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Structural  Geology 

of 

North  America 


HARPER'S     GEOSCIENCE     SERIES 

CAREY  CRONEIS,  Editor 


Structural   provinces  of  North  America,  shown  to  the  edge 
of  the  continental  shelf. 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

LYRASIS  Members  and  Sloan  Foundation 


http://archive.org/details/structuralOOeard 


Structural  Geology 

of 
North  America 


SECOND    EDITION 


A.  J.  EARDLEY 

Professor  of~(5eology  and  Dean 

College  of  Mines  and  Mineral  Industries 

University  of  Utah 


HARPER      &      ROW,      PUBLISHERS,      NEW     YORK      AND      EVANSTON 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA,  Second  Edition 

Copyright  1951   by  Harper  &  Row,  Publishers,  Incorporated 
Copyright  ©  1962  by  A.  J.  Eardley 

Printed  in  the  United  States  of  America 


,    IT 


All  rights  reserved.  No  part  of  the  book  may  be  used  or  reproduced 
in  any  manner  whatsoever  without  written  permission  except  in  the  case 
of  brief  quotations  embodied  in  critical  articles  and  reviews.  For  infor- 
mation  address   Harper  &  Row,   Publishers,    Incorporated 
49  East  33rd  Street,  New  York  16,  N.  Y. 

l-M 


Library  of  Congress  catalog  card  number:  62-17482 


3.   RESUMl  OF  STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 

Major  Tectonic  Divisions 


12 


CONTENTS 


EDITOR'S  INTRODUCTION 
PREFACE  TO  THE  FIRST  EDITION 
PREFACE  TO  THE  SECOND  EDITION 

1.  INTRODUCTION 

Purpose  of  Book  Method  of  Presentation  Kinds  of  Illustrations 
Maps  for  Collateral  Use  Authority  for  Stratigraphic  Correlations 
Exercises 

2.  STRUCTURAL  TERMINOLOGY 

Need  of  Standard  Terms  for  Regional  Structures  Meaning  and 
Choice  of  Terms  for  This  Book  Terms  for  Structural  Disturbances 
Classification  Used  for  Crustal  Disturbances 


XI 

xiii 
xv 

1 


4.  PRECAMBRIAN  TECTONIC  PROVINCES  22 

Distribution  of  Precambrian  Rocks  Canadian  Shield  Arctic  Stable 
Region      Precambrian  Provinces  of  the  United  States 

5.  CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES  37 

General  Characteristics  Pre-Devonian  Basins  Transcontinental  Arch 
Eastern  Interior  Basins  and  Arches  Northwestern  Interior  Basins  and 
Arches 

6.  PALEOZOIC  CORDILLERAN  GEOSYNCLINE  63 

Divisions  and  their  Characteristics  Basins  and  Uplifts  of  the  Western 
United  States  and  Southern  British  Columbia  Eugeosyncline  in 
Southeastern  Alaska,  Northern  British  Columbia,  and  the  Yukon  Sum- 
mary of  Orogenic  History 

7.  APPALACHIAN  MOUNTAINS  91 

Major  Structural  Divisions      Relations  to  Geomorphic  Provinces 

8.  SOUTHERN  AND  CENTRAL  APPALACHIANS  97 

Extent  and  Divisions  Major  Elements  of  Stratigraphy  Folded  and 
Thrust-Faulted  Appalachian  Mountains  Blue  Ridge  Province  Pied- 
mont Province      Summary  of  Orogenic  History 

9.  EASTERN  TRIASSIC   BASINS  128 

Distribution  of  Basins  Nature  of  Triassic  Rocks  Structure  of  Basins 
Origin  of  Basins      Late  Triassic  Phase  (Palisades  Orogeny) 

10.  ATLANTIC  COASTAL  PLAIN   AND  ADJACENT  OCEAN   BASIN      135 

Extent  and  Character  of  Sediments  Stratigraphy  Structure  Con- 
stitution of  Continental  Shelf  and  Adjacent  Atlantic  Ocean  Crust 

11.  NEW  ENGLAND  APPALACHIAN  SYSTEMS  154 

Divisions  of  New  England  Appalachians  Hudson  Valley-Lake  Cham- 
plain  Region  Central  and  Eastern  New  England  Carboniferous 
Basins 


VI 


CONTENTS 


12.  MARITIME  APPALACHIANS  189 

Definition  Geomorphic  Provinces  Stratigraphy  Igneous  Rocks 
Structures     Tectonic  History 

13.  NEWFOUNDLAND  APPALACHIANS  203 

Physical  Divisions  Stratigraphy  Intrusions  Major  Structural  Divi- 
sions and  Their  Characteristics  Tectonic  History  Major  Tectonic  Re- 
lations of  Greater  Acadia 

14.  OUACHITA,  MARATHON,  AND  COAHUILA  SYSTEMS  223 

Ouachita  System     Marathon  System     Coahuila  System 

15.  WICHITA  AND  ANCESTRAL  ROCKIES  SYSTEMS 

AND  THE  TEXAS  FORELAND  237 

Wichita  System     Texas  Foreland     Ancestral  Rockies  System 

16.  THE   LATE   PALEOZOIC  ZONES  OF  FAULTING  AND 
CRYPTOVOLCANIC  OR  METEORITE  IMPACT  STRUCTURES  253 

Foreland  Arcuate  Fault  Zone  Lake  Superior  Fault  Zone  Cryptovol- 
canic  or  Meteorite  Impact  Structures 

17.  MESOZOIC  SYSTEMS  ALONG  THE  PACIFIC  260 

Western  Nevada  Northwestern  Nevada  Central  and  Northern 
California  Oregon  Southern  California  Nevadan  Orogeny  An- 
cestral Coast  Range  System     Columbia  System 

18.  ROCKY  MOUNTAINS  IN  MESOZOIC  TIME  291 

Triassic  Geography  Early  Jurassic  Geography  Early  and  Mid-Cre- 
taceous Orogeny 

19.  LATE  CRETACEOUS  AND  EARLY  TERTIARY  ROCKY  MOUNTAIN 
SYSTEMS-THE  LARAMIDE  OROGENY  295 

Definition  of  Laramide  Orogeny  Belts  of  Deformation  Relation  of 
Belts  of  Deformation  to  Crustal  Constitution 

20.  CANADIAN  AND  MONTANA  ROCKIES  302 

Major  Systems  of  Canadian  Cordillera     Divisions  of  Canadian  and 


Montana  Rockies  Mountain  Belt  Foothill  Belt  Age  of  Thrusting 
The  Rocky  Mountain  Trench 

21.  IDAHO  BATHOLITH  AND  THE  OSBURN  FAULT  ZONE  319 

Extent     Composition     Age     Conclusions 

22.  CENTRAL  ROCKIES  327 

Spatial  Relations  Orogenic  Deposits  Southwestern  Montana 
Southeastern  Idaho  and  Western  Wyoming  Wasatch  Area  of  Utah 
Central  Utah     Southwestern  Utah     Western  Utah     Southern  Nevada 

23.  CENTRAL  MONTANA  ROCKIES  351 

General  Features  Central  Zone  of  Uplifts  Zones  of  En  Echelon 
Faults  Stages  of  Orogeny  Igneous  Centers  Structures  of  the 
Northern  Great  Plains 

24.  WYOMING  ROCKIES  361 

General  Characteristics  Teton— Gros  Ventre— Wind  River  Element 
Beartooth  Range  Owl  Creek  and  Washakie  Mountains  Heart 
Mountain  and  Related  Features  Absaroka  Range  and  Yellowstone 
Park  Big  Horn  Range  and  Big  Horn  Basin  Black  Hills  and  Powder 
River  Basin  Sweetwater  Range  Wind  River  Basin  Hanna  Basin 
Late  Tertiary  Downfaulting  of  Sweetwater  Range  Laramide  Pattern 
and  Cenozoic  Stages  in  the  Sweetwater  Range  Region  Rawlins  Up- 
lift Washakie  Basin  Green  River  Basin  Uinta  Mountains  Rock 
Springs  Uplift  Laramie  Range  and  Basin  and  Medicine  Bow  Range 
Hartville  Uplift     Regional  Uplift  in  Late  Cenozoic 

25.  COLORADO  AND  NEW  MEXICO  ROCKIES  389 

Extent  of  Laramide  Deformation  Colorado  Rockies  New  Mexico 
Rockies  Central  New  Mexico  Porphyry  Belt  Guadalupe  and  Mara- 
thon Uplifts 

26.  COLORADO  PLATEAU  407 

General  Geology  Asymmetrical  Arches  and  Basins  Salt  Anticlines 
Laccolithic  Mountains  Upheaval  Dome  Volcanic  Fields  High  Pla- 
teaus of  Utah  Age  of  Uplifts  and  Volcanism  Epeirogenic  Move- 
ments and  Isostatic  and  Seismic  Considerations 


CONTENTS 


27.  SOUTHERN  ARIZONA  ROCKIES  426 

Physiographic  Characteristics  and  Divisions  Paleozoic  and  Meso- 
zoic  Basins  Use  of  Terms,  Laramide  and  Nevadan  Orogenies  Mes- 
ozoic  and  Cenozoic  Geology  of  Southeastern  Arizona  Mesozoic  and 
Cenozoic  Geology  of  Southern  Arizona  Geology  of  West-Central 
Arizona  Nevadan  Orogeny  (?)  Igneous  Cycles  and  Mineraliza- 
tion Tertiary  Normal  Faulting  Conclusions  Regarding  Tectonic 
History 

28.  ROCKIES  OF  NORTHERN  MEXICO  440 

Mexican  Geosyncline  Sonoran  Region  El  Paso— Rio  Grande  Thrust 
Belt  Plateau  Central  and  Sierra  Madre  Oriental  Parras  Synclin- 
orium     Orogenic  History     Foothill  Belt 

29.  COAST  RANGES  OF  THE  PACIFIC  AND  THE  SAN   ANDREAS 
FAULT  SYSTEM  452 

Major  Divisions  Central  Coast  Ranges  of  California  Southern  Coast 
or  Transverse  Ranges  of  California  Northern  Coast  Ranges  of  Cali- 
fornia San  Andreas  Fault  System  Coast  Ranges  of  Oregon  and 
Washington 

30.  BAJA  CALIFORNIA  AND  SONORA  SYSTEMS  480 

Baja  California     Gulf  of  California     Sierra  Madre  Occidental 

31.  MIDDLE  AND  LATE  CENOZOIC  SYSTEMS 

OF  THE  CENTRAL  CORDILLERA  493 

General  Divisions  and  Their  Characteristics  Basin  and  Range  System 
Late  Cenozoic  Trenches  of  the  Rocky  Mountains  Geophysical  Evi- 
dence Exploring  Tensional  Tectonism  in  Western  North  America 
Seismic  Velocity  Layers  in  the  Eastern  Great  Basin 

32.  PACIFIC  SUBMARINE  PROVINCES  515 

Discovery  of  Strong  Submarine  Relief  Submarine  Provinces  Aleu- 
tian Trench  Bering  Sea  Floor  Pacific  Floor  off  Mexico  and  Central 
America  Fracture  Zones  Deep  Sea  Provinces  Hawaiian  Ridge 
Mid-Pacific  Mountains     Circum-Pacific  Tectonics 


33.  IGNEOUS  AND  TECTONIC  PROVINCES 

OF  THE  WESTERN  CORDILLERA  532 

Objectives     Concept  of  Igneous  Provinces 

34.  IGNEOUS  AND  TECTONIC   PROVINCES 

IN  SOUTH  AMERICA  537 

Chile  and  Argentina  Peru,  Bolivia,  Ecuador,  and  Columbia  Post- 
Batholithic  Belt      Parana  Basin  Basalt  Field 

35.  IGNEOUS  AND  TECTONIC  PROVINCES  IN  MEXICO  549 

Geosyncline  Batholithic  Belt  of  the  First  Cycle  Post-Batholithic 
Volcanism  Batholithic  Belt  of  the  Second  Cycle  Metamorphic  and 
Intrusive  Belt     Relation  to  Depressed  Belts 

36.  IGNEOUS  PROVINCES  IN  WESTERN  UNITED  STATES  553 

Eugeosynclinal  Province  Batholithic  Province  Post-Batholithic  Prov- 
inces of  the  Batholithic  Belt  Provinces  of  the  Miogeosyncline  and 
Shelf  Relation  of  Tectonic  to  Igneous  Provinces  Distribution  of 
Primary  Magmas 

37.  IGNEOUS  AND  TECTONIC  PROVINCES 

OF  WESTERN  CANADA  583 

Geosyncline  Orogenies  Beltian  Geanticline  Batholithic  Province 
Post-Batholithic  Volcanism  Relation  of  Volcanism  to  Tectonic  Prov- 
inces 

38.  SPATIAL  RELATIONS  OF  MAJOR  TECTONO-IGNEOUS 

ELEMENTS  AND  ORIGIN  OF  MAGMAS  588 

Relation  of  Batholithic  Belt  to  Eugeosyncline  Previous  Orogeny  in 
Eugeosyncline  Relation  of  Post-Batholithic  Compressional  Orogeny 
to  Geosyncline  and  Shelf  Relation  of  Post-Batholithic  Volcanics  to 
Batholithic  Belt  Relation  of  Post-Batholithic  Volcanic  Fields  to  Strato- 
volcanoes  Post-Batholithic  Volcanics  to  Trenches  Relation  of  Anti- 
clinoria  to  Other  Elements  Origin  of  Magmas  Techtono-lgneous 
Provinces  and  Deep-Seated  Earthquakes  Crustal  Tension  and  Mag- 
matism 


Vlll 


CONTENTS 


39.  ALASKA  AND  THE  YUKON  605 

Geomorphic  Provinces  of  Alaska  Paleozoic  Geosyncline  and  Related 
Orogeny  Triassic  and  Jurassic  Geanticline  and  Adjacent  Basins 
Cretaceous  Basins  and  Geanticlines  Mesozoic  and  Cenozoic  Oro- 
genies Tertiary  Volcanic  Rocks  Aleutian  Volcanic  Belt  Siberian 
Tectonic  Connections  Yukon  Territory  and  the  District  of  Mackenzie 
Cenozoic  Trenches  and  Faults 

40.  CANADIAN  ARCTIC  633 

Geography  and  Geologic  Provinces  of  the  Arctic  Archipelago  Low- 
lands and  Plateaus  Fold  Belts— The  Innuitian  Region  Arctic  Coastal 
Plain  Correlation  with  Alaska  and  the  Yukon  Pleistocene  Epeirog- 
eny  and  Climatic  Changes  Orogenic  Belts  of  Greenland  Arctic 
Ocean  Basin 


41.  GULF  COASTAL  PLAIN 

General  Characteristics  Structural  Geology  Igneous  Rocks  Tam- 
pico  Region,  Mexico  Florida  Platform  Crustal  Structure  of  Gulf 
of  Mexico 


650 


42.  ANTILLEAN-CARIBBEAN    REGION  670 

Geographic  Provinces  Greater  Antilles  Lesser  Antilles  Puerto 
Rico  Trench  and  Gravity  Anomalies  Caribbean  Region  and  Seismic 
Profiles  Origin  of  the  Caribbean  Basins,  Trenches,  and  Rises  Pos- 
tulated Eastward  Shift  of  Caribbean  Block 

43.  SOUTHERN  MEXICO  AND  CENTRAL  AMERICA  696 

Major  Geologic  Divisions  Crystalline  Belt  Permian  Fold  Belt  Late 
Cretaceous  and  Early  Tertiary  Fold  Belt  Southern  Gulf  Coastal 
Plain  Yucatan  Peninsula  Volcanic  Fields  and  Faulting  Isthmian 
Volcanic  Link  Relation  to  Greater  Antilles  Mammalian  Fossil  Record 
and  Land  Connections 

BIBLIOGRAPHY  709 

INDEX  739 


COLOR  PLATES 

The  signature  of  color  plates  follows  page  14. 


Plate  1.  Precambrian  Orogenic  Belts 

Plate  2.  Cambrian  Tectonic  Map 

Plate  3.  Ordovician  Tectonic  Map 

Plate  4.  Silurian  Tectonic  Map 

Plate  5.  Devonian  Tectonic  Map 

Plate  6.  Mississippian  Tectonic  Map 

Plate  7.  Pennsylvanian  Tectonic  Map 

Plate  8.  Permian  Tectonic  Map 

Plate  9.  Triassic  Tectonic  Map 

Plate  10.  Jurassic  Tectonic  Map 

Plate  11.  Early  Cretaceous  Tectonic  Map 

Plate  12.  Late  Cretaceous  Tectonic  Map 

Plate  13.  Tectonic  Map  of  the  Cretaceous-Tertiary  Transition 

Plate  14.  Early  Tertiary  Tectonic  Map 

Plate  15.  Late  Tertiary  and  Quaternary  Tectonic  Map 


IX 


EDITOR'S  INTRODUCTION 


A.  J.  Eardley's  Structural  Geology  of  North  America  has,  since  its  pub- 
lication in  1951,  become  something  of  a  landmark  in  the  geological  litera- 
ture of  the  New  World.  This  is  demonstrated  by  the  broad  base  of  its 
foreign  sales  and  the  fact  that,  at  home  and  abroad,  the  volume  has  re- 
ceived heavy  use  by  stratigraphers,  geophysicists  and  other  specialists, 
as  well  as  by  the  structural  geologists  for  whom  it  was  written.  Moreover, 
although  originally  conceived  as  a  textbook  for  advanced  undergraduates, 
Structural  Geology  soon  became  a  handy  and  valued  general  source  book 
for  nonacademic  professional  and  economic  geologists. 

Dr.  Eardley,  however,  has  always  considered  that  his  magnum  opus 
was  somewhat  out  of  date  even  before  the  first  edition  was  put  through 
the  publishing  mill.  Accordingly,  immediately  after  the  book  was  issued, 
he  set  about  the  onerous  task  of  revising  it.  For  a  full  decade  now  he  has 
devoted  a  considerable  amount  of  his  time  and  efforts  to  the  current  re- 
vision. The  self-imposed  "labor  of  Hercules"  has  been  particularly  frus- 
trating and  time  consuming  because  during  the  fifties  numerous  basic 
concepts  of  structural  geology  have  undergone  radical  change.  Thus, 
fondly  held  theories  of  less  than  ten  years  ago  are  now  either  discarded 


or  seriously  challenged.  In  addition,  a  vast  quantity  of  new  field  data  hai 
been  accumulating  so  rapidly  that  revisions  can  scarcely  keep  up  with 
the  scientific  progress. 

Dr.  Eardley  has  taken  full  cognizance  of  the  rapidK  evolving  theo- 
retical concepts,  as  well  as  of  the  flood  of  new  information.  As  a  result 
this  edition  of  Structural  Geology  is  far  from  being  a  reprint — in  many 
chapters  it  is  so  extensively  revised  as  to  be  essentiall)  a  new  volume. 
But  in  addition,  much  of  the  best  of  the  first  edition  reinainv  .iud  thus 
it  is  likely  that  this  volume  will  continue  to  be  the  standard  text  and 
reference  work  in  a  subdiscipline  of  geologv  that  is  of  prime  significance 
in  the  proper  understanding  of  all  other  phases  of  the  subject 

The  structural  evolution  of  a  continent!  Relatively  few  scientific  writers 
have  painted  on  such  a  broad  canvas  as  Dr.  Eardley.  Hi'  is  something  of 
a  rarity  even  among  such  artists,  for  he  not  only  works  with  a  broad 
brush  but  also  takes  pains  to  fill  in  the  details. 

The  geological  fraternity  has  been  indebted  to  Dr.  Eardley  for  an  ex- 
cellent compendium  on  structural  geology,  and  that  indebtedness  is  now- 
increased  through  an  exceptional  initial  task  that  has  become  even  better 
done  in  its  redoing. 

( '  u.i  ■>   (.  I    iNl  is 

Rice  University 
June,  1962 


XI 


PREFACE 

TO  THE  FIRST  EDITION 


This  book  is  addressed  especially  to  advanced  undergraduates  in  geol- 
ogy. I  doubt  that  it  could  have  been  written  on  a  more  elementary  level 
and  still  presume  to  use  the  common  terminology  of  the  numerous  source 
publications  and  the  language  of  the  professional  geologists.  In  fact,  some 
instructors  may  consider  the  book  too  advanced  for  undergraduates.  I 
have  endeavored,  however,  to  take  such  measures  as  will  make  it  under- 
standable to  the  student  who  has  had  basic  courses  in  mineralogy, 
lithology,  and  structural  geology.  It  will  be  well  if  he  has  had  a  course 
in  stratigraphy  in  which  correlation  problems  have  been  discussed  and 
in  which  some  attention  has  been  given  to  the  sedimentary  environments 
and  sources. 

The  reader's  attention  is  lost  most  frequently  by  the  use  of  unfamiliar 
formational,  fossil,  and  geographic  names.  Generally  I  have  not  used 


formational  names  in  the  text  but,  instead,  have  referred  to  the  dep< 
by  period,  epoch,  or  stage,  and  have  listed  the  formational  names  in 
charts.  This  has  the  advantage  of  easing  the  reading  of  the  text  and  still 
making  the  student  aware  of  the  many  formations  in  the  various  parts  ot 
the  country.  At  the  same  time  it  sets  the  stage  for  meaningful  stratigraphic 
studies  in  other  courses. 

I  have  discussed  stratigraphic  correlations  only  where  necessary,  anil 
have  relied  on  the  latest  authoritative  correlations  in  the  literati.: 
graphic  names  have  been  treated  with  care,  and  I  believe  all  that  have 
been  mentioned  are  on  accompanying  maps  and  figures,  or  on  other  well- 
known  maps  which  are  referred  to  as  the  occasion  arises.  Where  petro- 
graphic  research  has  been  referred  to,  I  have  attempted  to  discuss  it  in 
such  terms  that  the  student  with  a  knowledge  of  the  common  roik  names 
will  understand. 

Several  professors  who  teach  structural  geology  have  expressed  to  me 
the  need  for  a  text  that  treats  structural  geology  from  a  regional  point  of 
view,  hut  I  doubt  it  the  present  volume  is  what  they  want,  or  that  it  can 
be  used  as  a  substitute  for  the  standard  textbooks  on  principles.  It  may 
be  that  in  those  departments  where  structural  geology  is  taught  as  a  senior 
course,  the  hook  could  be  used,  and  principles  could  he  developed  col- 


xui 


XIV 


PREFACE  TO  THE  FIRST  EDITION 


laterally.  I  think,  however,  that  principles  will  suffer  this  way.  I  have 
the  book  in  mind  for  an  advanced  course  in  regional  or  structural  geology. 

I  hope  also  that  the  book  will  prove  attractive  to  professional  geologists, 
because  some  of  the  maps  and  ideas  about  the  many  fascinating  problems 
of  continental  growth  may  be  new  to  them.  I  also  trust  that  they  will  not 
hesitate  to  set  me  right  about  any  errors  I  have  made. 

Parts  of  the  North  American  continent  are  so  well  known  that  it  did 
not  seem  worth-while  to  do  more  than  describe  them  briefly  and  sum- 
marize the  conclusions  that  have  been  so  well  presented  by  others.  In 
certain  areas,  however,  I  had  to  marshal  the  evidence  and  present  it  in 
some  detail  in  order  to  sustain  an  original  interpretation.  For  this  reason, 
all  parts  of  the  continent  may  not  seem  equally  treated.  I  had  to  bear  in 
mind  the  professional  geologist  as  a  reader  when  drawing  original  con- 
clusions. 

A  series  of  paleogeologic  maps  and  paleotectonic  maps  is  included  in  the 
book.  These,  I  hope,  will  be  referred  to  repeatedly.  They  differ  decidedly 
from  the  familiar  paleogeographic  map,  and  for  structural  studies  are 
much  more  illuminating.  As  geologic  studies  progress,  the  maps  will  un- 
doubtedly bear  correction,  but  I  have  been  impressed  repeatedly  with  the 
adequacy  of  our  knowledge  to  date  in  establishing  many  important  rela- 
tionships. 


left 


Where  possible  I  have  referred  to  late  summary  reports,  and  have  left 
the  reader  to  go  to  these,  if  he  wishes  all  the  original  references.  Where 
good  summary  reports  are  lacking,  I  have  referred  to  the  basic  investi- 
gations. Our  literature  bearing  on  die  structural  development  of  the  con- 
tinent is  so  extensive  that  I  have  been  continuously  beset  by  the  fear  that 
I  have  missed  an  important  reference,  especially  for  those  regions  with 
which  I  am  least  familiar. 

The  research  and  writing  of  this  book  was  done  at  the  University  of 
Michigan,  where  the  geologic  library  is  extensive,  the  departmental  facil- 
ities are  all  that  were  needed,  the  time  to  do  research  work  was  abundant, 
and  my  former  associates  on  the  staff  were  most  helpful  and  congenial.  I 
remain  very  appreciative  of  these  facilities  and  opportunities  at  the  Uni- 
versity of  Michigan. 

Miss  Dolores  Marsik  has  helped  over  several  years  as  typist,  and  Dr. 
Ruth  Bastanchury  Boeckerman  has  assisted  in  editorial  work  and  has 
done  the  final  typing.  Mr.  Derwin  Bell  assisted  in  the  drafting  of  many 
of  the  figures  and  plates. 

A.  J.  Eardley 


January,  1951 


PREFACE 

TO  THE  SECOND  EDITION 


The  second  edition  is  an  extensively  revised  version  of  the  first.  Seven 
new  chapters  have  been  added,  one  on  the  Precambrian  orogenic  belts 
and  six  on  the  igneous  provinces  of  the  western  cordillera.  Igneous  rocks 
are  accorded  a  more  significant  place  here  than  in  the  first  edition.  South- 
ern Mexico  and  Central  America  are  treated  in  a  separate  chapter  as  is 
also  the  Canadian  Arctic.  The  colored  maps  of  the  summary  in  Chapter  3 
have  been  extensively  revised,  and  several  new  ones  are  included. 

Better  index  maps  have  been  added  throughout  and  an  attempt  has 
been  made  to  produce  an  understandable  text  independent  of  outside 
sources  of  information.  However,  such  maps  as  the  geologic  and  tectonic 
maps  of  the  United  States  and  Canada  and  the  several  state  maps  will 
be  indispensable  for  instructional  purposes  and  should  be  available  to 
the  student  or  professional  geologist  reading  the  book. 


The  second  edition  marks  a  time  of  major  transition  in  structural  geol- 
ogy. In  the  past  geologists  have  seen  evidence  in  nearly  every  mountain 
system  of  crustal  compression,  but  now  a  number  of  authorities  postulate 
earth  expansion,  differential  uplift,  and  crustal  tension.  The  folds  and 
thrust  sheets  are  being  interpreted  as  gravity  slide  phenomena  from  re- 
gions of  marked  uplift.  Vertical  movements  along  with  distention  and 
wrenching  are  considered  to  be  the  primary  aspects  of  crustal  deforma- 
tion— not  horizontal  compression. 

The  writer  sees  much  in  favor  of  the  hypothesis  of  primary  vertical 
movements  and  has  perhaps  accorded  it  greater  attention  than  some  will 
like.  However,  he  has  also  attempted  to  present  the  geology  of  the  several 
provinces  as  the  authorities  have  depicted  them.  Certain  sections  of  the 
book,  therefore,  reflect  the  orthodox  concepts  of  compression,  win 
other  parts  will  seem  to  emphasize  primary  vertical  movements  with  sec- 
ondary folding  and  thrusting.  It  will  take  another  ten  years  to  resoK  e  the 
irregularities  and  to  warrant  the  preparation  of  a  more  definitive  third 
edition. 

A.  J.  Eardli  v 

June,  1962 


xv 


Structural  Geology 

of 

North  America 


1. 


described.  Theories  of  diastrophism  thai  have  been  proposed  for  certain 

structural  systems  are  summarized,    and    current    concept!   of    mmintalii 
building  and  continental  development  .ire  presented  where  approprj 


INTRODUCTION 


PURPOSE  OF  BOOK 

The  purpose  of  the  book  is  to  describe  the  structural  evolution  of  the 
North  American  continent.  The  chapters  concern  the  formation  and  con- 
stitution of  the  mountain  systems,  basins,  arches,  and  volcanic  archi- 
pelagos; the  beveling  of  the  highlands;  and  the  filling  of  the  basins.  In 
short,  they  treat  of  the  procession  of  deformational  and  sedimentary 
events.  Not  only  does  the  book  seek  to  chronicle  the  crustal  unrest  of 
the  continent,  but  it  also  tries  to  summarize  the  supporting  evidence. 

The  igneous  provinces  and  their  relation  to  the  tectonic  provinces  are 
treated.  The  advances  in  geophysics  in  deciphering  deep  crustal  structure 
are  referred  to,  and  the  constitution  of  the  crust  in  several  regions  is 


METHOD  OF  PRESENTATION 

The  structural  history  of  the  continent  is  one  both  of  time  and  of  geo- 
graphic position.  The  major  scheme  of  organization  of  the  book  could, 
therefore,  follow  one  or  the  other.  For  instance,  if  organized  on  a  time 
basis,  all  the  structural  events  over  the  whole  continent  would  be  re- 
viewed period  by  period.  If  on  a  geographic  basis,  the  structural  history 
of  each  major  province  would  be  followed  from  the  beginnil  .'en- 

zoic  time  to  the  present.  Neither  course  when  rigidly  pursued  worked  out 
well,  but  if  the  chapter  headings  are  scanned,  it  will  he  apparent  that  l 
phasis  in  organization  has  been  placed  on  geographic  position. 

The  necessity  of  treating  a  succession  of  deformational  events  in  a  cer- 
tain province  without  serious  interruption  early  became  plain,  and  it 
decided  that  the  great  mountain  systems  whose  histories  run  through 
several  periods  of  time  must  be  treated  as  units.  The  growth  of  the  con- 
tinent in  its  several  provinces  has  been  described  first  during  the  Paleo- 
zoic, and  then,  in  general,  the  great  structural  units  of  the  MesozotC  and 
Cenozoic  have  been  considered.  In  the  resume  of  the  structural  evolution 
of  the  continent,  Chapter  3,  the  paleogeologic  and  paleotectonic  maps  are 
presented,  and  there  the  development,  period  by  period,  is  reviewed. 

KINDS  OF   ILLUSTRATIONS 

Considerable  effort  has  been  made  to  illustrate  every  important  point 
developed  in  the  text.  Maps,  cross  sections,  and  block  diagrams  are  used. 
Photographs  have  little  value  because  the  structural  features  described 
are  usually  immensely  larger  than  photographs  reveal.  If  the  reader  de- 
sires to  know  the  nature  of  the  topographv,  other  books  with  a  wealth  of 
photographs  should  be  referred  to,  such  as  Fenneman's  Physiography  of 
the  United  States,  Lobeck's  Gcomorplwlogy.  Hinds's  Geomorphology,  and 
Atwood's  Physiography  of  North  America. 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


MAPS  FOR  COLLATERAL  USE 

The  book  is  not  intended  to  stand  entirely  alone.  The  reader  or  in- 
structor should  have  the  following  maps  for  ready  reference,  preferably 
mounted  and  hanging  on  the  wall  at  short  range. 

The  Geologic  Map  of  the  United  States,  1932  edition 

The  Geologic  Map  of  Canada,  1957  edition 

The  Geologic  Map  of  North  America,  1946  edition 

The  Tectonic  Map  of  the  United  States,  1944  edition 

Landforms  of  the  United  States,  1939.  Map  by  Erwin  Raisz 

The  Tectonic  Map  of  Canada,  1950 

The  Geologic  Map  of  South  America,  1950 

These  maps  will  be  referred  to  repeatedly.  Although  the  book  contains 
many  illustrations,  it  does  not  reproduce  the  features  of  the  above  maps, 
and  if  they  are  not  consulted  when  referred  to,  the  continuity  will  be 
interrupted,  the  evidence  not  clearly  understood,  and  perhaps  the  con- 
clusions not  appreciated  or  properly  evaluated. 


AUTHORITY  FOR  STRATIGRAPHIC  CORRELATIONS 

Most  field  work  in  structural  geology  is  based  on  previous  paleontologic 
and  stratigraphic  work.  A  report  on  the  structural  geology  of  an  area  is 
not  considered  worth  while  unless  the  formations  are  dated.  The  principal 
method  of  dating  is  by  the  fossils  present,  and  therefore,  the  structural 
geologist  is  dependent  upon  the  paleontologist,  except  in  Precambrian 
terranes.  It  is  conceivable,  but  not  probable,  that  a  sequence  of  deforma- 
tional  events  could  be  worked  out  in  a  local  area  without  reference  to 
fossils  or  to  nearby  stratigraphic  columns,  but  to  date  the  events  and  to 
relate  them  to  others  in  widely  separated  areas  is  generally  impossible 
without  fossils. 

A  series  of  articles  has  appeared  in  the  last  few  years  in  the  Bulletins 
of  the  Geological  Society  of  America  that  summarize  the  formational  cor- 
relations throughout  North  America  for  each  geologic  period.  They  have 
been  prepared  by  the  Committee  on  Stratigraphy  of  the  National  Re- 
search Council,  and  are  taken  in  this  book  as  authority  in  relating  the 


numerous   orogenic   episodes   throughout   the   continent.   They   are   as 
follows : 

Chart  No. 

1.  Cambrian  formations  of  North  America,  Howell  et  al.,  Bull.  Geol.  Soc. 
Am.,  vol.  55,  pp.  993-1004,  1944. 

2.  Ordovician  formations  of  North  America,  W.  H.  Twenhofel  et  al.,  Bull. 
Geol.  Soc.  Am.,  vol.  65,  No.  3,  1954. 

3.  Silurian  formations  of  North  America,  C.  K.  Swartz  et  al.,  Bull.  Geol.  Soc. 
Am.,  vol.  53,  pp.  533-538,  1942. 

4.  Devonian  formations  of  North  America,  G.  Arthur  Cooper  et  al.,  Bull. 
Geol.  Soc.  Am.,  vol.  53,  pp.  1729-1794,  1942. 

5.  Mississippian  formations  of  North  America,  J.  Marvin  Weller  et  al.,  Bull. 
Geol.  Soc.  Am.,  vol.  59,  pp.  91-196,  1948. 

6.  Pennsylvania  formations  of  North  America,  R.  C.  Moore  et  al.,  Bull.  Geol. 
Soc.  Am.,  vol.  55,  pp.  657-706,  1944. 

7.  Permian  formations  of  North  America,  A.  A.  Baker  et  al.,  Bull.  Geol.  Soc. 
Am.,  vol.  71,  pp.  1763-1801,  1960. 

8.  Cretaceous  formations  of  the  western  interior  of  the  United  States,  Bull. 
Geol.  Soc.  Am.,  vol.  63,  pp.  1011-1044,  1952. 

9.  Cretaceous  formations  of  the  Greater  Antilles,  Central  America  and  Mexico, 
R.  W.  Imlay,  Bull.  Geol.  Soc.  Am.,  vol.  55,  pp.  1005-1046,  1944. 

10.  Marine  Cenozoic  formations  of  western  North  America,  C.  E.  Weaver 
et  al,  Bull.  Geol.  Soc.  Am.,  vol.  55,  pp.  569-598,  1944. 

11.  Cenozoic  formations  of  the  Atlantic  and  Gulf  Coastal  Plain  and  Caribbean 
Region,  C.  Wythe  Cooke  et  al.,  Bull.  Geol.  Soc.  Am.,  vol.  54,  pp.  1713- 
1724,  1943. 

Additional  correlations  charts 

Thickness  and  general  character  of  the  Cretaceous  deposits  in  the  western 
interior  of  the  United  States,  Preliminary  Map  No.  10,  J.  B.  Reeside,  Jr.,  U.S. 
Geol.  Survey,  Oil  and  Gas  Investigations,  1944. 

Nomenclature  and  correlation  of  the  North  American  Continental  Tertiary, 
H.  E.  Wood,  2nd,  et  al.,  Bull.  Geol.  Soc.  Am.,  vol.  52,  pp.  1-48,  1941. 

Paleotectonic  maps  of  the  Jurassic  system,  U.S.  Geol.  Survey,  Miscellaneous 
Geological  Investigations,  Map  1-175,  1956. 

Paleotectonic  maps  of  the  Triassic  system,  U.S.  Geol.  Survey,  Miscellaneous 
Geological  Investigations,  Map  1-300,  1959. 

EXERCISES 

Four  types  of  assignments  and  exercises  are  feasible.  The  first  is  the 
reading  and  reporting  of  original  articles  in  the  literature.  It  is  hoped  that 


INTRODUCTION 


all  articles  of  outstanding  importance  are  referred  to  in  the  text.  All  publi- 
cations referred  to  are  listed  in  the  bibliographic  index.  For  emphasis 
on  local  areas  of  interest,  die  instructor  can  assign  additional  publica- 
tions. 

The  second  type  of  exercise  is  the  detailing  of  stratigraphic  successions 
in  the  different  basins  and  mountain  systems.  This  in  itself  would  consti- 
tute an  extensive  course  in  stratigraphy,  but  perhaps  for  local  interest, 
certain  stratigraphic  details  can  be  fitted  into  the  structural  picture. 

The  third  type  of  exercise  is  the  assembling  from  the  book  of  all  the 
structural  events  that  occurred  nation-wide  for  each  of  the  periods.  Since 
the  book  is  organized  chiefly  on  a  geographic  or  provincial  basis,  it  will 


be  an  excellent  review  to  cut  across  provinces  on  a  time  basis  and  sum- 
marize  the   events   over   the   entire   continent    for    each    period.    'Ih< 
paleogeologic  and  paleotec  tonic  maps   and   the-  bri<  i    discussion   that 
companies  them  in  Chapter  3  already  do  this,  hut  no  part  of  the  text  is 
devoted  in  detail  to  it. 

The  fourth  type  of  exercise  is  the  tracing  of  the  geologic  history  of  a 
county  or  a  state.  The  commonest  types  of  reports  are  those  that  de- 
scribe the  geology  of  an  area  with  political  boundaries,  and  it  will  ser\e 
the  student  as  a  good  lesson  to  write  a  history  of  such  a  region.  He  will 
have  to  draw  his  information  from  several  structural  provinces  and  will 
find  his  organization,  if  complete,  both  long  and  complex. 


2. 


STRUCTURAL  TERMINOLOGY 


NEED  OF  STANDARD  TERMS  FOR  REGIONAL  STRUCTURES 

The  posthumous  work  of  Schuchert  (1943)  is  an  example  of  the  ir- 
regular use  of  names  for  the  large  structural  features  of  the  United  States. 
He  speaks  of  the  Cincinnati  anticline  and  the  Cincinnati  geanticline,  evi- 
dently interchangeably,  and  the  Nashville  dome  in  the  same  sense  as  the 
Cincinnati  anticline.  McFarlan  (1943),  in  his  book  on  the  geology  of 
Kentucky,  defines  the  Cincinnati  arch  as  a  major  structure  which  includes 
the  Jessamine  dome  and  the  Nashville  dome,  but  in  several  places  he 
refers  to  the  arch  as  a  dome.  In  Colorado  the  Ancestral  Rockies  are  com- 
monly called  highlands  and  geanticlines,  in  New  Mexico  they  are  land- 


masses,  in  Texas  they  are  uplifts  and  arches.  The  buried  Nemaha 
"Mountains"  in  Oklahoma  and  Kansas  have  been  called  a  ridge.  There  are 
a  number  of  other  terms  for  which  no  standard  structural  meaning  has 
evolved.  The  professional  geologist  may  not  experience  any  difficulty  or 
inconvenience  in  this  loose  and  local  application  of  names  for  the  large 
structural  features  of  the  earth's  crust,  but  for  the  student  it  is  confusing. 
I  have  felt  impelled  to  define  and  classify  for  his  sake,  because  the  book  is 
addressed  to  him.  In  so  doing,  however,  I  feel  at  many  turns  there  will 
be  objections,  largely  on  the  grounds  of  provincial  usage. 

In  view  of  the  undesirability  of  multiplying  technical  words,  it  seems 
necessary  to  assign  specific  meanings  to  common  words  in  their  several 
fields  of  usage.  For  instance,  the  word  system  when  used  in  stratigraphy 
denotes  the  rocks  formed  during  a  period  of  geologic  time;  when  used 
geographically  it  generally  signifies  a  group  of  ranges  with  unifying  char- 
acteristics; and  when  used  structurally  it  indicates  a  group  of  related 
joints,  faults,  dikes,  or  the  like.  It  is  probably  better  to  give  a  word  such 
as  system  several  meanings  rather  than  use  a  new  word,  or  a  less  common 
and,  perchance,  a  less  appropriate  one.  The  commonest  usage  of  a  term 
should  weigh  heavily  in  formulating  a  definition  for  it. 

MEANING  AND  CHOICE  OF  TERMS  FOR  THIS  BOOK 

Arch  and  Dome 

From  1891  to  1903  Foerste  spoke  of  the  Cincinnati  uplift  as  an  anti- 
cline, then  in  1904  as  a  geanticline,  and  Schuchert  continued  the  use  of 
these  two  terms  apparently  interchangeably.  The  first  mention  of  the 
terms  arch  and  dome  for  the  structure  has  not  been  located  in  the  litera- 
ture, but  since  1900  they  have  been  used  very  commonly  and  usually 
synonymously.  They  are  the  terms  used  both  provincially  and  nationally 
most  frequently  today.  McFarlan  ( 1943 )  has  distinguished  the  two  in  the 
sense  that  the  Cincinnati  arch  is  an  elongate  structure  and  includes  two 
dome-shaped  uplifts  on  it,  the  Jessamine  dome  and  the  Nashville  dome, 
separated  by  a  sag  or  saddle.  Tennesseans  will  probably  not  accept  the 
subordination  of  their  Nashville  dome  to  a  division  of  the  Cincinnati  arch, 
but  the  principle  of  the  distinction  of  arch  and  dome  is  appealing.  Since 


STRUCTURAL  TERMINOLOGY 


the  Cincinnati  and  Nashville  structures  are  the  earliest  of  the  broad, 
gentle  uplifts  studied  in  the  United  States,  they  probably  should  be 
taken  as  types,  and  definitions  should  be  fashioned  after  their  character- 
istics. At  the  completion  of  the  present  study  of  the  uplifts  and  depres- 
sions of  the  central  stable  region  of  the  United  States,  nothing  undesirable 
is  recognized  in  taking  the  Cincinnati  and  Nashville  structures  as  types 
for  the  United  States,  if  a  little  latitude  in  characteristics  is  tolerated.  The 
terms  in  this  report  will  be  used  as  follows: 

An  arch  is  a  gentle,  broad  uplift  with  an  evident  width  of  25  to  200 
miles  and  a  length  conspicuously  greater  than  the  width.  The  structural 
relief  may  amount  to  10,000  feet  or  more  between  a  bed  at  the  top  of  the 
arch  and  one  of  similar  age  at  the  bottom  of  the  adjacent  basin,  but  the 
dip  of  the  beds  will  generally  not  exceed  100  feet  per  mile.  The  struc- 
tural relief  may  have  been  acquired  in  part  by  subsidence  of  the  adjacent 
basins  at  a  greater  rate  than  the  arch  area,  so  that  the  arch  may  actually 
only  at  times  have  been  an  emergent  landmass. 

A  dome  is  a  gentle,  round  or  elliptical  uplift  of  arch  proportions.  It 
usually  occurs  along  an  arch  and  expands  the  arch  locally.  This  regional 
structural  meaning  of  dome  must  be  distinguished  from  the  usage  in  con- 
nection with  igneous  rock  masses  (Rice,  1940)  and  from  the  much 
smaller  oil-  and  gas-producing  structures  such  as  salt  domes  or  plugs. 

Swell 

Schuchert  ( 1923 )  used  the  term  swell  to  mean  all  large,  domed  areas 
within  the  nuclear  part  of  the  continent.  Rucher  ( 1933 )  defined  a  swell  as 
"an  essentially  equidimensional  uplift  without  connotation  of  size  or 
origin."  In  discussing  the  structures  of  the  United  States  the  terms  arch 
and  dome  are  sufficient  for  all  broad  gentle  uplifts,  to  which  the  term 
swell  would  generally  apply,  and  therefore  it  has  not  been  necessary  to 
use  swell  in  the  following  pages,  and  no  attempt  to  define  it  further  will 
be  made  here. 

Uplift  and  Upwarp 

Uplift  and  upwarp  are  used  for  a  wide  variety  of  structural  elevations, 
and,  therefore,  should  be  reserved  as  noncommittal  terms  in  regard  to 


size,  shape,  internal  structure,  and  origin.  If  it  is  desired  to  distinguish 
the  two,  uplift  might  be  conceived  as  implying  both  small   and  lai 
round  and  elongate  elevations,  with  sharp  and  gentle  variations;  whan 
upwarp  would  imply  simply  broad  and  gentle  archings.  Nfo  precedent 

can  be  cited  for  this  distinction,  but  a  perusal  of  the  literature  leaves  me 
with  the  impression  that  this  is  the  most  general  usage,  l'rovmc  iallv,  how- 
ever, uplift  may  mean  a  rather  definite  type  of  structure.  I  will  use  the 
terms  only  in  case  I  am  in  doubt  about  the  nature  of  a  structural  el 
tion,  or  desire  to  use  them  as  synonyms  of  structures  being  discussed  in 
order  to  eliminate  repetition. 

Basin 

Rucher  (1933)  uses  the  term  basin  in  a  structural  sense  to  mean  any 
essentially  equidimensional  depression  without  connoting  size  or  origin, 
and  then  gives  the  Michigan  basin  as  an  example.  Swell  is  his  antithetical 
structure  of  basin.  Since  the  drill  in  several  places  has  extensively  ex- 
plored the  subsurface  distribution  of  the  stratified  rocks  of  the  continent. 
a  number  of  downwarps  have  become  firmly  entrenched  as  basins  in  the 
literature.  Some  embrace  more  than  a  large  state,  and  some  are  of  county 
size.  Some  are  fairly  elongate,  and  most  all  have  axial  directions.  Some 
are  troughlike  or  furrowlike.  It  has  not  proved  disturbing  in  compiling 
the  present  review  to  have  basin  used  in  this  loose  sense,  and  I  believe  the 
variations  in  meaning  will  be  evident  to  the  student,  so  there  is  little  urge 
to  attach  limitations  to  the  term.  The  word  basin  is  applied  a  thousand 
times  each  day  by  petroleum  geologists  in  many  variations  of  meaning, 
and  it  would  appear  unwise  to  attempt  standardization. 

Coal  basins  have  not  proved  to  be  the  same  as  oil  basins  or  water 
basins  in  several  places,  and  also  the  extent  of  the  commercial  materials 
has  not  coincided  with  the  greatest  thickness  of  the  strata  and.  therefore, 
the  greatest  depression.  It  seems  to  me  that  the  major  geological  features 
should  govern  the  choice  of  a  geographic  name,  rather  than  the  distribu- 
tion of  an  economic  deposit  of  little  relative  volume. 

The  site  of  maximum  subsidence  during  an  epoch,  period,  or  era  may 
not  coincide  with  that  of  a  later  one,  and  some  confusion  has  resulted  in 
the  meaning  of  the  term  basin  in  certain  areas.  This  is  particularly  true 


6 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


on  tectonic  maps  which  attempt  to  show  all  structures  evolved  through 
three  eras.  I  have  found  it  desirable  to  think  of  certain  basins  in  a  re- 
stricted time  as  well  as  restricted  geographic  aspect,  and  to  prepare  ac- 
cordingly the  tectonic  maps  that  accompany  this  book. 

Geosyncline 
According  to  Kay  ( 1951 ) : 

The  term  geosyncline  should  be  restricted  to  a  surface  of  regional  extent  sub- 
siding through  a  long  time  while  contained  sedimentary  and  volcanic  rocks  are 
accumulating;  great  thickness  of  these  rocks  is  almost  invariably  the  evidence 
of  subsidence,  but  not  a  necessary  requisite.  Geosynclines  are  prevalently 
linear,  but  non-linear  depressions  can  have  properties  that  are  essentially 
geosynclinal. 

Classifications  of  geosynclines  are  discussed  by  Kay,  who  takes  the 
position  that  all  basins  having  a  thick  sequence  of  sediments  are  one  kind 
or  another  of  geosyncline.  However,  only  two  geosynclinal  terms  will  be 
used  in  this  text,  namely,  miogeosyncline  and  eugeosyncline,  which  are 
the  large  linear  basins  along  the  margins  of  North  America. 

Miogeosyncline 

A  miogeosyncline  is  part  of  the  great  linear  border  geosyncline.  It  lies 
between  the  shelf  regions  of  the  stable  interior  of  the  continent  and  the 
outer  part  of  the  geosyncline.  Its  sediments  are  dominantly  sandstone, 
shale,  chert,  limestone,  and  dolomite,  almost  free  of  volcanic  rock. 

Eugeosyncline 

An  eugeosyncline  is  the  outer  part  of  the  border  geosyncline  and  is 
characterized  by  an  abundance  of  volcanic  rock.  In  addition  there  is  much 
graywacke,  arkose,  dark  shale,  and  chert.  The  strata  are  generally  altered 
by  low-grade  metamorphism. 

Landmass 

Landmass  has  no  specific  structural  meaning  unless  used  locally  as  in 
the  Ancestral  Rockies  of  New  Mexico,  for  instance,  where  an  ancient 
range  is  referred  to  as  the  Pedernal  Landmass.  The  term  usually  con- 


notes a  land  area  whose  elevation,  climate,  and  life  are  the  special  object 
of  study  through  the  intermediary  of  the  sediments  derived  from  it,  or 
whose  changing  shore  fines  form  the  basis  of  some  paleogeographic  study. 
The  term  does  not  usually  imply  size,  relief,  or  origin,  and  no  specific 
attributes  will  be  affixed  to  it  in  this  book. 

Highland 

In  Colorado,  two  principal  uplifts  dominated  the  structural  evolution 
of  the  area  in  late  Paleozoic  time,  and  they  have  been  referred  to  by 
most  writers  as  highlands.  They  are  about  50  miles  wide  and  200  miles 
long  and  structurally  were  rather  abrupt,  asymmetrical  anticlines  which 
may  have  been  faulted  in  part  along  their  steep  flanks.  Except  in  appli- 
cation to  the  Colorado  uplifts,  the  term  is  used  very  broadly  in  the  United 
States,  and  no  one  to  my  knowledge  has  attempted  to  define  it;  nor  is  it 
necessary  here  to  do  so.  It  does  not  seem  consistent,  however,  to  say  a 
certain  highland  was  a  Zotu-lying  area,  but  the  statement  may  appro- 
priately be  made  of  a  landmass. 

Ridge 

The  buried  Nemaha  uplift  of  Oklahoma,  Kansas,  and  Nebraska  is  gen- 
erally spoken  of  as  the  Nemaha  Mountains,  but  the  term  Nemaha  ridge 
has  also  been  used,  with  the  implication  that  ridge  has  a  certain  structural 
significance.  The  use  is  almost  unique  to  this  area,  as  far  as  I  know.  A 
ridge,  topographically,  is  generally  less  than  5  miles  long,  and  its  use 
structurally  for  the  Nemaha  Mountains,  200  miles  long,  is  somewhat  mis- 
leading. It  is  not  necessary  to  use  the  term  in  the  present  review. 

The  term  is  used  in  oceanography  to  depict  very  large  linear  relief 
features  on  the  ocean  floor,  such  as  the  Mid-Atlantic  Ridge  (also  Rise) 
or  the  Beata  Ridge  in  the  Caribbean  Sea. 

Geanticline 

The  term  geanticline  was  proposed  by  Dana  in  1873  ( Schuchert,  1923 ) 
for  "the  upward  bendings  in  the  oscillations  of  the  earth's  crust — the 
geanticlinal  waves  or  anticlinoria."  According  to  Schuchert,  Dana's  typi- 
cal example  was  the  Cincinnati  arch,  though  later  on,  Dana  also  included 


STRUCTURAL  TERMINOLOGY 


far  greater,  even  continental  arching.  Schuchert  generally  recognized 
geanticlines  and  geosynclines  as  "complementary  structures,"  but  called 
the  land  that  divided  the  Cordilleran  geosyncline  during  Mesozoic  time 
into  an  eastern  geosyncline  and  a  western,  the  greatest  of  North  American 
geanticlines. 

Although  Schuchert  attempted  to  clarify  Dana's  most  confused  defini- 
tion, he  introduced  contradictory  thoughts,  and  therefore  did  not  clarify 
the  meaning  of  the  term.  Others  have  confused  the  meaning  still  more. 
According  to  Willis  ( 1934 ) ,  "a  geanticline  is  a  very  large  elevation  of  the 
earth's  surface.  The  rocks  of  the  geanticline  may  not  be  folded — may  not 
even  be  stratified — and  the  anticlinal  significance  is  lost."  Lahee  ( 1941 ) 
states  that  a  "geanticline  is  a  very  extensive  uplift,  generally  anticlinal  in 
nature  (also  called  a  regional  anticline)."  He  gives  as  examples  the  "Ar- 
buckle  Mountain  Uplift  and  the  Central  Mineral  Region  of  Texas,"  which 
are  two  greatly  different  kinds  of  tectonic  elements.  According  to  Nevin 
( 1942 )  a  geanticline  is  a  "great  upwarp  .  .  .  whose  dimensions  are  meas- 
ured in  hundreds  of  miles.  .  .  .  The  Ozark  Mountains  and  the  Arbuckle 
Uplift  are  true  geanticlines."  These,  again,  are  dissimilar  structures.  Bill- 
ings (1942)  defines  a  geanticline  as  "the  counterpart  of  a  geosyncline,  (it) 
is  an  area  from  which  the  sediments  are  derived.  The  geanticline  that  lay 
southeast  of  the  Appalachian  geosyncline  is  known  as  Appalachia."  In 
the  Dictionary  of  Geologic  Terms  (Rice,  1940)  a  geanticline  is  "a 
large,  broad,  and  usually  very  gentle  anticline,  commonly  many  miles  in 
width." 

Most  of  these  definitions  are  widely  divergent,  and  the  examples  are 
structures  of  contrasting  size,  composition,  history,  and  relation  to  the 
central  stable  interior  of  the  continent.  Some  of  the  definitions  are  synony- 
mous with  terms  already  defined,  such  as  arch,  dome,  and  landmass. 

The  confusion  in  American  literature  is  paralleled  by  the  European. 
Brouwer  (1925)  of  Holland  says  that  a  geanticline  is  a  major  uplift  of 
island  arc  size,  complementary  to  the  geosyncline.  Collet  ( 1927 ) ,  follow- 
ing Argand  (1916),  defines  a  geanticline  as  an  anticlinal  ridge  that  ap- 
pears on  the  bottom  of  a  geosyncline  and  expresses  itself  as  a  land  barrier 
between  the  seas  of  the  geosyncline.  It  is  at  first  a  long,  narrow  anticline 
of  considerable  size  and  later  evolves  into  a  great  nappe.  Whether  the  de- 


velopment of  a  nappe  is  necessary  to  demonstrate  a  true  geanticline  in  not 
stated  or  implied.  Most  Alpine  geologists,  it  is  my  impression,  follow  tin- 
usage  of  Collet. 

King  (1937)  exemplifies  the  Alpine  usage  in  his  treatise  of  die  evolu- 
tion of  the  Marathon  system.  A  structure  in  west-central  Nevada  tint 
rose  out  of  the  Paleozoic  Cordilleran  geosyncline  is  i  ailed  a  geantu  line  In 
Nolan  (1928).  I  have  decided  to  follow  the  specific  usage  of  Collet,  King, 
and  Nolan  and  will  denote  a  geanticline  as  a  large,  elongate,  anticlinal 
fold  that  develops  in  the  sediments  of  a  geosyncline.  It  is  not  a  'geanticline 
if  an  uplift  in  the  foreland  or  shelf  area.  Two  or  more  geanticlines  ma) 
develop  at  the  same  time  or  following  each  other  in  a  great  geos\  ncline. 
After  the  early  anticlinal  uplift,  the  great  fold  usually  becomes  a  complex 
anticlinorium,  several  imbricate  thrust  sheets,  or  a  nappe.  It  may  be 
largely  submarine,  and  suffer  little  erosion. 

Range 

The  synonymous  use  of  the  terms  highland,  landmass,  mountains,  up- 
lift, arch,  and  geanticline,  all  to  describe  uplifts  of  the  Ancestral  Rockies 
and  Wichita  systems  with  fairly  similar  size  and  shape,  poses  a  difficult 
problem,  especially  because  of  the  provincial  nature  of  the  usage.  It  is  so 
commonplace  to  say  Electra  arch  and  Uncompahgre  highland  that  a 
change  of  name  of  one  or  both  is  not  easily  accepted  by  all.  For  the  sake 
of  the  student  who  is  trying  to  get  an  understanding  of  the  rather  com- 
plex, regional,  structural  relations  of  the  continent,  uniformity  of  meaning 
is  desirable.  Many  geologists  long  since  out  of  school  recognize  the  need. 
It  is  a  matter  of  clear  composition. 

Nearly  all  the  structural  features  to  which  the  names  highland,  land- 
mass,  uplift,  arch,  and  geanticline  in  the  Ancestral  Rockies  and  Wichita 
systems  have  been  attached  are  the  size  of  a  range  like  the  Bighorn,  the 
Uinta,  or  the  Selkirk  ranges.  It  seems,  therefore,  that  the  word  range 
would  be  very  expressive  of  the  sharp  and  linear,  now  buried  or  nearly 
buried,  late  Paleozoic  uplifts  of  the  interior  part  of  the  United  States. 

Geographers  have  agreed  on  the  usage  of  range  and  mountain  svstem 
as  follows:  A  range  is  a  mountain  mass  within  limits  the  size  of  the  Big- 
horns or  the  Selkirks,  and  a  number  of  these  ranges  with  certain  unifying 


s 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


features  in  the  region  constitute  a  mountain  system.  In  working  over 
the  structural  features  of  North  America  I  find  that  the  divisions  of  the 
major  structural  provinces  can  fittingly  be  called  ranges  and  that  many  of 
the  major  provinces  themselves,  systems.  Range,  therefore,  will  be  used 
to  denote  a  sharp  uplift  about  10  to  75  miles  wide  and  50  to  200  miles 
long.  Commonly  the  structure  is  an  asymmetrical  anticline.  In  some,  the 
steep  flank  has  broken  into  a  high-angle  fault  or  a  thrust.  Others  may 
consist  of  several  folds  or  even  thrust  slices.  Probably  all  ranges  that  were 
eventually  buried  suffered  considerable  erosion  beforehand. 

Platform  and  Shelf 

The  terms  platform  and  shelf  in  a  structural  sense  are  logically  used 
by  King  ( 1942a )  in  the  Permian  area  of  west  Texas  and  southeastern  New 
Mexico.  There  previously  existing  range-sized  uplifts  were  buried,  and 
as  sediments  continued  to  accumulate,  the  adjacent  basins  were  depressed 
more  than  the  old  uplifts,  so  that  although  sediments  accumulated  on 
the  uplifts  themselves,  broad  anticlinal  structures  developed  over  them. 
These  are  called  platforms.  Beyond  the  basins,  shallow  seas  existed,  but 
the  crust  subsided  much  more  slowly  there  than  in  the  basins,  and  a 
much  thinner  deposit  of  sediment  accumulated.  These  are  called  shelves. 
A  platform  is  similar  to  a  shelf  in  regard  to  thickness  of  sediments  on  it, 
but  much  more  restricted  in  size  and  bounded  on  the  two  sides  by  ba- 
sins. This  is  the  sense  in  which  the  terms  will  be  used  in  the  following 
pages. 

Welt  and  Furrow 

Bucher  (1933)  defines  welt  and  furrow  as  crustal  elevations  and  de- 
pressions that  show  a  distinct  linear  development.  No  special  size  or 
origin  is  implied.  A  welt  may  be  as  large  as  a  great  deformed  geosyncline; 
viz.,  note  Bucher's  reference  to  Hobbs's  phrase,  "the  gigantic  welt  of  the 
Himalayas."  In  Bucher's  analysis  of  the  deformation  of  the  crust  on  a 
world-wide  scale,  he  needed  these  noncommittal  terms,  but  in  the  present 
attempt  to  picture  the  structural  evolution  of  the  North  American  conti- 
nent, the  names  do  not  seem  necessary,  and  they  will  not  be  used. 


Hinterland  and  Foreland 

Hinterland  and  foreland  are  terms  introduced  by  the  European  ge- 
ologists to  distinguish  the  landmass  or  resistant  elements  of  the  earth's 
crust  on  either  side  of  an  orogenic  belt.  In  the  Alps  great,  intricately 
folded  masses  of  sediments  of  the  geosyncline,  plus  injected  rock,  moved 
northward  many  miles.  The  north  stable  land  toward  which  they  were 
moved  is  called  the  foreland,  and  the  landmass  south  of  the  geosyncline 
is  called  the  hinterland.  In  the  main,  the  great  thrust  sheets  of  the  Ap- 
palachian and  Rocky  Mountain  orogenic  belt  have  overridden  toward  the 
interior  stable  part  of  the  continent,  and  this  ( at  least  the  parts  adjacent 
to  the  orogenic  belts)  has  generally  been  called  the  foreland.  The  land- 
masses  or  borderlands  on  the  oceanward  side  have  been  referred  to  as  the 
hinterlands.  It  is  apparent  that  confusion  must  arise  in  the  use  of  the 
terms  when  some  thrust  sheets  have  overridden  toward  the  oceans  and 
when,  perhaps,  no  great,  stable  borderland  existed.  Some  geologists  also 
contended  that  outward  from  the  continent  is  the  foreland.  As  for  usage 
in  this  book,  foreland  will  mean  the  part  of  the  stable  interior  adjacent  to 
a  marginal  orogenic  belt,  and  lands  oceanward  of  a  marginal  trough  of 
sedimentation,  created  by  previous  orogeny  and  from  which  sediments 
were  derived  will  be  called  the  hinterland. 


TERMS  FOR  STRUCTURAL  DISTURBANCES 

Revolution  and  Synonyms 

The  term  revolution  is  deeply  intrenched  in  geologic  literature,  al- 
though a  number  of  authors,  both  here  and  abroad,  have  avoided  its  use, 
and  one  has  recommended  its  abandonment  (Spieker,  1946). 

Schuchert's  (1924)  definition  of  a  revolution  is  more  complete  than  any 
found,  and  characterizes  many  usages  of  the  term. 

Near  the  close  of  the  eras  .  .  .  occur  the  most  extensive  times  of  mountain 
making,  .  .  .  These  times  of  major  diastrophism  are  the  critical  periods  or 
revolutions  in  the  history  of  the  earth,  and  they  divide,  as  it  were,  the  book 
of  geologic  time  into  chapters.  The  critical  periods  are  marked  by  the  fol- 
lowing features: 


STRUCTURAL  TERMINOLOGY 


1.  By  wide-spread  deformation  of  the  earth's  crust,  transmitted  from  place 
to  place.  This  leads  to  the  elevation  of  many  and  widely  separated  mountain 
ranges,  .  .  .  Each  revolution  ...  is  named  after  one  of  the  prominent  moun- 
tain ranges  formed  at  the  time  designated,  for  example,  Laramide  and  Ap- 
palachian revolutions. 

2.  By  wide-spread  changes  in  the  physical  geography  .  .  . 

3.  By  marked  and  wide-spread  destruction  of  the  previously  dominant, 
prosperous,  and  highly  specialized  organic  types. 

4.  By  marked  evolution  of  new,  dominant,  organic  types  out  of  the  small- 
sized  and  less  specialized  stocks,  and  by  the  development  of  hordes  of  new 
species. 

With  revolutions  reserved  to  close  eras,  Schuchert  used  the  term  dis- 
turbance to  terminate  periods.  Thus  the  crustal  movements  at  the  close  of 
the  Devonian  period  in  New  England  and  Acadia  would  be  called  the 
Acadian  ( Schickshockian )  disturbance. 

In  light  of  recent  research,  certain  disturbances  are  known  to  have  oc- 
curred within  periods,  and  three  (Taconic,  Acadian,  Nevadan)  are  equal 
or  exceed  in  size  and  certainly  exceed  in  intensity  the  Appalachian  (as 
orthodoxly  known)  and  the  Laramide  revolutions.  In  the  Alps,  the  di- 
astrophic  history  is  followed  from  the  middle  Carboniferous  to  the  close 
of  the  Oligocene,  and  it  seems  difficult  to  apply  the  term  revolution  in 
Schuchert's  sense.  The  great  paroxysms  in  which  the  nappes  were  formed 
occurred  in  middle  Oligocene  time,  and  to  these  and  all  other  deforma- 
tions of  early  Tertiary  time,  Argand  ( 1916)  applies  the  name  Alpine  cycle. 
Thus  he  speaks  as  follows:  "The  regime  of  deformation  of  Asia  during 
the  Alpine  cycle,  .  .  .  etc."  (1922).  He  refers  to  the  Hercynian  cycle 
and  the  Caledonian  cycle,  apparently  in  the  same  general  way  as  others 
do  with  the  words  orogeny,  revolution,  disturbance,  and  phase. 

Rucher  ( 1933)  adapts  the  term  revolution  to  his  own  nomenclature  and 
theory  by  the  following:  ".  .  .  the  juxtaposition  of  the  high  welt  and  the 
deep  sediment-filled  furrow  leads  to  the  violent  deformation  traditionally 
known  as  'revolutions.' " 

Refore  deciding  what  terms  or  classification  to  use  in  this  book,  a  few 
other  words  need  to  be  discussed.  The  terms  orogeny  and  epeirogeny, 
according  to  Gilbert  (1890)  are  processes  of  deformation.  He  defined 
orogeny  as  the  process  of  mountain  building,  and  epeirogeny  as  the 
process  of  continental  displacement  to  form  the  large  swells  and  basins. 


The  two  processes  collectively  he  called  diastrophism.  Orogenic  struc- 
tures, according  to  Stille  (1924)  are  visible  to  the  eye,  such  is  faults 
folds,  and  thrusts;  whereas  epeirogenic  structures  arc  so  gentle  thai  dips 
are  scarcely  noticeable,  and  are  due  to  broad  warping.  The  usage  in 
America  today  is  fairly  uniform  in  the  respect  that  orogenic  movement  is 
of  the  nature  of  folding,  thrusting,  and  block  faulting  or  rifting  and  for 
the  most  part  takes  place  in  the  geosynclinal  belts.  Epeirogenic  move- 
ment is  vertical,  of  gentle  nature,  and  affects  regional  parts  of  the  trust. 
The  arches,  domes,  and  large  basins  of  the  central  stable  region  of  the 
continent  are  examples  of  epeirogenic  movements,  and  the  interruption  of 
cycles  of  erosion  in  the  deformed  geosynclinal  belts  by  elevation  is  an  ex- 
ample of  epeirogenic  movements  in  the  marginal  and  older  orogenic  belts. 
It  is  in  this  sense  that  the  terms  will  be  used  in  this  book. 

A  point  that  is  confusing  is  the  interchangeable  use  in  our  literature  of 
orogeny  and  revolution.  It  would  seem  from  Gilbert's  early  usage  that 
orogeny  is  a  process,  and  to  say  Appalacliian  orogeny  would  be  to  focus 
attention  on  the  processes  of  deformation  in  the  geosyncline — to  em- 
phasize the  mechanical  relations.  On  the  other  hand,  to  say  Appalachian 
revolution  would  be  to  broaden  one's  vista  structurallv  to  the  events  in 
the  hinterland  and  the  foreland  as  well  as  in  the  geosyncline,  and  to  in- 
clude the  climates  and  changes  in  the  organic  world.  Current  usage  of  the 
term  orogeny  is  also  often  synonymous  simply  with  crustal  disturbance. 
Angular  unconformities  and  coarse,  thick,  basal  conglomerates  are  com- 
monly the  evidence  of  orogenies,  and  the  orogenies  are  given  names  such 
as  the  Diablan,  Santa  Lucian,  and  early  Laramide.  Refore  deciding  on 
definite  usages  of  the  terms,  it  is  best  to  consider  their  time  and  geo- 
graphic limits. 

Phase 

The  term  phase  has  been  used  structurally  as  well  as  stratigraphicallv. 
In  nearly  all  structural  uses  it  is  a  division,  either  spatial  or  time,  of  a 
revolution.  For  instance,  Argand  (1922)  in  explaining  his  tectonic  map  of 
Asia  says,  ".  .  .  we  have  concluded  .  .  .  that  a  classification  of  the  ele- 
ments (shows)  only  the  age  of  the  principal  folding  .  .  .  neglecting  the 
phases  but  retaining  the  orogenic  cycles."  And  again.  ".  .  .  all  the  pli 


10 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


of  all  the  orogenic  cycles  that  have  affected  each  part  of  the  country,  etc." 
Collet  (1927)  uses  the  word  phase  as  a  tectonic  unit  of  the  Middle 
Oligocene  orogenic  paroxysms  of  the  Alps,  viz.,  the  St.  Bernard  phase,  the 
Dent  Blanc  phase,  the  Monte  Rosa  phase,  the  phase  of  Adriatic  sub- 
sidence, and  the  phase  Insurbrienne.  This  usage  emphasizes  the  mass  and 
spatial  aspect  because  all  the  nappes  mentioned  evolved  within  a  short 
time — a  succession  of  events  is  not  implied.  On  the  other  hand,  van 
Waterschoot  van  der  Gracht  ( 1931 )  uses  the  term  more  in  a  time  aspect 
in  describing  the  structural  relations  in  the  Mid-Continent  area,  for  he 
designates  the  successive  episodes  of  disturbance  as  the  early  Wichita 
phase,  the  late  Wichita  phase  (early  Pennsylvanian ) ,  and  the  Arbuckle 
phase  (late  Pennsylvanian). 

Others  terms  such  as  epoch,  stage,  and  impulse,  have  been  used  but  to 
a  lesser  extent  than  phase. 

CLASSIFICATION  USED  FOR  CRUSTAL  DISTURBANCES 

Revolution 

If  revolutions  are  chapters  of  diastrophism  in  earth  history,  it  is  clear 
that  they  have  both  time  and  spatial  aspects.  To  say  they  terminate  the 
great  eras  of  time  reflects  the  state  of  advancement  of  the  science  45 
year  ago.  Most  of  the  time  divisions  were  originally  set  apart  by  uncon- 
formities, and  early  became  more  or  less  fixed  by  the  fossil  content  of 
formations  between  the  unconformities  at  the  type  localities.  Since  then, 
evidence  of  many  new  and  important  disturbances  has  been  discovered 
within  the  periods  and  eras  thus  set  apart.  Crustal  deformation  has  come 
to  be  known  not  as  a  repetition  of  pulsations  that  occurred  precisely  at 
the  close  of  periods  and  eras,  but  as  developmental  sequences  of  deforma- 
tional  events  which  frequently  occurred  over  protracted  periods  of  time 
with  shifting  scenes  of  activity. 

A  revolution  will  be  considered  to  encompass  the  deformational  events 
of  the  hinterland,  the  geosyncline,  and  the  foreland,  and  to  include  both 
orogenic  and  epeirogenic  processes.  Setting  time  limits  is  an  arbitrary  pro- 
cedure, and  in  doing  so  one  must  be  mindful  of  usage  which  will  help 
determine  the  best  limits  of  the  revolution  in  question. 


System 

The  major  structural  divisions  of  revolutions  will  be  called  systems.  A 
system  is  thus  primarily  a  spatial  division  and  is  determined  by  a  unity 
of  the  structural  features  in  it,  such  as  the  folds  and  thrusts  of  a  geo- 
syncline in  contrast  to  the  basins,  shelves,  and  arches  of  the  foreland,  or 
by  isolation  of  a  somewhat  similar  structural  assemblage  from  another 
by  younger  overlapping  deposits,  such  as  separate  the  Ouachita  Moun- 
tains from  the  Marathon  Mountains. 

As  far  as  noted,  systems  have  been  named  after  the  outstanding  range 
or  geographic  feature  in  the  division.  This  precedent  will  be  followed 
structurally  where  possible,  but  some  exceptions  seem  necessary.  For 
instance,  in  organizing  the  structures  of  the  central  stable  region  of  the 
United  States  the  area  proved  so  large  that  no  one  geographic  name 
seemed  suitable  for  the  greatest  arch,  so  its  outstanding  structural  char- 
acter was  used,  namely,  the  Transcontinental  Arch. 

Phase 

Each  system  has  its  developmental  history,  and  the  structural  events 
of  this  history  will  be  called  phases.  Although  the  types  and  extent  of  the 
structures  developed  will  be  considered  part  of  the  phase,  emphasis  is 
laid  on  the  time  aspect.  It  may  be  necessary  to  consider  as  phases  two 
contemporaneously  evolving  parts  of  a  system,  but  in  organizing  structural 
elements  of  the  continent  I  have  not  run  into  this  difficulty. 

In  the  Alps,  the  phases  have  been  given  geographic  names,  and  the 
practice  was  followed  in  this  country  by  Van  der  Gracht  (1931),  who 
discussed  the  Wichita  and  Arbuckle  phases  of  the  Wichita  system.  Since 
in  this  book  the  emphasis  will  be  placed  on  time,  I  have  concluded  that 
time  names  will  be  most  meaningful.  For  instance,  if  it  is  written,  the 
early  Pennsylvanian  phase  of  the  Ancestral  Rockies  system,  the  student 
cannot  miss  the  intended  meaning;  but  if  the  Wichita  phase  of  the  An- 
cestral Rockies  appears,  the  student  may  be  confused  if  he  has  not  read 
the  chapter  on  the  Wichita  system. 

Time  names  can  be  inappropriate  only  where  the  time  of  the  disturb- 
ance is  not  accurately  known  and  future  research  shows  the  designation 


STRUCTURAL  TERMINOLOGY 


11 


wrong.  A  geographic  name  avoids  this  difficulty,  it  is  true,  but  for  the 
most  part  stratigraphy  has  advanced  to  the  point,  in  the  United  States  at 
least,  that  the  times  of  the  deformation  are  fairly  accurately  known  and 
not  likely  to  be  changed  much  in  the  future.  The  advantage  to  the  student 
weighs  so  heavily  against  the  possible  chance  of  error  that  time  names  for 
the  phases  will  be  used. 

Most  of  the  chapters  deal  with  systems  and  their  phases.  Such  organiza- 
tion seems  adequate  to  explain  the  structural  evolution  of  the  continent. 
Originally  it  was  planned  to  organize  the  book  according  to  revolutions, 
but  setting  limits  led  to  many  difficulties,  and  the  idea  was  abandoned. 
As  a  result,  the  concept  of  revolution  is  not  emphasized. 

Orogeny 

With  the  decision  reached  to  divide  the  great  deformational  belts  into 
mountain  systems,  and  to  treat  the  several  episodes  of  deformation  of  each 


system  as  phases,  the  proper  usage  of  the  term  orogeny  teemed  d- 
each  phase  is  an  orogeny.  Thus  we  speak  of  the  "I. .it.-  (  retaceoui  and 
Early  Tertiary  Rocky  Mountain  systems,"  and  for  one  ol   th< 
the  Central  Rockies,  we  note  its  episodes  of  deformation,  namely,  the 
Montana  phase,  the  Paleocene  phase,  and  the  Eocene  phase.  These  pb 
are  commonly  the  orogenies,  which   respectively  would   be   the  earl) 
Laramide  orogeny,  middle  Laramide  orogeny,  and  late  1  •aramide  OXOgi 
See  table  of  contents   for   the  various   orogenies    recognized    in    North 
America. 

An  orogeny  should  be  given  a  geographic  name,  like  a  formation,  and 
if  the  time  of  deformation  is  found  to  be  earlier  or  later  than  previously 
recognized  on  the  basis  of  later  research,  then  the  name  remains  the  same, 
but  a  somewhat  different  age  is  assigned  it. 

An  orogeny  should  not  be  limited  to  a  phase  of  folding  and  thrusting, 
but  should  include  all  forms  of  diastrophism,  according  to  Billings  ( 1960). 


3. 


RESUME  OF  STRUCTURAL 
GEOLOGY  OF  NORTH  AMERICA 


MAJOR  TECTONIC  DIVISIONS 

Canadian  Shield 

The  Canadian  Shield  has  been  the  great  stable  portion  of  the  North 
American  continent  since  Proterozoic  time.  It  consists  of  Precambrian 
rock  except  along  the  southern  margin  of  Hudson  Bay,  where  Ordovician, 
Silurian,  and  Devonian  strata,  about  1000  feet  thick,  occur  and  probably 
continue  northward  under  much  of  the  bay.  Small  outliers  of  Paleozoic 
strata,  fossil  affinities,  and  the  absence  of  shore  facies  in  many  places 
indicate  that  the  Paleozoic  formations  were  once  much  more  widespread 


over  the  shield  than  now,  and  that  they  have  been  stripped  off  by  a  long 
interval  of  erosion  during  the  Mesozoic  and  Cenozoic  eras. 
Hudson  Bay  is  an  epeiric  sea  of  fairly  modern  time. 

Central  Stable  Region 

The  Central  Stable  Begion  consists  of  a  foundation  of  Precambrian 
crystalline  rock,  which  is  a  continuation  of  the  Canadian  Shield  south- 
ward and  westward,  and  a  veneer  of  sedimentary  rock.  The  veneer  varies 
greatly  in  thickness  from  place  to  place,  and  several  broad  basins,  arches, 
and  domes  are  present.  A  number  of  unconformities  attest  the  rise  of 
the  arches  and  their  erosion,  and  of  great  transgressions  and  overlaps. 
For  the  most  part  the  strata  have  only  gentle  dips,  and  aside  from  the 
slow  and  prolonged  vertical  movements  that  created  the  basins,  arches, 
and  domes,  the  geologic  province  properly  deserves  the  name,  the  Central 
Stable  Begion.  It  and  the  Canadian  Shield  compose  the  great  stable  in- 
terior of  the  continent. 

The  arches  and  basins  developed  chiefly  in  the  Paleozoic  era,  but  later, 
during  the  Mesozoic  and  Tertiary,  vast  amounts  of  clastic  sediments  from 
the  evolving  Cordilleran  mountain  systems  were  spread  eastward  over 
the  Paleozoic  strata  beyond  the  Missouri  Biver  as  far  as  Lake  Superior. 

In  the  southwestern  corner  of  the  Central  Stable  Begion  a  system  of 
ranges  was  elevated  in  Pennsylvanian  time,  and  then  during  the  late 
Pennsylvanian,  Permian,  and  Mesozoic  it  was  largely  buried.  The  ranges 
are  known  as  the  Ancestral  Bockies  in  Colorado  and  New  Mexico,  and 
as  the  Wichita  Mountain  system  in  Kansas,  Oklahoma,  and  Texas.  The 
Late  Cretaceous  and  Early  Tertiary  Laramide  structures  were  partly 
superposed  on  the  Ancestral  Bockies  in  Colorado  and  New  Mexico. 

Orogenic  Belts  of  the  Atlantic  Margin 

The  Paleozoic  orogenic  belts  bound  effectively  the  southern,  as  well  as 
the  eastern,  margin  of  the  continent.  The  major  belt  is  known  as  the 
Appalachian,  and  it  consists  of  an  inner  folded  and  thrust-faulted  division 
from  Alabama  to  New  York,  and  a  metamorphosed  and  intruded  division 
from  Alabama  to  Newfoundland.  One  major  orogeny  occurred  in  the 


12 


RESUME  OF  STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


I  . 


inner  belt,  and  this  in  late  Paleozoic  time.  Several  orogenies  beset  the 
outer  belt:  the  earliest  one  of  significance  occurred  at  the  close  of  the 
Ordovician,  the  major  one  during  the  Late  Devonian  and  the  last  one  in 
Pennsylvanian  and  Permian  time.  The  Carboniferous  orogenic  belt  in 
the  outer  crystalline  division  is  recognized  on  the  north  along  the  eastern 
margin  of  New  England,  the  Maritime  Provinces,  and  Newfoundland. 

Volcanic  rocks  and  great  batholiths  are  important  components  of  the 
crystalline  division  of  the  Appalachian  orogenic  belt,  but  the  inner  folded 
and  thrust-faulted  belt  is  comparatively  free  of  them.  Roth  divisions  are 
made  up  of  very  thick  sedimentary  sequences  which  are  characterized 
as  geosynclinal,  in  contrast  to  generally  thinner  sequences  in  the  Central 
Stable  Region. 

The  orogenic  belt  bordering  the  southern  margin  of  the  stable  interior 
is  mostly  concealed  by  overlapping  coastal  plain  deposits.  Where  exposed, 
as  in  the  Ouachita  Mountains  of  Arkansas  and  eastern  Oklahoma,  the 
Arbuckle  Mountains  of  south  central  Oklahoma,  and  the  Marathon  Moun- 
tains of  western  Texas,  it  is  a  folded  and  thrust-faulted  complex,  some- 
what similar  to  the  inner  Appalachian  division.  The  crystalline  division, 
if  it  parallels  the  inner  noncrystalline  division,  is  nowhere  exposed,  but 
deep  wells  through  the  coastal  plain  deposits  have  penetrated  low-grade 
metamorphic  rocks. 

Orogenic  Belts  of  the  Pacific  Margin 

The  great  complex  of  orogenic  belts  along  the  Pacific  margin  of  the 
continent  has  evolved  through  a  very  long  time.  The  oldest  strata  recog- 
nized from  their  fossils  are  Ordovician,  and  deformed  strata  of  Pleistocene 
age  mark  the  belt  in  places  from  Mexico  to  Alaska.  In  Paleozoic  time,  the 
Pacific  margin  of  the  continent  was  a  volcanic  archipelago  in  outward 
appearance  and  internally  a  belt  of  deformation  and  intrusion.  The 
Permian,  Triassic,  and  Early  and  Middle  Jurassic  were  times  of  excessive 
volcanism,  and  represent  a  continuation  of  essentially  the  same  Paleozoic 
conditions  well  into  the  Mesozoic.  In  Late  Jurassic  and  early  Late 
Cretaceous  time,  intense  folding  and  batholithic  intrusions  (Nevadan 
orogeny)   occurred  which  are  now  characteristic  of  large  parts  of  the 


Coast  Range  of  British  Columbia,  the  rangei  along  the  International 
border  in  British  Columbia,  Washington,  and  Idaho,  the  Klamath  Moun- 
tains of  southwestern  Oregon  and  northern  California,  the  Sierra  Nevadi 
of  California,  and  the  Sierra  of  Baja  California.  The  same  Nevadan  ele- 
ments may  also  continue  into  southern  Mexico  and  eastward  through 
Central  America. 

Following  the  orogeny,  in  California  at  least,  a  new  trough  of  accumu- 
lation and  a  new  volcanic  archipelago  formed  outside  the  Nevadan  belt, 
and  a  complex  history  of  deformation  and  sedimentation  tarries  down 
through  the  Cretaceous  and  Tertiary  to  the  present,  to  result  in  the  Coast 
Ranges  of  Washington,  Oregon,  and  California. 

Orogenic  Belts  of  the  Rocky  Mountains 

During  the  complex  and  long  orogenic  history  of  the  Pacific  margin, 
the  adjacent  zone  inward  was  one  of  gentle  subsidence  and  sediment 
accumulation,  comparatively  free  of  volcanic  materials,  during  the 
Paleozoic.  By  Triassic  time,  the  troughs  of  deposition  along  the  Pacific 
had  become  effectively  separated  by  a  medial,  linear  uplift  from  those 
in  the  Rocky  Mountain  area,  and  in  the  Mesozoic  much  coarse  debris 
came  from  the  uplift  or  geanticline  and  filled  the  basins  in  eastern  British 
Columbia,  western  Alberta,  Idaho,  western  Wyoming,  central  Utah,  and 
southern  Nevada.  Orogeny  from  place  to  place  along  the  eastern  margin 
of  the  geanticline  cast  several  floods  of  conglomerate  eastward  during 
the  Cretaceous. 

The  Paleozoic  and  all  the  Mesozoic  sediments  except  the  Upper 
Cretaceous  of  the  Rocky  Mountains  may  be  divided  into  thick  geosyn- 
clinal facies  on  the  west  and  fairly  thin  shelf  facies  on  the  east.  The  line 
dividing  the  two  lies  approximately  along  the  west  side  of  the  Colorado 
Plateau  and  thence  runs  northward  through  western  Wyoming  and 
Montana  to  western  Alberta.  The  shelf  facies  were  part  of  the  Central 
Stable  Region  until  the  Late  Cretaceous  and  Early  Tertiary  ( Laramide ) 
orogeny  in  whose  belts  both  geosynclinal  and  shelf  facies  were  deformed. 
The  western  division  of  the  Laramide  belt  (in  the  miogeosyncline)  is 
characterized  by  folds,  thrusts,  and  numerous  small  stocks.  The  eastern 


14 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Laramide  division  extended  through  the  shelf  region  of  central  and 
eastern  Wyoming,  central  Colorado,  eastern  Utah,  and  central  New 
Mexico,  and  is  characterized  by  large,  elliptical  uplifts. 

The  Laramide  belt  of  orogeny  extends  southward  through  Mexico, 
where  thick  sediments  of  the  Mexican  geosyncline  of  Upper  Jurassic  and 
Cretaceous  age  are  fairly  tightly  folded.  The  same  belt  of  orogeny  is 
believed  to  veer  eastward  through  Central  America. 

Following  well  after  the  Nevadan  and  Laramide  orogenies  of  western 
North  America,  an  episode  of  high-angle  faulting  occurred,  that  created 
the  Great  Basin  physiographic  province  and  gave  sharp  definition  to 
many  of  its  ranges  and  to  those  of  central  and  western  Mexico.  The 
high-angle  faults  were  superposed  on  both  the  Nevadan  and  Laramide 
belts;  most  of  them  are  Late  Tertiary  in  age  and  some  are  still  active.  A 
long  zone  of  the  faults  extends  northward  from  central  Utah  to  British 
Columbia  and  probably  beyond  to  Yukon  Territory  to  form  a  belt  of 
trenches  with  local  relief  of  3000  to  5000  feet.  The  faults  cut  the  older 
folds  and  thrusts  both  discordantly  and  concordantly,  and  the  activating 
forces  appear  deep-seated. 

Coastal  Plains 

Following  the  Appalachian  orogeny  in  Triassic  time,  the  outer  meta- 
morphosed division  was  broken  by  a  belt  of  high-angle  faults  that  has 
been  traced  discontinuously  from  South  Carolina  to  the  Bay  of  Fundy, 
between  New  Brunswick  and  Nova  Scotia.  Long  and  narrow  downfaulted 
basins  trapped  thick  series  of  generally  red  elastics.  The  Triassic  lowland 
of  Maryland,  New  Jersey,  and  Pennsylvania,  and  the  central  lowland  of 
Connecticut  are  the  best  known  of  the  basins. 

The  eastern  extent  or  breadth  of  the  Appalachian  orogenic  system 
and  the  nature  and  condition  of  the  crust  that  lay  east  of  it  are  not 
known,  but  the  continental  margin  had  begun  to  subside,  at  least  by 
Early  Cretaceous  time,  if  not  before.  The  peneplained  surface  on  the 
crystalline  rocks  has  been  traced  eastward  under  a  Cretaceous  and 
Tertiary  sedimentary  cover  to  a  depth  of  10,000  feet,  which  is  near  the 
margin  of  the  present  continental  shelf.  Most  sedimentary  units  of  the 
cover  dip  gently  and  thicken  like  a  wedge  oceanward  as  far  as  they  have 


been  traced  by  deep  drilling  and  by  seismic  traverses.  The  zone  of 
Cretaceous  and  Tertiary  overlap  on  the  older  rocks  of  the  eastern  con- 
tinental margin  is  known  as  the  Atlantic  Coastal  Plain,  but  because  the 
same  sediments  continue  out  beyond  the  present  ephemeral  shore  line, 
the  submerged  part  belongs  to  the  same  province.  Coastal  plain  sedi- 
ments are  known  to  exist  in  Georges  Bank  off  Rhode  Island  and  prob- 
ably make  up  part  of,  or  all,  the  shallow  continental  shelf  to  and 
including  the  Banks  of  Newfoundland. 

The  Gulf  Coastal  Plain  is  continuous  with  the  Atlantic  Coastal  Plain, 
and  counting  its  shallowly  submerged  portions,  it  nearly  encloses  the 
Gulf  of  Mexico.  The  oldest  known  sediments  of  its  marginal  areas  are 
Permian.  The  Mississippi,  Rio  Grande,  and  other  rivers  draining  the 
interior  of  the  continent  have  deposited  a  great  weight  of  sediments  at 
their  mouths  and  the  crust  has  subsided  along  the  Texas,  Louisiana,  and 
Mississippi  coast  to  the  extent  of  25,000  to  30,000  feet. 

Deep  drilling  in  Florida  and  the  Bahamas  indicates  that  the  coastal 
plain  province  extends  southeastward  almost  to  the  orogenic  belt  of 
Cuba  and  Hispaniola. 

Canadian  Arctic 

The  Precambrian  rocks  of  the  Canadian  Shield  are  overlapped  on  the 
north  by  nearly  flat-lying  sedimentary  strata  of  Paleozoic  age.  Basins 
and  arches  are  recognized  in  this  province  as  in  the  Central  Stable 
Region  of  the  United  States.  North  of  the  arches  and  basins  is  a  fold 
belt  developed  in  geosynclinal  sediments.  The  fold  belt  extends  across 
northern  Greenland,  northern  Ellesmere  Island  and  farther  to  the  south- 
west through  other  islands  of  the  Arctic  Archipelago.  Folding  first  oc- 
curred in  pre-Pennsylvanian  time.  After  erosion  a  voluminous  sequence  of 
Pennsylvanian  to  Tertiary  sediments  accumulated,  and  then  these  were 
somewhat  folded  in  Tertiary  time.  A  narrow  Tertiary  coastal  plain  is 
terminated  on  the  north  by  the  Arctic  Ocean  basin. 

Alaska 

Alaska  continues  the  broad  and  complex  western  cordillera  across  to 
Asia,  and  has  had  basically  the  same  history  but  with  variations  and 
singular  details. 


Meaning  of  Colors  on  Tecfonic  Maps 
(Plates  2-15) 

BLUE       Denotes  regions  of  accumulations  of   sediments.   Contours   indicate    thickness   of    sediments   and 
thus,  approximately,   the  amount  of  subsidence.   Thickness  figures   indicate   thousands   of   feet. 

GREEN       Denotes  ocean  basins;  i.e.,  regions  underlain   by  oceanic  crust. 


ORANGE      Denotes  significant  deformation.  Where  sediments   have   been   deformed   during   the   period   in 
which  they  were  deposited  such  has  been  printed  on  the  blue. 


RED  Denotes  belts  of  batholithic  intrusion  and  appreciable  metamorphism  on  all  Plates  except 
1,  14,  and  15.  On  Plate  1  various  intensities  of  red  plus  orange  and  yellow  denote  orogenic 
belts   of   different   ages.    On    Plates    14    and    15,    red    denotes    igneous    rock,    chiefly    volcanic. 

YELLOW      Denotes  regions  of  comparative  stability  of  the  earth's  crust.  It  includes  on  some  maps  regions 
of  broad  and  gentle  uplift  (Plate   1    excepted). 


PLATE     1 
Precambrian  Orogenic  Belts 

Position  of  belts  older  than  the  Beltian  is  determined  principally  by  absolute 
isotope  ages.  A,  P,  and  G  are  dates  of  Algoman,  Penokean,  and  Grenville 
orogenies,  respectively. 


PLATE     2 
Cambrian  Tectonic  Map 

Upper  Cambrian  seas  were  probably  more  widespread  in  the  Transcontinental 
Arch  region  than  shown;  the  strata  have  been  eroded  away  there.  The 
Cambrian  beds  of  eastern  Newfoundland,  although  evidently  in  the  Acadian 
trough,  are  mostly  miogeosynclinal  in  lithology. 


PLATE     3 
Ordovician  Tectonic  Map 

Westward  thrusting  occurred  at  the  close  of  the  Ordovician  in  eastern  New 
York  against  the  Adirondack  dome.  Some  ultrabasic  intrusions  may  have  been 
emplaced  in  the  Maritime  Provinces  and  Newfoundland  at  the  close  of  the 
Ordovician.  W.  A.  Waverly  arch  of  Early  Ordovician  time. 


PLATE     4 
Silurian  Tectonic  Map 

The  Atlantic  Ocean  and  Gulf  of  Mexico  are  left  uncolored  because  accumu- 
lating evidence  suggests  that  North  America  was  once  attached  to  and  part 
of  a  single  great  continent  which  cracked  and  drifted  apart.  The  spreading 
apart  is  presumed  to  have  brought  these  ocean  basins  into  existence,  starting 
in  late  Paleozoic  time. 


PLATE     5 
Devonian  Tectonic  Map 

The  eugeosynclinal  regions  in  Acadian  orogenic  belt  preceded  the  orogeny; 
their  sediments  were  intensely  deformed  and  invaded  by  the  large  batholiths, 
and  hence  are  not  shown  in  blue. 


/^  **. 


^J        v; 


PLATE     6 

Mississippian  Tectonic  Map 

Stanley,  Jack  Fork,  and  Johns  Valley  elastics  of  Ouachita  Mountains  are 
shown  as  a  Mississippian  basin.  They  may  be  in  part  Pennsylvanian.  LS  means 
La  Salle  anticlinal  belt.  It  rose  gently,  was  eroded,  and  buried  before  the 
Mississippian  period  ended.  Orange  here  indicates  areas  of  orogeny,  signifi- 
cant uplift,  or  mountains  of  an  immediately  prior  orogeny.  In  the  Antler 
orogenic  belt  both  sedimentation  and  orogeny  occurred. 


PLATE     7 
Pennsylvania/}  Tectonic  Map 


Uplifts  shown  by  dotted  lines  were  mostly  buried  by  end  of  Pennsylvanian. 
The  Baja  California  block  lay  several  hundred  miles  to  the  southeast.  A, 
Marathon  basin;  B,  Fort  North  basin;  C,  Ouachita  basin;  D,  Southern  Ap- 
palachian basin;  E,  Central  Appalachian  basin;  F,  Diablo  Range;  G,  Pecos 
Range;  H,  Pedernal  Range;  I,  Zuni  uplift;  J,  Circle  Cliffs  uplift;  K,  Emery  up- 
lift; L,  Oquirrh  basin;  M,  Central  Colorado  basin;  N,  Wood  River  basin; 
P,  Ardmore  basin;  T,  Matador  Range;  W,  Amarillo-Wichita  Range. 


PLATE     8 
Permian  Tectonic  Map 

Orange  color  over  the  Marathon,  Ouachita,  and  Appalachian  Mountains  indi- 
cates the  site  of  an  orogenic  belt  and  mountains  of  the  previous  Pennsylvanian 
period.  Uplift  probably  occurred  there  during  the  Permian.  U.R.,  Uncom- 
pahgre  Range;  C.R.,  Colorado  Range;  F,  Florida  uplift;  O.B.,  Oquirrh  basin; 
A.B.,  Anadarko  basin;  C.B.P.,  Central  basin  platform. 


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PLATE     9 

Triassic  Tectonic  Map 

Baja  California  block  lay  several  hundred  miles  to  the  southeast. 


PLATE     10 
Jurassic  Tectonic  Map 

Baja  California  block  lay  several  hundred  miles  to  the  southeast. 


o 


PLATE     11 
Early  Cretaceous  Tectonic  Map 


PLATE     12 

Late  Cretaceous  Tectonic  Map 

Only  Dakota  and  Colorado  deposits  in  Rocky  Mountains  are  represented. 
Montana  time  is  shown  on  Plate  13.  Main  batholiths  of  Nevadan  orogenic 
belt  were  intruded  in  very  early  Late  Cretaceous  time. 


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PLATE     13 
Tectonic  Map  of  the  Cretaceous-Tertiary  Transition 

Thickness  of  latest  Cretaceous  and  Early  Tertiary  deposits  in  Rocky  Mountain 
basins  not  shown.  For  detail  see  Figs.  22.4,  22.5,  and  22.6.  The  crypto- 
volcanic  structure  in  Iowa  is  Late  Cretaceous  or  Early  Tertiary;  the  others  are 
not  dated  but  are  presumed  to  be  of  the  same  age. 


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PLATE     14 
Early  Tertiary  Tectonic  Map 

Laramide  uplifts  and  basins  not  shown  except  for  Green  River  Lake  in  Utah, 
Colorado,  and  Wyoming,  and  Uinta  Range,  although  thick  Eocene  deposits 
accumulated  in  most  of  them.  The  Rocky  Mountain  front  is  a  result  of  previous 
orogeny.  The  volcanics  are  Eocene,  Oligocene,  and  in  places  Miocene  in  age; 
most  Miocene  volcanics,  however,  are  shown  on  Plate  15.  Numerous  volcanic 
cones,  not  shown,  were  built  in  the  eastern  Pacific  and  the  Gulf  of  California. 


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PLATE     15 
Late  Tertiary  and  Quaternary  Tectonic  Map 

Red,  besides  denoting  volcanic  rocks,  shows  laccolithic  clusters  in  the  Colorado 
Plateau.  Numerous  centers  of  volcanism  throughout  the  Basin  and  Range 
province  are  not  shown.  The  blue  color  extends  to  lines  of  maximum  trans- 
gression of  seas  during  the  time  represented  by  the  map.  Hudson  Bay  and 
St.  Lawrence  submergence  pre-dates  the  post-glacial  uplift.  The  submerged 
coastland  of  British  Columbia  has  been  uplifted  600  feet  in  post-glacial  time. 
See  Fig.  31.25  for  regional  vertical  movements  of  the  western  Cordillera  in 
late  Cenozoic  time. 


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RESUME  OF  STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Central  America 

Southern  Mexico,  Guatemala,  Honduras,  El  Salvador,  and  Nicaragua 
contain  a  belt  of  metamorphic  rocks  which  sweeps  from  southwestern 
Mexico  in  an  easterly  direction  to  the  Caribbean  Sea.  A  belt  of  deformed 
Permian  strata  with  Permian  ( ? )  granitic  and  ultrabasic  intrusives  makes 
up  part  of  the  crystalline  complex.  A  fold  belt  of  Jurassic  and  Cretaceous 
strata  borders  the  crystalline  belt  on  the  north. 

The  major  geologic  feature  of  southern  Mexico  and  Central  America 
is  an  extensive  accumulation  of  Tertiary  volcanic  rocks  which  masks 
much  of  the  underlying  older  rocks  mentioned  above.  All  the  Isthmus  of 
Costa  Rica  and  Panama  is  made  up  of  an  igneous  complex,  mostly 
Tertiary,  or  of  sediments  derived  from  the  volcanics. 

Antillean  Region 

The  Greater  Antilles,  composed  of  Cuba,  Hispaniola,  Puerto  Rico,  and 
the  Virgin  Islands,  have  a  late  Mesozoic  and  Ccnozoic  history.  Thick 
limestones  made  up  a  northern  facies  in  Jurassic  and  Cretaceous  times 
and  a  volcanic  assemblage  a  southern  facies.  Folding,  thrusting,  and  in- 
1  trusions  followed.  Tertiary  time  saw  extensive  flooding  and  reuplift  of 
the  islands  but  not  much  deformation  of  the  strata. 

The  Lesser  Antilles  or  Caribbees  are  a  Cenozoic  volcanic  arc  developed 
on  the  oceanic  crust. 

Precambrian  (Plate  1) 

Absolute  age  determinations  on  Precambrian  rocks  are  now  sufficiently 
numerous  so  that  divisions  of  different  ages  are  becoming  defined.  The 
ages  denote  the  time  of  origin  of  the  mineral  of  which  the  analysis  was 
made,  and  this  denotes  the  time  of  an  igneous  intrusion  or  of  an  episode 
of  metamorphism.  In  other  words,  the  ages  appear  to  indicate  belts  of 
orogeny.  They  define  a  continent  made  up  of  a  rather  small  central 
region  of  greatest  age,  and  belts  on  the  northwest  and  southeast  of 
progressively  younger  age.  The  strange  aspect  of  the  belts  older  than 
800  million  years  is  that  they  project  out  to  the  Pacific  Ocean  basin,  as 
if  the  continent  at  this  time  continued  to  the  southwest  farther  than  its 


present    boundary.   The    Beltian   basin   or   geosyncline,   about    S00  million 

years  old,  lies  unconformably  across  the  older  belts,  and  apparently,  for 
the  first  time  marked  a  direction   subparalle]   with   the   existing   mar 

Subsequently,  all  orogenesis  occurred  in  belts  conformable  to  the  present 
margin. 

Cambrian  (Plate  2) 

Cambrian  seas  and  sediments  defined  major  tectonic  divisions  of  the 
continent  which  lasted  until  the  end  of  the  Paleozoic  era.  The  Canadian 
Shield  of  Precambrian  rocks  formed  the  central  and  northeastern  part 
of  the  continent,  and  it  probably  was  a  vast  region  of  low  relief.  By  way 
of  an  extension  to  the  southwest,  the  Transcontinental  Arch,  the  United 
States  was  divided  into  western  and  eastern  seaways,  and  a  svinmetrial 
arrangement  of  shelves,  miogeosynclines,  and  eugeosvnclines  resulted. 
No  Cambrian  strata  are  known  along  the  western  margin  or  the  eastern 
margin  south  of  Maine,  and  the  conditions  in  these  regions  in  Cambrian 
times  are  not  well  known.  The  hypothesis  that  North  America  was  at 
this  time  part  of  a  much  larger  continent,  which  cracked  and  spread 
apart,  seems  to  help  most  in  understanding  the  paleotectonic  elements. 
Southern  Europe,  Africa,  and  South  America  are  postulated  by  some  to 
have  lain  close  together,  and  hence,  it  is  suggested  that  the  Atlantic- 
Ocean  and  Gulf  of  Mexico,  with  associated  coastal  plains  or  continental 
shelves,  did  not  exist  at  this  time. 

Ordovician  (Plate  3) 

The  broad  Williston  basin  became  well-defined  during  the  Ordovician 

and  a  narrow  basin  of  diick  carbonate  sediments  formed  in  Oklahoma. 
and  extended  to  the  shallow  Colorado  sag  nearlv  across  the  Transconti- 
nental Arch.  Extensive  regions  of  the  Canadian  Shield  were  invaded  by 
epeiric  seas.  The  margins  of  the  continent  are  still  problematical.  Flat- 
lying,  unmetamorphosed  strata  in  northern  Florida  south  ot  the  eastern 
orogenic  belt  seem  to  require  continental  connections  where  now  is  the 
Atlantic  Ocean.  The  Taconic  orogeny  of  folding  and  thrusting  occurred 
in  eastern  New  York,  Vermont,  and  southeastern  Quebec. 


16 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Silurian  (Plate  4) 

The  Transcontinental  Arch  became  very  wide  and  well-defined.  The 
Michigan  Basin,  in  which  extensive  deposits  of  salines  accumulated,  and 
one  in  Pennsylvania  and  West  Virginia  took  lasting  form.  The  Ozark 
dome  and  Texas  arch  became  prominent. 

Devonian  (Plate  5) 

During  Devonian  time,  the  Transcontinental  Arch  rose,  but  was  only 
gently  emergent;  and  strata  previously  deposited  across  its  site  were 
removed  by  the  close  of  the  period,  except  for  the  Colorado  sag  where 
100  to  200  feet  of  beds  remained.  In  Canada,  the  great  arch  bifurcated 
into  a  broad  arch  west  of  Hudson  Bay  and  another  one  east  of  Hudson 
Bay,  but  this  condition  probably  did  not  arise  until  the  close  of  the 
Devonian.  During  the  Devonian  the  arches  were  at  least  partly  sub- 
mergent,  because  Manitoba  fossil  faunas  are  very  similar  to  those  of 
Michigan  and  the  Hudson  Bay  region. 

Transverse  arches  also  developed.  The  Ellis-Ozark  uplift  extended 
from  Kansas  around  the  south  end  of  the  Illinois-Indiana-Kentucky  basin 
to  the  Nashville  dome,  and  thence  northward  to  the  Cincinnati  dome. 
The  Illinois-Indiana-Kentucky  basin,  with  the  intervening  Kankakee  arch 
or  area  of  much  less  subsidence  came  into  prominence  for  the  first  time. 

A  basin  of  subsidence  centered  in  Pennsylvania  during  the  Devonian, 
and  sediments  were  supplied  from  the  eastern  Taconic  orogenic  belt 
which  was  being  elevated  adjacent  to  the  basin  and  undergoing  unrest 
premonitory  to  the  Acadian  orogeny.  The  basin  sank  mostly  in  late 
Devonian  time,  and  its  dominantly  clastic  and  subaerial  sediments  coarsen 
toward  the  east.  The  western  and  northern  marine  facies  constitute  the 
classic  Devonian  section  of  the  continent. 

A  Devonian  trough  extended  northward  through  New  England,  the 
Maritime  Provinces,  and  Newfoundland,  in  which  much  volcanic  material 
was  deposited  along  with  various  clastic  sediments.  In  New  England  sedi- 
mentation was  mostly  east  of  the  main  Taconic  belt,  but  in  Quebec  it 
occurred  directly  on  the  eroded  Taconic  structures.  The  entire  region, 
beginning  perhaps  in  mid-Devonian  time  in  places,  gradually  became 


involved  in  the  great  Acadian  orogeny.  The  strata  were  folded,  intruded, 
metamorphosed,  and  thrust-faulted  to  form  a  complex  of  dominantly 
crystalline  rock.  The  Acadian  belt  extended  southward  through  the 
Crystalline  Piedmont  of  the  eastern  United  States,  where  numerous 
large  batholiths  were  emplaced  and  considerable  metamorphism  occurred. 

At  the  close  of  Devonian  time  a  belt  of  orogeny,  the  Antler,  formed  j' 
in  the  central  part  of  the  western  geosyncline.  The  belt  continued  active 
by  way  of  folding  and  thrusting  through  Pennsylvanian,  Permian,  and 
Mesozoic  time  with  a  number  of  phases  of  orogeny  fairly  accurately 
documented.  It  effectively  separated  the  miogeosyncline  on  the  east  from 
the  eugeosyncline  on  the  west. 

Devonian  and  Silurian  strata  have  been  identified  on  the  Pacific  margin 
of  the  continent  in  the  Klamath  Mountains,  and  therefore  it  is  concluded 
that  the  continental  margin  was  then  about  where  it  is  now. 

Mississippian  (Plate  6) 

Mississippian  seas  were  widespread  and  in  the  Rocky  Mountain  region 
a  small  basin  subsided  10,000  feet  along  the  Idaho-Montana  boundary.  A 
long  eastward-extending  basin  sank  through  central  Montana,  and  is 
known  as  the  Big  Snowy.  A  broad  eugeosyncline  of  poorly  known  limits 
extended  through  northern  California,  southern  Oregon,  and  north- 
western Nevada  west  of  the  Antler  orogenic  belt.  The  amount  of  subsid- 
ence is  unknown.  The  Antler  oros;enic  belt  in  central  Nevada  was 
marked  by  major  thrusting  and  complex  folding. 

The  Transcontinental  Arch  sagged  gently  through  its  central  area  and 
was  covered,  but  by  the  close  of  Early  Pennsylvanian  time  it  had  risen 
enough  to  have  suffered  erosion,  and  the  Precambrian  was  again  exposed. 
The  Texas  arch  was  covered  in  central  Texas  and  the  Ozark-Nashville 
arch  was  severed  from  the  Transcontinental  Arch. 

In  latest  Mississippian  or  earliest  Pennsylvanian  time,  a  deep  and  prob- 
ably large  basin  sank  rapidly  in  eastern  Texas,  southern  Oklahoma,  and 
western  Louisiana,  and  received  about  17,000  feet  of  clastic  sediments. 

The  La  Salle  anticlinal  belt  first  began  to  rise  at  the  close  of  the 
Mississippian  and  continued  to  grow  during  the  Pennsylvanian.  It  split 
the  Illinois-Indiana-Kentucky  basin  in  two  parts. 


RESUME  OF  STRUCTURAL  CKOLOCY  OK  NOHTII   AMKHK.\ 


IT 


The  Ozark  uplift  developed  into  a  broad,  continuous  arch  with  the 
Nashville  and  Cincinnati  arches,  and  the  northern  arms  of  the  Cincinnati 
arch,  the  Kankakee  and  Findlay  arches,  became  well  established.  Gentle 
,  erosion  probably  occurred  throughout  this  system  of  arches. 

Subsidence  continued  in  the  Appalachian  trough  area,  and  a  maximum 
of  4000  feet  of  sandstones,  shales,  and  limestones  accumulated. 

In  the  Maritime  Provinces  and  Newfoundland,  a  basin  sank  within  the 
older  Taconic  and  Acadian  orogenic  belts,  and  received  about  5000  feet 
of  clastic  sediments,   presumably   from   a   rising   orogenic   belt   on   the 
i  east. 

Pennsylvanian  (Plate  7) 

3  The  south-central  part  of  the  continent  was  one  of  considerable  and 
widespread  unrest  in  Early  Pennsylvanian  time,  and  a  number  of  ranges 
and  basins  were  formed.  The  Wichita  Mountain  system  of  Oklahoma  and 
northern  Texas  was  uplifted  together  with  the  Ancestral  Rockies  of  New 
Mexico  and  Colorado.  The  Pecos  and  Diablo  ranges  in  west  Texas  ap- 
peared. The  long,  narrow  Nemaha  Range  rose  sharply,  and  at  the  same 

i  time  basins  on  the  east  sank.  The  previously  formed  La  Salle  anticlinal 

,  belt  was  mostly  buried. 

The  trough  of  the  deep  basin  in  eastern  Texas  of  latest  Mississippian 
and  earliest  Pennsylvanian  time  shifted  northward  to  central  Arkansas, 

,  and  over  10,000  feet  of  sediments  accumulated  there. 

The  Arkansas  basin  was  probably  continuous  with  one  in  the  southern 
Appalachians,  where  10,000  feet  of  sediments,  mostly  clastic,  accumu- 
lated. Such  a  thick  and  clastic  deposit  undoubtedly  means  vigorous  uplift 
immediately  on  the  southeast  and  south.  The  area  of  deposition  in  the 
southern  Appalachians  in  Early  Pennsylvanian  time  shifted  to  the 
central  Appalachians  in  Late  Pennsylvanian  time,  and  somewhat  more 
that  3000  feet  of  coal-bearing  strata  were  deposited  there.  Although  de- 
position had  proceeded  at  variable  rates  here  and  there  during  the 
Paleozoic  in  the  southern  and  central  Appalachians,  which  lay  to  the 
west  of  the  Taconic  orogenic  belt,  it  is  generally  stated  that  more  than 

j  30,000  feet  of  sediments  had  accumulated.  In  Late  Pennsylvanian  time 
or  possibly  in  Early  Permian  time,  the  thick  succession  of  strata  from 


Oklahoma  and  Arkansas  to  Pennsylvania  suffered  folding  and  thrusting 

toward  the  continental  interior,  and  the  Ouachita  Mountains  and  (  lassical 
Appalachian  Mountains  (Valley  and  Ridge  Province)  WOt  brought 
into  being. 

The  Marathon  orogeny  of  west  Texas  occurred  in  Late  Pennsylvania!! 
time  and  several  thrust  sheets  moved  northward  toward  the  shelf.  The 
Arbuckle  Mountain  system  was  formed  hy  considerable  folding  and 
thrusting  of  the  sediments  of  the  Ardmore  basin,  and  the  structures 
were  appressed  tightly  against  the  early  Wichita  Range. 

In  New  England,  the  Maritime  Provinces,  and  Newfoundland,  sub- 
sidence followed  somewhat  the  same  pattern  as  that  of  the  Mississippian. 
and  coarse  red  Pennsylvanian  elastics  rest  there  on  the  'laconic  and 
Acadian  complex,  and  also  in  places  in  angular  unconformity  on  the 
Mississippian. 

Extensive  subsidence  occurred  during  the  Pennsylvanian  in  the  Cordil- 
leran  geosyncline  with  the  deposition  of  more  sand  than  in  any  time 
since  the  Cambrian.  A  local  basin  in  west-central  Utah  subsided  greatly 
and  was  filled  in  one  place  with  about  25,000  feet  of  beds.  The  Antler 
orogenic  belt  dominated  the  sedimentary  conditions  east  of  it,  and  coarse 
elastics  were  spread  there.  Allochthonous  masses  were  translated  25  to  75 
miles  eastward. 

The  volcanic  orogenic  archipelago  persisted  along  the  west  margin  of 
the  continent,  and  was  the  source  of  volcanic  contributions  to  the  sedi- 
ments of  the  adjacent  seas,  and  the  cause  of  unconformities  and  low- 
grade  metamorphism  in  the  deposits. 

Ry  Late  Pennsylvanian  time  the  Transcontinental  Arch  was  almost 
entirely  overlapped  and  buried,  and  the  Early  Pennsylvanian  uplifts  of 
Kansas,  Oklahoma,  and  Texas  were  covered.  Only  the  Ancestral  Rockies 
in  Utah,  Colorado,  and  New  Mexico  remained  as  islands  above  the  ac- 
cumulating sediments. 

Permian  (Plate  8) 

An  eugeosyncline  of  deep  and  broad  proportions  developed  in 
Permian  time  along  the  Pacific  and  was  filled  largely  with  volcanic  ma- 
terials. The  Permian  was  a  time  of  most  extensive  volcanism,  and  the  site 


18 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


of  maximum  subsidence  and  fill  later  became  the  locale  of  the  great 
Nevadan  batholiths. 

Orogeny  continued  in  central  Nevada,  and  a  small  deep  trough  in 
western  Utah  filled  with  sandstone,  shale,  and  limestone.  Extensive 
shelf  seas  stretched  eastward  and  southward. 

The  Colorado  and  Uncompahgre  ranges  of  the  Ancestral  Rockies 
remained  as  islands  in  the  surrounding  seas. 

The  previously  compressed  Marathons  were  elevated  epeirogenically, 
and  in  front  of  them  several  basins  sank  to  considerable  depth.  The 
platforms  of  little  subsidence  between  were  the  sites  of  the  previous 
Pecos  and  Diablo  ranges.  The  Anadarko  basin  also  subsided  appreciably. 

The  Carboniferous  basins  and  adjacent  areas  of  New  England  were 
intensely  deformed  either  in  Late  Pennsylvanian  or  Permian  time,  and 
in  places  intruded  by  granitic  batholiths.  The  deformation  is  not  defi- 
nitely dated,  but  presumably  it  occurred  after  the  beds  of  the  Permian 
basin  of  Pennsylvania  and  West  Virginia  had  been  deposited.  It  seems 
probable,  also,  that  folding  in  Pennsylvania  and  West  Virginia  occurred 
at  this  time. 

The  crustal  movements  and  spread  of  seas  in  Late  Pennsylvanian 
and  Permian  time  profoundly  altered  the  geologic  outcrop  pattern  of  the 
continent.  The  greatest  change  comes  from  the  extensive  overlap  of  the 
pre-middle  Pennsylvanian  structures  by  the  Upper  Pennsylvanian  and 
Permian  sediments.  All  the  Transcontinental  Arch  southwest  of  Wis- 
consin was  buried,  the  structures  of  Kansas  and  parts  of  the  Ozarks  dome, 
the  Wichita  and  Arbuckle  mountain  systems,  and  the,  ranges  of  west 
Texas  vanished  beneath  the  deposits.  Only  the  Colorado  and  Uncom- 
pahgre ranges  of  the  Ancestral  Rockies  remained  visible,  not  because  of 
renewed  uplift,  but  because  of  considerable  relief  inherent  from  their 
original  development. 

Triassic  (Plate  9) 

Eugeosynclinal  conditions  continued  in  the  west  with  extensive  vol- 
canic accumulations.  Crustal  unrest  continued  in  central  and  western 
Nevada.  In  northern  Utah  a  basin  subsided  and  collected  8000  feet  of 


carbonates  and  elastics.  Eastward  the  Triassic  deposits  are  largely  con- 
tinental and  red.  An  emergent  corridor  connected  the  Canadian  Shield 
with  northern  Mexico  and  southern  Arizona. 

The  Colorado  and  Uncompahgre  ranges  still  stood  as  islands  in  the 
surrounding  deposits. 

The  Marathon-Ouachita  orogenic  belt  of  earlier  development  was  still  j| 
mountainous  and  had  a  broad  piedmont  generally  free  of  deposits.  The 
mountainous  belt  may  have  risen  gently  as  its  rocks  were  eroded  and 
carried  away,  but  orogeny  there  had  ended. 

Within  the  metamorphic  and  igneous  core  of  the  Paleozoic  orogenic 
belts  of  the  Atlantic  margin,  a  zone  of  high-angle  faults  dropped  basins 
and  raised  blocks  of  mountainous  proportions.  Volcanism  was  a  prom- 
inent accompaniment  of  the  faulting.  The  basins  were  the  site  of  ac- 
cumulation of  thick,  red,  clastic  sediments  which  were  mostly  derived 
from  the  uplifted,  adjacent  blocks.  The  basins  are  narrow  and  long,  and 
because  of  their  fault  origin,  their  size  was  probably  not  much  larger 
originally  than  now.  The  faulting  and  igneous  activity  ran  its  course  in 
Late  Triassic  time,  and  the  orogeny  is  known  as  the  Palisades. 

Jurassic  (Plate  10) 

The  Cordilleran  geanticline  developed  in  Early  Jurassic  time  and 
separated  a  western  trough  effectively  from  an  eastern.  The  western 
again  was  one  of  extreme  subsidence,  and  about  30,000  feet  of  volcanics, 
black  shale,  and  other  sediments  accumulated  in  it.  Central  Nevada  con- 
tinued to  experience  orogeny,  and  thrusting  of  large  proportions  oc- 
curred. Late  Jurassic  was  also  a  time  of  considerable  batholithic  intrusions 
in  central  and  northern  California  and  possibly  western  Nevada. 

The  eastern  trough  was  generally  the  site  of  marine  transgression  and 
deposition,  but  the  Jurassic  deposits  are  less  extensive  than  the  earlier 
Permian,  Triassic,  and  the  later  Upper  Jurassic  and  Cretaceous.  The 
Jurassic  overlap  on  the  Paleozoic  strata  of  Montana,  Alberta,  and  Saskatch- 
ewan, particularly  on  the  Mississippian,  is  striking.  The  Mexican  geosyn- 
cline  began  to  form.  It  was  separated  on  the  north  by  a  peninsula,  the 
Coahuila,  from  the  seas  of  the  Gulf  of  Mexico.  The  wide  basin  of  the 


RESUME  OF  STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


10 


Gulf  of  Mexico  had  come  into  existence.  Much  salt  was  precipitated  in  an 
evaporite  sequence  in  the  Mexican   geosyncline  as  well   as  along  the 
northern  part  of  the  Gulf  in  Louisiana  and  Texas. 
The  interior  of  the  continent  was  extensively  emergent. 

Early  Cretaceous  (Plate  11) 

The  Cordilleran  geanticline  widened  and  stretched  from  Rritish  Colum- 
1  bia  to  Mexico,  and  from  eastern  California  to  central  Utah.  A  broad 
branch  extended  across  Arizona  and  central  New  Mexico  into  Texas. 
'Further  deformation  is  noted  in  northwestern  Nevada. 

Basins  sank  greatly  on  the  west  in  California,  Oregon,  and  Washington. 
Volcanism  continued  there  from  previous  times.  The  geanticline  was 
flanked  on  the  east  by  a  trough  of  sedimentation  from  Alberta  to  northern 
Utah  into  which  clastic  sediments  were  shed.  The  Ancestral  Rockies 
were  buried  save  for  a  small  island  in  central  Colorado.  The  Mexican 
'  geosyncline  enlarged  and  sank  over  15,000  feet.  It  received  considerable 
volcanic  material  from  the  west.  The  seas  spread  over  the  Coahuila  penin- 
sula to  make  it  a  platform,  and  were  more  extensive  now  over  the 
southern  and  western  part  of  the  country  than  at  any  previous  Mesozoic 
time. 

The  Rocky  Mountain  sea  merged  with  the  Gulf  of  Mexico,  and  the 
Gulf  Coastal  Plain  sediments  accumulated  to  an  appreciable  extent.  Only 
the  northern  part  of  Florida  was  emergent.  It  was  otherwise  a  platform 
and  with  the  Bahama  platform  made  up  a  large  region  of  carbonate 
deposition  and  slow  subsidence.  It  bordered  on  the  south  with  a  volcanic 
belt  in  Cuba  where  a  carbonate  facies  on  the  north  grades  into  a 
volcanic  facies  on  the  south. 

Late  Cretaceous  (Plate  12) 

The  Late  Cretaceous  was  a  time  of  widespread  and  intensive  crustal 
unrest  along  the  western  margin  of  the  continent.  The  climatic  phase 
of  the  Nevadan  orogeny  occurred  at  the  very  beginning  of  Late  Cre- 
taceous time  when  most  of  the  batholiths  that  characterize  the  belt  were 
intruded.  Narrow  basins  subsided  to  considerable  depths  on  the  west 


margin  of  the  belt  where  again  volcanoes  contributed  some  material. 

The   Nevadan   belt   of  orogeny   became   part   of    the    broad    Cordilleran 
geanticline,   along  whose   eastern   margin   strong   uplift    with    thrusting 
occurred.  Floods  of  coarse  conglomerate  were  poured  into  an  adja 
trough  in  Utah  and  western  Wyoming,  and  in  places  thrust  sheets  over- 
rode the  elastics. 

The  Late  Cretaceous  seas  and  deposits  were  even  more  widespread 
over  the  Rocky  Mountains  and  Great  Plains  states  than  those  of  the 
Early  Cretaceous,  and  the  deposits  were  much  thicker.  East  of  the  deep 
trough  in  central  Utah,  only  thin  deposits  had  previously  accumulated 
under  shelf  sea  conditions.  Now  sediments  in  excess  of  5000  feet  thick 
collected  over  a  wide  area  of  the  shelf. 

The  Mexican  geosyncline  had  shrunk  and  changed  decidedly  from  its 
Early  Cretaceous  form.  A  trough  extending  from  southeastern  Arizona 
into  northern  Mexico  contains  much  coarse  conglomerate  and  volcanic 
material.  South  of  the  Coahuila  platform  a  deep  east-west  trough,  the 
Parras,  sank  and  received  over  15,000  Eeet  of  sediments,  mostly  lime- 
stones and  shales. 

Florida  sank  progressively  through  Late  Cretaceous  time,  tilting  south- 
ward to  a  trough  that  centered  in  Cuba  where  some  10,000  feet  of 
carbonaceous  sediments  accumulated.  As  the  carbonates  thin  northward 
through  Florida,  they  change  into  argillaceous  and  arenaceous  facies.  Tne 
Atlantic  margin  of  the  continent  was  widely  invaded,  and  a  wedge  of 
sediments  that  thickens  seaward  was  deposited.  The  sediments  overlap 
the  Lower  Cretaceous  strata  in  most  places. 

Cretaceous-Tertiary  Transition  (Plate  13) 

During  the  latest  Cretaceous  (Montanan)  and  earliest  Tertiary  (Paleo- 
cene)  the  main  structures  of  the  Rocky  Mountains  of  Canada  and  the 
United  States  came  into  existence,  and  Plate  13  has  been  prepared  prin- 
cipally to  show  these  features.  The  crustal  unrest  is  known  as  the 
Laramide  orogeny.  The  Cordilleran  geanticline  was  broadly  deformed 
with  its  eastern  margin  and  the  adjacent  basin  deposits  of  the  Triassic, 
Jurassic,    and   Cretaceous    folded   and    thrust-faulted.    Major    overtlrrust 


20 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


sheets  rode  eastward  from  the  Yukon  to  southern  Utah,  and  repeated 
floods  of  coarse  elastics  occurred  in  this  marginal  belt.  Several  phases  of 
deformation  are  documented  in  most  places. 

East  of  the  thrust  belt  including  the  large  region  from  Montana  to 
southern  New  Mexico  and  generally  in  the  shelf  region  of  sedimentation 
anticlinal  uplifts,  mostly  elliptical  in  ground  plan  and  asymmetrical  in 
cross  section  rose  in  latest  Cretaceous  and  Paleocene  time.  They  are  75 
to  150  miles  long  and  20  to  50  miles  wide.  Where  the  uplift  has  been 
great  enough  to  result  in  erosion  exposing  the  Precambrian  rocks,  thrust- 
faulting  has  occurred  on  the  steep  margin.  The  elliptical  uplifts  compose 
the  major  mountain  ranges  of  the  region.  Retween  are  intermountain 
valleys  where,  particularly  in  Wyoming  and  Montana,  considerable 
amounts  of  Early  Tertiary  continental-type  sediments  were  caught. 

The  western  or  Pacific  margin  of  the  geanticline  continued  to  shed 
sediments  to  the  adjacent  basins,  and  no  strong  disturbance  is  indicated. 
The  San  Andreas  fault  had  probably  come  into  existence  and  the  west- 
lying  block  at  this  time  was  lodged  several  hundred  miles  to  the  south, 
but  now  had  started  to  shift  northwestward  along  the  fault,  as  indicated 
by  the  arrows. 

Major  deformation  of  previously  deposited  Jurassic  and  Cretaceous 
sediments  occurred  in  the  Greater  Antilles  with  northward  thrusting 
in  Cuba. 

Early  Tertiary  (Plate  14) 

The  most  conspicuous  and  probably  most  significant  feature  of  Early 
Tertiary  time  in  the  western  cordillera  was  magmatic  activity,  especially 
volcanic.  As  can  be  seen  from  the  map  that  the  Great  Rasin  region  of 
Nevada,  western  Utah,  and  central  and  southern  Arizona,  together  with 
the  vast  region  of  western  Mexico,  was  mostly  covered  with  volcanic 
materials.  Southern  Idaho  was  also  extensively  covered.  Significant  al- 
though scattered  fields  occur  in  New  Mexico,  Colorado,  and  Montana. 
The  central  Cordillera  of  Canada  developed  a  large  field.  Several  hun- 
dred small  stocks  also  were  intruded  in  the  Great  Rasin,  southern  Ari- 
zona, and  northern  Mexico.  All  this  activity  followed  the  Nevadan  and 
Laramide  orogenies  and,  in  places  at  least,  marked  the  beginning  of 


block  faulting  and  rifting  that  dominated  the  Late  Tertiary  activities. 

A  eugeosyncline  formed  in  Oregon  and  Washington,  which  is  made  ; 
up  of  a  very  thick  mass  of  sediments  and  volcanics.  Deep  but  restricted 
basins  between  uplifts  developed  in  central  and  southern  California. 
The  San  Andreas  fault  was  very  active  and  the  west  block  moved  north- 
ward, but  was  still  considerably  south  of  its  present  position.  The 
Atlantic  and  Gulf  of  Mexico  continental  margins  continued  to  subside 
during  the  Tertiary,  but  only  in  one  or  two  places,  particularly  the 
Mississippi  embayment,  did  the  Tertiary  beds  overreach  the  Upper 
Cretaceous  deposits.  The  Cretaceous  and  Tertiary  sediments  form  the 
present  Gulf  Coastal  and  Atlantic  Coastal  Plains. 

As  the  Atlantic  margin  of  the  continent  subsided  in  Late  Cretaceous 
and  Tertiary  time,  the  Appalachian  orogenic  belt  arched  gently,  and 
successive  erosion  surfaces  record  the  epeirogenic  uplift. 

The  Greater  Antilles  sank  and  appeared  as  a  belt  of  islands  around 
which  Tertiary  sediments  accumulated.  Florida  and  the  Rahama  plat- 
forms also  continued  to  sink  and  to  be  built  up  by  carbonate  sediments. 

Late  Tertiary  and  Quaternary  (Plate  15) 

Volcanism  continued  prominent  in  the  Late  Tertiary  with  basalt  fissure 
eruptions  in  Washington  and  Oregon  building  the  Columbia  River  field. 
To  the  south  in  southern  Oregon  and  Idaho  another  extensive  basalt  field 
formed  chiefly  from  vent  eruptions.  The  west  margin  of  these  two  large 
basalt  fields  has  been  built  especially  high  by  additional  volcanoes  to 
form  the  Cascade  Range.  A  row  of  majestic  stratovolcanoes  of  Quaternary 
age  dominates  the  Cascades  and  extends  into  southern  Rritish  Columbia 
beyond  the  basalt  fields.  The  Cascade  volcanics  are  chiefly  andesite. 

Rlock  faulting  of  major  proportions  spread  from  the  Sierra  Nevada  of 
California  to  the  Wasatch  Mountains  of  Utah.  It  also  extended  through 
southern  Arizona  and  southward  along  the  west  coast  of  Sonora,  Mexico. 
An  arm  of  the  faulting  extended  northward  through  eastern  Idaho, 
western  Wyoming,  and  western  Montana  to  the  Rocky  Mountain  Trench 
of  Rritish  Columbia.  The  block,  trench,  or  rift  faulting  is  believed  to  be 
of  tensional  origin  and  to  penetrate  deeply  into  the  crust. 

The  San  Andreas  fault  block  moved  northward  to  its  present  position 


RESUME  OF  STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


:i 


■' 


and  drifted  apart  from  the  continent  at  the  south  end  to  form  the  Gulf 
of  Raja  California  which  is  floored  by  oceanic  crust.  Deep  but  local 
basins  sank  in  southern  California. 

The  Colorado  Plateau  block  was  uplifted  with  associated  subsidence 
on  the  south  and  west.  Several  laccolithic  groups  were  intruded  into  the 
Plateau  strata,  and  several  volcanic  piles  accumulated  around  the  southern 
and  eastern  margins.  In  central  Wyoming  certain  blocks  were  depressed 
along  normal  faults,  particularly  the  Laramide  Sweetwater  Range.  The 
Great  Plains  came  into  existence  by  uplift  progressively  greater  toward  the 
west.  The  Laramide  Rockies  were  also  uplifted,  starting  a  new  erosion 
cycle. 

The  marginal  areas  of  the  Gulf  Coastal  Plain  continued  to  subside 


greatly  under  a  heavy  load  of  deltaic  sediments.  An  area  in  northwestern 

Florida  became  emergent.  The  Atlantic  Coastal  Plain  south  of  Ixmg 
Island  gradually  rose  and  the  sea  retreated,  but  north  of  Long  Island 
submergence  and  overlap  of  the  sea  occurred.  The  submergence  has 
also   been   effective   in    Quaternary   time   southward    where   emergence 

has  occurred  previously. 

Broad  arching  in  the  Appalachian  region  continued. 

The  Canadian  Shield  had  been  depressed  under  the  weight  of  the 
ice  sheets  but  in  post-glacial  time  has  lifted  progressively  to  the  north. 
The  tilting  starts  at  the  hinge  line  shown  on  Plate  15  and  amounts  to 
700  feet  along  the  northern  shores  of  Lake  Superior,  and  possibly  900 
feet  along  the  eastern  side  of  James  Bay  at  the  south  end  of  Hudson  Bay. 


! 


4. 


PRECAM  BRIAN 
TECTONIC  PROVINCES 

DISTRIBUTION  OF  PRECAMBRIAN  ROCKS 

The  continent  of  North  America  is  made  up  in  a  broad  way  of  a  stable 
interior  and  surrounding  belts  of  deformed,  intruded,  and  metamorphosed 
rocks.  The  stable  interior  has  been  free  of  orogeny  since  a  time  in  the 
late  Precambrian,  or  approximately  for  the  last  billion  years.  Before  that 
time,  however,  a  number  of  intense  and  widespread  orogenies  occurred. 

The  Canadian  Shield  is  the  greatest  expanse  of  Precambrian  rock 
exposures.  These  same  rocks  are  blanketed  by  Paleozoic,  Mesozoic,  and 
Cenozoic  strata  over  most  of  western  Canada  and  the  United  States;  only 


in  areas  of  local  uplift  or  doming  have  the  old  rocks  been  exposed. 
The  Crystalline  Piedmont  of  the  Atlantic  margin  of  the  continent  con- 
tains much  rock  of  Precambrian  age,  and  the  western  Cordillera  exposes 
the  ancient  rocks  of  several  ages  and  complex  relations  in  a  number 
of  places. 


CANADIAN  SHIELD 

Physiography 

The  Canadian  Shield  is  characterized  by  a  vast  expanse  of  Precambrian 
rock.  Its  upland  surfaces  are  uniform  in  height  over  large  areas  and, 
although  now  dissected,  represent  an  old  age  erosion  surface  as  large 
as.  any  in  existence  today.  The  extensive  surface  rises  1000  to  2000  feet 
above  sea  level  north  of  the  St.  Lawrence  River  and  Lake  Superior. 
Around  Hudson  Bay,  especially  on  the  south  and  west,  is  a  wide  lowland 
that  ranges  from  sea  level  to  500  feet  in  elevation.  In  northern  Labrador 
along  the  coast  just  southeast  of  Ungava  Bay,  the  surface  rises  to  5000 
feet  and  is  extensively  dissected.  Hudson  Bay  is  a  great  modern  epeiric 
sea;  it  is  a  marine  invasion  from  the  north  due  to  gentle  subsidence  in  j 
the  heart  of  the  shield  in  pre-Pleistocene  or  early  Pleistocene  time.  The  I 
ice  caps  imposed  such  a  weight  on  the  shield  in  and  around  Hudson  j 
Bay  that  the  area  sank  over  a  thousand  feet  in  addition  to  the  previous 
subsidence,  and  then  with  the  melting  of  the  ice  it  has  risen  about  900 
feet. 

Post-Proterozoic  History 

Paleozoic  strata  lap  upon  the  shield  from  the  Canadian  plains  on  the 
west,  and  from  the  southwest  in  Saskatchewan  and  Manitoba.  In 
northern  Minnesota  the  Precambrian  rocks  lie  exposed  and  extend  south- 
ward into  Wisconsin  and  eastward  into  northern  Michigan.  Paleozoic 
rocks  continue  to  overlap  the  Precambrian  across  southern  Ontario  and 
Quebec  to  the  Frontenac  axis,  where  the  Precambrian  extends  southeast- 
ward and  forms  the  Adirondack  dome  in  New  York.  See  the  Geologic 
Map  of  North  America.  For  the  most  part,  the  Paleozoic  rocks  that  skirt 


22 


PRECAMBRIAN  TECTONIC  PROVINCES 


23 


ithe  shield  are  Devonian  and  Silurian,  and  are  chemical  deposits  or  fine 
elastics.  Along  the  southern  margin  of  Hudson  Bay  is  a  fairly  large  area 
pf  flat-lying  Devonian,  Silurian,  and  Ordovician  sedimentary  rocks,  and 
:rom  fossil  studies  it  seems  probable  that  the  Manitoba,  Hudson  Bay,  and 
Michigan  Devonian  deposits  were  once  continuous  (G.  M.  Ehlers,  per- 
sonal communication).  The  thickness  of  the  Devonian  and  Silurian  south 
af  Hudson  Bay  is  at  least  1000  feet,  but  their  extension  northward  under 
;he  Bay's  waters  is  not  known.  It  can  easily  be  imagined  that  they  are 
continuous  to  Coats  and  Mansel  islands  at  the  entrance  of  Hudson  Bay 
ind  thence  to  the  nearly  horizontal  Paleozoic  strata  of  Southampton 
island  and  the  Arctic  Archipelago.  If  continuous,  one  wonders  if  some- 
where in  that  large  area  the  beds  are  not  thick  and  form  a  trough  or 
basin,  perhaps  similar  to  the  Michigan  basin.  In  fact,  basins  and  arches 
have  been  recognized  in  the  far  north,  and  are  described  in  Chapter  40. 

It  has  been  thought  until  lately  that  the  Canadian  Shield  was  com- 
paratively free  of  epeiric  seas  in  the  past;  but  now,  by  the  discovery 
pf  a  number  of  small  erosional  remnants  of  Paleozoic  strata  far  within 
'the  crystalline  rocks  (W.  Sinclair  and  J.  Tuzo  Wilson,  personal  com- 
jmunications ) ,  it  is  believed  that  large  areas  were  blanketed  by  sediments. 
Perhaps  very  little  escaped  submergence.  What  seems  more  important  is 
'that  no  orogenic  belts  developed  across  it  during  all  of  post-Proterozoic 
time.  The  same  is  true  with  some  exceptions  of  the  stable  region  of  the 
United  States. 

In  the  iron  ore  belt  of  central  Labrador  (the  Redmond  iron  deposit) 
downfaulting  of  a  trench  occurred  in  early  Late  Cretaceous  time,  and  in 
jit  various  argillites  and  ferric  concretionary  deposits  accumulated.  The 
Redmond  deposit  is  in  a  basin  1  mile  long,  1000  feet  wide,  and  600  feet 
deep.  Abundant  plant  fossils  in  certain  beds  serve  to  date  the  deposits 
|and  the  faulting.  The  extent  of  the  Cretaceous  faulting  is  not  known 
!(R.  A.  Blais,  1959). 

From  simple  map  examination,  it  looks  probable  that  Greenland  was 
part  of  the  Canadian  Shield  until  Cretaceous  time  when,  perhaps,  a 
Cretaceous  trough  extended  as  far  north  as  Disco  Island.  Greenland  was 
further  severed  from  the  shield  either  by  Tertiary  downfaulting  or  by 
drifting  apart.  See  Chapter  40. 


Geologic  Provinces 

The  Canadian  Shield  until  recently  has  been  difficult  of  access,  and 
this  with  the  extensive  "bush"  cover  has  made  geologic  exploration 
pensive  of  energy  and  slow.  The  advent  of  airplanes  and  aerial  photos 
has  hastened  the  work  immensely,  and  a  beginning  has  now  been  made 
in  analyzing  the  composition  of  the  great  Precambrian  shield.  But  the 
time  has  not  yet  arrived,  according  to  M.  E.  Wilson,  when  the  vast  region 
can  be  broken  down  into  divisions  with  confidence.  He  draws  approxi- 
mate boundaries  between  five  provinces  (see  map,  Fig.  4.1),  namely, 
the  Western  or  Churchill,  the  Ungava,  the  Arctic  Island,  the  Greenland, 
and  the  St.  Lawrence.  The  last  is  divided  into  subprovinces,  the  North- 


Fig.  4.1.      Geologic  provinces  of  the  Canadian  Shield  best  suited  at  present  for  individual  forma- 
tional    names.   After  M.   E.  Wilson,    1958. 


24 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Erm 
(HfYeen) 

Penod-Syilem 

Major  Sequence 

Formation 

Orogeny 

Intrusive  Rocka 

Ptlcoxoic 

C»mbnmn 

Grenville 
.  Penokean 

.  Algoman 
-Lauxentiaa 

(0*  b,y.) 
(11  bjr.) 

lati  mtawa 

Keweenawan 

Hinckley  sandstone 
Fond  du  Lac  sandstone 

North  Shore  volcanic   Undivided 
group 

Duluth  complex,  sills  at  DulurJi,  Beaver  Bay 

complex,  Logan  intrusive* 

Puckwunge 

Sioux  quartxite  (?) 

=  Thomson 
Gunflint 

Granite:  St.  Cloud  Red,  Rockville  (?)  granite  at 

Granite  Falls,  Bellingham  (?) 
Gneiss:  McGralh.  Montevideo  (?) 

(1.7  bj.) 

Haiooiu 

Animikie  froup 

Virginia  argHlile  =  Rove 
Biwabik  iron-formation  = 

Tonalites:    St  Cloud  Gray.  Warman,  Hillman. 
Freedbem,  Montevideo 

MwMlr  Preewrabrita 

Pokegama  quartxile 

Granite:    Gold    Island,    Giants   Range,    Sacred 

«•»  bjr.) 
(fbjr.) 

Early  Pircambriao 

Tuxttskaraiao 

OnUnui 

Knife  Lake  group 
Keevatin  group 

Undivided 

Soudan  iron- formation 

Ely  greenstone 

Gneiss:  Giants  Range,  Vermilion,  Morton 
Saganaga  granite,  Grassy  Island  lonalile  (?) 

Coulchiching  (?) 

Undivided 

Older  rocka 

Fig.  4.2.  Stratigraphic  succession  and  geochronology  of  the  Precambrian  of  Minnesota.  Repro- 
duced from  Goldich  ef  a/.,  1961. 

west,  the  Southern,  the  Timiskaming,  and  the  Grenville.  The  provinces 
and  the  subprovinces  thus  defined  represent  natural  divisions  and  the 
limits  to  which  attempts  should  be  made  to  correlate  rock  units.  Wilson 
recommends  separate  names  for  formations,  series,  or  intrusive  bodies 
within  each  of  these  divisions  at  least  for  the  present. 

Geologists  in  recent  culminating  studies  in  the  iron  and  copper  region 
of  Lake  Superior  recognize  a  threefold  division  of  the  rocks  ( Grout  et  ah, 
1951,  James,  1955,  and  Goldich  et  ah,  1961).  The  Precambrian  of  Minne- 
sota is  classified  by  Goldich  et  ah  after  many  radioactivity  age  determina- 
tions, as  shown  in  Fig.  4.2. 

Previously,  in  1934,  a  committee  of  the  Royal  Society  of  Canada  on 
stratigraphical  nomenclature  had  recommended  that  Precambrian  time 
be  divided  into  two  eras,  Archean  and  Proterozoic,  and  since  then  this 
classification  has  been  used  on  most  geologic  maps  issued  by  the 
Geological  Survey  of  Canada.  M.  E.  Wilson  in  1958  contends  that  the  dual 
classification  is  still  the  best  and  includes  the  Middle  Precambrian  rocks 
of  Grout  and  James  in  the  Proterozoic.  In  all  provinces  of  the  Canadian 
Shield  a  profound  unconformity  is  known,  by  reference  to  which  the 
rocks  can  be  divided  into  two  great  groups  (M.  E.  Wilson,  1958).  The 
standard  of  reference,  for  instance,  is  the  rock  succession  on  Lake  Timis- 


kaming where  the  Huronian  (Cobalt  series)  rests  "with  great  uncon- 
formity" on  granite — the  Laurentian. 

The  Archean  rocks  consist  of  clastic  sediments  and  various  volcanic 
rocks  conformably  interbedded,  and  even  though  extremely  old  they  are 
so  little  affected  by  metamorphism  in  places  that  original  sedimentary 
structures  are  clearly  visible.  In  many  other  places  they  are  meta- 
morphosed to  various  degrees.  According  to  Pettijohn  (1943)  one  may 
study  the  bedding  in  certain  argillites  in  the  finest  detail,  and  the  asso- 
ciated volcanics  show  pillow  structures,  amygdules,  spherulitic  structures, 
the  same  as  in  lavas  of  much  later  geologic  time.  Metamorphism  is  mainly 
of  the  low-grade  variety,  and  orogeny  has  left  the  very  ancient  rocks  of 
many  areas  untouched.  Recognizing  the  near-absence  of  metamorphism 
in  places,  however,  it  must  also  be  understood  that  enormous  volumes  of 
intrusive  igneous  rocks  occur,  and  estimates  have  been  made  that  these 
intrusive  rocks  constitute  as  much  as  80%  of  the  shield.  The  great  bulk 
of  these  are  granites  of  various  types,  with  relatively  small  but  important 
amounts  of  basic  rocks  such  as  gabbro,  norite,  and  peridotite.  Need- 
less to  say,  much  metamorphism  has  occurred  and  gneisses  and  schists 
(migmatites)  are  extensively  developed. 

The  Archean  sediments  of  the  southern  Canadian  Shield  are  mainly  gray- 
wacke.  Much  conglomerate,  a  litde  slate,  and  still  less  iron-bearing  formation 
are  also  present.  Excessive  thickness,  especially  of  the  conglomerates,  abundance 
of  graded  bedding,  rarity  of  cross-bedding  and  absence  of  ripple  mark,  the 
graywacke  nature  of  the  arenaceous  beds,  the  absence  of  true  quartzites  and 
limestones,  and  the  scarcity  of  normal  argillaceous  sediments,  and  the  associa- 
tion with  greenstones  and  tuffs  are  all  the  earmarks  of  a  geosynclinal  facies  of 
sedimentation  (Pettijohn,  1943). 

In  particular,  these  types  characterize  the  eugeosyncline,  and  since  they 
are  repeated  in  later  Precambrian  rock  series,  it  is  little  wonder  that 
confusion  in  correlations  has  resulted. 

In  eastern  Ontario  and  adjacent  parts  of  Quebec  the  oldest  rocks  are 
sedimentary  gneisses  associated  with  great  thicknesses  of  crystalline 
limestone  and  a  little  basic  metavolcanics.  These  rocks  are  termed  the 
Grenville  series.  They  appear  to  have  been  originally  shales,  sandstones, 
limestones,  and  some  lavas,  but  owing  to  the  intense  metamorphism,  they 
are  now  biotite  schists  and  sillimanite-garnet  gneisses,  vitreous  quartzite, 
and  crystalline  limestones. 


PRECAMBRIAN  TECTONIC  PROVINCES 


In  southern  Ontario,  particularly  in  Hastings  County  a  younger  series, 
the  Hastings,  overlies  the  Grenville  with  erosional  unconformity  but, 
apparently  with  little  structural  discordance.  The  series  consists  of 
gray,  blue-weathering  limestone  interstratified  with  argillite,  except  near 
the  base  where  beds  of  congolmerate  interstratified  with  argillite,  buff- 
weathering  dolomite,  graywacke,  and  mica  schist  occur.  Both  Grenville 
and  Hastings  rocks  are  intruded  by  a  group  of  gabbros,  anorthosites, 
pyroxene  diorites,  and  pyroxene  syenites.  Later  still  are  dikes,  sills,  and 
batholiths  of  granite  and  syenite,  and  their  gneissic  equivalents. 

The  Grenville  subprovince  is  believed  to  be  separated  from  the  Timis- 
kaming  subprovince  by  a  great  fault  called  the  "Lake  Mistassini-Lake 
Huron  fault"  by  M.  E.  Wilson  (1956)  and  the  Grenville  front  or  fault 
zone"  on  the  Tectonic  Map  of  Canada  (1950).  The  fault  marks  a  zone 
of  considerable  disturbance,  and  in  the  Lake  Mistassini  area  it  seems 
evident  that  the  Grenville  rocks  have  been  thrust  over  those  of  the  Timis- 
kaming  subprovince.  The  theoretical  fault  lies  under  lakes  and  glacial 
deposits  for  most  of  its  length,  and  considerable  controversy  centers 
about  it. 

For  further  discussion  of  the  many  rock  units  already  described  over 
the  vast  Canadian  Shield  read  M.  E.  Wilson  1956  and  1958,  and  Harrison, 
1957.  A  recent  symposium  publication,  "The  Grenville  Problem,"  pub- 
lished by  the  University  of  Toronto  Press,  presents  a  fascinating  picture 
of  the  many  problems  involved. 

Tectonic  Provinces 

With  the  advent  of  physiochemical  age  determinations  (about  1931) 
Imuch  new  light  has  been  shed  on  the  relative  ages  of  rocks  in  the 
Canadian  Shield.  The  ages  are  actually  for  minerals  occurring  in  igneous 
rocks  or  in  reconstituted  rocks,  metamorphosed  during  an  orogeny;  the 
|  original  age  of  the  graywacke,  shale  or  lava  is  not  determined  but  rather 
the  age  of  the  orogeny.  Therefore,  with  the  absolute  age  determinations 
has  come  an  increased  attention  to  orogenic  belts,  and  certain  geologists 
have  postulated  a  division  of  the  Canadian  Shield  into  tectonic  provinces 
or  orogenic  belts,  in  place  of  the  "geological  provinces."  See  Fig.  4.3. 

The  oldest  orogeny  in  Minnesota  is  called  the  Laurentian  by  Goldich 
et  al.  (1961),  but  this  he  regards  as  an  early  phase  of  folding  to  the 


Fig.  4.3.      Precambrian  orogenic  belts  of  North  America  defined   by  isotope  oges. 


26 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


greater  Algoman  orogeny  ( see  Fig.  4.2 ) .  The  latter  occurred  about  2500 
m.y.  ago,  although  the  very  ancient  dates  range  from  2200  to  2600  m.y. 
The  name  Algoman  is  here  used  for  the  belt  of  ancient  dates  through  the 
southern  part  of  the  Canadian  Shield.  It  has  been  variously  called  the 
Keewatin  and  Superior  by  other  writers. 

The  Algoman  and  the  Slave  (also  called  Yellowknif e )  provinces  are 
the  oldest  known  and  possibly  parts  of  the  original  nucleus  of  the  con- 
tinent. They  have  a  high  ratio  of  lavas  to  sediments  which  are  of  the 
graywacke  facies,  presumably  deposited  in  geosynclinal  basins.  The 
Churchill  province  is  considered  an  orogenic  belt  by  which  the  two 
nuclei  were  welded  together  (J.  Tuzo  Wilson,  1949,  1954).  See  also 
Farquhar  and  Russell  (1957)  and  Lowdon  (1960). 

A  belt  of  Huronian  rocks  extending  from  Minnesota  through  Wisconsin 
into  Michigan  and  lying  south  of  the  main  Algoman  belt  has  ages  of  about 
1700  m.y.  Goldich  et  al.  ( 1961 )  call  it  the  Penokean  orogenic  belt,  and 
the  name  has  been  applied  in  this  book  to  adjacent  regions  on  the  south- 
west in  the  United  States  and  on  the  northwest  in  Canada. 

The  Grenville  subprovince  of  M.  E.  Wilson  approximately  is  postulated 
as  an  orogenic  belt  about  1000  m.y.  old.  Its  deformed  front  borders 
directly  on  the  Algoman  province.  Southeast  of  the  Grenville  belt  are 
the  Taconic  and  Acadian  orogenic  belts,  about  400  and  300  m.y.  old, 
respectively. 

Eighty-three  isotopic  age  analyses  on  biotite,  K-feldspar,  and  whole- 
rock  samples  from  forty-five  localities,  using  both  K-Ar  and  Rb-Sr 
methods  have  been  made  on  igneous  rocks  and  a  few  metasediments  in 
the  Sudbury-Blind  River  area  of  the  Grenville  belt  by  Fairbairn  et  al. 
(1960). 

The  numbers  obtained,  forming  an  almost  continuous  age  spectrum  from 
1.0  b.y.  to  2.2  b.y.,  are  correlative  with  widespread  and  repeated  diastrophism 
in  the  region.  Whole-rock  analyses  of  igneous  material,  where  available,  show 
higher  ages  than  coexisting  minerals  in  most  examples,  and  there  is  reason  to 
believe  that  these  are  close  approximations  to  the  true  age.  There  is  consider- 
able evidence  by  both  K-Ar  and  Rb-Sr  methods,  of  orogenic  events  at  ap- 
proximately 1.0  b.y.,  1.2  b.y.,  and  1.6  b.y. 

The  oldest  igneous  rock  found  thus  far  is  the  Copper  Cliff  "rhyolite"  (2200 
m.y.),   which   intrudes   the   basal   section   of   a   thick   series   of   conformable 


metasediments  and  volcanics  southeast  of  Sudbury.  At  Quirke  Lake  granite  in 
the  basement,  uncomformably  beneath  U-bearing  pebble  beds,  is  2050  m.y. 
old.  As  the  time  of  uranium  mineralization  in  these  Huronian  sediments  is 
placed  at  1700  m.y.,  and  gabbro  which  intrudes  them  may  possibly  be  older 
than  1800  m.y.,  their  deposition  must  have  been  in  the  age  bracket  1800-2050 
m.y. 


ARCTIC  STABLE  REGION 

South  of  the  orogenic  belt  of  northern  Greenland  and  Ellesmere  Island 
and  north  of  the  Precambrian  Canadian  Shield  is  a  stable  region  com- 
posed of  a  Precambrian  crystalline  basement  with  a  veneer  of  nearly 
horizontal  Paleozoic  sedimentary  rocks.  It  includes  most  of  the  Arctic 
islands,  and  the  shallow  sea-covered  areas  between.  See  the  Geologic 
Map  of  North  America  or  the  Geologic  Map  of  Canada.  The  Precambrian 
rocks  of  the  shield  extend  northward  into  Baffin  and  Devon  islands,  and 
exposed  extensively  in  Melville  and  Boothia  peninsulas,  but  the  Paleozoic 
blanket  indicates  that  much,  if  not  all,  of  the  Arctic  islands  region 
(also  called  Arctic  Archipelago)  and  the  northern  part  of  the  Canadian 
Shield  were  submerged  at  times  during  the  Paleozoic.  The  part  south 
of  the  fold  belt  ( Chapter  35)  has  suffered  only  gentle  vertical  movements 
since  the  Proterozoic,  and  is  therefore  part  of  the  great  stable  interior  of 
the  continent.  The  Precambrian  crystalline  rocks  extend  southward  into 
the  United  States  under  a  veneer  of  Paleozoic  sedimentary  rocks  com- 
monly called  the  Central  Stable  Region.  It  seems  appropriate,  therefore, 
to  speak  of  the  similar  northern  geologic  province  as  the  Arctic  Stable 
Region. 

PRECAMBRIAN  PROVINCES  OF  THE  UNITED  STATES 

Isotope  Age  Determinations 

Recent  age  determinations  fall  into  a  pattern  that  marks  successive 
orogenic  belts  in  the  central,  southern,  and  western  states  of  the  United 
States,  and  these  are  shown  in  Fig.  4.3.  The  ages  pertain  to  rocks  gen- 
erally called  Archean  or  basement  complex.  In  Arizona,  Utah,  Idaho,  and 
Montana,  younger  and  much  less  metamorphosed  strata  rest  unconform- 


PRECAMBRIAN  TECTONIC  PROVINCES 


ably  on  the  crystalline  basement,  and  are  variously  called  Algonkian, 
Proterozoic,  Beltian,  or  Upper  Precambrian.  These  are  shown  on  the  map 
iby  the  dotted  lines.  Extending  southwestward  from  the  western  part 
of  Lake  Superior  is  another  belt  of  late  Precambrian  rocks,  namely  the 
Keweenawan  Series  with  its  included  large  gabbro  sills.  Beneath  the 
Paleozoic  and  Mesozoic  sedimentary  cover  of  Texas  and  southeastern 
New  Mexico  still  other  young  Precambrian  sediments,  volcanics,  and 
gabbro  sheets  have  been  recognized,  resting  on  an  older  granitic  terrane. 

Algoman  Oogenic  Belt 

The  ages  thus  far  published  for  north-central  Wyoming  and  south- 
central  Montana  are  very  old  (2500  to  2760  m.y.)  and  stand  apart  from 
other  ages  in  the  Rocky  Mountains  (Aldrich  et  al.,  1957;  Gast  and  Long, 
1957;  Hayden  and  Wehrenberg,  1959 ) .  An  absolute  age  determination  in 
southeastern  Manitoba  between  Winnipeg  River  and  Johnston  Lake  indi- 
cates that  a  plutonic  and  metamorphic  cycle  occurred  2650  =■=  100  m.y. 
ago  (Eckelmann  and  Gast,  1957).  These  ages  are  400  to  500  m.y.  older 
than  those  recorded  for  the  "Superior"  Province  in  Canada,  but  even  so 
iare  much  closer  to  it  than  to  those  of  the  adjacent  younger  orogenic 
;belt,  and  hence  are  regarded  related. 

Penokean  Orogenic  Belt 

A  number  of  isotope  ages  to  date  seem  to  establish  an  orogenic  belt 
;of  intermediate  age  between  the  very  old  Algoman  and  the  younger 
Mazatzal.  These  are  in  the  range  of  1600  to  1750  m.y.  See  Fig.  4.3.  The 
belt  contains  a  mixture  of  the  old  dates  and  the  younger,  and  this  is 
taken  to  mean  that  the  younger  orogeny  was  superposed  on  the  older.  The 
analyses  are  so  few  to  date  that  the  northern  limit  of  the  belt  is  poorly 
defined,  and  not  much  reliance  for  tectonic  interpretive  purposes  can 
yet  be  placed  on  the  distribution.  The  southern  limit  is  somewhat  better 
defined,  with  none  of  the  older  dates  in  the  general  field  of  the  1250 
to  1450  m.y.  dates. 

On  the  basis  of  the  geology  of  the  rocks  of  southwestern  Montana  the 
two  ages  are  understandable.  Perhaps  even  more  ages  within  the  belt  will 
be  recognized.  A  brief  description  of  the  recognized  units  is  as  follows: 


(1)   The  oldest  units  underlie  the  Cherry  Creek  Group  and   Include 
of  the  Poiin'  Group  as  well  as  other  pre-Cherry  Creek  rocks  which  probably 
an-  not  time  equivalents  ol  the  Pony.  Main  types  present  are  bioriti 
gneiss,  granite  gneiss,  injection  gneiss,  and  amphibole  gneiss.    1    The  CI* 
Creek  Group  consists  of  mctascdiincnts  including  marble,  quaitzite,  micai  i 
schists,     sillimanitc    schist,     handed     ironstones     with     Intercalated     layers     of 
amphibole  gneiss,  and  amphibolite  representing  metamorphosed  mafic  silk  and 
flows.  (3)  A  number  of  post-Cherry  Creek  intrusives,  all  of  which  show  - 
ing  degrees  of  metamorphism,  include,  among  others,  the  Dillon  granite  gn< 
widespread  in  Beaverhead  and   Madison  counties,   the  granite  of    the   [ardine 
district,  and  the  Pinto  metadiorite  in  the  Little   licit    Mountains.    (4)    Wider) 
distributed  bodies  of  unmetamorphosed   peridotite   and    associated    ultrainafu 
rocks  have  as  their  largest  representatives  the  Stillwater  Complex.    (5)    Post- 
Stillwater  intrusives  are  represented  mainly  by   the  granite  of  the  Beartooth 
Range.   (6)   Numerous  and  widespread  diabase  dikes  that  cut  all  these  older 
units  but  do  not  extend  into  Beltian  rocks   (Ileinrich,  1953). 

The  crystalline  basement  of  the  Beartooth  Range  from  what  is  known 
consists  of  schists  and  gneisses,  possiblv  the  Cherrv  (.'reck.  On  the  north- 
east is  the  Stillwater  ultramafic  complex  which  has  been  intruded  into  a 
series  of  dense  gray  hornfels,  an  iron  formation,  and  light-colored  quartz- 
ites.  It  may  be  part  of  the  Cherrv  Creek  group.  A  light  gray  gneissoid 
biotite  granite  cuts  the  ultramafic  complex.  At  Cook  City  two  granites  are 
recognized  (Parsons  and  Bryden,  1952). 

The  roof  of  a  granitic  batholith  is  exposed  in  the  Teton  Range  of 
western  Wyoming.  The  deep  canyons  that  dissect  the  range  show  gigantic 
zenoliths  and  an  irregular  roof  of  gneiss  and  schist. 

Mazatzal  Orogenic  Belt 

Distribution  of  Dates.  A  good  scatter  of  age  determinations  has  been 
made  in  the  Rockies  from  the  Black  Hills  to  Arizona  and  southern 
Nevada  and  defines  a  belt  of  rather  consistent  age  between  1300  and 
1400  m.y.  old.  A  low  age  is  given  for  the  Front  Range  of  central  Colorado 
of  1100  m.y.,  a  high  age  for  the  Black  Hills  of  South  Dakota  of  1600  m.v., 
and  a  high  age  of  1590  m.y.  for  the  Central  Wasatch  Mountains  in  Utah, 
Other  than  these  three,  ten  other  ages  fall  fairly  close  to  1350  m.y. 

No  orogenic  belt  or  province  in  the  Canadian  Shield  has  yielded  such 
ages.  The  1350-m.y.-old  belt  of  the  western  United  States  appears  to 


28 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


PINE    RIDGE 


CHISTOPHER 
MOUNTAIN   RIDGE 


CHEDISKI   RIDOE 


REDWALL    LM    (M) 


MARTIN    FM.    (D) 


_^V  /  J  «-7-    //^  MAKTIN     I..     101  ■<-.■    X  •  ,>^\V\\V   ^-TN. 

■/■  //;wA.:^-KSff!h»J*2*!?ss:wiJ5^.v-\.  "MMSgV.  TROY     >A«I>?Z"       OUARTZITE 


70  MILES    APP.- 


Fig.  4.4.      Restored   section   across  the   northern   part  of  Mazatzal   Land.   After   Huddle   and    Dob- 
rovolny,    1950. 

project  into  the  Grenville  belt  or  wedge  out  to  the  northeast  in  the  Great 
Lakes  region. 

Arizona.  The  1350-m.y.  orogenic  belt  is  here  called  the  Mazatzal  from 
relations  in  central  Arizona  (Fig.  4.4).  A  correlation  of  the  Precambrian 
rocks  of  Arizona  by  Anderson  (1951)  is  given  in  Table  4.1,  and  in  it  will 
be  seen  that  the  Mazatzal  quartzite  is  regarded  as  the  youngest  of  a 
group  of  old  rock  units,  mostly  schists.  E.  D.  Wilson  (1939)  showed  that 

Table  4.1.      Correlation  of  Precambrian  Rocks  of  Arizona  (C.  A.  Anderson,  1951) 


Grand 

Canyon 

(Noble    and 

Hunter 

1917;     Darton, 

1925) 


Bradshaw  Mtns. 

(Lindgren, 

1926) 


Mazatzal    Mtns. 

(E.   D.   Wilson, 

1939) 


Globe 

(Ransome, 

1903) 


Younger 
Precambrian 


Grand 

Canyon 

Series 


Chuar   group 
Unkar    group 


Unconformity 


Apache   group 


Apache 
group 


Orogeny— Intrusion     of    granitoid     magmas 


Older 
Precambrian 


Vishnu   schist 


Yavapai    schist 


Mazatzal     quartzite 
Maverick   shale 
Deadman    quartzite 

Alder  series 

Red  Rock  rhyolite 

Yaeger  greenstone 


Pinal    schist 


granite,  and  thus  dated  the  orogeny  and  intrusions  as  post-Mazatzal. 
the  Mazatzal  quartzite  was  folded  and  faulted  prior  to  the  intrusion  of 
He  named  the  orogeny  the  Mazatzal  revolution,  and  this  event  now  seems  j 
to  be  dated  by  the  new  isotope  age  determinations,  and  therefore  is  ap- 
plied to  the  entire  belt  up  through  Colorado,  Wyoming,  and  South 
Dakota. 

It  should  be  noted  that  the  Vishnu  schist  is  25,000  feet  thick  where  ex- 
posed in  the  Grand  Canyon  of  the  Colorado,  and  was  originally  fine- 
grained argillaceous  sandstones  and  sandy  shales.  A  sequence  of  basaltic 
lavas  and  tuffs  is  now  represented  by  amphibolites  in  which  relict  pillow 
and  anygdaloidal  structures  prove  the  volcanic  character.  The  Vishnu 
schist  is  intruded  by  plutonic  rocks  that  range  from  quartz  diorite  to 
granite.  In  fact,  granite  is  more  widespread  in  outcrop  in  Arizona  than  the 
host  rocks,  and  therefore  the  Mazatzal  orogeny  must  be  considered,  there 
at  least,  to  be  identified  with  great  batholithic  intrusions  of  fairly  acidic 
rock. 

Colorado.  The  largest  exposure  of  basement  crystalline  rocks  in  the 
Rockies  is  in  the  core  of  the  Front  Range  of  Colorado.  It  consists  essen- 
tially of  granite,  schist,  and  gneiss  (Lovering  and  Goddard,  1950). 

The  oldest  rocks  in  the  Front  Range  are  the  schists  and  gneisses  of  the 
Idaho  Springs  formation,  which  are  highly  metamorphosed  sedimentary  rocks 
of  early  pre-Cambrian  age.  The  thickness  is  approximately  20,000  feet.  The 
hornblende  schist  and  gneiss  of  the  Swandyke  hornblende  gneiss  is  overlain 
by  a  series  of  quartzites  and  quartz  pebble  conglomerates  at  least  14,000  feet 
thick.  These  formations  are  all  cut  by  an  extensive  series  of  granite  intrusives, 
the  oldest  of  which  is  a  quartz  monzonite  gneiss.  It  occurs  chiefly  in  small  stocks 
peripheral  to  granite  batholiths  or  as  a  lit-par-lit  injection  of  the  older  schists 
and  gneisses.  Gneissic  granite,  gneissic  aplite,  and  gneissic  diorite  are  found 
in  abundant  but  small  masses  within  the  metamorphic  terrain  and  are  believed 
to  be  related  to  nearby  granite  batholiths  of  different  ages. 

The  earliest  of  the  batholithic  granites  is  the  Boulder  Creek  granite;  it  is 
common  in  stocks  and  small  batholiths  in  the  central  part  of  the  Front  Range. 
Its  dark-gray  color  and  faindy  banded  appearance  distinguish  it  from  the 
pink  coarse-grained  Pikes  Peak  granite,  which  is  somewhat  younger  and  forms 
the  extensive  batholith  of  the  southern  part  of  the  Front  Range.  The  appearance 
and  age  relations  of  the  Pikes  Peak  granite  are  the  same  as  those  of  the  Sherman 
granite  exposed  in  the  large  batholith  extending  from  the  northern  part  of 
the  Front  Range  well  into  Wyoming.  Small  batholiths  and  stocks  of  the  younger 
fine-grained  to  medium-grained  light  pinkish-gray  Silver   Plume   granite  are 


PRECAMBRIAN  TECTONIC  PROVINCES 


widely  distributed,  and  locally  have  been  given  different  names.  Lead-uranium 
ratios  indicate  that  the  age  of  the  Pikes  Peak  granite  is  approximately  1  billion 
years  and  that  of  the  Silver  Plume  granite  approximately  940  million  years 
(Lovering  and  Goddard,  1950). 

The  lead-uranium  ratio  age  determinations  for  the  granites  are  younger 
than  those  yielded  elsewhere  by  the  potassium-argon  and  rubidium- 
strontium  methods,  and  it  seems  probable  that  these  will  be  recognized 
as  too  young  and  replaced  by  new  age  determinations. 

Utah.  The  Precambrian  rock  succession  in  central  Utah  is  shown  in 
the  correlation  chart  of  Fig.  4.5.  The  Farmington  Canyon  complex  is  the 
basement  rock  and  consists  of  gneisses,  schists,  and  granulites,  about 
20,000  feet  thick,  once  a  stratified  sequence  of  arkose,  calcareous  shale, 
impure  dolomitic  and  tuffaceous  beds,  and  very  pure  quartz  sandstone. 
Metamorphism  is  of  the  lower  amphibolite  facies  and  therefore  medium- 
grade  (Larson,  1957;  Bell,  1951).  The  metamorphism  is  dated  as  1590 
m.y.  (Gast  and  Long,  1957). 

Another  sequence  of  beds,  the  Willow  Creek  and  Harrison,  seems  to 
be  of  intermediate  age,  and  it  is  not  clear  yet  whether  they  were  in- 
volved in  the  Mazatzal  orogeny.  The  Farmington  Canyon  complex  is 
overlain  unconformably  by  the  Big  Cottonwood  quartzite  and  argillite 
series  and  did  not  participate  in  the  metamorphism  of  the  older  gneisses 
and  schists. 

The  Big  Cottonwood  and  Uinta  series  are  generally  correlated  with  the 
Belt  series  of  western  Montana  which  is  very  thick  and  widespread.  These 
will  be  referred  to  under  the  next  heading. 

Beltian  Orogenic  Belt 

A  major  trough  or  geosyncline  of  sediments  and  volcanic  rocks  of  post- 
Mazatzal  age,  yet  pre-Paleozoic  age,  extends  north  and  south  from  the 
Mexican  border  through  Arizona,  Utah,  Idaho,  western  Montana,  eastern 
Washington,  western  Alberta,  and  eastern  British  Columbia  to  the 
Yukon,  and  possibly  into  Alaska.  Its  stratigraphy  is  complex,  and  much 
remains  to  be  discovered  and  worked  out.  Two  major  divisions  appear 
to  stand  out,  namely,  a  lower  one,  the  Beltian,  and  an  upper  one,  which  is 
typified  by  a  thick  and  well-described  succession  in  the  western  Purcell 


Range  (Reesor,  1957)  and  in  northeastern  Washington   (Park  and  Can* 
non,   1943).   It  has  been  referred  to  as   the    Upper   Purcell    b)    1 
(1957)  and  also  as  the  Lipalian  series  by  Gussow   (  L957).   In  northern 
Utah,  it  may  find  representation  in  the  Mineral  Fork  tillite  and   Mutual 
formation  (Crittenden  et  al.,  1952). 

Angular  unconformities  have  been  recognized  in  a  number  of  places  up 
and  down  the  trough  between  the  Beltian  and  Metaline  sequences  and 
between  them  and  the  overlying  Cambrian.  In  central  Arizona  Mazatzal 
Mountains)  the  Apache  (Beltian)  group  is  tilted,  beveled,  and  overlain 
by  the  Cambrian.  In  the  Grand  Canyon  of  northern  Arizona,  the  Grand 
Canyon  series  (Beltian)  group  is  tilted,  faulted,  beveled,  and  overlain  by 
the  Cambrian.  In  north-central  Utah  12,000  to  15,000  feet  of  the  Big 
Cottonwood  series  (Beltian)  and  the  Mutual  formation  are  cut  out 
beneath  the  basal  Cambrian  angular  unconformity. 

In  western  Montana  and  southeastern  British  Columbia  Deiss  (1935) 
believes  the  Beltian  strata  were  strongly  uplifted,  tilted,  mildly  folded, 
and  eroded  before  the  Cambrian  beds  were  laid  down.  In  the  Purcell 
Range  Cambrian  beds  lie  across  various  Purcell  formations  (Beltian) 
through  a  stratigraphic  interval  of  8000  feet,  and  although  the  dis- 
cordance is  generally  slight,  in  one  place  it  is  90  degrees  (White,  1959). 
Large  sills  and  dikes  are  present  in  this  region  and  probably  accompanied 
the  orogeny.  Campbell  (1959)  recognizes  an  unconfromity  between 
Middle  Cambrian  and  Beltian  strata  in  northwestern  Montana  and  north- 
ern Idaho  in  which  up  to  18,000  feet  of  Beltian  is  missing. 

Stimulated  by  a  paper  by  Weiss  (1959)  the  writer  has  prepared  a 
cross  section  from  northeastern  Washington  across  southern  British- 
Columbia  to  Waterton,  Alberta,  showing  postulated  conditions  at  the 
beginning  of  Middle  Cambrian  time  (Fig.  4.6).  The  Beltian  correlatives 
would  be  the  Deer  Trail,  Priest  River,  and  Lower  Purcell  groups.  The 
LTpper  Purcell  group  would  include  the  Monk,  Three  Sisters,  and  Horse- 
thief  Creek  association,  the  Huckleberry,  Leola,  Irene,  and  Purcell  vol- 
canics,  and  the  basal  Huckleberry,  Shedroof,  and  Toby  conglomerates.  It 
may  be  seen  that  the  Upper  Purcell  group  rests  unconformly  on  the 
Beltian  and  is  introduced  by  a  thick  and  widespread  conglomerate.  This 
unconformity  is  taken  specifically  to  mark  the  orogeny  of  the  Beltian 


30 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


PROMONTORY 
RANGE  (Olsen) 


WESTERN 
UINTA  WITS. 

ILARSEN) 
€   QTZ. 


RED  PINE 
SHALE 


\, 

x3 

\4_ 

S 

UTAH 

Fig.   4.5.      Correlation    chart    of    Precambrian    formations    in    northern    Utah.   After    Larson,    1957. 


orogenic  belt,  and  its  extent  is  assumed  to  be  approximately  that  of  the 
Beltian  trough.  The  conglomerates  appear  to  have  come  from  the  west, 
and  if  so,  the  orogeny  was  most  severe  along  the  western  margin  of  the 
trough. 

The  age  of  the  Beltian  orogeny  cannot  be  accurataely  fixed  with  exist- 


ing data.  A  sample  of  illite  from  a  shale  in  the  Siyeh  formation  in  Glacier 
National  Park  (Goldich  et  al,  1959)  yielded  a  date  of  740  m.y.  by  the 
potassium-argon  method  and  780  m.y.  by  the  strontium-rubidium  method. 
Goldich  et  al.  reason  that  this  age  is  not  a  time  of  metamorphism  but 
more  probably  marks  the  time  of  deposition.  The  Siyeh  formation  is  near 


PRECAMBRIAN  TECTONIC  PROVINCES 


TURTLE 
LAKE 
QUAD. 


MAGNESITE 
BELT 


METALINE 
QUAD. 


LITTLE 
SALMO 


PURCELL      RANGE  CRANBROOK  GALTON 

WESTERN  DIVIDE  RANGE 


WATERTON 


MIDDLE   CAMBRIAN 


PEND   OREILLE 
METALINE  LS.  GR. 


LARDEAU   SER 


LOWER  CAMBRIAN::::  :•■••••■.  •.••.•;  •.••.;••.■:•.• 

;   •.AppYQUARTZITE'-.':- 


MAITLANO   PHYLLITE     LAIB  GR 
•QUARTZ  IT  E  R 


"UPPER  PURCELL       s  M  F  PPARD--KJNJ' L_A 
^PURCELL    LAVA 


10,000 


■  20,000 


130,000 
VERTICAL    SCALE 
IN    FEET 


Fig.   4.6.      Suggested   correlation   of   Precambrian   formations  of   southern    British    Columbia    and    northeastern 
Washington,  after  Reesor  (1957)  and  Weiss  (1959),  restored  to  Middle  Cambrian  time. 


the  top  of  the  Belt  series,  and  the  Beltian  orogeny  occurred  soon  after  its 
deposition,  so  the  date  is  about  as  good  for  the  time  of  deposition  as  for 
the  metamorphism,  if  any,  or  orogeny. 

In  conflict  with  the  illite  date  we  note  that  samples  of  uraninite  in  a 
vein  system  in  the  Coeur  d'Alene  district  of  Idaho  that  cuts  folded  meta- 
sedimentary  rocks  of  the  St.  Regis  formation  of  the  Belt  series  have 
yielded  a  date  of  approximately  1190  m.y.  (Eckelmann  and  Kulp,  1957). 


Although  different  laboratories  have  confirmed  this  date,  Wehrenberg 
(personal  communication)  thinks  there  is  still  justification  to  question  its 
validity  in  dating  the  age  of  the  strata  and  their  folding.  The  St.  Regis 
is  about  three-quarters  of  the  way  up  from  the  lowermost  beds  of  the 
Belt  exposed.  From  samples  of  galena  in  the  same  mine  Farquhar  and 
Cummings  (1954)  give  the  age  as  1030  =*=  290  m.y. 

It  is  clear  from  Fig.  4.3  that  the  Belt  sediments  and  correlatives  lie  in 


32 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


a  great  elongate  basin  generally  north-south  and  parallel  to  the  Pacific 
margin  of  the  continent,  and  that  the  basin  is  discordant  with  the  older 
orogenic  belts,  across  which  it  lies.  This,  if  true,  is  of  great  significance. 
It  suggests  that  following  the  Mazatzal  orogeny  that  a  major  part  of  the 
western  margin  of  the  continent  was  removed,  because  the  older  belts  of 
orogeny  now  extend  at  nearly  right  angles  to  the  continental  margin. 
It  also  suggests  that  in  Beltian  time  the  processes  of  sedimentation  and 
orogeny  first  became  established  along  and  parallel  to  the  present  con- 
tinental margin. 

The  discordant  relation  of  the  Beltian  trough  and  orogenic  belt  to  the 
older  belts  emphasizes  the  concern  that  must  be  attached  to  the  uraninite 
date.  It  is  almost  as  old  as  the  Mazatzal  orogeny,  and  presumably  should 
be  separated  from  it  by  considerable  time. 

Not  only  is  the  Beltian  orogenic  belt  discordant  with  the  Mazatzal 
orogenic  belt,  but  also  are  the  Antler  and  Shuswap  belt  and  Nevadan  belt 
which  lie  west  and  parallel  with  the  Beltian  ( see  Chapters  6  and  17 ) .  If 
the  theory  is  held  that  the  nucleus  of  the  continent  has  been  added  to  by 
successively  younger  orogenic  belts,  then  some  major  change  occurred 
to  the  southwest  margin  of  the  North  American  continent  in  Beltian  or 
pre-Beltian  time.  Perhaps  a  major  part  of  the  southwest  margin  as  it  ex- 
isted in  pre-Beltian  time  is  missing,  but  no  plausible  theory  of  translation 
or  foundering  has  been  thought  of  to  restore  the  missing  part.  It  is  con- 
ceivable that  a  major  change  occurred  in  the  constitution  and  assembly 
of  the  continents  in  the  interval  of  time  immediately  preceding  the 
Beltian. 

Purcell  Orogenic  Belt 

Following  the  Beltian  orogeny  in  the  southern  British  Columbia  and 
northeastern  Washington  region  a  thick  conglomerate  was  deposited,  and 
then  extensive  volcanic  rocks  were  spread  all  the  way  from  the  Columbia 
River  in  Washington  to  Waterton,  Alberta.  These  were  followed  by  sand- 
stones and  argillites,  particularly  in  a  main  trough  in  the  Purcell  Range 
area.  After  this  depositional  and  volcanic  cycle  another  disturbance  oc- 
curred in  which,  in  the  Purcell  Divide  area,  the  entire  series  was  removed 
together  with   a   considerable  thickness   of  the   underlying   Belt   series 


(Weiss,  1959).  This  unconformity  attests  the  removal  of  a  greater  thick- 
ness of  strata  than  the  one  at  the  base  of  the  Shedroof-Toby  con- 
glomerates, according  to  Weiss.  See  Fig.  4.6. 

The  overlying  Lower  Cambrian  quartzite  appears  to  have  been  derived 
from  the  west,  like  the  basal  Huckleberry-Shedroof-Toby  conglomerate, 
and,  if  so,  indicates  that  the  major  axis  of  orogeny  lay  to  the  west.  The 
zone  from  the  Purcell  Range  to  the  front  of  the  present  Rockies  was  a 
broad  geanticline  across  which  the  Early  Cambrian  seas  failed  to  spread. 
The  Middle  Cambrian  seas,  however,  probably  transgressed  much  of  the 
geanticlinal  area  (Campbell,  1959). 

The  orogeny  of  post-Monk  and  Three  Sisters  age,  yet  of  pre-Early 
Cambrian  age,  will  here  be  called  the  Purcell. 

In  dealing  with  Precambrian  formations  distant  correlations  are  gener- 
ally questionable,  and  this  is  especially  so  when  assuming  that  the 
Mineral  Fork  tillite  and  Mutual  strata  of  northern  Utah  are  equivalent 
to  the  Upper  Purcell  group.  If  valid,  however,  an  orogeny  can  be  said 
to  have  occurred  after  the  close  of  Mutual  time  and  before  the  late 
Lower  Cambrian  sands  were  spread  across  the  beveled  edges  of  these 
formations  as  well  as  those  of  the  Big  Cottonwood  series.  It  is  not  clear 
how  discordant  the  tillite  and  Mutual  are  to  the  underlying  Big  Cotton- 
wood strata  because  of  limited  exposures,  but  Crittenden  et  al.  (1952) 
note  that  the  tillite  occupies  broad  smooth-bottomed  basins  scooped  out 
of  the  upper  part  of  the  Big  Cottonwood  series. 

Both  the  Beltian  and  Purcell  orogenies  may  be  combined  in  one  angular 
unconformity  in  the  Grand  Canyon  of  the  Colorado  in  northern 
Arizona.  It  is  evident  that  information  on  the  extent  of  the  Beltian  and 
Purcell  orogenies  in  scanty  and  that  the  pronouncements  of  the  preceding 
paragraphs  are  postulates  of  fairly  tenuous  nature. 

Keweenawan  Belt 

The  Keweenawan  series  of  the  Lake  Superior  region  is  the  youngest 
of  the  Precambrian  rocks  there  and  is  well  known  because  of  the  great 
value  of  its  copper  mineralization.  An  imposing  sill  dated  1100  m.y.  by 
Goldich  (personal  communication)  and  believed  to  be  part  of  the  Ke- 
weenawan series,  crops  out  along  the  northwest  shore  of  Lake  Superior. 


PRECAMBRIAN  TECTONIC  PROVINCES 


33 


It  is  called  the  Duluth  gabbro.  Three  divisions  of  the  Keweenawan  are 
recognized,  namely,  a  lower  clastic  sequence  1400  feet  thick,  then  a 
thick  unit  of  basic  amydaloidal  lava  flows  interbeddcd  with  sandstones 
and  conglomerates,  and  at  the  top  a  continental  clastic  sequence  possibly 
reaching  a  thickness  of  25,000  feet  in  the  center  of  the  basin  of  ac- 
cumulation. The  widespread  extent  of  the  flows  and  the  paucity  of  ash 
suggest  that  the  flows  issued  from  a  system  of  fissures  rather  than  central 
vents.  Associated  with  the  flows  and  intruded  into  them  are  numerous 
dikes  and  sills,  dominantly  basic.  The  most  prominent  sill  is  the  Duluth 
gabbro. 

The  thick  upper  Keweenawan  elastics  consist  of  red  feldspathic  shaly 
sandstones  at  the  base  and  these  grade  upward  into  arkosic  and  quartzose 
sandstones.  They  accumulated  as  the  basin  foundered  in  response,  pre- 
sumably, to  the  extrusion  of  the  large  volume  of  volcanics.  Highlands 
existed  on  both  sides  of  the  basin  (Hamblin  and  Horner,  1961). 

Several  large  faults  break  the  Keweenawan  series.  The  Douglas  and 
Keweenawan  are  found  on  opposite  sides  of  the  synclinal  or  basin  axis 
with  thrusting  away  from  the  axis.  See  map,  Fig.  4.3  and  cross  sections 
of  Fig.  4.7.  Vertical  displacements  up  to  4  miles  are  indicated  by  the  cross 
sections.  The  North  Shore  fault,  postulated  from  physiographic  data 
solely  (principally  from  the  straight  shorelines)  was  not  detected  by 
gravity  surveys,  but  the  surveys  do  not  rule  out  its  existence.  If  it  is  a 
reality,  it  may  be  a  normal  fault  and  of  later  age  than  the  reverse  faults. 
The  orogeny  of  post-Keweenawan  time  consisting  of  volcanism  and  fault- 
ing has  been  called  the  Killarnean  and  is  dated  at  about  950  m.y.  ( Fair- 
bairn  et  al,  1960). 

The  sills  and  volcanic  rocks  are  strongly  reflected  by  positive  gravity 
anomalies,  and  the  deep  basins  of  clastic  rocks  by  negative  anomalies. 
Thiel  (1956)  has  recognized  this  fact  and  traced  the  Keweenawan  series 
under  the  Paleozoic  sedimentary  rock  cover  by  means  of  these  strong 
anomalies  southwestward  to  the  Salina  basin  of  Kansas.  The  positive 
feature  has  an  average  width  of  30  miles  and  an  amplitude  of  100  miligals 
above  the  regional  gravity  value.  For  the  greater  part  of  its  length  it  is 
flanked  on  both  sides  by  gravity  lows.  The  igneous  rock  masses  are 
responsible  for  the  gravity  highs  and  the  clastic-filled  basins,  the  lows. 


CLASTICS 


RED-ROCK 
PHASE 


DULUTH     GABBRO 


-I 


20     MILES 
Fig.  4.7.      Keweenawan   orogenic  belt.  Sections  in  the  Duluth  area   after  Thiel,   1956. 

The  Keweenawan  belt  projects  toward  the  volcanic  and  gabbroic 
terranes  of  Oklahoma  and  Texas,  and  perhaps  these  are  part  of  the  same 
tectono-igneous  belt.  No  strong  gravity  anomalies  are  known  between 
Kansas  and  Texas,  but  the  grain  of  gravity  contours  (Lyons,  1950)  is 
southwesterly,  and  thus  the  belt  may  be  marked  by  sedimentary  rocks 
and  an  absence  of  volcanic  in  this  region. 

The  Precambrian  rocks  of  the  Wichita  Mountains  of  Oklahoma  rep- 
resent   the    upper    granitic    part    of    a    large    gabbroic    lopolith    which 


34 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


CENTRAL  TEXAS 

NORTH  TEXAS 

TEXAS  PANHANDLE 

WICHITA  MOUNTAINS- 
BURIED  AMARILLO 
MOUNTAINS 

ARBUCKI.E  MOUNTAINS 

VAN  HORN  AREA 

WEST  MARGIN  OF  TEXAS 

CRATON ;  FRANKLIN 

MOUNTAINS;  SOUTHEAST 

NEW  MEXICO 

LATE 
PRECAMBRIAN 

sedimentary  rocks 
(Van  Horn  sandstone) 

SWISHER  GABBROIC 

TERRANE 
emplacement  of  gabbro 
(lopolith?)  ;  contact 
metamorphism  of  sedi- 
mentary rocks 

WICHITA  IGNEOUS 
PROVINCE 

gabbro-granite  (670m.y.) 
intrusion;  contact  meta- 
morphism of  sedimentary 
rocks  (Meers  quartzite) 

local  orogeny — cata- 
clastic  metamorphism; 
diorite  intrusion 

subsidence;  sedimentary 
rocks  (carbonate  rocks 
and  siltstones) 

sedimentary  rocks 
Meers  quartzite) 

sedimentary  rocks 
(Allamoore  and  Hazel 
formations) 

PANHANDLE 
VOLCANIC  TERRANE 
lavas,  tuffs,  shallow 
intrusives — mostly 
rhyolite 

rhyolite  intrusions? 
(East  and  West  Timbered 
Hills  porphyries) 

rhyolite  intrusions 

rhyolite  intrusions  and 
extrusions 

FISHER 
METASEDIMENTARY 

TERRANE 
regional  metamorphism 
of  sedimentary  rocks 

RED  RIVER 
MOBILE  BELT 
regional  metamorphism 
of  sedimentary  rocks; 
intrusion 

synorogenic?  granite 
intrusions 

VAN  HORN 
MOBILE  BELT 
regional  metamorphism 
(Carrizo  Mountain 
group  pre-rhyolite) 

regional  metamorphism 
of  sedimentary  rocks 
(Lanoria  quartzite?) 

MIDDLE 
PRECAMBRIAN 

TEXAS CRATON 
granitic  intrusions 
(about  1000  m.y.) 

Texas  era  ton  to  south 

TEXAS  CRATON 
granitic  intrusions 

Texas  craton  to  north 
and  northeast 

Texas  craton  to  east 

regional  metamorphism 
and  intrusion  (Valley 
Spring  gneiss,  Pack- 
saddle  schist,  older 
gneissic  meta-igneous 
rocks. 

Fig.   4.8.      Tentative   correlation   of   Precambrian    rocks   and   structural   events   in   Texas,   southern   Oklahoma, 
and  southeast  New  Mexico.  Reproduced  from   Flawn,   1956. 


Hamilton    (1956c)    thinks    might    correlate    with    the    Duluth    gabbro. 

The  lithologies  and  age  relations  recognized  by  Flawn  (1956)  of  the 
Texas  Precambrian  rocks  leave  considerable  to  be  desired  for  a  conclusive 
tie  with  the  Keweenawan  belt.  The  volcanics  are  mostly  rhyolite  and 
not  basic  varieties  as  in  the  Keweenawan  series,  and  orogeny  including 
acidic  intrusions  and  some  metamorphism  appears  to  be  indicated.  This 
is  not  characteristic  of  the  Keweenawan  belt. 

J.  Tuzo  Wilson  (1956)  has  suggested  that  the  sediments  of  the  Ke- 
weenawan, Huronian,  and  Mistassini  groups  along  the  Grenville  front 


in  Ontario  and  Quebec  have  been  derived  from  the  Grenville  orogenic 
belt,  and  that  a  secondary  mountain  belt  has  resulted  by  their  deforma- 
tion at  a  later  time.  The  Huronian  rocks  in  Minnesota,  Wisconsin,  and 
Michigan  have  a  much  wider  distribution  than  the  Keweenawan  series 
with  its  flanking  faults,  and  are  not  so  clearly  a  narrow  belt  as  the 
Keweenawan.  The  writer  sees  in  the  Keweenawan  belt  one  somewhat 
like  the  Triassic  basins  of  the  Piedmont  crystalline  province  of  the  greater 
Appalachian  mountain  systems.  See  Chapter  9.  These  are  long  narrow 
fault-formed  basins  filled  with  thick  sections  of  continental  clastic  sedi- 


PRECAMBRIAN  TECTONIC  PROVINCES 


35 


PRECAMBRIAN 
STRUCTURAL 
TRENDS 


MINERAL 
PROVIN 


DATE 
CES 


Fig.  4.9.      Precambrian  structural  trends  (left  map)  and   mineral  date  provinces  (right  map)   of   North 
America.  Reproduced  from   Gastil,   1960. 


ments  and  basic  flows,  sills,  and  dikes.  The  basalts  have  been  described 
as  tholeiitic  in  both  belts  (Turner  and  Verhoogen,  1951).  The  signifi- 
cance of  tholeiitic  basalt  is  discussed  in  Chapter  33,  and  the  occurrence  is 
believed  to  be  evidence  that  the  belts  formed  under  similar  tectonic 
settings.  Both  are  on  the  inside  (toward  the  continent)  of  master  orogenic 
belts  involving  extensive  metamorphism  and  great  batholithic  intrusions. 
According  to  this  interpretation  the  Keweenawan  belt  should  mark  ap- 
proximately the  inner  front  of  the  Grenville  orogenic  belt  or  province. 
Regarding  the  succession  in  Texas,  it  is  possible  that  the  Swisher 


gabbroic  terrane  and  parts  of  the  Wichita  igneous  terrane  arc  Keweena- 
wan equivalents,  and  that  the  metasedimentary  and  volcanic  (rhyolite) 
terranes  are  Huronian  or  somewhat  older  than  the  Keweenawan. 

Texas  Precambrian  Rocks 

In  Texas  and  southeastern  New  Mexico  a  subsurface  study  of  well 
samples  penetrating  the  Precambrian  has  enabled  Flawn  (1956">  to 
delimit  several  rock  assemblages,  which  he  calls  terranes  I  Fig.  Is  .  The 
basement  rock  is  a  granite  dated  about  100  m.y.  old,  and  this  is  overlain 


36 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


apparently  unconformably  by  metasedimentary  and  volcanic  rocks,  and  in 
one  place  by  a  gabbro  sheet  (?).  The  granitic  intrusion  therefore,  cor- 
related in  age  with  the  Grenville  and  Piedmont  orogenies,  and  the  meta- 
sediments  and  volcanics  presumably  with  the  Keweenawan  series  of  the 
Lake  Superior  region.  The  Mazatzal  orogenic  belt  appears  to  separate  the 
Texas  Precambrian  assemblage  from  the  Grenville,  and  hence,  the  most 
natural  tectonic  tie  of  the  Texas  assemblage  appears  to  be  with  the  Pied- 
mont (Fig.  4.3). 

Crystalline  Piedmont 

A  broad  belt  of  crystalline  rocks  extends  from  Alabama  and  Georgia 
northeastward  along  the  Atlantic  margin  of  the  continent  to  New  Jersey, 
and  its  relation  to  the  Appalachian  Mountains  will  be  explained  in  some 
detail  in  Chapters  8  and  9.  In  summary,  its  rocks  are  now  believed  to  be 


Precambrian  and  early  Paleozoic  in  age,  and  to  have  been  metamorphosed 
and  intruded  particularly  during  the  Taconic  and  Acadian  orogenies  of 
Late  Ordovician  and  Late  Devonian  ages,  respectively.  Age  determina- 
tions on  the  rocks  of  the  Piedmont  indicate  two  ages,  namely,  an  older 
one  of  Grenville  age  and  a  younger  one  of  Paleozoic  age.  In  fact,  in  one 
sample  the  zircon  grains  yielded  an  age  of  1050  m.y.,  and  the  feldspars 
an  age  of  300  =*=  m.y.  (Wetherill  et  al.,  1959).  It  is  reasoned  that  this 
means  an  early  orogeny  in  which  the  zircons  were  created,  and  a  late 
orogeny  in  which  the  feldspars  were  formed  but  the  zircons  of  the 
early  orogeny  left  unaltered. 

The  distribution  of  dates  so  far  published  is  shown  on  Fig.  4.3  and  a 
comprehensive  compilation  and  interpretation  of  Precambrian  trends  and 
orogenic  belts  of  North  America  by  Gastil  (1960)  is  reproduced  in  Fig. 
4.9. 


5. 


CENTRAL  STABLE  REGION 
OF  THE  UNITED  STATES 


other  structures  of  the  Central  Stable  Region,  with  few  <-\(  eptions,  formed 
during  the  Paleozoic  era,  and  many  of  them  yield  <  \  idenoe  ol  a  prolonged 
history  of  development. 

Up  to  Pennsylvania!!  time,  there  was  a  certain  bilateral  symmetry  to 
the  stable  region,  with  a  great  medial  transcontinental  arch,  and  basins 
and  smaller  arches  on  either  side.  An  approximate  parallelism  of  a  s<n<s 
of  arches  with  the  Ouachita  and  Appalachian  orogenic  belts  was  existent 
and  is  still  apparent  today. 

During  Mississippian,  Pennsylvanian,  and  Permian  time,  great  overlaps 
on  some  of  the  arches  occurred.  Others  were  either  not  completely  buried 
or  have  since  been  partially  exhumed  by  erosion.  In  some  areas  the 
Triassic  overlapped  on  the  Central  Stable  Region  beyond  the  limits  of  the 
Permian,  and  especially  in  late  Cretaceous  time  did  epeiric  seas  exten- 
sively invade  the  region  of  arches  and  basins. 

The  large  arches  and  basins  are  rippled  and  checked  with  numerous 
folds  and  faults;  and  these,  with  the  unconformities  created  by  the  great 
overlaps,  constitute  immensely  valuable  structures  for  oil  and  gas  accumu- 
lation. The  strata  also  contain  great  coal  deposits  and  numerous  other 
nonmetallic  mineral  resources.  Each  basin  and  each  arch  will,  therefore, 
be  considered  separately.  The  geologic  and  tectonic  maps  of  Chapter 
3  will  be  especially  helpful  in  relating  the  diastrophic  histories  of  the 
various  major  structures,  and  should  be  referred  to  repeatedly. 


GENERAL  CHARACTERISTICS 

The  Central  Stable  Region  of  the  United  States  is  made  up  of  a  founda- 
tion of  Precambrian  crystalline  rock  previously  described,  with  a  veneer 
of  sedimentary  rock.  The  veneer  varies  greatly  in  thickness  from  place 
1  to  place.  For  the  most  part,  the  Central  Stable  Region  has  suffered  vertical 
movements,  and  broad  basins  and  arches  have  formed.  Some  of  the 
basins  have  more  than  10,000  feet  of  strata  in  them,  and  in  the  cores  of 
some  of  the  arches  the  Precambrian  crystalline  rock  is  exposed.  Some  of 
the  arches  and  sharper  uplifts  are  not  expressed  in  the  surficial  layers  and 
have  been  revealed  only  by  drilling  operations.  The  arches,  basins,  and 


PRE-DEVONIAN  BASINS 

The  basins  of  greatest  extent  and  deepest  subsidence  in  early  Paleozoic 
time  were  the  geosynclines  along  the  western  and  eastern  margins  of  the 
continent.  Each  constitutes  an  important  part  of  our  continent  and  will 
be  discussed  in  separate  chapters:  the  Paleozoic  Cordilleras  geosyncline 
in  Chapter  6,  and  the  Appalachian  geosyncline  in  Chapters  7.  8,  11.  12.  and 
13.  Refer  to  the  map  of  Plate  2,  Chapter  3,  in  the  following  paragraphs. 

The  Appalachian  geosyncline  subsided  most  in  West  Virginia,  Virginia, 
Tennessee,  and  Alabama.  In  a  small  area  across  the  border  of  Virginia 
and  Tennessee,  sediments  accumulated  to  a  thickness  in  excess  of  25.(KX) 
feet  during  Cambrian,  Ordovician,  and  Silurian  time.  A  distinct  sag  in  the 


37 


38 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


form  of  an  embayment  from  Texas  into  southern  Oklahoma  resulted  in 
the  local  accumulation  of  more  than  6000  feet  of  strata,  the  chief  forma- 
tion of  which  was  the  Arbuckle  limestone.  Another  embayment  possibly 
extended  to  the  western  Texas  region,  where  later  the  Pecos  Range  de- 
veloped. The  pre-Devonian  sediments  are  thin  in  the  Marathon  and 
Ouachita  systems  as  compared  with  the  Appalachian  system. 

A  rather  deep  basin  formed  in  Michigan,  Indiana,  and  Illinois  in  pre- 
Devonian  time,  approximately  parallel  with  the  Appalachian  geosyncline. 
Its  largest  and  deepest  part  is  the  present  Michigan  basin. 

The  great  western  geosyncline  of  early  Paleozoic  time  extended  from 
Alaska  to  southern  California.  It  sank  15,000  to  20,000  feet  across  Nevada, 
and  at  the  Nevada-California  boundary  it  contained  over  20,000  feet  of 
beds  (Nolan,  1943).  No  information  is  available  farther  southwest  in 
California  because  of  the  extensive  Mesozoic  and  Cenozoic  cover,  in- 
tensive metamorphism,  and  widespread  Jurassic  intrusions.  The  south 
termination  of  the  geosyncline  shown  on  the  map  is,  therefore,  hypo- 
thetical. The  inner  trough  of  the  geosyncline  becomes  progressively  deeper 
to  the  southwest  and  undeniably  heads  into  the  later  Jurassic  orogenic 
belt,  which  with  still  younger  tectonic  elements  determines  the  margin  of 
the  continent  today. 

TRANSCONTINENTAL  ARCH 

General  Features 

During  Devonian  and  Mississippian  time  the  great  Central  Stable 
Region  of  North  America  consisted  of  three  major  divisions,  a  central 
northeast-southwest-trending  Transcontinental  Arch,  and  large  basins, 
shelves,  and  arches  and  domes  of  various  sizes  on  each  side  (Plates  3  and 
5).  The  arch  had  three  peninsular  extensions  to  the  southeast,  one  into 
Kansas  and  Missouri,  the  Ellis  and  Chautauqua  arches  and  the  Ozark 
dome;  one  into  Wisconsin,  the  Wisconsin  dome;  and  possibly  one  into 
Texas.  It  is  also  known  to  have  sagged  below  sea  level  in  two  places 
where  thin  lower  Paleozoic  sediments  were  deposited,  one  in  Colorado 
and  one  in  Arizona.  Until  the  rise  of  the  ranges  of  the  Ancestral  Rockies 
and  the  Wichita  systems,  the  Transcontinental  Arch  and  its  flanking 


basins  dominated  the  landscape.  The  Transcontinental  Arch  may  have 
bifurcated  north  of  Lake  Superior,  with  one  arm  extending  northward 
on  the  west  side  of  the  Hudson  Bay  basin,  and  the  other  extending  first 
eastward  and  then  northward  along  the  east  side  of  the  basin.  This  sup- 
position is  based  on  present  Precambrian  exposures,  but  paleontological 
evidence  and  newly  found  erosional  outliers  suggest  that  much  of  the 
area  of  the  arms  may  have  been  submerged  in  early  Paleozoic  time. 

Northeast  of  Colorado 

The  arch  in  Nebraska,  South  Dakota,  and  Minnesota  was  recognized 
by  Schuchert  and  called  Souxia.  It  was  later  clearly  depicted  by  Levorsen 
(1931,  PI.  1),  and  then  still  later  mapped  by  Ballard  (1942).  The 
boundaries  of  the  formations  shown  on  the  geologic  maps  of  the  close 
of  the  Devonian  and  the  close  of  the  Mississippian  are  those  preserved 
under  the  extensively  overlapping  Pennsylvanian  strata  (Plate  7)  which 
covered  most  of  the  arch.  Ballard  has  gathered  together  the  available  well 
records  of  the  area  and  believes  enough  data  is  at  hand  to  establish  defi- 
nitely the  existence  of  the  arch  and  fairly  well  the  formational  contacts 
on  either  side  of  it. 

The  arch  was  referred  to  as  the  continental  backbone  by  Keith  (1928) 
in  his  notable  paper  on  "Structural  symmetry  of  North  America,"  and 
later,  also,  by  Levorsen.  The  name  implies  that  it  was  a  strong,  resistant, 
centrally  located  tectonic  element  with  flanking  basins  and  marginal  oro- 
genic belts  in  bilateral  symmetry.  With  the  exception  of  the  peninsulas 
and  sags  previously  mentioned,  the  bilateral  symmetry  of  the  United 
States  part  of  the  continent  in  a  northeast  direction  was  pronounced  until 
the  Pennsylvanian  transgression.  The  building  of  the  Ancestral  Rockies 
altered  conspicuously  the  aspect  of  the  Transcontinental  Arch,  and  then 
the  late  Mesozoic  and  early  Cenozoic  mountain  building  disturbances 
left  the  southwest  half  unrecognizable  on  a  geologic  map  of  the  present 
time. 

The  Transcontinental  Arch  appears  very  dominant  on  a  pre-Pennsyl- 
vanian  geologic  map,  but  this  appearance  should  not  be  misinterpreted. 
During  the  Devonian  and  Mississippian,  the  arch  was  very  low-lying  and 
furnished  chiefly  chemical  sediments  to  its  flanking  basins  (Weller,  1931). 


CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES 


39 


The  "backbone"  was  also  not  very  strong  in  resisting  deformation.  In  its 
southwestern  part,  as  previously  mentioned,  it  was  the  site  of  Pennsvlva- 
nian  and  Cretaceous-Tertiary  mountain  building,  and  its  other  parts  have 
been  almost  completely  covered  by  Pennsylvanian,  Permian,  Mesozoic, 
jand  Cenozoic  strata,  in  places  of  considerable  thickness. 

Wisconsin  Dome 

The  area  of  central  Wisconsin  was  probably  uplifted  several  times  in 
the  Paleozoic,  but  evidence  both  for  time  and  spatial  relations  is  scarce 
and,  therefore,  all  the  geologic  boundaries  cannot  be  definitely  fixed. 
The  isopach  maps  of  the  Ninth  Annual  Field  Conference  of  the  Kansas 
Geological  Society  have  been  used  as  the  chief  source  of  information  in 

i  making  the  interpretations  shown  on  the  maps  of  this  book.  The  isopach 
maps  generally  show  the  existing  thickness  of  the  various  formations  or 
groups,  and  their  compilers  say  that  the  original  thickness  and  extent 
over  the  Wisconsin  dome  area  is  not  certain.  However,  some  of  the 
formations  thicken  basinward  under  cover  of  protecting  formations,  and 

!  such  contacts  can  be  projected  and  the  limits  before  burial  located  ap- 
proximately. 

Two  pre-Devonian  times  of  significant  uplift  are  recognized;  the  first 
preceded  the  deposition  of  the  St.  Peter  formation  in  Early  Ordovician 
time,  and  the  second  followed  the  deposition  of  the  Silurian  beds.  During 

;  the  second  uplift,  an  arch  was  formed  that  extended  southeastward  from 
Wisconsin  into  Illinois,  almost  to  the  city  of  Kankakee  (Fig.  220,  Ninth 
Annual  Field  Conference,  Kansas  Geological  Society). 

By  the  close  of  Mississippian  time,  a  pronounced  dome  had  appeared 
(Plate  6).  A  strip  of  Cambrian  sediments  extending  southwest  from  the 
Keweenaw  peninsula  of  Michigan  indicates  that  the  dome  was  separated 
from  the  Transcontinental  Arch  by  a  fairly  broad,  gentle  syncline.  A 
broad,  noselike  uplift  extended  southeastward  from  the  Wisconsin  dome 
in  approximately  the  position  of  the  post-Silurian  arch  and  connected  with 
the  Kankakee  arch  of  Illinois  and  Indiana  (Plate  6).  How  far  the 
Mississippian  sediments  spread  over  the  dome  area  is  not  ascertainable, 
but  following  the  late  Mississippian  uplift  they  were  eroded  back  appre- 
ciably. 


Colorado  and  Arizona 

The  rise  of  the  Ancestral  Rockies  in  late  Mississippian  and  Pennsylva- 
nia!) time  destroyed  the  Transcontinental  Arch  in  Colorado.  The  pre- 
Pennsylvanian  sediments  present  are  very  thin,  and  cover  the  arch 
throng!)  central  Colorado  in  a  /one  100  miles  wide.  The  zone  was  i 
dently  the  site  of  a  gentle  sag  in  the  arch  norma]  to  its  length,  and  as 
Burbank's  (1933)  map  shows,  it  lines  up  almost  precisely  with  the 
Wichita  trough  that  others  have  shown  in  Oklahoma  and  Kans.is.  It 
seems,  therefore,  that  the  Wichita  trough  extended  northwestward  toward 
the  Colorado  sag,  and  not  in  the  direction  of  the  Amarillo  Mountains  in 
the  Panhandle  of  Texas  as  has  been  suggested  by  some  writers. 

Arizona  was  mostly  above  water  during  the  early  Paleozoic  (Stoyanow, 
1942).  The  Mazatzal  orogeny  of  Precambrian  time  (sec  previous  dis- 
cussion in  this  chapter)  produced  a  chain  of  mountains  that  extended 
from  southwestern  Arizona  to  southwestern  Colorado  with  subparalli  1 
folds  and  thrust  faults  trending  northeastward  (Huddle  and  Dobrovolny, 
1950). 


The  orogeny  and  associated  intrusions  took  place  after  the  Mazatzal  quartzite 
was  deposited.  The  mountains  subsequently  were  well  worn  down  by  erosion, 
but  the  very  resistant  Mazatzal  quartzite  formed  ridges  along  the  core  of  the 
old  mountain  chain.  The  ridges  served  to  separate  the  basins  in  which  the 
rocks  of  the  Apache  and  Unkar  groups  were  deposited.  .  .  .  Both  were  con- 
siderably eroded  before  the  Troy  quartzite  and  Tapeats  sandstone  of  Cambrian 
age  were  deposited.  .  .  .  After  the  deposition  of  the  Cambrian  sandstones. 
Mazatzal  land  probably  was  up-arched  slightly  and  eroded,  because  the 
Martin  formation  in  central  Arizona  rests  on  a  surface  of  some  relief.  Then- 
are  neither  Ordovician  nor  Silurian  rocks  in  central  Arizona,  and  probably 
there  never  have  been  any.  Cambrian  rocks  may  have  extended  through  the 
Mogollon  sag,  and  a  considerable  thickness  of  them  may  have  been  removed 
from  Mazatzal  land  during  the  long  erosional  interval  between  the  retreat  oi 
the  Late  Cambrian  seas  and  the  spread  of  the  Late  Devonian  sets.  The 
gradual  burial  of  the  mountains  and  Mazatzal  land  before  Pennsylvanian  tunc 
is  summarized  diagrammatically  in  Fig.  4.4.  Because  the  Martin  formation 
was  not  deeplv  eroded  prior  to  the  deposition  of  the  RedwaD  limestone,  prob- 
ably no  diastrophic  disturbances  of  Mazatzal  land  occurred  at  the  close  of 
the  Devonian.  After  the  Mississippian  limestone  was  laid  down,  however, 
Mazatzal  land  again  was  uparched.  as  shown  by  the  great  erosional  reduction 


40 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


of  the  Redwall  limestone  on  Mazatzal  land  and  the  related  increase  in  the 
thickness  of  the  red  residual  member  of  the  Naco  formation  nearby  (Huddle 
and  Dobrovolny,  1950). 

EASTERN   INTERIOR   BASINS  AND  ARCHES 

General  Features 

Three  basins  of  subsidence  and  sedimentation  had  become  clearly 
established  by  late  Devonian  time  southeast  of  the  Transcontinental  Arch, 
namely,  the  Michigan  basin,  the  Illinois-Indiana-Kentucky  basin  (East- 
ern Interior  basin),  and  the  West  Virginia-Pennsylvanian  basin  (Appala- 
chian basin).  In  Pennsylvanian  time  a  fourth  became  defined,  which  is 


Fig.   5.1.      Basins   southeast   of  the   Transcontinental    Arch   showing   areas  of   sand   accumulation 
early  Pennsylvanian  time  and  the  direction  of  stream  transport.  After  Potter  and   Siever,   1956. 


called  the  Western  Interior  basin  as  a  coal  province,  and  the  Forest  City 
basin  as  an  oil  province.  See  map,  Fig.  5.1,  and  Plate  7.  The  Western 
Interior  and  Eastern  Interior  basins  were  first  so  labeled  when  studied 
as  coal  basins  of  Pennsylvanian  age,  and  although  the  nomenclature  is 
not  consistent  with  the  state  name  applied  to  the  Michigan  basin,  also  a 
coal  basin,  it  is  generally  retained  and  used  today. 

Appalachian  Basin 

The  history  of  the  Appalachian  basin  is  recounted  in  Chapter  7  in 
connection  with  the  Appalachian  Mountains.  As  shown  on  the  map,  Fig. 
5.1,  it  lies  between  the  Valley  and  Ridge  Province  of  the  Appalachians 
and  the  Cincinnati  arch,  but  in  its  development  its  deepest  part  lay  in 
the  mountainous  belt;  the  eastern  half  of  the  basin  became  involved  in 
folding  and  thrusting  in  late  Paleozoic  time  leaving  the  western  half 
relatively  undeformed  and  what  is  now  called  the  Appalachian  basin. 
See  Figs.  8.11  and  8.12.  It  is  filled  with  a  remarkable  succession  of 
miogeosynclinal  and  shelf  strata  ranging  in  age  from  Cambrian  to 
Permian. 

Michigan  Basin 

In  pre-Devonian  time,  the  Michigan  and  Illinois-Indiana-Kentucky 
basins  were  continuous;  but  beginning  in  the  Devonian,  the  Kankakee 
arch  began  to  form,  and  the  two  basins  became  increasingly  individual- 
istic thereafter.  The  Michigan  basin  today  is  circumscribed  by  the 
Great  Lakes  depressions  on  the  west,  north,  and  east,  and  by  the  Cin- 
cinnati dome  on  the  south.  It  consists  of  a  sequence  of  beds  representative 
of  all  periods  of  the  Paleozoic,  cast  in  saucer  fashion,  each  one  of  which 
is  smaller  than  the  preceding  on  which  it  rests.  The  youngest  strata  are 
thin  and  patchy  red  beds  of  either  Upper  Pennsylvanian  or  Permian  age. 
All  Paleozoic  strata  are  overlain  and  nearly  completely  blanketed  by  a 
layer  of  glacial  drift  which  ranges  in  thickness  from  a  few  feet  to  1200 
feet.  As  the  basin  subsided  through  the  Paleozoic,  its  crystalline  pre- 
cambrian  floor  acquired  the  configuration  shown  in  Figs.  5.2  and  5.3. 
The  total  thickness  of  sediments  in  the  basin  is  about  14,000  feet  ( Cohee, 
1948). 


CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES 


41 


The  major  unconformity  in  the  Paleozoic  sequence  is  at  the  base  of  the 
St.  Peter  sandstone  and  the  Trenton  and  Black  River  limestones.  See 
Figs.  5.4  and  5.5.  The  St.  Peter  sandstone  is  late  Lower  Ordovician,  and 
marks  the  time  of  uplift  and  erosion.  When  traced  eastward  from  Indiana 
to  Ohio  and  northeastward  into  Ontario  in  well  logs,  the  Lower  and 
Middle  Ordovician  formations  rest  successively  across  the  several  forma- 
tions of  the  Upper  Cambrian,  and  finally  come  to  rest  directly  on  the 
Precambrian  crystallines  of  the  Canadian  Shield.  Through  western 
Ontario,  the  Cambrian  beds  are  absent. 

Significant  units  in  the  Michigan  basin  are  the  evaporite  series  of  the 
Silurian  and  Devonian.  A  number  of  beds  of  salt  are  present  throughout 
much  of  the  basin  and  southwestern  Ontario  which  in  places  may  aggre- 
gate over  2000  feet  in  thickness.  Porous  dolomites  in  these  evaporite  series 
are  reservoir  rocks  for  oil  and  gas,  and  many  oil  fields  have  been  developed 
in  the  basin.  Very  gentle  folds  or  "highs"  ripple  the  basin  beds  and 
take  an  irregular  northwest-southeast  direction.  They  have  served  to  trap 
the  oil  (Fig.  5.4). 

In  the  Straits  of  Mackinac  region,  the  most  prominent  outcrops  are  a 
limestone  breccia.  It  is  noted  for  its  resistance  to  erosion  and  forms  the 
scenic  pillars  and  cliffs  of  the  region.  The  map  of  Fig.  5.6  shows  its  known 
distribution. 

The  columns  of  breccia,  according  to  Landes  ( 1945 ) ,  may  range  up  to 
1500  feet  in  vertical  dimension.  The  solution  of  Silurian  salt  has  resulted 
in  subsidence  and  roof  collapse,  and  the  breccias  are  the  result.  Certain 
blocks  can  be  shown  to  have  fallen  or  settled  600  feet.  The  formations 
involved  and  the  nature  of  the  breccias  are  illustrated  in  the  cross  section 
of  Fig.  5.7.  Supporting  the  salt  solution  and  collapse  theory  is  the  map 
showing  the  abrupt  thinning  of  the  Salina  salt  in  the  Mackinac  Straits 
region  (Fig.  5.8).  The  solution  of  salt  and  the  collapse  of  the  overlying 
layers  of  limestone  and  dolomite  took  place  chiefly  in  pre-Dundee  time 
( Middle  Devonian ) ,  but  even  now  some  leaching  may  be  occurring. 

Great  Lakes  Depressions 

The  Salina  salt  emerges  from  the  basin  in  a  horseshoe-shaped  pattern 
that  corresponds  closely  with  Lake  Michigan  and  Lake  Huron.  The  out- 


ILLINOIS 


Fig.   5.2.      Configuration    of   the   Precambrian   floor   in   the   Michigan    basin    and   adjoining    areas. 
Contours  in  thousands  of  feet.  After  Cohee,    1948. 


CAMBRIAN  8  ORDOVICIAhT 


Fig.  5.3.  Cross  section  of  the  Michigan  basin,  after  American  Association  of  Petroleum  Geolo- 
gists, 1954,  Geo/ogic  Cross  Section  of  Paleozoic  Rocks,  central  Mississippi  to  northern  Michigan. 
The   Cambrian    is    mostly   a   sandstone   and   shale   sequence;   the    Black    River   through   Traverse    a 


limestone,   dolomite,   and   evaporite   sequence,   the   Antrim   through   Michigan   a    shale   and   sand- 
stone sequence. 


CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES 


43 


I 


TRENTON    AND   BLACK  RIVER    LIMESTONES 


0 »    30         tfo  ^j, 


XATION  OF   SECTION 


Fig.  5.4.      Cross  section  from  Illinois  to  western  Ontario  showing  the  unconformity  at  the  base  of 
the  St.   Peter  sandstone  and  the  Trenton   and   Black  River  limestones.  Top  of  Trenton  is  taken  as 


horizontal    datum.    Younger    formations    and    present    structures    not    shown.    By    George    Cohee, 
U.S.  Geological  Survey. 


crop  then  swings  eastward  through  the  basins  of  Lake  Erie  and  Lake 
Ontario.  The  salt  would  emerge  mostly  under  water,  and  since  the 
aggregate  thickness  of  salt  beds  that  once  may  have  cropped  out  was 
several  hundred  feet,  it  has  been  suggested  ( Newcombe,  1933 )  that  the 
depressions  of  the  Great  Lakes  (excepting  Superior)  may  be  due  to  salt 
solution  and  consequent  subsidence.  The  basins  do  not  correspond  to 


faults  or  folds,  and  were  probably  existent  long  before  the  Pleistocene 
ice  lobes  occupied  them.  The  theory  of  salt  solution  seems  the  most  logi- 
cal explanation  yet  advanced. 

The  Lake  Superior  depression  is  north  of  the  belt  of  salt  outcrop  and  is 
mostly  in  Precambrian  rocks.  The  northwest  shore  may  correspond  to  a 
fault,  and  the  lake  bottom  topography  suggests  fault  scarps.  Because  the 


44 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Fig.    5.5.     Thickness   of    Upper    Cambrian    and    Lower    Ordovician    Rocks   in    the    Michigan    Basin. 
After   Cohee,    1948. 


SURFACE  EVIDENCE  OF  COLLAPSE 
x  SUBSURFACE  EVIDENCE  OF  COLLAPSE 
o        WELLS       WITH      NO     EVIDENCE     OF     COLLAPSE 


Fig.  5.6.      Map   of  Mackinac  Straits  areas  showing   zone  of  collapse  and   exposures  of  Mackinac 
breccia.    Reproduced   from    Landes,    1945. 


faults  have  been  regarded  as  either  Precambrian  or  late  Paleozoic  in  age, 
they  are  very  ancient,  and  any  scarps  would  be  erosional  features  of  the 
fault-line  variety.  Previous  conjecture  places  the  Grenville  front  in  the 
position  of  the  lake,  and  later  subsidence  along  this  zone  may  have  oc- 
curred to  form  the  lake  basin.  It  must  be  conceded,  however,  that  the 
origin  of  the  Lake  Superior  basin,  over  1000  feet  deep  in  places,  has  not 
yet  been  worked  out  satisfactorily. 


Eastern  Interior  Basin 

The  Eastern  Interior  or  Illinois-Indiana-Kentucky  basin  is  deepest  in 
Wayne,  White,  and  Hamilton  counties  where  the  base  of  the  Mississippian 


CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES 


45 


H /AG  ARAN 


Fig.    5.7.      Hypothetical    section    of    the    Mackinac    Straits    region    showing    collapse    formations    above    the 
Niagara  limestone,  and  the  breccia  chimneys  and  stacks.   Reproduced  from   Landes,   1945. 


tOo 


Fig.  5.8.      Isopach  map  showing  aggregate  thickness  of  Salina  salt.  Reproduced  from  Landes,  1945. 


shales  is  4800  feet  below  sea  level.  As  previously  explained,  the  Eastern 
Interior  basin  was  part  of  a  depression  that  included  the  Michigan  in  pre- 
Devonian  time,  but  from  then  on  the  two  basins  sank  separately,  leaving 
the  Kankakee  arch  between. 

The  La  Salle  anticlinal  belt  (see  Fig.  5.9)  is  a  row  of  anticlines 
arranged  en  echelon,  and  it  extends  over  200  miles  from  north  central  to 
southeastern  Illinois.  The  north  end  of  the  en  echelon  belt  may  be  con- 
nected with  the  east-west  trending  Savanna-Sabula  anticline  ( Eckblaw, 
personal  communication),  which  extends  into  eastern  Iowa.  The  south 
end  may  merge  with  the  Wabash  River  anticline.  The  La  Salle  anticlinal 
belt  formed  chiefly  during  the  Pennsylvanian  period  and  divided  the  pre- 
Pennsylvanian  Illinios-Indiana-Kentucky  basin  into  two  parts,  the  larger 
and  western  of  which  is  generally  known  as  the  Illinois  basin.  The  Oak- 
land anticline  borders  the  La  Salle  closely  on  the  east. 

The  first  deformation  took  place  in  post-Chester,  pre-Pennsylvanian 
time  (Fig.  5.10).  Further  deformation  continued  during  the  Pennsylva- 
nian progressively  southward.  In  La  Salle  and  Douglass  counties  at  the 
north  end,  the  early  movements  were  the  greatest,  and  the  crest  of  the 
anticline  was  elevated  900  to  1400  feet  above  the  adjacent  basins.  In 
Lawrence  and  Wabash  counties  to  the  south,  the  greatest  movements 
occurred  within  the  Pennsylvanian.  Since  the  Pennsylvanian  beds   are 


46 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


LAKE 


MICHIGAN 


^^LLE    OUTG$", 


MILES 


slightly  folded  over  the  anticline,  it  is  possible  that  some  movement 
occurred  after  they  were  deposited  as  well  as  during  the  time  of  de- 
position. 

At  the  beginning  of  the  Pennsylvanian  there  was  a  regional  southwest 
slope  furrowed  by  numerous  subparallel  valleys  as  deep  as  200  feet.  An 
eastward  slope  prevailed  along  the  western  border  of  the  basin  with 


Fig.  5.9  Structure  contour  map  of  Eastern  Interior  basin.  Contours  on  Illinois  Coal  No.  2,  in 
hundreds  of  feet.  After  Wanless,  1955.  Oak.  A.,  Oakland  anticline;  M-S  Syn.,  Marshall-Sidell 
syncline;   D.M.,  Duquoin   monocline;   R.C.F.,   Roush  Creek  fault  zone. 


Fig.  5.10.  Cross  section  of  the  Illinois  basin,  after  American  Association  of  Petroleum  Geologists 
1954,  Geo/ogic  Cross  Section  of  Paleozoic  Rocks,  central  Mississippi  to  northern  Michigan.  The 
Eau  Claire  and  older  beds  of  the  Cambrian  are  sandstone  and  shaly  sandstone;  from  the  upper 
part  of  the  Eau  Claire  through  the  Ordovician,  Silurian,  Devonian,  and  the  Mississippian  to  the 
Upper  Mississippian  Chester  series  the  sequence  is  dominantly  limestone  and  dolomite  with  much 
chert.  The  St.  Peter  is  conspicuous  sandstone  in  the  Ordovician,  and  the  Osage  of  the  Mississippian 
has  considerable  sandstone  and  shale  toward  the  La  Salle  anticlinal  belt.  The  Chester  and  Penn- 
sylvanian strata  are  sandstone  and  shale  with  several  thin  limestone  beds,  and  coal  in  the 
Pennsylvania. 


48 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


smaller  valleys.  The  geologic  map  at  this  time  would  have  appeared  as  in 
Fig.  5.11,  when  formations  from  the  Middle  Ordovician  St.  Peter  sand- 
stone to  the  Upper  Mississippian  Kinkaid  limestone  cropped  out.  The 
southeast  border  of  the  basin  sank  progressively  and  resulted  in  a  regular 
increase  in  thickness  of  the  uppermost  Pennsylvanian  strata  in  that  direc- 
tion (Wanless,  1955). 

The  assemblage  of  faults  in  southern  Illinois,  shown  on  the  map  of 
Fig.  5.9,  consists  principally  of  the  following  trends:  (1)  the  east- west 
trend  of  the  Rough  Creek-Shawneetown  system  which  extends  west  into 
Illinois  as  the  Cottage  Grove  and  associated  faults;  (2)  a  prominent 
northeast-southwest  system  of  faults  which  is  dominant  in  the  fluorspar 
district;  and  (3)  the  Wabash  Valley  fault  system  with  north-northeast 
trend,  a  few  of  which  cross  and  offset  the  Rough  Creek  fault.  These 
faults  are  post-Pennsylvanian  in  age  and  the  maximum  throw  is  about 
800  feet  along  the  Rough  Creek  fault. 

Studies  of  crossbedding  and  stratigraphic  relations  indicate  that  the 
late  Mississippian  Chester  sands  as  well  as  those  of  the  Pennsylvanian 
came  mostly  from  the  northeast  (Potter  et  al.,  1958,  Potter  and  Siever, 
1956,  and  Wanless,  1955),  and  some  were  probably  carried  by  streams 
from  the  site  of  the  Michigan  basin  across  the  site  of  the  previous  Kanka- 
kee arch.  A  minor  amount  of  sand  came  from  the  Transcontinental  Arch. 
See  Fig.  5.1. 

Nashville  Dome 

The  Nashville  dome  is  at  present  the  site  of  a  topographic  basin,  with 
surrounding  escarpments  of  successively  younger  rocks.  Ordovician  strata 
are  the  oldest  rocks  exposed  in  the  core,  and  the  escarpments  are  in  the 
overlapping  Mississippian  and  Pennsylvanian  formations.  The  dome  ex- 
perienced several  movements  in  pre-Chattanooga  (early  Mississippian) 
time,  synchronous  with  those  of  the  hinterland  of  the  Appalachian  geo- 
syncline,  according  to  Wilson  ( 1935 ) .  The  dome  was  below  sea  level  dur- 
ing several  epochs  of  various  lengths  of  time,  and  during  other  times  the 
central  part  was  above  sea  level  but  probably  so  slightly  emergent  that 
little  erosion  occurred.  The  structure  is  a  broad,  gentle  arch,  less  because 
of  uplift  than  because  of  greater  subsidence  of  the  adjacent  basins.  Its 


domal  structure  was  acquired  by  gentle  sags  between  it  and  the  Ozark 
dome  on  the  west  (Wilson,  1939)  and  the  Cincinnati  dome  on  the  north 
(MacFarlan,  1943).  See  cross  section  of  Fig.  5.12. 

The  first  major  uplift  in  which  considerable  truncation  of  the  beds  oc- 
curred was  in  late  Devonian  time.  The  Chattanooga  shale  rests  on  the 
Trenton  (Ordovician),  showing  that  about  500  feet  of  beds  had  been 
eroded  away  in  the  central  part  of  the  dome  consequent  to  this  pre- 
Mississippian  doming  (Wilson  and  Born,  1943). 

The  second  major  uplift  was  in  late  Mississippian  and  early  Pennsyl- 
vanian time,  when  its  associated  domes,  the  Ozark  and  Cincinnati,  were 
also  elevated  (Plate  5).  The  Chattanooga  shale  was  domed  gently,  pro- 
ducing regional  dips  of  16  feet  per  mile  on  the  flanks,  and  along  the  axis, 
both  northeast  and  southwest,  of  about  8  feet  per  mile.  A  structural  re- 
lief of  700  feet  was  acquired  by  the  dome  above  the  saddle  separating  it 
from  the  Cincinnati  dome  on  the  north.  The  structural  relief  of  the  dome 
over  the  flanking  basins  was  at  least  twice  as  much  (Wilson  and  Spain, 
1936). 

Detailed  structure  contour  maps  reveal  many  local  irregularities  in  the 
Nashville  dome.  A  conspicuous  "grain"  to  the  northwest  is  noted  by  Wil- 
son and  Born  (1943),  and  axes  of  folds  may  be  drawn  in  a  few  places.  A 
structure  contour  map  of  the  Pencil  Cave  ( Ordovician )  formation  shows 
the  grain  equally  as  well  as  one  drawn  on  the  Chattanooga  shale  ( Missis- 
sippian), but  the  local  structures  are  not  closely  superposed.  It  may, 
therefore,  be  inferred  that  part  of  them  originated  in  pre-Chattanooga 
time,  and  part  in  post-Chattanooga. 

Cincinnati  Dome 

The  Cincinnati  dome  is  much  like  the  Nashville  dome,  and  is  separated 
from  it  by  a  shallow  structural  saddle.  Several  writers  refer  to  the  two 
domes  together  as  the  Cincinnati  arch,  with  the  central  part  of  the 
northern  structure,  the  Jessamine  dome,  and  the  Nashville  dome  as  ele- 
ments of  it.  The  Cincinnati  dome  splits  into  two  branches  on  the  north, 
one  extending  to  the  west-northwest  and  the  other  to  the  north-northeast, 
which  are  known,  respectively,  as  the  Kankakee  arch  and  the  Findlay 
arch. 


CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES 


CENTRAL        BASIN 


49 


CUMBERLAND 
PLATEAU 


Fig.  5.12.  Section  across  the  Nashville  dome,  after  C.  W.  Wilson,  Jr.,  1935.  1,  Lower  and  Middle  Devonian; 
2,  Decatur;  3,  Lobelville;  4,  Beach  River,  Bob,  and  Dizon;  5,  Lego,  Waldron,  Laurel,  and  Osgood;  6,  Brass- 
field;  7,  Richmond. 


The  Cincinnati  dome  probably  had  an  early  Paleozoic  history  much  like 
the  Nashville  dome,  but  the  first  elevation  in  which  appreciable  erosion 
occurred  preceded  slightly  the  one  in  the  Nashville  dome.  MacFarlan 
(1943)  shows  that  the  Middle  Devonian  (Boyle)  limestone  overlaps  suc- 
cessively older  formations  toward  the  center  of  the  dome  where  it  rests 
on  the  Ordovician  ( Richmond  and  Maysville ) .  The  Lower  Mississippian 
shale  (Ohio  shale,  probably  the  Chattanooga  equivalent)  has  been  found 
to  "cut  out"  the  Boyle  limestone  in  a  few  places,  and  therefore  locally 
some  late  Devonian  movement  has  been  suggested. 

Preceding  the  Mid-Devonian  uplift  of  the  Cincinnati  dome  and  about 
100  miles  east  of  it,  arose  the  Waverly  arch  in  Early  Ordovician  time.  It 
has  a  structural  relief  of  750  feet  ( Woodward,  1961 ) . 

The    Pennsylvanian-Mississippian    contact    is    one    of    marked    dis- 


conformity  and  one  of  considerable  relief  as  shown  in  a  number  of 
Pottsville-filled  valleys.  The  post-Mississippian  uplift  represented  by  the 
unconformity  was  much  broader  than  the  doming  of  Middle  Devonian 
time.  Compare  Plates  5  and  6.  It  is  generally  regarded  that  after  the  late 
Mississippian  arching,  the  Cincinnati  dome  was  submerged,  and  that 
Pennsylvanian  beds  from  the  Appalachian  region  spread  westward  across 
it  so  that  the  Appalachian  and  central  interior  coal  fields  were  connected. 
Several  of  the  conglomerates,  fireclays,  and  limestones  have  been  corre- 
lated across  the  dome.  See  Plate  7. 

In  order  to  produce  the  present  distribution  of  the  Pennsylvanian  strata, 
still  another  broad,  gentle  arching  is  required  in  post-Pennsvlvanian  time. 
This  is  shown  on  the  tectonic  map  of  Plate  8. 

Some  faults  cut  the  dome,  and  these  will  be  described  later  as  part  of 


50 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


a  large  fault  zone  that  extends  across  several  states.  Local  structures  are 
not  as  well  mapped  as  in  the  Nashville  dome;  but  as  far  as  known,  the 
perceptible  northwest  "grain"  does  not  exist.  Instead,  one  or  two  "highs" 
have  been  described  on  the  eastern  flank  of  the  dome  that  trend  parallel 
with  the  main  axis.  It  may  be  that  with  better  contouring,  a  northwest 
direction  of  local  structures  will  be  noted. 

Kankakee  Arch 

The  Kankakee  arch,  as  defined  by  Ekblaw  (1938),  is  the  northwest 
branch  of  the  Cincinnati  dome,  and  passes  in  a  northwest  direction  across 
Indiana  and  Illinois,  connecting  with  the  Wisconsin  dome.  Kankakee  is 
preferred  to  Wabash,  a  name  sometimes  used.  The  earliest  significant 
uplift  preceded  the  deposition  of  the  St.  Peter  sandstone,  as  in  the  Wis- 
consin dome.  The  St.  Peter  sandstone  rests  on  Cambrian  beds  at  Oregon, 
Illinois,  indicating  arching  above  sea  level  and  removal  of  500  to  600  feet 
of  rock  in  this  early  movement.  The  Cambrian  and  Prairie  du  Chien  ( pre- 
St.  Peter)  beds  are  believed  to  be  about  4000  feet  thick,  both  on  the 
Kankakee  arch  and  in  the  Illinois  basin,  and  therefore  the  arch  was  evi- 
dently an  area  of  subsidence  just  as  much  as  the  basin  until  Early  Ordo- 
vician  time. 

Oil  wells  show  that  the  structural  relief  at  present,  if  measured  on  the 
top  of  the  Trenton  limestone,  is  about  6000  or  more  feet  in  relation  to 
the  Illinois  basin  and  10,000  feet  in  relation  to  the  Michigan  basin.  As  the 
Trenton  is  above  the  St.  Peter,  the  arch  has  acquired  this  much  additional 
structural  relief  since  the  pre-St.  Peter  uplift.  It  is  clear  that  the  large  part 
of  this  structural  relief  is  a  result  of  subsidence  of  the  basins  on  either 
side  of  the  arch,  and  that  the  upward  movements  of  the  arch  itself,  suffi- 
cient to  cause  it  to  be  eroded,  contributed  only  in  small  part  to  the  relief. 
See  Figs.  5.4  and  5.5  for  pre-St.  Peter  structural  relations. 

The  only  reflection  of  the  Middle  and  Late  Devonian  uplifts  of  the 
nearby  Cincinnati  and  Nashville  domes  is  the  conspicuous  thinning  of  one 
of  the  zones  of  the  Traverse  group  in  the  Michigan  basin  toward  the 
arch  (Cohee,  personal  communication).  The  greater  subsidence  of  the 
basin  area  than  the  arch  area,  as  indicated  by  this  zone  in  the  Traverse, 
occurred  in  late  mid-Devonian.  The  basin  had  previously  sunk  rapidly, 
and  a  thick  evaporite  series  was  deposited  during  the  Silurian  and  pre- 


Traverse  Devonian.  These  thick  salt,  gypsum,  limestone,  and  dolomite 
beds  are  represented  by  thinner  nonevaporite  series  in  the  Illinois  basin, 
and  hence  the  structural  relief  of  the  arch  is  not  so  great  to  the  southwest 
as  to  the  northeast. 

The  early  Mississippian  seas  probably  spread  over  the  arch  even  though 
Lower  Mississippian  rocks  are  not  there  today.  This  is  concluded  because 
the  beds  do  not  display  any  characteristics  of  overlap  on  a  land  area.  The 
Upper  Mississippian  (Chester)  beds  of  Illinois  are  not  represented  in 
the  Michigan  basin,  nor  anywhere  north  of  the  Kankakee  arch,  and  it 
therefore  seems  that  in  late  Mississippian  time  the  arch  and  the  area  to 
the  northeast  were  gently  emergent,  and  from  this  region  and  still  farther 
north  the  Chester  sands  were  derived.  Since  the  present  structure  dis- 
plays the  geologic  pattern  of  a  broad  anticline  with  Silurian  rocks  in  the 
core  and  Devonian  and  Mississippian  successively  away  on  either  side,  it 
follows  that  in  addition  to  regional  uplift  over  the  Great  Lakes  region  in 
late  Mississippian  time  there  must  also  have  been  local  uplift  along  the 
arch.  This  movement  occurred  at  the  same  time  as  the  one  described  in 
the  Cincinnati  dome  with  which  the  Kankakee  arch  merges. 

The  deposition  of  Pennsylvanian  sediments  across  the  Cincinnati  dome 
on  a  surface  of  appreciable  relief  corresponds  to  the  well-known  Pennsyl- 
vanian overlap  in  Illinois  south  of  the  Kankakee  arch  and  over  the  La 
Salle  anticlinal  belt.  The  Upper  Mississippian  and  pre-Pennsylvanian  up- 
lift along  the  arch  was  probably  a  movement  of  only  a  few  hundred  feet. 
Again  it  was  the  appreciable  subsidence  of  the  adjacent  basins  that  con- 
tributed most  to  the  arch  structure. 

Recause  the  Pennsylvanian  strata  were  gently  arched  and  eroded  back 
from  the  Cincinnati  arch,  a  post-Pennsylvanian  uplift  of  gentle  but  broad 
dimensions  is  indicated.  It  appears  that  the  uplift  spread  northward  so  as 
to  embrace  the  Kankakee  arch,  the  Wisconsin  dome,  the  Michigan  basin, 
and  the  southern  part  of  the  Canadian  shield. 

In  summary,  the  Kankakee  arch  acquired  its  structural  relief  chiefly  by 
greater  subsidence  of  the  basins  on  its  sides  than  by  actual  uplift.  It  was 
lifted  out  of  water  in  early  Ordovician  time,  and  in  one  place  it  suffered 
600  feet  of  erosion.  Again  it  rose  out  of  water  in  late  Mississippian  time, 
and  finally  participated  in  a  regional  uplift  of  the  Great  Lakes  region  in 
the  late  Pennsylvanian. 


CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES 


51 


A  sag  between  Peru  and  Logansport  across  the  arch  is  called  the 
Logansport  sag,  and  many  other  minor  irregularities  make  up  the  oil  field 
structures  in  the  area. 

Findlay  Arch 

The  Findlay  arch  is  the  right  arm  of  the  Cincinnati  dome,  and  extends 
north-northeastward  into  the  peninsular  area  of  Ontario  and  thence  to 
the  Canadian  Shield  (Plate  5).  It  is  similar  in  size  and  relief  to  the 
Kankakee  arch  and,  since  the  early  Ordovician  uplift,  it  has  had  a  similar 
history  (Cohee,  personal  communication).  It  was  not  an  area  where 
thick  pre-St.  Peter  sediments  accumulated,  and  may  actually  have  been 
a  low  ridge  of  Precambrian  rock  at  the  beginning  of  Cambrian  deposition 
(Cohee,  personal  communication). 

The  uplift  along  the  Findlay  arch  was  localized  and  of  somewhat 
greater  magnitude  than  along  the  Kankakee  arch  (Cohee,  personal  com- 
munication ) .  The  cross  section,  Fig.  5.4,  shows  the  base  of  the  Black  River 
and  the  progressive  overlap  northward  to  the  Precambrian  crystallines 
of  southeastern  Ontario. 

The  names  Lima  axis  and  Sandusky  arch  (Phinney,  1891),  Algonquin 
axis  (Kay,  1942),  and  Cataract  axis  have  been  used  for  all  or  part  of  the 
arch,  but  Findlay  arch  is  preferred  by  Ekblaw  ( 1938 )  and  others.  A  sag 


in  the  axis  near  Chatham,  as  contoured  by  Cohee  (personal  communica- 
tion),  reflects  movements  at  the  same  time  approximately  as  those  in  the 
arch.  The  cross  structure  is  called  the  Chatham  sag. 

Arches  of  Central  Kansas 

The  geologic  map  of  mid-Pennsylvanian  time  (Plate  7)  shows  the 
superposition  of  one  arch  over  another  in  central  Kansas,  with  axes  trend- 
ing in  slightly  different  directions.  At  the  close  of  the  Devonian,  a  broad 
arch,  for  which  the  name  Ellis  is  reserved  (Moore  and  Jewett,  1942), 
rose  (Plate  5)  and  was  eroded  so  that  the  Lower  Ordovician  Arbuckle 
limestone  was  exposed  in  the  core.  The  Mississippian  seas  then  lapped 
onto  the  Ellis  arch  and  perhaps  covered  it.  Post-Mississippian  arching 
in  a  somewhat  more  northerly  direction  and  in  a  narrower  zone  resulted  in 
the  erosion  of  the  Mississippian  strata  and  the  exposing  of  the  strata  in 
the  Ellis  arch  again.  This  new  uplift  is  called  the  central  Kansas  arch. 
However,  the  local  folds  that  developed  parallel  with  the  major  axis  of 
the  Ellis  arch  trend  obliquely  across  the  core  of  the  central  Kansas  arch. 
Examine  the  cross  section  of  Fig.  5.13  and  the  map  of  Fig.  14.1. 

The  Ellis  arch  continued  eastward  as  the  Chautauqua  to  the  Ozark 
dome.  The  Chautauqua  connection  existed  only  at  the  close  of  the  De- 
vonian. 


ELLIS  ARCH  (PRE-MI5SI3SIPPIAN)   AND    CENTRAL  KANSAS 
ARCH  (POST   MISSISSIPPIAN) 


NEMAHA 
RANGE 


MILC3 

Feci 


BOURBON  ARCH 


Fig.  5.13.      Section  along  central  Kansas  arch,  Nemaha  Range,  and   Bourbon  arch,  taken  from  cross  section 
by   Betty   Kellett  (1932).   Line  of  cross  section  shown   on    map  of   Fig.    14.1. 


52 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Nemaha  Range 

A  very  sharp  uplift,  the  Nemaha  Range,  trends  south-southwest  from 
Omaha  through  southeastern  Nebraska  across  Kansas  into  northern  Okla- 
homa, but  is  now  buried.  See  Figs.  5.13  and  14.1  and  Plate  6.  It  came 
into  mountainous  relief  during  early  Pennsylvanian  time,  because  the 
Mississippian  strata  are  tilted  up  and  truncated  along  its  sides.  Uplift 
and  dissection  were  sufficient  to  expose  Precambrian  crystalline  rocks  in 
the  core  before  burial.  See  cross  section  of  Fig.  5.14.  Structural  relief  is 
3600  feet  in  the  central  part  of  the  range,  and  the  east  flank  is  so  steep 
and  straight  that  a  block-fault  movement  has  been  visualized  ( Lee  et  al., 
1946).  The  range  was  eroded  rapidly  so  that  the  Pennsylvanian  strata, 
partly  derived  from  the  range  itself,  encroached  on  its  flanks  and,  to- 
gether with  much  exotic  material  perhaps  in  part  from  the  early  Ouachi- 
tas,  finally  buried  the  range.  The  present  depth  of  the  "granite"  at  the 
Kansas  and  Nebraska  line  is  only  about  400  feet  (500  feet  above  sea 
level),  but  at  the  Kansas  and  Oklahoma  line,  it  is  over  3000  feet  below 
the  surface  (2500  feet  below  sea  level). 

The  Nemaha  Range  contrasts  strongly  with  the  central  Kansas  arch  in 
relief  and  symmetry.  The  Nemaha  Range  has  3600  feet  of  relief,  whereas 
the  arch  has  1500.  The  range  has  a  very  steep  eastern  front  and  gentle 
back  slope,  whereas  the  arch  is  symmetrical  and  gentle.  The  nearly  north- 
south  trend  of  the  Nemaha  Range  is  unlike  the  northwest  trend  of  the 
broad,  gentle  arches,  and  this  sets  it  apart  from  the  arches  as  a  different 
structural  type.  It  resembles  the  Colorado  Range  of  the  Ancestral  Rockies, 
and  therefore  the  characterization  of  it  as  a  range  is  more  appro- 
priate than  as  an  arch,  anticline,  or  ridge,  as  it  has  variously  been 
called. 

Bourbon  Arch 

Slightly  north  of  the  site  of  the  previous  Chautauqua  arch,  a  later  but 
narrower  one  rose  in  early  Pennsylvania  time.  It  was  probably  a  shallow 
platform  between  the  Forest  City  basin  on  the  north  and  the  Cherokee 
basin  on  the  south  (Moore  and  Jewett,  1942).  See  Fig.  5.13. 


Ozark  Dome 

At  present,  the  Ozark  dome  is  a  broad,  nearly  circular  area  of  Cambrian 
and  Ordovician  limestones,  surrounded  by  escarpments  of  Mississippian 
limestone.  In  the  east  central  part,  knobs  of  pre-Cambrian  crystalline 
rocks  project  through  the  Cambrian  and  Ordovician  strata  to  the  surface. 
The  crystalline  outcrops  occur  in  southeastern  Missouri,  the  area  of  the 
St.  Francis  Mountains,  and  the  strata  dip  everywhere  away  from  them 
(Croneis,  1930).  The  dome  itself  spreads  over  two-thirds  of  the  state, 
and  also  into  northern  Arkansas  where  the  Boston  Mountains  make  up 
the  southern  flank.  The  Precambrian  surface  had  considerable  relief,  and 
the  younger  strata  were  deposited  on  it  with  initial  dips  in  places  up  to 
30  degrees  (Bridge,  1930). 

The  first  major  unconformity  in  the  Paleozoic  succession  around  the 
Ozark  dome,  especially  on  the  west  side  in  the  Forest  City  basin,  is  at  the 
base  of  the  St.  Peter  sandstone.  Lee  et  al.  (1946)  summarize  the  subsur- 
face geology  in  maps  and  cross  sections  and  show  that  subsidence  took 
place  in  the  Ozark  region  in  pre-St.  Peter  time,  while  upwarping  took 
place  in  southeastern  Nebraska  and  northeastern  Kansas  (the  Nebraska 
arch).  The  structural  relief  between  basin  and  uplift  was  about  2000 
feet. 

With  the  coming  of  St.  Peter  time,  the  crustal  movements  were  re- 
versed, and  the  Ozark  basin  now  started  to  rise  as  the  Nebraska  arch 
started  to  subside.  At  the  end  of  Silurian  time,  widespread  erosion  oc- 
curred, with  the  greatest  amount  around  the  rising  Ozark  dome.  The 
Devonian  strata  not  only  rest  on  the  truncated  Silurian  and  older  rocks 
around  the  dome,  but  themselves  in  turn  are  truncated  and  covered  by 
the  Mississippian  strata. 

The  Mississippian  overlap  is  most  extensive  and  very  well  known  from 
many  well  records  on  the  west  side  of  the  dome.  Consult  the  geologic 
map  of  the  close  of  the  Devonian,  Plate  5,  and  cross  sections  of  Figs.  5.15 
and  5.16.  The  unconformity  indicates  that  the  dome  was  again  uplifted  in 
late  Devonian  time  and  considerably  eroded.  The  pre-Mississippian  geo- 
logic maps  of  the  region  (Moore  and  Jewett,  1942;  Wrather,  1933;  Lee 
et  al.,  1946),  together  with  surface  outcrops,  indicate  that  the  Ellis  arch, 


NORTHERN         PART  OF  SALINA  BASIN 


Fig.  5.14.      Cross  section  of  the  Nemaha  Range  and  Forest  City  basin.  Reproduced  from  Wallace  Lee  er  o/., 
1946.   Note  the  several   unconformities. 


ST.    FRANCOIS       MOUNTAINS 


HORIZONTAL        SCALE 


Fig.  5.15.     Taken  from  Geologic  Map  of  Missouri  (1939).  Section  runs  from  Mt.  Vernon  to  Perry- 
ville.   Mo.   The   wedge   of    Pennsylvanian    strata   at   the    left   is   added    to   show   the    Mississippian 


and   Pennsylvanian   unconformity  as  it  occurs  about  50   miles   north   of  the  line   of  cross   section. 
Section   B-B'  on   map  of  Fig.   14.1. 


Fig. 

Fi9- 


5.16. 
14.1. 


Section  across  northeastern  Oklahoma.  Taken  from  White  (1926,  PI.  1).  Section  C-C  on  map  of 


CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES 


55 


the  Chautauqua  arch,  and  the  Ozark  dome  made  up  one  continuous 
broad  arch  which  left  the  Transcontinental  Arch  at  right  angles  and 
veered  eastward  in  southern  Missouri. 

The  dome  was  uplifted  again  slightly  in  the  late  Mississippian  (Plate 
6).  This  time  the  movement  was  not  in  company  with  the  Ellis  and 
Chautauqua  arches,  but  apparently  with  the  Hunton  arch  to  the  south- 
west in  Oklahoma  (Dott,  1934).  The  great  Pennsylvanian  transgression 
nearly,  if  not  entirely,  covered  the  dome  (Plate  6),  and  no  recurrences 
of  uplift  during  the  Pennsylvanian  or  Permian  have  been  described.  The 
Devonian  and  Mississippian  uplifts  left  the  dome  wrinkled  with  very 
gentle  narrow  folds  that  trend  in  a  northwest  direction. 

The  Arkansas  Valley  lies  south  of  the  Ozark  dome  and  north  of  the 
complexly  folded  and  thrust-faulted  Ouachita  Mountains.  It  is  a  structural 
basin  as  well  as  valley,  and  will  be  described  in  Chapter  14  under  the 
heading,  "Ouachita  System." 

Cambridge  Arch 

A  number  of  wells  which  have  penetrated  "granite"  have  been  drilled 
through  the  Pennsylvanian  formations  in  a  line  running  northwesterly 
across  Nebraska  (Ballard,  1942).  Isopach  maps  along  this  row  of  wells 
suggest  that  the  central  Kansas  arch,  well  known  from  many  wells, 
continues  northwestward  to  the  Black  Hills  and  beyond  to  the  south- 
eastern corner  of  Montana.  The  arch  across  Nebraska  is  known  as  the 
Cambridge  arch  (Plate  7).  Geologic  contacts  determined  from  both  sur- 
face and  subsurface  data,  however,  do  not  reveal  the  arch,  because  it  lies 
mostly  within  the  Precambrian  rocks  of  the  larger  Transcontinental  Arch 
(Plates  4  and  5).  No  wells  have  yet  been  drilled  to  the  Precambrian 
northeast  of  the  Cambridge-central  Kansas  arch,  and  therefore  the  bound- 
aries of  the  pre-Pennsylvanian  formations  along  the  Transcontinental  Arch 
may  have  to  be  shifted  considerably  at  a  later  date. 

NORTHWESTERN  INTERIOR  BASINS  AND  ARCHES 
Williston  and  Alberta  Basins 

The  Williston  basin  was  first  thought  of  as  a  gentle  Tertiary  downwarp 
in  western  North  Dakota  and  eastern  Montana,  and  was  named  after 


the  town  of  Williston,  N.D.,  on  the  Missouri  River.  Cretaceous  strata 
were  known  to  underlie  the  Tertiary  and  these  to  cover  Paleozoic  rocks 
of  the  extensive  region  of  South  and  North  Dakota,  Montana,  south- 
western Manitoba,  and  southern  Saskatchewan.  With  the  discovery  of 
commercial  oil  in  1951  in  North  Dakota,  the  term  Williston  basin  became 
applied  to  the  Paleozoic  strata  more  particularly  than  to  the  Tertiary 
or  Mesozoic,  and  with  the  drilling  of  many  holes  the  distribution  of 
formations  and  systems  has  become  well  known.  Isopach  maps  of  the 
several  systems  important  in  the  Williston  basin  are  shown  in  Figs.  5.17, 
5.18,  and  5.19. 

A  vast  region  in  Alberta,  western  Saskatchewan,  northeastern  British 
Columbia,  and  the  Mackenzie  area  of  the  Northwest  Territories  is  a 
continuation  of  the  Paleozoic  sequence  of  the  Williston  basin,  and  the 
accompanying  maps  show  the  close  relationship  of  the  geology  of  the 
two  regions,  although  they  are  generally  treated  separately  in  oil  field 
parlance.  The  term  "Alberta  shelf"  has  been  applied  to  the  Paleozoic 
sedimentary  province  under  the  Great  Plains  of  western  Canada,  because 
it  is  a  shallowing  shelf  region  to  the  Cordilleran  geosyncline  or  Alberta 
trough  on  the  west  for  most  of  the  systems  (Webb,  1954).  It  is  also 
commonly  referred  to  as  the  Alberta  basin  as  a  region  for  oil  exploration 
and  structurally  as  the  Alberta  syncline.  During  the  Devonian  period  a 
broad  basin  did  develop  (see  Fig.  5.17C),  but  otherwise  the  region  can 
more  properly  be  called  a  shelf.  The  syncline  developed  as  the  result  of 
Cretaceous  and  Tertiary  subsidence,  mountain  building  on  the  west,  and 
sedimentation,  but  the  synclinal  axis  is  not  reflected  under  the  Great 
Plains  in  the  thicknesses  of  any  of  the  pre-Cretaceous  systems. 

The  Cambrian  strata  are  dominantly  clastic  with  a  sandstone  generally 
at  the  base  and  a  sequence  of  green  and  maroon  shales  and  light  gray 
calcareous  siltstones  and  fine-grained  sandstones  above.  These  beds  were 
deposited  unconformably  on  a  Precambrian  terrane  as  the  seas  invaded 
the  shield  region  from  the  west  and  southwest  (Fig.  5.17A). 

The  Ordovician  beds  are  extensive  under  the  Williston  basin  but 
generally  absent  on  the  Alberta  plains.  The  outcrops  in  Manitoba  contain 
a  50-  to  100-foot  basal,  white  quartz  sandstone  with  interbedded  shales 


56 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


B.    ORDOVICIAN 

JL*T 

c 

MAN. 

C     DEVONIAN 
"EVAPORITE    BASIN 


Fig.  5.17.  Thickness  map  of  Williston  and  Alberta  basins:  Cambrian,  Ordovician  and  Devonian. 
Cambrian,  after  Webb  (1954)  and  Sloss  (1950);  Ordovician,  after  Webb  (1954)  and  Sloss  (1950); 

and  then  a  sequence  of  400  feet  of  limestones  and  dolomites.  The  car- 
bonates are  the  chief  rocks  encountered  in  wells;  the  basal  elastics  appear 
to  wedge  out  to  the  northwest  (Webb,  1954). 

The  Silurian  is  represented  in  east-central  Alberta  Plains  by  an  evapo- 
rite  sequence  and  is  generally  included  with  beds  which  may  be  Middle 
Devonian.  The  Silurian  and  Middle  (?)  Devonian  beds  are  the  Elk 
Point  formation  of  the  stratigraphic  chart,  Figs.  5.20  and  5.21,  and  con- 
tain a  composite  salt  thickness  of  1200  feet  in  1700  feet  of  beds.  The  Silu- 
rian is  present  in  Manitoba,  North  Dakota,  much  of  Saskatchewan  and 
northern  Montana,  but  with  the  Ordovician,  is  absent  in  the  Sweetgrass 
arch  region.  It  consists  of  light  yellowish  gray  and  yellowish  orange,  finely 
crystalline  to  dense  dolomite  (the  Interlake  group). 

The  Upper  Devonian  strata  in  western  Canada  are  much  more  wide- 


Devonian  with  evaporite  region,  after  Webb  (1954),  Sloss  (1950),  and  Baillie  (1955). 

spread  than  the  Middle,  and  the  original  extent  was  still  greater.  Post- 
Paleozoic  erosion  has  removed  the  beds  over  considerable  areas.  The 
Upper  Devonian  is  characterized  by  thick  deposits  of  limestones,  dolo- 
mites, shales,  and  evaporites.  It  marks  a  time  of  limestone  reef  growth 
on  widespread  banks  with  numerous  local  bioherm  and  biostrom  deposits 
and  abrupt  facies,  changes,  all  holding  large  oil  reserves. 

The  Devonian  succession  of  the  Williston  basin  is  shown  on  the  chart 
of  Fig.  5.21,  and  its  distribution  in  Fig.  5.17C.  It  is  divided  into  four 
major  lithologic  units,  which  in  ascending  order  are,  Elk  Point  group, 
Manitoba  group,  Saskatchewan  group,  and  Qu'Appele  group.  The  lower 
three  are  chiefly  carbonates  but  the  upper  is  composed  of  red  shales 
and  siltstones.  An  extensive  evaporite  sequence  occurs  in  the  lower  Elk 
Point  group  and  also  in  the  Manitoba  group.  In  north-central  Montana 


CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES 


57 


Fig.   5.18.      Thickness   map   of  the   Williston   and   Alberta    basins:    Lower   and   Upper   Mississippian 
and   Pennsylvanian.   Lower  Mississippian   (Kinderhookian,  Osagian,  and  Meramecian  series),  after 

a  third  evaporite  sequence  occurs  at  a  still  higher  stratigraphic  position, 
in  the  top  of  the  Jefferson. 

The  Mississippian  beds  which  rest  on  an  erosion  surface  on  the  De- 
vonian are  marked  at  the  base  by  black  shale  in  the  Williston  basin.  The 
Mississippian  is  more  restricted  in  the  Alberta  region,  but  the  beds 
possibly  extended  east  at  the  time  of  deposition  as  far  as  the  present 
margin  of  the  Canadian  Shield.  The  beds  in  Alberta  start  with  a  lower 
dark  gray  calcareous  shale  or  dark  brown-gray  argillaceous  limestone 
with  fine-grained  sandstone  beds  in  the  south.  The  upper  beds  are  buff 
crystalline  to  dense  limestones.  The  succession  in  the  Williston  basin 
beginning  with  the  Kinderhookian  and  Osagian  strata  is  largely  lime- 
stone. These  beds  make  up  the  Lodgepole  and  Mission  Canyon  forma- 
tions. The  Meramecian  is  dominated  by  dolomites  which  compose  the 


Webb  (1954)  and  Sloss  (1950);  Upper  Mississippian  (Chesterian),  after  Sloss  (1950);  Pennsyl- 
vanian,  includes    Permian   in   Canada,   after   Webb    (1954)   and    Sloss   (1950). 

Charles  formation.  See  Fig.  5.22.  The  Charles  contains  considerable 
thicknesses  of  evaporites.  See  map,  Fig.  5.18D. 

The  Upper  Mississippian  or  Chester  beds  lie  in  an  east-west  basin 
through  central  Montana,  called  the  Big  Snowy.  The  eastern  part  of  this 
basin,  however,  is  in  the  general  region  of  the  Williston  basin  and  hence 
it  is  considered  part  of  the  Williston.  The  strata  are  dominantly  clastic 
in  contrast  to  the  chemical  precipitates  of  the  Lower  Mississippian  and 
compose  the  Kibbey,  Otter,  and  Heath  formations.  Also  part  of  the 
overlying  Amsden  formation  is  Chester  in  age. 

The  Alberta  shelf  region  was  emergent  and  suffered  long-continued 
erosion  during  the  Pennsylvanian.  In  the  front  ranges  of  the  Rockies, 
however,  a  thin  sequence  of  sandy  dolomites  and  quartzitic  and  cherty 
sandstones  are  Pennsylvanian  and  Permian  in  age,  and  are  known  as 


58 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


t-   PRESENT    PRECAMBRIAN    SURFACE 


Fig.  5.19.  Thickness  maps  of  Williston  and  Alberta  basins:  Jurassic  and  Lower  Cretaceous.  Also 
contour  map  on   Precambrian  surface.  Jurassic,  after  Webb  (1954),   Francis  (1957),  and    Peterson 

the  Rocky  Mountain  formation.  Farther  north  in  adjacent  parts  of  Yukon 
and  Northwest  Territories  equivalent  sandstones  with  a  chert  member  at 
the  top  attain  a  maximum  thickness  of  1200  feet.  The  erosion  surface 
on  the  Mississippian  in  the  Peace  River  region  has  local  sharp  relief,  and 
beds  believed  to  be  Pennsylvanian  and  Permian  cover  the  surface  and 
range  up  to  500  feet  thick. 

In  the  Montana  and  South  Dakota  area  (see  map,  Fig.  5.18F)  elastics 
predominate  over  non-elastics,  and  clean  quartzose  sandstones  are  the 
rule,  making  up  the  Quadrant  sandstone  in  central  and  western  Montana 
and  the  Tensleep  sandstone  over  the  Wyoming  shelf.  In  the  southern 
part  of  the  Williston  basin  a  wedge  of  Pennsylvanian  is  preserved,  and 
consists  of  dolomite  interbedded  with  sandstone,  red  shale,  and  evapo- 
rites. 


(1957);    Lower   Cretaceous,   after   Webb    (1954)    and    Reeside    (1944);    Precambrian    surface,   from 
Tectonic  Map  of  Canada  (1954)  and  Moss  (1936). 

Triassic  time  was  marked  by  widespread  emergence,  but  in  the  Peace 
River  Country  a  thick  sequence  of  marine  elastics,  impure  limestones  and 
anhydrite  accumulated.  Thicknesses  up  to  3000  have  been  measured  in 
the  adjacent  Rockies. 

A  group  of  red  beds  has  been  charted  across  part  of  the  Williston 
basin  by  Ziegler  ( 1956 ) .  The  beds  lie  between  the  Permian  Minnekahta 
limestone  and  the  Piper  beds  of  the  Jurassic.  See  map,  Fig.  5.22.  A  lower 
shale  and  siltstone  unit  is  thought  to  correlate  with  the  Spearfish  red  beds 
of  the  Black  Hills  which  are  Triassic,  and  three  overlying  units,  a  salt,  a 
siltstone  and  sandstone,  and  an  upper  salt  are  thought  to  be  lower 
Jurassic  but  may  also  be  Triassic. 

The  Jurassic  beds  in  Alberta  have  about  the  same  distribution  as  the 
Triassic  except  for  a  wider  transgression  in  the  southern  Foothill  belt 


CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES 


59 


TERTIARY 


CRETACEOUS 


JURASSIC 


TRIASSIC 


PERMO-PENNSYL 


MISSISSIPPIAN 


DEVONIAN 


ORDOVICIAN 


PRECAMBRIAN 


Pliocene 

Miocene 

Oligocene 

Eocene 

Paleocene 


■!■■*■  *»^  ^i  H'Nw^t  ^jlllMW^I%,UWll^' 


Upper 


Lower 


Upper 

Middle 

Lower 


Upper 

Middle 

Lower 


inn 


Upper 
Lower 


Upper 

Middle 
Lower 


Upper 

Middle 

Lower 


Upper 

Middle 

Lower 


Upper 

Middle 

Lower 


Front  Range 
and  Foothills 


Paskapoo 


Edmonton 
Belly  River 

Wapiabi 

Bighorn  (Cardium) 

Blackstone 

Blairmore 

Upper  Kootenay 


Lower  Kootenay 
Fernie 


Spray  River 


3SC  L-l— L-l— l-i.-l. 


Rocky  Mountain 


■^I^O^^^-l^^^.i^^U^M-^1' 


Rundle 
Banff 


Exshaw 
Palliser 
Fairholme 
Ghost  River  ? 


[Ghost  River  ?] 


Cathedral 


Late   Proterozoic 
sediments 


Central   and 
Southern    Plains 


Cypress  Hills 
Swift  Current 
Ravenscrag 


I  \     i         i_[.i 


Edmonton 
Bearpaw 
Pale  Beds 
Foremost 
Pakowki 
Milk  River 


Lea 
Park 


Alberta  (Colorado) 

Blackleaf  (Viking) 
member  (Bow  Id.) 
Blairmore   


Ellis  group 


Madison  group 


Exshaw 

Wabamun  (Potiatch) 

Wmterburn   (Jefferaon) 

Woodbend 

Beaverhill  (Waterways) 

Elk  Point  (upper) 
(part) 


Elk  Point 


(lower) 
(part) 


Upper  Cambrian 


Southeastern 
Plains 


Wood  Mountain 


Turtle  Mountain 


J>i  i!«m'h    L  iJ  ■  L  i»k    J  ■ 


Boissevain 
Riding  Mountain 


Boyne 

Morden 

Favel 

Ashville 

Swan   River 


Jl.l.l.1.1     1 


Morrison   ? 
Sundance 
Gypsum  Springs 
(Amaranth    ? ) 


Charles 
Madison 
Kinderhook 


Exshaw 

Lyleton 

Jefferson 

Manitoban 
Winnipegosan 
Elm    Point 


group 

Stonewall 


Stony  Mountain 
Red   River 
Winnipeg 


Chiefly  Archean   Intrusives    and 
met amorphics 


Fig.  5.20.      Generalized   correlation   chart  of  western   Canada   basin,   southern   part,   after  Webb, 
1954. 


Fig.  5.21.  Devonian  correlation  chart  of  the  Williston  and  Alberta  basins.  Reproduced  from 
Boillie,   1955. 

near  Calgary.  There,  a  fairly  thick  succession  representing  Lower,  Mid- 
dle, and  Upper  Jurassic  occurs.  Over  the  Sweetgrass  arch  (Fig. 
5.19G)  only  a  thin  marine  sequence  of  shales  and  sandstones  of  Middle 
and  Upper  Jurassic  beds  is  present.  These  rest  on  an  irregularly  eroded 
surface  of  the  Mississippian.  Peterson  (1957)  traces  the  depositional 
history  of  western  Montana,  and  for  the  intermittently  positive  area 
where  thinning  and  overlap  occurred  he  uses  the  term  Belt  Island,  but 
explains  that  it  was  rarely  emergent  and  then  only  in  small  areas.  It  had 
been  emergent  in  early  Jurassic  time  and  probably  furnished  some  of 
the  clastic  material  for  the  adjacent  Middle  Jurassic  formations.  See 
chart,  Fig.  5.23.  Another  area  that  tended  toward  shoal  conditions  during 
parts  of  mid-  and  late  Jurassic  time,  although  not  emergent,  was  the 
Sheridan  arch.  Middle  and  Upper  Jurassic  beds  are  widespread  over  the 
Williston  basin  and  define  it  in  about  the  position  of  the  older  Mis- 
sissippian basin  but  centered  somewhat  south  of  the  Devonian  basin. 


Fig  5.22.      Distribution  of  formational  outcrops  before  Mesozoic  strata  were  deposited   unconform- 
ably  over  the  Paleozoic  strata.  The  hachured  line  indicates  extent  of  Triassic  (?)   red  bed  deposi- 


tion  (from   Ziegler,    1956).   Jurassic   sediments   spread   over  almost   entire   area.   Map   reproduced 
from  Francis  (1956). 


CENTRAL  STABLE  REGION  OF  THE  UNITED  STATES 


61 


By  Jurassic  time  the  rise  of  the  Cordilleran  geanticline  had  become  ex- 
tensive (see  Plate  10  of  Chapter  3),  and  considerable  sediment  was 
shed  from  it  eastward  to  the  subsiding  areas  of  accumulation.  Part  of 
the  geanticline  became  engrossed  in  major  mountain  building  in  Early 
Cretaceous  time,  and  this,  The  Nevadan  orogeny,  resulted,  in  British 
Columbia,  in  the  uplifting,  disruption,  and  widespread  intrusion  of  the 
sedimentary  rocks  of  the  Cordilleran  geosyncline.  A  new  restricted  trough 
or  longitudinal  basin  formed,  as  shown  in  Figs.  5.19  and  5.20,  in  about 
the  position  of  the  present  Canadian  Rockies.  The  Nevadan  Orogeny 
engrossed  the  Selkirk  Range  on  the  west  as  well  as  a  vast  region  west- 
ward to  the  continental  margin.  The  earliest  Lower  Cretaceous  sediments 
deposited  were  a  thick  coal-bearing  series,  the  Kootenay  formation,  and 
then  after  a  brief  erosion  interval  elastics  of  the  Blairmore  formation 
spread  eastward  over  the  Kootenay  and  extensively  over  the  Alberta  shelf 
region.  See  Fig.  5.19H.  The  coarse  elastics  along  the  foothills  and  front 
ranges  of  the  Rocky  Mountains  and  maximum  thickness  there  indicate 
that  the  rise  of  the  mountain  belt  on  the  west  was  rapid,  and  that  it  was 
suffering  active  erosion. 

The  distribution  of  Upper  Cretaceous  sediments  is  about  that  of  the 
Lower  Cretaceous  and  follows  about  the  same  pattern  of  thickening 
westward  into  the  trough.  The  Upper  Cretaceous  are  much  thicker  than 
the  lower  Cretaceous  in  the  Williston  basin  and  attain  thicknesses  of 
4000  feet  in  eastern  Montana  and  the  western  part  of  the  Dakotas.  The 
Upper  Cretaceous  beds  reflect  the  growth  of  the  later  Laramide  Rockies 
and  become  involved  themselves  in  deformation.  They,  with  a  central 
blanket  of  Tertiary  beds,  have  been  deposited  and  gently  folded  adjacent 
to  the  major  belt  of  mountain  building  on  the  west  to  form  the  Alberta 
syncline. 

A  contour  map  of  the  pre-Paleozoic  surface  reflects  the  summation  of 
all  subsidences  and  uplifts  in  the  Alberta-Williston  region,  and  it  will  be 
seen  (Fig.  5.191)  that  the  center  of  the  Williston  basin  is  about  at  the 
international  boundary  and  the  North  Dakota-Montana  line.  All  told,  it 
now  holds  over  7000  feet  of  sediment.  Its  position  and  extent  are  some- 
what modified  by  the  central  Montana  and  Black  Hills  uplifts  of  Late 
Cretaceous  age.  The  Sweetgrass  arch  is  a  strong  element  of  4000  feet 


Fig.  5.23.  Jurassic  correlation  chart  of  the  Williston  basin  and  adjacent  areas.  Reproduced  from 
Peterson,  1957. 

relief.  The  Alberta  basin  centers  between  Peace  River  and  Edmonton, 
and  contains  there  in  front  of  the  disturbed  belt  over  10,000  feet  of 
sediments.  Within  the  disturbed  belt  the  thickness  is  much  greater,  and 
had  the  Precambrian  surface  not  been  broken  and  deformed  in  the 
Nevadan  and  Laramide  orogenies  it  would  lie  very  deep,  indeed. 

Utah-Wyoming  Shelf 

The  Williston  basin  and  its  relation  to  the  Alberta  shelf  has  already 
been  described.  Southward  through  central  and  eastern  Wyoming  and 
the  Colorado  Plateau  of  Colorado  and  Utah  relatively  thin  layers  of 
Cambrian,  Ordovician,  Devonian,  Mississippian,  Pennsylvanian,  and 
Permian  strata  occur.  They  represent  the  transition  from  the  geosyncline 
on  the  west  to  the  Transcontinental  Arch  on  the  east.  The  influence  of 
the  Ancestral  Rockies  and  other  land  movements  in  Carboniferous  time 


62 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


SOUTHEASTERN 
IDAHO 


WIND  RIVER 
MTNS. 


DEVONIAN 


NORTHERN 
BLACK  HILLS 

I 
WHITEWOOD  DOLry 
GREEN  SHALE  ft  L 
SCOLITHUS   SS-7/ 


Stratigraphic  diagram  showing  the  relations  of  Cambrian  and  Ordo- 
vician  rocks  between  southeastern  Idaho  and  the  northern  Black  Hills. 


Fig.    5.24.      Relation    of   shelf   in    Wyoming    to   Transcontinental    Arch    and    Cordilleran    geosyncline.    Repro- 
duced  from    Thomas,    1949. 


on  the  sites  of  deposition  is  shown  on  Plate  7,  and  Fig.  6.7.  Figure  5.24 
is  a  cross  section  to  illustrate  the  shelf  and  its  relation  to  the  Trans- 
continental Arch  and  the  Cordilleran  geosyncline. 
The  formations  of  the  Wyoming  and  Montana  part  of  the  Utah- 


Wyoming  shelf  differ  somewhat  from  those  of  the  Utah  and  Arizona 
part.  The  formations  have  been  the  object  of  numerous  stratigraphic 
studies  because  of  their  importance  as  oil  and  gas  producers.  See  cor- 
relation charts  listed  in  Chapter  1. 


6. 


PALEOZOIC 

CORDILLERAN  GEOSYNCLINE 

DIVISIONS  AND  THEIR  CHARACTERISTICS 

Schuchert  is  probably  more  responsible  than  anyone  else  for  the  use 
of  the  expression  Cordilleran  geosyncline  in  describing  the  basins  of 
accumulation  of  sediments  along  the  western  margin  of  the  continent. 
He  also  used  the  term  Rocky  Mountain  geosyncline.  During  the  Mesozoic, 
his  "Cordilleran  intermontane  geanticline"  split  the  overall  broad  and 
irregular  basins  into  two  longitudinal  divisions,  but  before  the  geanticline 
became  pronounced,  the  divisions  were  already  evident  by  the  nature  of 
their  sediments,  the  western  being  an  eugeosynclinal  assemblage  and  the 
eastern  a  miogeosynclinal.  The  eugeosyncline  extended  from  mid-Nevada 


to  the  Pacific  Coast,  and  the  miogeosyncline  from  mid-Nevada  to  central 
Utah  (Fig.  6.1).  The  miogeosyncline  is  much  better  known  than  the 
eugeosyncline.  The  basins  of  sedimentation  and  geography  shifted  some- 
what from  one  period  to  another,  but  the  broad  overall  relations  remained 
fairly  constant.  The  change  from  the  thick  sedimentary  sequence  of  the 
miogeosyncline  to  the  thin  sediments  of  the  shelf  has  been  called  the 
Wasatch  line  (Kay,  1951),  and  for  all  Paleozoic  periods  except  Silurian 
the  change  is  fairly  abrupt  and  in  much  the  same  position.  The  broad 
divisions  as  outlined  were  probably  first  recognized  by  Stille  (1941)  and 
later  elaborated  on  by  Kay  (1942,  1951,  1960)  and  Eardley  (1947). 

The  eugeosyncline  probably  sank  more  and  received  a  greater  thickness 
of  sediments  than  the  miogeosyncline,  but  the  extent  of  sediments  in 
both  was  great.  The  major  difference  lies  in  the  character  of  the  sedi- 
ments. The  eugeosyncline  received  a  dominant  amount  of  volcanic 
material  and  graywacke,  whereas  the  miogeosyncline  was  filled  with 
sandstones,  quartzites,  shales,  limestones,  and  dolomites.  The  volcanic 
material  in  the  eugeosyncline  is  in  several  forms:  flows,  volcanic  con- 
glomerates, and  various  pyroclastics.  The  volcanics  and  graywackes  occur 
in  every  stratigraphic  system  from  Upper  Cambrian  to  Cretaceous.  The 
Permian  especially  was  a  time  of  excessive  volcanism,  and  the  volcanics 
of  that  period  have  been  traced  from  California  and  western  Nevada  to 
Alaska  (Wheeler,  1939;  White,  1959).  In  the  Humboldt  Range  of  north- 
western Nevada,  over  10,000  feet  of  Permian  strata,  largely  volcanic,  have 
been  identified. 

Roberts  et  al.  (1958)  estimate  that  the  miogeosynclinal  strata  in  east- 
ern Nevada  and  western  Utah  above  the  thick  basal  quartzite  of  the 
Cambrian  consist  of  60  per  cent  limestone,  30  percent  dolomite,  8  percent 
shale,  and  2  percent  quartzite.  They  estimate  that  the  eugeosvnclinal 
strata,  on  the  other  hand,  in  the  Sonoma  Range  and  vicinity  consist  of 
20-40  percent  shale,  10-30  percent  sandstone,  graywacke,  and  quartzite, 
up  to  30  percent  of  chert,  with  shale  partings,  and  up  to  30  percent  of 
volcanic  and  pyroclastic  rocks. 

The  units  are  characteristically  lenticular,  and  thin  or  thicken  abrupdy 
parallel  with  and  normal  to  the  geosynclinal  trend.  Limestone,  generally  shah' 
or  sandy,  locally  forms  thin,  discontinuous  layers.  The  shale  units  are  commonlv 


63 


64 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Fig.  6.1.  Major  Paleozoic  tectonic  elements  of  western  United  States.  The  eugeosynclinal 
bondary  was  farther  east  than  shown  in  Permian  time.  The  Wasatch  line  through  southern 
Nevada  has  been  called  the  Las  Vegas  line  (Welch,  1959). 


sandy  and  few  are  calcareous.  The  quartzites  are  generally  nearly  pure,  but 
the  sandstones  are  either  graywackes  or  feldspathic  sandstones.  The  chert  units, 
partly  of  volcanic  derivation,  range  from  a  few  inches  to  several  hundred  feet 
thick;  individual  chert  layers  are  lenticular  and  range  from  a  fraction  of  an 
inch  to  3  feet.  They  are  separated  by  shaly  partings  which  are  also  lenticular; 
laterally,  chert  units  grade  into  siliceous  shale  units  with  subordinate  chert. 
The  volcanic  rocks  are  largely  andesitic  or  basaltic  pillow  lavas  and  pyroclastics 
that  accumulated  mainly  in  a  marine  environment;  most  are  highly  albitic. 
Siliceous  pyroclastic  rocks  locally  form  thick  sections.  The  volcanic  rocks  are 
highly  lenticular,  and  probably  formed  around  many  source  centers  (Roberts 
etal,  1958). 

Another  characteristic  of  the  sediments  of  the  eugeosyncline  is  their 
metamorphism.  The  thick  sequences,  especially  in  the  Sierra  Nevada, 
Klamath  Mountains,  western  British  Columbia,  and  southeastern  Alaska, 
are  made  up  of  phyllites;  slates;  argillites;  quartz,  chlorite,  hornblende, 
and  calcareous  schists;  hornblende  gneiss;  recrystallized  chert;  marble; 
meta-conglomerate;  meta-andesite;  and  various  metamorphosed  pyro- 
clastics. Still  another  characteristic  is  the  presence  of  great  intrusive 
bodies  of  later  age,  and  the  metamorphism  of  the  sediments  about  the 
intrusions. 

The  sediments  of  the  miogeosyncline,  on  the  other  hand,  are  not 
metamorphosed.  Many  of  the  sands  are  cemented  with  silica  and  termed 
quartzite,  but  little  dynamic  metamorphism  incident  to  Paleozoic, 
Mesozoic,  or  Tertiary  orogeny  has  occurred. 

The  medial  belt  in  central  Nevada  contains  transitional  types  of  the 
two  environments,  and  became  not  only  a  geanticline  but  a  belt  of 
orogeny  in  late  Devonian  time.  The  western  eugeosynclinal  strata  were 
thrust  many  miles  eastward  to  rest  on  miogeosynclinal  strata  of  strikingly 
different  lithology. 

BASINS  AND  UPLIFTS  OF  THE  WESTERN  UNITED  STATES 
AND  SOUTHERN   BRITISH   COLUMBIA 

Cambrian  Basins 

The  miogeosyncline  is  noted  for  its  Cambrian  sections  (Fig.  6.2).  At 
one  locality  in  southern  Nevada  and  California  17,000  feet  of  Lower, 
Middle,  and  Upper  Cambrian  beds  have  been  measured. 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


65 


The  oldest  Cambrian  rocks  over  much  of  eastern  and  southern  Nevada 
and  southwestern  Utah  is  the  Prospect  Mountain  quartzite,  which  may 
be  over  5000  feet  thick  in  places.  The  Osgood  Mountain  quartzite  in 
north-central  Nevada,  the  equivalent  of  the  Prospect  Mountain,  may  be 
as  much  as  10,000  feet  thick.  Overlying  the  quartzite  are  shale,  dolomite, 
and  limestone  formations  of  uniform  and  wide  occurrence.  Stratigraphic 
sections  from  the  eugeosyncline  to  the  miogeosyncline  of  north-central 
Nevada  are  shown  in  Fig.  6.9,  and  of  the  miogeosyncline  of  western  and 
northern  Utah  in  Figs.  6.9  and  6.10. 

In  southeastern  British  Columbia  is  another  succession  of  Cambrian 
strata  which  totals  about  10,000  feet  in  maximum  thickness.  From  the 
Burgess  shale  of  this  succession  Wolcott  took  an  amazing  assortment  of 
fossils  and  greatly  enriched  our  knowledge  of  life  at  the  beginning  of 
Paleozoic  time.  Lower  Cambrian  beds  are  absent  at  the  international 
boundary,  but  further  north  in  the  Mount  Robson  vicinity  they  are 
present  and  consist  of  3900  feet  of  quartzitic  sandstone,  siliceous  shale, 
and  limestone.  Upper  Cambrian  strata  are  restricted  and  consist  mostly 
of  limestone  ( Lord  et  al.,  1947 ) . 

Another  thick  Cambrian  sequence  is  known  in  northeastern  Washington 
where  at  least  12,000  feet  of  beds  dated  by  fossils  occur.  The  Gypsy 
quartzite  lies  at  the  base;  over  this  is  the  Maitlen  phyllite,  and  over  this 
the  Metaline  limestone  (Park  and  Cannon,  1938;  Campbell,  1947).  The 
assemblage  is  miogeosynclinal  in  aspect  and  contains  elements  of  the 
same  fauna  as  the  miogeosyncline  of  western  Utah  and  eastern  Nevada 
( Wm.  Lee  Stokes,  personal  communication). 

Representative  of  the  eugeosynclinal  assemblage  in  Cambrian  time  is 
the  Scott  Canyon  formation  in  Battle  Mountain.  It  is  composed  of  green- 
stone, chert,  and  some  shale,  and  is  about  5000  feet  thick  ( Roberts  et  al., 
1958). 

Lower  and  Middle  Cambrian  sediments  are  just  about  entirely  re- 
stricted to  the  geosyncline,  but  Upper  Cambrian  strata  are  spread  widely 
over  the  Central  Stable  Region  of  the  United  States  as  far  as  Wisconsin 
and  Ohio.  Here  they  are  overlapped  by  Ordovician  sediments  which 
extend  to  the  north  and  northeast  over  the  Precambrian  rocks  of  the 
Canadian  Shield. 


CAMBRIAN 


Fig.  6.2.     Thickness  and  paleographic  map  of  the  Cambrian. 


66 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


ORDOVICIAN 


Fig.  6.3.      Thickness  and  paleographic  map  of  the  Ordivician. 


In  Chapter  4  the  Precambrian  Mazatzal  and  Reltian  orogenic  belts  have 
been  described.  Although  the  Beltian  trough  of  sedimentation  and  later 
belt  of  orogeny  marked  the  first  tectonic  development  parallel  with  the 
present  Pacific  margin  of  the  continent,  the  older  Mazatzal  belt  seems  to 
have  made  an  impress  on  the  Paleozoic  geosynclinal  basins.  The  Trans- 
continental Arch,  which  reflects  the  Mazatzal  orogenic  belt,  borders 
directly  on  the  arch  in  southeastern  Utah,  Arizona,  and  Colorado,  and 
the  two  have  the  same  trend  to  the  southwest.  See  maps,  Figs.  6.1  to 
6.5 

An  uplift  here  called  the  Raft  River  geanticline,  is  identified  in  north- 
western Utah  (Stokes,  1952;  Felix,  1956)  and  southwestern  Montana 
( Scholten,  1957)  on  the  south  and  north  sides  of  the  Snake  River  volcanic 
field  respectively  (see  Fig.  6.11).  Its  extent  northwestward  cannot  be  told 
because  of  the  cover  of  Tertiary  volcanic  rocks  and  the  intrusion  of  the 
great  Idaho  batholiths,  but  in  the  interpretation  rendered  on  Fig.  6.2  it 
appears  as  a  geanticlinal  uplift  between  the  eugeosyncline  basin  in  north- 
ern Nevada  and  the  miogeosyncline  of  Utah.  An  unconformity  in  the 
Upper  Cambrian  detected  in  the  South  Stansbury  Mountains  (Rigby, 
(1958)  with  700  feet  of  beds  removed  may  be  a  lateral  affect  of  the  Raft 
River  geanticline  (see  Fig.  6.10).  The  erosion  surface  lies  beneath  the 
Cole  Canyon  dolomite. 

Still  farther  north  in  northwestern  Montana,  northern  Idaho,  and 
British  Columbia  is  an  extensive  region  of  Precambrian  strata,  the  Belt 
series,  and  this  is  here  interpreted  to  have  been  a  fairly  persistent  struc- 
tural feature  from  Cambrian  time  on.  Evidence  cannot  be  sited  for 
shoreline  deposits  and  overlapping  relations,  but  this  is  mostly  due  to 
the  extensive  batholithic  intrusions  and  metamorphism.  Early  geologists 
considered  the  Beltian  terrane  the  shore  of  an  extensive,  west-lying  land 
which  they  called  Cascadia,  but  later  ones  have  considered  the  Paleozoic 
strata,  beginning  with  Middle  Cambrian,  to  have  been  deposited  across 
and  then  eroded  away  incident  to  the  emergence  of  the  modern  gean- 
ticline in  Cretaceous  and  Tertiary  times.  Sloss  ( 1950 )  however,  suggests 
a  small  uplift  there,  and  his  interpretation  is  reflected  on  the  maps  of  the 
Williston  basin,  Figs.  5.17,  5.18,  and  5.19.  The  writer  takes  the  view  that 
it  has  been  a  significant  feature  from  Cambrian  time  on  ( see  Chapter  33 ) . 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


67 


No  Cambrian  or  Ordovician  fossils  have  been  found  in  northern  Cali- 
fornia, Oregon,  and  all  Washington  except  the  northeast  corner.  The 
lack  of  information  about  the  western  margin  of  the  continent  in  Cam- 
brian time,  and  in  Ordovician  as  well,  is  disappointing.  The  oldest  fossils 
yet  discovered  along  the  Pacific  margin  in  the  United  States  and  British 
Columbia  are  Silurian.  These  have  been  found  in  the  Klamath  Mountains 
by  Wells  (1956).  Three  metamorphic  series  underly  the  fossiliferous 
Devonian  strata  there,  according  to  Hinds  (1939),  and  one  or  more  of 
these  might  be  Ordovician  and  Cambrian.  See  Fig.  6.3.  In  southeastern 
Alaska  Buddington  reports  Ordovician  fossils,  but  no  Cambrian.  In  con- 
clusion it  may  be  assumed  that  the  entire  region  west  of  central  Nevada 
was  eugeosynclinal  from  Ordovician  time  to  the  close  of  the  Paleozoic. 

Ordovician  Basins 

A  broad  Ordovician  basin  exists  in  western  Utah  and  Nevada  with 
miogeosynclinal  type  sediments  in  the  eastern  and  eugeosynclinal  type  in 
the  western  part  ( see  Fig.  6.3 ) .  The  formations  and  their  lithologies  are 
shown  in  Fig.  6.9,  which  is  a  section  across  central  Nevada  and  marks  the 
change  from  the  eugeosyncline  to  the  miogeosyncline.  The  miogeo- 
synclinal sediments  of  western  Utah  are  reviewed  by  Hintze  ( 1951 )  and 
summarized  in  the  table  of  Fig.  6.12. 

Another  basin,  which  was  narrower  and  completely  miogeosynclinal  in 
character  (Fig.  6.12,  Logan  area),  existed  in  southeastern  Idaho  and 
northern  Utah.  For  a  review  of  the  stratigraphy  see  Ross  ( 1953 ) .  In 
both  basins  the  rocks  are  dominantly  limestones  and  dolomites,  but  con- 
spicuous quartzite  formations  exist  in  each.  The  Swan  Peak  quartzite 
of  southeastern  Idaho  and  northern  Utah  is  about  500  feet  thick,  and  the 
Eureka  quartzite  and  the  Swan  Peak  quartzite  of  western  Utah  and 
eastern  Nevada  are  nearly  800  feet  thick  together.  The  Eureka  quartzite, 
537  feet  thick  at  Ibex,  Utah,  overlies  an  85-foot  dolomite  member,  and 
this  overlies  the  Swan  Peak  quartzite,  249  feet  thick.  The  dolomite  mem- 
ber wedges  out  east  of  Ibex,  and  there  the  upper  quartzite  rests  directly 
on  the  lower.  The  absence  or  near  absence  of  these  sandstones  together 
with  a  thinner  Ordovician  section  in  Utah  southwest  of  Great  Salt  Lake 
indicates  an  uplift  there  which  Webb  (1958)  has  defined  and  named  the 


Fig.  6.4.     Thickness  and  paleogeographic  map  of  the  Silurian. 


68 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Tooele  arch.  The  arch  and  erosion  is  pre-Fish  Haven  (see  Fig.  6.12). 

A  deep  and  evidently  narrow  trough  of  Ordovician  sediments  exists  in 
the  Canadian  Rockies  of  western  Alberta  and  eastern  Rritish  Columbia. 
It  is  interpreted  to  lie  east  of  the  Reltian  geanticline  and  to  be  separated 
by  it  from  the  basin  of  northeastern  Washington  containing  the  Ordo- 
vician Ledbetter  slate,  also  of  miogeosynclinal  type.  The  Ordovician  strata 
of  the  Canadian  Rockies  consist  of  3000  to  7000  feet  of  limestone,  shale, 
and  slate  beds  with  fossils  representing  a  range  from  Lower  to  Upper 
in  different  places  ( Lord  et  al.,  1947 ) . 

According  to  Roberts  et  al.  (1958): 

Rocks  of  Ordovician  age  that  belong  to  the  western  assemblage  (eugeosyn- 
cline)  are  widely  exposed  throughout  north-central  Nevada.  They  underlie 
large  areas  in  the  Sulphur  Spring  Range,  Roberts  Mountains,  Tuscarora  Moun- 
tains, Cortez  Mountains,  northern  Shoshone  Range,  Toyabe  Range,  Batde  Moun- 
tain, and  the  Sonoma  Range.  So  far  as  known  they  are  allochthonous. 

Merriam  and  Anderson  (1942,  p.  1694)  used  the  name  Vinini  formation 
for  rocks  of  Ordovician  age  of  the  western  assemblage  in  the  Roberts  Moun- 
tains. They  divided  the  formation  into  two  units.  The  lower  part  of  the  Vinini, 
Early  Ordovician  in  age,  consists  of  quartzite,  limestone,  and  calcareous  sand- 
stone, and  silty  and  shaly  sediments  with  minor  amounts  of  andesitic  lava  flows 
and  tuffs;  perhaps  the  relatively  abundant  limestone  here  suggests  an  approach 
to  the  transitional  assemblage.  The  upper  part  of  the  Vinini,  of  Middle 
Ordovician  age,  is  composed  of  bedded  chert  and  black  organic  shale,  clearly 
of  normal  western  lithologic  type. 

The  most  complete  stratigraphic  section  of  the  Vinini  formation  thus  far 
seen  is  in  the  Tuscarora  Mountains,  northern  Eureka  County,  about  5  miles  north 
of  U.S.  Highway  40.  Strata  of  Early,  Middle,  and  probably  late  Ordovician 
age  are  present;  no  detailed  measurements  were  made,  but  it  is  estimated  that 
the  section  is  at  least  7,000  feet  thick. 

In  the  Shoshone  Range,  Battle  Mountain,  and  Sonoma  Range  the  proportion 
of  massive  quartzite,  chert,  and  volcanic  material  in  the  Ordovician  rocks  of 
the  western  assemblage  is  larger  than  in  the  Vinini  formation.  These  rocks  were 
named  the  Valmy  formation  in  Battle  Mountain  (Roberts,  1949,  1951)  where 
they  have  been  subdivided  into  two  members.  The  lower  part  of  the  Valmy 
consists  mainly  of  rather  pure,  generally  light-colored  quartzite,  dark  gray  and 
greenish  chert,  some  gray  to  black  siliceous  shale,  and  a  significant  amount 
of  greenstone.  The  upper  member  consists  principally  of  dark  thin-bedded 
chert  interbedded  with  dark  shale  and  a  little  greenstone.  The  base  of  the 
Valmy  is  concealed  but  at  least  4,000  feet  is  present.  The  upper  beds  of  the 
Valmy  are  highly  contorted,  but  are  estimated  to  be  3,000  or  more  feet  thick. 
[Refer  also  to  Ross  (1961).] 


In  the  shelf  region  the  Transcontinental  Arch  was  nearly  completely 
emergent,  or  at  least  no  Ordovician  strata  occur  on  it  under  a  Devonian 
and  Mississippian  cover,  except  for  the  Colorado  sag.  This  embayment 
probably  did  not  extend  all  the  way  through  to  the  western  geosyncline 
or  the  Williston  basin  because  in  the  eastern  Uinta  Mountains  of  Utah 
the  Mississippian  beds  (possibly  Devonian)  rest  directly  on  the  Cam- 
brian. 

The  ancestral  Sweetgrass  arch  was  broadly  emergent  and  well-defined. 

Silurian  Basins 

The  Silurian  seas  were  more  restricted  than  any  others  in  Paleozoic 
time.  The  Laketown  dolomite  of  northern  Utah  and  southeastern  Utah 
has  been  traced  widely  over  western  Utah  and  is  the  sole  representative 
of  the  Silurian  thus  far  recognized  there.  In  eastern  and  central  Nevada 
the  Roberts  Mountain  formation  and  overlying  Lone  Mountain  dolomite 
correlate  with  the  Laketown.  The  entire  section  is  carbonate  rock,  and 
over  half  of  it  is  dolomite  (see  Figs.  6.9  and  6.12). 

Silurian  rocks  of  eugeosynclinal  aspect  appear  to  be  widespread  in 
north-central  Nevada,  but  because  they  resemble  the  Ordovician  units 
they  may  not  have  been  recognized  in  mapping. 

On  the  east  side  of  Pine  Valley  about  8  miles  south  of  Carlin,  unnamed 
black  shale  and  tawny  to  buff  tuffaceous  shale  and  calcareous  shale  have 
yielded  Monograptus  determined  by  R.  J.  Ross,  Jr.,  to  be  of  Silurian  age. 
The  thickness  of  these  beds  is  not  known. 

Black  shale  containing  Monograptus  is  reported  by  C.  W.  Merriam  (oral 
communication)  from  the  vicinity  of  McClusky  Pass  in  the  northern  part  of 
the  Simpson  Park  Mountains.  C.  A.  Nelson  (oral  communication)  also  reports 
Monograptus  in  shale  on  the  east  side  of  Pine  Valley  near  Mineral  Hill.  On 
the  west  side  of  the  Tuscarora  Mountains  in  the  valley  of  Mary's  Creek, 
graptolites  that  according  to  R.  J.  Ross,  Jr.,  have  affinities  with  Silurian  forms 
were  collected  by  Roberts  in  1954.  Silurian  strata  (R.  J.  Ross,  Jr.),  including 
about  4000  feet  of  sandstone,  arkose,  shale,  and  a  little  chert,  from  part  of 
the  overriding  plate  of  the  Roberts  Mountains  thrust  in  the  northern  Shoshone 
Range  and  in  the  Cortez  Mountains. 

The  beds  containing  graptolites  of  Silurian  age  are  on  the  whole  less  cherty, 
and  contain  more  calcareous  shale  and  limestone  layers  than  the  Vinini  and 
Valmy  formations.  On  the  other  hand,  the  Silurian  beds  of  the  western 
assemblage  appear  much  less  calcareous  than  the  Silurian  of  the  transitional 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


'assemblage.  The  western  rocks  contain  some  siliceous  pyroclastics,  which  have 
not  been  recognized  in  the  other  assemblages  (Roberts  et  al.,  1958). 

Silurian  strata  have  been  recognized  in  the  northern  Klamath  Moun- 
tains by  Wells  et  al.  (1951),  and  rest  on  highly  foliated  schists  which 
may  be  metamorphosed  Ordovician  and  Cambrian  or  Precambrian  in 
age.  The  Silurian  beds  had  formerly  been  considered  Devonian,  but 
patches  of  Devonian  limestone  of  undetermined  stratigraphic  relations 
crop  out  nearby.  The  sequence  of  units  now  recognized  by  Wells  and  co- 
workers is  as  shown  in  Fig.  6.13,  and  is  compared  with  the  assemblage 
of  rock  units  in  the  southern  Klamath  Mountains.  Since  no  Ordovician 
or  Cambrian  beds  are  yet  known  west  of  north-central  Nevada,  the 
possibility  of  correlating  the  Salmon  and  Abrams  schists  with  the  Ordo- 
vician and  Cambrian  is  suggestive.  The  Copley  and  Chanchellula  are 
questionably  correlated  with  the  "Silurian  strata"  of  the  northern  Klamath 
Mountains. 

Devonian  Basins 

The  Devonian  basins  are  in  much  the  same  pattern  as  the  Ordovician 
although  the  strata  are  not  so  thick.  The  Transcontinental  Arch  in  Utah 
and  Arizona  was  more  widely  covered,  however  (Fig.  6.5). 

Although  Devonian  strata  are  found  nearly  everywhere  west  of  the 
Transcontinental  Arch  ( Rrooks  and  Andrichuk,  1953 ) ,  they  are  over  1000 
feet  thick  only  in  the  western  part  of  the  general  Rocky  Mountain  area. 
In  the  Roberts  Range,  Nevada,  Merriam  ( 1940 )  has  described  4465  feet 
of  Devonian  beds,  and  at  nearby  Eureka  he  has  found  4000  to  5000  feet 
of  them.  They  are  composed  chiefly  on  limestones  and  dolomites,  their 
fossil  content  indicates  a  rather  complete  section,  and  the  broad  trough 
in  which  they  accumulated  subsided  during  most  of  Devonian  time.  ( See 
Fig.  6.9.) 

Devonian  rocks  of  the  Sulphur  Spring  and  Pinyon  ranges  have  been  recently 
described  by  Carlisle  and  others,  who  showed  that  northward  from  the 
Roberts  Mountains  the  Nevada-Devils  Gate  sequence  thickens,  becomes  more 
dolomitic,  and  less  fossiliferous.  The  sequence  contains  vitreous  quartzite  units 
as  much  as  400  feet  thick  that  grade  into  carbonate  quartz  arenites  and  thus 
resembles  the  Devonian  section  near  Eureka  more  than  the  section  at  Lone 
Mountain. 


DEVONIAN 


Fig.  6.5.  Thickness  and  paleogeographic  map  of  the  Devonian.  Antler  orogenic  belt,  Sta 
bury  anticline,  and  Beaverhead  dome  made  appearance  in  Late  Devonian.  Most  of  sedime 
are  Middle  Devonian. 


ns- 

nts 


70 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Devonian  rocks  of  the  western  assemblage  appear  to  be  widespread  through- 
out north-central  Nevada,  but  are  most  abundant  from  the  Shoshone  Range 
eastward.  These  lack  the  basic  volcanic  flows  and  pyroclastics  characteristic  of 
Cambrian  and  Ordovician  rocks  of  the  western  assemblage,  but  locally  contain 
silicic  pyroclastics,  much  chert  and  shale,  and  a  litde  calcareous  shale. 

In  Slaven  Canyon  in  the  Shoshone  Range  and  elsewhere  in  the  Mt.  Lewis 
Quadrangle,  there  are  at  least  4,000  feet  of  strata  composed  dominantly  of  dark 
gray  to  black  chert  with  some  dark  shale,  a  little  sandstone,  and  very  small 
amounts  of  limestone.  These  have  yielded  ostracods  and  conodonts  of  Middle 
Devonian  age.  Similar  rocks  on  and  south  of  Bald  Mountain,  in  the  northern 
Toyabe  Range  southwest  of  Cortez,  are  probably  correlative. 

Tuffaceous  shale  and  calcareous  shale  on  the  east  side  of  Pine  Valley  about 
8  miles  south  of  Carlin  have  also  yielded  conodonts  of  Devonian  age.  These 
rocks  are  associated  with  Silurian  and  Ordovician  rocks  in  the  upper  plate  of 
the  Roberts  Mountains  thrust  (Roberts  et  al.,  1958). 

In  the  southern  Klamath  Mountains  siliceous  black  shales  and  slates 
containing  thin  beds  of  sandstone  and  fossiliferous  limestone,  now  largely 
recrystalized,  make  up  the  Kennett  formation  of  Devonian  age.  It  crops 
out  in  two  restricted  belts,  and  rests  unconformably  on  the  older  rocks. 
Devonian  strata  are  not  known  in  the  Sierra  Nevada  or  Coast  Ranges 
south  of  the  Klamath  Mountains  in  California. 


Late  Devonian  Orogeny 

Toward  the  end  of  the  Devonian  period,  according  to  Nolan  ( 1943 ) ,  a 
geanticline  began  to  rise  in  central  Nevada,  approximately  along  the 
transition  zone  of  eugeosynclinal  and  miogeosinclinal  sediments.  See  Fig. 
6.5.  The  uplift  divided  the  geosyncline  into  a  western  and  an  eastern 
trough,  and  the  distribution  of  Devonian  sediments  is  reflected  in  two 
ways,  viz.,  by  the  almost  complete  removal  of  the  earlier  Devonian 
deposits  along  the  axis  of  the  arch,  and  by  an  eastward  shift  to  the  vicinity 
of  Eureka,  Nevada,  of  the  zone  of  maximum  sedimentation.  The  geanti- 
cline was  later  named  the  Manhattan  (Eardley,  1947).  Since  then  a  large 
amount  of  significant  field  work  has  been  done  and  the  geanticline  has 
come  to  be  recognized  as  a  belt  of  major  orogeny,  and  has  been  called 
the  Antler  orogenic  belt  ( Roberts  et  al.,  1958 ) . 

At  the  close  of  the  Devonian,  fundamental  changes  took  place  along 
the  western  part  of  the  area  of  predominantly  carbonate   deposition 


(miogeosyncline).  The  carbonate  rocks  were  folded  and  overridden  by 
the  Roberts  Mountains  thrust  plate  that  brought  clastic  and  volcanic 
rocks  of  equivalent  age  but  different  facies  from  the  west  or  northwest. 
Clastic  rocks  eroded  from  the  rising  upland  in  the  west  marked  the  end 
of  the  broad  geosyncline  in  north-central  Nevada  as  it  had  existed  earlier, 
and  introduced  a  change  to  narrow  straits  and  embayments  in  the 
orogenic  belt  during  the  remainder  of  the  Paleozoic.  The  clastic  rocks 
do  not  resemble  the  assemblages  laid  down  in  the  geosyncline  during 
early  and  middle  Paleozoic,  but  overlap  all  of  them.  On  the  west,  over- 
lapping rocks  rest  with  angular  unconformity  on  rocks  of  the  western 
and  transitional  assemblages;  in  the  Carlin  area,  west  of  Elko,  the  un- 
conformity is  much  less  marked;  and  on  the  east,  the  discordance  fades 
out  and  the  overlapping  rocks  interfinger  with  the  eastern  assemblage 
rocks  and  grade  eastward  into  the  carbonate  section  of  late  Paleozoic 
age  of  eastern  Nevada  and  western  Utah.  Examine  Figs.  6.9,  6.14,  and 
6.15. 

In  latest  Devonian  or  earliest  Mississippian  time  a  sharp  anticline  rose 
in  the  site  of  the  Stansbury  Range  of  west-central  Utah.  It  was  eroded 
down  to  the  Cambrian  before  early  Mississippian  seas  covered  it  (see 
Fig.  6.12).  Coarse  slide  debris  accumulated  on  its  northwest  flank,  and 
sand  dunes  were  blown  northward  for  several  miles  to  build  a  sandstone 
unit  several  hundred  feet  thick.  The  angular  unconformity  and  the  com- 
pleteness of  the  anticline,  about  30  miles  long  and  5  miles  wide  as  mapped 
by  Rigby  ( 1958 ) ,  are  particularly  impressive. 

No  Devonian  strata  are  known  in  the  Raft  River  Mountains  of  north- 
western Utah;  only  Pennsylvanian  strata  in  fault  contact  with  Precam- 
brian  rocks  have  been  mapped,  and  the  Devonian  relations  have  not 
been  specifically  deciphered  (Felix,  1956).  Small  remnants  of  al- 
lochthonous  Paleozoic  (?)  strata  occur  on  the  Precambrian  rocks,  and 
the  possibility  exists  that  this  area  may  be  a  continuation  of  the  Stans- 
bury anticline  and  a  belt  where  orogeny  was  more  severe  than  to  the 
south.  The  belt  may  join  the  Antler  orogenic  belt  to  the  northwest.  See 
Fig.  6.5.  More  details  of  the  Antler  orogenic  belt  will  be  given  in  the 
discussion  of  the  Mississippian,  Pennsylvanian,  and  Permian  strata. 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


71 


Mississippian  Basins 

Major  miogeosynclinal  deposits  extend  from  the  Big  Snowy  basin  of 

: Montana  in  a  fairly  narrow  trough  southward  through  eastern  Idaho 

into  Utah  and  then  southwesterly  into  southern  Nevada.  The  greatest 

thickness  is  reached  in  the  Lemhi  and  Lost  River  ranges  of  Idaho  (Figs. 

'6.6  and  6.11). 

Characteristic  formations  of  the  trough  are  shown  in  Fig.  6.16.  In 
summary  of  the  strata  of  the  eastern  trough  it  may  be  said  that  they 
consist  mostly  of  limestones,  but  that  the  limestones  grade  into  a  thick 
shale  (now  argillite)  section  in  Idaho,  which  may  savor  of  the  eugeosyn- 
cline.  Also  the  Manning  Canyon  shale  of  western  Utah  is  thick  (1100 
feet)  and  marks  the  transition  from  the  Mississippian  to  the  Pennsyl- 
jjvanian.  For  references  see  Scholten  (1957),  Morris  (1957),  and  Gilluly 
•i(1932). 

The  change  from  shelf  to  miogeosyncline  is  shown  in  Figs.  6.11  and 
6.17.  The  Raft  River  geanticline  just  southwest  of  the  Montana-Idaho 
^boundary  is  well  illustrated  in  Fig.  6.11. 

Antler  Orogenic  and  Post-Orogenic  Stratigraphy 

Coarse  elastics  in  places  10,000  feet  thick  were  spread  eastward  and 
westward  from  the  Antler  orogenic  belt,  and  overlap  the  pre-existing 
:3ugeosynclinal,  transitional,  and  miogeosynclinal  assemblages.  According 
to  Roberts  et  al,  (1958): 

The  lithologic  character  of  the  overlap  assemblage  is  variable  from  place  to 
ilace,  and  different  names  have  been  applied  to  correlative  beds.  In  the  east, 
he  Eureka-Carlin  sequence  includes  the  Chainman  shale,  Diamond  Peak 
formation,  Ely  limestone,  Carbon  Ridge,  and  Garden  Valley  formations  of  the 
iureka  area,  and  correlative  formations  in  the  Carlin  area.  In  the  west,  the 
Antler  sequence  includes  the  Battle  formation,  Highway  limestone,  Ander  Peak 
iimestone,  and  Edna  Mountain  formation.  Because  of  local  variations  in  source 
ireas,  in  conditions  of  deposition,  and  subsequent  history  of  these  rocks,  it  is 
mpossible  to  make  precise  correlations  of  the  units  in  the  different  sequences. 
Regional  lithologic  similarities  indicate,  however,  that  similar  environmental 
jjonditions  prevailed  over  broad  areas.  The  Havallah  formation  of  the  Sonoma 
md  East  ranges  was  probably  laid  down  50-100  miles  west  of  the  orogenic 
|)elt  and  was  thrust  eastward  into  juxtaposition  with  the  Antler  sequence  during 
vlesozoic  orogeny.  It  therefore  has  had  a  somewhat  different  history  and  is 


MISSISSIPPIAN 


Fig.  6.6.  Thickness  and  paleographic  map  of  the  Mississippian.  A-S.G.  AR.  is  Apishapo- 
Sierra  Grande  arch.  Uncompahgre  and  Colorado  uplifts  first  became  emergent  in  latest  Missis- 
sippian, and  developed  into  major  ranges  in  Early  Pennsvlvanian. 


72 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


not   strictly   comparable   with   the   approximately   contemporaneous    Eureka- 
Carlin  and  Antler  sequences. 

The  basal  sediments  of  the  overlap  assemblage  differ  in  age  throughout 
north-central  Nevada.  In  the  Eureka  area  the  intertonguing  Chainman  shale 
and  Diamond  Peak  formation  of  Late  Mississippian  age  are  the  earliest  orogenic 
sediments  recognized.  In  the  Carlin  area  the  Tonka  formation  of  Dott  (1955, 
pp.  2222-33)  and  correlative  units  farther  southeast  in  Pine  Valley  mapped  by 
J.  Fred  Smith  and  Keith  Ketner  included  Lower  Mississippian  clastic  beds 
that  overlap  the  upper  plate  of  the  Roberts  Mountains  thrust  fault,  indicating 
that  the  thrust  reached  the  Carlin  area  during  Late  Devonian  or  Early 
Mississippian  time. 

Orogenic  movements  continued  along  the  belt  in  Pennsylvanian  and 
Permian  time,  and  also  throughout  the  Mesozoic.  Examine  the  structure 
cross  sections  of  Chapter  17,  Figs.  17.3-17.6. 

Walter  Sadlick  and  F.  E.  Schaeffer  (personal  communication)  recog- 
nize an  angular  unconformity  at  the  base  of  the  Chainman  formation  in 
western  Utah  and  are  calling  the  disturbance  represented  by  it  the 
Wendover  phase  of  the  Antler  orogeny.  They  are  of  the  opinion  that 
this  time  (early  Valmeyer  of  the  early  Mississippian)  marks  the  begin- 
ning of  the  Antler  orogeny.  They  recognize  beveled  folds  covered  by  the 
Chainman,  and  the  axes  of  the  folds  trend  to  the  northwest. 

Klamath  Mountains  and  Sierra  Nevada 

The  Mississippian  is  made  up  of  two  formations  in  the  Klamath  Moun- 
tains, the  Bragdon  and  the  Baird  (Fig.  6.13).  They  are  probably  the  most 
widespread  formations  in  the  region.  The  Bragdon  is  chiefly  shale  and 
slate,  generally  gray,  in  contrast  to  the  black  shale  and  slate  of  the  older 
Kennett  formation  of  Devonian  age.  Some  sandstones  are  conglomeratic 
near  the  base  and  contain  fragments  of  both  the  Kennett  and  Copley 
formations.  Within  the  Redding  quadrangle,  a  volcanic  sequence  called 
the  Bass  Mountain  basalt  is  present.  The  Bragdon  may  exceed  6000  feet 
in  thickness  in  places.  The  Bass  Mountain  volcanic  sequence  contains 
many  tuff  beds.  Its  position  on  Bass  Mountain,  according  to  Hinds  ( 1939), 
is  in  the  lower  part  of  the  Bragdon  formation. 

The  Baird  formation  consists  largely  of  sandstone  and  tuff,  but  the 
upper  part  has  calcareous  and  siliceous  slates.  It  is  about  700  feet  thick 
and  apparently  rests  conformably  on  the  Bragdon  (Hinds,  1939). 


In  the  northern  Sierra  Nevada,  the  metamorphic  Calaveras  formation 
of  Carboniferous  age  is  widespread.  It  consists  chiefly  of  black  phyllite 
with  subordinate  fine-grained  quartzite,  limestone,  and  chert.  Associated 
and  in  part  interbedded  with  the  formation  are  green  amphibolite  schists 
of  contemporaneous  age.  From  fossils,  found  chiefly  in  the  limestone,  the 
Calaveras  formation  is  known  to  be  at  least  in  part  of  Carboniferous 
age,  but  parts  of  it  as  mapped  may  be  Devonian  and  Triassic.  Because 
of  the  metamorphosed  condition  of  the  rocks  in  which  the  fossils  are 
found,  it  has  been  difficult  for  paleontologists  to  determine  to  what  part 
of  the  Carboniferous  the  faunas  belong.  Groups  of  Calaveras  fossils  from 
the  Taylorsville  region  are  more  closely  related  to  the  Baird,  now  recog- 
nized as  Mississippian,  than  to  the  McCloud  limestone,  now  believed  to 
be  Permian. 

The  amphibolite  schists  were  originally  fine  pyroclastics  (Knopf,  1929). 
The  bedded  rocks  are  most  abundant  in  the  northern  Sierra  Nevada, 
but  southward  become  increasingly  metamorphosed,  and  progressively 
greater  areas  are  occupied  by  granitic  intrusives.  In  the  Tehachapi  Moun- 
tains and  the  southern  Coast  Ranges,  pre-granitic  rocks  are  present,  but 
highly  altered. 

A  thick  sedimentary  deposit,  now  schist,  in  southern  California,  has 
yielded  Mississippian  fossils  ( Larsen,  1948 ) .  The  sequence  appears  to  be 
miogeosynclinal  in  type  and  at  the  same  time  seemingly  out  of  place  in 
the  geosynclinal  setting. 

Pennsylvanian  Basins 

Of  the  miogeosyncline  the  Oquirrh  basin  is  the  most  striking  feature 
of  Pennsylvanian  and  Permian  time.  It  appears  to  have  been  a  sharp  and 
small  basin  in  which  over  15,000  feet  of  strata  accumulated.  The  thickest 
section  is  in  the  Provo  part  of  the  Wasatch  Mountains  of  central  Utah 
where  Baker  ( 1947)  reports  26,000  feet  of  beds.  The  upper  9800  feet  is  of 
Permian  age.  A  short  distance  to  the  southeast  20,000  feet  of  beds  have 
been  estimated  in  the  Mt.  Nebo  district  (Eardley,  1934),  and  in  the 
range  to  the  west,  the  Stansbury,  15,000  feet  (Rigby,  1958).  The  basin 
has  been  contoured  with  a  northwest  trend  and  an  abrupt  northeast 
margin   (Stokes  and  Heylmun,   1958).   This  permits  the  interpretation 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


:  - 


that  the  Uncompahgre  Range  of  the  Ancestral  Rockies   (Chapter  15) 
extends  through  in  subdued  form  to  a  small  uplift  in  northwestern  Utah. 
The  sharp  margin  was  not  a  fault  scarp,  however,  because  no  coarse 
flanking  debris  is  known  as  in  Paradox  basin.  The  conspicuous  change 
from  shelf  to  basin  is  illustrated  in  Fig.  6.17.  The  basin  was  filled,  at  least 
on  the  north  by  progressive  overlap  from  south  to  north,  with  the  oldest 
Pennsylvanian  Morrowan  sediments  on  the  Manning  Canyon  shale  on 
the  south  and  with  Atokan,  Desmoinesian,  and  Missourian  successively 
deposited  on  the  shale  to  the  north  (Rigby,  1958).  Limestone  and  sand- 
j  stone  are  the  principal  lithologies  in  the  thick  succession,  and  cyclical 
■j  sediments  dominate  the  Desmoinesian  section  in  the  Stansbury  Moun- 
tains. Quartzite  and  sandstone  dominate  over  limestone  in  the  Missourian 
and  Virgilian  section. 
A  deep  and  evidently  large  basin  developed  in  Idaho  in  which  the 
i  Wood  River  formation  accumulated  possibly  12,000  feet  thick.  The  forma- 
'  tion  extends  westward  from  the  Lost  River  Range  an  unknown  distance. 
i  The  shelf  deposits  in   southwestern   Montana   are  represented  by  the 
Quadrant  quartzite  which  attains  a  maximum  thickness   of  2600  feet 
(Scholten,  1957).  The  Wood  River  contains  fusilinids  of  Desmoinesian, 
i  Virgilian,  and  Wolfcampian  ages   (Rostwick,  1955),  and  therefore  was 
deposited  simultaneously  with  the  upper  part  of  the  Oquirrh  formation. 

The  basal  Wood  River  consists  of  several  hundred  feet  of  conglom- 
erates, consisting  of  angular  to  well-rounded  chert  and  quartzite  pebbles. 
Dark  arenaceous  limestone  beds  overlie  the  conglomerate,  and  then  the 
rest  of  the  formation,  which  is  the  bulk  of  it,  is  a  monotonous  sequence 
of  calcareous  sandstones  and  sandy  limestones.  Recrystallization  and  re- 
placement are  common.  The  sandstones  are  mostly  made  up  of  quartz 
jgrains  with  5  percent  or  less   of  feldspar,   moscovite,   magnetite,   and 
Jzircon.  The  formation  is  characterized  as  miogeosynclinal  by  Rostwick. 
Although  the  sandstones  may  resemble  those  of  the  Quadrant  to  the 
'east,  it  is  difficult  to  see  how  the  conglomerate  could  have  been  derived 
rom  an  eastern  source  and  transported  over  the  region  of  sand  deposition. 
jft  seems  more  logical  to  think  of  the  chert  and  quartzite  pebbles  coming 
rom  the  west,  and  thus  the  inference  is  drawn  that  the  Antler  orogenic 
'Selt   extended   from    Nevada   northward    through   central    Idaho,    and 


was  the  source  of  the  conglomerate  and,  possibly,  of  much  of  the  sand. 

The  relation  of  Pennsylvanian  rocks  to  the  Antler  orogenic  belt  is 
diagrammed  in  Figs.  6.14  and  6.15. 

In  Nevada  the  Pennsylvanian  rocks,  like  the  underlying  Mississippian 
are  particularly  thick  east  of  the  orogenic  belt,  but  not  quite  so  coarse. 

Basal  beds  in  the  overlap  assemblage  near  the  orogenic  belt,  expecially  in 
Mississippian  and  Early  Pennsylvanian,  are  usually  coarse  conglomerates  which 
grade  laterally  into  finer  conglomerates  and  sands,  then  into  silt,  clays,  and 
limestone.  These  clastic  beds  may  be  terrestrial  locally  within  the  belt,  but 
they  are  mainly  marine  adjacent  to  it.  The  belt  may  have  been  largely  sub- 
merged at  times,  for  widespread  marine  limestone  units  interfinger  with  the 
elastics.  The  lenticularity  of  the  overlap  sediments  as  a  whole  suggests  deposi- 
tion in  several  separate  basins,  possibly  in  a  series  of  straits  separated  by 
peninsulas  and  islands.  The  presence  of  coarse  elastics  throughout  much  of 
the  Pennsylvanian  indicates  continued  orogenic  activity  from  time  to  time, 
perhaps  continuing  into  the  Permian  (Roberts  et  al.,  1958). 

Volcanoes  were  active  west  of  the  orogenic  belt  as  attested  by  the 
presence  of  volcanic  materials  particularly  in  the  Pumpernickel  and 
Havallah  formations.  These  deposits  are  believed  by  Roberts  et  al.  to 
have  been  moved  as  an  allochthonous  mass  a  number  of  miles  from  the 
vicinity  of  the  Nevada-California  border  eastward  to  the  west  side  of 
the  orogenic  belt,  because  they  have  no  lithic  counterparts  nearby.  The 
Calaveras  beds  in  the  Sierra  Nevada  appear  to  have  been  metamorphosed 
more  than  associated  Jurassic  beds  (refer  to  Chapter  17),  and  since  no 
Pennsylvanian  rocks  have  been  recognized  in  the  Sierra  Nevada  or 
Klamath  Mountains,  an  episode  of  low-grade  dynamic  metamorphism 
has  been  postulated  in  Pennsylvanian  time.  Accordingly  on  the  map  of 
Fig.  6.7  an  orogenic  belt  is  shown  in  the  California  region. 

A  thick  quartzite  formation  overlies  a  Mississippian  schist  in  southern 
California  and  is  here  placed  in  the  Pennsylvanian  although  no  fossils 
have  been  found  in  it  (Larsen,  1948). 

Permian  Basins 

The  Permian  was  a  time  of  extensive  volcanism  in  the  west,  and  various 
kinds  of  volcanic  rocks  were  spread  from  the  Klamath  Mountains  on  the 
Pacific  coast  to  central  Nevada.  The  sequence  is  5000  feet  deep  at 
Rlairsden  in  the  Sierra  Nevada  and  thickens  eastward  to  12,000  feet  in 


74 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


PENNSYLVANIAN 


Fig.  6.7.      Thickness  and   paleogeographic  map  of  the  Pennsylvanian. 


the  Humboldt  Range,  Nevada  ( Nolan,  1943 ) .  Northwestward  into  central 
Idaho,  it  thins  to  about  4000  feet.  See  Figs.  6.8  and  6.13. 

In  the  Klamath  Mountains  the  Nosoni  formation  occurs  and  is  com- 
posed of  basaltic  agglomerates,  lithic  crystal  tuffs,  flows  of  andesite  and 
of  olivine  basalt,  dark  brown,  fossiliferous,  shaly  limestone,  and  dark 
gray  to  brown  tuffaceous  shales  and  slates.  The  maximum  thickness 
measured  by  Hinds  is  1200  feet.  It  is  considered  to  be  upper  Lower 
Permian  (Wheeler,  1933). 

The  Nosoni  rests,  probably  unconformably  (Hinds,  1939),  on  the  Mc- 
Cloud  limestone  which  is  highly  fossiliferous.  It  was  probably  a  massive 
cherty  limestone,  but  now  owing  to  the  Jurassic  intrusions  it  is  mostly 
metamorphosed  in  various  degrees  to  marble.  It  reaches  a  maximum 
thickness  of  2000  feet.  Its  fossils  were  first  thought  to  represent  a  Penn- 
sylvanian age,  but  a  recent  study  by  Wheeler  ( Hinds,  1939 )  shows  them 
to  be  Lower  Permian. 

The  McCloud  limestone  overlies  the  Mississippian  Baird  formation  dis- 
conformably,  so  it  appears  that  most  of  the  Pennsylvanian  was  a  time  of 
emergence. 

Central  and  Eastern  Oregon.  A  heterogeneous  group  of  east-west 
trending  ranges  and  dissected  lava  plateaus  known  collectively  as  the 
Blue  Mountains  uplift  or  the  Blue  Mountains-Ochoco  Mountains  uplift 
(Waters,  1933)  extends  from  central  to  eastern  Oregon.  The  ranges  are 
formed  of  Paleozoic  and  Mesozoic  sediments  and  lavas  and  Mesozoic 
plutons,  and  the  complex  protrudes  island-fashion  through  the  Columbia 
River  lava  fields.  The  oldest  beds  that  crop  out  are  Lower  Carboniferous 
limestones  and  calcareous  sandstones  (Merriam  and  Berthiaume,  1943). 
See  Fig.  6.18.  About  1000  feet  of  them  are  exposed,  and  they  are  called 
the  Coffee  Creek  formation.  No  volcanic  materials  have  been  noted. 

Overlying  the  Coffee  Creek  formation  is  the  Spotted  Ridge  formation. 
The  exact  contact  relations  have  not  been  observed,  but  if  an  unconform- 
ity does  exist,  it  is  probably  not  angular  and  does  not  represent  much  of  a 
time  break.  The  Spotted  Ridge  consists  of  plant-bearing  sandstones  and 
mudstones,  conglomerates  containing  diorite,  andesite,  and  dacite 
boulders,  and  bedded  chert.  It  may  be  1500  feet  thick.  The  plants  are 
believed  to  be  Lower  Pennsylvanian. 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


75 


The  Coffee  Creek  and  Spotted  Ridge  formations  are  reported  as  in- 
tensely folded,  but  no  mention  is  made  of  metamorphism  (Merriam  and 
Berthiaume,  1943).  They  lie  in  a  tectonic  belt  of  deformed  strata  in  which 
'  the  rocks  on  the  west  ( Klamaths )  and  on  the  east  ( Baker  area )  are  meta- 
morphosed, and  it  is  puzzling  that  these  also  are  not  metamorphosed. 

The  Spotted  Ridge  is  overlain  by  the  Coyote  Butte  formation.  A  slight 
i  angular  unconformity  separates  the  two.  The  Coyote  Butte  is  made  up 
almost  entirely  of  massive  limestones.  Some  chert  pebble  conglomerates 
i  are  present  near  the  base.  The  age  is  probably  Lower  Permian. 

A  prominent  angular  unconformity  exists  between  the  Paleozoic  beds 
i  of  central  Oregon  and  the  overlying  Triassic  conglomerates  which  attain 
1  a  thickness  of  4000  feet. 

In  the  Baker  quadrangle  of  eastern  Oregon,  Gilluly  (1937b)  described 
a  formation,  the  Burnt  River  schist,  which,  chiefly  because  of  greater 
metamorphism  than  that  of  known  Carboniferous  rocks  nearby,  he  cau- 
tiously treats  as  older.  The  rock  varieties  are  greenstone  schists,  quartz 
]  schist,  conglomerate  schist,  limestone,  slate,  and  quartzite,  and  make  up  a 
series  at  least  5000  feet  thick,  maybe  several  times  as  much.  The  various 
1  types  mentioned  grade  into  each  other. 

Gilluly  visualizes  the  origin  of  the  strata  as  follows: 

.  .  .  pyroclastic  material  was  added  in  amounts  varying  from  time  to  time 
^to  a  basin  of  sedimentation  to  which  at  some  times  sand  and  at  others  clay, 
widi  some  carbonates,  were  being  supplied.  When  volcanic  contributions  were 
small,  the  deposits  were  such  as  have  yielded  the  quartzites  and  carbonaceous 
Ulates  now  found,  but  when  the  volcanic  material  increased  relative  to  the 
}  normal  terrigenous  sediment  the  deposits  were  such  as  have  yielded  the  inter- 
mediate rocks.  At  times  such  floods  of  volcanic  material  were  contributed  that 
practically  unmixed  tuff  was  formed. 

The  Burnt  River  schist  has  lithologic  similarities  with  the  Calaveras  for- 
mation, but  differs,  it  seems,  in  generally  having  greater  metamorphism 
md  an  absence  of  chert.  The  Burnt  River  appears  from  published  de- 
scriptions to  be  surprisingly  similar  to  the  Salmon  schist  of  the  Klamaths, 
which  is  probably  pre-Silurian.  See  Figs.  6.17  and  6.18. 
j   Above  the  Burnt  River  schist  is  the  Elkhorn  Ridge  argillite  about  5000 
eet  thick.  It  is  probably  the  most  widespread  of  the  pre-Tertiary  forma- 
ions  and  is  a  thick  series  of  argillite,  tuff,  and  chert  with  subordinate 


C     /   /  »6—        /        I  ^        -"    PHOSPHATE       ■ 


PERMIAN 


Fig.  6.8.     Thickness  and  paleogeographic  map  of  the  Permian.  S.G.  and  L.A.  ARCH  means  Sierra 
Grande  and  Las  Animas  arch,  which  rose  at  end  of  Permian. 


76 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


WESTERN    ASSEMBLAGE        TRANSITIONAL  ASSEMBLAGE 
3  4  12 

"Hi 


EASTERN    ASSEMBLAGE 
5  6 


liOGEOSYNCUNe 


INFERRED    FORI   OF    GEOSYNCUNE   BEFORE   SHORTENING   IN   ANTLER   OROGENY 


Fig.  6.9.  Stratigraphic  sections  of  pre-Late  Mississippian  rocks  in  north-central  Nevada.  Repro- 
duced from  Roberts  ef  a/.,  1958.  1,  Hot  Springs  Range;  2,  Osgood  Mountains;  3,  Battle  Moun- 
tain; 4,  northern  Shoshone  Range;  5,  Cortez  Mountains;  6.  Roberts  Mountains;  7,   Eureka. 

limestone  and  greenstone  masses.  A  number  of  large  intrusive  bodies 
have  been  noted  in  the  east-west  belt  of  argillite;  and  these,  together 
with  the  overlapping  Cenozoic  rocks,  effectively  prevent  the  recognition 
of  contacts  and  the  determination  of  stratigraphic  relationships.  The  beds 
are  Pennsylvanian  in  age,  because  of  Fusulina  fossils  found  in  the  lime- 
stones. Reds  younger  than  Pennsylvanian  may  have  been  included  in  the 
formation  as  mapped  (Gilluly,  1937). 

The  whole  formation  is  provisionally  considered  marine.  The  tuffaceous 
argillite,  the  tuff,  and  the  tuffaceous  limestone  all  clearly  attest  notable 
pyroclastic  contributions  to  the  formation,  and  it  is  highly  probable  that 
cherts  so  numerous  and  thick  as  those  in  this  formation  may  be  considered 
evidence  of  igneous  contribution  also. 

The  association  of  limestone  with  volcanic  materials  may  have  no 
genetic  significance,  but  a  dependency  is  suspected  because  volcanism 


might  have  raised  the  temperature  of  the  sea  and  hence  decreased  the 
solubility  of  the  lime  (Gilluly,  1937). 

The  Clover  Creek  greenstone  overlies  the  Elkridge  argillite  and  con- 
sists of  altered  volcanic  flows  and  pyroclastic  rocks,  with  subordinate  con- 
glomerate, limestone,  chert,  and  argillite.  It  is  known  to  extend  as  far 
eastward  as  the  Snake  River  Canyon,  and  is  therefore  probably  the  same 
as  the  "Permian  volcanics"  of  several  areas  in  eastern  Idaho.  It  is  at  least 
4000  feet  thick  (Gilluly,  1937). 

The  effusive  rocks  in  order  of  abundance  are  quartz  keratophyre  ( lava- 
bearing  albite),  quartz  keratophyre  tuff,  and  meta-andesite.  Fossils  col- 
lected from  the  formation  betray  a  Permian  age. 

The  marine  limestone  and  associated  fossiliferous  tuffs  demonstrate  a 
marine  origin  for  part  of  the  formation,  at  least.  The  type  of  albitization 
which  most  of  the  volcanic  rocks  have  undergone  is  common  in  demon- 
strably submarine  volcanic  rocks,  and  the  association  here  with  marine 
limestone  suggests  rather  strongly  that  the  Clover  Creek  greenstone  is  in 
large  part  of  submarine  origin. 

Northern  Washington  and  Southern  British  Columbia.  Where  the 
Okanogan  River  crosses  the  international  boundary,  extensive  areas  of 
pre-Tertiary  rocks  are  found.  The  pre-intrusives  (pre- Jurassic)  meta- 
morphic  rocks  are  called  the  Anarchist  series;  they  crop  out  in  the 
Okanogan  Range  adjacent  to  the  Okanogan  Valley  on  the  west  and  exten- 
sively in  the  Okanogan  highlands  on  the  east.  According  to  Krauskopf 
( 1939)  neither  the  top  nor  the  bottom  of  the  Anarchist  series  has  been 
found,  but  at  least  10,000  feet  of  beds  exist.  They  can  be  divided  rather 
vaguely  into  three  divisions.  The  lower  consists  chiefly  of  gray  to  jet  black 
phyllites  with  some  interbedded  quartzite  and  a  little  chlorite  schist;  the 
middle  consists  of  limestone,  massive  quartzite,  graywacke,  conglomerate, 
some  phyllite,  and  to  the  north  and  east  of  much  greenstone;  the  upper 
consists  for  the  most  part  of  greenstone  with  some  interbedded  phyllite 
and  quartzite.  The  albite  in  the  greenstones  of  the  upper  division  suggests 
a  correlation  with  the  keratophyres  of  eastern  Oregon. 

Regional  metamorphism  has  converted  the  original  sedimentary  and 
volcanic  rocks  to  a  typical  chlorite  zone  assemblage.  Near  some  of  the 
plutonic  bodies  higher-grade  contact  metamorphism  has  been  superim- 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


77 


HOUSE  RANGE 

Wheeier  and  Steele  1951 
Benliey  1958 


SHEEPROCK  MTS. 

Cohenour  1957 


EAST  TINTIC  MTS. 

Morns  1957 
Benlley  1953 


OQUIRRH   MTS. 

Gilluly  1932 

Bissell  ond  R1o,py(notes) 


S.STANSBURY 
MOUNTAINS 


N   STANSBURY 
MOUNTAINS 


LAKESIDE  MTS. 

Young  1955 


PROMONTORY  MTS.      LOGAN  AREA 

Oiton  1957  Win, ara  1946 


Bunder bera^ 


Cole  Conyon 


Ophir  Group 


Dunderbefq^ 


Cote  Conyon 


Lynch 


Worm  Creek  mem 


Bnghom 


Morjurn 


S«osev 


Condor 


Fig.   6.10.      Cambrian   formations   of   central    and    northern    Utah.    Reproduced    from    Rigby,    1958. 


.posed,  yielding  biotite  and  amphibolite  schists  and  diopside  rocks  ( Kraus- 
kopf,  1939). 

A  few  fossils  establish  a  marine  origin  for  part  of  the  series  at  least, 
and  a  late  Paleozoic  age. 

In  Stevens  County  in  northeastern  Washington,  Weaver   ( 1920 )   de- 


scribed the  Stevens  series,  a  group  of  metamorphic  rocks  with  the  great 
thickness  reportedly  of  42,900  feet.  It  consists  of  quartzites,  argillites, 
phyllites,  dolomitic  limestones,  and  schists.  It  is  believed  to  be  in  part  of 
Carboniferous  age,  but  the  lower  parts  are  undoubtedly  older.  Bancroft 
(1914)  had  previously  found  fragmentary  plant  fossils  which  appeared 


78 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


0  10  20  3.0 

MILES 


TEMDOr 
RANGE 

' 


B»e    of    Btot 


Severol  hundred  feel  of  or  - 

c  Qillaceous  rocks  In  this  oreo> 

may  be  L.-M.  Mississippi 

litf.-l  P*nnJ 


x  k  x  x  x  x  : 


K/'^lOjrj-Dj     Jeffenonft  Grand  View  doll. 
-  w.$llurion[|  ""    |S|  taketown  dolomite 

I  I  On 

M-UCoir.tirioii[lA\Ntf  , 
E3»ou 


Precombnon 


SOturdoy  Mountain  dol. 
Kinmhinic  quartxitt 
notheod  tandttont  to  Pilgrim  dol. 
fttlt   quarliife 


Llil^jJPBim      Pre-Beltion  crystalline:  rock* 


0  feet 

1000 

2000 

3000 

4000 

5000 

-$000 

-7000 

-SOOO 

9000 

io.ooq 


Fig.   6.11.      Geosyncline,    geanticline,   and    shelf   of   southwestern    Montana    and    adjacent    Idaho. 
After  Scholten,   1957. 


to  be  Carboniferous.  The  Carboniferous  part  of  the  Stevens  series  is  prob- 
ably equivalent  to  part  of  the  Anarchist  series  on  the  west  and  to  the  Pend 
Oreille  group  (Daly,  1912)  on  the  northeast  along  the  49th  parallel.  The 
Pend  Oreille  is  also  considered  in  part  Carboniferous.  It  and  equivalents 
rest  on  the  immensely  thick  Beltian  strata  of  Proterozoic  age  which  form 
a  north-south  belt  in  northern  Idaho,  western  Montana,  and  British  Co- 
lumbia east  of  Kootenay  Lake. 

The  lower  part  of  the  Stevens  series  was  later  divided  into  a  number  of 
formations  by  Park  and  Cannon  ( 1943 )  after  Cambrian,  Ordovician,  and 
Devonian  fossils  had  been  found.  Their  section  is  as  follows: 


Formation 


Thickness,  Feet 


Limestone  (Devonian) 

Ledbetter  slate  (Ordovician) 

Metaline  limestone  (Middle  Cambrian) 

Maitlen  phyllite  (Lower  or  Middle  Cambrian) 

Gypsy  quartzite  (Lower  or  Middle  Cambrian) 

Monk  formation  (Cambrian?) 

Unconformity 
Leola   volcanics   (Precambrian) 
Shedroof  conglomerate   (precambrian) 

Unconformity 
Priest  River  group  (Precambrian) 


700 
2500 
3000 

3000  plus 
5300-8500 
3800 

5000  plus 
5000  plus 


The  Cambrian  formations  of  Park  and  Cannon  have  been  traced  to 
northeastern  Stevens  County  by  Campbell  (1947),  where  diagnostic 
early  Middle  Cambrian  fossils  were  found. 

Cache  Creek  Sequence  of  British  Columbia.  Upper  Permian  sediments 
are  widespread  and  very  thick  over  much  of  British  Columbia  ( Fig.  6.8 ) . 
A  number  of  formations  and  groups  have  been  collected  under  the  gen- 
eral term  Cache  Creek  sequence  by  White  ( 1959 ) .  Cherts  are  very  abun- 
dant in  several  forms,  as  well  as  interbedded  andesite  and  basalt  flows 
and  related  pyroclastics.  Limestone  units  range  from  thin  intercalated 
laminae  to  massive  beds  thousands  of  feet  thick.  In  places  the  Cache 
Creek  beds  have  been  involved  in  sharp  folding  and  metamorphism,  in- 
cident to  later  orogenies,  but  where  their  relations  to  older  beds  have 


;  i 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


79 


been  clearly  noted,  they  generally  rest  in  angular  unconformity  on  de- 
formed, metamorphosed,  and  intruded  rocks. 

The  zone  of  maximum  subsidence  extends  through  the  center  of  British 
Columbia  with  reported  thickness  ranging  from  10,000  feet  at  the  south- 
ern border  to  24,000  feet  in  the  northern  part  of  the  province. 

The  Cache  Creek  strata  have  yielded  Upper  Permian  fossils  in  a  num- 
ber of  places  but  lower  beds  in  the  sequence  may  be  Carboniferous. 

Shuswap  Terrane  and   Orogeny 

A  large  complex  of  metamorphosed  rocks  in  southern  British  Columbia 
is  known  as  the  Shuswap  terrane.  Its  location  is  shown  on  the  map  of 
Fig.  17.14.  The  metamorphism  has  long  been  attributed  to  Mesozoic 
batholithic  processes,  but  now  certain  positive  information  indicates  that 
extensive  parts  were  metamorphosed  in  Pre-Cache  Creek  time.  An  au- 
thoritative summary  of  the  nature  of  the  Shuswap  terrane  by  Cairnes 
(1939)  is  quoted  below  in  which  he  leans  toward  metamorphism  in 
Mesozoic  time  but  recognizes  that  early  metamorphism  may  have  oc- 
curred. 

The  rocks  of  this  Shuswap  terrane  are  a  metamorphic  complex,  and  their 
transformation  is  attributed  to  processes  connected  with  Mesozoic  batholithic 
intrusions,  of  which  those  of  the  Nelson  batholith  of  the  West  Kootenay  region 
have  played  a  principal  part.  The  nature  of  these  processes  is,  however,  not 
entirely  clear,  though  certain  probable  conditions  may  be  surmised  from  the 
available  evidence.  On  the  one  hand  it  is  apparent  that,  in  part  and  over  large 
areas,  the  Nelson  batholith,  together  with  other  adjacent  or  comagmatic  in- 
trusives,  has  been  emplaced  to  the  accompaniment  of  much  deformation  in  the 
invaded  formations.  On  the  other  hand  it  seems  equally  plain  that,  within  the 
broad  areas  occupied  by  much  of  the  Shuswap  terrane,  the  mechanics  of  batho- 

j  lithic  intrusion  have  been  of  a  quite  different  sort.  There  is  little  evidence  here 
of  those  pronounced  deformations  with  which  batholithic  invasion  is  so  gen- 
erally associated  in  mountainous  regions;  nor  of  that  abrupt  shouldering  aside  of 
formations  flanking  the  irruptive  mass  which  elsewhere  characterizes  the  in- 
vaded strata  bordering  the  Nelson  batholith.  On  the  contrary,  batholithic  inva- 
sion within  the  Shuswap  terrane  has  apparendy  progressed  under  conditions  of 

h  comparative  stability  by  a  process  or  processes  of  gradual  soaking  of  the  super- 
incumbent rocks  with  tenuous  and  mobile  products  from  the  underlying  magma 
reservoir.  The  nature  of  these  products  can  perhaps  best  be  judged  from  the 
occurrence  of  abundant  bodies  of  pegmatitic  granite  throughout  the  Shuswap 
terrane;  from  the  many  associated  aplitic  dykes;  and  from  the  aplitic  injection 
material  that  is  such  an  important  constituent  of  the  gneissic  members  of  tire 


Shuswap  complex.  The  fact,  too,  that  large  areas  of  massive  granite  contain 
many  bodies  of  pegmatitic  granite  of  precisely  the  same  mineral  composition  as 
the  granite,  and  show  every  textural  gradation  into  these  pegmatitic  bodies,  is 
further  indication  of  the  character  and  composition  of  the  magmatic  products 
effecting  the  transformations  in  the  Shuswap  terrane.  These  products  are  be- 
lieved to  have  been  essentially  of  the  nature  of  pegmatitic  and  aplitic  differenti- 
ates, high  in  volatile  constituents  and  extremely  mobile.  The  principal  processes 
have  seemed  to  involve  a  gradual  upward  seepage  of  this  material,  infiltration 
along  bedding  planes,  replacement  or  partial  replacement  of  intervening  rock 
matter,  and  the  growth,  in  situ,  of  perhaps  much  of  the  pegmatitic  granite.  In 
places  the  continued  supply  of  magmatic  material  resulted  in  the  complete  con- 
version of  large  bodies  of  the  original  strata  into  massive  granitoid  rock  which, 
under  the  conditions  of  transformation,  became  partly  plastic  or  molten  and, 
where  subjected  to  local  stresses,  behaved  much  as  a  normal  intrusive  rock  in 
its  contact  relations  with  adjoining  rock  masses. 

An  important  fact  in  the  history  of  the  Shuswap  rocks,  and  one  that  has  been 
stressed  adequately  by  Daly,  is  the  great  depth  at  which  their  transformation 
has  been  achieved.  Unquestionably  the  Shuswap  terrane  at  that  time  was 
deeply  buried,  and  unquestionably  the  temperatures  within  the  zone  of  trans- 
formation were  extremely  high  and  long  sustained.  That  this  zone  lay,  in  part 
and  at  times,  within  the  zone  of  plastic  flow  is  indicated  in  many  places  by 
numerous  local  sigmoid  folds  in  which  the  Shuswap  gneisses  are  involved.  That 
temperatures  within  the  metamorphic  zone  were  high  is  indicated  alone  by  the 
abundant  and  widespread  occurrence  of  pegmatitic  bodies  everywhere  within 
the  terrane.  That  this  condition  of  deep  burial  may,  as  Daly  points  out,  afford 
an  explanation  of  why  the  Shuswap  terrane  as  a  whole  has  escaped  the  severe 
deformations  effecting  more  superficial  formations  (such  as  are  now  found  bor- 
dering the  Shuswap  area),  must  be  kept  in  mind  in  any  interpretation  of  the 
origin  and  mode  of  formation  of  these  rocks.  That  conditions  implied  by  depth 
of  burial  would  be  most  effective  on  the  stratigraphicallv  oldest  formations  is 
evident  from  the  fact  that  for  any  sizable  area  of  Shuswap  rocks  it  is  the  oldest 
formations,  or  basal  strata,  the  alteration  of  which  has  been  most  complete. 
Thus  it  is  quite  probable  that  within  the  principal  area  of  the  Shuswap  terrane. 
as  about  Shuswap  Lake,  die  formations  principally  effected  are,  as  suggested 
also  by  the  general  structural  trend  of  their  foliation,  of  pre-Cambrian  (Beltian?'* 
age.  In  other  areas,  however,  it  is  known  that  metamorphism  lias  extended  up- 
ward to  include  late  Paleozoic  and  probably  Triassic  formations,  but  that  the 
effects  of  this  metamorphism  have  been  less  intense  as,  in  general,  the  depth  of 
burial  has  decreased. 

Since  1950  evidence  has  been  accumulating  that  points  to  the  conclu- 
sion, if  not  the  fact,  that  the  Permian  strata  rest  unconformably  on  the 
Shuswap  and  are  not  affected  by  the  same  orogenic  and  intrusive  activity. 
Reesor  (1957)  summarizes  recent  opinion  as  follows: 


80 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


SHEEPROCK  MTS. 
Cohenour  1957 


EASTTINTIC  MTS. 

Morris  1957 


S.STANSBURY  MTS. 

Teicherl  1958 
(modified) 


N.  STANSBURT  MTS. 

Arnold  1956 
(modified) 


LAKESIDE  MTS. 

Young   1955 


PROMONTORY  MTS. 

Olson  1957 


LOGAN  AREA 

Williams  1957 


Fig.  6.12.  Ordovician,  Silurian, 
Devonian,  and  Mississippian  forma- 
tions of  central  and  northern  Utah. 
Reproduced   from   Rigby,    1958. 


No  reasonable  doubt  exists  that  rocks  of  the  Cache  Creek  (Permian  and 
possibly  in  part  Carboniferous)  lie  with  profound  unconformity  over  rocks  of 
the  Shuswap  terrain.  Basal  conglomerates  of  the  Cache  Creek  contain  boulders 
of  metamorphosed  Shuswap  rocks.  Thus  metamorphism  and  deformation  of 
the  Shuswap  rocks  took  place  before  the  Permian. 

White  (1959)  sites  a  striking  example  of  the  basal  Permian  uncon- 
formity in  the  Cariboo  district.  There,  the  Cariboo  group  of  Early  Cam- 
brian age  is  closely  folded  into  synclinoria  and  anticlinoria,  and  clastic 


members  are  regionally  metamorphosed  to  the  chlorite-muscovite  grade. 
The  Slide  Mountain  group  of  Permian  age  of  entirely  different  lithology 
unconformably  overlies  the  Cariboo  group.  It  is  mildly  folded  and  not 
metamorphosed.  Because  of  the  clear-cut  relationship  here,  White  pro- 
poses the  name,  Cariboo  orogeny,  and  includes  all  deformational  events 
from  Early  Ordovician  to  Pennsylvanian  in  it  that  occurred  throughout 
the  entire  Canadian  Cordillera. 

Attention  on  previous  pages  to  Devonian,  Mississippian,  and  Pennsyl- 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


81 


vanian  data  in  the  western  United  States  from  which  the  maps  of  Figs. 
6.5-6.7  were  constructed  lead  to  the  suggestion  that  the  Antler  orogenic 
belt  of  Nevada  extends  northward  through  western  Idaho  and  eastern 
Oregon  and  Washington  to  the  Shuswap  terrane  of  southern  British 
Columbia.  If  so,  we  would  infer  that  the  Shuswap  orogeny  is  of  the  same 
age  as  the  Antler;  that  is,  it  started  in  Late  Devonian  and  continued  vigor- 
ously through  the  Mississippian  and  early  Pennsylvanian.  The  Shuswap 
is  marked  by  considerable  metamorphism  and  perhaps  batholithic  intru- 
sion and  related  processes,  whereas  the  Antler  belt  is  marked  especially 
by  great  thrust  sheets. 

The  term  Shuswap  orogeny  as  here  used  will  denote  tectonic  events 
in  the  Shuswap  terrane  region  that  occurred  during  the  same  time 
approximately  as  those  of  the  Antler  belt,  and  the  term  Cariboo  orogeny 
as  proposed  by  White  will  be  considered  to  have  wider  and  longer  conno- 
tation. 

White  (1959)  summarizes  information  which  suggests  that  the  Shu- 
swap belt  extends  into  northern  British  Columbia  and  the  Yukon  Terri- 
tory, and  when  so  conceived  the  Antler  and  Shuswap  orogenic  belt  is 
continuous  from  southern  California  to  Alaska. 

EUGEOSYNCLINE  IN  SOUTHEASTERN  ALASKA,  NORTHERN  BRITISH 
COLUMBIA  AND  THE  YUKON 

Southeastern  Alaska.  The  Paleozoic  rocks  in  southeastern  Alaska  from 
54°  30'  to  60°  N.  Lat.  are  of  geosynclinal  thickness  and  make  up  a 
number  of  formations  of  Ordovician,  Silurian,  Devonian,  Mississippian, 
Pennsylvanian,  and  Permian  ages  (Buddington  and  Chapin,  1929).  The 
stratigraphic  succession  is  given  in  the  table  on  p.  82. 

One  of  the  commonest  types  of  rock  is  andesite  in  various  forms.  It 
occurs  in  at  least  seven  formations  of  Permian  age  to  Ordovician,  and 
perhaps  older.  Many  of  the  volcanic  rocks  are  now  greenstone  schist. 
Pillow  lava  is  abundant  in  the  Lower  and  Middle  Ordovician,  Silurian, 
Middle  and  Upper  Devonian,  Lower  Permian,  and  Upper  Triassic. 

The  other  predominant  rock  types  are  sheared  graywacke,  slate,  and 
phyllite.  The  vast  amount  of  greenish  graywacke  with  associated  slate  is 


SOUTHERN   KLAMATH    MOUNTAINS 


NORTHERN    KLAMATH    MTS  . 


REDDING   QUAD. 
(HINDS       ET   AL. ) 

WEAVERVTLLE   QUAD. 
(HINDS    ET   AJ..  ) 

WELLS    EJ.   AL. 

U.    TRIASSIC 

APPLEGATE   GROUP,    METAVOLCANICS 
AND    METASEDIMENTS.       FORMERLY 
CALLED   DEVONIAN   OR   CARBONIFEROUS 

PERMIAN 

NOSONI    VOLCANICS_ 

McCLOUD    LIMESTONE 

MISSISSIPPIAN 

BAIRD    FM. 

DRAGDON    FM.    WITH    BASS 
MOUNTAIN   BASALT 

BRAGDON    FM. 

DEVONIAN 

KENNETT   FM. 

DEVONIAN    LIMESTONE    PATCHES 

SILURIAN 

COPLEY   META-ANDESITE 
(POSSIBLY   SILURIAN) 

COPLEY    META-ANDESITE 
CHANCHELLULA    FM. 
(POSSIBLY   SILURIAN) 

SALMON   SCHIST 
ABRAMS   SCHIST 

SILURIAN   STRATA    (NOT    NAMED) 

PRE -SILURIAN 

HIGHLY    FOLIATED   SCHIST 

Fig.  6.13.      Correlation  of  Paleozoic  formations  in   Klamath   Mountains. 

the  most  striking  feature  of  the  stratigraphic  sequence  of  southeastern 
Alaska.  Graywacke  is  found  in  every  system  of  the  Paleozoic  and  Meso- 
zoic,  and  in  many  places  it  is  difficult  or  impossible  to  tell  one  graywacke 
unit  from  another. 

Limestone  forms  a  very  considerable  part  of  each  Paleozoic  formation 
except  the  Ordovician.  The  thickest  unit  is  in  the  Upper  Silurian  and  is  a 
very  high   calcite  variety.   Some   limestone   carries   considerable   chert. 

Beds  of  cobble  and  boulder  conglomerate  form  conspicuous  and  thick 
members  of  the  Silurian  and  Devonian  formations.  A  peculiar  but  com- 
mon form  is  composed  of  andesite  and  limestone  pebbles  and  cobbles  in 
a  tuffaceous  matrix.  The  same  lithology  is  found  in  the  Middle  Devonian. 
Coarse  conglomerate  beds  occur  at  the  base  of  the  Devonian. 

Another  characteristic  lithology  in  the  Paleozoic  systems  in  southeastern 
Alaska  is  coarse,  waterworn  intraformational  limestone  conglomerate. 
Beds  occur  in  the  Silurian,  Devonian,  Permian,  and  Triassic  formations, 
and  in  all  of  them  the  cobbles  of  limestone  carry  the  same  fauna  as  the 
formation  in  which  the  conglomerate  occurs.  Buddington  believes  the 
intraformational  conglomerates  originated  from  crustal  movements  ac- 
companying the  volcanic  activity  during  these  periods. 

Black  slate  and  argillite  are  widely  distributed,  and  thin-layered  black 
chert  several  hundred  feet  thick  occurs  in  the  Ordovician  and  Missis- 


82 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Series 


Character 


Thickness,    Feet 


Series 


Character 


Thickness,  Feet 


Unconformity 
Andesitic  rocks,  including  breccia,  with  limestone  matrix 
and  lava  flows  (in  part  with   pillow  structure),  locally 
interbedded  with  slate  and  other  sediments  1400   plus 

Unconformity 
Conglomerate,      sandstone,      and      limestone;      in      the 
Ketchikan    district    includes    considerable    black    slate 
in  upper  part  1600   plus  or  minus 

Unconformity 

Thick-bedded  limestone;  with  common  to  abundant  in- 
tercalated layers  of  white  chert  1000 

Conglomerate,  limestone,  sandstone,  andesitic  and  ba- 
saltic  lava,   tuff,   and    locally   rhyolitic  volcanic   rocks    3000  plus  or  minus 

Unconformity 
White   massive   limestone  100   plus 

Interbedded  coarsely  crystalline  limestone  and  black 
chert,  overlain  by  interlayered  dense  gray  quartzite 
and  cherty  limestone;  sparse  conglomerate  1000 

Basalt,   andesite    (in    part    pillow    lava),    tuff,    limestone, 

sandstone,  slate,  and   conglomerate  1000 

Unconformity  (?) 
Limestone  600   plus 

Andesitic  green  to  gray  tuff  (locally  cherty)  and  gray- 
wacke,  with  locally  fine,  conglomeratic  layers,  inter- 
calated limestone,  and  a  minor  amount  of  andesitic 
lava  and  breccia  2400  plus 

Andesitic  lava  (in  part  pillow  lava),  breccia,  tuff,  con- 
glomerate  and   locally   rhyolitic   lava  2000 

Interbedded  limestone,  slate,  chert,  andesitic  lava, 
breccia,   tuff,   and    locally   conglomerate 

Conglomerate  and  graywacke-like  sandstone,  with  lo- 
cally interbedded   limestone  2000 

Unconformity 

Green-gray  graywacke  with  sparse  conglomerate  beds. 
Interbedded  red,  green-gray,  and  gray  graywacke, 
like  sandstone  with   small  amount  of  shale  5000   plus 

Green-gray  shale  with  intercalated  red  beds  and  thin- 
layered  fine-grained  gray  sandstone,  shale,  and 
dense   limestone  500   plus 


Jurassic 
Upper  Triassic 
Permian 

Pennsylvanian  (?) 
Mississippian 

Upper  Devonian 
Middle  Devonian 


Silurian 


Predominantly  thick-bedded  dense  limestone;  interca- 
lated with  thick  beds  of  coarse  conglomerate,  thin- 
layered  limestone,  nodular  and  shaly  argillaceous 
limestone  and  sandstone  Ls,  3000;  Congl.   1500  4500   plus  or   minus 

Andesite  (in  part  pillow  lava)  and  andesite  porphyry 
lava;  conglomerate;  with  some  associated  gray- 
wacke, tuff,  breccia,   and    limestone  3000   plus  or   minus 

Unconformity  (?) 
Indurated    graywacke   with    associated    black   slate    and 

sparse  conglomerate  and   limy  sediments  ? 

Unconformity   (?) 

Indurated  graywacke  with  associated  black  slate  and 
sparse  conglomerate  and  limy  beds;  locally  andesitic 
pillow-lava    and    volcanic    rocks  ? 

Thin-layered  black  chert  with  black  graptolitic  slate  part- 
ings, graywacke,   and   locally  andesitic  volcanic  rocks  ? 

Greenstone     schist     with     intercalated     or     interbedded 

limestone  ? 

Limestone  ? 

Schist  with  beds  of  limestone  and  slate  ? 

Schist  ? 


Middle 
Ordovician 

Lower  Ordovician 

Probably  pre- 
Ordovician    to 
Devonian  Wales 
group  (meta- 
morphic  rocks) 


sippian  formations.  Thick-bedded  chert  and  cherty  tuff  occur  in  the  Mid- 
dle Devonian,  and  white  chert  is  common  in  the  Upper  Permian. 

Schists  and  gneisses  are  also  common,  and  are  the  result  principally  of 
permeating  hot  solutions  attendant  upon  the  emplacement  and  solidifica- 
tion of  the  vast  volume  of  magma  in  addition  to  orogenic  stresses  (Bud- 
dington  and  Chapin,  1929). 

Northern  British  Columbia  and  the  Yukon.  The  Geologic  Map  of 
Canada  summarizes  what  is  known  of  the  distribution  of  Paleozoic  rocks 
in  northern  British  Columbia  and  the  Yukon.  Great  areas  are  still  marked 
"Paleozoic,  mainly  sedimentary  rocks,"  but  other  large  areas  are  labeled 
"Carboniferous  and  Permian  sedimentary  rocks."  Geology  and  Economic 
Minerals  of  Canada,  1947,  summarizes  the  distribution  as  follows: 

During  the  Carboniferous  and  Permian  periods  apparendy  nearly  the 
whole  of  the  Western  Cordilleran  region  (west  of  the  Rocky  Mountain  trench) 
lay  beneath  the  sea,  and  great  thicknesses  of  sedimentary  and  volcanic  material 


HAVALLAH    SEQUENCE 


EUREKA-CARLIN    SEQUENCE 


ANTLER    SEQUENCE 


i 

SONOMA    RANGE 
Kolpoto  formation 


Hovoiloh  formation 


CARLIN  AREA 

(Modified  after 

Dott,  1955. 

Fails,  I960) 


EUREKA    AREA 

(After  Nolon,  1956,   fig  I, 

and  pp  56  to  68) 


Pumpernickel 

formotion 

IMississippian 

or  older) 


\   EDNA 


MOUNTAIN 


BATTLE   MOUNTAIN 


Middi"e  —- ^'"<"Hoo^ 

Pennsylvanion  ~    -— 

Highwoy  limestone 


Preble  formotion 
(Combr  ion) 


„  Woo"*0' 

rn«£2ei—  - — 

■ — Bottle  formotion 


'  Volmy  formotion 
(Ordovicion) 


ks?5*??2S2e: 


K^%Vtbuntain 

i  mw 

™  Winnemucco  '~J  ft///. 
Lovelocks       Eferg/afef 

s.     tr*  La  s//w 


City 


k 


N 


Monhotian 

/ 


!...       '■  Sonomo  Range 

140* 
2.   Edno    Mountoln 

|  3.   Bottle  Mountain 

i  4.  Corlin  orea 

!  5    Eureko  orea 


Pioche 


\ 

N 

100  Miles  \ 
p  > 


-Of- 


J 


") 


Bosins  of  deposition  of  overlap  sequences 


K^Vj 


EXPLANATION 

feists! 


(Section  Is  75 

miles  south  of 

Carlln) 


r6000  fttt 


Chert 


Shole 


Greenstone 


Sandy  limestone 


sre^i 


Sondstone 


Intermediote  ond 

siliceous  volcanic 

rocks 


Cherty  limestone 


Conglomerate 


-4000 


2000 


Vertical  scoi« 


Fig.    6.14.      Detail    of    Mississippian,    Pennsylvanian,    and    Permian    formations    involved    in    Antler    orogeny 
of   north-central    Nevada.   Reproduced   from   Roberts   ef   a/.,    1958. 


84 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


EUGEOSYNCLINE 


MIOGEOSYNCLINE 


•  OLfCAMPlAK 


MISSISSIP 
AND    OLD 


ORDOVICIAN 


NORTH-CENTRAL 
NEVADA 
LAND    AXIS 


»00  f 
i  too 

IOOO 

-  soo 


PROBABLE  NORTH  EDGE 
OF  LATE  PENN.  EMERGE 
AREA 


NT 


Fig.    6 

strata 
1955. 


15.     Antler    orogenic    belt    of    central    Nevada    showing    Mississlppian,    Pennsylvanian,    and    Permian 
restored  to  early  Wolfcampian  time.  Section  extends  from  Winnemucca  to  Elko.  Reproduced  from  Dott, 


accumulated.  Wide  areas  of  almost  unexplored  country  in  eastern  Yukon  are 
presumed  to  be  underlain  chiefly  by  Paleozoic  strata,  but  may  also  contain 
rocks  of  Mesozoic  and  Precambrian  age.  In  northern  British  Columbia,  where 
exposed  strata  are  thought  to  represent  much  of  Paleozoic  time,  no  important 
disturbance  has  been  recognized.  In  a  number  of  localities  sedimentation  and 
volcanism  probably  proceeded  more  or  less  continuously  from  late  Paleozoic 
into  early  Mesozoic  time,  but  in  places  an  interval  of  uplift  and  erosion  without 
marked  tilting  or  folding  may  have  intervened. 

A  report  on  the  Cassiar  Mountains,  Finley  River  district  between  lati- 
tudes 56  and  58,  and  longitudes  of  124  and  126,  by  Dolmage  (1928)  de- 
scribes a  series  of  metamorphosed  rocks  of  Carboniferous  age.  They  are 
"green  ash  rocks  pressed  and  altered  into  schists,  interbedded  with  layers 
of  graywacke,  felsite,  halle-flinta,  serpentine,  and  argillite."  Along  Takla 
and  Stuart  lakes  and  vicinity  the  series  is  made  up  of  limestones,  argillites, 
cherty  quartzities,  green  schists,  slates,  volcanic  flows,  tuffs  and  breccias, 
and  narrow  bands  of  dolomite.  Fusulina  and  other  Carboniferous  fossils 
have  been  found  in  some  of  these  beds. 

Underlying  the  Carboniferous  series,  great  belts  of  schist  and  quartzite 


occur.  Quartz  mica  schist  constitutes  about  three-fourths  of  the  whole. 
In  many  places,  the  schist  grades  into  quartzite,  both  of  which  were  de- 
rived undoubtedly  from  siliceous  sediments  (Dolmage,  1928).  Such  rocks 
as  these  are  widespread  and  have  been  correlated  with  the  Shuswap 
terrane  of  southern  Rritish  Columbia,  which  now  as  previously  explained, 
is  believed  to  be  made  up  of  rocks  of  several  Paleozoic  periods  as  well  as 
Precambrian.  Also  some  coarse  quartzites,  quartz  pebble  conglomerates, 
and  limestones  have  been  likened  to  the  Cambrian  strata  of  the  southern 
Canadian  Rockies,  previously  described. 

The  areas  of  such  rocks  are  shown  on  the  map  of  Fig.  33.12.  A  great 
medial  area  of  Proterozoic  (Beltian?)  rocks  separates  the  western  areas 
of  Carboniferous  rocks  from  the  eastern  Paleozoic  rocks,  but  whether  or 
not  this  was  a  highland  in  Paleozoic  time  is  unknown. 

SUMMARY  OF  OROGENIC   HISTORY 

The  maps,  Figs.  6.1  to  6.8,  are  fairly  expressive  of  our  present  know- 
ledge and  postulates  of  the  evolution  of  the  western  margin  of  the  con- 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


B5 


tinent  during  Paleozoic  time.  That  the  western  margin  has  a  belt  of  major 
orogeny  with  associated  intrusive  and  extrusive  igneous  activity  and 
metamorphism  needs  no  longer  to  be  defended.  At  the  time  of  writing 
of  the  first  edition  of  this  book  the  profession  was  just  accepting  the  view 
and  abandoning  the  older  one  of  a  small  continental  borderland,  now 
partly  submerged  beneath  the  Pacific  Ocean. 

It  may  be  stated  that  we  have  no  information  on  conditions  in  Cam- 
brian time  west  of  northwestern  Nevada.  Cambrian  strata  are  recognized 
farther  south  in  California  in  the  Death  Valley  region,  but  these  lie  on 
the  projection  of  the  eastern  miogeosynclinal  assemblage.  Ordovician 
rocks,  like  the  Cambrian,  are  not  known  for  sure  west  of  northwestern 
Nevada.  In  southeastern  Alaska,  however,  they  have  been  identified  very 
close  to  the  Pacific  margin  of  the  continent,  and  are  part  of  an  extensive 
eugeosynclinal  assemblage.  Silurian  rocks  have  now  been  recognized  near 
the  Pacific  in  the  Klamath  Mountains,  but  the  paleogeography  of  the  entire 
region  from  northwestern  Nevada  to  the  Pacific  is  practically  unknown. 
The  presence  of  Silurian  strata  in  the  Klamath  Mountains  and  sequences 
under  them  which  might  be  Ordovician  and  Cambrian  lead  to  the  con- 
clusion that  the  western  margin  of  the  continent  as  early  as  Cambrian 
time  was  about  where  it  now  is;  and  that  the  continent  has  not  grown 
appreciably  since. 

We  must  also  postulate  several  phases  of  major  orogeny  together  with 
the  accumulation  of  eugeosynclinal  sequences  in  adjacent  and  associ- 
ated basins  or  troughs  in  early  Paleozoic  times  along  the  western  margin 
of  the  continent.  The  transitional  zones  of  the  eugeosynclinal  and  miogeo- 
synclinal assemblages  are  now  fairly  well  positioned,  and  the  basins  of 
the  miogeosyncline  are  beginning  to  take  on  specific  shape  and  distribu- 
tion in  light  of  our  present  knowledge.  Geanticlines,  the  Beltian  and  Raft 
River,  are  postulated,  and  the  Tooele  arch  seems  clear.  These  add  com- 
plexity to  what  was  previously  considered  a  simple  broad  basin. 

A  major  and  unsolved  problem  is  the  relation  of  the  southwesterly 
trending  Paleozoic  tectonic  elements  in  southern  Nevada,  Arizona,  and 
California  to  the  continental  margin — they  are  distinctly  discordant 
rather  than  approximately  concordant  or  unilateral.  The  problem  has  been 
discussed  in  Chapter  5. 


BAYHORSE   QUAD. 
IDAHO 

LOST    RIVER   RANGE 
IDAHO 

TENDOY   RANGE 
S.    W.    MONT. 

NORTHEASTERN 
UTAH 

OQIIRRH    MTS., 
CENTRAL    UTAH 

AMSDLN    FM.» 

MANNING   CAN.    SH.» 

MANNING  CAN.    SH.' 

"BRAZER"* 

BIG  SNOWY    GR. 

GREAT   BLUE   LS. 
HUMBUG   FM. 

GREAT   BLUE    LS . 
HUMBUG   FM. 

MILLIGEN 

DESERET    LS. 

DESERET   LS. 

ARGILLITE 

z 
o 
to 

MISSION   CAN.    LS. 

MILLIGEN 
ARGILLITE 

a 
3 

MADISON    LS. 

MADISON    LS. 

LODGEPOLE    LS . 

SAPPINGTON    FM.+ 

LEATHAM 

PARTLY    L.    PENNSYLVANIA 
+   OCCURS    EASTWARD   AS    PART   OF  SHELF  SEQUENCE 

Fig   6.16.      Correlation   of  Mississippian   formations  of  southwestern   Montana,   eastern    Idaho   and 
northern    Utah. 


A  major  orogenic  belt  began  to  develop  in  central  Nevada  in  late 
Devonian  time,  and  through  several  phases  of  folding  and  thrusting  con- 
tinued development  through  the  rest  of  the  Paleozoic.  The  belt  is  pro- 
jected northward  through  eastern  Oregon  and  Washington  into  southern 
British  Columbia  in  Mississippian  and  Pennsylvanian  time  to  the  Shuswap 
orogenic  belt  in  British  Columbia.  Another  orogenic  belt  lay  to  the  west 
in  Pennsylvanian  and  Permian  time,  and  it  seems  to  have  been  separated 
from  the  central  Nevada  belt  by  a  basin  of  sedimentation.  The  entire 
region  including  both  belts  and  the  intervening  basin  become  involved  in 
orogeny,  volcanism,  and  intrusive  activity  thereafter,  starting  in  Permian 
time. 

Shifting  basins  and  the  appearance  of  uplifts  of  several  kinds  add  com- 
plexity to  the  miogeosyncline  and  its  relation  to  the  shelf  in  the  late 
Paleozoic. 

The  Canadian  cordillera  is  not  as  wide  as  that  of  the  western  United 
States,  and  perhaps  its  development  is  more  regular.  From  what  is  known 
it  appears  that  a  geanticline  of  Beltian  strata  developed  early  in  Paleozoic 
time  and  separated  a  western  eugeocynclinal  trough  of  sedimentation 
from  an  eastern  miogeosynclinal  trough.  The  eugeosynclinal  region  was 
subjected  to  repeated  orogeny,  metamorphism,  and  igneous  activity.  In 
this  connection  it  is  pertinent  to  review  Buddington's  observations  in 
southeastern  Alaska. 


SILVER     IS.  RANGE 
SCHAEFFER,  PERSONAL 
COMMUNICATION 


OQUIRRH 

STANSBURY    MTS. 
RIGBY.I958 


BASIN 

WASATCH    MTS. 

PROVO    SECTION 

BAKER,  1947 


DUCHESNE    RIVER 
UTAH 


SHELF 

SOLS   CANYON 

10  MILES    SW    MANILA, UTAH 


RANGELY  FIELD 
W.  COLORADO 


Fig.  6.17.  Mississippian,  Pennsylvanian,  and  Permian  formations  in  Utah  showing  change  from  the  shelf 
assemblage  to  the  miogeosyncline  assemblage.  Sections  of  shelf  were  furnished  by  Walter  Sadlick,  who  also 
assisted  in  the  general  correlations. 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


87 


NORTHWEST      SECTION 


NORTHEAST    SECTION 


GRINDSTONE- TWELVEMILE   CREEKS   AREA,     CENTRAL    OREGON     (MERR1AM    AND    BERTHIAUME) 

Cc,  Coffee  Creek  fm.  (Lower  Carb.)    Cs,  Spotted  Ridge  fm. (Penn.)    Pc,  Coyote  BuTte  fm.  (Perm.) 

I     MILE 


^^K^-mmMM^WMSm, 


Tv 


MlBl 


cm$m*m 


NORTH-SOUTH     SECTION     NEAR      BAKER,    OREGON    (GILLULY) 

brs,  Burnt  River  schist;    Ce,  Elkhorn  Ridge  argillite  (Penn.  ?)     Ccg,    Clover  Creek  greenstone  (Perm.) 
qd,  biotite-quartz   dionte;     sg,   silicified  gabbro;     mg,  metagcbbro;     gb,    gabbro 

,  5    Ml  LELS 


Fig.  6.18.      Cross   sections  in   central   and   eastern   Oregon. 


The  Silurian  graywackes  in  general  of  southeastern  Alaska  are  com- 
posed of  particles  of  rock  similar  to  the  kinds  that  form  the  pebbles  and 
cobbles  in  the  conglomerates  with  which  they  are  interbedded,  and  in 
addition,  of  a  considerable  percentage  of  plagioclase,  potassic  feldspar, 
and  quartz  grains.  The  conglomerates  are  largely  made  of  andesite 
pebbles  and  boulders,  but  slate,  diorite,  rhyolite,  and  limestone  pebbles 
are  abundant,  if  not  dominant,  in  some  conglomerates.  One  specimen  of 
graywacke  of  Devonian  or  Silurian  age,  for  example,  consisted  of  particles 
of  andesite,  felsite,  plagioclase,  granophyre,  quartz,  spherulitic  rhyolite, 
and  orthoclase,  with  a  chloritic  and  slightly  calcareous  groundmass. 

The  association  of  the  graywackes  and  conglomerates  that  Buddington 
describes  is  very  revealing  of  their  origin.  The  conglomerates  in  them- 
I  selves  are  indicative  of  a  volcanic  archipelago  and  deserve  further  men- 
tion. The  following  is  a  reume  of  the  Silurian  conglomerates  according  to 
Buddington.  Varieties  of  conglomerates  are  as  follows: 


1.  A  conglomerate  composed  almost  wholly  of  well-rounded  andesite  or  an- 
desite porphyry  cobbles  and  boulders;  the  matrix  may  be  calcareous,  and 
lenses  of  limestones  are  intercalated  but  limestone  cobbles  are  sparse. 

2.  A  conglomerate  composed  almost  wholly  of  limestone  cobbles  or  boulders 
in  a  limestone  or  andesitic  tufflike  matrix;  this  type  is  rare,  but  beds  100 
feet  thick  have  been  noted. 

3.  Peculiar  conglomerates  intermediate  between  1  and  2,  consisting  of  pebbles 
and  cobbles  of  andesite  and  limestone  in  a  greenish  tufflike  matrix. 

4.  A  homogeneous-appearing  rock  composed  of  fragments  of  andesite  in  a 
matrix  of  the  same  material;  the  structure  is  that  of  a  conglomerate  or 
water-wom  breccia. 

The  limestone  fragments  are  usually  of  a  dense-textured  limestone 
typical  of  the  Silurian,  and  many  carry  fossils  of  Silurian  age.  The  fossils 
are  the  same  as  from  the  overlying  limestone.  It  is,  therefore,  believed 
that  the  limestone  conglomerates  are  intraformational  and  that  the  lime- 
stone fragments  are  of  practically  the  same  age  as  the  volcanic  fragments. 
Vertical  movements  of  the  sea  bottom,  perhaps  local,  must  have  accom- 


88 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Fig.  6.19.  Map  showing  coincidence  of 
Permian  volcanic  trough  (stippled  margins) 
and  zone  of  Sierran  intrustives  (lines).  Dots 
indicate  location  of  Carboniferous,  Perm- 
ian, and  Triassic  areas  referred  to  the 
text.  Pennsylvanian  and  Permian  basins 
combined  isopached.  Zone  of  Sierran  in- 
trusives  includes  nearly  all  satellites  and 
palingenetic   areas. 


panied  the  volcanism  and  resulted  in  contemporaneus  erosion  and  sub- 
marine slumping  of  slightly  compacted  fine  lime  mud.  A  part  of  the 
volcanic  material,  at  least,  must  have  been  erupted  from  central  vol- 
canoes, which  were  built  up  above  the  surface  of  the  ocean  and  were 
thus  subjected  to  erosion. 

Although  recognizing  unsolved  elements  in  the  problem  of  the  origin 
of  the  graywackes,  conglomerates,  and  limy  argillaceous  beds,  Budding- 
ton  visualizes  a  sedimentary  environment  as  follows:  the  great  lens- 
shaped  beds  of  conglomerate  may  be  local  deposits  made  by  torrential 
streams,  and  the  graywacke  may  be  in  part  the  more  finely  comminuted 
peripheral  marine  equivalent.  The  calcareous  shale  and  argillaceous  limy 
beds  which  are  locally  intercalcated  with  the  clean,  thick-bedded  lime- 
stone may  be  in  part  the  more  distant  offshore  equivalent  of  the  con- 
glomerate and  graywacke. 

The  limestone  is  in  part  dense  white  on  fresh  surfaces,  and  massive 
with  only  rare,  if  any,  evidence  of  stratification.  Beds  as  thick  as  2000  feet 
have  been  observed.  In  part  it  is  interbedded  with  thin-layered  limestone, 
nodular  and  shaly  limestone,  calcareous  shaly  argillite,  dense  platy  si- 
liceous layers,  green-gray  shale,  and  sparse  buff-weathering  sandstone. 
The  massive  limestone  seems  to  be  due  to  rapid  deposition,  and  where 
clean  the  site  of  accumulation  was  sufficiently  distant  from  land  so  not  to 
have  received  any  clastic  material.  Volcanic  activity  has  been  thought  of 
as  contributing  to  the  deposition  of  the  limestone,  through  the  activity  of 
magmatic  waters  or  meteoric  waters  draining  from  a  volcanic  terrane  or 
by  the  warming  of  the  marine  water,  but  the  chemistry  and  oceanography 
of  the  problem  have  not  been  worked  out. 

Schofield  ( 1941 )  discussed  the  problem  of  granitoid  pebbles  and 
cobbles  in  the  conglomerates  of  several  periods,  especially  the  Triassic. 
Buddington  refers  to  them  also.  In  one  locality,  the  Britannia  map  area 
of  British  Columbia,  an  arkose  is  described  as  composed  of  irregular 
grains  of  quartz,  plagioclase,  orthoclase,  and  sericite  schist.  The  lack  of 
rounding  of  the  grains,  the  freshness  of  the  plagioclase,  and  the  consider- 
able thickness  of  the  unstratified  beds,  prove  that  the  material  accumu- 
lated rapidly  and  was  transported  only  a  short  distance  from  a  source  of 
granitoid  plutonic  rocks.  Buddington  failed  to  trace  the  granitoid  elastics 


PALEOZOIC  CORDILLERAN  GEOSYNCLINE 


to  their  source,  despite  the  fact  that  their  size  and  abundance  indicated 
to  him  a  nearby  local  origin.  It  seems  necessary,  he  believes,  to  assume 
that  granitoid  intrusions  existed  in  a  land  that  formerly  stood  to  the 
west  where  only  the  Pacific  Ocean  now  lies. 

Krynine  (1941)  has  studied  the  tectonic  significance  of  arkoses,  and 
concludes  that  they  are  deposited  when  a  granitoid  terrane  has  just  been 
uplifted  and  is  being  vigorously  dissected.  They  are  related  to  the  de- 
formed geosyncline  into  which  granitoid  rocks  have  been  intruded.  The 
plutons  have  become  exposed  by  erosion  of  the  mountains  created  by 
the  orogeny,  and  then  uplifted  in  a  further  stage  of  deformation,  and 
vigorously  eroded. 

Granite  plutons  are  seldom  exposed  in  arcs  of  small  volcanic  islands. 
We  must  look  to  the  larger  islands  of  an  archipelago  for  the  source  of 
granitoid  conglomerates  and  arkoses.  The  geologic  map  of  the  Japanese 
Archipelago,  Fig.  6.20,  shows  extensive  areas  of  granitic  intrusions  and 
Precambrian  gneisses  which  could  furnish  the  necessary  material.  The 
major  archipelago  like  the  Japanese  has  had  a  long  orogenic  history  and 
is  composed  not  only  of  rocks  that  will  make  graywackes  but  also  arkoses. 
Such  a  one  seems  to  have  been  the  sourceland  of  the  sediments  of  the 

■  western  part  of  the  Cordilleran  geosyncline. 

Great  beds  of  chert  are  present  in  the  sediments  of  the  volcanic  archi- 
pelago. Extensive  beds  of  chert  and  cherty  limestone  are  present  in  the 

1  miogeosyncline  as  well  as  in  the  inland  basins  and  shelfs  of  the  main- 
land, and  so  the  factors  governing  the  precipitation  of  the  silica  are 

j  probably  several.  Its  transportation  in  solution  in  marine  currents  may  re- 

1  suit  in  precipitation  a  great  distance  from  its  source.  I  find  it  easy  to  be- 
lieve that  a  large  part  of  the  silica  originated  in  the  volcanic  activity  of 
the  archipelago,  that  some  of  it  was  carried  by  currents  across  the  seas 
between  the  archipelago  and  the  mainland  free  from  the  area  of  deposi- 


I  Fig.  6.20.  Generalized  geologic  map  of  the  Japanese  Archipelago  and  the  easten  part  of  Asia. 
Isobaths  are  in  meters.  Coarsely  stippled  areas  are  those  chiefly  of  sedimentary  rocks  but  with 
large  areas  of  Archean  gneiss  and  schist  and  some  smaller  areas  of  intrusive  and  extrusive  rock. 

;  Finely  stippled  areas  denote  alluvium.  Hachured  areas  are  those  of  plutonic  rocks,  chiefly  granite 
and  granadiorite,  but  with  considerable  areas  of  Archean  gneiss  and  schist  and  some  sedimentary 
rocks.  Solid  black  areas  are  andesite.  Horizontally  ruled  is  basalt  and  verticlly  ruled  is  trachyte. 


300      MILES 


90 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


tion  of  volcanic  material,  and  that  it  was  precipitated  copiously  in  the 
shallow  seas  of  the  eastern  trough  and  mainland  shelf  where,  from  place 
to  place  and  time  to  time,  clay,  lime  mud,  or  sand  were  accumulating. 
Perhaps  the  tectonic  conditions  of  the  eugeosyncline  of  the  western 
margin  of  North  America  can  be  visualized  better  if  reference  is  made  to 
the  Japanese  Archipelago  (see  Fig.  6.20).  It  is  believed  that  there  a 
fairly  good  example  and  close  parallel  of  conditions  exists  now  as  ex- 
isted in  times  past  along  the  west  coast  of  North  America. 


In  the  first  place  the  scale  and  shape  of  the  arcuate  features  are  the 
same.  In  the  second  place,  the  geology  of  the  Japanese  Archipelago  is 
somewhat  the  same  as  that  postulated  for  the  sourceland  of  the  sediments 
of  the  Pacific  trough  of  the  Paleozoic  Cordilleran  geosyncline.  The  most 
abundant  rocks  mapped  in  the  Japanese  Archipelago  are  as  follows: 
andesite,  granite,  syenite,  schistose  granite,  gneiss,  schist,  slate,  chert, 
sandstone,  limestone,  diorite,  pyroxenite,  amphibolite,  gabbro,  and 
trachyte,  in  approximate  descending  order  of  abundance. 


7. 


APPALACHIAN  MOUNTAINS 


MAJOR  STRUCTURAL  DIVISIONS 

The  index  map  of  Fig.  7.1  shows  the  structural  divisions  of  the  east- 
ern margin  of  the  continent  from  New  York  to  Alabama.  The  interior 
stable  region  of  the  continent  is  represented  by  the  Appalachian  plateaus 
province,  where  the  strata  are  nearly  horizontal  and  dissected  by  an 
elaborate  arborescent  drainage  system.  In  southern  New  York,  central 
Pennsylvania,  and  northern  West  Virginia,  the  strata  are  cast  into  very 
gentle  folds  which  are  the  site  of  extensive  gas  and  oil  fields.  The  folding 
is  so  gentle  that  the  drainage  is  little  affected,  and  the  arborescent  plateau 
type  exists,  scarcely  distinguishable  from  the  region  farther  west. 


The  folded  and  thrust-faulted  province  represents  the  Appalachian 
Mountains  proper.  It  is  the  well-known  region  of  flat-topped,  parallel,  or 
subparallel  ridges  and  valleys  that  are  carved  out  of  anticlines,  synclines, 
and  thrust  sheets.  The  drainage  pattern  is  rectangular  (trellis),  and  stands 
conspicuously  apart  from  the  arborescent  pattern  of  the  Appalachian 
plateaus.  The  strata  are  of  Paleozoic  age  in  both  provinces  but  thicken 
from  the  shelf  along  the  western  margin  of  the  plateaus  to  the  geosyn- 
cline  in  the  eastern  part  of  the  plateaus  and  in  the  folded  and  thrust- 
faulted  belt.  See  Fig.  7.2. 

The  Blue  Ridge  province  is  made  up  of  Cambrian  and  Late  and  prob- 
ably Early  Precambrian  metamorphic  and  igneous  rocks,  which  are  older 
than  those  of  the  Appalachians  to  the  west,  and  are  more  or  less  meta- 
morphosed. It  is  widest  in  the  south,  and  highest  in  the  Great  Smoky 
Mountains  of  Tennessee  and  North  Carolina  (Fig.  7.1).  It  dies  out  in 
southern  Pennsylvania  only  to  take  up  again  in  eastern  Pennsylvania, 
New  Jersey,  and  New  York.  The  Blue  Ridge  province  is  generally  one  of 
conspicuous  relief  east  of  the  Great  Valley  of  the  folded  Appalachians 
and  west  of  the  crystalline  Piedmont.  The  Piedmont  province  is  broad  and 
generally  of  low  relief.  Its  rocks  are  not  well  exposed  and,  as  yet, 
thoroughly  known  in  only  a  few  places.  They  are  chiefly  metamorphosed 
Precambrian  and  Paleozoic  sediments  and  volcanics,  and  Paleozoic 
plutons,  a  number  of  which  are  of  batholithic  proportions. 

Several  long,  narrow  basins  of  Triassic  sediments  rest  unconformably 
on  the  older  rocks  of  the  Piedmont,  and  in  one  place  on  the  Blue  Ridge 
belt.  They  are  down-faulted  troughs,  all  apparently  part  of  a  major  fault 
or  rift  zone.  The  Triassic  sediments  are  mostly  red  standstones  and  shales, 
and  are  cut  by  numerous  large  dikes  and  sills  of  diabase,  also  of  Triassic 
age. 

The  Atlantic  Coastal  Plain  is  a  continuation  of  the  Gulf  Coastal  Plain, 
and  is  made  up  of  Cretaceous  and  Tertiary  sediments  that  rest  uncon- 
formably on  the  older  rocks  of  all  the  structural  systems  of  the  Appala- 
chian Mountains.  They  overlap  the  Triassic  deposits  slightly  in  New 
Jersey.  They  dip  gently  seaward  and  probably  extend  out  under  water 


91 


Fig.  7.1.      Index   map  of  the  structural  systems  of  the  eastern   margin   of  the  continent. 


APPALACHIAN  MOUNTAINS 


93 


CUMBERLAND 
PLATEAU 


VALLEY   AND    RIDGE   PROVINCE 


BLUE       RIDGE      PROVINCE 


INNER    PIEDMONT 


GREAT     SMOKY   MOUNTAINS 


BREVARD    BELT 


ASHEVILLE  I  ,    i 

-•■.'■Vv,;^'->/---::;--^:-".---:  ■;'..■:■■'■  sv.;:' s'Vm^^Sg 


INNER     PIEDMONT 


KINGS   MTN.  BELT 


OUTER 

CHARLOTTE     BELT 


PIEDMONT 


COASTAL     PLAIN 


■  CAROLINA     SLATE      BELT. 


SHELBY 


10 


20 


30 

l_ 


40 


Jj      MILES 


Fig.  7.2..  Cross  section  of  Appalachian  system  from  Cumberland  Plateau  to  Atlantic  Coastal  Plain, 
from  King,  1955  and  1959.  Section  B-B',  Fig.  7.1  "Es,  Triassic  Newark  group;  PM,  Mississippian 
and  Pennsylvanian  rocks;  SO,  Middle  and  Upper  Ordovician  and  Silurian  rocks;  OC,  Cambrian 
and    Lower   Ordovician   rocks;   Cc,    basal   Cambrian    Chilhowee   group;    pCO2,    Great   Smoky   con- 


glomerate and  related  rocks;  pCo',  Hiwassee  slate  and  Snobird  fm.;  pCs,  gneiss  and  schist 
(mainly  Carolina  and  Roan  gneisses);  pCg,  Cranberry  and  Max  Patch  granites;  vol,  slate, 
tuff,  rhyolite  and  andesite  flows  and  breccia  interbedded;  gr2,  massive  granites;  gr',  foliated 
granites;    di,   diorite   and    gaboro;    gd,    granite-diorite    injection    complex;    gn,    gneiss    and    schist. 


in  the  Atlantic  Ocean  to  the  margin  of  the  continental  shelf,  so  that  the 
province  geologically  should  be  considered  to  include  the  continental 
shelf.  It  is  clear  that  coastal  plain  sediments  are  being  deposited  today. 
In  addition  to  the  great  longitudinal  structural  divisions  of  the  Atlantic 
margin  of  the  continent  just  described,  a  traverse  division  is  also  com- 
monly made,  and  the  terms  central  Appalachians  and  southern  Appala- 
chians are  used.  Generally,  the  three  structural  systems,  the  folded  and 
faulted  Appalachians,  the  Blue  Ridge,  and  the  Piedmont  provinces  in  the 
states  of  Alabama,  Georgia,  Tennessee,  North  Carolina,  and  Virginia 
are  included  in  the  southern  Appalachian  region,  and  the  same  three 
divisions  in  northern  West  Virginia,  Maryland,  Pennsylvania,  and  New 
Jersey  are  included  in  the  central  Appalachian  region,  although  some 
authors  call  the  whole  structural  complex  south  of  New  York  the 
southern  Appalachians. 


RELATIONS  TO  GEOMORPHIC  PROVINCES 


Appalachian  Plateaus  Province 


The  structural  divisions  or  systems  are  in  large  part  reflected  in  the 
geomorphic  provinces  and,  therefore,  except  for  minor  variations,  their 
boundaries  are  the  same.  See  Fig.  7.3.  The  Appalachian  plateaus  province 
includes  two  main  plateaus,  the  Cumberland  on  the  south,  and  the 
Allegheny  on  the  north.  The  province  is  one  of  mature  or  submature 
dissection,  and  stands  throughout  four-fifths  of  its  periphery  higher  than 
its  neighbors;  and  parts  of  it  are  properly  called  mountains.  The  province 
is  a  broad,  gentle,  synclinal  basin,  whose  youngest  rocks  are  the  Dunkard 
group  or  "upper  barren  measures"  (Permian).  They  are  mainly  a  thick 
mass  of  red  shale  and  sandstone,  and  occupy  a  belt  extending  southwest 
from  near  Pittsburgh  to  near  Huntington,  West  Virginia.  Cropping  out 


94 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 
APPALACHIAN        PLATEAU 


Hudson,  R. 


Fig.  7.3.  Block  diagram  of  the  geomorphic  provinces  of  the  central  Appalachians  and  the 
Atlantic  Coastal  Plain,  reproduced  from  Johnson,  Bascom,  and  Sharp,  1933.  M,  Manhattan; 
Sb,    Stroudsburg;    P.    Pottsville;    R,    Reading;    Hb,    Harrisburg;    CI,    Carlisle    G,    Gettysburg;    Ch, 

around  it  in  successive  elliptical  zones  are  the  Monongahela  ("upper 
productive"),  Conemaugh  ("lower  barren"),  Allegheny  ("lower  produc- 
tive"), and  finally  the  fairly  thin  Pottsville.  Most  of  the  limestone  and 
the  best  coal  beds  are  in  the  Monongahela  formation. 


Chambersburg;    Mr,    Mercersburg;    H,    Hagerstown;    HF,    Harpers    Ferry;    F,    Frederick;    Rv,    Rock- 
ville;    Wash,    Washington;    Bal,    Baltimore;    Phil,    Philadelphia;    Tr,    Trenton. 


The  Allegheny  plateau  is  continuous  with  the  Cumberland  plateau,  and 
any  boundary  is  arbitrary.  The  southern  plateau  is  somewhat  less  dis- 
sected, and  the  nearly  flat-lying  strata  are  largely  the  sandstones,  shales, 
and  basal  conglomerates  of  the  Pottsville  formation. 


APPALACHIAN  MOUNTAINS 


95 


...  in  southern  Ohio  the  Mississippian  rocks  on  the  western  margin  of  the 
Allegheny  Plateau  form  cuestas  rising  to  the  full  height  of  the  plateau.  The 
prominence  of  these  cuestas  diminishes  toward  the  south,  but  they  continue 
to  form  a  narrow  belt  included  in  the  plateau  as  far  as  latitude  37°  30',  beyond 
which  the  Mississippian  rocks  (all  except  the  uppermost)  spread  widely  to  the 
west  at  a  lower  level  and  belong  to  a  different  province.  Farther  south  the  strong 
conglomerates  or  sandstones  at  the  base  of  the  Pottsville  (Rockcastle  group) 
underlie  and  support  the  margin  of  the  plateau.  All  beds  here  dip  slighdy  to 
the  east,  and  the  strong  basal  formations  are  to  some  extent  stripped,  leaving 
at  places  a  decided  eastward  dip  slope.  As  the  stripped  belt  widens  toward 
the  south,  and  the  province  narrows,  the  entire  width  of  the  Cumberland 
Plateau  in  Tennessee  and  Alabama  comes  to  be  on  the  strong  formations  here 
|  known  as  Walden  and  Lookout  sandstones. 

For  nearly  200  miles  along  the  median  line  of  the  province  in  Tennessee  and 
Alabama,  runs  the  straight  Sequatchie  anticline,  broken  on  the  west  by  a  thrust 
fault.  If  left  uneroded,  it  would  form  a  range  of  mountains,  as  it  still  does  at 
its  northern  end  where  the  Crab  Orchard  Mountains  are  in  line  with  the  perfect 
anticlinal  valley  which  marks  the  rest  of  the  uplift.  Like  the  more  extensive 
and  complex  Allegheny  and  Cumberland  Mountains,  this  anticline  represents 
the  propagation  into  the  plateau  of  the  compressive  stress  by  which  the  Valley 
and  Ridge  province  was  folded.  Parallel  to  this  feature,  and  15  miles  to  the 
east  is  the  similar  Wills  Creek  anticline,  marked  by  the  valley  west  of  Lookout 
Mountain  (Fenneman,  1937). 

Valley  and  Ridge  Province 

The  folded  and  thrust-faulted  Appalachian  structural  system  is  the 
geomorphic  Valley  and  Ridge  province,  which  as  already  stated  consists 
of  parallel  or  subparallel  ridges  and  valleys  of  1000  to  2000  feet  local 
relief.  It  has  been  spoken  of  as  the  newer  Appalachians  in  contradistinc- 
tion to  the  older  Appalachians  which  would  include  the  Blue  Ridge  and 
|  Piedmont  provinces. 

The  Valley  and  Ridge  province  can  readily  be  divided  longitudinally  into  a 
northwestern  section,  in  which  high  ridges  alternate  with  valleys  of  moderate 
width  (the  "Valley  and  Ridge"  section),  and  a  broad  southeastern  lowland 
section  (the  "Great  Valley").  This  division  is  more  or  less  apparent  throughout 
the  length  of  the  province. 

Except  for  a  short  distance  in  New  York,  the  entire  northwestern  boundary 
of  the  province  is  an  erosional  escarpment  formed  on  gendy  dipping  or  horizon- 

i  tal  sediments   of  the  Appalachian   Plateau.    From   southern   Pennsylvania   to 
Alabama,  the  southeastern  boundary  is  formed  by  the  resistant  rocks  of  the 

1  Blue  Ridge,  towering  above  the  Great  Valley.  This  boundary  is  erosional  in 
origin,  weaker  Paleozoic  sediments  having  been  stripped  from  the  Precambrian 


surface   (in  some  places  from  resistant  Cambrian   quartzites)   on  which  till 
were  deposited.  In  other  localities  the  contact  of  weak  Paleozoic  sediments  with 
resistant  crystalline  rocks  takes  place  along  a  low-angle  thrust  fault,  and  erosion 
has  lowered  the  sediments  northwest  of  the  Fracture  plane. 

The  rocks  of  the  province  are  Paleozoic  sediments  ranging  in  age  from  Cam- 
brian to  Pennsylvanian.  Their  resistance  to  erosion  varies  gready  and  has  a  very 
important  effect  upon  the  topograph}'.  The  broad  low  land  composing  the  Great 
Valley  is  due  to  the  weakness  of  the  Cambro-Ordovician  limestones  (Kittatinnv 
and  other  formations)  and  Ordovician  shales  (Martinsburg).  The  ridges  of  the 
Valley  and  Ridge  belt  are  composed  of  very  resistant  middle  and  upper  Paleo- 
zoic sandstones  and  conglomerates,  particularly  the  Tuscarora  quartzite  and 
conglomerate  (Silurian),  the  Pocono  sandstone  (Mississippian),  and  the  Potts- 
ville conglomerate  (Pennsylvanian). 

At  the  end  of  Paleozoic  time  the  sediments  in  the  Newer  Appalachian 
province  were  subjected  to  strong  pressure  from  the  southeast  and  folded  into 
great  anticlines  and  synclines,  in  places  overturned  toward  the  northwest. 
Reverse  faults  were  also  commonly  developed  in  the  zone  of  greatest  pressure, 
the  horizontal  attitude  of  the  beds  was  scarcely  disturbed.  The  region  of 
undisturbed  rocks  today  forms  the  Appalachian  Plateau;  the  folded  area  has 
become  the  Newer  Appalachians.  In  the  latter  province  the  structural  trends 
are  northeasterly,  and  owing  to  the  remarkable  development  of  subsequent 
streams  the  topographic  features  trend  in  the  same  direction  (Fenneman,  l937). 

Blue  Ridge  Province 

The  Blue  Ridge  province  rises  in  southern  Pennsylvania  as  the  Carlisle 
prong  and  continues  southwestward  in  accordance  with  the  general  trend 
of  the  Appalachian  systems  to  northern  Georgia.  It  stands  conspicuously 
above  the  Great  Valley  section  of  the  Valley  and  Ridge  province  on  the 
northwest  and  the  much  lower  Piedmont  province  on  the  southeast.  The 
province  takes  its  name  from  the  Blue  Ridge  in  Virginia,  which  is  a  rela- 
tively narrow  mountainous  ridge  that  extends  from  the  Potomac  River 
200  miles  southwestward  to  Roanoke.  It  has  an  altitude  of  about  1000  feet 
near  the  Potomac,  but  attains  an  elevation  of  more  than  1000  feet  to  the 
southwest.  Southwest  of  Roanoke,  the  Blue  Ridge  province  is  a  rolling 
plateau,  about  10  to  65  miles  wide  ami  with  an  average  elevation  of 
3000  feet.  Its  bounding  escarpments  are  1000  to  2000  feet  high.  This  part 
of  the  province  includes  the  Great  Smokies  which  are  the  highest  land 
east  of  the  Rockies.  Mount  Rogers,  near  the  northwestern  escarpment 
in  Virginia  has  an  altitude  of  5719  feet,  and  Mount  Mitchell  in  North 
Carolina  has  an  elevation  of  6711  feet. 


96 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


The  Blue  Ridge  geomorphic  province  terminates  southward  in  northern 
Georgia,  just  north  of  Gainsville,  where  the  Piedmont  and  the  Valley 
and  Ridge  provinces  seem  to  close  around  the  Great  Smokies.  The  Blue 
Ridge  structural  belt,  however,  extends  on  southward  into  Alabama, 
where  it  is  buried  by  the  coastal  plain  sediments;  but  because  it  has 
been  eroded  down  to  the  level  of  the  Piedmont,  it  is  generally  included 
in  the  Piedmont  province  by  the  geomorphologists. 

The  Piedmont  province  emerges  from  the  Triassic  lowlands  in  New 
Jersey,  where  it  is  known  as  the  Trenton  prong  (see  Fig.  7.3),  and  extends 
southwestward  to  Alabama.  It  is  only  a  few  miles  wide  in  Pennsylvania, 
Maryland,  and  northern  Virginia,  but  widens  conspicuously  to  about  170 
miles  in  North  Carolina,  from  which  place  southwestward  it  continues 
wide.  The  surface  of  the  Piedmont  rises  gradually  westward  to  the  foot 
of  the  Blue  Ridge,  where  it  reaches  an  altitude  of  500  feet  at  the  north 
and  1500  feet  at  the  south.  It  is  a  vast  plain  along  the  horizon,  but  is 
maturely  dissected  to  a  local  relief  of  a  few  hundred  feet  in  places. 


Numerous  hills  and  ridges  rise  as  monadnocks  200  to  1000  feet  above 
the  general  plains  surface,  and  are  more  numerous  near  the  Blue  Ridge 
escarpment. 

The  rocks  of  the  Piedmont  province  are  mostly  granites,  gneisses,  and 
schists,  with  some  belts  of  marble  and  quartzite,  partly  of  Paleozoic  age 
but  also  in  part  of  Precambrian  age.  A  belt  of  basic  rocks  containing 
talc  and  soapstone  is  found  near  the  western  border.  Several  elongate 
basins  of  Upper  Triassic  sandstones  and  shales,  cut  by  diabase  dikes  and 
sills,  are  found  in  the  province.  The  Richmond  basin  contains  coal, 
which  was  the  first  mined  in  North  America  in  about  1750. 

The  Piedmont  crystallines  are  overlapped  on  the  east  by  the  Cretaceous 
and  Tertiary  sediments,  and  the  boundary  of  the  two  provinces  is  called 
the  fall  zone.  Baltimore,  Washington,  Fredericksburg,  Richmond,  Peters- 
burg, and  other  cities  are  located  along  it,  and  also  mark  approximately 
the  points  to  which  the  tide  extends  up  the  estuaries. 


8. 


SOUTHERN  AND 
CENTRAL  APPALACHIANS 


EXTENT  AND  DIVISIONS 

The  southern  and  central  Appalachians  extend  from  Alabama  to  New 
York  and  the  Hudson  River,  and  include  the  area  shown  on  the  index 
map  of  Fig.  7.1.  They  will  be  treated  under  their  three  longitudinal  divi- 
sions, the  folded  and  thrust-faulted  Appalachian  Mountains  province, 
the  Blue  Ridge  Cambrian  and  Precambrian  province,  and  the  Piedmont 
crystalline  province.  The  use  of  the  words  southern  and  central  implies 
that  a  northern  division  is  also  recognized,  but  this  is  referred  to  as  the 
New  England  province.  New  Brunswick  and  Nova  Scotia  will  be  in- 
cluded in  the  northern  division  because  of  their  close  geological  relation 
to  New  England. 


MAJOR  ELEMENTS  OF  STRATIGRAPHY 

Appalachian  Geosyncline 

From  the  time  tiiat  James  Hall  contributed  voluminously  to  geologic- 
literature  (1840  to  1860)  to  about  1920,  the  following  views  were  widely 
held  regarding  the  Appalachian  geosyncline.  It  extended  from  New- 
foundland to  Alabama  and  beyond,  over  3000  miles;  subsided  most  in  the 
site  of  the  present  Valley  and  Ridge  province  and  the  eastern  side  of  the 
Allegheny  synclinorium,  where  more  than  30,000  feet  of  sediments  ac- 
cumulated in  places;  shallow  shelf  seas  extended  inland  from  the  geosyn- 
cline over  the  Central  Stable  Region;  and  a  great  borderland,  Appala- 
chia,  lay  along  its  southeast  side,  from  which  came  much  of  the  sediment 
that  filled  the  subsiding  trough. 

Failure  to  appreciate  facies  changes  and  the  absence  of  detailed 
mapping,  especially  in  the  Blue  Ridge  and  Piedmont  provinces,  militated 
against  a  correct  understanding  of  the  tectonic  development  of  the  region. 
It  appears  now  that  the  Blue  Ridge  province  marks  approximately  the 
boundary  between  a  west-lying  miogeosyncline  and  an  east-lying  eugeo- 
syncline  in  Cambrian  time,  but  in  post-Cambrian  Paleozoic  time  the 
Blue  Ridge  and  Piedmont  were  generally  emergent.  The  concept  of  a 
borderland  that  extended  beyond  the  present  continental  shelf  into  the 
Atlantic  ocean  is  discredited. 

Because  of  the  metamorphosed  nature  of  the  strata  in  the  Piedmont 
and  the  almost  complete  failure  to  find  fossils  in  them,  the  work  of 
unraveling  their  stratigraphy  and  structure  has  been  slow.  The  stratig- 
raphy of  the  Valley  and  Ridge  province,  however,  has  received  a  gnat 
deal  of  attention.  It  will  be  seen  that  geosynclinal  subsidence  in  the  site 
of  the  Appalachians  and  the  plateaus  shifted  from  time  to  time  and 
place  to  place  so  that  a  strict  coincidence  of  structural  divisions  and  the 
sedimentary  provinces  does  not  exist.  In  a  broad  way,  however,  the 
western  half  of  the  miogeosyncline  is  undeformed  or  cast  only  into  very 
gentle  folds — it  is  structurally  the  Allegheny  svnclinorium  and  physio- 
graphically  the  Plateaus  province — whereas  the  eastern  half  of  the  mio- 
geosyncline is  the  folded  and  thrust-fanlted  province. 


97 


98 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


East-central  Ten- 
nessee (Chilhowee 
Mountain) 

Northeastern  Ten- 
nessee  (Johnson, 
Carter  and  Unicoi 
Counties) 

Northern  Virginia 
(Elkton  and  Har- 
pers Ferry  areas) 

Shady  dolomite 
(in  Miller  Cove) 

Shady  dolomite 

Tomstown  dolomite 

— 

3 

o 

E 

s 

o 

o 

Hesse  quartzite 

Erwin 
quartzite 

Antietam 

c 

Murray  shale 

quartzite 

£ 

cS 

Nebo  quartzite 

Nichols  shale 

Hampton  shale 

Harpers   shale 

o 

Cochran 
conglomerate 

Unicoi  formation 
(with  basalt  flows 
1000-1500  feet 
below  top) 

Weverton 
quartzite 

Loudoun  formation 
(with  tuffaceous 
slate  and  rare 
flows) 

c 

.5 

£ 

CIS 

CJ 

<1) 

s- 

Ocoee  series 

Volcanics  of  Mt. 
Rogers  area 

Cranberry  granite 

Injection  complex 

Fig.    8.1. 
1949. 


Formations    of    the    Chilhowee    group    in    Tennessee    and    Virginia.    From    P.    B.    King, 


Major  Sedimentary  Divisions  of  the  Miogeosyncline 

Lower  Cambrian  Marine  Clastics.  The  oldest  beds  of  the  Cambrian, 
referred  to  as  basal  Cambrian,  are  conglomerates,  arkoses,  and  shales, 
that  pass  upward  into  quartzites.  They  make  up  the  Chilhowee  group 
(Fig.  8.1)  and  attain  a  thickness  of  5000  to  6000  feet.  Tentative  correla- 
tions with  metamorphic  units  of  the  Piedmont  suggest  that  these  strata 
of  the  miogeosyncline  grade  southeasterly  into  eugeosynclinal  facies 
in  the  manner  illustrated  in  Fig.  8.2. 

The  basal  Chilhowee  beds  rest  in  places  unconformably  on  the  vol- 
canics and  greenstones  of  the  Ocoee  series,  and  hence  are  believed  to  be 


part  of  the  Lower  Cambrian  sequence.  They  are  limited  to  a  trough 
which  runs  the  length  of  the  central  and  southern  Appalachians  and 
are  absent  over  the  foreland  or  shelf  region. 

Cambrian  and  Lower  Ordovician  Carbonates.  The  miogeosyncline 
with  its  clastic  deposits  from  Alabama  to  Pennsylvania  became  one 
dominantly  of  limestone  and  dolomite  deposition.  Some  9000  feet  of 
carbonates  representing  the  remainder  of  the  Lower  Cambrian,  the  entire 
Middle  and  Upper  Cambrian,  and  the  Lower  Ordovician  accumulated 
to  a  fairly  uniform  thickness  up  and  down  the  entire  trough.  In  the 
southern  and  northern  ends  of  the  geosyncline  carbonate  deposition 
continued  into  Middle  Ordovician  time.  A  correlation  chart  of  the  im- 
portant formations  of  this  period  is  given  in  Fig.  8.3.  The  carbonates 
grade  into  shale  facies  toward  the  northwest  side  of  the  miogeosyncline 
and  the  shelf  in  the  manner  illustrated  in  Fig.  8.4. 

The  basal  Cambrian  clastics  and  the  succeeding  thick  carbonate 
sequence  are  typically  miogeosynclinal  and  correspond  in  distribution 
approximately  with  the  later  orogenic  belts  of  the  Blue  Ridge  and 
Valley  and  Ridge  provinces  (King,  1959).  The  clastics  were  derived  from 
an  emergent  stable  interior,  and  the  carbonates  were  deposited  on  a 
broad  continental  shelf,  evidently  without  off-lying  tectonic  lands  or  a 
volcanic  archipelago.  The  eugeosynclinal  equivalents  of  the  carbonates, 
if  ever  deposited,  are  not  yet  clearly  recognized  in  the  Piedmont. 

Middle  Ordovician  Clastic  Wedge.  The  regimen  of  erosion  and  sedi- 
mentation characterized  by  an  emergent  interior  and  a  gently  sub- 
merging continental  border  gave  way  abruptly  in  Middle  Ordovician 
time  to  a  reversed  situation  in  which  an  uplifted  borderland  now 
furnished  the  sediments  to  a  subsiding  inside  basin.  The  sediments  were 
mostly  clastic  (Fig.  8.5),  and  the  main  source  was  in  western  Virginia, 
western  North  Carolina,  and  eastern  Tennessee.  A  great  fan  of  sedi- 
ments is  visualized  to  have  apexed  in  this  region  in  about  the  Great 
Smoky  Mountains  area  and  extended  radially  to  the  west,  northwest, 
and  north  (P.  B.  King,  1959).  See  Fig.  8.31.  It  spread  considerably 
beyond  the  later  deformed  belt  of  the  Valley  and  Ridge  province,  and 
unlike  the  Cambrian  and  Lower  Ordovician  sediments  was  not  confined 
to  an  elongate  basin  parallel  with  the  continental  margin.  The  wedge 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


99 


Fig.    8.2.      Stratigrauhic    relations    of    Late    Precambrian    and    Early    Cambrian    formations    in    Blue    Ridge 
of  Virginia.  After   Bloomer  and   Werner,    1955. 


or  fan  was  about  8000  feet  thick  near  its  apex  but  thinned  toward  its 
edges.  Beds  representing  the  Middle  Ordovician,  as  well  as  the  Upper, 
are  only  500  feet  thick  to  the  southwest  in  Alabama,  and  are  carbonates. 
Likewise  to  the  northeast  in  Pennsylvania  Middle  Ordovician  beds  are 
carbonates  and  only  700  feet  thick. 

Late  Ordavician-Devonian  Clastic  Wedge.  Apexing  in  east-central 
Pennsylvania  is  another  great  wedge  of  clastic  sediments  which  began 
to  accumulate  in  Late  Ordovician  time  and  continued  through  the 
Silurian  and  Devonian.  The  greatest  subsidence  and  sediment  accumula- 
tion occurred  during  the  Late  Devonian,  which  deposit  is  commonly 
referred  to  as  the  Catskill  delta.  It  has  a  maximum  thickness  of  over 
8000  feet.  Isopach  maps  of  the  Late  Ordovician  and  Silurian  deposits  are 
shown  in  Fig.  8.6,  and  detail  of  facies  relations  in  Fig.  8.7.  A  cross 
section  of  the  Devonian  wedge  is  given  in  Fig.  8.8,  and  a  map  of  the 
deposit  in  Fig.  8.9.  Further  detail  on  the  stratigraphy  may  be  found  in 
publications  by  Willard  (1936). 

Mississippian  Deposits.  In  eastern  Tennessee  in  the  Great  Valley 
a  sheet  of  black  shale  may  be  seen  transgressing  across  the  Silurian  strata 
and  on  the  southeast  side  of  the  Valley  to  be  resting  on  Middle  Ordovician 
rocks.  See  Fig.  8.5.  It  is  known  as  the  Chattanooga  shale  and  probably 
ranges  in  age  from  latest  Devonian  to  earliest  Mississippian   (Rodgers, 


1953).  It  thickens  northeastward  and  eastward  to  a  maximum  of  400  feet 
at  Cumberland  gap.  The  Chattanooga  shale  is  extremely  widespread  in 
the  Nashville  and  Cincinnati  arch  areas  and  represents  a  marine  facies 
of  the  upper  continental  beds  of  the  Catskill  delta. 

The  Mississippian  above  the  Chattanooga  in  eastern  Tennessee  may 
have  attained  a  maximum  thickness  of  6000  feet  at  the  time  of  deposi- 
tion near  the  Blue  Ridge  source  region,  but  is  generally  much  thinner 
than  this  in  sections  now  preserved.  It  consists  of  three  units  each  ex- 
hibiting a  parallel  gradation  from  finer,  thinner,  and  less  detrital — 
more  carbonate  sediments  on  the  northwest  side  of  the  Great  Valley  to 
coarser,  thicker,  and  more  detrital  sediments  on  the  southeast  side. 

In  Alabama,  the  thin  Mississippian  limestones  of  the  foreland  change 
toward  the  southeast  into  5000  feet  of  sandstones  and  shales.  In  north- 
ern Virginia,  Maryland,  and  Pennsylvania,  the  lower  1000  to  2000  feet 
of  the  Mississippian  is  shale  and  sandstone,  the  middle  formations  are 
limestone  with  a  maximum  thickness  of  4000  to  5000  feet,  and  the  upper 
formations  are  calcareous  shale,  red  mudrock,  and  red  and  gray  sand- 
stones. The  Pocono  and  similar  sandstones  of  the  lower  division  are  thick 
bedded  and  conglomeratic.  The  thickening  of  most  all  units  of  the 
Mississippian  from  the  western  shelf  to  the  eastern  geosynclinal  trough  is 
conspicuous,  and  the  coarsest  material  occurs  where  the  section  is  thickest. 


100 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


TIME    SCALE 

CENTRAL 
PENNSYLVANIA 

SUSQUE- 
HANNA- 
NEW    RIVER 

NEW  RIVER- 
TENNESSEE 

TENNESSEE- 
ALABAMA 

z 
< 
a 
< 
z 
< 
u 

LARKE 

BEEKMAN- 
T0WN 

CHEPULTEPEC 

CHEPULTEPEC 

z 

4 

E 
■ 

2 

< 

O 

tt 
in 
<L 

a. 

3 

MADISON 
TREMPEALEAU 

o 
a 
r*- 

o 
o 

IS 

(9 

IE 

a> 
■a 

ui 

4 
(9 

MINES 
150-200 

ORE  HILL 
STACY 

C0N0C0- 
CHEAGUE 
1600-2000 

COPPER  RIDGE 
1200-2800 

COPPER  RIDGE 
1200-2800 

BIBB 

250-500 
KETONA 

400-600 
BRIERFIELD 

1500 

FRANCONIA 

DRESBACH 

WARRIOR 
1250 

NOLICHUCKY 
400-750+ 

4 
O 

Z> 
4 

n 

4 
Z 
O 

o 

NOLICHUCKY 

r 
< 

E 

00 

2 

4 
U 

M 

_l 
o 

a 

z 

MARJUM 

ELBROOK 
1800-3000 

K 
HI 
3£ 

4 
Z 
O 

X 

MARYVILLE 
150-750 

MARYVILLE 

WHEELER 

PLEASANT  HILL 
600 

ROGERSVILLE 
70-250 

ROGERSVILLE 

SWASEY 

DOME 

RUTLEDCE 
200-500 

RUTLEDGE 

OPHIR 

HOWELL 

Fig.  8.3.  Middle  and  Upper  Cambrian  formations  of  central  and  southern  Appalachians.  After 
Resser,  1938. 

The  Mississippian  trough  coincides  with  the  Valley  and  Ridge  province 
and  does  not  reflect  the  great  westward  bulging  wedges  of  the  Ordovician 
and  Devonian.  See  Plate  6.  It  is  probable  that  the  Mississippian  seas 
shored  at  about  the  Rlue  Ridge. 

Mississippian  rocks  may  never  have  been  deposited  in  the  northern 
part  of  the  geosyncline  in  southeastern  and  eastern  New  York.  The 
coarsest  beds  in  eastern  Pennsylvania  were  deposited  nearest  the  high- 


lands that  formed  in  New  England  in  the  Devonian,  and  with  reduction 
of  the  highlands  the  earlier  Mississippian  elastics  were  succeeded  by 
calcareous  sediments  (Kay,  1942). 

Pennsylvanian  Clastics.  The  Pennsylvanian  strata  are  distinctly  clastic, 
both  in  the  shelf  and  the  geosynclinal  areas.  They  are  the  great  coal- 
bearing  formations  of  the  Allegheny  Plateaus  and  Valley  and  Ridge 
provinces.  A  cross  section  from  Virginia  to  Illinois  that  does  not  contain 
the  present  structural  details  is  shown  in  Fig.  8.10.  The  trough  is  deep- 
est in  Alabama,  where  a  maximum  of  10,000  feet  of  strata — all  Pottsville 
— is  known.  The  Pottsville  thins  gradually  northeastward  until  in  Pennsyl- 
vania it  is  only  200  to  400  feet  thick.  As  the  Pottsville  thins,  younger 
Pennsylvanian  formations  appear,  and  in  West  Virginia  and  Pennsylvania 
the  Allegheny  formation  is  300  feet  thick,  the  Conemaugh  600  feet,  and 
the  Monongahela  with  the  extremely  valuable  Pittsburgh  coal  at  the  base, 
250  feet.  The  maximum  thickness  of  the  Upper  Pennsylvanian  is  estimated 
to  be  3000  feet. 

The  10,000  feet  of  Pottsville  beds  in  Alabama  in  the  Coosa  coal  field 
area  is  rather  restricted  in  east-west  distribution  because  of  the  nearness 
of  the  Nashville  arch  to  the  Blue  Ridge,  but  probably  the  original  dis- 
tribution was  in  the  form  of  a  wedge  which  spread  westward  over  the 
site  of  the  arch.  This  is  the  representation  of  King,  1959. 

Permian  System.  Overlying  the  Monongahela  formation  in  an  oval 
area  in  West  Virginia  and  Ohio,  entirely  in  the  Plateau  province,  is  the 
Dunkard  group  or  "upper  barren  measures"  of  Permian  age.  It  is  com- 
posed of  shale,  partly  red,  and  sandstone  with  thin  coal  beds.  Its  maxi- 
mum thickness  is  about  1500  feet. 

FOLDED  AND  THRUST-FAULTED  APPALACHIAN  MOUNTAINS 

Salients  and  Recesses 

When  viewed  as  a  whole,  the  folded  and  thrust-faulted  belt  of  the 
central  and  southern  Appalachians  consists  of  two  major  salients  and 
three  recesses.  These  are  terms  used  by  Keith  (1923)  in  his  well-known 
"Outlines  of  Appalachian  structure."  The  salients  are  the  arclike  portions 
of  the  belt  that  are  convex  inland,  and  the  recesses  are  the  arclike  portions 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


101 


NORTHWESTERN 
FACIES 


CENTRAL 
FACIES 


SOUTHEASTERN 
FACIES 


SOUTHWEST 
VIRGINIA 


Copper  Ridge  dolomite 


dolomite 


Conococheogue  limestone 


-2000 


_      LJ 


—    '— '—^  *—  Pumpkin  Valley    shale  znz^z 


-1500 


Ul 

1000  < 
o 
if) 


-500 


< 
o 

h- 

rr 

UJ 
> 


Rome 


formation 


Fig.  8.4.      Middle  and   Upper  Cambrian  sedimentary  rocks  of  eastern   Tennessee  and   southwestern  Virginia. 
After  Rogers,   1953. 


that  are  convex  toward  the  ocean.  The  southern  salient  is  principally  in 
Tennessee  and  southeastern  Kentucky  (see  Tectonic  Map  of  the  United 
States),  and  the  northern  salient  is  in  central  Pennsylvania.  They  are 
about  400  miles  apart.  Keith  points  out  two  other  salients  in  the  northern 
Appalachians  which  will  be  described  later. 

Structural  Characteristics  in  Alabama,  Georgia,  and  Tennessee 

If  the  Tectonic  Map  of  the  United  States  is  studied,  it  will  be  seen  that 
the  southern  half  of  the  Valley  and  Ridge  province  is  characterized  by 
thrust  faults,  whereas  the  northern  half  is  chiefly  one  of  long  parallel 
anticlines  and  synclines.  In  the  southern  part,  the  thrust  sheets  are 
stacked  in  imbricate  fashion  on  top  of  each  other,  and  in  eastern  Ten- 
nessee a  succession  of  nine  such  sheets  has  been  mapped.  Some  of  the 
thrust  sheets  carry  almost  the  entire  Paleozoic  succession;  others  du- 
plicate the  lower  Paleozoic   succession   only.   Precambrian   rocks   have 


nowhere  in  the  belt  been  exposed  as  the  result  of  thrusting  and  erosion. 

The  belt  is  made  up  almost  entirely  of  thrust  sheets  in  Tennessee,  but 
southward,  especially  along  the  northwest  margin,  the  beds  are  cast  into  a 
long  anticline  (Sequatchie)  and  syncline  (Coalburg),  which  extend  from 
central  Tennessee  almost  to  the  Cretaceous  cover  in  Alabama.  Also  along 
the  southeast  side  of  the  belt  in  northwestern  Georgia,  a  number  of  folds 
are  evident.  They  occur  in  a  conspicuous  embayment  of  the  Blue  Ridge 
front. 

The  nature  of  the  thrusts  and  folds  is  illustrated  in  sections  1  to  4  and 
8  to  12  of  Figs.  8.11  to  8.17.  The  location  of  the  sections  is  given  on  the 
index  map  of  Fig.  7.1.  Most  all  the  thrust  sheets  have  moved  toward  the 
stable  interior  of  the  continent;  only  a  few  exceptions  are  known.  One  of 
these  is  illustrated  in  section  2,  Fig.  8.12. 

The  Rome  sheet  was  thrust  forward  at  least  10  miles  and  then  folded 
into  anticlines  and  synclines.  See  section  3,  Fig.  8.12.  Some  of  the  folds 


102 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


MAYNARDVILLE   QUADRANGLE 


KNOXVILLE   QUADRANGLE 


Northwest  of 
Wallens  Ridge 


5 


Southeast  of 
Wallens  Ridge 


Northwest  of 
Bays  Mountain 

I 


Chilhowee 
Mountain 


■1-yzv-v":"---*  Chattanooga" shale \  -_-_j-l= ~r-_ -r'-~-  -  -  -~~  -  =  ~  ~  ~~~ ~~~~  """  "" 


S^^agjb»^£^evrer"j  jjiii  ~£?&S^%£ 


•.!.-.:.v.-:.'-..fpllico   sandstone";  •„•: 


2  * 

33 
<: 

4.t; 

*■» 

5  Co 


Conglomerate  locally 


Fig.  8.5.      Stratigraphic  diagram  of  Middle  and   Upper  Ordovician  and  Silurian   rocks  of  Valley  and   Ridge 
province   of  eastern   Tennessee.  After   P.   B.    King,    1950a. 


of  the  strata  below  the  thrust  sheet  are  in  the  same  position  as  those  of 
the  thrust  sheet,  but  in  detail  the  contacts  are  discontinuous  against  the 
thrust,  and  in  other  areas  a  complete  lack  of  coincidence  occurs.  This 
suggests  three  episodes  of  compressional  orogeny,  perhaps  almost  in 
continuous  succession:  first  the  folding  and  erosion  of  the  strata  in  front 
of  the  thrust  and,  perhaps,  the  early  development  of  the  thrust  itself; 
then  the  movement  of  the  great  sheet  out  over  the  folded  and  eroded 
terrane;  and  third,  further  folding,  involving  both  the  thrust  sheet  and 
the  underlying  strata.  Immediate  waste  products  of  the  folds  and  thrusts 
which  have  been  overridden  and  preserved,  or  which  partially  bury  the 


structures,  are  not  apparent.  Such  waste  products  in  the  form  of  coarse 
piedmont  elastics  are  present  in  some  of  the  Rocky  Mountain  thrusts  and 
serve  to  date  the  various  stages  of  deformation.  Regarding  the  Rome 
thrust,  however,  all  three  closely  related  episodes  of  deformation  are 
younger  than  the  Lower  Pennsylvanian  Pottsville,  which  is  involved  in 
the  deformation. 

Another  conspicuous  structural  division  of  the  Valley  and  Ridge 
province  of  the  southern  Appalachians  is  the  zone  of  shallow,  flat  thrust 
sheets,  like  the  Rome,  along  its  eastern  margin.  These  are  largely  part 
of  the  Rlue  Ridge  province,  and  involve  Cambrian  and  Ordovician  strata, 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


103 


but  in  part  are  in  the  Great  Valley.  Modern  interpretations  show  a  num- 
ber of  fensters  and  klippes.  See  sections  4,  10,  and  12  of  Figs.  8.13,  8.16, 
and  8.17,  respectively. 

In  northeastern  Tennessee  and  southeastern  Kentucky,  the  Appalachian 
front  is  characterized  by  an  unusual  thrust.  Elsewhere  the  Appalachian 
front  is  one  of  fairly  sharp  folds  that  start  abruptly  from  the  flat-lying 
plateaus  sediments.  As  seen  in  Figs.  8.14  and  8.15,  an  extensive  block  of 
the  flat  plateau  strata  has  been  torn  loose  and  thrust,  with  only  gentle 
deformation,  toward  the  stable  interior.  The  great,  basal  fault  is  known 
as  the  Pine  Mountain  and  the  two  lateral  tears  as  the  Jackson  and  Russell 
Fork.  Although  the  large  mass  is  a  thrust  sheet,  the  strata  from  Pine 
Mountain  to  Cumberland  Mountain  are  so  flat  that  an  arborescent  drain- 
age has  developed  and  the  region  is  considered  geomorphically  part  of 
the  plateaus  province.  The  thrust  mass  is  known  as  the  Cumberland  block 
and  is  125  miles  long  and  25  miles  wide.  Its  displacement  has  been  cal- 
culated as  5.8  miles  (Miller  and  Fuller,  1947).  Along  the  Powell  Valley 
anticline  in  the  thrust  sheet,  erosion  has  cut  several  small  fensters,  and 
the  Rose  Hill  oil  field  has  been  developed  in  the  underlying  beds  with 
production  from  the  Moccasin  limestone. 

Structural  Characteristics  in  the  Virginias,  Maryland,  and  Pennsylvania 

The  southern  part  of  the  Appalachian  belt,  characterized  by  thrust- 
ing, is  narrow;  but  toward  the  north  in  west-central  Virginia  a  number 
of  folds  begin  to  show  and  the  belt  broadens.  Sharp  asymmetrical  folds 
and  mild  metamorphism  characterize  the  Great  Valley,  strong  upright 
! folds  the  main  Valley  and  Ridge  province,  and  very  gentle  folds,  a 
western  belt.  See  index  map,  Fig.  7.1.  The  folds  of  the  westernmost  zone 
are  so  gentle  that  the  region  is  considered  part  of  the  Plateaus  province, 
and  the  Appalachian  structural  front  here  is  regarded  as  the  western 
boundary  of  the  zone  of  sharp  folds.  The  plateaus  generally  stand  in  relief 
above  the  valleys  and  ridges  of  the  strongly  folded  belt,  and  the  eastward- 
facing  escarpment  is  called  the  Allegheny  front,  which  is  a  geomorphic 
feature,  whereas  the  Appalachian  front  is  a  structural  feature. 

The  chief  faults  are  the  Pulaski  and  North  Mountain  overthrusts.  They 
may  be  parts  of  one  great  thrust  which  extends  from  southern  Penn- 


f  ^' 

!4c 

>r~  7SO  — "~ 

-^- 

I         \         P               / 

V    * ' 

/s^ 

\     / 

A    j 

/                 " 

s 

i     \ 

\\                 \             ' 

- 

Fig.   8.6.      Basins  of  deposition   in    middle  and   late   Ordovician   time  and   in   Silurian   time   in   the 
Pennsylvania-New  York  region.  After  Kay,   1942. 


104 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


sylvania  to  northeastern  Tennessee,  over  500  miles  long.  Rack  of  the 
Pulaski  thrust  front  are  several  fensters,  as  illustrated  in  sections  12  and 
13  of  Fig.  8.17.  See  also  Fig.  8.16.  Sections  14,  16,  and  17  of  Figs.  8.18  and 
8.19  also  illustrate  the  thrusts  of  the  central  and  eastern  parts  of  the  belt. 

The  nature  of  the  strong  folds  is  illustrated  in  sections  15,  16,  18-21, 
and  24  of  Figs.  8.17  to  8.20.  Most  of  the  folds  are  asymmetrical  and 
steepest  on  the  northwest  flank.  According  to  the  orthodox  view,  this 
marks  active  pressure  from  the  southeast,  as  do  almost  all  the  thrusts. 

SILURIAN 


The  folds  of  this  region  are  some  of  the  best  known  in  North  American 
geology,  and  some  are  markedly  long  and  regular.  See  the  Tectonic  Map 
of  the  United  States.  Keith  ( 1923 )  points  out  that  the  troughs  of  the  folds 
extend  downward  to  almost  a  common  level,  whereas  the  anticlines 
extend  upward  to  variable  elevations.  Some  of  the  anticlines  are  over- 
turned and  have  broken  into  thrust  faults.  Most  of  the  more  eastern 
thrust  sheets  have  extensively  flat  or  folded  lower  surfaces. 

The  faults  die  out  in  southern  Pennsylvania,  and  from  there  northwest- 


6ASS    ISLAND 


L. KEVSER  7 


10   N    T   A    R    I    0 
I 
CAPE    HORD  OWEN    SOUND 


NEW  YORK 

! 
GUELF      HAMILTON        LAKE  ERIE 


CINCIN  N  ATI  A  N 


PENNSYLVANIA 
I 
ALLEGHENY     FRONT 


HARRISBURG 


30      MILES  . 


Fig.    8.7.      Late    Ordovician    and    Silurian    stratigraphy    of    Pennsylvania,    western    New    York,    and    western 
Ontario.  After  Kay,  1942. 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


105 


ERIE,  PA.     PA 


N.Y. 


WARREN,  PA.         PORTAGE,  N.Y.  NAPLE5 


WATKINS   GLEN       BINGHAMPTON 


CAT5KILL   MT5. 


Hamilton    gr. 
'    '   h 

Onondaga  /j  /* 


0r/sX 


any 


/)  snoK  an 


Fig.  8.8.      Upper  cross  section,  the  great  Catskill  delta  from  Erie,   Pa.,  to  the  Catskill  Mountains, 
N.Y.  After  Schuchert,   1924. 

Black  is  black  shale  and  white  is  conglomerate,  sandstone,  shale,  and  calcareous  shale.  The 
elastics  are   dominantly   red   and   generally  coarsest  in   the  eastern    part.   Vertical   scale   much   ex- 

ward  almost  the  entire  belt  is  one  of  anticlines  and  synclines.  See  section 
29,  Fig.  8.20.  They  veer  markedly  eastward  in  central  and  eastern  Penn- 
sylvania, and  by  southern  New  York  both  the  gently  folded  belt  and  most 
of  the  strongly  folded  belt  die  out.  The  folds,  if  projected,  would  run 
into  the  Adirondack  uplift  and  the  lower  Hudson  Valley.  A  narrow  eastern 
zone  of  the  folded  and  thrust-faulted  Appalachians,  which  is  intimately 
connected  with  the  Rlue  Ridge  province,  extends  up  the  Hudson  Valley.  It 
seems  very  crowded  between  the  Adirondacks  and  the  New  England 
metamorphic  masses.  See  section  30,  Fig.  8.21. 

As  far  as  the  folded  and  thrust-faulted  Appalachians  are  concerned, 
and  aside  from  the  narrow  belt  up  the  Hudson,  it  can  be  said  that  they 
begin  in  southern  New  York  in  gentle  folds  and  become  stronger  south- 


Onona'aga     J 

Or/5Honyi  fte/a".,  r  Decker 

aggerated.  Thickness  may  be  judged  by  reference  to  the  isopach  map  of  Fig.  8.9. 

Lower  cross  section,  the  Catskill  Mountains  and  Hudson  Valley  north  of  Kingston,  N.  Y.,  after 
Chadwick  and  Kay,  1933.  It  shows  the  present  eastern  erosional  termination  of  the  Catskill 
delta,  and  presents  the  relations  concerned  with  the  problem  of  the  source  highlands. 

ward.  Thrust  faults  appear  and  become  the  dominant  structure  in  the 
southern  Appalachians.  Also,  in  general,  it  can  be  said  that  the  intensity' 
of  deformation  across  the  belt  becomes  greater  toward  the  southeast, 
and  in  the  Great  Valley  and  at  the  Blue  Ridge  front  it  is  the  greatest. 

Regarding  metamorphism,  Keith  (1923)  pointed  out  long  ago  that  a 
distinct  change  in  constitution  of  the  strata  occurs  along  the  eastern 
margin  of  the  Valley  and  Ridge  province  in  the  Great  Valley,  and  in  the 
adjacent  Blue  Ridge.  Shales  have  taken  on  a  slatv  character,  limestones 
and  dolomites  are  somewhat  marmorized,  and  sandstones  are  quartzitic. 
The  slate  belt  of  northeastern  Pennsylvania  and  southeastern  New  York 
in  the  tightly  appressed  and  narrow  belt  of  deformation  east  of  the  Blue 
Ridge  is  well  known.  The  change  from  bituminous  to  semibituminous  to 


MICH     OHIO 


Fig.  8.9.  Restored  section  of  the  Paleozoic  rocks  across  the  Allegheny  basin  and  Cincinnati  arch. 
The  line  of  cross  section  is  shown  on  the  inset  map,  but  it  continues  across  Ohio  to  the  southern 
Michigan    line.    After    Tafferty,    1941,    personal    communication.    The    inset   map    shows    the    great 


Catskill  delta  and  is  taken  from  Barrell,  in  Schuchert's  Historical  Geology,  1924.  The  heavy  lines 
are  isopachs  in  feet. 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


107 


anthracite  coal  eastward  through  Pennsylvania  has  been  emphasized  re- 
peatedly as  a  demonstration  of  greater  intensity  of  deformation  from  west 
to  east.  Although  the  coals  have  been  metamorphosed  within  the  belt 
west  of  the  Great  Valley,  the  associated  shales,  sandstones,  and  carbonates 
have  not  been  much  altered.  Some  doubts  exist  that  the  devolatilization 
is  entirely  a  result  of  folding,  because  of  anomalies  in  the  relations, 
especially  in  West  Virginia.  Farther  south  the  Knoxville,  Tennessee, 
"marble"  in  the  highly  thrust-faulted  belt  is  a  slightly  recrystallized  rock. 


StCllON      I 


I L.LIN0I5 


OHIO 


W.  VIRGINIA 


o 
z 
— o 
r  z 
o  o 
2£ 


VIRGIL 


MISSOURI 


°E3    MOINES 


^""MSAS 


QokeritpO-"- 

_CjL>Lt°2 


__ > 


:ig.  8.10.  Correlation  and  relative  thickness  diagram  of  Pennsylvania  strata  from  West  Virginia 
o  Illinois.  After  committee  report,  Chart  No.  6  G.S.A.,  Vol.  55,  1944.  The  Cincinnati  arch  and 
)ther  structures  are  not  shown,  nor  is  the  section  restored  to  any  one  time.  The  dashed  lines  are 
he  various  coal  beds. 


Cby 
CrCpv/      £01.  -.         COcr 


-"--S& 


r^t^; 


vr 


RED 

M7N. 

Dc,C(p,CwJ.g  Ch 


0e'i?m 


1  CwrCsr  Cpv 


Fig.  8.11.  Cross  section  (No.  1  of  index  map,  Fig.  7.1)  of  the  Bessemer  and  Vandiver  quad- 
rangles, Alabama,  after  Butts,  1927.  Cr,  Rome  fm.;  COK,  Ketona  dol.;  COcr,  Copper  Ridge  dol.; 
COc,  Chepultepec  dol.;  Olv,  Longview  Is.;  On,  Odenville,  Newala,  Lenoir  and  Mosheim  Iss.; 
Oa,  Athens  sh.;  Ol,  Little  Oak  Is.;  Dc  Chattanooga  sh.  and  Frog  Mtn.  ss.;  Cfp,  Fort  Payne 
chert;  Cf,  Floyd  sh.;  Cpw,  Parkwood  sh.  and  ss.;  Cs,  Cpv,  Cpi,  Cwr,  Pottsville  ss.,  sh.,  congl., 
and   coal   beds. 

The  change  in  constitution  of  the  rock  along  the  east  side  of  the 
Great  Valley  is  taken  as  a  good  boundary  between  the  Valley  and  Ridge 
and  Blue  Ridge  provinces  by  King  (1950a). 

Intrusive  igneous  rocks  are  almost  entirely  absent  in  the  Valley  and 
Ridge  province,  and  hence  no  metamorphism  incident  to  heat  and 
volatiles  is  known. 


BLUE  RIDGE  PROVINCE 

Divisions 

In  the  Blue  Ridge  and  Piedmont  provinces,  we  are  confronted  with  a 
geology  mostly  of  metamorphic  and  igneous  rocks,  only  in  part  studied 


108 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


€c 


GAYLOR 
RIDGE 


5r   5c 


SIMS 
MTN. 


ROME    THRUST 


HORSE 
MTN. 


SECTION     3 


SECTION     2 

Fig.  8.12.  Upper  cross  section  (No.  3  of  index  map,  Fig.  7.1)  of  Rome  quadrangle,  Georgia  and 
Alabama.  After  Hayes,  1902. 

Lower  cross  section  (No.  2  of  index  map)  of  Birmingham  quadrangle,  Alabama.  After  Butts, 
1910. 

Cr,  Rome  fm.;  €c,  Conasauga  Is.;  Cbr,  Beaver  Is.;  €Ok  and  £sk,  Knox  dolomite;  Oc,  Chicka- 
mauga  Is.;  Sc.  Clinton  ss.  and  sh.;  Sr,  Rockwood  fm.;  Da,  Armuchee  chert;  Cfp,  Fort  Payne  chert; 
Ch,  Floyd  ss.  member;  Cb,  Bangor  Is.;  Cp,  Pennington  sh.;  Cby  and  Cpv,  Pottsville  gr. 

and  understood,  and  with  an  extensive  literature  that  reveals  a  striking 
evolution  of  interpretation. 

The  Blue  Ridge  province  embraces  two  rather  distinct  tectonic  ele- 


ments, about  coincident  with  the  geomorphic  divisions.  Northeastward 
from  the  vicinity  of  French  Broad  River  in  eastern  Tennessee  and  western 
North  Carolina,  the  Blue  Ridge  is  narrow,  whereas  southwestward,  it  is 
broad  and  more  complex.  See  Fig.  8.22. 

Stratigraphy  and  Structure— Potomac  to  the  French  Broad  River 

The  northeastern  division,  where  most  typically  developed  in  northern 
Virginia,  is  composed  of  a  core  of  older  Precambrian  crystalline  base- 
ment rocks  which  are  overlain  and  flanked  by  a  considerable  body  of 
later  Precambrian  metavolcanics  and  metasediments  (Catoctin  green- 
stone and  related  units),  and  by  Lower  Cambrian  clastic  rocks 
(Chilhowee  group).  This  segment  is  known  as  the  Blue  Ridge-Catoctin 
Mountain  anticlinorium. 

The  structure  and  stratigraphy  of  the  north  end  of  the  Blue  Ridge  belt 
of  Fig.  8.22  across  Catoctin  Mountain  and  South  Mountain  is  shown  in 
Fig.  8.23.  This  sction  is  north  of  Harpers  Ferry.  Just  south  of  the  city 
the  structure  across  Short  Hill  and  the  Blue  Ridge  is  given  in  Fig.  8.24. 
Farther  south  in  the  Elkton  area  of  Virginia  a  section  on  the  west  side  of 


GREAT 


VALLEY 


BLUE 


RIDGE 


Pu 
Pine  Mountoin   foult 


MDc    DSu 


Fig.  8.13.  Cross  section  of  folded  and  thrust  faulted  Appalachians  in  eastern  Tennessee.  After 
Rodgers,  1953.  (Section  4.)  Pu,  Pennsylvanian  rocks;  Mp,  Pennington  formation;  Mn,  Newman 
limestone;  Mg,  Grainger  formation;  MDu,  Lower  Mississippian  and  Upper  Devonian  rocks  (Fort 
Payne,  Grainger,  and  Chattanooga  formations);  MDc,  Chattanooga  shale;  MDs,  Basal  Missis- 
sippian and  Devonian  shale;  DSu,  Lower  Devonian  and  Silurian  rocks  (Hancock  limestone,  Rock- 
wood  formation,  and  Clinch  sandstone);  Os,  Sequatchie  formation;  Oj,  Juanita  formation;  Ouc, 
Upper  part  of  Chickamauga  limestone,  including  Reedsville  shale;  Omb,  Martinsburg  shale; 
Olmc,   Lower  and  Middle   parts  of   Chickamauga   limestone,   undivided;   Ob,   Bays  formation;   Oo. 


Ottosee  shale;  Oh,  Holston  formation,  Ol,  Lenoir  limestone;  Oa,  Athens  shale;  Osv,  Sevier 
shale;  OCk,  Knox  dolomite  or  group,  undivided;  Cc,  Conasauga  shale  or  group,  undivided;  Ccu, 
Upper  Cambrian  part  of  Conasauga  group;  €hk,  Monaker  dolomite;  Cr,  Rome  formation;  Ss, 
Shady  dolomite;  Ce,  Erwin  formation  and  equivalent  rocks  (Hesse  sandstone,  Murray  shale,  and 
Nebo  sandstone);  Che,  Hesse  sandstone;  Cnb,  Nebo  sandstone;  Ch,  Hampton  formation;  Cni, 
Nichols  shale;  €u;  Unicoi  formation;  €ch,  Cochrane  conglomerate;  ocu,  Ocoee  series,  undivided; 
ocss,  Sandsuck  shale;  ocsb,  Snowbird  formation;  pCc,   Precambrian  crystalline  complex. 


; 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


109 


:ig.  8.14.  Major  structural  features  of  the  Cumberland  overthrust  block  (upper  map).  Area 
)f  fensters  ruled  and  shown  in  more  detail  in  smaller  map  (lower).  The  area  of  fensters  is  now 
an   oil   field   and   is   known   as  the   Rose    Hill   district.   Reproduced   from   Miller   and    Fuller,    1947. 

the  anticlinorial  belt  is  as  shown  in  Fig.  8.25.  These  recent  interpretations 
of  the  structure  show  no  important  thrusts  along  the  inner  side  of  the 
Blue  Ridge  belt,  but  rather  folded  normal  sequences.  Southward,  espe- 
cially south  of  the  James  River,  reverse  faults  are  numerous  and  thrusting 
Jbecomes  dominant,  as  will  be  seen  in  the  following  discussion  of  the 
Great  Smokies. 

The  old  Precambrian  crystalline  complex  is  composed  of  granite, 
granodiorite,  and  gneiss.  Cutting  through  it  are  basic  dikes  believed  to 
be  feeders  of  the  overlying  basaltic  Catoctin  greenstone.  The  whole 
Catoctin  mass  has  undergone  low-grade  metamorphism,  and  a  slaty  or 


schistose  cleavage  pervades  it,  which  dips  southeastward  as  shown  in  tin- 
sections  just  referred  to.  A  distinct  lineation  occurs  along  the  general 
boundary  of  the  Precambrian  and  Paleozoic  rocks,  and  in  northern  Vir- 
ginia, Maryland,  and  Pennsylvania,  the  cleavage  in  which  the  lineation 
lies  extends  into  the  Beekmantown  beds  according  to  Cloos  ( 1957 )  and 
into  the  Martinsburg  shale  according  to  Nickelsen  (1956).  See  Fig.  8.24. 
Lineation  and  cleavage  is  limited  to  the  Precambrian  from  Roanoke 
southwestward  where  thrusting  has  brought  the  basement  rocks  into 
abrupt  contact  with  the  unaltered  Paleozoic  rocks. 

The  shear  type  of  deformation  accompanied  by  thickening  along  the 
fold  axes  and  thinning  along  the  flanks  is  most  characteristic  of  the  Blue 
Ridge,  and  sets  it  apart  from  the  Valley  and  Ridge  structures. 

Only  one  deformation  has  been  detected  from  the  lineation  north  of 
the  Potomac  River  in  the  South  Mountain  anticlinorium.  Since  the  Pre- 
cambrian Catoctin  greenstone  as  well  as  the  Cambro-Ordovician  lime- 
stones and  shales  of  the  Great  Valley  are  affected  and  since  the  lineation 
is  remarkably  regular  along  the  Blue  Ridge  from  Pennsylvania  to  the 
French  Broad  River  in  North  Carolina,  Cloos  ( 1957)  thinks  that  this  one 
deformation  is  post-Ordovician,  and  therefore  either  Taconian  or  Acadian 
in  age.  These  orogenies  will  be  described  presently. 

Great  Smoky  Mountains 

South  of  the  French  Broad  River  the  Blue  Ridge  belt  loses  its  weltlike 
form,  and  a  broad,  high,  and  geologically  complex  terrane  sets  in.  Along 
the  Tennessee-North  Carolina  boundary  between  the  cities  of  Knoxville 
and  Ashville  are  the  Great  Smoky  Mountains  where  16  peaks  rise  above 
6000  feet.  The  general  expansion  of  the  Blue  Ridge  in  this  region  is  shown 
on  Fig.  8.22,  and  a  geological  map  by  P.  B.  King  is  presented  in  Fig. 
8.26.  A  small-scale  cross  section  is  part  of  Fig.  7.2,  and  a  more  detailed 
section  is  given  in  Fig.  8.27.  Most  of  the  Great  Smokies  is  a  thrust  com- 
plex of  the  Ocoee  Late  Precambrian  series. 

This  is  a  body  of  terrigenous  clastic  sedimentary  rocks,  which  has  minor 
intercalations  of  limestone  and  dolomite  but  no  volcanic  components  or  known 
fossils.  The  series  is  probably  30,000  feet  or  more  thick.  It  lies  unconforniahly 
on  a  basement  of  earlier  Precambrian  granitic  and  gneissic  rocks,  and  on  the 


MIDDLESBORO        SYNCLINE 


-* ROSE      HILL      DISTRICT--- 


CUMBERLAND      MOUNTAIN 
MONOCLINE 


POWELL 


VALLEY        ANTICLINE 


X 

s 


■X. 
<r 
o 


z 

o 
o 

2 

CC 

Q 

V 

>.  Z 

UJ 

2< 

KEN! 
CUMB 
VIRGI 

IT 
O 

2 

"  I  _J 


<  CO 

Z  W 


<E 

UJ 

> 
cc 


o      w 
_i      Q 


4' 

SE. 


Fig.    8.15.      Section    across   Cumberland    overthrust    block    along    line    A-A'    of    Fig.    8.14.    Length 
of    section,    27    miles.    Displacement    along    Pine    Mountain    fault,    5.8    miles.    Reproduced    from 


Miller   and    Fuller,    1947.   Section   line   A-A',   is   line   8   on   index   map   of   Fig.   7.1. 


110 


Fig.  8.16.  Geologic  map  and  section  of  the  area  from  Bristol,  Va.,  to  Mountain  City,  Tenn.  Re- 
produced from  Butts  ef  a/.,  1933.  Section  10  of  index  map,  Fig.  7.1.  Oa,  Athens  shale;  Olm, 
Lenoir,  and  Mosheim  limestones;  Ob,  Beekmantown  dolomite  (Nittany  and  post-Nittany);  Cc,  Cono- 


cocheague  limestone;  Cn,  Nolichucky  shale;  Chk,  Honaker  dolomite;  Cr,  Rome  formation;  Cs, 
Shady  dolomite;  Ce,  Erwin  quartzite;  Cq,  Cambrian  quartzite  and  shale,  undifferentiated;  gr, 
Precambrian  granite. 


Ill 


LITTLE 
MTN. 


WARM 

SPRINGS 

MTN. 


LITTLE 
MARE 
MTM 


Offset 


MILL 
MTN. 


SECTION    15 


SECTION     13 


READ    MTN 
FENSTER 


^/SjAj  _  fht 


xO 


& 


cj 


<     Pa/aski  thrust e$        *      ^  .      A$> 


&    V 


SECTION       12 


Fig.   8.17.      Sections    in    the   folded    and    thrust-faulted    Appalachians   of   western    Virginia,    after 
Butts  ef   a/.,   1933.   Section    15   is  from   Warm   Springs  to   Goshen;   Section    13   is  through    Hollins 


College;  and  Section  12  is  through  Newport  and  Christiansburg.  See  index  map.  Fig.  7.1. 


112 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


113 


JP      MONTEREY 
<?^°  MTN. 


fY  £&_ 


/. 


5  to 


SECTION      16 


Dph 


5HENAND0AH 

MTN. 

Dch 


Dck 


/O    MIL  £5 


BLUE 

RIDGE 


V  C 


i>> 


BRUSHY 
MTN. 

5cc 


SECTION     14 


BIG  LITTLE 

HOUSE        HOUSE" 

MTN.  MTN. 

Sec 


Oc    Om 


Fig.  8.18.  Section  in  the  folded  and  thrust-faulted  Appalachians  of  west-central  Virginia,  after  Butts  et  a/., 
1933.  Section  14  runs  through  Lexington  and  Section  16  from  the  West  Virginia  line  to  Waynesboro  and 
Afton.  See  index  map,  Fig.  7.1. 


northwest  side  of  the  mountains  it  is  overlain  by  the  Cochran  formation,  or  basal 
unit  of  the  Chilhowee  group,  which  is  of  Cambrian  and  Precambrian  (?)  age. 
South  of  the  mountains  it  is  overlain  by  rocks  of  the  Murphy  marble  belt;  here, 
the  top  of  the  Ocoee  is  placed  tentatively  at  the  base  of  the  Nantahala  slate. 
The  Ocoee  series  is  divisible  into  three  broad  units  of  regional  extent  and 
contrasting  lithologic  character,  which  are  herewith  designated  groups  and 
named  the  Snowbird  group,  the  Great  Smoky  group,  and  the  Walden  Creek 
group.  The  groups  consist  of  local  intergrading  and  intertonguing  formations 
and  have  complex  stratigraphic  and  structural  relations.  The  Ocoee  series  is 
split  by  major  thrust  faults  into  three  sequences,  a  southern,  central,  and 
northern,  none  of  which  contains  more  than  two  groups  of  the  series  (King 
etal.,1958). 

The  west  front  of  the  Great  Smokies  and  the  Blue  Ridge  belt  south- 
westwardly  is  characterized  by  great  folded  thrusts,  described  in  part 
under  the  previous  Valley  and  Ridge  province.  Where  the  overridden 
rocks  are  exposed  as  re-entrants  or  windows  and  composed  of  limestone 
or  dolomite,  they  form  "coves"  or  valleys  lying  within  the  mountains  of 


*; 

3'MENANDOAM     VALLEY 

o^cy-c/  ooob'  .-..osX. 

T)m 

MASSANUTTEN 

.  Dohl 

MOUNTAIN 

Dr 

-V\               1 

BURKETOWN 


0a   Oh 


.5"  M/lES 


Fig.  8.19.  Sections  in  the  folded  and  thrust-faulted  Appalachians  of  Virginia.  After  Butts  et  at., 
1933.  Section  17  is  about  10  miles  north  of  Staunton,  and  Section  18  is  10  miles  north  of 
Shenandoah  Caverns.  See  index  map,   Fig.  7.1. 


114 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


w. 


ALLEGHENY         PLATEAU 

Fr°si^urgJMd^'coa/ measures  " 


ALLEGHENY 
FRONT 

\3I 


Corriganville 

DEVILS 
BACKBONE 
0/~!         WILLS 
JO'       MOUNTAIN 


IRON  ORE 
RIDGE 

Flintstone 


RAGGED 
MOUNTAIN 
POLISH 
MOUNTAIN 


SIDELING 
HILL 

•pg  j  Roconoss. 
"***■  """rboniferous) 


CACAPON 
_-.,-,.,.,...       MOUNTAIN  F 

RIDGE  ANTICLINE  t" 

oei  C/osely  folded       Hanco^ 


U.  MILES 


Fig.   8.20.      Section   from   Allegheny   plateau   to   Cacapon   Mountain   anticline   at    Hancock,   Md.   Reproduced 
from   Butts  et  a/.,   1933.   Section  21    of  index   map,   Fig.  7.1. 


granitic  or  clastic  rocks.  One  of  the  windows,  such  as  that  containing 
Grandfather  Mountain,  North  Carolina,  lies  35  miles  southeast  of  the 
northwest  boundary  of  the  Rlue  Ridge  province  (King,  1951). 

PIEDMONT  PROVINCE 

Principal  Foliate  Rocks 

The  most  voluminous  rocks  in  the  crystalline  Piedmont  of  Penn- 
sylvania, Maryland,  and  Virginia  is  a  great  schist  series  which  exhibits 
in  part  high-grade  metamorphism  (Jonas,  1932).  It  contains  in  places 
various  metavolcanics.  In  Cecil  and  Harford  counties,  Maryland,  a 
volcanic  sequence  well  described  by  Marshall  (1937)  shows  considerable 
variation,  grading  from  massive  amygdaloids  and  even-textured  volcanics 


through  schistose  amygdaloids  to  fine-grained  hornblende  schists  which 
in  places  are  indistinguishable  from  sheared  gabbro  except  by  micro- 
scopic examination.  Several  bodies  of  mylonitized  granite  in  the  schist 
series  have  been  recognized. 

The  most  troublesome  and  yet  unsolved  problem  is  the  age  of  the 
schist.  It  has  been  correlated  with  the  Glenarm  series  of  Pennsylvania 
and  Maryland,  and  to  this  most  authorities  agree;  but  the  age  of  the 
Glenarm  is  not  yet  known.  It  is  generally  believed  to  be  late  Precambrian 
or  early  Paleozoic. 

A  few  anticlines  and  domes  of  older  rocks,  the  Raltimore  gneiss,  are 
found  within  the  schist  series,  in  Maryland  and  Pennsylvania,  and  pre- 
sumably others  occur  in  Virginia. 

The  Piedmont  and  eastern  part  of  the  Blue  Ridge  in  North  and  South 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


115 


Carolina  consists  of  a  complex  of  contorted  gneisses,  containing  granite 
plutons  and  satellitic  offshoots,  swarms  of  small  ultrabasic  intrusives,  and 
narrow  zones  of  metasedimentary  rocks.  The  boundary  of  the  Piedmont 
and  Rlue  Ridge  provinces  is  here  indistinct  on  the  basis  of  bedrock 
geology.  The  dominant  unit  of  this  complex  is  the  Carolina  gneiss.  It 
consists  of  quartz,  feldspar,  mica,  gneiss,  and  hornblende  gneiss  and  these 
are  considered  to  be  originally  sedimentary  and  volcanic  rocks  but  altered 
incident  to  the  batholithic  intrusions.  King  (1951)  points  out  that  no 
clear  break  exists  between  the  gneiss  complex  and  the  Ocoee  and  Tal- 
ladega series  in  the  Great  Smokies  to  the  northwest,  and  a  considerable 


part  of  it  may  be  a  highly  altered  phase  of  these   late   Precambrian 
geosynclinal  deposits. 

Metamorphism 

As  noted  by  King  (1951,  1959)  the  metamorphism  increases  progres- 
sively southeastward  from  the  Great  Valley  across  the  Blue  Ridge,  into 
the  Piedmont  province,  and  climaxes  with  the  development  of  silimanite 
in  the  central  part  of  the  Piedmont  between  the  Brevard  and  Kin-js 
Mountain  belts  (see  Fig.  7.2).  Southeast  of  the  silimanite  zone  the  meta- 
morphism is  less  intense.  The  belt  of  decreased  metamorphism  is  marked 


: 


T  r  i  a  s  s  i  c        Lowland     province 

HookMfn.            Wafchun?  Mb.  Palisades 
Schooley p  e  n  e  p I 


Manha  tt  a  n     prong 
New  England  Upland  prov. 

Ma  nhattan     island 


Coastal  Plain  province 
Long    Island 


/./:>  -,V^  .C .  R  Y    $  T  A  L-  LI    N  *E ..  R  '0   C   K  vS£.W-«^}£/r>^ 


Miles 


KITTATINNY   MOUNTAIN 
St 


GODFREY    RIDGE 


Brodhead 


SECTION    30 


J  M.le 


Fig.  8.21.  Upper  section  across  Triassic  basin  and  Manhattan  Island  to  Long  Island,  N.  Y.  Re- 
produced from  Johnson  ef  a/.,  1933.  No.  31,  Fig.  7.1.  Lower  section  through  Delaware  Water 
Gap.    Johnson    et    a/.,    1933,    after    Willard.    Om,    Martinsburg    shale;    St.    Tuscarora     ss.;    Scl, 


Clinton   ss.;   Shf,   High   Falls  sh.;   Spi,   Paxono   Island   sh.;   Dhb,   Helderberg   Is.;   Do,   Onondago  ss.; 
De,    Esopuc   grit;    Don,    Onondago    Is.;    Dm,    Marcellus   shale;    Dh,    Hamilton    ss.    No.   26,    Fig.    7.1. 


YOUNGER  THAN 
CHILHOWEE 

Poleozoic 


CHILHOWEE 
GROUP 
Lower 

Combnan 


MURPHY  MARBLE  CATOCTIN 

BELT  GREENSTONE 

Age  Lote 


OCOEE  SERIES 
Pre-Catoctin, 


CRYSTALLINE 
COMPLEX 

Early 


V  GRANITE    INTRUDED 

\     INTO    OCOEE    SERIES 


Myc  luic  r  r  c     ^u  iui*i  in,  t_uiiy 

uncertain Precambrian       Late  Precambnon    Precombnan 


X 


Paleozoic  ? 


Lynchburg    James  R 
0 


100 


\'\  Washing- 


Fig.  8.22.  The  Blue  Ridge  province  from  Georgia  to  Pennsylvania  showing  principally  the 
Lower  Cambrian  clastic  group  (Chilhowee)  and  the  Late  Precambrian  Catoctin  greenstone  and 
Ocoee    series    The    Catoctin    greenstone    includes    volcanics    and    sediments   of    Mt.    Rogers    area. 


After    P.    B.    King    (1949).    E.R.,    Elk    Ridge;    S.M.,    South    Mountain;    S.H.,    Short    Hill;    I.M.,    Iron 
Mountain 


Catoc+in  Mta 


10      MILES 


Fig.    8.23.      Change    from    open    to    close    folding    along    east    side    of    Great    Valley,    in    vicinity 
of  South  Mountain,  Md.  After  P.   B.   King,   1950a.  pCv,  volcanic  rocks;  Cc,   Lower  Cambrian   Chil- 


howee    gr.;    COl,     Cambrian     and     Ordovician     Is.,     dol.,     and     some     sh.;     Ordovician     shade. 
See   Fig.   8.22. 


SOUTHERN  AND  CENTRAL  APPALACHIANS 
Osp  Om\      Osp 


Oc  V 
OpsUsP  QrrV 


117 


Mm 


Orr 


MMk 


Os    ». 


\ 


0€c 


Os         Orr 


0€c 


mm« 


a\\\ 


Os 


0€c  0€c 

GREAT     VALLEY,      MARYLAND 


AFTER  SANDO,  1957 


0 

i— 


I 


2 
i 


3   Miles 


BLUE  RIDGE 


BLUE    RIDGE,    LOUDOUN  COUNTY,  VIRGINIA 


SHORT  HILL 
€wu  €wm  €wl 


AFTER   NICKELSEN,I956 


Fig.  8.24.  The  Great  Valley  (Shenandoah)  and  Blue  Ridge  in  Maryland  and  northern  Virginia. 
For  location  see  Fig.  8.22.  Om,  Martinsburg  shale;  Oc,  Chambersburg  limestone;  Osp,  St.  Paul 
group  (limestone);  Ops,  Pinesburg  Station  dolomite;  Orr,  Rockdale  Run  formation;  Os,  Stonehenge 

chiefly  by  the  Carolina  slate  belt,  which  extends  from  Virginia  through 
the  Carolinas  into  Georgia  (see  Fig.  7.1).  Its  rocks  are  slates,  graywackes, 
pyroclastics,  and  lavas,  which  are  only  moderately  folded  or  meta- 
morphosed except  near  some  granitic  body.  Still  farther  southwest  in 


limestone;  OCs,  Conococheague  formation;  Cc,  Tomstown  formation;  Ca,  Antietam  quartzite;  €h. 
Harpers  formation;  €wu,  €wm,  and  Cwl,  Weverton  quartzite;  CI,  Loudon  formation;  pCc,  Catoctin 
metabasalt;  p€sr,  Swift  Run  phyllite;  pCg,  gneissic  basement. 

southwestern  Georgia  and  southeastern  Alabama  is  the  smaller  Pine 
Mountain  belt  of  quartzite,  marble,  and  schist.  The  age  of  the  rorks 
of  both  the  Carolina  slate  belt  and  Pine  Mountain  belt  is  unknown,  but 
recent  workers  are  inclined  to  think  they  may  be  early  Paleozoic  and 


118 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Cambrian      ,  •''     ,. 

aol    v  /s      /    Ch.lho^ee   gr 


Chilhowee  gr 


I  oudoun  fm 
c°TocTin       ~~       '9reer>srone 


Fig.   8.25.      Blue   Ridge   near   Elkton,   Va.   After   P.   B.   King,    1950b. 

somewhat    metamorphosed    during    the    later    Taconian    or    Acadian 


Batholiths 

A  number  of  plutons,  most  of  batholithic  proportions,  occur  in  the 
Piedmont  province.  Their  distribution  is  shown  on  the  Tectonic  Map  of 
the  United  States,  on  the  Geologic  Map  of  the  United  States,  and  on  the 
Geologic  Map  of  North  America.  Major  differences  in  distribution  appear 
on  the  three  maps;  the  later  one  shows  a  far  less  extent  of  the  plutons  in 
South  Carolina  and  Georgia  than  the  earlier  one.  According  to  Keith 
(1923)  most  of  the  plutons  are  granite  and  are  little  deformed  or  non- 
deformed.  According  to  Jonas  (1932)  the  Petersburg  granite  of  Virginia 
is  not  deformed;  it  cuts  across  older  structures  without  disturbing  them 
and  enters  the  rock  by  replacing  those  already  there. 

The  plutons  are  known  today,  however,  to  be  both  concordant  and 
discordant.  The  former  are  foliated,  and  in  the  older  reports  are  con- 
sidered early  Precambrian.  The  more  or  less  discordant  plutons  are  the 
massive  ones,  and  according  to  the  older  reports  ( Keith,  1923,  and  others) 
are  of  late  Paleozoic  age  and  associated  in  time  with  the  folding  and 
thrusting  of  the  Valley  and  Ridge  province.  The  separation  into  two 
vastly  different  time  groups  is  now  held  to  be  unwarranted  for  two 
reasons:  (1)  A  similar  complex  is  well-worked  out  in  New  England 
(Chapter  11),  and  on  the  basis  of  fossils  and  stratigraphic  succession  the 
intrusions  range  in  age  from  Late  Ordovician  to  Carboniferous;  (2) 
isotope  age  determinations  now  date  the  intrusions  as  Paleozoic.  It  seems 
probable  that  the  metamorphism  of  the  Blue  Ridge  and  crystalline  Pied- 
mont developed  progressively  during  Paleozoic  time  as  a  result  of 
orogeny,  possibly  several  phases  of  orogeny.  The  silimanite  schist  and 


gneiss  zone  of  the  inner  Piedmont  evolved  as  a  result  of  the  invasion 
of  the  vast  granitic  plutons. 

Structure  of  the  Piedmont 

From  within  the  central  metamorphic  and  plutonic  belt  northwestward 
to  the  Great  Valley  nearly  all  the  faults,  folds,  and  cleavage  are  steeply 
inclined  but  have  a  northwestward  asymmetry;  i.e.,  the  fault  planes,  fold 
axial  planes,  and  cleavage  planes  dip  to  the  southeast.  Toward  the 
Coastal  Plain  a  tendency  is  noted  for  the  opposite  asymmetry.  The 
northwest  asymmetry  of  the  inner  zone  (Fig.  7.2)  is  more  one  of  folia- 
tion than  major  displacement  along  a  few  discrete  faults,  with  relatively 
slight  movement  along  an  infinite  succession  of  foliation  planes  ( Bloomer, 
1950). 


-J L 


Fig.  8.26.  Geologic  map  of  Greaf  Smoky  AAountains  and  vicinity.  After  King  ef  a/.,  1958.  A, 
Early  Precambrian  granitic  and  gneissic  rocks;  b,c,d,e,  groups  of  the  Ocoee  series  (later 
Precambrian);  P.  Chiihowee  group  (Cambrian  and  Precambrian(?));  h,  Mississippian,  Ordovician, 
and   Cambrian    rocks. 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


119 


ENGLISH     MTN 

Chilhowee  gr 
v\   ^ Cochron      SonasucA 


GftEAT    SMOKY     PITS     (COST    END) 


SECTION    5A 


Fig.  8.27.  Northeast  part  of  Great  Smoky  Mountains  and  adjacent  foothills  on  north. 
After  P.  B.  King,  1950a.  The  Great  Smoky  conglomerate,  the  Nantahala  slate,  the  Pigeon 
siltstone,  and  the  Sandsuck  shale,  are  part  of  the  Ocoee  series  (Late  Precambrian)  which 
forms  most  of  the  Great  Smokies.  The  Cochran  conglomerate  is  basal  Cambrian.  For  location 
see  Fig.  8.22. 

Infolded  Belts  of  Metasedimentary  Rocks 

Besides  the  gneisses,  the  metamorphic  and  plutonic  belt  contains  other 
metamorphic  rocks  that  are  clearly  of  sedimentary  origin.  These  characteristi- 
cally form  narrow  belts  or  bands  of  considerable  linear  extent.  The  principal 
belts  of  metasedimentary  rocks  are: 

1.  The  Arvonia  slate  belt,  near  the  James  River,  and  the  Quantico  slate  belt, 
near  the  Potomac  River,  in  Virginia.  These  are  synclines  of  fossiliferous  Ordovi- 
cian  rocks,  lying  uncomformably  on  older  schists  and  granites. 

2.  A  belt  of  quartzite,  schist,  and  marble  in  North  and  South  Carolina,  which 
has  been  mapped  by  Keith  (1931)  in  the  Kings  Mountain  area.  Further  details 
have  been  given  by  Kesler  (1944),  whose  interpretations  differ  from  those  of 
Keith. 

3.  The  Brevard  schist  belt  [Figs.  7.1  and  8.30],  which  is  by  far  the  longest, 
and  extends  from  central  North  Carolina  through  South  Carolina,  Georgia,  and 
Alabama  to  the  Gulf  Coastal  Plain.  Jonas  (1932)  states  that  similar  rocks  con- 
tinue northeastward  from  central  North  Carolina  into  southern  Virginia.  The 
rocks  of  the  Brevard  belt  consist  of  contorted  dark  slates  and  schists,  with 
lenses  of  limestones,  apparently  of  a  somewhat  lower  grade  of  metamorphism 
than  the  rocks  which  flank  them  on  either  side. 

4.  The   Murphy  marble   belt   of   western   North   Carolina    and   Northwest 
'■  Georgia  (Fig.  8.22),  has  many  features  similar  to  the  others  just  described,  but 

differs  in  that  it  is  not  flanked  by  crystalline  rocks,  but  by  altered  sedimentary 
i  rocks  of  the  Ocoee  series. 

No  fossils  have  been  found  in  the  belts  south  of  Virginia  and  the  age  of  the 
!  rocks  which  compose  them  is  unknown.  They  have  been  variously  assigned  to 

the  Paleozoic  and  the  Precambrian  (King,  1950a). 

Carolina  Slate  Belt 

In  the  southeast  part  of  the  Piedmont  province,  highly  metamorphosed 
rocks  give  place  to  less  metamorphosed  sedimentary  and  volcanic  rocks 
which  make  up  the  Carolina  slate  belt  (Fig.  7.1).  Granite  intrusions  are 


present,  but  they  appear  to  be  small  and  widely  scattered  and  also  cross- 
cutting  rather  than  concordant.  The  most  extensive  rock  unit  is  the 
"volcanic  series."  It  is  composed  of  flows,  breccias,  and  bedded  tuffs  of 
volcanic  origin  with  some  interbedded  slates  and  sandstones.  To  the 
southwest  in  southwestern  Georgia  and  northeastern  Alabama  is  the 
shorter  and  narrower  Pine  Mountain  belt.  It  is  composed  of  quartzite, 
marble,  and  schist  clearly  of  sedimentary  origin  and  intruded  bv  a 
gneissic  granite.  The  beds  are  broadly  rather  than  steeply  folded.  The 
age  of  both  the  rocks  of  the  Carolina  slate  belt  and  the  Pine  Mountain 
belt  is  uncertain;  they  have  been  assigned  to  both  the  Precambrian  and 
Paleozoic. 

Paleozoic  of  Florida 

Within  the  area  embracing  northern  Florida  and  adjacent  parts  of 
southern  Alabama  and  Georgia,  recent  drilling  has  shown  that  the  Meso- 
zoic  rocks  are  underlain  by  volcanic  rocks  and  by  sedimentary  rocks  of 
Paleozoic  age  (Applin,  1949). 

In  the  Ocala  uplift,  pre-Mesozoic  rocks  are  reached  in  places  at  depths 
of  less  than  4000  feet,  but  elsewhere  they  may  lie  as  much  as  10,000 
feet  below  the  surface.  Penetration  of  the  pre-Mesozoic  rocks  has  not 
been  sufficient  to  establish  a  sequence;  in  other  words,  different  rock 
types  have  been  found  in  different  wells,  but  have  not  been  found  in 
superposition. 

The  sedimentary  rocks  are  mainly  sandstones  and  shales.  Some  of  the 
sandstones  contain  worm  tubes  of  Scolithus  type,  not  unlike  those  found 
in  the  older  Paleozoic  rocks  of  the  Appalachians;  others  contain  large 
quantities  of  detrital  mica.  The  shales  are  gray,  black,  and  even  red. 
Graptolites  have  been  found  in  places,  as  well  as  various  other  fossils. 
The  only  Paleozoic  systems  whose  existence  has  been  definitely  proved 
paleontologically  are  the  Ordovician  and  Silurian,  although  others  might 
be  present.  The  volcanics  may  be  related  to  the  "volcanic  series"  of  the 
southeast  part  of  the  Piedmont  area,  but  like  this  series,  their  age  has 
not  been  established. 

Well  cores  show  that  these  rocks  are  little  deformed.  Metamorphic 
effects,  such  as  cleavage  and  recrystallization,  are  lacking.  Bedding  dips 


120 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Fig.   8.28.      Serpentine   belt  of  the  Appalachians.   By   H.   H.   Hess,    Princeton   University;   and   pub- 
lished with   his  permission.  Circles   represent  known   bodies  of  serpentine. 


at  low  angles;  in  some  places  the  strata  are  flat,  and  the  maximum  in- 
clination is  25°  to  30°.  Drilling  is  too  widely  spaced  to  permit  determina- 
tion of  more  than  the  gross  structural  pattern.  As  the  rocks  have  been 
encountered  over  an  extensive  area,  even  these  low  dips  would  be  suffi- 
cient to  account  for  a  sedimentary  and  volcanic  sequence  of  considerable 
thickness. 

These  discoveries  are  of  great  interest,  as  they  show  that  southeast  of 
the  Appalachian  system  there  is  a  foreland  or  shelf  of  little  deformed 
rocks,  just  as  there  is  northwest  of  it. 

Ultrabasic  Intrusives 

Hess  ( 1937a )  has  charted  the  serpentinized  ultramafic  intrusives  of  the 
Appalachians  and  finds  they  form  a  narrow  belt  lengthwise  of  the  Pied- 
mont crystalline  province  through  New  England  to  Quebec  City,  thence 
through  the  Taconic  and  Acadian  belt  of  Quebec  to  the  Gaspe  Peninsula, 
and  again  in  a  belt  through  Newfoundland.  See  the  map  of  Fig.  8.28.  In 
his  work  in  the  Greater  and  Lesser  Antilles,  he  has  concluded  on  the  basis 
of  considerable  evidence  (see  Chapter  42)  that  the  serpentines  occur  in 
the  arcuate,  highly  deformed,  orogenic  belt,  and  as  a  conclusion,  that  in 
certain  ancient  orogenic  belts,  now  obscured  by  metamorphism  and 
blanketing  deposits,  they  can  be  taken  to  indicate  the  position  of  the 
zone  of  maximum  orogeny.  The  serpentinites  are  chiefly  associated  with 
the  Taconian  orogenic  belt  in  New  England  and  the  Maritime  Provinces, 
and  they  are  strong  evidence,  it  seems  to  Hess,  that  the  core  of  the 
Taconian  orogeny  stretched  through  the  crystalline  Piedmont  of  the 
southern  and  central  Appalachians. 

Resides  the  granite  plutons,  the  metamorphic  and  plutonic  belt  con- 
tains a  group  of  intrusives  of  ultrabasic  composition — peridotites,  dunites, 
pyroxenites,  and  others,  now  in  part  altered  to  serpentine.  Unlike  the 
granites,  they  mostly  occupy  small  areas,  but  in  many  places  they  form 
well-defined  zones,  indicating  that  they  were  intruded  under  the  in- 
fluence of  some  sort  of  tectonic  control.  The  most  prominent  zone  lies 
toward  the  northwest  edge  of  the  metamorphic  and  plutonic  belt,  in  the 
southeast  part  of  the  Rlue  Ridge  province  of  western  North  Carolina;  it 
continues  northeastward  into  Virginia,  and  southwestward  into  Georgia. 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


121 


i 


j  Fig.  8.29.  Map  of  part  of  the  Blue  Ridge  and  Piedmont  provinces  of  western  North  Carolina, 
|  showing  the  distribution  of  ultrabasic  igneous  rocks.  After  P.  B.  King,  1950a.  Stippled  areas 
I  are  those  of  sedimentary  rocks,  mainly  Paleozoic,  but  including  the  Ocoee  series,  probably   Pre- 

Other  less  well-defined  groups  of  intrusives  occur  toward  the  southwest 

edge  of  the  metamorphic  and  plutonic  belt,  as  near  the  inner  margin  of 
1  the  Coastal  Plain  in  Georgia.  The  age  of  the  ultrabasic  intrusives  in  the 

southern  Appalachians  is  unknown.  Pratt  and  Lewis,  on  very  tenuous 
f  evidence,  conclude  that  they  are  of  older  Paleozoic  age  (King,  1950b). 

See  Fig.  8.29. 

J  Crystallines  of  Maryland  and  Southern  Pennsylvania 

The  Piedmont  of  Maryland  and  southern  Pennsylvania  merits  special 
j  attention  because  of  the  considerable  detailed  work  done  there  by  Ernst 


Cambrian,  and  Brevard  schist  of  unknown  age.  Blank  areas  east  of,  and  within,  stippled  area 
are  those  of  gneiss  and  schist  with  bodies  of  intrusive  granite.  Small  black  areas  are  ultra- 
basic   igneous  rocks.   Heavy   lines   are   faults.   After   P.   B.   King,    1950a. 

Cloos,  students,  and  colleagues.  Cloos  (1953)  has  divided  the  region  into 
twelve  divisions  or  zones,  the  first  being  the  Coastal  Plain.  See  map, 
Fig.  8.30.  The  second  division  is  the  belt  of  most  intense  metamorphism 
of  the  Piedmont  province  (Wasserburg  ct  ol,  1957)  and  contains  a 
number  of  gneiss  domes.  Six  of  these  are  in  the  vicinity  of  Baltimore  and 
their  cores  are  made  up  of  gneiss  and  migmatite  (Baltimore  gneiss) 
which  are  mantled  by  the  metasedimcnts  of  the  Glenarm  series  (Tilton 
et  at,  1958).  The  lowest  formation  of  the  Glenarm  is  the  Setters  quartzitc, 
the  next  above  the  Cockeysville  marble,  and  the  last  the  Wissahickon 


Fig.  8.30.      Tectonic  map  of  Maryland  and   southern   Pennsylvania.   Reproduced   from   Cloos,    1953. 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


123 


schist.  Granitic  stocks  and  pegmatite  dikes  cut  the  domes  and  meta- 
sedimentary  mantle. 

Foliation  in  the  Baltimore  gneiss  parallels  the  contact  with  the  mantle 
and  arches  over  the  domes  in  asymmetrical  form  with  the  steep  flanks 
to  the  southeast.  Lineation  appears  like  raindrops  running  off  an  umbrella 
(Cloos,  1953). 

The  Baltimore  gneiss  has  been  considered  Precambrian  in  age  and 
possibly  as  old  as  any  rock  in  the  Piedmont.  The  Glenarm  sediments  are 
thought  to  have  been  deposited  in  late  Precambrian  or  early  Paleozoic 
time  unconformably  upon  the  gneiss.  It  is  clear,  however,  that  the  same 
degree  of  metamorphism  pervades  the  overlying  Glenarm  rocks  as  the 
Baltimore  gneiss,  and  since  the  foliation  of  one  parallels  the  other,  it 
has  been  assumed  that  metamorphism  and  doming  of  the  mantle  has 
obliterated  the  original  basement  structures  and  produced  a  new  con- 
cordant foliation. 

If  the  unconformity  existed,  two  periods  of  tectonism  are  implied,  one  prior 
to  Glenarm  sedimentation  and  another  following  it.  If  the  unconformity  did 
not  exist,  a  single  period  of  deformation,  metamorphism,  and  injection  can 
explain  observed  relationships.  All  previous  investigators  of  the  domes  favor 
existence  of  the  unconformity,  but  conclusive  proof  is  lacking  (Tilton  et  al., 
1958). 

The  age  of  the  post-Glenarm  tectonism  is  generally  considered 
Taconian  or  Acadian.  Evidence  bearing  on  this  conclusion  will  be  pre- 
sented later.  The  age  of  the  Precambrian  tectonism  will  also  be  taken 
up  later. 

The  third  division  of  the  Piedmont  shown  on  Fig.  8.26  consists  mostly 
of  the  Glenarm  series  with  generally  horizontal  fold  axes.  Foliation  is 
vertical  on  the  east  border  and  is  inclined  to  the  southeast  on  the  west 
border.  The  fold  axial  planes  dip  to  the  southeast  also.  Metamorphism 
lessens  toward  the  west,  and  mica  schists  become  phyllites;  amphibolites 
become  epidote-  and  chlorite-rich  greenschists. 

The  rocks  of  this  zone  have  not  yet  been  correlated  with  the  fossil- 
bearing  early  Paleozoic  strata  west  of  the  Martic  line.  It  is  possible, 
according  to  Cloos,  that  the  Cambro-Ordovician  limestones  of  the 
westerly  zone  (6)  are  facies  of  the  once  sandy  rocks  of  the  Glenarm. 


Zone  four  encompasses  the  Sugarloaf  structure  which,  as  shown  by 
the  closure  of  the  bedding,  is  an  anticlinal  dome.  The  western  limb  is 
overturned.  Cleavage  confirms  the  domal  structure.  The  rocks  arc  in 
the  chlorite  and  greenschist  facies  of  zone  three.  The  local  phyllites  are 
correlated  with  the  Cambrian  Harpers  phyllite,  and  the  quartzites  which 
are  below  the  Harpers  are  most  likely  the  Lower  Cambrian  Weverton 
quartzite  (Scotford,  1951). 

The  Martic  line  is  called  division  five.  It  was  first  recognized  as  an 
overthrust  in  which  the  then  presumed  older  YVissahickon  schist  was 
thrust  westward  over  the  presumed  younger  Paleozoic  strata,  and  all 
rocks  southeast  of  the  "fault"  were  regarded  as  Precambrian  and  north- 
west of  it  as  Paleozoic.  Careful  work  has  shown  that  the  line  is  not  a 
discrete  plane  of  major  displacement,  but  that  in  most  places  complicated 
conditions  pertain  (Cloos  and  Heitanen,  1941).  It  was  also  presumed 
that  the  Martic  "thrust"  is  a  boundary  between  highly  metamorphosed 
schists  and  little  metamorphosed  Paleozoic  strata.  Cloos  and  Heitanen 
have  demonstrated  that  metamorphism  is  not  restricted  to  the  YVis- 
sahickon schist  but  that  all  rocks  including  the  Cambrian  Antietam  schist, 
Vintage  dolomite,  and  Ordovician  Conestoga  limestone  show  the  same 
intensity  of  metamorphism.  At  one  place  the  sequence  is  repeated  five 
times,  where  the  Conestoga  is  capped  by  the  YVissahickon  schist,  which 
in  several  ways  is  similar  to  the  Antietam.  At  another  place  the  Antietam 
schist  almost  meets  a  spur  of  YVissahickon. 

Along  the  Martic  line  the  fold  axes  are  horizontal  or  plunge  predominantly 
to  the  southwest.  All  folds  are  overturned  southward.  Flow  cleavage  is  an 
axial  plane  cleavage  and  dips  to  the  north.  Bedding  is  intensely  crumpled  and 
at  manv  localities  is  entirely  obscured  by  later  cleavage.  Since  all  members  of 
the  sequence  are  thin  and  underlie  large  areas,  it  can  safely  be  assumed  that 
bedding  is  roughly  parallel  to  the  boundary  planes  and  thus  largely  conform- 
able in  all  members  of  the  sequence  (Cloos  and  Heitanen.  194H. 

Zone  six  consists  mainly  of  Cambro-Ordovician  limestones  which  are 
strongly  cleaved  and  overturned  to  the  west.  The  zone  is  covered  in  large 
part  with  the  Triassic  deposits  (division  seven). 

Zone  eight  is  the  Blue  Ridge  belt  previously  described,  and  cleavage 
and  lineation  extend  northwestward  to  the  position   labeled  "tectonite 


124 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


front."  From  this  line  westward  the  sedimentary  rocks  are  non-tectonites. 
The  other  zones  have  been  described  in  previous  parts  of  this  chapter. 

Age  Determinations  by  Radioactivity 

The  first  isotope  age  determinations  on  the  minerals  of  the  crystalline 
Piedmont  were  published  in  1941  (Goodman  and  Evans),  and  since  then 
methods  and  calculations  have  been  refined,  new  methods  developed, 
and  a  fair  number  of  presumably  reliable  dates  have  been  determined. 

Two  groups  of  ages  are  now  fairly  well  established,  namely,  one 
ranging  from  1000  to  1100  m.y.  and  one  ranging  from  250  to  390  m.y. 
References  to  all  significant  dates  may  be  found  in  recent  publications  by 
Tilton  et  al.  (1958),  Hurley  et  al.  (1958,  1959),  and  Carr  and  Kulp 
( 1957 ) .  An  abstract  by  Kulp  et  al.  ( 1957 )  is  significant  for  ages  in  the 
southern  Piedmont. 

The  older  ages  (1000-1100  m.y.)  come  principally  from  zircon  sub- 

U238      U235      Pb207         ,  Th232 

jected  to  ,  , ,  and analyses. 

Pb206     Pb207     Pb206  Pb208 

Three  of  the  mantled  domes  in  the  Baltimore  area  (zircon  from  the 
Baltimore  gneiss ) ,  two  gneisses  from  Bear  Mountain,  New  York,  a  gneiss 
from  Shenandoah  National  Park,  Virginia,  and  two  gneisses  from 
Hibernia.  New  York,  were  sampled  and  the  zircons  run.  The  results  range 
from  1030  to  1170.  Rubidium-strontium  age  measurements  were  also 
made  on  microcline  from  the  three  Baltimore  gneiss  domes  and  a  value 
is  fixed  for  one  at  1200  plus  100  or  minus  200  m.y.  and  for  another  at 
about  1040  m.y.  It  is  concluded  by  Tilton  et  al.  ( 1958 )  that  the  zircon 
and  microcline  ages  record  a  1000-1100-m.y.  crystallization  in  the  Pied- 
mont. 

Now,  from  the  same  specimens  of  Baltimore  gneiss  from  which  the 

iv                             i_     •     j    i..     •      i.      K40        j    Rb87 
zircon  and  microcline  ages  were  obtained,  biotite  by  and  — 

5  y   A40  Sr87 

analyses  gave  ages  of  305-339  m.y.  For  the  older  and  younger  dates  of 
the  same  rock  two  interpretations  can  be  thought  of: 

(1)  The  gneiss  was  crystallized  or  recrystallized  1000-1100  m.y.  ago  (2) 
The  gneiss  was  originally  a  clastic  sediment  metamorphosed  300-350  m.y.  ago, 


and  the  zircon  and  microcline  were  relict  detrital  grains  eroded  from  a  terrain 
1000-1100  m.y.  old.  The  first  interpretation  is  favored,  chiefly  because  of  the 
non-clastic  character  of  the  microcline  grains.  Their  irregular  shapes,  with  deli- 
cate projections  and  interlocking  contacts  with  other  minerals,  were  clearly 
formed  during  crystallization  of  the  gneiss.  Possible  detrital  origin  for  the 
zircon  cannot  be  excluded,  although  if  this  were  the  case  a  greater  age  than 
that  of  the  microcline  might  be  expected.  It  is  concluded  that  the  microcline 
and  the  zircon  probably  record  a  1000-1100  m.y.  crystallization  in  the  Balti- 
more gneiss,  while  biotite  records  a  second  crystallization  300-350  m.y.  ago.  It 
should  be  noted  that  these  conclusions  allow  either  a  sedimentary  or  igneous 
origin  for  the  gneiss  (Tilton  et  al.,  1958). 

Kulp  et  al.  (1957)  report  a  granite  from  eastern  Georgia  about  250 
m.y.  old.  They  also  give  "apparent  ages"  of  320-370  m.y.  for  the  "meta- 
morphic  series"  in  western  Virginia  and  North  Carolina  as  well  as  the 
pegmatite  swarms  in  the  Spruce  Pine  and  Bryson  City  districts  of  North 
Carolina. 

In  New  England  a  number  of  radioactivity  age  measurements  have 
been  made  on  plutons  where  the  intrusive  relations  to  well-dated  fos- 
siliferous  strata  are  visible,  and  it  is  concluded  that  the  Devonian  period 
began  approximately  400  m.y.  ago  and  ended  slightly  less  than  250  m.y. 
ago.  These  data  will  be  presented  in  Chapter  11  on  New  England.  It 
appears,  therefore,  that  the  recrystallization  and  plutonism  (tectonism) 
in  the  Piedmont  province  ran  its  course  during  the  Devonian  period.  This 
is  younger  than  the  Taconian  orogeny  of  New  England  and  the  Maritime 
provinces  which,  from  angular  unconformities,  is  dated  as  late  Ordo- 
vician.  The  Acadian  orogeny  is  generally  regarded  as  having  occurred 
during  the  upper  half  of  Devonian  time,  so  the  dates  over  300  m.y.  seem 
too  old  for  it,  unless  extended  by  definition. 

SUMMARY  OF  OROGENIC  HISTORY 

The  major  lines  of  evidence  of  orogeny  in  the  Appalachian  mountain 
system  come  from  the  sedimentary  domains,  the  structures  and  structural 
relations,  metamorphism,  plutonism,  and  isotope  age  determinations. 
These  have  all  been  reviewed,  and  now  may  be  integrated  and  the  fol- 
lowing conclusions  reached. 

1.  An  orogeny  occurred  along  the  Atlantic  margin  of  the  United 
States  south  of  New  York  City  in  which  previously  existing  rocks  were 


Fig.  8.31.  Regimen  of  Appalachian  sedi- 
mentation in  the  early  Paleozoic.  Partly  after 
P.  B.  King,  1959. 


:\A:v.: 


APPALACHIAN 
:  STRUCTURAL 
FRONT 


■ORDOVICIAN    CLASTICS 


*2  /  NW  EDGE 

\^      /    OF   BlUE 
\  '   RIDGE   BELT 


SILURIAN   AND  OEVONIAN   CLASTICS 


..APPALACHIAN 
j  STRUCTURAL 
FRONT 


/  NW  EDGE 
/  OF  BLUE 
'    RIDGE   BELT 


Fig.  8.32.  Regimen  of  Appalachian  sedi- 
mentation during  Middle  and  Late  Paleozoic. 
Partly  after  P.  B.  King,  1959. 


SOUTHERN  AND  CENTRAL  APPALACHIANS 


127 


recrystallized  1000-1100  m.y.  ago.  This  correlates  in  time  with  the  Gren- 
ville  orogeny  of  Ontario  and  Quebec. 

2.  The  continental  margin  was  subparallel  with  the  present,  but  may 
have  been  extended  by  a  continental  shelf  and  slope  type  of  deposit  in 
times  following  the  Grenville  orogeny,  particularly  in  Late  Precambrian 
and  Early  Cambrian  time.  This  was  the  time  of  accumulation  of  the 
Ocoee  series  and  the  Chilhowee  group. 

3.  The  Atlantic  margin  of  the  continent  was  beset  with  deformation 
beginning  in  the  last  part  of  early  Ordovician  time,  and  the  previous 
region  of  sedimentation  now  was  elevated  and  became  the  source  land 
of  sediments  to  the  west.  See  Fig.  8.31.  A  great  fan  or  wedge  of  clastic 
sediment  was  spread  northwesterly  from  the  Great  Smoky  region  during 
the  Middle  Ordovician  and  another  one  in  Late  Ordovician  time  in  New 
England.  The  crustal  deformation  must  have  been  mostly  elevatory  at 
this  time  because  the  metamorphic  and  plutonic  activity  occurred  some- 
what later.  The  New  England  clastic  wedge  records  part  of  the  Taconian 
orogeny  as  defined,  but  no  name  has  been  proposed  for  the  Middle 
Ordovician  uplift. 

4.  Clastic  sedimentation  on  a  large  scale  shifted  during  Silurian 
and  Devonian  time  to  New  York,  Pennsylvania,  and  West  Virginia,  and 
another  great  fan  of  sediments  was  deposited  there,  also  derived  from 
uplifted  lands  on  the  east.  See  Fig.  8.32.  The  Silurian  and  Lower  Devo- 
nian elastics  were  not  very  thick,  about  5000  feet,  but  then  a  flood  of 
sediments  reached  10,000  feet  in  thickness  in  late  Devonian  time.  Strong 
compression  and  plutonic  tectonism  started  in  early  Devonian  time,  ac- 
cording to  the  isotope  age  measurements,  but  evidently  high  mountains 
were  not  created  until  the  beginning  of  the  Late  Devonian. 

Figure  8.33  is  an  idealized  section  of  the  southern  Appalachian  system 
and  illustrates  the  central  belt  of  most  profound  Devonian  metamorphism 
and  plutonism.  This,  when  much  eroded,  became  the  crystalline  Pied- 


CUMBERLAND 
PLATEAU 


BlUC  RIDGC  PICDM0NT   PROVINCt 

VALLCY  1  RIDCt  ..tferomorphic   f  flutomc  belt 

\  V.  1  ill  Coro/mo i/ofe 


PROVINCE 


He/t 


ATLANTIC  COAJT- 
al  plain 


Fig.  8.33.  Idealized  cross  section  of  the  southern  Appalachian  Mountains  system.  After  P.  B. 
King,    1950a. 

mont.  The  age  of  the  Carolina  slate  belt  sediments  is  unknown  but  evi- 
dently older  than  the  Devonian  tectonism.  It  may  be  speculated  that  they 
were  a  collateral  eastern  deposit  of  the  Middle  Devonian  clastic  wedge 
on  the  west  of  a  medial  uplift,  but  their  age  must  be  known  first  before 
they  can  be  correctly  fitted  into  the  picture. 

5.  Uplift  of  the  orogenic  belt  was  general  along  its  entire  length 
during  the  Mississippian  and  sediments  were  carried  westward  and  added 
to  the  miogeosyncline.  However,  in  Early  Pennsylvania!!  time  uplift  was 
particularly  great  in  the  southern  Piedmont  and  another  thick  wedge 
accumulated  on  the  west.  Later,  sedimentation  shifted  to  the  West 
Virginia  and  New  York  and  considerable  clastic  material  of  continental 
environment  accumulated  during  Late  Pennsylvanian  and  Permian  time. 

6.  The  eastern  part  of  the  miogeosyncline  including  the  thickest  parts 
of  the  clastic  wedges  and  the  eastern  part  of  the  great  Cambro-Ordovician 
carbonate  sequence  was  then  compressed  and  cast  into  folds  and  thrusts 
as  exemplified  in  the  Valley  and  Ridge  province  of  Fig.  8.33.  The  de- 
formation is  generally  referred  to  as  the  Appalachian  orogeny.  It  may 
have  started  in  Mid-  or  Late  Pennsylvanian  time  in  the  south  but  farther 
north  Valley  and  Ridge  deformation  could  not  have  occurred  until  the 
close  of  Pennsylvanian  time,  and  it  may  not  have  happened  until  near 
the  close  of  the  Permian. 


9. 


site  of  a  large  Triassic  basin,  and  under  the  Bay  of  Fundy  and  along  its 
east  shore  in  Nova  Scotia  another  such  basin  exists.  See  Plate  9. 

The  Triassic  areas  are  generally  sites  of  lowlands  because  the  basin 
beds  have  yielded  to  erosion  more  than  the  adjacent  crystallines.  The 
Triassic  lowlands  is  the  physiographic  name  generally  given  to  the  Penn- 
sylvania-New Jersey  basin.  The  lowlands  are  marked,  however,  by  ridges 
of  trap  rock  that  stand  rather  prominently  above  the  lowland  plain. 


EASTERN  TRIASSIC  BASINS 


DISTRIBUTION  OF  BASINS 

A  series  of  long,  narrow  basins  of  Triassic  deposits  occurs  along  the 
eastern  margin  of  the  continent.  It  will  be  seen  by  reference  to  the  Geo- 
logic Map  of  the  United  States  or  Geologic  Map  of  North  America  that 
the  basins  start  at  the  north  boundary  of  South  Carolina  in  the  Piedmont 
crystalline  province  and  extend  through  North  Carolina,  Virginia,  Mary- 
land, Pennsylvania,  and  New  Jersey  to  the  lower  Hudson  River  Valley  in 
New  York.  The  basin  in  Pennsylvania  and  New  Jersey  is  the  largest  of  any 
in  the  United  States,  and  for  a  distance  between  the  Carlisle  prong  and 
Reading  prong  of  the  Blue  Ridge  element,  it  borders  on  the  Ridge  and 
Valley  province. 

The  Connecticut  River  Valley  in  Connecticut  and  Massachusetts  is  the 


NATURE  OF  TRIASSIC  ROCKS 

General  Character 

The  Triassic  sedimentary  rocks  of  the  eastern  basins  are  chiefly  clastic 
and  dominantly  red.  Fanglomerates,  conglomerates,  sandstones,  arkoses, 
siltstones,  shales,  and  argillites  are  the  common  sedimentary  types.  Much 
basic  magma  has  invaded  the  sediments  and  now  exists  as  thick  sills  and 
long  dikes  of  diabase.  Basalt  flows  from  the  same  magma  are  also  inter- 
calated in  the  shales  and  sandstones.  The  intrusive  rocks  have  commonly 
altered  the  red  sediments  to  blue  or  gray  along  the  contacts  in  zones  50 
to  several  hundred  feet  thick. 

New  Jersey-Pennsylvania-Maryland-Virgina  Basin 

Newark  Group.  The  sediments  of  the  New  Jersey-Pennsylvania-Mary- 
land-Virginia basin  are  known  as  the  Newark  group.  The  basin  has  a 
maximum  width  of  30  miles  and  is  over  300  miles  long.  Part  of  it  is  shown 
in  Fig.  9.1.  The  Newark  group  has  been  classified  in  three  formations,  the 
Stockton,  Lockatong,  and  Brunswick,  the  last-named  being  the  youngest. 
These  subdivisions  are  clearly  separable  along  the  Delaware  River  and 
northeastward  in  New  Jersey,  where  they  were  first  established  and 
named. 

The  Stockton  formation  in  general  comprises  arkosic  sandstone  with 
some  red-brown  sandstone  and  red  shale,  in  irregular  succession  and  pre- 
senting many  local  variations  in  stratigraphy.  It  lies  unconformably  on 
Paleozoic  and  pre-Paleozoic  crystalline  rocks.  The  sandstones  are  in  places 
cross-bedded,  and  the  finer-grained  rocks  exhibit  ripple  marks,  mud 
cracks,  and  raindrop  impressions,  which  indicate  shallow-water  conditions 


128 


EASTERN  TRIASSIC  RASINS 


129 


during  deposition.  The  arkose,  a  sandstone  containing  more  or  less  feld- 
spar or  kaolin  derived  from  granite  or  gneiss,  indicates  proximity  at  the 
time  of  deposition  to  a  shore  of  Precambrian  crystalline  rocks. 

The  Lockatong  formation  consists  chiefly  of  dark-colored  fine-grained 
hard  and  compact  argillaceous  rocks.  Some  beds  are  massive,  and  others 
are  flaggy.  They  show  mud  cracks  and  other  evidences  of  shallow-water 
deposition,  but  their  materials  are  clay  and  very  fine  sand,  some  of  the 
beds  also  contain  carbonaceous  material. 

The  Rrunswick  formation,  in  its  typical  development,  consists  mainly  of 
a  great  thickness  of  soft  red  shale  with  local  and  thin  layers  of  sandstone. 
Northward  and  westward  the  sandstone  increases  in  amount  and  coarse- 
ness. It  overlaps  irregularly  older  Traissic  formations  and  Paleozoic  and 
pre-Paleozoic  formations. 

The  three  formations  are  not  sharply  separated  by  abrupt  changes  of 
material,  but  usually  merge  into  one  another  through  beds  of  passage 
which  appear  to  vary  somewhat  in  thickness  and  possibly  also  in  strati- 
graphic  position  in  different  areas. 

The  thickness  of  the  Stockton  is  estimated  to  range  from  1000  to  3000 
feet,  the  Lockatong  from  1500  to  3000  feet,  and  the  Brunswick  from  12,000 
to  16,000  feet.  The  total  thickness  of  the  Newark  group  as  generally  men- 
tioned is  about  20,000  feet,  but  figures  up  to  35,000  feet  have  been  pro- 
posed. This  great  amount  is  computed  by  the  dip  angle  and  the  distance 
across  dip  of  the  homoclinal  beds,  but  several  writers  have  suggested  the 
possibility  of  duplication  of  certain  beds  by  faulting,  and  hence  that  the 
figure  may  be  excessive.  Stose  and  Stose  ( 1944)  suggest  that  the  beds  over- 
lapped from  east  to  west  in  somewhat  the  manner  shown  in  Fig.  9.2  and 
that  therefore  the  combined  thickness  of  all  the  beds  will  not  be  found  in 
any  one  place.  It  cannot  be  doubted,  however,  that  the  long,  narrow 
troughs  containing  the  Triassic  sediments  are  very  deep,  undoubtedly 
over  10,000  feet,  and  probably  20,000  in  places. 

The  age  of  the  Newark  group  is  probably  Upper  Triassic,  but  the  high- 
est beds  may  be  lowermost  Jurassic.  According  to  Bascom  and  Stose 
(1938), 

A  comparison  of  fossil  plants,  crustaceans,  and  vertebrates  of  the  Newark 
with  simliar  forms  of  the  Jura  and  Trias  of  Europe  establishes  a  correspondence 


»         2*    milCS 


Fig.  9.1.  Triassic  basin  in  western  New  Jersey,  Pennsylvania,  and  Maryland.  Stippled  area, 
Triassic  sedimentary  rocks;  solid  black  areas  and  heavy  black  lines,  Triassic  diabase  sills  and 
dikes;  light  black  lines,  faults.  Reproduced  from  Stose  and  Stose,   1944. 

within  general  limits,  but  a  correlation  of  exact  horizons  is  not  practicable. 

The  Newark  strata  did  not  share  in  the  folding  that  occurred  at  the  end  of 
Carboniferous  time  and  therefore  must  be  of  later  date;  they  are,  however, 
clearly  older  than  the  lowest  Cretaceous  formations,  which  overlap  them  un- 
conformably.  They  are  thus  separated  from  earlier  and  later  deposits  by  inter- 
vals of  upheaval  and  erosion  of  unknown  duration,  but  their  position  in  geo- 
logic history  cannot  be  determined  more  closely  than  by  the  general  correlation 
of  fossils  above  indicated. 

Igneous  Rocks.  The  map  of  Fig.  9.1  shows  the  distribution  of  outcrop- 
ping sills,  lava  flows,  and  dikes  in  the  Newark  group  and  in  adjacent 
rocks  of  the  Piedmont.  The  sills  and  flows  are  confined  to  the  Triassic 
basin,  but  some  of  the  dikes  cross  out  into  the  older  rocks  of  the  Piedmont 
and  persist  for  many  miles.  The  Conshohocken  and  Downington  dikes 


130 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


NW. 


SE. 


A 


Fig.  9.2.  Origin  of  the  Newark  Triassic  basin.  Reproduced  from  Stose  and  Stose,  1944.  The 
sediments  are  postulated  to  have  first  been  derived  almost  entirely  from  the  east.  After  intrusion 
of  the  diabase  dikes  and  sills  and  renewed  faulting,  much  fanglomerate  was  washed  in  from 
the  west. 


are  60  to  70  miles  long,  and  the  Safe  Harbor  dike  extends  an  equal  length 
before  it  is  covered  by  the  Cretaceous  of  the  Coastal  Plain. 

The  largest  sill  in  the  southern  part  of  the  Newark  basin  is  the  Gettys- 
burg, which  is  1800  feet  thick.  Farther  northeast  in  New  Jersey  four 
great  sheets  of  trap  rock  occur  and  form  the  Watchung  Mountains  which 
are  more  prominent  that  the  ridges  of  the  great  Gettysburg  sill.  The  low- 
est of  the  four  sheets  is  intrusive  and  in  places  reaches  a  thickness  of  1000 
feet.  It  forms  the  Palisades  of  the  Hudson.  See  section  31  of  Fig.  8.21. 
Above  the  Palisades  sill  and  separated  from  it  and  each  other  by  several 
hundred  feet  of  intervening  Triassic  shales  are  three  extensive  (buried) 
basalt  flows  which,  from  bottom  to  top,  are  650,  850,  and  350  feet  thick. 

The  dikes  are  believed  to  follow  tension  cracks  which  in  places  become 
faults  and  offset  the  Triassic  beds.  According  to  Stose  and  Stose  ( 1944) 
the  dikes  and  the  normal  faults  that  the  dikes  follow  represent  major  lines 
of  Triassic  fractures.  They  cut  across  older  structural  lines,  which  are 
nearly  at  right  angles  to  them.  Many  of  the  diabase  dikes  originate  in  or 
join  the  diabase  sills  which  are  most  abundant  along  the  northwestern 
part  of  the  basin.  See  map,  Fig.  9.1. 

The  diabase  sills,  with  which  many  of  the  dikes  connect  at  their  northwestern 
ends,  coalesce  to  form  extensive  intrusive  bodies  in  the  northwestern  part  of 
the  Triassic  area  of  Pennsylvania.  The  larger  sills  are  the  Haycock,  Ziegler,  Saint 
Peters,  Yorkhaven,  and  Gettysburg.  They  parallel  the  strike  of  the  sedimentary 
rocks  for  long  distances,  and  then  the  intrusive  body  cuts  across  the  strike  at 
right  angles.  Most  of  these  crosscutting  bodies  extend  to  the  northwestern  edge 
of  the  Triassic  basin  where  they  terminate  against  the  faults  that  form  the 
boundary  of  the  basin.  Each  of  these  intrusive  bodies,  therefore,  has  the  form 
of  a  great  tilted  trough  bounded  on  the  southeast  side  by  the  west-dipping  sills 
and  at  the  ends  by  the  crosscutting  bodies  and  open  at  the  west. 

The  fissures  through  which  the  diabase  entered  the  Triassic  rocks  are  be- 
lieved to  lie  near  the  northwest  edge  of  the  basin  where  the  greatest  amount  of 
progressive  sinking  and  faulting  occurred  during  Triassic  deposition.  The 
rising  magma  broke  through  the  Triassic  beds  near  the  vents  in  the  form  of 
crosscutting  bodies,  and  injected  the  beds  to  the  southeast  in  the  form  of  sills. 
The  magma  extended  still  farther  southeastward  as  dikes  that  followed  vertical 
fractures  in  the  Triassic  sedimentary  rocks  and  continued  into  the  older  under- 
lying rocks  southeast  of  the  limits  of  the  basin  of  Triassic  sedimentation.  Some 
of  these  dikes  in  the  area  southeast  of  the  Triassic  outcrops  may  have  been 
feeders  of  large  diabase  bodies  in  Triassic  sedimentary  rocks  that  are  now  re- 


EASTERN  TRIASSIC  BASINS 


131 


moved  by  erosion,  but  the  evidence  is  not  available  to  support  such  a  view 
(Stose  and  Stose,  1944). 

Border  Conglomerate.  Along  the  northwest  border  of  the  Triassic 
basin  occur  deposits  of  fanglomerate,  generally  called  conglomerate  and 
breccia.  They  make  up  the  "Border  conglomerates."  In  width  of  exposure 
they  range  from  less  than  half  a  mile  to  about  8  miles  and  lie  in  discon- 
tinuous patches  along  the  Precambrian  and  lower  Paleozoic  rocks  of  the 
northwestern  border.  The  largest  area  is  south  of  Reading,  Pennsylvania, 
which  extends  across  the  Gettysburg  (Brunswick)  formation  to  the  New 
Oxford  (Stockton).  Most  of  the  gravel  fragments  were  derived  from 
Lower  Paleozoic  limestones,  dolomites,  sandstones,  and  quartzites,  but 
some  came  from  beds  as  high  as  the  Devonian,  and  some  are  Precambrian 
rocks.  In  one  place  Triassic  basalt  forms  boulders  and  cobbles  in  the 
fanglomerate  (Carlston,  1946). 

The  Border  conglomerate  is  for  the  most  part  of  Brunswick  age,  and  as 
depicted  in  certain  cross  sections  is  the  top  and  youngest  layer  of  the 
Triassic  group.  It  seems  to  lie  unconformably  across  the  older  Triassic 
beds  in  places,  and  in  others  rests  directly  on  the  pre-Triassic.  On  the 
other  hand,  the  conglomerate  beds  pass  into  sandstones  and  shales  and 
are  undoubtedly  mostly  a  northwestward  marginal  facies  of  the  Bruns- 
wick. Even  Border  conglomerate  wedges  have  been  observed  in  the  Stock- 
ton and  Lockatong,  and  although  the  conglomerate  is  chiefly  of  Bruns- 
wick age,  local  bodies  of  it  may  be  of  any  age  within  the  Newark  group 
(McLaughlin,  1931,  1958). 

Although  the  Border  conglomerates  clearly  betray  a  northwest  origin, 
most  of  the  material  washed  into  the  Triassic  basin  is  thought  to  come 
from  the  southeast.  The  reason,  according  to  Stose  and  Bascom  ( 1929 ) 
lies  in  the  composition  of  the  basin  beds.  The  "poorly  assorted  arkosic 
grits,  containing  feldspar  and  mica  derived  from  disintegrating  granitic 
rocks"  were  exposed,  they  believe,  only  in  the  land  southeast  of  the  basin. 
Except  for  a  stretch  of  about  75  miles  in  southeastern  Pennsylvania  to 
which  Stose  and  Bascom  refer  specifically,  the  Triassic  basins  in  the  Pied- 
mont are  bordered  on  both  sides  by  crystalline  rocks  that  could  have  sup- 
plied feldspar  and  mica,  but  the  Paleozoic  pebbles  in  the  border  con- 


glomerate indicate  that  little  Precambrian  was  exposed  on  the  northwest 
at  the  time  of  Triassic  deposition  in  the  southeastern  Pennsylvania  area. 

Deep  River  Basin 

The  Deep  River  basin  is  in  North  Carolina  and  is  generally  regarded 
as  made  up  of  the  Cumnock  basin  on  the  southwest  and  the  Durham 
basin  on  the  northeast.  The  southwestern  basin  is  noted  for  its  Triassic 
coal.  The  deposits  in  these  basins  are  much  like  those  of  the  New  ark  basin 
with  an  abundance  of  gray  arkosic  beds  lensing  into  red  sandstones  and 
shales  and  gray  to  buff  sandstones.  Locally  thin  carbonaceous  shale  beds 
occur.  Conglomerates,  fanglomerates,  and  in  places  landslide  breccias 
mark  the  border  zones,  but  here,  unlike  in  the  Newark  basin,  both  bor- 
ders are  marked  by  the  coarse  deposits.  Thin  conglomerates  with  an  abun- 
dance of  quartz  pebbles  occur  also  in  the  central  areas  (Prouty,  1931). 

The  torrential  fanglomerates  are  more  voluminous  along  the  eastern 
margin  of  the  basin  than  the  west,  which  shows  that  the  eastern  margin 
was  the  steeper  and  that  an  area  of  land  existed  there  as  well  as  on  the 
west. 

Connecticut  Valley  Basin 

The  Triassic  sedimentary  rocks  of  the  Connecticut  Valley  are  all  clastic 
and,  if  anything,  coarser  than  those  in  New  Jersey,  Pennsylvania,  and 
Maryland.  Red  colors  dominate,  and  they  are  also  interlayered  with  trap- 
rock  sheets.  The  basin  is  bordered  in  part  on  both  sides  by  faults,  and  is 
thus  a  graben;  but  the  eastern  fault  is  by  far  the  greatest  and  is  known  as 
the  Great  Fault.  All  beds  dip  generally  eastward  into  it,  as  the  beds  dip 
generally  westward  into  the  border  fault  of  the  Newark  basin.  See  map 
of  Fig.  9.3.  The  Great  Fault  has  a  throw  estimated  variously  between 
17,000  and  35,000  feet,  but  the  basin  beds  and  floor  have  not  been  re- 
garded in  the  same  way  as  Bascom  and  Stose  conceived  the  structure  of 
the  Newark  basin.  As  diagrammed  in  the  cross  sections  of  Fig.  9.4  the 
throw  would  be  of  the  great  magnitude  mentioned,  but  if  diagrammed  as 
it  is  in  Fig.  9.2,  the  displacement  would  be  much  less. 

According  to  Krynine  (1941a)  the  wedge  of  sediments  is  built  of  coa- 


132 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


EXPLANATION 


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Fig.    9.3.     Triassic    basin    of   Connecticut   and    Massachusetts.    Reproduced    from    Longwell,    1933. 


Fig.    9.4.      Generalized    east-west   sections    across    the    Triassic    basin    in    Connecticut   and    Massa- 
chusetts. Somewhat  modified  after   Longwell,   1933. 

lescing  alluvial  fans  that  radiate  westward  from  the  Great  Fault  and  thin 
from  16,000  to  1500  feet  in  some  32  miles. 

The  stratigraphic  units  are  (1)  Lower:  New  Haven  arkose,  up  to  8550  feet, 
relatively  coarse  fluvial  gray  and  pink  arkoses,  conglomerates,  red  feldspathic 
sandstones,  and  subordinate  red  siltstones  and  shales;  (2)  Middle:  Meriden 
formation,  up  to  2800  feet,  fine-grained  lacustrine  and  paludial  variegated  and 
dark  siltstones,  shales,  limestones,  light  feldspathic  sandstones,  subordinate 
coarse  elastics,  and  three  basaltic  lava  flows;  (3)  Upper:  Pordand  formation, 
up  to  4000  feet,  fluvial  deposit  similar  to  New  Haven. 

Conglomerates  form  10%,  sandstones  64%,  siltstones  and  shales  25%,  red 
color  is  present  in  52%.  Near  the  Great  Fault  sediments  pass  into  fanglomerates. 

Two  main  groups  of  alluvial  fans  are  present:  Central  Connecticut  (indicolite 
and  little  epidote)  and  Southern  Connecticut  (no  indicolite,  much  epidote). 
Almost  all  the  sedimentary  detritus  is  derived  from  a  source  area  only  5  to  10 
miles  wide  east  of  the  steep,  moderately  high  Great  Fault,  whose  recurrent 
rejuvenation  controlled  sedimentation. 

Four  formations  have  been  mapped  on  the  state  geologic  map  of  Mas- 
sachusetts (1916),  but  their  distribution  as  continuous-layered  units  could 
hardly  be  shown  on  cross  sections.  The  central  part  of  the  basin  at  the 


EASTERN  TRIASSIC  RASINS 


1  ,, 


surface  is  marked  by  the  Chicopee  shale;  this  is  bordered  on  both  sides 
and  the  north  by  the  Longmeadow  sandstone,  and  this  in  turn  by  the 
Sugarloaf  Arkose.  Along  the  east  side  is  a  coarse  border  aggregate  called 
the  Mount  Toby  conglomerate.  These  formations  are  clearly  facies  and 
grade  into  each  other  or  are  interdigitated.  The  Mount  Toby  conglomer- 
ate is  a  fanglomerate  in  large  part  and  an  actual  talus  in  others.  There 
can  be  little  doubt  about  its  relation  to  a  great  border  fault;  but  in  places 
bedrock  crops  out  surounded  by  conglomerate,  and  the  position  of  the 
fault  is  obscure. 

Intercalated  in  the  elastics  and  grouped  close  together  in  their  cen- 
tral part  are  three  lava  sheets  of  diabase.  The  middle  one,  the  Holyoke 
diabase,  is  the  thickest  and  in  places  reaches  400  feet.  Between  it  and  the 
upper  are  sandstones  that  contain  large  and  small  reptile  tracks  which  are 
very  well  known.  Shortly  after  the  third  lava  outpouring,  an  explosive 
eruption  took  place;  and  fragments  and  dust  of  diabase  were  spread  over 
a  large  area  to  form  the  Granby  tuff.  Over  the  tuff  was  spread  rusty  sand 
in  which  most  of  the  tracks  have  been  preserved.  In  the  southern  part  of 
the  basin  "dolerite"  sheets  have  been  intruded.  Dikes  are  few. 

Here  as  in  the  other  Triassic  basins,  normal  faults  cut  and  displace  the 
beds  and  volcanic  sheets.  See  sections,  Fig.  9.4. 

The  red  color  and  salt  crystal  impressions  have  led  a  number  of  writers 
to  envision  a  semiarid  climate;  but  Krynine,  on  the  other  hand,  contends 
that  the  flora  and  swamps  suggests  a  precipitation  of  about  50  inches  a 
year  and  a  temperature  of  70°  to  80°  F.  Fresh  arkoses  and  fanglomerates 
can  easily  form  under  tropical  humid  climate  in  regions  of  steep  topogra- 
phy. Desiccation  marks  indicate  alternating  dry  and  wet  seasons. 

STRUCTURE  OF  BASINS 

All  the  Triassic  basins  in  the  eastern  United  States  are  bordered  on  one 
side  or  the  other  by  major  normal  faults.  A  great  fault,  although  irregular 
and  with  branches  and  perhaps  steps  borders  the  Newark  basin  on  the 
west.  The  Deep  River  basin  has  a  major  fault  on  each  side.  The  Con- 
necticut Valley  Triassic  is  bordered  on  the  east  by  a  major  fault,  also  of 
a  complex  nature.  The  long  and  very  narrow  basin  that  stretches  from 


North  Carolina  into  Virginia  is  bordered  on  the  west  by  a  fault.  The  sev- 
eral other  small  and  detached  basins  are  shown  with  faults  on  either  the 
east  or  west  sides  on  the  Geologic  Map  of  the  United  States. 

Associated  with  all  the  great  border  faults  and  perhaps  due  to  them  is 
a  general  dip  of  the  beds  and  sills  toward  them.  See  cross  sections  of  Fi'_is. 
9.2  and  9.3.  The  dips  range  from  5  to  50  degrees  and  are  more  generally 
10  to  20  degrees.  The  Triassic  beds  are  not  folded  as  the  underlying 
Paleozoics  and  metamorphics,  upon  whose  beveled  edges  they  rest  un- 
conformably. 

Strike  faults  within  the  sediments  are  known,  somewhat  parallel  with 
the  border  faults,  and  many  transverse  faults  cut  and  offset  the  beds  and 
sills.  In  places  the  transverse  faults  terminate  against  normal  strike  faults 
and  produce  a  rhombic  pattern.  Some  of  the  transverse  normal  faults  have 
been  traced  out  into  the  folded  and  thrust-faulted  Paleozoic  rocks  which 
they  also  offset. 

The  normal  faults  within  the  basin  cut  the  Triassic  sediments  and  sills, 
yet  some  of  the  dikes  associated  with  the  sills  follow  cross  faults.  It  is  gen- 
erally concluded  that  the  faulting  is  later  than  most  of  the  beds,  but  before 
the  end  of  the  period  of  volcanic  activity,  so  that  most  of  the  sills  are  cut 
by  the  faults,  yet  some  dikes  were  injected  immediately  into  the  fractures 
when  they  formed. 

ORIGIN  OF  BASINS 

The  Triassic  basins  of  the  Piedmont  province  and  of  the  Connecticut 
Valley  have  a  similar  history.  The  troughs  in  which  the  sediments  were 
deposited  are  due  mainly  to  downfaulting  with  a  major  fault  or  chain  of 
faults  on  either  the  outer  or  inner  side.  The  trough  block  rotated  by  set- 
tling most  adjacent  to  the  border  fault.  The  border  faulting  is  conceived 
as  a  fairly  continuous  process  during  which  the  sediments  accumulated  in 
the  basins  as  they  were  progressively  deepened.  Stose  and  Bascom  ( 1929) 
represent  sedimentation  in  the  Newark  basin  to  have  started  considerably 
before  the  border  faulting  began  (see  Fig.  9.2);  then  with  the  onset  of 
faulting  the  previously  deposited  beds  which  came  from  the  southeast 
were  tilted,  and  the  site  of  later  sedimentation,  with  continued  faulting. 


134 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


shifted  more  toward  the  northwest.  Also,  with  the  onset  of  faulting,  fan- 
glomerates  were  washed  in  by  torrential  streams  from  the  uplifted  block. 
In  the  Deep  River  basin,  with  faulting  on  both  sides,  the  fanglomerates 
came  from  both  directions.  If  Triassic  sedimentation  started  before  fault- 
ing, it  may  have  been  due  to  one  of  two  causes :  ( 1 )  a  broad  syncline  may 
have  developed  which  later  broke  into  faults  on  one  or  both  sides,  or  (2) 
a  change  may  have  occurred  from  a  warm  humid  climate  in  whch  red 
soils  were  developed  on  the  surrounding  lands  to  an  arid  or  semiarid  one 
in  which  salt  crystals  developed  in  the  sediments  from  time  to  time,  and  in 
which  torrential  floods  were  common. 

The  throw  of  the  border  faults  according  to  the  cross  sections  of  Fig.  9.4 
would  equal  the  total  thickness  of  the  basin  sediments,  and  therefore, 
would  be  of  the  magnitude  of  20,000  feet.  This  is  twice  as  much  as  postu- 
lated or  computed  for  any  other  post-Proterozoic  normal  fault  in  North 
America,  and  leads  one  to  regard  the  large  figure  critically.  Stose  and 
Bascom  ( 1929 )  compute  the  throw  at  6000  feet  in  the  southeastern  Penn- 
sylvania area  by  means  of  their  postulated  origin  of  the  Newark  basin. 

The  nature  of  the  faults  of  the  Triassic  basins,  both  in  vertical  and 
horizontal  position  and  movement,  and  the  general  plan  of  the  entire  zone 
of  faults  from  the  Carolinas  to  Nova  Scotia  reminded  Bain  ( 1941 )  of  the 
Rift  Valleys  of  Africa,  and  he  considers  them  a  rift  zone. 

LATE  TRIASSIC  PHASE  (PALISADES  OROGENY) 

The  onset  of  faulting  that  formed  the  troughs  in  which  the  Triassic  sedi- 
ments accumulated  marked  the  beginning  of  the  Palisades  orogeny.  It 
started  in  late  Triassic  time  and  probably  ran  its  course  before  the  end  of 
the  period.  After  the  border  faults  had  become  major  faults  and  great 


thicknesses  of  sediments  had  accumulated,  vast  amounts  of  basic  magma 
entered  the  basins,  chiefly  along  the  border  faults,  and  spread  into  the 
sediments  as  numerous  sills,  some  exceedingly  thick,  and  as  great  dikes. 
In  places  the  dikes  cut  long  distances  into  the  country  rock.  Great  amounts 
of  magma  reached  the  surface  as  basalt  flows,  which  were  immediately 
buried  by  the  accumulating  sediments.  Accompanying  the  igneous  activity 
was  an  additional  episode  of  faulting.  Both  strike  and  transverse  parallel 
faults  provided  avenues  of  ingress  of  the  magma,  and  continued  faulting 
broke  and  offset  some  of  the  sills  as  well  as  the  sediments.  The  great 
border  faults  undoubtedly  also  continued  active  in  places,  dropping  the 
basins  farther  and  inviting  new  floods  of  fanglomerate. 

The  entire  activity  from  the  inception  of  the  border  faulting  through 
the  intrusive  and  extrusive  activity  and  additional  faulting  seems  to  have 
been  fairly  continuous  and  hence  not  separable  into  early  and  late  phases. 
It  will  all  be  recognized  here  as  the  late  Triassic  phase,  or  the  Palisades 
orogeny. 

The  faulting  and  dike  intrusions  spread  into  rocks  adjacent  to  the 
Triassic  basins,  and  it  is  clear  that  at  the  time  of  maximum  accumulation 
the  sediments  were  much  more  extensive  than  now.  Their  beds  are  bev- 
eled on  the  sides  opposite  the  border  faults,  and  the  fanglomerates  still 
bury  in  places  the  fault  scarps  and  spread  considerable  distances  over  the 
upthrown  blocks.  Whitcomb  (1942)  considers  the  Spitzenberg  conglomer- 
ate as  a  Triassic  outlier  20  miles  north  of  the  present  margin  of  the  New- 
ark basin.  The  now  separate  basins  may  easily  have  been  confluent  in 
places,  but  such  cannot  be  proved,  it  seems.  It  is  also  possible  that,  while 
the  Palisades  orogeny  was  taking  place  in  the  Piedmont  and  folded  Appa- 
lachians, the  continental  margin  lay  100  to  200  miles  eastward  and  Triassic 
sediments  were  accumulating  there. 


10 


How  toward  the  Atlantic.  The  Virginia,  Delaware,  Maryland,  and  New 
Jersey  section  of  the  Coastal  Plain  is  one  of  great  estuaries  in  which  tide 
waters  reach  across  the  plain  to  the  Piedmont.  These  are  regarded  as 
drowned  river  valleys. 

The  Coastal  Plain  as  a  geologic  unit  extends  out  into  the  Atlantic  Ocean 
and  forms  the  broad  and  well-known  continental  shelf  there.  Off  Cap< 
Hatteras,  the  shelf  is  only  30  miles  wide,  but  both  northeastward  and 
southwestward  from  the  cape  it  broadens.  Off  New  England,  it  is  over 
250  miles  wide.  See  the  Tectonic  Map  of  the  United  States  and  Fig.  7.1  of 
this  book. 

The  Atlantic  Coastal  Plain  is  continuous  with  the  Gulf  Coastal  Plain, 
which  is  described  in  Chapter  41.  Florida  has  been  included  in  the  Gulf 
Coastal  Plain,  so  will  not  be  treated  here. 


ATLANTIC  COASTAL  PLAIN 
AND  ADJACENT  OCEAN  BASIN 

EXTENT  AND  CHARACTER  OF  SEDIMENTS 

The  Atlantic  Coastal  Plain  is  underlain  by  poorly  consolidated  Quater- 
nary, Tertiary,  and  Cretaceous  sediments  that  dip  gently  seaward.  The 
Cretaceous  sediments  form  a  narrow  inland  belt  of  outcrop,  and  the  Ceno- 
zoic  sediments  a  broad  outer  belt.  In  places,  the  Cenozoic  sediments  over- 
lap the  Cretaceous  entirely  and  rest  on  the  crystalline  rocks  of  the  Pied- 
mont. See  the  Geologic  and  Tectonic  maps  of  the  United  States.  The 
surface  is  nearly  a  plain,  as  the  term  coastal  plain  implies.  The  interrup- 
tions to  the  plain  are  low,  inland-facing  questas  and,  in  places,  slightly 
intrenched  streams  that  cross  the  Cretaceous  and  Tertiary  rocks  as  they 


STRATIGRAPHY 

The  stratigraphy  of  the  Atlantic  Coastal  Plain  is  illustrated  by  a  chart, 
Fig.  10.1  and  five  cross  sections,  viz.,  numbers  32,  33,  34,  35,  and  36  of 
Figs.  10.2,  10.3,  and  10.4.  Refer  to  the  index  map,  Fig.  7.1,  for  the  position 
of  the  sections.  Three  of  the  sections  across  the  Coastal  Plain  and  two  of 
them  run  lengthwise  of  it. 

The  chief  elements  of  the  stratigraphy  are  the  Upper  Cretaceous,  Eo- 
cene, and  Miocene.  Lower  Cretaceous  beds  have  been  noted  in  the  north- 
ern half  of  the  Coastal  Plain,  and  Oligocene  beds  in  the  southern  part 
(South  Carolina  and  Georgia).  A  thin  Quaternary  cover  is  fairly  extensive 
in  the  area  between  Chesapeake  and  Delaware  bays  and  in  North  Caro- 
lina. For  details  of  the  stratigraphy,  see  Richards  (1945,  1947). 

A  well  in  Maryland  penetrated  169  feet  of  dark  red,  argillaceous  sand- 
stone, apparently  of  Triassic  age.  See  section  36,  Fig.  10.4. 

STRUCTURE 

Coastal  Plain 

Regional  Dip.  With  few  exceptions,  the  beds  dip  gently  toward  the 
Atlantic.  The  crystalline  floor  upon  which  the  sediments  rest  dips  the 


135 


Macrofauna 


Microfauna 


New  Jersey 


Europe 


Texas 


Epochs 
.and 

Groups 


Per- 
iods 


No  fossils  known 
from  outcrops 


Beacon  Hill 


Cohonsey 


Well  preserved  Mollusks 
neor  Shiloh, equivalent  to 
Calvert  of   Maryland 


Neritic  founo  from  wells 


Poorly  preserved  Mollusks 


Poorly  preserved  Mollusks 


Large  neritic  founa  in  wells 
only 


Kirkwood 
Shark  River 


Auversion 


Lutetian 


Arenaceous  species  in  outcrop 


Monosauan 


Cuisian 


Bryozoo  abundont 
in  South 


Lorge  well  preserved  founo 
with  mony  plonktonic 


Ypresian 


Vincentown 


Sparnacian 


Cuculloea.Oleneothyns, 
Gryphoeo   Founo 


\  Cuculloea   Fauna 


Diagnostic  Danian  ond  Thone- 
~~~X  tion  Species  / 


Thanetian 


Danian 


Lucino  Fauna 


Well  preserved  neritic  founa. 
Latest  Marine  Cretaceous  NA 


Red  Bank 


Cucullaea  Fauna 


Large,  well  preserved 
neritic  founo 


Navesink 


Maestrichtian 


Lucina   Fauna 


Mt  Laurel 


Wenonah 


Cucullaea  Fauna 


Well  preserved  neritic  fauna 
southern  port  of  stole 


Marshalltown 


No  fossils   known 
from    outcrops 


Englishtown 


Companion 


Lucina  Fauna 


Chiefly  Arenaceous  species  in 
outcrop. 


Woodbury 


Cucullaea  Fauna 


Arenaceous  species. 


Merchantville 


Lucina   Fauna 

(Extensive  Flora) 


Brockish-woter  and 
Monne   Mollusks 
(  Extensive  Flora  ) 


Magothy 


Santonian 

? 

Coniacian 


Turonian 


Arenaceous  species  in 
surfoce  exposures; 

Calcareous  forms  downdip 
in  wells 


Raritan 


Cenomanian 


Claiborne 


Wilcox 
? 


Midway 


? 

Navarro 


Taylor 


Austin 


Eagle  Ford 


Woodbine 


Plio. 


UJ 

Pol 


2  °- 

OO 


o  o 
o  tj5 


fr   Glouconitic 

_i_    Calcareous 


Fig.    10.1.      Cretaceous    and    Tertiary    formations    in    the    Coastal    Plain    of    New    Jersey.    Reproduced    from 
Dorf  and   Fox,   1957. 


ATLANTIC  COASTAL  PLAIN  AND  ADJACENT  OCEAN  BASIN 


137 


greatest  amount,  because  most  all  the  formations  thicken  seaward,  and 
each  successively  higher  sedimentary  surface  dips  somewhat  less  than  the 
"basement"  floor.  From  a  number  of  deep  wells  that  have  penetrated  the 
crystallines,  the  ancient  surface  can  be  contoured  as  shown  in  Fig.  10.6. 
Its  gentlest  slope  is  in  North  Carolina,  where  a  dip  of  10  to  14  feet  per 
mile  exists  from  the  inner  margin  ( fall  line )  to  the  coast  in  the  southeast- 
ern part  of  the  state. 

It  then  breaks  seaward  into  a  steeper  slope  of  122  to  124  feet  per  mile 
(Berry,  1948).  Two  deep  wells  in  northern  Maryland  demonstrate  an  off- 
shore dip  there  of  about  100  feet  per  mile  (Balsley  et  al.,  1946),  and  a 
uniform  slope  is  indicated.  The  two  slopes  in  North  Carolina  are  taken 
to  mean  two  peneplains  by  Berry  ( 1948 ) ,  but  their  local  development  is 
puzzling  if  this  theory  is  true. 

Unconformities.  The  great  unconformity  at  the  base  of  the  Cretaceous 
has  already  been  implied  in  the  discussion  of  the  slope  of  the  surface  of 
the  crystallines.  This  ancient  erosion  surface,  buried  by  the  Cretaceous 
sediments,  has  been  called  the  fall  zone  peneplain.  See  block  diagrams 
2  and  3  of  Fig.  10.8.  Since  an  outer  and  sharper  slope  has  recently  been 
defined,  the  ancient  surfaces  appear  more  complicated.  It  will  be  dis- 
cussed further  when  the  continental  shelf  is  considered. 

The  Lower  Cretaceous  beds  do  not  crop  out  anywhere  along  the  At- 
lantic Coastal  Plain;  they  form  a  subsurface  wedge  between  the  crystalline 
floor  and  the  Upper  Cretaceous.  The  dashed  lines  of  Fig.  10.6  show  the 
extent  and  thickness  variations  of  the  Lower  Cretaceous.  It  will  be  seen 
that  the  wedge  corresponds  in  position  approximately  to  the  outer  steeper 
slope  of  the  crystalline  floor.  The  isopachs  should  be  related  to  those  of 
Plate  11  which  depicts  the  distribution  of  Lower  Cretaceous  strata  in  the 
Gulf  Coastal  Plain  and  the  Caribbean  regions.  Not  enough  is  known  of  the 
Lower  Cretaceous  and  Upper  Cretaceous  contact  to  decipher  the  rela- 
tions. The  Lower  Cretaceous  Potomac  formation  is  regarded  as  nonma- 
rine,  and  the  overlying  Tuscaloosa  as  marine  (Richards,  1945). 

According  to  Richards'  ( 1945 )  correlations  the  Eocene  bevels  the  Up- 
per Cretaceous  beds  near  Asbury,  New  Jersey  ( section  32,  Fig.  10.2 )  and 
rests  on  the  Lower  Cretaceous  in  parts  of  Virginia  ( section  33,  Fig.  10.3 ) . 


Fig.  10.2.  Cross  sections  of  the  Atlantic  Coastal  Plain,  after  Richards,  1945.  Section  32,  from 
Allentown,  N.  J.,  to  Asbury  Park,  N.  J.  Section  34,  from  Goldsboro,  N.  C,  to  Cape  lookout, 
N.  C   See  index   map,   Fig.  7.1,  for  location   of  sections. 


138 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


SECTION    )S 


■£ 

£ 

5: 

Q 

£ 

■SJ 

5 

^ 

I 


Fig.  10.3.  Crojs  sections  of  the  Atlantic  Coastal  Plain,  after  Richards,  1945.  Section  33, 
Richmond,  Va.,  to  Norfolk,  Va.  Section  35,  Wilmington,  N.  C,  to  Parris  Island,  S.  C.  See 
index  map.   Fig.  7.1. 


SECTION    J6 


Fig.    10.4.      Section    of    the   Atlantic    Coastal    Plain    from    Virginia    to    Long    Island,    N.    Y.,    after 
Richards,   1947. 

Evidently,  therefore,  an  unconformity  of  considerable  magnitude  exists 
between  the  Tertiary  and  Cretaceous  systems. 

The  absence  of  Oligocene  beds,  except  in  the  south,  suggests  an  un- 
conformity between  the  Miocene  and  Eocene.  In  most  of  Richards'  sec- 
tions, however,  the  Miocene  seems  conformable  on  the  Eocene.  One  ex- 
ception is  noted  near  Summerville,  South  Carolina.  A  break,  however, 
occurs  between  Lower  and  Upper  Miocene  in  the  area  between  Norfolk, 
Virginia  and  Wilmington,  North  Carolina,  where  the  Yorktown-Duplin 
formation  rests  across  the  entire  Lower  Miocene,  Eocene,  and  most  of 
the  Upper  Cretaceous  succession.  The  Geologic  Map  of  the  United  States 
shows  very  clearly  the  unconformity  between  the  Yorktown  beds  and  the 
entire  Upper  Cretaceous,  Eocene,  and  Lower  Miocene  succession  in  the 
region  adjoining  the  states  of  North  and  South  Carolina.  Inspection  of  the  i 
map  also  reveals  an  unconformity  between  the  Pliocene  beds  and  older 
ones  in  this  region. 

Cape  Fear  Arch.  The  most  conspicuous  feature  of  the  Coastal  Plain 
is  the  Cape  Fear  arch  of  North  and  South  Carolina.  See  index  map,  Fig. 
7.1,  and  the  Geologic  and  Tectonic  Map  of  the  United  States.  Structure 
contours  on  the  top  of  the  Cretaceous  bulge  outward  at  this  place  and 
reveal  a  very  broad  nose  on  the  regional  seaward  dip,  so  the  structure  is 


ATLANTIC  COASTAL  PLAIN  AND  ADJACENT  OCEAN  BASIN 


139 


not  truly  an  arch  as  defined  in  Chapter  2.  The  Eocene  and  Miocene  con- 
tacts with  the  Cretaceous  also  reflect  the  broad  nose.  The  unconformities 
around  the  Cape  Fear  arch  indicate  the  principal  times  of  uplift  and  ero- 
sion to  have  been  at  the  close  of  the  Cretaceous  and  again  at  the  close  of 
the  early  Miocene. 

In  the  New  Jersey  region  Dorf  and  Fox  ( 1957 )  recognize  eight  trans- 
gressive-regressive  cycles  of  sedimentation  in  the  history  of  the  Coastal 
Plain  from  Raritan  ( Upper  Cretaceous )  to  Cohansey  ( close  of  Miocene ) 
time  (Fig.  10.1).  If  these  prove  to  be  of  local  extent,  then  it  would  be 
concluded  that  the  continental  margin  pulsed  up  and  down  locally  this 
many  times,  but  if  the  cycles  are  found  to  be  widespread  and  recorded 
in  the  Gulf  Coastal  Plain  sediments,  then  eustatic  changes  in  sea  level 
would  be  the  more  probable  cause.  The  subject  will  be  considered  in 
Chapter  41  on  the  Gulf  Coastal  Plain. 


known  outcrops  and  well  records;  and  two  submarine  traverses  were  run 
across  the  continental  shelf,  one  from  Woods  Hole  southward,  and  one 
from  Cape  Henry,  Virginia,  eastward  (section  37  of  index  map.  Fig.  7.1 
The  Cape  Henry  section  is  the  most  significant.  Many  reflection  surfaces 
were  recorded  in  the  sediments  above  the  crystalline  floor,  and  two  par- 
ticularly strong  ones  were  measured  by  refraction  beyond  the  present 
shore  line.  See  Fig.  10.5.  The  seismic  data  on  the  crystalline  floor  are  in 
fair  agreement  with  the  deep-well  records  and  indicate  that  at  a  point 
60  miles  at  sea  off  Cape  Henry  the  basement  would  be  12,000  feet  deep. 
The  significance  of  the  other  two  surfaces  is  not  altogether  clear.  Miller 
( 1937 )  suggests  that  the  "unconsolidated"  zone  consists  of  Cenozoic  and 
Cretaceous,  and  the  "semiconsolidated"  zone  consists  of  Jurassic  and 
Triassic.  The  surface  separating  the  two  is  known  as  the  M  /one  to  the 
geophysicists,  and  this  has  later  been  considered  as  a  reflection  horizon 


CONSTITUTION  OF  CONTINENTAL  SHELF  AND 
ADJACENT  ATLANTIC  OCEAN  CRUST 

Composition  of  Basement 

As  a  result  of  seismic  refraction  studies  in  the  Atlantic  Coastal  Plain 
between  Virginia  and  New  Jersey,  Ewing  et  al.  ( 1939 )  believe  that  the 
^ocks  of  the  crystalline  Piedmont,  as  known  in  the  exposed  belt,  are  also 
^present  in  the  basement  complex  below  the  Cretaceous.  They  recognize 
|the  Petersburg  granite  and  the  Wissahickon  schist  into  which  the  granite 
ijis  intrusive,  under  the  unconsolidated  sediments  east  of  Petersburg,  Vir- 
ginia, and  think  they  can  trace  the  belts  northward  through  Maryland, 
^Delaware,  and  New  Jersey.  It  would  appear,  they  say,  that  the  Peters- 
burg granite  is  a  correlative  of,  or  is  continuous  with,  the  late  Devonian 
granites  of  Connecticut  and  Rhode  Island. 

Deposits  of  Continental  Shelf 

■ 

The  continental  shelf  off  the  Atlantic  Coastal  Plain  has  been  investi- 
gated geophysically  in  the  past  12  years,  and  some  interesting  results 
have  been  obtained  (Ewing  et  al.,  1937,  1940).  Several  seismic  traverses 
were  run  across  the  Coastal  Plain  in  order  to  check  the  seismic  data  with 


WOODS        HOLE        SECTION 

CONTINENTAL         SHELF 


sea  level 


c« 


STATUTE 


^cojsolk) 


Sf*'C>NS0L 


-■"^PL  OATEI) 


t**F 

StlUT  H 


PAF  A  L  L 


CAPE 

HENRY       SECTION 

V- CONTINENTAL 

■HELP 

*•.■  m ' 

o— c 

J 

•"•CONSOLIOHTio           L_____-o— — -°          A 

MM' 

C    R 

VST 

*    "•'■<»,. 

-^ 

^"co, 

sO(_l|>ATED 

V 
\ 

«:■:.* 

s 

r*-* 

•oeo' 

> 

.    .. 

■  300' 

INI 

STA 

U  TE 

M  1  I 

E  S 

EAST 

OF 

PET    :  RS  B  J  RC 

V 

v 

; 

q 

•  0 

i 

>Q 

o 

r^^o 

• 

Fig.  10.5.  Seismic  traverses  on  the  Atlantic  Coastal  Plain  and  continental  shelf,  after  Ewing. 
Crary,  and  Rutherford,  1937.  Small  circles  represent  elevations  determined  by  the  refraction 
seismograph.  The  Cape  Henry  section  is  section  37  of  the  index  map  of  Fig.  7.1.  The  Woods 
Hole  section  runs  southward  from  Woods  Hole,  Mass.  The  M  Zone  is  probably  a  horizon 
within    the    Upper   Cretaceous. 


140 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


in  the  Upper  Cretaceous  ( Ewing  et  al.,  1939 ) .  Richards  thinks  the  M  zone 
in  the  Upper  Cretaceous  is  the  contact  between  the  Magothy  and  Mata- 
wan  or  Magothy  and  Merchantville  formations.  See  section  32,  Fig.  10.2. 
If  so,  about  700  feet  of  Upper  Cretaceous  strata,  which  generally  underlie 
the  Magothy,  and  1000  feet  or  more  of  Lower  Cretaceous  would  be  in  the 
semiconsolidated  layer.  In  southeastern  Virginia  the  Eocene  rests  on 
the  Lower  Cretaceous,  and  the  M  zone  is  probably  absent;  but  perhaps 
seaward  the  Upper  Cretaceous  comes  in  again,  and  the  zone  is  present. 

Contour  of  Crystalline  Basement  Surface 

In  a  paper  of  1950,  Ewing  et  al.,  report  on  profiles  off  Cape  May,  New 
York,  and  Woods  Hole,  and  concluded  that  the  Precambrian  surface  does 
not  slope  constantly  toward  the  Atlantic  Ocean  basin  floor  but  has  a  pro- 
nounced reversal  of  dip  at  a  depth  of  16,000  feet  before  the  margin  of  the 
shelf  is  reached  off  Long  Island  and  Delaware  Ray.  Structure  contours 
on  the  surface  are  shown  on  Fig.  10.6.  Farther  south  off  the  Cape  Fear 
arch  the  slope  of  the  crystalline  floor  reflects  the  arch  nearly  to  the  mar- 
gin of  the  shelf  (Richards,  1945,  1947;  Rerry,  1948;  Hersey  et  al,  1959). 
The  surface  is  lost  seaward  over  the  Rlake  Plateau,  where  no  seismic 
record  of  it  or  deeper  boundaries  of  velocity  layers  were  obtained.  See 
Fig.  10.7.  The  strike  of  the  surface  veers  westward  in  South  Carolina 
and  northern  Florida.  Near  Jackson,  Florida,  the  surface  dips  steeply 
southward  and  is  lost  at  a  depth  of  19,000  feet.  The  basement  contours 
here  are  distinctly  discordant  to  contours  drawn  on  the  top  of  the 
Cretaceous  (Fig.  10.6). 

In  the  shelf  profiles  off  Long  Island  and  Delaware  Ray  the  unconsoli- 
dated sediments  thicken  gradually  outward  under  the  shelf.  In  the  upper 
section  of  Fig.  10.7  Heezen  et  al.  (1959)  show  a  ridge  of  basement  rock 
at  the  shelf  margin  and  then  an  abrupt  fall-off  apparently  of  fault  nature. 
Oceanward  is  a  second  basin  in  which  the  unconsolidated  and  consoli- 
dated sediments  attain  a  maximum  thickness  of  33,000  feet  ( 10.3  kilome- 
ters). The  unconsolidated  layer  thins  over  the  deep  Atlantic  floor  to  about 
2  kilometers,  but  becomes  much  thicker  again  on  the  approaches  to  the 
Rermuda  Rise  and  Mid-Oceanic  Ridge. 

The  seismic  profiles  across  the  Atlantic  Coastal  Plain  and  continental 
shelf  to  date  have  been  summarized  by  Drake  et  al.  (1960),  and  these 


writers  point  out  that  a  ridge  of  basement  rock  near  the  edge  of  the  shelf 
is  a  common  feature.  It  separates  two  sedimentary  troughs,  one  under  the 
shelf,  and  another  in  deeper  water  under  the  shelf  slope  and  rise.  The 
ridge  and  basins  can  be  seen  in  the  upper  section  of  Fig.  10.7  and  section 
A-A'  of  Fig.  11.34.  The  sediments  in  the  inner  or  shelf  trough  have  been 
drilled  in  several  places  along  the  Atlantic  Coastal  Plain  and  are  mostly 
shallow  water  sands,  silts,  and  clays.  Cores  of  the  upper  part  of  the  sedi- 
ments of  the  outer  trough  have  revealed  features  attributed  to  slump- 
ing, sliding,  and  turbidity  currents,  and  are  in  part  similar  to  graywackes. 
Drake  et  al.  point  out  that  the  size  of  the  troughs  and  the  thickness  and 
character  of  sediments  in  them  are  similar  to  the  early  Paleozoic  troughs 
of  the  Appalachians  as  restored  by  Kay  (1951)  and  that  here  is  a  good 
representation  of  the  miogeosyncline  (inner  trough)  and  eugeosyncline 
(outer  trough).  Compare  with  Figs.  11.17,  6.6,  and  6.15.  Evidence  of  past 
volcanism  in  the  outer  trough  is  present  in  the  form  of  partially  buried 
seamounts  with  large  magnetic  anomalies. 

The  eugeosyncline,  according  to  the  above  view,  develops  largely  on 
the  oceanic  crust,  and  represents,  when  uplifted,  an  accretion  to  the 
continent.  The  theory  appears  very  attractive  when  related  to  the  Paleo- 
zoic Cordilleran  geosyncline. 

Submarine  Canyons.  Comprehensive  submarine  surveys  of  the  whole 
of  the  continental  shelf  and  slope  of  the  northeastern  United  States  have 
been  made  since  1930,  using  the  most  advanced  methods,  and  the  results 
were  published  in  1939.  Chart  1  of  the  publication,  "Atlantic  submarine 
valleys  of  the  United  States  and  the  Congo  submarine  valley"  (Veatch 
and  Smith,  1939)  is  a  composite  of  all  the  modern  work  from  Cape 
Hatteras  to  Georges  Rank.  The  same  results  are  presented  in  reduced 
scale  and  somewhat  simplified  on  the  Tectonic  Map  of  the  United 
States. 

The  shelf  is  a  fairly  smooth  plain  and  a  continuation  of  the  emerged 
Coastal  Plain.  The  most  prominent  feature  is  the  Hudson  channel,  which 
is  entrenched  50  to  150  feet  in  the  shelf  from  the  mouth  of  the  Hudson 
River  to  near  the  edge  of  the  shelf.  South  of  the  channel  are  many  shallow 
depressions  and  low,  irregular  ridges  trending  generally  parallel  with  the 
shore.  They  have  been  likened  to  bars  and  lagoons.  Northeast  of  the  chan- 
nel, the  shelf  is  a  regular  oceanward  slope,  perhaps  rilled  with  many 


[Fig.  10.6.  Structure  of  Atlantic  Coastal  Plain  and  adjacent  ocean  crust  from  Cape  Canaveral 
to  Cape  Cod.  Thin  contour  lines  are  on  the  ocean  floor  and  are  in  fathoms.  The  following 
contours    are    in    feet.    Heavy    continuous    lines    are    structure    contours    on    the    top    of    the    Pre- 


cambrian  crystalline  basement.  Heavy  dashed  lines  are  on  the  base  of  velocity  layers  interpreted 
to  be  sediments.  Dotted  contours  are  on  top  of  Cretaceous.  Compiled  from  Ewing  ef  a/.,  1950 
and    Hersey   ef   a/.,    1959. 


142 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


FROM   NEW  YORK  SOUTHEASTERLY   NEARLY   TO  BERMUDA  PEDESTAL 


400 


500  600 

KILOMETERS 


700 


800 


FROM     SOUTH      OF     CAPE      CANAVERAL    EASTERLY     TO   BLAKE     BAHAMA     BASIN,     THEN     NORTHEASTERLY 


1200 


200  KILOMETERS  400 


500 


700 


1100 


Fig.   10.7.      Sections  of  the  crust  of  the  Atlantic  Coastal   Plain   and  adjacent  ocean. 


shallow  valleys.  The  shelf  breaks  abruptly  at  about  the  600-foot  depth  to 
a  steeper  slope,  known  as  the  "slope"  which  carries  down  to  8000  feet  and 
more  below  sea  level  in  approximately  50  miles.  In  a  few  sections,  the 
slope  is  as  steep  as  700  feet  per  mile  (732  degrees). 

The  slope  is  riven  by  two  kinds  of  dip-slope  features;  canyons  that  ex- 
tend headward  into  the  shelf  10  to  30  miles  from  the  outer  margin,  and 
numerous  deep  parallel  rills  that  are  limited  entirely  to  the  slope.  The 
bottoms  of  the  submarine  canyons  range  from  2000  to  3700  feet  below 
the  floor  of  the  shelf  at  the  outer  margin.  Those  south  of  the  submarine 


Hudson  channel  and  canyon  generally  lose  their  identity  on  the  slope, 
merging  with  the  many  rill-like  canyons  or  not  being  larger  than  the 
canyons  limited  to  the  slope.  The  Hudson  canyon  and  others  that  indent 
the  shelf  to  the  eastward  along  Georges  Rank  more  clearly  retain  their 
identity  down  the  slope.  Only  one  submarine  canyon  in  this  section  of 
continental  shelf  can  be  related  with  any  assurance  to  a  major  river  on 
land.  This  singular  relation  is  the  Hudson,  whose  channel  from  New  York 
has  been  mapped  about  100  statute  miles  across  the  shelf  to  the  head  of 
the  deep  shelf-indenting  and  slope  canyon. 


Rejuvenated  Appalachians  in  post-Newark  time 


The  Fall  Zone  peneplain 


Encroachment  of  Cretaceous  sea  and  deposition  of  Coastal  Plain  beds 

Fig.    10.8.      Early    stages    in    Appalachian    epeirogeny.    Reproduced    from    Johnson,    1931.    Diagrams    1,    2, 
and   3   from   top   to   bottom. 


143 


Arching  of  Fall  Zone  peneplain  and  its  Coastal  Plain  cover;  regional  superposition  of  southeastward-flowing  streams 


The  Schooley  peneplain 


Arching  of  Schooley  peneplain 


Fig.    10.9.      Tertiary    stages    in    Appalachian    epeirogeny.    Reproduced    from    Johnson,    1931.    Diagrams    4, 
5,   and   6  from   top   to   bottom. 


144 


Dissection  of  Schooley  peneplain  and  development  of  Harrisburg  peneplain  on  belts  of  nonresistant  rock 


Uplift  and  dissection  of  Harrisburg  peneplain  and  development  of  Somerville  peneplain  on  the  weakest  rock  belts 


Allegheny    Front* — * 
APPALACHIAN    PLATEAU   — ♦ 


Ridge  and  Valley  belt 

NEWER    APPALACHIANS 


-Great  Valley-#-Readingprong-»TriasLovvl'd-»- Piedmont  ,0- 

-*—        OLDER    APPALACHIANS  ^-*COASTAL    PLAIN 


Uplift  and  dissection  of  Somerville  peneplain  to  give  present  conditions 

Fig.     10.10.      Late    Tertiary    and     Quaternary    stages    of    epeirogeny    and    erosion     in     the     Appalachians. 
Reproduced   from   Johnson,    1931.   Diagrams  7,   8,   and   9   from   top   to   bottom. 


145 


146 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


80*  75' 


Fig.   10.11.      Physiographic  provinces,  Atlantic  Ocean.  Reproduced  from   Heezen  et  a/.,   1959. 


The  Atlantic  continental  shelf  is  most  probably  constructional  and  due 
to  sedimentation  influenced  by  fluctuating  sea  level  during  the  Pleisto- 
cene. Although  certain  early  writers  during  a  vigorous  controvery  ( 1930- 
1940)  contended  that  the  canyons  are  due  to  subaerial  erosion,  and 
therefore  that  the  Atlantic  coast  has  subsided  5000-10,000  feet  subse- 
quently, the  theory  is  generally  held  today  that  the  canyons  are  due  to 


submarine  slumping,  mud  flows,  and  turbidity  currents.  See  discussion 
in  Chapter  32  of  submarine  canyons  off  the  California  coast. 

Appalachian  Epeirogeny 

Following  the  Appalachian  orogeny  in  the  late  Paleozoic  and  the 
Palisades  orogeny  in  the  late  Triassic,  a  long  period  of  erosion  set  in  and 


ATLANTIC  COASTAL  PLAIN  AND  ADJACENT  OCEAN  BASIN 


147 


lasted  during  all  of  the  Jurassic.  By  the  beginning  of  Cretaceous  time,  an 
extensive  and  very  subdued  surface  across  the  folded  and  thrust-faulted 
Appalachians,  and  across  the  Blue  Ridge,  the  Triassic  basins,  and  the 
Piedmont  had  formed.  This  is  known  as  the  fall  zone  peneplain.  Study 
diagrams  1  and  2  of  Fig.  10.8.  The  entire  area  as  far  westward  as  the 
plateaus  province,  according  to  Johnson  ( 1931 ) ,  was  then  invaded  by 
shallow  epicontinental  seas,  and  in  them  Cretaceous  sediments  were  de- 
posited (diagram  3).  From  subsurface  studies  of  the  Coastal  Plain  sedi- 
ments, it  has  been  shown  that  the  Lower  Cretaceous  is  entirely  buried  by 
the  Upper,  and  it  appears  that  the  extensive  overlap  that  Johnson  visual- 
izes occurred  in  Upper  Cretaceous  time.  Others  admit  that  the  Cretaceous 
extended  farther  inland  than  the  present  erosional  margin  but  do  not  be- 
lieve that  it  extended  beyond  the  Blue  Ridge.  Johnson  and  later  Strahler 
(1945)  believe  the  overlap  necessary  to  explain  the  stream  pattern  of  the 
Ridge  and  Valley  province. 

The  fall  zone  peneplain  was  then  arched  broadly  with  the  crest  in  the 
Ridge  and  Valley  and  Blue  Ridge  provinces  and  the  flanks  far  westward  in 
the  plateaus  and  far  eastward  in  the  site  of  the  present  Coastal  Plain  and 
continental  shelf.  Another  episode  of  base-leveling  followed,  which,  like 
the  previous  one,  established  an  extensively  subdued  surface,  but  lower 
and  younger.  This  is  known  as  the  Schooley  peneplain.  See  diagrams  4 
and  5  of  Fig.  10.9.  The  only  remnant  of  the  fall  zone  peneplain  is  that 
buried  beneath  the  Cretaceous  sediments  of  the  Coastal  Plain.  The 
Schooley  surface  is  now  generally  recognized  in  remnants  as  the  highest 
flat  tops  of  ridges  in  the  Appalachian  region. 

Broad  arching  again  occurred,  and  the  Schooley  peneplain  was  dis- 
sected in  the  manner  represented  in  diagrams  6  of  Fig.  10.9  and  7  of  Fig. 
10.10.  A  few  master  streams  persisted  across  the  folds  and  thrusts,  while 
many  subsequent  streams  etched  out  the  resistant  formations  to  produce 
the  first  appearance  of  flat-topped,  subparallel,  ridges  and  valleys.  The 
new  base  level  below  the  flat-topped  ridges  is  known  as  the  Harrisburg 
peneplain.  See  diagram  7  of  Fig.  10.10.  Still  third  and  fourth  stages  of 
arching  are  recognized  in  the  dissection  of  the  Harrisburg  peneplain  and 
the  establishment  of  the  lower  Somerville  surface,  and  the  dissection  of  the 
Somerville  to  the  present  stream  bottoms.  See  diagrams  8  and  9  of  Fig. 


10.10.  An  extensive  literature  may  be  found  on  the  geomoiphology  <>i  the 
Appalachians,  and  most  premises  and  conclusions  of  the  above  summary 
of  Johnson's  work  have  been  contested.  Most  authorities  recognize  the 
vertical  uplift,  but  some  contend  that  a  symmetrical  arching  did  not  occur. 
It  may  also  be  argued  that  the  arching  was  a  slow,  continuous  pro< 
and  not  one  of  four  stages  with  interims  of  standstill. 

Physiographic  Provinces  of  North  Atlantic  Floor 

Echo  sound  tracts  of  fifty  expeditions  in  the  North  Atlantic  including 
over  200,000  miles  by  vessels  of  the  Lamont  Geological  Observatory  with 
the  Luskin  precision  depth  recorder  were  compiled  by  Heezen  ct  at 
(1959),  and  a  physiographic  relief  map  of  the  ocean  floor  was  prepared. 
From  it  the  physiographic  provinces  are  resolved  as  shown  on  the  map  of 
Fig.  10.11.  Profiles  to  accompany  the  map  are  reproduced  in  Fig.  10.12. 
There  are  three  major  divisions,  each  with  its  subdivisions  as  follows: 

Continental  Margin 
Category  I 

Continental  Shelf 

Epicontinental  Seas 

Marginal  Plateaus 
Category  II 

Continental  Slope 

Marginal   Escarpments 

Landward  Slopes  of  Trenches 
Category  HI 

Continental  Rise 

Marginal  Trench-Onter  Ridge  Complex 

Marginal  Rasin-Outer  Ridge  Complex 
Ocean  Rasin  Floor 
Abyssal  floor 

Abyssal  Plains 

Abyssal  Hills 

Abyssal  Gaps  and  Mid-Ocean  Canyons 
Oceanic  Rises 
Seamount  Groups 
Mid-Oceanic  Ridge 
Crest   Provinces 

Rift  Valley 

Rift  Mountains 

High  Fractured  Plateau 


148 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


kiA  R  7 HA  S     VMe  YARD 


Azores 

Soo    Miguel 


■*—»      sZ'JSfi"  emum* 


moo  nmous 


Fig.  10.12.      Relief  profiles  across  the  Atlantic.  Reproduced  from  Heezen  ef  a/.,  1959.  Letters  a  to  q  indicate 
where  sounding  profiles  of  different  cruises  were  joined. 


Flank  Provinces 
Upper  Step 
Middle  Step 
Lower  Step 

For  further  information  the  reader  is  referred  to  the  work  of  Heezen 
et  ah,  Geological  Society  of  America  Special  Papers  65.  A  tectonic  map 
to  supplement  the  publication  is  yet  to  appear,  but  the  gross  details  as 
now  conceived  by  Heezen  and  colleagues  of  Lamont  Geological  Labora- 
tory are  portrayed  in  the  cross  section  of  Fig.  10.13. 

Blake  Plateau,  Blake  Bahama  Basin,  and  Outer  Ridge 

As  shown  on  Fig.  10.11  the  continental  shelf  breaks  into  two  steps 
south  of  Cape  Hatteras,  and  the  lower  step  is  known  as  the  Blake  Plateau. 


East  of  the  Blake  Plateau  is  the  Blake  Bahama  basin,  and  east  and  north 
of  it  is  the  low  Outer  Ridge.  The  Outer  Ridge  swings  northwestward  at 
29°  N.  Lat.,  73°  W.  Long.,  and  heads  toward  the  Cape  Fear  arch  to 
merge  with  the  Blake  Plateau.  Details  are  given  on  Fig.  10.6.  The  outer 
escarpment  of  the  Blake  Plateau  is  probably  a  fault  scarp,  according  to 
Heezen  et  al.  ( 1959 ) .  See  lower  diagram  of  Fig.  10.7. 

A  seismic  refraction  survey  of  part  of  the  Blake  Plateau  was  made  by 
Hersey  et  al.  ( 1959 ) ,  and  the  principal  profiles  are  shown  on  Fig.  10.6. 
The  same  letter  designations  are  retained  for  the  profiles  as  in  the  original 
article.  The  purpose  of  the  study  was  to  determine  the  relation  of  the 
Plateau  crust  to  the  continental  crust  on  one  side  and  to  the  oceanic  crust 
on  the  other.  Four  characteristic  profile  sections  are  shown  in  Figs.  10.14 
and  10.15. 


MID- ATLANTIC     RISE 


AFRICA 


Fig.    10.13.      Crustal   structure  across   North  Atlantic.   After   Heezen   ef  al.,    1959,   with   minor  changes  taken 
from   new  section   furnished   by  Tharp  and   Heezen. 


KILOMETERS 


Fig.  10.14.  Crustal  structure  sections  C-C  and  E-E'  of  Fig.  10.6.  After  Hersey  et  al.,  1959.  Numbers  are 
velocities  per  second  of  the  various  layers.  Stippled  layers  are  interpreted  as  unconsolidated  and  con- 
solidated sediments. 


150 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


0 

D 

D 

1.83) 

1.83, 

1.83  k 

1.83,      2.77? 

WATER 

1.74:-.  v;:  I.83-V-'?-.  :"i". . 

■••.'•  2.6I.V 

315        2.78 

J-? 

.  I.83-. 
4.11 

3.84             3  87          3.80 

2 

Ir       ^_ 

4.89 

1 

4.45    '4.6 

A 

6 

/■"     5.5 

55         62Z 

552 

1 

1 

4   • 

1 

1 

1    —  - 
\ 



*•*  *~ 

fl 

—                   b.85 

639  S,                  / 
•  X / 

6.21 

12 
14 

ToV 

MANTLE 

10 

0 

KILOMETERS 

200 

300 

100  KILOMETERS 


Fig.  10.15.  Crustal  structure  sections  D-D'  and  G— G'  of  Fig.  10.6.  After  Hersey  ef  a/.,  1959.  Numbers  are 
velocities  in  kilometers  per  second.  Stippled  layers  are  interpreted  as  unconsolidated  and  consolidated 
sediments. 


The  results  on  the  continental  shelf  are  correlated  with  adjacent  continental 
geology.  The  deepest  horizon  traced  along  the  shelf  is  interpreted  as  granitic 
basement,  which  has  compressional  velocities  of  5.82-6.1  km/sec.  At  the 
southern  extremity  it  is  at  a  depth  of  6  km.,  shoals  to  0.86  km.  near  Cape 
Fear,  and  deepens  north  of  Cape  Hatteras  to  more  than  3  km.  North  of 
Charleston,  South  Carolina,  there  is  excellent  depth  correlation  with  granitic 
basement  in  coastal  wells;  to  the  south  all  deep  wells  are  inland.  Age  correla- 
tions are  based  on  well  data  near  the  coast,  which  indicate  to  us  that  most  of 
the  observed  section  is  Cretaceous. 

On  the  Blake  Plateau,  several  layers  (1.83-4.5  km/sec.)  are  interpreted 
as  sedimentary.  A  5.5-km/sec.  layer  is  found  only  south  of  a  line  from  30°30' 
N.,  78°W.  to  Cape  Canaveral.  Velocities  higher  than  5.5  km/sec.  have  been 
measured  on  six  profiles  on  the  Blake  Plateau.  The  5.5-km/sec.  layer  and  a 
6.2-km/sec.  layer  appear  to  form  a  positive  feature  to  the  south  of  the  above- 
mentioned  line  [indicated  as  fault  on  Fig.  10.6].  Higher  velocities,  8.0  km/sec, 
and  7.28  and   7.3  km/sec,   which  are  probably  not  the   same  horizon,   are 


found  at  markedly  different  depths.  Possibly  these  represent  the  M  layer  and 
ultrabasic  material,  depending  on  relations  not  now  known. 

[The  Outer  Ridge  along  section  G— C]  is  underlain  by  thick  low-velocity 
layers  (1.83-2.96  km/sec),  interpreted  as  sediments,  and  higher-velocity 
layers  which  form  a  distinct  linear  structure  having  the  same  general  trend  as 
the  ridge.  At  its  northwestern  end  this  trend  treminates  against  a  thick 
lower-velocity  section  interpreted  as  a  sediment-fuled  trough  (Hersey  et  ah, 
1959,  p.   1). 

An  attempt  is  made  on  Fig.  10.6  to  contour  the  base  of  the  interpreted 
sedimentary  layers  (velocities  less  than  4.5  km/sec)  from  the  profiles  of 
Hersey  et  al.  The  results  are  to  be  taken  simply  as  pictorial.  There  seems 
little  doubt,  however,  that  a  major  fault  transects  the  Blake  Plateau,  but 
of  a  date  preceding  the  deposition  of  the  upper  two  velocity  layers  of  sedi- 
ments, because  they  bury  the  escarpment.  This  fault,  extended  south- 


ATLANTIC  COASTAL  PLAIN  AND  ADJACENT  OCEAN  BASIN 


151 


easterly,  probably  forms  the  south  boundary  of  the  Outer  Ridge,  described 
above  by  Hersey  et  al.,  but  if  so,  it  does  not  show  in  section  H-H'.  The 
Blake  Plateau  south  of  the  fault,  at  any  rate,  stands  15,000^30,000  feet 
above  the  block  on  the  north,  in  reference  to  the  base  of  the  interpreted 
sedimentaries.  The  deeply  filled  block  extends  northward  at  least  to 
32°  N.  Lat. 

Regarding  the  origin  of  the  Outer  Ridge,  Hersey  et  al.  point  out  that 
two  velocity  layers  appear  there  that  are  unusual,  namely  the  5.20-5.67- 
km/sec  layer  and  the  7.21-7.73-km/sec  layer.  The  5.2-km/sec  layer  is 
interposed  between  the  sedimentary  layers  and  the  basaltic  "oceanic 
layer"  (6.5  =*=  km/sec),  and  the  7.5-km/sec  layer  interposed  between  the 
oceanic  layer  and  the  mantle.  Since  profile  D-D'  shows  a  5.22-5.52- 
km/sec  layer  under  the  Blake  Plateau  the  rock  represented  by  this 
velocity  range  is  probably  not  unique  to  the  Outer  Ridge.  The  7.5-km/sec 
layer,  however,  seems  more  restricted  to  the  Ridge,  but  it,  nevertheless,  is 
known  to  extend  as  far  north  as  the  northern  end  of  profile  H-H'. 

The  5.2-km/sec  layer  is  regarded  as  a  mass  of  extruded  volcanic  mate- 
rial, lighter  and  more  porous  than  the  basaltic  "oceanic  crust"  layer,  and 
the  7.5-km/sec  layer  is  taken  to  be  a  mixture  of  mantle  rock  with  the 
oceanic  crust,  probably  by  intrusion  of  peridotitic  magma  into  basalt,  in 
the  manner  postulated  for  the  Mid-Atlantic  Ridge  (Fig.  10.13). 

Hersey  et  al.  (1959)  speculate  that  the  ultrabasic  intrusions  fed  the 
volcanic  extrusions,  then  at  the  surface,  and  that  the  two  are  comple- 
mentary. Another  theory  might  be  one  in  which  basalt  is  formed  by 
partial  melting  of  the  mantle,  with  the  basalt  rising  to  concentrate  in  mesh 
fashion  in  the  upper  part  of  the  mantle.  This  basalt  could  then  rise  in 
fissures  and  vents  through  the  oceanic  crust  to  eruption  at  the  surface. 
See  Chapter  33  on  igneous  rock  provinces. 

Mid-Atlantic  Ridge 

Topography.  The  Mid-Atlantic  Ridge  is  a  broad  arch  or  swell  that 
occupies  approximately  the  center  third  of  the  ocean  (Figs.  10.11  and 
10.12).  The  higher  and  central  part  is  less  than  1600  fathoms  below  sea 
level,  and  the  flanks  fall  between  1600  and  2500  fathoms.  The  Ridge  is 
very  rough  as  the  profiles  indicate,  and  the  most  striking  feature  is  a 
deep  notch  or  cleft  in  the  crest  of  the  arch,  called  the  Rift  Valley.  On  an 


average  profile  the  floor  of  the  valley  lies  at  about  20CK)  fathoms  below  sea 
level,  whereas  the  adjacent  peaks  average  about  1000  fathoms.  The  re- 
lief from  floor  to  adjacent  peaks  ranges  from  700  to  2100  fathoms.  The 
width  of  the  valley  between  crests  of  the  adjacent  peaks  ranges  between 
15  and  30  miles;  at  an  elevation  of  500  fathoms  above  its  floor  the  width 
is  from  5  to  22  miles  (Heezen  et  al.,  1959). 

On  either  side  of  the  Rift  Valley  are  terranes  of  sharp  and  strong  relief 
called  the  Rift  Mountains.  Immediately  adjacent  to  the  central  Rift 
Valley  are  the  High  Fractured  Plateaus  with  local  relief  of  400  fathoms 
and  ranges  8  to  20  miles  apart.  Flanking  the  High  Fractured  Plateaus 
is  a  succession  of  provinces  known  as  the  Upper  Step,  Middle  Step,  and 
the  Lower  Step.  The  topography  here  likewise  is  rough  with  local  relief 
of  200  fathoms.  Peaks  over  200  fathoms  high  occur  at  about  the  fre- 
quency of  7  per  each  100  miles.  The  steps  appear  to  be  separated  from 
each  other  by  scarps  of  considerable  length. 

Seismicity.  The  High  Fractured  Plateaus  and  Rift  Valley  make  up  a 
zone  of  considerable  seismicity.  See  Fig.  10.16.  Another  zone  extends  from 
the  Rift  Valley  through  the  Azores  eastward  to  Gibraltar. 

Sediments.  Photos  taken  on  the  sides  of  seamounts  in  the  Rift  Moun- 
tains show  scour  and  ripple  marks  indicating  deep-ocean  currents.  Cores 
taken  in  intermontane  basins  show  interlayering  as  turbidity  current 
deposits. 

Rocks.  The  lithology  of  the  Mid-Atlanic  Ridge  is  known  from  three 
sources:  (1)  rocks  dredged  from  the  sea  floor,  (2)  detrital  rock  frag- 
ments found  in  sediment  cores,  and  (3)  rocks  exposed  on  the  islands  of 
the  Ridge.  These  all  point  to  olivine  gabbro,  serpentine,  basalt,  and  dia- 
base as  the  predominating  rock  types.  One  limestone  sample  probably 
of  Tertiary  age  was  collected  from  the  Rift  Valley  at  about  30°  N.  Lat. 
(Heezen  et  al,  1959). 

Crustal  Structure.  Seismic  refraction  records  have  been  obtained  in 
about  twenty  places  on  the  Mid-Atlantic  Ridge,  and  the  following  layer- 
ing is  reported  (Heezen  et  al,  1959).  See  Fig.  10.13. 

.  .  .  the  average  crustal  structure  of  the  crest  provinces  and  Upper  Step 
consists  of  0.4  km  of  low-velocity  sediment  and  2.8  km  of  rock  with  a  velocity 
of  5.1  km/sec.  overlying  a  substratum  in  which  the  velocity  is  7.3  km  sec. 
The  thickness  of  the  layer  of  low-velocity  sediment  varies  considerably  From 


152 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


^e^J 


*n" — ^~ '/•   ■•••   : 

*  *•  •>  ••  • 


Fig.   10.16.      Earthquake  epicenters,   North  Atlantic.  Reproduced  from   Heezen  ef  a/.,   1959. 


place  to  place.  In  the  crest  provinces  the  5.1  km/sec  layer  is  commonly 
exposed.  In  the  flank  provinces  appreciable  thicknesses  (to  1  km)  of  sediment 
have  been  measured. 

Under  the  abyssal  floor  of  the  ocean  the  low  velocity  sediment  layer 
is  underlain  by  a  6.7-km/sec  layer,  and  this  by  a  8.1-km/sec  layer.  The 
lower  is  considered  the  mantle  of  peridotite  and  the  overlying  layer  a 


gabbroic  or  firm  basalt  layer.  Under  the  Ridge  neither  of  these  two  are 
present  but  instead  layers  of  5.1-km/sec  and  7.3-km/sec. 

Ewing  and  Ewing  (in  press)  suggest  that  this  intermediate  velocity 
(7.3  km/sec.)  is  the  result  of  a  physical  mixture  of  oceanic  crustal  rocks  and 
mande  rocks.  To  explain  such  large-scale  mixing  they  propose  that  extensive 
vulcanism   and   intrusion   along   the   Mid-Adantic    Ridge   have   produced   an 


ATLANTIC  COASTAL  PLAIN  AND  ADJACENT  OCEAN  BASIN 


153 


intermingling  of  the  crustal  and  mantle  rocks,  and  that  this  was  associated  with 
convection  cells  in  the  deep  mantle  which  supply  large  quantities  of  basaltic 
magma  and  produce  extensional  forces  on  the  crust  and  upper  mantie  ( Heezen 
et  d.,  1959). 

In  a  paper  (in  press)  Heezen  and  Ewing  compare  in  detail  the  topography 
and  seismicity  of  the  African  rift  valleys  and  the  Rift  Valley  of  the  Mid-Adantic 
Ridge.  Their  conclusion  is  that  the  two  areas  are  of  basically  the  same  structure, 
and  in  fact  both  form  parts  of  the  same  continuous  structural  feature.  Since 


the  African  rift  valleys  seem  clearly  to  be  the  result  of  normal  faulting  resulting 
from  extension  of  the  crust,  Heezen  and  Ewing  conclude  that  the  topo£raphy 
of  the  Mid-Adantic  Ridge  is  largely  the  result  of  normal  faulting.  Whether 
the  forces  are  the  result  of  horizontal  extension  or  vertical  uplift  remains  the 
most  important  unsolved  problem  in  connection  with  the  origin  of  the  con- 
tinental as  well  as  the  sub-oceanic  rift-valley  systems.  Hess  ( 1954)  has  proposed 
a  mechanism  relating  suboceanic  uplift  to  expansion  due  to  serpentization 
of  the  upper  mande  (Heezen  et  al.,  1959). 


11. 


HUDSON  VALLEY  LAKE  CHAMPLAIN  REGION 

Relief  Features 

The  relief  features  of  the  Taconic  erogenic  system  stretch  along  the 
general  Hudson  Valley,  Lake  Champlain  lowlands,  and  St.  Lawrence 
Valley.  In  addition  to  hills  and  ridges  within  the  lowland,  it  is  convenient 
under  this  heading  to  discuss  the  Hudson  highland  and  Catskill  and 
Adirondack  Mountains  on  the  west,  the  Laurentian  highlands  on  the 
northwest,  and  the  Taconic  and  Green  Mountains  on  the  east.  The 
Taconic  orogeny  culminated  in  late  Ordovician  time,  and  most  of  the 
structures  of  the  Hudson  and  Lake  Champlain  valleys  and  of  the  ranges 
along  its  eastern  margin  are  Taconic.  The  Catskills  and  Adirondacks, 
however,  are  part  of  the  stable  interior.  See  index  map,  Fig.  11.1  and 
geologic  map,  Fig.  11.2. 


NEW  ENGLAND 
APPALACHIAN  SYSTEMS 

DIVISIONS  OF  NEW  ENGLAND  APPALACHIANS 

The  New  England  Appalachian  systems  will  be  divided  for  purposes  of 
discussion  into  a  western  belt  and  an  eastern.  The  western  belt  includes 
those  structures  in  and  on  either  side  of  the  Hudson  Valley  and  Lake 
Champlain  lowlands,  and  the  eastern  belt  includes  a  north-south  zone 
through  central  and  eastern  Vermont,  New  Hampshire,  and  Maine.  The 
western  zone  is  essentially  the  core  of  the  Late  Ordovician  Taconic 
orogeny  and  the  eastern  the  site  of  the  Late  Devonian  Acadian  orogeny. 
A  third  division  may  be  recognized  through  Rhode  Island  and  Massa- 
chusetts on  the  far  east  where  Carboniferous  basins  and  related  igneous 
activity  indicate  a  still  later  orogenic  belt. 


Catskill  Mountains 

The  Catskill  Mountains  are  west  of  the  Hudson  River  and  about  100 
miles  north  of  the  city  of  New  York.  See  geomorphic  diagrams  of  Figs. 
11.3  and  11.4.  They  are  a  dissected  plateau  with  highest  summit  levels 
about  5000  feet  above  sea  level  and  local  relief  of  over  3000  feet.  They 
were  the  site  of  pioneer  geologic  studies  in  North  America,  and  in  them 
the  stratigraphic  sequence  of  the  Silurian  and  Devonian  systems  was  early 
established.  The  Catskills  proper  consist  of  nearly  flat-lying  beds,  gently 
inclined  toward  the  west,  and  as  such  are  part  of  the  Appalachian 
Plateaus  geomorphic  province.  The  most  widespread  rocks  are  the 
Devonian.  Along  the  east  margin  and  in  the  adjacent  Hudson  Valley, 
the  strata,  especially  the  Cambrian  and  Ordovician,  are  highly  deformed; 
and  the  Devonian  and  Silurian  beds  rest  on  their  beveled  edges.  The 
classic  angular  unconformity  between  the  Ordovician  and  Silurian  beds, 
which  here  marks  the  Taconic  orogeny,  is  displayed  along  the  southeast 
margin  of  the  Catskills.  See  the  Geological  Map  of  the  United  States. 
Also,  the  system  of  folded  and  thrust-faulted  Appalachians  of  the  south 
narrows  here  into  a  belt  a  few  miles  wide,  and  some  of  its  late  Paleozoic 
structures  may  here  be  impressed  on  the  strata  and  in  part  superposed 


154 


Fig.  11.1.      Principal  physical  features  of  New  England  and  the  Maritime  Provinces.  M.  H.  means 
Montarigian   Hills. 


Fig.  11.2.      Generalized  geologic  map  of  New  England.  Reproduced  from  Billings,  1956. 


Fig.    11.3.      Block   diagram   of   lower   Hudson   River    region    by   Raisz.    Reproduced   from    /nfernaf. 
Geo/.  Congr.  Guidebook    1,   1933,  Eastern  New  York  and  Western   New  England. 


Fig.   11.4.      Block   diagram   of   lower   Hudson   River   region.  Joins  opposite  figure  on   north. 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


157 


on  the  older  structures  of  the  Taconic  orogeny.  The  section  along  the 
Catskill  aqueduct,  Fig.  11.5,  gives  a  good  idea  of  the  composition  and 
structure  of  the  Catskills  and  adjacent  Hudson  Valley. 

The  regional  stratigraphy  including  the  Catskills  has  been  presented  in 
Chapter  8  on  the  southern  and  central  Appalachians.  See  Figs.  8.10  to 
8.12. 

Regarding  the  structural  history,  Chadwick  and  Kay  (1933)  say  the 
following: 

There  is  evidence  in  the  region  of  at  least  two  periods  of  deformation.  In 
several  exposures,  Ordovician  beds  lie  in  close  contact  with  angular  uncon- 
formity beneath  the  basal  Silurian  sediments.  Formations  as  young  as  Middle 
Devonian  have  been  folded  and  affected  by  faults  of  low  angle  showing  relative 
overthrust  from  the  east. 

The  first  of  these  deformations  is  definitely  assigned  to  the  Taconian  dis- 
turbance, for  which  this  is  the  classical  area  of  study.  The  later  deformation  may 
have  been  produced  either  in  the  Acadian  disturbance  at  the  end  of  the 
Devonian  or  in  the  Appalachian  revolution,  or  in  both.  Inasmuch  as  late 
Paleozoic  rocks  are  not  present  in  the  disturbed  areas,  it  is  not  possible  to  date 
the  movements  precisely.  The  tectonic  movements  that  produced  the  coarse 
clastic  Upper  Devonian  sediments  to  the  west  may  have  been  accompanied  by 
this  folding  and  faulting;  if  so,  the  structures  are  Acadian.  On  the  other  hand, 
the  structures  are  similar  to  those  formed  farther  to  the  southwest  and  north- 
east in  the  Appalachian  revolution,  and  it  is  probable  that  some  of  the  effects 
were  produced  at  that  time. 

Erosion  has  been  dominant  in  the  region  since  the  end  of  Paleozoic  time. 
Remnants  of  a  peneplain  may  be  preserved  in  the  accordant  summits  of  the 
higher  peaks  in  the  western  part  of  the  region,  of  which  Plateau  Mountain  is 
typical.  The  high  areas  that  bear  these  remnants  seem  to  stand  above  an  erosion 
level  represented  by  the  open  upper  valleys  of  the  Catskills  and  by  the  beveled 
surface  of  the  Helderberg  Plateau,  to  the  north,  seen  from  Windham  Notch. 
This  lower  level  lies  2,500  feet  (750  meters)  below  the  supposed  summit 
peneplain  and  has  been  correlated  by  some  geologists  with  the  Schooley  pene- 
plain of  Pennsylvania,  by  others  with  the  Harrisburg  peneplain,  of  later  Tertiary 
age.  Further  elevation  and  subsequent  erosion  produced  a  peneplain  that  bevels 
the  weaker  folded  rocks  in  the  Hudson  Paver  Valley  west  of  the  river.  This  later 
Tertiary  surface  is  1,500  feet  (450  meters)  below  the  last  and  has  been  called 
the  Albany  peneplain.  More  recent  movements  have  elevated  this  surface  a  few 
hundred  feet  (100  meters  or  more)  above  present  base-level,  permitting  the 
excavation  of  valleys  in  the  weakest  rock  belts.  Thus  erosion  has  brought  about 
the  removal  of  a  great  mass  of  later  Paleozoic  sediments  through  several  cycles 
of  erosion  with  intervening  uplifts,  exposing  early  Paleozoic  rocks  in  the  eastern 
part  of  the  region. 


Adirondack  Mountains 

The  Adirondack  Mountains  constitute  a  nearly  circular  uplift  about  150 
miles  across,  which  extends  from  Lake  Ontario  on  the  west  to  Lake  Cham- 
plain  on  the  east,  and  from  the  Mohawk  Valley  on  the  south  to  the  St. 
Lawrence  lowland  on  the  north.  The  northwestern  part  of  the  Adiron- 
dacks  is  a  rolling  upland  of  gentle  relief  and  a  mean  altitude  of  about 
1000  feet  above  sea  level,  whereas  the  southeastern  part  is  a  rugged  moun- 
tain mass,  individual  ridges  of  which  reach  3000  above  the  valley 
floors,  and  the  highest  peak,  Mount  Marcy,  stands  5344  feet  above  the  sea. 

The  Adirondacks  consist  mainly  of  Precambrian  rocks.  These  are  sur- 
rounded by  gently  upturned  Cambro-Ordovician  sediments,  except  near 
Kingston,  Ontario,  along  the  St.  Lawrence,  where  a  neck  of  the  Pre- 
cambrian rocks  connects  with  the  Precambrian  of  the  Canadian  Shield 
( the  Frontenac  axis )  and  along  Lake  Champlain  where  highly  deformed 
strata  of  the  Taconic  system  bound  the  dome. 

According  to  Balk  ( Longwell,  1933 ) : 

The  unconformity  between  pre-Cambrian  and  Paleozoic  rocks  is  exposed  in 
numerous  places,  although  in  the  southeast  the  primary  relations  are  somewhat 
blurred  by  post-Ordovician  faults  along  which  the  Adirondacks  have  been 
elevated  with  reference  to  the  surrounding  younger  rocks.  One  of  these  faults 
passes  through  Saratoga;  another  one  forms  the  escarpment  northwest  of  town 
and  is  followed  by  the  road  from  Saratoga  to  Glens  Falls  for  many  miles. 
Escarpments  near  Lakes  George  and  Champlain  are  due  to  additional  border 
faults  along  the  eastern  margin  of  the  Adirondacks. 

The  pre-Cambrian  sedimentary  rocks  of  the  Adirondacks  appear  to  be 
identical  with  rocks  of  the  same  general  age  in  the  Provinces  of  Quebec  and 
Ontario,  so  that  the  whole  region  is  to  be  regarded  as  an  outlier  of  die  Canadian 
shield. 

Sedimentation  in  and  around  the  Adirondack  region  in  Cambrian  and 
Ordovician  time  is  illustrated  in  the  paleograpbic  maps  of  Fig.  11.6 
and  by  the  cross  section  of  Fig.  11.7.  The  Adirondack  dome  persisted  with 
some  irregularities  as  an  area  of  gentle  uplift  during  the  Cambrian  and 
Ordovician,  and  by  late  Cincinnatian  time  a  broad  domal  structure  was  in 
existence.  Then  the  Taconic  orogeny  occurred  along  the  east  side  and 
following  the  orogeny  closely  the  dome  was  broken  by  block  faults.  Figure 
11.13  is  a  cross  section  that  restores  the  Adirondack  uplift  and  adjacent 


158 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Fig.    11.5.      Cross    section    along    the    Catskill    aqueduct.    Reproduced    from    Geological   Society   of    America 
Guidebook  of  Excursions,  1948. 


areas  to  this  time.  The  distribution  of  faults  and  the  Taconic  front  are 
shown  in  Fig.  11.12  in  relation  to  the  Lower  Ordovician  facies. 

Lower  Hudson  Valley  Crystallines 

Definition.  The  block  diagrams  of  Figs.  7.3  and  11.3  show  the  lower 
Hudson  Valley  area  to  be  made  up  of  the  Triassic  basin  sediments  and 
sills,  and  the  New  England  upland.  The  following  paragraphs  concern 
the  New  England  upland  thus  designated,  but  the  term  is  general  for 
much  of  New  England,  and  more  specific  names  have  been  given  to  the 
features  of  the  lower  Hudson  Valley  area.  The  Reading  prong  of  Penn- 
sylvania and  the  New  Jersey  highland  merge  on  the  northeast  with  the 
Hudson  highland,  whose  upland  surface  is  about  1000  feet  above  sea 
level.  The  Hudson  River  cuts  a  fairly  narrow  valley  without  flood  plain 
through  the  highland  between  Newburgh  and  Peekskill.  See  map  of  Fig. 
11.3.  The  Hudson  highland  continues  northeastward  into  Connecticut  as 
the  Housatonic  highland. 

Lower  Hudson  Valley.  From  Peekskill  to  Manhattan  Island,  the  Hud- 
son is  bounded  on  the  west  by  the  Triassic  rocks,  mostly  thick  diabase  sills 
that  form  the  Palisades  of  the  Hudson,  and  on  the  east  by  rounded  hills 
of  a  metamorphic  and  plutonic  complex.  The  rocks  along  the  route  from 
New  York  City  to  Peekskill  consist  of  gneisses  intruded  and  injected  by 
granite  with  infolded  belts  of  limestone  and  schist.  See  cross  section  of 
Fig.  11.8.  The  major  structural  axes  trend  north-northeast  and  are  strongly 
reflected  in  the  general  arrangement  of  ridges  and  valleys.  Along  the 
lower  part  of  the  river  in  the  vicinity  of  Yonkers,  the  structures  trend 
about  N.  20°  E.  and  are  parallel  with  the  river,  but  a  few  miles  above 


Yonkers  they  strike  more  easterly,  whereas  the  course  of  the  river  is  nearly 
due  north. 

Hudson  and  Housatonic  Highlands.  Balk  (1937)  and  Barth  (1937) 
have  made  a  thorough  study  of  the  Hudson  and  Housatonic  highlands 
and  adjacent  areas,  and  report  a  complex  of  Precambrian  crystalline 
rocks  and  a  series  of  three  sedimentary  formations  of  Cambrian  and 
Ordovician  age.  The  highlands  themselves  are  formed  of  a  complex  of 
gneisses  of  granitic  and  syenitic  composition.  Associated  are  injection 
gneisses  as  well  as  narrow  tracts  of  amphibolite,  marble,  and  other  highly 
metamorphic  rocks.  Along  the  northwestern  border  of  the  highlands, 
medium-  to  coarse-grained  granites  and  granite  gneisses  are  fairly  abun- 
dant. 

The  Paleozoic  strata  are  described  by  Balk  (1937)  as  follows: 

The  oldest  Paleozoic  rock  is  a  pink  or  white  quartzite  (Poughquag  quartzite) 
that  rests  unconformably  upon  the  various  pre-Cambrian  rocks.  At  the  base,  a 
conglomerate  may  be  present,  though  rarely  more  than  a  few  feet  thick.  Quartz 
pebbles,  about  an  inch  across,  and  an  occasional  black  chert  fragment,  are  the 
most  abundant  constituents.  Fossils  of  Lower  Cambrian  age  have  been  described 
from  several  localities  in  southeastern  New  York. 

The  quartzite  is  succeeded  by  a  sequence  of  carbonate  rocks  to  which,  in 
the  Poughkeepsie  area,  the  name,  Wappinger  terrane,  has  been  applied.  As 
elsewhere  in  the  Appalachian  region,  the  rocks  include  members  of  Cambrian 
and  Ordovician  age,  but  Quaternary  deposits  obscure  so  much  of  the  bedrock 
that  no  complete  section  is  available.  Fossils  ranging  from  Lower  Cambrian 
to  Middle  Ordovician  have  been  reported  from  various  localities,  but  it  is 
believed  that  there  are  several  disconformities  within  the  terrane.  The  thickness 
of  the  series  is  difficult  to  estimate,  but  may  well  exceed  1,000  feet. 

A  series  of  slates  and  similar  rocks,  resting  on  the  carbonate  rocks,  is  called 
the  Hudson  River  pelite.  Fossils  of  Middle  Ordovician  age  have  been  found  in 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


L50 


the  western  portion  of  Poughkeepsie  quadrangle,  but  farther  east,  cleavage 
seems  to  have  destroyed  them.  Hudson  River  slates  of  black,  gray,  greenish, 
and  red  color  are  known;  commonly,  argillaceous  layers  are  interbedded  with 
thousands  of  thin,  fine-grained  sandy  layers,  or  aphanitic  cherty  beds  that 
weather  whitish.  Scattered  through  the  series  are  hundreds  of  lenses  of  sand- 
stone, or  quartzite,  conglomerate,  and  graywacke,  and  quartz  veins  penetrate 
the  rock  in  almost  every  outcrop.  On  account  of  the  intricate  folding,  and 
absence  of  continuous  exposures,  the  thickness  of  the  Hudson  River  series  is 
unknown,  but  it  may  exceed  that  of  the  carbonate  rocks  below. 

Balk's  interpretation  of  the  structure  of  the  region  may  best  be  under- 
stood by  the  study  of  the  lower  cross  section  of  Fig.  11.9.  Of  first  im- 
portance is  the  unconformity  at  the  base  of  the  Poughquag  quartzite 
which  clearly  reveals  the  Precambrian  age  of  the  gneiss  and  granite  com- 
plex of  the  Hudson  and  Housatonic  highlands. 

The  highlands  are  regarded  as  uplifted  blocks.  As  the  uplift  occurred, 
the  Paleozoic  succession  along  the  west  side  was  tilted  westward,  and  in 
addition  was  broken  by  a  number  of  faults,  most  of  which  are  thrusts  of 
medium  to  steep  southeasterly  dip.  Thrust  faults  are  also  recognized  along 
the  east  flank  of  the  northeast  end  of  the  Hudson  highland.  That  the 
Precambrian  highlands  are  uplifted  masses  is  shown  by  the  general  basin 
distribution  of  the  youngest  rocks,  the  Hudson  River  pelites,  in  the  middle 
of  the  intervening  areas,  and  then  the  next  older  rocks,  the  Wappinger 
limestone  and  Poughquag  quartzite  next  to  the  gneiss. 

Between  the  Hudson  and  Housatonic  highlands  is  a  Paleozoic  area 
which  is  regarded  as  a  faulted  syncline.  It  has  the  special  significance  of 
affording  a  connection  between  the  known  Cambrian  and  Ordovician 
strata  on  the  west  of  the  highlands  to  unfossiliferous  and  more  meta- 
morphosed strata  on  the  east,  and  it  is  here  that  Balk  and  Barth  have 
demonstrated  the  progressive  metamorphism  of  the  Hudson  River  slates 
and  phyllites  to  schist  and  even  injection  gneisses,  and  the  increase  in 
marmorization  of  the  carbonates. 

The  general  basin  structure  of  the  strata  between  the  masses  of  Pre- 
cambrian gneisses  is  greatly  marred  and  distorted  by  normal  and  thrust 
faults  which  have  cut  the  quartzite  for  miles  along  the  gneiss  borders, 
and  at  many  places  have  brought  the  limestone  to  the  level  of  the  pelite. 
Most  of  the  faults  strike  north-northeast  or  north-south;  hence,  the  rock 


CAMBRIAN     5ERIES 


CANADIAN      SERIES 


CHAZYAN      SERIES 


LOWEST     MOHAWKIAN  (PAMELIA)    LIME- 
STONE   ON    PRE- MOHAWKIAN  GEOLOGY 


Fig.  11.6.  Cambrian  and  Ordovician  paleogeography  of  the  New  York  and  St.  Lawrence 
region,  after  Kay,  1942.  The  ruled  areas  represent  the  spread  of  deposits,  and  the  Taconic 
allochthone  as  postulated  in  Figs.  11.12  and  11.13  is  shown  in  both  present  ^left)  and 
original   (right)   position. 


160 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


units  are  arranged  in  belts  of  north-southerly  trend.  The  horizontal  forces 
that  caused  the  thrusts  are  also  believed  to  have  cast  the  sedimentary 
rocks  into  folds  which  are  overturned  to  the  west.  The  folds,  however, 
are  very  small  ones  in  otherwise  gently  downfolded  beds. 

Cleavage  pervades  the  crenulated  sediments  widely.  It  is  everywhere 
parallel  to  the  axial  planes  of  the  crenulations,  and  is  best  developed  in 
the  slate  phases  northeast  of  Poughkeepsie. 

The  metamorphic  rocks  of  the  lower  Hudson  River  Valley  have  been 
regarded  as  Precambrian,  but  in  light  of  Ralk's  and  Barth's  work  it  seems 
probable  that  only  the  Fordham  gneisses  is  Precambrian  and  that  the 
Inwood  limestone  is  equivalent  to  the  Wappinger  limestone  and  the  Man- 
hattan schist  to  the  Hudson  River  pelite,  both  of  Cambro-Ordovician  age. 
Refer  to  cross  sections  of  Figs.  11.5  and  11.8.  For  discussion  of  the  prob- 


DENKIARK 


WEST     CANADA 
CREEK 


lem  see  Balk,  1937.  Paige  (1956)  has  correlated  undoubted  Cambro- 
Ordovician  rocks  west  of  the  Hudson  River  near  Peekskill  with  the 
Inwood  marble  and  Manhattan  schist  east  of  the  river. 

Potassium-argon  age  determinations  on  the  micas  of  the  Manhattan 
schist,  the  Inwood  marble,  the  Fordham  gneiss,  some  discordant  pegma- 
tites, and  a  diorite  were  made  by  Long  and  Kulp  (1958).  An  average  age 
for  the  generation  of  the  micas  of  the  post-Fordham  gneiss  formations  is 
given  as  366  =*=  9  m.y.,  which  they  say  may  tentatively  be  correlated 
with  the  Late  Ordovician  Taconic  orogeny.  Very  recent  interpretations 
by  Hurley  et  al.  ( 1959 )  indicate  that  this  absolute  age  may  be  post-Early 
Devonian,  and  in  connection  with  orogeny  in  New  Hampshire  their  work 
will  be  referred  to  again. 

Biotite  from  the  Fordham  gneiss  is  slightly  older;  the  "apparent  age" 


MOHAWK     VALLEY 


WELL5 


LAKE  CHAMPLAIN     CANAJOHARIE 


z 


Zone 


or 


/}  m  /o/  ex  og  f*  a  jo  f  </sjtz-T~z.  am  r>  / '  e.  jt  /  c  a  <y  / '/\s  _r~  _ 

CAnAO,AN  'S^^^~~^T 8=7 h 

[z 

^oJvv^ — £HO/7EHflM  *  f  H 

ADIRONDACK      AYIS  0*p 

u 

a 
o 

h 

vo 
hi 


Fig.   11.7.      Restored     section     of     pro-Middle     Trenton     formations    across 
York,    after    Kay,    1942. 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


161 


Fig.  11.8.  Cross  section  along  Kenisco  bypass  tunnel  of  the  Delaware  aqueduct.  Kenisco  Dam  is 
just  east  of  Croton  Lake  in  the  lower  Hudson  Valley.  Reproduced  from  Geological  Sociefy  of  America 
Guidebook    of    Excursions,    1948. 


of  two  samples  is  given  as  400  and  440  m.y.  The  authors  suggest  that  the 
Fordham  gneiss  being  demonstrably  older  and  probably  the  Precambrian 
basement  did  not  lose  all  its  argon  during  the  365  m.y.  recrystallization 
I  process,  and  hence  its  micas  yield  somewhat  older  dates.  It  will  be  re- 
called that  zircons  from  the  Baltimore  gneiss  of  the  crystalline  Piedmont 
yielded  ages  of  about  1100  m.y.,  whereas  the  micas  from  the  same  rock 
gave  ages  of  300  to  350  m.y. 

The  age  of  the  sediments  themselves  is  not  indicated  by  the  isotope 
age  determinations  but,  at  least,  the  time  of  the  last  major  orogeny  and 
metamorphism  is  sufficiently  young  so  that  the  sediments  could  well  be 
Cambro-Ordovician. 

Green  Mountains 

The  Hudson  and  Housatonic  highlands,  if  followed  northerly,  lead 
to  the  Taconic  Mountains  and  northeasterly  to  the  "western  highland"  of 
Connecticut  and  Massachusetts,  of  which  the  Berkshires  are  a  part.  See 


Precambrian  area  in  western  Massachusetts,  Figs.  11.2  and  11.9.  East 
of  die  western  highland  is  the  Triassic  lowland.  The  Berkshire  Mountains 
extend  to  the  Green  Mountains  at  about  the  Massachusetts  and  Vermont 
border,  and  the  Green  Mountains  continue  northward  through  central 
Vermont  to  Quebec.  See  Cady,  1960.  The  Taconic  Range  extends 
northerly  along  the  New  York-Vermont  border  to  about  central  western 
Vermont,  and  between  it  and  the  Berksire-Green  Mountain  element  is 
the  "marble  belt."  For  the  broad  relations  of  these  geologic  units  see  the 
tectonic  map,  Fig.  11.10.  The  Green  Mountains  are  comparable  in  eleva- 
tion with  the  Adirondacks  which  lie  across  the  Lake  Champlain  Valley, 
but  the  other  highlands  and  ranges  are  comparatively  low. 

The  core  of  the  southern  end  of  the  Green  Mountains  is  made  up  of 
granites  and  gneisses  of  Precambrian  age.  These  ancient  rocks  are  over- 
lapped on  the  flanks  by  quartizites  of  lowest  Cambrian  age.  See  lower 
cross  section  of  Fig.  11.11.  The  northern  part  of  the  range  is  a  gneiss  and 
schist  anticlinorium  which  plunges  northerly,  and  although  somewhat  like 


162 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


TACONIC   RANGE   EAST   OF   TROY 


GREEN  MTS. 


TACONIC      RANGE       NEAR     CHATHAM 


Chatham 
thrust 


HUDSON        HIGHLAND 


p€g 


EAST      OF     POUGHKEEPSIE 
Ohr 


HOUS  ATONIC 
Ohr 


HIGHLAND 
p€g 


Fig.  11.9.  Cross  sections  of  central  and  southern  Taconic  Range.  Section  east  of  Troy,  N.  Y.,  after 
Balk,  1953.  p€g,  Precambrian  gneiss;  Cc,  Lower  Cambrian  Cheshire  quartzite;  CO,  Cambro-Ordo- 
vician  limestone  and  dolomite;  Oa,  gray,  purple,  and  black  slate  and  quartz-chlorite  schist. 

Section   near  Chatham,   N.  Y.,   after  Craddock,   1957.  €s,   green   slate   with    interbedded   gray- 


wacke   and    quartzite;    Oc,   carbonate    rock;    Ode,    green    shale;    Ons,    red    shale    member;    Onm, 
Mount  Merino  dark  shale  wtih   interbedded  chert;  Ona,  Austin  Glen  graywacke  and  dark  shale. 
Section    east    of    Poughkeepsie,    N.    Y.,    after    Balk,    1937;    pCg,    Precambrian    gneiss;    €Ow, 
Wappinger   dolomitic    limestone;    Ohr,    Hudson    River    pel  lite,    phyllite,   and    schist. 


the  southern  core  is  believed  by  Cady  ( 1945 )  to  be  part  of  the  Taconic 
allochthone.  See  map  of  Fig.  11.10.  In  its  east  flank  the  Green  Mountain 
anticlinorium  contains  a  discontinuous  belt  of  ultrabasic  intrusives  which 
are  associated  with  volcanics  including  pillow  basalt. 

Taconic  Mountains 

The  Taconic  Mountains  are  a  low  range  of  hills  composed  mostly  of 
argillaceous  rocks  such  as  phyllite,  slate,  and  shale.  This  clastic  sequence 
is  surrounded  in  the  adjacent  lowlands  by  rocks,  chiefly  carbonates.  In  the 
Taconic  sequence,  as  it  is  called,  there  is  one  thin  quartzite  formation 
and  one  very  thin  limestone  which  together  form  perhaps  5  percent 
of  the  section.  There  are  three  slate  formations  of  Middle  Ordovician  age 


and  six  of  Lower  Cambrian.  No  Middle  or  Upper  Cambrian  is  present 
and  no  Lower  Ordovician.  The  Lower  Cambrian  of  the  Taconic  Range 
lies  beside  the  Lower  Cambrian  of  the  valleys  and  the  two  groups  have 
no  features  in  common  except  that  of  age  (Keith,  in  Longwell,  1933). 
Similarly,  most  of  the  Ordovician  of  the  mountains  differs  from  the  Ordo- 
vician of  the  surrounding  valleys.  These  relations  have  led  through  a  long 
controversy  to  the  interpretation  of  the  Taconic  clastic  sequence  as  a 
klippe,  which  represents  an  eastern  trough  facies  that  has  been  thrust 
westward  30  to  50  miles  or  more  on  a  western  trough  sequence.  It  is  part 
of  the  Taconic  allochthone.  The  carbonates  of  the  western  trough  sup- 
posedly are  the  autochthone.  See  cross  section  D-D',  Fig.  11.11.  The 
details  and  relations  will  be  taken  up  later. 


Fig.  11.10.  Tectonic  and  palinspastic  maps  of  the 
Taconic  system  in  eastern  New  York,  western  New 
England,  and  southern  Quebec,  after  Cady,  1945. 
The  palinspastic  map  attempts  to  restore  the  thrust 
slices  to  their  approximate  position  before  they 
were  moved  westward.  Since  the  Devonian  strata 
were  deposited  after  the  Taconic  orogeny,  they 
were  not  displaced  by  it  and  do  not  participate 
in  the  restoration.  S.L.  means  slice  or  thrust  sheet 
and  the  abbreviations  in  the  tectonic  map  may  be 
identified  by  comparison  with  the  palinspastic 
map. 


HINESBUBG      SYNCLINORIUM 
CHAMPLAIN   THRUST  HINESBURG    THRUST  A> 


B 


CHAMPLAIN    THRUST 
r ORWELL    TH.  / 


MIDDLEBURY      SYNCLINORIUM 

0  o 


0      £i€m£dh€f^-1    B' 


ORWELL     THRUST 


OrcJov/cion 


SUDBURY   THRUST 


MIDDLEBURY      SYNCLINORIUM 

O  0      €d     £w      €m  £dh  _£c 


C 


5     MILES 


TACONIC     MTS. 


GREEN      MTS. 

p£q 


•"gv-''-''7:r~rv?-N-€f-q  _^^=^££ll         Osc       _£4  £q^-rr^rr^r^r-r^^€q 


€Q   €d        cis 


D' 


-TACONIC    THRU5T 


Fig.  11.11.  Cross  sections  of  the  Taconic  system  of  western  Vermont,  A-A',  B-B',  and  C-C, 
after  Cady,  1945.  Refer  to  map  of  Fig.  11.16.  £?md,  Mendon  series;  Cc,  Cheshire  quartzite; 
Cdh,  Dunham  dolomite;  £p,  Perker  shale;  Cm,  Monkton  quartzite;  Cw,  Winooski  dolomite;  €d, 
Danby  formation;  O,  several  Ordovician  formations;  Obm,  Bascom  formation. 

Cross  section   of  Taconic  and   Green   Mountains  along   Vermont-Massachusetts   border  and   into 


/O     MILES 


eastern  New  York,  D-D',  after  Knopf  and  Prindle  in  Longwell,  1923.  pCq,  granite  gneiss;  €q, 
quartzite,  including  phyllite  and  conglomerate;  Cd,  dolomite;  €rg,  graywacke;  Cs,  black  shale; 
Olm,  limestone  and  marble;  Osc,  black  shale,  red  shale,  and  chert;  gph,  Cambrian  (?)  green  , 
phyllite;   as,   Cambrian   (?)   albite   schist. 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


165 


The  manner  of  thrusting,  as  conceived  by  Kay,  in  map  view  is  graphi- 
cally illustrated  in  Fig.  11.12,  and  in  cross  section  in  Fig.  11.13. 

Two  cross  sections  of  the  central  and  southern  Taconic  Range  are  pre- 
sented in  Fig.  11.9  and  should  be  referred  to  in  the  following  discussion 
against  the  klippe  hypothesis. 

In  a  study  of  the  Taconic  Range  west  of  Troy,  Ralk  ( 1953 )  recognizes 
thrusting  and  an  eastern  allochthonous  sequence  and  a  western  autoch- 
thonous sequence,  but  concludes  that  dense  vegetation  cover  and  much 
drift  leave  so  few  outcrops  that  the  existence  of  a  great  Taconic  klippe 
cannot  be  proved  or  disproved.  In  a  study  farther  south  near  Pough- 
keepsie  (1937)  he  believes  there  is  little  evidence  to  support  the  thrust 
and  klippe  hypothesis. 

Thrust  sheets  and  klippen  are  postulated  because  of  anomalous  stratigraphic 
successions,  not  otherwise  explainable;  or  because  of  structure  anomalies  not 
understandable  from  other  points  of  view;  or  because  the  klippen,  although 
closely  related  to  rocks  nearer  the  root  zones,  were  obviously  out  of  their 
proper  geologic  setting;  or  on  the  evidence  of  intensely  crushed  subhorizontal 
zones  of  deformation;  or  on  the  evidence  of  exposed  soles.  None  of  these 
criteria  appears  to  be  fully  applicable  here.  There  is  no  proof  of  an  anomalous 
stratigraphic  succession  in  the  gap  of  Wingdale;  the  deformation  of  the 
supposed  thrust  sheet  of  pelite  is,  to  all  appearances,  synchronous  with  that 
of  the  autochthonous  formations;  the  gneiss  of  the  supposed  klippen  is  known 
to  underlie  the  sedimentary  rocks  a  few  thousand  feet  below  the  surface;  no 
crush  horizons,  or  exposures  of  indubitable  soles,  have  been  observed  (Balk, 
1937). 


Craddock  (1957)  also  concludes  against  the  major  klippe  hypothesis 
(middle  cross  section  of  Fig.  11.9)  in  a  study  of  the  southern  cud  ol  tin- 
Taconic  Range.  He  says: 


Fig.  11.12.  Distribution  of  Canadian  (Lower  Ordovician)  facies  in  New  England  and  New 
York,  after  Kay,  1942.  The  map  on  left  shows  the  present  distribution  as  a  result  of  the 
Taconic  (post-Ordovician)  thrusting,  and  the  map  on  right  shows  the  inferred  distribution 
before  thrusting  (a  palinspastic  map).  Vertically  ruled  sediments  are  carbonates;  horizontally 
dashed  sediments  are  shales. 


GREEN 

MT5.       CONNECTICUT 


/? D/ROND^CM    AXIS 
Fig.   11.13.      Section   of   Adirondack   dome   and   Taconic   system   restored   to   early   Silurian   time    (after    Kay,   1942). 


AXIS 


BELT 


166 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


<  > 

_i  — 

m  or 


uj  oc 

Q.  CD 

o-  Z 

D3 


z 
UJ  <x 

_l  — 

OK 

Q  CD 


"J  CD 


STANDARD 


RICHMOND 


MAYSVILLE 


EDEN 


GLOUCESTER 


COLLINGWOOD 


COBOURG 


SHERMAN  FALL 


ROCKLAND 


CHAUMONT 


LOWVILLE 


PAMELIA 


VALCOUR 


V///////A 

? ?. — ? — 

MIOOLEBURY  LS. 
8EL0ENS    FM 


CROWN  POINT 


DAY   POINT 


///////// 


SMITHVILLE 


COTTER- POWELL 


ROUB1DOUX 


GASCONADE 


TREMPEALEAU 


FRANCONIA 


DRESBACH 


MARJUM 


WHEELER 


SWASEY 


DOME 


HOWELL 


SPENCE 


LANGSTON 


ROME 


SHADY 


ERWIN 


HAMPTON 


UNICOI 


WEST-CENTRAL 
VERMONT 


HORTONVILLE    SL 
GLEN    FALLS    LS. 


ORWELL  LS. 


BURCHAROS 


BRIDPORT   OOL .. 


BASCOM     FM. 


CUTTING     OOL. 

SHELBURN.MARBIE 
CLARENDON  SPRINGS 


-■? ? ? 

WINOOSKI     DOL. 

MONKTON    OT2ITE. 

DUNHAM     DOL. 

CHESHIRE  OTZITE 

-? ? ?  — 

"MENDON   SERIES" 

"MT    HOLLY  SERIES" 


NORTHWESTERN 
VERMONT 


TstanbridgeI 

L    si-    J 


[mystic  congl] 
? 


grandge  sl. 
corliss  congl. 
highgate  sl. 


ROCKLEOGE   CONGL 
HUNGERFORO  SL. 
SAXE  BROOK  DOL. 
SKEELS  CORNERS  F 
MILL  RIVER  CONGL. 
ST.  ALBANA  SL. 


RUGG   BROOK  FM. 
PARKER    SL. 
DUNHAM   OOL. 
GILMAN  OTZITE. 


WEST  SUTTON  SL 
WHITE  BROOK  OOL. 
PINNACLE  GRAYWCK. 
CALL  MILL    SL. 
TIBBIT  HILL  SCHT. 


EASTERN 
NEW   YORK 


INDIAN  LADDER  BED 


ISLE    LAMOTTE    LS 
AMSTERDAM    LS. 


CHAUMONT  LS 


LOWVILLE  LS. 


VALCOUR  LS 
CROWN  PT.  LS. 
OAY    POINT  LS. 


BEEK.E 
CASSIN  FM  I  SEEK. 


A 


BEEK.  01  a  02     ?- 
BEEK.C    * 


—  ■ TRIBES  HILL 

BEEK  B    WHITEHALL 


LITTLE   FALLS 

DOL. 

THERESA   FM. 


NEW  YORK 
QUEBEC 


SNAKE    HILL  SH.  ? 


NORMANSKILL  SH 


OEEPSKILL    SH. 


SCHAGHTICOKE 


SILLERY   SL.  ? 


?  ? 


SCHODACK  SH.B  LS. 


BOMOSEEN    GRIT 


NASSAU     BEOS 


Fig.   11.14.      Stratigraphic  correlations  in  west-central  Vermont  and  adjoining  areas,  after  Cady, 
1945. 


Evidence  for  the  existence  of  the  "Taconic  klippe"  was  not  found  in  mapping 
this  quadrangle.  Analysis  of  the  development  of  the  klippe  hypothesis  indicates 
that  it  is  based  principally  upon  stratigraphic  considerations;  available  struc- 
tural evidence  weighs  against  this  interpretation.  While  the  klippe  hypothesis 
seems  to  explain  well  the  relations  at  the  north  end  of  the  Taconic  Range, 
the  problem  of  adequately  defining  the  boundaries  of  this  'Tdippe"  causes 
serious  doubt  about  its  existence. 

An  alternative  interpretation  of  the  regional  relations  is  suggested,  involving 
unconformities  and  facies  changes  in  a  single  indigenous  sequence.  Trentonian 
rocks  lie  unconformably  on  rocks  as  old  as  Precambrian  from  Vermont  to 
Pennsylvania  and  pass  indiscriminately  in  and  out  of  the  "Taconic  klippe." 
The  Normanskill  and  Deepkill  rocks  (mainly  shale)  are  interpreted  as  passing 
transitionally  into  limestone  to  the  west.  The  Deepkill  is  believed  to  rest 
unconformably  on  rocks  of  Early  Cambrian  to  middle  Canadian  age.  Middle 
Canadian  formations  in  the  kinderhook  quadrangle  are  carbonate  rocks  and 
appear  to  rest  unconformably  upon  Lower  Cambrian  slates;  their  striking 
similarity  to  equivalent  rocks  in  the  near-by  "autochthonous"  series  suggests 
they  have  not  been  displaced  any  great  distance.  The  lower  Cambrian  is  a 
thick  series  of  argillite,  graywacke,  and  quartzite  with  some  thin  carbonate 
rocks  near  the  top.  The  thick,  lower  part  of  this  series  is  considered  a  southward 
continuation  of  the  Mendon  Series  of  Vermont.  The  upper  strata  are  interpreted 
as  the  offshore  equivalents  of  shallow-water  quartzites  and  carbonate  rocks 
deposited  marginal  to  an  eastern  welt  in  later  Early  Cambrian  time. 

Lake  Champlain  and  St.  Lawrence  Lowlands 

The  Champlain  Valley  lies  partly  in  New  England.  In  the  largest  view 
it  is  bounded  on  the  east  by  the  Green  Mountains  and  on  the  west  by  the 
Adirondack  Mountains,  and  at  the  south  it  is  split  by  a  minor  group  of 
mountains,  the  Taconic  Range.  A  large  part  of  the  valley  is  occupied  by 
Lake  Champlain,  the  surface  of  which  is  100  feet  (30  meters)  above  sea 
level  and  the  bottom  is  below  sea  level.  The  valley  passes  northward  into 
Canada  and  curves  northeastward,  merging  into  the  St.  Lawrence  Valley 
(Keith,  in  Longwell,  1933). 

The  valley  is  divided  by  the  Taconic  Mountains  into  a  western  part 
which  is  continuous  with  the  Hudson  River  Valley,  and  an  eastern  part 
which  extends  along  the  eastern  side  of  the  range  nearly  to  Long  Island 
Sound.  This  eastern  part  of  the  valley  is  known  as  the  Rutland  Valley  in 
Vermont  and  the  Stockbridge  Valley  in  Massachusetts. 

The  St.  Lawrence  lowlands  are  of  two  divisions  separated  by  the  fault 
known  as  Logan's  line  ( Fig.  12.2 ) .  Southeast  of  the  fault  is  the  deformed 


( 


! 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


187 


SOUTH 


NORTH 


Fig.  11.15.  North-south  section  in  north- 
western Vermont  of  the  Cambrian  and 
Lower  Ordovician  formations,  restored  to 
early   Ordovician.   Reproduced    from    Shaw, 


1958. 


OUNHAM  DOLOMITE 
MIOOLEBURY        SYNCLINORIUM 


FRANKLIN    BASIN 


OUARTZITE 


DOLOMITE 


SLATE 


LIMESTONE    CONGL. 


Taconic  belt  and  northwest  of  it  is  the  undeformed  shelt  sediments  which 
lay  onto  the  Canadian  Shield. 

Stratigraphij.  The  stratigraphic  columns  presented  in  Fig.  11.14  are 
by  Cady  ( 1945)  and  represent  a  long  endeavor  by  numerous  geologists  to 
unravel  the  succession  and  to  correlate  the  different  formations  in  the 
region.  As  previously  noted,  it  appears  that  two  lower  Paleozoic  succes- 
sions of  approximately  equivalent  age  exist  within  the  same  area,  and 
1  the  tendency  of  most  workers  is  to  regard  the  argillaceous  sequence  as  an 
allochthone  from  the  east  now  reposing  on  a  calcareous  western  sequence. 
The  Cambro-Ordovician  limestones  and  dolomites  grade  westward  into 
foreland  sandstones  of  the  Adirondack  area,  and,  it  is  believed,  eastward 
into  shales  of  geosynclinal  thickness.  Cambrian  and  early  Ordovician 
sandstone  tongues  extend  far  to  the  east.  The  geosynclinal  trough  mi- 
grated westward  later  in  Ordovician  time  and  resulted  in  the  deposition 
of  a  shale  facies  over,  and  in  places  uncomformably  on,  the  calcareous 
and  sandy  succession.  This  was  the  occasion  of  the  Vermontian  disturb- 
ance (Kay,  1942). 

Kay's   (1942)   map  of  Fig.   11.11  restores   the  distribution  of  Lower 


Ordovician  strata  in  the  region.  He  names  the  eastern  trough  in  which  the 
shale  facies  was  deposited,  the  Magog;  a  postulated  barrier  to  the  west. 
the  Quebec;  and  the  shallower  trough  in  which  the  carbonates  were  de- 
posited, the  Champlain. 

In  the  St.  Alban's  area  of  northwesternmost  Vermont,  north  of  Cady's 
mapping,  Shaw  (1958)  reports  some  unexpected  facies  changes  in  the 
Cambrian  and  Lower  Ordovician  along  the  structural  strike.  These  are 
illustrated  in  Fig.  11.15.  A  northern  basin,  the  Franklin,  was  partially 
restricted  from  a  southern  bv  an  east-west  high,  the  Milton,  and  streams 
carried  considerable  clastic  material  into  it  from  the  Adirondack  and 
Laurentian  land  area.  Throughout  Cambrian  and  Early  Ordovician  times 
the  basin  was  one  of  considerable  crustal  unrest,  as  evidenced  by  the 
several  unconformities. 

Structure.  Although  considerable  doubt  exists  about  the  Taconic 
klippe  hypothesis  south  of  Albany,  there  seems  Little  question  in  the 
minds  of  those  who  have  worked  in  the  Lake  Champlain  lowlands  about 
the  reality  of  major  cast  to  west  thrusting. 

A  number  of  thrusts  other  than  the  great  Taconic  thrust,  but  of  the 


168 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


GREEN 


M     O      U      N     T     A     I      N 


Fig.  11.16.  Tectonic  map  of  west-central  Vermont,  after  Cady, 
1945.  Ruled  areas  are  Ordovician  strata  in  the  synclinoria. 
Faults  with   knobbed    bars   are   normal   faults. 


same  orogeny,  have  been  mapped.  All  are  interpreted  as  having  moved 
from  east  to  west.  The  chief  ones  of  these  are  the  Champlain  and  Hines- 
burg-Oak  Hill.  The  Champlain  thrust  trends  parallel  to  Lake  Champlain 
and  extends  from  a  point  near  the  south  end  of  the  lake  northward  about 
60  miles  to  the  Canadian  border.  About  3  miles  north  of  the  border,  near 
the  village  of  Rosenberg,  it  becomes  obscure  in  a  shale  terrane  (Cady, 
1945).  See  Fig.  11.16.  The  thrust  at  the  north  end  is  known  as  the  Rosen- 
berg slice  (sheet).  According  to  Cady,  near  the  south  end: 

At  Snake  Mountain  Lower  Cambrian  beds  of  the  mountain  proper  are 
thrust  westward  across  and  beyond  Upper  Cambrian  and  Beekmantown  rocks 
of  the  Orwell  thrust  plate  onto  the  Middle  Trenton  limestones  and  shales  next 
west  and  structurally  continuous  with  those  found  along  the  lake;  the  Champlain 
thrust  apparently  truncates  the  Orwell  thrust. 

The  Hinesburg-Oak  Hill  thrust  complex  floors  a  tectonic  unit  east  of 
the  Champlain  thrust  and  it  in  turn  is  bounded  on  the  east  by  the  Green 
Mountains.  The  southern  part  is  called  the  Hinesburg  thrust,  and  the 
northern  the  Oak  Hill.  The  Oak  Hill  thrust  sheet  passes  beneath  the 
Hinesburg. 

The  rocks  of  both  the  Hinesburg  and  Oak  Hill  thrust  slices  grade  eastward 
into  the  schist  and  gneiss  terrane  of  the  Green  Mountains.  Both  of  these  slices, 
so  far  as  they  have  been  delineated,  apparendy  have  undergone  considerable 
displacement,  as  evidenced  by  the  depth  of  erosional  re-entrants  and  by  the 
outlying  position  of  klippes.  The  Hinesburg  and  Oak  Hill  thrusts  form  the 
eastern  boundary  of  the  Rosenberg  slice. 


^  The  rather  highly  deformed  quartzose  slates,  phyllites,  and  graywackes  east 
of  the  Hinesburg  thrust,  a  short  distance  north  and  east  of  Hinesburg  village, 
lie  with  angular  discordance  across  the  east  limb  of  the  Hinesburg  synclinorium, 
where  the  thrust  plane  truncates  minor  folds  which  are  made  up  of  beds  from 
Lower  Cambrian  to  Beekmantown  age.  The  thrust  plane  has  not  been  observed 
at  any  point,  but  the  depth  of  the  re-entrants  suggests  that  it  dips  at  a  very 
low  angle  to  the  east.  Non-quartzose  black  slates  and  phyllites  crop  out  west 
of  the  quartzose  rocks  along  the  thrust  front  in  St.  George  and  Williston  town- 
ships. These  latter  Upper  Cambrian  argillaceous  rocks  comprise  the  Muddy 
Brook  thrust  slice,  which  was  apparently  dragged  up  along  the  sole  of  the 
Hinesburg  thrust.  These  same  slates  and  Upper  Cambrian  sandy  dolomites 
crop  out  in  the  re-entrant  west  of  Williston  village.  Northwest  of  Williston 
village  the  quartzose  rocks  are  thrust  over  a  closely  folded  syncline  of  the 
Oak  Hills  slice.  In  this  syncline  are  formations  from  Lower  Cambrian  to  prob- 
ably Upper  Cambrian  age. 

In  general,  the  rocks  east  of  the  Oak  Hill  thrust  are  less  deformed  and  less 
uniform  in  appearance  than  those  east  of  the  Hinesburg  thrust.  The  lower 
Cambrian  Dunham  dolomite  is  everywhere  recognizable,  and  at  many  places 
along  the  thrust  front,  where  structures  involving  the  Dunham  are  truncated 
at  erosional  re-entrants  or  at  klippes  such  as  Cobble  Hill  in  Milton  township,  it 
locates  the  fault.  Where  argillaceous  rocks  are  near  the  contact,  the  fault  is 
much  more  difficult  to  locate,  inasmuch  as  the  eastern  exposures  of  the 
Rosenberg  slice  are  in  a  predominandy  argillaceous  terrane  (Cady,  1945). 

Two  synclinoria  lie  on  a  common  north-south  axis  and  are  separated 
by  the  Monkton  cross  anticline.  See  Fig.  11.16.  They  are  bounded  on  the 
west  by  the  Adirondack  dome  and  Champlain  thrust  and  on  the  east  by 
the  Hinesburg-Oak  Hill  thrust  and  the  Green  Mountains. 

The  southern  synclinorium,  known  as  the  Middleburg,  makes  up  the 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


169 


structure  of  the  area  between  Snake  Mountain  on  its  west  limb  and  the 
Green  Mountain  front  on  its  east  limb.  The  center  of  the  synclinorium  is 
covered  by  the  great  Taconic  klippe  south  of  the  latitude  of  Brandon. 
The  east  limb  may  be  traced  fairly  continuously  into  the  marble  belt  south 
of  this  latitude  (Cady,  1945).  The  west  limb  loses  its  identity  in  an  area 
of  high  angle  faults  southwest  of  Orwell.  The  nature  of  the  numerous 
small  folds  of  the  synclorium  are  best  shown  in  the  cross  sections  B  and 
C  of  Fig.  11.11. 

The  northern  synclinorium,  known  as  the  Hinesburg,  composes  the 
structure  of  most  of  the  area  between  Lake  Champlain  and  the  Green 
Mountain  front.  See  section  A,  Fig.  11.11.  Most  of  the  east  limb  is  covered 
by  the  Hinesburg-Oak  Hill  thrust  slices.  The  Hinesburg  synclinorium  is 
not  so  symmetrical  as  the  Middleburg  synclinorium,  and  the  folding  is 
limited  to  the  development  of  a  series  of  moderately  broad  basin  struc- 
tures (Cady,  1945). 

The  normal  faults  of  the  Adirondacks  have  already  been  described. 
The  eastern  border  of  the  crystalline  mass  is  formed  in  part  by  these 
faults,  and  they  seem  to  be  genetically  related  to  the  uplift  of  the  dome. 
They  do  not  intersect  the  major  thrusts  of  the  Lake  Champlain  region, 
but  they  parallel  the  Orwell  and  Champlain  thrusts,  and  for  a  distance 
the  bends  in  the  normal  faults  coincide  with  bends  in  the  thrust  fronts.  It 
lis  suggested  (Cady,  1945)  that  the  thrust  fronts  may  have  retreated  by 


erosion  eastward  after  they  were  trimmed  by  the  normal  faults,  and  thus 
the  parallelism  has  resulted. 

Tectonic  History 

Champlain  and  Magog  Troughs.  In  1923  on  the  occasion  of  his  presi- 
dential address  on  North  American  geosynclines,  Schuchert  postulated  a 
western  trough,  the  St.  Lawrence,  through  the  Lake  Champlain  and  St. 
Lawrence  region,  a  medial  divide  or  geanticline,  and  then  an  eastern 
trough,  the  Acadian,  principally  through  Nova  Scotia  and  New  Bruns- 
wick. The  geanticline  included  the  Green  Mountains  of  Vermont  and 
the  White  Mountains  of  New  Hampshire  and  Maine.  The  rocks  of  these 
mountains  were  then  regarded  as  Precambrian.  Since  then  several  groups 
of  fossils  have  been  found,  and  most  of  the  metamorphosed  sediments 
of  Schuchert's  geanticline  have  turned  out  to  be  Lower  and  Middle 
Paleozoic  in  age.  Still  two  troughs  seem  necessary,  but  the  eastern  one 
must  have  occupied  approximately  the  site  of  Schuchert's  geanticline.  It 
has  been  called  the  Magog  eugeosyncline  by  Kay  ( 1942),  and  the  western 
has  been  called  the  Champlain  miogeosyncline.  The  Magog  is  character- 
ized by  shales,  cherts,  and  various  volcanics,  the  western  by  carbonates. 
Until  Mid-Ordovician  time,  the  separation  of  the  two  troughs  was  prob- 
ably a  matter  of  facies,  but  then  a  land  barrier  called  Vermontia  rose 
within  the  western  part  of  the  Magog  trough  and  caused  the  deposition  of 
elastics  over  the  carbonates  of  the  western  trough.  See  Fig.  11.17.  Later  in 


: 


WEST  ERA! 
NX 


SITE    OF    UPPER    DEVONIAN  "DELTA" 


MIOGEOSYNCLINE 
Lower    Devonion'}  S-) 


,  VT               i                                               \SOUTH 
NYMUASS.     VT.W.H                               N.H\MAINE        GULF    OF    MAINE 
-+-     '  --LATER   ACADIAN     BELT- *• 


ATLANTIC 


VERMONTIA 
GEANTICLINE     .      EUGEOSYNCLINE 


Lower  Devonion'; 


APPALACHIA 


Fig.  11.17.  Basins  of  deposition  across  New  England  just  prior  to  Acadian  orogeny.  Compiled 
from  Kay  (1951),  Billings  (1956),  and  other  sources.  Vermontia  had  risen  in  Mid-Ordovician 
time  and  evidently  was  considerably  wider  than  present  dimensions  indicate  to  supply 
the  voluminous  elastics  to   the   miogeosyncline   in   Mid-   and    Late   Ordovician   time.   Vermontia    as 


---0   _---' 
Grenville  orogenic    complex 

shown  was  also  essentially  the  site  of  the  Taconic  orogeny  at  the  close  of  Ordovician  time.  The 
eugeosyncline  was  the  site  of  much  volcanism,  and  Vermontia  the  site  of  ultramafic  intrusions,  cm, 
Cincinnatian;  moh,  Mohawkian;  and  ch-can,  Chazyan  and  Canadian.  The  region  of  Vermontia  in 
places  probably   received   Silurian  and   Devonian   sediments,  so  its  history  and    nature   is  complex. 


170 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


NORTHWESTERN 
VERMONT 

Montpelier  Quad. 
Cady,  1956 

CENTRAL  AND  EAST 
CENTRAL  VERMONT 

White  and  Jahns,  1950 

WESTERN,  CENTRAL 

AND  NORTHERN 

NEW  HAMPSHIRE 

Billings,  1956 

SOUTHEASTERN 
NEW  HAMPSHIRE 

Billings,  1956 

LOWER 
DEVONIAN 

SILURIAN 

?Meeting  House  slate 
Gile  Mountain  fm. 

Littleton  fm. 
15,000'+ 

Littleton  fm. 

15,000'± 

Waits  River  fin. 
Northfield  slate 

"Standi fig  Pond  vols. 
Waits  River  fm. 

Northfield  slate 

Fitch,  fm. 
0-769' 

Berwick  fm. 
10,000'+ 

Eliot  fm. 
6,500'i 

ORDOVICIAN 

Shaw  Mtn.  fm. 

Serpentine,  talc- 
carbonate  rock, 
and  steatite 

Shaw  Mountain  fm. 
Ultramafic  rocks 

Clough  quartzite 
0-1200' 

Partridge  fm. 
0-2000' 

Ammonoosuc  vols. 
2000-5000' 

Kittery  quartzite 
1,500'± 

Rye  fm. 

2,000'i 

Moretown  fm. 
Stowe  fm. 

Cram  Hill  fm. 

Arenites  of  the  Brain- 
tree-Northf ield  Range 

Albee  fm. 
5000' 

Orfordville  fm. 
3500-4000' 

CAMBRIAN 

Ottauquechee  fm. 
Camels  Hump  gr. 

Ottauquechee  phyllite 

Pinney  Hollow  schist 

Quartzose  schist, 
quartzite,  dolomite, 
and  conglomerate 

PRECAMBRIAN 

(To  the  southwest) 

Fig.  11.18.  Correlation  chart  of  pre-Acadian  Paleozoic  formations  across  Vermont  and  New 
Hampshire.  The  Standing  Pond  volcanics  and  Meeting  House  slate  are  listed  by  Billings  for 
westernmost  New  Hampshire  in  the  stratigraphic  order  shown  but  not  included  by  Cady  for 
Vermont.  The  total   Vermont  section   is  immensely  thick. 


Ordovician  time,  another  uplift,  the  Oswegan  disturbance,  occurred  and 
spread  westward  past  the  Adirondack  axis  into  the  Allegheny  basin. 

Taconic  Orogeny.  At  the  close  of  the  Ordovician  period  the  major 
Taconic  orogeny  occurred,  and  the  argillaceous  rocks  of  the  Magog  trough 
were  thrust  far  westward.  The  Quebec  barrier  and  eastern  part  of  the 
Champlain  trough  were  concealed  by  it.  The  amount  of  horizontal  dis- 
placement probably  exceeded  40  miles  (Kay,  1942). 

The  thrust  sediments  are  in  tectonic  contact  on  Queenston  shale  in  south- 
eastern Quebec,  and  the  autochthonous  Cincinnatian  has  been  folded  con- 
siderably. The  overthrust  rocks  are  overlain  at  Becraft  Mountain,  New  York, 
and  in  the  Catskill  Front  by  latest  Silurian  Manlius  limestone.  Thus,  there  is 
direct  evidence  that  the  principal  lateral  movements  were  pre-Manlius  and 
post-Queenston.    Folds    in    autochthonous    Ordovician    are    truncated   by    the 


Shawangunk  and  Tuscarora  quartzites  of  the  earliest  Silurian  in  southeastern 
New  York  and  Pennsylvania;  if  the  folding  accompanied  Taconic  thrusting,  the 
revolution  is  pre-Silurian. 

The  front  of  the  thrust  sheet  is  not  very  high.  Middle  Ordovician  sediments 
are  preserved  near  to  the  westernmost  remnant  of  the  sheet  and  probably  never 
were  buried  deeply.  On  Anticosti  Island  in  the  Gulf  of  St.  Lawrence,  there  is 
essentially  continuous  section  of  Cincinnatian  and  early  Silurian  calcareous  shale 
and  limestone  in  the  Champlain  belt  within  50  miles  of  the  overthrust  rocks 
of  Gaspe;  the  allochthone  was  beneath  the  sea  or  not  high  enough  to  produce 
significant  detritus  after  the  revolution.  Though  the  quantity  of  Silurian  terrig- 
enous sediments  is  distinctly  smaller  than  that  of  the  Ordovician,  .  .  .  this 
reflects  repeated  uplift  and  continued  presence  of  Vermontian  highlands  in 
later  Ordovician,  in  contrast  to  progressive  reduction  of  the  transposed  Taconia 
in  the  Silurian.  The  greatest  quantity  of  eroded  material  was  laid  down  in  the 
latitude  of  Pennsylvania,  as  shown  by  isopachs;  that  the  greatest  elevation  was 
there  is  also  shown  by  the  coarser  texture  of  the  sediments.  The  lateral  move- 
ment of  the  allochthone  may  have  been  as  great  or  even  greater  in  Quebec,  but 
Vermontia  and  its  transposed  descendant,  Taconia,  were  more  continually  high 
farther  south. 

Acadian  Orogeny.     The  next  great  influx  of  clastic  sediments  was  in  the 
Middle  Devonian,  and  the  sediments  generally  coarsen  upward  and  east-  j 
ward.  They  came  from  rising  highlands  on  the  east.  The  elevation  termi- 
nated in  the  Acadian  orogeny  which  was  followed  by  the  deposition  of  " 
Mississippian  elastics  to  the  west  of  the  orogenic  belt. 

The  Acadian  belt  is  known  best  in  New  Hampshire  and  the  Maritime 
Provinces  and  will  be  described  later,  but  it  is  possible  that  it  spread 
westward  to  the  Hudson  Valley  and  Lake  Champlain  lowlands  and  im- 
pressed additional  folds  on  the  Taconic  structures.  It  is  possible,  also, 
that  the  later  structures  are  Appalachian  in  age. 

Unsolved  Problems.  The  above  summary  of  the  history  of  the  Taconic 
system  savors  of  those  who  postulate  the  great  Taconic  allochthone,  and 
this  is  the  general  opinion  of  those  who  have  worked  in  northern  Massa- 
chusetts, Vermont,  and  eastern  New  York.  Yet  Balk  and  Craddock  in  very 
thorough  work,  at  the  south  end  of  the  Taconic  klippe  where  the  great 
thrust  and  its  roots  should  be  found,  do  not  find  evidence  of  it,  and 
they  do  not  believe  the  thrust  theory  necessary  to  explain  the  facies  and 
metamorphism  there.  Similarly,  the  roots  of  the  thrust  are  not  yet  estab- 
lished at  all  well  in  the  Green  Mountains. 


tchq 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 

HYDE    PARK      QUADRANGLE,      NW     VERMONT 

€chq    £0  Oi 


171 


J 


MONTPELIER      QUADRANGLE,      NW     VERMONT 

Os    o,sgo 


Om       5i"!J"^       5* 


Fig.  11.19.  Cross  sections  of  northwestern  Vermont  in  Green  Mountains.  Hyde  Park  section 
;after  Albee,  1957.  Montpelier  quadrangle  after  Cady,  1956.  €ch,  Camels  Hump  group;  Cchg, 
.albite   and   tremolite   greenstone;   Co,    Ottanquechee   fm.;    Os,    Stowe   fm.;    Osga,    middle    unit   of 

CENTRAL  AND  EASTERN  NEW  ENGLAND 

Definition 

The  Acadian  orogeny  of  Late  Devonian  time  affected  much  of  New 
jEngland  and  the  Maritime  Provinces,  and  undoubtedly  spread  southward 
through  the  Piedmont  crystalline  province  of  the  Atlantic  margin.  It 
treated  a  mountain  system  that  was  superposed  in  part  on  the  earlier 
Taconic  system.  Where  best  known  and  perhaps  best  displayed  in  New 
Hampshire,  New  Brunswick,  and  Nova  Scotia,  it  is  an  irregular  north- 
south  belt  east  of  the  Taconic  system,  but  its  western  limit  is  as  yet  poorly 
defined. 

The  region  here  discussed  lies  east  of  the  crest  of  the  Green  and  Berk- 
shire Mountains  and  includes  the  New  England  seaboard  lowland,  the 
New  England  upland  and  the  White  Mountains  in  the  United  States  and 
Canada.  See  map  of  Fig.  11.1  and  11.2.  The  seaboard  lowland  extends 
along  the  Atlantic  coast  as  a  narrow  zone  from  Rhode  Island  to  the 
border  of  Maine  and  New  Brunswick. 


Os  consisting  of  greenstone  and  amphibolite;  Om,  Moretown  fm.;  Omsp,  carbonaceous  and 
slate  member;  Ssm,  Shaw  Mountain  fm.;  Sn,  Northfield  slate;  Swr,  Waits  River  fm.;  Da, 
Adamant   granite. 

Stratigraphy  and  Structure  of  Vermont 

An  immensely  thick  section  of  stratified  rocks  exists  in  northwestern, 
central,  and  east-central  Vermont,  probably  reaching  a  thickness  of  100.- 
000  feet  (White  and  Jahns,  1950).  The  strata  except  some  lamprophyre 
dikes  are  folded  and  metamorphosed  sedimentary  and  volcanic  rocks.  A 
number  of  units,  members  or  formations  of  volcanic  rock  throughout  the 
section  from  Cambrian  to  Lower  Devonian  attest  the  eugeosynclinal 
nature  of  the  deposits.  See  correlation  chart  of  Fig.  11.18. 

Northwestern  Green  Mountains 

Two  quadrangles,  the  Hyde  Park  and  Montpelier,  have  been  mapped 
by  Albee  (1957)  and  Cady  (1956),  and  depict  the  structure  and  stratig- 
raphy near  the  north  end  of  the  Green  Mountains  a  few  miles  east  of  the 
crest.  The  sections  of  Fig.  11.19  show  the  thick  succession  of  folded  beds 
from  Cambrian  to  Devonian. 

The  axis  of  the  Green  Mountain  anticlinorium  trends  north-northeast  across 
the  northwest  corner  of  the  Hyde  Park  quadrangle.  This  anticlinorium.  which 


172 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


is  the  principal  structural  feature  of  the  bedrock  of  Vermont,  extends  north- 
northeast  from  the  Massachusetts- Vermont  border  the  full  length  of  the  state 
and  about  50  miles  into  Quebec,  a  total  distance  of  about  210  miles.  The 
stratigraphic  sequence  and  lithologic  character  of  the  rocks  on  the  west  limb 
of  the  anticlinorium  are  different  from  those  on  the  east  limb,  and  a  generally 
accepted  correlation  of  the  two  is  not  yet  possible.  In  the  Hyde  Park  quad- 
rangle, and  in  the  Montpelier  quadrangle  (Cady,  1956),  which  borders  on 
the  south  edge  of  the  Hyde  Park  quadrangle,  the  general  eastward  dip  of 
the  rocks  is  interrupted  by  a  group  of  anticlines  whose  axes  parallel  the  axis 
of  the  Green  Mountain  anticlinorium.  [See  Fig.  11.18.] 

The  bedrock  of  the  quadrangle (s)  comprises  chiefly  metamorphosed  sedi- 
mentary and  volcanic  rocks,  principally  schist,  phyllite,  slate,  granulite, 
quartzite,  greenstone,  amphibolite,  crystalline  limestone,  and  conglomerate, 
that  range  in  age  from  Cambrian  probably  to  Devonian.  Intrusive  igneous 
rocks,  some  of  which  are  metamorphosed,  underlie  less  than  1  percent  of 
the  area  and  comprise  serpentinite  and  its  derivatives  (talc-carbonate  rock 
and  steatite ) ,  granite,  and  diabase  that  range  in  age  from  Ordovician  probably 
to  Mississippian. 

All  the  rocks  in  this  erea  except  the  lamprophyre  dikes  have  been  affected 
by  regional  metamorphism.  In  this  area,  chlorite,  garnet,  and  kyanite  have 
been  interpreted  as  successively  general  indicators  of  increasing  metamorphic 
grade  in  the  schists.  Similarly,  chlorite,  actinolite,  and  hornblende  are  indicators 
in  the  greenstone  and  amphibolite.  Most  of  the  Hyde  Park  quadrangle  is  in 
the  chlorite  zone  of  metamorphism  (Cady,  1956). 

Bodies  of  serpentinite  or  its  alteration  products,  talc  carbonate  rock  and 
steatite,  are  numerous,  having  been  noted  in  fifteen  places  by  Albee  and 
in  five  by  Cady.  They  occur  chiefly  in  the  Stowe  formation. 

The  serpentinite  (or  its  derivatives)  forms  tabular,  lenticular,  or  pod- 
shaped  masses  that  strike  north-northeast  and  dip  steeply,  parallel  with  the 
schistosity  and  commonly  also  with  the  bedding  of  the  enclosing  rocks.  The 
serpentinite  is  dark  green  to  dark  greenish  black  on  the  fresh  surface  but 
weathers  to  a  characteristic  pale  greenish-white  or  light-buff  rind  traversed 
by  a  reticulate  system  of  sharply  cut  lines;  it  is  composed  almost  entirely  of 
the  mineral  serpentine,  probably  of  the  antigorite  variety.  The  talc-carbonate 
rock  is  mottled  greenish  gray  and  weathers  brown;  it  is  composed  of  the 
minerals  talc,  magnesite,  and  locally  small  amounts  of  dolomite.  The  steatite 
ranges  from  white  to  green  and  greenish  gray  and  weathers  grayish  tan;  it 
is  composed  of  the  mineral  talc  (Albee,  1957). 

Thick  sills  of  granite  invade  the  Waits  River  formation  of  the  Mont- 
pelier quadrangle,  and  have  generated  cordierite  and  diopside  as  contact 
metamorphic  effects.   These  sills   are  probably   a  late   element   of   the 


Acadian  folding  which  took  place  in   Mid-   and  Late  Devonian  time 
(Cady,  1956). 
The  minor  folds  do  not  accord  with  the  major  folds. 

The  axes  of  most  of  the  minor  folds  and  granular  quartz  columns,  as  well 
as  the  intersections  of  fold  bands  and  of  slip-cleavage  lamellae  with  bedding, 
are  nearly  vertical.  This  attitude  implies  that  most  of  these  minor  structural 
features  were  not  produced  by  shearing  movements  in  a  nearly  east-west 
oriented  vertical  plane,  such  as  were  evidently  responsible  for  the  gently 
plunging  structures  of  the  Green  Mountain  anticlinorium.  Instead  they  were 
probably  either  formed  before  folding  of  the  anticlinorium  by  shearing  move- 
ments in  a  north-south  vertical  plane,  or  after  folding  and  tilting  of  the  limbs 
of  the  anticlinorium  by  shearing  movements  in  a  north-south  vertical  plane, 
or  after  folding  and  tilting  of  the  limbs  of  the  anticlinorium  to  near  vertical, 
by  shearing  movements  in  a  horizontal  plane.  The  pattern  of  movement  of 
these  minor  folds  is  uniform  over  rather  wide  areas;  thus  most  of  the  folds  in 
the  fold  bands  in  the  Moretown  formation  southeast  of  the  Worcester  Mountains 
are  dextral  in  plan  (see  White  and  Jahns,  1950,  p.  197,  for  usage  of  terms 
"dextral"  and  "sinistral"),  and  it  appears  that  the  rocks  to  the  east  have  moved  i 
south  relative  to  those  to  the  west.  This  relationship  is  well  shown  at  the 
previously  cited  exposures  of  the  Moretown  formation  in  Middlesex  Gorge 
(Albee,  1957). 


Central  and  East-Central  Vermont 

The  outcrop  pattern  of  three  key  formations  in  central  and  eastern 
Vermont  is  broadly  shown  on  the  map  of  Fig.  11.20,  and  the  stratigraphic 
succession  in  Fig.  11.18.  According  to  White  and  Jahns: 

The  formations  of  central  and  east-central  Vermont  are  exposed  as  a  series 
of  parallel  belts  that  strike  nearly  north.  Most  of  the  rocks  dip  steeply,  and 
many  are  overturned.  With  one  possible  exception,  there  seem  to  be  no 
major  repetitions  within  the  sequence,  and  the  order  of  formations  from 
west  to  east  appears  to  be  the  same  as  the  order  of  their  deposition.  The 
formations  are  dominantly  schist  or  phyllite,  with  varying  proportions  of 
arenaceous  material.  One  thin  formation,  the  Shaw  Mountain,  contains  quartz 
conglomerate,  calcareous  tuff,  and  crinoidal  limestone.  The  third-from-highest 
formation,  the  Waits  River,  is  very  thick  and  contains  a  large  proportion  of 
calcareous  beds.  The  distance  from  the  base  of  the  lowest  formation  to 
the  top  of  the  highest,  measured  normal  to  bedding,  is  more  than  100,000 
feet;  this  large  apparent  thickness  is  believed  to  be  not  very  much  greater 
than  the  original  thickness. 

The   metasediments   have   been   intruded   by   granitic    dikes    and    plutons 

afic  dikes,  and  small  ultramafic  plutons. 


^Yn 


NEW  ENGLAND  APPALACHIAN   SYSTEMS 


173 


Two  principal  stages  of  deformation  are  distinguished.  During  the  earlier 
stage  the  rocks  were  folded,  and  a  schistosity  was  developed  nearly  parallel  to 
bedding.  Throughout  the  area  the  minor  folds  of  this  stage  indicate  a  consistent 
upward  movement  of  rocks  on  the  east  with  respect  to  those  on  the  west.  The 
folds  plunge  at  low  to  moderately  steep  angles,  typically  northward. 

Phenomena  associated  with  the  later  stage  of  deformation  decrease  in 
intensity  both  eastward  and  westward  from  the  belt  underlain  by  the  calcareous 
Waits  River  formation.  At  a  distance  from  this  formation,  the  rocks  have 
prominent  slip  cleavage,  and  the  earlier  schistosity  is  folded.  The  minor  folds 
plunge  moderately  to  steeply  northward  on  the  western  side  of  the  area  and 
^ore  gendy  northward  on  the  eastern.  As  the  Waits  River  formation  is 
approached,  slip  cleavage  passes  gradually  into  a  schistosity  that  obliterates 
the  earlier  schistosity,  and  the  intensity  of  later  folding  increases.  In  both 
the  eastern  and  the  western  parts  of  the  area  the  later  minor  folds  indicate 
"that  the  rocks  of  the  Waits  River  formation  have  moved  upward  with  respect 
|  to  the  formations  on  either  side. 

1  The  central  part  of  the  belt  underlain  by  the  Waits  River  formation  is  marked 
(lby  a  huge  arch,  10—20  miles  across,  whose  axis  is  more  or  less  parallel  to  the 
1  belt  and  plunges  gently  northward.  This  is  shown  to  be  an  arch,  not  in  bedding, 
)!but  in  the  later  schistosity  and  in  the  axial  planes  of  large  isoclinal  folds  that 
1  were  formed  during  the  later  stage  of  deformation.  The  axial  planes  of  three 
1  of  these  large  isoclinal  folds  can  be  correlated  across  the  crest  of  the  cleavage 
arch  at  Strafford  Village. 

Western,  Central,  and  Northern  New  Hampshire 

i     Stratigraphy.     A  series  of  metasedimentary  and  metavolcanic  rocks  in 
1  western,  central,  and  northern  New  Hampshire  ranges  in  age  from  Ordo- 
vician (?)  to  Lower  Devonian  and  has  an  aggregate  thickness  of  16,000 
feet.  See  Fig.  11.18.  Figure  11.21  is  a  columnar  section  of  the  Littleton- 
,i  Moosilauke  area  in  the  White  Mountains  of  west  central  New  Hampshire. 
The  stratified  rocks  fall  into  six  major  units.  The  Albee,  Ammonoosuc, 
and  Partridge  formations  are  of  pre-Silurian,  probably  Upper  Ordovician 
age,  the  unconformably  overlying  beds  are  the  Clough  conglomerate  and 
J  Fitch  formation  of  Silurian  age,  and  the  Littleton  formation  is  of  Lower 
;  Devonian  age.  The  Albee  was  originally  a  shale  and  sandstone  formation, 
land  although  no  fossils  have  been  found  in  it,  it  appears  to  be  above  the 
i fossilif erous  Middle  Ordovician  of  Vermont  (Billings,  1937). 

The  Ammonoosuc  volcanics  consist  principally  of  soda-rhyolite,  soda- 
rhyolite  volcanic  conglomerate,  meta-andesite  porphyry  breccia,  and  slate 
and  impure  quartzite.  The  Partridge  formation  is  largely  a  black  slate.  In 


WHITE    MOUNTAIN 
I       PLUTONIC-VOLCANIC    SERIES 


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t''"j;J3   NE*    HAMPSHIRE  _    fiU£B££. 

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);-/J  PROBABLY    OF   NEW    HAMPSHIRE 
PLUTONIC     SERIES^ 


OLIVERIAN     PLUTONIC 
SERIES     FORMING    CORES 
OF    D 


Fig.  11.20.  Major  structures  of  eastern  Vermont  and  New  Hampshire.  After  White  and 
Jahns  (1950)  and  Billings  (1956).  The  narrow  Connecticut  Valley  synclinorium  lies  between  the 
Northey  Hill  and  Ammonoosuc  thrusts  and  is  not  labeled  on  the  map.  Osp,  Standing  Pond 
volcanics;  On,   Northfield   slate;   Oo,  Ottauquechee   phyllite. 


UTHOLOGY  IN  LOW-GRADE 
ZONE     (EPIZONE) 


5 


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ICKNESS 
N  FEET 


£ 


INTRUSIVE  ROCKS 


GLACIAL  TILL  8.  OUTWASH,  ALLUVIUM 


»LATE   AND  SANDSTONE,  WITH   VOL- 
CANIC  MEMBER   CONSISTING    OF 
CHLORITE    SCHIST   AND   META- 
BASALT    (Olc),  SODA-RHYOLITE 
VOLCANIC    CONGLOMERATE   (Dive), 
AND    SODA-RHYOLITE,  SODA- 
RHYOLITE    TOFF    AND    BRECCIA  , 
AND   SODA-TRACHYTE     (Dlr). 


LIMESTONE,  MARBLE,  DOLOMITIC 
SLATE,  ARENACEOUS    DOLOMITE, 
CALCAREOUS    SLATE,  ARENACEOUS 
LIMESTONE,  CALCAREOUS     SAND- 
STONE, IMPURE    QUARTZ  I TE,  ARKOSE, 
QUARTZ    CONGLOMERATE,    AND 
GRAY     SLATE. 


5000 


WHITE   MOUNTAIN 
MAGMA  SERIES    (wm)' 

NEW  HAMPSHIRE 
MAGMA    SERIES    (nh) 

OLIVERIAN    MAGMA 
SERIES      (ol) 


SODA 
AND 


-RHYOLITE    DIKES 
SILLS     (sr)      


QUARTZ    CONGLOMERATE    AND 
QUARTZ  I TE. 


BLACK  SLATE,  WITH  THIN-BEDDED 
QUARTZITE,  SLATE,  AND  VOLCANIC 
MATERIAL    AT    BASE. 


SODA-RHYOLITE   TUFF,  BRECCIA, 
AND    VOLCANIC     CONGLOMERATE; 
CHLORITE    SCHIST;  CHLORITE- 
EPIDOTE    SCHIST;   SLATE    AND 
IMPURE    QUARTZITE. 


QUARTZITE,  ARGILLACEOUS 
QUARTZITE  ,  GREEN    SLATE,  AND 
BLACK    SLATE. 


2000  k 


4000  * 


HIGHLANDCROFT 
MAGMA    SERIES  (h) 


Fig.  11.21.  Columnar  section  of  the  Littleton  Moosilauke  area.  Reproduced  from  Billings,  1937.  In  addi- 
tion to  the  sequence  and  character  of  the  sedimentary  and  volcanic  rocks,  the  time  of  intrusion  of  igneous 
rocks   is   shown. 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


175 


places  at  the  base,  black  slate  and  fine-grained,  light  quartzite  alternate 
in  beds  a  quarter  of  an  inch  thick. 

The  Clough  conglomerate  is  one  of  the  best  key  horizons  in  western 
New  Hampshire,  and  although  thin,  it  is  resistant  and  exceptionally  well 
represented  in  outcrops.  It  apparently  continues  southward  to  the  Massa- 
chusetts boundary.  Its  outcrops  are  generally  white  cliffs.  The  pebbles  in 
the  conglomerate  are  chiefly  vein  quartz,  but  some  are  quartzite,  jasper, 
greenstone,  or  soda-rhyolite.  In  places  only  a  few  pebbles  are  present;  in 
others  they  constitute  over  60  percent  of  the  rock  (Billings,  1937).  The 
matrix  is  pure  or  slightly  impure  quartzite. 

The  Clough  conglomerate  directly  underlies  the  Fitch  formation  which 
carries  middle  Silurian  fossils.  Moreover,  the  two  formations  are  closely  related 
in  age,  for  a  few  beds  of  quartz  conglomerate  are  found  in  the  Fitch.  The 
Clough  conglomerate,  however,  is  separated  from  the  underlying  strata  by  an 
unconformity.  It  is  apparent  that  the  formation  is  either  middle  or  lower 
Silurian.  In  many  respects  the  Clough  is  similar  to  the  Shawangunk  conglomer- 
ate of  New  York,  although  the  former  is  thinner  and  purer.  The  Clough  under- 
lies fossiliferous  middle  Silurian,  and  the  Shawangunk  carries  middle  Silurian 
fossils  in  its  upper  part.  The  two  are  closely  related,  if  not  identical,  in  age 
(Billings,   1937). 

The  Fitch  formation  in  its  least  altered  form  consists  of  white  to  buff 
marble;  gray  limestone  and  marble;  buff  dolomitic  slate;  buff  to  brown 
arenaceous  dolomitic  limestone;  gray  calcareous  slate  ("trilobite  slate"  of 
earlier  workers);  white  to  gray  arenaceous  limestone  and  calcareous, 
arkosic  conglomerate;  gray  impure  quartzite;  white  to  gray  arkose;  white 
quartz  conglomerate;  and  gray  slate.  Fossils  have  been  found  at  two 
localities  in  the  Fitch  formation  southeast  of  the  Ammonoosuc  thrust,  and 
are  recognized  as  of  Middle  Silurian  (Niagaran  age). 

The  Littleton  formation  of  Lower  Devonian  age  consists  in  its  least 
metamorphosed  condition  chiefly  of  slate  and  sandstone,  with  subordinate 
amounts  of  soda-rhyolite  conglomerate,  tuff  and  breccia,  and  some  green- 
stone. 

Formations  older  than  those  listed  in  the  chart  of  Fig.  11.21  are  known. 
The  Orfordville  formation,  first  recognized  in  west  central  New  Hamp- 
shire (Kruger,  1946)  underlies  the  Albee  formation,  and  the  Waits  River 
formation  first  found  in  central  Vermont,  underlies  the  Orfordville  ( Cur- 


rier and  Jahns,  1941).  The  base  of  the  Waits  River  is  2000  feet  abo' 
crinoidal  limestone  which  appears  to  be  Middle  Ordovician.  If  so,  both 
the  Waits  River  and  Orfordville  are  Middle  Ordovician  or  vounger.  The 
Orfordville  formation  was  originally'  a  shale  with  very  thin  beds  of  sand- 
stone, and  the  Waits  River  a  calcareous  shale  and  limestone  formation. 

Structure 

General  Statement.  In  Massachusetts  and  southern  New  Hampshire 
the  structures  trend  northerly;  in  northern  New  Hampshire  they  veer 
northeasterly.  A  succession  of  anticlinoria  and  synclinoria  make  up  the 
major  elements  of  the  structure.  See  Figs.  11.20  and  11.26.  Proceeding 
eastward  from  the  great  monocline  of  central  and  eastern  Vermont  three 
thrust  faults  occur,  and  between  the  middle  ( Ammonoosuc )  and  eastern 
( Northey  Hill )  is  the  Connecticut  Valley  synclinorium.  This  lies  approxi- 
mately astride  the  boundary  line  of  Vermont  and  New  Hampshire.  Next 
east  is  the  Bronson  Hill  anticline,  the  Merrimack  synclinorium  and  in 
southeastern  New  Hampshire  the  Rockingham  anticlinorium.  The  Coos 
anticlinorium  is  in  the  northern  part  of  the  state  and  lies  between  the 
Monroe  and  Ammonoosuc  thrusts. 

The  older  plutonic  series,  especially  the  Oliverian  and  New  Hampshire 
series,  participate  in  the  northerly  and  northeasternly  trend.  This  may 
be  seen  by  the  Oliverian  series  making  up  the  cores  of  the  domes  along 
the  Bronson  anticline,  and  by  the  foliated  Mt.  Clough  and  Cardigan 
plutons  of  the  New  Hampshire  series  striking  along  the  western  flank  of 
the  Merrimack  synclinorium. 

Bronson  Hill  Anticline.  The  Bronson  Hill  anticline  extends  from 
Massachusetts  to  Maine,  a  length  of  150  miles.  It  ranges  from  6  to  16 
miles  wide.  The  core  is  composed  of  the  Ammonoosuc  volcanics  and  the 
Oliverian  plutons  with  the  Clough,  Fitch,  and  Littleton  formations  on 
both  flanks. 

Rockingham  Anticlinorium.  The  Rockingham  anticlinorium.  lies  in 
southeastern  New  Hampshire,  between  the  Atlantic  Ocean  and  the  Fitch- 
burg  pluton.  The  individual  folds  of  the  anticlinorium  are,  from  south- 
east to  northwest,  the  Rye  anticline,  the  Great  Bay  (Eliot)  syncline.  and 
the  Exeter  anticline  (largely  occupied  by  the  Exeter  pluton). 


176 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Merrimack  Synclinorium.  East  of  the  Bronson  Hill  anticline  and 
northwest  of  the  Rockingham  anticlinorium  is  a  large  area  of  Littleton 
formation,  all  in  the  sillimanite  zone  of  metamorphism.  Inasmuch  as  this 
band  of  the  Littleton  formation  is  bordered  on  either  side  by  older  strata, 
it  must  occupy  a  synclinorium.  This  structural  feature  is  called  the  Mer- 
rimack synclinorium,  because  much  of  it  is  drained  by  the  Merrimack 
River  and  its  tributaries. 

Throughout  much  of  western  New  Hampshire  the  western  limb  of  the 
Merrimack  synclinorium  is  invaded  by  large  bodies  of  the  New  Hamp- 
shire plutonic  series.  These  relations  are  well  shown  on  sections  A-A'  and 
B-B'-B"  of  Fig.  11.26. 

Thrust  Faults.  The  Ammonoosuc  thrust  is  marked  generally  by  Am- 
monoosuc  volcanics  being  thrust  over  the  Littleton  formation  with  a 
stratigraphic  displacement  of  7000  feet.  The  fault  dips  from  32  to  50 
degrees  westerly.  It  is  younger  than  the  regional  metamorphism. 

The  Northey  Hill  thrust  predates  the  metamorphism  because  there  is 
no  break  in  grade  of  metamorphism  across  it.  This  feature  renders  recog- 
nition of  the  fault  a  little  difficult,  yet  mapping  shows  the  Littleton  forma- 
tion lies  in  contact  with  several  different  formations  along  it,  and  a 
maximum  stratigraphic  displacement  of  12,000  feet  may  be  measured.  A 
steep  dip  characterizes  much  of  its  length,  and  this  is  believed  due  to 
later  deformation. 

The  Monroe  thrust  is  about  as  long  as  the  Ammonoosuc  (85  miles). 
It  is  nearly  vertical  throughout  most  of  its  length,  but  in  places  dips 
southeasterly.  It  is  mostly  older  than  the  regional  metamorphism,  but  later 
deformation  steepened  it  and  also  caused  some  renewed  movements 
along  it. 

Magma  Series 

Plutonic  rocks  are  abundant  and  varied  in  form  and  composition.  Four 
magma  series  have  been  worked  out  (Billings,  1937).  The  oldest  is  known 
as  the  Highlandcroft  magma  series  and  is  probably  of  late  Ordovician 
age.  See  chart,  Fig.  11.21  and  map,  Fig.  11.20.  Some  time  after  the  Lower 
Devonian,    probably    in    Mid-    and    Late    Devonian    time,    other   large 


quantities  of  magma  invaded  the  region.  The  Oliverian  magma 
series  preceded  the  folding  and  was  followed  by  the  New  Hampshire 
magma  series,  the  earlier  members  of  which  were  contemporaneous  with 
the  main  period  of  folding,  and  the  later  members  of  which  were  slightly 
younger  than  the  folding.  The  White  Mountain  magma  series  is  the 
youngest  of  the  plutonic  rocks,  and  it  appears  less  extensive  than  the 
others.  It  is  probably  early  Mississippian  in  age  (Billings,  1945). 

The  Highlandcroft  magma  series  is  represented  by  the  Highlandcroft 
granodiorite  and  small  bodies  of  diorite,  quartz  diorite,  and  quartz 
monzonite.  The  Oliverian  magma  series  is  represented  by  the  pink  Owls 
Head  granite  in  the  Littleton  area  and  by  other  units  in  the  Rumney,  Mt. 
Cube,  and  Mascoma  quadrangles.  Many  sills  in  the  Ammonoosuc  vol- 
canics are  of  this  series. 

The  White  Mountain  magma  series  is  characterized  by  ring-dikes, 
stocks,  a  batholith,  and  by  eruptive  differentiates.  According  to  Billings, 
1945: 

Much  of  the  magma  of  the  White  Mountain  magma  series  was  erupted  on 
the  surfaces  to  from  the  Moat  volcanics.  Tuffs,  breccias,  and  lavas,  composed 
chiefly  of  rhyolite,  andesite,  and  basalt,  but  also  including  some  trachyte,  are 
typical.  Rhyolite  is  by  far  the  most  common;  trachyte  is  rare. 

The  intrusive  rocks  range  in  composition  from  gabbro  to  granite,  and  a  great 
variety  of  intermediate  types  are  developed.  Chapman  and  Williams,  in  a 
careful,  detailed  study,  have  shown  that  the  mafic  rocks  are  the  oldest  and  the 
felsic  are  the  youngest.  They  have  also  determined  the  areal  extent  of  the 
plutonic  rocks  and  calculated  the  percentage  of  each  compared  to  the  whole 
magma  series.  The  order  of  intrusion,  from  oldest  to  youngest,  and  the  percent- 
age of  each  as  exposed  at  the  surface,  are  gabbro,  norite,  diorite,  and  quartz 
diorite  (0.5  per  cent);  monzodiorite  and  monzonite  (1.5  per  cent);  syenite,  in- 
cluding some  nepheline-sodalite  syenite  (9  per  cent);  quartz  syenite  (10  per 
cent);  granite  and  granite  porphyry  (79  per  cent).  Although  the  rocks  in  gen- 
eral became  more  siliceous  as  differentiation  progressed,  this  is  not  true  in 
detail.  Especially  important  is  the  fact  that  the  Albany  quartz  syenite  is  younger 
than  the  granite  porphyry.  This  is  significant  in  considering  the  tectonic  evolu- 
tion of  the  area. 

Chapman  and  Williams  have  also  shown  that  fractional  crystallization  con- 
trolled the  evolution  of  the  series,  but  that  abyssal  assimilation  played  an  im- 
portant role. 

The  Moat  volcanics,  in  large  part  contemporaneous  with  the  granite  por- 
phyry, are  older  than  the  Albany  type  of  quartz  syenite,  but  their  age  relative 
to  the  more  mafic  plutonic  rocks  is  uncertain. 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


177 


Metamorphism 

All  the  sedimentary  and  metamorphic  rocks  have  been  deformed  and 
metamorphosed  to  various  degrees.  The  metamorphism  increases  gen- 
erally to  the  southeast,  and  three  zones  have  been  recognized  by  Billings, 
namely,  the  low-grade,  the  middle-grade,  and  the  high-grade.  See  map 
of  Fig.  11.22. 

The  distinction  between  the  zones  is  based  primarily  on  their  mineralogy. 
The  low-grade  zone  is  characterized  by  chlorite,  epidote,  albite,  sericite,  and 
dolomite;  the  middle-grade  zone,  by  staurolite,  garnet,  hornblende,  actinolite, 
diopside,  biotite,  and  intermediate  and  calcic  plagioclase.  The  mineralogical 
contrast  between  these  two  zones  is  striking.  The  high-grade  zone  differs  from 
the  middle-grade  zone  chiefly  in  that  sillimanite  is  present  and  staurolite  is 
absent  or  is  in  small  crystals.  Thus,  if  aluminous  sediments  are  not  present,  it 
is  difficult  or  impossible  to  distinguish  the  middle-grade  and  the  high-grade 
zones  on  mineralogical  criteria  alone.  In  general,  the  high-grade  rocks  are 
coarser  than  the  middle-grade,  but  this  criterion  is  difficult  to  apply,  and, 
wherever  the  rocks  might  belong  to  either  of  the  two  higher  zones,  they  have 
been  assigned  to  the  middle-grade  zone. 

The  change  in  the  degree  of  metamorphism  in  a  southeasterly  direction  is 
readily  apparent.  The  cumulative  effect  of  these  changes  is  so  great  that,  for  a 
long  time,  rocks  now  known  to  belong  to  the  same  formations  were  believed  to 
be  of  very  different  ages.  Whereas,  northwest  of  the  Ammonoosuc  thrust  the 
rocks  are  dominandy  sandstone,  slate,  calcareous  slate,  dolomitic  slate,  rhyo- 
lite  tuff,  and  greenstone,  composed  of  such  minerals  as  sericite,  chlorite,  albite, 
dolomite,  calcite,  quartz,  and  epidote,  to  the  southeast  the  rocks  are  mica  schist, 
calcite-biotite  schist,  actinolite-diopside  granulite,  biotite  gneiss,  and  amphibo- 
lite,  composed  of  such  minerals  as  biotite,  garnet  (almandite),  staurolite,  silli- 
manite, actinolite,  diopside,  hornblende,  calcite,  quartz,  and  calcic  plagioclase. 
Moreover,  there  is  a  general  coarsening  in  grain.  These  changes  clearly  repre- 
sent progressive  metamorphism  toward  the  southeast,  for  the  new  rocks  are 
farther  and  farther  removed  mineralogically  from  the  original  rocks  from  which 
they  were  derived. 

A  number  of  the  intrusive  rocks  are  older  than  the  regional  metamor- 
phism and  were  affected  to  different  degrees.  The  Highlandcroft  grano- 
diorite  was  in  the  zone  of  low-grade  metamorphism,  and  its  original 
andesine  plagioclase  has  been  replaced  by  albite-oligoclase,  epidote,  and 
sericite.  Green  biotite,  which  is  found  in  places  as  a  shell  around  the  horn- 
blende, is  of  metamorphic  origin.  The  Moulton  diorite  has  been  subjected 
to  low-grade  metamorphism,  and  its  original  condition  is  much  altered. 


7I-4S" 


Scale  of  Miles 


LEGEND 


DRIFT    AND 
ALLUVIUM 


WHITE   MOUNTAIN 
MAGMA   SERIES? 


NEW   HAMPSHIRE 
MAGMA    SERIES 


OLIVERIAN 
MAGMA  SERIES 


HIGHLANDCROFT 
MAGMA  SERIES 


METAMORPHIC 
ZONES 


HIGH-GRADE  ZONE 
WHERE  SILLIMANITE 
HAS  RETROGRESSED 
TO    STAUROLITE 


HIGH-GRADE  ZONE 
(KATAZONE) 


_J 


middle-grace  zone 
(mesozone) 


TRANSITION 
BETWEEN    LOW- 
GRADE  ANO  MIDDLE- 
GRADE    ZONES 


i 


LOW-GRADE  ZONE 
(EPIZONE) 

FOSSIL  LOCALITIES 
SOUTHEAST    OF 
AMMONOOSUC  THRUS1 


Fig.    11.22.      Metamorphic    zones    in    the    Littleton-Moosilauke    area.    Metamorphism    is    progressive 
toward  the  southeast.  Reproduced  from  Billings,  1937. 


178 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Rasic  dikes  and  sills  have  attained  equilibrium  under  the  new  metamor- 
phic  conditions. 

Rillings  regards  the  main  alteration  to  have  occurred  after  the  Northey 
Hill  thrust  and  during  the  intrusions  of  the  New  Hampshire  magma 
series.  Then  the  Ammonoosuc  thrust  brought  different  metamorphic 
zones  into  sharp  contact  with  each  other.  Also  in  certain  places  retro- 
grade metamorphism  set  in  with  the  formation  of  much  chlorite. 

The  cause  of  the  metamorphism  is  apparently  the  intrusions  of  the  vari- 
ous plutons  of  the  New  Hampshire  magma  series.  Northwest  of  the 
Ammonoosuc  thrust  where  metamorphism  is  least,  the  intrusions  of  the 
New  Hampshire  magma  series  are  absent  except  that  a  few  small  bodies 
of  the  Bethlehem  gneiss  and  Kinsman  quartz  monzonite  appear.  Billings 
points  out  that,  as  intrusions  are  common  eastward  to  the  Maine  border, 
and  as  the  sedimentary  rocks  almost  invariably  are  recrystallized  to  high- 
grade  metamorphic  rocks,  there  must  be  a  causal  connection  between  the 
increase  in  metamorphism  and  these  intrusions.  Not  only  is  there  a  gen- 
eral increase  in  the  intensity  of  metamorphism  toward  the  area  where 
igneous  intrusions  are  most  abundant,  but  there  is  an  increase  locally 
toward  individual  bodies.  Such  high-grade  zones  surrounding  intrusive 
masses  are  not  well  defined  in  the  map  of  Fig.  11.22,  but  it  is  suggested 
that  the  contact  metamorphic  zones  vary  in  width  greatly,  and  that  cer- 
tain zones  betray  the  presence  of  unexposed  plutons. 

Mechanics  of  Instrusion 

Introduction.  The  post-tectonic  White  Mountain  magma  series  is 
characterized  by  ring-dikes,  stocks,  and  a  batholith  (Billings,  1945).  The 
ring-dikes,  most  of  which  range  in  composition  from  monzonite  to  quartz 
syenite,  intruded  arcurate  and  circular  vertical  fracture  zones  by  piece- 
meal stoping  and  related  mechanisms.  Cauldron  subsidence,  although 
associated  with  some  ring-dikes,  is  not  essential  for  their  intrusion.  The 
stocks  of  the  White  Mountain  magma  series  were  emplaced  by  under- 
ground cauldron  subsidence. 

The  New  Hampshire  magma  series,  emplaced  during  the  Acadian 
^orogeny,  occurs  chiefly  as  great  sheets,  lenses,  and  stocks,  forcefully 
injected  into  the  older  formations. 


Ring-Dikes.  Altogether,  36  ring-dikes  associated  with  the  White 
Mountain  magma  series  have  been  discovered  in  New  Hampshire.  A  ring- 
dike  complex  is  a  structural  unit  containing  one  or  more  ring-dikes.  Ac- 
cording to  Billings  ( 1945 ) : 

There  are  five  ring-dikes  at  Mt.  Tripyramid,  four  each  in  the  Pliny  region  and 
the  Franconia  quadrangle,  and  six  in  the  Belknap  Mountains,  although  the  six 
separate  intrusions  could  be  considered  to  belong  to  two  composite  ring-dikes. 
Ring-dikes  have  also  been  described  from  adjacent  areas  in  Quebec  and  Maine. 

Complete  ring-dikes  that  encompass  360  degrees  are  rare,  but  the  ring-dike 
of  the  Ossipee  Mountains  and  some  of  those  on  Mt.  Tripyramid  are  of  this  type. 
Most  ring-dikes  are  arcuate  in  plan  and  those  in  New  Hampshire  encompass, 
on  the  average,  170  degrees  of  the  total  possible  360  degrees.  The  average 
radius  of  ring-dikes  in  New  Hampshire,  measured  from  the  outer  margin  of  the 
ring-dike  to  its  center  of  curvature,  is  three  miles.  A  ring-dike  composed  of 
Albany  quartz  syenite  in  the  Franconia  quadrangle  has  a  radius  of  9.2  miles 
and  is  one  of  the  largest  known  anywhere  in  the  world.  The  smallest  ring-dike 
in  New  Hampshire,  with  a  radius  of  only  0.8  mile,  is  on  Mt.  Tripyramid.  The 
average  width  of  ring-dikes  in  New  Hampshire  is  1900  feet.  The  arcuate  body 
of  amphibole  granite  in  the  southern  part  of  the  Franconia  quadrangle  is  14,000 
feet  wide,  but  this  may  not  be  a  true  ring-dike. 

Inside  some  of  the  ring-dikes  are  accumulations  of  extrusive  rocks, 
known  as  the  Moat  volcanics.  They  are  never  found  outside  the  ring-dike. 
The  volcanics  also  have  the  same  composition  as  the  ring-dike  within 
which  they  have  subsided. 

The  Moat  volcanics  are  at  least  10,000  feet  thick  and  rest  with  pronounced 
angular  unconformity  on  the  older  metamorphic  rocks  of  the  Litdeton  forma- 
tion and  the  plutonic  rocks  of  the  New  Hampshire  magma  series.  It  is  almost 
always  impossible  to  determine  the  attitude  of  the  Moat  volcanics,  because 
many  of  the  pyroclastic  rocks  and  lavas  are  devoid  of  bedding  and  flow  struc- 
ture. Available  data  indicate,  however,  that  near  the  ring-dikes  the  volcanics 
are  essentially  vertical,  but  toward  the  center  of  the  complex  the  dips  become 
progressively  less  [Fig.  11.23]. 

Unfortunately,  precise  data  concerning  the  amount  of  subsidence  are  diffi- 
cult to  obtain  in  New  Hampshire.  The  key  horizon  used  for  such  studies  is  the 
base  of  the  Moat  volcanics.  It  is  apparent  from  Fig.  11.23  that  the  center  of  the 
subsided  block  has  settled  10,000  feet  relative  to  the  margins  of  the  block  near 
the  ring-dike.  Moreover,  the  edge  of  the  subsiding  block  just  inside  the  ring-dike 
has  apparendy  settled  at  least  5,000  feet  relative  to  the  rocks  some  distance  out- 
side of  the  ring-dike.  Therefore,  the  center  of  the  subsided  block  has  dropped 
at  least  15,000  feet  relative  to  the  rocks  some  distance  outside  of  the  ring-dike. 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


L79 


sw 


Mt.  Faraway 


NE 

S.Nickerson  Mtn. 


I  Albany 

I  quartz   syenite 


Moat  volcanics 


"iyZ'-tfy,  Winnipesaukee 
?/?t'/;'4  quartz  diorite 


Scale  In  Miles 


Scale  in  Kilometers 


Fig.  11.23.  Section  through  the  Ossipee  Mountains,  N.  H.  Reproduced  from  Billings,  1945,  after 
Kingsley. 

It  is  apparent  that  the  intrusion  of  some  ring-dikes  is  associated  with  the  sub- 
sidence of  a  central  block.  It  does  not  follow,  however,  that  all  ring-dikes  are 
associated  with  central  subsidence. 

Billings  (1945)  believes,  because  the  ring-dikes  are  vertical  in  New 
Hampshire,  that  their  intrusion  was  controlled  by  an  annular  vertical 
fracture  zone,  the  width  of  which  was  comparable  to  the  width  of  the 
ring-dike.  Such  a  fracture  zone  would  be  susceptible  to  piecemeal  stoping. 
Various  combinations  of  the  annular  or  partially  annular  fracture  zone  ■ 
with  sagging  or  doming  are  shown  in  Fig.  11.24. 

Stocks.  For  most  of  the  stocks  there  are  few  data  to  indicate  whether 
they  are  concordant  or  discordant  because  many  of  them  have  been  in- 
truded into  areas  already  occupied  by  relatively  massive  or  weakly  foli- 
ated older  plutonic  rocks.  The  Mt.  Ascutney  stock  has  been  shown  to  cut 
discordantly  across  the  steeply  dipping  older  strata,  and  the  lineation  and 
fold  axes  of  the  older  strata  have  not  been  modified  by  the  intrusion 
(Chapman  and  Chapman,  1940).  A  process  of  underground  cauldron  sub- 
sidence, whereby  large  blocks  with  outward-dipping  walls  approximately 
the  size  of  the  present  stocks  sank,  is  visualized,  and  is  illustrated  in  Fig. 
11.25.  The  activity  occurred  in  the  last  stages  of  the  evolution  of  the 
White  Mountain  magma  series.  The  remarkable  uniformity  of  the  White 
Mountain  magma  series  through  New  Hampshire  suggests  that  a  single 
reservoir  underlay  much  of  the  state  (Billings,  1945). 

Plutons  of  Forceful  Injection.  Many  plutons  belonging  especially  to 
the  New  Hampshire  magma  series  have  been  emplaced  bv  forceful  in- 


Fig.   11.24.      Origin  of  ring-dikes.  Reproduced  from  Billings,   1945.  Broken   line   is  present  erosion 
surface. 


180 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Fig.    11.25.      Evolution   of  the   syenite-granite   stock   of  Ascutney   Mountain,   Vt.   Reproduced   from 
Chapman  and   Chapman,    1940. 

jection.  Notable  of  these  are  the  Kinsman  quartz  monzonite  and  the 
Bethlehem  gneiss. 

According  to  Billings  (1945): 

The  Mt.  Clough  pluton,  composed  of  Bethlehem  gneiss,  is  undoubtedly  the 
longest  intrusion  in  New  Hampshire.  The  main  body  extends  southward  for  90 
miles  from  the  northern  part  of  the  Franconia  quadrangle  to  the  south  end  of 
the  Lovewell  Mountain  quadrangle,  which  is  beyond  the  limits  of  Fig.  11.20. 
The  width  ranges  from  half  a  mile  to  7  miles.  In  the  Moosilauke  quadrangle  the 
contacts  are  essentially  vertical  and  the  pluton  is  a  vertical  sheet.  Further  south, 
however,  the  contacts  dip  to  the  east  and  along  the  eastern  border  of  the  Mas- 
coma  quadrangle  and  the  western  border  of  the  Cardigan  quadrangle,  the  upper 
and  lower  contacts  dip  30  degrees  east.  Here  the  pluton  is  a  huge  sheet  inclined 
to  the  east  [Fig.  11.26]. 

A  series  of  plutons  composed  of  Kinsman  quartz  monzonite  lie  east  of  the 
Mt.  Clough  pluton.  The  most  northerly  of  these,  which  may  be  called  the  Kins- 
man pluton  ...  is  a  gigantic  lens,  essentially  vertical  in  the  surrounding  schists. 

In  the  western  part  of  New  Hampshire,  some  ten  miles  east  of  the  Connecti- 
cut River,  the  crest  of  a  major  anticline  is  occupied  by  a  series  of  "domes."  In 
their  essential  features  these  domes,  nine  of  which  have  been  mapped,  are  re- 
markably similar.  A  central  oval-shaped  core  of  plutonic  rocks,  ranging  in  com- 


position from  granodiorite  through  quartz  monzonite  to  granite,  has  a  foliation 
that  dips  outward.  The  plutonic  rocks,  overlain  by  Ordovician  (?),  Silurian, 
and  Devonian  strata,  include  the  Ordovician  (?)  rocks  in  many  localities  and 
the  Silurian  rocks  in  at  least  one  locality.  The  upper  contact  of  the  plutonic 
rocks  is  at  essentially  the  same  stratigraphic  horizon  in  all  the  domes,  approxi- 
mately 500  feet  below  the  top  of  the  Ammonoosuc  volcanics,  but  ranges  from 
the  top  to  an  horizon  1,000  feet  below  the  top.  The  overlying  formations  like- 
wise participate  in  the  domical  structure. 

Originally  considered  to  be  laccoliths  or  "bottomless"  plugs  that  had  bowed 
up  their  roof,  it  is  possible  that  they  all  belong  to  a  single  great  concordant 
sheet,  originally  horizontal,  that  has  been  buckled  up  during  orogeny. 

Tectonic  History 

Ordovician  Sedimentation.  The  oldest  rocks  known  so  far  in  the  eu- 
geosyncline  of  New  Hampshire  are  Middle  Ordovician  limestone,  cal- 
careous shale,  and  shale,  7000  to  8000  feet  thick.  Over  these  accumulated 
the  Upper  Ordovician  Ammonoosuc  volcanics,  about  4000  feet  thick,  and 
over  the  volcanics  another  500  to  2000  feet  of  shale. 

Taconic  Orogeny.  Near  the  close  of  Ordovician  time  the  previously 
deposited  sediments  and  volcanics  were  mildly  folded  and  eroded.  The 
disturbance  here  probably  marks  the  subdued  effects  of  die  Taconic 
orogeny  of  the  Hudson-Champlain  region  farther  west. 

Silurian  and  Lower  Devonian  Sedimentation.  In  a  Middle  Silurian 
sea  that  moved  in  from  the  southwest,  conglomerates  and  sands  of  the 
Clough  formation  and  the  dolomitic  sandstones  and  shales  of  the  Fitch 
formation,  not  over  800  feet  thick,  were  deposited.  Late  Silurian  history 
is  obscure,  but  during  early  Devonian  time  about  10,000  feet  of  sand- 
stone, shale,  and  volcanic  materials  accumulated.  See  upper  left  section 
of  Fig.  11.27. 

Acadian  Orogeny.  During  Mid-  or  Late  Devonian,  die  strata  were 
caught  in  a  major  orogeny.  Even  before  the  deformation,  or  at  least  in 
its  early  stages,  successive  injections  of  the  Oliverian  magma  series 
formed  a  great  sheet  in  the  Ammonoosuc  volcanics,  later  to  be  domed 
in  several  places  along  the  western  margin  of  New  Hampshire.  The 
Ordovician,  Silurian,  and  Devonian  strata  were  thrown  into  a  series  of 
anticlinoria  and  synclinoria  whose  axes  trend  north  and  northeast,  and 
countless  minor  folds  were  impressed  upon  the  larger.  Also  the  Northey 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


1S1 


•COOS    ANTICLINORIUM- 


A 

Ot 


BRONSON 

«*—  HILL 

ANTICLINE 


Om3<C>       5 fog  5jLD_Djf0b£?k£^^ 


Monroe      Ammonoosuc     Northey  Hill 
thrust  thrust  thrust 


9P 


MERRIMACK        SYN  CLI  NORIUM- 

WHITE  MOUNTAIN  BATHOLITH 

CO        ,9£      P'q     mo  syj^  C9    PV. 


Mm 


irfMWTi 


A' 


CONNECTICUT 

■*VALLEY->-«-BRONSON    HILL    ANTICLINE- 
SYNCLINORIUM 

UNITY    DOME     "*" MT   CLOUGH^ 
PLUTON 


CARDIGAN    PLUTON 


MERRIMACK      SYNCLINORIUM 


B' 

big   Dl      gqg 


Osp      0       D,    0      D   5i bg  PI    /Jlk kqtn  Pig  Dl  big  Dl  big  Dl       big  Dl     gqg 

Mn,+  h,a„   1-1,1 1  5d 


Northey  Hill 
thrust  (overturned) 


FITCHBURG      PLUTON- 


B' 

949  Dl 


PAWTUCKAWAY 
RING-DIKE   COMPLEX 

■  m,  nn      „S0, 
d  id/  Q<W  i  \ 


ROCKINGHAM 

EXETER 
PLUTON 


ANTICLINORIUM 


GREAT  BAY 
SYNCLINE 


B 


ii 


_!3    MILES 


RYE    ANT.       BAY  OF   MAINE 
50rv       .'5o""vSOr« 


349  Dl         949  d  ,d/  gg^Tx 30  /di       v'\       30  50rv      .-jy^sOrv 


Fig.   11.26.      Cross  section  of  New   Hampshire.  After  Billings,   1956.   Section  A-A'  is  across  northern   part  of 
state  and  B-B'-B"  across  southern   part.  Refer  to  map,  Fig.   11.20. 


Hill  thrust  occurred.  Schistosity  parallel  to  the  bedding  formed  during 
the  earlier  stages  of  the  folding,  and  fracture  cleavage,  essentially  parallel 
to  the  axial  planes  of  the  minor  folds,  formed  during  the  later  stages. 
The  rocks  were  subjected  to  low-grade  metamorphism  northwest  of  the 
Ammonoosuc  thrust,  and  to  medium  and  high-grade  alteration  southeast 
of  it.  The  main  metamorphism  occurred  after  the  Northey  Hill  thrust 
and  during  the  intrusions  of  the  New  Hampshire  magma  series  which 
were  chiefly  responsible  for  the  medium-  and  high-grade  metamorphism. 
See  third  section  in  Fig.  11.27. 


Succeeding  the  metamorphism  was  the  Ammonoosuc  thrusting  and, 
following  this,  some  normal  faulting.  Then  the  Moat  volcanics  were 
erupted,  and  the  plutons  of  the  White  Mountain  magma  series  wore 
emplaced  to  complete  the  bedrock  complex.  This  may  have  occurred  in 
Mississippian  time.  Examine  the  last  four  diagrams  of  Fig.  11.27. 

Isotope  Ages  and  the  Acadian  Orogeny 

It  is  becoming  evident  that  die  Devonian  period  began  almost  400 
m.y.  ago,  and  that  our  previous  estimates  that  designate  this  age  for 


182 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


^\f  r  f"i'W»TC' 

" 

«V 

jVlVj 

'OJn 

'./--■■■ 

Oiil                                                                                                -".■- 

£n0   OF  LOwca    PE.ONU 


LATE    OEvOniam?     IfftCTS  Of    COMTEMPORAWEOwS   E«03iON  OM.TTEO 


£ABLT     C*«&ON(fE«0OS? 


Fig.  11.27.  Evolution  of  the  Franconia  quadrangle  terrane,  White  Mountains,  N.  H.  Reproduced 
from  Williams  and  Billings,  1938.  Oal,  Albee  formation;  Oam,  Ammonoosuc  volcanics;  Sc,  Clough 
conglomerate;  Sf,  Fitch  formation;  Dl,  Littleton  formation;  bg,  Bethlehem  gneiss;  kqm,  Kinsman 
quartz  monzonite;  mv,  Moat  volcanics;  ml,  Mt.  Lafayette  granite  porphyry;  mq,  Mt.  Garfield 
prophyritic  quartz  syenite;  eg,  Conway  granite  and  Mt.  Osceola  granite.  Bethlehem  and  Kins- 
man  belong  to  the   New   Hampshire  magma   series. 


the  Late  or  Mid-Ordovician  must  be  revised.  Hurley  et  al.  ( 1959 )  report 
the  age  of  a  quartz  monzonite  stock  in  northwestern  Maine  which  in- 
trudes well-documented,  fossiliferous,  Lower  Devonian  slate  as  360  m.y. 
The  metamorphism  of  the  beds  is  believed  to  have  occurred  along  with 
the  intrusion. 

Therefore,  the  Oriskany  sedimentation  took  place  prior  to  this  time.  This  is 
in  agreement  with  findings  of  Fairbairn  in  Nova  Scotia  where  sediments  of 
similar  age  have  been  intruded  by  granitic  rocks  .  .  .   (Hurley  et  al.  1959). 

Ages  in  the  320-380  m.y.  range  category  have  generally  been  correlated 
with  the  Taconic  orogeny,  but  if  they  indicate  Acadian  orogeny,  then 
we  must  conclude  that  nearly  all  the  metamorphism  and  most  of  the 
plutonic  activity  is  Acadian  in  New  England  and  the  crystalline  Pied- 
mont. 


CARBONIFEROUS  BASINS 


Location 


Emerson  in  1917  recognized  five  major  Carboniferous  basins  and  a 
number  of  minor  ones  in  eastern  Massachusetts,  southeastern  New  Hamp- 
shire, and  Rhode  Island,  and  they  are  shown  on  the  Geological  Map  of 
the  U.S.  ( 1932)  accordingly.  The  new  geological  map  of  New  Hampshire 
by  Billings  (1956),  however,  recognizes  the  "Carboniferous"  basins  of 
Emerson  in  New  Hampshire  as  Devonian  and  older,  and  therefore  it 
appears  that  only  two  major  basins  are  now  to  be  considered,  the  Nar- 
ragansett  and  the  Boston.  Two  smaller  basins  in  northern  Rhode  Island 
also  are  definitely  demonstrated,  and  they  will  be  referred  to  as  the 
Woonsocket  basins,  following  Emerson.  The  above  basins  are  shown 
on  the  map  of  Fig.  11.28. 

The  Carboniferous  stratified  rocks  are  in  the  slope  from  the  New 
England  upland  to  the  Seaboard  lowland  and  in  the  lowland  itself. 

Narragansett  Basin 

The  generalized  stratigraphy  of  the  three  basins  shown  on  the  map  of 
Fig.  11.28  is  illustrated  on  the  correlation  chart  of  Fig.  11.29.  The  igneous 
intrusive  rocks  are  also  shown.  It  will  be  noted  that  the  basement  com- 
plex consists  of  metamorphosed  Precambrian  sediments  and  intrusives 
and  various  Acadian  intrusives.  Some  fossiliferous  Lower  Cambrian  beds 
are  known  in  eastern  Massachusetts  (Chute,  1950). 

According  to  Emerson  (1917)  the  strata  of  the  Narragansett  basin 
are  in  large  part  coarse  elastics  with  an  aggregate  thickness  of  12,000 
feet.  At  the  base  is  the  Pondville  quartz  conglomerate,  which  is  a  coarse, 
white,  granitic  waste  or  arkose  100  feet  thick.  Above  the  Pondville  is  the 
Wamsutta  group  of  dominantly  red  conglomerates,  sandstones,  shales, 
slates,  and  felsite  flows,  breccias,  and  conglomerates,  some  1000  feet 
thick.  Above  these  strata  are  the  thick  Rhode  Island  coal  measures  that 
include  dominantly  dark  gray  conglomerate,  pebbly  sandstone,  sandstone 
and  gray wa eke,  shale,  and  coal  beds.  They  contain  the  Odontopteris 
flora  and  insect  beds,  and  are  about  10,000  feet  thick.  Above  the  coal 
measures   is   the  Dighton   conglomerate  of  the  northern  field  and   the 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


183 


Purgatory  conglomerate  of  the  southern  field.  The  basin  beds  become 
metamorphosed  to  slates  and  quartzites  to  the  south  and  the  pebbles  of 
the  conglomerates  are  elongated  and  indented.  They  are  regarded  as 
Carboniferous  in  age  and  probably  Pennsylvanian. 

Recent  detailed  work  by  Richmond  (1952)  Quinn  et  al.  (1949),  Quinn 
(1951,  1952),  Nichols  (1956),  Quinn  and  Springer  (1954),  and  Chute 
(1950)  is  responsible  for  the  correlation  chart  (Fig.  11.29),  and  the 
following  generalizations.  The  succession  of  formations  given  by  Emer- 
son is  not  found  in  any  one  quadrangle.  The  unconformity  at  the  base  of 
the  Pennsylvanian  beds  in  the  Narragansett  basin  is  striking,  and  is 
shown  by  the  near  right  angle  discordance  of  the  contacts  of  older  forma- 
tions with  the  Pennsylvanian,  and  by  the  discordance  in  outcrop  of  bed- 
ding and  schistosity.  Three  episodes  of  metamorphism  may  be  detected 
(Quinn,  1952).  The  beds  of  the  Blackstone  series  were  first  moderately 
affected — sandstone  to  quartzite,  mudstones  to  amphibolite  schist.  The 
later  Esmond  granite  is  mildly  metamorphosed  as  are  the  volcanics  of 
the  East  Greenwich  group.  Since  the  East  Greenwich  beds  contain  peb- 


Fig.   11.28.      Carboniferous   basins  of   Rhode   Island   and  Massachusetts. 


NARRAGANSETT  DASIN 

W00NS0CKET  BASINS 

BOSTON  BASIN 

Sedimentary 

Igneous 

Sedimentary 

Igneous 

Sed lmentary 

Igneous 

TRIASSIC 

Diabase  d  ikes 

Diorite  and 
diabase  dikes 

PERMIAN*? 
PENNSYLVANIAN 

Dighton  congl. 
Rhode  Island  fm. 
Wamsutta  gr. 
Pondville  congl. 

Narragansett  Pier 
granite  b   peg. 

Pegmatite  and 
aplite 

Bell ingham 
congl . 

Cambridge 

slate 
J  fSquantun 
u   tillite 

Dorchester 
£  .   slate 
a   Brook  line 
X    cgl.  & 

£  I  vols. 

MISSISSIPPI.** 

East  Greenwich 

group 
(granite  ff   vols .  ) 

tiuincy  granite 

DEVONIAN 

OR 
EARLIER 

Esmond  granite 
?Scituate  granite 

Fine  grained 

gran . 
Esmond  granite 
Metadiabase 

dikes 
Scituate  gr.  gn. 

Fossil iferous 
Lower  CaAbnan 

Dedhaa 

granodionte 
Salem  gabbro- 

d  lorite 
Volcanic  rocks 

PRECAMBRIAN 

Amp 

0 

JL  IT 

■a 

hibolite 
hist 
Sneech  Pond 

schist 
Westboro 

qtz. 
Mussey  Brook 
. schist 

Blackstone 

ser, 

Woonasqua- 
tucket  fm. 

Absalona  fm. 

Sipsachuck 
gneiss 

Porphyritic 
metadiorite 

Fig.   11.29.        Some  sedimentary  and   igneous   rocks  of  Rhode   Island   and   Massachusetts. 


184 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


wq,m 


SOUTHERN 

apg 


WOONSOCKET 

wq,m 


eg         fg  eg 


ngn 


wqm 


NARRAGANSETT       BASIN,        PAWTUCKET       QUAD.,      R.I. 


eg  __q.d       h-^-L..llg_        wq.a  hg  Cgp   hg dd        gg C u 

mb  wq  wq  as  ss 


NARRAGANSETT      PIER 
sga  qbs  Pr'lS 


QUAD.,     R.I. 


Pris 


MILES 


P      P 


npg 


Fig.  11.30.  Cross  sections  of  Woonsocket  and  Narragansett  basins.  Top  section  after  Richmond, 
1952.  ngn,  Nipsachuck  gneiss;  apg,  Absalona  fm.;  wqm,  Woonsasquatucket  fm.;  pmd,  metadiorite; 
Sg,  Scituate  granite  gneiss;  eg,  Esmond  granite;  fg,  fine-grained  granite;  Pb,  Bellingham  con- 
glomerate. 

Middle  section  after  Quinn  ef  a/.,  1949.  mb,  Mussey  Brook  schist;  wa,  Westboro  quartzite;  wqa, 

bles  of  the  Esmond  granite,  their  metamorphism  was  later  than  that  of 
the  Blackstone  series.  The  later  intrusives  rocks  of  the  East  Greenwich 
group  are  essentially  unmetamorphosed.  The  Pennsylvanian  rocks  are 
folded  and  fault-tilted,  and  schistosity  is  widespread.  It  is  commonly 
not  parallel  to  the  bedding,  and  chloritoid,  garnet,  amphibole,  biotite, 
and  muscovite  are  developed. 


Albion    schist    member;    ss,    Sneech    Pond    schist;    hg,    Hunting    Hill    greenstone;    gg,    Grant    Mills 
granodiorite;  Cqp,  Quiney  granite;  Cu,  Carboniferous  undifferentiated;  dd,  diabase  dike. 

Lower  section   after   Nichols,   1956.  sgg,  Scituate   granite   gneiss;   qbs,   Blackstone   quartz-biotite 
schist;  Pris,  Rhode  Island  formation;  npg,  Narragansett  Pier  granite;  p,  pegmatite. 


In  the  Narragansett  Pier  quadrangle  a  reddish,  massive  to  gneissic 
granite  is  clearly  intrusive  into  the  Pennsylvanian  beds.  It  has  been 
named  the  Narragansett  Pier  granite  by  Nichols  ( 1956 ) .  A  cross  section 
is  shown  in  Fig.  11.30.  Elsewhere  granites  intrusive  into  the  Penn- 
sylvanian beds  have  been  reported  but  the  modern  mapping  casts  doubt 
on  such  relations. 


NEW  ENGLAND  APPALACHIAN  SYSTEMS 


185 


Woonsocket  Basins 


A  section  across  the  southern  of  the  two  small  basins,  here  called  the 
Woonsocket,  is  given  in  Fig.  11.30.  The  western  margin  of  the  Penn- 
sylvanian  basin  dips  steeply,  although  it  is  a  sedimentary  contact.  The 
east  margin  is  a  high-angle  normal  fault  contact  ( Richmond,  1952 ) .  The 
Bellingham  conglomerate  which  fills  the  small  basins  generally  dips  east- 
ward although  it  has  many  small  and  closely  spaced  folds.  The  west 
margin  is  a  sedimentary  overlap.  The  conglomerate  pebbles  are  stretched 
in  the  plane  of  schistosity  and  the  long  axes  point  down  dip.  The  matrix 
in  places  is  a  mica  or  chlorite  schist  which  tends  to  enwrap  the  pebbles. 
The  conglomerate  in  the  southern  basin  is  more  sandy  and  less  meta- 
morphosed, and  contains  beds  of  graywacke,  biotite-sericite  schist,  dark 
phyllite,  and  slate. 

Boston  Basin 

The  strata  of  the  Boston  basin  comprise  the  Roxbury  conglomerate 
below,  and  the  Cambridge  slate  or  argillite  above.  The  Roxbury  lies  un- 
conformably  on  the  Dedham  granodiorite  of  Precambrian  (?)  age,  and 
is  possibly  Pennsylvanian  and  probably  Permian  in  age,  according  to 
Billings  et  al.  (1939).  The  conglomerate  is  over  3500  feet  thick,  and  the 
slate  about  3500  feet;  both  constitute  the  Boston  Bay  group.  Part  of  the 
I  Roxbury  conglomerate  is  volcanic  and  part  sedimentary.  The  volcanic 
!  rocks  include  not  only  effusive  lavas  but  also  thick  beds  of  tuff,  ag- 
glomerate, volcanic  breccia,  and  conglomerate. 

The  Roxbury  conglomerate  above  most  of  the  volcanics  is  described  by 
Emerson  as  consisting  of  the  Brookline  conglomerate  at  the  base,  the 
Dorchester  slate  in  the  middle,  and  the  Squantum  tillite  at  the  top.  Ac- 
cording to  La  Forge  the  threefold  division  does  not  persist  throughout 
the  area  occupied  by  the  formation  with  sufficient  definiteness  to  warrant 
mapping  the  members  separately.  In  some  areas,  beds  like  the  Dorchester 
!  slate  are  intercalated  in  most  of  the  formation  below  the  tillite.  The 
Brookline  conglomerate  is  massive,  coarse,  and  in  some  areas  1200  feet 
thick.  It  contains  cobbles  and  boulders,  many  of  which  are  of  the  under- 
lying Dedham  granodiorite  or  of  the  volcanic  complex.  The  slate  mem- 
ber is  red  and  purple,  and  in  one  place  possibly  2000  feet  thick.  Much  of 


Northern 


Soufhrrn 


•  Roxbury    conglomerate  - 


Dec/horri  orono  - 
O/orite 


Cambridge*^    „  '     •  / 

argillite      x /roxbury      cong/omerore 


Decfharn  grono&iorite 
zooo  rSET 


Fig.  11.31.  Cross  sections  of  Boston  basin.  Upper  section  from  northwest  to  southeast  across  entire 
basin.  Cr,  Roxbury  conglomerate;  Cc,  Cambridge  slate;  blank,  pre-Carboniferous,  mainly  igneous 
(LaForge,  1932). 

Middle  section  across  Nantasket  area.  Section  about  4000  feet  in  length.  After  Billings,  Loomis, 
and  Stewart,  1939. 

Lower  section  across  the  Hingham  area.  After  Billings  et  al.,  1939. 


it  is  reworked  basaltic  and  andesitic  tuff,  and  layers  of  purple  sandstone 
and  grit  are  common.  The  Squantum  tillite  is  exposed  in  many  places  in 
the  southern  part  of  the  Boston  basin,  and  is  about  600  feet  thick.  It 
possesses  many  characteristics  of  glacial  drift  and  is  generally  believed  to 
have  been  deposited  by  local  mountain  glaciers. 

The  various  lithologic  types  of  the  Roxbury  conglomerate  interfinger  in 
a  complex  fashion  in  the  Nantasket  area,  according  to  Billings  ( 1939 ) , 
and  the  formation  consists  of  numerous  lenses  of  sedimentary  and  vol- 
canic materials  overlapping  one  another.  See  cross  sections,  Fig.  11.31. 

The  Cambridge  slate,  over  the  Roxbury  conglomerate,  underlies  nearly 
all  the  northern  part  of  the  Boston  basin  and  occupies  several  long  belts 
in  the  southern  part.  The  rock  is  practically  nowhere  a  true  slate,  but  it 
generally  has  a  dominant  cleavage  parallel  with  the  bedding.  It  has  vari- 


186 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Fig.    11.32.      Gulf   of   Maine    and   contnental    shelf   off    Nova    Scotia    showing    location    of   seismic 
profiles  and  Triassic  basin  in  Bay  of  Fundy. 

ously  been  called  a  pelite,  shale,  argillite,  and  slate.  It  contains  some 
quartzite  beds. 

Dott  ( 1961 )  believes  the  Roston  Ray  group  may  be  mid-Paleozoic  and 
not  Carboniferous,  and  also  that  the  Squantum  is  not  a  tillite  but  rather 
an  orogenic  clastic  interfingered  in  the  other  lithologies. 

Gulf  of  Maine 

Cenozoic  and  Cretaceous  Geology.  The  continental  shelf  extends  east- 
ward from  Nantucket  and  Cape  Cod,  and  a  broad  peninsula-like  platform 


under  less  than  500  feet  of  water,  bounded1  on  the  north  by  the  Gulf  of 
Maine  and  on  the  south  by  the  deep  Atlantic,  is  known  as  Georges 
Rank  (Fig.  11.32).  The  Atlantic  margin  of  the  bank  is  trenched  by  deep 
submarine  canyons,  and  from  their  walls  have  been  dredged  rock  samples 
carrying  both  Tertiary  and  Upper  Cretaceous  fossils.  Fragments  of  a 
coarse  sandstone,  Lower  Monmouth  or  Upper  Matawan   (both  Upper 


MT.  KATAHDIN 


LATE        PLIOCENE 


MODERN     WAVE-SMOOTHED  BANK 


Gulf    of    Maine 


GEORGt'J     BAr. 


Po/eozo/l  ~  ,   ~  r"/-  -V-'J~  ~ 


"'-•  v  rocki 


OP  <-\U]=. 


Fig.  11.33.  Evolution  of  the  Gulf  of  Maine  and  Georges  Bank,  generalized  after  a 
chart  exhibited  at  the  Geological  Society  of  America  meetings,  1948,  by  G.  H.  Chadwick  and 
with  his  permission.  Vertical  scale  greatly  exaggerated. 


Halifax 


ANOMALOUS       LAYER 
7.07   AT    40,000" 


5000 


10,000 


15,000' 


20,000' 


25,000' 


B-»-"«"r- 


Fig.   11.34.      Seismic   profiles  of  Gulf  of  Maine   and   continental   shelf   off   Nova   Scotia.   See    Fig.    11.32   for 
location  of  profiles.  After  Drake  ef  a/.,   1954,  and  Officer  and   Ewing,   1954. 


188 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Cretaceous);  of  a  glauconitic  greensand,  Navarro  (equivalent  of  Mon- 
mouth); of  an  indurated  green  silt  not  older  than  Miocene;  and  of  an 
impure  glauconitic  sandstone,  late  Tertiary  in  age,  were  broken  from 
the  walls  of  newly  charted  canyons  cutting  the  southern  margin  of 
Georges  Bank  (Stetson,  1936).  The  thickness  of  the  Tertiary  sediments 
cannot  exceed  1500  feet,  and  the  top  of  the  Upper  Cretaceous  ranges 
between  1450  and  1800  feet  below  sea  level.  Glacial  drift  and  recent 
material  mantle  the  gentler  slopes,  but  in  several  places  the  older  forma- 
tions crop  out  on  the  steeper  slopes.  It  is  clear,  therefore,  that  the  Atlantic 
Coastal  Plain,  made  up  of  Tertiary  and  Cretaceous  sediments,  continues 
eastward  from  the  New  York  region  and  forms  Georges  Bank. 

George  H.  Chadwick  has  prepared  sections  across  the  Gulf  of  Maine 
and  Georges  Bank  showing  the  composition  and  evolution  of  the  sub- 
merged coastal  plain,  and  he  has  given  permission  to  reproduce  them, 
although  they  have  not  been  published.  See  Fig.  11.33.  These  sections 
integrate  the  erosional  surfaces,  the  sediments  of  Georges  Bank  as  recog- 
nized by  Stetson,  an  extension  of  the  Nova  Scotian  Triassic  trough, 
eustatic  changes  in  sea  level,  and  two  stages  of  glaciation.  The  Lower 
Cretaceous  Potomac  is  a  projection  from  the  New  Jersey  coastal  plain 
and  has  not  been  sampled  by  the  dredge. 

Seismic  Profiles.  Refraction  profiles  have  been  run  by  Drake  et  al. 
(1954)  and  Officer  and  Ewing  (1954)  of  the  Gulf  of  Maine  and  con- 
tinental shelf  off  Nova  Scotia.  These  support  the  conclusions  of  Chad- 
wick and  Stetson  as  far  as  the  unconsolidated  and  semiconsolidated  sedi- 
ments go  (Cenozoic  and  Cretaceous).  Compare  Figs.  11.32  and  11.34, 
B-B'.  It  will  be  seen  that  the  unconsolidated  sediments  are  very  thin 


over   the    Gulf    of    Maine    and    only    thicken    under    the    shelf    slope. 

The  Triassic  trough  sediments  are  believed  to  exist,  as  Chadwick 
pictured  them,  on  the  basis  of  the  layer  that  yielded  the  3.7-4.02-km/sec 
velocities  (Drake  et  al.,  1954). 

The  crystalline  basement  appears  complicated  by  layers  with  lower 
than  normal  velocities.  The  4.6-km/sec  velocity  layer  south  of  Yarmouth 
(section  C-C),  the  4.52-5. 13-km/sec  layer  under  the  shelp  slope  and 
rise  off  Nova  Scotia  (sectionA-A'),  and  the  5.11-4.78-km/sec  layer  in 
the  same  place  off  Georges  Bank  (section  B-B')  are  the  cases  in  point. 
They  have  been  interpreted  by  Drake  et  al.  to  be  part  of  the  crystalline 
basement  on  the  grounds  that  Katz  et  al.  (1953)  found  two  layers  in 
Maine,  recording  at  Falmouth,  with  a  velocity  of  5.34  km/sec  for  the 
upper  and  6.24  km/sec  for  the  lower.  These  are  both  somewhat  higher 
than  the  presumed  equivalents  under  the  Gulf  of  Maine.  In  a  study  of 
the  Outer  Ridge  and  Blake-Bahama  basin  (reviewed  in  Chapter  10)  a 
5.2-km/sec  velocity  layer  on  a  =•=  6.5-km/sec  velocity  layer  was  theorized 
to  be  a  mass  of  extruded  basalt  on  the  typical  "oceanic  basalt"  layer.  The 
Gulf  of  Maine  "anomalous  layer"  has  velocities  somewhat  slower  than  the 
'Volcanic"  layer  under  the  Outer  Ridge,  and  also  lies  on  the  crystalline 
basement—not  on  the  ocean  basalt  layer.  It  would  appear,  therefore,  that 
the  anomalous  layer  is  part  of  the  Paleozoic  complex  of  New  England.  It 
could  be  a  mildly  metamorphosed  Carboniferous  basin  type  of  deposit, 
or  conceivably  a  Mississippian  (?)  volcanic  accumulation. 

The  floor  of  the  continental  shelf  and  shelf  slope  sediments  off  Nova 
Scotia  and  Georges  Bank  show  a  depression  or  trench  similar  to  that  off 
New  Jersey.  Refer  to  Fig.  10.6. 


12. 


MARITIME  APPALACHIANS 


DEFINITION 

The  Maritime  Appalachians  will  here  include  the  Paleozoic  mountain 

systems  of  Nova  Scotia,  New  Brunswick,  Prince  Edward  Island,  and  the 

,  continuation  of  the  structural  elements  of  New  York,  Vermont,  and  New 

Hampshire  in  Quebec.  The  folded  and  thrust-faulted  chains  south  of  the 

St.  Lawrence  River  extend  northeastward  into  the  Gaspe  Peninsula,  and 

j  all  are  intrinsically  part  of  the  Maritime  geologic  province.  See  index  map 

1  of  Fig.  11.1.  The  Maritime  Appalachians,  as  here  defined,  are  also  known 

as  the  Appalachian-Acadian  region   ( Alcock,   1947 )   and  together  with 

New  England  and  Newfoundland,  as  Greater  Acadia   ( Schuchert  and 

Dunbar,  1934). 


GEOMORPHIC  PROVINCES 

General  Characteristics 

The  Martime  Appalachians  are  made  up  of  dissected  uplands  and 
broad  lowlands.  The  shoreline  is  notably  long  and  irregular,  with  many 
deep  embayments.  It  is  a  fine  example  of  a  ria  coast  in  which  the  linear 
structural  elements  run  out  under  the  sea.  Figure  12.1  shows  the  physical 
divisions  of  New  Brunswick  and  Nova  Scotia  which  correspond  to  the 
following  descriptions  by  Alcock  (1947). 

Nova  Scotia 

Nova  Scotia  is  made  up  of  five  upland  and  as  many  lowland  areas.  The 
former  comprise:  (1)  the  large  Southern  Upland,  which  embraces  the  southern 
and  central  part  of  the  peninsula  and  slopes  from  elevations  of  about  600  feet 
southeastward  towards  the  Atlantic  Ocean  and  also  southwestward  towards  the 
Gulf  of  Maine;  (2)  North  Mountain,  a  narrow,  flat-topped  belt,  averaging  about 
550  feet  high,  that  extends  along  the  southeast  side  of  the  Bay  of  Fundy  from 
Cape  Blomidon  in  Minas  Basin  southwest  for  120  miles  to  Brier  Island;  (3) 
the  Cobequid  Mountains,  lying  north  of  Minas  Basin  and  stretching  for  75 
miles  across  Cumberland  County  from  the  head  of  the  Bay  of  Fundy  almost 
to  Northumberland  Strait;  this  region  shows  broad,  rounded  summits  blending 
to  form  a  somewhat  rolling  surface  with  an  average  elevation  of  a  little  more 
than  900  feet;  (4)  the  highlands  of  eastern  Pictou  and  Antigonish  counties 
between  New  Glasgow  and  Antigonish  and  stretching  northeastward  to  Cape 
George;  in  the  southern  part  the  average  elevation  is  about  800  feet,  but  near 
Arisaig  it  is  more  nearly  900  feet;  (5)  the  upland  belts  and  northern  tableland 
is  the  largest  of  these  areas  and  presents  an  even  flat-topped  surface  about 
1,200  feet  high. 

The  lowlands  are  underlain  by  less  resistant  rocks,  such  as  sandstone,  shales, 
limestone,  and  gypsum  and  show  a  considerable  diversity  of  elevation  and  form. 
They  comprise:  (6)  the  Annapolis  Cornwallis  Valley,  a  long  trough-like  depres- 
sion lying  between  the  steep,  straight  wall  of  North  Mountain  and  Colchester 
counties  surrounding  Minas  Basin  on  the  north,  east,  and  south,  and  merging 
into  Cornwallis  Valley  on  the  west;  (7)  the  lowlands  of  Hants  and  Colchester 
counties  surrounding  Minas  Basin  on  the  north,  east,  and  south,  and  merging 
into  Cornwallis  Valley  on  the  west;  (8)  the  Cumberland-Pictou  area  occupying 
all  that  part  of  the  isthmus  of  Chignecto  lying  north  and  east  of  Cobequid 
Mountains;  (9)  the  lowland  of  Antigonish  and  Guysborough  counties,  which 
lies  south  and  east  of  the  highlands  extending  towards  Cape  George:  and 
(10)  the  lowlands  of  Cape  Breton  Island,  areas  lying  between  the  upland  belts 
and  occupied  by  undulating  country  of  landlocked  lakes. 


189 


Fig.     12.1.      Physical     divisions     of    the     Maritime     Provinces,     New     Brunswick,     Nova     Scotia,     and     Prince 
Edward   Island.   Reproduced   from   Alcock,    1947. 


MARITIME  APPALACHIANS 


191 


New  Brunswick  and  Prince  Edward  Island 

New  Brunswick  falls  naturally  into  four  major  topographic  divisions  whose 
boundaries,  however,  in  most  places  are  not  sharply  defined.  The  first,  which 
may  be  regarded  as  the  main  axis  of  the  province,  is  known  as  the  Central  High- 
lands, an  upland  region  developed  largely  on  resistant  granitic,  volcanic,  and 
metamorphic  rocks.  It  trends  northeast  through  the  central  part  of  the  province 
and  is  made  up  of  ridges  and  hills,  most  of  which  have  flat  summits.  Its  eleva- 
vation  varies  considerably,  but  much  of  it  has  an  average  height  of  about  1,000 
feet.  The  highest  part  is  where  the  tributaries  of  Miramichi,  Nipisiguit,  and 
Tobique  Rivers  take  their  rise.  Here  broad  summits  have  a  general  elevation  of 
about  2,200  feet,  with  some  ridges  and  peaks  rising  to  still  greater  heights.  For 
example,  Mount  Carleton,  the  highest  point  in  the  province,  has  an  elevation  of 
2,690  feet. 

To  the  northwest  of  the  Central  Highlands  is  a  second  division,  which  may 
be  termed  the  Northern  Upland.  It  stands  at  an  elevation  of  800  to  1,000  feet 
above  sea  level  and  is  developed  on  folded  Paleozoic  strata.  The  upland  pre- 
sents a  remarkably  uniform,  flat-topped  surface  whose  regularity  is  broken  only 
by  a  few  peaks  and  ridges  rising  slighdy  above  the  general  level  and  by  valleys 
such  as  those  of  the  St.  John  and  the  Restigouche,  which  are  deeply  entrenched 
in  it.  The  Stewart  highway  from  Campbellton  to  St.  Leonard  crosses  this  belt. 
The  third  division,  the  Eastern  Plain,  lies  to  the  east  of  the  Central  High- 
lands, and  makes  up  almost  one-half  of  the  province.  It  is  a  region  of  low  relief, 
rarely  more  than  600  feet  high,  sloping  gendy  to  the  Gulf  of  St.  Lawrence.  Its 
underlying  rocks  are  mosdy  flat  or  gendy  dipping  Carboniferous  sediments. 
Prince  Edward  Island  may  be  regarded  as  an  outlier  of  this  division,  and  the 
Cumberland-Pictou  lowland  area  of  Nova  Scotia  is  continuous  with  it. 

The  fourth  division,  termed  the  Southern  Highlands,  lies  along  the  Bay  of 
Fundy.  It  is  mainly  an  upland  belt  of  ridges  of  which  the  most  important  is  the 
II  flat-topped  Caledonis  Mountain  belt  of  Albert,  Kings,  and  St.  John  counties, 
'J  which  reaches  a  maximum  elevation  of  1,350  feet  southeast  of  Markhamville. 
j  To  the  southwest,  in  Charlotte  county,  the  belt  merges  into  the  Central  High- 
I  lands.  The  region  shows  considerable  topographic  diversity  and  a  great  variety 
of  rock  types.  The  ridges  are  composed  mainly  of  hard  volcanic  and  intrusive 
,  rocks,  whereas  minor  lowland  areas  within  the  belt  have  been  carved  from 
-  weaker  strata. 

i    Quebec 

In  Quebec  the  Appalachian  region  is  bordered  on  the  northwest  by  the  St. 
ji  Lawrence  Lowlands  into  which  it  merges  imperceptibly.  In  fact,  considered 
|  from  the  point  of  view  of  topography,  the  lowland  belt  overlaps  the  Appalachian 
geological  region.  To  the  southwest  the  upland  region  includes  three  parallel 
groups  of  ridges  and  isolated  hills  and  mountains.  These  are  highest  in  the  south, 
and  decrease  in  elevation  towards  the  northeast.  The  highest  point  is  Round 
Top  on  Sutton  Mountain,  elevation  3,175  feet,  near  the  Vermont  border. 


The  most  easterly  of  the  three  belts  is  known  as  the  Megantic  anticline.  It 
forms  part  of  the  International  Boundary,  and  to  the  northeast  passes  into 
Maine.  To  the  west  the  Stoke  Mountain  anticline  extends  as  far  as  Lake  St. 
Francis,  where  it  loses  its  identity.  Still  farther  west,  a  little  beyond  Lake  Mem- 
phremagog,  the  third  range,  the  Sutton  Mountain  anticline,  is  a  continuation 
of  the  Green  Mountains  of  Vermont.  Between  the  anticlinal  ranges  the  country 
varies  from  900  to  1,000  feet  in  elevation,  presenting  in  places  a  remarkably 
level  surface.  To  the  northeast,  it  continues  as  an  upland  belt  of  ridges  and  roll- 
ing country  cut  across  by  deep  valleys  such  as  those  of  the  St.  Francis  and 
Chaudiere.  It  decreases  in  elevation  to  a  point  about  opposite  Quebec  City,  but 
farther  northeast  it  rises  again  and  in  the  central  part  of  the  Gaspe  Peninsula 
becomes  the  Shickshock  Mountains,  with  elevations  ranging  up  to  more  than 
4,200  feet.  The  individual  members  of  this  range  show  broad  flat  summits  and 
the  range  is  bordered  both  to  the  north  and  south  by  another  flat-topped  upland 
at  a  lower  level  into  which  the  present  river  valleys  are  deeply  incised.  On  the 
north  side  of  the  Shickshock  the  descent  to  the  lower  upland  is  for  the  most  part 
abrupt;  on  the  south  it  is  more  gradual.  The  lower  surface  slopes  off  both  to  the 
north  and  to  the  south,  and  to  the  southwest  merges  with  the  Northern  Upland 
of  New  Brunswick. 


STRATIGRAPHY 

Introduction 

The  Maritime  Appalachians  are  a  continuation  of  the  New  England 
Appalachians  and  present  much  the  same  geology.  See  geologic  map  of 
Fig.  12.2.  They  are  composed  mostly  of  Paleozoic  rocks,  both  sedimentary 
and  igneous,  but  some  older  Precambrian  and  some  younger  Triassic 
rocks  are  also  present.  The  chart  of  Fig.  12.3  correlates  the  principal  for- 
mations of  Nova  Scotia,  New  Brunswick,  and  Quebec,  and  may  be  re- 
ferred to  in  the  following  brief  enumeration  of  the  stratigraphic  systems. 
Several  groups  such  as  the  Green  Head,  the  George  River,  and  the  Cold- 
brook  are  known  definitely  to  be  Precambrian,  and  others  such  as  the 
Meguma  and  Macquereau  are  regarded  as  Precambrian  but  on  less  satis- 
factory evidence.  They  may  be  Cambrian.  Certain  granite  intrusions  of 
the  southern  highlands  of  New  Brunswick  and  in  Cape  Breton  Island  are 
also  probably  Precambrian,  but  absolute  proof  of  this  has  not  been  estab- 
lished. Other  belts  of  rock  shown  on  early  maps  as  Precambrian  arc  now 
either  definitely  known  or  else  inferred  to  be  of  Paleozoic  age  ( Alcock, 
1947). 


SO 

■•'■'■ 


SCALE     OF    MILES 
O  SO  lOO 


Fig.     12.2.      Geologic    map    of    the    Maritime     Provinces     and     Quebec.     Reproduced     from     Alcock,     1947. 


MARITIME  APPALACHIANS 


193 


Cambrian  System 

Alcock  (1947)  reports  that  Cambrian  rocks  are  found  in  southeastern 
Quebec,  in  Gaspe  Peninsula,  in  southern  New  Brunswick,  and  in  Cape 
Breton  Island,  Nova  Scotia.  In  southeastern  Quebec  most  of  the  rocks  of 
this  age  are  metamorphosed  to  a  greater  or  less  degree,  and  some  are 
highly  schistose.  In  the  Oak  Hill  region  near  the  Vermont  border  a  series 
of  Lower  Cambrian  strata  3000  to  4000  feet  thick  consist  of  slate,  quartz- 
ite,  dolomite,  graywacke,  and  sericite  schist.  Rocks  presumably  of  Cam- 
brian age  of  the  Thetford-Beauceville  region,  known  as  the  Caldwell 
group,  consist  of  nearly  pure  quartzites,  slates,  and  pillow  lavas  of  basaltic 
composition.  A  Cambrian  seaway  and  trough  of  deposition  probably 
extended  from  the  Lake  Champlain  region  to  Quebec  City  and  hence  to 
Gaspe  where  some  hard,  gray  limestone  and  ribboned,  shaly  limestone 
of  late  Cambrian  age  occur. 

At  St.  John,  southern  New  Brunswick,  strata  from  Lower  Cambrian  to 
Lower  Ordovician  crop  out,  and  these  are  known  collectively  as  the  St. 
John  group.  It  consists  of  quartzites,  limestones,  and  black  shales.  Similar 
beds  occur  on  Cape  Breton  Island.  They  range  in  age  from  Lower  to 
Upper  Cambrian  and  consist  of  gray  and  black  shales  and  slates  with 
some  quartzite  and  conglomerate,  red  sandstone  and  red  and  gray  argillite 
carrying  hematite,  and  greenish  gray  and  reddish  gray  argillites. 

Ordovician  System 
According  to  Alcock  (1947): 

In  the  Appalachian  belt  of  Quebec,  strata  of  Lower,  Middle,  and  Upper 
!  Ordovician  age  are  known,  but  in  most  places  fossils  are  not  sufficiently  well 
preserved  to  permit  an  exact  age  determination.  In  the  long  belt  from  the  Ver- 
mont border  to  the  east  end  of  Gaspe  the  deformed  Ordovician  strata  were 
formerly  referred  to  as  the  "Quebec  group."  This  term  had  first  been  applied 
by  Logan  in  1860  to  beds  at  Quebec  City  that  had  been  thrust  against  and 
over  the  younger  strata  of  Middle  Ordovician  age.  Later  the  term  became  a  con- 
venient one  to  include  all  those  early  rocks  whose  exact  age  was  unknown. 

In  Nova  Scotia,  Ordovician  rocks  are  known  to  occur  in  the  Pictou-Antigonish 
upland.  They  comprise  metamorphosed  sedimentary,  volcanic,  and  intrusive 
varieties.  The  Browns  Mountain  group,  consisting  of  argillites,  slates  and  gray- 
wacke, is  regarded  on  the  evidence  of  a  few  fossil  linguloids,  as  of  Lower  Ordo- 
vician age.  Locally  associated  with  the  sediments  are  interbedded  volcanic  flows 


Era 

Period 

Epoch 

Nova  Scotia 

New  Brunswick 

Quebec 

Mesozoic 

Triassic 

Annapolis 

Ouaco;  Lepreau 

Permian 

Carboniferous 

Pennsylvania 

Pictou;  Morien; 

Stellarton 
Cumberland 
Riversdale 

Clifton       \ 

Lancaster  f 

>Petit- 
i       codiac 

Mispek 

Bon  a  venture 

Mississipian 

Canso 

Windsor 
Horton 

Hopewell 
Windsor 

Moncton 

Albert 

Memramcook 

Paleozoic 

Devonian 

Upper  Devonian 

Perry 

Escuminac 
Fleurant 
Pirate  Cove 

Middle  Devonian 

Gaspe 

Gaspe;   Malbaie; 

Heppel 

Lower  Devonian 

McAdom  Lake;  Tor- 
brook;  Knoydart 

Dalhousie 

Grand  Greve 
Bon  Ami 

St.  Albans;  Dalhousie; 
Lake  Aylmer 

Silurian 

Arisaig;  Kentville 

Chaleur  Bay;  Mas- 
carene 

Chaleur  Bay 

Ordovician 

Upper  Ordovician 

Matapedia 

Matapedia;  Paboi; 
White  Head 

Middle  Ordovician 

Malignant  Cove; 
Stewart  Brook 

Browns  Mountain 
Boisdale 

Tetagouche 

Pohenagamooke; 
Mictaw;  Quebec 
City;   Beaucevitle; 
Farnham;  St.  Fran- 
cis 

Lower  Ordovician 

Saint  John 

Levis 
Sillery 

Cambrian 

Murphy  Creek;  Cald- 
well; Sutton;  L'Met 

ProTerozolc 

Meguma    (Gold- 
bearing) 

Coldbrook 

Macquereau;    Tibbit 
Hill 

Archean 

George  River 

Green  Head 

Fig.  12.3.  Correlation  chart  of  the  principal  formations  of  Nova  Scotia,  New  Brunswick,  and 
Quebec.   Reproduced   from   Alcock,    1947. 

and  tuffs,  and  cutting  them  is  a  stock  of  granite  and  dvkes  and  stocks  of  rh\  o- 
lite  and  quartz  porphyry.  In  the  Arisaig  region,  strata  of  this  group  are  overlain 
by  coarse  conglomerate,  and  grit  of  the  Malignant  Cove  formation,  which  is 
believed  to  be  of  Middle  Ordovician  age.  In  the  Pictou  region  purplish  red.  ar- 
kosic  conglomerate,  purplish  gray,  arkosic  grit,  and  purplish  red  argillite  form 
what  is  known  as  the  Stewart  Brook  formation,  which  is  probably  correlative 
with  the  Malignant  Cove. 

In  New  Brunswick,  rocks  of  Middle  Ordovician  age  occur  near   Bathurst. 
Stretching  to  the  southwest  is  a  wide  belt  of  sedimentary  rocks,  with,  in  places, 


194 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


associated  volcanic  varieties.  Much  of  this  complex  may  be  of  Ordovician  age. 
In  the  southwestern  part  of  the  province  the  Charlotte  group  is  probably  of  Or- 
dovician age.  It  is  made  up  of  two  divisions,  one  known  as  the  Dark  Argillite, 
the  other  as  the  Pale  Argillite.  The  former  lies  unconformably  below  strata  of 
Silurian  age  and  is  composed  of  argillite,  slate,  quartzite,  mica  schist,  gneiss, 
and  minor  amounts  of  volcanic  rocks.  It  is  intruded  by  masses  of  granite  and 
gabbro.  The  Pale  Argillite  consists  of  argillite,  sandstone,  arkose,  slate,  and 
mica  schist.  In  the  St.  Stephen  area  the  beds  are  apparently  comformable  with 
and  grade  into  those  of  Dark  Argillite.  On  early  maps  the  Pale  Argillite  was 
classed  as  Devonian  on  account  of  the  reported  finding  on  Cox  Brook,  a  tributary 
of  Magaguadavic  River,  of  a  Lepidodendron-like  form.  Later  work  has  failed 
to  find  any  fossils  whatever  in  these  rocks. 

In  the  Thetford  area,  the  Quebec  group  (Sillery  and  Levis)  consists  of  black 
slates  with  a  basal  conglomerate  and  some  interbedded  impure  quartzite  or 
graywacke,  overlying  unconformably  the  Cambrian  Caldwell  group.  In  the 
Beauceville  region  volcanic  tuffs  and  flows  are  interbedded  with  the  sediments, 
and  in  places  the  series  is  so  altered  that  it  is  difficult  to  distinguish  the  volcanic 
from  the  sedimentary  members.  Still  farther  southwest,  near  Phillipsburg  in  the 
Lake  Champlain  region,  a  thick  series  of  fossiliferous  Beekmantown  sediments 
consisting  of  shales  and  limestones  overlies  Upper  Cambrian  beds  and  is  fol- 
lowed by  strata  of  Chazy  of  Middle  Ordovician  age. 

To  the  northeast  of  Levis,  rocks  consisting  of  red,  green,  gray,  and  black 
slates,  quartzites,  and  conglomerates  form  a  belt  in  places  20  miles  wide.  These 
beds  have  been  correlated  with  the  Sillery,  but  both  younger  and  older  strata 
may  be  included.  An  interesting  feature  in  these  rocks  is  the  presences  of  belts 
of  limestone  conglomerates.  These  occur  at  various  horizons  in  both  the  Sillery 
and  the  Levis,  forming  bands  from  about  a  foot  to  more  than  100  feet  in  thick- 
ness. The  pebbles  and  boulders  consist  of  gray  limestone,  and  weigh  from  less 
than  an  ounce  to  many  tons.  Similar  limestone  conglomerates  are  found  in  New- 
foundland to  the  northeast  and  Vermont  to  the  southwest.  They  have  been  in- 
terpreted as  the  result  of  local  slipping  and  breaking  up  of  limestone  along  the 
sea  bottom  by  earthquakes  in  a  zone  where  faulting  was  prevalent.  Another 
feature  of  the  Sillery  is  the  occurrence  of  belts  of  quartzite,  locally  called  the 
Kamouraska  formation.  These  belts  are  lenticular  but  extensive,  and  their  thick- 
ness varies  greatly. 

Interbedded  arkose  and  volcanic  rocks  of  Ordovician  age  are  known 
in  the  Shickshock  Mountains;  and  dark  shales,  limestones,  conglomerates, 
argillites,  quartzose  sandstone,  and  volcanic  flows  and  tuffs  occur  to  the 
south  on  both  sides  of  Chaleur  Bay. 

Silurian  System 

The  best  Silurian  section  in  Nova  Scotia  is  at  Arisaig  where  3800  feet  of 
highly  fossiliferous  sandstones  and  shales  occur.  The  series  is  overlain  by 


Lower  Devonian  beds,  and  it  overlies  a  flow  of  rhyolite  probably  of 
Lower  Ordovician  age.  The  faunas  can  be  correlated  better  with  British 
than  with  American;  even  the  resemblances  with  the  Chaleur  Bay  Silurian 
faunas  are  slight. 

On  the  north  side  of  Chaleur  Bay  is  probably  the  thickest  marine 
Middle  Silurian  succession  in  North  America.  At  the  top  of  the  sequence 
are  volcanic  flows  interbedded  with  sediments,  chiefly  elastics,  and  flows 
are  present  also  in  other  formations  farther  down  in  the  succession.  A 
total  of  8427  feet  or  more  of  sedimentary  rocks  and  4626  feet  of  volcanic 
rocks  are  present  in  the  Black  Cape  area. 

In  southern  New  Brunswick,  on  the  Bay  of  Fundy,  great  quantities  of 
volcanic  rocks,  chiefly  rhyolites  and  andesites,  are  interbedded  with  sedi- 
ments. At  Oak  Bay  a  basal  Silurian  coarse  conglomerate  rests  unconform- 
ably on  the  dark  argillite  of  the  Charlotte  group  of  Ordovician  age.  The 
belt  is  a  continuation  of  one  extending  from  the  Eastport  area  of  Maine, 
where  a  number  of  formations  of  Middle  and  Upper  Silurian  age  occur. 

Devonian  System 

Rocks  of  Lower  Devonian  age  occur  in  Quebec,  New  Brunswick,  and 
Nova  Scotia.  Sedimentation  at  this  time  was  accompanied  by  widespread 
volcanism,  and  at  the  close  of  the  epoch  the  main  phase  of  the  Acadian 
orogeny  took  place.  In  the  Middle  Devonian,  great  thicknesses  of  clastic 
sediments  accumulated  in  the  Gaspe  Peninsula,  and  in  Upper  Devonian 
time  sedimentation  progressed  locally  in  the  Chaleur  Bay  and  Bay  of 
Fundy  regions  ( Alcock,  1947 ) . 

A  well-known  Lower  Devonian  section  is  at  the  eastern  end  of  Gaspe 
Peninsula,  where  about  2000  feet  of  limestone  and  limy  shale  beds  have 
been  described.  Within  central  Gaspe  Lower  Devonian  shales  and  lime- 
stones, associated  with  thick  deposits  of  volcanic  rocks,  are  widespread. 
At  the  west  end  of  the  peninsula,  shales  and  argillaceous  limestones  of  the 
same  age  are  2200  feet  thick. 

The  Lower  Devonian  rocks  at  Dalhousie  consist  of  highly  fossiliferous 
marine  sediments,  volcanic  flows,  and  tuffs,  dikes,  and  volcanic  rocks. 
The  principal  Nova  Scotian  Lower  Devonian  section  is  southwest  of 
Arisaig,  where  fine-grained,  red,  arenaceous  slates  and  gray  sandstones 


MARITIME  APPALACHIANS 


195 


1000  feet  thick,  and  apparently  of  continental  origin,  overlie  with  marked 
erosional  unconformity  Silurian  strata  of  the  Arisaig  series. 
.  Much  of  the  interior  of  Gaspe  is  underlain  by  sandstones,  conglom- 
erates, and  arenaceous  shales  varying  in  color  from  green  and  drab  to  red. 
The  type  locality  is  on  Gaspe  Bay  where  a  section  7000  feet  thick  rests  on 
the  Lower  Devonian  limestones. 

Upper  Devonian  beds  are  present  on  the  north  side  of  Chaleur  Bay  in  a 
three-unit  sequence.  The  lower  formation  consists  of  pebble  conglom- 
erates and  sandstones  and  450  feet  of  coffee-colored  shale.  The  middle 
formation  consists  of  a  coarse  pebble-and-boulder  conglomerate  with 
gray  matrix.  It  is  only  45  feet  thick.  The  upper  formation  is  385  feet 
thick  and  consists  of  gray  shales  and  shaly  sandstones. 


On  the  western  side  of  Passamaquoddy  Bay,  in  the  St.  Andrews  region  of 
'  New  Brunswick,  near  the  Maine  border,  on  the  opposite  side  of  the  bay  on 
Mascarene  Peninsula,  at  Black  Harbour  south  of  St.  George,  and  on  some  of 
the  adjacent  islands  are  areas  underlain  by  beds  of  red  sandstone  and  conglom- 
erate that  are  correlated  with  the  Perry  conglomerate  of  Maine. 

The  beds  lie  for  the  most  part  with  low  dips  and  in  gende  folds.  In  places 

they  rest  unconformably  on  the  Silurian  rocks,  and  in  places  are  in  fault  contact 

i  against  them.  The  conglomerates  contain  boulders   of  the  Silurian   and  pre- 

Silurian  rocks  and  of  the  St.  George  granite  intrusive  rocks.  On  Hill  Island  two 

basic  amygdaloidal  lava  flows  are  interbedded  with  the  red  sediments,  and  simi- 

;  lar  volcanic  rock  shows  on  Howard  Island.  Locally  the  beds  are  cut  by  dark 

j  dykes.  Similar  dykes  and  flows  are  associated  with  the  conglomerate  beds  at  St. 

j  Andrews  (Alcock,  1947). 

Carboniferous  System 

Carboniferous  strata  underlie  extensive  areas  of  New  Brunswick  and 
i  Nova  Scotia.  They  also  underlie  all  of  Prince  Edward  Island  and  the  Mag- 
dalen Islands  in  the  Gulf  of  St.  Lawrence,  and  they  crop  out  along  the 
north  shore  of  Chaleur  Bay.  They  represent  Mississippian,  Pennsylvanian, 
and  possibly  part  of  Permian  time,  and  are  the  source  of  coal,  oil,  gas,  and 
gypsum  in  New  Brunswick  and  Nova  Scotia.  They  are  generally  softer 
i  and  more  susceptible  to  erosion  than  the  older  Paleozoics  and  form  the 
lowlands.  The  lowlands  of  the  geomorphic  map  of  Fig.  12.1  are,  therefore, 
I  about  coincident  with  the  Carboniferous  beds.  See  also  the  Geologic  Map 
of  North  America. 


Fig.    12.4.      Correlation    chart    of    the    Carboniferous    formations    of    New    Brunswick    and    Nova 
Scotia.   Reproduced  from   Alcock,    1947. 


196 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


The  Carboniferous  strata  make  up  extremely  thick  sequences,  are 
dominantly  conglomerates,  sandstones,  and  shales;  they  contain  several 
angular  unconformities,  and  are  particularly  instructive  of  crustal  unrest 
and  of  the  tectonic  history  of  the  region.  The  correlation  chart  of  Fig.  12.4 
gives  the  important  formations  of  the  Carboniferous  rocks  in  the  Maritime 
Provinces.  From  it  some  idea  of  the  numerous  units,  large  thicknesses, 
and  unconformities  can  be  gained.  The  sedimentary  and  tectonic  history 
is  even  more  detailed  than  the  chart  indicates.  For  instance,  the  Missis- 
sippian  strata  of  Nova  Scotia  belong  to  two  groups,  the  Horton  and  the 
Windsor;  and  along  the  lower  part  of  the  Avon  River,  the  Horton  group 

...  is  made  up  of  two  formations,  a  lower  known  as  the  Horton  Bluff,  con- 
sisting of  some  3,400  feet  of  dark  shale,  sandstone,  and  conglomerate,  and  an 
upper,  the  Cheverie,  made  up  of  600  feet  of  red  and  grey  shales,  sandstone  and 
arkose.  The  Horton  Bluff  formation  rests  unconformably  on  pre-Carboniferous 
metamorphic  and  igneous  rocks;  it  contains  plant  remains,  buried  forests,  and 
soils,  and  has  a  fauna  of  ostracod,  crustaceans,  and  fish  remains.  The  Cheverie 
rests  with  an  angular  unconformity  on  the  Horton  Bluff  and  is  succeeded,  also 
unconformably,  by  the  Windsor  group  of  marine  sediments.  The  latter  comprise 
limestone,  gypsum,  shale,  sandstone  and  limestone  conglomerate,  the  whole 
having  a  thickness  of  about  1,550  feet.  The  limestone  members  are  rich  in  fos- 
sils and  have  yielded  one  hundred  and  twenty-seven  species,  chiefly  molluscs 
and  brachiopods. 

The  Mississippian  rocks  extend  eastward  through  the  lowland  belt  to  the 
Strait  of  Canso,  and  also  occupy  much  of  the  lowlands  of  the  southwestern  part 
of  Cape  Breton  Island.  In  the  Lake  Ainslie  area,  the  Horton  group  includes 
about  6,000  feet  of  conformable,  dominantly  clastic  sediments  containing  a 
meagre  flora  and  fauna.  They  are  intruded  by  diabase  dykes  and  sills.  The  suc- 
ceeding Windsor  beds  have  here  a  thickness  of  about  2,000  feet.  In  the  Arisaig 
region,  diabase  and  basalt  dykes  and  stocks  intrude  red  conglomerate,  sand- 
stone, and  sandy  shale  of  the  Mississippian  McAras  Brook  formation,  but  are 
apparently  older  than  the  limestone  of  the  Ardness  formation  of  Mississippian 
age  (Alcock,  1947). 

The  Pennsylvanian  rocks  of  Nova  Scotia  are  wholly  nonmarine,  as  far 
as  known,  are  dominantly  clastic  and  red,  and  contain  locally  beds  of  coal 
and  thin  limestones.  Pennsylvanian  rocks  also  cover  much  of  the  plain  of 
eastern  New  Brunswick,  being  made  up  of  red  and  gray  shales,  sand- 
stones, grits,  and  conglomerates. 

The  north  shore  of  Chaleur  Bay  is  bordered  for  considerable  distances  by  red 
clastic  beds  of  the  Bonaventure  formation,  which  takes  its  name  from  the  Bona- 


venture  Island  at  Perce.  The  strata  consists  chiefly  of  coarse  conglomerates  and 
sandstones,  with  associated  red  shales,  shaly  sandstones,  and  locally  limestone. 
The  beds  for  the  most  part  lie  horizontally,  but  are  locally  tilted  and  in  places 
faulted. 

For  relations  along  the  north  shore  of  Chaleur  Bay  see  Fig.  12.5. 

Magdalen  Islands  are  composed  of  folded  sedimentary  and  volcanic 
rocks  of  Mississippian  age,  surrounded  by  flat-lying  beds  of  red  sandstone 
of  probable  Pennsylvanian  age. 

Triassic  System 

Red  sandstones,  shales,  and  conglomerates  of  Triassic  age  occur  in  the 
Bay  of  Fundy  region.  They  are  most  extensive  on  the  southeast  side  of 
the  bay,  where  a  belt  stretches  along  the  entire  length  of  the  bay  and 
borders  both  sides  of  Minas  Basin.  See  Fig.  11.31.  They  rest  uncon- 
formably on  various  Paleozoic  and  Precambrian  formations  and  are 
capped  by  about  1000  feet  of  basaltic  lavas  that  form  the  North  Moun- 
tain upland.  On  the  northwest  side  of  the  Bay  of  Fundy,  patches  of 
similar  red  conglomerate  and  sandstone  occur.  The  beds  of  all  these 
patches  dip  to  the  northwest  and  are  in  fault  contact  with  the  older 
formations.  It  has  been  concluded  that  they  are  deposits  in  a  down- 
faulted  basin  similar  to  those  of  the  Triassic  red  beds  in  the  Connecticut 
and  New  Jersey  basins.  This  is  the  northeasternmost  of  the  known  Trias- 
sic fault  basins  in  the  Appalachian  mountain  systems.  It  is  believed  to 
extend  under  the  Gulf  of  Maine  nearly  to  Boston.  See  Fig.  11.31. 

IGNEOUS  ROCKS 

Extrusive  Rocks 

Interbedded  volcanic  rocks  of  various  kinds  have  already  been  men- 
tioned in  the  account  of  the  stratigraphy.  They  are  known  in  the  Cam- 
brian and  Lower  Ordovician  of  the  Thetford-Beauceville  region  of  Que- 
bec, in  the  Middle  Ordovician  in  the  central  Shickshock  Mountains,  and 
on  the  south  side  of  Chaleur  Bay.  They  are  also  known  in  the  Middle 
Silurian  in  various  places  on  the  Gaspe  Peninsula  on  the  north  side  of 
Chaleur  Bay,  along  the  New  Brunswick  side  of  the  Bay  of  Fundy,  and 


DETAILS    OF 

ESCUMINAC    BAY  SECTION 

GASPE  PENIN.  QUEBEC 


>     Red  shale  and  conglomerate 


SCALE  OP  MILES 
10  0  10         20         30 


G  S.C. 


Fig.   12.5.      Diagrammatic   section   along   the   north   shore   of   Chaleur   Bay.   Reproduced    from   Alcock,    1947. 
Gaspe  sandstone  is  middle  Devonian. 


198 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


in  the  Eastport  area  of  Maine.  The  Silurian  outpourings  were  especially 
voluminous  and,  where  identified,  are  chiefly  andesites  and  basalts,  al- 
though acidic  varieties  have  been  noted.  Volcanism  was  again  widespread 
and  voluminous  in  the  Devonian.  Lower  Devonian  volcanics  are  known 
in  the  Gaspe  Peninsula,  in  northern  New  Brunswick,  and  in  the  Lake 
Ainslie  area  of  Nova  Scotia;  Upper  Devonian  lavas  have  been  noted  in 
the  St.  Andrews  region  of  New  Brunswick  near  the  Maine  border.  The 
Devonian  volcanics  are  mostly  andesites. 

The  Carboniferous  was  unremitting  in  volcanic  activity,  and  consid- 
erable amounts  of  lavas  and  tuffs  were  extruded.  The  Mississippian 
rocks  of  the  Magdalen  Islands  contain  basaltic  lavas  and  fragmentals,  and 
those  of  the  Hampstead  area  of  New  Brunswick  contain  rhyolite.  Penn- 
sylvanian  rocks  in  the  St.  John  region  of  the  Bay  of  Fundy  contain  ex- 
trusive and  intrusive  rocks,  and  the  Bonaventure  formation  along  the 
north  shore  of  Chaleur  Bay  contains  amygdaloidal  basalt  flows. 

Lavas,  chiefly  andesitic  and  basaltic,  and  graywackes  and  arkoses  with 
sandstones,  shales,  and  limestones  compose  a  stratified  assemblage  typical 
of  the  eugeosyncline  of  Kay  (1951). 

Intrusive  Rocks 

Intrusive  rocks  are  widespread  in  Nova  Scotia  and  New  Brunswick. 
They  are  granites  and  associated  differentiates,  that  accompanied  the 
Acadian  orogeny  at  the  close  of  Lower  Devonian  time.  The  granites  are 
exposed  over  much  of  the  southern  upland  of  Nova  Scotia,  and  the  central 
highlands  of  New  Brunswick. 

A  belt  of  ultrabasic  plutons,  now  largely  serpentinized,  extends  through 
the  Quebec  Appalachians  from  Vermont  to  Gaspe,  and  their  intrusion  is 
thought  to  have  accompanied  the  Taconic  orogeny.  See  Fig.  8.29. 

Many  dikes  and  sills  are  mentioned  in  the  literature,  and  these  prob- 
ably relate  to  the  volcanic  series. 

A  group  of  eight  small  intrusions  in  southern  Quebec  form  the  Mon- 
terigian  Hills.  The  most  westerly  is  Mount  Royal  at  Montreal.  Except  for 
one,  they  lie  along  a  curved  line  that  extends  easterly  from  Montreal.  Five 
of  them  rise  well  over  1000  feet  above  the  surrounding  plain;  the  others  to 
heights  of  600  to  700  feet.  The  five  westerly  ones  intrude  the  flat-lying 


beds  in  front  of  Logan's  line,  and  the  three  easterly  ones  cut  the  folded 
and  faulted  Paleozoics  east  of  the  line.  According  to  Caley  ( 1947 ) : 

Brome  and  Shefford  Mountains  are  thought  to  be  unroofed  laccoliths,  or  per- 
haps parts  of  a  single  laccolith  still  covered  by  sedimentary  strata  in  the  2%  mile 
interval  of  lower  land  between  the  hills.  The  remaining  hills  appear  to  be  vol- 
canic necks  with  nearly  vertical  walls. 

The  age  of  the  intrusions  is  Devonian  or  younger.  Evidence  for  this,  in  addi- 
tion to  that  supplied  by  the  St.  Helen  Island  breccia,  is  afforded  by  Yamaska, 
Shefford,  and  Brome  Mountains,  which  lie  within  the  folded  Appalachian  re- 
gion. The  intrusive  masses  show  no  effects  of  deformation,  and  hence  must 
have  been  intruded  after  the  last  folding  that  affected  this  region  in  Middle 
Devonian  time.  It  has  also  been  noted  that  in  the  Monterigian  intrusive  rocks 
pleochroic  haloes  surrounding  crystals  of  zircon  and  titanite  are  invariably 
poorly  developed  and  immature.  In  this  they  resemble  those  in  Tertiary  intru- 
sive rocks,  whereas  in  certain  Devonian  granites  haloes  are  numerous  and  prom- 
inent. The  suggestion  has,  therefore,  been  advanced  that  the  igneous  rocks  of 
the  Monterigian  Hills  may  be  as  young  as  Tertiary. 

STRUCTURES 

Unconformities 

The  Paleozoic  section  is  replete  with  unconformities  and  conglomerates 
which  indicate  intermittent  orogeny  from  place  to  place  over  a  long 
time. 

A  coarse  conglomerate  of  Lower  Cambrian  age  containing  large  gra- 
nitic boulders  rests  on  rocks  of  the  same  material  as  the  boulders  near 
St.  John,  New  Brunswick.  Lower  Ordovician  black  slates  with  a  basal 
conglomerate  and  some  interbedded  impure  quartzite  or  graywacke 
overlie  unconformably  the  Caldwell  group  of  the  Cambrian  in  the  Thet- 
ford  area  of  southern  Quebec.  Limestone  conglomerates  of  Lower 
Ordovician  age  occur  in  places  from  Vermont  through  Quebec  to  New- 
foundland and  have  been  interpreted  as  the  result  of  local  slipping  and 
breaking  up  of  limestones,  just  deposited,  along  the  sea  bottom  by  earth- 
quakes in  a  zone  of  crustal  deformation. 

In  Nova  Scotia,  a  coarse  conglomerate  and  grit  of  Middle  Ordovician 
age  overlies  beds  of  Lower  Ordovician  age.  On  the  north  side  of  Chaleur 
Bay,  coarse  conglomerates  of  Middle  Ordovician  age  made  up  largely  of 
the  Proterozoic  (?)  Macquereau  rocks,  rest  on  the  Macquereau.  In  the 


MARITIME  APPALACHIANS 


199 


same  general  area  is  a  broad  belt  of  Upper  Ordovician  conglomerate  and 
grit  about  2000  feet  thick.  Its  relations  to  underlying  beds  are  not  noted. 

The  Arisaig  Silurian  series  of  Nova  Scotia  contains  conglomerates  and 
rests  on  Lower  Ordovician  volcanics.  At  Oak  Bay  in  southern  New  Bruns- 
wick, the  base  of  the  Silurian  succession  is  a  coarse  conglomerate  which 
rests  unconformably  on  the  dark  argillite  of  Ordovician  age. 

Lower  Devonian  red  slates  and  gray  sandstones  southwest  of  Arisaig 
overlie  with  a  marked  unconformity  Silurian  strata.  Arkoses  and  con- 
glomerates occur  in  the  Lower  Devonian  of  Cape  Breton  Island.  Much  of 
the  interior  of  the  Gaspe  Peninsula  is  underlain  by  Middle  Devonian 
sandstones,  conglomerates,  and  arenaceous  shales.  The  change  from  lime- 
stones of  the  Lower  Devonian  to  elastics  of  the  Middle  Devonian  is  gen- 
erally regarded  here  as  marking  the  principal  phase  of  the  Acadian 
orogeny.  In  the  zinc  and  lead  district  of  Berry  Mountain  and  Brandy 
Brooks,  the  limestones  are  cut  and  mineralized  by  granitic  and  syenitic 
intrusive  rocks,  but  not  the  overlying  sandstones. 

Upper  Devonian  beds  on  the  north  side  of  Chaleur  Bay  consist  at 
the  base  of  about  600  feet  of  coarse  conglomerates  and  sandstone.  These 
have  been  cast  into  a  broad  syncline,  eroded,  and  are  unconformably 
overlain  by  the  Pennsylvanian  Bonaventure  conglomerate.  More  con- 
glomerates of  the  Late  Devonian  age  occur  in  New  Brunswick  near 
the  Maine  border;  they  are  correlated  with  the  Perry  conglomerate  of 
Maine.  These  beds  are  seen  to  rest  unconformably  on  the  Silurian  rocks, 
and  they  contain  boulders  of  the  Silurian  and  pre-Silurian  rocks  of  the 
St.  George  granitic  intrusives. 

The  Carboniferous  sediments  rest  everywhere,  it  is  believed,  in  marked 
angular  unconformity  on  older  rocks,  which  range  from  Precambrian 
to  Late  Devonian  in  age.  They  are  thousands  of  feet  thick  and  contain 
great  quantities  of  coarse  elastics,  particularly  the  Pennsylvanian.  In 
Nova  Scotia,  the  Horton  Bluff  elastics  at  the  base  of  the  Mississippian 
rest  unconformably  on  pre-Carboniferous  metamorphics  and  igneous 
rocks,  and  are  in  turn  separated  by  an  angular  unconformity  from  the 
overlying  Cheverie,  also  of  Mississippian  age. 

Mississippian  limestones  and  volcanics  are  folded,  eroded,  and  over- 
lain unconformably  by  Pennsylvanian  (?)  strata  on  the  Magdalen  Islands. 


Gussow's  (1953)  studies  in  New  Brunswick  lead  to  the  conclusion  that 
the  Lower  Mississippian  strata  rest  unconformably  on  the  older  Acadian 
complex,  and  in  turn  are  overlain  unconformably  by  the  Upper  Missis- 
sippian strata.  The  Upper  Mississippian  strata  were  in  turn  strongly 
folded  and  faulted,  eroded,  and  overlain  unconformably  by  the  Penn- 
sylvanian elastics.  The  structure  imposed  on  the  Mississippian  strata, 
both  during  and  at  the  close  of  the  period,  is  typically  Appalachian-type 
folding  and  thrust  faulting.  The  Pennsylvanian  strata  have  not  been  dis- 
turbed to  any  extent  since  deposition  and  are  essentially  flat.  The  great 
amount  of  conglomerate  attests  the  vigorous  elevation  of  sizable  high- 
lands immediately  before  and  during  deposition. 

Folds  and  Thrusts 

All  pre-Carboniferous  rocks  are  considerably  deformed  and  in  part 
metamorphosed.  In  places,  the  Carboniferous  strata  are  also  deformed. 
The  chief  structures  are  folds.  Some  thrusts  have  been  observed  and 
mapped,  particularly  in  New  Brunswick,  but  for  the  most  part  mapping 
has  not  been  sufficiently  detailed  to  bring  out  the  existence  of  long  and 
great  thrust  sheets.  The  linear  elements  in  the  compressional  structures 
trend  generally  northeastward  in  continuation  of  those  of  New  England. 
The  folds  and  thrusts  of  the  Taconic  and  Acadian  systems  of  New  York 
and  Vermont  pass  into  southern  Quebec,  and  the  Taconic  front  reaches 
the  St.  Lawrence  at  Quebec  City.  There  the  Quebec  formation  carries 
Trenton  fossils,  and  consists  of  limestone  and  shale  and  thin  beds  of  lime- 
stone conglomerate.  See  Fig.  12.6.  Its  beds  have  been  altered  and  cleaved. 
Beds  of  the  older  Levis  formation  have  been  thrust  from  the  southeast 
against  the  Quebec  City,  whereas  on  the  northeast  the  Quebec  City  is 
thrust  against  and  over  younger  Upper  Ordovician  beds,  the  Utica- 
Lorraine.  The  Utica-Lorraine  in  turn  is  in  contact  with  the  Precambrian 
of  the  Canadian  Shield.  Resting  horizontally  and  free  from  disturbance, 
directly  on  the  Precambrian,  are  Trenton  limestones  unlike  the  beds  of 
the  Quebec  City  formation  of  similar  age.  This  boundary  between  the 
highly  deformed  and  the  undeformed  strata  has  long  been  known  as 
Logan's  line  or  Logan's  fault  (see  map,  Fig.  12.2).  From  Quebec  City 
the  line  runs  under  the  waters  of  the  St.  Lawrence,  and  sweeps  in  a 


200 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


North 


trent<5n 


XXX 

xxx 

XXX 

xxx 
xxx 

V     X     X 

PRECAMBRIAN 

XX     X  X  X  X  X 

XXX  X  X  x  X 

X    X     X  X  X  X  X 

X    X     X  X  X  X  X 

X    X     X  X  X  X  X 


Fig.   12.6.      Section   across  the  St.   Lawrence  at  Quebec   City.   Reproduced   from   Alcock,   1947. 


smooth  curve  easterly  to  the  tip  of  Gaspe,  passing  between  Anticosti 
Island  and  the  peninsula.  Where  information  is  available,  the  faults  in 
the  great  arcuate  zone  of  deformation  south  of  the  St.  Lawrence  are 
known  to  be  overthrusts  from  the  southeast.  The  rocks  of  this  belt, 
particularly  those  of  Gaspe,  can  be  divided  into  four  main  assemblages 
according  to  the  number  of  orogenies  by  which  they  have  been  affected. 
The  metamorphic  rocks  of  the  Macquereau  group  were  deformed  by  a 
late  Proterozoic  to  early  Cambrian  orogeny;  the  Upper  Cambrian  and 
Ordovician  rocks  were  deformed  by  the  Taconic  orogeny;  the  Silurian 


and  Devonian  rocks  were  affected  by  the  Acadian  orogeny;  the  Car- 
boniferous is  comparatively  little  disturbed  (Alcock,  1935).  Figure  12.5 
illustrates  the  structures  in  a  small  way. 

Ry  reference  to  the  Geologic  Map  of  Canada,  it  will  be  seen  that  the 
lower  and  outer  part  of  Nova  Scotia  is  made  up  of  Precambrian  rock,  as 
well  as  a  belt  through  St.  John,  New  Rrunswick.  These  were  not  immune 
to  Paleozoic  orogeny,  however,  because  overlying  and  marginal  Paleozoic 
strata  are  much  deformed  and  the  Precambrian  rocks  are  intruded  by 
many  plutons  of  Paleozoic  age. 


^Qc  ^/i 


-?-'' 


\  \5Wff  )gfly 


Cb 


Cb 


--?_ 


tf*  tf  & 


77777/    T-^     — 


•  —  •    • 7^ 


SJ^P^^??^ 


L 


5"   MILES 


\  Fig.  12.7.  Cross  sections  in  the  Maritime  Provinces.  Upper  two  sections  are  near  Port  Daniel 
Bay  or  the  south  coast  of  Gaspe  Peninsula.  After  Northrop,  1939.  €?m,  Macquerean  metaclastics, 
either  Cambrian  or  Precambrian;  Om,  Mictaw  elastics;  Sc,  Clemville  formation;  Sac,  Anse  Cascon 
formation;  Slv,  LaVieille  formation;  Sg,  Gascons  formation;  Sb,  Bouleaux  formation;  Swp,  West 
Point  formation;  Cb,   Bonaventure  formation.  All   Silurian  formations  are  Middle  Silurian   in  age. 

1 


Lower  section  is  of  the  St.  John  area,  New  Brunswick.  After  Hayes  and  Howell,  1937.  pCc, 
Cold  Brook  volcanics;  pCst,  St.  Martin  volcanics,  conglomerates  and  intrusives;  Ce,  Etcheminian 
sandstone;  Ch,  Hanfordian  formation;  CI,  Loch  Lomond  slate;  Cj,  Johanian  sandstone;  Ck,  Kenne- 
becasis  conglomerate;  Cw,  Windsor  limestone;  Chr,  Red  Head  conglomerate;  Ct,  Tynemouth 
Creek  conglomerate;  Trq,  Quaco  elastics. 


202 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


The  Arisaig  region  of  Nova  Scotia  was  affected  by  folding  and  in- 
trusives  at  the  close  of  Lower  Ordovician  and  probably  again  at  the  close 
of  the  period,  when  the  Taconic  orogeny  spread  over  much  of  the  Mari- 
time Provinces.  Numerous  plutons,  mostly  of  Middle  Devonian  age,  were 
emplaced  in  the  Nova  Scotian  Precambrian  and  in  the  pre-Devonian 
strata  of  central  New  Brunswick  as  previously  described.  Similar  in- 
trusions occurred  in  the  Gaspe  Peninsula.  The  strata  of  New  Brunswick 
and  Nova  Scotia  were  cast  into  northeasterly  trending  folds  at  this  time, 
which  probably  paralleled  former  structures.  Figure  12.7  shows  the  folds 
and  faults  of  the  St.  John  area  in  New  Brunswick. 

Normal  faults  are  shown  in  a  number  of  cross  sections  in  the  literature 
but  are  not  much  discussed.  They  are  evidently  later  than  the  compres- 
sional  orogenies  or  due  to  late  adjustments  of  the  individual  orogenies. 
Some  may  be  related  to  the  Triassic  basin  faults  and  some  even  to 
Tertiary  faulting. 

TECTONIC  HISTORY 

Most  writers  emphasize  two  great  orogenies  in  the  Maritime  Provinces, 
the  Taconic  at  the  close  of  the  Ordovician  and  the  Acadian  or  Shicksho- 
kian  that  ran  its  course  through  middle  and  late  Devonian  time.  If  the 
geologist  is  not  influenced  unduly  by  the  interpretations  and  conclusions 
of  numerous  writers  and  considers  only  the  numerous  coarse  conglom- 
erates, unconformities,  and  volcanic  series  without  previous  impressions, 
it  would  be  natural  to  conclude  that  a  long  succession  of  compressional 
impulses  with  accompanying  intermittent  volcanic  and  magmatic  ac- 
tivity affected  the  Maritime  Provinces.  At  intervals  from  Proterozoic  to 


late  Triassic  time,  vigorous  deformation  occurred  from  place  to  place. 
It  does  not  seem  altogether  sound  to  the  writer  to  conclude  that  two 
orogenies  stand  apart  as  clear-cut  and  distinct.  Perhaps  orogenic  events 
reached  maxima,  and  these  maxima  are  to  be  considered  the  Taconic  and 
Acadian  orogenies.  The  great  angular  unconformity  at  the  base  of  the 
Carboniferous  emphasizes  the  superior  nature  of  the  orogenic  phases 
that  preceded  the  Mississippian. 

The  Mississippian  beds  are  folded  in  places,  and  so  are  the  Penn- 
sylvanian,  but  the  phases  of  Carboniferous  orogeny  are  not  so  severe  as 
the  earlier  ones.  Over  the  New  Brunswick  lowlands  the  beds  are  fairly 
flat.  Bordering  highlands  were  intermittently  and  sharply  elevated,  how- 
ever, throughout  the  Mississippian  and  Pennsylvanian  to  supply  the  great 
amounts  of  coarse  elastics  that  make  up  the  thick  deposits.  One  of  these 
source  areas  probably  was  the  Precambrian  area  of  Nova  Scotia;  another 
possibly  lay  to  the  northeast  along  the  St.  Lawrence. 

During  the  succession  of  orogenies  that  beset  the  Maritime  Provinces, 
several  ranges  were  undoubtedly  elevated  and  several  troughs  of  deposi- 
tion undoubtedly  sank,  and  this  activity  was  accompanied  by  voluminous 
volcanism.  With  the  sea  extensively  invading  the  cordillera,  a  condi- 
tion is  visualized  much  like  the  partially  submerged  Andean  system  of 
southern  Chile,  Patagonia,  and  Tierra  del  Fuego.  The  changing  geo- 
graphic scene  during  the  Paleozoic  has  not  been  set  down  on  maps — 
perhaps  the  geological  information  is  not  yet  sufficient  to  perform  such  a 
snythesis. 

The  fronts  of  the  orogenic  belts,  however,  seem  clear  by  now,  and  after 
the  geology  of  Newfoundland  has  been  presented,  an  attempt  will  be 
made  to  relate  the  orogenic  belts  of  Greater  Acadia. 


13. 


NEWFOUNDLAND 
APPALACHIANS 


PHYSICAL  DIVISIONS 

Newfoundland  may  be  divided  into  upland  and  lowland.  Examine  the 
map  of  Fig.  13.1.  The  upland  over  large  areas  has  remarkably  little  relief, 
and  generally  breaks  off  in  steep  slopes  to  the  lowland.  Most  lowland 
areas  are  on  weak  rocks,  and  a  number  of  the  steep  slopes  between  up- 
land and  lowland  are  known  to  be  fault-line  scarps;  others  are  thought  to 
I  be.  An  article  of  Twenhofel  and  MacClintock  (1940)  discusses  the  physi- 
ography of  Newfoundland  and  is  the  basis  for  the  following  review. 

The  highest  part  of  the  upland  is  the  Long  Range  topographic  feature 
along  the  west  margin  of  Newfoundland.  It  has  been  referred  to  as  a 


Fig.  13.1.  Physical  divisions  of  Newfoundland.  After  A.  K.  Snelgrove,  Newfoundland  Geological 
Survey.  The  horizontally  ruled  areas  are  upland  and  the  unruled  areas,  lowland.  Small  num- 
bered uplands  are  1,  Hare  Bay  serpentine  hills;  2,  Highlands  of  St.  John;  3,  Indian  Head  Range. 
The  lowlands  take  appropriate  names  such  as  West  Coast  Lowland;  Grand  Lake-White  Bay  basin; 
Notre   Dame   Bay  basin;   Bay  d'   Espoir  basin;  Trinity   Bay  basin;  and   Conception   Bay  basin. 


203 


204 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


plateau  because  of  a  fairly  flat  top.  Actually  only  remnants  of  a  high,  flat 
surface  exist,  and  these  are  about  2000  feet  above  sea  level.  High  valleys 
of  late  mature  aspect  range  in  elevation  from  1300  to  1700  feet  and  are 
correlated  with  the  highest  surface  in  the  central  plateau  at  1400  to  1600 
feet.  This  same  surface  declines  to  about  1000  feet  in  the  Baie  d'Espoir 
region,  and  700  to  800  feet  at  St.  Johns.  A  third  surface  in  the  western 
Long  Range  is  at  500  to  1000  feet  above  sea  level.  In  the  central  plateau 
this  surface  is  believed  to  mark  the  mature  upland  of  500  to  1000  feet  at 
Grand  Lake — White  Bay  basin,  and  the  200-foot  level  at  Notre  Dame  Bay 
and  the  lower  Exploits  basin,  and  the  350-  to  400-foot  level  at  St.  Johns. 
The  three  surfaces,  or  peneplains,  are  regarded  as  sloping  to  the  east  and 
representing  corresponding  tilt  of  the  island  in  that  direction.  The  pene- 
plains were  developed  through  fluvial  erosion,  not  marine;  and  as  in  the 
southern  and  central  Appalachians  were  eroded,  it  is  believed,  in  Tertiary 
time.  Perhaps  the  highest  Long  Range  peneplain  formed  in  the  late 
Cretaceous. 

The  Anguille  Mountains  have  an  upland  surface  much  like  that  of  Long 
Range.  The  highest  points  are  at  about  1800  feet  above  sea  level.  The 
Serpentine  Range  includes  the  Lewis  Hills  and  Blow-me-down  Moun- 
tains south  of  the  Bay  of  Islands,  Arm  Mountain  on  the  north  side  of  the 
bay,  the  St.  Gregory  highland  on  the  north  entrance  of  the  bay,  Table 
Mountain  on  the  south  side  of  Bonne  Bay,  and  Lookout  Hills  on  the 
south  entrance  of  Bonne  Bay.  These  several  relief  features  are  parts  of  a 
basic  intrusive  complex.  Lewis  Hills  have  a  remarkably  flat  surface  at 
about  2300  feet  above  sea  level,  a  well-preserved,  mature  surface  at  1300 
to  1700  feet,  and  a  surface  shown  by  upland  valleys  at  700  to  over  1100 
feet. 

STRATIGRAPHY 

Introduction 

The  stratigraphy  of  western  Newfoundland  was  first  summarized  by 
Schuchert  and  Dunbar  (1934).  The  report  also  reviews  the  stratified  units 
of  the  rest  of  the  island  in  the  light  of  information  up  to  1934.  Several 
Bulletins  and   Information  Circulars  of  the  Newfoundland  Geological 


Survey  under  the  direction  of  A.  K.  Snelgrove  contain  additional  informa- 
tion; and  a  few  journal  articles  by  Twenhofel  (1947),  Twenhofel  and 
Shrock  (1937),  Dorf  and  Cooper  (1943),  Kindle  and  Whittington  (1958), 
and  others  present  new  stratigraphic  and  paleontologic  information. 

The  island  has  been  divided  into  four  sections  in  the  chart  of  Fig.  13.2 
for  the  purpose  of  listing  representative  sequences.  A  fifth  section  is 
added  on  the  west  for  the  coast  of  Labrador,  and  still  a  sixth  for  the 
Canadian  Shield.  The  chart  attempts  to  summarize  not  only  the  stratified 
sections,  but  also  the  tectonic  history.  It  can  be  referred  to  later  when  the 
structure  and  tectonic  history  of  the  island  are  discussed.  The  sections 
from  west  to  east  may  represent  the  major  stratigraphic  provinces,  since 
they  are  taken  across  the  strike  of  the  linear  structural  elements.  The 
Notre  Dame  Bay  section  in  the  north-central  part  of  the  island  and  the 
Fortune  Bay  section  in  the  south-southeastern  part  of  the  island  may  be 
parts  of  a  common  central  province,  the  details  of  which  are  not  yet 
known. 

Cambrian  System 

In  western  Newfoundland  limestones,  dolomites,  siltstones,  and  shales 
predominate  and  build  up  a  sequence  3000  to  3500  feet  thick.  Along  the 
west  coast  for  a  distance  of  800  miles,  and  especially  at  Cows  Head 
(between  Bonne  Bay  and  St.  John  Bay,  Fig.  12.1)  a  succession  of  lime- 
stone conglomerates  interbedded  in  shales  and  limestone,  about  1000 
feet  thick  represent  Middle  Cambrian  to  Middle  Ordovician  time  ( Kindle 
and  Whittington,  1958).  The  conglomerates  consist  of  small,  flat  chips, 
angular  to  subangular  boulders,  and  scattered  large  blocks  up  to  600 
feet  in  length.  The  matrix  is  a  mudstone.  The  fragments  came  from  a 
source  area  where  calcarenites,  oolites,  calcilutites,  and  dense  fine- 
grained, varicolored  porcellanous  limestones,  in  places  with  shale  part- 
ings, were  accumulating.  The  boulders  have  fossils  of  the  same  age  as 
the  matrix.  These  observations  lead  Kindle  and  Whittington  to  con- 
clude that  the  conglomerates  are  not  thrust  breccias  but  intraforma- 
tional  units  in  a  flysch  sequence.  The  source  direction  could  not  be  deter- 
mined. 

The  Burin  Peninsula  has  Cambrian  beds  of  carbonates,  shale,  and 


NEWFOUNDLAND  APPALACHIANS 


205 


sandstone  plus  manganiferous  shales  and  limestones,  and  about  1000  feet 
of  sandstone  and  shale  in  the  Conception  Bay  area.  In  the  Rencontre 
East  area  of  Fortune  Bay,  a  section  of  Lower  Cambrian  or  Proterozoic 
rocks  is  composed  of  more  than  6000  feet  of  conglomerate,  sandstone, 
arkose,  limestone,  and  shale.  So  far,  no  volcanic  rocks  have  been  recog- 
nized in  the  Cambrian  in  Newfoundland. 

In  the  Conception  Bay  area,  it  is  interesting  to  note  the  occurrence  of 
a  great  volcanic  series,  the  Avalon,  that  underlies  the  Cambrian.  Within 
the  Avalon  volcanic  series  at  least  three  Precambrian  epochs  of  sedi- 
mentation and  volcanism  are  recognized,  and  each  was  terminated  by 
folding,  uplift,  and  erosion.  The  last  disturbance  probably  preceded 
the  deposition  of  the  Cambrian  only  a  short  time,  and  the  whole  of  the 
Avalon  peninsula  probably  sank  thereafter  and  was  covered  by  the 
Cambrian  sediments. 

The  fossils  of  all  Cambrian  sections  have  European  affinities. 

Ordovician  System 

The  Ordovician  strata  of  western  Newfoundland  consist  of  a  lower 
sequence  of  6700  feet  of  sandstones,  shales,  limestones,  and  dolomites, 
and  an  upper  sequence,  some  5000  to  10,000  feet  thick,  of  dark  and 
variegated  shales  and  sandstones  with  minor  amounts  of  conglomerate, 
arkose,  and  limestone.  Some  lava  flows,  agglomerate,  and  ash  beds  have 
also  been  noted  in  the  upper  or  Humber  Arm  series.  These  are  the  first 
evidence  of  volcanism  in  western  Newfoundland,  and  they  were  prob- 
ably extruded  near  the  close  of  the  Ordovician. 

The  two  thick  sequences  are  separated  by  a  disturbance  that  involved 
considerable  faulting  and  erosion.  The  lower  is  massive  and  more  compe- 
tent; the  upper  is  generally  thin-bedded  and  incompetent.  It  is  much  dis- 
torted in  nearly  all  outcrops.  The  volcanics  in  the  upper  sequence 
probably  preceded  ultramafic  serpentine  intrusions  that  penetrate  the 
beds  extensively. 

The  Ordovician  in  the  Notre  Dame  Bay  and  in  Fortune  Bay  areas  is  re- 
plete with  volcanics.  The  sequences  are  very  thick  and  generally  associ- 
ated with  elastics  containing  the  impure  varieties  of  sandstone — arkose 
and  graywacke.  Only  at  the  base  of  the  Ordovician  section,  in  the  Fortune 


CANAOIAN 
SHIELD 

COAST      OF 
LABRADOR 

WESTERN 
NEW  FOUNDLAN0 

NOTRE         0»ME 
BAY       AREA 

FORTUNE  BAT    AND 
BURIN   PENINSULA 

AVALON 
PENINSULA 

_  1 

z 
-z. 

a 

A 

FOLDING, THRUSTING 

FAULTING 

FAULTING 

FAULTING 

BARACHOIS        SER. 
COWL,  SS,  SH. 
COAL,   3,000' 

EROSION 

SHARP     UPLIFT 

UPLIFT 

UPLIFT 

UPLIFT 

Z 

o 

EROSION 

CODROY  SERIES      « 
CONGL  ,  SS,  SH,  LS 
GYPSUM 

ANGUILLE    SER 
CONGL  ,  SS,  SH 

SPRINGDALE  GROUP 

RED  CLASriCS, 

VOLCANICS 

EROSION 

z 
< 
z 

o 

> 

o 

a. 

SHARP  UPLIFT 

DISTURBANCE 
INTRUSIONS 

SHARP    UPLIFT 

BATHOLITHIC 
INTRUSIONS 

UPLIFT 

EROSION 

CLAM  BANK  SERIES 

COARSE  CONGL,  SS., 

1,700' 

?             ?             ? 

FOLDING,  FAULTING 
INTRUSIONS 

ORE AT    BAY     OE 

L'EAU    CONGL 

3,000' 

9 

z 
< 

K 
in 

< 
a. 

z 

SHARP    UPLIFT 

FOLDING,   EROSION  f 

FOLDING,    EROSION' 

SHARP   UPLIFT 

EROSION 

? 

SILURIAN   IN    WHITE 
BAY.  CLASTIC,  2g00' 

SILURIAN  IN    NOTRE 

DAME  BAT,  CLASTIC 

2,000' 

RENCONTRE  FM 
OTZ, GRAYWACKE, 
VOLCANICS, 

3J00' 

2 

ULTRABASIC 
INTRUSIONS 

DISTURBANCE      ? 

DISTURBANCE      ? 

' 

z 

o 

> 
O 

o 
a 
o 

1 

a 

? 

3 

a. 

3 

GREEN   SS. 

% 

o 
It 

* 

HUMBER  ARM  SERIES 
WITH  RED  CLIFF  VOL 

\      CROSS  POND 
VOLCANICS 

SNOOKS  ARM    VOLCAN 
TABLE  HEAD  SERIES 
SH 

LATE  STCEORCE  SER 
SLATES, VOLCANICS 

MOORING    COVE 
VOLCANICS,  1,500' 
ANDERSON   COVE 
SLATES   1,500 

BELL    BAY 
VOLCANICS 
13.000'* 

POOLS   COVE  CONGL 
5.000' 

WABANA     SH.   HEMA- 
TITE    3.000' 
BELL  ISLE        6.000' 
CLARENVILLE  SH ,  SS 

DISTURBANCE 

BAY  DEST    LS. 
2.000' 

z 
< 

■ 
2 
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3 

< 

Z 

o 

? 

? 

LABRADOR  SER. 
SS,LS.,     470' 

7 
7 

DISTURBANCE    AND 
EROSION 

JOHANNIAN           500' 
MANUELS     SH.     300' 

HANFOROIAN  SH .  LS 

KELLIGRE  WS     SH 
LONG    POND      SH 
CHAM8ERLAINS  BR  SH 

EROSION 

LABRADOR    SERIES 
SS.LS.OTZ,    2.600' 

HANFOROIAN  SH..  LS. 

EROSION 

EROSION 

BRIGUS     CLASTICS 
AND   LS. 

ETCHEMINIAN    SERIES 
CONGL. SS.SH.LS,  200' 

o 
o 

Q 

a. 

o 
a. 

a 

UPLIFT,  EROSION 

UPLIFT.   EROSION 

FOLDING,  INTRUSION 

FOLDING.  INTRUSIONS 

z 
o 

c 
a 

, 

EROSION 

EROSION 

EROSION 

BAY  O'ESPOIR 
SERIES.   I5.0OO' 
GRAYWACKE.    BASAL 

VOLCANICS 
HARBOUR  MAIN    VOL- 
CANICS OF  BURI H     ° 

AVALON  VOLCANIC 
SERIES    I5.OO0' 
TWO   OROGENIES 
WITHIN   SERIES 

Fig.  13.2.  Representative  sections  and  crustal  disturbances  of  Newfoundland.  Compiled  from 
various  reports  mentioned  in  the  text  and  with  the  aid  of  Daniel  A.  Bradley,  University  of 
Michigan.  The  age  of  the  folding,  faulting  and  intrusions  of  the  Notre  Dame  Bay  area  as  in- 
dicated between  the  Silurian  and  Mississippian  beds  is  doubtful;  they  may  be  Acadian  rather 
than  Caledonian. 


206 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Bay  area,  is  a  nonvolcanic  series  present.  There  about  2000  feet  of  lime- 
stone occur. 

In  Conception  Bay  on  the  east  the  volcanics  are  absent,  or  if  deposited, 
have  been  eroded  away.  The  Belle  Isle  and  Wabana  formations,  the  latter 
carrying  sedimentary  iron-ore  beds,  are  chiefly  sandstones  and  shales, 
about  9000  feet  thick. 

The  thick  Ordovician  sections  in  central  Newfoundland  with  their 
abundant  volcanics  resemble  the  Ordovician  Ammonoosuc  volcanics  of 
New  Hampshire  more  than  any  strata  of  similar  age  in  the  Maritime 
Provinces. 

Silurian  System 

Strata  of  Silurian  age  are  not  known  in  either  the  western  or  eastern 
divisions  of  Newfoundland,  but  in  the  central  belt  various  elastics  are 
fairly  voluminous.  In  the  White  Bay  and  Notre  Dame  Bay  areas  over 
2000  feet  of  Silurian  sandstones  and  shales  have  been  noted.  In  the  For- 
tune Bay  area,  the  Rencontre  formation  consists  of  quartzite,  graywacke, 
and  volcanics,  about  3500  feet  thick.  Other  sequences  in  the  central  divi- 
sion may  prove  to  be  Silurian. 

Devonian  System 

The  Clam  Bank  series  along  the  western  shore  of  St.  George  peninsula 
is  a  coarse,  red  conglomerate,  with  intercalated  masses  of  soft,  coarse 
brown  sandstone  and  shaly  sandstone  of  early  Devonian  age.  The  well- 
rounded  and  polished  pebbles  in  the  conglomerates  are  of  many  kinds  and 
range  up  to  4  inches  in  diameter.  The  beds  resemble  the  Triassic  sedi- 
ments of  the  Connecticut  Valley.  In  places  they  appear  nearly  flat,  but  in 
others  they  are  on  end.  They  indicate  a  sharp  uplift  immediately  preced- 
ing and  collateral  with  their  deposition,  and  their  deformation  indicates  a 
following  orogeny. 

In  the  Fortune  Bay  area,  the  Great  Bay  de  l'Eau  conglomerate  is  3000 
feet  thick,  and  is  also  believed  to  be  early  Devonian. 

Early  Devonian  plant  impressions  were  discovered  in  the  La  Poile  Bay 
area  of  southeastern  Newfoundland  east  of  Long  Range  in  1940  (Dorf 
and  Cooper,  1943)  in  the  Bay  du  Nord  series  which,  because  of  its  meta- 


morphosed character,  had  previously  been  thought  of  as  Precambrian. 
The  fossils  occur  in  a  grayish-black  slate  which  is  associated  with  gray- 
wacke and  conglomerate.  Much  of  the  central  plateau  is  metamorphic 
and  igneous  rock,  and  a  belt  of  schistose  character  flanks  Long  Range 
on  the  east.  The  early  Devonian  fossils  occurring  in  rocks  of  this  terrane 
open  up  the  possibility  that  much  of  the  stratified  altered  rock,  previously 
called  Precambrian,  is  Paleozoic;  and  that  the  numerous  and  large  cross- 
cutting  plutons  are  Acadian  in  age.  Recognizing  the  well-established 
Acadian  orogenic  history  in  the  Maritime  Provinces  and  in  New  England, 
which  includes  much  metamorphism  and  plutonic  activity,  a  number  of 
modern  investigators  are  classifying  the  stratified,  altered,  lithologic  units 
as  Paleozoic  rather  than  Precambrian.  It  seems  probable  that  much  of 
central  Newfoundland  will  prove  to  be  underlain  by  Paleozoic  rocks.  The 
recent  Geologic  Map  of  North  America  shows  most  of  it  as  Ordovician 
strata  and  Devonian  intrusives.  Undoubtedly  more  Paleozoic  systems  will 
be  recognized  in  this  complex  in  future  investigations. 

Mississippian  System 

Mississippian  rocks  are  present  abundantly  in  the  St.  George  Bay  area 
and  in  the  White  Bay — Grand  Lake  lowland.  They  are  also  known  at 
Cape  Rouge  and  Groais  Island,  and  in  part  of  the  Notre  Dame  Bay  area. 
The  chart  of  Fig.  13.3  correlates  the  Mississippian  formations  of  these 
areas.  They  are  chiefly  elastics.  The  St.  George  Bay  series  contains  in 
addition  some  evaporites,  and  the  Notre  Dame  Bay  area,  some  volcanics. 
Up  to  3500  feet  of  beds  have  been  noted  in  these  sections. 


ST      GEORGES 
SAT     AREA 


WOOOT   POINT    SS 
WOOOT  COVE  SH.LS 
BLACK  POINT     LS. 
COOROT  SH , GYP 
SNAKE  BRIGHT  SH. 
CAPE  ANCUILLE  SS 


DEER       LAKE 


UPPER    GRAY 

AND 

LOWER    RED 

SHALES 


WHITE     BAY 


SPEAR  POINT  SS.SH 


CAPE     ROUGE  - 
GROAIS      ISLAND 


CAPE  ROUGE    SH., 
SS..   SILTSTONE 


PILIER  CONGL..SS 


REO      INDIAN 
LAKE 


SHALE,  CONGL.  AND 
LIMESTONE 


NOTRE     DAME 
BAY 


SPRINGOALE     GRP. 

REO   CLASTICS, 

VOLCANICS 


Fig.    13.3.      Mississippian    formations    of    Newfoundland,    after    Betz,    1948.    All    are    regarded    as 
Lower  Mississippian. 


NEWFOUNDLAND  APPALACHIANS 


207 


Pennsylvanian  System 

A  body  of  coarse  elastics,  the  Barachois  series,  rests  on  the  Mississip- 
pian  Codroy  series  in  the  St.  George  Bay  area.  It  consists  of  5000  or  more 
feet  of  coarse  conglomerate,  sandstone,  arkose,  and  shale,  with  some  thin 
coal  beds,  presumably  all  continental,  and  indicates  a  new  sharp  uplift 
nearby.  No  other  Pennsylvanian  strata  are  known  in  Newfoundland. 

INTRUSIONS 

Serpentine  Belts 

Two  belts  of  ultrabasic  plutons  occur  in  Newfoundland.  They  are 
known  as  the  eastern  and  the  western  serpentine  belts.  Not  only  serpen- 
tine but  also  chromite  are  common  associates  of  the  basic  intrusions 
(Snelgrove,  1934).  The  principal  rocks  are  peridotite,  pyroxenite,  and 
gabbro.  See  map,  Fig.  13.4. 

The  eastern  serpentine  belt  extends  from  Carmanville  to  the  head- 
waters of  the  Gander  Biver.  Serpentine  masses  are  exposed  intermittently 
over  120  miles  in  a  general  northeast-southwest  direction.  According  to 
Snelgrove: 

This  part  of  the  island  is  relatively  low-lying  and  is  characterized  by  undu- 
lating topography.  The  ultrabasic  rocks  of  this  belt,  in  contrast  with  those  on 
the  west  coast,  are  only  partly  exhumed  by  erosion  and  consequently  lack  any 
striking  topographic  expression.  The  serpentines  form  low,  bare  ridges,  with 
few  prominent  peaks  or  knolls. 

At  the  north  tip,  it  has  an  outcrop  width  of  one-half  mile,  and  dips  westward. 
Highly  serpentinized  dunite  is  confined  to  a  band  varying  from  one  hundred  to 
five  hundred  feet  in  width,  flanked  by  pyroxenite.  The  serpentine  band  forms 
small  prominences.  The  country  rocks  beneath  the  intrusives  are  chloritized  vol- 
canics,  locally  fragmental,  underlain  by  micaceous  black  slate  and  quartzite. 
Above  the  ultrabasic  rocks  are  black  slate,  gray  quartzitic  sandstones,  and  con- 
glomerate. These  sedimentary  and  volcanic  rocks  are  probably  of  early  Paleo- 
zoic age;  they  appear  to  have  been  intruded  conformably  by  the  plutonic  rocks. 

The  section  of  the  belt  exposed  near  the  headwaters  of  the  Gander  River, 
central  Newfoundland,  consists  of  serpentinized  dunite  with  lenticular  segre- 
gations of  medium-grained  to  pegmatitic  pyroxenite.  Its  width  was  not  deter- 
mined. Structurally,  the  intrusion  appears  to  be  nearly  vertical;  it  is  invaded  by 
a  granite  batholith  lying  to  the  south  and  east. 

The  Western  Serpentine  Belt  consists  of  a  series  of  four  main  intrusions, 
which  seem  to  have  been  injected  concordantly  at  different  horizons  into  a 


Fig.   13.4.      Ultramafic   plutons  of   Newfoundland.   Reproduced   from   Snelgrove,    1938. 

folded  sedimentary  and  volcanic  series  (Humber  Arm  series),  probably  of 
upper  Ordovician  age,  which  underlies  this  part  of  the  lowland  of  the  west 
coast  of  Newfoundland. 

South  of  Bay  of  Islands,  the  eastern  section  of  this  belt,  as  exposed  in  Blow- 
me-down  Mountain,  is  a  pseudo-stratified  complex  and  is  composed  ol  a  wide 
zone  of  various  types  of  peridotites  at  the  base,  succeeded  by  more  siliceous 
rocks  toward  the  top.  Both  the  intrusives  and  the  country  rocks  of  sandstones, 
slates,  argillites,  and  lavas  have  a  general  westward  dip  near  Blow-me-down 
Mountain.  In  the  section  south  of  Bay  of  Islands,  a  lopolithic  structure  is  indi- 
cated. Five  miles  to  the  east  of  the  southernmost  intrusive  ol  the  western  belt 
is  a  satellitic  serpentine  mass  containing  an  asbestos  prospect.  The  structural 


208 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


relations  of  the  mass  are  unknown.  A  smaller  satellite  some  1,000  feet  thick  and 
well-differentiated  occurs  in  Lark  Mountain,  south  of  the  mouth  of  Bay  of 
Islands. 

North  of  Bay  of  Islands,  also,  the  basal  portion  of  the  ultrabasic  rocks  com- 
posing the  serpentine  belt  is  composed  of  a  wide  zone  of  peridotites  which  dip 
westward. 

Since  no  igneous  rocks  are  known  to  cut  the  Carboniferous  of  western  New- 
foundland, the  intrusives  are  referred  to  either  the  Taconic  (late  Ordovician) 
or  the  Acadian  (late  Devonian)  orogeny. 

The  western  serpentine  belt  extends  adjacent  to  the  west  coast  from 
Port  au  Port  Ray  to  Ronne  Ray  and  forms  the  flat-topped  Serpentine 
Range,  previously  mentioned,  with  summit  elevations  around  2000  feet. 

Other  areas  of  serpentine  not  included  in  the  eastern  and  western  belts 
are  on  the  east  side  of  the  northern  peninsula  at  Hare  Ray,  and  at  Raie 
Verte  and  Ming's  Right.  At  Hare  Ray  considerable  thicknesses  of  perido- 
tites have  an  eastward  dip  and,  with  the  enclosing  sediments,  form  the 
eastern  limb  of  the  northern  peninsula  anticline. 

At  Raie  Verte,  the  formation  of  that  name,  which  consists  of  greenstone 
and  greenstone  schist  with  minor  amounts  of  graywacke,  tuff,  agglom- 
erate, lava,  slate,  ferruginous  chert,  sandstone,  and  marble,  has  been  in- 
truded by  large,  dominantly  concordant  bodies  of  ultramafic  rock  and 
gabbro  (Watson,  1943).  Much  of  the  ultramafic  rock  has  undergone  in- 
tense serpentinization  and  steatitization.  The  gabbro  has  suffered  saus- 
suritization,  uralitization,  silicification,  carbonatization,  and  alteration  to 
zoisite-quartz  and  zoisite-prehnite  rock.  Granite,  quartz-porphyry,  and 
quartz-diorite  intrusions  occur  in  the  Raie  Verte  formation.  Adjacent  to 
the  latter,  the  greenstone  and  gabbro  have  been  metamorphosed  to  the 
amphibolite  fades.  Small  sills  and  dikes  of  mafic  gabbro,  porphyrite, 
diorite,  and  kersantite  were  observed  in  the  area. 

The  above  areas  of  ultramafic  rocks  are  shown  on  the  map  of  Fig.  13.4. 
These  occurrences  in  Newfoundland  are  considered  part  of  a  major  ser- 
pentine belt  from  Georgia  through  the  crystalline  piedmont  belt  to  the 
Hudson  Valley  and  through  the  Taconic  system  to  the  St.  Lawrence  and 
the  Gaspe  Peninsula.  They  have  been  compiled  by  Hess,  and  his  map  is 
reproduced  in  Fig.  8.29.  Hess  has  developed  the  theory  that  serpentine 
plutons  occur  in  linear  arrangement  and  mark  the  heart  of  the  belts  of 


great  compressional  deformation,  especially  of  the  volcanic  arc  type.  If 
the  linear  belt  of  ultramafic  plutons  be  interpreted  in  this  way,  we  have 
to  deal  with  additional  evidence  of  a  great  orogenic  belt,  and  can  point  to 
its  core  of  greatest  deformation. 

In  the  St.  Lawrence-Gaspe  belt,  most  of  the  serpentinized  plutons  are 
Taconic  in  age,  but  some  may  be  Devonian.  About  the  same  can  be  said 
of  their  age  in  Newfoundland.  Their  age  is  not  known  in  the  crystalline 
piedmont,  but  it  is  inviting  to  think  of  the  entire  serpentine  belt  as  one 
of  the  manifestations  of  the  great  Taconic  orogeny. 

Granitic  Plutons 

Many  large  discordant  granitic  to  dioritic  plutons,  some  of  batholithic 
proportions,  occur  in  the  central  part  of  Newfoundland  between  the  Pre- 
cambrian  of  Long  Range  and  the  Precambrian  of  Avalon  peninsula. 
Some  lie  within  the  Precambrian  areas  also.  For  the  most  part  they  have 
not  yet  been  mapped  and  differentiated.  They  are  now  regarded  as  prob- 
ably Acadian  in  age,  since  one  has  been  found  intruding  the  early 
Devonian  beds  of  the  La  Poile  Ray  area  and  another  one  cuts  the  De- 
vonian beds  of  the  Fortune  Ray  area.  Some  may  be  late  Silurian  (Cale- 
donian ) ;  most  are  known  to  cut  the  Ordovician  strata,  and  pebbles  of  the 
granite  are  found  in  a  Mississippian  conglomerate. 

Instructive  examples  are  the  Ray  du  Nord  granodiorite  and  Ackley 
granite  batholiths  of  the  Fortune  Ray  and  Rurin  peninsula  region.  See 
map,  Fig.  13.5.  According  to  White  (1940): 

The  (Ackley)  batholith  intrudes  the  northwest  limb  of  a  large  syncline,  the 
major  structure  of  the  Fortune  Bay  synclinorium.  The  invaded  rocks  are  largely 
the  Ordovician  (?)  Belle  Bay  volcanics,  and  to  a  lesser  extent,  tuffaceous  slates 
conformably  overlying  the  volcanics,  and  Cambrian  quartzites.  The  mapped 
extent  of  the  batholith  is  over  160  square  miles,  but  this  is  probably  less  than 
half  of  the  total.  The  long  axis  of  the  intrusion  is  oriented  approximately  north- 
east, parallel  to  the  dominant  regional  structural  trends.  The  dip  of  the  contact, 
where  it  could  be  determined,  is  25°  to  45°  outward  from  the  batholith. 

The  topography  of  the  batholith  is  of  low  relief,  with  elevations  averaging 
about  750  feet,  in  contrast  to  the  higher  elevations  and  considerably  greater 
local  relief  of  the  volcanics  to  the  south. 

The  intrusion  consists  mainly  of  granite  ("white  granite")  and  alaskite  ("red- 
granite"),  with  the  latter  the  more  abundant,  in  the  southern  part  of  the  batho- 


. 


NEWFOUNDLAND  APPALACHIANS 


209 


lith.  These  two  phases  are  generally  gradational,  but  sharp  contacts  and  local 
cross-cutting  relationships  have  been  observed. 

Basic  and  intermediate  rocks  are  completely  absent,  although  early  phases  of 
the  differentiation  series  may  be  represented  by  the  nearby  Bay  du  Nord  batho- 
lith. 

The  Bay  du  Nord  and  Ackley  batholiths  are  in  turn  cut  by  the  Belle- 
orum  granite,  which  is  known  to  intrude  the  Great  Bay  de  l'Eau  con- 
glomerate of  Devonian  age  (D.  A.  Bradley,  personal  communication). 
The  three  plutons  are  regarded  by  Bradley  as  closely  related  genetically. 

Composite  batholiths  have  been  noted  in  the  St.  Lawrence  area  of  the 
Burin  peninsula  where  the  Lawn  (?)  metagabbro,  possibly  of  Taconic 
age,  is  succeeded  by  the  St.  Lawrence  granite  of  Acadian  age  (Van  Al- 
stine,  1948);  in  the  Trinity  Bay  area  where  the  Powder  Horn  diorite  is 
intruded  by  the  Northern  Bight  granite  (Hayes  and  Bose,  1948);  and  in 
j  the  Notre  Dame  Bay  area  where  a  pink  granite  batholith  with  satellites  in 
the  Hodges  Hills  vicinity  intrudes  a  gray  hornblende  diorite.  The  latter 
diorite  has  gabbro  facies  and  exhibits  all  the  characters  of  xenolithic 
assimilation  (John  J.  Hayes,  personal  communication). 

MAJOR  STRUCTURAL  DIVISIONS  AND  THEIR  CHARACTERISTICS 

Tectonic  Map 

The  tectonic  map  of  Fig.  13.6  is  an  attempt  to  classify  the  major  struc- 
tural divisions  of  Newfoundland,  and  to  show  some  of  the  important  fold 
axes  and  faults  of  the  large  island.  It  is  based  chiefly  on  Snelgrove's  Geo- 
logic Map  of  Newfoundland  (1938)  and  on  additions  that  he  has  made 
on  a  copy  loaned  to  the  writer.  The  faults  and  folds  of  the  Notre  Dame 
Bay  area  were  taken  from  a  work  map  of  John  J.  Hayes. 

Considerable  field  work  has  been  done  that  is  not  yet  in  print;  much 
of  the  central  plateau  has  never  been  seen  by  geologists;  and  areas  of 
crystalline  rock  are  now  being  considered  more  as  Acadian  orogenic  com- 
plex rather  than  Precambrian.  These  factors  lead  to  an  almost  hopeless 
task  of  bringing  the  geologic  map  up  to  date  and  making  it  tolerably 
correct,  even  if  generalized.  As  a  substitute,  a  generalized  tectonic  map 
was  constructed  (Fig.  13.6)  that  divides  Newfoundland  into  four  major 


Fig.   13.5.      Geologic  map  of  Recontre  Bay  area.  Reproduced  from  White,   1940. 

geologic  zones,  each  with  distinguishing  characteristics.  In  addition,  the 
Carboniferous  basins,  basic  plutons,  principal  fold  axes  and  faults,  and 
Cambrian  outcrops,  as  far  as  known,  are  shown.  Each  zone  will  be  de- 
scribed separately. 

Principal  Structural  Directions 

Overall,  the  fold  axes,  the  faults,  and  the  foliation  take  a  north-north- 
easterly direction;  but  upon  closer  observation,  some  structures  trend 
more  easterly,  especially  in  the  Notre  Dame  Bay  area.  The  stratigraphic 
and  structural  composition  is  much  like  that  of  the  Maritime  Provinces 
and  New  England,  and  undoubtedly  Newfoundland  is  part  of  the  great 
Appalachian  Mountain  systems. 

Relation  to  Physiographic  Provinces 

The  Long  Bange  highland  of  the  physiographic  map,  Fig.  13.1,  is 
coincident  with  the  crystalline  Precambrian  (?)  rocks  of  zone  1  of  the 
tectonic  map,  Fig.  13.6;  the  serpentine  plutons  are  generally  strong  relief 


210 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


THRUST    FAULT 

SAW    TEETH    ON    SIDE 
OF     UPPER    PLATE 


s     1    MAJOR   ANTICLINE      OR 
r  ANTICLINORIUM 

/K    MINOR    FOLD    AXIS 

w'     HIGH    ANGLE     FAULTS 

^^r  SERPENT  I  NIZEO 
I  NTRUSIONS 

GABBRO  OR    PERIOOTITE 


>'>''   CARBONIFEROUS    3ASI  N 


Fig.  13.6.  Tectonic  map  of  Newfoundland,  taken  mostly  from  Snelgrove's  Geo/ogic  Map  of  New- 
foundland, Newfoundland  Geological  Survey.  Interpretations  assisted  by  J.  J.  Hayes,  D.  Bradley, 
and  Joe  Kerr.  Zone  I  consists  of  schists,  gneisses,  and  intrusives,  believed  to  be  chiefly  Pre- 
cambrian,  which  in  part  may  be  metamorphosed  volcanics.  It  was  actively  deformed  during 
Taconic  and  Acadian  orogenies.  Zone  II  is  the  Paleozoic  orogenic  belt  of  Ordovician,  Silurian, 
and  Devonian  metasediments,  metavolcanics,  and  batholiths.  It  may  contain  both  older  and 
younger  rocks,  but  in  exposure  they  are  of  minor  importance.  Zone  III  is  a  Paleozoic  orogenic 
belt,  but  in  addition  to  the  rocks  of  zone  II  it  contains  major  Precambrian   linear  elements.  Zone 


features;  and  the  Carboniferous  areas  are  for  the  most  part  lowlands; 
but  the  uplands  and  lowlands  east  of  these  do  not  clearly  indicate  in- 
dividualized geologic  provinces,  as  far  as  known. 

Characteristics  of  Tectonic  Zones 

Zone  One.  Zone  one  is  the  Long  Range  highland,  and  it  consists  chiefly 
of  schists  and  gneisses  similar  to  those  of  the  nearby  Canadian  Shield  of 
Labrador.  At  the  south  and  between  La  Poile  Ray  and  Cape  Ray,  how- 
ever, part  of  the  rocks  may  be  metamorphosed  Paleozoic.  George  Phair 
has  mapped  the  coast  from  La  Poile  Ray  westward,  according  to  Joe  Kerr 
(personal  communication),  and  finds  at  the  bay  a  fossiliferous  Lower 
Devonian  formation  with  the  argillaceous  members  slaty  and  sharply 
folded.  As  the  upturned  succession  is  traversed  westward,  it  becomes  phyl- 
litic  and  finally  schistose.  No  contacts  could  be  found  between  the 
Devonian  slates  and  the  phyllites,  and  the  schists,  previously  called  Pre- 
cambrian. Phair  visualizes  the  southern  end  of  the  Long  Range  as  an  anti- 
clinorium  of  isoclinal  folds,  pitching  north-northeastward,  and  with 
increasing  metamorphism  toward  the  core;  perhaps  Precambrian  rock  is 
exposed  in  the  core,  but  contact  relations  are  not  evident  to  prove  it. 

At  the  north  end  of  the  range  and  along  its  flanks  at  intervals — Ray  of 
Islands  area  on  the  west  and  White  Ray  on  the  east — Cambrian  beds  rest 
on  the  schists  and  gneisses,  and  hence  demonstrate  the  Precambrian  age 
there  of  the  foliate  rocks. 

Zone  Two.  Zone  two  east  of  Long  Range  appears  to  be  basically  the 
Acadian  orogenic  complex.  It  is  made  up  principally  of  the  great  Ordo- 
vician and  Silurian  volcanic  sequences  and  numerous  great  batholiths, 
presumably  of  Caledonian  or  Acadian  age.  The  stratified  sequences  are 
much  folded  and  generally  subject  to  low-grade  metamorphism.  Some 
Precambrian  rocks  may  exist,  but  this  possibility  seems  less  as  work 


IV  consists  principally  of  Precambrian  sediments  and  volcanics  with  small  infolded  or  faulted 
basins  of  Cambrian  and  Ordovician  strata.  The  zone  is  generally  much  less  deformed  than  the 
others.  Carboniferous  basins  are  stippled  and  postdate  the  major  orogeny,  but  were  affected  by 
Appalachian  faulting.  Black  areas  with  smooth  borders  are  serpentinized  intrusions,  and  black 
areas  with  hachured  edges  are  gabbros  and  peridotites.  Numbers  1  to  1 1  are  lines  of  cross 
sections. 


NEWFOUNDLAND  APPALACHIANS 


211 


v;  l 


\  / 


CODROY       \    ■•'••  \ ,    lj .         .    "-*,„■>      ,   ••— V*    *     V 


/ingu/7/e  se 

/     MILE 


SECTION     I 


Codroy     ser/es 


STORMY  PT. 

CODROY   RIV. 

\\\»   Baracho/5  ser/es 


BAY  ST.  GEORGE 


SECTION     2 


WEST 


COAST 


L     O     W     L     A     N 


Carboniferous 


LONG     RANGE 


'7W  \/\'\/WW\/\/\  / 


W.WPR  E- CAM  BRIAN  s  L> 
\\\/\  ir  \"V\  jwwuw"/  \ 

/\  /\  /  \/\/W  \/\/\/\/ 

■^    M  I  L  E3 


_i 


WHITE         6  AY 


O/c/er  Pa/e ozo/ cs  \         <5//ur/ar?         x"     M /js  / ss/pp/on 

— /V/A  £''5 i  Quartz  porphyry,   tn/cf-  Pcr/eozo/c 


SECTION    3 


Fig.   13.7.      Representative  cross   sections  of   Newfoundland.   Section    1    after   Hayes  and   Johnson, 
1938;  section  2  after  Betz,   1943;  section  3  after  Betz,   1948. 


progresses.  Much  of  the  region  is  unknown.  Several  serpentinized  ultra- 
|  mafic  intrusions  occur  in  a  line  southwest  of  Carmanville. 

Zone  two  west  of  the  Long  Range  Mountains  consists  of  folded  and 
faulted  Cambrian,  Ordovician,  and  Devonian  strata,  with  the  Ordovician 
\  thickest  but  with  volcanic  rocks  present  in  only  one  formation.  It  repre- 
sents the  front  of  the  Taconic  and  Acadian  systems.  It  contains  the  major 


Carboniferous  basin  and  the  principal  belt  of  serpentine  intrusions. 

The  Long  Range  has  been  elevated  in  a  steep  reverse  fault  against  the 
Carboniferous  basin.  See  section  2,  Fig.  13.7.  Section  1  shows  the  faulted 
and  folded  nature  of  the  Carboniferous  rocks  themselves.  They  are  gen- 
erally far  less  folded,  however,  than  the  underlying  Ordovician.  Folded 
Carboniferous  is  also  shown  in  section  4B  resting  unconformably  on  the 


212 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 

Tab/e.  Head  fc.p    5f-  Georpp 


J 


V77 


/'/// 


7  '  /  &rff'''// 

WJJJ )  ! }  I '  Si'M  ' 


5ECTI0N    4A 


/<$/        5f.    George  ser/es 
Tab/e  /ieod  /s. 

Carbon/ ferous 


SECTION  43 

C.  FOX     PEN. 
CONCtiE   HSR. 


M  u  m  b  e  r      Arm      s  e.  r  /  e  s  -    Or  do  v  /  c  /  a n 


Tab/e.  Head 
As. 


S   A7/L  £S 


<5t.    George  ser/es 
O  r  do  v/  c  /on 


GR0AI5       15. 


GULL    15. 


Ordov.   '  M/Js/js/pp/'an 
5ECTI0N    5 


/^re  -  Ca/rrbr/on  ? 


Fig.    13.8.      Representative   cross   sections   of    Newfoundland.   Section   4A   and   4B   after   Walthier, 
1949;  section  5  after  H.  Johnson,  1941. 


Humber  Arm  series  of  the  Ordovician. 

The  upfaulting  of  Long  Range  on  the  west  started  in  early  Mississip- 
pian  time  and  resulted  in  the  deposition  on  the  downfaulted  block  of  the 
coarse  Anguille  series.  Movement  continued  during  the  deposition  of  the 
entire  Mississippian  and  Pennsylvanian  sequence,  or  at  least  recurred 
after  the  Mississippian  sediments  were  deposited,  because  the  Precam- 
brian  is  now  in  fault  contact  with  the  Mississippian.  Faulting  recurred 
after  the  Pennsylvanian  Barachois  beds  were  deposited. 

The  structure  along  the  east  flank  of  the  Long  Range  uplift  is  illustrated 


in  sections  3  and  5,  Figs.  13.7  and  13.8.  High-angle  thrust  faulting  seems 
the  dominant  structure,  but  probably  a  large  syncline  or  synclinorium 
exists  between  the  mainland  and  Groais  Island.  Groais  and  Bell  islands 
are  presumably  Precambrian  schists  and  gneisses,  and  hence  are  believed 
to  mark  an  anticlinal  fold. 

Representative  of  the  folding  and  faulting  in  the  Notre  Dame  Bay  area 
are  sections  6  and  7  of  Fig.  13.9.  Through  the  islands  and  headlands  of 
Notre  Dame  Bay  area,  a  system  of  faults  with  an  east-west  bearing  oc- 
curs. Those  shown  on  the  tectonic  map  were  taken  from  a  compilation 


NEWFOUNDLAND  APPALACHIANS 


2J3 


RED    CLIFF 
POND 


SECTION       6 


6  5 


I    I    I 


SNOOKS 
ARM 


Iwrrtf 


SECTION 


TOMMYS 

ARM         SOPS    ARM 


SHOAL 
ARM 


BEAVER 
7     BIGHT 


WILD  BIGHT 

2_ 


ROTI 


15LE  AU 
N^BOIS 

////ft 


BAIE 
I/D'ESPOIR 


5ECTION  8 


Schist 


•5  Safes,  phy///fes,    qucrrfz/tes,  groywocAes 


\  i  s  /  k~/  ri 
/\ '/  n/w  w ' 

/www  C7 

Devon /on  (?)  gron/f'e 


Bo/e   cf  ' £spo/r  ser/e5 


L 


4   MILES 


J 


Fig.  13.9.  Representative  cross  sections  of  Newfoundland.  Section  6  after  Snelgrove,  1931;  1 
to  5  make  up  the  Snooks  Arm  series  of  Ordovician  age.  1,  andesite  pillow  lava;  2,  andesite;  3, 
rhyolite;  4,  pyroclastics;  5,  slates,  argillite,  sandstone,  chert.  Nos.  6  to  8  are  post-Ordovician. 
6,  gabbro;  7,  diabase  and  basalt;  8,  Burtons  Pond  granite  porphyry.  Section  7  after  Espenshade, 

by  J.  J.  Hayes.  Some  of  the  northeast  are  probably  horizontal  shears,  and 
the  main  east-west  faults  are  high-angle  ones  with  movement  in  the  ver- 
tical direction.  The  fold  axes  trend  acute  to  the  major  faults,  and  to  put 
them  in  the  same  mechanical  frame  as  the  folds  seems  impossible.  The 
folds  appear  to  the  writer  to  be  Acadian,  and  the  faults  more  likely  to  be 
associated  with  the  faulting  of  the  Carboniferous  basins  and  later  than 
with  the  Acadian  folding. 

Zone  Three.     Zone  three  is  much  like  zone  two  but  includes  several 
Precambrian  linear  masses.  These  may  be  upfaulted  blocks  or  cores  of 


1937.  1,  pillow  basalts;  5,  andesites;  4,  shales  and  sandstone;  3,  coarse,  massive  sandstone;  6, 
argillaceous  graywacke  and  chert;  2,  shales,  tuffs  and  cherts;  7,  gabbro.  All  units  are  probably 
Ordovician.  Section  8  is  after  Jewell,   1939. 


anticlinoria.  Cross  sections  8,  Fig.  13.9  and  9A  and  9B,  Fig.  13.10,  are  rep- 
resentative of  the  structure.  They  show  especially  the  trans gressive  grani- 
toid intrusions.  The  Precambrian  rocks  that  appear  in  zone  three  are 
sediments  and  volcanics,  and  are  considered  later  than  the  schists  and 
gneisses  of  Long  Range. 

Zone  Four.  Zone  four  is  predominantly  a  late  Precambrian  sedimen- 
tary and  volcanic  series,  with  infolded  or  downfaulted  Cambrian  and 
Ordovician  sediments  in  several  places.  On  Belle  Isle  of  Conception  Bay, 
Ordovician  sediments  occur  which  carry  iron  ore.  See  map  and  sections, 


214 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 

Harbor  Ma/r? 


Litf/e.  Lawn   5/?.,  groyivacAe, 
arg/'//fte  -  Orc/ov/c/0/7  (?) 


3er/e3 


SECTION    9A 


Granrfe  -  Qevon/cm(?) 
4   rrrL.ES 


\\  //  f/  ?/  l/tf/e.  low/'?   fm 

/Jy'y/J'/J,t/f//;*/ffIli/rtli  h" >///■■  ///■/■■/  //■/^r>/ •<  »  »  \  »  V\  \  v  *  »  »  v  *  *•   v    •  .»     •    y  >    '  /  /  ' 


Harbor  Ma/n  £3 r /get 5  S3.,^h.,_ 

vo/can/c  jer/es        to.  -L.  Combr/0/7 

SECTION   9B 


Sarin   series  -bo^o/fic 
/ Qva^  y-  ^ea/n7e.t7t3  -  Orcfov/c/'an  (?) 


Oc 


Oc    £ec 


5MITH 
•Tb        £.f*2    £b     50UND  RANDOM     15. 


SECTION    10 


Fig.  13.10.  Representative  sections  of  Newfoundland.  Sections  9A  and  9B  after  Van  Alstine,  1947;  section 
10  after  Hayes  and  Rose,  1948;  pCm,  Musgravetown  granite;  pCcp,  Connecting  Point  granite;  £r,  Randon 
quartzite;  €b,  Brigus  conglomerate,  quartzite,  shale;  Gee,  Elliott  Cove  shale;  Oc,  Clarenville  shale,  sandstone. 


(locality  11)  Fig.  13.11.  The  Cambrian  and  Ordovician  sediments  have 
largely  escaped  metamorphism.  Along  the  west  side  of  Trinity  Bay  (sec- 
tion 10)  the  Cambrian  and  Ordovician  sediments  are  rather  tightly 
folded,  whereas  to  the  east  in  Avalon  peninsula,  the  Paleozoic  beds  are 


less  folded  and  chiefly  faulted.  The  impression  is  conveyed  that  zone  two 
east  of  the  Long  Range  Mountains  suffered  the  most  intense  deformation, 
and  that  zones  one  and  three,  although  deformed  and  intruded  exten- 
sively, are  marginal;  and  that  the  eastern  part  of  zone  four  escaped  the 


NEWFOUNDLAND  APPALACHIANS 


215 


Fig.    13.11.     Map   and   sections   of   Conception    Bay   and   the   Wabana    iron   ore   deposits.    Repro- 
duced from  Hayes,  1931. 


sharp  folding  and  metamorphism  common  to  zones  one,  two,  and  three 
but  was  faulted  and  elevated  in  post-Ordovician  time,  probably  in  the 
Appalachian  orogeny. 


TECTONIC  HISTORY 

Early  Cambrian  Phase 

By  reference  again  to  the  chart  of  Fig.  13.2,  the  numerous  disturbances 
and  orogenies  that  characterized  the  Appalachian  systems  in  Newfound- 
land can  be  reviewed.  Nine  orogenic  phases  are  fairly  clear.  When  cor- 
relations are  more  precise,  this  number  may  be  increased. 

It  is  evident  from  the  angular  unconformity  at  the  base  of  the  Cambrian 
and  the  coarse,  basal  elastics  that  an  orogeny  immediately  preceded  or 
accompanied  the  early  Cambrian  sedimentation.  This  is  noted  in  the 
west  along  the  coast  of  Labrador  and  the  western  lowland  of  Newfound- 
land, and  in  the  east  from  the  Bay  d'Espoir  to  the  Avalon  peninsula.  In 
the  east  the  orogenic  phase  is  the  last  of  three  or  more  that  accompanied 
the  deposition  of  a  great  Precambrian  volcanic  series.  It  is  not  yet  pos- 
sible to  define  the  distribution  of  land  and  sea  in  the  orogenic  belt  in 
Cambrian  time.  For  that  matter,  the  same  can  be  said  of  the  belt  in  all 
pre-Carboniferous  time.  Volcanic  activity  was  pronounced  in  eastern 
Newfoundland  in  the  Proterozoic  but  abated  everywhere,  it  seems,  during 
the  Cambrian  period. 

After  the  early  Cambrian  Brigus  and  Eteheminian  elastics  had  been  de- 
posited in  the  Fortune  Bay  and  Trinity  Bay  areas  respectively,  a  slight 
disturbance  occurred  which  resulted  in  uplift  and  erosion  before  the  next 
Lower  Cambrian  Hanfordian  beds  were  deposited. 

Late  Cambrian  Phase 

In  the  Burin  peninsula,  a  disturbance  occurred  in  late  Cambrian  time  in 
which  the  Middle  Cambrian  beds  were  tilted  and  somewhat  eroded  be- 
fore covered  with  the  Ordovician  strata  (Van  Alstine,  194S).  Deposition 
of  carbonates  occurred  apparentlv  undisturbed  on  the  east  and  on  the 
west  while  the  uplift  was  taking  place. 


216 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Early  Orodovician  Phase 

With  the  beginning  of  Ordovician  time,  western  Newfoundland  started 
to  sink  more  rapidly  and  became  the  site  of  deposition  of  a  thick  clastic 
series,  and  later  of  considerable  limestone  and  dolomite.  The  central 
area  around  Fortune  Ray  received  much  limestone,  at  least  in  places.  East 
Newfoundland  also  sank  considerably  and  received  over  6000  feet  of  fine 
elastics  and  carbonates.  It  seems  necessary  to  picture  the  western  New- 
foundland Lower  Ordovician  elastics  coming  from  the  Canadian  Shield 
where  a  rather  sharp  uplift  set  in  (see  Plates  2  and  3),  but  the  source  of 
the  shales  in  eastern  Newfoundland  is  not  clear. 

After  early  Ordovician  time,  the  whole  central  part  of  Newfoundland 
became  a  site  of  profound  volcanic  activity,  much  of  it  submarine,  with 
the  passive  emission  of  flows;  but  there  was  also  abundant  pyroclastic 
activity,  probably  both  submarine  and  subaerial.  The  Ordovician  must 
also  have  been  a  time  of  tumultuous  crustal  activity  in  the  volcanic  zone 
because  various  elastics,  such  as  graywacke,  conglomerate,  sandstone, 
and  shale,  are  commonly  interbedded  in  the  volcanics,  or  mixed  with  tuf- 
faceous  material,  and  they  necessarily  must  have  come  from  nearby  up- 
lifts. Chert  and  carbonate  were  also  deposited,  which  with  the  above 
lithologies  are  the  common  associates  of  volcanic  orogenic  belts.  In  places 
upward  of  20,000  feet  of  volcanics  and  sediments  accumulated. 

Andesites  are  the  most  common  of  eruptive  rocks  in  the  orogenic  belts, 
but  in  the  Relle  Ray  volcanic  series  of  Fortune  Ray,  about  13,000  feet 
thick,  most  of  the  volcanics  are  rhyolite  (D.  A.  Bradley,  personal  com- 
munication). This  is  indeed  a  great  outpouring  of  rhyolite  in  an  orogenic 
belt.  Hobbs  ( 1944)  has  found  that  andesites  are  the  first  eruptives  in  new 
orogenic  belts  in  the  southwest  Pacific,  but  after  a  period  of  growth,  other 
less  basic  forms  appear,  with  rhyolite  one  of  the  late  entrants.  Since  vol- 
canic activity  continued  long  after  the  Belle  Bay  rhyolites  in  central  New- 
foundland, it  appears  that  new  volcanic  cycles  followed  the  early  Ordo- 


vician one. 


Late  Ordovician  Phase  (Taconic  Orogeny) 

The  Taconic  orogeny  is  generally  held  to  have  been  pronounced  in 
Newfoundland,  not  because  of  a  great  angular  unconformity  between 


Ordovician  and  Silurian  rocks,  but  first,  because  the  Ordovician  sequences 
are  more  metamorphosed  than  the  younger  ones  ( Schuchert  and  Dunbar, 
1934);  second,  because  the  Silurian  has  much  conglomerate  in  it;  and 
third,  because  the  Taconic  orogeny  of  the  Gaspe  and  Maritime  Provinces 
could  not  very  well  end  abruptly  without  extension  into  Newfoundland. 
Silurian  beds  are  relatively  not  very  abundant  in  Newfoundland,  and 
good  exposures  of  their  contact  with  the  Ordovician  sequences  have  so 
far  escaped  detection.  Twenhofel  and  Shrock  wrote  in  1937  that  so  far  as 
known  there  is  no  angular  unconformity  between  the  Ordovician  and 
Silurian  systems.  However,  White  ( 1940  and  Ph.D.  thesis,  Princeton, 
1939)  recognized  evidence  of  the  Taconic  orogeny  in  the  Rencontre  East 
area  of  Fortune  Ray,  where  the  Long  Harbour  volcanics  of  Ordovician 
age  were  folded  and  extensively  eroded,  he  believes,  before  the  Silurian 
Rencontre  series  was  deposited. 

The  contention  that  the  Ordovician  sequences  are  more  metamorphosed 
than  younger  ones  is  correct  only  in  so  far  as  the  "younger  ones"  are 
Carboniferous  sequences  or,  perhaps  in  a  few  places,  Devonian.  Some  of 
the  granitic  batholiths  are  now  known  to  be  Acadian,  and  most  of  the 
metamorphism  may  be  incident  to  them,  in  which  both  Silurian  and 
certain  Devonian  strata  are  altered  as  much  as  the  Ordovician.  Aside  from 
the  Rencontre  East  area,  it  is  difficult  to  find  tangible  evidence  of  a  sharp 
orogeny  in  Newfoundland  at  the  close  of  the  Ordovician.  The  Silurian  se- 
ries, with  its  volcanics  and  elastics,  resembles  the  Ordovician  of  central 
Newfoundland,  and  it  seems  more  logical  to  regard  the  central  belt  as  one 
of  continuing,  but  intermittent,  orogenic  and  volcanic  activity  into  and 
through  the  Silurian. 

The  ultrabasic  intrusions  of  western  Newfoundland  are  regarded  as  Late 
Ordovician  mostly  by  relation  to  those  of  the  Gaspe  and  Quebec  Taconic 
belt  (Snelgrove,  1934).  Some  of  the  ultrabasic  plutons  are  known  to  in- 
trude the  Ordovician  volcanic  series  and  are  therefore  not  older  than  the 
Taconic. 

Late  Silurian  Phase  (Caledonian  Orogeny) 

The  Clam  Bank  conglomerate  of  western  Newfoundland  and  the  Great 
Bay  de  l'Eau  conglomerate  of  Fortune  Bay,  both  of  early  Devonian  age, 


NEWFOUNDLAND  APPALACHIANS 


217 


indicate  sharp  uplift  nearby,  and  the  influx  of  much  coarse  clastic  mate- 
rial. Since  Devonian  plant  fossils  have  been  found  in  schistose  strata  in 
the  La  Poile  Bay  area,  it  now  seems  probable  that  considerable  of  the 
metamorphic  rocks  of  central  Newfoundland,  aside  from  the  batholiths, 
will  prove  to  be  Devonian,  and  therefore  a  site  of  deposition  during  part 
of  Devonian  time,  at  least.  The  sources  of  the  Lower  Devonian  conglom- 
erates and  sandstones  must  have  been  along  the  Labrador  coast  on  the 
west  and  in  an  uplift  through  the  Avalon  peninsula  on  the  east. 

A  Caledonian  orogeny  in  the  White  Bay  and  Notre  Dame  Bay  region 
has  been  suggested  by  Heyl  ( 1937a )  in  view  of  the  lithologic  similarity  of 
the  Devonian  and  Mississippian  there,  in  contrast  to  the  Silurian  and  older 
rocks.  Also,  the  amount  of  deformaton  of  the  Devonian  and  Carbonifer- 
ous is  less  than  that  of  the  older  beds.  Schuchert  and  Dunbar  ( 1934)  note 
that  the  Devonian  sediments  in  the  St.  George  Bay  area  are  not  strongly 
deformed,  except  along  Appalachian  phase  faults;  they  are  apparently  no 
more  disturbed  than  the  Mississippian  strata,  and  much  less  disturbed 
than  the  Ordovician  Humber  Arm  series. 

If  an  orogeny  occurred  in  the  White  Bay  and  Notre  Dame  Bay  region, 
it  is  not  unlikely  that  intrusive  activity  accompanied  the  deformation. 
Some  of  the  plutons  of  that  region  may,  therefore,  be  Caledonian.  They 
may  also  have  come  in  during  the  Devonian  or  at  its  close  (Acadian). 
Composite  relations  undoubtedly  exist  (Hayes,  personal  communication). 

Late  Devonian  Phase  (Acadian  Orogeny) 

Like  the  Taconic  orogeny  the  Acadian  is  also  illusive.  Mississippian 
elastics  in  themselves  indicate  sharp  uplift  nearby,  and  are  generally  be- 
lieved to  rest  in  angular  relation  on  much  deformed  Ordovician  strata 
in  western  Newfoundland  and  in  the  White  Bay  and  Notre  Dame  Bay 
area,  although  the  contact  is  seen  in  only  a  few  places.  The  Mississippian 
strata  have  suffered  little  metamorphism,  however,  and  this  sets  them  off 
strikingly  from  the  older  deformed  and  altered  rocks.  Nowhere  in  New- 
foundland has  an  angular  unconformity  yet  been  recorded  between  the 
Mississippian  and  Devonian  systems.  Nevertheless,  all  workers  in  New- 
foundland are  aware  of  profound  folding,  batholithic  intrusions,  volcan- 
ism,  and  metamoq:>hism  that  occurred  sometime  between  the  Ordovician 


and  Mississippian;  and  since  in  two  places  the  batholiths  are  found  in- 
truding the  Lower  Devonian  series,  it  seems  probable  that  many  plutons, 
similar  in  composition,  are  of  the  same  age.  The  Acadian  orogeny,  pro- 
ceeding through  the  late  Devonian  and  into  early  Mississippian  in  the 
Maritime  Provinces  and  New  England,  was  one  of  superior  and  wide- 
spread proportions,  and  it  is  highly  unlikely  that  Newfoundland,  with  its 
similar  geosynclinal  assemblages  and  lying  in  the  projection  of  the  great 
belt  of  orogeny,  could  have  escaped  it. 

Mississippian  Phase 

The  desposition  of  the  Anguille  conglomerates  in  the  St.  George  Bay 
area  attended  the  upfaulting  of  the  Long  Range  mass,  and  the  same  ac- 
tivity is  probably  indicated  by  the  Pilier  conglomerate  at  Groais  Island. 
The  Springdale  elastics  in  the  Notre  Dame  Bay  area,  if  correctly  dated,  in- 
dicate orogeny  nearby. 

Early  Pennsylvanian  Phase 

The  coarse  and  thick  Barachois  series  of  the  St.  George  Bay  area  rests 
conformably  on  the  Lower  Mississippian  Codroy  formation,  but  the 
abrupt  change  from  fine-grained,  mottled  red  and  green  sandstones  of  the 
Codroy  to  the  coarse,  red,  feldspathic  sandstone  of  the  Barachois  is  strik- 
ing. The  influx  of  coarse  red  elastics  signifies  another  sharp  uplift,  proba- 
bly in  the  Labrador  coast  area. 

No  other  Pennsylvanian  rocks  are  known  in  Newfoundland,  and  hence 
nothing  is  known  of  the  early  Pennsylvanian  disturbance  outside  the  St. 
George  Bay  area. 

Post-Early  Pennsylvanian  Phase  (Appalachian  Orogeny) 

The  major  fault  zone  that  extends  from  the  southwestern  coast  of  New- 
foundland in  a  northeasterly  direction  to  Grand  Lake,  White  Bay,  and  up 
the  east  coast  of  the  northern  peninsula  postdates  the  youngest  sediments 
of  Newfoundland.  These  are  the  Barachois  series  of  lower  or  middle  Potts- 
ville  (Early  Pennsylvanian)  age.  Relief  features  and  escarpments  in  other 
parts  of  the  island  trend  northeasterly  and  parallel  the  western  fault  zone. 
These  in  part  may  also  be  due  to  faults  of  the  same  phase.  Betz  ( 1943 ) 


218 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


suggests  that  the  orogeny  is  an  extension  of  the  Appalachian  orogenic  belt 
of  the  Canadian  and  United  States  Appalachians. 

Volcanic  activity  had  died  out  by  the  Pennsylvanian  after  very  little  in 
the  Mississippian,  and  no  Carboniferous  intrusions  have  yet  been  noted. 
The  post-Barachois  faulting  and  thrusting  mark,  as  far  as  known,  the  last 
compressional  deformation  in  the  Appalachian  mountain  systems  of  New- 
foundland. 

Post-Appalachian  History 

No  Triassic  fault  basin  sediments  are  known  as  in  Nova  Scotia  and  New 
England,  and  no  coastal  plain  sediments  of  Cretaceous  or  Tertiary  age  oc- 
cur above  water  on  Newfoundland.  Without  these  signs  of  submergence, 
it  is  concluded  that  the  island  has  been  mostly  above  sea  level  since  the 
Appalachian  orogeny,  and  has  been  a  site  of  erosion.  It  undoubtedly  has 
had  broad  connections  with  the  Maritime  Provinces  and  the  Gaspe  in  the 
Mesozoic.  Likewise,  the  region  of  its  northeastward  projection  into  the 
Atlantic  must  have  been  extensively  emergent  in  times  past. 

The  broad  banks  off  Newfoundland  continue  the  continental  shelf  from 
Nova  Scotia,  and  as  late  Cretaceous  fossils  have  been  dredged  off  Nova 
Scotia  (see  Chapter  10),  one  could  assume  the  same  fossil-bearing  beds 
will  be  found  under  the  Banks  of  Newfoundland.  An  enticing  experiment 
would  be  the  drilling  of  a  deep  well  on  Sable  Island. 

Twenhofel  and  MacClintock  ( 1940 )  have  described  three  fluvial  erosion 
surfaces  in  Newfoundland  in  much  the  same  aspects  as  in  the  central 
Appalachians,  and  hence  assign  a  similar  history  of  Cenozoic  epeirogenic 
uplift  to  the  island.  The  major  difference  is  that  the  Maritime  Provinces 
and  Newfoundland  have  not  emerged  as  much  as  the  Appalachians  south 
of  New  York  City.  If  they  should  rise  another  1000  feet,  then  much  of  the 
continental  shelf  would  be  land  and  probably  a  large  bordering  coastal 
plain  with  Cretaceous  and  Tertiary  sediments  would  appear. 

Cabot  Strait  Fault  (?)  and  Seismic  Profile 

The  Tectonic  Map  of  Canada  (1950)  shows  a  fault  along  Cabot  Strait 
between  Nova  Scotia  and  Newfoundland,  with  the  implication  that  it  is  a 
transcurrent  fault  offsetting  the  structural  elements  of  the  two  provinces. 


Fig.  13.12.  Paleozoic  orogenic  belts  of  Greater  Acadia.  In  addition  to  the  Taconic,  Acadian,  and 
Appalachian  orogenies  there  were  several  others  in  various  places  that  are  not  represented.  The 
post-Silurian  Caledonian  orogeny  was  pronounced  in  Newfoundland  and  Nova  Scotia.  A  mid- 
Ordovician  Vermontian  is  known  in  the  Vermont-Gaspe  region. 


NEWFOUNDLAND  APPALACHIANS 


219 


Reference  to  the  map  of  Fig.  13.12  will  indicate  the  position  of  the  pre- 
sumed fault.  The  structural  front  passes  between  Anticosti  Island  and  the 
Gaspe  Peninsula  and  between  Labrador  and  the  Northern  Peninsula  of 
Newfoundland  under  the  Straight  of  Belle  Isle  (Figs.  13.1  and  13.6).  Since 
the  front  is  entirely  submerged,  its  position  as  shown  on  Fig.  13.12  is  only 
a  guess.  Nevertheless,  the  conclusion  must  be  drawn  that  a  deep  recess  in 
the  structural  front  exists  between  the  Champlain-Gaspe  salient  and  the 
Newfoundland  salient.  Perhaps  this  is  the  result  of  horizontal  offset  along 
a  transcurrent  fault. 

The  submarine  trough  of  the  Gulf  of  St.  Lawrence  extends  out  under 
Cabot  Straight  to  the  edge  of  the  continental  shelf.  See  Fig.  13.12.  It  has 
a  depth  of  over  600  feet  for  a  distance  of  750  miles,  and  from  a  point 
midway  south  of  Anticosti  Island  to  the  shelf  rim  is  over  1200  feet  deep. 
At  two  places  it  is  1800  feet  deep,  and  has  a  closed  basin  in  this  area 
about  150  miles  long  below  the  1320-foot  contour.  One  large  tributary  of 
the  trough  extends  up  toward  the  Straight  of  Belle  Isle,  and  another  ex- 
tends along  the  north  side  of  Anticosti  Island. 

Six  seismic  profiles  were  shot  on  the  extensive  banks  off  Nova  Scotia 
and  Newfoundland  by  Press  and  Beckmann  ( 1954),  and  a  combination  of 
three  of  them  across  the  outer  end  of  the  Cabot  Straight  trough  is  shown 
in  Fig.  13.13.  The  position  of  the  section  is  indicated  on  Fig.  13.12. 

The  seismic  section  indicates  for  one  thing  that  the  trough  is  erosional 
into  the  unconsolidated  sediment  layer,  and  this  is  the  conclusion  that 
Shepard  (1930)  reached.  From  a  study  of  the  shape  of  the  submarine 
valley  he  concluded  that  it  was  first  a  subaerial  stream  valley  and  then 
was  modified  by  glaciers  flowing  seaward  along  it.  Glacial  striations  and 
roches  moutonees  on  the  southern  tip  of  Newfoundland  and  on  St.  Paul 
Island  off  the  north  end  of  Nova  Scotia  demonstrate  the  past  ice  flow. 
The  present  depth  of  the  trough  is  no  greater  than  fiords  elsewhere.  The 
trough  walls  do  not  resemble  fault  scarps — they  are  straight  segments 
with   hanging   valleys. 

In  interpreting  the  seismic  section,  Press  and  Beckmann  say  that  it  sup- 
ports the  thesis  that  the  trough  is  of  fault  origin,  yet  at  the  same  time  say 
that  the  faulting  occurred  during  the  deposition  of  the  sediments  of  the 
3.80-km/sec  layer.  They  regard  the  3.8-km/sec  layer  under  the  north  side 


Banquereau 
Bank 

Cabot     Strait     Trough 

St  Pierre 

Bank 

1  70 

2  94 

r  .  ■.-,•. 

— 10  ooo- 

'•.'•"■  .'•"•*•  3.0  V-V 

v.: 

— "' ' "  ""*     TIT 

4.6 

3.80 

1 
I 
/ 

3.30 

15,000- 

MB****"^ 

/ 
/ 

20.000' 

1 

—  25,000' 

—  30.OO0- 

e  S3 

Fig.  13.13.  Seismic  profile  across  Cabot  Strait,  Nova  Scotia,  and  Newfoundland.  See  section 
line  A-A',  Fig.   13.12.   Figures  are  velocities  in  km/sec. 

of  the  trough  (Fig.  13.13)  as  demonstrating  the  faulting.  It  is  possible 
that  the  wedge  shape  of  this  layer  does  indicate  faulting,  but  not  in  post- 
unconsolidated  sediment  time.  The  3.80-km/sec  layer  is  logically  inter- 
preted as  consolidated  sediment.  Consolidated  sedimentary  rocks  would 
be  either  Triassic  red-beds  or  Carboniferous  of  the  nature  of  the  basin 
sediments  of  southwestern  Newfoundland,  and  faults  of  this  age  are  long 
since  dead,  according  to  the  history  of  the  Piedmont  and  Greater  Acadia. 

Mild  earthquake  activity  is  cited  as  evidence  for  the  fault  origin  of  the 
Cabot  Strait  trough.  Two  earthquakes  whose  epicenters  were  on  the  shelf 
slope  immediately  off  the  trough  mouth  have  caused  submarine  land- 
slides and  numerous  Trans-Atlantic  cable  breaks.  Shepard  questions  the 
presumed  connection  between  these  earthquakes  and  continuing  displace- 
ment along  faults  causing  the  trough. 

Both  sides  of  the  modern  trough  are  about  the  same,  yet  the  seismic 
profile  indicates  the  possibility  of  a  fault  on  one  side  only.  The  conclusion 
is  reached  that  in  Carboniferous  or  Triassic  time  a  trough  formed,  pos- 
sibly bv  downfaulting,  but  that  since  then  no  further  movement  has 
occurred. 

Now,  to  the  original  question;  could  the  structural  elements  of  the 
Maritime  Provinces  and  Newfoundland  be  offset  appreciably  by  horizontal 
motion  along  a  transcurrent  fault?  The  seismic  profiles  have  demonstrated 
the  possibility  of  a  late  Paleozoic  or  Triassic  fault  along  the  outer  stretch 
of  the  Cabot  Strait  trough.  If  this  fault  is  part  of  the  Triassic  fault  system, 
it  would  probably  be  one  of  vertical  displacement.  If  like  the  fault  that 


220 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


bounds  the  east  side  of  the  Carboniferous  basin  of  the  St.  Georges  Ray 
area  of  southwestern  Newfoundland,  it  would  also  be  one  of  vertical  dis- 
placement. The  wedge  of  sediments  of  the  3.80-km/sec  layer  suggest  a 
vertical  fault.  The  major  structural  elements  from  Newfoundland  to  Nova 
Scotia  may  be  drawn  across  to  Nova  Scotia  with  reasonable  continuity 
and  without  a  horizontal  offset,  as  shown  in  Fig.  13.12.  Although  none  of 
these  is  compelling  evidence  against  horizontal  movement,  they  lead  the 
writer  to  conclude  that  considerable  transcurrent  movement  has  not 
occurred. 

MAJOR  TECTONIC  RELATIONS  OF  GREATER  ACADIA 

Definition 

Greater  Acadia  has  been  defined  by  Schuchert  and  Dunbar  ( 1934 )  as 
the  combined  regions  of  New  England,  the  Maritime  Provinces,  the  St. 
Lawrence-Gaspe  area  of  Quebec,  and  Newfoundland.  Much  of  the  area  is 
now  covered  by  shallow  waters,  and  from  an  historical  point  of  view 
Greater  Acadia  includes  all  the  lands  of  the  past  in  the  great  geosynclinal 
and  orogenic  belt  seaward  to  the  continental  shelf  slope. 

Major  Geocynclinal  Characteristics 

Numerous  series  of  beds  in  Greater  Acadia  have  thicknesses  of  5000  to 
15,000  feet,  and  the  total  thickness  in  places  ranges  up  to  100,000  feet. 
Thick  and  coarse  elastics  in  every  stratigraphic  system  of  the  Paleozoic 
and  numerous  unconformities  within  and  between  systems  attest  long- 
continued  crustal  unrest  in  the  geonsyncline  and  at  times  in  belts 
adjacent  to  it.  A  dominant  lithology  of  the  materials  in  the  geosyncline 
is  volcanic  rocks  of  all  descriptions.  They  consist  chiefly  of  andesites  and 
basalts,  but  other  varieties,  especially  rhyolites,  are  by  no  means  absent. 
A  very  thick  accumulation  of  Ordovician  rhyolite  marks  the  central  part 
of  the  geosyncline  in  Newfoundland.  The  volcanics  occur  as  flows,  in 
large  part  submarine,  and  as  various  pyroclastics.  They  are  especially 
concentrated  in  the  medial  part  of  the  geosyncline,  if  the  Precambrian 
rocks  of  Nova  Scotia  and  the  Avalon  peninsula  of  Newfoundland  mark 
the  site  of  the  outer  or  southeastern  portion.  The  inner  belt  of  the  Taconic 


Mountains-Lake  Champlain-St.  Lawrence-Gaspe  region  was  compara- 
tively free  of  volcanics  until  late  Ordovician  and  Silurian  time  when  the 
igneous  activity  spread  to  the  Gaspe  Peninsula  and  to  western  New- 
foundland in  the  western  belt.  Aside  from  Devonian  volcanic  activity 
in  the  Gaspe  Peninsula  the  western  belt  was  again  free  of  volcanism 
after  Silurian  time.  Eruptive  activity  had  died  out  in  all  Newfoundland 
by  late  Mississippian  time  but  not  in  the  Maritime  Provinces  and  in  the 
eastern  part  of  New  England.  Volcanism  continued  exceedingly  active 
there  in  places,  and  was  accompanied  and  followed  in  the  Carboniferous 
basins  of  New  England  by  intrusive  activity. 

Batholiths 

The  central  zone  of  the  geosyncline,  along  with  tumultuous  volcanic  ac- 
tivity, was  the  site  of  great  batholithic  intrusions.  Where  better  known,  as 
in  New  Hampshire,  four  magma  series  are  recognized,  the  first  about  of 
Taconic  age  and  the  other  three  of  Acadian,  which  there  started  in  mid- 
Devonian  and  lasted  probably  until  early  Mississippian.  Of  the  three  Aca- 
dian magma  series,  the  first  preceded  the  major  compressional  orogeny, 
the  second  was  synorogenic,  and  the  third  followed  the  orogeny. 

As  studies  progress  in  the  Maritime  Provinces  and  in  Newfoundland,  it 
is  becoming  clearer  that  most  of  the  dioritic  to  granitic  batholiths  there 
are  Acadian  also.  The  batholiths  are  not  limited  to  the  medial  volcanic 
zone  of  the  geosyncline  but  some  have  intruded  the  inner,  less  volcanic 
complement  of  geosynclinal  sediments  and  others  in  great  volume, 
the  outer  zone,  now  mostly  of  Precambrian  rocks. 

Metamorphism 

A  striking  character  of  the  stratified  rocks  of  the  geosyncline  of  Greater 
Acadia  is  their  metamorphism.  Where  distant  from  the  batholiths  they 
are  generally  slates,  phyllites,  argillites,  quartzites,  and  metavolcanics. 
Where  close  to  the  altering  influence  of  the  intrusions  they  are  schistose 
and  gneissic.  The  very-low-grade  and  low-grade  metamorphism  is  more 
characteristic  of  the  inner  belt,  and  also  the  outer  where  Paleozoic  sedi- 
ments are  preserved,  as  in  the  Conception  Ray  area  of  Newfoundland. 
Medium-grade  metamorphism  is  more  characteristic  of  the  central  belt. 


NEWFOUNDLAND  APPALACHIANS 


221 


Ultramafic  Intrusions 

A  zone  of  serpentinized  ultramafic  intrusions  extends  from  Georgia 
through  the  crystalline  Piedmont  to  New  York  City,  and  from  New  York 
northward  through  the  Taconic  system  to  the  St.  Lawrence  and  Gaspe. 
From  there  it  is  believed  to  continue  through  western  Newfound- 
land. 

Fronts  of  Successive  Orogenies 

An  attempt  was  made  by  Schuchert  in  his  early  paleogeographic  maps 
and  later  by  Schuchert  and  Dunbar  ( 1934 )  to  show  the  major  structural 
elements  of  Greater  Acadia.  They  postulated  a  western  trough  of  sedimen- 
tation, the  St.  Lawrence  geosyncline;  a  central  land  barrier,  the  New 
Brunswick  geanticline;  and  eastern  trough  of  sedimentation,  the  Acadian 
geosyncline;  and  beyond  this,  a  borderland,  Novascotica.  As  described 
on  previous  pages,  the  "New  Brunswick  geanticline"  has  been  found  to 
be  approximately  the  heart  of  the  geosyncline — a  site  of  such  sedimenta- 
tion and  prodigious  igneous  and  orogenic  activity.  Crustal  movements 
within  the  orogenic  belt  were  numerous,  and  the  island  barriers  and  pen- 
insulas were  too  many  and  transitory  to  be  charted  satisfactorily  with 
present  knowledge. 

Kay  (1947)  has  illustrated  the  Taconic,  Acadian,  and  Appalachian 
orogenic  systems  of  Greater  Acadia  to  have  been  formed  by  deforma- 
tion of  the  sediments  of  the  eugeosyncline.  This  great  sedimentary 
province  includes  the  volcanic  assemblages  of  sediments,  the  batholiths 
and  serpentinites,  in  contrast  to  the  relatively  igneous-rock-free  inner  mio- 
geosyncline  typified  by  the  sediments  of  the  Bidge  and  Valley  province. 
It  is  clear  that  the  belts  of  deformation  of  the  eugeosyncline  impinge  on 
the  Canadian  Shield  in  the  Greater  Acadia  region,  and  that  the  belt  of 
deformation  of  the  inner  miogeosyncline  terminates  approximately  at  the 
Adirondacks. 

Some  progress  can  be  made  toward  an  understanding  of  the  spatial 
relations  of  Greater  Acadia  if  the  distribution  of  the  orogenic  belts  is 
charted,  rather  than  the  poorly  documented  and  transitory  shore  lines. 
The  fronts  of  the  Taconic,  Acadian,  and  Appalachian  orogenic  belts  are 


known  in  places  with  considerable  precision  and  in  others  only  approxi- 
mately. Figure  13.12  shows  these  fronts,  as  well  as  the  zones  of  superposi- 
tion of  one  belt  over  the  other.  Evidence  of  the  locations  for  the  most  part 
has  already  been  presented,  and  when  composed  for  the  entire  Greater 
Acadia,  yields  the  picture  recorded  on  the  map.  In  the  lower  left-hand 
corner,  the  northern  end  of  the  Appalachian  folded  and  thrust-faulted  belt 
of  the  Valley  and  Bidge  province  is  seen.  The  Taconic  front  then  faces  the 
shield  (with  its  thin  sedimentary  veneer).  At  Quebec  City  on  the  St.  Law- 
rence, the  front  of  the  Acadian  orogenic  belt  impinges  on  the  shield,  and 
as  far  as  known  from  Quebec  City  to  the  tip  of  Gaspe  and  beyond,  the 
Taconic  and  Acadian  belts  are  superposed.  The  two  belts  in  the  Gaspe 
Peninsula  swing  eastward,  and  even  somewhat  southward  of  east,  and 
project  in  that  direction  into  the  Gulf  of  St.  Lawrence. 

Where  next  observable  in  southwestern  Newfoundland,  the  front  of  the 
Appalachian  belt  faces  the  shield,  and  is  impressed  on  all  older  belts.  It, 
therefore,  appears  that  from  Vermont  northeastward  successively  younger 
orogenic  belts  overlap  inward  and  front  on  the  Canadian  Shield.  The 
equivalent  of  the  Bidge  and  Valley  folded  and  thrust-faulted  province 
does  not  exist  north  of  the  Catskills.  In  Keith's  terminology  the  Taconic 
and  Acadian  orogenic  systems  compose  a  pronounced  "salient"  toward 
the  shield  in  the  Vermont-St.  Lawrence-Gaspe  region. 

The  map  also  shows  linear  Precambrian  masses  that  were  uplifted  dur- 
ing the  Appalachian  orogeny  and,  if  once  covered  by  Paleozoic  strata, 
were  later  subject  to  erosion  and  stripped  of  their  mantle.  The  Long 
Bange  Mountains  element  of  western  Newfoundland  is  fairly  definitelv 
of  this  origin.  It  seems  to  find  continuation  in  northern  Nova  Scotia,  in 
Precambrian  exposures  on  the  western  side  of  the  Bav  of  Fundv,  and 
perhaps  even  in  Precambrian  rocks  in  the  Boston  basin  region.  Pre- 
cambrian rock  forms  most  of  the  Avalon  peninsula  of  Newfoundland 
and  also  crops  out  in  several  places  west  of  the  peninsula.  It  has  not  been 
proved  that  this  region  is  one  of  late  Paleozoic  uplift,  but  only  inferred 
because  of  the  numerous  escarpments  and  shore  fines  that  parallel  the 
known  Appalachian  elements  of  western  Newfoundland,  and  the  faults  of 
Conception  Bay  which  resemble  those  of  the  western  Carboniferous 
basins.  It  ties  in  well  with  the  extensive  Precambrian  area  of  eastern 


222 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Nova  Scotia  in  relation  to  the  Appalachian  front,  and  in  having  a 
similar  thick  Proterozoic  volcanic  sequence  of  rocks.  The  zone  marks 
the  site  of  a  great  Proterozoic  trough  in  which  volcanic  rocks  accumu- 
lated voluminously  and  were  frequently  deformed.  The  Avalon  peninsula 
contains  no  sedimentary  rocks  younger  than  early  Ordovician  and  may 
have  been  an  area  of  erosion  since  then.  The  Great  Ray  de  1'Eau  con- 
glomerate suggests  a  sharp  uplift  of  eastern  Newfoundland  in  late 
Silurian  or  early  Devonian  time,  and  the  region  was  probably  affected 


by  the  Acadian  movements  and  intrusions.  The  Precambrian  of  Nova 
Scotia  contains  numerous  batholiths,  presumably  of  Acadian  age.  It  is 
entirely  possible  that  the  outer  Precambrian  uplift  is  one  that  dates  back 
to  mid-Paleozoic  time  and  is  complex. 

The  presence  of  the  geanticline  of  Precambrian  rocks  along  the  outer 
exposed  margin  of  Greater  Acadia  is  rather  significant  in  demonstrating 
that  the  continent  has  not  been  added  to  appreciably,  or  has  not  grown 
seaward  much,  since  Proterozoic  time. 


14. 


OUACHITA,  MARATHON, 
AND  COAHUILA  SYSTEMS 


OUACHITA  SYSTEM 

Location  and  Topography 

The  Ouachita  Mountains  occupy  a  belt  50  to  60  miles  broad  and 
200  miles  long  in  southeastern  Oklahoma  and  western  Arkansas.  See 
maps,  Figs.  14.1  and  14.2.  They  are  somewhat  like  the  Appalachians  in 
topographic  appearance,  although  not  generally  so  high.  Their  level- 
topped  subparallel  east-west  ridges  reflect  structure  and  dissection  of 
erosion  surfaces.  The  ridges  rise  scarcely  250  feet  above  the  valley  west 
of  Little  Rock  but  gradually  increase  in  height  toward  the  Oklahoma- 
Arkansas  border,  where  the  highest  point  is  2900  feet  above  sea  level 


and  nearly  2000  feet  above  the  valley  floors.  Their  eastern,   western, 
and  southern  margins  are  blanketed  by  the  Gulf  Coastal  Plain  sediments. 

Stratigraphy 

The  oldest  rocks  of  the  Ouachita  Mountains  are  Cambrian,  and  these 
are  exposed  in  the  central  anticlinorium.  The  section  of  the  anticlinorium 
or  "core  area"  of  southeastern  Oklahoma  in  McCurtain  County  as 
measured  by  Pitt  (1955)  is  as  follows: 


Bigfork  chert 

p 

Womble  shale 

66+ ft 

Mazarn  shale 

600  ft 

Crystal    Mountain   sandstone 

50-100  ft 

Collier  shale 

180  ft 

Lukfata   sandstone 

150  + ft 

Northwestward  each  thrust  sheet  has  elements  of  its  stratigraphy,  and 
these  are  given  by  Hendricks  ( 1943 )  in  Fig.  14.3. 

The  Arkansas  novaculite  is  a  conspicuous  formation  of  the  pre- 
Mississippian  sequence.  It  has  a  counterpart  in  the  Marathon  uplift  of 
west  Texas,  the  Caballos  chert,  but  is  not  present  in  the  southern  Appa- 
lachians. The  Bigfork  chert,  Pinetop  chert,  and  Woodford  chert,  as  well 
as  the  siliceous  nature  of  the  limestones  and  shales  indicate  that  a 
dominant  characteristic  of  these  formations  is  silica.  Pitt  (1955)  thinks 
that  much  of  the  silica  is  secondary,  having  been  introduced  by  ground- 
water after  extensive  fracturing. 

The  combined  thickness  of  the  Cambrian,  Ordovician,  Silurian,  and 
Devonian  rocks  is  hardly  3000  feet,  and  they  are  regarded  as  a  shelf  or 
platform  type  of  deposit,  although  the  high  silica  content  is  unusual  in 
such  a  setting.  The  Mississippian  and  Pennsylvania!)  strata  are  almost 
entirely  clastic — shale  and  sandstone — and  are  very  thick.  A  measure- 
ment of  18,950  feet  for  the  Ouachita  Mountains  sequence  of  Stanley, 
Jackfork,  and  Johns  Valley  formations  is  given  by  Cline  and  Moretti 
(1956),  and  17,000  feet  for  the  foredeep  sequence  of  Atoka  (Hendricks 
et  al,  1936). 

The  terms  Ouachita  facies  and  Arbuckle  facies  have  been  widely  used 
to  compare  or  contrast  the  sequences  of  the  Ouachita  Mountains  and 


223 


aw 


'♦  H»ROE«AN        {MS  IN      :  V      ?»i^     '  ^    °"  <     V^ 

ij -, >~svi — I ■•"•/•     %  ;.%    ^v  ,\\Xv 


0% 


vaiiYmrn  •   '  .1,  /  5     i 

^■-Wsr,--  *\         v'      I) 

*-*■.*■       i     %  i       .'///■■    <W 


s 


12     ..- 

<■ 

am 


s  /; 


Fig.  14.1.  Composite  map  of  the  tectonic 
features  developed  in  the  late  Paleozoic  in 
the  Mid-Continent  region.  Taken  from  R.  E. 
King  et  al.  (1942),  Moore  and  Jewett 
(1942),  and  other  publications.  In  Kansas 
the  dotted  names  designate  the  older  fea- 
tures.  A. A.,   Arbuckle   anticline. 


OUACHITA,  MARATHON,  AND  COAHUILA  SYSTEMS 


225 


-^r 


PRE-MISSISSIPPIAN 
FORMATIONS 


r^L. 


Fig.    14.2.      Generalized   structure   map  of   the   Ouachita   and   Arbuckle   Mountains.   MC,    Magnet   Cove. 


the  Arbuckle  Mountains.  The  Ouachita  facies  is  characterized  by  an 
abundance  of  silica  in  the  pre-Mississippian  formations  and  by  the  very 
thick  Carboniferous  clastic  sequences.  Also  it  appears  that  incipient 
metamorphism  is  included  by  some  as  a  mark  of  the  facies.  This  is  all 
a  misuse  of  the  term  facies  as  defined,  but  for  local  paleogeologic  studies 
it  is  convenient,  if  properly  understood. 

Structure 

The  Ouachita  Mountains  may  be  divided  into  a  western  division,  re- 
plete with  thrust  faults,  and  an  eastern  division,  intensely  folded  but 
not  appreciably  faulted. 

According  to  Miser  (1929)  there  are  five  thrust  sheets  in  the  Okla- 
homa Ouachitas  (see  cross  section  D-D',  Figs.  14.1  and  14.4),  but  in 
light    of    Hendricks'    additional    work    there    are    four    "independent" 


thrusts.  They  are,  from  northwest  to  southeast:  (1)  the  Choctaw  fault, 
(2)  the  Pine  Mountain  fault,  (3)  the  Ti  Valley  fault,  and  (4)  the  Wind- 
ingstair  fault.  See  Fig.  14.5.  Each  sheet  has  been  thrust  from  south  to 
north  and  has  been  broken  by  numerous  smaller,  high-angle  reverse 
faults  that  presumably  join  the  main  thrusts  at  depth.  Minor  cross  faults 
are  numerous,  and  larger  cross  faults  are  present  in  several  settings.  The 
stratigraphy  of  each  thrust  sheet  is  somewhat  different  and  is  sum- 
marized in  Fig.  14.3. 

In  front  of  the  thrust  sheets  is  the  Arkansas  Valley  basin  whose  beds 
have  been  cast  into  open  folds  which  gradually  decrease  in  intensity 
toward  the  north.  These  folds  partake  of  some  of  the  characteristics  (4 
both  its  bounding  provinces,  the  beds  on  the  south  being  rather  close!) 
folded  near  the  Ouachitas  but  progressively  more  open  farther  north 
toward  the  Ozark  dome.  Normal  faults  on  the  north  side  of  the  valley 


COAL     BASIN 

BLOCK   S.E. 

of  the 

CHOCTAW  FAULT 

BLOCK  S.E. 

of  the 

KATY  CLUB  FAULT 

BLOCK    S.E. 
of  the 
PINE  MTN.  FAULT 

BLOCK  S.E. 
of  the 
Tl  VALLEY  FAULT 

CO 

o 

K 

UJ 
U. 

z 
o 

K 

< 
O 

z 
< 

z 
< 

> 

> 

CO 

z 
z 

UJ 

a 

McAlester  sh. 
Hartshorne  s  s. 
Atoka    fm. 
Wapanucka   Is. 

Springer  fm. 

Atoka  fm. 
Wapanucka  Is. 

Springer  fm. 

Atoka   fm. 

Chickachoc 

chert 
Springer  fm. 

Atoka    fm. 
Springer  fm. 

Atoka    fm. 
Johns  Valley  sh. 

Jackfork  ss. 
Stanley    sh. 

CO 
CO 

Caney  sh. 
Sycamore    Is. 

Caney    sh. 

Caney  sh. 

Caney    sh. 
Sycamore   Is.  (?) 

DEVON- 
IAN  ? 

Woodford  chert 

Bois  d'Arc    Is. 
Haragar.   sh. 

Woodford  chert 

Pinetop   chert 
Unnamed    Is. 

Arkansas 
novaculite 

DEVON- 
IAN 

a 

3 

o 
a. 
o 

z 
o 

1- 
t- 

X 

z 
< 
S 

_l 

Henryhouse  sh. 
Chimneyhill    Is. 

Missouri 
Mountain  sh. 

Z 
< 

o 

> 
o 
o 

K 
O 

J 

Sylvan  sh. 
Fernvale  Is. 
Viola    Is. 
Simpson   group 

Arhii^klA    nrnnn 

Polk  Creek  sh. 

Bigfork  chert 
Womble    sh. 

CAM^~ 
BRlAf* 

Reagan   ss. 

Fig.   14.3.      Sequence  of  strata  characteristic  of  each   of  the  structural   blocks  of  the   Black   Knob 
Ridge   area   of   the  western   end   of   the   Ouachita   Mountains.    After    Hendricks,    1943.    Katy    Club 


fault  is   a   minor   shear  along   the   line   of  cross  section   in    Fig.    14.5.   The   Stanley   shale   is   now 
considered  Upper  Mississippian. 


OUACHITA,  MARATHON,  AND  COAHUILA  SYSTEMS 


227 

D' 


ARKANSAS         VALLEY 


COASTAL  PLAIN  OUACHITA  MOUNTAINS 

window  .Jockfork  ,'      .      WINDOW      „ 


BOSTON       MOUNTAINS 


-Cambrian  'S'S'->,  '-/c/\'\> 


)° 


Mississippion 


Formations     in     Ooachitas 
Atoka  -formation 
Johns  Volley  shale 
dock  fork   sandstone 
Stanley  shale. 
Coney  shale 
Arkansas  novacu/ite 
Missouri  Mountain  slate 
Blaylock  sandstone  Silurian 

Polk   Creek  shale 
Big  fork  chert 

Womble  shale  (Stringtownj  \  Ordovician 
Bloke ly  sandstone 
Mazarn  shale  i 

Crystal  Mountain  sondstoneX  Cambrian 
Collier    shale  J 


Formations    in    Arkansas  Valley 
Boggy    shale 
5a  van  a  sandstone 
McAlester  shale 
Hartshorne  sandstone 
Atoka  formation -9,ooo' 
thick  in  southern  part 


L  Pennsylvanian 


Vertical t  horizontal  scale  in  miles 


Fig.   14.4.      North-south  cross  section  through   Ouachita  Mountains  and  Arkansas  Valley.  Section   D-D',   Fig. 
14.1.  Somewhat  idealized  from  Miser,   1929,  and  Hendricks  et  a/.,  1936. 


are  common  (Croneis,  1930).  Their  south  sides  are  generally  down, 
thereby  augmenting  the  basin  structure. 

The  thrust  faults  appear  to  die  out  eastward  into  Arkansas  where  a 
fold  complex  indicates  also  considerable  compression.  See  Fig.  14.6. 
An  anticlinorium  is  the  dominant  structure  in  the  approximate  center  of 
the  exposed  fold  belt.  The  minor  folds  on  the  major  anticline  are  sharp 
and  mostly  asymmetrically  inclined  northward.  Two  large  anticlines  with 
amplitudes  of  7000-10,000  feet  dominate  the  belt  north  of  the  intricately 
folded  anticlinorium.  Precambrian  rock  is  nowhere  exposed  in  the 
Ouachitas — a  condition  similar  to  that  in  the  Valley  and  Ridge  province 
of  the  Appalachians. 

In  Arkansas  it  is  not  clear  just  where  the  line  should  be  drawn 
separating  the  folds  of  the  Arkansas  Valley  basin  and  those  of  the 
Ouachitas.  The  Choctaw  thrust  is  considered  the  northern  boundary  of 


the  Ouachitas  in  Oklahoma.  Numerous  folds  in  the  Arkansas  Valley 
basin  sediments  are  conspicuous  on  the  Tectonic  Map  of  Oklalioma 
(Arbenz,  1956). 

The  turn  of  the  thrusts  of  the  west  end  of  the  Ouachitas  to  the  south 
is  very  conspicuous.  The  number  of  thrust  slices  increases  also,  and  it 
appears  that  the  strata  were  more  crowded  here  than  elsewhere.  The 
junction  with  the  Arbuckles  is  unfortunately  covered  by  the  Cretaceous 
sediments,  but  a  number  of  wells  and  some  geophysical  work  help  to 
explain  the  obscure  relationship.  The  strike  of  the  structures  and  trend 
of  the  Arbuckles  is  nearly  at  right  angles  to  the  southward  veering 
Ouachita  structures,  and  the  formations  are  in  part  conspicuously  differ- 
ent. The  problem  of  the  relation  of  the  Arbuckles  to  the  Ouachitas  will 
be  taken  up  later. 

No  rocks  or  structural  elements  resembling  the   Rlue  Ridge  or  the 


228 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Fig.    14.5.      Cross  section   of  the    Black   Knob    Ridge   area   of   the   western    end   of   the   Ouachita    Mountains. 
After  Hendricks,   1943.  Formations  may  be  identified  by  reference  to  chart,  Fig.  14.3. 


crystalline  Piedmont  are  exposed  on  the  south  flank  of  the  folded  and 
thrust-faulted  Ouachitas.  These  tectonic  units  have  been  looked  for  in 
numerous  wells  which  have  penetrated  the  Cretaceous  and  Jurassic  cover, 
but  the  wells  are  apparently  not  sufficiently  far  enough  down  dip  and 
seaward  to  discern  the  units. 

/Aetamorphism 

The  pre-Mississippian  formations  of  the  central  anticlinorium  or 
"core"  of  the  Ouachita  Mountains  in  both  Oklahoma  and  Arkansas  are 
slightly  metamorphosed.  The  shales  are  dynamically  altered  to  argillites, 
meta-argillites,  and  in  places  to  phyllites  (Goldstein  and  Reno,  1952; 
Flawn,  personal  communication  and  1956).  The  novaculite  and  chert 
units  are  most  metamorphosed  at  the  eastern  end  of  the  anticlinorium 
near  Little  Rock  and  at  the  southwestern  end  in   McCurtain  County, 


Oklahoma  (Miser,  1943).  In  McCurtain  County  the  fissility  of  the 
Cambro-Ordovician  shales  is  parallel  or  subparallel  with  the  bedding 
(Pitt,  1955).  The  small  folds  around  the  central  core  are  overturned 
southward  and  slaty  cleavage  has  developed  which  dips  generally  steeply 
north. 

The  position  of  the  Ouachita  front  under  the  Cretaceous  and  Tertiary 
cover  is  recognized  on  the  basis  of  metamorphism  and  high  dips  in 
contrast  to  the  lack  of  metamorphism  and  very  low  dips  of  the  beds 
of  the  foreland.  See  Fig.  14.6.  The  siliceous  nature  of  the  Devonian  to 
Cambrian  rocks  of  the  Ouachitas  is  an  additional  guide. 

Structural  Problems 

The  Geological  Map  of  Oklahoma  (Miser,  1954)  shows  the  Hendricks 
version  of  the  multiple  thrust  structure  as  well  as  two  windows,  the 


OUACHITA,  MARATHON,  AND  COAHUILA  SYSTEMS 


22') 


Fig.  14.6.      Cross  section  of  Ouachita  Mountains  in  Arkansas.  After  cross  section  on  Geo/ogic  Mop 
of  Arkansas,   1929.  Gc,  Collier  shale;  Owe,  Womble  shale,  Blakely  sandstone,  Mazarn  shale,  and 


Crystal  Mountain  sandstone;  DSO,  Arkansas  novaculite,  etc;  Cs,  Stanley  shale;  Cj,  Jackfork  sand- 
stone; Ca,  Atoka  formation;  Csh,  Savanna,  Paris,  Fort  Smith,   Spadra,  and   Hartshorne  formations. 


Potato  Hills  and  the  McCurtain  County  core  area  (also  called  the 
Choctaw  anticlinorium ) .  These  have  been  reproduced  in  Fig.  14.2. 
Hendricks'  synthesis  of  the  thrust  structure  involves  translation  of  rocks 
considerable  distances,  a  seeming  requisite  of  the  Ouachita  overthrusting 
of  the  Arbuckles.  See  Figs.  14.1  and  14.6.  Hendricks  postulates  that  a 
deep-seated  thrust  plane  exists,  the  Powers,  along  which  rocks  of 
"Arbuckle  facies"  were  thrust  southeastward,  and  then,  slightly  later,  the 
strata  involving  the  thick  Carboniferous  clastic  sequences  were  thrust 
northward  to  rest  as  allochthonous  sheets  on  a  foreign  ( Arbuckle)  founda- 
tion. 

The  Tectonic  Map  of  Oklahoma  (Arbenz,  1956)  shows  the  thrust 
complex  of  the  Geologic  Map  including  Potato  Hills  window,  but  not 
the  core  window.  The  core  area  was  remapped  and  reported  on  by  Pitt 
in  1955,  and  he  concluded  that  a  normal  sequence  of  formations  exists 
on  and  around  a  rather  simple  dome — that  no  klippe  is  indicated;  the 
previous  need  for  a  fault  was  due  to  erroneous  reading  of  bedding  and 
an  inadequate  understanding  of  the  stratigraphic  succession. 

In  1957  Misch  and  Oles  took  issue  with  Hendricks  on  the  basis  of  their 
own  detailed  mapping  of  the  Ouachitas.  They  concur  with  Pitt  on  the 
structure  of  the  "core"  and  also  recognize  no  window  in  the  Potato 
Hills.  They  conclude  that  Potato  Hills  is  an  anticlinorium  of  closely 
spaced,  steep,  and  partly  overturned  folds. 

The  overturning  is  both  to  north  and,  against  the  direction  of  the  supposed 
overthrusting,  to  south.  Some  overturned  anticlinal  limbs  have  ruptured,  and 
steep  reverse  faults  have  developed.  Some  of  these  faults  yield  to  the  north; 
others  yield  to  the  south.  All  of  these  reverse  faults  die  out  along  the  strike, 
generally  in  the  steep  limbs  of  anticlines. 

The  Arkansas  anticlinorium  displays  the  same  fold  pattern  as  that  seen  in 


the  Potato  Hills.  Steep  northward  and  southward  overturning  of  folds  are  about 
equal.  The  greatest  stratigraphic  and  structural  depth  is  exposed  in  the  core 
of  the  western  part  of  the  anticlinorium  (south  of  Mt.  Ida),  and  there  is  the 
same  continuous  change  in  tectonic  style  as  that  found  in  the  core  of  the 
Choctaw  anticlinorium. 

Misch  and  Oles  contend  that  the  mapped  overthrusts,  both  major  and 
minor,  are  partly  steep  reverse  faults  and  partly  no  faults  at  all.  The  large 
exotic  boulders  of  Arbuckle  rocks  in  the  Johns  Valley  shale  are  considered 
evidence  of  thrusting  by  Hendricks,  but  Misch  and  Oles  believe  they  are 
of  "deposition  origin" — apparently  not  associated  with  an  advancing 
thrust  front. 

Misch  and  Oles  also  believe  that  the  differences  between  the  "Ouachita 
facies"  and  the  "Arbuckle  facies"  have  been  overemphasized. 

Some  units  are  indentical,  as  for  example,  the  upper  Arkansas  novaculite  of 
the  Ouachitas  and  the  Woodford  chert  of  the  Arbuckle  region.  Others  differ 
relatively  litde,  as  the  Bigfork  "chert"  and  the  major  part  of  the  Viola  lime- 
stone, or  the  Stanley  shale  and  the  Caney  shale.  Others  differ  more  strongly, 
as  the  Ouachita  Mountains  correlatives  of  the  Simpson  group.  And  some  units 
differ  very  strongly,  as  the  Missouri  Mountain  shale  and  the  lower  Hunton 
limestone.  However,  contrasted  facies  are  not  disconnected  as  the  hypothesis 
of  overthrusting  requires.  Most  of  the  contrasted  facies  have  transitional  re- 
lationships. Some  of  the  transitions  are  very  gradual;  others  are  pronounced 
and  also  have  been  accentuated  by  the  intense  shortening  resulting  from  folding 
and  faulting.  None  of  these  changes,  however,  exceeds  those  often  encountered 
in  adjacent  and  connecting  basins,  or  different  parts  of  the  same  basin.  More- 
over, the  fact  is  often  overlooked  that  there  are  marked  facies  changes  within 
the  Arbuckle  region  itself,  as  well  as  within  the  Ouachita  Mountains. 

For  a  review  of  the  problems  in  the  Ouachita  Mountains  see  Tomlin- 
son  (1959). 


230 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Phases  of  Ouachita  System 

Early  Mississippian  Phase.  Elevations  precursory  to  the  late  Paleozoic 
orogeny  seem  to  be  indicated  by  an  unconformity  between  the  Arkansas 
novaculite  (Devonian)  and  the  Upper  Mississippian  elastics  (Chaney 
shale).  Chert  conglomerates  rest  on  the  novaculite  in  the  Potato  Hills 
section  of  the  Ouachitas  and  they  are  found  at  the  base  of  the  Stanley 
shale  (Lower  Pennsylvanian)  in  southern  outcrops.  In  addition  to  this 
suggested  late  Mississippian  disturbance,  the  rise  in  the  foreland  of  the 
Ellis-Chautauqua-Ozark  arch  in  late  Devonian  time  may  be  mentioned. 

Late  Mississippian  Phase.  The  deposition  of  more  than  17,000  feet  of 
clastic  sediments  of  the  Stanley,  Jackfork,  and  Johns  Valley  formations 
all  within  a  very  short  time  indicates  a  great  and  sudden  uplift  nearby, 
which  undoubtedly  was  one  of  active  orogeny  because  a  sedimentary 
mass  of  the  character  and  quantity  noted  requires  actively  rising  moun- 
tain chains.  The  elastics  were  deposited  in  a  foredeep. 

Whereas  van  der  Gracht  and  others  before  him  postulated  the  orogeny 
in  the  hinterland  to  the  south,  Hendricks  (1943)  believes  that  early 
thrust  sheets  came  from  the  north  and  pushed  southward  to  form  a  land- 
mass.  The  Stanley,  Jackfork,  and  Johns  Valley  shales  were  deposited 
in  a  basin  to  the  south  of  this  landmass,  and  the  thrusting  culminated  in 
Johns  Valley  time.  The  Atoka  sediments  were  then  spread  thickly  over  the 
sites  of  both  facies.  Van  der  Gracht  believes  the  Atoka  came  from  a 
southern  highland;  Hendricks  does  not  comment  on  the  source.  The  Atoka 
sediments  reflect  the  second  pulsation  this  time  in  the  Early  Pennsyl- 
vanian. 

In  eastern  Texas,  a  foreland  basin  to  the  southward-trending  chains 
of  the  hinterland  came  into  existence,  and  in  the  basin  the  Strawn  and 
Millsap  formations  were  deposited,  having  been  derived  from  an  eastern 
source. 

Mid-Pennsylvanian  (?)  Phase.  The  age  of  the  major  deformation  of 
the  Ouachitas  is  believed  by  several  authors  to  have  occurred  in  post- 
Atoka  and  pre-Boggy  time.  According  to  Fitts  (1950); 

The  unconformity  at  the  base  of  the  Boggy  formation  is  the  largest  within 
the  Pennsylvanian  of  Oklahoma  and  is  probably  the  most  widespread.  Along  the 
line   of  outcrop,   it   is   progressively   underlain   by   Pennsylvanian   beds   from 


Savanna  to  Atoka,  locally  in  the  Tri-State  area  upon  Mississippian  and  in  wes- 
tern areas  of  Oklahoma  all  formations  down  to  granite. 

The  top  of  the  Boggy  is  marked  by  another  unconformity,  this  one  of  more 
importance  locally  and  to  the  westward  in  the  Seminole  region.  The  section  of 
beds  above  this  unconformity  is  generally  devoid  of  any  angular  discordance 
and  for  the  first  time  can  be  seen  a  relationship  which  will  persist  through  the 
rest  of  the  Pennsylvanian  and  lower  Permian;  i.e.,  predominandy  limestone  in 
the  north  grading  to  shales  and  elastics  in  the  central  to  coarser  elastics  and  red 
beds  as  the  Arbuckle  Mountains  are  approached. 

The  deformation  of  the  Arbuckles  in  the  Mid-Pennsylvanian  influenced 
the  development  of  the  red-bed  facies  in  the  upper  Cisco  and  Lower 
Permian,  but  later  in  Permian  time  much  clastic  material  in  the  Wichita 
system  came  from  an  eastern  source  (Cheney,  1929). 

Drilling  operations  have  penetrated  a  formation,  the  Morehouse, 
under  the  coastal  plain  sediments,  in  northern  Louisiana,  which  contains 
"late  Paleozoic  fossils"  (Imlay  and  Williams,  1942).  Its  areal  relations 
have  been  worked  out  for  a  limited  distance  in  southern  Arkansas  and 
also,  to  some  extent,  its  stratigraphic  relations  (Philpott  and  Hazzard, 
1949;  Fisher  et  al,  1949).  See  Fig.  14.6.  It  occurs  above  the  Eagle  Mills 
formation  and  below  the  Louann  salt  and  Werner  formation.  (Philpott 
and  Hazzard,  1949).  According  to  the  usage  of  Imlay  and  Williams,  the 
Louann  sail  and  Werner  formation  make  up  the  Eagle  Mills.  At  any 
rate,  the  Eagle  Mills  seems  to  overlie  the  folded  Ouachita  facies  uncon- 
formably,  and  if  such  is  the  case,  the  Ouachita  thrusting  predates  the 
Eagle  Mills  and  Morehouse.  When  their  age  eventually  is  fixed,  the  age 
of  the  Ouachita  thrusting  possibly  will  be  fixed  more  definitely  than  is 
now  possible. 


Connection  of  Ouachitas  and  Appalachians 

Spatial  Relations.  The  relation  of  the  Ouachita  system  to  the  Appa- 
lachian is  hidden  by  the  Cretaceous  and  Tertiary  rocks  of  the  Mississippi 
embayment,  but  they  have  been  traced  by  deep  wells  to  within  60  miles 
of  each  other.  See  map,  Fig.  14.7.  Both  are  strongly  folded  and  faulted, 
and  in  both  there  has  been  thrusting  toward  the  central  stable  region  of 
the  continent.  In  both  areas  there  is  a  thick  development  of  Early  Pennsyl- 


OUACHITA,  MARATHON,  AND  COAHUILA  SYSTEMS 


231 


Fig.  14.7.  Relation  of  Ouachita  Mountains  to  southern  Appalachians  under  the  Coastal  Plain 
cover.  The  pre-Upper  Cretaceous  geology  of  Arkansas  and  Louisiana  is  by  Fisher,  Kirkland,  and 
Burroughs  (1949).  Fredericksburg,  Paluxy,  Mooringsport,  Ferry  Lake  anhydrite,  Lower  Glen 
Rose,  and  Hosston  formations  are  Lower  Cretaceous;  the  Smackover  and  Cotton  Valley  are 
Upper  Jurassic;  the  Eagle  Mills  is  possibly  Lower  Jurassic  (King,  1950a)  or  Permian  (Philpott  and 
Hazzard,   1949). 

vanian  clastic  rocks  derived  from  the  hinterlands.  See  paleotectonic 
maps,  Plates  5  and  6. 

According  to  King  ( 1950a ) : 

The  sequence  of  Paleozoic  deposits  in  the  Ouachita  Mountains  resembles 
that  in  the  Valley  and  Ridge  province  in  that  it  is  composite,  the  older  part 
indicating  quiet  deposition,  and  the  younger  part  deposition  during  a  time  of 
considerable  crustal  mobility.  It  differs  in  that  the  boundary  between  the  older 
and  younger  parts  is  post-Devonian  rather  than  Middle  Ordovician  as  in  the 
Valley  and  Ridge  province,  so  that  there  is  no  representation  of  the  Taconian 
orogeny.  Moreover,  the  deposits  of  the  older  part  are  black  graptolite  shales, 
bedded  cherts,  novaculites,  and  fine  sandstones,  rather  than  carbonates,  and 
hence  are  of  "eugeosynclinal"  facies,  as  contrasted  with  the  "miogeosynclinal" 
facies  of  the  Valley  and  Ridge  province  to  the  east,  and  of  the  Arbuckle  and 
Wichita  Mountains  farther  west  in  Oklahoma.  Deposits  of  the  younger  part, 
laid  down  under  conditions  of  greater  crustal  mobility,  are  of  early  Pennsyl- 
vanian  (Springer)  age,  and  probably  formed  in  response  to  the  Wichita  period 
of  orogeny.  They  are  similar  to  the  thick  late  Mississippian  and  early  Pennsyl- 
vanian  deposits  of  the  Valley  and  Ridge  province  in  Alabama.  The  deposits  of 


the  Ouachita  geosynclinal  were  remarkably  persistent  in  character,  for  nearly 
the  same  units  are  present  in  the  extension  of  the  system  in  the  Marathon 
region,  Texas,  many  hundreds  of  miles  to  the  southwest. 

The  Appalachian  folds  have  been  traced  as  far  southwest  as  Marengo  Counts . 
Alabama,  on  line  of  strike  from  the  exposed  structures  of  the  Valley  and  Ridge 
province  in  the  Birmingham  district,  where  wells  have  encountered  Ordovician 
limestones  and  dolomites  directly  beneath  the  Mesozoic. 

The  Ouachita  folds  have  been  traced  southeastward  from  their  outcrops  in 
the  Ouachita  Mountains,  across  the  Mississippi  Embayment  and  into  central 
Mississippi.  Here,  the  boundary  between  Paleozoic  rocks  of  Ouachita  facies  and 
the  foreland  rock  trends  southeastward.  That  this  is  likewise  the  strike  of  the 
folding  is  suggested  by  the  fact  that  folds  in  the  adjacent  Black  Warrior  Basin 
trend  southeast.  In  Newton  and  Neshoba  Counties,  Mississippi,  near  the  bound- 
ary between  the  Ouachita  area  and  the  foreland,  wells  have  encountered  Ordo- 
vician limestones  and  dolomites  below  the  Mesozoic.  These  are  of  Appalachian 
or  Arbuckle  facies,  rather  than  Ouachita  facies,  which  indicates  the  existence 
of  an  intermediate  slice  between  the  Ouachita  folds  and  the  foreland. 

The  Appalachian  and  Ouachita  systems  have  thus  been  traced  by  drilling  to 
within  about  60  miles  of  each  other,  and  they  seem  to  be  approaching  at  an 
acute  angle.  Southward,  they  pass  beneath  the  thick  Jurassic  and  Lower  Cre- 
taceous deposits  of  the  Gulf  Coastal  Plain,  so  that  their  point  of  junction  is 
beyond  the  reach  of  the  drill. 

Connection  of  Ouachitas  and  Marathons 

The  Ouachita  thrust  sheets  not  only  overlie  the  east  end  of  the  Wichita 
system,  but  continue  southward  under  the  Cretaceous  rocks  of  the  Gulf 
Coastal  Plain.  If  not  the  thrust  sheets,  the  deformed  strata  of  the  orogenic 
belt  wrap  around  the  Llano  uplift  of  Texas  and  connect  with  the  Mara- 
thon Mountains  to  the  west.  Miser  and  Sellards  (1931)  have  traced  the 
Ouachita  front  under  the  Cretaceous  strata  by  means  of  well  records  south 
to  the  Llano  uplift,  and  Sellards  ( 1931 )  has  traced  the  geosynclinal  rocks 
westward  from  the  uplift  to  the  Marathon  exposures,  also  by  means  of 
well  records.  Flawn  (personal  communication  and  1956)  more  recently 
has  mapped  this  front  in  considerable  detail. 

MARATHON  SYSTEM 

Location  and  Principal  Structures 

Paleozoic  formations  appear  in  the  Marathon  basin  of  trans-Pecos 
Texas,  and  there  reveal  another  great  orogenic  system.  The  Marathon 


232 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


I 1  oermun  1---;  -I :.  7  ";j  cretaceous  \lll^  TvoL«mcs        [ 

*•*    TERTIARY     INTRUSIVES  »""■ 


PRE-PERMIAN     PALEOZOIC    STRATA 
FOLDED     AND     FAULTED 


PENNSYLVANIAN     THRUSTS 


CONTOURS     BASE    COMANCHE    SER. 
?    MILES 


Fig.    14.8.      Structure   map   of   the   Marathon   uplift.   After   King,    1937.   Black   Peak   thrust   is   post- 
Cretaceous.  A  number  of  Cretaceous  outliers  in   the   Paleozoic  area   not  shown. 


region  lies  on  the  edge  of  the  Mexican  highlands  physiographic  province 
which  merges  with  the  Great  Plains  on  the  east.  Structurally,  the  region 
is  a  broad  dome  of  Cretaceous  rocks,  from  whose  central  part  the  Creta- 
ceous cover  has  been  stripped  away,  leaving  an  area  of  low  country  in 
the  center,  the  Marathon  basin.  See  Figs.  14.1  and  14.8  and  cross-section 
M-M'-M",  Fig.  14.9.  Here,  strongly  folded  Paleozoic  rocks  are  exposed. 
The  Paleozoic  rocks  in  the  basin,  and  in  the  Glass  Mountains  which  flank 
it  on  the  northwest,  have  a  thickness  of  21,000  feet.  The  greater  part  of 
them  was  laid  down  in  a  subsiding  trough  commonly  referred  to  as  the 
Llanorian  geosyncline.  The  oldest  rocks  are  Upper  Cambrian  sandstones 
and  shales,  whose  base  is  not  exposed.  Overlying  them  are  2000  feet  of 
Ordovician  rocks  composed  of  shaly  limestone  and  shale,  with  some  beds 
of  chert.  The  Ordovician  is  overlain  by  the  Caballos  novaculite,  possibly 
of  Devonian  age,  which  reaches  600  feet  in  thickness.  The  Caballos  no- 
vaculite is  over-lain  by  a  great  series  of  clastic  rocks  of  Pennsylvanian  age, 
as  much  as  12,000  feet  thick  in  the  southeastern  part  of  the  area  but 
much  thinner  in  the  northwest. 

Llanoria  and  the  Llanorian  Geosyncline 

The  belt  of  folded  sedimentary  rocks  of  the  Ouachita  Mountains  ex- 
tends around  the  Llano  uplift  to  the  Marathon  region  and  thence  south- 
westward  across  the  Solitario  near  the  Rio  Grande  and  on  into  Mexico. 
See  Plate  8.  The  early  Paleozoic  trough  lay  about  100  miles  north  of  the 
present  mountains  (Rarton,  1945).  See  Fig.  14.10.  In  Permian  time,  a 
trough  of  geosynclinal  proportions  existed  in  Coahuila,  200  miles  south  of 
the  Solitario. 

Pre-Carboniferous  sediments  of  the  Marathon  and  Solitario  uplifts, 
like  those  of  the  Ouachitas,  are  rather  thin  and  include  much  clastic  ma- 
terial. They  are  composed  of  sandstones,  conglomerates,  boulder  beds  of 
debated  origin,  and  impure  limestone  with  much  shale,  chert,  and,  con- 
spicuously, novaculite.  Some  of  the  sediments  evidently  accumulated  at 
no  great  distance  from  shore;  others  such  as  the  shales  may  have  been 
carried  much  farther  away  from  their  source.  In  the  foreland  areas  of 
both  the  Ouachitas  and  Marathons,  the  sediments  are  mostly  limestones. 
It  is  generally  concluded  that  the  early  Paleozoic  sediments  came  from  a 


M 


OUACHITA,  MARATHON,  AND  COAHUILA  SYSTEMS 

M 

rcd,-?   ct  j 


GLASS  MOUNTAINS  i 
I 
I 


MARATHON        ANTICLINORIUM 


DUOOU 


T  CREEK     THRuTF  g^-Tgfg  ..€.0^1 


7 


233 


M' 


Ct 


J^'  DAGGER  FLAT  ANTICLINORIUM 


ARDEN    DRAW 
vx\       '^>  \\.  THRUST  v 

Ct Dc         r  ->\  \  jQ\  ^  Cd 


HELL'S 


^  V. 


€d-J 


HALF  ACRE  V      ^\\     ^     J     Kf 
>T  *         x>  "^i 


TRES  HERMANAS    MTN. 
Kt 


M 


Kf 


Kt 


Vet' 


10 

—I 


HORIZONTAL    AND    VERTICAL     SCALE     IN    MILES 


|  Fig.   14.9.      Cross  section   of  Marathon   uplift  and   Permian   basin.  Taken  from   King  (1937,   PI.  23, 

1  section  B-B').  Cd,  Dogger  Flat  sandstone  (Cambrian);   O,  Maravillas  chert,  Woods   Hollow  shale, 

Fort  Pena  formation,  Alsate  shale,  and  Marathon  limestone  (Ordovician);  De,  Caballos  novaculite 

(Devonian    ?);    Ct,    Tesnus    formation,    Cd,    Dimple    limestone,    Ch,    Hamond    formation,    and    Cg, 

landmass  to  the  south  or  southeast  and  accumulated  in  a  sea  whose  shore 

lines  moved  back  and  forth,  but  the  propriety  of  calling  the  basin  of  depo- 

I  sition  of  that  time  a  geosyncline  with  only  1500  to  3100  feet  of  sediment 

i  has  been  questioned  (Sellards  and  Baker,  1934).  Deep  wells  have  enabled 

Barton  ( 1945)  to  diagram  the  extent  of  the  pre-Pennsylvanian  deposits 


Gaptank  formation  (Pennsylvanian);  Cwc,  Wolfcamp  formation,  CI,  Leonard  formation,  Cw, 
Wood  formation,  and  Cc,  Capitan  limestone  (Permian);  lb,  Besset  conglomerate  (Triassic  ?);  Kt, 
Trinity  group,  and   Kf,   Fredericksburg   group   (Lower  Cretaceous). 


with  more  detail  than  heretofore.  See  Fig.  14.10.  He  shows  that  the  axis 
of  the  basin  was  considerably  north  of  the  later  Pennsylvanian,  and  also 
that  the  basin  was  too  shallow  to  deserve  the  name  geosyncline. 

In  both  of  the  regions,  the  deposits  of  Carboniferous  time  attained  a 
great  thickness,  possibly  over  20,000  feet  in  the  Ouacbitas  and  12,000  or 


App.  loo   Miles  ■ 


SITE     OF      LATER 
'MARATHON    MOUNTAINS 


LL  ANOBIA 


M/ss/ss ippign  hj 


Woodford  sh. 


Tpyrpyr_.. 

\  AA  /_\  A  A  S^STT^Ty^^'^6 
a  A  a  a  A  a  A  a  a  A  aaa/ 

\aaaaa/\aaaaaaa"aa~aaaa/  \  a/  "\~a~a~7  \A7  \~7  <7  \~/\~  www  \";\"/\"a"/\"/ "/  \~V\7  \i  \i  \7  v>  ~i  \/~/\/\/\/  \i  \7  \~>  \7  \>  \7  \7  \~  \7  \7  v/  \~>  \~  \~  \~  \~  \ 


A  A  A  A  A /_\  A  AM / 

v  A  A  A  '_>  A  A  <_>  <_y_> 

A  A  A  A  A  A  A  A  A  / 
\  A  A  A  A  A  A  A  A  A 
A  A  A  A  /  \  A  A  AA  / 
\  A  A  A AA A  A  A  A 
A  A  A.  A  A  A  A  A  A  / 
\  /_\  A  A  A  A  A  A  A  A 
/  \  A  A  /  \  A  A  A  A  A  / 
\  A  A  A  A  A  A  A  A  A 
A  A/  \A  A  A  Aa  A/ 


Fig.    14.10.      Pre-Pennsylvanian    basin    of   deposition    in    the    region    of   the    Marathon    Mountains, 
after   Barton,   1945.   The   section   extends   approximately   north-south   through    the   Marathons   and 


into   the    Delaware    basin,    and    restores   the    strata    diagrammatically    to    their    pre-Pennsylvanian 
condition. 


234 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


more  feet  in  the  Marathons.  The  trough  in  which  these  Carboniferous 
sediments  accumulated  appears  to  have  extended  uninterrupted  from  the 
Ouachita  to  the  Marathon  and  Solitario  regions.  This  Pennsylvanian 
trough  is  referred  to  as  the  Llanorian  geosyncline.  The  Fort  Worth 
( Strawn )  and  Kerr  basins  seem  to  be  expansions  of  the  geosyncline  over 
the  margin  of  the  foreland. 

The  land  area  of  Llanoria,  southeast  of  the  Llanorian  geosyncline,  ap- 
pears to  have  been  composed  largely  of  crystalline  rocks  and  probably 
stood  as  a  highland  or  mountain  area  during  a  large  part  of  Paleozoic 
time.  For  the  most  part,  the  former  highland  is  now  buried  beneath 
Cretaceous  and  younger  strata,  and  the  hypothesis  of  its  former  existence 
is  based  largely  on  evidence  supplied  by  the  composition  of  the  Paleozoic 
sediments  in  the  geosyncline  (Miser,  1929;  King,  1937). 

Both  Pennsylvanian  clastic  and  Devonian  cherty  formations  thicken 
southeastward  across  the  Llanorian  geosyncline  in  the  Marathons;  lime- 
stones are  replaced  by  shales  or  cherts;  and  the  clastic  deposits  contain 
grains  of  schistose  or  granitic  rocks,  pebbles  of  vein  quartz,  and  cobbles 
of  igneous  rocks.  The  distance  south  at  which  the  land  lay  during  Paleo- 
zoic time  is  unknown,  but  it  may  have  been  100  or  more  miles  away. 
Examine  Fig.  14.10. 

Phases  of  Marathon  System 

Early  Pennsylvanian  Phase.  The  lowest  of  the  Pennsylvanian  forma- 
tions, the  Tesnus,  was  deposited  in  the  Llanorian  geosyncline,  probably  in 
early  Pennsylvanian  time  (King,  1937).  It  is  a  great  mass  of  inter- 
bedded  sandstone  and  shale  in  thin  and  thick  beds,  nearly  barren  of  fos- 
sils. In  the  southeastern  part  of  the  basin  it  exceeds  6500  feet  in  thickness, 
and  it  is  predominantly  sandstone  with  many  arkose  layers  and  several 
prominent  massive  layers  of  white  quartzite.  In  the  northwestern  part  of 
the  basin,  it  is  about  300  feet  thick  and  is  nearly  all  black  shale  with  a  few 
sandstone  beds.  The  Tesnus,  the  Dimple  limestone,  and  the  lower  part 
of  the  Raymond  formation  make  up  the  flysch  facies — a  European  term 
to  signify  sediments  deposited  during  the  time  of  a  rising  hinterland  and  a 
sinking  geosyncline.  The  Dimple  limestone  is  over  1000  feet  thick  in  the 
Marathon  basin,  and  thins  southward.  The  Ilaymond  formation  is  a  mass 
of  arkosic  sandstones  and  shales  3000  feet  thick. 


Overthrusting  in  the  southern  part  of  the  Marathon  area  began  at  this 
stage,  as  is  suggested  by  a  remarkable  layer  of  mudstone  in  the  upper 
part  of  the  Haymond,  in  which  are  embedded  large  blocks  of  older  rocks. 
The  blocks  are  believed  to  have  been  derived  from  the  erosion  of  ad- 
vancing thrust  sheets  and  to  mark  the  first  strong  compression  in  the 
region  (King,  1937). 

Late  Pennsylvanian  Phase.  The  uppermost  Pennsylvanian  formation, 
the  Gaptank  (Upper  Pennsylvanian  in  age),  consists  of  conglomerate  and 
sandstone  derived  from  the  erosion  of  rising  folds.  The  strong  deformation 
to  which  the  Paleozoic  rocks  of  the  Marathon  basin  have  been  subjected 
apparently  culminated  after  the  deposition  of  this  Upper  Pennsylvanian 
formation.  The  Permian  rocks  of  the  Glass  Mountains  to  the  northwest 
rest,  at  least  in  places,  with  great  angular  unconformity  on  the  disturbed 
older  beds.  See  section  M-M'-M",  Fig.  14.9.  The  structural  features  con- 
sist of  close  folds  that  trend  northeast  and  are  overturned  to  the  north- 
west, and  several  thrust  faults.  The  faulting  culminated  on  the  northwest 
in  the  nearly  flat-lying  Dugout  overthrust,  with  a  known  displacement  of 
more  than  six  miles.  Farther  southeast  the  other  thrusts  have  miles  of  dis- 
placement and  some  are  folded  and  therefore  older  than  the  frontal  fault 
(P.  B.  King,  1937). 

COAHUILA  SYSTEM 

Known  Geologic  History 

Exposures  of  Late  Pennsylvanian  (?)  and  Permian  rock  in  the  south- 
western part  of  the  Mexican  state  of  Coahuila,  some  250  miles  south  of  the 
Marathon  region  of  Texas,  are  believed  to  reveal  a  continuation  of  the 
Llanorian  geosyncline  and  the  approximate  position  of  the  west  margin  of 
Llanoria.  In  the  Acatita-Las  Delicias  area,  according  to  Kelly  (1936)  and 
R.  E.  King  et  al.  (1944),  a  series  of  sediments  and  interstratified  igneous 
rocks  over  10,000  feet  thick  was  deposited  in  a  subsiding  trough.  The 
sediments  came  from  the  landmass  of  Llanoria,  and  the  lava  flows,  sills, 
fragmental  igneous  material,  and  graywacke  came  from  the  west.  The 
volcanics  are  rhyolite,  andesite,  and  basalt  flows  and  tuffs. 

Late  Pennsylvanian  ( ? )  limestones,  possibly  in  part  of  reef  origin,  were 
deposited    simultaneously    with    products    of    volcanic    activity.    Coarse 


OUACHITA,  MARATHON,  AND  COAHUILA  SYSTEMS 


235 


W-E    SECTION  PASSING    2  KM.  NORTH  OF    LA  DIFUNTA 
K 


POST-PERMIAN    PRE-CRETA. 
GRANITE    INTRUSION 


CRETACEOUS 


POST- PERMIAN  '  PRE-'WeTACEOUS    GRANITE     INTRUSION 


WSW-ENE    SECTION    PASSING    I  KM.    NORTH   OF  THE    NORIA  DE   MALASCACHAS 


MILES 


!  Fig.    14.11.      Cross   sections    near    Las    Delicias,    Coahuila,   Mexico.   The    Permian    strata    consist   of 
1  interbedded   conglomerate,   graywacke,   sandstone,   shale,   limestone,   and   intermediate   and    basic 

,  detritus  from  these  and  older  rocks  accumulated  in  the  western  part  of 

1  the  area  either  contemporaneously  with  the  reefs  or  as  a  clastic  wedge 

i  on  the  flank  of  an  early  Permian  uplift.  The  coarseness  and  unsorted  char- 

j  acter  of  the  boulder  conglomerates  indicate  that  the  boulders  must  have 

]  been  transported  by  unusual  processes.  During  the  remainder  of  Permian 

time,  the  geosyncline  received  deposits  of  clay  from  Llanoria  on  the  east, 

flows  of  lava  from  fissures  in  the  basin  to  the  west,  and  volcanic  detritus 

derived  from  the  reworking  of  pyroclastic  deposits  and  possibly  by  action 

of  waves  on  the  lava  flows. 


lavas.   The   graywacke   and    lava    make   up   about  60   percent   of   the   sequence.   After   R.    E.    King 
ef  al.,   1944. 

At  some  time  beween  Late  Permian  and  Late  Jurassic,  the  Pennsvl- 
vanian  (?)  and  Permian  rocks  were  intensely  folded  and  overthrust.  See 
cross  section,  Fig.  14.11.  If  the  deformation  took  place  in  Late  Permian 
time,  it  was  the  last  phase  of  orogeny  affecting  the  sediments  of  the  Paleo- 
zoic geosyncline.  Possibly  it  occurred  in  Early  Jurassic  or  Triassic  time,  but 
not  as  late  as  the  Nevadan  disturbance  (Late  Jurassic),  because  the 
Upper  Jurassic  Oxfordian  sediments  rest  unconformably  upon  the  trun- 
cated Permian.  The  geosyncline  is  shown  as  deformed  in  Late  Permian 
time  on  the  tectonic  map  of  Plate  8.  See  Chapter  17  and  Fig.  17.9. 


236 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


The  folded  rocks  were  intruded  by  batholiths  of  granite  and  grano- 
diorite  before  Oxfordian  time. 

Structural  Trends 

The  dominant  strike  of  the  beds  in  the  northern  part  of  the  main  Per- 
mian area  is  N.  35°  to  N.  50°  E.  The  strike  of  secondary  cleavage  is 
N.  75°  E.  and  may  indicate  the  trend  of  the  axis  of  the  folds.  In  the  south- 
ern part  of  the  Permian  area  the  strike  of  the  beds  swings  sharply  to 
S.  40°  E.  R.  E.  King  et  al.  (1944)  suggest  that  this  may  mean  that  the 
Las  Delicias  area  is  a  salient  part  of  a  mountain  arc  in  the  Paleozoic  struc- 
ture which  possibly  controlled  the  outline  of  the  Coahuila  peninsula  of 
Upper  Jurassic  and  Lower  Cretaceous  time.  Post-Cretaceous  folds  in  con- 
tinuation of  this  S.  40°  E.  trend  may  have  been  controlled  by  Permian 
folds,  and  thus  indicate  the  trend  of  the  older  structures.  King's  sug- 
gestion is  illustrated  on  the  tectonic  map. 

Relation  to  Marathon  System 

On  previous  pages  it  has  been  explained  that  the  folding  and  thrusting 


in  the  Marathons  reached  a  climax  in  late  Pennsylvanian  time.  See  Plate  7. 
Thereafter  the  compressed  structures  were  deformed  only  by  epeirogenic 
uplift.  The  Pennsylvanian  and  older  rocks  were  deeply  eroded,  and  even- 
tually Permian  deposits  overlapped  them  progressively  southward.  The 
tectonic  map  of  the  Permian  shows  the  previously  deformed  belt  as  one 
of  epeirogenic  uplift.  The  Permian  Delaware  and  Marfa  basins  were  con- 
tinuous with  the  Coahuila  Permian  basin;  but  while  saline  residues  were 
being  deposited  in  the  northern  basins,  waters  of  normal  salinity  persisted 
in  the  south  basin  and  probably  replenished  the  evaporating  waters  to  the 
north.  After  the  Permian  deposition  in  both  the  north  and  south  basins, 
the  folding  and  intrusions  of  the  Coahuila  area  occurred. 

The  Coahuila  structures  have  commonly  been  tied  to  the  Marathon 
belt,  which  lies  250  miles  to  the  north.  The  Permian  volcanics  and  the 
post-folding  granitic  intrusions  present  characteristics  foreign  to  the 
Ouachitas  and  Marathons  in  late  Paleozoic  time,  and  the  writer  is  inclined 
to  favor  a  connection  with  the  early  Nevadan  belt  of  western  Nevada  and 
California,  where  the  same  characteristics  hold.  This  correlation,  however, 
presents  problems  in  working  out  logical  map  relations. 


15. 


WICHITA  AND  ANCESTRAL 

ROCKIES  SYSTEMS 

AND  THE  TEXAS  FORELAND 


WICHITA  SYSTEM 

i 
Ranges  and  Basins  of  the  System 

Wichita  Mountains.  The  Wichita  Mountains  in  southwestern  Okla- 
homa rise  1100  feet  above  the  plains  and  2480  feet  above  sea  level.  The 
hills  are  chiefly  granite  surrounded  and  embayed  with  nearly  horizontal 
Permian  strata.  Outcrops  of  Arbuckle  limestone  of  the  same  facies  as  in 
the  Arbuckle  Mountains  are  numerous,  especially  along  the  north  side; 
and  others  on  the  soutii  side  and  within  the  hills  indicate  that  three  en 


Fig.  15.1.      Configuration  of  the  Precambrian  surface  in  Oklahoma  and  Texas.  After  Flawn     1956 
and   others.   Numbers  on  contours  are  in   thousands  of  feet   below  sea   level. 

echelon  anticlines  are  present,  with  granite  in  the  cores,  Arbuckle  lime- 
stone on  the  flanks,  and  both  overlapped  unconformably  by  the  Permian 
strata.  The  relief  of  the  buried  Precambrian  surface  is  shown  in  Fig.  15.1. 
and  a  cross  section  at  the  eastern  end  of  tire  range  reveals  the  structure 
( Fig.  15.2 ) .  Intricate  folding  is  described  by  Hayes  ( 1952 ) . 

Amarillo  Range.  The  Amarillo  Range  in  the  Texas  Panhandle  is  a 
series  of  buried  hills  without  surface  expression,  and  is  cored  by  Pre- 
cambrian crystalline  rocks.  The  buried  hills  are  known  to  extend   125 


237 


238 


Cp 


WICHITA 


&*^<f\i  W  ~i  \i  w  \i  \i  w  ~i  w  w  w  w  w  W  ~i  \<  ~i  \i  \i\i  \i\i  \  i\  /  w/T i  \i  w  w  \" 
_\  /W\7\7  \"/  \i\l\l~t\i  ~>\    PRE- CAMBRIAN/)   ~y  N~    ~,  v")  x~  />  Q  s~y  s"///  WW  WW 

7  w  w  \7  w  w  \-/  w  ~/  w  w  w  w  w  \~/  w  w  "/  w  CV  w  w  w  w  \~/  C7  w  w  w  /" /  w  w  w  w  \ 

\/\'\/\/s  /  w  w  "'  w  w  wO  w  w  w  w  w  w  www  \-/  \-/_x_/  V-/_N_/  v_/  v,_'l/  '  "O"7  x~'  x_/  X"Z? 

/  w  \  if  W  W  \  I  WW  W  W  W  W  W  W  W  W  W  W  WWW  W  W  \  /WWW  W  W  w  \  /  W  W  \  I  \ 
\l\  l\  '_~s  W  W  W  W  \t  W  w  w  w  W  W  W  W  W  W  W  W  W  s  I  W  W  W  W  W  W  W  W  \-/  ~l \l 

I  \i\  I  \  I  \i\  1^  l\  l\i  w  W  W  W  W  W  W  W  W  w  W  W  \~/  "/  ~/  W  ~'  w  w  w  W_\_/  W  ~l  w  \" 
W  W  \V  W  W  W  W  W  W  W  W  \7  W  \7  W  \  /_~'_W  W  W  w  W  W  W  W  W  W  WWW  W  W  \_/  w 

/  \  /  \  /  \  /  \  /  \  I  ~i  \  I  s  /  \  /  \  /  \-/  \  /  \  /  \  /  \  /  \  /  \  /  W  w  w  W  W  W  \  /  ~l  w  w  \~/  \-/  w  W  W  w  ^ 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


MOUNTAINS 
-Cp. 


ANADARKO      BASIN 


G' 


HORIZONTAL    AND    VERTICAL    SCALE 


J      MILES 


Fig.  15.2.  Section  through  Wichita  Mountains  and  Anadarko  basin.  Compiled  from  Taff  (1904)  and  Millison 
and  Reed  (1939).  Os,  Simpson  group;  Dv,  Viola  limestone;  Osh,  Silvan  and  Hunton  formations;  Mw,  Wood- 
ford formation. 


AMARILLO     DISTRICT 


J' 


ANADARKO      BASIN 


BUSH    DOME 


JOHN  RAY    DOME 


MILES 


LEILA      DOMfr 


HORIZONTAL     SCALE 


Fig.   15.3.      Sections  J-J'  and   H-H'  of  Fig.   14.1   across  the  buried  Amarillo  Range.  Taken  from  Cotner  and 
Crum,  1933. 


miles  east-west  across  the  Panhandle.  See  Fig.  15.1.  The  highest  peaks 
reached  by  the  drill  are  about  1300  feet  above  sea  level  and  2000  feet 
below  the  surface.  Some  of  the  granite  peaks  are  overlain  directly  by 
the  Permian  beds,  but  others  are  covered  with  the  Pennsylvanian.  See 
cross  sections,  Fig.  15.3.  En  echelon  faults  bound  some  hills  and  help 
produce  ridges  in  en  echelon  arrangement.  The  Armillo  Range  and  the 
Wichitas  are  continuous  as  shown  in  Fig.  15.4. 


Las  Animas  Arch.  The  Amarillo  Range  probably  extended  to  south- 
eastern Colorado  and  northeastern  New  Mexico,  where  it  joined  other 
ranges  and  an  arch  known  as  the  Las  Animas  (Maher,  1946).  See  the 
tectonic  map  of  the  Early  Pennsylvanian  and  Fig.  15.5.  The  Precambrian 
rocks  may  have  been  exposed  above  sea  level  in  Early  and  Mid-Pennsyl- 
vanian  time  along  the  Las  Animas  arch,  but  the  thinning  of  the  Pennsyl- 
vanian and  Permian  strata  over  the  arch  is  chiefly  due  to  subsidence  of 


WICHITA  AND  ANCESTRAL  ROCKIES  SYSTEMS  AND  THE  TEXAS  FORELAND 


239 


the  crust  on  either  side  at  a  more  rapid  rate  than  the  arch  itself.  A 
structural  relief  of  3000  to  4000  feet  appears  to  have  formed  during 
these  times.  Still  further  arching  occurred  in  post-Paleozoic  time,  accentu- 
ating the  structural  relief. 

Muenster  anticline.  The  Muenster  anticline  or  arch  is  the  south- 
eastern end  of  the  Amarillo  Wichita  uplift.  See  Fig.  15.4.  Like  the 
Amarillo  Range  it  is  completely  buried  and  was  rangelike  at  the  time 
of  uplift,  during  the  Pennsylvanian.  Altogether  the  Amarillo-Wichita- 
Muenster  alignment  makes  up  an  uplift  with  a  Precambrian  core  and 
flanking  truncated  Lower  and  Middle  Paleozoic  strata  350  miles  long. 

Criner  Hills.     The  Criner  Hills  are  a  complexly  faulted  horst  con- 
sisting largely  of  Arbuckle  limestone  which  is  exposed  at  the  surface 
and  is  flanked  by  Pennsylvanian  and  Permian  strata.  The  horst  is  the  east 
end  of  an  anticline  off  the  Amarillo-Wichita  uplift.  See  Figs.  15.4  and 
'  15.6. 

Matador  Arch.     The  Matador  arch  as  here  defined  is  made  up  of  a 

narrow  series  of  east-west-trending  buried  granite  hills  which  extend 

from  the  New  Mexico  line  across  the  Llano  Estacado  to  Wichita  Falls 

and  beyond,  a  length  of  some  300  miles.  If  the  overlying  Cretaceous 

and  late  Paleozoic  deposits  were  removed,  the  uplift  would  be  found 

j  to  consist  of  scattered  peaks  rising  above  an  upland.  Strong  faults  and 

folds  trend  obliquely  across  the  uplift  in  a  northwest  direction,  and  these 

;  have  produced  an  en  echelon  character  to  the  topography  (the  buried 

J  peaks)    and  to   the  "highs"  of   the   overlying   formations.   The    Upper 

!  Pennsylvanian  rests  directly  on  the  Precambrian  in  some  localities. 

Parts  or  all  of  the  Matador  arch  have  variously  been  called  the  Red 

River  uplift,  the  Electra  arch,  and  the  Matador  arch.  The  term  Matador 

arch  appears   to  be   gaining  general  acceptance.   The  string  of  small 

uplifts  produced  islands  in  the  Pennsylvanian  seas  and  because  of  this 

j  the  feature  has  also  been  called  the  Matador  archipelago. 

Palo  Duro  and  Hardeman  Basins.     The  general  depression  between 

j  the  Amarillo-Wichita  uplift  and  the  Matador  arch  is  filled  with  Pennsyl- 

!  vanian  and  Permian  sediments,  and  has  a  western  and  an  eastern  divi- 

j  sion,  as  may  be  seen  on  Fig.  15.4.  The  western  is  the  Palo  Duro  basin  and 

the  eastern  the  Hardeman  basin.  Various  names  have  been  used  for  the 


Fig.  15.4.  Generalized  paleogeologic  map,  Texas  and  Oklahoma,  of  pre-Pennsylvanian  rocks. 
Black  is  sub-Pennsylvanian  and  Permian  outcrop  of  Cambrian,  Ordovician,  Silurian,  ond  De- 
vonian formation.  Hachured  area  is  Precambrian.  Mississippian  outcrops  not  shown.  After  Totten 
(1956),  Flawn  (1956),  and  others.  The  Pennsylvanian  and  Permian  cover  has  been  eroded  away 
in  places  in  the  Wichita  and  Arbuckle  and  in  the  Llano  uplift.  Doming  of  the  Marathon  uplift 
is  post-Cretaceous.  H.A.,  Hunton  arch;  A. A.,  Arbuckle  anticline;  C.H.,  Criner  Hills  anticline;  M.A., 
Muenster  anticline;   Cent.   Bas.   Pf.,   Central   Basin   platform;   O.C.A.,   Oklahoma    City   anticline. 

features  of  this  region  as  drilling  has  progressed  and  the  geology  become 
better  understood. 

Arbuckle  Mountains.     Topographically  the  Arbuckle   Mountains   are 
the  hills  between  Davis  and  Ardmore,  and  are  the  surface  expression  of 


INDEX    MAP     SHOWING    LINE    OF     SECTION 

30  M.les 


Horizontal    scale 
SEA     LEVEL    DATUM 


GROUPS  AND   FORMATIONS 


Nippewalla    group 


Sumner,  Chase,    and 
Council  Grove   groups 


Admire    shale 


Wabaunsee     group 


Shawnee,  Douglas   and 
Pedee   groups 


Lansing,   Kansas   City, 
and    Bronson    groups 


Marmaton     group    and 
Cherokee    shale 


Ste.   Genevieve     Is. 


Louis    Is. 


Spergen  ond  Worsow   Iss 


Keokuk  and   Burlington  ls». 


Gilmore    City     Is. 


Misener    sd." 


Simpson  (T)       oroup 


Arbuckle     Is. 


GUADALUPIAN 


LEONARDIAN 

and 
WOLFCAMPIAN 


DESMOINESIAN 


MERAMECIAN 


KINDERHOOKIAN 


BEDS   OF  TRENTON    AGE 


BEDS    OF    BLACK  RIVER 
AND    CHAZYAN     AGE 


BEDS  OF    BEEKMANTOWN- 
IAN    AND  ST.  CROIXIAN 
AGE 


as 
a:< 

oo 


Fig.  15.5.  Correlation  of  Paleozoic  rocks  across  the  Las  Animas  arch  in  Baca,  Las  Animas,  and  Otero 
Counties,  Colorado.  Stratigraphic  classification  on  right  is  mainly  after  State  Geological  Survey  of  Kansas; 
that  on  left  follows  common   usage  in   Colorado.  From  Maher,   1946. 


WICHITA  AND  ANCESTRAL  ROCKIES  SYSTEMS  AND  THE  TEXAS  FORELAND 


241 


Cp     Pontotoc  for.    (Permian) 

Ch      Hoxbor  group  (Missouri  •*  Virgil) 

Cd      Dcese  group  ( Des  Moines) 

Cdh    Dornick  Hills  group  (U. Morrows  Lamp.) 

CS      Springer    group  (  L.  Morrow) 

|>|w    Woodford     (Mississippion) 

Mc     Coney  shale  (Mississippion) 

Osh  Sylvan  and  hunton' 

Ov      Viola  limestone      JOrdovician 

03     Simpson  group 

OCo  Arbuckle    limestone (Ord  i-Comh) 

Cr     Reagon  sandstone   (Cambnon) 

p-G  Pre -Cambrian  crystallines 


/  w  w  w  \7  w 


Fig.    15.6.      Cross   sections    through    the    Ardmore    basin,    Arbuckle    Mountains,    and    Hunton    arch,    compiled 
from  Dott  (1934),  Tomlinson  (1929),  and  Moore  ei  al.  (1944). 


a  large,  complex  anticline.  In  the  core  of  the  anticline,  two  prominent 
peaks  of  Precambrian  porphyry  ( the  Timbered  Hills)  rise  700  feet  above 
the  valley  of  the  Washita  River  and  1400  feet  above  sea  level.  Geologically 
the  term  Arbuckle  Mountians  applies  also  to  the  hilly  area  to  the  north 
and  east  in  which  lower  Paleozoic  rocks  crop  out  and  where  structural 
features  of  mountain  proportions  are  located.  A  thick  sequence  of  rocks 
from  Precambrian  to  Late  Pennsylvanian  is  exposed  in  the  range.  See 
cross  sections,  Fig.  15.6. 

The  regional  structure  of  the  Arbuckle  Mountains  is  a  series  of  much- 
faulted  subparallel  folds  trending  northwest  and  southeast.  They  are 
shown  on  the  map  of  Fig.  14.2,  where  it  will  be  seen  from  north  to  south 


the  several  divisions  are  as  follows;  Lawrence  uplift,  Franks  graben, 
Hunton  anticline,  Mill  Creek  syncline,  and  Tishomingo  anticline.  On 
Fig.  15.4  the  Hunton  anticline,  Franks  graben,  and  Lawrence  uplift  are 
combined  under  the  general  term,  Hunton  arch.  The  Arbuckle  anticline 
is  next  south  of  the  Tishomingo  anticline  but  offset  to  the  west.  The 
Washita  syncline  and  fault  zone  separate  the  Tishomingo  anticline  from 
the  Arbuckle  anticline.  The  structures  are  compressional  in  nature,  and 
especially  in  the  Arbuckle  anticline  and  south-lving  Ardmore  basin 
thrust  faults  and  tight  folds  are  pictured  by  Dott  ( 1934 )  and  confirmed 
by  Swesnik  and  Green  (1950).  The  overriding  is  northward.  Study 
sections  in  Fig.  15.6. 


242 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Ardmore  Basin.  The  Ardmore  basin  is  a  folded  and  faulted  basin 
between  the  Arbuckle  anticline  (Mountains)  and  Criner  Hills.  It  con- 
tains a  thick  and  deeply  depressed  Pennsylvanian  sequence  of  clastic 
sediments,  overlying  a  rather  thick  Cambro-Ordovician  carbonate  se- 
quence with  unconformable  relations  attesting  two  principal  times  of 
orogeny.  These  will  be  outlined  presently. 

Over  30,000  feet  of  Paleozoic  sediments  are  involved,  about  13,000  feet 
of  which  are  Pennsylvanian  and  include  the  Springer,  Dornick  Hills, 
Deese,  Hoxbar,  and  Pontotoc  formations,  from  oldest  to  youngest.  Most 
of  the  pre-Pennsylvanian  beds  are  limestone,  and  the  Pennsylvanian  are 
mostly  sandstone  and  shale.  The  Ardmore  basin  is  considered  a  foredeep 
by  van  der  Gracht,  north  of  the  Wichita  and  Criner  Hills  anticlinorium. 
At  the  time  of  deposition  of  the  beds,  the  basin  spread  over  the  site  of 
the  present  Arbuckle  Mountains  as  well  as  the  present  Ardmore  syncline, 
and  extended  to  the  Hunton-Tishomingo  landmass  (Dott,  1934). 

Anadarko  Basin.  North  of  the  Wichitas  is  the  extensive  Anadarko 
basin.  It  occupies  the  greater  part  of  western  Oklahoma.  Its  axis  runs 
west-northwest  and  approximately  parallels  the  Wichita-Amarillo  up- 
lift. The  Permian  beds  thicken  to  4500  feet  just  25  miles  north  of  the  near- 
est granite  outcrop.  The  thickness  of  the  Pennsylvanian  in  the  center  of  the 
basin  is  unknown  but  may  be  rather  great,  notably  in  the  eastern  part, 
and  may  be  an  extension  of  the  Ardmore  basin.  Becker  (1930)  cal- 
culates the  highest  part  of  the  Wichita  anticlorinium  to  have  been 
elevated  structurally  about  19,000  feet  above  the  axis  of  the  Anadarko 
"foredeep." 

The  Ardmore  trough  trends  into  the  Anadarko  basin  under  the  blanket 
of  Permian  red-beds  and  Cretaceous.  It  is  not  known  how  much  Pennsyl- 
vanian subsidence  occurred  in  the  Anadarko  basin,  but  it  is  clear  that 
most  of  the  subsidence  in  the  Ardmore  basin  is  Pennsylvanian,  and  at 
least  4500  feet  of  subsidence  in  the  Anadarko  is  Permian. 

Paleogeology  of  the  Wichita-Ouachita  Region 

The  history  of  sedimentation  in  Oklahoma  is  in  two  distinct  divisions, 
both  in  time  and  space.  An  uplift  and  peninsula  through  Texas  from 
Mid-Ordovician  to  Mid-Mississippian  separated  the  West  Texas  basin 


Fig.  15.7.  Mid-Ordovician  to  Early  Mississippian  tectonic  features  of  Texas  and  adjacent  areas. 
After   Adams,    1954. 

from  the  Oklahoma  basin.  See  Fig.  15.7.  The  Cambro-Ordovician 
Arbuckle  limestone  sea  spread  across  the  arch  in  platform  fashion  where 
about  1000  feet  of  carbonates  accumulated,  but  in  the  Oklahoma  basin 
on  the  northeast  4000  to  6000  feet  accumulated.  On  top  of  these 
deposits,  while  the  Texas  arch  was  emergent,  an  additional  3000  feet  of 
sediments  were  deposited  in  Late  Ordovician,  Silurian,  and  Early 
Devonian  time.  These  were  also  mostly  carbonates.  To  the  north  in 
Kansas  the  equivalent  strata  are  only  about  1000  feet  thick.  The  region 


WICHITA  AND  ANCESTRAL  ROCKIES  SYSTEMS  AND  THE  TEXAS  FORELAND 


243 


of  subsidence,  defined  by  the  pre-Mississippian  strata,  the  Oklahoma 
basin,  extended  west-northwesterly  toward  the  Colorado  sag  in  central 
Colorado.  The  core  area  of  the  Ouachitas  received  about  3000  feet  of 
sediments  during  this  time,  so  the  axis  of  the  Oklahoma  basin  appears 
to  have  lain  in  the  northern  part  of  the  Ouachitas  and  under  the 
Arkansas  Valley,  and  to  have  extended  eastward  to  a  connection  with 
the  Appalachian  geosyncline.  See  Plates  2,  3,  and  4. 

In  Late  Mississippian  time  and  during  the  Pennsylvanian  a  new 
regimen  of  sedimentation  dominated  the  region,  and  over  the  carbonates 
and  cherts  great  volumes  of  shales  and  sandstones  were  deposited.  The 
basin  of  sharp  subsidence  and  accumulation  followed  mainly  the  belt  of 
later  orogeny  of  the  Ouachita  system.  The  site  of  the  present  Ouachita 
Mountains,  the  Arkansas  Valley  and  the  Wort  Worth  basin  marked  the 
region  of  heavy  deposition,  but  a  spur  of  this  arcuate  basin  projected  off 
to  the  west  through  the  Ardmore  and  Anadarko  basins  where  at  least 
10,000  feet  of  clastic  sediments  accumulated.  See  Plate  8  of  the  Early 
Pennsylvanian.  The  history  of  Pennsylvanian  sedimentation  is  complex 
because  of  deformational  impulses  from  time  to  time  and  place  to  place. 
These  will  be  discussed  under  the  next  heading. 

Phases  of  Orogeny 

Late  Mississippian  Phase.  The  great  flood  of  Stanley,  Jackfork,  and 
Johns  Valley  elastics  in  the  Ouachitas  and  the  equivalent  Springer  group 
in  the  Ardmore  basin  reflect  major  uplift  and  associated  deformation. 
This  was  a  belt  in  the  hinterland,  toward  the  Gulf  of  Mexico,  most  prob- 
ably, because  there  is  no  plausible  source  area  to  the  north. 

Early  Pennsylvanian  Phase.  The  first  disturbance  within  the  basin  of 
accumulation  is  detected  in  a  post-Springer  and  pre-Dornick  Hills  or 
Deese  unconformity,  in  the  Criner  Hills-Ardmore  basin  area.  See  Fig. 
15.6.  This  probably  marked  the  beginning  of  rise  of  the  entire  Amarillo- 
Wichita  element  (Swesnik  and  Green,  1950).  See  tectonic  correlation 
chart,  Fig.  15.8. 

The  Ardmore  basin  then  proceeded  to  sink  and  received  an  addi- 
tional 17,000  feet  of  sediments  making  up  the  Dornik  Hills,  Deese,  and 
Hoxbar  groups. 


Late  Pennsylvanian  Phase.  By  McAlester  time  (late  Lampasas), 
the  crest  of  the  Hunton-Tishomingo  uplift  had  been  eroded  to  the 
Hunton  limestone,  while  the  northeastern  flank  was  being  submerged  by 
encroaching  seas.  Erosion  of  the  crest,  due  to  intermittent  uplifts,  had 
exposed  the  Viola  limestone.  Then  followed  a  rather  extensive  sub- 
mergence, and  by  Missouri  time  the  entire  northwest  end  of  the  Hunton- 
Tishomingo  landmass  had  been  covered.  The  Ardmore  basin,  received 
sediments  from  the  Hunton-Tishomingo  and  Wichita  land  areas  as  well 
as  the  previously  elevated  Ouachita  Mountains.  The  basin  spread  over 
the  site  of  the  present  Arbuckle  Mountains.  A  series  of  rocks  was  de- 
posited in  this  basin  that  differs  in  fades  and  sequence  from  the  material 
that  was  being  laid  down  simultaneously  in  the  McAlester  basin  north- 
east of  the  Hunton-Tishomingo  land  mass.  The  two  basins  were  probably 
never  connected. 

Late  in  Hoxbar  time,  compressive  forces  from  the  southwest  re- 
juvenated the  older  folds  of  the  Wichita  uplift,  and  the  entire  element 
was  moved  northward  toward  the  Hunton-Tishomingo  buttress.  The 
Amarillo  Mountains  were  also  rejuvenated,  and  the  erosional  detritus  of 
the  "granite  wash,"  was  formed.  The  sediments  of  the  Ardmore-Arbuckle 
basin  were  greatly  compressed,  and  the  Arbuckle  anticline  originated. 
As  the  forces  continued  to  move  the  southern  elements  northward,  the 
eastern  part  of  the  Wichita  system  was  thrust  still  farther  north,  ap- 
parently moving  as  a  pivot,  with  the  west  end  of  the  Amarillo  Mountains 
remaining  about  stationary.  The  thrusting  at  the  eastern  end  resulted  in 
minor  folds,  first  in  the  Arbuckle  anticline  and  later  in  the  Hunton- 
Tishomingo  arch.  Most  of  these  minor  folds  became  asymmetrical,  and 
many  were  finally  overturned  toward  the  northeast.  In  the  final  stages 
of  the  movement,  the  major  anticlines  broke  on  their  overturned  axes, 
finally  developing  into  thrusts  and  overriding  the  adjacent  synclines. 

Thirteen  small  erratic  masses  have  been  found  toward  the  west 
extension  of  the  Mill  Creek  syncline  (Lehman,  1945).  The  erratics  are 
remnants  of  an  extensive  thrust  sheet  which  overrode  at  this  place  the 
truncated  edges  of  the  Simpson  group  in  post-Hoxbar  and  pre-Pontotoc 
time. 

In  a  detailed  study  of  a  small  area  in  the  Arbuckle  anticline  Dun- 


Permian 


Virgil 


Missouri 


Des  Moines 


Atoka 


Morrow-  Springer 


Mississippian 


Devonian 


Silurian 


Ordovician 


Cambrian 


QUACHITA- 
McALESTER 
PROVINCE 


ARBUCKLE- 

HUNTON  ARCH 

PROVINCE 


m 


\ 


CRINER. 
WICHITA 
PROVINCE 


ANADARKO- 

ARDMORE 

BASIN 


/ 


\ 


NORTH  &  CENTRAL 
OKLA.  PLATFORM 
&  NEMAHA  RANGE 


OZARK 
PROVINCE 


TENTATIVE  CORRELATION  OF  MAIN  TECTONIC  MOVEMENTS  IN  OKLAHOMA 


Down  warps  of 
basins  and  sediment 
accumulation 


Orogenic  pulses 


Epeirogenic  pulses 
with  unconformities 

Positive  behavior 


Fig.  15.8.  Graphic  representation 
of  phases  of  deformation  in  Mid- 
Continent  region.  Reproduced  from 
Tectonic  Map  of  Oklahoma,    1956. 


WICHITA  AND  ANCESTRAL  ROCKIES  SYSTEMS  AND  THE  TEXAS  FORELAND 


245 


ham  (1955)  finds  evidence  by  way  of  conglomerates,  unconformities, 
and  fault  offset  of  fold  axes  that  the  deformation  there  began  in  Deese 
( Mid-Pennsylvanian)  time,  culminated  in  late  Pennsylvanian,  and  con- 
tinued on  into  early  Permian  by  tilting  the  Lower  Pontotoc  conglomerate 
beds  up  to  40  degrees. 

The  Arbuckle  anticline  was  thrust  far  northeast  of  its  original  position 
and  overrode  a  considerable  distance  onto  the  Hunton-Tishomingo  uplift. 
The  magnitude  of  the  overthrusting  decreased  a  great  deal  within  a  short 
distance  from  southeast  to  northwest  where  crustal  shortening  was  taken 
up  mainly  by  complex  folding.  It  probably  follows  that  the  thrust  along 
its  strike  continued  for  a  considerable  distance  southeast  under  what 
is  now  the  Ouachita  Mountains.  The  Tishomingo  anticline  was  shoved 
northward  in  an  overthrust  second  in  magnitude  only  to  the  one  in 
the  southeast  end  of  the  Arbuckle  anticline,  and  overrode  the  syncline 
to  the  north.  The  Franks  graben,  Wapanucka  syncline,  and  other  minor 
folds  and  thrusts  were  formed  in  the  Hunton  arch. 

Tomlinson  ( 1929 )  has  estimated  the  amount  of  crustal  shortening  in 
the  Ardmore  basin  as  16  miles;  and  Dott  (1934),  whose  theory  of 
structural  evolution  the  above  summary  depicts,  suggests  in  his  illustra- 
tion (Fig.  15.6)  a  net  shortening  at  right  angles  to  the  trend  of  the  struc- 
tures, in  late  Pennsylvanian  time  only,  of  several  scores  of  miles.  It  is, 
therefore,  probably  incorrect  to  show  the  positions  of  structural  elements 
as  they  existed  in  times  past  in  the  places  where  the  features  now  re- 
pose, but  so  many  uncertainties  attend  the  construction  of  palinspastic 
maps  (Kay,  1945)  in  this  region  that  it  seems  best  for  present  purposes 
to  crown  the  elements  so  as  to  conform  to  their  present  geographic 
positions.  Such  has  been  done  on  the  tectonic  maps  of  Plates  6,  7,  and 
8. 

During  the  great  late  Pennsylvanian  phase,  marine  deposits  of  Canyon 
age  and  older  were  highly  tilted  on  the  flanks  of  the  Arbuckle  Mountains, 
and  during  the  following  Cisco  time  erosion  removed  a  sedimentary 
mantle  probably  3  miles  thick,  and  cut  into  granite.  The  granite  thus 
removed  was  distributed  in  beds  of  Wo  If  camp  age  over  wide  areas.  North 
central  Texas  was  affected  to  some  extent  at  this  time,  as  shown  by 
thinning  over  the  Matador  arch. 


TEXAS  FORELAND 


Definition 


The  Texas  Foreland,  as  here  defined  is  the  fairly  undeformed  portion 
of  the  earth's  crust  north  and  west  of  the  Ouachita-Marathon  orogenic 
belt,  south  of  the  Wichita  system,  and  west  of  the  Laramide  cordillera. 
See  Fig.  14.1.  It  is  characterized  by  broad  arches,  basins,  platforms,  and 
shelves.  It  appears  to  be  a  small  part  of  the  Central  Stable  Region  cut 
off  by  the  Wichita  system.  In  reference  to  the  Precambrian  rock  area 
Flawn  (1959)  has  designated  large  parts  of  it  as  the  Texas  craton.  Con- 
siderable igneous  activity  and  probably  deformation  occurred  in  Pre- 
cambrian time,  but  from  the  beginning  of  the  Paleozoic  era  to  the 
present  it  has  been  a  fairly  stable  region  with  practically  no  igneous 
activity. 

For  purposes  of  discussion  the  Texas  Foreland  may  be  considered  to 
have  two  divisions,  the  Central  Texas  and  the  West  Texas-New  Mexico. 

Central  Texas 

Texas  Arch.  During  Cambrian  and  Early  Ordovician  time  Texas  was 
mostly  a  shelf  region  of  carbonate  deposition.  The  carbonate  deposit 
known  as  the  El  Paso  limestone  in  New  Mexico,  the  Ellenburger  in  West 
Texas  and  the  Arbuckle  in  Oklahoma  and  adjacent  north  Texas, 
thickens  southeasterly  from  a  thin  layer  on  the  northwest  to  a  massive 
deposit  over  2000  feet  thick  at  the  edge  of  what  may  have  been  the 
continental  shelf  at  the  time.  The  Oklahoma  basin  lay  to  the  north  and 
the  West  Texas  basin  to  the  west.  In  about  Mid-Ordovician  time  a 
broad  and  gently  emergent  peninsula  extending  southeastward  through 
Texas  rose  (Adams,  1954).  See  the  map  of  Fig.  15.7  and  stratigraphic 
column  of  Fig.  15.9. 

The  subsurface  outcrops  as  indicated  on  the  map  are  interpreted  to 
be  depositional  edges,  with  the  peninsula,  as  large  as  Florida,  emergent 
throughout  the  long  period  of  time.  The  deposits  in  general  gradually 
encroached  on  the  peninsula;  the  Simpson,  Viola,  Montova.  Sylvan,  and 
Hunter  being  Upper  Ordovician  and  Silurian,  and  the  Woodford  De- 
vonian. The  lithologies  are  remarkably  similar  on  either  side  of  the  arch. 


246 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


STRATIGRA    PHY 


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PL. 

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MEMBER 

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THRIFTY 
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CADDO  CREEK 
BRAD 

GRAFORD 
WHITT 

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Colony  Creek  Sh 
Ranger  Ls 
Placid  Sh 
Winchell 
Cedarton  Sh 
Adams  Branch 
Upper  Brownwood  Sh 
Palo  Pinto 
Keechi  Creek 
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Garner 

Brazos  River  cong. 
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MILLSAP  LAKE 

Grindstone  Creek 

Goen  Ls 
Santo  Ss 
Buck  Creek  Ss 

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(Restricted  ) 

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Kickapoo  Falls  Ls 
Dickerson  Sh 

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Upper  Marble  Falls 

Brister 
Lemons  Bluff 

Gibbons  cong. 

MORROW 

Comyn  of  Subsurface 
Lower  Marble  Falls 

Aylor 
Sloan 

SPRINGER 

Fig.   15.9.      Pennsylvanian   stratigraphy  of  the   Llano  uplift.  After  Cheney  and  Goss,   1952. 

Concho  Arch.  In  late  Mississippian  time  the  orogeny  of  the  hinter- 
land of  the  Ouachitas  resulted  in  the  depression  and  fill  of  the  Fort 
Worth  and  Kerr  basins  marginal  to  the  later  belt  of  compression.  This 
resulted  in  the  development  of  a  broad,  pronounced  asymmetrical  arch 
involving  the  previous  formations  and  the  top  of  the  Precambrian.  The 
situation  is  illustrated  in  the  lower  cross  section  of  Fig.  15.10.  Subsidence 
continued  through  the  Atoka  and  Kickapoo  elastics  (subdivisions  of  the 
Lampasas  according  to  Cheney  and  Goss  (1952).  The  asymmetrical  arch 
is  called  the  Concho.  With  the  deposition  of  the  thick  Permian  sedi- 
ments of  the  Midland  basin  (second  cross  section,  Fig.  15.10)  the  arch 
becomes  a  very  strong  and  large  feature.  The  present  contour  of  the 


Precambrian  surface  reflects  the  arch  essentially  as  it  was  at  the  close 
of  Permian  time.  See  Fig.  15.1.  It  pitches  gradually  to  the  north-north- 
west and  reaches  to  the  Matador  arch. 

Bend  Axis.  The  Permian  and  Upper  Pennsylvanian  beds  overlap  the 
Concho  arch  from  the  west  in  the  manner  illustrated  in  Fig.  15.11.  As  far 
as  these  beds  are  concerned  an  axis  of  down  tilting  to  the  west  is  in- 
volved, and  this  has  been  called  the  Bend  axis  or  arch.  There  may  be 
an  arch  in  the  Upper  Pennsylvanian  beds  but  probably  not  in  the 
Permian. 

Llano  Uplift.  The  southeast  end  of  the  Concho  arch  was  so  high 
that  all  beds  were  stripped  off  down  to  the  Precambrian  before  the  in- 
vasion of  the  Cretaceous  seas,  which  spread  a  cover  of  coastal  plain 
sediments  widely  over  the  south  and  east  flanks  of  the  arch.  These  sedi- 
ments have  since  been  mostly  removed  from  the  Precambrian  and  a 
domal  area  known  as  the  Llano  uplift  results.  This  is  the  most  prominent 
feature  evident  on  the  geologic  map  of  Central  Texas. 

The  Pennsylvanian  history  of  the  site  of  the  Llano  uplift  is  somewhat 
more  involved  than  the  cross-sectional  representation  of  the  Concho 
arch  in  Fig.  15.10.  According  to  Cheney  and  Goss  (1952): 

Mississippian  outcrops  in  the  Llano  region  transgress  the  truncated  Ordo- 
vician  Ellenburger  group.  Drilling  has  shown  an  increasing  loss  of  section  west 
of  the  Llano  uplift  so  that,  as  a  result  of  both  erosion  and  non-deposition, 
Upper  Pennsylvanian  (Canyon)  marine  sediments  locally  overlap  Cambrian 
rocks  in  and  near  northeast  Menard  County.  Farther  west  and  northwest, 
Middle  Pennsylvanian  beds  rest  on  truncated  Mississippian  and  Ordovician 
or  older  rocks  in  a  large  region,  heretofore  called  the  Concho  arch,  where 
local  as  well  as  regional  tectonic  features  had  developed  mainly  along  trends 
varying  from  north-northeast  to  northwest.  Thin  Middle  Pennsylvanian  marine 
sediments  of  the  Lampasas  and  Strawn  series  deposited  across  this  base-levelled 
region  are  chiefly  limestones  and  shales  of  the  platform  type  in  contrast  to 
thick  basinal  type  deposits  on  the  east  and  south. 

A  system  of  large  faults  extending  northward  from  the  present  Llano 
uplift  into  die  Fort  Worth  basin  developed  during  very  late  Lampasas 
time.  The  faults,  well  known  from  surface  mapping  in  the  Llano  uplift, 
have  now  been  followed  by  geophysical  work  and  drilling  for  more  than 
100  miles  northward  into  the  Forth  Worth  basin.  Some  of  the  faults  have 
displaced  upper  Lampasas  and  older  beds  as  much  as  1100  feet  in  the 


WICHITA  AND  ANCESTRAL  ROCKIES  SYSTEMS  AND  THE  TEXAS  FORELAND 


247 


WESTERN    EPEIRIC    SEA 


CRETACEOUS     LAND 


GULF     COASTAL    PLAIN 


MIDLAND     BASIN 


CONCHO  ARCH 


OUACHITA     SYSTEM 


PENN. 


o  a  s-7     € 

WEST    TEXAS    BASIN 


CONCHO  ARCH 

(Mid-Pennsylvonian) 


FORT    WORTH    BASIN 


Fig.   15.10.      Evolution   of  central  Texas  as  idealized 
the  Ouachita  orogenic  belt. 

Strawn  basin.  The  faults  in  the  Llano  uplift  have  formed  narrow  grabens, 
and  the  three  most  prominent  horsts  over  which  the  later  strata  are 
flexed  are  called,  from  west  to  east,  the  Richland  Springs,  San  Saba, 
and  Lampasas  "axes."  The  Richland  Springs  axis  forms  the  southern  part 
of  the  present  Rend  arch.  See  map,  Fig.  14.1. 

The  time  of  deformation  of  the  Ouachita  orogenic  belt  is  believed 
to  be  post-Kickapoo.  As  cited  in  the  treatment  of  the  Ouachita  Moun- 
tains a  major  unconformity  across  the  Atoka,  McAlester,  Hartshorne,  and 


along   an   eastwest  section   from  the   Midland    basin   to 

Savanna  beneath  the  Roggy  shale  in  the  west  end  of  the  Arkansas  Valley 
is  believed  to  mark  the  time  of  main  deformation  in  the  Ouachitas.  This 
accords  with  Cheney  and  Goss's  interpretation  of  the  Pennsylvanian 
around  the  north  and  east  sides  of  the  Llano  uplift. 

West  Texas-New  Mexico  Region 

During  Permian  time,  the  foreland  area  in  front  of  the  Marathons  was 
divided  into  a  number  of  irregularly  shaped  provinces  which  received 


248 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


different  types  of  deposits  and  which  were  probably  tectonically  unlike. 
Refer  to  Figs.  14.1  and  15.12.  Some  were  basin  areas,  like  the  Delaware 
basin  in  which  a  total  of  10,000  feet  of  sediments  accumulated.  Others 
were  shelf  areas.  Akin  to  the  shelves  were  several  narrow  masses,  or 
platforms,  lying  between  the  basins.  The  basins  were  areas  of  greater 
subsidence;  the  platforms  and  shelves,  areas  of  lesser  subsidence.  The 
Central  Rasin  Platform  was  covered  with  2000-4000  feet  of  sediments, 
as  were  also  the  shelf  areas.  The  provinces  appear  to  have  been  inherited 
from  the  pre- Wolfcamp  foreland  features,  and  each  platform  is  underlain 
by  one  of  the  more  important  pre-Wolfcamp  uplifts.  The  Permian  tectonic 
features  may  have  been  formed  during  a  time  of  dominant  crustal  ten- 
sion, following  the  pre-Wolfcamp  time  of  dominant  crustal  compression 
(King,  1937).  The  basins  were  centers  of  accumulations  of  clastic  rocks, 
first  black  shales  and  later  sandstones,  and  the  total  thickness  of  beds 
deposited  in  them  was  greater  than  elsewhere.  Limestone  tended  to  form 
over  all  the  higher  standing  areas.  Landward,  because  of  climatic  condi- 
tions that  favored  evaporation,  evaporites  were  laid  down  in  the  fringing 
seas.  On  the  margins  of  these  seas,  red-beds  were  deposited  which  were 
derived  from  the  bordering  lands. 

The  subsidence  in  Permian  time  that  led  to  the  burial  of  the  Penn- 
sylvanian  ranges  also  resulted  in  the  burial  of  the  Matador  and  Amarillc— 
Wichita  ranges  to  the  north,  and  the  northern  part  at  least  of  the  folded 
and  thrust  Marathons.  Much  of  the  sediment  in  the  extensive  Permian 
basin  came  from  the  Ouachitas  which  were  actively  being  elevated  at 
this  time.  Some  debris  from  the  Marathons  reached  surprising  distances 
northward.  The  subsidence  was  regional  in  aspect  and  accentuated  the 
Concho  arch. 

Extending  across  the  larger  features  of  the  Marathon  foreland  and  im- 
parting a  distinctive  grain  to  their  surfaces  are  numerous  minor  tectonic 
features  in  which  the  linear  element  dominates.  These  include  the 
flexures  in  the  Guadalupe  Mountains  region,  the  minor  folds  on  which 

Fig.  15.11.  Concho  arch,  Bend  axis,  and  Llano  uplift,  after  Cheney  and  Goss,  1952.  Forma- 
tional  contacts  generalized.  Heavy  contours  are  isopachs  on  the  Paleozoic  interval  below  the 
Strawn  formation  and  illustrate  the  nature  of  the  resulting  Concho  arch  in  Mid-Pennsylvanian 
time. 


WICHITA  AND  ANCESTRAL  ROCKIES  SYSTEMS  AND  THE  TEXAS  FORELAND 


249 


Delaware    Basin 


Central 


Basin 


Platform 


Miolano 


Basin 


l-^I.-TriaVsic; 


Eastern  Platform 


CRtTACtOua? 


5a/odo 
Votes 
5even  Rivera 
Queen 

Croyburg 


3  an  Andre  3 


Clear  Fork  -  Wich/to 
£/o7fcomp 


^ffcon,p 


PfNNSYLVANIAN  -------^ 


-'-'_5trown 


SITE    OF   PECOS    RANGE,  ELEVATED     IN    EARLY    AND 
IN   LATE      rENNSTLVANIAN 


.Scale 


Fig.  15.12.      Principal  stratigraphic  units  and  structural  features  of  the  South   Permian  basin  of  New  Mexico 
and  Texas.  Line  of  cross  section  shown  on  map,  Fig.  14.1.  Taken  from  Plate  2,   King  ef  a/.,  1942. 


many  of  the  oil  fields  are  located,  and  various  faults.  Some  were  formed 
in  pre-Wolfcamp  time,  but  most  of  them  were  formed  during  the 
Permian.  Some  suffered  movement  again  in  the  Cenozoic.  They  may  be 
grouped  into  four  systems,  viz.,  northwest  trending,  northeast  trending, 
north-northwest  trending,  and  east-west  trending;  but  much  yet  remains 
to  be  learned  regarding  the  systems  because  those  mentioned  may  not 
be  natural  units  and  may  include  some  unrelated  features.  The  systems 
apparently  include  features  of  several  different  ages,  as  well  as  features 
that  were  formed  during  several  periods  of  movement. 

ANCESTRAL  ROCKIES  SYSTEM 

Major  Structural  Features 

A  group  of  imposing  uplifts  in  Colorado  and  New  Mexico  of  Penn- 
sylvanian  age,  the  Ancestral  Rockies,  has  long  been  known.  Considering 


the  far  greater  length  and  breadth  of  the  modern  Cordillera  known  as 
the  Rocky  Mountains,  the  Ancestral  Rockies  only  partially  deserve  their 
name.  Deep  basins  are  associated  with  the  uplifts,  and  collectively  repre- 
sent a  rather  important  orogenic  system  in  the  foreland.  The  Ancestral 
Rockies  are  separated  from  the  Wichita  system  and  the  Texas  foreland 
chiefly  for  purposes  of  discussion,  but  probably  are  continuous  with  and 
intimately  related  to  them. 

By  reference  to  the  map  of  Fig.  6.7  the  several  uplifts  of  the  Ancestral 
Rockies  and  the  adjacent  basins  may  be  seen.  Two  of  these,  the  Un- 
compahgre  and  Colorado,  were  particularly  bold  and  high.  The  Colorado 
Range  is  frequently  referred  to  as  the  Front  Range  highland.  The 
Pedernal  uplift  is  not  yet  very  well  defined,  but  seems  to  be  an  emergent 
area  in  east-central  New  Mexico  which  connects  southward  with  the 
Diablo  uplift.  The  Zuni  uplift,  like  the  Pedernal,  seems  to  have  been  wide 
and  not  particularly  high. 


250 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


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UNCOMPAHGRE 
UPLIFT 


Fig.  15.13.      Pennsylvanian  deposits  of  the  Paradox  basin.  After  Herman  and  Barkell,  1957. 

Pre-Pennsylvanian  Setting 

The  total  thickness  of  the  Paleozoic  formations  present  in  central 
Colorado  by  the  end  of  Lower  Mississippian  (Leadville)  time  was  only 
1000  feet.  In  southwestern  Colorado,  only  400-500  feet  existed,  and  in  the 
northern  part  of  the  Front  Range,  they  were  still  thinner.  Since  the  fairly 
pure  Mississippian  limestones  occur  in  areas  close  to  the  Pennsylvanian 
ranges  and  no  lithologic  changes  are  evident  in  the  limestones  as  the 
ranges  are  approached,  the  Mississippian  seas  probably  spread  over  the 
sites  of  the  highlands  (Lovering,  1933). 

Evidence  of  thinning,  probably  by  erosion,  is  evident  when  isopachs 
are  worked  out,  and  it  appears  that  some  of  the  ranges  first  began  to  be 
expressed  in  latest  Mississippian  time,  as  illustrated  in  Fig.  6.6.  The  New 
Mexico  arch  of  Mississippian  age  exposed  Precambrian  rock  over  much 
of  central  New  Mexico. 

Uncompahgre  and  Colorado  Ranges 

The  Uncompahgre  and  Colorado  ranges  were  flanked  by  basins  as 
indicated  on  the  map  of  Fig.  6.7;  the  Paradox,  the  Central  Colorado,  and 
the  Denver.  The  extreme  and  abrupt  facies  changes  of  sediments  de- 
posited against  their  flanks  is  the  evidence  of  the  sharp  uplifts.  One  of 
the  flanking  basins,  the  Paradox,  is  illustrated  in  Fig.  15.13.  The  south- 


west margin  of  the  Uncompahgre  Range  was  a  fault  scarp,  and  the  thin 
pre-Pennsylvanian  sedimentary  veneer  was  soon  stripped  from  the  rising 
block,  with  the  Precambrian  crystallines  furnishing  flood  deposits  of 
arkose  to  the  adjacent  subsiding  basin.  During  part  of  Pennsylvanian 
time  evaporite  conditions  prevailed  and  four  evaporite  sequences — 
cyclothems — resulted  (Herman  and  Rarkell,  1957).  This  part  of  the 
Hermosa  formation  is  the  Paradox  facies  or  member. 

The  Molas  is  Atoka  in  age  and  the  Hermosa  spans  the  Des  Moines, 
Missouri,  and  Virgil.  The  Cutler  extends  on  into  the  Permian.  The  time 
of  the  most  vigorous  uplift,  then,  is  clearly  Atokan  through  to  the  begin- 
ning of  the  Permian. 

The  Pennsylvanian  and  Permian  sediments  overlap  the  gently  beveled 
edges  of  the  older  Paleozoic  rocks  and  rest  on  Precambrian  crystallines 
in  the  cores  of  the  old  ranges  ( Lovering,  1933;  Rurbank,  1933;  Glockzin 
and  Roy,  1945).  See  Fig.  15.14.  The  crystalline  rock  was  the  source  of 
many  of  the  Pennsylvanian  and  Permian  strata  which  are  commonly 
coarse  and  arkosic  near  the  old  landmasses.  For  instance,  Rrill  (1944) 
describes  the  sediments  of  the  central  Colorado  basin  as  consisting  mostly 
of  red  and  gray  arkoses,  arkosic  conglomerates,  sandstones,  siltstones,  and 
gypsum  which  thicken  to  13,000  feet  in  the  deepest  part  of  the  basin. 
Lateral  variations  are  abrupt  and  extreme.  During  the  most  active  time 
of  uplift  of  the  adjacent  ranges,  the  coarse  elastics  were  deposited  as 
deltas  along  the  margins  of  the  trough,  and  the  fine-grained  sediments 
were  carried  into  the  center.  Identical  mineral  assemblages  in  the  elastics 
on  both  sides  of  the  basin  indicate  that  the  exposed  bedrock  of  both  the 
Uncompahgre  and  the  Colorado  Range  was  much  the  same. 

Pedemal  Uplift 

The  Pedernal  landmass,  named  by  Thompson  (1942)  from  the  Pedemal 
Hills,  is  a  large  north-south-trending  range  in  east  central  New  Mexico, 
about  midway  between  the  Rio  Grande  and  the  Pecos  rivers.  Red  shales, 
sandstones,  variegated  shales,  and  limestones  of  Permian  age  rest  directly 
on  igneous  and  metamorphic  rocks  of  Precambrian  age  in  an  area  ex- 
tending  from   the   eastern   side   of   the   Sacramento    Mountains,   Otero 


WICHITA  AND  ANCESTRAL  ROCKIES  SYSTEMS  AND  THE  TEXAS  FORELAND 


251 


WEST 


cast 


f\/w\/\  /  \  /  \ 

7  \~/\  /\/\  /  \/ 


V  \"/  \"/  \"/  \~/  \~/  \"/  O  \"7  \  /  w  \~  \~/  T/  ~/  ~/  ~/  \  /  \  /  \7  w  w  w  "/ \7  \~/  \"/  w  ~/  w  y~/  \~/  \  /  \~/  \  /  w  \  /  \  /  \ /  \7  \  /  s  /  -.  /  \  /  \  /  \  /  \/  \  / \~/  \  /  \  /  \~  w  s  /  \  /  \  ^  \  /  \  /  \  /  s /  \~  \  / 


Fig.  15.14.  Idealized  section  after  Lovering  (1929)  of  the  Colorado  Range  near  the  close  of 
Pierre  time  (Upper  Cretaceous)  and  before  deformation  during  the  Laramide  revolution.  Kp, 
Pierre  sh.;  Kn,  Niobrara  Is.;  Kb,  Benton  sh.;  Kd,  Dakota  Si.;  Jm,  Morrison  fm.;  Je,  Entrada  ss.;  Js, 
Sundance   fm.;   Cp,    Belden   sh.;   Maroon   fm.    (Des  Moines)   and   State   Bridge   siltstone    (Permian); 

County,  apparently  continuously  to  northern  Torrance  County.  Very 
coarse  conglomerates  with  cobbles  of  quartzite  and  other  metamorphic 
rocks  are  present  in  the  Pennsylvanian  rocks  in  the  Sacramento  Moun- 
tains on  the  west  side  of  the  uplift.  From  these  and  other  similar  data, 
Thompson  concludes  that  the  Pedernal  Range  was  in  existence  from 
early  Pennsylvanian  time  until  well  after  the  beginning  of  Permian  time. 

The  Colorado  Range  probably  extended  southward  into  New  Mexico 

through  Colfax  and  Mora  counties.  Very  thick  sections  of  Pennsylvanian 

j   rocks  of  Des  Moines  age  or  older  crop  out  on  the  eastern  edge  of  the 

|   Sangre  de  Cristo  Range  from  the  region  of  Pecos  River  almost  to  the 

!  Colorado  border.  These  rocks  include  arkoses,  arkosic  conglomerates  and 

I  sandstones,  and  black  shales. 

i 

i 

1   Zuni  Uplift 

In  northwestern  New  Mexico  and  northeastern  Arizona  evidence  of 

Pennsylvanian  uplift  is  noted  in  the  modern  Zuni  and  Defiance  ranges. 

With  additional  subsurface  evidence  from  drilling  the  configuration  of 

;   the  range  appears  to  be  like  that  illustrated  in  Fig.  6.7.  Red  sandstones 

and  shales  identified  as  the  Permian  Ajo  formation  rest  on  Precambrian 


Cml,  Leadville  Is.  (Mississippian  ?);  DO,  Devonian  and  Ordovician  formations;  Cs,  Sawatch 
quartzite;  Cpf  and  Cpl,  Fountain  fm.  and  Lykins  fm.  (Pennsylvanian  and  Permian  ?  red  arkosic 
ss.  and  congl.);  Cmm,  Millsap  fm.  (Mississippian);  Ofhm,  Fremont  Is.  (Ordovician);  Cq,  Cambrian 
quartzite.  Vertical  scale  exaggerated  and  relative  thicknesses  of  formations  only  approximate. 

crystalline  rock  in  the  Zuni  Range,  and  the  Permian  Moenkopi  formation 
rests  on  the  crystallines  in  the  Defiance  Range.  The  old  uplift  is  desig- 
nated both  as  the  Zuni  and  Defiance,  but  Zuni  seems  to  be  preferred. 

Florida  Uplift 

In  the  Florida  Mountains  of  southwestern  New  Mexico,  Permian  lime- 
stone rests  on  Ordovician  limestone;  and  a  short  distance  to  the  north 
in  the  Cooks  Range,  the  Permian  rests  on  Mississippian  limestone.  The 
absence  of  Pennsylvanian  strata  is  due  to  a  Pennsylvanian  or  post-Penn- 
sylvanian  disturbance,  probably  at  the  same  time  as  those  in  the  south 
end  of  the  Hueco  Mountains  and  the  Diablo  Mountains  near  El  Paso. 
The  direction  in  which  the  elevated  land  trends  is  believed  to  be  south- 
easterly. It  will  be  called  the  Florida  Range. 

Burial  of  the  Ancestral  Rockies 

During  Triassic,  Jurassic,  and  Cretaceous  time  the  Ancestral  Rockies 
were  gradually  buried  by  accumulating  sediments.  Immediately  around 
them  were  their  own  waste  products,  but  marine  epeiric  seas  brought 
carbonates  and  fine  elastics  from  adjacent  regions,  and  these  sediments 


252  STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 

helped  in  the  burial  process.  Jurassic  desert  conditions  brought  great  the  early  Upper  Cretaceous  before  the  last  peaks  were  drowned.  See 

volumes  of  wind-transported  sand  from  the  western  Cordilleran  geanti-  Fig.  15.14.  Ry  this  time  the  early  manifestations  of  crustal  unrest  in  the 

cline.  Rocky  Mountains  are  evident,  and  the  old  buried  ranges  with  over- 

The  Zuni  and  Pedernal  uplifts  were  buried  by  the  Permian  deposits,  tying  sediments  were  considerably  deformed.  An  array  of  new  super- 

the  Uncompahgre  lasted  in  a  number  of  small  islands  until  late  Jurassic  posed  structures  and  ranges  developed,  which  will  be  reviewed  in  later 

before  final  burial,  and  the  Colorado  Range  lasted  until  Pierre  time  in  chapters. 


16. 


THE  LATE  PALEOZOIC 
ZONES  OF  FAULTING 
AND  CRYPTOVOLCANIC 
OR  METEORITE 
IMPACT  STRUCTURES 

FORELAND  ARCUATE  FAULT  ZONE 

An  arcuate  zone  of  faults  extends  from  the  Llano  dome  in  Texas  north- 
ward to  Oklahoma,  northeastward  to  the  Ozark  dome  and  eastward  across 
Kentucky  to  West  Virginia.  The  faults  are  subparallel  with  the  zone  for 
the  most  part,  but  some  are  divergent,  especially  two  long  faults  in  Mis- 
souri which  strike  northwestward  directly  athwart  the  zone.  See  Tectonic 
Map  of  the  United  States,  1944.  The  zone  crosses  domes  and  basins  alike, 
and  therefore  does  not  seem  to  be  controlled  by  them.  On  the  other  hand, 
the  fault  zone  wraps  around  the  Ouachita  arc  of  the  marginal  orogenic 
belt  of  the  continent,  and  although  the  fault  zone  has  a  lesser  curvature 


than  the  Ouachita  arc  and  departs  from  it  a  considerable  distance  on  the 
north,  the  subparallelism  may  mean  that  a  genetic  relationship  exists. 

Most  of  the  faults  are  known  to  have  originated  in  Pennsylvanian  time 
or  immediately  thereafter.  A  few  others  are  post-Devonian.  Thus  the  time 
relation  as  well  as  the  spatial  indicates  that  the  zone  of  faults  is  a  single 
tectonic  element. 

The  faults  in  the  Llano  uplift  are  known  from  surface  mapping.  Oil 
wells  and  geophysical  prospecting  have  extended  the  known  length  of 
some  of  the  faults  more  than  100  miles  to  the  north-northeast  into  the 
Strawn  basin  (Cheney,  1940).  The  faults  are  probably  of  the  high-angle, 
normal  variety,  and  have  blocked  out  narrow  grabens  and  horsts.  The 
high  blocks  have  been  named  from  west  to  east,  the  Richland  Springs, 
Pontotoc,  San  Saba,  and  Lampasas  axes.  According  to  geophysical  work 
in  the  Fort  Worth  basin,  some  of  these  faults  have  displaced  the  Smith- 
wick  formation  1100  feet,  so  the  movement  occurred  in  post-Smithwick 
(Early  Pennsylvanian)  time.  However,  beds  only  slightly  younger  than 
Smithwick,  namely  middle  Strawn,  are  only  slightly  disturbed  along  a 
major  fault  near  Regency  in  the  Colorado  River  area,  and  the  faults  are 
not  known  in  still  younger  Pennsylvanian  beds.  Cheney,  therefore,  con- 
cludes that  the  faulting  in  the  Llano  dome  and  Strawn  basin  occurred 
in  early  Pennsylvanian  time. 

The  Stonewall  fault  in  the  Hunton  arch  area  of  southern  Oklahoma  is 
said  to  have  occurred  in  about  middle  Strawn  time  and  to  have  a  displace- 
ment of  about  3500  feet  (Morgan,  1924),  but  from  Dott's  (1934)  discus- 
sion the  fault  may  be  one  of  the  Arbuckle  group  of  thrust  faults  and  not  a 
part  of  the  arcuate  fault  zone. 

A  group  of  faults  in  the  northeastern  corner  of  Oklahoma  bound  six 
small  crustal  blocks,  each  about  6  miles  wide  (Wilson,  1937).  The  faults 
trend  in  general  northeastward,  and  some  have  been  traced  for  50  miles. 
One  block  is  tilted  to  the  north;  two  are  tilted  to  the  south,  and  the  re- 
maining three  are  about  level.  Their  throws  range  from  90  to  600  feet,  but 
these  figures  apply  only  to  surface  offsets.  The  faults,  as  well  as  the  folds 
in  this  region,  become  more  pronounced  in  the  older  underlying  forma- 
tions. Where  it  is  possible  to  trace  the  stratigraphy  at  depth  by  oil  wells, 
the  structural  relief  decreases  upward  through  the  conformable  sand- 


253 


254 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


stones  and  shales  of  the  Atoka,  Hartshorne,  McAlester,  Savanna,  and 
Boggy  formations.  Bloesch  (1919)  believed  that  this  decrease  is  due  to 
recurring  deformation  during  the  deposition  of  the  above  formations, 
which  are  of  the  late  Early  Pennsylvanian  age. 

North  of  the  six  fault  blocks  and  parallel  with  them  is  the  hundred- 
mile-long  Seneca  fault.  It  extends  into  the  southwest  corner  of  Missouri. 
Surface  evidence  for  the  fault  is  not  conclusive  everywhere  along  the 
structure,  and  it  may  be  a  syncline  rather  than  a  fault  in  several  places 
(Weidman,  1939). 

Several  rows  of  small  faults  are  well  known  in  Creek  and  Osage  coun- 
ties, Oklahoma,  just  west  of  the  previously  mentioned  Seneca  fault.  The 
individual  faults  are  arranged  en  echelon  and  trend  northwest.  The  rows 
trend  nearly  north  and  make  an  angle  of  about  45  degrees  with  the  in- 
dividual faults.  On  Plate  8  the  rows  are  indicated  by  dashed  lines.  The 
largest  stratigraphic  throw  at  the  surface  is  about  130  feet,  and  the  great- 
est length  is  3/4  miles;  yet  the  length  of  one  of  the  rows  is  80  miles.  They 
are  all  normal  faults. 

Fath  (1920)  analyzed  the  en  echelon  faults  as  follows.  The  Precam- 
brian  crystalline  rocks  were  cut  by  a  system  of  faults  before  the  Paleozoic 
veneer  of  sediments  was  laid  down.  In  fact,  peneplanation  had  removed 
most  of  the  relief  incident  to  the  faulting  before  the  Paleozoic  beds  started 
to  accumulate.  Beginning  in  Early  Pennsylvanian  time,  the  faults  in  the 
basement  complex  again  became  active,  this  time,  however,  with  hori- 
zontal (strike-slip)  movement.  The  overlying  veneer  was  shear-strained 
along  the  underlying  faults  and  broke  in  rows  of  small  faults  arranged 
en  echelon.  The  east  side  of  each  fault  in  the  Precambrian  moved  north- 
ward. The  movement  recurred  several  times  during  the  Pennsylvanian,  so 
that  the  throw  of  the  faults  is  greater  at  depth.  Some  rows  of  en  echelon 
faults  may  not  even  show  in  the  Pennsylvanian  beds  at  the  surface  today, 
and  others  are  reflected  in  small  asymmetrical  anticlinal  flexures  over  the 
faults.  Several  such  rows  of  anticlines  farther  west  in  Oklahoma  and  north 
in  Kansas  may  belong  to  the  same  system. 

The  postulate  that  the  great  arcuate  fault  zone  is  related  to  the  Ouach- 
ita lobe  of  the  marginal  orogenic  belt  is  supported  by  Fath's  mechanical 
analysis.  As  would  be  expected  in  this  theory,  the  foreland  block  directly 


in  front  of  the  lobe  would  be  moved  horizontally  ahead  of  its  left-hand 
neighbor,  which  is  the  direction  of  shear  indicated  by  the  en  echelon 
faults. 

In  eastern  Missouri,  two  stages  of  faulting  are  recognized  (Weller  and 
St.  Clair,  1928),  one  in  late  Devonian  and  one  in  post-Mississippian.  The 
faults  form  a  complex  system,  and  the  total  displacement  in  the  fault  zone 
ranges  up  to  1200  feet. 

The  eastern  Missouri  faults  continue  eastward  across  the  southern  tip 
of  Illinois  into  Kentucky,  where  a  region  of  widespread  and  intensive 
faulting  exists.  Along  the  north  side  of  this  complex  of  faults  is  the  Shaw- 
neetown  fault  of  southern  Illinois,  and  its  eastward  continuation,  the 
Rough  Creek  fault  zone  of  Kentucky.  The  Shawneetown-Rough  Creek 
fault  zone  is  really  an  uplift  that  varies  in  structural  relief  and  detail  from 
place  to  place  (McFarlan,  1943).  Most  characteristic  of  the  uplift  is  its 
anticlinal  structure.  At  places,  a  series  of  anticlines  is  developed,  in  part 
asymmetrical  to  the  north  and  broken  to  form  reverse  faults.  Normal  faults 
arranged  en  echelon  are  also  present.  The  structural  relief  of  the  uplift 
ranges  from  a  few  hundred  feet  to  2500  feet,  and  Mississippian  beds  in 
places  are  brought  into  outcrop.  The  complex  structural  zone  divides  the 
Pennsylvanian  coal  basin  into  a  northern  and  a  southern  division. 

Just  south  of  the  Shawneetown-Rough  Creek  structure  in  western  Ken- 
tucky is  a  cluster  of  high-angle  faults,  the  main  ones  of  which  trend  north- 
east and  east  and  have  displacements  up  to  1500  feet.  They  are  joined  by 
smaller  cross  faults.  The  area  is  semicircular,  about  60  miles  in  diameter, 
and  is  the  most  intensely  faulted  area  in  the  interior  lowlands.  Along  with 
the  faults,  peridotite  dikes  and  highly  commercial  veins  of  fluorspar  occur. 
The  faults  are  post-Pennsylvanian  and  pre-Cretaceous. 

The  Rough  Creek  fault  zone  is  continued  after  a  gap  of  a  few  miles  to 
central  and  eastern  Kentucky  by  the  Kentucky  River  fault  and  its  asso- 
ciates, the  West  Hickman  fault,  the  Irvine-Point  Creek  fault,  and  other 
smaller  ones  (McFarlan,  1943).  Maximum  displacement  on  the  Kentucky 
River  fault  is  600  feet.  Some  suggestion  of  pre-Pennsylvanian  movement 
and  progressive  movement  has  been  made,  but  McFarlan  believes  the 
faulting  occurred  in  post-Pennsylvanian  time. 


LATE  PALEOZOIC  ZONES  OF  FAULTING  AND  CRYPTOVOLCANIC  OR  METEORITE  IMPACT  STRUCTURES 


255 


LAKE  SUPERIOR  FAULT  ZONE 

The  Tectonic  Map  of  the  United  States  shows  a  group  of  long  and 
subparallel  faults  extending  from  the  Lake  Superior  region  southwest- 
ward  into  Wisconsin  and  Minnesota.  The  Keweenawan  fault  is  probably 
the  best  known.  It  runs  lengthwise  and  approximately  in  the  center  of 
the  Keweenawan  peninsula  of  Michigan  and  separates  the  copper-bearing 
Keweenawan  volcanic  series  from  the  Cambrian  (?)  sandstones.  The  fault 
is  clearly  a  thrust  in  one  exposure  near  Houghton,  but  probably  a  fairly 
high-angle  one,  with  the  Keweenawan  series  displaced  southwestward 
over  the  Cambrian  (?)  sandstone. 

North  of  the  Keweenawan  fault,  the  volcanic  series  is  downfolded  into 
a  broad  syncline  with  dips  on  the  southeast  flank  of  about  30  degrees. 
The  beds  rise  and  crop  out  on  Isle  Royal  in  Lake  Superior.  A  fault  which 
cuts  the  north  flank  of  the  syncline  has  been  postulated  just  north  of  Isle 
Royal.  This  northern  fault  has  been  connected  with  the  Douglas  fault, 
which  runs  almost  east-west  south  of  Superior,  Wisconsin,  and  which, 
according  to  Thwaites  (1912,  1935)  dips  38  to  60  degrees  southward.  He 
believes  the  south  block  has  been  thrust  northward  6  to  12  miles.  The 
Douglas  fault  swings  southward  after  entering  Minnesota,  and  there  it 
has  been  studied  by  geophysical  means.  Near  Pine  City,  the  fault  is 
believed  to  be  nearly  vertical,  with  the  east  side  upthrown  about  9000 
feet  (Welch,  1941). 

The  great  syncline  between  the  oppositely  dipping  Keweenawan  and 
Douglas  faults  is  thought  by  Thwaites  to  contain  numerous  minor  folds 
in  Wisconsin  and  hence  to  be  a  synclinorium.  The  structure  is  discussed 
in  Chapter  4  and  illustrated  in  Figs.  4.3  and  4.7.  He  also  states  that  part 
of  the  displacement  could  have  occurred  in  late  Keweenawan  time,  but 
that  part  of  it  probably  occurred  later.  The  complementary  relation  of 
the  Keweenawan  and  Douglas  faults  suggests  they  are  of  the  same  age. 
The  syncline  in  the  Keweenawan  peninsula  region  appears  to  have  sub- 
sided partly  at  the  time  the  volcanic  flows  and  conglomerates  were  ac- 
cumulating, according  to  Broderick  (personal  communication),  but 
considerable  faulting  undoubtedly  occurred  later.  Thwaites  ( 1943 )  agrees 
in  substance  with  this  view. 


A  fault  along  the  north  coast  of  Lake  Superior  has  been  surmised, 
chiefly  on  physiographic  evidence  (Martin,  1908),  but  this  is  not  sup- 
ported by  gravity  surveys. 

Ten  miles  southeast  of  the  Keweenawan  fault  in  Michigan,  two  hills, 
Limestone  Mountain  and  Sherman  Hill,  are  made  up  of  a  basal  sandstone 
and  overlying  dolomites  and  limestones.  The  sandstone,  according  to 
Case  and  Robinson  (1915)  is  either  Cambrian  or  Lower  Ordovician,  and 
the  limestones  and  dolomites  are  Ordovician,  Silurian,  and  Devonian. 
According  to  Thwaites  (1943)  the  sandstone  is  Upper  Keweenawan,  and 
the  dolomites  and  limestones  are  Trenton-Black  River.  The  strata  are 
cut  by  small  faults  and,  along  the  east  side,  exhibit  dips  up  to  55  degrees. 
A  major  fault  may  exist  along  the  east  margin,  and  the  high  dips  may  be 
drag  along  the  fault  which  would  be  approximately  parallel  with  the 
Keweenawan.  The  Ordovician  beds  in  Limestone  Mountain  are  80  miles 
from  the  nearest  Ordovician  outcrops;  and  the  Devonian,  if  present,  150 
miles  from  the  nearest  Devonian  outcrops. 

Dating  the  faults  in  Limestone  Mountain  and  Sherman  Hill  is  difficult 
because  of  lack  of  agreement  on  the  age  of  the  sandstones  associated  with 
them  (Cambrian  or  Precambrian ) ,  and  the  extensive  swamp  and  drift 
cover  that  prevents  working  out  the  geologic  relations.  Opinion  seems 
to  favor  an  early  episode  of  subsidence  in  which  the  Keweenawan  basins 
were  formed,  and  a  later  episode  of  faulting  in  which  the  Paleozoic  rocks 
were  affected. 

The  disposition  of  an  immense  amount  of  material  that  came  from 
the  truncation  of  thousands  of  feet  of  Keweenawan  strata  along  the 
Douglas  and  Keweenawan  faults  poses  another  problem.  If  most  of  the 
movement  were  Precambrian,  representative  deposits  possibly  should 
occur  in  the  Cambrian,  but  the  orogenic  waste  products  do  not  seem 
to  make  up  any  of  the  Paleozoic  rocks  nearby  in  Wisconsin  or  Michi- 
gan. 

If  all  but  a  small  part  of  the  faulting  were  Precambrian  and  associated 
with  the  downfaulting  of  a  basin  in  which  the  Keweenawan  series  ac- 
cumulated, and  if  the  Keweenawan  series  is  1100  m.y.  old  as  recounted 
in  Chapter  4,  then  during  the  next  500  m.y.  before  the  basal  Cambrian 
sands  were  spread  across  the  region,  all  relief  could  have  disappeared. 


256 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


and  the  Cambrian  sediments  need  not  necessarily  contain  the  Kewee- 
nawan  lithologies. 

CRYPTOVOLCANIC  OR  METEORITE  IMPACT  STRUCTURES 

Definition 

Eight  small  circular  structures,  one  of  known  volcanic  origin,  and  the 
others  supposedly  of  volcanic  origin,  have  been  mapped  in  the  Central 
Stable  Region  of  the  United  States,  and  possibly  a  ninth  one  in  the 
Colorado  Plateau  of  Utah.  See  map  of  Fig.  16.1.  They  are  described  by 
Bucher  (1933)  as  characterized  by  a  nearly  circular  outline,  a  central 
uplift  with  intense  structural  derangement,  and  a  marginal,  ring-shaped 


Fig.  16.1.  Cryptovolcanic  or  meteorite  impact  structures  in  the  United  States.  1,  Jeptha  Knob, 
Shelby  County,  Ky.;  2,  Serpent  Mount  structure,  Adams  and  Highland  counties,  O.;  3,  Flynn 
Creek  disturbance,  Tenn.;  4,  Wells  Creek  basin,  Houston  and  Stewart  counties,  Tenn.;  5, 
Decaturville  structure,  Camden  and  Maclede  counties,  Mo.;  6,  Kentland  structure,  Newton 
County,  Ind.;  7,  Magnet  Cove,  Hot  Springs  County,  Ark.;  8,  Upheaval  dome,  San  Juan  County, 
Ut.  After  Bucher,   1933.  9,  Manson,   la. 


Fig.  16.2.  Geologic  map  of  the  Wells  Creek  basin,  Tenn.  Reproduced  from  Bucher,  1933.  1, 
Wells  limestone  (L.  Ordovician);  2,  mid-Ordovician  limestone;  3,  Hermitage  formation  (mid- 
Ordovician);  4,  Silurian  and  Devonian  formations;  5,  Lower  Mississippian  formations;  6,  War- 
saw limestone  (mid-Mississippian);  7,  St.  Louis  limestone  (mid-Mississippian);  8,  alluvium. 


LATE  PALEOZOIC  ZONES  OF  FAULTING  AND  CRYPTOVOLCANIC  OR  METEORITE  IMPACT  STRUCTURES 


257 


depression  with  irregular  and  local  faulting.  Including  the  marginal  ring, 
they  range  in  diameter  from  2  to  8  miles.  The  inner  intensely  deranged 
core  may  be  only  part  of  a  mile  across  in  some,  but  in  others  up  to  2 
miles. 

The  faults  make  both  an  approximate  concentric  pattern  and  a  radial 
pattern.  In  some,  the  radial  pattern  is  resolved  strongly  into  a  northwest- 
southeast  direction.  Examine  the  representative  illustrations  of  Figs.  16.2 
and  16.3. 

i  Distribution 

The  map  of  Fig.  16.1  shows  the  distribution  of  the  cryptovolcanic 
structures.  Numbers  1  to  6,  and  9  are  in  the  general  arch  and  dome  area 
of  the  central  Mississippi  Valley.  Numbers  1  to  4  are  in  the  Cincinnati 
and  Nashville  domes,  number  5  in  the  Ozark  dome,  and  number  6  in  the 
|  Kankakee  arch.  They  avoid  the  Illinois  basin  fairly  well.  Number  7  is 
I  in  the  orogenic  belt  of  the  Ouachita  Mountains,  but  it  is  dissimilar  to 
the  rest  in  having  igneous  rocks  exposed  in  the  core,  in  being  free  of 
faults,  and  in  being  the  site  of  considerable  mineralization.  See  Fig.  14.2. 
Number  8  is  in  the  Colorado  Plateau  and  is  complexly  associated  with 
salt  dome  upheaval. 

Origin  and  Age 

No  volcanic  rocks  are  associated,  at  least  at  the  surface,  with  the  small 
circular  structures  of  the  Central  Stable  Region,  yet  their  circular  shape, 
their  upheaved,  broken,   and  in  places   brecciated  condition,   and  the 

J  presence  of  a  number  of  dikes  cutting  the  near  horizontal  Paleozoic  rocks 
in   surrounding   areas,   lead   Rucher  to   imagine   an   explosive  volcanic 

i  origin. 

These  cryptovolcanic  structures  are  thought  to  be  the  result  of  a  sudden  lib- 
eration of  pent-up  volcanic  gases,  which  had  accumulated  near  the  surface,  the 
;  explosion  having  been  too  weak  to  produce  a  shallow  crater  such  as  formed  in 
]  the  Ries  Basin,  southern  Germany  (Bucher,  1933). 

These  unique  structures  in  the  United  States  have  been  eroded  more 
than  those  of  Tertiary  age  in  Germany,  and  so  Rucher  regards  them  as 
older  and  of  probable  late  Paleozoic  or  Mesozoic  age. 


Fig.    16.3.      Structure   contour   map   of   Serpent   Mound,   O.   The    length    of   each    square    is   about 
2200  feet.  Reproduced  from  Bucher,  1933. 

Recently  a  new  cryptovolcanic  (?)  structure  has  been  found  near 
Manson,  Iowa.  It  is  number  9  on  Fig.  16.1.  Unlike  the  others  it  has  a 
Precambrian  crystalline  core  about  lM  square  miles  in  area  which  lay 
unknown  because  of  a  cover  of  glacial  drift  until  discovered  by  core 
drilling  (Hoppin  and  Dryden,  1958).  In  this  area  a  thin  Paleozoic  veneer 
of  sedimentary  rocks  plus  a  cover  of  Cretaceous  shale  is  the  normal 
expectation  under  the  drift.  The  contact  of  the  crystalline  rock  with  the 
surrounding  sedimentary  rocks  dips  outward  350  feet  per  mile  to  the 


R.  17  W. 


t-       If       L.    1    ft 

-,   V     r     v      B 


Fig.  16.4.  Geologic  map  of  Magnet  Cove,  Arkansas.  Reproduced  from  Bucher,  1933;  after  Landes,  1931. 
1,  Pleistocene  (T,  tufa);  2,  sandstone  and  shale  (Mississippian);  3,  novaculite  (Devonian);  4,  metamorphosed 
sandstone  and  shale;  5,  metamorphosed  limestone;  6,  igneous  rocks  (M,   magnetite). 


LATE  PALEOZOIC  ZONES  OF  FAULTING  AND  CRYPTOVOLCANIC  OR  METEORITE  IMPACT  STRUCTURES 


256 


southeast  and  290  feet  per  mile  to  the  west.  The  relief  of  this  rather 
sharp,  small  dome  is  at  least  1500  feet.  Surrounding  the  crystalline  core 
is  a  "disturbed  area"  20  miles  in  diameter  in  which  the  sedimentary  rocks 
are  severely  deformed.  Mississippian  limestone  and  Lower  ( ? )  Cretaceous 
shale  have  been  sampled  in  drill  cores  in  the  disturbed  area,  and  there- 
fore the  structure  was  formed  in  post-Early  Cretaceous  time.  The  upper 
200  feet  of  the  Precambrian  rock  beneath  the  drift  is  badly  shattered. 

The  writers  believe  that  the  crystalline  rock  was  forced  upward  into 
the  limestone  and  shale,  and  in  the  process  was  badly  shattered.  The 
mechanism  responsible  is  postulated  to  be  a  hidden  igneous  intrusion. 

Magnet  Cove 

The  Magnet  Cove  structure  is  included  by  Rucher  in  his  resume  of 
cryptovolcanic  structures,  although  it  consists  of  an  elliptical  intrusive 
complex  about  3  miles  across  and  is  within  the  compressional  structures 
of  the  Ouachita  Mountains.  See  map  of  Fig.  16.4.  The  igneous  rocks  are 
alkaline,  and  for  the  most  part  belong  to  the  nephelite-syenite  group 
(Landes,  1931).  The  peripheral  intrusives,  which  are  more  resistant  to 
erosion  than  those  toward  the  center  of  the  complex,  form  a  circular  ring. 
Metamorphosed  sandstone  and  shale  border  the  intrusions  in  places. 

Some  time  after  the  folding  of  the  Ouachitas,  a  stock  of  highly  alkalic 
magma  was  intruded  into  the  Paleozoic  rocks,  and  then  either  by  differ- 
entiation or  through  separate  intrusions  several  rock  types  were  formed 
and  an  unusual  suite  of  minerals  was  emplaced.  Compounds  of  titanium 
are  especially  abundant. 

Upheaval  Dome 

The  Upheaval  dome  is  in  the  flat-lying  red-beds  of  the  Colorado 
Plateau  and  is  sharply  conical  with  a  surrounding  ring-like  syncline.  From 


the  axis  of  the  syncline  on  one  side  to  the  axis  of  the  syncline  on  tin- 
other  is  only  2  miles,  and  the  diameter  of  the  entire  affected  area  is  3 
miles.  The  White  Rim  sandstone  member  of  the  Cutler  formation  appears 
as  huge,  up-ended  blocks  the  size  of  a  house  in  the  highly  disturbed 
central  area  (McKnight,  1940),  and  the  cliff-making  Wingate  sandstone 
rings  a  spectacular  crater  about  a  mile  in  diameter. 

Roth  aeromagnetic  and  gravity  surveys  have  been  made  of  the  area. 
The  magnetic  contours  resolve  two  strong  and  symmetrical  highs,  one 
directly  over  the  Upheaval  dome  and  the  other  about  7  miles  to  the 
southeast.  The  gravity  survey  also  indicates  two  structures  in  about  the 
same  places  but  not  so  distinctly.  Joesting  and  Plouff  (1958)  conclude 
that  the  broad  magnetic  and  gravity  highs  each  require  the  rise  of  a 
mass  of  Precambrian  crystalline  rock  about  5  miles  in  diameter  2000 
feet  above  its  normal  position.  Salt  flow  emphasized  the  one  dome 
( Upheaval )  but  failed  to  materialize  for  some  unknown  reason  in  the 
other.  Lastly,  because  the  gravity  anomalies  are  not  entirely  satisfied  by 
the  salt  plug,  a  small  igneous  intrusion  into  the  salt  of  the  dome  is  postu- 
lated. The  process  took  place  in  several  steps  from  Permian  to  the 
Miocene.  Refer  to  "salt  anticlines"  in  Chapter  26  on  the  Colorado  Plateau. 

Meteorite  Impact  Origin 

With  the  space  age  has  come  increased  interest  in  terrestrial  meteorite 
impact  craters,  and  Dietz  (1960)  has  called  attention  to  this  theory  of 
origin,  especially  for  such  structures  as  Serpent  Mound  (Fig.  16.3)  and 
the  Wells  Creek  basin  (Fig.  16.2).  Evidence  for  the  impact  theory  comes 
from  the  presence  of  shatter  cones  (small  percussion  fractures  in  conical 
shape)  and  coesite  powder,  a  high  pressure  crystalline  form  of  silica, 
supposedly  generated  at  the  time  of  impact.  According  to  some  geologists, 
the  theory  is  gaining  much  favor. 


17. 


MESOZOIC  SYSTEMS 
ALONG  THE  PACIFIC 


WESTERN   NEVADA 

Central  and  western  Nevada  and  all  California  were  involved  in 
orogeny  during  the  Mesozoic  era,  and  the  index  map,  Fig.  17.1,  shows 
the  chief  areas  and  features  with  which  the  following  discussion  is  con- 
cerned. The  map  also  extends  eastward  to  central  Utah  where  late 
Mesozoic  disturbances  occurred.  These  will  be  discussed  in  Chapter  18. 

A  trough  of  geosynclinal  proportions  centered  in  western  Nevada  in 
Triassic  and  early  Jurassic  time.  It  has  already  been  referred  to  in  con- 
nection with  the  Permian  and  Mesozoic  geanticline  in  central  Nevada. 
See  tectonic  maps,  Plates  8,  9,  and  10.  In  general,  its  axis  probably  lay 
slightly  east  of  the  axis  of  the  Permian  trough.  In  the  Hawthorne  and 


Tonapah  quadrangles,  Nevada,  it  sank  and  received  a  total  thickness  of 
sediments  of  about  30,000  feet  (Muller  and  Ferguson,  1936).  The  sedi- 
ments are  predominantly  marine  elastics,  cherts,  and  limestones  with  a 
considerable  proportion  of  more  or  less  altered  pyroclastic  rocks  and 
lavas  in  the  lower  and  upper  parts  of  the  section. 

The  table,  Fig.  17.2,  shows  the  sequence  of  Mesozoic  formation  there 
and  elsewhere  in  western  Nevada,  California,  and  southern  Oregon. 
The  Lower  Triassic  Candelaria  formation  rests  with  marked  erosional 
unconformity  on  the  thin  Permian  sandstones  and  grits  and  in  places  on 
the  beveled  Ordovician  strata.  A  slight  disturbance,  therefore,  affected 
the  area  in  late  Permian  time  and  probably  reflects  greater  orogeny  in  the 
westward-lying  orogenic  belt.  During  the  deposition  of  the  Candelaria 
formation,  the  area  of  sedimentation  as  well  as  the  western  highland  were 
comparatively  quiet,  and  shales,  sandy  shales,  sandstones,  some  of  tuf- 
faceous  aspect,  and  scattered,  thin  layers  of  limestone  were  deposited. 
Then  marked  volcanism  and  orogeny  occurred  to  the  west  in  middle 
Triassic  time,  and  over  12,000  feet  of  strata,  chiefly  pyroclastics  and  lavas, 
accumulated.  This  group  of  rocks  is  known  as  the  Excelsior  formation. 
The  lavas  range  in  composition  from  andesite  through  quartz  latite  to 
rhyolite.  Alteration,  principally  epidotization  and  chloritization,  has  af- 
fected the  formation  over  wide  areas.  Volcanic  breccias,  especially  those 
containing  altered  andesite  fragments,  are  abundant;  and  in  some  sections 
they  exceed  the  effusive  rocks  in  amount.  In  the  Pilot  and  Excelsior 
ranges,  a  considerable  thickness,  estimated  to  exceed  8000  feet,  consists 
of  massively  bedded  chert.  Examination  under  the  microscope  shows  this 
rock  to  be  an  extremely  fine-grained  water-laid  tuff,  cemented  and  largely 
replaced  by  cryptocrystalline  quartz.  Interbedded  with  the  chert  are  dark 
tuffaceous  slate,  a  little  impure  sandstone,  and  some  lava  and  breccia. 

The  volcanics  were  then  subjected  to  erosion  for  a  time  but  not  much 
disturbed  before  the  thick  Upper  Triassic  sequence  accumulated.  Dark 
limestone  and  dolomite  predominate,  but  siliceous  argillite,  argillite, 
calcareous  shale,  shale,  and  chert  pebble  conglomerates  are  not  uncom- 
mon. These  beds  are  known  as  the  Luning  formation.  Above  the  limestone 
and  dolomite  sequence  are  420  feet  of  purple  to  black  shale  and  dark 
brown  limestone,  known  as  the  Gabbs  formation.  The  Gabbs  is  conforma- 


260 


MESOZOIC  SYSTEMS  ALONG  THE  PACIFIC 


261 


Fig.  17.1.  Index  map  showing  significant  features 
and  localities  of  Mesozoic  orogeny  in  the  western 
Cordillera.  G.P.,  Grants  Pass  quadrangle;  Med.,  Med- 
ford  quadrangle;  Winn.,  Winnemucca  quadrangle; 
Gol.,  Golconda  quadrangle;  Tobin,  Mt.  Tobin  quad- 
rangle; Moses,  Mt.  Moses  quadrangle;  Gun.  P.,  Gun- 
nison  Plateau. 


TERTIARY 


WINN 

GOL. 

TOBIN 

% 

MOSES 

» 

t 

OLCimcs 


IDAHO  

~ NEVADA  I   UTAH 


SIERRA    NEVADA    AND 
KLAMATH     BATHOLITHS 
AND     SATELLITES 


\ 


\ 


UINTA 

t     -*  * 

"\   »    \       t— • 


CANYON,     ; 
RANGE ,'     I 


IRON 
SPRINGS 
OISTRICJ--^ 


UTAH      _ 
~ARlZQN* 


\ 


\J 


ble  with  underlying  and  overlying  formations.  Deposition  was  continuous 
from  Triassic  to  Jurassic  time,  while  the  western  orogenic  belt  remained 
fairly  quiet.  Its  relief  was  evidently  low,  and  volcanism  is  not  recorded  in 
the  shales,  limestones,  and  sandstones  of  the  Sunrise  formation  which 
were  deposited  in  the  trough. 

At  this  stage  in  early  Jurassic  time,  the  sediments  of  the  trough  were 
sharply  folded  ( Ferguson  and  Muller,  1937 ) .  The  most  intense  deforma- 
tion was  approximately  coextensive  with  the  area  of  deposition  of  the 
Upper  Triassic  deposits.  The  orogeny  began  apparently  with  the  forma- 
tion of  a  marginal  trough  at  the  border  of  the  geosyncline.  In  the  trough, 


the  Dunlap  formation  of  Early  Jurassic  age  was  deposited.  It  consists 
dominantly  of  fanglomerate,  conglomerate,  and  sandstone  with  an  upper 
volcanic  member  of  andesitic,  quartz-latitic,  and  rhyolitic  composition. 
The  fanglomerates  and  conglomerates  were  derived  chiefly  from  the 
limestones  of  the  Luning  formation  and  only  locally  from  the  great  Ex- 
celsior volcanic  series.  The  Dunlap  has  been  observed  resting  on  upturned 
cherts  of  the  Excelsior  formation  with  an  angular  discordance  of  90  de- 
grees, and  also  to  be  truncating  folds  of  the  Luning  limestones.  The 
Dunlap  is  characteristically  an  orogenic  deposit,  and  Ferguson  and  Muller 
(1937)   recognize  a  continuation  of  deformation  during  its  deposition. 


262 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


These  movements  were  the  beginning  of  thrusting,  at  least  in  the  area  of 
former  deposition.  Later  compression  resulted  in  thrusting  on  a  large 
scale,  and  the  earlier  structures  were  greatly  complicated.  The  thrusting 
postdates  the  Dunlap  Lower  Jurassic  formation,  and  precedes  the  in- 


EUROPEAN 
STAGES 


MAESTR1CHTIAN 


CENOMANIAN 


HAUTERIVIAN 


VALANGINIAN 


BERRlASIAN 


(TITHONIAN) 
PORTLANDIAN 


KIMMERIDGIAN 


I 


WEST   SIDE 
SACRAMENTO 
VALLEY    AND 
COAST   RANGES 


MORENO 
FM 


Ws<" 


MORSE- 
TOWN 


U.S  KNOKVILLE 


EAST- 
CENTRAL 
CALIFORNIA 


MARIPOSA 
SLATE 


AMADOR 
GR 


EASTERN 

CALIFORNIA 

WESTERN 

NEVADA 


EXCELSIOR 

FM 

(VOLCANICS) 


CANOELARIA 


SOUTH- 
WESTERN 
OREGON 


GALICE     FM 


ROGUE     FM. 


DOTHAN    FM 


NORTH- 
EASTERN 
CALIFORNIA 


TTi'm'rTTfm.rr 


IINCHMANSS 


BICKNELL    SS 


UJ-IJJJJl 

VOLCANICS 


MORMON    SS. 


THOMPSON     LS 
FANT  ANDESITE 


HARGRAVE    SS 


LOWER  UPPER 

PLATE  PLATE 

FACIES       FACIES 


RASPBERRY  F 


WINNEMUCCA 


DUN  GLEN  F 


NATCHEZ 
PASS    FM 

PRIDA    FM 


CANE  SPRING 


FAVRET   FM 


Fig.  17.2.  Principal  Mesozoic  formations  of  California  and  western  Nevada.  West  side,  Sacra- 
mento Valley  and  Coast  Ranges,  taken  from  Irwin  (1957)  and  Briggs  (1953).  Potassium  argon 
dating  of  Nevadan  orogeny  by  Evernden  et  al.,  1957.  Jurassic  correlations  from  McKee  ef  al., 
1956.  Triassic  of  eastern  Nevada  from  Ferguson  and  Muller  (1937),  of  west-central  Nevada 
(Mount  Tobin  Quadrangle)  by  Muller  et  al.  (1951),  and  of  southwestern  Oregon  by  Wells  (1956). 


-         s^-r^ZLlW^&'^-J*!*       TH"     tH*J<<»          ■><>* 

_jas__ 

^S^'Ji==J-.=-S^'^ 

-7%-^    «*     Jd.                       "Rid         ^g-pSmygT**.  /M,J    L       ?^SS 

•  •••••  •.■•■•'-> -   -  . i  -  <•  °      - J_S i                ~   - 1 

^<7>  i  i  1 1 1  ' T~tsftii I  i  /s»J?*  <W  , ■  i»  nnrTT~i     i   i  i    i  1 1 1  nTi Tii  ft     ■  ■ ,     *■  ■ 

•'  * '  "  \/  //" *  *  i  •  i  •  '  •       * 


Fig.  17.3.  Cross  sections  in  the  Hawthorne  and  Tonopah  quadrangles,  reproduced  from  Ferguson 
and  Muller,  1949.  Top  section,  north  of  Garfield  Flat  showing  relation  of  Dunlap  formation  to 
Luning  and  Excelsior  formations.  Middle  section,  south  of  Sunrise  Flat,  Gabbs  Valley  Range, 
showing  thrusting  and  later  normal  faulting.  Bottom  section,  south  of  Redlich  siding,  showing 
relations  of  Ordovician  and  Permian  and  the  Excelsior  formation.  Symbols,  top  section:  Jdf, 
Dunlap  fanglomerate  and  congl.;  Jdg,  Dunlap  vols.;  Jds,  Dunlap  ss.;  Jdl,  Dunlap  Is.;  Ilu, 
Luning  upper  Is.;  lis,  Luning  slate;  Teg,  Excelsior  vols.;  Tec,  Excelsior  chert  and  tuff.  Middle 
section;  Jdv,  Dundap  vols.;  Jds,  Dunlap  ss.;  Jdc,  Dunlap  congl.;  lid,  Luning  dol.;  Jdt,  thrust 
cong.  Bottom  section:  le,  Excelsior  vols.;  1c,  Candelaria  formation;  Pc,  Permian  congl.;  Os, 
Ordovician  slate  and   tuff. 

trusion  of  the  Sierra  Nevada  batholith,  whose  satellites  are  present  in  the 
western  part  of  the  sediments  of  the  Triassic  and  Jurassic  trough. 

The  thrusting  in  general  was  easterly  along  the  eastern  margin  of  the 
trough  and  southerly  along  the  southern  border. 

Representative  sections  from  the  Hawthorne  and  Tonopah  quadrangles 
are  reproduced  in  Fig.  17.3,  and  the  evolution  of  the  complex  thrust 
structure  in  Dunlap  and  post-Dunlap  time  is  shown  in  Fig.  17.4. 


MESOZOIC  SYSTEMS  ALONG  THE  PACIFIC 


263 


In  the  Winnemucca,  Golconda,  Mt.  Tobin,  and  Mt.  Moses  quadrangles 
of  west-central  Nevada  (column  7,  Fig.  17.2;  area  denoted  as  W-G— T-M 
on  Fig.  17.7)  the  late  Paleozoic  Antler  orogeny  is  strikingly  displayed,  as 
well  as  strong  orogeny  in  mid-Permian  time.  Volcanism  in  late  Permian 


^OUNLAP 
FOR. 


[Jdv  -  voiconics  and  sediments 


Jdt  •  Conglomerates  ond  fonglomerate 


I  Jds  •  Sondstone 


STAGE     J 


SUNRISE  AND  „    , 

GABBS  FOR.   Js    "  Limestone   ond  sholt 

i*ptlu  -Massive  limestone  and  dolomite 
Tils  -Shale  with  conglomerate  lenses 
XI  -  Thin  oedded  limestone 
>ec-Chert 
,tteg-Greenstone  ond   breccia 


EXCELSIOR 
FOR. 


yn^^" "  frj 

rW^N 

)'     MM 

p$~2 

^Sff^^^ 

/jfcss 

Z.^^9r 

Wz 

/*'t»^ 

j&y 

W^Mi^S 

b^    HI'/ 

I 

Fig.   17.4.      Development  of  complex  structure  in  the  northwestern   port  of  Pilot  Mountains,   Haw- 

'  thorne   and    Tonopah    quadrangles,    Nev.    From    Plate   3,    Ferguson    and    Muller,    1949.    Stage    1, 

*  folding  near  margin   of  Luning  embcyment  and   deposition  of  conglomerate  and  fanglomerate  of 

the   Dunlap  formation.   Stage  2,   development  of   Mac  thrust.   Deposition   of   coarse   material   and 

folding   of  Mac  thrust.  Stage  3,  further  folding  with   development  of   Spearfish   thrust.  Movement 

toward    the   trough    was   along   an   erosion    surface   cut   on    the    upper    plate    of   the    Mac    thrust. 

I,  Stage  4,  development  of  five  other   thrusts  and   intricate   folds.   The   relative   length   of   the   four 

diagrams   indicates   the    postulated   shortening    of   the   stratigraphic   section    involving   the   Triassic 

and  Jurassic  sediments. 


QOLOONOA    QUAO) 


Fig.    17.5.      Map    showing     inferred    extent    of    Tobin    and    Golconda    thrusts.    Reproduced     from 
Ferguson  et  al.,   1951. 


264 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


TOBIN    THRUST. 


_TpBIN_THRUST 
"ftnp 


CpPh 


GOLCONDA 

THRUST 
C 


'Cp 


SECTION    IN     MOUNT     TOBIN     QUADRANGLE  <> 


I   MILES 


SECTION      IN     WINNEMUCCA      QUADRANGLE 


Tidg     pk 


Fig.  17.6.  Representative  cross  sections  of  northwest  central  Nevada.  Top  section  shows  the 
Tobin  thrust  of  Late  Jurassic  age  and  the  angular  unconformity  between  the  Permian  Koipato 
and  Havallah  formations.  Middle  section  shows  the  Dewitt  thrust  of  late  Mississippian  or  Early 
Pennsylvanian   age   and   the   associated   angular   unconformity   between   the    Pennsylvanian   Battle 

and,  again,  mild  orogeny  at  the  end  of  the  Permian  is  noted.  See  top 
and  middle  sections  of  Fig.  17.6. 

Large-scale  thrusting  occurred  in  the  late  Jurassic  probably  correspond- 
ing in  time  to  the  major  deformation  in  the  Hawthorne  and  Tonopaw 
quadrangles.  Considering  the  time  of  intense  deformation  of  the  Mariposa 
slate  in  eastern  California,  to  be  discussed  immediately,  the  orogeny  is 
thought  to  have  culminated  in  Kimmeridgian  time  of  the  Late  Jurassic. 
The  distribution  of  the  major  thrusts  of  this  age,  the  Tobin  and  Golconda, 
is  shown  in  Fig.  17.6.  The  two  may  actually  be  one  and  the  same.  At 
least,  the  horizontal  translation  has  been  so  great  that  two  suites  of 
formations  of  different  facies  probably  deposited  an  appreciable  distance 
apart,  have  been  brought  into  juxtaposition.  In  the  four  quadrangles  the 
upper  thrust  plate  covers  an  area  extending  50  miles  from  north  to 
south   and  40   miles   from   east  to  west.   The   Permian   formations   are 


Mountain  formation  and  the  Ordovician  Comus  formation.  Lower  section  shows  the  succession  of 
thrusts;  first  the  Thomas,  then  the  Sonoma,  and  then  the  Clear  Creek,  all  of  Late  Jurassic  age. 
The  Tobin  thrust  nearby  cuts  the  Clear  Creek  thrust. 


common  to  both  plates.  The  direction  of  relative  movement  of  the  upper 
plate  is  uncertain.  In  the  Sonoma  Range  a  succession  of  four  thrusts,  all 
occurring  in  the  Late  (?)  Jurassic  orogeny,  is  recognized,  and  the  three 
lower  ones  moved  from  east  to  west.  It  seems  possible  that  the  Tobin 
thrust  plate  could  have  moved  toward  the  north  (Ferguson  et  al.,  1951). 
See  lower  section  of  Fig.  17.6. 


NORTHWESTERN  NEVADA 

Lower  and  probably  Upper  Cretaceous  rocks  have  been  found  in  north- 
western Nevada,  and  these  record  a  continuation  of  deformational  phases 
beyond  the  Late  Jurassic  Tobin  and  Golconda  thrusting.  According  to 
Willden  (1958): 


MESOZOIC  SYSTEMS  ALONG  THE  PACIFIC 


263 


u  u 
a.  < 

3  U 


Danian 

Maestrichtian 

Senonian 

Turonian 

Cenomanian 

95-101- 

Albian 

Apt i an 

Barremian 
Hauterivian 
Valanginian 
Berriasian 


133 

Portlandian 
(Tithonian) 

Kimmeridgian 
Oxford ian 
Callovian 

Bathonian 
Bajocian 

Lias 

17S 


Rhaetian 

Norian 

Karnian 

Ladinian 

Anisian 

Scythian 


■185-200 


Ochoa 
Guadalupe 
Leonard 
Wolfe amp 
210- 


Virgil 
Missouri 
Des  Moines 
Lamp ass  as 
Morrow 


MISSISSIPPIAN 


Folding  and  faulting  in  northwestern  Nevada. 


Thrusting  of  Permian  volcanics  over  King  Lear  and 

Pansy   Lee  elastics . 
Deposition  of  Pansy   Lee  conglomerate  in  north— 

western  Nevada. 
Santa  Lucian  phase  in  Central  Coast  Ranges. 
Intrusion  of  great  batholiths  of  Sierra  Nevada 

and  Coast  Ranges. 


r    Folding  and  erosion  of  King  Lear  fm. 
I 

y    Uplift  and  deposition  of  King  Lear  fm.  in  north- 
west Nevada. 


Subsidence  of  Luning  Embayment. 

Strong,  local  orogeny  and  volcanism;  folding  and 
thrusting  in  Hawthorne  and  Tonopaw  Quadrangles. 

.*-  Mild,  local  disturbance  resulting  in  angular 
unconformity. 


4-" 


Mild  orogeny  in  central  and  western  Nevada 
resulting  in  unconformity.   


*— Volcanism,  extensive.   Folding  in  central  Oregon* 
•*-  Orogeny  in  Western  Nevada:   Golconda  thrust 


Strong  orogeny,  folding  and  thrusting  in  central 
and  western  Nevada.   Sharp  folding  and  low- 
grade  metamorphism  of  Calaveras  fm.  in  eastern 
California  possibly  at  this  time. 


Continued  orogeny  probably  in  several  phases. 


Beginning  of  geanticlinal  uplift  in  central 
Nevada,  and  compressional  orogeny  in  part. 


«  v 


«  c 

>  o 

O  111 

z  o 


jss 


■o  So 

ffl  c 

>  o 

c  BO 

z  o 

I  u 

■o  o 


Intrusion   of  batholiths    in   southern   Klamath  Mts. 

and   northwestern   foothills   of  Sierra   Nevada. 
•Strong   orogeny;    Tobin    and    related     thrusts    of 

VM5-T-M   Quadrangles.       Mariposa   slate    of    eastern 

California    isoclinally   folded  with  resulting 

low-grade    metamorphism. 
Volcanism  and    local    folding   and   thrust-faulting 

during  deposition  of   Dunlap   fm.    in  Hawthorne 

and   Tonopah  Quadrangles. 


O  M 

c  O 

O  Ih 

en  o 


Fig.    17.7.      Sequence    of    disturbances    in    central    and    western    Nevada    and    California    from    the 

|  central   Coast  Ranges  to  the   Sierra   Nevada.   Numbers  are  absolute  ages  in   terms  of   millions  of 

years  and  in  part  are  modifications  of  the  Holmes  time  scale  as  proposed  by  Curtis  ef  a/.,   1958. 


\n\  vnWklamath 

1     M^— wxMTS. 

I  Z      \ 

/  o        s 

-I 

^>1'34.4 

pi 

HR7 

<?v 

^ 
kv 

k    * 

131.5  812 

o^ : 

Fig.  17.8.  Location  and  age  of 
granitic  rocks  in  California 
dated  by  potassium-argon 

method.  Stippled  areas  are 
granitic  plutons.  After  Curtis 
et  al.,   1958. 


W. 


rY0SEMITE 

^9  plutons  ranging 
trom  83.3  to 
953 

fa 


SOUTHERN 
vCALIFORNIi 

THOLIT/ 


A  formation  of  Early  Cretaceous  age  composed  of  locally  derived  clastic- 
rocks,  including  pebble  to  boulder  conglomerate,  siltstone,  coarse  graywacke. 
and  finely  crystalline  limestone  is  exposed  at  several  places  in  the  central  and 
northern  part  of  the  Jackson  Mountains,  Humboldt  County,  Nevada.  This  for- 
mation (King  Lear)  was  folded  and  at  two  places  probably  completelv  eroded 
before  deposition  of  the  next  younger  unit — a  pebble  conglomerate  com- 
posed of  exotic  pebbles  of  chert  and  quartzite  derived  from  rocks  of  early 
Paleozoic  age.  This  younger  pebble  conglomerate  (Pansy  Lee)  may  be  of  Late 
Cretaceous  or  early  Tertiary  age  and  may  be  equivalent  to  rocks  of  similar 
stratigraphic  position  and  lithologic  character  exposed  over  a  considerable  area 
of  eastern  Nevada  and  western  Utah.  Both  of  these  coarse  clastic  formations 
have  been  overridden  by  a  thrust  sheet  of  Permian  or  older  volcanic  rocks.  The 
dimensions  of  the  thrust  sheet  are  not  known  exactly  but  remnants  arc  exposed 
over  a  25-mile-long  segment  of  the  range.  Upper  Tertiary  volcanic  rocks  ex- 
posed in  the  range  are  not  involved  in  the  thrusting. 

The  Cretaceous  and  younger  rocks  of  the  Jackson  Mountains  record  a  long 
period  of  orogenic  unrest  that  included:  (1)  uplift  of  the  source  area  of  and 
deposition  of  the  Lower  Cretaceous  rocks;  (2)  folding  and  beveling  by  erosion: 
(3)   deposition  of  the  exotic-pebble  conglomerate;    (4)   thrusting  of  the  Per- 


266 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


mian  or  older  volcanic  rocks  over  the  two  coarse  clastic  formations;  and   (5) 
later  folding,  faulting,  and  erosion  providing  the  present  outline  of  the  range. 

These  relations  record  orogeny  of  Laramide  age  and  undoubtedly  mean 
that  the  Laramide  belt  of  the  Central  Rockies  ( Chapter  22)  spread  west- 
ward over  most  of  Nevada.  The  folding  of  the  King  Lear  elastics  before 
the  deposition  of  the  Pansy  Lee  conglomerate  records  deformation  prob- 
ably in  Early  Cretaceous  time,  and  this  has  been  labeled  the  mid- 
Nevadan  orogeny  on  Fig.  17.7. 

CENTRAL  AND  NORTHERN  CALIFORNIA 

In  the  California  Sierra  Nevada  region,  Taliaferro  (1942)  summarizes 
an  eastern  belt  of  Triassic  and  Jurassic  rocks  and  a  western  belt  of  Juras- 
sic rocks.  The  two  were  probably  continuous,  but  due  to  the  Nevadan 
orogeny  (to  be  described  immediately)  a  dividing  mass  25  to  50  miles 
wide  of  Calaveras  rocks  and  granite  of  the  Sierra  Nevada  batholith  exists. 
The  eastern  belt  consists  of  discontinuous  areas  of  Upper  Triassic  and 
Jurassic  sediments  and  volcanics.  Doubtless  these  formed  a  continuous 
belt  at  one  time,  but  as  they  lie  in  the  region  of  maximum  plu tonic  in- 
vasion and  maximum  Tertiary  uplift,  they  have  been  obliterated  or  re- 
moved by  erosion  in  many  places.  Near  the  northern  end  of  the  Sierra 
Nevada,  the  Milton  formation  represents  the  Triassic  and  Jurassic  rocks, 
and  where  not  engulfed  by  the  plutons  or  removed  by  erosion  it  lies  in  a 
broad,  steep-limbed  syncline,  practically  free  from  minor  crumbling, 
thrusting,  and  overturning  (Taliaferro,  1942).  The  conglomerates  contain 
abundant  debris  of  the  Paleozoic  rocks  (Calaveras)  and  thicken  and 
coarsen  westward.  It  seems  clear,  therefore,  that  the  Milton  was  derived 
from  the  west. 

The  best-exposed  and  most  complete  section  of  the  east  belt  is  on  the 
north  fork  of  the  American  River  in  Placer  County.  On  the  west  limb  of 
the  syncline,  basic  and  intermediate  volcanics  and  radiolarian  cherts,  200 
feet  thick,  are  followed  by  12,800  feet  of  conglomerates,  sandstones,  hard 
slaty  shales,  and  fine-grained  andesitic  tuffs.  The  center  of  the  syncline  is 
occupied  by  9500  feet  of  intermediate  and  basic  flows,  agglomerates,  and 


tuffs.  Only  about  900  feet  of  sediments  and  tuffs  lie  below  the  volcanics 
on  the  east  limb  of  the  syncline,  the  lower  part  having  been  obliterated  by 
batholithic  intrusions.  Well-preserved  Upper  Triassic  fossils  are  found 
at  and  near  the  base  of  the  sediments  on  the  west  limb  of  the  syncline, 
Lower  Jurassic  fossils  2500  feet  above  the  base,  and  Middle  Jurassic  fos- 
sils 9500  feet  above  the  base;  no  fossils  have  been  found  in  the  upper 
13,000  feet  of  the  sediments  and  volcanics.  The  section  is  well  exposed 
and  no  unconformities  or  disconformities  have  been  observed.  Possibly 
part  of  the  upper  13,000  feet  is  equivalent  to  the  Mariposa  slate  of  the 
western  belt.  The  upper  volcanics  are  possibly  equivalent  to  the  extensive 
Logtown  Ridge  volcanics  lying  between  Amador  and  Mariposa  west 
of  the  Mother  Lode.  No  evidence  supports  the  idea  that  the  Milton  of 
the  eastern  belt  was  separated  from  the  Mariposa  and  Logtown  Ridge  of 
the  western  belt  either  by  deposition  in  separate  basins  or  by  a  period  of 
batholithic  intrusion  and  orogeny  (Taliaferro,  1942).  See  column  2, 
Fig.  17.2. 

In  comparing  the  sediments  of  the  eastern  belt  of  the  Sierras  with  those 
of  the  trough  of  western  Nevada,  it  appears  that  Lower  and  Middle 
Triassic  sediments  were  deposited  in  the  central  part  of  the  trough  which 
lay  in  western  Nevada,  and  then  Upper  Triassic  sediments  overlapped  on 
highlands  both  westward  and  eastward.  See  Fig.  17.8.  Great  subsidence 
occurred  in  early  Middle,  and  early  Late  Jurassic  time;  the  center  of  the 
Jurassic  trough  migrated  west  of  that  of  the  Triassic  trough;  and  over- 
lap on  the  western  volcanic  orogenic  belt  was  extensive. 

The  western  belt  is  made  up  of  the  Amador  group  and  the  Mariposa 
slates  in  the  Sierra  Nevada  and  northwestward  in  Oregon,  of  the  Dothan 
and  Galice.  The  Amador  and  Dothan  are  probably  Middle  Jurassic  in 
age,  with  their  upper  beds  containing  Late  Jurassic  fossils.  The  Mariposa 
and  Galice  are  early  Late  Jurassic.  The  great  bulk  of  the  Amador  consists 
of  volcanics  and  elastics,  but  red  and  green  radiolarian  cherts  and  dense, 
unfossiliferous  limestones  are  common.  On  the  Cosumnes  River,  1200 
feet  of  conglomerates  and  sandstones  are  at  the  base  of  the  Amador.  On 
the  Merced  River,  radiolarian  cherts,  tuffs,  and  shales  are  over  1500  feet 
thick,  and  these  overlie  about  1400  feet  of  pillow  basalts.  The  entire 
Amador  group  ranges  in  thickness  from  5000  to  15,000  feet,  and  usually 


MESOZOIC  SYSTEMS  ALONG  THE  PACIFIC 


267 


grades  upward  into  the  Mariposa  (Taliaferro,  1942),  but  between  the 
Merced  and  Mariposa  rivers,  conglomerates  are  at  the  base  of  the 
Mariposa.  The  pebbles  are  presumably  from  the  underlying  Amador.  See 
column  4,  Fig.  17.2. 

The  Mariposa  formation  consists  of  black  slate  and  graywacke,  with 
which  greenstone  is  closely  associated  (Knopf,  1929).  Conglomerate 
occurs  locally,  and  sericite  schist  and  limestone  in  a  very  few  places.  The 
greenstone,  because  of  its  intimate  interbedding  with  the  normal  sedi- 
mentary rocks,  is  in  many  places  an  inseparable  part  of  the  formation,  and 
locally  predominates  in  volume.  The  conglomerate  contains  a  variety  of 
rocks,  namely:  quartz  keratophyre  (submarine  lava  flow  origin),  quartz- 
ite,  chert,  quartz,  aplite,  and  biotite  granophyre.  The  last  two  point  to 
plutonic  intrusions  older  than  those  of  the  Sierra  Nevada  ( Knopf,  1929 ) . 
The  graywacke  contains  grains  of  quartz,  plagioclase,  slate,  quartzite,  and 
keratophyre  (?).  On  the  one  hand  they  grade  into  slate  and  graywacke 
slate,  and  on  the  other,  by  the  presence  of  augite,  into  augite  tuff.  The 
greenstones  were  principally  augite  basalt  breccias,  tuffs,  and  lavas, 
now  somewhat  metamorphosed  (Knopf,  1929).  It  appears  that  some  of 
jthe  volcanics  included  by  Knopf  in  the  Mariposa  are  what  Taliaferro 
places  in  the  Amador. 

j  The  great  thickness  of  volcanics  is  a  striking  feature  of  practically  all 
Jurassic  units  in  California  and  southwestern  Oregon.  The  volcanic  rocks 
range  from  rhyolite  to  basalt,  but  augite  andesites  predominate.  Practi- 
pally  all,  if  not  all,  are  submarine,  as  they  are  interbedded  with  marine 
Isediments  (Taliaferro,  1942).  Pyroclastics  predominate  over  flows.  Cen- 
ters of  volcanism  have  been  recognized  in  the  form  of  necks,  both  breccia 
sand  solid,  and  great  accumulations  of  flows,  tuffs,  and  very  coarse  brec- 


cias. 

I    Intrusions  of  peridotite  and  dunite,  now  largely  serpentinized,  together 

with  their  closely  associated  gabbroic  and  diabasic  differentiates,  are  com- 
mon in  the  Jurassic  of  California  and  southwestern  Oregon.  They  occur  as 

r>ills,  dikes,  plugs,  and  large  masses  of  undetermined  form.  The  great  ma- 
jority were  intruded  prior  to  folding  of  the  Jurassic  sediments  and  before 
the  Sierra  Nevadan  batholith  was  emplaced.  The  basic  intrusions  of  the 
Mother  Lode  were  serpentinized  immediately  after  their  emplacement 


(Knopf,  1929).  They  were  slightly  metamorphosed  by  the  folding,  and 
greatly  altered  at  the  contacts  of  the  granodiorite  plutons. 

OREGON 

In  central  Oregon,  a  fairly  complete  Jurassic  section  has  been  described 
by  Lupher  ( 1941 ) .  He  sets  apart  ten  formations  which  range  in  age  from 
Early  to  Late  Jurassic,  perhaps  to  Early  Cretaceous,  and  altogedier  are 
over  11,000  feet  thick.  These  beds  show  only  a  succession  of  gentle  emer- 
gent and  submergent  movements.  The  lithology  is  in  conspicuous  contrast 
to  that  of  the  Jurassic  of  the  Sierra  Nevada  in  lacking  volcanics  and  having 
only  minor  amounts  of  coarse  elastics.  It  is  nearly  all  sandstone  and  shale, 
and  in  part  it  is  very  fossiliferous. 

The  Oregon  Jurassic  rests  with  marked  angular  discordance  on  a  base- 
ment of  highly  folded  Upper  Triassic  and  Mississippian  rocks.  Some  of  the 
beds  called  Upper  Triassic  may  be  Lower  Jurassic,  because  a  sequence 
of  shales,  sandstones,  and  conglomerates,  many  thousands  of  feet  thick, 
overlies  the  fossiliferous  Upper  Triassic  but  underlies  the  great  unconform- 
ity. The  folds  in  the  Jurassic  beds  trend  at  divergent  angles  from  those 
of  the  Upper  Triassic,  and  basic  plutons  now  largely  altered  to  serpentine 
invade  the  Upper  Triassic  but  not  the  Jurassic.  It  is,  therefore,  apparent 
that  an  orogeny  of  considerable  proportions  is  indicated.  It  will  be  re- 
called that  a  similar  unconformity  separates  two  formations  of  Early  Juras- 
sic age  in  western  Nevada,  and  it  is  evident,  therefore,  that  the  two  may 
be  the  same,  perhaps  with  slightly  different  ages.  It  seems  necessary,  in 
order  to  account  for  the  different  lithologies  of  the  Jurassic  beds  of  central 
Oregon  and  those  of  the  Sierra  Nevada,  to  separate  the  central  Oregon 
beds  from  the  volcanic  belt  by  a  nonvolcanic  highland  or  Piedmont.  See 
the  tectonic  maps,  Plates  11  and  12.  The  pebbles  are  cherts  and  lime- 
stones, evidently  from  Paleozoic  formations  (Lupher,  1941). 

SOUTHERN  CALIFORNIA 

Larsen  (1948)  has  summarized  the  geology  of  the  region  southeast  of 
Los  Angeles  in  southern  California,  especially  in  relation  to  the  great 


268 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Nevadan  intrusions  there;  and  he  also  reviews  the  southern  continuation 
of  the  batholithic  province  into  Baja  California.  A  group  of  slates  and 
argilhtes,  with  some  quartzites,  lie  west  of  the  main  batholith  and  form 
most  of  the  Santa  Ana  Mountains.  Triassic  fossils  have  been  collected  there 
in  several  places.  Somewhat  more  metamorphosed  remnants  of  these 
rocks  occur  within  the  batholith.  The  group  is  known  as  the  Bedford  Can- 
yon formation,  and  about  20,000  feet  of  beds  are  exposed  in  the  Santa  Ana 
Mountains.  Parts  of  the  formation  may  be  older  than  Triassic  and  parts 
may  be  Jurassic.  The  uniform  argillaceous  lithology  is  a  dominant  char- 
acter. 

A  group  of  volcanic  beds,  mostly  mildly  metamorphosed,  andesitic 
agglomerates,  overlies  the  Bedford  Canyon  formation  unconformably. 
The  extrusives  have  been  called  the  Santiago  Peak  volcanics  (Larsen, 
1948),  and  they  are  probably  many  thousands  of  feet  thick.  They  are 
older  than  the  batholithic  intrusions  and,  therefore,  are  probably  Jurassic 
in  age. 

Along  the  east  side  of  the  main  batholithic  region  are  coarsely  crystal- 
line schists,  all  of  which  contain  much  quartz.  Interbeds  of  limestone 
have  yielded  Mississippian  fossils  (Larsen,  1948).  A  quartzite  sequence 
with  interbedded,  coarse,  mica  schist  is  also  thought  to  be  Carboniferous. 
It  is  some  12,000  feet  thick.  Larsen  believes  that  the  Paleozoic  sediments 
were  metamorphosed  and  intruded  by  granite  rocks  before  the  deposition 
of  the  Triassic  rocks,  and  that  this  older  metamorphism  was  more  intense 
than  the  later  metamorphism  of  the  Triassic  rocks. 

NEVADAN  OROGENY 

History  of  Concept 

The  literature,  up  to  the  last  few  years,  suggests  that  the  Late  Jurassic 
folding  and  thrusting  was  followed  very  shortly  by  the  great  batholithic 
intrusions,  and  that  the  two  events  occurred  between  the  Kimmeridgian 
and  Portlandian.  See  Figs.  17.2  and  17.7.  Recent  isotope  age  determina- 
tions have  demonstrated  fairly  conclusively,  however,  that  the  intrusions 
are  mid-  or  early  Late  Cretaceous  in  age.  Also  new  fossil  finds  have  re- 
sulted in  a  revision  of  concepts  of  the  Upper  Jurassic  and  Lower  Creta- 


ceous stratigraphy  which  is  not  incompatible  with  a  Mid-Cretaceous  age 
of  the  batholiths. 

Additional  sampling  and  potassium-argon  age  determinations  by  Curtis 
et  al.  (1958)  indicate  that  granitic  rocks  along  the  northwest  foothills  of 
the  Sierra  Nevada  and  in  the  southern  Klamath  Mountains  are  Tithonian 
( Portlandian )  in  age,  as  the  early  geologists  had  concluded.  Furthermore, 
they  found  that  several  plutons  in  the  Central  Coast  Ranges  are  early 
Late  Cretaceous  (about  Cenomanian  to  Senonian),  the  same  age  as  the 
plutons  of  Yosemite  National  Park.  The  various  potassium-argon  ages 
to  date  in  California  are  shown  in  Fig.  17.8.  Curtis  et  al.  conclude  that  the 
bulk  of  the  great  batholiths  of  California  are  of  the  later  date,  but  that 
some  are  late  Jurassic,  and,  as  the  earlier  writers  concluded,  are  closely 
associated  with  the  post-Kimmeridgian  folding  and  thrusting. 

The  term  Nevadan  orogeny  has  been  used  to  denote  those  tectonic 
events  that  occurred  in  the  general  region  of  the  Sierra  Nevada  in  a  rather 
limited  interval  of  time  between  the  Kimmeridgian  and  Portlandian.  The 
great  batholiths  are  indelibly  impressed  in  the  literature  as  an  outstand- 
ing characteristic  of  the  orogeny,  so  now  with  die  recognition  that  the 
main  batholiths  are  much  younger  we  are  faced  with  a  redefinition  of  the 
term,  Nevadan  orogeny.  It  is  here  proposed  to  call  those  disturbances 
and  intrusions  in  Late  Jurassic  time  (post-Bathonian )  the  early  Nevadan 
orogeny,  those  of  Early  Cretaceous  time  the  mid-Nevadan  orogeny,  and 
those  of  Mid-  and  early  Late  Cretaceous  time  the  late  Nevadan  orogeny 
(see  Fig.  17.7). 

General  Characteristics 

The  Jurassic  and  pre-Jurassic  rocks  thus  far  described  were  severely 
folded  and  thrust-faulted  in  the  Sierra  Nevada,  and  then  invaded  by 
granitic  magma.  The  maximum  deformation  seems  to  have  been  con- 
centrated along  what  is  now  the  western  slopes  of  the  Sierra  Nevada  in 
the  zone  of  the  western  belt  of  Jurassic  deposits.  Overturned  folds,  some 
of  great  amplitude,  great  thrusts,  such  as  the  Mother  Lode  zone,  and  mild 
dynamic  metamorphism  were  widespread.  The  eastern  belt  of  Triassic  and 
Jurassic  rocks,  near  the  present  crest  of  the  Sierra  Nevada,  is  strongly 
folded,  but  less  dynamically  metamorphosed.  The  eastern  belt  of  Triassic 


MESOZOIC  SYSTEMS  ALONG  THE  PACIFIC 


269 


and  Jurassic  rocks  continued  southward  into  southern  California,  but  is 
much  obscured  there  by  Tertiary  lavas  and  late  Cenozoic  faulting.  See 
Kg.  17.9. 

Central  and  Northern  California 

At  the  north  end,  in  the  Taylorsville  region,  the  Paleozoic  rocks  are 
thrust  eastward  over  the  Jurassic,  overturning  them  toward  the  east,  just 
the  opposite  of  the  thrusting  along  the  Mother  Lode  on  the  west  flank 
jof  the  Sierra  Nevada.  It  will  be  recalled  that  the  Late  ( ? )  Jurassic  thrust- 
''ing  in  western  Nevada  was  both  toward  die  east  and  west  and  locally 
(probably  southward  and  northward.  In  the  Grass  Valley  area  of  the 
northern  Sierra  Nevada,  Johnston  (1940)  finds  the  rocks  to  have  been 
compressed  into  northwest-trending  isoclinal  folds.  The  metamorphism 
swas  of  the  feeblest  kind.  The  Mariposa  was  compacted  and  cemented, 
land  some  of  the  andesitic  rocks  acquired  schistocity;  but  the  chemical 
sand  physical  changes  were  much  less  severe  than  those  imposed  upon 
the  Calaveras  formation  in  late  Paleozoic  orogeny. 

Regarding  the  post-Mariposa  plutons,  Knopf  (1929)  says  that  in  the 
'Mother  Lode  belt  the  oldest  of  these  rocks  there  are  peridotites  which, 
•soon  after  intrusion,  were  transformed  into  serpentines.  Smaller  masses 
■of  gabbro  and  hornblendite  were  then  intruded  into  the  peridotite,  to 
iwhich  they  seem  to  have  a  predilection.  The  peridotite,  gabbro,  and  horn- 
blende appear  to  represent  the  "basic  prelude"  to  tremendous  intrusions 
jof  granodiorite  that  form  the  bulk  of  the  present  Sierra  Nevada. 

The  granodiorite  is  uniform  in  texture  and  composition,  and  contains 
Jbasic  clots  which  are  very  common  in  the  high  Sierra.  Quartz  diorite 
porphyry  is  intrusive  into  the  Mother  Lode  belt  south  of  Placerville.  It 
[grades  into  the  granodiorite  and  has  exerted  no  perceptible  contact  meta- 
morphism. Knopf  believes  that  the  granodiorite  ascended  to  a  high  level 
"in  the  earth's  crust  in  the  gold  belt  area.  Dikes  and  small  intrusive  masses 
?lof  a  white  rock  composed  almost  entirely  of  albite  complete  the  intrusive 
licycle.  Allied  varieties  of  the  granodiorite  are  quartz-monzonite,  granite, 
'and  alaskite.  The  Mariposa  is  affected  by  contact  metamorphism  as  much 
as  a  mile  away  from  the  granodiorite  contact. 

In  the  northern  Sierra  Nevada,  Johnston  (1940)  finds  essentially  the 


CALIF.     I    NEV 


NARROW  I 

VOLCANIC  CALIFORNIA    TROUGH 

ARCHIPELAGO       i 


ASUNCION   GR 


WAIN  6ATH0LITHIC    INTRUSIONS 
(NEVADAN    OROGENY)  AND  OEPOSITION    DVRINt 
AL61AN     AND    CENOMANlAN    TIME 


POST-KIMMERIOGIAN    FOLD1NO    AND  THRUSTING 
DEPOSITION   FROM  LATE   JURASSIC  IT1THON1AN) 
THROUGH    LATE    EARLT   CRETACEOUS 
(APTIAN)    IN    NEW  WESTERN   TROUGH 


I 
i 
i 

I 


6ATH0LITHIC   INTRUSIONS  IN    TlTHONlAN 


DEPOSITION    THROUGH   EARLT   LATE   JURASSIC 
(KIHMERIDGIAN)  WITH   DISTURBANCE    IN 
EARLY   JURASSIC 


OEPOSITION  THROUGH  TRIASSIC  WITH 
DISTURBANCE  8ETWEEN  MIDDLE  AND 
UPPER    TRIASSIC  


Fig.  17.9.  Evolution  of  the  Sierra  Nevada  through  Mesozoic  time.  C  is  Calaveras  formation  of 
late  Mississippian  (?)  age;  F  is  Franciscan  group;  K,  Knoxville  formation;  P,  Pashenta  formation; 
and   H,   Horsetown  formation. 

same  batholitic  cycle  as  Knopf  does  to  the  south  in  the  Mother  Lode, 
namely,  an  intrusive  succession  of  ultrabasic  rocks,  gabbro,  diabase, 
granodiorite,  granite,  and  aplite.  Granodiorite  was  intruded  in  tremendous 
batholithic  masses  that  now  form  the  backbone  of  the  high  Sierra.  On  the 
western  slope,  smaller  masses  of  granodiorite  are  satellitic  to  the  main 
mass.  The  earlier  formations  were  shoved  aside  and  possibly  in  part  as- 
similated, and  contact  metamorphic  zones  were  developed  in  the  sedi- 
mentary rocks.  From  the  last  emanations  of  the  granitic  intrusions  were 
formed  die  gold  quartz  veins  of  the  Sierra  Nevada. 

In  the  southern  part  of  the  Sierra  Nevada,  Mayo  ( 1941 )  in  reviewing 
the  work  of  others  and  himself,  finds  that  hornblende  gabbro  and  horn- 
blende diorite  were  forerunners  to  the  main  granitic  intrusions.  These 


270 


MT.    McGEE 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


MT.  EMERSON 


ZONE     OF      GRANODIORITE 


NORTH     PALISADE 


DEVIL'S    CRAGS 


^•r.  ■■'-..: 


5  BASIC   COMPLEX 


TABLE    MTN 


LOOKOUT 


"1 — ^T~— — ■ 


Gr         5     Gr  3         Di        Gr 


COYOTE    RIDGE 


Gr 


ROUND     MTN. 


6r 


. '  '     T.i.'l ■■!■■■•'   ■   jl      - 


Gr 


5     3     Di 


Gr  Gr 

SCALE        IN      MILES 


5     6r  5 


Fig.  17.10.  Structure  sections  across  southern  Sierra  Nevada  Mountains.  Upper  section  is  north 
of  Connecting  Link;  second  section  is  south  of  it.  Lower  two  sections  are  across  the  northern  part 
of  Coyote  Salient,  s,  septum;  Gr,  granitic  rocks;  Di,  Diorite  and  gabbro.  After  Mayo,   1941. 

basic  intrusions  now  appear  widely  distributed  as  dark  zones,  strips,  and 
masses  of  various  shapes  and  simulate  the  remnants  of  the  metamorphic 
rocks.  According  to  Mayo,  the  bulk  of  the  Sierra  Nevada  core  ranges  in 
composition  from  granodiorite  to  granite,  with  quartz  monzonite  predomi- 
nating. All  members  of  the  intrusive  sequence  are  penetrated  by  dikes  of 
aplite  and  pegmatite.  Some  basic  dikes  were  late  comers  also. 

The  groups  of  intrusions  are  separated  at  many  places  by  long,  narrow 
strips  and  by  local  broad  areas  of  metamorphic  rocks.  The  metamorphic 
rocks  are  divisible  into  two  groups:  an  older  series  of  metasediments  of 
probable  Paleozoic  age,  and  a  series  of  metavolcanics,  part  of  which 
Knopf  has  assigned  to  the  Triassic. 

The  metamorphic  rocks  are  remnants  of  septa  (Fig.  17.10)  that  divided 
the  intrusions  to  unknown  depths.  During  the  earliest  recorded  deforma- 


tion, the  original  bedding  and  other  layered  structures  were  thrown  into 
a  series  of  closely  appressed,  nearly  vertical-sided,  isoclinal  folds.  Cleavage 
developed  approximately  parallel  to  the  axial  planes  of  the  folds,  and 
was  followed  by  many  small  shears  and  a  few  upthrusts.  Linear  structures 
that  vary  greatly  in  pitch  were  formed  in  the  planes  of  cleavage,  bedding, 
shears,  and  upthrusts.  These  metamorphic  rock  structures  are  separated 
from  the  intrusions  by  contacts  that  are  usually  very  steep  and  sharp. 
Gradational  contacts  are  suggested  in  a  few  places. 

Within  the  granitic  rocks,  a  parallel  arrangement  of  inclusions,  min- 
erals, and  schlieren  reveals  layered  and  linear  traces  of  flow  that  are  as- 
signed to  the  plastic  stage  of  intrusion.  These  structures  of  the  plastic 
stage,  by  grading  into  fractures,  locally  record  the  stage  of  transition. 
The  stage  of  transition  was  followed  by  the  solid  stage,  when  adjustments 
resulted  in  fracturing. 

In  the  Huntington  Lake  area  of  the  western  slope  of  the  central  Sierra 
Nevada,  Hamilton  (1956a)  has  concluded  that  the  crystalline  rocks  there 
consist  of  ten  separate,  sharply  bounded,  plutons  which  range  in  size 
from  one  square  mile,  approximately,  to  several  hundred  square  miles. 
Only  small  parts  of  this  area  consist  of  metamorphic  rocks.  See  Fig.  17.11. 

The  granite  rocks  range  from  alaskite  to  quartz  diorite,  but  it  is  impor- 
tant to  note  that  a  rock  type  does  not  constitute  a  separate  intrusion,  but 
rather,  each  intrusion  may  be  made  up  of  two  or  more  rock  types.  Two  of 
the  plutons  range  from  quartz  diorite  through  granodiorite  to  quartz 
monzonite.  In  another,  the  content  of  ferromagnesian  minerals  varies  from 
2  to  19  percent.  The  abundance  of  ferromagnesian  minerals  and  of  the 
dark  inclusions  are  closely  parallel.  The  inclusions  are  xenolithic,  and 
some  and  possibly  most  of  the  mafic  minerals  are  products  of  assimilation 
of  metamorphic  rocks.  Most  of  the  granite  rocks  are  believed  to  have 
formed  from  the  upward  intrusion  of  mobile  materials. 

The  western  group,  consisting  of  the  Tamarack  Creek,  Huntington 
Lake,  Sheepthief  Creek,  and  Kaiser  Peak  plutons,  is  considered  the  older, 
and  eastern  group,  consisting  of  the  Mt.  Givens,  Red  Lake,  Rodeo 
Meadow,  Dinkey  Lake,  Coyote  Creek,  and  Helms  Creek  plutons,  the 
younger. 

The  relative  aerial  abundances  of  the  rock  types  are  as  follows: 


MESOZOIC  SYSTEMS  ALONG  THE  PACIFIC 


271 


alaskite 

granite 

quartz  monzonite 

granodiorite 

quartz  diorite 


5  percent 

4  percent 

47  percent 

33  percent 

11  percent 


This  confirms  Mayo's  observation  that  quartz  monzonite  is  the  most 
voluminous  rock  type  in  the  Sierra  Nevada  where  studied  petrographi- 
cally. 

Age  of  the  Batholiths 

The  first  determination  of  the  age  of  the  Sierra  Nevada  batholith  by 
isotope  methods  was  made  by  Larson  et  al.  in  1954.  Lead-alpha  activity 
ratios  were  determined  on  the  accessory  minerals  zircon,  monozite,  and 
xenotime.  Seven  samples  yielded  an  average  age  of  100  m.y.  Twenty-five 
samples  were  run  from  the  batholith  of  southern  California,  and  these 
gave  an  average  age  of  105  m.y.  (Larson  et  al.,  1954). 

A  few  years  later  samples  were  taken  by  Evernden  et  al.  ( 1957 )  from 
eight  individual  intrusions  in  the  Yosemite  Canyon  area  of  the  Sierra 
Nevada  batholithic  complex,  plus  a  pegmatite  of  one  of  the  plutons  and 
their  ages  determined  by  the  potassium-argon  method.  The  major  plutonic 
bodies  had  been  mapped  by  Calkins  (1930)  and  Rose  (1957)  who  had 
established  for  the  most  part  the  relative  ages  of  the  intrusions  on  con- 
vincing field  evidence.  From  youngest  to  oldest  the  seven  plutons  are 
named  as  follows:  Johnson  granite  porphyry,  Cathedral  Peak  granite, 
Half  Done  quartz  monzonite,  Sentinel  granodiorite,  El  Capitan  granite, 
Gateway  granodiorite,  and  Arch  Rock  granite.  The  Hoffman  quartz  mon- 
zonite, which  is  noted  to  have  intrusive  relations  to  the  Cathedral  Peak 
granite,  was  also  sampled.  The  experimental  age  determinations  agreed 
perfectly  with  the  relative  ages  determined  by  geological  field  relations. 
The  youngest,  the  Johnson  granite  porphyry,  yielded  a  date  of  82.4 
(  ±  1-2%)  m.y.,  and  the  oldest,  the  Arch  Rock  granite,  95.3  (  ±  1-2%).  The 
authors  from  theoretical  considerations  regard  these  ages  as  slightly 
younger  than  the  true  absolute  ages  of  the  plutons,  but  believe  any  change 
made  ultimately  will  be  in  the  order  of  a  few  percent  at  most. 

A  pegmatite  in  the  Hoffman  pluton  (83.3^1-2%  m.y.)  yielded  an  age 


of  76.9  m.y.,  and  the  range  from  this  youngest  rock  to  the  oldest  is  there- 
fore approximately  18  m.y.  This  intrusive  activity  would  have  occurred 
according  to  Curtis  et  al.  (1958)  during  the  Cenomanian,  Turonian,  and 
Senonian  (see  Fig.  17.7)  epochs. 

If  the  series  of  nine  plutons,  including  a  late  pegmatite,  were  intruded 
during  an  interval  of  18  m.y.,  a  separate  intrusion  approximately  each 
2  m.y.  would  have  been  emplaced.  Evernden  et  al.  (1957)  review  the 
field  evidence  to  the  effect  that  most  of  these  intrusions  were  almost  com- 
pletely crystallized  at  the  time  die  succeeding  pluton  was  emplaced, 
and  thus  conclude  that  crystallization  of  each  would  require  somewhat 
less  than  2  m.y. 


Fig.  17.11.      Plutons  and  rock  types  of  the  Huntington  Lake  area;  Sierra   Nevada  batholithic  com- 
plex. Direction  of  pattern   lines  has  no  significance. 


272 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


The  granitic  rocks  were  exposed  by  erosion  at  the  time  the  Turonian 
sediments  were  deposited  (see  Figs.  17.7  and  17.8)  and  hence,  only  a 
short  time  separated  the  last  intrusion  from  its  exposing.  It  may  thus  be 
assumed  that  uplift  and  erosion  kept  close  pace  with  granitic  emplace- 
ment. From  this  Evernden  et  al.  deduce  that  the  space  for  the  batholiths 
was  produced  by  the  elevation  of  the  roof  slowly  and  by  small  increments, 
and  that  the  overlying  sedimentary  rocks  were  stripped  by  erosion  as 
rapidly  as  they  rose. 

ANCESTRAL  COAST  RANGE  SYSTEM 

Franciscan  Basin 

Following  the  post-Kimmeridgian  folding  and  thrusting  (Fig.  17.9) 
a  trough  or  basin  sank  on  the  west  in  California,  and  in  it  an  exceedingly 
thick  sequence  of  sediments  accumulated.  These  are  those  of  the  Fran- 
ciscan group  and  equivalents  (Fig.  17.2).  West  of  this  trough  lay  a 
sourceland  of  sediments,  viewed  as  a  narrow  volcanic  archipelago  by 
Taliaferro  ( 1942 ) .  The  strata  known  as  Franciscan  crop  out  in  the  Coast 
Ranges  and  the  Shasta  and  Upper  Cretaceous  strata  occur  in  the  Sacra- 
mento Valley.  The  thickness  of  the  Franciscan  is  about  35,000  feet.  That 
of  the  Shasta  series  is  about  10,000  feet  and  of  the  Upper  Cretaceous  on 
the  west  side  of  Sacramento  Valley  is  15,000  feet. 

According  to  Irwin  ( 1957 ) : 

The  Franciscan  group  consists  dominandy  of  detrital  sedimentary  rocks 
with  interbedded  chemical  sedimentary  and  volcanic  rocks.  The  detrital 
rocks  are  chiefly  sandstones  of  the  graywacke  type,  with  interbedded  shale 
and  conglomerate.  Reliable  criteria  have  not  yet  been  described  for  dis- 
tinguishing, either  in  hand  specimen  or  under  the  microscope,  between 
detrital  rocks  of  the  Franciscan  group  and  those  of  the  Sacramento  Valley 
sequence.  The  most  obvious  and  significant  difference  between  the  lithologic 
character  of  the  Franciscan  group  and  that  of  the  Sacramento  Valley  sequence 
is  the  presence  and  local  abundance  of  interbedded  volcanic  rocks  and  as- 
sociated chemical  sedimentary  rocks  in  the  Franciscan.  The  chemical  sedimen- 
tary rocks  include  rhythmically  thin-bedded  chert,  and,  much  less  abundandy, 
a  distinctive  foraminiferal  limestone.  In  addition,  the  Franciscan  group  includes 
small  areas  of  glaucophane  schists.  In  some  areas,  strata  of  the  Franciscan  group 
have  been  metamorphosed  to  slates  and  phyllites. 

The  Franciscan  group  has  been  intruded  by  mafic  and  serpentinized  ultra- 


mafic  rocks,  and  has  been  highly  faulted  and  pervasively  sheared.  The  general 
appearance  of  the  Franciscan  terrane,  because  of  the  net  effect  of  the  lithologic 
heterogeneity  and  complex  structural  deformity,  is  in  striking  contrast  to  areas 
underlain  by  strata  of  the  Sacramento  Valley  sequence. 

The  Knoxville  formation  as  exposed  along  the  west  side  of  Sacramento  Valley 
between  Wilbur  Springs  and  Paskenta  is  perhaps  10,000  feet  in  average  thick- 
ness. The  base  is  unknown,  as  along  most  of  the  valley  the  lowest  exposed  beds 
are  in  fault  contact  with  the  belt  of  ultramafic  rock.  The  Knoxville  formation  is 
generally  considered  to  consist  typically  of  a  thick  section  of  thin-bedded  shales 
with  small  lenses  of  limestone,  but  interbedded  sandstones  and  conglomerates 
are  locally  abundant.  Fossils  indicate  that  it  is  Late  Jurassic  (Tithonian)  in 
age.  One  of  its  most  characteristic  and  abundant  fossils  is  Aucella  piochii  Gabb. 

The  contact  between  the  Knoxville  formation  and  overlying  Shasta  series  is 
marked  by  a  fairly  abrupt  and  complete  change  in  fauna,  and  at  many  places 
by  beds  of  conglomerate.  Here,  as  well  as  at  other  places,  the  concept  of  a 
"basal  conglomerate"  has  much  influenced  the  subdivision  of  the  Sacramento 
Valley  sequence.  Along  much  of  Sacramento  Valley  the  transition  from  one 
unit  to  the  other  is  one  of  nearly  continuous  deposition  and,  judged  from  broad 
structural  conformity,  was  accomplished  with  litde  disturbance. 

The  strata  referred  to  the  Shasta  series  have  a  higher  ratio  of  sandstone  to 
shale  than  has  the  Knoxville  formation. 

Upper  Cretaceous  strata  along  the  west  side  of  Sacramento  Valley  consist 
of  sandstones  and  shales  and  are  about  15,000  feet  in  average  thickness.  They 
represent  only  the  lower  part  of  the  Upper  Cretaceous  section  of  northern 
California. 

Mid-Cretaceous  Phase  (Mid-Cretaceous  Orogeny) 

In  many  places  in  the  Coast  Ranges  there  is  either  a  definite  discon- 
formity  or  a  strong  unconformity  or  overlap  between  the  Shasta  series 
and  the  Upper  Cretaceous  strata.  Especially  in  the  Santa  Lucian  Range, 
there  is  evidence  of  deep  erosion  and  overlap.  Along  the  crests  of  some 
of  the  folds  produced  during  this  disturbance,  the  Lower  Cretaceous 
and  Upper  Jurassic  beds  were  removed,  so  that  the  Shasta  trough  was 
lifted  in  subparallel  fragments.  Other  parts  of  the  Shasta  beds  were 
little  affected.  The  orogeny  represented  by  the  unconformity  has  been 
called  the  Mid-Cretaceous  by  Taliaferro  (1943b). 

Mid-Upper  Cretaceous  Phase  (Santa  Lucian  Orogeny) 

The  Upper  Cretaceous  strata  in  the  Coast  Ranges  are  divisible  into 
two  groups,  the  Pacheco  and  the  Asuncion,  which  together  make  up 
the  Chico  (Taliaferro,  1943b).  See  Fig.  17.2.  The  Pacheco  consists  in 


Fig.  17.12.  Evolution  of  structure  along  cross  section  through  south 
central  part  of  Adelaida  quadrangle,  Calif.,  showing  relations  between 
various   units  of   Cretaceous  and   relations  to  older  and   younger   rocks. 

1.  Structure  as  it  exists  at  present. 

2.  Structure  along  same  section  during  deposition  of  Middle  Miocene. 

3.  During   deposition   of   Asuncion,   late   Upper   Cretaceous. 

4.  During    deposition    of   Jack    Creek    formation,    early    Upper    Creta- 
ceous. 

(After  Taliaferro,    1944.) 


sw 


Middle   Miocene 
Rhyolite    flows  and   shallow 


Middle  Miocene 
Siliceous  shales,  marls, 

cherts  and   limestones. 


Unconformity 

•^Y^A    Late   Upper   Cretace 
rJ^^Asuncon   Group 


Unconformity 

Lower    Cretaceous 
MarmoleJO  Formation. 
^J-^j  basal   breccia.   Kmb 


^SjZI       Middle  Miocene  k.      I      Lower  Miocene 

^■%{  Analcile  Diabase-   sills  and  |  ^|  Voqueros    sandstone 

dikes. 

I    i    i    i    9  1 


.       Early  Upper  Cr«taceou» 
.'-,^ic,';    Jack  Creek  Formation 


Jurasilc 
„  JffcJ  Francican- Knoivlll* 
d.fferent.aUd 


Horizontal     Scale  and  Vertical  Scale  The  Same 


274 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


the  central  Coast  Ranges  of  7000  to  8000  feet  of  gray  sandy  shales,  silts, 
sandstones,  and  conglomerates.  If  it  was  not  removed  by  erosion  before 
the  Asuncion  group  was  deposited,  it  rests  on  the  erosion  surface  that 
followed  the  Diablan  orogeny.  The  Pacheco  sediments  may  be  less  widely 
distributed  in  the  central  Coast  Ranges  than  the  Asuncion  but  probably 
more  widely  in  the  northern  Coast  Ranges  (Taliaferro,  1943b). 

The  Pacheco  and  Asuncion  groups  are  separated  by  an  unconformity 
which  in  places  in  the  central  Coast  Ranges  is  as  angular  as  80  degrees. 
See  Fig.  17.12.  The  disturbance  represented  by  this  unconformity  has 
been  named  the  Santa  Lucian  by  Taliaferro  ( 1943b).  Where  the  Asuncion 
laps  over  older  rocks  than  the  Pacheco,  which  it  does  in  a  number  of 
places,  it  is  difficult  if  not  impossible  to  distinguish  the  two  disturbances 
— in  fact,  to  recognize  that  more  than  one  disturbance  has  occurred  ( Tal- 
iaferro, 1943b). 

The  Santa  Lucian  orogeny  was  strongest  in  the  Santa  Lucia  Range  and 
died  out  eastward.  During  the  orogeny,  the  Gabilan  mesa  rose  for  the  first 
time  (Taliaferro,  1944).  This  has  been  called  the  Diablo  uplift  by  Reed 
( 1933 ) .  Another  land  projection  into  the  general  north-south  trough  lay 
to  the  south  and  has  been  called  Catalina.  At  the  north  various  authors 
have  recognized  the  Klamath  Island  or  Klamathonia.  All  three  are  here 
treated  as  peninsulas,  branching  off  the  volcanic  archipelago,  which  as 
a  whole  has  been  called  Pacifica.  See  the  tectonic  map  of  the  Late  Cre- 
taceous, Plate  12. 

As  with  other  diastrophisms  in  California,  the  Santa  Lucian  appears  to 
have  taken  but  a  relatively  short  time.  Although  there  was  deep  erosion 
and  widespread  stripping,  subsidence  again  took  place,  and  the  sea  spread 
rather  rapidly  over  an  area  of  considerable  relief.  The  latest  Upper  Cre- 
taceous, the  Asuncion,  is  the  most  widespread  Cretaceous  unit  in  the  Coast 
Ranges.  The  Asuncion  is  predominantly  coarse  grained,  being  made  up 
of  arkosic  sandstone  and  coarse  conglomerates  perhaps  10,000  feet  thick. 
Fine  sediments  increase  eastward.  Franciscan  debris  increases  toward  the 
west.  Near  the  present  coast,  the  basal  conglomerates  contain  large  angu- 
lar to  subrounded  blocks  of  Franciscan  chert,  basalt,  diabase,  and  sand- 
stone, as  well  as  well-rounded  pebbles,  cobbles,  and  boulders  of  the 
ancient  crystalline  complex   (Sur  series  and  Santa  Lucia  granodiorite). 


To  the  east  in  what  is  now  the  great  valley  of  California,  the  Upper 
Cretaceous  deposits  have  been  divided  into  twelve  foraminiferal  zones, 
and  these  grouped  into  seven  stages  (Goudkoff,  1945).  During  the  first 
three  stages,  the  sea  was  transgressive  eastward  on  the  early  Sierra  Ne- 
vadan  landmass,  and  reached  a  maximum  distance  at  the  end  of  the  third 
stage  except  in  the  most  northerly  part.  Near  the  end  of  the  Upper  Cre- 
taceous (beginning  of  seventh  stage)  a  low  land  barrier  just  south  of 
Stockton  divided  the  region  into  two  basins.  The  extent  of  the  barrier 
westward  into  the  site  of  deposition  of  the  Chico  strata  has  not  been 
worked  out.  During  the  earlier  stages,  the  sediments  came  from  the  west 
as  pointed  out  by  Taliaferro,  but  in  the  later  stages  considerable  material 
came  from  the  east  according  to  Goudkoff,  and  some  from  the  northwest. 
The  eastern  source  suggests  slight  uplift  in  the  closing  phase  of  the 
Cretaceous  in  the  Sierra  Nevadan  landmass. 

Evidence  of  igneous  activity  is  present  in  many  formations  of  the  Meso- 
zoic  and  Cenozoic  in  the  central  Coast  Ranges  of  California,  and  Talia- 
ferro,  emphasizes  the  fact  that  volcanism  was  nearly  continuous  in  one 
place  or  another  nearby  during  these  eras. 

COLUMBIA  SYSTEM 

Extent 

The  term  Columbia  system  will  here  be  used  to  signify  the  mountains 
and  troughs  of  the  Mesozoic  era  in  British  Columbia,  southeastern  Alaska, 
the  Yukon,  Washington,  western  Idaho,  and  eastern  Oregon.  It  is  defined 
approximately  by  the  extent  of  the  Triassic  and  Jurassic  troughs  and  the 
volcanic  archipelago  on  the  west  that  supplied  much  of  the  material  to 
the  troughs.  In  many  respects  it  is  a  parallel,  if  not  a  continuation,  of  the 
great  Sierra  Nevada  and  Ancestral  Coast  Range  systems  of  the  United 
States.  See  tectonic  maps,  Plates  10,  11,  and  12,  and  Fig.  17.13. 

Triassic  and  Early  Jurassic  Phase 

In  the  southern  interior  of  British  Columbia  and  more  particularly 
southward  from  Kamloops  Lake,  strata,  presumably  of  Triassic  age,  are 
widely  displayed.  See  map,  Fig.  17.14.  This  assemblage  is  generally  re- 


MESOZOIC  SYSTEMS  ALONG  THE  PACIFIC 


275 


ferred  to  as  the  Nicola  series  and  consists  largely  of  volcanic  intrusives 
and  effusives,  tuffs,  and  agglomerates  with  argillites  and  limestone  at 
several  horizons.  The  total  thickness  in  places  is  10,000  to  15,000  feet,  but 
the  uppermost  part  may  be  of  early  Jurassic  age.  In  the  vicinity  of  Kam- 
loops,  the  Triassic  beds  with  a  basal  conglomerate  rest  without  angular 
unconformity  on  Carboniferous  beds,  and  possibly  the  same  general  re- 
lation holds  elsewhere.  The  Triassic  strata  occur  also  west  of  the  Fraser 
River,  and  consist  of  dark  green  massive  andesite  and  basalt,  chert,  argil- 
lite,  limestone,  and  tuffaceous  shales  (Cairnes,  1936).  Volcanic  rocks 
with  minor  amounts  of  sediments  occupy  a  great  part  of  Vancouver  Island 
and  of  Queen  Charlotte  Islands.  See  map,  Fig.  17.18.  The  bedded  char- 
acter of  the  fragmental  volcanic  rocks,  the  presence  of  a  few  limestone 
members  which  in  some  places  are  several  thousand  feet  thick,  and  the 
marine  fossils  found  in  tuffs  and  other  sediments  indicate  that  the  gen- 
eral assemblage  is  marine  in  origin.  It  seems  probable  that  the  beds  formed 
in  a  sea  which,  like  that  of  Carboniferous  time,  extended  over  the  greater 
part,  if  not  all,  of  the  Canadian  Cordilleran  region. 

In  Queen  Charlotte  Islands,  a  thick  clastic  series  with  some  pyroclastic 
material  ranges  in  age  from  Late  Triassic  to  Jurassic  and  grades  upwards 
into  a  volcanic  assemblage  of  tuffs  and  effusives,  5000  feet  or  more 
thick.  The  tuffs  are  fossiliferous,  evidently  were  laid  down  in  the  sea,  and 
are  of  Jurassic  and,  presumably,  Middle  Jurassic  age.  The  thick  assem- 
blage of  Triassic  volcanics  and  sediments  which  is  widely  displayed  over 
Vancouver  Island  and  known  as  the  Vancouver  group  also  may  be  suc- 
ceeded by  beds  of  Jurassic  age.  Strata,  resembling  the  Vancouver  group 
and  related  series  but  in  places  much  metamorphosed,  occur  at  intervals 
along  the  mainland  coast  and  as  included  masses  in  the  granitic  rocks  of 
the  Coast  Range.  Along  the  eastern  side  of  the  Coast  Range,  within  the 
basins  of  Nass  and  Skeena  rivers,  is  a  thick  assemblage  of  sedimentary  and 
volcanic  rocks  known  as  the  Hazelton  group  and  which,  as  indicated  by 
an  imperfectly  known  flora  and  fauna,  is  of  Jurassic,  possibly  Mid- Jurassic, 
age.  The  proportions  of  sedimentary  and  volcanic  material  composing  the 
Hazelton  group  varies  from  district  to  district  with  some  indication  that 
the  nonvolcanic  sedimentary  rocks  become  more  and  more  preponderant 
as  the  formation  is  followed  eastward  from  the  margin  of  the  Coast 


Fig.  17.13.  Batholiths  of  the  North 
American  Cordillera.  Heavy  dashed 
lines  indicate  axes  of  anticlinoria,  syn- 
clinoria,  belts,  and  general  trends  of 
the  late  Jurassic  and  early  Cretaceous 
phase.  The  dashed  line  north  of  the 
Nelson  batholith  is  an  anticlinorium  in 
Proterozoic  strata  and  may  be  Lara- 
mide   in   age. 


276 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


SHUSWAP  TERRANE 


Fig.  17.14.  Generalized  distribution  of  major  rock  units  of  southern  British  Columbia.  After 
Smith  and  Stevenson,  1955.  The  Shuswap  terrane  has  some  Paleozoic  and  Belt  outcrops  and  the 
Belt  terrane  has  some  small   patches  of  Paleozoic.  All  are  invaded   by  great  plutons,   not  shown, 

Range.  The  strata  are,  in  part  at  least,  marine;  but  the  presence  of  plant 
remains  and  other  features  indicates  that  the  sea  was  shallow  and  that 
possibly  some  parts  of  the  assemblage  may  be  nonmarine.  In  southern 
British  Columbia,  various  assemblages  of  sediments  or  of  sedimentary  and 
volcanic  strata  are  known,  and  others  are  believed  to  be  of  Jurassic  age, 
as  in  the  Kootcnay  Lake  district  where  fossiliferous  Jurassic  beds  rest  on 
Paleozoic  strata.  In  general,  the  Jurassic  beds  appear  to  be  as  widely,  or 
even  more  widely,  distributed  than  the  Triassic;  and  as  yet  there  is  no 
evidence  of  any  interval  of  orogenic  movements  that  separated  the  two 


except  the   Upper  Cretaceous   of   Vancouver    Island   and   the   strata   east   of   the    Rocky  Mountain 
trench. 


periods.  Thick  assemblages  of  sediments  and  pyroclastics,  as  well  as  great 
volumes  of  extrusive  and  intrusive  volcanic  strata,  occur  in  northern  Brit- 
ish Columbia  and  southern  Yukon  and  apparently  correspond  to  the 
Hazelton  group  in  the  south.  For  more  detail,  see  Canadian  Geological 
Survey,  Economic  Geology  Series,  No.  1,  1957. 

Daly  (1912)  describes  Triassic  strata  in  northwestern  Washington  that 
have  a  thickness  between  3000  and  7000  feet.  They  are  principally  dark 
gray  to  black  argillite,  in  part  bituminous,  generally  associated  with  bands 
of  gray  to  greenish  gray  sandstone  and  grit  and  in  a  few  places  with  fine 


MESOZOIC  SYSTEMS  ALONG  THE  PACIFIC 


277 


conglomerate.  The  gritty  beds  are  charged  commonly  with  small  angular 
fragments  of  black  argillite.  All  the  coarser  types  are  decidedly  feld- 
spathic.  Some  of  these  sediments  could  probably  be  called  graywacke. 

In  southeastern  Alaska,  Buddington  and  Chapin  (1929)  have  noted 
numerous  outcrops  of  Triassic  rocks  and  others  that  may  be  Triassic.  All 
the  strata  that  carry  fossils  are  Upper  Triassic,  and  they  seem  to  be 
divisible  into  three  units,  one  consisting  of  sediments  and  the  other  two 
of  volcanic  rocks  with  a  little  intercalated  sedimentary  material.  The 
volcanic  formations  are  differentiated  from  volcanic  formations  of  other 
periods  on  the  basis  of  their  faunas.  Their  character  and  structural  rela- 
tions over  wide  areas  are  insufficiently  known,  and  their  lithology  is  too 
similar,  to  separate  them  otherwise.  They  comprise  green  andesitic  flows, 
breccia,  and  tuffs.  The  lava  predominantly  shows  pillow  structure  but  is 
in  part  amygdaloidal  and  in  part  polygonally  jointed.  Much  of  the  breccia 
has  a  limestone  matrix  and  is  in  considerable  part  the  result  of  primary 
disaggregation  of  the  radial-jointed  pillows.  The  basal  part  of  the  volcanic 
rocks  on  Kuiu  Island  consists  of  interbedded  limestone  and  green 
andesitic  tuff  and  lava  with  local  conglomeratic  beds.  On  Kupreanof 
Island,  the  volcanic  formation  has  a  bed  of  conglomerate  150  to  200  feet 
thick  in  local  areas  at  its  base.  The  basal  Triassic  conglomerates  and  the 
unconformable  relations  to  the  Paleozoics  have  been  discussed  previously 
in  the  section  on  the  late  Permian  or  early  Triassic  orogenic  phase. 

On  Kupreanof  Island  and  the  islands  southeast  of  Kake,  Upper  Triassic 
sediments  overlie  the  upper  limestone  division  of  the  Permian  and  are 
overlain  in  apparent  conformity  by  volcanic  rocks  of  late  Triassic  age. 
Locally  there  is  a  thick  bed  of  coarse  conglomerate  of  the  Upper  Triassic 
volcanic  rocks.  On  the  northeast  side  of  Kuiu  Island,  however,  the  Upper 
Triassic  volcanic  rocks  overlie  the  lower  division  of  the  Permian  without 
any  apparent  angular  unconformity.  The  volcanic  rocks  of  Kuiu  Island 
also  carry  a  different  fauna  from  those  on  Kupreanof  Island.  Uncon- 
formities are  indicated,  therefore,  not  only  at  the  base  of  the  Upper 
Triassic,  but  within  it  (Buddington  and  Chapin,  1929). 

The  Triassic  occurrences  in  British  Columbia  and  Washington  are  so 
little  known  that  unconformities  within  the  beds  assigned  to  this  period, 
if  they  exist,  are  not  known.  It  is  of  interest,  however,  to  recall  the  un- 


conformities below  and  above  the  Upper  Triassic  beds  of  western  Nevada, 
and  to  note  the  same  position  of  breaks  in  southeastern  Alaska. 

Another  series  of  beds  that  was  intruded  by  the  great  Coast  Range 
batholith  in  southeastern  Alaska  has  been  assigned  questionably  to  the 
Jurassic.  Some  of  these  beds  may  be  Lower  Cretaceous  and  some  Triassic 
and  Paleozoic.  They  have  been  divided  into  two  groups  for  mapping  pur- 
poses, namely,  a  predominantly  sedimentary  facies  consisting  of  gray- 
wacke, black  slate,  and  conglomerate;  and  a  predominantly  volcanic 
facies  consisting  of  schistose  greenstone  made  up  of  breccia,  flows  and 
tuffs,  and  black  slate  and  graywacke. 

These  questionable  Jurassic  and  Lower  Cretaceous  rocks  are  believed 
to  overlie  the  Paleozoic  and  Triassic  formations  unconformablv.  A  pro- 
nounced angular  unconformity  separates  Jurassic  from  Devonian  forma- 
tions at  the  north  end  of  Kupreanof  Island,  but  where  the  Jurassic  rests 
on  the  Triassic  the  break  is  more  in  the  nature  of  a  disconformity  ( Bud- 
dington and  Chapin,  1929). 

The  Jurassic  ( or  Lower  Cretaceous )  slate  and  graywacke  appear  to  be 
much  less  metamoq)hosed  than  the  older  Mesozoic  formations,  but  this  is 
certainly  in  part  due  to  their  character.  In  all  the  formations,  the 
argillaceous  beds  are  most  resistant  to  recrystallization,  and  their  abun- 
dance in  this  series  gives  the  Jurassic  formations  a  misleading  appearance 
of  minor  metamorphism.  The  pebbles  and  cobbles  of  the  intercalated 
conglomerates  are  very  markedly  flattened  as  a  result  of  very  strong 
pressure. 

To  summarize,  map,  Fig.  17.14  may  be  referred  to  again.  Triassic  and 
Jurassic  strata  were  deposited  east  of  the  present  Canadian  Rockies,  and 
this  basin  of  deposition  was  separated  from  a  broad  region  of  deposition 
by  a  Mesozoic  geanticline  which  now  is  displayed  chiefly  as  the  Beltian 
terrane.  The  sediments  of  the  eastern  basin  are  miogeosynclinal  and  shelf 
types,  whereas  the  sediments  west  of  the  geanticline  are  eugeosynclinal. 
and  may  have  accumulated  in  several  deep  troughs.  Due  to  the  great 
batholiths  that  occupy  much  of  the  region  of  southern  British  Columbia 
it  is  apparently  impossible  to  recognize  the  original  extent  of  the  basins  or 
their  number.  Triassic  and  Jurassic  strata  occur  in  places  from  Kootenay 
lake  westward  to  the  Pacific  Ocean.  Since  thev  are  laden  with  volcanic 


278 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 

la 


SCALE 


IN     MILES 
10 


20 


Fig.  17.15.  Diagrammatic  east-west  section  through  the  Okanogan  composite  batholith.  s,  schists 
and  associated  Paleozoic  rocks;  Cr,  Pasayton  lower  Cretaceous  arkose  sandstones;  la,  Chopaka 
peridotite;  lb,  Basic  complex;  2,  Ashnola  gabbro;  3a,  Remmel  batholith,  western  phase;  3b, 
Remmel  batholith,  eastern  phase;  3c,  Osoyoos  batholith;  4,  Kruger  alkaline  body;  5,  Similkameen 

materials  a  west-lying  volcanic  archipelago  and  orogenic  belt  may  be 
postulated  similar  to  that  of  California  and  western  Nevada,  but  possibly 
the  regions  of  sedimentation  were  complicated  by  geanticlines  which 
also  were  sites  of  volcanic  activity. 

Cretaceous  strata  have  a  more  restricted  distribution.  Lower  Cretaceous 
deposits  of  interior  basin  type  occur  in  the  Rockies  and  eastward.  A 
narrow  trough  of  them  is  recognized  west  and  south  of  Kamloops  Lake  in 
mid-interior  and  east  of  the  great  Coast  Range  batholith.  A  small  deposit 
occurs  on  the  west  coast  of  Vancouver  Island.  It  would  appear  that  the 
Belt  geanticline  had  widened  westward  from  Jurassic  time,  and  perhaps 
another  broad  geanticline  existed  in  the  site  of  the  Coast  Range  batholith 
and  Vancouver  Island. 

In  Late  Cretaceous  time  the  entire  interior  from  the  Rocky  Mountains 
to  the  Strait  of  Georgia  had  become  emergent  and  only  flanking  deposits 
accumulated.  This  was  undoubtedly  a  consequence  of  the  great  batho- 
lithic  intrusions  and  previous  compressional  orogeny  of  the  broad  cordil- 
leran  region. 

Nevadan  Orogeny 

Batholiths  of  the  International  Border.  An  almost  continuous  succes- 
sion of  batholiths  stretches  more  than  350  miles  along  the  international 


batholith;  6a,  Cathedral  batholith,  older  phase;  6b,  Park  granite  stock;  7,  Cathedral  batholith, 
younger  phase. 

The  components  of  the  batholith  are  numbered  in  order  of  intrusion.  Vertical  scale  is  exag- 
gerated twice  the  horizontal.  After  Daly,   1912. 

border  between  Washington  and  British  Columbia.  These  have  been  de- 
scribed by  Daly  (1912),  Smith  and  Calkins  (1904,  1906),  and  Smith 
(1904),  and  later  studies  have  been  made  by  Waters,  Krauskopf,  Camp- 
bell, and  Pardee  (see  references  in  Waters  and  Krauskopf,  1941).  It  is 
highly  probable  that  the  plutons  form  the  basement  southward  under  vast 
areas  of  lavas  of  the  Columbia  Plateau  because  granitic  rocks  appear  in 
the  Ochoco-Blue  Mountains  uplift  of  central  and  eastern  Oregon  midway 
to  the  Klamaths  and  Sierra  Nevada  (Waters,  1933)  and  also  southeast- 
ward under  more  lavas  through  the  Thatuna  batholith  to  the  great  Idaho 
batholith. 

Intrusions  of  peridotite,  gabbro,  and  diorite  are  associated  with  the 
prevailing  granodiorite  of  the  great  batholiths.  Quartz  monzonite,  quartz 
diorite,  and  granite  are  locally  widespread.  In  certain  areas  where  the 
succession  of  intrusions  has  been  worked  out,  it  is  a  cycle  similar  to  that  of 
the  Sierra  Nevada,  viz.,  first  the  smaller  bodies  of  ultrabasic  rock,  then 
gabbros  and  diorites,  and  finally  the  great  granitoid  bodies.  Pegmatites  are 
rare  in  the  batholiths  along  the  border  in  Washington,  but  aplite  masses 
locally  of  almost  batholithic  proportions  crosscut  the  earlier  intrusions. 
The  borders  of  the  batholiths  commonly  show  discordant  relations  to  the 
country  rock,  and  extensive  masses  of  contact  breccia  are  found  along  the 
intrusive  margins   (Waters,   1933).   Some  of  the  best  examples  of  dis- 


MESOZOIC  SYSTEMS  ALONG  THE  PACIFIC 


279 


SCALE       IN      MILES 
I  2  3 


;  Fig.  17.16.  Cross  sections  in  the  Similkameen  District,  British  Columbia,  Latitude  49,  Longitude 
|  120.  1,  Vaseaux  fm.,  paragneiss,  schist,  quartzite;  3,  Koban  group,  schist,  greenstone;  6,  Barslow 
|  fm.,  argillite;  8,  Shoemaker  fm.,  chert,  some  tuff,  greenstone;  9,  Old  Tom  fm.,  greenstone,  basalt 
j  flows,  sills,  bosses,  some  diorite;  10,  altered  rocks  of  dioritic  composition;  11a,  Osoyoos  grano- 
f  diorite;    lib,    Fairview    granodiorite;    12a,    hornblendite;    12b,    pyroxenite;    14a,    Kruger    syenite; 

rcordant  batholiths,  as  well  as  some  of  the  most  conclusive  evidence  of 
Utoping,  may  be  found  in  the  northern  Cascades  (Daly,  1912).  See  Figs. 
$7.15  and  17.16. 

The  igneous  bodies  generally  designated  by  the  names  Osoyoos  and 
.  Colville  batholiths  (see  map,  Fig.  17.13)  are  really  complex  associations  of 
|  eight  plutons.  Contact  metamorphism  is  intense  near  some  but  almost 
i  absent  near  others  ( Krauskopf ,  1941 ) .  Detail  along  the  border  of  the  Col- 
j  ville  batholith  has  been  worked  out  by  Waters  and  Krauskopf  ( 1941 ) .  See 


14b,   Oliver  syenite;    15,   granodiorite;    16a,   Oliver   granite;    17,   Springbrook   fm.,   conglomerate, 
some  sandstone  and  shale;  18,  maroon  fm.,  basaltic  lava,  some  breccia,  tuff,  conglomerate. 

1    and   3,  Carboniferous.  6,   8,  and   9,  Triassic  or  older.   11    and    12,  Jurassic  (?).    14,    15,   and 
16,  Jurassic  and   (or)  younger.   17  and   18,   Eocene.  After   Daly,    1912. 


Fig.  17.17.  The  batholith  is  a  complex  plutonic  mass  that  intrudes  folded 
and  dynamometamorphosed  sedimentary  and  volcanic  rocks  of  late  Paleo- 
zoic and  Triassic  age.  Along  the  sharply  discordant  contact,  the  wall  rocks 
are  much  fractured  and  granulated,  but  contact  metamorphism  is  slight  or 
absent.  The  batholith  is  remarkably  heterogeneous,  both  structurally  and 
petrographically.  A  central  mass  of  structureless  granodiorite  grades  out- 
ward into  a  belt  of  foliated  igneous  rock  which  commonly  shows  intricate 
swirling  of  the  foliation.  The  swirled  rocks  grade  into  a  peripheral  belt  of 


280 


STRUCTURAL  GEOLOGY  OF  NORTH  AMERICA 


Fig.  17.17.  Structural  map  of  part  of  the  border  of  the  Colville  batholith.  Reproduced  from 
Waters  and   Krauskopf,   1941. 

variable  but  well-foliated  migmatitic  gneisses  ( magmatic  injection  and