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Geology of the Harper Ranch Group (Carboniferous-Permian) and Nicola Group (upper Triassic) northeast… Smith, Randall Blain 1979

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GEOLOGY OF THE HARPER RANCH GROUP (CARBONIFEROUS-PERMIAN) AND NICOLA GROUP (UPPER TRIASSIC) NORTHEAST OF KAMLOOPS, BRITISH COLUMBIA by RANDALL BLAIN SMITH A.B., C o r n e l l U n i v e r s i t y ,  1974  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in THE FACULTY OF GRADUATE Department o f G e o l o g i c a l  STUDIES Sciences  We a c c e p t t h i s t h e s i s as c o n f o r m i n g to t h e r e q u i r e d s t a n d a r d  THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1979  <c) Randall B l a i n Smith, 1979  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives.  It is understood that copying or publication  of this thesis for financial gain shall not be allowed without my written permission.  Department nf  Geological Sciences  The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5  D  a  t  e  A p r i l 10,  1979  ABSTRACT  The actually Harper  "Cache consists  Ranch The  limestone This  Lower  Permian  dacitic  sequence  of  Paleozoic of  Late  the  in  ages,  the  Late  is  with  a  in  part  detail.  deep water  lenses  found  near  period  of  volcanic  of  the  In  this  quiescence  shallow  and  marine  metres  Only  the  of  lower  andesitic  eruptions, and  high  con-  limestone  sequence.  shallowing  to  then  bioclastic  the  of  Pennsylvanian  hundred  currents  of  sequence  portion,  marine  base  of  group.  Mississippian the  Group.  Middle  several  turbidity  Upper  is  to  area  Paleozoic  km-thick  by  shallow  by  Nicola  5  rare  overlain  upper  thin  Kamloops  Mississippian  produced by  A  the  Triassic  Group  tuff  fauna  arc  orogenic  (1977).  arc  was  an  and  Group,  Mt.  the  Roberts  Triassic  old  Groups  above  to  deformation  and and  low  of  southern  closure  of  the  terrane  to  elastics  the  rocks  orogenic  bounded  Eastern grade  British  back-arc the  parts  It  of  the  a  on  of  the  east  Late zone.  by  Caribooan the  Late  assemblage  orogeny.  Paleozoic of  Monger  metamorphism  of  Columbia  have  basin,  east.  of  subduction  Mississippian  l i t h i c - r i c h  Formation,  probably  east-dipping  basin  Devonian  the  were  an  back-arc  Late  supplied  eugeoclinal  the  formed  "oceanic"  Permo-Triassic  with  Chilliwack  which  formed by  Pre-Late  by  arc  terrane  Paleozoic  caused  Ranch  volcanic  lands  Anarchist  the  Harper  the  orogenic  Late  a  ash  Upper  Ranch  studied  flows.  marine  the  in  floor. The  This  redeposited  during  of  forming  consist  subaqueous  and  mapped  different  disconformably  tuffs and  of  Harper  fossils  is  previously  redeposited  were  accumulated  East  and  limestone  diverse  basin  the  section  centration a  name),  of  yield  as  sequences  the  reworked  with  (new  mudstone  age.  Group"  two  part  which  km o f  of  Group  lower  hemipelagic  2.3  Creek  and  may  collision  the been of  A new  v o l c a n i c a r c formed i n the L a t e T r i a s s i c i s r e p r e s e n t e d  v o l c a n i c flows and b r e c c i a s o f the N i c o l a Group west o f Kamloops. Kamloops, the N i c o l a Group c o n s i s t s o f 3 km which accumulated i n deep water w i t h i n  sandstone and  deposited  t u r b i d i t y currents  s i v e and and  by  a back-arc b a s i n .  of  hemi-  redeposited  l i m e s t o n e , a l l o f which were  concentration  density  flows.  Mas-  p i l l o w e d b a s a l t i c o r a n d e s i t i c v o l c a n i c flows o c c u r near the base  top o f the sequence, which has  units.  P e l a g i c and  are i n t e r b e d d e d w i t h  conglomerate, and and h i g h  East  o f sediments and v o l c a n i c l a s t i c s  p e l a g i c mudstones dominate the s e c t i o n , but tuff, lithic  by  Conodonts e x t r a c t e d  been s u b d i v i d e d  into five  lithologic  from l i m e s t o n e s y i e l d K a r n i a n ages.  Redeposited t u f f s i n the N i c o l a Group were p r o b a b l y d e r i v e d v o l c a n i c a r c t o the west, and the e a s t .  conglomerates c o n t a i n  c a n i c d e t r i t u s , i n c l u d i n g abundant c h e r t and  exposed i n the  the  a l s o from submarine v o l c a n o e s i n the b a s i n  L i t h i c sandstones and  have been d e r i v e d  from  sedimentary and  c h e r t y mudstone.  These  to  volmay  from a c c r e t e d o c e a n i c r o c k s o f the Cache Creek Group,  emergent P i n c h i g e a n t i c l i n e west o f the v o l c a n i c a r c .  Detrital  b l u e amphiboles i n f i n e - g r a i n e d t u r b i d i t e l i m e s t o n e s suggest t h i s sediment was  also derived  from s h a l l o w waters s u r r o u n d i n g the P i n c h i t e r r a n e .  N i c o l a v o l c a n i c arc therefore paleoslope. stretched The trending  b a c k - a r c b a s i n was  Harper Ranch and  east-facing  f l o o r e d by o l d e r e u g e o c l i n a l  from the a r c eastward to the  rocks,  f a u l t the  and  miogeocline.  N i c o l a Groups are s e p a r a t e d by a northwest-  v e r t i c a l f a u l t , p r o b a b l y of L a t e Mesozoic o r E a r l y T e r t i a r y  E a s t o f the w i t h few  The  seems to have been b u i l t on an  The  age.  lower Harper Ranch Group forms an e a s t - f a c i n g homocline  d i s c e r n i b l e mesoscopic f o l d s .  To  the west, l i t h i c u n i t s i n the  N i c o l a Group o u t l i n e a p a i r o f f a u l t e d n o r t h w e s t - t r e n d i n g f o l d s :  an  upright  s y n c l i n e on the e a s t , and a westward-overturned a n t i c l i n e on the west. Deformation  p r o b a b l y took p l a c e d u r i n g the L a t e s t T r i a s s i c t o E a r l i e s t  J u r a s s i c I n k l i n i a n orogeny.  The T r i a s s i c rocks are i n t r u d e d by the P a u l  Peak Stock, a zoned i n t r u s i o n r a n g i n g from p y r o x e n i t e t o g r a n i t e i n composition.  T h i s p l u t o n i s s i m i l a r t o zoned Alaskan-type m a f i c - u l t r a m a f i c  i n t r u s i o n s i n composition the 200 m.y.  and t e c t o n i c s e t t i n g , and i s p r o b a b l y p a r t o f  p l u t o n i c s u i t e o f s o u t h e r n B r i t i s h Columbia.  Numerous  a n d e s i t i c to r h y o l i t i c d i k e s o f p r o b a b l e Eocene t o O l i g o c e n e age o t h e r rock  cut a l l  units.  P r e h n i t e - p u m p e l l y i t e f a c i e s metamorphism has a f f e c t e d a l l rock u n i t s i n the a r e a , i n c l u d i n g the d i k e s .  A l t e r a t i o n of v o l c a n i c l a s t i c rocks i n  the Harper Ranch Group i s much more complete than i n the younger r o c k s , s u g g e s t i n g t h a t the P a l e o z o i c rocks were a f f e c t e d by the P e r m o - T r i a s s i c low grade metamorphic event r e c o r d e d elsewhere  i n southern B r i t i s h  Columbia.  V  TABLE OF CONTENTS  ABSTRACT LIST OF TABLES LIST OF ILLUSTRATIONS LIST OF PLATES ACKNOWLEDGEMENTS  i i viii ix xii xiii  Chapter I.  INTRODUCTION  1  P r e l i m i n a r y Statement L o c a t i o n , Physiography, and S u r f i c i a l Regional Geologic S e t t i n g Stratigraphy Structure II.  HARPER RANCH GROUP (MAP  1 5 6 7 10  Geology  UNIT 1)  12  Introduction S t r u c t u r a l S e t t i n g , P h y s i c a l S t r a t i g r a p h y , and Biostratigraphy Sedimentology Mudstones V o l c a n i c Sandstones o r Redeposited T u f f s D e s c r i p t i o n o f Sedimentary S t r u c t u r e s F i n e t o medium-grained sandstone Coarse t o v e r y c o a r s e sandstone Sandstone Petrography . . . Source and D e p o s i t i o n o f the V o l c a n i c D e t r i t u s . . Deep Water C a l c i r u d i t e Shallow-marine Limestone Summary o f D e p o s i t i o n a l S e t t i n g Regional C o r r e l a t i o n s E a s t e r n Assemblage Cache C r e e k - B r i d g e R i v e r Assemblage Southern B r i t i s h Columbia Assemblage and Suggested Revision T e c t o n i c S i g n i f i c a n c e o f the Harper Ranch Assemblage . . III.  12  o  12 19 21 25 25 25 26 28 37 40 43 54 55 57 60 62 66  NICOLA GROUP (MAP-UNITS 2 THROUGH 6) Introduction Physical Stratigraphy Structural Setting Description of Units Unit 2 Unit 3 Unit 4 Unit 5 Unit 6  .  76 76 76 76 78 79 80 80 82  vi  Biostratigraphy Sedimentology Mudstone Thin  85  and  and to  Submarine  Basinal  Tuff Sandstone  and  Turbidites  Redeposited  and  94  Tuff  106  Conglomerate  113  Implications  119  Depositional Between  Setting  the  119  Nicola  and  Harper  Groups  Provenance of  Flows  or  Regional  Relationship Ranch  91 92  110  and of  88  Limestone  Pyroclastic Sandstone  Lithic Summary  Mudstone  Mudstone  Vitric Discussion  88 88  Medium-bedded  Redeposited  Petrology  Siltstone  Laminated  Volcanic  Sedimentary  119  of  Clastic  Detritus  the  Quesnel  Trough  Tectonic  Setting  and  and  Paleogeography 121  Evolution  of  the  Nicola  Group IV.  INTRUSIVE Paul  128  ROCKS  Peak  Field  134  Stock  (Map-Unit  7)  134  Relations  134  Petrography Olivine  136 Clinopyroxenite  Leucogabbro Hornblende Quartz  and  136  Diorite  Gabbro  and  Monzodiorite  136  Diorite  and  141  Hornblende  Granite  .  .  .  .  Petrogenesis Origin  143  of  the  Rock  Series  the  Ultramafic  Leucogabbro  to  Granite Origin Age Small  and  143  of  Regional  Plugs,  S i l l s ,  Description Thick  of  Dikes  Intrusive  Porphyry  8)  Rocks  .  152 .  .  .  Plug  Andesite  Rhyolite  .  .  .  .  .  153  Dikes  154 Plug  Andesite  Hornblende-Pyroxene  V.  148  (Map-Unit  153  Non-porphyritic  and  146  Correlation and  Minor  Porphyritic  Age  Rocks  S i l l s  Dacite  143  and  Correlation  of  154 Dikes  Andesite  and  S i l l s  Dikes  155  S i l l s Minor  155 156  Intrusive  METAMORPH I S M  Rocks  156 158  Introduction  158  Low  158  Grade  Metamorphism  General  Features  Triassic Paul Dikes  158  Rocks  160  Peak  Stock  and  S i l l s  Carboniferous  Volcaniclastic  Conditions  Metamorphism  of  164 165 Rocks  167 169  Contact  Metamorphism  .  Albite-Epidote-Hornbels Hornblende-Hornfels Effects  of  Conditions VI.  STRUCTURAL  . • . - .  .  .  Low  172 Grade  Metamorphism  175  Metamorphism  175  GEOLOGY  176  Introduction  176  Folding  176  Harper  Ranch  Nicola  Group  Group  .  SUMMARY  I.  AND  CONCLUSIONS  REPORT (NTS  II.  .  176  183  188 ON C O N O D O N T  LIMESTONE  APPENDIX  .  181  BIBLIOGRAPHY APPENDIX  .  177  Faulting VII.  169 169  Facies  Subsequent of  .  Facies  92  SAMPLES  1/9)  STRUCTURAL  ,  COLLECTIONS FROM  SOUTH-CENTRAL  DATA  EXTRACTED  T H E KAMLOOPS B.C  FROM  MAP-AREA 200 203  viii-  TABLES  Table I.  II.  Modal a n a l y s e s o f v o l c a n i c sandstones Ranch Group Allochem  from t h e Harper  content o f d i f f e r e n t m i c r o f a c i e s o f M i s s i s s i p p i a n  l i m e s t o n e , U n i t 1A, Harper Ranch Group III. IV. V.  VII. VIII. IX. X.  XI.  45  V i s u a l l y e s t i m a t e d modes o f r e d e p o s i t e d t u f f s  95  Average compositions  98  o f zoned p l a g i o c l a s e from U n i t 3 . . . .  V i s u a l l y e s t i m a t e d modes o f v o l c a n i c sandstones o r r e d e p o s i t e d t u f f s from U n i t s 2, 4, and 5  VI.  29  V i s u a l l y e s t i m a t e d modes o f v i t r i c  tuffs  107 I l l  Modal a n a l y s e s o f c l a s t i c rocks from U n i t 5  117  V i s u a l l y e s t i m a t e d modes o f p l u t o n i c r o c k s from P a u l Peak Stock A n o r t h i t e c o n t e n t o f p l a g i o c l a s e f e l d s p a r s from P a u l Peak Stock  137 138  Low grade metamorphic m i n e r a l s found i n r o c k s o f d i f f e r e n t age and l i t h o l o g y i n the study a r e a  161  A l b i t e - e p i d o t e - h o r n f e l s f a c i e s m i n e r a l assemblages i n the c o n t a c t metamorphic a u r e o l e o f P a u l Peak Stock . . . .  173  ix,  ILLUSTRATIONS  Figure 1.  Map  of  southern  -.1 " t o w n s  British  and-map-areas  tectonic  Columbia  "mentioned  subdivisions  of  the  showing in- the  the  location  text.  Cordillera  Inset  in  of  shows  British  Columbia 2.  Geologic  3.  Sketch  of  the  region  surrounding  geologic  map  of  Harper  South 4.  2  map  Thompson  Stratigraphic Harper  section  Ranch  the  River  east of  of  the  Kamloops  Ranch  Group  .  8  along  the  Kamloops  lower  13  portion  of  the  Group  .  15  5.  Laminated  mudstone  and  siltstone,  Harper  Ranch  Group  .  .  .  .  22  6.  Laminated  mudstone  and  siltstone,  Harper  Ranch  Group  .  .  .  .  22  7.  Q-F-L the  8.  plot  of  Harper  Polished  modal Ranch  slab  of  data  from  volcaniclastic  rocks  from  Group  30  volcanic  sandstone  from  the  Harper  Ranch  Group 9. 10.  Polished  14.  Polished Harper  15.  of  thin-section,  Harper  Sample  Ranch  MK-186,  Group  of  thin-section,  Sample  MK-186,  33 of  thin-section,  Sample  MK-186,  Harper 34  of  thin-section,  Sample  MK-193,  Harper  Group  34 of  Ranch  Ranch  31  Harper  Group  slab  . . .  Harper  Group  Photomicrograph Harper  sandstone,  33  Photomicrograph Ranch  volcanic  Group  Photomicrograph Ranch  13.  of  Photomicrograph Ranch  12.  slab  Photomicrograph Ranch  11.  31  poorly  sorted  calcirudite,  Group of  the  Group  . alga  Solenopora,  Loc.  .  Loc.  F-2, 41  F-2, 42  X  16.  17.  18.  19.  20.  Photomicrograph o f t h e a l g a Parachaetetes, Harper Ranch Group  L o c . F-2, 42  Upper P a l e o z o i c e u g e o c l i n a l assemblages i n B r i t i s h 'Columbia "  58  R e v i s e d Upper P a l e o z o i c e u g e o c l i n a l assemblages i n southern B r i t i s h Columbia and n o r t h e r n Washington  63  Sketch c r o s s - s e c t i o n showing i n f e r r e d p a l e o g e o g r a p h i c and p a l e o t e c t o n i c elements o f southern B r i t i s h Columbia during the Late M i s s i s s i p p i a n t o E a r l y Pennsylvanian . . .  71  S t r a t i g r a p h i c r e l a t i o n s h i p s o f u n i t s w i t h i n the N i c o l a Group  77  21.  P o o r l y d e f i n e d v e s i c u l a r p i l l o w s i n U n i t 6B  83  22.  T h i n t o medium-bedded mudstone i n U n i t 5  90  23.  P o l i s h e d s l a b o f thin-bedded mudstone, showing numerous f l a t t e n e d burrows p a r a l l e l  t o bedding  90  24.  Photomicrograph o f t h i n - s e c t i o n o f t u f f from U n i t 3  97  25.  Photomicrograph o f t h i n - s e c t i o n o f t u f f from U n i t 3  97  26.  P o l i s h e d s l a b o f conglomerate from U n i t 3, c o n s i s t i n g e n t i r e l y o f pebbles o f p o r p h y r i t i c d a c i t e o r a n d e s i t e P o l i s h e d s l a b o f submarine t u f f from U n i t 3 showing a Bouma BC sequence: p l a n a r l a m i n a t i o n s o v e r l a i n by cross-laminations  27.  28.  29.  30.  31.  . . .  P o l i s h e d s l a b o f submarine t u f f from U n i t 3 showing t h e base o f a graded t u r b i d i t e bed, w i t h a c o n c e n t r a t i o n o f c o a r s e p l a g i o c l a s e , pyroxene, and hornblende c r y s t a l s  101  104  .  105  Photomicrograph o f t h i n - s e c t i o n , Sample MK-151, v o l c a n i c sandstone o r r e d e p o s i t e d t u f f from U n i t 4  109  Photomicrograph o f t h i n - s e c t i o n , Sample MK-215, v o l c a n i c sandstone o r r e d e p o s i t e d t u f f i n U n i t 5  109  Photomicrograph o f t h i n - s e c t i o n (Sample MK-150) o f vitric  tuff  from U n i t 2  32.  Outcrop o f l i t h i c  conglomerate i n U n i t 5, Dome H i l l s  33.  Polished slab of l i t h i c Dome H i l l s  112 . . . .  115  conglomerate from U n i t 5, 115  xi  34.  Photomicrograph o f t h i n - s e c t i o n , Sample MK-132, l i t h i c v o l c a n i c sandstone from U n i t 5  118  L o c a t i o n map o f Ouesnel t r o u g h and s u r r o u n d i n g Mesozoic t e c t o n i c elements o f c e n t r a l and southern B r i t i s h Columbia  122  36.  G e o l o g i c map o f t h e P a u l Peak Stock  135  37.  Photomicrograph o f leucogabbro, MK-98  140  38.  Photomicrograph o f hornblende gabbro, MK-195  142  39.  Photomicrograph o f hornblende g r a n i t e , MK-104  142  40.  P r e h n i t e v e i n i n p y r o c l a s t i c t u r b i d i t e from U n i t 3, Dome H i l l s  162  35.  41.  Map o f m i n e r a l assemblages and i s o g r a d s from t h e c o n t a c t metamorphic a u r e o l e o f t h e P a u l Peak Stock  . . . .  171  x i i  PLATES  Plate I.  Geologic Dome  Map  of  Hills,  Paul  Ridge  Nicola  and  map-area,  the  southwestern  British  Columbia  -in-~s?ear'••  -  pocket  -f  t f i  o\\ II.  Microfauna Harper  III.  Microfacies IA,  IV.  Group, VI.  from  extracted  Structural  map  Ridge and  limestone,  IA)  Mississippian  18 limestone,  Unit  Group  upper  Ranch  Paul  Mississippian (Unit  upper  Ranch  Harper  Conodonts  upper Group  from  Harper  Microfacies IA,  V.  from  Ranch  47  Mississippian  limestone,  Unit  Group from and  49 limestones Dome  Hills  cross-sections  in  the  Nicola 87 -in_r.ear^ £ 3 pocket  •  -f  '  ^.jj  x i i i  ACKNOWLEDGEMENTS  W. Creek  R.  Danner  Group,"  him  and  with  the  Paleozoic  Barnes,  P.  Paterson, B.  for  the  P.  B.  from  United  the  on  R.  their  so  Geological  of  California  at  and  W.  like Indian  to  him  Barnes  to  a l l  of  who  Also, times  also  R.  and  use the  the when  give  understanding  of  K.  B.  W.  B.  Nielsen,  I.  A.  Travers.  of  Canada  of  laboratory  SEM  "Cache  Columbia:  identified  the  f a c i l i t i e s  photomicrographs. by  Armstrong  Cruz  J .  T.  Dutro,  provided  boundary. provided  J r . ,  of  information  Eugenio  technical  Gonzales help  in  illustrations. earlier  drafts  of  the  thesis,  greatly.  me  interest  people to  for  conduct  and  completion  special  W.  the  with  Monger,  identified L.  these  allowed  my  of  Discussions  British  H.  reviewed  text  Band,  the  Santa  the  the I  B.  thank  W.  taking  and  work.  Survey  were  improved  lands.  through  in  problems  improved  Triassic-Jurassic  Danner  comments  this  Solberg,  Survey.  the  J .  and  Group  photographs  reservation  indeed,  assisted  to  southern  Geological advice  Ranch  of  P.  the  would  me  and  of  Grette,  of  Kamloops  helped  the  of  greatly  Ross,  provided  dating  preparation  V.  of  Harper  University  I the  Cameron  States  of  W.  J .  J .  attention  stages  geology  Duncan,  Read,  the  radiometric  and  I.  a l l  my  people  Mesozoic  extraction,  on  the  following  and  B.  directed  supervised  conodonts,  their  Fossils  the  Bond,  E.  Triassic  and  f i r s t  of  thanks.  their much  help, of  encouragement this  work  and  this of  seemed  especially  f i e l d  J .  W.  far  work  H. away  Monger  1  CHAPTER I .  INTRODUCTION  PRELIMINARY STATEMENT  Upper P a l e o z o i c e u g e o c l i n a l rocks o c c u r w i d e l y i n southern Columbia, but t h e i r s t r a t i g r a p h y , i n t e r n a l s t r u c t u r e , and the  British  sedimentary  and t e c t o n i c environments i n which they formed are p o o r l y known. attempt by Monger  (1977) t o d i v i d e them i n t o a number o f  A recent  tectonostrati-  g r a p h i c assemblages p o i n t s out the d i v e r s i t y of these r o c k s , and the ficulties  dif-  i n h e r e n t i n attempts to d e c i p h e r t h e i r o r i g i n a l t e c t o n i c s e t t i n g  '  and e x p l a i n t h e i r p r e s e n t r e l a t i v e p o s i t i o n s w i t h i n the C o r d i l l e r a n orogen. D e t a i l e d s t u d i e s o f each assemblage are necessary  i n o r d e r t o r e s o l v e these  problems. The  o r i g i n a l purpose of t h i s study was  sedimentology,  t o a n a l y z e the s t r a t i g r a p h y ,  and s t r u c t u r e o f Upper P a l e o z o i c sedimentary  "Cache Creek Group" i n N i c o l a map-area ( F i g . 1 ) . by C o c k f i e l d  (1948) as c h i e f l y a r g i l l i t e ,  minor v o l c a n i c rock, and  limestone.  The  rocks o f the  rocks had been d e s c r i b e d  q u a r t z i t e , conglomerate and b r e c c i a ,  T h i s Pennsylvanian  and Permian sequence  l i e s between c o e v a l m i o g e o c l i n a l s t r a t a to the e a s t and o c e a n i c rocks t o the west, and Monger (1975a) and Monger and o t h e r s  (1972) suggested  part of a Late Paleozoic v o l c a n i c i s l a n d a r c .  P r e v i o u s work on the area  p r i m a r i l y r e g i o n a l mapping and r e c o n n a i s s a n c e 1915;  Cockfield,  (Dawson, 1879,  t h a t i t forms  1895;  was  Daly,  1948).  The b e s t exposures o f the "Cache Creek Group" i n N i c o l a map-area are i n the North and Danner  and South Thompson R i v e r v a l l e y s , and b i o s t r a t i g r a p h i c work by Sada (1974) e a s t and n o r t h e a s t o f Kamloops p r o v i d e d a s t a r t i n g p o i n t  Fig.  1. Map o f southern B r i t i s h Columbia showing the l o c a t i o n o f towns and mapa r e a s mentioned i n the t e x t . I n s e t shows t e c t o n i c s u b d i v i s i o n s o f the C o r d i l l e r a i n B r i t i s h Columbia.  3  for  further  carried River,  out from  Danner, mapped  from be  of  stratigraphic  study.  at  1:12,500  a  Kamloops  and  also  in  of  eastward the  about  25  square  The  scope  of  the  dark  gray,  argillaceous  Late  Triassic of  the  area:  study  a  age.  west-trending  vertical  fault.  or  such  as  deep  water  rocks  are  mapping  Usage  zoic  only  of  by  rocks  oceanic  belt  the  central  the  type  Kamloops. be  excluded  area  The  of  Upper  from  the  when  of  to  the  north  1975,  mapping  side  of  area  studied  of  the  was  South by  Kamloops.  of  group  Paleozoic group  on  with  2).  Thompson  Sada  The  and  area  flows  currents.  the  deep  of  mafic two  by  a  by  minerals  sequences  in  two  and  a  north-  mudstone  turbidity  lithologic shallow  to  within  east,  water  deposited  presence  the  to  that  present  separated of  proved  reveals  are  However,  unaltered  features  water in  versus  pyroclastic  regional  control.  "Cache  proposes  These  Creek  to  chert  and  rocks  the  rocks  town in  basis  the of  Group"  restrict  a  belt  of  the  pelite,  form  Intermontane  the  are  extracted  mudstones  mapping,  primarily  mudstones,  conodonts  sequence  They  pyroclastic  of  of  lithology  Permian  consist  term  at  the  similar  (Fig.  (bedded  the  collections  distinguish  He  rocks).  part  the  of  interbedded with  to  density  fossil  aspect  ultramafic  of  Hills  along  abundance  (1975b).  and  ing  and  stratigraphic  canics, in  and  scattered  Monger  of  Dome  Both  sufficient  the  limits  grossly  characteristics  probably  the  west  sandstones  limestones,  with  discussed  the  high-concentration  parting  north  Mississippian to  currents  the  data,  but  sequence  volcahiclastic  along  limestones  Triassic  with  summer  expanded  This  ages  Late  the  kilometres.  study  different  to  southern  is  sequences  Late  scale  During  Cache  their  recently  term  Upper  Paleo-  limestone,  basic  vol-  British Creek,  and  been  to  discontinuous of  Nicola  has  Columbia,  70  Vernon  differing  elongate  km w e s t map-areas  lithology.  includof would  4  Application conodont  of  vertently  be  that  found  for  be  extend  in  map-areas  use which  Upper  km  the  were  Nicola  associated  sediments,  Triassic  rocks which  by  type  of  laterally priate. and  This  Okulitch  The logic  in  Nicola  the  to  usage  the  bulk  and  area.  to  this  been  Group. thus  been  in  rocks  thesis  the  study  metamorphism,  area  and  and  area. the  of  of  Late  deeper  The  facies  two  inclusion by  in  with  in the  regional  this  petrology  Creek  Nicola flow,  w i l l  Group." I  age  include about  and  distal  probably is  (1976)  similar  1970).  represented  and  group  60  tuffs,  (Schau,  centers  Cameron  the  Vernon  breccias.,  same  approand  in  Read  age  and  study. stratigraphy,  correlations  of  and  mudstones  are  term  Group,  the  for  informally  Group"  coeval  physical  Additional  should  This  Creek  are  which  and  Group  also  Triassic  and  names  Nicola  volcanic  Okulitch map-area  in  water  inad-  (1948)  Ranch  w i l l  the  andesitic  or  the  (1976)  were  River.  "Cache  "Cache  from  described  and  as  erupted  Vernon  deals  petrography, in  type  their  applied  rocks  Triassic  of  Groups  and  as  are  I  that  map-areas.  Harper  lithology  workers  rocks  name  Thompson  in  Cameron  Cockfield  Vernon  name  mapped  Kamloops  by  discussion,  limestones,  have  Nicola  has  (1977)  description,  structure  may  gradational,  lithology  and  the  of  and  the  and  basaltic  reef  east  volcaniclastics rocks  are  of  the  and  Triassic  Group"  South  previous  in  Okulitch  Nicola  age  unfortunate  stratigraphic  the  formerly  Rocks  and  in  more  Upper  proposes  similar  rocks  by  by  new  along  by  even  Creek  purposes  mapped  Kamloops,  a  rocks  1978)  of  Group.  of  reasons,  For  is  and  "Cache  exposed  rocks  Triassic  southwest  Upper  to  herein  the  comm.,  paper.  region  underlain  Paleozoic  rocks  this  its  these  (pers.  Paleozoic  used  with  For  this  areas  within  Upper  Danner  in  reported  large  included  (1959).  Upper  name  collections  demonstrate  Jones  the  chapters the  of  the  deal  varied  l i t h o -  Harper  with  Ranch  their  intrusive  rocks  5  LOCATION,  The  study  map-area,  The  east  the  is  by  a  in  the  North  and  probably  are  Tertiary walled  valleys  The trending unnamed in  lakes,  Peter  region  Creek  ridge  such  to and  occur  western  flanks  the  and  slope  forest  of  Paul  cover.  as  Kamloops  northeast  on  Dome  Ridge The  of  Hills.  higher  of  the  of  broad  upland  valleys  near  which  bedrock  only  gently  limited of  to  from  units  the  and  erosion  on  an  produced  deposits,  and  structures, Early steep-  and  containing  the  northeast-  Lakes.  lying  to  by the  terminates  north at  as  Paul  Ridge.  flank  of  Paul  Ridge,  rolling  summit  exposure, Dome  with Hills  and  its  i t  the  north  are  Thompson  developed  bisected  ridge  refer  elevations  is  Hills  southern  The  flow  blocks Kamloops  west-flowing  Shuswap  This  w i l l  steep  have  Dome  I). I  plateau  taken.  glacial  Kamloops  geo-  interior  the  at  and  Fulton  originally  and  geology  Nicola  by  unconsolidated  the  and  the  of  in  length  large  form  valleys  thick  (Plate  exposures  to  trend  by  Peaks,  region  Pleistocene  south  bedrock  north  stream  with  Paul  of  the  the  The  Kamloops  Quaternary  largely  of  of  described  Rivers,  Kamloops  valley,  the  portion  valleys.  Late  floored  been is  GEOLOGY  northeast  The  elevated  across  surface.  upland Paul  cut  has  Thompson  at  antecedent  now  large  South  SURFICIAL  and  summary  an  major  joining  valleys  erosion  numerous  of  is  east  area  southern  This  AND  Columbia.  following  and  respectively, These  British  the  system  River.  end  the  Cordillera.  of  immediately  Nicola-Vernon  which  area  separated those  of  from  Canadian  is  south-central  morphology (1975),  area  PHYSIOGRAPHY,  western The and  surface  extensive are  an  also  best the  and grass heavily  forested.  Surficial drumlinoid  deposits  deposits  in  mantle  the most  area of  are  Paul  extensive Creek  and  valley  varied.  and  the  T i l l  eastern  and Dome  6  Hills.  The  r o l l i n g summit s u r f a c e o f P a u l Ridge may  t h i n veneer o f t i l l , o f the summit.  The  as suggested by a few  l a r g e l y covered  by  exposures a l o n g the southern  o r i e n t a t i o n o f s t r e a m l i n e d bedrock r i d g e s and  d e p o s i t s i n d i c a t e s t h a t i c e flow was  toward the s o u t h e a s t .  the s t r i k e o f the T r i a s s i c bedrocks u n i t s , and ice  be  This  a  edge  morainal parallels  suggests some c o n t r o l o f  local  movement o r the p r e - g l a c i a l topography by the bedrock s t r u c t u r e . Along the South Thompson R i v e r are prominent t e r r a c e s o f varved  trine s i l t .  These s i l t s  lacus-  were d e p o s i t e d by a s e r i e s o f p r o g l a c i a l l a k e s formed  d u r i n g d e g l a c i a t i o n o f the r e g i o n .  The  d e s c r i b e d by Mathews (1944) and F u l t o n s t r a n d l i n e s can be r e c o g n i z e d  h i s t o r y o f these (1965, 1969).  l a k e s has  been  A number o f o l d l a k e  a t d i f f e r e n t e l e v a t i o n s on the west f l a n k o f  Paul Peak. Alluvial  fans c o n s i s t i n g o f p o o r l y s o r t e d g r a v e l , sand, s i l t ,  and  clay  have accumulated a t the base o f the steep w a l l s o f the North and South Thompson v a l l e y s , m a n t l i n g  the s i l t  t e r r a c e s i n the l a t t e r .  Fulton  (1975) suggests  t h a t the fans formed p r i m a r i l y d u r i n g the p e r i o d o f a g g r a d a t i o n following deglaciation. s l o p e s o f Paul and The  and  southwestern  P e t e r Peaks, formed by mass w a s t i n g o f the c l i f f s  l a k e t e r r a c e s , and  r i v e r s , and  Large t a l u s cones cover the southern  directly  above.  l o c a l l y the a l l u v i a l f a n s , have been i n c i s e d by  the modern v a l l e y bottoms are covered  the  by f l o o d p l a i n d e p o s i t s .  REGIONAL GEOLOGIC SETTING  The  study  area i s i n the e a s t e r n p a r t o f the Intermontane b e l t ,  a  e u g e o c l i n a l t e r r a n e f l a n k e d on the e a s t by the Omineca C r y s t a l l i n e b e l t , on the west by the Coast C r y s t a l l i n e b e l t b e l t c o n s i s t s predominantly of oceanic  and  ( F i g . 1, i n s e t ) . i s l a n d arc-type  The  and  Intermontane  sedimentary  and  7  volcanic clastic Eocene  time.  the  of  Late  sediments  plateau of  rocks  accumulated  Mesozoic  volcanics:  and  t i a l l y  unmetamorphosed  to  blueschist  Harakal,  and  mantle  sedimentary  the  Paleozoic in  Jurassic  successor  basins  plutons  rocks  volcanic  facies  Early  Tertiary  older  to  to  over  rocks  is  are  known  from  Middle  areas.  typically  locally  Marine  abundant,  large,  prehnite-pumpellyite are  age.  low,  (Monger,  to  Tertiary  metamorphic  ranging  facies.  nonmarine  Jurassic  and  The  and  Rocks  1975b);  from  grade  essen-  transitional  Paterson  and  1974).  Stratigraphy  The of  Late  (1959)  as  "Cache  of  an  by  recognized Low the  Lake, of  in  tuff  from  the  phyllite,  sive  into  other  ages  (Okulitch  present.  greenstone, Group, mentary  but  No  these  rocks  of  occur  a  rocks  (Okulitch  mapped  the  Lower  l i e and  Cockfield  the  Harper  of  limestone,  and  the  Eagle  northeast  and  unit,  been  The  but  yield  Eagle  up  1976).  most  time-equivalent near  granitic  rocks  m.y.)  the  below  Upper  schist, of  intru-  radiometric  from  rest  consists  conodonts  Mississippian  the  Shuswap  Formation  than  of  is  1974).  Mississippian  (372  mudstone  limestone  part  Bay  of  They  disconformably  Kamloops,  Devonian  recovered  make  in  Jones  Group.  Danner,  foliated  younger  stratigraphically Cameron,  of  limestone.  Rocks  that  probably  1959).  Bay  1975).  are  Rocks  and  sequence  (Sada  which  2.  (1948)  of  Kamloops  Fig.  Ranch  Pennsylvanian  lenses  in  Permian  (Jones,  gneiss  shown  Upper  to  have  by  is  limestone.  limestone  fossils and  east  region  designated to  rocks  others,  marble,  are  greenstone,  from  parts and  age,  Permian  Group  quartzite,  recovered  Kamloops  discontinuous  Group Ida  been  be  with  locality  Ranch  have  also  Group,"  metamorphic  Mount  the  Permian  Lower  one  grade  of  Mississippian  massive  Harper  to  Creek  Upper  redeposited  overlain  to  geology  Mississippian  consist and  general  age  quartzite,  the  Triassic  may  Mount  Ida  metasedi-  LEGEND TERTIARY Tv: E o c e n e to P l i o c e n e v o l c a n i c and sedimentary rocks.  W W W  0.  2  W W W  UPPER TRIASSIC Nicolo Group u'Rvibasalt and andesite flows, breccia, and tuff, v o l c a n i c sandstone and mudstone, limestone. uDs-. m u d s t o n e , v o l e j n i c s a n d s t o n e and tuff, minor lime turbidites a n d basalt or a n d e s i t e flows. u~Asm.-equivalent m e t a m o r p h o s e d r o c k s , including S i c a m o u s Formation near Shuswap L c k e . MISSISSIPPIAN TO PERMIAN Harper Ranch Group MPhr: mudstone, v o l c a n i c sandstone, limestone, volcanic flows.  F i g . 2.  P A L E O Z O I C AND 0 L D E R 7 Mount Ida Group Pmi: s c h i s t , q u a r t z i t e , greenstone, m a r b l e , gneiss. Includes Chapperon Group west of Okanagan Lake. Peb: Eogle Bay Formation: phyllite, q u a r t z i t e , greenstone, marble, arqillite. Shuswap Metomorphic Complex gns: gneiss, schist, and pegmatite.  ++++ ++++ ++++  INTRUSIVE ROCKS, MESOZOIC TO TERTIARY gr: d i o r i t e to g r a n i t e or s y e n i t e .  Geologic High-ongle  contact. fault.  G e o l o g i c map o f the r e g i o n s u r r o u n d i n g Kamloops.  9  Upper rocks  of  mostly low  Paleozoic  the  type  bedded  water  Cache  chert  and  The  two  clastic and  a  rocks  highly  Near the  Late to  not  been  Triassic  Shuswap  Lake,  graphitic, South  allow and  and  area,  no  The  fossils  a l l  but  westernmost  the  In have  Bonaparte  mapped  logically Group. 2,  a  Lower  nearly  Some  Plutonic  and  deposited  in  of  limestone from of  of  the  have  of  rocks  yet  of  map-area  age  eastern the  and  1974)  region  of  and  lenses,  suggests is  units  that  Upper  Kamloops,  the  volcanic  included the  range  with  arc the  unit  Kamloops  and  volcani-  to  become 1974).  collections  of  Paleozoic the  remain  undiffer-  Nicola  and  Nicola  map-area, in  age.  Tipper  which  facies  study  Pennsylvanian  Paleozoic  Campbell  of  (Okulitch,  with in  The  map-area.  Upper  some  a  Metamorphosed  North  the  and  west  fossil  volcanic-clastic  from be  Formation  1976).  shal-  above.  change  into  of  1977).  Vernon  facies  are  Pennsylvanian,  basin.  in  Group"  terrane  of  Jurassic  part  Creek  deformed, of  oceanic  rocks  sedimentary  Triassic  found,  this  a  Sicamous  limestone  north  may  occur  are  bodies  breccias  back-arc  Cameron,  been  Danner,  portion  this  in  a  Late  "Cache  numerous and  the  Kamloops,  (Okulitch  Middle  the  in  2)  described  basinal  undergoes  indistinguishable  rocks  particularly  to  flows  unit  (Sada  Lake  volcanic  The  large  (Monger,  were  arc.  Fig. These  rocks  Group  sedimentary  fossils  Permian  present  facies  units  and  but  both  division  presence  out,  are  and  complexly  of  southeast  Triassic  entiated.  were  equivalents the  Triassic  of  worked  on  map-area.  Nicola  volcanic  east  p h y l l i t i c  preliminary  Upper  belt  shown  volcanics,  exposed,  age  the  (not  Ashcroft  basic  has  Triassic  deformed  in  poorly  comprising  the  Kamloops  are  north-northwest-trending represents  Group  mudstone,  Late  facies  of  They  sequence perhaps  west  Creek  and  limestone.  stratigraphic Permian,  rocks  of  is  l i t h o -  the  Group  (1971)  in  Nicola Fig.  area.  from  Late  Triassic  to  Tertiary  (?)  10  i n age.  Most were p r o b a b l y  emplaced d u r i n g L a t e s t T r i a s s i c t o E a r l y J u r a s s i c  and Middle t o Upper J u r a s s i c p l u t o n i c p u l s e s Quartz d i o r i t e , g r a n o d i o r i t e , and rocks.  ( G a b r i e l s e and  Reesor, 1974).  q u a r t z monzonite are the common i n t r u s i v e  D i o r i t i c t o u l t r a m a f i c types occur  to g r a n i t i c s t o c k s are a l s o p r e s e n t . u n d e r l i e l a r g e areas i n the r e g i o n .  l o c a l l y , and  several small  T e r t i a r y v o l c a n i c rocks  and  syenitic  sediments  Middle Eocene b a s a l t , a n d e s i t e ,  and  d a c i t e l a v a s and b r e c c i a s and minor sediments are unconformably o v e r l a i n by f l a t - l y i n g , Miocene t o P l i o c e n e p l a t e a u l a v a s , c h i e f l y o l i v i n e b a s a l t .  Structure  The  e a s t e r n p o r t i o n o f the Intermontane b e l t forms the h i n t e r l a n d o f  the Columbian Orogen  (Wheeler and  G a b r i e l s e , 1972).  orogen i s the Omineca C r y s t a l l i n e b e l t , r e p r e s e n t e d Shuswap Metamorphic Complex and e a s t o f F i g . 2.  The  Foreland  The  core zone o f  the  a t t h i s l a t i t u d e by  the  Kootenay A r c , which l i e s u c c e s s i v e l y to  the  Thrust  and  F o l d b e l t l i e s i n the Rocky Mountains  to the e a s t o f the Omineca b e l t . S t r u c t u r e s are b e s t known i n the F o r e l a n d  and Omineca b e l t s .  F o r e l a n d b e l t i s a zone o f e a s t e r l y - d i r e c t e d t h r u s t s and developed i n the P a l e o z o i c m i o g e o c l i n e wedge d e p o s i t s .  The  and  concentric folds  Mesozoic t o Lower T e r t i a r y c l a s t i c  Omineca b e l t s t r a d d l e s the boundary between P r o t e r o z o i c  to Lower P a l e o z o i c sediments o f the d i s t a l m i o g e o c l i n e , t o Mesozoic v o l c a n i c and  and  the  mid-Paleozoic  sedimentary r o c k s o f the Intermontane b e l t .  t u r e s i n t h i s r e g i o n are complex, and amphibolite  The  Struc-  vary w i t h the s t r u c t u r a l l e v e l .  f a c i e s rocks o f the Shuswap Complex and  Upper  the lower grade rocks  of  the Mount Ida Group have undergone polyphase d e f o r m a t i o n i n which e a r l y isoclinal  f o l d s have been r e f o l d e d by more open, n o r t h t o  northwest-trending  11  folds.  Metamorphism a f f e c t s r o c k s as young as E a r l y J u r a s s i c  Gabrielse, The  (Wheeler  and  1972). s t r u c t u r e o f the southern Intermontane  Evidence f o r pre-Upper  b e l t i s known o n l y s k e t c h i l y .  T r i a s s i c d e f o r m a t i o n i s found l o c a l l y and has been  summarized by Read and O k u l i t c h  (1977) .  Steep f a u l t s and open f o l d s predom-  i n a t e i n the v o l c a n i c a r c f a c i e s o f the N i c o l a Group (Schau, 1970) .  Folds  i n the a r g i l l a c e o u s f a c i e s t o the e a s t are a t l e a s t l o c a l l y t i g h t e r ,  over-  t u r n e d toward  the west, and c u t by s t e e p f a u l t s  (data from t h i s s t u d y ) .  Major d e f o r m a t i o n o f these r o c k s p r o b a b l y took p l a c e i n the E a r l y (Schau, 1970,  and t h i s s t u d y ) .  Jurassic  12  CHAPTER I I .  HARPER RANCH GROUP (MAP UNIT 1)  INTRODUCTION  The Harper Ranch Group, i n exposures  a l o n g t h e South Thompson R i v e r  e a s t o f Kamloops, can be d i v i d e d i n t o two s t r a t i g r a p h i c i n t e r v a l s  separated  by a major d i s c o n f o r m i t y ( F i g . 3 ) . The lower s e c t i o n , o f L a t e M i s s i s s i p p i a n to Middle P e n n s y l v a n i a n  age, c o n s i s t s o f more than 5,000 m o f marine mud-  stone and v o l c a n i c l a s t i c r o c k s , w i t h r a r e d i s c o n t i n u o u s l e n s e s o f l i m e s t o n e . A l i m e s t o n e c o n t a i n i n g E a r l y and Middle P e n n s y l v a n i a n forms t h e t o p o f t h i s sequence  (Sada and Danner, 1974).  i s a steeply-dipping, northwest-trending the west.  fusulinids generally The base o f t h e group  f a u l t w i t h Upper T r i a s s i c r o c k s t o  O v e r l y i n g the C a r b o n i f e r o u s rocks d i s c o n f o r m a b l y  i s a massive  Lower Permian l i m e s t o n e , p r o b a b l y s e v e r a l hundred metres t h i c k .  Upper Permian  f o s s i l s a r e found i n one i s o l a t e d l i m e s t o n e o u t c r o p near t h e Lower Permian limestone. Triassic  T h i s sequence i s o v e r l a i n above a n g u l a r u n c o n f o r m i t i e s by Upper  (?) sedimentary  T h i s study concerns the Harper Ranch Group.  and v o l c a n i c rocks and by T e r t i a r y v o l c a n i c f l o w s . the lower 2,300 m o f the C a r b o n i f e r o u s s t r a t a i n Study was c o n f i n e d t o s t r a t a below t h e Lower Penn-  s y l v a n i a n . l i m e s t o n e s a t l o c a l i t i e s Harper Ranch and South Thompson No. 1 o f Sada and Danner  (1974) ( F i g . 3 ) .  STRUCTURAL SETTING, PHYSICAL STRATIGRAPHY, AND BIOSTRATIGRAPHY  The  lowermost p o r t i o n o f the Harper Ranch Group forms a  t r e n d i n g , e a s t - f a c i n g homocline.  Bedding  northwest-  dips steeply e i t h e r t o the northeast  LEGEND QUATERNARY DEPOSITS AND COVERED AREAS MIOCENE?  SCALE  BASALT  UPPER TRIASSIC OR LOWER JURASSIC SEDIMENTARY AND VOLCANIC ROCKS UPPER TRIASSIC SEDIMENTARY AND VOLCANIC ROCKS UPPER PERMIAN LIMESTONE LOWER PERMIAN  INTERMITTENT STREAM ^  GEOLOGIC CONTACT  MILE  i KM  J  tr~r  FAULT  LIMESTONE .•vv>  T~T  '•vv!  LOWER PENNSYLVANIAN LIMESTONE  )i  UPPER MISSISSIPPIAN TO LOWER PENNSYLVANIAN SEDIMENTARY ROCKS  XT  r \  UPPER MISSISSIPPIAN LIMESTONE : S  *—::  r  / V  (  LOC. HARPER RANCH  LOC  r-t  LOC. F-I;  ./^  T T ' l • • !•• 1 ,7A A a A A  i  A A A A , A A A A A A A  i - i -A 0AA AA tA  -TO  Fig.  KAMLOOPS  7.5 KM  3 . S k e t c h g e o l o g i c map o f t h e Harper Ranch Group a l o n g the South Thompson R i v e r e a s t o f Kamloops, showing f o s s i l l o c a l i t i e s .  14  o r southwest.  Although  o n l y s i x f a c i n g d e t e r m i n a t i o n s were o b t a i n e d , no  r e v e r s a l s i n f a c i n g d i r e c t i o n were observed  t h a t would suggest t h e presence  of major f o l d c l o s u r e s , and few mesoscopic f o l d s a r e p r e s e n t .  S t r i k e s and  d i p s a r e i r r e g u l a r , however, and t h i s f a c t i n combination w i t h the l a c k o f complete exposures thickness.  makes i t i m p o s s i b l e t o a c c u r a t e l y measure t h e s t r a t i g r a p h i c  The t h i c k n e s s o f 2,300 m was e s t i m a t e d assuming an average  strike  o f 140°, and a v e r t i c a l d i p . The  s t r a t i g r a p h i c s e c t i o n has been s u b d i v i d e d ( F i g . 4) i n t o two sequences  o f mudstone and v o l c a n i c sandstone  o r r e d e p o s i t e d t u f f , s e p a r a t e d by l i m e s t o n e .  F u r t h e r s u b d i v i s i o n o f the t h i c k sequence o f noncarbonate r o c k s has n o t been possible.  S i n c e t h e l i m e s t o n e b o d i e s i n t h e Harper Ranch Group a r e n o t l a t e r -  a l l y c o n t i n u o u s , even t h i s g r o s s s u b d i v i s i o n would be d i f f i c u l t t o apply a l a r g e r area.  over  However, t h e l i m e s t o n e b o d i e s a t Harper Ranch and South Thomp-  son No. 1, a l t h o u g h p h y s i c a l l y n o t connected,  c o n t a i n s i m i l a r Lower P e n n s y l -  v a n i a n f u s u l i n i d faunas, and can be p r o j e c t e d one i n t o t h e o t h e r a l o n g  strike.  I t i s t h e r e f o r e r e a s o n a b l e t o conclude t h a t they occupy n e a r l y the same s t r a t i graphic p o s i t i o n r e l a t i v e t o the e n c l o s i n g c l a s t i c rocks.  Careful structural  mapping and c o r r e l a t i o n between l i m e s t o n e s may a l l o w t h e o v e r a l l r e g i o n a l s t r a t i g r a p h y o f the Harper Ranch Group t o be d e c i p h e r e d . The b a s a l p o r t i o n o f the s e c t i o n c o n s i s t s o f 50 t o 100 m o f massive mudstone, l a m i n a t e d mudstone, and r a r e f i n e - g r a i n e d sandstone.  Where the  o v e r l y i n g l i m e s t o n e u n i t i s absent, t h i s sequence cannot be d i f f e r e n t i a t e d from the h i g h e r c l a s t i c sequence.  The v e r t i c a l  f a u l t which t r u n c a t e s t h i s  s e c t i o n a t i t s base g e n e r a l l y t r e n d s p a r a l l e l t o the s t r i k e o f bedding, b u t l o c a l divergences lead t o the recorded v a r i a t i o n s i n thickness. A s m a l l fauna o f b r a c h i o p o d s ,  c o l l e c t e d from massive mudstone near t h e  5 </>  STANDARD SUCCESSIONS LITHOLOGY  Limestone of localities Harper Ranch and South Thompson No. I of Soda and Danntr, 1974  NORTH AMERICA 2 < Z < >  2000CO Z Z LU 0.  < UJ  oo  EURASIA  U. N  z < o  rr rr  o 5  Z <  20  rr <  tO  rr <  rr  UJ  LU rUi  1900-  Mattivt and laminated mudstone, fine to very coarse-grained volcanic sandstone (redeposited tuff or pyroclastic sandstone)  !fl tO LU Z  u  Exact location of Mississippian / Pennsylvanian boundary unknown  I rUJ  19  1000-  < X  o  rr a.  o. <  ioo-:  <  a. a. CO  Loc. F-2  Bioclastic limestone  Lcc. F-  Massive and laminated mudstone, rare fine-grained volcanic sondtton*  to to to 2 UJ  <  18 Z <  rr UJ  \-  to LU  x o  rr 3 2 < 2  ?  I7 1  VISEAN?  Fault  F i g . 4. S t r a t i g r a p h i c s e c t i o n o f the lower p o r t i o n o f t h e Harper Ranch Group.  I6  16  base o f the s e c t i o n  (Loc. F - l ) , were i d e n t i f i e d by Dr. J . T. Dutro, J r . , o f  the U. S. G e o l o g i c a l Survey: The brachiopods are medium-sized p r o d u c t i d s t h a t p r o b a b l y i n c l u d e Inflatia and Flexaria. Not w e l l enough p r e s e r v e d to hazard s p e c i f i c i d e n t i f i c a t i o n s . However, these two genera are a s s o c i a t e d i n many p l a c e s i n Late M i s s i s s i p p i a n r o c k s o f the n o r t h e r n Rockies ( w r i t t e n commun. t o W. R. Danner, 1976). S i n c e they were found i n f i n e - g r a i n e d mudstone, the brachiopods  are  clearly  an autochthonous b e n t h i c fauna, and were not t r a n s p o r t e d p r i o r t o b u r i a l . The o v e r l y i n g l i m e s t o n e  (Unit 1A)  v a r i e s from 0 t o 10 m i n t h i c k n e s s .  The p r e s e n t d i s c o n t i n u i t y o f t h i s l i m e s t o n e i s due f a u l t s and t o l a c k o f exposure, u l a r as w e l l .  but the u n i t was  i n p a r t to o f f s e t  probably o r i g i n a l l y  The gray, b i o c l a s t i c l i m e s t o n e c o n t a i n s a v a r i e t y o f  o l o g i e s , from wackestones and packstones  to grainstones.  u n d e r l y i n g and o v e r l y i n g c l a s t i c r o c k s are abrupt but The h e t e r o c o r a l Hexaphyllia A c c o r d i n g t o Dr. D. H i l l  occurs i n s e v e r a l limestone  samples.  ( c i t e d i n Sada and Danner, 1973), Hexaphyllia has  The v a r i e d fauna o f b e n t h i c f o r a m i n i f e r s i n c l u d e s Endothyra, Climacammina,  f i c a t i o n s were attempted,  remainder  and Tetrataxis,  Columbia. Eostaffella, identi-  specified  T h i s fauna i s shown i n P l a t e I I .  o f the s e c t i o n , some 2,200 m t h i c k , c o n s i s t s o f massive  and l a m i n a t e d mudstone, f i n e t o medium-grained v o l c a n i c t u r b i d i t e and coarse t o v e r y c o a r s e v o l c a n i c sandstones subaqueous mass f l o w s . L o c a l l y sandstone  is  found i t i n  but s i n c e no s p e c i f i c  the age o f t h i s l i m e s t o n e cannot be  more p r e c i s e l y than C h e s t e r i a n . The  lith-  C o n t a c t s w i t h the  (=Upper C h e s t e r i a n ) l i m e s t o n e i n n o r t h e r n B r i t i s h  Paleotextularia,  lentic-  conformable.  r e s t r i c t e d t o the V i s e a n , but B. L. Mamet (1976, p. 108) E a r l y Namurian  by  may  sandstones,  d e p o s i t e d by h i g h - d e n s i t y  The p r o p o r t i o n o f sandstone  t o mudstone i s v a r i a b l e .  make up as much as 70% o f the s e c t i o n , but mudstone  17  PLATE  II.  MICROFAUNA HARPER  A  through  D,  Scale  E  photomicrographs  B.  Eostafella,  saggital  C.  Eostafella,  axial  D.  Paleotextularia,  E.  RANCH  GROUP  MISSISSIPPIAN  LIMESTONE,  (UNIT 1A)  thin-sections.  b a r = 100 m i c r o m e t r e s -  Endothyra,  saggital  section. section.  section. longitudinal  G, photomicrographs  Scale  UPPER  from  A.  through  FROM  from  section.  acetate  peels.  bar = 1 millimetre  Hexaphyllia,  cross  section  of corallum  surrounded  by  algal  cross  section  o f corallum  surrounded  by  algal  coat. F.  Hexaphyllia, coat.  G.  . oblique  Hexaphyllia, coat.  .  •  section  of corallum  surrounded  by  algal  19  p r o b a b l y makes up more than 50% o f the t o t a l t h i c k n e s s o f the  section.  The o n l y f o s s i l s r e c o v e r e d from t h i s s e c t i o n o c c u r i n a c o a r s e - g r a i n e d bed composed mostly o f r e d e p o s i t e d s h a l l o w water carbonate d e b r i s , 100 150 m above l i m e s t o n e IA Solenopora  and Parachaetetes,  (Loc. F - 2 ) .  Two  to  genera o f c a l c a r e o u s a l g a e ,  are abundant.  These genera range  throughout  the P a l e o z o i c , but o n l y a s i n g l e o c c u r r e n c e o f s o l e n o p o r i d a l g a e has been r e p o r t e d from P e n n s y l v a n i a n r o c k s  (Heckel, 1975).  Lower P e n n s y l v a n i a n  f u s u l i n i d s o c c u r i n the l i m e s t o n e s o v e r l y i n g t h i s s e c t i o n i t i e s Harper  Ranch and South Thompson No.  boundary thus l i e s determined  due  1).  (Unit IB, L o c a l -  The M i s s i s s i p p i a n / P e n n s y l v a n i a n  somewhere w i t h i n t h i s s e c t i o n , but i t s p o s i t i o n cannot  t o the l a c k o f c l o s e r f o s s i l c o n t r o l .  be  The bed c o n t a i n i n g  s o l e n o p o r i d a l g a e i s not f a r above the Upper M i s s i s s i p p i a n l i m e s t o n e , and i s p r o b a b l y a l s o L a t e M i s s i s s i p p i a n i n age. warranted,  F u r t h e r study o f these a l g a e i s  f o r t h e i r p r e s e r v a t i o n i s e x c e l l e n t , and a P e n n s y l v a n i a n age  can-  not be r u l e d out.  SEDIMENTOLOGY  Exposures  o f the Harper Ranch Group are adequate t o r e v e a l the g e n e r a l  nature o f the l i t h o l o g i e s i n the s e c t i o n , but inadequate analysis.  for detailed  facies  No continuous marker beds were found, i n d i v i d u a l beds cannot  be  t r a c e d l a t e r a l l y , and e x t e n s i v e o u t c r o p s which r e v e a l v e r t i c a l sequences o f l i t h o l o g i e s are r a r e and c o n f i n e d t o steep c l i f f s access. of  which are d i f f i c u l t  of  S e d i m e n t o l o g i c a n a l y s i s i s a l s o hampered by the extreme i n d u r a t i o n  both sandstone  and mudstone.  p a r a l l e l t o bedding,  Each e x h i b i t s l i t t l e  and the mudstones are l i t t l e  and e r o s i o n than the c o a r s e sandstones.  tendency  for parting  l e s s r e s i s t a n t t o weathering  As a r e s u l t , l a y e r i n g e x e r t s  little  20  c o n t r o l on the geometry o f o u t c r o p s .  The  s o l e s o f sandstone beds are  exposed; no bottom markings or o t h e r measurable p a l e o c u r r e n t  seldom  i n d i c a t o r s were  observed. In s p i t e o f these l i m i t a t i o n s , the g e n e r a l environment o f the s e c t i o n i s c l e a r .  Deposition  b a s i n w i t h i n a v o l c a n i c a r c system, p r o b a b l y p o r t i o n o f the b a s i n was  d e p o s i t i o n a l and t e c t o n i c took p l a c e i n a marine  w i t h i n the f r o n t a l a r c .  r e l a t i v e l y d i s t a n t from the v o l c a n i c c e n t e r s ,  none o f the v o l c a n i c d e t r i t u s i s c o a r s e r than very coarse s i z e , and  no  flows are p r e s e n t  c o n s i s t of v o l c a n i c l i t h i c  i n the s e c t i o n .  The  Most o f the d e t r i t u s i s p r o b a b l y  produced by s h a l l o w  submarine e r u p t i o n s .  The  pyroclastic The  granule  v o l c a n i c sandstones  pyroclastic in origin,  T h i s m a t e r i a l was  reworked  subaqueous flows,  and  termed r e d e p o s i t e d  o f U n i t 1A i s l i t h o l o g i c a l l y v a r i e d and i n v e r t e b r a t e s and  tuffs  contains  a t normal marine  accumulated on a shallow  s h e l f at a considerable  v o l c a n i c c e n t e r s , o r d u r i n g a p e r i o d of v o l c a n i c  The  and  d i s t a n c e from the  quiescence.  f o l l o w i n g s e c t i o n s , b a s i c sedimentologic  i n t e r p r e t a t i o n s are p r e s e n t e d  a diverse  salinities.  I t c o n t a i n s v i r t u a l l y no v o l c a n i c d e t r i t u s c o a r s e r than c l a y s i z e ,  Group.  or  rare encrusting algae, i n d i c a t i n g  d e p o s i t i o n a t depths w i t h i n the p h o t i c zone and  and  mud-  sandstones.  limestone  In the  high-  i s i n t e r l a y e r e d with hemipelagic  v o l c a n i c sandstones c o u l d thus be  fauna o f marine b e n t h i c  probably  and  i n deeper water below wave base by t u r b i d i t y c u r r e n t s and  concentration stones.  sand o r  since  fragments and p h e n o c r y s t s i n d i c a t i n g an a n d e s i t i c  to d a c i t i c source.  redeposited  This  and p e t r o g r a p h i c  data  f o r each l i t h o l o g y i n the Harper Ranch  d e p o s i t i o n a l model w i l l then be developed a t g r e a t e r  length.  21  Mudstones  Mudstones w i t h i n the Harper Ranch Group are s i l i c e o u s and indurated.  They l a c k bedding p l a n e f i s s i l i t y o r p e n e t r a t i v e c l e a v a g e ,  c o u l d thus be termed a r g i l l i t e s as d e f i n e d by the AGI (Gary and  o t h e r s , 1972,  p.  37).  i s avoided  i t s emphasis on p o s t - d e p o s i t i o n a l h i s t o r y ,  laminated  mudstones occur  are i n t e r l a y e r e d and perhaps e q u a l l y abundant. i n t h i n t o t h i c k beds (terminology to very  b u r r o w - m o t t l i n g was i n the f i e l d  uniform  i n the s e c t i o n ,  and  Homogeneous mudstone  a f t e r Ingram, 1954).  occurs  Homogeneity may  be  i n t e n s e b i o t u r b a t i o n o f o r i g i n a l l y l a y e r e d muds.  No  observed, but the mudstone was  f o r these f e a t u r e s .  deep sea c o r e s  G l o s s a r y o f Geology  i n this discussion.  Both homogeneous and  primary o r due  and  Because o f the i n c o n s i s t e n c i e s i n d e f i n i -  t i o n and usage o f t h i s term, and i t s use  extremely  (Reineck and  not examined c a r e f u l l y  Primary homogeneous muds are known from  Singh, 1975,  p. 406),  and  represent  i n t e r v a l s of  sedimentation.  Laminated mudstones c o n s i s t o f t h i n  (1-3 mm)  and  thick  (3-10  laminae and v e r y t h i n t o t h i n beds o f gray t o b l a c k mudstone and t o cream-colored s i l t s t o n e .  Layering  S i l t s t o n e l a y e r s range up to 5 cm fine horizontal lamination, stone l a y e r s c o u l d be  and  gray  undulating.  t h i c k , w i t h t h i c k e r l a y e r s showing very  sometimes f a i n t g r a d i n g .  Some l a y e r s o f s i l t s t o n e and v e r y  These t h i c k  sequences  (Fig. 5).  do not show o t h e r a s p e c t s  and  t h e r e f o r e d i f f i c u l t to a t t r i b u t e to t u r b i d i t y c u r r e n t s .  centi-  occasional  These beds do not appear t o  o f the Bouma sequence.  silt-  (Bouma, 1962).  f i n e sandstone up to s e v e r a l  meters t h i c k show m u l t i p l e s e t s o f r i p p l e c r o s s - l a m i n a t i o n ,  graded, and  light  i s u s u a l l y p l a n a r or g e n t l y  i n t e r p r e t e d as t u r b i d i t e DE  minute l o a d c a s t s a t the base  mm)  be  They are  These beds may  be  Fig.  5. Laminated mudstone and s i l t s t o n e , Harper Ranch Group. White c r o s s - l a m i n a t e d s i l t s t o n e l a y e r a t t o p , w i t h m i c r o - l o a d c a s t s a t base. Slump f o l d a t bottom.  Fig.  6. Laminated mudstone and s i l t s t o n e , Harper Ranch Group l a m i n a t e d s i l t s t o n e deformed by a slump f o l d .  (right).  Center of slab, c r o s s -  23  the r e s u l t o f reworking o f t u r b i d i t e s i l t s  and  Hsu  (1964) p o s t u l a t e d  and  f i n e sands i n t e r l a y e r e d w i t h t u r b i d i t e s and  Pliocene  sands by bottom  currents.  t h i s o r i g i n for s i m i l a r t h i n cross-laminated  P i c o Formation o f  silts  deep water mudstones i n the  California.  I observed no b i o t u r b a t i o n s t r u c t u r e s i n the l a m i n a t e d mudstones. T h i s i n d i c a t e s d e p o s i t i o n o f mud  a t a r a t e much g r e a t e r than the r a t e o f  reworking by burrowers, and perhaps a l a c k o f abundant b e n t h i c  infauna.  In the s i n g l e t h i n - s e c t i o n o f l a m i n a t e d mudstone which was the mudstone c o n s i s t s o f c r y p t o c r y s t a l l i n e m a t e r i a l w i t h low wispy b l a c k  streaks of organic  o f f e l d s p a r and/or q u a r t z . and  m a t e r i a l , and  Layering  o f gray c o l o r . the mudstone. mudstone.  changes i n g r a i n s i z e  p y r i t e are s c a t t e r e d through  P o s s i b l e r a d i o l a r i a n remains are a l s o p r e s e n t (about 0.1  clear m i c r o c r y s t a l l i n e quartz. l a y e r i n g , suggesting  The  mm  throughout  parallel  shape r e s u l t s from f l a t t e n i n g o f  o r i g i n a l l y s p h e r i c a l bodies during  compaction o f the e n c l o s i n g mud.  i n t e r n a l s t r u c t u r e s are p r e s e r v e d ,  but these are p r o b a b l y i n t e r n a l molds  of r a d i o l a r i a n t e s t s .  R a d i o l a r i a n s were p r o b a b l y an important  Only a few  from the d i s s o l u t i o n o f r a d i o l a r i a n t e s t s d u r i n g  s c a t t e r e d molds have s u r v i v e d t h i s  Coarse s i l t s t o n e and v e r y and  No  constituent  o f these s i l i c e o u s mudstones, and most o f t h i s d i s s e m i n a t e d s i l i c a probably derived  the  diameter) e l l i p s o i d a l b o d i e s o f  l o n g axes o f the e l l i p s o i d s  t h a t the p r e s e n t  grains  m a t e r i a l , p r o d u c i n g d i f f e r e n t shades  Very s m a l l cubes o f a u t h i g e n i c  These are s m a l l  birefringence,  scattered s i l t - s i z e d  i s d e f i n e d by  v a r i a t i o n s i n the amount o f o r g a n i c  examined,  was diagenesis.  process.  f i n e sandstone l a y e r s c o n s i s t o f  a p h a n i t i c v o l c a n i c rock fragments, w i t h v e r y  l i t t l e o r no  A l t e r a t i o n o f the v o l c a n i c fragments i s so e x t e n s i v e  t h a t the  feldspar  quartz. original  24  clastic  texture  diffraction primarily  is  analysis  of  constituents  are At  least  since  mudstones and  to  this  the  polished  slab,  inferred  from  of  divergence  the  occur base  upper  few  No  Thus  1972; the  the  centimetres  Walker  fact  current  that  of  feature  is  are  which of  of  the  common  in  1973),  from  mudstones the  suite  deep and  is of  water,  this  interbedded with  of to  siltstone. beds,  a  so  hemipelagic  turbidite  laminae.  of  from  the a  true  during  shear  stress  These  features stress  These of  at  are  the  slope.  any  particular  mudstones  found (Bouma,  strengthened  sandstones.  the  sense  motion  structures  is  (Fig.  as  reflects  movement  sedimentary  interpretation  interface,  from  either.  indicative  5).  sample  shear  submarine  folds  (Fig.  determined  probably  downslope on  one  direction  responsible  deposited  recumbent  direction  attributed  the  the  the  Con-  overlying  in  be  direction  turbidite be  probably  thick  by  present  This  be  are  sediment-water  truncated are  the  deposited  sediment  the  opposite  cannot  resulting  scale  current  and  cannot  small  apparent the  X-ray  consist  deformation.  cannot  overlying  However,  Mutti,  they  in  direction  currents  setting.  and  the  deformation  features,  mudstones  that  These  features  lamination.  turbidity  single  these  contorted  absence  slump  siltstones  the  in  the  cases  layers  centimetres  at  is  currents  depositional these  of  several  some  section.  fragments.  very  occurred  in  of  and  thin  these  soft-sediment  cross-bedding  bottom  of  are  evident  show  only  deformation  geometry  is  between  by  probably  in  i t the  deformation.  also  layers  in  plagioclase.  volcanic  laminae  cross-laminated  true  overturning  exerted  of  contortedJlayers  While  lesser  commonly  siltstone  groups  of  and  mineralogically  microcrystalline  the  Contorted, 6).  that  of  some  the  reveals feldspar  mudstone  confined  o b l i t e r a t e d when ^observed  alkali  Laminated torted  nearly  by  25  P r o c e s s e s o f d e p o s i t i o n o f these muds might have i n c l u d e d p e l a g i c s e t t l i n g , low d e n s i t y t u r b i d i t y c u r r e n t s ( R e i n i c k and S i n g h , 1975, 381), and d e p o s i t i o n from a n e p h e l o i d l a y e r d i k e , 1969).  ( E i t t r e i m , Ewing, and  The c r o s s - l a m i n a t e d s i l t s t o n e and f i n e sandstone  evidence f o r some reworking o f the sediment  p.  380-  Thorn-  l a y e r s are  by bottom c u r r e n t s .  The dark c o l o r o f the mudstones i s p r o b a b l y i n d i c a t i v e o f a h i g h o r g a n i c c o n t e n t , and t o g e t h e r w i t h the l a c k o f b i o t u r b a t i o n and presence s c a t t e r e d a u t h i g e n i c p y r i t e suggests a q u i e t , low-oxygen environment  of  without  an abundant bottom fauna.  V o l c a n i c Sandstones o r Redeposited  Tuffs  D e s c r i p t i o n o f Sedimentary  Sandstones i n the Harper d e p o s i t e d as sediment  Ranch Group are o f v o l c a n i c o r i g i n , and were  g r a v i t y flows  depths below storm wave base  Structures  (sensu M i d d l e t o n and Hampton, 1973)  (a few tens o f m e t r e s ) .  at  Some o f these beds  are t u r b i d i t e s , but o t h e r s were p r o b a b l y d e p o s i t e d by o t h e r mechanisms o f subaqueous mass flow. For purposes two  classes:  sandstone.  o f d e s c r i p t i o n , the sandstones have been d i v i d e d  f i n e t o medium-grained sandstone, Although based  and c o a r s e t o v e r y c o a r s e  i n i t i a l l y on g r a i n s i z e , t h i s d i v i s i o n  r e f l e c t s d i f f e r e n c e s i n bed t h i c k n e s s , i n t e r n a l sedimentary p r o b a b l y i n mode o f d e p o s i t i o n . are i d e n t i c a l .  c l a s t i c sequences, sandstones  also  structures,  C o m p o s i t i o n a l l y , however, t h e s e  F i n e - g r a i n e d sandstones  into  sandstones  are found i n both upper and  a l t h o u g h they are r a r e i n the l a t t e r .  lower  The c o a r s e - g r a i n e d  are r e s t r i c t e d t o the upper c l a s t i c s u c c e s s i o n .  F i n e - t o medium-grained sandstone:  and  These t u r b i d i t e sandstones  are  26  abundant i n the Harper Ranch Group.  Bed t h i c k n e s s ranges from 15 cm t o 1.5  m, b u t most beds are l e s s than 1.0 m t h i c k . stone beds a r e sharp,  The b a s a l c o n t a c t s o f t h e sand-  and may be p l a n a r o r have obscure s o l e markings which  have o n l y been observed i n c r o s s - s e c t i o n .  Normal s i z e - g r a d i n g i s f r e q u e n t l y  v i s i b l e , and the upper p o r t i o n s o f the beds a r e g r a d a t i o n a l w i t h o v e r l y i n g mudstones.  P l a n a r l a m i n a t i o n s a r e sometimes p r e s e n t w i t h i n t h e upper p o r -  t i o n o f t h e beds, b u t c r o s s - l a m i n a t i o n has n o t been observed. These beds can be d e s c r i b e d i n t h e t e r m i n o l o g y and ABE sequences.  T h i s type o f incomplete  " c l a s s i c a l " proximal  o f Bouma (1962) as AE  Bouma sequence i s t y p i c a l o f  t u r b i d i t e s , the t u r b i d i t e f a c i e s C o f Walker and M u t t i  (1973). Coarse t o very coarse high-density  sandstone:  sediment g r a v i t y flows.  These sandstones were d e p o s i t e d by T h i s i n t e r p r e t a t i o n i s based on t h e i r  t h i c k n e s s and g r a i n s i z e , t h e i r a s s o c i a t i o n w i t h normal t u r b i d i t e s and deep water mudstones, and the l a c k o f f a m i l i a r t u r b i d i t e f e a t u r e s w i t h i n the beds. The  t h i c k n e s s o f i n d i v i d u a l beds commonly exceeds t h e dimensions o f  the a v a i l a b l e s m a l l o u t c r o p s .  Beds more than 1 m t h i c k a r e t y p i c a l , and  s i n g l e beds more than 5 m t h i c k have been observed.  The sharp b a s a l con-  t a c t s may be p l a n a r , o r i r r e g u l a r as t h e r e s u l t o f e r o s i o n o f t h e u n d e r l y i n g mudstone d u r i n g t r a n s p o r t . the presence o f l a r g e  E r o s i o n o f t h e s u b s t r a t e i s a l s o i n d i c a t e d by  (up t o 30 cm) e l o n g a t e  which are o f t e n p r e s e n t  r i p - u p c l a s t s o f mudstone  i n t h e lower p a r t o f t h e sandstone beds.  Identifica-  t i o n as r i p - u p c l a s t s i s based on t h e i r v e r y l a r g e s i z e compared t o the e n c l o s i n g sand g r a i n s ; t h e i r elongate  and i r r e g u l a r shapes which suggest  short distances o f transport; t h e i r s i m i l a r i t y to the interbedded and  t h e i r i r r e g u l a r , embayed margins where s u r r o u n d i n g  mudstone;  sand g r a i n s have  27  pressed  into  the  Obvious stone,  tus.  The  beds,  the  stones  upward  density  be  these  fluidized  action  strength. process these tion  a  mechanism  for  distinct  from  that  be  may  can be  a  given  observed  in  the  paucity  of  exposures  the  vague  grading  Walker  by  to  and  unstable  into  the  sandof detri-  laminae.  overlying  describe Mutti  coarse  volcanic  horizontal  show  support would  It  these  (1973),  incomplete types  Middleton and  Often  mudstone.  beds.  They  massive  sand-  deposit. in the  As  their Bouma  diffuse  and  Hampton flow,  various  group,  lack  fluid  of  to  which  flow,  fact of  Beds  these  are  lamination.  They  :  include support  direct  inter-  with  finite  a  of  more  a  higher-  possible  each  than  transport  postulate  however,  In  grain  deposits  in  stages  are  matrix  well-defined  sequence.  horizontal  and  structures  (1973).  in  the  character-  sequences.  support  differentiate  hazardous a  Bouma  by  are  sedimentary  i n t e r s t i t i a l  unknown,  during  of  suspension  deposits  grain  debris  an  clearly  thus  of  intergranular by  in  resulting  successions  presently  is  maintained  The  or  flow,  upward  operate  by  is  other by  grain  are  turbidites  or  vertical  flows,  and  flow.  described  massive  of  of  applied  sediment  complete  which  might  single  the  show  show  usefully  summarized  others  mechanisms of  as  grains,  the  or  turbulence.  and  respectively  from  w i l l  B2  from  alteration  massive,  be  fluid  flow,  Criteria  infrequently  result  of  facies  gravity  been  between  only  structure.  described  sediment  achieved  appear  bedding,  have  compaction.  part  currents,  of  sediment  in  cannot  dish  graded  is  centimetres  turbidity  can  during  effects  turbidite  component  by  which  they few  without In  ized  to  may  the  sequence  correspond  is  and  upper  Bouma  and  this  Commonly,  only  mud  size-grading  although  complete  soft  one  and  of  deposi-  particular deposits  sedimentary commonly Graded  are structures  thick,  bedding,  and reverse  28  graded flow  bedding,  and  deposits. The  respond  turbidite their  to  with  mass  Any  of  this  sandstone  of  incorporating  not  turbulent  It  fragments  enough  to  of  totally  provenance. plagioclase in are  from  The  major  feldspar,  hand-specimen blurred  by  and 8  and  matrix,  volcanic  These  l i t h i c i f  not  clearly  and  in  what  of  aphanitic  cannot  be  accurately  Modal Table  I.  volcanic  analyses  Modal  thin-section.  enough  appears  to  and  the  modal  data  four  warrant  as  cor-  non-  comes  from  water  mud-  have  produced  capable  of  internal  eroding  flow  Ranch  overwhelmingly  volcanic  texture  is  but of  l i t h i c  was  between  thin-sections  of  Group from  recalculated  to  the  l i t h i c  of  is  and  detrital (Dickinson, seven  showed  analysis,  original  sandstones  evident  significant  provenance  counts  of  modal  include  although  fragments,  boundaries  unstable  "epimatrix"  may  volcanic  generally grain  quantitative  "matrix"  determined  were  but  an  diagenetic  determination  were  may  distinction  specified,  Harper  deep  were  thin-section,  Only  be  beds.  mudclasts.  are  clastic  Fortunately,  four  flows  have  material.  of  above  large  Group  make  to  and  mass  sandstones  interpretation  substrate, the  the  interpreted  recrystallization  effects  percentages The  and  in  impossible.  textures these  The  and  Group  sandstones  constituents  fragments,  original even  9)  be  of  from  Petrography  Ranch  quartz.  devitrification  components.  d i f f i c u l t  Harper  framework  (Fig.  mineral  1970)  the  the  reported  base  Ranch  thus  these  mud  been  the  discussed  disrupt  Sandstone Sandstones  for  that  their  near  can  turbidite  clear  a l l  Harper  and  mechanisms is  have  common  Support  with  the  beds.  and  are  description,  deposits.  a l l  grading  coarse-grained  association  or  size  mudclasts  very  flow  intimate  stones. these  Large  coarse  well  lack  amounts  textures s t i l l  possible.  are  presented  400  points  parameters  Q,  in  per F,  and  TABLE  I.  MODAL A N A L Y S E S HARPER  SAMPLE  MK-175  Devitrified in  VOLCANIC  RANCH  SANDSTONES  FROM  THE  GROUP  MK-180  MK-186  MK-193  glass  volcanic  rock  OF  50%  51%  62%  61%  14  fragments  Plagioclase  10  8  7  Alkali  Tr  Tr  3  Tr  6  2  Tr  Tr  4  Tr  feldspar  Quartz Plutonic  rock  fragments? Mudstone  clasts  Mafics Carbonate Matrix  Tr  Tr  Tr  1  Tr  1  1  Tr  Tr  1  36  33  19  19  3  1  Tr  2  clasts  and  epimatrix  Cement  Grain  Size  M to  Sorting  C  Moderate  Tr  =  Trace  F  =  Fine-grained  M  =  Medium-grained  C  =  Coarse-Grained  VC  =  Very  coarse-grained  F Moderate  —  C  to Poor  2  VC  C  to  Very  VC Poor  30  Fig.  7  Q-F-L p l o t o f modal d a t a from v o l c a n i c l a s t i c r o c k s from the Harper Ranch Group. Q = q u a r t z + c h e r t ; F = t o t a l f e l d s p a r ; L = t o t a l unstable l i t h i c s .  31  Fig.  8. P o l i s h e d s l a b o f v o l c a n i c sandstone from the Harper Ranch Group. C o n s i s t s mostly o f dense v o l c a n i c l i t h i c fragments and p l a g i o c l a s e feldspar. X 1.37.  Fig.  9. P o l i s h e d s l a b o f v o l c a n i c sandstone, Harper Ranch Group, c o n s i s t i n g o f v o l c a n i c l i t h i c fragments, pumice, and p l a g i o c l a s e f e l d s p a r . Wispy t e x t u r e s i n d i c a t i v e o f pumice c l a s t s are e v i d e n t , e s p e c i a l l y i n c e n t r a l p a r t o f the specimen. X 1.44.  32  L  of  Dickinson  grain  size  roundness (1968).  (1970),  was  estimated  were  visually  Examples  Figures  10  of  through  similar  aries  have  intervals suggests stones as  more  the  been  that  as  (1970) , tive  by  within  rock  and  species.  As  Table  Alkali  higher  are  thick  rims  clumps  of  I.  grains, most  amounts  These  in  The  section,  and  Fig.  7.  sorting  comparison  are  Median  and  charts  textures  seven  also  in  Folk  shown  the  beds,  can  come  in  only  be  grain  in  character  lateral  and  from  uniformity  overall or  examined, although  samples  their  vertical  single  were  composition,  and  represent  fragments  shown  in  standard  in  they bound-  irregular  composition of  the  petrologic  revealed  by  sand-  trends, further  sampling.  is  2%  plot  eyepiece,  sandstones  Significant  fragments  than  triangular  volcaniclastic  sandstones  adequately  volcanic  carbonate  other  entire  phenocrysts""-" w i t h i n  in  a  using  obliterated.  plagioclase  mineral  on  micrometre  preserved  three  the  variations  Volcanic followed  of  section.  detailed  a  estimated  well  nearly  they  the  shown  using  analyzed  covering  in  well  to  are  13.  Thin-sections are  and  and  Volcanic  from  l i t h i c  volcanic a  result,  feldspar,  Only  alkali  perthitic  crystals  quartz.  mudstone  one  a  fragments for 5%  fragments  each  composite clasts  sample (3%)  and  or  the  than  are  or  hypabyssal  variety  of  as  their  respec-  of  framework  the  volume  of  glass  grains, in  These  plutonic  minerals, less  significantly  feldspar  euhedral  mafic  amounts  contains  of  Dickinson  volume  present  10).  constituents,  the  feldspar  composite  (Fig.  a  counted  sample  (MK-186)  grains,  exhibit  framework procedure  were  greater  feldspar  volcanic  abundant  Following  plagioclase  alkali  most  rip-up  feldspar  polycrystalline of  the  approximately  samples. of  are  grains  plagioclase might  (4%). with  represent  source.  textures.  Most  are  33  Fig.  10. Photomicrograph o f t h i n - s e c t i o n , Sample MK-186, Harper Ranch Group. Composite f e l d s p a r g r a i n w i t h c o r e s o f p l a g i o c l a s e f e l d s p a r (PI) surrounded by t h i c k rims o f p e r t h i t i c a l k a l i f e l d s p a r (A, s t a i n e d yellow). Plane l i g h t , X 40.  Fig.  11. Photomicrograph o f t h i n s e c t i o n , Sample MK-186, Harper Ranch Group. M i c r o l i t i c v o l c a n i c fragments (V), pumice (P), a l k a l i f e l d s p a r (A), and q u a r t z (Q). Plane l i g h t , X 40.  34  Fig.  12. Photomicrograph o f t h i n - s e c t i o n , Sample MK-186, Harper Ranch Group. Broken zoned p l a g i o c l a s e c r y s t a l ( P I ) , p o r p h y r i t i c v o l c a n i c fragment (V), pumice (P), a l k a l i f e l d s p a r (A), q u a r t z (Q). Plane l i g h t , X 40.  Fig.  13. Photomicrograph o f t h i n - s e c t i o n , Sample MK-193, Harper Ranch Group. Angular v o l c a n i c q u a r t z (Q), dark mudclast (M), v a r i o u s v o l c a n i c fragments (V).  35  dense m i c r o l i t i c g r a i n s ( F i g . 11), w i t h p l a g i o c l a s e m i c r o l i t e s i n h y a l o p i l i t i c , t r a c h y t i c , or f e l t e d textures. felsite  The groundmass i n these g r a i n s may  ( c r y p t o c r y s t a l l i n e mosaic o f q u a r t z and f e l d s p a r ) o r c h l o r i t e .  g r a i n s have f e l s i t i c t e x t u r e s .  A  few  Pumice i s p r e s e n t i n most samples, and abun-  dant i n s e v e r a l ( F i g . 9, 11, 12).  Both round-bubble and long-tube  o c c u r , but the l a t t e r i s more d i f f i c u l t of  be c r y p t o -  t o r e c o g n i z e due  the i n t e r n a l s t r u c t u r e d u r i n g replacement  varieties  t o the o b l i t e r a t i o n  by c h l o r i t e and c e l a d o n i t e .  Such g r a i n s can be i d e n t i f i e d by t h e i r wispy i n t e r n a l s t r u c t u r e , equant t o h i g h l y e l o n g a t e shape, and by the e f f e c t s o f c o l l a p s e and squashing o f the o r i g i n a l l y porous g r a i n s between a d j a c e n t more competent g r a i n s d u r i n g compaction  ( F i s k e , 1969).  Clinopyroxene  i s the o n l y r e l i c t m a f i c m i n e r a l , and i s u s u a l l y  r e p l a c e d by c h l o r i t e .  D i s c r e t e framework g r a i n s and m i c r o p h e n o c r y s t s  partially which  are c o m p l e t e l y r e p l a c e d by c h l o r i t e p r o b a b l y were once mafic m i n e r a l g r a i n s , but t h e i r o r i g i n a l i d e n t i t y cannot be  determined.  Most q u a r t z g r a i n s can be c l a s s e d as "common" q u a r t z  ( F o l k , 1968) :  a n h e d r a l , subequant, m o n o c r y s t a l l i n e g r a i n s w i t h s t r a i g h t t o s l i g h t l y e x t i n c t i o n , and few i n c l u s i o n s o r v a c u o l e s . i n d i c a t i v e o f a p a r t i c u l a r source.  T h i s type o f q u a r t z i s not  Composite and seim-composite g r a i n s are  a l s o p r e s e n t , but are much l e s s abundant. phenocrysts  i n v o l c a n i c rock fragments,  Quartz o c c u r s r a r e l y as  ( F i g . 13).  micro-  and some f r e e g r a i n s o f d e f i n i t e  v o l c a n i c o r i g i n , w i t h a n g u l a r o r hexagonal o u t l i n e s and margins, are a l s o p r e s e n t  undulose  i r r e g u l a r l y embayed  Much o f the "common" q u a r t z may  also  have a v o l c a n i c o r i g i n . Carbonate g r a i n s are s i n g l e c r y s t a l s o f c a l c i t e , o f t e n m i n u t e l y and can be i d e n t i f i e d on t h i s b a s i s as echinoderm p l a t e s , p r o b a b l y columnals.  porous,  crinoid  36  P l a g i o c l a s e o c c u r s as e u h e d r a l , broken e u h e d r a l , and s u b h e d r a l g r a i n s . Zoning i s common ( F i g . 12), and i t i s e v i d e n t t h a t most o f these g r a i n s are v o l c a n i c phenocrysts which have been p a r t i a l l y t o completely f r e e d t h e i r v o l c a n i c m a t r i x d u r i n g e r u p t i o n o r subsequent  transport.  from  Small rem-  nants o f a p h a n i t i c groundmass can be observed rimming some g r a i n s ,  although  d i s t i n g u i s h i n g t h i s m a t e r i a l from d e t r i t a l o r d i a g e n e t i c m a t r i x i s o f t e n impossible.  Replacement by s e r i c i t e o r f i n e - g r a i n e d s a u s s u r i t e i s e x t e n s i v e ;  consequently, the o r i g i n a l a n o r t h i t e c o n t e n t c o u l d not be determined. important i n d i c a t o r o f the o r i g i n a l magma compositions i s thus l o s t .  One However,  m i c r o l i t i c t e x t u r e s are most common i n i n t e r m e d i a t e l a v a s ( D i c k i n s o n , 1970), and the s u r v i v i n g p h e n o c r y s t mineralogy ene)  ( p l a g i o c l a s e , q u a r t z , and c l i n o p y r o x -  a l s o suggests an a n d e s i t i c t o d a c i t i c s o u r c e .  might i n d i c a t e a minor r h y o l i t e  The r a r e f e l s i t i c g r a i n s  source.  The problems i n r e c o g n i z i n g the o r i g i n a l t e x t u r e o f these rocks have a l r e a d y been o u t l i n e d , but some c o n c l u s i o n s can be drawn.  The v o l c a n i c  sand-  stones are g r a i n - s u p p o r t e d , w i t h i n t e r s t i c e s f i l l e d by murky d e t r i t a l o r diagenetic matrix.  Minor amounts ( l e s s than 3%)  of clear,  monomineralic  c h l o r i t e , a l b i t e , and c a l c i t e have been d e s i g n a t e d as cement i n T a b l e I , and may  have f i l l e d i n t e r s t i t i a l v o i d s r a t h e r than r e p l a c i n g m a t r i x .  between l i t h i c g r a i n s show the e f f e c t s o f p r e s s u r e - s o l u t i o n and lization.  S o r t i n g o f the framework g r a i n s i s moderate t o poor.  g r a i n e d sandstones  show,better  Contacts recrystalThe  finer-  s o r t i n g , but much h i g h e r p r o p o r t i o n s o f m a t r i x ,  than the coarse t o v e r y c o a r s e samples.  The h i g h e r p r o p o r t i o n o f m a t r i x  r e f l e c t the r e a l abundance o f o r i g i n a l d e t r i t a l m a t r i x , but i t may  a l s o be  the r e s u l t o f the g r e a t e r d i f f i c u l t y i n d i s t i n g u i s h i n g framework g r a i n s from m a t r i x i n the f i n e r - g r a i n e d r o c k s .  may  37  Source and D e p o s i t i o n o f t h e V o l c a n i c D e t r i t u s The m a j o r i t y o f t h e v o l c a n i c d e t r i t u s i n t h e Harper Ranch Group i s p y r o c l a s t i c i n o r i g i n , produced by e r u p t i o n s c o e v a l w i t h  sedimentation.  T h i s i s i n d i c a t e d by t h e presence o f pumice and u n s t a b l e m i n e r a l s such as clinopyroxene,  and t h e abundance o f euhedral  g r a i n s i n these d e p o s i t s .  and broken, a n g u l a r  mineral  Pumice makes up o n l y a s m a l l f r a c t i o n o f t h e ash;  most o f t h e fragments a r e n o n v e s i c u l a r , equant, and sometimes p o l y g o n a l i n shape. T h i s m a t e r i a l i s s i m i l a r t o t h a t produced by p h r e a t i c e r u p t i o n s (Heiken,  1972), o r by g r a v i t a t i o n a l c o l l a p s e o f domes o r t h i c k flows o f  h i g h l y v i s c o u s magma ( F r a n c i s and o t h e r s , 1974).  According t o Fiske  (1963),  t h i s type o f a s h i s u s u a l l y l e s s voluminous than pumiceous ash i n s u b a e r i a l a n d e s i t i c t o d a c i t i c volcanoes,  due. presumably t o t h e l a c k o f abundant >  groundwater and t h e predominance o f v e s i c u l a t i n g magmas. t i v e estimates  Although  quantita-  o f r e l a t i v e volumes o f t h e two types o f s u b a e r i a l ash a r e n o t  a v a i l a b l e , s e v e r a l p e t r o g r a p h i c s t u d i e s o f ashes c o n f i r m t h i s c o n c l u s i o n (Heiken,  1972, 1974; F r a n c i s and o t h e r s , 1974; Roobol and Smith, 1974).  The  predominance o f n o n v e s i c u l a r ash can be e x p l a i n e d i f t h e e r u p t i o n s were subaqueous ( F i s k e , 1963), w i t h l a r g e volumes o f water a v a i l a b l e t o quench and  fragment t h e e r u p t i n g magma. Fiske  (1963) i n f e r r e d a subaqueous o r i g i n f o r s e v e r a l types o f p y r o -  c l a s t i c d e p o s i t i n t h e Eocene Ohanapecosh Formation i n western Washington, and was a b l e t o s u b s t a n t i a t e t h i s i n f e r e n c e by i d e n t i f y i n g t h e source of the tephra.  vents  The most common type i s v e r y s i m i l a r t o t h e p y r o c l a s t i c  d e p o s i t s i n t h e Harper Ranch Group, c o n t a i n i n g a v a r i e t y o f n o n v e s i c u l a r lithic  fragments, and v a r i a b l e b u t g e n e r a l l y s m a l l amounts o f pumice.  This  38  tephra tered  was the  probably magma  ing  very  the  pyroclastic from  The  (Fiske  upward—a  eruption.  the  settling  The Group  occur  marine an  as  to  eruptions  eruption  size-sorted  with  Ranch  the  Group,  probably  lack  the  graded  These by  and  the  of  the  entire  series  massive  result  of  the  graded  vent  material  downslope  is  from  the  volcaniclastic  turbidite coarse  sequences,  finer-grained  of  the  as  a  coarse stages  and of  originate  submarine  of  beds,  and  pyroclastic  so  they  do  not  beds  not  beds as are  appear  Matsuda  (1964).  Production  would  explain  the  of  submarine would  lack  eruption  probably  doubly  column  have  to  in  from  eruption  accumulated  part not  of  of  place  Harper  the  Ranch  doubly  overlain  graded  necessary take  the  similar  and  sequence  to  a  currents.  thick,  a  pyroclastic  tuffaceous  early  thought  transport  of  from  interpreted  the  of  material  submarine  movement  during  sequence  much  described  becoming  is  downslope  for  sequence  thin-bedded  tuff  form-  c h a r a c t e r i z e d by  series  The  finer  are  a  around  doubly  units  been deep  vent,  some  well.  relatively  shat-  origin  as  have  which  the  present  which  1964).  around  although  structures of  eruptions  likely  Group  medium-grained  Fiske  is  Ranch  periodic  isolated  The  by  by  tephra  Harper  overlain  flow,  phreatic  and  This  is  sequence.  upper  lava  products  progressively  turbidite  described  bed  turbidity  fine  sequences. graded  tuff  submarine  Harper  the  accumulated  accompanied as  the  graded  The of  in  Matsuda,  each  which  the  material  be  pyroclastic  debris  the  volcanoes  beds  massive  doubly  subaqueous  to and  with  in  of  tephra.  sedimentary  believed  turbidites,  mixed  material  and  thick,  column,  pre-existing  pyroclastic  eruptions  dense  the  subaerial  types  deposits  single  product  heterogeneous  reworked  bedding  and  the  to  graded  by  the  tephra  doubly deposits  by  sequences,  to  produce  at  depths  shallow since  such of  a  several  hundred  metres  ossicles  also  accumulated present  volcanic  The  in  eruptions  section  "classical"  not  grain  size,  bed.  The  the  processes  by  fans,  dispersal  and  canic from  Ranch  water. have  produced  of  (stalked and  Transport  occurred  slumping  not  each  to  abyssal  of  during  may  echinoderm)  have  this  temporarily  material  eruptions,  unconsolidated  within  mudstones,  Walker  or  material  the  presence  Mutti,  into  its  interaround  or  lack  the  dispersal and  of fan  beds,  and  a  make  however, beds,  are and  channeling  sequences  form  the  canyons  associations  are  the .pyroclastic systems,  more coarse  but  probably or  less  mass  by  defined  sedimentary or  facies  are  channels,  for  sediment  debris  was  location  dispersed  flow  such  integral  from  random  in  criteria  absent  the  assign-  structures  and  framework  flow  structure.  are  regular  turbi-  these  of  systems,  T e p h r a was  producing  to  as  mass  dish  sequence  (submarine  which  facies  of  coarse  was  deposits.  identified  turbidite  of  elements  plains)  and  (1973)  flow  without  used  individual  development  basin.  turbidite  and  terrigenous  canyon  center,  type  mass  the  sandstones criteria  Mutti  were  and  and  than  and  pyroclastic  turbidites  The  thickness,  rather  Walker  turbidites,  correct.  of  of  the  massive  These  because  submarine  volcanic  B2,  In  deposition.  by  proximal  and  the  describe  physiographic  and  Group  sources  bedded  was  pyroclastic  beds,  ratio  lead  the  submarine  trolled  bed  definitions.  which  controlled  to  facies  of  sandstone-shale  Harper  pelmatozoan  classification  facies  s t r i c t l y  sequences  of  facies  turbidite is  the of  parts  by  of  tephra  could  medium-grained C,  as  were  terms as  to  usage  within  the  shallow  setting  previous  facies  ments  water  turbidite  a  deposits This  that  presence  vent.  fine-  dite  The  relatively  between  The used  more.  suggests  in  deep  mittently  or  the conof  vol-  radially  sequence  deposits.  of  inter-  40  Deep Water C a l c i r u d i t e  A s i n g l e bed o f p o o r l y - s o r t e d c a l c i r u d i t e o c c u r s about above the l i m e s t o n e o f U n i t 1-A, sandstones  (Loc. F - 2 ) .  100  i n t e r b e d d e d w i t h mudstone and  t o 150  m  turbidite  The p o o r l y exposed, s t r u c t u r e l e s s packstone  up mostly o f v e r y coarse sand t o pebble s i z e f o s s i l m a t e r i a l i n an  i s made argilla-  ceous m i c r i t e m a t r i x , which i s l o c a l l y r e c r y s t a l l i z e d t o s p a r r y c a l c i t e . The most abundant c o n s t i t u e n t s are pelmatozoan o s s i c l e s ,  f o l l o w e d by s o l e n o -  p o r i d a l g a e , b r a c h i o p o d s h e l l s and s h e l l fragments,  and o s t r a c o d s .  s m a l l rugose  fragments  c o r a l s , e c h i n o i d s p i n e s , and t r i l o b i t e  few  are a l s o  p r e s e n t , as w e l l as minor amounts o f p l a g i o c l a s e , v o l c a n i c rock and q u a r t z .  A  fragments,  Rip-up c l a s t s o f mudstone and v o l c a n i c s i l t s t o n e are common  ( F i g . 14) . The  s o l e n o p o r i d a l g a e and o t h e r f o s s i l organisms  a s h a l l o w water environment  o r i g i n a l l y inhabited  ( w i t h i n the p h o t i c zone), but t h e i r p r e s e n t depo-  s i t i o n a l s e t t i n g i n d i c a t e s t h a t they have been r e d e p o s i t e d i n deeper  water  genera o f a l g a e , Solenopora  and  by submarine mass flow p r o c e s s e s . Parachaetetes tetes  The  two  Parachae-  ( F i g . 15 and 16), develop as n o d u l a r a t t a c h e d forms.  i s found i n Upper Devonian r e e f complexes i n the immediate b a c k - r e e f  f a c i e s , o r i n the f o r e - r e e f zone (Wara,: 1972). P e n n s y l v a n i a n o c c u r r e n c e s o f Parachaetetes  Heckel  (1975) notes  are r e s t r i c t e d t o c a l c a r e n i t e s  a s s o c i a t e d w i t h p h y l l o i d algal-mud b u i l d u p s .  T h i s s e t t i n g appears  o f most s o l e n o p o r i d s ; they are abundant mainly i n r e e f - a s s o c i a t e d but were not important r e e f b u i l d e r s  that  (Heckel, 1975).  t o be  that  calcarenites,  Such c a l c a r e n i t e s  and  c a l c i r u d i t e s are then the l i k e l y immediate source f o r the c a l c a r e o u s d e t r i t u s which makes up the r e d e p o s i t e d bed. R e e f - l i k e b u i l d u p s and t h e i r a s s o c i a t e d carbonate  sediment  probably  41  F i g . 15. Photomicrograph o f the a l g a Solenopora, Harper Ranch Group. T h i n - s e c t i o n , X 32.  F i g . 16. Photomicrograph o f the a l g a Parachaetetes, Harper Ranch Group. T h i n - s e c t i o n , X 32.  Loc. F-2,  Loc. F-2,  43  r i n g e d the v o l c a n i c i s l a n d s or s h a l l o w l y submerged v o l c a n i c summits which were the sources  o f the v o l c a n i c d e t r i t u s i n the Harper Ranch Group.  p o r t o f t h i s c a l c a r e o u s d e t r i t u s i n t o t h i s p a r t o f the b a s i n s m a l l amounts i n c o r p o r a t e d i n v o l c a n i c sandstones) was event, s i n c e o n l y one  such bed was  c a l c a r e o u s m a t e r i a l was ume  (except  Transas  obviously a rare  found i n the s e c t i o n .  In most cases  overwhelmed by and mixed w i t h the much g r e a t e r  the vol-  of p y r o c l a s t i c material a v a i l a b l e for transport.  Shallow-marine Limestone  B i o c l a s t i c limestone  ( U n i t lA) crops out d i s c o n t i n u o u s l y 50 t o 100  m  s t r a t i g r a p h i c a l l y above the b a s a l t e c t o n i c c o n t a c t o f the Harper Ranch Group. Where p r e s e n t ,  the limestone  m.  f a u l t s and poor exposure i n c e r t a i n areas  O f f s e t s by  o f the s m a l l en echelon  has  a r e l a t i v e l y uniform  10  (both e a s t and west  segments) combine to p a r t i a l l y account f o r the mapped  d i s c o n t i n u i t y o f the l i m e s t o n e .  However, the e a s t e r n t e r m i n a t i o n o f the u n i t  i s b e s t e x p l a i n e d as a s t r a t i g r a p h i c p i n c h o u t , are good and no evidence  t h i c k n e s s o f about  f o r f a u l t o f f s e t was  s i n c e exposures t o the observed  t a c t o f the Harper Ranch Group i s not o f f s e t ) . s t r a t a i n t h i s r e g i o n are g e n e r a l l y l e n t i c u l a r  east  (the nearby b a s a l con-  Limestones w i t h i n ( C o c k f i e l d , 1948;  correlative Sada  and  Danner, 1974). The  limestone  i s medium t o l i g h t gray i n c o l o r .  In most outcrops i t  appears massive, but i n some c a s e s , where i t has been i n c i s e d by s m a l l streams, bedding i s v i s i b l e . ranging outcrops  At these  from 3 t o 30 cm.  l o c a l i t i e s bedding i s p l a n a r , w i t h  thicknesses  I t i s l i k e l y t h a t the massive c h a r a c t e r o f many  r e s u l t s from s u r f i c i a l weathering and perhaps from s l i g h t  l i z a t i o n d u r i n g r e g i o n a l low  grade metamorphism.  primary s t r u c t u r a l f e a t u r e s o f the l i m e s t o n e .  recrystal-  These e f f e c t s mask the  However, t h i c k , massive  44  bedding may  be  a p r i m a r y d e p o s i t i o n a l f e a t u r e o f some p o r t i o n s o f the  lime-  stone . Fine- to coarse-grained up the u n i t . allochems.  Whole and  wackestones, packstones, and  fragmentary c a l c a r e o u s  grainstones  make  f o s s i l s are the most abundant  Ooids and p e l l e t s are abundant i n some samples.  Skeletal debris  i s d i v e r s e , but g e n e r a l l y f o r a m i n i f e r s , b r a c h i o p o d s h e l l fragments and and pelmatozoan present  ( s t a l k e d echinoderm) o s s i c l e s are most abundant, and  i n n e a r l y a l l samples.  Other types i n c l u d e o s t r a c o d s ,  are  echinoid  s p i n e s , bryozoans, c o r a l s , c a l c i s p h e r e s , and p o s s i b l y pelecypods. d i v e r s i t y o f f o s s i l types suggests t h a t d e p o s i t i o n took p l a c e  spines,  The  in subtidal,  open marine s h e l f c o n d i t i o n s . I have r e c o g n i z e d allochem c o n t e n t . The p e e l s , and was  s i x microfacies  d e f i n e d on the b a s i s o f t e x t u r e  m a t e r i a l examined i n c l u d e s p o l i s h e d s l a b s ,  t h i n s e c t i o n s o f 17 samples from v a r i o u s  not adequate t o r e v e a l whether s y s t e m a t i c  butions  of microfacies  e x i s t , and  n i z e d w i t h f u r t h e r sampling. given  i n Table I I , and Microfacies 1  wackestone. matrix.  The  Abundant and  diverse  Ostracods are a r t i c u l a t e d and  t o wash and  Sampling distri-  c o u l d p r o b a b l y be  recog-  a l l o c h e m c o n t e n t o f each m i c r o f a c i e s  i s very poorly skeletal debris  IV.  "floats" in a micrite  the f r a g i l e s h e l l s are unbroken.  f i l l e d w i t h spar, as are forams and  f o s s i l debris.  No  is  s o r t e d s k e l e t a l lime  i n a v e r y q u i e t environment w i t h l i t t l e  fragment the  acetate  lateral  they are i l l u s t r a t e d i n P l a t e s I I I and  ( P l a t e I I I , A)  took p l a c e  v e r t i c a l and  other microfacies  Brachiopods are d i s a r t i c u l a t e d , but  Deposition  localities.  and  gastropods.  current  evidence o f b i o t u r b a t i o n  activity was  observed. Microfacies 2  ( P l a t e I I I , B and  C)  c o n s i s t s of f i n e - to  coarse-grained,  45  TABLE I I . ALLOCHEM CONTENT OF DIFFERENT MICROFACIES OF MISSISSIPPIAN LIMESTONE, UNIT IA, HARPER RANCH GROUP. X INDICATES PRESENCE OF ALLOCHEM.  X X  Brachiopods  X X  Pelecypods  ? ?  Forams  Gastropods Crinoid o s s i c l e s Echinoid spines Ostracods Calcispheres Bryozoans Corals Peloids Ooids Intraclasts  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 X  X X X  X X  X X X  X  X  46  PLATE  III. UNIT  MICROFACIES 1 A , HARPER  FROM  RANCH  UPPER  GROUP.  MISSISSIPPIAN SCALE  LIMESTONE,  B A R =. 0 . 5 mm  A.  Microfacies  1,  skeletal  lime  wackestone.  B.  Microfacies  2,  skeletal  lime  packstone.  C.  Microfacies  2,  skeletal  lime  packstone.  D.  Microfacies  3,  peloidal  lime  packstone.  48  PLATE IV. MICROFACIES FROM UPPER MISSISSIPPIAN LIMESTONE, UNIT 1A, HARPER RANCH GROUP.  SCALE BAR = 0.5 mm.  A.  M i c r o f a c i e s 4a, s k e l e t a l o o i d g r a i n s t o n e  (well s o r t e d ) .  B.  M i c r o f a c i e s 4b, s k e l e t a l o o i d g r a i n s t o n e  (poorly  C.  M i c r o f a c i e s 5, p e l o i d a l lime  D.  Fine-grained  skeletal  grainstone.  grainstone.  sorted).  50  poorly  s o r t e d s k e l e t a l lime packstone.  Most samples c o n t a i n abundant  finely  comminuted and m i c r i t i z e d s k e l e t a l d e b r i s and s c a t t e r e d l a r g e r fragmentary and whole f o s s i l s .  The i n t e r n a l f a b r i c ranges from n e a r l y s t r u c t u r e l e s s ,  w i t h randomly o r i e n t e d e l o n g a t e g r a i n s , t o h i g h l y o r g a n i z e d ,  w i t h good p a r -  a l l e l alignment o f e l o n g a t e g r a i n s as a r e s u l t o f weak c u r r e n t One  activity.  sample c o n s i s t e d o f i n t e r l a y e r e d packstone and burrow-mottled m i c r i t e ,  w i t h the packstone c u t by m i c r i t e - f i l l e d burrows. these rocks  i s commonly somewhat a r g i l l a c e o u s .  The m i c r i t e m a t r i x i n  Skeletal debris i s of diverse  and s e v e r a l samples c o n t a i n the h e t e r o c o r a l Hexaphyllia,  types,  c y l i n d r i c a l corallum  a t l e a s t several centimetres  l o n g , surrounded by a con-  c e n t r i c a l l y layered m i c r i t e coat, probably o f a l g a l Microfacies  3 ( P l a t e I I I , D) i s a p o o r l y  o f abundant p e l o i d s  (Bathurst,  material i n a m i c r i t e matrix.  with a slender  origin.  s o r t e d packstone c o n s i s t i n g  1971, p. 84) and l e s s abundant s k e l e t a l The p e l o i d s a r e rounded e l l i p s o i d s o f homo-  geneous m i c r i t e from 0.1 t o 0.25 mm i n maximum diameter.shape and s i z e suggests t h a t they a r e f e c a l p e l l e t s .  Their  regular  The sediment i s s t r u c -  t u r e l e s s and homogeneous, and t h i s f a b r i c as w e l l as t h e abundant p e l o i d s may r e s u l t from very  thorough reworking by burrowing d e t r i t u s  M i c r o f a c i e s 4 i s composed o f s k e l e t a l - o o i d g r a i n s t o n e s , g r a d a t i o n a l l y from w e l l s o r t e d and w e l l washed s o r t e d and p o o r l y washed contains filling  feeders. which range  (4a, P l a t e IV, A) t o p o o r l y  (4b, P l a t e IV, B ) . The p o o r l y washed  grainstone  i r r e g u l a r l a y e r s o f m i c r i t e i n a rock o t h e r w i s e cemented by v o i d sparry c a l c i t e .  Most samples a r e medium-grained.  Ooids have few  t o many l a y e r s , and commonly have n u c l e i o f pelmatozoan o s s i c l e s , o r l e s s commonly o f f o r a m i n i f e r s o r p e l o i d s .  D e t a i l s o f the o o l i t i c coatings are  g e n e r a l l y obscured by r e c r y s t a l l i z a t i o n , b u t i n some g r a i n s ghosts o f the  51  radiaxial-fibrous structure are s t i l l are abundant, b u t o t h e r  visible.  f o s s i l s a r e uncommon.  Uncoated pelmatozoan o s s i c l e s The o o i d s  and s k e l e t a l d e b r i s  o r i g i n a t e d i n shallow, h i g h l y a g i t a t e d water, b u t were t r a n s p o r t e d  into  q u i e t e r water, s i n c e t h i s m i c r o f a c i e s o c c u r s i n t e r l a y e r e d w i t h M i c r o f a c i e s 2, s k e l e t a l lime packstone, and M i c r o f a c i e s 6, f i n e - g r a i n e d s k e l e t a l Lime mud i n t r a c l a s t s , p r o b a b l y i n c o r p o r a t e d but  rare.  Small-scale  during  grainstone.  transport, are present  c r o s s - b e d d i n g has been observed i n t h i n - s e c t i o n s , b u t  not i n o u t c r o p . M i c r o f a c i e s 5 ( P l a t e IV, C) i s a p e l o i d a l lime g r a i n s t o n e .  It is  moderately s o r t e d and f i n e - g r a i n e d , w i t h abundant p e l o i d s and l e s s abundant s k e l e t a l g r a i n s cemented by s p a r r y c a l c i t e .  Thorough washing o f the p e l o i d a l  muds c o u l d have produced t h i s sediment, perhaps w i t h l i t t l e  transport o f the  p e l o i d s and s k e l e t a l g r a i n s . M i c r o f a c i e s 6 ( P l a t e IV, D) c o n s i s t s o f f i n e - g r a i n e d s k e l e t a l S o r t i n g i s moderate, and there  i s some alignment o f e l o n g a t e g r a i n s  t o bedding, i n d i c a t i n g working by c u r r e n t s . are the most common a l l o c h e m s .  grainstone. parallel  Pelmatozoan d e b r i s and p e l o i d s  A few m i c r i t e - f i l l e d burrows can be seen i n  thin-section. The  d i v e r s i t y of microfacies  and organisms found i n t h i s l i m e s t o n e i s  c h a r a c t e r i s t i c o f s h a l l o w s u b t i d a l carbonates d e p o s i t e d e f f e c t i v e wave base  (Laporte,  1971).  Deposition  above, o r j u s t below,  a t depths w i t h i n the p h o t i c  zone i s i n d i c a t e d by t h e a l g a l s t r u c t u r e s c o a t i n g t h e c o r a l l a o f On  t h e o t h e r hand, f e a t u r e s  tidal  flats  (laminated  i n d i c a t i v e o f very  Hexaphyllia.  s h a l l o w r e s t r i c t e d lagoons o r  a l g a l s t r u c t u r e s , mudcracks, abundant i n t r a c l a s t s ,  d o l o m i t e , and low f a u n a l d i v e r s i t y ) a r e absent. from wackestones t o o o l i t i c g r a i n s t o n e s  records  The range i n textu'ral types a wide v a r i a t i o n i n c u r r e n t  52  i n t e n s i t y which i s t o be expected Although  i n the shallow s u b t i d a l  environment.  the r e l a t i v e p r o p o r t i o n s o f the d i f f e r e n t m i c r o f a c i e s are  d i f f i c u l t t o a s s e s s , wackestones and packstones  a r e a t l e a s t as abundant,  and p r o b a b l y more abundant, than g r a i n s t o n e s , and formed i n bottom e n v i r o n ments w i t h abundant l i m e mud, d i v e r s e b e n t h i c fauna, and low t o moderate c u r rent a c t i v i t y .  G r a i n s t o n e s seem t o be i n t i m a t e l y i n t e r b e d d e d w i t h t h e  m i c r i t e - r i c h rocks. stones  P e l o i d a l g r a i n s t o n e s and f i n e - g r a i n e d s k e l e t a l  ( M i c r o f a c i e s 5 and 6) c o u l d have been produced  s o r t i n g e s s e n t i a l l y in  situ,  extended  by c u r r e n t washing and  s i n c e t h e i r framework g r a i n s a r e s i m i l a r t o ,  though l e s s v a r i e d than, t h e i n t e r b e d d e d packstones s k e l e t a l - o o i d grainstones  and wackestones.  The  ( M i c r o f a c i e s 4a and 4b), however, were formed by  and repeated c u r r e n t a g i t a t i o n , p r o b a b l y on shoal-water  sand banks.  grain-  carbonate  Some o f these sands were p e r i o d i c a l l y c a r r i e d i n t o t h e q u i e t  water s e t t i n g s , where they a r e now p r e s e r v e d , by e x t r a o r d i n a r i l y s t r o n g wave o r c u r r e n t a c t i v i t y , perhaps d u r i n g  storms.  V o l c a n i c and o t h e r noncarbonate g r a i n s c o a r s e r than c l a y s i z e a r e c o n s p i c u o u s l y absent ing  from t h i s l i m e s t o n e , i n marked c o n t r a s t t o t h e u n d e r l y -  and o v e r l y i n g c l a s t i c r o c k s .  Furthermore,  these e l a s t i c s a r e h e m i p e l a g i c  muds and t u r b i d i t e s d e p o s i t e d below wave base, and p o s s i b l y a t moderate t o g r e a t depths,  compared w i t h t h e s h a l l o w marine c h a r a c t e r o f t h e l i m e s t o n e .  These c o n t r a s t s , i n a d d i t i o n t o t h e l a t e r a l d i s c o n t i n u i t y o f t h e l i m e s t o n e , demand c a r e f u l examination  o f t h e s t r a t i g r a p h i c r e l a t i o n s h i p s o f these  units,  s i n c e they suggest t h e p o s s i b i l i t y t h a t t h e l i m e s t o n e i s n o t i n d e p o s i t i o n a l sequence w i t h the e n c l o s i n g r o c k s , b u t may o c c u r as submarine s l i d e b l o c k s or  as t e c t o n i c s l i v e r s w i t h i n t h e deep water sequence.  field  evidence  i s i n support o f a conformable  However, a l l o f t h e  depositional succession.  53  The o n l y good exposure o f the c o n t a c t s of the l i m e s t o n e o c c u r s i n a s m a l l dry stream channel which c u t s a c r o s s the easternment segment o f U n i t 1A.  Here bedded l i m e s t o n e i s i n conformable  stone.  c o n t a c t w i t h the o v e r l y i n g mud-  The change from l i m e s t o n e t o mudstone i s , however, sudden, w i t h  i n t e r v a l of interbedding.  The o v e r a l l t r e n d o f the u n i t i s a l s o  no  conformable  w i t h the a t t i t u d e o f the e n c l o s i n g r o c k s , which are u s u a l l y mudstone i n outcrops n e a r e s t t o the c o n c e a l e d c o n t a c t s . l o c a l i t y South Thompson No.  C o n t a c t s o f the l i m e s t o n e a t  1 (Unit IB) are much more f u l l y exposed, and  too are seen t o be conformable.  Furthermore,  they  a l t h o u g h the lower c o n t a c t w i t h  mudstone i s abrupt, t h i s l i m e s t o n e i s o v e r l a i n by a sequence a t l e a s t 10 m t h i c k o f i n t e r b e d d e d mudstone, dark gray m i c r i t e , and f i n e - t o medium-grained c a l c a r e o u s and n o n c a l c a r e o u s  sandstone.  I i n t e r p r e t these rocks as an assem-  b l a g e t r a n s i t i o n a l between the shallow water carbonates deeper water c l a s t i c r o c k s .  and the  overlying  T h i s t r a n s i t i o n r e c o r d s the renewed i n f l u x o f  v o l c a n i c l a s t i c s , and p r o b a b l y p r o g r e s s i v e deepening  o f the b a s i n  W i t h i n the e n t i r e Harper Ranch Group i n t h i s a r e a , the  floor.  stratigraphic  s u c c e s s i o n o f p a l e o n t o l o g i c a l l y dated l i m e s t o n e u n i t s i s c o n s i s t e n t w i t h f a c i n g d i r e c t i o n o f the e n c l o s i n g sedimentary b r e c c i a s and megabreccias, stone s l i d e b l o c k s  which would be expected  Coarse  limestone  t o accompany l a r g e l i m e -  (Conaghan and o t h e r s , 1976) , are absent, and even  g r a i n e d a l l o d a p i c carbonates d e s c r i b e d below.  rocks.  are n o t a b l y r a r e , l i m i t e d t o the s i n g l e  T h e r e f o r e , I conclude  t h a t these l i m e s t o n e s are  onous, and are n e i t h e r submarine s l i d e b l o c k s nor t e c t o n i c These l i m e s t o n e u n i t s accumulated  the  finerbed  autochth-  slices.  d u r i n g p e r i o d s when p o r t i o n s o f the  b a s i n f l o o r had t e m p o r a r i l y reached s h a l l o w s u b t i d a l depths, as a r e s u l t o f basin f i l l i n g ,  u p l i f t o f the b a s i n f l o o r , o r e u s t a t i t i c s e a - l e v e l  lowering.  54  The  absence o f v o l c a n i c d e t r i t u s o r a s h - f a l l t u f f s i n the l i m e s t o n e  t h a t v o l c a n i c a c t i v i t y may  have ceased.  e x i s t e d on the b a s i n f l o o r a t t h i s time.  suggests  Subdued t o p o g r a p h i c r e l i e f .probably Carbonate p r o d u c t i o n and  accumula-  t i o n took p l a c e on those p o r t i o n s w i t h i n the p h o t i c zone, w h i l e slow d e p o s i t i o n o f t e r r i g e n o u s mud  and minor e p i c l a s t i c v o l c a n i c d e t r i t u s c o u l d have  c o n t i n u e d i n deeper p o r t i o n s . of t h i s  T h i s would e x p l a i n the l a t e r a l  discontinuity  limestone.  From the s e d i m e n t o l o g i c f e a t u r e s o f the v o l c a n i c l a s t i c s t r a t a , I i n f e r t h a t they were d e p o s i t e d a t g r e a t e r water depths than the s h a l l o w water l i m e stone.  The v e r t i c a l t r a n s i t i o n from the l i m e s t o n e o f U n i t 1A t o the o v e r l y i n g  deeper water mudstone and r e d e p o s i t e d t u f f p r o b a b l y r e c o r d s a r a p i d deepeni n g o f the b a s i n f l o o r which r o u g h l y c o i n c i d e d w i t h the resumption activity  ( i f i t indeed had c e a s e d ) .  o f deepening  of volcanic  No q u a n t i t a t i v e e s t i m a t e o f the amount  can be made, because no c r i t e r i a are p r e s e n t t o suggest  depths o f accumulation  o f the v o l c a n i c l a s t i c  exact  strata.  SUMMARY OF DEPOSITIONAL SETTING  Coarse  c l a s t i c d e t r i t u s i n the Harper Ranch Group i s e n t i r e l y v o l c a n i c  i n o r i g i n , except f o r common but minor admixed carbonate a l o g y and t e x t u r e o f v o l c a n i c l i t h i c t h i s d e b r i s was  produced  debris.  fragments and p h e n o c r y s t s  The  miner-  suggests t h a t  by p y r o c l a s t i c e r u p t i o n s o f a n d e s i t i c t o d a c i t i c  l a v a a t s h a l l o w l y submerged v o l c a n i c c e n t e r s .  T h i s m a t e r i a l was  subsequently  reworked and r e d e p o s i t e d i n marine waters below wave base by t u r b i d i t y  cur-  r e n t s and h i g h - c o n c e n t r a t i o n subaqueous f l o w s , and i s i n t e r b e d d e d w i t h  sili-  ceous h e m i p e l a g i c mudstones.  During p e r i o d s o f v o l c a n i c quiescence  and  s h a l l o w i n g o f the b a s i n f l o o r , b i o c l a s t i c l i m e s t o n e composed o f a v a r i e t y  55  o f l i t h o f a c i e s accumulated i n shallow  marine, s u b t i d a l waters.  v o l c a n i c a c t i v i t y accompanied by r a p i d i n c r e a s e i n water depth renewed d e p o s i t i o n o f deeper water v o l c a n i c l a s t i c sediments. t i o n a l megacycle i s r e p e a t e d  Renewal o f initiated This  deposi-  a t l e a s t f o u r times i n t h e M i s s i s s i p p i a n t o  Lower P e n n s y l v a n i a n p o r t i o n o f the Harper Ranch Group. Deposition  took p l a c e w i t h i n a v o l c a n i c a r c h i p e l a g o which was  an a c t i v e v o l c a n i c i s l a n d a r c a s s o c i a t e d w i t h a s u b d u c t i o n t h i s p o r t i o n o f the d e p o s i t i o n a l b a s i n was some d i s t a n c e c e n t e r s , s i n c e coarse flows which occur are absent.  The b a s i n p r o b a b l y  f o r e - a r c o r back-arc regions.  from t h e v o l c a n i c  (Jones,  1967; M i t c h e l l , 1970)  was w i t h i n t h e f r o n t a l a r c r a t h e r than t h e Sediments d e p o s i t e d  i n t h e l a t t e r two areas  o f deep water type i n v o l c a n i c a r c s w i t h  o f sediment from an a d j a c e n t 1974).  However,  v o l c a n i c b r e c c i a s , d e b r i s flow d e p o s i t s , and v o l c a n i c  near i s l a n d a r c v o l c a n i c vents  are u s u a l l y u n i f o r m l y  zone.  probably  c o n t i n e n t a l landmass  little  influx  ( D i c k i n s o n , 1976; K a r i g ,  The f r o n t a l a r c , on the o t h e r hand, may c o n t a i n a range o f e n v i r o n -  ments from s u b a e r i a l t o moderately deep water, and i s s u b j e c t t o r e c u r r e n t episodes o f u p l i f t and subsidence  (Tracey  c o r r e l a t i o n o f episodes o f limestone  and o t h e r s ,  1964; K a r i g , 1971).  My  deposition with periods of v o l c a n i c  q u i e s c e n c e suggests a t e c t o n i c r a t h e r than e u s t a t i c c o n t r o l o f t h e i n f e r r e d v a r i a t i o n i n paleobathymetry.  Such i n s t a b i l i t y i s thus c o n s i s t e n t w i t h the  i n f e r r e d f r o n t a l a r c d e p o s i t i o n a l s e t t i n g f o r t h e Harper Ranch Group.  REGIONAL CORRELATIONS  Rocks mapped as "Cache Creek Group" and " e a s t e r n Cache Creek Group" by Cockfield  (1948) and Campbell and T i p p e r  (1971) extend northward from Kamloops  through the N i c o l a and Bonaparte Lake map-areas t o a t l e a s t l a t i t u d e 51° 30'N,  56  where they a r e f a u l t e d a g a i n s t Upper T r i a s s i c v o l c a n i c s and t h e P a l e o z o i c (?) greenstone  o f t h e F e n n e l Formation,  by J u r a s s i c and T e r t i a r y s t r a t a .  i n t r u d e d by Mesozoic  Although  p l u t o n s , and covered  t h e "Cache Creek Group" as p r e -  v i o u s l y mapped i s now known t o i n c l u d e Upper T r i a s s i c r o c k s i n N i c o l a map-area, most o f the e a s t e r n p o r t i o n o f t h e u n i t i n both map-areas i s p r o b a b l y P a l e o z o i c i n age.  Late  Common l i t h o l o g i e s a r e v o l c a n i c a r e n i t e and graywacke,  s i l i c e o u s a r g i l l a c e o u s r o c k s , and minor c a r b o n a t e , an assemblage which i s s i m i l a r t o t h a t near Kamloops.  B a s i c and i n t e r m e d i a t e v o l c a n i c f l o w s ,  near Kamloops, may be p r e s e n t i n these a r e a s .  absent  S i m i l a r l i t h o l o g i e s a r e found  i n t h e "Cache Creek Group" west o f Vernon and Kelowa .in Vernon map-area 1959), and e x t e n d i n g eastward  (Jones,  from Vernon t o Monashee Pass, where they a r e  o v e r l a p p e d by T r i a s s i c r o c k s o f t h e S l o c a n Group and e n g u l f e d by Mesozoic p l u t o n i c rocks sion, I w i l l  (Wheeler and o t h e r s , 1972, F i g . 2 ) . I n t h e f o l l o w i n g d i s c u s -  i n c l u d e these C a r b o n i f e r o u s and Permian s t r a t a w i t h t h e Harper  Ranch Group i n o r d e r t o emphasize t h e i r g e n e r a l s i m i l a r i t y , and t o d i s t i n g u i s h them from nearby groups o f s i m i l a r age b u t d i s s i m i l a r l i t h o l o g y and t e c t o n i c setting. Monger (1977) has grouped t h e Harper Ranch Group w i t h o t h e r u n i t s o f Late P a l e o z o i c age i n t h e s o u t h e r n Intermontane b e l t , and r e f e r s t o them as the Southern  B r i t i s h Columbia assemblage.  Other groups o f Upper P a l e o z o i c  e u g e o c l i n a l s t r a t a a r e d e s i g n a t e d as t h e E a s t e r n assemblage and Cache CreekB r i d g e R i v e r assemblage.  P u b l i s h e d d e s c r i p t i o n s o f t h e r o c k s grouped by  Monger w i t h t h e Harper Ranch Group suggest t h a t they have l i t t l e with i t , The  i n common  and a r e b e t t e r r e f e r r e d t o these o t h e r Upper P a l e o z o i c assemblages.  assemblages d e f i n e d by Monger (1977) a r e b r i e f l y d e s c r i b e d below, f o l l o w e d  by my suggested Columbia.  r e v i s i o n o f Upper P a l e o z o i c assemblages i n southern  British  57  Eastern  Assemblage  The from  Eastern  southern  Crystalline lain  by  a  British  belt.  gabbro,  from  mudstones  intermediate  which  on  in  and to  the  Equivalent Group  and  erates  of  a  the  in  rocks  mafic  volcanics,  clasts  chert been  and made  are  are  the  Bonaparte Nelson  make  up  which  of  along  derived  up  Lower  with  metamorphosed  detritus,  volcanic  underlying  and  from  i t  the  same  older  clasts  suggest  that  Paleozoic  oceanic  crust.  that  of  Portions  the  Group and  17).  of  found  Ida 1976).  intra-  in  and  conglom-  the  Yukon.  Group  Therefore local  sedimentary The  terrane i t  Late  a r g i l l i t e ,  are  with  of  fault  Cameron,  terrane.  this  or  Mount  Lardeau  rocks  source  part  the  Columbia  the  to  chert,  boulders.  to  deposits,  (Fig.  and  are  metamorphosed  likely  acid  map-area,  of  dia-  range  Mountain  suggests  schist  argillaceous  is  Lake  over-  chert,  and  Slide  mainly  Monger  granitic  section  prior  (Okulitch  are  Omineca  depositional  portions  map-area  the  portion  map-areas  British  mafic of  and  of  minor  metamorphosed  in  stretches  miogeoclinal  northern  Group,  volcanic  water  in  the  with  with  assemblage  Milford  the  lies  sandstone of  flanks  limestone  and  in  of  a l l  age,  lower  phyllite  present  some  and  minor  region  Vernon  the  of  from  provided  in  basalt in  in  sedimentary  clasts  derived  composed  this  probably  conglomerate  clasts  terrane  were  Lardeau  the  Similar  older  deep  Formation  Formation  Eastern  the  in  Fennel  Groups  However,  assemblage  Columbia  included  with  to  the  mainly  elastics  shallow  Bay  in  and  The  Permian  along  mostly  conglomerates,  older  the  lower,  rock,  to  Yukon  section,  British  Kaslo  origin. of  consists  metamorphosed  Clasts  basinal  or  map-area,  Eagle  carbonate,  the  rocks.  Strata  and  to  coarse  southernmost  Milford  Columbia  ultramafic  Devonian  McBride  Mississippian  volcanic  volcanic  Mississippian. in  It  dominantly  base,  contact  assemblage,  may  may be  are an plutons  and abundant have  UPPER PALEOZOIC EUGEOCLiNAL ASSEMBLAGES Eastern South central British Columbia Cache Creek-Bridge River Stikine Chilli wack E>S§|  Sicker-Skolai Fault Thrust fault  F i g . 17. Upper P a l e o z o i c e u g e o c l i n a l assemblages i n B r i t i s h a c c o r d i n g t o Monger, 1977.  Columbia  59  r e p r e s e n t e d by the E a g l e Bay quartzite  Formation,  (metachert?), greenstone,  which i n c l u d e s p h y l l i t e ,  and l i m e s t o n e , and i s i n t r u d e d by  t o i d rocks y i e l d i n g z i r c o n ages o f 372 m.y. o t h e r s , 1975).  phyllitic grani-  (Late Devonian; O k u l i t c h and  B e s i d e s t h i s example, p r e - M i s s i s s i p p i a n e u g e o c l i n a l r o c k s  have not been p o s i t i v e l y i d e n t i f i e d i n the Intermontane b e l t o r Omineca Crystalline  belt.  Monger and o t h e r s  (1972) concluded t h a t the source t e r r a n e f o r the  E a s t e r n assemblage e l a s t i c s l a y t o the west o f the Omineca C r y s t a l l i n e  belt.  The Late Devonian t o Middle M i s s i s s i p p i a n o r o g e n i c event which produced  this  deformed, l o c a l l y metamorphosed and i n t r u d e d t e r r a n e and the e l a s t i c s d e r i v e d from i t has been r e f e r r e d t o as the Caribooan Orogeny 1970,  p. 415).  (Douglas  and o t h e r s ,  I t i s r o u g h l y synchronous w i t h the A n t l e r Orogeny o f Nevada  (Roberts and o t h e r s , 1958; which i n v o l v e d eastward  1975;  Speed, 1977),  t h r u s t i n g o f deformed o c e a n i c o r m a r g i n a l b a s i n r o c k s  onto the o l d m i o g e o c l i n e . Late P a l e o z o i c produced  B u r c h f i e l and D a v i s , 1972,  Continued  u p l i f t o f the A n t l e r b e l t d u r i n g the  c l a s t i c sequences, such as the H a v a l l a h  Formation  (Stewart and o t h e r s , 1977), which resemble the e l a s t i c s i n the lower E a s t e r n assemblage. In the Yukon and n o r t h e r n B r i t i s h Columbia, b a s a l t and u l t r a m a f i c rocks o f the upper p o r t i o n o f the E a s t e r n assemblage form an a l l o c h t h o n t h r u s t eastward  over m i o g e o c l i n a l s t r a t a , i n i t i a l l y  K l u i t and o t h e r s , 1976).  Elsewhere  v o l c a n i c s are demonstrably lower sedimentary  (Tempelman-  T h i s a l l o c h t h o n has been i n t e r p r e t e d as P a l e o z o i c  o c e a n i c c r u s t by Monger and o t h e r s Monger (1977).  i n the L a t e T r i a s s i c  (1972), Wheeler and G a b r i e l s e (1972),  and  i n n o r t h e r n and s o u t h e r n B r i t i s h Columbia, the i n d e p o s i t i o n a l c o n t a c t and i n t e r f i n g e r w i t h the  s t r a t a , which are a l s o i n t r u d e d by gabbro s i l l s  interpreted  60  as f e e d e r s t o t h e o v e r l y i n g v o l c a n i c s .  The t e c t o n i c s i g n i f i c a n c e o f t h e upper  p a r t o f t h e E a s t e r n assemblage i s t h e r e f o r e s t i l l  Cache Creek-Bridge  not c l e a r .  R i v e r Assemblage  The Cache Creek-Bridge  R i v e r assemblage i s a w e l l d e f i n e d b e l t o f  o c e a n i c rocks extending from n o r t h e r n Washington t o a t l e a s t t h e southern Yukon.  T h i s assemblage i n c l u d e s t h e type a r e a o f t h e Cache Creek Group and  perhaps t h e lower d i v i s i o n o f t h e P a v i l i o n Group i n A s h c r o f t map-area west o f Kamloops, t h e B r i d g e R i v e r o r Ferguson the Hozameen Group i n Hope map-area. chert, a r g i l l i t e ,  Group i n Pemberton map-area, and  Typical l i t h o l o g i e s are r a d i o l a r i a n  carbonate, mafic v o l c a n i c s , and u l t r a m a f i c r o c k .  c a n i c s a r e mainly b a s a l t i c flows which a r e l o c a l l y p i l l o w e d .  Vol-  Limestones,  which a r e common o n l y i n t h e Cache Creek Group, a r e massive and form pods up t o tens o f k i l o m e t r e s l o n g , a p p a r e n t l y d e p o s i t e d i n shallow water on v o l c a n i c substrates. No o l d e r r o c k s a r e known t o o c c u r s t r a t i g r a p h i c a l l y beneath t h e Cache Creek-Bridge  R i v e r assemblage.  The sediments and v o l c a n i c s comprise t h e  upper l e v e l s o f Late P a l e o z o i c o c e a n i c c r u s t , whose deeper l e v e l s a r e exposed i n a number o f s e r p e n t i n i z e d u l t r a m a f i c b o d i e s .  F u s u l i n i d s and o t h e r  fos-  s i l s a r e common i n t h e l i m e s t o n e s , and range from E a r l y M i s s i s s i p p i a n t o Late Permian i n n o r t h e r n B r i t i s h Columbia, and from P e n n s y l v a n i a n the type a r e a o f the Cache Creek Group.  t o Permian i n  R a d i o l a r i a from c h e r t s a t one  l o c a l i t y i n t h e l a t t e r a r e a , however, a r e o f p r o b a b l e L a t e T r i a s s i c o r p o s s i b l e E a r l y J u r a s s i c age ( T r a v e r s , 1978).  Middle T r i a s s i c  o c c u r i n s m a l l carbonate pods i n t h e B r i d g e R i v e r Group. has  so f a r proven u n f o s s i l i f e r o u s .  f u s u l i n i d s have Tethyan  The Hozameen Group  The Permian and perhaps  faunal a f f i n i t i e s ,  conodonts  Pennsylvanian  and a r e u n l i k e c o e v a l faunas i n  61  other  Upper  American  stratigraphy  bodies  chert  and  of  a r g i l l i t e .  discontinuous,  the  difference  and  the  Lake  the  (J.  schists  and  northern  British  Columbia,  of  assemblage  blue  British part  Pinchi  Lake  the  or  from  the  the  North  locally  211  218  to  these  ages m.y.  surrounded  lenticular  on  Due  to  bodies  pods  almost  are  recognized in  the  1975b);  1977);  by  volcanic  are  Monger,  (Paterson,  Pod-  originally  developed  terrane;  K-Ar  are  and  melanges  1976).  from  of  complex.  discontinuity.  carbonate  tectonic  (Atlin  rocks  this  boundaries  are  are  certainly  enhanced  province  commun., range  were  massive  amphiboles  of  oral  has  Possible  Columbia  ultramafic  units  between  cherts,  this  and  these  deformation  faulted.  Grette,  near  of  bedded  central  F.  volcanics,  competence  Metamorphic  in  Creek  in  sheared  in  in  structure  Some  but  surrounding  locally. Group  and  carbonate,  and  always  assemblages  craton.  The like  Paleozoic  and  white  (Paterson  Cache near  south mica and  only  Pinchi  of  in  Creek  Cache  blue-  Harakal,  1974). The and  Cache  others  oceanic  (1972)  If  the  North  the  assemblage  at  stratigraphic to  blueschists  the  least  (200  suggest  subduction  in  the  Paleozoic  part  of  by  this  the  age  and  the  are  sediments in  age  Triassic cooling  complex  Triassic.  rocks  (Tipper,  restricts Middle  older  Late  tectonic  Late  Jurassic  Lower  uplift  i n t e r p r e t e d by  scraped  by  or  been  material  and  m.y.)  has  as  Triassic  evidence Early  assemblage  (1976)  continent  with  River  Anderson  during  overlain  Jurassic  terrane  so,  American  locally  Early  and  lithosphere  Mesozoic.  is  Creek-Bridge  and  early  (Monger, of  this  and/or  was  a l l  1977).  by  and in  the  the  of  but  i t  plutons  of  Structural in  to  contacts  faults,  deformation  terrane  early  accreted  intruded  1975b)  downgoing  external  nearly  Monger, of  The  off  Monger  the  and Atlin  Pinchi  Late  Lake  Triassic.  62  T h i s u p l i f t i s p r o b a b l y a l s o e v i d e n c e d by o p h i o l i t i c and c h e r t d e t r i t u s i n K a r n i a n t o N o r i a n r o c k s near P i n c h i Lake (Paterson, 1977), and c h e r t d e t r i t u s i n K a r n i a n r o c k s near Kamloops, as r e p o r t e d i n the f o l l o w i n g c h a p t e r .  The  l a t t e r a l s o c o n t a i n d e t r i t a l b l u e amphiboles f o r which the Cache Creek Group i s the o n l y known nearby s o u r c e .  T h i s Middle t o L a t e T r i a s s i c  deformation,  low grade metamorphism, and u p l i f t i s known as the T a h l t a n i a n Orogeny and o t h e r s , 1970, Creek-Bridge  p. 431;  Read and O k u l i t c h , 1977).  R i v e r assemblage may,  T r i a s s i c and i n t o the J u r a s s i c s u b d u c t i o n which produced  A c c r e t i o n o f the Cache  however, have c o n t i n u e d through the L a t e  (Anderson,  1976)  during eastward-directed  m a f i c t o i n t e r m e d i a t e v o l c a n i c s o f the Upper T r i -  a s s i c N i c o l a Group, and s i m i l a r Lower J u r a s s i c r o c k s . s t r a t a d e p o s i t e d on the Cache Creek-Bridge o r younger i n age  (Douglas  The  first  R i v e r assemblage are  widespread Cretaceous  (Monger, 1977).  Southern B r i t i s h Columbia Assemblage and Suggested R e v i s i o n The Southern  B r i t i s h Columbia assemblage i s perhaps the l e a s t known, as  these rocks have been s t u d i e d i n d e t a i l i n o n l y a few p l a c e s .  The  grouping  o f Upper P a l e o z o i c r o c k s i n t h i s assemblage i s l a r g e l y g e o g r a p h i c , and Monger (1977) suggests  t h a t more than one  In f a c t , he d i s t i n g u i s h e s two  t e c t o n o - s t r a t i g r a p h i c assemblage i s p r e s e n t .  sequences w i t h d i f f e r e n t l i t h o l o g i e s w i t h i n  the assemblage, but I b e l i e v e t h a t t h r e e are p r e s e n t .  One  o f these sequences  can be r e f e r r e d t o the E a s t e r n assemblage, but f o r the o t h e r two new  assemblage names:  the Old Tom  and Harper Ranch assemblages.  I propose The  loca-  t i o n s o f these assemblages are shown i n F i g . 18. The O l d Tom Formations  assemblage i n c l u d e s the Old Tom,  Shoemaker, and  Independence  i n P r i n c e t o n and K e t t l e R i v e r map-areas, and t h e i r p o s s i b l e  63  REVISED UPPER PALEOZOIC EUGEOCLINAL ASSEMBLAGES  F i g . 18. Revised Upper P a l e o z o i c e u g e o c l i n a l assemblages i n southern B r i t i s h Columbia and n o r t h e r n Washington. Sources o f d a t a i n text.  64  metamorphosed  equivalent,  the  area  belong  this  may  also  volcanic bedded  be  rocks  in  are  a r g i l l i t e ,  the  includes  are  the  Group  of  i t  once  sequences  arc  terrane  of  assemblage, Covada  rocks L i t t l e ,  in  and Group  (Rinehart  I  Mount  and  Devonian  I  refer  to  as  Columbia  with  are  metamorphosed  sequence  of  1976;  Pardee,  a r g i l l i t e ,  breccia,  age  (Read  and  Ranch  and  and  I  infer  to  to  Fox  Group the  with  the  1918)  Eastern  and  be  It  Washington.  A l -  assemblage, These  parts  several  composition, of  rock  Group,  adjacent  an  from  the  that  quartzite minor  are  the  Mis-  and  Ranch  along of  Okulitch,  they  to  Harper  descriptions 1977;  units  northern  assemblage,  others,  siltstone,  limestone,  and  distinct  reveal  1977).  C h i l l i -  separate  Anarchist  Published and  these  age.  map-areas  the  to  they  bioclastic  intermediate  them  Permian  Ranch  River  of  l i t h -  assemblage.  northwestern  elastics  are  Okulitch,  probably  a  the  from  Carboniferous  assemblage.  Washington.  1972,  Fossils  map-  1977),  suggests  Ranch  Formation,  belong  Monger  the  Harper  rocks  to  as  lithologically  they  a  Harper  and  similar  Group  Harper  Kettle  and  above,  Vernon  Okulitch,  Chilliwack  associated  the  are  and  study.  in  in  the  described  the  Roberts  1967;  and  as  Mississippian  Muessig,  conglomerate  clasts  in  metamorphosed  These  detailed  Early  limestones,  1960;  wacke,  more  Group  (Read  assemblage,  although  and  northern Fox,  River  or  and  believe  composition  limestone.  British  grouped  groups  of  andesitic  Group  Late  Nelson  These  less  continuous  marine  A r g i l l i t e  The  age,  volcanics  the  assemblage.  following  in  shallow  southeast:  Chapperon  established  probably  Washington.  the  i t  Ranch  (1977)  (1977)  The  minor  subdivision  include  Group.  Creek-Bridge  southwestern  Monger  sion  and  with  island  or  Silurian  Harper  Monger  was  late  second  though  the  Cache  Carboniferous  The  along  basaltic  included within  limestone  wack  of  chert,  ologies may  flows  with  Kobau  a  these 1973;  variably  (metachert?),  basaltic  or  with  gray-  andesitic  65  volcanics.  The c l a s t s i n the conglomerates a r e mainly c h e r t ,  sandstone, m a f i c v o l c a n i c s , and l i m e s t o n e .  The l i t h i c  argillite,  s i m i l a r i t y of this  sequence t o the lower sedimentary p o r t i o n o f the E a s t e r n assemblage i s e v i d e n t , and i n c o n t r a s t w i t h the v o l c a n i c l a s t i c n a t u r e o f the Harper Ranch assemblage.  F o s s i l s i n n o r t h e r n Washington a r e m o s t l y Permian i n age, b u t  i n B r i t i s h Columbia range from L a t e M i s s i s s i p p i a n t o Permian.  The A n a r c h i s t  Group i n n o r t h e r n Washington i s d i s c o n f o r m a b l y o v e r l a i n by the Palmer Mount a i n Greenstone, c o n s i s t i n g o f metamorphosed b a s a l t i c f l o w s , p y r o c l a s t i c s , and i n t r u s i v e r o c k s o f Permian and/or T r i a s s i c age.  T h i s u n i t i s perhaps  e q u i v a l e n t t o the upper v o l c a n i c p o r t i o n o f the E a s t e r n assemblage i n s o u t h e a s t e r n B r i t i s h Columbia. The Harper Ranch assemblage i s unique w i t h i n Monger's Southern B r i t i s h Columbia assemblage i n b e i n g a c l a s t i c sequence d e r i v e d from an a c t i v e arc,  d e s p i t e the i n f e r e n c e by O k u l i t c h and P e a t f i e l d  Group r e p r e s e n t s an i s l a n d a r c sequence. not  island  (1977) t h a t the A n a r c h i s t  The Harper Ranch assemblage  does  appear t o extend southward i n t o the southernmost p a r t o f the p r o v i n c e ,  where the O l d Tom assemblage i s i n c l o s e p r o x i m i t y t o the A n a r c h i s t  Group.  P o s s i b l y such r o c k s a r e p r e s e n t i n the western p a r t o f the A n a r c h i s t which has n o t been w e l l s t u d i e d .  Group,  The b u l k o f the A n a r c h i s t Group i s a p p a r e n t l y  p a r t o f the E a s t e r n assemblage, however. The C h i l l i w a c k Group, which crops out i n the western f o o t h i l l s o f the n o r t h e r n Cascade Mountains, i s s t r i k i n g l y s i m i l a r t o the Harper Ranch in  i t s l i t h o l o g i e s and s t r a t i g r a p h i c s u c c e s s i o n  1977a).  (Monger, 1966; Danner,  Group 1972,  I t c o n s i s t s o f f i n e - g r a i n e d c l a s t i c r o c k s , v o l c a n i c sandstone, l i m e -  stone, and l o c a l l y abundant v o l c a n i c rocks o f v a r i e d c o m p o s i t i o n .  The  sequence c o n t a i n s rocks b o t h o l d e r and younger than those o f the Harper Ranch  66  Group.. of ing  Devonian and Lower P e n n s y l v a n i a n  l i m e s t o n e s are s e p a r a t e d by hundreds  metres o f u n f o s s i l i f e r o u s f i n e e l a s t i c s and v o l c a n i c sandstones t u r b i d i t e s ) which c o u l d i n c l u d e r o c k s o f M i s s i s s i p p i a n age.  Pennsylvanian  (includ-  The  Lower  l i m e s t o n e , c o n t a i n i n g a f u s u l i n i d fauna s i m i l a r t o t h a t found  near Kamloops, i s d i s c o n f o r m a b l y o v e r l a i n by conglomerate,  graywacke, and  a r g i l l i t e which are i n t u r n o v e r l a i n by a t h i c k Lower t o Middle Permian limestone.  Permian rocks above t h i s l i m e s t o n e are a r g i l l i t e ,  v o l c a n i c sand-  stone, l i m e s t o n e l e n s e s , and v o l c a n i c flows and p y r o c l a s t i c r o c k s o f b a s a l t i c to  d a c i t i c composition.  Permian c l a s t i c r o c k s have not been r e c o g n i z e d i n  the Harper Ranch Group, but may  be p r e s e n t .  TECTONIC SIGNIFICANCE OF THE HARPER RANCH ASSEMBLAGE  The Harper Ranch assemblage r e p r e s e n t s p a r t o f an i s l a n d a r c t e r r a n e o f Late P a l e o z o i c age.  The v o l c a n i c c e n t e r s from which these e l a s t i c s were  d e r i v e d do not seem t o be p r e s e n t l y exposed, b u t they may e x t e n s i v e Upper T r i a s s i c s t r a t a t o the west.  be covered  by  V o l c a n i c flows i n the sequence  seem t o be minor i n e x t e n t , and some areas where flows have been mapped in  f a c t b e l o n g t o the Upper T r i a s s i c N i c o l a Group.  Coeval r o c k s t o the west  are the o c e a n i c sediments and v o l c a n i c s o f the Cache Creek-Bridge b l a g e , and the O l d Tom  assemblage.  R i v e r assem-  To the e a s t are the v o l c a n i c and  rocks o f the E a s t e r n assemblage, the l a t t e r d e r i v e d l a r g e l y from an and deformed p r e - M i s s i s s i p p i a n o c e a n i c t e r r a n e .  may  clastic uplifted  C o n t a c t s between these assem-  b l a g e s are u s u a l l y e i t h e r covered by Upper T r i a s s i c and younger s t r a t a , o r o b l i t e r a t e d by Mesozoic  and T e r t i a r y p l u t o n s , but i n s o u t h e r n Bonaparte Lake  map-area p o s s i b l e Harper Ranch Group i s f a u l t e d a g a i n s t the Fennel  Formation  67  and  the  Eagle  Bay  Possible exposed  Eberlein,  and  others, Irwin  others,  clastic  Jones  Middle  and  and  volcanic general they  in  far  later  The exposed, a  and  of  Late a  events  and  submerged Group  is  which  the  in  also  northern  a  between  volcanic  Klamath  in  arc  Commonly,  and  carbonates  are  of  elastics  mafic  have arc  to  of  terrane  covered by  Ranch  show to  no  the  which  elastics  or  continental older  lower  been  of The  that  disrupted  by  rocks.  an  the  directly  a  portion.  suggests  accumulated  of  from  composition.  has  of  separ-  assemblage  areas  younger  evidence  deposited  but  varied  these  Group  been  exposed,  a  intermediate  history  Harper  and  its  Ross,  also  disconformity  in  and  and  stratigraphy  Mountains.  limestone  volcani-  (Monger  elastics  thick  widely  setting,  Pennsylvanian a  and  these and  a  by  (Irwin,  (D'Allura  faunas  similarities  (Vallier  California  volcanic  fusulinid  Churkin  Oregon  Nevada  of  1977;  and  contrast  not  Stevens,  eastern  Sierra  suggests  discontinuously  missing,  the  island  of  1971).  are  sequence  may  and  abundance  eastern  strata  are  Correlations  Permian  partially  the  Group  the  once-continuous  in  source,  on  Paleozoic  elastics  Ranch  as  pyroclastics in  1975).  Striking  limestone  which  older  Chilliwack  the  on  Harper  Cowan,  Tipper,  1975a;  central  northern  dominated  basement  sediment  an  above  (Monger,  and  the  and  terrane  Mountains  1972).  Lower  arc  Klamath  primarily  south  sequence  portions  tectonic  and  Pennsylvanian to  island  non-Tethyan  others,  (Campbell  include  sequences,  their  as  areas  1977),  the  east  Cordillera  eastern  based  in  similarity  are  These  the  are  Upper  flows  the  Schweickert  least  rocks  in  others,  and  Permian  Permian  on  south  Mississippian  Lower  The  this  material  at  as  of  areas  exist,  ates  correlatives  1977).  similarity  1971;  the  1977),  1977;  separated  the  to  farther  and  1977;  Formation  is  older  terrane  Eastern on  basement.  nowhere  assemblage.  oceanic The  metaplutonic  base  rocks  acting  crust, of  or  the  yielding  68  P r o t e r o z o i c and S i l u r i a n r a d i o m e t r i c ages  (Mattinson, 1972) o c c u r as t e c t o n i c  s l i c e s i n t h r u s t f a u l t s c u t t i n g the C h i l l i w a c k s t r a t a , and i n t h e metamorphic core zone o f t h e Cascades t o t h e e a s t . C h i l l i w a c k Group may have accumulated o l d e r magmatic a r c r o c k s .  These o c c u r r e n c e s suggest t h a t t h e on a basement o f c o n t i n e n t a l c r u s t o r  In t h e Klamath Mountains, t h e Devonian t o Permian  arc sequence o v e r l i e s an O r d o v i c i a n o p h i o l i t e sheet and a complex assemblage of O r d o v i c i a n t o Lower Devonian sediments,  some o f which a r e a r c - d e r i v e d  elastics. The Cache Creek-Bridge  R i v e r assemblage c o n t a i n s r o c k s which formed  i n an o c e a n i c environment c o e v a l w i t h L a t e P a l e o z o i c a r c a c t i v i t y .  Tectonic  a c c r e t i o n o f t h i s m a t e r i a l t o t h e a r c p r o b a b l y began d u r i n g e a s t w a r d - d i r e c t e d s u b d u c t i o n which produced  the a r c t e r r a n e .  However, r o c k s as young as L a t e  T r i a s s i c may be p r e s e n t i n the o c e a n i c assemblage, s u g g e s t i n g t h a t a c c r e t i o n c o n t i n u e d i n t o the Mesozoic. The T r a f t o n Sequence  (Danner, 1966, 1977a) i n t h e Cascade f o o t h i l l s and  the San Juan I s l a n d s west o f t h e C h i l l i w a c k Group i s l i t h o l o g i c a l l y t o the Cache Creek-Bridge  R i v e r assemblage.  similar  The C h i l l i w a c k Group and T r a f t o n  Sequence p r o b a b l y r e p r e s e n t the same p a i r e d t e c t o n o - s t r a t i g r a p h i c u n i t s as the Cache Creek Group and Harper Ranch Group near Kamloops (Danner 1977a and b; F i g . 1 8 ) . The T r a f t o n Sequence, however, i s a s s o c i a t e d w i t h a v a r i e t y o f Mesozoic  r o c k s u n i t s o f o c e a n i c c h a r a c t e r i n a s t r u c t u r a l l y complex r e g i o n .  U l t r a m a f i c r o c k s , l a y e r e d gabbro and a m p h i b o l i t e which a r e i n t r u d e d by d i o r i t e dated a t 170 ± 10 m.y. may comprise lite  a Middle o r L a t e J u r a s s i c  (Brown, 1977)„. - ' R a d i o l a r i a n " c h e r t s of. J u r a s s i c , t o Cretaceous  ophio-  age a r e  abundant; i n t h e s u r r o u n d i n g u n i t s , and t h e T r a f t o n Jsequerice i t s e l f p r o b a b l y  \  i n c l u d e s l a r g e areas o f T r i a s s i c c h e r t (Danner, 1977a, and o r a l commun., 1978;  69  Whetten and o t h e r s , 1978).  Cretaceous p l a n k t o n i c f o r a m i n i f e r a have been  found i n t u f f s a s s o c i a t e d w i t h p i l l o w b a s a l t o t h e r s , 1978).  (Danner, 1966;  S i m i l a r p o s t - T r i a s s i c rocks may  i n the Cache Creek-Bridge  Whetten  be p r e s e n t but  and  unrecognized  R i v e r assemblage, o r the T r a f t o n Sequence  may  have undergone a l o n g e r p e r i o d o f a c c r e t i o n than the o t h e r o c e a n i c t e r r a n e s in B r i t i s h  Columbia.  An o c e a n i c assemblage o f c h e r t , a r g i l l i t e , p i l l o w b a s a l t , u l t r a m a f i c r o c k s , and l i m e s t o n e s w i t h Tethyan  Permian faunas i s exposed s p o r a d i c a l l y  f a r t h e r south i n the C o r d i l l e r a , l y i n g west o f the Late P a l e o z o i c a r c t e r r a n e . T h i s complex l i e s e a s t o f and i s o l d e r than the a c c r e t e d J u r a s s i c t o Eocene rocks o f the F r a n c i s c a n Complex, and i s t h e r e f o r e s i m i l a r i n t e c t o n i c p o s i t i o n t o the Cache Creek-Bridge  R i v e r assemblage.  and n o r t h e a s t e r n Oregon ( V a l l i e r and o t h e r s , 1977; Brooks and V a l l i e r ,  1978); the western  and o t h e r s , 1977); and the western and o t h e r s , 1977;  Such rocks o c c u r i n c e n t r a l D i c k i n s o n and Thayer,  Klamath Mountains  f o o t h i l l s o f the S i e r r a Nevada  Davis and o t h e r s , 1978).  However, T r i a s s i c and  rocks are common i n the complex i n some a r e a s , and may than the P a l e o z o i c r o c k s extending through  ( I r w i n , 1977;  Irwin  (Schweickert Jurassic  even be more abundant  ( I r w i n , 1977), a g a i n s u g g e s t i n g t e c t o n i c  the T r i a s s i c and  1978;  accretion  Jurassic.  C l a s t i c sediments i n the Harper Ranch assemblage and E a s t e r n assemblage have v e r y d i f f e r e n t provenances.  Sediment d e r i v e d from the Caribooan  orogenic  t e r r a n e i s abundant i n the E a s t e r n assemblage, but absent i n the Harper Ranch assemblage.  The v o l c a n i c a r c and t h i s o l d e r o c e a n i c t e r r a n e were p r o b a b l y  w i d e l y s e p a r a t e d d u r i n g the L a t e P a l e o z o i c .  Assuming t h a t no  t r a n s c u r r e n t motion has o c c u r r e d between these two  significant  assemblages, they were  p r o b a b l y s e p a r a t e d by a deep marine b a s i n o f unknown width.  From the  spatial  70  distribution  of  that  was  the  oceanic  arc rocks  on  the  is  correct,  arc  A  coeval  and  coarse  rane  of  the  event,  I ern  of  by  the  l i t h i c - r i c h the  the  the  that  the  the  derived  with  Sonoma  the  Antler largely  to  Early  Middle  to  Late  and  the  presence  of  thick,  widespread  age  may  indicate  that  subduction  Speed,  the the  1977;  from  this  basin,  belt,  a  basin  closed,  During was  Golconda  this  thrust allochthon.  eugeocline  in  south-  Subduction  of  Pennsylvanian,  and  perhaps  longer.  the  terrane,  limestones  age of  volcanism  subduction  may  have  of  the  arc  in  Lower ceased  continued terrane  arc  to for  until  from  Middle much the  resulted  in  ter-  oceanic  continued  Pennsylvanian  the  cherts,  arc  arc  uplift  Paleozoic  volcanic  and  time  back-  deformed  Sequence  events.  the  or  marginal  east.  course the  the  of  the  form  of  Late  orogenic  a  of  which  of  of  beneath  marginal  includes  evolution  rocks  at  unit  Havallah to  inference  separated  now  Paleozoic similar  this  is  Late  through  miogeocline  If  1972;  floor  belt  the  accrete  Davis,  and  of  Pennsylvanian,  Antler  that  to  the  belt  east,  Alternatively,  the  and  began  a  Permo-Triassic,  Orogeny,  absence  interval.  This  composed  the  for  and  oceanic  inferred  19).  terrane  from  and  During  followed  toward  the  have  zone,  probably  postulated  arc  I  Paleozoic.  (Fig.  Sequence.  east  age.  Antler  Mississippian  the  was  (Burchfiel the  Havallah  on  type  been  There,  collided as  has  elastics  Paleozoic  Columbia  crust  oceanic  rocks,  assemblage  Late  arc  type  subduction  River  the  the  representing  basin  terrane  of  California  1977).  basalts  believe  British  oceanic Late  crust  arc  east-dipping  during  paleogeography  and  over  arc  by  and  and  Creek-Bridge  east  referred to  eastward  the  an  basin  Nevada  Early arc  Cache of  others,  flanking  rocks and  of  above  oceanic  the  miogeocline  quartzites, and  then  floored  eugeocline Stewart  the  side  similar  Paleozoic  built  of  western  basin  Late  the The  Permian of  end  this of  the  erosion  ACCRETIONARY PRISM  CACHE CREEK-BRIDGE RIVER A S S E M B L A G E (IN P A R T )  VOLCANIC  BACK-ARC  ARC  BASIN  HARPER RANCH ASSEMBLAGE  CARIBOOAN  MIOGEOCLINE  OROGEN  EASTERN ASSEMBLAGE  F i g . 19. Sketch c r o s s - s e c t i o n showing i n f e r r e d paleogeographic and p a l e o t e c t o n i c elements o f southern B r i t i s h Columbia d u r i n g the Late M i s s i s s i p p i a n t o E a r l y Pennsylvanian. Not t o s c a l e .  72  of  the Middle t o Upper P e n n s y l v a n i a n  rocks.  C l o s u r e o f the back-arc b a s i n p r o b a b l y began i n the l a t e E a r l y Permian or  L a t e Permian.  C o l l i s i o n o f the a r c t e r r a n e w i t h the o l d e r r o c k s t o the  e a s t i n the E a r l y T r i a s s i c may  account  f o r the p r e - L a t e T r i a s s i c  deformation  and low grade metamorphism which a f f e c t the Harper Ranch Group and E a s t e r n assemblage south o f the l a t i t u d e o f Kamloops. The mechanism .of b a s i n c l o s u r e i s u n c e r t a i n . (1975) suggested  Davis  t h a t the L a t e P a l e o z o i c back-arc b a s i n i n Nevada c l o s e d by  s u b d u c t i o n o f the o c e a n i c basement eastward w h i l e the v o l c a n i c and sedimentary o v e r the c o n t i n e n t a l margin. of  B u r c h f i e l and  the b a s i n f i l l  fill  beneath the c o n t i n e n t a l margin,  o f the b a s i n was  t r a n s p o r t e d upward  I t h i n k i t u n l i k e l y t h a t such eastward  thrusting  c o u l d have o c c u r r e d except d u r i n g a c t u a l c o l l i s i o n between  the a r c and the c o n t i n e n t a l margin.  At t h i s time, sediments and v o l c a n i c s  a c c r e t e d t o the margin above the s u b d u c t i n g s l a b would have been caught the c o l l i s i o n a l v i s e and squeezed out over the margin, i n a manner to  analagous  the p r e s e n t Molucca Sea c o l l i s i o n zone ( S i l v e r and Moore, 1978).  t h i s p r o c e s s , s u b d u c t i o n continued on the west s i d e o f the a r c , u n t i l s i o n was  completed  i n the E a r l y  An a l t e r n a t i v e model was  in  During colli-  Triassic. p r e s e n t e d by Speed  (1977), which assumed t h a t  the b a s i n c l o s e d by s u b d u c t i o n o f the b a s i n f l o o r toward the west, beneath the v o l c a n i c a r c .  Sediments and v o l c a n i c s a c c r e t e d t o the e a s t e r n s i d e o f  the a r c d u r i n g t h i s s u b d u c t i o n p r o c e s s were t h r u s t over the c o n t i n e n t a l margin as i t reached the s u b d u c t i o n zone i n the E a r l y T r i a s s i c .  In B r i t i s h  Columbia,  t h i s model would r e q u i r e a r e v e r s a l i n s u b d u c t i o n p o l a r i t y d u r i n g the Permian, if  my p r e v i o u s assumptions are c o r r e c t . One  o f the drawbacks t o the concept o f a L a t e P a l e o z o i c m a r g i n a l b a s i n  73  i n southern B r i t i s h Columbia i s t h a t t h e r e are no rocks t o the e a s t o f a r c t e r r a n e t h a t seem r e p r e s e n t a t i v e o f the m a r g i n a l b a s i n i t s e l f . northern  the  In  B r i t i s h Columbia the upper p a r t o f the E a s t e r n assemblage may  an o v e r t h r u s t  sheet o f o c e a n i c  c r u s t , but  be  i n the southern p a r t o f the  pro-  v i n c e the upper m a f i c v o l c a n i c s o f t h i s assemblage appear t o conformably o v e r l i e the lower o r o g e n i c  elastics  (Monger, 1977;  Davis and  others,  1978).  One  c o u l d p o s t u l a t e w i t h e i t h e r o f these models t h a t most o f the b a s i n  was  subducted a l o n g w i t h  fill  i t s basement.  F u r t h e r data are needed t o t e s t these models.  Geochemical t r e n d s  of  the L a t e P a l e o z o i c v o l c a n i c rocks might be u s e f u l i n the f o l l o w i n g ways: 1) i n d e t e r m i n i n g  whether s u b d u c t i o n  west o r e a s t , and whether i t r e v e r s e d  beneath the a r c t e r r a n e was i n the Permian; 2) i n  toward  the  determining  whether the m a f i c v o l c a n i c s o f the E a s t e r n assemblage are r e l a t e d to format i o n of the b a c k - a r c b a s i n , or t o eastward s u b d u c t i o n margin i n the B u r c h f i e l and Davis model. l i t h o l o g i e s and  beneath the  continental  F u r t h e r d e t a i l e d s t u d i e s of  the  d e p o s i t i o n a l environments o f a l l the e u g e o c l i n a l assemblages  w i l l c e r t a i n l y h e l p c l a r i f y these t e c t o n i c i n t e r p r e t a t i o n s . The  p r e s e n t p o s i t i o n o f the C h i l l i w a c k Group and  T r a f t o n Sequence r e l a -  t i v e to the o t h e r Upper P a l e o z o i c sequences i s a t l e a s t i n p a r t due  to t r a n s -  current f a u l t i n g .  system  R i g h t - l a t e r a l s l i p on the Yalakom-Pasayten f a u l t  ( F i g . 18), which bounds the B r i d g e amount t o hundreds o f k i l o m e t r e s  R i v e r and Hozameen Groups on the e a s t ,  ( T i p p e r , 1977) , and moved the B r i d g e  Group to a p o s i t i o n west o f the Cache Creek Group. C h i l l i w a c k Group, and juxtaposed  The  River  T r a f t o n Sequence,  the metamorphic core zone o f the North Cascades were  west o f the Hozameen Group by r i g h t - l a t e r a l s l i p on the  R i v e r - S t r a i g h t C r e e k ! f a u l t system and  an a n c e s t r a l Ross Lake f a u l t .  may  Fraser Davis  74  and o t h e r s  (1978) proposed a mid-Cretaceous phase o f f a u l t i n g a l o n g the l a t -  t e r f a u l t zone which moved the Cascade and San Juan I s l a n d t e r r a n e s n o r t h westward from the a r e a o f s o u t h e a s t e r n Washington and n o r t h e a s t e r n Oregon now covered by the Columbia R i v e r B a s a l t s .  Subsequent Cretaceous movement  on the F r a s e r R i v e r - S t r a i g h t Creek f a u l t system i s a t l e a s t 75 km 1977), and may be as much as 200 km  (Tipper,  (Misch, i n Monger, 1977, F i g . 8 ) .  North o f Bonaparte Lake map-area, rocks s i m i l a r t o the Harper Ranch Group are n o t exposed e a s t o f the Cache C r e e k - B r i d g e R i v e r assemblage, which i s s e p a r a t e d from the E a s t e r n assemblage by f a u l t s and Mesozoic v o l c a n i c and plutonic rocks.  I t does n o t seem l i k e l y t h a t the Upper P a l e o z o i c i s l a n d a r c  t e r r a n e , i f p r e s e n t , would be c o m p l e t e l y obscured by younger d e p o s i t s and i n t r u s i o n s f o r such a g r e a t d i s t a n c e a l o n g the C o r d i l l e r a . zones  The major  fault  ( P i n c h i and T e s l i n f a u l t s ) which bound the Cache C r e e k - B r i d g e R i v e r  assemblage on the e a s t a r e s t e e p , p o s s i b l y t r a n s c u r r e n t f e a t u r e s ; major westward t e c t o n i c t r a n s p o r t o f the Omineca C r y s t a l l i n e b e l t  ( i n c l u d i n g the  E a s t e r n assemblage), which might have b u r i e d the a r c complex, has not been documented. In n o r t h - c e n t r a l B r i t i s h Columbia, s c a t t e r e d exposures o v e r a v e r y l a r g e r e g i o n b e l o n g t o t h e ' S t i k i n e assemblage, an Upper P a l e o z o i c i s l a n d a r c t e r r a n e which l i e s west o f the Cache C r e e k - B r i d g e R i v e r assemblage i n the western Intermontane b e l t .  I t i n c l u d e s Upper M i s s i s s i p p i a n and Lower Permian  b a s a l t i c , a n d e s i t i c , and l o c a l r h y o l i t i c flows and p y r o c l a s t i c s , a l o n g w i t h s h a l e and carbonate.  A d i s t i n c t i v e Lower Permian c a r b o n a t e u n i t i s wide-  spread, and some evidence suggests t h a t i t r e s t s unconformably on Upper M i s s i s s i p p i a n rocks.  F u s u l i n i d s from the carbonate form a non-Tethyan  fauna s i m i l a r t o Permian faunas from the a r c t e r r a n e i n the e a s t e r n Klamath  75  Mountains.  Enough s i m i l a r i t i e s e x i s t between the S t i k i n e assemblage and  the  Harper Ranch Group and i t s c o r r e l a t i v e s t o the south t o suggest t h a t the S t i k i n e assemblage i s the m i s s i n g n o r t h e r n c o n t i n u a t i o n o f t h i s Upper P a l e o z o i c arc terrane.  I f so, the p r e s e n t o c c u r r e n c e o f the S t i k i n e assemblage  west o f the Cache Creek-Bridge  R i v e r assemblage must be e x p l a i n e d .  (1977) suggests t h a t the o c e a n i c r o c k s were t h r u s t eastward  (obducted)  the broad a r c t e r r a n e , p r o b a b l y i n the E a r l y o r Middle J u r a s s i c . posed a l l o c h t h o n must be c o m p l e t e l y detached S t i k i n e assemblage.  The  Monger  The  over pro-  from i t s r o o t zone west o f the  g r e a t d i s t a n c e o f t h r u s t i n g i n v o l v e d (over 200  km),  and i n c o n s i s t e n c i e s w i t h s t r u c t u r a l d a t a from the o c e a n i c r o c k s are problems o f t h i s h y p o t h e s i s , as was  p o i n t e d out by Monger.  A l t e r n a t i v e l y , the S t i k i n e assemblage and Harper Ranch Group may  never  have been c o n t i n u o u s , h a v i n g formed on o p p o s i t e s i d e s o f the L a t e P a l e o z o i c ocean b a s i n .  Emplacement o f the S t i k i n e assemblage by a combination  of  b a s i n c l o s i n g and p o s s i b l e s t r i k e - s l i p motion d u r i n g the Late T r i a s s i c have been accompanied by eastward B r i t i s h Columbia and the Yukon  may  o b d u c t i o n o f ocean f l o o r i n n o r t h e r n  (Monger, 1977;  i m p l i e s t h a t most o f the Cache Creek-Bridge  Tempelman-Kluit, 1976).  R i v e r assemblage was  This  accreted to  North America by the L a t e T r i a s s i c , although i n southern B r i t i s h Columbia i t c o u l d have remained open t o the P a c i f i c u n t i l a t l e a s t Middle J u r a s s i c as suggested by Cole and Tennyson  (1977).  time  76  CHAPTER I I I .  NICOLA GROUP (MAP-UNITS 2 THROUGH 6)  INTRODUCTION  The N i c o l a Group i n t h e study a r e a c o n s i s t s o f a t l e a s t 3000 m o f marine mudstone, submarine p y r o c l a s t i c flows and v o l c a n i c l a s t i c minor v o l c a n i c f l o w s , l i t h i c sandstone b a s i n a l limestones.  and conglomerate,  sequence i n t o f i v e u n i t s , map-units 2 through  Ridge.  and r e d e p o s i t e d  Mudstone i s by f a r t h e most abundant l i t h o l o g y .  N e i t h e r the base n o r t o p o f t h e sequence i s exposed.  pocket).  turbidites,  I have d i v i d e d t h e  6, shown on P l a t e I ( i n  Each i s w e l l exposed i n p l a c e s a l o n g the south s l o p e o f P a u l U n i t s 3, 4, and 5 extend northwestward i n t o t h e southern Dome  Hills,  although U n i t 5 undergoes a profound  P a u l Creek v a l l e y .  change i n f a c i e s i n c r o s s i n g  Such r a p i d f a c i e s changes imply t h a t these u n i t s may  o n l y be r e c o g n i z a b l e l o c a l l y  ( F i g . 20).  PHYSICAL STRATIGRAPHY  Structural  Setting  The N i c o l a Group on P a u l Ridge i s deformed i n t o a p a i r o f northwestt r e n d i n g mappable f o l d s , t h e P a u l Ridge a n t i c l i n e on t h e west and P a u l Ridge s y n c l i n e to the east.  The a n t i c l i n e i s o v e r t u r n e d toward t h e west, and t h e  o v e r t u r n e d limb a l s o crops o u t i n t h e southern Dome H i l l s . cut  The f o l d s a r e  by s e v e r a l s t e e p f a u l t s which c o m p l i c a t e t h e map p a t t e r n .  The o l d e s t  T r i a s s i c r o c k s a r e f a u l t e d a g a i n s t t h e Harper Ranch Group t o the e a s t , and the t o p o f t h e s e c t i o n i s covered by a l l u v i u m i n t h e North Thompson R i v e r Valley.  WESTERN P A U L RIDGE COVERED  LITHOLOGIC  SYMBOLS  Thin-bedded  mudstone  Laminated mudstone and siltstone, thin-bedded mudstone, turbidite limestone tiltttone, rbidite  DOME  HILLS  thin-bedded  eandttone  tiltttone,  thin-beddsd  ne a n d c o n g l o m e r a t e  pyroclattic flows  EASTERN PAUL RIDGE MISSING  -. — ~ ~ .TI  3 VERTICAL  COVERED  Fig.  20.  Stratigraphic  relationships  FAULT  o f u n i t s w i t h i n the N i c o l a Group.  78  Description of Units  Unit 2 U n i t 2 i s t h e o l d e s t exposed T r i a s s i c u n i t .  The u n i t o c c u p i e s t h e  core o f t h e P a u l Ridge a n t i c l i n e , and i s f a u l t e d a g a i n s t M i s s i s s i p p i a n on the e a s t limb o f t h e P a u l Ridge s y n c l i n e .  rocks  In a d d i t i o n , t h e i n t e r n a l  s t r u c t u r e o f t h i s u n i t i s complex, w i t h common mesoscopic f o l d s , so o n l y a g e n e r a l e s t i m a t e o f s e v e r a l hundred meters can be g i v e n f o r t h e minimum thickness o f the unit. The  e a s t e r n p o r t i o n o f t h e u n i t c o n s i s t s mostly o f thin-bedded mud-  stone, w i t h a l e n s o f massive m a f i c v o l c a n i c r o c k , U n i t 2A. the igneous  rocks w i t h t h e e n c l o s i n g mudstone a r e c o n c e a l e d , b u t t h e mafic  rocks a r e amygdaloidal, The western  Contacts o f  i n d i c a t i n g t h a t they o r i g i n a t e d as an e x t r u s i v e flow.  p o r t i o n o f t h e u n i t a l s o c o n s i s t s predominantly  bedded mudstones, b u t i n t e r b e d d e d s p o r a d i c a l l y through  o f t h i n t o medium-  the s e c t i o n are i n t e r -  v a l s o f l a m i n a t e d mudstone and s i l t s t o n e and dark, f i n e - g r a i n e d t u r b i d i t e limestones.  These l i t h o l o g i e s become i n c r e a s i n g l y abundant h i g h e r i n t h e  s e c t i o n , and predominate i n t h e upper 50 t o 100 m.  In t h i s upper i n t e r v a l ,  f i n e - g r a i n e d p y r o c l a s t i c r o c k s appear i n t e r b e d d e d w i t h t h e s i l t s t o n e s and l i m e s t o n e s , h e r a l d i n g t h e p y r o c l a s t i c s e d i m e n t a t i o n o f U n i t 3.  The c o n t a c t  between these u n i t s i s g r a d a t i o n a l , and i s drawn where massive p y r o c l a s t i c rocks become predominant i n t h e s e c t i o n , mudstones become s u b o r d i n a t e , and t u r b i d i t e limestones disappear. The mafic v o l c a n i c s o f U n i t 2A a r e massive i n o u t c r o p . t o s e v e r a l m i l l i m e t e r s i n diameter Small phenocrysts  V e s i c l e s up  a r e f i l l e d by c a l c i t e and c h l o r i t e .  o f c l i n o p y r o x e n e and p l a g i o c l a s e make up about 5 t o 10%  o f the rock, and a r e s e t i n an a p h a n i t i c m a t r i x o f p l a g i o c l a s e m i c r o l i t e s  79  and a l t e r e d g l a s s w i t h a h y a l o p i l i t i c t e x t u r e .  Glass i s a l t e r e d to c h l o r i t e ,  sphene, and l e s s abundant q u a r t z , c a l c i t e , and a l b i t e .  Plagioclase i s  l a r g e l y a l t e r e d t o s e r i c i t e , and i t s c o m p o s i t i o n i s i n d e t e r m i n a b l e .  The  composition o f the v o l c a n i c s i s e i t h e r b a s a l t i c o r a n d e s i t i c .  Unit 3 T h i s u n i t crops out i n the core o f the P a u l Ridge s y n c l i n e , and i n the u p r i g h t and o v e r t u r n e d limbs o f the f a u l t e d P a u l Ridge a n t i c l i n e .  I t con-  s i s t s o f a n d e s i t i c p y r o c l a s t i c m a t e r i a l r e d e p o s i t e d by t u r b i d i t y c u r r e n t s and h i g h - c o n c e n t r a t i o n mass f l o w s , and i n t e r b e d d e d w i t h gray t o green mudstone.  Dense v o l c a n i c fragments and l e s s e r amounts o f p l a g i o c l a s e and  mafic  p h e n o c r y s t s make up the d e p o s i t s , which range i n g r a i n s i z e from f i n e t o very coarse sand  (ash), w i t h some s i l t s t o n e and r a r e pebble  conglomerate.  Weathered s u r f a c e s o f these rocks o f t e n have a d i s t i n c t i v e l i g h t r e d d i s h brown c o l o r . E a s t e r n and western  exposures  of the u n i t d i f f e r i n f a c i e s .  Outcrops  i n the e a s t e r n p o r t i o n o f t e n l a c k l a y e r i n g , and s t r u c t u r a l d a t a from area i s sparse.  Many o u t c r o p s c o n s i s t o f massive,  graded,  this  o r laminated  t u f f , w i t h n e i t h e r the top nor bottom o f the bed exposed, so beds s e v e r a l meters t o tens o f meters t h i c k must dominate the s e c t i o n . i n the western  p o r t i o n are much t h i n n e r ( u s u a l l y l e s s than one meter),  t u r b i d i t e sedimentary The  In c o n t r a s t , beds and  s t r u c t u r e s are p r e s e n t .  e s t i m a t e d t h i c k n e s s o f the western  f a c i e s i s about 400 m.  To  the  e a s t , the top o f the u n i t has been eroded away, and the base i s i n p a r t f a u l t e d , but the minimum t h i c k n e s s i s s u b s t a n t i a l l y g r e a t e r , perhaps 500 600  m.  to  80  Unit  This v i t r i c The  unit  tuff,  contact  thick with  pyroclastic to  unit  cludes the  on  the  unit. On  stone  grained the  Paul  coarse  Unit  is  thin-bedded  mudstone,  laminated  sandstones,  and  redeposited  unexposed 3  giving  interbedded Ridge  is  of  Ridge,  in  the  interbedded  of  intrusive the  Dome and  siltstones  the  volcaniclastics  way  within and  upper  are  In  is  525  This  occurs  in  about of  in  than  10  thickness  the  4  m of  ex-  middle  are  of  mostly  Thick,  mudstone  however,  the  the  estimate  limestones.  H i l l s ,  occur  less  with  m.  Unit  subordinate  Dome  and  550  rare  limestone.  The  m.  portions  with  of  limestones. to  mudstone,  conformable,  distance  turbidite  the  uncommon,  a  which  Hills  sandstones unit.  475  s i l l  and  minor  apparently  siltstones  lower  turbidite  portion  but  approximately  the  thickness  volcanic  middle  of  thickness The  with  volcanic 3  with Paul  of  Unit  rocks  mudstones  the  consists  4  coarse-  make  medium  upper  100  mud-  up to  m of  the  unit.  Unit This Dome  unit  Hills.  On  shows Paul  bedded mudstone. The  only  Peak, crop  out  coarse  on  the  thin-bedded assessed Mount  On  Ridge  of  l i t h i c  mudstones.  Stock,  the  the  of  slopes The  is  southwestern  rocks  on  are  of  the  peak, of  slope  of  between  Paul  Ridge  entirely  thin  to  coarse  elastics  structural order  almost  pebbly  thickness  the  change  and  coarse  sandstone,  erratic  but  facies  limestones  abundant  eastern  because  Paul  pronounced  Turbidite  occurrence  where  a  5  the  is  Dome  near  sandstone,  are  the and  unit  1,000  Hills,  cannot and  the  the  medium-  very  summit  rare. of  Peter  conglomerate  interbedded with  attitudes of  elastics  and  be  laminated  and  accurately  intrusion  of  the  m.  the  character  of  the  unit  is  81  very to  different.  homogeneous  pebbly other  chiefly bedded  with  mudstone,  turbidite of  valley,  but  the  pronounced  Ridge  these of  and  evidence  interpretation. Unit or  4.  The  stone  with  elastics Hills. mudstone coarse  the  the  northwest  tion trend  of to  the  and  differ of  by is  The  alluvium similar  1.5  the  a  the  that the  in  is  deep  on  rapid  in  a  both  is  Peak  drawn of  are  along  on  4,  in  to  This is  Ridge  across  last  above  become  Dome  conformably  the  identical  several  Paul  southeast  Unit  strike  which  includes  above  elastics  section  unit,  sequences  to  trend  nearly  the  of  is  a l l  proportion  mudstone of  consistent  of  volcanic  while  coarse with  alluvium-filled  in  of the  or  The  coarse Dome  thin-bedded proportion in  The  extrapolation Creek  mud-  in  the  southeast,  elastics.  Paul  sandstones  size  evident  the  overlie  mudstone  grain  5  plausible  lithologies.  particularly  Unit  gradationally  similar  northwest,  intervals is  the  more  thin-bedded  dominant  those  Hills, the  exposures  which  the  and  of  several  that  is  Ridge.  suggest  suggest  facies  Thompson  might  However,  change  water  Paul  sections  fragments,  inter-  North  northwest,  the  l i t h i c  breccia  of  to  between  to  those  probably  lithology km  from  subordinate  sandstone,  non-volcanic  therefore  covered  only  coarse-grained  limestone.  is  are  juxtaposed.  increases.  elastics  abundance  but  structurally  decreases  of  elastics  and  in  to  present,  been  the  elastics  portion  Hills,  limestones  Within  fine  thickness  difference  First,  Peter  is  exposed  l i t h i c - r i c h  on  unit  s t i l l  have  contact  turbidite  their  sandstones,  Dome  sequences  in  These  sandstone,  the  are  mudstones,  breccia. units  top  Paul  lines,  and  The  The  that  laminated  Triassic  chert,  deposit.  on  and  sandstone, Upper  River  Thin-bedded mudstones  of  of basal  but  to  proporthis  valley.  82  Unit 6 The h i g h e s t exposed u n i t i n the T r i a s s i c s u c c e s s i o n i s U n i t 6, which crops out a t the western  end o f P a u l Ridge,  j u s t n o r t h o f Kamloops.  The  u n i t c o n s i s t s o f a v a r i e t y o f c l a s t i c and v o l c a n i c r o c k s , and has a t h i c k ness o f about 800  t o 850 m, w i t h the top covered by the a l l u v i u m o f the  North Thompson R i v e r v a l l e y .  These r o c k s are i n t r u d e d by the P a u l Peak  Stock, and have undergone c o n t a c t metamorphism t o the  hornblende-hornfels  facies. The b a s a l 140 m o f the u n i t c o n s i s t s o f massive o r l a m i n a t e d ,  fine  to medium-grained a n d e s i t i c p y r o c l a s t i c r o c k s s i m i l a r t o those i n U n i t 3. These p y r o c l a s t i c s are a p p a r e n t l y conformable o f U n i t 5, although the c o n t a c t i s c o n c e a l e d . i n t e r v a l i s a coarse pebble conglomerate  upon the u n d e r l y i n g mudstones Near o r a t the top o f t h i s  w i t h subrounded p o r p h y r i t i c  v o l c a n i c c l a s t s , i r r e g u l a r mudstone r i p - u p s , and a few l i m e s t o n e T h i s conglomerate P a u l Peak.  pebbles.  forms the c r e s t o f the prominent s o u t h e a s t e r n spur o f  Above i t are about 225 m o f l a m i n a t e d mudstone, minor f i n e t o  medium-grained l i t h i c - v o l c a n i c sandstone e l a s t i c s i n U n i t 5.  and conglomerate,  s i m i l a r t o the  Very r a r e t u r b i d i t e l i m e s t o n e s a l s o o c c u r i n t h i s  section. These e l a s t i c s are o v e r l a i n by about 240 m o f dark green t o b l a c k , massive and p i l l o w e d m a f i c v o l c a n i c flows  (Unit 6B).  L a y e r i n g i s not  e v i d e n t w i t h i n the v o l c a n i c s , and no sediments are i n t e r l a y e r e d w i t h them. P i l l o w s were observed  i n o n l y a few o u t c r o p s , and are obscure,  visible  mainly as c l u s t e r s o f c a l c i t e - f i l l e d amygdules, sometimes surrounded an a p h a n i t i c , n o n - v e s i c u l a r s h e l l which shows f i s s i l i t y the p i l l o w  ( F i g . 21).  by  concentric with  The p i l l o w s are c l o s e l y - p a c k e d , w i t h some i n t e r p i l l o w  83  F i g . 21. P o o r l y d e f i n e d v e s i c u l a r p i l l o w s i n U n i t 6B. i s 24 mm i n diameter.  Coin  84  voids  f i l l e d by f i n e - g r a i n e d  v o l c a n i c ash, now n e a r l y non-vesicular  pillows.  l i m e s t o n e , b u t most a r e f i l l e d by f i n e - g r a i n e d  i n d i s t i n g u i s h a b l e i n c o l o r and t e x t u r e  Many o u t c r o p s which appear massive a r e p r o b a b l y  p i l l o w e d , w i t h t h e presence o f p i l l o w s r e v e a l e d p i l l o w limestone patches. and  from t h e  o n l y by s c a t t e r e d i n t e r -  The l i m e s t o n e p r o b a b l y formed by t h e p e r c o l a t i o n  e v e n t u a l accumulation o f p o s t - e r u p t i v e  i n t e r p i l l o w v o i d spaces, as d e s c r i b e d  carbonate sediment through t h e  by G a r r i s o n  (1972).  Where not  r e c r y s t a l l i z e d by contact-metamorphic e f f e c t s o f t h e P a u l Peak Stock, the limestone i s m i c r i t i c , contains  abundant conodonts, and shows no e f f e c t s  o f thermal a l t e r a t i o n due t o c o n t a c t w i t h h o t v o l c a n i c The  rocks.  l e a s t a l t e r e d v o l c a n i c rock samples c o n s i s t s o f about 40% randomly  o r i e n t e d p l a g i o c l a s e l a t h s surrounded by a l t e r e d g l a s s i n an i n t e r s e r t a l t o hyaloophitic texture.  The g l a s s i s r e p l a c e d by a f i n e - g r a i n e d aggregate o f  sphene, c h l o r i t e , and c a l c i t e , w i t h minor s t i l p n o m e l a n e . c r y s t s a r e p r e s e n t i n t h i s rock, b u t c l i n o p y r o x e n e  No m a f i c pheno-  (now l a r g e l y r e p l a c e d by  a c t i n o l i t e ) makes up about 20% o f samples from w i t h i n the c o n t a c t Where o r i g i n a l t e x t u r e s  aureole.  a r e d i s c e r n i b l e , t h e c l i n o p y r o x e n e o c c u r s as s m a l l  g r a n u l e s i n t e r s t i t i a l t o p l a g i o c l a s e , and l a r g e r c r y s t a l s molded around the p l a g i o c l a s e l a t h s . determinable.  P l a g i o c l a s e i s a l b i t i c where i t s c o m p o s i t i o n i s  The o r i g i n a l rock c o m p o s i t i o n was p r o b a b l y b a s a l t , based on  the p h e n o c r y s t mineralogy and t e x t u r e s . Overlying  t h e v o l c a n i c s a r e s e v e r a l hundred meters o f mudstone, minor  sandstone, and r a r e t u r b i d i t e l i m e s t o n e s .  The sediments d i r e c t l y  above  the v o l c a n i c s a r e mostly mudstone and thin-bedded s i l i c e o u s mudstone o r c h e r t w i t h abundant r a d i o l a r i a n s .  Attitudes within t h i s i n t e r v a l are  e r r a t i c , and l o c a l r e v e r s a l s i n f a c i n g d i r e c t i o n were observed,  85  so  the  thickness  thickness  was  may  have  probably  been  on  the  increased order  of  by  150  folding, to  200  but  the  original  m.  BIOSTRATIGRAPHY  The  only  conodonts donts acid  identifiable  found  were  in  and  insoluble  residue  Dr.  B.  B.  E.  report, the  turbidite  extracted  solution,  are  collections  conodont  Metapolygnathus  Triassic,  probably  limestone  from  navicula  and  in  6  yielded  dominated  by  Neogondolella  are  then  The ing  modes  two of  interpillow the  water  contrasting sedimentation  voids  column  is and  a  of  probably then  in  is  a  are  were  found  Cono-  1.74  fraction  Canada.  2  and  4  N  of  acetic the  identified His  in  ages  Two  by  complete  Appendix  these  in  the  indicates  bar,  of  I,  and  different yielded  platform a  Late  interpillow  blade,  and  Neogondolella  collections  A l l  the  samples)  samples  of  conodonts  Karnian.  Karnian  (four  form  units.  of  found  form-species,  assemblages  early  the  were  This  platform  conodont of  of  single  these  The  Group  heavy  conodonts  Survey  Units  only  the  possibly  study  The  the  Group  limestones.  samples  assemblage  diverse  and  the  limestone  abstracted,  in  for  sp.  Nicola  interpillow  polygnathiformis. age  the  V.  limestones  Triassic—Karnian, in  is  conodont  containing  from  separating  Geological  of  and  liquids.  Plate  Karnian  Unit  the  by  following  types  Turbidite  conodonts,  the  shown  abundant  form  heavy  of  the  different  limestones.  dissolving  using  recovered  limestones  concentrated  from which  Two  by  Cameron  conodonts  fossils  units  of  are the  plat-  navicula Late Nicola  age.  assemblages enclosing  can  be  related  limestones.  Lime  mostly  pelagic  sediment  which  percolated  through  the  of  pile  to mud  the  f i l l i n g  settled  pillows  d i f f e r -  on  through the  86  PLATE V. CONODONTS EXTRACTED FROM LIMESTONES IN THE NICOLA GROUP, PAUL RIDGE AND DOME HILLS  Fig.  1.  Neospathodus s p . c f . N. newpassensis (Mosher). L a t e r a l view, X 215; G.S.C. L o c . 93450.  Fig.  2.  Ozarkodina t o r t i l i s (Tatge). G.S.C. Loc. 93450.  Fig.  3, 4.  Cypridodella s p . c f . C. muelleri (Tatge). 3, l a t e r a l view, X 330; G.S.C. L o c . 93450. 4, l a t e r a l view, X 160; G.S.C. L o c . 93451.  Fig.  5.  Enantiognathus ziegleri (Diebel). G.S.C. L o c . 93451.  Fig.  6, 7.  Neogondolella navicula navicula (Huckriede). 6, o b l i q u e - l a t e r a l view o f elongate form, X 90; 7, o b l i q u e view o f o r a l s u r f a c e o f more e l l i p t i c a l form, X 95. Both G.S.C. L o c . 93450.  Fig.  8, 9.  Neogondolella s p . ( p o s s i b l e n. sp. s i m i l a r t o N. regale (Mosher) ) . 8, o b l i q u e view o f o r a l s u r f a c e , X 70. 9, o b l i q u e view o f o r a l s u r f a c e o f b e t t e r p r e s e r v e d specimen, X 130. Both completely r e c r y s t a l l i z e d , G.S.C. L o c . 93451.  Fig.  10, 11, 12.  Note:  L a t e r a l view, X 180;  L a t e r a l view, X 300;  Metapolygnathus polygnathiformls (Budurov and S t e f a n o v ) . 10, o b l i q u e view o f o r a l s u r f a c e , X 95. G.S.C. L o c . 93452. 11, o b l i q u e view o f o r a l s u r f a c e , X 95, G.S.C. L o c . 93453. 12, o b l i q u e view o f a b o r a l s u r f a c e , X 125. G.S.C. Loc. 93453.  L o c a l i t i e s shown i n P l a t e I . A l l f i g u r e s a r e SEM photomicrographs, and m a g n i f i c a t i o n s a r e approximate.  88  seafloor.  The e n c l o s e d conodonts o r i g i n a t e d somewhere w i t h i n t h e water  column d i r e c t l y above t h e i r p l a c e o f d e p o s i t i o n .  In c o n t r a s t , conodonts  w i t h i n the t u r b i d i t e l i m e s t o n e s were t r a n s p o r t e d l a t e r a l l y and downslope a f t e r accumulating  i n a s h a l l o w e r environment.  M. polygnathiformis  isa  l a r g e , r o b u s t form, and i t may be t h a t s e l e c t i v e removal o r d e s t r u c t i o n o f s m a l l e r , more f r a g i l e conodont elements b e f o r e o r d u r i n g t u r b i d i t y c u r r e n t t r a n s p o r t i s r e s p o n s i b l e f o r t h e absence o f o t h e r form-taxa i n these d e p o s i t s .  However, t h e absence o f M. polygnathiformis  from the i n t e r -  p i l l o w l i m e s t o n e s i n d i c a t e s t h a t two d i s t i n c t faunas a r e r e p r e s e n t e d . These d i f f e r i n g conodont assemblages appear t o r e p r e s e n t faunas o f two  d i f f e r e n t environments and water depths, which now both o c c u r i n d e p o s i t s  o f r e l a t i v e l y deep water o r i g i n .  S i m i l a r d a t a accumulating  s e v e r a l years has shown t h a t many conodont faunas a r e indeed  over t h e p a s t facies-  c o n t r o l l e d , and c a l l s i n q u e s t i o n p r e v i o u s c o n c l u s i o n s t h a t t h e conodontb e a r i n g animal was p e l a g i c and f a c i e s - i n d e p e n d e n t Barnes and Fahraeus,  (Seddon and Sweet, 1971;  1975; Barnes and Nowlan, 1975).  SEDIMENTOLOGY AND SEDIMENTARY PETROLOGY  Mudstone and S i l t s t o n e  Mudstone i s t h e predominant l i t h o l o g y i n a l l the T r i a s s i c u n i t s U n i t 3.  except  Two broad types o f mudstone can be d i f f e r e n t i a t e d i n t h e f i e l d :  t h i n t o medium-bedded mudstone, and l a m i n a t e d mudstone and s i l t s t o n e .  T h i n t o Medium-Bedded Mudstone T h i n t o medium-bedded mudstone comprises o f U n i t 5 on P a u l Ridge,  t h i c k s e c t i o n s o f U n i t 2, most  and o c c u r s s p o r a d i c a l l y i n t h e o t h e r u n i t s .  These  89  mudstones have v e r y w e l l developed bedding p l a n e p a r t i n g s , w i t h bed ness u s u a l l y r a n g i n g from 5 t o 13 22). and  The  cm,  but  some are as t h i c k as 20  thick-  cm  (Fig.  mudstone i s dark gray, weathering to l i g h t e r gray or brown shades,  i s extremely i n d u r a t e d  and  locally siliceous.  Rare c h e r t s  a l s o occur.  Some beds are i n t e r n a l l y s t r u c t u r e l e s s , but more t y p i c a l l y a d i f f u s e c o l o r banding i s p r e s e n t .  These muds have been i n t e n s e l y b i o t u r b a t e d  burrowing d e t r i t u s - f e e d i n g organisms. cross-sections t h i c k and  The  burrows are most e v i d e n t  o f beds, where they appear as f l a t t e n e d l e n s e s ,  5 t o 30 mm  long,  the s u r r o u n d i n g rock angle t o b e d d i n g .  f i l l e d w i t h mud  ( F i g . 23).  1 to 2  They are e l o n g a t e p a r a l l e l or a t a  as simple tubes which wander through the mud,  small  w i t h o u t complex, h i g h l y  B a c k - f i l l s t r u c t u r e s are p r e s e n t i n some burrows. . The  compaction o f the mud.  The  burrows observed do not resemble the  deep water t r a c e f o s s i l s o f the Zoophycus  and  Nereites  f a c i e s of  during  complex Seilacher  the n e a r l y h o r i z o n t a l o r i e n t a t i o n o f almost a l l the  burrows i s t y p i c a l o f deep water d e p o s i t s . rows c h a r a c t e r i z e a b y s s a l the Deep Sea  mm  the burrows appear  burrows were o r i g i n a l l y s u b c i r c u l a r tubes, but have been f l a t t e n e d  (1964, 1967), but  in  which i s d a r k e r i n c o l o r than  When observed on bedding s u r f a c e s ,  organized patterns.  by  muds r e c o v e r e d from the P a c i f i c Ocean f l o o r  D r i l l i n g Project  Thin-sections  S i m i l a r simple h o r i z o n t a l bur-  (Ekdale,  1974,  p.  by  51-52).  o f mudstone r e v e a l t h a t i t c o n s i s t s o f a c r y p t o c r y s t a l -  l i n e p a s t e w i t h low b i r e f r i n g e n c e , i n which s i l t - s i z e d g r a i n s o f p l a g i o clase, quartz,  and  some v o l c a n i c fragments are s c a t t e r e d .  bands r e s u l t from somewhat h i g h e r p r o p o r t i o n s o f dark o r g a n i c organic  matter than the  of s i l t  s u r r o u n d i n g sediment.  matter i n the burrows causes t h e i r dark c o l o r .  and  Lighter-colored lower  proportions  Concentrations of  90  F i g . 23. P o l i s h e d s l a b o f thin-bedded mudstone, showing numerous f l a t t e n e d burrows p a r a l l e l t o bedding.  91  Chert i s d i f f i c u l t the f i e l d , ness.  to differentiate  from mudstone and s i l i c e o u s mudstone i n  s i n c e i t i s a l s o dark gray i n c o l o r and has a s i m i l a r bed t h i c k -  One t h i n - s e c t i o n showed the c h e r t t o be composed o f c r y p t o c r y s t a l -  l i n e q u a r t z w i t h numerous r e c r y s t a l l i z e d r a d i o l a r i a , each f i l l e d w i t h c o a r s e r - g r a i n e d q u a r t z o r chalcedony.  The c h e r t i s h i g h l y f r a c t u r e d , and  the d i s t r i b u t i o n o f dark o r g a n i c matter seems t o be r e l a t e d t o the f r a c t u r e s , o c c u r r i n g mostly a l o n g them o r c o n c e n t r a t e d i n p a r t i c u l a r  fracture-bounded  p o r t i o n s o f the c h e r t . The t h i n bedding,  fine grain s i z e , extensive h o r i z o n t a l bioturbation,  and presence o f r a d i o l a r i a n c h e r t suggests t h a t these r o c k s were d e p o s i t e d i n r e l a t i v e l y deep water, mainly by p e l a g i c s e t t l i n g o f f i n e muds and at  silt,  r a t e s slow enough t o p e r m i t thorough reworking by the deep water benthos.  Coarse c l a s t i c i n t e r b e d s a r e r a r e i n s e c t i o n s o f thin-bedded mudstone, supporting this  interpretation.  Laminated  Mudstone  Laminated mudstone and r a r e s i l t s t o n e d i f f e r from thin-bedded mudstone i n c o n t e n t o f c o a r s e m a t e r i a l , presence o f p l a n a r l a m i n a t i o n , and l e s s intense bioturbation. d i t e sandstones  T h i s type o f mudstone i s a s s o c i a t e d w i t h t h i c k  and l i m e s t o n e s .  turbi-  P a r t i n g p l a n e s a r e more w i d e l y spaced than  i n the thin-bedded f a c i e s , and a r e g e n e r a l l y from 8 o r 10 cm t o over a meter apart.  Coarse laminae i n the mudstones are composed o f s i l t  or f i n e  and i n the s i l t s t o n e s , c o a r s e laminae are o f f i n e t o medium sand. ness o f the laminae ranges than 5 mm  from 1 mm  sand,  The t h i c k -  t o s e v e r a l c e n t i m e t e r s , w i t h most l e s s  thick.  The l a m i n a t i o n i s g e n e r a l l y p l a n a r , b u t c o n t o r t e d laminae a r e f r e q u e n t l y observed i n mudstones beneath  t u r b i d i t e l i m e s t o n e beds, o f t e n forming s m a l l  92  recumbent f o l d s which do n o t a f f e c t o v e r l y i n g and u n d e r l y i n g beds. f e a t u r e s may have been produced of  These  by t r a c t i o n d u r i n g t h e flow and d e p o s i t i o n  the o v e r l y i n g t u r b i d i t e bed, o r by slumping  preceding t u r b i d i t e deposition.  Laminated s i l t s t o n e s appear i n t h i n - s e c t i o n t o be made up p r i m a r i l y o f s i l t to sand-sized chert or f e l s i t i c  v o l c a n i c fragments,  w i t h l e s s abundant  q u a r t z , p l a g i o c l a s e , mudstone c l a s t s , and f i n e r - g r a i n e d m a t r i x . are t o o f i n e - g r a i n e d f o r c h e r t and f e l s i t i c  These rocks  fragments t o be d i f f e r e n t i a t e d ,  b u t the dark gray t o b l a c k c o l o r o f some o f the s i l t s t o n e l a y e r s t h a t much o f the d e t r i t u s i s c h e r t .  Some green, p r o b a b l y  suggests  volcanic-rich  s i l t s t o n e s also occur. The  l a m i n a t e d mudstones a r e a s s o c i a t e d w i t h t u r b i d i t e s and o t h e r  d e n s i t y flow d e p o s i t s .  They p r o b a b l y i n c l u d e h e m i p e l a g i c and low d e n s i t y  t u r b i d i t y c u r r e n t d e p o s i t s , r e f l e c t i n g h i g h e r r a t e s o f d e p o s i t i o n than t h e thin-bedded The  f a c i e s , and consequently  show l e s s i n t e n s e b i o t u r b a t i o n .  l a m i n a t e d s i l t s t o n e s form t h e upper p a r t o f some t h i c k  beds, b u t a l s o r a r e l y o c c u r i n d e p e n d e n t l y , stone and t u r b i d i t e l i m e s t o n e s . reworking  of turbidite s i l t s  turbidite  i n t e r b e d d e d w i t h l a m i n a t e d mud-  These s i l t s t o n e s may have formed by t h e  and f i n e sands by bottom c u r r e n t s , p r o d u c i n g  w e l l developed p l a n a r l a m i n a t i o n s and good s o r t i n g .  Redeposited B a s i n a l Limestone  Redeposited  m i c r i t e , lime s i l t s t o n e , and f i n e - g r a i n e d c a l c - a r e n i t e  occur i n U n i t s 2, 4, and 6, b u t make up o n l y a v e r y s m a l l p r o p o r t i o n o f the s e c t i o n . siltstones.  They a r e u s u a l l y i n t e r b e d d e d w i t h l a m i n a t e d mudstones and Most o f these beds a r e dark gray m i c r i t e and l i m e  a few t o 30 cm t h i c k , w i t h r a r e beds up t o about 1 metre t h i c k .  siltstone, Basal  c o n t a c t s o f the beds a r e commonly sharp, w i t h s c o u r i n g sometimes e v i d e n t  93  beneath c o a r s e r beds, which c o n t a i n dark mudclasts diameter.  a few m i l l i m e t r e s i n  I n t e r n a l l y t h e beds a r e u s u a l l y s t r u c t u r e l e s s , and g r a d i n g i s  not v i s i b l e , perhaps due t o t h e f i n e g r a i n s i z e and t h e e f f e c t s o f r e c r y s tallization.  P l a n a r and c o n v o l u t e l a m i n a t i o n s can be observed  beds, although some o f these a r e composite  i n some  beds, c o n s i s t i n g o f i n t e r l a m i n -  a t e d m i c r i t e and l i m e s i l t s t o n e , w i t h i n d i v i d u a l laminae  from a few m i l l i -  metres t o 1 cm t h i c k . In t h i n s e c t i o n , o r i g i n a l c l a s t i c t e x t u r e s a r e obscure  due t o t h e  g e n e r a l f i n e g r a i n s i z e and t h e e f f e c t s o f r e c r y s t a l l i z a t i o n .  Several  samples c o n s i s t mostly o f i n t e r l o c k i n g a n h e d r a l c a l c i t e g r a i n s , 1 t o 4 p m i n diameter  ( m i c r i t e ) , and 4 t o 10 p m i n diameter  spar was o r i g i n a l l y  (microspar).  The m i c r o -  f i n e r - g r a i n e d lime mud which has been r e c r y s t a l l i z e d .  T h i s p r o c e s s has p r o g r e s s e d even f a r t h e r i n o t h e r samples, which now c o n s i s t of i n t e r l o c k i n g f i n e t o c o a r s e - g r a i n e d a n h e d r a l c a l c i t e , c o m p l e t e l y a t i n g the o r i g i n a l texture. i n a t e d through  obliter-  Dark, o r g a n i c - r i c h noncarbonate mud i s dissem-  t h e m i c r i t e , p r o b a b l y c o m p r i s i n g a few p e r c e n t o f t h e r o c k s ,  and g i v i n g them t h e i r dark c o l o r .  S c a t t e r e d noncarbonate g r a i n s i n c l u d e  p l a g i o c l a s e , q u a r t z , v o l c a n i c r o c k fragments,  pumice, and mudstone c l a s t s .  Heavy m i n e r a l c o n c e n t r a t e s from t h e i n s o l u b l e r e s i d u e s c o n t a i n e p i d o t e , and t h e b l u e amphibole c r o s s i t e . r e p l a c e d by h e m a t i t e ,  hornblende,  A u t h i g e n i c p y r i t e cubes,  i n part  a r e common.  S k e l e t a l d e b r i s i n these l i m e s t o n e s i s e x c e e d i n g l y r a r e , l i m i t e d t o a few t e n t a t i v e l y i d e n t i f i e d echinoderm p l a t e s i n b a d l y rocks.  recrystallized  The o n l y common o r g a n i c remains v i s i b l e i n t h i n - s e c t i o n a r e s m a l l  s p h e r i c a l b o d i e s , mostly  10 t o 20 p m i n diameter, made up o f s e v e r a l i n t e r -  l o c k i n g c a l c i t e g r a i n s (sometimes w i t h a r a d i a l arrangement),  and a dark  94  a r g i l l a c e o u s outer coating.  These may  be the remains o f c a l c a r e o u s a l g a e .  P l a t f o r m conodonts were e x t r a c t e d from 6 of 24 samples, and may in  be  abundant  c e r t a i n samples. The o c c u r r e n c e o f i s o l a t e d beds o f f i n e - g r a i n e d carbonate  i n deep  water mudstones, t o g e t h e r w i t h the i n t e r n a l s t r u c t u r e s o f the l i m e s t o n e s , suggest d e p o s i t i o n by t u r b i d i t y c u r r e n t s .  The source o f the sediment  was  p r o b a b l y i n p a r t the s h a l l o w waters s u r r o u n d i n g v o l c a n i c i s l a n d s , but  the  presence  o f d e t r i t u s from a metamorphic source  (epidote, crossite)  suggests p r o x i m i t y t o a landmass composed o f o l d e r r o c k s . the t u r b i d i t e l i m e s t o n e s were undoubtedly p r o b a b l y s e p a r a t e d accumulation  Conodonts w i t h i n  t r a n s p o r t e d , but l i t t l e  o f carbonate  also  time  sediment i n s h a l l o w water  and  r e d e p o s i t i o n i n deeper water, so b i o s t r a t i g r a p h i c ages based on the conodonts are v a l i d .  The c o n s i s t e n t o c c u r r e n c e o f the same conodont taxon i n  these samples makes i t v e r y u n l i k e l y t h a t they were reworked from o l d e r rocks.  Submarine P y r o c l a s t i c Flows and  Turbidites  A n d e s i t i c p y r o c l a s t i c d e b r i s c h a r a c t e r i z e s the b u l k o f U n i t 3, and b a s a l p o r t i o n o f U n i t 6. p y r o c l a s t i c sandstones tuff).  the  These rocks are p r i m a r i l y r e d e p o s i t e d t u f f s o r  and s i l t s t o n e s , w i t h minor pebble  conglomerate  (lapilli-  They are i n t e r l a y e r e d w i t h deep water mudstones and t u r b i d i t e s ,  and  were d e p o s i t e d by t u r b i d i t y c u r r e n t s and h i g h - c o n c e n t r a t i o n submarine f l o w s . V i s u a l l y e s t i m a t e d modes o f the p y r o c l a s t i c rocks from U n i t 3 are shown i n T a b l e I I I .  Samples from U n i t 6 have undergone severe  l i z a t i o n d u r i n g c o n t a c t metamorphism, l a r g e l y o b l i t e r a t i n g the textures.  recrystaloriginal  They appear t o be s i m i l a r t o the e l a s t i c s o f U n i t 3 i n c o m p o s i t i o n .  TABLE  III.  rock  ESTIMATED  MODES  OF  MK-128  MK-127  Sample  Volcanic  VISUALLY  REDEPOSITED  TUFFS  FROM U N I T  MK-158  MK-198  3  MK-201  MK-217  fragments 60%  40%  50-60%  55-65%  50%  40%  Plagioclase  20-25  40  20-25  20-25  30  40  Clinopyroxene  10-15  15  7-10  5-7  10  15  1-2  5-7  2  1  —  Tr  Tr  Tr  (excluding  phenocrysts)  Hornblende  2  Orthopyroxene?  1  4  Biotite  Tr  —  —  —  Tf  Mudstone  —  Tr  3-5  Tr  —  Matrix  and  cement  Magnetite Echinoderm  Average sand  —  =  plates  grain or  ash  size  (in  Absent  TR = T r a c e VF = Very f i n e - g r a i n e d "F = F i n e - g r a i n e d  C  '  — —  10  *  5-10  5-10  5-10  —  1  —  Tr  Tr  Tr  Tr  —  Tr  —  —  —  range)  1  to  M  VC  M  to  C  C  to  = Medium-grained  C  =  VC  =  Coarse-grained Very  coarse-grained  VC  M  .  to  C  VF  *  Matrix  5  to  F  F  and cement  differentiated volcanic  rock  fragments.  to  not  from  M  96  The most abundant c o n s t i t u e n t s i n these r o c k s are dense, n o n v e s i c u l a r v o l c a n i c rock fragments  ( F i g . 24 and  i n g the volume o f p h e n o c r y s t s . (1970), and counted species.  25), which range from 40 t o 65%,  exclud-  I have f o l l o w e d the s u g g e s t i o n o f D i c k i n s o n  a l l sand-sized phenocrysts  T h i s a l l o w s o b j e c t i v e comparison  as t h e i r r e s p e c t i v e m i n e r a l  between samples o f  different  g r a i n s i z e , s i n c e the p r o p o r t i o n o f f r e e g r a i n s t o e n c l o s e d p h e n o c r y s t s i n c r e a s e s as g r a i n s i z e d i m i n i s h e s .  I t a l s o p r o v i d e s a measure o f c o n s i s -  tency, s i n c e as a l t e r a t i o n obscures o r i g i n a l v o l c a n i c l a s t i c t e x t u r e s , the d i s t i n c t i o n between v o l c a n i c rock fragments phenocrysts  and  f r e e m i n e r a l g r a i n s , becomes d i f f i c u l t ,  (as i n sample MK-128).  i f not impossible  Free m i n e r a l and p h e n o c r y s t phases i n c l u d e p l a g i o -  c l a s e , c l i n o p y r o x e n e , hornblende, tite.  and m a t r i x , and hence between  orthopyroxene,  C l i n o p y r o x e n e and hornblende  and r a r e b i o t i t e and magne-  t o g e t h e r t o t a l 15 t o 20% o f the r o c k s ,  and t h e i r abundance i n hand specimens d i s t i n g u i s h e s the p y r o c l a s t i c d e p o s i t s o f these u n i t s from a l l o t h e r v o l c a n i c l a s t i c r o c k s i n the study a r e a . r i p - u p c l a s t s and  Mud  echinoderm p l a t e s are p r e s e n t i n t r a c e amounts i n s e v e r a l  samples. O s c i l l a t o r y z o n i n g i s common i n most o f the p h e n o c r y s t phases, b e s t developed  i n plagioclase.  c i t e and a l b i t e ,  A l t e r a t i o n o f p l a g i o c l a s e , commonly t o  i s v a r i a b l e , and o r i g i n a l compositions  s e v e r a l samples, r a n g i n g from Ang2 t o A n Q 6  c l i n o p y r o x e n e may tered.  The No  both be  (Table I V ) .  zoned, and are t y p i c a l l y  c l i n o p y r o x e n e has  f r e s h orthopyroxene  but i s  a 2V o f about  seri-  are p r e s e r v e d i n Hornblende  little  and  a l t e r e d or unal-  55°, and i s p r o b a b l y d i o p s i d e .  i s p r e s e n t i n any o f the samples examined.  T e n t a t i v e i d e n t i f i c a t i o n o f t h e s e c o m p l e t e l y a l t e r e d g r a i n s i s based the i d e n t i t y and c o n f i g u r a t i o n o f the a l t e r a t i o n p r o d u c t s , and the  upon  form  Fig.  24. Photomicrograph o f t h i n - s e c t i o n o f t u f f from U n i t 3 Abundant p o r p h y r i t i c v o l c a n i c rock fragments (V), w i t h p h e n o c r y s t s o f p l a g i o c l a s e (PI) , hornblende (H), and c l i n o p y r o x e n e (C). Plane l i g h t , X 40.  Fig.  25. Photomicrograph o f t h i n - s e c t i o n o f t u f f from U n i t 3 P o r p h y r i t i c v o l c a n i c rock fragments (V) and f r e e m i n e r a l grains: zoned p l a g i o c l a s e ( P I ) , c l i n o p y r o x e n e (C), and hornblende (H). Plane l i g h t , X 40.  TABLE IV.  AVERAGE COMPOSITIONS OF ZONED PLAGIOCLASE FROM UNIT 3  Sample  A n o r t h i t e Content (Wt  MK-127 MK-128  An An o, 6  8 2  An  6 1  , An  MK-198  An _5  MK-201  ^0-5  MK-161  0  ^62'  A n  66  7 1  99  of  the e u h e d r a l pseudomorphs.  r e p l a c e d by c h l o r i t e and The  The  f o u r o r e i g h t - s i d e d g r a i n s are  completely  f i n e l y g r a n u l a r sphene, and perhaps some  leucoxene.  sphene i s commonly a l i g n e d a l o n g two  s e t s o f p l a n e s w i t h i n the g r a i n s ,  which i n t e r s e c t a t angles r a n g i n g from about 60 t o 90°, p r o b a b l y  replacing  l a m e l l a e o f i l m e n i t e o r t i t a n o m a g n e t i t e e x s o l v e d from the o r i g i n a l o r t h o pyroxene.  I t i s h i g h l y improbable  t h a t these are a l t e r e d hornblendes  c l i n o p y r o x e n e s , s i n c e the l a t t e r are t y p i c a l l y l i t t l e t i o n from l i t t l e  a l t e r e d , and no  a l t e r e d g r a i n s t o pseudomorphs o c c u r s .  or transi-  Orthopyroxene  pseudomorphs are a l s o p r e s e n t as i n c l u s i o n s i n u n a l t e r e d c l i n o p y r o x e n e . In  the c o a r s e r - g r a i n e d r o c k s , n e a r l y a l l o f the v o l c a n i c fragments are  porphyritic. fragment.  Phenocrysts may  be s p a r s e , o r make up more than 60% o f the  E i t h e r p l a g i o c l a s e , c l i n o p y r o x e n e , o r hornblende  may  abundant p h e n o c r y s t , b u t i n fragments w i t h h i g h p r o p o r t i o n s o f to  be the most phenocrysts  groundmass, p l a g i o c l a s e i s more abundant than m a f i c phases, and t h i s i s  r e f l e c t e d by the o v e r a l l abundance o f the m i n e r a l s i n the t u f f s . mass may  be f e l s i t i c  In the m i c r o l i t i c g r a i n s , o r i g i n a l  g l a s s i s r e p l a c e d by a c r y p t o c r y s t a l l i n e aggregate A few  ground-  or m i c r o l i t i c , with p l a g i o c l a s e m i c r o l i t e s i n p i l o t a x -  i t i c , h y a l o p i l i t i c , or t r a c h y t i c t e x t u r e s .  feldspar.  The  o f c h l o r i t e and  alkali  lathwork g r a i n s o c c u r , w i t h c r u d e l y a l i g n e d , crowded p l a g i o -  c l a s e p h e n o c r y s t s w i t h i n t e r s t i t i a l g r a n u l e s o f c l i n o p y r o x e n e , and w i t h g r a n u l e s o f sphene r e p l a c i n g i n t e r s t i t i a l The t u f f s are g r a i n supported, D e t r i t a l c r y s t a l s range from a n g u l a r  chlorite  glass.  and p o o r l y t o moderately (broken o r euhedral)  well sorted.  t o subrounded.  V o l c a n i c fragments are u s u a l l y i r r e g u l a r t o somewhat p o l y g o n a l i n shape, range from very a n g u l a r t o subangular.  Roundness i s d i f f i c u l t t o  because b o u n d a r i e s between v o l c a n i c g r a i n s are o f t e n s u t u r e d and  and  determine indistinct  100  due  t o t h e e f f e c t s o f compaction, p r e s s u r e  metamorphic r e c r y s t a l l i z a t i o n .  T h i s a l s o l e a d s t o c o n f u s i o n between v o l -  c a n i c fragments and i n t e r s t i t i a l m a t e r i a l . and o r g a n i c - r i c h matrix  evident.  s o l u t i o n , d e v i t r i f i c a t i o n , and  In none o f t h e rocks  In the c o a r s e - g r a i n e d  i s a clay  t u f f s , where t e x -  t u r e s a r e c l e a r e s t , framework g r a i n s a r e c l o s e l y packed, and i n t e r s t i t i a l m a t e r i a l does n o t exceed 10% o f the r o c k .  Much o f t h i s m a t e r i a l i s o f  d i a g e n e t i c o r metamorphic o r i g i n , and c o n s i s t s o f an i n d i s t i n c t paste  ( e p i m a t r i x ) , b u t some monomineralic patches o f c h l o r i t e ,  p r e h n i t e and p u m p e l l y i t e larly  a l s o occur,  granular calcite,  and c o u l d be c a l l e d cement.  Particu-  i n some o f t h e ' f i n e r - g r a i n e d t u f f s , d i s t i n g u i s h i n g v o l c a n i c framework  g r a i n s from i n t e r s t i t i a l m a t r i x  i s almost i m p o s s i b l e .  This i s a r e s u l t o f  i n c r e a s e d r e c r y s t a l l i z a t i o n , b u t whether t h i s i n t u r n r e s u l t s from proportions  o f o r i g i n a l unstable  matrix m a t e r i a l i s u n c e r t a i n .  c l a y - s i z e d d e t r i t a l m a t e r i a l was o r i g i n a l l y p r e s e n t ,  increased  I f s i l t to  i t was mostly  very  f i n e v o l c a n i c m a t e r i a l , r a t h e r than a c l a y - r i c h mud. The  r a r e pebble conglomerate ( F i g . 26) i s v e r y p o o r l y s o r t e d ,  subrounded t o rounded v o l c a n i c c l a s t s up t o s e v e r a l c e n t i m e t e r s and v a r i a b l e amounts o f mudstone r i p - u p c l a s t s . framework supported, w i t h of volcanic s i l t  10 t o 20% m a t r i x  with  i n diameter,  The conglomerates a r e  o f dark mud and v a r i a b l e amounts  and f i n e t o medium-grained v o l c a n i c sand.  The mineralogy, and t e x t u r e o f t h e v o l c a n i c fragments i d e n t i f y them as a n d e s i t e  or dacite.  Except f o r some v a r i a t i o n i n g r a i n s i z e and r e l a t i v e  proportions  of mineral  s p e c i e s and v o l c a n i c fragments, the p y r o c l a s t i c rocks  are c o m p o s i t i o n a l l y  and t e x t u r a l l y homogeneous throughout the s e v e r a l hundred  metres o f U n i t 3, and a p p a r e n t l y  i n the b a s a l p o r t i o n o f U n i t 6 as w e l l .  They may have been d e r i v e d from a s i n g l e v o l c a n i c c e n t e r which produced  101  F i g . 26. P o l i s h e d s l a b o f conglomerate from U n i t 3, c o n s i s t i n g e n t i r e l y o f pebbles o f p o r p h y r i t i c d a c i t e o r andesite. X 1.33.  102  andesitic  or  dacitic  Subaerial vesicular and  as  that  this  by  volcano.  The  contact  vesicular that  the  spines, a  a  of  or  flows  setting  Fiske  (1963)  abundant  consists amounts  of of  from  metres posed  grading  were  in  the  and  medium was  tephra  of  thick  to  of  as  might  the  grading  flow.  and  be  might  The  of  a  of  Source unlikely  i t  was  subaerial  eruptions  (1963).  He  caused  non-  inferred  homogeneous  water.  This  in  too  in  density  Unit  lower beds  3,  domes,  also  seems  while  most subtle  are  flows at  thick. a  of  few  be  6  cases the  pyroare  probably lesser  mudstone. are  least The  outcrops to  Thick  Unit  deep  which  interlayered with  pyroclastic  In  flows,  turbidites  bioturbated  flows  present  flows.  portion are  its  mass  pyroclastic  metres  tephra. but  is  that  from  debris  sometimes  typical  be  under  of  These  tens  field,  Fiske  high  individual  outcrops,  or  i t  of  3.  facies  laminated,  think  II,  homogeneous,  disintegration  portion.  of  Similar  by  subaqueous  deposits.  I  quantities  Chapter  explosive  pyroclastic  currents  in  originating  water.  variation. large  source,  submarine  Unit  the  coarse-grained in  flows  extruded  eastern  and  discussion  subaerial  explosive were  the  the  some  evident  part  a  of  a  produce  Therefore  described  they  portions  to  although  were  western  types  only  from  abundant  turbidity  (see  Detritus).  deposited  dominate  ash  probably  by  referred  ungraded, of  the  which  size  thick, of  for  as  homogeneous  the  with  tuffs  flows  both  Usually but  lava  were  compositional  volcanoes  pyroclastic  produced  has  flows  of  l i t t l e  dacitic  reworked  eruptions  lava  water  more  was  was  to  Volcanic  series  source  The  clastic  the  hot  showing  nonvesicular  subaqueous ash  likely  as  of  tephra  deposited  by  andesitic  well  Deposition  lavas  several  flows normal rocks  observed  exposed,  in  are  com-  size appear a  small  103  The mentary are  pyroclastic  structures,  usually  stone.  medium  The  sand  tion,  sometimes  sions  B  coarse  and  C  overlain  rather  the  the  coarse  layer the  mudstone  turbidite before  The ship  the  change the  of  of  turbulence  due  the  Both  The volcano movement  to  from  of  next  within  decrease  east  to  pyroclastic  and  chance  Unit  by  in  and  are  debris  thin  not  the  after  d i v i of  thin  graded, tuff  known.  sinking  The  turbidites,  to  some  be  of  coarse  implying  material  is  28).  base  the  In  in  and  (Fig.  of  mud-  lamina-  to  is  deposition.  fine  of  the  thick,  decrease at  the  and  a  cases, rapid  deposited  turbidites  eastern high  currents,  in  density  head  with  by  portion  density  and  this  the  deposited  apparently  probably and  the  both  increase  in  interface  of  size  and  by  decrease  interpretation.  from  the  collapse on  relation-  and  flows  upper  grain  originated  probably  originally  proximal-distal  maximum  consistent  eruptions,  is  and  layer  layer  visibly  They  planar  a  laminated  turbidity  average  siltstone show  This  implies  flows  into  cm o r  sedi-  flow.  3  The  more.  into  not  by  for  50  corresponding  B.  size  shortly  primary  Sometimes  is  disrupted  seawater  west  flows  between  grain  portion.  with  bed,  turbidity  movement  mixing  27).  successive  material,  pyroclastic or  mud  pyroclastic  western  the  in  l i t t l e  facies  coarse  during  the  downslope  deposition  thickness  soft  tuff,  division  the  to  abundant  always  finer-grained,  been  between  thick  the  during  flow.  in  much  commonly  of  of  change  with  almost  (Fig.  underlies  1  upward  cross-laminated  by  underlying  arrival  turbidites  in  has  beds  contain  from  grading  tuff  thickness  abrupt  graded,  thickness  sequence  tephra  intervenes  between  evolved  Bouma  deposition,  the  by  abruptly  for  in  s i l t - s i z e d  the  are  fine-grained,  total  reason  into  range  overlain  The  no  to  crystal-rich to  tuff  and  to  of  relation  turbidites  submarine and  unstable  downslope  slopes  Fig.  27. P o l i s h e d s l a b o f submarine t u f f from U n i t 3 showing a Bouma BC sequence.  105  F i g . 28. P o l i s h e d s l a b o f submarine t u f f from U n i t 3 showing the base o f a graded t u r b i d i t e bed, w i t h a c o n c e n t r a t i o n o f coarse p l a g i o c l a s e , pyroxene, and hornblende c r y s t a l s . Base of l a y e r i s d i s r u p t e d by l o a d c a s t s . Thin c r o s s laminated t u r b i d i t e bed below.  106  around the vent.  The  rounding o f the l a r g e r v o l c a n i c c l a s t s and  o f doubly-graded sequences t h a t the vent was  ( F i s k e and Matsuda, 1964)  only shallowly  submerged, and  have accumulated around the vent and t r a n s p o r t and  interbedded  i n t e r m i t t e n t , as shown by  i n U n i t 3 suggests  t h a t some o f the t e p h r a  Transport  may  o f the tephra  into  the presence o f mudstones  w i t h the p y r o c l a s t i c d e p o s i t s , but  the i n t e r v a l s between flows  were p r o b a b l y s h o r t , because the mudstone l a y e r s are t h i n , and a s m a l l p a r t of the t o t a l t h i c k n e s s  lack  undergone s i g n i f i c a n t c u r r e n t or wave  a b r a s i o n p r i o r to r e d e p o s i t i o n .  the deep b a s i n was  the  make up  only  o f the u n i t s .  V o l c a n i c Sandstone o r Redeposited T u f f  V o l c a n i c sandstones d e p o s i t e d i n U n i t 4, but  a l s o r a r e l y i n U n i t s 2 and  l e s s than 15 cm t o over 2.5m, middle p o r t i o n o f U n i t 4. base, g r a d i n g  by t u r b i d i t y c u r r e n t s  f i n e - g r a i n e d sandstone.  laminated B - i n t e r v a l t o g e t h e r  the  The  at  the  Complete Bouma  massive A - i n t e r v a l and h o r i z o n t a l l y  account f o r most o f the t h i c k n e s s  E each o n l y a few  from  m t h i c k are common i n the  These t h i c k sandstones are c o a r s e - g r a i n e d  sequences were found i n s e v e r a l beds.  and  They range i n t h i c k n e s s  and beds 1 to 2.5  upward t o medium and  w i t h i n t e r v a l s C, D,  5.  are found p r i m a r i l y  centimeters  o f the beds,  t h i c k a t the top  of  bed. P e t r o g r a p h i c a l l y these rocks  are shown i n T a b l e V.  are q u i t e v a r i e d .  A l l of the rocks  fragments and p l a g i o c l a s e , but  Modes o f t h r e e  samples  are dominated by v o l c a n i c rock  t h e i r textures  vary  dramatically.  Sample MK-222 i s s i m i l a r i n c o m p o s i t i o n t o the p y r o c l a s t i c s o f U n i t but  i t s constituent mineral  equant and  g r a i n s and  rounded, the rocks  3,  v o l c a n i c rock fragments are more  are moderately w e l l s o r t e d , and  i t i s cemented  TABLE V. VISUALLY ESTIMATED MODES OF VOLCANIC SANDSTONES OR REDEPOSITED TUFFS FROM UNITS 2, 4, AND 5  S  a  m  p  l  MK-151 Unit 2  e  V o l c a n i c rock  MK-215 Unit 4  MK-222 Unit 5  fragments  ( e x c l u d i n g phenocrysts)  65-70%  Plagioclase Quartz  30%  25  40  1  Tr  20-25% 35  Clinopyroxene  —  —  5  Hornblende  —  —  1  Biotite  —  —  Tr  Clastic Calcite  —  Tr  Tr  M a t r i x and Pseudomatrix  5-10  C a l c i t e Cement  —  G r a i n s i z e (sand t o ash range)  — = Absent Tr = Trace  F = Fine-grained M = Medium-grained  30% —  VC  40  F-M  C = Coarse-grained VC = Very c o a r s e - g r a i n e d  108  by  sparry c a l c i t e .  The sand i s g r a i n supported, b u t t h e g r a i n s a r e o n l y  l o o s e l y packed, so i t seems t h a t cementation took p l a c e e a r l y i n t h e d i a genetic h i s t o r y , before place.  deep b u r i a l and s i g n i f i c a n t compaction c o u l d take  T h i s ash c l e a r l y underwent s i g n i f i c a n t t r a n s p o r t , s o r t i n g , and  abrasion before  r e d e p o s i t i o n i n t o t h e deep b a s i n .  Both sample MK-151 and MK-215 c o n t a i n some c h l o r i t i z e d pumice c l a s t s in addition to nonvesicular c l e a r angular  v o l c a n i c fragments, and v e r y s m a l l amounts o f  quartz, probably  also volcanic i n o r i g i n .  p o o r l y s o r t e d and c l o s e l y packed, w i t h probably  Both samples a r e  a murky i n t e r s t i t i a l m a t r i x ,  i n c l u d e s some a l t e r e d v o l c a n i c g r a i n s  ( F i g . 29 and 30).  which  Volcanic  g r a i n o u t l i n e s and shapes a r e b l u r r e d by d i a g e n e t i c and metamorphic e f f e c t s , but  i n o v e r a l l composition  and t e x t u r e these rocks  t u f f s o f t h e Harper Ranch Group. produced by shallow  T h i s p y r o c l a s t i c m a t e r i a l was  probably  marine o r s u b a e r i a l e r u p t i o n s , and was t r a n s p o r t e d t o  deeper water and d e p o s i t e d The  resemble t h e r e d e p o s i t e d  by t u r b i d i t y c u r r e n t s and h i g h d e n s i t y mass  predominance o f n o n v e s i c u l a r  flows.  v o l c a n i c grains-, over pumice suggests t h a t  the e r u p t i o n s which produced t h e ash were submarine, o r t h a t l e s s dense v e s i c u l a r and pumiceous g r a i n s were removed from s u b a e r i a l ash d u r i n g stream t r a n s p o r t t o t h e marine environment. S e v e r a l samples o f p o o r l y s o r t e d p y r o c l a s t i c rocks show p a r t i a l replacement o f m a t r i x calcite.  and framework g r a i n s by  Sample MK-151 grades from a rock w i t h  which i s over 70% c a l c i t e .  microgranular  almost no c a l c i t e t o one  Small opaque granules  p y r i t e ) a r e a l s o common i n s e v e r a l o f these rocks lacks c a l c i t e ) .  ( i n c l u d i n g MK-151)  o f yellow  sulfide  (probably  ( i n c l u d i n g MK-215, which  Because o f r e c r y s t a l l i z a t i o n , i t i s n o t c l e a r whether  mud was o r i g i n a l l y p r e s e n t  i n the matrix  lime  o f these r o c k s , b u t i f s o , a d d i t i o n a l  109  Fig.  29. Photomicrograph o f t h i n - s e c t i o n , Sample MK-151, v o l c a n i c sandstone o r r e d e p o s i t e d t u f f from U n i t 4. V o l c a n i c rock fragments (V), p l a g i o c l a s e ( P I ) , and c a l c i t i z e d v o l c a n i c fragment ( C c ) . Plane l i g h t , X 40.  Fig.  30. Photomicrograph o f t h i n - s e c t i o n , Sample MK-215, v o l c a n i c sandstone o r r e d e p o s i t e d t u f f i n U n i t 5. P l a g i o c l a s e ( P I ) , p o r p h y r i t i c v o l c a n i c fragment, and c h l o r i t i z e d pumice c l a s t (P). Plane l i g h t , X 40.  -  110  c a l c i t e a l s o had observed.  t o be i n t r o d u c e d t o account f o r the amount o f replacement  I f c a l c i t i z a t i o n o f these  rocks o c c u r r e d a t the same stage  cementation i n sample MK-222, then i t was took p l a c e d u r i n g shallow  Vitric  as  an e a r l y d i a g e n e t i c e f f e c t which  burial.  Tuff  Beds o f v i t r i c  t u f f occur near the top o f U n i t 2, and  near the base  o f U n i t 4, o r , i n o t h e r words, j u s t below and above the subaqueous p y r o c l a s t i c flows and  t u r b i d i t e s o f U n i t 3.  w i t h mudstone, laminated  They o c c u r i n t h i c k graded beds  s i l t s t o n e , and  Samples from each u n i t (Table VI) g l a s s shards and pumice  ( F i g . 31).  v o l c a n i c fragments are p r e s e n t ,  limestones.  c o n s i s t o f 80 t o 90%  Only a few m i c r o l i t i c ,  devitrified  non-vesicular  a l o n g w i t h v a r i a b l e but s m a l l amounts o f  p l a g i o c l a s e , quartz, clinopyroxene, content  turbidite  interbedded  hornblende, and b i o t i t e .  The  mineral  o f the samples suggests t h a t they are d a c i t i c t o a n d e s i t i c i n compo-  sition.  Glass i n sample MK-150 i s a l t e r e d to c a l c i t e , c h l o r i t e ,  f e l d s p a r , and perhaps a l b i t e .  potassium  In sample MK-125, g l a s s i s a l t e r e d t o  chlorite,  potassium f e l d s p a r , o c c a s i o n a l c a l c i t e , and brown t o green, amorphous m a t e r i a l w i t h anomalous b i r e f r i n g e n c e , perhaps masked by  i t s color.  i s s i m i l a r to c h l o r o p h a e i t e , an amorphous a l t e r a t i o n p r o d u c t  This material of b a s a l t i c  glasses. The  t u f f s a r e w e l l i n d u r a t e d , but  p r e f e r r e d o r i e n t a t i o n of elongate 125.  The  s m a l l mudclasts may  show no s i g n s o f w e l d i n g .  shards and pumice i s p r e s e n t  Strong  i n sample  MK-  be a c c i d e n t a l fragments i n c o r p o r a t e d i n t o the  g l a s s y t e p h r a d u r i n g i t s e r u p t i o n , but more l i k e l y they are r i p - u p  clasts,  which i m p l i e s t h a t the t u f f s were emplaced as t u r b i d i t y c u r r e n t s w i t h c i e n t e r o s i v e c a p a c i t y to m i l d l y erode u n d e r l y i n g muds.  This i s also  suffi-  TABLE V I . VISUALLY ESTIMATED MODES OF VITRIC TUFFS  S  a  m  p  Devitrified  l  e  MK-125 Unit 4  glass  shards and pumice Volcanic  MK-150 Unit 2  rock fragments  Plagioclase Quartz  85-90%  80%  Tr  Tr  1  5  Tr  Clinopyroxene Hornblende  —  Tr  Biotite  Tr  Tr  Mudstone c l a s t s  Tr  Tr  Matrix  10  10  Plagioclase composition  —  = Absent  T r = Trace  Ang^, Angg  Ani^  F i g . 31. Photomicrograph o f t h i n - s e c t i o n (Sample MK-150) o f v i t r i c t u f f from U n i t 2. B u b b l e - w a l l shards (Sh), pumice, (P), and minor p l a g i o c l a s e (PI) and hornblende (H). Plane l i g h t , X 40.  113  r e f l e c t e d by t h e i r moderate t o poor s o r t i n g , and presence r i c h matrix.  o f a murky, o r g a n i c -  The homogeneity and a n g u l a r n a t u r e o f the p y r o c l a s t i c m a t e r i a l  i m p l i e s t h a t s e d i m e n t a t i o n took p l a c e d u r i n g o r s h o r t l y a f t e r i t s e r u p t i o n .  L i t h i c Sandstone and  The presence  Conglomerate  o f an a p p r e c i a b l e p r o p o r t i o n o f n o n v o l c a n i c l i t h i c  clasts  d i s t i n g u i s h e s the coarse c l a s t i c sediments o f U n i t 5 from most o t h e r s i n the section.  The r o c k s are mostly  b l e conglomerate  and b r e c c i a .  f i n e - g r a i n e d sandstone  and s i l t s t o n e , and peb-  U n f o r t u n a t e l y , these r o c k s a r e f o r the most  p a r t p o o r l y exposed i n ephemeral stream channels, so o n l y a v e r y g e n e r a l d e s c r i p t i o n can be p r e s e n t e d .  S i m i l a r sedimentary  rocks a l s o o c c u r beneath  the v o l c a n i c r o c k s o f U n i t 6. As a group, these r o c k s appear t o have a s t r o n g l y bimodal distribution.  Pebble conglomerates  g r a i n e d m a t r i x o f f i n e sand, s i l t , l a y e r e d w i t h the conglomerates c o a r s e - g r a i n e d sandstones  and b r e c c i a s have a d i s t i n c t l y o r more r a r e l y mud.  size  finer-  Sandstone beds i n t e r -  are a l s o u s u a l l y f i n e - g r a i n e d .  Medium t o  are r a r e .  F i n e - g r a i n e d sandstone t h i n beds  grain  and s i l t s t o n e t y p i c a l l y o c c u r i n sequences o f  (to s e v e r a l c e n t i m e t e r s t h i c k ) , w i t h the sequence t o t a l l i n g a meter  o r more i n t h i c k n e s s .  Each t h i n bed has a sharp b a s a l c o n t a c t , and shows  normal s i z e g r a d i n g from f i n e sandstone mudstone i s p r e s e n t i n these sequences.  upward t o s i l t s t o n e .  They p r o b a b l y r e p r e s e n t r a p i d l y  d e p o s i t e d sequences o f f i n e - g r a i n e d t u r b i d i t e s . h o r i z o n t a l l y l a m i n a t e d f i n e sandstone Pebble and sharpstone  L i t t l e o r no  O c c a s i o n a l t h i c k beds o f  or s i l t s t o n e are a l s o present.  conglomerate  beds are c o m p l e t e l y  showing n e i t h e r s t r a t i f i c a t i o n nor i m b r i c a t i o n .  Some beds may  structureless, be tens o f  114  metres Basal  thick,  of  the  beds  but  (Fig.  generally  quite  as  these  bed  (Fig.  beds  and  model  "resedimented" water,  flow  process,  dites.  The  gest  Walker  to  slopes that  as  the  are  and  spaced the  less  unit.  conglomerates traced than  two  or  are  Stratigraphic  rare  given  sample.  turbidite  of  internal  limit  breccia  The  of  size, the  outcrop.  conglomerates  comprising  On  and  10  to  of  is  most  numerous  are  20%  rounding  average,  contain  found and  they  in  200  Unit are on  5 may  the  southwest and  sandstones  with  pinchout  their of  to  a  are up  clasts  angular  are  another,  apparent  conglomerate  on  the  type  evidence  shoestring,  slope  of  Dome  the but  in  be  turbisug-  submarine  to  which  between  The  gullies  the  strike  disorganized  lithologies,  equivalents  cannot  and  suggests  Hills.  generally  shal-  density  gullies  perpendicular  dominant  in  channelized  stream  m thick,  term  deposits  steep  of  100  of  mudstones  relatively Field  The  accumulated  some  setting  disorganized-  1975).  series  lateral beds  by  fine-grained  deep water  disorganized-bed  nearly to  fits  deep water  indeed be in  The  originally  channels.  and  gully  of  rapidly  exposed  m apart,  one  which  mudstone,  (Walker,  deeper water  intervals  from  structures  nature  submarine  turbidite  limestones.  interbedded with  accumulated  elevation than  into  chaotic  in  laminated  conglomerates  conglomerates  deposits  three,  matrix  exceed pebble  Stratigraphic  laterally  the  interbedded with  lack  perhaps  ft  the  conformable.  designated  transported  conglomerates  2000  are  to  coarseness  These  a  resedimented  were  lags,  deposits. 1500  for  that  within  be  with  clasts  rocks  their  and  packed, few  and  refers  then  to  exceeds  33).  sandstones,  facies  low  the  conglomerates  turbidite  of  variable but  well  The  Very  generally  appear  closely  32).  subangular,  clasts  of  thickness  sorted,  rock  are  bed  contacts  poorly the  and  appear being  proven,  but  in  can no  be  more  mudstone. confinement  115  Fig.  33. P o l i s h e d s l a b o f l i t h i c Hills.  conglomerate from U n i t 5, Dome  116  of  i n d i v i d u a l conglomerate  observations.  beds t o submarine channels c o u l d e x p l a i n these  No c o n s i s t e n t o f f s e t s o f these i n t e r v a l s which might be  a t t r i b u t e d t o f a u l t i n g were noted. P e t r o g r a p h i c d a t a on these e l a s t i c s were d e r i v e d from f o u r t h i n - s e c t i o n s and a number o f hand-specimens o f sandstone  and conglomerate,  o b s e r v a t i o n o f c l a s t c o n t e n t o f conglomerates. counted,  clasts  (mostly c h e r t and mudstone) a r e an important o r  even dominant component o f these e l a s t i c s . i s an extreme example:  exceed  Two t h i n - s e c t i o n s were p o i n t -  and t h e r e s u l t s a r e p r e s e n t e d i n T a b l e V I I .  Sedimentary  fragments  and f i e l d  The conglomerate  sample MK-211  others contain greater proportions o f volcanic  ( F i g . 32) and p h e n o c r y s t s , although sedimentary  50% o f t h e framework.  i n t h i n - s e c t i o n , and grade  rock  clasts generally  C h e r t c l a s t s a r e g e n e r a l l y c o l o r l e s s t o brown  i n t o mudstones.  Many c o n t a i n r a d i o l a r i a , which  are r e c r y s t a l l i z e d t o a c o l o r l e s s , m i c r o g r a n u l a r q u a r t z aggregate which i s c o a r s e r than t h e s u r r o u n d i n g c h e r t ( F i g . 34). Mudstone c l a s t s a r e equant and o f t e n a n g u l a r , and were c l e a r l y l i t h i f i e d p r i o r t o i n c o r p o r a t i o n i n t h e conglomerate; or  they a r e n o t i n t r a b a s i n a l r i p - u p c l a s t s .  homogeneous, and some c o n t a i n s i l t  They may be laminated  to sand-sized plagioclase grains.  stone and s i l t s t o n e c l a s t s c o n s i s t mostly o f p l a g i o c l a s e and v o l c a n i c fragments  w i t h some m a f i c m i n e r a l s , i n c l u d i n g  V o l c a n i c rock fragments  Sand-  rock  hornblende.  may be f e l s i t i c , and d i f f i c u l t  to distinguish  from c h e r t , b u t most a r e p o r p h y r i t i c , w i t h p l a g i o c l a s e and sometimes hornblende o r b i o t i t e m i c r o p h e n o c r y s t s .  Other v o l c a n i c c o n s t i t u e n t s a r e f r e e  p h e n o c r y s t g r a i n s , i n c l u d i n g p l a g i o c l a s e , hornblende,  and c l i n o p y r o x e n e .  U n a l t e r e d p l a g i o c l a s e g r a i n s i n sample MK-132 have compositions o f An3g, Ani4g, and Angij., c o n s i s t e n t w i t h t h e i n f e r r e d i n t e r m e d i a t e c o m p o s i t i o n o f t h e  TABLE V I I .  MODAL ANALYSES OF CLASTIC ROCKS FROM UNIT 5  Sample  MK-132 Coarse Sandstone  Pebble  MK-211 Conglomerate  Chert  17%  463  Mudstone  16  19  7  8  19  10  13  3  Volcanic  sandstone and  siltstone Volcanic  r o c k fragments  Plagioclase Hornblende -Clinopyroxene  5 5  Tr  10  9  8  4  T o t a l Counts  328  296  T o t a l determinable framework counts  268  255  Matrix Indeterminate  Sedimentary c l a s t s (Chert + mudstone + sandstone + s i l t s t o n e )  48%  85%  Volcanic c l a s t s ( v o l c a n i c rock fragments + p l a g i o c l a s e + hornblende + clinopyroxene)  52  15  —  = Absent  Tr = Trace  F i g . 34. Photomicrograph o f t h i n - s e c t i o n , Sample MK-132, l i t h i c v o l c a n i c sandstone from U n i t 5. C l a s t s o f r a d i o l a r i a n c h e r t ( C t ) , v o l c a n i c s i l t s t o n e ( S t ) , and p l a g i o c l a s e ( P I ) . Plane l i g h t , X 40.  119  volcanic material.  However, the wide range i n a n o r t h i t e  t h a t v o l c a n i c c l a s t s may  have been d e r i v e d  content suggests  from s e v e r a l d i s t i n c t  volcanic  sources. These c l a s t i c r o c k s r e c o r d a mixed provenance, w i t h most o f the tus d e r i v e d activity.  from an o l d e r sedimentary t e r r a n e The  v o l c a n i c sandstone and  i f i e d before being incorporated from an o l d e r v o l c a n i c  from c o e v a l  volcanic  s i l t s t o n e c l a s t s were p r o b a b l y  i n these d e p o s i t s ,  and  may  lith-  have been  derived  terrane.  DISCUSSION AND  Summary o f D e p o s i t i o n a l  REGIONAL IMPLICATIONS  Setting  Rocks o f the N i c o l a Group i n the and  and  detri-  study area are a deep water sedimentary  v o l c a n i c f a c i e s assemblage which accumulated i n a b a s i n l y i n g t o the  east  (using p r e s e n t d i r e c t i o n s ) o f the a c t i v e N i c o l a v o l c a n i c a r c h i p e l a g o .  Pelagic  and h e m i p e l a g i c mudstones are abundant or dominant i n most u n i t s .  vol-  c a n i c l a s t i c rocks, were d e p o s i t e d  by  lithic  sandstones and  t u r b i d i t y currents  and  B a s i c v o l c a n i c s were e r u p t e d on the sea ing  massive and p i l l o w e d  flows.  The  conglomerates, and  limestones  high  density  concentration  f l o o r l o c a l l y and  Deposition  flows.  s p o r a d i c a l l y , form-  o f a l l these s t r a t a took  place  i n q u i e t waters a t an i n d e r m i n a b l e depth below storm wave base, s i n c e dence o f reworking o f the  Relationship  The  The  sediments i s meager.  Between the N i c o l a and  Harper Ranch Groups  c o n t a c t between the N i c o l a and  i n the study a r e a , but f a u l t truncates  evi-  Harper Ranch Groups i s not  exposed  i s i n t e r p r e t e d as a s t e e p , n o r t h w e s t - t r e n d i n g  l i t h o l o g i c u n i t s w i t h i n the N i c o l a Group a t a low  faults. angle,  120  and the rock sequences fault.  on e i t h e r s i d e o f i t become younger away from the  However, a t depth the N i c o l a Group may  older rocks.  Read and O k u l i t c h  unconformity beneath  l i e unconformably  on the  (1977) have d e s c r i b e d a r e g i o n a l angular  Middle and Upper T r i a s s i c r o c k s on the west s i d e o f the  Omineca C r y s t a l l i n e b e l t i n the r e g i o n south o f Kamloops. and o l d e r r o c k s beneath  In p l a c e s Permian  the unconformity have undergone i n t e n s e d e f o r m a t i o n  and low grade metamorphism.  Evidence f o r p r e - T r i a s s i c d e f o r m a t i o n i s l a c k -  i n g i n the study a r e a , b u t the v o l c a n i c l a s t i c r o c k s o f the Harper Ranch Group are s i g n i f i c a n t l y more a l t e r e d than those o f the N i c o l a Group, sugg e s t i n g the p o s s i b i l i t y o f P e r m o - T r i a s s i c low grade metamorphism a f f e c t i n g the Harper Ranch Group.  The a n g u l a r unconformity has not been r e c o r d e d  n o r t h o f Kamloops, b u t the Harper Ranch Group does not extend beyond Bonaparte  northwestward  Lake map-area.  About 13 km e a s t o f Kamloops a l o n g the South Thompson R i v e r , near Campbell  Creek  j u n c t i o n , an a n g u l a r unconformity between the Harper Ranch  Group and rocks mapped as N i c o l a Group i s exposed 1948;  Sada and Danner, 1974;  (Daly, 1915;  Read and O k u l i t c h , 1977).  The  Cockfield,  unconformity  t r u n c a t e s massive Lower Permian and Lower P e n n s y l v a n i a n l i m e s t o n e , and i s o v e r l a i n by 45 m o f pebble t o b o u l d e r conglomerate, stone.  My  sandstone, and l i m e -  examination showed t h a t c l a s t s o f p u r p l e f e l d s p a r porphyry  common i n the conglomerate,  a l o n g w i t h l i m e s t o n e , mudstone, and  sandstone p r o b a b l y d e r i v e d from the Harper Ranch Group.  The  rocks above the unconformity d i p g e n t l y (15 t o 30°) eastward, l a i n by massive  a u g i t e porphyry v o l c a n i c b r e c c i a s .  are  volcanic  sedimentary and are o v e r -  A t t i t u d e s i n the s e d i -  mentary s t r a t a are q u i t e r e g u l a r , i n c o n t r a s t t o those i n the Harper Ranch Group and N i c o l a Group to the west.  121  The v o l c a n i c r o c k s o v e r l y i n g the conglomerate are l i t h o l o g i c a l l y s i m i l a r t o the v o l c a n i c a r c f a c i e s o f the N i c o l a Group, and they have been mapped as such by C o c k f i e l d .  However, no f o s s i l s have been r e p o r t e d from  the v o l c a n i c sequence a t t h i s l o c a l i t y , o r from r o c k s c o n t i g u o u s w i t h them, and a Lower J u r a s s i c age f o r t h e s e r o c k s i s p o s s i b l e . Quesnel Lake map-areas, Campbell and T i p p e r Lower t o Middle J u r a s s i c  In Bonaparte Lake and  (1970, 1971)  have mapped a  (Sinemurian and younger) v o l c a n i c and  volcaniclastic  u n i t which i s l i t h o l o g i c a l l y i n d i s t i n g u i s h a b l e from p a r t s o f the N i c o l a In some p l a c e s the base o f t h i s sequence i s a c o a r s e conglomerate c l a s t s o f the N i c o l a and Harper Ranch Groups, and g r a n i t i c c l a s t s .  Group.  containing Although  g r a n i t i c c l a s t s have not been found i n the conglomerate a t Campbell Creek, i n o t h e r r e s p e c t s i t resembles the conglomerate d e s c r i b e d by Campbell Tipper. Preto  and  Lower and perhaps M i d d l e J u r a s s i c r o c k s have a l s o been found by  (1977) i n the N i c o l a Group south o f N i c o l a Lake  map-areas).  ( N i c o l a and P r i n c e t o n  With p a l e o n t o l o g i c c o n t r o l l a c k i n g a t Campbell Creek, i t i s  not a d v i s a b l e t o assume a T r i a s s i c age f o r t h i s u n c o n f o r m i t y .  However, un-  c o n f o r m i t i e s beneath dated Upper T r i a s s i c r o c k s o c c u r west and northwest o f Vernon, and the P e r m o - T r i a s s i c u n c o n f o r m i t y may  extend as f a r as the study  area.  Provenance o f C l a s t i c D e t r i t u s and Paleogeography o f the Quesnel Trough  The Quesnel trough i s a n o r t h w e s t - t r e n d i n g b e l t o f Upper T r i a s s i c Lower J u r a s s i c v o l c a n i c and sedimentary r o c k s l y i n g west o f the Omineca C r y s t a l l i n e b e l t , and s t r e t c h i n g from n o r t h e r n Washington B r i t i s h Columbia  ( F i g . 35).  e i t h e r s i d e by o l d e r r o c k s .  to northern  T h i s f a u l t - b o u n d e d "trough" i s f l a n k e d on On t h e e a s t s i d e a r e the Upper P a l e o z o i c  and  122  F i g . 35. L o c a t i o n map o f Quesnel trough and s u r r o u n d i n g Mesozoic t e c t o n i c elements o f c e n t r a l and southern B r i t i s h Columbia. M o d i f i e d from Wheeler (1970).  123  e u g e o c l i n a l rocks which form t h e western  margin o f t h e Omineca b e l t .  To t h e  west l i e s t h e P i n c h i g e a n t i c l i n e , c o n s i s t i n g o f t h e Cache Creek Group.  Late  T r i a s s i c u p l i f t and emergence o f t h e P i n c h i g e a n t i c l i n e may have p r o v i d e d a source f o r some o f t h e c l a s t i c sediments i n t h e Quesnel some q u a r t z o s e sediments i n t h e southernmost Quesnel d e r i v e d from t h e Omineca g e a n t i c l i n e a strongly positive J u r a s s i c deformation  trough.  Although  trough may have been  (Wheeler and o t h e r s , 1972), i t was n o t  f e a t u r e d u r i n g t h e Late T r i a s s i c .  Middle t o L a t e  and u p l i f t i n t h e Omineca b e l t p r o b a b l y ended marine  d e p o s i t i o n i n t h e trough  (Campbell  During t h e Late T r i a s s i c  and T i p p e r , 1970'; E i s b a c h e r , 1974) .  (Karnian t o N o r i a n ) , t h e western  the trough was a v o l c a n i c a r c h i p e l a g o which produced  portion of  t h e v o l c a n i c rocks o f  the N i c o l a Group, and t h e T a k l a Group i n n o r t h e r n B r i t i s h Columbia.  The  N i c o l a Group i n i t s type a r e a around N i c o l a Lake, 50 km south o f Kamloops, i s a complex assemblage o f b a s a l t i c a n d e s i t e and a n d e s i t e f l o w s , b r e c c i a s , and t u f f s , w i t h a s s o c i a t e d c l a s t i c sediments and l i m e s t o n e s  (Schau,  Flows and d i k e s a r e common near the v o l c a n i c c e n t e r s , a l o n g w i t h b r e c c i a s and agglomerates.  A t l e a s t some o f t h e s e d i -  i n shallow water, as evidence by r i p p l e marks,  scour marks, and c r o s s - b e d d i n g . islands.  coarse  E q u i v a l e n t s t r a t a f a r t h e r from t h e c e n t e r s a r e  f i n e t u f f s and v o l c a n i c o r c a l c a r e o u s wackes. ments p r o b a b l y accumulated  1970).  C o r a l - a l g a l reefs fringed the v o l c a n i c  F o s s i l s from r e e f l i m e s t o n e s and o t h e r sediments,  although  rare,  i n d i c a t e these rocks c o u l d range i n age from l a t e K a r n i a n t o l a t e N o r i a n . •few  kilometres  (A  t o t h e south, f o s s i l s o f E a r l y J u r a s s i c age a r e found i n  rocks i n c l u d e d by P r e t o  (1977) w i t h t h e N i c o l a Group.)  E a s t o f t h e v o l c a n i c a r c h i p e l a g o l a y a marine b a s i n i n which t h e mudstone, v o l c a n i c l a s t i c r o c k s , and l i m e s t o n e o f the d i s t a l N i c o l a Group  124  accumulated. was  The  sedimentary f a c i e s and  s t r u c t u r e s suggest t h a t the  r e l a t i v e l y deep, c e r t a i n l y w e l l below s h e l f depths.  basin  Conodonts from  the  b a s i n a l sediments found a t s e v e r a l l o c a l i t i e s are K a r n i a n t o e a r l y N o r i a n i n age,  i n d i c a t i n g t i m e - e q u i v a l e n c e w i t h a t l e a s t the  p r o x i m a l v o l c a n i c f a c i e s ( O k u l i t c h and  f a c i e s has  However, south o f Kamloops, C o c k f i e l d  culty consistently separating  the  Cameron, 1976).  A mappable l a t e r a l t r a n s i t i o n between these two been r e c o g n i z e d .  lower p o r t i o n o f  not  (1948) had  yet  diffi-  h i s "Cache Creek Group" (almost c e r t a i n l y  rocks o f the b a s i n a l f a c i e s o f the N i c o l a Group) from the v o l c a n i c rocks o f the  type N i c o l a Group.  zons w i t h i n the two o f the  the  Breccias  and  conglomerates o c c u r a t d i f f e r e n t h o r i -  "Cache Creek Group," and  groups a t the p l a c e  C o c k f i e l d drew the boundary between  i n the s e c t i o n where v o l c a n i c flows and  type N i c o l a Group become predominant.  breccias  Where a t t i t u d e s c o u l d be  deter-  mined, t h i s d i v i s i o n s e p a r a t e s rocks which are conformable.  I t would appear  then t h a t the K a r n i a n rocks o f the study area pass u p s e c t i o n  southwestward  i n t o the p r o x i m a l v o l c a n i c t h a t the  two  the r e g i o n ,  f a c i e s o f the N i c o l a Group, w i t h some s u g g e s t i o n  facies interfinger.  In f a c t , a t s e v e r a l l o c a l i t i e s  the b a s i n a l sediments and  f i n e - g r a i n e d v o l c a n i c l a s t i c s are  l a i n conformably by v o l c a n i c flows and b r e c c i a s o f presumed L a t e age  (Campbell and  i n the N o r i a n , and  Tipper,  1970;  Read and  Okulitch,  1977).  over-  Triassic  I t appears  that  perhaps l a t e N o r i a n , v o l c a n i s m became widespread over  the b a s i n , perhaps a s s o c i a t e d w i t h s h a l l o w i n g or  throughout  o f the b a s i n  f l o o r by  infilling  uplift. The  volcanic t u r b i d i t e s of Units  from the N i c o l a v o l c a n i c c e n t e r s  2, 4,  t o the west.  and  5 were p r o b a b l y  derived  T h e i r mineralogy c l o s e l y  resembles t h a t o f the lower v o l c a n i c assemblage o f the N i c o l a Group  described  125  by Schau (1970).  Both the p r o x i m a l  i z e d by v o l c a n i c fragments w i t h r a r e a l t e r e d mafic m i n e r a l s . both i n the t u r b i d i t e s and u n i t d e s c r i b e d by Not  abundant p l a g i o c l a s e phenocrysts  Quartz-bearing  and  volcanic clasts also  only  occur  i n the sediments i n the upper p o r t i o n o f  a l l the v o l c a n i c l a s t i c rocks i n the study  the  The  a r e a were d e r i v e d  p y r o c l a s t i c rocks o f U n i t s 3 and  from  6 are u n l i k e  rocks y e t d e s c r i b e d from the v o l c a n i c f a c i e s t o the west, i n t h a t  c o n t a i n hornblende and b i o t i t e i n a d d i t i o n to c l i n o p y r o x e n e The  character-  Schau.  these v e n t s , however. any  rocks and the t u r b i d i t e s are  and p l a g i o c l a s e .  upper u n i t o f the N i c o l a Group d e s c r i b e d by Schau c o n t a i n s  a u g i t e and  abundant  some p l a g i o c l a s e , but hornblende has o n l y been d e s c r i b e d  one b r e c c i a u n i t .  they  from  Furthermore, the f a c i e s r e l a t i o n s o f U n i t 3 i n d i c a t e t h a t  these d e p o s i t s were d e r i v e d from a v o l c a n i c c e n t e r or c e n t e r s l y i n g t o e a s t o r n o r t h e a s t o f the study The  a r e a , and  thus w i t h i n the b a s i n .  c h e r t - r i c h e l a s t i c s o f U n i t s 5 and  the P i n c h i g e a n t i c l i n e t o the west, although  6 may  have been d e r i v e d from  the s i l i c e o u s mudstones  and  p y r o c l a s t i c r o c k s o f the Harper Ranch assemblage are another p o s s i b l e The  coarse, angular  u p l i f t o f the source The  nature  the  source.  o f the c h e r t and mudstone c l a s t s suggests t h a t  t e r r a n e was  r a p i d , and  l o c a l r e l i e f was  considerable.  emergent P i n c h i g e a n t i c l i n e l a y west o f the b e l t o f N i c o l a v o l c a n i c  centers.  The  coarse d e b r i s d e r i v e d from i t was  d e n s i t y flows which funneled  through low  out i n t o deeper waters beyond.  t r a n s p o r t e d eastward by  p o i n t s between the volcanoes  This i n t e r p r e t a t i o n requires that  N i c o l a v o l c a n i c c e n t e r s were b u i l t on an e a s t - f a c i n g p a l e o s l o p e  and  the  (using  p r e s e n t geographic d i r e c t i o n s ) c u l m i n a t i n g t o the west i n the emergent Cache Creek t e r r a n e .  L o c a l b a s i n s trapped between the emergent t e r r a n e  and  126  the v o l c a n i c c h a i n would c o n t a i n v o l c a n i c l a s t i c s from the Studies  by  Travers  l i t h i c d e t r i t u s derived  from the west  and  east. (1978) o f sedimentary and  v o l c a n i c rocks o f  N i c o l a Group near Cache Creek support t h i s i n t e r p r e t a t i o n .  the  These rocks  l i e between the o u t c r o p b e l t s o f the Cache Creek Group t o the west and p r o x i m a l v o l c a n i c f a c i e s o f the N i c o l a Group to the e a s t .  The  the  lower p a r t  of the N i c o l a Group (Karnian) c o n s i s t s o f v o l c a n i c flows and  breccias,  cherts, a r g i l l i t e s ,  calcarenites.  t u r b i d i t e sandstones, conglomerates, and  Conglomerates c o n t a i n c l a s t s o f c h e r t , a r g i l l i t e , derived  from the Cache Creek Group, but  sequence suggest t r a n s p o r t  s t r a t a c o u l d thus be and  lithic  The  (mostly c a l c a r e o u s  abundant p a l e o c u r r e n t  and  from the  lith-  east are  sandstones o r c a l c a r limestone,  argillite,  from the Cache Creek  data i n d i c a t e transport  to  southeast.  t u r b i d i t e l i m e s t o n e s i n the study a r e a are composed o f  carbonate mud  and  silt  derived  from s h a l l o w water a r e a s .  fine-grained  Shallow water  r e e f s formed near v o l c a n i c i s l a n d s i n the N i c o l a Group (Schau, 1970), carbonates may  a l s o have f r i n g e d p o r t i o n s  rane, as suggested by  current  and  o f the emergent Cache Creek t e r -  d i r e c t i o n s o f the N o r i a n c a l c a r e n i t e s r e c o r d e d  by T r a v e r s .  The  sections  i n s o l u b l e residues  and  the  these  o v e r l y i n g N o r i a n beds  These c l a s t s were p r o b a b l y d e r i v e d  Group to the west, and the e a s t or  The  conglomerate l e n s e s w i t h c l a s t s o f c h e r t ,  graywacke.  s p e c i f y the  d i r e c t i o n s were d e r i v e d ,  from the west.  mudstones w i t h abundant sandstones  and  T r a v e r s does not  indicators i n  a mixture o f v o l c a n i c d e t r i t u s d e r i v e d  detritus derived  e n i t e s ) , and  limestone p o s s i b l y  rare paleocurrent  t o the west.  o l o g i e s o f beds from which the c u r r e n t  and  presence o f both v o l c a n i c and o f the  metamorphic d e t r i t u s i n t h i n -  l i m e s t o n e s near Kamloops suggests  127  d e r i v a t i o n o f sediment from b o t h a r e a s . b l u e amphibole ( c r o s s i t e )  T h i s d e t r i t u s i n c l u d e s metamorphic  f o r which the Cache Creek Group i s the o n l y known  source-, i n the Canadian C o r d i l l e r a .  K-Ar ages o f b l u e s c h i s t s from P i n c h i  Lake, c e n t r a l B r i t i s h Columbia, r e c o r d u p l i f t and c o o l i n g a t 211 t o 218 or  m.y.,  L a t e K a r n i a n t o N o r i a n , roughly c o i n c i d e n t w i t h the age o f the N i c o l a  Group. The e a s t e r n l i m i t s o f t h i s marine b a s i n a r e not known f o r c e r t a i n , and to  i t p r o b a b l y s t r e t c h e d a c r o s s the p r e s e n t p o s i t i o n o f the Omineca the western margin o f the T r i a s s i c m i o g e o c l i n e  1970; Wheeler and o t h e r s , 1972).  Metamorphosed  belt  (Campbell and T i p p e r ,  e q u i v a l e n t s o f the b a s i n a l  rocks can be t r a c e d d i s c o n t i n u o u s l y a c r o s s the metamorphic c u l m i n a t i o n o f the  Omineca b e l t e a s t o f Vernon, and i n t o the T r i a s s i c S l o c a n and Ymir  Groups on the e a s t s i d e o f the c r y s t a l l i n e b e l t , i n the Rossland trough (Wheeler and o t h e r s , 1972, F i g . 2; O k u l i t c h and Cameron, 1976).  These  "troughs" are n o t narrow d e p o s i t i o n a l f e a t u r e s , b u t remnants o f widespread Upper T r i a s s i c d e p o s i t s which have been removed from most o f the Omineca b e l t and P u r c e l l and western Rocky Mountains by p o s t - T r i a s s i c u p l i f t  and  erosion. Most o f the b a s i n a l r o c k s i n t h e r e g i o n , i n c l u d i n g the S l o c a n and Ymir Groups, a r e mudstones w i t h some c o a r s e v o l c a n i c and l i t h i c b a s i n a l limestones.  Near Shuswap Lake, t h e i r metamorphosed  e q u i v a l e n t i s the g r a p h i t i c , p h y l l i t i c s c h i s t o f the Sicamous Formation. bedded mudstone Lake by O k u l i t c h Vernon  e l a s t i c s and stratigraphic  l i m e s t o n e , marble, p h y l l i t e ,  The f a c i e s change from mudstone  and to i n t e r -  and a r g i l l a c e o u s l i m e s t o n e has been mapped west o f Adams (1974).  Upper T r i a s s i c l i m e s t o n e a l s o o c c u r s e a s t o f  ( O k u l i t c h and Cameron, 1976).  The Sicamous Formation i s s e v e r e l y  128  deformed and metamorphosed, so s p e c u l a t i o n s on i t s d e p o s i t i o n a l h i s t o r y hazardous.  However, d e s c r i p t i o n s o f the u n i t  (Jones, 1959;  Fyson,  are  1970)  suggest t h a t i t o r i g i n a t e d as muddy b a s i n a l l i m e s t o n e s i n t e r b e d d e d w i t h mudstone, r a t h e r than i n a s h a l l o w water s e t t i n g . microorganisms  are unknown b e f o r e the J u r a s s i c , these l i m e s t o n e s  p r o b a b l y not p e l a g i c i n o r i g i n .  and the lime mud  than i n the N i c o l a and S l o c a n Groups,  have been t r a n s p o r t e d from the s h e l f area t o the n o r t h -  In t h i s i n t e r p r e t a t i o n the Sicamous Formation  accumulation slope.  may  The  are  The b a s i n a l l i m e s t o n e s are a p p a r e n t l y more  abundant i n the Sicamous Formation  east.  Since p e l a g i c calcareous  o f l i m e mud  i s viewed as a l o c a l  near the base o f the L a t e T r i a s s i c c o n t i n e n t a l  a x i s o f the L a t e T r i a s s i c b a s i n would then l i e between the  Kamloops area and Shuswap Lake, perhaps c o i n c i d e n t w i t h the b e l t o f T r i a s s i c metasediments e a s t o f Vernon.  But a w e s t e r l y  d e r i v a t i o n o f the Sicamous  l i m e s t o n e s cannot be r u l e d out, i n which case the L a t e T r i a s s i c  depocenter  would l i e f a r t h e r e a s t .  T e c t o n i c S e t t i n g and E v o l u t i o n o f the N i c o l a Group  E a r l y T r i a s s i c o r o g e n e s i s brought  t o a c l o s e the L a t e P a l e o z o i c c y c l e  o f i s l a n d a r c v o l c a n i s m i n southern B r i t i s h Columbia.  T h i s deformation  low grade metamorphism i s documented i n p a r t by an a n g u l a r beneath T r i a s s i c r o c k s .  Rocks above the unconformity  and  unconformity  young westward  from  E a r l i e s t T r i a s s i c i n the southern Rocky Mountains t o Late T r i a s s i c west o f the Omineca C r y s t a l l i n e b e l t  (Read and O k u l i t c h , 1977).  By the L a t e  a s s i c , n e a r l y the whole e u g e o c l i n a l regime e a s t o f the Cache R i v e r assemblage had s u b s i d e d below sea l e v e l .  Tri-  Creek-Bridge  The N i c o l a d e p o s i t i o n a l  b a s i n s t r e t c h e d from the Late T r i a s s i c c o n t i n e n t a l margin  (miogeocline)  129  westward t o the a c c r e t e d o c e a n i c  rocks o f the emergent P i n c h i g e a n t i c l i n e .  A n o r t h - t r e n d i n g b e l t o f submarine v o l c a n i c c e n t e r s separated rocks:  two deeper b a s i n s  and v o l c a n i c i s l a n d s  dominated by sedimentary and v o l c a n i c l a s t i c  a narrow western b a s i n and a much wider e a s t e r n b a s i n .  d e t r i t u s eroded from the P i n c h i g e a n t i c l i n e was p e r i o d i c a l l y  Clastic  funneled  through low p o i n t s i n t h e v o l c a n i c c h a i n , and accumulated i n t h e e a s t e r n as w e l l as western b a s i n .  Carbonate sediment accumulated i n shallow  waters  around v o l c a n i c i s l a n d s and the emergent P i n c h i g e a n t i c l i n e , and p e r i o d i c a l l y was t r a n s p o r t e d  i n t o t h e deeper marine b a s i n s by t u r b i d i t y c u r r e n t s .  Some  carbonate sediment i n the e a s t e r n b a s i n may have been d e r i v e d from the miog e o c l i n e t o the e a s t . D i f f e r e n t p a r t s o f t h e N i c o l a Group formed i n d i f f e r e n t t e c t o n i c settings.  The N i c o l a v o l c a n i c flows  and b r e c c i a s r e p r e s e n t  a Late  v o l c a n i c a r c complex which formed above an e a s t - d i p p i n g s u b d u c t i o n (Monger and o t h e r s ,  1972; Anderson, 1976; Davis and o t h e r s , 1978).  mudstones, v o l c a n i c l a s t i c s and minor flows  Triassic zone Coeval  accumulated i n a narrow f o r e - a r c  b a s i n west o f the a r c , and i n a broad back-arc b a s i n e a s t o f the a r c . b a c k - a r c b a s i n was a "trapped"  b a s i n formed by subsidence o f an o l d e r  e u g e o c l i n a l basement; no b a c k - a r c s p r e a d i n g P i n c h i g e a n t i c l i n e separated the west.  The  o c c u r r e d w i t h i n the b a s i n .  The  t h e f o r e a r c b a s i n from a deep ocean b a s i n t o  Although the P i n c h i g e a n t i c l i n e was composed i n p a r t o f o c e a n i c  sediments a c c r e t e d d u r i n g Late P a l e o z o i c s u b d u c t i o n , Late T r i a s s i c was caused by renewed s u b d u c t i o n  i t s r i s e d u r i n g the  and consequent a c c r e t i o n o f  a d d i t i o n a l sediments a t the toe o f t h e a c c r e t i o n a r y wedge. S i m i l a r t e c t o n i c elements can be r e c o g n i z e d Cordillera.  V o l c a n i c rocks  f a r t h e r south i n the  s i m i l a r t o the N i c o l a Group occur  on o r west  130  o f the Late T r i a s s i c c o n t i n e n t a l margin from n o r t h e r n B r i t i s h Columbia t o the S i e r r a Nevada o f C a l i f o r n i a  (Monger, 1975a; Monger and Church, 1977;  B u r c h f i e l and Davis, 1972, 1975; Schweickert,  1976).  In t h e southern  S i e r r a Nevada, t h e Late T r i a s s i c a r c developed on a c o n t i n e n t a l margin t r u n c a t e d by enigmatic P e r m o - T r i a s s i c s t r i k e - s l i p movements ( B u r c h f i e l and D a v i s , 1972).  F u r t h e r n o r t h , the Late P a l e o z o i c e u g e o c l i n a l t e r r a n e s form  the basement o f the a r c , which was s e p a r a t e d from the m i o g e o c l i n e by a deep, marine b a s i n . Speed  Remnants o f t h i s b a s i n have been r e c o g n i z e d i n Nevada by  (1978a and b ) .  Complexly deformed o c e a n i c rocks o f Late P a l e o z o i c  and younger age o c c u r west o f t h e v o l c a n i c b e l t , and p r o b a b l y i n c l u d e rocks a c c r e t e d d u r i n g Late P a l e o z o i c and Late T r i a s s i c t o E a r l y J u r a s s i c c y c l e s of subduction  (see Chapter I I ) .  S c a t t e r e d b l u e s c h i s t t e r r a n e s o c c u r w i t h i n t h i s o c e a n i c complex a l o n g the l e n g t h o f t h e C o r d i l l e r a . t h i s b e l t y i e l d remarkably  With a few e x c e p t i o n s , the b l u e s c h i s t s  c o n s i s t e n t K-Ar ages o f 214 t o 220 m.y.  1975a; Hotz and o t h e r s , 1977; P a t e r s o n and H a r a k a l , 1974).  from  (Monger,  By the r e v i s e d  t i m e - s c a l e o f Armstrong and McDowell (1974; Armstrong, 1978), the u p l i f t and c o o l i n g which these dates r e c o r d a r e c o e v a l w i t h L a t e T r i a s s i c a r c v o l c a n i s m . The b l u e s c h i s t s p r o b a b l y formed i n the deeper l e v e l s o f the Late P a l e o z o i c to E a r l y T r i a s s i c a c c r e t i o n a r y wedge.  T h e i r synchronous u p l i f t may r e c o r d  an i n t e r v a l o f very r a p i d s u b d u c t i o n a l o n g most o f the l e n g t h o f the a r c . Rapid a c c r e t i o n o f m a t e r i a l t o the wedge caused h i g h r a t e s o f u p l i f t , and the r e s u l t a n t complex motions w i t h i n the wedge ( S i l l i n g and Cowan, 1977) e l e v a t e d the b l u e s c h i s t s upward o v e r younger rocks t o the s u r f a c e .  This  model would e x p l a i n the u p l i f t o f the P i n c h i g e a n t i c l i n e , the appearance of d e t r i t u s d e r i v e d from i t w i t h i n the N i c o l a Group, and the f a c t t h a t the  131  b l u e s c h i s t s i n s e v e r a l areas o c c u r i n h i g h s t r u c t u r a l p o s i t i o n s near e a s t e r n margin o f the a c c r e t e d t e r r a n e , as p r e d i c t e d by the s t u d i e s o f S i l l i n g and Cowan  the  scale-model  (1977).  In B r i t i s h Columbia, the Cache Creek-Bridge  R i v e r assemblage i s  t y p i c a l l y s e p a r a t e d from the Upper T r i a s s i c a r c v o l c a n i c s by s t e e p zones such as the P i n c h i , Hozameen, and F r a s e r f a u l t zones. and movement h i s t o r i e s o f these f a u l t s are u n c e r t a i n .  The  They may  fault  significance have o r i g i n a t e d  as the t e c t o n i c c o n t a c t (upper s l o p e d i s c o n t i n u i t y o f K a r i g and Sharman,  1975)  s e p a r a t i n g the a c c r e t i o n a r y p r i s m from the P a l e o z o i c and younger a r c t e r r a n e t o the e a s t , but l a t e r movements have almost c e r t a i n l y o c c u r r e d on them as well. was  I f a s i g n i f i c a n t p o r t i o n o f the Cache Creek-Bridge  R i v e r assemblage  a c c r e t e d d u r i n g the Late P a l e o z o i c t o E a r l y T r i a s s i c , i t i s u n l i k e l y  t h a t any o f these f a u l t s r e p r e s e n t the t r a c e o f the L a t e J u r a s s i c s u b d u c t i o n zone, as suggested  Triassic-Early  f o r the Hozameen f a u l t by Anderson  (1976) . The  composition o f the Upper T r i a s s i c v o l c a n i c rocks i s not  o f simple c a l c - a l k a l i n e a r c s o f Andean o r Cascade t y p e .  typical  M a f i c l a v a s and  b r e c c i a s predominate over those o f i n t e r m e d i a t e c o m p o s i t i o n , and most o f the rocks are a l k a l i n e r a t h e r than c a l c - a l k a l i n e (1977) proposed  (Souther, 1977).  Paterson  t h a t the upper T r i a s s i c v o l c a n i c s i n B r i t i s h Columbia were  r e l a t e d p r i m a r i l y to t r a n s f o r m p l a t e motions r a t h e r than t o s u b d u c t i o n .  He  i d e n t i f i e d the P i n c h i f a u l t as a Late T r i a s s i c , r i g h t - l a t e r a l  transform  f a u l t c o n n e c t i n g s h o r t , east-west  In t h i s model,  t r e n d i n g s u b d u c t i o n zones.  the P i n c h i b l u e s c h i s t s were " l e a k e d " t o the s u r f a c e a l o n g the t r a n s f o r m fault.  Recent v o l c a n i c s s i m i l a r i n composition t o the T a k l a and N i c o l a  v o l c a n i c s are found i n s e v e r a l i s l a n d c h a i n s i n the southwest P a c i f i c  132  where present-day p l a t e motions are mainly s t r i k e - s l i p Carmichael, Turner, and Verhoogen, 1974, Considering  p.  542-544).  a l l along  s h o r t segments o f s u b d u c t i o n  N i c o l a - T a k l a v o l c a n i c s may  zones.  1977;  The  chemistry  probably  Davis and o t h e r s ,  of  1978).  again  arc volcanism  oblique  zone i t s e l f ,  or  arc  the  on  terrane;  Such s t r i k e - s l i p f a u l t s w i t h i n modern  a r c systems have been d e s c r i b e d by F i t c h Subduction and  the  Motion p a r a l l e l to  f a u l t zones w i t h i n o r between the a c c r e t i o n a r y wedge and  perhaps on the P i n c h i f a u l t i t s e l f .  and  transform  the r e s u l t o f  a r c c o u l d have been accomodated w i t h i n the s u b d u c t i o n steep  "leaky"  a c c u r a t e l y r e f l e c t a s t r i k e - s l i p component o f  p l a t e motion a t t h i s time, but t h i s was (Souther,  in  the c o n t i n e n t a l margin a t t h i s time, i t i s  u n l i k e l y t h a t they c o u l d have been produced s o l e l y by  subduction  1977;  the l a r g e volume o f Upper T r i a s s i c v o l c a n i c s erupted  B r i t i s h Columbia and  f a u l t s and  (Paterson,  (1972).  occurred  i n the E a r l y J u r a s s i c , but  through the Karnian  and  Norian,  i n B r i t i s h Columbia both the a r c  terrane  and b a c k - a r c b a s i n were t e c t o n i c a l l y d i s r u p t e d i n the E a r l i e s t J u r a s s i c by the  " I n k l i n i a n Orogeny."  Evidence f o r t h i s event i n c l u d e s a r e g i o n a l uncon-  f o r m i t y beneath Lower J u r a s s i c s t r a t a , commonly o f Sinemurian age  (Douglas  and o t h e r s ,  faulting  1970,  p. 440;  o f the v o l c a n i c a r c rocks ing  Campbell and  Tipper,  (Schau, 1970) ; and  1970); warping and  i n t r u s i o n and  o f p l u t o n s w i t h i n the v o l c a n i c a r c which y i e l d K-Ar  around 200  m.y.  (Campbell and T i p p e r ,  the w e s t e r l y - o v e r t u r n e d formed a t t h i s time  1970).  e r o s i o n a l unroof-  ages c l u s t e r i n g  In a d d i t i o n , I b e l i e v e t h a t  f o l d s w i t h i n the N i c o l a Group i n the study  (see f o l l o w i n g c h a p t e r s ) .  i n terms o f p l a t e t e c t o n i c s i s not o b v i o u s .  area  An e x p l a n a t i o n o f t h i s However, examination o f  s t r a t i g r a p h i c r e c o r d o f T e r t i a r y i s l a n d a r c s i n the western P a c i f i c ,  event the such  133  the Marianas  ( K a r i g , 1971; Tracey and o t h e r s , 1964), New Hebrides  and Warden, 1971), and F i j i  ( R i c k a r d , 1963, 1966; Ibbotson,  (Mitchell  1969) show t h a t  arc v o l c a n i s m occurs i n p u l s e s o f 10 t o 15 m.y. d u r a t i o n , punctuated by s h o r t p e r i o d s o f u p l i f t , b l o c k - f a u l t i n g , and u n r o o f i n g o f p l u t o n s .  These  i n t e r r u p t i o n s may mark c e s s a t i o n s o r changes i n r a t e o f s u b d u c t i o n , o r changes i n r e l a t i v e motion o f n e i g h b o r i n g p l a t e s , b u t c l e a r l y do not r e f l e c t major c o l l i s i o n a l events i n v o l v i n g t h e a r c i t s e l f .  The " I n k l i n i a n Orogeny"  may be a s i m i l a r event which a l s o i n v o l v e d f o l d i n g i n the back-arc r e g i o n .  134  CHAPTER IV.  INTRUSIVE ROCKS  PAUL PEAK STOCK (MAP-UNIT 7)  Field  Relations  This small, compositionally v a r i e d pluton occupies f l a n k s o f the r i d g e between Paul Peak and P e t e r Peak.  the saddle and  I t i s highly  elongate  (3.8 km l o n g and up t o 1.25 km w i d e ) , t r e n d i n g northwestward a t a s m a l l angle t o the s t r i k e o f the Upper T r i a s s i c rocks o f U n i t s 5 and 6 which i t intrudes. the  P l e i s t o c e n e d e p o s i t s cover  the northwest and southeast  ends o f  pluton. The  northeastern  margin appears t o be roughly  concordant w i t h the  l a y e r i n g i n U n i t 5, b u t the c o n t a c t i s nowhere exposed. c o n t a c t i s much more i r r e g u l a r , c u t t i n g a t h i g h angles i n c l u d i n g the c o n t a c t between U n i t s 5 and 6. adjacent  across l a y e r i n g ,  L o c a l l y , thin-bedded mudstones  t o the p l u t o n have been deformed d u r i n g i n t r u s i o n , and have anom-  alous a t t i t u d e s p a r a l l e l t o t h e i n t r u s i v e The  The southwestern  p l u t o n i s c o n c e n t r i c a l l y zoned  contact. ( F i g . 36), although  the zoning i s  t r u n c a t e d by the exposed c o n t a c t s , and c o n t i n u i t y o f a l l the zones a t depth cannot be assumed.  Two outcrops  o f o l i v i n e c l i n o p y r o x e n i t e are i n f e r r e d t o  form p a r t s o f a narrow band which o c c u p i e s band i s completely  t h e core o f the p l u t o n .  This  surrounded by leucogabbro and d i o r i t e , which a r e suc-  ceeded outward t o the e a s t and west by hornblende gabbro and d i o r i t e . blende-quartz  monzodiorite  zones a t the s o u t h e a s t  Horn-  and f i n a l l y hornblende g r a n i t e form i s o l a t e d  end o f the p l u t o n .  The nature  o f t h e zone c o n t a c t s  c o u l d not be determined i n t h e f i e l d owing t o poor exposure.  However,  TYPE OF COMPOSITIONAL DATA  0.5 km  •  Field description  •  Hand specimen  *  Thin-section  | Q | Quaternary  deposits  LOWER JURASSIC PAUL PEAK STOCK Hornblende granite Hornblende quartz monzodiorite Hornblende gabbro and diorite Leucogabbro and diorite  vr;tV*V-i. yJ IIIK-l95 1  Olivine clinopyroxenite  T  t  :AVtV,v-.  UPPER TRIASSIC  /--'.t 1 1 1 • -t t IT  NICOLA GROUP 6b  Mafic volcanic rocks Mudstone, lithic sandstone, andesitic pyroclastics Thin-bedded mudstone  MK-91 »  v  "v7'-''-r>'->''.--"-~'inK-ipr.-4> i  MK  ..•6b  • WiiK-iql' ** * • - #  * - * ' * * * » - "\ '^"•'•••".•; ;/ ;  Q  .• Q  Fig.  36.  G e o l o g i c map o f t h e P a u l Peak Stock.  oo  136  t e x t u r a l s i m i l a r i t i e s w i t h i n the s e r i e s l e c o g a b b r o - g r a n i t e suggests  these  contacts are gradational. Most o f t h e p l u t o n i c r o c k s a r e medium-grained and e q u i g r a n u l a r . outcrops of  a r e massive,  l a c k i n g primary  v e r y c o a r s e - g r a i n e d hornblende  a few p l a c e s , and p i n k potassium quartz monzodiorite  igneous  layering or f o l i a t i o n .  c u t t h e hornblende  The Veins  gabbro and d i o r i t e i n  f e l d s p a r v e i n s a r e common i n t h e hornblende-  and hornblende  granite.  Petrography  Table VIII gives the v i s u a l l y Peak Stock. T a b l e IX.  e s t i m a t e d modes o f samples from t h e P a u l  The a n o r t h i t e c o n t e n t s o f p l a g i o c l a s e f e l d s p a r s a r e g i v e n i n The rock c l a s s i f i c a t i o n used  i s t h a t g i v e n by t h e IUGS Sub-  commission on t h e S y s t e m a t i c s o f Igneous Rocks  ( S t r e c k e i s e n , 1974).  Olivine Clinopyroxenite O l i v i n e c l i n o p y r o x e n i t e i s composed o f 70% c l i n o p y r o x e n e ( d i o p s i d e or  a u g i t e ) and 30% o l i v i n e .  grains i n t e r s t i t i a l pyroxenes. of  The o l i v i n e o c c u r s as aggregates  t o and p a r t i a l l y  s u r r o u n d i n g s u b h e d r a l t o rounded  P l a g i o c l a s e i s l a c k i n g i n t h e samples examined.  interstitial  by hornblende  o f anhedral  b i o t i t e a r e p r e s e n t , and minor replacement  Trace amounts o f clinopyroxene  has o c c u r r e d .  Leucogabbro and D i o r i t e These a r e gray e q u i g r a n u l a r r o c k s composed l a r g e l y o f s u b h e d r a l , zoned p l a g i o c l a s e and c l i n o p y r o x e n e . from leucogabbro ing  ( p l a g i o c l a s e a v e r a g i n g >An ) t o d i o r i t e  <An^Q) w i t h o u t  tuents.  There appears t o be a continuous  50  gradation  (plagioclase  any s i g n i f i c a n t change i n t h e p r o p o r t i o n o f m a f i c  I n t e r p e n e t r a t i n g g r a i n c o n t a c t s between some p l a g i o c l a s e and  averagconsti-  TABLE V I I I .  Sample  Lithology  VISUALLY ESTIMATED MODES OF PLUTONIC ROCKS FROM PAUL PEAK STOCK  MK-99b  MK-195  MK-98  MK-91  Olivine Clinopyroxenite  Leucogabbro  Diorite  Hornblende Diorite  68%  Plagioclase  —  73%  78%  Potassium feldspar  —  2  3  Tr  Quartz  —  —  —  —  Clinopyroxene  72%  20  12  9  Hornblende  Tr  —  —  20  Biotite  Tr  3  6  3  Olivine  28  2  Tr  —  Sample  Lithology  MK-101  MK-194  MK-104  MK-103  Hornblende Gabbro  Hornblende Gabbro  Quartz Monzodiorite  Hornblende Granite  Plagioclase  65%  Potassium feldspar  —  Quartz Clinopyroxene  60%  54%  35%  1  28  42  1  3  12  20  2  15  —  —  Hornblende  30  8  Biotite  Tr  13  —  —  Olivine  —  —  —  —  Tr = Trace  6  = Absent  3  138  TABLE IX.  ANORTHITE CONTENT OF PLAGIOCLASE PAUL PEAK STOCK  Core  Sample  MK-195  Rim  An  5 1  ,  An  5 1 >  An  5 8  ,  An  6 8  An  MK-98  FELDSPARS FROM  ,  6 9  A n i » Ani+g, t2  Ani+Q,  An^g,  An^g  A n  ^50  ^50  MK-91  Ani^,  An  MK-101  An  An g,  MK-194  Small,  7 6  ,  3 5  5 0  7  a p p a r e n t l y unzoned An  3tt  , An  4 0  , An  5 7  ,  crystals:  An  S 2  Compositions determined i n t h i n - s e c t i o n p r i m a r i l y by t h e C a r l s b a d - a l b i t e method.  139  c l i n o p y r o x e n e g r a i n s i n d i c a t e simultaneous as s k e l e t a l p o i k i l i t i c grains.  g r a i n s , and potassium  Biotite  f e l d s p a r as s m a l l  occurs  interstitial  T y p i c a l t e x t u r e s are shown i n F i g . 37.  P l a g i o c l a s e shows complex zoning. o s c i l l a t o r y zones was normally Ani 2-  crystallization.  zoned rim.  Commonly a l a r g e c o r e w i t h numerous  p a r t i a l l y r e s o r b e d , and surrounded Average compositions  by a s i n g l e  thick,  f o r the cores range from Ang^  W i t h i n a s i n g l e sample the a n o r t h i t e component o f the cores may  +  up to 20%.  Average r i m compositions  were determined  on o n l y two  to vary  crystals i n  one sample, and were both An35. S e v e r a l samples c o n t a i n up to 2% o l i v i n e , almost always i n rounded, anhedral g r a i n s which were p r o b a b l y p a r t l y r e s o r b e d by r e a c t i o n w i t h the The o l i v i n e g r a i n s are t y p i c a l l y f r a c t u r e d , and p a r t i a l l y a l t e r e d t o t i n e o r reddish-brown " i d d i n g s i t e " and magnetite. coronas  melt.  serpen-  Complex r e a c t i o n rims o r  o c c u r between o l i v i n e and p l a g i o c l a s e , forming a s e r i e s o f c o n c e n t r i c  s h e l l s around the o l i v i n e s . c o l o r l e s s hypersthene, green b i o t i t e .  The i n n e r s h e l l c o n s i s t s o f b l o c k y c r y s t a l s o f  and the second one o f r a d i a l l y or t a n g e n t i a l l y o r i e n t e d  In most examples t h e r e i s a t h i r d s h e l l o f r a d i a l l y  wormy a c i c u l a r c r y s t a l s o f an u n i d e n t i f i e d m i n e r a l . l e s s , has  This mineral i s color-  i n c l i n e d e x t i n c t i o n , moderate t o h i g h r e l i e f ,  amphibole o r c l i n o p y r o x e n e . t i n u o u s , but the i n n e r one  E i t h e r o f the two i s always p r e s e n t .  arranged,  and perhaps i s an  o u t e r s h e l l s may  be d i s c o n -  Replacement o f o l i v i n e  has  taken p l a c e p r e f e r e n t i a l l y a l o n g f r a c t u r e s , l e a d i n g t o the f o r m a t i o n o f very complex coronas.  In some cases, the o l i v i n e has been completely  by a g r a n u l a r aggregate core o f  o f hypersthene  and magnetite,  replaced  usually leaving a  "iddingsite."  P r e s e r v a t i o n o f the d e l i c a t e corona t e x t u r e s i n d i c a t e s t h a t they formed  140  Fig,  37. Photomicrograph o f leucogabbro, MK-98. Subhedral p l a g i o c l a s e (PI) and c l i n o p y r o x e n e (C) w i t h i n t e r s t i t i a l b i o t i t e (B) and potassium f e l d s p a r (K). T h i n - s e c t i o n , X 40.  141  a f t e r most movement between c r y s t a l s w i t h i n the p l u t o n had ceased. such coronas might  Although  form d u r i n g l a t e r h i g h grade metamorphism o f p l u t o n i c  r o c k s , i n t h i s case post-emplacement metamorphism i s l i m i t e d t o the p r e h n i t e p u m p e l l y i t e f a c i e s , w i t h o n l y minimal e f f e c t s on the p l u t o n i c r o c k s (see Chapter V ) .  Thus the f o r m a t i o n o f the h i g h temperature phases which make  up the coronas must have taken p l a c e by a r e t r o g r a d e r e a c t i o n between p l a g i o c l a s e and o l i v i n e d u r i n g c o o l i n g o f the p l u t o n from i t s o r i g i n a l magmatic temperatures  ( G r i f f i n and H e i e r , 1973; S a p o u n t z i s , 1975).  Hornblende Hornblende  gabbro  Gabbro and D i o r i t e  and d i o r i t e a r e t e x t u r a l l y s i m i l a r t o the r o c k s  j u s t d e s c r i b e d , b u t c o n t a i n up t o 30% hornblende. pyroxene  P l a g i o c l a s e and c l i n o -  a r e s u b h e d r a l , w h i l e b i o t i t e , q u a r t z , and p o t a s s i u m f e l d s p a r show  i n t e r s t i t i a l textures.  P l a g i o c l a s e compositions range from An 5 t o A^i,., 8  and much o f i t i s p a r t l y a l t e r e d t o s e r i c i t e .  This a l t e r a t i o n i s nearly  absent i n the d i o r i t i c r o c k s l a c k i n g hornblende. Hornblende green hornblende  o c c u r s i n two d i f f e r e n t forms w i t h i n these r o c k s .  Pale  (or perhaps a c t i n o l i t e ) r e p l a c e s c l i n o p y r o x e n e m a r g i n a l l y  and a l o n g c l e a v a g e s , and more s t r o n g l y c o l o r e d green hornblende o c c u r s as overgrowths fill  around the a l t e r e d pyroxenes  ( F i g . 38).  These overgrowths  often  i n t e r s t i c e s between p l a g i o c l a s e l a t h s , and i n one sample form v e r y  large p o i k i l i t i c  g r a i n s , s u g g e s t i n g c r y s t a l l i z a t i o n from a l a t e - s t a g e m e l t  or f l u i d w i t h which c l i n o p y r o x e n e was no l o n g e r i n e q u i l i b r i u m .  Inter-  growths o f hornblende w i t h b i o t i t e suggest t h a t some replacement o f b i o t i t e has a l s o taken p l a c e . R e a c t i o n coronas around o l i v i n e g r a i n s i n t h e hornblende gabbro cummingtonite  i n p l a c e o f hypersthene, s u g g e s t i n g t h a t the coronas  contain  formed  Fig.  38. Photomicrograph o f hornblende gabbro, MK-195. Single l a r g e p o i k i l i t i c hornblende (H) surrounds c l i n o p y r o x e n e ( C ) , a l t e r e d p l a g i o c l a s e ( P i ) , and magnetite (Mt). Thin-section, p l a n e l i g h t , X 40.  Fig.  39. Photomicrograph o f hornblende g r a n i t e , MK-104. Subhedral zoned p l a g i o c l a s e (Pi) and e u h e d r a l hornblende (H) and sphene (S) surrounded by i n t e r s t i t i a l q u a r t z (Q) and p o i k i l i t i c p o t a s sium f e l d s p a r (K). T h i n - s e c t i o n , c r o s s e d n i c o l s , X 40.  143  p r i o r t o o r d u r i n g the episode o f hornblende  replacement  and growth.  Quartz M o n z o d i o r i t e and Hornblende G r a n i t e Quartz m o n z o d i o r i t e  and hornblende  g r a n i t e a r e m i n e r a l o g i c a l l y and  t e x t u r a l l y s i m i l a r t o each o t h e r , d i f f e r i n g o n l y i n t h e i r r e l a t i v e t i o n o f p l a g i o c l a s e t o potassium  feldspar.  P l a g i o c l a s e and hornblende a r e  e u h e d r a l t o s u b h e d r a l , and a r e commonly zoned. o s c i l l a t o r y z o n i n g surrounded for  propor-  P l a g i o c l a s e has c o r e s w i t h  by normally zoned r i m s .  Average  compositions  the cores range from An^^ t o A n 5 , and f o r t h e rims from An£g t o An282  Quartz o c c u r s as aggregates c l a s e , w h i l e potassium  o f anhedral c r y s t a l s p a r t i a l l y e n c l o s i n g p l a g i o -  f e l d s p a r o f t e n forms l a r g e p o i k i l i t i c c r y s t a l s  rounding a l l o t h e r phases  ( F i g . 39).  Both potassium  sur-  f e l d s p a r and p l a g i o c l a s e  are m i l d l y a l t e r e d t o s e r i c i t e .  Petrogenesis  O r i g i n o f the Rock S e r i e s Leucogabbro t o G r a n i t e The o v e r a l l s i m i l a r i t y i n t e x t u r e o f rocks w i t h i n t h i s s e r i e s , w i t h the p r o g r e s s i v e v a r i a t i o n i n modal mineralogy zone, suggests  t h a t t h i s may be a continuous  formed by f r a c t i o n a l c r y s t a l l i z a t i o n .  coupled  and t e x t u r e from zone t o  d i f f e r e n t i a t i o n s e r i e s which  P l a g i o c l a s e i n a l l the rocks i s  s u b h e d r a l t o e u h e d r a l , and commonly has a n o r m a l l y zoned r i m s u r r o u n d i n g a p a r t i a l l y r e s o r b e d core w i t h numerous o s c i l l a t o r y zones.  Both core and r i m  compositions become p r o g r e s s i v e l y more s o d i c i n the more f e l s i c r o c k s . i n n e r leucogabbro  and d i o r i t e c o n t a i n c l i n o p y r o x e n e as the primary  mafic  phase, w h i l e the m o n z o d i o r i t e and g r a n i t e c o n t a i n o n l y hornblende. l i e the hornblende  The  In between  gabbro and d i o r i t e i n which e a r l y c l i n o p y r o x e n e became  u n s t a b l e w i t h r e s p e c t t o the i n t e r s t i t i a l melt, and was r e p l a c e d and  144  overgrown by hornblende. These r e l a t i o n s h i p s suggest t h a t t h e g a b b r o i c by s e g r e g a t i o n  and d i o r i t i c rocks  o f e a r l y p l a g i o c l a s e and c l i n o p y r o x e n e  melt i n which hornblende r a t h e r than c l i n o p y r o x e n e phase as the melt c o o l e d and P  increased.  formed  from a l a r g e r body o f  became the s t a b l e m a f i c  This melt eventually  crystal-  H2O  l i z e d t o form the h o r n b l e n d e - q u a r t z m o n z o d i o r i t e and hornblende g r a n i t e . was  It  n o t p o s s i b l e t o determine from t h e f i e l d r e l a t i o n s h i p s whether t h e c l i n o -  pyroxene and h o r n b l e n d e - b e a r i n g p o r t i o n s o f t h e i n t r u s i o n were emplaced s e p a r a t e l y o r as p a r t o f a s i n g l e mass.  However, t e x t u r e s w i t h i n the h o r n -  blende gabbro and d i o r i t e demonstrate r e a c t i o n between t h e two p o r t i o n s a s i g n i f i c a n t amount o f i n t e r s t i t i a l m e l t remained i n t h e d i o r i t i c suggesting The zonation  rocks,  emplacement as a s i n g l e coherent magma body. mechanism o f c r y s t a l s e g r e g a t i o n  are problematic.  Murray  and o r i g i n o f t h e crude c o n c e n t r i c  (1972) and James (1971) invoked flowage  d i f f e r e n t i a t i o n as a model t o e x p l a i n the c o n c e n t r i c z o n a t i o n type zoned u l t r a m a f i c complexes.  i n Alaskan-  T h i s mechanism depends upon t h e tendency  o f suspended p a r t i c l e s w i t h i n a f l o w i n g f l u i d t o move away from the and  while  walls  toward t h e r e g i o n o f l e a s t shear s t r e s s i n t h e m e d i a l o r a x i a l p o r t i o n  o f the c o n d u i t .  In t h i s way, e a r l y c r y s t a l s c o u l d be c o n c e n t r a t e d  c e n t e r o f a magma body f l o w i n g through a v e r t i c a l c y l i n d r i c a l producing Smith  a c o n c e n t r i c a l l y zoned i n t r u s i o n .  i n the  conduit,  But w h i l e B h a t t a c h a r j i and  (1964) demonstrated t h a t t h i s mechanism can o p e r a t e i n s m a l l models,  Barriere  (1976) has shown t h e o r e t i c a l l y t h a t t h e inward movement should  decrease r a p i d l y away from t h e w a l l s o f t h e c o n d u i t . flowage d i f f e r e n t i a t i o n c o u l d n o t e x p l a i n zoning about 100 m i n diameter.  He c o n c l u d e d t h a t  i n i n t r u s i o n s l a r g e r than  145  Textures o f the g a b b r o i c and d i o r i t i c rocks suggest t h a t these rocks may  be cumulates o f p l a g i o c l a s e and c l i n o p y r o x e n e formed by  crystal settling. and hornblende  Intercumulus  phases are b i o t i t e , q u a r t z , a l k a l i  (excluding that replacing clinopyroxene).  have i n t e r s t i t i a l o r p o i k i l i t i c  gravitative feldspar,  These m i n e r a l s  t e x t u r e s , and make up 6% t o about 20%  the r o c k s , g i v i n g a crude minimum e s t i m a t e o f the amount o f  of  interstitial  melt p r e s e n t w i t h i n the cumulates p r i o r t o f i n a l c r y s t a l l i z a t i o n .  (The  n o r m a l l y zoned o u t e r rims o f the p l a g i o c l a s e c r y s t a l s p r o b a b l y a l s o formed from the intercumulus  l i q u i d , but t h i s volume i s n o t e a s i l y measured o r  estimated). F r a c t i o n a l c r y s t a l l i z a t i o n and c r y s t a l s e t t l i n g alone cannot e x p l a i n the c o m p o s i t i o n a l z o n i n g w i t h i n the p l u t o n , s i n c e these p r o c e s s e s would form a s t r a t i f o r m p l u t o n .  I f these p r o c e s s e s d i d produce the o r i g i n a l  c o m p o s i t i o n a l v a r i a t i o n , then upward r e m o b i l i z a t i o n o f the cumulates  and  the remaining melt must have taken p l a c e d u r i n g f i n a l emplacement o f the pluton.  Movement o f the cumulates would have been f a c i l i t a t e d by the  s t i t i a l melt, which would a c t as a l u b r i c a n t . r e a c t i o n coronas were a f f e c t e d by hornblende cumulates p r o b a b l y ceased b e f o r e hornblende i n the remaining  inter-  Since o l i v i n e - p l a g i o c l a s e a l t e r a t i o n , movement o f the  became the s t a b l e mafic phase  melt.  Upward i n t r u s i o n o f the cumulates and melt may r e g i o n a l compressive  s t r e s s e s which a l s o produced  the N i c o l a Group p r i o r to i n t r u s i o n .  have r e s u l t e d  from  the l a r g e s c a l e f o l d s i n  T h i s would account  o f the p l u t o n a t o n l y a s m a l l angle t o the f o l d t r e n d s .  f o r the e l o n g a t i o n Diapiric  z a t i o n o f s t r a t i f o r m cumulates d u r i n g r e g i o n a l f o l d i n g was  remobili-  also postulated  by F i n d l a y (1969) t o e x p l a i n the geometry o f the Tulameen u l t r a m a f i c - g a b b r o  146  complex, which i n t r u d e s t h e N i c o l a Group about 150 km south o f Kamloops, and i s probably  about t h e same age as t h e P a u l Peak Stock.  O r i g i n o f t h e U l t r a m a f i c Rocks The  o r i g i n o f t h e o l i v i n e c l i n o p y r o x e n i t e which crops o u t i n t h e  core o f t h e Paul Peak Stock i s u n c e r t a i n . are d i s c u s s e d , b u t l i t t l e d i r e c t evidence  Several possible interpretations e i t h e r supports  o r r e f u t e s any o f  them. The  o l i v i n e c l i n o p y r o x e n i t e c o u l d have formed as a p y r o x e n e - o l i v i n e  cumulate a t the bottom o f t h e magma chamber, b e f o r e p l a g i o c l a s e began t o c r y s t a l l i z e t o form t h e s u r r o u n d i n g mafic  gabbroic  and d i o r i t i c r o c k s .  cumulates would have been deformed and i n t r u d e d a l o n g w i t h  o f t h e cumulates. resorbed  the r e s t  The presence o f s m a l l amounts o f rounded, p r o b a b l y  o l i v i n e i n t h e gabbro and d i o r i t e i s c o n s i s t e n t w i t h  The p y r o x e n i t e  c o u l d a l s o have formed as a s e p a r a t e  e a r l i e r o r l a t e r than t h e gabbro. necessary  The u l t r a -  t h i s model.  intrusion, either  S i n c e temperatures i n excess o f 1300° a r e  f o r p y r o x e n i t e melts t o e x i s t a t low p r e s s u r e s  the p y r o x e n i t e would p r o b a b l y  partly  (Presnall,  have been emplaced as a l a r g e l y  1966),  crystalline  mush, perhaps formed by f r a c t i o n a l c r y s t a l l i z a t i o n from a b a s i c magma. O l i v i n e c l i n o p y r o x e n i t e o f s i m i l a r modal p r o p o r t i o n s t o t h a t i n t h e Paul Peak Stock i s a major c o n s t i t u e n t o f zoned, Alaskan-type u l t r a m a f i c complexes.  These complexes u s u a l l y c o n s i s t o f d u n i t e , o l i v i n e  clinopyroxen-  i t e , magnetite c l i n o p y r o x e n i t e , and hornblende-magnetite c l i n o p y r o x e n i t e i n a c r u d e l y c o n c e n t r i c z o n a l p a t t e r n , w i t h more o l i v i n e - r i c h r o c k s the c e n t e r .  The zones a r e commonly d i s c o n t i n u o u s  toward  i n map view, and one o r  more rock types may be absent from e i t h e r end o f t h e s e r i e s , b u t t h e i r order i s u s u a l l y maintained.  Orthopyroxene and p l a g i o c l a s e a r e absent from  147  the u l t r a m a f i c r o c k s , which almost always i n t r u d e g a b b r o i c t o d i o r i t i c rocks o f v a r y i n g k i n d s . I suggest t h a t t h e P a u l Peak Stock i s such a zoned complex, although o n l y one u l t r a m a f i c rock type i s p r e s e n t .  F i n d l a y (1969) reached t h e same  c o n c l u s i o n f o r t h e Tulameen complex, where t h e complete s u i t e o f u l t r a m a f i c rocks from d u n i t e t o hornblende  clinopyroxenite i s present.  A major  p e t r o l o g i c problem c o n c e r n i n g these complexes i s t h e r e l a t i o n s h i p between the u l t r a m a f i c rocks and t h e s u r r o u n d i n g g a b b r o i c r o c k s .  T h e i r almost  i n v a r i a b l e s p a t i a l association implies that t h e i r r e l a t i o n s h i p i s not accidental.  However, t h e g a b b r o i c r o c k s may be e i t h e r  (tholeiitic)  as i n A l a s k a , o r u n d e r s a t u r a t e d and a l k a l i c , as i n t h e Tulameen  complex.  silica-saturated  T h o l e i i t i c and a l k a l i n e l i q u i d s cannot be d e r i v e d one from t h e  o t h e r by simple c r y s t a l f r a c t i o n a t i o n a t t h e low p r e s s u r e s which would p r e v a i l d u r i n g emplacement o f these complexes 1971,  p. 190-208).  (Yoder and T i l l e y ,  1962; W y l l i e ,  T h e r e f o r e i t i s d i f f i c u l t t o see how both s a t u r a t e d and  u n d e r s a t u r a t e d gabbros c o u l d be d e r i v e d from a s i n g l e p a r e n t melt type which g i v e s r i s e t o such a c o n s i s t e n t sequence o f u l t r a m a f i c d i f f e r e n t i a t e s . Irvine  (1973, 1974) proposed  t h a t t h e g a b b r o i c and u l t r a m a f i c rocks  o f zoned complexes r e s u l t from i n t r u s i o n o f s u c c e s s i v e magmas i n t h e f e e d e r pipes o f volcanoes.  In the Duke I s l a n d complex i n s o u t h e a s t e r n A l a s k a , t h e  u l t r a m a f i c rocks a r e c l e a r l y cumulates formed by f r a c t i o n a l and c r y s t a l s e t t l i n g , and I r v i n e suggests u n d e r s a t u r a t e d mafic magma.  crystallization  t h a t t h e p a r e n t melt was a s i l i c a -  The c o n c e n t r i c z o n a t i o n r e s u l t s from  i n t r u s i o n o f t h e s t r a t i f o r m mass o f cumulates,  diapiric  t h e same mechanism o u t l i n e d  above f o r t h e g a b b r o i c rocks o f t h e Paul Peak Stock.  The r e s i d u a l melt may  have been vented t o t h e s u r f a c e t o form mafic a u g i t e porphyry  volcanics,  148  which i n s o u t h e a s t e r n A l a s k a o c c u r i n the same r e g i o n as the zoned complexes, and a r e approximately a u g i t e porphyry  c o e v a l w i t h them ( C r e t a c e o u s ) .  Significantly,  similar  v o l c a n i c s o c c u r i n the Upper T r i a s s i c and Lower J u r a s s i c i n  B r i t i s h Columbia, approximately  c o e v a l w i t h t h e emplacement o f t h e P a u l  Peak Stock and the Tulameen complex.  A p o s s i b l e g e n e t i c l i n k between the  Tulameen complex and t h e N i c o l a v o l c a n i c s was f i r s t suggested by F i n d l a y (1969). Comparison o f the P a u l Peak Stock w i t h zoned m a f i c - u l t r a m a f i c complexes thus suggests  t h a t t h e p y r o x e n i t e core o f the p l u t o n formed as a s e p a r a t e ,  l a t e r i n t r u s i o n o f c r y s t a l mush d e r i v e d by c r y s t a l f r a c t i o n a t i o n from a m a f i c , p o s s i b l y a l k a l i n e melt, and may have been g e n e t i c a l l y r e l a t e d t o Nicola  Age  volcanism.  and Regional  Correlation  The P a u l Peak Stock i n t r u d e s deformed Upper T r i a s s i c t a r y and v o l c a n i c rocks o f t h e N i c o l a Group.  (Karnian)  sedimen-  Major d e f o r m a t i o n o f the  T r i a s s i c rocks predates o r was synchronous w i t h emplacement o f the s t o c k . L o c a l s t r a t i g r a p h i c evidence does n o t p l a c e a c l o s e upper l i m i t on t h e age of  i n t r u s i o n ; the o l d e s t d e p o s i t s o v e r l y i n g the p l u t o n a r e P l e i s t o c e n e t o  Recent l a c u s t r i n e s i l t s  and a l l u v i a l f a n d e p o s i t s .  G r a n i t i c p l u t o n i s m i n the c e n t r a l and e a s t e r n Canadian C o r d i l l e r a has r e c e n t l y been summarized by G a b r i e l s e and Reesor (1974).  They were a b l e t o  d i s t i n g u i s h s e v e r a l groups o f p l u t o n i c rocks based on age, c o m p o s i t i o n , and tectonic setting.  The c o m p o s i t i o n , s e t t i n g , and i n f e r r e d p e t r o g e n e s i s o f  the Paul Peak Stock suggest c o r r e l a t i o n w i t h the Late T r i a s s i c t o E a r l y J u r a s s i c p l u t o n i c s u i t e , a l s o r e f e r r e d t o as the 200 m.y. p l u t o n i c  suite  149  by Campbell and T i p p e r (1970).  T h i s s u i t e i n c l u d e s numerous l a r g e g r a n i t i c  b o d i e s and many s m a l l s t o c k s and p l u g s .  Most o f these p l u t o n s i n t r u d e the  Upper T r i a s s i c v o l c a n i c rocks of the Quesnel range from 193  t o 215 m.y.,  trough.  c l u s t e r i n g between 197  K-Ar  m i n e r a l ages  and 206 m.y.  The  Iron  Mask B a t h o l i t h , the n e a r e s t p l u t o n o f t h i s group t o the study a r e a , i n t r u d e s the v o l c a n i c f a c i e s o f the N i c o l a Group 5 km The  southwest o f Kamloops.  l a r g e r p l u t o n s o f t h i s group (Guichon, Thuya, Takomkane) are  i n a n t l y g r a n o d i o r i t e i n c o m p o s i t i o n , b u t range from q u a r t z d i o r i t e o r to q u a r t z monzonite.  domdiorite  In many t h e r e i s a r e l a t i v e l y m a f i c border phase, w i t h  p r o g r e s s i v e l y younger and more f e l s i c phases toward the c e n t e r o f the p l u t o n . The s m a l l e r b o d i e s  (Copper Mountain, I r o n Mask) are a l k a l i n e , composed o f  d i o r i t e , monzonite, and s y e n i t e .  O f t e n these are a l s o s t r o n g l y zoned, w i t h  gabbro or p y r o x e n i t e margins and s y e n i t i c c o r e s . group o f zoned Alaskan-type  F i n a l l y , there i s a small  m a f i c - u l t r a m a f i c b o d i e s , i n c l u d i n g the Tulameen  complex, probably the P a u l Peak Stock, and a group d e s c r i b e d by I r v i n e from n o r t h c e n t r a l B r i t i s h Columbia. be d e s c r i b e d from the Quesnel from 155 complex.  to 164 m.y.  trough.  Many such b o d i e s p r o b a b l y remain t o A few d i s c o r d a n t K-Ar  f o r the n o r t h e r n b o d i e s , and 186 m.y.  ages range  f o r the Tulameen  However, the a s s o c i a t i o n o f these p l u t o n s w i t h Upper T r i a s s i c  v o l c a n i c s , and s t r u c t u r a l evidence a t Tulameen, suggests contemporaneous w i t h the r e s t o f the 200 m.y. The  (1976)  plutonic  t h a t they may  be  suite.  l o c a t i o n o f many o f the p l u t o n s c o i n c i d e s w i t h the t h i c k e s t accum-  u l a t i o n s o f Upper T r i a s s i c v o l c a n i c flows and b r e c c i a s . g e n e r a l correspondence  T h i s f a c t , p l u s the  i n composition between the a l k a l i n e s t o c k s and  m a f i c , a l k a l i n e v o l c a n i c s , has  the  l e d many authors t o the c o n c l u s i o n t h a t both  are d e r i v e d from the same magma, and the p l u t o n s mark the l o c a t i o n s o f  former  150  volcanic centers.  However, the p l u t o n s reached  t h e i r f i n a l l e v e l o f emplace-  ment a f t e r , o r d u r i n g l a t e r stages o f , an episode o f d e f o r m a t i o n which formed v a r i a b l e but g e n e r a l l y n o r t h t o n o r t h w e s t - t r e n d i n g g e n t l e warps and s t e e p f a u l t s w i t h i n the v o l c a n i c sequence 1969;  Schau, 1970).  The  (Wheeler and o t h e r s , 1972;  Findlay,  g e n e r a l concordance o f the l a r g e b a t h o l i t h s  some s m a l l e r p l u t o n s w i t h r e g i o n a l f a u l t and f o l d t r e n d s , and the  and  internal  s t r u c t u r e and i n f e r r e d emplacement mechanism o f i n t r u s i o n s such as the T u l a meen complex suggest t h a t i n t r u s i o n accompanied r e g i o n a l deformation. b e l i e v e t h i s same episode o f d e f o r m a t i o n produced  the  I  northwest-trending  f o l d s which a f f e c t the K a r n i a n rocks o f the N i c o l a Group i n the study and which are c u t by the P a u l Peak Stock.  U p l i f t and e r o s i o n f o l l o w e d  r a p i d l y a f t e r i n t r u s i o n , f o r c l a s t s d e r i v e d from the 200 m.y. common i n Lower J u r a s s i c conglomerates (Campbell  area,  which are as o l d as  p l u t o n s are  Sinemurian  and T i p p e r , 1971).  G r a n i t i c c l a s t s are found s p o r a d i c a l l y i n v o l c a n i c b r e c c i a s mapped as N i c o l a Group southwest o f Kamloops  (Northcote, 1974;  Schau, 1970).  North-  c o t e has i n f e r r e d from t h i s evidence t h a t i n t r u s i o n o f the I r o n Mask bathol i t h was  c o e v a l w i t h N i c o l a v o l c a n i s m , and t h a t the p l u t o n was  and c a n n a b a l i z e d w h i l e N i c o l a v o l c a n i s m c o n t i n u e d . s i s t e n t w i t h K-Ar  con  A suggested  a v e r a g i n g 200  m.y.;  i f the T r i a s s i c - J u r a s s i c boundary  i s taken a t the w i d e l y accepted age o f 195 H i n t e , 1976).  T h i s c o n c l u s i o n i s con-  ages f o r the p l u t o n (190 t o 205 m.y.,  N o r t h c o t e , p e r s o n a l communication, 1976)  unroofed  t o 200 m.y.  (Lambert, 1971;  van  r e v i s i o n o f t h i s boundary by Armstrong and Besan-  (1970) and Armstrong and McDowell (1974) would push i t back t o 208  210 m.y.,  i n which case the 200 m.y.  J u r a s s i c i n age.  p l u t o n i c s u i t e would be  or  earliest  T h i s i s c o n s i s t e n t w i t h the c o n c l u s i o n o f Campbell  and  151  Tipper  (1970) t h a t p l u t o n i s m accompanied u p l i f t and e r o s i o n  the T r i a s s i c , ending marine d e p o s i t i o n has  o f the N i c o l a  been r e f e r r e d t o as the I n k l i n i a n Orogeny  a t the c l o s e o f  Group.  This  episode  (Douglas and o t h e r s , 1970,  p. 440), and i t s e f f e c t s a r e widespread i n the Intermontane b e l t . R e c o n c i l i a t i o n o f N o r t h c o t e ' s s t r a t i g r a p h i c evidence f o r the time o f u n r o o f i n g w i t h the r e v i s e d  radiometric  age f o r the p l u t o n may be p o s s i b l e .  North o f Kamloops, i n Bonaparte Lake and Quesnel Lake map-area, Campbell and Tipper  (1970, 1971) have mapped a Lower t o Middle J u r a s s i c v o l c a n i c and  v o l c a n i c l a s t i c u n i t which i s l i t h o l o g i c a l l y i n d i s t i n g u i s h a b l e the N i c o l a  Group, except f o r the presence a t i t s base o f a coarse conglom-  erate containing 200  from p a r t s o f  c l a s t s o f the N i c o l a and "Cache Creek" Groups, and o f the  m.y. i n t r u s i o n s .  i n southern N i c o l a  J u r a s s i c rocks a r e a l s o i n c l u d e d  and i n P r i n c e t o n map-areas (Preto,  i n the N i c o l a 1977).  Group  F o s s i l s are  sparse both i n the J u r a s s i c u n i t and i n t h e N i c o l a Group, and the p l u t o n i c bearing breccias  south o f Kamloops appear t o be i n c l u d e d  Group p r i m a r i l y on l i t h o l o g i c grounds.  w i t h the N i c o l a  I suggest t h a t these rocks may  a c t u a l l y be Lower J u r a s s i c i n age, c o r r e l a t i v e w i t h the J u r a s s i c  volcanic  sequence.  Search f o r f o s s i l s i n these beds i s o b v i o u s l y n e c e s s a r y i n o r d e r  to r e s o l v e  this question.  plutonic  An a l t e r n a t e p o s s i b i l i t y i s t h a t the s p o r a d i c  c l a s t s i n the N i c o l a  Group a r e i n c l u s i o n s brought from p l u t o n s a t  depth below the v e n t s , and do n o t r e c o r d o r o t h e r 200 m.y.  u n r o o f i n g o f the Iron Mask b a t h o l i t h  plutons.  In summary, the P a u l Peak Stock i s p r o b a b l y c o r r e l a t i v e w i t h o t h e r zoned m a f i c - u l t r a m a f i c tonic suite.  p l u t o n s which make up a p o r t i o n  o f t h e 200 m.y.  plu-  I t was emplaced d u r i n g the l a t e stages o f a phase o f r e g i o n a l  compressive d e f o r m a t i o n which produced f a u l t s and open f o l d s i n the p r o x i m a l  152  v o l c a n i c f a c i e s o f the N i c o l a Group, and westward o v e r t u r n e d f o l d s i n the b a s i n a l f a c i e s o f the N i c o l a Group i n the study a r e a . deformation  i s thus determined  The age o f t h i s  t o be L a t e s t T r i a s s i c to E a r l i e s t  SMALL PLUGS, SILLS, AND  DIKES (MAP  Jurassic.  UNIT 8)  Small i n t r u s i v e b o d i e s o f a n d e s i t i c t o r h y o l i t i c composition are common  i n the a r e a .  Most o f these are t h i n d i k e s and s i l l s , but s e v e r a l s m a l l  p l u g s and t h i c k s i l l s of  o c c u r as w e l l .  These r o c k s e x h i b i t a wide v a r i e t y  t e x t u r e s , b u t most have a p h a n i t i c and/or p o r p h y r i t i c t e x t u r e s .  samples examined showed e x t e n s i v e a l t e r a t i o n o f phenocrysts produced  by hydrothermal  and  All  groundmass,  a l t e r a t i o n or low grade r e g i o n a l metamorphism.  However, the o r i g i n a l t e x t u r e s are l a r g e l y p r e s e r v e d , and p h e n o c r y s t are  phases  identifiable. Most o f the r o c k s s t u d i e d are a n d e s i t e s o r d a c i t e s w i t h  and/or microphenocrysts  of p l a g i o c l a s e and hornblende  phenocrysts  in a felsitic  matrix.  Some o f the rocks c o n t a i n q u a r t z p h e n o c r y s t s , o r q u a r t z i n a m i c r o g r a n i t i c m a t r i x , and are i d e n t i f i e d as d a c i t e s .  The remainder  o f the rocks l a c k  o p t i c a l l y i d e n t i f i a b l e q u a r t z , and c o u l d be a n d e s i t e s , d a c i t e s , o r t r a c h y a n d e s i t e s depending on the r e l a t i v e p r o p o r t i o n o f potassium  f e l d s p a r and  q u a r t z hidden i n the groundmass, b u t were t e n t a t i v e l y i d e n t i f i e d as andesites.  A s m a l l number o f h i g h l y a l t e r e d r h y o l i t e d i k e s and s i l l s  also occur.  P e t r o g r a p h i c d e s c r i p t i o n s o f the d i f f e r e n t v a r i e t i e s o f minor i n t r u s i v e rocks are g i v e n i n the f o l l o w i n g paragraphs. is  d i s c u s s e d i n Chapter  V.  The  secondary  mineralogy  153  D e s c r i p t i o n o f Minor I n t r u s i v e Rocks  Thick S i l l s Two  s i l l s up t o s e v e r a l tens o f metres t h i c k i n t r u d e U n i t 4 on P a u l  Ridge, and U n i t 5 i n Dome H i l l s .  The s i l l  on P a u l Ridge i s composite,  an a n d e s i t i c lower p a r t and a d a c i t i c upper p a r t .  Outcrops  with  o f these two  types a r e u s u a l l y no c l o s e r than 30 meters a p a r t , s e p a r a t e d by a covered interval.  They may be s e p a r a t e i n t r u s i o n s w i t h an i n t e r v e n i n g septum o f  sedimentary  rock, b u t a r e shown as a s i n g l e u n i t on P l a t e I . The s i l l i n  Dome H i l l s ,  a l o n g w i t h a number o f d i k e s , a r e l i t h o l o g i c a l l y v e r y  to t h e upper p o r t i o n o f t h e P a u l Ridge The d a c i t i c s i l l s 30% p h e n o c r y s t s  minor q u a r t z .  and d i k e s a r e gray, p o r p h y r i t i c r o c k s , w i t h 25 t o  are p l a g i o c l a s e  of unzoned cores surrounded  of  T h i n - s e c t i o n s o f two samples show  (10 t o 25%) , hornblende  f r e s h i n p o r t i o n s o f one sample, and c o n s i s t s  by t h i c k rims w i t h o s c i l l a t o r y  o f Arn+7 and An^i^ were determined  two g r a i n s .  (5 t o 10%) , and  A few pseudomorphs a f t e r pyroxene a r e p r e s e n t i n one sample.  P l a g i o c l a s e remains r e l a t i v e l y  sitions  sill.  i n an a p h a n i t i c m a t r i x .  that phenocrysts  similar  Hornblendes a r e stubby  zoning.  Compo-  on t h e i n n e r p o r t i o n s o f t h e rims  t o e l o n g a t e , up t o 6 mm l o n g , w h i l e  p l a g i o c l a s e i s g e n e r a l l y l e s s than 3 mm i n diameter.  The groundmass  s i s t s o f microphenocrysts  assemblage,  identical  t o the phenocryst  con-  surrounded  by a f e l s i t i c m a t r i x . The  a n d e s i t e making up t h e lower p o r t i o n o f t h e s i l l  more s p a r s e l y p o r p h y r i t i c , and t h e p l a g i o c l a s e phenocrysts  a r e mostly o n l y 1 t o 2 mm l o n g .  a f i n e - g r a i n e d aggregate secondary  minerals.  (5%)  on P a u l Ridge i s  and hornblende (10%)  The l i g h t gray groundmass i s  which c o n s i s t s mostly o f a l t e r e d f e l d s p a r p l u s  L i t t l e o r no q u a r t z i s e v i d e n t .  154  D a c i t e Porphyry Low  outcrops o f d a c i t e porphyry  Plug  o c c u r s c a t t e r e d over an area of a  few hundred square metres on the top o f P a u l Ridge, p o r t i o n o f U n i t 2.  i n t r u d i n g the e a s t e r n  Abundant f l o a t o f t h i s porphyry was  a l s o observed  to  the s o u t h e a s t , near the southern edge o f the r o l l i n g upland s u r f a c e o f the ridgetop.  T h i s f l o a t was  no bedrock exposures out o f t i l l  found near the c o n t a c t between U n i t s 1 and  were found.  The porphyry  2, but  cobbles p r o b a b l y are weathered  which l o c a l l y mantles the r i d g e t o p , and d e r i v e from the  outcrops  previously described. The porphyry 1.5  mm  c o n t a i n s about 20%  i n diameter, and  zoned p l a g i o c l a s e phenocrysts  5 t o 10% e l o n g a t e hornblende  up t o 6 mm  long.  p l a g i o c l a s e composition i s a l b i t e , p r o b a b l y r e p l a c i n g a more c a l c i c plagioclase. blende  The  gray,  The  primary  " s a l t and pepper" groundmass c o n t a i n s s m a l l e r horn-  and p l a g i o c l a s e c r y s t a l s surrounded  q u a r t z and potassium  up t o  by n e a r l y equal amounts o f anhedral  f e l d s p a r , both as s e p a r a t e g r a i n s and i n g r a p h i t i c  growths, and a l s o secondary v i s i b l e but not i d e n t i f i a b l e  minerals.  The  inter-  groundmass g r a i n s are b a r e l y  i n hand-specimen, so the groundmass i s a c t u a l l y  a f i n e - g r a i n e d p h a n e r i t e r a t h e r than an a p h a n i t e , and the rock might be called  a porphyritic micro-granodiorite.  and potassium  The modal p r o p o r t i o n s o f q u a r t z  f e l d s p a r i n t h i s groundmass c l e a r l y  show t h a t the rock has  a  b u l k composition o f g r a n o d i o r i t e o r d a c i t e , r a t h e r than a n d e s i t e , d e s p i t e the l a c k o f q u a r t z p h e n o c r y s t s .  P o r p h y r i t i c A n d e s i t e Plug A s m a l l a n d e s i t e p l u g i n t r u d e s the e a s t e r n p o r t i o n o f U n i t 2 a d j a c e n t to a prominent n o r t h - t r e n d i n g f a u l t .  Exposures are too poor t o show whether  the p l u g i n t r u d e s a l o n g the f a u l t or t h a t the f a u l t c u t s the p l u g .  The  155  a n d e s i t e i s gray, w i t h phenocrysts o f p l a g i o c l a s e (5 t o 10%).  (5 t o 10%) and hornblende  The b l o c k y p l a g i o c l a s e phenocrysts a r e 1 t o 2 mm i n diameter,  b u t much o f the hornblende by secondary m i n e r a l s .  i s much s m a l l e r , and i s completely r e p l a c e d  The groundmass i s f e l s i t i c , w i t h numerous b l o c k y  p l a g i o c l a s e microphenocrysts  and secondary m i n e r a l s .  N o n - p o r p h y r i t i c A n d e s i t e Dikes and S i l l s T h i n , l i g h t green d i k e s and s i l l s , not uncommon.  u s u a l l y l e s s than a metre wide, a r e  In hand-specimen these a r e g e n e r a l l y a p h a n i t e s o r v e r y  g r a i n e d p h a n e r i t e s , and l a c k p h e n o c r y s t s .  fine-  In t h i n - s e c t i o n i t can be seen  t h a t p l a g i o c l a s e l a t h s make up 50% o f t h e r o c k , e l o n g a t e hornblendes 5 t o 10%, w i t h t h e r e s t o f the rock composed o f i n t e r s t i t i a l  another  feldspar, quartz,  c h o r i t e , and o t h e r secondary m i n e r a l s .  The e l o n g a t e p l a g i o c l a s e and horn-  blende c r y s t a l s a r e randomly o r i e n t e d .  The i n t e r s t i t i a l m a t e r i a l may r e p r e -  sent a l t e r e d  glass.  Hornblende-Pyroxene A n d e s i t e Dikes Another out the a r e a .  type o f i n t e r m e d i a t e c o m p o s i t i o n d i k e i s v e r y common throughT h i s i s a gray p o r p h y r i t i c a n d e s i t e w i t h p l a g i o c l a s e ,  horn-  b l e n d e , and c l i n o p y r o x e n e phenocrysts i n about equal p r o p o r t i o n s , t o t a l l i n g about  20% o f t h e r o c k .  The d i s t i n c t i v e f e a t u r e o f these d i k e s i s the  presence o f l a r g e hornblende  c r y s t a l s , up t o 1 cm l o n g .  C l i n o p y r o x e n e and  p l a g i o c l a s e a r e g e n e r a l l y much s m a l l e r , and t h e l a t t e r a r e s i m i l a r i n c o l o r to  t h e gray groundmass, and t h e r e f o r e i n c o n s p i c u o u s i n hand-specimen.  blende i s f r e s h , o f t e n c o n c e n t r i c a l l y zoned, and l o c a l l y surrounds and replaces clinopyroxene.  The groundmass c o n s i s t s o f r a n d o m l y - o r i e n t e d  p l a g i o c l a s e and hornblende  microphenocrysts w i t h i n t e r s t i t i a l  p r e h n i t e , and o t h e r secondary  m i n e r a l s , perhaps  replacing  chlorite,  glass.  Horn-  156  R h y o l i t e Dikes and  Sills  T h i n r h y o l i t e d i k e s are common i n the e a s t e r n p o r t i o n o f U n i t 2, several larger s i l l s  are p r e s e n t i n the western  p a r t o f the u n i t .  r h y o l i t e i s white t o p i n k , and i s e x t e n s i v e l y a l t e r e d .  comprise  10% o f the  R e l i c t z o n i n g and a l b i t e t w i n n i n g are  e v i d e n t i n t h i n - s e c t i o n , b u t the m i n e r a l i s c o m p l e t e l y r e p l a c e d by and white mica.  B i o t i t e and hornblende  l e s s than a few p e r c e n t i n one  sample.  amounts o f anhedral q u a r t z and white  Age  The  P l a g i o c l a s e i s the  o n l y p h e n o c r y s t i d e n t i f i a b l e i n hand-specimen, and may rock, but commonly much l e s s .  and  albite  pseudomorphs are p r e s e n t i n amounts The  groundmass c o n s i s t s o f v a r i a b l e  mica.  and C o r r e l a t i o n o f Minor I n t r u s i v e Rocks  The ages o f these i n t r u s i v e rocks a r e u n c e r t a i n .  A n d e s i t i c to d a c i t i c  and r h y o l i t i c rocks cut both M i s s i s s i p p i a n and T r i a s s i c s t r a t a , and d i k e s w i t h low grade metamorphic m i n e r a l assemblages c u t h i g h e r grade rocks i n the c o n t a c t a u r e o l e o f the P a u l Peak Stock. o r younger i n age.  T h e r e f o r e they are p r o b a b l y  Jurassic  A more p r e c i s e age e s t i m a t e can be given by c o n s i d e r i n g  the p o s t - T r i a s s i c r e c o r d o f v o l c a n i s m i n the r e g i o n . t i o n s o f these v o l c a n i c rocks  (Campbell  Lithologic descrip-  and T i p p e r , 1971;  Cockfield,  1948)  suggest t h a t the minor i n t r u s i v e rocks i n the study a r e a are r e l a t e d t o the Eocene t o Oligocene Kamloops Group. are predominantly  hornblende  V o l c a n i c rocks i n the Kamloops Group  and a u g i t e a n d e s i t e s and d a c i t e s , b a s a l t s ,  some l i g h t - c o l o r e d f e l s i t e s and r h y o l i t e s . these v o l c a n i c rocks  The abundance o f hornblende  (and i n the i n t r u s i v e r o c k s i n the study area)  and in  distin-  guishes them from v o l c a n i c s o f o t h e r ages i n the r e g i o n . The r h y o l i t i c i n t r u s i v e s are abundant o n l y i n the e a s t e r n p a r t o f U n i t 2, a d j a c e n t t o the n o r t h w e s t - t r e n d i n g  f a u l t s e p a r a t i n g the N i c o l a and Harper  157  Ranch Groups.  S e v e r a l d a c i t e p l u g s a l s o o c c u r i n the u n i t , one a d j a c e n t t o  a north-trending f a u l t .  The i n t r u s i o n s were e v i d e n t l y emplaced p r e f e r e n -  t i a l l y a l o n g the f a u l t zones, perhaps contemporaneous the  faults.  w i t h movement a l o n g  158  CHAPTER V.  METAMORPHISM  INTRODUCTION  Low grade metamorphism o r hydrothermal o f t h e rock u n i t s i n t h e study a r e a .  a l t e r a t i o n has a f f e c t e d a l l  Prehnite-pumpellyite facies mineral  assemblages occur i n C a r b o n i f e r o u s and T r i a s s i c v o l c a n i c l a s t i c s t r a t a and mafic v o l c a n i c f l o w s , and i n p o s t - T r i a s s i c d i k e s and s i l l s o f i n t e r m e d i a t e composition.  Mudstones and l i m e s t o n e s show few r e c o g n i z a b l e e f f e c t s o f  this alteration.  In a d d i t i o n , P a u l Peak Stock i s surrounded  by a c o n t a c t -  metamorphic a u r e o l e which i n i t s i n n e r p o r t i o n a t t a i n s t h e hornblendehornfels facies.  Upper T r i a s s i c rocks w i t h a v a r i e t y o f compositions  are i n v o l v e d i n t h e a u r e o l e .  The o c c u r r e n c e o f low grade m i n e r a l assem-  b l a g e s w i t h i n t h e o u t e r p o r t i o n o f P a u l Peak Stock, and i n d i k e s c r o s s c u t t i n g t h e h i g h grade a u r e o l e s u r r o u n d i n g t h e p l u t o n , demonstrates t h a t s i g n i f i c a n t low grade metamorphism p o s t d a t e s emplacement o f t h e p l u t o n . The d i f f e r e n c e i n degree o f a l t e r a t i o n between C a r b o n i f e r o u s and Upper T r i a s s i c v o l c a n i c l a s t i c s t r a t a o f s i m i l a r composition p o s s i b i l i t y o f a post-Permian,  suggests t h e  p r e - L a t e T r i a s s i c low grade metamorphic  event.  LOW GRADE METAMORPHISM  General  Features  Low grade metamorphic m i n e r a l s r e p l a c e p l a g i o c l a s e and m a f i c m i n e r a l s , cement d e t r i t a l g r a i n s , f i l l  v e i n s and v e s i c l e s , and o c c u r i n t h e groundmass  159  o f v o l c a n i c rocks and rock fragments.  T h e i r f i n e g r a i n s i z e o f t e n makes  i d e n t i f i c a t i o n d i f f i c u l t , and some m i n e r a l s may have been o v e r l o o k e d . f o r e , the m i n e r a l assemblages p r e s e n t e d below may be incomplete.  There-  Minerals  such as c a l c i t e , c h l o r i t e , a l b i t e , sphene, a c t i n o l i t e , and e p i d o t e a r e readily identifiable i n thin-section.  P r e h n i t e i s a l s o o f t e n coarse enough  f o r p o s i t i v e o p t i c a l i d e n t i f i c a t i o n , and has been confirmed by X-ray f r a c t i o n a n a l y s i s o f a m i n e r a l s e p a r a t e from a v e i n .  dif-  Pumpellyite, stilpnom-  e l a n e , and c e l a d o n i t e were o n l y t e n t a t i v e l y i d e n t i f i e d i n t h i n - s e c t i o n , because many o f the m i n e r a l p r o p e r t i e s a r e n o t measurable due t o the f i n e g r a i n s i z e and s c a r c i t y o f these phases.  These f a c t o r s a l s o p r e c l u d e  i d e n t i f i c a t i o n by simple X-ray d i f f r a c t i o n t e c h n i q u e s . d i f f r a c t i o n o r microprobe  Single crystal  X-ray  a n a l y s e s a r e p r o b a b l y n e c e s s a r y t o c o n f i r m these  identifications. In the rocks w i t h these metamorphic m i n e r a l assemblages,  chemical  d i s e q u i l i b r i u m a t the s c a l e o f a t h i n - s e c t i o n i s the r u l e r a t h e r than the exception.  T h i s i s p a r t i c u l a r l y t r u e o f the T r i a s s i c v o l c a n i c l a s t i c  and the Paul Peak Stock. hornblende,  R e l i c t h i g h temperature  rocks  igneous phases such as  pyroxene, and i n t e r m e d i a t e p l a g i o c l a s e a r e common i n rocks i n  which low grade m i n e r a l assemblages o c c u r i n v e i n s , cement o r e p i m a t r i x , and i n a p h a n i t i c v o l c a n i c rock fragments.  The secondary  m i n e r a l s were  p r e c i p i t a t e d i n v o i d s , and r e a d i l y r e p l a c e d v o l c a n i c g l a s s (or an e a r l i e r , fine-grained d e v i t r i f i c a t i o n product), but replaced pre-existing phases i n c o m p l e t e l y and s e l e c t i v e l y .  crystalline  T h i s does n o t mean t h a t l o c a l  equili-  brium may n o t have been a c h i e v e d i n i n d i v i d u a l v e i n s , and among the m i n e r a l s replacing individual volcanic clasts.  With t h i s p o s s i b i l i t y i n mind, com-  mon m i n e r a l assemblages i n which a l l phases a r e i n mutual c o n t a c t were  160  noted, a l o n g w i t h t h e i r s e t t i n g .  These assemblages may  r e p r e s e n t an approach  to chemical e q u i l i b r i u m between a f l u i d phase and the o r i g i n a l l y g l a s s y p o r t i o n s o f the r o c k s . Low  grade m i n e r a l s observed  T a b l e IX.  i n each group o f rocks are l i s t e d i n  In the s e c t i o n s t h a t f o l l o w , s i g n i f i c a n t t e x t u r a l and m i n e r a l o g i c a l  f e a t u r e s and m i n e r a l assemblages are p r e s e n t e d f o r each such group.  T r i a s s i c Rocks  Low  grade m i n e r a l assemblages are p r e s e n t i n v o l c a n i c l a s t i c s t r a t a o f  i n t e r m e d i a t e c o m p o s i t i o n , and i n b a s i c v o l c a n i c f l o w s . In the v o l c a n i c l a s t i c r o c k s , growth o f secondary  minerals w i t h i n  v o l c a n i c fragments and i n the pore spaces o r m a t r i x between the c l a s t s b l u r r e d g r a i n o u t l i n e s , but not o b l i t e r a t e d the c l a s t i c t e x t u r e .  has  Chlorite,  sphene, a l b i t e , p r e h n i t e ( F i g . 40), and c a l c i t e are the most abundant secondary  minerals.  Common m i n e r a l assemblages i n c l u d e , a l o n g w i t h u b i q u i -  tous sphene:  prehnite + c h l o r i t e + c a l c i t e ± a l b i t e ± quartz  (a)  prehnite + pumpellyite ± quartz ± a l b i t e  (b)  pumpellyite + c h l o r i t e  (c)  P u m p e l l y i t e was U n i t 3.  found o n l y i n t h r e e p y r o c l a s t i c sandstone  samples  from  I t o c c u r s as s m a l l a n h e d r a l g r a n u l e s b a r e l y v i s i b l e a t a m a g n i f i c a -  t i o n o f 125X.  I t i s c h i e f l y r e c o g n i z a b l e by i t s c o l o r and s t r o n g p l e o c h r o i s m ,  from p a l e y e l l o w t o b r i g h t b l u e - g r e e n .  I t s r e l i e f i s somewhat l e s s than t h a t  o f e p i d o t e , and i t e x h i b i t s anomalous b l u e - g r e e n i n t e r f e r e n c e c o l o r s . Mafic phenocrysts hornblende  such as c l i n o p y r o x e n e and b i o t i t e are g e n e r a l l y f r e s h ,  i s f r e s h o r s l i g h t l y a l t e r e d t o c h l o r i t e and sphene, but o r t h o -  pyroxene i s completely r e p l a c e d by a f i n e aggregate  of the l a t t e r m i n e r a l s .  TABLE X.  LOW GRADE METAMORPHIC MINERALS FOUND IN ROCKS OF DIFFERENT AGE AND LITHOLOGY IN THE STUDY AREA  Triassic Volcaniclastics  Triassic Basic Volcanics  Mississippian Volcaniclastics  Actinolite Albite  X  X  X  Calcite  X  X  X  Epidote  X Group  Zoisite Clinozoisite Epidote  X  X  X  X  X  X  Prehnite  X  Pumpellyite*  X  Quartz  X  X  Sphene  X  X  X = Mineral present  X  X X  X  X X  X  X X  X  Potassium feldspar  S t ilpnome1ane *  Mesozoic o r Tertiary Dikes and S i l l s  X  Celadonite* Chlorite  Jurassic Paul Peak Stock  X  X X X  X  X  X  X  X X X  X X  X  X  * = T e n t a t i v e i d e n t i f i c a t i o n based on incomplete  X X  optical  data  40. P r e h n i t e v e i n i n p y r o c l a s t i c t u r b i d i t e from U n i t 3, Dome H i l l s . The i r r e g u l a r r a d i a t i n g c l u s t e r s o f c r y s t a l s are the t y p i c a l h a b i t o f p r e h n i t e found i n the study a r e a . T h i n - s e c t i o n , c r o s s e d n i c o l s , X 40.  163  A l t e r a t i o n o f p l a g i o c l a s e i s s l i g h t to n e a r l y complete, mediate igneous  compositions  are o f t e n p r e s e r v e d .  but o r i g i n a l  inter-  Large v a r i a t i o n s i n  degree o f p l a g i o c l a s e a l t e r a t i o n are f r e q u e n t l y observed w i t h i n a s i n g l e thin-section.  The u s u a l p r o d u c t s are s e r i c i t e o r v e r y f i n e - g r a i n e d s a u s s u r -  i t e i n which i n d i v i d u a l m i n e r a l s p e c i e s cannot be i d e n t i f i e d  optically.  Less commonly, i t i s p a r t i a l l y r e p l a c e d by c h l o r i t e , c h l o r i t e + c a l c i t e , z o i s i t e , or pumpellyite. The b a s i c v o l c a n i c rocks c o n t a i n a s i m i l a r a r r a y o f secondary but l a c k p u m p e l l y i t e , and c o n t a i n s t i l p n o m e l a n e .  minerals,  Observed m i n e r a l assem-  b l a g e s i n c l u d e , a l o n g w i t h sphene:  c h l o r i t e + stilpnomelane  (d)  c a l c i t e + stilpnomelane  (e)  prehnite + c h l o r i t e + c a l c i t e  (a)  Veins and amygdules i n the v o l c a n i c s c o n t a i n c a l c i t e ± q u a r t z , z o i s i t e ,  or  assemblage ( d ) . Stilpnomelane  occurs i n the groundmass i n o v o i d , f i n e - g r a i n e d r a d i a t i n g  aggregates.  I t resembles  brown b i o t i t e , b u t l a c k s b i r d s - e y e m o t t l i n g a t  extinction.  Because the m a t e r i a l i s so f i n e - g r a i n e d , i t cannot be  distin-  guished from b i o t i t e s o l e l y on the b a s i s o f o p t i c a l p r o p e r t i e s , s i n c e they are v e r y s i m i l a r .  The i d e n t i f i c a t i o n i s based p r i m a r i l y on the h a b i t  i s t y p i c a l o f s t i l p n o m e l a n e ) , f i n e g r a i n s i z e , and o c c u r r e n c e as a  (which  secondary  phase a s s o c i a t e d w i t h o t h e r low-grade m i n e r a l s . The metamorphic m i n e r a l assemblages i n the Upper T r i a s s i c rocks are those o f the p r e h n i t e - p u m p e l l y i t e f a c i e s .  There are no a r e a l v a r i a t i o n s i n  the m i n e r a l assemblages, except those c o n t r o l l e d by the b u l k  composition  o f the r o c k s , o r a s s o c i a t e d w i t h the c o n t a c t a u r e o l e s u r r o u n d i n g the P a u l Peak Stock.  164  P a u l Peak Stock  A l t e r a t i o n o f the primary igneous mineralogy i s l i m i t e d t o the h o r n b l e n d e - b e a r i n g ,  o f the P a u l Peak Stock  o u t e r p o r t i o n o f the p l u t o n .  c l a s e and c l i n o p y r o x e n e i n the c e n t r a l d i o r i t e and gabbro are fresh.  A l t e r a t i o n w i t h i n the h o r n b l e n d e - b e a r i n g  Plagio-  completely  rocks i s r e l a t i v e l y minor.  P l a g i o c l a s e i n a l l samples i s m i l d l y s a u s s u r i t i z e d .  Much o f the amphibole  i s p a l e green, but shows the anomalous green and brown i n t e r f e r e n c e c o l o r s t y p i c a l o f hornblende. p i n k potassium  The most severe a l t e r a t i o n i s found a s s o c i a t e d w i t h  feldspar veins.  In one  p l a g i o c l a s e i s r e p l a c e d by potassium hornblende  sample o f hornblende  diorite,  f e l d s p a r , and b o t h c l i n o p y r o x e n e  are r e p l a c e d by p a l e green a c t i n o l i t e .  and  B i o t i t e i n the same rock  i s p a r t i a l l y r e p l a c e d by c h l o r i t e o r c h l o r i t e + p r e h n i t e . The s i n g l e sample o f q u a r t z monzonite s t u d i e d has hornblende r e p l a c e d a l o n g c l e a v a g e s by c h l o r i t e + sphene. between hornblende  Small a n g u l a r  partially  interstices  and p l a g i o c l a s e c r y s t a l s are f i l l e d w i t h the f o l l o w i n g  assemblages:  p u m p e l l y i t e + sphene + c a l c i t e pumpellyite + c h l o r i t e + epidote  P u m p e l l y i t e i n t h i s sample o c c u r s as c l u s t e r s o f r a d i a t i n g f i b r o u s  crystals  w i t h s l i g h t l y i n c l i n e d e x t i n c t i o n , and the same s t r o n g p l e o c h r o i s m  noted  above.  I t s i n t e r f e r e n c e c o l o r s are anomalous deep b l u e and brown. A l t e r a t i o n w i t h i n the o u t e r p o r t i o n o f the p l u t o n i s patchy.  e x p l a n a t i o n i s t h a t c o n t a c t between the rock and a f l u i d phase was f o r low grade metamorphic r e a c t i o n s to take p l a c e .  likely  necessary  S i n c e the p l u t o n i c  l a c k s s i g n i f i c a n t i n t e r g r a n u l a r p o r o s i t y , the f l u i d was s m a l l areas around l o c a l  A  rock  o n l y a b l e t o permeate  f r a c t u r e systems i n the o u t e r p o r t i o n o f the s t o c k .  165  Rocks i n the core o f the p l u t o n , and even some q u i t e c l o s e t o the p r e s e n t c o n t a c t , remained u n a l t e r e d . The secondary  m i n e r a l s w i t h i n the P a u l Peak Stock a r e compatible  with  the p r e h n i t e - p u m p e l l y i t e f a c i e s m i n e r a l assemblages o f t h e s u r r o u n d i n g T r i a s s i c rocks.  These assemblages a r e p r o b a b l y the p r o d u c t s o f a s i n g l e  episode o f low grade metamorphism sometime a f t e r the emplacement o f the s t o c k , d u r i n g the E a r l y J u r a s s i c o r l a t e r .  Dikes and S i l l s  A n d e s i t i c and d a c i t i c d i k e s and s i l l s metamorphic m i n e r a l assemblages.  c o n t a i n w e l l developed  The range o f secondary  low grade  m i n e r a l s found i n  these r o c k s i s g e n e r a l l y s i m i l a r t o t h a t o f t h e s u r r o u n d i n g  Triassic  v o l c a n i c l a s t i c s t r a t a , which have a s i m i l a r b u l k c o m p o s i t i o n .  However,  a c t i n o l i t e , s t i l p n o m e l a n e , and c e l a d o n i t e o c c u r i n t h e d i k e s b u t n o t i n the v o l c a n i c l a s t i c s t r a t a , a t l e a s t w i t h i n the p r e s e n t sample o f these rocks.  In a d d i t i o n , the d i k e s c o n t a i n e p i d o t e and c l i n o z o i s i t e as w e l l as  zoisite.  More than one member o f t h e e p i d o t e group may be p r e s e n t w i t h i n  a s i n g l e sample.  The degree o f a l t e r a t i o n i s g e n e r a l l y g r e a t e r i n these  rocks than i n any o t h e r group, w i t h t h e e x c e p t i o n o f t h e P a l e o z o i c v o l c a n i c l a s t i c rocks. P l a g i o c l a s e i s g e n e r a l l y moderately and e i t h e r s e r i c i t e o r s a u s s u r i t e . i s p r e s e r v e d i n some samples.  to strongly altered to albite  However, o r i g i n a l igneous  plagioclase  Other phases which may r e p l a c e p l a g i o c l a s e  are c h l o r i t e , c a l c i t e , p r e h n i t e , and z o i s i t e .  Hornblende i s the common  mafic m i n e r a l i n these r o c k s , and i t i s p a r t i a l l y a l t e r e d t o one o f s e v e r a l m i n e r a l assemblages, each dominated by c h l o r i t e :  166  c h l o r i t e ± p r e h n i t e ± c a l c i t e ± sphene c h l o r i t e ± z o i s i t e ± c a l c i t e ± q u a r t z ± sphene chlorite  + celadonite  chlorite  ± stilpnomelane  ± calcite  The most abundant secondary m i n e r a l s a l b i t e , sphene, c a l c i t e , and p r e h n i t e .  i n the groundmass a r e c h l o r i t e ,  In one sample, primary  i n the groundmass has been r e p l a c e d by p a l e green a c t i n o l i t e . of minerals o f these  hornblende Assemblages  i n mutual c o n t a c t have n o t been determined f o r the groundmass  rocks.  A v e i n assemblage i n one sample c o n s i s t s o f :  pumpellyite  + z o i s i t e + c a l c i t e + quartz  T h i s i s the o n l y o c c u r r e n c e  o f p u m p e l l y i t e noted  i n these  rocks.  C e l a d o n i t e i s v e r y f i n e - g r a i n e d , and i s intergrown w i t h I t s d i s t i n g u i s h i n g f e a t u r e s a r e i t s h a b i t , moderate r e l i e f , c o l o r and p l e o c h r o i s m , The d i k e s , s i l l s ,  and an anomalous b l u e - g r e e n and o t h e r s m a l l i n t r u s i v e  same episode o f a l t e r a t i o n Peak Stock.  dant b i o t i t e and a c t i n o l i t e Paul Peak Stock. i n the country  b o d i e s have undergone t h e strata  and the Paul  rocks which c o n t a i n abun-  formed d u r i n g c o n t a c t metamorphism around the  The d i k e s do n o t show the severe r e c r y s t a l l i z a t i o n  evident  r o c k s , and c o n t a i n the same low grade assemblages found i n  d i k e s and country  rocks o u t s i d e the c o n t a c t a u r e o l e .  dence t h a t major low grade a l t e r a t i o n Peak Stock.  s t r o n g green  interference t i n t .  which a f f e c t e d t h e T r i a s s i c  S e v e r a l o f these d i k e s c u t T r i a s s i c  chlorite.  I f my suggested  postdates  correlation  This i s further e v i -  emplacement o f the Paul  o f these i n t r u s i v e  rocks w i t h the  Eocene t o O l i g o c e n e  v o l c a n i c s o f the Kamloops Group i s v a l i d , then  alteration  a l s o took p l a c e d u r i n g Eocene t o O l i g o c e n e  probably  perhaps even l a t e r .  this  volcanism, or  167  C a r b o n i f e r o u s V o l c a n i c l a s t i c Rocks  Upper M i s s i s s i p p i a n t o Lower P e n n s y l v a n i a n  andesitic to d a c i t i c  v o l c a n i c l a s t i c s t r a t a are s e v e r e l y a f f e c t e d by low grade metamorphism. The  r e c r y s t a l l i z a t i o n i s so i n t e n s e t h a t i n some samples a l t e r e d  v o l c a n i c fragments, consistently.  and m a t r i x b l e n d t o g e t h e r and  cannot be d i s t i n g u i s h e d  E x t e n s i v e a l t e r a t i o n o f p l a g i o c l a s e to s e r i c i t e or s a u s s u r -  i t e p r e v e n t s d e t e r m i n a t i o n o f i t s c o m p o s i t i o n , but i t i s albitized.  feldspars,  undoubtedly  R e l i c t c l i n o p y r o x e n e , found i n a s i n g l e sample, i s the o n l y  s u r v i v i n g mafic phase, and i t i s a l t e r e d around i t s margins t o c h l o r i t e . Other samples c o n t a i n pseudomorphs o f c h l o r i t e a f t e r u n i d e n t i f i e d  mafic  minerals. The most abundant secondary  m i n e r a l s i n rock fragments,  epimatrix or  cement, and v e i n s , are c h l o r i t e , a l b i t e , sphene, and c a l c i t e .  Pumpellyite  has been found i n a s i n g l e sample  (MK-191), where i t occurs as t i n y b r i g h t  green g r a n u l e s w i t h i n a v o l c a n i c rock fragment.  Celadonite i s present i n  another sample (MK-193), where i t o c c u r s intergrown w i t h c h l o r i t e i n altered clasts.  P r e h n i t e has not been  found.  The m i n e r a l assemblages p r e s e n t i n most o f the C a r b o n i f e r o u s  volcani-  c l a s t i c rocks c o u l d o c c u r i n e i t h e r the p r e h n i t e - p u m p e l l y i t e o r g r e e n s c h i s t facies.  However, the l o c a l presence  o f p u m p e l l y i t e and c e l a d o n i t e , and  absence o f a c t i n o l i t e , i n d i c a t e t h a t the metamorphism which produced assemblages was (Bishop, 1972; been produced younger r o c k s .  the  these  no h i g h e r i n grade than the p r e h n i t e - p u m p e l l y i t e f a c i e s Wise and E u g s t e r , 1964).  These assemblages thus c o u l d have  by the p o s t - T r i a s s i c metamorphic episode which a f f e c t s However, the e x t e n s i v e a l t e r a t i o n o f the  the  Carboniferous  r o c k s , compared w i t h the m i l d a l t e r a t i o n o f the T r i a s s i c r o c k s ,  suggests  168  t h a t a p r e - L a t e T r i a s s i c episode o f metamorphism was of  this alteration.  r e s p o n s i b l e f o r much  T h i s metamorphic event p r o b a b l y a l s o produced  assemblages i n the z e o l i t e o r p r e h n i t e - p u m p e l l y i t e f a c i e s . m i n e r a l s i n d i c a t i v e o f g r e e n s c h i s t f a c i e s o r h i g h e r grades  No  mineral  relict  are p r e s e n t .  I f such m i n e r a l s had been produced, t h e i r complete replacement  d u r i n g the  p o s t - T r i a s s i c metamorphic event would have been u n l i k e l y , i n view o f the widespread  relict  igneous m i n e r a l s i n the T r i a s s i c r o c k s , and h i g h grade  phases i n the contact-metamorphosed r o c k s . T e x t u r a l evidence w i t h i n the C a r b o n i f e r o u s rocks themselves  does not  r e q u i r e an i n t e r p r e t a t i o n o f more than one metamorphic event, and  specific  m i n e r a l s cannot be a s s i g n e d t o one  or the o t h e r event.  The  absence o f  p r e h n i t e and l i m i t e d o c c u r r e n c e o f p u m p e l l y i t e i n the o l d e r rocks i s i n t e r e s t i n g , s i n c e they are p r o b a b l y s i m i l a r i n b u l k c o m p o s i t i o n t o the younger v o l c a n i c l a s t i c and i n t r u s i v e rocks which do c o n t a i n these phases.  A  p o s s i b l e i n f e r e n c e i s t h a t the e a r l i e r low grade assemblages d i d not c o n t a i n p r e h n i t e and p u m p e l l y i t e , and t h a t changes i n the assemblages d u r i n g p o s t T r i a s s i c metamorphism were r e l a t i v e l y minor. Both experimental and t h e o r e t i c a l s t u d i e s (Winkler, 1976, G l a s s l e y , 1974)  p. 196-197;  i n d i c a t e t h a t p r e h n i t e - p u m p e l l y i t e f a c i e s m i n e r a l assemblages  w i l l o n l y e x i s t i n e q u i l i b r i u m w i t h a f l u i d phase i n which t h e r e i s a  low  mole f r a c t i o n o f CO2  may  ( u s u a l l y much l e s s than 0.1).  This r e l a t i o n s h i p  e x p l a i n the absence o f p r e h n i t e and near absence o f p u m p e l l y i t e i n the Carboniferous rocks. may  During the e a r l i e r metamorphic episode, pore  have c o n t a i n e d enough d i s s o l v e d CO2 t o p r e v e n t  m i n e r a l s , g e n e r a t i n g the observed and c a l c i t e .  fluids  f o r m a t i o n o f these  assemblages dominated by c h l o r i t e ,  albite,  Under low grade c o n d i t i o n s , m a t e r i a l t r a n s p o r t necessary f o r  169  m i n e r a l r e a c t i o n s t o take p l a c e probably depends h e a v i l y on the presence a f l u i d phase (Zen and Thompson, 1974). the f i r s t metamorphic episode may  Growth o f secondary  of  minerals during  have reduced p o r o s i t y and p e r m e a b i l i t y  o f the v o l c a n i c l a s t i c r o c k s enough t o p r e v e n t the f r e e c i r c u l a t i o n o f such pore  f l u i d s d u r i n g the l a t e r e p i s o d e , and thus i n h i b i t i n g  recrystallization.  An a l t e r n a t i v e e x p l a n a t i o n f o r the d i f f e r e n c e i n i n t e n s i t y o f a l t e r a t i o n between the rocks o f d i f f e r e n t ages i s t h a t two d i f f e r e n t p r e s s u r e temperature faulting.  regimes o f p o s t - T r i a s s i c metamorphism have been juxtaposed by However, the s m a l l p l u t o n s i n t r u d e d a l o n g and near the f a u l t zone  s e p a r a t i n g the C a r b o n i f e r o u s and T r i a s s i c rocks a l s o c o n t a i n p r e h n i t e p u m p e l l y i t e f a c i e s m i n e r a l assemblages.  E v i d e n t l y the f a u l t i n g  predates  p o s t - T r i a s s i c metamorphism, and both assemblages e x p e r i e n c e d s i m i l a r p r e s sures and temperatures  d u r i n g t h i s metamorphism.  C o n d i t i o n s o f Metamorphism  Experimental phase e q u i l i b r i a s t u d i e s a l l o w broad  l i m i t s t o be p l a c e d  on metamorphic c o n d i t i o n s d u r i n g f o r m a t i o n o f p r e h n i t e - p u m p e l l y i t e f a c i e s m i n e r a l assemblages  (Zen and Thompson, 1974;  Winkler,  1976).  Temperatures  were p r o b a b l y between 200°C and 400°C, and the p r e s s u r e l e s s than 2.5  to  kb.  from  The  analcime  low-temperature l i m i t i s p r o v i d e d by the f o r m a t i o n o f a l b i t e  3.0  + q u a r t z , taken by some authors as a convenient boundary between  d i a g e n e s i s and low grade metamorphism.  The high-temperature  l i m i t i s the  breakdown o f p r e h n i t e t o z o i s i t e + g r o s s u l a r + q u a r t z + water.  The  high-  p r e s s u r e l i m i t i s p r o v i d e d by the f o r m a t i o n o f l a w s o n i t e from v a r i o u s o t h e r Ca-Al s i l i c a t e s .  P r e h n i t e and p u m p e l l y i t e can p e r s i s t t o p r e s s u r e s above  t h i s , but l a w s o n i t e would p r o b a b l y be p r e s e n t as w e l l .  170  A c t i n o l i t e i s p r e s e n t w i t h i n the Paul Peak Stock, and i n one d i k e which i n t r u d e s metavolcanic  rocks near the margin o f t h e s t o c k  ( F i g . 41).  Although  c h a r a c t e r i s t i c o f b a s i c rocks i n the g r e e n s c h i s t f a c i e s , a c t i n o l i t e a l s o o c c u r s w i t h p u m p e l l y i t e i n m i n e r a l parageneses t r a n s i t i o n a l between t h e p r e h n i t e - p u m p e l l y i t e and g r e e n s c h i s t f a c i e s , sometimes r e f e r r e d t o as t h e pumpellyite-actinolite facies.  However, p u m p e l l y i t e i s absent  samples, and p r e h n i t e , u s u a l l y absent (Bishop, 1972), i s p r e s e n t .  from these  i n the p u m p e l l y i t e - a c t i n o l i t e  facies  In both samples t h e a c t i n o l i t e r e p l a c e s e i t h e r  hornblende o r c l i n o p y r o x e n e , and i t i s n o t i n c o n t a c t and may n o t be i n e q u i l i b r i u m w i t h the p r e h n i t e - b e a r i n g m i n e r a l assemblages. s i g n i f i c a n c e o f t h e occurrences  Therefore the  i s unknown.  CONTACT METAMORPHISM  The passes  c o n t a c t metamorphic a u r e o l e s u r r o u n d i n g t h e Paul Peak Stock encom-  Upper T r i a s s i c mudstone, v o l c a n i c and l i t h i c  v o l c a n i c s i n U n i t s 5 and 6.  sandstones,  Contact metamorphic e f f e c t s can be r e c o g n i z e d  up t o 600 m away from the exposed i n t r u s i v e c o n t a c t . is  and b a s i c  Most o f t h e a u r e o l e  c h a r a c t e r i z e d by m i n e r a l assemblages o f t h e a l b i t e - e p i d o t e h o r n f e l s  facies.  A t l e a s t l o c a l l y , an i n n e r zone i n t h e h o r n b l e n d e - h o r n f e l s  can be r e c o g n i z e d  facies  (Fig. 41).  Albite-Epidote-Hornfels Facies  Rocks o f t h e a l b i t e - e p i d o t e - h o r n f e l s f a c i e s a r e t y p i f i e d by t h e p r e s ence o f a c t i n o l i t e and b i o t i t e .  The mudstones possess  t e x t u r e i n hand-specimen and t h i n - s e c t i o n . stones and b a s i c v o l c a n i c s show l i t t l e  a typical  hornfelsic  The v o l c a n i c and l i t h i c  sand-  effect of recrystallization i n  KEY  TO SYMBOLS  | Q | Quaternary deposits  Biotite + K - f e l d s p a r + a n d e s i n e H o r n b l e n d e + b i o t i t e or  0.5 km  LOWER JURASSIC Paul Peak Stock  clinopyroxene  Actinolite + biotite  UPPER TRIASSIC NICOLA GROUP  A c t i n o l i t e + c h l o r i te  | 6b | Mafic volcanic rocks  Chlorite + stilpnomelane -•"—u--u'—•—  Actinolite  /.  | 5 | Thin-bedded mudstone  isogrod side,  \  dotted w h e r e i n f e r r e d b e n e a t h Quaternary  f  : T|43  I 6 | Mudstone, lithic sandstone, andesitic pyroclastics  isograd  ( T i c k m a r k s on h i g h g r a d e  /,  6b .  Hornblende  \  deposits)  \  I  \ 0 '• 93  1  s  I -'  /  \  A, \ \ 0  \6b\/  '  *• » ' \  -A +  , ' . . ^ . ' ti * t . 1 . 4 <  '  r - v 6  ,  A  5  +X. 4  \  ^N.  5 \  <  <  1  \  V. •. 136 '• • ..  \  \  * \ 135 \  • ' . .  \  Fig.  41.  Map  o f m i n e r a l assemblages  P a u l Peak S t o c k .  and  isograds  from t h e c o n t a c t metamorphic a u r e o l e o f t h e ,_,  172  hand-specimen, b u t i n t h i n - s e c t i o n both m i n e r a l o g i c and t e x t u r a l changes are e v i d e n t .  B i o t i t e , a c t i n o l i t e , and o t h e r metamorphic m i n e r a l s grow i n  random o r i e n t a t i o n w i t h i n and between v o l c a n i c and l i t h i c t a l l i z a t i o n i s incomplete, however, as high-temperature as c l i n o p y r o x e n e and hornblende  fragments.  Recrys-  igneous phases such  a r e o n l y p a r t i a l l y r e p l a c e d by a c t i n o l i t e +  b i o t i t e , o r by a c t i n o l i t e + magnetite  + sphene.  A c t i n o l i t e also replaces  hornblende. Metamorphic f e l d s p a r i s p r e s e n t i n s e v e r a l samples, b u t i s t o o f i n e g r a i n e d f o r exact i d e n t i f i c a t i o n .  V o l c a n i c p l a g i o c l a s e , probably  originally  andesine o r l a b r a d o r i t e , has been r e p l a c e d i n some cases by a c t i n o l i t e and b i o t i t e , s u g g e s t i n g t h a t a l b i t e i s s t a b l e r a t h e r than a more c a l c i c c l a s e , as i t s h o u l d be i n t h i s  facies.  Some common m i n e r a l assemblages noted i n rocks o f d i f f e r e n t are p r e s e n t e d i n Table XI.  These have n o t been checked  Numbers i n parentheses  composition  f o r mutual c o n t a c t  o f a l l phases, so a l l m i n e r a l s may n o t be p a r t o f a s i n g l e assemblage.  plagio-  equilibrium  a r e sample numbers shown on P i g . 41.  I f rocks o f lower grade than t h i s were formed f a r t h e r from the p l u t o n d u r i n g c o n t a c t metamorphism, they a r e i n d i s t i n g u i s h a b l e from those w i t h p r e h n i t e - p u m p e l l y i t e f a c i e s metamorphic assemblages.  Thus t h e e a r l i e s t  r e c o g n i z a b l e c o n t a c t metamorphic e f f e c t as t h e p l u t o n i s approached i s t h e appearance o f a c t i n o l i t e , as sketched i n F i g . 41.  The p o s i t i o n o f t h i s zone  boundary i s n o t w e l l c o n t r o l l e d .  Hornblende-Hornfels  The  Facies  i n n e r zone o f h o r n b l e n d e - h o r n f e l s  f a c i e s i s r e p r e s e n t e d by t h r e e  samples, a l l found w i t h i n 100 m o f t h e i n t r u s i v e c o n t a c t . t e r i z e d by t h e presence o f hornblende  They a r e charac-  r a t h e r than a c t i n o l i t e , and a more  TABLE X I .  Rock  Composition  Pelitic  Basic  Hornfels  volcanic  V o l c a n i c and l i t h i c elastics  ALBITE-EPIDOTE-HORNFELS FACIES MINERAL ASSEMBLAGES IN THE CONTACT METAMORPHIC AUREOLE OF PAUL PEAK STOCK  Sample Number  Mineral  Assemblage  106  A c t i n o l i t e , b i o t i t e , quartz,  141  Actinolite, biotite, plagioclase, chlorite,  105, 134 102 135, 136 132  A c t i n o l i t e , b i o t i t e , quartz,  feldspar  feldspar  Actinolite, biotite,  f e l d s p a r , sphene,  Actinolite, biotite,  sphene,  Actinolite, chlorite,  sphene  calcite  (epidote)  sphene, z o i s i t e ,  calcite  174  c a l c i c p l a g i o c l a s e (andesine)  where i t s c o m p o s i t i o n  was  determinable.  Static  r e c r y s t a l l i z a t i o n i s more e x t e n s i v e i n these r o c k s , and metamorphic m i n e r a l s are somewhat c o a r s e r - g r a i n e d than i n the lower grade r o c k s . be absent  or very t h i n around the s o u t h e a s t e r n  o l i t e - b e a r i n g rocks were found w i t h i n 100 One  sample o f p e l i t i c  T h i s zone  end o f the i n t r u s i o n .  m o f the c o n t a c t i n t h i s  h o r n f e l s i n t h i s zone (130)  may  Actin-  area.  c o n t a i n e d the  mineral  assemblage: q u a r t z , potassium  f e l d s p a r , b i o t i t e , p l a g i o c l a s e (An 42-44),  epidote.  B i o t i t e i n t h i s rock i s p a r t i a l l y r e p l a c e d by  c h l o r i t e , a retrograde  effect  which o c c u r r e d d u r i n g c o o l i n g or d u r i n g subsequent low grade metamorphism. A l e u c r o c a t i c v e i n w i t h i n t h i s sample  q u a r t z , potassium  contained:  feldspar, plagioclase, tremolite, diopside,  calcite.  C a l c i t e occurs  i n very s m a l l q u a n t i t i e s , but i f i t i s p a r t o f the e q u i l i b r i u m  assemblage, then the f o l l o w i n g r e a c t i o n assemblage may  be  present:  tremolite + c a l c i t e + quartz = diopside.  Two  d i f f e r e n t m i n e r a l assemblages were found  i n basic  metavolcanic  rocks:  hornblende, p l a g i o c l a s e , b i o t i t e , sphene  (93)  c l i n o p y r o x e n e , hornblende, p l a g i o c l a s e , b i o t i t e  M i c r o t e x t u r e s o f the c l i n o p y r o x e n e morphic phase, not a r e l i c t  demonstrate t h a t i t i s a prograde meta-  igneous m i n e r a l .  by a c t i n o l i t e + c h l o r i t e , another  (143)  retrograde  However, i t i s p a r t l y effect.  replaced  175  E f f e c t s o f Subsequent Low Grade Metamorphism  M i n e r a l o g i c changes which c o u l d be a t t r i b u t e d t o subsequent low grade metamorphism a r e r e l a t i v e l y minor.  These i n c l u d e the replacement o f b i o -  t i t e and c l i n o p y r o x e n e i n the h o r n b l e n d e - h o r n f e l s f a c i e s rocks d e s c r i b e d above, although t h i s c o u l d a l s o have o c c u r r e d d u r i n g c o o l i n g o f the i n t r u sion.  However, a v e i n i n a b a s i c m e t a v o l c a n i c sample  (143) w i t h i n the horn-  b l e n d e - h o r n f e l s f a c i e s zone c o n t a i n s the assemblage:  prehnite + chlorite + c a l c i t e  which i s t y p i c a l o f the l a t e r low grade metamorphic assemblages.  C o n d i t i o n s o f Metamorphism  From e x p e r i m e n t a l work on metamorphic m i n e r a l e q u i l i b r i a , T u r n e r (1968) suggests t h a t m i n e r a l assemblages o f the a l b i t e - e p i d o t e - h o r n f e l s f a c i e s form a t temperatures o f 300° to 450°C w i t h i n the p r e s s u r e range P„ „ = 1 t o 3 kb. H2O  The h o r n b l e n d e - h o r n f e l s f a c i e s r e p r e s e n t s a b r o a d e r  range o f temperatures, from 400° t o 600° o r 700°C i n the same p r e s s u r e range.  176  CHAPTER V I .  STRUCTURAL GEOLOGY  INTRODUCTION  The Harper Ranch Group and N i c o l a Group a r e s e p a r a t e d w i t h i n the study a r e a by a n o r t h w e s t - t r e n d i n g , v e r t i c a l f a u l t .  Both sequences have  been f o l d e d on a r e g i o n a l s c a l e , and a l s o e x h i b i t some s m a l l - s c a l e f o l d s . The p o r t i o n o f the study area u n d e r l a i n by the Harper Ranch Group i s too s m a l l t o r e v e a l the major r e g i o n a l s t r u c t u r e o f t h e group, o r t o a f f o r d adequate comparison o f i t s s t r u c t u r a l geometry w i t h t h a t o f the N i c o l a Group.  In a d d i t i o n , t h e s t r u c t u r a l s t y l e o f these rocks v a r i e s w i t h  lithology.  T h e r e f o r e , t h e s t r u c t u r a l h i s t o r i e s o f these juxtaposed  their sequences,  and t h e i r s i m i l a r i t i e s o r d i f f e r e n c e s , remain u n c e r t a i n . None o f the rocks i n t h e study a r e a possess a r e g i o n a l p e n e t r a t i v e cleavage, b u t f r a c t u r e s and j o i n t s w i t h extremely are v e r y common.  variable  orientations  The low metamorphic grade o f t h e rocks i m p l i e s t h a t a l l  deformation took p l a c e a t shallow b u r i a l  depths.  A map o f the d i f f e r e n t s t r u c t u r a l domains i s shown i n P l a t e VI ( i n p o c k e t ) , a l o n g w i t h c r o s s - s e c t i o n s and e q u a l - a r e a p l o t s o f t h e s t r u c t u r a l data.  FOLDING  Harper Ranch Group  The Harper Ranch Group i n t h e study area forms a n o r t h w e s t - t r e n d i n g , e a s t - f a c i n g homocline.  Bedding  dips very s t e e p l y to the northeast o r  177  southwest, b u t s t r a t i g r a p h i c tops a r e c o n s i s t e n t l y towards the e a s t .  The  l a r g e r map p a t t e r n o f t h e Harper Ranch Group e a s t o f t h e study a r e a ( F i g . 3), p a r t i c u l a r l y the d i s t r i b u t i o n o f the P e n n s y l v a n i a n  and Permian l i m e -  stone n o r t h e a s t o f McGregor Creek, shows t h e r e g i o n a l s t r u c t u r e t o be much more complex, p r o b a b l y i n v o l v i n g s e v e r a l g e n e r a t i o n s o f major f o l d s w i t h d i f f e r i n g a x i a l trends. Mesoscopic observed  f o l d s a r e uncommon i n t h e Harper Ranch Group, and were  i n o n l y a few o u t c r o p s .  A l l o f these f o l d s were open and concen-  t r i c , w i t h axes p l u n g i n g moderately  t o the s o u t h e a s t o r southwest.  An e q u a l - a r e a p r o j e c t i o n o f s t r u c t u r a l d a t a from t h e Harper Ranch Group ( P l a t e VI) shows t h e predominance o f n e a r - v e r t i c a l d i p s i n the n o r t h w e s t - t r e n d i n g homocline. o f p o l e s t o bedding  The few d i v e r g e n t a t t i t u d e s suggest t h a t t h e l o c u s  can be approximated  by a g r e a t c i r c l e w i t h a p o l e a t  143/50, n e a r l y c o i n c i d e n t w i t h t h e measured a x i s o f one o f the few minor folds.  A d d i t i o n a l s t r u c t u r a l d a t a o v e r a l a r g e r area a r e needed t o e v a l u a t e  the p o s s i b l e s i g n i f i c a n c e o f t h i s o b s e r v a t i o n and t o determine  whether  these rocks were a f f e c t e d by t h e r e g i o n a l P e r m o - T r i a s s i c o r o g e n i c d e s c r i b e d by Read and O k u l i t c h  event  (1977).  N i c o l a Group  The map u n i t s which comprise  t h e N i c o l a Group d e f i n e two major n o r t h -  w e s t - t r e n d i n g f o l d s , t h e P a u l Ridge a n t i c l i n e on t h e west and t h e P a u l Ridge s y n c l i n e on t h e e a s t .  The c o r e s and common limb o f t h e f o l d s a r e  complicated by s t e e p f a u l t s , making t h e i r i n f e r r e d geometry somewhat speculative. The P a u l Ridge a n t i c l i n e i s a t i g h t f o l d o v e r t u r n e d toward the west.  178  The  o v e r t u r n e d limb  the Dome H i l l s , and ward d i p s .  crops out along  the western p a r t of Paul  i s c h a r a c t e r i z e d by v a r i a b l e but  S t r a t i g r a p h i c tops face u n i f o r m l y  Ridge and  generally steep  east-  westward on t h i s limb.  The  f o l d i s i n f e r r e d to c l o s e w i t h i n the western p a r t o f U n i t 2, west o f narrow s l i v e r o f U n i t 3 which crops out on the summit o f Paul Ridge VI).  Bedding w i t h i n t h i s s l i v e r appears to be  U n i t 2 j u s t t o the e a s t o f t h i s s l i v e r , and  upright.  separated  The  i t s e a s t e r n margin d i p s and  from i t by  f a c e s eastward.  the  f o l d c l o s u r e , o f f s e t from t h a t t o the west by  may  be p r e s e n t  i n the southwest c o r n e r  westward d i p s , one section C-C). by  a vertical anticline;  However, p a r t  the aforementioned  w i t h bedding f a c i n g west ( P l a t e I; P l a t e VI,  of  fault, several  cross-  A moderate northwestward plunge „for the f o l d i s i n d i c a t e d  the t r e n d and plunge o f minor f o l d s i n the core  l i e near the hinge o f the The  (Plate  o f t h i s a r e a , as i n d i c a t e d by  bedding a t t i t u d e s w i t h east-west s t r i k e s and may  the  p o r t i o n of  f a u l t , i s i n t e r p r e t e d as p r i m a r i l y p a r t o f the u p r i g h t limb o f the bedding a l o n g  in  zone, and by  a  few  moderate northward d i p s , which  fold.  core o f the Paul Ridge s y n c l i n e i s c u t by  the  northwest-trending  f a u l t which bounds the e a s t e r n p o r t i o n o f U n i t 3 on i t s west s i d e .  The  p y r o c l a s t i c flows i n t h i s p a r t o f U n i t 3 are massive and very t h i c k l y bedded, so bedding a t t i t u d e s are r a r e l y o b t a i n a b l e .  However, where bedding  observed, d i p s were moderately t o s t e e p l y westward, and  although no  i n d i c a t o r s were found, I i n f e r t h i s s e c t i o n t o be u p r i g h t , and eastern  limb o f the Paul Ridge s y n c l i n e .  east of t h i s p o r t i o n of Unit  The  top  t o form the  r e p e t i t i o n of Unit 2 to  3 supports t h i s i n t e r p r e t a t i o n .  limb of the s y n c l i n e i s the u p r i g h t U n i t 2.  The  was  limb o f the Paul  The  western  Ridge a n t i c l i n e  hinge zone o f the s y n c l i n e a t t h i s s t r u c t u r a l l e v e l  the  has  within  179  a p p a r e n t l y been e n t i r e l y e l i m i n a t e d by f a u l t i n g , and d i f f e r e n t  stratigraphic  l e v e l s on t h e two limbs a r e juxtaposed a c r o s s t h e f a u l t . In the easternmost p o r t i o n o f U n i t 2, bedding d i p s n e a r l y and g e n e r a l l y northeastward.  vertically,  No t o p i n d i c a t o r s were found here, b u t t h e  s e c t i o n p r o b a b l y f a c e s westward, and r e p r e s e n t s a s l i g h t l y o v e r t u r n e d port i o n o f t h e e a s t e r n limb o f t h e P a u l Ridge s y n c l i n e .  However, i t i s separ-  ated from U n i t 3 by another v e r t i c a l f a u l t , so t h i s i n t e r p r e t a t i o n i s n o t certain. The geometry o f t h e P a u l Ridge a n t i c l i n e r e s u l t s from c o n s i d e r a b l e compressive  strain.  The rocks w i t h i n t h e a x i a l r e g i o n o f t h e f o l d possess  no s l a t y cleavage o r o t h e r i n d i c a t o r s o f p e n e t r a t i v e s t r a i n w i t h i n beds (aside from f e a t u r e s which can be a t t r i b u t e d t o sedimentary normal  t o bedding).  compaction  T i g h t e n i n g o f the f o l d must t h e r e f o r e have been  a c h i e v e d by removal o f m a t e r i a l from t h e core zone by bedding-plane r a t h e r than by homogeneous p e n e t r a t i v e s t r a i n .  shear,  The n e c e s s a r y i n t e r b e d  s t r a i n c o u l d e a s i l y have been accomodated by t h e thin-bedded mudstone o f U n i t 2, which forms t h e core o f t h e f o l d . Mesoscopic  f o l d s a r e common o n l y i n t h e thin-bedded mudstone f a c i e s  o f t h e N i c o l a Group.  Thus they a r e found mostly i n U n i t s 2 and 5.  The  geometry o f these f o l d s i s q u i t e v a r i a b l e , b u t t h e most common f o l d s a r e open t o c l o s e , c o n c e n t r i c and n e a r l y p a r a l l e l , w i t h l a y e r t h i c k n e s s remaini n g n e a r l y c o n s t a n t around t h e f o l d s  (Class l b o f Ramsay, 1967).  t i g h t f o l d s o c c u r , which have n o t i c e a b l y t h i c k e n e d hinges Ramsay).  A few  (Class I c o f  None o f these f o l d s possess an a x i a l p l a n e c l e a v a g e .  The o r i e n t a t i o n s o f t h e f o l d s a r e a l s o q u i t e v a r i a b l e . Paul Ridge, t h e f o l d s plunge s h a l l o w l y t o moderately  In c e n t r a l  northwestward,  and a r e  180  p r o b a b l y c o a x i a l with t h e P a u l Ridge a n t i c l i n e . the a n t i c l i n e  On t h e o v e r t u r n e d limb o f  (Western Paul Ridge and Dome H i l l s ) ,  t h e f o l d s plunge moder-  a t e l y t o s t e e p l y t o the west, n o r t h , and n o r t h e a s t . vergence  In a l l t h r e e a r e a s , t h e  o f n o r t h t o n o r t h w e s t - t r e n d i n g minor f o l d s , where  i s c o n s i s t e n t w i t h t h e i r p o s i t i o n on t h e major f o l d : t u r n e d limb, and S-type on t h e u p r i g h t limb.  determinable,  Z-type on the over-  Thus a t l e a s t these  folds  p r o b a b l y a r e g e n e t i c a l l y r e l a t e d t o and formed synchronously w i t h t h e major folds. The o r i g i n o f t h e n o r t h e a s t - t r e n d i n g minor f o l d s on t h e o v e r t u r n e d limb i s more p r o b l e m a t i c . can be approximated  The l o c u s o f p o l e s t o bedding  i n t h e Dome H i l l s  by a g r e a t c i r c l e w i t h a p o l e a t 42/56, n e a r l y c o i n c i d e n t  w i t h t h e axes o f a group o f n o r t h e a s t - t r e n d i n g minor f o l d s . f o l d s form a l a t e r g e n e r a t i o n superimposed on t h e e a r l i e r major and minor f o l d s .  P o s s i b l y these  northwest-trending  However, s u p e r p o s i t i o n o f t h e two t r e n d s has n o t  been observed i n o u t c r o p .  No c l e a r s e p a r a t i o n can be made between t h e two  p o s s i b l e f o l d s e t s on the b a s i s o f a x i a l t r e n d o r f o l d s t y l e , and n e a r l y a l l o f t h e minor f o l d s have n o r t h w e s t - t r e n d i n g a x i a l p l a n e s which d i p to s t e e p l y n o r t h e a s t .  moderately  Thus an i n t e r p r e t a t i o n o f more than one f o l d  gener-  a t i o n cannot be s u b s t a n t i a t e d with t h e p r e s e n t d a t a . The o v e r t u r n e d limb o f t h e P a u l Ridge a n t i c l i n e i s c u t by t h e P a u l Peak Stock. assic  In Chapter  IV I p r e s e n t e d arguments i n support o f a Lower J u r -  (about 200 m.y.) age f o r t h e s t o c k .  T h i s l i m i t s t h e time o f f o r m a t i o n  of these major f o l d s t o t h e L a t e s t T r i a s s i c o r E a r l i e s t J u r a s s i c . deformation was p r o b a b l y p a r t o f t h e " I n k l i n i a n orogeny" (Douglas  This and o t h e r s ,  1970), which r e s u l t e d i n r e g i o n a l u p l i f t and e r o s i o n , warping and f a u l t i n g o f the p r o x i m a l f a c i e s o f t h e N i c o l a Group (Schau,  1970) , and i n t r u s i o n and  181  u n r o o f i n g o f the 200  m.y.  p l u t o n s w i t h i n the N i c o l a a r c .  Schau (1970) c a l -  c u l a t e d the r e s u l t a n t s t r a i n w i t h i n the type a r e a o f the N i c o l a Group a t l e s s than 5 p e r c e n t .  The  presence of major o v e r t u r n i n g w i t h i n the N i c o l a  Group i n the study area suggests t h a t d e f o r m a t i o n was  much more i n t e n s e  and  s t r a i n much g r e a t e r w i t h i n the b a s i n a l f a c i e s o f the N i c o l a Group e a s t o f the arc  terrane.  FAULTING  Northwest-trending, steeply dipping o f the N i c o l a Group, and The  f a u l t s postdate  separate  f a u l t s segment the e a s t e r n  i t from the Harper Ranch Group to the  the major f o l d s i n the N i c o l a Group.  the f a u l t s were found, and  t h e i r t r a c e s can be  No  specified.  t r e n d i n g f a u l t s o f f s e t the c o n t a c t between the N i c o l a and These f a u l t s have r i g h t - l a t e r a l s e p a r a t i o n s  s e v e r a l hundred metres. common i n the s u r r o u n d i n g Tipper,  along  However, the  V e r t i c a l apparent o f f s e t s on the f a u l t s exceed  but the sense o f motion on the f a u l t s cannot be  Groups.  exposures o f  r e l i e f on the s u r f a c e f a u l t t r a c e s shows the f a u l t s to be  essentially vertical. m,  east.  located accurately only  the southern s l o p e o f Paul Ridge where exposures are b e s t . topographic  part  1971;  North and  northwest-trending  Smaller  north-  Harper Ranch  o f a few  tens  to  f a u l t systems are  p o r t i o n s o f the Intermontaine b e l t  Schau, 1970).  1000  (Campbell  These f a u l t s are g e n e r a l l y o l d e r than  and  the  Miocene and younger v o l c a n i c s which mantle l a r g e p a r t s o f the r e g i o n . major f a u l t which separates  the N i c o l a and  area p r o j e c t s t o the southeast trace i s apparently canics  ( F i g . 2).  across  Harper Ranch Groups i n the  The study  the South Thompson R i v e r , where i t s  covered by a l a r g e body o f these L a t e T e r t i a r y v o l -  Campbell and T i p p e r  (1971) document o f f s e t s o f Eocene  182  v o l c a n i c s along f a u l t s w i t h these  t r e n d s , but r e c o r d a much g r e a t e r  o f f a u l t s and f r a c t u r e s i n T r i a s s i c and J u r a s s i c r o c k s . t h a t f a u l t i n g began i n the Mesozoic and c o n t i n u e d early Tertiary.  density  They p o s t u l a t e  i n t e r m i t t e n t l y i n t o the  183  CHAPTER V I I .  The  SUMMARY AND CONCLUSIONS  "Cache Creek Group" as p r e v i o u s l y mapped i n t h e Kamloops area  a c t u a l l y c o n s i s t s o f two sequences o f d i f f e r e n t ages, s e p a r a t e d by a northwest-trending v e r t i c a l f a u l t .  To t h e e a s t l i e t h e M i s s i s s i p p i a n t o  Permian mudstone, r e d e p o s i t e d t u f f , and l i m e s t o n e d e s i g n a t e d as the Harper Ranch Group.  Upper T r i a s s i c rocks o f the N i c o l a Group l i e west o f t h e  f a u l t , and c o n s i s t o f marine mudstone, submarine p y r o c l a s t i c flows and t u r b i d i t e s , minor v o l c a n i c f l o w s , l i t h i c sandstone rare basinal The  and conglomerate,  and  limestone.  study area i n c l u d e s o n l y the lower p a r t o f t h e Harper Ranch Group  (Unit 1 ) , which forms a n o r t h w e s t - t r e n d i n g , e a s t - f a c i n g homocline.  Nearly  a l l o f t h e s e c t i o n , more than two k i l o m e t e r s t h i c k , c o n s i s t s o f mudstone and v o l c a n i c l a s t i c r o c k s .  A t h i n marine l i m e s t o n e near the base c o n t a i n s  f o s s i l s o f Late M i s s i s s i p p i a n age.  A Lower P e n n s y l v a n i a n  the t o p o f t h e s e c t i o n s t u d i e d , although exposures T h i s sequence accumulated  l i m e s t o n e forms  c o n t i n u e t o the e a s t .  i n a marine b a s i n w i t h i n a v o l c a n i c a r c system,  p r o b a b l y w i t h i n the f r o n t a l a r c .  T h i s p o r t i o n o f t h e b a s i n was r e l a t i v e l y  d i s t a n t from t h e v o l c a n i c c e n t e r s , s i n c e none o f t h e v o l c a n i c d e t r i t u s i s c o a r s e r than very coarse sand o r g r a n u l e s i z e , and no flows a r e p r e s e n t i n the s e c t i o n .  The v o l c a n i c sandstones  and phenocrysts  consist of volcanic l i t h i c  i n d i c a t i n g an a n d e s i t i c t o d a c i t i c s o u r c e .  d e t r i t u s i s p r o b a b l y p y r o c l a s t i c i n o r i g i n , produced eruptions.  fragments  Most o f the  by shallow submarine  T h i s m a t e r i a l was reworked and r e d e p o s i t e d i n deeper water  below wave base by t u r b i d i t y c u r r e n t s and h i g h - c o n c e n t r a t i o n subaqueous f l o w s , and i s i n t e r l a y e r e d w i t h h e m i p e l a g i c mudstones.  184  The  l i m e s t o n e o f U n i t l A i s made up o f wackestones, packstones,  and  g r a i n s t o n e s , and c o n t a i n s a d i v e r s e marine fauna, i n d i c a t i n g shallow marine deposition.  I t c o n t a i n s v i r t u a l l y no v o l c a n i c d e t r i t u s c o a r s e r than  s i z e , and probably accumulated  clay  on a s h a l l o w s h e l f a t a c o n s i d e r a b l e d i s t a n c e  from the v o l c a n i c c e n t e r s , o r d u r i n g a p e r i o d o f v o l c a n i c q u i e s c e n c e .  Rela-  t i v e changes i n the p o s i t i o n o f sea l e v e l w i t h r e s p e c t t o the b a s i n f l o o r , of  e i t h e r t e c t o n i c or e u s t a t i c o r i g i n , must be p o s t u l a t e d to e x p l a i n the  j u x t a p o s i t i o n o f deep water mudstones and t u r b i d i t e s o v e r l y i n g shallow marine  mudstone. T h i s l a t e P a l e o z o i c a r c t e r r a n e was  e n t a l margin by a back-arc b a s i n .  p r o b a b l y s e p a r a t e d from the c o n t i n -  C l o s i n g of t h i s basin resulted i n c o l -  l i s i o n o f the a r c w i t h o l d e r t e r r a n e s t o the e a s t , which may  account f o r  the p r e - L a t e T r i a s s i c deformation and low grade metamorphism which a f f e c t P a l e o z o i c e u g e o c l i n a l r o c k s i n the r e g i o n south o f Kamloops. study area, P e r m o - T r i a s s i c deformation  Within  the  cannot be demonstrated w i t h the p r e s -  ent d a t a , but the rocks appear t o have undergone low grade metamorphism p r i o r t o the L a t e  Triassic.  Subsequent t o the E a r l y T r i a s s i c o r o g e n e s i s , a new  v o l c a n i c a r c system  formed i n the L a t e T r i a s s i c above an e a s t - d i p p i n g s u b d u c t i o n zone. volcanic arc i t s e l f  i s r e p r e s e n t e d by the v o l c a n i c rocks o f the N i c o l a  Group west of Kamloops.  W i t h i n the study a r e a , rocks of the N i c o l a Group  c o n s i s t o f a t l e a s t t h r e e k i l o m e t e r s o f sediments and which accumulated arc.  The  volcaniclastics  i n deep water w i t h i n a b a c k - a r c b a s i n e a s t o f the v o l c a n i c  P e l a g i c and h e m i p e l a g i c mudstones are abundant o r predominant i n the  section.  The v o l c a n i c l a s t i c r o c k s , l i t h i c sandstones  and  conglomerates,  and limestones were d e p o s i t e d by t u r b i d i t y c u r r e n t s and h i g h - c o n c e n t r a t i o n  185  d e n s i t y flows.  B a s a l t i c or a n d e s i t i c v o l c a n i c s were erupted  s p o r a d i c a l l y , forming massive and p i l l o w e d flows v a r i a t i o n s i n the r e l a t i v e p r o p o r t i o n s u n i t s , numbered 2 through 6. y i e l d Karnian  i n U n i t s 2 and  Conodonts e x t r a c t e d from the  comparison o f p h e n o c r y s t mineralogy.  and  o r i g i n a t e d from shallow resulted i n a lateral  five  limestones  to the west, based on  a  the lower p o r t i o n o f U n i t  and  t u r b i d i t e s , which  marine v o l c a n i c vents l y i n g t o the e a s t .  f a c i e s t r a n s i t i o n w i t h i n U n i t 3 from very  probably  This t h i c k pyro-  i n the e a s t to well-bedded t u r b i d i t e s i n the west.  L i t h i c sandstone and  conglomerate i n U n i t s 5 and  and v o l c a n i c d e t r i t u s , i n c l u d i n g abundant c h e r t .  6 contain  rocks o f the Cache Creek Group. grained redeposited  limestones  c o n t i n e n t a l margin (miogeocline)  an e a s t - f a c i n g p a l e o s l o p e  waters s u r r o u n d i n g  s t r e t c h e d from the Late  Triassic  rocks  of  v o l c a n i c c e n t e r s o f the N i c o l a a r c formed on  on the western s i d e o f the b a s i n .  Clastic  thus a b l e t o f i l t e r  accumulate i n the b a s i n t o the  Marine d e p o s i t i o n o f the N i c o l a Group was or E a r l i e s t J u r a s s i c by  carbonate  the P i n c h i t e r r a n e .  westward t o the a c c r e t e d o c e a n i c  m a t e r i a l d e r i v e d from the P i n c h i t e r r a n e was the v o l c a n i c c h a i n and  oceanic  suggest t h a t a t l e a s t some o f t h i s  N i c o l a d e p o s i t i o n a l basin probably  The  derived  D e t r i t a l b l u e amphiboles found i n f i n e -  d e r i v e d from shallow  the P i n c h i g e a n t i c l i n e .  sedimentary  They were p r o b a b l y  from the emergent P i n c h i g e a n t i c l i n e to the west, which exposed  The  Vertical  5 are composed o f reworked t u f f  U n i t 3 and  6 are composed of a n d e s i t i c p y r o c l a s t i c flows  sediment was  floor  ages f o r the e n t i r e sequence.  d e r i v e d from the N i c o l a v o l c a n i c c e n t e r s  c l a s t i c flows  6.  o f these l i t h o l o g i e s d e f i n e  V o l c a n i c t u r b i d i t e s i n U n i t s 2, 4, probably  on the sea  through  east.  ended i n the L a t e s t T r i a s s i c  the " I n k l i n i a n orogeny," which produced a r e g i o n a l  186  angular unconformity  beneath Lower J u r a s s i c r o c k s .  w i t h i n the a r c t e r r a n e was  Although  deformation  m i l d , the N i c o l a Group i n the study area  deformed i n t o a p a i r o f n o r t h w e s t - t r e n d i n g major f o l d s .  was  The Paul Ridge  a n t i c l i n e on the west i s a t i g h t f o l d o v e r t u r n e d toward the west.  The  P a u l Ridge s y n c l i n e i s a p p a r e n t l y u p r i g h t and more open, but i t s a x i a l r e g i o n has been e l i m i n a t e d by l a t e r f a u l t i n g .  A number o f  northwest-  p l u n g i n g minor f o l d s appear t o be c o a x i a l w i t h the major f o l d s . a t i o n took p l a c e a t shallow depths,  The  deform-  and d i d not l e a d t o f o r m a t i o n o f a pene-  t r a t i v e f a b r i c w i t h i n the r o c k s . The o v e r t u r n e d limb o f the P a u l Ridge a n t i c l i n e i s c u t by the P a u l Peak Stock, which was  p r o b a b l y emplaced d u r i n g the l a t e r stages of the  " I n k l i n i a n orogeny," around 200 m.y.  ago.  The p l u t o n shows  incomplete  c o n c e n t r i c zoning, w i t h i t s composition v a r y i n g from o l i v i n e c l i n o p y r o x e n i t e i n the core t o hornblende  g r a n i t e a t the s o u t h e a s t e r n e x t r e m i t y .  The p l u t o n  i s s i m i l a r t o zoned "Alaskan" type m a f i c - u l t r a m a f i c complexes i n i t s compos i t i o n and t e c t o n i c s e t t i n g .  The  c o m p o s i t i o n a l v a r i a t i o n and zoning i n the  o u t e r p a r t o f the p l u t o n c o u l d have been produced  by  fractional  crystalliza-  t i o n and c r y s t a l s e t t l i n g o f a s i l i c a - s a t u r a t e d melt o f i n t e r m e d i a t e composition,  f o l l o w e d by upward d i a p i r i c i n t r u s i o n o f the s t r a t i f o r m  cumulates.  The u l t r a m a f i c core p r o b a b l y i s a somewhat l a t e r i n t r u s i o n , which was  emplaced  as a c r y s t a l mush which formed by f r a c t i o n a l c r y s t a l l i z a t i o n o f a m a f i c , a l k a l i n e melt.  Contact metamorphism o f the s u r r o u n d i n g sedimentary  v o l c a n i c rocks reaches the hornblende  h o r n f e l s f a c i e s i n outcrops  the i n t r u s i v e c o n t a c t , although most o f the a u r e o l e i s i n the amphibolite The  and  nearest  albite-epidote  facies.  t i m i n g o f subsequent events  i s not w e l l c o n s t r a i n e d .  Northeast-  187  t r e n d i n g minor f o l d s i n the N i c o l a Group may have formed a t a l a t e r , i n d e t e r minate time than the major f o l d s i n t h e a r e a .  Northwest and n o r t h - t r e n d i n g  v e r t i c a l f a u l t s i n t h e study area may have formed i n mid-Mesozoic t o E a r l y T e r t i a r y time, based on t h e r e c o r d o f f a u l t i n g i n a d j a c e n t a r e a s . of  small dikes, s i l l s ,  Ranch Group.  and p l u g s i n t r u d e b o t h t h e N i c o l a Group and Harper  Most o f these are a n d e s i t e s o r d a c i t e s , w i t h some r h y o l i t e s  also present. suggests  A variety  The composition and p h e n o c r y s t mineralogy  o f these  intrusives  t h a t they a r e r e l a t e d t o t h e Eocene t o O l i g o c e n e v o l c a n i c s o f the  Kamloops Group.  The i n t r u s i o n s were emplaced p r e f e r e n t i a l l y a l o n g f a u l t  zones,  perhaps contemporaneous w i t h movement a l o n g t h e f a u l t s . P r e h n i t e - p u m p e l l y i t e f a c i e s metamorphism has a f f e c t e d a l l o f t h e rock u n i t s i n the study a r e a , i n c l u d i n g t h e d i k e s o f p r o b a b l y Eocene t o Oligocene age.  The e f f e c t s o f t h i s metamorphism a r e most pronounced i n the v o l c a n i c  and v o l c a n i c l a s t i c rocks and the d i k e s and s i l l s .  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H., 1964, C e l a d o n i t e : s y n t h e s i s , thermal s t a b i l i t y , and o c c u r r e n c e : American M i n e r a l o g i s t , v. 49, p. 1031-1083. Wray, J . L., 1972, Environmental d i s t r i b u t i o n o f c a l c a r e o u s algae i n Upper Devonian r e e f complexes: G e o l o g i s c h e Rundschau, v. 61, p. 578-584. W y l l i e , P. J . , 1971, The Dynamic E a r t h : Textbook i n G e o s c i e n c e s : New York, W i l e y , 416 p. Yoder, H. S., and T i l l e y , C. E., 1962, O r i g i n o f b a s a l t i c magmas: an e x p e r i m e n t a l study o f n a t u r a l and s y n t h e t i c rock systems: J o u r n a l o f P e t r o l o g y , v. 3, p. 342-532.  .199  E., and Thompson, A. B., 1974, Low grade r e g i o n a l metamorphism: m i n e r a l e q u i l i b r i u m r e l a t i o n s : Annual Reviews o f E a r t h and P l a n e t a r y S c i e n c e , v. 2, p. 179-212.  200  APPENDIX I . REPORT ON CONODONT COLLECTIONS EXTRACTED FROM LIMESTONE SAMPLES FROM THE KAMLOOPS MAP-AREA (NTS 92 1/9), SOUTH-CENTRAL B. C.  by  B. E. B. Cameron G e o l o g i c a l Survey o f Canada V i c t o r i a , B. C.  Conodonts a r e i l l u s t r a t e d i n P l a t e V.  G.S.C. Loc. 93450 F i e l d No. M2, NTS 92 1/9, Kamloops, Lat.  G r i d . No. 897189,  50° 41.8'N, Long. 120° 18.6'W.  Conodonts Neogondolella navicula navicula (Huckriede) - about 40 specimens. ( P l a t e V, F i g . 6 and 7) Xaniognathurs?  sp. - 2 specimens-  Enantiognathus  ziegleri  Neospathodus  (Diebel) - 1 specimen  sp. - 3 specimens  N. sp. c f . N. newpassensis F i g . 1)  (Mosher) - 1 specimen ( P l a t e V,  Cypridodella sp. c f . C. muelleri ( P l a t e V, F i g . 3) Ozarkodina Hindeodella?  tortilis  (Tatge) - about 3 specimens  (Tatge) - 2 specimens  ( P l a t e V, F i g . 2)  sp. - 1 specimen  v a r i o u s o t h e r fragments. Age and Remarks L a t e T r i a s s i c , K a r n i a n , p o s s i b l y e a r l y K a r n i a n on t h e b a s i s of N. newpassensis and h i g h degree o f v a r i a b i l i t y i n N. navicula navicula. The l a t t e r i n c l u d e v a r i a t i o n i n shape from e l o n g a t e t o e l l i p t i c a l , v a r i a t i o n i n i n c l i n a t i o n o f prominent p o s t e r i o r d e n t i c l e from e r e c t t o p o s t e r i o r l y p r o j e c t i n g , and i n some t h e development o f l a t e r a l l y c r e n u l a t e a n t e r i o r margins o f t h e p l a t f o r m . These v a r i a t i o n s have been observed i n o t h e r c o l l e c t i o n s o f t h i s f o r m - s p e c i e s o f K a r n i a n age.  G.S.C. Loc. 93451 F i e l d No. M4, NTS 92 1/9, Kamloops, G r i d . No. 894194, L a t . 50° 42.2'N, Long. 120° 18.9'W. Conodonts Enantiognathus F i g . 5)  ziegleri  (Diebel) - 1 specimen  Cypridodella s p . c f . C. muelleri ( P l a t e V, F i g . 4) Neogondolella navicula specimen  navicula  ( P l a t e V,  (Tatge) - 1 specimen  (Huckriede)  - 1  N. sp. ( p o s s i b l e n. sp. s i m i l a r t o N. regale Mosher i n i t s h i g h prominent c a r i n a and d i s c r e t e d e n t i c l e s ) • about 8 specimens ( P l a t e V, F i g . 8 and 9) Age  T r i a s s i c , probably  Karnian  G.S.C. Loc. 93452 F i e l d No. M10, NTS 92 1/9, Kamloops, G r i d . No. 926192, L a t . 50° 42.0'N, Long. 120° 16.3'W. Conodonts Metapolygnathus polygnathiformis (Budurov and Stefanov) about 13 specimens ( P l a t e V, F i g . 10) Age T r i a s s i c , t h e range o f t h i s taxon i s l a t e L a d i n i a n t o l a t e Karnian. In abundance, however, i t i s most chara c t e r i s t i c o f K a r n i a n age r o c k s .  G.S.C. Loc. 93453 F i e l d No. M23, NTS 92 1/9, Kamloops, G r i d . No. 952199, L a t . 50° 42.4'N, Long. 120° 13.9'W. Conodonts Metapolygnathus polygnathiformis (Budurov and Stefanov) about 15 specimens ( P l a t e V, F i g . 11 and 12) Age Late T r i a s s i c , K a r n i a n , as i n G.S.C. L o c . 93452.  G.S.C. L o c . 93454 F i e l d No. M25, NTS 92 1/9, Kamloops, Lat.  G r i d No. 907226,  50° 43.8'N, Long. 120° 17.7'W.  Conodonts Metapolygnathus polygnathiformis 2 specimens  (Budurov and Stefanov)  Age Triassic,  probably Karnian  G.S.C. Loc. 93455 F i e l d No. M27, NTS 92 1/9, Kamloops, Lat.  G r i d No. 905229,  50° 44.0'N, Long. 120° 17.9'W.  Conodonts a s i n g l e a n t e r i o r fragment, p o s s i b l y o f or Metapolygnathus Age probably  Triassic  Neogondolella  203  APPENDIX I I . STRUCTURAL DATA  G r i d numbers r e f e r t o M i l i t a r y G r i d shown on P l a t e s  I and V I .  HARPER RANCH GROUP  / d i p o f bedding  Grid  East  G r i d North  139/85 E  98.35  20.1  108/90 144/82 145/61 135/81 150/87 130/68  E E W W W (Overturned)  98.3 98.65 98.45 98.6 98.75 98.8  19.75 19.75 19.55 19.5 19.6 19.35  110/82 151/81 145/80 162/63 138/85 171/42 163/78 156/80  W W W W E E E W  99.05 99.25 99.35 99.15 99.2 99.3 99.7 99.9  19.2 19.3 19.2 19.1 19.15 19.1 19.05 19.02  98/64 111/58 121/59 116/88 123/83 142/72 145/83 154/83 131/79 135/78 84/77 127/68 146/75 130/81 131/90 153/83 106/83  S S S N W E W  99.1 99.05 99.05 99.2 99.7 99.8 99.7 99.8 99.9 99.4 99.55 99.5 99.55 99.7 100.0 99.9 99.95  18.85 18.8 18.75 18.7 18.95 18.9 18.85 18.8 18.8 18.55 18.45 18.45 18.65 18.85 18.7 18.55 18.5  149/77 137/85 137/84 153/71 163/90  W E E E  100.1 100.15 100.25 100.6 100.7  18.85 18.9 18.85 18.8 18.85  w w w s w E W (Overturned) E  s  S t r i k e / d i p o f bedding  Grid  East  G r i d North  160/74 157/81 123/88 141/88 116/79 131/74 140/77 141/90  E E W (Overturned) W (Overturned) W E W  100.7 100.85 100.1 100.15 100.2 100.35 100.05 100.15  18.85 18.8 18.65 18.7 18.75 18.7 18.5 18.5  145/85 171/80 157/87 119/72 146/83 146/78 153/73 140/75  E E E E E E E E  101.25 101.5 101.05 101.2 101.4 101.45 101.5 101.6  18.8 18.85 18.65 18.5 18.55 18.6 18.6 18.7  154/85 162/85 159/71 44/42 156/79 38/65 171/62 20/66  W E E E E E E E  102.5 102.55 102.65 102.85 102.9 102.85 102.85 102.95  17.15 17.15 17.1 17.15 17.4 17.05 16.85 16.75  152/78 E 16/57 E  103.05 103.05  17.05 16.9  Trend/plunge o f f o l d axes 200/27 140/43  Grid East  G r i d North  102.98 99.1  16.9 18.9  NICOLA GROUP Dome H i l l s Grid East  G r i d North  126/56 E 120/48 E  88.8 88.85  23.6 23. 3  129/48 130/45 129/68 124/72 124/34 142/36  89.0 89.05 89.05 89.15 89.35 89.4  23.5 23.5 23.3 23.3 23.3 23.2  S t r i k e / d i p o f bedding  E E (Overturned) E E E E (Overturned)  205  S t r i k e / d i p o f bedding  Grid East  G r i d North  120/61 E  89.4  23.1  157/88 161/60 151/68 160/60 125/88  90.5 90.6 90.7 90.9 • 90.9  23.1 23.45 23.3 23.25 23.5  148/75 E 124/73 E 118/90  88.6 88.75 88.6  22.95 22.3 22.3  140/49 169/64 155/46 155/54 100/59 117/53 145/72 57/24 128/44 142/65 165/58 165/70 112/58 142/61 128/42 109/53 132/81 143/35 142/56 146/64 100/62 101/44 158/47 175/65 108/63 127/85 143/65 124/74 169/83  E E E E E E E W E E E E E E E E E E E E E E E E E E E E E  (Overturned) (Overturned) (Overturned) (Overturned)  89.2 89.25 89.4 89.5 89.5 89.6 89.85 89.8 89.8 89.7 89.6 89.1 89.05 89.2 89.3 89 .4 89.35 89.8 89.55 89.8 89.8 89.8 89.45 89.45 89.3 89.25 89.2 89.05 89.05  22.9 22.8 22.9 22 .9 22.8 22.8 22 .8 22.75 22.7 22.7 22.6 22.6 22.55 22.45 22.3 22.3 22 .25 22.6 22.35 22.3 22.1 22.05 22.15 22.1 22.1 22.1 22.15 22.15 22.05  151/40 150/52 125/53 153/57 135/70 148/46 151/57 154/59 128/62 174/68  E (Overturned) E (Overturned) E E E E E E E E  90.05 90.2 90.6 90.25 90.65 90.2 90.25 90.4 90.05 90.05  22.75 22.85 22.95 22.7 22.7 22.5 .. 22.6 22.55 22.35 22.15  W E E E E  (Overturned) (Overturned)  (Overturned) (Overturned)  (Overturned) (Overturned)  (Overturned) (Overturned)  206  S t r i k e / d i p o f bedding  Grid East  G r i d North  125/75 E  88.5  21.75  160/63 E  89.2  21.9  Trend/plunge o f minor f o l d axes 335/24 23/61 34/40 41/46 358/50  Strike/dip of a x i a l planes o f minor f o l d s 158/86 105/61 105/44 114/46 84/50  Grid East  E N N N N  89.45 89.75 90.0 90. 88.  G r i d North 22.1 22.7 22.4 22.6 21.75  Western P a u l Ridge Grid East  G r i d North  89.45  20.2  89.15 89.4 89.4 89.4 89.65  19.2 19.2 19.2 19.2 19.4  126/56 E  89.7  18.9  165/56 E 168/88 E  90.65 90.98  20.6 20.4  155/55 132/57 145/79 150/55 146/78 171/47 136/71 134/41 134/68  E E E E E E E E E  90.0 90.2 90.1 90.1 90.3 90.6 90.7 90.75 90.8  19.4 19.3 19.15 19.15 19.15 19.15 19.2 19.15 19.2  120/41 158/82 149/89 146/58  E W W E  90.35 90.5 90.6 90.8  18.95 18.9 18.98 19.0  115/80 144/73 136/87 127/87 156/77  E E E W E  91.15 91.1 91.6 91.7 91.9  20.4 20.3 20.02 20.05 20.05  91.3  19.9  / d i p o f bedding 131/90 128/47 161/69 117/71 76/60 168/67  W W E W E  68/63 E  207  S t r i k e / d i p o f bedding  Grid East  G r i d North  E E E E E E E E W W E E W E E E E E E E  91.3 91.5 91.25 91.35 91.5 91.55 91.65 91.25 91.3 91.4 91.5 91.5 91.85 91.98 91.98 91.65 91.7 91.8 91.95 91.98  19.85 19.95 19.75 19.75 19.7 19.7 19.7 19.5 19.5 19.5 19.45 19.4 19.45 19.55 19.4 19.35 19.3 19.3 19.25 19.3  153/22 E  92.95  20.3  162/77 06/62 04/68 156/47 146/51 142/58 160/78 134/63 155/69 142/68 171/75 125/28 07/42 05/38 158/41 162/90 131/43 162/63 110/22 156/78 153/82 08/57 05/67 173/51 02/71 171/72 14/65  92.1 92.3 92.3 92.5 92.9 92.05 92.1 92.2 92.3 92.3 92.4 92.45 92.65 92.75 92.8 92.3 92.3 92.4 92.55 92.5 92.6 92.7 92.8 92.9 92.75 92.8 92.9  19.85 19.9 19.8 19.95 19.9 19.5 19.6 19.55 19.6 19.5 19.5 19.55 19.65 19.7 19.6 19.4 19.3 19.35 19.4 19.3 19.25 19.45 19.35 19.4 19.1 19.15 19.25  93.5  20.2  27/81 131/87 166/73 128/70 156/81 39/60 130/71 151/81 151/81 176/81 150/67 152/73 74/52 158/50 165/68 156/78 166/81 147/81 161/77 164/85  E E E E (Overturned) E E E E E E E E E E (Overturned) E (Overturned) E E E E E E E E E E E  150/55 E  (Overturned) (Overturned) (Overturned)  208  S t r i k e / d i p o f bedding  Grid East  G r i d North  158/66 172/58 158/41 151/54 175/77 167/75 151/51 175/46 179/61 157/74 172/71 167/77 145/55 154/65 145/50 160/58 154/80 171/63  E E E E W E (Overturned) E E E E E (Overturned) E E E E E E E (Overturned)  93.02 93.1 93.2 93.7 93.2 93.3 93.35 93.45 93.7 93.8 93.9 93.97 93.1 93.4 93.5 93.7 93.9 93.0  19.9 19.7 19.75 19.75 19.5 19.55 19.55 19.5 19.4 19.4 19.4 19.45 19.25 19.35 19.3 19.2 19.15 19.25  165/73 163/87 158/89 147/74 152/83 160/86  E W W W E E  94.05 94.02 94.1 94.2 94.15 94.3  19.35 19.2 19.25 19.15 18.95 18.95  Trend/plunge o f minor f o l d axes 310/73 35/81 92/59 65/58 26/52 44/43 59/54 330/12 07/53  Strike/dip of a x i a l planes o f minor f o l d s  106/81 132/65 130/63 61/62 84/67 41/78  89.4 91.5 91.1 91.1 92.4 92.4 92.4 92.55 92.05  N E E W N E  Central Paul  S t r i k e / d i p o f bedding  Grid East  G r i d North 19.17 19.7 20.05 20.05 19.3 19.3 19.3 19.35 19.5  Ridge  Grid East  G r i d North  130/54 E 127/63 E 132/88 W  93.7 93.85 93.9  20.6 20.35 20.2  150/73 E  93.8  19.95  S t r i k e / d i p o f bedding  Grid East  G r i d North  132/50 E 159/76 E  93.9 93.9  19.95 19.7  129/78 135/67 140/43 133/52  E E E E  94.3 94.6 94.85 94.9  20.1 20.05 20.05 20.1  165/55 163/72 157/90 147/84 161/54 02/54 166/50 85/50 136/70 90/57 146/35 139/47 153/46 120/48 136/70 140/67 163/80 149/66 140/64 146/29 133/90 146/66 145/50 156/76 90/36 150/79 161/45 142/54 146/77 157/77 84/44 143/42 163/26 150/83 147/71 143/75 134/86 133/65  E E  94.1 94.05 94.1 94.15 94.25 94.3 94.35 94.5 94.6 94.6 94.75 94.85 94.95 94.7 94.8 94.9 94.02 94.1 94.2 94.3 94.75 94.9 94.25 94.35 94.5 94.5 94.55 94.65 94.8 94.9 94.95 94.64 94.8 94.3 94.65 94.8 94.95 94.4  19.85 19.8 19.75 19.75 19.8 19.7 19.7 19.8 19.8 19.7 19.8 19.8 19.8 19.65 19.7 19.7 19.65 19.6 19.6 19.5 19.5 19.6 19.4 19.4 19.3 19.35 19.45 19.35 19.35 19.45 19.4 19.25 19.2 19.1 19.0 19.1 19.1 19.9  142/51 E  95.05  20.05  163/61 E 156/61 E 146/90  95.15 95.25 95.3  19.98 19.98 19.9  E E E E N E N E E E E E E W E E E E E E N E E E E W N E W W E W W W  (Overturned)  210  S t r i k e / d i p o f bedding 155/47 142/59 124/59 123/73 154/61 156/65 140/81 173/74 141/73 136/68 143/83 169/76 150/55 156/77 134/51 160/76 156/76 158/80  Grid East  E E E E E E E W E E E W E W E E W W  162/83 E 143/77 W  Trend/plunge o f minor f o l d axes 340/57 05/28 326/16 340/0 317/40 324/31 330/09 328/42  G r i d North  95.02 95.1 95.3 95.1 95.25 95.3 95.4 95.0 95.1 95.2 95.4 95.15 95.3 95.5 95.15 95.2 95.45 95.5  19.7 19.6 19.7 19.5 19.5 19.5 19.55 19.3 19.35 19.4 19.45 19.2 19.3 19.3 19.1 19.1 19.1 19.2  95.2 95.4  19.0 19.0  Strike/dip of a x i a l planes o f minor f o l d s  Grid East 95. 2 95. 5 94. 75 95. 1 95. 25 95. 3 94. 15 94. 1  86/59 N 115/35 N 25/40 W 114/62 N 98/42 N  G r i d North 18.95 19.25 19.05 19.35 19.4 19.35 19.85 19.75  E a s t e r n P a u l Ridge  S t r i k e / d i p o f bedding  Grid East  G r i d North  165/84 W  95.6  20.0  149/81 W  95.55  19.7  143/83 E 150/88 W  96.2 96.4  21.95 21.0  147/78 176/69 171/21 140/43  96.7 96.2 96.45 96.8  19.7 19.45 19.2 19.35  W W W W  S t r i k e / d i p o f bedding  Grid East  154/56 E 119/58 E 125/78 W  97.55 97.6 97.6  20.05 20.1 20.15  114/88 131/70 115/48 116/63 174/60  W E E E W  97.5 97.9 97.9 97.9 97.3  19.9 19.85 19.8 19.8 19.2  149/58 W  97.1  18.85  101/90 91/85 109/72 117/78 158/62 118/82 98/82 143/87  N E E E E E E  98.25 98.2 98.35 98.25 98.3 98.4 98.5 98.3  19.6 19.35 19.3 19.15 19.15 19.17 19.13 19.05  123/90 171/58 107/71 112/86 134/74 130/50 137/69  E W W E E W E  98.55 98.25 98.8 98.75 98.75 98.75 98.95  18.9 18.55 18.85 18.7 18.6 18.5 18.4  128/83 123/77 95/78 109/90 107/62 108/79  E E S  99.0 99.05 99.4 99.4 99.45 99.6  18.35 18.3 18.45 18.4 18.15 18.15  E W  Trend/plunge o f minor f o l d axes 306/38 111/68 287/02 128/69  S t r i k e / d i p of a x i a l planes o f minor f o l d s 54/40 149/84 107/80 143/82  W W N N  Grid  Grid East 98.25 98.8 99.3 99.35  North  G r i d North 19.15 18.8 18.25 18.3  

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