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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 i n THE FACULTY OF GRADUATE STUDIES Department of Geological Sciences We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1979 <c) Randall Blain 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 A B S T R A C T T h e " C a c h e C r e e k G r o u p " a s p r e v i o u s l y m a p p e d i n t h e K a m l o o p s a r e a a c t u a l l y c o n s i s t s o f t w o s e q u e n c e s o f d i f f e r e n t a g e s , t h e L a t e P a l e o z o i c H a r p e r R a n c h G r o u p (new n a m e ) , a n d t h e U p p e r T r i a s s i c N i c o l a G r o u p . T h e l o w e r p a r t o f t h e H a r p e r R a n c h G r o u p i s a 5 k m - t h i c k s e q u e n c e o f h e m i p e l a g i c m u d s t o n e a n d r e d e p o s i t e d t u f f w i t h r a r e l e n s e s o f s h a l l o w m a r i n e l i m e s t o n e w h i c h y i e l d f o s s i l s o f L a t e M i s s i s s i p p i a n t o M i d d l e P e n n s y l v a n i a n a g e . T h i s s e q u e n c e i s d i s c o n f o r m a b l y o v e r l a i n b y s e v e r a l h u n d r e d m e t r e s o f L o w e r P e r m i a n l i m e s t o n e f o r m i n g t h e u p p e r p a r t o f t h e g r o u p . O n l y t h e l o w e r 2 . 3 km o f t h e s e c t i o n w e r e s t u d i e d i n d e t a i l . I n t h i s p o r t i o n , a n d e s i t i c t o d a c i t i c t u f f s c o n s i s t o f a s h p r o d u c e d b y s h a l l o w m a r i n e e r u p t i o n s , t h e n r e w o r k e d a n d r e d e p o s i t e d i n d e e p w a t e r b y t u r b i d i t y c u r r e n t s a n d h i g h c o n -c e n t r a t i o n s u b a q u e o u s f l o w s . A t h i n U p p e r M i s s i s s i p p i a n b i o c l a s t i c l i m e s t o n e w i t h a d i v e r s e m a r i n e f a u n a i s f o u n d n e a r t h e b a s e o f t h e s e q u e n c e . I t a c c u m u l a t e d 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 a n d s h a l l o w i n g o f t h e b a s i n f l o o r . T h e H a r p e r R a n c h a n d C h i l l i w a c k G r o u p s w e r e p r o b a b l y p a r t s o f a L a t e P a l e o z o i c v o l c a n i c a r c w h i c h f o r m e d a b o v e a n e a s t - d i p p i n g s u b d u c t i o n z o n e . E a s t o f t h e a r c was a n " o c e a n i c " b a c k - a r c b a s i n b o u n d e d o n t h e e a s t b y o r o g e n i c l a n d s f o r m e d b y t h e L a t e D e v o n i a n t o M i s s i s s i p p i a n C a r i b o o a n o r o g e n y . T h i s o r o g e n i c t e r r a n e s u p p l i e d t h e l i t h i c - r i c h e l a s t i c s o f t h e L a t e P a l e o z o i c A n a r c h i s t G r o u p , M t . R o b e r t s F o r m a t i o n , a n d t h e E a s t e r n a s s e m b l a g e o f M o n g e r ( 1 9 7 7 ) . P r e - L a t e T r i a s s i c d e f o r m a t i o n a n d l o w g r a d e m e t a m o r p h i s m o f t h e L a t e 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 o f s o u t h e r n B r i t i s h C o l u m b i a may h a v e b e e n c a u s e d b y P e r m o - T r i a s s i c c l o s u r e o f t h e b a c k - a r c b a s i n , a n d c o l l i s i o n o f t h e a r c w i t h t h e o l d o r o g e n i c t e r r a n e t o t h e e a s t . A new volcanic arc formed i n the Late T r i a s s i c i s represented by volcanic flows and breccias of the Nicola Group west of Kamloops. East of Kamloops, the Nicola Group consists of 3 km of sediments and v o l c a n i c l a s t i c s which accumulated i n deep water within a back-arc basin. Pelagic and hemi-pelagic mudstones dominate the section, but are interbedded with redeposited t u f f , l i t h i c sandstone and conglomerate, and limestone, a l l of which were deposited by t u r b i d i t y currents and high concentration density flows. Mas-sive and pillowed b a s a l t i c or andesitic volcanic flows occur near the base and top of the sequence, which has been subdivided i n t o f i v e l i t h o l o g i c u n i t s. Conodonts extracted from limestones y i e l d Karnian ages. Redeposited t u f f s i n the Nicola Group were probably derived from the volcanic arc to the west, and also from submarine volcanoes i n the basin to the east. L i t h i c sandstones and conglomerates contain sedimentary and v o l -canic d e t r i t u s , i n c l u d i n g abundant chert and cherty mudstone. These may have been derived from accreted oceanic rocks of the Cache Creek Group, exposed i n the emergent Pinchi g e a n t i c l i n e west of the volcanic arc. D e t r i t a l blue amphiboles i n fine-grained t u r b i d i t e limestones suggest t h i s sediment was also derived from shallow waters surrounding the Pinchi terrane. The Nicola volcanic arc therefore seems to have been b u i l t on an east-facing paleoslope. The back-arc basin was f l o o r e d by older eugeoclinal rocks, and stretched from the arc eastward to the miogeocline. The Harper Ranch and Nicola Groups are separated by a northwest-trending v e r t i c a l f a u l t , probably of Late Mesozoic or Early T e r t i a r y age. East of the f a u l t the lower Harper Ranch Group forms an east-facing homocline with few 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 units i n the Nicola Group o u t l i n e a p a i r of f a u l t e d northwest-trending f o l d s : an upright syncline on the east, and a westward-overturned a n t i c l i n e on the west. Deformation probably took place during the Latest T r i a s s i c to E a r l i e s t Jurassic I n k l i n i a n orogeny. The T r i a s s i c rocks are intruded by the Paul Peak Stock, a zoned i n t r u s i o n ranging from pyroxenite to granite i n compo-s i t i o n . This pluton i s s i m i l a r to zoned Alaskan-type mafic-ultramafic intrusions i n composition and tectonic s e t t i n g , and i s probably part of the 200 m.y. plutonic suite of southern B r i t i s h Columbia. Numerous andesitic to r h y o l i t i c dikes of probable Eocene to Oligocene age cut a l l other rock u n i t s . Prehnite-pumpellyite facies metamorphism has affected a l l rock units i n the area, in c l u d i n g the dikes. 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 rocks, suggesting that the Paleozoic rocks were affected by the Permo-Triassic low grade metamorphic event recorded elsewhere i n southern B r i t i s h Columbia. V TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES v i i i LIST OF ILLUSTRATIONS i x LIST OF PLATES x i i ACKNOWLEDGEMENTS x i i i Chapter I. INTRODUCTION 1 Preliminary Statement 1 Location, Physiography, and S u r f i c i a l Geology 5 Regional Geologic Setting 6 Stratigraphy 7 Structure 10 I I . HARPER RANCH GROUP (MAP UNIT 1) 12 Introduction 12 S t r u c t u r a l Setting, Physical Stratigraphy, and Biostratigraphy 12 Sedimentology 19 Mudstones 21 Volcanic Sandstones or Redeposited Tuffs 25 Description of Sedimentary Structures 25 Fine to medium-grained sandstone 25 Coarse to very coarse sandstone 26 Sandstone Petrography . . . 28 Source and Deposition of the Volcanic Detritus . . o 37 Deep Water C a l c i r u d i t e 40 Shallow-marine Limestone 43 Summary of Depositional Setting 54 Regional Correlations 55 Eastern Assemblage 57 Cache Creek-Bridge River Assemblage 60 Southern B r i t i s h Columbia Assemblage and Suggested Revision 62 Tectonic Significance of the Harper Ranch Assemblage . . 66 I I I . NICOLA GROUP (MAP-UNITS 2 THROUGH 6) Introduction 76 Physical Stratigraphy 76 S t r u c t u r a l Setting . 76 Description of Units 76 Unit 2 78 Unit 3 79 Unit 4 80 Unit 5 80 Unit 6 82 v i B i o s t r a t i g r a p h y 85 S e d i m e n t o l o g y a n d S e d i m e n t a r y P e t r o l o g y 88 M u d s t o n e a n d S i l t s t o n e 88 T h i n t o M e d i u m - b e d d e d M u d s t o n e 88 L a m i n a t e d M u d s t o n e 91 R e d e p o s i t e d B a s i n a l L i m e s t o n e 92 S u b m a r i n e P y r o c l a s t i c F l o w s a n d T u r b i d i t e s 94 V o l c a n i c S a n d s t o n e o r R e d e p o s i t e d T u f f 106 V i t r i c T u f f 1 1 0 L i t h i c S a n d s t o n e a n d C o n g l o m e r a t e 1 1 3 D i s c u s s i o n a n d R e g i o n a l I m p l i c a t i o n s 1 1 9 Summary o f D e p o s i t i o n a l S e t t i n g 1 1 9 R e l a t i o n s h i p B e t w e e n t h e N i c o l a a n d H a r p e r R a n c h G r o u p s 1 1 9 P r o v e n a n c e o f C l a s t i c D e t r i t u s a n d P a l e o g e o g r a p h y o f t h e Q u e s n e l T r o u g h 121 T e c t o n i c S e t t i n g a n d E v o l u t i o n o f t h e N i c o l a G r o u p 1 2 8 I V . I N T R U S I V E ROCKS 134 P a u l P e a k S t o c k ( M a p - U n i t 7) 134 F i e l d R e l a t i o n s 134 P e t r o g r a p h y 136 O l i v i n e C l i n o p y r o x e n i t e 136 L e u c o g a b b r o a n d D i o r i t e 136 H o r n b l e n d e G a b b r o a n d D i o r i t e 141 Q u a r t z M o n z o d i o r i t e a n d H o r n b l e n d e G r a n i t e . . . . 1 4 3 P e t r o g e n e s i s 1 4 3 O r i g i n o f t h e R o c k S e r i e s L e u c o g a b b r o t o G r a n i t e 143 O r i g i n o f t h e U l t r a m a f i c R o c k s 146 A g e a n d R e g i o n a l C o r r e l a t i o n 1 4 8 S m a l l P l u g s , S i l l s , a n d D i k e s ( M a p - U n i t 8) 152 D e s c r i p t i o n o f M i n o r I n t r u s i v e R o c k s . . . . . . . . . 1 5 3 T h i c k S i l l s 1 5 3 D a c i t e P o r p h y r y P l u g 154 P o r p h y r i t i c A n d e s i t e P l u g 154 N o n - p o r p h y r i t i c A n d e s i t e D i k e s a n d S i l l s 155 H o r n b l e n d e - P y r o x e n e A n d e s i t e D i k e s 155 R h y o l i t e D i k e s a n d S i l l s 1 5 6 A g e a n d C o r r e l a t i o n o f M i n o r I n t r u s i v e R o c k s 156 V . METAMORPH I SM 1 5 8 I n t r o d u c t i o n 1 5 8 Low G r a d e M e t a m o r p h i s m 158 G e n e r a l F e a t u r e s 158 T r i a s s i c R o c k s 1 6 0 P a u l P e a k S t o c k 1 6 4 D i k e s a n d S i l l s 165 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 R o c k s 167 C o n d i t i o n s o f M e t a m o r p h i s m 1 6 9 C o n t a c t M e t a m o r p h i s m . . . • . - . . . 1 6 9 A l b i t e - E p i d o t e - H o r n b e l s F a c i e s 1 6 9 H o r n b l e n d e - H o r n f e l s F a c i e s 172 E f f e c t s o f S u b s e q u e n t Low G r a d e M e t a m o r p h i s m 1 7 5 C o n d i t i o n s o f M e t a m o r p h i s m 1 7 5 V I . S T R U C T U R A L GEOLOGY 176 I n t r o d u c t i o n 1 7 6 F o l d i n g 176 H a r p e r R a n c h G r o u p . . . . 1 7 6 N i c o l a G r o u p 1 7 7 F a u l t i n g 1 8 1 V I I . SUMMARY AND CONCLUS IONS 1 8 3 B I B L I O G R A P H Y 1 8 8 A P P E N D I X I. REPORT ON CONODONT C O L L E C T I O N S E X T R A C T E D FROM L I M E S T O N E SAMPLES FROM T H E KAMLOOPS M A P - A R E A (NTS 9 2 1/9) , S O U T H - C E N T R A L B . C 2 0 0 A P P E N D I X I I . S T R U C T U R A L DATA 203 v i i i -TABLES Table I. Modal analyses of volcanic sandstones from the Harper Ranch Group 29 II . Allochem content of d i f f e r e n t microfacies of Mis s i s s i p p i a n limestone, Unit 1A, Harper Ranch Group 45 I I I . V i s u a l l y estimated modes of redeposited t u f f s 95 IV. Average compositions of zoned plagioclase from Unit 3 . . . . 98 V. V i s u a l l y estimated modes of volcanic sandstones or redeposited t u f f s from Units 2, 4, and 5 107 VI. V i s u a l l y estimated modes of v i t r i c t u f f s I l l VII. Modal analyses of c l a s t i c rocks from Unit 5 117 VIII. V i s u a l l y estimated modes of plutonic rocks from Paul Peak Stock 137 IX. Anorthite content of plagioclase feldspars from Paul Peak Stock 138 X. Low grade metamorphic minerals found i n rocks of d i f f e r e n t age and l i t h o l o g y i n the study area 161 XI. Albite-epidote-hornfels facies mineral assemblages i n the contact metamorphic aureole of Paul Peak Stock . . . . 173 i x , I L L U S T R A T I O N S F i g u r e 1. Map o f s o u t h e r n B r i t i s h C o l u m b i a s h o w i n g t h e l o c a t i o n o f -.1 " towns a n d - m a p - a r e a s " m e n t i o n e d i n - t h e t e x t . I n s e t s h o w s t e c t o n i c s u b d i v i s i o n s o f t h e C o r d i l l e r a i n B r i t i s h C o l u m b i a 2 2 . G e o l o g i c map o f t h e r e g i o n s u r r o u n d i n g K a m l o o p s . 8 3. S k e t c h g e o l o g i c map o f t h e H a r p e r R a n c h G r o u p a l o n g t h e S o u t h T h o m p s o n R i v e r e a s t o f K a m l o o p s 13 4 . S t r a t i g r a p h i c s e c t i o n o f t h e l o w e r p o r t i o n o f t h e H a r p e r R a n c h G r o u p . 15 5 . L a m i n a t e d m u d s t o n e a n d s i l t s t o n e , H a r p e r R a n c h G r o u p . . . . 22 6 . L a m i n a t e d m u d s t o n e a n d s i l t s t o n e , H a r p e r R a n c h G r o u p . . . . 22 7 . Q - F - L p l o t o f m o d a l d a t a f r o m v o l c a n i c l a s t i c r o c k s f r o m t h e H a r p e r R a n c h G r o u p 30 8 . P o l i s h e d s l a b o f v o l c a n i c s a n d s t o n e f r o m t h e H a r p e r R a n c h G r o u p 31 9 . P o l i s h e d s l a b o f v o l c a n i c s a n d s t o n e , H a r p e r R a n c h G r o u p . . . 31 1 0 . P h o t o m i c r o g r a p h o f t h i n - s e c t i o n , S a m p l e M K - 1 8 6 , H a r p e r R a n c h G r o u p 33 1 1 . P h o t o m i c r o g r a p h o f t h i n - s e c t i o n , S a m p l e M K - 1 8 6 , H a r p e r R a n c h G r o u p 33 1 2 . P h o t o m i c r o g r a p h o f t h i n - s e c t i o n , S a m p l e M K - 1 8 6 , H a r p e r R a n c h G r o u p 34 1 3 . P h o t o m i c r o g r a p h o f t h i n - s e c t i o n , S a m p l e M K - 1 9 3 , H a r p e r R a n c h G r o u p 34 1 4 . P o l i s h e d s l a b 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 , L o c . F - 2 , H a r p e r R a n c h G r o u p . . 41 1 5 . P h o t o m i c r o g r a p h o f t h e a l g a Solenopora, L o c . F - 2 , H a r p e r R a n c h G r o u p 42 X 16. Photomicrograph of the alga Parachaetetes, Loc. F-2, Harper Ranch Group 42 17. Upper Paleozoic eugeoclinal assemblages i n B r i t i s h 'Columbia " 58 18. Revised Upper Paleozoic eugeoclinal assemblages i n southern B r i t i s h Columbia and northern Washington 63 19. Sketch cross-section showing i n f e r r e d paleogeographic and paleotectonic elements of southern B r i t i s h Columbia during the Late Miss i s s i p p i a n to Early Pennsylvanian . . . 71 20. St r a t i g r a p h i c r e l a t i o n s h i p s of units within the Nicola Group 77 21. Poorly defined v e s i c u l a r pillows i n Unit 6B 83 22. Thin to medium-bedded mudstone i n Unit 5 90 23. Polished slab of thin-bedded mudstone, showing numerous flatt e n e d burrows p a r a l l e l to bedding 90 24. Photomicrograph of thin - s e c t i o n of t u f f from Unit 3 97 25. Photomicrograph of th i n - s e c t i o n of t u f f from Unit 3 97 26. Polished slab of conglomerate from Unit 3, co n s i s t i n g e n t i r e l y of pebbles of p o r p h y r i t i c dacite or andesite . . . 101 27. Polished slab of submarine t u f f from Unit 3 showing a Bouma BC sequence: planar laminations o v e r l a i n by cross-laminations 104 28. Polished slab of submarine t u f f from Unit 3 showing the base of a graded t u r b i d i t e bed, with a concentration of coarse pl a g i o c l a s e , pyroxene, and hornblende c r y s t a l s . 105 29. Photomicrograph of th i n - s e c t i o n , Sample MK-151, volcanic sandstone or redeposited t u f f from Unit 4 109 30. Photomicrograph of thi n - s e c t i o n , Sample MK-215, volcanic sandstone or redeposited t u f f i n Unit 5 109 31. Photomicrograph of thin - s e c t i o n (Sample MK-150) of v i t r i c t u f f from Unit 2 112 32. Outcrop of l i t h i c conglomerate i n Unit 5, Dome H i l l s . . . . 115 33. Polished slab of l i t h i c conglomerate from Unit 5, Dome H i l l s 115 x i 34. Photomicrograph of thi n - s e c t i o n , Sample MK-132, l i t h i c -v olcanic sandstone from Unit 5 118 35. Location map of Ouesnel trough and surrounding Mesozoic tectonic elements of cent r a l and southern B r i t i s h Columbia 122 36. Geologic map of the Paul Peak Stock 135 37. Photomicrograph of leucogabbro, MK-98 140 38. Photomicrograph of hornblende gabbro, MK-195 142 39. Photomicrograph of hornblende granite, MK-104 142 40. Prehnite vein i n p y r o c l a s t i c t u r b i d i t e from Unit 3, Dome H i l l s 162 41. Map of mineral assemblages and isograds from the contact metamorphic aureole of the Paul Peak Stock . . . . 171 x i i P L A T E S P l a t e I. G e o l o g i c Map o f P a u l R i d g e a n d t h e s o u t h w e s t e r n -in-~s?ear'•• -Dome H i l l s , N i c o l a m a p - a r e a , B r i t i s h C o l u m b i a p o c k e t t f i -f o\\ I I . M i c r o f a u n a f r o m u p p e r M i s s i s s i p p i a n l i m e s t o n e , H a r p e r R a n c h G r o u p ( U n i t IA ) 18 I I I . M i c r o f a c i e s f r o m u p p e r 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 I A , H a r p e r R a n c h G r o u p 47 I V . M i c r o f a c i e s f r o m u p p e r 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 I A , H a r p e r R a n c h G r o u p 49 V . C o n o d o n t s e x t r a c t e d f r o m l i m e s t o n e s i n t h e N i c o l a G r o u p , P a u l R i d g e a n d Dome H i l l s 87 V I . S t r u c t u r a l map a n d c r o s s - s e c t i o n s - i n _ r . e a r ^ £ 3 ^.jj • -f p o c k e t ' x i i i ACKNOWLEDGEMENTS W. R. D a n n e r f i r s t d i r e c t e d my a t t e n t i o n t o p r o b l e m s o f t h e " C a c h e C r e e k G r o u p , " a n d s u p e r v i s e d a l l s t a g e s o f t h i s w o r k . D i s c u s s i o n s w i t h h i m a n d w i t h t h e f o l l o w i n g p e o p l e g r e a t l y i m p r o v e d my u n d e r s t a n d i n g o f t h e P a l e o z o i c a n d M e s o z o i c g e o l o g y o f s o u t h e r n B r i t i s h C o l u m b i a : W. B . B a r n e s , P. B o n d , I. D u n c a n , J . G r e t t e , J . W. H . M o n g e r , K. N i e l s e n , I. A . P a t e r s o n , P. B . R e a d , J . V . R o s s , P. S o l b e r g , a n d W. B . T r a v e r s . B . E . B . C a m e r o n o f t h e G e o l o g i c a l S u r v e y o f C a n a d a i d e n t i f i e d t h e T r i a s s i c c o n o d o n t s , p r o v i d e d a d v i c e a n d t h e u s e o f l a b o r a t o r y f a c i l i t i e s f o r t h e i r e x t r a c t i o n , a n d a s s i s t e d i n t a k i n g t h e SEM p h o t o m i c r o g r a p h s . F o s s i l s f r o m t h e H a r p e r R a n c h G r o u p w e r e i d e n t i f i e d b y J . T . D u t r o , J r . , o f t h e U n i t e d S t a t e s G e o l o g i c a l S u r v e y . R. L . A r m s t r o n g p r o v i d e d i n f o r m a t i o n o n r a d i o m e t r i c d a t i n g o f t h e T r i a s s i c - J u r a s s i c b o u n d a r y . E u g e n i o G o n z a l e s o f t h e U n i v e r s i t y o f C a l i f o r n i a a t S a n t a C r u z p r o v i d e d t e c h n i c a l h e l p i n t h e p r e p a r a t i o n o f t h e p h o t o g r a p h s a n d i l l u s t r a t i o n s . W. R. D a n n e r a n d W. B . B a r n e s r e v i e w e d e a r l i e r d r a f t s o f t h e t h e s i s , a n d t h e i r c o m m e n t s i m p r o v e d t h e t e x t g r e a t l y . I w o u l d l i k e t o t h a n k a l l o f t h e s e p e o p l e f o r t h e i r h e l p , a n d e s p e c i a l l y t h e K a m l o o p s I n d i a n B a n d , who a l l o w e d me t o c o n d u c t m u c h o f t h i s f i e l d w o r k o n r e s e r v a t i o n l a n d s . A l s o , t h e i n t e r e s t a n d e n c o u r a g e m e n t o f J . W. H . M o n g e r h e l p e d me t h r o u g h t h e t i m e s w h e n c o m p l e t i o n o f t h i s w o r k s e e m e d f a r away i n d e e d , s o t o h i m I a l s o g i v e s p e c i a l t h a n k s . 1 CHAPTER I. INTRODUCTION PRELIMINARY STATEMENT Upper Paleozoic eugeoclinal rocks occur widely i n southern B r i t i s h Columbia, but t h e i r stratigraphy, i n t e r n a l structure, and the sedimentary and tectonic environments i n which they formed are poorly known. A recent attempt by Monger (1977) to divide them into a number of t e c t o n o s t r a t i -graphic assemblages points out the d i v e r s i t y of these rocks, and the d i f -f i c u l t i e s inherent i n attempts to decipher t h e i r o r i g i n a l tectonic s e t t i n g ' and explain t h e i r present r e l a t i v e positions within the C o r d i l l e r a n orogen. Detailed studies of each assemblage are necessary i n order to resolve these problems. The o r i g i n a l purpose of t h i s study was to analyze the stratigraphy, sedimentology, and structure of Upper Paleozoic sedimentary rocks of the "Cache Creek Group" i n Nicola map-area (Fig. 1). The rocks had been described 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 , q u a r t z i t e , conglomerate and breccia, minor volcanic rock, and limestone. This Pennsylvanian and Permian sequence l i e s between coeval miogeoclinal s t r a t a to the east and oceanic rocks to the west, and Monger (1975a) and Monger and others (1972) suggested that i t forms part of a Late Paleozoic volcanic i s l a n d arc. Previous work on the area was p r i m a r i l y regional mapping and reconnaissance (Dawson, 1879, 1895; Daly, 1915; Cock f i e l d , 1948). The best exposures of the "Cache Creek Group" i n Nicola map-area are i n the North and South Thompson River 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 and Danner (1974) east and northeast of Kamloops provided a s t a r t i n g point F i g . 1. Map of southern B r i t i s h Columbia showing the lo c a t i o n of towns and map-areas mentioned i n the text. Inset shows tectonic subdivisions of the C o r d i l l e r a i n B r i t i s h Columbia. 3 f o r f u r t h e r s t r a t i g r a p h i c s t u d y . D u r i n g t h e summer o f 1 9 7 5 , m a p p i n g was c a r r i e d o u t a t a s c a l e o f 1 : 1 2 , 5 0 0 a l o n g t h e n o r t h s i d e o f t h e S o u t h T h o m p s o n R i v e r , f r o m K a m l o o p s e a s t w a r d t o t h e l i m i t s o f t h e a r e a s t u d i e d b y S a d a a n d D a n n e r , a n d a l s o i n t h e s o u t h e r n Dome H i l l s n o r t h o f K a m l o o p s . T h e a r e a m a p p e d i s a b o u t 25 s q u a r e k i l o m e t r e s . T h e s c o p e o f t h e s t u d y e x p a n d e d w h e n c o l l e c t i o n s o f c o n o d o n t s e x t r a c t e d f r o m d a r k g r a y , a r g i l l a c e o u s 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 m u d s t o n e s p r o v e d t o b e o f L a t e T r i a s s i c a g e . T h i s d a t a , a l o n g w i t h t h e m a p p i n g , r e v e a l s t h a t t w o s e q u e n c e s o f d i f f e r e n t a g e s b u t g r o s s l y s i m i l a r l i t h o l o g y a r e p r e s e n t w i t h i n t h e s t u d y a r e a : a L a t e M i s s i s s i p p i a n t o P e r m i a n s e q u e n c e t o t h e e a s t , a n d a L a t e T r i a s s i c s e q u e n c e t o t h e w e s t ( F i g . 2 ) . T h e y a r e s e p a r a t e d b y 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 . B o t h c o n s i s t p r i m a r i l y o f d e e p w a t e r m u d s t o n e w i t h v o l c a h i c l a s t i c s a n d s t o n e s a n d p y r o c l a s t i c f l o w s d e p o s i t e d b y t u r b i d i t y c u r r e n t s o r h i g h - c o n c e n t r a t i o n d e n s i t y c u r r e n t s . H o w e v e r , l i t h o l o g i c f e a t u r e s s u c h a s p a r t i n g c h a r a c t e r i s t i c s o f m u d s t o n e s , p r e s e n c e o f s h a l l o w w a t e r v e r s u s d e e p w a t e r l i m e s t o n e s , a n d a b u n d a n c e o f u n a l t e r e d m a f i c m i n e r a l s i n p y r o c l a s t i c r o c k s a r e p r o b a b l y s u f f i c i e n t t o d i s t i n g u i s h t h e t w o s e q u e n c e s i n r e g i o n a l m a p p i n g w i t h o n l y s c a t t e r e d f o s s i l c o n t r o l . U s a g e o f t h e s t r a t i g r a p h i c t e r m " C a c h e C r e e k G r o u p " h a s r e c e n t l y b e e n d i s c u s s e d b y M o n g e r ( 1 9 7 5 b ) . He p r o p o s e s t o r e s t r i c t t h e t e r m t o U p p e r P a l e o -z o i c r o c k s o f o c e a n i c a s p e c t ( b e d d e d c h e r t a n d p e l i t e , l i m e s t o n e , b a s i c v o l -c a n i c s , a n d u l t r a m a f i c r o c k s ) . T h e s e r o c k s f o r m a d i s c o n t i n u o u s e l o n g a t e b e l t i n t h e c e n t r a l p a r t o f t h e I n t e r m o n t a n e b e l t o f B r i t i s h C o l u m b i a , i n c l u d -i n g t h e t y p e a r e a o f t h e g r o u p a t t h e t o w n o f C a c h e C r e e k , 70 km w e s t o f K a m l o o p s . T h e U p p e r P a l e o z o i c r o c k s i n t h e N i c o l a a n d V e r n o n m a p - a r e a s w o u l d b e e x c l u d e d f r o m t h e g r o u p o n t h e b a s i s o f t h e i r d i f f e r i n g l i t h o l o g y . 4 A p p l i c a t i o n o f t h e name i n t h i s r e g i o n i s e v e n m o r e u n f o r t u n a t e i n t h a t t h e c o n o d o n t c o l l e c t i o n s r e p o r t e d h e r e i n a n d b y O k u l i t c h a n d C a m e r o n (1976 ) d e m o n s t r a t e t h a t l a r g e a r e a s u n d e r l a i n b y U p p e r T r i a s s i c r o c k s w e r e i n a d -v e r t e n t l y i n c l u d e d w i t h i n t h e " C a c h e C r e e k G r o u p " b y C o c k f i e l d ( 1 9 4 8 ) a n d J o n e s ( 1 9 5 9 ) . F o r t h e s e r e a s o n s , a new s t r a t i g r a p h i c name o r names s h o u l d b e f o u n d f o r U p p e r P a l e o z o i c r o c k s i n N i c o l a a n d V e r n o n m a p - a r e a s . D a n n e r ( p e r s . c o m m . , 1 9 7 8 ) p r o p o s e s t h e name H a r p e r R a n c h G r o u p f o r t h e U p p e r P a l e o z o i c r o c k s e x p o s e d a l o n g t h e S o u t h T h o m p s o n R i v e r . T h i s t e r m w i l l b e u s e d i n t h i s p a p e r . F o r p u r p o s e s o f d i s c u s s i o n , I w i l l a l s o i n f o r m a l l y e x t e n d i t s u s e t o r o c k s o f s i m i l a r a g e a n d l i t h o l o g y i n N i c o l a a n d V e r n o n m a p - a r e a s w h i c h w e r e m a p p e d b y p r e v i o u s w o r k e r s a s " C a c h e C r e e k G r o u p . " U p p e r T r i a s s i c r o c k s f o r m e r l y m a p p e d a s " C a c h e C r e e k G r o u p " I i n c l u d e w i t h t h e N i c o l a G r o u p . R o c k s i n t h e t y p e a r e a o f t h e N i c o l a G r o u p , a b o u t 60 km s o u t h w e s t o f K a m l o o p s , a r e b a s a l t i c a n d a n d e s i t i c f l o w , b r e c c i a s . , t u f f s , a s s o c i a t e d s e d i m e n t s , a n d r e e f l i m e s t o n e s , o f L a t e T r i a s s i c a g e ( S c h a u , 1 9 7 0 ) . U p p e r T r i a s s i c r o c k s e a s t o f K a m l o o p s a r e d e e p e r w a t e r m u d s t o n e s a n d d i s t a l v o l c a n i c l a s t i c s w h i c h may h a v e b e e n e r u p t e d f r o m v o l c a n i c c e n t e r s r e p r e s e n t e d b y r o c k s o f t h e t y p e N i c o l a G r o u p . T h e t w o f a c i e s a r e c o e v a l a n d p r o b a b l y l a t e r a l l y g r a d a t i o n a l , a n d t h u s t h e i r i n c l u s i o n i n t h e same g r o u p i s a p p r o -p r i a t e . T h i s u s a g e h a s b e e n a p p l i e d b y O k u l i t c h a n d C a m e r o n ( 1 9 7 6 ) a n d R e a d a n d O k u l i t c h ( 1 9 7 7 ) t o r o c k s i n V e r n o n m a p - a r e a w h i c h a r e s i m i l a r i n a g e a n d l i t h o l o g y t o t h e T r i a s s i c r o c k s d e s c r i b e d i n t h i s s t u d y . T h e b u l k o f t h i s t h e s i s d e a l s w i t h t h e p h y s i c a l s t r a t i g r a p h y , l i t h o -l o g i c d e s c r i p t i o n , p e t r o g r a p h y , a n d r e g i o n a l c o r r e l a t i o n s o f t h e H a r p e r R a n c h a n d N i c o l a G r o u p s i n t h e s t u d y a r e a . A d d i t i o n a l c h a p t e r s d e a l w i t h t h e i r s t r u c t u r e a n d m e t a m o r p h i s m , a n d t h e p e t r o l o g y o f t h e v a r i e d i n t r u s i v e r o c k s i n t h e a r e a . 5 L O C A T I O N , P H Y S I O G R A P H Y , AND S U R F I C I A L GEOLOGY T h e s t u d y a r e a i s i m m e d i a t e l y e a s t a n d n o r t h e a s t o f K a m l o o p s i n N i c o l a m a p - a r e a , s o u t h - c e n t r a l B r i t i s h C o l u m b i a . T h e Q u a t e r n a r y g e o l o g y a n d g e o -m o r p h o l o g y o f t h e N i c o l a - V e r n o n a r e a h a s b e e n d e s c r i b e d a t l e n g t h b y F u l t o n ( 1 9 7 5 ) , f r o m w h i c h t h e f o l l o w i n g summary i s l a r g e l y t a k e n . T h e a r e a i s i n t h e s o u t h e r n p o r t i o n o f t h e i n t e r i o r p l a t e a u o f t h e C a n a d i a n C o r d i l l e r a . T h i s i s a n e l e v a t e d r e g i o n o f b r o a d u p l a n d b l o c k s s e p a r a t e d b y a s y s t e m o f m a j o r v a l l e y s . T h e l a r g e v a l l e y s n e a r K a m l o o p s a r e t h o s e o f t h e N o r t h a n d S o u t h T h o m p s o n R i v e r s , w h i c h f l o w f r o m t h e n o r t h a n d e a s t r e s p e c t i v e l y , j o i n i n g a t K a m l o o p s t o f o r m t h e w e s t - f l o w i n g T h o m p s o n R i v e r . T h e s e v a l l e y s c u t a c r o s s t h e t r e n d o f b e d r o c k u n i t s a n d s t r u c t u r e s , a n d a r e p r o b a b l y a n t e c e d e n t s t r e a m v a l l e y s o r i g i n a l l y d e v e l o p e d o n a n E a r l y T e r t i a r y e r o s i o n s u r f a c e . L a t e P l e i s t o c e n e g l a c i a l e r o s i o n p r o d u c e d s t e e p -w a l l e d v a l l e y s now f l o o r e d b y t h i c k u n c o n s o l i d a t e d d e p o s i t s , a n d c o n t a i n i n g n u m e r o u s l a r g e l a k e s , s u c h a s K a m l o o p s a n d S h u s w a p L a k e s . T h e u p l a n d r e g i o n n o r t h e a s t o f K a m l o o p s i s b i s e c t e d b y t h e n o r t h e a s t -t r e n d i n g P a u l C r e e k v a l l e y , w i t h t h e Dome H i l l s l y i n g t o t h e n o r t h a n d a n u n n a m e d r i d g e t o t h e s o u t h ( P l a t e I ) . T h i s r i d g e t e r m i n a t e s a t i t s w e s t e r n e n d i n P e t e r a n d P a u l P e a k s , a n d I w i l l r e f e r t o i t a s P a u l R i d g e . T h e b e s t b e d r o c k e x p o s u r e s o c c u r o n t h e s t e e p s o u t h e r n f l a n k o f P a u l R i d g e , a n d t h e w e s t e r n f l a n k s o f t h e Dome H i l l s . T h e g e n t l y r o l l i n g s u m m i t s u r f a c e a n d n o r t h s l o p e o f P a u l R i d g e h a v e o n l y l i m i t e d e x p o s u r e , w i t h e x t e n s i v e g r a s s a n d f o r e s t c o v e r . T h e h i g h e r e l e v a t i o n s o f t h e Dome H i l l s a r e a l s o h e a v i l y f o r e s t e d . S u r f i c i a l d e p o s i t s i n t h e a r e a a r e e x t e n s i v e a n d v a r i e d . T i l l a n d d r u m l i n o i d d e p o s i t s m a n t l e m o s t o f P a u l C r e e k v a l l e y a n d t h e e a s t e r n Dome 6 H i l l s . The r o l l i n g summit surface of Paul Ridge may be l a r g e l y covered by a t h i n veneer of t i l l , as suggested by a few exposures along the southern edge of the summit. The o r i e n t a t i o n of streamlined bedrock ridges and morainal deposits indicates that i c e flow was toward the southeast. This p a r a l l e l s the s t r i k e of the T r i a s s i c bedrocks u n i t s , and suggests some control of l o c a l ice movement or the p r e - g l a c i a l topography by the bedrock structure. Along the South Thompson River are prominent terraces of varved lacus-t r i n e s i l t . These s i l t s were deposited by a s e r i e s of p r o g l a c i a l lakes formed during d e g l a c i a t i o n of the region. The h i s t o r y of these lakes has been described by Mathews (1944) and Fulton (1965, 1969). A number of o l d lake strandlines can be recognized at d i f f e r e n t elevations on the west flank of Paul Peak. A l l u v i a l fans c o n s i s t i n g of poorly sorted gravel, sand, s i l t , and clay have accumulated at the base of the steep walls of the North and South Thomp-son v a l l e y s , mantling the s i l t terraces i n the l a t t e r . Fulton (1975) suggests that the fans formed p r i m a r i l y during the period of aggradation d i r e c t l y following d e g l a c i a t i o n . Large talus cones cover the southern and southwestern slopes of Paul and Peter Peaks, formed by mass wasting of the c l i f f s above. The lake terraces, and l o c a l l y the a l l u v i a l fans, have been i n c i s e d by the r i v e r s , and the modern v a l l e y bottoms are covered by f l o o d p l a i n deposits. REGIONAL GEOLOGIC SETTING The study area i s i n the eastern part of the Intermontane b e l t , a eugeoclinal terrane flanked on the east by the Omineca C r y s t a l l i n e b e l t , and on the west by the Coast C r y s t a l l i n e b e l t (Fig. 1, i n s e t ) . The Intermontane b e l t consists predominantly of oceanic and i s l a n d arc-type sedimentary and 7 v o l c a n i c r o c k s o f L a t e P a l e o z o i c t o E a r l y J u r a s s i c a g e . M a r i n e a n d n o n m a r i n e c l a s t i c s e d i m e n t s a c c u m u l a t e d i n s u c c e s s o r b a s i n s f r o m M i d d l e J u r a s s i c t o E o c e n e t i m e . M e s o z o i c a n d T e r t i a r y p l u t o n s a r e a b u n d a n t , a n d T e r t i a r y p l a t e a u v o l c a n i c s : m a n t l e o l d e r r o c k s o v e r l a r g e , a r e a s . T h e m e t a m o r p h i c g r a d e o f t h e s e d i m e n t a r y a n d v o l c a n i c r o c k s i s t y p i c a l l y l o w , r a n g i n g f r o m e s s e n -t i a l l y u n m e t a m o r p h o s e d t o 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 . R o c k s t r a n s i t i o n a l t o t h e b l u e s c h i s t f a c i e s a r e k n o w n l o c a l l y ( M o n g e r , 1 9 7 5 b ) ; P a t e r s o n a n d H a r a k a l , 1 9 7 4 ) . S t r a t i g r a p h y T h e g e n e r a l g e o l o g y o f t h e K a m l o o p s r e g i o n i s s h o w n i n F i g . 2 . R o c k s o f L a t e M i s s i s s i p p i a n t o P e r m i a n a g e , m a p p e d b y C o c k f i e l d ( 1 9 4 8 ) a n d J o n e s ( 1 9 5 9 ) a s " C a c h e C r e e k G r o u p , " a r e d e s i g n a t e d t h e H a r p e r R a n c h G r o u p . T h e y c o n s i s t o f a n U p p e r M i s s i s s i p p i a n t o L o w e r P e n n s y l v a n i a n s e q u e n c e o f m u d s t o n e a n d r e d e p o s i t e d t u f f w i t h 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 , d i s c o n f o r m a b l y o v e r l a i n b y m a s s i v e L o w e r P e r m i a n l i m e s t o n e . U p p e r P e r m i a n l i m e s t o n e i s r e c o g n i z e d f r o m o n e l o c a l i t y e a s t o f K a m l o o p s ( S a d a a n d D a n n e r , 1 9 7 4 ) . Low g r a d e m e t a m o r p h i c r o c k s w h i c h a r e p r o b a b l y i n p a r t t i m e - e q u i v a l e n t t o t h e H a r p e r R a n c h G r o u p o c c u r t o t h e n o r t h e a s t o f K a m l o o p s , n e a r S h u s w a p L a k e , i n t h e M o u n t I d a G r o u p ( J o n e s , 1 9 5 9 ) . T h e E a g l e B a y F o r m a t i o n c o n s i s t s o f p h y l l i t e , q u a r t z i t e , g r e e n s t o n e , a n d l i m e s t o n e . M i s s i s s i p p i a n c o n o d o n t s h a v e b e e n r e c o v e r e d f r o m a l i m e s t o n e u n i t , b u t f o l i a t e d g r a n i t i c r o c k s i n t r u -s i v e i n t o o t h e r p a r t s o f t h e E a g l e B a y y i e l d D e v o n i a n (372 m . y . ) r a d i o m e t r i c a g e s ( O k u l i t c h a n d o t h e r s , 1 9 7 5 ) . R o c k s y o u n g e r t h a n M i s s i s s i p p i a n a g e may a l s o b e p r e s e n t . No f o s s i l s h a v e b e e n r e c o v e r e d f r o m t h e s c h i s t , q u a r t z i t e , g r e e n s t o n e , m a r b l e , a n d g n e i s s t h a t m a k e u p m o s t o f t h e r e s t o f t h e M o u n t I d a G r o u p , b u t t h e s e r o c k s l i e s t r a t i g r a p h i c a l l y b e l o w U p p e r T r i a s s i c m e t a s e d i -m e n t a r y r o c k s ( O k u l i t c h a n d C a m e r o n , 1 9 7 6 ) . 0. 2 W W W W W W L E G E N D T E R T I A R Y Tv: Eocene to Pliocene volcanic and sedimentary rocks. UPPER TR IASS IC Nicolo Group u'Rvibasalt and andesite flows, breccia, and tuff, volcanic sandstone and mudstone, limestone. uDs-. mudstone, volejnic sandstone and tuff, minor lime turbidites and basalt or andesite flows. u~Asm.-equivalent metamorphosed rocks, including Sicamous Formation near Shuswap Lcke. MISSISSIPPIAN TO PERMIAN Harper Ranch Group MPhr: mudstone, volcanic sandstone, l imestone, volcanic flows. ++++ ++++ ++++ PALEOZOIC AND 0 L D E R 7 Mount Ida Group Pmi: schist, quartz ite, greenstone, marble, gneiss. Includes Chapperon Group west of Okanagan Lake. Peb: Eogle Bay Formation: phyllite, quartzite, greenstone, marble, arqillite. Shuswap Metomorphic Complex gns: gneiss, schist, and pegmatite. INTRUSIVE ROCKS, MESOZOIC TO TERT IARY gr: diorite to granite or syenite. Geologic contact . High-ongle fault. F i g . 2. Geologic map of the region surrounding Kamloops. 9 U p p e r P a l e o z o i c r o c k s w e s t o f K a m l o o p s ( n o t s hown o n F i g . 2) a r e o c e a n i c r o c k s o f t h e t y p e C a c h e C r e e k G r o u p i n A s h c r o f t m a p - a r e a . T h e s e r o c k s a r e m o s t l y b e d d e d c h e r t a n d m u d s t o n e , b a s i c v o l c a n i c s , a n d l a r g e b o d i e s o f s h a l -l o w w a t e r l i m e s t o n e . T h e y a r e p o o r l y e x p o s e d , c o m p l e x l y d e f o r m e d , a n d a s t r a t i g r a p h i c s e q u e n c e h a s n o t b e e n w o r k e d o u t , b u t r o c k s o f P e n n s y l v a n i a n , P e r m i a n , a n d p e r h a p s L a t e T r i a s s i c a g e a r e p r e s e n t ( M o n g e r , 1 9 7 7 ) . T h e t w o f a c i e s c o m p r i s i n g t h e N i c o l a G r o u p w e r e d e s c r i b e d a b o v e . T h e n o r t h - n o r t h w e s t - t r e n d i n g b e l t o f v o l c a n i c f l o w s a n d b r e c c i a s w e s t o f K a m l o o p s r e p r e s e n t s a L a t e T r i a s s i c v o l c a n i c a r c . T h e b a s i n a l s e d i m e n t a r y a n d v o l c a n i -c l a s t i c r o c k s t o t h e e a s t w e r e d e p o s i t e d i n a b a c k - a r c b a s i n . M e t a m o r p h o s e d a n d h i g h l y d e f o r m e d e q u i v a l e n t s o f b o t h f a c i e s o c c u r i n V e r n o n m a p - a r e a . N e a r S h u s w a p L a k e , t h e s e d i m e n t a r y u n i t u n d e r g o e s a f a c i e s c h a n g e t o b e c o m e t h e g r a p h i t i c , p h y l l i t i c l i m e s t o n e o f t h e S i c a m o u s F o r m a t i o n ( O k u l i t c h , 1 9 7 4 ) . S o u t h a n d s o u t h e a s t f r o m K a m l o o p s , L a t e T r i a s s i c f o s s i l c o l l e c t i o n s a l l o w p r e l i m i n a r y d i v i s i o n o f t h e " C a c h e C r e e k G r o u p " i n t o U p p e r P a l e o z o i c a n d U p p e r T r i a s s i c u n i t s ( O k u l i t c h a n d C a m e r o n , 1 9 7 6 ) . N o r t h o f t h e s t u d y a r e a , n o T r i a s s i c f o s s i l s h a v e y e t b e e n f o u n d , a n d t h e u n i t s r e m a i n u n d i f f e r -e n t i a t e d . T h e p r e s e n c e o f n u m e r o u s l i m e s t o n e l e n s e s , some w i t h P e n n s y l v a n i a n a n d P e r m i a n f o s s i l s ( S a d a a n d D a n n e r , 1 9 7 4 ) s u g g e s t s t h a t i n N i c o l a m a p - a r e a , a l l b u t t h e w e s t e r n m o s t p o r t i o n o f t h i s t e r r a n e i s U p p e r P a l e o z o i c i n a g e . I n B o n a p a r t e L a k e m a p - a r e a n o r t h o f K a m l o o p s , C a m p b e l l a n d T i p p e r ( 1 9 7 1 ) h a v e m a p p e d a L o w e r t o M i d d l e J u r a s s i c v o l c a n i c - c l a s t i c u n i t w h i c h i s l i t h o -l o g i c a l l y n e a r l y i n d i s t i n g u i s h a b l e f r o m t h e v o l c a n i c a r c f a c i e s o f t h e N i c o l a G r o u p . Some r o c k s o f t h i s a g e may b e i n c l u d e d w i t h t h e N i c o l a G r o u p i n F i g . 2 , p a r t i c u l a r l y i n t h e e a s t e r n p a r t o f t h e a r e a . P l u t o n i c r o c k s i n t h e r e g i o n r a n g e f r o m L a t e T r i a s s i c t o T e r t i a r y (?) 10 i n age. Most were probably emplaced during Latest T r i a s s i c to Early J u r a s s i c and Middle to Upper Jurassic plutonic pulses (Gabrielse and Reesor, 1974). Quartz d i o r i t e , granodiorite, and quartz monzonite are the common i n t r u s i v e rocks. D i o r i t i c to ultramafic types occur l o c a l l y , and several small s y e n i t i c to g r a n i t i c stocks are also present. T e r t i a r y volcanic rocks and sediments underlie large areas i n the region. Middle Eocene basal t , andesite, and dacite lavas and breccias and minor sediments are unconformably o v e r l a i n by f l a t - l y i n g , Miocene to Pliocene plateau lavas, c h i e f l y o l i v i n e b a s a l t . Structure The eastern portion of the Intermontane b e l t forms the hinterland of the Columbian Orogen (Wheeler and Gabrielse, 1972). The core zone of the orogen i s the Omineca C r y s t a l l i n e b e l t , represented at t h i s l a t i t u d e by the Shuswap Metamorphic Complex and Kootenay Arc, which l i e successively to the east of F i g . 2. The Foreland Thrust and Fold b e l t l i e s i n the Rocky Mountains to the east of the Omineca b e l t . Structures are best known i n the Foreland and Omineca b e l t s . The Foreland b e l t i s a zone of e a s t e r l y - d i r e c t e d thrusts and concentric folds developed i n the Paleozoic miogeocline and Mesozoic to Lower T e r t i a r y c l a s t i c wedge deposits. The Omineca b e l t straddles the boundary between Proterozoic to Lower Paleozoic sediments of the d i s t a l miogeocline, and the mid-Paleozoic to Mesozoic volcanic and sedimentary rocks of the Intermontane b e l t . Struc-tures i n t h i s region are complex, and vary with the s t r u c t u r a l l e v e l . Upper amphibolite f a c i e s rocks of the Shuswap Complex and the lower grade rocks of the Mount Ida Group have undergone polyphase deformation i n which early i s o c l i n a l folds have been refolded by more open, north to northwest-trending 11 f o l d s . Metamorphism a f f e c t s rocks as young as Early Jurassic (Wheeler and Gabrielse, 1972). The structure of the southern Intermontane b e l t i s known only s k e t c h i l y . Evidence for pre-Upper T r i a s s i c deformation i s found l o c a l l y and has been summarized by Read and Okulitch (1977) . Steep f a u l t s and open folds predom-inate i n the volcanic arc f a c i e s of the Nicola Group (Schau, 1970) . Folds i n the argillaceous f a c i e s to the east are at l e a s t l o c a l l y t i g h t e r , over-turned toward the west, and cut by steep f a u l t s (data from t h i s study). Major deformation of these rocks probably took place i n the Early J u r a s s i c (Schau, 1970, and t h i s study). 12 CHAPTER I I . HARPER RANCH GROUP (MAP UNIT 1) INTRODUCTION The Harper Ranch Group, i n exposures along the South Thompson River east of Kamloops, can be divided into 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 disconformity (Fig. 3). The lower section, of Late M i s s i s s i p p i a n to Middle Pennsylvanian age, consists of more than 5,000 m of marine mud-stone and v o l c a n i c l a s t i c rocks, with rare discontinuous lenses of limestone. A limestone containing Early and Middle Pennsylvanian f u s u l i n i d s generally forms the top of t h i s sequence (Sada and Danner, 1974). The base of the group i s a steeply-dipping, northwest-trending f a u l t with Upper T r i a s s i c rocks to the west. Overlying the Carboniferous rocks disconformably i s a massive Lower Permian limestone, probably several hundred metres thick. Upper Permian f o s s i l s are found i n one i s o l a t e d limestone outcrop near the Lower Permian limestone. This sequence i s o v e r l a i n above angular unconformities by Upper T r i a s s i c (?) sedimentary and volcanic rocks and by T e r t i a r y volcanic flows. This study concerns the lower 2,300 m of the Carboniferous s t r a t a i n the Harper Ranch Group. Study was confined to s t r a t a below the Lower Penn-sylvanian . limestones at l o c a l i t i e s Harper Ranch and South Thompson No. 1 of Sada and Danner (1974) (Fig. 3). STRUCTURAL SETTING, PHYSICAL STRATIGRAPHY, AND BIOSTRATIGRAPHY The lowermost portion of the Harper Ranch Group forms a northwest-trending, east-facing homocline. Bedding dips steeply e i t h e r to the northeast T~T LEGEND QUATERNARY DEPOSITS AND COVERED AREAS MIOCENE? BASALT UPPER TRIASSIC OR LOWER JURASSIC SEDIMENTARY AND VOLCANIC ROCKS UPPER TRIASSIC SEDIMENTARY ^ AND VOLCANIC ROCKS UPPER PERMIAN LIMESTONE LOWER PERMIAN LIMESTONE LOWER PENNSYLVANIAN LIMESTONE SCALE MILE INTERMITTENT STREAM GEOLOGIC CONTACT tr~r i K M J FAULT UPPER MISSISSIPPIAN TO LOWER PENNSYLVANIAN SEDIMENTARY ROCKS UPPER MISSISSIPPIAN LIMESTONE : S ) . • v v > '•vv! LOC r-t LOC. F-I; LOC. HARPER RANCH \ / V ( i r *—:: XT r ./^  T T ' l • • !•• 1 ,7A A a A A i - i - 0 A A A A , A A A A A A A i A A A A A A t -TO KAMLOOPS 7.5 KM F i g . 3 . Sketch geologic map of the Harper Ranch Group along the South Thompson River east of Kamloops, showing f o s s i l l o c a l i t i e s . 14 or southwest. Although only s i x facing determinations were obtained, no reversals i n facing d i r e c t i o n were observed that would suggest the presence of major f o l d closures, and few mesoscopic folds are present. Strikes and dips are i r r e g u l a r , however, and t h i s f a c t i n combination with the lack of complete exposures makes i t impossible to accurately measure the s t r a t i g r a p h i c thickness. The thickness of 2,300 m was estimated assuming an average s t r i k e of 140°, and a v e r t i c a l dip. The s t r a t i g r a p h i c section has been subdivided (Fig. 4) into two sequences of mudstone and volcanic sandstone or redeposited t u f f , separated by limestone. Further subdivision of the thick sequence of noncarbonate rocks has not been possible. Since the limestone bodies i n the Harper Ranch Group are not l a t e r -a l l y continuous, even t h i s gross subdivision would be d i f f i c u l t to apply over a larger area. However, the limestone bodies at Harper Ranch and South Thomp-son No. 1, although p h y s i c a l l y not connected, contain s i m i l a r Lower Pennsyl-vanian f u s u l i n i d faunas, and can be projected one in t o the other along s t r i k e . I t i s therefore reasonable to conclude that they occupy nearly 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 to the enclosing c l a s t i c rocks. Careful s t r u c t u r a l mapping and c o r r e l a t i o n between limestones may allow the o v e r a l l regional stratigraphy of the Harper Ranch Group to be deciphered. The basal portion of the section consists of 50 to 100 m of massive mudstone, laminated mudstone, and rare fine-grained sandstone. Where the overlying limestone unit 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 higher c l a s t i c sequence. The v e r t i c a l f a u l t which truncates t h i s section at i t s base generally trends p a r a l l e l to the s t r i k e of bedding, but l o c a l divergences lead to the recorded v a r i a t i o n s i n thickness. A small fauna of brachiopods, c o l l e c t e d from massive mudstone near the L I T H O L O G Y STANDARD SUCCESSIONS NORTH AMERICA EURASIA 5 </> < UJ oo U. N 2 0 0 0 -1 9 0 0 -tO rr LU r -Ui !fl tO LU Z u I r-UJ 1 0 0 0 -< X o rr a. o. < ioo-: Loc. F-2 Lcc. F-Limestone of localities Harper Ranch and South Thompson No. I of Soda and Danntr, 1974 2 < Z < > CO Z Z LU 0. rr < UJ z < o rr rr o 5 Z < rr < 20 19 Mattivt and laminated mudstone, fine to very coarse-grained volcanic sandstone (redeposited tuff or pyroclastic sandstone) Exact location of Mississippian / Pennsylvanian boundary unknown Bioclastic limestone Massive and laminated mudstone, rare fine-grained volcanic sondtton*  < a. a. CO to to to 2 UJ < Z < rr UJ \-to LU x o rr 3 2 < 2 ? 1 VISEAN? 18 I 7 I 6 Fault F i g . 4. Stratigraphic section of the lower portion of the Harper Ranch Group. 16 base of the section (Loc. F - l ) , were i d e n t i f i e d by Dr. J . T. Dutro, J r . , of the U. S. Geological Survey: The brachiopods are medium-sized productids that probably include Inflatia and Flexaria. Not well enough preserved 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 associated i n many places i n Late Mississippian rocks of the northern Rockies (written commun. to W. R. Danner, 1976). Since they were found i n fine-grained mudstone, the brachiopods are c l e a r l y an autochthonous benthic fauna, and were not transported p r i o r to b u r i a l . The overlying limestone (Unit 1A) varies from 0 to 10 m i n thickness. The present d i s c o n t i n u i t y of t h i s limestone i s due i n part to o f f s e t by f a u l t s and to lack of exposure, but the unit was probably o r i g i n a l l y l e n t i c -u l a r as w e l l . The gray, b i o c l a s t i c limestone contains a v a r i e t y of l i t h -ologies, from wackestones and packstones to grainstones. Contacts with the underlying and overlying c l a s t i c rocks are abrupt but conformable. The heterocoral Hexaphyllia occurs i n several limestone samples. According to Dr. D. H i l l (cited i n Sada and Danner, 1973), Hexaphyllia i s r e s t r i c t e d to the Visean, but B. L. Mamet (1976, p. 108) has found i t i n Early Namurian (=Upper Chesterian) limestone i n northern B r i t i s h Columbia. The varied fauna of benthic foraminifers includes Endothyra, Eostaffella, Paleotextularia, Climacammina, and Tetrataxis, but since no s p e c i f i c i d e n t i -f i c a t i o n s were attempted, the age of t h i s limestone cannot be s p e c i f i e d more p r e c i s e l y than Chesterian. This fauna i s shown i n Plate I I . The remainder of the section, some 2,200 m thick, consists of massive and laminated mudstone, f i n e to medium-grained volcanic t u r b i d i t e sandstones, and coarse to very coarse volcanic sandstones deposited by high-density subaqueous mass flows. The proportion of sandstone to mudstone i s v a r i a b l e . L o c a l l y sandstone may make up as much as 70% of the section, but mudstone 17 P L A T E I I . M ICROFAUNA FROM U P P E R M I S S I S S I P P I A N L I M E S T O N E , HARPER RANCH GROUP (UN IT 1A) A t h r o u g h D, p h o t o m i c r o g r a p h s f r o m t h i n - s e c t i o n s . S c a l e b a r = 1 0 0 m i c r o m e t r e s -A . Endothyra, s a g g i t a l s e c t i o n . B. Eostafella, s a g g i t a l s e c t i o n . C . Eostafella, a x i a l s e c t i o n . D. P a l e o t e x t u l a r i a , l o n g i t u d i n a l s e c t i o n . E t h r o u g h G , p h o t o m i c r o g r a p h s f r o m a c e t a t e p e e l s . S c a l e b a r = 1 m i l l i m e t r e E . Hexaphyllia, c r o s s s e c t i o n o f c o r a l l u m s u r r o u n d e d b y a l g a l c o a t . F . Hexaphyllia, c r o s s s e c t i o n o f c o r a l l u m s u r r o u n d e d b y a l g a l c o a t . . G . Hexaphyllia, o b l i q u e s e c t i o n o f c o r a l l u m s u r r o u n d e d b y a l g a l c o a t . . • 19 probably makes up more than 50% of the t o t a l thickness of the section. The only f o s s i l s recovered from t h i s section occur i n a coarse-grained bed composed mostly of redeposited shallow water carbonate debris, 100 to 150 m above limestone IA (Loc. F-2). Two genera of calcareous algae, Solenopora and Parachaetetes, are abundant. These genera range throughout the Paleozoic, but only a si n g l e occurrence of solenoporid algae has been reported from Pennsylvanian rocks (Heckel, 1975). Lower Pennsylvanian f u s u l i n i d s occur i n the limestones overlying t h i s section (Unit IB, Local-i t i e s Harper Ranch and South Thompson No. 1). The Mississippian/Pennsylvanian boundary thus l i e s somewhere within t h i s section, but i t s p o s i t i o n cannot be determined due to the lack of c l o s e r f o s s i l c o n t r o l . The bed containing solenoporid algae i s not f a r above the Upper Mi s s i s s i p p i a n limestone, and i s probably also Late M i s s i s s i p p i a n i n age. Further study of these algae i s warranted, for t h e i r preservation i s excellent, and a Pennsylvanian age can-not be ruled out. SEDIMENTOLOGY Exposures of the Harper Ranch Group are adequate to reveal the general nature of the l i t h o l o g i e s i n the section, but inadequate for d e t a i l e d f a c i e s analysis. No continuous marker beds were found, i n d i v i d u a l beds cannot be traced l a t e r a l l y , and extensive outcrops which reveal v e r t i c a l sequences of l i t h o l o g i e s are rare and confined to steep c l i f f s which are d i f f i c u l t of access. Sedimentologic analysis i s also hampered by the extreme induration of both sandstone and mudstone. Each exhibits l i t t l e tendency for pa r t i n g p a r a l l e l to bedding, and the mudstones are l i t t l e less r e s i s t a n t to weathering and erosion than the coarse sandstones. As a r e s u l t , l a y e r i n g exerts l i t t l e 20 control on the geometry of outcrops. The soles of sandstone beds are seldom exposed; no bottom markings or other measurable paleocurrent i n d i c a t o r s were observed. In spite of these l i m i t a t i o n s , the general depositional and tectonic environment of the section i s c l e a r . Deposition took place i n a marine basin within a volcanic arc system, probably within the f r o n t a l arc. This portion of the basin was r e l a t i v e l y d i s t a n t from the volcanic centers, since none of the volcanic d e t r i t u s i s coarser than very coarse sand or granule s i z e , and no flows are present i n the section. The volcanic sandstones consist of volcanic l i t h i c fragments and phenocrysts i n d i c a t i n g an andesitic to d a c i t i c source. Most of the d e t r i t u s i s probably p y r o c l a s t i c i n o r i g i n , produced by shallow submarine eruptions. This material was reworked and redeposited i n deeper water below wave base by t u r b i d i t y currents and high-concentration subaqueous flows, and i s i n t e r l a y e r e d with hemipelagic mud-stones. The volcanic sandstones could thus be termed redeposited t u f f s or p y r o c l a s t i c sandstones. The limestone of Unit 1A i s l i t h o l o g i c a l l y varied and contains a diverse fauna of marine benthic invertebrates and rare encrusting algae, i n d i c a t i n g deposition at depths within the photic zone and at normal marine s a l i n i t i e s . I t contains v i r t u a l l y no volcanic d e t r i t u s coarser than clay s i z e , and probably accumulated on a shallow s h e l f at a considerable distance from the volcanic centers, or during a period of volcanic quiescence. In the following sections, basic sedimentologic and petrographic data and i n t e r p r e t a t i o n s are presented for each l i t h o l o g y i n the Harper Ranch Group. The depositional model w i l l then be developed at greater length. 21 Mudstones Mudstones within the Harper Ranch Group are s i l i c e o u s and extremely indurated. They lack bedding plane f i s s i l i t y or penetrative cleavage, and could thus be termed a r g i l l i t e s as defined by the AGI Glossary of Geology (Gary and others, 1972, p. 37). Because of the inconsistencies i n d e f i n i -t i o n and usage of t h i s term, and i t s emphasis on post-depositional h i s t o r y , i t s use i s avoided i n t h i s discussion. Both homogeneous and laminated mudstones occur i n the section, and are i n t e r l a y e r e d and perhaps equally abundant. Homogeneous mudstone occurs i n t h i n to thick beds (terminology a f t e r Ingram, 1954). Homogeneity may be primary or due to very intense bioturbation of o r i g i n a l l y layered muds. No burrow-mottling was observed, but the mudstone was not examined c a r e f u l l y i n the f i e l d f o r these features. Primary homogeneous muds are known from deep sea cores (Reineck and Singh, 1975, p. 406), and represent i n t e r v a l s of uniform sedimentation. Laminated mudstones consist of t h i n (1-3 mm) and thick (3-10 mm) laminae and very t h i n to t h i n beds of gray to black mudstone and l i g h t gray to cream-colored s i l t s t o n e . Layering i s usually planar or gently undulating. S i l t s t o n e layers range up to 5 cm thick, with thicker layers showing very fine h o r i z o n t a l lamination, and sometimes f a i n t grading. These thick s i l t -stone layers could be interpreted as t u r b i d i t e DE sequences (Bouma, 1962). Some layers of s i l t s t o n e and very f i n e sandstone up to several c e n t i -meters thick show multiple sets of r i p p l e cross-lamination, and occasional minute load casts at the base (Fig. 5). These beds do not appear to be graded, and do not show other aspects of the Bouma sequence. They are therefore 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 currents. These beds may be F i g . 5. Laminated mudstone and s i l t s t o n e , Harper Ranch Group. White cross-laminated s i l t s t o n e layer at top, with micro-load casts at base. Slump f o l d at bottom. F i g . 6. Laminated mudstone and s i l t s t o n e , Harper Ranch Group ( r i g h t ) . Center of slab, cross-laminated s i l t s t o n e deformed by a slump f o l d . 23 the r e s u l t of reworking of t u r b i d i t e s i l t s and sands by bottom currents. Hsu (1964) postulated t h i s o r i g i n for s i m i l a r t h i n cross-laminated s i l t s and f i n e sands inte r l a y e r e d with t u r b i d i t e s and deep water mudstones i n the Pliocene Pico Formation of C a l i f o r n i a . I observed no bioturbation structures i n the laminated mudstones. This indicates deposition of mud at a rate much greater than the rate of reworking by burrowers, and perhaps a lack of abundant benthic infauna. In the s i n g l e t h i n - s e c t i o n of laminated mudstone which was examined, the mudstone consists of c r y p t o c r y s t a l l i n e material with low birefringence, wispy black streaks of organic material, and scattered s i l t - s i z e d grains of feldspar and/or quartz. Layering i s defined by changes i n grain s i z e and v a r i a t i o n s i n the amount of organic material, producing d i f f e r e n t shades of gray color. Very small cubes of authigenic p y r i t e are scattered through the mudstone. Possible r a d i o l a r i a n remains are also present throughout the mudstone. These are small (about 0.1 mm diameter) e l l i p s o i d a l bodies of clear m i c r o c r y s t a l l i n e quartz. The long axes of the e l l i p s o i d s p a r a l l e l l a y e ring, suggesting that the present shape r e s u l t s from f l a t t e n i n g of o r i g i n a l l y s p h e r i c a l bodies during compaction of the enclosing mud. No i n t e r n a l structures are preserved, but these are probably 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 . Radiolarians were probably an important constituent of these s i l i c e o u s mudstones, and most of t h i s disseminated s i l i c a was probably derived from the d i s s o l u t i o n of r a d i o l a r i a n t e s t s during diagenesis. Only a few scattered molds have survived t h i s process. Coarse s i l t s t o n e and very f i n e sandstone layers consist of feldspar and aphanitic volcanic rock fragments, with very l i t t l e or no quartz. A l t e r a t i o n of the volcanic fragments i s so extensive that the o r i g i n a l 24 c l a s t i c t e x t u r e i s n e a r l y o b l i t e r a t e d w h e n ^ o b s e r v e d i n t h i n s e c t i o n . X - r a y d i f f r a c t i o n a n a l y s i s r e v e a l s t h a t m i n e r a l o g i c a l l y t h e s e l a y e r s c o n s i s t p r i m a r i l y o f a l k a l i f e l d s p a r a n d l e s s e r p l a g i o c l a s e . T h e s e a r e p r o b a b l y t h e c o n s t i t u e n t s o f t h e m i c r o c r y s t a l l i n e v o l c a n i c f r a g m e n t s . L a m i n a t e d m u d s t o n e s c o m m o n l y show s o f t - s e d i m e n t d e f o r m a t i o n . C o n -t o r t e d m u d s t o n e a n d s i l t s t o n e l a m i n a e a n d v e r y s m a l l s c a l e r e c u m b e n t f o l d s a r e c o n f i n e d t o g r o u p s o f l a y e r s o n l y s e v e r a l c e n t i m e t r e s t h i c k ( F i g . 5 ) . A t l e a s t some o f t h i s d e f o r m a t i o n o c c u r r e d a t t h e s e d i m e n t - w a t e r i n t e r f a c e , s i n c e t h e c o n t o r t e d J l a y e r s a r e i n some c a s e s t r u n c a t e d b y o v e r l y i n g l a m i n a e . C o n t o r t e d , c r o s s - l a m i n a t e d s i l t s t o n e s a r e p r e s e n t i n o n e s a m p l e ( F i g . 6 ) . W h i l e t h e t r u e g e o m e t r y o f t h e s e f e a t u r e s c a n n o t b e d e t e r m i n e d f r o m t h e p o l i s h e d s l a b , i t i s e v i d e n t t h a t t h e a p p a r e n t c u r r e n t d i r e c t i o n a s i n f e r r e d f r o m t h e c r o s s - b e d d i n g i s i n t h e o p p o s i t e d i r e c t i o n f r o m t h e s e n s e o f o v e r t u r n i n g o f t h e c o n t o r t e d l a m i n a t i o n . T h i s p r o b a b l y r e f l e c t s a t r u e d i v e r g e n c e b e t w e e n c u r r e n t d i r e c t i o n a n d t h e d i r e c t i o n o f m o t i o n d u r i n g d e f o r m a t i o n . T h u s t h e d e f o r m a t i o n c a n n o t b e a t t r i b u t e d t o s h e a r s t r e s s e x e r t e d b y b o t t o m c u r r e n t s w h i c h d e p o s i t e d t h e s i l t s t o n e . T h e s e f e a t u r e s a l s o o c c u r i n t h e a b s e n c e o f o v e r l y i n g t u r b i d i t e b e d s , s o s h e a r s t r e s s a t t h e b a s e o f t u r b i d i t y c u r r e n t s c a n n o t b e r e s p o n s i b l e e i t h e r . T h e s e a r e p r o b a b l y s l u m p f e a t u r e s , r e s u l t i n g f r o m t h e d o w n s l o p e m o v e m e n t o f t h e u p p e r f e w c e n t i m e t r e s o f s e d i m e n t d e p o s i t e d o n a s u b m a r i n e s l o p e . No s i n g l e f e a t u r e o f t h e m u d s t o n e s i s i n d i c a t i v e o f a n y p a r t i c u l a r d e p o s i t i o n a l s e t t i n g . H o w e v e r , t h e s u i t e o f s e d i m e n t a r y s t r u c t u r e s f o u n d i n t h e s e m u d s t o n e s i s common i n d e e p w a t e r , h e m i p e l a g i c m u d s t o n e s ( Bouma , 1 9 7 2 ; W a l k e r a n d M u t t i , 1 9 7 3 ) , a n d t h i s i n t e r p r e t a t i o n i s s t r e n g t h e n e d b y t h e f a c t t h a t t h e y a r e i n t e r b e d d e d w i t h t u r b i d i t e s a n d s t o n e s . 25 Processes of deposition of these muds might have included pelagic s e t t l i n g , low density t u r b i d i t y currents (Reinick and Singh, 1975, p. 380-381), and deposition from a nepheloid layer (Eittreim, Ewing, and Thorn-dike, 1969). The cross-laminated s i l t s t o n e and f i n e sandstone layers are evidence for some reworking of the sediment by bottom currents. The dark color of the mudstones i s probably i n d i c a t i v e of a high organic content, and together with the lack of bioturbation and presence of scattered authigenic p y r i t e suggests a quiet, low-oxygen environment without an abundant bottom fauna. Volcanic Sandstones or Redeposited Tuffs Description of Sedimentary Structures Sandstones i n the Harper Ranch Group are of volcanic o r i g i n , and were deposited as sediment gravity flows (sensu Middleton and Hampton, 1973) at depths below storm wave base (a few tens of metres). Some of these beds are t u r b i d i t e s , but others were probably deposited by other mechanisms of subaqueous mass flow. For purposes of d e s c r i p t i o n , the sandstones have been divided into two classes: f i n e to medium-grained sandstone, and coarse to very coarse sandstone. Although based i n i t i a l l y on grain s i z e , t h i s d i v i s i o n also r e f l e c t s differences i n bed thickness, i n t e r n a l sedimentary structures, and probably i n mode of deposition. Compositionally, however, these sandstones are i d e n t i c a l . Fine-grained sandstones are found i n both upper and lower c l a s t i c sequences, although they are rare i n the l a t t e r . The coarse-grained sandstones are r e s t r i c t e d to the upper c l a s t i c succession. Fine- to medium-grained sandstone: These t u r b i d i t e sandstones are 26 abundant i n the Harper Ranch Group. Bed thickness ranges from 15 cm to 1.5 m, but most beds are less than 1.0 m th i c k . The basal contacts of the sand-stone beds are sharp, and may be planar or have obscure sole markings which have only been observed i n cross-section. Normal size-grading i s frequently v i s i b l e , and the upper portions of the beds are gradational with overlying mudstones. Planar laminations are sometimes present within the upper por-t i o n of the beds, but cross-lamination has not been observed. These beds can be described i n the terminology of Bouma (1962) as AE and ABE sequences. This type of incomplete Bouma sequence i s t y p i c a l of " c l a s s i c a l " proximal 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 of Walker and Mutti (1973). Coarse to very coarse sandstone: These sandstones were deposited by high-density sediment gravity flows. This i n t e r p r e t a t i o n i s based on t h e i r thickness and grain s i z e , t h e i r a ssociation with normal t u r b i d i t e s and deep water mudstones, and the lack of f a m i l i a r t u r b i d i t e features within the beds. The thickness of i n d i v i d u a l beds commonly exceeds the dimensions of the available small outcrops. Beds more than 1 m thick are t y p i c a l , and single beds more than 5 m thick have been observed. The sharp basal con-tacts may be planar, or i r r e g u l a r as the r e s u l t of erosion of the underlying mudstone during transport. Erosion of the substrate i s also indicated by the presence of large (up to 30 cm) elongate rip-up c l a s t s of mudstone which are often present i n the lower part of the sandstone beds. I d e n t i f i c a -t i o n as rip-up c l a s t s i s based on t h e i r very large si z e compared to the enclosing sand grains; t h e i r elongate and i r r e g u l a r shapes which suggest short distances of transport; t h e i r s i m i l a r i t y to the interbedded mudstone; and t h e i r i r r e g u l a r , embayed margins where surrounding sand grains have 27 p r e s s e d i n t o t h e s o f t mud d u r i n g c o m p a c t i o n . O b v i o u s s i z e - g r a d i n g i s o n l y i n f r e q u e n t l y o b s e r v e d i n t h e c o a r s e s a n d -s t o n e , a l t h o u g h t h i s may i n p a r t r e s u l t f r o m t h e p a u c i t y o f e x p o s u r e s o f c o m p l e t e b e d s , a n d t h e e f f e c t s o f a l t e r a t i o n o f t h e u n s t a b l e v o l c a n i c d e t r i -t u s . C o m m o n l y , t h e y a p p e a r m a s s i v e , o r s how v a g u e h o r i z o n t a l l a m i n a e . O f t e n o n l y t h e u p p e r f e w c e n t i m e t r e s w i l l s how g r a d i n g i n t o t h e o v e r l y i n g m u d s t o n e . T h e Bouma s e q u e n c e c a n n o t b e u s e f u l l y a p p l i e d t o d e s c r i b e t h e s e b e d s . T h e y c o r r e s p o n d t o t u r b i d i t e f a c i e s B2 o f W a l k e r a n d M u t t i ( 1 9 7 3 ) , m a s s i v e s a n d -s t o n e s w i t h o u t d i s h s t r u c t u r e . I n t u r b i d i t y c u r r e n t s , s e d i m e n t i s m a i n t a i n e d i n s u s p e n s i o n b y t h e u p w a r d c o m p o n e n t o f f l u i d t u r b u l e n c e . T h e r e s u l t i n g d e p o s i t s a r e c h a r a c t e r -i z e d b y g r a d e d b e d d i n g , a n d v e r t i c a l s u c c e s s i o n s o f s e d i m e n t a r y s t r u c t u r e s w h i c h c a n b e d e s c r i b e d a s c o m p l e t e o r i n c o m p l e t e Bouma s e q u e n c e s . I n h i g h e r -d e n s i t y s e d i m e n t g r a v i t y f l o w s , o t h e r t y p e s o f g r a i n s u p p o r t a r e p o s s i b l e : a n d t h e s e h a v e b e e n s u m m a r i z e d b y M i d d l e t o n a n d H a m p t o n ( 1 9 7 3 ) . T h e y i n c l u d e f l u i d i z e d s e d i m e n t f l o w , g r a i n f l o w , a n d d e b r i s f l o w , i n w h i c h g r a i n s u p p o r t i s a c h i e v e d r e s p e c t i v e l y b y u p w a r d i n t e r g r a n u l a r f l u i d f l o w , d i r e c t i n t e r -a c t i o n b e t w e e n g r a i n s , a n d s u p p o r t b y a n i n t e r s t i t i a l m a t r i x w i t h a f i n i t e s t r e n g t h . C r i t e r i a w h i c h w o u l d c l e a r l y d i f f e r e n t i a t e d e p o s i t s o f e a c h p r o c e s s f r o m t h e o t h e r s a r e p r e s e n t l y u n k n o w n , a n d i n f a c t m o r e t h a n o n e o f t h e s e m e c h a n i s m s m i g h t o p e r a t e d u r i n g v a r i o u s s t a g e s o f t r a n s p o r t a n d d e p o s i -t i o n o f a s i n g l e f l o w . I t i s t h u s h a z a r d o u s t o p o s t u l a t e a p a r t i c u l a r m e c h a n i s m f o r a g i v e n d e p o s i t . A s a g r o u p , h o w e v e r , t h e s e d e p o s i t s a r e d i s t i n c t f r o m t u r b i d i t e s i n t h e i r l a c k o f w e l l - d e f i n e d s e d i m e n t a r y s t r u c t u r e s t h a t c a n b e d e s c r i b e d b y t h e Bouma s e q u e n c e . B e d s a r e c o m m o n l y t h i c k , a n d may b e m a s s i v e o r s how d i f f u s e h o r i z o n t a l l a m i n a t i o n . G r a d e d b e d d i n g , r e v e r s e 28 g r a d e d b e d d i n g , a n d l a c k o f s i z e g r a d i n g h a v e a l l b e e n r e p o r t e d f r o m m a s s f l o w d e p o s i t s . L a r g e m u d c l a s t s a r e common n e a r t h e b a s e o f t h e b e d s . T h e c o a r s e t o v e r y c o a r s e - g r a i n e d H a r p e r R a n c h G r o u p s a n d s t o n e s c o r -r e s p o n d w e l l w i t h t h i s d e s c r i p t i o n , a n d c a n t h u s b e i n t e r p r e t e d a s n o n -t u r b i d i t e m a s s f l o w d e p o s i t s . S u p p o r t f o r t h e i n t e r p r e t a t i o n c o m e s f r o m t h e i r i n t i m a t e a s s o c i a t i o n w i t h t u r b i d i t e s a n d s t o n e s a n d d e e p w a t e r m u d -s t o n e s . A n y o r a l l o f t h e m e c h a n i s m s d i s c u s s e d a b o v e may h a v e p r o d u c e d t h e s e s a n d s t o n e b e d s . I t i s c l e a r t h a t t h e s e f l o w s w e r e c a p a b l e o f e r o d i n g a n d i n c o r p o r a t i n g f r a g m e n t s o f t h e i r mud s u b s t r a t e , b u t i n t e r n a l f l o w was n o t t u r b u l e n t e n o u g h t o t o t a l l y d i s r u p t t h e l a r g e m u d c l a s t s . S a n d s t o n e P e t r o g r a p h y S a n d s t o n e s f r o m t h e H a r p e r R a n c h G r o u p h a v e a n o v e r w h e l m i n g l y v o l c a n i c p r o v e n a n c e . T h e m a j o r f r a m e w o r k c o n s t i t u e n t s a r e v o l c a n i c l i t h i c f r a g m e n t s , p l a g i o c l a s e f e l d s p a r , a n d q u a r t z . T h e c l a s t i c t e x t u r e i s g e n e r a l l y e v i d e n t i n h a n d - s p e c i m e n ( F i g . 8 a n d 9) a n d i n t h i n - s e c t i o n , b u t g r a i n b o u n d a r i e s a r e b l u r r e d b y d e v i t r i f i c a t i o n a n d r e c r y s t a l l i z a t i o n o f u n s t a b l e l i t h i c a n d m i n e r a l c o m p o n e n t s . T h e s e e f f e c t s make t h e d i s t i n c t i o n b e t w e e n d e t r i t a l m a t r i x , v o l c a n i c l i t h i c f r a g m e n t s , a n d d i a g e n e t i c " e p i m a t r i x " ( D i c k i n s o n , 1 9 7 0 ) d i f f i c u l t i f n o t i m p o s s i b l e . O n l y f o u r t h i n - s e c t i o n s o f s e v e n s h o w e d o r i g i n a l t e x t u r e s c l e a r l y e n o u g h t o w a r r a n t q u a n t i t a t i v e m o d a l a n a l y s i s , a n d e v e n i n t h e s e w h a t a p p e a r s t o b e " m a t r i x " may i n c l u d e s i g n i f i c a n t a m o u n t s o f a p h a n i t i c v o l c a n i c m a t e r i a l . F o r t u n a t e l y , a l t h o u g h o r i g i n a l t e x t u r e s c a n n o t b e a c c u r a t e l y s p e c i f i e d , d e t e r m i n a t i o n o f p r o v e n a n c e i s s t i l l p o s s i b l e . M o d a l a n a l y s e s o f f o u r H a r p e r R a n c h G r o u p s a n d s t o n e s a r e p r e s e n t e d i n T a b l e I. M o d a l p e r c e n t a g e s w e r e d e t e r m i n e d f r o m c o u n t s o f 4 0 0 p o i n t s p e r t h i n - s e c t i o n . T h e m o d a l d a t a w e r e r e c a l c u l a t e d t o t h e p a r a m e t e r s Q , F , a n d T A B L E I. MODAL A N A L Y S E S OF V O L C A N I C SANDSTONES FROM T H E HARPER RANCH GROUP SAMPLE M K - 1 7 5 M K - 1 8 0 M K - 1 8 6 M K - 1 9 3 D e v i t r i f i e d g l a s s i n v o l c a n i c 50% r o c k f r a g m e n t s P l a g i o c l a s e 10 A l k a l i f e l d s p a r T r Q u a r t z T r P l u t o n i c r o c k f r a g m e n t s ? M u d s t o n e c l a s t s T r M a f i c s T r C a r b o n a t e c l a s t s 1 M a t r i x a n d e p i m a t r i x 36 C e m e n t 3 5 1 % 62% 6 1 % 8 7 14 T r 3 6 2 T r T r 4 T r T r — 2 1 T r 1 T r T r 1 33 19 19 1 T r 2 G r a i n S i z e M t o C F C t o V C C t o VC S o r t i n g M o d e r a t e M o d e r a t e P o o r V e r y P o o r T r = T r a c e F = F i n e - g r a i n e d M = M e d i u m - g r a i n e d C = C o a r s e - G r a i n e d VC = V e r y c o a r s e - g r a i n e d 30 F i g . 7- Q-F-L p l o t of modal data from v o l c a n i c l a s t i c rocks from the Harper Ranch Group. Q = quartz + chert; F = t o t a l feldspar; L = t o t a l unstable l i t h i c s . 31 Fi g . 8. Polished slab of volcanic sandstone from the Harper Ranch Group. Consists mostly of dense volcanic l i t h i c fragments and plagioclase feldspar. X 1.37. F i g . 9. Polished slab of volcanic sandstone, Harper Ranch Group, con s i s t -ing of volcanic l i t h i c fragments, pumice, and plagioclase feldspar. Wispy textures i n d i c a t i v e of pumice c l a s t s are evident, e s p e c i a l l y i n central part of the specimen. X 1.44. 32 L o f D i c k i n s o n ( 1 9 7 0 ) , a n d a r e s h o w n o n a t r i a n g u l a r p l o t i n F i g . 7 . M e d i a n g r a i n s i z e was e s t i m a t e d u s i n g a m i c r o m e t r e e y e p i e c e , a n d s o r t i n g a n d r o u n d n e s s w e r e v i s u a l l y e s t i m a t e d u s i n g s t a n d a r d c o m p a r i s o n c h a r t s i n F o l k ( 1 9 6 8 ) . E x a m p l e s o f w e l l p r e s e r v e d v o l c a n i c l a s t i c t e x t u r e s a r e s h o w n i n F i g u r e s 10 t h r o u g h 1 3 . T h i n - s e c t i o n s o f t h r e e o t h e r s a n d s t o n e s w e r e a l s o e x a m i n e d , a n d t h e y a r e s i m i l a r t o t h e a n a l y z e d s a n d s t o n e s i n c o m p o s i t i o n , a l t h o u g h g r a i n b o u n d -a r i e s h a v e b e e n n e a r l y o b l i t e r a t e d . T h e s e v e n s a m p l e s come f r o m i r r e g u l a r i n t e r v a l s c o v e r i n g t h e e n t i r e s e c t i o n , a n d t h e i r u n i f o r m i t y i n c o m p o s i t i o n s u g g e s t s t h a t t h e y a d e q u a t e l y r e p r e s e n t t h e o v e r a l l c h a r a c t e r o f t h e s a n d -s t o n e s i n t h e s e c t i o n . S i g n i f i c a n t v e r t i c a l o r l a t e r a l p e t r o l o g i c t r e n d s , a s w e l l a s v a r i a t i o n s w i t h i n s i n g l e b e d s , c a n o n l y b e r e v e a l e d b y f u r t h e r m o r e d e t a i l e d s a m p l i n g . V o l c a n i c r o c k f r a g m e n t s a r e t h e m o s t a b u n d a n t f r a m e w o r k c o n s t i t u e n t s , f o l l o w e d b y p l a g i o c l a s e a n d q u a r t z . F o l l o w i n g t h e p r o c e d u r e o f D i c k i n s o n (1970 ) , phenocry s t s " " - " w i t h i n v o l c a n i c f r a g m e n t s w e r e c o u n t e d a s t h e i r r e s p e c -t i v e m i n e r a l s p e c i e s . A s a r e s u l t , f o r e a c h s a m p l e t h e v o l u m e o f f r a m e w o r k v o l c a n i c f r a g m e n t s i s a p p r o x i m a t e l y 5% g r e a t e r t h a n t h e v o l u m e o f g l a s s s h o w n i n T a b l e I. A l k a l i f e l d s p a r , c o m p o s i t e f e l d s p a r g r a i n s , m a f i c m i n e r a l s , c a r b o n a t e g r a i n s , a n d m u d s t o n e r i p - u p c l a s t s a r e p r e s e n t i n a m o u n t s l e s s t h a n 2% i n m o s t s a m p l e s . O n l y o n e s a m p l e (MK -186 ) c o n t a i n s s i g n i f i c a n t l y h i g h e r a m o u n t s o f a l k a l i f e l d s p a r (3%) a n d c o m p o s i t e f e l d s p a r g r a i n s ( 4 % ) . T h e s e a r e p o l y c r y s t a l l i n e p l a g i o c l a s e g r a i n s , o r e u h e d r a l p l a g i o c l a s e w i t h t h i c k r i m s 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 ( F i g . 1 0 ) . T h e s e m i g h t r e p r e s e n t c l u m p s o f c r y s t a l s f r o m a v o l c a n i c o r h y p a b y s s a l p l u t o n i c s o u r c e . V o l c a n i c l i t h i c f r a g m e n t s e x h i b i t a v a r i e t y o f t e x t u r e s . M o s t a r e 33 F i g . 10. Photomicrograph of thin- s e c t i o n , Sample MK-186, Harper Ranch Group. Composite feldspar grain with cores of plagioclase feldspar (PI) surrounded by thick rims of p e r t h i t i c a l k a l i feldspar (A, stained yellow). Plane l i g h t , X 40. Fig . 11. Photomicrograph of t h i n section, Sample MK-186, Harper Ranch Group. M i c r o l i t i c volcanic fragments (V), pumice (P), a l k a l i feldspar (A), and quartz (Q). Plane l i g h t , X 40. 34 F i g . 12. Photomicrograph of thin-section, Sample MK-186, Harper Ranch Group. Broken zoned plagioclase c r y s t a l (PI), p o r p h y r i t i c volcanic fragment (V), pumice (P), a l k a l i feldspar (A), quartz (Q). Plane l i g h t , X 40. Fi g . 13. Photomicrograph of thi n - s e c t i o n , Sample MK-193, Harper Ranch Group. Angular volcanic quartz (Q), dark mudclast (M), various volcanic fragments (V). 35 dense m i c r o l i t i c grains (Fig. 11), with plagioclase 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. The groundmass i n these grains may be crypto-f e l s i t e ( c r y p t o c r y s t a l l i n e mosaic of quartz and feldspar) or c h l o r i t e . A few grains have f e l s i t i c textures. Pumice i s present i n most samples, and abun-dant i n several (Fig. 9, 11, 12). Both round-bubble and long-tube v a r i e t i e s occur, but the l a t t e r i s more d i f f i c u l t to recognize due to the o b l i t e r a t i o n of the i n t e r n a l structure during replacement by c h l o r i t e and celadonite. Such grains 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 structure, equant to highly elongate shape, and by the e f f e c t s of collapse and squashing of the o r i g i n a l l y porous grains between adjacent more competent grains during com-paction (Fiske, 1969). Clinopyroxene i s the only r e l i c t mafic mineral, and i s usually p a r t i a l l y replaced by c h l o r i t e . Discrete framework grains and microphenocrysts which are completely replaced by c h l o r i t e probably were once mafic mineral grains, 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 quartz grains can be classed as "common" quartz (Folk, 1968) : anhedral, subequant, monocrystalline grains with s t r a i g h t to s l i g h t l y undulose e x t i n c t i o n , and few in c l u s i o n s or vacuoles. This type of quartz i s not i n d i c a t i v e of a p a r t i c u l a r source. Composite and seim-composite grains are also present, but are much less abundant. Quartz occurs r a r e l y as micro-phenocrysts i n volcanic rock fragments, and some free grains of d e f i n i t e volcanic o r i g i n , with angular or hexagonal o u t l i n e s and i r r e g u l a r l y embayed margins, are also present (Fig. 13). Much of the "common" quartz may also have a volcanic o r i g i n . Carbonate grains are single c r y s t a l s of c a l c i t e , often minutely porous, and can be i d e n t i f i e d on t h i s basis as echinoderm p l a t e s , probably c r i n o i d columnals. 36 Plagioclase occurs as euhedral, broken euhedral, and subhedral grains. Zoning i s common (Fig. 12), and i t i s evident that most of these grains are volcanic phenocrysts which have been p a r t i a l l y to completely freed from t h e i r volcanic matrix during eruption or subsequent transport. Small rem-nants of aphanitic groundmass can be observed rimming some grains, although d i s t i n g u i s h i n g t h i s material from d e t r i t a l or diagenetic matrix i s often impossible. Replacement by s e r i c i t e or fine-grained saussurite i s extensive; consequently, the o r i g i n a l anorthite content could not be determined. One important i n d i c a t o r of the o r i g i n a l magma compositions i s thus l o s t . However, m i c r o l i t i c textures are most common i n intermediate lavas (Dickinson, 1970), and the surviving phenocryst mineralogy (plagioclase, quartz, and clinopyrox-ene) also suggests an a n d e s i t i c to d a c i t i c source. The rare f e l s i t i c grains might indicate a minor r h y o l i t e source. The problems i n recognizing the o r i g i n a l texture of these rocks have already been outlined, but some conclusions can be drawn. The volcanic sand-stones are grain-supported, with 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 or diagenetic matrix. Minor amounts (less than 3%) of c l e a r , 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 designated as cement i n Table I , and may have f i l l e d i n t e r s t i t i a l voids rather than replacing matrix. Contacts between l i t h i c grains show the e f f e c t s of pressure-solution and r e c r y s t a l -l i z a t i o n . Sorting of the framework grains i s moderate to poor. The f i n e r -grained sandstones show,better s o r t i n g , but much higher proportions of matrix, than the coarse to very coarse samples. The higher proportion of matrix may r e f l e c t the r e a l abundance of o r i g i n a l d e t r i t a l matrix, but i t may also be the r e s u l t of the greater 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 grains from matrix i n the finer-grained rocks. 37 Source and Deposition of the Volcanic Detritus The majority of the volcanic d e t r i t u s i n the 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 eruptions coeval with sedimentation. This i s indicated by the presence of pumice and unstable minerals such as clinopyroxene, and the abundance of euhedral and broken, angular mineral grains i n these deposits. Pumice makes up only a small f r a c t i o n of the ash; most of the fragments are nonvesicular, equant, and sometimes polygonal i n shape. This material i s s i m i l a r to that produced by phreatic eruptions (Heiken, 1972), or by g r a v i t a t i o n a l collapse of domes or thick flows of highly viscous magma (Francis and others, 1974). According to Fiske (1963), t h i s type of ash i s usually le s s voluminous than pumiceous ash i n subaerial andesitic to d a c i t i c volcanoes, due. presumably to the lack of abundant > groundwater and the predominance of v e s i c u l a t i n g magmas. Although quantita-t i v e estimates of r e l a t i v e volumes of the two types of subaerial ash are not ava i l a b l e , several petrographic studies of ashes confirm t h i s conclusion (Heiken, 1972, 1974; Francis and others, 1974; Roobol and Smith, 1974). The predominance of nonvesicular ash can be explained i f the eruptions were subaqueous (Fiske, 1963), with large volumes of water a v a i l a b l e to quench and fragment the erupting magma. Fiske (1963) i n f e r r e d a subaqueous o r i g i n for several types of pyro-c l a s t i c deposit i n the Eocene Ohanapecosh Formation i n western Washington, and was able to substantiate t h i s inference by i d e n t i f y i n g the source vents of the tephra. The most common type i s very s i m i l a r to the p y r o c l a s t i c deposits i n the Harper Ranch Group, containing a va r i e t y of nonvesicular l i t h i c fragments, and variable but generally small amounts of pumice. This 38 t e p h r a was p r o b a b l y t h e p r o d u c t o f s u b m a r i n e p h r e a t i c e r u p t i o n s w h i c h s h a t -t e r e d t h e magma a n d t h e p r e - e x i s t i n g l a v a a n d t e p h r a a r o u n d t h e v e n t , f o r m -i n g v e r y h e t e r o g e n e o u s m i x e d t e p h r a . T h i s i s t h e l i k e l y o r i g i n f o r m u c h o f t h e p y r o c l a s t i c m a t e r i a l i n t h e H a r p e r R a n c h G r o u p , a l t h o u g h some m a t e r i a l r e w o r k e d f r o m s u b a e r i a l v o l c a n o e s i s p r o b a b l y p r e s e n t a s w e l l . T h e p y r o c l a s t i c b e d s i n t h e H a r p e r R a n c h G r o u p l a c k t h e s e q u e n c e o f b e d d i n g t y p e s a n d s e d i m e n t a r y s t r u c t u r e s w h i c h h a v e b e e n d e s c r i b e d f r o m d e p o s i t s b e l i e v e d t o b e t h e p r o d u c t s o f r e l a t i v e l y d e e p s u b m a r i n e p y r o c l a s t i c e r u p t i o n s ( F i s k e a n d M a t s u d a , 1 9 6 4 ) . T h e s e u n i t s a r e c h a r a c t e r i z e d b y a s i n g l e t h i c k , m a s s i v e t u f f o v e r l a i n b y a s e r i e s o f t h i n - b e d d e d t u f f a c e o u s t u r b i d i t e s , w i t h e a c h b e d g r a d e d a n d t h e e n t i r e s e r i e s b e c o m i n g f i n e r - g r a i n e d u p w a r d — a d o u b l y g r a d e d s e q u e n c e . T h e m a s s i v e t u f f i s i n t e r p r e t e d a s a s u b a q u e o u s p y r o c l a s t i c f l o w , t h e r e s u l t o f d o w n s l o p e m o v e m e n t o f c o a r s e a n d d e n s e d e b r i s w h i c h a c c u m u l a t e d a r o u n d t h e v e n t d u r i n g t h e e a r l y s t a g e s o f t h e e r u p t i o n . T h e u p p e r d o u b l y g r a d e d s e q u e n c e i s t h o u g h t t o o r i g i n a t e f r o m t h e s e t t l i n g o f p r o g r e s s i v e l y f i n e r m a t e r i a l f r o m t h e s u b m a r i n e e r u p t i o n c o l u m n , a c c o m p a n i e d b y p e r i o d i c d o w n s l o p e t r a n s p o r t o f t h e a c c u m u l a t e d m a t e r i a l a s t u r b i d i t y c u r r e n t s . T h e f i n e t o m e d i u m - g r a i n e d v o l c a n i c l a s t i c b e d s i n t h e H a r p e r R a n c h G r o u p o c c u r a s i s o l a t e d t u r b i d i t e b e d s , a n d n o t a s p a r t o f d o u b l y g r a d e d s e q u e n c e s . T h e t h i c k , c o a r s e p y r o c l a s t i c b e d s a r e n o t o v e r l a i n b y d o u b l y g r a d e d t u r b i d i t e s e q u e n c e s , s o t h e y d o n o t a p p e a r s i m i l a r t o t h e d e p o s i t s d e s c r i b e d b y F i s k e a n d M a t s u d a ( 1 9 6 4 ) . P r o d u c t i o n o f t h e t e p h r a b y s h a l l o w m a r i n e e r u p t i o n s w o u l d e x p l a i n t h e l a c k o f d o u b l y g r a d e d s e q u e n c e s , s i n c e a n e r u p t i o n w i t h a s u b m a r i n e e r u p t i o n c o l u m n n e c e s s a r y t o p r o d u c e s u c h a s i z e - s o r t e d s e q u e n c e w o u l d p r o b a b l y h a v e t o t a k e p l a c e a t d e p t h s o f s e v e r a l h u n d r e d m e t r e s o r m o r e . T h e p r e s e n c e o f p e l m a t o z o a n ( s t a l k e d e c h i n o d e r m ) o s s i c l e s a l s o s u g g e s t s t h a t t h e t e p h r a was p r o d u c e d a n d may h a v e t e m p o r a r i l y a c c u m u l a t e d i n r e l a t i v e l y s h a l l o w w a t e r . T r a n s p o r t o f t h i s m a t e r i a l i n t o i t s p r e s e n t d e e p w a t e r s e t t i n g c o u l d h a v e o c c u r r e d d u r i n g e r u p t i o n s , o r i n t e r -m i t t e n t l y b e t w e e n e r u p t i o n s b y s l u m p i n g o f u n c o n s o l i d a t e d m a t e r i a l a r o u n d t h e v o l c a n i c v e n t . T h e t u r b i d i t e f a c i e s c l a s s i f i c a t i o n o f W a l k e r a n d M u t t i ( 1973 ) w a s u s e d i n a p r e v i o u s s e c t i o n t o d e s c r i b e t h e p y r o c l a s t i c m a s s f l o w d e p o s i t s . T h e f i n e - t o m e d i u m - g r a i n e d p y r o c l a s t i c t u r b i d i t e s w e r e i d e n t i f i e d a s t u r b i -d i t e f a c i e s C , " c l a s s i c a l " p r o x i m a l t u r b i d i t e s , a n d t h e c o a r s e m a s s f l o w d e p o s i t s a s t u r b i d i t e f a c i e s B 2 , m a s s i v e s a n d s t o n e s w i t h o u t d i s h s t r u c t u r e . T h i s u s a g e i s n o t s t r i c t l y c o r r e c t . T h e c r i t e r i a u s e d t o m a k e t h e s e a s s i g n -m e n t s w e r e g r a i n s i z e , b e d t h i c k n e s s , a n d t y p e a n d s e q u e n c e o f s t r u c t u r e s w i t h i n t h e b e d . T h e f a c i e s o f W a l k e r a n d M u t t i , h o w e v e r , a r e d e f i n e d i n t e r m s o f s e q u e n c e s o f b e d s , r a t h e r t h a n i n d i v i d u a l b e d s , a n d c r i t e r i a s u c h a s s a n d s t o n e - s h a l e r a t i o a n d p r e s e n c e o r l a c k o f c h a n n e l i n g a r e i n t e g r a l p a r t s o f t h e d e f i n i t i o n s . I n t e r r i g e n o u s t u r b i d i t e s y s t e m s , s e d i m e n t a r y p r o c e s s e s w h i c h l e a d t o t h e d e v e l o p m e n t o f r e g u l a r s e q u e n c e s o r f a c i e s a r e c o n t r o l l e d b y t h e p h y s i o g r a p h i c e l e m e n t s ( s u b m a r i n e c a n y o n s a n d c h a n n e l s , s u b m a r i n e f a n s , a n d a b y s s a l p l a i n s ) w h i c h f o r m t h e f r a m e w o r k f o r s e d i m e n t d i s p e r s a l a n d d e p o s i t i o n . T h e s e f a c i e s a s s o c i a t i o n s a r e a b s e n t f r o m t h e H a r p e r R a n c h G r o u p b e c a u s e d i s p e r s a l o f t h e . p y r o c l a s t i c d e b r i s wa s c o n -t r o l l e d n o t b y s u b m a r i n e c a n y o n a n d f a n s y s t e m s , b u t b y t h e l o c a t i o n o f v o l -c a n i c s o u r c e s w i t h i n t h e b a s i n . T e p h r a was p r o b a b l y d i s p e r s e d r a d i a l l y f r o m e a c h v o l c a n i c c e n t e r , p r o d u c i n g a m o r e o r l e s s r a n d o m s e q u e n c e o f i n t e r -b e d d e d m u d s t o n e s , t u r b i d i t e b e d s , a n d c o a r s e m a s s f l o w d e p o s i t s . 40 Deep Water C a l c i r u d i t e A single bed of poorly-sorted c a l c i r u d i t e occurs about 100 to 150 m above the limestone of Unit 1-A, interbedded with mudstone and t u r b i d i t e sandstones (Loc. F-2). The poorly exposed, struc t u r e l e s s packstone i s made up mostly of very coarse sand to pebble si z e f o s s i l material i n an a r g i l l a -ceous mi c r i t e matrix, which i s l o c a l l y r e c r y s t a l l i z e d to sparry c a l c i t e . The most abundant constituents are pelmatozoan o s s i c l e s , followed by soleno-porid algae, brachiopod s h e l l s and s h e l l fragments, and ostracods. A few small rugose co r a l s , echinoid spines, and t r i l o b i t e fragments are also present, as well as minor amounts of p l a g i o c l a s e , volcanic rock fragments, and quartz. Rip-up c l a s t s of mudstone and volcanic s i l t s t o n e are common (Fig. 14) . The solenoporid algae and other f o s s i l organisms o r i g i n a l l y inhabited a shallow water environment (within the photic zone), but t h e i r present depo-s i t i o n a l s e t t i n g indicates that they have been redeposited i n deeper water by submarine mass flow processes. The two genera of algae, Solenopora and Parachaetetes (Fig. 15 and 16), develop as nodular attached forms. Parachae-tetes i s found i n Upper Devonian reef complexes i n the immediate back-reef f a c i e s , or i n the fore-reef zone (Wara,: 1972). Heckel (1975) notes that Pennsylvanian occurrences of Parachaetetes are r e s t r i c t e d to calcarenites associated with p h y l l o i d algal-mud buildups. This s e t t i n g appears to be that of most solenoporids; they are abundant mainly i n reef-associated c a l c a r e n i t e s , but were not important reef builders (Heckel, 1975). Such calcarenites and c a l c i r u d i t e s are then the l i k e l y immediate source for the calcareous d e t r i t u s which makes up the redeposited bed. Reef-like buildups and t h e i r associated carbonate sediment probably 41 F i g . 15. Photomicrograph of the alga Solenopora, Loc. F-2, Harper Ranch Group. Thin-section, X 32. Fi g . 16. Photomicrograph of the alga Parachaetetes, Loc. F-2, Harper Ranch Group. Thin-section, X 32. 43 ringed the volcanic islands or shallowly submerged volcanic summits which were the sources of the volcanic d e t r i t u s i n the Harper Ranch Group. Trans-port of t h i s calcareous d e t r i t u s into t h i s part of the basin (except as small amounts incorporated i n volcanic sandstones) was obviously a rare event, since only one such bed was found i n the section. In most cases the calcareous material was overwhelmed by and mixed with the much greater v o l -ume 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 (Unit lA) crops out discontinuously 50 to 100 m s t r a t i g r a p h i c a l l y above the basal tectonic contact of the Harper Ranch Group. Where present, the limestone has a r e l a t i v e l y uniform thickness of about 10 m. Offsets by f a u l t s and poor exposure i n c e r t a i n areas (both east and west of the small en echelon segments) combine to p a r t i a l l y account for the mapped di s c o n t i n u i t y of the limestone. However, the eastern termination of the u n i t i s best explained as a s t r a t i g r a p h i c pinchout, since exposures to the east are good and no evidence for f a u l t o f f s e t was observed (the nearby basal con-ta c t of the Harper Ranch Group i s not o f f s e t ) . Limestones within c o r r e l a t i v e s t r a t a i n t h i s region are generally l e n t i c u l a r (Cockfield, 1948; Sada and Danner, 1974). The limestone i s medium to l i g h t gray i n color. In most outcrops i t appears massive, but i n some cases, where i t has been i n c i s e d by small streams, bedding i s v i s i b l e . At these l o c a l i t i e s bedding i s planar, with thicknesses ranging from 3 to 30 cm. I t i s l i k e l y that the massive character of many outcrops 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 r e c r y s t a l -l i z a t i o n during regional low grade metamorphism. These e f f e c t s mask the primary s t r u c t u r a l features of the limestone. However, thick, massive 44 bedding may be a primary depositional feature of some portions of the lime-stone . Fine- to coarse-grained wackestones, packstones, and grainstones make up the u n i t . Whole and fragmentary calcareous f o s s i l s are the most abundant allochems. Ooids and p e l l e t s are abundant i n some samples. Skeletal debris i s diverse, but generally foraminifers, brachiopod s h e l l fragments and spines, and pelmatozoan (stalked echinoderm) o s s i c l e s are most abundant, and are present i n nearly a l l samples. Other types include ostracods, echinoid spines, bryozoans, co r a l s , calcispheres, and possibly pelecypods. The d i v e r s i t y of f o s s i l types suggests that deposition took place i n s u b t i d a l , open marine shelf conditions. I have recognized s i x microfacies defined on the basis of texture and allochem content. The material examined includes polished slabs, acetate peels, and t h i n sections of 17 samples from various l o c a l i t i e s . Sampling was not adequate to reveal whether systematic v e r t i c a l and l a t e r a l d i s t r i -butions of microfacies e x i s t , and other microfacies could probably be recog-nized with further sampling. The allochem content of each microfacies i s given i n Table I I , and they are i l l u s t r a t e d i n Plates III and IV. Microfacies 1 (Plate I I I , A) i s very poorly sorted s k e l e t a l lime wackestone. Abundant and diverse s k e l e t a l debris " f l o a t s " i n a micrite matrix. Brachiopods are d i s a r t i c u l a t e d , but the f r a g i l e s h e l l s are unbroken. Ostracods are a r t i c u l a t e d and f i l l e d with spar, as are forams and gastropods. Deposition took place i n a very quiet environment with l i t t l e current a c t i v i t y to wash and fragment the f o s s i l debris. No evidence of bioturbation was observed. Microfacies 2 (Plate I I I , B and C) consists 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. Forams X X X X X X X Brachiopods X X X X X Pelecypods ? ? • Gastropods X X Crinoid ossicles X X X X X X X Echinoid spines X X X Ostracods X X Calcispheres X X X Bryozoans X X Corals X Peloids X X X X X Ooids X X Intraclasts X 46 P L A T E I I I . M I C R O F A C I E S FROM U P P E R 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 1 A , HARPER RANCH GROUP. S C A L E BAR =. 0 . 5 mm A . M i c r o f a c i e s 1, s k e l e t a l l i m e w a c k e s t o n e . B. M i c r o f a c i e s 2 , s k e l e t a l l i m e p a c k s t o n e . C . M i c r o f a c i e s 2 , s k e l e t a l l i m e p a c k s t o n e . D. M i c r o f a c i e s 3 , p e l o i d a l l i m e p a c k s t o n e . 48 PLATE IV. MICROFACIES FROM UPPER MISSISSIPPIAN LIMESTONE, UNIT 1A, HARPER RANCH GROUP. SCALE BAR = 0.5 mm. A. Microfacies 4a, s k e l e t a l ooid grainstone (well sorted). B. Microfacies 4b, s k e l e t a l ooid grainstone (poorly sorted). C. Microfacies 5, p e l o i d a l lime grainstone. D. Fine-grained s k e l e t a l grainstone. 50 poorly sorted s k e l e t a l lime packstone. Most samples contain abundant f i n e l y comminuted and m i c r i t i z e d s k e l e t a l debris and scattered 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 nearly s t r u c t u r e l e s s , with randomly oriented elongate grains, to highly organized, with good par-a l l e l alignment of elongate grains as a r e s u l t of weak current a c t i v i t y . One sample consisted of int e r l a y e r e d packstone and burrow-mottled m i c r i t e , with the packstone cut by m i c r i t e - f i l l e d burrows. The mi c r i t e matrix i n these rocks i s commonly somewhat a r g i l l a c e o u s . S k e l e t a l debris i s of diverse types, and several samples contain the heterocoral Hexaphyllia, with a slender c y l i n d r i c a l corallum at l e a s t several centimetres long, 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 of a l g a l o r i g i n . Microfacies 3 (Plate I I I , D) i s a poorly sorted packstone c o n s i s t i n g of abundant peloids (Bathurst, 1971, p. 84) and less abundant s k e l e t a l material i n a mic r i t e matrix. The peloids are rounded e l l i p s o i d s of homo-geneous m i c r i t e from 0.1 to 0.25 mm i n maximum diameter.- Their regular shape and size suggests that they are f e c a l p e l l e t s . The sediment i s struc-tureless and homogeneous, and t h i s f a b r i c as well as the abundant peloids may r e s u l t from very thorough reworking by burrowing d e t r i t u s feeders. Microfacies 4 i s composed of sk e l e t a l - o o i d grainstones, which range gradationally from well sorted and well washed (4a, Plate IV, A) to poorly sorted and poorly washed (4b, Plate IV, B). The poorly washed grainstone contains i r r e g u l a r layers of m i c r i t e i n a rock otherwise cemented by void-f i l l i n g sparry c a l c i t e . Most samples are medium-grained. Ooids have few to many layers, and commonly have n u c l e i of pelmatozoan o s s i c l e s , or less commonly of foraminifers or peloi d s . Details of the o o l i t i c coatings are generally obscured by r e c r y s t a l l i z a t i o n , but i n some grains ghosts of the 51 r a d i a x i a l - f i b r o u s structure are s t i l l v i s i b l e . Uncoated pelmatozoan o s s i c l e s are abundant, but other f o s s i l s are uncommon. The ooids and s k e l e t a l debris originated i n shallow, highly agitated water, but were transported into quieter water, since t h i s microfacies occurs i n t e r l a y e r e d with Microfacies 2, sk e l e t a l lime packstone, and Microfacies 6, fine-grained s k e l e t a l grainstone. Lime mud i n t r a c l a s t s , probably incorporated during transport, are present but rare. Small-scale cross-bedding has been observed i n thin-sections, but not i n outcrop. Microfacies 5 (Plate IV, C) i s a p e l o i d a l lime grainstone. I t i s moderately sorted and fine-grained, with abundant peloids and less abundant s k e l e t a l grains cemented by sparry c a l c i t e . Thorough washing of the p e l o i d a l muds could have produced t h i s sediment, perhaps with l i t t l e transport of the peloids and s k e l e t a l grains. Microfacies 6 (Plate IV, D) consists of fine-grained s k e l e t a l grainstone. Sorting i s moderate, and there i s some alignment of elongate grains p a r a l l e l to bedding, i n d i c a t i n g working by currents. Pelmatozoan debris and peloids are the most common allochems. A few m i c r i t e - f i l l e d burrows can be seen i n thin- s e c t i o n . The d i v e r s i t y of microfacies and organisms found i n t h i s limestone i s c h a r a c t e r i s t i c of shallow subtidal carbonates deposited above, or ju s t below, e f f e c t i v e wave base (Laporte, 1971). Deposition at depths within the photic zone i s indicated by the a l g a l structures coating the c o r a l l a of Hexaphyllia. On the other hand, features i n d i c a t i v e of very shallow r e s t r i c t e d lagoons or t i d a l f l a t s (laminated a l g a l structures, mudcracks, abundant i n t r a c l a s t s , dolomite, and low faunal d i v e r s i t y ) are absent. The range i n textu'ral types from wackestones to o o l i t i c grainstones records a wide v a r i a t i o n i n current 52 i n t e n s i t y which i s to be expected i n the shallow subtidal environment. Although the r e l a t i v e proportions of the d i f f e r e n t microfacies are d i f f i c u l t to assess, wackestones and packstones are at l e a s t as abundant, and probably more abundant, than grainstones, and formed i n bottom environ-ments with abundant lime mud, diverse benthic fauna, and low to moderate cur-rent a c t i v i t y . Grainstones seem to be intimately interbedded with the m i c r i t e - r i c h rocks. P e l o i d a l grainstones and fine-grained s k e l e t a l grain-stones (Microfacies 5 and 6) could have been produced by current washing and sort i n g e s s e n t i a l l y in situ, since t h e i r framework grains are s i m i l a r to, though les s varied than, the interbedded packstones and wackestones. The ske l e t a l - o o i d grainstones (Microfacies 4a and 4b), however, were formed by extended and repeated current a g i t a t i o n , probably on shoal-water carbonate sand banks. Some of these sands were p e r i o d i c a l l y c a r r i e d into the quiet water se t t i n g s , where they are now preserved, by e x t r a o r d i n a r i l y strong wave or current a c t i v i t y , perhaps during storms. Volcanic and other noncarbonate grains coarser than clay s i z e are conspicuously absent from t h i s limestone, i n marked contrast to the underly-ing and overlying c l a s t i c rocks. Furthermore, these e l a s t i c s are hemipelagic muds and t u r b i d i t e s deposited below wave base, and possibly at moderate to great depths, compared with the shallow marine character of the limestone. These contrasts, i n addition to the l a t e r a l d i s c o n t i n u i t y of the limestone, demand c a r e f u l examination of the 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 of these units, since they suggest the p o s s i b i l i t y that the limestone i s not i n depositional sequence with the enclosing rocks, but may occur as submarine s l i d e blocks or as tectonic s l i v e r s within the deep water sequence. However, a l l of the f i e l d evidence i s i n support of a conformable depositional succession. 53 The only good exposure of the contacts of the limestone occurs i n a small dry stream channel which cuts across the easternment segment of Unit 1A. Here bedded limestone i s i n conformable contact with the overlying mud-stone. The change from limestone to mudstone i s , however, sudden, with no i n t e r v a l of interbedding. The o v e r a l l trend of the u n i t i s also conformable with the attitu d e of the enclosing rocks, which are usually mudstone i n out-crops nearest to the concealed contacts. Contacts of the limestone at l o c a l i t y South Thompson No. 1 (Unit IB) are much more f u l l y exposed, and they too are seen to be conformable. Furthermore, although the lower contact with mudstone i s abrupt, t h i s limestone i s o v e r l a i n by a sequence at l e a s t 10 m thick of interbedded mudstone, dark gray m i c r i t e , and f i n e - to medium-grained calcareous and noncalcareous sandstone. I i n t e r p r e t these rocks as an assem-blage t r a n s i t i o n a l between the shallow water carbonates and the overlying deeper water c l a s t i c rocks. This t r a n s i t i o n records the renewed i n f l u x of v o l c a n i c l a s t i c s , and probably progressive deepening of the basin f l o o r . Within the e n t i r e Harper Ranch Group i n t h i s area, the s t r a t i g r a p h i c succession of p a l e o n t o l o g i c a l l y dated limestone units i s consistent with the facing d i r e c t i o n of the enclosing sedimentary rocks. Coarse limestone breccias and megabreccias, which would be expected to accompany large lime-stone s l i d e blocks (Conaghan and others, 1976) , are absent, and even f i n e r -grained a l l o d a p i c carbonates are notably rare, l i m i t e d to the si n g l e bed described below. Therefore, I conclude that these limestones are autochth-onous, and are neither submarine s l i d e blocks nor tectonic s l i c e s . These limestone units accumulated during periods when portions of the basin f l o o r had temporarily reached shallow subtidal depths, as a r e s u l t of basin f i l l i n g , u p l i f t of the basin f l o o r , or e u s t a t i t i c sea-level lowering. 54 The absence of volcanic d e t r i t u s or a s h - f a l l t u f f s i n the limestone suggests that volcanic a c t i v i t y may have ceased. Subdued topographic r e l i e f .probably existed on the basin f l o o r at t h i s time. Carbonate production and accumula-t i o n took place on those portions within the photic zone, while slow deposi-t i o n of terrigenous mud and minor e p i c l a s t i c volcanic d e t r i t u s could have continued i n deeper portions. This would explain the l a t e r a l d i s c o n t i n u i t y of t h i s limestone. From the sedimentologic features of 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 that they were deposited at greater water depths than the shallow water lime-stone. The v e r t i c a l t r a n s i t i o n from the limestone of Unit 1A to the overlying deeper water mudstone and redeposited t u f f probably records a rapid deepen-ing of the basin f l o o r which roughly coincided with the resumption of volcanic a c t i v i t y ( i f i t indeed had ceased). No quantitative estimate of the amount of deepening can be made, because no c r i t e r i a are present to suggest exact depths of accumulation of the v o l c a n i c l a s t i c s t r a t a . 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 volcanic i n o r i g i n , except for common but minor admixed carbonate debris. The miner-alogy and texture of volcanic l i t h i c fragments and phenocrysts suggests that t h i s debris was produced by p y r o c l a s t i c eruptions of andesitic to d a c i t i c lava at shallowly submerged volcanic centers. This material was subsequently reworked and redeposited i n marine waters below wave base by t u r b i d i t y cur-rents and high-concentration subaqueous flows, and i s interbedded with s i l i -ceous hemipelagic mudstones. During periods of volcanic quiescence and shallowing of the basin f l o o r , b i o c l a s t i c limestone composed of a v a r i e t y 55 of l i t h o f a c i e s accumulated i n shallow marine, subtidal waters. Renewal of volcanic a c t i v i t y accompanied by rapid increase i n water depth i n i t i a t e d renewed deposition of deeper water v o l c a n i c l a s t i c sediments. This deposi-t i o n a l megacycle i s repeated at l e a s t four times i n the Mis s i s s i p p i a n to Lower Pennsylvanian portion of the Harper Ranch Group. Deposition took place within a volcanic archipelago which was probably an active volcanic i s l a n d arc associated with a subduction zone. However, t h i s portion of the depositional basin was some distance from the volcanic centers, since coarse volcanic breccias, debris flow deposits, and volcanic flows which occur near i s l a n d arc volcanic vents (Jones, 1967; M i t c h e l l , 1970) are absent. The basin probably was within the f r o n t a l arc rather than the fore-arc or back-arc regions. Sediments deposited i n the l a t t e r two areas are usually uniformly of deep water type i n volcanic arcs with l i t t l e i n f l u x of sediment from an adjacent continental landmass (Dickinson, 1976; Karig, 1974). The f r o n t a l arc, on the other hand, may contain a range of environ-ments from subaerial to moderately deep water, and i s subject to recurrent episodes of u p l i f t and subsidence (Tracey and others, 1964; Karig, 1971). My c o r r e l a t i o n of episodes of limestone deposition with periods of volcanic quiescence suggests a tectonic rather than e u s t a t i c c o n t r o l of the 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 consistent with the in f e r r e d f r o n t a l arc depositional s e t t i n g f o r the Harper Ranch Group. REGIONAL CORRELATIONS Rocks mapped as "Cache Creek Group" and "eastern Cache Creek Group" by Cock f i e l d (1948) and Campbell and Tipper (1971) extend northward from Kamloops through the Nicola and Bonaparte Lake map-areas to at l e a s t l a t i t u d e 51° 30'N, 56 where they are faulted against Upper T r i a s s i c volcanics and the Paleozoic (?) greenstone of the Fennel Formation, intruded by Mesozoic plutons, and covered by Jurassic and T e r t i a r y s t r a t a . Although the "Cache Creek Group" as pre-viously mapped i s now known to include Upper T r i a s s i c rocks i n Nicola map-area, most of the eastern portion of the un i t i n both map-areas i s probably Late Paleozoic i n age. Common l i t h o l o g i e s are volcanic arenite and graywacke, s i l i c e o u s a rgillaceous rocks, and minor carbonate, an assemblage which i s s i m i l a r to that near Kamloops. Basic and intermediate volcanic flows, absent near Kamloops, may be present i n these areas. S i m i l a r l i t h o l o g i e s are found i n the "Cache Creek Group" west of Vernon and Kelowa .in Vernon map-area (Jones, 1959), and extending eastward from Vernon to Monashee Pass, where they are overlapped by T r i a s s i c rocks of the Slocan Group and engulfed by Mesozoic plutonic rocks (Wheeler and others, 1972, F i g . 2). In the following discus-sion, I w i l l include these Carboniferous and Permian s t r a t a with the Harper Ranch Group i n order to emphasize t h e i r general s i m i l a r i t y , and to d i s t i n g u i s h them from nearby groups of s i m i l a r age but d i s s i m i l a r l i t h o l o g y and tectonic s e t t i n g . Monger (1977) has grouped the Harper Ranch Group with other units of Late Paleozoic age i n the southern Intermontane b e l t , and refer s to them as the Southern B r i t i s h Columbia assemblage. Other groups of Upper Paleozoic eugeoclinal s t r a t a are designated as the Eastern assemblage and Cache Creek-Bridge River assemblage. Published descriptions of the rocks grouped by Monger with the Harper Ranch Group suggest that they have l i t t l e i n common with i t , and are better referred to these other Upper Paleozoic assemblages. The assemblages defined by Monger (1977) are b r i e f l y described below, followed by my suggested r e v i s i o n of Upper Paleozoic assemblages i n southern B r i t i s h Columbia. 57 E a s t e r n A s s e m b l a g e T h e E a s t e r n a s s e m b l a g e , M i s s i s s i p p i a n t o P e r m i a n i n a g e , s t r e t c h e s f r o m s o u t h e r n B r i t i s h C o l u m b i a t o t h e Y u k o n a l o n g t h e f l a n k s o f t h e O m i n e c a C r y s t a l l i n e b e l t . I t c o n s i s t s o f a l o w e r , m a i n l y s e d i m e n t a r y s e c t i o n o v e r -l a i n b y a d o m i n a n t l y v o l c a n i c s e c t i o n , m o s t l y b a s a l t w i t h m i n o r c h e r t , d i a -b a s e , g a b b r o , a n d u l t r a m a f i c r o c k , e l a s t i c s i n t h e l o w e r p o r t i o n r a n g e f r o m m u d s t o n e s t o c o a r s e c o n g l o m e r a t e s , w i t h m i n o r l i m e s t o n e a n d a c i d t o i n t e r m e d i a t e v o l c a n i c r o c k s . T h e a s s e m b l a g e l i e s w i t h d e p o s i t i o n a l o r f a u l t c o n t a c t o n D e v o n i a n o r o l d e r s h a l l o w t o d e e p w a t e r m i o g e o c l i n a l d e p o s i t s , w h i c h i n s o u t h e r n m o s t B r i t i s h C o l u m b i a w e r e m e t a m o r p h o s e d p r i o r t o t h e L a t e M i s s i s s i p p i a n . S t r a t a i n c l u d e d i n t h i s r e g i o n a r e t h e S l i d e M o u n t a i n G r o u p i n M c B r i d e m a p - a r e a , t h e F e n n e l F o r m a t i o n i n B o n a p a r t e L a k e m a p - a r e a , a n d t h e M i l f o r d a n d K a s l o G r o u p s i n L a r d e a u a n d N e l s o n m a p - a r e a s ( F i g . 1 7 ) . E q u i v a l e n t m e t a m o r p h o s e d r o c k s p r o b a b l y make u p p o r t i o n s o f t h e M o u n t I d a G r o u p a n d E a g l e B a y F o r m a t i o n i n V e r n o n m a p - a r e a ( O k u l i t c h a n d C a m e r o n , 1 9 7 6 ) . C l a s t s i n t h e c o n g l o m e r a t e a n d s a n d s t o n e a r e m a i n l y c h e r t , a r g i l l i t e , c a r b o n a t e , a n d m a f i c v o l c a n i c s , a l l o f w h i c h M o n g e r s u g g e s t s a r e o f i n t r a -b a s i n a l o r i g i n . H o w e v e r , c l a s t s o f p h y l l i t e a n d s c h i s t a r e f o u n d i n c o n g l o m -e r a t e s o f t h e E a s t e r n a s s e m b l a g e i n n o r t h e r n B r i t i s h C o l u m b i a a n d t h e Y u k o n . S i m i l a r c l a s t s d e r i v e d f r o m t h e u n d e r l y i n g m e t a m o r p h o s e d L a r d e a u G r o u p a r e p r e s e n t i n t h e M i l f o r d G r o u p , a l o n g w i t h g r a n i t i c b o u l d e r s . T h e r e f o r e a n o l d e r t e r r a n e c o m p o s e d o f m e t a m o r p h o s e d a r g i l l a c e o u s r o c k s w i t h l o c a l p l u t o n s p r o v i d e d some o f t h e d e t r i t u s , a n d i t i s l i k e l y t h a t t h e s e d i m e n t a r y a n d v o l c a n i c c l a s t s a r e d e r i v e d f r o m t h e same o l d e r s o u r c e t e r r a n e . T h e a b u n d a n t c h e r t a n d m a f i c v o l c a n i c c l a s t s s u g g e s t t h a t p a r t o f t h i s t e r r a n e may h a v e b e e n made u p o f L o w e r P a l e o z o i c o c e a n i c c r u s t . P o r t i o n s o f i t may b e U P P E R P A L E O Z O I C E U G E O C L i N A L A S S E M B L A G E S Eastern South central British Columbia Cache Creek-Bridge River Stikine Chilli wack E>S§| Sicker-Skolai Fault Thrust fault F i g . 17. Upper Paleozoic eugeoclinal assemblages i n B r i t i s h Columbia according to Monger, 1977. 59 represented by the Eagle Bay Formation, which includes p h y l l i t e , p h y l l i t i c quartzite (metachert?), greenstone, and limestone, and i s intruded by grani-t o i d rocks y i e l d i n g z i r c o n ages of 372 m.y. (Late Devonian; Okulitch and others, 1975). Besides t h i s example, pre-Mississippian eugeoclinal rocks 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 or Omineca C r y s t a l l i n e b e l t . Monger and others (1972) concluded that the source terrane for the Eastern assemblage e l a s t i c s lay to the west of the Omineca C r y s t a l l i n e b e l t . The Late Devonian to Middle M i s s i s s i p p i a n orogenic event which produced t h i s deformed, l o c a l l y metamorphosed and intruded terrane and the e l a s t i c s derived from i t has been re f e r r e d to as the Caribooan Orogeny (Douglas and others, 1970, p. 415). I t i s roughly synchronous with the Antler Orogeny of Nevada (Roberts and others, 1958; B u r c h f i e l and Davis, 1972, 1975; Speed, 1977), which involved eastward th r u s t i n g of deformed oceanic or marginal basin rocks onto the o l d miogeocline. Continued u p l i f t of the Antler b e l t during the Late Paleozoic produced c l a s t i c sequences, such as the Havallah Formation (Stewart and others, 1977), which resemble the e l a s t i c s i n the lower Eastern assemblage. In the Yukon and northern B r i t i s h Columbia, basalt and ultramafic rocks of the upper portion of the Eastern assemblage form an allochthon thrust eastward over miogeoclinal s t r a t a , i n i t i a l l y i n the Late T r i a s s i c (Tempelman-K l u i t and others, 1976). This allochthon has been interpreted as Paleozoic oceanic crust by Monger and others (1972), Wheeler and Gabrielse (1972), and Monger (1977). Elsewhere i n northern and southern B r i t i s h Columbia, the volcanics are demonstrably i n depositional contact and i n t e r f i n g e r with the lower sedimentary s t r a t a , which are also intruded by gabbro s i l l s interpreted 60 as feeders to the overlying volcanics. The tectonic s i g n i f i c a n c e of the upper part of the Eastern assemblage i s therefore s t i l l not cl e a r . Cache Creek-Bridge River Assemblage The Cache Creek-Bridge River assemblage i s a well defined b e l t of oceanic rocks extending from northern Washington to at l e a s t the southern Yukon. This assemblage includes the type area of the Cache Creek Group and perhaps the lower d i v i s i o n of the P a v i l i o n Group i n Ashcroft map-area west of Kamloops, the Bridge River or Ferguson Group i n Pemberton map-area, and the Hozameen Group i n Hope map-area. Typ i c a l l i t h o l o g i e s are r a d i o l a r i a n chert, a r g i l l i t e , carbonate, mafic volcanics, and ultramafic rock. Vol-canics are mainly b a s a l t i c flows which are l o c a l l y pillowed. Limestones, which are common only i n the Cache Creek Group, are massive and form pods up to tens of kilometres long, apparently deposited i n shallow water on volcanic substrates. No older rocks are known to occur s t r a t i g r a p h i c a l l y beneath the Cache Creek-Bridge River assemblage. The sediments and volcanics comprise the upper l e v e l s of Late Paleozoic oceanic crust, whose deeper l e v e l s are exposed i n a number of serpentinized ultramafic bodies. Fusulinids and other fos-s i l s are common i n the limestones, and range from Early M i s s i s s i p p i a n to Late Permian i n northern B r i t i s h Columbia, and from Pennsylvanian to Permian i n the type area of the Cache Creek Group. Radiolaria from cherts at one l o c a l i t y i n the l a t t e r area, however, are of probable Late T r i a s s i c or possible Early J u r a s s i c age (Travers, 1978). Middle T r i a s s i c conodonts occur i n small carbonate pods i n the Bridge River Group. The Hozameen Group has so far proven u n f o s s i l i f e r o u s . The Permian and perhaps Pennsylvanian f u s u l i n i d s have Tethyan faunal a f f i n i t i e s , and are unlike coeval faunas i n 61 o t h e r U p p e r P a l e o z o i c a s s e m b l a g e s i n B r i t i s h C o l u m b i a , o r f r o m t h e N o r t h A m e r i c a n c r a t o n . T h e s t r a t i g r a p h y a n d s t r u c t u r e o f t h i s a s s e m b l a g e a r e c o m p l e x . P o d -l i k e b o d i e s o f c a r b o n a t e , v o l c a n i c s , a n d u l t r a m a f i c r o c k s a r e s u r r o u n d e d b y c h e r t a n d a r g i l l i t e . Some o f t h e s e u n i t s w e r e c e r t a i n l y o r i g i n a l l y l e n t i c u l a r a n d d i s c o n t i n u o u s , b u t d e f o r m a t i o n h a s e n h a n c e d t h i s d i s c o n t i n u i t y . Due t o t h e d i f f e r e n c e i n c o m p e t e n c e b e t w e e n m a s s i v e c a r b o n a t e a n d v o l c a n i c b o d i e s a n d t h e s u r r o u n d i n g b e d d e d c h e r t s , t h e b o u n d a r i e s o f t h e s e p o d s a r e a l m o s t a l w a y s s h e a r e d a n d f a u l t e d . P o s s i b l e t e c t o n i c m e l a n g e s a r e r e c o g n i z e d o n l y l o c a l l y . M e t a m o r p h i c b l u e a m p h i b o l e s a r e l o c a l l y d e v e l o p e d i n t h e C a c h e C r e e k G r o u p i n n o r t h e r n B r i t i s h C o l u m b i a ( A t l i n t e r r a n e ; M o n g e r , 1 9 7 5 b ) ; n e a r P i n c h i L a k e i n t h e c e n t r a l p a r t o f t h e p r o v i n c e ( P a t e r s o n , 1 9 7 7 ) ; a n d s o u t h o f C a c h e C r e e k ( J . F . G r e t t e , o r a l c o m m u n . , 1 9 7 6 ) . K - A r a g e s o n w h i t e m i c a i n b l u e -s c h i s t s n e a r P i n c h i L a k e r a n g e f r o m 211 t o 218 m . y . ( P a t e r s o n a n d H a r a k a l , 1 9 7 4 ) . T h e C a c h e C r e e k - B r i d g e R i v e r a s s e m b l a g e h a s b e e n i n t e r p r e t e d b y M o n g e r a n d o t h e r s ( 1972 ) a n d A n d e r s o n ( 1 9 7 6 ) a s m a t e r i a l s c r a p e d o f f d o w n g o i n g o c e a n i c l i t h o s p h e r e d u r i n g s u b d u c t i o n i n t h e L a t e P a l e o z o i c a n d / o r e a r l y M e s o z o i c . I f s o , a t l e a s t p a r t o f t h i s t e c t o n i c c o m p l e x was a c c r e t e d t o t h e N o r t h A m e r i c a n c o n t i n e n t b y t h e L a t e T r i a s s i c . T h e e x t e r n a l c o n t a c t s o f t h e a s s e m b l a g e w i t h T r i a s s i c a n d o l d e r r o c k s a r e n e a r l y a l l f a u l t s , b u t i t i s l o c a l l y o v e r l a i n b y L o w e r J u r a s s i c s e d i m e n t s a n d i n t r u d e d b y p l u t o n s o f E a r l y J u r a s s i c ( 200 m . y . ) a g e ( T i p p e r , i n M o n g e r , 1 9 7 7 ) . S t r u c t u r a l a n d s t r a t i g r a p h i c e v i d e n c e r e s t r i c t s t h e a g e o f e a r l y d e f o r m a t i o n i n t h e A t l i n t e r r a n e t o t h e E a r l y o r M i d d l e T r i a s s i c ( M o n g e r , 1 9 7 5 b ) a n d t h e P i n c h i L a k e b l u e s c h i s t s s u g g e s t u p l i f t a n d c o o l i n g o f t h i s t e r r a n e i n t h e L a t e T r i a s s i c . 62 This u p l i f t i s probably also evidenced by o p h i o l i t i c and chert d e t r i t u s i n Karnian to Norian rocks near Pinchi Lake (Paterson, 1977), and chert d e t r i t u s i n Karnian rocks near Kamloops, as reported i n the following chapter. The l a t t e r also contain d e t r i t a l blue amphiboles for which the Cache Creek Group i s the only known nearby source. This Middle to Late T r i a s s i c deformation, low grade metamorphism, and u p l i f t i s known as the Tahltanian Orogeny (Douglas and others, 1970, p. 431; Read and Okulitch, 1977). Accretion of the Cache Creek-Bridge River assemblage may, however, have continued through the Late T r i a s s i c and i n t o the Jurassic (Anderson, 1976) during eastward-directed subduction which produced mafic to intermediate volcanics of the Upper T r i -a s sic Nicola Group, and s i m i l a r Lower Jurassic rocks. The f i r s t widespread s t r a t a deposited on the Cache Creek-Bridge River assemblage are Cretaceous or younger i n age (Monger, 1977). Southern B r i t i s h Columbia Assemblage  and Suggested Revision 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 studied i n d e t a i l i n only a few places. The grouping of Upper Paleozoic rocks i n t h i s assemblage i s l a r g e l y geographic, and Monger (1977) suggests that more than one tectono-stratigraphic assemblage i s present. In f a c t , he distinguishes two sequences with d i f f e r e n t l i t h o l o g i e s within the assemblage, but I believe that three are present. One of these sequences can be r e f e r r e d to the Eastern assemblage, but for the other two I propose new assemblage names: the Old Tom and Harper Ranch assemblages. The loca-tions of these assemblages are shown i n F i g . 18. The Old Tom assemblage includes the Old Tom, Shoemaker, and Independence Formations i n Princeton and K e t t l e River map-areas, and t h e i r possible 63 REVISED UPPER PALEOZOIC EUGEOCLINAL ASSEMBLAGES F i g . 18. Revised Upper Paleozoic eugeoclinal assemblages i n southern B r i t i s h Columbia and northern Washington. Sources of data i n text. 64 m e t a m o r p h o s e d e q u i v a l e n t , t h e K o b a u G r o u p . T h e C h a p p e r o n G r o u p i n V e r n o n m a p -a r e a may a l s o b e l o n g w i t h t h i s a s s e m b l a g e . T h e l e s s m e t a m o r p h o s e d r o c k s a r e v o l c a n i c f l o w s o f b a s a l t i c o r a n d e s i t i c c o m p o s i t i o n ( R e a d a n d O k u l i t c h , 1 9 7 7 ) , b e d d e d c h e r t , a r g i l l i t e , a n d m i n o r l i m e s t o n e . T h e s e a r e s i m i l a r t o t h e l i t h -o l o g i e s i n t h e C a c h e C r e e k - B r i d g e R i v e r a s s e m b l a g e , a n d M o n g e r s u g g e s t s t h e y may b e i n c l u d e d w i t h i n i t f o l l o w i n g m o r e d e t a i l e d s t u d y . F o s s i l s f r o m t h e s e r o c k s a r e C a r b o n i f e r o u s i n a g e , a l t h o u g h c l a s t s i n a C a r b o n i f e r o u s b i o c l a s t i c l i m e s t o n e a r e l a t e S i l u r i a n o r E a r l y D e v o n i a n i n a g e ( R e a d a n d O k u l i t c h , 1 9 7 7 ) . T h e s e c o n d s u b d i v i s i o n I r e f e r t o a s t h e H a r p e r R a n c h a s s e m b l a g e . I t i n c l u d e s t h e H a r p e r R a n c h G r o u p a s d e s c r i b e d a b o v e , a n d p r o b a b l y t h e C h i l l i -w a c k G r o u p o f s o u t h w e s t e r n B r i t i s h C o l u m b i a a n d n o r t h w e s t e r n W a s h i n g t o n . A l -t h o u g h M o n g e r ( 1 9 7 7 ) e s t a b l i s h e d t h e C h i l l i w a c k G r o u p a s a s e p a r a t e a s s e m b l a g e , i t wa s o n c e p r o b a b l y c o n t i n u o u s w i t h t h e H a r p e r R a n c h a s s e m b l a g e . T h e s e s e q u e n c e s i n c l u d e v o l c a n i c s a n d a s s o c i a t e d e l a s t i c s 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 , a l o n g w i t h s h a l l o w m a r i n e l i m e s t o n e s , a n d I i n f e r t h e m t o b e p a r t s o f a n i s l a n d a r c t e r r a n e o f L a t e M i s s i s s i p p i a n t o P e r m i a n a g e . M o n g e r ( 1977 ) g r o u p e d t h e H a r p e r R a n c h G r o u p w i t h s e v e r a l r o c k u n i t s t o t h e s o u t h e a s t : t h e M o u n t R o b e r t s F o r m a t i o n , t h e A n a r c h i s t G r o u p , a n d t h e M i s -s i o n A r g i l l i t e i n N e l s o n a n d K e t t l e R i v e r m a p - a r e a s a n d a d j a c e n t n o r t h e r n W a s h i n g t o n . T h e s e g r o u p s a r e l i t h o l o g i c a l l y d i s t i n c t f r o m t h e H a r p e r R a n c h a s s e m b l a g e , a n d I b e l i e v e t h e y b e l o n g t o t h e E a s t e r n a s s e m b l a g e , a l o n g w i t h t h e C o v a d a G r o u p o f n o r t h e r n W a s h i n g t o n . 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 s e r o c k s ( R i n e h a r t a n d F o x , 1 9 7 2 , 1 9 7 6 ; F o x a n d o t h e r s , 1 9 7 7 ; O k u l i t c h , 1 9 7 3 ; L i t t l e , 1 9 6 0 ; M u e s s i g , 1 9 6 7 ; P a r d e e , 1 9 1 8 ) r e v e a l t h a t t h e y a r e a v a r i a b l y m e t a m o r p h o s e d s e q u e n c e o f a r g i l l i t e , s i l t s t o n e , q u a r t z i t e ( m e t a c h e r t ? ) , g r a y -w a c k e , c o n g l o m e r a t e a n d b r e c c i a , l i m e s t o n e , a n d m i n o r b a s a l t i c o r a n d e s i t i c 65 volcanics. The c l a s t s i n the conglomerates are mainly chert, a r g i l l i t e , sandstone, mafic volcanics, and limestone. The l i t h i c s i m i l a r i t y of t h i s sequence to the lower sedimentary portion of the Eastern assemblage i s evident, and i n contrast with the v o l c a n i c l a s t i c nature of the Harper Ranch assemblage. F o s s i l s i n northern Washington are mostly Permian i n age, but i n B r i t i s h Columbia range from Late Miss i s s i p p i a n to Permian. The Anarchist Group i n northern Washington i s disconformably o v e r l a i n by the Palmer Moun-t a i n Greenstone, c o n s i s t i n g of metamorphosed b a s a l t i c flows, p y r o c l a s t i c s , and i n t r u s i v e rocks of Permian and/or T r i a s s i c age. This u n i t i s perhaps equivalent to the upper volcanic portion of the Eastern assemblage i n south-eastern B r i t i s h Columbia. The Harper Ranch assemblage i s unique within Monger's Southern B r i t i s h Columbia assemblage i n being a c l a s t i c sequence derived from an active i s l a n d arc, despite the inference by Okulitch and P e a t f i e l d (1977) that the Anarchist Group represents an i s l a n d arc sequence. The Harper Ranch assemblage does not appear to extend southward into the southernmost part of the province, where the Old Tom assemblage i s i n close proximity to the Anarchist Group. Possibly such rocks are present i n the western part of the Anarchist Group, which has not been well studied. The bulk of the Anarchist Group i s apparently part of the Eastern assemblage, however. The Chilliwack Group, which crops out i n the western f o o t h i l l s of the northern Cascade Mountains, i s s t r i k i n g l y s i m i l a r to the Harper Ranch Group 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 succession (Monger, 1966; Danner, 1972, 1977a). I t consists of fine-grained c l a s t i c rocks, volcanic sandstone, lime-stone, and l o c a l l y abundant volcanic rocks of varied composition. The sequence contains rocks both older and younger than those of the Harper Ranch 66 Group.. Devonian and Lower Pennsylvanian limestones are separated by hundreds of metres of 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 volcanic sandstones (includ-ing t u r b i d i t e s ) which could include rocks of Mis s i s s i p p i a n age. The Lower Pennsylvanian limestone, containing a f u s u l i n i d fauna s i m i l a r to that found near Kamloops, i s disconformably 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 turn o v e r l a i n by a thick Lower to Middle Permian limestone. Permian rocks above t h i s limestone are a r g i l l i t e , volcanic sand-stone, limestone lenses, and volcanic flows and p y r o c l a s t i c rocks of 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 rocks have not been recognized i n the Harper Ranch Group, but may be present. TECTONIC SIGNIFICANCE OF THE HARPER RANCH ASSEMBLAGE The Harper Ranch assemblage represents part of an i s l a n d arc terrane of Late Paleozoic age. The volcanic centers from which these e l a s t i c s were derived do not seem to be presently exposed, but they may be covered by extensive Upper T r i a s s i c s t r a t a to the west. Volcanic flows i n the sequence seem to be minor i n extent, and some areas where flows have been mapped may i n f a c t belong to the Upper T r i a s s i c Nicola Group. Coeval rocks to the west are the oceanic sediments and volcanics of the Cache Creek-Bridge River assem-blage, and the Old Tom assemblage. To the east are the volcanic and c l a s t i c rocks of the Eastern assemblage, the l a t t e r derived l a r g e l y from an u p l i f t e d and deformed pre-Mississippian oceanic terrane. Contacts between these assem-blages are usually 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 , or o b l i t e r a t e d by Mesozoic and T e r t i a r y plutons, but i n southern Bonaparte Lake map-area possible Harper Ranch Group i s faulted against the Fennel Formation 67 a n d t h e E a g l e B a y F o r m a t i o n t o t h e e a s t ( C a m p b e l l a n d T i p p e r , 1 9 7 1 ) . P o s s i b l e c o r r e l a t i v e s o f t h i s i s l a n d a r c t e r r a n e a r e d i s c o n t i n u o u s l y e x p o s e d f a r t h e r s o u t h i n t h e C o r d i l l e r a ( M o n g e r , 1 9 7 5 a ; S t e v e n s , 1 9 7 7 ; C h u r k i n a n d E b e r l e i n , 1 9 7 7 ) . T h e s e a r e a s i n c l u d e c e n t r a l a n d e a s t e r n O r e g o n ( V a l l i e r a n d o t h e r s , 1 9 7 7 ) , t h e e a s t e r n K l a m a t h M o u n t a i n s o f n o r t h e r n C a l i f o r n i a ( I r w i n , 1 9 7 7 ; I r w i n a n d o t h e r s , 1 9 7 7 ) , a n d t h e n o r t h e r n S i e r r a N e v a d a ( D ' A l l u r a a n d o t h e r s , 1 9 7 7 ; S c h w e i c k e r t a n d C o w a n , 1 9 7 5 ) . C o r r e l a t i o n s b e t w e e n t h e s e w i d e l y s e p a r a t e d a r e a s a r e b a s e d p r i m a r i l y o n t h e a b u n d a n c e o f v o l c a n i c a n d v o l c a n i -c l a s t i c m a t e r i a l i n t h e s e q u e n c e s , w h i c h s u g g e s t s a v o l c a n i c a r c s e t t i n g , a n d t h e s i m i l a r i t y i n t h e i r n o n - T e t h y a n P e r m i a n f u s u l i n i d f a u n a s ( M o n g e r a n d R o s s , 1 9 7 1 ; J o n e s a n d o t h e r s , 1 9 7 2 ) . S t r i k i n g s i m i l a r i t i e s i n s t r a t i g r a p h y a l s o e x i s t , a t l e a s t a s f a r s o u t h a s t h e e a s t e r n K l a m a t h M o u n t a i n s . C o m m o n l y , M i d d l e a n d U p p e r P e n n s y l v a n i a n s t r a t a a r e m i s s i n g , a n d a d i s c o n f o r m i t y s e p a r -a t e s M i s s i s s i p p i a n t o L o w e r P e n n s y l v a n i a n e l a s t i c s a n d c a r b o n a t e s f r o m a L o w e r P e r m i a n s e q u e n c e d o m i n a t e d b y a t h i c k l i m e s t o n e i n i t s l o w e r p o r t i o n . P e r m i a n r o c k s a b o v e t h e l i m e s t o n e a r e e l a s t i c s a n d a v a r i e d a s s e m b l a g e o f v o l c a n i c f l o w s a n d p y r o c l a s t i c s o f m a f i c t o i n t e r m e d i a t e c o m p o s i t i o n . T h e g e n e r a l s i m i l a r i t y i n L a t e P a l e o z o i c h i s t o r y o f t h e s e a r e a s s u g g e s t s t h a t t h e y a r e p o r t i o n s o f a o n c e - c o n t i n u o u s t e r r a n e w h i c h h a s b e e n d i s r u p t e d b y l a t e r t e c t o n i c e v e n t s a n d p a r t i a l l y c o v e r e d b y y o u n g e r r o c k s . T h e b a s e m e n t o n w h i c h t h e H a r p e r R a n c h G r o u p a c c u m u l a t e d i s n o w h e r e e x p o s e d , e l a s t i c s i n t h e s e q u e n c e show n o e v i d e n c e o f a n o l d e r t e r r a n e a c t i n g a s a s e d i m e n t s o u r c e , i n c o n t r a s t t o t h e e l a s t i c s o f t h e E a s t e r n a s s e m b l a g e . T h e H a r p e r R a n c h G r o u p may h a v e b e e n d e p o s i t e d d i r e c t l y o n o c e a n i c c r u s t , o r o n a n o l d e r s u b m e r g e d i s l a n d a r c o r c o n t i n e n t a l b a s e m e n t . T h e b a s e o f t h e C h i l l i w a c k G r o u p i s a l s o n o t e x p o s e d , b u t o l d e r m e t a p l u t o n i c r o c k s y i e l d i n g 68 Proterozoic and S i l u r i a n radiometric ages (Mattinson, 1972) occur as tectonic s l i c e s i n thrust f a u l t s c u t t i n g the Chilliwack s t r a t a , and i n the metamorphic core zone of the Cascades to the east. These occurrences suggest that the Chilliwack Group may have accumulated on a basement of continental crust or older magmatic arc rocks. In the Klamath Mountains, the Devonian to Permian arc sequence o v e r l i e s an Ordovician o p h i o l i t e sheet and a complex assemblage of Ordovician to Lower Devonian sediments, some of which are arc-derived e l a s t i c s . The Cache Creek-Bridge River assemblage contains rocks which formed i n an oceanic environment coeval with Late Paleozoic arc a c t i v i t y . Tectonic accretion of t h i s material to the arc probably began during eastward-directed subduction which produced the arc terrane. However, rocks as young as Late T r i a s s i c may be present i n the oceanic assemblage, suggesting that accretion continued into the Mesozoic. The Trafton Sequence (Danner, 1966, 1977a) i n the Cascade f o o t h i l l s and the San Juan Islands west of the Chilliwack Group i s l i t h o l o g i c a l l y s i m i l a r to the Cache Creek-Bridge River assemblage. The Chilliwack Group and Trafton Sequence probably represent the same paired tectono-stratigraphic units as the Cache Creek Group and Harper Ranch Group near Kamloops (Danner 1977a and b; F i g . 18). The Trafton Sequence, however, i s associated with a v a r i e t y of Mesozoic rocks units of oceanic character i n a s t r u c t u r a l l y complex region. Ultramafic rocks, layered gabbro and amphibolite which are intruded by d i o r i t e dated at 170 ± 10 m.y. may comprise a Middle or Late J u r a s s i c ophio-l i t e (Brown, 1977)„. - ' Radiolarian" cherts of. Jurassic, to Cretaceous age are abundant; i n the surrounding units, and the Trafton Jsequerice i t s e l f probably \ includes large areas of T r i a s s i c chert (Danner, 1977a, and o r a l commun., 1978; 69 Whetten and others, 1978). Cretaceous planktonic foraminifera have been found i n t u f f s associated with pillo w basalt (Danner, 1966; Whetten and others, 1978). Similar p o s t - T r i a s s i c rocks may be present but unrecognized i n the Cache Creek-Bridge River assemblage, or the Trafton Sequence may have undergone a longer period of accretion than the other oceanic terranes i n B r i t i s h Columbia. An oceanic assemblage of chert, a r g i l l i t e , p i l l o w b a s a l t , ultramafic rocks, and limestones with Tethyan Permian faunas i s exposed sp o r a d i c a l l y farther south i n the C o r d i l l e r a , l y i n g west of the Late Paleozoic arc terrane. This complex l i e s east of and i s older than the accreted Jurassic to Eocene rocks of the Franciscan Complex, and i s therefore s i m i l a r i n tectonic p o s i -t i o n to the Cache Creek-Bridge River assemblage. Such rocks occur i n ce n t r a l and northeastern Oregon ( V a l l i e r and others, 1977; Dickinson and Thayer, 1978; Brooks and V a l l i e r , 1978); the western Klamath Mountains (Irwin, 1977; Irwin and others, 1977); and the western f o o t h i l l s of the S i e r r a Nevada (Schweickert and others, 1977; Davis and others, 1978). However, T r i a s s i c and J u r a s s i c rocks are common i n the complex i n some areas, and may even be more abundant than the Paleozoic rocks (Irwin, 1977), again suggesting tectonic accretion extending through the T r i a s s i c and J u r a s s i c . C l a s t i c sediments i n the Harper Ranch assemblage and Eastern assemblage have very d i f f e r e n t provenances. Sediment derived from the Caribooan orogenic terrane i s abundant i n the Eastern assemblage, but absent i n the Harper Ranch assemblage. The volcanic arc and t h i s older oceanic terrane were probably widely separated during the Late Paleozoic. Assuming that no s i g n i f i c a n t transcurrent motion has occurred between these two assemblages, they were probably separated by a deep marine basin of unknown width. From the s p a t i a l 70 d i s t r i b u t i o n o f L a t e P a l e o z o i c o c e a n i c a n d a r c t y p e r o c k s , I h a v e i n f e r r e d t h a t t h e a r c was b u i l t a b o v e a n e a s t - d i p p i n g s u b d u c t i o n z o n e , a n d t h a t o c e a n i c r o c k s o f t h e C a c h e C r e e k - B r i d g e R i v e r a s s e m b l a g e b e g a n t o a c c r e t e o n t h e w e s t e r n s i d e o f t h e a r c d u r i n g t h e L a t e P a l e o z o i c . I f t h i s i n f e r e n c e i s c o r r e c t , t h e n t h e b a s i n e a s t o f t h e a r c was p r o b a b l y a m a r g i n a l o r b a c k -a r c b a s i n f l o o r e d b y c r u s t o f o c e a n i c t y p e ( F i g . 1 9 ) . A s i m i l a r p a l e o g e o g r a p h y h a s b e e n p o s t u l a t e d f o r t h e L a t e P a l e o z o i c e u g e o c l i n e o f N e v a d a a n d C a l i f o r n i a ( B u r c h f i e l a n d D a v i s , 1 9 7 2 ; S p e e d , 1 9 7 7 ; S t e w a r t a n d o t h e r s , 1 9 7 7 ) . T h e r e , t h e a r c t e r r a n e i s now s e p a r a t e d f r o m t h e c o e v a l m i o g e o c l i n e b y t h e H a v a l l a h S e q u e n c e . T h i s u n i t i n c l u d e s c h e r t s , q u a r t z i t e s , a n d b a s a l t s r e p r e s e n t i n g t h e o c e a n i c f l o o r o f t h e m a r g i n a l b a s i n , a n d c o a r s e l i t h i c - r i c h e l a s t i c s d e r i v e d f r o m t h e A n t l e r o r o g e n i c b e l t , a t e r -r a n e f l a n k i n g t h e b a s i n o n t h e e a s t a n d c o m p o s e d l a r g e l y o f d e f o r m e d o c e a n i c r o c k s o f E a r l y P a l e o z o i c a g e . D u r i n g t h e P e r m o - T r i a s s i c , t h i s b a s i n c l o s e d , a n d t h e a r c t e r r a n e c o l l i d e d w i t h t h e A n t l e r b e l t t o t h e e a s t . D u r i n g t h i s e v e n t , r e f e r r e d t o a s t h e S o n o m a O r o g e n y , t h e H a v a l l a h S e q u e n c e was t h r u s t e a s t w a r d o v e r t h e A n t l e r b e l t a n d m i o g e o c l i n e t o f o r m t h e G o l c o n d a a l l o c h t h o n . I b e l i e v e t h a t t h e L a t e P a l e o z o i c e v o l u t i o n o f t h e e u g e o c l i n e i n s o u t h -e r n B r i t i s h C o l u m b i a f o l l o w e d a s i m i l a r c o u r s e o f e v e n t s . S u b d u c t i o n o f o c e a n i c c r u s t t o w a r d t h e e a s t , b e n e a t h t h e v o l c a n i c a r c c o n t i n u e d f r o m t h e L a t e M i s s i s s i p p i a n t h r o u g h t h e E a r l y P e n n s y l v a n i a n , a n d p e r h a p s l o n g e r . T h e a b s e n c e o f r o c k s o f M i d d l e t o L a t e P e n n s y l v a n i a n a g e i n t h e a r c t e r r a n e , a n d t h e p r e s e n c e o f t h i c k , w i d e s p r e a d l i m e s t o n e s o f L o w e r t o M i d d l e P e r m i a n a g e may i n d i c a t e t h a t s u b d u c t i o n a n d a r c v o l c a n i s m c e a s e d f o r m u c h o f t h i s i n t e r v a l . A l t e r n a t i v e l y , s u b d u c t i o n may h a v e c o n t i n u e d u n t i l t h e e n d o f t h e P e n n s y l v a n i a n , a t w h i c h t i m e u p l i f t o f t h e a r c t e r r a n e r e s u l t e d i n e r o s i o n A C C R E T I O N A R Y V O L C A N I C B A C K - A R C C A R I B O O A N M I O G E O C L I N E P R I S M A R C B A S I N O R O G E N C A C H E C R E E K - B R I D G E R I V E R H A R P E R R A N C H E A S T E R N A S S E M B L A G E (IN P A R T ) A S S E M B L A G E A S S E M B L A G E F i g . 19. Sketch cross-section showing i n f e r r e d paleogeographic and paleotectonic elements of southern B r i t i s h Columbia during the Late Mississippian to Early Pennsylvanian. Not to scale. 72 of the Middle to Upper Pennsylvanian rocks. Closure of the back-arc basin probably began i n the l a t e Early Permian or Late Permian. C o l l i s i o n of the arc terrane with the older rocks to the east i n the Early T r i a s s i c may account for the pre-Late 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 Eastern assemblage south of the l a t i t u d e of Kamloops. The mechanism .of basin closure i s uncertain. B u r c h f i e l and Davis (1975) suggested that the Late Paleozoic back-arc basin i n Nevada closed by subduction of the oceanic basement eastward beneath the continental margin, while the volcanic and sedimentary f i l l of the basin was transported upward over the continental margin. I think i t u n l i k e l y that such eastward thrusting of the basin f i l l could have occurred except during actual c o l l i s i o n between the arc and the continental margin. At t h i s time, sediments and volcanics accreted to the margin above the subducting slab would have been caught i n 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 analagous to the present Molucca Sea c o l l i s i o n zone ( S i l v e r and Moore, 1978). During t h i s process, subduction continued on the west side of the arc, u n t i l c o l l i -sion was completed i n the Early T r i a s s i c . An a l t e r n a t i v e model was presented by Speed (1977), which assumed that the basin closed by subduction of the basin f l o o r toward the west, beneath the volcanic arc. Sediments and volcanics accreted to the eastern side of the arc during t h i s subduction process were thrust over the continental margin as i t reached the subduction 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 require a rev e r s a l i n subduction p o l a r i t y during the Permian, i f my previous assumptions are correct. One of the drawbacks to the concept of a Late Paleozoic marginal basin 73 i n southern B r i t i s h Columbia i s that there are no rocks to the east of the arc terrane that seem representative of the marginal basin i t s e l f . In northern B r i t i s h Columbia the upper part of the Eastern assemblage may be an overthrust sheet of oceanic crust, but i n the southern part of the pro-vince the upper mafic volcanics of t h i s assemblage appear to conformably o v e r l i e the lower orogenic e l a s t i c s (Monger, 1977; Davis and others, 1978). One could postulate with e i t h e r of these models that most of the basin f i l l was subducted along with i t s basement. Further data are needed to t e s t these models. Geochemical trends of the Late Paleozoic volcanic rocks might be useful i n the following ways: 1) i n determining whether subduction beneath the arc terrane was toward the west or east, and whether i t reversed i n the Permian; 2) i n determining whether the mafic volcanics of the Eastern assemblage are r e l a t e d to forma-t i o n of the back-arc basin, or to eastward subduction beneath the continental margin i n the B u r c h f i e l and Davis model. Further d e t a i l e d studies of the l i t h o l o g i e s and depositional environments of a l l the eugeoclinal assemblages w i l l c e r t a i n l y help c l a r i f y these tectonic i n t e r p r e t a t i o n s . The present p o s i t i o n of the Chilliwack Group and Trafton Sequence r e l a -t i v e to the other Upper Paleozoic sequences i s at l e a s t i n part due to trans-current f a u l t i n g . 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 system (Fig. 18), which bounds the Bridge River and Hozameen Groups on the east, may amount to hundreds of kilometres (Tipper, 1977) , and moved the Bridge River Group to a p o s i t i o n west of the Cache Creek Group. The Trafton Sequence, Chilliwack Group, and the metamorphic core zone of the North Cascades were juxtaposed west of the Hozameen Group by r i g h t - l a t e r a l s l i p on the Fraser River-Straight Creek!fault system and an ancestral Ross Lake f a u l t . Davis 74 and others (1978) proposed a mid-Cretaceous phase of f a u l t i n g along the l a t -t e r f a u l t zone which moved the Cascade and San Juan Island terranes north-westward from the area of southeastern Washington and northeastern Oregon now covered by the Columbia River Basalts. Subsequent Cretaceous movement on the Fraser River-Straight Creek f a u l t system i s at l e a s t 75 km (Tipper, 1977), and may be as much as 200 km (Misch, i n Monger, 1977, F i g . 8). North of Bonaparte Lake map-area, rocks s i m i l a r to the Harper Ranch Group are not exposed east of the Cache Creek-Bridge River assemblage, which i s separated from the Eastern assemblage by f a u l t s and Mesozoic volcanic and plutonic rocks. I t does not seem l i k e l y that the Upper Paleozoic i s l a n d arc terrane, i f present, would be completely obscured by younger deposits and intrusions for such a great distance along the C o r d i l l e r a . The major f a u l t zones (Pinchi and T e s l i n faults) which bound the Cache Creek-Bridge River assemblage on the east are steep, possibly transcurrent features; major westward tectonic transport of the Omineca C r y s t a l l i n e b e l t (including the Eastern assemblage), which might have buried the arc complex, has not been documented. In north-central B r i t i s h Columbia, scattered exposures over a very large region belong to the'Stikine assemblage, an Upper Paleozoic i s l a n d arc terrane which l i e s west of the Cache Creek-Bridge River assemblage i n the western Intermontane b e l t . I t includes Upper Missi 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 , along with shale and carbonate. A d i s t i n c t i v e Lower Permian carbonate unit i s wide-spread, and some evidence suggests that i t rests unconformably on Upper Mississippian rocks. Fusulinids from the carbonate form a non-Tethyan fauna s i m i l a r to Permian faunas from the arc terrane i n the eastern 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 to the south to suggest that the St i k i n e assemblage i s the missing northern continuation of t h i s Upper Paleo-zoic arc terrane. I f so, the present occurrence of the S t i k i n e assemblage west of the Cache Creek-Bridge River assemblage must be explained. Monger (1977) suggests that the oceanic rocks were thrust eastward (obducted) over the broad arc terrane, probably i n the Early or Middle J u r a s s i c . The pro-posed allochthon must be completely detached from i t s root zone west of the Stikine assemblage. The great distance of thrusting involved (over 200 km), and inconsistencies with s t r u c t u r a l data from the oceanic rocks are problems of t h i s hypothesis, as was pointed 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 continuous, having formed on opposite sides of the Late Paleozoic ocean basin. Emplacement of the S t i k i n e assemblage by a combination of basin c l o s i n g and possible s t r i k e - s l i p motion during the Late T r i a s s i c may have been accompanied by eastward obduction of ocean f l o o r i n northern B r i t i s h Columbia and the Yukon (Monger, 1977; Tempelman-Kluit, 1976). This implies that most of the Cache Creek-Bridge River assemblage was accreted to North America by the Late T r i a s s i c , although i n southern B r i t i s h Columbia i t could have remained open to the P a c i f i c u n t i l at l e a s t Middle Jurassic time as suggested by Cole and Tennyson (1977). 76 CHAPTER I I I . NICOLA GROUP (MAP-UNITS 2 THROUGH 6) INTRODUCTION The Nicola Group i n the study area consists of at l e a s t 3000 m of 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 t u r b i d i t e s , minor volcanic flows, l i t h i c sandstone and conglomerate, and redeposited basinal limestones. Mudstone i s by far the most abundant l i t h o l o g y . Neither the base nor top of the sequence i s exposed. I have divided the sequence i n t o f i v e u n i t s , map-units 2 through 6, shown on Plate I (in pocket). Each i s well exposed i n places along the south slope of Paul Ridge. Units 3, 4, and 5 extend northwestward into the southern Dome H i l l s , although Unit 5 undergoes a profound change i n fac i e s i n crossing Paul Creek v a l l e y . Such rapid f a c i e s changes imply that these units may only be recognizable l o c a l l y (Fig. 20). PHYSICAL STRATIGRAPHY Structural Setting The Nicola Group on Paul Ridge i s deformed into a p a i r of northwest-trending mappable f o l d s , the Paul Ridge a n t i c l i n e on the west and Paul Ridge syncline to the east. The a n t i c l i n e i s overturned toward the west, and the overturned limb also crops out i n the southern Dome H i l l s . The folds are cut by several steep f a u l t s which complicate the map pattern. The oldest T r i a s s i c rocks are faulted against the Harper Ranch Group to the east, and the top of the section i s covered by alluvium i n the North Thompson River Valley. W E S T E R N P A U L R IDGE COVERED D O M E H I L L S 3 V E R T I C A L LITHOLOGIC S Y M B O L S Thin-bedded mudstone Laminated mudstone and siltstone, thin-bedded mudstone, turbidite limestone t i l t t t o n e , t h i n - b e d d e d r b i d i t e e a n d t t o n e t i l t t t o n e , t h i n - b e d d s d ne and c o n g l o m e r a t e pyroclattic flows E A S T E R N P A U L R IDGE MISSING -. — ~ ~ .TI COVERED FAULT F i g . 20. 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 of units within the Nicola Group. 78 Description of Units Unit 2 Unit 2 i s the oldest exposed T r i a s s i c u n i t . The un i t occupies the core of the Paul Ridge a n t i c l i n e , and i s faulted against Mississippian rocks on the east limb of the Paul Ridge syncline. In addition, the i n t e r n a l structure of t h i s unit i s complex, with common mesoscopic f o l d s , so only a general estimate of several hundred meters can be given for the minimum thickness of the unit. The eastern portion of the unit consists mostly of thin-bedded mud-stone, with a lens of massive mafic volcanic rock, Unit 2A. Contacts of the igneous rocks with the enclosing mudstone are concealed, but the mafic rocks are amygdaloidal, i n d i c a t i n g that they originated as an extrusive flow. The western portion of the unit also consists predominantly of t h i n to medium-bedded mudstones, but interbedded s p o r a d i c a l l y through the section are i n t e r -vals of laminated mudstone and s i l t s t o n e and dark, fine-grained t u r b i d i t e limestones. These l i t h o l o g i e s become increasingly abundant higher i n the section, and predominate i n the upper 50 to 100 m. In t h i s upper i n t e r v a l , fine-grained p y r o c l a s t i c rocks appear interbedded with the s i l t s t o n e s and limestones, heralding the p y r o c l a s t i c sedimentation of Unit 3. The contact between these units i s gradational, and i s drawn where massive p y r o c l a s t i c rocks become predominant i n the section, mudstones become subordinate, and t u r b i d i t e limestones disappear. The mafic volcanics of Unit 2A are massive i n outcrop. Vesicles up to several millimeters i n diameter are f i l l e d by c a l c i t e and c h l o r i t e . Small phenocrysts of clinopyroxene and plagioclase make up about 5 to 10% of the rock, and are set i n an aphanitic matrix of plagioclase m i c r o l i t e s 79 and al t e r e d glass with a h y a l o p i l i t i c texture. Glass i s al t e r e d to c h l o r i t e , sphene, and less abundant quartz, c a l c i t e , and a l b i t e . Plagioclase i s l a r g e l y altered to s e r i c i t e , and i t s composition i s indeterminable. The composition of the volcanics i s e i t h e r b a s a l t i c or a n d e s i t i c . Unit 3 This unit crops out i n the core of the Paul Ridge syncline, and i n the upright and overturned limbs of the f a u l t e d Paul Ridge a n t i c l i n e . I t con-s i s t s of andesitic p y r o c l a s t i c material redeposited by t u r b i d i t y currents and high-concentration mass flows, and interbedded with gray to green mud-stone. Dense volcanic fragments and l e s s e r amounts of plagioclase and mafic phenocrysts make up the deposits, which range i n grain s i z e from fine to very coarse sand (ash), with some s i l t s t o n e and rare pebble conglomerate. Weathered surfaces of these rocks often have a d i s t i n c t i v e l i g h t reddish-brown color. Eastern 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 eastern portion often lack layering, and s t r u c t u r a l data from t h i s area i s sparse. Many outcrops consist of massive, graded, or laminated t u f f , with neither the top nor bottom of the bed exposed, so beds several meters to tens of meters thick must dominate the section. In contrast, beds i n the western portion are much thinner (usually less than one meter), and t u r b i d i t e sedimentary structures are present. The estimated thickness of the western f a c i e s i s about 400 m. To the east, the top of the u n i t has been eroded away, and the base i s i n part faulted, but the minimum thickness i s s u b s t a n t i a l l y greater, perhaps 500 to 600 m. 80 U n i t 4 T h i s u n i t c o n s i s t s o f t h i n - b e d d e d m u d s t o n e , l a m i n a t e d m u d s t o n e , r a r e v i t r i c t u f f , t h i c k v o l c a n i c s a n d s t o n e s , a n d m i n o r r e d e p o s i t e d l i m e s t o n e . T h e c o n t a c t w i t h U n i t 3 i s u n e x p o s e d b u t a p p a r e n t l y c o n f o r m a b l e , w i t h t h e p y r o c l a s t i c r o c k s o f U n i t 3 g i v i n g way w i t h i n a d i s t a n c e o f l e s s t h a n 10 m t o m u d s t o n e s w i t h i n t e r b e d d e d s i l t s t o n e s a n d l i m e s t o n e s . T h e t h i c k n e s s o f t h e u n i t o n P a u l R i d g e i s a p p r o x i m a t e l y 4 7 5 t o 5 2 5 m. T h i s e s t i m a t e e x -c l u d e s t h e t h i c k n e s s o f t h e i n t r u s i v e s i l l w h i c h o c c u r s i n t h e m i d d l e o f t h e u n i t . T h e t h i c k n e s s i n t h e Dome H i l l s i s a b o u t 5 5 0 m. On P a u l R i d g e , t h e l o w e r a n d u p p e r p o r t i o n s o f U n i t 4 a r e m o s t l y m u d -s t o n e w i t h i n t e r b e d d e d s i l t s t o n e s a n d t u r b i d i t e l i m e s t o n e s . T h i c k , c o a r s e -g r a i n e d v o l c a n i c t u r b i d i t e s a n d s t o n e s w i t h s u b o r d i n a t e m u d s t o n e make u p t h e m i d d l e p o r t i o n o f t h e u n i t . I n t h e Dome H i l l s , h o w e v e r , m e d i u m t o c o a r s e v o l c a n i c l a s t i c s a r e u n c o m m o n , a n d o c c u r i n t h e u p p e r 1 0 0 m o f t h e u n i t . U n i t 5 T h i s u n i t s h o w s a p r o n o u n c e d f a c i e s c h a n g e b e t w e e n P a u l R i d g e a n d t h e Dome H i l l s . On P a u l R i d g e t h e r o c k s a r e a l m o s t e n t i r e l y t h i n t o m e d i u m -b e d d e d m u d s t o n e . T u r b i d i t e l i m e s t o n e s a n d c o a r s e e l a s t i c s a r e v e r y r a r e . T h e o n l y o c c u r r e n c e o f a b u n d a n t c o a r s e e l a s t i c s i s n e a r t h e s u m m i t o f P e t e r P e a k , w h e r e c o a r s e l i t h i c s a n d s t o n e , p e b b l y s a n d s t o n e , a n d c o n g l o m e r a t e c r o p o u t o n t h e e a s t e r n s l o p e s o f t h e p e a k , i n t e r b e d d e d w i t h l a m i n a t e d a n d t h i n - b e d d e d m u d s t o n e s . T h e t h i c k n e s s o f t h e u n i t c a n n o t b e a c c u r a t e l y a s s e s s e d b e c a u s e o f e r r a t i c s t r u c t u r a l a t t i t u d e s a n d t h e i n t r u s i o n o f t h e M o u n t P a u l S t o c k , b u t i s o n t h e o r d e r o f 1 , 0 0 0 m. On t h e s o u t h w e s t e r n s l o p e o f Dome H i l l s , t h e c h a r a c t e r o f t h e u n i t i s 81 v e r y d i f f e r e n t . T h i n - b e d d e d m u d s t o n e s a r e s t i l l p r e s e n t , b u t a r e s u b o r d i n a t e t o h o m o g e n e o u s a n d l a m i n a t e d m u d s t o n e s , f i n e t o c o a r s e - g r a i n e d s a n d s t o n e , p e b b l y s a n d s t o n e , a n d b r e c c i a . T h e s e e l a s t i c s d i f f e r f r o m t h o s e i n t h e o t h e r U p p e r T r i a s s i c u n i t s i n t h e i r a b u n d a n c e o f n o n - v o l c a n i c l i t h i c f r a g m e n t s , c h i e f l y c h e r t , m u d s t o n e , s a n d s t o n e , a n d l i m e s t o n e . T h e b r e c c i a i s i n t e r -b e d d e d w i t h t u r b i d i t e s a n d s t o n e s , a n d i s t h e r e f o r e p r o b a b l y a d e e p w a t e r d e p o s i t . T h e t o p o f t h e u n i t i s c o v e r e d b y a l l u v i u m o f t h e N o r t h T h o m p s o n R i v e r v a l l e y , b u t t h e e x p o s e d t h i c k n e s s i s s i m i l a r t o t h a t o n P a u l R i d g e . T h e p r o n o u n c e d d i f f e r e n c e i n l i t h o l o g y b e t w e e n t h e s e c t i o n s o f U n i t 5 o n P a u l R i d g e a n d Dome H i l l s , o n l y 1 .5 km t o t h e n o r t h w e s t , m i g h t s u g g e s t t h a t t h e s e s e q u e n c e s h a v e b e e n s t r u c t u r a l l y j u x t a p o s e d . H o w e v e r , s e v e r a l l i n e s , o f e v i d e n c e s u g g e s t t h a t r a p i d c h a n g e i n f a c i e s i s a m o r e p l a u s i b l e i n t e r p r e t a t i o n . F i r s t , b o t h s e q u e n c e s c o n f o r m a b l y a n d g r a d a t i o n a l l y o v e r l i e U n i t 4 . T h e c o n t a c t i s d r a w n a b o v e t h e l a s t e x p o s u r e s o f v o l c a n i c s a n d s t o n e s o r t u r b i d i t e l i m e s t o n e s o f U n i t 4 , a b o v e w h i c h t h i n - b e d d e d m u d s t o n e o r m u d -s t o n e w i t h l i t h i c - r i c h e l a s t i c s b e c o m e t h e d o m i n a n t l i t h o l o g i e s . T h e c o a r s e e l a s t i c s o n P e t e r P e a k a r e i d e n t i c a l t o t h o s e o f s i m i l a r g r a i n s i z e i n Dome H i l l s . W i t h i n t h e s e c t i o n i n Dome H i l l s , t h e p r o p o r t i o n o f t h i n - b e d d e d m u d s t o n e d e c r e a s e s a l o n g s t r i k e t o t h e n o r t h w e s t , w h i l e t h e p r o p o r t i o n o f c o a r s e e l a s t i c s i n c r e a s e s . T h i s t r e n d i s p a r t i c u l a r l y e v i d e n t i n t h e b a s a l p o r t i o n o f t h e u n i t , w h i c h i s n e a r l y a l l m u d s t o n e i n t h e s o u t h e a s t , b u t t o t h e n o r t h w e s t i n c l u d e s s e v e r a l i n t e r v a l s o f c o a r s e e l a s t i c s . T h e p r o p o r -t i o n o f e l a s t i c s o n P a u l R i d g e i s c o n s i s t e n t w i t h e x t r a p o l a t i o n o f t h i s t r e n d t o t h e s o u t h e a s t a c r o s s t h e a l l u v i u m - f i l l e d P a u l C r e e k v a l l e y . 82 Unit 6 The highest exposed unit i n the T r i a s s i c succession i s Unit 6, which crops out at the western end of Paul Ridge, j u s t north of Kamloops. The unit consists of a v a r i e t y of c l a s t i c and volcanic rocks, and has a t h i c k -ness of about 800 to 850 m, with the top covered by the alluvium of the North Thompson River v a l l e y . These rocks are intruded by the Paul Peak Stock, and have undergone contact metamorphism to the hornblende-hornfels f a c i e s . The basal 140 m of the u n i t consists of massive or laminated, fin e to medium-grained andesitic p y r o c l a s t i c rocks s i m i l a r to those i n Unit 3. These p y r o c l a s t i c s are apparently conformable upon the underlying mudstones of Unit 5, although the contact i s concealed. Near or at the top of t h i s i n t e r v a l i s a coarse pebble conglomerate with subrounded p o r p h y r i t i c volcanic c l a s t s , i r r e g u l a r mudstone rip-ups, and a few limestone pebbles. This conglomerate forms the crest of the prominent southeastern spur of Paul Peak. Above i t are about 225 m of laminated mudstone, minor fine to medium-grained l i t h i c - v o l c a n i c sandstone and conglomerate, s i m i l a r to the e l a s t i c s i n Unit 5. Very rare t u r b i d i t e limestones also occur 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 of dark green to black, massive and pillowed mafic volcanic flows (Unit 6B). Layering i s not evident within the volcanics, and no sediments are i n t e r l a y e r e d with them. Pillows were observed i n only a few outcrops, and are obscure, v i s i b l e mainly as c l u s t e r s of c a l c i t e - f i l l e d amygdules, sometimes surrounded by an aphanitic, non-vesicular s h e l l which shows f i s s i l i t y concentric with the p i l l o w (Fig. 21). The pillows are closely-packed, with some i n t e r p i l l o w 83 F i g . 21. Poorly defined v e s i c u l a r pillows i n Unit 6B. Coin i s 24 mm i n diameter. 84 voids f i l l e d by fine-grained limestone, but most are f i l l e d by fine-grained volcanic ash, now nearly i n d i s t i n g u i s h a b l e i n color and texture from the non-vesicular p i l l o w s . Many outcrops which appear massive are probably pillowed, with the presence of pillows revealed only by scattered i n t e r -pi l l o w limestone patches. The limestone probably formed by the percolation and eventual accumulation of post-eruptive carbonate sediment through the i n t e r p i l l o w void spaces, as described by Garrison (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 of the Paul 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 of thermal a l t e r a t i o n due to contact with hot volcanic rocks. The l e a s t a l t e r e d volcanic rock samples consists of about 40% randomly oriented plagioclase laths surrounded by a l t e r e d glass i n an i n t e r s e r t a l to hyaloophitic texture. The glass i s replaced by a fine-grained aggregate of sphene, c h l o r i t e , and c a l c i t e , with minor stilpnomelane. No mafic pheno-crysts are present i n t h i s rock, but clinopyroxene (now l a r g e l y replaced by a c t i n o l i t e ) makes up about 20% of samples from within the contact aureole. Where o r i g i n a l textures are d i s c e r n i b l e , the clinopyroxene occurs as small granules i n t e r s t i t i a l to pla g i o c l a s e , and larger c r y s t a l s molded around the plagioclase l a t h s . Plagioclase i s a l b i t i c where i t s composition i s determinable. The o r i g i n a l rock composition was probably basal t , based on the phenocryst mineralogy and textures. Overlying the volcanics are several hundred meters of mudstone, minor sandstone, and rare t u r b i d i t e limestones. The sediments d i r e c t l y above the volcanics are mostly mudstone and thin-bedded s i l i c e o u s mudstone or chert with 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 reversals i n facing d i r e c t i o n were observed, 85 s o t h e t h i c k n e s s may h a v e b e e n i n c r e a s e d b y f o l d i n g , b u t t h e o r i g i n a l t h i c k n e s s was p r o b a b l y o n t h e o r d e r o f 150 t o 2 0 0 m. B I O S T R A T I G R A P H Y T h e o n l y i d e n t i f i a b l e f o s s i l s r e c o v e r e d f r o m t h e N i c o l a G r o u p a r e c o n o d o n t s f o u n d i n t u r b i d i t e l i m e s t o n e s a n d i n t e r p i l l o w l i m e s t o n e s . C o n o -d o n t s w e r e e x t r a c t e d b y d i s s o l v i n g t h e l i m e s t o n e s a m p l e s i n a 1 .74 N a c e t i c a c i d s o l u t i o n , a n d c o n c e n t r a t e d b y s e p a r a t i n g t h e h e a v y f r a c t i o n o f t h e i n s o l u b l e r e s i d u e u s i n g h e a v y l i q u i d s . T h e c o n o d o n t s w e r e i d e n t i f i e d b y D r . B . E . B . C a m e r o n o f t h e G e o l o g i c a l S u r v e y o f C a n a d a . H i s c o m p l e t e r e p o r t , f r o m w h i c h t h e f o l l o w i n g i s a b s t r a c t e d , i s f o u n d i n A p p e n d i x I, a n d t h e c o n o d o n t s a r e s h o w n i n P l a t e V . Two d i f f e r e n t t y p e s o f c o n o d o n t a s s e m b l a g e w e r e f o u n d i n t h e d i f f e r e n t l i m e s t o n e s . T u r b i d i t e l i m e s t o n e s i n U n i t s 2 a n d 4 ( f o u r s a m p l e s ) y i e l d e d a b u n d a n t c o l l e c t i o n s c o n t a i n i n g o n l y a s i n g l e f o r m - s p e c i e s , t h e p l a t f o r m c o n o d o n t Metapolygnathus polygnathiformis. T h i s f o r m i n d i c a t e s a L a t e T r i a s s i c , p r o b a b l y K a r n i a n a g e f o r t h e s e u n i t s . Two s a m p l e s o f i n t e r p i l l o w l i m e s t o n e f r o m U n i t 6 y i e l d e d d i v e r s e a s s e m b l a g e s o f b a r , b l a d e , a n d p l a t -f o r m c o n o d o n t s , d o m i n a t e d b y t h e p l a t f o r m c o n o d o n t s Neogondolella navicula navicula a n d Neogondolella sp. T h e a g e s o f t h e s e c o l l e c t i o n s a r e L a t e T r i a s s i c — K a r n i a n , a n d p o s s i b l y e a r l y K a r n i a n . A l l u n i t s o f t h e N i c o l a G r o u p i n t h e s t u d y a r e t h e n o f K a r n i a n a g e . T h e t w o c o n t r a s t i n g c o n o d o n t a s s e m b l a g e s c a n b e r e l a t e d t o t h e d i f f e r -i n g m o d e s o f s e d i m e n t a t i o n o f t h e e n c l o s i n g l i m e s t o n e s . L i m e mud f i l l i n g i n t e r p i l l o w v o i d s i s p r o b a b l y m o s t l y p e l a g i c s e d i m e n t w h i c h s e t t l e d t h r o u g h t h e w a t e r c o l u m n a n d t h e n p e r c o l a t e d t h r o u g h t h e p i l e o f p i l l o w s o n t h e 86 PLATE V. CONODONTS EXTRACTED FROM LIMESTONES IN THE NICOLA GROUP, PAUL RIDGE AND DOME HILLS Fi g . 1. Neospathodus sp. c f . N. newpassensis (Mosher). Late r a l view, X 215; G.S.C. Loc. 93450. Fi g . 2. Ozarkodina t o r t i l i s (Tatge). La t e r a l view, X 180; G.S.C. Loc. 93450. Fi g . 3, 4. Cypridodella sp. c f . C. muelleri (Tatge). 3, l a t e r a l view, X 330; G.S.C. Loc. 93450. 4, l a t e r a l view, X 160; G.S.C. Loc. 93451. F i g . 5. Enantiognathus ziegleri (Diebel). L a t e r a l view, X 300; G.S.C. Loc. 93451. Fi g . 6, 7. Neogondolella navicula navicula (Huckriede). 6, o b l i q u e - l a t e r a l view of elongate form, X 90; 7, oblique view of o r a l surface of more e l l i p t i c a l form, X 95. Both G.S.C. Loc. 93450. Fi g . 8, 9. Neogondolella sp. (possible n. sp. s i m i l a r to N. regale (Mosher) ). 8, oblique view of o r a l surface, X 70. 9, oblique view of o r a l surface of better preserved specimen, X 130. Both completely r e c r y s t a l l i z e d , G.S.C. Loc. 93451. Fi g . 10, 11, 12. Metapolygnathus polygnathiformls (Budurov and Stefanov). 10, oblique view of o r a l surface, X 95. G.S.C. Loc. 93452. 11, oblique view of o r a l surface, X 95, G.S.C. Loc. 93453. 12, oblique view of aboral surface, X 125. G.S.C. Loc. 93453. Note: L o c a l i t i e s shown i n Plate I. A l l figures are SEM photomicrographs, and magnifications are approximate. 88 seafloor. The enclosed conodonts originated somewhere within the water column d i r e c t l y above t h e i r place of deposition. In contrast, conodonts within the t u r b i d i t e limestones were transported l a t e r a l l y and downslope af t e r accumulating i n a shallower environment. M. polygnathiformis i s a large, robust form, and i t may be that s e l e c t i v e removal or destruction of smaller, more f r a g i l e conodont elements before or during t u r b i d i t y current transport i s responsible for the absence of other form-taxa i n these deposits. However, the absence of M. polygnathiformis from the i n t e r -p i l l o w limestones indicates that two d i s t i n c t faunas are represented. These d i f f e r i n g conodont assemblages appear to represent faunas of two d i f f e r e n t environments and water depths, which now both occur i n deposits of r e l a t i v e l y deep water o r i g i n . S imilar data accumulating over the past several years has shown that many conodont faunas are indeed f a c i e s -c o n t r o l l e d , and c a l l s i n question previous conclusions that the conodont-bearing animal was pelagic and facies-independent (Seddon and Sweet, 1971; Barnes and Fahraeus, 1975; Barnes and Nowlan, 1975). SEDIMENTOLOGY AND SEDIMENTARY PETROLOGY Mudstone and S i l t s t o n e Mudstone i s the predominant l i t h o l o g y i n a l l the T r i a s s i c units except Unit 3. Two broad types of mudstone can be d i f f e r e n t i a t e d i n the f i e l d : t h i n to medium-bedded mudstone, and laminated mudstone and s i l t s t o n e . Thin to Medium-Bedded Mudstone Thin to medium-bedded mudstone comprises thick sections of Unit 2, most of Unit 5 on Paul Ridge, and occurs s p o r a d i c a l l y i n the other u n i t s . These 89 mudstones have very well developed bedding plane partings, with bed t h i c k -ness usually ranging from 5 to 13 cm, but some are as thick as 20 cm (Fig. 22). The mudstone i s dark gray, weathering to l i g h t e r gray or brown shades, and i s extremely indurated and l o c a l l y s i l i c e o u s . Rare cherts also 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 color banding i s present. These muds have been intensely bioturbated by burrowing de t r i t u s - f e e d i n g organisms. The burrows are most evident i n cross-sections of beds, where they appear as f l a t t e n e d lenses, 1 to 2 mm thick and 5 to 30 mm long, f i l l e d with mud which i s darker i n color than the surrounding rock (Fig. 23). They are elongate p a r a l l e l or at a small angle to bedding. When observed on bedding surfaces, the burrows appear as simple tubes which wander through the mud, without complex, highly organized patterns. B a c k - f i l l structures are present i n some burrows. . The 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 during compaction of the mud. The burrows observed do not resemble the complex deep water trace f o s s i l s of the Zoophycus and Nereites f a c i e s of Seilacher (1964, 1967), but the nearly h o r i z o n t a l o r i e n t a t i o n of almost a l l the burrows i s t y p i c a l of deep water deposits. Similar simple h o r i z o n t a l bur-rows characterize abyssal muds recovered from the P a c i f i c Ocean f l o o r by the Deep Sea D r i l l i n g Project (Ekdale, 1974, p. 51-52). Thin-sections of mudstone reveal that i t consists of a c r y p t o c r y s t a l -l i n e paste with low birefringence, i n which s i l t - s i z e d grains of p l a g i o -clase, quartz, and some volcanic fragments are scattered. Lighter-colored bands r e s u l t from somewhat higher proportions of s i l t and lower proportions of dark organic matter than the surrounding sediment. Concentrations of organic matter i n the burrows causes t h e i r dark color. 90 F i g . 23. Polished slab of thin-bedded mudstone, showing numerous flattened burrows p a r a l l e l to bedding. 91 Chert i s d i f f i c u l t to d i f f e r e n t i a t e from mudstone and s i l i c e o u s mudstone i n the f i e l d , since i t i s also dark gray i n color and has a s i m i l a r bed t h i c k -ness. One thi n - s e c t i o n showed the chert to be composed of c r y p t o c r y s t a l -l i n e quartz with 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 with coarser-grained quartz or chalcedony. The chert i s highly fractured, and the d i s t r i b u t i o n of dark organic matter seems to be r e l a t e d to the fractures, occurring mostly along them or concentrated i n p a r t i c u l a r fracture-bounded portions of the chert. The t h i n bedding, f i n e grain s i z e , extensive h o r i z o n t a l bioturbation, and presence of r a d i o l a r i a n chert suggests that these rocks were deposited i n r e l a t i v e l y deep water, mainly by pelagic s e t t l i n g of fine muds and s i l t , at rates slow enough to permit thorough reworking by the deep water benthos. Coarse c l a s t i c interbeds are rare i n sections of thin-bedded mudstone, sup-porting t h i s i n t e r p r e t a t i o n . Laminated Mudstone Laminated mudstone and rare s i l t s t o n e d i f f e r from thin-bedded mudstone i n content of coarse material, presence of planar lamination, and les s intense bioturbation. This type of mudstone i s associated with thick t u r b i -d i t e sandstones and limestones. Parting planes are more widely spaced than i n the thin-bedded f a c i e s , and are generally from 8 or 10 cm to over a meter apart. Coarse laminae i n the mudstones are composed of s i l t or f i n e sand, and i n the s i l t s t o n e s , coarse laminae are of f i n e to medium sand. The th i c k -ness of the laminae ranges from 1 mm to several centimeters, with most less than 5 mm th i c k . The lamination i s generally planar, but contorted laminae are frequently observed i n mudstones beneath t u r b i d i t e limestone beds, often forming small 92 recumbent folds which do not a f f e c t overlying and underlying beds. These features may have been produced by t r a c t i o n during the flow and deposition of the overlying t u r b i d i t e bed, or 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 th i n - s e c t i o n to be made up pr i m a r i l y of s i l t to sand-sized chert or f e l s i t i c volcanic fragments, with less abundant quartz, p l a g i o c l a s e , mudstone c l a s t s , and finer-grained matrix. These rocks are too fine-grained f o r chert and f e l s i t i c fragments to be d i f f e r e n t i a t e d , but the dark gray to black color of some of the s i l t s t o n e layers suggests that much of the d e t r i t u s i s chert. Some green, probably v o l c a n i c - r i c h s i l t s t o n e s also occur. The laminated mudstones are associated with t u r b i d i t e s and other density flow deposits. They probably include hemipelagic and low density t u r b i d i t y current deposits, r e f l e c t i n g higher rates of deposition than the thin-bedded f a c i e s , and consequently show less intense bioturbation. The laminated s i l t s t o n e s form the upper part of some thick t u r b i d i t e beds, but also r a r e l y occur independently, interbedded with laminated mud-stone and t u r b i d i t e limestones. These s i l t s t o n e s may have formed by the reworking of t u r b i d i t e s i l t s and f i n e sands by bottom currents, producing well developed planar laminations and good s o r t i n g . Redeposited Basinal Limestone Redeposited m i c r i t e , lime s i l t s t o n e , and fine-grained c a l c - a r e n i t e occur i n Units 2, 4, and 6, but make up only a very small proportion of the section. They are usually interbedded with laminated mudstones and s i l t s t o n e s . Most of these beds are dark gray m i c r i t e and lime s i l t s t o n e , a few to 30 cm thi c k , with rare beds up to about 1 metre thick. Basal contacts of the beds are commonly sharp, with scouring sometimes evident 93 beneath coarser beds, which contain dark mudclasts a few millimetres i n diameter. I n t e r n a l l y the beds are usually s t r u c t u r e l e s s , and grading i s not v i s i b l e , perhaps due to the fine grain s i z e and the e f f e c t s of recrys-t a l l i z a t i o n . Planar and convolute laminations can be observed i n some beds, although some of these are composite beds, c o n s i s t i n g of interlamin-ated m i c r i t e and lime s i l t s t o n e , with i n d i v i d u a l laminae from a few m i l l i -metres to 1 cm thick. In t h i n section, o r i g i n a l c l a s t i c textures are obscure due to the general f i n e grain s i z e and the e f f e c t s of r e c r y s t a l l i z a t i o n . Several samples consist mostly of i n t e r l o c k i n g anhedral c a l c i t e grains, 1 to 4 p m i n diameter ( m i c r i t e ) , and 4 to 10 p m i n diameter (microspar). The micro-spar was o r i g i n a l l y finer-grained lime mud which has been r e c r y s t a l l i z e d . This process has progressed even farther i n other samples, which now consist of i n t e r l o c k i n g f i n e to coarse-grained anhedral c a l c i t e , completely o b l i t e r -ating the o r i g i n a l texture. Dark, organic-rich noncarbonate mud i s dissem-inated through the m i c r i t e , probably comprising a few percent of the rocks, and giving them t h e i r dark color. Scattered noncarbonate grains include pla g i o c l a s e , quartz, volcanic rock fragments, pumice, and mudstone c l a s t s . Heavy mineral concentrates from the insoluble residues contain hornblende, epidote, and the blue amphibole c r o s s i t e . Authigenic p y r i t e cubes, i n part replaced by hematite, are common. Ske l e t a l debris i n these limestones i s exceedingly rare, l i m i t e d to a few t e n t a t i v e l y i d e n t i f i e d echinoderm plates i n badly r e c r y s t a l l i z e d rocks. The only common organic remains v i s i b l e i n thin - s e c t i o n are small spherical bodies, mostly 10 to 20 p m i n diameter, made up of several i n t e r -locking c a l c i t e grains (sometimes with a r a d i a l arrangement), and a dark 94 argillaceous outer coating. These may be the remains of calcareous algae. Platform conodonts were extracted from 6 of 24 samples, and may be abundant i n c e r t a i n samples. The occurrence of i s o l a t e d beds of fine-grained carbonate i n deep water mudstones, together with the i n t e r n a l structures of the limestones, suggest deposition by t u r b i d i t y currents. The source of the sediment was probably i n part the shallow waters surrounding volcanic i s l a n d s , but the presence of d e t r i t u s from a metamorphic source (epidote, crossite) also suggests proximity to a landmass composed of older rocks. Conodonts within the t u r b i d i t e limestones were undoubtedly transported, but l i t t l e time probably separated accumulation of carbonate sediment i n shallow water and redeposition 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 cono-donts are v a l i d . The consistent occurrence of the same conodont taxon i n these samples makes i t very u n l i k e l y that they were reworked from older rocks. Submarine P y r o c l a s t i c Flows and Turbidites Andesitic p y r o c l a s t i c debris characterizes the bulk of Unit 3, and the basal portion of Unit 6. These rocks are p r i m a r i l y redeposited t u f f s or p y r o c l a s t i c sandstones and s i l t s t o n e s , with minor pebble conglomerate ( l a p i l l i -t u f f ) . They are i n t e r l a y e r e d with deep water mudstones and t u r b i d i t e s , and were deposited by t u r b i d i t y currents and high-concentration submarine flows. V i s u a l l y estimated modes of the p y r o c l a s t i c rocks from Unit 3 are shown i n Table I I I . Samples from Unit 6 have undergone severe r e c r y s t a l -l i z a t i o n during contact metamorphism, l a r g e l y o b l i t e r a t i n g the o r i g i n a l textures. They appear to be s i m i l a r to the e l a s t i c s of Unit 3 i n composition. T A B L E I I I . V I S U A L L Y E S T I M A T E D MODES OF R E D E P O S I T E D T U F F S FROM U N I T 3 S a m p l e M K - 1 2 7 M K - 1 2 8 M K - 1 5 8 M K - 1 9 8 M K - 2 0 1 M K - 2 1 7 V o l c a n i c r o c k f r a g m e n t s ( e x c l u d i n g p h e n o c r y s t s ) 60% 40% 5 0 - 6 0 % 5 5 - 6 5 % 50% 40% P l a g i o c l a s e 2 0 - 2 5 40 2 0 - 2 5 2 0 - 2 5 30 40 C l i n o p y r o x e n e 1 0 - 1 5 15 7 - 1 0 5 - 7 10 15 H o r n b l e n d e 2 4 1-2 5 - 7 2 1 O r t h o p y r o x e n e ? 1 — T r T r T r 1 B i o t i t e T r — — — T f ' — M u d s t o n e — T r 3 - 5 T r — — M a t r i x a n d c e m e n t 10 * 5 - 1 0 5 - 1 0 5 - 1 0 5 M a g n e t i t e — 1 — T r T r T r E c h i n o d e r m p l a t e s — — T r — . T r — A v e r a g e g r a i n s i z e ( i n s a n d o r a s h r a n g e ) C t o VC M t o C C t o V C M t o C V F t o F F t o M — = A b s e n t M = M e d i u m - g r a i n e d * M a t r i x a n d c e m e n t n o t TR = Trace VF = Very fine-grained "F = Fine-grained C = C o a r s e - g r a i n e d V C = V e r y c o a r s e - g r a i n e d d i f f e r e n t i a t e d f r o m v o l c a n i c r o c k f r a g m e n t s . 96 The most abundant constituents i n these rocks are dense, nonvesicular volcanic rock fragments (Fig. 24 and 25), which range from 40 to 65%, exclud-ing the volume of phenocrysts. I have followed the suggestion of Dickinson (1970), and counted a l l sand-sized phenocrysts as t h e i r respective mineral species. This allows objective comparison between samples of d i f f e r e n t grain s i z e , since the proportion of free grains to enclosed phenocrysts increases as grain s i z e diminishes. I t also provides a measure of consis-tency, since 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 textures, the d i s t i n c t i o n between volcanic rock fragments and matrix, and hence between phenocrysts and free mineral grains, becomes d i f f i c u l t , i f not impossible (as i n sample MK-128). Free mineral and phenocryst phases include pl a g i o -clase, clinopyroxene, hornblende, orthopyroxene, and rare b i o t i t e and magne-t i t e . Clinopyroxene and hornblende together t o t a l 15 to 20% of the rocks, and t h e i r abundance i n hand specimens distinguishes the p y r o c l a s t i c deposits of these units from a l l other v o l c a n i c l a s t i c rocks i n the study area. Mud rip-up c l a s t s and echinoderm plates are present i n trace amounts i n several samples. O s c i l l a t o r y zoning i s common i n most of the phenocryst phases, but i s best developed i n p l a g i o c l a s e . A l t e r a t i o n of p l a g i o c l a s e , commonly to s e r i -c i t e and a l b i t e , i s v a r i a b l e , and o r i g i n a l compositions are preserved i n several samples, ranging from Ang2 to An 6Q (Table IV). Hornblende and clinopyroxene may both be zoned, and are t y p i c a l l y l i t t l e a l t e r e d or unal-tered. The clinopyroxene has a 2V of about 55°, and i s probably diopside. No fresh orthopyroxene i s present i n any of the samples examined. Tentative i d e n t i f i c a t i o n of these completely a l t e r e d grains i s based upon the i d e n t i t y and configuration of the a l t e r a t i o n products, and the form F i g . 24. Photomicrograph of th i n - s e c t i o n of t u f f from Unit 3 Abundant p o r p h y r i t i c volcanic rock fragments (V), with phenocrysts of plagioclase (PI) , hornblende (H), and clinopyroxene (C). Plane l i g h t , X 40. F i g . 25. Photomicrograph of th i n - s e c t i o n of t u f f from Unit 3 Por p h y r i t i c volcanic rock fragments (V) and free mineral grains: zoned plagioclase (PI), clinopyroxene (C), and hornblende (H). Plane l i g h t , X 40. TABLE IV. AVERAGE COMPOSITIONS OF ZONED PLAGIOCLASE FROM UNIT 3 Sample Anorthite Content (Wt MK-127 MK-128 MK-198 MK-201 MK-161 A n 8 2 An 6 o , A n 6 1 , A n 7 1 An 0 _5 ^ 0 - 5 ^ 6 2 ' A n 6 6 99 of the euhedral pseudomorphs. The four or eight-sided grains are completely replaced by c h l o r i t e and f i n e l y granular sphene, and perhaps some leucoxene. The sphene i s commonly aligned along two sets of planes within the grains, which i n t e r s e c t at angles ranging from about 60 to 90°, probably replacing lamellae of ilmenite or titanomagnetite exsolved from the o r i g i n a l ortho-pyroxene. I t i s highly improbable that these are a l t e r e d hornblendes or clinopyroxenes, since the l a t t e r are t y p i c a l l y l i t t l e a l t e r e d , and no t r a n s i -t i o n from l i t t l e a l t e r e d grains to pseudomorphs occurs. Orthopyroxene pseudomorphs are also present as in c l u s i o n s i n unaltered clinopyroxene. In the coarser-grained rocks, nearly a l l of the volcanic fragments are p o r p h y r i t i c . Phenocrysts may be sparse, or make up more than 60% of the fragment. Ei t h e r p l a g i o c l a s e , clinopyroxene, or hornblende may be the most abundant phenocryst, but i n fragments with high proportions of phenocrysts to groundmass, plagioclase i s more abundant than mafic 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 of the minerals i n the t u f f s . The ground-mass may be f e l s i t i c or m i c r o l i t i c , with plagioclase 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 textures. In the m i c r o l i t i c grains, o r i g i n a l glass i s replaced by a c r y p t o c r y s t a l l i n e aggregate of c h l o r i t e and a l k a l i feldspar. A few lathwork grains occur, with crudely aligned, crowded p l a g i o -clase phenocrysts with i n t e r s t i t i a l granules of clinopyroxene, and c h l o r i t e with granules of sphene replacing i n t e r s t i t i a l glass. The t u f f s are grain supported, and poorly to moderately well sorted. D e t r i t a l c r y s t a l s range from angular (broken or euhedral) to subrounded. Volcanic fragments are usually i r r e g u l a r to somewhat polygonal i n shape, and range from very angular to subangular. Roundness i s d i f f i c u l t to determine because boundaries between volcanic grains are often sutured and i n d i s t i n c t 100 due to the e f f e c t s of compaction, pressure s o l u t i o n , d e v i t r i f i c a t i o n , and metamorphic r e c r y s t a l l i z a t i o n . This also leads to confusion between v o l -canic fragments and i n t e r s t i t i a l material. In none of the rocks i s a clay and organic-rich matrix evident. In the coarse-grained t u f f s , where tex-tures are c l e a r e s t , framework grains are c l o s e l y packed, and i n t e r s t i t i a l material does not exceed 10% of the rock. Much of t h i s material i s of diagenetic or metamorphic o r i g i n , and consists of an i n d i s t i n c t granular paste (epimatrix), but some monomineralic patches of c h l o r i t e , c a l c i t e , prehnite and pumpellyite also occur, and could be c a l l e d cement. Part i c u -l a r l y i n some of the'finer-grained t u f f s , d i s t i n g u i s h i n g volcanic framework grains from i n t e r s t i t i a l matrix i s almost impossible. This i s a r e s u l t of increased r e c r y s t a l l i z a t i o n , but whether t h i s i n turn r e s u l t s from increased proportions of o r i g i n a l unstable matrix material i s uncertain. I f s i l t to cl a y - s i z e d d e t r i t a l material was o r i g i n a l l y present, i t was mostly very f i n e volcanic material, rather than a c l a y - r i c h mud. The rare pebble conglomerate (Fig. 26) i s very poorly sorted, with subrounded to rounded volcanic c l a s t s up to several centimeters i n diameter, and v a r i a b l e amounts of mudstone rip-up c l a s t s . The conglomerates are framework supported, with 10 to 20% matrix of dark mud and va r i a b l e amounts of volcanic s i l t and f i n e to medium-grained volcanic sand. The mineralogy, and texture of the volcanic fragments i d e n t i f y them as andesite or dacite. Except for some v a r i a t i o n i n grain s i z e and r e l a t i v e proportions of mineral species and volcanic fragments, the p y r o c l a s t i c rocks are compositionally and t e x t u r a l l y homogeneous throughout the several hundred metres of Unit 3, and apparently i n the basal portion of Unit 6 as we l l . They may have been derived from a sing l e volcanic center which produced 101 F i g . 26. Polished slab of conglomerate from Unit 3, consist-ing e n t i r e l y of pebbles of p o r p h y r i t i c dacite or andesite. X 1.33. 102 a n d e s i t i c o r d a c i t i c l a v a s s h o w i n g l i t t l e c o m p o s i t i o n a l v a r i a t i o 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 v o l c a n o e s p r o d u c e l a r g e q u a n t i t i e s o f v e s i c u l a r a s w e l l a s n o n v e s i c u l a r a s h ( s e e d i s c u s s i o n i n C h a p t e r I I , S o u r c e a n d 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 ) . T h e r e f o r e I t h i n k i t i s u n l i k e l y t h a t t h i s t e p h r a was r e w o r k e d f r o m a s u b a e r i a l s o u r c e , o r t h a t i t was d e p o s i t e d b y a s e r i e s o f p y r o c l a s t i c f l o w s o r i g i n a t i n g f r o m a s u b a e r i a l v o l c a n o . T h e e r u p t i o n s w e r e p r o b a b l y s u b m a r i n e e x p l o s i v e e r u p t i o n s c a u s e d b y c o n t a c t o f h o t l a v a w i t h a b u n d a n t w a t e r . S i m i l a r h o m o g e n e o u s , n o n -v e s i c u l a r s u b a q u e o u s t u f f s w e r e d e s c r i b e d b y F i s k e ( 1 9 6 3 ) . He i n f e r r e d t h a t t h e a s h was p r o d u c e d b y e x p l o s i v e d i s i n t e g r a t i o n o f h o m o g e n e o u s d o m e s , s p i n e s , o r l a v a f l o w s a s t h e y w e r e e x t r u d e d u n d e r w a t e r . T h i s a l s o s e e m s a l i k e l y s o u r c e f o r t h e t e p h r a o f U n i t 3 . T h e f l o w s w h i c h d e p o s i t e d t h e p y r o c l a s t i c d e b r i s i n i t s p r e s e n t d e e p w a t e r s e t t i n g w e r e t u r b i d i t y c u r r e n t s a n d h i g h d e n s i t y m a s s f l o w s , w h i c h F i s k e ( 1963 ) h a s r e f e r r e d t o a s s u b a q u e o u s p y r o c l a s t i c f l o w s . T h i c k p y r o -c l a s t i c f l o w s d o m i n a t e t h e e a s t e r n f a c i e s o f U n i t 3 , w h i l e t u r b i d i t e s a r e m o r e a b u n d a n t i n t h e w e s t e r n p o r t i o n . T h e l o w e r p o r t i o n o f U n i t 6 p r o b a b l y c o n s i s t s o f b o t h t y p e s o f d e p o s i t s . T h e s e b e d s a r e i n t e r l a y e r e d w i t h l e s s e r a m o u n t s o f h o m o g e n e o u s a n d l a m i n a t e d , s o m e t i m e s b i o t u r b a t e d m u d s t o n e . U s u a l l y o n l y p o r t i o n s o f i n d i v i d u a l p y r o c l a s t i c f l o w s a r e e x p o s e d , b u t f r o m t h e s i z e o f t h e o u t c r o p s , t y p i c a l f l o w s a r e a t l e a s t s e v e r a l m e t r e s t h i c k , a n d some m i g h t b e t e n s o f m e t r e s t h i c k . T h e f l o w s a r e c o m -p o s e d o f m e d i u m t o c o a r s e - g r a i n e d t e p h r a . I n a f e w c a s e s n o r m a l s i z e g r a d i n g was e v i d e n t i n t h e f i e l d , b u t i n m o s t o u t c r o p s t h e r o c k s a p p e a r u n g r a d e d , a l t h o u g h g r a d i n g m i g h t b e t o o s u b t l e t o b e o b s e r v e d i n a s m a l l p a r t o f a t h i c k f l o w . 1 0 3 T h e p y r o c l a s t i c t u r b i d i t e s a r e g r a d e d , c o n t a i n a b u n d a n t p r i m a r y s e d i -m e n t a r y s t r u c t u r e s , a n d r a n g e i n t h i c k n e s s f r o m 1 t o 50 cm o r m o r e . T h e y a r e u s u a l l y m e d i u m t o f i n e - g r a i n e d , g r a d i n g u p w a r d i n t o s i l t s t o n e a n d m u d -s t o n e . T h e s a n d t o s i l t - s i z e d t u f f b e d s a l m o s t a l w a y s show p l a n a r l a m i n a -t i o n , s o m e t i m e s o v e r l a i n b y c r o s s - l a m i n a t e d t u f f , c o r r e s p o n d i n g t o d i v i -s i o n s B a n d C o f t h e Bouma s e q u e n c e ( F i g . 2 7 ) . S o m e t i m e s a l a y e r o f c o a r s e c r y s t a l - r i c h t e p h r a u n d e r l i e s d i v i s i o n B . T h i s l a y e r i s t h i n i n r e l a t i o n t o t h e t o t a l t h i c k n e s s o f t h e b e d , i s n o t v i s i b l y g r a d e d , a n d i s o v e r l a i n r a t h e r a b r u p t l y b y much f i n e r - g r a i n e d , l a m i n a t e d t u f f ( F i g . 2 8 ) . T h e r e a s o n f o r t h e a b r u p t c h a n g e i n g r a i n s i z e i s n o t k n o w n . T h e b a s e o f t h e c o a r s e l a y e r h a s c o m m o n l y b e e n d i s r u p t e d b y t h e s i n k i n g o f t h e c o a r s e t u f f i n t o t h e u n d e r l y i n g s o f t mud s h o r t l y a f t e r d e p o s i t i o n . I n some c a s e s , n o m u d s t o n e i n t e r v e n e s b e t w e e n s u c c e s s i v e t h i n t u r b i d i t e s , i m p l y i n g r a p i d t u r b i d i t e d e p o s i t i o n , w i t h l i t t l e c h a n c e f o r f i n e m a t e r i a l t o b e d e p o s i t e d b e f o r e t h e a r r i v a l o f t h e n e x t t u r b i d i t y f l o w . T h e c h a n g e i n f a c i e s w i t h i n U n i t 3 i m p l i e s a p r o x i m a l - d i s t a l r e l a t i o n -s h i p b e t w e e n t h e t h i c k p y r o c l a s t i c f l o w s o f t h e e a s t e r n p o r t i o n a n d t h e t u r b i d i t e s o f t h e w e s t e r n p o r t i o n . T h e t h i c k , h i g h d e n s i t y f l o w s a p p a r e n t l y e v o l v e d d u r i n g d o w n s l o p e m o v e m e n t i n t o t u r b i d i t y c u r r e n t s , p r o b a b l y b o t h b y d e p o s i t i o n o f c o a r s e m a t e r i a l , a n d b y d e c r e a s e i n d e n s i t y a n d i n c r e a s e i n t u r b u l e n c e d u e t o m i x i n g w i t h s e a w a t e r a t t h e h e a d a n d u p p e r i n t e r f a c e o f t h e f l o w . B o t h t h e d e c r e a s e i n a v e r a g e a n d max imum g r a i n s i z e a n d d e c r e a s e i n t h i c k n e s s f r o m e a s t t o w e s t a r e c o n s i s t e n t w i t h t h i s i n t e r p r e t a t i o n . T h e p y r o c l a s t i c f l o w s a n d t u r b i d i t e s o r i g i n a t e d f r o m t h e s u b m a r i n e v o l c a n o d u r i n g o r b e t w e e n e r u p t i o n s , p r o b a b l y b y t h e c o l l a p s e a n d d o w n s l o p e m o v e m e n t o f p y r o c l a s t i c d e b r i s o r i g i n a l l y d e p o s i t e d o n u n s t a b l e s l o p e s F i g . 27. Polished slab of submarine t u f f from Unit 3 showing a Bouma BC sequence. 105 F i g . 28. Polished slab of submarine t u f f from Unit 3 showing the base of a graded t u r b i d i t e bed, with a concentration of coarse plagioclase, pyroxene, and hornblende c r y s t a l s . Base of layer i s disrupted by load casts. Thin cross-laminated t u r b i d i t e bed below. 106 around the vent. The rounding of the larger volcanic c l a s t s and the lack of doubly-graded sequences (Fiske and Matsuda, 1964) i n Unit 3 suggests that the vent was only shallowly submerged, and that some of the tephra may have accumulated around the vent and undergone s i g n i f i c a n t current or wave transport and abrasion p r i o r to redeposition. Transport of the tephra into the deep basin was intermittent, as shown by the presence of mudstones interbedded with the p y r o c l a s t i c deposits, but the i n t e r v a l s between flows were probably short, because the mudstone layers are t h i n , and make up only a small part of the t o t a l thickness of the u n i t s . Volcanic Sandstone or Redeposited Tuff Volcanic sandstones deposited by t u r b i d i t y currents are found p r i m a r i l y i n Unit 4, but also r a r e l y i n Units 2 and 5. They range i n thickness from less than 15 cm to over 2.5m, and beds 1 to 2.5 m thick are common i n the middle portion of Unit 4. These thick sandstones are coarse-grained at the base, grading upward to medium and fine-grained sandstone. Complete Bouma sequences were found i n several beds. The massive A - i n t e r v a l and h o r i z o n t a l l y laminated B - i n t e r v a l together account for most of the thickness of the beds, with i n t e r v a l s C, D, and E each only a few centimeters thick at the top of the bed. Petrographically these rocks are quite varied. Modes of three samples are shown i n Table V. A l l of the rocks are dominated by volcanic rock fragments and plagioclase, but t h e i r textures vary dramatically. Sample MK-222 i s s i m i l a r i n composition to the p y r o c l a s t i c s of Unit 3, but i t s constituent mineral grains and volcanic rock fragments are more equant and rounded, the rocks are moderately well sorted, and i t i s cemented TABLE V. VISUALLY ESTIMATED MODES OF VOLCANIC SANDSTONES OR REDEPOSITED TUFFS FROM UNITS 2, 4, AND 5 MK-151 MK-215 MK-222 S a m p l e Unit 2 Unit 4 Unit 5 Volcanic rock fragments (excluding phenocrysts) 65-70% 30% 20-25% Plagioclase 25 40 35 Quartz 1 Tr Clinopyroxene — — 5 Hornblende — — 1 B i o t i t e — — Tr C l a s t i c C a l c i t e — Tr Tr Matrix and Pseudomatrix 5-10 30% C a l c i t e Cement — — 40 Grain size (sand to ash range) VC F-M — = Absent F = Fine-grained C = Coarse-grained Tr = Trace M = Medium-grained VC = Very coarse-grained 108 by sparry c a l c i t e . The sand i s grain supported, but the grains are only loosely packed, so i t seems that cementation took place early i n the d i a -genetic h i s t o r y , before deep b u r i a l and s i g n i f i c a n t compaction could take place. This ash c l e a r l y underwent s i g n i f i c a n t transport, s o r t i n g , and abrasion before redeposition i n t o the deep basin. Both sample MK-151 and MK-215 contain some c h l o r i t i z e d pumice c l a s t s i n addition to nonvesicular volcanic fragments, and very small amounts of clear angular quartz, probably also volcanic i n o r i g i n . Both samples are poorly sorted and c l o s e l y packed, with a murky i n t e r s t i t i a l matrix, which probably includes some al t e r e d volcanic grains (Fig. 29 and 30). Volcanic grain outlines and shapes are blu r r e d by diagenetic and metamorphic e f f e c t s , but i n o v e r a l l composition and texture these rocks resemble the redeposited t u f f s of the Harper Ranch Group. This p y r o c l a s t i c material was probably produced by shallow marine or subaerial eruptions, and was transported to deeper water and deposited by t u r b i d i t y currents and high density mass flows. The predominance of nonvesicular volcanic grains-, over pumice suggests that the eruptions which produced the ash were submarine, or that less dense v e s i c u l a r and pumiceous grains were removed from subaerial ash during stream transport to the marine environment. Several samples of poorly sorted p y r o c l a s t i c rocks (including MK-151) show p a r t i a l replacement of matrix and framework grains by microgranular c a l c i t e . Sample MK-151 grades from a rock with almost no c a l c i t e to one which i s over 70% c a l c i t e . Small opaque granules of yellow s u l f i d e (probably pyrite) are also common i n several of these rocks (including MK-215, which lacks c a l c i t e ) . Because of r e c r y s t a l l i z a t i o n , i t i s not cl e a r whether lime mud was o r i g i n a l l y present i n the matrix of these rocks, but i f so, ad d i t i o n a l 109 F i g . 29. Photomicrograph of thi n - s e c t i o n , Sample MK-151, volcanic sandstone or redeposited t u f f from Unit 4. Volcanic rock fragments (V), plagioclase (PI), and c a l c i t i z e d volcanic fragment (Cc). Plane l i g h t , X 40. -F i g . 30. Photomicrograph of thin-section, Sample MK-215, volcanic sandstone or redeposited t u f f i n Unit 5. Plagioclase (PI), po r p h y r i t i c volcanic 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 also had to be introduced to account for the amount of replacement observed. If c a l c i t i z a t i o n of these rocks occurred at the same stage as cementation i n sample MK-222, then i t was an early diagenetic e f f e c t which took place during shallow b u r i a l . V i t r i c Tuff Beds of v i t r i c t u f f occur near the top of Unit 2, and near the base of Unit 4, or, i n other 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 of Unit 3. They occur i n thick graded beds interbedded with mudstone, laminated s i l t s t o n e , and t u r b i d i t e limestones. Samples from each unit (Table VI) consist of 80 to 90% d e v i t r i f i e d glass shards and pumice (Fig. 31). Only a few m i c r o l i t i c , non-vesicular volcanic fragments are present, along with v a r i a b l e but small amounts of plagioclase, quartz, clinopyroxene, hornblende, and b i o t i t e . The mineral content of the samples suggests that they are d a c i t i c to a ndesitic i n compo-s i t i o n . 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 , potassium feldspar, and perhaps a l b i t e . In sample MK-125, glass i s a l t e r e d to c h l o r i t e , potassium feldspar, occasional c a l c i t e , and brown to green, amorphous material with anomalous birefringence, perhaps masked by i t s c o l o r . This material i s s i m i l a r to chlorophaeite, an amorphous a l t e r a t i o n product of b a s a l t i c glasses. The t u f f s are well indurated, but show no signs of welding. Strong preferred o r i e n t a t i o n of elongate shards and pumice i s present i n sample MK-125. The small mudclasts may be accidental fragments incorporated into the glassy tephra during i t s eruption, but more l i k e l y they are rip-up c l a s t s , which implies that the t u f f s were emplaced as t u r b i d i t y currents with s u f f i -c i e n t erosive capacity to mildly erode underlying muds. This i s also TABLE VI. VISUALLY ESTIMATED MODES OF VITRIC TUFFS MK-150 MK-125 S a m p l e Unit 2 Unit 4 D e v i t r i f i e d glass shards and pumice 85-90% 80% Volcanic rock fragments Tr Tr Plagioclase 1 5 Quartz Tr Clinopyroxene Hornblende — Tr B i o t i t e Tr Tr Mudstone c l a s t s Tr Tr Matrix 10 10 Plagioclase composition Ang^, Angg Ani^ — = Absent Tr = Trace F i g . 31. Photomicrograph of thin-section (Sample MK-150) of v i t r i c t u f f from Unit 2. Bubble-wall shards (Sh), pumice, (P), and minor plagioclase (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 to poor s o r t i n g , and presence of a murky, organic-r i c h matrix. The homogeneity and angular nature of the p y r o c l a s t i c material implies that sedimentation took place during or shortly a f t e r i t s eruption. L i t h i c Sandstone and Conglomerate The presence of an appreciable proportion of nonvolcanic l i t h i c c l a s t s distinguishes the coarse c l a s t i c sediments of Unit 5 from most others i n the section. The rocks are mostly fine-grained sandstone and s i l t s t o n e , and peb-ble conglomerate and b r e c c i a . Unfortunately, these rocks are for the most part poorly exposed i n ephemeral stream channels, so only a very general des c r i p t i o n can be presented. Similar sedimentary rocks also occur beneath the volcanic rocks of Unit 6. As a group, these rocks appear to have a strongly bimodal grain s i z e d i s t r i b u t i o n . Pebble conglomerates and breccias have a d i s t i n c t l y f i n e r -grained matrix of f i n e sand, s i l t , or more r a r e l y mud. Sandstone beds i n t e r -layered with the conglomerates are also usually fine-grained. Medium to coarse-grained sandstones are rare. Fine-grained sandstone and s i l t s t o n e t y p i c a l l y occur i n sequences of th i n beds (to several centimeters t h i c k ) , with the sequence t o t a l l i n g a meter or more i n thickness. Each t h i n bed has a sharp basal contact, and shows normal s i z e grading from fin e sandstone upward to s i l t s t o n e . L i t t l e or no mudstone i s present i n these sequences. They probably represent r a p i d l y deposited sequences of fine-grained t u r b i d i t e s . Occasional thick beds of h o r i z o n t a l l y laminated fin e sandstone or s i l t s t o n e are also present. Pebble and sharpstone conglomerate beds are completely s t r u c t u r e l e s s , showing neither s t r a t i f i c a t i o n nor imbrication. Some beds may be tens of 114 m e t r e s t h i c k , a n d b e d t h i c k n e s s g e n e r a l l y e x c e e d s t h e l i m i t o f o u t c r o p . B a s a l c o n t a c t s o f t h e b e d s a p p e a r t o b e c o n f o r m a b l e . T h e c o n g l o m e r a t e s a r e p o o r l y s o r t e d , b u t c l o s e l y p a c k e d , w i t h t h e m a t r i x c o m p r i s i n g 10 t o 20% o f t h e r o c k ( F i g . 3 2 ) . V e r y f e w c l a s t s e x c e e d p e b b l e s i z e , a n d r o u n d i n g i s g e n e r a l l y q u i t e v a r i a b l e w i t h i n a g i v e n s a m p l e . On t h e a v e r a g e , m o s t c l a s t s a r e s u b a n g u l a r , b u t t h e r o c k s d e s i g n a t e d b r e c c i a c o n t a i n n u m e r o u s a n g u l a r c l a s t s a s w e l l ( F i g . 3 3 ) . T h e c o n g l o m e r a t e s a r e i n t e r b e d d e d w i t h l a m i n a t e d m u d s t o n e , f i n e - g r a i n e d t u r b i d i t e s a n d s t o n e s , a n d r a r e t u r b i d i t e l i m e s t o n e s . T h e d e e p w a t e r s e t t i n g o f t h e s e b e d s a n d t h e i r l a c k o f i n t e r n a l s t r u c t u r e s f i t s t h e d i s o r g a n i z e d -b e d f a c i e s m o d e l f o r r e s e d i m e n t e d c o n g l o m e r a t e s ( W a l k e r , 1 9 7 5 ) . T h e t e r m " r e s e d i m e n t e d " r e f e r s t o c o n g l o m e r a t e s w h i c h o r i g i n a l l y a c c u m u l a t e d i n s h a l -l o w w a t e r , t h e n w e r e t r a n s p o r t e d i n t o d e e p e r w a t e r b y some t y p e o f d e n s i t y f l o w p r o c e s s , a n d a r e f o u n d i n t e r b e d d e d w i t h d e e p w a t e r m u d s t o n e s a n d t u r b i -d i t e s . T h e c o a r s e n e s s a n d c h a o t i c n a t u r e o f d i s o r g a n i z e d - b e d d e p o s i t s s u g -g e s t t o W a l k e r t h a t t h e y a c c u m u l a t e d r a p i d l y o n r e l a t i v e l y s t e e p s u b m a r i n e s l o p e s a s l a g s , p e r h a p s i n s u b m a r i n e c h a n n e l s . F i e l d e v i d e n c e s u g g e s t s t h a t t h e c o n g l o m e r a t e s i n U n i t 5 may i n d e e d b e s h o e s t r i n g , c h a n n e l i z e d d e p o s i t s . T h e s e d e p o s i t s a r e e x p o s e d i n a s e r i e s o f s t r e a m g u l l i e s b e t w e e n 1500 a n d 2000 f t e l e v a t i o n o n t h e s o u t h w e s t s l o p e o f Dome H i l l s . T h e g u l l i e s a r e s p a c e d l e s s t h a n 200 m a p a r t , a n d a r e n e a r l y p e r p e n d i c u l a r t o t h e s t r i k e o f t h e u n i t . S t r a t i g r a p h i c i n t e r v a l s u p t o 100 m t h i c k , i n w h i c h d i s o r g a n i z e d c o n g l o m e r a t e s a n d t u r b i d i t e s a n d s t o n e s a r e t h e d o m i n a n t l i t h o l o g i e s , c a n b e t r a c e d l a t e r a l l y f r o m o n e g u l l y t o a n o t h e r , b u t g e n e r a l l y a p p e a r i n n o m o r e t h a n t w o o r t h r e e , w i t h t h e i r a p p a r e n t l a t e r a l e q u i v a l e n t s b e i n g m u d s t o n e . S t r a t i g r a p h i c p i n c h o u t o f c o n g l o m e r a t e b e d s c a n n o t b e p r o v e n , b u t c o n f i n e m e n t 115 Fi g . 33. Polished slab of l i t h i c conglomerate from Unit 5, Dome H i l l s . 116 of i n d i v i d u a l conglomerate beds to submarine channels could explain these observations. No consistent o f f s e t s of these i n t e r v a l s which might be att r i b u t e d to f a u l t i n g were noted. Petrographic data on these e l a s t i c s were derived from four thin-sections and a number of hand-specimens of sandstone and conglomerate, and f i e l d observation of c l a s t content of conglomerates. Two thin-sections were point-counted, and the r e s u l t s are presented i n Table VII. Sedimentary c l a s t s (mostly chert and mudstone) are an important or even dominant component of these e l a s t i c s . The conglomerate sample MK-211 i s an extreme example: others contain greater proportions of volcanic rock fragments (Fig. 32) and phenocrysts, although sedimentary c l a s t s generally exceed 50% of the framework. Chert c l a s t s are generally c o l o r l e s s to brown i n t h i n - s e c t i o n , and grade into mudstones. Many contain 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 to a c o l o r l e s s , microgranular quartz aggregate which i s coarser than the surrounding chert (Fig. 34). Mudstone c l a s t s are equant and often angular, and were c l e a r l y l i t h i f i e d p r i o r to incorporation i n the conglomerate; they are not i n t r a b a s i n a l rip-up c l a s t s . They may be laminated or homogeneous, and some contain s i l t to sand-sized plagioclase grains. Sand-stone and s i l t s t o n e c l a s t s consist mostly of plagioclase and volcanic rock fragments with some mafic minerals, in c l u d i n g hornblende. Volcanic rock fragments may be f e l s i t i c , and d i f f i c u l t to d i s t i n g u i s h from chert, but most are p o r p h y r i t i c , with plagioclase and sometimes horn-blende or b i o t i t e microphenocrysts. Other volcanic constituents are free phenocryst grains, i n c l u d i n g p l a g i o c l a s e , hornblende, and clinopyroxene. Unaltered plagioclase grains i n sample MK-132 have compositions of An3g, Ani4g, and Angij., consistent with the i n f e r r e d intermediate composition of the TABLE VII. MODAL ANALYSES OF CLASTIC ROCKS FROM UNIT 5 Sample MK-132 MK-211 Coarse Sandstone Pebble Conglomerate Chert 17% 463 Mudstone 16 19 Volcanic sandstone and s i l t s t o n e 7 8 Volcanic rock fragments 19 10 Plagioclase 13 3 Hornblende 5 -Clinopyroxene 5 Tr Matrix 10 9 Indeterminate 8 4 Total Counts 328 296 Total determinable framework counts 268 255 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 (volcanic rock fragments + plagioclase + hornblende + clinopyroxene) 52 15 — = Absent Tr = Trace F i g . 34. Photomicrograph of t h i n - s e c t i o n , Sample MK-132, l i t h i c -volcanic sandstone from Unit 5. Clasts of r a d i o l a r i a n chert (Ct), volcanic s i l t s t o n e (St), and plagioclase (PI). Plane l i g h t , X 40. 119 volcanic material. However, the wide range i n anorthite content suggests that volcanic c l a s t s may have been derived from several d i s t i n c t volcanic sources. These c l a s t i c rocks record a mixed provenance, with most of the d e t r i -tus derived from an older sedimentary terrane and from coeval volcanic a c t i v i t y . The volcanic sandstone and s i l t s t o n e c l a s t s were probably l i t h -i f i e d before being incorporated i n these deposits, and may have been derived from an older volcanic terrane. DISCUSSION AND REGIONAL IMPLICATIONS Summary of Depositional Setting Rocks of the Nicola Group i n the study area are a deep water sedimentary and volcanic facies assemblage which accumulated i n a basin l y i n g to the east (using present directions) of the active Nicola volcanic archipelago. Pelagic and hemipelagic mudstones are abundant or dominant i n most units. The v o l -c a n i c l a s t i c rocks, l i t h i c sandstones and conglomerates, and limestones were deposited by t u r b i d i t y currents and high concentration density flows. Basic volcanics were erupted on the sea f l o o r l o c a l l y and s p o r a d i c a l l y , form-ing massive and pillowed flows. Deposition of a l l these s t r a t a took place i n quiet waters at an inderminable depth below storm wave base, since e v i -dence of reworking of the sediments i s meager. Relationship Between the Nicola and Harper Ranch Groups The contact between the Nicola and Harper Ranch Groups i s not exposed i n the study area, but i s interpreted as a steep, northwest-trending f a u l t s . The f a u l t truncates l i t h o l o g i c units within the Nicola Group at a low angle, 120 and the rock sequences on either side of i t become younger away from the f a u l t . However, at depth the Nicola Group may l i e unconformably on the older rocks. Read and Okulitch (1977) have described a regional angular unconformity beneath Middle and Upper T r i a s s i c rocks on the west side of the Omineca C r y s t a l l i n e b e l t i n the region south of Kamloops. In places Permian and older rocks beneath the unconformity have undergone intense deformation and low grade metamorphism. Evidence for p r e - T r i a s s i c deformation i s lack-ing i n the study area, but the v o l c a n i c l a s t i c rocks of the Harper Ranch Group are s i g n i f i c a n t l y more al t e r e d than those of the Nicola Group, sug-gesting the p o s s i b i l i t y of Permo-Triassic low grade metamorphism a f f e c t i n g the Harper Ranch Group. The angular unconformity has not been recorded north of Kamloops, but the Harper Ranch Group does not extend northwestward beyond Bonaparte Lake map-area. About 13 km east of Kamloops along the South Thompson River, near Campbell Creek junction, an angular unconformity between the Harper Ranch Group and rocks mapped as Nicola Group i s exposed (Daly, 1915; Cockfield, 1948; Sada and Danner, 1974; Read and Okulitch, 1977). The unconformity truncates massive Lower Permian and Lower Pennsylvanian limestone, and i s ove r l a i n by 45 m of pebble to boulder conglomerate, sandstone, and lime-stone. My examination showed that c l a s t s of purple feldspar porphyry are common i n the conglomerate, along with limestone, mudstone, and volcanic sandstone probably derived from the Harper Ranch Group. The sedimentary rocks above the unconformity dip gently (15 to 30°) eastward, and are over-l a i n by massive augite porphyry volcanic breccias. Attitudes i n the s e d i -mentary s t r a t a are quite regular, i n contrast to those i n the Harper Ranch Group and Nicola Group to the west. 121 The volcanic rocks overlying the conglomerate are l i t h o l o g i c a l l y s i m i l a r to the volcanic arc facies of the Nicola Group, and they have been mapped as such by Coc k f i e l d . However, no f o s s i l s have been reported from the volcanic sequence at t h i s l o c a l i t y , or from rocks contiguous with them, and a Lower Jurassic age for these rocks i s poss i b l e . In Bonaparte Lake and Quesnel Lake map-areas, Campbell and Tipper (1970, 1971) have mapped a Lower to Middle Jurassic (Sinemurian and younger) volcanic and v o l c a n i c l a s t i c unit 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 parts of the Nicola Group. In some places the base of t h i s sequence i s a coarse conglomerate containing c l a s t s of the Nicola and Harper Ranch Groups, and g r a n i t i c c l a s t s . Although g r a n i t i c c l a s t s have not been found i n the conglomerate at Campbell Creek, i n other respects i t resembles the conglomerate described by Campbell and Tipper. Lower and perhaps Middle Jurassic rocks have also been found by Preto (1977) i n the Nicola Group south of Nicola Lake (Nicola and Princeton map-areas). With paleontologic control lacking at Campbell Creek, i t i s not advisable to assume a T r i a s s i c age for t h i s unconformity. However, un-conformities beneath dated Upper T r i a s s i c rocks occur west and northwest of Vernon, and the Permo-Triassic unconformity may extend as f a r as the study area. Provenance of C l a s t i c Detritus and Paleogeography of  the Quesnel Trough The Quesnel trough i s a northwest-trending b e l t of Upper T r i a s s i c and Lower Jurassic volcanic and sedimentary rocks l y i n g west of 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 northern Washington to northern B r i t i s h Columbia (Fig. 35). This fault-bounded "trough" i s flanked on eit h e r side by older rocks. On the east side are the Upper Paleozoic 122 F i g . 35. Location map of Quesnel trough and surrounding Mesozoic tectonic elements of ce n t r a l and southern B r i t i s h Columbia. Modified from Wheeler (1970). 123 eugeoclinal rocks which form the western margin of the Omineca b e l t . To the west l i e s the Pinchi g e a n t i c l i n e , c o n s i s t i n g of the Cache Creek Group. Late T r i a s s i c u p l i f t and emergence of the Pinchi g e a n t i c l i n e may have provided a source for some of the c l a s t i c sediments i n the Quesnel trough. Although some quartzose sediments i n the southernmost Quesnel trough may have been derived from the Omineca gean t i c l i n e (Wheeler and others, 1972), i t was not a strongly p o s i t i v e feature during the Late T r i a s s i c . Middle to Late Jurassic deformation and u p l i f t i n the Omineca b e l t probably ended marine deposition i n the trough (Campbell and Tipper, 1970'; Eisbacher, 1974) . During the Late T r i a s s i c (Karnian to Norian), the western portion of the trough was a volcanic archipelago which produced the volcanic rocks of the Nicola Group, and the Takla Group i n northern B r i t i s h Columbia. The Nicola Group i n i t s type area around Nicola Lake, 50 km south of Kamloops, i s a complex assemblage of b a s a l t i c andesite and andesite flows, breccias, and t u f f s , with associated c l a s t i c sediments and limestones (Schau, 1970). Flows and dikes are common near the volcanic centers, along with coarse breccias and agglomerates. Equivalent s t r a t a farther from the centers are fine t u f f s and volcanic or calcareous wackes. At l e a s t some of the s e d i -ments probably accumulated i n shallow water, as evidence by r i p p l e marks, scour marks, and cross-bedding. C o r a l - a l g a l reefs fringed the volcanic islands. F o s s i l s from reef limestones and other sediments, although rare, i n d i c a t e these rocks could range i n age from l a t e Karnian to l a t e Norian. (A •few kilometres to the south, f o s s i l s of Early J u r a s s i c age are found i n rocks included by Preto (1977) with the Nicola Group.) East of the volcanic archipelago lay a marine basin i n which the mud-stone, v o l c a n i c l a s t i c rocks, and limestone of the d i s t a l Nicola Group 124 accumulated. The sedimentary facies and structures suggest that the basin was r e l a t i v e l y deep, c e r t a i n l y well below sh e l f depths. Conodonts from the basinal sediments found at several l o c a l i t i e s are Karnian to early Norian i n age, i n d i c a t i n g time-equivalence with at l e a s t the lower portion of the proximal volcanic facies (Okulitch and Cameron, 1976). A mappable l a t e r a l t r a n s i t i o n between these two f a c i e s has not yet been recognized. However, south of Kamloops, Cockfield (1948) had d i f f i -c u l t y c o n s i s t e n t l y separating h i s "Cache Creek Group" (almost c e r t a i n l y rocks of the b a s i n a l facies of the Nicola Group) from the volcanic rocks of the type Nicola Group. Breccias and conglomerates occur at d i f f e r e n t h o r i -zons within the "Cache Creek Group," and Cockfield drew the boundary between the two groups at the place i n the section where volcanic flows and breccias of the type Nicola Group become predominant. Where attitudes could be deter-mined, t h i s d i v i s i o n separates rocks which are conformable. I t would appear then that the Karnian rocks of the study area pass upsection southwestward into the proximal volcanic facies of the Nicola Group, with some suggestion that the two facies i n t e r f i n g e r . In f a c t , at several l o c a l i t i e s throughout the region, the b a s i n a l sediments and fine-grained v o l c a n i c l a s t i c s are over-l a i n conformably by volcanic flows and breccias of presumed Late T r i a s s i c age (Campbell and Tipper, 1970; Read and Okulitch, 1977). I t appears that i n the Norian, and perhaps l a t e Norian, volcanism became widespread over the basin, perhaps associated with shallowing of the basin f l o o r by i n f i l l i n g or u p l i f t . The volcanic t u r b i d i t e s of Units 2, 4, and 5 were probably derived from the Nicola volcanic centers to the west. Their mineralogy c l o s e l y resembles that of the lower volcanic assemblage of the Nicola Group described 125 by Schau (1970). Both the proximal rocks and the t u r b i d i t e s are character-iz e d by volcanic fragments with abundant plagioclase phenocrysts and only rare a l t e r e d mafic minerals. Quartz-bearing volcanic c l a s t s also occur both i n the t u r b i d i t e s and i n the sediments i n the upper portion of the unit described by Schau. Not a l l the v o l c a n i c l a s t i c rocks i n the study area were derived from these vents, however. The p y r o c l a s t i c rocks of Units 3 and 6 are unlike any rocks yet described from the volcanic f a c i e s to the west, i n that they contain hornblende and b i o t i t e i n addition to clinopyroxene and p l a g i o c l a s e . The upper unit of the Nicola Group described by Schau contains abundant augite and some plagioclase, but hornblende has only been described from one b r e c c i a u n i t . Furthermore, the facies r e l a t i o n s of Unit 3 i n d i c a t e that these deposits were derived from a volcanic center or centers l y i n g to the east or northeast of the study area, and thus within the basin. The c h e r t - r i c h e l a s t i c s of Units 5 and 6 may have been derived from the Pinchi g e a n t i c l i n e to the west, although the s i l i c e o u s mudstones and p y r o c l a s t i c rocks of the Harper Ranch assemblage are another possible source. The coarse, angular nature of the chert and mudstone c l a s t s suggests that u p l i f t of the source terrane was rapid, and l o c a l r e l i e f was considerable. The emergent Pinchi g e a n t i c l i n e lay west of the b e l t of Nicola volcanic centers. The coarse debris derived from i t was transported eastward by density flows which funneled through low points between the volcanoes and out i n t o deeper waters beyond. This i n t e r p r e t a t i o n requires that the Nicola volcanic centers were b u i l t on an east-facing paleoslope (using present geographic directions) culminating to the west i n the emergent Cache Creek terrane. Local basins trapped between the emergent terrane and 126 the volcanic chain would contain l i t h i c d e t r i t u s derived from the west and v o l c a n i c l a s t i c s from the east. Studies by Travers (1978) of sedimentary and volcanic rocks of the Nicola Group near Cache Creek support t h i s i n t e r p r e t a t i o n . These rocks l i e between the outcrop b e l t s of the Cache Creek Group to the west and the proximal volcanic f a c i e s of the Nicola Group to the east. The lower part of the Nicola Group (Karnian) consists of volcanic flows and breccias, cherts, a r g i l l i t e s , t u r b i d i t e sandstones, conglomerates, and c a l c a r e n i t e s . Conglomerates contain c l a s t s of chert, a r g i l l i t e , and limestone possibly derived from the Cache Creek Group, but rare paleocurrent i n d i c a t o r s i n the sequence suggest transport to the west. Travers does not specify the l i t h -ologies of beds from which the current d i r e c t i o n s were derived, and these s t r a t a could thus be a mixture of volcanic d e t r i t u s derived from the east and l i t h i c d e t r i t u s derived from the west. The overlying Norian beds are mudstones with abundant sandstones (mostly calcareous sandstones or c a l c a r -enites) , and conglomerate lenses with c l a s t s of chert, limestone, a r g i l l i t e , and graywacke. These c l a s t s were probably derived from the Cache Creek Group to the west, and abundant paleocurrent data ind i c a t e transport to the east or southeast. The t u r b i d i t e limestones i n the study area are composed of fine-grained carbonate mud and s i l t derived from shallow water areas. Shallow water reefs formed near volcanic islands i n the Nicola Group (Schau, 1970), and carbonates may also have fringed portions of the emergent Cache Creek t e r -rane, as suggested by current d i r e c t i o n s of the Norian cal c a r e n i t e s recorded by Travers. The presence of both volcanic and metamorphic d e t r i t u s i n t h i n -sections and i n s o l u b l e residues of the limestones near Kamloops suggests 127 derivation of sediment from both areas. This d e t r i t u s includes metamorphic blue amphibole (crossite) for which the Cache Creek Group i s the only known source-, i n the Canadian C o r d i l l e r a . K-Ar ages of blueschists from Pinchi Lake, ce n t r a l B r i t i s h Columbia, record u p l i f t and cooling at 211 to 218 m.y., or Late Karnian to Norian, roughly coincident with the age of the Nicola Group. The eastern l i m i t s of t h i s marine basin are not known for c e r t a i n , and i t probably stretched across the present p o s i t i o n of the Omineca b e l t to the western margin of the T r i a s s i c miogeocline (Campbell and Tipper, 1970; Wheeler and others, 1972). Metamorphosed equivalents of the b a s i n a l rocks can be traced discontinuously across the metamorphic culmination of the Omineca b e l t east of Vernon, and into the T r i a s s i c Slocan and Ymir Groups on the east side of the c r y s t a l l i n e b e l t , i n the Rossland trough (Wheeler and others, 1972, F i g . 2; Okulitch and Cameron, 1976). These "troughs" are not narrow depositional features, but remnants of widespread Upper T r i a s s i c deposits which have been removed from most of 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 of the b a s i n a l rocks i n the region, including the Slocan and Ymir Groups, are mudstones with some coarse volcanic and l i t h i c e l a s t i c s and bas i n a l limestones. Near Shuswap Lake, t h e i r metamorphosed s t r a t i g r a p h i c equivalent i s the g r a p h i t i c , p h y l l i t i c limestone, marble, p h y l l i t e , and s c h i s t of the Sicamous Formation. The facies change from mudstone to i n t e r -bedded mudstone and argillaceous limestone has been mapped west of Adams Lake by Okulitch (1974). Upper T r i a s s i c limestone also occurs east of Vernon (Okulitch and Cameron, 1976). The Sicamous Formation i s severely 128 deformed and metamorphosed, so speculations on i t s depositional h i s t o r y are hazardous. However, descriptions of the unit (Jones, 1959; Fyson, 1970) suggest that i t originated as muddy bas i n a l limestones interbedded with mudstone, rather than i n a shallow water s e t t i n g . Since pelagic calcareous microorganisms are unknown before the J u r a s s i c , these limestones are probably not pelagic i n o r i g i n . The b a s i n a l limestones are apparently more abundant i n the Sicamous Formation than i n the Nicola and Slocan Groups, and the lime mud may have been transported from the s h e l f area to the north-east. In t h i s i n t e r p r e t a t i o n the Sicamous Formation i s viewed as a l o c a l accumulation of lime mud near the base of the Late T r i a s s i c continental slope. The axis of the Late T r i a s s i c basin would then l i e between the Kamloops area and Shuswap Lake, perhaps coincident with the b e l t of T r i a s s i c metasediments east of Vernon. But a westerly d e r i v a t i o n of the Sicamous limestones cannot be ruled out, i n which case the Late T r i a s s i c depocenter would l i e farther east. Tectonic Setting and Evolution of the Nicola Group Early T r i a s s i c orogenesis brought to a close the Late Paleozoic cycle of i s l a n d arc volcanism i n southern B r i t i s h Columbia. This deformation and low grade metamorphism i s documented i n part by an angular unconformity beneath T r i a s s i c rocks. Rocks above the 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 to Late T r i a s s i c west of the Omineca C r y s t a l l i n e b e l t (Read and Okulitch, 1977). By the Late T r i -a s s i c, nearly the whole eugeoclinal regime east of the Cache Creek-Bridge River assemblage had subsided below sea l e v e l . The Nicola depositional basin stretched from the Late T r i a s s i c continental margin (miogeocline) 129 westward to the accreted oceanic rocks of the emergent Pinchi g e a n t i c l i n e . A north-trending b e l t of submarine volcanic centers and volcanic islands separated two deeper basins dominated by sedimentary and v o l c a n i c l a s t i c rocks: a narrow western basin and a much wider eastern basin. C l a s t i c d e t r i t u s eroded from the Pinchi g e a n t i c l i n e was p e r i o d i c a l l y funneled through low points i n the volcanic chain, and accumulated i n the eastern as well as western basin. Carbonate sediment accumulated i n shallow waters around volcanic islands and the emergent Pinchi 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 transported i n t o the deeper marine basins by t u r b i d i t y currents. Some carbonate sediment i n the eastern basin may have been derived from the mio-geocline to the east. D i f f e r e n t parts of the Nicola Group formed i n d i f f e r e n t tectonic s e t t i n g s . The Nicola volcanic flows and breccias represent a Late T r i a s s i c volcanic arc complex which formed above an east-dipping subduction zone (Monger and others, 1972; Anderson, 1976; Davis and others, 1978). Coeval mudstones, v o l c a n i c l a s t i c s and minor flows accumulated i n a narrow fore-arc basin west of the arc, and i n a broad back-arc basin east of the arc. The back-arc basin was a "trapped" basin formed by subsidence of an older eugeoclinal basement; no back-arc spreading occurred within the basin. The Pinchi g e a n t i c l i n e separated the forearc basin from a deep ocean basin to the west. Although the Pinchi g e a n t i c l i n e was composed i n part of oceanic sediments accreted during Late Paleozoic subduction, i t s r i s e during the Late T r i a s s i c was caused by renewed subduction and consequent accretion of add i t i o n a l sediments at the toe of the accretionary wedge. Similar tectonic elements can be recognized f a r t h e r south i n the C o r d i l l e r a . Volcanic rocks s i m i l a r to the Nicola Group occur on or west 130 of the Late T r i a s s i c continental margin from northern B r i t i s h Columbia to the S i e r r a Nevada of C a l i f o r n i a (Monger, 1975a; Monger and Church, 1977; Bu r c h f i e l and Davis, 1972, 1975; Schweickert, 1976). In the southern S i e r r a Nevada, the Late T r i a s s i c arc developed on a continental margin truncated by enigmatic Permo-Triassic s t r i k e - s l i p movements (Burchfiel and Davis, 1972). Further north, the Late Paleozoic eugeoclinal terranes form the basement of the arc, which was separated from the miogeocline by a deep, marine basin. Remnants of t h i s basin have been recognized i n Nevada by Speed (1978a and b). Complexly deformed oceanic rocks of Late Paleozoic and younger age occur west of the volcanic b e l t , and probably include rocks accreted during Late Paleozoic and Late T r i a s s i c to Early Jurassic cycles of subduction (see Chapter I I ) . Scattered b l u e s c h i s t terranes occur within t h i s oceanic complex along the length of the C o r d i l l e r a . With a few exceptions, the blueschists from t h i s b e l t y i e l d remarkably consistent K-Ar ages of 214 to 220 m.y. (Monger, 1975a; Hotz and others, 1977; Paterson and Harakal, 1974). By the revised time-scale of Armstrong and McDowell (1974; Armstrong, 1978), the u p l i f t and cooling which these dates record are coeval with Late T r i a s s i c arc volcanism. The blueschists probably formed i n the deeper l e v e l s of the Late Paleozoic to Early T r i a s s i c accretionary wedge. Their synchronous u p l i f t may record an i n t e r v a l of very rapid subduction along most of the length of the arc. Rapid accretion of material to the wedge caused high rates of u p l i f t , and the resultant complex motions within the wedge ( S i l l i n g and Cowan, 1977) elevated the blueschists upward over younger rocks to the surface. This model would explain the u p l i f t of the Pinchi g e a n t i c l i n e , the appearance of detritus derived from i t within the Nicola Group, and the fac t that the 131 blueschists i n several areas occur i n high s t r u c t u r a l positions near the eastern margin of the accreted terrane, as predicted by the scale-model studies of S i l l i n g and Cowan (1977). In B r i t i s h Columbia, the Cache Creek-Bridge River assemblage i s t y p i c a l l y separated from the Upper T r i a s s i c arc volcanics by steep f a u l t zones such as the Pinchi, Hozameen, and Fraser f a u l t zones. The s i g n i f i c a n c e and movement h i s t o r i e s of these f a u l t s are uncertain. They may have originated as the tectonic contact (upper slope d i s c o n t i n u i t y of Karig and Sharman, 1975) separating the accretionary prism from the Paleozoic and younger arc terrane to the east, but l a t e r movements have almost c e r t a i n l y occurred on them as w e l l . I f a s i g n i f i c a n t portion of the Cache Creek-Bridge River assemblage was accreted during the Late Paleozoic to Early T r i a s s i c , i t i s u n l i k e l y that any of these f a u l t s represent the trace of the Late T r i a s s i c - E a r l y J u rassic subduction zone, as suggested for the Hozameen f a u l t by Anderson (1976) . The composition of the Upper T r i a s s i c volcanic rocks i s not t y p i c a l of simple c a l c - a l k a l i n e arcs of Andean or Cascade type. Mafic lavas and breccias predominate over those of intermediate composition, and most of the rocks are a l k a l i n e rather than c a l c - a l k a l i n e (Souther, 1977). Paterson (1977) proposed that the upper T r i a s s i c volcanics i n B r i t i s h Columbia were rela t e d p r i m a r i l y to transform plate motions rather than to subduction. He i d e n t i f i e d the Pinchi 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 connecting short, east-west trending subduction zones. In t h i s model, the Pinchi blueschists were "leaked" to the surface along the transform f a u l t . Recent volcanics s i m i l a r i n composition to the Takla and Nicola volcanics are found i n several i s l a n d chains i n the southwest P a c i f i c 132 where present-day plate motions are mainly s t r i k e - s l i p (Paterson, 1977; Carmichael, Turner, and Verhoogen, 1974, p. 542-544). Considering the large volume of Upper T r i a s s i c volcanics erupted i n B r i t i s h Columbia and a l l along the continental margin at t h i s time, i t i s u n l i k e l y that they could have been produced s o l e l y by "leaky" transform f a u l t s and short segments of subduction zones. The chemistry of the Nicola-Takla volcanics may accurately r e f l e c t a s t r i k e - s l i p component of plate motion at t h i s time, but t h i s was probably the r e s u l t of oblique subduction (Souther, 1977; Davis and others, 1978). Motion p a r a l l e l to the arc could have been accomodated within the subduction zone i t s e l f , or on steep f a u l t zones within or between the accretionary wedge and arc terrane; perhaps on the Pinchi f a u l t i t s e l f . Such s t r i k e - s l i p f a u l t s within modern arc systems have been described by F i t c h (1972). Subduction and arc volcanism occurred through the Karnian and Norian, and again i n the Early J u r a s s i c , but i n B r i t i s h Columbia both the arc terrane and back-arc basin were t e c t o n i c a l l y disrupted i n the E a r l i e s t J u r assic by the " I n k l i n i a n Orogeny." Evidence for t h i s event includes a regional uncon-formity beneath Lower Jurassic s t r a t a , commonly of Sinemurian age (Douglas and others, 1970, p. 440; Campbell and Tipper, 1970); warping and f a u l t i n g of the volcanic arc rocks (Schau, 1970) ; and i n t r u s i o n and erosional unroof-ing of plutons within the volcanic arc which y i e l d K-Ar ages c l u s t e r i n g around 200 m.y. (Campbell and Tipper, 1970). In addition, I believe that the westerly-overturned folds within the Nicola Group i n the study area formed at t h i s time (see following chapters). An explanation of t h i s event i n terms of plate tectonics i s not obvious. However, examination of the s t r a t i g r a p h i c record of T e r t i a r y i s l a n d arcs i n the western P a c i f i c , such 133 the Marianas (Karig, 1971; Tracey and others, 1964), New Hebrides (Mitchell and Warden, 1971), and F i j i (Rickard, 1963, 1966; Ibbotson, 1969) show that arc volcanism occurs i n pulses of 10 to 15 m.y. duration, punctuated by short periods of u p l i f t , b l o c k - f a u l t i n g , and unroofing of plutons. These interruptions may mark cessations or changes i n rate of subduction, or changes i n r e l a t i v e motion of neighboring pla t e s , but 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 the arc i t s e l f . The "Ink l i n i a n Orogeny" may be a s i m i l a r event which also involved f o l d i n g i n the back-arc region. 134 CHAPTER IV. INTRUSIVE ROCKS PAUL PEAK STOCK (MAP-UNIT 7) F i e l d Relations This small, compositionally varied pluton occupies the saddle and flanks of the ridge between Paul Peak and Peter Peak. I t i s highly elongate (3.8 km long and up to 1.25 km wide), trending northwestward at a small angle to the s t r i k e of the Upper T r i a s s i c rocks of Units 5 and 6 which i t intrudes. Pleistocene deposits cover the northwest and southeast ends of the pluton. The northeastern margin appears to be roughly concordant with the lay e r i n g i n Unit 5, but the contact i s nowhere exposed. The southwestern contact i s much more i r r e g u l a r , c u t t i n g at high angles across layering, including the contact between Units 5 and 6. L o c a l l y , thin-bedded mudstones adjacent to the pluton have been deformed during i n t r u s i o n , and have anom-alous attitudes p a r a l l e l to the i n t r u s i v e contact. The pluton i s c o n c e n t r i c a l l y zoned (Fig. 36), although the zoning i s truncated by the exposed contacts, and continuity of a l l the zones at depth cannot be assumed. Two outcrops of o l i v i n e clinopyroxenite are i n f e r r e d to form parts of a narrow band which occupies the core of the pluton. This band i s completely surrounded by leucogabbro and d i o r i t e , which are suc-ceeded outward to the east and west by hornblende gabbro and d i o r i t e . Horn-blende-quartz monzodiorite and f i n a l l y hornblende granite form i s o l a t e d zones at the southeast end of the pluton. The nature of the zone contacts could not be determined i n the f i e l d owing to poor exposure. However, TYPE OF COMPOSITIONAL DATA | Q | Quaternary deposits 0.5 km • Field description • Hand specimen * Thin-section vr;tV*V-i. yJ t 1IIIK-l95 T-:AVtV ,v - . /--'.t 1 1 1 • - t t I T MK-91 » v "v7'-''-r>i'->''.--"-~'inK-ipr.-4> ..•6b LOWER JURASSIC PAUL PEAK STOCK Hornblende granite Hornblende quartz monzodiorite Hornblende gabbro and diorite Leucogabbro and diorite Olivine clinopyroxenite UPPER TRIASSIC NICOLA GROUP 6b Mafic volcanic rocks MK Mudstone, lithic sandstone, andesitic pyroclastics Thin-bedded mudstone • W i i K - i q l ' ** * • - # Q * - * ' * * * » - "\ ' ^ " • ' • • • " . • ; ; ; / .• Q F i g . 36. Geologic map of the Paul Peak Stock. oo 136 t e x t u r a l s i m i l a r i t i e s within the series lecogabbro-granite suggests these contacts are gradational. Most of the plutonic rocks are medium-grained and equigranular. The outcrops are massive, lacking primary igneous l a y e r i n g or f o l i a t i o n . Veins of very coarse-grained hornblende cut the hornblende gabbro and d i o r i t e i n a few places, and pink potassium feldspar veins are common i n the hornblende-quartz monzodiorite and hornblende granite. Petrography Table VIII gives the v i s u a l l y estimated modes of samples from the Paul Peak Stock. The anorthite contents of plagioclase feldspars are given i n Table IX. The rock c l a s s i f i c a t i o n used i s that given by the IUGS Sub-commission on the Systematics of Igneous Rocks (Streckeisen, 1974). Ol i v i n e Clinopyroxenite Ol i v i n e clinopyroxenite i s composed of 70% clinopyroxene (diopside or augite) and 30% o l i v i n e . The o l i v i n e occurs as aggregates of anhedral grains i n t e r s t i t i a l to and p a r t i a l l y surrounding subhedral to rounded pyroxenes. Plagioclase i s lacking i n the samples examined. Trace amounts of i n t e r s t i t i a l b i o t i t e are present, and minor replacement of clinopyroxene by hornblende has occurred. Leucogabbro and D i o r i t e These are gray equigranular rocks composed l a r g e l y of subhedral, zoned plagioclase and clinopyroxene. There appears to be a continuous gradation from leucogabbro (plagioclase averaging >An50) to d i o r i t e (plagioclase averag-ing <An^Q) without any s i g n i f i c a n t change i n the proportion of mafic c o n s t i -tuents. Interpenetrating grain contacts between some plagioclase and TABLE VIII. VISUALLY ESTIMATED MODES OF PLUTONIC ROCKS FROM PAUL PEAK STOCK Sample MK-99b MK-195 MK-98 MK-91 Lithology O l i v i n e Clinopyroxenite Leucogabbro D i o r i t e Hornblende D i o r i t e Plagioclase — 73% 78% 68% Potassium feldspar — 2 3 Tr Quartz — — — — Clinopyroxene 72% 20 12 9 Hornblende Tr — — 20 B i o t i t e Tr 3 6 3 Ol i v i n e 28 2 Tr — Sample MK-101 MK-194 MK-104 MK-103 Lithology Hornblende Gabbro Hornblende Gabbro Quartz Monzodiorite Hornblende Granite Plagioclase 65% 60% 54% 35% Potassium feldspar — 1 28 42 Quartz 1 3 12 20 Clinopyroxene 2 15 — — Hornblende 30 8 6 3 B i o t i t e Tr 13 — — O l i v i n e — — — — Tr = Trace = Absent 138 TABLE IX. ANORTHITE CONTENT OF PLAGIOCLASE FELDSPARS FROM PAUL PEAK STOCK Sample Core Rim MK-195 A n 5 1 , A n 5 1 > A n 5 8 , A n 6 8 , A n 6 9 MK-98 Ani t 2» Ani+g, Ani+Q, An^g, An^g ^50 A n 3 5 ^ 5 0 MK-91 A n i ^ , A n 5 0 MK-101 An 7 6 , An 7g, MK-194 Small, apparently unzoned c r y s t a l s : An 3 t t, A n 4 0 , A n 5 7 , A n S 2 Compositions determined i n thin - s e c t i o n p r i m a r i l y by the Carlsbad-albite method. 139 clinopyroxene grains indicate simultaneous c r y s t a l l i z a t i o n . B i o t i t e occurs as s k e l e t a l p o i k i l i t i c grains, and potassium feldspar as small i n t e r s t i t i a l grains. Typical textures are shown i n F i g . 37. Plagioclase shows complex zoning. Commonly a large core with numerous o s c i l l a t o r y zones was p a r t i a l l y resorbed, and surrounded by a s i n g l e thick, normally zoned rim. Average compositions for the cores range from Ang^ to Ani+2- Within a single sample the anorthite component of the cores may vary up to 20%. Average rim compositions were determined on only two c r y s t a l s i n one sample, and were both An35. Several samples contain up to 2% o l i v i n e , almost always i n rounded, anhedral grains which were probably p a r t l y resorbed by reaction with the melt. The o l i v i n e grains are t y p i c a l l y fractured, and p a r t i a l l y a l t e r e d to serpen-t i n e or reddish-brown " i d d i n g s i t e " and magnetite. Complex reaction rims or coronas occur between o l i v i n e and p l a g i o c l a s e , forming a ser i e s of concentric s h e l l s around the o l i v i n e s . The inner s h e l l consists of blocky c r y s t a l s of c o l o r l e s s hypersthene, and the second one of r a d i a l l y or t a n g e n t i a l l y oriented green b i o t i t e . In most examples there i s a t h i r d s h e l l of r a d i a l l y arranged, wormy a c i c u l a r c r y s t a l s of an u n i d e n t i f i e d mineral. This mineral i s color-l e s s , has i n c l i n e d e x t i n c t i o n , moderate to high r e l i e f , and perhaps i s an amphibole or clinopyroxene. E i t h e r of the two outer s h e l l s may be discon-tinuous, but the inner one i s always present. Replacement of o l i v i n e has taken place p r e f e r e n t i a l l y along fractures, leading to the formation of very complex coronas. In some cases, the o l i v i n e has been completely replaced by a granular aggregate of hypersthene and magnetite, usually leaving a core of " i d d i n g s i t e . " Preservation of the d e l i c a t e corona textures indicates that they formed 140 F i g , 37. Photomicrograph of leucogabbro, MK-98. Subhedral pla g i o -clase (PI) and clinopyroxene (C) with i n t e r s t i t i a l b i o t i t e (B) and potassium feldspar (K). Thin-section, X 40. 141 a f t e r most movement between c r y s t a l s within the pluton had ceased. Although such coronas might form during l a t e r high grade metamorphism of plutonic rocks, i n t h i s case post-emplacement metamorphism i s l i m i t e d to the prehnite-pumpellyite f a c i e s , with only minimal e f f e c t s on the plutonic rocks (see Chapter V). Thus the formation of the high temperature phases which make up the coronas must have taken place by a retrograde reaction between plag i o -clase and o l i v i n e during cooling of the pluton from i t s o r i g i n a l magmatic temperatures ( G r i f f i n and Heier, 1973; Sapountzis, 1975). Hornblende Gabbro and D i o r i t e Hornblende gabbro and d i o r i t e are t e x t u r a l l y s i m i l a r to the rocks just described, but contain up to 30% hornblende. Plagioclase and c l i n o -pyroxene are subhedral, while b i o t i t e , quartz, and potassium feldspar show i n t e r s t i t i a l textures. Plagioclase compositions range from An 85 to A^i,., and much of i t i s p a r t l y a l t e r e d to 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 rocks lacking hornblende. Hornblende occurs i n two d i f f e r e n t forms within these rocks. Pale green hornblende (or perhaps a c t i n o l i t e ) replaces clinopyroxene marginally and along cleavages, and more strongly colored green hornblende occurs as overgrowths around the a l t e r e d pyroxenes (Fig. 38). These overgrowths often f i l l i n t e r s t i c e s between plagioclase l a t h s , and i n one sample form very large p o i k i l i t i c grains, suggesting c r y s t a l l i z a t i o n from a late-stage melt or f l u i d with which clinopyroxene was no longer i n equilibrium. Inter-growths of hornblende with b i o t i t e suggest that some replacement of b i o t i t e has also taken place. Reaction coronas around o l i v i n e grains i n the hornblende gabbro contain cummingtonite i n place of hypersthene, suggesting that the coronas formed F i g . 38. Photomicrograph of hornblende gabbro, MK-195. Single large p o i k i l i t i c hornblende (H) surrounds clinopyroxene (C), altered plagioclase ( P i ) , and magnetite (Mt). Thin-section, plane l i g h t , X 40. Fig. 39. Photomicrograph of hornblende granite, MK-104. Subhedral zoned plagioclase (Pi) and euhedral hornblende (H) and sphene (S) surrounded by i n t e r s t i t i a l quartz (Q) and p o i k i l i t i c potas-sium feldspar (K). Thin-section, crossed n i c o l s , X 40. 143 p r i o r to or during the episode of hornblende replacement and growth. Quartz Monzodiorite and Hornblende Granite Quartz monzodiorite and hornblende granite are mineralogically and t e x t u r a l l y s i m i l a r to each other, d i f f e r i n g only i n t h e i r r e l a t i v e propor-t i o n of plagioclase to potassium feldspar. Plagioclase and hornblende are euhedral to subhedral, and are commonly zoned. Plagioclase has cores with o s c i l l a t o r y zoning surrounded by normally zoned rims. Average compositions for the cores range from An^^ to An5 2, and for the rims from An£g to An28-Quartz occurs as aggregates of anhedral c r y s t a l s p a r t i a l l y enclosing pl a g i o -clase, while potassium feldspar often forms large p o i k i l i t i c c r y s t a l s sur-rounding a l l other phases (Fig. 39). Both potassium feldspar and plagioclase are mildly a l t e r e d to s e r i c i t e . Petrogenesis O r i g i n of the Rock Series Leucogabbro to Granite The o v e r a l l s i m i l a r i t y i n texture of rocks within t h i s s e r i e s , coupled with the progressive v a r i a t i o n i n modal mineralogy and texture from zone to zone, suggests that t h i s may be a continuous d i f f e r e n t i a t i o n series 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 . Plagioclase i n a l l the rocks i s subhedral to euhedral, and commonly has a normally zoned rim surrounding a p a r t i a l l y resorbed core with numerous o s c i l l a t o r y zones. Both core and rim compositions become progressively more sodic i n the more f e l s i c rocks. The inner leucogabbro and d i o r i t e contain clinopyroxene as the primary mafic phase, while the monzodiorite and granite contain only hornblende. In between l i e the hornblende gabbro and d i o r i t e i n which early clinopyroxene became unstable with respect to the i n t e r s t i t i a l melt, and was replaced and 144 overgrown by hornblende. These re l a t i o n s h i p s suggest that the gabbroic and d i o r i t i c rocks formed by segregation of early plagioclase and clinopyroxene from a larger body of melt i n which hornblende rather than clinopyroxene became the stable mafic phase as the melt cooled and P increased. This melt eventually c r y s t a l -H2O l i z e d to form the hornblende-quartz monzodiorite and hornblende granite. I t was not possible to determine from the f i e l d r e l a t i o n s h i p s whether the c l i n o -pyroxene and hornblende-bearing portions of the i n t r u s i o n were emplaced separately or as part of a sing l e mass. However, textures within the horn-blende gabbro and d i o r i t e demonstrate reaction between the two portions while a s i g n i f i c a n t amount of i n t e r s t i t i a l melt remained i n the d i o r i t i c rocks, suggesting emplacement as a si n g l e coherent magma body. The mechanism of c r y s t a l segregation and o r i g i n of the crude concentric zonation are problematic. Murray (1972) and James (1971) invoked flowage d i f f e r e n t i a t i o n as a model to explain the concentric zonation i n Alaskan-type zoned ultramafic complexes. This mechanism depends upon the tendency of suspended p a r t i c l e s within a flowing f l u i d to move away from the walls and toward the region of l e a s t shear stress i n the medial or a x i a l portion of the conduit. In t h i s way, early c r y s t a l s could be concentrated i n the center of a magma body flowing through a v e r t i c a l c y l i n d r i c a l conduit, producing 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 . But while Bhattacharji and Smith (1964) demonstrated that t h i s mechanism can operate i n small models, Barriere (1976) has shown t h e o r e t i c a l l y that the inward movement should decrease r a p i d l y away from the walls of the conduit. He concluded that flowage d i f f e r e n t i a t i o n could not explain zoning i n intrusions larger than about 100 m i n diameter. 145 Textures of the gabbroic and d i o r i t i c rocks suggest that these rocks may be cumulates of plagioclase and clinopyroxene formed by g r a v i t a t i v e c r y s t a l s e t t l i n g . Intercumulus phases are b i o t i t e , quartz, a l k a l i feldspar, and hornblende (excluding that replacing clinopyroxene). These minerals have i n t e r s t i t i a l or p o i k i l i t i c textures, and make up 6% to about 20% of the rocks, giving a crude minimum estimate of the amount of i n t e r s t i t i a l melt present within the cumulates p r i o r to f i n a l c r y s t a l l i z a t i o n . (The normally zoned outer rims of the plagioclase c r y s t a l s probably also formed from the intercumulus l i q u i d , but t h i s volume i s not e a s i l y measured or 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 explain the compositional zoning within the pluton, since these processes would form a s t r a t i f o r m pluton. If these processes did produce the o r i g i n a l compositional v a r i a t i o n , then upward remobilization of the cumulates and the remaining melt must have taken place during f i n a l emplacement of the pluton. Movement of the cumulates would have been f a c i l i t a t e d by the i n t e r -s t i t i a l melt, which would act as a l u b r i c a n t . Since o l i v i n e - p l a g i o c l a s e reaction coronas were affected by hornblende a l t e r a t i o n , movement of the cumulates probably ceased before hornblende became the stable mafic phase i n the remaining melt. Upward i n t r u s i o n of the cumulates and melt may have resulted from regional compressive stresses which also produced the large scale folds i n the Nicola Group p r i o r to i n t r u s i o n . This would account for the elongation of the pluton at only a small angle to the f o l d trends. D i a p i r i c remobili-zation of s t r a t i f o r m cumulates during regional f o l d i n g was also postulated by Findlay (1969) to explain the geometry of the Tulameen ultramafic-gabbro 146 complex, which intrudes the Nicola Group about 150 km south of Kamloops, and i s probably about the same age as the Paul Peak Stock. Origin of the Ultramafic Rocks The o r i g i n of the o l i v i n e clinopyroxenite which crops out i n the core of the Paul Peak Stock i s uncertain. Several possible interpretations are discussed, but l i t t l e d i r e c t evidence e i t h e r supports or refutes any of them. The o l i v i n e clinopyroxenite could have formed as a pyroxene-olivine cumulate at the bottom of the magma chamber, before plagioclase began to c r y s t a l l i z e to form the surrounding gabbroic and d i o r i t i c rocks. The u l t r a -mafic cumulates would have been deformed and intruded along with the r e s t of the cumulates. The presence of small amounts of rounded, probably p a r t l y resorbed o l i v i n e i n the gabbro and d i o r i t e i s consistent with t h i s model. The pyroxenite could also have formed as a separate i n t r u s i o n , e i t h e r e a r l i e r or l a t e r than the gabbro. Since temperatures i n excess of 1300° are necessary for pyroxenite melts to e x i s t at low pressures (Presnall, 1966), the pyroxenite would probably have been emplaced as a l a r g e l y c r y s t a l l i n e 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 basic magma. Oli v i n e clinopyroxenite of s i m i l a r modal proportions to that i n the Paul Peak Stock i s a major constituent of zoned, Alaskan-type ultramafic complexes. These complexes usually consist of dunite, o l i v i n e clinopyroxen-i t e , magnetite clinopyroxenite, and hornblende-magnetite clinopyroxenite i n a crudely concentric zonal pattern, with more o l i v i n e - r i c h rocks toward the center. The zones are commonly discontinuous i n map view, and one or more rock types may be absent from either end of the s e r i e s , but t h e i r order i s usually maintained. Orthopyroxene and plagioclase are absent from 147 the ultramafic rocks, which almost always intrude gabbroic to d i o r i t i c rocks of varying kinds. I suggest that the Paul Peak Stock i s such a zoned complex, although only one ultramafic rock type i s present. Findlay (1969) reached the same conclusion for the Tulameen complex, where the complete su i t e of ultramafic rocks from dunite to hornblende clinopyroxenite i s present. A major pe t r o l o g i c problem concerning these complexes i s the r e l a t i o n s h i p between the ultramafic rocks and the surrounding gabbroic rocks. Their 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, the gabbroic rocks may be ei t h e r s i l i c a - s a t u r a t e d ( t h o l e i i t i c ) as i n Alaska, or undersaturated and a l k a l i c , as i n the Tulameen complex. 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 derived one from the other by simple c r y s t a l f r a c t i o n a t i o n at the low pressures which would pre-v a i l during emplacement of these complexes (Yoder and T i l l e y , 1962; Wyllie, 1971, p. 190-208). Therefore i t i s d i f f i c u l t to see how both saturated and undersaturated gabbros could be derived from a sing l e parent melt type which gives r i s e to such a consistent sequence of ultramafic d i f f e r e n t i a t e s . Irvine (1973, 1974) proposed that the gabbroic and ultramafic rocks of zoned complexes r e s u l t from i n t r u s i o n of successive magmas i n the feeder pipes of volcanoes. In the Duke Island complex i n southeastern Alaska, the ultramafic rocks are c l e a r l y cumulates 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 and c r y s t a l s e t t l i n g , and Irvine suggests that the parent melt was a s i l i c a -undersaturated mafic magma. The concentric zonation r e s u l t s from d i a p i r i c i n t r u s i o n of the s t r a t i f o r m mass of cumulates, the same mechanism outlined above for the gabbroic rocks of the Paul Peak Stock. The re s i d u a l melt may have been vented to the surface to form mafic augite porphyry vo l c a n i c s , 148 which i n southeastern Alaska occur i n the same region as the zoned complexes, and are approximately coeval with them (Cretaceous). S i g n i f i c a n t l y , s i m i l a r augite porphyry volcanics occur i n the Upper T r i a s s i c and Lower Jurassic i n B r i t i s h Columbia, approximately coeval with the emplacement of the Paul Peak Stock and the Tulameen complex. A possible genetic l i n k between the Tulameen complex and the Nicola volcanics was f i r s t suggested by Findlay (1969). Comparison of the Paul Peak Stock with zoned mafic-ultramafic complexes thus suggests that the pyroxenite core of the pluton formed as a separate, l a t e r i n t r u s i o n of c r y s t a l mush derived by c r y s t a l f r a c t i o n a t i o n from a mafic, possibly 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 to Nicola volcanism. Age and Regional C o r r e l a t i o n The Paul Peak Stock intrudes deformed Upper T r i a s s i c (Karnian) sedimen-tary and volcanic rocks of the Nicola Group. Major deformation of the T r i a s s i c rocks predates or was synchronous with emplacement of the stock. Local s t r a t i g r a p h i c evidence does not place a close upper l i m i t on the age of i n t r u s i o n ; the oldest deposits overlying the pluton are Pleistocene to 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 fan deposits. G r a n i t i c plutonism i n the cen t r a l and eastern Canadian C o r d i l l e r a has recently been summarized by Gabrielse and Reesor (1974). They were able to di s t i n g u i s h several groups of plutonic rocks based on age, composition, and tectonic s e t t i n g . The composition, s e t t i n g , and i n f e r r e d petrogenesis of the Paul Peak Stock suggest c o r r e l a t i o n with the Late T r i a s s i c to Early Jurassic plutonic s u i t e , also r e f e r r e d to as the 200 m.y. plutonic suite 149 by Campbell and Tipper (1970). This suite includes numerous large g r a n i t i c bodies and many small stocks and plugs. Most of these plutons intrude the Upper T r i a s s i c volcanic rocks of the Quesnel trough. K-Ar mineral ages range from 193 to 215 m.y., c l u s t e r i n g between 197 and 206 m.y. The Iron Mask Batho l i t h , the nearest pluton of t h i s group to the study area, intrudes the volcanic facies of the Nicola Group 5 km southwest of Kamloops. The larger plutons of t h i s group (Guichon, Thuya, Takomkane) are dom-i n a n t l y granodiorite i n composition, but range from quartz d i o r i t e or d i o r i t e to quartz monzonite. In many there i s a r e l a t i v e l y mafic border phase, with progressively younger and more f e l s i c phases toward the center of the pluton. The smaller bodies (Copper Mountain, Iron Mask) are a l k a l i n e , composed of d i o r i t e , monzonite, and syenite. Often these are also strongly zoned, with gabbro or pyroxenite margins and s y e n i t i c cores. F i n a l l y , there i s a small group of zoned Alaskan-type mafic-ultramafic bodies, in c l u d i n g the Tulameen complex, probably the Paul Peak Stock, and a group described by Irvine (1976) from north ce n t r a l B r i t i s h Columbia. Many such bodies probably remain to be described from the Quesnel trough. A few discordant K-Ar ages range from 155 to 164 m.y. for the northern bodies, and 186 m.y. for the Tulameen complex. However, the association of these plutons with Upper T r i a s s i c volcanics, and s t r u c t u r a l evidence at Tulameen, suggests that they may be contemporaneous with the r e s t of the 200 m.y. plutonic s u i t e . The l o c a t i o n of many of the plutons coincides with the th i c k e s t accum-ulations of Upper T r i a s s i c volcanic flows and breccias. This f a c t , plus the general correspondence i n composition between the a l k a l i n e stocks and the mafic, a l k a l i n e volcanics, has led many authors to the conclusion that both are derived from the same magma, and the plutons mark the locations of former 150 volcanic centers. However, the plutons reached t h e i r f i n a l l e v e l of emplace-ment a f t e r , or during l a t e r stages of, an episode of deformation which formed variable but generally north to northwest-trending gentle warps and steep f a u l t s within the volcanic sequence (Wheeler and others, 1972; Findlay, 1969; Schau, 1970). The general concordance of the large batholiths and some smaller plutons with regional f a u l t and f o l d trends, and the i n t e r n a l structure and i n f e r r e d emplacement mechanism of intrusions such as the Tula-meen complex suggest that i n t r u s i o n accompanied regional deformation. I believe t h i s same episode of deformation produced the northwest-trending folds which a f f e c t the Karnian rocks of the Nicola Group i n the study area, and which are cut by the Paul Peak Stock. U p l i f t and erosion followed r a p i d l y a f t e r i n t r u s i o n , for c l a s t s derived from the 200 m.y. plutons are common i n Lower Jurassic conglomerates which are as o l d as Sinemurian (Campbell and Tipper, 1971). Gr 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 volcanic breccias mapped as Nicola Group southwest of Kamloops (Northcote, 1974; Schau, 1970). North-cote has i n f e r r e d from t h i s evidence that i n t r u s i o n of the Iron Mask batho-l i t h was coeval with Nicola volcanism, and that the pluton was unroofed and cannabalized while Nicola volcanism continued. This conclusion i s con-s i s t e n t with K-Ar ages for the pluton (190 to 205 m.y., averaging 200 m.y.; Northcote, personal communication, 1976) i f the T r i a s s i c - J u r a s s i c boundary i s taken at the widely accepted age of 195 to 200 m.y. (Lambert, 1971; van Hinte, 1976). A suggested r e v i s i o n of t h i s boundary by Armstrong and Besan-con (1970) and Armstrong and McDowell (1974) would push i t back to 208 or 210 m.y., i n which case the 200 m.y. plutonic s u i t e would be e a r l i e s t Jurassic i n age. This i s consistent with the conclusion of Campbell and 151 Tipper (1970) that plutonism accompanied u p l i f t and erosion at the close of the T r i a s s i c , ending marine deposition of the Nicola Group. This episode has been referred to as the I n k l i n i a n Orogeny (Douglas and others, 1970, p. 440), and i t s e f f e c t s are widespread i n the Intermontane b e l t . Reconciliation of Northcote's s t r a t i g r a p h i c evidence for the time of unroofing with the revised radiometric age for the pluton may be possible. North of Kamloops, i n Bonaparte Lake and Quesnel Lake map-area, Campbell and Tipper (1970, 1971) have mapped a Lower to Middle Jurassic volcanic and v o l c a n i c l a s t i c unit 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 parts of the Nicola Group, except f o r the presence at i t s base of a coarse conglom-erate containing c l a s t s of the Nicola and "Cache Creek" Groups, and of the 200 m.y. int r u s i o n s . Jurassic rocks are also included i n the Nicola Group i n southern Nicola and i n Princeton map-areas (Preto, 1977). F o s s i l s are sparse both i n the Jurassic unit and i n the Nicola Group, and the p l u t o n i c -bearing breccias south of Kamloops appear to be included with the Nicola Group pr i m a r i l y on l i t h o l o g i c grounds. I suggest that these rocks may ac t u a l l y be Lower Jurassic i n age, c o r r e l a t i v e with the Jurassic volcanic sequence. Search f o r f o s s i l s i n these beds i s obviously necessary i n order to resolve t h i s question. An alternate p o s s i b i l i t y i s that the sporadic plutonic c l a s t s i n the Nicola Group are inclusions brought from plutons at depth below the vents, and do not record unroofing of the Iron Mask b a t h o l i t h or other 200 m.y. plutons. In summary, the Paul Peak Stock i s probably c o r r e l a t i v e with other zoned mafic-ultramafic plutons which make up a portion of the 200 m.y. p l u -tonic s u i t e . I t was emplaced during the l a t e stages of a phase of regional compressive deformation which produced f a u l t s and open folds i n the proximal 152 volcanic facies of the Nicola Group, and westward overturned folds i n the basinal facies of the Nicola Group i n the study area. The age of t h i s deformation i s thus determined to be Latest T r i a s s i c to E a r l i e s t J urassic. SMALL PLUGS, SILLS, AND DIKES (MAP UNIT 8) Small i n t r u s i v e bodies of andesitic to r h y o l i t i c composition are com-mon i n the area. Most of these are t h i n dikes and s i l l s , but several small plugs and thick s i l l s occur as w e l l . These rocks e x h i b i t a wide v a r i e t y of textures, but most have aphanitic and/or p o r p h y r i t i c textures. A l l samples examined showed extensive a l t e r a t i o n of phenocrysts and groundmass, produced by hydrothermal a l t e r a t i o n or low grade regional metamorphism. However, the o r i g i n a l textures are l a r g e l y preserved, and phenocryst phases are i d e n t i f i a b l e . Most of the rocks studied are andesites or dacites with phenocrysts and/or microphenocrysts of plagioclase and hornblende i n a f e l s i t i c matrix. Some of the rocks contain quartz phenocrysts, or quartz i n a microgranitic matrix, and are i d e n t i f i e d as dacites. The remainder of the rocks lack o p t i c a l l y i d e n t i f i a b l e quartz, and could be andesites, dacites, or trachy-andesites depending on the r e l a t i v e proportion of potassium feldspar and quartz hidden i n the groundmass, but were t e n t a t i v e l y i d e n t i f i e d as ande-s i t e s . A small number of highly a l t e r e d r h y o l i t e dikes and s i l l s also occur. Petrographic descriptions of the d i f f e r e n t v a r i e t i e s of minor i n t r u -sive rocks are given i n the following paragraphs. The secondary mineralogy i s discussed i n Chapter V. 153 Description of Minor Intrusive Rocks Thick S i l l s Two s i l l s up to several tens of metres thick intrude Unit 4 on Paul Ridge, and Unit 5 i n Dome H i l l s . The s i l l on Paul Ridge i s composite, with an a n d e s i t i c lower part and a d a c i t i c upper part. Outcrops of these two types are usually no closer than 30 meters apart, separated by a covered i n t e r v a l . They may be separate intrusions with an intervening septum of sedimentary rock, but are shown as a sing l e u n i t on Plate I. The s i l l i n Dome H i l l s , along with a number of dikes, are l i t h o l o g i c a l l y very s i m i l a r to the upper portion of the Paul Ridge s i l l . The d a c i t i c s i l l s and dikes are gray, p o r p h y r i t i c rocks, with 25 to 30% phenocrysts i n an aphanitic matrix. Thin-sections of two samples show that phenocrysts are plagioclase (10 to 25%) , hornblende (5 to 10%) , and minor quartz. A few pseudomorphs a f t e r pyroxene are present i n one sample. Plagioclase remains r e l a t i v e l y fresh i n portions of one sample, and consists of unzoned cores surrounded by thick rims with o s c i l l a t o r y zoning. Compo-s i t i o n s of Arn+7 and An^i^ were determined on the inner portions of the rims of two grains. Hornblendes are stubby to elongate, up to 6 mm long, while plagioclase i s generally less than 3 mm i n diameter. The groundmass con-s i s t s of microphenocrysts i d e n t i c a l to the phenocryst assemblage, surrounded by a f e l s i t i c matrix. The andesite making up the lower portion of the s i l l on Paul Ridge i s more sparsely p o r p h y r i t i c , and the plagioclase (5%) and hornblende (10%) phenocrysts are mostly only 1 to 2 mm long. The l i g h t gray groundmass i s a fine-grained aggregate which consists mostly of a l t e r e d feldspar plus secondary minerals. L i t t l e or no quartz i s evident. 154 Dacite Porphyry Plug Low outcrops of dacite porphyry occur scattered over an area of a few hundred square metres on the top of Paul Ridge, intruding the eastern portion of Unit 2. Abundant f l o a t of t h i s porphyry was also observed to the southeast, near the southern edge of the r o l l i n g upland surface of the ridgetop. This f l o a t was found near the contact between Units 1 and 2, but no bedrock exposures were found. The porphyry cobbles probably are weathered out of t i l l which l o c a l l y mantles the ridgetop, and derive from the outcrops previously described. The porphyry contains about 20% zoned plagioclase phenocrysts up to 1.5 mm i n diameter, and 5 to 10% elongate hornblende up to 6 mm long. The plagioclase composition i s a l b i t e , probably replacing a more c a l c i c primary plagioclase. The gray, " s a l t and pepper" groundmass contains smaller horn-blende and plagioclase c r y s t a l s surrounded by nearly equal amounts of anhedral quartz and potassium feldspar, both as separate grains and i n g r a p h i t i c i n t e r -growths, and also secondary minerals. The groundmass grains are barely v i s i b l e but not i d e n t i f i a b l e i n hand-specimen, so the groundmass i s a c t u a l l y a fine-grained phanerite rather than an aphanite, and the rock might be c a l l e d a p o r p h y r i t i c micro-granodiorite. The modal proportions of quartz and potassium feldspar i n t h i s groundmass c l e a r l y show that the rock has a bulk composition of granodiorite or dacite, rather than andesite, despite the lack of quartz phenocrysts. Po r p h y r i t i c Andesite Plug A small andesite plug intrudes the eastern portion of Unit 2 adjacent to a prominent north-trending f a u l t . Exposures are too poor to show whether the plug intrudes along the f a u l t or that the f a u l t cuts the plug. The 155 andesite i s gray, with phenocrysts of plagioclase (5 to 10%) and hornblende (5 to 10%). The blocky plagioclase phenocrysts are 1 to 2 mm i n diameter, but much of the hornblende i s much smaller, and i s completely replaced by secondary minerals. The groundmass i s f e l s i t i c , with numerous blocky plagioclase microphenocrysts and secondary minerals. Non-porphyritic Andesite Dikes and S i l l s Thin, l i g h t green dikes and s i l l s , usually l e s s than a metre wide, are not uncommon. In hand-specimen these are generally aphanites or very f i n e -grained phanerites, and lack phenocrysts. In thin-section i t can be seen that plagioclase laths make up 50% of the rock, elongate hornblendes another 5 to 10%, with the re s t of the rock composed of i n t e r s t i t i a l feldspar, quartz, chorite, and other secondary minerals. The elongate plagioclase and horn-blende c r y s t a l s are randomly oriented. The i n t e r s t i t i a l material may repre-sent a l t e r e d glass. Hornblende-Pyroxene Andesite Dikes Another type of intermediate composition dike i s very common through-out the area. This i s a gray p o r p h y r i t i c andesite with plagioclase, horn-blende, and clinopyroxene phenocrysts i n about equal proportions, t o t a l l i n g about 20% of the rock. The d i s t i n c t i v e feature of these dikes i s the presence of large hornblende c r y s t a l s , up to 1 cm long. Clinopyroxene and plagioclase are generally much smaller, and the l a t t e r are s i m i l a r i n color to the gray groundmass, and therefore inconspicuous i n hand-specimen. Horn-blende i s fresh, often 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 consists of randomly-oriented plagioclase and hornblende microphenocrysts with i n t e r s t i t i a l c h l o r i t e , prehnite, and other secondary minerals, perhaps replacing glass. 156 Rhyolite Dikes and S i l l s Thin r h y o l i t e dikes are common i n the eastern portion of Unit 2, and several larger s i l l s are present i n the western part of the unit. The r h y o l i t e i s white to pink, and i s extensively a l t e r e d . Plagioclase i s the only phenocryst i d e n t i f i a b l e i n hand-specimen, and may comprise 10% of the rock, but commonly much l e s s . R e l i c t zoning and a l b i t e twinning are evident i n thin-section, but the mineral i s completely replaced by a l b i t e and white mica. B i o t i t e and hornblende pseudomorphs are present i n amounts less than a few percent i n one sample. The groundmass consists of v a r i a b l e amounts of anhedral quartz and white mica. Age and C o r r e l a t i o n of Minor Intrusive Rocks The ages of these i n t r u s i v e rocks are uncertain. Andesitic to d a c i t i c and r h y o l i t i c rocks cut both Mississippian and T r i a s s i c s t r a t a , and dikes with low grade metamorphic mineral assemblages cut higher grade rocks i n the contact aureole of the Paul Peak Stock. Therefore they are probably Jurassic or younger i n age. A more precise age estimate can be given by considering the p o s t - T r i a s s i c record of volcanism i n the region. L i t h o l o g i c descrip-tions of these volcanic rocks (Campbell and Tipper, 1971; Cockfield, 1948) suggest that the minor i n t r u s i v e rocks i n the study area are re l a t e d to the Eocene to Oligocene Kamloops Group. Volcanic rocks i n the Kamloops Group are predominantly hornblende and augite andesites and dacites, b a s a l t s , and 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 . The abundance of hornblende i n these volcanic rocks (and i n the i n t r u s i v e rocks i n the study area) d i s t i n -guishes them from volcanics of other ages i n the region. The r h y o l i t i c i n t r u s i v e s are abundant only i n the eastern part of Unit 2, adjacent to the northwest-trending f a u l t separating the Nicola and Harper 157 Ranch Groups. Several dacite plugs also occur i n the un i t , one adjacent to a north-trending f a u l t . The intrusions were evidently emplaced preferen-t i a l l y along the f a u l t zones, perhaps contemporaneous with movement along the f a u l t s . 158 CHAPTER V. METAMORPHISM INTRODUCTION Low grade metamorphism or hydrothermal a l t e r a t i o n has affected a l l of the rock units i n the study area. Prehnite-pumpellyite facies mineral assemblages occur i n Carboniferous 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 volcanic flows, and i n p o s t - T r i a s s i c dikes and s i l l s of intermediate composition. Mudstones and limestones show few recognizable e f f e c t s of th i s a l t e r a t i o n . In addition, Paul Peak Stock i s surrounded by a contact-metamorphic aureole which i n i t s inner portion att a i n s the hornblende-hornfels f a c i e s . Upper T r i a s s i c rocks with a v a r i e t y of compositions are involved i n the aureole. The occurrence of low grade mineral assem-blages within the outer portion of Paul Peak Stock, and i n dikes cross-cutting the high grade aureole surrounding the pluton, demonstrates that s i g n i f i c a n t low grade metamorphism postdates emplacement of the pluton. The difference i n degree of a l t e r a t i o n between Carboniferous 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 of s i m i l a r composition suggests the p o s s i b i l i t y of a post-Permian, pre-Late T r i a s s i c low grade metamorphic event. LOW GRADE METAMORPHISM General Features Low grade metamorphic minerals replace plagioclase and mafic minerals, cement d e t r i t a l grains, f i l l veins and v e s i c l e s , and occur i n the groundmass 159 of volcanic rocks and rock fragments. Their f i n e grain s i z e often 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 minerals may have been overlooked. There-fore, the mineral assemblages presented below may be incomplete. 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 epidote are re a d i l y i d e n t i f i a b l e i n thin - s e c t i o n . Prehnite i s also often coarse enough for 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 d i f -f r a c t i o n analysis of a mineral separate from a vein. Pumpellyite, stilpnom-elane, and celadonite were only t e n t a t i v e l y i d e n t i f i e d i n thin-section, because many of the mineral properties are not measurable due to the fine grain s i z e and s c a r c i t y of these phases. These factors also preclude 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 techniques. Single c r y s t a l X-ray d i f f r a c t i o n or microprobe analyses are probably necessary to confirm these i d e n t i f i c a t i o n s . In the rocks with these metamorphic mineral assemblages, chemical dise q u i l i b r i u m at the scale of a thin - s e c t i o n i s the ru l e rather than the exception. This i s p a r t i c u l a r l y true of the T r i a s s i c v o l c a n i c l a s t i c rocks and the Paul Peak Stock. R e l i c t high temperature igneous phases such as hornblende, pyroxene, and intermediate plagioclase are common i n rocks i n which low grade mineral assemblages occur i n veins, cement or epimatrix, and i n aphanitic volcanic rock fragments. The secondary minerals were p r e c i p i t a t e d i n voids, and r e a d i l y replaced volcanic glass (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 pr e - e x i s t i n g c r y s t a l l i n e phases incompletely and s e l e c t i v e l y . This does not mean that l o c a l e q u i l i -brium may not have been achieved i n i n d i v i d u a l veins, and among the minerals replacing i n d i v i d u a l volcanic c l a s t s . With t h i s p o s s i b i l i t y i n mind, com-mon mineral assemblages i n which a l l phases are i n mutual contact were 160 noted, along with t h e i r s e t t i n g . These assemblages may represent an approach to chemical equilibrium between a f l u i d phase and the o r i g i n a l l y glassy portions of the rocks. Low grade minerals observed i n each group of rocks are l i s t e d i n Table IX. In the sections that follow, s i g n i f i c a n t t e x t u r a l and mineralogical features and mineral assemblages are presented for each such group. T r i a s s i c Rocks Low grade mineral assemblages are present i n v o l c a n i c l a s t i c s t r a t a of intermediate composition, and i n basic volcanic flows. In the v o l c a n i c l a s t i c rocks, growth of secondary minerals within volcanic fragments and i n the pore spaces or matrix between the c l a s t s has blurred grain outlines, but not o b l i t e r a t e d the c l a s t i c texture. C h l o r i t e , sphene, a l b i t e , prehnite (Fig. 40), and c a l c i t e are the most abundant secondary minerals. Common mineral assemblages include, along with ubiqui-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) Pumpellyite was found only i n three p y r o c l a s t i c sandstone samples from Unit 3. I t occurs as small anhedral granules barely v i s i b l e at a magnifica-t i o n of 125X. I t i s c h i e f l y recognizable by i t s color and strong pleochroism, from pale yellow to b r i g h t blue-green. Its r e l i e f i s somewhat les s than that of epidote, and i t exhibits anomalous blue-green interference colors. Mafic phenocrysts such as clinopyroxene and b i o t i t e are generally fresh, hornblende i s fresh or s l i g h t l y a l t e r e d to c h l o r i t e and sphene, but ortho-pyroxene i s completely replaced by a f i n e aggregate of the l a t t e r minerals. TABLE X. LOW GRADE METAMORPHIC MINERALS FOUND IN ROCKS OF DIFFERENT AGE AND LITHOLOGY IN THE STUDY AREA 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 i a s s i c Basic Volcanics M i s s i s s i p p i a n V o l c a n i c l a s t i c s Jurassic Paul Peak Stock Mesozoic or T e r t i a r y Dikes and S i l l s A c t i n o l i t e X X A l b i t e X X X X C a l c i t e X X X X X Celadonite* X X C h l o r i t e X X X X X Epidote Group X X X Z o i s i t e X X X C l i n o z o i s i t e X Epidote X X Potassium feldspar X X Prehnite X X X X Pumpellyite* X X X X Quartz X X X Sphene X X X X X S t ilpnome1ane * X X X = Mineral present * = Tentative i d e n t i f i c a t i o n based on incomplete o p t i c a l data 40. Prehnite vein i n p y r o c l a s t i c t u r b i d i t e from Unit 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 of c r y s t a l s are the t y p i c a l habit of prehnite found i n the study area. Thin-section, crossed n i c o l s , X 40. 163 A l t e r a t i o n of plagioclase i s s l i g h t to nearly complete, but o r i g i n a l i n t e r -mediate igneous compositions are often preserved. Large var i a t i o n s i n degree of plagioclase a l t e r a t i o n are frequently observed within a single thin-section. The usual products are s e r i c i t e or very fine-grained saussur-i t e i n which i n d i v i d u a l mineral species cannot be i d e n t i f i e d o p t i c a l l y . Less commonly, i t i s p a r t i a l l y replaced 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 basic volcanic rocks contain a s i m i l a r array of secondary minerals, but lack pumpellyite, and contain stilpnomelane. Observed mineral assem-blages include, along with 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 volcanics contain c a l c i t e ± quartz, z o i s i t e , or assemblage (d). Stilpnomelane occurs i n the groundmass i n ovoid, fine-grained r a d i a t i n g aggregates. I t resembles brown b i o t i t e , but lacks birds-eye mottling at ex t i n c t i o n . Because the material i s so fine-grained, i t cannot be d i s t i n -guished from b i o t i t e s o l e l y on the basis of o p t i c a l properties, since they are very 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 habit (which i s t y p i c a l of stilpnomelane), f i n e grain s i z e , and occurrence as a secondary phase associated with other low-grade minerals. The metamorphic mineral assemblages i n the Upper T r i a s s i c rocks are those of the prehnite-pumpellyite f a c i e s . There are no areal variations i n the mineral assemblages, except those c o n t r o l l e d by the bulk composition of the rocks, or associated with the contact aureole surrounding the Paul Peak Stock. 164 Paul Peak Stock A l t e r a t i o n of the primary igneous mineralogy of the Paul Peak Stock i s l i m i t e d to the hornblende-bearing, outer portion of the pluton. Plagio-clase and clinopyroxene i n the ce n t r a l d i o r i t e and gabbro are completely fresh. A l t e r a t i o n within the hornblende-bearing rocks i s r e l a t i v e l y minor. Plagioclase i n a l l samples i s mildly s a u s s u r i t i z e d . Much of the amphibole i s pale green, but shows the anomalous green and brown interference colors t y p i c a l of hornblende. The most severe a l t e r a t i o n i s found associated with pink potassium feldspar veins. In one sample of hornblende d i o r i t e , plagioclase i s replaced by potassium feldspar, and both clinopyroxene and hornblende are replaced by pale green a c t i n o l i t e . B i o t i t e i n the same rock i s p a r t i a l l y replaced by c h l o r i t e or c h l o r i t e + prehnite. The single sample of quartz monzonite studied has hornblende p a r t i a l l y replaced along cleavages by c h l o r i t e + sphene. Small angular i n t e r s t i c e s between hornblende and plagioclase c r y s t a l s are f i l l e d with the following assemblages: pumpellyite + sphene + c a l c i t e pumpellyite + c h l o r i t e + epidote Pumpellyite i n t h i s sample occurs as c l u s t e r s of r a d i a t i n g fibrous c r y s t a l s with 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 strong pleochroism noted above. Its interference colors are anomalous deep blue and brown. A l t e r a t i o n within the outer portion of the pluton i s patchy. A l i k e l y explanation i s that contact between the rock and a f l u i d phase was necessary for low grade metamorphic reactions to take place. Since the plutonic rock lacks s i g n i f i c a n t intergranular porosity, the f l u i d was only able to permeate small areas around l o c a l fracture systems i n the outer portion of the stock. 165 Rocks i n the core of the pluton, and even some quite close to the present contact, remained unaltered. The secondary minerals within the Paul Peak Stock are compatible with the prehnite-pumpellyite facies mineral assemblages of the surrounding T r i a s s i c rocks. These assemblages are probably the products of a sing l e episode of low grade metamorphism sometime a f t e r the emplacement of the stock, during the Early Jurassic or l a t e r . Dikes and S i l l s Andesitic and d a c i t i c dikes and s i l l s contain well developed low grade metamorphic mineral assemblages. The range of secondary minerals found i n these rocks i s generally s i m i l a r to that of the surrounding 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 , which have a s i m i l a r bulk composition. However, a c t i n o l i t e , stilpnomelane, and celadonite occur i n the dikes but not i n the v o l c a n i c l a s t i c s t r a t a , at l e a s t within the present sample of these rocks. In addition, the dikes contain epidote and c l i n o z o i s i t e as well as z o i s i t e . More than one member of the epidote group may be present within a si n g l e sample. The degree of a l t e r a t i o n i s generally greater i n these rocks than i n any other group, with the exception of the Paleozoic v o l c a n i -c l a s t i c rocks. Plagioclase i s generally moderately to strongly a l t e r e d to a l b i t e and either s e r i c i t e or saussurite. However, o r i g i n a l igneous plagioclase i s preserved i n some samples. Other phases which may replace plagioclase are c h l o r i t e , c a l c i t e , prehnite, and z o i s i t e . Hornblende i s the common mafic mineral i n these rocks, and i t i s p a r t i a l l y a l t e r e d to one of several mineral assemblages, each dominated by c h l o r i t e : 166 c h l o r i t e ± prehnite ± 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 ± quartz ± sphene c h l o r i t e + celadonite c h l o r i t e ± stilpnomelane ± c a l c i t e The most abundant secondary minerals i n the groundmass are c h l o r i t e , a l b i t e , sphene, c a l c i t e , and prehnite. In one sample, primary hornblende i n the groundmass has been replaced by pale green a c t i n o l i t e . Assemblages of minerals i n mutual contact have not been determined f o r the groundmass of these rocks. A vein assemblage i n one sample consists of: pumpellyite + z o i s i t e + c a l c i t e + quartz This i s the only occurrence of pumpellyite noted i n these rocks. Celadonite i s very fine-grained, and i s intergrown with c h l o r i t e . Its d i s t i n g u i s h i n g features are i t s habit, moderate r e l i e f , strong green color and pleochroism, and an anomalous blue-green interference t i n t . The dikes, s i l l s , and other small i n t r u s i v e bodies have undergone the same episode of a l t e r a t i o n which affected the T r i a s s i c s t r a t a and the Paul Peak Stock. Several of these dikes cut T r i a s s i c rocks which contain abun-dant b i o t i t e and a c t i n o l i t e formed during contact metamorphism around the Paul Peak Stock. The dikes do not show the severe r e c r y s t a l l i z a t i o n evident i n the country rocks, and contain the same low grade assemblages found i n dikes and country rocks outside the contact aureole. This i s further e v i -dence that major low grade a l t e r a t i o n postdates emplacement of the Paul Peak Stock. I f my suggested c o r r e l a t i o n of these i n t r u s i v e rocks with the Eocene to Oligocene volcanics of the Kamloops Group i s v a l i d , then t h i s a l t e r a t i o n probably also took place during Eocene to Oligocene volcanism, or perhaps even l a t e r . 167 Carboniferous V o l c a n i c l a s t i c Rocks Upper Mississippian to Lower Pennsylvanian 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 severely affected 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 intense that i n some samples alt e r e d feldspars, volcanic fragments, and matrix blend together and cannot be distinguished consistently. Extensive a l t e r a t i o n of plagioclase to s e r i c i t e or saussur-i t e prevents determination of i t s composition, but i t i s undoubtedly a l b i t i z e d . R e l i c t clinopyroxene, found i n a s i n g l e sample, i s the only surviving mafic phase, and i t i s al t e r e d around i t s margins to c h l o r i t e . Other samples contain pseudomorphs of 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 minerals i n rock fragments, epimatrix or cement, and veins, 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 si n g l e sample (MK-191), where i t occurs as t i n y b r i g h t green granules within a volcanic rock fragment. Celadonite i s present i n another sample (MK-193), where i t occurs intergrown with c h l o r i t e i n a l t e r e d c l a s t s . Prehnite has not been found. The mineral assemblages present i n most of the Carboniferous v o l c a n i -c l a s t i c rocks could occur i n e i t h e r the prehnite-pumpellyite or greenschist f a c i e s . However, the l o c a l presence of pumpellyite and celadonite, and the absence of a c t i n o l i t e , i n d i c a t e that the metamorphism which produced these assemblages was no higher i n grade than the prehnite-pumpellyite facies (Bishop, 1972; Wise and Eugster, 1964). These assemblages thus could have been produced by the p o s t - T r i a s s i c metamorphic episode which a f f e c t s the younger rocks. However, the extensive a l t e r a t i o n of the Carboniferous rocks, compared with the mild a l t e r a t i o n of the T r i a s s i c rocks, suggests 168 that a pre-Late T r i a s s i c episode of metamorphism was responsible for much of t h i s a l t e r a t i o n . This metamorphic event probably also produced mineral assemblages i n the z e o l i t e or prehnite-pumpellyite f a c i e s . No r e l i c t minerals i n d i c a t i v e of greenschist facies or higher grades are present. If such minerals had been produced, t h e i r complete replacement during 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 of the widespread r e l i c t igneous minerals i n the T r i a s s i c rocks, and high grade phases i n the contact-metamorphosed rocks. Textural evidence within the Carboniferous rocks themselves does not require an i n t e r p r e t a t i o n of more than one metamorphic event, and s p e c i f i c minerals cannot be assigned to one or the other event. The absence of prehnite and l i m i t e d occurrence of pumpellyite i n the older rocks i s i n t e r -esting, since they are probably s i m i l a r i n bulk composition to 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 contain these phases. A possible inference i s that the e a r l i e r low grade assemblages did not contain prehnite and pumpellyite, and that changes i n the assemblages during post-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 studies (Winkler, 1976, p. 196-197; Glassley, 1974) indicate that prehnite-pumpellyite facies mineral assemblages w i l l only e x i s t i n equilibrium with a f l u i d phase i n which there i s a low mole f r a c t i o n of CO2 (usually much less than 0.1). This r e l a t i o n s h i p may explain the absence of prehnite and near absence of pumpellyite i n the Carboniferous rocks. During the e a r l i e r metamorphic episode, pore f l u i d s may have contained enough dissolved CO2 to prevent formation of these minerals, generating the observed assemblages dominated by c h l o r i t e , a l b i t e , and c a l c i t e . Under low grade conditions, material transport necessary for 169 mineral reactions to take place probably depends heavily on the presence of a f l u i d phase (Zen and Thompson, 1974). Growth of secondary minerals during the f i r s t metamorphic episode may have reduced porosity and permeability of the v o l c a n i c l a s t i c rocks enough to prevent the free c i r c u l a t i o n of such pore f l u i d s during the l a t e r episode, and thus i n h i b i t i n g r e c r y s t a l l i z a t i o n . An a l t e r n a t i v e explanation for the difference i n i n t e n s i t y of a l t e r a -t i o n between the rocks of d i f f e r e n t ages i s that two d i f f e r e n t pressure-temperature regimes of p o s t - T r i a s s i c metamorphism have been juxtaposed by f a u l t i n g . However, the small plutons intruded along and near the f a u l t zone separating the Carboniferous and T r i a s s i c rocks also contain prehnite-pumpellyite facies mineral assemblages. Evidently 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 experienced s i m i l a r pres-sures and temperatures during t h i s metamorphism. Conditions of Metamorphism Experimental phase e q u i l i b r i a studies allow broad l i m i t s to be placed on metamorphic conditions during formation of prehnite-pumpellyite facies mineral assemblages (Zen and Thompson, 1974; Winkler, 1976). Temperatures were probably between 200°C and 400°C, and the pressure less than 2.5 to 3.0 kb. The low-temperature l i m i t i s provided by the formation of a l b i t e from analcime + quartz, taken by some authors as a convenient boundary between diagenesis and low grade metamorphism. The high-temperature l i m i t i s the breakdown of prehnite to z o i s i t e + grossular + quartz + water. The high-pressure l i m i t i s provided by the formation of lawsonite from various other Ca-Al s i l i c a t e s . Prehnite and pumpellyite can p e r s i s t to pressures above t h i s , but lawsonite would probably be present as w e l l . 170 A c t i n o l i t e i s present within the Paul Peak Stock, and i n one dike which intrudes metavolcanic rocks near the margin of the stock (Fig. 41). Although c h a r a c t e r i s t i c of basic rocks i n the greenschist f a c i e s , a c t i n o l i t e also occurs with pumpellyite i n mineral parageneses t r a n s i t i o n a l between the prehnite-pumpellyite and greenschist f a c i e s , sometimes re f e r r e d to as the pumpe l l y i t e - a c t i n o l i t e f a c i e s . However, pumpellyite i s absent from these samples, and prehnite, usually absent i n the pumpelly i t e - a c t i n o l i t e facies (Bishop, 1972), i s present. In both samples the a c t i n o l i t e replaces e i t h e r hornblende or clinopyroxene, and i t i s not i n contact and may not be i n equilibrium with the prehnite-bearing mineral assemblages. Therefore the si g n i f i c a n c e of the occurrences i s unknown. CONTACT METAMORPHISM The contact metamorphic aureole surrounding the Paul Peak Stock encom-passes Upper T r i a s s i c mudstone, volcanic and l i t h i c sandstones, and basic volcanics i n Units 5 and 6. Contact metamorphic e f f e c t s can be recognized up to 600 m away from the exposed i n t r u s i v e contact. Most of the aureole i s characterized by mineral assemblages of the albite-epidote hornfels f a c i e s . At l e a s t l o c a l l y , an inner zone i n the hornblende-hornfels facies can be recognized (Fig. 41). Albite-Epidote-Hornfels Facies Rocks of the albite-epidote-hornfels facies are t y p i f i e d by the pres-ence of a c t i n o l i t e and b i o t i t e . The mudstones possess a t y p i c a l h o r n f e l s i c texture i n hand-specimen and thi n - s e c t i o n . The volcanic and l i t h i c sand-stones and basic volcanics show l i t t l e e f f e c t of r e c r y s t a l l i z a t i o n i n 0 '• 0.5 km / . /, 6b . f : T|43 I 1 93 Is-' \ \6b\/ -A ' r - v , 6 V. KEY TO SYMBOLS Biotite + K-feldspar + andesine Hornblende + biotite or clinopyroxene Actinol ite + biot i te Act ino l i te + ch lo r i te Chlor i te + st i lpnomelane -•"—u--u- Hornblende isograd ' — • — Actinol ite i s o g rod (Tick marks on high g r a d e s ide , dotted where i n f e r r e d benea th Q u a t e r n a r y depos i t s ) A , 0 \ / \ 5 \ \ \ \ •. 136 * \ '• • .. 135 \ • ' . . | Q | Quaternary deposits LOWER JURASSIC Paul Peak Stock UPPER TRIASSIC NICOLA GROUP | 6b | Mafic volcanic rocks I 6 | Mudstone, lithic sandstone, andesitic pyroclastics | 5 | Thin-bedded mudstone \ \ \ \ ' *• » ' \ A 5 , ' . . ^ . ' t- + i * +X. t . 1 . 4 < 4 \ N^. < < 1 \ F i g . 41. Map of mineral assemblages and isograds from the contact metamorphic aureole of the Paul Peak Stock. ,_, 172 hand-specimen, but i n thin - s e c t i o n both mineralogic and text u r a l changes are evident. B i o t i t e , a c t i n o l i t e , and other metamorphic minerals grow i n random or i e n t a t i o n within and between volcanic and l i t h i c fragments. Recrys-t a l l i z a t i o n i s incomplete, however, as high-temperature igneous phases such as clinopyroxene and hornblende are only p a r t i a l l y replaced by a c t i n o l i t e + b i o t i t e , or 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 feldspar i s present i n several samples, but i s too f i n e -grained for exact i d e n t i f i c a t i o n . Volcanic p l a g i o c l a s e , probably o r i g i n a l l y andesine or labradorite, has been replaced i n some cases by a c t i n o l i t e and b i o t i t e , suggesting that a l b i t e i s stable rather than a more c a l c i c p l a g i o -clase, as i t should be i n t h i s f a c i e s . Some common mineral assemblages noted i n rocks of d i f f e r e n t composition are presented i n Table XI. These have not been checked for mutual contact of a l l phases, so a l l minerals may not be part of a sing l e equilibrium assemblage. Numbers i n parentheses are sample numbers shown on Pig. 41. If rocks of lower grade than t h i s were formed farther from the pluton during contact metamorphism, they are indis t i n g u i s h a b l e from those with prehnite-pumpellyite f a c i e s metamorphic assemblages. Thus the e a r l i e s t recognizable contact metamorphic e f f e c t as the pluton i s approached i s the appearance of 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 of t h i s zone boundary i s not well c o n t r o l l e d . Hornblende-Hornfels Facies The inner zone of hornblende-hornfels facies i s represented by three samples, a l l found within 100 m of the i n t r u s i v e contact. They are charac-t e r i z e d by the presence of hornblende rather than a c t i n o l i t e , and a more TABLE XI. ALBITE-EPIDOTE-HORNFELS FACIES MINERAL ASSEMBLAGES IN THE CONTACT METAMORPHIC AUREOLE OF PAUL PEAK STOCK Rock Composition Sample Number Mineral Assemblage P e l i t i c Hornfels 106 A c t i n o l i t e , b i o t i t e , quartz, feldspar Basic volcanic 141 A c t i n o l i t e , b i o t i t e , p l a g i o c l a s e , c h l o r i t e , sphene Volcanic and l i t h i c e l a s t i c s 105, 134 A c t i n o l i t e , b i o t i t e , quartz, feldspar 102 A c t i n o l i t e , b i o t i t e , feldspar, sphene, c a l c i t e 135, 136 A c t i n o l i t e , b i o t i t e , sphene, (epidote) 132 A c t i n o l i t e , c h l o r i t e , sphene, z o i s i t e , c a l c i t e 174 c a l c i c plagioclase (andesine) where i t s composition was determinable. S t a t i c r e c r y s t a l l i z a t i o n i s more extensive i n these rocks, and metamorphic minerals are somewhat coarser-grained than i n the lower grade rocks. This zone may be absent or very t h i n around the southeastern end of the i n t r u s i o n . A c t i n -o l i t e - b e a r i n g rocks were found within 100 m of the contact i n t h i s area. One sample of p e l i t i c hornfels i n t h i s zone (130) contained the mineral assemblage: quartz, potassium feldspar, b i o t i t e , p l a g ioclase (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 replaced by c h l o r i t e , a retrograde e f f e c t which occurred during cooling or during subsequent low grade metamorphism. A le u c r o c a t i c vein within t h i s sample contained: quartz, potassium feldspar, p l a g i o c l a s e , tremolite, diopside, c a l c i t e . C a l c i t e occurs i n very small q u a n t i t i e s , but i f i t i s part of the equilibrium assemblage, then the following reaction assemblage may be present: tremolite + c a l c i t e + quartz = diopside. Two d i f f e r e n t mineral assemblages were found i n basic metavolcanic rocks: hornblende, pl a g i o c l a s e , b i o t i t e , sphene (93) clinopyroxene, hornblende, pl a g i o c l a s e , b i o t i t e (143) Microtextures of the clinopyroxene demonstrate that i t i s a prograde meta-morphic phase, not a r e l i c t igneous mineral. However, i t i s p a r t l y replaced by a c t i n o l i t e + c h l o r i t e , another retrograde e f f e c t . 175 Ef f e c t s of Subsequent Low Grade Metamorphism Mineralogic changes which could be a t t r i b u t e d to subsequent low grade metamorphism are r e l a t i v e l y minor. These include the replacement of b i o -t i t e and clinopyroxene i n the hornblende-hornfels facies rocks described above, although t h i s could also have occurred during cooling of the i n t r u -sion. However, a vein i n a basic metavolcanic sample (143) within the horn-blende-hornfels facies zone contains the assemblage: prehnite + c h l o r i t e + c a l c i t e which i s t y p i c a l of the l a t e r low grade metamorphic assemblages. Conditions of Metamorphism From experimental work on metamorphic mineral e q u i l i b r i a , Turner (1968) suggests that mineral assemblages of the albite-epidote-hornfels facies form at temperatures of 300° to 450°C within the pressure range P„ „ = 1 to 3 kb. The hornblende-hornfels facies represents a broader H2O range of temperatures, from 400° to 600° or 700°C i n the same pressure range. 176 CHAPTER VI. STRUCTURAL GEOLOGY INTRODUCTION The Harper Ranch Group and Nicola Group are separated within the study area by a northwest-trending, v e r t i c a l f a u l t . Both sequences have been folded on a regional scale, and also e x h i b i t some small-scale f o l d s . The portion of the study area underlain by the Harper Ranch Group i s too small to reveal the major regional structure of the group, or to af f o r d adequate comparison of i t s s t r u c t u r a l geometry with that of the Nicola Group. In addition, the s t r u c t u r a l s t y l e of these rocks varies with t h e i r l i t h o l o g y . Therefore, the s t r u c t u r a l h i s t o r i e s of these juxtaposed sequences, and t h e i r s i m i l a r i t i e s or differences, remain uncertain. None of the rocks i n the study area possess a regional penetrative cleavage, but fractures and j o i n t s with extremely variable orientations are very common. The low metamorphic grade of the rocks implies that a l l deformation took place at shallow b u r i a l depths. A map of 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 Plate VI (in pocket), along with cross-sections and equal-area pl o t s of the s t r u c t u r a l data. FOLDING Harper Ranch Group The Harper Ranch Group i n the study area forms a northwest-trending, east-facing homocline. Bedding dips very steeply to the northeast or 177 southwest, but s t r a t i g r a p h i c tops are consistently towards the east. The larger map pattern of the Harper Ranch Group east of the study area (Fig. 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 of the Pennsylvanian and Permian lime-stone northeast of McGregor Creek, shows the regional structure to be much more complex, probably involving several generations of major folds with d i f f e r i n g a x i a l trends. Mesoscopic folds are uncommon i n the Harper Ranch Group, and were observed i n only a few outcrops. A l l of these folds were open and concen-t r i c , with axes plunging moderately to the southeast or southwest. An equal-area pro j e c t i o n of s t r u c t u r a l data from the Harper Ranch Group (Plate VI) shows the predominance of n e a r - v e r t i c a l dips i n the north-west-trending homocline. The few divergent attitudes suggest that the locus of poles to bedding can be approximated by a great c i r c l e with a pole at 143/50, nearly coincident with the measured axis of one of the few minor fol d s . Additional s t r u c t u r a l data over a larger area are needed to evaluate the possible s i g n i f i c a n c e of t h i s observation and to determine whether these rocks were affected by the regional Permo-Triassic orogenic event described by Read and Okulitch (1977). Nicola Group The map units which comprise the Nicola Group define two major north-west-trending f o l d s , the Paul Ridge a n t i c l i n e on the west and the Paul Ridge syncline on the east. The cores and common limb of the folds are complicated by steep f a u l t s , making t h e i r i n f e r r e d geometry somewhat speculative. The Paul Ridge a n t i c l i n e i s a t i g h t f o l d overturned toward the west. 178 The overturned limb crops out along the western part of Paul Ridge and i n the Dome H i l l s , and i s characterized by v a r i a b l e but generally steep east-ward dips. Stratigraphic tops face uniformly westward on t h i s limb. The f o l d i s i n f e r r e d to close within the western part of Unit 2, west of the narrow s l i v e r of Unit 3 which crops out on the summit of Paul Ridge (Plate VI). Bedding within t h i s s l i v e r appears to be upright. The portion of Unit 2 just to the east of t h i s s l i v e r , and separated from i t by a v e r t i c a l f a u l t , i s interpreted as p r i m a r i l y part of the upright limb of the a n t i c l i n e ; bedding along i t s eastern margin dips and faces eastward. However, part of the f o l d closure, o f f s e t from that to the west by the aforementioned f a u l t , may be present i n the southwest corner of t h i s area, as indicated by several westward dips, one with bedding facing west (Plate I; Plate VI, cross-section C - C ) . A moderate northwestward plunge „for the f o l d i s indicated by the trend and plunge of minor folds i n the core zone, and by a few bedding attitudes with east-west s t r i k e s and moderate northward dips, which may l i e near the hinge of the f o l d . The core of the Paul Ridge syncline i s cut by the northwest-trending f a u l t which bounds the eastern portion of Unit 3 on i t s west side. The p y r o c l a s t i c flows i n t h i s part of Unit 3 are massive and very t h i c k l y bedded, so bedding attitudes are r a r e l y obtainable. However, where bedding was observed, dips were moderately to steeply westward, and although no top indicators were found, I i n f e r t h i s section to be upright, and to form the eastern limb of the Paul Ridge syncline. The r e p e t i t i o n of Unit 2 to the east of t h i s portion of Unit 3 supports t h i s i n t e r p r e t a t i o n . The western limb of the syncline i s the upright limb of the Paul Ridge a n t i c l i n e within Unit 2. The hinge zone of the syncline at t h i s s t r u c t u r a l l e v e l has 179 apparently been e n t i r e l y eliminated by f a u l t i n g , and d i f f e r e n t s t r a t i g r a p h i c l e v e l s on the two limbs are juxtaposed across the f a u l t . In the easternmost portion of Unit 2, bedding dips nearly v e r t i c a l l y , and generally northeastward. No top indic a t o r s were found here, but the section probably faces westward, and represents a s l i g h t l y overturned por-t i o n of the eastern limb of the Paul Ridge syncline. However, i t i s separ-ated from Unit 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 not cer t a i n . The geometry of the Paul Ridge a n t i c l i n e r e s u l t s from considerable compressive s t r a i n . The rocks within the a x i a l region of the f o l d possess no s l a t y cleavage or other ind i c a t o r s of penetrative s t r a i n within beds (aside from features which can be at t r i b u t e d to sedimentary compaction normal to bedding). Tightening of the f o l d must therefore have been achieved by removal of material from the core zone by bedding-plane shear, rather than by homogeneous penetrative s t r a i n . The necessary interbed s t r a i n could e a s i l y have been accomodated by the thin-bedded mudstone of Unit 2, which forms the core of the f o l d . Mesoscopic folds are common only i n the thin-bedded mudstone facies of the Nicola Group. Thus they are found mostly i n Units 2 and 5. The geometry of these folds i s quite v a r i a b l e , but the most common folds are open to close, concentric and nearly p a r a l l e l , with layer thickness remain-ing nearly constant around the folds (Class lb of Ramsay, 1967). A few ti g h t folds occur, which have noticeably thickened hinges (Class Ic of Ramsay). None of these folds possess an a x i a l plane cleavage. The orientations of the folds are also quite v a r i a b l e . In central Paul Ridge, the folds plunge shallowly to moderately northwestward, and are 180 probably coaxial with the Paul Ridge a n t i c l i n e . On the overturned limb of the a n t i c l i n e (Western Paul Ridge and Dome H i l l s ) , the folds plunge moder-ately to steeply to the west, north, and northeast. In a l l three areas, the vergence of north to northwest-trending minor f o l d s , where determinable, i s consistent with t h e i r p o s i t i o n on the major f o l d : Z-type on the over-turned limb, and S-type on the upright limb. Thus at l e a s t these folds probably are ge n e t i c a l l y r e l a t e d to and formed synchronously with the major folds. The o r i g i n of the northeast-trending minor folds on the overturned limb i s more problematic. The locus of poles to bedding i n the Dome H i l l s can be approximated by a great c i r c l e with a pole at 42/56, nearly coincident with the axes of a group of northeast-trending minor f o l d s . Possibly these folds form a l a t e r generation superimposed on the e a r l i e r northwest-trending major and minor fo l d s . However, superposition of the two trends has not been observed i n outcrop. No clear separation can be made between the two possible f o l d sets on the basis of a x i a l trend or f o l d s t y l e , and nearly a l l of the minor folds have northwest-trending a x i a l planes which dip moderately to steeply northeast. Thus an in t e r p r e t a t i o n of more than one f o l d gener-ation cannot be substantiated with the present data. The overturned limb of the Paul Ridge a n t i c l i n e i s cut by the Paul Peak Stock. In Chapter IV I presented arguments i n support of a Lower Jur-assic (about 200 m.y.) age for the stock. This l i m i t s the time of formation of these major folds to the Latest T r i a s s i c or E a r l i e s t J u r a s s i c . This deformation was probably part of the "I n k l i n i a n orogeny" (Douglas and others, 1970), which resulted i n regional u p l i f t and erosion, warping and f a u l t i n g of the proximal facies of the Nicola Group (Schau, 1970) , and in t r u s i o n and 181 unroofing of the 200 m.y. plutons within the Nicola arc. Schau (1970) c a l -culated the resultant s t r a i n within the type area of the Nicola Group at less than 5 percent. The presence of major overturning within the Nicola Group i n the study area suggests that deformation was much more intense and s t r a i n much greater within the b a s i n a l facies of the Nicola Group east of the arc terrane. FAULTING Northwest-trending, steeply dipping f a u l t s segment the eastern part of the Nicola Group, and separate i t from the Harper Ranch Group to the east. The f a u l t s postdate the major folds i n the Nicola Group. No exposures of the f a u l t s were found, and t h e i r traces can be located accurately only along the southern slope of Paul Ridge where exposures are best. However, the topographic r e l i e f on the surface f a u l t traces shows the f a u l t s to be e s s e n t i a l l y v e r t i c a l . 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 1000 m, but the sense of motion on the f a u l t s cannot be s p e c i f i e d . Smaller north-trending f a u l t s o f f s e t the contact between the Nicola and Harper Ranch Groups. These f a u l t s have r i g h t - l a t e r a l separations of a few tens to several hundred metres. North and northwest-trending f a u l t systems are common i n the surrounding portions of the Intermontaine b e l t (Campbell and Tipper, 1971; Schau, 1970). These f a u l t s are generally older than the Miocene and younger volcanics which mantle large parts of the region. The major f a u l t which separates the Nicola and Harper Ranch Groups i n the study area projects to the southeast across the South Thompson River, where i t s trace i s apparently covered by a large body of these Late T e r t i a r y v o l -canics (Fig. 2). Campbell and Tipper (1971) document o f f s e t s of Eocene 182 volcanics along f a u l t s with these trends, but record a much greater density of f a u l t s and fractures i n T r i a s s i c and Jurassic rocks. They postulate that f a u l t i n g began i n the Mesozoic and continued i n t e r m i t t e n t l y into the early T e r t i a r y . 183 CHAPTER VII. SUMMARY AND CONCLUSIONS The "Cache Creek Group" as previously mapped i n the Kamloops area a c t u a l l y consists of two sequences of d i f f e r e n t ages, separated by a northwest-trending v e r t i c a l f a u l t . To the east l i e the Mississippian to Permian mudstone, redeposited t u f f , and limestone designated as the Harper Ranch Group. Upper T r i a s s i c rocks of the Nicola Group l i e west of the f a u l t , and consist of 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 volcanic flows, l i t h i c sandstone and conglomerate, and rare b a s i n a l limestone. The study area includes only the lower part of the Harper Ranch Group (Unit 1), which forms a northwest-trending, east-facing homocline. Nearly a l l of the section, more than two kilometers thick, consists of mudstone and v o l c a n i c l a s t i c rocks. A thi n marine limestone near the base contains f o s s i l s of Late Mis s i s s i p p i a n age. A Lower Pennsylvanian limestone forms the top of the section studied, although exposures continue to the east. This sequence accumulated i n a marine basin within a volcanic arc system, probably within the f r o n t a l arc. This portion of the basin was r e l a t i v e l y d i s t a n t from the volcanic centers, since none of the volcanic d e t r i t u s i s coarser than very coarse sand or granule s i z e , and no flows are present i n the section. The volcanic sandstones consist of volcanic l i t h i c fragments and phenocrysts i n d i c a t i n g an andesitic to d a c i t i c source. Most of the detritus i s probably p y r o c l a s t i c i n o r i g i n , produced by shallow submarine eruptions. This material was reworked and redeposited i n deeper water below wave base by t u r b i d i t y currents and high-concentration subaqueous flows, and i s interlayered with hemipelagic mudstones. 184 The limestone of Unit lA i s made up of wackestones, packstones, and grainstones, and contains a diverse marine fauna, i n d i c a t i n g shallow marine deposition. I t contains v i r t u a l l y no volcanic d e t r i t u s coarser than clay s i z e , and probably accumulated on a shallow s h e l f at a considerable distance from the volcanic centers, or during a period of volcanic quiescence. Rela-t i v e changes i n the p o s i t i o n of sea l e v e l with respect to the basin f l o o r , of e i t h e r tectonic or e u s t a t i c o r i g i n , must be postulated to explain the juxtaposition of deep water mudstones and t u r b i d i t e s overlying shallow mar-ine mudstone. This l a t e Paleozoic arc terrane was probably separated from the contin-ental margin by a back-arc basin. Closing of t h i s basin resulted i n c o l -l i s i o n of the arc with older terranes to the east, which may account for the pre-Late T r i a s s i c deformation and low grade metamorphism which a f f e c t Paleozoic eugeoclinal rocks i n the region south of Kamloops. Within the study area, Permo-Triassic deformation cannot be demonstrated with the pres-ent data, but the rocks appear to have undergone low grade metamorphism p r i o r to the Late T r i a s s i c . Subsequent to the Early T r i a s s i c orogenesis, a new volcanic arc system formed i n the Late T r i a s s i c above an east-dipping subduction zone. The volcanic arc i t s e l f i s represented by the volcanic rocks of the Nicola Group west of Kamloops. Within the study area, rocks of the Nicola Group consist of at l e a s t three kilometers of sediments and v o l c a n i c l a s t i c s which accumulated i n deep water within a back-arc basin east of the volcanic arc. Pelagic and hemipelagic mudstones are abundant or predominant i n the section. The v o l c a n i c l a s t i c rocks, l i t h i c sandstones and conglomerates, and limestones were deposited by t u r b i d i t y currents and high-concentration 185 density flows. B a s a l t i c or andesitic volcanics were erupted on the sea f l o o r s poradically, forming massive and pillowed flows i n Units 2 and 6. V e r t i c a l v a r i a t i o n s i n the r e l a t i v e proportions of these l i t h o l o g i e s define f i v e u n i t s , numbered 2 through 6. Conodonts extracted from the limestones y i e l d Karnian ages for the e n t i r e sequence. Volcanic t u r b i d i t e s i n Units 2, 4, and 5 are composed of reworked t u f f probably derived from the Nicola volcanic centers to the west, based on a comparison of phenocryst mineralogy. Unit 3 and the lower portion of Unit 6 are composed of andesitic p y r o c l a s t i c flows and t u r b i d i t e s , which probably o r i g i n a t e d from shallow marine volcanic vents l y i n g to the east. This resulted i n a l a t e r a l f a cies t r a n s i t i o n within Unit 3 from very thick pyro-c l a s t i c flows i n the east 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 Units 5 and 6 contain sedimentary and volcanic d e t r i t u s , including abundant chert. They were probably derived from the emergent Pinchi g e a n t i c l i n e to the west, which exposed oceanic rocks of the Cache Creek Group. D e t r i t a l blue amphiboles found i n f i n e -grained redeposited limestones suggest that at l e a s t some of t h i s carbonate sediment was derived from shallow waters surrounding the Pinchi terrane. The Nicola depositional basin probably stretched from the Late T r i a s s i c continental margin (miogeocline) westward to the accreted oceanic rocks of the Pinchi g e a n t i c l i n e . The volcanic centers of the Nicola arc formed on an east-facing paleoslope on the western side of the basin. C l a s t i c material derived from the Pinchi terrane was thus able to f i l t e r through the volcanic chain and accumulate i n the basin to the east. Marine deposition of the Nicola Group was ended i n the Latest T r i a s s i c or E a r l i e s t Jurassic by the " I n k l i n i a n orogeny," which produced a regional 186 angular unconformity beneath Lower Jurassic rocks. Although deformation within the arc terrane was mild, the Nicola Group i n the study area was deformed into a p a i r of northwest-trending major f o l d s . 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 overturned toward the west. The Paul Ridge syncline i s apparently upright and more open, but i t s a x i a l region has been eliminated by l a t e r f a u l t i n g . A number of northwest-plunging minor folds appear to be coaxial with the major fo l d s . The deform-ation took place at shallow depths, and d i d not lead to formation of a pene-t r a t i v e f a b r i c within the rocks. The overturned limb of the Paul Ridge a n t i c l i n e i s cut by the Paul Peak Stock, which was probably emplaced during 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 pluton shows incomplete concentric zoning, with i t s composition varying from o l i v i n e clinopyroxenite i n the core to hornblende granite at the southeastern extremity. The pluton i s s i m i l a r to zoned "Alaskan" type mafic-ultramafic complexes i n i t s compo-s i t i o n and tectonic s e t t i n g . The compositional v a r i a t i o n and zoning i n the outer part of the pluton could have been produced 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 and c r y s t a l s e t t l i n g of a s i l i c a - s a t u r a t e d melt of intermediate compo-s i t i o n , followed by upward d i a p i r i c i n t r u s i o n of the s t r a t i f o r m cumulates. The ultramafic core probably 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 of a mafic, a l k a l i n e melt. Contact metamorphism of the surrounding sedimentary and volcanic rocks reaches the hornblende hornfels facies i n outcrops nearest the i n t r u s i v e contact, although most of the aureole i s i n the albite-epidote amphibolite f a c i e s . The timing of subsequent events i s not well constrained. Northeast-187 trending minor folds i n the Nicola Group may have formed at a l a t e r , indeter-minate time than the major folds i n the area. Northwest and north-trending v e r t i c a l f a u l t s i n the study area may have formed i n mid-Mesozoic to Early T e r t i a r y time, based on the record of f a u l t i n g i n adjacent areas. A v a r i e t y of small dikes, s i l l s , and plugs intrude both the Nicola Group and Harper Ranch Group. Most of these are andesites or dacites, with some r h y o l i t e s also present. The composition and phenocryst mineralogy of these i n t r u s i v e s suggests that they are rela t e d to the Eocene to Oligocene volcanics of the Kamloops Group. The intrusions were emplaced p r e f e r e n t i a l l y along f a u l t zones, perhaps contemporaneous with movement along the f a u l t s . Prehnite-pumpellyite facies metamorphism has affected a l l of the rock units i n the study area, including the dikes of probably Eocene to Oligocene age. The e f f e c t s of t h i s metamorphism are most pronounced i n the volcanic and v o l c a n i c l a s t i c rocks and the dikes and s i l l s . Low grade minerals replace plagioclase and mafic minerals, cement d e t r i t a l grains, f i l l veins and v e s i c l e s , and occur i n the groundmass of the p o r p h y r i t i c rocks. 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M., and Cowan, D. S., 1977, A dynamic, scaled model of accre-t i o n at trenches and i t s implications for Franciscan tectonics (abstr.): Geological Society of America Abstracts with Programs, v. 9, no. 4, p. 499-500. S i l v e r , E. A., and Moore, J . C , 1978, The Molucca Sea c o l l i s i o n zone, Indonesia: Journal of Geophysical Research, v. 83, p. 1681-1691. 197 Souther, J . G., 1977, Volcanism and tectonic environments i n the Canadian C o r d i l l e r a — a second look: Geological Association of Canada Special Paper no. 16, p. 3-24. Speed, R. C , 1977, Island-arc and other paleogeographic terranes of Late Paleozoic age i n the western Great Basin: in Stewart, J . H., Stevens, C. H., and F r i t c h e , A. E. (eds.), Paleozoic Paleogeography of the Western United States: Society of Economic Paleonotologists and Mineralogists, P a c i f i c section, P a c i f i c Coast Paleogeography Sympo-sium 1, p. 349-362. , 1978a, Basinal terrane of the early Mesozoic marine province of the western Great Basin: in Howell, D. G., and McDougall, K. A. (eds.), Mesozoic Paleogeography of the Western United States: Society of Economic Paleontologists and Mineralogists, P a c i f i c Section, P a c i f i c Coast Paleogeography Symposium 2, p. 2 37-252. , 1978b, Paleogeographic and plate tectonic evolution of the early Mesozoic marine province of the western Great Basin: in Howell, D. G., and McDougall, K. A. (eds.), Mesozoic Paleogeography of the Western United States: Society of Economic Paleontologists and Mineralogists, P a c i f i c Section, P a c i f i c Coast Paleogeography Symposium 2, p. 253-270. Stevens, C. 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Wise, W. S., and Eugster, P. H., 1964, Celadonite: synthesis, thermal s t a b i l i t y , and occurrence: American Mineralogist, v. 49, p. 1031-1083. Wray, J . L., 1972, Environmental d i s t r i b u t i o n of calcareous algae i n Upper Devonian reef complexes: Geologische Rundschau, v. 61, p. 578-584. Wyllie, P. J . , 1971, The Dynamic Earth: Textbook i n Geosciences: New York, Wiley, 416 p. Yoder, H. S., and T i l l e y , C. E., 1962, Or i g i n of b a s a l t i c magmas: an experimental study of natural and synthetic rock systems: Journal of Petrology, v. 3, p. 342-532. .199 E., and Thompson, A. B., 1974, Low grade regional metamorphism: mineral equilibrium r e l a t i o n s : Annual Reviews of Earth and Planetary Science, 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 Geological Survey of Canada V i c t o r i a , B. C. Conodonts are i l l u s t r a t e d i n Plate V. G.S.C. Loc. 93450 F i e l d No. M2, NTS 92 1/9, Kamloops, Grid. No. 897189, Lat. 50° 41.8'N, Long. 120° 18.6'W. Conodonts Neogondolella navicula navicula (Huckriede) - about 40 specimens. (Plate V, F i g . 6 and 7) Xaniognathurs? sp. - 2 specimens-Enantiognathus ziegleri (Diebel) - 1 specimen Neospathodus sp. - 3 specimens N. sp. c f . N. newpassensis (Mosher) - 1 specimen (Plate V, Fi g . 1) Cypridodella sp. c f . C. muelleri (Tatge) - about 3 specimens (Plate V, F i g . 3) Ozarkodina t o r t i l i s (Tatge) - 2 specimens (Plate V, F i g . 2) Hindeodella? sp. - 1 specimen various other fragments. Age and Remarks Late T r i a s s i c , Karnian, possibly early Karnian on the basis of N. newpassensis and high degree of v a r i a b i l i t y i n N. navicula navicula. The l a t t e r include v a r i a t i o n i n shape from elongate to 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 of prominent p o s t e r i o r d e n t i c l e from erect to p o s t e r i o r l y pro-j e c t i n g , and i n some the development of l a t e r a l l y crenulate anterior margins of the platform. These v a r i a t i o n s have been observed i n other c o l l e c t i o n s of t h i s form-species of Karnian age. G.S.C. Loc. 93451 F i e l d No. M4, NTS 92 1/9, Kamloops, Grid. No. 894194, Lat. 50° 42.2'N, Long. 120° 18.9'W. Conodonts Enantiognathus ziegleri (Diebel) - 1 specimen (Plate V, Fig . 5) Cypridodella sp. c f . C. muelleri (Tatge) - 1 specimen (Plate V, F i g . 4) Neogondolella navicula navicula (Huckriede) - 1 specimen N. sp. (possible n. sp. s i m i l a r to N. regale Mosher i n i t s high prominent carina and di s c r e t e denticles) • about 8 specimens (Plate V, Fi 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, Grid. No. 926192, Lat. 50° 42.0'N, Long. 120° 16.3'W. Conodonts Metapolygnathus polygnathiformis (Budurov and Stefanov) about 13 specimens (Plate V, F i g . 10) Age T r i a s s i c , the range of t h i s taxon i s l a t e Ladinian to la t e Karnian. In abundance, however, i t i s most char-a c t e r i s t i c of Karnian age rocks. G.S.C. Loc. 93453 F i e l d No. M23, NTS 92 1/9, Kamloops, Grid. No. 952199, Lat. 50° 42.4'N, Long. 120° 13.9'W. Conodonts Metapolygnathus polygnathiformis (Budurov and Stefanov) about 15 specimens (Plate V, F i g . 11 and 12) Age Late T r i a s s i c , Karnian, as i n G.S.C. Loc. 93452. G.S.C. Loc. 93454 F i e l d No. M25, NTS 92 1/9, Kamloops, Grid No. 907226, Lat. 50° 43.8'N, Long. 120° 17.7'W. Conodonts Metapolygnathus polygnathiformis (Budurov and Stefanov) 2 specimens Age T r i a s s i c , probably Karnian G.S.C. Loc. 93455 F i e l d No. M27, NTS 92 1/9, Kamloops, Grid No. 905229, Lat. 50° 44.0'N, Long. 120° 17.9'W. Conodonts a single anterior fragment, possibly of Neogondolella or Metapolygnathus Age probably T r i a s s i c 203 APPENDIX I I . STRUCTURAL DATA Grid numbers r e f e r to M i l i t a r y Grid shown on Plates I and VI. HARPER RANCH GROUP /dip of bedding Grid East Grid North 139/85 E 98.35 20.1 108/90 98.3 19.75 144/82 E 98.65 19.75 145/61 E 98.45 19.55 135/81 W 98.6 19.5 150/87 W 98.75 19.6 130/68 W (Overturned) 98.8 19.35 110/82 W 99.05 19.2 151/81 W 99.25 19.3 145/80 W 99.35 19.2 162/63 W 99.15 19.1 138/85 E 99.2 19.15 171/42 E 99.3 19.1 163/78 E 99.7 19.05 156/80 W 99.9 19.02 98/64 S 99.1 18.85 111/58 S 99.05 18.8 121/59 S 99.05 18.75 116/88 N 99.2 18.7 123/83 W 99.7 18.95 142/72 E 99.8 18.9 145/83 W 99.7 18.85 154/83 w 99.8 18.8 131/79 w 99.9 18.8 135/78 w 99.4 18.55 84/77 s 99.55 18.45 127/68 w 99.5 18.45 146/75 E 99.55 18.65 130/81 W (Overturned) 99.7 18.85 131/90 100.0 18.7 153/83 E 99.9 18.55 106/83 s 99.95 18.5 149/77 W 100.1 18.85 137/85 E 100.15 18.9 137/84 E 100.25 18.85 153/71 E 100.6 18.8 163/90 100.7 18.85 S t r i k e / d i p of bedding Grid East Grid North 160/74 E 100.7 18.85 157/81 E 100.85 18.8 123/88 W (Overturned) 100.1 18.65 141/88 W (Overturned) 100.15 18.7 116/79 W 100.2 18.75 131/74 E 100.35 18.7 140/77 W 100.05 18.5 141/90 100.15 18.5 145/85 E 101.25 18.8 171/80 E 101.5 18.85 157/87 E 101.05 18.65 119/72 E 101.2 18.5 146/83 E 101.4 18.55 146/78 E 101.45 18.6 153/73 E 101.5 18.6 140/75 E 101.6 18.7 154/85 W 102.5 17.15 162/85 E 102.55 17.15 159/71 E 102.65 17.1 44/42 E 102.85 17.15 156/79 E 102.9 17.4 38/65 E 102.85 17.05 171/62 E 102.85 16.85 20/66 E 102.95 16.75 152/78 E 103.05 17.05 16/57 E 103.05 16.9 Trend/plunge of f o l d axes Grid East Grid North 200/27 102.98 16.9 140/43 99.1 18.9 NICOLA GROUP Dome H i l l s S t r i k e / d i p of bedding Grid East Grid North 126/56 E 88.8 23.6 120/48 E 88.85 23. 3 129/48 E 89.0 23.5 130/45 E (Overturned) 89.05 23.5 129/68 E 89.05 23.3 124/72 E 89.15 23.3 124/34 E 89.35 23.3 142/36 E (Overturned) 89.4 23.2 205 Str i k e / d i p of bedding Grid East Grid North 120/61 E 89.4 23.1 157/88 W 90.5 23.1 161/60 E 90.6 23.45 151/68 E (Overturned) 90.7 23.3 160/60 E (Overturned) 90.9 • 23.25 125/88 E 90.9 23.5 148/75 E 88.6 22.95 124/73 E 88.75 22.3 118/90 88.6 22.3 140/49 E 89.2 22.9 169/64 E 89.25 22.8 155/46 E (Overturned) 89.4 22.9 155/54 E (Overturned) 89.5 22 .9 100/59 E 89.5 22.8 117/53 E 89.6 22.8 145/72 E 89.85 22 .8 57/24 W 89.8 22.75 128/44 E 89.8 22.7 142/65 E 89.7 22.7 165/58 E 89.6 22.6 165/70 E (Overturned) 89.1 22.6 112/58 E (Overturned) 89.05 22.55 142/61 E 89.2 22.45 128/42 E 89.3 22.3 109/53 E 89 .4 22.3 132/81 E 89.35 22 .25 143/35 E 89.8 22.6 142/56 E 89.55 22.35 146/64 E (Overturned) 89.8 22.3 100/62 E (Overturned) 89.8 22.1 101/44 E 89.8 22.05 158/47 E 89.45 22.15 175/65 E 89.45 22.1 108/63 E 89.3 22.1 127/85 E (Overturned) 89.25 22.1 143/65 E (Overturned) 89.2 22.15 124/74 E (Overturned) 89.05 22.15 169/83 E (Overturned) 89.05 22.05 151/40 E (Overturned) 90.05 22.75 150/52 E (Overturned) 90.2 22.85 125/53 E 90.6 22.95 153/57 E 90.25 22.7 135/70 E 90.65 22.7 148/46 E 90.2 22.5 .. 151/57 E 90.25 22.6 154/59 E 90.4 22.55 128/62 E 90.05 22.35 174/68 E 90.05 22.15 206 Str i k e / d i p of bedding Grid East Grid North 125/75 E 88.5 21.75 160/63 E 89.2 21.9 Trend/plunge of minor f o l d axes 335/24 23/61 34/40 41/46 358/50 Str i k e / d i p of a x i a l planes of minor folds 158/86 E 105/61 N 105/44 N 114/46 N 84/50 N Grid East 89.45 89.75 90.0 90. 88. Grid North 22.1 22.7 22.4 22.6 21.75 Western Paul Ridge /dip of bedding Grid East Grid North 131/90 89.45 20.2 128/47 W 89.15 19.2 161/69 W 89.4 19.2 117/71 E 89.4 19.2 76/60 W 89.4 19.2 168/67 E 89.65 19.4 126/56 E 89.7 18.9 165/56 E 90.65 20.6 168/88 E 90.98 20.4 155/55 E 90.0 19.4 132/57 E 90.2 19.3 145/79 E 90.1 19.15 150/55 E 90.1 19.15 146/78 E 90.3 19.15 171/47 E 90.6 19.15 136/71 E 90.7 19.2 134/41 E 90.75 19.15 134/68 E 90.8 19.2 120/41 E 90.35 18.95 158/82 W 90.5 18.9 149/89 W 90.6 18.98 146/58 E 90.8 19.0 115/80 E 91.15 20.4 144/73 E 91.1 20.3 136/87 E 91.6 20.02 127/87 W 91.7 20.05 156/77 E 91.9 20.05 68/63 E 91.3 19.9 207 Str i k e / d i p of bedding Grid East Grid North 27/81 E 91.3 19.85 131/87 E 91.5 19.95 166/73 E 91.25 19.75 128/70 E 91.35 19.75 156/81 E 91.5 19.7 39/60 E 91.55 19.7 130/71 E 91.65 19.7 151/81 E 91.25 19.5 151/81 W 91.3 19.5 176/81 W 91.4 19.5 150/67 E 91.5 19.45 152/73 E 91.5 19.4 74/52 W 91.85 19.45 158/50 E 91.98 19.55 165/68 E 91.98 19.4 156/78 E 91.65 19.35 166/81 E 91.7 19.3 147/81 E 91.8 19.3 161/77 E 91.95 19.25 164/85 E 91.98 19.3 153/22 E 92.95 20.3 162/77 E 92.1 19.85 06/62 E 92.3 19.9 04/68 E 92.3 19.8 156/47 E (Overturned) 92.5 19.95 146/51 E 92.9 19.9 142/58 E 92.05 19.5 160/78 E 92.1 19.6 134/63 E 92.2 19.55 155/69 E 92.3 19.6 142/68 E 92.3 19.5 171/75 E 92.4 19.5 125/28 E 92.45 19.55 07/42 E 92.65 19.65 05/38 E (Overturned) 92.75 19.7 158/41 E (Overturned) 92.8 19.6 162/90 92.3 19.4 131/43 E 92.3 19.3 162/63 E 92.4 19.35 110/22 E 92.55 19.4 156/78 E 92.5 19.3 153/82 E 92.6 19.25 08/57 E (Overturned) 92.7 19.45 05/67 E 92.8 19.35 173/51 E (Overturned) 92.9 19.4 02/71 E (Overturned) 92.75 19.1 171/72 E 92.8 19.15 14/65 E 92.9 19.25 150/55 E 93.5 20.2 208 Str i k e / d i p of bedding Grid East Grid North 158/66 E 93.02 19.9 172/58 E 93.1 19.7 158/41 E 93.2 19.75 151/54 E 93.7 19.75 175/77 W 93.2 19.5 167/75 E (Overturned) 93.3 19.55 151/51 E 93.35 19.55 175/46 E 93.45 19.5 179/61 E 93.7 19.4 157/74 E 93.8 19.4 172/71 E (Overturned) 93.9 19.4 167/77 E 93.97 19.45 145/55 E 93.1 19.25 154/65 E 93.4 19.35 145/50 E 93.5 19.3 160/58 E 93.7 19.2 154/80 E 93.9 19.15 171/63 E (Overturned) 93.0 19.25 165/73 E 94.05 19.35 163/87 W 94.02 19.2 158/89 W 94.1 19.25 147/74 W 94.2 19.15 152/83 E 94.15 18.95 160/86 E 94.3 18.95 Trend/plunge of minor f o l d axes 310/73 35/81 92/59 65/58 26/52 44/43 59/54 330/12 07/53 St r i k e / d i p of a x i a l planes of minor folds 106/81 N 132/65 E 130/63 E 61/62 W 84/67 N 41/78 E Grid East 89.4 91.5 91.1 91.1 92.4 92.4 92.4 92.55 92.05 Grid North 19.17 19.7 20.05 20.05 19.3 19.3 19.3 19.35 19.5 Central Paul Ridge S t r i k e / d i p of bedding Grid East Grid 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 of bedding Grid East Grid North 132/50 E 93.9 19.95 159/76 E 93.9 19.7 129/78 E 94.3 20.1 135/67 E 94.6 20.05 140/43 E 94.85 20.05 133/52 E 94.9 20.1 165/55 E 94.1 19.85 163/72 E 94.05 19.8 157/90 94.1 19.75 147/84 E 94.15 19.75 161/54 E 94.25 19.8 02/54 E 94.3 19.7 166/50 E 94.35 19.7 85/50 N 94.5 19.8 136/70 E 94.6 19.8 90/57 N 94.6 19.7 146/35 E 94.75 19.8 139/47 E 94.85 19.8 153/46 E 94.95 19.8 120/48 E 94.7 19.65 136/70 E 94.8 19.7 140/67 E 94.9 19.7 163/80 W 94.02 19.65 149/66 E 94.1 19.6 140/64 E 94.2 19.6 146/29 E 94.3 19.5 133/90 94.75 19.5 146/66 E 94.9 19.6 145/50 E 94.25 19.4 156/76 E 94.35 19.4 90/36 N 94.5 19.3 150/79 E 94.5 19.35 161/45 E (Overturned) 94.55 19.45 142/54 E 94.65 19.35 146/77 E 94.8 19.35 157/77 W 94.9 19.45 84/44 N 94.95 19.4 143/42 E 94.64 19.25 163/26 W 94.8 19.2 150/83 W 94.3 19.1 147/71 E 94.65 19.0 143/75 W 94.8 19.1 134/86 W 94.95 19.1 133/65 W 94.4 19.9 142/51 E 95.05 20.05 163/61 E 95.15 19.98 156/61 E 95.25 19.98 146/90 95.3 19.9 210 Stri k e / d i p of bedding Grid East Grid North 155/47 E 95.02 19.7 142/59 E 95.1 19.6 124/59 E 95.3 19.7 123/73 E 95.1 19.5 154/61 E 95.25 19.5 156/65 E 95.3 19.5 140/81 E 95.4 19.55 173/74 W 95.0 19.3 141/73 E 95.1 19.35 136/68 E 95.2 19.4 143/83 E 95.4 19.45 169/76 W 95.15 19.2 150/55 E 95.3 19.3 156/77 W 95.5 19.3 134/51 E 95.15 19.1 160/76 E 95.2 19.1 156/76 W 95.45 19.1 158/80 W 95.5 19.2 162/83 E 95.2 19.0 143/77 W 95.4 19.0 St r i k e / d i p of Trend/plunge of a x i a l planes of minor f o l d axes minor folds Grid East Grid North 340/57 86/59 N 95. 2 18.95 05/28 115/35 N 95. 5 19.25 326/16 25/40 W 94. 75 19.05 340/0 95. 1 19.35 317/40 114/62 N 95. 25 19.4 324/31 98/42 N 95. 3 19.35 330/09 94. 15 19.85 328/42 94. 1 19.75 Eastern Paul Ridge S t r i k e / d i p of bedding Grid East Grid North 165/84 W 95.6 20.0 149/81 W 95.55 19.7 143/83 E 96.2 21.95 150/88 W 96.4 21.0 147/78 W 96.7 19.7 176/69 W 96.2 19.45 171/21 W 96.45 19.2 140/43 W 96.8 19.35 S t r i k e / d i p of bedding Grid East Grid North 154/56 E 97.55 20.05 119/58 E 97.6 20.1 125/78 W 97.6 20.15 114/88 W 97.5 19.9 131/70 E 97.9 19.85 115/48 E 97.9 19.8 116/63 E 97.9 19.8 174/60 W 97.3 19.2 149/58 W 97.1 18.85 101/90 98.25 19.6 91/85 N 98.2 19.35 109/72 E 98.35 19.3 117/78 E 98.25 19.15 158/62 E 98.3 19.15 118/82 E 98.4 19.17 98/82 E 98.5 19.13 143/87 E 98.3 19.05 123/90 E 98.55 18.9 171/58 W 98.25 18.55 107/71 W 98.8 18.85 112/86 E 98.75 18.7 134/74 E 98.75 18.6 130/50 W 98.75 18.5 137/69 E 98.95 18.4 128/83 E 99.0 18.35 123/77 E 99.05 18.3 95/78 S 99.4 18.45 109/90 99.4 18.4 107/62 E 99.45 18.15 108/79 W 99.6 18.15 Str i k e / d i p of Trend/plunge of a x i a l planes of minor f o l d axes minor folds Grid East Grid North 306/38 54/40 W 98.25 19.15 111/68 149/84 W 98.8 18.8 287/02 107/80 N 99.3 18.25 128/69 143/82 N 99.35 18.3 

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