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Sedimentology and stratigraphy of the southern Sustut basin, north central British Columbia McKenzie, Kathleen Jane 1985

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"I ^ y-A >-c^ J ( 7Q -SEDIMENTOLOGY AND STRATIGRAPHY OF THE SOUTHERN SUSTUT BASIN, NORTH CENTRAL BRITISH COLUMBIA By KATHLEEN JANE McKENZIE B . S c , The U n i v e r s i t y of Calgary, 1982 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 G e o l o g i c a l Sciences We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA January 1985 ©Kathleen Jane McKenzie In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of GftllofM/'/xl ScAjLiOCl/) The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date DE-6 (3/81) ABSTRACT The S u s t u t Group w i t h i n t h e s t u d y a r e a i s a n o n m a r i n e s u c c e s s i o n o f f i n e t o c o a r s e g r a i n e d e l a s t i c s , d e p o s i t e d i n an a l l u v i a l f a n e n v i r o n m e n t . R e g i o n a l l y , t h e S u s t u t Group i s d i v i s i b l e i n t o the Tango Creek and B r o t h e r s Peak F o r m a t i o n s . I n t h e s t u d y a r e a , t h e two f o r m a t i o n s a r e e n t i r e l y L a t e C r e t a c e o u s (Campanian t o M a a s t r i c h t i a n ) i n age, b a s e d on p a l y n o l o g i c a l e v i d e n c e . I n t h e s o u t h e r n S u s t u t B a s i n , o n l y the uppermost 400 m o f t h e T a t l a t u i Member o f t h e Tango C r e e k F o r m a t i o n i s e x p o s e d . S e d i m e n t s o f t h e T a t l a t u i Member a r e d i v i d e d i n t o f i n e and c o a r s e g r a i n e d l i t h o f a c i e s . The f i n e g r a i n e d l i t h o f a c i e s i s composed o f i n t e r b e d d e d mudstone, s i l t s t o n e and f i n e g r a i n e d sandstone, which i s i n t e r p r e t e d as an a l l u v i a l p l a i n d e p o s i t . P e b b l e c o n g l o m e r a t e i n t e r b e d d e d w i t h c o a r s e t o medium g r a i n e d s a n d s t o n e c o m p r i s e t h e c o a r s e g r a i n e d l i t h o f a c i e s w h i c h i s c o n s i d e r e d t o be a b r a i d e d r i v e r d e p o s i t . The B r o t h e r s Peak F o r m a t i o n c o m p r i s e s 1 000 m of d i v e r s e e l a s t i c s and t u f f s , w h i c h a r e d i v i s i b l e i n t o t h e l o w e r and upper L a s l u i Member, and the o v e r l y i n g S p a t s i z i Member. The lower L a s l u i Member c o n f o r m a b l y o v e r l i e s the T a t l a t u i Member of the Tango Creek F o r m a t i o n , and i s c h a r a c t e r i z e d by s e v e r a l f i n i n g upwards s e q u e n c e s o f c o b b l e c o n g l o m e r a t e t o medium g r a i n e d s a n d s t o n e , a t t r i b u t e d t o d e p o s i t i o n by h i g h e n e r g y b r a i d e d s t r e a m s i n t h e m i d - f a n r e g i o n o f an a l l u v i a l f a n c o m p l e x . S e d i m e n t s o f t h e u p p e r L a s l u i Member a r e d i v i d e d i n t o a f i n e g r a i n e d l i t h o f a c i e s c o n s i s t i n g o f mudstone, i n t e r b e d d e d w i t h l e s s e r amounts o f s i l t s t o n e , f i n e g r a i n e d i i s a n d s t o n e and t u f f beds, and a c o a r s e g r a i n e d l i t h o f a c i e s composed o f o r t h o c o n g 1 o m e r a t e , p a r a c o n g 1 o m e r a t e and c o a r s e g r a i n e d sandstone. The f i n e g r a i n e d l i t h o f a c i e s comprises the m a j o r i t y o f the sequence and i s i n t e r p r e t e d as an a l l u v i a l p l a i n d e p o s i t . Coarse g r a i n e d sediments of the upper L a s l u i Member were l i k e l y d e p o s i t e d d u r i n g s t a g e s o f h i g h water d i s c h a r g e , by major d i s t r i b u t a r i e s , s h e e t f l o o d s and d e b r i s f l o w s . The S p a t s i z i Member i s g r a d a t i o n a l from the upper L a s l u i Member and i s composed of sandstone/mudstone sequences i n t e r p r e t e d as sandy b r a i d e d s t r e a m d e p o s i t s o f an a l l u v i a l p l a i n . D e t r i t a l components of the Tango Creek and Brothers Peak sandstones are mainly c h e r t , q u a r t z , p l a g i o c l a s e and v o l c a n i c r o c k f r a g m e n t s . P a l e o c u r r e n t measurements and p r o v e n a n c e c o n s i d e r a t i o n s s u g g e s t s o u r c e t e r r a n e s were l o c a t e d t o the e a s t d u r i n g Tango Creek d e p o s i t i o n , and t o the west d u r i n g B r o t h e r s Peak d e p o s i t i o n . In the s o u t h e r n S u s t u t B a s i n , the Tango C r e e k F o r m a t i o n documents u p l i f t and e r o s i o n i n t h e Omineca B e l t and P a l e o z o i c rock u n i t s , f o l l o w i n g a c c r e t i o n of the f i r s t composite t e r r a n e (terrane I) to the North American Margin. The Broth e r s Peak Formation i s co n s i d e r e d a r e s u l t of l o c a l u p l i f t and v o l c a n i c a c t i v i t y , accompanying the a c c r e t i o n of a second composite t e r r a n e (terrane I I ) . i i i T A B L E O F C O N T E N T S ABSTRACT i i TABLE OF CONTENTS . . i v LIST OF TABLES : v i i LIST OF FIGURES v i i i LIST OF PLATES X ACKNOWLEDGEMENTS . . x i i INTRODUCTION 1 GENERAL STATEMENT 1 STUDY AREA 3 TECTONIC SETTING 6 STRUCTURAL SETTING 9 REGIONAL GEOLOGICAL SETTING 11 METHODS AND DATA 16 LITHOSTRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS 18 TANGO CREEK FORMATION 18 TATLATUI MEMBER - LITHOFACIES DESCRIPTION 20 Coarse Grained L i t h o f a c i e s 20 Fine Grained L i t h o f a c i e s 22 TATLATUI MEMBER -INTERPRETED DEPOSITIONAL ENVIRONMENT 2 3 i v BROTHERS PEAK FORMATION 2 8 LOWER LASLUI MEMBER - LITHOFACIES DESCRIPTION 29 Conglomeratic L i t h o f a c i e s 29 Fine Grained L i t h o f a c i e s 32 LOWER LASLUI MEMBER -INTERPRETED DEPOSITIONAL ENVIRONMENT . .. 32 UPPER LASLUI MEMBER - LITHOFACIES DESCRIPTION 37 Coarse Grained L i t h o f a c i e s 37 Interbedded Fine Grained L i t h o f a c i e s 41 UPPER LASLUI MEMBER -INTERPRETED DEPOSITIONAL ENVIRONMENT 43 SPATSIZI MEMBER - LITHOFACIES DESCRIPTION 49 SPATSIZI MEMBER -INTERPRETED DEPOSITIONAL ENVIRONMENT 51 PETROLOGY OF THE SUSTUT GROUP 5 4 PETROGRAPHY AND MINERALOGY 54 HEAVY MINERALS 75 DIAGENESIS 80 PALYNOLOGY 86 COALIFICATION LEVEL 87 PALEOCURRENT ANALYSIS 90 PROVENANCE 91 DEPOSITIONAL HISTORY AND TECTONIC SIGNIFICANCE OF THE SOUTHERN SUSTUT BASIN 95 SUMMARY AND CONCLUSIONS 101 V REFERENCES 104 APPENDIX 116 v i LIST OF TABLES Table 1. Modal a n a l y s i s of the Tango Creek Formation. Table 2 . Modal a n a l y s i s of the lower L a s l u i Member. Table 3 . Modal a n a l y s i s of the upper L a s l u i Member. Table 4. Modal a n a l y s i s of the S p a t s i z i Member. Table 5. C o a l i f i c a t i o n l e v e l of samples from the southern Sustut B a s i n . v i i LIST OF FIGURES F i g u r e 1. L o c a t i o n o f the n o r t h e r n and s o u t h e r n S u s t u t B a s i n s . F i g u r e 2. G e o l o g i c a l map of the s t u d y a r e a ( m o d i f i e d from R i c h a r d s , 1976). F i g u r e 3 . Major t e c t o n i c e l e m e n t s o f t h e C a n a d i a n C o r d i l l e r a (modified from Wheeler and G a b r i e l s e , 1972). F i g u r e 4. A l l o c h t h o n o u s t e r r a n e s of the Canadian C o r d i l l e r a (modified from P r i c e et a l , 1981). F i g u r e 5. C o r r e l a t i o n c h a r t o f T r i a s s i c t o T e r t i a r y r o c k u n i t s surrounding the Sustut B a s i n . F i g u r e 6 . R e g i o n a l g e o 1 o g y ( m o d i f i e d f r o m T i p p e r and Rich a r d s , 1976). F i g u r e s 7a-7g. Sustut Group s e c t i o n s S2-S8. F i g u r e 8. S t r a t i g r a p h i c c o r r e l a t i o n . F i g u r e 9. P r i n c i p a l r i v e r types (modified from M i a l l , 1977). F i g u r e 10. I n t e r p r e t e d d e p o s i t i o n a l e n v i r o n m e n t of t h e T a t l a t u i Member. Fi g u r e 11. I n t e r p r e t e d d e p o s i t i o n a l environment of the lower L a s l u i Member. Fi g u r e 12. I n t e r p r e t e d d e p o s i t i o n a l environment of the upper L a s l u i Member. F i g u r e 13. I n t e r p r e t e d d e p o s i t i o n a l e n v i r o n m e n t of the S p a t s i z i Member. F i g u r e 14. A t r i a n g u l a r diagram i l l u s t r a t i n g the composition of the Sustut Group sandstones. F i g u r e 15. The i n f e r r e d s o u r c e a r e a s and p a l e o c u r r e n t d i r e c t i o n s f o r the S u s t u t Group i n t h e s o u t h e r n S u s t u t B a s i n . F i g u r e 16. G e n e r a l i z e d s t r a t i g r a p h i c s e c t i o n of the Sustut Group i n the s o u t h e r n S u s t u t B a s i n , i 1 1 u s t r a t i n g the p a l e o c u r r e n t d i r e c t i o n s and i n f e r r e d source r o c k s . F i g u r e l 7 . D e p o s i t i o n a l model o f t h e B r o t h e r s Peak Formation. v i i i LIST OF PLATES P l a t e 1. The e a s t s i d e o f t h e C o n n e l l y Range showing the e x c e l l e n t exposure of the Sustut Group. l a l o o k i n g to the southwest, and l b l o o k i n g to the northwest. P l a t e 2. C h a r a c t e r i s t i c s of the T a t l a t u i Member. P l a t e 2a. Outcrops showing t h i c k l y bedded conglomerate interbedded with f i n e g r a i n e d sediments. P l a t e 2b. Outcrops showing interbedded f i n e g r a i n e d sediments. P l a t e 2c. Close-up of a p o o r l y s o r t e d , pebble conglomerate. P l a t e 3. C h a r a c t e r i s t i c s of the lower L a s l u i Member. P l a t e 3a, Imbricated c l a s t s a t the base of the lower L a s l u i Member. P l a t e 3b. I n t e r n a l l y complex and r a p i d v a r i a t i o n i n t e x t u r e , both v e r t i c a l l y and l a t e r a l l y . P l a t e 3c,d. Tabular c r o s s - s t r a t i f i c a t i o n . P l a t e 3e. Mudstone r i p - u p c l a s t s i n sandstone. P l a t e 3f. Log impression w i t h i n a very coarse sandstone sequence. P l a t e 4. Overview of the upper L a s l u i Member i l l u s t r a t i n g the d i s t i n c t i v e l e n t i c u l a r white t u f f beds. P l a t e 5. C h a r a c t e r i s t i c s of the upper L a s l u i Member o r t h o -conglomerates . P l a t e 5a. Orthoconglomerate "A" caps a sequence of i n t e r -bedded f i n e g r a i n e d sediments, i n c l u d i n g t u f f s . P l a t e 5b. L o n g i t u d i n a l s c ours, or " g u t t e r c a s t s " exposed on the base of orthoconglomerate "A". P l a t e 5c. Log impressions w i t h i n orthoconglomerate "A". P l a t e 5d. L a t e r a l l y d i s c o n t i n u o u s exposure of orthocon-glomerate "B", w i t h i n a sequence of interbedded f i n e g r a i n e d sediments. i x P l a t e 6. C h a r a c t e r i s t i c s of the upper L a s l u i Member paraconglomerate and t u f f s . P l a t e 6a. Paraconglomerate, l e s s r e s i s t a n t than above pebble orthoconglomerate. Note the o v e r a l l darker c o l o r of the paraconglomerate bed. P l a t e 6b. Paraconglomerate showing both normal and r e v e r s e gra d i n g l o c a l l y . P l a t e 6c. T u f f bed showing sharp lower and upper c o n t a c t s . P l a t e 7. C h a r a c t e r i s t i c s of the S p a t s i z i Member sandstone. P l a t e 7a. Small s c a l e t a b u l a r c r o s s - s t r a t i f i c a t i o n . P l a t e 7b. R i p p l e c r o s s - s t r a t i f i c a t i o n . P l a t e 7c. F a i n t l y convoluted and c o n t o r t e d bedding. P l a t e s 8-14. Thin s e c t i o n photomicrographs of the Sustut Group. P l a t e 8a. Thi n s e c t i o n photomicrograph of quartz w i t h n e e d l e -l i k e m i c r o l i t e i n c l u s i o n s . P l a t e 8b. Thin s e c t i o n photomicrograph showing quartz overgrowths. P l a t e 8c. Thi n s e c t i o n photomicrograph of a bimodal p o l y c r y s t a l l i n e quartz g r a i n with sutured i n t e r n a l c o n t a c t s . N i c o l s c r o s s e d . P l a t e 9a. Thi n s e c t i o n photomicrograph of c h e r t with a r g i l -laceous m a t e r i a l . N i c o l s c r o s s e d . P l a t e 9b. Thi n s e c t i o n photomicrograph of chalcedony ( z e b r a i c ? ) . N i c o l s c r o s s e d . P l a t e 9c. Thi n s e c t i o n photomicrograph of c h e r t with c i r c u l a r f o s s i l (?) remnants. N i c o l s c r o s s e d . P l a t e 10. Thi n s e c t i o n photomicrographs of p l a g i o c l a s e f e l d s p a r . P l a t e 10a. A l t e r a t i o n t o mica. P l a t e 10b. A l t e r a t i o n - t o c a l c i t e . P l a t e 11. Thi n s e c t i o n photomicrographs i l l u s t r a t i n g the v a r i o u s t e x t u r e s of v o l c a n i c rock fragments (a and b). P l a g i o c l a s e (PI) i s the main phenocryst. 10c T r a c h y t i c t e x t u r e of p l a g i o c l a s e l a t h s . x P l a t e 12a. Thin s e c t i o n photomicrograph of a metamorphic rock fragment. Note the elongate and s t r e t c h e d i n t e r n a l g r a i n s . Arrows p o i n t t o mica f l a k e s w i t h i n the rock fragment. N i c o l s c r o s s e d . P l a t e 12b. Thin s e c t i o n photomicrograph of a bent or kinked mica ( b i o t i t e ) . P l a t e 13a. T h i n s e c t i o n photomicrograph of subhedral z i r c o n (Zi) g r a i n s . P l a t e 13b. T h i n s e c t i o n photomicrograph of a u g i t e . P l a t e 13c. Thin s e c t i o n photomicrograph of d e t r i t a l (?) sphene. P l a t e 13d. T h i n s e c t i o n photomicrograph of a hornblende g r a i n . P l e o c h r o i c green to brown. P l a t e 14. T h i n s e c t i o n photomicrographs of cements. P l a t e 14a. T u f f showing c l a y cement o u t l i n i n g o r i g i n a l l y v i t r i c shards. H e u l a n d i t e i n f i l l s the shards (h). Other g r a i n s i n c l u d e quartz (q), and p l a g i o c l a s e (p). P l a t e 14b. E x c e l l e n t example of f i b r o u s c l a y cement around an o r i g i n a l v e s i c l e i n a t u f f which i s i n f i l l e d w ith b r i g h t green c e l a d o n i t e . P l a t e 14c-d. Tuffaceous sandstone showing c l a y rimming cement i n f i l l e d w ith quartz (q) and a l b i t e ( ? ) (A). 14a cro s s e d n i c o l s . P l a t e 14d-f. N o n - t u f f a c e o u s s a n d s t o n e showing e x c e l l e n t f i b r o u s c e l a d o n i t e (c) i n f i l l i n g pore s p a c e s . 14e c r o s s e d n i c o l s . P l a t e 14e-14f. Thin s e c t i o n photomicrograph showing f i b r o u s open space f i l l i n g , c l a y cement. 14e n i c o l s c r o s s e d . x i ACKNOWLEDGEMENTS I w i s h t o thank my a d v i s o r Dr. Marc B u s t i n f o r h i s a d v i c e , s u p p o r t and c r i t i c a l r e v i e w s of the t h e s i s . I a l s o w i s h t o thank Drs. W. C. Barnes and G. Rouse as members of my a d v i s o r y committee. I am g r a t e f u l t o Dr. G. Rouse and A. Sweet f o r p a l y n o l o g i c a l a n a l y s e s . I am indebted to E. Montgomery and the t e c h n i c a l s t a f f of the Department of G e o l o g i c a l S c i e n c e s f o r p h o t o g r a p h i c work and sample p r e p a r a t i o n . I w i s h t o thank G. Hodge and M. S u l l i v a n f o r t h e i r h elp and advice with d r a f t i n g . F i n a n c i a l support was p r o v i d e d by NSERC Grant no. A7337, a s c h o l a r s h i p from t h e Wyoming G e o l o g i c a l S u r v e y and a G r a d u a t e R e s e a r c h F e l l o w s h i p from the U n i v e r s i t y of B r i t i s h Columbia. M o s t i m p o r t a n t l y I t h a n k my f a m i l y , f r i e n d s , and e s p e c i a l l y M. P i c k e r i n g , f o r t h e i r encouragement, support and understanding. x i i INTRODUCTION GENERAL STATEMENT The S u s t u t G r o u p i s t h e y o u n g e s t r e g i o n a l l y c o r r e l a t i b l e sedimentary assemblage i n the Intermontane B e l t o f n o r t h - c e n t r a l B r i t i s h C o l u m b i a . A t h i c k n o n m a r i n e s u c c e s s i o n o f a l t e r n a t i n g f i n e and c o a r s e g r a i n e d s ediments accumulated i n the Sustut Basin which records the f i n a l stages of d e f o r m a t i o n and d e p o s i t i o n i n the C a n a d i a n C o r d i l l e r a . L o r d (1948), d e f i n e d t h e S u s t u t Group as "a t h i c k a s semblage of c o n s p i c u o u s l y bedded and banded c o n t i n e n t a l s t r a t a o f r e l a t i v e l y s imple s t r u c t u r e . " E i s b a c h e r (1974), o u t l i n e d the s e d i m e n t a r y h i s t o r y and t e c t o n i c e v o l u t i o n o f the S u s t u t B a s i n , b ut b e l i e v e d the sequence t o be L a t e C r e t a c e o u s (Cenomanian) t o T e r t i a r y (Eocene), however, p a l y n o l o g i c a l e v i - r a c e from the s t u d y a r e a i n d i c a t e s t h e s u c c e s s i o n i s e n t i r e l y L a t e C r e t a c e o u s (Campanian t o M a a s t r i c h t i a n ) . The p r e s e n t s t u d y p r o v i d e s a more d e t a i l e d and c o m p r e h e n s i v e a n a l y s i s of the Sustut Group i n the southern Sustut Basin with p a r t i c u l a r emphasis on the d e p o s i t i o n a l h i s t o r y and e v o l u t i o n of the s t r a t a . The p r i n c i p a l o b j e c t i v e s of t h i s t h e s i s are to: 1) d e s c r i b e t h e major c l a s t i c l i t h o f a c i e s o f the S u s t u t Group and p r o v i d e s t r a t i g r a p h i c c o r r e l a t i o n ; 2) determine the d e p o s i t i o n a l environments of the major c l a s t i c l i t h o f a c i e s ; 3) u t i l i z e t he m i n e r a l o g y and p a l e o c u r r e n t d a t a t o i n t e r p r e t the provenance; 4) r e s o l v e t h e age of the S u s t u t Group t h r o u g h t h e 1 i d e n t i f i c a t i o n and d a t i n g of palynomorphs; 5) document the c o a l i f i c a t i o n l e v e l of the Sustut Group; and 6 ) r e c o n s t r u c t the t e c t o n i c and d e p o s i t i o n a l h i s t o r y of the southern Sustut Basin. 2 STUDY AREA The S u s t u t Group o c c u r s i n two l a r g e o u t l i e r s , r e f e r r e d t o as t h e n o r t h e r n and s o u t h e r n S u s t u t B a s i n . C o l l e c t i v e l y , t h e two s u b - b a s i n s t r e n d n o r t h w e s t t o s o u t h e a s t b e tween t h e Skeena and Omineca Mo u n t a i n s , and c o v e r r o u g h l y 6 000 square k i l o m e t e r s ( F i g u r e 1 ) . T h i s s t u d y d e a l s w i t h t h e s o u t h e r n S u s t u t B a s i n and more s p e c i f i c a l l y t h e sediments t h a t make up t h e C o n n e l l y Range, l o c a t e d e a s t of Bear Lake on t h e M c C o n n e l l C r e e k map s h e e t , 94 D ( F i g u r e 2). P h y s i o g r a p h i c a 1 l y , t h e a r e a i s m o u n t a i n o u s , w i t h peak e l e v a t i o n s r a n g i n g f r o m 1 600 m t o 2 500 m. L o c a l r e l i e f i s g e n e r a l l y l e s s t h a n 2 000 m and t h e v a l l e y s a r e commonly deep and b r o a d l y U-shaped. R i d g e s o f t h e C o n n e l l y Range a r e a s y m m e t r i c a l w i t h the west s i d e of the r i d g e b e i n g a d i p - s l o p e (30 degrees SW), whereas th e e a s t s i d e i s c h a r a c t e r i z e d by n e a r l y v e r t i c a l c l i f f s and s t e e p t a l u s s l o p e s , a c c o u n t i n g f o r t h e e x c e l l e n t e x p o s u r e o f t h e u p p e r m o s t 1 000 m t o 1 500 m ( P l a t e 1 ) . Lower i n t h e s e c t i o n , e x p o s u r e i s l i m i t e d by g r a s s y s l o p e s and dense t r e e c o v e r . D r a i n a g e o f t h e s t u d y a r e a i s m a i n l y by t h e S u s t u t R i v e r , w h i c h f l o w s w e s t w a r d i n t o t h e Skeena R i v e r t h a t i n t u r n e m p t i e s i n t o t h e P a c i f i c O c e a n . E a s t w a r d d r a i n a g e i s p r i n c i p a l l y by t h e F i n l a y R i v e r t h a t i s l o c a l l y f e d by t h e Omineca R i v e r , w h i c h e v e n t u a l l y d r a i n s i n t o t h e M a c K e n z i e R i v e r and the A r c t i c Ocean ( F i g u r e 1). 3 U.S.A. Figure 1. Location of the northern and southern Sustut Basins 4 Mate 1. East side of the Connelly Range showing the excellent exposure of the Sustut Group. TECTONIC SETTING The l o c a t i o n of t h e S u s t u t B a s i n w i t h r e s p e c t t o the t e c t o n i c b e l t s of the Canadian C o r d i l l e r a i s shown on F i g u r e 3. The Canadian C o r d i l l e r a i s a " c o l l i s i o n orogen" i n v o l v i n g t h e a c c r e t i o n o f a c o l l a g e of a 11ochthonous t e r r a n e s t o t h e western margin of the North American c o n t i n e n t . A c c r e t i o n of t e r r a n e s i n M e s o z o i c time was accompanied by h i g h grade metamorphism, g r a n i t i c i n t r u s i o n s and u p l i f t a l o n g deep c r u s t a l f a u l t s . U p l i f t l e d t o the p r o g r a d a t i o n of t h i c k c l a s t i c wedges i n t o the Bowser B a s i n i n M i d d l e t o L a t e J u r a s s i c , and the S u s t u t B a s i n i n L a t e C r e t a c e o u s Time ( E i s b a c h e r , 1981). S e v e r a l t e r r a n e s are thought to have amalgamated p r i o r to a c c r e t i o n w i t h t h e a n c i e n t N o r t h American c o n t i n e n t and a r e r e f e r r e d t o as c o m p o s i t e t e r r a n e s (Monger, 1984). Composite t e r r a n e s I and I I a r e shown on F i g u r e 4. The a c c r e t i o n of t e r r a n e I i n m i d - J u r a s s i c t i m e and t e r r a n e I I i n m i d -C r e t a c e o u s time i s c o n s i d e r e d l a r g e l y r e s p o n s i b l e f o r t h e p r e s e n t c o n f i g u r a t i o n of t h e C a n a d i a n C o r d i l l e r a (Monger, 1984). B o u n d a r i e s f o r m e d by t h e s e a c c r e t i o n s c o i n c i d e s p a t i a l l y w i t h the b e l t s of i n t e n s e deformation, metamorphism, and g r a n i t i c i n t r u s i o n , t h e Omineca and t h e C o a s t P l u t o n i c B e l t s (Figure 4). During M i d d l e to Late J u r a s s i c time i n the Bowser Basin, t h i c k and e x t e n s i v e d e p o s i t s of marine and non-marine e l a s t i c s accumulated. F o l l o w i n g a h i a t u s i n the Upper J u r a s s i c - e a r l y Lower Cretaceous (Tipper and Richards, 1976), marine and non-marine s e d i m e n t s of t h e Lower C r e t a c e o u s Skeena Group were 6 Figure 2. Geological map of the study area. (modified from Richards, 1976) 7 400 K i l o m e t r e s Figure 3. Major tectonic elements of the Canadian Cordillera, (modified from Wheeler and Gabrielse, 1972) d e p o s i t e d . Skeena s e d i m e n t s c o n t a i n an abundance of q u a r t z and m u s c o v i t e s u g g e s t i n g u p l i f t o f a h i g h grade metamorphic complex, p r e s u m a b l y t h e Omineca B e l t ( T i p p e r and R i c h a r d s , 1976). By m i d - C r e t a c e o u s t i m e , t h e f i n a l a c c r e t i o n o f c o m p o s i t e t e r r a n e s t o the w e s t e r n edge of N o r t h America was c o m p l e t e (Monger, 1984). S e d i m e n t a t i o n resumed i n the L a t e Cretaceous, i n i t i a l l y r e f l e c t i n g high angle f a u l t i n g i n the Omineca B e l t ( E i s b a c h e r , 1981), and l a t e r i n r e s p o n s e t o v o l c a n i c a c t i v i t y and u p l i f t of the Coast P l u t o n i c b e l t . Both the high angle f a u l t i n g i n the Omineca B e l t and the a c c r e t i o n of t e r r a n e I I , r e s u l t i n g i n u p l i f t and v o l c a n i c a c t i v i t y , are documented by the p r o g r a d a t i o n of a l l u v i a l sediments i n t o the Upper Cretaceous Sustut Basin. STRUCTURAL SETTING W i t h i n the s t u d y a r e a , S u s t u t s t r a t a a r e f o l d e d i n t o a b r o a d n o r t h w e s t t r e n d i n g sync 1 i n e - a n t i c 1 i n e p a i r . At the s o u t h end of the C o n n e l l y Range, Eocene K a s t b e r g I n t r u s i o n s t r u n c a t e t h e S u s t u t Group ( F i g u r e 2). M i n o r , s m a l l e r s c a l e f o l d i n g and f a u l t i n g o c c u r a t the n o r t h end of the C o n n e l l y Range. Furt h e r north, however ( i n c l u d i n g the northern Sustut Ba s i n ) , the s t r a t a are s t r u c t u r a l l y more complex, deformed by c l o s e l y s p a c e d , n o r t h w e s t t r e n d i n g t h r u s t f a u l t s and f o l d s ( E i s b a c h e r , 1974). A d j a c e n t t o the e a s t e r n margin of the S u s t u t B a s i n a r e s e v e r a l r i g h t - l a t e r a l s t r i k e s l i p f a u l t s . The most w e s t e r l y i s the T a k l a F a u l t , f o l l o w e d by the more e a s t e r n V i t a l F a u l t and the P i n c h i - F i n l a y f a u l t system. 9 1 0 REGIONAL GEOLOGICAL SETTING F i g u r e 5 i s a c o r r e l a t i o n c h a r t o f T r i a s s i c t o T e r t i a r y r o c k u n i t s s u r r o u n d i n g the S u s t u t B a s i n . The main u n i t s adjacent to, or u n d e r l y i n g , the Sustut Group range i n age from P r o t e r o z o i c to E a r l y Cretaceous, r e p r e s e n t i n g v a r i o u s t e r r a n e s and events i n the Canadian C o r d i l l e r a , and w i l l be d i s c u s s e d below. D i s t r i b u t i o n o f the v a r i o u s r o c k u n i t s i s shown on F i g u r e 6. The Omineca B e l t c o n s i s t s of a m i d - P r o t e r o z o i c t o mid-P a l e o z o i c m i o g e o c l i n a l sequence, as w e l l as P a l e o z o i c and M e s o z o i c v o l c a n i c and p e l i t i c r o c k s . In m i d - M e s o z o i c t o T e r t i a r y time, these rocks were h i g h l y deformed and v a r i a b l y metamorphosed and i n t r u d e d by J u r a s s i c and Cretaceous p l u t o n s . The Cache Creek Group which o c c u p i e s a narrow b e l t t o t h e e a s t of t h e s t u d y a r e a , c o n s i s t s of r a d i o l a r i a n c h e r t , a r g i l l i t e , b a s a l t , u l t r a m a f i c s , c a r b o n a t e and l o c a l l y b l u e s c h i s t , r a n g i n g i n age from M i s s i s s i p p i a n t o Upper T r i a s s i c (Monger, 1984). The Cache Creek Group i s p a r t of composite t e r r a n e I. Patchy outcrop of the A s i t k a Group occurs to the east and n o r t h e a s t of the study area. The A s i t k a Group i s composed of c h e r t and t u f f a c e o u s limestone of Permian age, and a n d e s i t i c to r h y o l i t i c v o l c a n i c and v o l c a n i c l a s t i c rocks of unknown, but p o s s i b l y P e r m o - T r i a s s i c age (Monger and D a v i s , 1983). The A s i t k a Group o v e r l i e s the Cache Creek Group unconformably, and l o c a l l y i s unconformably o v e r l a i n by the Sustut Group (Monger, 1973). 11 W o o d s w o r t h e t a l . , 1 9 8 3 E i s b a c h e r , 1 9 7 4 T h i s S t u d y TERRACE AREA SOUTHERN BOWSER BASIN SOUTHERN SUSTUT BASIN TERTIARY TERTIARY S u s t u t G r o u p Brothers Peak Formation CRETACEOUS Upper B r i a n B o r u F o r m a t i o n Tango Creek Formation S u s t u t G r o u p B r o t h e r s P e a k F o r m a t i o n T a n g o C r e e k F o r m a t i o n CRETACEOUS S k e e n a G r o u p CRETACEOUS Lower S k e e n a G r o u p JURASSIC Upper Middle Lower B o w s e r L a k e G r o u p B o w s e r L a k e G r o u p B o w s e r L a k e G r o u p JURASSIC H a z e l t o n G r o u p H a z e l t o n G r o u p H a z e l t o n G r o u p JURASSIC TRIASSIC Upper Middle T a k l a G r o u p T a k l a G r o u p T a k l a G r o u p TRIASSIC Figure 5. Correlation chart of Triassic to Tertiary rock units surrounding the Sustut Basin 1 2 The T a k l a Group comprises b a s a l t i c and a n d e s i t i c v o l c a n i c rocks, (dominantly a u g i t e p o r p h y r i e s ) , p e l i t i c rocks and minor l i m e s t o n e s , t h a t c r o p out t o t h e n o r t h e a s t of the s o u t h e r n S u s t u t B a s i n . T i p p e r and R i c h a r d s (1976) c o n s i d e r the T a k l a Group to be mainly Late T r i a s s i c . The H a z e l t o n Group i s E a r l y to M i d d l e J u r a s s i c i n age and i s a t h i c k a s semblage of v a r i c o l o r e d b a s a l t i c t o a n d e s i t i c v o l c a n i c and v o l c a n i c l a s t i c rocks, sedimentary rocks and minor c a r b o n a t e r o c k s . The H a z e l t o n Group c r o p s out l o n g narrow b e l t s t o the e a s t and more e x t e n s i v e t o t h e west s u r r o u n d i n g southern outcrops of the Sustut Group. The A s i t k a , T a k l a and H a z e l t o n Groups form p a r t of the S t i k i n e t e r r a n e of composite t e r r a n e I. The Bowser Lake Group i s composed of a t h i c k marine t o non-marine assemblage of c h e r t r i c h c l a s t i c rocks which were de p o s i t e d i n the Bowser Ba s i n i n M i d d l e t o Late J u r a s s i c time. The Bowser Lake Group crops out over an e x t e n s i v e area to the west of the study area. The Skeena Group i s composed of i n t e r b e d d e d marine and non-marine sedimentary rocks with abundant d e t r i t a l muscovite ( T i p p e r and R i c h a r d s , 1976). Woodsworth e t a l . (1983) c o n s i d e r the Skeena Group t o be E a r l y C r e t a c e o u s i n age. T i p p e r and R i c h a r d s (1976) and E i s b a c h e r (1981), h a v e s p e c u l a t e d t h a t the Sustut Group i s the nonmarine e q u i v a l e n t of the upper p o r t i o n of the Skeena Group. •Outcrops of t h e Skeena Group occur to the south and west of the Sustut Group. 13 REGIONAL GEOLOGY L E G E N D T E R T I A R Y I 1 O o t s a L a k e a n d E n d a k o G r o u p s C R E T A C E O U S S k e e n a a n d S u s t u t G r o u p s B r i a n B o r u F o r m a t i o n M I D D L E T O U P P E R J U R A S S I C B o w s e r L a k e G r o u p L O W E R T O M I D D L E J U R A S S I C Iv v vl H a z e l t o n G r o u p U P P E R T R I A S S I C T O L O W E R J U R A S S I C 1 • I In t rus ive R o c k s U P P E R T R I A S S I C T a k l a G r o u p U P P E R P A L E O Z O I C A s i t k a G r o u p C a c h e C r e e k G r o u p L a y R a n g e A s s e m b l a g e C R Y S T A L L I N E T E R R A N E I"*"! O m i n e c a C r y s t a l l i n e Be l t Figure 6. Regional Geology (modified from Tipper and Richards, 1976) 1 4 Unconformably o v e r l y i n g t h e Skeena Group i s the v o l c a n i c B r i a n B o r u F o r m a t i o n composed o f c a l c - a l k a l i n e b a s a l t t o r h y o l i t e w i t h a p r e p o n d e r a n c e o f p 1 a g i o c 1 a s e - h o r n b 1 e n d e porphyry. C o g e n e t i c i n t r u s i v e b o d i e s have been da t e d as L a t e C r e t a c e o u s (70 - 84 Ma) (Woodsworth e t a l . , 1983). The B r i a n B o r u F o r m a t i o n c r o p s o u t s o u t h a n d e a s t o f t h e c i t y o f H a z e l t o n . The K a s t b e r g I n t r u s i o n s l o c a l l y o c c u r i n t h e s t u d y a r e a and c o n s i s t of grey t o b u f f p o r p h y r i t i c r o c k s of g r a n o d i o r i t e t o q u a r t z d i o r i t e c o m p o s i t i o n . They i n t r u d e S u s t u t Group r o c k s a t the s o u t h end o f the C o n n e l l y Range and have y i e l d e d K/Ar age d a t e s o f 48 and 45 my ( R i c h a r d s , 1976). A n d e s i t i c and b a s a l t i c T e r t i a r y o r Q u a t e r n a r y f l o w s , necks and numerous s m a l l d i k e s a l s o i n t r u d e t h e S u s t u t s t r a t a i n t h e C o n n e l l y Range. 15 METHODS AND DATA F i e l d Study F i e l d work was conducted d u r i n g the summer of 1983. The i n i t i a l base camp was s i t u a t e d immediately no r t h of Bear Lake w i t h s u b s e q u e n t f l y - c a m p s l o c a t e d on the e a s t s i d e of the C o n n e l l y Range. T r a n s p o r t a t i o n was by h e l i c o p t e r and l i g h t a i r c r a f t . Seven s t r a t i g r a p h i c s e c t i o n s were measured u s i n g a 1.5 m Jacob's s t a f f e q u i p p e d w i t h a c l i n o m e t e r . The s e c t i o n s l o c a t e d a l o n g the east s i d e of the C o n n e l l y Range, are shown i n F i g u r e 2. Over 200 samples were c o l l e c t e d f o r f u r t h e r a n a l y s i s i n the l a b o r a t o r y . P e t r o l o g y G r a i n s i z e was e s t i m a t e d u s i n g the Wentworth (1922) s c a l e , and b e d d i n g d e s c r i p t i o n s were based on t h i c k n e s s e s o u t l i n e d by Ingram (1954). Roundness and s p h e r i c i t y , s o r t i n g and e s t i m a t i o n of d e t r i t a l g r a i n percentages were determined by v i s u a l c o m p a r i s o n w i t h s t a n d a r d c h a r t s as p r e p a r e d by Powers (1953), F o l k (1968), and T e r r y and C h i l a n g a r i a n (1955), r e s p e c t i v e l y . Sandstones were c l a s s i f i e d u s ing Folk's (1968) t r i a n g u l a r diagrams. For heavy mineral a n a l y s i s , 17 samples ranging from f i n e sandstone to g r a n u l e conglomerate were crushed and s i e v e d to very f i n e sand s i z e (0.125 mm) , and then separated by g r a v i t y u s i n g h e a v y - l i q u i d s (Krumbein and P e t t i j o h n , 1938). A f t e r s e p a r a t i o n , a magnet was used to separate out magnetite, which presumably removed most of the i l m e n i t e . 16 A t o t a l o f 27 t h i n s e c t i o n s were s e l e c t e d f o r modal a n a l y s i s . These s e c t i o n s were s t a i n e d f o r K f and Na + to a i d i n t h e i d e n t i f i c a t i o n o f p o t a s s i u m f e l d s p a r and s o d i u m - r i c h p l a g i o c l a s e , r e s p e c t i v e l y , u s i n g the method o u t l i n e d by B a i l e y and S t e v e n s (1960). A p p r o x i m a t e l y 300 g r a i n s were p o i n t c o u n t e d p e r t h i n s e c t i o n . T h i s number was a r r i v e d a t by a p p r o x i m a t i n g the method o u t l i n e d by Solomon (1963) which t a k e s i n t o a c c o u n t t h e a v e r a g e g r a i n s i z e , t h e g r i d s p a c i n g and t h e t o t a l a r e a o f the g r i d i n an attempt t o m i n i m i z e t h e v a r i a n c e . F o r d e t e r m i n i n g c o a l i f i c a t i o n l e v e l s , s a m p l e s o f carbonaceous s h a l e and c o a l fragments were crushed to -850 um and formed i n t o p e l l e t s , u s i n g a t h e r m o - p l a s t i c t h a t melts at l e s s than 100° C, and p o l i s h e d with a f i n a l g r i t s i z e of 0.05 um. F o r each sample, maximum r e f l e c t a n c e measurements were made by r o t a t i n g the stage through 360° as the r e f l e c t a n c e was r e c o r d e d . A minimum of 50 maximum r e f l e c t a n c e measurements were made and the mean and standard d e v i a t i o n determined f o r each of the 6 samples. 17 LITHOSTRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS The S u s t u t Group i s an Upper C r e t a c e o u s assemblage of non-marine s e d i m e n t a r y and v o 1 c a n i c 1 a s t i c u n i t s . E i s b a c h e r (1971) r e c o g n i z e d two f o r m a t i o n s t h a t can be i d e n t i f i e d throughout the Sustut Basin; the Tango Creek and the Brothers Peak. E i s b a c h e r (1971) c o n s i d e r e d the Tango Creek Formation to be Late Cretaceous (Cenomanian to Turonian) i n age, based on the i d e n t i f i c a t i o n of f o s s i l f l o r a , and the Brothers Peak F o r m a t i o n t o be m a i n l y of Eocene age based on f o s s i l p l a n t s and two age dates obtained from t u f f samples. P a l y n o l o g i c a l r e s u l t s from the present study, as d i s c u s s e d l a t e r , i n d i c a t e however t h a t the Tango Creek Formation and the Brothers Peak F o r m a t i o n i n t h e s t u d y a r e a , a r e b o t h L a t e C r e t a c e o u s ( C a m panian t o M a a s t r i c h t i a n ) i n age and t h a t t h e y a r e conformable. Thick and e x t e n s i v e pebble conglomerate beds of the B r o t h e r s Peak Formation are i n e r o s i o n a l c o n t a c t with the u n d e r l y i n g r e c e s s i v e m udstone beds o f t h e Tango C r e e k F o r m a t i o n . T h i s c o n t a c t can be t r a c e d t h r o u g h o u t the S u s t u t B a s i n ( F i g u r e 2). The two f o r m a t i o n s can be s u b d i v i d e d i n t o members w h i c h a r e d i s c u s s e d f u r t h e r b e l o w . D e t a i l e d l i t h o l o g i c l o g s and accompanying d e s c r i p t i o n s f o r each of the measured s e c t i o n s are i n the pocket of the t h e s i s (Figures 7a-7g). F i g u r e 8, i s a s t r a t i g r a p h i c c o r r e l a t i o n o f t h e measured s e c t i o n s . TANGO CREEK FORMATION In the Sustut Basin, the Tango Creek Formation v a r i e s i n t h i c k n e s s from 400 m i n t h e s o u t h t o o v e r 1 400 m i n the 18 Figure 8. Stratigraphic correlation 19 Section S5 Locat ion Map north. E i s b a c h e r (1974) d e f i n e d two i n f o r m a l members t h a t can be i d e n t i f i e d t h r o u g h o u t most o f t h e b a s i n : the lower N i v e n Member and t h e upper T a t l a t u i Member. The c o n t a c t between these members i s g r a d a t i o n a l from predominantly red and green mudstone i n the Niven Member to mainly grey mudstones of the T a t l a t u i Member. In the study area, o n l y the uppermost 400 m of the T a t l a t u i Member i s exposed (for a d e t a i l e d d e s c r i p t i o n of the Niven Member, see E i s b a c h e r , 1974). TATLATUI MEMBER - LITHOFACIES DESCRIPTION The T a t l a t u i Member c o n s i s t s o f s e v e r a l l a t e r a l l y continuous conglomerate and medium to coarse g r a i n e d sandstone u n i t s , separated by t h i c k sequences of interbedded mudstone, s i l t s t o n e and f i n e g r a i n e d s a n d s t o n e . Two l i t h o f a c i e s a r e r e c o g n i z e d i n t h e T a t l a t u i s e q u e n c e : a c o a r s e g r a i n e d l i t h o f a c i e s and a f i n e g r a i n e d l i t h o f a c i e s ( P l a t e 2). Coarse Grained L i t h o f a c i e s The c o a r s e g r a i n e d l i t h o f a c i e s i s a minor component o f t h e T a t l a t u i Member, e x c e p t i n s e c t i o n S4 where t h e l i t h o f a c i e s c o m p r i s e s o v e r h a l f o f the measured s e c t i o n ( F i g u r e 8 ) . The c o a r s e g r a i n e d l i t h o f a c i e s c o m p r i s e s i n t e r n a l l y d i s c o n t i n u o u s sequences ranging from 2 m to 20 m i n t h i c k n e s s , composed of m a s s i v e t o t h i c k l y bedded p e b b l e c o n g l o m e r a t e s i n t e r b e d d e d w i t h , and l o c a l l y f i n i n g upwards i n t o , c o a r s e t o medium g r a i n e d , p e b b 1 y s a n d s t o n e . U n d e r l y i n g mudstone or s i l t s t o n e of the T a t l a t u i Member i s i n e r o s i o n a l c o n t a c t with the coarse g r a i n e d l i t h o f a c i e s . 20 P l a t e 2. C h a r a c t e r i s t i c s o f the T a t l a t u i Member P e b b l 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 w i t h a modal c l a s t s i z e of 1.5 cm ( P l a t e 2). L o c a l l y , i n s e c t i o n S4 c l a s t s up to 11 cm occur. Poor to moderately s o r t e d matrix comprises 10 t o 30% of t h e c o n g l o m e r a t e and r a n g e s from s i l t t o c o a r s e sand s i z e . S a n d s t o n e s a r e t y p i c a l l y c r o s s - s t r a t i f i e d i n t a b u l a r s e t s 40 to 50 cm t h i c k . Trough c r o s s bedding, massive t o medium h o r i z o n t a l s t r a t i f i c a t i o n and s c o u r s u r f a c e s a r e present to a l e s s e r extent. Mudstone r i p - u p c l a s t s , up t o 10 cm i n l e n g t h , commonly occur at the base of the conglomerates and w i t h i n some of the sandstones. Carbonaceous fragments, l o g impressions up to 3 m l o n g , and c a l c a r e o u s s a n d s t o n e n o d u l e s , 40 cm by 20 cm i n diameter, occur l o c a l l y throughout the l i t h o f a c i e s . F i n e Grained L i t h o f a c i e s The f i n e g r a i n e d l i t h o f a c i e s c o m p r i s e s i n t e r b e d d e d sequences up to 100 m t h i c k . Mudstone i s the main l i t h o l o g y , w ith l e s s e r amounts of s i l t s t o n e and f i n e to v e r y f i n e g r a i n e d s a n d s t o n e . I n d i v i d u a l l i t h o l o g i e s range from 30 cm ( f i n e g r a i n e d sandstone) t o 12 m (mudstone) i n t h i c k n e s s and a r e l a t e r a l l y d i s c o n t i n u o u s . R e s i s t a n t beds of s a n d s t o n e and l o c a l s i l t s t o n e occur w i t h i n the o v e r a l l r e c e s s i v e interbedded sequence. The v a r i o u s u n i t s are massive to t h i n l y bedded and h i g h l y f r a c t u r e d , a l t h o u g h zones of carbonaceous f l e c k s and mudstone r i p - u p c l a s t s are common i n some f i n e g r a i n e d sandstone u n i t s . 22 TATLATDI MEMBER - INTERPRETED DEPOSITIONAL ENVIRONMENT F a b r i c , t e x t u r e and morphology of the T a t l a t u i sediments s u g g e s t d e p o s i t i o n by f l u v i a l p r o c e s s e s . The f i n e g r a i n e d l i t h o f a c i e s i s i n t e r p r e t e d as a f l o o d p l a i n d e p o s i t . The c o a r s e g r a i n e d l i t h o f a c i e s has many f e a t u r e s i n d i c a t i v e of channel d e p o s i t s , such as e r o s i v e b a s a l c o n t a c t s and l a t e r a l d i s c o n t i n u i t y . Of the fou r p r i n c i p a l r i v e r types: s t r a i g h t , b r a i d e d , a n a s t o m o s i n g and meandering, d e s c r i b e d by M i a l l (1977) and i l l u s t r a t e d i n F i g u r e 9, t h e c o a r s e g r a i n e d l i t h o f a c i e s most c l o s e l y r e s e m b l e s d e p o s i t s o f a b r a i d e d r i v e r . B r a i d e d r i v e r s produce i n t e r n a l l y complex d e p o s i t s as a r e s u l t o f the b u i l d - u p and m i g r a t i o n o f l o n g i t u d i n a l and t r a n s v e r s e bars, and the r a p i d l a t e r a l m i g r a t i o n of channels a c r o s s t h e b r a i d p l a i n ( M i a l l , 1977). The c o a r s e g r a i n e d l i t h o f a c i e s i s c o n g l o m e r a t i c a t the base and fine's upwards i n t o h o r i z o n t a l l y and c r o s s - s t r a t i f i e d sandstone, w i t h l o c a l e r o s i o n a l s c o u r s f i l l e d w i t h c r o s s - s t r a t i f i e d s a n d s t o n e . A n a l o g o u s d e p o s i t s a r e foun d i n t h e b r a i d e d Donjek R i v e r , Yukon (Rust, 1972), which i s dominated by l o n g i t u d i n a l b a r s . S i m i l a r t o the c o a r s e g r a i n e d l i t h o f a c i e s o f the T a t l a t u i Member, the l o n g i t u d i n a l bars of the Donjek R i v e r are composed of a mixture of conglomerate and sandstone, and are commonly d i s s e c t e d by l o w - o r d e r c h a n n e l s , p r o d u c i n g l o c a l pods of c r o s s - s t r a t i f i e d s a n d s t o n e . G r o s s - s t r a t i f i e d s a n d s t o n e i s a l s o commonly a t t r i b u t e d to accumulation i n t r a n s v e r s e bars, as documented by Smith (1970) i n the P l a t t e R i v e r , Nebraska. 23 meandering FTHI bar surfaces covered during flood stages braided Figure 9 Principal braided river types (modified from Miall, 1977) 24 The abundance of c r o s s - s t r a t i f i e d sandstone w i t h i n the coarse g r a i n e d l i t h o f a c i e s s u g g e s t s d e p o s i t i o n o c c u r r e d i n b o t h t r a n s v e r s e and l o n g i t u d i n a l bars. Deposits w i t h complex i n t e r n a l v a r i a t i o n s i m i l a r to the c o a r s e g r a i n e d l i t h o f a c i e s o f the T a t l a t u i Member a r e a l s o a t t r i b u t e d to the e r o s i o n and d i s s e c t i o n of b r a i d bars d u r i n g waning f l o o d stages ( M i a l l , 1977). These e r o s i o n a l processes make t h e o r i g i n a l shape and s i z e o f t h e b a r i m p o s s i b l e t o d i s c e r n . Waning f l o o d s t a g e s may a l s o l e a d t o t h e a c c u m u l a t i o n o f a t h i n mud l a y e r on b a r t o p s , and i f s u b a e r i a l l y exposed, o f t e n leads to the formation of mudstone r i p - u p c l a s t s , which are i n c o r p o r a t e d as a l a g d e p o s i t i n the next f l o o d stage. Mudstone r i p - u p c l a s t s are abundant w i t h i n the T a t l a t u i s t r a t a , s u g g e s t i n g t h a t v a r i a t i o n i n water d i s c h a r g e was frequent d u r i n g d e p o s i t i o n of the coarse g r a i n e d l i t h o f a c i e s . C a r b o n i z e d l o g s up t o 3 m i n l e n g t h w i t h i n t h e c o a r s e g r a i n e d l i t h o f a c i e s a r e a l s o i n t e r p r e t e d as a l a g d e p o s i t , a n a l o g o u s t o the Cannes de Rouche F o r m a t i o n , Gaspe, i n which Rust (1978) recorded l o g s measuring 5 m i n length. V e r t i c a l l y and l a t e r a l l y , the f i n e g r a i n e d l i t h o f a c i e s of the T a t l a t u i Member i s e x t e n s i v e , w i t h the e x c e p t i o n o f s e c t i o n S 4 , where the c o a r s e g r a i n e d l i t h o f a c i e s c o m p r i s e s over h a l f of the measured s e c t i o n (Figure 7c). Organic b l a c k mudstone w i t h i n the f i n e g r a i n e d l i t h o f a c i e s suggests a humid c l i m a t e c a p a b l e of su p p o r t i n g v e g e t a t i o n ; however, the absence of c o a l seams i n d i c a t e s t h a t c o n d i t i o n s were not conducive to the accumulation and/or p r e s e r v a t i o n of peat. Discontinuous f i n e g r a i n e d sandstone u n i t s , present w i t h i n the f i n e g r a i n e d l i t h o f a c i e s , s u g g e s t t h a t minor d i s t r i b u t a r y c h a n n e l s were p e r i o d i c a l l y a c t i v e d u r i n g f l o o d stages, analogous to d i s t a l a l l u v i a l f a n d e p o s i t s ( N i l s e n , 1982). The a s s o c i a t i o n of o r g a n i c b l a c k mudstone, s i l t s t o n e and f i n e s a n d s t o n e t o g e t h e r w i t h c o n g l o m e r a t e and s a n d s t o n e s u g g e s t s t h a t t h e T a t l a t u i s e d i m e n t s were d e p o s i t e d i n an a l l u v i a l p l a i n environment, p e r i o d i c a l l y occupied by a b r a i d e d r i v e r complex ( F i g u r e 10). But, because o f the d i s t r i b u t i o n o f b r a i d e d r i v e r d e p o s i t s , and t h e i r l a c k o f l a t e r a l c o n t i n u i t y , i t i s i n t e r p r e t e d t h a t the m i g r a t i o n o f the b r a i d e d r i v e r t r a c t was somewhat co n f i n e d . I n a c t i v e areas on the a l l u v i a l p l a i n s u p p o r t e d v e g e t a t i o n and g e n e r a l l y a c c u m u l a t e d mud, r e c e i v i n g s i l t and s a n d v i a s m a l l d i s t r i b u t a r y channels and d u r i n g f l o o d stages. 26 Figure 10. Interpreted depositional environment of the Tatlatui Member BROTHERS PEAK FORMATION In the S u s t u t B a s i n , t h e B r o t h e r s Peak F o r m a t i o n v a r i e s i n t h i c k n e s s from 300 m t o o v e r 1000 m. E i s b a c h e r (1974) d i s t i n g u i s h e d two members w i t h i n the Brothers Peak Formation: the L a s l u i Member, and the o v e r l y i n g S p a t s i z i Member. In the s t u d y a r e a , t h e L a s l u i Member i s s u b d i v i d e d i n t o a lower s e q u e n c e c h a r a c t e r i z e d by a p r e d o m i n a n c e o f t h i c k conglomerates and an upper sequence of f i n e r g r a i n e d sediments i n t e r b e d d e d w i t h a s h - f a l l t u f f s . N u m e r o u s p e b b l y sandstone/black mudstone sequences c h a r a c t e r i z e the S p a t s i z i Member. The c o n t a c t between the L a s l u i and S p a t s i z i Members i s p l a c e d a t the base of the f i r s t sandstone/mudstone sequence, c o n t r a r y t o E i s b a c h e r (1974), who p l a c e d the c o n t a c t where a marked d e c r e a s e i n c o n g l o m e r a t i c b eds and a c h a n g e i n p a l e o c u r r e n t d i r e c t i o n s occurred. 28 LOWER LASLUI MEMBER - LITHOFACIES DESCRIPTION F i n i n g upwards s u c c e s s i o n s o f c o n g l o m e r a t e , s a n d s t o n e , s i l t s t o n e , and mudstone t y p i f y t h e l o w e r L a s l u i Member. S u c c e s s i o n s v a r y i n t h i c k n e s s from 100 t o 150 m. At the base of the sequence i s a r e s i s t a n t c o n g l o m e r a t e zone i n e r o s i o n a l c o n t a c t w i t h mudstones o f the T a t l a t u i Member. Sediments o f t h e l o w e r L a s l u i Member a r e d i v i d e d i n t o two l i t h o f a c i e s ; a c o n g l o m e r a t i c l i t h o f a c i e s , i n c l u d i n g b o t h s a n d s t o n e and c o n g l o m e r a t e , and a f i n e g r a i n e d l i t h o f a c i e s c o n s i s t i n g p r e d o m i n a n t l y o f mudstone and s i l t s t o n e . C o n g l o m e r a t i c L i t h o f a c i e s The c o n g l o m e r a t i c l i t h o f a c i e s w hich i s t h e main component o f t h e l o w e r L a s l u i Member f o r m s two and l o c a l l y t h r e e l a t e r a l l y c o n t i n u o u s , f i n i n g upwards s e q u e n c e s r a n g i n g i n t h i c k n e s s f r o m 30 t o 60 m. The l i t h o f a c i e s i s composed o f p e b b l e - c o b b l e o r t h o c o n g l o m e r a t e and medium g r a i n e d sandstone. A t t h e b a s e o f t h e l o w e r L a s l u i Member i s t h e t h i c k e s t and c o a r s e s t c o n g l o m e r a t e u n i t w i t h i m b r i c a t e d c l a s t s r a n g i n g up t o b o u l d e r s i z e ( P l a t e 3 a ) . Above t h e b a s e t h e modal g r a i n s i z e o f t h e c o n g l o m e r a t e d e c r e a s e s m a r k e d l y t o 1 cm, w i t h l o c a l c l a s t s up t o 25 cm. I n t e r n a l l y e a c h c o n g l o m e r a t e s e q u e n c e e x h i b i t s r a p i d l a t e r a l v a r i a t i o n i n t e x t u r e ( P l a t e 3b). I n s e c t i o n s S2 and S3, 2 t o 4 m t h i c k c o n g l o m e r a t e u n i t s a r e a l s o f o u n d i n t e r b e d d e d w i t h s a n d s t o n e and f i n e r g r a i n e d s e d i m e n t s . Conglomerate i s g e n e r a l l y m a s s i v e t o t h i c k l y bedded, b u t l o c a l l y h o r i z o n t a l o r t a b u l a r c r o s s - s t r a t i f i c a t i o n o c c u r s i n 29 Plate 3. Characteristics of the lower Laslui Member. 3a. Imbricated clasts at the base of the lower Laslui Member. 3b. Internally complex and rapid variation in texture, both v e r t i c a l l y and l a t e r a l l y . 3c,d. Tabular c r o s s - s t r a t i f i c a t i o n . 3e. Mudstone rip-up clasts in sandstone. 3f. Log impression within a very coarse sandstone sequence. 30 31 30 cm s e t s ( P l a t e 3c, 3d). The c o n g l o m e r a t e i s poor t o moderately s o r t e d and c o n t a i n s 10 to 30% matrix. M a t r i x ranges i n s i z e from f i n e t o c o a r s e sand and i s m o d e r a t e l y s o r t e d . Sandstone i s t h i c k l y bedded or t a b u l a r c r o s s - s t r a t i f i e d i n 10 to 20 cm s e t s . Scour channels up t o 5 m i n t h i c k n e s s and 10 m i n l a t e r a l e x t e n t a l s o o c c u r w i t h i n the s a n d s t o n e i n t e r v a l . Mudstone r i p - u p c l a s t s , c a r b o n a c e o u s f r a g m e n t s and l o g i m p r e s s i o n s a r e common t h r o u g h o u t t h e c o n g l o m e r a t i c l i t h o f a c i e s ( P l a t e 3e, 3 f ) . Fin e Grained L i t h o f a c i e s The f i n e g r a i n e d l i t h o f a c i e s i s a minor component and c o n s i s t s of 2 to 5 m t h i c k i n t e r v a l s of carbonaceous mudstone, s i l t s t o n e and l o c a l f i n e g r a i n e d s a n d s t o n e . In s e c t i o n s S4 and S6 the f i n e g r a i n e d l i t h o f a c i e s i s absent. When present, t h e f i n e g r a i n e d l i t h o f a c i e s i s g r a d a t i o n a l f r o m t h e con g l o m e r a t i c l i t h o f a c i e s , capping the o v e r a l l f i n i n g upwards sequences. The u n i t s a r e t h i n l y bedded and h i g h l y f r a c t u r e d . L o c a l l y , f i n e g r a i n e d sandstones c o n t a i n carbonaceous f l e c k s . LOWER LASLUI MEMBER - INTERPRETED DEPOSITIONAL ENVIRONMENT A c o m p l e x a s s o c i a t i o n o f c o n g l o m e r a t e s and p e b b l y s a n d s t o n e s , w i t h l e s s e r amounts of f i n e r g r a i n e d s e d i m e n t s c h a r a c t e r i z e s t h e l o w e r L a s l u i Member. O v e r a l l , t h e c o a r s e n e s s , t h i c k n e s s , and e x t e n t of the c o a r s e g r a i n e d d e p o s i t s , p l u s the complex i n t e r n a l f a c i e s r e l a t i o n s h i p a r e s u g g e s t i v e o f d e p o s i t i o n by a h i g h e n e r g y b r a i d e d r i v e r 32 complex i n a humid a l l u v i a l fan (mid-fan p o s i t i o n ) , s i m i l a r to the f a c i e s of the g l a c i a l outwash d e p o s i t s i n the San Joaquin V a l l e y (Cherven, 1984). At the base of the lower L a s l u i sequence a r e m a s s i v e t o p a r a l l e l l a m i n a t e d , l o c a l l y i m b r i c a t e d c o n g l o m e r a t e s i n t e r p r e t e d as l o n g i t u d i n a l bars, analogous to d e p o s i t s of the modern b r a i d e d Donjek R i v e r , Yukon (Rust, 1972), and b r a i d e d outwash f a n d e p o s i t s i n the n o r t h e a s t e r n G u l f of A l a s k a (Boothroyd and Ashley, 1975). The lower L a s l u i conglomerates a r e c o a r s e s t a t the base, l o c a l l y p o s s e s s i n g a l a g d e p o s i t which i s t h o u g h t t o i n i t i a t e the f o r m a t i o n o f l o n g i t u d i n a l bars (Boothroyd and A s h l e y , 1975; Cant, 1982), and v e r t i c a l l y g r ade i n t o p a r a l l e l l a m i n a t e d p e b b l y s a n d s t o n e s . T a b u l a r c r o s s - s t r a t i f i c a t i o n i s l e s s common but may d e v e l o p a t the down c u r r e n t end of the bar. Rust (1972) d e s c r i b e d a s i m i l a r sequence f o r l o n g i t u d i n a l bar d e p o s i t s i n the Donjek R i v e r . Pebbly c r o s s - s t r a t i f i e d sandstone t h a t l o c a l l y dominates the upper s e c t i o n s of the coarse g r a i n e d l i t h o f a c i e s , p r o b a b l y r e p r e s e n t t r a n s v e r s e bar d e p o s i t s as documented i n the P l a t t e R i v e r , Nebraska, by Smith (1970). Capping the o v e r a l l f i n i n g upwards sequences, i s the f i n e g r a i n e d l i t h o f a c i e s which r e p r e s e n t s f l o o d p l a i n d e p o s i t i o n d u r i n g decreased water f l o w l e v e l s , s i m i l a r t o F a c i e s A and B on the Donjek R i v e r ( W i l l i a m s and Rust, 1969). With s u s t a i n e d low l e v e l s o f d i s c h a r g e , c l a y , s i l t , and f i n e sand may accumulate o v e r the channel s u r f a c e , as a f l o o d p l a i n d e p o s i t . O t h e r w i s e , the f i n e s e d i m e n t s a r e removed d u r i n g s u b s e quent 33 f l o o d s , which e x p l a i n s the p a u c i t y of mudstone and s i l t s t o n e i n t h e l o w e r L a s l u i s e d i m e n t s . E r o s i o n of t h i n mud l a y e r s i s e v i d e n t by t h e i n c o r p o r a t i o n o f mudstone r i p - u p c l a s t s i n t o c h a n n e l l a g s a t the base of l o n g i t u d i n a l bar d e p o s i t s , i n d i c a t i n g r a p i d f l u c t u a t i o n of water d i s c h a r g e from stages of e r o s i o n to stages of d e p o s i t i o n . The o v e r a l l decrease i n c l a s t s i z e of s u c c e s s i v e f i n i n g upwards sequences i n d i c a t e d e p o s i t i o n by c y c l i c a l f l o o d s w h i c h d e c r e a s e d i n o v e r a l l w a t e r d i s c h a r g e t h r o u g h o u t d e p o s i t i o n o f t h e l o w e r L a s l u i Member. The c o m p l e x o v e r l a p p i n g and e r o s i o n of l o n g i t u d i n a l and t r a n s v e r s e bars r e s u l t s i n r a p i d i n t e r n a l l a t e r a l v a r i a t i o n s i n the t e x t u r e of t h e c o a r s e g r a i n e d l i t h o f a c i e s . A n a l o g o u s f i n i n g upwards sequences o c c u r i n modern st r e a m g r a v e l s d e s c r i b e d by Smith (1974), and i n a n c i e n t e q u i v a l e n t s d e s c r i b e d by S t e e l and Thompson (1983). Because o f the r a p i d l a t e r a l s h i f t i n g o f channels, b r a i d e d r i v e r s t y p i c a l l y produce e x t e n s i v e sheets of c o a r s e g r a i n e d s e d i m e n t s w i t h s u b o r d i n a t e amounts of f i n e s , a n a l o g o u s t o the c o a r s e g r a i n e d l i t h o f a c i e s of t h e l o w e r L a s l u i sequence. Braided r i v e r d e p o s i t s are a major component of a l l u v i a l f a n complexes as documented by many a u t h o r s , such as B u l l (1972), B o o t h r o y d and Numraedal (1978), C o l l i n s o n (1981), and Rust (1984). The l o w e r L a s l u i s t r a t a c o n t a i n many of t h e c h a r a c t e r i s t i c s of a l l u v i a l f a n d e p o s i t s as summarized by N i l s e n (1982), such as: 1) complex changes i n l a t e r a l and v e r t i c a l f a c i e s ; 2) p a u c i t y o f o r g a n i c m a t t e r ; 3) l i m i t e d s u i t e of s e d i m e n t a r y s t r u c t u r e s , most commonly medium t o 34 l a r g e - s c a l e c r o s s . - s t r a t a and p l a n a r s t r a t i f i c a t i o n ; 4) r a p i d down f a n decreases i n both average and maximum c l a s t s i z e ; 5) t y p i c a l l y poor s o r t i n g , c o n t a i n i n g a g r e a t range of g r a i n s i z e s ; and 6) d e p o s i t i o n by h i g h e n e r g y f l o w s . The absence o f g r a v i t y f l o w s w i t h i n the lower L a s l u i s t r a t a l i k e l y r e f l e c t s c o n t i n u a l s e d i m e n t a t i o n and s u s t a i n e d h i g h water d i s c h a r g e s d u r i n g d e p o s i t i o n , as g r a v i t y f l o w s a r e u s u a l l y prompted by abundant but s p o r a t i c water supply ( B u l l , 1972). The lower L a s l u i Member i s i n t e r p r e t e d t o have been d e p o s i t e d i n proximal b r a i d e d r i v e r s i n a mid-fan p o s i t i o n on an a l l u v i a l f a n complex (Figure 11). Both the l a t e r a l extent and a s s o c i a t i o n of f a c i e s w i t h i n the lower L a s l u i Member has many s i m i l a r i t i e s w i t h f i n i n g upwards p r o x i m a l b r a i d p l a i n d e p o s i t s o f t h e M a l b a i e F o r m a t i o n , E a s t e r n Gaspe, Quebec, d e s c r i b e d by Rust (1984). In the m i d - f a n p o s i t i o n , many c h a n n e l s a r e p r e s e n t and a r e f r e e t o m i g r a t e a c r o s s the a l l u v i a l f a n (McGowan and G r o a t , 1971). Thus, a m i d - f a n p o s i t i o n accounts f o r the coarseness of the sediments and the l a t e r a l c o n t i n u i t y of the d e p o s i t . 35 Figure 1 1. Interpreted depositional environment of the lower Laslui Member UPPER LASLUI MEMBER - LITHOFACIES DESCRIPTION Sediments of the upper L a s l u i Member a b r u p t l y o v e r l y the lower L a s l u i Member and comprise a d i s t i n c t i v e assemblage of interbedded f i n e g r a i n e d d e p o s i t s i n t e r s p e r s e d with r e s i s t a n t c o n g l o m e r a t e and s a n d s t o n e u n i t s ( P l a t e 4 ) . A p p r o x i m a t e l y 900 m t h i c k , t h e upper L a s l u i Member can be d i v i d e d i n t o a coarse g r a i n e d and an interbedded f i n e g r a i n e d l i t h o f a c i e s . Coarse Grained L i t h o f a c i e s S a n d s t o n e s and c o n g l o m e r a t e s o f t h e c o a r s e g r a i n e d l i t h o f a c i e s c o m p r i s e r o u g h l y one t h i r d o f t h e upper L a s l u i Member, and g e n e r a l l y form w i d e l y spaced, r e s i s t a n t and l a t e r a l l y d i s c o n t i n u o u s u n i t s 2 m t o 12 m t h i c k . Orthoconglomerates, paraconglomerates and sandstones a l l occur w i t h i n the coarse g r a i n e d l i t h o f a c i e s . The orthoconglomerates are d i v i d e d i n t o s u b - f a c i e s "A" and "B" as d e s c r i b e d below. Orthoconglomerate "A" forms two l a t e r a l l y continuous, 10 to 12 m t h i c k , massive to p o o r l y s t r a t i f i e d , g r a n u l e to pebble conglomerate sequences t h a t f i n e upwards i n t o pebbly, f i n e to medium g r a i n e d s a n d s t o n e ( P l a t e 5a). The bases of the sequences are i n e r o s i o n a l c o n t a c t with mudstones and l o c a l l y expose l o n g i t u d i n a l s c o u r s , s i m i l a r t o the g u t t e r c a s t s of C o l l i n s o n and Thompson (1982; P l a t e 5b). O r t h o c o n g l o m e r a t e "A" i s p o o r l y s o r t e d and c o n t a i n s 10 t o 20% m a t r i x . The matrix i s moderately s o r t e d and has a mean g r a i n s i z e of f i n e t o medium sand. Sandstone a s s o c i a t e d w i t h o r t h o c o n g l o m e r a t e 37 Overview of the upper Laslui Member, i l l u s t r a t i n g the d i s t i n c t i v e l e n t i c u l a r , white t u f f beds. 38 "A", i s commonly c r o s s - s t r a t i f i e d i n t a b u l a r s e t s 10 to 15 cm t h i c k . H o r i z o n t a l s t r a t i f i c a t i o n and t r o u g h c r o s s -s t r a t i f i c a t i o n a r e l e s s abundant. Sandstone a l s o o c c u r s i n e r o s i o n a l s c o u r s 50 cm t h i c k and 2 t o 3 m i n l a t e r a l e x t e n t . Carbonaceous f r a g m e n t s , l o g i m p r e s s i o n s ( P l a t e 5c) and mudstone r i p - u p c l a s t s are abundant throughout the sequences. In c o n t r a s t to orthoconglomerate "A", Orthoconglomerate "B" forms s e v e r a l t h i n n e r u n i t s r a n g i n g from 10 t o 25 cm i n t h i c k n e s s . L o c a l l y t h e s e t h i n , m a s s i v e c o n g l o m e r a t e s a r e l a t e r a l l y continuous f o r 50 m, but commonly p e r s i s t f o r o n l y a few meters, ( P l a t e 5d). O r t h o c o n g l o m e r a t e "B" i s p o o r l y s o r t e d and c l a s t s range i n s i z e from 1 cm t o 1 mm. M a t r i x comprises 10 to 30% of the rock, and ranges from s i l t to c l a y . P a r a c o n g 1 o m e r a t e s a r e a p p r o x i m a t e l y 2 m t h i c k and form l a t e r a l l y d i s c o n t i n u o u s , f i n g e r - l i k e lobes. Although a minor component, p a r a c o n g 1 o m e r a t e s o c c u r i n a l l the s e c t i o n s measured. These g r a n u l e c o n g l o m e r a t e s have a r e s i s t a n c e i n t e r m e d i a t e between a d j a c e n t s a n d s t o n e s and r e c e s s i v e f i n e g r a i n e d s e d i m e n t s ( P l a t e 6a). The p a r a c o n g 1 o m e r a t e s have s h a r p u p p e r and l o w e r c o n t a c t s , a r e b o t h n o r m a l l y and r e v e r s e l y g r a d e d ( P l a t e 6b), and a r e p o o r l y s o r t e d c o n t a i n i n g up to 50% m a t r i x . The m a t r i x has a mean g r a i n s i z e of s i l t to c l a y . Medium t o c o a r s e g r a i n e d , l a t e r a l l y d i s c o n t i n u o u s s a n d s t o n e u n i t s range i n t h i c k n e s s from 15 cm to 5 m. The t h i n n e r u n i t s form p a r t of the i n t e r b e d d e d f i n e g r a i n e d l i t h o f a c i e s . Sandstone f i n e s upwards from an e r o s i o n a l b a s a l 39 5c. Log impressions within orthocon-glomerate 'A'. 5d . Laterally discontinuous exposure of orthoconglomerate 'B', within a sequence of interbedded fine grained sediments. ¥0 c o n t a c t w i t h mudstone or s i l t s t o n e and a r e h o r i z o n t a l l y s t r a t i f i e d . Interbedded Fine Grained L i t h o f a c i e s The interbedded f i n e g r a i n e d l i t h o f a c i e s forms over h a l f of t h e upper L a s l u i Member. Mudstone i s the most abundant l i t h o l o g y w i t h l e s s e r amounts of s i l t s t o n e , f i n e g r a i n e d sandstone and t u f f beds. G r e e n , h i g h l y f r a c t u r e d mudstone f o r m r e c e s s i v e i n t e r v a l s of up t o 20 m t h i c k t h r o u g h o u t the upper L a s l u i Member. In the lower h a l f of the upper L a s l u i sequence, 1 to 2 m t h i c k r e d mudstone u n i t s a r e commonly i n t e r b e d d e d w i t h green mudstones, but are absent h i g h e r i n the s e c t i o n . B lack, c a r b o n a c e o u s mudstone and s i l t s t o n e a r e minor components of the interbedded f i n e g r a i n e d l i t h o f a c i e s . O c c u r r i n g as e i t h e r 15 to 20 cm t h i c k l a t e r a l l y d i s c o n t i n u o u s r e s i s t a n t u n i t s , or as 1 t o 3 m t h i c k r e c e s s i v e i n t e r v a l s . F i n e g r a i n e d s a n d s t o n e o c c u r s as 20 t o 30 cm t h i c k l a t e r a l l y d i s c o n t i n u o u s u n i t s w i t h i n t h e f i n e g r a i n e d l i t h o f a c i e s . C o n t a c t s a r e commonly s h a r p and l o c a l l y c h a n n e l e d bases o c c u r . F i n e g r a i n e d s a n d s t o n e e x h i b i t s h o r i z o n t a l s t r a t i f i c a t i o n i n 1 cm se t s . L o c a l l y , t u f f c o m p r i s e s about a q u a r t e r o f the upper L a s l u i Member. The t u f f u n i t s occur i n l e n t i c u l a r beds up to 40 m i n l e n g t h and average 40 cm i n t h i c k n e s s . Both upper and lower c o n t a c t s a r e s h a r p even though s u r r o u n d i n g u n i t s a r e commonly t u f f a c e o u s ( P l a t e 6c). T u f f s a r e m a s s i v e t o t h i n l y b e d d e d w i t h l o c a l o c c u r r e n c e s o f s m a l l s c a l e c r o s s -41 Plate 6. Characteristics of the upper Laslui Member paraconglomerate and tuff. 6b. Paraconglomerate showing both normal and reverse grading. HI s t r a t i f i c a t i o n . C l o s e l y a s s o c i a t e d with t u f f are t h i n , 5 to 10 cm b e n t o n i t e s . UPPER LASLUI MEMBER - INTERPRETED DEPOSITIONAL ENVIRONMENTS The upper L a s l u i Member i s dominated by f i n e g r a i n e d s e d i m e n t s , w i t h t h e c o a r s e g r a i n e d f a c i e s f o r m i n g d i s c o n t i n u o u s pods, e x c e p t f o r two l a t e r a l l y c o n t i n u o u s c o n g l o m e r a t e sequences. The f a c i e s a r e i n t e r p r e t e d as a l l u v i a l p l a i n d e p o s i t s . Many o f t h e f a c i e s p r e s e n t h a v e c h a r a c t e r i s t i c s s u g g e s t i v e of d e p o s i t i o n i n se m i - a r i d c o n d i t i o n s , however, the presence of palynomorphs from very hot and humid c l i m a t e f l o r a (Rouse, p e r s comm., 1985) i n d i c a t e s a l t e r n a t i n g wet and d r y c o n d i t i o n s e x i s t e d , at l e a s t l o c a l l y , d u r i n g d e p o s i t i o n of the upper L a s l u i sequence. The v a r i e t y of c o l o r s of mudstone i n the upper L a s l u i Member, a l s o s u g g e s t s f l u c t u a t i o n s i n the l e v e l of t h e water t a b l e . Red mudstone s u g g e s t s o x i d i z i n g c o n d i t i o n s , common i n a r e a s w i t h a low w a t e r t a b l e , f a c i l i t a t i n g t h e w e a t h e r i n g o f f e r r o m a g n e s i u m m i n e r a l s ( h o r n b l e n d e and b i o t i t e ) t o c l a y m i n e r a l s such as h e m a t i t e ( C o l l i n s o n , 1978). However, as the r e d mudstone u n i t s a r e subordinate to green mudstone u n i t s , o x i d i z i n g c o n d i t i o n s must have been l o c a l or of sh o r t d u r a t i o n . O v e r a l l , green mudstone dominates the upper L a s l u i sequence and i s i n d i c a t i v e o f e i t h e r a more humid c l i m a t e with a higher water t a b l e (Graham, 1975), o r r e p r e s e n t s d e p o s i t i o n i n a l o c a l l y d eeper, w e t t e r p o s i t i o n on t h e f l o o d p l a i n . The p r e s e n c e o f b l a c k , o r g a n i c mudstone, a l t h o u g h i n minor amounts, s u g g e s t s swampy or 43 vegetated areas, a l s o must have been l o c a l l y present. Hence, c o n d i t i o n s on the f l o o d p l a i n , with r e s p e c t to the water t a b l e l e v e l , were h i g h l y v a r i a b l e d u r i n g d e p o s i t i o n . In c l o s e a s s o c i a t i o n with the mudstone d e p o s i t s are sheet - l i k e d e p o s i t s of h o r i z o n t a l l y s t r a t i f i e d f i n e g r a i n e d s a n d s t o n e and s i l t s t o n e , s i m i l a r t o modern day f l o o d p l a i n d e p o s i t s . McKee e t a l . (1967), r e c o r d e d a h o r i z o n t a l l y laminated sheet d e p o s i t between 1 and 4 m t h i c k , i n the B i j o u Creek, C o l o r a d o and on f u r t h e r e x a m i n a t i o n , c o n c l u d e d t h a t sheet sedimentation on the f l o o d p l a i n o c c u r r e d as a r e s u l t of f l o o d i n g on s m a l l and i n s i g n i f i c a n t channels. In the upper L a s l u i Member, d e p o s i t s of s i l t s t o n e and f i n e sandstone up to 3 m t h i c k may have a s i m i l a r o r i g i n . W e l l p r e s e r v e d , t h i c k , c r o s s - s t r a t i f i e d , l e n t i c u l a r t u f f b e d s t h a t o c c u r t h r o u g h o u t t h e u p p e r L a s l u i Member n e c e s s i t a t e s a subaqueous environment f r e e of e r o s i o n , such as s m a l l l a k e s or ponds. T u f f a c e o u s mudstone and s i l t s t o n e i s common d i r e c t l y above and below the t u f f h o r i z o n s , suggesting a c l o s e a s s o c i a t i o n i n space and time between accumulation and d e p o s i t i o n of t h i c k ash d e p o s i t s , and sediment c a r r i e d by f l o o d s to the a l l u v i a l p l a i n . In a s s o c i a t i o n with lakes and f l o o d p l a i n d e p o s i t s , S t e e l (1974) has documented f i n g e r - s h a p e d d i s t a l l o b e s of stream c h a n n e l s a n d s t o n e and c o n g l o m e r a t e , and mudflows t h a t a r e enveloped v e r t i c a l l y and l a t e r a l l y by f i n e r g r a i n e d sediments, i n the New Red Sandstone, S c o t l a n d . S i m i l a r l y i n the upper L a s l u i s t r a t a , d i s c o n t i n u o u s lobes of orthoconglomerate "B", medium t o c o a r s e g r a i n e d s a n d s t o n e and p a r a c o n g l o m e r a t e a r e 44 p r e s e n t w i t h i n a d o m i n a n t l y f i n e g r a i n e d , f l o o d p l a i n s u c c e s s i o n . O r t h o c o n g l o m e r a t e " B " , and the medium t o c o a r s e g r a i n e d sandstone d e p o s i t s are t y p i c a l l y p o o r l y s o r t e d , t h i n , d i s c o n t i n u o u s u n i t s a n a l o g o u s t o stream c h a n n e l d e p o s i t s c h a r a c t e r i s t i c of a l l u v i a l fan d e p o s i t s d e s c r i b e d by S t e e l (1974). The p a r a c o n g 1 o m e r a t e s a r e i n t e r p r e t e d as g r a v i t y f l o w s s i m i l a r t o the d e b r i s f l o w s d e s c r i b e d by Wasson (1977) and Heward (1978). Debris flows are common on many a l l u v i a l fans of b o t h humid (Heward, 1978) and s e m i - a r i d c l i m a t e s ( B u l l , 1972; and A l l e n , 1981) and have become a c h a r a c t e r i s t i c f o r t h e r e c o g n i t i o n o f a l l u v i a l f a n d e p o s i t i o n . In t h e upper L a s l u i Member, b o t h mudf1ow and g r a i n f l o w d e p o s i t s o c c u r , g r a i n f l o w s b e i n g l e s s abundant. Mudflow d e p o s i t s a r e most abundant near the f a n apex, and g e n e r a l l y f o l l o w stream c h a n n e l s ( B u l l , 1972). However, S t e e l (1974), and S t e e l and Aasheim (1975), have documented d i s t a l mudflow d e p o s i t s beyond t h e n o r m a l r a n g e o f f a n a c t i v i t y i n a s s o c i a t i o n w i t h f l o o d p l a i n and p l a y a sediments, analogous to the upper L a s l u i s t r a t a . A c c o r d i n g t o B u l l (1972), mudflows a r e prompted by abundant but s p o r a t i c water supply, steep s l o p e s , and f u r t h e r r e q u i r e a f i n e g r a i n e d s o u r c e f o r the m a t r i x . In the upper L a s l u i Member, v o l c a n i c ash was the dominant s o u r c e f o r the f i n e g r a i n e d matrix as evidenced by the t u f f a c e o u s composition of the mudflows and g r a i n f l o w s . The g r a v i t y f l o w s e x h i b i t i n v e r s e and normal g r a d i n g and have a wide c o m p o s i t i o n a l v a r i e t y of v e r y a n g u l a r c l a s t s , suggesting r a p i d d e p o s i t i o n . 45 Debris f l o w s with s i m i l a r c h a r a c t e r i s t i c s have been d e s c r i b e d from s e m i - a r i d s e t t i n g s ( B u l l , 1972; L a r s o n and S t e e l , 1978) as opposed t o the d e b r i s f l o w s i n humid a r e a s t h a t a r e composed o f w e l l - r o u n d e d c l a s t s and which commonly l a c k s t r a t i f i c a t i o n (Wasson, 1977; Iwaniw, 1984). Two l a t e r a l l y e x t e n s i v e d e p o s i t s of o r t h o c o n g 1 o m e r a t e "A", i n the upper L a s l u i sequence have many f e a t u r e s of b r a i d e d stream d e p o s i t s such as complex i n t e r n a l v a r i a t i o n i n t e x t u r e , and an o v e r a l l f i n i n g upwards sequence from massive c o n g l o m e r a t e t o h o r i z o n t a l s t r a t i f i e d and c r o s s - s t r a t i f i e d sandstone, s i m i l a r to s h e e t f l o o d d e p o s i t s d e s c r i b e d by Muir and Rust (1982). S h e e t f l o o d sediments r e c o g n i z e d on a l l u v i a l fans ( N i l s e n , 1982), are de p o s i t e d by surges of sediment laden water spreading out from the main stream channel i n the form of many s h a l l o w d i s t r i b u t a r y channels and r e s u l t i n l a t e r a l l y e x t e n s i v e d e p o s i t s analogous to orthocong1omerate "A" of the u p p e r L a s l u i Member. F i n i n g upwards d e p o s i t s o f o r t h o c o n g 1 o m e r a t e "A" a r e l e s s than 12 m t h i c k , s u g g e s t i n g t h a t : 1) the d i s t r i b u t a r y c h a n n e l s were s h a l l o w , a l t h o u g h e x t e n s i v e ; and 2) the d e p o s i t s r e p r e s e n t s i n g l e f l o o d events. T y p i c a l l y , the a s s o c i a t i o n of ponds, swamp and s h e e t f l o o d d e p o s i t s i s c h a r a c t e r i s t i c of d i s t a l a l l u v i a l f a n s and a l l u v i a l p l a i n s i n humid c l i m a t e s (Heward, 1978). However, d e b r i s f l o w d e p o s i t s a r e u s u a l l y more abundant on a r i d t o s e m i - a r i d a l l u v i a l f a n s (Cherven, 1984). Thus, the upper L a s l u i Member has f e a t u r e s t y p i c a l o f b o t h wet and d r y c o n d i t i o n s , s u g g e s t i n g t h a t the water t a b l e l e v e l must have f l u c t u a t e d , a t l e a s t l o c a l l y , d u r i n g d e p o s i t i o n . 46 The wide v a r i e t y of f a c i e s p r e s e n t i n t h e upper L a s l u i Member i s s i m i l a r to f a c i e s a s s o c i a t i o n s from the mid-fan to d i s t a l f a n or a l l u v i a l p l a i n , d e s c r i b e d by M u i r and Rust (1982) f o r the S n o w b l i n d F o r m a t i o n , N.W.T., and Z a i t l i n and Rust (1983) f o r the B o n a v e n t u r e F o r m a t i o n , Gaspe and New Brunswick. D e p o s i t i o n on the d i s t a l a l l u v i a l f a n - a l l u v i a l p l a i n a c c o u n t s f o r t h e i n t e r f i n g e r i n g o f f i n e g r a i n e d s e d i m e n t s w i t h c o a r s e g r a i n e d s e d i m e n t s i n the upper L a s l u i Member (Figure 12). 47 Figure 1 2 . Interpreted depositional environment of the upper Laslui Member SPATSIZI MEMBER - LITHOFACIES. DESCRIPTION Up t o 600 m of the S p a t s i z i Member i s exposed i n the s t u d y a r e a . In c o n t r a s t t o the r e s t of the S u s t u t Group, the S p a t s i z i Member i s c y c l i c , c o m p o s e d o f m o n o t o n o u s sandstone/mudstone packages; as many as 22 c y c l e s o c c u r a t a s i n g l e l o c a l i t y . The sandstone/mudstone sequence i s l a t e r a l l y continuous, but c o r r e l a t i o n of i n d i v i d u a l sequences between s e c t i o n s was not p o s s i b l e . Medium g r a i n e d , moderately w e l l s o r t e d , sandstone u n i t s r a n g i n g from 2 t o 18 m i n t h i c k n e s s dominate the S p a t s i z i Member. S a n d s t o n e u n i t s h a v e c h a n n e l e d b a s e s and commonly c o n t a i n pebble l a g d e p o s i t s i n the lower p o r t i o n s of the Member. The m a j o r i t y of the s a n d s t o n e s e x h i b i t medium s c a l e h o r i z o n t a l s t r a t i f i c a t i o n . S m a l l s c a l e (5 t o 10 cm) t a b u l a r c r o s s - s t r a t i f i c a t i o n ( P l a t e 7a), trough, c r o s s - s t r a t i f i c a t i o n and r i p p l e c r o s s - s t r a t i f i c a t i o n ( P l a t e 7b) are l e s s abundant. C o n v o l u t e b e d d i n g i s a l s o p r e s e n t , b u t l i m i t e d t o t h e uppermost s a n d s t o n e s ( P l a t e 7c). L o c a l l y , p e b b l e zones, c a r b o n a c e o u s f r a g m e n t s and w i s p s , and c a l c a r e o u s n o d u l e s occur. R e c e s s i v e , b l a c k mudstone up t o 30 m t h i c k i s commonly the o n l y f i n e g r a i n e d l i t h o l o g y e x c e p t f o r l o c a l , t h i n f i n e g r a i n e d sandstone u n i t s c o n t a i n i n g mudstone r i p - u p c l a s t s and minor f l a s e r b e d d i n g . A l i m i t e d number of t u f f h o r i z o n s , up to 2 m t h i c k , are l o c a l l y present i n the lower p o r t i o n of the S p a t s i z i Member. 49 Plate 7. Characteristics of the Spatsizi Member sandstones. 60 SPATSIZI MEMBER - INTERPRETED DEPOSITIONAL ENVIRONMENT F i n i n g upwards s e d i m e n t s of the S p a t s i z i Member a r e c y c l i c a l , i n c o n t r a s t to sediments of the T a t l a t u i and L a s l u i Members. W e l l developed c y c l i c i t y r e s u l t s from topographic d i f f e r e n t i a t i o n between channels and overbank areas i n r i v e r systems (Rust, 1984). The f i n i n g upwards sequences of the S p a t s i z i Member have p r e v i o u s l y been i n t e r p r e t e d as meandering r i v e r d e p o s i t s (Eisbacher, 1974). However, both the b r a i d e d D o n j e k r i v e r , Yukon ( R u s t , 1972) and t h e b r a i d e d S o u t h Saskatchewan r i v e r (Cant, 1978) produce f i n i n g upwards c y c l i c a l d e p o s i t s s i m i l a r to the S p a t s i z i sequence. T h e r e a r e no a b s o l u t e c r i t e r i a f o r d i s t i n g u i s h i n g c y c l i c a l d e p o s i t s of a d i s t a l b r a i d e d r i v e r from meandering r i v e r d e p o s i t s . G e n e r a l l y though, t r o u g h c r o s s s t r a t a a r e more abundant t h a n p l a n a r c r o s s s t r a t a w i t h i n a meandering r i v e r d e p o s i t , i n c o n t r a s t t o the dominance o f p l a n a r c r o s s s t r a t a i n the S p a t s i z i Member. In meandering r i v e r d e p o s i t s , p l a n a r c r o s s s t r a t a a r e l i m i t e d t o s c r o l l b ar d e p o s i t i o n ( J a c k s o n , 1978), whereas i n b r a i d e d r i v e r d e p o s i t s , p l a n a r c r o s s - s t r a t a can d e v e l o p a t any l e v e l w i t h i n t h e sequence (Cant, 1978), and hence a r e more abundant, s i m i l a r t o the o c c u r r e n c e o f p l a n a r c r o s s - s t r a t a i n the S p a t s i z i sequence. A l s o , t h e s u b o r d i n a t e amount of o v e r b a n k mudstone d e p o s i t s w i t h i n the S p a t s i z i Member suggests t h a t the r i v e r system was f r e e t o m i g r a t e a c r o s s the a l l u v i a l p l a i n , u n r e s t r i c t e d by s t a b i l i z e d o v e r b a n k a r e a s . U n r e s t r i c t e d f l o w would f a v o r a b r a i d e d system over a meandering one (Schumm, 1981). 51 D e p o s i t s o f t h e b r a i d e d S o u t h S a s k a t c h e w a n r i v e r d e s c r i b e d by Walker (1976) and summarized by M i a l l (1977) very c l o s e l y resemble the r e p e t i t i v e sandstone/mudstone d e p o s i t s of the S p a t s i z i Member. Both d e p o s i t s f i n e upwards b e g i n n i n g w i t h i n t r a c l a s t s on a c h a n n e l e d s u r f a c e , i n t e r p r e t e d as a channel l a g . In the South Saskatchewan R i v e r , the channel l a g i s o v e r l a i n by trough c r o s s s t r a t a which are o v e r l a i n by se t s of p l a n a r c r o s s - s t r a t a i n t e r p r e t e d as d e p o s i t s o f sandy f o r e s e t bars (Walker, 1976). But o v e r l y i n g the b a s a l channel l a g i n t h e S p a t s i z i s e d i m e n t s a r e s a n d s t o n e s dominated by p l a n a r c r o s s - s t r a t i f i c a t i o n , almost to the e x c l u s i o n of trough c r o s s - s t r a t i f i c a t i o n . Both the South Saskatchewan and S p a t s i z i sequences end wi t h r i p p l e d sandstone and mudstone of v a r y i n g p r o p o r t i o n . Trough c r o s s - s t r a t i f i c a t i o n w i t h i n the South Saskatchewan r i v e r i s not a l w a y s w e l l - d e f i n e d (Cant, 1978), and thu s poor p r e s e r v a t i o n may e x p l a i n the s p a r s e occurrence of trough c r o s s - s t r a t i f i c a t i o n w i t h i n the S p a t s i z i sediments. L o c a l o c c u r r e n c e s o f c o n v o l u t e b e d d i n g i n t h e uppermost S p a t s i z i sediments are i n t e r p r e t e d as the product of i n c r e a s e d shear s t r e s s due to an i n c r e a s e d c u r r e n t v e l o c i t y as a r e s u l t of a sudden r i s e i n t u r b u l e n c e . Sediments of the S p a t s i z i Member are most s i m i l a r t o the br a i d e d a l l u v i a L model S-II of Rust (1978), and the model by M i a l l (1978) based on t h e South Saskatchewan R i v e r . Both models c o n s i s t of f i n i n g upward sandstone c y c l e s , d e p o s i t e d by br a i d e d r i v e r s t r a n s i t i o n a l to meandering r i v e r s t h a t occupy an a l l u v i a l p l a i n environment, (Figure 13). 5 2 r i pp l e 1 - b e d d e d p l a n a r b e d d e d p e b b l y s a n d s t o n e p l a n a r x - b e d d e d s a n d s tone t rough x - b e d d e d s a n d s t o n e mudst one B. G e n e r a l i z e d S e c t i o n o f t h e S p a t s i z i M e m b e r D i s t a l B r a i d e d S t r e a m -A l l u v i a l P l a i n Figure 13 Interpreted depositional environment of the Spatsizi Member PETROLOGY OF THE SDSTDT GROUP PETROGRAPHY AND MINERALOGY V o l c a n i c l a s t i c Sediments T u f f s range i n c o l o r from aqua t o g r e e n t o b u f f , and weather a c h a r a c t e r i s t i c c h a l k y white c o l o r . T u f f s commonly grade i n t o t u f f a c e o u s mudstone and s i l t s t o n e beds. Both v i t r i c and c r y s t a l t u f f s were o r i g i n a l l y d e p o s i t e d i n the Brothers Peak Formation. Subsequently, the v i t r i c shards have been r e p l a c e d by the z e o l i t e s , h e u l a n d i t e and laumontite as w e l l as q u a r t z , a l b i t e and c l a y • m i n e r a l s (see t h e s e c t i o n on d i a g e n e s i s f o r f u r t h e r d i s c u s s i o n ) . O t h e r framework g r a i n s i n c l u d e p l a g i o c l a s e , quartz and minor b i o t i t e . Weathering of t u f f beds has commonly produced b e n t o n i t e s , w hich v a r y i n c o l o r from l i g h t g r e e n t o dark y e l l o w . V o l c a n i c d i k e s Red-brown w e a t h e r i n g , v o l c a n i c d i k e s o c c u r l o c a l l y t h r o u g h o u t t h e s t u d y a r e a and a r e g e n e r a l l y v e s i c u l a r , p o r p h y r i t i c a n d e s i t e s . The di k e s are l e s s than 1 m t h i c k and a r e n e a r l y v e r t i c a l i n o r i e n t a t i o n . A u g i t e p h e n o c r y s t s a r e t y p i c a l l y t he l a r g e s t and most abundant, w i t h s u b o r d i n a t e p h e n o c r y s t s o f o r t h o p y r o x e n e , o l i v i n e , and p l a g i o c l a s e . O l i v i n e phenocrysts are a l t e r e d t o a r e d d i s h brown i d i n g s i t e . Roughly one q u a r t e r of the v e s i c l e s are p a r t i a l l y f i l l e d with c a l c i t e g i v i n g a l o c a l amygdaloidal t e x t u r e . Conglomerates P e b b l e o r t h o c o n g 1 o m e r a t e i s the main l i t h o l o g y i n the c o a r s e g r a i n e d l i t h o f a c i e s o f t h e T a t l a t u i Member. In t h e B r o t h e r s Peak F o r m a t i o n , c o b b l e - p e b b l e o r t h o c o n g 1 o m e r a t e dominates the lower L a s l u i Member, whereas the coarse g r a i n e d l i t h o f a c i e s o f t h e upper L a s l u i Member c o n s i s t s o f g r a n u l e o r t h o - and paraconglomerates. In the S p a t s i z i Member pebbles occur l o c a l l y i n sandstones as a l a g d e p o s i t but conglomerate i s absent. In the orthoconglomerates of the T a t l a t u i Member, c l a s t s a r e rounded t o subrounded and a r e d o m i n a n t l y composed of green, grey and b l a c k c h e r t , with l e s s e r amounts of v o l c a n i c , s e d i m e n t a r y and g r a n i t i c r o c k f r a g m e n t s . The m a t r i x i s composed of s u b a n g u l a r t o subrounded c h e r t ; s u b a n g u l a r v o l c a n i c and sedimentary rock fragments, q u a r t z , p l a g i o c l a s e f e l d s p a r , micas and c l a y m i n e r a l s . O r t h o c o n g 1 o m e r a t e s o f t h e lower L a s l u i Member, a r e composed o f subrounded, b l a d e d t o equant shaped c l a s t s . The c l a s t s c o n s i s t o f e q u a l amounts of b l a c k and g r e y c h e r t , q u a r t z and v o l c a n i c r o c k f r a g m e n t s w i t h l e s s e r amounts o f s e d i m e n t a r y and g r a n i t i c r o c k f r a g m e n t s . L o c a l l y , zones o f mudstone r i p - u p c l a s t s o c c u r . M a t r i x i s composed o f s u b a n g u l a r t o subrounded c h e r t , q u a r t z , v o l c a n i c and s e d i m e n t a r y r o c k 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 , micas and c l a y m i n e r a l s . The coarse g r a i n e d l i t h o f a c i e s of the Upper L a s l u i Member c o n s i s t s o f o r t h o c o n g 1 o m e r a t e "A" and "B" as w e l l as p a r a c o n g l o m e r a t e s . O r t h o c o n g 1 o m e r a t e "A" i s composed of .55 s u b r o u n d e d t o a n g u l a r c l a s t s . C l a s t s a r e composed o f g r e e n , g r e y a n d l o c a l l y r e d c h e r t , g r e e n v o l c a n i c r o c k f r a g m e n t s ( i n c l u d i n g t u f f ) a n d g r e y s e d i m e n t a r y r o c k f r a g m e n t s , i n a p p r o x i m a t e l y e q u a l a b u n d a n c e s . T h e m a t r i x i s c o m p o s e d o f s u b a n g u l a r t o s u b r o u n d e d c h e r t , q u a r t z , v o l c a n i c a n d s e d i m e n t a r y r o c k f r a g m e n t s w i t h l e s s e r amounts o f p l a g i o c l a s e f e l d s p a r , m i c a and c l a y m i n e r a l s . O r t h o c o n g 1 o m e r a t e B i s composed o f s u b a n g u l a r t o a n g u l a r c l a s t s o f d o m i n a n t l y r e d and g r e e n c h e r t and v o l c a n i c c l a s t s ( i n c l u d i n g t u f f ) , w i t h l e s s e r amounts o f g r e y c h e r t , q u a r t z , a n d g r a n i t i c a n d s e d i m e n t a r y r o c k f r a g m e n t s . The m a t r i x i s m a i n l y c o m p o s e d o f c l a y . O r t h o c o n g 1 o m e r a t e "B" i s c o m m o n l y w e a t h e r e d . T h e v e r y a n g u l a r t o s u b a n g u l a r c l a s t s o f t h e p a r a c o n g l o m e r a t e s a r e d o m i n a n t l y composed o f r e d , maroon and g r e e n v o l c a n i c r o c k f r a g m e n t s , g r e e n , r e d , b l a c k c h e r t , a n d s e d i m e n t a r y r o c k f r a g m e n t s , w i t h s u b o r d i n a t e q u a r t z a n d g r a n i t i c r o c k f r a g m e n t s . The t u f f a c e o u s m a t r i x w e a t h e r s t o a d a r k brown and f r e s h c o l o r s a r e v a r i o u s s h a d e s o f g r e e n . 5 6 Sandstone A t o t a l o f 75 s a n d s t o n e s were examined i n t h i n s e c t i o n ; 27 were s e l e c t e d f o r modal a n a l y s i s . The r e s u l t s , a l o n g with heavy m i n e r a l s , s o r t i n g and a v e r a g e c l a s t s i z e a r e shown i n T a b l e s 1-4. Using Folk's (1968) sandstone c l a s s i f i c a t i o n , 13 o f t h e s a m p l e s a r e 1 i t h a r e n i t e s , 7 a r e f e l d s p a t h i c 1 i t h a r e n i t e s , and 7 a r e l i t h i c a r k o s e s ( F i g u r e 14). The s a n d s t o n e s g e n e r a l l y c o n t a i n l e s s t h a n 5% o r i g i n a l m a t r i x , which a c c o r d i n g to F o l k (1968), c l a s s i f i e s them as submature. A v e r a g e g r a i n s i z e r a n g e s from v e r y f i n e sand t o v e r y c o a r s e sand and l o c a l l y i n c l u d e g r a n u l e t o p e b b l e s i z e d c l a s t s . Quartz, c h e r t , p l a g i o c l a s e f e l d s p a r and v o l c a n i c rock fragments are the main framework g r a i n s , with l e s s e r amounts of s e d i m e n t a r y and metamorphic r o c k f r a g m e n t s , o r t h o c l a s e , micas, c h l o r i t e , c a l c i t e and heavy m i n e r a l s . The m a t r i x i s composed of s m e c t i t e , c e l a d o n i t e , k a o l i n i t e , z e o l i t e s , q u a r t z , a l b i t e and minor c l i n o z o i s i t e and sphene. In the upper L a s l u i Member the m a t r i x i s commonly h i g h l y t u f f a c e o u s . Cement i s u b i q u i t o u s ; and t h e t y p e o f cement p r e s e n t i s c o n t r o l l e d by p o s t - d e p o s i t i o n a l a l t e r a t i o n . The degree of rounding, s o r t i n g and s p h e r i c i t y i s h i g h l y v a r i a b l e . Most samples are p o o r l y to moderately s o r t e d , with a n g u l a r q u a r t z , and subrounded c h e r t , f e l d s p a r , and v o l c a n i c r o c k f r a g m e n t s . G e n e r a l l y , q u a r t z has a low s p h e r i c i t y whereas c h e r t , f e l d s p a r and v o l c a n i c r o c k f r a g m e n t s have moderate to moderately h i g h s p h e r i c i t y . 57 Q u a r t z Q u a r t z o s e M e t a m o r p h i c R o c k F r a g m e n t s F e l d s p a r 2 5 5 0 2 5 R o c k F r a g m e n t s C h e r t Figure 14. A triangular diagram illustrating the composition of the Sustut Group sandstones 5 8 Tables 1-4 Location, grain s i z e , modal analysis of d e t r i t a l c l a s t s , heavy  minerals and cement types of representative samples from the Tango Creek and Brothers Peak Formations. Key Modal Analysis - Detrital Clasts Q - Quartz VR - Volcanic Rock Ch - Chert Fragments Ps - Plagioclase Feldspar MR - Metamorphic Rock Ks - Potassium Feldspar Fragments SR - Sedimentary Rock Mi - Mica Fragments Og - Organics Cement Types Grain Size CI - Clay eg - Conglomerate Ca - Calcite VCs- Very Coarse Sand Qtz- Quartz Cs - Coarse Sand Ab - Alb i t e Ms - Medium Sand HI - Heulandite Fs - Fine Sand Lm - Laumontite VFs- Very Fine Sand Heavy Mineral s* Ep - Epidote Ap - Apatite CI - CI i n o z o i s i t e CPy- CIino-pyroxene Zi - Zircon H - Hornblende R - Rutile OPy- Ortho-pyroxene T - Tourmaline Sl - Spinel Gt - Garnet Op - Opaques (Magnetite Sp - Sphene and Ilmenite) t r - trace * heavy minerals separated for analysis ( )- estimated percentages for samples not point counted 59 Table 1 Tango Creek Formation Metres Sample Above Gra i n Modal Analysis - Detrital C l a s t s % Heavy Cement No. Base Size Q Ch Ps Ks SR VR MR Mi Og Minerals Type S2-26 0 Cg (20)(30)(5) (-) (15)(25)(-) ( t r ) ( t r ) -- Ca,Cl,Qtz S2-28 25 Ms 32 16 6 5 10 21 t r t r t r Ep CI, Ca.Qtz(lO) S2-29 30 Fs (35)(15)(20)(-) (7) (9) (7) (4) ( t r ) Ep,Zi,R,Gt,Ap,H, Ca.Cl,Qtz SI ,0p S2-31 65 Ms 25 35 5 - 4 t r 3 3 - -- Ca.Cl (21) S2-36 115 Fs (no analysis) Zi,R,T,Gt,H,0p CI ,Ca S3-80 375 Ms 47 20 3 t r 11 7 3 4 t r Ep, Op CI (3) S6-173 160 Ms 23 27 1 5 11 6 9 3 t r - Ep,Zi,R,T,Gt,Sp CI (3) H,0Py,Sl,0p Table 2 lower Laslui Member Metres Sample Above Grain Modal Analysis - Detrital C l a s t s % Heavy Cement No. Base Size Q Ch Ps Ks SR VR MR Mi Qg Minerals Types S2-41 180 Cs 25 29 5 t r 11 15 t r - - Ep.Cl.Op Qtz,Ca,Cl(14) S2-42 195 Ms 18 9 29 4 4 14 3 t r t r CI,0p Qtz.Cl(14) S3-83 475 VCs 29 12 4 t r 8 26 4 3 - Ep, Op CI ,Qtz(12) ,lm(?) S3-84 490 Ms 26 17 30 9 2 8 4 - t r Ep,0p Ca,Cl(3), Qtz S4-128 450 Cs 35 14 20 3 8 16 2 t r - Ep,Zi,R,T,Gt,Sp * Cl ( t r ) ,Qtz Cpy,H,0p S5-156 10 Cs (no analysis) Ep,Zi,R,Gt,Sp, * Ap,Cpy,0p Ca.Cl S5-159 100 Fs 24 11 25 7 21 4 5 2 - Ep.Cl,Zi,R,Gt, * Sp,Ap,CPy,Op CI,Ca(3) S5-165 300 Ms 23 27 15 11 9 9 - t r - Ep.Cl,Zi,R,T(?)* Gt,Sp,CPy,H,Sl,0p Table 3 upper Laslui Member Metres Sample Above Gra i n Modal Analysis - Detrital C l a s t s % Heavy Cement No. Base Size Q Ch Ps Ks SR VR MR Mi Og Minerals Type S2-50 260 Ms (15)(25)(20)( -) (15)(25)(tr )(tr ) ( ) Ep,Zi,R,Gt,Sp, * Qtz.Cl ,Ab CPy,H,0P CI ,C1 (18) ,H1 S2-54 320 Ms 15 42 6 - 7 7 2 - Ep,0p S2-60 355 Ms 40 7 16 t r 4 5 3 t r - Ep,0p CI ,Ca(14),Qtz S3-95 625 Vcs 16 22 9 t r 18 16 2 - Ep,R,0p Cl,(16),Lm(?) S3-101 760 Vcs 31 19 18 - 6 23 t r t r - Ep,0p CI ,Qtz,Lm(?) S4-151 630 Ms 31 44 9 t r 3 5 tr 2 t r Ep,Cl,Z1,R,T, * CI ,Ca(3) Gt,Sp,CPy,H,Op Cl,Ca(10) S5-168 350 Ms 24 14 34 9 tr 5 t r 3 t r Ep.Cl,Zi,R,T(?) * Gt,Sp,Ap,CPy,H,Op Cl(2) ,Qtz,Ab S7-207 625 Cs 27 15 9 2 6 38 - t r - Ep,Zi,R,T(?),Gt, * Sp,CPy,H,0Py,Sl,0p S7-212 875 Cs 15 47 13 t r 3 19 - t r - Ep,Cl,Zi,R,T(?), * Cl.Ca(tr) Rt,Sp,CPy,H,0Py,0p S8-221 330 Cs 25 19 26 6 10 15 - t r - Ep,Zi,R,Gt, * CI, - Sp,CPy,H,0p Cl(tr).Qtz.Ab S8-225 400 Cg 7 47 4 3 30 6 t r - Ep.Op Table 4 Spatsizi Member Metres Sampl e Above Grain Modal Analysis - 1 Detrital C l a s t s % Heavy Cement No. Base Size Q Ch Ps Ks SR VR MR Mi Og Minerals Type S2-62 425 Ms 12 9 27 4 6 25 2 t r - Ep,0p CI,(10) S2-63 430 Ms 20 13 23 6 4 25 t r t r _ Ep.Cl,Zi,R,T, * CI ,Qtz(9),Ab Gt,Sp,CPy,H,Op CI,Ca(8) S2-65 500 Fs 18 14 25 26 t r 9 - t r - Ep,Zi,R,T,Gt, * Sp.H.Sl,0p S3-110 1160 VFs 17 18 27 6 t r 20 - 4 5 E'p.Op CI,(4) S5-169 410 Cs 24 27 15 2 10 17 2 t r - Ep.Op CI(tr),H1 S7-214 963 Ms 17 6 34 13 2 26 - t r - Ep,Cl,Zi,R,T(?), * Cl(2),Qtz Sp,CPy,H,0P Q u a r t z c o m p r i s e s 2 t o 60% of the framework g r a i n s , a v e r a g i n g 25%. The lowest percentage i s from the upper L a s l u i Member g r a v i t y f l o w s . Q u a r t z i s a m a j o r component i n s a n d s t o n e s o f t h e T a t l a t u i and l o w e r L a s l u i Members. M o n o c r y s t a 1 1 i n e q u a r t z w i t h s t r a i g h t t o s l i g h t l y u n d u l o s e e x t i n c t i o n i s s l i g h t l y more abundant t h a n p o l y c r y s t a 1 1 i n e quartz. N e e d l e - l i k e m i c r o l i t e i n c l u s i o n s are common w i t h i n m o n o c r y s t a 1 1 i n e q u a r t z ( P l a t e 8a). Q u a r t z o v e r g r o w t h s ( P l a t e 8b) a r e r a r e . P o l y c r y s t a 1 1 i n e q u a r t z g r a i n s a r e unimodal or bimodal with r e s p e c t to i n t e r n a l c r y s t a l s i z e , and show s u t u r e d or l e s s commonly s t r a i g h t i n t e r n a l c o n t a c t s ( P l a t e 8c). Q u a r t z g r a i n s a r e g e n e r a l l y a n g u l a r and have a low s p h e r i c i t y , e x c e p t i n the S p a t s i z i Member, where the g r a i n s are subrounded and have a moderate s p h e r i c i t y . C h e r t c o m p r i s e s 1 t o 50% o f t h e f r a m e w o r k g r a i n s a v e r a g i n g 30% The h i g h e r p e r c e n t a g e i s i n v a r i a b l y from c o a r s e r g r a i n e d samples. C h e r t o c c u r s i n a wide v a r i e t y o f c o l o r s i n c l u d i n g shades of grey, green, b l a c k and red and have a c r y p t o c r y s t a 1 1 i n e and/or m i c r o c r y s t a 1 1 i n e t e x t u r e . Some g r a i n s c o n t a i n a r g i l l a c e o u s m a t e r i a l or chalcedony c r y s t a l s and show c i r c u l a r remnant r a d i o l a r i a n ( ? ) s t r u c t u r e s ( P l a t e 9). E x t e r n a l g r a i n b o u n d a r i e s a r e i n d i s t i n c t i f c h e r t i s a l s o p r e s e n t as m a t r i x . C h e r t g r a i n s a r e subrounded t o rounded and have low to moderate s p h e r i c i t y . F e l d s p a r c o n t e n t r a n g e s from 5 t o 40% o f the t o t a l framework g r a i n s . P l a g i o c l a s e i s the p redominant f e l d s p a r comprising up to 75% of the t o t a l f e l d s p a r , w i t h subordinate amounts of o r t h o c l a s e . P l a g i o c l a s e i n v o l c a n i c rock fragments 64 Plate 8 . 8 a . Thin section photomicrograph of quartz with needle-l i k e m i c r o l i t e inclusions. 8 b . Thin section photomicrograph showing quartz overgrowths 8 c . Thin section photomicrograph of a bimodal p o l y c r y s t a l l i quartz grain with sutured internal contacts. Nicols crossed 65 Plate 9. 9a. Thin section photomicrograph of chert with argillaceous material. Nicols crossed. 9b. Thin section photomicrograph of chalcedony (zebraic?). NicoTs crossed. 9c. Thin section photomicrograph of chert with c i r c u l a r f o s s i l (?) remnants. Nicols crossed. 67 i s e x c l u ded from the f e l d s p a r component, thus where v o l c a n i c rock fragments are abundant the p l a g i o c l a s e count may be low. P l a g i o c l a s e i s h i g h l y v a r i a b l e i n h a b i t , r a n g i n g f r o m u n a l t e r e d c r y s t a l l a t h s to extremely a l t e r e d g r a i n s without c l e a r b o u n d a r i e s . A l t e r a t i o n i s g e n e r a l l y t o mica, e p i d o t e g r o u p m i n e r a l s , and c a l c i t e ( P l a t e 10). G e n e r a l l y , p l a g i o c l a s e (An 25 - An 45) w i t h i n t u f f s and t u f f a c e o u s s e d i m e n t s i s u n a l t e r e d , w h e r e a s w i t h i n n o n - t u f f a c e o u s s e d i m e n t s - i t i s h i g h l y a l t e r e d , m a k i n g c o m p o s i t i o n de t e r m i n a t i o n s d i f f i c u l t . O r t h o c l a s e was o n l y i d e n t i f i e d i n the p o i n t c o u n t e d s e c t i o n s , l a r g e l y b e c a u s e of the d i f f i c u l t y i n r e c o g n i z i n g u n s t a i n e d o r t h o c l a s e . O r t h o c l a s e i s a minor c o n s t i t u e n t c o m p r i s i n g l e s s t h a n 30% of t h e t o t a l f e l d s p a r . O r t h o c l a s e g r a i n s are subrounded and have moderate s p h e r i c i t y . V o l c a n i c r o c k f r a g m e n t s c o m p r i s e 0 t o 40% o f t h e f r a m e w o r k g r a i n s , a v e r a g i n g 20% and i n c l u d e m a f i c t o in t e r m e d i a t e rock fragments with p l a g i o c l a s e phenocrysts. The p h e n o c r y s t s a r e l a t h - l i k e , g e n e r a l l y u n a l t e r e d , and i n some samples have a t r a c h y t i c t e x t u r e ( P l a t e 11). The m a j o r i t y o f v o l c a n i c r o c k f r a g m e n t s a r e round t o subrounded and have a moderate t o hig h s p h e r i c i t y . Sedimentary rock fragments g e n e r a l l y comprise from 0 to 25% o f the framework g r a i n s , b ut may r e a c h up t o 50% i n the L a s l u i Member. S e d i m e n t a r y r o c k f r a g m e n t s a r e i n v a r i a b l y c l a s t i c and dominantly mudstone, s i l t s t o n e and t u f f with r a r e f i n e sandstone fragments. C o l o r ranges from brown to almost 69 Plate 10. Thin section photomicrographs of plagioclase feldspar. 10a. A l terat ion to mica. Nicols crossed. 10b. A l te rat ion to c a l c i t e . Nicols crossed. 70 Plate 11. Thin section photomicrographs i l l u s t r a t i n g the various textures of volcanic rock fragments Plagioclase (Pi) is the main phenocryst. 10c shows trachytic texture of the plagioclase laths. 10b. and 10c. nicols crossed. 71 r e d and i n c l u d e s v a r i o u s amounts of o r g a n i c m a t t e r i n the mudstones, s i l t s t o n e s and sandstones. T u f f fragments are a v a r i e t y o f c o l o r s i n c l u d i n g r e d , maroon, g r e e n , aqua, and b u f f . S e d i m e n t a r y r o c k f r a g m e n t s a r e round t o subrounded and have low to moderate s p h e r i c i t y . M etamorphic r o c k f r a g m e n t s a r e a minor c o n s t i t u e n t , r e a c h i n g a maximum of 5% of t h e framework g r a i n s i n t h e S p a t s i z i Member. Metamorphic r o c k f r a g m e n t s a r e l i m i t e d t o s c h i s t f r a g m e n t s composed o f e l o n g a t e q u a r t z c r y s t a l s , w i t h s u t u r e d c o n t a c t s , and an abundance of mica ( P l a t e 12a). St r e t c h e d p o l y c r y s t a l l i n e quartz g r a i n s with sutured c o n t a c t s , and l a c k i n g mica, were not recorded here as "Metamorphic rock f r a g m e n t s " , b ut r a t h e r as q u a r t z g r a i n s . Thus the o v e r a l l metamorphic r o c k fragment component may be u n d e r e s t i m a t e d . I d e n t i f i e d metamorphic rock fragments are subrounded and have a low s p h e r i c i t y . G r a n i t i c rock fragments are l i m i t e d to conglomerate and c o a r s e s a n d s t o n e where t h e y c o m p r i s e l e s s t h a n 5% of t h e c l a s t s . G r a n i t i c r o c k f r a g m e n t s t e n d t o d i s i n t e g r a t e on t r a n s p o r t , w hich e x p l a i n s t h e i r absence i n f i n e r s e d i m e n t s . Composition ranges between g r a n o d i o r i t e and g r a n i t e . A c c e s s o r y d e t r i t a l f r a m e w o r k g r a i n s i n c l u d e m i c a , c h l o r i t e , c a l c i t e and heavy m i n e r a l s . Mica i s present i n n e a r l y a l l samples, but g e n e r a l l y c o m p r i s e s l e s s t han 1% of the t o t a l g r a i n s . The main accessory m i n e r a l s i n the L a s l u i Member a r e c h l o r i t e and m u s c o v i t e , and i n t h e T a t l a t u i and S p a t s i z i Members a r e c h l o r i t e , m u s c o v i t e and b i o t i t e . T y p i c a l l y , the o r i g i n a l h a b i t o f mica g r a i n s i s h a r d t o 73 Plate 12. 12a. Thin section photomicrograph of a metamorphic rock fragment. Note the elongate and stretched internal grains. Arrows point to mica f lakes within the rock fragment. Nicols crossed. d i s t i n g u i s h owing t o d i f f u s e g r a i n b o u n d a r i e s . A l s o , c o l o r a p p e a r s t o have been " l e a c h e d " from b i o t i t e g r a i n s due t o w e a t h e r i n g ( F o l k , 1968). In the S p a t s i z i Member, d e t r i t a l b i o t i t e and muscovite are i n v a r i a b l y kinked and show sh a r p g r a i n b o u n d a r i e s ( P l a t e 12b). D e t r i t a l c h l o r i t e i s p l e o c h r o i c i n shades of g r e e n and has anomalous b l u e - b r o w n i n t e r f e r e n c e c o l o r s . O n l y a few g r a i n s of b l o c k y d e t r i t a l c a l c i t e were found, and w i t h i n a l i m i t e d number of samples. Heavy M i n e r a l s R e s u l t s of the heavy mineral a n a l y s i s are l i s t e d i n T a b l e 1. The heavy m i n e r a l s are d i v i s i b l e i n t o the f o l l o w i n g four s u i t e s based on p r o b a b l e o r i g i n . 1) STABLE SUITE: z i r c o n , r u t i l e , t o u r m a l i n e 2) VOLCANIC SUITE: a p a t i t e , c 1 i n o p y r o x e n e , hornblende, magnetite, i l m e n i t e , and z i r c o n ( ? ) . 3) PLUTONIC SUITE; a u g i t e , hornblende, sphene. 4) METAMORPHIC SUITE; garnet, c1inopyroxene, hornblende, e p i d o t e (group). The s t a b l e s u i t e i s composed of m i n e r a l s r e s i s t a n t t o w e a t h e r i n g and r e c r y s t a 1 1 i z a t i o n t o some degree. Thus z i r c o n , r u t i l e , and t o u r m a l i n e may be p o l y c y c l i c , d e r i v e d from p r e - e x i s t i n g s e d i m e n t s . M i n e r a l s of the s t a b l e s u i t e a r e p r e s e n t i n a l l the s e c t i o n s a n a l y z e d . Z i r c o n i s t h e most abundant s t a b l e m i n e r a l . I t i s c o l o r l e s s to l i g h t brown and i s s u b h e d r a l t o euhedra1 i n shape ( P l a t e 13a). R u t i l e , the n e x t most abundant, i s a n g u l a r w i t h an orange brown c o l o r i n plane p o l a r i s e d l i g h t . Tourmaline i s l e s s abundant o c c u r r i n g 75 i n t r a c e amounts or up t o 10's of g r a i n s p e r sample. I t i s p l e o c h r o i c i n shades of brown o r g r e e n and i s we 1 1 rounded. O v e r a l l , m i n e r a l s o f t h e v o l c a n i c s u i t e a r e the most a b u n d a n t . A p a t i t e i s a b u n d a n t i n a few s a m p l e s b u t r e p r e s e n t e d by o n l y 1 or 2 g r a i n s i n o t h e r samples. I t i s g e n e r a l l y euhedral and weakly p l e o c h r o i c . A p a t i t e i s thought to be i n d i c a t i v e of an e r u p t i v e v o l c a n i c source (Folk, 1968), a l t h o u g h may o c c u r i n o t h e r i g n e o u s r o c k s and i n some sediments. Magnetite and i l m e n i t e are u b i q u i t o u s and by f a r the most abundant heavy m i n e r a l s ranging i n g r a i n shape from a n g u l a r t o w e l l rounded. A u g i t e i s of minor abundance and g e n e r a l l y subrounded i n shape ( P l a t e 13b). A l s o , z i r c o n s showing an idiomorp h i c c r y s t a l o u t l i n e are l i k e l y d e r i v e d from a v o l c a n i c source (Folk, 1968). The p l u t o n i c s u i t e i s p o o r l y represented with sphene the o n l y c h a r a c t e r i s t i c m i n e r a l ( P l a t e 13c), and furthermore, some of t h e sphene may have formed a u t h i g e n i c a 1 1 y. Sphene i s of minor abundance and g e n e r a l l y o c c u r s as l a r g e g r a i n s w i t h i r r e g u l a r c r y s t a l o u t l i n e s , w h i c h a r e p r e s u m e d t o be a u t h i g e n i c . The few sphene g r a i n s with good c r y s t a l o u t l i n e s a r e s m a l l e r and i n t e r p r e t e d as d e t r i t a l . A l l sphene g r a i n s are c h a r a c t e r i s t i c a l l y brown i n p l a n e p o l a r i s e d l i g h t . Augite i s o f v a r i a b l e abundance and d i s t r i b u t i o n , i n t h e p l u t o n i c s u i t e , and i s subangular to subrounded i n shape. Hornblende i s o f minor abundance, t y p i c a l l y p l e o c h r o i c from brown t o green and has subrounded form. The metamorphic s u i t e i s c h a r a c t e r i z e d by g a r n e t and epid o t e (group), whereas c1inopyroxene, hornblende and sphene 76 Plate 13. 13a. Thin section photomicrograph of subhedral zircon (Zi) grains. 13b. Thin section photomicrograph of augite. 13c. Thin section photomicrograph of a hornblende grain. Pleochroic green to brown. 77 may a l s o r e p r e s e n t an igneous source. Garnet ranges from v e r y a n g u l a r t o w e l l rounded and i s c o l o r l e s s t o p i n k i n t h i n s e c t i o n . G a r n e t , p r o b a b l y a l m a n d i n e , i s o f moderate t o minor abundance, but i s n e a r l y u b i q u i t o u s . E p i d o t e and c l i n o z o i s i t e a r e i n v a r i a b l y p r e s e n t and commonly abundant. Ep i d o t e i s c o l o r l e s s , and c l i n o z o i s i t e i s p l e o c h r o i c y e l l o w -g r e e n i n t h i n s e c t i o n . The g r a i n s h a p e o f e p i d o t e and c l i n o z o i s i t e i s e i t h e r subrounded or a f i n e a g g r e g a t e . C l i n o z o i s i t e i s l i k e l y d e r i v e d from s a u s s u r i t i z a t i o n of f e l d s p a r s , based on appearance. H o r n b l e n d e g e n e r a l l y c o m p r i s e s l e s s t h a n 10 g r a i n s of any one sample but i s p r e s e n t i n most samples ( P l a t e 13d). I t i s subrounded to subangular and shows green to brown pleochroism. C1inopyroxene (augite predominantly) i s g e n e r a l l y subangular. 79 D i a g e n e s i s V o l c a n o g e n i c s e d i m e n t s a r e c h a r a c t e r i z e d by h i g h l y r e a c t i v e m a t e r i a l s such as g l a s s , p l a g i o c l a s e and v o l c a n i c rock fragments, a l l of which are v e r y s u s c e p t i b l e to h y d r a t i o n r e a c t i o n s . D i a g e n e t i c m i n e r a l s common i n v o l c a n o g e n i c s e d i m e n t s a r e c l a y m i n e r a l s , z e o l i t e s , a l b i t e and c a l c i t e (Surdam and B o l e s , 1979). E a r l y work c o n c e r n i n g t h e d i a g e n e s i s o f v o l c a n o g e n i c r o c k s r e l a t e d t h e a l t e r a t i o n mineralogy with s t r a t i g r a p h i c p o s i t i o n (Coombs e t a l . , 1959). However more re c e n t work by B o l e s and Coombs (1975); and Read and E i s b a c h e r (1974) has demonstrated t h a t the d i s t r i b u t i o n of d i a g e n e t i c m i n e r a l s i n v o l c a n o g e n i c sediments depends l a r g e l y on f l u i d f l o w and o r i g i n a l c o m p o s i t i o n o f the s e d i m e n t s , r a t h e r than s t r a t i g r a p h i c p o s i t i o n . In t h e s t r a t a of the s o u t h e r n S u s t u t B a s i n the main d i a g e n e t i c m i n e r a l s a r e h e u l a n d i t e , l a u m o n t i t e , a l b i t e , s m e c t i t e , c e l a d o n i t e , k a o l i n i t e , q u a r t z and c a l c i t e . I d e n t i f i c a t i o n was done o p t i c a l l y and by X - r a y d i f f r a c t i o n . In the samples a n a l y s e d there i s a c l o s e c o r r e l a t i o n between sample composition, cementing agents and d i a g e n e t i c h i s t o r y . In the t u f f s and t u f f a c e o u s mudstones the main framework g r a i n s are o r i g i n a l l y v i t r i c shards, p l a g i o c l a s e , quartz and minor b i o t i t e . The o r i g i n a l l y v i t r i c s h a r d s have been c o m p l e t e l y a l t e r e d : most commonly t o h e u l a n d i t e , l e s s commonly t o a l b i t e , and i n one f i n e g r a i n e d t u f f sample l a u m o n t i t e r e p l a c e s the v i t r i c s h a r d s . T h i n c o a t i n g s of s m e c t i t e , k a o l i n i t e and/or c e l a d o n i t e o u t l i n e the o r i g i n a l l y v i t r i c shards and v e s i c l e s . The shards and most v e s i c l e s are 80 i n f i l l e d w i t h b l a d e s of h e u l a n d i t e ( P l a t e 14a) and laumontite, or l a t h s o f a l b i t e , a l l o r i e n t e d p e r p e n d i c u l a r t o the c l a y r i m s . The v e s i c l e s a r e l o c a l l y i n f i l l e d w i t h c e l a d o n i t e ( P l a t e 14b). The n o n - v i t r i c framework g r a i n s i n t u f f s and t u f f a c e o u s mudstones r e m a i n u n a l t e r e d , e x c e p t f o r b i o t i t e which has l o c a l l y a l t e r e d to c e l a d o n i t e . In t u f f a c e o u s s a n d s t o n e s the framework g r a i n s c o n s i s t m a i n l y o f u n a l t e r e d p l a g i o c l a s e , q u a r t z , c h e r t , p o t a s s i u m f e l d s p a r , v o l c a n i c r o c k f r a g m e n t s , and l e s s e r amounts of a l t e r e d v i t r i c shards. Quartz and a l b i t e are common as pore f i l l i n g cement, w i t h l o c a l o c c u r r e n c e s o f h e u l a n d i t e , and c a l c i t e . Smectite and c e l a d o n i t e commonly rim the framework g r a i n s and a l s o l o c a l l y f i l l pore spaces ( P l a t e 14c,d). In the non-tuffaceous sandstones the main framework g r a i n s a r e q u a r t z , c h e r t , p l a g i o c l a s e , s e d i m e n t a r y r o c k f r a g m e n t s , and v o l c a n i c rock fragments, with minor amounts of metamorphic rock fragments, micas and heavy m i n e r a l s . C l a y m i n e r a l s and f i n e l y d i s s e m i n a t e d q u a r t z - a 1 b i t e ( ? ) a r e common as pore f i l l i n g cement ( P l a t e 14f). Laumontite occurs as a minor pore f i l l i n g cement. Read and E i s b a c h e r (1974) found laumontite to be more w i d e - s p r e a d i n the n o n - t u f f a c e o u s s e d i m e n t s o f t h e Sustut Group i n the northern Sustut Basin. Surdam and B o l e s (1979) o u t l i n e d t h r e e b a s i c t y p e s o f r e a c t i o n s f o r t h e f o r m a t i o n o f z e o l i t e s , c a l c i t e , c l a y s , a l b i t e and p o t a s s i u m f e l d s p a r as d i a g e n e t i c p h a s e s i n v o l c a n o g e n i c s e d i m e n t s : (1) h y d r a t i o n ; (2) c a r b o n a t i z a t i o n ( f o r m a t i o n o f c a r b o n a t e s ) ; and (3) d e h y d r a t i o n . Commonly 81 Plate 14. Thin section photomicrographs of cements. 14a. Tuff showing clay cement outlining o r i g i n a l l y v i t r i c shards. Heulandite i n f i l l s the shards (h). Other grains include quartz (q), and plagioclase (p). 14b. Excellent example of fibrous clay cement around an original vesicle in a t u f f which i s i n f i l l e d with bright green celadonite. 14c-d. Tuffaceous sandstone showing clay rimming cement i n f i l l e d with quartz (q) and albite(?) (a). 14a crossed ni c o l s . 14e-f. Non-tuffaceous sandstone showing excellent fibrous celadonite (c) i n f i l l i n g pore spaces. 14e crossed n i c o l s . 82 h y d r a t i o n and c a r b o n a t i z a t i o n c h a r a c t e r i z e e a r l y d i a g e n e s i s , and d e h y d r a t i o n c h a r a c t e r i z e s l a t e r d i a g e n e s i s . In t h e S u s t u t Group, i n i t i a l h y d r a t i o n r e a c t i o n s formed the n e a r l y u b i q u i t o u s c l a y rimming cement, f o l l o w e d by open space f i l l i n g by z e o l i t e s , a l b i t e , q uartz, c l a y m i n e r a l s and c a l c i t e . The p e r m e a b i l i t y and p o r o s i t y w i t h i n the sediments r e s u l t e d from p r i m a r y p o r o s i t y i n m a t r i x poor s a n d s t o n e s , secondary p o r o s i t y from the d i s s o l u t i o n of v i t r i c shards and l o c a l f r a c t u r e p o r o s i t y . V i r t u a l l y a l l of t h e p o r o s i t y has been i n f i l l e d by t h i s " e a r l y " phase of d i a g e n e s i s . The a l t e r a t i o n mineralogy i s r e l a t e d to the p r o x i m i t y to t u f f s o r t u f f a c e o u s s e d i m e n t s . H e u l a n d i t e g e n e r a l l y o c c u r s o n l y i n t u f f s , and a l b i t e i s most p r e v a l e n t i n the B r o t h e r s Peak F o r m a t i o n , s u g g e s t i n g t h a t t h e f o r m a t i o n of a l b i t e i s a l s o s p a c i a l l y r e l a t e d t o t u f f s and t u f f a c e o u s s e d i m e n t s . Laumontite and c a l c i t e occur throughout the Sustut Group, but p a r t i c u l a r l y i n non-tuffaceous sediments. C l a y m i n e r a l s and quartz are present throughout the Sustut Group. The u b i q u i t o u s a l t e r a t i o n of v i t r i c s h a r d s r e l e a s e d c a t i o n s and s i l i c a i n t o s o l u t i o n , s u p p l y i n g c a l c i u m f o r the formation of h e u l a n d i t e (and p o s s i b l e the anomalous occurrence of l a u m o n t i t e ) , and sodium f o r the f o r m a t i o n of a l b i t e . F u r t h e r c a l c i u m f o r the formation of laumontite, c a l c i t e and c l a y m i n e r a l s i n the n o n - t u f f a c e o u s s e d i m e n t s may have been s u p p l i e d by the d i s s o l u t i o n o f f r e s h water s h e l l s (Read and E i s b a c h e r , 1974). K-Ar, whole rock age determinations of t u f f s y i e l d e d d a t e s of 53 and 49 Ma (Read and E i s b a c h e r , 1974). These 84 ages l i k e l y r e f l e c t t h e t i m i n g of a l t e r a t i o n i n t h e S u s t u t Group as opposed t o the age of d e p o s i t i o n because of the e x t e n s i v e a l t e r a t i o n of t u f f s , t h e low amount of b i o t i t e p r e s e n t , and i n l i g h t o f t h e Campanian t o M a a s t r i c h t i a n p a l y n o l o g i c a l age dates. I n summary t h e f o l l o w i n g r e l a t i o n s h i p s t y p i f y t h e a l t e r a t i o n w i t h i n the Sustut Group: 1) the p r o x i m i t y to t u f f s u l t i m a t e l y c o n t r o l s the type of a l t e r a t i o n ; 2) h e u l a n d i t e , a l b i t e , q u a r t z and c l a y m i n e r a l s t y p i f y a l t e r e d t u f f s and t u f f a c e o u s sediments; 3) laumontite, a l b i t e , c a l c i t e , quartz and c l a y m i n e r a l s t y p i f y non-tuffaceous sandstones; 4) e a r l y h y d r a t i o n of v i t r i c shards s u p p l i e d the c a l c i u m f o r h e u l a n d i t e and some l a u m o n t i t e , and s u p p l i e d sodium f o r the formation of a l b i t e ; and 5) d i s s o l u t i o n of f r e s h water s h e l l s may have s u p p l i e d the remainder of the c a l c i u m f o r laumontite, smectite and c a l c i t e i n the non-tuffaceous sediments. 85 PALYNOLOGY An o v e r a l l age range o f Campanian t o M a a s t r i c h t i a n i s i n d i c a t e d by the palynomorphs present i n the southern Sustut B a s i n . T h i s age r a n g e i s b a s e d on t h e p r e s e n c e o f A q u i l l a p o l 1 e n i t e s which does n o t o c c u r i n r o c k s o l d e r than Campanian and d i s a p p e a r s a t t h e end of t h e M a a s t r i c h t i a n (Rouse, p e r s comm., 1985). Ot h e r palynomorphs i d e n t i f i e d i n samples l o c a t e d through out the study area by A. Sweet (pers comm., 1984) and G. Rouse (pers comm., 1985) a r e l i s t e d i n the Appendix, and i n c l u d e ; angiosperm p o l l e n , gymnosperm p o l l e n , spores, a l g a l c y s t s , and r e c y c l e d d i n o c y s t s of Late Cretaceous age. T h i s assemblage s u g g e s t s a v e r y warm and humid c l i m a t e e x i s t e d a t l e a s t i n p a r t d u r i n g d e p o s i t i o n o f t h e S u s t u t Group (Rouse, p e r s comm., 1985). 86 C O A L I F I C A T I O N L E V E L S i x r e p r e s e n t a t i v e samples of carbonaceous mudstone and p h y t o c l a s t s concentrated from sandstones, of the Tango Creek Formation and Broth e r s Peak Formation were a n a l y z e d f o r mean maximum v i t r i n i t e r e f l e c t a n c e (Ro max). The l a c k o f c o a l seams i n the measured s e c t i o n s c o n f i n e d the number and type of samples a v a i l a b l e f o r o r g a n i c m a t u r a t i o n s t u d i e s . T a b l e 5 l i s t s the determined v a l u e and l o c a t i o n of each sample. The samples were composed dominantly of s t r u c t u r e l e s s v i t r i n i t e and minor i n e r t i n i t e , e x c e p t f o r sample S4-129 which has a higher percentage of i n e r t i n i t e r e l a t i v e to the other samples. V i t r i n i t e g r a i n s with dark o x i d a t i o n rims and f r a c t u r e s were p r e s e n t i n a l l samples. Ro max v a l u e s r anged from 0.89% t o 1.30%, corresponding t o a c o a l rank of high v o l a t i l e bituminous A to medium v o l a t i l e bituminous c o a l ( T e i c h m u l l e r and T e i c h m u l l e r , 1982). An anomalous v a l u e o f 1.6% Ro max from sample S4-129 i s a t t r i b u t e d to l o c a l h e a t i n g from a dike. Assuming a normal geothermal g r a d i e n t of 25-30°C/km and a maximum d e p t h o f b u r i a l f o r the S u s t u t Group o f 2 000 m, a t e m p e r a t u r e i n the o r d e r o f 80* C would be e x p e c t e d . Such a temperature, with an e f f e c t i v e h e a t i n g time of 30 Ma, however sh o u l d r e s u l t i n a coa1 i f i c a t i o n l e v e l of 0.59% Ro max (Bustin e t a l . , 1983), s u b s t a n t i a l l y lower than the determined v a l u e s of up t o 1.3% Ro max. Thus i n o r d e r t o produce Ro max v a l u e s of 1.3%, the maximum temperature would have been i n the order of 122°C-147°C. Samples c o l l e c t e d i n the northern Sustut B a s i n by G. Ei s b a c h e r , y i e l d e d s i m i l a r l y high Ro max v a l u e s , r a n g i n g from 0.99% t o 1.7% ( B u s t i n , 1984). C o a l b e a r i n g 87 s e d i m e n t s of a s i m i l a r age t o t h e S u s t u t Group, l o c a t e d t o the n o r t h and s o u t h of the S u s t u t B a s i n , a r e o f a l i g n i t e rank (Coal Resources of B r i t i s h Columbia, 1975), corresponding to an Ro max v a l u e of between 0.28% and 0.39%. C o a l samples an a l y z e d from the M i d d l e to Upper J u r a s s i c Bowser Lake Group, u n d e r l y i n g the Sustut Group, y i e l d e d anomalously high v a l u e s of up t o 5.8% Ro max c o r r e s p o n d i n g t o a m e t a - a n t h r a c i t e rank ( B u s t i n , 1984). These r e g i o n a l l y h i g h v a l u e s i n d i c a t e b o t h the prolonged time p e r i o d and r e g i o n a l extent over which high h e a t f l o w must have been p r e s e n t a t l e a s t i n p a r t of t h e Canadian C o r d i l l e r a . Anomalously high c o a l i f i c a t i o n l e v e l s f o r b o t h the S u s t u t and Bowser Lake Groups, as s u g g e s t e d by B u s t i n (1984), may have r e s u l t e d from: 1) e x p o s u r e t o h i g h temperatures as a r e s u l t of igneous i n t r u s i o n accompanying the c o l l i s i o n o f t h e S t i k i n e t e r r a n e , of c o m p o s i t e t e r r a n e I, t o t h e N o r t h A m e r i c a n m a r g i n i n M e s o z o i c t i m e ; a n d / o r 2) r e g i o n a l l y h i g h heat f l o w i n a back-arc b a s i n a s s o c i a t e d with an e a s t e r l y - d i p p i n g s u b d u c t i o n zone u n d e r n e a t h the c o a s t a l p l u t o n i c - v o l c a n i c a r c complex t o t h e west. P r e s e n t l y , b o t h t h e o r i e s are f e a s i b l e f o r e x p l a i n i n g the r e g i o n a l l y high heat f l o w d u r i n g Mesozoic time i n the Canadian C o r d i l l e r a . 88 SAMPLE NO. %Ro max METRES ABOVE BASE 53- 92 0.89 ± 0.09 583 54- 129 1.50 * 0.08 460 S4-140 1.12 * 0.1 535 S7-188 0.97 * 0.12 130 S7-192 1.08 * 0.10 170 S7-211 1.20 ± 0.12 670 Ta b l e 5. Coa1 i f i c a t i o n l e v e l of samples from the southern Sustut B a s i n 89 PALEOCURRENT ANALYSIS P a l e o c u r r e n t measurements were determined on t a b u l a r and t r o u g h c r o s s - s t r a t i f i c a t i o n , and i m b r i c a t e d c o n g l o m e r a t e c l a s t s . Too few measurements were made i n the T a t l a t u i Member and thus w i l l not be co n s i d e r e d here. I n t h e B r o t h e r s Peak F o r m a t i o n , a t o t a l o f 286 measurements were made of which 119 were from i m b r i c a t e d p e b b l e s i n t h e lower L a s l u i Member, 99 were from c r o s s s t r a t i f i c a t i o n mainly i n the upper L a s l u i Member and 68 were from c r o s s - s t r a t i f i c a t i o n i n the S p a t s i z i Member. The p r i n c i p a l p a l e o c u r r e n t d i r e c t i o n was from t h e n o r t h or n o r t h w e s t d u r i n g d e p o s i t i o n o f t h e lower L a s l u i Member. However, t h e p r i n c i p a l p a l e o c u r r e n t d i r e c t i o n d u r i n g d e p o s i t i o n of the upper L a s l u i Member was from the southwest. D u r i n g d e p o s i t i o n o f t h e S p a t s i z i Member p a l e o c u r r e n t d i r e c t i o n was from the west to northwest, s i m i l a r to the lower L a s l u i Member. 90 PROVENANCE Sa n d s t o n e s and c o n g l o m e r a t e s o f t h e S u s t u t Group a r e c h a r a c t e r i z e d by low c o m p o s i t i o n a l s t a b i l i t y and a submature t o immature t e x t u r e . Thus the c o m p o s i t i o n o f s a n d s t o n e s and c o n g l o m e r a t e s r e f l e c t t he c o m p o s i t i o n o f t h e s o u r c e and, combined w i t h p a l e o c u r r e n t d a t a , s u g g e s t p r o b a b l e s o u r c e r o c k s . R e s u l t s o f t h e h e a v y m i n e r a l a n a l y s i s were n o t d i a g n o s t i c f o r d e t e r m i n i n g a s p e c i f i c s o u r c e r o c k o r a r e a . F u r t h e r , r e s u l t s o f t h e heavy m i n e r a l a n a l y s i s d i d not show any trends between the Members of the Tango Creek and Brothers Peak F o r m a t i o n s . F i g u r e 15 i l l u s t r a t e s t h e l o c a t i o n and d i s t r i b u t i o n o f the p r i n c i p a l l i t h o l o g i c a l u n i t s o f t h e i n f e r r e d source areas and p a l e o c u r r e n t d i r e c t i o n s throughout d e p o s i t i o n of the Sustut Group i n the southern Sustut Basin. In t h e T a t l a t u i Member o f the Tango Creek F o r m a t i o n s a n d s t o n e s and c o n g l o m e r a t e s a r e r e l a t i v e l y e n r i c h e d w i t h q u a r t z , c h e r t and g r a n i t i c r o c k f r a g m e n t s . The Omineca B e l t t o the e a s t o f the S u s t u t Group i s a l i k e l y s o u r c e f o r the s e d i m e n t s , s p e c i f i c a l l y from t h e u n r o o f i n g o f g r a n i t o i d p l u t o n s t h a t i n t r u d e d the Omineca B e l t , and from t h e Cache Creek assemblage, which i s r i c h i n c h e r t and a r g i l l i t e . S e diments of the lower L a s l u i Member a r e r i c h i n c h e r t , e s p e c i a l l y the conglomerates, p l u s p l a g i o c l a s e f e l d s p a r and quartz. P a l e o c u r r e n t d i r e c t i o n d u r i n g d e p o s i t i o n of the lower L a s l u i Member was towards the southeast, suggesting the Bowser G r o u p as a s o u r c e r o c k . The Bowser G r o u p c o n s i s t s p r e d o m i n a n t l y o f c h e r t p e b b l e c o n g l o m e r a t e s and q u a r t z o s e s a n d s t o n e s , v o l c a n i c s and a r g i l l i t e s ( T i p p e r and R i c h a r d s , 91 1 9 7 6 ) , s i m i l a r t o t h e c o m p o s i t i o n o f t h e l o w e r L a s l u i sandstones and conglomerates. Sediments of the upper L a s l u i Member a r e composed of a high percentage of v a r i c o l o r e d a n d e s i t i c to b a s a l t i c v o l c a n i c f r a g m e n t s , v a r i c o l o r e d t u f f f r a g m e n t s as w e l l as t u f f h o r i z o n s , i n c o n t r a s t t o t h e lower L a s l u i and the T a t l a t u i Members. P l a g i o c l a s e f e l d s p a r , q u a r t z and c h e r t a r e a l s o common i n t h e upper L a s l u i Member, but a r e not as d i a g n o s t i c f o r source determination. O r i e n t a t i o n of c r o s s - s t r a t i f i c a t i o n i n t he upper L a s l u i Member i n d i c a t e s an e a s t t o n o r t h e a s t d i p p i n g p a l e o s l o p e , which i s a s i g n i f i c a n t change from t h e s o u t h e r l y d i p p i n g p a l e o s l o p e of the lower L a s l u i Member. Both t h e a b u n d a n c e o f v a r i c o l o r e d v o l c a n i c r o c k s and t h e n o r t h e a s t e r l y p a l e o c u r r e n t d i r e c t i o n s u g g e s t t h e Lower t o M i d d l e J u r a s s i c H a z e l t o n Group as the s o u r c e r o c k s . The Ha z e l t o n Group i s composed of b a s a l t i c to r h y o l i t i c v o l c a n i c r o c k s , t h e i r t u f f a c e o u s e q u i v a l e n t s , s e d i m e n t a r y r o c k s and minor l i m e s t o n e ( T i p p e r and R i c h a r d s , 1976). The u p l i f t e d Bowser Group may have c o n t i n u e d t o s u p p l y c h e r t and r o c k f r a g m e n t s t o the S u s t u t B a s i n d u r i n g d e p o s i t i o n o f the upper L a s l u i Member. The upper L a s l u i Member a l s o c o n t a i n s abundant f i n e g r a i n e d t u f f s and t u f f a c e o u s h o r i z o n s . The abundance o f t u f f present, together with the f i n e g r a i n s i z e would suggest t h a t the v o l c a n i c c e n t e r was: 1) ve r y a c t i v e over a long p e r i o d of time; and 2) s i g n i f i c a n t l y removed from the Sustut Basin. The v o l c a n i c B r i a n Boru F o r m a t i o n , p r e s e n t l y exposed s o u t h and 92 w e s t o f t h e s t u d y a r e a , i s b a s a l t i c t o r h y o l i t i c i n c o m p o s i t i o n ; p l a g i o c l a s e - h o r n b l e n d e p o r p h y r y b e i n g t h e commonest l i t h o l o g y . These v o l c a n i c rocks are c o g e n e t i c with Late Cretaceous i n t r u s i o n s t h a t y i e l d e d K-Ar dates of 70 - 80 Ma (Woodsworth e t a l . , 1983). The B r i a n Boru F o r m a t i o n and r e l a t e d v o l c a n i c and p l u t o n i c rocks are thought t o re p r e s e n t p a r t of a c o n t i n e n t a l v o l c a n i c a r c (Souther, 1975; Woodsworth e t a l . , 1983) and i s t h e most p r o b a b l e e r u p t i v e v o l c a n i c source r e s p o n s i b l e f o r the t u f f h o r i z o n s i n the upper L a s l u i Member. D e t r i t a l g r a i n s o f t h e S p a t s i z i Member a r e d o m i n a n t l y c h e r t , q u a r t z , p l a g i o c l a s e f e l d s p a r and l e s s e r amounts o f v o l c a n i c rock fragments. P a l e o c u r r e n t data i n d i c a t e s an e a s t t o s o u t h e a s t e r l y t r a n s p o r t d i r e c t i o n , s i m i l a r t o t h e lower L a s l u i Member. C o m p o s i t i o n and p a l e o c u r r e n t d i r e c t i o n suggests once again the Bowser Group as the p r i n c i p a l source r o c k s w i t h minor c o n t r i b u t i o n s from t h e H a z e l t o n Group sediments. R e c y c l e d d i n o c y s t s of Turonian age found throughout the s e c t i o n i n d i c a t e i nput from a marine environment c o e v a l with the S u s t u t Group. However, t h e r e i s no e v i d e n c e o f t h e s e rocks h a v i n g been p r e s e r v e d w i t h i n the s t r a t i g r a p h i c r e c o r d i n the surrounding area. 93 126" REG IONAL G E O L O G Y L E G E N D T E R T I A R Y l**"! O o t s a L a k e a n d E n d a k o G r o u p s C R E T A C E O U S S k e e n a a n d S u s t u t G r o u p s B r i a n B o r u F o r m a t i o n M I D D L E T O U P P E R J U R A S S I C B o w s e r L a k e G r o u p L O W E R T O M I D D L E J U R A S S I C Ivvvl H a z e l t o n G r o u p U P P E R T R I A S S I C T O L O W E R J U R A S S I C Intrus ive R o c k s U P P E R T R I A S S I C T a k l a G r o u p U P P E R P A L E O Z O I C A s i t k a G r o u p C a c h e C r e e k G r o u p [13 L a y R a n g e A s s e m b l a g e C R Y S T A L L I N E T E R R A N E I "*») O m i n e c a C r y s t a l l i n e Be l t A. Tatlatui Member B. lower Laslui Member and Spatsizi Member C. upper Laslui Member Figure 15. The inferred source areas and paleocurrent directions of the Sustut Group in the southern Sustut Basin 94 DEPOSITIONAL HISTORY AND TECTONIC SIGNIFICANCE OF THE SOUTHERN SUSTUT BASIN F i g u r e 16 i s a g e n e r a l i z e d 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 S u s t u t Group i n t h e s o u t h e r n S u t u t B a s i n , i l l u s t r a t i n g t h e changing p a l e o c u r r e n t d i r e c t i o n s and i n t e r p r e t e d source rocks. The d e p o s i t i o n a l h i s t o r y of the Late Cretaceous Sustut B a s i n i s d i r e c t l y r e l a t e d t o the t e c t o n i c e v o l u t i o n of the Canadian C o r d i l l e r a . Composite t e r r a n e I a c c r e t e d t o the N o r t h A merican c o n t i n e n t i n m i d - J u r a s s i c time (Monger, 1984). In m i d - C r e t a c e o u s t i m e , the S u s t u t B a s i n i s t h o u g h t t o have formed i n response to high angle normal f a u l t i n g accompanying e x t e n s i v e r i g h t - l a t e r a l s t r i k e s l i p f a u l t i n g . The u p l i f t e d p o r t i o n s o f the a c c r e t e d t e r r a n e and t h e Omineca B e l t , r e s u l t e d i n the shedding of f i n e and coarse g r a i n e d sediment westward i n t o the b a s i n , d e p o s i t i n g the Tango Creek Formation. In the southern Sustut Basin, the mainly f i n e g r a i n e d T a t l a t u i Member of the Tango Creek Formation i s i n t e r p r e t e d as a d i s t a l a l l u v i a l f a n to a l l u v i a l p l a i n d e p o s i t . P e r i o d i c a l l y , b r a i d e d streams m i g r a t e d a c r o s s the a l l u v i a l p l a i n i n r e s p o n s e t o h i g h e r e n e r g y l e v e l s and d e p o s i t e d c o a r s e s a n d s t o n e and c o n g l o m e r a t e , r e l a t i v e l y e n r i c h e d i n q u a r t z , w i t h l e s s e r amounts o f c h e r t and i g n e o u s r o c k f r a g m e n t s , i n c l u d i n g g r a n i t i c c l a s t s . The c o m p o s i t i o n o f the T a t l a t u i Member suggest t h a t the hig h grade metamorphic rocks comprising the Omineca B e l t s u p p l i e d much of the q u a r t z t o the s o u t h e r n S u s t u t B a s i n . The p r e s e n c e o f ig n e o u s r o c k f r a g m e n t s and c h e r t c l a s t s p o s s i b l y r e p r e s e n t the u n r o o f i n g o f p l u t o n i c r o c k s w i t h i n the Omineca B e l t , and t h e e r o s i o n o f T a k l a -Q i; S p a t z i z i M e m b e r u p p e r L a s l u i M e m b e r l o w e r L a s l u i M e m b e r T a t l a t u i M e m b e r f in ing u p w a r d s d i s t a l b r a i d e d s t r e a m s o v e r b a n k d e p o s i t s sma l l c h a n n e l b r a i d e d r i ve r shee t d e p o s i t sma l l c h a n n e l g r a v i t y f low b r a i d e d r i ve r s h e e t d e p o s i t sma l l c h a n n e l g r a v i t y flow m i d - f a n p r o x i m a l b r a i d e d s t r e a m P A L E O C U R R E N T D I R E C T I O N N d i s t a l b r a i ded s t ream overbank O o o o o o) a^y. o 0 o o o \ ^55^° ° ° a °) a>rtg o o Q v L e g e n d !il Conglomerate Sandstone [Hi] S i l t a t o n e / M u d a t o n e Tuff T rough x - b e d d e d //// P l ana r x - b e d d e d = P a r a l l e l x - b e d d e d --<*• R i p p l e s I N T E R P R E T E D S O U R C E B o w s e r G r o u p T a k l a / H a z e l t o n G r o u p (B r i a n B o r u \ F o r m a t i o n / B o w s e r G r o u p O m i n e c a B e l t C a c h e C r e e k G r o u p Figure 16. Generalized stratigraphic section of the Sustut Group illustrating the paleocurrent directions and inferred source rocks 96 H a z e l t o n v o l c a n i c s and Cache Creek c h e r t . P a l e o c u r r e n t data from t h e T a t l a t u i s e d i m e n t s i s s p a r s e and c o u l d n ot be u t i l i z e d to support the proposed source l o c a l i t i e s east of the Sustut Basin. A c c r e t i o n of composite t e r r a n e II to the North American margin i n m i d - C r e t a c e o u s time formed the v o l c a n i c - p 1 u t o n i c C o a s t P l u t o n i c B e l t t o t h e west of t h e S u s t u t B a s i n (Monger, 1984). C o n s e q u e n t L a t e C r e t a c e o u s u p l i f t o f t h e C o a s t P l u t o n i c B e l t and r e l a t e d f o l d i n g and f a u l t i n g of the Bowser Lake Group, terminated the d e p o s i t i o n of e a s t e r l y d e r i v e d f i n e g r a i n e d T a t l a t u i sediments, and t r i g g e r e d the p r o g r a d a t i o n of a l l u v i a l f a n complexes which d e p o s i t e d the t h i c k conglomerate sequences of the b a s a l B r o t h e r s Peak Formation (Figure 17a). Thick f i n i n g upward sequences of the lower L a s l u i Member i n d i c a t e d e p o s i t i o n i n s e v e r a l p u l s e s by high energy b r a i d e d s t r e a m s . C l a s t s o f t h e l o w e r L a s l u i s a n d s t o n e s and c o n g l o m e r a t e s a r e m a i n l y v a r i c o l o r e d c h e r t , q u a r t z , p l a g i o c l a s e and v o l c a n i c rock fragments. Such a composition combined w i t h a p r i n c i p a l n o r t h - n o r t h e a s t p a l e o c u r r e n t d i r e c t i o n , i n d i c a t e d by c r o s s - s t r a t i f i c a t i o n and i m b r i c a t e d c l a s t s , s u g g e s t s t h a t lower L a s l u i s e d i m e n t s were m a i n l y d e r i v e d from the u p l i f t e d , c h e r t r i c h , Bowser Lake Group. With d e n u d a t i o n o f t h e s o u r c e a r e a , c o a r s e g r a i n e d s e d i m e n t s o f t h e lower L a s l u i Member were p r o g r e s s i v e l y r e p l a c e d by t h i c k sequences o f f i n e g r a i n e d s e d i m e n t s , i n c l u d i n g t u f f beds, o f t h e upper L a s l u i Member. The f i n e g r a i n e d s e d i m e n t s a r e t h o u g h t t o have a c c u m u l a t e d on an a l l u v i a l f a n d i s t a l t o the lower L a s l u i Member or on an 97 Spatsizi Member Figure 17. Depositional model of the Brothers Peak Formation 98 a l l u v i a l p l a i n (Figure 17b). Sm a l l t r i b u t a r i e s t r a n s p o r t e d s i l t and f i n e sand which, d u r i n g f l o o d s t a g e s , d e p o s i t e d s h e e t - l i k e u n i t s . In ephemeral l a k e s v o l c a n i c ash, which emanated from v o l c a n i c c e n t r e s to the southwest accumulated. One l i k e l y v o l c a n i c c e n t e r c o i n c i d e s with the upper Cretaceous B r i a n Boru v o l c a n i c s . P e r i o d i c a l l y l a r g e r d i s t r i b u t a r i e s and high energy b r a i d e d streams migrated over the a l l u v i a l p l a i n , d e p o s i t i n g t h i n u n i t s o f c o a r s e s a n d s t o n e and c o n g l o m e r a t e . L o c a l l y , g r a v i t y f l o w s r e p r e s e n t i n g m a t r i x s u p p o r t e d c o n g l o m e r a t e i n t e r f i n g e r w i t h the f i n e g r a i n e d s e d i m e n t s of the upper L a s l u i Member. C o m p o s i t i o n a 1 l y , c l a s t s o f the coarse g r a i n e d sediments are mainly v a r i c o l o r e d v o l c a n i c rock fragments- s i m i l a r t o t h e c o m p o s i t i o n of b o t h t h e T a k l a and H a z e l t o n F o r m a t i o n s , as w e l l as p l a g i o c l a s e , c h e r t , and quartz. C r o s s - s t r a t i f i c a t i o n i n conglomerate, sandstone and t u f f beds i n d i c a t e a p r i n c i p a l p a l e o c u r r e n t d i r e c t i o n from the west to southwest, s u p p o r t i n g both the proposed v o l c a n i c and sedimentary source areas. C y c l i c a l sandstone and mudstone sequences of the S p a t s i z i Member, which are g r a d a t i o n a l from the upper L a s l u i sediments, a r e t h o u g h t t o r e p r e s e n t an e n t r e n c h e d sandy b r a i d e d stream complex d i s t a l t o an a l l u v i a l f a n . The b r a i d e d streams m i g r a t e d a c r o s s t h e a l l u v i a l p l a i n d e p o s i t i n g c h a n n e l and o v e r b a n k s e d i m e n t s ( F i g u r e 17c). V o l c a n i c a c t i v i t y had d e c r e a s e d s i g n i f i c a n t l y d u r i n g d e p o s i t i o n o f t h e S p a t s i z i Member as e v i d e n t by the l a c k of t u f f s . S i m i l a r to the lower L a s l u i Member, S p a t s i z i s a n d s t o n e s a r e m a i n l y composed of c h e r t , q u a r t z , p l a g i o c l a s e and v o l c a n i c rock fragments which suggests t h a t the Bowser Lake Group and p o s s i b l y the T a k l a and H a z e l t o n Groups were s o u r c e r o c k s . C r o s s - s t r a t i f i c a t i o n w i t h i n the S p a t s i z i Member sandstones i n d i c a t e s t h a t the main p a l e o c u r r e n t d i r e c t i o n was from the west to northwest. The Bowser Lake Group i s p r e s e n t l y exposed i n t h i s d i r e c t i o n . 100 SUMMARY AND CONCLUSIONS The Sustut Group of n o r t h - c e n t r a l B r i t i s h Columbia i s a non-marine s u c c e s s i o n of a l t e r n a t i n g f i n e and coarse g r a i n e d e l a s t i c s which i s d i v i s i b l e i n t o the Tango Creek and Brothers Peak F o r m a t i o n s . In t h e s o u t h e r n S u s t u t B a s i n t h e t o t a l t h i c k n e s s of the Sustut Group i s a t l e a s t 1 500 m. The Tango Creek Formation and the Brothers Peak Formation a r e c o n f o r m a b l e w i t h i n t h e s t u d y a r e a and a r e e n t i r e l y L a t e C r e t a c e o u s (Campanian t o M a a s t r i c h t i a n ) i n age, based on p a l y n o l o g i c a l evidence. An e n t i r e l y Late Cretaceous age f o r the Sustut Group i s s i g n i f i c a n t as p r e v i o u s work by Ei s b a c h e r (1971, 1974), d e f i n e d t h e Tango Creek F o r m a t i o n as Upper Cretaceous and the Brothers Peak Formation as Eocene. In the southern Sustut B a s i n o n l y the uppermost 400 m of the T a t l a t u i Member of t h e Tango Creek F o r m a t i o n i s exposed. The T a t l a t u i Member i s m a i n l y composed o f f i n e g r a i n e d sediments i n t e r p r e t e d as d i s t a l a l l u v i a l f a n - a l l u v i a l p l a i n d e p o s i t s . The f i n e g r a i n e d s e d i m e n t s a r e i n t e r b e d d e d w i t h c o a r s e g r a i n e d s a n d s t o n e s and c o n g l o m e r a t e s t h a t r e p r e s e n t the p e r i o d i c m i g r a t i o n of b r a i d e d stream d e p o s i t s across the a l l u v i a l p l a i n . The B r o t h e r s Peak Formation comprises 1 000 m of d i v e r s e e l a s t i c s and t u f f beds, and i s d i v i s i b l e i n t o a lower and upper L a s l u i Member and the S p a t s i z i Member. Sediments of the lower L a s l u i Member are composed mainly of t h i c k sequences of conglomerates and coarse g r a i n e d sandstones r e s u l t i n g from the pr o g r a d a t i o n of a l l u v i a l fans. The upper L a s l u i sequence i s composed mainly of f i n e g r a i n e d d i s t a l a l l u v i a l f a n - a l l u v i a l 101 p l a i n s e d i m e n t s , i n c l u d i n g t u f f beds, which a r e i n t e r b e d d e d w i t h coarse g r a i n e d d i s t r i b u t a r y , s h e e t f l o o d , and d e b r i s f l o w d e p o s i t s . C y c l i c a l sandstone/mudstone sequences comprise the S p a t s i z i sequence and are i n t e r p r e t e d as sandy b r a i d e d stream d e p o s i t s on an a l l u v i a l p l a i n . D e t r i t a l components of the Tango Creek and Brothers Peak sandstones are mainly c h e r t , q u a r t z , p l a g i o c l a s e and v o l c a n i c rock fragments. Cementation by c l a y m i n e r a l s and a l t e r a t i o n of v i t r i c s h a r d s t o z e o l i t e s i s common. The s a n d s t o n e s a r e c l a s s i f i e d as 1 i t h a r e n i t e s , f e l d s p a t h i c 1 i t h a r e n i t e s , and l i t h i c arkoses. Anomalously high c o a l i f i c a t i o n l e v e l s , c o rresponding to a r a n k o f h i g h v o l a t i l e b i t u m i n o u s A t o medium v o l a t i l e b i t u m i n o u s c o a l ( T e i c h m u l l e r and T e i c h m u l l e r , 1982), were foun d t h r o u g h o u t t h e S u s t u t Group. Such r e g i o n a l l y h i g h coa1 i f i c a t i o n l e v e l s may have r e s u l t e d from exposure to high temperature as a r e s u l t of igneous i n t r u s i o n and/or r e g i o n a l l y h i g h h e a t f l o w a s s o c i a t e d w i t h a J u r a s s i c t o e a r l y T e r t i a r y back-arc b a s i n . The d e p o s i t i o n a l h i s t o r y of the S u s t u t B a s i n can be c o r r e l a t e d t o t h e t e c t o n i c e v o l u t i o n o f t h e C a n a d i a n C o r d i l l e r a . The S u s t u t B a s i n f o r m e d i n r e s p o n s e t o e x t e n s i o n a l f a u l t i n g r e s u l t i n g from s t r i k e - s l i p f a u l t i n g s u bsequent t o the a c c r e t i o n of c o m p o s i t e t e r r a n e I t o t h e North American Continent i n M i d - J u r a s s i c time (Monger, 1984). Based on c o m p o s i t i o n , the T a t l a t u i s e d i m e n t s o f the Tango Creek F o r m t a i o n a r e i n t e r p r e t e d as o r i g i n a t i n g from the 102 u p l i f t e d Omineca B e l t and o t h e r P a l e o z o i c r o c k s e a s t o f t h e S u s t u t B a s i n . P a l e o c u r r e n t measurements and p r o v e n a n c e c o n s i d e r a t i o n s s u g g e s t t h a t d e p o s i t i o n of t h e B r o t h e r s Peak F o r m a t i o n was t r i g g e r e d by t e c t o n i c u p l i f t and v o l c a n i c a c t i v i t y west of the Sustut B a s i n r e s u l t i n g from the a c c r e t i o n of c o m p o s i t e t e r r a n e I I t o the N o r t h American c o n t i n e n t . S o u r c e a r e a s t o t h e w e s t c o n t i n u e d t o s u p p l y s e d i m e n t throughout Brothers Peak d e p o s i t i o n . 103 REFERENCES A l l e n , J.R.L. 1981. 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The sedimentology of a b r a i d e d r i v e r . J o u r n a l of Sedimentary P e t r o l o g y , v. 39, pp. 649-679. 114 Woodsworth, G.J., C r a w f o r d , M.L., and H o i l i s t e r , L.S. 1983. Metamorphism and s t r u c t u r e of the Coast P l u t o n i c Complex and adjacent b e l t s , P r i n c e Rupert T e r r a c e Areas, B r i t i s h Columbia. GAC, MAC, CGU F i e l d T r i p Guidebook 14, p.5. Z a i t l a n , B.A., and Rust, B.R. 1983. A spectrum of a l l u v i a l d e p o s i t s i n the Lower Ca r b o n i f e r o u s Bonaventure Formation of western C h a l e u r Bay Area, Gaspe, New Brunswick, Canada. Canadian J o u r n a l of E a r t h S c i e n c e s , v. 20, pp. 1098-1110. 115 A P P E N D I X PALYNOLOGY Sample No. Palynomorphs Age Range No. Above Base S3-81 390 Angiosperm p o l l e n : Campanian-Maastrichtian A g u i l l a p o l e n i t e s sp. c f . A_^  dolium Comp1exiopo1 l i s ? sp. Based on the p r e s e n c e C u p a n e i d i t e s sp. o f A q u i l a p o l l e n i t e s . L i l i a c i d i t e s sp. N y s s a p o l l e n i t e s a l b e r t e n s i s Spores: C y a t h i d i t e s sp. G l e i c h e n i i d i t e s sp. A l g a l c y s t s : a c r i t a r c h s S i g m o p o l l i s sp. D i n o c y s t s - r e c y c l e d Palaeoperidinium pyrrophorum  I s a b e l i d i n i u m acuminata  Amphidiodema nucula A l t e r b i a r e c t i c o r n i s S3-100 715 Angiosperm p o l l e n : monosulcate p o l l e n t r i c o l p a t e p o l l e n Indeterminate other than A l b i a n or younger Gymnosperm p o l l e n : E p h e d r i p i t e s sp. A l g a l c y s t s : a c r i t a r c h s 116 S3 -106 1055 A n g i o s p e r m p o l l e n : C a m p a n i a n - M a a s t r i c h t i a n S4 -124 310 S4 -143 550 S6 -171 60 A q u i l a p o l l e n i t e s p u l c h e r  A g u i l a p o l l e n i t e s sp . A . s p . c f . A ^ r e d u c t u s  E r d t m a n i p o l l i s s p . L i l i a c i d i t e s s p . t r i c o l p a t e p o l l e n t r i p o r a t e p o l l e n Gymnosperm p o l l e n : C l a s s i o p o l l i s s p . E p h e d r i p i t e s s p . S p o r e s : L a e v i g a t o s p o r i t e s s p . L i b r u n i s p o r i s s p . L y c o p o d i u m s p o r i t e s s p . S t e r e i s p o r i t e s s p . D i n o c y s t s - r e c y c l e d : P a l a e o s t o m o c y s t i s l a e v i g a t a S p o r e s and p o l l e n : G l e i c h e n i i d i t e s s e n o n i c u s D i n o c y s t s - r e c y c l e d : I s a b e l i d i n i u m a c u m i n a t a A n g i o s p e r m p o l l e n : A q u i l a p o l l e n i t e s s p . S p o r e s : C y a t h i d i t e s s p . M i c r o r e t i c u l a t i s p o r i t e s s p . T a u o r c u s p o r i t e s s p . B a s e d on t h e p r e s e n c e o f A q u i l a p o l l e n i t e s and E r d t m a n i p o l l i s C a m p a n i a n - M a a s t r i c h t i a n Upper C r e t a c e o u s S a n t o n i a n - M a a s t r i c h t i a n C a m p a n i a n - M a a s t r i c h t i a n B a s e d on t h e p r e s e n c e o f A q u i l a p o l e n i t e s 117 S6-182 660 Angiosperm p o l l e n : Campanian-Maastrichtian A q u i l a p o l l e n i t e s sp. c f . A.reductus Cranwe 11 i a sp.  Erdtmanipo11 i s sp. L i l i a c i d i t e s sp. R e t i t r i c o l p i t e s sp. c f . h e p a t i c u l u s t r i p o r a t e p o l l e n U l m i p o l l e n i t e s sp. Spores: Fora m i n i s p o r i s sp. fungal spores Gabonisporis sp. ?Ghoshispora sp. G l e i c h e n i i d i t e s sp. L a e v i g a t o s p o r i t e s sp. Lycopodiumsporites sp. Rou s e i s p o r i t e s sp. Based on the combined presence of A q u i l a p o l - l e n i t e s , Cranwe1lia, and Erdtmanipo11 i s S6-183 890 Angiosperm p o l l e n : Campanian-Maastrichtian A q u i l a p o l l e n i t e s sp. C r a n w e l l i a s p. t r i c o l p a t e p o l l e n t r i p o r a t e p o l l e n U l m i p o l l e n i t e s sp. Based on the presence o f A q u i l a p o l l e n i t e s and C r a n w e l l i a Spores: Gabonisporis sp. Ghoshipora sp. S7-185 15 Angiosperm p o l l e n : A. sp. c f . A_^  ceriocorpus?  E r d t m a n i p o l l i s sp. P r o t e a c i d i t e s sp. t r i c o l p a t e p o l l e n Gymnosperm p o l l e n : b i s a c c a t e p o l l e n Campanian or Campanian-M a a s t r i c h t i a n Based on the combined presence of the species l i s t e d 118 S p o r e s : S7 -196 320 S7 -197 305 A p p e n d i c i s p o r i t e s p r o b l e m a t i c u s ?  C i c a t r i c o s i s p o r i t e s s p . F o r a m i n i s p o r i s s p . F o v a e o s p o r i t e s l a b i o s u s  G h o s h i s p o r a s p . L i b r u n i s p o r i s s p . L y c o p o d i u m s p o r i t e s s p . N e o r a i s t r i c k i a s p . R o u s e i s p o r i t e s s p . S e l a g i n e l l a s p . A n g i o s p e r m p o l l e n : A q u i l a p o l l e n i t e s s p . S p o r e s : C y a t h i d i t e s s p . D i s t a l t r i a n g u l i s p o r i t e s s p . G l e i i c h e n i d i t e s s p . L a e v i g a t o s p o r T t e s s p . L y c o p o d i u m s p o r i t e s s p . A n g i o s p e r m p o l l e n : A q u i l a p o l l e n i t e s s p . c f . A^ _ d o l ium Gymnosperm p o l l e n : E u c o m m i i d i t e s s p . S p o r e s : C y a t h i d i t e s s p . G l e i c h e n i i d i t e s s p . C a m p a n i a n - M a a s t r i c h t i a n Ba sed on t h e p r e s e n c e o f A q u i l a p o l l e n i t e s Campan ian B a s e d on t h e p r o b a b l e p r e s e n c e o f A. d o l i u m S7 -206 605 S8-223 360 S p o r e s : C y a t h i d i t e s s p . L a e v i g a t o s p o r i t e s s p . A n g i o s p e r m p o l l e n : A q u i l a p o l l e n i t e s s p . c f .A. p u l c h e r t r i c o l p a t e p o l l e n no age d i a g n o s t i c p a l y n o m o r p h s C a m p a n i a n - M a a s t r i c h t i a n Ba sed on t h e p r e s e n c e o f A q u i l a p o l l e n i t e s 119 Spores: C y a t h i d i t e s sp. Fora m i n i s p o r i s sp. fungal spores Gabonisporis sp. Lycopodiumsporites sp. 120 

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