A Discussion on the Origin Of

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A DISCUSSION ON THE ORIGIN OFCLAY MINERALS IN SEDIMENTARY ROCKS

ByC H A R L E S E . WE A V E RShell Oil Company, Houston, Texas

A B S T R A C TX-ray ana lyses o f the c lay minera ls f rom thousands o f sed iments ind ica te tha t any o f themajor c lay minera ls can occur in abundance in any o f the major depos i t iona l env iron-men ts and there is no consis tent coincidence between specific c lay m inerals and specificdepo sit ional environments . I t is concluded that the g reat ma jority of c lay minerals in sedi-menta ry rocks a re de t r i ta l in o r ig in , s t rong ly re f lec t the charac te r o f the i r source mate r ia l ,and a re on ly s l igh t ly modif ied in the i r depos i t iona l env ironments .The most comm on process acting on the c la y m inerals in m arine environments is cationadsorp t ion . The m odif ica t ions p roduced by th is p rocess a re secondary bu t because o f theoveremphasis of names ra ther than processes , they have been considered fundamentalchanges a nd the process has been called diagenesis . From the g eologis t 's v iewpoint, thebasic c lay mineral la t t ice , which is inherited from the source materia l , is the most s ignifi-can t pa ram ete r o f the c lay minera ls and m odif ica tions caused by the adsorbed ca t ions a resecondary, derived parameters reflecting the character of the deposit ional environment.

This concept of dualism is essentia l to the unders tanding of c lay genesis , and the s ignifi-cance o f the two param ete rs mus t be unders tood be fore a gene t ic c lass i f ica tion can beconstructed a nd befo re c lays can b e used for geologic interp reta tio n.I N T R O D U C T I O N

C l a y p e t r o l o g y h a s f i n a l ly c o m e o f ag e a n d c a n b o a s t t h e d e v e l o p m e n t o fw i d e l y d i v e r g e n t v i e w p o i n t s su c h a s c h a r a c t e r i z e s o m e o f t h e o l d e r g e o l o g i cd i s c i p l i n e s ; e. g. , g r a n i t i z a t i o n a n d t h e g r a y w a c k e c o n f u s i o n . T h e m o s t i m p o r -t a n t a r e a o f d i s a g r e e m e n t o r s p e c u l a t i o n i n c l a y p e t r o l o g y c o n c e r n s t h e o r i g i no f t h e c l a y m i n e r a l s i n s e d i m e n t s ; a r e t h e y p r i m a r i l y d e t r i t a l o r d i a g e n e t i c i no r i g i n ? M i l l o t ( 1 94 9 , 1 9 5 3 ) , G r i m ( 1 9 5 3 ) , P o w e r s ( 1 9 5 7 ) , a n d o t h e rs h a v ea b l y p r e s e n t e d th e c as e f o r d i a g e n e s i s o r n e o f o r m a t i o n . R i v i g r e ( 1 9 5 3)a p p e a r s t o h a v e b e e n t h e o n l y o n e t o a t t e m p t a d e f e n se o f t h e " d e t r i t a l " c o n -c e pt . I n g e n e r a l t h e p r e v a i l i n g o p i n i o n s a r e b a s e d u p o n r a t h e r s c a n t d a t a . ,

D u r i n g t h e p a s t f e w y e a r s , i n c o n n e c t i o n w i t h v a r i o u s i n v e s t i g a t i o n s , x - r a yd i f f r a c t i o n a n a l y s e s of t h e c l a y f r o m t h o u s a n d s o f s e d i m e n t a r y r o c k s h a v eb e e n a v a i l a b l e f o r i n t e r p r e t a t i o n . T h e p u r p o s e o f co l l e ct i n g t h e se d a t a h a sb e e n t h e g e o l o g i c i n t e r p r e t a t i o n o f a r g i l l a c e o u s s e d i m e n t s a n d i n a l l c a s es t h ec l a y m i n e r a l d a t a h a v e b e e n c l o s e ly i n t e g r a t e d w i t h a l l o t h er a v a i l a b l e g e o l o g ici n f o r m a t i o n . T h e i n t e n t o f t h i s p a p e r i s t o p r e se n t s o m e o f t h e p r e l i m i n a r yi d e a s o b t a i n e d f r o m e x a m i n i n g t h i s m a s s o f d a t a . T h e o v e r w h e l m i n g i m p r e s -s i o n g a i n e d f r o m e x a m i n i n g t h e c l a y s f r o m s u c h a la r g e n u m b e r o f r o c k s i st h a t t h e m a j o r i t y o f t h e c l a y m i n e r a l s i n s e d i m e n t a r y r o c k s a r e d e t r i t a l i no r i g i n a n d s t r o n g l y r e f l ec t t h e c h a r a c t e r o f t h e i r s o u r c e a r e a .

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16 0 ORIGIN OF CLAY MINERALS IN SEDIMENTARY ROCKSR E L A T I O N O F C L A Y M I N E R A L S T O D E P O S I T I O N A LE N V I R O N M E N T S

General ObservationsF i g u r e s 1 a n d 2 i l l u s t r a t e t h e v a r i e t y o f c l a y m i n e r a l s f o u n d i n s e d i m e n t sd e p o s i t e d u n d e r s i m i l a r e n v i r o n m e n t a l c o n d i t i o n s a n d a l s o t h e v a r i e t y o fe n v i r o n m e n t s in w h i c h t h e s a m e c l a y m i n e r a l s c a n o c c u r . A l l s a m p l es a r e o fa n c i e n t r o c k a n d a r e n o t s e le c te d fr e a k s a m p l e s b u t a r e r e p r e s e n t a ti v e o f t e n so r h u n d r e d s o f s am p l e s. A l t h o u g h a n a t t e m p t w a s m a d e t o s e le c t e x a m p l e s i nw h i c h o n e t y p e o f c l a y p r e d o m i n a t e s , m a n y o t h e r e x a m p l e s c o u l d h a v e b e e nc h o s e n t o s h o w v a r i o u s m i x t u r e s o f c l a y m i n e r a l s w h i c h o c c u r i n s e d i m e n t s

d e p o s i t e d u n d e r w i d e l y d i f f e r i n g e n v i r o n m e n t a l c o n d i t i o n s .P o s t d e p o s i t i o n a l a lt e r a t io n o f t h e c l ay m i n e r a l s i n p o r o u s a n d p e r m e a b l es a n d s to n e s i s r e l a ti v e l y c o m m o n ; f o r t h is r e a s o n o n l y x - r a y p a t te r n s o f t h ec l a y f r o m s h a le a n d c a r b o n a t e s am p l e s a r e s h o w n i n F i g u r e s 1 a n d 2 . F i g u r e 3i s a s e r i e s o f x - r a y p o w d e r - d i f f r a c t i o n p a t t e r n s o f o r g a n i c a n d p y r i t e - r i c hb la c k sha le s . Ag a in , a l l t he ma jo r c l a y mine r a l t ype s , e xc e p t c h lo r i t e , oc c u r a sd o m i n a n t m i n e r a l s i n t h e s e s h a l e s t h a t r e p r e s e n t s i m i l a r c h e m i c a l e n v i r o n -m e n t s . S o m e o f t h e i n f e re n c e s t h a t c a n b e m a d e f r o m t h e s e d a t a a n d t h e b u l kd a t a f r o m w h i c h t h e y a r e d r a w n a r e : ( 1 ) n o p a r t i c u l a r c l a y m i n e r a l isr e s t r ic t e d t o a p a r t ic u l a r e n v i r o n m e n t ; ( 2 ) i ll it e, m o n t m o r i l lo n i t e , a n d m i x e d -l a y e r il l it e -m o n t m o r i l lo n i t e c a n o c c u r i n a b u n d a n c e , f r e q u e n t l y a s t h e o n l yc l a y m i n e r a l s p r es e n t , i n a n y o f t h e m a j o r d e p o s i t i o n a l e n v i r o n m e n t s ; ( 3 )k a o l i n i t e i s d o m i n a n t m a i n l y i n f l u v i a t i l e e n v i r o n m e n t s a l t h o u g h i t o c c u r s i na b u n d a n c e i n a l l e n v i r o n m e n t s ; ( 4 ) c h l o r i t e is se l d o m i f e v e r a d o m i n a n t c l a ym i n e r a l ; ( 5 ) n o n m a r i n e s ha le s a r e s e l d o m i f e v e r m o n o m i n e r a l i c .T h e s e d a t a i n d i c a te t h a t ( 1 ) a s a w h o l e, c l a y m i n e r a l s d o n o t o r i g i n a t e intoto i n t h e i r d e p o s i t io n a l e n v i ro n m e n t , a n d ( 2 ) g e n e r a l ly t h e y a r e n o t s t r o n g l ym o d i f i e d b y t h e d e p o s i t i o n a l e n v i r o n m e n t . T h i s s u g g e s ts t h a t t h e p r o c e s s o fd i a g en e s i s i s n o t a s e f fe c t iv e a s i s c o m m o n l y t h o u g h t a n d t h a t c l a y m i n e r a l sa r e p r e d o m i n a n t l y d e t r i ta l in o r i g i n a n d r e f l e c t p r i m a r i l y t h e c h a r a c t e r o ft h e i r s o u r c e a r e a . T h e r e i s s t r o n g e v i d e n c e t h a t c l a y s a r e a l t e re d ( u s u a l lyd e g r a d e d ) t o s o m e e x t e n t i n f lu v i a t il e a n d s u b a e r i a l c o n t i n e n t a l e n v i r o n m e n t s ,b u t i n t h e o t h e r m a j o r e n v i r o n m e n t s t h e r e i s l i t t l e d i r e c t e v i d e n c e t o i n d i c a t et h a t a l t e r a ti o n i n t h e b a s i n o f d e p o s i t i o n i s a m a j o r f a c t o r i n d e t e r m i n i n g t h eu l t i m a t e m i n e r a l o g i c c h a r a c t e r o f t h e c l a y s u i t e .

._.yFIsuRz 1 . - Typ es of clay minerals occurring in m arine environments: (1) W ills Creek,Upper Silurian, Pennsylvania; (2) So da La ke , Lo w er M iocene, California; (3) Sod aLake, Lo w er M iocene, California; (4) So da Lak e, Lo w er Miocene, California; (5) Fay -etteviUe, Upp er M ississippian, Arkansas; (6) Le ban on , M idd le Ordov ician, Tennessee;(7) U pp er Cretaceous, Florida; (8) Nolichucky , Up per Cam brian, Virginia; (9) M agda-lena, Low er Pennsylvanian, Texas; (1 0 ) Sm ackover, Upper Jurassic, Louisiana; (11)Seven Rivers, Up per Permian, Texas; (12 ) U pper Cretaceous, Florida; (1 3) Lo w er Cre-taceous, Florida; (1 4) G len Rose, Low er Cretaceous, Texas; (1 5) Ly lton, Upper Devon-ian, Montana.


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CHARLES E. WEAVER 161

I L L I T E

M O N T M O R I L L O N I T E

M I X E D - L A Y ERI L L I T E -


K A O L I N I T E

C H L O R I T E

S H A L E C A R B O N A T E E V A P O R I T E

I . 6 . I I .

2. 7. 12.

3. 8. 13.

a23a4 .5.

9 . 14.

I0. 15.


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] 6 2 ORIGIN OF CLAY MINERALS IN SEDIMENTARYROCKS

I L L I T E

MONTMORILLONITE

M I X E D - L A Y E RI L L I T E -


K A O L I N I T E

C H L O R I T E

DELTA I C LA C U S TR IN FLUVIAT ILE

16. 21. 26 .

18. ~ 23 . 2 8 .

19 .

20.

24 . 2 9 .

2 5 . 30.


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CHARLES E. WEAVER 163T h e r a r i t y o f m o n o m i n e r a l i c d e l t a i c s h a l e s p r o b a b l y r e s u l t s f r o m t h e r a p i ddu m ping ty pe o f de pos i t i on wh ic h o c c u r s i n de lt a s . Th e de l t a ic l oc us o f se d i-m e n t a t i o n i s a n e n v i r o n m e n t w h e r e t h e r e i s l i t t l e w i n n o w i n g o r c h e m i c a ls o r t i n g .P o w e r s ( 1 9 5 7 ) h a s p r e s e n t e d so m e f a i r l y c o n v i n c i n g e v i d e n c e t h a t c h l o r i t em a y f o r m i n a m a r i n e e n v i r o n m e n t , b u t e v e n h e r e i t i s p o s t u l a t e d t h a t t h eba s i c l a t ti c e is de t r i t a l in o r ig in a n d tha t o n ly the in t e r l a ye r m a te r i a l i s a u th i -ge n ic . Th a t c h lo r i t e i s s e ldom a dom ina n t min e r a l i n sha l es a nd l ime s tone sc a n be e xp la ine d by the f a c t t ha t c h lo r i t e i s r a the r e a s i ly we a the r e d a nd se l -d o m i s t h e d o m i n a n t m i c a i n a n y o f t h e c o m m o n s o u r c e ro c k s . I f c h l o ri t e i sc o m m o n l y f o r m e d a u t h i g e n ic a l l y u n d e r n o r m a l m a r i n e c o n d i t io n s , i t s h o u l d

f r e qu e n t ly f o r m the bu lk o f a c l a y m ine r a l su it e . Ac tua l ly , it a ppe a r s t ha tc h l o r i t e m a y b e m o r e a b u n d a n t i n c la y s d e p o s it e d in b r a c k i s h a n d f r es h - w a t e re n v i r o n m e n t t h a n i n t h o s e d e p o s i t e d u n d e r o p e n m a r i n e c o n d i t i o n s .T h e i n v e s t i g a t o r s o f R e c e n t m a r i n e m u d s i n d i c a t e t h a t d i a g e n e s i s i s a ni m p o r t a n t p r o c e s s i n d e t e r m i n i n g t h e m i n e r a l o g i c c h a r a c t e r o f t h e c l a y m i n -e r a l su i te . D i r e c t p r o o f o f t he r e l a t ive e f f e c tive ne ss o f t he d i a ge ne t i c a ndde t r i t a l p r oc e s se s i s e x t r e me ly d i f f ic u l t a nd in ne a r ly a l l s tud ie s o f R e c e n t a nda nc ie n t s e d ime n t s on ly ind i r e c t e v ide nc e c a n be c i te d . I n m os t c a se s the da t ao b t a i n e d f r o m t h e c l a y p e t r o l o g y o f a l a r g e n u m b e r o f f o r m a t i o n s a n d b a s i n swe r e be s t i n t e g r a t e d in to the ove r - a l l ge o log ic h i s to r y by a s suming tha t t hec l a y m ine r a l su i t es we r e la r ge ly de t r i t a l i n o r ig in . Aga in the e v ide nc e i s ind i -r e c t b u t f r o m t h e s t a n d p o i n t o f c o i n c i d e n c e t h e r e i s c o n s i s t e n t l y a g r e a t e rc o i n c i d e n c e b e t w e e n t h e b u l k c l a y s u i te a n d s o u r c e t h a n b e tw e e n t h e b u l k c l a ys u i t e a n d d e p o s i t i o n a l e n v i r o n m e n t .

Speci/ic ApproachA s p e c i f i c e x a m p l e o f t h e i n f l u e n c e o f s o u r c e o n t h e d i s t r i b u t i o n o f c l a ym i n e r a l s i n a t h i c k s h al e f o r m a t i o n i s s h o w n i n F i g u r e 4 . A t h i n g l a u c o n i t i csa nds tone is u se d a s a da tum l ine . Th e d i s t r ibu t ion o f t he c l a y m ine r a l f a c i e sa n d a d d i t i o n a l g e o l o g ic d a t a i n d i c a t e th a t a m o n t m o r i l lo n i t i c ( c h l o ri t e a n dka o l in i t e a l so p r e se n t ) de l t a wa s f o r m ing in the we s t e r n pa r t o f t he ba s in a t t hesa me t im e a s a n i l l i te ( ka o l in i t e , c h lo r i t e , a nd m ixe d - l a ye r i l li t e -mo n tmor i l l on -i t e a l so p r e se n t ) de l t a wa s f o r m ing in the e a s t e r n pa r t o f t he ba s in . Th e c la ysbe twe e n the se two de l t a s a r e a mix tu r e o f t he two c l a y su i t e s w i th e a c h su i t eg r a d ua l ly lo s ing i ts o r ig ina l c ha r a c t e r a wa y f r om i ts r e spe c t ive de l ta . Eve n tu -

,6==FI6URE 2 . - Types of clay minerals occurring in continental environments: (16) Catskill,Upper D evonian, Pennsylvania; (1 7 ) Sp ringer, U pp er M ississippian, Oklahoma; (18)Soda Lak e, Lo we r M iocene, California; (1 9) Ato ka, Lo w er Pennsylvanian, Texas; (20)Cantuar, Lo we r Cretaceous, Saskatchewan; (2 1) G reen River , Midd le Eocene, Utah;(22) G reen River, M iddle Eocene, Utah; (2 3) G reen River, M iddle Eocene, Utah; (24)M iocene, Venezuela; (2 5 ) C antu ar, Lo w er Cretaceous, Saskatchewan; (2 6 ) C antuar,Lower Cretaceous, Saskatchewan; (2 7) Fountain, Low er Pennsylvanian, Colorado; (28)Cantuar, Lo w er Cretaceous, Saskatchewan; (2 9) Cantuar, Lo we r Cretaceous, Saskatche-wan; (3 0 ) Cantuar, Low er Cretaceous, Saskatchewan.


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164 ORIClN OF CLAY MINERALS IN SEDIMENTARY ROCKS

I , K A O L I N I T E 3 . MO NT MO RILLO NIT E

2 . M I X E D - L A Y E RI L L I T E - M O N T M O R I L L O N I T E 4.1LLITEFicw ~ 3 . - Types ot clay minerals occurring in b lack shales: (1) Cretaceous, Saskatche-wan; (2)Devonian, Saskatchewan; (3) Eocene, California; (4) Ordovician, Oklahoma.a l l y t he bas in w as nea r l y f i l l ed ; dep os i t ion ceased i n t he wes t e rn , mo n tmor i l -l on i t i c de l t a and t he re was r enewed up l i f t i n t he sou rce a rea o f t he eas t e rn ,i ll it ic de l ta . The i ll i te f ac ies sp read w es tward over t he mo n tm or i l l on i t i c de lt a ,r e w o r k i n g t h e u n d e r l y i n g se d i m e n t s ( th e d e l t a ic s o d i u m m o n t m o r i l l o n i te w a sa l te r e d to a c a l c i u m m o n t m o r i ll o n i t e d u r i n g w e a t h e r i n g a n d r e w o r k i n g ) , a n dfo rm ing a t h in zone o f mixe d s ed imen t s a s i t m ig ra t e d t o the w es t. Th e g l au -con i t i c s ands tone i s u sua l l y a s soc ia t ed w i th t h i s sha l low-wate r , m ixed zone .In connect ion wi th sou rce a reas , i t i s o f i n t e res t t o no t e someth ing o f t hee ros iona l p roces ses wh ich p roduce t he detr i ta l c l ay ma te r i a l. S amples o f t hec l a y i n f l o o d w a t e r , t a k e n a t t h e c r e st , f ro m t h e S u s q u e h a n n a R i v e r a n d t w o o fi ts ma jo r t r i bu t a r ie s , P in e Creek and L oya l sock Creek , con t a in i l li te and ch lo r-i te . The s t r eams i n th i s r eg ion de r i ve mo s t o f t he i r d e t r i t u s f rom the su r roun d-ing Devon i an , Mi s s i s s i pp i an , and P ennsy lvan i an s ed imen t s wh ich a re p redom-inan t l y i ll it e and ch lo r i t e sha les . The f l ood wa t e r s o f a smal l t r i bu t a ry t o P ineCreek wh ich had e roded deep go rges t h rough a s e r i e s o f Mi s s i s s i pp i an sha l escon t a ined on ly i l l i t e and ch lo r i t e . The sha l e fo rming t he s i des o f t he go rgesa l so con t a ined on ly i l l i t e and ch lo r i t e ; however , t he heav i l y vege t a t ed fo res tso i l su r ro und ing t he s t r eam con t a ined m ixed- l ayer i lt i te -mon tmor i l lon i t e , kao -l in i te , an d a sm al l am ou nt of il ii te . Th e i l li t e - to-chlor i t e ra t io , 9 :1 , in the


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CHARLES E. WEAVER 165s t r e a m s i s s i m i l a r t o t h a t in t h e s u r r o u n d i n g s h a le f o r m a t i o n s . I t is a p p a r e n tt h a t , a s i n t h e V - s h a p e d g r a n i t i c c a n y o n s d e s c r i b e d b y K r y n i n e ( 1 9 4 9 ) , m o s to f t h e c l a y s i n t h es e m o u n t a i n o u s s t r ea m s a t f l o o d s ta g e a r e d e r i v e d f r o mm e c h a n i c a l d i s a g g r e g a t i o n o f r e l a t i v e l y f r e s h s h a l e m a t e r i a l w h i l e t h e w e a t h -e r e d so i l m a te r i a l c on t r ibu te s ve r y l i tt l e t o the s t r e a m loa d . I n th i s s i t ua t ion i ti s poss ib l e t o o b ta in tw o c l a y su it e s f r om one sou r c e a r e a .

S O U R C E V E R S U S D I A G E N E S I SKaolinite

I n d i sc uss ing d i a ge ne s i s , Gr im ( 1951) ha s no te d tha t ka o l in i t e i s r e l a t ive lyl e s s a b u n d a n t i n a n c i e n t s e d i m e n t s t h a n i n y o u n g e r s e d i m e n t s a n d c o n c l u d e dt h a t i t m u s t t h e r e f o r e b e c h a n g e d t o s o m e o t h e r c l ay m i n e r a l . G i l lu l y ( 1 9 4 9 )r e p o r t e d t h a t " T h e r e c o r d o f t h e c o a r s e r c l a s t i c b o r d e r z o n e s i s m u c h m o r el i a b le t o be de s t r oy e d by e r os ion tha n i s t ha t o f t he ba s in c e n te r . S t a t is t i c al ly ,we shou ld e xpe c t t ha t t he o lde r t he pe r iod , t he mor e l i ke ly i t i s t o be r e p r e -s e n t e d b y o f f s h o r e d e p o s i ts . " B e c a u s e k a o l i n i te i s m o s t a b u n d a n t i n c o n t i-n e n t a l a n d n e a r - s h o r e s e d im e n t s , a m o r e r e a s o n a b l e e x p l a n a t i o n o f th ede c r e a se in ka o l in i t e migh t be tha t t he se ka o l in i t e - r i c h , bo r de r z one se d ime n t sa r e p o o r l y r e p r e s e n t e d i n t h e o l d e r g e o l o g ic r e c o r d .Mi l lo t ( 1953) , i n bu i ld ing h i s c a se f o r ma r ine d i a ge ne s i s , r e po r t e d tha tm a r i n e s e d i m e n t s , p o o r i n c a l c i t e b u t r i c h i n o r g a n i c m a t t e r a n d s u l f i d e s , a r er e l a ti v e l y r i c h i n k a o l i n i te a n d c o n c l u d e d t h a t k a o l i n i t e is f o r m e d b y a n a c i dr e a c t i o n i n a n a n a e r o b i c m e d i u m . D a t a f r o m t h e C h a t t a n o o g a , W o o d f o r d ,Lodge po le , Te snus , C a ne y , He e bne r , P o lk C r e e k , F e r n ie , Exsha w, B a nf f , B a k -

I 2 3 4 5 6 7 8 9

[ ~ i I~L.TE ~ ILLITE ~LUS MO .T.O.~LO.~EFICURE 4.--Northwest-southeast cross section showing the distribution of clay mineralfacies.


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166 ORIGIN OF CLAY MINERALS IN SEDIMENTARY ROCKS

k e n , a n d D u v e r n a y f o r m a t i o n s i n d i c a t e t h a t m a r i n e b l a c k s h a l e s a r e d o m i -nan t l y composed o f i l l i t e o r mixed - l ayer i l l i t e -mon tmor i l l on i t e and usua l l ycon t a in no kao l i n i t e o r l es s t ha n 10 pe rcen t .Mo n t m o r i l l o n i t e

G rim (1951) a l so s t a ted t ha t t he re i s re l a t ive ly l es s m on tm or i l l on i t e i nanc i en t s ed imen t s and sugges t ed t he re fo re t ha t i t i s changed by d i agenes i s t os o m e o t h e r c l a y m i n e r a l . T h e r e i s s o m e d o u b t t h a t t i m e d i a g e n e s is h a s a n yef fec t on mo n tm or i l l on i t e , a s i t is qu i t e comm on in Ju ras s i c , P e rm ian , P enn-sy lvan i an , and Upper M i s s is s i pp ian rocks ( l oca ll y 5000 fee t t h i c k ) , and i sp resen t a s mixed - l ayer ch lo r i t e -mon tm or i l l on i te i n M idd l e and L ow er Ordo-v i c i a n a n d U p p e r a n d M i d d l e C a m b r i a n s e d i m e n t s . V o l c a n i c m a t e r i a l i s t h em a j o r s o u r c e o f m o n t m o r i l l o n i te a n d i t a p p e a r s t h a t t h e r e m a y h a v e b e e n le ssv o l c a n is m d u r i n g t h e e a r ly P a le o z o i c t h a n t h e T e r t i a ry . F u r t h e r , m u c h o f th eo lde r P a l eozo i c ben ton i t i c ma t e r i a l appear s t o have been a l t e red by r eg iona lm e t a m o r p h i s m ( v o l c a n i c s l a t e s o f t h e A p p a l a c h i a n M o u n t a i n s ) .l l l i t e

I l li t e i s t he d om inan t minera l i n l imes tones and i t i s genera l l y be l ieved t ha tt he re i s some re l a t i on be tween a ca l ca reous env i ronmen t and t he d i agenes i s o fi ll it e . How ever , t he da t a sum ma r i zed in F igu re 1 i nd i ca t e t ha t a ny o f t he c l ayminera l s , w i th t he pos s ib l e excep t i on o f kao l i n i t e , may ex i s t i n abundance i nc a r b o n a t e r o c k s. A l t h o u g h i ll it e i s t h e m o s t a b u n d a n t m i n e r a l i n c a r b o n a t erocks , it is a lso the mos t abu nd an t m inera l i n sha l es and t he p resen t d a t a i nd i -ca t e t ha t i t is no t no t i ceab ly m ore ab un dan t i n l imes tones t han i n sha l es . Insec t ions where l imes tones and sha l es a re i n t e rbedde d , t he re i s li tt le d i f f e rencebe tween t he c l ay m inera l su i te s . A l thoug h t he c l ay minera l in o lde r P a l eozo i cl imes tones is p red om inan t l y il li te , il li te i s a lso t he p red om inan t c l ay m inera l i nthe o lde r P a l eozo i c c l a s ti c s ed imen t s and i ts abu nda nce appa ren t l y i s a r e f l ec-t i o n o f s o u r c e m a t e r i a l a n d t y p e o f w e a t h e r i n g r a t h e r t h a n e n v i r o n m e n t a ld iagenes i s .

Rece n t l y Lev inson (1955) and Yoder and Eug s t e r (1955) have d is cus sedp o l y m o r p h i s m i n il li te m i n e r a ls . T h e l a tt e r a u t h o r s h a v e d e m o n s t r a t e d th a tt h e 1 M a n d 1 M d p o l y m o r p h s a r e t h e s t a b l e l o w - t e m p e r a t u r e s t r u c t u r e s a n dt h a t t h e 2M m i c a p o l y m o r p h i s t h e s ta b l e h i g h - t e m p e r a t u r e f o r m . E x a m i n a .t i on o f a number o f s ed imen ta ry i l l i t e s has sugges t ed t ha t t he 1M and 1Mdtypes t end t o be found as g l aucon i t e s , i l l i t e s fo rmed by t he a l t e ra t i on o f f e l d -spa r s , and m ixed- l ayer i l li t e -mon tmor i l lon i t e s wh ich have fo rm ed f ro m mon t -mo r i ll on i te s . S amples o f l eached muscov i t e , wh ich expa nd t o 16 . 6A whent rea t ed w i th e thy l ene g lyco l, s t il l r e t a i n t he i r o r i g ina l 2M s t ruc tu re . Thesed a t a , a lo n g w i th th e d a t a o f Y o d e r a n d E u g s t e r ( 1 9 5 5 ) , s t r o n g l y su g g e s t t h a ta n y s e d i m e n t a r y d i o c t a h e d r a l i l li te m i n e r a l w h i c h f o r m e d d i a g e n e t ic a l l y f r o ma m i n e r a l o t h e r th a n m u s c o v i te , o r a u t h i g e n i c a ll y f r o m s o lu t io n , w o u l d h a v e a1M or 1M d s truc tu re . In v i ew o f t he f ac t t ha t t he g l auco n i t e mine ra l , wh i ch i s


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CHAnLES E. W EAvrn 167c o n s i d e r e d t o f o r m d i a g e n e t i c a l l y u n d e r m a r i n e c o n d i t i o n s , a p p e a r s t o e x i s to n l y a s t h e 1 M p o l y m o r p h , i t w o u l d b e d i f f i c u l t t o i m a g i n e t h a t e l s e w h e r e i nt h e m a r i n e e n v i r o n m e n t t h e 2 M m i c a p o l y m o r p h w a s b e in g f o r m e d f r o m m a te -r i a l t h a t d i d n o t h a v e a p r e e x i s ti n g 2 M s t r u c t u r e . T h e o n l y s ig n i f i c a n t s o u r c eo f 2 M i l l i t e s i s m u s c o v i t e ( m o s t o f w h i c h p r o b a b l y w a s f o r m e d b y m e t a m o r -ph i sm o f 1M i ll it e s a nd m ixe d - l a ye r c l a ys ) a nd , a s t he 2M , 10A i l l it e s a ppe a rt o b e o v e r w h e l m i n g l y m o r e a b u n d a n t t h a n t h e 1 M v a r ie t ie s i n b o t h s h a le s a n dl ime s tone s , i t a ppe a r s t ha t mos t o f t he i l l i t e i n s e d ime n t s wa s de r ive d f r omm u s c o v i t e a n d i s t h e r e f o r e d e t r i ta l i n o r i g in .T h e n a t u r e o f t h e m a r i n e e n v i r o n m e n t a n d d i a g e n e t i c ch a n g e s i n i t a r e s u c ht h a t v a r i a t i o n s i n t h e c h a r a c t e r o f t h e s o u r c e m a t e r i a l a r e a l m o s t i n v a r i a b l yr e f l ec t e d i n th e s e d i m e n t a r y a c c u m u l a t i o n . T h i s d o e s n o t m e a n t h a t c l a y m i n -e r a ls c a n n o t b e u s e d f o r e n v i r o n m e n t a l i n t e r p r e t a ti o n b u t t h a t t h e e f fe c ts o fs o u r c e s h o u l d b e u n d e r s t o o d a n d e v a l u a t e d b e f o r e a n e n v i r o n m e n t a l i n t e r p r e -t a t i on i s a t t e mp te d .

S E D I M E N T A R Y P R O C E S S E S A F F E C T I N G C L A Y M I N E R A L STerminology of Sedimentary Processes

A r e e x a m i n a t i o n o f t h e b a s i c d a t a i n d i c a t e s t h a t m a n y o f t h e d e t r i t a l v s .d i a g e n e ti c d i f fe r e n c e s a r e m o r e a p p a r e n t t h a n r e a l a n d m a y b e i n p a r t a m a t -t e r o f s e m a n t ic s . M u c h m i s u n d e r s t a n d i n g i s a r e s u l t o f t h e f a i l u r e to s e p a r a t ea n d w e i g h o b j e c t i v e l y t h e c l a y m i n e r a l c h a r a c t e ri s t ic s w h i c h a r e o f d e t r i ta lo r i g i n a n d t h o s e d u e t o d e p o s i t i o n a l e n v i r o n m e n t . T h e d u a l c h a r a c t e r o f t h ec l a y mine r a l s i s a r e su l t o f t he unsa t i s f i e d c ha r ge wh ic h e x i s t s i n t he ba s i cl a tt i c e. Th e ba s i c c la y min e r a l l a t t ic e is f a i r l y s ta b l e a nd i ts o r ig ina l c h a r a c t e rw i l l n o t b e m a t e r i a l l y a l t e r e d e x c e p t u n d e r r e l a t i v e l y i n t e n s e w e a t h e r i n g a n dl e a c h i n g c o n d i t io n s . T h e p r o c e ss e s o p e r a t i v e in m a r i n e e n v i r o n m e n t s d o n o ta pp e a r t o be su f f i c i e n t ly s eve r e t o a l t e r a pp r e c i a b ly t he b a s i c c l a y l a tt i c e e xc e p ti n v o l u m e t r i c a l ly u n i m p o r t a n t e n v i r o n m e n t s . H o w e v e r , t h e c at i o n s w h i c h a r ea dso r be d on the su r f a c e o f t he c l a y she e t s a r e on ly l oose ly he ld a nd a r e r e a d i lye x c h a n g e d f o r o t h e r c a t i o n s a s th e c l a y pa s se s f r o m o n e c h e m i c a l e n v i r o n m e n ti n t o a n o t h e r . S o m e o f th e s e c a t i o n s a r e m o r e t i g h t ly b o u n d t h a n o t h e rs , b u te v e n i n t h e m i c a s w h e r e t h e y a r e m o s t t i g h t l y b o u n d , t h e b o n d i n g i s m u c hw e a k e r t h a n t h a t w i t h i n t h e l a t ti c e. T h i s c o n c e p t o f th e d u a l c h a r a c t e r o f t h ec l a y m i n e r a l s m u s t a l w a y s b e k ep t i n m i n d w h e n d i s cu s s in g t h e s e d i m e n t a r yp r oc e s se s a f f e c t ing c l a y mine r a l s .B e f o r e d i s c us s ing the p r oc e s se s in wh ic h c l a y mine r a l s pa r t i c ipa t e , i t i s ne c -e s s a r y t o r e v i e w t h e d e f i n i t i o n o f s o m e t e r m s c o m m o n l y u s e d i n c o n n e c t i o nw i th these processes . C las t ic i s "a d e s c r i p ti v e t e r m a p p l i e d t o a r o c k f o r m e df r o m t h e f r a g m e n t s o f o t h e r r o c k s " ( R i ce , 1 9 4 8 ) . C h e m i c a l i s d e f i n e d a s" . . . p r e ci p it a te s f r o m s o l u t i o n . . . " ( P e t ti j o h n , 1 9 4 9 ) . P e t t i jo h n ( 1 94 9 , p .476 - - 478 ) de f ine s a u th ige ne s i s a s " the f o r ma t ion o f ne w mine r a l s e i t he r byr e p l a c e m e n t o r b y r e c r y s t a l l i z a t i o n . . . [ a n d g r o w t h ] o n t h e s p o t , " a n d d i a g e n -esis as " . . . t h e b e g in n i n g o f m e t a m o r p h i s m . . . " a n d in a m o r e r es tr ic te ds e n s e , " t h e c h e m i c a l r e a r r a n g e m e n t s a n d r e p l a c e m e n t s t h a t o c c u r w h i l e t h e


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s e d i m e n t i s s ti ll o n t h e se a f l o o r . . . " T h u s , b o t h c l a st ic a n d c h e m i c a l m i n e r -a l s c a n b e m o d i f i e d a f t e r r e a c h i n g t h e d e p o s i ti o n e n v i r o n m e n t . T h e p r o c e s s e so f m o d i f i c a t i o n a r e c a l le d a u t h i g e n e s is i f t h e c h a n g e i s f u n d a m e n t a l ; i .e .,a r a g on i t e t o c a l c it e , s i li c a ge l t o qua r t z . T h e d i r e c t p r e c i p i t a t i on o f m i ne r a l sf r o m s o l u t io n i s a l so c o n s i d e r e d a u t h i g e n e s is b u t t h e p r o c e s s h e r e i s n o d i f fe r -e n t f r o m t h a t d e f i n e d b y th e t e r m c h e m i c a l . T h e t e r m d i a g e n e s is h a s b e e nu s e d to d e s c r i b e t h e v e r y m i n o r a n d l e a st i m p o r t a n t c h a n g e s w h i c h t a k e p l a c ei n p r e e x i s t in g m i n e r a l s , s u c h a s b a s e e x c h a n g e . H o w e v e r , t h e t e r m i s al sou s e d to d e s c r i b e a ll t y p e s o f m o d i f i c a t i o n e x t e n d i n g u p t o l o w - g r a d e m e t a m o r -p h i s m .

T h e t e r m d i ag e n e si s i s v e r y b r o a d i n m e a n i n g a n d s e ld o m m e a n s t h e s a m et h i n g t o a n y t w o p e o p l e ; a s a r e s u l t , t h e u s e o f t h i s t e r m c a u s e s u n n e c e s s a r ym i s u n d e r s t a n d i n g . D i a g e n e s i s i n g e n e r a l i m p l i e s a m o r e f u n d a m e n t a l m o d i -f i c a t i o n o r a l t e r a t i o n o f a m i n e r a l t h a n t h a t c a u s e d b y i n t e r c h a n g i n g t h ea d s o r b e d s u r f a c e c a ti o n s . S u c h a n i n t e r c h a n g e m o s t li k e ly o c c u r s w i t h t h e fe wc a t i o n s a d s o r b e d o n t h e s u r f a c e o f a c l a s t i c q u a r t z g r a i n w h e n i t s h i f t s t o d i f -f e r e n t c h e m i c a l e n v i r o n m e n t s . C e r t a i n ly , c h a n g i n g a N a - m o n t m o r i l l o n i t e t o aC a - m o n t m o r i l lo n i t e sh o u l d n o t b e c o n s i d e r e d d i a g e n e s is . Y e t i t is t h is t y p e o fr e a c t i o n w h i c h a p p a r e n t l y a c c o u n t s f o r m u c h o f t h e m a r i n e e n v i r o n m e n t a lm o d i f i c a t i o n o f c l a y m i n e r a l s . P e r h a p s i t i s t h e u s e o f cl a y m i n e r a l n a m e sw h i c h i m p l i es c h a n g e s g r e a t e r t h a n a c t u a l ly o c c u r , w h i c h h a s c a u s e d t h e u s e o ft h e t e r m d i a g e n e si s. T h u s , i t i s c o m m o n t o s p e a k o f t h e d i a g e n e s i s o f m o n t -m o r i l lo n i t e to i ll it e u n d e r m a r i n e c o n d i t io n s . T h e r e i s n o e v i d e n c e to s u g g e s tt h a t t h e c l a y m i n e r a l m o n t m o r i l l o n i t e , a s d e f i n e d b y t h e s t r u c t u r a l a n d c h e m i -c a l c ha r a c t e r o f i t s ba s i c l a t t i c e , a d s o r bs po t a s s i um a nd be c om e s i l l i t e .I l l i t e a n d m u s c o v i t e c a n h a v e s o m e o f t h e i r i n t e r l a y e r p o t a s s i u m r e m o v e da n d a r e t h e n d e s c r ib e d a s d e g r a d e d i l li te s ( G r i m , 1 9 5 1 ) , o r c a n h a v e p o ta s -s i u m r e m o v e d t o t h e e x t e n t t h a t w a t e r i s a d s o r b e d b e t w e e n t h e l a y e r s a n d t h ec l a y m i n e r a l s u p e r f i c ia l l y r e s e m b l e s a m o n t m o r i l l o n i t e o r v e r m i c u l it e . W h e nt h e s e c l a y s a r e p l a c e d i n a p o t a s s i u m s o l u t i o n , t h e y c o n t r a c t t o 1 0 A ( B r o w n ,1 9 5 3 ; K u n z e a n d Je f f r i e s, 1 9 5 3 ; V a n d e r M a r e l , 1 9 5 4 ; R i c h a n d O b e n s h a i n ,1 9 5 5 ; e t c . ) . T h e b a s ic l at ti c e o f t h e se w e a t h e r e d m i n e r a l s a p p a r e n t l y i s n o ts e r i o u s ly m o d i f ie d , f o r w h e n a s a m p l e o f th i s t y p e w a s e x p o s e d t o s e a w a t e r i tr e a d s o r b e d p o t a s s i u m a n d w a s r e j u v e n a t e d o r r e c o n s t i t u te d t o 2 M i ll it e. T h i sp r oc e s s s upe r f i c i a l l y l ooks l i ke d i a ge ne s i s bu t i s a c t ua l l y no m or e t ha n a na d s o r p t i o n p h e n o m e n o n . M u c h le ss i s k n o w n a b o u t t h e f o r m a t i o n o f c h l o r i teu n d e r m a r i n e c o n d i t io n s , b u t i t i s l ik e l y t h a t m u c h o f t h e c h l o r i t e is f o r m e df r o m d e g r a d e d c h l o r i t e s o r c h l o r i t e s t h a t h a v e h a d m o s t o f t h e b r u c i t e l a y e rr e m o v e d a n d a c t a s v er m i c u l it e s .

M i x e d - l a y e r i l l i t e - m o n t m o r i l l o n i t e a p p e a r s t o f o r m b y t h e a l t e r a t i o n o fm o n t m o r i l lo n i t e u n d e r m a r i n e co n d i ti o n s ( W e a v e r , 1 9 5 3 ) . H e r e a g a i n th ec h a n g e i s m a g n i f i e d b y th e n o m e n c l a t u r e . N o m i x e d - l a y e r il li t e- m o n t m o r i ll o n -i te h a s b e e n r e p o r t e d w h i c h h a s a b a s i c l a tt ic e c h a r a c t e r n e a r t h a t o f m o n t m o r -i l lon i t e ; i. e. , p r e do m i na n t l y oc t a h e d r a l l a t ti c e s ubs t i t u t i on . T h e m i xe d - l a ye rc l a y s h a v e a l a r g e r t o t a l c h a r g e a n d l a r g e r a m o u n t o f t e t r a h e d r a l s u b s t i t u t i o n .


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C la ys ha v ing ba s i c l a t t i c e s o f t h i s l a t t e r t ype a r e f r e que n t ly f ound in c on -t i n e n t a l d e p o s i t s w h e r e t h e y c o n t a i n h y d r a t e d C a 2 M g z and N a ase x c h a n g e a b l e c a ti o n s a n d a r e u s u a l ly r e f e r r e d t o a s m o n t m o r i ll o n i t es . I f t h es ec l a y s a r e t r a n s p o r t e d t o a m a r i n e e n v i r o n m e n t , t h e l a y e r s w i t h t h e h i g h e rt o t a l a n d t e t r a h e d r a l c h a r g e ( m i c a -l ik e b a s ic l a tt ic e ) w o u l d p r e s u m a b l ye xc h a nge the i r C a 2+ f o r K a nd c on t r a c t t o a mic a - l ike l a ye r , whe r e a s thel o w e r a n d o c t a h e d r a l - c h a r g e d l a y e r s w o u l d r e t a i n t h e i r w a t e r a n d r e m a i ne x p a n d e d . A g a i n t h e a l t e r a t io n i s m e r e l y o n e o f a d s o r p t i o n w h e r e i n t h e v a r i-o u s l y c h a r g e d , d e t r i t al c l a y l a tt ic e s c o m e t o e q u i l i b r i u m w i t h t h e i r s u r r o u n d -i n g e n v i r o n m e n t .The se sa me c l a ys , on the ba s i s o f t he i r l a t t i c e d i f f e r e nc e s , a r e mixe d - l a ye rl a t t i c e s e ve n unde r c on t ine n ta l c ond i t ions , bu t be c a use po ta s s ium i s no t a va i l -a b l e , a l l t h e l a y e r s r e m a i n e x p a n d e d a n d , b e c a u s e o f t h e o v e r e m p h a s i s o f t h ef e a t u r e s o f e x p a n s i o n a n d c o n t r a c t i o n , th e y a r e c o m m o n l y c o n s i d e r e d to b em on tm or i l l on i t e s . W i th a c la s s i f i c a t ion ba se d on the na tu r e o f t he ba s i c l a t-t ic e , t h e y w o u l d a n d s h o u l d b e m i x e d - l a y e r c la y s r e g a r d le s s o f t h e c o m p o s i t i o no f the a dso r be d c a t ions . I f suc h r e a c t ions a r e to be c a l le d d i a ge ne s is , the p r o -c es s i n v o l v e d m u s t b e m o r e e x a c t l y d e f in e d . T h e t e r m a d s o r p t i o n , p r e f i x e d b ythe c a t ion invo lve d , a s K- a dso r p t ion o r a dso r p t ion d i a ge ne s i s , i s a mor e r e a l i s -t ic s ta t e m e n t o f t h e m o d i f i c a t i o n . P e r h a p s t h e t e r m d i a g e n e s is s h o u l d b er e s t r i c t e d to inc lude on ly a l t e r a t ions wh ic h mod i f y the ba s i c l a t t i c e .

A g r o n o m i s t s a n d c h e m i s t s , w h o h a v e l o n g b e e n i n t e r e s t e d i n t h e c h e m i c a lr e a c t iv i ty o f t he c l a y mine r a l s , ha ve t e nde d to s t r e s s t he r o l e o f t he a dso r be dc a t i o n , b u t t o t h e g e o l o g i s t , w h o m u s t b e c o n c e r n e d w i t h t h e w h o l e m i n e r a l ,t h e e p h e m e r a l a d s o r b e d c a t io n s a r e o f o n l y s e c o n d a r y i m p o r t a n c e t o t h e b a s icc lay la t t ice .The E]tects of Sedimentary Processes on Detrital Material

The r e i s l i t t l e que s t ion tha t c l a y mine r a l s f o r m by a u th ige ne s i s a nd d i a ge ne -s is u n d e r c o n t i n e n t a l c o n d i t i o n s ; h o w e v e r , t h e r e i s c o n s i d e r a b l e d i s a g r e e m e n tc o n c e r n i n g t h e i r f o r m a t i o n u n d e r m a r i n e c o n d i t io n s . T h e fo l l o w i n g p r o c es s e sm a y o c c u r i n m a r i n e e n v i r o n m e n t s : ( 1 ) C l a y m i n e r a l f o r m e d f r o m g la ss, g e l ,o r c o l l o id a l m a t e r i a l ; ( 2 ) c l a y m i n e r a l f o r m e d b y a l t e r i n g th e b a s i c l a tt ic e o fa p r e e x i s t i n g m i n e r a l ; ( 3 ) c l a y m i n e r a l a lt e r e d b y c h a n g i n g t h e ty p e o fa d s o r b e d s u r f a c e c a t i o n ; a n d ( 4 ) c l a y m i n e r a l u n a f f e c te d b y c h e m i c a le n v i r o n m e n t .T h e s e f i r s t t w o p r o c e s s e s m a y b e c o n s i d e r e d a s r e p r e s e n t i n g d i a g e n e s i s ;c l a s s i f y ing the th i r d p r oc e s s a s d ia ge ne s i s i s que s t iona b le a nd th e f ou r th c a nbe c ons ide r e d a s de f in i t e ly de t r i t a l . P r oc e s se s 3 a nd 4 a p pe a r t o be the mos ti m p o r t a n t v o l u m e t r i c a l l y .

M o n t m o r i l l o n i t e f o r m e d f r o m v o l c a n i c m a t e r i a l u n d e r m a r i n e c o n d i t i o n s i sa t r ue e xa mple o f Type 1 ma r ine d i a ge ne s i s , bu t e ve n he r e i t i s l i ke ly tha t t heu l t i m a t e c h a r a c t e r o f t h e b a s i c l a t t i c e o f t h e m o n t m o r i l l o n i t e w i l l d e p e n ds t r o n g l y o n th e c h e m i c a l c o m p o s i t i o n a n d s e m b l a n c e o f s t ru c t u r a l o r d e r o f t h evo lc a n ic ma te r i a l .


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G l a u c o n i te , t h o u g h v o l u m e t r ic a l l y u n i m p o r t a n t , i s s o m e t im e s c i t e d a s a ne x a m p l e o f m a r i n e d i a g e n e s is o f t h e s e c o n d ty p e . G l a u c o n i te , a n i r o n - r i c hi l l i t e , i s e s se n t i a l l y a f e mic mine r a l , a nd i s f r e que n t ly be l i e ve d to ha ve be e nd e r i v e d l a r g e l y f r o m p r e e x i s t in g f e m i c m i n e r a l s s u c h a s b i o t i t e , a u g it e , a n d o li -v i n e ( G a l l ih e r , 1 9 3 5 ; H e n d r i c k s a n d R o s s, 1 9 4 1 ) . S o m e o f t h e s e m i n e r a l sa p p e a r t o h a v e a l t e r e d t o g l a u c o n i t e u n d e r m a r i n e c o n d i t i o n s a n d m a y t h e r e -f o r e r e p r e s e n t d ia g e n e si s . I n o t h e r c a se s m u c h o f t h e a l t e r a ti o n c o u l d h a v eb e e n a c c o m p l i s h e d b y s u b a e r i a l w e a t h e r i n g a n d o n l y m i n o r m o d i f i c a t i o n s w e r ep r o d u c e d in t h e m a r i n e e n v i r o n m e n t . W a l k e r (1 94 .9 ) h a s s h o w n th a t d u r i n gs o i l w e a t h e r i n g t h e c o m p o s i t i o n o f b i o t i t e t e n d s t o s h i f t t o w a r d t h a t o f g l a u -c on i t e . I n a ny e ve n t g l a uc on i t e d i a ge ne s i s is a c c omp l i she d unde r pe r h a ps t hem o s t i d e a l c o n d i t i o n s f o r m a r i n e c l a y d i a g e n e s i s : f o r m e d f r o m e a s i l y a l t e r e df e m i c m i n e r a l s d u r i n g t i m e s o f s lo w o r n e g a t i v e s e d i m e n t a t i o n a n d f r e q u e n t l yw i t h t h e a id o f o r g a n i c a g e n ts ( H e n d r i c k s a n d R o s s, 1 9 4 1 ) . U n d e r t h e se id e a lc ond i t i ons t he m or e su b t l e f e a tu r e s o f t he g l a uc on i t e m ine r a l a nd the F e 3+ toF e 2 r a t i o a pp e a r t o be a f unc t io n o f the de po s i t i ona l e n v i r on m e n t , w he r e a sthe c oa r se r f e a tu r e o f the g l a uc on i t e , a h igh i r on c on te n t , i s u sua l ly i nh e r i t e df r o m t h e d e t r i ta l s o u r c e m a t e r i a l . I f fe m i c m i n e r a l s c a n r e t a i n t h is m u c h o fthe i r o r ig ina l i de n t i t y , i t i s no t su r p r i s ing tha t t he mor e s a l i c mine r a l s wou ldbe e ve n le ss a f f e c t e d by d i a ge ne s i s . F u r the r , r e c e n t wor k ha s i nd i c a t e d tha tg l a u c o n it e li k e p e ll et s c a n b e c o m p o s e d o f i r o n - r i c h c h lo r i t e ( t h u r i n g i t e ? ) a n dm o n t m o r i l l o n i t e , w h i c h s u g g e st s t h a t t h e t y p e o f g l a u c o n it e f o r m e d d e p e n d s o nt h e ty p e o f s o u r c e m a t e r ia l .T h e t h i r d p r o c es s , c a t i o n a d s o r p t i o n , h a s b e e n d i s cu s s e d u n d e r t h e p r e v i o u she a d ing a nd , a s sugge s t e d the r e , t h i s p r oc e s s shou ld no t be c ons ide r e d a s r e p -r e se n t ing d ia ge ne s i s . F o r t he va s t m a jo r i t y o f c l ays in a r g i l l a c e ous r oc ks , t heb a s ic l a t ti c e c a n b e c o n s i d e r e d t o b e d e t r i ta l a n d t o h a v e r e t a i n e d m o s t o f t h ec h a r a c t e r i t o r ig i n a l l y h a d i n t h e s o u r c e a r e a , w h e r e a s th e a d s o r b e d c a t io n sc a n be c l a s se d a s e i t he r a u th ige n ic , i f t he y ha ve be e n a c qu i r e d in t he de pos i -t i o n a l e n v i r o n m e n t , o r d e t r i t a l i f t h e y a r e t h e o r i g i n a l c a t i o n s o b t a i n e d a t t h es o u r c e a r e a ( T y p e 4 ) . S i m i l a r d u a li s m i s c o m m o n in t h e c o a r s e r m i n e r a l s ;i . e . , a q u a r t z g r a i n d e p o s i t e d u n d e r m a r i n e c o n d i t i o n s i s c o n s i d e r e d t o b ed e t r i t a l b u t q u a r t z o v e r g r o w t h s w h i c h f o r m o n t h e g r a i n a r e a u t h i g e n i c .T h e a m o u n t o f c la y m a t e ri a l u n a f fe c t ed b y t h e m a r i n e e n v i r o n m e n t ( T y p e4 ) i s qu i t e la r ge . R e la t ive ly unm od i f i e d musc ov i t e , b io t i t e , a nd c h lo r i t e a r ec om m on in s a nd - si z e a nd f ine r s e d ime n t s . I f de pos i t i on i s r a p id , a s i n mio -g e o s y n c l i n e s a n d e u g e o s y n c l i n e s , a n d t h e n e a r b y s o u r c e a r e a s h a v e r e l a t i v e l yh igh r e l i e f , t he p r oc e s se s a c t ing on the c l a y ma te r i a l a r e l a r ge ly phys i c a l a ndthe r e i s l i tt l e i f a ny m od i f i c a t ion o f t he c l a y . Ge o sync l ina l sha l e s de r ive d f r omn e a r b y m u s c o v i t e a n d c h l o r i t e s c h i s t s f r e q u e n t l y a f f o r d x - r a y r e f l e c t i o n s a ssha r p a nd d i s t i nc t a s t hose ob ta ine d f r om the s c h i s t ma te r i a l .

N E E D F O R A G E N E T I C C L A S S I F IC A T I O NTh e de g r e e o f c on t r a c t ion o r e xpa n s ion o f a c l a y l a t t ic e i s a c tua l ly a de r ive dpa r a m e te r , one tha t i s de pe n de n t up on the ba s i c p r ope r t i e s , f o r i t is no t t he


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po ta s s ium ion be twe e n the c l a y l a ye r s wh ic h c a use s a c l a y to c on t r a c t bu t i t i st h e t y p e a n d a m o u n t o f c h a r g e o n t h e b a s i c l a t t i c e w h i c h p r i m a r i l y p r o v i d e sthe c l a y w i th i t s c on t r a c t a b l e c ha r a c t e r . A ge ne t i c c la s s i f i c a tion o f sha le s m us tinc lude th i s f und a m e n ta l c onc e p t o f c l a y mine r a l s . I f c la y mine r a l s a r e c l as s i-f i e d o n t h e b as i s o f d e r i v e d p r o p e r t i e s r a t h e r t h a n b a s i c p r o p e r t i e s , t h e n t h e r ei s li t tl e c ha n c e f o r e s t a b l i sh ing a ge ne t i c c la s s i f i c a tion o f sha le s . F o r e xa m ple ,i f t he be l i e f pe r s i s ts t ha t i ll i te s f o r m f r o m m on tm or i l l on i t e s i n a m a r in e e nv i-r onme n t r a the r t ha n f r om l e a c he d i l l i t e s a nd musc ov i t e s , i t w i l l be d i f f i c u l t t ode ve lop a un i f i e d the o r y o f c la y o r sha l e gene s is . Th i s do e s no t ne c e s sa r i l yimp ly a ny r a d i c a l r e c l a s s i f i c a t ion o f t he c l a y mine r a l s , f o r t he na me i l l i t e i s a su s a b l e as t h e n a m e f e l d s p a r . I t i s t h e d e f i n i t io n a n d t h e p h y s i c al a n d c h e m i c a ln a t u r e o f th e v a r i o u s i ll it e c l a y m i n e r a l s a n d h o w t h e y r e a c t i n g i v e n e n v i r o n -m e n t s w h i c h n e e d t o b e c l a r if i ed .P e t t i j ohn ( 1949) s t a t e s " . . . t h e b a s is o f al l s o u n d t a x o n o m i c w o r k m u s t b es e le c ti o n o f s i g n i f i c a n t c h a r a c t e r s f o r c l a s s if i c a to r y p u r p o s e s a n d a v o i d a n c e o fi r r e l e va n t pe c u l i a r i t i e s , " a nd " the on ly t e s t o f s ign i f i c a nc e i s whe the r t hec h a r a c t e r is t i c s a r e o r a r e n o t b a s i c t o t h e u n d e r s t a n d i n g o f o r i g i n . " T h u s ,ou r p r e se n t c l a s s i f i c a t ion i s no t u sa b le i f we c ons ide r suc h th ings a s t he t ypeo f a d s o r b e d c a t i o n a n d t h e a m o u n t o f w a t e r b e t w e e n c l a y l a y e r s a s t h e m o s ts ign i f i c a n t c ha r a c t e r i s t i c s . The se a r e on ly loc a l pe c u l i a r i t i e s o f t he imme d ia t ee n v i r o n m e n t w h i c h a r e s u b j e c t to s u b s e q u e n t c h a n g e , w h e r e a s t h e c h a r a c t e r o fthe ba s i c l a t t i c e i s r e l a t i ve ly una f f e c t e d by loc a l mod i f i c a t ions e xc e p t unde re x t r e m e c o n d i t io n s a n d i s a m o r e s i g n i f ic a n t c h a r a c t er i s ti c . A t t h e p r e s e n tt ime , on ly a de sc r ip t ive c l a s s i f i c a tion c a n be c ons t r uc t e d . I n d e ve lopng a c l as -s i f ic a t io n o f t h i s t y p e , a n y n u m b e r o f d e s c r ip t i v e p a ra m e t e r s c a n b e u s e d b u ti t wou ld be w i se t o c hoose pa r a m e te r s t ha t , on the ba s i s o f p r e se n t da t a , a f f o r dthe be s t p r ospe c t s o f u l t ima te ly ha v ing ge ne t i c imp l i c a t ions . C e r t a in ly w i thp r e s e n t t e c h n i q u e s i t is e a s i er to s t u d y a n d m e a s u r e t h e d e r i v e d p r o p e r t i e s t h a nt h e b a s i c p r o p e r t i e s b u t t h a t i s n o e x c u s e f o r a l t e r i n g t h e i r o r d e r o f i m p o r -t a nc e .

S U M M A R YX - r a y a n a l y s es o f th e c l a y m i n e r a l s f r o m t h o u s a n d s o f s e d i m e n t s i n d i c a tet h a t a n y o f t h e m a j o r c l a y m i n e r a l s c a n o c c u r i n a b u n d a n c e i n a n y o f t h em a j o r d e p o s i t i o n a l e n v i r o n m e n t s a n d t h e r e i s n o c o n s i s t e n t c o i n c i d e n c ebe twe e n spe c i fi c c l a y m ine r a l s a nd sp e c i f i c de po s i t i ona t e nv i r onm e n t s . I t i sb e l i e v e d t h a t m a n y o f t h e g e n e r a l i z e d t h e o r i e s c o n c e r n i n g t h e d i a g e n e s i s o fc l a y m i n e r a l s a r e b a s e d o n i n a d e q u a t e a n d n o n r e p r e s e n t a t i v e d a t a .I t is c o n c l u d e d th a t t h e g r e a t m a j o r i t y o f c la y m i n e r a l s i n s e d i m e n t a r y r o c k sa r e d e t r i t a l i n o r i g i n , a n d t h a t t h e y s t r o n g l y r e f l e c t t h e c h a r a c t e r o f t h e i r

s o u r c e m a t e r i a l a n d a r e o n l y s l i g h t l y m o d i f i e d i n t h e i r d e p o s i t i o n a l e n v i r o n -m e n t s .A r e v i e w o f th e t e r m i n o l o g y u s e d t o d e s c r ib e t h e o r i g i n o f c l a y m i n e r a lsa n d t h e p r o c es s e s af f e c ti n g th e c l a y m i n e r a l s i n d i c a te s t h a t t h e m o s t c o m m o np r o c e s s a c t i n g o n t h e c l a y m i n e r a l s i n m a r i n e e n v i r o n m e n t s i s c a t i o n a d s o r p -


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172 ORIGIN OF CLA Y MINERALS IN SEDIMENTARY ROCKSt i o n . T h e m o d i f i c a t i o n s p r o d u c e d b y th i s p r o c e s s ar e s u p e r f i c i a l b u t b e c a u s eo f t h e o v e r e m p h a s i s o f n a m e s r a t h e r t h a n p r o c e s se s , t h e y h a v e b e e n c o n s i d e r e df u n d a m e n t a l c h a n g e s a n d t h e p r o c e s s h a s b e e n c a ll e d d i a g n e s i s . F r o m t h eg e o l o g i s t 's a n d p e t r o g r a p h e r ' s v i e w p o i n t , t h e b a s i c c l a y m i n e r a l l a t t ic e , w h i c hi s i n h e r i t e d f r o m t h e s o u r c e m a t e r i a l , i s t h e m o s t s i g n i f i c a n t p a r a m e t e r o f th ec l a y m i n e r a l s ; a n d m o d i f i c a t i o n s c a u s e d b y t h e a d s o r b e d c a t i o n s a r e s e co n d -a r y , d e r i v e d p a r a m e t e r s r e f l e c t i n g t h e c h a r a c t e r o f t h e d e p o s i t i o n a l e n v i r o n -m e n t . T h i s d u a l i s m i s e s s e n ti a l t o th e u n d e r s t a n d i n g o f c l a y g e n e si s a n d t h es i g n i f i c a n c e o f t h e s e t w o p a r a m e t e r s m u s t b e u n d e r s t o o d b e f o r e a g e n e t i cc l a s s i f ic a t i o n c a n b e c o n s t r u c t e d .

A C K N O W L E D G M E N T SS p e c i a l t h a n k s a r e d u e R . A . R o w l a n d a n d R . G . S t e v e n s o n , w h o h a v e c o n -

t r i b u t e d m u c h t o th e i d e a s p r e s e n t e d . T h e w r i t e r i s g r a t e f u l to t h e m a n y g e o lo -g i s t s o f t h e S h e ll O i l C o m p a n y , p a r t i c u l a r l y A . R . E d w a r d s , R . V . W a r d , a n dF . T . C o n n o l l y , w h o h a v e p r o v i d e d s a m p l e s a n d b a c k g r o u n d d a t a f o r t h e s es t u d i e s .

R E F E R E N C E SBrown, George, 1953, The dioc tahe dral analogue of ver m iculi te : Clay M in. Bull ., v . 2 , p .64-70.Galliher, E. W., 1935, Geology of glauconite : Amer. Assoc. Petroleum Geologis ts Bull . , v .19, p. 1569-1601.Gilluly , James, 1949, Dis tributio n of mou ntain b uild ing in geologic t im e: Geol. Soc.Am er. B ull., v. 60, p. 561-590.Grim, R. E., 1951, The d eposit io nal environment of red and green sha les : J . Sed. P etrol-ogy, v. 21, p. 226-232.Grim, R. E. , 1953, Clay miner alog y: McG raw-H ill Book Com pany, Inc . , New York, , 384 p.H end rick s, S. B., and Ross, C. S., 1941, Chem ical com position and genesis of glauc on iteand celadonite : Am. Min. , v . 26, p . 683-708.Kry nine, P. D ., 1949, The origin of red bed s: New Yo rk Acad . Sci. Trans . , ser. 2 , v . 2 , p .60-68.Kunze, G. W., and Je ffries , C. D., 1953, X-ray chara cteris t ic s of c lay m inerals as r e la te d topotassium fixation: Soil Sci. Soc. Amer. Proc., v. 17, p. 242-244.Lev inson , A. A. , 1955 , S tud ies in the mica g ro up : Po lymorph ism among i l l i te s and hydrousmicas: Am. Min., v. 40, p. 41-49.M illot , Georges, 1949, Relation s entre la con sti tution e t la gen~se des roches s6dim entairesargileu ses: G 6ol. Ap pliq . e t Prosp. Min. , v . 2 , Nancy, Fran ce, 352 p.M illot , Georges, 1953, H6 ritage e t n6oformation dans la s6dimentation argile use: Congr~sG~ologique In ternatio nal, 1952, Fasc icule 18, 163-175.Pett i j ohn , F. J . , 1949, Sedim entary rocks: H arp er & Brothers, New York, 526 p.Powers , M . C. , 1957 , The ad jus tm ent o f land de r ived c lays to the ma r ine env ironm ent : J .Sed. Petrology, v. 27, p. 355-372.Rice , C . M. , 1948 , Dic t ionary o f geo log ica l te rms : Edw ards B ro the rs, Inc . , Ann Arbo r ,Michigan, 461 p.Rich, C. I . , and Obenshain, S. S. , 1955, Chemical and c lay miner al prop erties of a Red-Yel-low Podzolic soil deriv ed from m uscovite s ch ist: Soil Sci. Soc. Am er. Proc., v. 19, p.334-339.Rivi~re , An dre , 1953, Sur l 'orig ine des argiles s~dimentaires , Congrbs G6ologique Interna -tional, 1952, Fascicule 18, p. 177-180.Van de r M are l , H. W . , 1954 , Po tass ium f ixa t ion in D utch so i ls : Minera log ica l ana lyses :Soil Sci., v. 78, p. 267-287.


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CHARL ES E . W E AVE R 1 7 3W a lk e r , G . F . , 1949, The decompos i t ion o f b io t i te in the so i l : Min . Mag . , v . 28 , p . 693-703 .W eaver , C. E ., 1953 , M inera logy and pe t ro logy o f some O rdov ic ian K-ben ton i tes and

rela ted l imestones: Geol . Soc. Amer. Bull . , v . 64, p . 921-943.Yoder , H. S ., and E ugs te r , H. P . , 1955 , Syn the t ic and na tu ra l musc ov i tes : Geoch im ica e tCosmochimica Acta , v . 8 , p . 225-280.

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