Organic geochemistry of cretaceous black shale deposits from Italy and France

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ORGANIC GEOCHEMISTRY

OF CRETACEOUS B L A C K S H A L E DEPOSITS

FROM ITALY AND F R A N C E

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O R G A N I C G E O C H E M I S T R Y

O F C R E T A C E O U S B L A C K S H A L E DEPOSITS

F R O M ITALY A N D F R A N C E

PROEFSCHRIFT

ter verkrijging van de graad

van doctor in de technische wetenschappen

aan de Technische Hogeschool Delft

op gezag van de rector magnificus,

prof. ir. B.P.Th. Veltman

voor een commissie

aangewezen door het college van dekanery'

te verdedigen op

donderdag 7 oktober te 14.00 uur

DOOR

GERARDUS WIJNANDUS V A N G R A A S

Scheikundig ingenieur,

geboren te Gouda

1

Dit proefschrift is goedgekeurd door de promotor,

PROF. DRS. P.A. S C H E N C K

Het t o t s t a n d komen v a n d i t p r o e f s c h r i f t i s a l l e e n m o g e l i j k geweest d a n k z i j de b i j d r a g e n v a n v e l e mensen. I n de e e r s t e p l a a t s z i j n d i t de l e d e n v a n de g r o e p O r g a n i s c h e Geochemie, maar d a a r n a a s t ook a n d e r e l e d e n v a n de v a k g r o e p Algemene S c h e i k u n d e en v a n de m a s s a s p e k t r o m e t r i s c h e a f d e l i n g v a n de v a k g r o e p O r g a n i s c h e Chemie. B u i t e n de TH D e l f t b e t r e f t h e t de l e d e n v a n de a f d e l i n g B i o m o l e c u l a i r e F y s i c a v a n h e t F O M - i n s t i t u u r v o o r Atoom- en M o l e c u u l f y s i c a t e Amsterdam en de o v e r i g e d e e l n e m e r s aan h e t ' B l a c k S h a l e ' o n d e r z o e k , d i e v o o r n a m e l i j k werkzaam z i j n op h e t I n s t i t u u t v o o r A a r d w e t e n s c h a p p e n t e U t r e c h t . Ik w i l hen a l l e n g r a a g bedanken v o o r de p r e t t i g e samenwerking, d i e i k heb e r v a r e n en d i e h e t m i j moge-l i j k maakt om met v e e moge-l p moge-l e z i e r aan de a f g e moge-l o p e n j a r e n t e r u g t e denken.

The r e s e a r c h d e s c r i b e d i n t h i s t h e s i s was s u p p o r t e d by t h e N e t h e r l a n d s F o u n d a t i o n f o r E a r t h S c i e n c e R e s e a r c h (AWON) w i t h f i n a n c i a l a i d f r o m t h e N e t h e r l a n d s O r g a n i z a t i o n f o r t h e Advancement o f P u r e R e s e a r c h (ZWO). Cover p h o t o g r a p h : A l b i a n p a r t o f t h e e x p o s u r e n e a r M o r i a , I t a l y ( C h a p t e r 2 ) . The r h y t h m i c a l t e r -n a t i o -n o f l i m e s t o -n e s a-nd m a r l s c a -n be e a s i l y o b s e r v e d .

CONTENTS

1. CRETACEOUS BLACK SHALES: AN INTRODUCTION 1

O c c u r r e n c e 1 M o d e l s o f f o r m a t i o n 2 P a l e o - o c e a n o g r a p h y 5 O r g a n i c g e o c h e m i c a l i n v e s t i g a t i o n s 6 C y c l i c i t y . 7 Scope o f t h i s t h e s i s 8 O r g a n i c g e o c h e m i c a l r e s e a r c h d e s c r i b e d i n t h i s t h e s i s 10 R e f e r e n c e s 10

2. ORIGIN OF THE ORGANIC MATTER IN A CRETACEOUS BLACK SHALE DEPOSIT IN THE

CENTRAL APENNINES (ITALY) 15

A b s t r a c t 15 I n t r o d u c t i o n 16 E x p e r i m e n t a l 17 R e s u l t s 18 D i s c u s s i o n 20 Acknowledgements 23 R e f e r e n c e s 23

3. A STUDY OF THE SOLUBLE AND INSOLUBLE ORGANIC MATTER FROM THE LIVELLO BONARELLI, A CRETACEOUS BLACK SHALE DEPOSIT IN THE CENTRAL APENNINES

(ITALY) 25 A b s t r a c t 25 I n t r o d u c t i o n 1 26 E x p e r i m e n t a l 26 R e s u l t s 28 D i s c u s s i o n 31 Acknowledgements 37 R e f e r e n c e s 38

4. INVESTIGATION OF THE ORGANIC MATTER FROM THE 'MARNES NOIRES' AT

COL DE PALLUEL, FRANCE 41 I n t r o d u c t i o n 41 E x p e r i m e n t a l 42 R e s u l t s and d i s c u s s i o n 42

R e f e r e n c e s 44

5. A-NOR-STERANES, A NOVEL CLASS OF SEDIMENTARY HYDROCARBONS 45

6. DE-A-STEROID KETONES AND DE-A AROMATIC STERANES: POSSIBLE INDICATORS

FOR A NEW DIAGENETIC PATHWAY OF STEROIDAL COMPOUNDS 51

7. THEORETICAL ORGANIC GEOCHEMISTRY. I . THE THERMODYNAMIC STABILITY OF

SEVERAL CHOLESTANE ISOMERS CALCULATED BY MOLECULAR MECHANICS 55

A b s t r a c t 55 I n t r o d u c t i o n 56 M o l e c u l a r m e c h a n i c s 57 R e s u l t s and d i s c u s s i o n 59 Acknowledgement 62 R e f e r e n c e s 62

8. KEROGEN OF TOARCIAN SHALES OF THE PARIS BASIN. A STUDY OF ITS

MATURATION BY FLASH,PYROLYSIS TECHNIQUES 65

A b s t r a c t 65 I n t r o d u c t i o n 66 E x p e r i m e n t a l 67 R e s u l t s 69 D i s c u s s i o n . 73 Acknowledgements 79 R e f e r e n c e s 79 9. EPILOGUE 83 R e f e r e n c e s 84 APPENDIX 85 SUMMARY ' 91 SAMENVATTING 93

C H A P T E R 1 C R E T A C E O U S B L A C K S H A L E S : AN I N T R O D U C T I O N OCCURRENCE ' B l a c k s h a l e s ' i s an o l d term used by g e o l o g i s t s t o d e s i g n a t e a r g i l l a c e o u s r o c k s r i c h i n o r g a n i c m a t t e r ( e . g . H o w e l l , 1957). I n the l i t e r a t u r e t h e r e i s no u n a n i m i t y c o n c e r n i n g a more p r e c i s e d e f i n i t i o n b u t C u r t i s (1980) summarized t h e e s s e n t i a l c h a r a c t e r i s t i c s as f o l l o w s : a) h i g h o r g a n i c c a r b o n c o n t e n t ; b) low c a r b o n a t e c o n t e n t ; c ) h i g h p y r i t e c o n t e n t ; d) f i s s i l i t y a r i s i n g from l a m i n a t i o n . T h i s i s s t i l l a r a t h e r vague d e s c r i p t i o n as i t does n o t m e n t i o n a b s o l u t e amounts f o r the v a r i o u s c o n s t i t u e n t s . B e s i d e s , t h e r e a r e many s e d i m e n t s w h i c h do n o t show a l l o f t h e s e c h a r a c t e r i s t i c s b u t s h o u l d n e v e r t h e l e s s be c o n s i d e r e d when d i s c u s s i n g the o r i g i n o f b l a c k s h a l e s ( A r t h u r , 1979). The p a s t decade has shown a r e v i v e d i n t e r e s t f o r b l a c k s h a l e d e p o s i t s . T h i s i s p r i n c i p a l l y due t o t h e i r o i l s o u r c e r o c k p o t e n t i a l ( A r t h u r and S c h l a n g e r , 1979).

A t t e n t i o n i s f o c u s s e d m a i n l y on C r e t a c e o u s b l a c k s h a l e s s i n c e t h e r e c o g n i -t i o n o f -t h i c k f o r m a -t i o n s o f -t h e s e s e d i m e n -t s i n a l l major o c e a n i c b a s i n s d u r i n g the Deep Sea D r i l l i n g P r o j e c t (DSDP) ( F i g . l ) . The g e o g r a p h i c d i s t r i b u t i o n o f t h e d e p o s i t s - w h i c h were a l r e a d y known from l a n d e x p o s u r e s i n t h e M e d i t e r r a n e a n a r e a , E n g l a n d , the C a r i b b e a n a r e a and C a l i f o r n i a - p r o v e d t o be s u b s t a n t i a l l y w i d e r b e c a u s e o f the p r e s e n c e o f C r e t a c e o u s o r g a n i c r i c h s e d i m e n t s i n t h e N o r t h and S o u t h A t l a n t i c (DSDP l e g s 1,11,14,36,40,41,43,44,47,48,50,51,52 and 5 3 ) , t h e I n d i a n Ocean (DSDP l e g s 25, 26 and 2 7 ) , and t h e P a c i f i c (DSDP l e g s 32 and 3 3 ) . More i n f o r m a t i o n c a n be found i n the a p p r o p r i a t e I n i t i a l Reports of the

Deep Sea Drilling Project.

The w i d e s p r e a d d i s t r i b u t i o n o f C r e t a c e o u s b l a c k s h a l e s s u g g e s t s t h a t t h e i r f o r m a t i o n i s r e l a t e d to g l o b a l o c e a n o g r a p h i c phenomena termed ' o c e a n i c a n o x i c e v e n t s ' ( S c h l a n g e r and J e n k y n s , 1976). T h r e e such e v e n t s c a n be r e c o g n i z e d d u r i n g the C r e t a c e o u s ( f i g . 2 ; S c h l a n g e r and J e n k y n s , 1976; Ryan and C i t a , 1977;

Fig. 1. Location of DSDP sites with recovery of organic r i c h Cretaceous

sediments (compiled from various sources). Paleoreconstruction for

100 My B.P. (after Smith and Briden, 1977).

A r t h u r and S c h l a n g e r , 1979). The f i r s t one t a k e s p l a c e from L a t e B a r r e m i a n t h r o u g h A l b i a n time (100-117 M y r B . P . ) . A second e v e n t l o c a t e d a r o u n d the C e n o m a n i a n - T u r o n i a n boundary (90-95 M y r B.P.) i s o f h i g h e r i n t e n s i t y b u t more r e s t r i c t e d i n t i m e . A t h i r d and l e s s w i d e s p r e a d event o c c u r s d u r i n g C o n i a n c i a n and S a n t o n i a n (78-86 M y r B . P . ) .

MODELS OF FORMATION

The f o r m a t i o n o f o r g a n i c r i c h s e d i m e n t s i s t h o u g h t t o o c c u r when t h e e n v i r o n m e n t o f d e p o s i t i o n becomes l o c a l l y o r f u l l y a n o x i c . Two models o f s e d i -m e n t a r y e n v i r o n -m e n t s a r e g e n e r a l l y used t o a c c o u n t f o r t h e develop-ment o f

a n a e r o b i c c o n d i t i o n s ( S c h l a n g e r and J e n k y n s , 1976; Ryan and C i t a , 1977; T h i e d e and Van A n d e l , 1977; Demaison and Moore, 1980) ( f i g . 3 ) .

I n t h e f i r s t c a s e a d e n s i t y s t r a t i f i c a t i o n o f t h e w a t e r column c a u s e s a s t a g n a t i o n thus i n h i b i t i n g the t r a n s p o r t o f oxygen t o deep w a t e r s . A t t h e b o t t o m t h e a v a i l a b l e o x y g e n i s consumed b y t h e o x y d a t i o n o f dead o r g a n i c m a t t e r t h a t r a i n s down from the p h o t i c zone l e a d i n g t o an a n a e r o b i c e n v i r o n -ment o f s e d i m e n t a t i o n . Such a d e n s i t y s t r a t i f i c a t i o n c a n o c c u r i n s e v e r a l s i t u a t i o n s . The B l a c k Sea i s t h e c l a s s i c a l example o f a r e s t r i c t e d b a s i n w h i c h has o n l y a s h a l l o w w a t e r c o n n e c t i o n t o o t h e r p a r t s o f t h e o c e a n g i v i n g r i s e t o

s t a g n a t i o n i n the d e e p e r p a r t s o f the b a s i n (Degens and R o s s , 1974). D e n s i t y s t r a t i f i c a t i o n and the r e s u l t i n g s t a g n a t i o n c a n a l s o be i n i t i a t e d by t h e i n f l u x o f a dense b o t t o m l a y e r o f w a t e r (Summerhayes, 1981) o r a l i g h t s u r f a c e l a y e r ( R o s s i g n o l - S t r i c k et al.3 1982). M Y B P 6 5 -S T A G E C H A N G E S O F SEA LEVEL F o i l i n g - " >—Rising O C C U R R E N C E A N D M A E S T R I C H T I A N

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135-Fig. 2. Occurrence of 'oceanic anoxia events' in r e l a t i o n to sea level

changes (after Arthur and Schlanger, 1979).

I n the s e c o n d c a s e a n o x i c c o n d i t i o n s o f s e d i m e n t a t i o n a r e p r e s e n t a t the i n t e r f a c e o f an expanded, o x y g e n - d e p l e t e d oxygen-minimum l a y e r and the s e d i m e n t . I n t h i s model the d e e p e r p a r t s o f the b a s i n a r e o x y g e n a t e d . E x p a n s i o n o f and o x y g e n d e p l e t i o n i n the oxygen-minimum l a y e r c a n be the r e s u l t o f u p w e l l i n g o f n u t r i e n t r i c h w a t e r w h i c h l e a d s to a h i g h p r o d u c t i v i t y i n the s u r f a c e w a t e r s . The h i g h oxygen demand f o r the r e c y c l i n g o f l a r g e amounts o f dead o r g a n i c m a t t e r i n the u n d e r l y i n g w a t e r l a y e r s c a u s e s the d e v e l o p m e n t o f a n o x i c c o n d i t -i o n s . A s -i m -i l a r s -i t u a t -i o n can a l s o d e v e l o p w -i t h o u t a h -i g h p r o d u c t -i v -i t y when the v e r y l a r g e d i s t a n c e to a s o u r c e o f deep o x y g e n a t e d w a t e r g i v e s r i s e to a g r a d u a l e x h a u s t i o n o f o x y g e n . P r e s e n t - d a y examples o f t h e s e s i t u a t i o n s a r e f o u n d o f f s h o r e N a m i b i a i n f l u e n c e d by the B e n g u e l a C u r r e n t and i n t h e N o r t h e r n I n d i a n Ocean r e s p e c t i v e l y (Demaison and Moore, 1980).

b) The Blaak Sea, an anoxia silled basin.

2 5 0 K m . A N O X I C S E P . O R G . C A R S , 1 - 1 5 % Ô X I C S E P . O R G . C A R B . <2.5% U: 5 - 3 0 c m / 1 0 0 0 Y r s SIMILAR SETTINGS: B A L T I C S E A • S A A N I C H I N L E T L A K E M A R A C A I B O Fig. 3. Present-day examples of anoxia environments of sedimentation (after Demaison and Moore, 1980).

a) The western shelf of India, interface with the oxygen-minimum layer.

The two models a r e n o t m u t u a l l y e x c l u s i v e . The development o f f u l l y a n o x i c c o n d i t i o n s i n t h e oxygenminimum l a y e r w i l l be f a c i l i t a t e d by a s l u g g i s h c i r c u -l a t i o n and i n case o f a c o m p -l e t e s t a g n a t i o n oxygen d e p -l e t i o n i s -l i k e -l y t o s t a r t i n the m i d - w a t e r oxygen-minimum zone. I t i s n o t c l e a r w h i c h model a p p l i e s t o the C r e t a c e o u s b l a c k s h a l e d e p o s i t s . I n ' the P a c i f i c the oxygen-minimum zone mechanism i s v e r y p l a u s i b l e s i n c e b l a c k s h a l e s a r e o n l y f o u n d a t t h e t o p s and

f l a n k s o f seamounts and r i s e s whereas i n d e e p e r p a r t s o f the b a s i n o x y g e n a t e d s e d i m e n t s o c c u r ( S c h l a n g e r and J e n k y n s , 1976; Ryan and C i t a , 1977). The r e s -t r i c -t e d b a s i n model i s p r o b a b l y more a p p l i c a b l e -t o -the s i -t u a -t i o n i n -the C r e t a c e o u s A t l a n t i c Ocean w h i c h a t t h e time was a young and r e l a t i v e l y n a r r o w o c e a n d i v i d e d i n t o s e v e r a l b a s i n s by s i l l s , t h r e s h o l d s and r i d g e s ( B e r n o u i l l i ,

1972; Ryan and C i t a , 1977; L a n c e l o t and S e i b o l d , 1977; T u c h o l k e and V o g t , 1979).

The s i m u l t a n e o u s o c c u r r e n c e and t h e s i m i l a r i t y o f C r e t a c e o u s b l a c k s h a l e d e p o s i t s a l l o v e r the w o r l d have i n i t i a l l y l e d t o the s u g g e s t i o n t h a t t h e i r

f o r m a t i o n c o u l d be d e s c r i b e d by one g e n e r a l l y a p p l i c a b l e s e d i m e n t a r y e n v i r o n -ment. However, as more d e t a i l e d s t u d i e s were u n d e r t a k e n i t became c l e a r t h a t c o n d i t i o n s o f s e d i m e n t a t i o n may v a r y s i g n i f i c a n t l y when comparing b l a c k s h a l e s from d i f f e r e n t l o c a t i o n s and c o n s e q u e n t l y s e v e r a l models f o r p a l e o e n v i r o n m e n t a r e n e c e s s a r y . I n g e n e r a l one can say t h a t the C r e t a c e o u s has i n d e e d b e e n a p e r i o d d u r i n g which a n a e r o b i c c o n d i t i o n s o f s e d i m e n t a t i o n c o u l d e a s i l y d e v e l o p d e p e n d i n g on the l o c a l s i t u a t i o n as w i l l be d i s c u s s e d b e l o w .

PALEO-OCEANOGRAPHY

S e v e r a l t e c t o n i c and c l i m a t i c f a c t o r s made the C r e t a c e o u s ocean as a whole more p r o n e t o the development o f a n o x i c c o n d i t i o n s . S c h l a n g e r and J e n k y n s

(1976) o b s e r v e d a c o i n c i d e n c e o f t h e i r ' o c e a n i c a n o x i c e v e n t s ' and m a j o r t r a n s g r e s s i o n s ( f i g . 2 ) . These t r a n s g r e s s i o n s were caused by an enhanced r a t e o f s p r e a d i n g o f the o c e a n i c p l a t e s and the r e l a t e d i n c r e a s e i n t h e volume o f the m i d - o c e a n i c r i d g e s (Hays and P i t m a n , 1973). Due t o the t r a n s g r e s s i o n s v a s t a r e a s o f c o a s t a l p l a i n s were f l o o d e d . D u r i n g the C r e t a c e o u s the c l i m a t e was m i l d and e q u a b l e ( F r a k e s , 1979) l e a d i n g t o a r e l a t i v e l y low c i r c u l a t i o n v e l o c

-i t y o f o c e a n -i c w a t e r and hence a d e c r e a s e -i n t h e r e p l e n -i s h m e n t o f oxygen -i n deep w a t e r s can be e x p e c t e d .

The f l o o d i n g o f the c o a s t a l p l a i n s may have c a u s e d the seaward t r a n s p o r t -a t i o n o f l -a r g e -amounts o f t e r r e s t r i -a l b i o m -a s s thus p r o m o t i n g the f o r m -a t i o n o f b l a c k s h a l e s . T h i s mechanism, w h i c h i s s u p p o r t e d by the d e t e c t i o n o f s i g n i f i -c a n t amounts o f t e r r e s t r i a l o r g a n i -c m a t t e r i n a number o f A t l a n t i -c b l a -c k s h a l e s

( T i s s o t et at., 1980), has p r o b a b l y b e e n o n l y o f l o c a l i m p o r t a n c e dependent o f p a l e o g e o g r a p h y . The s u g g e s t i o n o f J e n k y n s (1980) t h a t 'much o f the C r e t a c e o u s o c e a n was s i m p l y awash w i t h wood' i s n o t i n agreement w i t h the r a t e o f the C r e t a c e o u s t r a n s g r e s s i o n s which were too s l o w t o a c c o u n t f o r a c a t a s t r o p h i c t r a n s f e r o f t e r r e s t r i a l o r g a n i c m a t t e r i n t o the o c e a n b a s i n s .

B e s i d e s b e i n g a p o t e n t i a l s o u r c e f o r t e r r e s t r i a l m a t e r i a l t h e f l o o d e d p l a i n s a r e t u r n e d i n t o h i g h l y p r o d u c t i v e s h e l f a r e a s w h i c h can a c c o u n t f o r a

l a r g e p r o d u c t i o n o f m a r i n e o r g a n i c m a t t e r t h a t c a n be t r a n s p o r t e d towards the o c e a n . The e x t r a c t i o n of l a r g e amounts o f m a r i n e o r g a n i c m a t t e r and i t s i n -c o r p o r a t i o n i n the s e d i m e n t would r e s u l t i n a h i g h e r 1 3C /1 2C r a t i o i n the

c a r b o n a t e s o f the s u r f a c e w a t e r s . S e v e r a l a u t h o r s ( F i s c h e r and A r t h u r , 1975; S c h o l l e and A r t h u r , 1980) e x p l a i n the o c c u r r e n c e o f 'heavy' c a r b o n a t e s i n s e d i m e n t s w i t h a h i g h o r g a n i c c a r b o n c o n t e n t by t h i s mechanism. A n o t h e r ex-p l a n a t i o n f o r t h e s e 'heavy' c a r b o n a t e s i s g i v e n by W e i s s e r t et at. (1979) who a t t r i b u t e the h i g h 1 3C /1 2C r a t i o t o a d e c r e a s e d u p w e l l i n g o f deep w a t e r s r i c h

i n l i g h t c a r b o n i s o t o p e s . De Boer (1982b) s u g g e s t s the 'heavy' c a r b o n a t e s i n the o r g a n i c r i c h l a y e r s t o be t h e r e s u l t o f a d i a g e n i c p r o c e s s thus a v o i d i n g t h e n e c e s s i t y o f a h i g h p r o d u c t i v i t y i n t h e w a t e r column d u r i n g the f o r m a t i o n of b l a c k s h a l e s . F o r m a t i o n o f b l a c k s h a l e s w i t h o u t an enhanced p r o d u c t i o n o f o r g a n i c m a t e r i a l i s a l s o s u g g e s t e d by the low r a t e o f s e d i m e n t a t i o n i n a

number o f c a s e s ( T u c h o l k e and V o g t , 1979; de B o e r , 1982a; J o h n s o n I b a c h , 1982).

ORGANIC GEOCHEMICAL INVESTIGATIONS

A major p a r t o f t h e r e s e a r c h on C r e t a c e o u s b l a c k s h a l e s has been p e r f o r m e d on s e d i m e n t s f r o m the A t l a n t i c Ocean t h a t have become a v a i l a b l e t h r o u g h t h e Deep Sea D r i l l i n g P r o j e c t . Whereas t h e f i r s t p a r t o f t h i s p r o j e c t showed o n l y l i t t l e a c t i v i t y o f o r g a n i c g e o c h e m i s t s ( e . g . S i m o n e i t et al., 1972 and 1973), f r o m l e g 41 on the number o f o r g a n i c g e o c h e m i c a l i n v e s t i g a t i o n s has i n c r e a s e d m a r k e d l y . The C r e t a c e o u s b l a c k s h a l e s o f l e g s 43,44,47/2, 48 and 50 have r e -c e i v e d the a t t e n t i o n o f s e v e r a l o r g a n i -c g e o -c h e m i s t s ( s e e t h e a p p r o p r i a t e

I n i t i a l Reports of the Deep Sea drilling P r o j e c t ) .

B o t h t h e s o l u b l e and the i n s o l u b l e o r g a n i c m a t t e r have b e e n i n v e s t i g a t e d . C h a r a c t e r i z a t i o n o f the i n s o l u b l e m a t e r i a l was c a r r i e d o u t by m i c r o s c o p y ( e . g . Dow, 1978; C o r n f o r d , 1980), e l e m e n t a l a n a l y s i s ( e . g . Erdman and S c h o r n o , 1979), c a r b o n i s o t o p e measurements ( e . g . Stuermer and S i m o n e i t , 1978), and v a r i o u s p y r o l y s i s t e c h n i q u e s ( e . g . C l a y p o o l and B a y s i n g e r , 1978; K e n d r i c k , 1979; Deroo

et al., 1979). E x t r a c t s were a n a l y z e d i n d e t a i l a f t e r s e p a r a t i o n i n t o s e v e r a l

c l a s s e s such as s a t u r a t e d and a r o m a t i c h y d r o c a r b o n s , f a t t y a c i d s , k e t o n e s , a l c o h o l s , and p o r p h y r i n s ( e . g . B a k e r et al., 1978; C a r d o s o et al., 1978; M c l v e r and R o g e r s , 1978; B a r n e s et al.-, 1979; S i m o n e i t , 1979; B r a s s e l l et al., 1980).

S e v e r a l a u t h o r s (Van A n d e l et al., 1977; A r t h u r , 1979; T i s s o t et al., 1980; Summerhayes, 1981) have summarized the r e s u l t s o f t h e a n a l y s e s o f o r g a n i c m a t t e r i n C r e t a c e o u s b l a c k s h a l e s f r o m the A t l a n t i c Ocean. T h e i r c o n c l u s i o n s a r e g e n e r a l l y i n good agreement. No u n i f o r m model f o r t h e o c c u r r e n c e o f a l l b l a c k s h a l e d e p o s i t s can be a p p l i e d . The o r g a n i c m a t t e r c o n t e n t v a r i e s o v e r a wide r a n g e ( f r o m l e s s t h a n 1% up t o more t h a n 15% o r g a n i c c a r b o n ) . The r e l a t i v e amounts o f m a r i n e and t e r r e s t r i a l o r g a n i c m a t t e r depend on t h e p a l e o l o c a t i o n o f the s i t e w i t h r e g a r d t o the p r e s e n c e o f landmasses and t h e o c c u r r e n c e o f up-w e l l i n g phenomena.

D u r i n g L a t e C e n o m a n i a n - E a r l y T u r o n i a n time h i g h amounts o f m a i n l y m a r i n e o r g a n i c m a t t e r have been i n c o r p o r a t e d i n t h e s e d i m e n t s . T h i s e v e n t w h i c h i s i d e n t i c a l to the s e c o n d ' o c e a n i c a n o x i c e v e n t ' as i d e n t i f i e d by S c h l a n g e r and J e n k y n s (1976) i s s u g g e s t e d t o have o c c u r r e d a f t e r the r e a l i z a t i o n o f a deep

w a t e r c o n n e c t i o n between the N o r t h and South A t l a n t i c and the r e s u l t i n g n o r t h -ward t r a n s p o r t a t i o n o f dense s a l i n e b o t t o m w a t e r . T h i s d e n s e w a t e r may have c a u s e d an upward t r a n s p o r t o f n u t r i e n t r i c h w a t e r s g i v i n g r i s e t o an enhanced p r o d u c t i v i t y o f m a r i n e o r g a n i c m a t t e r i n the s u r f a c e l a y e r (Summerhayes, 1981). A t a number of l o c a t i o n s t h e o r g a n i c m a t t e r i s o f the r i g h t t y p e t o be a p o t e n t i a l o i l s o u r c e b u t i n a l l o f t h e s e c a s e s t h e s e d i m e n t s have n o t y e t m a t u r e d enough to g e n e r a t e o i l ( T i s s o t et at., 1980). CYCLICITY A c o n s p i c u o u s f e a t u r e o f many b l a c k s h a l e d e p o s i t s i s the r h y t h m i c i n t e r -b e d d i n g w i t h l i g h t e r c o l o r e d ( g r e e n to g r a y ) mud, m a r l o r l i m e s t o n e ( A r t h u r , 1979). G e n e r a l l y c a r b o n a t e p o o r , o r g a n i c r i c h , l a m i n a t e d o r homogeneous s e d i -ments a r e a l t e r n a t e d w i t h c a r b o n a t e r i c h , o r g a n i c p o o r , b i o t u r b a t e d s e d i m e n t s .

S e v e r a l e x p l i c a t i o n s f o r t h e c y c l i c i t y have b e e n o f f e r e d ( B e r g e r and Von Rad, 1972; Dean et at., 1977): 1) p e r i o d i c i n f l u x o f t u r b i d i t e s c a u s i n g a r e d e -p o s i t i o n o f s h a l l o w c a r b o n a t e s i n an a n o x i c e n v i r o n m e n t b e l o w the c a r b o n a t e c o m p e n s a t i o n d e p t h (CCD); 2) changes o f d i a g e n e t i c c o n d i t i o n s i n s i d e t h e s e d i m e n t s u c h as r e d o x p o t e n t i a l and c a r b o n a t e p r e c i p i t a t i o n / d i s s o l u t i o n ; 3) v a r i a t i o n s i n the CCD; 4) p e l a g i c c y c l e s o f h i g h m a r i n e p r o d u c t i v i t y and/or a d i l u t i o n by t e r r i g e n e o u s m a t e r i a l . S e v e r a l o f the p r o p o s e d mechanisms a r e t h o u g h t t o be r e l a t e d t o c l i m a t i c v a r i a t i o n s (Dean et at.,. 1977; McCave, 1979; M e l i e r e s , 1979).

The r h y t h m i c i t y i n a s e t o f p e l a g i c l i m e s t o n e s and m a r l s o f A p t i a n t o Cenomanian age f r o m the Umbrian A p e n n i n e s n e a r M o r i a , I t a l y , h a s b e e n s t u d i e d e x t e n s i v e l y by de Boer and Wonders (1981, 1982). They f o u n d a mean d e p o s i t i o n time f o r a l i m e s t o n e / m a r l c o u p l e t o f 21,000-23,000 y e a r s . T h i s i s w i t h i n t h e r a n g e f o u n d f o r s i m i l a r f o r m a t i o n s a t o t h e r l o c a t i o n s (17,00-50,000 y e a r s ; Dean et at., 1977; A r t h u r and F i s c h e r , 1977; McCave, 1979). As t h e s e d i m e n t -a t i o n r -a t e o f t h e n o n - c -a r b o n -a t e m -a t e r i -a l -a p p e -a r s t o be more o r l e s s c o n s t -a n t i n b o t h l i m e s t o n e s and m a r l s ( s e e a l s o T u c h o l k e and V o g t , 1979) and the f o r " a m i n i f e r a i n t h e m a r l y l a y e r s do n o t show s i g n s o f d i s s o l u t i o n the c y c l i c i t y o b s e r v e d i n t h e s e d i m e n t s must be the r e s u l t o f a v a r i a t i o n i n the s u r f a c e p r o d u c t i v i t y o f b i o g e n i c c a r b o n a t e ( s e e a l s o A r t h u r and F i s c h e r , 1977). De B o e r and Wonders (1981, 1982) s u g g e s t t h a t t h e p r e c e s s i o n c y c l e , one o f the s o - c a l l e d M i l a n k o v i t c h p a r a m e t e r s i n f l u e n c i n g t h e e a r t h ' s o r b i t ( K e r r , 1981), w i t h a p e r i o d o f 23,000 y e a r s c a u s e s a c y c l i c v a r i a t i o n o f the c l i m a t e . As a c o n s e q u e n c e o f t h e s e c l i m a t i c v a r i a t i o n s the p o s i t i o n o f t h e ' h i g h p r o d u c t i v -i t y e q u a t o r -i a l zone' w -i l l v a r y -i n s u c h a way t h a t a r e a s a t 25 t o 35 d e g r e e s

o f l a t i t u d e w i l l a l t e r n a t e l y f a l l i n s i d e and o u t s i d e t h e i n f l u e n c e o f t h i s zone. I n c a s e o f t h e M o r i a s e d i m e n t s t h i s i m p l i e s t h a t t h e c a r b o n a t e r i c h beds were d e p o s i t e d when t h e a r e a was w i t h i n t h e i n f l u e n c e o f t h e ' h i g h

p r o d u c t i v i t y e q u a t o r i a l zone' c a u s i n g u p w e l l i n g c o n d i t i o n s , a h i g h p r o d u c t i v i t y and a good r e p l e n i s h m e n t o f oxygen i n deep w a t e r s . The m a r l y l a y e r s were formed d u r i n g t i m e s of a s l u g g i s h c i r c u l a t i o n r e s u l t i n g i n a low p r o d u c t i v i t y and a s i t u a t i o n i n w h i c h oxygen d e p l e t i o n i n deep w a t e r s c o u l d e a s i l y o c c u r .

Fig. 4. Locations of the sampled sections in France and Italy.

SCOPE OF THIS THESIS

The o r g a n i c g e o c h e m i c a l i n v e s t i g a t i o n s d e s c r i b e d i n t h i s t h e s i s a r e p a r t o f a more e x t e n s i v e r e s e a r c h p r o j e c t on the o c c u r r e n c e and f o r m a t i o n o f C r e t a c e o u s b l a c k s h a l e d e p o s i t s i n n o r t h e r n I t a l y and s o u t h e r n F r a n c e . T h i s p r o j e c t combines t h e r e s u l t s o f v a r i o u s d i s c i p l i n e s s u c h as s e d i m e n t o l o g y , p a l e o n t o l o g y , p a l y n o l o g y , and o r g a n i c g e o c h e m i s t r y i n o r d e r to o b t a i n an i n t e g r a t e d model f o r the f o r m a t i o n o f the b l a c k s h a l e s . The m a j o r p a r t o f the g e o l o g i c a l r e s e a r c h has been p e r f o r m e d by P.L. de Boer o f t h e C o m p a r a t i v e S e d i m e n t o l o g y D i v i s i o n , I n s t i t u t e o f E a r t h S c i e n c e s , U t r e c h t .

The s e d i m e n t s u n d e r i n v e s t i g a t i o n have b e e n d e p o s i t e d i n the now e x t i n c t T e t h y s Ocean o f w h i c h the M e d i t e r r a n e a n i s a remnant. A s e r i e s o f t e c t o n i c e v e n t s have o c c u r r e d s i n c e t h e C r e t a c e o u s and h a v e c r e a t e d s e v e r a l w e l l -e x p o s -e d o u t c r o p s o f C r -e t a c -e o u s b l a c k s h a l -e d -e p o s i t s . Th-e p r -e s -e n c -e o f t h -e s -e o u t c r o p s i n I t a l y and s o u t h e r n F r a n c e makes t h e a r e a v e r y s u i t a b l e f o r our p u r p o s e s . As t h e b i o s t r a t i g r a p h y and the geometry o f t h e s e d i m e n t a r y b a s i n s

a r e r a t h e r well-known a c o r r e l a t i o n o f the s e c t i o n s from d i f f e r e n t l o c a t i o n s i s p o s s i b l e and t h e d i f f e r e n c e s between samples from an open m a r i n e and a n e a r - s h o r e e n v i r o n m e n t o f s e d i m e n t a t i o n c a n be o b s e r v e d . The a v a i l a b i l i t y o f o u t c r o p s a l s o e n a b l e s t h e c o l l e c t i o n o f l a r g e samples. Hence i t i s p o s s i b l e to p e r f o r m v a r i o u s s t u d i e s on i d e n t i c a l samples and the o r g a n i c g e o c h e m i c a l a n a l y s i s o f samples w i t h a v e r y low o r g a n i c c a r b o n c o n t e n t becomes f e a s i b l e . These a r e i m p o r t a n t advantages o f o u t c r o p samples o v e r t h e c o r e samples t h a t c a n be o b t a i n e d from the Deep Sea D r i l l i n g P r o j e c t . DSDP samples a r e g e n e r a l -l y -l i m i t e d i n number and g e o g r a p h i c a -l d i s t r i b u t i o n o f t h e samp-les and i n sample amount. The m a i n d i s a d v a n t a g e o f the use o f o u t c r o p samples i s the p o s s i b l e e f f e c t o f w e a t h e r i n g on the o r g a n i c m a t t e r .

Our r e s e a r c h has been f o c u s s e d on s e d i m e n t s from two a r e a s ( f i g . 4 ) : 1) the Umbrian A p e n n i n e s n e a r C a g l i , I t a l y , and 2) t h e A l p e s M a r i t i m e s i n s o u t h -e a s t -e r n F r a n c -e .

The Umbrian A p e n n i n e s a r e renowned f o r the p r e s e n c e o f s e v e r a l c o n t i n u -ous e x p o s u r e s o f C r e t a c e o u s open m a r i n e p e l a g i c f a c i e s ( A r t h u r and F i s c h e r , 1977; Wonders, 1980). Our samples come from a l o c a t i o n n e a r C a g l i , P r o v i n c e o f P e s a r o and U r b i n o . T h i s s e c t i o n , w h i c h r a n g e s from the A l b i a n i n t o the P a l e o c e n e , i s c h a r a c t e r i z e d by a r h y t h m i c a l t e r a t i o n o f l i m e s t o n e s and m a r l s . Two i n t e r v a l s were sampled i n d e t a i l : a) a s e c t i o n from t h e A l b i a n p a r t o f t h e e x p o s u r e c o m p r i s i n g 13 l i m e s t o n e / m a r l c o u p l e t s i n c l u d i n g s e v e r a l b l a c k c o l o r e d m a r l s ( c h a p t e r 2 ) ; b) the L i v e l l o B o n a r e l l i , a c a r b o n a t e p o o r , l a m i n a t e d i n t e r v a l a t the C e n o m a n i a n - T u r o n i a n b o u n d a r y ( c h a p t e r 3 ) .

The F r e n c h samples come from the 'Marnes N o i r e s ' , g r e y to o l i v e - b l a c k s h a l e s o f A p t i a n t o A l b i a n age. T h i s f o r m a t i o n does show a r h y t h m i c o c c u r r e n c e o f more c o n s i s t e n t b e d s w i t h a h i g h e r c a r b o n a t e c o n t e n t but i t i s much l e s s

Fig. 5.

Paleoreconstruation of the

Voaontian Trough, a

side-arm of the Tethys Ocean,

and the location of the

sampled sections.

Massif * Central

o u t s p o k e n t h a n i n t h e I t a l i a n e x p o s u r e . As t h e F r e n c h s e d i m e n t s have a l s o b e e n a l t e r e d by d i a g e n e t i c p r o c e s s e s (de Boer, p e r s o n a l communication) we l i m i t e d o u r s e l v e s t o a s t u d y o f two samples f r o m C o l de P a l l u e l ( c h a p t e r 4) . These s e d i m e n t s have been d e p o s i t e d i n the V o c o n t i a n T r o u g h , a s i d e - a r m o f t h e T e t h y s Ocean ( f i g . 5 ) . Due t o t h i s more n e a r - s h o r e l o c a t i o n we e x p e c t e d t o f i n d a s u b s t a n t i a l t e r r e s t r i a l c o n t r i b u t i o n to the o r g a n i c m a t t e r o f t h e samples f r o m C o l de P a l l u e l .

ORGANIC GEOCHEMICAL RESEARCH DESCRIBED IN THIS THESIS

B o t h t h e s o l u b l e and t h e i n s o l u b l e o r g a n i c m a t e r i a l have been i n v e s t i g a t e d . E x t r a c t e d s e d i m e n t s were c h a r a c t e r i z e d u s i n g C u r i e - p o i n t p y r o l y s i s - m a s s

s p e c t r o m e t r y , C u r i e p o i n t p y r o l y s i s g a s c h r o m a t o g r a p h y , and C u r i e p o i n t p y r o -l y s i s - g a s chromatography-mass s p e c t r o m e t r y . A s u b s t a n t i a -l amount o f r e s e a r c h has been d e v o t e d t o t h e d e v e l o p m e n t o f d a t a p r o c e s s i n g t e c h n i q u e s f o r t h e i n t e r p r e t a t i o n of l a r g e s e r i e s o f p y r o l y s i s mass s p e c t r a (van G r a a s et at., 1980a, 1980b, 1981). F o r t h i s p u r p o s e we u s e d s e v e r a l model s e r i e s among w h i c h a s u i t e of samples f r o m the P a r i s B a s i n , F r a n c e ( c h a p t e r 8 ) .

The e x t r a c t s were s e p a r a t e d i n t o a number o f f r a c t i o n s s u c h as s a t u r a t e d and a r o m a t i c h y d r o c a r b o n s , k e t o n e s , a c i d s , and a l c o h o l s . Our a t t e n t i o n has b e e n f o c u s s e d m a i n l y on the s a t u r a t e d h y d r o c a r b o n f r a c t i o n s b e c a u s e t h e s e a p p e a r e d t o be v e r y u s e f u l f o r a c o m p a r i s o n o f the v a r i o u s s a m p l e s .

I n the c o u r s e o f t h e e x t r a c t a n a l y s e s s e v e r a l unknown compounds were en-c o u n t e r e d . Some o f t h e s e en-c o u l d be i d e n t i f i e d t h r o u g h s y n t h e s i s o f r e f e r e n en-c e compounds ( c h a p t e r s 5 and 6 ) . The mass s p e c t r a o f s e v e r a l o t h e r h i t h e r t o un-i d e n t un-i f un-i e d compounds a r e shown un-i n t h e a p p e n d un-i x .

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C H A P T E R 2

O R I G I N OF T H E O R G A N I C M A T T E R I N A C R E T A C E O U S B L A C K S H A L E D E P O S I T I N T H E C E N T R A L A P E N N I N E S ( I T A L Y ) *

Ger v a n G r a a s , T.C. V i e t s , J.W. de Leeuw and P.A. Schenck D e l f t U n i v e r s i t y o f T e c h n o l o g y Department o f C h e m i s t r y and C h e m i c a l E n g i n e e r i n g O r g a n i c G e o c h e m i s t r y U n i t De V r i e s v a n H e y s t p l a n t s o e n 2 2628 RZ D e l f t , The N e t h e r l a n d s ABSTRACT

The o r g a n i c m a t t e r i n a C r e t a c e o u s sequence o f a l t e r n a t i n g l i m e s t o n e s and m a r l s f r o m t h e c e n t r a l A p e n n i n e s , I t a l y , has been i n v e s t i g a t e d m i c r o s c o p i c a l l y and t h r o u g h d e t a i l e d a n a l y s i s o f t h e e x t r a c t s . B l a c k l a y e r s a r e d i f f e r e n t f r o m o t h e r l a y e r s i n t h a t t h e y c o n t a i n remains o f b a c t e r i a i n t h e i n s o l u b l e mate-r i a l ; t h e c o m p o s i t i o n o f t h e e x t mate-r a c t s p o i n t s t o a b a c t e mate-r i a l c o n t mate-r i b u t i o n t o o .

A p a l e o r e c o n s t r u c t i o n based on c h e m i c a l d a t a shows a low p r o d u c t i v i t y i n t h e water column and an o x i c e n v i r o n m e n t o f s e d i m e n t a t i o n f o r t h e b l a c k m a r l s . E o l i a n i n p u t p r o b a b l y a c c o u n t s f o r t h e p r e s e n c e o f n - a l k a n e s o f t e r r e s t r i a l o r i g i n i n a l l samples. T h i s r e c o n s t r u c t i o n i s i n agreement w i t h p a l e o n t o l ó -g i c a ! and s e d i m e n t o l o -g i c a l d a t a .

INTRODUCTION

D u r i n g some i n t e r v a l s o f t h e C r e t a c e o u s ( 140 t o 65 My B . P . ) , d a r k c o l o u r e d ( b l a c k ) s h a l e s , whether o r n o t i n t e r b e d d e d w i t h l i g h t e r c o l o u r e d , c a r b o n a t e - r i c h e r b e d s , have been d e p o s i t e d more f r e q u e n t l y and more a b u n d a n t l y t h a n d u r i n g any o t h e r g e o l o g i c a l p e r i o d . C r e t a c e o u s b l a c k s h a l e s a r e encoun-t e r e d e s p e c i a l l y i n encoun-t h e N o r encoun-t h and S o u encoun-t h A encoun-t l a n encoun-t i c ( e . g . DSDP l e g 11, H o l l i s encoun-t e r

et al., 1972; l e g 40, B o l l i et al., 1978; l e g 44, Benson et al., 1978; l e g 48,

M o n t a d e r t et al.,1979; e t c . ) b u t a l s o i n t h e P a c i f i c a t t h e f l a n k s o f s e a -mounts and c o n t i n e n t s ( e . g . l e g 32, L a r s o n et aZ.,1975; l e g 33, S c h l a n g e r et

al. , 1976).

S e v e r a l a u t h o r s have d i s c u s s e d t h e o r i g i n o f t h e C r e t a c e o u s b l a c k s h a l e s . S c h l a n g e r and J e n k y n s (1976) and T h i e d e and Van A n d e l (1977) s u g g e s t t h a t t h e e x p a n s i o n o f t h e mid-water oxygen minimum l a y e r and i t s oxygen e x h a u s t i o n c a u s e d t h e f o r m a t i o n o f t h e d a r k c o l o u r e d , o f t e n o r g a n i c r i c h l a y e r s , w h i l e Ryan and C i t a (1977) emphasize t h e p o s s i b i l i t y o f an ocean-wide s t a g n a t i o n . T h e s e t h e o r i e s a r e n o t c o n f l i c t i n g ; a f u l l d e p l e t i o n o f oxygen i n t h e oxygen minimum l a y e r w i l l be f a v o u r e d by a waning o f c i r c u l a t i o n v e l o c i t y . I n c a s e o f

c o m p l e t e s t a g n a t i o n ( i f p o s s i b l e ) , oxygen e x h a u s t i o n i s l i k e l y t o s t a r t i n t h e mid-water oxygen minimum zone.

The f r e q u e n t d e p l e t i o n o f o x y g e n i n d e e p e r p a r t s o f t h e M i d - C r e t a c e o u s o c e a n s , w h i c h a l l o w e d t h e f o r m a t i o n o f o r g a n i c r i c h p e d i m e n t s , i s o b v i o u s l y r e l a t e d t o b o t h t e c t o n i c and c l i m a t i c f a c t o r s . The M i d - C r e t a c e o u s (110-85 My B.P.) i s c h a r a c t e r i z e d by r e l a t i v e l y h i g h t e m p e r a t u r e s and low t e m p e r a t u r e d i f f e r e n c e s between h i g h and low l a t i t u d e s ( F r a k e s , 1979) as a c o n s e q u e n c e o f a g r e a t r i s e o f t h e s e a l e v e l (up t o 350 m; P i t m a n , 1978) w h i c h i n t u r n was c a u s e d by an i n c r e a s e o f t o t a l volume o f m i d - o c e a n i c r i d g e s ( v a n S t r a a t e n ,

1973; Hays and P i t m a n , 1973). I n s u c h a s i t u a t i o n a r e l a t i v e l y low c i r c u l a t i o n v e l o c i t y o f o c e a n i c w a t e r r e s u l t s and hence a d e c r e a s e i n r e p l e n i s h m e n t o f oxygen i n deep water i s e x p e c t e d . T h i s d e p l e t i o n o f oxygen has f a v o u r e d t h e d e p o s i t i o n o f o r g a n i c r i c h s e d i m e n t s i n t h e o c e a n s . D e p e n d i n g on t h e p l a c e o f d e p o s i t i o n r e l a t i v e t o t h e p o s i t i o n o f l a n d a r e a s , t h e o r g a n i c m a t t e r i n M i d - C r e t a c e o u s p e l a g i c s e d i m e n t s i s composed o f v a r y i n g r a t i o s o f t e r r e s t r i a l and m a r i n e o r g a n i c m a t t e r ( T i s s o t et al., 1980). I n s p i t e o f i t s l a r g e s i z e , t h e r a t e o f s e a l e v e l r i s e d u r i n g t h e C r e t a c e o u s has been r e l a t i v e l y s m a l l . T h e r e f o r e , i t i s u n l i k e l y t h a t t h e C r e t a c e o u s t r a n s g r e s s i o n would have c a u s e d a c a t a s t r o p h i c t r a n s f e r o f t e r r e s t r i a l l y d e r i v e d o r g a n i c m a t t e r i n t o t h e o c e a n s , as was s u g g e s t e d by J e n k y n s ( 1 9 8 0 ) . 16

Our c u r r e n t r e s e a r c h i s p a r t o f a p r o j e c t c o n c e r n i n g s e d i m e n t o l o g i c a l , p a l e o n t o l o g i c a l and o r g a n i c g e o c h e m i c a l i n v e s t i g a t i o n s o f M i d d l e C r e t a c e o u s b l a c k s h a l e d e p o s i t s f r o m o u t c r o p s i n N o r t h e r n I t a l y and S o u t h e r n F r a n c e . I n t h i s p a p e r we r e p o r t about t h e r e s u l t s o b t a i n e d on samples f r o m a l o c a t i o n i n t h e n o r t h c e n t r a l A p e n n i n e s , I t a l y , w h i c h c o v e r s a l a r g e p a r t o f t h e

C r e t a c e o u s i n t h i s a r e a . The sampled s e c t i o n forms p a r t o f a p e l a g i c s e q u e n c e . T h i s sequence c o n s i s t s o f a more o r l e s s r e g u l a r a l t e r n a t i o n o f c a r b o n a t e - r i c h and c a r b o n a t e - p o o r e r b e d s , t h e l a t t e r o f w h i c h a r e c h a r a c t e r i z e d by a g r e y t o b l a c k c o l o u r and t h e r e f o r e a r e i n d i c a t e d as b l a c k s h a l e s . The c a r b o n a t e o f t h e samples c o n s i s t s m a i n l y o f t h e r e m a i n s o f c o c c o -l i t h o p h o r e s and t o a s m a -l -l e r e x t e n t o f p -l a n k t o n i c and b e n t h o n i c f o r a m i n i f e r a (Wonders, 1980).

De Boer and Wonders (1981) show t h e r h y t h m i -c i t y o f t h e -c a r b o n a t e - m a r l a l t e r n a t i o n s i n t h e A l b i a n - C e n o m a n i a n i n t e r v a l t o be t h e r e s u l t o f a r h y t h m i c v a r i a t i o n o f p r o d u c t i o n o f c a r b o n a t e , w h i c h i s r e l a t e d t o t h e i n f l u e n c e o f a s t r o n o m i c a l p a r a m e t e r s upon t h e e a r t h ' s c l i m a t e . A n a l y s i s o f t h e e x t r a c t a b l e o r g a n i c m a t t e r f r o m t h e l i m e s t o n e s and m a r l s , i n c o m b i n a t i o n w i t h m i c r o s c o p i c , s e d i m e n t o l o g i c a l and p a l e o n t o l o g i c a l d a t a , made p o s s i b l e t h e c o n s t r u c t i o n o f a model f o r t h e o r i g i n o f t h i s s e d i m e n t a r y s e q u e n c e . EXPERIMENTAL

The samples have been t a k e n f r o m a l o c a t i o n a l o n g t h e M o r i a - M o n t e P e t r a n o r o a d n e a r t h e ceme-t e r y o f M o r i a (43°33'N, 1 2 ° 4 1 ' S ) , 6.5 km s o u ceme-t h w e s ceme-t o f C a g l i i n t h e n o r t h c e n t r a l A p e n n i n e s , I t a l y

(Wonders, 1980),from t h e lower p a r t o f t h e S c a g l i a B i a n c a F o r m a t i o n w h i c h i s o f L a t e A l b i a n age (108-100 My B . P . ) . An i n t e r v a l o f 1.30 m w i t h 13 l i m e s t o n e / m a r l c o u p l e t s was sampled ( F i g . 1 ) . I n a number o f c o u p l e t s t h e m a r l y l a y e r i s v e r y t h i n . S e v e r a l m a r l y l a y e r s a r e p a r t i a l l y o r t o t a l l y d a r k c o l o u r e d . I n c a s e o f p a r t i a l l y d a r k c o l o u r e d m a r l s (samples 5, 14, 16 and 24) a s u b d i v i s i o n was made as i n d i c a t e d i n F i g . 1. I n o r d e r t o o b t a i n f r e s h

§§§

Fig. 1.

Stratigraphy of the

sampled section.

m a t e r i a l about 30 cm o f r o c k were removed b e f o r e a c t u a l s a m p l i n g .

I n t h e l a b o r a t o r y s i x samples have been s e l e c t e d f o r a d e t a i l e d a n a l y s i s o f t h e e x t r a c t s : two c a r b o n a t e l a y e r s (27 and 2 9 ) ; two i n t e g r a l m a r l y l a y e r s , one w i t h a b l a c k m i d d l e p a r t ( 2 4 - t o t a l ) and one w i t h o u t a b l a c k m i d d l e p a r t

(28) and t h e b l a c k p a r t s o f two m a r l y l a y e r s (24 B and 2 6 ) . The samples were ground i n a r o t a r y d i s c m i l l and S o x h l e t e x t r a c t e d w i t h t o l u e n e / m e t h a n o l (1/3 v / v ) f o r 20 h r s . The o r g a n i c c a r b o n c o n t e n t o f t h e e x t r a c t i o n r e s i d u e s was measured a f t e r r e m o v a l o f c a r b o n a t e w i t h 2n HC1. The c a r b o n a t e c o n t e n t o f t h e

samples was c a l c u l a t e d f r o m t h e w e i g h t l o s s upon 2n HC1 t r e a t m e n t .

The t o t a l e x t r a c t s were i n v e s t i g a t e d by TLC u s i n g an I a t r o n I a t r o s c a n TH-10 i n s t r u m e n t e q u i p p e d w i t h Chromarods S I I ; h e x a n e / d i e t h y l e t h e r / f o r m i c a c i d

(95/5/1 v / v / v ) was u s e d a s e l u e n t (Kramer et al., 1980). The h y d r o c a r b o n s were i s o l a t e d by p r e p a r a t i v e TLC o n s i l i c a g e l w i t h p e t r o l e u m e t h e r 4 0 6 0 / d i e t h y l -e t h -e r / a c -e t i c a c i d (89/10/1 v / v / v ) a s d -e v -e l o p -e r . G a s - c h r o m a t o g r a p h y (GLC) was p e r f o r m e d u s i n g a C a r l o E r b a 4160 i n s t r u m e n t e q u i p p e d w i t h a 25 m. g l a s s WC0T column ( I . D . 0.31 mm.) c o a t e d w i t h SE-52.

Gas chromatography-mass s p e c t r o m e t r y (GCMS) was c a r r i e d o u t on a V a r i a n 3700 gas c h r o m a t o g r a p h e q u i p p e d w i t h a 25 m. g l a s s WCOT column ( I . D . 0.25 mm.) c o a t e d w i t h C P - s i l - 5 , c o u p l e d t o a MAT 44 q u a d r u p o l e mass s p e c t r o m e t e r o p e r a t i n g a t 70 eV w i t h mass r a n g e m/z 50-500 and a c y c l e t i m e o f 2 s. I n b o t h GC and GCMS h e l i u m was u s e d as c a r r i e r g a s .

A b l a n k p r o c e d u r e was c a r r i e d o u t u s i n g q u a r t z sand w h i c h was f i r s t h e a t e d f o r 16 h r s . a t 900°C. Samples 26, 27, 28 and 29 have been i n v e s t i g a t e d by i n c i d e n t l i g h t (UV, 365 nm.) m i c r o s c o p y . RESULTS C a r b o n a t e and o r g a n i c c a r b o n c o n t e n t o f t h e samples a r e l i s t e d i n T a b l e 1. E x t r a c t i o n y i e l d s a r e i n t h e o r d e r o f m a g n i t u d e o f 10-100 ppm. F u r t h e r q u a n t i t a t i o n was n o t a t t e m p t e d . TLC a n a l y s i s showed t h a t t h e e x t r a c t s c o n t a i n m a i n l y s a t u r a t e d h y d r o c a r b o n s (Rf 0.95-1.0) and h i g h l y p o l a r m a t e r i a l (Rf 0.0-0 . 1 ) . S e p a r a t e bands o f a r o m a t i c h y d r o c a r b o n s were n o t p r e s e n t . The s a t u r a t e d h y d r o c a r b o n f r a c t i o n s o f t h e e x t r a c t s were a n a l y s e d b y GLC and GC-MS. The chromatograms o f t h e h y d r o c a r b o n f r a c t i o n o f samples 26 and 28 a r e shown i n F i g . 2. I d e n t i f i c a t i o n o f t h e numbered compounds i s g i v e n i n T a b l i 2> I d e n t i f i c a t i o n o f hopanes and hopenes i s b a s e d on mass s p e c t r a l and GLC -r e t e n t i o n d a t a ( E n s m i n g e -r , 1974; V a n D o -r s s e l a e -r , 1974; W a -r d -r o p e -r , 1979).

• * A l l samples c o n t a i n n - a l k a n e s w i t h a m o d e r a t e odd/even p r e d o m i n a n c e ( C P I 2 4 - 3 4 2 ) and s q u a l e n e . The p r e s e n c e o f t h e l a t t e r compound i s due t o