Origin of Organic Matter in North American Basin Cretaceous Black

6 Origin of Organic Matter in North American Basin Cretaceous Black Shales Rosanne M. Joyce and Edward S. Van Vleet Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 29, 2018 | https://pubs.acs.org Publication Date: April 21, 1986 | doi: 10.1021/bk-1986-0305.ch006

Department of Marine Science, University of South Florida, St. Petersburg,FL33701

The expansion of the oxygen minimum zone in the incipient North Atlantic during the Upper Cretaceous enhanced the preservation of sedimentary organic matter. Organic carbon values ranging from 1.7 to 13.7% and the proportions of unbound lipid to total lipid content (>70%) support this premise. A present point of contention is the origin of the organic matter-rich Upper Cretaceous deep-sea sediments. With eustatic sea level transgression and flooding of continental lowlands, transport of terrigenous organic matter into the North American basin may have increased. Analyses of Upper Cretaceous sediments from DSDP Site 603B, lower continental rise east of Cape Hatteras, indicate that the organic matter was continentally derived. δC values of -23.5 to -27.1 /oo, C/N ratios of 32 to 72, and l i p i d class maxima of unbound alkanes (C and C ), unbound fatty acids (C and C ) and bound fatty acids (C28, C and C ) provide supportive evidence for the terrigenous nature of the organic matter. 13

o

31

30

26

29

28

24

The Upper Cretaceous has been described as a period of many important global events. Enhanced sea-floor spreading (up to 18 cm/yr) at many mid-ocean ridge systems led to a reduction in ocean basin volume (D particularly in the restricted, incipient North Atlantic. Sea level transgressed, surpassing present levels by as much as 350 m 02). As latitudinal temperature gradients diminished, deep-water circulation in the oceans waned. In the North Atlantic basin (3), stagnation and consequent expansion of the oxygen minimum zone to the deep-sea floor may account for the observed preservation of thick organic matter - r i c h sequences in mid-Cretaceous sediments (}}Γ§_)· sluggish deep-water circulation which favored anoxic expansion may have also reduced nutrient recycling to surface waters, decreasing f e r t i l i t y and productivity in the euphotic zone of the open-ocean (7). Paleofertility estimates derived from organic carbon accumulation T n e

0097-6156/ 86/ 0305-0091 $06.00/ 0 © 1986 American Chemical Society

Sohn; Organic Marine Geochemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

ORGANIC MARINE GEOCHEMISTRY

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r a t e s of mid-Cretaceous deep-sea d e p o s i t s suggest t h a t primary p r o d u c t i v i t y was as much as an order of magnitude lower than p r o d u c t i v i t y measured i n t o d a y s oceans ( 8 ) . I f these s c e n a r i o s are c o r r e c t , i n c r e a s e d i n p u t of t e r r e s t r i a l " o r g a n i c m a t t e r from the p r o g r a d i n g c o n t i n e n t a l s h e l f ( 9 ) , c o u p l e d w i t h reduced s e a - s u r f a c e p r o d u c t i v i t y , would produce an o b v i o u s t e r r e s t r i a l i n f l u e n c e on the s e d i m e n t a r y o r g a n i c matter d e p o s i t e d on the c o n t i n e n t a l s h e l f and slope. A l t e r n a t i v e l y , Jenkyns (9) proposed t h a t w i t h the e x t e n s i o n of the s u b a e r i a l c o n t i n e n t , t e r r i g e n o u s r u n - o f f not o n l y enhanced p r i m a r y p r o d u c t i v i t y i n s h e l f s u r f a c e w a t e r s by i n c r e a s i n g n u t r i e n t a v a i l a b i l i t y , but a l s o i n c r e a s e d the d e p o s i t i o n of t e r r i g e n o u s o r g a n i c matter i n the marine environment. In c o n s i d e r a t i o n of these s c e n a r i o s , b o t h marine o r g a n i c matter and t e r r i g e n o u s o r g a n i c matter may have been important components of the sediment. The g o a l s of the p r e s e n t s t u d y a r e t o a s s e s s the l o c a l e x t e n t of a n o x i a on the lower c o n t i n e n t a l r i s e , e a s t of Cape H a t t e r a s , d u r i n g s p e c i f i c i n t e r v a l s of the Upper C r e t a c e o u s , to evaluate r e l a t i v e c o n t r i b u t i o n s t o the b u l k o r g a n i c matter by marine and t e r r i g e n o u s s o u r c e s , and t o determine the e x t e n t of m i c r o b i a l a l t e r a t i o n ^ Of s p e c i f i c l i p i d c l a s s e s . The above assessments are based on 6 C, o r g a n i c c a r b o n / o r g a n i c n i t r o g e n r a t i o s , and a n a l y s e s of s e l e c t e d l i p i d c l a s s e s of Upper C r e t a c e o u s b l a c k s h a l e and v a r i e g a t e d c l a y s t o n e samples from DSDP S i t e 603B.

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 29, 2018 | https://pubs.acs.org Publication Date: April 21, 1986 | doi: 10.1021/bk-1986-0305.ch006

f

Experimental

Methods

Sediment was d r i l l e d from DSDP S i t e 603B (lower c o n t i n e n t a l r i s e , 43J5 km e a s t of Cape H a t t e r a s , water depth 4643 m, latitude 35 29.71'N, l o n g i t u d e 70°01.71·Ε) by the D/V Glomar C h a l l e n g e r ( F i g u r e 1 ) . S u b s u r f a c e sampling depths ranged from 1081 t o 1146 m (Table I ) . Based on the e v i d e n c e of sharp b a s a l c o n t a c t s and graded s i l t s , i t i s presumed t h a t the sediments were t u r b i d i t i c a l l y emplaced t o S i t e 603B ( 1 0 ) .

Table

I.

Site

d e s c r i p t i o n of DSDP S i t e 603B lower r i s e , U.S. e a s t c o a s t ( 1 0 ) .

Core 29 S e c t i o n (cm) 1(48-53) Depth (m) 1050 variegated Lithology claystone ConiacianAge Santonian 84-89 Ma a

m i l l i o n s of

continental

33 Ρ Ρ 36 CC(1-8) 1(13-116) 2(136-139) 1(39-43) 1127 1128 1130 1146 b l a c k carbonaceous claystones*" "

a

89-91

Ma

91-98

Ma

years

Unbound lipid methanol/toluene/H 0

was for

extracted by refluxing sediment in t h r e e hours f o l l o w i n g s o n i c a t i o n ( 6^.



JOYCE AND VAN VLEET

Organic Matter in Cretaceous Black Shales

F i g u r e 1. L o c a t i o n map w i t h p h y s i o g r a p h i c f e a t u r e s o f t h e N o r t h American B a s i n , and l o c a t i o n o f DSDP S i t e 603 and o t h e r DSDP d r i l l s i t e s i n t h e N o r t h A t l a n t i c Ocean. Bathymetry a f t e r U c h u p i , 1971 ( 1 0 ) .


94

ORGANIC MARINE GEOCHEMISTRY

A f t e r p a r t i t i o n i n g and hexane e x t r a c t i o n , the unbound l i p i d e x t r a c t was c o n c e n t r a t e d t o near d r y n e s s and d i l u t e d t o a known volume. A l i q u o t s o f unbound l i p i d were p a r t i t i o n e d employing a m o d i f i e d s e r i a l - e l u t i o n column chromatography procedure (J5, VI_) t o i s o l a t e aliphatic hydrocarbons and fatty acids. Fatty acids were m e t h y l a t e d (12) and p u r i f i e d by t h i n - l a y e r chromatography ( 6 ) . Bound l i p i d was e x t r a c t e d by r e f l u x i n g r e s i d u a l sediment i n 0.5N KOH i n m e t h a n o l / t o l u e n e / H 0 and then s e p a r a t e d , d e r i v i t i z e d and p u r i f i e d t o o b t a i n the bound l i p i d c l a s s e s . A l i q u o t s o f unbound and bound t o t a l l i p i d were measured g r a v i m e t r i c a l l y a f t e r d r y i n g t o constant weight. Identification and quantitative determinations of lipid compounds were made by s p l i t l e s s i n j e c t i o n c a p i l l a r y g a s - ^ l i q u i d chromatography (GC). Samples were a n a l y z e d on a H e w l e t t - P a c k a r d 5880A FID gas chromatograph equipped w i t h a 15 m χ 0.2 mm i . d . DB-5 f u s e d s i l i c a c a p i l l a r y column, temperature programmed from 90 t o 255°C a t 4°C/min. u s i n g H as a c a r r i e r gas. I n d i v i d u a l compounds were i d e n t i f i e d by comparison o f r e t e n t i o n t i m e s w i t h those o f a u t h e n t i c s t a n d a r d s and c o n f i r m e d by combined h i g h - r e s o l u t i o n gas chromatography-mass s p e c t r o m e t r y 06). Q u a n t i f i c a t i o n o f i n d i v i d u a l c o n s t i t u e n t s was based on r e l a t i v e p e r c e n t s of i n t e g r a t e d peak areas extrapolated to g r a v i m e t r i c a l l y determined t o t a l lipid f r a c t i o n weights. A n a l y t i c a l v a r i a t i o n o f sample replicates q u a n t i f i e d by GC g e n e r a l l y ranges from ±10 t o 37$ (13-1*0. S t a b l e carbon i s o t o p e s were a n a l y z e d on a F i n n i g a n MAT 250 i s o t o p e r a t i o mass s p e c t r o m e t e r a c c o r d i n g t o the p r o c e d u r e o f C r a i g (15). R e s u l t s a r e r e p o r t e d r e l a t i v e t o the Chicago PDB s t a n d a r d i n terms o f δ C d e f i n e d a s :


2

2

Γ

l 3

c/

1 2

L

c

standard

Ί

_J

(15). Average a n a l y t i c a l v a r i a b i l i t y o f sample p r e p a r a t i o n and s t a b l e carbon i s o t o p e r a t i o a n a l y s i s i s ±0.2$ (J_6). A Carlo-Erba Model 1106 E l e m e n t a l A n a l y z e r was employed t o determine p e r c e n t o r g a n i c carbon and n i t r o g e n i n each sediment sample. Analytical v a r i a t i o n o f sample a n a l y s i s i s ±20$ ( 1 7 ) . R e s u l t s and D i s c u s s i o n 13 T o t a l o r g a n i c carbon (TOC), δ C, and t o t a l l i p i d data a r e summarized i n T a b l e I I (more d e t a i l e d r e s u l t s can be found i n Joyce [6]). Total organic carbon was highest in the Cenomanian-Turonian b l a c k s h a l e samples, w i t h ranges from 3.4$ t o 13.7$. The C o n i a c i a n - S a n t o n i a n v a r i e g a t e d c l a y s t o n e had the l o w e s t T0C (1.7$) i n t h e sample s e t . TOC i n Core 34-1 r e p r e s e n t s one o f the h i g h e s t v a l u e s measured i n sediments sampled from the N o r t h American b a s i n . C o n d i t i o n s i n the n e a r - s h o r e environment and lower continental rise following turbiditic emplacement of these sediments must have f a v o r e d o r g a n i c matter p r e s e r v a t i o n s i n c e v a l u e s >0.6$ TOC a r e not t y p i c a l of deep-sea sediments ( 1 8 ) . A l t h o u g h an environment e n t i r e l y d e p l e t e d i n oxygen i s not a


6.

Organic Matter in Cretaceous Black Shales

J O Y C E A N D VAN V L E E T

95

r e q u i s i t e f o r b l a c k s h a l e f o r m a t i o n 0_8), t h e u n b i o t u r b a t e d n a t u r e of t h e sediments i n the present study suggests that an oxygen-stressed system p r e v a i l e d d u r i n g their d e p o s i t i o n and burial.

Table

II.

O r g a n i c geochemical d a t a , DSDP S i t e c o n t i n e n t a l r i s e , U.S. e a s t c o a s t .


Core a

T 0 C ($) C/N r a t i o yC (°/oo) T o t a l l i p i d (mg/g) L i p i d i n TOC ($) Bound l i p i d ($ o f total lipid) 0

5

a

29-1 1050 1.7 72.0 24.7 0.3 1.5 27

t o t a l o r g a n i c carbon; ratio

33-CC 1127 3.4 38.6 -24.7 0.7 2.2 7

34-1 1128 13.7 43.8 -23.6 3.3 2.4 6

b o r g a n i c carbon t o o r g a n i c

603B

34-2 1130 4.8 40.0 -23.5 1.4 2.8 19

nitrogen

lower

36-1 1146 3.9 32.0 -27.1 1.9 4.8 9

atomic

Unbound l i p i d s , compounds which a r e g e n e r a l l y more l a b i l e than t h e i r bound c o u n t e r p a r t s 09.), represented the greatest proportion o f t o t a l l i p i d i n each sediment sample. More than 80? o f t h e t o t a l l i p i d was unbound i n t h e b l a c k s h a l e s ; Core 34-1 had t h e h i g h e s t proportion o f unbound l i p i d (94?) as w e l l as t h e h i g h e s t concentration o f T0C (13.7$) and t o t a l lipid (3.3 mg/g). C o n v e r s e l y , t h e v a r i e g a t e d c l a y s t o n e (Core 29-1) had t h e l o w e s t p r o p o r t i o n o f unbound l i p i d ( 7 3 $ ) , T0C (1.7$) and t o t a l l i p i d ( 0 . 3 mg/g). L i p i d c o n c e n t r a t i o n and t h e p r o p o r t i o n o f unbound t o bound l i p i d may be coupled w i t h t h e o x i d a t i o n p o t e n t i a l . During the Cenomanin-Turonian, black shale deposition and/or formation p r o b a b l y o c c u r r e d under c o n d i t i o n s o f reduced o x i d i z i n g p o t e n t i a l , and t h a t o f t h e C o n i a c i a n - S a n t o n i a n variegated claystone during elevated oxidation potential conditions. The percentage o f l i p i d i n TOC i n c r e a s e d w i t h depth (1.5 t o 4.8$). Dean e t a l . (20) have r e l a t e d i n c r e a s e s i n l i p i d c o n t e n t t o enhanced methanogenic b a c t e r i a l a c t i v i t y , a p r o c e s s t h a t may have produced l i g h t e r δ C v a l u e s . Work by P a u l y (2Λ) has shown t h a t the i n p u t o f a r c h a e b a c t e r i a l l i p i d s t o these sediment samples i s v e r y low (

Origin of Organic Matter in North American Basin Cretaceous Black

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