CONTINENTAL MARGIN, LEG 79, SITES 545 AND 547 · 33. ORGANIC MATTER ALONG THE SEDIMENTARY SEQUENCES OF THE MOROCCAN CONTINENTAL MARGIN, LEG 79, SITES 545 AND 5471 Bernd R.T. Simoneit,

33. ORGANIC MATTER ALONG THE SEDIMENTARY SEQUENCES OF THE MOROCCANCONTINENTAL MARGIN, LEG 79, SITES 545 AND 5471

Bernd R.T. Simoneit, College of Oceanography, Oregon State UniversityVassil T. Vuchev, Kansas Geological Survey, University of Kansas

andJoan O. Grimalt, College of Oceanography, Oregon State University2

ABSTRACT

The lipids and kerogens of 15 sediment samples from Site 547 (ranging from Pleistocene to Early Jurassic/Triassic)and 4 from Site 545 (Cretaceous) have been analyzed. A strong terrestrial contribution of organic matter was found,and significant autochthonous inputs were also present, especially at Site 545. Both strongly reduced and highly oxi-dized sediments have been found in the Cenozoic and Jurassic samples of Site 547. On the contrary, all the Cretaceoussections of Sites 547 and 545 are anoxic. Sediments from anoxic paleoenvironments are immature and have a high con-tent of sterenes, diasterenes, steradienes, hopenes, and ßß hopanes. Samples from oxic paleoenvironments are mainlymature and their content of hopenes and steriod structures is below the detection level. Nevertheless, their hopane dis-tributions have the immature ßß homologs as the predominant molecular markers. For Site 545 the most abundant mo-lecular markers are ring A monoaromatic steranes, and their presence is attributed to microbial and chemical transfor-mations during early diagenesis.

INTRODUCTION

Leg 79 is of interest from many geological aspectsand particularly from an organic geochemical point ofview. The eastern Atlantic has turned out to be one ofthe segments of the world ocean studied most duringthe entire history of deep sea drilling. A diverse andthick sequence of sediments was cored, ranging in agefrom Jurassic to Pleistocene and deposited in variousand changing environments, interrupted by distinctivehiatuses overlapping or interspersed with block faultingof crystalline basement and diapiric salt movement. Sucha sequence provides a unique opportunity for organicgeochemical studies. The drilling results summarized ini-tially (Hinz et al., 1982) and described in detail (sitechapters, this volume) have provided such samples. Ofparticular interest is Site 547, which was drilled with re-entry capability through the thickest sedimentary col-umn (1030 m) and would probably have almost reachedcrystalline basement. This chapter is based primarily ondata for specially selected samples from Site 547 withadditional samples from Site 545 (the second deepest)taken for the Organic Geochemistry Panel. All possibleon-board measurements were performed on the Site 547samples during the cruise.

The goals of this study are to consider this thick sedi-mentary sequence in terms of general organic geochem-istry. Three organic-rich facies are present within thissequence that require special attention, namely, Eoceneclaystones and chalks, Middle Cretaceous claystones, and

Hinz, K., Winterer, E. L., et al., Ink Repts. DSDP, 79: Washington (U.S. Govt. Print-ing Office).

2 Addresses: (Simoneit) College of Oceanography, Oregon State University, Corvallis,OR 97331; (Vuchev, permanent address) Geological Institute, Bulgarian Academy of Science,1113 Sofia, Bulgaria; (Grimalt permanent address) Instituto de Quimica Bio-organica,C.S.I.C., Jorge Girona Salgado, Barcelona 34, Spain.

Early Jurassic claystones and calcarenites. This varietyof facies was deposited in a passive marginal basin, whichhas undergone a long and interruptive geological evolu-tion starting with salt and red bed deposition in the Ear-ly Jurassic or Triassic and giving way to a hemipelagicand a pelagic deposition during the Late Jurassic throughCenozoic.

The analytical approach considers the content, types,sources, and maturity of the bulk organic matter, thatis, the kerogen; the sources, diagenetic, and catageneticchanges of the extractable organic matter, that is the bi-tumen; and the overall petroleum potential of the sedi-mentary formations.

EXPERIMENTAL

Materials

The core samples studied here were taken from both holes at Site547 and from Site 545. Site 547 is located in slope sediments of thestructural high seaward of the regional Mazagan Slope (Fig. 1). Thewater depth at this site is 3940.5 m. Site 545 is located near the foot ofthe Mazagan Escarpment and is closest to the carbonate platform. Atthis location there is a major hiatus between the Mesozoic and Ceno-zoic, with the Cenomanian sequence covered by about 250 m of Pleis-tocene to Neogene chalks and oozes. The water depth is 3150 m.

All major units of the section were sampled at Site 547, includingthe three organic-rich intervals (Fig. 2, Table 1). Four samples at Site545 are from the Middle Cretaceous claystones (Unit III), enriched inorganic matter. All samples are considered to be geologically repre-sentative for the corresponding confidence limits (Fig. 2). Several ex-ceptions, mainly with respect to carbonate content, are observed forthe samples at Site 547, but they are'within the confidence intervals.

Three analyses were carried out on samples from very close inter-vals of Section 547B-20-1 to elucidate the lithologic diversity of theLower Jurassic sediments.

Lipids

The samples were freeze dried and then exhaustively extracted withchloroform and methanol (1:1) in a Soxhlet apparatus. The extractswere concentrated on a rotary evaporator and treated with BF3 inmethanol to derivatize free fatty acids. The extracts were then subject-

807

B. R. T. SIMONEIT, V. T. VUCHEV, J. O. GRIMALT

Sialic basement high

- O _ X > • A| |A' -m m-Diapiric structure Line of section Normal fault

Figure 1. Mazagan Escarpment area, showing the location of Leg 79Sites 545 and 547.

ed to thin-layer chromatography (TLC) on silica gel; hexane and di-ethyl ether (9:1) were used for eluent. The bands (after developmentwith iodine vapor) corresponding to hydrocarbons, esters, and ketoneswere scraped off the TLC plates and eluted with methylene chloride.The hydrocarbon and some ester and ketone fractions were analyzedby gas chromatography (GC) and gas chromatography/mass spectrom-etry (GC/MS).

The GC analyses were carried out on a Varian Vista 44 gas chro-matography system using a 25 m × 0.20 mm fused silica capillary col-umn coated with DB-5 and programed from 40 to 280°C at 4°C permin.; He was the carrier gas.

The GC/MS analyses were performed on a Finnigan 4021 quadru-pole mass spectrometer interfaced directly to a Finnigan 9610 gas chro-matograph, equipped with a 30 m × 0.25 mm fused silica capillarycolumn coated with SE-54. The GC conditions for the GC/MS analy-ses were the same as those employed in the analytical GC system. Themass spectrometric data were acquired and processed with a Finnigan-Incos 2300 data system.

Bulk Organic Matter

The measurements of CaCO3, Corg, and Norg shown in Figure 2and associated with the samples taken for the Organic GeochemistryAdvisory Panel (OGP) were carried out on small amounts taken fromjust below and above the 30-cm sections of the bulk samples. All col-ors including those of the bitumens were determined conventionallyfollowing the Rock-Color Chart of the Geological Society of America.

The Hewlett-Packard CHN-Analyzer was utilized on-board and itworked perfectly with samples of 20 mg. Rock-Eval pyrolysis analyseswere carried out on board with the Girdel instrument. The sample,weights were kept around 100 mg, but smaller amounts of about 25-30 mg were found adequate when richer sediments were pyrolyzed.The Rock-Eval instrument is designed to measure hydrocarbon poten-tial and maturity of source rock samples, based on the selective detec-tion and quantitation of hydrocarbons and CO2 by programmed py-rolysis (Espitalié et al., 1977; Roucaché et al., 1979). Several parame-ters are obtained by this technique (Peters and Simoneit, 1982). The

free hydrocarbons (bitumen) are thermally distilled from the sampleand the quantity (mg HC/g sample) determined by a flame ionizationdetector represents the first peak (SI). The second peak (S2) comprisesthe hydrocarbons generated by pyrolytic degradation of the remainingorganic matter (kerogen) (mg HC/g sample). The carbon dioxide gen-erated from organic matter is separated and analyzed as a third peak(S3) (mg CO2/g sample) using a thermal conductivity detector. Thetemperature of maximum hydrocarbon yield (Tmax) is also monitored.The hydrogen index (HI) corresponds to the amount of hydrocarbons(S2) normalized to the total organic carbon (TOC) content of the sam-ple (mg HC/g Corg). The oxygen index (OI) corresponds to the amountof CO2 (S3) normalized to TOC (mg CO2/g Corg). The HI and OI cor-relate well with atomic H/C and O/C, respectively (Espitalié et al.,1977).

RESULTS AND DISCUSSION

Lithological and Organic Matter Measurements

A few comments should be added to the basic resultsof the contents and distributions of CaCO3 and Corg alongthe sedimentary section studied. The data are shown inFigure 2 for Sites 547 and 545, discussed in further de-tail in the corresponding site chapters (this volume), andlisted in Table 1. There are two major subdivisions ofthis section: (1) medium and highly calcareous, uniformoozes in the Cenozoic with a low Corg content; (2) lowand medium to highly calcareous sediments in the Me-sozoic, with a gradually increasing and then decreasingcarbonate content versus depth, and a moderate to lowCorg content, which reaches a maximum in the middleCretaceous nanno-bearing chalks.

Each subdivision has an interval anomalously rich inCorg. Unit III of Hole 547A is late Eocene in age andconsists mainly of a matrix with claystones and chalks,containing clasts and conglomerate beds of similar sedi-ments. Samples 547A-18-1, 57-73 cm and 547A-20-4,120-125 cm are from this unit, and they are among therichest in organic carbon content of the whole sequence.R. Mark Leckie carried out a quantitative examinationof Sample 547A-18-1, 57-73 cm with respect to the com-position and contents of foraminifers and found thatamong a total of 435 tests there were 227 (52.2%) plank-tonic and 208 (47.8%) calcareous benthic specimens.All were well preserved with many juvenile forms, es-pecially among the planktonic species. The assemblageappears to have a minimal component from recycling,though Sample 547A-18-1, 57-73 cm is itself part of theclast of middle Eocene age. Resedimentation is consid-ered responsible for the clasts and debris flows of theentire unit (Site Chapter, this volume).

The lowest part of Subunit VIB (891-924 m) of Hole547B is from the Mesozoic subdivision. It is Early Ju-rassic in age and contains several layers of organic-richclaystones and calcarenites among a lithologically di-verse and disturbed sequence. Some layers appear very"coaly" and shaley, although claystones within the unitcontain well-preserved benthic foraminifers.

There are a few significant correlations between thenoncarbonate material and Corg for both Sites 547 and545 (Site Chapters, this volume). At Site 547 Units I,IIA, IVA, and IVB, VB, and VII show positive correla-tions. These are sequences with presumed uniform sedi-mentation, where the sediment and organic matter accu-mulations can be related to similar factors. This is not

808

ORGANIC MATTER IN SEDIMENTS OF THE MOROCCAN CONTINENTAL MARGIN

the case for the two organic-rich intervals in the late Eo-cene and Early Jurassic discussed previously. The samekind of correlation was found for all Cenozoic units atSite 545, again marking the intervals of stable sedimen-tation.

The contents and distribution of Norg for all unitsand samples studied (Table 1) parallel those of Corg. Theratios of Corg to Norg for the organic-rich Jurassic sam-ples were anomalously high, which may indicate a con-tribution of terrestrially derived organic matter the sedi-ments. This may also be the case for the Eocene samplesthat are enriched in Corg. The terrestrial influx of organ-ic detritus is, however, not indicated by the Rock-Evaldata and the high C/N ratio may thus reflect increasedmaturity or degradation of the organic matter (e.g., Si-moneit, 1982).

Extractable Organic Matter (bitumen)

Good yields and percentages of extractable bitumenwere obtained with few exceptions, namely, from Sam-ples 547A-4-1, 110-116 cm and 547A-10-2, 120-136 cm.Varicolored claystone and mudstone comparatively poorin Corg from the lowest part of the section at Site 547also contained a significant amount of bitumen. Thereis one remarkable feature of the extract data: the bi-tuminosity of the organic matter (beta) is low and indi-cates the syngenetic character of the extractable organicconstituents in the samples (Table 2). The bituminosityor bitumen extraction ratio has been used to estimateorganic matter transformation (maturation) and to di-agnose bitumen migration (i.e., allochthonous bitumencontent) (Vuchev, 1974). The colors of the bitumens, al-though dissolved in CH2C12, match, at least partly, thecolors of the corresponding sediments (Tables 1 and 2).

Hydrocarbons

The GC traces of most of the hydrocarbon fractionsare shown in Figures 3 and 4. The resolved componentsconsist primarily of n-alkanes and cyclic molecular mark-ers (sterenes and triterpenes), and various envelopes ofthe unresolvable branched and cyclic compounds are alsoevident. Such chromatograms have been described earli-er from other drill sites in the Cretaceous of the easternAtlantic (e.g., Rullkötter et al., 1982). The distributiondiagrams of the w-alkanes are shown in Figure 5 to clar-ify their distribution patterns and ranges in some ofthese complex mixtures.

The rt-alkanes of all samples have a dominant contri-bution from terrestrial plant waxes (Simoneit, 1978). Theodd carbon number alkanes > C24 are most abundant inall samples, except for the Eocene example (Section547A-18-1) where the maximum around C21 is present atan equivalent concentration. These allochthonous ter-rigenous hydrocarbons exhibit different carbon-numbermaxima, depending on their geologic age and the loca-tion of the drill site. Thus, all samples examined fromSite 545 have a maximum of n-C25 and those from Site547 have maxima at «-C31 (Pleistocene to late Eoceneand Jurassic) or at «-C27 (late Eocene to late Albian).This aspect is emphasized further by the ratio of (n-C29

+ /z-C31)/(n-C25 + n-C27) given in Table 2. Values greaterthan about 1.3 reflect the higher carbon number maxi-ma and those less than 1.3 indicate lower ones. The plantwax signatures with a maximum at w-C31 may reflect asource from grassland or swamp vegetation and thosewith a maximum at n-C27 may be derived from marsh orsea grasses (Simoneit and Mazurek, 1979b). In fact, then-alkane patterns in the core sections from Site 547 par-allel those from Site 397 further to the south, where thePleistocene samples exhibit a maximum at «-C3i and theCretaceous samples at n-C27 (cf. Figs. 5R and S, Simo-neit and Mazurek, 1979b). The maximum at n-C29 forSection 547B-4-2 in the late Albian (Fig. 5H) has alsobeen observed for a claystone of the same age from Site398 at the Vigo Seamount (Simoneit and Mazurek, 1979a).The n-C31 predominance for the Jurassic samples fromSite 547 was also observed in the same geologic age se-quence at Site 391 in the Blake-Bahama Basin (cf. Fig.5T; Stuermer and Simoneit, 1978).

Autochthonous marine hydrocarbons are more evi-dent at Site 545 where the w-alkanes exhibit a maximumat C17 with no carbon number preference from C14 toC20, which is indicative of an algal source. At Site 547,the hydrocarbons from Sections 547A-18-1 and 547A-63-3 only exhibit a microbial autochthonous component.

The concentrations of pristane (Pr) and phytane (Ph)can be correlated with the degree of anoxicity duringsedimentation and subsequent diagenesis (Didyk et al.,1978). In very oxidized sediments (cf. HI and OI corre-lation of the kerogens below) there is a tendency towardsa higher content of pristane than phytane (Pr/Ph < 1,Table 2) and their overall concentrations are low (Fig. 5).Sections 547A-4-1, 547A-10-2, 547A-41-1, 547B-20-1, and547B-26-1 reflect oxic sedimentary conditions. Further-more, it should be noted that the quantities of these iso-prenoid hydrocarbons are so low in some cases that thePr/Ph may be subject to some degree of uncertainty dueto the analytical constraints. However, in the case of highisoprenoid concentrations (anoxic sedimentary environ-ment) this is a clearly not a problem. In this respectthere are three coincident parameters that define the ox-ic sections of Site 547 mentioned previously: (1) a lowcontent of organic carbon (<1%, carbonate-free); (2)the kerogen (discussed later) has a high oxygen indexand low hydrogen index; and (3) a low content of iso-prenoid hydrocarbons (Pr + Ph/n-alkmax < 0.2) withPr/Ph > 1. The anoxic sediments are characterized bytheir enhanced organic matter contents, high phytaneconcentrations, and hydrogen-rich kerogen.

The total concentrations of n-alkanes in these sam-ples are related to their overall organic matter contentsand to the environmental conditions during their sedi-mentation. The lean and oxic sections have n-alkane con-centrations in the range of 250-500 ng/g of dry sedimentand the more anoxic and organic-rich samples range upto 1400 ng/g. Considering the n-alkane concentration ver-sus organic carbon content (Table 2), it is obvious thatsome of the organic-rich sediments have anomalouslylow amounts of hydrocarbons (e.g., Sections 547A-18-1,547A-20-4 and 547B-20-1). In these cases, the strong an-

809


Site 547, Holes 547A, 547B: Lat. 33°46.8'N, Long. 9°21.0'W, Depth 3940.5 m

1 0 0 -

2 0 0 -

3 0 0 -

400 -i

5 0 0 -

6 0 0 -

700 H

800-

900-

1000-

CoreNo.

oo•o

o#

o

o

o

•

o

o

o

o

o•o

o

o

o

o

o

o

soo•

- 2 A

- 5 A

-

- 1 0 A

-

-15A

- 2 0 A

- 2 5 A

- 3 0 A

= 35A

- 4 0 A

-

- 4 5 A

- 5 0 A

- 5 5 A

- 6 0 A

- 6 5 A

-

^ 7 0 A

- 7 3 A

Lithology

o o.1

Pale yellow brownforaminiferal-nannofossil ooze

Pale yellow brownslightly clayeynannofossil ooze

Greenish gray slightlyclayey firmnannofossil ooze

Greenish gray clayeynannofossil chalkDebris flows of nannoclayst. and chalk. Clastsof Paleoc, upper K.,and Cenomanian

Greenish gray siliceousand cherty nannochalk and claystone

Mainly debris flows ofgreenish gray clayeynanno chalk.

Greenish nannofossil-bearing claystonewith layers of flat-pebble claystoneconglomerate

Micritic nodularlimestone andlimestone breccia

Mainly micriticnodular limestone

Claystone, nodular1st. Stromatolite<?)at base

Grayish red and darkgray sandy mudstone.Rare gypsum veins,dolomite patchesand concretions.

Age Unit

HA

3•.Eoc.-πB

e. Oligo.

.?

III

IVA

IVB

VA

VB

VII

M e a n s a n d c o n f i d e n c e l i m i t s ( x i t r — )

° v nCaCO,

30 60

~!

Neocomian

VIA

VIB

C o r g < % )

MlIIn

I

TTl

I I1 1 .

3

T. D. = 1030.0 m

Figure 2. Sediment lithology, ages, mean concentrations of organic and carbonate carbon for sedimentary units, and locations of samplestaken from this study.

810


Site 545: Lat. 33° 39.86'N, Long. 9°21.88'W, Depth 3150 m

1 0 0 -

2 0 0 -

3 0 0 -

α 400-Q

5 0 0 -

6 0 0 -

700-

^ oα •?E ra

= O

= o

o

— O

= o

— Φ==

CoreNo.

Lithology

Clayey foraminiferal-nannofossil ooze

Firm clayey foram-iniferal nannofossilooze. Limestonebreccia layers.

Greenish clayeynannofossil chalk,siliceous

Green nannofossilclaystone. Small-scale slump foldsand microfaultscommon

Yellow gray dolomiticooze/chalk

Fossiliferous dolo-mitic limestone anddolomite. Commonlybrecciated

Dolomite, gradingdown to dolomiticsandy limestone andcalcareous siltstone

Age Unit

IA

IB

IIIA

IV

Means and confidence limits ( x ± 1 5 -j=

CaCO

30T~

60T~

±. LI 1 p i

•T-H

„ LLl

IIIB

-IIIC- .-z.-z.-.-zszAlr----.

C o r g ( % )

IV

T. D. = 701.0 m

• This studyO OGP sample

— OB

Figure 2. (Continued).

oxic environmental conditions have perhaps preserved asignificant fraction of the lipids as more polar compo-nents (e.g., fatty acids, alcohols, ketones, etc.) so thatthe hydrocarbons constitute a relatively minor fractionof the total.

The unresolved complex mixture (UCM, hump) ofbranched and cyclic hydrocarbons of the many samplesfrom Site 547 are bimodal (Fig. 3), with maxima at aboutC2 0 or C21 and at C2 9 or C30. Since all these samples arerelatively immature, the UCM at lower retention time isattributable to a marine origin and the other one may be

Mean value

j Range of values

derived from diagenesis of heavier, mostly terrestrial lip-id residues. Only Section 547B-26-1 exhibits a unimodalhump, maximizing at about C25 It is the oldest sectionsampled and may reflect the effects of a higher geother-mal gradient that caused the onset of bitumen genera-tion from kerogen. A large amount of UCM is presentin the samples from Site 545 and maximizes around theretention time of n-Cxη (Fig. 4). The relatively low con-centration of n-alkanes < C2 0 may indicate a strong in-fluence of hydrocarbon degradative microorganisms ac-tive during sedimentation. This phenomenon is common

811


Table 1. Carbonate, Corg, and Norg contents of samples from Sites 547 and 545.

Sample(interval in cm)

Hole 547A

4-1, 110-116

10-2, 120-136

18-1, 57-73

20-4, 120-125

41-1, 34-50

63-3, 110-128

72-2, 24-40

Hole 547B

4-2, 110-126

4-3, 85-101

4-5, 10-26

20-1, 13-14^

20-1, 5-23 ( I I )

20-1, 5-23*111)

22-2, 36-55

26-1, 20-36

Hole 545

29-1, 145-150

37-2, 145-150

43-4, 145-150

55-5, 120-123

Sub-bottomdepth(m)

99.5

158.2

232.1

256.2

440.9

653.6

726.4

755.7

757.1

759.5

891.1

891.1

891.1

907.0

941.7

266.9

343.9

403.9

519.2

Unit/Subunit

I

IIA

III

III

VA

VB

VB

VB

VB

VB

VIB

VIB

VIB

VIB

VII

IIIA

IIIB

IIIB

me

Age

Pliocene

middle Miocene

late Eocene

late Eocene

late Cenoma-nian

late Albian

late Albian

late Albian

late Albian

late Albian

Early Jurassic

Early Jurassic

Early Jurassic

Early Jurassic

Early Jurassic/late Triassic

late Cenoma-nian

late Albian

middle Albian

late Aptian

Lithology

Nanno ooze, clayey,pinkish gray

Nanno ooze, clayey,bluish white

Nanno chalk,clayey, slightlysilty, light olivegray


Claystone, lightolive gray,nanno-bearing

Nanno chalk,clayey, lightolive gray





Claystone, olivegray

Calcarenite, green-ish gray, slightlysilty

Claystone, darkgreenish gray,waxy

Calcareous clay-stone, lightolive gray

Calcareous mud-stone, silty,grayish olive

Nannofossil clay-stone, green

Nanno chalk,clayey, green

Nanno chalk,clayey, silty,green

Nanno chalk,clayey, silty,green

CaCO3

(%)

80.4

73.3

68.2

57.5

15.7

32.5

58.0

38.5

48.8

41.1

9.5

63.4

12.9

28.4

34.2

33.6

50.8

41.3

53.6

c orgNoncar-bonateresidue

0.38

0.73

17.15

7.19

0.57

1.38

1.86

1.89

1.39

1.50

7.47

5.51

10.21

0.66

0.42

1.52

1.49

2.90

2.07

(%)

Totalsediment

0.07

0.19

5.45

3.06

0.48

0.93

0.78

1.16

0.71

0.88

6.76

2.02

8.89

0.44

0.28

1.01

0.73

1.70

0.96

NOrg

Noncar-bonateresidue

0.09

0.10

0.79

0.27

0.06

0.10

0.12

0.12

0.10

0.11

0.16

0.15

0.18

0.06

0.05

0.11

0.10

0.16

0.10

(%)

Totalsediment

0.02

0.03

0.25

*0.11

0.05

0.07

0.05

0.07

0.05

0.06

0.14

0.05

0.16

0.04

0.03

0.07

0.05

0.09

0.05

CorgNorg

4.2

7.3

21.7

26.6

9.5

13.8

15.5

15.8

13.9

13.6

46.7

36.7

56.7

11.0

8.4

13.8

14.9

18.1

20.7

in recent sediments with some degree of anoxicity and ahigh rate of hydrocarbon accumulation (Wakeham andCarpenter, 1976; Reed, 1977), and usually the shorterchain hydrocarbons are degraded first (Giger et al.,1980).

Molecular Indicators

The dominant molecular markers found in the hydro-carbon fractions are steroid and triterpenoid derivativesand they are summarized in Table 3. The salient features

812


Table 2. Bitumen in sediments from Sites 547 and 545.

Core-section

Hole 547A

4-1

10-2

18-1

20-4

41-1

63-3

72-2

Hole 547B

4-2

4-3

4-5

20-1

22-2

26-1

Hole 545

29-1

37-2

43-4

55-5

C orgin total

sediment(dry wt.%)

0.07

0.19

5.45

3.06

0.48

0.93

0.78

1.16

0.71

0.88

8.89

0.44

0.28

1.01

0.73

1.70

0.96

g

0.0022

0.0028

0.1000

0.0576

0.0113

0.0454

0.0539

0.0751

0.0653

0.0441

0.1249

0.0084

0.0135

0.0297

0.0250

0.0501

0.0238

Yield

Dry wt.%of sediment

0.004

0.006

0.242

0.113

0.020

0.073

0.073

0.110

0.098

0.060

0.169

0.011

0.018

0.050

0.057

0.103

0.042

mg/eCOrg

63

32

44

37

42

78

94

95

138

68

19

25

64

50

78

61

44

Bitumen(extractable)

color(GSA, rock-color

chart)

Grayish yellow(5Y 8/4)

Light olive brown(5Y 5/6)

Grayish olive green(5GY 3/2)

Grayish olive green(5GY 3/2)

Moderate brown(5YR 3/4)

Dusky brown(5YR 2/2)












Bituminosity

beta - b i t u m e n

COrg

6.3

3.2

4.4

3.7

4.2

7.8

9.4

9.5

13.8

6.8

1.9

2.5

6.4

5.0

7.8

6.1

4.4

yield(ng/g)a

250(660)360

(490)1200

(70)830

(HO)510

(890)950

(690)770

(410)

1180(620)750

(540)900

(600)1300(240)460

(700)290

(690)

1050(690)760

(510)1400(480)950

(460)

Hydrocarbons(n-alkanes)

CPI b

3.2

3.3

2.4

2.0

2.4

2.1

1.8

2.5

2.6

2.4

3.1

3.2

1.4

2.0

1.9

2.7

2.2

*-max

29,3!

29,31

21,29,31

25,27,31

25,27,29

Ph,23,25,27

25,27,31

Ph,25,27,31

25,27,31

25,27,31

29,31

Ph, 29, 31

18,25

25,27

23,25,27

25,35

17,25,31

Pr/Ph d

0.63

1.00

0.44

0.59

1.25

0.68

0.30

0.53

0.45

0.36

0.36

0.50

0.67

1.30

0.80

0.56

1.07

/1-C29 + n-C^/J-C25 + n-C27

2.34

2.43

1.33

0.82

0.83

0.69

0.78

1.34

0.74

0.71

1.50

1.76

0.58

0.69

0.76

0.51

0.92

Hydrocarbon yield expressed as ng/g dry sediment and in parentheses as ng/g organic carbon.Carbon preference index is summed from C14 to C38, odd-to-even ratio.Homologs with maximum concentration; dominant homolog is underscored.Pristane to phytane ratio (Didyk et al., 1978).

of typical mass chromatograms (m/z 191, 257, 215, 217,and 211) for these molecular indicators are shown fortwo examples in Figures 6 and 7.

The oxic samples (e.g. Sections 547A-4-1 and 547B-26-1) contain no detectable levels of steroid compoundsand only traces of triterpenoids. No inferences can bedrawn from the limited triterpane content of Section547A-4-1 and those of the other sample are immaturebased on the stereomer distribution.

The samples coming from anoxic paleoenvironmentscontain major concentrations of triterpenoids and ste-roidal compounds (Table 3), in some cases exceeding the«-alkane concentrations. The late Eocene sample (Sec-tion 547A-18-1) contains mainly sterenes and varioushopanoids. The sterenes are immature and are com-prised of Δ4 and Δ5 - monounsaturated (I) and traces ofΔ5'22 - diunsaturated C2 7 to C2ç homologs, with some 5αr(H)-steranes (II). The hopanoids are also immature andconsist primarily of the 17j8(H),21/3(H)-series (III) rang-ing from C27 to C31 without C28 and various olefins. Iso-

hop-13(18)-ene (IV) is the dominant triterpenoid, withlesser amounts of trisnorhop-17(21)-ene (V, R = H);hop-17(21)-ene (V, R = C3H7); fern-7-ene (VI, Δ7); fern-8-ene (VI, Δ8); and unknown C2 7 and C3 0 isomers. Thelate Albian samples (Sections 547A-72-2, 547B-4-2,547B-4-3, and 547B-4-5, e.g., Fig. 6) contain predomi-nantly sterenes and lesser amounts of hopanoids, alsowith stereochemistries indicative of immature organicmatter. The sterenes are composed of Δ4- and Δ5-mono-unsaturated (I), diasterenes (VII), and 5α(H)-steranes(II) [ » 5j8(H)-steranes], ranging from C27 to C29 with apredominance of C27 and significant amounts of the C29homologs. Monoaromatic steranes (VIII) are present asminor components with a predominance of C27. The tri-terpenoids consist of 17/3(H)-hopanes (III) ranging fromC27 to C31 without C2s and various olefins and unknowncompounds. Isohoρ-13(18)-ene (IV); hop-17(21)-ene (V,R = C3H7); another isomer; and trisnorhop-17(21)-ene(V, R = H) are the major triterpenes present. Similarmolecular marker distributions have been identified in

813

Time —*-

Time

JJ

2931

2733

Figure 3. Capillary gas chromatograms (operating conditions are given in the text) of the hydrocarbon fractions from samples at Site 547 (arabic numerals indicate n-alkanes): A. 547A-4-1, 110-116cm. B. 547A-10-2, 120-136 cm. C. 547A-18-1, 57-73 cm. D. 547A-20-4, 120-125 cm. E. 547A-41-1, 34-50 cm. F. 547A-63-3, 110-128 cm. G. 547A-72-2, 24-40 cm. H. 547B-4-3, 85-101 cm. I.547B-4-5, 10-26 cm. J. 547B-20-l(II), 5-23 cm. K. 547B-22-2, 36-55 cm. L. 547B-26-1, 20-36 cm.


r r

Figure 4. Capillary gas chromatograms of the hydrocarbon fractions from the samples at Site 545 (arabic numerals indicate n-alkanes): A. 545-29-1,145-150 cm. B. 545-37-2, 145-150 cm. C. 545-43-4, 145-150 cm. D. 545-55-5, 120-123 cm.

other Cretaceous samples from the eastern Atlantic(e.g., Rullkötter et al., 1982). The Early Jurassic sample(Section 547A-20-1) also contains immature sterenes andtriterpenoids. The dominant compounds are the triter-penes: isohop-13(18)-ene (IV), hop-17(21)-ene (V), andtrisnorhop-17(21)-ene (V), with lesser amounts of the17jS(H)-hopane series (III) from C27 (no C28) to C33 andtraces of moretanes and 17α(H)-hopane. Monounsat-urated sterenes (Δ4 and Δ5) and 5α(H)-steranes are pres-ent as minor components.

Three mid-Cretaceous samples from Site 545 containpredominantly immature and possibly oxidized steroidresidues and lesser amounts of triterpenoids (Table 3).The major steroid residues for these samples are mono-aromatic steranes (VIII), ranging from C27 to C29, witha strong maximum at C29 and three different isomers ateach carbon number (e.g., Fig. 7). The mass spectromet-ric fragmentation pattern of the dominant isomer (e.g.,Fig. 7C) fits with that of an authentic standard de-scribed by Spyckerelle (1975) and Hussler et al. (1981).These compounds were also identified in other DSDPsamples of Cretaceous age from the eastern North Atlan-tic (Hussler et al., 1981), but their origin could not bedefined. We suggest that these compounds may repre-

sent an oxidized steroid component, and based on themaximum concentration at C29, derived from terrestrialsources since other terrigenous lipids are also present.The Δ4 and Δ5-sterenes (I) are the next significant mark-ers, ranging from C2 7 to C29, with lesser concentrationsof 5>22-diunsaturated sterenes, diasterenes (VII), and5α(H)-steranes, in these cases with a predominance ofC27. The minor amounts of triterpenoids consist of the17|8(H)-hopanes, ranging from C27 to C33 (no C28) (III),and some hop-17(21)-ene, isohop-13(18)-ene, fern-7-ene(VI), other isomers of olefins, 17α(H)-hopane, and mo-retane (e.g., Fig. 7).

Varying amounts of sesquiterpenoid and diterpenoidresidues are found in the Jurassic and Cretaceous sec-tions of both sites. The sesquiterpenoidal compoundsare mainly cadalene (IX), with in some cases 5,6,7,8-tet-rahydrocadalene, and they occur in the Cretaceous sam-ples. The major diterpenoidal compounds are retene(X), dehydroabietin (XI), simonellite (XII), and 13-meth-ylpodocarpa-8,ll,13-triene (XIII). These compounds areindicative of a terrigenous origin, and the absence of themore reduced species (e.g., fichtelite, dehydroabietane)suggests some oxidative diagenesis during transport (Si-moneit, 1977; in press).

816


31

10 20

10 20 10 20 30 40 10 20 30 40

10

•

0-

Q

17

i

25

fi•i•i

27 31i l1n35

i•i l•

10 20C•

30 40 10

Figure 5. Distribution diagrams (concentration versus carbon number) of n-alkanes for all samples analyzed ( . . . = isoprenoids): A. 547A-4-1,110-116 cm. B. 547A-10-2, 120-136 cm. C. 547A-18-1, 57-73 cm. D. 547A-20-4, 120-125 cm. E. 547A-41-1, 34-50 cm. F. 547A-63-3, 110-128cm. G. 547A-72-2, 24-40 cm. H. 547B-4-2, 110-126 cm. I. 547B-4-3, 85-101 cm. J. 547B-4-5, 10-26 cm. K. 547B-20-l(II), 5-23 cm. L. 547B-22-2,36-55 cm. M. 547B-26-1, 20-36 cm. N. 545-29-1, 145-150 cm. O. 545-37-2, 145-150 cm. P. 545-43-4, 145-150 cm. Q. 545-55-5, 120-123 cm. R.396-6-3, 120-135 cm (Simoneit and Mazurek, 1979b). S. 397A-51-4, 100-112 cm (Simoneit and Mazurek, 1979b). T. 391C-52-2, 3-10 cm (Stuer-mer and Simoneit, 1978).

The molecular markers of these samples are imma-ture, even into the Jurassic. The oxidized samples con-tain very low levels of molecular markers and they aremore mature than those of the anoxic sediments. Theanoxic samples from the Cretaceous and Jurassic con-tain mainly steroid residues and triterpenoids whose car-

bon skeleton distributions indicate a mixed origin fromprincipally marine, autochthonous and from lesser ter-rigenous, allochthonous sources. This is based primari-ly on the significant concentrations of the C29 steroidskeleton versus the C2η homolog (Huang and Meins-chein, 1979) and possibly the monoaromatic steroid se-

817


Table 3. Molecular markers in sediments from Sites 547 and 545.

Core-section Characteristics Age

Mainhopanoids a

Mainsteroids8

Mainditerpenoidsa Aromatics Others

4-1

18-1

41-1

72-2

4-2

4-3

4-5

Oxic

Anoxic

Oxic

Anoxic

Anoxic

Anoxic

Anoxic

Pleistocenelate Miocene

late Eocene

late Cenomanian

late Albian

late Albian

late Albian

late Albian

Very weak

Isohop-13(18)-eneHop-17(21)-eneTrisnorisohop-13(18)-ene17/3,21/3(H)-hopane17/3(H)-trisnorhopane17/3,2 l/3(H)-norhopane17/8,21 /3(H)-homohopane17α,21/3(H)-hopaneWeak17/3,2 l/3(H)-hopane17/3,21 /3(H)-homohopane

17|8(H)-trisnorhopane

Unknown17/3,2 l/3(H)-hopane17/3,21 0(H)-homohopaneTrisnorisohop-13( 18)-ene

Hop-17(21)-eneIsohop-13(18)-ene17/3(H)-trisnorhopaneTrisnorisohop-13(18)-eneUnknownTrisnorhop-17(21 )-ene

UnknownUnknownHop-17(21)-eneIsohop-13(18)-ene17/3,21/3(H)-hopane

Under detectable level

5α, 14α, 17α(H)-cholestaneΔ -sterenes C29>C27Δ -sterenes C29 > C27A monoaromatic steranes C27

5 2 2steradienes C28

Diasterenes C29>C27

Diasterenes C27 > C295α, 14α, 17α(H)-cholestaneΔ -sterenes C27>C29Δ4-sterenes C27 > C29Δ 5 22-steradienes C28

Δ5-sterenes C27 > C29Δ4-sterenes C27 > C29Δ 5 22-steradienes C28

5α,14α,17α(H)-steranes C27>C29A monoaromatic steranes C-£I>C Λ

Δ -sterenes C 2 7 » C 2 9Δ -sterens C 2 7 » C 2 9Diasterenes C27--C295q,14α,17α(H)-steranes C27>C29Δ5 '2 2-steradienes C28

5α,14α,17α(H)-steranes C29>C27Δ -sterenes C29>C27Δ4-sterenes C29>C27Diasterenes C29>C27Δ5>22-steradienes C28

Not found

Not determined

DehydroabietaneDehydroabietin19-norabieta-8,11,13-

trieneDehydroabietin19-norabieta-8,ll,13-

triene13-methylpodocarpa-8,11,

13-triene5,6,7,8-tetrahydrocadalene

Simonellite13-methylpodocarpa-8,11,13

trieneCadalene19-norabieta-4,8,11,13-

IQ tetraene

Simonellite13-methylpodocarpa-8,11,13

triene19-norabieta-4,8,ll,13-

tetraeneAbieta-7,13-dieneCadaleneNot determined

Trimethylnaphthalenes

22-2

26-1

Site 545

29-1

Jurassic (Plien-bachian/Sinemurian)

Jurassic(Sinemurian)

Early Jurassic/late Triassic

Anoxic

Anoxic

Anoxic

late or middleCenomanian

late Albian

late Aptian

17/3(H)-trisnorhopane17/3,21 /3(H)-homohopane17α,21/3(H)-hopaneTrisnorhop-17(21 )-eneTrisnorisohop-13(18)-eneHop-17(21)-ene17/3-Trisnorhopane17/3,21/3(H)-norhopane17/3,21/3(H)-hopane17/3,21 /3(H)-homohopane17α,21/3(H)-hopane17/3,21/3(H)-hopane17/3,21 i8(H)-homohopane3-methyl-17α,21/3(H)-

hopaneUnknown17/3,2 lα(H)-hopane17/3(H)-trisnorhopane17/3,21/3(H)-norhopane17/3,2 l/3(H)-homohopane17α,21(3(H)-hopane17α,18α,21/3(H)-28,30-

bisnorhopane17/3,21/3(H)-hopaneC37 homolog, unsatu-

rated in side chain

17/3(H)-trisnorhopaneTrisnorisophop-13( 18)-

ene17/3,21/3(H)-hopane17/3,21 /3(H)-homohopaneIsohop-13(18)-ene17α,21/3(H)-hopane17/3,21/3(H)-hopane17/3,21/3(H)-homohopaneTrisnorisohop-13(18)-eneIsohop-13(18)-ene17/3(H)-trisnorhopane17α,21,8(H)-hopane17/3,21/3(H)-norhopane17/3,21/3(H)-homohopane17/3,21/3(H)-hopane17α,21/3(H)-hopane17/3,2 l/3(H)-norhopaneIsohop-13(18)-ene

A monoaromatic steranes C27 > C29

A monoaromatic steranes5α,14α,17α(H)-steranes

Under detectable level

Norsimonellite13-methylpodocarpa-8,11,13-

triene

Cadalene

Under detectable level Not found

Diasterenes C27 > C29A monoaromatic steranes C27 > C29

A monoaromatic steranes C27 > C29Diasterenes C28

5q, 14α, 17α(H)-steranesΔ^-stereΔ 4-sterenesC27>C 29

3 > z z-steradienes C28

A monoaromatic steranes

5α,14α,17α(H)-steranes C27

Δ -sterenes C27

Δ -sterenes C27

Cadalene5,6,7,8-tetrahydro-

cadaleneDehydroabietane

13-methylpodocarpa-8,11,13-triene

CadaleneSimonellite

TetramethylnaphthalenesTrimethylnaphthalenesDimethylnaphthalenes

TrimethylnaphthalenesTetramethylnaphthalenes

a Listed from more to less abundant.

818


30?

1 900Scan number

2600

-

m/z215 _

-

m/z217 _

-

27

Δ 4

27(5/3)

if

27

Δ 5

28 28

Δ 5 ' 2 2 Δ 4 Δ 5

ill III

27 (5α)

28 α

28/3 |

—j *—i—

2J

iá !

Δ5

H i I. A

2

29/3

II *

9α

1\

—i—ii ,

C

D

1 ' 12200

Figure 6. Salient features of the GC/MS data for an example of the hydrocarbon fraction from Albian Sample 547B-4-2,110-126 cm. (Numerals indicate carbon numbers of compounds). A. Mass chromatogram m/z 191, triterpenoids. B.Mass chromatogram m/z 257, diasterenes. C. Mass chromatogram m/z 215, sterenes. D. Mass chromatogram m/z 217,steranes.

819


m/z131 .

30(3

30α130:1 30 ßa

27ß29/3

310

320

13M 1438

m/z211 .

-

B

1500 1698

291554

R27 'Y2 N[

1445 j | 2 8

JJJU2 8

I 1574

1783

163329

!

i;

1808

2916441

1S93 2008 •"

13θβ

lββ.β-i

8,1 31

IHV* 4*vr+TWZ 68 83 102 128 143 15β 188

lββ.β-i

233 223 243 263 293 380 343 368 38β

159

i i 1 5 3

'••i••U•••, L•̂ . i l . , J l i . i • , , l | l | l i . , t i | Φ l l U , '

6 8 8 8 1 8 3 143 163 24β 266 233 303 320 340 368

' ' i ' ; " " I ' l ' ' i • I vv. r p v r .yvvr \•\•\-r

lθβ 120 148 ISβ 228 240 260 288 328 340 360 38β

Figure 7. Salient features of the GC/MS data for the hydrocarbon fraction from Sample 545-55-5, 120-123 cm: A. Mass chromatogram m/z 191,triterpenoids. B. Mass chromatogram m/z 211, monoaromatic steranes, VIII. C. Mass spectrum, scan 1603 in Fig. 7B, l-methyl-24-ethyl-19-nor-cholesta-l,3,5(10)-triene. D. Mass spectrum, scan 1554 in Fig. 7B, another C29-isomer. E. Mass spectrum, scan 1644 in Fig. 7b, another C29-iso-mer.

ries. Furthermore, the presence of the uncommon triter-penes, as, for example, isohopanes and fernenes, mayindicate in the case of these samples some higher plantorigin, since the paleoreconstruction of the depositionalenvironments of both sites indicates rapid wash in of

terrestrial detritus from wet zones (Simoneit and Stuer-mer, 1982). A terrigenous origin for some of the molec-ular markers is also supported by the dominant n-al-kanes derived from vascular plant waxes and the TypeIII kerogens described later.

820


Rock-Eval Data and Organic Potentials of Sediments

The Rock-Eval data are given in Table 4 for samplesfrom Site 547 and the results of the hydrogen index (HI)are plotted versus the oxygen index (OI) in Figure 8.There are three distinctive groups of samples based ontheir HI, namely, with high, moderate, and low valuesof HI, as is evident from the regions indicated on theVan Krevelen type diagram (Fig. 8). The conventionallabels of the evolution paths are also indicated, but theyshould be considered as approximate trends. The firstgroup consists of the organic-rich Jurassic and Tertiarysamples and includes the I.F.P. standard 27251, which isa lower Toarcian organic-rich shale, an alginite and withan advanced path of kerogen evolution (Tissot et al.,1974; Espitalié et al., 1977). The second group includesall middle Cretaceous samples with moderate HI values,whereas the third group comprises all samples lean inCorg and derived from the youngest and oldest sedimentscored. The same kind of grouping was observed for allsites of Leg 79 based on the on-board Rock-Eval mea-surements of many other samples (Site Chapters, thisvolume).

The Tmax of all Cretaceous and Upper Jurassic sam-ples ranges from 405 to 426°C. These low values, coup-led with a negligible SI peak (free hydrocarbons), indi-cate that these sediments are immature. This immaturityis supported further by the transformation ratio, SI/(SI + S2) (Tissot and Welte, 1978), which is approxi-mately zero for all samples. The hydrocarbon-generat-ing potential, based on S2, ranges from poor to excel-lent.

The Tmax of 509°C for the Pliocene sample (Unit I,Sample 547A-4-1, 110-116 cm), coupled with the highOI and low HI, indicate oxidized, mature, and probablyrecycled organic detritus. The low Tmax (388°C) of themiddle Miocene sample (Subunit IIA, Sample 547A-10-2,120-136 cm) with the low HI and relatively high OI indi-cate oxidized but immature organic detritus. These in-ferences are also obvious from the plot of HI versus OI(Fig. 8), where these samples fall on the Type III kerogenpath (vitrinitic).

600

500

1"<£ 400

300

200

100

I 20-1

J20-1(H) I I Alginites

Types of kerogenmaturation pathsSamples

18-1.IOI .F.P. standard 27241

_s y

| 4*2 ^ ! " E × i " i t e S

! 7*2 1

I~S ' III Vitrinites

f / 26-l 10-2 \ _

200 400 600 800 1000 1200 1400

Oxygen index (mg I

Figure 8. Rock-Eval data for the bulk organic matter plotted as hydro-gen index versus oxygen index.

Sample 547A-18-1, 57-73 cm (Unit III, late Eocene)has an excellent hydrocarbon potential and the organicmatter is an immature alginite (Type I kerogen). TheEarly Jurassic samples (Subunit VIB, Sample 547B-20-1,5-23 cm, organic-rich vs. lean) also contain immaturealginite organic matter (Type I kerogen) with only a rela-tive concentration difference, probably due to mineraldilution of the organic detritus.

The late Cenomanian (Subunit VA, 547A-41-1, 34-50 cm); Early Jurassic (Subunit VIB, 547B-22-2, 36-55cm); and the Jurassic/Triassic (Subunit VII, 547B-26-1,20-36 cm) samples all fall on the Type III kerogen path(vitrinitic), have a very low hydrocarbon potential andelevated Tmax, especially the Jurassic sample (503°C).These data indicate that the organic matter is probablyderived from terrigenous sources, was partially oxidizedduring transport, and has also matured (mainly Sample547B-22-2, 36-55 cm).

All samples from the late Albian (Subunit VB) clus-ter on the HI/OI plot (Fig. 8) and fall on both paths for

Table 4. Rock-Eval pyrolysis data for samples from Site 547.

Sample(interval in cm)

Hole 547A

4-1, 110-116

10-2, 120-13618-1, 57-7341-1, 34-5063-3, 110-12672-2, 24-40

Hole 547B

4-2, 110-1264-3, 85-1014-5 10-262001). l, 5-2320<m>-l,5-2322-2, 36-5526-1, 20-36

Sub-bottomdepth

(m)

99.5

158.2232.1440.9553.6726.4

755.7757.1759.5891.1891.1907.0941.7

(I.F.P. standard 27251)

Unit

I

IIAIIIVAVBVB

VBVBVB

VIDVIDVIDVII

Age

Pleistocene/Miocene

Miocenelate Eocenelate Cenomanianlate Albianlate Albian

late Albianlate Albianlate AlbianJurassicJurassicJurassicJurassic/Triassiclower Toarcian

c org

0.07

0.195.450.480.930.78

1.160.710.882.028.900.470.282.48

s l S2 S3(mg/g sediment)

0.0

0.00.00.00.00.0

0.00.00.00.00.00.00.00.0

0.05

0.0948.5

0.140.960.20

2.111.381.97

10.648.5

0.050.148.2

0.91

0.892.270.981.170.89

0.850.991.021.272.771.610.580.85

Hydrogenindex(HI)

(mg HC/gcorg)

66

47339

28103153

182194224526546

1049

330

Oxygenindex(OI)

(mg Cθ2/gCorg)

1297

47042

205126115

741391166331

343209

34

πiβx

509

388423425420426

423417417408405503450426

821


Type I and Type II kerogens (alginites and exinites). Theresolution of type I versus II is not possible from thesedata and would require microscopic maceral analysis.However, based on the meager hydrocarbon-generatingpotential (S2 range 0.1-2.1, Table 4), these samples ap-pear to contain immature, degraded microbial detritus.

CONCLUSIONS

1. A strong terrestrial lipid input is observed for allthe samples studied. In this respect, the correspondingn-alkane distributions have a dominant contribution ofodd carbon number homologs >n-C24, indicative of ahigher plant wax origin. These profiles have different max-ima (Fig. 5) depending on the location and age of thesections. Those from Site 545 (mid-Cretaceous) maxi-mize at Λ-C2 5, some from Site 547 (late Eocene to lateAlbian) at n-C2η, and others from Site 547 (Pleistoceneto late Eocene and Jurassic) at «-C31. The n-hydrocar-bon distributions from Site 547 parallel those of Site 397(located further to the south) and the predominance of«-C31 in Jurassic sections has also been observed for thesame age interval at Site 391 (Stuermer and Simoneit,1978). This alternation between the maxima at n-C31 toΛ-C27 and again to «-C31 may be due to terrestrial hydro-carbons coming from grassland or swamp vegetation inthe first and third cases and from marsh or sea grassesin the second.

2. The autochthonous inputs are more evident forSite 545 where the w-alkanes exhibit a lower maximumat «-C17 with essentially no carbon number preferencefrom «-Cj4 to /2-C20 (indicative of an algal origin). Amarine origin may also be attributed to the major humpmaximizing around «-C17. In general these sections con-tain a relatively low concentration of n-alkanes below n-C20, which may indicate strong microbial hydrocarbondegradation during deposition.

In some sections of Site 547 marine inputs are alsoevident. Thus, a maximum around «-C21, attributableto algal/microbial products, is observed in Section 547 A-18-1, and a high content of n-C17 and n-C19 in Section547A-63-3 is indicative of bacterial detritus. On the oth-er hand, Rock-Eval analyses of some samples of this site(Sections 547A-18-1, 547A-20-1) characterized their ker-ogens as alginites.

3. The oxicity or anoxicity of these sediments can besubstantiated by means of two parameters: (a) the pris-tane and phytane concentrations (Didyk et al., 1978);and (b) the Rock-Eval indexes HI and OI (Tissot et al.,1974). In the first case, oxic samples (Sections 547A-4-1,547A-10-2, 547A-41-1, 547B-22-2, and 547B-26-1) aredistinguished by a higher amount of pristane over phy-tane and a very low content of both, whereas the anox-ic sediments (Sections 547A-18-1, 547A-20-4, 547A-63-3, 547A-72-2, 547B-4-2, 547B-4-3, 547B-4-5, 547B-20-1)have a greater content of phytane than pristane at ahigher overall concentration. With respect to the recordparameter, there is a high OI and low HI for the oxicsections and a low OI with a high HI for the anoxicones.

4. The degree of oxicity and the organic matter ma-turity generally correlate for Site 547. In this sense, the

Rock-Eval analyses indicated that the sections from themid-Cretaceous, Sections 547A-18-1 (Eocene) and 547B-20-1 (Jurassic), were immature (negligible Sλ peaks andlow temperature maxima for hydrocarbon yield, Tm a x),and they could be classified either as alginites or exini-tes. Furthermore, the low amounts of normal hydrocar-bons versus total organic carbon or their low yields maybe related to their immaturity, which would support thepresence of more polar material (carboxylic acids, ke-tones, etc.) in the bitumen.

With the exception of Section 547A-10-2 (Miocene),the oxic sections of Site 547 can be classified as maturedue to their high Tm a x (509° C) and low hydrocarbon yieldpotential. In contrast, Section 547A-10-2 displays a lowT m a x (388°C) and the HI and OI are indicative of an oxi-dized but immature example. The unique n-alkane dis-tribution and hump of the oldest sample (Section 547B-26-1, Triassic-Jurassic) can be explained in terms of geo-thermal processes, which would have caused its matura-tion and would have altered the original hydrocarbonprofile with alkanes produced from the kerogen.

5. The molecular markers are mainly steroidal and tri-terpenoidal compounds. Samples from the mid-Creta-ceous and late Eocene (Section 547A-18-1) have a high-er amount of sterenes than hopanoids. Δ4 and Δ5-sterenesare the most common with a lower amount of stera-dienes (Δ5-22). C27 and C2 9 homologs are found in com-parable amounts pointing to a mixed marine and terres-trial origin. C27 and C2 9 5α(H)-steranes are also present.The hopanoid distribution ranges from C2 7 to C33 (noC28) with a predominance of the ßß stereomers. Otherunsaturated hopenes, trisnorhopenes, and fernenes arealso found in these samples. Section 547B-20-1 (EarlyJurassic) also contains the same kinds of compounds,with a predominance of the hopanoid over the steroidstructures. Strong reducing paleoenvironmental condi-tions are indicated for these samples according to thesemolecular marker distributions (many unsaturated struc-tures and the predominance of the ßß hopane series).The mid-Cretaceous samples of Site 545 contain ringA monoaromatized steroids (VIII) as major molecularmarkers, along with the same types of sterenes, steranes,steradienes, hopenes, and hopanes as those describedpreviously. The presence of monoaromatized steranes hasbeen reported for other Cretaceous black shales (Sites364 and 365, Angola and Cape Verde basins, Hussler etal., (1981), which are also immature and from reductivepaleoenvironments. These compounds were inferred toresult from microbial and chemical transformation dur-ing early diagenesis; it is thus noteworthy that strongmicrobial activity was also observed for Site 545. Theoxic samples contain no steroidal structures at the ana-lytical level of detection and only minor amounts of sat-urated hopanoids. Nevertheless, it has to be pointed outthat they are predominantly of the 17j3(H), 21/3(H) ste-reochemistry, even for the oldest sample (Section 547B-26-1, Jurassic-Triassic).

ACKNOWLEDGMENTS

We thank the National Science Foundation for access to the coresamples by the direct participation of one of us (V.T.V.) aboard Glo-

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mar Challenger as organic geochemist. We thank the Interdepartment-al Commission for Research and Technological Investigation (CIRIT,Generalitat de Catalunya) for a research fellowship (J.O.G.); J. Le-Claire and the shipboard technical staff for valuable assistance duringsample collection and preliminary laboratory evaluations on Leg 79;Mrs. A. Vucheva, Geological Institute, Bulgarian Academy of Sci-ences, Sofia, for technical assistance while at O.S.U.; R. Mark Leckie(University of Colorado) for the determination of the foraminiferalassemblages; and Drs. P. A. Meyers and R. Cunningham for review ofthis manuscript.

REFERENCES

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Hussler, G., Chappe, B., Wehrung, P., and Albrecht, P., 1981. C27-C29 ring A monoaromatic steroids in Cretaceous black shales. Na-ture, 294:556-558.

Peters, K. E., and Simoneit, B. R. T., 1982. Rock-Eval pyrolysis ofQuaternary sediments from Leg 64, Sites 479 and 480, Gulf of Cali-fornia. In Curray, J. R., Moore, D. G., et al., Init. ReptsDSDP, 64,Pt 2: Washington (U.S. Govt. Printing Office), 925-931.

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Simoneit, B. R. T., 1977. Diterpenoid compounds and other lipids indeep-sea sediments and their geochemical significance. Geochim.Cosmochim. Acta, 41:463-476.

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Date of Initial Receipt: August 9, 1983Date of Acceptance: October 28, 1983

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APPENDIXChemical Structures Cited in the Text

|R = H , C H 3 , C 2 H 5

I. Δ4- or Δ5- Sterenes

VII. Diasterenes

f

I I . 5α(H)• Steranes

R = H, C 2 H 5 - C 7 H 1 5

I I I . Mß (H)-Hopanes

X. Reteπe

VII I . Monoaromatic steranes

X I . Dehydroabietin X I I . Simonellite

IX. Cadalene

X I I I . 13-Methylpodo-carpa-8, 11-13-triene

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Documents

CONTINENTAL MARGIN, LEG 79, SITES 545 AND 547 · 33. ORGANIC MATTER ALONG THE SEDIMENTARY SEQUENCES OF THE MOROCCAN CONTINENTAL MARGIN, LEG 79, SITES 545 AND 5471 Bernd R.T. Simoneit,