13.3 ORGANIC GEOCHEMISTRY OF SOME NEOGENE CORES FROM SITES 374, 375, 377,AND 378: LEG 42A, EASTERN MEDITERRANEAN SEA

G. Deroo, J. P. Herbin, and J. Roucaché Institut Français du Petrole, 1 et 4 avenue de Bois Preau,92502 Rueil-Malmaison, France

ABSTRACT

Two different types of organic matter were defined in easternMediterranean sediments of late Neogene age which were sampledfrom cores of the DSDP Leg 42A cruise.

Pyrolysis assay and chloroformic extraction were techniques thatwere used together with analysis of humic compounds and kerogenfraction. Organic matter from Messinian evaporitic levels of theIonian Basin (Site 374) could be of marine origin. For the otherNeogene samples taken from the Mediterranean Ridge Cleft (Site377), the Cretan Basin (Site 378), and the Florence Rise (Site375), the organic material mainly originated from continentalsources. All the analyzed samples are immature but the samples ofSerravallian age from the Florence Rise were the most evolved andhad reached the stage of late diagenesis or early catagenesis. It isshown that rich organic black sediments (many of which arereferred to as sapropels) may have a number of origins andinferred environments of deposition.

INTRODUCTION

The aim of this paper is to define the different typesand the origin of the organic matter in eastern Mediter-ranean sediments of late Neogene age.

Since burial depths were low and the geological ageof the sediments relatively young only minor evolutionof hydrocarbons would be expected. Neverthelessgeochemical analyses were performed to confirm thispoint.

A pyrolysis assay for hydrocarbon detection on rawmaterial and some chloroform solvent extractions werefirst performed. They were useful to characterize an-cient sediments. Then followed a study of the remain-ing insoluble organic fraction on some selected sam-ples. The characterization of the latter is reached fromthe study of humic compounds on one hand and thekerogen fraction on the other. The elemental composi-tion of kerogen, and the proportion of humic com-pounds in organic matter give valuable indications as

465

G. DEROO, J. P. HERBIN, J. ROUCACHE

to its origin; marine autochtonous versus continentaldetrital. Furthermore, humic compounds are well rep-resented in immature sediments while kerogen frac-tions are present in both immature and mature materi-als.

SAMPLINGThirty-two samples of some 10 grams each (5 to 20

g) were received from the cores of Sites 374, 375, 377,and 378 drilled during the Leg 42A of D.S.D.P. cruisein eastern Mediterranean Sea. They mainly belong toupper and middle Miocene while two have Plioceneages (Figure 1) according to the shipboard report,1975. Their updated stratigraphy and lithologic termi-nology are given on Table 1.

ANALYTICAL METHODSAs they were received, the 32 samples were freeze

dried. Then they were ground in an AUREC pulverizer(Grain size 90µ). The successive analytical processesare schematized on Figure 2. Organic carbon wasanalyzed with a LECO apparatus. A pyrolysis assay isapplied on raw samples as a method of source rockand maturation characterization (Espitalie et al., 1977).The method is deduced from kerogen experimentalstudies (Durand and Espitalie, 1973; Espitalie et al,

EASTERN MEDITERRANEAN

IONIANBASIN

3 7 4

MEDITERRANEAN CRETANRIDGE CLEFT BASIN

377 378

FLORENCERISE

375

£ 500-

800

Figure

r~7| Interbedded|X I lithologies

_r-rj Muds and• ÷M Mudstones

NannofossilOoze

Marls andMarlstones

I 9g9| Gypsum

AAAA Anhydrite

Dolomitic Mudsand Mudstones

Dolomitic Marlsand Marlstones

Dolomitic limestone

H Cored interval(11) Sampled Cores

1973; Tissot et al, 1974). Equivalent parts of groundsamples are extracted with chloroform and the extractsfractionated according to a method described in Hue etal. (1977). On the insoluble part of rock the totalhumic compounds are extracted and humic acids(H.A.) are separated from fulvic acids (F.A.) (Hue etal., in press). The new insoluble part corresponds tohumin and the non-hydrolysable fraction is the kero-gen (Durand et al., 1972; Robin et al., in press).Determination of organic carbon content from totalhumic compounds and from fulvic fraction is per-formed with a Carmnograph Wosthoff (MAJ) appa-ratus. Elemental analysis (C, H, O, N, S and Fe) andash content are measured on kerogen and calculatedon a mineral-free basis.

DETAILED RESULTS

Mineral Carbon (Table 1)There is a good agreement between the mineral

carbon data for analyzed samples and the petrographicdefinition of series used in the cruise report. Samples oflimestones from Site 374 close to the Miocene-Pliocenecontact have some 70 percent of carbonates and thecontent is clearly low for the Messinian evaporite levels

TABLE 1Location of Samples, Lithology and Age, and Carbon Data and

Pyrolysis Temperatures

800

1. Stratigraphic location of sites and samples.

Sample(Interval in cm)

37411, CCii, ce

17-1, 72-7819-1, 148-15020-1,2220-1,25-28

3773-2, 60-65

3788-2, 26-32

3755-2, 82-885-3, 02-045-4, 1506-2, 13-176-3, 45-4864 , 85-877-2, 105-1087-2, 138-1407-4, 26-287-6, 26-307-6, 54-578-1, 41448-2, 110-1138-3, 55-578-3, 128-1309-1, 05-079-1, 102-1069-2, 139-1429-3, 47-569-3, 53-579-3, 130-1339A, 16-209-5, 06-109-6, 24-28

DepthBelow

SeaFloor

(m)

381.5381.5

411.8419.5420.2420.3

259.1

225.3

362.3363364.5462.6464.4466.3567.5567.9569.8572.7573622.4624.6625.5626.3650.5651.5653.4654654654.8655.2656.6658.2

Lithologyand Age

Dolomite withsapropelitic layers(early Pliocene)Dolomitic mud-stone overlyinggypsum(Messinian)

Mudstone (mid-dle Miocene)

Nannofossilmarlstone (latePliocene)

Msrlstoπc(Tortonian)

.Msiistonc(Serravallian)

CaCOo(%)

6871

25341412

16

37

23305932263022211922231510

83127

928222310232427

OrganicCarbon (%)

BeforeHCC23

Extrac-tion

2.081.83

5.572.224.444.14

0.71

4.08

2.311.180.230.504.350.532.660.440.700.450.411.920.180.520.400.764.760.683.451.075.623.042.750.36

AfterHCCS3

Extrac-tion

1.951.91

4.661.914.123.50

0.70

3.96

2.301.180.190.474.310.472.540.460.710.430.402.000.220.480.400.694.100.623.820.975.063.152.800.36

Pyrol-ysis

Temper-ature(°C)

432439

430427433433

428

436

432434

412422432434437440

440

434440434444439424426426426

Note: Updated using Site Report data, Chapters 2 to 8.

466

ORGANIC GEOCHEMISTRY OF SOME NEOGENE CORES

GRINDFREEZE-DRIED

ROCK

Pyrolysis

Mineral andOrganicCarbons

HCCI3extraction

L_

Hand 0Indexes

Pyrolysis max.I temperature 'I 1

ROCKRESIDUE

soluble

HCChEXTRACT

NaOH (IN)Na4p2°7

Fractionatiqn(Thin layer or liquidchromatography)

soluble

HUMINin ROCKRESIDUE

HUMICCOMPOUNDS

NSOCOMPOUNDS

AROMATICHYDROCARBONS

SATURATED ANDUNSATURATED

HYDROCARBONS

rHCIand

HCI + HFOrganiccarbon

HCI(pH=2)

KEROGEN

1I

Elementalanalysis

J

HUMICACIDS(HA)

soluble

FULVICACIDS

(FA)

—

I GasI Chromatography

II I

"1l II Gas fI Chromatography I

I II J

Organiccarbon

Figure 2. Schematic analytical procedures.

467

G. DEROO, J. P. HERBIN, J. ROUCACHE

with a 12 to 25 and 34 percent range. The only samplefrom the middle Miocene mudstones of Site 377 was16 percent against 37 percent for the late Pliocenemarlstone sample of Site 378. In Site 375 the Tortonianmarlstones have a carbonate range between 19 to 32and 59 percent. The content is somewhat lower in theSerravallian marlstones with an 8 to 31 percent range.

Organic Carbon (Table 1)

In Site 374 the organic carbon content is relativelyimportant for both the Pliocene dolomite (around 2%)and the dolomitic mudstone in the Messinian below(1.91 to 4.66%) samples. The content is low for theMiocene sample of Site 377 (0.70%) and again higherfor the Pliocene sample of Site 378 (3.96%).

For the samples of Site 375 two groups of organiccontent, one above and one below 1 percent should beconsidered but their vertical distribution both in Torto-nian and Serravallian series is irregular (Figure 3).

Pyrolysis Assay and Organic MatterCharacterization (Figures 3 and 4)

The maximum of hydrocarbon production duringpyrolysis assays was reached at relatively low tempera-tures in the 412° to 444°C range for all the studiedsamples. This low temperatures range (Table 1) ischaracteristic of an immature stage of evolution.

The four samples in the Messinian evaporitic seriesof Site 374 (Figures 3, 4) can easily be distinguishedfrom the others. They belong to good potential sourcerocks of petroleum, close to the reference type 2

(Figure 4). Their hydrogen indexes of 265 to 335 mgof hydrocarbon compounds related to 1 g of organiccarbon can be compared with the 550-600 values forimmature material of type 2 which have the same lowoxygen indexes.

All the other samples of Site 374 and other sites(Figures 3, 4) reveal lower hydrogen indexes (less than198) and higher oxygen indexes.

The samples of Site 375 show a wide dispersion ofthe oxygen index (75 to 600) but the variation falls to75-250 if we only consider the samples with more than0.50% of organic carbon. They can be compared to thereference type 3 (Figure 4) but their relatively largevariation of the oxygen index (75 to 250) cannot beexplained by catagenetic effects.

The type 3 kerogens mainly correspond to higherplant detritus and humic continental matter. Theirpetroleum potential for oil is lower than for types 1and 2 even if their petroleum yield could be of thesame importance. The type 2 kerogens are common inmarine sediments. They are rich in saturated C-Hgroups and their potential for oil is good.

Study of Chloroformic Extracts

The six samples of Messinian to early Pliocene agefrom Site 374, the single sample from Site 378 plus theselected Serravallian samples from core 9 of Site 375provided some extract (7 to 188 mg). The middleMiocene sample of Site 377 and the Tortonian samplesfrom Site 375, i.e., the separate samples from Core 5and the two composite samples taken respectively fromCores 6 and 7 were devoid of extract (Table 2); the

SITE

378

375

CORE

and

SEC-

TION

ORG. CARBON

( % weight)

HYDROGEN INDEXmg hydroc. compounds

g. org. carbon

0 150 300 450 6OO

OXYGEN INDEX

mg. C02

g. org. carbon

100 200 300 400

DEPTHbelowseafloor(m)

381,5381.5411.8419.5420.2420.3

259 1

253.3

362.3363.0364.5426.6464.4466.3567.5567.9569.8572.7573.0

622 4624 6625.5626.3650.1651.5653.4654.06540654.86552656.66582

O 300•

O>-X

Typei

Type 2

II

! ! •11 19/1|

II

IIII

(47-56)9/1

(102-1061

•

•

o

*20/1

122)

Site

-

-

-

Cor

On,

374

375

377

378

β/sβction

rval, cm)

8/3(55-57)

v> Type 3 / r j ‰

(53-57)

8/3(128-130)

• 7/β •L7/2 (26-30) B/*~

(138-140) 9 < * - 1

150 200 250 300 350 400

OXYGEN INDEX (mg.C02/g.org.carbon)

Figure 3. Pyrolysis assays,to organic carbon).

Geochemical logs (data related Figure 4. Pyrolysis assays. Hydrogen and oxygen indexes(data related to organic carbon).

468

ORGANIC GEOCHEMISTRY OF SOME NEOGENE CORES

TABLE 2Chloroformic Extracts

Sample(Interval in cm)

374-11, CC11,CC17-1,72-7819-1, 148-15020-1, 2220-1,25-28

377-3-2, 60-65378-8-2, 26-32375-5-2, 82-88

5-3,02-045-4, 1506-2,13-17

to6-4,85-877-2,105-108

to7-6, 54-579-1,102-1069-3, 47-569-3,130-133

DepthBelow

SeaFloor(m)

381.5381.5411.8419.5420.2420.3259.1225.3362.3363.364.5462.6

to466.3567.5

to573.651.5654.654.8

HCCS3Extract(Weight

mg)

6.98.8

188.321.572.138.5

0.017.00.00.00.0

0.0

0.08.8

16.48.5

Extractto

RockRatio

(Weight%)

0.070.061.240.180.520.49

0.11

0.070.070.08

Extractto

OrganicRatio

Carbon(Weight)

0.0330.0320.2220.0810.1170.118

0.024

0.0180.0260.015

Thin LayerChromatography

NSOCom-

pounds(%)

83728584

76

416840

Hydro-carbon

FractionsAro Sat.(%) (%)

12 513 15

7 87 9

8 16

5 5417 152 58

latter samples of Cores 6 and 7 were grouped forstudying the HCC13 insoluble organic matter.

As the extract content was generally poor, fractiona-tion was performed using the thin layer chromatogra-phy (TLC) method. At this point of study it should benoted, the two Pliocene dolomite samples of Site 374were not fractionable because of insufficient material.The other extracts mainly correspond to NSO com-pounds and their hydrocarbon content is low (Table 2;Figures 5 and 6) as found for immature sediments.

The Messinian evaporite samples of Site 374 have amedium yield of extract (0.08 to 0.11 and 0.22, relatedto organic carbon) and fractions obtained with TLCpreparation revealed figures on thin layer preparationswhich were different from the usual hydrocarbonpatterns. The same was found for the late Pliocenesample of Site 378. All these were controlled with gaschromatography (GC) analysis upon the unsaturatedfractions. The chromatograms show peak distributionswith retention times quite different from those knownfor normal alkanes and isoprenoids. From a thermalevolution point of view, the above characteristicswould be typical of a diagenetic stage and not of acatagenetic one.

The three Serravallian samples selected for theirorganic carbon richness gave a low ratio of extract(0.015 to 0.026 versus organic carbon) but true hydro-carbon fractions were collected by TLC fractionation.They were confirmed with GC on the saturated frac-tion. On the chromatogram, besides the C1 5 to C3 1

normal alkanes and related isoprenoid distribution, ahump in the range of C29-C33 was present and didcorrespond mainly to unsaturated and saturated poly-cyclic compounds (Figure 7). The N-alkanes distribu-tion revealed an even-upon-odd predominance of C16-C 1 8 range. Besides a high odd-upon-even carbon num-ber predominance of n-alkanes from C2 1 or C2 3 to C3 1

was present (Figure 5). This predominance and theabundance of polycyclics in the C3 0 range would be

ORGANIC CARBON

(% weight)

1 2 3 4 5 6

EXTRACT

HCCI3

sxtrαct

Jlαible

extract

alaible

no extract

avalaible

AROMATICHC

\ HC

GC OF SATURATED HC

5 20 25 3 0 '

CARBON ATOM NUMBER

Figure 5. Site 375 organic carbon content. Gross composi-tion of chloroformic extracts and distribution of normalalkanes and isoprenoids.

indicative of an early stage of catagenesis compared tothe theoretically preceding stage of evolution, i.e., thelate step of the diagenesis. The large proportion ofC25+ odd normal alkanes would suggest an importantcontribution of higher plant waxes.

In the aromatic fraction, complex molecules with ahigh carbon number were largely present in the FIDaromatic chromatogram (Figure 8) for a compositesample of Site 375 Core 9. They would suggest a lowcatagenesis. The very poor distribution of thiopheniccompounds on the FPD chromatograms can also bementioned.

Study of Humic Compounds

First, some samples had to be combined to supplyenough material (50 to 100 g) to perform humic andkerogen analysis. For Site 374 one sample was acombination of the samples of the evaporitic Messinian(Cores 17 to 20). For Site 375 two samples fromTortonian Cores 5 to 7 were combined and anothercombination gathered some of the samples of Serraval-lian age from Core 9 (Table 3).

The sample from evaporitic series of Site 374 had avery poor content of humic compounds correspondingto 2.4 percent total organic carbon. As the other

469

G. DEROO, J. P. HERBIN, J. ROUCACHE

AROMATIC-LIKECOMPOUNDS

SITE 374" 375" 378

SATURATED-LIKECOMPOUNDS

(7O)A3O

NSOCOMPOUNDS

10070 60 50 40 30 20 10 0

Figure 6. Cross composition of chloroformic extracts.

Figure 8. Site 375. Extracts. Gas chromatography ofaromatic fraction (FID) and gas chromatography ofthiophenic compounds (FPD).

TABLE 3Humic Compounds and Carbon Organic Content

Sample(Interval in cm)

374-17-1,72-78to

20-1, 25-28375-5-2, 82-88

to6-4, 85-877-2,105-108

to7-6, 54-579-1,05-07

to9-6, 24-28

DepthBelow

SeaFloor(m)

411.8to

420.3362.3

to466.3567.5

to573.650.5

to658.2

TotalOrganicCarbon(Weight

%)

4.09

1.51

0.93

1.44

Carbon Content(% Total Organic Carbon)

HumicCom-

pounds(FA

+ HA)

2.42

70.86

30.68

29.23

FulvicAcids(FA)

0.97

10.26

8.58

4.58

HumicAcids(HA)

1.45

60.59

22.10

24.65

FA/HA

0.67

0.17

0.38

0.18

CORE 9section 1(W2-WScm)

CORE 9section 3(130-135 cm)

CORE 9sections 1 to 4

CARBON ATOM NUMBERS

Figure 7. Site 375. Extracts. Gas chromatography ofsaturated fraction.

characteristics such as pyrolysis and chloroformic ex-tracts correspond to a very immature material the lowcontent of humics could not be explained by an evolu-tion effect. This low content must reflect an organicmatter so well preserved during sedimentation andlater that no humic process was engaged.

At Site 375 the contents of humic material inTortonian samples were respectively 70 and 30 percenttotal organic carbon. It was close to 30 percent for theSerravallian sample but its fulvic acids (FA)-upon-humic-acids (HA) ratio was somewhat lower (0.18against 0.38) than for the nearest Tortonian sample(Table 3). Such a high proportion of humic material ina moderate evolutionary stage (end of diagenesis,beginning of catagenesis) is typical of continentaldetrital organic matter (Hue et al., 1977). Thus—in thesame manner as with the pyrolysis assays—humiccompound data suggest a major continental contribu-tion for the Tortonian and Serravallian analyzed sam-ples. For the Serravallian, the chloroformic extract andthe low FA/HA ratio would be indicative of a moreadvanced thermal evolution (early step of catagene-sis?) than that of the other mentioned samples studied.

Study of Kerogen

The four samples selected for humic analysis werethen used for a kerogen study. The elemental composi-tion of their kerogen fraction (Table 4) allows to

470

ORGANIC GEOCHEMISTRY OF SOME NEOGENE CORES

TABLE 4Elemental Analysis of Kerogens

DepthBelow

Sea Atomic AshesSamples Floor Weight Per Cent, on Ash Free Basis H / c Q / c ( W d g h t

(Interval in cm) (m) C H O S N (X 102) %)

374-17-1,72-78 411.8to to 62.55 7.72 10.92 16.97 1.85 1.48 13.09 9.46

20-1,25-28 420.3375-5-2,82-88 362.3

to to 41.31 5.37 25.06 27.06 1.19 1.56 45.50 50.056-4,85-87 466.37-2,105-108 567.5

to to 63.66 6.47 22.46 4.55 2.85 1.22 26.46 35.947-6,54-57 573.9-1,05-07 650.5to to 72.00 7.49 17.65 0.0 2.86 1.25 18.38 57.90

9-6,24-28 658.2

consider the H/C and O/C atomic ratios on a VanKrevelen diagram (Figure 9) in order to define thetypes of related organic matter (Tissot et al., 1974).

First the data of the Tortonian sample (Cores 5-6)from Site 375 should not be used because the elemen-tal analysis revealed an abnormally high content ofunexplained ashes (about 60% total ashes).

The sample from evaporitic series of Site 374 waslocated (Figure 9) halfway between the beginning ofpaths I and II. It would be compared with aliphatic-rich kerogens of types I and II which were commonlyfound in the organic matter of marine environments.

The two other samples from Site 375 belong, respec-tively, to the Tortonian (Core 7) and the Serravallian(Core 9). In the latter a high ash content which wasonly issued from pyrite (58%) could be noted. The tworelated kerogens had a lower H/C and a higher O/Catomic ratios (Figure 9) than the previous sample ofSite 374. They were located in the area between theorigin of paths II and III. So they would be composedof mixed continental and marine organic materials. Asfor the previous sample of Site 374 the vicinity of theorigin of paths would be indicative of a low evolution-ary range. However, it must be kept in mind that thekerogen of the two latter samples was not representa-tive of the entire organic matter because humic com-pounds and hydrolysable fractions were also present.

DISCUSSION AND CONCLUSIONSThe organic matter encountered in the Messinian

evaporitic levels of the Site 374 is of marine origin andthese would represent good potential oil source rocks.Their low level of evolution is attested by pyrolysisindices and kerogen data. It cannot account for theirpoor content of humic compounds so that poornessmust be related to an original absence of humicprocesses in evaporitic environments.

The organic content of all other samples studiedfrom Sites 374, 377, 378, and 375 would mainly bederived from continental sources. They show, frompyrolysis and chloroformic extract data, the charac-teristics of poorly evolved or immature material. Conti-nental input is confirmed for the Tortonian and Serra-

^ _ w _ • Direction of increasing evolution_ _ _ _ _ Domain of existence of kerogensTTT- I I I Evolution paths of kerogen types

Domain of existence of vitrinites• Site 374• Site 375

7/2-6 Core/sections

0.4 0 5

O/C ( ATOMIC RATIO )

Figure 9. Kerogens. H/C and O/C diagram.

vallian samples studied from Site 375 by a highcontent of humic compounds although the continentalmaterial was less abundant in their kerogen fraction.Higher plant characteristics were found in the saturatedfraction of the Serravallian extracts. These wouldrepresent a more advanced stage of evolution thanrevealed by the other extracts. Its stage would corre-spond to a late diagenesis or early catagenesis.

From these data, it appears that black sediments,even with a comparatively rich organic content mayhave a variety of origins. Some can be of a detritalorigin as in most of the samples studied from the upperMiocene. The term "sapropel" should be avoided forthat material and a stagnant environment would notnecessarily be inferred.

ACKOWLEDGMENTS

The authors are indebted to Dr. J. M. Hunt, Woods HoleOceanographic Institution, for comments and review of thepresent paper.

471

G. DEROO, J. P. HERBIN, J. ROUCACHE

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Durand, B. and Espitalie, J., 1973. Etude de la matièreorganique au cours de 1'enfouissement des sediments:C.R. Acad. Sci., Paris, v. 276, p. 2253-2256.

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Espitalie, J., Laparte, J.-L., Madec, N., Marquis, F., Leplat,P., Paulet, J., and Bautefeu, A., 1977. Methode rapide decaracterisation des caches mères de leur potential pétrolieret de leur degré devolution: Rev. Inst. Franc Pétrole, v.32, p. 23-42.

Hue, A. Y. and Durand, B., 1977. Occurrence and signifi-cance of humic acids in ancient sediments: Fuel, v. 56, p.73-80.

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Hue, A.Y., Durand, B., Monin, J.C., in press. Humic com-pounds and kerogens in cores from Black Sea sediments.Leg 42B-Sites 379A, 379B, and 38OA. In Ross, D.,Neprochnov, I., et al, Initial Reports of the Deep SeaDrilling Project, Volume 42B: (U.S. Government PrintingOffice), Washington

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