35. HUMIC COMPOUNDS AND KEROGENS IN CORES FROM BLACK SEA SEDIMENTS,LEG 42B — HOLES 379A, B, AND 380A

A.Y. Huc, B. Durand, and J.C. Monin, Institut Français du Pétrole, Division Géologie, France

ABSTRACTSamples from Sites 379 and 380 (DSDP Leg 42B) in the Black Sea

have been analyzed for their organic content. Subbottom depth ofsamples ranges from 4 meters to 621 meters at Site 379 (ages to600,000 years B.P.) and from 600 meters to 1063 meters at Site 380(ages from 750,000 to 3 × 106 years B.P. or more). The main organicfractions consist of humic compounds and of alkali-insolublematerial, called humin, including its non-hydrolyzable fraction,kerogen.

The genetic properties of humic acids show great variety in thesedimentary columns suggesting important changes in the input ofparental organic matter (autochthonous versus allochthonous [landderived] balance) during the course of sedimentation.

Moreover it is observed that organic matter changes as a functionof burial, i.e., we observe: a decrease in the hydrolyzable fraction, adecrease in humic compounds content, a decrease in proteinaceous-like material in humic acids (amide bond vibrations in IR spectradisappear with increasing sample depth) and a decrease in theoxygen content in the more autochthonous-derived humic acids,while the more land-derived humic acids undergo burial withoutsuch a decrease. This fact suggests various ways of oxygenincorporation in the different kinds of humic acids. All thesechanges lead the bulk of the organic matter towards the kerogenstatus as it is found in ancient sediments. As a result, from thecomparison between Sites 379 and 380 we might claim that kerogenformation has terminated at the deepest samples of Site 380, while itis still occurring at Site 379.

INTRODUCTION

Using previous research to compare the mainproperties of organic matter from both shallow youngsediments (buried at depths less than 10 m) and ancientsediments, great differences appear. In young deposits,besides a very low fraction of organic matter soluble inordinary organic solvents, alkali soluble organic matteris high in most cases (Rashid and King, 1970;Nissenbaum et al., 1972). The remaining insolublefraction (humin) cannot be studied with any validitybecause of the destruction of most of it during kerogenisolation using acids. On the other hand, in ancientsediments the extractability of organic matter by alkalisis low, and extractability by organic solvents which islow in the immature stage may be high in the cata-genetic stage. Here the insoluble organic matter ispractically not destroyed by kerogen isolation.Moreover, other differences occur in the properties ofthe organic matter. For instance, the oxygen content ofhumic acids is generally higher in young sedimentsthan in ancient ones.

Changes in sedimentary organic matter, leading fromyoung to older sediment status during the course of asedimentary cycle, previously have not been detectedbecause of a lack of sampling for geochemicalpurposes. However, these changes may be detectable in

long cores such as those obtained by the Deep SeaDrilling Project. The JOIDES project in the Black Seais well suited to such an attempt, which is outlined here.In this respect the humic compounds are considered tobe the most suitable fraction of the sedimentary organicmatter. They are obtained by a non-degradatingprocedure and are abundant in young sediments.Previous research has shown that they make up asubstantial fraction of the sedimentary organic matter(Hue and Durand, 1973; Hue and Durand, 1977).However, it should be noted that in sediments thedetrital input might imply the presence of evolved allo-chthonous organic matter which is derived fromweathering and erosion of more ancient sediments, or ofcrystalline and metamorphic rocks. This evolvedorganic matter may amount in some cases to a largeproportion of the total sedimentary organic matter(Debyser et al., in press). The methods used here do notprovide information about such a fraction. In thisrespect it would be worthwhile to complete the presentstudy by optical and electron diffraction analyses of theorganic matter.

SAMPLES

The samples were taken from Holes 379A, B and380A, which were drilled during DSDP Leg 42B, in the

737

A. Y. HUC, B. DURAND, J. C. MONIN

44"

42

40

1 ' 1

N

ROMANIA (

. • Λ

BULGARIA f\f^

J '

/ ~ " ' •%' .

>-

i

i

y *

/"

i

V 1

;;k.;

f

c1

"-

, '"> , ' \ ' "

i

; ' • ' ; . ' ; •• • ' Λ

T

U.

u

1s.

V

::•:.•;;••:

W

R

|

S.

• ,

/ - >

K

R

ry

1 1

_.

379A•

yft •>"**—»

HUMIC COMPOUNDS AND KEROGEN IN BLACK SEA SEDIMENT CORES

IFP SAMPLES

CORES'•'UNITS

IFP SAMPLES

CORES^UNITS

Q.

Q

50 A

100^

200 A

250 J

_L_

3

4

5

8

9

2021222324252627

—

*

3

3(

4

= 5 3E

1-125,000

I BP*

)0

50

400

6B

* A450

*7 son

2829

3435

363738393D:424344454647484950

54

550-

600-

IFP SAMPLES

C O R E S ^ UNITS

•+- +h5556575859

60

6164

666768

M M

• - • -

9

ft 600,000I BP

IFP SAMPLES

CORES^UNITS

IFP SAMPLES

CO RES'*'UNITS

HOLES 379A, B

-250,000BP

600 A

650 H

700 J

750 A

800 A

* *HUMIC COMPOUNDS ANDKEROGENS INVESTIGATIONS

850 A

303132333435363738394041424344454647484950515253545556

ft*••.- ••mm

*B3

900|~75O,OOU

I BPB4a

950

**

1000

*

1050

B4b

t

575859606162636465666768697071

737475767778

µ —

^B4c

*B4d

B5

~3x106

BPORMORE

HOLE 380A

Figure 2. Lithologic units and sampling.

1) Determination of soluble organic carbon inaliquot portions from total humic compounds solutionsand supernatant fulvic fractions is performed using aCarmograph Wosthoff apparatus.

2) Elemental analysis is performed by ATX(Suresnes, France), according to our indications. TheC, H, O, N, S (+ Fe in the case of kerogens), and ashcontents are measured on samples after drying at 80°C(HA) or 100°C (kerogens) in a vacuum. Calculationsfor corrected elemental analysis of kerogens on amineral-free basis are made, assuming Fe to belongentirely to FeS2 minerals and the organic matter to becomposed solely of C, H, O, N, and organic S.Accordingly, organic S is calculated by taking thedifference between total S and S from pyrite.

3) Infrared absorbance spectra with quantitativeinterpretation are recorded with a Beckman 42-40spectrometer. Kerogen or humic acids are dispersed ina KBr pellet, with a known concentration, pressedunder 8000 kg/cm2. In order to remove moisture, KBrpellets are stored 10 days in a dry atmosphere (Robinand Rouxhet, 1976). Absorbance of the differentbands is determined by planimetry of the areas shownin Figure 8. The absorption coefficient K is obtained byrelating the intensity to the effective concentration oforganic material in mg/cm2 (wave number ×absorbance unit × (mg × cim^XRobin et al., inpress).

RESULTS

Organic Carbon (100 samples)Organic carbon data are presented in Table 1 and

Figure 4. Most values are low and cannot be correlated

with stratigraphic units except with the "black varves"and "black shales" units where organic carbon contentsare the highest.

Mineral Carbon (100 samples)The values are presented in Table 1 and Figure 4. We

see no definite correlation between these data and thestratigraphic units.

Hydro lyzable Organic Carbon (52 samples)The hydrolyzable fraction of the organic carbon falls

in the 2%-43% range (Table 1). This fraction decreasesas a function of the depth of burial, and in samplesfrom Site 379 the rate of decrease is the highest during thefirt 250 meters. In deep samples from Hole 380A the con-centrations are low, i.e., 6%-2% (Figure 5).

Distribution of Analytical Fractions in Organic MatterThe organic substances soluble in CHCb amount to

l%-5% or the total organic substances in the sediments(21 samples), Figure 6. These values are practically thesame as those found in soils and other sediments (Hunt,1961). According to thin-layer chromatography (Hue etal., 1976), the polar compounds comprise about 70%-90% of the organic solvent-soluble substances.

Humic compounds extractable with alkalis rangebetween 6.0% and 29.1% of the total organic substances(Table 2, Figure 6); in samples from Site 380, theconcentrations are lower than those from Site 379.Moreover the FA content appears to decreaseprogressively as a function of depth of burial and,except for Section 31-3, the FA/HA ratios are higher inshallow samples (1-4; 5-3; 8-3; 28-5).

739

A. Y. HUC, B. DURAND, J. C. MONIN

TABLE 1Data on Samples From Holes 37 9A, 37 9B, and 380A (organiccarbon, hydrolyzable organic carbon as % of the total organic

carbon, mineral carbon)

TABLE 1 - Continued

FragmentCore Section (IFP)

Depth(m)

Org. C Min. C Hydr. C

Core SectionFragment

(IFP)Depth

(m)Org. C Min. C Hydr. C

Hole 379B

89

Hole 379A

20

20

202123252627282930313234

3434

237414543620

03

343536373839404243

45464748495051515152535454

CC45274544

33512205

CC2200

4.5

49.777.8

133.7

134.3149.5

179.6

179.6

181.2190.7216.0230.2236.6249.2260.3268.2277.7290.4295.2311.0

311.0314.2

320.5327.6336.3342.7358.5364.8374.3382.2393.3

409.2418.7432.9434.5445.6455.1463.0470.9472.5474.1485.2491.5

0.410.420.460.450.480.170.590.440.400.430.420.410.410.70

0.540.540.510.490.520.410.450.720.360.440.540.590.960.390.320.770.750.760.800.590.450.630.560.610.500.280.650.370.320.380.250.580.250.210.250.260.240.250.330.260.430.480.280.330.300.350.490.290.520.430.430.41

2.882.982.622.782.761.621.482.542.622.162.362.542.820.70

2.842.642.902.902.791.243.122.043.243.102.843.043.122.303.303.402.822.902.502.903.523.744.143.143.922.703.023.422.842.263.283.442.983.243.202.903.123.143.243.063.162.322.922.602.842.223.643.443.763.843.843.60

43.

41.20.

32.36.

29.27.31.14.25.27.32.22.22.26.27.

26.29.20.31.22.28.28.20.

22.21.20.15.24.28.25.26.24.24.22.

Hole 379A Continued

545556575859606264656667

336634534331

68 4

Hole 380A

31 3

41414242465763737678

0CC0

CC1

CC1436

496.2505.7520.0529.5532.7543.7554.8564.7583.3591.2599.2607.1

621.3

612.7

703.0712-5718.5722.0750.5864.591210131040.01063

0.410.420.510.410.300.630.750.290.450.330.250.340.520.410.470.330.180.420.30

0.770.580.530.630.592.201.711.321.962.263.261.801.701.142.20

3.953.424.003.803.123.084.824.483.523.463.262.806.583.803.022.161.883.603.28

1.281.621.681.360.670.370.390.301.541.102.201.411.621.281.17

23.

21.15.21.16.25.21.25.29

17.

21.

11.18.19.12.16.10.76

12.12.

"Humin," or the organic substances remaining afteralkali treatment, ranges between 70% and 94% of thetotal organic substances. The organic matter lostduring kerogen isolation is close to that obtained byhydrolysis of the humin (6N HCl)(Table 3).

Properties of Humic Acids—Elemental CompositionThe results of elemental analysis of humic acids from

Sites 379 and 380 are given in Table 4. The data areplotted in a Van Krevelen diagram (H/C versus O/C)together with data from humic acids from variousknown sources (Figure 7). Site 379 and Site 380 plotsappear to be very scattered in this frame. This suggestsdiversity in the nature and origin of the humic acids inthese sedimentary columns. However the properties ofthese compounds cannot be correlated withstratigraphic units. We can see that O/C values aregenerally lower at Site 380 than at Site 379. The resultsof elemental analysis of hydrolyzed humic acids aregiven in Table 5. After hydrolysis O/C ratios becomevery close to each other for all samples. H/C ratiosfollow this trend to uniformization, but it remains asignificative difference between samples.

Properties of Humic Acids in Infrared SpectroscopyThe absorption spectra of humic acids (Figure 8)

show bands in the regions of: 2700-3400 cm~'(H bonded

740

HUMIC COMPOUNDS AND KEROGEN IN BLACK SEA SEDIMENT CORES

CRUSHEDFREEZE-DRIED

SEDIMENT

HYDROLYSIS

HYDROLYZABLEORGANIC CARB.

MINERAL andORG. CARB.

p INSOLUBLE

RESIDUE

NaOHO.IN+Na 4 P 2 O 7

SOLUBLE mm

EXTRACT

SOLUBLE

HUMICCOMPOUNDS

PH2(HCI)

SOLUBLE • * INSOLUBLE

FULVIC ACIDS(FA)

HUMIC ACIDS(HA)

RESIDUE"HUMIN"

HCI4N70° C

HCI4NHF40%

(1/3-2/3)

KEROGEN(KB)

KEROGEN(KC)

EXTRACT

Figure 3. Flow diagram for analytical procedure.

HOLES 379A, B

ORGANIC CARBON

0 1 2 3

MINERAL CARBON

0

100

200

300

400 ^

500

600-

• > *

;*••

.•v

W- 0 2 4 6 9

• 4 -―*•

— 5 —— 6 —

— 7 —

_ . -

— 9 —

•

•yf•

HOLE 380A

ORGANIC CARBON MINERAL CARBONunits

0 1 2 3 % 0 2 4 6 %

500-

600-

700-

800-

900-

1000-

1100-

- B 3 —

- B4 —

— B 5 ^

HOLES379A,

0 50

U f

100-

200-

300-

400-

500-

600-

1* I

I

B

100%

600-

700-

800-

900-

1000-

1100-

HOLE 380A

0 50 100%

«

•

t

Figure 5. Variations in the hydrolyzable organic carbonfraction versus depth of burial.

HOLES 379A, B

I

0 0.05 0.1g0

0-

100-

200-

300-

400-

500-

600-

CD FA

• l HA?Zft HUMIN

HOLE 380A

I CHLOROFORM EXTRACT:g/g of total org. carbon 800-

HUMIC COMPOUNDS:g of humic carbon/g of total org. carb.

900-

1100-

0 0.05 0.1g0 0.05 ig= ^ —

—

-

•Figure 4. Organic and mineral carbon data.

Figure 6. Distribution of analytical fractions in organicmatter.

741

A. Y. HUC, B. DURAND, J. C. MONIN

TABLE 2Humic Compound Contentsa

TABLE 4Elemental Analysis of Humic Acids

Core-Section

TotalOrganicCarbon

HumicCompound(% of total

Org. C) FA/HA

FA(% of total

Org. C)

HA(% of total

Org. C)Core-

Section

Elemental Analysis

H 0 N

Atomic Ratios

0/C N/C

H/C X 102 X 102

Hole 379B

1-41 45-38-3

Hole 379A

20-228.532-234-CC42451-067-1

Hole 3 80A

31-341-041-346-157-CC63-173-4

76-3

0.410.460.590.44

0.540.540.320.500.580.300.47

0.772.201.712.263.26i onl . o U

1.701.14

28.624.025.419.7

28.029.629.126.121.023.528.6

7.813.411.7

9.86.0A 1

4. /10.419.6

0.600.671.381.03

0.470.620.380.450.350.480.27

1.160.390.350.370.46r\ c i

U.M0.180.44

10.79.6

14.710.0

9.011.3

7.98.24.97.76.0

4.23.73.12.61.9i r1.01.65.9

17.914.410.79.7

19.018.321.217.916.115.822.6

3.69.78.67.24.1i 13.18.8

13.7

Hole 379B

1 41-45-384

Hole 379A

20-228-532-234-CC4 2 451-067-1

Hole 380A

31-341-041-346-157-CC63-173476-3

56.8757.4054.0056.89

56.4656.3953.9455.6656.3954.8360.50

57.9261.2360.5661.8562.3262.0459.8261.58

5.085.285.225.05

4.005.424.434.895.534.365.51

4.404.764.755.706.465.355.165.02

32.1331.2931.7832.34

33.9831.6833.9733.0032.1034.8428.49

32.0528.2328.9526.6924.4526.7328.4027.48

3.863.993.423.74

3.255.263.113.563.323.513.00

3.254.093.773.983.332.513.082.75

2.052.045.581.98

2.301.254.552.902.662.462.50

2.381.681.961.783.443.383.553.17

1.07

1.101.161.06

0.851.150.991.051.180.951.09

0.910.930.941.111.241.031.030.98

42.37

40.8944.1342.63

45.1442.1347.2344.4742.7047.6635.31

41.5034.5835.8532.3729.4232.3135.6033.47

5.82

5.965.425.64

4.948.004.945.485.045.484.25

4.815.725.345.524.583.474.483.83

aFA fulvic acids carbon; HA = humic acids carbon.

TABLE 3Hydrolyzable Proportion of Humic Acids and Humins

Core-Section

Hole 379B

1 4145-38-3

Hole 379A

20-232-234, CC4 2 451-067-1

Hole 380A

31-341-041-346-157, CC76-3

TotalHydrolyzable

OrganicCarbon (%)

43392437

282726202529

211118161012

HydrolyzableHumic

Carbon (%)

131612-

510

8923

0_0020

HydrolyzableHum in

Carbon (%)

363623

302825232728

18

21131314

Loss ofOrganic CarbonDuring Kerogen

Isolation (%)

37363135

323531283927

13172413

111

OH) including two broads bands: around 3200 cm and2600 cm-1 (acidic OH); 2920 cm"1 (aliphatic C-Hstretching from CH2 and CH3);1720 cm-

1 (C = Ostretching from COOH, COOR and ketonic C = O);1630 cm~1 (aromatic C = C; olefinic C = C; quinonic C= O); 1455 cπr1 (CH deformation from CH2 and CHa);1375 cm-1 (CH deformation from CH3); 1040 cm"

1 (C-O of polysaccharide-like substances); however SiO may

be responsible for absorption near 1000 cm"1 andaccordingly the assignment to carbohydrates must beassumed with care in humic acids with high ashcontent. This band disappears in hydrolysis residues(Figure 12) when it is really related to carbohydrates.

The spectra of the near sea-bottom humic acids showadditional absorption bands due to peptide linkages,i.e., 1650 cm"1 (amide C = O) which may shift themaximum of the 1630 cm band, and 1540 cm'1 (amideNH + CN) (Bellamy, 1958; Stevenson and Goth, 1971;Ishiwatari, 1967; Robin et al., in press).

Infrared spectra of humic acids from Sites 379 and380 are shown in Figures 9 and 10. For comparativepurposes, quantitative data on the absorption bandsare given in Table 6, including K3400, K2920, K1720,K1630, K1540, and K1375/K1455. The ratioK1375/K1455 provides an estimate of the ratioCH3/CH2 + CH3. There is a reverse relationship betweenthis ratio and the intensity values of K2920 of CH groupsgiven by K2920 (Figure 14). The infrared spectra show greatvariety in their main features, especially in the saturated C-Hvalues (Table 6), which is in good agreement with the H/Cratio values (Figure 11).

We can also observe the occurrence of the absorptionbands assigned to peptide linkages (1650 cm~1 and 1540cm-1) in humic acids associated with shallow samples(1-4 [a], 1-4 [c], 5-3) and their disappearance as afunction of depth (Table 6).

Properties of Kerogens

Nineteen kerogens were isolated, but only 11 wereanalyzed because of the high ash content (>40%) of theother eight. The loss of organic matter during theisolation of kerogen or during óiVHCl hydrolysis of thehumin is higher than the loss of organic matter during67V HC1 hydrolysis of the humic acids (Table 3).

742

HUMIC COMPOUNDS AND KEROGEN IN BLACK SEA SEDIMENT CORES

1.5

I.U

0.5

n

PARIS BASIN(Lower Toarcian)

\SI

;N Δ

Λ Δ

^ *•

^7

Λ •

.6b

DOUALA BASIN(Upper Cretaceous)

•

AUTOCHTHONOUS ORGANIC MATTER INPUT• Kerguelen IslandA Aiguillon BayT Bourgneuf Bay• Black Sea (Atlantis 1 )

DETRITAL ORGANIC MATTER INPUT(• Guinea Gulf)

O HOLES 379A, B

Δ HOLE 380A

0.2 0.4 0.6 0.8

O/C

Figure 7. H/C versus O/C diagram - humic acids from Sites 379 and 380 compared withhumic acids from various origins.

TABLE 5Elemental Analysis of Hydrolyzed Humic Acids

Core-Section C

Elemental

H O N S

Atomic Ratios

O/C

H/C X 102N/C

X 102

Hole 379B

1-41-45-3

Hole 379A

63.7463.5562.99

20-2 57.7132-2 60.0534, CC 63.0842-451-067-1

Hole 380A

31-3

41-346-157, CC76-3

65.2058.9262.70

60.9762.2564.0265.8862.04

4.845.085.06

3.674.334.735.194.195.40

4.024.635.286.064.73

26.9625.8425.06

31.3929.2425.7523.5830.0925.33

30.0025.2924.0421.0324.02

2.912.772.39

2.642.673.053.032.822.94

2.803.363.982.912.19

1.562.764.50

4.603.713.333.003.983.63

2.224.472.684.127.01

0.91 31.72 3.910.96 30.50 3.740.96 29.84 3.26

0.760.870.910.960.851.03

0.790.890.991.100.92

40.7936.5330.6227.1338.3030.30

36.9130.4728.1723.9529.04

3.923.814.153.984.104.02

3.934.635.333.793.02

Data on elemental composition of kerogens arerecorded in Table 7 and plotted in a H/C versus O/Cdiagram (Figure 12).

In many cases, by reason of an important amount ofashes, the infrared spectra of kerogens with high ashcontents are unreliable. However when elementalanalysis shows a low ash content infrared spectra weresuccessfully recorded. In these cases, by comparisonwith humic acids and hydrolyzed humic acids thefollowing observations were made (Figure 13):

1) The peaks around 2900 cm"1 are similar in humicacids, hydrolysis residue, and kerogen.

2) The peaks at 1720 cm"1 and 1630 cm~1 are alwayssmaller in kerogen.

3) The region 1200-1300 cm-1, assigned to several -C-O- bands (acids, phenols, aromatic ethers) is alwayssmaller in kerogen.

Aromatic C=CQuinonic C=OOlefinic C=C

WAVE NUMBER

Figure 8, Infrared spectrum of sedimentary humic acids,assignment of bands.

4) The region 1370-1460 cm~1, shows an interestingdifference: in kerogen the band around 1455 cm~1 isrelatively higher than the band around 1375 cm"1.Hence the ratio CH3/CH2 +CH3 tentatively providedby the ratio K1375/K1455, which is shown in Figure14, is higher in humic acids and hydrolysis residue thanin related kerogen.

DISCUSSION

Nature of Organic Matter

Previous research has pointed out that in recent andancient sediments the properties of humic acids wererelated to the nature of parent organic matter (Hue etal., 1974; Hue and Durand, 1977). In a gen-eral way two extreme types can be distinguished.Parent organic matter derived largely from land-plant,has high humic acid extratibility, and the humic acidsare hydrogen poor, which is related to a low H/C ratioand a low intensity of CH groups in infrared spectra. Soare the humic acids which are isolated from sedimentstaken from the Gulf of Guinea (Hue and Durand,

743

A. Y. HUC, B. DURAND, J. C. MONIN

42-4

51-0

67-1

3600 2800 2000 1600 1200 3600 2800 2000 1600 1200 3600 2800 2000 1600 1200

WAVE NUMBER CM-1

Figure 9. Infrared spectra of humic acids from Site 379.

1973), deposited in a deltaic environment (Klingebiel etal., 1975), and from an Upper Cretaceous series fromthe Douala Basin (Hue and Durand, 1977) deposited in adetrital environment (Dunoyer de Segonzac, 1969).

On the other hand, organic matter which is devoid ofproducts derived from land plants has lower humicacids extractibility, and the humic acids are hydrogenrich, which is related to high H/C ratio and highabsorbance of CH groups in infrared spectra. Thisoccurs in humic acids from Aiguillon Bay (Hue, 1973),Bourgneuf Bay (Debyser et al., 1975), young BlackSea sediments (Debyser and Pelet, in preparation),Kerguelen Island, and Toarcian shales from the ParisBasin (Tissot et al., 1971; Hue and Durand, 1977). In thesecases the parent organic material is mainly marine organism,i.e., diatoms are the main organic source in Aiguillon Bayand Bourgeuf Bay (Gouleau, 1975). Algae have beenrecognized to amount to as much as two-thirds of thesedimentary organic material in the Black Sea Basin(Shimkus and Trimonis, 1974). Bethic algae are the solesource in the Kerguelen Island sample (Debyser et al.,1977). (Figure 15).

Thus H/C ratio and intensity of C-H bands frominfrared spectra of humic acids can be used in thisrespect to make some distinctions between their parentorganic matter. These parameters reveal variations inthe nature of the organic matter input during the courseof sedimentation (Figure 11). We deduce from lowvalues of H/C and of intensity of CH infrared bandsthat the organic matter input is more allochthonous;higher values are related to more autochthonousorganic matter input. However, we must keep in mindthat the balance of the allochthonous-autochtonouscontribution to the humic acids obviously does notcorrelate with the stratigraphic units as previouslydescribed in the shipboard report.

Transformation of Organic Matter With Depth

We can follow the transformation of sedimentaryorganic matter during approximately 3 × 106 years: 0-

600, 000 B.P. at Site 379 and 750,000-3 × 106 years B.P.at Site 380 (according to data from the shipboardreport). {Ed. comment: base of Site 380 may be upperMiocene or about 5 X 106 B.P.)

The decrease in the hydrolyzable fraction of totalorganic matter, humic acids and humins occurs as afunction of depth of burial within the cores studied.These observations agree to some extent with theresults noted in short cores by Bordovskiy (1965) inBering Sea sediments and by Hue and Durand (1973) inGulf of Guinea sediments. In Site 379 and 380sediments, this trend is observed for the first time over alarge depth range (0-1000 m). This indicates thatstructural changes occur at depth in the organic matter,leading it towards a resistant status.

We can see a decrease in the FA content and inFA/HA ratio between near sea-bottom samples andthe deeper ones. In the case of soils, these valuesdecrease with the increasing degree of humification.Moreover, the obvious decrease in the humic-compounds content from Site 379 to the older Site 380might be connected to changes in the organic matterlosing hydrophilic groups, hence its extractability bydiluted alkali solutions.

The rapid decrease and disappearance ofproteinaceous-like material associated with humicacids, as inferred from the decrease in IR absorptionbands at 1650 cm~1 and 1540 cm-1, agrees with theobservations made by Ishiwatari (1972) on humic acidsfrom Japanese lakes and from Sea of Japan and by Hueand Durand (1973) on humic acids from the Gulf ofGuinea.

From the Van Krevelen diagram it appears that theO/C ratio in humic acids is, as a mean, lower in deepersamples from Sites 379 and 380. This result wasexpected from the comparison between humic acids ofancient and recent sediments (Figure 7) (Hue andDurand, 1977). The samples from Leg 42B fill thegap between recently deposited and ancient organicmatter (commonly sampled in petroleum prospects).Moreover it is interesting to see that as the H/C ratio

744

HUMIC COMPOUNDS AND KEROGEN IN BLACK SEA SEDIMENT CORES

TABLE 6Infrared Absorption Measurements K3400,

K2920, K1720, K1630, K1540, andK1375/K1455 of Humic Acids (infrared units)

3600 2800 2000 1600 1200 800

,-1WAVE NUMBER CM"

Figure 10. Infrared spectra of humic acids from Site380.

is high, the O/C ration decreases more easily. This mightmean that at these stages of evolution in the O/C decrease ismore important in autochthonous organic matter than inland-derived organic matter. We are inclined to considerthat, in humic acids from autochthonous material, the oxy-gen might be included in the molecule as a labile form, withrespect to their evolution in this early diagenesis. In land-derived humic acids, oxygen is more firmly incorporated inthe structure.

Formation of Kerogen

The kerogen in a sedimentary rock can beanalytically defined as the insoluble organic matter

Core-Section

Hole 379B

1 41-45-38-3

Hole 379A

20-228-532-234, CC42-451-067-1

Hole 380A

31-341-041-346-157, CC63-17 3 476-3

K2920

20.428.426.623.5

11.732.416.622.428.617.729.1

17.423.925.028.536.930.025.323.1

K1720

46.153.145.150.1

53.157.049.850.144.552.549.6

53.952.947.545.541.553.749.153.6

K1630

50.549.239.952.6

51.646.644.545.941.447.339.2

46.551.052.649.031.839.146.345.7

K1540

3.12.41.4-

——_—-

———_——-

K1375/K1455

2.101.471.671.65

2.951.831.922.581.841.681.69

2.501.301.841.750.981.381.181.02

Note: Absorption measurement K is obtained by relatingthe intensity (planimetered absorbance peak areas) tothe effective concentration of organic material inmg/cm : [(wave number X absorbance unit X (mg Xcm2)'1)].

remaining after destruction of the mineral material byhydrochloric and hydrofluoric acids. In ancientsediment this procedure ineffectively degrades organicmatter, and the resulting kerogen is representative ofthe insoluble part of the organic matter. On the otherhand, in young deposits, the insoluble organic matter,called humin, is easily hydrolyzable and the remainingkerogen represents only a fraction of it. Hence, naturalevolution leads from a kerogen poorly representative ofthe bulk of the insoluble organic matter towards arepresentative kerogen. This might explain the differentkerogen locations (between Site 379 and Site 380) in aVan Krevelen Diagram (Figure 13). It would beworthwhile to study the hydrolyzable fraction of theorganic matter. This investigation is not easy withpresent analytical procedures. However, this fraction isof interest because of its behavior, i.e., it seems to beincorporated into kerogen through natural evolution.

CONCLUSIONIn spite of a possible contribution of evolved detrital

organic matter by detrital input that may causescattering in the results, this study reveals someinteresting trends as follows:

1) The differences in humic acids properties in thesedimentary column suggest that organic matter inputsand prevailing sedimentary environments have beenchanging during the last 3 million or 5 million years in

745

A. Y. HUC, B. DURAND, J. C. MONIN

10 20 30

HOLES 379A, B

HOLE 380A

I H/C (atomic ratio)

10 20 30

Figure 11. Variations in H/C ratio and absorption measurement K 2920 cm~* values.

TABLE 7Elemental Analysis of Kerogens

Core-Section

Hole 379B

L-41-4

Hole 379A

32-234, CC42-451-067-1

Hole 3 80A

41-041-346-157, CC

l a

41.6442.82

41.3746.1946.5341.5043.82

60.1260.9851.0448.77

C

2 b

67.1064.99

68.6067.1567.5268.0165.73

69.0769.7970.4968.66

AtomicRatio(H/C)

0.931.04

0.810.991.040.821.07

1.271.261.301.38

AtomicRatio(o/ç

X102)

22.2822.63

22.3223.8222.3424.4226.40

19.2218.6618.8818.19

AtomicRatio(N/C

X102)

3.443.26

2.593.192.032.562.61

3.053.173.442.92

AtomicRatio

(Sorg/CX102)

2.854.20

2.321.942.721.741.86

1.901.590.682.44

Minerals

Pyrite

11.0111.46

3.964.59

10.352.27

21.75

10.017.46

23.5125.65

Others

26.9322.65

35.8526.6320.7436.7110.62

2.825.174.013.06

aOrganic carbon content.Organic carbon content on a mineral-free basis.

the Black Sea Basin, i.e., more terrestrial organicmatter inputs alternate with more autochthonousinputs.

2) Organic matter has undergone transformation asa function of burial, especially as inferred by a decreasein the hydrolyzable portion of the organic mattertowards a more resistant material. This is accompaniedby a decrease in the fulvic-acid fraction, suggesting ahumification process, and by an overall decrease inhumic compounds suggesting changes in thehydrophylic functions responsible for the extractability.

3) Specific transformations might be related to thedifferent kinds of organic matter. Terrestrial-derivedorganic matter can undergo burial with fewtransformations, but in the more autochthonousorganic matter we observe a decrease in the oxygencontent as a function of evolution. This fact suggeststhat a large proportion of the oxygen associated withthe latter is included as labile groups.

4) All these changes lead the bulk of the organicmatter towards the kerogen status that is found inancient sediments.

From this point of view we might claim that theforming of kerogen is over in Site 380, while it is stilloccurring in the core from Site 379.

REFERENCESBordovskiy, O.K., 1965. Accumulation and transformation

of organic substance in marine sediments: Marine Geol.,v. 3, p. 3-114.

Bellamy, L.J., 1958. The infrared spectra of complexmolecules, 2nd Ed.: New York (John Wiley).

Debyser, Y. and Pelet, R., in preparation. More organicgeochemistry in Black Sea sediments.

Debyser, Y., Leblond, C , Dastillung, M., and Gudel, F., 1977.Etude géochimique de sediments Marins et lacustres: Advancesin organic géochem.

Debyser, Y., Pelet, R., and Dastillung, M., 1975.Géochimie organique de sediments marins récents: MerNoire, Baltique, Atlantique (Mauritanie): Adv. in Org.Geochem.

Dunoyer de Segonzac, G., 1969. Les minéraux argileux dansla diagenèse. Passage au métamorphisme: Thesis, U. ofStrasbourg.

746

o/c

Figure 12. H/C versus O/C diagram - kerogens and associ-ated humic acids.

Durand, B., Espitalié, J., Nicaise, G. and Combaz, A., 1972.Contribution à 1'etude de la matière organique insoluble dessédimets anciens (kéroghes) par différentes méthodes physico-chiminques (Ire partie): Rev. Inst. Franc, du Pétrole, v. 27. p.865-884.

379, 20-2

HUMIC COMPOUNDS AND KEROGEN IN BLACK SEA SEDIMENT CORES

Gouleau, D., 1975. Les premiers stades de la sedimentationsur les vasières littorales: Thesis, U. of Nantes.

Hue, A.Y., 1973. Contribution à 1'étude de 1'humus marin etde ses relations avec les kérogènes: Thesis, U. of Nancy.

Hue, A.Y. and Durand, B., 1973. Etude des acides humiqueset de 1'humine de sediments récents considérés commeprécurseurs des kérogènes: Adv. in Org. Geochem., p. 53-72.

, 1977. Occurrence and significance ofhumic acids inancient sediments: Fuel, v. 56, p. 73-80.

Hue, A.Y., Durand, B., and Jacquin, F., 1974.Caractérisation des acides humiques de sediments marinsrécents et comparaison avec leurs homologues terrestres:Bull. ENSAIA, Nancy, v. 16, p. 59-75.

Hue, A.Y., Roucaché, J., Bernon, M., Caulet, G. and DaSilva, M., 1976. Application de la chromatographie sur couchemince à l'étude quantitative et qualitative des extraits deroches et des huiles: Rev. Inst. Franc, du Pétrole, v. 31, p.67-98.

Hunt, J., 1961. Distribution of hydrocarbons in sedimentaryrocks: Geochim. Cosmochim. Acta, v. 22, p. 37-49.

Ishiwarati, R., 1967. Infrared Absorption band at 1540 cm-1of humic acids from a Recent lake sediment: Geochem. J.Japan, v. 1, p. 61-70.

, 1972. Transformation of sedimentary humic acids,facts and speculations: Int. Meet. Humic Substances Proc,Nieuwersluis Pudoc. Wagening en.

Klingebiel, A., Boltenhagen, C, Caratini, C, Debyser, Y.,Delteil, J.R., Durand, B., Etienne, J., Hue, A.Y.,Latouche, C, Millepieds, P., Parra, M., Pujol, C, Sauvan,P., and Sommer, F., 1975. Etudes stratigraphique,sédimentologique et géochimique de sediments carottés

379, 42-4 380, 57, CC

3600 2800 2000 1600 1200 3600 2800 2000 1600 1200

— WAVE NUMBER CM'1 -

3600 2800 2000 1600 1200

a: Humic acids b: Hydrolyzed humic acids c: Kerogen

Figure 13. Infrared spectra ofhumic acids, hydrolyzed humic acids, and related kerogens.

747

A. Y. HUC, B. DURAND, J. C. MONIN

30 -

20 -

10 -

A\

\

\

\

1

A

k

\

\

\ \A \A

\

\\

\

\

A

Site 379 #

Site 380 •

\

\\

# \

K1375cm'

K1455cm•

Figure 14. Relationship between absorption measurementK 2920 cm-i and K 1375/K 1455 ratio in humic acidsfrom Sites 379 and 380.

o•z.<COccOCOGO<

3600

dans le Golfe de Guinée au cours de la campagne Benin1971: Bull. Inst. Géol. Bassin Aquitaine, v. 17, p. 101-232.

Kononova, M.M. and Bel'Chikova, N.P., 1960. A study ofsoil humus substances by fractionation: Pochvovedeniye,v. 11, p. 1.

Nissenbaum, A., Baedecker, M.J., and Kaplan, R., 1972.Organic Geochemistry of Dead Sea Sediments: Geochim.Cosmochim. Acta, v. 36, p. 709-727.

Rashid, M.A. and King, L.H., 1970. Major oxygencontaining functional groups in humic and fulvic acidfractions isolated from contrasting marine environments:Geochim. Cosmochim. Acta, v. 34, p. 193-201.

Robin, P.L. and Rouxhet, P.G., 1976. Contribution of molecµlarwater in the infrared spectra of kerogen and coals: Fuel, v. 55,p. 177-183.

Robin, P.L., Rouxhet, P.G., and Durand, B., in press.Caractérisation des kérogènes et de leur evolution parspectroscopie infra rouge: Adv. in Org. Geochem.

Stevenson, F.J. and Goth, K.M., 1971. Infrared spectra ofhumic acids and related substances : Geochim.Cosmochim. Acta, v. 35, p. 471-483.

Shimkus, K.M. and Trimonis, E.S., 1974. Modernsedimentation in the Black Sea. In Degens, E.T., Ross,D.A. (Eds.), The Black Sea—geology, chemistry andbiology: Am. Assoc. Petrol. Geol. Mem. 20.

Tissot, B., Califet-Debyser, Y., Deroo, G., and Oudin, J.L.,1971. Origin and evolution of hydrocarbons in earlyToarcian shales: France (Paris Basin), Bull. Am. Assoc. Petrol.Geol., v. 55, p. 2177.

2800 2000 1600 1200 3600

WAVE NUMBER CM'1 •

2800 2000 1600 1200

Figure 15. Infrared spectra ofhumic acids from Sites 379 and 380, comparison with humic acids from well-known depositi-tional environments.

748