29. GEOCHEMICAL AND OPTICAL STUDY OF ORGANIC MATTER IN SOME PLEISTOCENEAND PLIOCENE SEDIMENT FROM THE GULF OF CALIFORNIA: LEG 64, HOLES 474 TO 481A1

G. Deroo, J. P. Herbin, J. Roucaché, and J. P. Boudou, Institut Français du Pétrole,Syntheses Géologiques et Géochimie, Rueil-Malmaison, France

andP. Robert, S. Jardiné, and P. Marestang, Societé Nationale Elf-Aquitaine,

Centre Recherches Boussens, Saint-Martory, France

ABSTRACT

Pleisto-Pliocene hemipelagic and diatomaceous mud was recovered from Deep Sea Drilling Project (DSDP) Sites474 through 481 in the Gulf of California. The organic matter is mostly marine and mainly derived from diatomaceousprotoplasm. We found some continental organic matter in sediments near the bottom basalts or near dolerites (Holes474A and 478). The organic matter in most of the samples is in an early stage of evolution.

INTRODUCTION

This chapter describes geochemical analyses of or-ganic matter in the Pleisto-Pliocene sediment in DSDPHoles 474A, 475, 476, 478, 479, and 481-481A abovebasalt or dolerite sills. We describe a pyrolysis assay anda humic extraction of eight samples, mostly from Hole479. We performed both procedures before preparingand analyzing the samples for kerogen. We conductedan optical study on the same material. The applicationof reflected light and fluorescence to the whole rock pro-duced no chemical effects. We also conducted a palyno-logical examination of acid-treated samples.

SAMPLESIn the Cabo San Lucas area, we recovered nine Pleis-

tocene-to-early Pliocene samples from Holes 474A, 475,and 479. The sediment from Hole 474A comprises turbi-dite, silt, and claystone. Hole 475 and Hole 476 arecomposed of hemipelagic and diatomaceous mud.

In the Guaymas Basin, we obtained 27 samples ofQuaternary-Pleistocene sediment from Hole 479 and,to the south, from Holes 478, 481, and 481 A. The hemi-pelagic-diatomaceous mud in the latter holes is similarto that in Hole 479. The sediment in Holes 478 and 481Afor the upper series varies from diatomaceous ooze tomudstone with some turbidites. The lower series includeslaminations in Hole 478 and mudflows in Hole 481 A. InHoles 478 and 481 A, some dolerite sills are interlayeredwith the sediment.

GEOCHEMICAL STUDY

METHODThe analytical procedures are outlined in Figure 1. Using a Leco

apparatus, we determined organic carbon in acid-treated samples. Weconducted a pyrolysis assay on raw samples with a Rock Eval (Espi-talié et al., 1977). With chloroform, we extracted equivalent parts of

Curray, J. R., Moore, D. G., et al., Init. Repts. DSDP, 64: Washington (U.S. Govt.Printing Office).

samples. The humic compounds were then isolated and their carboncontent analyzed with a carmhograph WOSTHOFF apparatus beforethe kerogen was prepared (Hue et al., 1978). Carbon content was alsoanalyzed in the hydrolyzable fraction obtained after HC1 (6N) treat-ment on humin. We then performed elemental analysis on the kerogenconcentrate.

Results

Mineral Carbon (Table 1)Low mineral carbon (0.24-1.64 wt.% i.e., 2-14% car-

bonates) characterizes the samples from various holes.

Organic Carbon (Table 1)In the Cabo San Lucas area, the organic carbon

range is 1.63 to 3.00 wt.%, except for samples neareruptive series, where the content decreases (0.89 and1.22 in Holes 474A and 476, respectively).

In the Guaymas Basin, we also found the lowest con-tent in the bottom samples (1.33 in Hole 479 and 0.64 inHole 478). But the other samples reveal a 2.40-to-4.00range in Hole 479 and 1.52 to 2.44 in Hole 478. Weobserved a similar range (0.97-2.27) in Holes 481 and481 A, which lie to the north of Site 478.

Pyrolysis Assay on Raw Samples (Table 1)The method of pyrolysis described in Espitalié et al.

(1977), using a Rock Eval apparatus, defines three typesof kerogen (Tissot et al., 1974), which can be used tocharacterize organic matter in ancient sediments.

According to the hydrogen index (Hl)-versus-oxygen-index (OI) diagram (Fig. 2A, B), some samples are nearthe initial evolution path of kerogen Type III and can beconsidered immature continental organic matter. Somecorrespond to the bottom sediments in Holes 474A and478 and the top of the mudflows in Hole 481 A. The datafor the other samples are relatively dispersed (HI =127-450; OI = 57-244) and are not near ReferencePaths I, II, or III. This distribution is common for im-mature material. Considerable oxygenated molecules insuch material contribute to rich oxygen indexes. When

855

G. DEROO ET AL.

Grindfreeze-dried

rock

PyrolysisMineral and

organiccarbons

L I

HCCIg

extraction

H andOindexes

Pyrolysis max.temperature

I Soluble

Rockresidue

HCCIg

extract

HCI,2/VNaQH,N/1O

* i

Soluble

Huminin rockresidue

Humiccompounds

HC I, 6/V

r•

I Organiccarbon

Soluble

HF

1L.

Kerogen

1Elementalanalysis

11

. J

Hydrolyzablefraction

Organiccarbon

Figure 1. Schematic analytical processes.

diagenesis increases, defunctionalization modifies thisorganic material so that the oxygen indexes decrease andtend to reach the range of the reference paths of ancientsediments.

In a pyrolysis assay, the temperature at the top of thepyrolysis peak (Table 1) corresponds to the immature oilzone in the 400-to-440°C range, to the main oil zone ormature zone from 440 to 460°C, and to the cracking orgas zone beyond 460°C. The samples can be assigned to

the early stages of the immature zone. A 418-to-423°Crange occurs in nearly all Cabo San Lucas samples and a403-to-423°C range occurs in the Guaymas Basin sam-ples, except for the deepest sample from Holes 478 and479 with temperatures of 428 and 426°C, respectively.The Section 481 A-13-6 sample has a maximum pyrolysistemperature beyond the 550° final temperature for py-rolysis assay. This must be caused by ancient, reworked,overmatured material.

856

GEOCHEMICAL AND OPTICAL STUDY

Table 1. Data from carbon and pyrolysis assays on raw samples, Leg 64.

Sample(interval in cm)

Hole 479

3-2, 112-1305-3, 125-1397-5, 135-1409-2, 125-13013-1, 110-13015-5, 123-12917-5, 120-14019-5, 110-11522-5, 134-14027-4, 120-14029-5, 134-14034-5, 125-13037-5, 130-150394, 110-11543-1, 130-13547-4, 110-130

Hole 481

8-2, 125-130

Hole481A

8-2, 110-11713-6, 0-524-5, 110-11630-5, 133-140

Hole 474A

7-2, 110-11521-6, 48-5332-2, 145-14041-3, 120-125

Hole 475

6-5, 120-12916-2, 120-130

Hole 476

3-4, 120-12711-4, 110-11619-1, 140-145

Hole 478

7-5, 120-14011-4, 120-12514-4, 120-12717-4, 139-14528A 120-12535-5, 110-116

Sub-bottomDepth

(m)

16.1236.2557.8582.75

109.60135.23154.20183.10201.34246.70267.34313.75342.30362.60393.30433.60

33.75

111.60162.50267.10334.33

222.60352.98452.95539.20

52.20142.70

25.70101.60173.40

58.2093.70

122.70151.89247.70305.10

MineralCarbon(wt.%)

0.580.700.461.480.960.380.160.720.360.620.240.680.260.321.201.64

1.04

0.901.141.001.52

0.681.620.980.88

1.040.66

0.840.760.44

1.040.740.921.000.841.12

Carbonates(wt.%)

4.85.83.8

12.38.03.21.36.03.05.22.05.72.22.7

10.013.7

8.7

7.59.58.3

12.7

5.713.58.27.3

8.75.5

7.06.33.7

8.76.27.78.37.09.3

OrganicCarbon(wt.%)

3.032.882.562.622.983.142.402.582.932.543.083.303.714.002.751.33

1.93

2.210.971.372.27

1.631.652.040.89

2.272.49

3.082.301.22

1.891.982.441.522.430.64

HydrogenIndex

(mg HC/g org. C)

362275348335391418391307332346314352445450392201

344

3211796

292

150222216

64

199302

322234199

12722234788

30891

OxygenIndex

(mg CO2/g org. C)

20716911815814711411212610712067

100635795

179

488

23344

185137

155160112245

15890

160142125

244179190213116191

HydrogenIndex

(mg HC/g rock)

10.967.938.928.77

11.6513.139.387.929.748.809.67

11.6316.5118.0110.782.67

6.63

7.090.171.316.63

2.453.664.410.57

4.517.53

9.925.392.43

2.404.40S.461.347.490.58

OxygenIndex

(mg CO2/g rock)

6.284.883.024.154.373.582.693.253.133.042.073.302.322.272.622.38

9.41

5.150.432.543.12

2.532.642.282.18

3.582.24

4.943.271.53

4.613.554.633.232.811.22

PyrolysisTemperature

CO

411421403404409419411411416410410416413410416426

421

418

423415

423421430421

418422

41942142!

420420412423408428

Humic Compounds and HydrolyzableFraction of Humin

In Hole 479, the organic carbon in the hydrolyzablefraction of humin related to the weight of rock or to thetotal organic carbon, shows a decrease with depth (Fig.3A, B). The variation may be caused by diagenesis.

In the same hole, a low proportion of the total car-bon (15-5%) belongs to the humic fractions (Table 2).Hue and Durand (1977) showed that Type III humicfractions revealed a larger proportion (30% and more)of the total organic carbon than Types I and II (< 10%)when maturation corresponded to a 0.35-to-0.45 reflec-tance range. If we extend this observation to the lowerstages of maturation, the humic compounds in Hole 479would be related to Type I or II material. A 36.9% con-tent for Section 478-7-5 would indicate a Type III humicfraction.

Kerogen Fraction

Elemental analysis of the kerogen concentrate fromSection 479-13-1 (Table 3) was inconclusive because of alarge amount (>50%) of nonorganic material, mainlypyrite. We plotted other data on a Van Krevelen dia-

gram (Fig. 4) and compared them to the three referenceevolution paths for Types I, II, and III kerogens of an-cient sediment (Tissot et al., 1974), deducing a relativehomogeneity from the low dispersion of the data. Thesamples are immature and occur near the beginning ofthe evolution paths. Thus, to identify kerogens theymust be compared with material in the earliest stageof diagenesis. Accordingly, we selected representativemarine material from Orgon III (Debyser et al., 1979),cored in a profile off northern Mauritania, and a typicalhuminolignitic sediment from the present MahakamDelta in eastern Kalimantan.

We also examined some more mature samples ofabout 0.45 reflectance (Hue and Durand, 1977) fromReference Paths II and III. Compared to the previousreference samples, the kerogens appear to be on thereference trend of early, immature, Type II material,though the H/C ratio is lower than in Reference Path II.It can be explained as a mixture of Type II kerogen withsome material of low H/C ratio derived from a moreoxygenated Type II or Type III material—or even froma residual type (Tissot et al., 1979). Moreover, a de-crease of the O/C ratio with increasing depth for theHole 479 samples is apparent on the diagram (Fig. 4)

857

G.DEROO ET AL.

900-1

800

700^

600-

•g 500

400

300

200

100-

/ICABO SAN LUCAS AREA

Hole474A < )Hole 475 OHole 476

16-2 = Core 16, Section 2j

Organic Carbon (wt. %)

QQooo

3.01-4.00

2.01-3.00

1.51-2.00

1.01-1.50

0.51-1.00

/ - .

®

900

800

700

600

500

300

200

100

/I

n

17-5

GUAYMAS BASIN

Hole 478 #Hole 479 O

Holes 481, 481A (?)

39-4 = Core 39, Section 4

Organic Carbon (wt. %)

Q 3.01-4.00Q 2.01-3.00

O 1.51-2.00O 1.01-1.50O 0.51-1.00

®

47-4

)7-5

®50 100 150 200 250

Oxygen Index300 350 400 50 100 150 200 250

Oxygen Index

300 350 400

Figure 2. Pyrolysis assays and hydrogen and oxygen indexes, Cabo San Lucas and Guaymas Basin areas.

Hydrolyzable Fraction of Humin

Organic Carhon Organic Carbon(wt. % of total rock) (% of total organic carbon)

0 .1 .2 .3 .4 .5 .6 .7 0 5 10 15

Table 2. Organic carbon content of humic compounds and hydrolyz-able fraction.

100

Q.200

300

Hole 475 OHole 478

4 7 " 4 Hole 479 O3-2 = Core 3, Section 2

400

Figure 3. Organic carbon in hydrolyzable fraction of humin versusdepth.

and is regular in Figure 5. This decrease depends ondiagenesis and probably corresponds to a loss of oxygenin molecules of immature material.

Data for the eight samples discussed in the precedingparagraph indicate the area where most of the other

Sub-bottomSample Depth

(interval in cm) (m)

TotalOrganicCarbon(wt.%)

Hydrolyzable FractionHumic Compounds (HC1, 6JV)

Carbon Humic C Carbon Hyd. C Vs.(% of rock) Total C (%) (% of rock) Total C (%)

475-16-2478-7-5,479-3-2,479-13-1479-17-5479-274479-37-5479.47^

120-130120-140112-130

110-130120-140120-140130-150110-130

142.7058.2016.12

109.60154.20246.70342.30433.60

1.913.042.992.402.543.711.33

0.360.700.460.130.240.320.200.08

14.536.915.24.29.9

12.65.35.7

0.140.220.420.27

0.210.140.170.09

5.511.613.89.18,95.64.57.0

samples are localized (Fig. 2). Thus we assign a pre-dominant aquatic marine origin and an early stage ofmaturation to this sample population. Exceptions in theGuaymas Basin correspond to the reworked old mate-rial of Section 481A-13-6 and to an immature continen-tal organic matter in the samples from Sections 478-17-4, 478-37-5, and 481A-24-5. In the Cabo San Lucasarea, the sample from Section 474A-41-3 is the onlycontinental material.

OPTICAL STUDY

METHOD

Reflected Light and Fluorescence. This method deals with wholerock, before chemical treatment, on polished sections (with organicmatter concentrated by gravity) and thin sections. Fluorescenceenables us to examine both types of sections under reflected fluores-

858

GEOCHEMICAL AND OPTICAL STUDY

Table 3. Kerogen data from elemental analysis.

Sample(interval in cm)

475-16-2, 120-130478-7-5, 120-140479-3-2, 112-130479-13-1, 110-130479-17-5, 120-140479-27-4, 120-140479-37-5, 130-150479-47-4, 110-130

Orgon III.KL 15Palan Island,Mahakam DeltaWell G.2 7.5Toarcian, Paris BasinJouy aux Arches,outcrop, Toarcian,Paris BasinWell Logbaba 102-1,Cameroon

Sub-bottomDepth

(m)

142.7058.2016.12

109.60154.20246.70342.30433.60

6.000.00

32.50

0.00

775.00

AtomicRatio

H/C

1.161.221.230.941.091.191.211.09

1.201.02

1.16

1.26

0.87

o/c0.230.210.240.490.220.200.190.18

0.300.39

0.14

0.10

0.22

Weight Percentage on Ash-Free Basis

C

34.9146.2943.1727.1940.3441.6052.4236.61

H

3.384.714.412.133.664.135.293.32

N

1.962.412.321.352.092.092.512.05

O

10.9713.4213.8117.8211.8711.3013.548.88

S

26.3918.4719.3730.8022.9920.8814.4126.15

Fe

18.0510.4611.9524.9714.1612.449.28

19.11

Ash, Freeof Pyrite(wt.%)

4.344.244.97—

4.897.562.553.88

•^^^—~— Direction of increasing evolution

— — - Kerogens

I ~ H ~ I H Evolution paths of kerogen types

Vitrinites

Hole 475 OHole 478 ®Hole 479 Q

3-2 = Core 3, Section 2

oA

•

Orgon IIIKL15

Mahakam(bottom)

G2Toarcian

JouyToarcian

Logbaba201

0.2 0.3

O/C (atomic ratio)

0.4 0.5

Figure 4. Kerogen: H/C and C/O diagram.

cent and white light and under transmitted light to recognize the sam-ple in polarized light (Robert, 1979).

We measured vitrinite and bitumen reflectances in the concen-trated polished section, using a Leitz Orthoplan microscope pho-tometer in monochromatic (546 nm) light and oil immersion. We per-formed fluorescence observations using a Zeiss photomicroscope (ex-citation range = 350-450 nm; barrier filter at 470 nm). A globalfluorescence estimate was obtained by a comparison to standards, andthe maximum index (5) accorded with the best fluorescent ground-masses (Green River shales). Such an index correlates well with thecharacteristics of hydrocarbon source rocks. We obtained comple-mentary source rock information from the fading fluorescence (Teich-müller and Ottenjann, 1977), which was applied to the groundmassesand indicated the materiaPs ability to generate hydrocarbon.

Palynological Study. Sample processing was divided into twosteps: treatment by HCL + HF to obtain the total organic material(TOM in Fig. 6) and treatment with HNO3 (25% for 15 min.) and

gravity separation with alcohol-bromide to obtain insoluble organicmaterial (IOM in Fig. 6). These two steps allowed us to estimate thedegradation of organic material from light-oxidation and the dissolu-tion of soluble constituents.

We summarize the observations on transmitted light in Figure 6 asfollows:

1) Percentage (of slide surface) of the various particles constitut-ing the palynofacies;

2) Thermal alteration index (TAI) estimated on the color andtransparency of the pollen grains and dinoflagellates.

Results

Site 479

Hole 479 comprises early-to-late Pleistocene sediment.We studied six samples from Cores 3, 13, 17, 27, 37, and

859

G. DEROO ET AL.

0

50

100-

_ 150

J£200α

o 250n

Sub

-b<

350

400-

450

) .020 ^

" ^

_J

Kerogen O/C

$ .180 .200

i

17-5

J/

/27'-4 θ /

737-5 Cf

(J47-4

>

.250 .270

O3-2

(7 5 /

/ 13-1 Q (

/ O-16-2 °•491

r

Hole 475 O

Hole 478 Φ

Hole 479 O

3-2 = Core 3, Section 2

Figure 5. Kerogen: variations with depth of O/C ratio.

47. The locations appear in Figure 1 of Simoneifs intro-duction to shore-based organic geochemistry (this vol-ume), and the vertical positions are presented in Table 1.The main results are given in Figure 6.

On the whole, vitrinite (huminite) is rare, with max-imum reflectance values of 0.35% in Core 27; somebitumens occur at the same level (Ro = 0.1-0.3%) butare rare in the rest of the hole.

Fluorescence is active and is quite strong in somesamples and indicates a good source rock. The globalestimation, based mainly on the reddish-to-gray ground-rnass, varies between Indices 2 and 3. This fluorescenceis caused by diffuse sapropelic (algal) matter (Robert,1979) impregnating an argillaceous ooze. There is verylittle detritic quartz in Core 27, and some calcite occursin Core 47.

Numerous organisms occur and are visible in whitelight, but their fluorescence coloration varies with depth.Thus, because of thermal alteration, all samples (exceptthat from Core 47) are very rich in diatoms (Plate 1) anddeserve the name diatomaceous ooze. Diatoms probablycompose more than 90% Of the sample. Most organicmatter probably originates from diatom protoplasm.

Monocellular algae are present, but not abundant, intwo samples (Cores 27 and 47); dinoflagellate cysts arecommon in Core 37 and form continuous beds; pinepollen occurs in Cores 3, 17, and 27.

The sample from Core 47 is pure shale without dia-toms, and the groundmass fluoresces gray.

Diatoms fluoresce strongly green in Core 3, weakly inCore 13, and not at all below. The fluorescence color isthe same as the cellulose coloration, and it defines quitewell the fine structure of the organisms. An attempt todestroy cellulose by dissolving it in the Schweitzer liquidwas ineffective, probably because of the opal protectionof the test. The absence of this fluorescence in the hole

correlates with the changing coloration of pine pollen(green in Core 3; yellow in Core 17). These color varia-tions by thermal alteration are well known (Ottenjann etal., 1974). Correlatively, spores and dinoflagellates areyellow in Samples 479-37-5, 130-150 cm and 479-47-4,110-130 cm; unicellular algae are yellow and darkyellow in Samples 479-27-4, 120-140 cm and 479-47-4,110-130 cm.

The absence of this questionable cellulose is wellknown for lignites under thermal evolution in coal ba-sins (Stach et al., 1975).

The palynological study confirms most of our pre-vious observations. In all the samples, the TOM slidesshow an amorphous material made up of large yellow-brown flaky masses with no definite shape. They alsocontain abundant small crystals of pyrite. This amor-phous material corresponds to more massive and darkerflakes with more accurate margins in Samples 479-37-5,130-150 cm and 479-47-4, 110-130 cm.

The palynological slides (IOM) show the predomi-nance of sapropelic amorphous material in yellow flakesof small-to-medium size. The change in color is causedby the disaggregation of pyrite. The disaggregation ofthe large flakes in TOM has produced tiny globular par-ticles (< 1 µm), small-to-medium sized flakes, and trans-parent "membranes." This proves that the flakes com-prise more-or-less dense and polymerized matter andmaterial soluble in alcohol-bromide. The treatmentcauses the appearance of a few ligneous, terrigenousparticles (light brown or opaque). Microfossils are alsosometimes abundant, as, for example, in Samples 479-13-1, 110-130 cm and 479-17-5, 120-140 cm (angio-sperms) and in Samples 479-27-4, 120-140 cm and 479-37-5, 130-150 cm (gymnosperm pollen grains [pinus]and dinoflagellate cysts). The TAI values are low (1.5-2-) but higher in Sample 479-47-4, 110-130 cm (2+).Sample 479-37-5, 130-150 cm has a lower maturationindex because of transparent dinocysts. The highervalue in Sample 479-47-4, 110-130 cm could be cor-related with denser and darker flakes, which would thusbe caused by a higher degree of maturation.

In sum, the samples comprise highly fluorescent,sapropelic groundmasses and amorphous palynofa-cies, generally corresponding to potential hydrocarbonsource rocks. The geochemical results indicate satis-factory hydrogen indices (about 300-400). In good agree-ment is the strong fading effect in fluorescence (Plate 1),though negative, due to the low maturation.

The progression of maturation is shown by the varia-tions in fluorescence (as explained in the column ofobservations on the nature of organic matter) and thepalynological TAI. Such a relatively high diagenesis, notfar from the onset of oil generation, is exceptional insuch a recent and shallow section and is probably relatedto the rift-heated location in the Gulf of California.

Site 478

The Holocene sediment in Sample 478-7-5, 120-140cm is very similar to Sample 479-3-2, 112-130 cm. Thediatomaceous ooze fluoresces strongly green and theshaly groundmass fluoresces dark red (Index 3). Vitri-

860

Sample(interval in cm)

478-7-5,120-140

479-3-2,112-130

479-13-1, 110-130

479-17-5, 120-140

479-27-4, 120-140

479-375,130-150

479-47-4,110-130

475-16-2,120-130

Str

atig

raph

yH

olo

cen

eearl

y P

leis

toce

ne

la

te P

leis

toce

ne

earl

y P

lioce

ne

Tota

l O

rgan

icC

arbo

n (%

)

1.89

3.03

2.98

2.40

2.54

3.71

1.33

2.49

×

Hyd

roge

n Im

(pyr

olys

is

127

362

391

391

346

445

201

302

Reflected Light

Reflectance (%)

0 0.5 0.8

JL

_r

J

mI,

Ml

J L

i—

1 π

] Vitrinite1 Bitumen

Fluorescence

Global

Estimation

1 2 3 4

-J

Nature of Organic Matter

Abundant strong green diatoms;

sapropelic groundmass (shaly)

Abundant green diatoms;pine pollen (green); sapropelicgroundmass (shaly)

Abundant pale green diatoms;dinoflagellates. Foraminifers;sapropelic groundmass (shaly)

Abundant diatoms(not fluorescent); pine pollen(clear yellow); sapropelicgroundmass (shaly)

Abundant diatoms(not fluorescent);pine pollen (yellow);algae (yellow); sapropelicgroundmass (shaly; quartz rare)

Abundant yellow dinoflagellates

No diatoms; filamentousalgae; small foraminifers;sapropelic groundmass(shaly—carb.)

Abundant diatoms(not fluorescent); filamentousalgae (yellow); sapropelicgroundmass (shaly; quartz rare)

Transmitted Light (palynology)

Organic Facies

T O M (%)

20 40 60 80

ITI IU

•i

IOM (%)

20 40 60 80

AmLigrMic

u-

l 1 1

orplleoiirofo

IOUS

s dessils

1

matbris

1

1

ter

TAI

1 2 3

-

mm

Observations

Ligneous debrisfairly abundant

Large flakes ofamorphous matterin the TOMSmall and mediumflakes with "membranes"in the IOMAngiosperm pollencommon in Samples479-13-1, 110-130 cmand 479-17-5.120—140 cm; pinuspollen common in479-17-5, 120-140 cm;dinoflagellates commonin Samples 479-37-5,130-150 cm and479-47-4,110-130 cm

Darker and moremassive flakes

TAI higher

Same as in Sections479-3-2 to479-27-4

Figure 6. Synopsis: optical analysis of organic matter.

G. DEROO ET AL.

nites, more common than in the Hole 479 sample, pro-duce dispersed reflectances (0.15-0.65%) because of re-worked material. The youth, shallow burial, and fluo-rescence of diatoms indicate that maturation is low (orabsent).

The palynological study of Sample 478-7-5, 120-140cm emphasizes characteristic differences with the paly-nofacies in Hole 479. The Hole 478 sample containsmixed pálynofacies. In the MOT slide, the amorphousmaterial makes up 10% of the total, whereas the in-herited terrigenous material is abundant (up to 30%).

In the IOM palynological slide, the ligneous materialis common and correlates with the presence of vitrinite(light-brown and dark particles [tracheids, ligneous tis-sues, and fibers]). Abundant Pinus pollen grains occurtogether with angiosperm pollen and dinoflagellates.The amorphous matter comprises small flakes.

These observations (Fig. 6) confirm the difference ingeochemical data between the Hole 479 samples and theHoie 478 sample. The hydrogen index, much lower thanfor the Hole 478 sample, correlates with the high con-tent of terrigenous woody remains. The terrigenous re-mains could be caused, in part, by reworking. The TAIvalue is low (about 2).

Site 475

Sample 475-16-2, 120-130 cm (early Pliocene) is simi-lar to the deepest samples in Hole 479. Diatoms aboundbut do not fluoresce, some filamentous algae are yellow,and the sapropelic groundmass (shaly; rare quartz) has agood brown-red fluorescence. One peculiarity is the pres-ence of bitumen with low (0.2%) reflectance—not a reli-able indicator of maturation. Fluorescence observationssuggest a certain thermal maturation, and the presenceof bitumen confirms the generation of hydrocarbons;but its reflectance underestimates the true degree of ther-mal evolution.

The TOM and IOM palynological slides show thesame pálynofacies and TAI as in Samples 479-3-2, 112-130 cm through 479-27-4, 120-140 cm.

The samples from Holes 478 and 475 are good con-trols for observations on the nature of organic matterand maturation in the Hole 479 sample. The composi-tion of the organic matter agrees with the geochemicalresults (see HI, Fig. 6).

CONCLUSIONS

The organic matter in Pleistocene and lower Pliocenemarine hemipelagic and diatomaceous mud or oozeoverlying igneous material in Holes 474A, 475, 476,478, 479, and 481-481A is commonly marine and de-rived mainly from diatoms. Its range is immature, butdiagenetic effects with depth are obvious and can berelated to the active rifting. Terrigenous immatureorganic material is also present, particularly near theeruptive contact in Holes 474A and 478 or at the top ofmudflows in Hole 481 A.

ACKNOWLEDGMENTS

The authors are indebted to A. Hood and B. R. T. Simoneit forreviewing the manuscript.

REFERENCES

Debyser, Y., and Gadel, R, 1979. Geochimie des kérogènes dans lessediments. Geochimie Organique des sediments marins profonds,Orgon III: Paris (Editions CNRS), pp. 375-403.

Espitalié, J., Laporte, J. L., Madec, M., et al., 1977. Méthode rapidede caractérisation des roches mères, de leur potentiel pétrolier et deleur degré devolution. Rev. Inst. Fr. Pet., 32:23-42.

Hue, A. Y., and Durand, B., 1977. Occurrence and significance ofhumic acids in ancient sediments. Fuel, 56:73-89.

Hue, A. Y., Durand, B., and Monin, J. C , 1978. Humic compoundsand kerogens in cores from Black Sea sediments, Leg 42B—Holes379A, B, and 380A. In Ross, D. A., Neprochnov, Y. P., et al.,Init. Repts. DSDP, 42, Pt. 2: Washington (U.S. Govt. Printing Of-fice), 737-748.

Ottenjann, K., Teichmüller, M., and Wolf, M., 1974. Mesures spec-trales de fluorescence sur sporinites en lumière réfléchie, une mé-thode microscopique de determination du rang des charbons peuhouillifiés. Fortsch. Geol. Rheinl. Westfalen, 24:1-184 (Frenchtranslation BRGM 5477).

Robert, P., 1979. Classification des matières organiques en fluores-cence. Application aux roches méres pétrolières. Bull. Cent. Rech.Explor. Prod. Elf-Aquitaine, 3:223-263.

Stach, E., Mackowsky, M. Th., Teichmüller, M., et al., 1975. Stach'sTextbook of Coal Petrology: Berlin (Gebrüder Borntraeger).

Teichmüller, M., and Ottenjann, K., 1977. Liptinite und LipoideStoffe in einem Erdölmuttergestein. Erdoel Kohle, 9:387-398.

Tissot, B., Durand, B., Espitalié, J., et al., 1974. Influence of thenature and diagenesis of organic matter in the formation of petro-leum. Am. Assoc. Pet. Geol. Bull., 58:499-506.

Tissot, B., Deroo, G., and Herbin, J. P., 1979. Organic matter in Cre-taceous sediments of the North Atlantic: Contribution to sedi-mentology and paleogeography. In Talwani, M., Hay, W., andRyan, W. B. F. (Eds.), Deep Drilling Results in the AtlanticOcean: Continental Margins and Paleoenvironment: Washington(American Geophysical Union), pp. 362-376.

862

GEOCHEMICAL AND OPTICAL STUDY

Plate 1. Fluorescence of Sample 479-3-2, 112-130 cm. (Scale bar = 50 µm.) 1. Fluorescent (red) groundmass and fluorescent (green) diatoms. 2.Fading fluorescence in the groundmass: A = before exposure. B = after exposure (2 hr.) of the right half.

863

G.DEROO ET AL.

^ J

Plate 2. Palynofacies from Holes 475, 478, and 479. (Scale bar = 100 µm, except where noted; TOM = total organic material, IOM = insoluble or-ganic material). 1A. Sample 475-16-2, 120-130 cm (TOM). IB. Sample 475-16-2, 130-130 cm (IOM). 2A. Sample 478-7-5, 120-140 cm(TOM). 2B. Sample 478-7-5, 120-140 cm (IOM). 3A. Sample 479-37-5, 130-150 cm (TOM). 3B. Sample 479-37-5, 130-150 cm (IOM). 4A.Sample 479-47^, 110-130 cm (TOM). 4B. Sample 479-47-4, 110-130 cm (IOM). 4C. Sample 479-47 A 110-130 cm (IOM; scale bar =

864