38. ROCK-EVAL PYROLYSIS OF QUATERNARY SEDIMENTS FROM LEG 64,SITES 479 AND 480, GULF OF CALIFORNIA1

K. E. Peters, Chevron Oil Field Research Company, Box 446, La Habra, Californiaand

B. R. T. Simoneit,2 Institute of Geophysics and Planetary Physics, University of California—Los Angeles,Los Angeles, California

ABSTRACT

Geochemical analyses were carried out on Quaternary sediments from cores at Sites 479 and 480. The amount oforganic matter indicates that these sediments have good to very good source-rock potential. Rock-Eval pyrolysis andmicroscopic examination show that many of the samples contain thermally immature, oil-prone, marine organic mat-ter. Preliminary results show that Rock-Eval pyrolysis can distinguish oxic (bioturbated) and anoxic (laminated)organic facies in the cores.

More than 10% of the organic carbon in these immature sediments is normally lost as hydrolysate during conven-tional acid treatment for the removal of carbonates. The protokerogen remaining after solvent extraction and acidmaceration constitutes only a fraction of the total organic matter. Elemental analysis, pyrolysis, and vitrinite reflec-tance of the kerogenous residue show that it is considerably less oil prone than the total organic matter.

INTRODUCTION

Demaison and Moore (1980) have suggested thatstudying the interaction of the oceanic oxygen-mini-mum layer with organic matter (OM) deposited in slopesediments will enhance our understanding of oil source-bed genesis. Alternating laminated (anoxic) and homo-geneous, bioturbated (oxic) zones were found in coresfrom the Deep Sea Drilling Project (DSDP)-Interna-tional Phase of Ocean Drilling (IPOD) cores from Leg64, Sites 479 and 480 (Curray et al., 1979; Schrader etal., 1980). These zones represent a unique opportunityto study the effects of periodic displacement of the oxy-gen-minimum layer on the geochemical and sedimento-logical parameters of young sediments. Both sites weredrilled primarily in Quaternary marine sediments on theslope of the Guaymas Basin in the central Gulf of Cal-ifornia. These unlithified sediments appear to representmodern analogs of shales, such as the Miocene Monte-rey Formation in California, which are rich in organicmatter.

The concept of sedimentary organic facies is based on(1) the types of organisms that act as a source, (2) thedepositional environment, and (3) conditions during ear-ly diagenesis. In ancient sediments, organic facies aremappable subdivisions of a stratigraphic unit that canbe distinguished on the basis of the chemical composi-tion of the organic matter. Examples of the use of vari-ous geochemical parameters in differentiating the or-ganic facies characteristic of oxic and anoxic sedimen-tary environments include Pelet and Debyser (1977), Di-dyk et al., (1978), Byers and Larson (1979), and Jones

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

2 Present address: School of Oceanography, Oregon State University, Corvallis, Oregon.

and Demaison (1980). Facies determination by Rock-Eval pyrolysis produced negative (Favero et al., 1979)and positive (Demaison et al., 1980) results.

The purpose of this preliminary work is twofold: (1)to determine the quantity, quality, and degree of matu-ration of organic matter in these sediments to assesstheir hydrocarbon potentials and generative histories,and (2) to investigate the relation between Rock-Evalpyrolysis response and organic facies at Sites 479 and480.

METHODSConventional "filtering" acidification procedures for the removal

of carbonate prior to total organic carbon (TOC) analyses were con-ducted by DSDP. Each sample was acidified with 6N HC1 in Lecofiltering crucibles, and spent acid and wash water were removed byvacuum filtration. The dried residue was combusted, and organic car-bon was measured as CO2 (Gehman, 1962).

Our "nonfiltering" acidification was modified from Wimberley(1969). Aliquots of 100 mg of sediment were weighed into Leco non-filtering combustion crucibles (No. 528-038). The samples were treat-ed drop-wise with 6N HC1 until all CO2 evolution ceased and werethen allowed to react overnight. Crucibles containing the samples wereoven-dried at 100°C for about 30 min. and analyzed as usual on theLeco carbon analyzer.

"Rock-Eval" is a pyrolysis instrument designed to rapidly mea-sure hydrocarbon potential and generative history from whole-rocksamples (Espitalié et al., 1977). The method is based on the selectivedetection of hydrocarbon compounds and carbon dioxide generatedfrom organic matter in the rock during programmed heating in an in-ert atmosphere.

Several parameters are obtained by this technique. A flame ioniza-tion detector (FID) senses any hydrocarbons generated during pyro-lysis. The first peak (S1) represents the quantity of free hydrocarbons(HC—bitumen) that is thermally distilled from the rock (mg HC/gsample). The second peak (S2) comprises hydrocarbons generated bypyrolytic degradation of the insoluble organic matter (kerogen) (mgHC/g sample). Carbon dioxide generated from the organic matter isanalyzed as a third peak (S3) (mg CO2/g) using a thermal conductivitydetector (TCD). Carbonate lithologies can pose a problem since someinorganic S3 can be produced (Peters, unpubl. data).

During pyrolysis the temperature is monitored by a thermocouple.The temperature at which the maximum amount of hydrocarbons are

925

K. E. PETERS, B. R. T. SIMONEIT

generated is called Traax. The hydrogen index (HI) corresponds to thequantity of hydrocarbon compounds from S2 normalized to the TOCof the sample (mg HC/g organic carbon). The oxygen index (01) cor-responds to the quantity of CO2 normalized to the TOC of the sample(mg CO2/g organic carbon). As previously demonstrated (Espitalié etal., 1977), the HI and OI show good correlation with atomic H/C andatomic 0/C, respectively.

Operating parameters for Rock-Eval pyrolysis were identical tothose in Clementz et al. (1979). Homogenized samples of untreated oracid-treated dry sediments were pyrolyzed from 250 to 55O°C in ahelium atmosphere at a program rate of 25°C/min. Peak areas werecalculated by digital integration.

Selected sediment samples were treated using the standard pro-cedure for kerogen isolation applied to source rocks. Kerogen is de-fined as the acid-resistant, insoluble organic material isolated fromancient sediments. Site 479 and 480 samples were exhaustively ex-tracted in a Soxhlet apparatus using carbon disulfide. The remainingmaterial was treated with 6N hydrochloric acid for carbonate removalfollowed by repeated washing with water. Hydrofluoric acid (60%)removed most silicate minerals. The residue was rinsed with dichloro-methane prior to drying at 40°C in a vacuum oven. Because of thethermally immature nature of these young sediments, we prefer to usethe term "protokerogen" (Peters et al., 1981) to describe the insolubleresidue. Protokerogen may contain a variety of biopolymers—such aslignin, cell wall debris, and weakly bound lipids or humic acids—sub-ject to alteration during diagenesis. Our preliminary studies did not in-volve extraction of humic substances using basic solution. Thus, theprotokerogen residues may contain some humic acids.

Carbon, hydrogen, and nitrogen contents of the protokerogen weremeasured using a Carlo Erba MOD 1106 elemental analyzer. Polishedslides for microscopic analysis were prepared using the method de-scribed by Baskin (1979). Vitrinite reflectance measurements were com-pleted by B. Alpern (CERCHAR, France).

DISCUSSION

Whole-Sediment Analyses

Total organic carbon, based on the nonfilter acid-ification procedure and Rock-Eval pyrolysis data forwhole-sediment samples from Sites 479 and 480, arefound in Tables 1 and 2, respectively. Total organic car-bon values determined by DSDP on these samples arereported in parentheses in the tables. Four replicate ana-lyses are included in these data. The average standarddeviations, expressed as percentages of the respectivemeasured values of TOC, HI, OI, and Tmax, are 0.5,6.1,5.5, and 0.7%.

Figure 1 plots TOC values for the nonfilter (hydro-lysate-retained) versus filter (hydrolysate-lost) methods.It shows that, on the average, more than 10% of theorganic carbon in a sample is lost as hydrolysate duringconventional acid treatment. Additional loss of col-loidal organic matter through the porous Leco filteringcrucibles is possible. These results agree with those ofRoberts et al. (1973), who showed a loss of up to 44% ofthe organic matter from Recent sediments in the acidfiltrate. We have observed that sediments and rocksolder than those found at these sites generally containdiagenetically mature organic matter, which is moreresistant to hydrolysis.

Figure 2 is a plot of TOC versus total hydrocarbonyield (S1 + S2) obtained by Rock-Eval pyrolysis of thewhole-sediment samples. These nonlinear results appearto result from differences in composition of the organicmatter among samples. Preliminary optical studies byB. Alpern, for example, suggest that a difference in mac-eral composition exists between low- (<2.5%) and bigh-t s . 5 % ) TOC sediments at these localities. Low-TOC

sediments commonly represent oxidizing depositional re-gimes dominated by recycled, hydrogen-poor macerals.Higher TOC sediments are characteristic of more reduc-ing environments dominated by hydrogen-rich rnacer-als. Upon pyrolysis, hydrogen-rich macerals yield morehydrocarbons per gram organic carbon than do hydro-gen-poor macerals (Tissot et al., 1974). Low-TOC sedi-ments at these localities seem to contain proportionallymore recycled organic matter than high-TOC sediments.The variation in total hydrocarbon yield for sampleswith more than 2.5% organic carbon may also reflectdifferences in maceral composition. Additional opticalstudies are in progress.

An alternative explanation for the results in Figure 2is absorption of pyrolytic hydrocarbons by the kerogen/mineral matrix (Espitalié et al., 1980). This absorptiveeffect can be likened to the behavior of a sponge. Whenthe supply of hydrocarbons to the sponge is low (lowTOC), much of the hydrocarbon material is absorbed bythe sponge. Once a specific threshold of hydrocarbonsupply is reached, however, the sponge becomes satu-rated, and hydrocarbons flow through as rapidly as theyare supplied.

All TOC values at Site 479 (Table 1) are greater than1%, and most are over 2%. In more mature sedimentsthis would indicate good to very good quantities ofsource rock organic material for hydrocarbon genera-tion. (Organic carbon content does not, however, speci-fy the proportion of the organic matter convertible tohydrocarbons.) Tmax values range from 403 to 427°C.These low values, combined with negligible S1 (free hy-drocarbon) content, verify the immaturity of the sedi-ments. The transformation ratio, S1/(S1 + S2) (Tissotand Welte, 1978), for all these samples is approximatelyzero. Hydrocarbon-generating potential, as measuredby S2, ranges from fair to very good. The variabilitywith depth for values such as S2/S3, HI, and OI far ex-ceeds the standard deviation for their measurement.

Rock-Eval and TOC results for Site 480 are similar tothose from Site 479. TOC values range from 2.5 to3.4%, indicating very good source rock potential interms of quantities of organic matter. Tmax values (400-420 °C) and negligible S1 hydrocarbons again indicateimmature sediments.

Figures 3 and 4 are HI versus OI plots based onpyrolysis results for Sites 479 (Table 1) and 480 (Table2). Pathways I, II, and III represent the changing com-positions of the principal types of organic matter insource rocks (Espitalié et al., 1977). Each pathway ap-proaches the origin of the figure as a result of thermalmaturation during burial. Organic matter plotting onthe Type I pathway, such as that from shales of theGreen River Formation, originates as very oil-prone ma-terial. Type II source rocks, such as those of the lowerToarcian of the Paris Basin, are moderately oil prone.Type III source rocks, such as the Upper Cretaceousrocks of the Douala Basin, are only gas prone. Mostrocks contain mixtures of the principal types of organicmatter.

By using different symbols, the data for each site aredivided into three arbitrary depth intervals to show gen-eral depositional trends. At Site 479 (Fig. 3) the shallow

926

ROCK-EVAL PYROLYSIS

Table 1. Rock-Eval pyrolysis and TOC results, Site 479.

Sample(interval in cm)

3-2, 99-1015-3, 107-1096-4, 80-827-5, 108-1108-3, 45-479-3, 99-10110-4, 65-6710-7, 24-2612-6, 111-11313-1, 110-11214-2, 52-5415-2, 97-9915-5, 108-11016-3, 126-12818-1, 82-8421-5, 110-11222-5, 101-10323^, 73-7524-3, 86-8825-2, 131-13326-1, 82-8427-4, 72-7431-5, 69-7131-5, 70-7232-1,63-6534-2, 84-8634-5, 108-11034-5, 139-14136a-3, 70-7236-3, 70-7237-2, 78-8038a-5, 129-13138-5, 129-13139-4, 107-10940-6, 110-11241-1, 99-10143a-2, 82-8443-2, 82-8444-3, 93-9545-1, 81-8347a-4, 108-11041 A, 108-110

Sub-bottomDepth

(m)

14.9936.5746.3056.5863.4573.4984.1589.24

106.61108.60119.02128.97133.58140.26155.82190.60200.01207.73215.86224.31231.82245.72285.19285.20288.63309.34314.08322.39329.70329.70337.78352.29352.29360.07372.60374.49394.82394.82405.93412.31436.08436.08

TOCb

(wt.%)

3.19(2.8)2.92 (2.7)2.54 (2.3)2.96 (2.7)2.73 (2.4)2.60 (3.0)2.72 (2.3)2.68 (2.4)2.59 (2.4)3.26 (2.9)2.83 (2.6)3.16(2.8)3.34 (2.9)3.48 (3.2)2.09(1.9)2.82 (2.5)2.98 (2.6)2.34 (2.3)2.80 (2.5)2.70 (2.5)1.77(1.6)2.66 (2.5)3.03 (2.6)3.09 (2.8)2.80 (2.5)2.82 (2.7)3.20 (3.0)2.58 (2.3)3.24 (2.9)3.21 (2.9)3.02 (2.8)3.46 (3.0)3.48 (3.0)3.80 (3.5)2.32(2.1)3.06 (2.7)2.90 (2.6)2.91 (2.6)2.08(1.9)2.22(1.9)1.37(1.2)1.36(1.2)

S1(mg HC/g)

000.20000000000.400000000000.3000000000000000000

S2(mg HC/g)

24.819.110.531.214.512.114.415.715.318.424.319.422.927.210.912.416.812.017.814.76.9

20.824.321.311.619.317.513.614.917.118.827.725.725.213.512.014.714.75.9

9.83.63.2

S3(mg CO2/g)

8.810.68.97.0

10.79.0

12.08.77.7

10.38.27.58.59.34.9

75.47.28.16.05.45.35.73.96.38.55.16.76.57.26.8

10.07.27.29.09.88.6

10.110.88.16.33.73.0

‰ax(°C)

415417413405419415420413417411413413415415403412410420410415413413418410413412All410418421410416413419418418418413427407418418

S1/(S1 +S2)

000000000000000000000000000000000000000000

S2/S3

2.8

t

.8

.21.5.4.4.2.8

2.01.83.03.42.71.82.20.92.31.53.02.71.33.66.23.41.43.82.62.12.12.51.93.83.62.81.41.41.51.40.71.61.01.0

HI(mg HC/gC)

111654413

1054531467529586591564858614686782522440564513636544390781801689416684546527460533623800739663581392507505285441265235

OI(mg CO2/gC)

276363350236342346441325297316290221254267234191242346214200299214129204304181209252222212331208207237422281348371389284270221

a Replicate analyses." TOC data using conventional acid treatment for carbonate removal in parentheses (DSDP data).

Table 2. Rock-Eval pyrolysis and TOC results, Site 480.

Sample

3,CC5,CC6,CC7,CC9,CC

11,CC13.CC17.CC19,CC21,CC23, CC25.CC27,CC29,CC31.CC

Sub-bottomDepth

(m)

14.2023.6028.4033.1042.6049.1066.3085.4094.90

104.20113.90123.40132.90142.40151.90

TOCa

(wt.%)

2.68 (2.9)3.09 (2.8)2.86 (2.5)2.94 (2.9)3.36 (3.0)2.50 (2.5)2.69 (2.4)2.99 (2.7)2.73 (2.5)3.06 (3.2)2.74 (2.2)3.03 (2.8)2.90 (2.7)2.62 (2.3)2.56 (2.2)

S1(mg HC/g)

000000000000000

S2(mg HC/g)

18.527.117.613.316.511.814.515.619.616.423.528.429.725.420.8

S3(mg CO2/g)

8.77.76.18.8

14.07.96.06.54.89.95.35.45.84.24.1

‰ax( ° Q

418415420411417412410413417415413416408411400

S1/(S1 + S2)

000000000000000

S2/S3

2.13.52.91.51.21.52.42.44.11.74.45.35.16.05.1

HI(mg HC/gC)

690876763550491472539522718536858937

1024969813

OI(mg CO2/gC)

325249265365417316223217176324193178200160160

TOC data using conventional acid treatment for carbonate removal are in parentheses (DSDP data).

927

K. E. PETERS, B. R. T. SIMONEIT

| 2

• Site 479

• Site 480

• • /•/

Filter TOC (wt.%)

Figure 1. Nonfilter (hydrolysate-retained) versus conventional filter(hydrolysate-lost) TOC results for whole sediments, Sites 479 and480. (Dashed line represents ideal correlation.)

1000

900

800

700

J 600

- 500

^.400I

300

200

100

Sub-bottom Depths (m):

G 14.99-108.60

B 119.02-360.07

• 372.60-436.08

B B BB

BB

* •D

D D

B •• BB °

100 200 300Oxygen Index (mg CC^/g C)

400

Figure 3. Hydrogen index versus oxygen index for whole-sedimentsamples, Site 479.

_ 3

• Site 479

• Site 480

10 15 20 25

Total Hydrocarbon Yield (mg HC/g)

30 35

Figure 2. Nonfilter TOC versus total hydrocarbon yield (S1 + S2)from Rock-Eval pyrolysis of whole-sediment samples, Sites 479and 480.

interval (14.99-108.60 m) shows a range of HI and OIresults, but most points cluster between the immatureportions of the Type II (oil-prone) and Type III (gas-prone) pathways. Thus, most of these sediments in theshallow interval are only weakly oil prone. Data for theintermediate interval (119.02-360.07 m) show that thegeneral quality (oil-generating potential) of the organicmatter was better than that deposited subsequently inthe shallow interval. Most of the intermediate depthsamples plot near the immature portion of the Type IIpathway in Figure 3. Samples from the deep interval(372.60-436.08 m) are predominantly weakly gas prone,for they plot between immature Type II and Type IIIpathways.

1000

900

800

700

ε 600

- 500

400

300

200

100

O

Sub-bottom Depths (m):

O 14.20-28.40

Φ 33.10-104.20

• 113.90-151.90

G

Φ

θ

100 200 300

Oxygen Index (mg CO2/g C)

400

Figure 4. Hydrogen index versus oxygen index for whole-sedimentsamples, Site 480.

At Site 479 the sediments were severely disturbed bybiogenic gas partings and drilling. Unfortunately, thedisturbed nature of the core does not allow a strict com-parison of Rock-Eval pyrolysis results with lithology.

At Site 480, deposition of very oil-prone organic mat-ter with a composition intermediate between immature

928

ROCK-EVAL PYROLYSIS

Types I and II (Fig. 4) occurred in the deep interval(113.90-151.90 m). In an intermediate interval (33.10-104.20 m) most of the organic matter plots between im-mature Types II and III and is of lower quality than thatof the overlying shallow interval (14.20-28.40 m) thatplots near the immature Type II pathway.

The unlithified samples from Site 480 are core-catchermaterial, which is sometimes disturbed during collec-tion. The core lithology is divided almost equally be-tween two alternating sediment types (Schrader et al.,1980). Laminated zones, consisting of rhythmic cou-plets, are mixtures of diatom ooze and terrigenous clays.Homogeneous zones consist of diatomaceous mud tomuddy ooze with evidence of extensive burrowing. Thelatter probably reflect times with a less-pronounced oxy-gen-minimum zone that allowed the existence of epifaunaand infauna. The causes of these fundamentally differ-ent lithologies also appear to have determined the distri-bution of organic facies at this site.

Figure 5 plots TOC and some Rock-Eval parametersversus lithology at Site 480. An inverse relation existsbetween HI and OI as a function of depth. The resultssuggest different types of organic matter in the oxic,

homogenous zones (low HI, high OI) than in the anoxic,laminated zones (high HI, low OI).

Note the striking change in HI, OI, and S2/S3 be-tween 104.20 and 151.90 meters sub-bottom. The deeperinterval is laminated and of sufficient thickness to beunaffected by mixing with homogenous layers fromabove during collection. The S2/S3 ratios and HI valuesfor the deeper samples are significantly larger than thoseof the shallower sediments. The OI and Tmax values ofthe deeper samples are smaller than those of the shal-lower sediments. The significance of these preliminaryresults is that Rock-Eval pyrolysis has been used suc-cessfully to differentiate organic facies in this core.

Protokerogen Analyses

Table 3 shows the results of elemental analysis, Rock-Eval pyrolysis, and microscopic examination of proto-kerogens isolated from selected Site 479 and 480 sam-ples. The S2/S3 and HI and OI pyrolysis results in thetable show that most of these residues are less oil pronethan the total organic matter in the same sediment. Thisis particularly apparent for the very oil-prone organicmatter in the deeper samples (113.90-151.90 m) at Site

Lithology

5 0 -

Q.α>

Q

E

8o•9.α

500 600

Hydrogen Index (HI)

700 800 900 1000

S2/S3

3 5

100-

150-

T0C(wt.%)200 250 300 350 400

Oxygen Index (OI)

break in record

laminated orfaintly laminated

homogeneous

Figure 5. Nonfilter TOC and Rock-Eval parameters versus lithology as a function of depth, Site 480. (The two columns labeled "Lithology" repre-sent simplified lithology [left] and simplified textural interpretation [right] modified after Schrader et al. [1980].)

929

K. E. PETERS, B. R. T. SIMONEIT

Table 3. Microscopic, elemental analysis, and Rock-Eval pyrolysis results, Sites 479 and 480 kerogens.

Sub-bottomSample Depth

(level in cm) (m) Atomic H/CS1

(mg HC/g)S2

(mg HC/g)S3

(mg CO2/g)HI OI

S2) S2/S3 (mgHC/gC) (mg CO2/gC)

479-7-5, 108479-12-6, 111479-23-4, 73479-36-3, 70479-43-2, 82479-47-4, 108

480-5,CC480-11,CC480-13.CC480-17,CC480-19.CC480-21,CC480-23.CC480-25 ,CC480-29.CC480-3 l.CC

56.58106.61207.73329.70394.82436.08

23.6049.1066.3085.4094.90

104.20113.90123.40 ]142.40151.90

.18

.07

.09

.15

.09

.19

.16

.14

.08

.20

.15

.18

.11

.20

.13

.10

0.260.250.280.350.350.38

0.350.280.250.250.270.280.310.250.340.30

01.20.21.71.27.1

2.806.61.801.803.001.3

240.8108.5116.8221.9172.399.4

148.0126.3142.1386.9166.3311.2230.8243.8246.8153.2

74.460.652.668.079.424.0

96.693.890.1

138.884.4

109.9118.0119.7129.174.6

409410422413421429

415409410413409413407408413410

000000.1

0000000000

3.21.82.23.32.24.1

1.51.31.62.82.02.82.02.01.92.1

553341355474384406

418359424859509688715525577363

17119016014517798

273267269308258243366258302177

a Oil immersion vitrinite reflectance of about 50 randomly oriented vitrinite particles per sample (by B. Alpern).

480. These residues constitute only a fraction of thetotal organic matter in the untreated samples. Apparent-ly, oil-prone materials are preferentially removed fromthese immature sediments during acid maceration andsolvent extraction (see Fig 1). Unlike the sediments atSites 479 and 480, we find a general agreement betweenwhole-rock and kerogen determinations of organic mat-ter quality in older sediments and rocks. These resultssuggest that the Quaternary sediments at these localitieson the Guaymas Slope are diagenetically immature. Theproduction of kerogen from protokerogen, lipids, hu-mic substances, and other classes of organic materials isstill in progress (Peters et al., 1981).

Mean vitrinite reflectance values (Table 3) rangefrom 0.25 to 0.38% at Site 479 and from 0.25 to 0.35%at Site 480. These values are characteristic of immatureorganic matter and agree with conclusions based onpyrolysis. Simoneit et al. (1979), reached similar conclu-sions by using elemental and isotopic analyses of proto-kerogens isolated from sediments near these locations.The reflectance studies also show varying quantities ofrecycled organic matter in Site 479 and 480 sediments.

Figure 6 is an atomic H/C versus O/C plot for theprotokerogens and is based on data from Table 3. Loca-tion of points on the figure was determined using atomicH/C and vitrinite reflectance measurements (Jones andEdison, 1978). Lines I, II, and III in the figure areevolutionary pathways followed by the three principaltypes of kerogens during burial maturation (Tissot etal., 1974). This plot shows that samples from Sites 479and 480 contain immature, moderately oil-prone pro-tokerogen, whose composition is intermediate betweenTypes II and III. The protokerogens are generally lessoil prone than the whole-sediment samples shown inFigures 3 and 4.

CONCLUSIONSRock-Eval pyrolysis of whole sediments from Sites

479 and 480 shows that many consist of thermally im-mature, oil-prone, marine organic matter. In general,protokerogen isolated from these samples is less oil

1.5 -

oI.« 1.0E

0.5 -

0.5

_1

-

. 1 0s

1.

2.0_

4.0/

X

0

K\\ /5 ü\

M

/

\\

A

/ ̂4.0

I

s

^1.0

\ > c2.0 ' •5

J0.1

• Site 479

9 Site 4801 III

. evolutionary pathways

Principal Productsof Kerogen Evolution:

P771 CO2 ,H2O

1 1 oil

E l ^s

1 1 J,0.2

Atomic O/C

Figure 6. Atomic H/C versus O/C plot for protokerogens isolatedfrom selected Site 479 and 480 sediments.

prone than the total organic matter. Hydrolysis and lossof labile, oil-prone organic matter are significant duringacid maceration and solvent extraction of young sedi-ments. Preliminary results suggest that Rock-Eval py-rolysis is a useful geochemical method of mapping fa-des boundaries.

ACKNOWLEDGMENTSWe thank the management of the Chevron Oil Field Research

Company for permission to publish this work. B. Alpern (CER-CHAR, France) completed vitrinite reflectance and maceral analysesof the kerogen isplates. We thank H. Halpern and P. C. Henshaw, Jr.for their reviews of this chapter. Special thanks are due R. W. Jonesand G. J. Demaison for helpful suggestions and discussions. Con-tribution 2094 from the Institute of Geophysics and Planetary Phys-ics, UCLA.

930

ROCK-EVAL PYROLYSIS

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Byers, C. W., and Larson, D. W., 1979. Paleoenvironments of MowryShale (Lower Cretaceous), western and central Wyoming. Am.Assoc. Pet. Geol. Bull., 63:354-361.

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