Pisciotto, K. A., Ingle, J. C, Jr., von Breymann, M. T., Barron, J., et al., 1992Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 127/128, Pt. 1

35. PYROLYTIC ASSAY OF SAMPLES FROM SITE 7991

Barry J. Katz2

ABSTRACT

Pyrolysis techniques were used to characterize the organic matter contained within the penetrated section and to assess thepresence of heavy hydrocarbon shows. The Rock-Eval data indicate a change in organic hydrogen enrichment within the middleMiocene sequence. It appears that the level of organic enrichment may be controlled by sedimentation rate, while the organichydrogen enrichment, as shown in the hydrogen index, may reflect differences in preservation potential. Higher sedimentationrates would result in higher organic carbon contents. Higher hydrogen index values would reflect higher degrees of organicpreservation resulting from more restricted circulation.

The entire penetrated section is thermally immature and has not entered into the main phase of thermal hydrocarbon generation. Neitherthe Rock-Eval nor the pyrolysis-gas chromatographic data indicate the presence of thermally mature, migrated, heavy hydrocarbons. Thisabsence of mature, heavy hydrocarbons includes Cores 128-799B-65R and 128-799B-66R, which exhibited cut fluorescence onboard theship. Therefore, the fluorescence is considered to have resulted from indigenous, thermally immature bitumens.

INTRODUCTION

Site 799 is located in the Kita-Yamato Trough in the south-centralJapan Sea (Fig. 1). Three holes drilled at the site penetrated 1084 mof sediment. The oldest sediment recovered is early Miocene in age.

The primary objective of Site 799 was to examine the depositionaland tectonic environments of massive sulfide mineralization in afailed backarc rift. A secondary objective was to obtain a detailedpaleoceanographic record of this backarc setting, including possibleevidence of low-oxygen water masses during the initial formation ofthe basin. The original drilling plans called for total penetration ofapproximately 1610 mbsf (including 50 m of basement). However,drilling was terminated at 1084 mbsf prior to reaching this objectivefor safety reasons when samples from Cores 128-799B-65R and128-799B-66R exhibited a slow, pale, yellowish-white cut fluores-cence (Shipboard Scientific Party, 1990).

This study was initiated (1) to supplement the available shipboardorganic geochemical data with information about downhole variabil-ity of the sedimentary organic matter and (2) to determine the signifi-cance of the cut fluorescence in Cores 128-799B-65R and128-799B-66R. This was to include a determination about whethermigrated, thermally mature, heavy hydrocarbons (C10+) are presentin the stratigraphic column and whether the penetrated section isactively generating heavy hydrocarbons.

ANALYTICAL METHODS

One hundred and eight samples were selected for analysis, basedon shipboard measurements of organic carbon (Shipboard ScientificParty, 1990). The stratigraphic distribution of these samples is pre-sented in Figure 2. Upon receipt, each sample was oven-dried at 60° Cand ground to approximately 325 mesh (44 µm). Organic carboncontent (Corg) and total sulfur were determined for each sample usinga LECO analyzer after decarbonation with HC1. Each sample was alsosubjected to whole-rock pyrolytic assay using the Rock-Eval systemdescribed by Espitalié et al. (1977). Selected samples underwentpyrolysis-gas chromatography, as described by Colling et al. (1986).This technique utilizes a pyroprobe which flash heats the sample to700° C for 5 s, trapping the products in a liquid nitrogen cold trap.The products were then permitted to achieve thermal equilibrium with

Pisciotto, K. A., Ingle, J. C, Jr., von Breymann, M. T., Barron, J., et al., 1992. Proc.ODP, Sci. Results, 127/128, Pt. 1: College Station, TX (Ocean Drilling Program).

2 Texaco Inc., E.TP.D., 3901 Briarpark, Houston, TX 77042.

the initial gas chromatograph oven temperature (50° C). After 18 min,the oven temperature was increased to 225° C at a rate of 8° perminute, and then to 310° C at a rate of 6° per minute. This finaltemperature was held for 6 min.

ANALYTICAL RESULTS

Organic Carbon and Total Sulfur

Organic carbon contents ranged from 0.90 to 5.08 wt%. These dataare detailed in Table 1 and Figure 2. All of the samples containabove-average quantities of organic carbon (> 0.3 wt%) relative todeep-sea sediments (Mclver, 1975), and all except seven samplescontain above-average quantities of organic carbon (> 1.0 wt%)relative to all fine-grain sedimentary rocks (Bissada, 1982). In gen-eral, the lower and middle Miocene sections, below 454 mbsf (Core128-799A-50X), display slightly greater levels of organic carbonenrichment than the younger sediments.

The shore-based organic carbon values measured as part of thisstudy differ slightly from the shipboard measurements (ShipboardScientific Party, 1990). In general, the shipboard measurements areslightly greater than the shore-based measurements (Fig. 3). Becausethere appears to be a systematic difference among the paired values,much of the difference may be attributable to a difference in analyticaltechniques. As noted previously, shore-based measurements wereperformed using a LECO analyzer, while shipboard values weredetermined by difference, with total carbon being determined usinga Perkin Elmer (model 240C) CHN-elemental analyzer, while car-bonate carbon was determined using a Coulometrics 5030 carbonatecarbon apparatus. The generally depressed shore-based measure-ments may reflect losses of organic matter as a result of hydrolysisduring decarbonation or depressed shipboard carbonate-carbon val-ues because of the presence of both dolomite and siderite.

The few values that differ substantially from the observed trendmay reflect sample inhomogeneity. Although measurements wereperformed using samples from the same intervals, they were notperformed on splits of a homogenized powder.

Total sulfur data also are included in Table 1. Total sulfur contentsrange from 0.04 to 3.06 wt%. The observed carbon/sulfur ratios donot appear typical of open marine sediments (Fig. 4). In general, thesediments appear to contain a slight excess of sulfur. However, thesulfur excess is less than would be expected from a euxinic environ-ment in which free H2S is present in the water column and sedimen-tary iron is available (Berner and Raiswell, 1983). The observedcarbon/sulfur ratios may reflect an iron deficiency rather than differ-

623

B. J. KATZ

40°N

39° -

133°E

Figure 1. Location map for Site 799.

134C 135° 136° 137e

ences in the availability of either O2 or H2S in the water column. Theseobservations are consistent with those of the Shipboard ScientificParty (1990).

Rock-Eval Pyrolysis

Pyrolytic assay provides information about hydrocarbon genera-tion potential, organic character, the extent of thermal diagenesis, andthe presence of "reservoired" hydrocarbons. Pyrolysis results aresummarized in Table 1 and Figure 2.

Total pyrolytic hydrocarbon yields (S + S2 = free distillablehydrocarbons [HC] + generatable HC) range from 0.69 to 18.83 mgHC/g rock. Good potential and/or effective hydrocarbon source rocksyield > 6 mg HC/g rock (Tissot and Welte, 1984). Within the presentsample suite, sediments of this quality are limited principally to thesection below 741 m (Core 128-799B-32R), i.e., the lower half of themiddle Miocene and lower Miocene sequences. However, cautionshould be exercised when evaluating these data because of the sus-pected low levels of thermal maturity of the sediments. In sampleshaving very low levels of thermal maturity, both the S! and the S2

peaks may not contain exclusively hydrocarbons, but may insteadcontain significant amounts of hetero compounds (i.e., moleculescontaining O, N, and S). The presence of these labile compounds mayresult in a slight overestimation of the hydrocarbon yields.

Although complicated by such factors as thermal maturity (Espi-talié et al, 1985), organic enrichment and mineral matrix effects(Katz, 1983), pyrolysis can be used to provide insight into the natureof the sedimentary organic matter. This interpretation is accomplished

using the hydrogen (mg "S2" HC/g Corg) and oxygen (mg CO2/g Corg)indexes and a modified van Krevelen-type diagram, as described byEspitalié et al. (1977).

Both the hydrogen and oxygen indexes samples from Site 799exhibit wide variability (Fig. 5). However, these data do indicate thata marked change occurs in organic facies within the middle Miocenesection (Fig. 2). The organic matter in the lower portion of the column,below 740 mbsf (Core 128-799B-32R), is more hydrogen enrichedthan the preserved organic matter contained within the upper portionof the stratigraphic column. The sediments in the lower portion of thestratigraphic column display hydrogen indexes of -400. This organicmaterial might be classified type II according to the scheme of Tissotet al. (1974). Type II organic material is typically well-preservedmarine organic matter. In the shallower portion of the column thehydrogen indexes typically range between 100 and 200. This materialshould be classified as type III organic matter according to the schemeof Tissot et al. (1974). Type III material typically is either oxidizedmarine or terrestrially derived organic matter. The elevated oxygenindexes (> ~150) are probably the combined result of an inorganicCO2 contribution from the various carbonate minerals present (cal-cite, dolomite, and siderite; Palacas et al., 1981; Katz, 1983), as wellas a contribution from the more functionalized components, includinghumic acids, typical of very thermally immature sediments.

An examination (Table 1) of the two pyrolysis thermal maturityindicators, T , ^ (temperature at which maximum pyrolytic hydrocar-bon generation occurs) and the transformation ratio (TR = S^fSj +S2]), suggests that the penetrated section is thermally immature (i.e.,has not entered the main phase of the thermal hydrocarbon genera-

624

PYROLYTIC ASSAY OF SAMPLES, SITE 799

0 m

4 0 0 -

500

600

700

800

900

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1000-******************

OrganicCarbon

FreeHydrocarbons

(S )mg HC/g rock)

QβneratableHydrocarbons

(S 2 )mg HC/g rock)

HydrogenIndex

mg HC/g C o r g )S /(S +S2)

max

0 5 0 1.0 2.0

Figure 2. Lithostratigraphic and geochemical summary for Site 799.

10 20 30 0 200 400 600 0 0.2 0.4 0.6 410 430 450 470

tion). This is manifested by the typically low Tm a x values of < 430° C andthe TR values of < 0.10 in the lower half of the sedimentary sequence.

These data further suggest that several samples (e.g., 128-799 A-3H-6, 10-15 cm, and 128-799A-25X-4, 113-117 cm) contain highproportions of secondary, recycled, or inert organic matter. This ismanifested by these samples' bimodal S2 peak. Samples showing abimodal S2 peak appear to be largely restricted to the upper portionof the stratigraphic column. The presence of "residual" material isconsistent with the suggested kerogen type, based on the hydrogenand oxygen indexes.

Although the TR values do indicate that the penetrated section isthermally immature, the observed trend in TR is anomalous and does

not represent a typically observed thermal maturation trend or profile.The highest TR values are observed in the upper portion of thesequence (Fig. 2). The inverted TR trend most probably reflects adecrease in the relative concentration of initial bitumens as a functionof organic diagenesis. This inverted trend may, in part, be a result ofthe conversion from biopolymers represented largely in the S, frac-tion to geopolymers represented by the S2 fraction (i.e., the kerogeni-zation process).

Although anomalously high TR values may sometimes indicate thepresence of migrated heavy hydrocarbons (petroleum), such is notconsidered to be the case at Site 799. Hydrocarbon shows or occurrencesare normally restricted to discrete intervals and typically do not display

625

B. J. KATZ

Table 1. Organic carbon and pyrolysis data, Site 799.

interval (cm)

799A

1H-1,44-492H-4, 74-783H-6, 10-144H-4, 20-254H-6, 20-255H-4, 20-256H-2, 20-256H-4, 20-257H-4, 40-458H-6, 50-549H-2, 30-35

15H-6, 54-5816H-4, 60-6516H-6, 60-6517H-2, 55-6017H-4, 40-4518H-4, 40-4518H-6, 40-4520H-2, 20-2522X-2, 77-8123X-2, 29-3323X-4, 20-2424X-2, 132-13624X-4, 98-10224X-6, 24-2925X-4,113-11727X-2, 25-2929X-2, 25-3029X-4, 22-2730X-6, 50-5532X-4, 50-5539X-4, 40-4439X-6, 40-4442X-6, 80-8543X-6, 40-4544X-2,10-1545X-4, 47-5246X-4, 20-2547X-4, 126-13047X-6, 144-14850X-2, 88-9250X-4, 93-97

799B

5R-1,90-946R-1, 33-386R-2, 10-157R-1,20-257R-3, 30-358R-6, 16-209R-2, 91-959R-4, 123-127

10R-2, 127-13110R-4, 64-6711R-5, 29-3111R-7, 32-3512R-4, 71-7413R-1, 56-6113R-3, 60-6514R-1, 85-9014R-3, 55-6015R-1, 25-3015R-4, 5-1016R-1,80-8516R-3,110-11517R-1, 25-3017R-3, 35^017R-5, 30-3518R-1, 143-14718R-3, 89-9118R-4, 139-14119R-1,77-8119R-3, 80-84

Depth(mbsf)

0.446.44

18.3025.0028.0034.6041.2044.2054.0066.7070.10

134.14140.90143.90147.55150.40160.10163.10176.20196.07205.29208.20215.92218.58222.84228.43243.15252.65255.62268.55283.20350.80353.80383.30392.50395.90408.87418.30429.06432.24454.68457.73

490.50494.93496.20499.90503.00516.96521.41524.73531.37533.74544.59547.62553.11558.16561.20568.15570.85577.25581.55587.40590.70596.55599.65602.60607.33609.79611.79616.37619.40

Organiccarbon(wt%)

1.251.011.110.993.341.011.361.011.102.700.901.361.321.411.501.421.741.751.251.121.531.431.051.391.190.961.041.400.951.740.901.201.051.741.990.911.111.071.371.692.123.07

3.614.922.423.103.852.851.772.402.022.571.673.781.582.101.932.223.035.084.923.212.711.881.961.461.963.201.922.473.10

Totalsulfur(wt%)

0.040.700.850.401.300.890.840.661.301.060.920.810.900.810.730.810.871.200.660.900.540.810.620.870.640.450.830.790.501.120.770.680.730.741.060.500.870.540.931.161.091.15

1.172.070.971.001.181.291.571.631.121.100.611.450.511.601.521.561.471.622.161.970.880.980.680.821.231.011.301.010.87

s, S2

(mg HC/g rock)

0.590.310.380.170.940.370.280.470.330.910.140.170.280.260.340.340.510.380.300.380.470.430.330.320.180.430.370.380.370.410.260.410.330.300.260.330.280.250.150.080.310.34

0.630.610.190.320.360.350.230.240.150.150.220.210.040.070.150.080.230.890.430.430.15

. 0.040.040.030.050.110.050.070.15

2.781.321.580.843.870.781.281.940.705.300.640.831.301.162.031.492.392.221.112.452.462.761.721.230.691.501.482.161.232.621.231.671.442.082.571.201.040.971.041.292.012.75

4.326.692.474.065.503.062.373.511.702.101.493.620.651.171.310.851.878.094.242.162.070.981.190.671.072.711.131.783.11

HIa

22213014284

1157694

19163

19671619882

13510513712789

2171611921638858

155142154129150136138137119129132939075769489

119136102130142107134146838189954155673861

15986677652604554845871

100

OIb

12814095

21383

47820875

23178

29228320329216620211422623277

19934

136218466

434

1307

16916835

141211183374544

44934326353

465757527050

1097250

1323961

394174222380212139235860

11211911270536324

TRC

0.180.190.190.170.200.320.180.200.320.150.180.170.180.180.140.190.180.150.210.130.160.140.160.210.210.220.200.150.230.140.180.200.190.130.090.220.210.200.130.060.130.11

0.130.080.070.070.060.100.090.060.080.070.130.050.060.060.100.090.110.100.090.170.070.040.030.040.040.040.040.040.05

T

420dBBB

415B

412B

<400437420407417415

B409411424414443423414

B418418

B408425

<400429410414415425432

<400<400

405430440427412

410417415421422409420417417420400421427433421415416414400

<400412422430428418420419420412

626

PYROLYTIC ASSAY OF SAMPLES, SITE 799

Table 1 (continued).

Core, section,interval (cm)

19R-5, 55-5920R-5, 108-11221R-3, 80-8422R-1, 6-923R-2, 50-5525R-1,60-6525R-3, 90-9526R-1, 120-12527R-1, 108-11227R-3,112-11728R-1, 40-4528R-3, 40-4528R-5, 40-4529R-2, 100-10529R-4, 75-8030R-1, 85-8732R-1,59-6133R-1, 69-7235R-2, 42-4436R-1, 137-14138R-1, 65-6739R-1, 103-10548R-2, 96-10051R-2, 78-8253R-2, 0-454R-1, 19-2362R-2, 13-1762R-4, 44-4863R-1,119-12364R-1, 0-465R-1, 83-8565R-2, 130-13265R-3, 14-1665R-3, 42-4466R-2, 53-5567R-1, 51-5367R-3, 72-74

Depth(mbsf)

622.15632.28638.70644.66656.20674.10677.40684.40693.58696.62702.50705.50708.50714.30717.05722.25741.09750.89771.42780.57799.15809.13897.06925.58944.10952.39

1031.131034.441040.291048.801059.231061.201061.541061.821069.221078.211081.42

Organiccarbon(wt%)

2.432.401.533.171.171.781.092.851.100.981.192.011.581.702.201.622.402.113.911.981.471.692.861.721.403.522.332.441.731.613.383.683.022.802.943.253.04

Totalsulfur(wt%)

1.001.000.390.990.810.940.720.981.231.150.990.981.270.770.991.401.071.421.971.090.740.881.391.081.001.831.541.310.741.022.002.582.172.762.742.433.06

s, S2

(mg HC/g rock)

0.070.260.090.340.150.240.100.300.090.060.120.140.180.120.210.170.370.351.170.320.230.270.620.260.170.560.330.320.150.080.500.660.590.490.590.650.51

2.704.641.206.421.823.212.276.041.300.721.963.682.612.354.414.078.326.90

18.838.475.406.85

11.685.724.20

14.9410.849.765.443.24

12.7514.0613.6510.4311.2611.7011.18

HIa

11119378

20215418020721211773

164182165138200251347326481428366405407331300424464400313201377381451372382360367

OIb

3019

102192220545924

1133291253848

463169

236217842

3312367917069

1112

TRC

0.030.050.070.050.080.070.040.050.060.080.060.040.060.050.050.040.040.050.060.040.040.040.050.040.040.040.030.030.030.090.040.040.040.040.050.050.04

Tmax(°C)

425419417421411413419418413417416425411421423414413402403408410412408409418410420417428430418424418423420420421

a Hydrogen Index (mg "S2" HC/g Corg).b Oxygen Index (mg CO2/g Corg).c Transformation Ratio S,/(S[ + S2).d Bimodal S2 peak.

a depth trend. In addition, the samples with the elevated TR values donot consistently display unusually low Tmax values (< 400° C), whichwould be typical for a hydrocarbon show.

The general absence of nonindigenous (stains and/or drillingcontaminants) hydrocarbons is consistent with the relationship be-tween TR and Tmax (Fig. 6), although several samples from Cores128-799A-29X, 128-799 A-44X, 128-799A-45X,and 128-799B-16Rdisplay slightly elevated TR values. The absence of nonindigenoushydrocarbons is also consistent with the relationship between S! andCorg (Fig- 7), in which all samples display low S^C^ values.

It is important to emphasize that the Rock-Eval data do not indicatethe presence of migrated hydrocarbons in Cores 128-799B-65R,128-799B-66R, or 128-799B-67R.

Pyrolysis-Gas Chromatography

Pyrolysis-gas chromatography provides additional informationabout the nature of kerogen (Larter and Douglas, 1980), as well asqualitative assessment of principal hydrocarbon products that mayhave been generated upon thermal maturation (Dembicki et al., 1983).

The chromatographic signatures obtained for all of the analyzedsamples generally lack higher-molecular-weight, waxy, alkane-alkene doublets. The best developed alkane-alkene doublets typicallyrange from C13 to C19. The lighter-end fraction is a complex hydro-carbon mixture that includes numerous aromatic species. In the highermolecular-weight range, a single peak tends to dominate in all sam-

ples independent of stratigraphic position or hydrogen index. Thispeak has tentatively been identified through its mass spectrum assqualene. Several samples (e.g., 128-799B-35R-2, 42-44 cm;Fig. 8D) also exhibit a well-developed naphthenic envelope. Thesesame samples also appear to display the best-developed and mostcomplete series of alkane-alkene doublets. In addition, these samplesdisplay a clearly defined harmonic decrease in peak height withincreasing carbon number.

These characteristics may be largely independent of the hydrogenindex value. Note the similarity in the chromatograms obtained fromSamples 128-799B-6R-1, 33-38 cm, and 128-799B-35R-2, 42-44 cm (Figs. 8B and 8D), with hydrogen indexes of 136 and 481,respectively. This similarity in chromatographic character suggeststhat some of the hydrogen indexes may be depressed by the presentof "inert" (strongly oxidized or recycled) organic matter, whichcontributes to the total organic carbon content but does not contributeto the hydrocarbon yield (Katz, 1988).

The poor peak development in samples (such as 128-799A-8H-6,50-54 cm; Fig. 8A) is typical of samples containing organic matterthat includes a large inert component. Such an interpretation isconsistent with the slightly elevated Tmax value of 437° C comparedto the expected level of thermal maturity, based on the sample's age(Quaternary), depth of burial (66.70 mbsf), and in situ temperature(~7°C; Shipboard Scientific Party, 1990).

The absence of abundant waxy components (nC22+) suggests thatthe reactive or "live" organic matter does not contain a significant

627

B. J. KATZ

2 4 6 8

Shore based measurement TOC (wt.%)10

Figure 3. Comparison of shipboard with shore-based organic carbon determinations.

terrestrial component and was, in general, autochthonous (i.e., ma-rine-derived). Such an interpretation is consistent with the presenceof a naphthenic envelope, a harmonic decrease in peak height in somesamples, as well as the presence of squalene, which has been foundin planktonic organic detritus (Saliot et al., 1988). Differences in thecalculated hydrogen indexes may reflect differences in the degree ofpreservation of the organic matter and/or the relative abundance ofresidual organic matter. The lower hydrogen index values mightindicate poorer organic preservation and/or a larger relative propor-tion of residual organic matter. A common "live" organic mattersource for the entire stratigraphic sequence is also consistent with theabundance of squalene in all of the pyrolysates.

The pyrolysis-gas chromatograph may also be used to thermallyextract and analyze the S! hydrocarbons. These results are presentedin Figure 9. Unlike mature extracts, which should be dominated byn-alkanes, these chromatograms are dominated by the isoprenoidspristane and phytane. rc-alkanes are either absent or present in onlytrace quantities relative to the two isoprenoids. Such a chromatographicpattern is consistent throughout the penetrated section, includingCores 128-799B-65R and 128-799B-66R, which exhibited cut fluo-rescence on-board the ship.

As expected, a downhole increase in the complexity of the chro-matographic pattern reflects the onset of thermal hydrocarbon gen-eration, but not the presence of thermally mature hydrocarbons.

These thermal extracts also display variations in the pris-tane/phytane ratio and the relative abundance of specific compounds.For example, the pristane/phytane ratio of Sample 128-799B-65R-3,14-16 cm, is ~l.O (Fig. 9D) compared with 0.44-0.66 observed inthe other samples. Such differences probably reflect temporal changesin both the biomass and the depositional environment.

DISCUSSION

Although all of the samples selected for this study were organi-cally enriched, samples from the lower portion of the stratigraphicsection (deeper than 454 mbsf; lower and middle Miocene) generallycontain more organic matter than the shallow section. In addition,samples deeper than 740 mbsf display the most elevated hydrogenindexes. The discordance between organic enrichment and organic-

1 2 3 4 5Total organic carbon (wt.%)

Figure 4. Relationship between total organic carbon and total sulfur. Dashed line =observed relationship for normal, modern marine sediments. Solid line = observedrelationship for euxinic sediments of the Black Sea (Berner and Raiswell, 1983).

hydrogen enrichment suggests possibly independent enrichmentmechanisms. It is possible that the differences in organic carbonreflect differences in sedimentation rate, with higher TOCs associ-ated with higher sedimentation rates (Muller and Suess, 1979), whiledifferences in the hydrogen indexes may reflect differences in pres-ervation efficiencies, with higher hydrogen index values reflectingbetter preservation, possibly as a result of more restricted circulation.

Kayoma et al. (1973) observed that organic hydrogen decreases at agreater rate than organic nitrogen, which in turn decreases at a more rapidrate than organic carbon during biochemical degradation of organicmatter. Thus, the depletion in organic hydrogen associated with relativelyconstant organic carbon contents observed at Site 799 is probably theresult of differences in the relative rates of elemental decomposition.

Possibly the most important results of this work are associatedwith the findings concerning the presence and generation of heavyhydrocarbons. The Rock-Eval maturity indexes clearly indicate thatthe penetrated section is thermally immature and has not yet enteredinto the main phase of hydrocarbon generation. This is consistent withthe sediment's age, depth of burial, and geothermal gradient(98°C/km; Shipboard Scientific Part, 1990). In addition, these dataindicate that migrated heavy hydrocarbons are not present within thepenetrated section. No heavy hydrocarbon anomalies were detected,and those hydrocarbons that were observed appear to be thermallyimmature. Although the thermal extracts display increased complex-ity with depth, probably as a result of thermal hydrocarbon genera-tion, such changes in composition are most probably associated withthe earliest phases of thermogenic hydrocarbon generation. Thisinterpretation is consistent with the Rock-Eval data and the interpre-tation of the volatile hydrocarbons by the shipboard party (ShipboardScientific Party, 1990), who noted the presence of significant quanti-ties of neopentane.

Although it was prudent and necessary to terminate drilling priorto reaching Site 799's objective, because of the observed cut fluores-cence and the lack of shipboard data to determine the nature of thefluorescing material, this post-cruise investigation indicates that drill-ing might have proceeded safely if a more complete hydrocarbonmonitoring program had been in use. This interpretation is significant

62 X

PYROLYTIC ASSAY OF SAMPLES, SITE 799

1000

800

×V 600

cCDCHO

•σ

I400

200

TYPE

- -TYPE

r I /

- I•• # V TYPt

50 100 150 200

Oxygen index

250 300 350

Figure 5. Modified van Krevelen-type diagram using the pyrolysis-derived hydrogen and oxygen indexes.

because a re-entry cone was left at the site and drilling might resumeat Site 799 if the JOIDES Resolution returns to the Japan Sea.

SUMMARY

1. The lower portion (middle and lower Miocene) of the strati-graphic section is generally more enriched in both organic carbon andorganic hydrogen. It appears that there may be different causes forthe organic carbon and organic hydrogen enrichment. Organic carbonenrichment may reflect elevated sedimentation rates, while organichydrogen enrichment may reflect increased preservation resultingfrom more restricted circulation.

2. Rock-Eval data do not indicate the presence of migrated heavyhydrocarbons in Cores 128-799B-65R, 128-799B-66R,or 128-799B-67R. Nor do these data indicate that the penetrated section experienc-ed the necessary burial/thermal history for beginning the catagenicgeneration and expulsion of heavy hydrocarbons. This low level ofthermal maturity is manifested in both Rock-Eval indexes.

3. The chromatographic fingerprint of the S! peaks obtained fromCores 128-799B-65R, 128-799B-66R, and 128-799B-67R are con-sistent with thermally immature bitumens and are similar to those ob-tained in the shallow portion of the section (Core 128-799A-4H). Thethermal extracts are dominated by the isoprenoids pristane and phytane.

4. A decision to continue drilling could have been justified if amore complete shipboard hydrocarbon monitoring program had beenin use on Leg 128.

ACKNOWLEDGMENTS

The author thanks Texaco Inc. for permission to publish thisresearch. Samples were supplied by Matta T. von Breymann of theOcean Drilling Program. Analytical support was provided by TheolaBreaux, Mike Darnell, and Thomas Jorjorian. Mary Hill providededitorial assistance with the original manuscript. Vaughn D. Robison,George E. Claypool, and Kay Emeis provided critical reviews of anearlier version of this manuscript.

REFERENCES

Berner, R. A., and Raiswell, R., 1983. Burial of organic carbon and pyritesulfur in sediments over Phanerozoic time: a new theory. Geochim. Cos-mochim. Acta, 47:855-862.

Bissada, K. K., 1982. Geochemical constraints on petroleum generation andmigration—a review. Proc. 2nd ASCOPE Conf. Exhib., 69-87.

Colling, E. L., Burda, B. H., and Kelley, P. A., 1986. Multidimensionalpyrolysis-gas chromatography: applications in petroleum geochemistry.J. Chromatogr. Sci., 24:7-12.

Dembicki, H., Jr., Horsfield, B., and Ho, TTY., 1983. Source rock evaluationby pyrolysis-gas chromatography. AAPG Bull., 67:1094-1103.

Espitalié, J., Deroo, G., and Marquis, F, 1985. La pyrolyse Rock-Eval et sesapplications. Rev. Inst. Fr. Pet., 40:563-579.

Espitalié, J., Madec, M., Tissot, B., Menning, J. J., and Leplat, P., 1977. Sourcerock characterization methods for petroleum exploration. Proc. 9th Anna.Offshore Technol. Conf., 3:439-443.

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Katz, B. J., 1983. Limitations of "Rock-Eval" pyrolysis for typing organicmatter. Org. Geochem., 4:194-199.

, 1988. Clastic and carbonate lacustrine systems: an organic geo-chemical comparison (Green River Formation and East African lakesediments). In Fleet, A. J., Kelts, K., and Talbot, M. R. (Eds.), LacustrinePetroleum Source Rocks. Geol. Soc. Spec. Publ. London, 81-90.

Koyama, T., Nikaido, M., Tomino, T., and Hayakawa, H., 1973. Decomposi-tion of organic matter in lake sediments. Proc. Symp. Hydrogeochem.Biogeochem., 2:512-535.

Larter, S. R., and Douglas, A. G., 1980. A pyrolysis-gas chromatographicmethod for kerogen typing. In Douglas, A., and Maxwell, J. R. (Eds.),Advances in Organic Geochemistry, 1979: New York (Pergamon Press),584-597.

Mclver, R. D., 1975. Hydrocarbon occurrences from JOIDES Deep SeaDrilling Project cores. Proc. 9th World Pet. Congr.: London (AppliedScience Publ.), 2:269-280.

Muller, P. J., and Suess, E., 1979. Productivity, sedimentation rate and sedi-mentary organic carbon in the oceans. I. Organic carbon preservation.Deep Sea Res. Part A, 26A: 1347-1362.

Palacas, J. G., Daws, T. A., and Applegate, A. V, 1981. Preliminary petroleumsource-rock assessment of Pre-Punta Gorda rocks (lowermost Cretaceous-Ju-rassic?) in south Honda. Trans. Gulf Coast Assoc. Geol. Soc, 31:369-376.

Saliot, A., Tronczynski, J., Scribe, P., and Letolle, R., 1988. The applicationof isotopic and biogeochemical markers to the study of biogeochemistryof organic matter in a macrotidal estuary, the Loire, France. Est. Coast.Shelf Sci., 27:645-669.

Shipboard Scientific Party, 1990. Site 799. In Ingle, J. C , Jr., Suyehiro, K.,von Breymann, M. T., et al., Proc. ODP, Init. Repts., 128: College Station,TX (Ocean Drilling Program), 237^02.

Tissot, B., Durand, B., Espitalié, J., and Combaz, A., 1974. Influence of natureand diagenesis of organic matter in formation of petroleum. AAPG Bull.,58:499-506.

Tissot, B. P., and Welte, D. H., 1984. Petroleum Formation and Occurrence(2nd ed.): New York (Springer-Verlag).

Date of initial receipt: 30 January 1991Date of acceptance: 29 August 1991Ms 127/128B-163

500

480

460oo

440

420

400

Inert carbonpresent

Post-mature

T

- Hi

Main Stage ofhydrocarbongeneration

Non-indigenous hydrocarbons present

Immature 7

o.oo 0.20 0.40 0.60

Transformation ratio

0.80 1.00

Figure 6. Relationship between Tmax and TR, permitting an assessment of thermal maturity, the presence of inert carbon, and nonindigenous hydrocarbons.

630

PYROLYTIC ASSAY OF SAMPLES, SITE 799

100r

0.0110

Total organic carbon (wt.%)

Figure 7. Relationship between S{ yield and total organic carbon. Any samplesplotting above the dashed line typically are contaminated or contain migratedhydrocarbons.

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B. J. KATZ

Squalene

Squalene

Figure 8. Pyrolysis-gas chromatograms. A. Sample 128-799A-8H-6, 50-54 cm. B. Sample 128-799B-6R-1, 33-38 cm. C. Sample 128-799B-22R-1, 6-9 cm.D. Sample 128-799B-35R-2, 42-44 cm. E. Sample 128-799B-67R-3, 9-11 cm.

632

PYROLYTIC ASSAY OF SAMPLES, SITE 799

Phytane

B

Phytane

Pristane

Pristane

Phytane

Pristane

Pristane Phytane

Phytane

Figure 9. Gas chromatograms of thermally extracted S] hydrocarbons. A. Sample 128-799A-4H-6, 20-25 cm. B. Sample 128-799B-35R-2, 42-45 cm. C. Sample128-799B-65R-2, 130-132 cm. D. Sample 128-799B-65R-3, 42-44 cm. E. Sample 128-799B-66R-2, 53-55 cm. E Sample 128-799B-67-1, 51-53 cm.

633