deep sea drilling project reports and publications - 37 ...organic geochemical investigation of...

37. PRELIMINARY RESULTS, ORGANIC GEOCHEMICAL INVESTIGATIONOF BLACK SEA SEDIMENTS: DEEP SEA DRILLING PROJECT LEG 42B

Donald F. Anders, George E. Claypool, Sister Carlos M. Lubeck, and John M. Patterson,U.S. Geological Survey, Box 25046, Denver Federal Center, Denver, Colorado

INTRODUCTION

Black Sea sediments of Pleistocene age cored duringDSDP Leg 42B were deposited mostly under lacustrineconditions. The shipboard summary of this legmentions certain similarities between these Black Seasediments and those of the Eocene Green RiverFormation of Wyoming, Colorado, and Utah. A suiteof samples has been analyzed in order to test fororganic geochemical similarities. It is believed that theresults provide a useful analog for lacustrine sedimentsof Tertiary age in the western United States.

The latitude, longitude, water depth, and depth ofpenetration of each drilling site is summarized in Table1. The general stratigraphy of the penetrated section isshown in Figure 1.

ANALYTICAL PROCEDURES

Organic carbon: Samples of 0.25 to 0.75 g weretreated with 1 to 3 ml cone. HC1 in LECO filteringcrucibles. The solution was evaporated to dry ness toremove excess HC1 and to promote precipitation oforganic material possibly solubilized in the acidtreatment. The crucibles were lightly washed withdistilled water under suction, and then oven dried at105°C. After addition of combustion accelerators, thesamples were burned in a stream of oxygen. The CO2produced was measured gravimetrically in ascarite-magnesium perchlorate absorption bulbs.

Thermal analysis: The MP-3 thermal chromatographwas used following the general procedure described byClaypool and Reed (1976). About 0.05 to 0.15 g offreeze-dried sediment was heated at a rate oftemperature increase of 40°C/min, from 30° to 800°Cin a stream of helium. Organic-carbon-containingcompounds evolved as a function of temperature weretransported from the furnace by a heated line (250°C)and monitored by a hydrogen flame ionizationdetector. The total millivolt signal was integrated overthe time of the analysis, normalized by the sampleweight, and related to the quantity of volatile organicmatter evolved from the rock by empirical calibrationcurves.

Solvent extraction and column chromatography:Samples of freeze=dried sediment, weighing from 63 to104 g were disaggregated and lightly ground in aporcelain mortar and pestle, then extracted withchloroform in a soxhlet apparatus. The chloroform-soluble bitumen was isolated by distillation of thechloroform under reduced pressure, followed byevaporation under nitrogen to an arbitrarily defined

TABLE 1Location, Water Depth, and Depths of Penetration for Black Sea

Drilling Sites, Leg 42B

Site Latitude Longtitude

WaterDepth

(m)

Depth ofPenetration

(m)

379 43°00.29' 36°00.68' 2172 624

380/380A 42°06' 29°37' 2115 1074381 41°40.25' 29°24.96' 1751 503

constant weight (weight loss after 15-minuteevaporation period is less than 0.2 mg or 5% of previousnet weight). The total bitumen, or an aliquot, was

SITE381

EXPLANATION

t • ^ r r J Terrigenous

^--λ Dolomite—"--a

S I Siderite

A I Aragonite

Z 1 Zeolites

Breccia

Figure 1. General stratigraphy of Black Sea sediments, Leg42B drilling sites.

755

D. E. ANDERS, G. E. CLAYPOOL, C. M. LUBECK, J. M. PATTERSON

fractionated over silica gel into heptane, benzene, andbenzene-methanol eluates, which were isolated andweighed using the same procedure applied to thebitumen.

Gas chromatography of heptane eluate: The heptaneeluate of each sample was redissolved in an amount ofheptane sufficient to give a concentration of about 10mg/ml. 2.4 µl of each sample was injected by a Varian8000 automatic sampling device and analyzed in aVarian 2800 on 2.0 mm X 1.8 meter columns packedwith 3.0% GCSE-30 on 100-120 mesh Gas Chrom Q,He flow was 40 ml/min. Column temperature was 80°Cat injection and was programmed to rise 12°C/min for10 minutes, then 10°C/min for 12 minutes to a finaltemperature of 320°C.

Gas chromatography-mass spectrometry of heptaneeluate: Each of the heptane eluates was injected intoanother gas chromatograph (HP5710A) connected by a2.3 cm Watson Biemann Helium separator to a HitachiRMU-6H mass spectrometer equipped with an AEIDS-50 data system. Prior to enrichment, the materialwas separated by gas chromatography on a stainlesssteel 2 meter × 3.2 mm ID column packed with 3% SE-30 on 80-100 mesh Gas Chrom Q (8O-3OO°C @10°C/min). The Helium flow rate of 30 cc/min wassplit at the exit of the column, allowing 20 cc/min to goto the Helium separator (maintained at 300°C) and 10cc/min to go to the FID detector. The ion sourcetemperature was approximately 220°C. The ionizingvoltage was 70 eV with a filament emission of 80 µA.Scan rate was 3 sec/decade for the mass range 28-560AMU. Spectra were recorded on an AEI DS50 datasystem. Background spectra were also recorded. PFK(perfluorokersene) was used as mass marker. Allreported spectra have had the background subtractedand have been normalized to the most intense fragmention above m/e 100.

RESULTS AND DISCUSSION

Organic Carbon and Thermal AnalysisSixty-seven samples from Leg 42B were analyzed for

organic carbon by combustion of an acid-insoluableresidue. These results are given in Table 2. Thirty-fourof these samples were also analyzed by the thermalanalysis-pyrolysis technique. The integrated flameionization response is converted to Pyrolytichydrocarbon yield by an empirical calibration curveand is also summarized in Table 2.

Figure 2 is a plot of organic carbon versus thermalanalysis (pyrolysis) hydrocarbon yield. Also shown onFigure 2 for comparison are results from five blackshale samples of Aptian and Albian Age from Hole391, Leg 44. Figure 2 illustrates that there is aconsistent non-linear relationship between the yield ofvolatile pyrolysis products and the amount of organiccarbon. The slope of this curved line is apparently acharatceristic of the type of organic matter depositedand preserved in a particular sedimentary environment.In the case of Black Sea sediments, one possibleinterpretation of the relationship shown in Figure 2 isthat there is a mixture of two dominant types of organic

TABLE 2Organic Carbon and Pyrolytic Hydrocarbon

Yield Leg 42B

Section

Hole 379A

21-522-523-324-125-627-629-231-234-536-338-340-142-243-245-346-547-348-549-650-651-352-454-756-056-457-258-159-260-162-165-165-566-167-368-268-6

Hole 379B

4-25-18-59-3

Hole 380

0-119-525-3

Hole 380A

3-114-121-337-248-053-464-370-174-1

Site 381

2-36-18-2

Organic Carbon(wt %)

0.460.490.380.401.720.300.370.460.720.610.490.230.680.280.210.200.300.180.240.430.380.290.300.140.370.390.130.350.500.270.270.390.280.790.500.37

0.502.420.340.36

0.570.800.61

1.010.950.430.831.892.012.351-.111.52

0.450.310.40

Pyrolytic HCYield(wt %)

—---

0.31—--

0.087—-—

0.061---

0.020--------

0.035---——

0.023—---

_0.85

—-

0.0630.0680.041

0.0720.0910.0470.100.550.560.970.210.35

0.0110.0110.009

756

ORGANIC GEOCHEMICAL INVESTIGATION OF BLACK SEA SEDIMENTS

TABLE 2 - Continued

SectionOrganic Carbon

(wt %)

Pyrolytic HCYield

(wt %)

Site 381

9-012-313-215-116-317-223-626-133-537-354-054-5

— Continued

0.780.480.730.630.510.611.371.591.035.321.271.54

0.0340.0140.0880.0400.0230.0430.220.470.373.180.140.19

aLeaders (-) indicate sample was not analyzedfor Pyrolytic hydrocarbon.

Oil yield (wt %)0.4 0.6

DSDP SAMPLES

• Atlantic

O Black Sea

1 2 3

Detector response (10° i.u./mg)

Figure 2. Organic carbon content versus Pyrolytic hydro-yield.

matter. The sediments appear to contain a constantminimum of about 0.4% organic carbon which isrefractory and yields little or no volatile product uponpyrolysis. This component may be recycled kerogen orcharcoal. Added to this refractory carbon is a variablecomponent of labile organic carbon which mayrepresent organic matter produced in the water columnoverlying the sediment, or otherwise close to the site ofdeposition.

Extractable Organic Matter

Twelve samples from Site 380 were analyzed byconventional petroleum source-rock evaluationtechniques. The results are summarized in Table 3. Thecontent of chloroform-extractable bitumen ranges from37 to 1520 ppm by weight, or from 0.9% to 6.4% of theorganic carbon. In general, the deeper calcareous anddolomitic sediments contain more organic matter thanthe shallower, dominantly terrigenous part of thesection.

When the chloroform-extractable organic matter isfractionated on silica gel, the heptane eluate iscomposed predominantly of alkane and cycloalkanehydrocarbons; the benzene eluate contains aromatichydrocarbons and, in thermally immature sediments,abundant nonhydrocarbons such as esters andalcohols; the 1:1 benzene-methanol eluate contains themost polar compounds, i.e., the asphalticnonhydrocarbons.

Generally, the sum of the three fractions does notequal the theoretical quantity of bitumen placed on thesilica-gel column, as indicated by the percentages in thelast column of Table 3. This discrepancy is due to(1) the weight of unevaporated chloroform in sampleswith the highest bitumen concentrations, (2) a smallamount of column hold-up, (3) additional evaporationlosses in subsequent solvent evaporation steps. For verysmall samples these factors are minimal; however,column blank or hygroscopic material in the benzene-methanol fraction may cause recoveries slightly greaterthan 100%.

The extractable organic matter from dominantlyterrigenous sediment appears to contain the highestproportion of saturated hydrocarbons (heptane eluate),and the lowest proportion of asphaltics. Diatomaceous,calcareous, and dolomitic sediments containextractable organic matter which is lower in relativeamounts of saturated hydrocarbons.

There is no apparent variation in the relativeamounts of the various classes of extractable organicmatter with depth of burial and/or with age andtemperature history.

Gas Chromatography

The detailed composition of the heptane eluate isindicated by the gas chromatograms shown in Figures3(A-L). The hydrocarbon composition appears to begenerally related to the stratigraphy, or to thecomposition of the organic matter deposited andpreserved at different stages during the geologicalhistory of the Black Sea.

Odd-numbered «-alkanes in the range of n-d to n-C35 are the major constituents of the saturatedhydrocarbons extracted from all samples analyzed inHoles 38O/38OA, except for Section 380A-53-4 at 821 m(Figure 3[I]), which is dominated by (95%) tetracyclic andpentacyclic triterpane hydrocarbons. Samples from theshallower, dominantly terrigenous part of the sectionalso contain appreciable amounts of mono-, di-, andtricyclic alkanes, which are expressed in thechromatogram as a hump of unresolved compoundsoccurring between n•Cu and /1-C25. Samples deeperthan 380A-37-2, which is at 667 meters, contain noappreciable Cu-to-C25 cycloalkane hydrocarbon hump.

Sediment samples from depth intervals shown asdiatomaceous in the general stratigraphic section(Figure 1) contain one or both of two compoundswhich may be biological markers characteristic ofdiatoms. These compounds are shown as the majorpeaks in th n-Czs region in Figures 3(B,D,E,H, and I).

Tetracyclic and pentacyclic hydrocarbons areabundant in all of the samples from 380A-48-0 at 770meters to the deepest sample, 380A-74-1, at 1017meters. The appearance of significant amounts of these

757


TABLE 3Extractable Organic Matter, Black Sea Sediments, Site 380

SampleInterval in cm

380-0-1,126-150380-19-5, 85-97380-25-3, 102-113380A-3-1, 66-78380A-14-1, 67-80380A-21-3, 40-50380A-37-2, 60-72380A-48-0, 1-12380A-5 3-4, 8-17380A-64-3, 12-24380A-70-1, 25-36380A-74-1, 89-100

Depth (m)

1178231352457526667770821925979

1017

OrganicCarbon(wt %)

0.60.80.71.01.00.40.81.92.02.41.11.5

CH3CI-solubleBitumen(wt ppm)

153206108210175

3781

250119015 20

175279

HeptaneEluate

(wt ppm)

1814161113

58

1194631414

BenzeneEluate

(wt ppm)

2324193125

91841

101249

3051

Benzene-Methanol

Eluate(wt ppm)

88141

60141132

2557

184639640105150

PercentRecovery

84.386.988.087.197.1

1054102.5

94.470.162.685.177.1

compounds roughly corresponds with a transition fromdominantly terrigenous, detrital sediments todominantly calcareous or dolomitic marls. These twosediment types probably contain different types oforganic matter. The end=member composition ofsaturated hydrocarbons associated with these two typesof organic matter may be represented by Sections380A-21-3 and 380A-53-4 (Figures 3[F and J]).

Mass Spectral Evidence for Structure of ProminentCompounds

The compounds which occur prominently in samplesfrom Black Sea Holes 38O/38OA are listed in Table 4. Adiscussion of polycyclic compounds follows.

Compounds M+330 and m+328: These compoundsare suggested as biological markers derived fromorganic matter deposited with diatomaceous sediments.The mass spectrum of the M+330 (C24H42) compoundindicates intense parent and M-CH3 (m/e 315) ions,with other major fragmentions at M-CòHn (m/e 245),m/e 191, m/e 179, and m/e 177 (see Figure 4).Interpretation of ions at m/e 245, 191, and 179 suggeststhe structure shown in Figure 4. The structure of m+328(C24H40) and a homolog M+314 (C23H38) isolated fromthe leading edge of peak M+328 could not bedetermined from their mass spectra, shown in Figures 5and 6, respectively.

Compounds M+372 and M+370: The M+372 (C27H48)compound has the fragmentation pattern of 5 -cholestane with typical sterane fragment ions at m/e149, 163, 177, 217, and 218. The M+370 (C27H46) peakrepresents at least two geometric isomers having massspectral fragmentation patterns (Figure 7)characteristic of C27 sterenes (Rubinstein et al., 1975;Rhead et al., 1971). The leading edge of the peak givesM+370 (100%), 355 (38%, M-CH3), 257 (83% M-sidechain from C-17), and 215 (40%, cleavage of D ring atbonds 13-17 and 14-15). The top of the GC peak givesthe following mass spectral characteristics: M+370(100%), 355 (40%, M-CH3), 257 (50%, M-side chainfrom C-17), and 215 (97% M-cleavage of D ring atbonds 13-17 and 14-15). The mass spectralfragmentation pattern of the latter M+370 peakresembles somewhat the cholest-5-ene spectrumdescribed by Rhead et al., (1971); except that the m/e

275 and 301 ions are less intense in the Black Seasamples.

Compound M+384: The GC-MS peak correspondingto M+384 (C28H48) is a pentacyclic triterpane of thedegraded moretane-lupane-hopane variety. The massspectrum is shown in Figure 8. Cleavage of the 9-11 and8-14 bonds gives the m/e 191 ion. Cleavage of the 12-13and 8-14 bonds gives the m/e 163 ion. Ethyl loss at M-29 is also seen. The absence of an M-43 ion and a majorfragment ion corresponding to cleavage of a five-membered ring at bonds 18-19 and 17-21 suggests thatring E is of the type group 8b described by Kimble etal., (1974).

Compound M+398 (sterene): Fragmentationcharacteristics of the M+398 (C29H50) compound shownin Figure 9 suggest a C29 sterene (Steel and Henderson,1972). This compound appears as a small peak on thefront edge of the M+410 peak in Sample 380A-53-4(Figure 3[I]) and as a major peak in Sections 380A-64-3(Figure 3[J]), 380A-70-1 (Figure 3[K]), and 380A-74-1(Figure 3[L]). Key diagnostic fragment ions for this GCpeak are M+398 (64%), 383 (35%, M-CH3), 257 (51%,M-C10H21 from cleavage of side chain at C-17), 215(100% M-cleavage of D ring at bonds 13-17 and 14-15),149 (66%), and 147 (86%). If this compound is derivedfrom a dehydrated C29 sterol, such as B-sistosterol orstigmastanol, the double bond is probably in the 5-6position, unless rearrangement has taken place. Thesuggested structure is conjecture at this point.

Compound M+410 (pentacyclic triterpene): Theprincipal mass spectral fragment ions (Figure 10) forthe GC-MS, M+410 (C30H50) peak (Figure 3[I])areasfollows: M+410 (20%), 367 (36%, M-C3H7), 231 (41%),191 (73%), 189 (38%), 177 (18%), 175 (31%), 163 (23%),161 (59%), 149 (19%), 147 (22%), 137 (46%), and 135(100%). The ion pairs at m/e 191-189, 177-175, 163-161,and 149-147, and the ions m/e 107, 121, and 135suggest an unsaturated pentacyclic triterpenoid. Theonly natural pentacyclic triterpenoids showing a C3H7loss contain an isopropyl group attached to a five-membered ring. Also, the only C30 pentacyclic tri-terpenoids showing no cleavage of their five-memberedring are of the lupane-hopane variety (Kimble et al.,1974). The m/e 189 and 191 ion pair, with the 191 iondouble the intensity of the 189 ion, suggests a non-

758


D

352m

B178m E

457m

C231m F

526m

Figure 3A-F. Gas chromatigraphic analysis of saturated hydrocarbons from Hole 380/380A sediments.

759


G

821m

J

925m

K979m


TABLE 4Occurrence of Major Gas Chromatographic Peaks Examined

by Mass Spectrometry in Black Sea Samples

Section

Compound, (s)

η-alkanespristanephytanemono-, di-, tricyclic alkanes

(unresolved)m + 328m + 330m + 370 (cholest-5-ene)m + 372 (5-α-cholestane)m + 384 (C28 pentacyclic triterpane)m + 398 (C29 sterene)m + 398 (C29 pentacyclic triterpane)m + 410 (pentacyclic triterpane)m + 412 (pentacyclic triterpane)m + 426 (pentacyclic triterpane)

Depth (m)

.-H CO f N

o o o o o o o o o o o oo o o o o o o o o o o o o o o o o o o o o o o oc o c o c o c o c o c o c o c o c o c o c o c o

X X X X X XXX ? X ? XX X X X ? X

X X X X X XX X XX

X X X XX X

X X X X

X X X X X

X X X X XX X X X XX X X X X

XX XX XX X X X X

X X X X X XX X X X X X

X X X X XX X

X X X X X XX X X

X X X X

>•o r— o ~* m ON C~CN VO t ^ CN ( N (― - H>o \o r— oo os σ * o

245 -+ 1

191- ^179& 2H 177-«

179&-2H=177

- 191

M-43287

J I

Figure 4. Mass spectra of compound M 330.


symmetrical nucleus. The more intense 191 ionprobably results from the D and E ring fragment(Kimble et al., 1974). The presence of intense ions at 79,



×-- m

L L 1. I

M-29 M-15355 369


93, 107, 121, and 135, lead us to believe that the doublebonds resides in ring A. Again, without an authenticsample for comparison, any suggested structure isconjecture.

Compound M+398 (pentacyclic): The M+398 (C29H50)compound eluting as the major component in Section380A-53-4 (Figure 3 [I]) is probably of the degradedoleanane-gammacerane (Figure 11) variety containing

761


LJLJ U i

Figure 9. Mass spectra of compound M 398 (sterene).

Figure 10. Mass spectra of compound M+ 410.

Figure 11. Mass spectra of compound M+ 398 (penta-cyclic).

five six = membered rings, two of which have the A-Bring configuration (giving the intense m/e 191 ion) andtwo of which have the D-E ring configuration minusone methyl substituent (giving the m/e 177 ion). Nofragment ions were seen to suggest a five-member ring

(i.e., m/e 327) or a side chain larger than methyl. Themass spectrum resembles the C29H50 pentacyclic tri-terpenoid isolated by Gallegos (1971) from Green Rivershale.

Compound M+412: Mass spectral fragmentation ofthe M+412 (C30H52) compound (Figure 12) in Section380A-53-4 (Figure 3[I]) suggests a structure similar to theAdianane variety of pentacyclic triterpenoids (Kimbleet al., 1974). Fragmentation producing the m/e 179 andm/e 191 cleavage products in Adianane type triterpanesappears to be controlled by the substituents at C-13 andC-14. The m/e 327 ion results from cleavage of the 18-19 and 17-21 bonds of the five-member ring. The m/e259 ion comes from cleavage of the 13-18 and 14-15bonds of ring D.

Compound M+426: The M+426 (C31H54) compoundin Sample 380A-53-4 is resolved by gaschromatography (Figure 3[I3); however, it is also presentin every sample throughout the core. Its mass spectrum,shown in Figure 13, appears to be similar to the penta-cyclic triterpane, Homomoretane, isolated by Andersand Robinson (1971) from Green River shale. For adiscussion of fragmentation routes of such compounds,with extended chains, see Kimble et al., (1974).



162


GENERAL OBSERVATIONS

The Black Sea sediments penetrated in Holes38O/38OA are of dominantly terrigenous origin in theupper part of the section, while the lower part of thesection contains abundant dolomitic marls. The hydro-carbons extracted from the sediments may reflect, in asimilar way, provenance or origin of the organicmatter. In the upper part of the section «-alkanes arethe predominant hydrocarbon constituents, while in thelower part of the section steranes (and sterenes) andpentacyclic triterpanes (and triterpenes) are majorconstituents, although w-alkanes are usually importantthroughout the section. There is no clear evidence forthermal diagenetic effects in the heavy hydrocarbonfraction of these samples. The organic matter in theupper part of the section may be predominantly thatwhich has washed in with the terrigenous sediment, i.e.,an allochthonous component which is resistant tooxidative decomposition during sedimentary trans-port, such as higher plant tissues. In the lower part ofthe section, a major component of the organic matterpreserved in the sediments may be that which isproduced at the site of deposition (i.e., anautochthonous component), which would tend to bebetter preserved during carbonate-depositing phases ofthe Black Sea lake.

The terrigenous allochthonous component ischaracterized by a saturated hydrocarbon assemblageof predominantly odd-numbered n-alkanes withmaxima at n-Cn, and by 1-, 2-, and 3-ring cyclo-alkanes. The hydrocarbon assemblage of the lacustrine,autochthonous component appears to be uniquelycharacterized by the presence of C27 and C29 sterenes,and by the absence of 1-, 2-, and 3-ring cycloalkanes. Inaddition, pristane, phytane, and a variety of tetracyclicand pentacyclic hydrocarbons are present atconcentration levels greater than or subequal to thoseof the w-alkanes. The samples in Holes 38O/38OA fromdepths of 1 to 526 meters contain predominantlyallochthonous organic matter, while the samples from770 to 1017 meters contain mostly autochthonousorganic material. The sample at 667 meters appears tobe transitional.

The average organic carbon content of the sevenshallowest samples in Holes 380/380A is 0.9%, while itis 1.8% for the five deepest samples. Moreover, the yieldof Pyrolytic hydrocarbons is 0.03% to 0.08% for theshallow interval containing the allochthonous organicmatter, and 0.20% to 0.97% for the deeper interval

containing the autochthonous organic matter. Theresult is that the average yield of Pyrolytichydrocarbons per unit of organic carbon is about fourtimes higher for organic matter in the deeper part of thesection. These differences illustrate the importance ofthe environment of deposition to the generation ofhydrocarbons; apparently the type of organic matterpreserved during carbonate deposition has a greatercapacity to form hydrocarbons.

Although the organic matter is very well preserved inthese cores, it is not present in unusually highconcentrations. This is most likely due to the extremelyrapid sedimentation rate and consequent dilution of theorganic matter by noncarbonaceous, but possiblybiogenic, sedimentary constituents. Thus, while theBlack Sea sediments are in many respects qualitativelysimilar to Green River oil shale, they have only aboutone-tenth of the organic matter content ofeconomically important oil shales.

ACKNOWLEDGMENTSThis manuscript was reviewed by Robert E. Miller, U.S.

Geological Survey, Reston, Virginia.

REFERENCESAnders, D.E. and Robinson, W.E., 1971. Cycloalkane

constituents of the bitumen from Green River Shale:Geochim. Cosmochim. Acta, v. 35, p. 661-678.

Claypool, G.E. and Reed, P.R., 1976. Thermal-analysistechnique for source-rock evaluation: quantitativeestimate of organic richness and effects of lithologicvariation: Am. Assoc. Petrol. Geol. Bull., v. 60, p. 608-611.

Gallegos, E.J., 1971. Ide2tification of new sterones,triterpanes and branched paraffins in Green River Shaleby capillary chromatography and mass spectrometry:Anal. Chem., v. 43, p. 1151-1161.

Kimble, B.J., Maxwell, J.R., Philp, R.P., and Eglinton, G.,1974. Identification of steranes and triterpanes in geolipedextracts by high-resolution gas chromatography and massspectrometry: Chem. Geol., v. 14, p. 173-198.

Rhead, M.M., Eglinton, G., and Draffan, G.H., 1971.Hydrocarbons produced by the thermal alteration ofcholesterol under conditions simulating the maturation ofsediments: Chem. Geol., v. 8, p. 277-297.

Rubinstein, I., Sieskind, O., and Albrecht, P., 1975.Rearranged sterenes in a shale: occurrence and simulatedformation: J. Chem. Socl, p. 1833-1836.

Steel, G. and Henderson, W., 1972. Isolation and char-acterization of stanols from Green River Shale: Nature,v. 238, p. 148-149.

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