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Stepwise chemical degradation involving cleavage of ester bonds (KOH/MeOH), sulfide and remaining ester bonds (Li/EtNH2), ether bonds (HI/LiAlH4) and sub-units linked to aromatic moieties (RuO4) has been carried out on the kerogens of two immature sulfur-rich marls (IV-1.4 and 1.8, TOC ca. 1.5%) from evaporitic cycle IV of the Gesosso-solfifera Formation (Messinian, Vena del Gesso, Italy). Up to 80% of the organic matter was converted to solvent-soluble material, with the greatest proportion released by Li/EtNH2. The majority by far of the extracts comprises polar macromolecular material which is thought to correspond to high molecular weight sub-units of the kerogen. Quantification of the small amounts (

Messinian marls from evaporitic cycle IV of the Gessoso-solfifera formation (Italy) are known to contain in high abundance the diaromatic carotenoid isorenieratene of green sulfur bacterial (Chlorobiaceae) origin along with a second diaromatic carotenoid. The previous tentative assignment of the latter as a cis diastereomer of isorenieratene has now been confirmed; this indicates that double bond isomerization occurs during early diagenesis and provides further evidence for the pathway proposed previously to link isorenieratene to a number of aromatic isoprenoid hydrocarbon biomarkers. Stable carbon isotopic data confirm the Chlorobiaceae origin of the intact all-trans isorenieratene isomer and indicate that the isomerization is accompanied by little or no kinetic isotope effect. Comparison of the δ13C values of each of the isolated carotenoids (measured as isorenieratane after hydrogenation) with those of their sulfide-bound counterpart in the polar fraction of the extracts (also measured as isorenieratane) indicates that sulfurization resulted in little depletion in 13C.

3 β -Hydroxy-5 α -androstan-17-one (epiandrosterone), 5 α -androstan-3,17-dione, 3 α -hydroxy-5 α -androstan-17-one (androsterone), 5 α -androstan-3 β ,17 β -diol and 5 α -androstan-3 α ,17 β -diol have been identified in the solvent soluble fraction of peat from Bolton Fell Moss (Cumbria, U.K.). The structures and δ 13 C values of these androstane derivatives indicate a diagenetic origin in sterols also present in the peat and provide the first evidence that cleavage of the C-17 side-chain can occur during early diagenesis, microbial oxidation being the most likely mechanism.

Biomarker distributions based on GC and GC-MS data supplemented by stable carbon isotopic compositions based on irm (isotope ratio monitoring) GC-MS data have been used to investigate changes in depositional conditions in a number of samples from a 2 m core (Rheinberger Heide) covering the entire deposition of the Permian Kupferschiefer (Lower Rhine Basin, northwest Germany). Compound classes investigated are aliphatic and aromatic hydrocarbons and maleimides (1H-pyrrole-2,5-diones). The core has been previously divided into four sections: TI, TIIA, TIIB and TIII based on lithology. The biomarker distributions and the δ13C values of components indicate contributions from cyanobacteria, algae, green sulphur bacteria and higher plants (minor) throughout Kupferschiefer deposition. All of the phytoplanktonic components show 13C enrichment in the lowest section, suggesting a greater productivity. The occurrence of components derived from green sulphur bacteria (Chlorobiaceae) indicates that the entire deposition was characterised by periods of photic zone anoxia. Such conditions were rapidly established after the initial transgression of the Zechstein Sea and may have been productivity-driven, but were less prevalent during deposition of the upper core sections.

A study of the distributions of free and S-bound biomarkers and their δ13C values in the extract of a bulk sample of the Permian Kupferschiefer from the Lower Rhine Basin has been carried out to provide a more detailed characterization of the biological inputs. The distributions and isotopic compositions of selected components released from nickel boride desulphurization have been compared with those of components in the free fraction. The free biomarkers occur in greater abundance than their S-bound counterparts. The distribution and carbon isotopic composition of both free and bound components in the extract indicate a major cyanobacterial and algal input. Likewise, the free and bound aromatic hydrocarbons contain components which reveal an origin from the carotenoids of Chlorobiaceae (green sulphur bacteria), providing molecular evidence for the occurrence of photic zone anoxia in the water column. Most of the components in the complex mixture of mono-, di-, tri- and tetra-aromatics in the free aromatic hydrocarbon fraction result from cyclization and aromatization reactions.

Kerogens isolated from nine samples from a single marl bed of the Gessoso-solfifera formation in the Vena del Gesso basin (Upper Miocene, Italy) were treated with CrCl 2 and Li/EtNH 2 to remove inorganic and organic sulphur, respectively. The untreated and “desulphurized” (CrCl 2 and Li/EtNH 2 ) kerogens were qualitatively and quantitatively analyzed by flash pyrolysis-gas chromatography-mass spectrometry. Typically, significant variations in the relative contributions and abundances of n -alk-1-enes/ n -alkanes, alkylated pyrroles, thiophenes and supposedly S-bound moieties released as phytenes and sterenes were observed. The first series of products ( n -hydrocarbons) contributed relatively more to the pyrolyzates of the desulphurized kerogens, suggesting an enrichment of microalgal-derived aliphatic macromolecules. These marine micro-organisms are thought to belong in part to the class of Eustigmatophyceae. Alkylated pyrroles were barely detectable in the untreated kerogen pyrolyzates, whereas they contributed significantly to those from the treated kerogens. Similar treatment of a porphyrin, octaethylporphyrin, revealed that alkyl porphyrins are thermally too stable to be cleaved upon pyrolysis. However, Li/EtNH 2 treatment reduced the porphyrin standard, such that it could generate mainly monopyrroles upon pyrolysis. It is concluded that Li/EtNH 2 treatment reduced tetrapyrrole moieties bound to the desulphurized kerogen network.

Bacterial populations and activity were quantified at three sites in the Cascadia Margin accretionary wedge, off the West Canadian/American coast (ODP Leg 146). At two sites sediments contained gas hydrates, Site 889/890 had a discrete zone of hydrate approximately 10 m above a bottom simulating reflector (BSR) at 225 m below sea floor (mbsf) and Site 892 had disseminated hydrate in the upper 20 mbsf and a BSR at 74 mbsf. Site 888 was a control site without gas hydrates. The control site (888) and top approximately 90 mbsf of Site 889/890 had bacterial distributions similar to previous Pacific Ocean sites. In the upper approximately 30 m of Site 892, however, bacterial populations were much lower, suggesting inhibition by the high concentrations of H 2 S within the hydrate zone. Below this depth bacterial populations rose to concentrations consistent with other sites. The control site was dominated by SO 4 reduction and rates of CH 4 oxidation in the top 90 m were low (0.002–0.033 nmol cm −3 d −1 ). At Site 889/890 bacterial populations and activity were stimulated in the discrete hydrate zone. CH 4 oxidation rates increased in the middle of this zone to 134.5 nmol cm −3 d −1 (ca. 9 times the average rate at other depths), resulting in a significant (× 10) increase in the total bacterial population. The anaerobic process(es) responsible for this oxidation remain unclear, despite SO 4 -reducing bacteria, previously associated with CH 4 oxidation, also being stimulated in this zone. Fluid flux into accretionary wedge sediments may be an important process in providing electron acceptors to maintain these relatively high rates of CH 4 oxidation. This first microbiological study of gas hydrates indicates that bacterial processes are influenced by gas and fluid venting, and they play a major role in geochemical changes within these deep (> 200 mbsf) sediments.

The iron porphyrin fraction of Kupferschiefer, an organic-rich sedimentary rock deposited in the Zechstein Sea during the Permian (ca. 235Myr before present) contains three minor components characterised by 1 H NMR spectroscopy. The carbon skeletons correlate specifically with members of one series of the bacteriochlorophylls d of the Chlorobiaceae, which are obligate anaerobes. Their structures therefore reveal the occurrence of anoxic conditions extending up into the zone of light penetration in the water column of the original depositional setting in the Lower Rhine Basin.

A sensitive, semi-automated method has been developed for the rapid estimation of the total concentration of chlorophyll a transformation products (chlorins) in solvent extracts of aquatic sediments. The methodology utilizes a laboratory robot for sample extraction and work up and a high pressure liquid chromatography (HPLC) system operated under off-column conditions. Use of an on-line tuneable fluorescence detector allows measurement of total chlorin concentration at greater sensitivity than conventional u.v./vis spectrophotometric detection, and allows reproducible results to be obtained from smaller sediment samples. This is relevant to palaeoceanographic studies at high stratigraphic resolution or where sample demand is high for other stratigraphic studies.

Kerogens of nine samples from a single marl bed of the Gessoso-solfifera Formation in the Vena del Gesso basin (Messinian, Italy) were qualitatively and quantitatively studied by analytical pyrolysis. Relationships between the nature of the pyrolysis products and the source organisms were determined. The high abundance of (i) algal-derived components (n-alkanes and n-alk-1-enes) and (ii) sulphur-containing and sulphur-bound products signifying a high degree of early diagenetic sulphurization were observed. Presence of photic zone anoxia during the deposition of these sediments was discussed via the presence of 1,2,3,4-tetramethylbenzene in the pyrolysates. Unusual distributions were found for three series of pyrolysis products (i.e. C13 and C14n-alkylated thiophenes and thiolanes and C12 and C13n-1,3-alkadienes were by far the major products of these series) in the pyrolysates of two samples corresponding to the middle of the cycle (samples 3 and 5) which also have the highest δ13CTOC values and the highest pyrolysis yields. Therefore, the contribution of organisms biosynthesizing resistant algal biopolymer was considered as much more important during the deposition of the sediments associated with samples 3 and 5. We finally proposed partial structural elements from which the specific low molecular weight compounds of samples 3 and 5 can be derived upon pyrolysis.

The porphyrins and carotenoids of marl horizons within the Messinian evaporitic cycles of the Vena del Gesso basin show variations in abundance and composition throughout a sequence of ten cycles. Significant variations are also apparent within individual marl horizons. The differences in pigment distribution reflect significant changes in the environmental conditions during sediment deposition. The presence of significant amounts of isorenieratene and co-occurrence of an alkyl porphyrin with a C 34 skeleton provide evidence for anoxic conditions extending into the photic zone of the palaeo-water column. Variations in the free pigment contents of the marls reflect a regressive trend both during deposition of an individual marl, and over the entire sequence.

Lithium in ethylamine ( Li EtNH 2 ) treatment has been carried out on sulphur-rich kerogens from 10 sub-samples of the cycle IV marl from the Vena del Gesso evaporitic sediments (Upper Miocene, Italy). The treatment releases, after chromatography of the resulting solvent extracts, up to 30% of the kerogen total organic carbon. The biomarkers released are dominated by components of algal origin. The concentrations of the aliphatic hydrocarbons obtained are of the same order of magnitude as the bound alkanes released upon desulphurization of polar fractions from organic extracts and show similar distributions. The presence of diaromatic isoprenoids derived from Chlorobiaceae indicates that photic zone anoxia occurred during the deposition of the cycle IV marl, such conditions being more prevalent at the middle of the section. Polar material makes up by far most of the organic material released and contains in particular alcohols and amides which may result from the cleavage of ester bonds present in these immature kerogens, the amides being secondary products formed by reaction with the EtNH2. In the case of the alcohols, however, these components could also arise from cleavage of sulphide-bound moieties.

Isotope ratio monitoring GC-MS (irm-GCMS) analyses of individual hydrocarbons isolated from the surface sediment of a small eutrophic lake (Priest Pot, U.K.) and a phytoplankton tow sample from the upper water column have been undertaken in order to assign sources of sedimentary lipids. The δ 13C values for the sedimentary n-alkanes showed no clear distinction between lower molecular weight components (C17–C19) of presumed algal origin and higher members (C23–C33) of presumed higher plant origin, thus indicating a limitation to the use of compound specific isotope analysis in the freshwater system studied. In contrast, the δ 13C values of sedimentary hopenes were markedly depleted (by over 20%) compared with those in the phytoplankton sample from the upper water column. Hop-22(29)-ene in the surficial sediment had a δ 13C value of −55.2%, which contrasts witht he value of the phytoplankton component (−32.7%), attributed to cyanobacteria. These values indicate that a highly 13C-depleted source provides a major contribution to the sedimentary component. It is proposed that the sedimentary hopenes originate in part from methanotrophic bacteria, demonstrating the presence of a bacterial methane cycle in this environment.

The abundances and distribution patterns of mono-, di- and trimethylated 2-methyl-2-(4,8,12-trimethyltridecyl) chromans (MTTCs) and long-chain alkylbenzenes in extracts of marl (66 samples), anhydrite (15) and halite (1) strata of the Salt IV Formation of the Oligocene Mulhouse Basin are reported. The distributions of the methylated MTTCs indicate salinity changes of the upper part of a density stratified water column of the basin. These variations are explained by a tectonically or climatically induced change in the supply of water of relative lower salinity to form a layer overlying the deeper water brine. Hence, it is suggested that mesohaline (3.5–15%) conditions in the surface waters were established as a result of periodic incursions of marine water and subsequent evaporation. Conversely, during periods when the surface water was derived mainly from fresh water from the hinterland, lower average salinity in the surface layer resulted. The distributions of long-chain alkylbenzenes also appear to record these changes.

The major esterified tetrapyrrole in a Miocene oil shale (Marau, Brazil) is a free base chlorin, most likely pyrophaeophorbide a, esterified to 24-ethyl-4α-methyl-5α(H)-cholestan-3β-ol, the structure being assigned by FAB-MS and 1H NMR, and by GC-MS analysis of the sterol liberated by hydrolysis. FAB-MS and electronic absorption spectrophotometric data for the second most abundant component are consistent with the mesopyrophaeophorbide counterpart. Only one other minor esterified chlorin was detected, implying a highly specific and, hence, biologically-mediated esterification. It is not clear whether the reaction took place during biosynthesis of an unknown precursor chlorophyll or resulted from esterification of a hydrolysis product(s) from a known chlorophyll (most likely chlorophyll a) after cellular disruption, although the second possibility is considered more likely.

An unusual series of quinone pigments in a pink Eocene (c. 45x106 yr) sepiolite (quincyte, France) has been characterised by spectroscopy. The structure of the major pigment (c. 75% of total), 2,8-di-isopropyl-peri-xanthenoxanthene-4,10-quinone, was confirmed by synthesis. Spectroscopy revealed six minor related components with various oxygenated C-2 substituents (C1–C3) and, generally, a C-8 isopropyl group. Although the origin of the pigments is unknown, they (or their precursors) appear to have been biosynthesised by the acyl-malonate pathway.

The identities of the two major tetrapyrroles in the bottom sediment of a eutrophic lake, assigned previously by spectral comparison with standards, have been confirmed as phaeophytin a and pyrophaeophytin a through the use of 2D COSY and nOe difference NMR techniques. This provides the first unambiguous characterization of sedimentary chlorins, the components being early products in the degradative pathway of chlorophyll a in the aquatic environment.

The major chlorin in Messel oil shale (Eocene, lacustrine, F.R.G.) has been isolated and assigned as the nickel complex of mesopyrophaephorbide a by spectral comparison with a synthesised standard. The component, whose structure clearly indicates a chlorophyll origin and which co-occurs with its free-base counterpart, has the same carbon skeleton as the major nickel porphyrin acid assigned previously, but is present in much lower abundance and still retains the C-131 carbonyl group found in all chlorophylls. It appears that mesopyrophaeophorbide a represents the major part of the residual chlorin fraction which has survived aromatisation and carbonyl reduction and, like the alkyl porphyrins and carboxylic acids, has become metallated with nickel.

A multi-user integrated suite of instruments designed to optimize the search for evidence of life on Mars is described. The package includes: - Surface inspection and surface environment analysis to identify the potential Mars landing sites, to inspect the surface geology and mineralogy, to search for visible surficial microbial macrofossils, to study the surface radiation budget and surface oxidation processes, to search for niches for extant life. - Subsurface sample acquisition by core drilling- Analysis of surface and subsurface minerals and organics to characterize the surface mineralogy, to analyse the surface and subsurface oxidants, to analyse the mineralogy of subsurface aliquots, to analyse the organics present in the subsurface aliquots (elemental and molecular composition, isotopes, chirality). - Macroscopic and microscopic inspection of subsurface aliquots to search for life's indicators (paleontological, biological, mineralogical) and to characterize the mineralogy of the subsurface aliquots. The study is led by ESA Manned Spaceflight and Microgravity Directorate.

Low molecular weight hydrocarbon (LMWH) distributions were examined in sediments from Sites 1109 and 1115 in the western Woodlark Basin using purge-trap thermal adsorption/desorption gas analysis. A number of different hydrocarbon components >C1, which were not detected during shipboard gas analysis, were detected at both sites using the purge-trap procedure. Concentrations of ethane, propane, and butane remained relatively low (

An immature sulfur-rich marl from the Gessosso-solfifera Formation of the Vena del Gesso Basin (Messinian, Italy) has been subjected to hydrous pyrolysis (160 to 330°C) to simulate maturation under natural conditions. The kerogen of the unheated and heated samples was isolated and the hydrocarbons released by selective chemical degradation (Li/EtNH2 and HI/LiAlH4) were analysed to allow a study of the fate of sulfur- and oxygen-bound species with increasing temperature. The residues from the chemical treatments were also subjected to pyrolysis–GC to follow structural changes in the kerogens. In general, with increasing hydrous pyrolysis temperature, the amounts of sulfide- and ether-bound components in the kerogen decreased significantly. At the temperature at which the generation of expelled oil began (260°C), almost all of the bound components initially present in the unheated sample were released from the kerogen. Comparison with an earlier study of the extractable organic matter using a similar approach and the same samples provides molecular evidence that, with increasing maturation, solvent-soluble macromolecular material was initially released from the kerogen, notably as a result of thermal cleavage of weak carbon–heteroatom bonds (sulfide, ester, ether) even at temperatures as low as 220°C. This solvent-soluble macromolecular material then underwent thermal cleavage to generate hydrocarbons at higher temperatures. This early generation of bitumen may explain the presence of unusually high amounts of extractable organic matter of macromolecular nature in very immature S-rich sediments.

Bacterial populations and activity were quantified at four Ocean Drilling Program Leg 146 sites in the Cascadia Margin accretionary wedge, off the west Canadian/American coast. At two sites the sediments contained gas hydrates: Site 889/890 had a discrete hydrate zone for -10 m above the bottom-simulating reflector (BSR) at 225 m below the sea floor (mbsf), and Site 892 had disseminated hydrate in the top -20 mbsf and a BSR at 73 mbsf. Site 891 had fault zones and discrete zones of active fluid venting. The other site, 888, was a control site without gas hydrates or substantial fluid venting. Bacterial populations were present at all sites with deepest samples from Site 888 at 564 mbsf. The control Site 888 and the top -90 mbsf of Site 889/890 had bacterial distributions similar to previous sites studied in the Pacific Ocean. In the top -20 m of Site 892, however, bacterial populations were much lower than in the other two sites; they may have been inhibited by the high concentrations of hydrogen sulfide within the hydrate zone. Below this depth, bacterial populations increased to concentrations consistent with other sites, apart from local decreases in Hole 892A associated with thermally generated aromatic hydrocarbons, which might be toxic to a portion of the bacterial community. Near-surface bacterial populations at 891A were -4.5 times higher than expected, probably reflecting fluid venting near this site. Below about 50 mbsf at this site (Hole 891B), bacterial populations were also elevated and peaks corresponded to geochemical anomalies resulting from fluid venting. Bacterial processes generally decreased with increasing depth at the control site, which was dominated by sulfate reduction, and rates of methane oxidation in the top 90 m were low, ranging from 0.002 to 0.033 nmol/cm3/d. Fluid and gas venting have a marked effect on deep bacterial processes at Sites 891 and 889/890: in contrast to the control site, maximum bacterial activities occur and bacterial populations are elevated at depth (sub-200 mbsf), reflecting marked increases in methane oxidation. At Site 889/890, bacterial populations and activity were stimulated in the discrete hydrate zone. Methane oxidation rates increased in the middle of this zone to 134.5 nmol/cm3/d, and this resulted in a significant increase in the total bacterial population. The anaerobic process(es) responsible for methane oxidation remain unclear, but fluid flux into accretionary wedge sediments may be an important process in providing electron acceptors to maintain these high rates of methane oxidation. Variation in bacterial profiles between cores at the same site (891 and 892), only a few meters apart, closely reflect spatial heterogeneity in geochemistry and fluid expulsion in these accretionary sediments, demonstrating that bacterial processes are a sensitive index for the fluid and gas venting that may drive many of the geochemical changes.

Sedimentary rock from the Gessoso-solfifera Formation (Messinian) in the Vena del Gesso Basin (northern Italy) containing immature (Ro = 0.25%) S-rich organic matter was artificially matured by hydrous pyrolysis at temperatures from 160 to 330°C for 72 h to study the diagenetic fate of n-C37 and n-C38 di- and tri-unsaturated methyl and ethyl ketones (alkenones) biosynthesised by several prymnesiophyte algae. During early diagenesis, the alkenones are incorporated into the kerogen by both sulphur and oxygen cross-linking as indicated by chemical degradation experiments with the kerogen of the unheated sample. Heating at temperatures between 160 and 260°C, which still represents early stages of thermal maturation, produces large amounts (up to 1 mg/g TOC) of S-bound, O-bound, and both S- and O-bound n-C37 and n-C38 skeletons, saturated n-C37 and n-C38 methyl, ethyl, and mid-chain ketones, C37 and C38 mid-chain 2,5-di-n-alkylthiophenes, C37 and C38 1,2-di-n-alkylbenzenes, and C37 and C38 n-alkanes. With increasing thermal maturation, three forms of the n-C37 and n-C38 skeletons are relatively stable (saturated hydrocarbons, 1,2-di-n-alkylbenzenes and saturated ketones), whereas the S- and O-bound skeletons are relatively labile. These results suggest that in natural situations saturated ketones with an n-C37 and n-C38 skeleton can be expected as well as the corresponding hydrocarbons.

A computer method is described for the automatic classification of triterpanes and steranes into gross structural type from their mass spectral characteristics. The method has been applied to the spectra obtained by gas-chromatographic/mass-spectroscopic analysis of two mixtures of standards and of hydrocarbon fractions isolated from Green River and Messel oil shales. Almost all of the steranes and triterpanes identified previously in both shales were classified, in addition to a number of new components. The results indicate that classification of such alkanes is possible with a laboratory computer system. The method has application to diagenesis and maturation studies as well as to oil/oil and oil/source rock correlations in which rapid screening of large numbers of samples is required.

The distributions of steroidal and triterpenoidal alkanes and aromatic hydrocarbons and, where appropriate, triterpenoid alkenes and ketones, in nine oils, nine coals and three shales from the Mahakam Delta have been examined by gas chromatography-mass spectrometry. In all of the fractions there are high relative abundances of components of higher-plant origin, in keeping with the previous assignment of the organic matter in Mahakam sediments as type III. Comparison of molecular maturity measurements for the sediments and the oils extends earlier ideas that the source for the Handil oils must have a present depth of at least 3000 m. No major difference was observed here in the maturity (based on the molecular measurements) measured for coal-shale pairs with similar burial depths. In the oils, variations in the relative abundances of the monoaromatic steroid hydrocarbons relative to the triaromatic steroid hydrocarbons, taken with the results of earlier studies of the oils, have been ascribed tentatively to a migration effect.

Immature samples of the Permian Kupferschiefer from the Lower Rhine Basin in N.W. Germany were analysed for tetrapyrrole pigment type and abundance. The sediment, thought to have been deposited in a marine regime with enhanced salinity, was found to contain high concentrations of metalloporphyrins. The porphyrins are complexed to nickel (Ni) and oxovanadium (V=0), but high abundances of iron (Fe) porphyrins were also detected using UV/visible spectroscopy and mass spectrometry. The presence in the latter of series of aetioporphyrins, cycloalkanoporphyrins, di-cycloalkanoporphyrins and benz-cycloalkanoporphyrins was confirmed by accurate mass measurements; HPLC co-injection of deoxophylloerythroetioporphyrin (C32 DPEP) with the demetallated iron porphyrins indicated its presence in the sediment as an iron complex. The study provides the first evidence for the occurrence of Fe porphyrins in geological samples other than coals and lignites, and reports the highest concentrations in sedimentary organic matter to date.

The major carotenoids at three levels (3, 40, and 175 m below the sediment-water interface) in a core from a marine sediment (Cariaco Trench, off Venezuela) have been examined. Mass and electronic spectral data have provided evidence for the onset of a progressive reduction of carotenoids in the geological column. The time scale of the process appears to depend on the particular carotenoid. Reduction of up to two double bonds is observed for the diol, zeaxanthin, in the oldest sediment (about 340,000 years old) but no reduction is observed in the younger samples (about 5000 and 56,000 years old). The diketone, canthaxanthin, shows evidence of reduction of up to two double bonds in the 56,000-yr sample and up to five double bonds in the oldest sample. No reduction of beta-carotene was observed in any of the samples.

Treatment of 4-methylcholest-4-ene under mild acid conditions at low temperatures gives chemical evidence for certain features seen in the distributions of sedimentary 4-methyl steroid hydrocarbons, and further indicates that many low temperature diagenetic reactions of steroids are explicable in terms of acid catalysed rearrangements. Specifically, the results provide: (i) Indirect evidence that the 4-ene skeleton is a key intermediate in the dehydration of 4-methyl stanols in sediments. (ii) An explanation for the distribution of 4-methyl sterenes and A-nor sterenes in the lacustrine Messel shale (Eocene). (iii) An explanation for the presence of 4β-methyl steranes in relatively immature sedimentary rocks, despite the precursor stanols having the 4α-methyl configuration. With increasing maturity in the Paris Basin shales (Lower Toarcian), the less stable 4β-methyl steranes decrease gradually in abundance relative to their 4α-methyl counterparts, at a rate fairly similar to the change in pristane stereochemistry.

Three series of de-A-diasterenes have been observed in a variety of immature marine shales. Two of them have been identified by comparison with authentic standards and the structures of the third assigned by extrapolation. The greater complexity in the number of series compared with diasterenes indicates that the ring A degradation occurred to differing extents. The rate of C-20 diagenetic isomerisation in the de-A-diasterenes proceeds at a similar rate to that in diasterenes. Two series of B-ring monoaromatic de-A-steroid hydrocarbons have also been found. Comparison with the B-ring monoaromatic anthrasteroids indicates that the de-A-compounds are 14α(H) and 14β(H) isomers. Diagenetic isomerisation of the 14α(H) isomers to the more stable 14β(H) isomers occurs at a rate similar to that in the B-ring monoaromatic anthrasteroid series.

An immature Toarcian shale from the Paris Basin (Semecourt, reported maximum burial depth 700m) was heated in the laboratory under reduced pressure at different temperatures (201, 257, 285°C) for different times (6–91 days). We measured in the resulting extracts by gas chromatography or combined gas chromatography-mass spectrometry: 1. (a) extent of configuational isomerisation at (i) C-6 and C-10 in pristane, (ii) C-20, and C-14 and C-17 in 5α(H),14α(H),17α(H)-steranes, (iii) C-17 and C-22 in hopanes; 2. (b) extent of aromatisation in aromatic steroid hydrocarbons. Both configurational isomerisation and aromatisation occur during heating, but the latter process is accelerated relative to the former, in comparison with the maturation effect experienced by the Toarcian shales as a result of burial depth and the associated temperature rise. The results suggest that it may be possible to distinguish the thermal histories of sedimentary sequences by comparison of the relative extents of isomerisation at C-20 in steranes with the extent of aromatisation in aromatic steroid hydrocarbons.

The distributions of nickel (II) and vanadyl alkyl porphyrins in a suite of Toarcian shales from the Paris Basin have been examined as the demetallated compounds by high performance liquid chromatography and mass spectrometry. The suite covers a wide range of burial history. Among the major changes which occur in the vanadyl species with increasing maximum depth of burial are: (1) conversion of DPEP components to etio components, (2) a decrease in the chain lengths of the β alkyl substituents, and (3) a decrease in the ratio of Ni to VO porphyrins. In addition, evidence is presented for the generation of higher molecular weight species (C 35 C 39 ) below 2000 m maximum burial depth. These appear to arise by thermal cracking of the kerogen. Within the shallow samples the Ni species undergo the DPEP to etio conversion and decrease of alkyl chain length before the VO species. These changes indicate, for the shallow samples, an increase in the extent of maturation from north to south across the basin.

The distributions of the alkanes and aromatic steroid hydrocarbons of eleven oils and six shales from the Shengli oilfield (Zhanhua depression), have been examined by gas chromatography and gas chromatography-mass spectrometry. Particular attention has been paid to the so-called biological marker compounds (steranes, triterpanes and aromatic steroid hydrocarbons). Where metalloporphyrins are present, their distributions have been examined by high-performance liquid chromatography and mass spectrometry. The shales show progressive increases in the extent of aromatisation of aromatic steroid hydrocarbons and the extent of configurational isomerisation in the triterpanes which correlate well with present burial depth. They are less mature than all of the oils when maturity assessment is based on the degree of sterane configurational isomerisation. One oil (Yi-18) is less mature than all the other oils from most of the measurements. A number of ratios and compound distributions thought to be indicative of either maturity or palaeoenvironment (or both) suggest the Upper Shahejie (Oligocene) as the most appropriate source for the Yi-18 oil. The same ratios and distributions rule out the Lower Shahejie (as represented by the sample examined here) as a possible source for any of the oils (even in a more mature state). The main source(s) for all the other oils is more mature (by extent of sterane isomerisation) than all the shales examined. Suitable sources for these oils have not been found in this study. There is no correlation between oil maturity and reservoir depth, suggesting that the present maturity of the oils relates mainly to maturation effects in the source rocks and not the reservoir. All oils pooled at depths of ⪝ 1500 m (∼70°C) show the effect of biodegradation ( n -alkanes removed) whilst those pooled at depths ⪞ 1500 m appear to be unaffected.

Crude-oil samples from three oilfields in the east and west of the Tertiary Niger delta, Nigeria, were analysed for pentacyclic triterpanes by gas chromatography and gas chromatography—mass spectrometry. Previously identified pentacyclanes such as 18αH-oleanane; 1(10→5)-abeo-3β-methyl-24β-nor-25α-18αH-oleanane (spirotriterpane); 30-nor-17αH,21βH-hopane; 17αH,21βH-hopane and 22,29,30-trisnor-18αH-hopane-II were recognised in the crudes. In addition, 17βH,21αH-hopane (moretane) and 17βH,21αH-homohopane (homomoretane) were identified for the first time. Results obtained in the present study indicate that the Nigerian petroleum pentacyclanes belong to at least three homologous series, namely, the 17αH,-21βH-hopanes (αβ); 17βH,21αH-hopanes (βα) and a novel “ K 1 ” series distinguished by members with retention times that were considerably shorter than those of the corresponding αβ hopanes with the same number of C atoms. Mass-spectral and retention-time characteristics of the “ K 1 ” triterpanes classified them neither as the 17αH-hopanes (αα hopane series) nor the recently-discovered methylhopane series. The preponderant pentacyclic triterpanes in the oils sampled from either side of the delta were the αβ hopanes and oleananes. However, the triterpane fingerprint of the western crudes differed significantly from that of their eastern counterparts in the distribution of the oleananes. The relatively higher concentration of the oleananes in the eastern oils apparently reflects a greater input of higher plants to their source sediments, presumably the shale of the paralic Agbada Formation. The relatively lower concentration of the oleananes in the western oils resulted in a dominantly hopane fingerprint, expected for petroleum generated in mainly non-terrigenous source rocks. Therefore, it would appear that the concentration of oleananes in Nigerian petroleum is sufficiently variable with source facies to permit dependable oil—source rock correlation based on triterpane finger-printing.

An investigation of bulk, isotopic and molecular features of a wide selection of source rocks and oils from Brazilian marginal basins, ranging from Lower Cretaceous to Tertiary in age, provides a number of organic geochemical criteria that characterise and distinguish their depositional palaeo-environments. The methods employed include evaluation of organic carbon contents, Rock-Eval pyrolysis, vitrinite reflectance measurements, determination of carbon isotope ratios, elemental and visual kerogen analysis, assessment of oils and solvent extracts by liquid and gas chromatography, and quantitative biological marker investigations using GC-MS for aliphatic hydrocarbons and UV/Vis spectrophotometry for metalloporphyrins. Selected data were evaluated using principal component analysis. The results enable the recognition and differentiation of seven depositional regimes: lacustrine freshwater; lacustrine saline water; marine evaporitic; marine carbonate; marine deltaic; marine highly anoxic with a predominance of calcareous mudstone lithology, and marine anoxic with predominance of siliciclastic lithology. Diagnostic features in the biological markers from these depositional environments include: the carbon number distributions of n -alkanes, pristane/phytane ratios; absolute concentrations of β-carotane, higher acyclic isoprenoids, C 30 αβ hopane and steranes, and the abundance of the latter relative to 4-methylsteranes; the occurrence and abundance of particular biological markers such as gammacerane, tricyclic and tetracyclic terpanes, 18α (H)-oleanane, 28,30-bisnorhopane and 25,28,30-trisnorhopane, and the relative abundances of nickel and vanadyl porphyrins.

The lipids of 6 sections from the Deep Sea Drilling Project's transect (Legs 56 and 57) of the Japan Trench have been examined. Five of these form a downhole sequence at a site on the landward side of the trench, the other is on the distal side. Gas chromatographic and computerised-gas chromatography-mass spectrometric data for aliphatic and aromatic hydrocarbons, ketones, alcohols, acids and polyfunctional components are reported. The lipid components are considered as indicators of terrestrial, marine (non-bacterial) and bacterial inputs. The marked similarity in these respects of 2 sections is discussed, and the input contributions to other sections deduced. The lipid distributions of Site 440 sections are illustrated, with especial reference to diagenetic transformations in relation to depth of C30 hopenes and of steroidal, cyclic diterpenoid and acyclic isoprenoid components.

Certain features of the distributions of sedimentary 4-methyl steroid hydrocarbons have been investigated: (i) competitive dehydration experiments with stanols adsorbed on a shale suggests a possible explanation for the low abundance of 4-methyl sterenes relative to their desmethyl counterparts in immature sediments, (ii) a 4-methyl spirostene which is a minor product of the backbone rearrangement of 4-methylcholest-4-ene in the laboratory has been tentatively assigned; its presence in a Toarcian black shale with a second isomer provides further evidence that the sedimentary backbone rearrangement of 4-methyl sterenes is analogous to that of their desmethyl counterparts and (iii) the major C30 4-methyl steranes in Semecourt shale (Toarcian, Paris Basin) differ from those in an Eocene lacustrine shale from China; this indicates the potential complexity of C30 steroidal alkanes (both 4-methyl and desmethyl) which can occur in sedimentary organic matter and shows that care must be taken in using m/z 217 mass chromatograms alone for routine input and maturity assessment using steroidal alkanes.

Immature shale of the Agbada Formation of the Tertiary Niger delta, Nigeria, cored at various depths A simulation experiment carried out by heating the immature shale at 300°C in vacuo (0.4 Torr) for ten days resulted in a triterpane composition similar to that of the delta oils. The disappearance of olean-13 (18)-ene and the generation of oleananes had apparently occurred simultaneously with reported structural changes in the hopane components. The presence of the triterpene in immature shale and its apparent transformation to 18αH-oleanane by in vitro thermal alteration was consistent with the current hypothesis of the origin of oleananes in Nigerian petroleum.

A combined geochemical and molecular characterization of a wide selection of oils from the major Brazilian offshore basins has been undertaken. The elemental (sulphur, nickel and vanadium) and bulk (oAPI and δ13C) properties of each sample been considered, together with its molecular composition determined using liquid and gas chromatography, and quantitative biological marker investigations using gas chromatography-mass spectrometry for alkanes. The results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups. The distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils. Each group is correlated tentatively with source rocks laid down in a specific depositional regime, namely lacustrine freshwater, lacustrine saline water, marine evaporitic, marine carbonate or marine deltaic. The diagnostic features that allow this classification are: the relative abundance and carbon number distributions of n-alkanes; pristane/phytane ratios; sulphur, nickel and vanadium contents; carbon isotope data; the absolute concentrations of hopanes and steranes, and their abundance relative to 4-methylsteranes and, also the occurrence and abundance of several specific biological markers, including 18α(H)-oleanane, gammacerane, β-carotane, tricyclic terpanes, higher acyclic isoprenoids, 28, 30-bisnorhopane and 25, 28, 30-trisnorhopane. This investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils.

Series of (20R)- and (20S)-Δ8(14) and Δ145α(H)-sterenes have been identified in an immature marl from a hypersaline deposit (northern Apennines, Italy) by co-injection studies with authentic compounds. These alkenes co-occur with Δ13(17) 5α(H)-spirosterenes and transient (20R)- and (20S)-Δ14 5α(H), 17β(H)-sterenes. The source of these isomeric steroid alkenes is probably Δ7 (and Δ8(14)) 5α(H)sterols via (Δ2,7), Δ2,8(14) and Δ2,14 5α(H)-steradienes. Reduction processes in the sediment, via the Δ14 5α(H),17β(H)-sterenes, can give rise to the C-20 isomeric 5α(H),14β(H),17β(H)-steranes present in “anomalously” high relative abundances from a thermal maturity viewpoint. This diagenetic pathway is supported by laboratory rearrangement/hydrogenation experiments of 5α(H)-cholest-7-ene and from considerations of carbon number distributions of various steroid hydrocarbons in the sediment extract.

Naturally occurring plant and animal pigments have long aroused intense scientific interest. The vivid red organic pigments, the petroporphyrins, present as minor components of many sediments and petroleums, are now receiving increasing attention in the field of organic geochemistry. First observed 50 years ago, and thought to arise in part from the green photosynthetic pigment chlorophyll in ancient organisms, they provided the first firm evidence for a biogenic origin for petroleum. Recent improvements in microanalytical chemical techniques have shown that the petro porphyrins are generally complex mixtures of a variety of closely related structural types. The distributions of the components as revealed by direct insertion probe mass spectrometry (MS), high-performance liquid chromatography (HPLC) and computerised gas chromatography-mass spectrometry (CGCMS) can provide a record of the original depositional palaeoenvironment and subsequent thermal history of the sedimentary matrix. The petropor...

The occurrence of pyrochlorophyll a and pyrophaeophytins a and b in the bottom sediments of a small eutrophic lake (Priest Pot, Cumbria, U.K.) is reported on the basis of HPLC coinjection with standards. Assignment of pyrophaeophytins a and b was confirmed by FAB mass spectrometric and nuclear magnetic resonance studies of the isolated components and comparison with standards. The co-occurrence of pyrochlorins with their non-pyro counterparts, even in a surface sediment, shows that decarbomethoxylation can occur at the very earliest stages of the Treibs diagenetic pathway linking the chlorophylls and sedimentary porphyrins.

A C25 alkane (1) proposed previously to occur in Methanobacterium barkeri and M. thermoautotrophicum 1 and to be a sedimentary biological marker for methanogenic bacteria9, has been synthesised and its occurrence confirmed.

Four basic structural types of alkyl porphyrins have been reported frequently to occur in sedimentary organic matter as metallocomplexes. The purpose of this note is: i) to report the structural assignment of two representatives (C32, C33) of the so-called “di-DPEP” series, isolated from El Lajjun shale, a bituminous limestone of central Jordan (Upper Cretaceous, El Lajjun Basin); ii) to evaluate a previous suggestion that this type of compound and sedimentary monobenzoporphyrins are related in structure and origin.

Methane and deuteromethane released from Apollo 11 and 12 lunar fines by deuterated acid etch, using gas chromatography for carbon compounds separation

METHANE (up to 5 µg g−1 carbon) and material behaving as carbide (releasing up to 23 µg g−1 carbon as CD4) on deuterated acid dissolution, are ubiquitous components of lunar fines1–4. The abundances of both components correlate with a number of parameters related to the extent of exposure of the samples on the lunar surface2,3. Also, location studies show that the CH4 and carbide are apparently concentrated at particle surfaces4,5. We have suggested therefore that the principal origins for each species involve processes occurring directly at the lunar surface, notably solar wind implantation for formation of CH4 and both solar wind implantation and meteorite impact for the formation of carbide1–4.