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To investigate possible reasons for the discrepancy between the abundance of 4-methyl components in free sterols and steryl chlorin esters (SCEs) which is commonly observed in sediments, experiments in which the copepod Calanus helgolandicus grazed on the dinoflagellates Prorocentrum micans and Alexandrium tamarense were carried out. With P. micans all the algal sterols were esterified as SCEs in the faecal pellets, but there was clear discrimination against the uptake of 4-Me sterols. This discrimination was also evident with A. tamarense. To investigate changes in the faecal pellet SCE and the free sterol distributions during pellet ageing in the P. micans experiment, portions were allowed to stand for up to 29 days in seawater in the dark. Although degradation of SCEs occurred, their esterified sterol distribution remained unchanged. The free sterols were degraded more rapidly than the SCEs and changes in the distribution were observed. This provides further laboratory evidence that sedimentary SCE sterols are more robust markers of phytoplankton communities than the corresponding free sterol distributions. Comparison of the SCE abundance in sterilised and unsterilised pellets indicated that the degradation was a result of microbial activity.

The production of steryl chlorin esters (SCEs) of both pyrophaeophorbide a and pyrophaeophorbide b has been demonstrated in a laboratory experiment in which the copepod Calanus helgolandicus grazed on the prasinophyte Tetraselmis suecica. Both algal sterols were converted into SCEs a and b with equal efficiency, indicating that in this case the SCE sterols were directly representative of the substrate. The sterols of the animal were also converted to SCEs, although with some change in the distribution as a result of cholesterol demand by the copepod. The results show that during herbivory chlorophyll b undergoes the same biotransformation to SCEs as reported for chlorophyll a and predict that SCEs b should occur in sediments beneath a phytoplankton population containing a significant contribution of chlorophyll b.

Steryl esters of the chlorophyll a transformation product pyrophaeophorbide a (SCEs), were formed when the copepod Calanus helgolandicus was allowed to graze on the marine diatom Thalassiosira weissflogii , confirming an earlier preliminary experiment. All of the animal and algal sterol components were found in the SCEs although there were distributional changes attributed to alteration prior to esterification to pyrophaeophorbide a , which resulted from utilisation by the copepod to produce cholesterol. This indicates that where there is insufficient cholesterol in the zooplankton diet in the natural environment, sedimentary SCE sterol distributions may not accurately reflect the original phytoplanktonic free sterol distribution. Although the concentration of SCEs dropped markedly as a result of pellet ageing, their abundance relative to the other major chlorins increased. This relative stability provides an explanation for a previous observation that SCEs in surface sediments are present in higher abundance than in the corresponding water column particulates and accounts for their significant abundance in the solvent extractable chlorins in sediments. Two novel products, tentatively proposed as the phytyl ester and the 24-methylcholesta-5,24(28)-dien-3β-yl ester of 13 2 -oxopyrophaeophorbide a were also observed in the pellets, although the widely occurring rearranged sedimentary chlorin 13 2 -hydroxychlorophyllone a (chlorophyllone) was only detected in aged pellets.

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.

To investigate the effect of bacterial diagenesis on the distributions of algal lipids, the marine haptophyte Emiliania huxleyi was incubated with estuarine sediment slurries under defined conditions (oxic, sulfate reducing and methanogenic). Rapid initial degradation of lipids corresponded to increased bacterial populations, both of which subsequently declined. Under oxic conditions the algal C31 dienes were rapidly and completely degraded within 178 days. Extensive degradation of the characteristic C37 methyl alkenones occurred under all conditions (up to 85% under oxic conditions); however, the U37K′ index remained essentially constant, except for a slight increase at the longest oxic incubation time. Under anoxic conditions the alkyl alkenoates were preferentially degraded relative to the alkenones and changes in the AA36 index occurred. These results demonstrate that lipids are part of the “labile” organic matter; however, they were generally degraded at multiple rates which slowed during incubation, resulting in their partial preservation. Hence, laboratory experiments conducted over only short periods cannot predict the preservation potential of lipid components. Furthermore, preservation differed between sulfate reducing and methanogenic conditions, so the roles of anaerobic processes need to be considered individually with regard to oxic vs. anoxic preservation.

Pyrophaeoporphyrins c 1 and c 2 ( I a, b ), transformation products of chlorophylls c 1 and c 2 ( II a, b ) occur as minor pigments in the surface sediment (0–5 cm) of Priest Pot, a small eutrophic lake (Cumbria, U.K.) and in the products from feeding the diatom Thalassiosira weissflogii to the copepod Calanus helgolandicus . These findings, based on comparisons with standards prepared from the chlorophylls c 1 and c 2 , indicate that enzymatic removal of the C-13 2 carbomethoxy substituent, a prerequisite for the diagenetic transformation pathway of the chlorophylls c to a number of sedimentary alkyl porphyrins, occurs mainly in the water column as a result of zooplankton herbivory.

The sterol distributions in the steryl chlorin esters (SCEs) from three marine and two lacustrine sediments have been compared with the free sterols and known water column sterol distributions. The comparison provides further evidence that the SCE sterol distributions are more representative of the original phytoplanktonic sterol distribution than are the free sterol distributions. This is most clearly seen in the relative abundance of C 26 sterols and 4-methyl sterols, and in the stanol/stenol ratios. It appears that in general the SCE sterols are less susceptible to selective biodegradation than the free sterols.

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.

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.

An abundant chlorophyll a transformation product, found previously in a lake sediment (chlorophyllone a ) has been identified by LC-MS in sediments from five aquatic environents, both marine and lacustrine. Its previously unrecognized wide sedimentary occurrence and apparent post burial stability suggest it is an important preservational sink for the chlorophyll produced in the euphotic zone. It contains a seven-membered ring fused to a five-membered ring, and therefore provides further evidence for a transformation pathway linking chlorophyll a to a recently reported sedimentary bicycloalkanochlorin and a suite of sedimentary porphyrins of the bicycloalkanoporphyrin (bi-CAP) type.

The transformations undergone by chlorophyll a under anoxic conditions have been simulated by using the widespread marine prymnesiophyte Emiliania huxleyi as a substrate for a mixed bacterial community by incubation in a sediment slurry under sulphate reducing conditions. This resulted in the formation of pyrophaeophytin a after 77 days, along with smaller amounts of phaeophorbide a, pyrophaeophorbide a and mesopyrophaeophorbide a, from an original pigment distribution comprising mainly phaeophytin a, with a lower abundance of chlorophyll a. Mesopyrophaeophorbide a has not been reported previously as a product of any chlorophyll a defunctionalization study. Its formation under the conditions used suggests that the reduction of the C-3 vinyl substituent, required for transformation of chlorophyll a to a number of sedimentary porphyrins and chlorins, is a process which involves anaerobic bacterial communities.

A study of the pigment composition in the water column particulates and bottom sediment column of an anoxic lake, Lake Ciso (Catalonia, Spain), has been carried out. The depth-dependencies of the carotenoid and chlorophyll distributions in the water column during stratification and holomixis, as well as during the diurnal cycles, have been determined. In the sediment, the composition of the pigments has been studied over the top 25 cm. The analyses were carried out by high performance liquid chromatography (HPLC) and HPLC coupled to mass spectrometry. The distributions of carotenoids, bacteriochlorophylls and chlorophylls in the water particulates closely follow the population dynamics of the photosynthetic organisms during stratification and holomixis. Among these, only chlorophyll a transformation products are found in the water column, namely phaeophytin a , pyrophaeophytin a and pyrophaeophorbide a . These derivatives also occur in the sediment, where they are found together with bacteriophaeophytin a and pyrobacteriophaeophytin a . This compartment-dependent occurrence corresponds to a higher degree of preservation of the bacterial vs algal pigments. The former occur in the anoxic hypolimnion or mixed water column during holomixis, and the latter in the oxic epilimnion. The presence of these compounds and the very low abundance of phaeophorbide a and absence of bacteriophaeophorbide a point to a transformation pathway where, in the absence of zooplankton grazing or high abundances of the enzyme chlorophyllase, the loss of the phytyl chain occurs predominantly after loss of the C-13 2 carbomethoxyl group. Okenone, alloxanthin, α-carotene and zeaxanthin/lutein are the major water column carotenoids. Their relative abundances contrast with their distribution in the sediments where okenone is the predominant compound and zeaxanthin/lutein are below detection limit. This effect may be in part a consequence of a more uniform okenone concentration in the water particulates over the year, leading to a higher annual sedimentation flux. Again, it may also be influenced by the higher degree of preservation of the bacterial vs algal carotenoids. A similar situation is observed for the relative abundances of chlorophyll a and bacteriochlorophyll a in water particulates and sediments.

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.

To obtain further information about the origin of sedimentary tetrapyrroles such as the alkyl porphyrin desoxophylloerythroaetioporphyrin, the defunctionalization of chlorophyll a has been studied in batch cultures of the marine diatom Phaeodactylum tricornutum, which were induced to undergo senescence by the exclusion of light. Identification of pigments by combined reversed phase high-performance liquid chromatography-mass spectrometry (LC-MS), with on-line photo-diode array detection, revealed conversion of chlorophyll a to phaeophytin a and pyrophaeophorbide a. The results demonstrate that certain chlorophyll a transformation products which occur commonly in aquatic sediments can be formed in part by the action of algal enzymes in the water column. The study provides the first unambiguous identification of pyrophaeophorbide a during senescence of a non-mutant alga.

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 lower Oligocene evaporite sequence of the Mulhouse Basin (France) contains organic matter-rich marl deposits. These marls display an overall cyclic variation of sedimentation rate, organic carbon content, hydrogen index and selected molecular parameters over a 30 m thick stratigraphic interval. The integration of all sedimentological and geochemical parameters has allowed the reconstruction and characterization of the paleoenvironment of deposition. The marls were deposited in a perennial lake that was at times connected to the sea. Two organic facies end members could be assigned to a lake stage with a marine connection and a lake stage that received dominantly continental water input. The overall stratigraphic variation in the organic matter content is interpreted to reflect the adaptation of the Oligocene flora to the changing paleoclimate and environmental conditions.

Principal components analysis (PCA) has been used to investigate changes in concentrations of the components of the hydrocarbon fractions extracted from 71 marl samples, selected to cover two total organic carbon (TOC) maxima in the lower part of the Salt IV formation, a Lower Oligocene evaporitic sequence from the Mulhouse Basin, France. The analysis indicates that the fractions can be ascribed as lying between two end member distributions. The changes in these distributions are gradual, suggesting that they resulted from fairly gradual changes in the depositional palaeoenvironment. These changes are related to increased algal productivity associated with the evolution of a restricted lacustrine environment through to one with a greater marine influence. Systematic variations in the concentrations of selected components relative to the TOC profile point to a repeated sequential evolution in the biological assemblage during deposition of the sequence.

Reduction of a sulphur-rich asphaltene from a crude oil (Rozel Point) with lithium in ethylamine (Li/EtNH2) affords an alkane fraction similar to that obtained from desulphurisation with Raney nickel, but in higher yield. Using Li/EtND2, deuterium-labelled alkanes were obtained, thereby confirming the presence of sulphide linkages in the asphaltene fraction. Reduction of two sulphur-rich kerogens with similar sulphur contents, Serpiano shale (M. Triassic) and Jurf Ed Darawish (JED, U. Cretaceous) afforded significant quantities of polar solvent-extractable material. Both kerogens also yielded low amounts of hydrocarbons although the amount released from JED kerogen was significantly higher. The results indicate that, whereas the kerogens contain hydrocarbon moieties intermolecularly linked by sulphide bridges, the distributions of the precursors lipids which were incorporated were different. For example, GC-MS analysis of the labelled products from JED kerogen revealed them to be dominated by steranes of algal origin, with the position(s) of deuterium labelling providing evidence of sulphide linking and cross-linking. On the other hand, the labelled products from Serpiano kerogen were dominated by hopanes of bacterial origin which were linked terminally via the side chain.

Combined liquid chromatography-mass spectrometry studies of the pigment distributions of a variety of lake and marine sediments from different depositional settings reveal the presence of steryl chlorin esters as significant components of the chlorin assemblages. The components are water column transformation products of phytoplankton chlorophyll a, and it is suggested that they form through an enzymatic esterification or transesterification process during senescence or decay. Remarkably, the steroidal alcohols are esterified mainly to a common nucleus, pyrophaeophorbide a. The transformation pathway involved appears to be a ubiquitous one in marine and lacustrine environments, and the components represent a significant sedimentary “sink” for the chlorophyll biosynthesised in the euphotic zone. Future water column studies of the changes in photosynthetic pigments in phytoplankton blooms and of pigment fluxes should take into account the likely presence of steryl chlorin esters.

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.

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.

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.

Abundant volatile lipids of Methanobacterium thermoautotrophicum and Methanosarcina barkeri include isoprenoid hydrocarbons (≤ C30), and C15, C20 and C25 isoprenoid alcohols. M. barkeri contains 2,6,10,15,19-pentamethyleicosane, whose relative stereochemistry is the same as found in marine sediments, indicating that it is a marker of methanogenic activity. The C20, C30 and C25 alkenes in M. thermoautotrophicum also have a preferred sterochemistry; the latter have the 2,6,10,14,18-pentamethyleicosanyl skeleton, suggesting that the alkane in marine sediments may derive from methanogens. The stereochemistry of squalane in a marine sediment is also compatible with an origin in methanogens; in contrast, the stereochemistry of pristane in M. thermoautotrophicum indicates a fossil fuel contaminant origin, suggesting that this and certain other alkanes reported in archaebacteria might also be of contaminant origin. There is, therefore, little evidence at present that the pristane in immature marine sediments originates in methanogens. The C15 and C20 saturated alcohols in M. thermoautotrophicum have mainly the all-R configuration. If this is generally true for methanogens, the C20 alcohol in the Messel shale may originate mainly from methanogens, whereas that in the Green River shale may originate mainly from photosynthetic organisms.

The kinetics of the aromatisation of both rearranged and non-rearranged monoaromatics have been investigated in the laboratory under free radical conditions. These studies have indicated that the aromatisation rate constant for the non-rearranged is greater than that for the rearranged isomers at any one particular temperature. Since the members of the rearranged series coelute with their non-rearranged counterparts when both series are present in geological extracts, these results suggest that care needs to be exercised when assessing extents of maturation using monoaromatic and triaromatic steroid hydrocarbons.

This paper describes the main results of a study of hydrocarbon migration in the Mesozoic in the Paris Basin, as obtained from the geochemical analysis of cuttings from 41 petroleum boreholes. The analytical methods used were pyrolysis, gas chromatography, mass spectrometry and the determination of stable isotopes. Hydrocarbon formation and migration were simulated using the Temispack mathematical model. The following results were found: Concerning the primary migration, pyrolysis of numerous samples of freshly-cleaned cuttings allowed the computation of a Migration Efficiency Ratio for each sample, by comparing the HC contents actually produced with those remaining in the rock. They also allowed the compilation of migration maps for each source rock level. As indicated by the Migration Ratios, the HC expulsion starts below the beginning of the oil window (2100 m), at a depth of about 2350 m, for a Transformation Ratio of the Lias OM of 25%. These Migration Ratios increase strongly with depth, reaching 88% at 2700 m. Migration maps served to locate the true source rocks at the base of the Lias, and to calculate the total quantity of oil expelled (2 billion tons of HC ∗ ). Analysis of rock extracts from drained levels shows, by comparison with the oil analyses, that migration occurred without any variation in HC composition. Concerning the secondary migration, the migration maps used to estimate the amounts of migrated HCs revealed lateral migration phenomena in some rocks (Toarcian). With respect to the other secondary migration paths, faults played an important role, but failed to favor vertical downward migration by more than 50 m below the Lias source rocks, as shown by the Temispack model. The deep Trias reservoirs could only be filled laterally when the faults (like the Bray fault) placed the mature Hettangian/Sinemurian source rocks in contact with the Trias. Furthermore, the hypotheses of a regional hydrodynamic flow trending NE/SW were taken into account in the model to explain the lateral HC migrations to distances often far from their “oil kitchen”, and the rarity of shows northeast of the Bray fault.

The distributions of proposed reactants and products of stages of early diagenesis of steroid hydrocarbons have been studied by GC and GC-MS in a variety of downhole sequences of DSDP cores of various ages, which include the San Miguel Gap, Walvis Ridge, Gulf of California and Falkland Plateau. The compounds comprise aliphatic and aromatic hydrocarbons such as diasterenes, monoaromatic anthrasteroids and spirosterenes. From the study of the progress of proposed reactions and of presumed product/reactant relationships a pattern emerges that extractable lipid distributions can provide a means of distinguishing levels of early diagenesis which cannot be recognised readily from other methods. A number of diagentic trends are evident such as progressive isomerisation at C 20 in diasterenes, which occurs at different relative rates and temperature ranges in sediment sequences with different heat fluxes. Such studies allow investigation of the changes in biological marker compounds in the part of the continuum between changes during sediment deposition and the advent of catagenesis.

A stepwise extraction technique, based on that of Beletskaya (1972), has been aplied to sedimentary rock samples of variable grain size and maturity from a Neogene sequence in the Pannonian Basin (S.E. Hungary). The resulting chloroform extracts, claimed by Beletskaya (1978) to sample “open” and mineralogically “closed” pores, have been analysed by gas chromatography and gas chromatography-mass spectrometry. Differences in the concentrations of the two extracts and the concentrations of their hydrocarbon fractions, and in the distributions of n -alkanes and steroid hydrocarbons suggest that either the “open” pores are impregnated with mature oil which has migrated from depth, or that movement of organic material from the “closed” to “open” pores occurs with considerable fractionation based on both polarity and molecular size. The implications of these differences for source rock-oil correlation studies are discussed and an assessment of mechanisms for primary migration is given.

Laboratory heating experiments have been carried out using a mixture of isomeric C 27 monoaromatic steroid hydrocarbons and 6(R), 10(S) pristane as organic substrate, each on a different sediment matrix. Under free radical conditions in the presence of elemental sulphur triaromatic steroid hydrocarbons and the 6(R), 10(R) and 6(S), 10(S) isomers of pristane were formed, respectively. Both the aromatisation and isomerisation reactions follow pseudo-first-order kinetics and rate constants have been measured. A qualitative investigation of the isomerisation of 5α(H)-cholestane shows that a complex mixture of C 27 isomeric steranes is formed.

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.

The distributions of the major ring C monoaromatic and triaromatic steroid hydrocarbons of a number of oils, biodegraded under natural conditions to differing extents, have been examined by combined gas chromatography-mass spectrometry. Three major effects are observed: (i) loss of low molecular weight triaromatics, possibly from preferential water solubility; (ii) preferential degradation of mono- and triaromatics with the original 20R biological configuration; (iii) resistance of low molecular monoaromatics to biodegradation in comparison with their high molecular weight counterparts. In the laboratory, aerobic biodegradation of aromatic steroid hydrocarbons has also been demonstrated. Some of the effects are similar to those observed in the field studies.

A combined geochemical and micropalaeontological study of Cenomanian to Maastrichtian pelitic sediments from the Brazilian continental margin has been undertaken. The organic carbon contents, Rock-Eval pyrolysis results and biological marker distributions, together with the taxonomic selection and distribution patterns of microfossil assemblages indicate that intermittent anoxic events occurred in the Brazilian marginal basins during the Cenomanian-Santonian with deposition taking place in progressively deeper waters from neritic to bathyal. Such events are characterised by the following: 1. (i) a predominance among the benthonic foraminifera of low-diversity, small-sized specimens (mainly composed of gavelinellids, buliminids and nodosariids) indicating “dysaerobic” bottom conditions; 2. (ii) levels with virtually no benthonic foraminifera and a well-developed planktonic biota (foraminifera, radiolarians and diatoms) indicating “anaerobic” bottom conditions with oxygenated surface waters; 3. (iii) the occurrence of organic rich calcareous mudstone sediments; 4. (iv) features in the biological marker distributions such as high concentrations of 28,30-bisnorhopane and 25,28,30-trisnorhopane (up to 130 ppm), a predominance of phytane over pristane, and medium to high concentrations of nickel and vanadyl porphyrins (up to ca 5700 ppm). The widely recognized Cenomanian-Turonian and Santonian “oceanic anoxic events” (Schlanger and Jenkyns, 1976; Ryan and Cita, 1977 and Jenkyns, 1980) are therefore manifest in the Cassipore, Ceara, Sergipe/Alagoas and Campos basins within the Brazilian continental margin, as is the presence of such events in the Coniacian. In contrast, the Campanian-Maastrichtian appears to be a time interval when deposition under oxygenated conditions produced sediments with low organic carbon contents and poor hydrocarbon source potential, containing highly diversified and abundant calcareous and agglutinated benthonic foraminifera.

The isoprenoid alkane 2,6,10-trimethyl-7(3-methylbutyl)-dodecane, a related monoene and a pseudohomologous C25 diene have been identified in field specimens of the green alga Enteromorpha prolifera. The identifications were based on gas chromatographic retention data, microscale hydrogeneration, mass spectral evidence and, for the C20 alkane, comparison with the synthesised hydrocarbon. The same compounds, and related hydrocarbons with the same two carbon skeletons, appear to occur widely in freshwater and marine sediments and sedimenting particles from different parts of the globe. Some of these highly branched sedimentary compounds may be algal in origin.

Recent literature reports have suggested the use of long chain ( n -C 37 ) alken-2-ones in Quaternary marine sediments as a palaeoclimate indicator. They occur as di-, tri- and tetra-unsaturated components whose relative abundances are measured as an internal ratio (U 37 k ). Since the precise structures of the compounds were unknown, both the all- Z and all- E isomers of the gross structures assigned previously have been synthesised. GC coinjection studies indicate that the natural components in the alga Emiliania huxleyi and in marine sediments have the unusual and unexpected E configuration. The synthesised compounds offer promise as standards for the development of more sensitive and specific methods for measurement of U 37 k ratios.

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.

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.

A novel series of C26 to C28 5β(H)-A-norsteran-3-ones (Ia to c) has been identified in a Late Miocene and two Pliocene sediments from the San Miguel Gap (California continental borderland). Their presence suggests that the bottom waters might have periodically contained sufficient oxygen to allow benthic fauna to survive.

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 re-investigation of the acid catalysed rearrangement of Δ 4 and Δ 5 sterenes and of 4-methyl- Δ 4 sterenes, and comparison of the product distributions (including diasterene and rearranged spirosterene components) with those of steroid alkenes and 4-methyl steroid alkenes respectively in immature sediments, confirms that in each case the rearrangement occurs naturally during diagenesis. In the case of Δ 4 and Δ 5 sterenes, the distributional changes observed during a time-course study parallel those seen with increasing extent of diagenesis. A related study of the rearrangement of Δ 7 sterenes indicates that other sterenes and spirosterenes arise from Δ 7 sterols and that reduction of these isomeric sterenes in immature sediments could give rise to the (20R)- and (20S)-5α, 14β, 17β(H)- and (20S)-5α-steranes commonly used for maturity assessment.

Heating of C 20 (Ia) and C 28 (Ie, 20R) triaromatic steroid hydrocarbons on bentonite at 200°C results in their presumed degradation to unknown products, although traces of Δ 15 and 20S (for the C 28 compound) components were observed. No short chain, C 20 (Ia) and C 21 (Ib) triaromatics were obtained from the C 28 triaromatic. Competitive heating of equal amounts of C 20 and C 28 components showed a faster rate of degradation for the long chain homologue. This suggests that the increase in short chain triaromatics in sediments upon increasing maturation may be due to preferential degradation of the long chain homologues.