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Summary This abstract provides an overview of the workflows and methodologies implemented in generating a UKCS wide geochemical and geological database, to be used in conducting petroleum systems analysis. As a truly integrated study, it provides a rationale to the various technical scopes involved in executing the work and shows the value in bringing these various results together into an integrated database to be used by industry and academia. The results of this study provide a unique tool to improve subsurface understanding across the UKCS, and assist in the continued drive to enhance exploration and development opportunities in all areas of the UKCS.

The Barmer Basin is a failed continental rift of late Cretaceous–Eocene age in Rajasthan, NW India, containing prolific hydrocarbon resources, with 33 discoveries having been made in the last decade. The basin is predominantly oil-prone, although gas discoveries have been made in the deeper parts of the basin. Oils in the Barmer Basin are highly waxy, a result of the lacustrine nature of the source rocks that dominate the sedimentary fill of the basin. Detailed interpretation of the molecular composition of the oils defines three main oil groups that can be related to differing sources. The oils are all distinctively lacustrine in origin, although differing in specific source-facies characteristics. All of the oils are isotopically light, mostly in the −29‰ to −33‰ range. Most oils in the northern Barmer Basin (groups 1A and 1B) are interpreted to have been generated from the Late Paleocene Barmer Hill Formation, an excellent oil-prone source rock with predominantly Type I lacustrine algal and bacterial kerogen. Group 2 oils are subordinate in abundance, occurring only in the southern part of the basin, and are interpreted to be at least partly sourced from the overlying Early Eocene Dharvi Dungar Formation, which is characterized by mixed Type I and Type III kerogen, and attains oil maturity only in the southern basin. Group 3 oils are less common, and are of higher maturity than the Group 1 oils, but also appear to have been generated from the Barmer Hill Formation where it was buried more deeply in the central and southern parts of the basin. However, recognition of probable Mesozoic sediments in sub-basins beneath the Tertiary Barmer Basin introduces a further source-rock candidate for the Group 3 oils. A high maturity hydrocarbon charge that is recognized in the gasoline-range hydrocarbons in the Group 2 oils of the southern Barmer Basin may also be from a Mesozoic source rock, or from the Barmer Hill Formation that is much more deeply buried in this part of the basin than in the north, and represents a more mixed oil- and gas-prone source.

The Sea Lion Field, lying approximately 220 km north of the Falkland Islands in the northern rift of the North Falkland Basin, contains waxy oil in Lower Cretaceous reservoir sands. The oil is likely to be sourced from Lower Cretaceous lacustrine source rocks lying beneath the reservoir sands. A significant complication in interpreting the geochemical data for the Sea Lion oils comes from their overprinting by leaching of bitumen components (especially biomarkers) from immature organic-rich claystones that are interbedded with the reservoir. Accordingly, best estimates of maturity are obtained from gasoline-range and aromatic hydrocarbons. A higher maturity charge is seen in oils from some of the more western wells, consistent with their higher gas–oil ratios. Basin modelling has shown that the source rocks are more mature to the south of the Sea Lion Field, and the observed differences in oil maturity can be related to sourcing from different parts of this kitchen area and/or different stratigraphic intervals of the source-rock package. Gasoline-range hydrocarbons provide evidence for phase fractionation, with some oils having lost a more volatile fraction whilst others have received additional gas charge. A gas leg in the Beverley and Casper South reservoirs in Well 14/15-4Z appears to have been the original fluid charge, and has not displaced oil, although gas compositions suggest that gas was co-generated with oil, and subsequently separated into two phases, at least in some parts of the field.

The discovery of oil and gas in the Barmer Basin in northwest India was one of the more significant global discoveries in the decade 2001–2010. The basin’s presence was suspected from gravity and magnetic data in the late 1980s but not confirmed until 1999 from seismic and drilling. The basin is a lacustrine failed rift. Biostratigraphic data, however, indicate it was intermittently connected to marine waters via either the Cambay Basin, the Kutch Basin, or across the Devikot high, temporarily forming a large, shallow estuary. At least six major tectono-stratigraphic events have caused relative lake level falls and translation of clastic reservoirs basinward. Upward of 6 km (∼20,000 ft) of Cenozoic and Mesozoic sedimentary rocks have been preserved. Prolific source rocks occur from the Mesozoic through Eocene strata. Tectonically, the basin is divided into a northern and a southern province. The north province continues to undergo inversion and erosion, and has not been buried as deeply as the south. Kinetics of the major source facies in the north are substantially different from those in the south, as well as the present-day and paleo-heat flow. These differences have made the northern part of the basin predominantly an oil province and the southern part a mixed oil and gas province. The prolific Paleocene Fatehgarh Formation contains the bulk of the 7.3 billion barrels of stock tank oil in place (STOIP) identified to date, but other reservoirs from the Mesozoic to the late Cenozoic are common and may yield significant future resource additions.

This paper documents the findings based on interpretation of the geochemical composition of oils from the Bualuang Field located in the western Gulf of Thailand, and how these oils compare with other oils and potential source rocks in the region. The Bualuang Field is located in Block B8/38, on the eastern flank of one of a series of north-south trending, Tertiary half-grabens which are part of the greater Western Basin. Eight oil samples from five wells on the Bualuang Field were analysed using gas chromatography (GC), gas chromatography-mass spectroscopy (GC-MS) and carbon isotopic techniques. Selected samples were further analysed by GC-MS-MS. This paper provides a review of these analyses, presenting key geochemical evidence for the likely age and facies of the source of this oil. A comparison is then made between the Bualuang Field oils and other oils from the immediate surrounding area as well as more regionally. In addition, the oils are considered against potential Mesozoic source rocks observed in peninsular Thailand. The molecular and isotopic analysis of the Bualuang oils show strong similarity, and origin from a carbonate facies (probably marly) as indicated by dominance of C29 hopane over C30 hopane, presence of significant C30 30-norhopane, abundance of C24 tetracyclic terpane and low amounts of diasteranes. Furthermore, the oils are believed to have a marine origin due to the presence of C30 steranes (confirmed by GC-MS-MS), a C26/C25 tricyclic terpane ratio in excess of 1, and the stable carbon isotopic composition. The source of the Bualuang oil is considered older than Tertiary because of the absence of oleanane (typically significant in Tertiary oils), the dominance of 27-norcholestanes (24-norcholestane ratio ca.0.18) and a low C28/C29 sterane ratio (0.58-0.65). Correlation with other oils near Bualuang indicates that this source facies extends further north, with some subtle differences. More regionally clear differences can be observed between the Bualuang oils and other Tertiary oils recognized as either lacustrine or terrestrial in origin. The current study confirmed Jurassic-aged potential source in shales in peninsular Thailand; however, these are quite different to the source for the Bualuang oil. Previous published data for Cretaceous-aged potential source rocks onshore also do not provide a strong correlation. Importantly this paper provides strong, albeit indirect, geochemical evidence for an additional oil-prone source to consider within the western Gulf of Thailand, which is believed to be Mesozoic in age. One of the key exploration challenges is related to identifying the presence and extent of such a Pre-Tertiary source on seismic data.

A suite of black shales, calcareous shales and limestones, representing the Toarcian anoxic event (Jurassic, ∼ 192 Ma), was collected from a 14-m length of core taken from the Belluno Trough, northern Italy, and examined in detail to assess variations in depositional environment during this interval. Geochemical and optical data indicate organic matter of algal and bacterial origin, with only trace contribution from terrestrial sources. Detailed biological marker data, interpreted with the aid of multivariate statistics, demonstrate fluctuations in primary producers and bacterial populations during black shale deposition. The onset of the anoxic event was not abrupt, but characterized by an apparent gradual development of anoxia and consequent enhanced organic-matter preservation. Different hopane biomarkers proved especially useful in recognizing preservation potential in the section, and correlate well with other “preservation” indicators. Increased oxygenation at the end of the event may have been associated with changes in primary productivity.

This study reports the results of organic geochemical characterisation of oil extracts from cores through an oil reservoir column within the Grane field, North Sea. The results show small gradients in composition attributed to ongoing biodegradation occurring at the oil–water contact. Biodegradation is affecting the labile constituents that have been replenished by recent charging of this mixed oil and there is no apparent ongoing biodegradation effect upon the resistant compounds associated with earlier oil charge. The use of principal component analysis has allowed compositional changes due to evaporation during storage to be distinguished from the effects of biodegradation, and has highlighted the C19+ n-alkanes/(hopanes + steranes) ratio as a biodegradation sensitive parameter that shows a gradient in composition through the oil column. The concentration of the C19+ n-alkanes though the oil column confirms that the n-alkanes are depleted towards the oil–water contact. This approach has shown that biodegradation related trends, indicative of ongoing biodegradation, can be identified in reservoirs that contain multiple altered oil charges even when affected by subsequent compositional changes during sample storage.

Bacteriohopanepolyols (BHPs) are membrane lipids produced by a wide range of bacteria including cyanobacteria, nitrogen fixing bacteria, purple non-sulfur bacteria, acetic acid bacteria, methanotrophs and methylotrophs. The diverse range of BHPs produced by these organisms and the degree of taxonomic specificity enables their use as molecular biomarkers for bacterial processes and populations in both modern and ancient environments. Here we show that the diversity of intact BHP structures from a number of UK soils indicates significant differences between soil bacterial populations. We also identify a group of BHP structures that appear to be highly specific to soils and which could be used to track the movement of soil to sediments.

We investigated relationships between sedimentary solvent-extractable long-chain alkenone (LCA) concentration and composition and environmental factors in a suite of endorheic lakes from inland Spain. LCAs were found in 14 of the 54 lakes examined, with concentrations comparable with those from previously published lacustrine settings. The composition of LCAs in our sites, however, contrast from the majority of those previously reported from lake environments; in our study the tri-unsaturated component is the most abundant component at most sites where LCAs are detected, and C38:3 is the most abundant LCA in the majority of sites. LCA occurrence appears to be restricted to brackish-hypersaline sites and C37 LCAs are absent above a salinity of ∼40 g L−1 suggesting a salinity control on LCA-producing organisms in these sites. Low concentrations of C37 LCA components means U 37 k and U 37 k ′ temperature indices are generally not applicable. Instead we find good relationships between C38 components and (in particular mean autumn) temperature and the strongest LCA–temperature relationships are found when using a combination of all C37 and C38 compounds. We propose a new alkenone temperature index for lakes with elevated salinity and where the C38 components dominate the LCA distributions. This is expressed as U 3738 k = 0.0464 × MAutAT - 0.867 (r2 = 0.80, n = 13). In this paper, we provide the first account of sedimentary LCA distributions from lakes in inland Spain, extending the range of environments within which these compounds have been found and highlighting their significance as indicators of both salinity and temperature in saline, endorheic lake environments. This has important implications for extending the potential role of LCAs as palaeoclimatic indicators in lacustrine environments.

Exploratory analysis of petroleum geochemical data seeks to find common patterns to help distinguish between different source rocks, oils and gases, and to explain their source, maturity and any intra-reservoir alteration. However, at the outset, one is typically faced with (a) a large matrix of samples, each with a range of molecular and isotopic properties, (b) a spatially and temporally unrepresentative sampling pattern, (c) noisy data and (d) often, a large number of missing values. This inhibits analysis using conventional statistical methods. Typically, visualisation methods like principal components analysis are used, but these methods are not easily able to deal with missing data nor can they capture non-linear structure in the data. One approach to discovering complex, non-linear structure in the data is through the use of linked plots, or brushing, while ignoring the missing data. In this paper we introduce a complementary approach based on a non-linear probabilistic model. Generative topographic mapping enables the visualisation of the effects of very many variables on a single plot, while also dealing with missing data. We show how using generative topographic mapping also provides an optimal method with which to replace missing values in two geochemical datasets, particularly where a large proportion of the data is missing.

In addition to previously reported 25-norhopanoic acids with the 17α(H), 21β(H) and 17β(H), 21α(H) configurations, for the first time we report the identification of 25-norhopanoic acids bearing the 17β(H), 21β(H) configuration in a suite of heavily biodegraded oils from China. The 17β(H), 21β(H) stereochemistry is a thermally unstable biologically-derived structure, suggesting that the 17β(H), 21β(H) 25-norhopanoic acids may derive from petroleum-degrading microbes. Rather than representing a direct input, we propose that demethylation of 17β(H), 21β(H) hopanoic acids derived from bacteria in the reservoir may give rise to 17β(H), 21β(H) 25-norhopanoic acids, implying that microbial reworking of biomass is occurring alongside petroleum degradation.

Bacteriohopanepolyols (BHPs) are membrane lipids produced by a wide range of prokaryotes, including many methanotrophs, methylotrophs, cyanobacteria, nitrogen fixing bacteria and purple non-sulfur bacteria. As a result of the taxanomic variation expressed by the producer organisms, BHPs offer great potential as molecular markers of bacterial populations and processes and can be used to fingerprint hopanoid-producing bacterial populations in modern environments as well as having the potential to provide a valuable record of past bacterial community structure. Here we show that the diversity of BHPs in many recent sedimentary environments is considerably more complex than previously envisaged and can be used to readily identify organic matter derived from diverse groups of organisms as well as environmentally significant bio- and geochemical processes.

The lipid geochemistry of lake sediments can provide information on past environmental change. Detailed interpretation is, however, often hampered by a limited understanding of the provenance of many compounds and the multiple factors influencing their distributions in modern lake sediments. We have quantified the solvent extractable lipid compositions of modern surface sediments from fifty four Spanish lakes covering a range of hydrochemical (fresh to hypersaline) and hydrological (shallow ephemeral to deep permanent) conditions. Lipid compositions across the dataset are dominated by carboxylic acids (up to 86% total solvent extractable lipids), alkanols (up to 63%) and sterols (up to 58%), with smaller relative proportions of alkanes, alkenes, ketones (including long chain alkenones) and hopanols. Here we employ the distributions of these dominant compounds to explore relationships between lipid composition, source inputs and lake type. Source input is the major factor influencing the lipid composition, but there are also some indicators of early stages of lipid diagenesis in these surface sediments. Multivariate data analysis (non-metric multidimensional scaling ordination and cluster analysis) of normalised lipid concentrations shows a distinction between compounds originating primarily from algal, bacterial, macrophyte or terrestrial plant sources. This statistical technique enables sites to be grouped according to their dominant lipid compositional characteristics as well as enabling us to identify broad trends in groups of sites in terms of their environmental features (e.g. shallow or deep lakes). This modern training set study provides insight into patterns of contemporary lipid distributions and lipid source and site relationships across diverse lacustrine environments, which can then be useful in environmental monitoring and palaeoenvironmental studies using sediment cores.

Bacteriohopanepolyols (BHPs) are membrane lipids produced by a wide range of eubacteria. Their use, however, as molecular markers of bacterial populations and processes has until recently been hampered by the lack of a suitable rapid method for fingerprinting their composition in complex environmental matrices. New analytical procedures employing ion trap mass spectrometry now allow us to investigate the occurrence of BHPs in diverse biological and environmental samples including bacterial cultures, soils, and recent and ancient sediments. Here, we describe the structural characterisation using atmospheric pressure chemical ionisation liquid chromatography/ion trap mass spectrometry (APCI-LC/MSn) of a number of previously identified but less commonly occurring BHPs such as adenosylhopane and ribonylhopane. Many of the structures described here have previously only been reported in one or just a small number of cultured organisms having been isolated from large amounts of cellular mass (4–26 g) and identified by nuclear magnetic resonance (NMR) techniques after purification of individual compounds. Now, having established characteristic APCI fragmentation patterns, it is possible to rapidly screen many more bacterial cultures using only small amounts of material (

Lipid compositions preserved in stalagmites have significant potential for use in reconstruction of global climate change and regional vegetation cover, but the low organic content of stalagmites poses a problem both for clean extraction and for obtaining a high temporal resolution in palaeoenvironmental records. Here, we present an acid digestion method optimised for cleanliness and maximum lipid recovery. The use of acid digestion and hydrolysis improves lipid yields not only by releasing organic matter trapped within individual calcite crystals, but also by allowing access to the chemically-bound pool of lipids, particularly acidic compounds such as alkanoic acids, hydroxy acids, and alkanedioic acids. The technique also considerably reduces contamination problems in comparison to conventional soxhlet extraction.

Quantitative data from petroleum systems in China (Liaohe basin) and Canada (Athabasca tar sands) support the theory that 25-norhopanes are produced during biodegradation of petroleum in the subsurface. Within a single oil column, both case histories showed increasing severity of degradation, indicated by destruction of hopanes and production of 25-norhopanes downward to the oil–water contact. In the Athabasca samples between the [Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood Cliffs, New Jersey, p. 363] scale of biodegradation levels 5–9, concentrations of C28 20S triaromatic steroids and other biodegradation-resistant compounds increased by 35%, reflecting a concentration effect as a consequence of removal of more degradable compounds. Over the same interval, the concentrations of C28 17α 25-norhopane and C29 17α 25-norhopane increased by an order of magnitude, thus requiring that the balance be met by their net production during degradation. A detailed molecular investigation of the Athabasca bitumen revealed that C30 17α hopane degrades faster than C29 17α hopane, whilst the rate of formation of both C29 17α 25-norhopane and C28 17α 25-norhopane are similar, complicating a straightforward interpretation of demethylation of hopanes to form 25-norhopanes. Hopane degradation in the Athabasca tar sand may also occur without the production of 25-norhopanes. The results show that even within a single petroleum accumulation, a number of mechanisms control changes in the abundance and composition of hopanes and 25-norhopanes.

Microbial adaptations associated with extreme growth environments, including high temperatures and low pH, are of interest to astrobiologists and origin of life researchers. As part of a survey of microbial lipids present in terrestrial geothermal settings, we examined four silica sinters associated with three different hot spring areas of the Taupo Volcanic Zone (TVZ), New Zealand. Dominant bacterial lipids include free fatty acids, 1,2-diacylglycerophospholipids, 1,2-di-O-alkylglycerols, 1-O-alkylglycerols, wax esters, alkanols, alkan-1,2-diols and various hopanoids, whereas dominant archaeal lipids include both archaeol and glycerol dialkyl glycerol tetraethers. Although many of these compounds occur in other settings, in the TVZ sinters their distributions (with high abundances of β-OH fatty acids and high-molecular-weight (> C18) fatty acyl components) and carbon isotopic compositions (ranging from −40 to +4, with up to 25 variability in a single sample) are unusual. In addition, we have identified a range of unusual compounds, including novel macrocyclic diethers and hopanoids. The distributions of these compounds differ among the study sites, suggesting that, where preserved in ancient sinters, they could serve as an important tool in studying past hydrothermal environments.

Soluble and insoluble fractions of the Jet Rock sedimentary organic matter have been subjected to hydropyrolysis to evaluate their biomarker content. Hydropyrolysis is the temperature-programmed pyrolysis of organic matter in an open system fixed bed reactor under high hydrogen pressure in the presence of a sulfided molybdenum catalyst. The hydrocarbon products contain fossil lipids and biomarkers including high carbon number homologues and compounds with stereochemical configurations that are sensitive to exposure to high temperatures. Distinct differences exist between the concentrations and composition of biomarkers present in the different organic matter fractions. The sterane carbon number distribution, the dominant hopane carbon number and the proportions of tricyclic terpanes and extended tricyclic terpanes are different in each fraction, so biomarker parameters measured for different fractions are not directly comparable. The samples are of early oil window maturity and yet the quantities of biomarkers covalently bound into the kerogen fraction are of equal magnitude to the quantities that are present in the extractable aliphatic hydrocarbon fraction. However, the quantities of biomarkers in the polar resin and asphaltene fractions are two orders of magnitude lower and these two organic matter fractions contain biomarkers that are compositionally very different from the bulk of the biomarkers present in the total sedimentary organic matter. Isorenieratene derivatives were found in all fractions, indicating that green sulfur bacteria were present during sedimentation and that water column anoxia extended into the photic zone periodically if not continuously during the deposition of the Jet Rock.

Anaerobic oxidation of methane (AOM) is common in ocean-margin sediments, where it is mediated by consortia of Archaea and Bacteria and can result in the formation of authigenic carbonate, including extensive carbonate crusts. Previous work indicates that AOM is associated with Gulf of Mexico hydrocarbon seeps and is mediated by similar organisms as identified in other settings; however, biological investigations have not been done on the associated 13C-depleted carbonates. Here, we show that 13C-depleted archaeal and bacterial biomarkers are abundant in Gulf of Mexico authigenic carbonate rocks, revealing that AOM-mediating organisms are closely associated with carbonate authigenesis. Moreover, the rocks share general characteristics of the background (soft) sedimentary archaeal and bacterial community inferred from biomarker analysis, suggesting that the organisms associated with carbonate authigenesis are the same as those that live elsewhere in the hydrocarbon seep environment. This provides further evidence that AOM by Archaea and sulfate-reducing bacteria can result in the sequestration of significant quantities of methane-derived carbon in carbonate rocks.

Flash pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) was applied to freeze dried cells of eleven bacterial species. Six species known to synthesise bacteriohopanepolyols (BHPs) were found to produce easily identifiable C27–C35 hopenes and hopanes upon flash pyrolysis. These compounds could not be observed in the pyrolysis products of five species, two of which are known not to produce BHPs. In the search for BHP-containing bacteria this rapid screening approach prevents unnecessary time-consuming laboratory work to characterise species that would produce negative results.

Biogenic silicates from the Taupo Volcanic Zone (North Island, New Zealand) are shown to contain a number of unusual polyfunctionalised bacteriohopanepolyols. Hopanoid fractions isolated from the Rotokawa hot spring (80–82 °C) contained significant amounts of 32,35-anhydrobacteriohopanetetrol and two isomers of a related trihydroxylated compound. The origin of these unusual hopanoid side chains is unclear and they may result either from novel biosynthetic or diagenetic transformation pathways of known biohopanoid precursors such as bacteriohopanetetrol (via cyclisation) or reductive removal of adenine from adenosylhopane.

Methylhopanoids are organic compounds synthesized by certain bacteria, that when preserved in sediments act as molecular fossils or biomarkers for organic matter inputs from specific bacterial sources. Two series of methylhopanoids occur, each mainly deriving from a distinct bacterial source: cyanobacteria (2-methyl) and methanotrophic bacteria (3-methyl). The abundance and composition of methylhopanoids within sediments of modern depositional environments varies widely, apparently due to different bacterial communities contributing to the sedimentary organic matter. Comparable molecular characteristics are found in oils and their source rocks. Consequently, methylhopanoids are valuable in oil-oil and oil-source rock correlations, distinguishing between samples related to different depositional environments. In particular, abundant 3β-methylhopanoids (from methanotrophic bacteria or an additional unknown bacterial source) are characteristic of some modern alkaline saline lake environments. Comparable compositional features in the methylhopanes of oils allow the assignment of lacustrine oils offshore West Africa to two distinct lacustrine source rock facies, and to distinguish between different marine source facies, thus refining oil-source rock correlation.

Molecular stratigraphic analyses using gas chromatograph-mass spectrometry have been performed in the upper section (S0, L1, S1) of the Yuanbo loess–paleosol sequences in northwest China, with a record extending from the last interglaciation through the present interglaciation. The CPI (Carbon Preference Index) values of both n-alkanols and n-alkan-2-ones display variations between loess deposits and paleosols, showing a correlation with the magnetic susceptibility record, an indicator of the East Asian summer monsoon. The observed variations in the indexes in relation to changes in lithology/paleoclimate are proposed to result from microbial degradation of higher plant lipids in the paleosols. The CPI values of n-alkanes, n-alkanols, and n-alkan-2-ones are negatively correlated with δ13C of bulk organic matter. The correlations suggest that the observed glacial–interglacial variations of δ13C data in the loess stratigraphy reflect the relative importance of the contribution of paleovegetation compared with microorganisms (including both the degradation and the addition of organic matter) and allochthonous loess/soil parent materials. It is thus necessary to evaluate the contributions of the latter two before the paleovegetation can be reconstructed based on the δ13C analysis of bulk organic matter in some loess–paleosol sequences of the Chinese Loess Plateau.

Biohopanoid compositions were determined for modern sediments from 27 lacustrine environments and 1 near coastal lagoon. GC–MS analysis of existing hopanols and those produced by a side-chain cleavage reaction (periodic acid and sodium borohydride) of the bacteriohopanepolyols provided quantitative data for bacteriohopanetetrol (BHT), bacteriohopanepentol, and composite tetra-, penta- and hexafunctionalised biohopanoids. Additional analysis of acetylated total extracts by HPLC–APCI–MS has allowed us to identify up to seven intact bacteriohopanepolyols in these environments, including the first direct observation of 35-aminobacteriohopanepentol in environmental samples. This method is complementary to the periodic acid approach in providing more specific compositional information. The lacustrine environments exhibit a wide range of compositions, many with high inputs of hexafunctionalised biohopanoids (up to 60% of total tetra-, penta- and hexafunctionalised biohopanoids), indicative of major contributions to the sediment from Type I methanotrophic bacteria. Several methylated biohopanoids were also detected in most of the samples with 2β as the dominant configuration of the methyl group; 2β-methylbacteriohopanetetrol was by far the most abundant and most commonly occurring compound of this type and comprised the most abundant bacteriohopanepolyol in one saline lake (Laguna Grande, Spain). Such compounds are believed to be derived from cyanobacteria, currently the only known quantitatively-significant source of 2β-methylated biohopanoids. Biohopanoids containing a methyl group at C-3 were also detected in a limited number of environments. These data demonstrate the wide variability in bacteriohopanepolyol compositions among depositional environments, and the potential of these compounds to preserve bacterial source information and, thereby, to record environmental change.

Hopanoids bound into the insoluble organic matter (kerogen) of Recent sediments from a freshwater lake (Priest Pot) and an anoxic sulphidic fjord (Framvaren) were released by hydropyrolysis and examined by gas chromatography-mass spectrometry. Bound hopanoids are present in high concentration (190–1400 μg/g TOC) and represent 22 to 86% of the total analysable hopanoids (i.e., bound and solvent-soluble), this proportion increasing with depth in Framvaren Fjord. The hopanes generated by hydropyrolysis contain higher amounts of the C35, C32, and C30 homologues, reflecting the carbon number distribution of the bound hopanoids and indicating that both biohopanoids (C30 and C35) and their diagenetic products (dominated by C32) are incorporated into the kerogen on a timescale of only 0 to 350 years. Sequential (multiple temperature) hydropyrolysis experiments gave an indication of the relative strengths of bonds being cleaved in association with hopane generation: The hopanoids of a sediment from Priest Pot are almost entirely bound by strong covalent bonds, interpreted to be mainly ether linkages, whilst a Framvaren sediment contains hopanoids that are bound by a mixture of weak di-/polysulphide linkages and stronger ether bonds. Labelling with deuterium indicated that the strong covalent linkages dominate, even for the Framvaren sediment.

Bacteriohopanepolyols (BHPs) fragment via characteristic pathways during atmospheric pressure chemical ionisation liquid chromatography/ion trap mass spectrometry (APCI-LC/MS(n)). Comparison of the MS(2) spectra of bacteriohopane-32,33,34,35-tetrol (BHT) and 2 beta-methylbacteriohopane-32,33,34,35-tetrol has confirmed the previously proposed ring-C cleavage occurring between C-9 and 11 and C-8 and 14. This fragmentation, diagnostic of all hopanoids, also occurs in BHPs containing an amino group (-NH(2)) at C-35 although the higher relative stability of the ion limits this fragmentation to a minor process after protonation of the basic nitrogen function. Studies of a number of cell cultures including a prochlorophyte (Prochlorothrix hollandica) and a cyanobacterium (Chlorogloeopsis LA) demonstrate the power of this technique to detect composite BHPs with a complex biological functionality at C-35. We also report the first observation of intact pentafunctionalised bacteriohopanepolyols using this method.

Atmospheric pressure chemical ionisation liquid chromatography/multi-stage ion trap mass spectrometry (APCI-LC/MSn) has been applied to the study of intact bacteriohopanepolyols. Spectral characterisation of bacteriohopanepolyols of known structure present in bacterial extracts (Zymomonas mobilis and a fermenter containing methanotrophs including Methylococcus capsulatus) has revealed greater structural detail than previous liquid chromatography/mass spectrometry (LC/MS) methods and identified characteristic fragmentations indicative of numerous biohopanoid structures. Analysis of a Recent sedimentary extract from Lake Druzhby (Antarctica) has demonstrated the power of this technique to detect biohopanoids in complex samples including at least partial characterisation of previously unknown composite structures. Copyright © 2003 John Wiley & Sons, Ltd.

Hopanoic acids were found in all but the two most mature of a suite of 30 Triassic to Cretaceous sedimentary rocks. Their carbon number distributions generally maximise at C 32 , consistent with hopanoic acids found in modern sediments. The extent of isomerisation (measured by %ββ and %22S αβ parameters) is less for the acids than for associated hopanes, possibly due to increased isomerisation of hopanes in association with their generation from macromolecules and functionalised precursors. In immature samples the hopane carbon number distributions are consistent with an origin from defunctionalisation of hopanoic acids and other early diagenetically-formed hopanoids, whilst hopanes in more mature samples exhibit broader carbon number distributions indicative of side-chain cleavage during generation of macromolecularly-bound hopanoids.

The sediment of a highly productive lake (Priest Pot, UK) contains the biosynthesised hopanoid bacteriohopanetetrol (BHT) and a series of hopanediols and triols. These polyols represent intermediate stages in the conversion of biologically produced hopanoids to the diagenetic products, hopanes. Two of these geohopanoids, assigned as trishomohopane-32,33-diol and bishomohopane-30,31,32-triol have not been previously reported in recent sediments, and their identification, in addition to that of tetrakishomohopane-32,33,34-triol and a bishomohopanediol gives valuable information on the original composition and subsequent diagenesis of bacteriohopanepolyols within recent sediments.

Bacteriohopanepolyols are the biological precursors of extended hopane biomarkers which are ubiquitous in the geosphere. The abundance and composition of these biohopanoids were determined for modern sediments from eight depositional environments by GC-MS analysis of hopanols derived from a side-chain cleavage reaction (periodic acid and sodium borohydride) of the bacteriohopanepolyols. We report quantitative data for bacteriohopanetetrol (BHT), composite tetrafunctionalised biohopanoids, pentafunctionalised biohopanoids and hexafunctionalised biohopanoids. BHT was found in concentrations higher than previously reported (up to ca. 1500 μg/g TOC), but comprised only a relatively small proportion (0–26%) of the total biohopanoids in all except one sample. Composite tetrafunctionalised biohopanoids were the dominant group of bacteriohopanepolyols in all other sediments, and are likely to be a major source of the geologically occurring extended hopanes. Hexafunctionalised biohopanoids were most abundant in lake sediments, particularly two small highly productive stratified lakes (where they comprised 20–40% of total biohopanoids). This feature is interpreted to be due to greater contribution to the organic matter of these sediments from Type I methanotrophic bacteria (which produce dominantly hexafunctionalised biohopanoids), consistent with the environmental settings. In the marine environments where sulphate reduction is dominant, hexafunctionalised biohopanoids are relatively minor constituents (2–6% of total biohopanoids). These data comprise the first clear demonstration that bacteriohopanepolyols vary in composition between depositional environments, and have the potential to preserve specific bacterial source information in sedimentary organic matter.

The effects of thermal maturation upon the abundance and composition of the tricyclic terpanes have been investigated within a single sedimentary horizon within the Dun Caan Shale Member (Isle of Skye, Scotland) intruded by a 0.9 m thick Tertiary dolerite dyke. Heating by the igneous body caused the concentrations of all 13β(H),14α(H) and 13α(H),14α(H) tricyclic terpanes to increase towards or within the effective ‘oil window’, recording generation from abundant non-hydrocarbon precursors, such as kerogen- and asphaltene-bound components. Progressive changes in tricyclic terpane composition accompany these concentration changes. An increase in the C23 βα/αα maturity parameter towards the dyke resulted from the relatively greater rate of generation of the βα isomer, combined with the earlier decline in concentration (by degradation or isomerisation) of the αα component. The tricyclics/(tricyclics+hopanes) parameter shows a dramatic increase within the latter part of the oil window, due to the greater relative thermal stability of the tricyclic terpanes. The quantitative data demonstrate the importance of the processes of generation (from non-hydrocarbon fractions of the sedimentary organic matter) and thermal degradation in the operation of tricyclic terpane maturity parameters.

A rapid method for the extraction of RNA from the indigenous bacterial communities in environmental samples was developed. The method was tested using anoxic sediment samples from a productive freshwater lake (Priest Pot, Cumbria, UK). The simple protocol yielded rRNA and mRNA of a purity suitable for amplification by reverse transcriptase PCR (RT-PCR). The integrity of the RT-PCR was demonstrated by amplifying 16S rRNA and mRNA for the mercury resistance regulatory gene merR. The diversity of 16S rRNA sequences recovered from RNA and DNA extracted from anoxic Priest Pot sediments was analysed. The 5' end of extracted 16S rRNA was amplified by RT-PCR and the 16S rRNA PCR products were cloned and sequenced to identify active constituents of the sediment bacterial community. Corresponding analyses were performed upon DNA templates from the same sediment samples. Partial 16S rRNA sequences were obtained from a total of 147 clones (71 rRNA-derived and 76 rDNA-derived). The clone libraries included sequences related to Pirellula staleyi, an aerobic planktonic member of the Planctomycetales, and the recently described candidate bacterial division OP5. Sequences from these groups were recovered in libraries generated from a DNA template but were also present in RNA-derived libraries. Previous studies of anoxic environments have identified sequences most closely related to Pirellula spp. This study, which utilized RT-PCR of 16S rRNA, has provided the first evidence that Pirellula-like bacteria are active in situ in an anoxic environment. Furthermore, members of the recently described candidate division, OP5, were also identified as active constituents of the bacterial community of anoxic Priest Pot sediments. This not only supports the widespread occurrence of OP5 members in diverse environments but suggests that they are active under anoxic conditions.

The distribution of free bio- and geohopanoids were studied in a short (46 cm) core from Recent sediments of Lake Pollen, Norway. Bacteriohopanepolyols are abundant components of the sediments (totalling up to 321 μ g/g dry sediment; 7485 μ g/g TOC), being dominated by C-32,33,34,35 tetrafunctionalised hopanoids. Significantly, bacteriohopanetetrol only accounts for between 7 to 62% of these (24% on average), indicating that composite bacteriohopanoids are more abundant sedimentary constituents, and thus more important precursors of geohopanoids than previously recognised. Downcore profiles of bio- and geohopanoid abundance show maxima at ca . 25 to 30 cm, with a marked decrease in abundance above this depth which coincides with a well-documented change in environment from fjord to isolated lake. A second maximum in biohopanoid abundance occurs at ca . 5 to 12 cm depth. Specific biohopanoids were affected to different extents by the change in environment, suggesting that they have, at least partly, different sources. Our data thus indicate that biohopanoids, and their geohopanoid products, may be sensitive to changes in depositional environment and that they have potential to act as markers for environmental conditions.

The effects of burial maturation upon seven molecular maturity parameters, and the concentrations of individual biomarkers employed in these parameters, have been studied in a well in the Barents Sea. The depth interval between 1400 and 3000 m comprises homogenous Eocene claystones with effectively uniform organic carbon content (0.4–0.6%) and kerogen type (HI of 100–200 mg HC/g TOC). The quantitative biomarker data thus contain minimal interference from organic facies, hydrocarbon expulsion effects and the presence of migrated hydrocarbons. Bulk geochemical data define the hydrocarbon generation threshold (or “oil window”) at around 2300 m. Molecular maturity parameters proceed to equilibrium, and in some cases demonstrate inversion at high maturity. These molecular changes are associated with major changes in biomarker concentrations. The % ββ hopane, %22 S C 31 αβ hopane and %20 S C 29 ααα sterane parameters proceed as a result of the balance between the relative rates of generation and thermal degradation of the different isomers. Increased concentrations of the individual isomers are interpreted to be the result of biomarker generation from the kerogen (mainly) and other macromolecular/polar fractions. The % αββ C 29 sterane parameter and the three parameters involving rearranged hopanes (%Ts, %29Ts and %diahopane) operate at higher maturity levels, and proceed as a result of the relative rates of thermal degradation of the compound pairs. Isomerisation in the bitumen may also influence the operation of the parameters involving stereoisomers, but must be a relatively minor contribution.

We report the new application of negative ion atmospheric pressure chemical ionization (APCI) to the detection of composite bacteriohopanepolyols in bacterial and sedimentary (or other natural environmental) samples. The method employs the addition of dichloromethane to the high performance liquid chromatography eluent prior to APCI to stimulate formation of chlorine addition/association ions from the hopanoid alcohols. This approach provided the first direct analysis of composite bacterial hopanoids in a sediment, identifying bacteriohopanetrol and bacteriohopanetetrol cyclitol ether. © 1998 John Wiley & Sons, Ltd.

Solvent-extracted Kimmeridge Clay Formation kerogen was heated to 315°C for 72 h in the presence of excess water (H2O) or heavy water (D2O). Hydrocarbons generated from the kerogen during the D2O experiments contained variable amounts of deuterium atoms [0 to as high as 12 deuterium atoms per molecule in the compounds we examined (mean of

Hydropyrolysis was used to determine the concentrations of kerogen-bound hopanoid hydro- carbons. The samples characterized were a Recent sediment (Priest Pot, English Lake District) and three source rock kerogens (Green River shale, Draupne shale and Jet Rock shale). The hydropyroly- zate of a hopanoid producing bacterium (Methylobacterium organophilum) showed that this procedure does not overly obscure the original isomer compositions of the samples characterized, although signifi- cant side-chain cleavage does occur, which is inevitable with any pyrolysis method. Notable diAerences are observed between the composition of pyrolyzates and bitumen extracts. For each of the source rock kerogens, the overall level of hopane isomerization within the pyrolyzate is significantly lower than in the corresponding extracts. This is particularly the case for the Draupne sample, the pyrolyzate of which contains 17b,21b-hopanes though these are absent in the bitumen. DiAerences in isomeric com- position of the pyrolyzates are in line with the isomer contents of the bitumen extracts. The abundance of kerogen-derived hopanes is highly variable, both in terms of absolute concentration and also relative to the concentration of hopanes in the bitumen. This is in part due to maturity diAerences, but deposi- tional environment and diagenetic conditions may also exert a control on kerogen-bound hopane con- centration. These results show that hydropyrolysis provides valuable data on the concentration of kerogen-bound hopanes, whilst largely preserving their original isomeric composition. # 1998 Elsevier Science Ltd. All rights reserved

Absolute concentrations of various bio- and geohopanoids have been determined in a 24 cm long core from anoxic Recent sediments of Priest Pot, a small highly productive lake in the English Lake District. Samples were Soxtherm extracted, derivatised by methods targeted at specific hopanoid groups, and quantified by GC-MS. Periodic acid/sodium borohydride treatment was used to cleave the side-chains of highly functionalised hopanoids, producing products more amenable to our detection methods. Biohopanoids are extremely abundant (totalling up to 3000 μg/g dry sediment), particularly those with composite or highly (penta- and hexa-) functionalised side-chains, suggesting that these are important precursors to sedimentary hopanoids in Priest Pot. Downcore biohopanoid abundance profiles show a general diagenetic decline with a marked dip at 5–8 cm, which we interpret as a change in bacterial input. Since this is most marked in the composite hopanoids rather than bacteriohopanetetrol, we suggest that these two hopanoid groups have at least partly different sources, and may thus have potential as environmental markers. The geohopanoids are also abundant (totalling up to 1700 μg/g dry sediment) being dominated by the ββ and αβ bishomohopanoic acids, ββ and αβ bishomohopanol and hop-17(21)-ene. Downcore plots show no apparent conversion of free bio- to geohopanoids with depth, which suggests that incorporation into kerogen may be commencing at an early diagenetic stage in the sediments.

A suite of 36 shales and marls from the Toarcian Oceanic Anoxic Event section at three localities in northern Italy was found to contain variable contents of three series of rearranged hopanes: 17α-diahopanes (C 27 and C 29–34 ; and trace C 35 ), 18α-neohopanes (C 27 and C 29–30 ) and an unidentified early-eluting series (C 27 and C 29–35 ). Principal component analysis (PCA) shows the 17α-diahopanes and the early-eluting rearranged hopanes to closely covary, suggesting a related diagenetic mechanism for the formation of their rearranged skeletons. A general covariance with diasteranes is also noted. The 18α-neohopanes show no covariance with diasteranes or the other two series of rearranged hopanes. We also report 2α-methyl analogues of the 17α-diahopanes and early-eluting rearranged hopanes. We propose that the neohopanes may be at least partly derived from different biohopanoid precursors than the other two series of rearranged hopanes, and that the diagenetic origin of the neohopane structure differs from that of the 17α-diahopanes and the unidentified early-eluting series

The thermal effects of an igneous intrusion (0.9 m thick dyke) upon the abundance and composition of hopanes and hopenes are reported for a suite of samples within a single sedimentary horizon (a carbonate concretion > 1.6 m in diameter) from the Jurassic Dun Caan Shale Member (Bearreraig Bay, Isle of Skye, Scotland). The conventional hopane maturity parameters show normal trends towards the dyke and through the “oil window” (approximately 22–45 cm from the dyke, i.e. 25–50% dyke thickness), with the exception of the Ts (Ts + Tm) parameter which shows a progressive fall with increasing maturity, until the middle of the oil window when it increases markedly. Molecular abundances demonstrate that the observed changes in the hopane maturity parameters result from the combined effects of generation (presumed to be from kerogen) and degradation of individual compounds, with isomerization in the free phase being minimal or unimportant. The unexpected behaviour of Ts (Ts + Tm) results from the minimal generation of Ts compared with Tm. Our data indicate that the Ts skeleton is not present in the kerogen, and at least under the elevated heating associated with an igneous intrusion may be derived from 18α(H)-22,29,30-trisnorneohop-13(18)-ene in the bitumen. Thermally induced modifications to hopane carbon number distributions are also reported, and show that oil-source rock correlations between samples of different maturity must consider the effects of generation/degradation of kerogen-bound hopanes.

Bulk and molecular geochemical, micropalaeontological, and carbon-isotopic data are used to address the different local and global factors influencing the environment of sedimentation of the La Luna Formation (Cenomanian-Campanian, approximate palaeolatitude 15°N) in a single section in western Venezuela. Based on the constructed chronostratigraphic framework, oxygen-depleted bottom-water conditions and black-shale deposition started in western Venezuela well before the widespread occurrence of organic-rich sediments in higher palaeolatitude regions such as the Tethys and the North Atlantic near or at the Cenomanian-Turonian boundary. In the La Luna Formation, palaeoenvironmental conditions that allowed the preservation of organic matter (mainly of marine origin), prevailed until Santonian times in a distal platform facies with very low siliciclastic input. Changes in lithology appear to reflect the local response to eustatic sea-level variations and the presence of a migrating upwelling belt affecting the bioproductivity of silica and carbonate. A marked δ13Corg isotopic excursion is recognised in the middle part of the section, and is apparently unrelated to local palaeoenvironmental changes in bioproductivity and oxygen depletion. Biological marker data show no variations in association with the isotopic excursion, being mainly controlled by local fluctuations in organic-matter input and preservation.

Organic matter accumulation and preservation in lakes with different geomorphological and climatic regimes, is directly influenced not only by local but also by regional and more global climatic conditions. Thus, compositional variations in lacustrine organic matter can be used as good indicators of paleoenvironmental conditions of deposition. Relatively high average TOC (1.0–6.5 wt%) and good lamination characterize most of the Holocene sequence of Lake St. Moritz, an Alphine lake located in SE Switzerland. However, variations in the type and quality of the organic matter at discrete intervals have been distinguished using bulk parameters and biomarker distributions. The most prominent change occurs at the Late Glacial-Holocene boundary, where δ 13 C (OM) , Hydrogen Index and lipid concentrations indicate a substantial increase in primary productivity. Organic matter production and preservation appear to dominate from the early Holocene until approximately 3.8 Ka BP, although variations in sterol contents and fatty acid distributions indicate superimposed fluctuations, such as between 8.3 and 8.1 Ka BP and 5.1 to 4.8 Ka BP. These variations in the lake trophic-state can be correlated with other proglacial lakes in the region, as well as with similar lacustrine records on both sides of the Alps. The result of this comparison indicates a synchronous character of major to medium-amplitude climatic shifts on a European scale.

A Flandrian peat bed near Low Hauxley (Northumberland, UK) was studied both optically and geochemically to compare the pollen and lipid records of changing plant input during its accumulation. A progressive change in the predominant plant inputs from woodland trees to a more diverse assemblage with herbs, shrubs and Sphagnum is recorded in the pollen data, and associated lipid records. However, the pollen and lipid records do not correlate in detail; samples with near-identical lipid distributions can have markedly different pollen assemblages and vice versa. This apparent inconsistency between data sets is interpreted to be the result of different modes of incorporation of the signals. While the lipids will be largely derived from plant debris in situ, the pollen may have been transported over considerable distances, and will record an average signal of flora over a wider area. The records of local plant input (lipid data) and regional vegetation cover (pollen data) are complementary in the reconstruction of past environmental conditions.

Variations in extended hopane distributions are now routinely applied in assessing anoxia in ancient marine sediments and for oil-source correlation studies. Current parameters based on the extended hopanes focus on the predominance of the C35 17α homologues (22S + R isomers), and thus reveal little information on the overall distribution. We present here a new method of characterising extended hopane distributions, using a combination of a C31:C33:C35 ternary diagram, and a hopane odd/even predominance parameter (HOEP). This allows the distinction of virtually all extended hopane distributions. The ternary figure is particularly useful in characterising large numbers of distributions and for correlation purposes. The application of this figure to a set of North Sea data, reveals the existence of a continuum of extended hopane distributions.

What are the consequences for organic matter diagenesis of the observation in two recently published articles of a strong correlation between surface area and organic content in marine sediments? The findings suggest that the typical mode of occurrence of organic matter in marine sediments is as a monolayer (or equivalent concentration) sorbed to the surface of mineral grains. This comment considers the theoretical factors which may influence adsorption and propagation of polymeric organic matter on mineral surfaces, and looks at the likely diagenetic fate of adsorbed material. Both adsorption and condensation have been suggested as possible mechanisms for the preservation of labile biopolymers, but neither process is satisfactory as a stand-alone mechanism; adsorption of monomers can merely retard their biodegradation, and condensation is not favoured in solution. However, if the two processes operate in concert, the criticisms levelled against each process considered in isolation are cancelled out, adsorption promoting condensation and condensation enhancing the strength of adsorption of the products. We suggest that the diagenetic modifications of surface adsorbed organic molecules will tend to strengthen their binding to the mineral surface, such that the geomacromolecules will evolve on the mineral surface towards strongly bound monolayers. The hypothesis overcomes many of the objections to the so-called classical condensation pathway of kerogen formation.

A series of diahopanes and a second, unknown, early-eluting series of triterpanes are reported in lacustrine oil samples from three different basins. We suggest that these compounds, together with 18α(H) 30-norneohopane, show distributions which vary with the salinity of the depositional environment.