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We have analyzed the solvent extracts from three different types of native bitumens from the Uinta Basin in northeastern Utah by a variety of analytical techniques, including GC-IRMS, to evaluate variations in the paleodepositional environment during two periods of Lake Uinta deposition. The gilsonite and tabbyite bitumens are associated with Parachute Creek Member sediments deposited during a major expansion of ancient Lake Uinta. Compound specific isotopic analyses of s-carotane and phytane ( δ 13 C = −32.6 to −32.1% 0 ) from these bitumens reflect input from primary photosynthetic producers such as cyanobacteria. Sterane δ 13C values (−34.5 to −29.2%0) refflect contributions from lacustrine algae, while extremely depleted δ 13C values for methylhopanes (−58.1 to −61.5%0) suggest input from methanotrophic bacteria. Variations in the δ 13C values of the αβ-hopanes (−51.4 to 37.7%0) imply additional input from other bacterial sources. The wurtzilite bitumen was generated from the Saline Facies of the Green River Formation deposited during a later regression of Lake Uinta. Compound specific isotopic analyses of phytane ( δ 13 C = −30.1% 0 ) and steranes δ 13 C = −29.6 to −26.7% 0 ) from this bitumen indicate continued input from primary producers and eukaryotes. The higher relative concentrations of gammacerane ( δ 13 C = −26.9% 0 ) indicate increasing input from aerobic protozoa. We observed a slight enrichment in δ 13C in the wurtzilite extract (and several biomarkers) and suggest that this is a result of sulfate-reducing bacteria outcompeting methanogens, thereby, eliminating the influence of methanotrophs in this later saline stage of deposition.

Hydrocarbon exploration and environmental forensics may appear to be two unrelated topics but in many ways are closely related. Techniques that have been developed and utilized in the hydrocarbon exploration and exploitation industry for many decades have found their way to the forefront of environmental forensics area over the past decade. Whereas hydrocarbon exploration is geared towards finding new resources, environmental forensics is directed to looking at what happens to those resources as they, or products derived from them, are spilled into the environment. In the former one uses sophisticated techniques to correlate oils, or gases, with their suspected sources and in the later, one is trying to correlate the spilled product with its suspected source. The source may be a tanker, pipeline, underground storage tank or something similar. The most widely used techniques in both of these areas for many years have been gas chromatography (GC) and gas chromatography mass spectrometry (GCMS) but recent years have seen an exponential increase in the utilization of stable isotopes. There is nothing new about applying stable isotopes to exploration problems but the majority of the older applications utilized bulk isotope numbers for crude oil correlation studies. The availability of the combined gas chromatography-isotope ratio mass spectrometer systems (GCIRMS) over the past 10–20 years, has played an important role in the increased number of applications where stable isotopes have to be used to investigate problems in both of these areas.

Bitumens collected in the east zone of the Cigar Lake deposit have been analyzed by 13C nuclear magnetic resonance, pyrolysis – gas chromatography, Rock-Eval, and C. H, and O methods. Carbon and hydrogen isotopic compositions and uranium contents have been determined. Results indicate that the bitumens consist mainly of aromatic structures (Fa ≈ 60%) and have undergone a late oxidation process. Similarities in carbon isotopic composition (−27.5‰ > δ13C > −28.2‰) between barren bitumens (U 13C-enriched bitumens could have formed directly by hydrogenation of amorphous carbon, whereas mineralized, isotopically light bitumens from Cluff Lake (δ13C ≈ 48‰) may result from the polymerization of light hydrocarbons around uraninite grains.

We evaluated the ability of the native microbiota in a low-temperature, sulfidic natural hydrocarbon seep (Zodletone) to metabolize short-chain hydrocarbons. n-Propane and n-pentane were metabolized under sulfate-reducing conditions in initial enrichments and in sediment-free subcultures. Carbon isotope analysis of residual propane in active enrichments showed that propane became enriched in (13)C by 6.7 (+/-2.0) per thousand, indicating a biological mechanism for propane loss. The detection of n-propylsuccinic and isopropylsuccinic acids in active propane-degrading enrichments provided evidence for anaerobic biodegradation via a fumarate addition pathway. A eubacterial 16S rRNA gene survey of sediment-free enrichments showed that the majority of the sequenced clones were phylogenetically affiliated within the Deltaproteobacteria. Such sequences were most closely affiliated with clones retrieved from hydrocarbon-impacted marine ecosystems, volatile fatty acid metabolizers, hydrogen users, and with a novel Deltaproteobacterial lineage. Other cloned sequences were affiliated with the Firmicutes and Chloroflexi phyla. The sequenced clones were only distantly (95%) related to other reported low-molecular-weight alkane-degrading sulfate-reducing populations. This work documents the potential for anaerobic short-chain n-alkane metabolism for the first time in a terrestrial environment, provides evidence for a fumarate addition mechanism for n-propane activation under these conditions, and reveals microbial community members present in such enrichments.

Isotope fractionation has been used with increasing frequency as a tool to quantify degradation of chlorinated aliphatic pollutants in the environment. The objective of this research was to determine if the electron donor present in enrichment cultures prepared from uncontaminated sediments influenced the extent of isotope fractionation of tetrachloroethylene (PCE), either directly, or through its influence on microbial community composition. Two PCE-degrading enrichment cultures were prepared from Duck Pond (DP) sediment and were incubated with formate (DPF) or H(2) (DPH) as electron donor. DPF and DPH were significantly different in both product distribution and extent of isotope fractionation. Chemical and isotope analyses indicated that electron donors did not directly affect the product distribution or the extent of isotope fractionation for PCE reductive dechlorination. Instead, restriction fragment length polymorphism (RFLP) and sequence analysis of the 16S rRNA clone libraries of DPF and DPH identified distinct microbial communities in each enrichment culture, suggesting that differences in microbial communities were responsible for distinct product distributions and isotope fractionation between the two cultures. A dominant species identified only in DPH was closely related to known dehalogenating species (Sulfurospirillum multivorans and Sulfurospirillum halorespirans) and may be responsible for PCE degradation in DPH. Our study suggests that different dechlorinators exist at the same site and can be preferentially stimulated by different electron donors, especially over the long-term (i.e., years), typical of in-situ ground water remediation.

The development of tandem mass spectrometry (MS-MS) and its combination with gas chromatography (GC-MS-MS) has greatly enhanced our ability to analyze exceedingly complex mixtures from a wide variety of sources, including fossil fuels. This paper describes a comparison of the conventional electron impact (El) mass spectral fragmentation patterns, obtained in the MS-MS precursor – product mode, of three oleanane isomers and one ursene, all of which are used as indicators of higher plant input to the sedimentary environment Results show that El and collision-activated dissociation (CAD) spectra are most similar at collision energies between −15 and −20 eV.The presence of methyl substituents in these pentacyclic terpenes plays an important role in the process of ring fragmentation: the daughter spectra of the M – 15 fragments can be used to obtain structural information, such as the positions of the double bonds.

Reductive dechlorination of tetrachloroethylene (PCE) and trichloroethylene (TCE) was studied in well-defined microcosms prepared with aquifer materials from three locations. Electron donors and terminal electron acceptors were added to both stimulate microbial activity and generate reactive minerals via microbial iron and sulfate reduction. The relative importance of abiotic and microbial PCE and TCE reductive dechlorination was then assessed by analysis of reaction products and kinetics and, in some cases, by stable carbon isotope fractionation. The predominant PCE and TCE transformation pathway in most microcosms was microbial reductive dechlorination. Rates of abiotic transformation were similar in magnitude to those for microbial reductive dechlorination in only a few cases where the activity of dechlorinating bacteria was low. Comparison of geochemical conditions with abiotic product recoveries showed thatthe greatest extent of abiotic reductive dechlorination occurred under iron- and sulfate-reducing conditions. Under these two geochemical conditions, high concentrations of Fe(II) and S(-II) solid species were present, suggesting the involvement of Fe(II) and S(-II) minerals in abiotic reductive dechlorination. Both abiotic and microbial dechlorination of PCE and TCE took place under almost all microcosm conditions; the relative rates of the two processes under field conditions will depend on factors such as the abundance of dechlorinating bacteria, soil properties, and the mass loading of reactive minerals.

Twelve oils from the Sirikit field of the Phisanulok Basin, Thailand, have been examined to determine the nature of their source materials, depositional environment, relative maturity and extent of biodegradation. The geochemical analyses performed in this study suggested that all of the oils were derived from similar types of organic source matter consisting of a mixture of bacterial, algal and higher plant material. The sterane contents of the oils were relatively low and conventional maturity parameters based on sterane ratios suggested the oils were relatively immature. Extensive strike/slip faults in the Phisanulok Basin may have led to rapid burial of the sediments during deposition preventing these ratios from having attained their equilibrium ratios.

The formation of melanoidins from d -lysine in the presence of H 2 S and N 2 was examined to clarify the effect of H 2 S on the condensation of sugars and amino acids. Significant amounts of dark brown-colored precipitates formed in a mixture of glucose and lysine heated at 80°C for 20 days under N 2 . However, the same solution heated at 80°C for 30 days under H 2 S showed no major change apart from a slight change in color to light brown. This observation indicates that the condensation of glucose and lysine proceeds very slowly in the presence of H 2 S compared to their condensation in the presence of N 2 . Instead, significant amounts of organosulphur compounds formed from the glucose-lysine solution and H 2 S as confirmed by py-GC (pyrolysis gas chromatography) using both FID (flame ionization detector) and FPD (flame photometric detector). The rapid reaction of H 2 S with reactive carbonyl groups of reducing sugars is proposed to hinder the progess of the condensation between reducing sugars and amino acids. The incorporation of sulphur from H 2 S into sedimentary organic matter in the very early stage of diagenesis could be one of important controlling factors governing the formation of melanoidin-like geopolymers in Recent sediments. The organic geochemical characteristics of kerogens in carbonate rocks (relatively low abundance and high organic sulphur contents) could be interpreted by the rapid reaction between H 2 S and reducing sugars in the very early stage of diagenesis.

Organonitrogen compounds are present in varying concentrations in aromatic fractions of various organic-rich geologic samples. Quinolines, benzoquinolines and carbazoles are the most important families of organonitrogen compounds in the aromatic fractions of crude oils and Phosphoria Formation pyrolysates. Aromatic fractions of oils generated from phosphatic shales contain higher concentrations of organonitrogen compounds than those from carbonate source rocks. Artificial maturation experiments on Phosphoria rocks at about 300°C yield high concentrations of quinolines relative to benzoquinolines and carbazoles, while higher temperature experiments yield high concentrations of benzoquinolines and carbazoles relative to quinolines. Organonitrogen compounds are potentially useful as indicators of the depositional environment of source rocks and maturity of crude oils.

The Tertiary Thrace Basin located in NW Turkey comprises 9 km of clastic-sedimentary column ranging in age from Early Eocene to Recent in age. Fifteen natural gas and 10 associated condensate samples collected from the 11 different gas fields along the NW-SE extending zone of the northern portion of the basin were evaluated on the basis of their chemical and individual C isotopic compositions. For the purpose of the study, the genesis of CH 4, thermogenic C2+ gases, and associated condensates were evaluated separately. Methane appears to have 3 origins: Group-1 CH4 is bacteriogenic (Calculated ?13CC1-C = -61.48‰; Silivri Field) and found in Oligocene reservoirs and mixed with the thermogenic Group-2 CH4. They probably formed in the Upper Oligocene coal and shales deposited in a marshy-swamp environment of fluvio-deltaic settings. Group-2 (?13CC1-C = -35.80‰; Hamitabat Field) and Group-3 (?13C 1-C = -49.10‰; Degirmenköy Field) methanes are thermogenic and share the same origin with the Group-2 and Group-3 C 2+ gases. The Group-2 C2+ gases include 63% of the gas fields. They are produced from both Eocene (overwhelmingly) and Oligocene reservoirs. These gases were almost certainly generated from isotopically heavy terrestrial kerogen (?13C = -21‰) present in the Eocene deltaic Hamitabat shales. The Group-3 C2+ gases, produced from one field, were generated from isotopically light marine kerogen (?13C = -29‰). Lower Oligoce ne Mezardere shales deposited in pro-deltaic settings are believed to be the source of these gases. The bulk and individual n-alkane isotopic relationships between the rock extracts, gases, condensates and oils from the basin differentiated two Groups of condensates, which can be genetically linked to the Group-2 and -3 thermogenic C2+ gases. However, it is crucial to note that condensates do not necessarily correlate to their associated gases. Maturity assessments on the Group-1 and -2 thermogenic gases based on their estimated initial kerogen isotope values (?13C = -21‰; -29‰) and on the biomarkers present in the associated condensates reveal that all the hydrocarbons including gases, condensates and oils are the products of primary cracking at the early mature st age (Req = 0.55-0.81%). It is demonstrated that the open-system source conditions required for such an early-mature hydrocarbon expulsion exist and are supported by fault systems of the basin. © 2005 Elsevier Ltd. All rights reserved.

The topic of thermal analytical methods in organic geochemistry covers many methods ranging from bulk characterization of organic matter in terms of total organic carbon content (TOC) and weight loss through thermal gravimetric analysis (TGA) to sophisticated fingerprinting of organic matter using microscale pyrolysis techniques combined with analytical techniques such as gas chromatography (GC), gas chro-matography-mass spectrometry (GCMS) and more recently gas chromatography-isotope ratio mass spectrometry (GCIRMS). In general, the methods can be divided into those which either involve degradation of organic matter or thermal desorption of extractable organic matter from various types of matrices. Organic geochemistry itself covers a broad spectrum of disciplines including environmental and forensic geochemistry (see for example Kaplan et al., 1997; Murphy and Morrison, 2001) as well as the more traditional topics of petroleum geochemistry (Hunt, 1996), fate of organic matter (Engel and Macko, 1992), or origin of life type studies (Calvin, 1964). The main idea behind this chapter will be to discuss and review the techniques associated with the thermal analytical methods, and examples of applications will be given wherever it might be deemed appropriate. For each technique a brief overview will be given along with a few key references and examples of applications. It is not proposed that this chapter be an exhaustive review of the all the pyrolysis work of the past few decades.

Petroleum geochemistry has played an important role in many areas of exploration and production for fossil fuels. Many of the more recent developments can be seen to have developed in parallel with developments in analytical chemistry such as gas chromatography and gas chromatography−mass spectrometry. For the past two decades such analytical techniques have been used to search for trace amounts of compounds known as biomarkers present in oils and source rock extracts which can be used to provide valuable information on the origin and history of the oil. In the past two or three years much more effort has been placed on the development and utilization of such techniques as an aid to solving reservoir and production problems. In this paper it is proposed to provide an overview of major developments that have occurred in a number of areas of geochemistry in recent years. This will include developments in reservoir geochemistry such as the use of high-resolution gas chromatography for reservoir continuity st...

Biomarkers are compounds, generally hydrocarbons, present in crude oils and source rocks whose carbon skeletons can be readily related to a precursor molecule occurring in the original source material. The use of biomarkers in source rock extracts and crude oils for the purpose of determining source materials, thermal maturity, extent of biodegradation and migration and for making oil/oil and oil/source rock correlation studies has been well documented. One of the major problems with this approach is the possibility of contamination either naturally, through crude oil migration, or artificially during sample collection or work-up procedures. A solution to this potential problem can be found in the use of biomarkers produced by kerogen pyrolysis. The actual isolation of the kerogen eliminates any potential contaminants and pyrolysis of the kerogen produces indigenous biomarkers. In this paper it is intended to review progress that has been made in the study of biomarkers produced by kerogen pyrolysis. The various techniques that have been used in this approach will be discussed and examples given to show, in particular, the distributions of triterpanes and steranes produced by kerogen pyrolysis. In addition, results obtained from a combination of hydrous pyrolysis to artificially mature kerogens, and anhydrous pyrolysis to characterize the artificially matured kerogens, will be discussed. Certain biomarkers such as the C 28 -bisnorhopane and gammacerane are not produced during anhydrous pyrolysis and possible reasons for these observations will be discussed. Finally, the production of sulphur-containing compounds during pyrolysis reactions will be briefly discussed with reference to their role as possible indicators of maturity and depositional environments.

The classic organic chemical studies by the German chemist Alfred Treibs on the structures of tetrapyrrole-type compounds in crude oils led him to propose a biological origin for crude oils (Treibs 1934, 1 936). Treibs based his proposal on structural determinations, made by classical chemical methods, of porphyrins (I) in the oils and their structural relationship with chlorophyll (II) molecules (known to be widely distributed in plants) and compounds with similar structures in animals and bacteria. These obser­ vations can be thought of as the beginning of the biomarker concept and precursor/product relationships. Although the idea was initially proposed in the 1 930s, it was not widely exploited until major analytical advances occurred in the 1 960s and 1 970s. In this time period major breakthroughs were made in the coupling of gas chromatographs and mass spectrometer systems and the development of capillary gas chromatography columns.

The average stable carbon isotope ratio of 21 oils from the Taranaki Basin of New Zealand suggests that the source rocks date from the Cretaceous period, when sedimentation in this basin began. Stable carbon isotope ratios also confirm the grouping of these oils into the genetic families which were previously suggested by the correlation of source-related biomarkers. Stahl isotope type-curves for the oils also reflect the correctness of these relationships. A plot of the saturate versus aromatic δ13C values for the New Zealand oils is particularly valuable for oil correlation in this basin and clearly demonstrates that the Ahuroa and Stratford oils, while separated from the McKee field by some 30 km, probably originate from the same oil-source formation as do the oils of the McKee field. The plot also indicates, that the Kaimiro, Mangahewa, Pukearuhe and Waihapa oils are discrete in situ accumulations of petroleum which do not have the characteristics of oils from adjacent fields. These conclusions are further supported by the values of the Sofer canonical variable for all of the oils. Additionally, the Sofer plot provides clear evidence of the predominantly terrigenous origin of the oils in the Taranaki basin. Consideration of the data for these oils, leads to a hypothesis that three independent sources of organic material, microbes, gymnosperms and angiosperms, gave rise to the oils in this region.

The study of natural products in plants, animals, bacteria, fungi, and other living systems has long been of interest to chemists, biochemists, and analytical chemists. Generally, however, these scientists are concerned only with the isolation and identification of compounds present in living systems. A relatively small but rapidly growing scientific discipline has emerged over the past two decades involving scientists primarily interested in the fate of organic material and associated natural products after their demise and deposition in the sedimentary record and conversion into fossil fuels or chemical fossils. Organic compounds present in the original source material whose carbon skeleton is preserved throughout the geological record are referred to as biomarkers. In this Report the authors will introduce some of the basic concepts of petroleum geochemistry and the key role that analytical chemistry has played in the development of this discipline. They will also discuss areas in which geochemical research is most likely to develop in the next few years, and they will examine the major analytical challenges the organic geochemist will meet in conducting geochemical research during the next decade.

The bi-, tri- and tetracyclic terpenoids in crude oils from the Taranaki basin of New Zealand have been studied. The distribution of C14, C15 and C16 bicyclanes was essentially invariant amongst the various fields. A suggestion is made that the proportion of rearranged to total drimanes may be related to maturity and the ratio of homodrimane to drimane may be related to depositional environment. Mass spectra are reported for a number of unidentified sesquiterpanes, including possibly norbisabolane and bisabolane. The distribution of bi-, tri- and tetracyclic diterpanes was very similar to that of crude oils from the Gippsland basin of south-east Australia. The occurrence of rimuane was confirmed, 8α(H)-labdane was identified and 4α(H)-18-norisopimarane was tentatively identified. Isopimarane dominated the diterpane distribution of oils from the Maui field in the south-west of the basin and its abundance gradually diminished in a north-westerly direction until it became a minor component of oil from the New Plymouth field. This trend coincided with an increase in the complexity of the triterpane distribution and with the oleanane content of the oils. These northwards trends also followed the evolution of coal deposits in the region. The diterpanes in these oils had the same structure as those which occur in extant trees of the Araucariaceae and Podocarpaceae which flourish in New Zealand today and did so even more extensively in the past. Coal measures, formed from forests of such trees, are probably the source of the diterpanes, a situation analogous to that in the Gippsland basin of south-eastern Australia. Tricyclanes of the cheilanthane series were not detected in any of the Taranaki oils, lending support to the view that these tricyclanes occur most abundantly in oils derived from marine sources. C24-Tetracyclanes (secotriterpanes) occurred abundantly in all the oils as they do in terrigenous oils from other parts of the world.

In the past decade, environmental forensics has emerged as a discipline directed toward determining parties liable for causing spills of contaminants into the environment. Such investigations, while geared toward determining the guilty parties in order to recover costs of the cleanup and remediation, require various questions to be addressed. These include determination of the nature of the product; Where did it come from?; Extent of weathering, if any; How long has it been there?; and Is it degrading naturally? Traditionally, these studies have been addressed through utilization of techniques such as gas chromatography (GC) and gas chromatography–mass spectrometry (GCMS). However, in recent years, stable isotopes, primarily determined through the use of combined gas chromatography–isotope ratio mass spectrometry (GCIRMS), have emerged as an equally important tool in environmental forensics. For relatively low molecular, volatile compounds such as MTBE, BTEX, or chlorinated solvents, the isotopes, primarily carbon and hydrogen, have been used extensively for evaluating the onset of natural attenuation. For larger molecules such as PCBs or PAHs, in which the effects of biodegradation on the isotope composition of these molecules is minimal, the isotopic fingerprints of the individual compounds can be used for correlation purposes. In this paper, a brief introduction to isotope geochemistry will be given, followed by a review of applications of stable isotopes to a variety of environmental problems. While the review may not necessarily be exhaustive, it will provide a comprehensive overview of areas where isotopes have been used and potential applications for the future. Most of the review is concerned with carbon and hydrogen isotopes, although a brief overview of the emerging area of chlorine isotopes will also be discussed.