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A comprehensive regional organic geochemical study was performed on outcrop and core samples from the Eagle Ford Group with the aim of determining variations in organic matter source, thermal maturity, and depositional environments. Total organic carbon (TOC) and Rock-Eval pyrolysis parameters show that the Eagle Ford Group has excellent hydrocarbon source rock potential and is dominated by type II kerogen. Distributions of regular steranes, hopanes, and monoaromatic steroids confirm a marine carbonate depositional environment. Aryl isoprenoid ratios suggest the occurrence of intermittent photic zone anoxia. The n-alkane and sterane distributions and the presence of pregnanes, homopregnanes, and gammacerane suggest deposition under hypersaline conditions particularly in west and east Texas. In east Texas, biomarkers indicate that the Eagle Ford Group was partially sourced from terrigenous organic matter and deposited under oxic–suboxic conditions. Thermal maturity parameters including the temperature at which the peak corresponding to the compounds produced from the thermal degradation of kerogen in the Rock-Eval chromatogram maximizes (Tmax), vitrinite reflectance, and biomarker ratios indicate that in west and central Texas, the Eagle Ford Group is immature to marginally mature; in southwest Texas it is in the oil to dry gas window; and in east Texas, the Eagle Ford is in the main stage of oil generation. Geochemical logs of biomarker ratios show that the Lower Eagle Ford Formation has the highest TOC and hydrogen index, particularly in the Lozier Canyon Member; experienced stronger anoxic conditions during deposition; and has lower clay content compared with the Upper Eagle Ford Formation. Geochemical parameters show that the latter may have received an additional siliciclastic and terrigenous organic matter input under oxic–dysoxic conditions. Isotope data indicate a marine organic matter source for the Eagle Ford Group, but surprisingly, δ13C values do not show significant organic facies, depositional environment, or thermal maturity variations.

Understanding the environmental features and processes responsible for the formation of organic-rich, laterally extensive source rocks of appreciable thickness, such as the Late Devonian–Early Mississippian Woodford Shale, is necessary to refine current depositional models. In this study, a detailed assessment of the paleowater column was undertaken via examination of molecular fossil (biomarker) data. Specifically, C40 aromatic carotenoids were used to delineate the nature and severity of photic-zone euxinia concomitant with the deposition of the lower, middle, and upper Woodford. The immature character of the Woodford in the study area ensured that biomarker interpretations were reflective of the depositional environment and not altered by secondary processes. Twenty-nine Woodford Shale samples from the Lawrence uplift of the western Arkoma Basin were subjected to bulk and molecular geochemical analyses, with the objective to enhance the understanding of the paleowater column. A suite of C40 aromatic carotenoids—paleorenieratane, isorenieratane, renieratane, and renierapurpurane—was identified for the first time in the Woodford Shale. Paleorenieratane, the predominant C40 aromatic carotenoid, was found to be isotopically enriched (δ13C e −12‰ ± 1.5‰). This was interpreted as a product of carbon fixation via the reverse tricarboxylic acid cycle, a diagnostic trait of Chlorobiaceae. Additional biomarker parameters sensitive to changes in redox assisted in substantiating interpretations of Chlorobiaceae derivatives, with the severity of photic-zone euxinia inferred by the effects that this environmental state imposed on the overlying microbial community and algal populations. Previously unrecognized inter- and intramember variations in water-column structure and redox state were documented. The lower Woodford was characterized by isolated pulses of photic-zone euxinia, with the middle Woodford deposited during persistent photic-zone euxinia, as evinced by elevated concentrations of the C40 aromatic carotenoids. A deep, persistent chemocline likely typified upper Woodford deposition, but lack of sampling intensity in this member may belie a more episodic nature. Effects of photic-zone euxinia appeared to be most severe in the middle Woodford, where progressively increasing C40 aromatic-carotenoid concentrations coincide with rising gammacerane indices and a systematic decrease in sterane/hopane values. Environmental conditions (e.g., oxygen minimum zone, restriction) that facilitate the development of euxinia in the photic zone were interpreted to reconstruct the paleoenvironment on a local to subregional scale.

The Central Sumatra Basin (CSB), formed during the Late Eocene (?) to Early Oligocene, is the most prolific hydrocarbon basin in Indonesia. The Brown Shale Formation of the Pematang Group is the sole known source rock for the tens of billions of barrels of oil located in the CSB. Samples analyzed in this study were from the Karbindo coal mine in the Kiliran graben of the Kiliran sub-basin, located on the western side of the CSB. This study incorporates advanced organic geochemical and petrographical data of samples from the Brown Shale Formation, as well as interpretations from previous studies at this location, to construct a detailed paleoenvironment model for this Tertiary lake. The lacustrine source rock was deposited under fresh water conditions, with subtle changes in the environment that resulted in significant changes in ecologies. Based on new data from organic petrography, biomarkers, microscale sealed vessel pyrolysis, and characterization of the polyaromatic hydrocarbons, the organic matter in the Brown Shale Formation was determined to be sourced primarily from lacustrine organisms with a small amount of terrestrial plant input. 4-Methylsterane concentrations and n -alkane distributions indicate that non-marine dinoflagellates and Botryococcus braunii (A race) were likely a significant portion of the local biosphere.

It has been estimated that technically recoverable reserves from shales in the continental U.S. are believed to be approximately 24 billion barrels of oil (BBO) and 750 trillion cubic feet (Tcf) of gas. In Oklahoma the most important hydrocarbon source rock is the Woodford Shale, proposed to be the source of some 70% of the state's liquid hydrocarbon reserves. Such a regionally widespread source rock provides potential for both academic study and industrial opportunities. In this study representative samples of the Woodford Shale from the McAlister Quarry outcrop have been characterized by a variety of geochemical techniques. TOC values range from 0.07 to 15.6 wt% and, based on Rock-Eval Pyrolysis, most of the samples plot within the Type I/II kerogen range, with several low TOC samples plotting in the Type III kerogen range. TOC and biomarker parameters, suggests that two sections of the Upper Woodford are immature paleosols, having been subaerially exposed due to abrupt episodes of sea level fall during the Late Devonian. Evidence for these zones of paleoweathering includes highly depleted TOC, increased oxygen index (OI) values, loss of n-alkanes, decreases in the aryl isoprenoid ratio (AIR), sesquiterpenoids, cheilanthanes, hopanoids, and decreases in many of the polycyclic aromatic hydrocarbons (PAHs). The values of several paleoenvironmental proxies for samples immediately following the Frasnian-Famennian (F–F) Stage extinction boundary within the Upper Woodford suggests that a large influx of weathered terrigenous material occurred at that time. The presence of pyrogenic compounds implies that paleowildfires were widespread throughout the Middle and Late Devonian in the North American midcontinent. It is possible that these influxes of weathered terrestrial organic material stimulated algal blooms that led to the anoxic water column conditions often attributed to the F–F Stage extinction event. Investigation of the stratigraphic framework of these source rocks assists in evaluating their potential as hydrocarbon producers and/or unconventional reservoirs. Integration of geochemical data adds another powerful dimension to this approach. It has been proposed that the Woodford Shale was deposited during a 2nd order depositional sequence. The lower member represented the transgressive systems tract (TST), the Upper member the highstand systems tract (HST), and the Middle member bridging the transition between the two. Numerous 3rd order parasequences were also identified as being part of the overall 2nd order sequence and could be correlated to the Devonian sea level curve. The major objectives of the study were: While this study focuses locally on the McAlister Quarry samples, it is also of regional importance. The Woodford is a prolific source rock throughout the Anadarko Basin and has been the subject of extensive exploration and production efforts, particularly in the past decade with the development of horizontal drilling and hydrofracturing techniques. Continued investigation of the heterogeneity of the shale will greatly enhance the ability to predict more productive facies within the formation throughout the basin.

1,2-Dibromethane (EDB) is a toxic fuel additive that likely occurs at many sites where leaded fuels have impacted groundwater. This study quantified carbon (C) isotope fractionation of EDB associated with anaerobic and aerobic biodegradation, abiotic degradation by iron sulfides, and abiotic hydrolysis. These processes likely contribute to EDB degradation in source zones (biodegradation) and in more dilute plumes (hydrolysis). Mixed anaerobic cultures containing dehalogenating organisms (e.g., Dehaloccoides spp.) were examined, as were aerobic cultures that degrade EDB cometabolically. Bulk C isotope enrichment factors (ebulk) associated with biological degradation covered a large range, with mixed anaerobic cultures fractionating more (ebulk from −8 to −20‰) than aerobic cultures (ebulk from −3 to −6‰). ebulk magnitudes associated with the abiotic processes (dihaloelimination by FeS/FeS2 and hydrolysis) were large but fairly well constrained (ebulk from −19 to −29‰). As expected, oxidative mechanisms fra...

Molecular and isotopic compositions of 51 gas and 7 condensate samples produced from the Barnett Shale were determined by gas chromatography–isotope ratio mass spectrometry to investigate their origin and maturity at the time of generation. Additionally, two hydrous pyrolysis experiments were performed to calibrate maturity values predicted for gas generation. Molecular and carbon and hydrogen isotopic compositions of the gases indicate that gas produced from the Barnett is thermogenic. To estimate generation maturity, additional analyses were performed on the condensates and available core samples. Diamondoid indices combined with vitrinite reflectance (Ro) measurements, isotopic and molecular composition, and hydrous pyrolysis experiments suggest that gas produced from the Barnett Shale was generated within the condensate–wet gas window (1.3–2.0% Ro) at a later stage than hydrocarbons accumulated in shallower reservoirs. The origin of the gas is thermogenic, probably derived from both kerogen cracking and secondary cracking of previously generated nonmigrated hydrocarbons. Additionally, the occurrence of a methane isotope reversal in group 1 gases corroborates that in-situ oil or gas cracking is occurring in the easternmost part of the study area.

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 (

Representative samples of crude oils from Cusiana, Cupiagua, Apiay, Castilla and Chichimene fields in the Eastern Llanos Basin of Colombia were analyzed to determine its compound-specific stable carbon isotope composition (CSIA) using gas chromatography–isotopic ratio–mass spectrometry (GC–IRMS). GC–IRMS analyses of n-alkanes allowed differentiating between Cretaceous and Cretaceous/Tertiary oil samples. Cretaceous sourced samples have δ13C-enriched values than Cretaceous/Tertiary sourced samples; the heavier isotope composition of these samples is due to their major terrigenous organic matter input. Their isotope distribution patterns suggest significant algal and/or bacterial contribution (marine origin). The analysis of the n-alkane fractions by GC–IRMS confirms that the organic matter has marine origin in those samples from Cusiana, Cupiagua and Apiay while Castilla and Chichimene have marine origin with terrestrial inputs. The results were confirmed by gas chromatography/FID and gas chromatography/mass spectrometry (GC/MS). Basic geochemical composition show that samples from Cupiagua/Cusiana fields and Apiay/Castilla/Chichimene fields in the Llanos basin, Colombia present different characteristics reflecting a specific for each depositional environment.

Significant carbon isotope fractionation was observed during FeS-mediated reductive dechlorination of tetrachloroethylene (PCE) and trichloroethylene (TCE). Bulk enrichment factors (E(bulk)) for PCE were -30.2 +/- 4.3 per thousand (pH 7), -29.54 +/- 0.83 per thousand (pH 8), and -24.6 +/- 1.1 per thousand (pH 9). For TCE, E(bulk) values were -33.4 +/- 1.5 per thousand (pH 8) and -27.9 +/- 1.3 per thousand (pH 9). A smaller magnitude of carbon isotope fractionation resulted from microbial reductive dechlorination by two isolated pure cultures (Desulfuromonas michiganensis strain BB1 (BB1) and Sulfurospirillum multivorans (Sm)) and a bacterial consortium (BioDechlor INOCULUM (BDI)). The E(bulk) values for biological PCE microbial dechlorination were -1.39 +/- 0.21 per thousand (BB1), -1.33 +/- 0.13 per thousand (Sm), and -7.12 +/- 0.72 per thousand (BDI), while those for TCE were -4.07 +/- 0.48 per thousand (BB1), -12.8 +/- 1.6 per thousand (Sm), and -15.27 +/- 0.79 per thousand (BDI). Reactions were investigated by calculation of the apparent kinetic isotope effect for carbon (AKIEc), and the results suggest that differences in isotope fractionation for abiotic and microbial dechlorination resulted from the differences in rate-limiting steps during the dechlorination reaction. Measurement of more negative E(bulk) values at sites contaminated with PCE and TCE may suggest the occurrence of abiotic reductive dechlorination by FeS.

Stable carbon isotopes have been used in various applications for approximately 50 years, in many applications including the fields of medicine, criminology, and biology and recently has been used in the remediation field to track the degradation of various organic compounds. It is a commercially available investigation technology that is gaining in popularity and has unique applications related to monitored natural attenuation (MNA). To further discuss this technology and how it is used at MNA sites, we presented the following question to five guest panel members. © 2007 Wiley Periodicals, Inc.

Environmental forensics has emerged as an important area of environmental studies over the past two decades. One of the major areas of interest in environmental forensic investigations is to determine the origin or point of release of a spilled product. A wide variety of analytics are used to fingerprint the contaminant and potential sources in order to determine whether or not there is any relationship between them. If there are multiple possible sources in the area it may be difficult to narrow it down to a specific source. Furthermore, fingerprinting tools that may be useful with complex mixtures may not be directly applicable to single-component mixtures. In situations such as this, utilization of stable isotopes of the individual compounds becomes a particularly powerful tool for undertaking the correlations. The purpose of this chapter will be to provide a review along with some recent examples of the nature of the stable isotope information that is typically obtained in environmental forensic investigations and how this information may be interpreted. Examples will involve hydrocarbons, chlorinated solvents, and MTBE and BTEX compounds. Techniques will include gas chromatography (GC), gas chromatography–mass spectrometry (GCMS), stable isotopes—both bulk and gas—and chromatography–isotope ratio mass spectrometry (GCIRMS).

N-alkanes in extracts from possible carbonate source rocks of the Lower Ordovician Majiagou Formation in the central gas field of the Shanganning Basin and the Upper Sinian Dengying Formation in the Weiyuan gas field of the Sichuan Basin, are characterized by bimodal distributions with the dominant carbon numbers in the range C17-C21 and C25-C29. In most samples, the lower carbon number components are present in greater abundance than the higher carbon number ones. Most samples contain significant concentrations of waxy hydrocarbons (C22+) with C21-/C22+ ratios between 0.50 to 3. 16, and an average value of 1. 34. The n-alkanes in extracts of outcrops and shallow core samples of Upper Proterozoic and Lower Palaeozoic carbonate rocks in the western and southern parts of the North China Basin are of unimodal distributions dominated by n-alkanes maximizing in the C25-C29 range. These extracts have very high concentrations of waxy hydrocarbons with C21-/C22+ ratios all < 1. 0, ranging from 0. 14 to 0. 90 and averaging 0. 36. All of the extracts have a marked odd/even predominance in the high molecular weight n-alkane range regardless of whether they are from shallow or deep cores or out-crop samples. Simulation experiments were performed using typical sapropelic-type kerogens from the immature Sinian Lower Xiamalin Formation carbonate-rich shales collected at Jixian, Hebei Province, North China Basin, and the contemporary microplanktonic blue-green algaeSpirulina subsala. Results indicate that the unusual distribution of n-alkanes in the extracts of Upper Proterozoic and Lower Palaeozoic carbonate rocks possibly originated from algae in the source rocks at high levels of maturity and overmaturity.

Petroleum geochemistry is the outgrowth of the application of the principles and methods of organic chemistry to petroleum refining and petroleum geology. This paper reviews 120 years of petroleum geochemistry, from about 1860 to 1980, and includes a discussion of the formal recognition of petroleum geochemistry as an earth-science discipline starting in 1959 when a general petroleum geochemistry symposium was first organized at Fordham University, New York. A chronology of significant events, including concepts, techniques, and textbook publications, is presented. Because petroleum geochemistry has been a tool for petroleum exploration from the beginning, the early developments of surface prospecting, source-rock identification, and oil/oil and oil/source correlation are discussed, along with the application of geochemistry to petroleum migration, accumulation, and alteration. In addition the paper deals with the biomarker revolution, which began in earnest about 1964, and with early models of geothermal history. Concepts in petroleum geochemistry have continually evolved, enhanced by the development of new analytical techniques, leading to new discoveries concerning the origin and occurrence of petroleum.

A large number of underground gasoline storage facilities in the United States continuously leak gasoline into the subsurface, which makes gasoline a major groundwater contaminant. Gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) are used currently to characterize contaminated groundwater and soils. Correlations of contaminants with suspected source(s) are extremely difficult by these techniques because many gasolines have similar hydrocarbon distributions. The present study applied the technique of isotope ratio monitoring gas chromatography–mass spectrometry (irmGC–MS) to 19 gasoline samples from different areas of the USA. This allows a much better correlation of gasoline contaminants to source. Data obtained indicate a wide range of δ 13 C values for 16 ubiquitous compounds in the gasolines The majority of samples could be distinguished from each other on the basis of δ 13 C hydrocarbon composition. The oxygenated additive methyl tertiary butyl ether (MTBE) was present in ten of the gasolines analyzed, and had a relatively narrow range of δ 13 C values (−30.4 to −28.3‰). Preliminary investigations were also made to determine the extent of carbon isotopic fractionation after simple water washing and evaporation experiments. Results indicate that the majority of compounds did not undergo significant carbon isotopic fractionation as a result of these processes.

Correlation of crude oils, or refined products, in the environment with suspected sources is typically undertaken through the use of GC and GCMS and in certain cases bulk carbon isotope compositions. However, with crude condensates, or refined products in particular, the absence, or low concentration, of biomarkers precludes their successful use for making unique correlations. An alternative and, sometimes, complimentary technique for correlation of such products is evolving through the use of combined gas chromatography-isotope ratio mass spectrometry (GCIRMS). This approach permits determination of the carbon and hydrogen isotopic composition of individual compounds in the crude oil or refined product to produce isotopic fingerprints for use in correlation studies. In this paper, it is proposed to review applications of GCIRMS to the correlation of various spilled products with their suspected sources in different environments. Whilst not proposing that this technique will replace GC or GCMS; it is prop...

The recent controversy over the use of MTBE within gasoline to boost oxygen content and decrease carbon monoxide emissions to the atmosphere has led to a proposed phase-out of this compound by 2002. This paper is a preliminary investigation into the use of gas chromatography isotope-ratio mass spectrometry (GCIRMS) to determine both carbon and hydrogen isotopic compositions of MTBE as a means of differentiating sources of MTBE. Three pure MTBE samples were purchased from chemical distributors. Little variation of the δ 13 C values were observed although the samples had isotopically distinct δ-D values. Four different methods of obtaining carbon isotope ratios of neat MTBE, MTBE in gasoline, and MTBE in water are described, and the precision and accuracy of each is discussed. The carbon isotopic compositions of MTBE within 10 gasoline samples from three different areas of the United States show a wide range of carbon isotope compositions. This novel method of MTBE analysis could be valuable in forensic investigations.

High-temperature gas chromatography (HTGC) has enhanced our ability to characterize hydrocarbons extending to C120 in crude oils. As a result, hydrocarbons in waxes (> C20) have been observed to vary significantly between crude oils, even those presumed to originate from the same source. Prior to this development, microcrystalline waxes containing hydrocarbons above C40 were not characterized on a molecular level due to the analytical limitations of conventional gas chromatography. Routine screenings of high pour-point crude oils by high-temperature gas chromatography has revealed that high molecular weight hydrocarbons (> C40) are very common in most oils and may represent 2% of the crude oil. Precise structures, origins, and significance of these high molecular weight compounds remain elusive. As a preliminary step to expand our knowledge of these compounds their general molecular structures and formulas have been investigated in this study. Initial results suggest that the major high molecular weight compounds include a homologous series of n-alkanes, methylbranched alkanes, alkylcyclopentanes, alkylcyclohexanes, alkylbenzenes and alkylcycloalkanes. # 2000 Elsevier Science Ltd. All rights reserved.

The occurrence of high molecular weight hydrocarbons in a selected solid bitumen (ozocerite) and a waxy yellow crude oil from the Uinta Basin (Utah) have been studied by field ionization-mass spectrometry (FIMS). The FIMS spectra consisted predominantly of molecular ions ranging up to near mass 2000, and correspond to several series of hydrocarbons ranging up to C110. The use of FIMS permits the range of hydrocarbons identified in geological materials to be extended far beyond that identified by the usual chromatographic techniques. Moreover, from the FIMS spectra it was possible to extract the molecular ions corresponding to series of hydrocarbons with different degree of unsaturation or ring closures (different Z-numbers). The ozocerite solid bitumen consisted mainly of series of branched alkanes (CnH2n+2) and cyclic alkanes (CnH2n and CnH2n−2) up to C110 with a predominance of monocyclic alkanes in the high molecular weight region (above C40). The waxy yellow crude oil, on the other hand, contained only acyclic compounds, mainly n-alkanes, ranging up to C100.

Results of extraction experiments performed on immature Green River Formation source rock samples from the Black Shale Facies (Uinta Basin, Utah) demonstrate the potential of extracting high molecular weight hydrocarbons (HMWHC) with sequential dichloromethane:methanol/soxhlet and p -xylene/sonication techniques. The first soxhlet extraction step with DCM:MeOH removes lower molecular weight alkanes from the source rock while the HMWHC remain in the rock residue. Sonication of the rock residue with p -xylene recovers these HMWHC, showing distinct hydrocarbon distributions and preferences in high temperature gas chromatograms. Extracts obtained by using p -xylene/soxhlet with original source rocks and sequential soxhlet extraction instead of sonication have relatively lower concentrations of HMWHC. Sequential extraction of two other source rock types (Mahogany Shale and Black Shale Facies coal) did not result in detection of similar HMWHC in the extract. This indicates that the presence of these compounds in the Black Shale Facies of the Green River Formation is a primary source signal and a specific characteristic of this source rock.

Results are presented on changes in the content and composition of waxes and asphaltenes of oil produced during the transition from primary to secondary recovery following water flooding. Oil samples have been collected for a period of about three years from one well in Prairie Gem field in central Oklahoma. Wax and asphaltene fractions have been isolated from the produced oils and analyzed, qualitatively and quantitatively, by high temperature gas chromatography. The results demonstrate significant variations in the asphaltene and wax content of the oil produced during the transition period from primary to secondary water flood recovery, ranging from 0.7 to 5 wt%, and 11 to 33 wt%, respectively. Moreover, these variations are found to be accompanied by changes in wax composition and to precede specific production events. The oil produced a month before the response of the well to water flooding indicated an enhanced concentration of nC 22 –C 35 alkanes in the wax. The following episode of wax plugging in well equipment was preceded by increased amounts of asphaltenes and high molecular weight (nC 35 –C 50 ) alkanes in the wax of produced oils. Changes in the asphaltene and wax compositions are discussed in terms of processes displacing weakly adsorbed organic material from the pore spaces of the reservoir under increased reservoir pressure and flowing fluid volumes related to water flooding.

the macromolecular structure of the pyrobitumen wurtzilite has been examined by a variety of chemical and analytical techniques, including desulfurization with lithium in ethylamine. The results of these analyses provide strong evidence for the presence of intermolecular sulfur linkages in the wurtzilite geopolymer matrix, which are thought to have formed via a process of low temperature “natural vulcanization”. The polymerized hydrocarbon components appear to be a complex mixture of n -alkanes, isoprenoids, and heterocompounds, offering further insight toward a bulk structural model for wurtzilite.

In order to investigate the formation of organosulphur compounds during the very early stage of diagenesis, experiments were designed to simulate sulphur incorporation from H2S, or elemental sulphur, into recently deposited natural sedimentary organic matter (cyanobacterial mats from salt ponds in Baja California) and performed under relatively mild reaction conditions (40°C, 2 to 30 days, hydrous and anhydrous). The sulphur-containing moieties in the reaction products were examined by pyrolysis-gas chromatography (GC) using a GC equipped with a flame photometric detector (FPD) and a flame ionization detector (FID), and pyrolysis-gas chromatography/mass spectrometry (GC/MS). Sulphur incorporation from H2S into recently deposited cyanobacterial mats occurred fairly readily, but elemental sulphur does not react as readily with the cyanobacterial mats. Sulphur incorporation into humic acids occurred more rapidly than into proto-kerogens. Sulphur incorporation into lipid fractions was not observed. Two major sulphur incorporation stages are proposed, with the formation of thiols by reaction between H2S and active carbonyl groups considered to be the most likely mechanism of sulphur incorporation in the first stage. The second stage of sulphur incorporation is proposed to be related to the reaction between H2S and proteinaceous organic matter.

Isotope ratios of volatile organic compounds (VOCs) in the environment are often of interest in contaminant fate studies. Adsorbent preconcentration-thermal desorption of VOCs can be used to collect environmental vapor samples for compound-specific isotope analysis (CSIA). While active adsorbent samplers offer logistic benefits in handling large volumes of air, their performance in preserving VOCs isotope ratios was not previously tested under sampling conditions corresponding to typical indoor air sampling conditions. In this study, the performance of selected adsorbents was tested for preconcentration of TCE (for determination of C and Cl isotope ratios), PCE (C and Cl) and benzene (C and H). The key objective of the study was to identify the adsorbent(s) permitting preconcentration of the target VOCs present in air at low μg/m3 concentrations, without significant alteration of their isotope ratios. Carboxen 1016 was found to perform well for the full range of tested parameters. Carboxen 1016 can be recommended for sampling of TCE, PCE and benzene, for CSIA, from air volumes up to 100 L. Variable extent of isotope ratio alteration was observed in the preconcentration of the target VOCs on Carbopack B and Carbopack X, resulting from partial analyte loss via adsorbent bed breakthrough and (possibly) via incomplete desorption. The results from testing the Carbopack B and Carbopack X highlight the need of adsorbent performance validation at conditions fully representative of actual sample collection conditions, and caution against extrapolation of performance data toward more challenging sampling conditions.

For the past two or three decades geochemists have been concerned with the analyses and characterization of compounds, generally hydrocarbons, ranging from C1C40. Significant amounts of information have resulted from these studies which have been extremely useful in many geochemical and environmental studies. However, in the past two or three years the commercial development and availability of high temperature gas chromatography columns has lead to the investigation of the occurrence and distribution of high molecular weight hydrocarbons (HMWHC), and other compounds, in the carbon number range C40C100, present in oils, waxes, bitumens and rock extracts. The ability to study these compounds represents a major advance in organic geochemistry. In some samples these compounds may represent the bulk of the organic components but prior to development of the high temperature columns it was impossible to study their distributions. This paper will review advances that have occurred in terms of the application of high temperature gas chromatography (HTGC) to the analyses of fossil fuel samples and discuss the possible origin and significance of these compounds that have been identified. In addition, some of the potential problems involved in the analyses of these compounds will also be discussed.

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.

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.

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.

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 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.