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Based on the systematic analyses of fifteen typical crude oils and ten typical potential source rocks collected from the Qaidam, Tarim and Turpan basins, Northwest China, the geochemical characteristics of the oils and source rocks were investigated and oil-source rock correlations undertaken. The oils and source rocks deposited in saline lacustrine environment from the western Qaidam Basin were characterized by n-alkanes with even carbon-number preference in the C-C range, low pristane/phytane (Pr/Ph) ratios (less than 0.5), and high abundances of C steranes, gammacerane and C hopanes. The oils and source rocks deposited in marine environment from the Tarim Basin were characterized by n-alkanes with even carbon-number preference in the C-C range, relatively low Pr/Ph ratios (near to 1), high abundance of C steranes, and relatively high gammacerane. In contrast, the oils and source rocks deposited in terrigenous bog environment from the Turpan Basin were characterized by relatively high Pr/Ph ratios (oil samples greater than 6) high abundance of C steranes, and relatively low gammacerane and C hopanes. The higher amounts of C and C n-alkanes of source rocks from the western Qaidam Basin and the Tarim Basin suggest an origin of these alkanes from functionalized C and C n-alkadienes and alkenones in prymnesiophytes living in lacustrine and marine environments. Oil-source rock correlations suggest oils in the western Qaidam Basin were derived from the Oligocene Lower Ganchaigou Formation (E), oils in the Tabei and Tazhong uplifts from the Tarim Basin have a genetic relationship with the Middle-Upper Ordovician source beds. Oils in the Turpan Basin generally fall into two genetic types. Most oils in the Taibei depression from the Turpan Basin were derived from the Lower-Middle Jurassic coal measures, but the fewer oils in this region are a mixed source derived from the Lower-Middle Jurassic coal measure and the Upper Permian source rocks. [ABSTRACT FROM AUTHOR]

Abstract: The Central Sumatra Basin (CSB) is a prolific oil producing basin in Indonesia where a single source rock has been identified, the Brown Shale Formation of the Paleogene Pematang Group. Despite the presence of a single source rock, the oils in the Central Sumatra Basin and particularly in the Aman Trough, exhibit variable molecular and isotopic compositions, previously described as reflective of lateral facies variations within the source rock. Analyses by gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS) and gas chromatography–isotope ratio mass spectrometry (GC–IRMS) of 15 oil samples from the Aman Trough allowed identification of vertical and lateral facies changes within the Brown Shale Formation as well as paleoproductivity and paleoclimatic changes that took place during deposition of this prolific source rock. The molecular and isotopic data indicate the source rock for these oils was deposited in a fresh to brackish water stratified lake in which CO2 limiting conditions prevailed. Compound specific isotopic data also indicate that changes in paleoclimatic conditions, possibly associated with the Eocene–Oligocene paleoclimatic transition, had an effect on the geochemical composition of the source rock in the Aman Trough. [Copyright &y& Elsevier]

The kinetics and in some cases stable carbon isotope fractionation associated with abiotic reductive dechlorination of tetrachloroethylene (PCE) and trichloroethylene (TCE) by model Fe(II)-bearing minerals present in anaerobic soils were measured. The minerals studied were chloride green rust (GR-Cl), sulfate green rust (GR-SO4), pyrite, magnetite, and adsorbed Fe(II) or FeS formed at the surface of goethite by treatment with dissolved Fe(II) or S(-II). We observed some abiotic transformation of PCE and TCE in every system studied, as evidenced by the presence of abiotic reaction products. Bulk enrichment factors (ε bulk values) for TCE transformation by GR-Cl and pyrite were −23.0±1.8‰ and −21.7±1.0‰, respectively, which are more negative than reported values for microbial TCE dechlorination and could provide one means for distinguishing microbial from abiotic dechlorination of TCE in the environment. Considering the time scale of subsurface remediation technologies, including natural attenuation, minerals such as green rusts, pyrite, and magnetite have the potential to contribute to the transformation of PCE and TCE at contaminated sites. [Copyright &y& Elsevier]

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 proposed that GCIRMS is a very powerful tool to be used in conjunction with GC and GCMS to make such correlations. Although isotopic fractionation has been observed in some of the lighter components such as benzene and toluene, higher carbon numbered compounds, say above C10, do not appear to undergo any significant isotopic fractionation as a result of weathering. Furthermore with refined products, isotopic fractionation of the lighter components has the potential to demonstrate the onset of natural attenuation of refined products in the environment. [Copyright &y& Elsevier]

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 δ13C values for 16 ubiquitous compounds in the gasolines The majority of samples could be distinguished from each other on the basis of δ13C 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 δ13C 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. [Copyright &y& Elsevier]