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Adamantane hydrocarbons have been isolated from Cenomanian heavy naphthenic oil of the Russkoe field using the thiocarbamide adduction method. Steam distillation of the oil has given a fraction (boiling range 105-150°C) containing 0.36 wt % adamantane, from which a concentrate containing 18.2 wt % C-C adamantane derivatives has been obtained. Adamantane and its derivatives in the crude oil, oil fractions, and concentrate have been identified, and adamantane has been quantified using the gas chromatography-mass spectrometry technique. [ABSTRACT FROM AUTHOR]

Transformation of organic matter (OM) in Holocene sediments of Lake Ochki (southern coast of Lake Baikal) at the early stages of diagenesis has been studied using pyrolytic methods of Rock Eval (RE-pyrolysis) and pyrolysis-gas chromatography-mass spectrometry (Pyr-GC-MS). OM has been analyzed in lacustrine sediments and their main producers, phytoplankton and zooplankton. Data on the distribution of hydrocarbon-biomarkers in sediments indicate an uninterrupted influx of terrigenous OM and transformation of OM precipitated by microorganisms. The analysis of molecular composition of pyrolysates makes it possible to assume a sharp change of sedimentation conditions in the upper part of sedimentary sequence (0-60 cm). It is shown that the macromolecular aliphatic kerogen structure begins to form in incoherent sediment at the very early stages of diagenesis. [ABSTRACT FROM AUTHOR]

A number of rare sterane hydrocarbons untypical of younger Phanerozoic petroleum systems have been found by gas chromatography-mass spectrometry in crude oils from the Nepa-Botuoba anteclise of the Siberian platform and the South Oman salt basin of the Arabian platform (Huqf family oils). Among regular steranes, a continuous series of C to C hydrocarbons including the previously unknown C-C isomers have been identified. It has been noted that short-chain C and C steranes are represented by the most thermally stable pregnane species diginane and methyldiginane. Another series of steroids is represented by A-norsteranes, the structures demethylated at C10 (main fragment ion in the mass spectrum at m/ z 203). Tricyclic hydrocarbons C-C identified by m/ z 219 have been attributed to the homologous series of 8,14-secosteranes. These chemofossils have a wide stratigraphic range of occurrence and, like modern minor secosterynes, can be associated with lipid membranes of sponge and their bacterial synbiotics. [ABSTRACT FROM AUTHOR]

A number of previously unknown or less common sterane and terpane hydrocarbons in crude oils of the Nepa-Botuoba anteclise (NBA) have been found by gas chromatography-mass spectrometry. The former include pregnane structures demethylated at C10 (principal fragment ion at m/ z 203) and C-C tricyclic secosteranes ( m/ z 219). By the m/ z 123 mass chromatogram, a number of bicyclic sesquiterpanes with the drimane or tricyclic norisopimarane structure have been identified for the first time in NBA oils. The origin of these terpenoid hydrocarbons is usually associated with the involvement of higher plant debris in sedimentary source rocks. Their presence in Neoproterozoic oils suggests other precursors of these hydrocarbons. Like 10-desmethylpregnanes, 12- and 13-monomethylalkanes, which are unique biomarkers for Neoproterozoic oils of the Siberian platform, have been found in Vendian and Lower Cambrian oils of the Arabian platform and provide evidence for a close similarity between biotas that existed in these ancient basins. [ABSTRACT FROM AUTHOR]