Chromato-mass-spectrometric studies made it possible to identify a wide spectrum of hydrocarbon biomarkers in crude oils from Cenomanian pools of northern West Siberia (Russkoe, Pangodinskoe, Van-Eganskoe, Severo-Komsomol’skoe). The distribution pattern of the main hydrocarbon components (n-alkanes, acyclic isoprenanes, steranes, terpanes) shows that most of the oils underwent intense microbial oxidation. We have established high concentrations of 25-norhopanes typical of high-degree degradation; demethylated hopanes are also revealed in “alkane” crude oils. Among low-molecular chemofossils, bi- and tricyclic mono- and sesquiterpanes have been recognized, whose precursors are usually biomolecules synthesized by plants. Unsaturated precursors of mono- and sesquiterpanes might have been the starting material for thermocatalytical synthesis of framework adamantanoid structures, whose high concentrations have been found in alkane-free crude oils.

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