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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]

The article discusses the organic matter (OM) sedimentation in rocks of the Bazhenovskaya Suite in Western Siberia in Russia which is the evidence from hydrocarbons' distributions as conducted by biomarkers. It highlights the main type among oil-bearing formations in the Western Siberia Basin. It mentions the results of analysis of chromate-mass-spectrometric (GCMS) probes of aliphatic and aromatic fractions from bazhenovites and argillites to reconstruct the accumulation of these rocks. It also notes that based from the processes of diagenetic transformation and estimation of primary productivity of OM of the Bazhenovskaya Suite, the sedimentation rate was higher for argillites compared to bazhenovites which increase its cycle duration and decrease in argillites.