We have studied for the first time the organic geochemistry of the Vendian thick section stripped by the parametric well Vostok-3 in the depth range 5002-3870 m in southeastern West Siberia. The results point to the aquagene-plankton-derived and bacterial nature of the buried organic matter (OM). At some depth levels, the deposits are enriched in OM (up to 0.7-9.6%). The study of kerogens has shown that the OM is transformed to the apocatagenesis stage. The composition of biomarker hydrocarbons in bitumens has been studied, and the geochemical criteria for the petroleum presence prediction are considered
