Biomarker hydrocarbons in the organic matter of Paleogene sediments in southern West Siberia

Results of geochemical studies of chloroform extracts from the organic matter (OM) of argillaceous-aleuritic Paleogene rocks drilled by wells in southern West Siberia are reported. Judging from the prevalence of odd over even n-alkanes, as well as the simultaneous presence of terpenes, biohopanes, and regular petroleum hopanes (in 17a(H),21β(H) configuration), the OM of the sediments passed the step of the diagenetic transformation but did not exit from the protocatagenesis zone, i.e., it did not reach the oil window. Taraxerene and olean-12-ene were detected at depths of 90–120 m. At depths greater than 400 m, oleanane and a number of quite rare triterpenoids, such as 28,30-bisnorhopane-17(21)-ene and its reduced analog 28,30-bisnorhopane, appear in trace amounts. Most of the array of triterpenoids are characteristic of terrigenous OM, whereas the pattern of the distribution of tricyclic cheilanthanes in some samples is typical of marine sediments. In character, it is close to the set of the biomarker molecules identified in extracts of Holocene and Miocene deep-sea sediments from Baffin Bay.