A GEOCHEMICAL INVESTIGATION OF SAMPLES FROM THE VOLGIAN BAZHENOV FORMATION, WESTERN SIBERIA, RUSSIA

In this paper we present analyses of five core samples from the Volgia n Bazhenov Formation. Three different organic facies (A, B, and C) are proposed based on microscopical, bulk and biomarker analyses. Facies A and B have much in common, including low hopane/sterane ratios, C35/ C34 hopane ratios slightly above 1.0, small amounts of tricyclic terpa nes, and a range of alkylthiophenes in their pyrolysates. However, Fac ies A and B show some differences. For example, Facies A shows a sligh t even/odd (C22-C27) n-alkane predominance in some of the samples, whi le Facies B lacks 28,30-bisnorhopane, and shows significantly differen t n-alkane/isoprenoid ratios. These findings contrast with those of Fa cies C, which shows very low organic sulfur, an odd/even predominance in the higher n-alkanes, a high C29/C27 sterane ratio, a very high hop ane/sterane ratio, and is very low in tricyclic terpanes. The timing o f hydrocarbon generation from Facies A, together with the type and amo unt of organic matter, appears to be similar to that of the Upper Jura ssic of the Norwegian continental shelf. It appears that Facies A and B have similar types of organic matter, with a somewhat higher input o f terrestrial debris in the latter and, contrastingly, in Facies C an even greater proportion of terrestrial organic matter.