Geochemistry of phenanthrenes, dibenzothiophenes and aromatic steroids in the Bazhenov formation’s source rock of the south-east of Western Siberia (Tomsk region)

The paper presents the results of studying aromatic compounds (phenanthrenes, dibenzothiophenes, aromatic steroids) in source rock extracts (bitumoids) from the Bazhenov Formation of the Tomsk Region (south-east of Western Siberia, Russia). In addition to holonuclear and monomethyl-substituted structures of the phenanthrene and dibenzothiophene series we also identified their di- and trimethyl-substituted homologues. A comparative analysis of the relative concentrations of the main groups of aromatic compounds calculated by two methods (with and without diand trimethylphenanthrenes and dibenzothiophenes) showed their identity. The main factor controlling the content and distribution of aromatic compounds has been established as the degree of maturity of organic matter. The most informative molecular maturity indices for the Bazhenov Formation’s organic matter whose maturity corresponds to low and medium gradations of catagenesis (PK 3 -MK 1 2 ) are the ratios of 4-MDBT/1-MDBT, TASI, TAS/MAS, and TMTGP/1,7,8-TMP.