Home – Home – Jornals – Russian Geology and Geophysics 2018 number Неопубликованное

The organic matter (OM) of the terrigenous coal-bearing strata of the Tunguska series (C₂-P) and the Khanar formation (C_2-3), as well as the Devonian carbonate rocks of the North Tunguska OGR, have experienced a complex geological history due to strong heating by traps. Because of this, the values of biomarker genetic parameters C₂₇/C₁₇ in n-alkanes, C₂₉/C₂₇ in steranes, hopanes/tricyclanes decrease in a number of terrestrial bitumens, and the tricyclane index I_TC is likely to be altered by the migration effects of accumulation/dispersion of low-molecular compounds. The sterane maturity coefficient in most samples has undergone thermal inversion and is unsuitable for determining the level of catagenesis. Devonian samples as a whole probably contain marine OM (low δ¹³C; high HI in the insoluble residue and in kerogen, H/C_at in kerogen; in the diagram Pr/nC₁₇ – Ph/nC₁₈ are at the boundary or in the field of type II kerogen; low nC₂₇/nC₁₇ and C₂₉/C₂₇ are characteristic), although in the kerogen of the Manturovka formation (D₁), isotopic and pyrolytic characteristics are distorted, possibly due to high catagenesis. The coal-bearing strata contain terrestrial OM (low HI in kerogens; high nC₂₇/nC₁₇, C₂₉/C₂₇ in steranes, hopanes/tricyclanes for the Khanar formation). The genetic characteristics of the saturated fractions of bitumen nC₂₇/nC₁₇, C₂₉/C₂₇ in steranes, hopanes/tricyclanes in several samples of the Upper Paleozoic are significantly distorted due to the catagenetic redistribution of compounds in favor of low-molecular compounds. According to the elemental composition of kerogen, half of the samples of the Khanar formation and the Tunguska series can be attributed to type III kerogen, and the other half to type IV, probably due to the high level of thermal transformation by the introductions of traps. In this regard, catagenesis for carbon–permian increases generally from the bottom up along the section from the MK₂ gradation to apocatagenesis (changes in R^o_vt, MPI-1 in the aromatic fraction of bitumen, H/C_at in kerogens and asphaltenes).