—A combination of modern analytical methods was used to study terrestrial organic matter from upper Paleozoic rocks in the central part of the Vulyui hemisyneclise (East Siberia) sampled from the depth interval 3370–6458 m penetrated in the Srednevilyuiskaya-27 superdeep well. In this study, we used 71 core samples to trace depth variations in the geochemical characteristics of organicmatter during middle–late mesocatagenesis and apocatagenesis: organic carbon content (Corg), Rock-Eval pyrolysis parameters (HI, Тmax), carbon isotope composition, thermal maturity (RVto, %), hydrocarbon type composition (hydrocarbons, resins, and asphaltenes), distributions of n-alkanes (TIC), steranes (m/z 217), and terpanes (m/z 191), and standard biomarker indices with increasing degree of thermal maturity. It is shown that during late mesocatagenesis and apocatagenesis, the pyrolysis parameters and biomarker indicators are no longer effective as indicators of organic-matter maturity and genesis.

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