PRIMARY MIGRATION AND DEGRADATION OF BITUMENS IN LOWER AND MIDDLE CAMBRIAN ROCKS IN THE NORTHEASTERN SIBERIAN PLATFORM

The paper outlines concepts about the migration of dispersed bitumens and the formation of oil accumulations in black-shale deposits, whose development has been advanced largely by Russian researchers. We present new results of the study of organic matter in the lower and middle Cambrian Kuonamka Formation using a comprehensive technique developed for the analysis of high-carbon rocks. The study has revealed the compositional specifics of organic matter in Cambrian deposits spread within the Muna arch on the eastern slope of the Anabar anteclise. A number of samples display similar compositions, ratios, and distributions of hydrocarbon isomers and homologs. A genetic relationship is observed between open-pore bitumen and residual autochthonous closed-pore bitumen. It has been established that oil-producing and oil-saturated rocks with hydrocarbon potential have undergone intense postsedimentary and postdiagenetic alterations during their geologic history. The residual organic matter of certain crushed and uncrushed samples has poorly preserved the composition and distribution of hydrocarbons that originated from Cambrian biologic communities. The low contents of open-pore bitumens and significant changes in their group composition and in the contents and ratios of individual hydrocarbons are the result of primary migration within the Kuonamka Formation, emigration into the underlying and overlying sediments, and active destructive weathering processes. In the hypergene zone, light oil components were dispersed from parautochthonous and allochthonous rock bitumens throughout their open-pore system, which was accompanied by biotic and abiotic oxidation of organic-matter components.