PRIMARY MIGRATION AND DEGRADATION OF BITUMENS IN LOWER AND MIDDLE CAMBRIAN ROCKS IN THE NORTHEAST SIBERIAN PLATFORM
T.M. Parfenova, A.E. Kontorovich, D.S. Melnik
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: dispersed organic matter, bitumens, hydrocarbons, catagenesis, primary migration, hypergenesis, Kuonamka formation, Cambrian, Siberian Platform.
Abstract
The article presents ideas about the migration of dispersed bitumen and the formation of oil accumulations in black shale deposits, to the development of which Russian researchers have made a major contribution. New results are presented from a study of organic matter in the Lower and Middle Cambrian Kuonamka Formation using a comprehensive methodology developed for the analysis of high-carbon rocks. Features of its composition were revealed in Cambrian deposits distributed on the Munsky arch of the eastern slope of the Anabar anteclise. It is shown that a number of samples exhibit similar compositions, ratios, and distributions of hydrocarbon isomers and homologues, and a genetic relationship is observed between open-pore bitumen and residual autochthonous closed-pore bitumen. It is established that potentially oil-producing and oil-saturated rocks have undergone intense postsedimentation and postdiagenetic changes during their geological history. Furthermore, the residual organic matter of some crushed and uncrushed samples poorly preserved the composition and distribution of hydrocarbons, which originated from Cambrian biological communities. Low contents of open-pore bitumen and significant changes in their group composition, as well as 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 hypergenesis zone, light petroleum components were dispersed from paraautochthonous and allochthonous rock bitumen throughout their open-pore system, along with bacterial and nonbacterial oxidation of organic matter components.
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