Lithological and geochemical evidence of catagenetic transformations of black shales on the example of the Bazhenov formation in Western Siberia

Abstract

The regularities of changes in the lithological and geochemical composition of Bazhenov Formation (BF) rocks characterized by different degrees of organic matter transformation are determined. From МК1 2–МК2 (140–170 C–170–195 C), the following tendency is revealed: a) increasing of the number of calcareous-dolomitic interlayers and content of the dolomite in them; b) reducing of the content of S in the whole section; c) reducing of the OM and sulfide sulfur contents in “pyrite-kerogen” layers of roof of BF; d) reducing of the ratios of C/S; d) increasing of the “pyrite” layer thickness in the transition zone of BF and the overlying sediments and the content of pyrite in it. It is concluded that in the period between the stages corresponding to the grades МК1–МК2, there is a transformation of OM, migration of its transformation products, dolomitization of rocks, and pyritization of low-carbon rocks of the overlying BF Podachimov strata.