Abstract

An integrated lithofacies analysis of the Middle–Upper Bathonian petroleum horizon J2 in the northeastern part of the latitudinal Ob’ region was carried out. The new data were used to supplement and refine the available data. The recognized lithofacies and their associations clearly mark off the boundaries of reconstructed sedimentation conditions. A petrographical study of the silt–sandy rocks of the horizon was carried out with a detailed calculation of their grain size and petrographic compositions. Grain size coefficients were analyzed with the use of genetic, dynamic, and dynamogenetic diagrams. The new data permitted a considerable refinement of the reconstructed sedimentation conditions of the horizon. It has been found that the transgressive change of sedimentation conditions is reflected in regular changes in some characteristics of the studied sediments: a decrease in the total number and thickness of coal interbeds, an increase in the degree of sediment bioturbation, a change of ichnofossils, and an increase in the amount of pyrite. More detailed paleogeographical schemes have been constructed for the formation of the lower (continental), middle (transitional), and upper (littoral marine) parts of the horizon. They provide a better understanding of the regularities of development of the Middle–Late Bathonian sedimentary basin in the study area.

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