Based on new geological and geophysical data obtained in recent years, the types of Lower Carboniferous sections were updated, and the boundaries of their distribution were refined within the southeastern slope of the North-Tatarian Arch in the Republic of Tatarstan. A.K. Shelnova identified four typical Lower Carboniferous sections in 1966: Saraylinsky, Aktashsky, Kabyk-Kupersky and Saitovsky types. Using well geophysical survey data and core material studies, reference charts were created for each section type, allowing the identification of new variations: Kabyk-Kupersky type 1, Kabyk-Kupersky type 2, and a transitional type, which were previously included into the Kabyk-Kuper section type. As a result, the definition of the Saraylinsky formation was refined. It represents a complex of carbonate-siliceous-terrigenous rocks with high organic matter content, extending from the lower boundary of the Tournaisian stage to the base of overlying Tournaisian carbonate rocks or terrigenous deposits of a different (post-Tournaisian) age. The stratigraphic position of the Saraylinsky formation within the Lower Carboniferous and its high organic matter content were established through lithological, bio-sedimentological, and paleontological core studies from two wells: one located in the axial part of the Nizhnekamsk Trough and the other on the northern flank of the trough. For the first time, seismic data enabled the stratification and tracking of the reflecting horizon associated with the top of the Saraylinsky formation within the Nizhnekamsky Trough of the Kama-Kinel system. The revision of section types and distribution boundaries of Lower Carboniferous deposits enhances and expands the understanding of the structural-facies zonation of the region.
References
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