Model of Upper Famennian-Tournaisian Formations within the Axial and Margin Zones of the Saraylinsky Depression (Republic of Tatarstan, Russia)

The study focused on the Upper Famennian-Tournaisian formations in the southeastern part of Tatarstan, which constitute the stratigraphic sections of various segments of the Saraylinsky depression. The research aimed to develop a sedimentation model for the Upper Devonian-Tournaisian depositional complex within the Saraylinsky depression. Typical stratigraphic sections were constructed for different segments of the depression, and sedimentation patterns were examined for the margin, slope, and depression zones, based on a detailed analysis of core material from several wells. A consistent lithological succession was identified within the depression profile, revealing a rapid decrease in the proportion of carbonate deposits toward the axial zones, accompanied by an increase in mixed clay-carbonate-siliceous rocks with a high content of syngeneic organic matter. In the same direction, the thickness of coeval deposits decreases. The sections of the margin zone were formed in shallow-water carbonate shelf environments, whereas the axial zone sections represent more deepened intrashelf basins with signs of condensed sedimentation. Slope-type sections, in terms of lithological composition, show greater affinity with depression-type sections, although they exhibit characteristics of somewhat shallower sedimentary settings. A sedimentation model for the Upper Famennian-Tournaisian deposits within the Saraylinsky depression has been presented and described. The margin zones of the Saraylinsky depression are considered highly prospective for oil exploration, while the slope and depression-type sections may be regarded as potentially promising targets for shale hydrocarbon development with the application of appropriate technologies. The results of this study can be used in sedimentological research of other elements of the Kamsky-Kinelsky system of depressions, including the prediction of potentially promising areas for development.