LITHOLOGICAL-FACIAL STRUCTURE OF THE UFA SEDIMENTS IN THE CENTRAL PART OF THE PERM KRAI

Abstract

The relevance of the study is caused by the need to clarify the lithological-facies and sequence-stratigraphic structure of the sediments of the Uralian section of the Permian system. Today, there is a problem of the stratigraphic position and independence of the Ufa stage. Over the past three decades, researchers have expressed various assumptions about changes in the volumes of the longline. Due to the peculiarities of sedimentation, the main biostratigraphic groups for the Volga-Kama region are: ostracods, pelecypods, spores and pollen, plant remains, fragments of fish and vertebrates, the distribution intervals of which are limited by the boundaries of facies zones. Hence, there is a limitation of biostratigraphic methods, due to which researchers have not been able to clearly define the boundaries and volume of the stage until now. Purpose: division of sediments into fourth order sequences and clarification of the lithological-facies structure. Objects: geological sections and oil wells in the central part of the Perm region. Methods: geo-mapping of geological sections; borehole correlation; lithological-facies description; paleogeographic reconstructions. Results. Correlation of the most typical sections helped the authors describe the structure, material composition and build a composite section of the Ufa stage. The submeridional profile for the studied wells made it possible to show a change in the types of the section over the area from the maximum thickness in the area of the Solikamsk and Visim depression to the normal platform part of the Perm territory. In the section of the Ufa stage, two fourth-order sequences have been identified. The first sequence corresponds in volume to the Lower Solicam sub-formation. The second sequence is identified in the volume of the Verkhnesolikamsk subformation and Sheshminskaya formation. Stratigraphic unconformities with signs of subaerial exposure were recorded at the border of the Kungurian and Ufa stages and the lower and upper Solikamsk subformation.

Keywords

• stratigraphy
• permian system
• ufa stage
• sequence stratigraphy
• lithofacies variability