Tectonic structure and stages of geological development of the Sterlitamak shikhans

Abstract

The article considers the features of the tectonic structure and geological development of the Lower Permian single mountains – shikhans on the left bank of the Belaya River near the city of Sterlitamak (Republic of Bashkortostan). The analysis of published and archival materials, field research, the study of core material, lithological and structural observations allowed us to get an idea of the tectonics of single mountains (shikhans). The Shikhans are part of a single chain of carbonate massifs composed of reef facies and located submeridionally (from south to north) in the western side of the Pre-Uralian Foredeep. In the area of Sterlitamak four massivеs are brought to the surface of the Earth as part of a single Shikhan block. The tectonic structure of the territory is determined by paleotectonic (the period from 3600 to 23 million years) and neotectonic (23 – 5 million years).years and up to the present) events that are combined into periods and are divided into stages. The formation of reef complexes composing the shikhans was controlled by paleotectonic events of the collision stage of development, which led to the formation of the continental shelf margin with conditions favorable for the formation of reef communities on the border of the Pre-Uralian Foredeep during the Asselian and Sakmarian epochs (for 15 million years). Subsequent geological events – in the Artinskian and Kungur time, in the Late Permian-Early Mesozoic stage and in the Middle Jurassic-Miocene platform stage caused the destruction and leveling of the Early Permian relief, erosion of sediments and their overlap with younger sediments. The tectonic impact of the last Pliocene-Quaternary neo-orogenic stage (5 – 0 million years) is most intensively manifested in the rocks of Shikhans. It is expressed in intense fracturing and fragmentation of rocks, their recrystallization with loss of primary structural and textural features. The neotectonic movements of the blocks of the Earth's crust contributed to the removal to the surface of individual sections of the reef complexes distribution zone. The isolation of reef shikhans was a result of presence of an evaporites оver them, which were easily eroded. The tectonic effect on the carbonate rocks of reef nature contributed to the formation of zones of increased fracturing observed in the rocks of the Sterlitamak shikhans and penetration of oil-containing solutions and fluids, which formed areas of rocks with increased reservoir properties. Leaching and karst zones with residual bitumen are observed on almost all shikhans.