Geologicheskii Vestnik

Lithofacial analysis of carbonate rocks of the Upper Carboniferous and Lower Permian in the stratotypic section of the Usolka showed the presence of several types of sediments differing in composition and mechanism of formation. Background sediments include fine grained limestones – wackstones with radiolarians and sponge spicules of LFT1, LTF2, and LTF3 lithofacies and their dolomitized and phosphatized differences. They indicate the quietness and depth of the sedimentary basin in this zone of the Preuralian foredeep. The sediments with introduced components include granular limestones – grainstones and rudstones LTF4 with fragments of reef fauna and calcareous siltstones LFT5 with tuff (ash) material. The intermediate type of precipitation is dark gray pelitic clay-siliceous-carbonate deposits – marls and argillites or mudstones LTF6. They contain background siliceous-carbonate mud with an admixture of introduced clay material. The irregular alternation of these types of sediments in the Usolka section indicates the conditions of the slope of a deep-sea basin into which clastic and volcanogenic ash material was pulsed. The main removal of carbonate fragments in the rudstones and grainstones of LTF4 occurred as a result of earthquakes from the reef zone bordering the western side of the Preuralian foredeep. The facies environment corresponds to the area of transition from the deep-sea shelf of the western part of the Preuralian foredeep to the central zone of the basin.

Southern Urals, Zilmerdak Formation, Bederysh Subformation, traces of runoff jets, storm deposits, glauconite

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