Lithofacies Peculiarities and Bionomic Specification of the Fossil Remnants Complexes of the Lower Permian in the Yuryuzan-Ai Depression in the Southern Urals (on the Example of the Mechetlino Section)

Abstract

A lithofacies and bionomic study of the boundary Artinskian-Kungurian deposits of the Cisuralian Series of the Permian system in the Yuryuzan-Ai Depression was carried out on the example of the Mechetlino section (Southern Urals). The section was a candidate GSSP of the lower boundary of the Kungurian. In terrigenous-carbonate deposits, eight lithophacial types of rocks – lithofacies – are identified. According to their combination, the section is divided into packages composed of carbonate-terrigenous flysch rocks, carbonate clastic deposits initiated by storms, and blocky underwater landslide deposits. Six ecological complexes of small foraminifera are identified, reflecting sedimentation conditions in the areas of benthic fauna denudation. The mechanisms of mixing and movement of plant remains, benthic, planktonic and nectonic fossils are indicated. A model of the formation of sedimentary complexes of the Lower Permian in the Yuryuzan-Ai depression of the Pre-Ural trough is proposed, reflecting the bionomic specificity of the complexes of organic residues on the border of the Artinskian and Kungurian stages.