Paleosols in the Kashira deposits in the south of the East European Craton (Republic of Bashkortostan): characteristics, paleoecological and stratigraphic significance

Abstract

Research subject. Paleosols discovered in the Kashira sequence of the Pennsylvanian in the southeastern part of the East European platform. Aim. To study the structure and composition of the paleosols.Materials and methods. Core material from wells was studied by X-ray analysis, scanning electron microscopy and a detailed description of the core and thin sections.Results. Four types of paleosols were identified, three of which are developed on a dolomite substrate. The dolomites are characterized by the following features: microcrystalline structure with a crystal size of 5–10 microns; predominantly euhedral form of crystals, high intercrystalline porosity (up to 38%), inclusions of in situ halite, gypsum and anhydrite, ubiquitous filaments of sepiolite. In paleosols based on a limestone substrate, beta-calcretes with Microcodium were found. The study of fossil roots (rhizoliths) revealed the correlation between their types and substrate composition. Thus, petrified rhizoliths and root casts filled with sedimentary rock and developed clay cutans were found on a dolomite substrate, while calcite tubules around root channels were developed on a limestone substrate. The latter show the presence of abundant Microcodium formations.Conclusions. The revealed morphological and compositional features of the paleosols under study, such as the presence of in situ halite and sulfates (anhydrite and gypsum), sepiolite, and beta calcretes, point to the semiarid climate during the Kashira age on the area under study.