Upper Permian paleosols developed from limestone in the middle reaches of the Volga River: Morphology and genesis

Abstract

The results of the study of paleosols preserved in the Upper Permian deposits in the central part of the Russian plate are presented. The paleosol profiles consist of the medium loamy dark brown BMg,ca horizon and the hard cemented calcareous Mm,ca and Mca horizons. The imprints of plant roots in the Mm,ca horizon and in the upper part of the Mca horizon serve as a vivid diagnostic feature of these paleosols. Two paleosol morphotypes are distinguished according to the development of the structural-metamorphic BMg,ca horizon and the micromorphological features. These paleosols were developed from highly calcareous lacustrine deposits that were initially loose and then subjected to cementation. The processes of leaching and redistribution of carbonates, as well as the development of the soil structure, vertic properties, eluvialgley processes, lessivage, and soil creep, can be identified in the studied paleosols. They bear the record of the geomorphic conditions on a flat plain with recurrently drying inland water reservoirs in a semiarid paleoclimate with well-pronounced seasons.