The Tologoi Key Section (Upper Cenozoic, Transbaikalia): Reconstruction of the Peculiarities and Depositional Environment

Abstract

Abstract —This paper presents new data on the structure and lithologic, geochemical, and granulometric features of the Quaternary deposits of the Tologoi key section (upper Cenozoic, Transbaikalia). These data made it possible to determine the location of paleosol horizons throughout the section and their thicknesses. Four main sedimentation cycles have been identified; each of them terminated with the formation of soil horizons. It is shown that the climate during the formation of the deposits had a cyclic nature: Wet periods were changed by dry epochs of different durations. During warming and the formation of soil horizons, distant and medium-range provenance areas prevailed. In situ biochemical postsedimentary transformations of the deposits dominated in the periods of the most intense pedogenesis, as reflected in the changes in their chemical composition. It is shown that the warmest climate and the activation of weathering and leaching processes during the Pleistocene were in the period of the accumulation of a paleosol horizon in the section interval 16.4–15.0 m. It was a period of pedogenic and biologic activity and reduced salinization and carbonation. Stages with prevailing cryogenic environments are clearly recorded in the studied geochemical profile as involutions, pseudomorphs after ice wedges, and thick carbonate lenses. The deposits formed at these stages are characterized by minimum salinization, high calcification, and low leaching (hydrolysis) and oxidation indices as well as a positive Eu anomaly and high ΣCe/ΣY and low La/Sm values.