THE TOLOGOI KEY SECTION (upper Cenozoic, Transbaikalia): RECONSTRUCTION OF THE PECULIARITIES AND DEPOSITIONAL ENVIRONMENT
V.V. Ivanova1,2,3, M.A. Erbaeva4, A.A. Shchetnikov5,2,6,7, A.Yu. Kazansky8,3, G.G. Matasova3,9, N.V. Alekseeva4, I.A. Filinov5,7,3, M.I. Kuzmin2
1I.S. Gramberg All-Russia Scientific Research Institute for Geology and Mineral Resources of the Ocean, Angliiskii pr. 1, St. Petersburg, 190121, Russia
2Vinogradov Institute of Geochemistry, ul. Favorskogo 1a, Irkutsk, 664033, Russia
3Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017, Russia
4Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh’yanovoi 61, Ulan-Ude, 670047, Russia
5Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
6Irkutsk Scientific Center, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 134, Irkutsk, 664033, Russia
7Irkutsk State University, ul. Karla Marksa 1, Irkutsk, 664003, Russia
8Lomonosov Moscow State University, Leninskie Gory 1, Moscow, 119991, Russia
9Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Pleistocene, Pliocene, geochemical composition of loose deposits, environmental changes, lithology, Tologoi key section, Transbaikalia
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.
DOI: 10.15372/RGG2020141
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