Holocene Morpholithogenesis of the Onon–Torei Plain

• Published in: Geography and natural resources 2022-12, Vol.43 (4), p.351-362
• Main Authors: Bazhenova, O. I., Cherkashina, A. A.
• Format: Article
• Language: English
• Subjects: Decomposing organic matter; Earth and Environmental Science; Economic Geography; Eolian deposits; Eolian processes; Geography; Geomorphology; Holocene; Humus; Lake basins; Lakes; Landscape/Regional and Urban Planning; Phases; Physical characteristics; Radiocarbon dating; Radiometric dating; Ravines; Regional Problems of the Study of Nature and Use of Natural Resources; Rivers; Sediments; Soil formation; Soil horizons; Soils; Solifluction; Steppes; Valleys
• ISSN: 1875-3728; 1875-371X
• DOI: 10.1134/S1875372822040047

On the basis of long-term station-based studies and soil-sedimentary sequences, a reconstruction of the morpholithogenesis of the Onon–Torey Plain in the Holocene has been performed. A rhythmicity of the functioning of geomorphological systems is revealed. It manifests itself in a regular change in the dynamic phases of relief formation. Characteristics of morphological, lithological, and dynamic parameters of each phase are obtained. The sequence of their change in geomorphological cycles at different hierarchical levels is determined. It is shown that the largest cycle, encompassing the entire Holocene on the Onon–Torei plain is most fully represented in sections of the valleys of the Imalka and Onon rivers. In eolian deposits, 1800-year cycles are especially clearly pronounced by periods of pedogenesis. A change in the conditions of aeolian accumulations in dune sections occurs every 260 years. In the mouths of the ravines opening into the basin of Lake Zun-Torei and the valley of the Builesan River, in the proluvial and proluvial-solifluction deposits of the Atlantic and Subatlantic periods, 130-year and intra-secular Brickner cycles are recorded, the duration of which is about 50 years. A regional scheme of alternation in the Holocene of extreme fluvial and arid phases with normal zonal dynamic phases of relief formation has been compiled. The horizons of fluvial genesis comprise the lower part of the sediments of the Holocene macrocycle. A strong manifestation of fluvial processes was noted in the Preboreal and Atlantic periods of the Holocene, as well as in the transitional time from the Atlantic to the Subborial period. The normal zonal phase of matter integration in systems is evidenced by buried humus soil horizons. Soils aged about 8000, 6400, and 1200–1400 calendar years ago received regional formation. A tendency towards a reduction in the area of the lakes and an increase in the role of eolian processes against the background of a general aridization of the climate over the past 10 000 years has been established. According to radiocarbon dating, sedimentation–accumulation rates are obtained. In general, the high dynamism of morpholithogenesis in the steppes of Central Asia is shown, which causes planation.