LATE HOLOCENE CRYOGENIC DEFORMATIONS IN FLOODPLAIN SEDIMENTS OF RIVER VALLEYS IN THE SELENGA RIVER BASIN
Yu.V. Ryzhov1,2,3, V.L. Kolomiets4, M.V. Smirnov1
1Institute of the Earth's Crust, SB RAS, Lermontova str. 128, Irkutsk, 664033, Russia
2Sochava Institute of Geography, SB RAS, Ulan-Batorskaya str. 1, Irkutsk, 664033, Russia
3Irkutsk State University, Lenina str. 1, Irkutsk, 664003, Russia
4Geological Institute, SB RAS, Sakhyanovoy str. 6a, Ulan-Ude, 670047, Russia
Keywords: frost cracking, ground wedge, cryoturbation, floodplain, Late Holocene, Selenga River basin
Abstract
The morphology and age of cryogenic deformations (cryoturbations and ground wedges) in the Holocene floodplain sediments of river valleys in the Selenga River basin within the areas of seasonal, discontinuous, sporadic, and isolated permafrost were studied. Late Holocene ground wedges and cryoturbations were identified in the seasonally frozen layer of floodplain sections of the Itantsa, Il’ka, and Orkhon rivers. The time of formation of the cryogenic deformations was determined on the basis of detailed morphological descriptions and dating of low and high floodplain sediments of these rivers. The age of the alluvium with cryoturbation on the low floodplain is less than 2 kyr. Cryogenic deformations on the high floodplain formed in the Late Holocene (the last 4.2 kyr). It was determined that alluvium layers with cryoturbation are underlain by moderately wet to satiated wet loamy sands and loams. Cryogenic deformations are considered a paleoclimatic indicator of the Late Holocene in the Transbaikal region and northern and central Mongolia.
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