The Cyclical Structure of the Isotopic Diagram of a Lithalsa and Its Radiocarbon Age, Sentsa River Valley, Eastern Sayan

This paper reports on the nature and history of the mineral-rich frost heave mounds—lithalsas—developed on the first terrace of the Sentsa River in Okinsky District of Buryatia. An ice core of the lithalsa was exposed by drilling of a 20-m borehole. The most typical feature of the isotopic diagrams,...

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Bibliographic Details
Published in:Doklady earth sciences 2019-12, Vol.489 (2), p.1456-1460
Main Authors: Vasil’chuk, Yu. K., Vasil’chuk, J. Yu, Alexeyev, S. V., Budantseva, N. A., Alexeyeva, L. P., Vasil’chuk, A. C., Kozyreva, Ye. A., Svetlakov, A. A.
Format: Article
Language:English
Subjects:
Archaeological dating
Boreholes
Carbon 14
Coring
Drilling
Earth and Environmental Science
Earth Sciences
Evaporation
Flooding
Frost
Frost heaving
Geography
Heaving
Ice
Ice cores
Ice formation
Isotopes
Lakes
Mounds
Permafrost
Radiocarbon dating
Radiometric dating
River valleys
Rivers
Soil
Terraces
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Summary:This paper reports on the nature and history of the mineral-rich frost heave mounds—lithalsas—developed on the first terrace of the Sentsa River in Okinsky District of Buryatia. An ice core of the lithalsa was exposed by drilling of a 20-m borehole. The most typical feature of the isotopic diagrams, which we obtained for the ice core, is their cyclical pattern illustrating isotope minima at depths of about 3–5 m, 9–12 m, and 18–21 m, separated by two distinct isotope maxima. Most likely, this demonstrates the cyclicity of the triple flooding of the growing frost heave mound and the subsequent active evaporation of lake-march waters, which are the main source of moisture for the lithalsa ice core. Based on the detailed radiocarbon dating of organic material from the upper horizons of the highest and surrounding lithalsas, we determined the time of their formation. Organic material in drained frost-susceptible soils was intensely accumulated during the period from 0.5 to 0.2 ka BP. This is the time of the beginning of the formation of permafrost, active ice-formation, and the associated frost heave and lithalsa growth. The age of at least three of four mounds studied is not older than 200 years, it coincides with the cooling at the beginning of the 19th century.
ISSN:1028-334X
1531-8354
DOI:10.1134/S1028334X19120158