Выпуск: 5 , Том: 34 , Год издания: 2026

The chronology, size, and drainage patterns of ice-dammed lakes in the high-mountain depressions of the Russian Altai, as well as their influence on topography changes and sedimentation of the main valleys during the Pleistocene, remain highly debatable. The main reason is different interpretation of key sections and landforms; the different sets of research methods; the objective difficulties of applying numerical dating techniques; and the discrepancies in chronological determinations obtained by different dating techniques. A comprehensive geological and geomorphological study based on OSL and ¹⁴C dating allowed us to propose our own version of Pleistocene events in the upper Chuya River basin. The age of glaciolacustrine deposits in the Chagan key section indicates powerful glaciation in the mountainous framing of the Chuya Depression as early as the Middle Pleistocene-ca 160-180 ka ago (MIS 6). However, the ice-dammed (probably single) lake, which left the highest (up to similar to 2100 m a.s.l.) shorelines preserved in the topography on the slopes of the Chuya and Kurai Depressions, existed no earlier than 90-80 ka ago, i.e., in the Late, not Middle Pleistocene, probably in MIS 4. The view that the Chuya Depression was filled in MIS 4 to a level of 2250 m a.s.l. does not yet have a geochronological basis; existing calculations of the volume of the single Kurai-Chuya lake at this level are purely hypothetical. The last lake in the Chuya depression, with a level of about similar to 1890 m a.s.l., existed during the Last Glacial Maximum (MIS 2) about 37 (25)-16 (14) ka ago, and was drained over a short period of time. The Kurai Depression in MIS 2 was occupied by lake at least 25 ka ago. Around 19 ka ago the Kurai paleolake had a water level of 1730 m a.s.l. (depth up to 270 m near the dam) and extended as a narrow bay into the Chuya Valley between the Kurai and Chuya depressions. Sharp and significant drop in the lake's level occurred at that time, but about 16 ka ago its level was still no lower than 1570 m a.s.l. No later than similar to 16-14 ka ago the main part of the Kurai Depression had completely drained. The damming of not only the old but also the new Chuya River valley at the outlet of the Kurai Depression by the Maashey Glacier, and subsequently by its moraines, was a key reason for the change of direction of flow of the Chuya River. At the beginning of the Holocene, small lakes of non-glacial origin existed at the mouths of both depressions and in the Chuya Valley between them. The comprehensive description of studied sections applying geochronological, geological, paleontological and geomorphological methods allows us to classify them as key sections for reconstructing the Pleistocene evolution history of the Chuya and Kurai Depressions and the Altai highlands as a whole. Refinement of the stratigraphic scale of the Altai Quaternary deposits should be considered based on the results of these studies.