Experience of applying the cosmogenic dating method (¹⁰Be) to assess the age and scale of the Pleistocene Glaciation in North-Eastern Siberia (based on the example of glacier complexes of the Chersky Ridge)

The history of studying glacial complexes in North-Eastern Siberia goes back more than 150 years. During this period, extensive geological and geomorphological features were obtained, which made it possible to determine the stages, nature and extent of glaciations. At the same time, the lack of direct dating of the glacial relief obtained by geochronological methods does not allow for full-fledged paleogeographic reconstructions. This leads to discussions in both Russian and English literature about the possibility of the existence of glaciation in the mountains of North-Eastern Siberia. In this regard, to determine the size and time of glaciation in the southern part of the Chersky Range, we carried out a complex of geomorphological and geochronological studies, which are part of the international project “Searching for the missing ice sheet in Eastern Siberia”. Because of fieldwork in the Ohandya Ridge, in the Malyk-Sien River valley, three terminal moraine ridges have been identified, reflecting different stages of glaciation. Based on the dating of exposed boulders within three terminal moraine complexes, 22 10Be cosmogenic dates were obtained. The average exposed age for the outer moraine is 120.8±13.7 ka, for the middle one North-Eastern 37.7±4.9 ka and for the internal moraine North-Eastern 13.8±2.2 ka. The age of the terminal moraine complexes testifies to the mountain-valley character of the glaciation of the Chersky Range in the Middle and Late Pleistocene, and emphasizes the trend towards a gradual decrease in the maximum length of glaciers in Northeast Asia. The successive reduction of glaciers from MIS 6 to MIS 2 indicates an increase in the deficit of atmospheric precipitation and a significant cryoaridization of the region. The decreasing trend may be related to the sharply continental conditions observed in the interior of Eurasia and western North America. This trend contrasts with much of the glaciated areas in the Northern Hemisphere, where the maximum area of Late Pleistocene glaciers is reconstructed for LGM time (MIS 2). The obtained datings of the glacial complexes of the Chersky Ridge confirm that at the end of the Middle and Late Pleistocene glaciations here were of a limited nature and there was no single ice cover in the mountains.