LATE QUATERNARY GLACIATION IN NORTHERN CENTRAL ASIA

Late Pleistocene glaciers in a large area east from the central Tien Shan to the Khangai Nuruu, and north from the Gobi Desert to the Gornii Altai and the Saian ranges of southern Siberia, appear to have advanced and retreated substantially in phase with glacier fluctuations in much of Europe and North America. Thus, the glaciers of the "Last Glacial Maximum" (LGM)(~20 ka: "Sartan" in Russia) were generally as large or larger than those earlier in the last glacial cycle, ~110-14 ka, as demonstrated by ¹⁰Be dates from 18 drainages distributed across this vast region. These findings are consistent with those of F. Lehmkuhl in western Mongolia, and with inferences made from sediment cores taken from Lake Baikal by the Baikal Drilling Project. Equilibrium-line altitudes (ELAs) of modern glaciers generally rise from north to south, and also from west to east, especially across the first mountains encountered by winter low-pressure systems. ELAs reconstructed using the AAR, THAR, and maximum-moraine techniques show that throughout much of northern Central Asia south of Siberia, the depression during the LGM compared to modern values was generally ~300-600 m, abut half that for North America. However, on the windward side for the westernmost mountains the depression was as much as ~900 m. The ELA depression also increased similarly from 49° to 51°N.

In the Darhat depression of northern Mongolia, the headwaters of the Yenesei River (Shishhid Gol) were dammed to a depth of as much as ~250 m by glaciers from a tributary (Tingis Gol) at their maximum extent. This happened repeatedly, causing outburst floods of ~150-500 km³. Thermoluminescence, ¹⁰Be and ¹⁴C dating of varved sediments suggests that glacial dams existed ~35-45 ka and 16-18 ka. The last high stand of the lake was at 9300 ¹⁴C yr B.P. However, the dam from this high stand has not been identified. Dating of Darhad sediments complements climatic inferences made from the Lake Baikal core because the timing of maximum glaciations can be identified unambiguously.