Distribution and timing of Holocene and late Pleistocene glacier fluctuations in western Mongolia

Frank Lehmkuhl,Michael Klinge,Daniela Hülle,Henrik Rother

doi:10.3189/2016aog71a030

Abstract

Abstract.Despite being a key location for paleoglaciological research in north-central Asia, with the largest number of modern and Pleistocene glaciers, and in the transition zone between the humid Russian Altai and dry Gobi Altai, little is known about the precise extent and timing of Holocene and late Pleistocene glaciations in western Mongolia. Here we present detailed information on the distribution of modern and late Holocene glaciers, and new results addressing the geomorphological differentiation and numerical dating (by optically stimulated luminescence, OSL) of Pleistocene glacial sequences in these areas. For the Mongolian Altai, geochronological results suggest large ice advances correlative to marine isotope stages (MIS) 4 and 2. This is in contrast to results from the Khangai mountains, central Mongolia, showing that significant ice advances additionally occurred during MIS3. During the Pleistocene, glacial equilibrium-line altitudes (ELAs) were ~500 to >1000m lower in the more humid portion of the Russian and western Mongolian Altai, compared to 300-600 m in the drier ranges of the eastern Mongolian Altai. Pleistocene ELAs in the Khangai mountains were depressed by 700-1000 m, suggesting more humid conditions at times of major glaciation than in the eastern Mongolian Altai. This paleo-ELA pattern reveals that the precipitation gradient from the drier to the more humid regions was more pronounced during glacial times than at present.

Highlights

This paper aims to summarize the extent and timing of Holocene and Pleistocene glaciations in western Mongolia based on selected region in the Altai and western Khangai mountains (Figs 1–6; see Fig. 1a for locations)
Several Holocene and Pleistocene stages of glaciation can be differentiated based on geomorphological criteria
Close to the C2 site, glaciofluvial sands, exposed stratigraphically below the moraine, yielded consistent optically stimulated luminescence (OSL) dates of >25.1 2.4 and >27.1 2.1 ka (O3), suggesting deposition slightly before the last major ice advance. Both data sources, cosmogenic radionuclide (CRN) and OSL, place this ice advance into MIS2 between >27.1 and 17.7 ka. These results provide evidence suggesting the correlation of the M1c moraines to ice advances during MIS3 and the M1b moraines are part of the MIS2 sequence

Summary

Introduction

This paper aims to summarize the extent and timing of Holocene and Pleistocene glaciations in western Mongolia based on selected region in the Altai and western Khangai mountains (Figs 1–6; see Fig. 1a for locations). Towards the southeast the Mongolian Altai extend into the Gobi Altai. East of the Mongolian Altai, the socalled ‘Valley of Great Lakes’ separates the Altai from the Khangai mountains in central Mongolia, which trend 600 km from northwest to southeast (Fig. 1a). The highest amount of annual precipitation occurs in the western Altai (above 1000 mm), in regions climatically influenced by the westerlies. In the basins of the Valley of Great Lakes the annual precipitation decreases to 400 mm. There is a pronounced seasonal precipitation distribution, with 70–80% of annual precipitation falling during the summer months

Objectives

Results

Discussion

Conclusion