Palaeoglaciology of Bayan Har Shan,NE Tibetan Plateau: exposure ages reveal a missing LGM expansion |
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| Authors: | Jakob Heyman Arjen P Stroeven Marc W Caffee Clas Hättestrand Jonathan M Harbor Yingkui Li Helena Alexanderson Liping Zhou Alun Hubbard |
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| Institution: | 1. Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, CAS, Beijing 100101, China;2. Centre for Glaciology, Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY233DB, UK |
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| Abstract: | The Bayan Har Shan, a prominent upland area in the northeastern sector of the Tibetan Plateau, hosts an extensive glacial geological record. To reconstruct its palaeoglaciology we have determined 10Be exposure ages based on 67 samples from boulders, surface pebbles, and sediment sections in conjunction with studies of the glacial geology (remote sensing and field studies) and numerical glacier modelling. Exposure ages from moraines and glacial sediments in Bayan Har Shan range from 3 ka to 129 ka, with a large disparity in exposure ages for individual sites and within the recognised four morphostratigraphical groups. The exposure age disparity cannot be explained by differences in inheritance without using unrealistic assumptions but it can be explained by differences in post-depositional shielding which produces exposure ages younger than the deglaciation age. We present a palaeoglaciological time-slice reconstruction in which the most restricted glaciation, with glaciers less than 10 km long, occurred before 40–65 ka. More extensive glaciations occurred before 60–100 ka and 95–165 ka. Maximum glaciation is poorly constrained but probably even older. The Bayan Har Shan exposure age dataset indicates that glaciers on the northeastern Tibetan Plateau have remained surprisingly restricted for at least 40 ka, including the global last glacial maximum (LGM). This case of a missing LGM is further supported by high-resolution glacier modelling experiments. |
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