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Disscusion on the Evolution of the Puruogangri Ice Field Based on Proglacial Dune Geomorphology

LI Xiao-ze, YAO Tan-dong, QU Jian-jun, ZHANG Wei-min (Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou Gansu 730000, China)  
There are proglacial dunes and gobi planes in the west side of the Puruogangri Ice Field at the central Tibetan Plateau, China. Different from the other deserts in general, there are the following five features of the proglacial dunes and gobi planes: 1) In spatial, they are distributed near to their correlative glaciers; 2) They are based on the layers of till formed by correlative glacier movement; 3) Gobi planes and gravel ventifacts are well-developed; 4) The dunes are of active, with single direction of lunar type and very slow movement; 5) There are laminae-slice layers of humic materials in the laminae system of dunes. ;The proglacial dunes better reflect the evolution of the ice field. Because the dunes formed after glacier retreating and after exposure of till, followed by providing plentiful sand materials. So, in this way, the proglacial eolian sandy geomorphology mainly depends on the retreat of glacier in the west edge of the ice field, and on the yield of sand materials. Also the eolian geomorphology indicates the trajectory of retreating glacier. ;From the eolian geomorphology and deposits one can see: 1) The ice field formed at 18 ka BP at least, which can be inferred from the age of dune section, 10^8 ka BP ({} 14C dating), and the correlation with Guliya ice core records; 2) Precipitation on the ice field is mainly due to planetary westerly, which can be reconstructed from the dune s morphology and attitudes of fore laminae bedding of dunes; 3) In the west edge, the equilibrium line of the ice field has retreated with the mean rate of 0^88~1^02 m5a+{-1} in the horizontal direction and 24~32 mm5a+{-1} in the vertical direction, respectively, since 10^8 ka BP.
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