从冰前风沙地貌初看普若岗日冰原的形成演变

野外实地考察和室内样品分析表明,位于普若岗日冰原西侧冰川前缘带的大片风沙地貌,直接发育在冰碛之上,并以冰碛为主要物质来源,与冰川运动和冰原环境具有密切的联系,是相关冰川和冰原形成演化过程的良好反映与记录.结合沙丘沉积序列中的沉积构造测量、粒度分析及腐殖质夹层的¹⁴C测年等结果,初步得出:普若岗日冰原至少形成于18kaBP;冰原降水可能主要来自西风降水;18kaBP以来,冰原在总体上处于收缩过程,在约108kaBP来,冰原西缘的零平衡线的年均水平退缩速率约为088～102m·a^-1,铅直升高速率约为24～32mm·a^-1。

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

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 mm·a^-1 in the vertical direction, respectively, since 10.8 ka BP.