HOLOCENE CLIMATIC RECORDS FROM PROGLACIAL DUNES IN CENTRAL AREA OF QINGHAI-TIBET PLATEAU

There is about 100 Km2 of proglacial dunes and gobi planes, with altitude range from 5200 to 5500 m asl., in the west side of the ice field Puruogangri which is the biggest ice field in Asia, at the central Qinghai-Tibetan Plateau in China. The dunes and gobies are developed on layers of tills made by the correlated glacier°¯s movement, and spatially, located near to its correlated glaciers. Both the gobi planes and its gravel ventifact are developed. The dunes are of active and mostly lunar type with single direction and very slow movement from west to east, and with laminae layers of humic materials in laminae system of dunes. This proglacial desert sediment is infrequent in the world, first example in middle latitude and high altitude area in China and records for environment and climate change in the central area of the Plateau in Holocene time. Based on a 35 meter thick section of dune laminae series, 13 layers of humus laminae have been obtained, and gained a series of ages of carbon 14 as 12709 a.BP, 10792 a.BP, 9274 a.BP, 8167 a.BP, 6791 a.BP, 6171 a.BP, 4985 a.BP, 4750 a.BP, 3694 a.BP, 2460 a.BP, 2326 a.BP, 1720 a.BP, 922a.BP, etc. These humus ages are mostly correspond to warm times identified by oxygen sotopic curves of ice core Guliya at west Kunlun Mt. and ice core Dunde at Qilian Mt. which both Mt. are all located on the north edge of the Qinghai°ªTibetan Plateau. So these humus and eolian sand layers may indicate the vertical shifts of bioclimatic zone. Statistically, the atitudes of foreset laminae of different dunes distributed as 40~130°ã°Ï20~34°ã, and the recovered wind direction is 220~310°ã, average as 260°ã. This is in line with the locally west wind. The dunes have been formed at a site after the correlated glacier had retired and tills exposited and plentiful sand materials could provided from the tills. So, in this way, the proglacial eolian sandy geomorphology is mainly depended on the movement of the glacier in the west edge of the ice field by the way of making sand materials, and also is a indication to trajectory of a retiring glacier.