FORMATION AND ENVIRONMENTAL EVOLUTION OF SAND WEDGES ON THE TIANSHUIHAI NORTH LAKESHORE IN THE WESTERN KUNLUN MOUNTAINS
Chang Xiaoli Jin Huijun He Ruixia(State Key Laboratory Frozen Soils Engineering,Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences,Lanzhou 730000)
Qinghai-Tibet Plateau is one of the most well developed periglacial areas within the low-middle latitude regions in the world.Tianshuihai,located in the Western Kunlun Mountains regions in the north-west of the Plateau,spreads widely with sand-wedges and other periglacial features.The sand-wedges,which were developed in cold climate conditions,are of important significance for paleo-climate or paleo-environment reconstruction.At the 570km of Xin-Zang Highway(i.e.G219)on the Tianshuihai North Lakeshore,a typical sand-wedge was found with the exact location 35°32.968'N,79°31.821'E and the elevation about 4850m.It is irregular with 37cm in width at the top of sand-wedge but 50cm at the depth of 30cm from ground surface and 98cm in depth,with periglacial involution on the left side of sand-wedge and large compressed deformation and tilt on the right side of sand-wedge.There is a right-ward convex on the left at the depth of 60cm,and then the width of sand-wedge tapers off with the value of 6 ～ 8cm at the bottom of sand-wedge.As to lithology,surrounding rock is principally composed of gray silty soil interbedded,sandy loam and loam.The grain-size distribution,~(14)C dating of organism and mineral composition were analyzed in the sand-wedge and the surrounding rock.The key findings are as follows. (1)The sand-wedge is mainly comprised of light minerals with debris accounting for 75% in weight,which indicates the provenance of infill materials of the wedge is nearby. (2)The sand-wedge could be distinctively divided into three sub-parts with respect to texture,grain-size and figure of the infill,of the results of ~(14)C dating indicates that these three parts were formed in 11.5kaB.P., 11.9kaB.P.and 13.9kaB.P.,respectively,from the center to the periphery. (3)Compared with the climate changing pattern derived from the ostracods research in the Sumxi Co Lake and Bangong Co Lake in the vicinity,these three sub-parts were all formed in the climate cooling period. (4)According to the temperature and moisture condition for frost cracking in different materials,the corresponding mean air temperatures were about 1.8℃,1 ℃ and 4℃ less than present temperature in Tianshuihai region in the Western Kunlun Mountains,respectively.At last,sand-wedges could be considered as an important indicator for cold-arid climate condition and could be used to reconstruct the paleo-climate or paleo-environment.
【Fund】： 国家自然科学基金创新群体项目(批准号:40821001);; 中国科学院寒区旱区环境与工程研究所冻土工程重点实验室专项子课题(批准号:SKLFSE-ZT-01)共同资助
【CateGory Index】： P532;P942
【CateGory Index】： P532;P942