Abstract:

The climbing dunes are widely distributed in Dinggye area of Zigaze Prefecture, Tibet, China, and the surface sediment grain size characteristics are of great significance for exploring the development process of sand dunes. In this paper, six climbing dunes sand were collected in the area. In order to reveal the grain size characteristics, the study analyzed the morphological parameters, mechanical composition and grain size parameters of surface sediments of the dunes, which provide a theoretical basis to reveal the climbing dune’s formation mechanism on the Qinghai-Tibet Plateau. The current researches were mainly concentrated on the climbing dunes in coastal areas rather than that in arid areas. Studying the climbing dunes on the Qinghai-Tibet Plateau can explore the grain size characteristics of climbing dunes in inland arid regions. The results are summarized as follows：The surface sediments of climbing dunes are mainly composed of silver sand and medium sand, accounting for 55.25% and 32.73% respectively. Fine sand accounts for 9.98%.The content of silty and coarse sand are less than 3%.The frequency curves of grain size are showing an approximate symmetrical unimodal distribution, and sand dunes have a slender tail on one side of the fine particles. The range of Mz is 1.98-2.41 Ф and the mean value is 2.23 Ф.The range ofσis 0.45-0.75 and the mean value is 0.57,which is good for middling sorting. The range of SK is 0.01-0.12,the mean value is 0.04,and kurtosis is positive. The range of KG is 0.94-1.01,the mean value is 0.97,and kurtosis presents a single peak. As the height and distance increasing, the Mz of the climbing dunes trends to be thinner first and later coarser, the sorting gets better.The variation trend of grain size characteristics of different parts of sand dunes is as follows: The Mz from the windward and the leeward slope to the top of the leeward is generally coarser, and the sorting is worse. The variation trend of SK is from near symmetry to positive deviation, and the KG has a medium sharp. The reason for its differentiation is mainly affected by the source and wind sorting. The analysis of the sources of the sediment reveals that the dune surface sediment is mainly from the floodplain. Comparing with the climbing dunes in the Yarlung Tsangpo River and the eastern Kunlun Mountains, the surface sediments of the climbing dunes in the study area is coarser and the sorting is relatively better. It indicates that the climbing sand dunes are closer to the source area, and the wind sorting effect is stronger in Dinggye than the other two areas.

Key words: Times New Roman", ,serif, font-size:10.5pt, climbing dune')">">climbing dune, grain size characteristics, Dinggye area