西藏定结地区爬坡沙丘粒度特征分析

通过对西藏定结地区典型爬坡沙丘表层沉积物的形态参数、粒度组成和粒度参数等进行分析，揭示其粒度特征。结果表明：（1）爬坡沙丘表层沉积物以细砂和中砂为主，极细砂含量较少，同时含有少量粉砂和粗砂，不含粘土成分。（2）沙丘平均粒径范围1.98~2.41 Ф，分选系数变化范围为0.45~0.75，属中等分选，偏度变化范围为0.01~0.12，呈近对称至正偏分布，峰度变化范围为0.94~1.01，呈中等尖锐峰态。（3）从样品PPSQ1~PPSQ6，随着高度和距离的增加，沙丘表层沉积物平均粒径先变细后变粗，分选不断变好。（4）爬坡沙丘表层沉积物主要来源于河漫滩。（5）与雅鲁藏布江、东昆仑山地区爬坡沙丘对比可知，定结地区的沙丘粒径较粗，分选较好，主要是物源及风力分选作用的共同结果。

Grain size characteristics of the climbing dunes in Dinggye area of Tibet

Theclimbing dunes are widely distributed in Dinggye area of Zigaze Prefecture, Tibet,China, and the surface sediment grain size characteristics are of greatsignificance for exploring the development process of sand dunes. In thispaper, six climbing dunes sand were collected in the area. In order to revealthe grain size characteristics, the study analyzed the morphologicalparameters, mechanical composition and grain size parameters of surface sedimentsof the dunes, which provide a theoretical basis to reveal the climbing dune’s formation mechanism on theQinghai-Tibet Plateau. The current researches were mainly concentrated on theclimbing dunes in coastal areas rather than that in arid areas. Studying theclimbing dunes on the Qinghai-Tibet Plateau can explore the grain sizecharacteristics of climbing dunes in inland arid regions. The results aresummarized as follows：The surface sediments ofclimbing dunes are mainly composed of silver sand and medium sand, accountingfor 55.25% and 32.73% respectively. Fine sand accounts for 9.98%.The content ofsilty and coarse sand are less than 3%.The frequency curves of grain size areshowing an approximate symmetrical unimodal distribution, and sand dunes have aslender 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 is0.57,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. Therange of KG is 0.94-1.01,the mean value is 0.97,and kurtosis presents a singlepeak. As the height and distance increasing, the Mz of the climbing dunes trends to be thinner first and latercoarser, the sorting gets better.The variation trend of grain sizecharacteristics of different parts of sand dunes is as follows: The Mz from the windward and the leewardslope to the top of the leeward is generally coarser, and the sorting is worse.The variation trend of SK is fromnear symmetry to positive deviation, and the KG has a medium sharp. The reason for its differentiation is mainlyaffected by the source and wind sorting. The analysis of the sources of thesediment reveals that the dune surface sediment is mainly from the floodplain. Comparingwith the climbing dunes in the Yarlung Tsangpo River and the eastern KunlunMountains, the surface sediments of the climbing dunes in the study area iscoarser and the sorting is relatively better. It indicates that the climbingsand dunes are closer to the source area, and the wind sorting effect isstronger in Dinggye than the other two areas.