库姆塔格沙漠典型线形沙丘粒度特征

对库姆塔格沙漠不同区域典型线形沙丘不同地貌部位的表层沉积物进行了粒度分析。结果表明：线形沙丘沙物质组成的优势粒级为中沙、细沙和极细沙，所占比重分别为28.85%、30.92%和25.98%。根据沙丘剖面形态和粒度特征，该沙漠的线形沙丘可分为两大类，第一类剖面形态不对称，沙物质由沙丘两翼底部向脊部逐渐细化、分选变好，分布于沙漠的东北部、中部、南部和西部；第二类剖面形态较为对称，沙物质在两翼中部最细，脊部最粗，坡脚次之，分选性无明显变化规律，分布于沙漠的东部。对这两类线形沙丘粒度特征的形成原因做了探讨，初步认为第一类是沙物质经风选的结果，而第二类则是风选、物源风化等综合影响的结果。

Grain-size Characteristics of Typical Linear Dunes in the Kumtagh Desert

The sediment samples from different geomorphological positions of typical linear dunes were collected in the northeastern, eastern, central, southern and western parts of the Kumtagh Desert which is located in the west of China, and analyzed by means of sieving. The results show that the main grain composition of linear dunes is medium sand, fine sand and very fine sand, their proportions being 28.85%, 30.92% and 25.98% respectively, and the cumulative content of these three size fractions accounts for different percentages in the surface sediments of the foot and middle of windward slope, the top of the dune, the middle and foot of leeward slope, being 69.45%, 90.62%, 91.72%, 96.22% and 80.72% respectively. The linear dunes in the Kumtagh Desert are divided into two categories according to the profile shape and the characteristics of grain size parameters of the dunes. The profile shape of the first type is not symmetrical, their sediments gradually tend to become finer, better sorted from the foot to the top on both slopes, and the dunes of the first type are distributed in the northeast, central, southern and western desert. The profile shape of the second type is more symmetrical than that of the first type, the sediments on two middle slopes are the finest, those on the top are the coarsest and those at the foot take second place, and the sorting characteristics show no obvious regularity. The dunes of the second type are located in the east of desert. This paper discussed the causation of grain size characteristics of two types of linear dunes, and drew a preliminary conclusion that the formation of the first type of linear dunes is mainly caused by wind sorting, while the second type of linear dunes are the results of wind sorting and the source of sediments, and may be caused by underlying physiognomy, weathering and wind sorting as well.