新月形沙丘粒度分布的交替过程——以甘肃省河西沙区绿洲边缘积沙带为例

新月形沙丘是一种常见的沙丘类型，甘肃河西走廊沙区绿洲边缘积沙带上存在大量新月形沙丘。通过对河西走廊沙区新月形沙丘全面调查取样和在民勤沙区重复取样测定，分析了新月形沙丘的粒度特征。结果表明，新月形沙丘和新月形沙丘链表层0~5 cm深度以细沙和中沙为主，其中古浪沙区沙粒较细且与金昌、临泽、金塔和民勤沙丘的粒度差异较大；主风向（NW）过程从沙丘迎风坡底部到沙丘顶部粒度由粗变细，即沙丘顶部粉沙最多，其次是背风坡中部；迎风坡底部粗沙最多，其次是迎风坡中部。反风向（SE）过程从沙丘迎风坡底部到沙丘顶部粒度由粗变细再变粗，即迎风坡中部粉沙最多，其次是沙丘顶部；迎风坡底部粗沙最多，其次是迎风坡中部。主风向过程沙丘粒度的标准差和变异系数较大，而反风向过程沙丘粒度的标准差和变异系数相对较小。主风向和反风向2种过程，导致了沙丘各部位粒度的交替变化。由于观测的季节不同，才导致了有关新月形沙丘迎风坡粒度分布的2种不同结论。 

Alternating Processes of Distribution of Grain Size over Barchan Dunes:A Case Study of Accumulated Sand-belts of Oasis Edge of Hexi Desert Area of Gansu Province

Barchan dunes is a common dune type.There are a lot of barchan dunes at accumulated sand-belts of the oasis edge of Hexi desert area of Gansu.Characteristic of grain size were analyzed by comprehensive investigation and sampling in the Hexi Corridor desert area，and repeated sampling and determination in Minqing desert area.The surface layer of crescent dunes and crescent dunes was mainly composed of fine sand and medium sand at 0-5 cm depth.The sand grains in Gulang sandy area were finer and grain sizes were quite different from those of Jinchang，Linze，Jinta and Minqin dunes.The grain size of the main wind direction （NW） process from the bottom of windward slope to the top of dune changes from coarse to fine; the bottom of windward slope has the most coarse sand，followed by the middle of the windward slope.The grain size of reverse wind direction （SE） process from the bottom of the windward slope of dune to the top of dune changes from coarsening to fining and then to coarsening.The bottom of windward slope has the most coarse sand，followed by the middle of windward slope.The standard deviation and variation coefficients of dune grain size in the main wind direction process were larger than those in reverse wind direction process.The two processes of main wind direction and reverse wind direction lead to the alternate change of grain size in each part of the dune.Because of the different of seasons observed，two different conclusions about the distribution of grain size of windward slope of crescent dune were drawn.