新疆艾勒逊乌拉沙漠沙丘表层沉积物粒径及分形特征

Granularity and Fractal Characteristics of Surface Sediment in Sand Dunes of Arexunula Desert in Xinjiang Uygur Autonomous Region

[目的]对新疆艾勒逊乌拉沙漠表层沉积物粒度特征进行研究,旨在了解其地表沉积物粒度特征及影响沉积物粒度分布的因素。[方法]对沙漠及沙丘表层沉积物粒度进行粒级划分,并对粒度参数、分形维数分析。[结果]①研究区表层沉积物平均粒径为284.63μm,中砂为主,占48.93%;偏度为-0.18,呈负偏,距沙源近,搬运介质动力强;分选系数为1.10,分选性极好;峰度值为1.01,属常峰态,沉积物颗粒分布较均匀。②流动性沙丘和半固定沙丘表层沉积物偏度值分别为-0.13和-0.08,分别呈负偏、中等,两类沙丘粗砂砾较多;分选系数分别为1.66和1.76,均呈中等,沉积物粒度分布较均匀;峰度值分别为1.10和1.12,为常峰态和较窄峰,说明沙丘的粗颗粒沉积物在沙漠中相对集中。③流动性沙丘和半固定沙丘从迎风坡底到背风坡底表层沉积物的粒度平均粒径值依次分别为289.58,310.44,290.92,277.64,275.36μm和310.34,306.68,337.78,290.36,277.68μm,两类沙丘粗颗粒沉积物均集中在迎风坡。半固定沙丘迎风坡粗颗粒沉积物含量高于流动性沙丘迎风坡粗颗粒沉积物含量,半固定沙丘截沙能力更强;流动性沙丘和半固定沙丘的分选系数从迎风坡底到背风坡底变化趋势,前者波动大,呈W形变化,后者变化小,呈V形变化,灌丛植被使分选系数变化趋势在丘顶转折;④沙漠表层沉积物粒度的分形维数值是1.35,半固定沙丘和流动性沙丘表层沉积物粒度的分形维数分值别为1.59和1.34。分形维数的波动强度影响沉积物颗粒分布的均匀度、土壤肥力和植被生长。[结论]艾勒逊乌拉沙漠距沙源近,沙丘的粗颗粒沉积物在沙漠中相对集中,灌丛是影响表层沉积物粒度分布特征的因素之一。

[Objective]The granularity characteristics of surface sediments in the Arexunula Desert in Xinjiang Uygur Autonomous Region were studied in order to understand the characteristics of surface sediments in the study area and the factors affecting the granularity distribution of sediments.[Methods]Granularity was divided into grains,granularity parameters,and fractal dimension of the surface sediments for the Arexunula Desert and sand dunes in Xinjiang were analyzed.[Results]①The granularity size of surface sediments in the study area was 284.63μm,with medium sand dominant,accounting for 48.93%.The skewness was-0.18,with a negative bias,close to the sand source.The transport medium had strong dynamics.The sorting coefficient was 1.10,and the sorting performance was excellent.The kurtosis value was 1.01,which was a normal peak state,and the sediment particles were evenly distributed.②The skewness values of surface sediments of mobile sand dunes and semi-fixed sand dunes were-0.13 and-0.08,respectively,which indicated negative skewness and medium skewness,respectively,and there was a large amount of coarse gravel in both types of dunes.The sorting coefficients were 1.66 and 1.76,both of which were medium,and the sediment granularity distribution was relatively uniform.The kurtosis values were 1.10 and 1.12,respectively,which were normal and narrow peaks,indicating that the coarse-grained sediments of sand dunes were relatively concentrated in the desert.③The average granularity values of surface sediments from the bottom of the windward slope to the bottom of the leeward slope were 289.58,310.44,290.92,277.64,275.36,310.34 and 306.68,337.78,290.36,277.68μm,respectively.The coarse-particle sediments of the two types of sand dunes were concentrated in the windward slope.The coarse particle sediment content of the semi-fixed dune windward slope was higher than that of the mobile dune windward slope,and the semi-fixed sand dune had stronger sand interception ability.The sorting coefficients of mobile sand dunes and semi-fixed sand dunes changed from the bottom of the windward slope to the bottom of the leeward slope.The former fluctuated greatly and showed a W-shape,and the latter changed little and was V-shaped.Shrub vegetation made the sorting coefficient change trend turn at the top of the dune.④The fractal dimension value of the grain size of desert surface sediments was 1.35,and the fractal dimension values of the particle size of semi-fixed sand dunes and mobile sand dunes were 1.59 and 1.34,respectively.The fluctuation intensity of fractal dimension affected the uniformity of sediment particle distribution,soil fertility,and vegetation growth.[Conclusion]The Arexunula Desert is close to the sand source,and the coarse-grained sediments of the dunes were relatively concentrated in the desert.Shrubland is one of the factors affecting the granularity distribution characteristics of surface sediments.