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

[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] ① The granularity size of surface sediments in the study area was 284.63 μm, 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. ② The 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. ③ The 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, 277.68 μm, 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. ④ The 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.