Abstract:

Dendritic dune is a unique type of dune landform in Gurbantunggut desert. This paper analyzes the grain size and micromorphological characteristics of the surface sediments of the dendritic dunes in the Gurbantunggut Desert. The results show that： （1） The dendritic dunes are dominated by medium sand， followed by fine sand and coarse sand. There is a good linear relationship between the average particle size and the separation coefficient. The smaller the average particle size， the better the sorting coefficient. The sedimentary environment is dominated by rivers and lakes. The shape of quartz grains is mainly round and long and the roundness is moderate. Dished pits are widely distributed and accompanied by the phenomenon of silicon precipitation， indicating that the deposition is mainly mechanical and accompanied by chemical action. （2） On the whole， the coarse sand and extremely coarse sand account for the most in the west while fine sand in the south， which is the result of wind separation. The sorting in the west is better than that in other regions while the sorting in the east is worse. The roundness in the west is the best while the roundness in the south is the worst. The medium sand at the top of the slope accounts for a large proportion. The content of coarse sand on the windward slope is higher than that of the leeward slope while the fine sand and medium sand content at the foot of the windward slope is much higher than that on the leeward slope. The proportion of grain size in the two wings of sand dune is relatively consistent. （3） The characteristics of grain size and micromorphology indicate that the dendritic sand dunes are mainly affected by wind separation as well as by material sources and vegetation， which jointly reveal the sedimentary environment of rivers and lakes.

Key words: Gurbantunggut Desert, dendritic sand dunes, grain size, micro-morphology, depositional environment