Variation of grain sizes on a mountain climbing dune in Mainling wide valley,Yarlung Zangbo River
雅鲁藏布江米林宽谷段爬升沙丘粒度分异特征研究

Mountain climbing dunes are widely distributed in the Mainling wide valley of Yarlung Zangbo River,southern Qinghai-Tibet Plateau.The climbing dunes studied are located on the right bank of Yarlung Zangbo River at an S-shaped meander,west of Wolong town.Samples are collected according to dune climbing height and sites of super-imposed dunes along prevailing wind(NE).As parts of the aeolian sand dune system in the valley,sediments are also sampled on dunes developing on the alluvial flat and terrace.Grain size analysis shows that sediments of the mountain climbing dune are generally characterized by fine and very fine sands(2.07 to 3.71Φ),moderately well sorting(0.20 to 1.41Φ),fine skewness(-0.33 to 0.61) and multi-mode grain size distribution with kurtosis ranging from 0.66 to 3.09,exhibiting some features of both succession and variation from those of sand dunes on the upwind marginal alluvial flat and river terrace.Grain size parameters vary with height in NE-SW wind direction from the toe to the top of the climbing dune with mean grain size getting finer,sorting better,skewness coarser and kurtosis lower.Also,grains on super-imposed dunes grow coarser and sorting poorer from toe to dune top.There are some correlations between grain size and height,which shows a positive correlation for very fine sands with height and a negative relation for fine sands and height.The variation of grain sizes with height reflects different climbing ability for grains with different sizes.There exist differences in grain size characteristics between ridges and inter-ridge grooves of strip-shaped dunes.