库布齐沙漠南缘抛物线形沙丘表面粒度特征

对库布齐沙漠南缘抛物线形沙丘特征断面上下层（0~5cm、5~10cm）沉积物采样分析结果表明，沙丘粒径与分选参数及其分布随沙丘形态、发育程度和植被生长状况发生变化。抛物线形沙丘丘体迎风坡下凹背风坡上凸，丘顶始终处于侵蚀亚环境。在顺风向断面，平均粒径从迎风坡脚到丘顶变粗，从丘顶到背风坡脚又变细，且这种变化在高大沙丘上更为明显；分选性在迎风坡为中等和较好，丘顶较差，顺风向到背风坡脚逐渐由中等变为较好；粒径频率曲线在丘顶双峰正偏，除迎风坡脚单峰正偏外，其余部位均单峰近对称。在垂直于风向的两翼断面，平均粒径在成熟沙丘由翼顶向两侧坡脚趋于变细，而在欠成熟沙丘无明显的变化趋势。翼间平地沉积物受植被等影响，平均粒径偏细但分选性差，偏度为正偏和极正偏，峰度为尖锐和非常尖锐。受不同时期风况的影响，成熟抛物线形沙丘上下层粒度参数在沙丘断面的分布较欠成熟沙丘一致。

Grain Size Distribution of Parabolic Dunes on the Southern Fringe of Hobq Desert

Choosing two parabolic dunes with different morphology on the Southern Fringe of Hobq Desert,we conducted sampling analysis on surface sediments both 0-5cm and 5~10 cm collected along typical transects.The results showed that grain size parameters and their distribution on parabolic dune were affected by dune morphology,vegetation cover,dune developmental stage,as well as their distance from the sand source.The parabolic dunes were characterized by concave stoss slope and convex lee slope,and dune apex was in a sub-environment which was eroded all the time.In the windward transects,particle size gradually became coarser from stoss slope toe to dune crest,and then became finer until lee slope toe.The higher the dune is,the more obvious the grain size varies with dune morphology.Sorting was moderate and good in the windward slope,poor on the dune top,and then became moderate and good until lee slope toe.Frequency curve of particle size was symmetrically unimodal except that dune apex was positively skewed and bimodal as well as stoss slope toe was positively skewed.In the two wings’ transect normal to wind direction,average grain diameter became finer from wing apex to bilateral slope in the mature dune,whereas no significant trends in the less mature dune.Compared with the body and two wings of parabolic dunes,the vegetation belt between arms received finer or more silty sand subsided by suspension,whereas sorting was poor for being mixed up with gravels.The frequency curve was bimodal and positively skewed.The grain size pattern on the less developed parabolic dune was more easily redistributed than the dune with a longer period development,which leads to differences in grain size parameters between 0-5cm and 5-10cm on the less mature dune.