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

Key words: 
•   /
• parabolic dune /
• grain size /
• Hobq /

Abstract: 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.