腾格里沙漠东南缘格状沙丘粒度特征与成因探讨*

腾格里沙漠南缘格状沙丘表面沉积物的系统采样分析结果表明,粒径与分选参数在沙丘断面具有规律变化是形态-气流相互作用的结果.文中根据沙丘形态和气流状况,对格状沙丘成因及类型归属等问题作了探讨.认为格状沙丘发育在双向低风能环境,其中主梁为主风(西北风)作用下形成的横向沙丘,副梁则发育在主梁基础上并受制于主风和次主风(东北风)交替作用,在形态,沉积和动力学方面具有纵向要素特征.因此,该区格状沙丘属纵向要素叠置于横向沙丘之上的一种复杂型沙丘.

GRAIN-SIZE CHARACTERITICS AND MECHANISM OF NETWORK DUNE IN THE SOUTHEASTERN TENGGER DESERT

Two transect of samples were obtained from the ridges of the network dune in the southeastern fringe of Tengger Desert. The result shows that the grain size and sorting parameters vary with position on the both ridges of the dune due to the interaction between forms and flows. On the main ridge, mean grain size decreases and sorting improves from the bottom to the top, which can be explained in terms of that avalanching sands down slipsurface give rise to accumalation of coarser grains on the base of slipsurface and this grading mechanism reappears on windward slope where deflation takes place. On the secondary ridge, mean grain size becomes coarser from the mid slop to both the base and the crest while sorting becomes better from the base to the crest. The reason is that, two directional winds operating alternatively on this rigde result in erosion to take place on both windward slope and the lower part of leeward slope and deposition on the upper part of leeward slope near crest. According to the analysis of dune morphology and wind regime and supplemental observation of surface processes, the network dune in Tengger Desert is a complex form of longitudinal element (seconday ridge) and transverse dune (main ridge), in which the main ridge was formed in the dominent northwest wind while the secondary ridge was developed and maintained in an alternative bi directional wind regime.