巴丹吉林沙漠高大沙山的形成发育研究

通过对巴丹吉林沙漠高大沙山的考察，以及沙丘形态和风况、沙山TL测年、古沙丘层理产状等的研究表明，高大沙山的形成发育受沙源、风系、底基地形和灌草植被等因素的影响。第四纪以来弱水古水系的变迁为沙漠及沙山的发育提供了丰富的沙物质来源。沙山发育的受西风和西北风两大盛行风系的控制，末次冰期以前为西风环流主导时期，地表盛行风向为西风，次为西北风；末次冰期以来为季风环流主导时期，地表盛 行风为西北风，次为西风。沙山底基地形的起伏不仅诱发近地表气流产生波伏运动，同时也是风沙流运行的障碍。气候湿润期发育的沙丘灌草植被通过抑制风蚀、扑捉风沙等作用加速沙山的发育。高大沙山是新月形沙丘和沙丘链、复合新月形沙丘和沙丘链演进而形成的大型稳定风积床面形态。

Formation and Growth of High Megadunes in Badain Jaran Desert

High megadunes in the Badain Jaran desert, with a height rangingfrom 200 to 300 m in general and maximum height of 500 m or more are seldom seen in the other sand seas of the world. Up to present no much work associated with the formation and growth of high megadunes have been done. On-the-spot investigations of the Badain Jaran desert and a series of research work, including sand dune types and their spatial features, megadunes strata and TL dating, palaeowind direction measurement and modern wind data analysis, indicate that the formation and growth of high megadunes in the Badain Jaran desert are controlled by sand source, pre vailing wind patterns, underlying relief of megadunes and vegetation on sand dun es. Ruoshui system developed in the western and northwestern Badain Jaran area w as a main sand source for the formation and growth of high megadunes. Dips from fossil sand dunes cross-bedding and steep-face orientations in three locaties distributed in the Badain Jaran desert demonstrate that the prevailing palaeowind patterns over the Badain Jaran desert are at variance throughout the Quaternar y period. Before last glaciations westerly winds originating from westerly circu lation predominated but that there were also important northwestly winds from East Asian monsoon circulation at the time of high megadune growth. Since last glaciations, northwestly winds have dominated the area but accompanied also with the relatively important westerly winds in the processes of megadune growth. Simul taneously, the initial stages of the magedunes are related to the wave-like air flow motion caused by the intimidation from underlying hilly relief which become an obstacle against moving wind blown sand. The shrub and grass on sand dunes, fed by rainfall during stronger summer monsoon, encourages the growth and development of megadunes by trapping and accumulating upwind windblown sand and combating wind erosion as well as promoting roughness over dune surface. Intergrated aeolian bedforms in the area went through a temporal development process from ba rchans, barchanic ridges, compound barchans, megabarchans to high megadunes sinc e the Quaternary.