关键词: 巴丹吉林沙漠, 高大沙山, 古沙山, 风系, 环境变化

Abstract: High mega dunes in the Badain Jaran desert, ranging generally from 200 to 300 m in height and maximum 500 m or more are seldom seen in other sand seas of the world. On-the-spot investigation for the Badain Jaran desert and a series of research work, including sand dune types and their spatial features, mega dunes strata and TL dating, paleo-wind direction measurement and modern wind data analysis etc. suggest that the Badain Jaran area can be zoned approximately into three landscape-sedimentation zones from NW to SE. Among them Ruoshui alluvial fan is characterized by an alternation between alluvial and lacustrine sedimentation. Yadan zone is characterized by an alternation between alluvial-lacustrine and eolian sand sedimentation. The wide dune field has been dominated by continuous wind-blown sand sedimentation since the Quaternary, which indicates that the formation and growth of high mega dunes in the Badain Jaran desert are controlled by sand source, prevailing wind patterns, underlying relief of mega dune and vegetation on sand dunes. Ruoshui system developed in the western and northwestern Badain Jaran area was a main sand source for the formation and growth of high mega dune. Dips from fossil sand dune cross-bedding and steep-face orientations in three localities distributed in the Badain Jaran desert demonstrated that the prevailing palaeo-wind patterns over the Badain Jaran desert was variant throughout the Quaternary. Before the last Glaciation westerly winds originating from westerly circulation predominated, but there were also important northwest winds from East Asian monsoon circulation. Since the last Glaciation northwest winds have been dominating the area but there were also relatively important westerly winds in the processes of mega dune growth. Simultaneously, the initialing of the mega dunes was related to the wave-like airflow motion caused by the intimidation from underlying hilly relief that become a obstacle against moving wind-blown sand. The shrubs and grasses on sand dunes fed by rainfall during stronger summer monsoon, encourages the growth and development of mega dunes by trapping and accumulating upwind wind-blown sand and combating wind erosion as well as promoting roughness over dune surface. With integrated respect to the four factors the eolian landform in the area experienced a development in time from barchans?barchanic ridges→compound barchans?mega barchans?high mega dunes during the Quaternary.

Key words: Badain Jaran desert, high mega dune, palaeo-sand dune, wind regime, environmental change