巴丹吉林沙漠沙山发育与环境演变研究

Study on Mega Dunes Development and Environmental Change in Badain Jaran Desert

通过对巴丹吉林沙漠风沙地貌、沙山地层结构、古沙山层理构造、沙山TL测年和区域输沙率等的综合研究表明 ,巴丹吉林地区自西北而东南大致可划分为河湖为主的弱水冲洪积扇、以河湖与风沙交替作用过度区和以风沙作用为主沙丘区。弱水冲洪积扇的发育为沙漠、沙山的发育提供了丰富的沙物质来源。高大沙山是更新世期间起伏的沙质下垫面与西风环流和季风环流相互作用的结果。末次冰期以前为西风环流为主时期 ,地表主导风向为西风 ,次为西北风 ,河湖环境发育 ;末次冰期以来为东亚季风环流为主时期 ,地表盛行风向为西北风 ,次为西风 ,风沙活动盛行。期间 ,风积床面经历了新月形、新月形沙丘链、复合新月形、复合沙丘链到复合型高大沙山的一系列复合、演变与发展过程。

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.