库姆塔格沙漠的形成时代与演化

Formative age and evolution of Kumtagh Desert

库姆塔格沙漠腹地广泛出露含古风成砂的第四纪地层剖面。根据含古风成砂地层剖面的野外调查与地层年代的室内分析结果,并与已有的周边区域地质资料对比分析,库姆塔格沙漠形成至少始于早更新世初,到中更新世晚期285.9±42.9 ka BP沙漠已大面积扩展形成,奠定了现代沙漠环境格局。沙漠最初从西南部开始形成,之后向北和东北扩展。依据梭梭沟地层剖面,沙漠在第四纪演化过程中至少经历了19个沙漠正、逆过程旋回,平均周期约为110 ka。新构造运动对沙漠的形成演化和地貌的形成发育具有重要作用,构造了山间断陷盆地并使其逐渐向封闭的干旱盆地演化形成沙漠,受四周断裂控制沙漠整体形态呈"扫帚状"。分布在沙漠北部的独特砾石体地貌形成于晚更新世末(285.9±42.9)ka BP之后。

The ancient aeolian sand has been thought of as the indicator that can indicate the formation and evolution of desert during the past time.Kumtagh Desert is located in the northen fringe of the Qinghai-Tibet Plateau.The first integrated scientific investigation of the desert had been completed in 2004-2006.Kumtagh Desert,where the Quaternary stratigraphic profile containing ancient aeolian sands is widely distributed,is a natural ideal model for studying the formation and evolution of desert.The comprehensive field investigation and studies on sedimentary,chronology and palynology of typcal profiles named Suosuo gully,Xiaoquan gully and gravel body with ancient aeolian sand layers showed that the Kumtagh Desert probably originated as early as（2 097.7±314.7） ka BP.During the period of（386.9±58.0）-（285.9±42.9） ka BP,the desert largely extended and established its modern distributional pattern.The desert developed originally in the southwest part of desert,subsequently,extended to the north and northeast.The sedimentary face of Suosuo gully profile revealed that the desert experienced at least 19 advance and inverse processes of desertification with average period of 110 ka during its evolution in the Quaternary.The neotectonic movements played an important role in the formation and development of the desert and its geomorphology.On the one hand,it caused the formation of intermontane fault basin,which was further developed towards the closed drought basin,and furthermore caused the formation of the natural environment for the desert formation.On the other hand,under the control of surrounding faults,the unique broom-shaped desert landscape was formed,and the gullies and sand ridges in this region experienced an abrupt directional change from north by west to north by east at the location of 39°45′-39°55′N.The unique landscape of gravel body occurred widely in the northern desert was formed after（285.9±42.9） ka BP.The results in this paper further provide scientific basis for investigating the formative age and evolutionary process of dry climate and environment in the north-western Chinese region,and the uplifting of Qinghai-Tibet Plateau as well as its responses to the global climatic changes.