毛乌素沙漠古河流湖泊的消退和风沙地貌演化过程研究

Located at the border of monsoon climate area, Mu Us Desert is more sensitive to the moonsoon activities. The sediments alternated among aeolian sands and fluvial sediments, lacustrine sediments or paleosol with the environment change. There are not only mobile dunes, semi-fixed dunes and fixed dunes, but also rivers and lakes in the Desert in the same time. The former researches suggested that fluvial sediments and lacustrine sediments were widespread during the late Pleistocene, then the river and lake contracted or disappeared and the aeolian activities expanded during phase periods, and resulted the landscape of modern Mu Us Desert. This project will survey geomorphologic pattern at present time, date some typical terrace or paleodunes and sediments sections, measure multi-proxies such as grain size, pollen, chemical composition, and magnetic susceptibility et al. By synthetical analyze the sedimentary faces and sediments characteristics of different locations of desert, we hope to recover the geomorphologic patterns of Mu Us Desert during different periods, reconstruct the extinction of rivers and lakes and aeolian landform evolution processes in Mu Us Desert since the Late Quaternary, and discuss the temporal-spatial coupling relationship among climatic changes, tectonic movement and geomorphologic patterns of desert, reveal the rules of desert development.

毛乌素沙漠位于我国季风边缘区，特点是对季风环流变化的反应更加敏感，特征是在时间上交替发育风成砂-河湖相沉积物或黑色砂质古土壤，空间上河流湖泊与流动沙丘、半固定沙丘、固定沙丘交错分布。在发展趋势上，自晚更新世早期广泛发育河湖相沉积物以来，河流湖泊呈阶段性消退，风沙活动的空间范围逐渐扩大，最终形成今天的地貌格局。本项目通过对毛乌素沙漠现代地貌格局进行野外调查，在对典型地貌体及沉积地层准确测年、环境演变代用指标分析测定的基础上，综合分析不同空间部位的沉积相和环境，重建晚更新世以来毛乌素沙漠河流湖泊消退与风沙地貌形成发育过程，恢复典型时段的河湖分布与风沙地貌格局，探讨毛乌素沙漠晚更新世以来气候变化、构造运动和沙漠地貌格局的时间与空间耦合关系。

毛乌素沙漠位于我国季风边缘区，空间上河流、湖泊与流动沙丘、半固定沙丘、固定沙丘交错分布，沙丘形态类型多样，不同类型沙丘可以相互转化。前人研究主要聚焦在该地区过去气候和环境的时间变化，而对于地表景观的空间变化关注较少。本项目通过对毛乌素沙漠现代地貌格局的野外调查，典型地貌体及沉积地层测年，环境代用指标分析测定，结合历史文献等综合分析重建了毛乌素沙漠河流湖泊消退、风沙地貌的形成演化过程。项目主要取得了以下研究进展：（1）出版了1:25万《毛乌素风沙地貌图》，查明了毛乌素沙漠不同活性和形态的沙丘类型及其空间分布特征。从活动性看，以半固定沙丘（地）为主，面积17633 km2，约占沙丘（地）面积的一半；从形态看，缓起伏沙地所占面积11616 km2，约占沙丘（地）面积的三分之一；（2）重建了全新世适宜期毛乌素沙漠湖泊的空间格局，该时期湖泊总面积为1697 km2，是现代湖泊总面积的5.8倍，当时普遍存在比现代湖面高出10~12 m的高湖面；（3）对孢粉、磁化率和色度等常用指标的环境意义进行了探讨，并运用于毛乌素沙漠晚更新世以来的环境重建。毛乌素沙漠8~3 ka BP为气候适宜期，早期较为湿润，湖泊发育；中后期较为温暖，湖沼、古土壤发育；3 ka BP以来风沙活动加强，逐渐接近现代环境；（4）全新世期间毛乌素沙漠并未出现统一的大湖，只是存在串珠状分布的小湖、浅滩。全新世晚期，无定河上游各条河流的溯源侵蚀贯通了被沙垄和沙地分割的大小湖泊；毛乌素东南部大量湖泊消亡，同时河流下切降低地下水位，对此时期活动沙地范围的扩大起到了重要作用；（5）以本项目第1标注发表的论文内容为素材，服务于国家高等教育人才选拔，获得了很好的效果。