晚更新世以来浑善达克沙地北部及毗邻地区古水文及气候、地貌演化

Although aeolian sand widely develop in the desert area of China, much less paleoenvironmental records have been obtained comparing with the other deserts in the world. The paleoenvironmental interpretation of the aeolian sand archive is complicated by the complexity and short memory of the aeolian sand deposit system, which is particularly true for the east part of the desert belt in northern China. Reconstruction of the geomorphic processes from the earth system perspective has emerged as an effective way to overcome the complexity of the deposit system of the desert. In the dryland, water deeply involved in the geomorphic processes. Critical information referring to the past environmental conditions could be obtained through paleohydrological studies. In this project, the northern Hunshandake Sandy Land and adjacent areas, which is located in the east part of north China desert belt and poorly studied in the past, is selected as the study area. An integration of geomorphological, sedimentological, geochronological, remote sensing and GIS approaches are used to reconstruct the late Pleistocene paleohydrology, followed by the investigation of the earth surface processes. The paleoclimatic conditions will be reconstructed quantitatively and mechanism for the environmental changes will be investigated. This project would provide not only valuable data of the late Pleistocene environmental conditions for the eastern desert belt of China, but also an insight into the connections between climate changes and earth surface processes in the dryland, which is of great importance for the desertification control in the north China.

相比于世界其它沙漠，我国沙丘覆盖面积虽大，但直接来自沙漠、沙地的古环境记录偏少，且由于风沙沉积过程复杂、记录的时间尺度较短，致使第四纪古环境研究相对薄弱，亟待深入和加强。这一问题在我国东部半干旱区尤为突出。从地球系统科学的角度出发，重建地表过程是破解沙漠地区沉积系统复杂性的有效途径和发展趋势。在干旱、半干旱区，水是地表过程的重要参与者，古水文遗迹蕴含着环境变化的关键信息。本项目拟以位于北方干旱区东缘的浑善达克沙地北部及毗邻地区为研究区，利用地貌学、沉积地层学和年代学等方法，结合遥感与地理信息系统等手段，以古水文重建作为切入点，对晚更新世以来的地表过程展开研究，进而定量重建古气候，探讨环境变化机制，揭示现代地貌格局的成因和演化过程。通过本项目的实施，可为我国东部半干旱区晚第四纪古环境研究提供宝贵的数据资料，提高对干旱区气候变化与地表过程的理论认识水平，为我国北方荒漠化防治决策提供科学支持。

干旱区古环境变化与地表过程研究对认识气候变化历史和评估全球变暖下的荒漠化具有重要意义。本项目以浑善达克沙地为研究区，重建了晚更新世以来的水文演化历史及古气候，探讨了湖泊演化与粉尘记录的关系，初步研究了浑善达克沙地沉积物粒度粒形特征及地表过程指示意义。本项目利用释光和铀系测年方法，建立了浑善达克地中西部晚更新世以来古水文演化年代框架。通过获取大量地质记录厘清和夯实了这一地区古水文演化过程。利用水量平衡模型对古降水进行了定量重建，研究认为MIS 5与全新世高湖面时期较现代降水量分别高120-150%和80-110%，广泛存在的湖相沉积露头与规模巨大的古河道指示浑善达达克沙地晚更新世湿润时期降水量可能高达1000 mm以上。地貌与地层年代结果显示，浑善达克沙地西部存在强烈的风蚀作用。MIS 5时期浑善达克沙地及戈壁荒漠地区显著湿润的气候可能是导致MIS 4时期东亚及北太平洋粉尘较MIS 2时期偏高的重要原因。浑善达克沙地不同沉积物粒度粒形分析表明，风力和植被因素导致风沙粒度自西向东逐渐变细。风沙沉积与河湖相沉积在粒形上具有显著差异，浑善达克沙地风沙可能是河湖相沉积物经历了长期地表过程作用的结果。