腾格里沙漠覆盖区晚第四纪大湖期的多手段测年及高湖面成因研究

过去认为我国西部地区深海氧同位素三阶段晚期的气候较为湿润，普遍出现高湖面"大湖期"，"腾格里大湖"就是其中一个典型实例。近年来对"大湖期"的时间提出了异议。本项目拟在位于"腾格里大湖"中心的白碱湖地区钻取完整地层记录，并对其高湖岸进行系统调查，运用OSL、AMS C-14和古地磁方法测定高湖面地质记录的年代，在交叉检验可靠性的基础上厘定白碱湖地区高湖面的确切时代。通过孢粉组合恢复晚第四纪最高湖面时段的植被状态，通过介形虫优势种属和主要易溶盐类型恢复湖水盐度，重建高湖面时段的气候状况。通过可能补给水源及地层中古湖水载体的87Sr/86Sr比值测量，分析晚第四纪湖泊不同发展阶段的主要补给水源，解析腾格里沙漠区晚第四纪高湖面的成因。本研究不仅有助于明确回答腾格里沙漠覆盖区晚第四纪高湖面的确切时间和成因，而且能为回答MIS3a时段我国西部地区的气候是否真正有别于全球其它地区这一科学问题提供依据。

MIS 3a was commonly considered a relatively humid period with high lake levels in large areas of western China, and Megalake Tengger (MTG) is a representative huge lake with high lake level at that time in the Tengger Desert. However the time of these high lake levels is being argued by recent researches. In this proposal, a comprehensive research focusing on timing and probing formation of the highest lake level based on complete sedimentary sequence as well as shorelines is proposed to be undertaken in the middle part of MTG, Lake Baijian. By using multiple dating methods including OSL, AMS radiocarbon and paleomagnetic dating, age of the sedimentary sequence as well as littoral sediments around Lake Baijian will be measured, and the definite age of the highest lake level will be determined based on cross-correction of the ages obtained. Through analysis of pollen assemblage and type of dominant soluble salt in the sedimentary documents, the ecological environment and salinity of lake water at the highest lake stage will be reconstructed. Basing on hydrological tracking, analysing the 87Sr/86Sr ratios of all potential water sources and water of the paleolake at different stage, the main water source of the highest lake level stage will be identified and formation of the highest lake will be discussed. This research will not only contribute to provide a definite age of the highest lake level in the area of Tengger Desert, helpful to answer whether climate of western China during MIS 3a stage is actually abnormally humid or not, but also provide insights to understand environmental evolvements in the present desert covered areas.