柴达木盆地盐湖周边灌丛沙丘年代学及演化

Qaidam basin is considered as a major source area for Asian mineral dust and the wind-sand activities are strong in this region. While great amount of dust was exported from the Qaidam basin, the aeolian sediments deposited in the margin of the basin could develop some aeolian landforms, for example, modern moving sand dunes, nebkhas and so on. Considered as an aeolian landform, the nebkhas must contain the regional sand process, the climatic variation, the paleoenvironmental evolution and some other information. At present, the chronology and evolution of the whole development process of nebkhas have not yet been systematically studied. Therefore, with the nebkhas as the research objects in Qaidam basin, the ground penetrating radar(GPR) technique by combining with the field observation of the natural outcrop sections and the artificial exploratory trench profiles will be used to detect the aeolian deposits sequences of the nebkhas. The chronological framework will be constructed with the optically stimulated luminescence(OSL) dating, and the reliability of OSL dating data will be tested by AMS14C dating. In the mean while, the grain-size analysis with high density sampling will be devoted to distinguish the formation of the different layers in nebkhas. Then, based on the OSL chronology, the evolution sequence of the nebkhas around salt lakes in Qaidam basin will be reestablished and the influence factors and dynamic mechanism of the nebkhas will be discussed. Besides, the changing process of the regional paleo-wind directions will be reestablished, and the wind strength change of the East Asian summer monsoon, the westerlies and the Indian monsoon will be discussed, too. This study is quite important to understanding the chronology of nebkhas and the response to regional environment change, it also will be very meaningful to enrich the researchment of the sand geomorphology and desertification science of the plateau inland basin in China.

柴达木盆地盐湖周边灌丛沙丘广泛发育，其在反映区域风沙活动及荒漠化方面已得到较多关注，但有关其整个发育过程的年代学及演化目前还未开展系统的研究。因此，本项目以柴达木盆地盐湖周边灌丛沙丘为研究对象，运用地质雷达（GPR）探测，结合天然剖面、人工探槽等获取灌丛沙丘的沉积构造，划分其沉积序列；采用OSL测年，结合AMS14C年龄校验，确立研究区灌丛沙丘发育的年代学框架；对灌丛沙丘典型剖面高密度采样，进行沉积物粒度参数实验和成因分析。以研究区灌丛沙丘沉积序列及年代学框架为基础，重建柴达木盆地盐湖周边灌丛沙丘演化过程，探讨其沉积演化的影响因素及成因机制，并初步尝试对区域古风向变化过程进行重建。本研究对深入了解柴达木盆地灌丛沙丘发育过程的年代学及沙丘演化对区域环境变化的响应等方面有重要作用，并在丰富和完善我国高寒、极旱的高原内陆盆地风沙地貌学和沙漠化科学研究方面有一定的理论和实践意义。

柴达木盆地盐湖周边灌丛沙丘广泛发育，但有关其发育年龄、物源及其对气候环境、风沙活动的响应过程尚不清楚。为此，对该区域灌丛沙丘进行了沙丘年代、沉积物稀土元素特征等方面的研究，并结合柴达木盆地周边区域风沙活动、古气候变化的研究成果，探讨了灌丛沙丘发育年龄及过程、物质来源及其对干旱环境的响应关系。结果表明：柴达木盆地盐湖周边灌丛沙丘自末次冰盛期以后开始发育，且沙丘年龄变量与深度变量之间存在Y=0.188X+0.276的方程式，其相关系数R2=0.539，置信水平为0.99，呈极显著相关。随气候变干，灌丛沙丘在中、晚全新世以后达到较大规模，其形成发育是对全新世干旱气候的响应过程，并对35°N夏季太阳辐射强度变化、新仙女木事件有较好反映。全球末次冰盛期以后，随气候转暖东昆仑山冰川融水携带的第四纪沉积物在山麓形成的冲洪积扇碎屑经风化、搬运、沉积过程，为灌丛沙丘发育提供了丰富的物质基础；其风沙物质来源并非气候干旱期湖水退缩后湖底沉积物的风化产物。此外，冰川融水可能为植被生长提供了必备条件，植被发育为灌丛沙丘发育提供了保障。