基于风积物光释光测年的末次盛冰期以来腾格里沙漠南缘演化研究

Quaternary climate was characterized by alternation of glacial and interglacial periods. Northern China’s deserts and their borders have changed significantly during these periods. The Last Glacial Maximum (LGM) and the Holocene Optimum (HO) were two important climate stages during the late Quaternary and northern China’s deserts were characterized respectively by mobilization (expansion) and stabilization (contraction). The Tengger Desert is a major source of dust for the Chinese Loess Plateau and its surrounding areas as well as being considered a key source of atmospheric dust loading in the Northern Hemisphere. Early studies of stratigraphic chronology in the south margin of the desert were mainly based on thermoluminescence (TL) dating and radiocarbon (14C) dating. Optical stimulated luminescence (OSL) dated sedimentary records are limited. In this project we intend to conduct systematic and multiple-site sampling and OSL dating in an area along the southern margin of the Tengger Desert to reveal history of aeolian activity in this region since the LGM. OSL chronologies, sedimentary records, and locations of various sections will be combined to reconstruct the south border of the Tengger Desert during the LGM and HO. The relationship between climate change and desert evolution will be investigated and major forcing factors that control the transition between mobilization and stabilization of sand dunes will be discussed to improve understanding of desertification and its forcing mechanism. This project may provide valuable insight into modeling and forecasting future desert evolution in arid region and have important practical significance for combating increasingly serious desertification.

第四纪气候以冰期–间冰期循环为主要特征，在此期间，中国北方沙漠与沙地分布格局发生了大幅变化。末次盛冰期（LGM）与全新世大暖期（HO）是晚第四纪以来的两个重要特征气候期，中国北方沙漠与沙地分别以活化扩张、固定收缩为主要特征。腾格里沙漠是中国黄土高原乃至北半球地区的重要粉尘物源区，先前对该地区的风积物地层年代研究以热释光与碳十四测年为主，光释光（OSL）年代较少。本项目拟对腾格里沙漠南缘地区进行系统性、高密度的风积物剖面OSL样品采集与年代测定，结合沉积地层重建该地区LGM时期以来的风沙活动历史；根据不同剖面的位置关系重建沙漠南缘LGM与HO时期的边界格局。探讨气候变化与沙漠空间分布格局变化之间的内在联系，揭示影响沙丘从流动向固定转变的主要强迫因子，以期加深对沙漠化过程及其驱动机制的认识。研究结果将为模拟与预测干旱地区未来沙漠演化提供科学支持，对治理日益严重的土地沙漠化具有重要实践意义。

腾格里沙漠是中国黄土高原乃至北半球地区的重要粉尘物源区，晚第四纪时期经历了显著的扩张与退缩。重建该地区历史时期的风沙活动记录对揭示气候变化与沙漠化之间的内在联系有重要意义。光释光（OSL）测年法是测定第四纪风积物埋藏年代的一种可靠方法，但之前对该腾格里沙漠南缘风积物地层的研究中OSL年代较少。本项目对腾格里沙漠南缘进行高密度风积物OSL采样，并使用单片再生（SAR）与标准生长曲线（gSGC）相结合的方法来估计这些样品的埋藏年代。在测得的91个风积物样品年代中，最老的风成砂堆积于氧同位素（MIS）3阶段，最老的黄土堆积于MIS6阶段。在MIS3与MIS2期间，黄土与风成砂均有发育。在45–23 ka、8–4 ka时段内风成砂堆积很少。对粒度与剖面沉积速率分析表明，腾格里沙漠南缘地表风力强度显著增加的3个时段为23–20 ka、18–15 ka、13–11 ka，与东亚夏季风强度减弱期一致。研究表明，不能笼统的将风成砂堆积作为沙丘活化而将黄土堆积作为沙丘固定的标志，在夏季风盛行时期，黄土沉积物会明显多于风成砂沉积物，地表风积物的沉积速率较低；而在弱夏季风条件下，黄土与风成砂都会发生堆积，风积物的沉积速率较高。