光释光年代学对腾格里沙漠化机制及风沙物源的指示

腾格里沙漠地处东亚夏季风现代影响区的西北边缘，长期以来被认为是东亚沙尘暴多发中心之一。近年来的研究较明确地支持腾格里沙漠晚更新世以来的沉积环境发生了巨大变化，但该区沙漠化的机制仍需进一步研究。文章基于石英矿物的光释光测年技术，研究了腾格里沙漠南部腹地系列剖面的沉积年代，结合已有研究结果，重建了该区风沙堆积历史，获得如下认识：1）腾格里沙漠末次冰盛期以来的风沙堆积主要集中在16~10 ka及约1.5 ka以来两个时段；2）腾格里地区16~10 ka的风沙堆积发生在区域由干变湿的时段，而7.3 ka、5.1 ka和3.8~3.3 ka的风沙堆积发生于区域湿度较高背景下的干旱时段。由于这些时段的气候环境有利于风沙的堆积与固定而不利于风沙的产生，因而推断16.0~3.3 ka时段腾格里地区的风沙主要来自上风向地区的输入；3）腾格里大面积地区的沙丘/沙山堆积于最近0.37 ka以来降水较少的时段，略晚于区域高强度的人类工程活动，表明现今可见的沙丘/沙山地貌景观的形成是人类高强度工程活动触发、就地起沙的结果。

OSL CHRONOLOGY OF SEDIMENTS IN THE TENGGER SANDY DESERT AND ITS INDICATION TO AEOLIAN SAND SOURCE AND DESERTIFICATION MECHANISM

Tengger Sandy Desert(TSD) (37°30'~40°00'N, 102°30'~106°00'E) lies at the northwest edge of the modern East Asian summer monsoon domain. This area has long been considered as one of the most important sources of the frequent sandstorm in East Asia. It was reported that the TSD was ultimately formed after a series of drastic environmental changes during the Late Pleistocene, however, the mechanism of desertification in vast area of the desert is unclear yet. In this study, more than 10 profiles in different locations in the southern hinterland of the TSD were studied and 27 OSL samples were collected and measured. This study reveals that in the southwestern hinterland of the desert, either lacustrine clay or aeolian sands accumulated during 13~10 ka, and lacustrine sediments developed in different areas >3.8 ka and >0.37 ka, and aeolian sands accumulated in different areas synchronously at around 16 ka, 10 ka, 7.3 ka and after 0.37 ka. In the southeastern hinterland, either greenish grey clay or brown clay developed during 7.90~0.80/0.37 ka, and aeolian sand started to accumulated in vast areas since 0.80/0.37 ka. Besides, either the layer of sandy clay was replaced by loess or the clay lay was replaced by sandy clay at the interval of 3.8~3.3 ka in the southern hinterland of the TSD. These results support that a dramatic expansion of desert environment since ca. 0.80 ka, especially after 0.37 ka. Combined with the previously studies from the lake shorelines and drill cores within the hinterland of the TSD, the OSL dating results from profiles within the hinterland of the desert support that there was an aeolian erosion environment during the last glacial maximum, and aeolian sand accumulation at 16 ka, 10 ka, 7.3 ka and after 1.5 ka, especially during the latest 0.37 ka. A comparison with the climatic background indicates that the aeolian sand accumulated during 15~12 ka and ca. 10 ka when the climate shifted from dry to wet, and at dry intervals of 7.3 ka and 5.1 ka and 3.8~3.3 ka under a generally humid climatic background. The climatic background during these intervals is more favorable to aeolian sand/dust accumulation than production of drift sand. Therefore, it can be inferred that the aeolian sands that accumulated in the modern TSD before 3.3 ka was mainly sourced from the upwind arid areas. Initiation of sand accumulation at the base of sand dunes/hills in vast area of the present-day TSD since 0.37 ka under the background of low precipitation, was somewhat later than the peak time of the intensified human activities in this area. This fact supports the idea that desertification in vast area of the TSD during the latest 0.37 ka is triggered by the intensified human activities, and the sands accumulated nearby the place where they were eroded from.