博斯腾湖湖泊沉积物光释光年代测量*

使用光释光年代学的单片再生法测量了博斯腾湖沉积剖面中碳酸盐泥及粉砂质泥底部的浅湖相灰色粉细砂和风成沙的年龄,对剖面上部碳酸盐层中陆生植物残体进行了AMS ¹⁴ C测年。通过不同测片的等效剂量(D_e)值的分布状况评价了样品的晒褪程度,选择不随灵敏度校正后的自然释光信号变化的相对集中的等效剂量(D_e)值计算了样品的埋藏年龄。通过这些年龄结果的对比,发现石英矿物的OSL年龄和AMS ¹⁴ C年龄在地层上是一致的,表明尽管在浅湖相细砂中存在不完全晒褪,但根据相对较小而集中的D_e值计算得到的年龄结果是可靠的。这些年龄结果和地层资料揭示末次冰消期以来至早全新世,博斯腾湖处于无水干盆地向深水湖泊转化的浅水湖泊状态,现代深水博斯腾湖大约形成于距今8ka前后。

OSL DATING OF LACUSTRINE SEDIMENTS FROM LAKE BOSTEN

The Lake Bosten is one of the largest fresh lakes in Western China, in a region of arid Central Asia dominated by westerly atmospheric circulation. Optical stimulated luminescence (OSL) was applied to the lacustrine grayish silty sand below the deep lake carbonate mud and silt mud from the cores. We calculated the burial ages based on bleaching assessing of these samples through the distribution of D_e values from different aliquots. Ages ranging from 8.53±1.94ka to 15.87±2.22ka were obtained from the shallow lake sandy sediments and 17.29±1.99ka from the below eolian sand. An accelerator mass spectrometer (AMS) ¹⁴ C age of 7250~7310cal.aB.P. was obtained from the terrestrial plant in the above carbonate mud layer. Comparison of these ages reveals that these OSL dating results of quartz from lacustrine silty fine sand and the AMS ¹⁴ C age are accordant with stratum, indicating that reliable OSL dating results can be obtained based on the concentrated D_e values free from sensitivity-corrected natural OSL signal, although it possibly had suffered incomplete bleaching before burial. Combination of the core sediments lithology and these dating results suggest that the Lake Bosten had experienced an environmental change from dry basin to catchment basin during the last deglaciation and Early Holocene, and the modern deep lake was formed at about 8ka ago.