基于光释光测年的共和盆地风沙活动历史研究

摘要

The Gonghe Basin, located on the northeastern of the Qinghai-Tibetan Plateau and in the arid and semi-arid areas controlled by the alternating circulation of the Asian summer monsoon and the westerly circulation, and a large area of desert is distributed in the basin.102 OSL dating results from 25 aeolian sections in the Gonghe Basin have been analyzed, and it is concluded that the aeolian sand activity in Gonghe Basin has occurred in the whole periods since the late Pleistocene.The loess deposits were mainly from late Pleistocene to early Holocene.The paleosols were mainly developed in the late Holocene.However previous dating works are short of high-density OSL dating test.In this paper, a systematic high-density OSL chronological study of the Yangqu section in the southwestern Gonghe Basin has been carried out.The Yangqu section is mainly deposited during the last Deglacial, aeolian activities in 9.6-7.1 ka were weakened rapidly and an obvious depositional hiatus appeared at 7.1-2 ka, which indicates that the environmental evolution and reconstruction based on a single section should be careful.Combined with the results of OSL dating published in the basin, aeolian sand activities have existed in the Gonghe Basin since the last Deglacial, and the strongest period is about 14-10 ka.The loess is mainly deposited from 14 to 10 ka during the last Deglacial, the paleosols development is mainly developed in 3-2 ka and 6-4 ka, and also developed in 9-8 ka.%位于青藏高原东北缘的共和盆地处于亚洲冬、夏季风和西风环流作用交替控制的干旱—半干旱区,盆地中分布着大面积的沙漠,是重建过去气候的重要载体.就前人对共和盆地25个风成剖面的102个光释光(OSL)年代结果进行分析,总结出晚更新世以来共和盆地的风沙活动在各个时期都有发生,黄土堆积主要是更新世末期到早全新世,古土壤主要是晚全新世发育的,但其测年工作缺乏高密度光释光测年检验.通过对共和盆地西南部的羊曲剖面进行系统的高密度光释光年代学研究发现,羊曲剖面主要是末次冰消期沉积的,9.6～7.1 ka风沙活动迅速减弱,7.1～2 ka存在明显的沉积间断,说明基于单个剖面进行环境演变重建需谨慎.结合盆地内已发表OSL年代结果,末次冰消期以来,风沙活动在共和盆地一直存在,其最强烈时期是14～10 ka左右,黄土主要是末次冰消期14～10 ka沉积的,古土壤发育主要集中在3～2 ka和6～4 ka,此外在9～8 ka也有发育.