柴达木盆地中部与西南部古沙丘的光释光年代学研究

OSL Chronology of Paleodunes in the Middle and Southwestern Qaidam Basin,China

青藏高原东北部的柴达木盆地广泛分布着风成沉积,其中古沙丘主要分布在盆地东部、中部三湖区和西南缘。柴达木盆地中部和西南部两处古沙丘集中分布区靠近柴达木盆地盐湖区,与盐湖的演化有着密不可分的联系,但是这些古沙丘的形成时代至今没有具体研究。本文应用光释光定年的单片再生剂量法对这两个区域典型的古沙丘进行了风成砂沉积年代测定。结果显示研究区古沙丘的堆积开始于约4～3ka,并延续至0.5ka之后被固定,其形成与柴达木盆地晚全新世气候的干旱和盆地内湖泊退缩引起的砂源增加有关;古沙丘下伏的河流相沉积物形成于末次冰消期(12.6±0.8ka)。古沙丘的固定事件对应青藏高原东北部的冰川前进期,冰川前进期的低温条件可以引起盆地内蒸发量下降和有效湿度相对增加,从而促使植被条件改善并最终使沙丘固定。

Aeolian sediments are widely distributed in the Qaidam Basin, northeastern Qinghai-Tibetan Plateau （QTP）. The paleodunes are mainly located at the southeastern, middle and southwestern Qaidam Basin. Chronology of the paleodunes in the southeastern Qaidam Basin have been well studied recently, however, ages of paleodunes in the middle and southwestern Qaidam Basin have not been reported, though they are close to and might connected to the evolution of the salt lakes in the central basin. In this study, we use sin- gle aliquot regeneration （SAR） protocol of Optically Stimulated Luminescence （OSL） to date the dune sand in the two regions. Results showed that： （1） Sand accumulation in these regions started at 4--3 ka and lasted to 0.5 ka when they were stabilized, according to the arid climate in the late Holocene. （2） The underlying fluvial sand was formed during the deglaciation at 12.6＋0.8 ka. （3） The stabilization periods of the paleodunes were corresponding to the advance stages of the glacier in the northeastern QTP, during which the lower temperature caused the decrease of the evaporation and increase of the effective moisture indirectly, and this caused the increase of the vegetation and stabilization of the dunes.