宁夏沙坡头沙漠扩张的时代: 来自黄河阶地光释光年龄证据

由于新构造运动作用,宁夏沙坡头地区从早更新世以来发育了多达9级的黄河阶地。在高阶地上部发育非水相结构的黄色粉砂-砂沉积物。光释光测年结果最老为74ka,大部分年龄处于末次冰期的早期。这与黄河阶地的形成时代不一致,推断这些沙沉积物并不是与阶地同时形成的,而是末次冰期干冷环境下的风成物质。这些风成沙沉降到阶地面后,进入以砾石为主的黄河阶地堆积物而保存下来,可能指示了腾格里沙漠东南缘沙漠在末次冰期干冷气候背景下的扩张。本研究提供了在末次冰期气候干冷背景下腾格里沙漠扩张和风沙活动增强的直接证据。

THE AGE OF THE SHAPOTOU DESERT EXPANSION BASED ON OSL AGES OF AEOLIAN SEDIMENTS IN THE YELLOW RIVER TERRACES,NINGXIA HUI AUTONOMOUS REGION,NORTHERN CHINA

There are nine river terraces developed on the left bank of Yellow River around Yemingshan hill which is on the upside of Xiangshan-Tianjingshan fault.The highest terrace above the river is about 140m.At the same time,on the right bank of the river,there are only three terraces near Dawancun village(37°27' 02″N,104°58'38″E) ,downside of the fault.The elevation of highest terrace is about 80m.The deposition of terraces on the right bank is obviously thicker than the ones on the left,and reach to 20m for the thickest one.Ages of the aeolian sand layers interbedded in upper part of the fluvial deposits in the Yellow River terraces in Shapotou area,Ningxia,were determined by Optically Stimulated Luminescence(OSL)dating method.12 OSL samples were collected from the Yellow River terraces around Yemingshan hill and Dawancun village near Shapotou,and 3 samples were taken from the sand deposition section near Mengjiawan village(37°26' 10″N,104°55'40″E) ,about 6km away from the left bank of Yellow River.Most of the ages are younger than 74ka.This obvious discrepancy with the time of terraces formation suggested that the dated sand layers were not deposited at the same time when the terraces were formed,but in the cold and dry climate in the Last Glacial period.It indicates a pulse of the Tengger desert expansion cross the Yellow River during this time.This study provides firstly direct evidence that the sandy sediments of Tengger desert were expanded during the cold and dry climate of the Last Glaciation,in that time the aeolian sand activity was significantly strengthened.