1.8 Ma BP以来陇西断岘黄土剖面沉积特征及其反映的腾格里沙漠演化

Loess Deposit Characteristic in Duanxian Section of Longxi Basin and Its Reflected Evolution of Tengger Desert at North of China since Last 1.8 Ma

六盘山作为青藏高原的东北构造边界,东西两侧有着明显的风成沉积差异。通过对陇西盆地六盘山西侧山麓剥蚀面上厚约223 m的断岘黄土-古土壤剖面的古地磁、磁化率和粒度分析,该剖面具有1.8 Ma BP以来完整的风成沉积旋回。主要应用砂粒百分含量(>63μm)作为指示风成物质来源区沙漠范围和气候干旱的直接指标,初步发现腾格里沙漠自1.8 Ma BP以来至少有2次大的扩张与变化过程,分别发生在1.1和0.8 Ma BP前后。研究表明腾格里沙漠的扩张与变化可能同全球性的冰量增加和冬季风增强以及区域性的青藏高原隆升有成因上的联系。

Liupan Mountain, located on the northeast margin of Qinghai-Xizang Plateau, shows obviously landform distinction between the east and the west of it. Recently, a pediment named as Gansu Period Peneplain is found, which lies at the northeast edge of Longzhong Basin. Analyses of paleomagnetic polarity reversals, magnetic susceptibility and grain size on the loess-paleosol sequence of Duanxian section, about 223m thick, on the pediment show that this sequence contains most of the stratigraphic units recorded in the standard loess-paleosol of section on the China Loess Plateau over the past 1.8 Ma BP and its age is in accordance with that of the peneplains distributed in Lanzhou＇ s and Linxia＇ s on the southwest of Longzhong Basin. Using sand particle percentage （〉63μm） of the aeolian sequence as a proxy indicator of desert extent and aridity in the dust source regions, a preliminary study on it is found that during the past 1.8 Ma, there were two important climatic events indicating the advance of the Tengger Desert. The events occurred at about 1.1 Ma BP and 0. 8 Ma BP, respectively. The stepwise advance and changes of the Tengger Desert may be linked closely to increase in global ice volume and monsoon change and uplift of the Tibetan Plateau in the late Cenozoic.