中文摘要：

亚洲内陆干旱区是与亚洲季风区密切关联的一个环境系统，其形成演化与青藏高原的隆起和全球变化等因素密切相关，揭示其干旱化过程和趋势具有重大的理论和现实意义。文章通过对亚洲内陆干旱区柴达木盆地中央鸭湖剖面孢粉和盐类化学指标的初步研究，表明5．3Ma时湖泊周围已分布着以蒿属、藜科、麻黄、禾本科等为主的草原，气候已经变干，由此期较高的氯离子、硫酸根离子及碳酸钙含量表明湖泊演化处于沉积碳酸盐和少量硫酸盐阶段；3．4Ma后草本植物含量略有增加，但离子含量普遍降低，推测气候季节性增强；2．6Ma后耐旱植物花粉含量与盐度指标均呈现明显长期增加趋势，气候快速向更干旱方向发展。

英文摘要：

As the largest temperate arid region, Central Asia has been attracting widely interests for its aridification,since it has long thought to relate strongly to the uplift of the Tibetan Plateau, the retreat of the North Tethys and the growth of Arctic ice. Therefore, a good understanding of the process and trend of Asian aridity is of great significance to both practical and theoretical study. However, most of the existed evidence on this issue are indirect, largely from the eolian records in the Chinese Loess Plateau, and little from inland arid area. Shortage of stable and continuous sediment records and convincing evidence is obvious. The Qaidam Basin, sitting on north Eastern Tibetan Plateau, develops continuous and well-exposed Cenozoic sediments,which provided an unique opportunity to study Asian aridity. We present a continuous lake sediment section from the Yahu anticline,a former playa lake in Central Qaidam Basin. It consists of Shizigou and Qigequan Formations. The age of the Yahu section was determined at ca. 5.30 ~ 1.83Ma with a stratigraphic lacuna of 4.2 ~ 3.7Ma,by paleomagnetism and fossils of ostracode and fish. Sporopollen and salinity proxy records indicate that there developed a steppe dominated by Artemisia, Chenopoidaceae,Ephedra, Gramineae around the Yahu area and the climate had already become dry at ca. 5.3Ma. Higher contents of CaCO3 , Cl- and SO4^2- lend support to this. From 3.4Ma to 2.6Ma, the percentage of arid herbs was increased slightly from 24.45% to 26.2%, but the contents of ions above decreased to some extent. We speculate that the seasonality was enhanced,accompanied with enlarged relief during this time. This would make higher mountains intercept more precipitation from the enhanced summer monsoon, and hence bringing more water into the lake, while the wide basin surface turned to more arid due to the foehn effect and enhanced winter monsoon. Since 2.6Ma,the average percentages of xerophilous plants increased from 26.2% to 37.58%, CaCO3 from 10.5% to 18.28%, Cl- from 70.4g