【作者】 张虎才； 雷国良； 杨明生； 樊红芳；

【Author】 ZHANG Hucai LEI Guoliang YANG Mingsheng FAN Hongfang Nanjing Institute of Geography and Limnology, Nanjing, Jiangsu, 210008 Key Laboratory of Western China ’ s Environments, MOE, College of Earth Sciences and Environments, Lanzhou University, Lanzhou , Gansu , 730000

【机构】 中国科学院南京地理与湖泊研究所； 中国西部环境教育部重点实验室兰州大学资源环境学院；

【摘要】 位于极端干旱区的额济纳盆地,是我国内陆地区代表性的盆地之一。这里不仅具有典型的大陆性气候、脆弱的生态系统,而且在平缓的戈壁滩下面,沉积有厚达200～400余米的古湖相地层。盆地东南与最高达近500 m沙丘的巴丹吉林沙漠比邻,构成了特征性的盆地一沙漠系统,是世界少有的自然景观,也是目前研究热点之一。更多还原

【Abstract】 Located in a hyperarid area, Ejina basin is one of the typical inland basins in China. This area not only possesses a typical continental climate but also has very fragile ecosystem. Under the flat Gobi desert the lacustrine deposits are 200-400 m in thickness. Ejina basin connects with Badain Jaran desert where the megadunes are more than 500 m high, forming a typical basin-desert system, which not only constitutes a rarely-seen landscape in the world but also is one of the areas which arouse scientists’ attention both in China and abroad. Field investigation reveals that there existed a humid period at about 30 ka B P, which can be correlated with the megalake development history in neighboring Tengger desert. Recent field work has found that there are several terraces formed by water erosion of the dune sand in the transitional area between southeastern Ejina basin and Badain Jaran desert. The upper parts of these terraces were covered by the carbonate-solidified sandy crusts. They possess nearly the same elevation and are extensively correlatable. Lake carbonate and root cast are widely distributed in the area. Geomorphologic features, lake deposits and fossil shells in sand-gravel layers indicate the existence of palaeolakes. 14-C ages indicate that the carbonate sampled from the second high platform was formed at ca. 25 ka B P (samples were dated at 25 630±270, 25 530±230 and 25 640±220, with a radiocarbon degradation half-life of 5 568 years), while the fossil shells taken from the northern part of the basin were formed at ca. 28 ka B P (samples were dated at 28 530±430, 28 630±320, 28 780±340 and 28 560±280 yr B P). The strontium isotope analyses (see the following table) demonstrate that 87Sr/86Sr ratios of the carbonate are much variable than those of the fossil shells, and that the average value of the 87Sr/86Sr ratios of the shells is smaller than that of carbonate. The 87Sr/86Sr ratio of the fossil shell and lake carbonate represents the 87Sr/86Sr ratio of the palaeolake water, and the 87Sr/86Sr ratio is related to the salinity of the lake water. It can therefore be deduced that the salinity of the palaeolake water coexisting with the shells is lower than that during the deposition of the carbonate, which implies that the palaeolake at the early stage had fresh water and the salinity increased at the late stage. This is consistent with the linving conditions of the shells that are fresh water species. The 87Sr/86Sr ratio of the carbonate became higher along with strong evaporation and quick lowering of the water level, and these processes were directly related to the climate change. Evidence shows that there existed megapalaeolakes and high water lake levels in Ejina basin which had experienced abrupt climate changes.更多还原