乌兰布和沙漠腹地古湖存在的沙嘴证据及环境意义

Evidence of Palaeolake Existence in Ulan Buh Desert and Its Environmental Evolution

通过大范围的系统野外考察发现,在乌兰布和沙漠腹地存在众多干盐湖,其周围存在不同高度的湖岸堤。其中,贺日木西尼沙嘴最为典型。该沙嘴呈NW-SE走向,海拔高度从1052m下降至1035m,长达11km,是古湖泊发育和存在的重要证据和标志。通过对湖滨沉积物的OSL年代测定,该沙嘴形成于全新世的8.6-7kaBP阶段,与中国西部许多沙漠出现的相对湿润环境状况相一致。其主要由强劲的风力作用和吉兰泰古湖沿岸流以及丰富的松散物质传输堆积而成。依据该沙嘴的海拔高程和形成年代来推测,在乌兰布和沙漠腹地曾经发育面积巨大的古湖,其范围西到吉兰泰盆地,东延河套盆地西部,形成早全新世的吉兰泰古湖。之后,受区域构造运动和干旱气候的影响,古湖水位下降,水域面积缩小,古大湖解体,导致该沙漠腹地的古湖部分水体逐渐向西退缩,形成了吉兰泰盐湖。在古湖退缩过程中,乌兰布和沙漠腹地残留众多湖泊,随着气候干旱化和蒸发作用的加剧,这些湖泊逐渐演变成盐湖。在强劲的风力驱动下,古湖周围的松散物质被侵蚀、搬运、扩散、堆积成现在的乌兰布和沙漠。

There are numerous dry salt lakes in the hinterland of the Ulan Buh Desert and around them are lakeshore terraces at different heights. The Herom Xil spit discovered in extensive field investigation is the most typical among them. The spit falls from northwest to southeast with elevations ranging between 1052-1035 m a.s.1, and has a length of 11 km. This is an important evidence for the existence and development of the palaeolake. The spit was formed during the period 8.6-7 ka B.P. in early Holocene, based on the OSL dating on beach sediment. The period was coincident with the moist environment observed in many deserts of western China. The strong palaeowind, rich lake sediment sources and currents of Jarantai and Hetao palaeolakes led to the formation of the spit. According to the elevation of the spit, we estimated that in the Ulan Buh Desert hinterland developed a relatively large palaeolake which extended to Jarantai basin westward and to Hetao basin eastward, and thus formed Jarantai megalake in Holocene. With the intensification of dry climate, the palaeolake level declined and the area shrank. Furthermore, numerous lakes remained and evolved into salt lakes in the hinterland of the Ulan Buh Desert. The sands around the palaeolake might have resulted in the formation of the present Ulan Buh Desert.