94–9ka察尔汗盐湖的气候环境演化过程

Chemical Elements in Core Sediments of the Qarhan Salt Lake and Palaeoclimate Evolution during 94–9 ka

本文依托柴达木盆地中东部察尔汗盐湖沉积中心102 m长钻孔(ISL1A)岩芯,应用AMS14C和不平衡U系测年方法建立了年龄-深度框架,对岩芯开展了元素地球化学分析,利用主成分分析提取影响察尔汗盐湖沉积物化学组成的2个主控因子:入湖径流量因子和湖泊蒸发量因子,结合孢粉、粒度、沉积物中石盐含量等环境代用指标,分析讨论察尔汗盐湖晚更新世湖泊波动与环境变化过程。结果表明:察尔汗古湖在晚更新世经历多次淡化期和咸化期,94–52 ka期间察尔汗古湖为微咸水-半咸水湖,湖泊入湖径流量较大,湖区植被为草原/荒漠草原植被;约52 ka各指标均反映了察尔汗古湖环境发生了显著变化,湖泊入湖径流量减小,蒸发量增加,湖泊由咸水湖退缩演化为盐湖,湖区植被由草原/荒漠草原演替为荒漠草原/荒漠。34–24 ka期间察尔汗盐湖入湖径流量增加,湖泊有所扩张,但湖水盐度较高;24–9 ka期间在冷干气候背景下,湖泊退缩演化为干盐湖。环境指标所指示的察尔汗盐湖波动演化过程得到了柴达木盆地及其周边地区其他环境变化记录的支持。

A 102 m long drill core （ISL1A） was obtained from the Qarhan Salt Lake in central eastern Qaidam Basin, northeastern Tibetan Plateau. An age-depth model was established with AMS 14C and 230Th dating. Chemical elements analysis was carried out for the core sediments, and two important factors including runoff of the lake and evaporation were identified using Principal Component Analysis. The chemical elements analysis results were combined with pollen analysis, grain size and percentage of halite in the sediments so as to reveal the evolution of the Qarhan Salt Lake during Late Pleistocene. The result indicates that the paleo-Qarhan Lake experienced several desalt and salinization stages. During 94-52 ka, environmental proxies indicated freshwater to oligohaline conditions of the paleo-Qarhan Lake, the runoff and detrital input to the lake were relatively high and the steppe/desert steppe vegetation developed around the lake. After 52 ka, lake level decreased significantly in volume and salinity compared with previous periods of the Late Pleistocene, and desert steppe/desert vegetation developed around the lake. The increasing of runoff of the lake diluted the water body from a hyper-saline concentration to a brackish concentration during 34-24 ka. However, it is further noted that the range of lake expansion was limited during this stage. During 24-9 ka, cold and dry climate prevailed in the basin and the Qarhan Salt Lake finally evolved into a dry playa. These environmental changes and the variations of the lake level reflected by the environmental proxies of Qarhan Salt Lake sediments are supported by other environmentalchange records in Qaidam Basin as well as adjacent areas.