对青藏高原东北部封闭咸水湖泊苦海水深最深处KH17钻孔进行沉积物粒度、烧失量和X射线荧光光谱(XRF)测试及XRF测试结果的主成分分析(PCA),以揭示14 ka以来苦海沉积物特征及其所反映的搬运与沉积过程变化,反演湖泊流域古环境。研究结果表明:第一主成分(PC1)主要包括Ti、Fe、K等元素,指示径流输入强弱;第二主成分(PC2)中载荷值较大的Ca和Sr与碳酸盐含量相关,指示湖泊蒸发强弱;Zr(第三主成分中载荷值最大)与砂组分、Rb与黏土组分含量相关,分别指示风力输入粗颗粒物质和径流输入细颗粒物质情况,其比值可反映化学风化弱强;Fe/Mn、Sr/Ca也能较好地指示沉积物氧化还原环境、湖水盐度和水位情况。基于上述记录所建立的古环境演变重建结果显示:13.6~13.0 ka B.P.苦海水位较低,径流输入相对强;13.0~11.5 ka B.P.受新仙女木事件影响,环境干旱且温度极低,风力作用强,输入物质多;早全新世升温显著,蒸发作用强,内生碳酸盐沉积增多,湖泊水位增加缓慢,中全新世期间达到最高水位;5.3 ka B.P.以后,湖泊经历干旱时期,盐度与碳酸盐沉积增加;2.7 ka B.P.以来水分供给波动,湖泊水位显著振荡。
英文摘要:
Lake basins on the northeastern Tibetan Plateau are regarded as important archives for the reconstruction of environmental and climate changes during the Upper Quaternary. Lake deposits serve as ideal indicators of various transport and depositional processes in changing hydro-climatic settings. Understanding such dynamic processes is of crucial interest when deciphering the process-response behavior of lakes from their sedimentary characteristics over time. The closed saline Kuhai Lake is an ideal location for unraveling sediment dynamics and related lake level changes during the last 14 ka B.P., as revealed by sediment core KH17 (around 7 m long) retrieved from the deepest part of the lake basin. Sediment grain size, loss on ignition (LOI) and X-ray fluorescence (XRF) were used to determine such depositional and transportation processes. Principal component analysis (PCA) shows that PC1, characterized by high positive loadings of K, Ti, Mn, Fe and Rb, is related to the detrital material transported by inflowing rivers. Ca and Sr in PC2 have high correlation coefficients indicating the varying intensity of local evaporation. Zr (high loadings on PC3) and Rb are related to coarse and fine sediment components respectively, which are mainly transported by wind and suspended load of inflows. The Zr/Rb ratio was used to judge the intensity of geochemical weathering. Fe/Mn and Sr/Ca indicate redox conditions and salinity, which are related to lake level changes. Based on the proxies, the environmental history over the past 14 ka was reconstructed as follows. During 13.6~13 ka B.P., the Kuhai Lake Basin was covered by a shallow water body, and strongly influenced by inflow variations. The Younger Dryas interval between 13 and 11.5 ka B.P. experienced cold, dry conditions and increased aeolian transport, which influenced the depositional environment. A 500-year warm and wet intermediate phase may have existed, according to the chronology. Temperatures increased to a large extent since the Early Holocene, which led to increased evaporation and the formation of carbonates following a slight lake level rise. The water depth peaked during the Middle Holocene, reaching the highest level experienced by the lake. After 5.3 ka BP, Kuhai Lake experienced a drier period, with high salinity and varying carbonate precipitation. Water supply has fluctuated greatly since the Late Holocene (2.7 ka B.P.).