西藏台错TT-1剖面的碳酸盐分布、元素地球化学特征及其古环境意义

根据台错TT-1剖面自生碳酸盐矿物的分布和共生组合、成盐物质的元素地球化学特征和变化规律研究,结合铀系不平衡法获得的准确可靠定年数据,本文重建了西藏台错古湖区晚更新世晚期至全新世中期的古气候、古环境演变。从万年尺度上,台错在>32.60～26.15kaBP间的6.45ka中,气候以湿润和温暖为大背景;在26.15～4.50kaBP的21.65ka间气候则以偏干和寒冷为大背景;在4.50kaBP,沉积记录终断,表明湖泊干枯。从百年-千年尺度上,更加详尽地描述了台错在32.60～4.50kaBP经历的16个演变阶段,完整再现了湖泊演化的全部过程:即湖泊的青年阶段——深水大湖,湖泊的成年阶段——逐步咸化萎缩、湖水变浅,湖泊的终年阶段——水位骤降、干枯而演化成干盐湖。

Distribution and Characteristics of Carbonate and Elementary Geochemistry of Profile TT-1 in Dahyab Tso(Tai Cuo), Tibet, and Its Palaeoenvironment Significance

The saline lake-Dahyab Tso (Taicuo) located in northern Tibetan Plateau was chosen as a study object. The environment around Dahyab Tso is primitive, and has not suffered any pollution. Field work was carried out in 2001. Samples were collected along the 369-cm-long Profile TT-1 in a high consistency, and the average thickness of each sample has been limited within 2.36cm. Based on the mineral distribution and assemblage of authigenic carbonate in profile TT-1, the geochemical characteristics of saline elements, and the credible dating data by Uranium-series chronology method, the paper reconstructed the paleoclimate and paleoenvironment from the Late Pleistocene to Middle Holocene of Dahyab Tso (Taicuo) in Tibet. By the ten-thousand timescales, two changing stages in climate took place in the Dahyab Tso area. The climate at 6.45ka from >32.6 kaBP to 26.15 kaBP was generally humid and warm, and from 26.15 kaBP to 4.50 kaBP, the climate was generally slightly dry and cold during 21.65ka. After 4.50 kaBP, missing of the upper part of the profile results in interruption of saline lake sedimentary record, indicating the lake was dried up. This study describes in great detail 16 changing stages in Dahyab Tso from 32.60 kaBP to 4.50 kaBP in the hundred-thousand timescale and reconstructed a complete evolution of a lake from the flush to the end: from a pan-lake in flush stage, to mature stage characterized by salinizing and shoaling gradually, and finally to the salty lake from the lake, which was accompanied by water-level falling and drying rot.