西藏当雄错盐湖碳酸盐沉积环境及其地质意义  

Sedimentary Environment of Carbonate Deposits and Its Geological Significance in Dangxiong Co,Tibet

作　　者：牛新生[1] 刘喜方[1] 马妮娜[1] 郑绵平[1] NIU Xinsheng;LIU Xifang;MA Nina;ZHENG Mianping(MNR Key Laboratory of Saline Lake Resources and Environments,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037)

机构地区：[1]中国地质科学院矿产资源研究所、自然资源部盐湖资源与环境重点实验室,北京100037

出　　处：《地球学报》2024年第5期743-756,共14页Acta Geoscientica Sinica

基　　金：中国地质调查局地质调查项目“我国重要含盐盆地钾盐重点调查区区块优选与综合评价”(编号:DD20230296);中国地质科学院矿产资源研究所基本科研业务费项目(编号:KK2210);国家青年科学基金项目(编号:41402076)联合资助。

摘　　要：西藏当雄错盐湖是一个碱性的富锂、硼资源盐湖,对其碳酸盐沉积物的研究有助于了解盐湖形成过程中沉积环境的变化以及锂、硼资源的富集过程。为此,本文从当雄错盐湖碳酸盐剖面自上而下采集了31件样品。对这些样品开展了铀系年龄、XRD、主-微量元素、碳-氧同位素测定以及介形类的鉴定分析。铀系年龄结果表明剖面沉积开始于(3788±120)a BP,结束于约2220 a BP。碳酸盐沉积的微量元素和稀土元素特征表明,其沉积水体为缺氧、还原环境下的咸水环境,沉积物形成于干旱、寒冷的气候环境,湖泊水体具有半开放-半封闭性质,但封闭程度较高。约3430 a BP时,当雄错水体盐度发生了较大改变。结合沉积物中介形类Candona gyrongensis的出现和沉积物的碳氧同位素特征,推测有地下淡水注入导致湖泊水体变淡和还原性减弱。当雄错水体的盐度在2220 a BP之前仍相对较低,湖水浓缩达到盐湖阶段的时间在2220 a BP以后。Dangxiong Co in Tibet is an alkaline lake containing abundant lithium and boron.Research on these carbonate sediments will enhance understanding of the changes of sedimentary environment and the enrichment process of lithium and boron resources during the formation of the salt lake.In this study,31 samples collected from a carbonate section in Dangxiong Co from above to below.The uranium series ages,X-ray diffraction peaks,major and trace elements,carbon and oxygen isotopes,and ostracod species were studied.The uranium age results showed that section deposition began at(3788±120)a BP and ended at~2220 a BP.Trace and rare earth element signatures of the carbonate deposits indicated that the sedimentary waters were brackish in an anoxic,reducing environment and that the sediments formed in an arid,cold climate.The lake’s waters were semi-open to semi-closed,but with a high degree of closure.At about 3430 a BP,the salinity of the Dangxiong Co water body changed greatly.Considering the presence of Candona gyrongensis in the sediments and the carbon–oxygen isotope signatures,it is speculated that the lake’s water body was diluted and its reducing conditions weakened due to freshwater injection from groundwater.The salinity of Dangxiong Co water remained relatively low until 2220 a BP,and the lake concentration reached the salt lake stage after 2220 a BP.

关 键 词：当雄错 碳酸盐沉积 盐湖 沉积环境 介形类 地球化学 

分 类 号：P343.3[天文地球—水文科学] P532[天文地球—地球物理学]