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

Dangxiong Co in Xizang 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 major and trace elements, carbon and oxygen isotopes, and ostracod species were studied. The uranium age results showed that section deposition began at（3 788±120） a BP and ended at ～2 220 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 3 430 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 2 220 a BP, and the lake concentration reached the salt lake stage after 2 220 a BP.