Palaeo-hydrochemistry reconstructed from fossil mollusc shells from dammed palaeo-lake sediments in the Yarlung Tsangpo valley, Tibet

Abstract Radix sp., Gyraulus sp. and Pisidium sp. are aquatic mollusc taxa. Although their fossil shells occur widely in dammed palaeo-lake sediments in the Yarlung Tsangpo valley in Tibet, their hydrochemical and hydrological implications are not fully understood. Moreover, vital effects on the trace element and stable isotope composition of the aragonite shells of these molluscs are unclear. We measured the values of δ13Cshell, δ18Oshell, Sr/Cashell and Mg/Cashell of the fossil shells of Radix sp., Gyraulus sp., and Pisidium sp. collected from the dammed lake sedimentary sequences at Xigaze and Lhainxiang in Tibet, with the aim of reconstructing the palaeo-hydrochemistry and palaeo-hydrology of the dammed palaeo-lake. The results show that the values of δ18Owater, Sr/Cawater and electrical conductivity (EC) of the dammed palaeo-lake water are higher than those of the modern Yarlung Tsangpo River water. Nevertheless, the dammed palaeo-lake still exhibited a through-flow status, together with freshwater characteristics. The values of δ18Oshell and δ13Cshell of Gyraulus sp. and Radix sp. have a positive relationship, but their ratios of Sr/Cashell and Mg/Cashell are not correlated. Moreover, δ18Oshell in the Radix sp. shells is ~2.97 ‰ more enriched and has a stronger relationship with δ18Owater than is the case for shells of Gyraulus sp. The values of δ18Oshell and δ13Cshell of Pisidium sp. are similar to those of the shells of Radix sp., and we conclude that the shells of Radix sp. are the most suitable mollusc shell for recording the δ18Owater of the ambient water of water bodies in the Tibetan Plateau.