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

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 delta C-13(shell), delta O-18(shell), Sr/Ca-shell and Mg/Ca-shell 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 delta O-18(water), Sr/Ca-water 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 delta O-18(shell) and delta C-13(shell) of Gyraulus sp. and Radix sp. have a positive relationship, but their ratios of Sr/Ca shell and Mg/Ca shell are not correlated. Moreover, delta O-18(shell) in the Radix sp. shells is similar to 2.97 parts per thousand more enriched and has a stronger relationship with delta O-18(water) than is the case for shells of Gyraulus sp. The values of delta O-18(shell) and delta C-13(shell) 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 delta O-18(water) of the ambient water of water bodies in the Tibetan Plateau.

Automated summary

The study on fossil shells of aquatic mollusc taxa found in dammed lake sediments in Tibet provides insights into the paleo-hydrochemistry and paleo-hydrology of the region, revealing important information on past water conditions.