Radiocarbon dating of aquatic gastropod shells and its significance in reconstructing Quaternary environmental changes in the Alashan Plateau of northwestern China

Using landform evolution and lake sediment records to reconstruct Quaternary environmental changes requires reliable chronology. However, there is an ongoing debate regarding the fossil shells of aquatic gastropods in carbonate rock area to be used for radiocarbon dating. The focus of this debate is whether living gastropods incorporate the dead carbon, which would affect the accuracy of the dating results. Living aquatic gastropods were selected from habitats on carbonate terrain in arid region. In this study, 64 shell samples from living gastropods, including Cipangopaludina chinensis, Gyraulus convexiusculus, and Radix auricularia, collected from the Alashan Plateau of northwestern China, were dated by accelerator mass spectrometry (AMS) 14C dating. The results revealed that only five samples (~8%) from the same site contained no dead carbon. The other 59 samples (~92%) contained dead carbon in various amounts: ~59% samples contained 0-10% dead carbon, and ~33% samples contained more than 10% dead carbon. Of the samples, 56 were Radix auricularia and their 14C ages varied from present to 3253 cal yr BP. Two of the samples were Gyraulus convexiusculus samples dated at 379 and 290 cal yr BP which are highly consistent with 14C ages of Radix auricularia samples from the same site. The other six Cipangopaludina chinensis samples were dated at 407-863 cal yr BP. Thus, most of living aquatic gastropods from habitats on carbonate terrain contained dead carbon. The amount of dead carbon in the gastropod shells was nonselective among the three species. Radiocarbon dating of aquatic gastropod shells may not be useful for studying processes that occurred over multi-millennial timescales at different localities in areas of carbonate rock. It is difficult to establish high-resolution chronologies using 14C ages of gastropod shells in arid regions with carbonate rocks unless the limestone effect has been corrected.