Terrestrial mollusk records in the loess sequences from eastern Central Asia since the last deglaciation and their paleoenvironmental significance

Abstract

A variety of proxies has been studied to document paleoclimatic changes in arid Central Asia (ACA). However, biological archives, which can be directly related to climatic conditions, are still scarce in this region. Here we report records of the total count fossils (TCF) of terrestrial mollusks, organic carbon isotopes (δ13Corg) and loss on ignition (LOI), since the last deglaciation in the Talede and XRBLK loess sections in Xinjiang, eastern Central Asia. Prior to the Holocene, the records show rare fossils with relatively low LOI and more positive δ13Corg, indicating low biomass/organic carbon content under dry conditions which were unfavorable for the survival of snails. In contrast, TCF increased abruptly at the beginning of Holocene, coincident with a prominent increase in LOI and a marked negative shift in δ13Corg. Furthermore, TCF increased gradually to its maximum and δ13Corg became progressively negative with constant high LOI from the early to late Holocene. The variations imply a trend towards wetter environment, with optimal moisture (precipitation/relative humidity) conditions occurring in the late Holocene. Overall, this Holocene moisture evolution history could be attributed to the variations of Westerlies strength modulated by the latitudinal temperature gradient and the insolation-related evaporation should also be concerned.