STABLE ISOTOPES OF CARBONATE AND FOSSIL SHELLS FROM THE SHELL BAR SECTION OF THE PALEOLAKE QARHAN, QAIDAM BASIN
柴达木盆地察尔汗古湖贝壳堤剖面碳酸盐和 瓣鳃化石碳氧稳定同位素*

Shell Bar, which is composed of abundant fossil shells of Corbicula fluminea Müller and Corbicula largillierti Philippi and located at the southeastern end (36°30'N, 96°12'E) of the paleolake Qarhan, is one of the sections with the most prominent features in the Qaidam Basin. Multi-method dating reveals that the high lake levels appeared between 39.6kaB.P. and 17.1kaB.P. The stable carbon and oxygen isotopes of fossil shells, bulk sedimentary carbonate and carbonate content in the lacustrine deposits in the Shell Bar section from the paleolake Qarhan in the Qaidam Basin were analyzed systematically to address the relationships between isotopes properties of shells and carbonate in bulk samples. Results show that during the period the high lake levels sustained. The stable isotopes of the shells and carbonate in bulk samples can be used as proxies of lake water temperature and salinity, while δ18 O is more sensitive to salinity of lake water, which closely relates to temperature changes. Based on these proxies, the paleoenvironment change history was reconstructed. During the period between 39.6kaB.P. and 35.5kaB.P. , the δ13 C and δ18 O values are generally high, together with high carbonate content, they imply a strong evaporation in the earlier stage of the lake development. During this stage, the climate was changed from cold-dry to warm and humid, the precipitation in the drainage, especially in mountainous regions surrounding the basin increased, and the lake began to develop with the lake level starting to rise. From 35.5kaB.P. , the climate was wetter than the earlier stage. It was the period during that the lake fully developed and lake level reached the maximum. Started from 22.1kaB.P. , the climate became relatively warm and dry, lake level decreased step by step and the salinity of lake water increased. Around 17.1kaB.P. , the climate deteriorated abruptly: lake level decreased suddenly, strong evaporation resulted in the decreasing of lake level and the formation of salt layer on the top of the studied section, and the high paleolake level history ended.