The Rb/Sr And ～(87)Sr/～(86)Sr Of Shell Bar Section At Charhan Lake, Qaidam Basin And Its Paleoenvironmental Significance

Qaidam Basin, situated at the northeastern Tibetan Plateau, is in the central part of the arid Asia, which is the biggest non-zonal aid area in temperate zone on the earth, and is the conjunction area among the Westerly jet, southeastern Asia Monsoon and Southwestern Asia Monsoon that influence the climate of China, therefore, it is very sensitive to the regional and global changes. Detailed researches can promote our understandings of the climate change in the central Asia to the global changes and the mechanisms behind these changes. The study on the climate change history in the arid-cold area of the northeastern Tibetan Plateau is of great theoretical and applied importance.Shell Bar is the only one which has been discovered at Qaidam Basin so far, it has an important significance. Based on the detailed discussions of the dating and chronology establishment, through the analyses of the sedimentological characteristics, ⁸⁷Sr/⁸⁶Sr, Rb/Sr and Sr content of the acetic acid soluble part and insoluble part of Shell Bar section at southeastern Charhan saline lake, Qaidam Basin, and grain size, TOC, CaCO₃, element ratio, other geochemical proxies, the environmental change history was reconstructed and the main results can be summarize as follows:1,According to the environmental significance of Rb/Sr ratio of lake sediments, The data showed that, ⁸⁷Sr/⁸⁶Sr ratio can effectively indicate the catchment chemical weathering intensity and the paleoenvironmental changes of the deposit area. The ⁸⁷Sr/⁸⁶Sr and Rb/Sr have a correlation with grain size, TOC, CaCO₃, and some other geochemical proxies.2,Based on chemical weathering intensity the sedimentary and geochemical proxies of the samples along the sequence, the environmental change history was reconstructed between 39.7 ka BP and 17.5 ka BP of the studied area. that are from 39.7ka BP to 35.2 ka BP is the period of lake formation, from 35.2-33.2ka BP the lake level was high and stable, temperature in the area was more warm-humid than that of today. The lake level reached it maximum between 33.2 and 26.9ka BP, both temperature and precipitation were higher than today. Between 26.9ka BP and 18.1ka BP, the climate was still warm, but the lake level started to lowering, most likely is because of the reduction of the precipitation amount and the deterioration of the environments. Start from 18.1ka BP, the lake retreated abruptly with a very strong increase of the evaporation, resulted in the salt formation. Then the lake shrank further and never reached the level again.