THE GRAIN SIZE AND ELEMENT RECORD OF THE DRY MID-HOLOCENE LAKE IN THE TENGGER NUUR, INNER MONGOLIA PLATEAU, CHINA

A 400-cm long core from Tengger Nuur of the Inner Monglia Plateau was collected and grain size, carbonate-content, TOC-content, metal elements and ratios analyzed in the environmental lab of Lanzhou University. 3 ¹⁴C AMS samples were determined by the NFS Arizona AMS Laboratory of Arizona University in the USA. Carbon reservoir effect was considered for calibration of the dating data using the about 1000 year data from researching results in the past. Environmental proxies of Mg/Ca、CEC、Rb/Sr、CIA and palaeoclimatic index C were used for construction of palaeoenvironmental change model since~9 000 cal aBP. A warm and dry palaeocliamtic environment was prevailed during the mid-Holocene (~9 000~4 500cal.aBP) with high lake level and low effective humidity. The lake remained high in the Early Holocene as summer monsoon strengthened with high rainfall and temperature. The lake approached its highest level about~8 000~6 200 cal. aBP. After 3 000~4 500 cal. aBP, palaeoclimate turned dry and cold, and the increase in effective humidity was in favor of vegetation in this area. However, with decreasing rainfall, the lake shrank gradually until it dried up.