CONTENT OF MG IN THE CALCITE AS A LAKE SALINITY PROXY IN THE NORTHWEST INLAND CHINA: A CASE OF PRIMARY RESEARCH IN LAKE KOUCHA

A-560 m-long core, namely core K-1, collected from the Lake Koucha, a closed to semi-closed lake in the southeastern part of the Tibet Plateau, was carefully studied. We analyzed the mineralogy and carbonate composition of the core samples since 30 kaBP, dated by the age model established upon 5 ¹⁴C AMS data. Results show that the content of Mg in the calcite can be used as a potential lake salinity proxy in such a closed to semi-closed lake. Based on the changes in salinity, six stages could be recognized since 30 kaBP. Stage 1, 560~410 cm(?30~15 kaBP), it was a fluvial environment. Stage 2, 410~320 cm(15~7.6 kaBP), the Lake Koucha started to germinate, and filled with fresh to oligohaline water. Stage 3, 320~180 cm(7.6~2.6 kaBP), the lake continued to develop and lake water became hyperhaline due to high evaporation. Stage 4, 180~100 cm(2.6~1.4 kaBP), the lake water changed back to fresh. Stage 5, 100~40 cm(1.4~0.6 kaBP), the Lake Koucha became a mesohaline lake again. Stage 6, 40~0 cm(0.6~kaBP), the salinity of the Lake Koucha decreased in the beginning but increased gradually since 3 000 kaBP.