Abstract: The Chagelebulu section lies in the southern fringe of Badain Jaran Desert, Inner Mongolia , China. In this paper, the compositions of bulk chemical element of fifty-seven sediments in the section were analyzed with the method of fluorescence X-ray, which reflect the climatic evolu-tion in this area in response to global change since the last interglacial period. The periodic swing of the East Asia summer monsoon rain fringe in this area is the main reason to explain the complex facies changes of the section since 128 ka BP, i.e. , lacustrine deposit, the layer of peb-ble with sand, loess, paleosoil and eolian sand interlaced with each other frequently from the bottom to the top of the section. The weathering degrees of those deposits are different from each other. We arranged those deposits according to their silica-alumina ratios that were thought to be the reflection of their weathering from low value to high value degrees as follow-ing:Eolian sand (Ⅰ)→Aeolian sand (Ⅱ )eolian sand(Ⅲ)→the layers of pebble with sand→Q₃² lacustrine deposits→Q₃¹ lacustrine deposits→loess→paleosoil.With the fluctuation of the Quaternary glacial climate, the East Asia summer monsoon rain fringe could reach and even exceed this area during interglacial periods or stages and post-glacial period when the desert environment was transformed into a kind of steppe one, and the dunes were fixed completely or partly. Lacustrine deposit, loess and paleosol were formed in those pe-riods in the section which silica-alumina ratio is 9-33, 7.58 and 7.51, respectively. Former fixed dunes activated again during glacial period or stages when the dry and cold winter monsoon dominated the area. and eolian sand spread extensively in this area. Eolian sand was formed in those periods in the section which could be divided into 3 kinds according to their activation de-grees, i. e. eolian sand (Ⅰ), eolian sand (Ⅱ) and eolian sand (Ⅲ) mentioned in this paper, which silica-alumina ratio is 15. 42, 15. 40 and 10. 32, respectively, reflecting the interim fromfluent dune sand to half fixed one.In fact, the geochemical characteristics of clay part is different to that of whole rock. The geochemical information store in whole rock is diluted by its coarse part which is the product of physical weathering.

Key words: Badain Jaran Desert, Chagelebulu Section, geochemistry, monsoon