微量元素记录的化学风化和气候变化——以巴丹吉林沙漠查格勒布鲁剖面为例

Chemical Weathering and Climatic Changes Recorded by the Trace Elements in Chagelebulu Section, Badain Jaran Desert, China

查格勒布鲁剖面包含 7种类型的沉积相。地层中微量元素的总质量分数大致按照“风成砂→湖相层→黄土→古土壤”的顺序递增。多数微量元素的质量分数在剖面中的演化趋势与沉积物的中值粒径和硅酸系数的大小呈负相关。与洛川剖面的马兰黄土相比 ,查格勒布鲁剖面上更新统地层处于相对微弱的化学风化环境。表明 ,晚更新世期间 ,巴丹吉林沙漠一带的干湿变化取决于东亚夏季风的盛衰 ,西风气流带来的降水到达不了巴丹吉林沙漠附近地区。

This paper deals with the variations of the chemical weathering and climatic change in Badain Jaran desert area that induced by the repeated advances and retreats of the East Asian monsoon since Late Pleistocene period. The Chagelebulu section, which located at the southeastern fringe of the Badain Jaran desert, is composed of seven sedimentary facies, i.e., three types of aeolian sands, loess, paleosol, lacustrine and peb-sends layers. The total mass fraction of 15 trace elements increased in the direction from aeolian sands to lacustrine layers, and to loess, and then to paleosol. The total mass fraction of most of those trace elements changed inversely in the section with the middle size and the silica-alumna ratio of the sediments. According to the variations in time of the trace elements in the Chagelebulu section it can be seen that the humidity in this area had been fluctuating from dry environment to relative humid one. A comparison of the chemical weathering degree was made between the Late Pleistocene stratum in the Chagelebulu section with the Malan loess stratum of the Loess Plateau in Luochuan section. The chemical weathering degree is relatively lower in Chagelebulu section than that in Malan loess of Luochuan section, Loess Plateau. The variations of the humidity in Badain Jaran desert area were depended upon the rise and fall of East Asian summer monsoon in the Late Pleistocene period, when the precipitation brought by the west wind could not arrived Badain Jaran desert area.