昆仑山北坡黄土粒度特征与环境意义初探

Grain-size characteristics of Kunlun Mountains loess and its environmental implication

昆仑山北坡沉积了极端干旱区巨厚的黄土,不仅记录了塔克拉玛干沙漠的发生发展过程,也蕴含了西风环流的演化信息。该地区气候干旱,成壤作用弱,靠近物源,黄土记录了沉积时的粒度特征,是研究风动力变化的良好载体。本文选取昆仑山北坡的普鲁剖面进行详细的粒度分析,结果表明黄土颗粒较粗,是沙漠的近源沉积,搬运动力较强。通过粒级一标准偏差变化计算,黄土粒度可以分为粉砂(<36μm)和细砂(>36μm)两个敏感粒级组分。依据塔里木盆地内的现代环流特征,粉砂组分主要与近地面较弱的环流风场有关,而细砂组分主要由盆地南缘频发的沙尘暴搬运,并且沙尘暴对沙尘的搬运作用可能更为显著。

The Kunlun Mountains loess, depositing on the southern of Tarim basin where formed theextensive Taklimakan desert, have recorded evolutions of desert and wind power. Although the loesshere has great potential in paleoclimate research, much less studies have been done by contrast withChina Loess Plateau. In this paper, we discuss bulk grain-size at length on a 29 m profile locate in thenorthern slope of Kunlun Mountains. The results illustrate that Kunlun Mountains loess is much coarserthan other areas and its medium diameter （Md） changes about from 32 μm to 50 μm, which is mainlydue to closing to the Taklimakan desert and weak pedogenesis. Previous researches have indicated thatthe Taklimakan desert tend to be steady since the Late Quaternary, and this could be inferred from theslight fluctuation of grain-size in this profile. Consequently, we attribute fluctuation of grain-size in thisprofile to wind power changes. Based on calculating standard deviation of each grain-size class, weidentify two sensitive sedimentary components, silty sand group whose grain-size is less than 36 μm,and fine sand group whose grain-size is over 36 μm. As different strength of wind power has differenttransporting capacity, the silty sand （〈 36 μm） group is more likely carried by weak prevailing wind, andfine sand （〉36 μm） group is carried by frequent sand storm. Moreover, the sand storm may play a moreimportant role in dust transporting than we used to realised in Southern Taklimakan desert, but whichstill need to be further studied.