塔里木盆地大气降尘初步观测研究

A PRELIMINARY OBSERVATION AND STUDY OF DUSTFALL IN TARIM BASIN

塔里木盆地降尘量分布规律是，塔南明显高于塔北，以昆仑山北麓平原区的民丰至策勒一带为最高，达１１２７．５ｔ·ｋｍ￣（－２）·ａ￣（－１）（策勒，１９９０）。以地区划分降尘量大小，其排列顺序依次为：和田地区、喀什地区、巴音郭楞蒙古自治州、阿克苏地区。大气降尘主要集中在春、夏两季，占全年降尘量的７６％，而秋、冬两季仅占２４％，降尘量最高月份为７－８月，最低月份为１２－１月。比较戈壁与绿洲在同一时间、同一高度和同一风向上的降尘量，绿洲内的降尘量是戈壁地区降尘量的三倍，由此证明，绿洲是大气沙尘的一个主要沉积区。从重矿物组合和粒度分析结果看，大气降尘与塔克拉玛干沙漠砂的背景值以及亚沙土、黄土具有较好的相似性，从而证实塔里木盆地的大气降尘主要来源于盆地内部沙漠砂的微砂和粉砂组分。而分布于昆仑山北坡的亚沙土与黄土正是由塔里木盆地内部地面盛行的西北和东北风吹蚀沙区沉积物，经风力长期搬运分选形成的。

The precipita tion of d ustfall in sou thern basin was obviously higher than that in northpart.The dustfall in the piedmont of Kunlun Mt.was the highest and attained to 1 127.5t· km￣(-2)·a￣(-1)(Qira county,1990).Based on the actual observation in April,1990,the dustfall inQira county was 61.52t·km￣(-2)·mon￣(-1).while that in Xiaotang,Luntai county was only 4.12t·km￣(-2)·mon￣(-1).The sequence in the dustfall quantity of district from high to low was Hoton.Kashi,Bayingolin Mongolian Autonomous District and Aksu.The observation during 1989 to 1990showed that a tmospheric dustfall mainly concentrated in two season of spring and sum mer,andoccupied 76%of annual dustfall,and that of fall and winter occupied 24%,The highest value ofdustfall occurred in July to August each year,and the lowest value occurred in December toJanuary,Spatial distri bution of dustfall in the basin correspOnded with the regional frequen cy(days)of dust storm and strong wind.The consistency became more obvious,espocially in southfringe of the basin. Comparison of dustfall quantity between gobi and oasis at the same time,height and winddirection suggests,that the dustfall in oasis is nearly 3 times higher than that in gobi,which showedthat oasis might be a main dustfall place. It is re ported that the sub -sandy loess and loess on north slope of Kunlun Mt.and Altun Mt.were aeolian,which might be related to the dustfall there, The analysis of hcavy mineral assemblageand the particle-size of dust showed that the d ustfall was well similar to the background value ofTaklimakan Desert and that of sub-sandy loess and loess,It is concluded that the atmospheric dustfallin the basin mainly came from the very-fine sand and coarse silt of dune field.Therefore,the sub-sandy loess and loess on north slope of Kunlun Mt.and Altun Mt.were wind- eroded depositstransported by northwest wind and northeast wind from the in terior of the basin.