DUSTSTORM, MONSOON AND UPLIFT OF QINGHAI-XIZANG PLATEAU

Recently, China has implemented a program of control sandstorms in surrounding areas of Beijing. This program is in order to bid farewell to sandstorms in Beijing by 2010. The sand and dust storms become a hot research topic in China. A North Pacific core (LL44-GPC3) has been used to evaluate changes in influence of strong duststorms. From this core, eolian sedimentation decreased from 70 to 50 Myr ago. Fine eolian grain size and the low accumulation rates in the Eocene and early Oligocene are in agreement with a vigorous trade wind, the evaporite formation in Southeast Asia and the South China was displaced by the tropical rain florist, which was connected with the uplift of the Tibet Plateau by 65-45 Myr ago. During 37-30 Myr ago large increases in grain size was connected with the uplift of eastern Tibet Plateau. A moisture channel from India Ocean to Lanzhou Basin formed. The evaporite formation in Lanzhou Basin disappeared at 32 Myr ago. It seems that the vigorous winter and summer monsoon formed at that time. A relatively arid temperate steppe or forest-grassland environment appeared, where the early strong duststorms happened. So did as significant change of eolian deposition at 25, 15 and after 3 Myr ago. Since 15 Myr ago the northwestern China has been getting worse to worse. It reflected the rainshadow effect by the Tibet Plateau. Eolian accumulation rates sharply increased at 3 and 1.2¨C0.7 Myr ago. From distribution of calcium soil and loess, the steppe or forest-grassland environment shifted from 104^oE to 106^oE, 112^oE and 114^oE respectively at 32, 29-8, 7-3.5, and 1.2-0.7 Myr ago. As the semiarid and arid area expands, and monsoon strengthens by uplift of Tebit Plateau, the frequency of strong duststorms or eolian accumulation rates sharply increase. The yearly expanding acreage of desertified land is from 1,560 square kilometers in the 1950s-1970s to 3,436 square kilometers during the last five years of the 1990s. It shows desertification-control projects do not change a deterioration situation . But the duststorm sharply decreased in the 1970s-1990s. It shows the frequency of strong duststorm is not directly connected with sandstorm and acreage of desertified land, a sky with floating dust in spring could never bid farewell in Beijing, even if the present desertified land situation recovered to 1950s.