GRAIN-SIZE DISTRIBUTION ALONG THETUMEN SECTION OF SOUTHERN TENGGER DESERT,NORTHWESTERN CHINA AND ITS PALEOCLIMATIC IMPLICATIONS DURING THE LAST DEGLACIAL
The Tumen sequence(41LD-52L)at the southern edge of the Tengger Desert in the northwestern China covers the time span of 14930-11640 aBP synchronously with the last Deglacial.It consists of 3 layers of loess-like sandy loams,2 layers of sandy loess,2 layers of lacustrine facies,and 2 layers of paleosol. The results of grain-size analysis show that silty sands dominate the major proportion ranging from 21.69%upto 79.47% with an average of 50.33%;Sands comes the second with a distribution range of 3.97%~75.37% and an average of 38.17%;The lowest proportion is clay,ranging from 2.34% to 34.02% with an average of 11.50%.Symmetrical changes in grain-sizes,Mz andsigmaare observed in vertical direction,indicating that the climate in southern Tengger Desert during the last deglacial had significantly varied for at least 4 warm-cold fluctuations,including warm-humid phase W1-W4 and cold-dry phase C1- C4.The W2,W3 and W4,are corresponding to the late Allerod,early Allerod and Bolling in the GRIP ice core record,respectively,while the C1,C2 and C3 are corresponding to Younger Dryas(YD)and Inter Allerod Cold Period(IACP).In addition,the Yonger Dryas(12650-11640 aBP)and Bolling-Allerod warm period(BA)(14930-12650 aBP)indicated by grain sizes are corresponded well and in phase with oxygen isotope records(delta~(18)O)in GRIP cores,demonstrating that the driving force of such a change in southern Tengger desert is chiefly related to the thermohaline circulation in high nothern latitudes represented by Greenland ice core.