Research On Quaternary River Terraces In The Upstream Of Yarkant River Watershed

Scholars in the domestic and overseas did some researches on the piedmontterraces in the analysis of quaternary river terraces in west Kunlun, and focused on thedownstream of Yarkand river watershed, but there were little researches on riverterraces within the west Kunlun hinterland. This paper was based on the regionalgeological survey projects with the scale of1:50000in Xinjiang Province, and thedata was from measured sections of quaternary river terraces in the upstream ofYarkant River watershed, and took sporopollen samples and OSL(OpticallyStimulated Luminescence) samples. With the analysis on sporopollen and OSL, weget the results as follows:1、The major types of river terraces developed in Yarkand River watershed werepedestal terraces and accumulation terraces, all of which had3levels. Sediments in allterraces were gravel, coarse sand and clay. Clay in pedestal terraces was less than thatin accumulation terraces, and the particle size kept the same in the both top andbottom. While there were more fine sands and clay in accumulation terraces,developed the parallel bedding, the particle size turned smaller from the bottom to thetop.2、The results of sporopollen released that the river terraces in the upstream ofYarkand river formed from Holocene, and the type keep the same, which suggest thatthe climate keep the same in the forming of all terraces, so tectogenesis have moreeffects on the formation of river terraces.3、The results of OSL released that there were3levels of river terraces in theupstream of Yarkand River, Level terrace formed in9.5±1.34ka, the relative heightwas21.3m, the uplift rate of west Kunlun was2.24m/ka at that time; Second terraceformed in28.8±4.9ka, the relative height was20.1m, the uplift rate of west Kunlunwas1.04m/ka at that time; Triple terraces formed in43.2±4.7ka, the relative heightwas24.8m, the uplift rate of west Kunlun was1.72m/ka at that time. The resultsreleased that the west Kunlun took3neo-tectonic uplift from upper Pleistocene(50ka).Previous researches on3Piedmont terraces of Tizinafu River and Kalakashi River inpiedmont belt of west Kunlun, released that there were four levels terraces in piedmont belt, which developed in100kaB.P.、50kaB.P.、30kaB.P. and8.5kaB.P.respectively, the uplift rates were1.8m/ka,0.57m/ka,1.75m/ka and0.22m/karespectively. All of those suggested that the time and uplift rates in the plateauhinterland was consistent with that in piedmont belt, but the types and levels wasdifferent. This may resulted from heavier uplift and erode the earlier Ⅳ levelterrace, but the accommodate space in piedmont belt was very big and suited todevelop and preserve the river terrace. However, neither in piedmont belt nor inplateau hinterland, tectonism was the major reason in the formation of river terrace.