Sedimentary characteristics of Yigeziyer River terraces of West Kunlun, China and its implications for river evolution

This study obtained heights, distribution, development and sedimentary characteristics of terraces through field geological investigation on Yigeziyer River terraces in the piedmont of West Kunlun. On this basis, authors further investigated development genesis of terraces and evolution process of river by analyzing sedimentary facies and paleo environments of different river terraces. The results show that the Yigeziyer River developed two pedestal terraces(T4 and T3)and two accumulation terraces(T2 and T1), which formed at about 80～100 ka B.P., 40～50 ka B.P., 18～30 ka B.P., 5～8ka B.P. respectively. The terraces resulted mainly from periodic tectonic uplifting, with limited effect from climate change, and the difference of terrace types was mainly influenced by river evolution. Terrace sedimentary facies analysis shows that the main sedimentary facies of T4 and T3 are debris flow sedimentary and alluvial-proluvial fan sedimentary respectively, with strong river erosion and intermittent accumulation. During the T2 sedimentary period, the river system changed greatly, the sediment shows multi-cycle braided river deposit, with enhanced accumulation. The sedimentary facies of T1 terrace was mainly channel-floodplain deposits, with the erosion-accumulation process towards to balance.