祁连山东段河流阶地的形成时代与机制探讨

第四纪期间祁连山东段发育了多级洪积台地与河流阶地，它们是研究区域构造活动与气候变化良好的载体。对该区主要河流阶地序列的野外考察，利用ESR、TL、IRSL以及^14C等测年方法，研究表明，第四纪期间石羊河上游的各大支流普遍发育了5～6级阶地，其中南营村附近金塔河五级河流阶地的形成时代大致为1．24 Ma B．P．(L)、0．78 Ma B．P．(4)、0．14 Ma B．P．(T3)、0．06 Ma B．P．(T2)和0．01 Ma B．P．(T1)，完全可以与该区沙沟河、黄河兰州段以及长江三峡段的阶地序列相对比。从各级阶地砾石层的堆积时代以及阶地的沉积特征分析，我们认为，即使在构造活动区域，气候变化在河流地貌演化过程之中起着重要的控制作用。

Age and Genesis of Alluvial Terraces in East Qilian Mountains

Based on field investigation, we find that the rivers generally developed 5-6 terraces in the east Qilian Mountains during the Quaternary. According to the ESR (Electron spin resonance) , TL (Luminescence) , IRSL (Infra-red stimulated luminescence) and 14C dating methods, the ages of the Jinta River terraces are 1. 24 Ma B.P. (T5), 0.78 MaB.P. (T4), 0.14 Ma B.P. (T3) , 0.06 Ma B. P. (T2), and 0.01 Ma B. P. (T1)from up to down. The Xiying River developed 6 terraces near the Xiying Reservoir, some ages are 0. 84 Ma B. P. (T6) , 0.25 Ma B. P. (T4) , 0. 14 Ma B. P. (T3) , 0. 06 Ma B. P. (T2). These terrace sequences can be roughly correlated with the stepped landforms found in upstream Yellow River and Yangtze River watersheds. After careful analyses on the ages of gravel bed accumulations and the ages of channel down-cuttings, we propose that climate variations play significant roles in controlling river terrace evolutions even within the tectonic active regions.