河流阶地形成过程及其驱动机制再研究

河流阶地的形成是在内因(河流内部动力变化)和外因(低频和高频气候变化、构造运动、基准面变化)共同作用下的结果.受单一气候变化制约的河流阶地发育模式可以解释由于沉积物通量和径流量变化引起的河流堆积-侵蚀过程,但它难以解释形成多级阶地的逐步(或间歇性)下切过程.多级阶地的形成可能同时受到构造抬升和周期性气候变化的制约.由于下切过程的滞后效应,侵蚀和冰川均衡抬升、河谷的侧向侵蚀过程等影响,山地的构造抬升与河谷的下切之间并非一种简单的线性关系,应当慎用河谷的下切速率来代表山地的抬升速率.

Formation Process and Driving Mechanisms of Fluvial Terrace

The formation of fluvial terraces results from the combination of internal factor(change in intrinsic fluvial system dynamics) and external factors(high-and low-frequency climate change,tectonic uplift,and base level change).Models of climate-controlled fluvial terrace formation can explain the tendencies towards riverbed aggradation and degradation resulting from changes in sediment and water supply.However,these models can not explain the progressive(intermittent) incision recorded by several terrace staircases.The formation of river terrace staircases might be the result of combination of climate changes and tectonic uplift.When the resisting power resulting from increment of sediment supply and decrement of river discharge exceeded the stream power resulting from increment of river gradient due to tectonic uplift,river aggradation occursed during glacial periods.However,river channels behaviored in a contrary way during glacial-interglacial periods,when river incision occurred and the effect of tectonic uplift was then released.Due to delay effect of river incision,glacial and denudational isostatic uplift,as well as process of lateral erosion,river incision was not linearly related to tectonic uplift.Utilization of vertical incision rate to represent uplift rate should be done cautiously.