嘉陵江曲流型叠置河谷成因对区域地质环境的响应

Origin of Meander Shape-Superimposed Valleys in the Middle Jialing River:Responses to Regional Geological Environment

为了明确嘉陵江曲流型叠置河谷形成原因及其对区域地质环境演化的响应,在综合分析区域地质地貌背景、水系演化模式等基础上,认为嘉陵江曲流型叠置河谷的成因可能是三峡贯通这一重大地质事件作用的结果.三峡贯通前,古分水岭两侧的四川盆地和江汉盆地水系相互独立发育;由于江汉盆地水系溯源侵蚀速率快,切穿其与四川盆地的古分水岭,分水岭西侧水系被袭夺后东流,两大水系完成统一;在三峡贯通事件作用下,嘉陵江古自由河曲快速下切嵌入基岩,形成了曲流型叠置河谷的壮观地貌景观.基于砾石层中冲积物的电子自旋共振(electron spin resonance dating,ESR)测年结果,表明三峡贯通的时间大致在早-中更新世之交.第四纪地壳活跃,三峡的贯通可能与该时期内的"昆仑-黄河运动"密切相关.

In order to define the formation of the Jialing meander shape-superimposed valley and response to the regional geological environment evolution,the regional geological background,together with the evolution model of water system are explored.It is found that origin of the meander shape-superimposed valley maybe controlled by cut-through of the Three Gorges.Water systems of the Sichuan basin and the Jianghan basin had developed separately due to the ancient watershed before the cut-through of the Three Gorges until the Jianghan basin drainage cut through the ancient watershed,captured the western drainage of watershed because of quick erosion rate in the eastern Jianghan basin,and the two drainages were unified at last.Ancient meander of the Jialing River was fast undercut,inset the bed rock and finally developed the meander shapesuperimposed valley,the spectacular landscape.Based on ESR（electron spin resonance dating）ages of river sediments in the gravel layers,we believe that cut-through of the Three Gorges happened approximately in the Early-Middle Pleistocene.The cut-through maybe closely related with the＂Kunlun-Huanghe Movement＂,which happened in this period because of the strong crustal activity in the Quaternary.