对我国西南地区河谷深厚覆盖层成因机理的新认识

近年来，在我国水能资源开发过程中，发现各河流现代河床以下普遍堆积厚达数十米甚至上百米的松散堆积物。河谷深厚覆盖层的存在，不仅严重制约了工程坝址的选择，影响相关流域水电资源的开发利用，也给坝工设计带来巨大的困难。由于深厚覆盖层埋藏于现代河床之下，其形成年代一般先于一二级阶地，有悖于河流发育演化的常理，其成因一直令人费解。首次将河谷深切和深厚堆积事件与全球气候变化、海平面升降运动、地壳运动等有机地联系起来，并提出冰期、间冰期全球海平面大幅度升降，是导致河流深切成谷并形成深厚堆积的主要原因的新观点。在此基础上，引入层序地层学原理，从理论上较好地解释了全球气候变化导致海平面和河流侵蚀基准面大幅变化，并产生河谷深切和深厚堆积的原因和过程。最后，进一步将沿河大型古滑坡的孕育和发生与河谷深切事件相联系，提出沿河大型古滑坡是在河谷深切期因前缘临空较好而形成的新观点，从而对沿河古滑坡前缘剪出口高程往往低于现代河床数十米的原因给出了较合理的解释。

New Views on Forming Mechanism of Deep Overburden on River Bed in Southwest of China

Recently, widespread thick ranging from 10 to even 100 meters loose accumulations were found below modern rivers bed during China's hydropower resources development process. Deep overburden on river bed not only seriously hampers the dam site selection, impacts correlation basin hydropower resources development and exploit, but also brings enormous difficulties to dam engineering design. Because deep overburden is buried under modern river bed and its formation ages priors to the first and second terrace, this phenomenon is contrary to common sense of the river evolution, so its causes have been confused. Deeply cut valley and deep accumulation events, global climate change, sea level eustacy motion and crustal movement organically linked up are reported for the first time in this paper. The author points out a new viewpoint that global sea level greatly change during ice age and interglacial stage is the main reason that causes deep river valley and forms deep accumulation. On this basis, this paper explain that global climate change result in sea level and erosion basis considerable growth, and causes and processing of production deeply cut valley and deep accumulation by applying the principle of sequence stratigraphy. Finally, this article further related large ancient landslides preparation and occurence along river and deeply cut valley events. The author propose a new perspective that along river large ancient landslides were formed by front free face better in the deeply cut valley period. Therefore, these new views provided a reasonable explanation on the elevation of landslide front shear opening below the modern river bed over 10 meters.