三峡库区奉节—云阳的低阶地与地壳运动、河谷深槽与古洪水的新解释

THE NEW VIEWPOINTS OF QURER AND CRUSTAL MOVEMENT,VALLEY DEEP TROUGH AND PALAEOFLOOD, FROM FENGJIE COUNTY TO YUNYANG COUNTY IN THREE GORGES RESERVOIR AREA

前人对三峡工程库区地壳运动与阶地类型的研究结果认为是间歇性抬升和基座阶地.文章从滑坡研究入手,对奉节白衣庵滑坡前沿深切古河湾中保存良好阶地的第四纪不同岩性沉积物的沉积关系、沉积年代、沉积气候等进行了重点研究;对云阳宝塔-鸡扒子滑坡及其附近的汤溪河口阶地与类型、阶(台)地沉积关系、沉积年代与成因、岩性等进行了对比分析;另外,对奉节白衣庵和云阳宝塔-鸡扒子两滑坡与河谷发育、深切河槽的发育关系、形成时代进行了讨论;同时还对旧县坪、故陵滑坡的发生年龄与其上阶地进行了分析.研究结果表明,峡区西云阳-奉节一带T1和T2阶地均为内叠(嵌入)阶地,地壳运动在最近50万年期间有4次上升,3次下降,在总体呈上升的背景下,近12万年期间升降幅度较前降低,频度则增加.此外,还讨论了与地壳运动、阶地形成有关的滑坡与河谷发育关系,发现深切河槽的形成时间是30万年前的MIS 9早中期;白衣庵、宝塔、旧县坪等大滑坡均是河谷深槽形成后发生的;证实'40～30kaB.P.的高温大降水'时期是古洪水发生期外,还存在更早期的古洪水沉积.

The crustal movement type is intermittent uplift and the terrace pattern is main bottom terrace in Three Gorges reservoir area, that are the former people viewpoint. The sediment relation, sediment time, and sediment climate of Quaternary terrace deposit in front of Baiyi＇an landslide are important to this study. On the basis of the comparative analysis of terrace deposit relation, deposit time, origin, and lithology in the Baota landslide, the relation between two landslides and valley development, incised channel, are studied. An analysis of the time and terrace of the Jiuxianping landslide and the Gulin landslide educed a type of second bottom and second terrace from Yunyang County to Fengjie County in the west reservoir area, an inset terrace. In the past five hundred thousands years, there was four times the uplift and three times the falloff of crustal movement. The amplitude of crustal movement reduced while the frequency of crustal movement rose with the uplift wholly in the past one hundred and twenty thousands years. Otherwise, the relation of landslide and valley development, the forming time of incised channel, the palaeoflood deposit and terrace are studied in the paper. The conclusions are as follows ： the formation time of deep troughs is early-middle of MIS 9, three hundreds thousands years B. P. The Baiyi＇an landslide, Baota landslide, and the Jiuxianping landslide occurred after the formation of deep trough. There are also older palaeoflood deposit before the palaeoflood period of “40 - 30kaB. P. megatemperature precipitation”.