关键词: 地下水库, 河型, 古河流, 古河道带, 相沉积, 古河道分期, 亚砂土, 截点, 亚粘土, 冲刷面

Abstract: Nangong Underground Beservior lies on the old channel zone of Damiug-Qinghe-Jingxian-Qingxian at Hebei Plain (code number: 112(1) B). Explorations and dissec-tions on the reservior have been made in recent years, and the results show that the deposit has the typical marks of river-facies deposit such as: a scoured surface and river-bed holdxip-f acies deposit; an progressively thincr upwards cycle of sedimentation; thin and fine deposits along river bed caused by one-way water flow; the remains of fresh water organism such as clam shells; "V" traces, pits and shallow channels on the surface of the quartz sand.The old river developed on a scoured s’lrfaee of brown redish clay in the drpth of about 30 m and it was accumulated successively into three stages. Stage I (about 20-30 m deep), stage II (about 8-20 m deep’i and stage III (about 0-8 m). Among them, stage T was a braided channel, transporting sand mainly by bed load and saltation load. Stage II was a braided-straightward one. transporting sand mainly by mixed load, and stage III was a straightward-curved one, transporting sand mainly by suspension load.The accumulation of three stages of the old channels represents three different geographical landscapes of Nangong Underground Eeservoir at late-recent geologic period: during stage I, the sea level was lower, the climate was cold and humid, the discharge of the river was large and the current velocity was swift, therefore a landscape of pouring and roaring flood was emerged on the river. During the stage II, the sea level uplifted, the climate was warm and humid, the discharge of the river was smaller and the current velocity slowed down. Therefore,a landscape of flurishiug biology lakes was emerged on the river. During stage III, the sea level lowered down, the climate was dry and cold, the discharge of the river was small and variable, a dry landscape with drought, waterlogging and salinization of soil occured alternatively.