华北山地的古河道与古水系*

华北山地早第三纪地貌奠定了现代水系格局的基础。至晚第三纪晚期河流已发育到中-老年阶段。第三纪末期至第四纪早期,山地差异活动剧烈,断陷盆地形成,内、外流水系并存,遗留下垭口与顺直-曲流型宽谷。第四纪中期,河流袭夺,内陆水系先后变成外流水系,并生成“U”形宽谷。第四纪晚期,河流下切,水系变迁,现代水系形成。

PALAEOCHANNEL AND PALAEODRAINAGE PATTERNS IN THE NORTH CHINA MOUNTAINS

Two drainage patterns are found in the North China Mountains:One is a longer river system across the ranges of the Taihang Mt.and the Yanshan Mt,it initiated in the Eocene.the first episde of the Himalaya Orogenesis,and subsequently passed through the primary stage of formation in the Eocene,and lateraly windening stage in the Neogene.The internal drainages coexisted with the exterior draginages from the Early Pleistocene to the Middle Pleistocene and the lateral continuity stage was in the Middle Pleistocene.The river incising and modern drainage forming stage was in the Late Pleistocene.The other is a shorter river system origined from the east pedimont area of the Taihang Mt.and the south pedimont area of the Yanshan Mt..It started in the beginning of the Early Pleistocene,the third episode of the Himalay Orogeny,and subsequently went on incising stage in the Early Pleistocene,lateral windening stage in the Middle Pleistocene,rivers dissecting and present drainage forming stage in the Late Pleistocene.Comparing the two drainage systems,there are two different valleys in the river geomorphology.The former has a three series supPerposition-tray-like valleys,broad valleys with"U"-like and"V"-like gorges.The later has a two series suPerposition-broad valleys with"U"-like and"V"-like gorges.