黄河上游的阶地与水系变迁

ON RIVER TERRACES OF THE UPPER REACHES OF THE HUANGHE RIVER AND CHANGE OF THE RIVER SYSTEM

黄河上游于贵德盆地和共和盆地中有7级阶地,再往上游方向存在阶地级数递减的趋势.共和盆地中还有3级古黄河阶地.黄河上游水系是通过一级级河流袭夺相继贯通的.共和盆地与贵德盆地间的黄河古道始于中更新世末期,龙羊峡河段始于60kaB.P.前后.玛多与唐乃亥间的峡谷河段是20ka B.P.才贯通的.

The upper reaches of the Huanghe (Yellow) River, a length of 1350 km from Gyaring Lake to Guide county, cuts through the great slope of the northeast part of the Qinghai-Xizang (Tibet) Plateau and it runs through a few of Mesozoic-Cenozoic depositional basins, for example, Guide basin, Gonghe basin, Xinghai basin, Zoige basin, Ngoring-Gyaring basin etc. , the sections between them are a series of gorges of the Huanghe Riv-er.Based on author's investigation, there is a terrace of 7 steps in the Huanghe River val-ley by Guide county, a terrace of 3 steps being formed by the ancient Huanghe River and 7 steps in Gonghe basin, 6 steps by Gamao Yangqu town, 5 steps by Tangnaihai town, Xinghai County, 3 steps by Maqu town, Gansu Province, and one step by Ngoring-Gyaring Lake.The overall upper reaches of the Huanghe River was linked up by a series of the stream captures occurred after strongly uplifting of the Qinghai-Xizang area into a plateau. A section of the ancient Huanghe River through the place Gahaitan located on northeastern Gonghe basin towards east into Guide basin was developed during the end of Middle Pleistocene to the middle of the Late Pleistocene, and then it migrated towards southeast to the place Longyangxia Gorge about 60000 years ago. And the gorge from Maqu to Tangnaihai was linked up about 20000 years ago.