• 责任者：Wang Xiaoyan (School of Geography ; Beijing Normal University ; Beijing 100875 ; China) ; Qiu Weili
• 刊名：Quaternary Sciences
• 出版年：2013
• 卷期：33(4)
• 关键词：流水地貌 ; fluvial features ; 冲积层 ; alluvium ; 山西 ; Shanxi Province ; 陕西 ; Shaanxi Province
• 页码：p.715-722
• 图表：3 illus., 3 tables, 40 refs.
• 分类号：1400
• issnNo：ISSN1001-7410
• isbnNo：CN11-2708/P

     Because of its complex history,the Yellow River is a good case for fluvial geomorphology studies.The Jinshaan Gorge is one of the key parts to understand the evolution of the Yellow River.Since 1922,researchers have made great progress in the study of the evolution of the Yellow River in the Jinshaan Gorge area.But there are some disputes still remained about the Tangxian Surface,an erosion surface formed in the Miocene and Pliocene,and the alluvium on it.The main divarication is whether the Tangxian Surface is a terrace of the Yellow River or the alluvium on the Tangxian Surface is formed by the ancient Yellow River.Baode-Fugu area,located in the north part of the Jinshaan Gorge,is famous for the Neogene red clay sediment in which Hipprion fauna is unearthed.The recent studies of red clay offer a chronological data to discuss the age of both the red clay,other contemporaneous sediment and the underneath erosion surface of Tangxian Stage.The present paper is based on the survey of eighteen sediment outcrops on the Tangxian Surface in the Baode-Fugu area.Twenty one samples were collected from gravel layers for sediment analysis.A topographic profile across the Yellow River shows that there is a wide bedrock valley stretching along the modern Yellow River,which is about 170m above the river level.According to the previous magnetostratigraphic studies of the red clay and fluvial sediment,the Tangxian Surface was formed at least 8.0Ma ago.Gravel statistic result shows that the gravel sitting on the Tangxian Surface is 〉1.5 in the complexity index of components and is characterized by an average roundness of ca.2 or 〉2,i.e.sub-rounded and rounded,with a variance of 〉0.5.The rock type of the gravels indicates a mixture of distant and local source.Combining the evidences above,it is reasonable to conclude that there used to be a river flowing along a similar course direction of modern Yellow River in this region during the Middle Miocene.Though it is much smaller than the Yellow River today,it is a part of the ancient river when the Yellow River connected the Weihe and Hetao basins and it can be named as the Ancient Yellow River.With the incision of the Jinshaan Gorge,the Tangxian Surface became the highest terrace of the Yellow River in the study area.On both side of the Tangxian Surface,gravels interbeded with the red clay are mainly deposits of the tributaries.Their relatively simple components （ca.1 in complexity index）,poor roundness （〈1.5 in average,sub-angular）and a small variance of less than 0.32 suggest a local source of the sediment.