Development of Holocene Fluvial Terraces in the Eastern Qilianshan Mountain and Its Relationship with Climatic Changes

详细信息   

• 责任者：Hu Xiaofei (Key Laboratory of Western China’s Environmental Systems ; Ministry of Education ; Lanzhou University ; Lanzhou 730000 ; China) ; Pan Baotian
• 刊名：Quaternary Sciences
• 出版年：2013
• 卷期：33(4)
• 关键词：河流阶地 ; river terraces ; 祁连山 ; Qilian Mountains
• 页码：p.723-736
• 图表：7 illus., 1 table, 52 refs.
• 分类号：1400
• issnNo：ISSN1001-7410
• isbnNo：CN11-2708/P

摘要

     Holocene terraces along most rivers in the NW China were well developed,while the process and mechanism about the Holocene terrace is poorly known.In the eastern Qilianshan Mountain（between 101°30＇E to 103°30＇E and 37°00＇N to 38°10＇N）,near Wuwei City,Holocene terrace is usually composed by 1~3 flights of sub-terraces,while this phenomenon is scarcely found with Pleistocene terraces.In order to disclose the mechanism of the formation the sub-terraces,we investigated the Holocene terraces in 13 river valley transections along 4 rivers（the Xiying,Jinta,Huangyang,and Gulang rivers） in the eastern Qilianshan Mountain.The depositing stratigraphy with each terrace was observed in detail and terrace age was accurately determined by 14 C dating method in the relative sediment of the Holocene terrace.Except the Xiying River,2~3 flights of Holocene sub-terraces were developed along other 3 rivers,especially along the Jinta River,the sub-terraces are distinct.Within each terrace stratigraphy,Holocene paleosol was usually developed in the overlying loess or colluvial sediment above the fluvial gravel layer.Analysis results of terrace ages indicate that river incisions mainly cumulated on the period of 7.5~3.0ka B.P.Based on the comparison between river incision ages and climatic records,we find that during the periods（5.9~7.2ka B.P. ,4.2~5.2ka B.P. and 2.4~3.3ka B.P.）of river incision,the climate was relative wet in the study area.This evidence may suggest that river incisions happened while the discharge increases and the sediment supply decreases according to increasing precipitation and better vegetation cover.The multiple incision periods in Holocene also suggest that one regular river incision（like Pleistocene terraces）is completed by multiple short-lived incisions and aggradations,and due to the local river valley situation,this process can be documented by small terraces staircases,or it will be erased by side erosion.Otherwise,different rivers with different sizes may have different responses to same climate changes that large rivers are sensitive to long-term climatic changes,while it is not sensitive to short-term climatic changes.