长江三峡地区夷平面分布特征及其形成年代

通过野外路线考察,典型地区填图,地质、地形图判读,航片、卫片验证、核对及前人资料分析和年代学方法,对长江三峡地区的地貌进行了研究。结果表明:该区现代河谷之上存在两级夷平面和一级剥夷面。高夷平面分布高度为海拔1700~2000m,完成于老第三纪末;低夷平面分布高度为海拔1200~1500m,完成于上新世末;剥夷面分布高度海拔为800~1200m,形成年代为3.4~1.8M a B.P.。高夷平面在地貌上表现为宽浅的坳谷洼地与低矮的缓丘相结合,呈现一派波状起伏的老年期地貌景观;低夷平面多表现为高大的岩溶丘陵与大型洼地相组合的岩溶台面,洼地两侧多有水平溶洞发育;剥夷面可以岩溶盆地、山间盆地、岩溶台面、河谷盆地、岩溶洼地及河流宽谷等多种地貌形式存在,没有大范围可比性。

FAETURES OF THE PLANATION SURFACE IN THE SURROUNDING AREA OF THE THREE GORGES OF YANGTZE

By way of interpretation of large-scale topographic maps and satellite images,field investigation,geomorphic mapping to typical regions,analysing the topographic surface features and chronological study,the topographic surfaces surrounding the Yangtze Gorges(the Three Gorges) were analyzed.Two planation surfaces and one pediment in the study area were found.The higher planation surface,1700m to 2000m above sea level,was formed in the latest period of Early Tertiary.The lower planation surface,1200m to 1500m above sea level,was formed in the Late Pliocene.The pediment was formed from 3.0~3.4 Ma B.P.to 1.8~2.04 Ma B.P..Thereafter the modern river system of Yangtze was stable and began its incision to form the present channels system.