金沙江“长江第一湾”段河谷地貌、沉积与发育

摘要

“长江第一湾”位于青藏高原东南边缘及其向云贵高原过渡的边缘地带，金沙江在该区深深切割了青藏高原东南边缘。按照河谷地貌与沉积特征，其宗—大具段金沙江可划分为其宗—下落鱼段、虎跳峡段和大具盆地段。详细描述了各河段的地貌与第四纪沉积特征，并根据同位素年龄等数据讨论了河流沉积物、湖相沉积物及冰川与冰水沉积物，特别是河谷中厚达150~250m的埋藏沉积物的成因与形成时代。在此基础上，讨论了研究区及邻区自中新世以来的金沙江河谷发育与青藏高原隆升问题。%The First Bend of the Yangtze River refers to a segment of incised valleys in the upper reaches of the Jinsha River where the river makes a 135° turn from SSE to NNE. This segment is located on the southeast margin of the Tibetan Plateau, that is, the transition zone from the Tibetan Plateau to the Yunnan-Guizhou Plateau. According to the geomorphic and sedimentary characteris⁃tics of valleys, it can be divided into three sectors:the Qizong-Xialuoyu sector, the Tiger Leaping Gorge sector, and the Daju Basin sector. Their landforms and Quaternary sedimentary characteristics are described in detail in this paper. The origins and formation ag⁃es of alluvial sediments, lacustrine sediments, and glacial and glaciofluvial sediments in these sectors, especially 150~250m thick bur⁃ied sediments, are also discussed on the basis of isotopic ages and related analytical data. The development of the Jinsha River valleys and the uplift of the Tibetan Plateau since the Miocene are also discussed.