Macroscopic and microscopic evidence of Quaternary glacial features and ESR dating in the Daweishan Mountain area, Hunan, eastern China

摘要

Whether Quaternary glaciers existed in the Daweishan Mountain area is of great significance to the reconstruction of the Quaternary environments in the Yangtze Valley. This study investigated the macroscopic and microscopic features of Quaternary glacial features in the Daweishan Mountain area, and applied Electron Spin Resonance (ESR) dating to the clay and gravel sediments to determine their age. ASTER GDEM with a resolution of 30 m, combined with field investigation, recognized the glacial landforms in the Daweishan Mountain area. Cirques and firn basins were distinguished using a flat index of F= L/2D and a length-width ratio of G = L/W. Scanning Electron Microscopy (SEM) identified glacial traces on quartz sand grains of the clay and gravel sediments. ESR dating of 6 sections showed that the sediments were formed in 2 stages, 205-262 ka and 377-425 ka, equivalent to the late stage and middle stage of the Middle Pleistocene, respectively. There were at least 2 glaciations in the Daweishan Mountain area. In the late stage and middle stage of the Middle Pleistocene, the Yangtze Valley was influenced by a cold trough, and promoted glaciations developed in the Daweishan Mountain area.