Evolution of glacial trough and influence factors of the Qingshui Valley in Luoji Mountain, Sichuan Province

Abstract

Luoji Mountain located at the southeast margin of the Qinghai-Tibet Plateau is one of the typical mountains in China where Quaternary glacier relics exist. The evolution of glacier landforms in the area plays an important role in the study of regional environmental change. In the Qingshui Valley on the east slope of the Luoji Mountain, two sets of ancient glacial trough valleys, namely the inner trough valley and lateral trough valley,are preserved. The inner trough valley is relatively intact. However, the lateral trough valley between 3450 m and3600 m in the shady slope is incomplete. Based on field investigation and model analysis, this study examines the evolution of the glacial trough valley. The model analysis shows that the A and B parameter values vary between 1.3101-15.2064 and 0.9695-3.2965 respectively and these values first increase and then decrease with decreasing altitudes. Both values indicate that the form of the glacial trough valley is atypical. The field investigation and model analysis indicate that lithology and headwater erosion have contributed to the shape of the trough valley. This study applied the ESR dating method to define the high and low moraine in the through valley. The result shows that the high lateral moraine was formed in ~58-84 ka BP, which was in the early stage of the last glacial cycle, corresponding to the Marine Isotope Stage 4(MIS4). The low lateral moraine was formed in 13-17 ka BP, which was during the last glacial maximum(LGM), corresponding to MIS 2. During the last glacial cycle two glaciations developed two sets of trough valleys respectively, that is, the early stage of the last glacial cycle contributed to the formation of the lateral trough valley, and the late stage of the last glacial cycle contributed to the formation of the inner trough valley. The glacial sequences in the Qingshui Valley also show that the glacial activities took place here accorded with other mountains in the surrounding areas of the Qinghai-Tibetan Plateau.