Palaeoglacial and palaeoenvironmental conditions of the Gangdise Mountains, southern Tibetan Plateau, as revealed by an ice-free cirque morphology analysis

摘要

Cirque morphology can be used to indicate patterns of palaeoglaciations and palaeoclimate. Many cirque morphological analyses have been conducted worldwide, but only a few studies focus on the Tibetan Plateau (TP). In this study, we mapped 1652 ice-free cirques in the western, central, and eastern sectors of the Gangdise Mountains, southern TP. We calculated the cirque size, shape, and topography, and categorized them into fifteen lithological units to study their morphological parameters. Results show that cirque size decreases from west to east, implying that the western sector frequently developed cirque-type glaciers or was eroded by dynamic glaciers during the initial period of cirque development. Bedrock type can also explain the difference in cirque size in the three sectors, as the dominating bedrocks of the cirques in the western sector are relatively 'soft'. The relatively small L/W ratios for the cirques in the western sector implies the important effect of widening on cirque planar enlargement in this sector. The decreasing trend of L/H and W/H ratios and the increasing trend of A(3D)/A(2D) ratios from west to east imply the importance of deepening for the cirques in the eastern sector. Moreover, the different bedrock types may be attributed to the different cirque shapes. The NE-facing bias for the cirques reveals the impact of solar radiation. This implies that the Gangdise Mountains were characterized by a relatively low cloudiness during the ablation season. The E bias for the cirques in the eastern sector reveals that the Indian Summer Monsoon was not strong. (C) 2020 Elsevier B.V. All rights reserved.