ABSTRACT Since the Cenozoic era, the central Yunnan region has been at the front of the southeastern Tibetan Plateau, and the release of plateau stresses has significantly influenced the evolution of drainage systems and geomorphic patterns. The Longchuan River in central Yunnan Province is a first‐level tributary of the southern bank of the Jinsha River, and its basin is a standard watershed zone of the Red River, Jinsha River, and Pearl River. This basin is a sensitive area for the evolution of large river systems. Consequently, this region offers an optimal setting for investigating the coupling relationship between tectonic activity, climatic variations, and river system evolution. In this study, optically stimulated luminescence (OSL) dating and identification of heavy minerals and palynology were conducted on the newly discovered river terrace sediments of the Longchuan River. The results indicated the following. (1) The Longchuan River began to develop during the late Quaternary, and the sedimentary periods of three terraces (T2, T1, and T0) in the middle Yuba area were 69 ± 1.2 ka, 54 ± 3.9 ka, and 5.6 ± 1.3 ka, respectively. The deduced downcutting rates are 0.40–0.42 mm/a, 0.18–0.21 mm/a, and 0.28–0.46 mm/a, are lower than those of the Jinsha River to the north, indicating that the crustal uplift in the Longchuan River Valley is weaker than that in the Jinsha River Valley. (2) Since the late Pleistocene, the vegetation in the Longchuan River Basin have been represented by Pinus , Betula , Ilex , Theaceae, and other mixed forests with fern growing under the forest, reflecting a regional climate that has become increasingly hot and humid. (3) During the T1 to T0 deposition period, the headward erosion direction of the upper reaches of the Longchuan River gradually evolved from the Shiguanshan area to the Tianzimiaopo area. (4) The Longchuan River system may have inherited extinct Quaternary lake basins in the region, with its development and evolution possibly influenced by tectonic faults as well as climatic factors. This study elucidates the detailed processes and mechanisms of river system evolution at the plateau margin under the coupled driving forces of tectonic activity and climate change. It provides a key case study for understanding the dynamics of the geomorphic system in the southeastern Tibetan Plateau, offering significant value for advancing the theory of tectonics‐climate interactions and predicting future regional environmental evolution trends.
Cao et al. (Tue,) studied this question.