When was the Yangtze River formed?

The Yangtze River, as the longest river in Asia, serves as a direct link connecting the Xizang Plateau and the Pacific Ocean. Delving into the formation and evolution of the Yangtze River can provide invaluable insights into the geological structure and climate changes occurring in East Asia. However, there is currently no consensus regarding the precise timing of its formation or the specific details of its evolutionary process.

To address this research gap, we conducted a comprehensive review, analysis, and comparison of existing sedimentological and geochemical data on the development and evolution of the Yangtze River Basin. Our study begins by examining the context of tectonic evolution and climate change, and subsequently delves into a discussion on the evolutionary process of the Yangtze River.

The results of our analysis reveal the followings: ① During the Late Mesozoic, a large river system formed in the Sichuan Basin that flowed southward. Additionally, tectonic subsidence during this period turned the Jianghan Basin and Wangjiang Basin into regional drainage centers. As a result, the upper, middle, and lower reaches of the Yangtze River Basin experienced segmented evolution. ② Between 60 Ma and 35 Ma, significant subsidence occurred in the Jianghan Basin, Wangjiang Basin, South Yellow Sea Basin, and East China Sea Basin, which continued to function as local drainage centers. During this time, the Jianghan Basin developed extensive salt lake deposits, suggesting the absence of major inflowing or outflowing rivers. However, the Paleo−Red River flowed into the South China Sea, marking the early phase of the evolution of the proto−Yangtze River during this time. ③ Approximately 20 Ma, the Xizang Plateau experienced vertical uplift and lateral extrusion, triggering extensive exhumation processes in the Yungui Plateau. As a result, the Paleo−Red River, which previously flowed southward, disintegrated entirely. In the Middle Miocene, the Three Gorges of the Yangtze River underwent significant incision, leading to the deposition of sedimentary material from the upstream Yangtze River in the Jianghan Basin, Nanjing area, and East China Sea Basin. Consequently, the Yangtze River, with a length exceeding 6000 km, emerged during the Miocene epoch, marking the onset of the evolutionary stage of the Yangtze River. ④ During the Pliocene, the downstream areas of rivers such as the Jinsha River, Yalong River, and Dadu River were affected by heavy rainfall to appear the large−scale landslides, leading to the formation of extensive Paleo−Xigeda Lake. Additionally, the formation of thick gravel layers was observed in various regions, including the Jianchuan Basin, Dadu River and Minjiang River basins, Wangjiang Basin, and the Nanjing area. The wide canyon formed in the Three Gorges region of the Yangtze River. These geological changes suggest a substantial enhancement of the hydraulic transport capacity of the Yangtze River compared to the Middle Miocene. During the Pliocene, the South China region exhibited a similar mountain−river−sea distribution pattern as is observed today, representing a developmental stage of the Yangtze River. ⑤ Between 2 and 1 Ma, Paleo−Xigeda Lake completely disintegrated, resulting in significant reorganization of the main and tributary streams in the Yangtze River. This process brought about notable changes in sediment sources in both the Jianghan Basin and the Yangtze River Delta. Subsequently, a new phase of rapid incision took place in the upstream Yangtze River around 0.7~0.5 Ma, leading to the reestablishment of river terraces in the Jinsha River, Dadu River, and the Three Gorges region. During the middle Pleistocene, as the East China Sea and Yellow Sea became submerged by seawater, the continued incision in the upstream Yangtze River combined with the influence of the seawater in the lower reaches resulted in a significant reduction in the topographic difference between the upstream and downstream erosion levels of the river. Consequently, there was a shift toward deposition processes in the lower reaches, leading to the gradual development of a deltaic landform. These changes indicate the entrance of the Yangtze River Basin into a mature stage during the Quaternary.

The development of fluvial landforms in the Yangtze River Basin was influenced by the interplay of tectonic processes, climate change, and local stochastic effects such as landslides, particularly during the uplift processes of the Xizang Plateau and the surrounding mountains.