Formation of the First Bend in the late Eocene gave birth to the modern Yangtze River, China

The First Bend on the Yangtze River (China), the point where the river ceases flowing toward the south and heads toward the northeast, has been one of the most strongly debated geomorphic features in Asia because it holds the key to understanding the history of the Yangtze River and is linked to the tectonically driven surface uplift of the southeastern Tibetan Plateau. Mid- to upper Eocene sedimentary rocks preserved in the Jianchuan Basin located immediately southwest of the First Bend demonstrate that a large river system, presumably the paleo-Jinshajiang River (the upper Yangtze), used to flow south through that region. Provenance analysis of sediments over the wider region, based mostly on U-Pb dating of detrital zircon grains, confirms that the once south-flowing paleo-Yangtze River originated in the Tibetan Plateau and flowed into the South China Sea. Inversion of the Jianchuan Basin, starting in or after the latest Eocene and associated with wider plateau surface uplift at that time, caused the river to be diverted toward the northeast where it was confined along tectonic lineaments associated with strike-slip faulting, giving birth to the First Bend, a major step in the formation of the modern Yangtze River.

Automated summary

The formation of the First Bend of the Yangtze River is closely related to the tectonic evolution of the Tibetan Plateau, with evidence from the paleo-Jinshajiang River indicating a southern source originating in the Tibetan Plateau flowing into the South China Sea. This diversion of the river towards the northeast due to tectonic movements ultimately led to the creation of the modern Yangtze River.