Evolving Yangtze River reconstructed by detrital zircon U‐Pb dating and petrographic analysis of Miocene marginal Sea sedimentary rocks of the Western Foothills and Hengchun Peninsula, Taiwan

The timing of the establishment of the Yangtze River, whether prior to the early Miocene (~24 Ma) or more recently (~2 Ma), has been a point of much debate. Here we applied detrital zircon U‐Pb dating to Miocene sedimentary rocks from Taiwan and to estuary sands from modern rivers in SE China to trace sediment provenance and to further constrain the evolution of the Yangtze River. Detrital zircon U‐Pb ages from Miocene sandstones of the Western Foothills show similar age spectra to Miocene and modern sediments in the Yangtze River drainage and some similarity to the Minjiang River sediments. However, they differ significantly from ages in some sandstones from the Hengchun Peninsula accretionary prism and from the estuary sands of the Jiulongjiang River. This information, together with petrographic and sedimentary facies analysis, argues that the Jiulongjiang and Minjiang Rivers were major sources to some Hengchun Peninsula turbidites (~12 Ma), while synchronous sedimentation in the Western Foothills was supplied from the Yangtze, Minjiang (or similar river), and possibly even the Yellow River. These sediments were transported southward/eastward via rivers or channels to the marginal sedimentary basins now inverted in the Western Foothills in Taiwan. The Yangtze River must have been established prior to the middle Miocene. Key Points Miocene sediments in the Western Foothills should not only receive detritus from Minjiang River, but also Yangtze River Oligocene‐Miocene coastline in SE China should be far away from the present location to facilitate materials being transported farther The Yangtze River evolved close to its modern state must be prior to 24 Ma