Provenance Shift During The Plio-Pleistocene In The Vertex Of Yangtze Delta And Its Geomorphological Implications

One of the key issues of the Source-to-Sink process is revealing the geomorphological evolutions of large rivers from the perspective of river sink areas. This study aims to reveal the provenance change near the vertex of the Yangtze delta during the late Cenozoic and provide insight into the Yangtze channelization into the sea due to regional tectonic subsidence. Heavy minerals and zircon geochronology in the Plio-Pleistocene sediments of the vertex of the modern Yangtze delta (core RGK15) reveal that a significant provenance shift occurred at similar to 2.6 Ma (the beginning of the Pleistocene). During the Pliocene, ultra-stable heavy minerals and pre-Mesozoic zircon grains predominated in the sediments, probably derived from contemporary outcrops of sedimentary rock that were widely distributed in the delta and its surrounding area. They are completely different from those in the Pliocene sediments of the south delta, indicating that decentralized, local, small watersheds dominated the Yangtze delta during the Pliocene. This resulted from the relatively elevated terrain of this region due to the adjacent ancient Zhejiang-Fujian Uplift (ZFU) at that time. However, diversified heavy minerals and zircon geochronology similar to those of the modern upper Yangtze fingerprints occur in the Pleistocene sediments of core RGK15, implying that a significant provenance shift to the Yangtze River occurred here at similar to 2.6 Ma. The provenance shift recorded by the cores in the south delta mainly occurred at similar to 1.2 Ma, indicating that the Yangtze River channel was dragged southward with the further subsidence of the ancient Zhejiang-Fujian Uplift. This study reveals the southward migration process of the Yangtze River channel with the regional tectonic subsidence from the perspective of provenance evolution, which contributes to an understanding of when the Yangtze River channelized into the sea.