Provenance changes of the Yangtze River Delta sediments since ∼3.6 Ma: Evidence from heavy mineral assemblages and detrital zircon U–Pb ages spectra

Abstract

The Yangtze River drains from the eastern Tibetan Plateau and provides insights into the evolution of the Asian monsoon and uplift of the Tibetan Plateau. The age and evolution of the Yangtze River have been investigated, yet consensus remains lacking. This study aimed to investigate the sediment source changes of the Yangtze Delta since approximately 3.6 Ma. A new sediment core (YZQK2, 300.36 m) was subjected to high-resolution magnetostratigraphic, zircon U–Pb age spectral, and heavy mineral assemblage analyses. Magnetostratigraphy showed that 79.65, 171.22, and 293.4 m reflected the Matuyama–Brunhes, Gaussian–Matuyama, and Gilbert–Gaussian boundaries, respectively. The bottom age of the core was approximately 3.60 Ma. Between 3.60 and 3.44 Ma, heavy mineral assemblies were characterized as high reductive heavy minerals, pyrite, and siderite with the dominant peak of the detrital zircon U–Pb ages being 400–450 Ma. The sediments were primarily fed by tributaries draining into the middle Yangtze River, which were the Han River oriented in the Tongbai-Dabieshan orogenic belt and Xiang River and Gan River oriented in the Cathaysia Block. Between 3.44 and 2.79 Ma, the reductive heavy minerals, pyrite, and siderite disappeared, while garnet, apatite, sphene, and ilmenite showed a sharp increase. The dominant peak of detrital zircon U–Pb ages exhibited an extremely narrow range of 100–150 Ma. The sediments originated from the rock basin in the lower Yangtze River, the dominant river system, and were sourced locally or regionally from the adjacent Cretaceous granite plutons and volcanic rocks. The zircon age spectrum similar to the mainstream of the Yangtze River, containing amphibole, pyroxene, and magnetite from the upper to the middle and lower reaches of Yangtze River, has formed the Yangtze drainage pattern since 2.79 Ma. The sediment in the middle Yangtze reached the Yangtze Delta no later than 3.6 Ma, while the integration of the upper Yangtze into the Yangtze Delta occurred no earlier than 2.79 Ma. Our results provide novel insights into the established timeline of the Yangtze River.