Tectonic-Driven Transformation of Sedimentary Provenance in the Late Miocene to Pliocene Dongfang Submarine Fan in the Yinggehai Basin, South China Sea

Abstract

The Late Miocene to Pliocene was a critical period of tectonic reorganization in the northern South China Sea, when changes in fault activity, basin subsidence, and sediment supply reshaped regional sediment-routing systems. However, the provenance evolution of the Yinggehai Basin, a key depocenter at the mouth of the Red River, and its controlling mechanisms remain poorly understood. This study integrates 3D seismic data, detrital zircon U–Pb geochronology, heavy mineral assemblages, geochemical data and inverse Monte Carlo mixing models to quantitatively evaluate sediment provenance evolution. The results reveal a systematic transition from a Late Miocene multi-source depositional system to a Pliocene regime dominated by axial sediment supply from the Red River. Late Miocene deposits are characterized by multi-directional progradational seismic geometries, mixed zircon age spectra with Indosinian, Jinningian and Yanshanian populations, low ZTR indices, limited abundances of high-grade metamorphic minerals, and geochemical signatures indicative of felsic upper crustal sources. Together, these features indicate hybrid sediment supply from the Red River (33%–73%), Central Vietnam (26%–67%), and Hainan Island (< 1%). In contrast, Pliocene sediments display regionally extensive north–south oriented progradational seismic clinoforms, increased proportions of Yanshanian zircons, and enrichment of high-grade metamorphic and stable heavy minerals, indicating pronounced Red River dominance (> 80%). The attenuation and termination of eastward-prograding seismic reflections record a substantial reduction in sediment supply from Central Vietnam. In contrast, consistently elevated REE contents and high ZTR indices indicate that Hainan Island acted as a persistent, though subordinate, sediment source throughout the same period. Provenance analysis indicates that the Late Miocene sedimentation was governed by a multi-source system. This system developed in response to regional stress-field reorganization and the presence of intrabasinal structural barriers. This pattern shifted during the Pliocene to a system dominated by Red River provenance, coinciding with dextral reactivation of the Red River Fault Zone and accelerated uplift of the southeastern Tibetan Plateau initiating at ~5.5 Ma. These findings collectively establish a tectonically driven source-to-sink evolution model for confined continental-margin basins. The model has direct implications for sediment routing and reservoir distribution in passive-margin settings.