Variability in the planform architecture of the Miocene paleo-Pearl River Delta, northern South China Sea: Records of longshore paleocurrent

Abstract The long-term growth of a continental-shelf delta records combined sea-level fluctuations and sediment supply, by mixed hydrodynamic processes; consequently, its morphology typically features complex asymmetry. Using extensive 3D seismic data, cores, well logs, and provenance data, we present a systematic anatomy of the Early–Middle Miocene Paleo-Pearl River Delta (PPRD). Results show that fifteen depositional sequences can be identified, spanning T60 (~23 Ma) to T35 (~13.8 Ma). Each sequence exhibits a typical four-fold systems tract structure, from each showing typical deltaic planform morphologies and sedimentary facies. Mineralogical data reveal a distinct two-source pattern: the western branch mainly supplied the Enping Sag, whereas the eastern branch fed the Xijiang and Huizhou sags. This pattern is corroborated by 2D and 3D seismic data. Seismic geomorphology further shows an asymmetric morphology, with river channels and mouth bars deflected southwestward and beach and shelf sand ridges widening in the same direction. This asymmetry records a dominant southwestward paleoflow. Considering modern hydrodynamics and regional paleoclimatic evidence, we propose that monsoon-driven longshore currents and the Guangdong Coastal Current (GDCC) likely generated this flow. Reconstructing this paleocurrent system improves our understanding of sediment dynamics and reservoir prediction in the PPRD and comparable marine deltas.