Why Did the Pearl River Deepwater Fan Progressively Expand Westward in the Northern South China Sea?

In contrast to the disordered development of deepwater fans along many shelf margins (e.g., Angola–Congo, LBG, Hammerhead, Washakie and Porcupine), the Early Miocene Pearl River Deepwater Fan System (PRDFS) in the northern South China Sea exhibits progressive westward expansion within a third‐order sequence. Using high‐resolution 3D seismic data, well logs and cores, integrated with seismic geomorphology and sequence stratigraphy, this study investigates the architectural elements, evolution and controlling factors of the PRDFS. Results show that four depositional elements were recognised within the PRDFS, including deepwater channels, sheet sands, delta‐fed apron deposits and lobes. The evolution of the PRDFS is divided into three stages, corresponding to the lowstand systems tract (LST), highstand systems tract (HST) and falling‐stage systems tract (FSST). Stage 1 (LST) marks initial development, with gravity‐flow deposits first forming in the eastern segment of the Pearl River shelf margin and dominated by long run‐out channels and associated lobes. Stage 2 (HST) records westward expansion into the central segment, with medium‐runout channels, lobes and locally developed sheet sands. Stage 3 (FSST) represents the maximum areal extent and depositional volume of the PRDFS, with broad sheet sands accumulating preferentially within upper‐slope ponded accommodation in the western segment. We infer that this progressive westward expansion was governed by the hierarchical interaction of three controls: (1) a westward increase in the accommodation‐to‐sediment supply ratio ( A / S ), (2) stage‐specific variations in shelf‐margin process regimes and (3) local slope morphology and topographic configuration. Lower A / S and persistently fluvial‐dominated conditions in the eastern segment favoured early and efficient sediment bypass to deepwater areas. In the central segment, moderate A / S and strengthening fluvial influence supported intermediate‐scale fan development. In the western segment, higher A / S and persistent wave dominance promoted shelf‐margin sediment storage and delayed substantial deepwater deposition until Stage 3, when increased sand‐prone sediment supply and upper‐slope ponded accommodation favoured broad sheet‐sand accumulation. This study demonstrates how along‐strike gradients in A / S , shelf‐margin process regimes and slope morphology can jointly organise margin‐scale, stage‐wise fan expansion, providing a predictive framework for the evolution of deepwater fans and reservoir prediction in the Pearl River Mouth Basin and analogous shelf margins.