Deep-Water Erosional Channels Associated with Fluid Escape Structures in the Qiongdongnan Basin, Northwestern South China Sea

Deep-water channels can deliver vast amounts of sediment from land to deep-water settings and potentially host or sequester hydrocarbon resources within associated sand-rich deposits. However, the fluid migration processes linking deep-sourced fluids with submarine channels remain poorly understood. Based on 3D seismic data from the Qiongdongnan Basin, northwestern South China Sea, this study identifies two buried channels and their underlying fluid escape systems. The channels exhibit erosional incisions, with high-amplitude anomalies at their bases, suggesting the occurrence of coarse-grained sediments. In shallower strata, extensively distributed high-amplitude reflections are interpreted as gas-bearing overbank sandy deposits, whereas some negative-polarity reflections are recognized as bottom-simulating reflectors, indicating the boundary between overlying gas hydrate-bearing sediments and underlying free gas. Erosional channel margins and adjacent enhanced amplitude reflectors further suggest that these margins serve as efficient pathways for fluid migration. Additionally, a fluid escape chimney, characterized by blanking and disrupted reflectors, has been identified beneath the channels, implying focused fluid ascent from deeper levels. Taken together, these features indicate that deep-sourced fluid migrates upward through fluid escape chimneys, accumulates at the channel bottom within sandy deposits, and subsequently disperses laterally along the erosional channel margins into the shallow horizontal overbank deposits. This coupling between submarine channels and fluid escape structures creates a complex fluid flow system characterized by diverse fluid migration pathways at different stratigraphic levels. The findings highlight the significance of submarine channels and fluid escape chimneys in fluid migration, offering insights that may be applicable to other basins.