The influence of inherited structural relief on the architecture of early post-rift deepwater systems

Deep-water submarine fans represent the largest sediment accumulations on Earth and serve as key reservoirs for hydrocarbons and carbon storage. Their morphology and architecture are strongly influenced by interactions with topography, particularly in rift basins where inherited structural relief affects sediment routing and deposition. However, uncertainties remain regarding how syn-rift topography controls the distribution and evolution of deep-water systems during early post-rift basin infill. This study investigates two contrasting early post-rift deep-water systems: the Angel Formation (North West Shelf, Australia) and the Agat Formation (North Sea, Norway). An integrated approach utilizing 3D seismic reflection, well logs, core data, and spectral reflectance analysis provides insights into sediment distribution from basin to bed scale. Results indicate that the degree of basin infill critically controls channel and lobe deposition. In underfilled basins, fault topography strongly influences sediment entry points and sandstone distribution, resulting in sand-rich lobe complexes that abruptly pinch out against fault scarps. Pinch-out rates vary due to rugose topography, but compensational stacking increases as the basin fills. In more infilled basins, direct fault interactions are less pronounced, but fault topography exerts a lasting influence by generating compaction hinges over buried faults. These hinges impact sediment pathways, with their effects varying according to fault geometry and throw. This research underscores the role of inherited structural relief in shaping deep-water deposits and highlights the importance of basin-fill state at rift cessation in controlling early post-rift sedimentation. These findings enhance our ability to predict reservoir architecture and connectivity in rift basins, with implications for hydrocarbon exploration and carbon sequestration.