Variability of shelf-edge processes and linked deep-water systems in an underfilled rift basin with structural inheritance (Porcupine Basin, offshore Ireland)

While it is accepted deep-water sand delivery is most efficient during periods of relative sea-level fall and lowstand, other parameters (e.g., sediment supply, hydrodynamic regime) can also influence when, where and how these sands are bypassed. In this context, it is critical to understand how tectonic and climatic settings modulate those parameters and impact shelf-to-basin sediment transfers. Availability of high-resolution and extensive 3D seismic data in the Porcupine Basin offers a unique opportunity to study the evolution of shelf-margin clinoforms developed during the Paleogene in a failed rift basin under greenhouse climatic conditions. Using advanced full-volume seismic interpretation methods, the Quantitative 3D Seismic Stratigraphy (QSS) approach is used to identify fifteen clinothems prograding over a period of ∼20.4 Myr during the Late Paleocene–Mid Eocene. Overall, the shelf margin presents low progradation rates and is developed under low rates of sediment supply. It appears that increasing fluvial influence along paleoshorelines developed at the shelf edge promotes deep-water sand delivery, which is consistent with previous published studies along other margins. The QSS analysis reveals that steeper clinoform slope gradients are associated with wave-dominated shorelines, whereas more gentle slope gradients are associated with fluvial-dominated shorelines. These results present opposite relationships to what is described in the literature, hence it is interpreted that in the absence of high sediment supply, the inherited rift topography (i.e., structural inheritance) controlled the shelf-margin architecture and its physiography by superseding relationships typically observed in other types of shelf margins. This study demonstrates the critical roles of sediment supply and inherited paleotopography in post-rift basins on shelf-margin architecture and associated sediment transfer mechanisms.