Cretaceous and Tertiary basin development west of Ireland

Abstract

The Porcupine, Rockall and Hatton–Rockall basins lie on the continental seaboard west of Ireland. Up to 9 km of Cretaceous and Tertiary strata are preserved in the Porcupine Basin, in contrast to 2–3 km in the Rockall and Hatton–Rockall basins. Differences in seismic stratigraphic sequences through the region are attributed to an interplay between the developing North Atlantic Ocean, post-rift thermal subsidence and sea-level changes. Localized Ryazanian fault-controlled alluvial fan clastic rocks in the Porcupine Basin are succeeded by Valanginian to Barremian marine deposits. Sea-level lowstands in Albian and Paleocene–Eocene times, interpreted as rift and ridge-push effects respectively, resulted in delta and submarine fan progradation. Rapid thermal subsidence in Early Oligocene times led to marine deposits and to the onset of geostrophic currents. Miocene slumping triggered shale-dominant turbidite development, followed by tranquil deep marine sediments as subsidence outstripped sedimentation. The Cretaceous sequence in the Rockall Trough is thought to contain extensive igneous bodies overlain by an Upper Cretaceous muddy chalk sequence which is cut by abundant Tertiary sills and dykes. A number of shale-prone Upper Tertiary sequences occur. The Upper Cretaceous to Lower Tertiary succession is thin and frequently absent in the Hatton–Rockall Basin.