The evolution of the Porcupine and Rockall basins, offshore Ireland: the geological template for carbonate mound development

Abstract

The margins of the deep-water sedimentary basins west of Ireland contain a number of large clusters (provinces) of spectacular carbonate mounds and build-ups. These basins have a complex development history involving the interplay of rift tectonics, thermal subsidence, igneous activity and oceanographic variations. The Porcupine and Rockall basins both rest upon thin continental crust, the consequence of major rift episodes in Permo-Triassic, Late Jurassic and Early Cretaceous times. Phases of volcanism occurred in the Early Cretaceous and especially in the Early Cenozoic. Fluid flow within the basins is likely to have been controlled by the overall basin geometry and by the distribution and linkage of permeable strata with fault systems, stratal surfaces and unconformities. A number of regional unconformities, controlled by both basin tectonic and regional oceanographic effects, can be mapped and correlated throughout the Porcupine and Rockall basins. The youngest of these unconformities (C10: Early Pliocene) can be traced throughout much of the NW European Atlantic margin. It forms the horizon on which virtually all the carbonate mounds in the basins develop, suggesting a geologically instantaneous mound nucleation and growth event. Although the control on their development is uncertain, the mound clusters show a spatial association with lithified strata, buried contourite and deltaic deposits, slope failure features and with the basin margins. Analysis of these relationships points to a combination of geological and oceanographic processes controlling mound initiation and growth.

The Enya mounds: a lost mound-drift competition

“…Although the origin of the Darwin mounds also is related to fluid escape (porewater) and pockmarks (Masson et al 2003), it is clear that fluid escape alone is not sufficient to support coral colonies. As such, no evidence for the presence of any directly associated seepage has been found near coral banks on the Rockall Trough margins or in the Porcupine Seabight (Bailey et al 2003;De Mol et al 2007;Huvenne et al 2003;Kenyon et al 2003;Mienis et al 2006;Shannon et al 2007).…”

“…Nevertheless, in a particular zone of the slope, one can observe the typical upslope migrating sigmoidal deposits, interpreted as a set of sediment waves (Van Rooij et al 2003). They might very well be demonstrating the first stages of Late Oligocene to Early Miocene alongslope sediment transport in the basin as suggested by Shannon et al (2007). The upper boundary of this unit is the slightly erosive RD2 unconformity which has been attributed a late Early Miocene to early Mid-Miocene age Van Rooij et al 2003).…”

“…1). The geological evolution of the basin has been extensively described by Croker and Shannon (1995), Shannon (1991) and Shannon et al (2007); the Porcupine Seabight is the surface expression of the underlying deep sedimentary Porcupine Basin, which is a failed rift of the proto-North Atlantic Ocean, filled in with a 10 km thick series of Mesozoic and Cenozoic sediments. The Cenozoic sedimentary succession of the basin has been cut by several major unconformities which can be correlated with the Rockall Basin.…”

“…1 Location map of the study area with respect to the Belgica mound province. The location of R/V Marion Dufresne Calypso cores, IODP 307 sites, R/V Pelagia TOBI track and the RCMG seismic profiles are overlain on AWI Bremerhaven multibeam bathymetry with a contour interval of 20 m (McDonnell and Shannon 2001;Shannon et al 2007;Stoker et al 2005;Van Rooij et al 2007a).…”

Cold-water coral carbonate mounds as unique palaeo-archives: the Plio-Pleistocene Challenger Mound record (NE Atlantic)

“…1). Formed as a failed-rift basin during the opening of the North Atlantic, its Neogene post-rift sedimentary history alternates contourite drift deposition with several regional erosion events (Van Rooij et al, 2003;Stoker et al, 2005;Shannon et al, 2007) (Fig. 1).…”