Marine geology of the Rockall Plateau and Trough

Abstract

The Rockall Plateau is an extensive shallow water area located south of Iceland and west of the British Isles: it is separated from the British Isles by the 3000 m deep Rockall Trough. Rockall Island, composed of 52 ± 9 Ma aegirine-granite is the sole subaerial expression. The Rockall Plateau is interpreted as a continental fragment or microcontinent isolated during the sea floor spreading evolution of the North Atlantic Ocean. A geological reconnaissance of the Rockall Plateau and Trough has been made by using a 650 cm 3 (40 in3) seismic reflexion profiling system, supplemented by sparker (8 kJ) profiles on Rockall Bank and arcer (60 kJ) profiles across the margin west of the British Isles. Stratigraphic interpretation of these profiles has been aided by deep sea drilling data, bottom sampling on Rockall Bank and by the relation between the various reflecting horizons and oceanic basement dated by oceanic magnetic anomaly identifications. Analysis of the microtopography of the area has given information on Post-Palaeogene sedimentation processes. Three major sedimentary basins are present in the area. The Hatton-Rockall Basin is developed in thinned continental crust on Rockall Plateau. The Rockall Trough is developed on continental crust and includes oceanic crust believed to have been generated in Late Jurassic-Early Cretaceous time. The Porcupine Seabight may be developed on thinned continental crust. All three basins have a faulted basement and exhibit a history of progressive and/or intermittent subsidence. The subsidence phases correlate closely with estimated changes in sea-floor spreading rate. This correlation and the regional pattern of uplift and subsidence is discussed with reference to the effects of thermal subsidence and differential loading of the lithosphere beneath continental margins. Post Upper Eocene sedimentation throughout the area was characterized initially by widespread chert deposition and subsequently by differential deposition of Early Miocene to Recent oozes. The onset of widespread differential deposition in the Early Miocene indicates the present near bottom-circulation was established at this time and may be related to subsidence of the Iceland-Faeroes Ridge. The relation between differential deposition, topography and circulation is discussed in terms of flow around obstacles.