The geology of the UK Hatton-Rockall margin

Abstract

Seismic, potential field, sea-bed sample and shallow drilling data have been used to investigate the geology of the UK part of the Rockall Plateau. Most of the Rockall Plateau is underlain by Early Proterozoic Rockall Bank/Islay terrane metamorphic basement although George Bligh Bank and the north-eastern end of Hatton Bank may be underlain, at depth, by Lewisian rocks. The basement crops out on Rockall Bank but occurs at a much deeper level beneath Hatton Bank and Hatton Basin. The widespread Palaeogene lavas of Rockall Plateau have been sourced from large central igneous complexes (Rockall, Swithin, Sandastre, Mammal, Lyonesse and Sandarro), local volcanoes and fissures. Some of the lavas may also have been derived from the incipient rift axis west of Hatton Bank at the time of continental break-up. Differences in seismic facies allow the extent of the lavas from the large centres to be mapped. Where the lavas are absent beneath parts of Hatton Bank, either due to non-emplacement or subsequent erosion during the Cenozoic, seismic data image the underlying Mesozoic (and ?older) rocks. Here BGS boreholes 99/1 and 99/2A have proved mid-Cretaceous (Albian) shales and sandstones respectively beneath a thin Cenozoic cover. The Mesozoic (and ?older) rocks appear to be quite extensive and are folded and faulted. Mesozoic strata are not observed on Rockall Bank in UK waters. The post-lava Cenozoic succession of Rockall Plateau can be sub-divided into three megasequences separated by two unconformities which, by analogy with Rockall Basin, have been designated ?C30 (intra Late Eocene) and ?C10 (intra Early Pliocene). The ages can be corroborated by DSDP/ODP boreholes in the Hatton Basin. The Cenozoic succession contains Eocene prograding fan sequences, contourite deposits on the flanks of the banks and shallow faulting, some of which affects the present day sea bed. Structurally, Rockall High appears mainly as a large basement block whereas Hatton High is more complex exhibiting half-grabens, inversion structures and reverse fault geometries due to Cenozoic tectonism. The northern end of Hatton High is a large anticline with its axis aligned ENE-WSW. The structural differences between the highs may be due to their locations with Rockall High exhibiting fewer tectonic effects due to its more landward, intraplate setting further away from plate-margin deformation.