Palaeogeographical evolution of the Rattray Volcanic Province, Central North Sea

The Rattray Volcanics Member, at the triple junction of the North Sea rift, is here subdivided into two informal sub-members based on analysis of core, wireline and seismic data. The Lower and Upper Rattray Volcanics were emplaced during two distinct phases of volcanism separated by a sustained volcanic hiatus. The presence of hyaloclastite and abundant freshwater algae at the base of the Lower Rattray indicates that large lakes were present in the area prior to the volcanism, possibly indicating that collapse of the regional Jurassic Central North Sea dome began prior to volcanism. Pulsed subsidence probably occurred through the duration of the volcanism with lacustrine conditions becoming re-established during the midvolcanic hiatus. Sediments were deposited across the Rattray Volcanic Province in fluvial systems and floodplain coal swamps after the final cessation of volcanism, with later marine transgression leading to drowning of the area in the Callovian to Oxfordian. In terms of hydrocarbon prospectivity, no evidence is currently found to confirm the presence of an intra-basaltic play analogous to the Rosebank Field in the Faroe-Shetland Basin, although post-volcanic Pentland Formation sedimentary sequences in the Fisher Bank Basin area indicate the possibility of supra-basaltic prospectivity in the triple junction.