Sediment-drift development on the continental margin off NW Britain

Abstract

Abstract The long-term record of sediment-drift development on the continental margin off NW Britain was investigated using seismic-reflection data calibrated with boreholes and short cores. These data indicate that the onset of bottom currents on the NW British margin occurred in the early late Eocene following a major phase of subsidence in the Rockall Trough and Hatton-Rockall Basin. Seismic reflection profiles reveal the downwarped and eroded surface of lower upper Eocene and older strata onlapped by middle to upper Cenozoic sediments. The latter consist predominantly of deep-marine contourites preserved both as mounded, elongate, and broad, sheeted, sediment drifts with associated sediment waves. Seismic-stratigraphical analysis of the drift succession has revealed a broad two-stage depositional history. A vigorous bottom-current regime in the late Eocene to mid-Miocene interval was accompanied by significant lateral migration of sediment by upslope accretion onto the flanks of the basins, including the construction of the bulk of the Feni Ridge. Mid-Miocene tectonism modified the palaeoceanographic and sedimentary regime. In the ensuing mid-Miocene to Holocene interval, drift accumulation persisted in the axial and eastern part of the Rockall Trough whereas a largely erosional regime prevailed on its western margin. The overall locus of drift sedimentation shifted westeards onto the Rockall Plateau.