Sediment drifts and contourite sedimentation in the northeastern Rockall Trough and Faroe-Shetland Channel, North Atlantic Ocean

Abstract

Abstract Seismic reflection profiles, shallow cores and seabed photography from the continental margin off NW Britain reveal the variety of bottom current influenced sedimentation in the northern Rockall Trough and Faroe-Shetland Channel. Types of sediment drifts identified include: (1) elongate drifts, both single, and multi-crested; (2) sheeted drift forms, varying from gently domed to flat-lying; and (3) isolated patch drifts, including moat-related drifts. Associated fields of localized sediment waves are developed with the elongate and gently domed, broad sheeted drifts. The contrasting style of sediment drift development reflects the complex interaction between bottom current regime, sediment supply and the bathymetry of the continental margin. The majority of the mounded/gently domed drifts occur in the northern Rockall Trough, with sheetform drifts commonly confined to the Faroe-Shetland Channel, a narrow basin which is an area of net sediment export rather than drift accumulation. Small patch drifts are present in both basins. Muddy, silty muddy and sandy contourites have been recognized from sediment cores sampling the uppermost parts of the drift sequences. Based on their glaciomarine character, the mid- to high-latitude contourites are referred to as glacigenic contourites. Both partial and complete con–tourite sequences are preserved; the former consist largely of sandy (mid-only) and top-only contourites. Modern sandy con–tourites have also been identified from seabed photographs on the Hebrides Slope. The contourites are recognized as a rippled mobile sand layer, reworked from a poorly sorted glaciomarine parent deposit.