Neogene-Quaternary contourite and related deposition on the West Shetland Slope and Faeroe-Shetland Channel revealed by high-resolution seismic studies

The Neogene and Quaternary sediments of the Faeroe-Shetland Channel and West Shetland shelf and slope rest upon a major regional unconformity, the Latest Oligocene Unconformity (LOU), and have been deposited through the interaction of downslope and parallel-to-slope depositional processes. The upper to middle continental slope is dominated by mass-transport deposits (debris flows), which progressively diminish downslope, and were largely generated and deposited during glacial cycles when ice sheets supplied large quantities of terrigeneous sediment to the upper slope and icebergs scoured sea-floor sediments on the outer shelf and uppermost slope. Large-scale sediment failures have also occurred on the upper slope and resulted in deposition of thick, regionally extensive mass-transport deposits on portions of the lower slope and channel floor. In contrast, large fields of migrating sediment waves and drift deposits dominate most of the middle to lower slope below 700 m water depth and represent deposition by strong contour currents of the various water masses moving northeastward and southwestward through the channel. These migrating sediment waves indicate strong northeastward current flow at water depths shallower than ∼700 m and strong southwestward current flow at water depths from ∼700 to >1,400 m. These flow directions are consistent with present-day water-mass flow through the Faeroe-Shetland Channel. The Faeroe-Shetland Channel floor is underlain by thin conformable sediments that appear to be predominantly glacial marine and hemipelagic with less common turbidites and debris flows. No evidence is observed in seismic or core data that indicates strong contour-current erosion or redistribution of sediments along the channel floor. Introduction and background The modern Faeroe-Shetland Channel is a narrow elongate basin that trends NE–SW between the West Shetland Shelf and the Faeroe Shelf and that provides a major passageway for the exchange of cold and warm water masses between the Norwegian Sea and the North Atlantic (Figure 1). The Faeroe Basin, which is a several kilometer thick accumulation of sediments beneath the channel floor and the West Shetland slope and shelf, has become an important hydrocarbon province. Exploration for hydrocarbons by Mobil North Sea Ltd. led us to participate in a detailed seismic-stratigraphic analysis of the Paleogene strata of the Faeroe Basin using conventional multi-fold seismic data (Mitchell et al., 1993). Concurrent with this study, we undertook a preliminary study of the depositional processes of the Neogene/Quaternary section of this area with a partial grid of high-resolution airgun (50–250 Hz) seismic data collected by the British Geological Survey for the purposes of developing depositional analogs for the Paleogene prospective deposits, and for assessing sea-floor geohazards (Damuth and Olson, 1993). This study revealed that a significant portion of the West Shetland Slope contains extensive fields of migrating sediment waves or drift deposits presumably deposited by contour-current activity. In addition, significant downslope movement of sediments through mass-transport and turbidity-current processes was also observed. The fairly wide spacing of the seismic lines available for this preliminary study left some uncertainties about the depositional processes in some portions of the study area (Damuth and Olson, 1993). The present study is an outgrowth of, and builds on, our original study, and was undertaken when a more robust data set consisting of the entire BGS grid of high-resolution (50–250 Hz) airgun seismic