1 * hast@bgs.ac.uk © 2012 European Association of Geoscientists & Engineers Near Surface Geophysics, 2012, 10, xxx-xxx doi:10.3997/1873-0604. 2012014 The timing and significance of gully incision on the eastern flank of the Faroe–Shetland Channel and its impact on seafloor infrastructure Heather A. Stewart* and David Long British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, UK Received May 2012, revision accepted May 2012 ABSTRACT The Faroe–Shetland Channel is an area of active offshore development and the safety of the sea- floor infrastructure is paramount. This study has concentrated on a system of down-slope linear gullies and associated debris fans located to the west of Shetland in water depths of between 465m and 995m. Three-dimensional seismic, two-dimensional seismic and multibeam echosounder data have been combined to map the sea-bed morphology and shallow sub-surface geology associated with these features. The localised debris fans and gullies are interpreted as the products of high energy mass-flow fed by an ancient ice-stream constrained to this part of the West Shetland Shelf. During decay of this ice-stream, melt-water plumes of sediment released from the retreating ice front have formed a thin (<5m) laminated sediment drape overlying the debris fans observed from seismic data. At present locally strong oceanic currents rework and redistribute sea-bed sediments into sediment drifts called contourites that cover much of the sea bed of the Faroe–Shetland Channel. These along-slope deposits have been shown to infill erosional features located further northeast along the continental slope, however, these deposits thin to the southwest reflecting the increasing strength of present day oceanic currents impeding deposition. This study shows that slope angles within the down-slope gullies exceed 20° and cut down into earlier contouritic sedi- ments. The high slope angles recorded on the multibeam echosounder data combined with video data confirm the presence of near-vertical sediment cliffs within the gullies. This is of significance to industry as there are currently producing hydrocarbon fields and continued exploration in and around these sea-bed features. has been in place for around the last 14,000 years although the strengths may have changed (Miller and Tucholke 1983; Rasmussen et al. 1996; 2002). The channel’s role in providing a conduit for exchanging Atlantic Ocean and Norwegian Sea waters may have influenced sediment accumulation on the shelf margins since Late Eocene and Oligocene times (Miller and Tucholke 1983; Rasmussen et al. 1996; 2002). The British Geological Survey began regional geological mapping of the area over 30 years ago with Stoker et al. (1993) presenting a summary of the regional geological setting. More recently the British Geological Survey and Jarðfeingi (the Faroese Earth and Energy Directorate) have published a sum- mary of the regional geology which includes the Faroese sector of the Faroe–Shetland Channel (Ritchie et al. 2011a) which was not included in the previous Stoker et al. (1993) publication. In this paper, we present a new interpretation of the sea-bed sediments and sea floor geomorphology of a system of down- slope linear gullies and their associated debris fans located in the Faroe–Shetland Channel (Fig. 1). By combining these new inter- INTRODUCTION The Faroe–Shetland Channel is located to the north and west of the Shetland Islands and separates the Faroe and West Shetland shelves (Fig. 1). The channel is around 400km in length from the Norwegian Basin to the Wyville–Thomson Ridge, is around 250km at its widest (shelf break to shelf break), and 1600m deep, narrowing to around 120km in width at the southwestern end where the sea floor is around 1000m in depth. The bathymetry of the region strongly influences the hydrodynamic regime. Oceanic currents are the predominant influence on the continental slope and channel floor (Stoker et al. 1993) with Turrell et al. (1999) describing five major water masses within the Faroe–Shetland Channel, some of which are known to create persistent, strong bottom currents capable of eroding and re-distributing sediments with grain sizes up to and including gravel (Masson et al. 2004). It has been suggested that the present day hydrodynamic regime of contrasting directions for the upper and lower water masses