From Ice to Deep Water Fans: Seismic Geomorphology Reveals the Story of a Glacigenic Basin Floor Fan offshore West of Shetland

This study uses 3D seismic reflection data to conduct a detailed seismic geomorphology analysis of a portion of a glacigenic basin fan system located offshore West of Shetland in water depths greater than 1000 m.

These deposits lie downslope from a gully system linked to the Foula wedge trough mouth fan, with both systems remarkably preserved at the present-day seafloor. While the seafloor morphology has received extensive attention in existing literature, the basin fan system subsurface structure, particularly its 3D geometry and distribution, remains less understood. This study lifts the veil, unveiling its basal surface and internal architecture in unprecedented detail. The 3D seismic characterisation reveals a complex basin channel network with linear, diverging erosional features and distinctive terminal lobes. These lobes exhibit stacked and backstepping patterns. The seismic geomorphology showcases features indicative of both debris flows and turbidites. This intricate interplay suggests a complex shelf-to-basin sediment transport and deposition mechanism.

The integration of this newfound evidence with existing regional bathymetry, helped pinpoint the source of the main basin distributary channels to two of the downslope gullies.  This suggests that, initially, high energy flows remained somewhat confined within the basin area allowing erosion. These local-scale insights shed light on different sediment delivery processes and their impact on basin fans development. Ultimately, these findings contribute to a more comprehensive understanding of the Foula wedge large-scale dynamics, particularly the influence of meltwater pulses driven by paleo-morphology, substrate characteristics, and unique ice-sheet behaviour during the Pleistocene glaciations.