Mixed sedimentation of the North Sea Fan – insights on volumes of contourites, plumites and downslope deposits during a full glacial-interglacial cycle

Trough mouth fans are important depocenters for glacial sedimentation in high latitude margins, recording sedimentological processes and their relationship with paleoclimatic fluctuations on short timescales - from decades to millennia. The volume of sediments accumulated in these fans varies significantly depending on the phase of the glacial cycle, with higher values typically reached during early retreats. The input of large volumes during short time intervals can potentially trigger submarine landslides and overpressure build-up, making the understanding of processes and proportions related to sedimentation in glaciated margins crucial, especially during periods of global warming. In this study we use high-quality 3D seismic cubes (vertical resolution of 2 m and bin size of 6.25 x 18.75 m) to delimitate different types of deposits on an area over 14000 km² on the North Sea Trough Mouth Fan during a full glacial-interglacial cycle of the last glaciation (Weichselian). After mapping the corresponding top and base surfaces of each type of deposit their volumes were calculated using the mean thickness of the beds multiplied by their extent. The base of the studied package comprises a contourite body deposited on top of the Tampen Slide, whose failure is estimated to have happened around 130 ka ago. Next we have a thick (> 400 m) mixed package of debris flows and meltwater turbidites, with its rapid deposition happening during approximately 4 ka (~23 to 19 ka). The package is then completed with plume settling related to the full retreat of the ice stream. Although not completely interpreted due to limitations of the dataset extent and remobilization of a part of the fan by the Storegga Slide in the northern part, the last glacial cycle comprises a total of 7160 km³ of sediments, with more than half of it (4850 km³) originated from the downslope processes. The plumites and contourites comprise volumes of 1105 km³ and 1205 km³. This accounts to a significant variability of the magnitude of sediment volume coming into the sink per year, with the downslope deposits having over 100 times more sediment input and the plumites 5 times more when compared to the contourites. These results highlight the range of sediment volume that can be delivered in a glaciated margin depending on changes in processes and climatic fluctuations, which may also entail changes in the potential geohazards.