Signatures of hydraulic jump-related scouring in a deep-marine rift basin, Wollaston Forland Group, NE Greenland

Supercritical high-density turbidity currents descending steep submarine slopes often transition to subcritical flow via hydraulic jumps at the base-of-slope break, causing scouring and plunge pool formation. On the slope, scour arrays from turbulent erosion by the flow head, can develop into chutes where supercritical flow is sustained, generating cyclic steps. However, little is known about the infill of hydraulic-jump-related scours and upper flow regime bedforms in coarse-grained, deep-water slope systems. This study examines conglomerate- and sandstone-rich sediment gravity flow deposits from an Upper Jurassic–Lower Cretaceous deep-water syn-rift succession in Wollaston Forland, NE Greenland. These coarse-grained deposits accumulated on a steep, subaqueous fan delta slope perched on the basin-bounding fault escarpment. The upper slope, with minimal scouring, is dominated by breccia and conglomerate beds from debris falls and non-cohesive debris flows. In contrast, the lower slope exhibits extensive scouring, diverse scour-and-fill elements, and complex bedding patterns suggesting hydraulic jump-related erosion and scour filling by strongly stratified, supercritical high-density turbidity currents. Arrays of asymmetric conglomeratic scour fills, frequently exhibiting variably inclined and laterally accreted stratification, may indicate the presence of cyclic steps. Abundant conglomerate-filled scours at the slope base further suggest that gravel from the basal, inertia-driven part of the flows were trapped in plunge pools carved by their faster-moving turbulent parts. The dominance of sandstone beds on the basin floor indicates that the sand-laden turbulent flows continued basinward before coming to rest. Our findings highlight the role of flow transformation and scouring in shaping submarine slopes and controlling deep-water architecture.