Repeated degradation and progradation of a submarine slope over geological timescales

ABSTRACT Submarine slopes prograde via accretion of sediment to clinoform foresets and degrade in response channel or canyon incision mass-wasting processes. The timescales over which progradation degradation occur, the large-scale stratigraphic record these processes, remain unclear due poor age constraints subsurface-based studies areally limited exposures exhumed systems. We here integrate 3D seismic reflection borehole data study geometry origin ancient slope canyons developed late Mesozoic strata Måløy Slope, offshore Norway. Slope commenced during Kimmeridgian, coincident with latter stages rifting. Later periods formation occurred Aptian Albian Cenomanian, early post-rift subsidence. are straight, up 700 m deep, 10 km wide on upper die out downdip onto lower slope. trend broadly perpendicular crosscut most rift-related normal faults, although syn-filling fault growth locally helped preserve thicker canyon-fill successions. headwalls oldest (late Kimmeridgian) located at a fault-controlled shelf edge, where younger overstep this fault, was inactive when they formed, extending across paleo-shelf. Downslope, either erode into older, Kimmeridgian Barremian fills, forming complicated set unconformities, case Cenomanian canyons, correlative conformities. Boreholes indicate that bases defined by sharp, erosional surfaces, we observe an abrupt upward shift from shallow- deep-marine facies (i.e., canyons), deep marine (Aptian canyons). Missing biostratigraphic zones relatively protracted (c. 2–17 Myr) structurally enhanced bypass, separated > Myr deposition accretion. trigger for is unclear, but it likely reflects basinward tilting tectonically active margin, erosive gravity flows. results our have implications may occur other slopes, complex geophysical geological also show can cause large volumes margin-derived bypass proximal sub-basins within rifted terranes, important process not currently captured rift-basin tectono-stratigraphic models.