We interpret a region of undulatory sediments adjacent to a major headwall of the Cape Fear submarine landslide system offshore of North Carolina, USA, as sediment waves rather than creep or fault-related deformation. The wave package extends 19 km upslope from the S4 landslide headwall and thickens upslope from approximately 250 to 450 m. The field of undulating sediments displays the continuity of seismic horizons, upslope-migrating crests, downslope thinning, and wave heights and lengths of approximately 26 m and approximately 1 km, respectively, which are consistent with sediment wavefields. The Western Boundary Undercurrent formed contourites on the nearby Blake Ridge and it is possible that these sediment undulations were deposited via similar mechanisms. Ocean Drilling Program (ODP) cores near the sediment undulation field suggest that the turbidity currents also may have played a role in wave formation. Although most of the 19 km long field comprises unaltered sediment waves, we observe an approximately 5 km long zone adjacent to the landslide scarp that expresses evidence of faults that offset and deform the sediment wave strata. We interpret this deformation as the result of reduction in stress following the removal of the landslide mass. Given that the Cape Fear system has generated several episodes of potentially tsunamigenic slope failure, the future stability of the system is pertinent. Redefining these undulatory sediments as sediment waves eliminates a major slope instability mechanism of the system and is important for understanding the future slope stability hazards of Cape Fear. Our analysis highlights the importance of understanding sediment waves in hybrid submarine landslide-sediment wave systems.

Geological feature:

Cape Fear submarine landslide sediment waves

Seismic appearance:

Continuous undulating horizons

Alternative interpretations:

Downslope creep or faults

Features with similar appearance:

Extensional slope failure

Formation:

Alongslope and downslope currents

Age:

Quaternary

Location:

Cape Fear submarine landslide complex, offshore North Carolina

Seismic data:

High resolution multichannel seismic data

Analysis tools:

Multichannel seismic data, multibeam bathymetry, sub-bottom Chirp

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