Undulating sediments of the Cape Fear submarine landslide system, offshore U.S. Atlantic margin

Abstract:

The Cape Fear submarine landslide system encompasses ~25,000 km² of seafloor on the continental slope offshore of North Carolina, USA. The system features a broad zone of seafloor and subsurface sediment undulations immediately upslope of the largest headwall scarp. The zone extends 19-km upslope of the headwall, in water depths of 1330-2400 m, and thickens upslope, from 280-400 m thickness. Early interpretations suggested a listric fault or creep origin, whereas modern high-resolution seismic data has led to the suggestion that these undulations could be sediment waves. Here, we examine the undulating sediments with bathymetry data and 2D seismic data to better understand their origin. The highest resolution seismic profile through this field was acquired in 2014, with vertical resolution <2 m of the internal architecture of the undulating sediments. Our preliminary findings support the interpretation of sediment waves, primarily due to: upslope-migrating crests, continuity of seismic reflectors, variable individual horizon thickness across the undulations and preferentially higher seismic amplitude on the downslope flanks and troughs. Furthermore, there are no discernible fault planes or offsets that would be indicative of faulting. The average observed wave heights of ~27 m and wavelengths of ~1 km are within commonly accepted values for sediment waves. These waves may be related to the contourites of nearby Blake Ridge, formed by the Western Boundary Undercurrent. Additionally, turbidity currents may have also played a role in their formation. While most of the 19-km long field exhibits unaltered sediment waves, we observe a ~5-km long zone immediately adjacent to the landslide headscarp containing listric faults that offset and deform the sediment wave strata. We interpret this near-scarp zone to have resulted from the reduction in lateral stress following the removal of the landslide mass. We also observe evidence of an irregular topography at the base of the sediment wave field, suggesting a possible feedback whereby past slope failure established an irregular seafloor, which in turn facilitated the development and growth of the sediment waves. Our analysis highlights the potential importance of understanding sediment waves in hybrid submarine landslide-sediment wave systems.