Mapping landslides and slope failure from seismic dataset on the Brazilian Equatorial Margin

The Brazilian Equatorial Margin developed due the break-up between Africa and South America during the Cretaceous, the opening left the Equatorial Atlantic marked large offset of transform faults. The investigated part on the margin is the offshore portion of the Potiguar Sedimentary Basin, NE-Brazil. Understand the seabed morphology of the region is imperative since the area is the new target for wind power offshore and exploration of oil in deep waters. Construction in areas of instability could represent hazards and cause accidents. The area beyond the shelf is not covered by high resolution bathymetrical dataset. To provide the first high resolution mapping of the continental shelf and slope we used two 3D high resolution seismic blocks. The dataset was conceded by the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP). With the seabed mapped the aim was: a) Provide the first high resolution mapping of the slope of the Potiguar Basin and b) Map the most representative geomorphological features, especially those that could indicate instability. In addition, the subbotom seismic interpretation was used to verify if: a) Any of those features were being controlled by Neotectonism related to a possible reactivation of an Ocean Fracture Zone or if b) They were related only with gravitational/erosional processes. To conduct the seismic interpretation Petrel E&P Software was used. The seabed mapping revelled that the continental slope is marked by submarine channels, slope failure, sediments deposits, gullies and at least 4 landslide scarps. The largest landslide scarp Ls1 has a semi-elliptical shape-oriented NW-SE and reaches a slope dip of ~14.4º. The subbotom seismic interpretation revealed at least three types of landslides processes occurred at the slope: slide, collapse and slumps. The tectonic interpretation did not evidence any tectonic faults affecting the sedimentary packages younger than the Miocene. This indicates that the present seabed morphology is probably not or little affected by neotectonic processes and a possible reactivation was not proved on the area covered by the dataset. The complex morphology revelled by the seabed mapping seems to be controlled only by gravitational, erosional, and sedimentary processes. Our dataset indicates that areas close to the channel’s walls, marked by scarps and close to landslide scars, are areas prone to collapse, due to the elevated steepness in which offshore constructions should be avoided.