The interplay between structural inheritance and morphology in the Equatorial Continental Shelf of Brazil

摘要

The primary objective of this study is to assess the control of faults of the rift and post-rift stages on the shelf morphology of the Potiguar Basin in northeastern Brazil. This aborted rift basin was generated during the opening of the Equatorial Atlantic in the Aptian. The offshore portion of the continental margin consists of a narrow (-40 km) and shallow (~70 m below present sea-level) continental shelf with a very steep continental slope (1:11). Our dataset encompasses gravity, bathymetric, shallow seismic and structural data. The results indicate that low sedimentation rates during the Quaternary period contributed to the identification of structural controls in pre-Holocene rocks. The key evidence for fault reactivation on the seafloor is the link between coastal and shelf features associated with pre-Cenozoic structures of the Potiguar Basin. During periods of low sea level, the incision of shelf valleys was readjusted longitudinally and transversally due to the structural controls. Shelf gradient breaks are associated with the occurrences of coplanar ESE-WNW-oriented faults, and uplifted and subsided areas occur in between these fault systems. The results indicate a strong correlation between the margin geometry, modern shelf surface, near-surface expression, and the rift-phase faults, which appear to be reactivated in concordance with the present-day margin stress field. We conclude that neotectonics has influenced both the sediment deposition and morphology of the NE Brazilian Equatorial margin during Quaternary times.