Regional assessment of gravity‐driven deformation offshore Namibia (West Africa)—Styles, distribution and controlling factors

Abstract

This paper presents a semi‐quantitative analysis of gravity‐driven deformation along the Namibian margin using extensive 2D depth converted seismic data. The geometries, internal characters and distribution of gravity‐driven systems were investigated through regional and detailed seismic studies. The research shows that surficial slumps are typically ca. 50 m thick and are characterised by contorted seismic facies commonly occurring along the slopes of the margin. They commonly funnel and cluster within high relief areas such as canyons and pre‐existing landslide scars. These contrast with coherent slides that are up to 2 km thick which extend laterally along the margin for tens to hundreds of kilometres. Slides preferentially occur in the proximal part of the margin and are constrained within the main margin depocenters. Here, high sedimentation rates and loading promote the generation of distinct, weak, overpressured layers that favour initiation of sliding of relatively coherent sediment masses. This research also shows that one‐third of volume of the post‐rift sediments on the Namibian margin were affected by slides and slumps. This demonstrates that gravity‐driven deformation is a key geological process that can strongly modify the evolution of rifted passive margins.