Post-rift stratigraphic evolution of the Atlantic margin of Namibia and South Africa: Implications for the vertical movements of the margin and the uplift history of the South African Plateau

Abstract : The aim of this study is to constrain the post-rift deformations of the Atlantic passive margin of Namibia and South Africa using an extensive industrial 2D reflection seismic dataset calibrated by wells and onshore outcrops that have been revaluated in age (biostratigraphy) in order to discuss the evolution of the South African Plateau uplift. The first-order evolution of the margin is tectonically driven and can be divided into three principal phases. The first (131–93.5 Ma) comprises an overall retrogradational trend that results from a rate of accommodation, created by the thermal flexure of the margin, that is higher than the sediment supply. The second (93.5–66 Ma) comprises an overall aggradational-progradational trend that results from a relative increase in sediment supply due to an uplift and subsequent erosion of the margin and the inland domain. The third (66–0 Ma) is retrogradational again in response to a decrease in sediment supply induced by a relative stability of the margin and climate conditions. This study demonstrates that the present-day configuration of the margin is acquired during the Late Cretaceous (from 81 to 66 Ma) with a strike, long-wavelength and seaward tilt of the margin which could be related to the growth of the onshore main escarpment. We also characterize a regional Oligocene unconformity marked by a significant downward shift of the shoreline which suggests a moderate uplift of the inland domain and could be associated with a reactivation of the relic late Cretaceous relief.