The Sedimentary Supply of African Sedimentary Basins Over the Last 250 Ma

Delphine Rouby, Francois Guillocheau, Catherine Helm, Cecile Robin, Stephane Bonnet, Jean Braun, Olivier Dauteuil, and Kerry Gallagher
Université de Rennes 1 -CNRS/INSU, Geosciences Rennes, Rennes, France

Our objective is to bring new constraints on the uplift and erosion of the African continent over the last 250 Ma from the perspective of the stratigraphic architecture of its passive margin sedimentary basins. The novel aspect of our approach is to integrate the evolution of both the domains in erosion and in sedimentation and to review published data to quantify the terrigeneous supply eroded in the drainage area and preserved in the basins.

We use three approaches with complementary spatial and temporal resolutions. (1) When data are available (e.g along the South African and Namibian Atlantic margins), we determine the long-term signal of sedimentary supply (x10 Ma) from 3D mass balance calculations comparing sedimentary volumes deduced from offshore isopach maps and erosion volumes deduced from the present day geometry of geomorphic markers and thermochronology data. (2) When isopach maps are available, we quantify the associated sedimentary volumes (the Kalahari and Zaire depressions, the Limpopo system and north African basins. (3) 3D dataset are not always available and allow most of the time only a long-term description of the sedimentary supply. We therefore develop a GIS database of 2D regional cross-sections across the major sedimentary basins established from published seismic lines. We homogenise the sections in spatial and temporal scale and then extrapolate them down to the most distal part of the basin so that geometries of our sedimentary wedges are not restricted to the platform domain. On each cross-section, we then measure the 2D area of each stratigraphic interval (x1 Ma) and, determine the average sedimentation “areas” and rates. We then determine the spatial extension of the basins for each time increment and use it to extrapolate average sedimentation “areas” and rate into sedimentation volumes.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery