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The Orange Basin offshore southwest Africa appears to represent a classical example of continental rifting and break up associated with large-scale, transient volcanism. The presence of lower crustal bodies of high seismic velocities indicates that large volumes of igneous crust formed as a consequence of lithospheric extension.We present results of a combined approach using subsidence analysis and basin history inversion models. Our results show that a classical uniform stretching model does not account for the observed tectonic subsidence. Moreover, we find that the thermal and subsidence implications of underplating need to be considered. Another departure from the uniform stretching model is renewed sub-crustal thinning and linked to that uplift in the Cenozoic that is necessary to reproduce the observed phases of erosion and the presentday depth of the basin. The dimension of these events has been examined and quantified in terms of tectonic uplift and sub-crustal thinning. Based on these forward models we predict the heat flow evolution not only for the available real wells but also for virtual wells over the entire study area. Finally, the hydrocarbon potential and the temperature evolution is presented and shown in combination with inferred maturation of the sediments for depth intervals which comprise potential source rocks.

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An integrated approach to investigate the petroleum system of the southern Orange Basin, South Africa reveals that the principal controls on hydrocarbon generation and leakage are spatial and temporal variations in post-rift overburden deposition. The model predicts present day gas seepage at the sea floor and this is calibrated against observed seepage events. D basin modelling of an east-west trending transect across the Orange Basin passive margin was undertaken accounting for variations in stratigraphy, structural deformation, source rock distribution and characteristics and heat flow variations associated with continental break-up. Petroleum generation and migration modelling was performed using compositional kinetic schemes, and migration and leakage routes calibrated to signs of current-day active leakage collected during seismic interpretation. The use of seismic indicators of hydrocarbon leakage as calibration data for constraining migration predictions is essential for the reconstruction of hydrocarbon generation and migration scenarios, as they provide the validation of the model with respect both to the physical properties and distribution of the sedimentary sequences as well as the dynamics of oil and gas migration. Modelling results indicate that the main period of hydrocarbon generation occurred in the Late Cretaceous, the time of maximum burial on the shelf. Following an erosion event at the end of the Cretaceous, deposition shifted over the shelf break and significant sediment volumes prograded into the deep basin. This led to a second pronounced maturation event focussed specifically under the prograding Tertiary wedges. The model predicts that the kitchen area is active today and is also the source of hydrocarbons that are observed to be seeping at the present day sea floor.