Print this pageAtlantic Marginal Basins of Africa
George T. Moore
The over 10,000-km long Atlantic margin of Africa is divisible into thirty basins or segments of the margin that collectively contain over 18.6 × 106 km3 of syn-breakup and post-breakup sediments. Twenty of these basins contain a sufficiently thick volume of sediments to be considered prospects. These basins lie, at least partially, within the 200 m disobath. The distribution of source rocks is broad enough to give potential to each of these basins.
The sedimentation patterns, tectonics, and timing of events differ from basin to basin and are related directly to the margin's complex history. Two spreading modes exist: rift and transform. Rifting dates from Late Triassic-Early Jurassic in the northwest to Early Cretaceous south of the Niger Delta. A complex transform fault system separated these two margins. Deep-water communication between the two basins became established in the middle Cretaceous. This Mesozoic-Cenozoic cycle of rifting and seafloor spreading has segmented the margin and, where observable, basins tend to be bounded by these segments.
The sediment distribution forms a band paralleling the margin; this band is elliptical in cross section and irregular in width. The thickness is variable with depocenters that locally exceed 10 km. Over 60% of the basins have a sediment column greater than 5 km in thickness. The top of the oil generation window averages about 3.3 km. Allowing an additional 2 km to the top of the gas generation window, any source rock interval that is buried deeper than 5.3 km is in a dry gas regime. The giant oil province, the Niger delta (20 × 109 bbl of oil), is associated with a triple junction. Five other basins, Gabon, Cabinda/Zaire, Ivory Coast, Cuanza, and Douala, each contain reserves in excess of 0.5 × 109 bbl of oil. A large volume of reserves in these major o l-producing basins is in settings dominated by delta-fan complexes.
AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.