A petroliferous transform-margin basin, Cote d'Ivoire, West Africa

Break-up transform margins, formed by large dominantly strike-slip faults as continents separate, are distinct in structural style and stratigraphic sequence from subduction or purely extensional margins. A continental margin defined by such a transform zone is sharp, precipitous, and places an essentially complete continental crust abruptly against oceanic or highly attenuated continental crust. Structures develop in stress fields dominated by horizontal translation, with an overprint of uplift and subsidence related to thermal effects of a laterally migrating asthenosphere plume. Stratigraphic sequences begin with relatively deep-water lacustrine deposits and are followed by marine conditions as ocean connections develop. Because bathymetry tends to be steep across the transform zone, marine deposits along this zone represent slope environments with many erosional canyons and canyons fills, and these facies are vertically stacked through time. The offshore Cote d'Ivoire Basin is an excellent example of a transform margin documented by more than 110 wells, an extensive 2-D seismic grid, a growing number of 3-D surveys, and several productive fields. The sedimentary section exceeds 5000m, beginning with Aptian( )-Albian deep lacustrine facies. Marine incursion occurred in the Albian, followed by deformation, uplift, and erosion in later Albian. A series of major uplifts developed offshore along strandsmore » of the St. Paul fracture zone. The uplifts contain many SE-trending normal splay faults. The uplifts and NE-tilted fault blocks are the major petroleum targets within the Albian section. Upper Cretaceous petroleum traps are mainly related to stratigraphic variations caused by submarine canyon cutting and filling. The Cote d'lvoire Basin provides a valuable model of transform margin processes and petroleum occurrences.« less