Abstract: Tectonic-Stratigraphy of the Aptian Salt Basin as Developed in the North Gabon, Lower Congo and Kwanza Basins

Ormerod, David; Jonathan Smith; and John Griffith - BHP

The Aptian Salt Basin comprises several distinct basins which have major hydrocarbon provinces associated with them. The overall stratigraphy throughout the Aptian Salt Basin however has very similar components with the major modifications controlled more by tectonic styles rather than timing of major events.

The general tectonic style in the southern Kwanza and Lower Congo basins is one of extensional platform, diapiric and salt withdrawal basins, compressional folds and thrusts with associated downbuilding moving from east to west. In the northern North Gabon basin the tectonic belts are similar with the main downbuilding into salt occurring within the extensional zone and the degree of shortening in the compressional generally being less.

The overall stratigraphy is similar throughout the Aptian Salt Basin with a two phase rifting episode within which localized rich lacustrine source rocks are developed. This is then overlain by a transitional phase which is predominantly comprised of a thick salt layer. Overlying this are extensive Albian platform carbonates with associated deep water marls providing source rocks. A major transgression in the Turonian provides a second laterally extensive source rock and this is then overlain by major regressive delta systems which are initiated by changes in river catchment areas and by significant uplifts in the Oligocene / Lower Miocene along the West African Margin. Within the deep water facies of the major deltas significant turbidite controlled by tectonically enhanced lowstands provide high quality reservoirs.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil