Namibe Basin: Geology and Hydrocarbon Potential, Angola

Syanga Abilio, Sriman N. M. Inkollu

Namibe basin is located in the south-central Atlantic off southern Angola. Its occurrence in Late Jurassic-Early Cretaceous continental rifting is coeval to the Santos of eastern Brazil. In this frontier-type, marginal sag basin, a 420-km sediment depocenter is estimated along a north-south elongation axis. Walvis Ridge bounds the basin's southern flank offshore, and desert sand covers the onshore strata.

The basin is divisible along its axis into a shallow shelf and deep basin, separated by north-northeast-trending gravity maxima. A steep plunge at the shelf edge is marked by basement hinge faults and the 200-m water-depth isobath. Prominent east-northeast-trending transcurrent faults dissect the basement. The shelf is narrow, ranging from 5 to 50 km, and is wider in the southern part of the basin. Oceanic crust near the shelf edge is interpreted from positive to rapidly converging negative Bouguer values toward the continent.

On the shelf, Early Cretaceous rifting is marked by extensive volcanism, tensional tectonism, graben formation, and thick fluvio-lacustrine sediment deposition. Minimal subsidence on the shelf led to moderate post-Aptian sediment accumulation with homocline structuring. In the deep basin, early Tertiary volcanism around the northern flank and thick sedimentation due to subsidence along the hinge fault are recognizable. Aptian salt is absent, except along the northern flank where its presence is inferred through apparent salt-induced post-Aptian structuring.

Regional unconformities are drawn from contiguous Kwanza and Congo basins. A potentially large reservoir is a 100-mi linear shelf-edge Albian carbonate inferred to be a buildup or bank. Other potential reservoirs are lacustrine sands/carbonates found near basement horst blocks and deep-basin Tertiary turbidites sourced from the shelf due to rapid sand deposition on a steep shelf-slope. The basin's excellent hydrocarbon potential is emphasized by marine and lacustrine source-rich shale deposition in optimal mature zones.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.