(1) Consulting Exploration Geologist, Houston, TX
(2) Geolearn LLC, Houston, TX
(3) Unocal, Sugarland, TX
Abstract: Paleogeography of the pre-salt and salt basins of the Angolan continental margin
Seismic data in deep and ultra-deepwater of West Africa has shed light on evolution of the continental margin. The origin of block faulted basement (volcanic?) west of the Salt Basin is postulated to represent a sub-aerial phase of early drift volcanism that predates seafloor spreading. This new feature along with the main structural elements that controlled sedimentation during Rift, Sag and Early Drift are illustrated using paleographic maps. These maps display the spatial as well as temporal relations of the main elements during evolution of the continental margin.
Early in the Rift phase, continental sediments rapidly accumulated in a series of tectonically linked grabens in a long rift valley with deep lakes, active block faulting, and local volcanism. Abandoned rift segments thermally subsided creating the Sag Basins. In the Sag phase, the lakes broadened while at the same time, active rifting was occurring in the west. Late in the Sag Phase, the eastern belt of rift basins was exposed while thick sediments, transitional to marine (?) accumulated in the Sag basins.
As the continents began moving apart, during the Early Drift phase, marine waters invaded the rift. Salt was deposited over the Sag basins, while a sub-aerial volcanic terrane continued to develop west of the continental boundary. Late Cretaceous shallow(?) Marine Early Drift sediments on-lap this faulted volcanic terrane.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana