Abstract: Map of Tectonics, Sedimentation and Hydrocarbon Distribution of the South Atlantic Margins

Davison, Ian and Royal Holloway - University of London

A tectonic map of the South Atlantic margins is presented which highlights the correlation of structures, source rocks and oil types across the margins. The correlation of opposing margins has been made using the recent Seasat gravity anomaly maps which allow some fracture zones to be traced up to the coastlines. Precambrian basement structures control the orientation of the margin causing the inflection of the Santos basement. The present day bathymetry is a good indication of the underlying tectonics except in regions of abnormal sedimentation such as the Amazonas cone and the Niger delta. The 3000-4000m bathymetric zone is approximately the depth where the oceanic-continental crust boundary is situated. The distance from the coastline to the 3000m isobath varies from 28 km in the Pernambuco-Paraíba Basin to a maximum of 600 km in the Santos Basin. The widest margin in Brazil is the Santos Basin, and this is juxtaposed against the narrowest basin on the African side, which is the Namibe Basin. This extreme asymmetry is probably caused by final separation of the margins taking place along one side of a symmetrically-stretched zone. The difference of the hydrocarbon distribution along narrow margins and wide margins is extreme with 90% of the produced oil along the margins trapped on wide margins. Most of this oil is trapped in turbidite sandstones of Late Cretaceous to Miocene age. However, narrow margin traps exist in deep waters, which have not been drilled yet.

The map will be available in CD ROM format, along with a series of maps covering the whole of the Brazilian margin. These will be published shortly in Davison (1998).

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