ABSTRACT: Early Cretaceous Paleogeography of Gabon/Northeastern Brazil--A Tectono-Stratigraphic Model based on Propagating Rifts

BRADLEY, C. H., Conoco Inc., Houston, TX, and M. N. FERNANDEZ, DuPont Nigeria, Lagos, Nigeria

Regional gravity and seismic data, the region's present-day structural and stratigraphic configuration and comparison with other rift systems worldwide, led to the development of a rift model for Gabon and Northeastern Brazil that involves two propagating megafracture systems which interacted in a very complex fashion. A series of paleogeographic reconstructions depict the development of the rift stratigraphy and illustrate how the dual rift model explains the geometry and subsidence history of both the Reconcavo/Tucano/Jatoba Rift system, the northward-propagating fracture system, and the Sergipe-Alagoas/Interior Basin/N'Komi Rift system, the southward-propagating fracture system. In both regions, the distribution of presalt Early Cretaceous reservoirs and source rocks was controlled by the rift phase in progress at the time of deposition.

The reconstructions show that during latest Jurassic through early Cretaceous (Valanginian) time, the Sergipe-Alagoas basin of northeast Brazil and the Gabon interior basin were linked by a transfer zone that formed opposing asymmetric half-grabens. Beginning as early as Hauterivian time, the locus of extension and deposition began to step westward in northern Gabon with the development of a new rift phase fault system. During Barremian-Aptian time, the southern\

interior basin was largely abandoned as active faulting and extension shifted further inboard, to the west of the Lambarene horst. A similar but opposite progression occurred in Brazil as active deposition and rifting moved to the east. By Aptian time, crustal attenuation was complete and the final stages of continental breakup were underway with the emplacement of proto-oceanic crust.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)