Published 1995 as part of Studies in Geology 40
Copyright © 1995 The American Association of Petroleum Geologists.  All Rights Reserved.
 

By the earliest Cretaceous, a meridionally oriented rift system began splitting Northern Gondwana into the respective continents of South America and Africa. The system terminates abruptly against the Falkland-Agulhas transform on the south and the St. Paul-Romanche transform to the north, which give the boundaries to the present-day South Atlantic Ocean. This 5000 km long system created an elongated, segmented, complex series of rift valleys that were the settings for lakes ranging in age from Neocomian through Barremian. Various geologic factors defined the major segmentations of the margin and ultimately controlled basin dimensions. Early in the history of these basins, the lakes occupying some basins became anoxic, allowing organic-rich sediments to accumulate. 

These source rocks and their generated oils have been shown through geochemistry and biomarker studies to change character north of the Rio Grande Rise-Walvis Ridge complex toward the interior of Northern Gondwana. The southern rift lake basins that evolved into the Santos, Campos, and Espirito Santo basins on the South American margin and the Angola, Congo, Cabinda basins on the African margin generated oils from source rocks originally deposited in saline to brackish water anoxic lakes. In the more continental interior basins of Sergipe-Alagoas, Potiguar (South America), and Gabon (Africa) the organic-rich sediments were deposited in freshwater lakes that were dysaerobic to anoxic. These relationships imply