Contrasting Structural Styles, Brazilian and West African South Atlantic Volcanic and Nonvolcanic Margins: The Impact on Presalt Petroleum Systems

Abstract

The South Atlantic presalt petroleum system has unique elements which are related to the basin bound-ing structural fabric, accommodation space and climatic conditions. The development of both high total organic carbon lacustrine source rocks and hypersaline/ hyperalkaline microbial carbonates requires sequestra-tion of these basins from marine conditions. Sequestration is accomplished by an outer-high which was isostatically elevated by magmatic under-plating. This magmatic under-plating is occurs along the mar-gin from the Santos Basin to the Espírito Santo Basin and the conjugate Kwanza Basin. Where the outer high is absent, such as in the Brazilian Pelotas Basin and Namibian basins, the presalt petroleum system fails to develop. In Gabon where under-plating and basin sequestration occurs, a Brazilian style presalt system fails to develop due to high clastic influx. Gabon lacks the microbial hypersaline carbonate reservoir. Similar Brazilian style presalt petroleum systems are likely however, to occur on other passive margins where sim-ilar structural styles create a sequestered basin. These basins should occur in regions which are transitional from classic volcanic margins to true nonvolcanic mar-gins. Through better understanding of the Brazilian presalt geodynamic setting we can position ourselves to identify new basins with similar petroleum systems which have created the giant Brazilian presalt discoveries.