AAPG ACE 2018

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Influence of Proterozoic Heritage on Development of Rift Segments in the Equatorial Atlantic

Abstract

The last phase of Atlantic Ocean opening was Late Albian rifting and separation of Africa and South America in the Equatorial Atlantic. Prior to the Albian, initiation and northward propagation of sea-floor spreading caused rotation of the South American plate and formation of two main rift systems in NE Brazil and West Africa: The Northeast Brazilian Rift System, consisting of the Reconcavo-Tucano-Jatoba rifts (RTJ); Sergipe Alagoas/Gabon (SAG) and Cariri-Potiguar (CP) rift valleys in Brazil and the West and Central African Rift System (WCARS) in Africa. The Brazilian basins were developed inside and around the Borborema Province, a key Proterozoic structure that controlled spatial and temporal differentiation between these rift systems. The E-W segment of the Borborema Province behaved as a large scale dextral transfer zone, balancing rift development between the future Equatorial and Central Atlantic branches of the South Atlantic. The RTJ developed as an early rift that was aborted when spreading developed in the SAG segment. This switch was partly driven by the stability of the Borborema Province, not allowing rifting to propagate through the zone. Our analysis of a new compilation of onshore and offshore faults of the Equatorial Atlantic led us to the conclusion that the segment bound by the Kribi and Bode Verde fracture zones south of Borborema acted as a link between intracontinental rifting to the north and late rifting stages in the Central Atlantic. During the Albian, this region acted as a buffer zone, balancing, kinematically, in time and space, dextral strike slip rifting in the Equatorial branch, with simultaneous sea floor spreading in the Central segment. In this paper we tie sequence stratigraphic rift sequences to plate kinematic changes described in our new plate model. Attempts to consider the thermal and tectonic evolution of the Central Salt Basin Segment of the South Atlantic as an analog for the Equatorial margin may lead to wrong predictions in oil exploration, and may explain the asymmetry in the distribution of oil and gas reserves between the two branches of the South Atlantic Margin.