Abstract The Equatorial Atlantic evolved from a transform margin to an oblique-passive margin from the early rifting to early drifting stages. The entire Equatorial region of the South Atlantic behaved as a global-scale accomodation zone linking the evolving Central and Southern Atlantic ocean basins. Lithospheric keels and the roots of thick, stable Proterozoic cratons worked as an anchor, preventing and postponing the continental rupture. The transition, from a continental transform margin to an oblique-passive margin, lasted approximatelly 10 m.y. Once oceanic lithosphere started to be created at the main transtensional segments, large offset transform faults developed. Remarkable differences are observed between adjacent basins. Deformation partitioning ocurred at the equatorial margin due to the coaxiality of the progressive deformation. Diachronous deformation occurred as a function of the degree of obliquity of each basin at a specific time. Individual segments of the margin are associated with individual strike-slip basins at early rifting stages and have different amounts of obliquity with a decrease in obliquity from south to north. Because, basement faults form and develop during rifting their geometry gets locked at the time of first emplacement of oceanic crust. Therefore, the geometry of the basement and basement faults can be used to reconstruct the geometries of the original strike-slip basins prior to oceanic spreading.

Abstract The Demerara Plateau is located on the northeast South America continental margin between 5° and 10° North, marking the northwest corner of the equatorial segment of the Atlantic Ocean. It is conjugate to the Guinea Plateau on the African margin, which rifted from the Demerara during the Early Cretaceous opening of the Central Atlantic. Published studies of the Demerara Plateau are focused on its Cretaceous history, when the northern edge of the platform was formed by trans-tensional deformation along Atlantic transform faults, and its eastern edge by extensional deformation during rifting. The platform itself is commonly interpreted as a continental block left behind following South Atlantic rifting. Seismic data across the plateau reveal significant compressional deformation beneath an Albian unconformity. We suggest that this deformation is the result of early opening of the South Atlantic, with a rotation pole located close to the present-day Amazon delta. Allowing for this compression in plate reconstructions of the South Atlantic results in restorations which do not require large amounts of intracontinental deformation in South America, and, consequently, in a relatively simple plate model for the South Atlantic.

Abstract Recent discoveries in Cretaceous presalt basins of the South Atlantic have brought industry’s attention to a new deep-water play on the conjugate margins of South America and Africa. Some of the key factors impacting exploration success in rifted basins are: basement composition, compartmentalization, and subsidence history. Definition of the continent-ocean boundary and configuration of the passive margin are generally inferred from the extent of identified oceanic magnetic anomalies, paleo plate reconstructions, and presence of evaporites. In the absence of magnetic lineations on oceanic crust during the “Cretaceous quiet period,” the margin configuration at the onset of oceanic spreading in the Atlantic is open for debate. The Equatorial Atlantic Transform Margin was dominated by shear deformation due to adjustment in relative plate motions during separation of North American and African plates to the north and South American and African plates to the south. Rifting along the passive margins adjusted to variations in spreading rate, mantle thermal structure, and rift geometry. To reveal the original basin shape, filtered Bougüer gravity and seismic reflection data were used and aided by modeling of South Atlantic opening. This approach provided boundary conditions for original basin shape and limits of extended continental crustal.