Abstract This paper first reviews the salt basins and depositional ages in the South Atlantic salt province. This comprises a series of salt basins separated by basement highs, deep graben (that never dried up), later volcanic highs and subaerial ocean spreading ridges. Initial halite and anhydrite deposition occurred first in the Sergipe-Alagoas Basin of NE Brazil at c. 124.8 Ma, and was closely followed by deposition in the Kwanza Basin, Angola between 124.5 and 121 Ma. The later potassium-magnesium-rich salts were deposited in the Sergipe-Alagoas and Gabon-Congo basins before 114.5 Ma. The age of the main Santos-Campos salt is not known precisely, but the latest anhydrites deposited on the southern margin of the Santos Basin post-date volcanic rocks dated at 113.2 Ma. The paper then compares the salt tectonics of the wide Campos-Santos Basin segment with the narrow South Bahia basins segment. Sediment loading in the Santos Basin produced a landward-dipping base salt, which led to the development of counter-regional faults, and inhibited downslope sliding, and enhanced later contractional effects caused by either gravity spreading or regional tectonic compression. Folding occurred in simultaneous pulses across the Santos Basin, suggesting that regional tectonic compression occurred. The narrow salt basins of South Bahia have a steeply dipping base salt horizon (4°) and pronounced folding, which initiates at the oceanward pinch-out of the salt and propagates back up the slope. The topographic highs, above fold anticlines, are rapidly eroded on narrow margin slopes, which allows the folds to grow more easily to large amplitudes at the top salt horizon.

Abstract Continental extension between West Africa and Brazil was responsible, directly or indirectly, for the development of the pre-salt sag basins and the evaporites of the South Atlantic salt basin. Subsidence mechanisms to explain these basins and their capping evaporites include: (1) deposition on Barremian-aged ocean crust; (2) rift propagation from east to west across the West African margin such that post-rift subsidence commenced in the east while rifting was still occurring to the west; and (3) depth-dependent lithospheric extension. Predicted thermal subsidence of oceanic crust or rifted lithosphere is inadequate to generate sufficient accommodation for the evaporites. Within the Santos Basin, extensional faulting within the pre-salt sag basin occurs up to the base of the evaporites; extension clearly continued to the late Aptian. Time-equivalent onshore and offshore pre-salt sections across the West African margin, and the inability to generate sufficient subsidence if the sections are considered to be post-rift, disqualifies east to west rift propagation as a mechanism for the observed pre-salt basins and evaporites. Barremian–Aptian depth-dependent extension best explains the general rift and post-rift development of the West African and Brazilian margins and the paucity of syn-rift faulting, the strain balance being achieved by the lateral emplacement of lower crust and continental mantle out from under the adjacent continental lithosphere. Regional exposure and truncation of the top pre-salt sag section attests to a climate-induced lake level drawdown during the mid Aptian, and offers a simple mechanism to generate the shallow water environments for evaporite precipitation across the West African–Brazilian rift system. In the subsequent marine transgression the Gabon and Angolan salts and the evaporites within the conjugate Camamu-Almada, Jequitinhonha and Cumuruxatiba basins were deposited. Santos and Campos basin evaporites are younger. The barrier to southern Atlantic marine incursions and the possible delay in Santos and Campos evaporite deposition relates to the magmatic constructions of a proto-Walvis Ridge and the long-lived anomalous topography of the southeastern Brazilian highlands; Campos and Santos basin extension was necessarily superimposed on a broad, high-relief plateau.

Abstract The South Atlantic Ocean evolved after rupture of the São Francisco–Congo–Rio de la Plata–Kalahari cratonic landmass and the Late Proterozoic fold belts. Break-up in the South Atlantic realm developed diachronously: rifting started in the south (Argentina) during the Jurassic and progressed towards the equatorial segment. The central portion was controlled by a rift-resistant cratonic nucleus (the São Francisco–Congo craton) and as a result underwent development of narrow basins; parts controlled by Neoproterozoic fold belts developed wide basins. The final break-up of western Gondwana and the onset of plate divergence were marked by thick wedges of seaward-dipping reflectors, located near the incipient ocean-ridge spreading centre that had already been formed by the time Aptian evaporites were deposited. Subsequently, a few episodes of intraplate tectonic and magmatic activity affected the Santos, Campos and Espírito Santo basins. Post-break up development of the offshore basins was affected by gravity gliding over the Aptian evaporites. Continental uplift may be invoked as the main cause of salt mobilization, generating prograding clastic wedges that thickened basin-wards and produced a loading effect on the salt basin. Coupled with onshore erosional unloading and the effects of the gravity gliding, this probably resulted in further flexural uplift of the continental margin.

Abstract An integrated, multidisciplinary study of the tectonic framework, sedimentation, and petroleum systems in the Sergipe–Alagoas Basin was carried out. The methodology was based on regional integration of geologic and geophysical data, particularly seismic reflection and potential field data (gravity and magnetics), results of exploratory drilling, paleontologic and paleoenvironmental analysis of the sedimentary succession, and geochemical data from oils and source rocks. The main topics addressed were the tectono-stratigraphic evolution of the sedimentary basins in northeastern Brazil, the crustal architecture of the Sergipe–Alagoas Basin, and the petroleum systems both onshore and offshore. Results of this study indicate that major synrift troughs are located in the proximal regions and are characterized by negative Bouguer anomalies. The proximal grabens are controlled by comparatively small synthetic and antithetic normal faults, while major rift blocks are controlled by crustal faults that dip seaward. These master faults cut through most of the crust and detach onto lower crustal horizons or even the seismic Moho. Deep-water rift blocks were affected by regional erosional episodes. The transition to pure oceanic crust is marked by wedges of seaward-dipping reflectors and igneous plugs. Some possible salt diapirs are located near the crustal limit. The petroleum systems for this basin include good source rocks in the transitional (evaporitic) and rift-phase sequences. Hydrocarbon generation and migration was effective from Late Cretaceous time onward. Exploratory plays include structural traps associated with synrift and postrift structures, as well as stratigraphic traps associated with deep-water turbidites.