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Abstract

Plate tectonic reconstructions and geophysical interpretations across the southern South Atlantic Ocean suggest geodynamic relationships between Brazilian and West African continental margin basins, particularly the correlation of synrift basins, transform faults, fracture zones, salt basins, and other geological markers. The analysis indicates a diversity of basin characteristics (rift and drift systems) on both sides of the South Atlantic that define them as different stratigraphic, structural, and geochemical entities. Marked differences are observed between the basins north and south of the Florianópolis (Rio Grande) Fracture Zone in Brazil and the Walvis Ridge in Africa, which are clearly expressed in the regional deep seismic profiles recently obtained in the conjugate margins. However, in terms of petroleum systems, the basins are characterized by several geochemical similarities in source rocks deposited during a continental, lacustrine synrift sequence.

This interpretation has been overlooked by several previous works comparing the South Atlantic margins, but it has been recently applied to the delineation of several exploratory targets in the southern Angola, Namibian, and South Africa offshore basins. Two end-end member basins have been suggested north and south of the Walvis Ridge–Florianópolis Fracture Zone, which experienced a different structural and stratigraphic evolution as a consequence of their geodynamic models. The southern African basins (located south of the Walvis Ridge), as well as the conjugate Pelotas Basin offshore Brazil, and the offshore Uruguay and Argentina basins, have been associated with the development of volcanic margins, formed during the emplacement of the Tristan da Cunha mantle plume. Due to the lack of significant hydrocarbon discoveries in the southernmost South Atlantic, doubts have been cast on the presence of the prolific Lower Cretaceous lacustrine source rock systems south of the Walvis Ridge, which occur in the northern basins (particularly in the Greater Campos basin) and are overlain by the massive salt offshore Angola. This work reports the comparison of the geological, geophysical, geochemical and consequently the petroleum system features of the Namibian and South African basins (Walvis, Lüderitz, and Orange) with the basins offshore Brazil, Uruguay, and Argentina.

The results of seismic, potential field, and geochemical analyses of oil samples recovered from offshore wells in the South Atlantic conjugate margins endorse the application of a unified model for source rock and petroleum system assessment in the offshore basins, heralding the existence of a new frontier for the petroleum exploration offshore Namibia, possibly containing giant lacustrine oil and gas reserves.

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