Abstract The synrift and breakup stages of the Pelotas basin in southeast Brazil are characterized by scarce siliciclastic deposits and widespread volcanism in the form of seaward-dipping reflectors (SDRs). Using high-quality seismic reflection and refraction profiles integrated with gravity, magnetics, and exploratory boreholes, a volcanostratigraphic analysis has been undertaken to understand the geological processes observed during the rifting and breakup stages of this segment of the South Atlantic continental margin. Ten volcanic units have been identified and mapped within the extended continental crust and into the transitional and oceanic crusts. The magmatic cycle began during the early synrift stage, with alkaline, high TiO 2 basalts produced at 125 Ma. This was followed by the formation of a series of voluminous tholeiitic, high TiO 2 SDR wedges during the late synrift and breakup stages. The end of the breakup process was marked by flat-lying, late synrift/early postrift, tholeiitic, low TiO 2 basalts at 118 Ma. During the Late Cretaceous and Early Paleogene, the magmatic activity continued only in the oceanic crust, forming igneous intrusions (volcanic cones or seamounts). A comparison between the Pelotas basin and the Lüderitz and Walvis basins offshore Namibia is discussed by integrating regional geological maps, potential field methods, seismic data, and results of exploratory drilling. The SDR province in the Pelotas basin coincides geographically with the Paraná basin continental flood basalts onshore Brazil, which crop out near the coastline. This makes the Pelotas basin an ideal place to understand the relationships between the tectonic-magmatic events that preceded and continued during the Gondwana breakup, which resulted in the development of continental margin rift basins and the formation of the South Atlantic Ocean.

Abstract The Red Sea and Gulf of Aden sedimentary basins are developed along the African and Arabian conjugate margins and are characterized by Late Tertiary rifts filled with siliciclastic, carbonate, and thick evaporite successions north of the Babel-Mandeb Strait in the Red Sea. Geodynamic models for the development of the Red Sea–Gulf of Aden continental margins include simple shear mechanisms associated with mantle exhumation, as described in the Iberian margin, and pure shear mechanisms, with continental breakup associated with magmatic intrusions and development of organized oceanic crust in some segments of the axial trough. The rifted continental margin in the southern segment of the South Atlantic is characterized by several Mesozoic rifts that extend from onshore to offshore Brazil, Uruguay, and Argentina; the onshore rift-border faults in Argentina are at high angle to the continental margin basins. These rifts and also the Pelotas basin in southern Brazil are essentially devoid of evaporites, which mainly occur northwards of the Florianópolis Fracture Zone. A mantle plume before continental breakup is interpreted to cause the massive volcanic outpouring both in the Red Sea–Gulf of Aden continental margins (Afar plume) as well as in the region between the Pelotas and Santos basins in Brazil (Tristão da Cunha plume). The basalts associated with the continental breakup include seaward-dipping wedges in the transition from continental to oceanic crust, and volcanic eruptions probably formed barriers isolating oceanic basins from an incipient gulf developed on continental crust with synrift sedimentation. Episodic marine incursions resulted in accumulation of thick layers of massive evaporites that were deposited before the development of active oceanic spreading centers. The oceanic ridges split the salt basins initially with localized igneous intrusions and subsequently by organized oceanic crustal spreading, with allochthonous salt flows advancing towards the axial trough and covering the volcanic basement.

Abstract The rifted continental margins off Brazil and West Africa encompass several morphological distinct regions that resulted from the plate separation and subsequent drift of South America and Africa. The main building blocks that controlled the development of the Atlantic-type continental margin basins consist of prerift, synrift, and postrift tectonic stages, and these events determined the basin infill. Oceanic fractures created by transform faults that indent the continental margins form basement highs that ultimately define the tectonic edges of the continental margin basins. These boundaries are involved in the marginal plateaus, marginal banks, and characteristic marginal volcanic ridges. Major petroleum producing provinces are situated in the rifted margin salt basins and also in the equatorial transform margin basins without salt. In the salt basins, the continental slope and rise are characterized by the development of massive salt walls that delineate minibasins that were in-filled with deep-water sediments. The hydrocarbon production from these deep-water reservoirs are mainly from postsalt Tertiary and Upper Cretaceous turbidite sands, plus added production from the cluster trends of presalt carbonate microbialite reservoirs. These reservoirs are all mainly sourced by Lower Cretaceous synrift lacustrine strata, but Upper Cretaceous source rocks have also been identified in the South Atlantic salt basins. The equatorial conjugate transform margin basins are also characterized by minor salt deposition in some regions (such as the Ceará basin). These basins produce hydrocarbons from combination traps of Tertiary and Upper Cretaceous turbidite reservoirs. All of the deep-water basins are influenced either by salt or shale tectonics and related to episodic volcanism. In the southernmost South Atlantic, volcanism dominates the conjugate margins, as indicated by thick wedges of seaward-dipping reflectors. There are two main types of South Atlantic continental margins: The transform margins shaped by the large offset equatorial fracture zones and in which the transverse structural lineaments are predominant, except for preexisting structuring that is not related to the Cretaceous transform directions. In these basins, where salt is absent, the typical exploratory play includes combination traps with turbidite reservoirs, generally exhibiting remarkable bright-spots amplitudes that reflect the associated deep-water channels and stratigraphic pinch-outs. The rifted conjugate margins shaped by salt tectonics, which extend from Sergipe-Alagoas to the Santos basin in Brazil and the corresponding conjugate margin basins from Cameroon to Angola. Here, the typical plays are predominantly associated with autochthonous salt. The salt basins account for most of the South Atlantic’s offshore petroleum production. The postsalt and presalt petroleum yields are explained by lacustrine source rock maturation during Tertiary times. Hydrocarbon migration is either into the synrift reservoirs proper or through salt windows into the postrift/postsalt reservoirs of mid-Cretaceous to Miocene. In the presalt plays, the synrift source rock and the carbonate reservoirs in the sag basin are capped either by massive salt or by a thick layered highly mobile evaporite sequence. Future exploration will need to tackle the ultra-deepwater provinces near the continent-ocean boundary, where there are several potential tectonic, structural and stratigraphic targets.

Abstract Geological reconstructions in the last two years involving the elements and processes of the petroleum systems across the southern South Atlantic rifted margins of Namibia and Brazil show evidence of great similarities in the geochemical affinity of petroleum systems in the conjugate margin basins, although some differences are present in their structural and stratigraphic framework. The results of three deep water wells drilled in 2013, in the Walvis and Orange basins, offshore Namibia, showed the presence of at least three prolific active petroleum systems; an early Barremian lacustrine saline, a Barremian marine siliciclastic, and a Cenomanian–Turonian marine anoxic, all of which are characterized by expressive correlations with world-class lacustrine and marine source rock entities. The occurrence of marine anoxic source rocks deposited in Barremian times suggests that sea incursions, in the synrift occurred earlier in the Namibian coast when compared with their Brazilian counterparts where the present of Late Aptian salt is observed (Santos and Campos basins). The recovery of a marine light oil (41° API), for the first time, offshore Namibia, tested from Barremian turbidite sandstones in the Wingat-1 well in the Walvis basin, together with the penetration of at least three source rock systems intervals in the Wingat-1, Murombe-1, and Moosehead-1 wells, confirmed the oil-charged character of a new underexplored petroliferous basin in the deep water province of Namibia.

Abstract The main objective of this book is to provide a global overview of divergent margins based on geological and geophysical interpretation of sedimentary basins along the South, Central and North Atlantic conjugate margins, from plate tectonics and crustal scales to a more detailed description of stratigraphical and structural elements that are responsible for petroleum plays. These themes are complemented by geodynamic concepts based on physical and numerical models, and by comparisons with present-day embryonic margins, which are succinctly discussed in some papers. Supplementary material: Three plate animations of the Atlantic Ocean are available at www.geolsoc.org.uk/SUP18620 .

Abstract This work addresses the geological and geophysical interpretation of salt structures in selected Brazilian sedimentary basins, from intracratonic Palaeozoic evaporites in the Amazon and Solimões basins to divergent margin evaporite basins formed during the Mesozoic break-up of Gondwana. There is an intriguing correlation between evaporite basins and hydrocarbon accumulations in all the selected basins discussed. The Solimões and Amazonas basins developed evaporite depositing environments as the Middle Carboniferous sea was closing during a plate convergence phase. The salt basin along the eastern Brazilian and western African margins developed along the Mesozoic rifts of the South Atlantic. Regional seismic interpretation and potential field (gravity and magnetic) data over the eastern Brazilian and west African margins suggest a very thick autochthonous salt layer deposited over rifted continental crust and particularly above the thick sag basin sediments over the hyperextended crust that marks the transition from continental to oceanic crust. Most of the hydrocarbon discoveries in the eastern Brazilian and western African margins are in post-salt turbidite and carbonate reservoirs, but recent discoveries in the deepwater salt basins along the southeastern Brazilian margin indicate that pre-salt plays will represent an important contribution to hydrocarbon production in the near future.

Abstract Industry, regional deep-resolution seismic reflection profiles along the shallow to ultra-deepwater regions of the South Atlantic sedimentary basins allow the interpretation of different salt tectonic compartments for the whole Aptian basin, which extends from the rift border towards the oceanic crustal limit. Geological and geophysical interpretation, particularly along regional seismic transects in the eastern Brazilian and western African margins, reveals six major salt tectonic provinces associated with gravitational sliding and spreading. These tectonic provinces are characterized by particular salt families that have counterpart structural elements in the Gulf of Mexico, which shows better development of Jurassic salt basins onland and much thicker clastic input offshore in the Late Tertiary. The tectonic domains in the offshore region (platform and in deep waters) are characterized by halokinetic structures that developed huge salt diapirs, an extensional province associated with turtle structures, roll-overs and evacuation grabens, and particularly, by major development of allochthonous salt tongues. Extensional elements predominate in the proximal and intermediate provinces, whereas compressional features characterize basinward provinces near the continental—oceanic crustal boundary. Volcanic features, igneous intrusions, and wedges of seaward-dipping reflectors characterize the transition from rifted continental to oceanic crust. The deep-resolution seismic profiles also allow the identification of autochthonous and allochthonous salt structures near the crustal boundary, forming bathymetric escarpments and salt nappes that extend towards the undeformed post-salt sedimentary sequences overlying oceanic crust. Physical modelling experiments and seismic restoration using balancing techniques can constrain the seismic interpretation. We also propose conceptual plays that have not been tested in the South Atlantic but have been proved elsewhere, both in the Gulf of Mexico and in the North Sea.