Abstract This work integrates the available geological information and geochronology data for the Cretaceous–Recent magmatism in the South Atlantic, represented by onshore and offshore magmatic events, including the oceanic islands along the transform faults and near the mid-ocean ridge. The analysis of the igneous rocks and their tectonic settings allows new insights into the evolution of the African and Brazilian continental margins during the South Atlantic opening. Following the abundant volcanism in the Early Cretaceous, the magmatic quiescence during the Aptian–Albian times is a common characteristic of almost all Brazilian and West African marginal basins. However, rocks ascribed to the Cabo Granite (104 Ma) are observed in NE Brazil. In West Africa, sparse Aptian–Albian ages are observed in a few coastal igneous centres. In the SE Brazilian margin, an east–west alkaline magmatic trend is observed from Poços de Caldas to Cabo Frio, comprising igneous intrusions dated from 87 to 64 Ma. Mafic dyke swarms trending NW also occur in the region extending from the Cabo Frio Province towards the Central Brazilian Craton. On the West African side, Early Cretaceous–Recent volcanism is observed in the Walvis Ridge (139 Ma), the St Helena Ridge (81 Ma) and the Cameroon Volcanic Line (Early Tertiary–Recent). Volcanic islands such as Ascencion (1.0–0.65 Ma), Tristão da Cunha (2.5–0.13 Ma) and the St Helena islands (12 Ma) most probably correspond to mantle plumes or hot spots presently located near the mid-Atlantic spreading centre. Within the South America platform and deep oceanic regions, the following volcanic islands are observed: the Rio Grande Rise (88–86 Ma), Abrolhos (54–44 Ma), the Vitória–Trindade Chain (no age), Trindade (2.8–1.2 Ma) and Fernando de Noronha (12–1.5 Ma). There are several volcanic features along the NW–SE-trending Cruzeiro do Sul Lineament from Cabo Frio to the Rio Grande Rise, but they have not been dated. The only known occurrence of serpentinized mantle rocks in the South Atlantic margin is associated with the Saint Peter and Saint Paul Rocks located along the São Paulo Fracture Zone. The Cameroon Volcanic Line in NW Africa is related to the magmatism that started in the Late Cretaceous and shows local manifestations up to the Present. The compilation of all available magmatic ages suggests an asymmetrical evolution between the African and South America platforms with more pre-break-up and post-break-up magmatism observed in the Brazilian margin. This is most likely to have resulted from the different geological processes operating during the South Atlantic Ocean opening, shifts in the spreading centre, and, possibly, the rising and waning of mantle plumes. Supplementary material: A complete table with radiometric dates that have been obtained by universities, government agencies and research groups is available at: www.geolsoc.org.uk/SUP18596

Abstract New seismic and well data in the deep-water basins of Campos, Santos, South Kwanza and Benguela, supported by plate reconstructions, help answer fundamental questions on the rifting history of the central South Atlantic, specifically on the amount and effect of fault-related deformation, and on when and where sea-floor spreading started. The Paraná mantle plume played a fundamental role – dynamically raising the plate, prolonging continental rifting by heat-softening the crust and, after break-up, delaying the onset of marine conditions. Previous discrepancies in extension and subsidence have been solved, and the location and age of the continent–ocean boundary can now be determined. Rifting involved approximately 450 km of homogeneous pure shear, equivalent to a β factor (lithosphere stretching factor) of 4.5. Break-up occurred at 123 Ma (Barremian–Aptian boundary), 7–8 Ma later than the southern South Atlantic but 6 Ma before widespread salt deposition. The mid-Atlantic ridge was initially subaerial, marked by a volcanic high. Sea-floor spreading was at a rate of 24 mm year −1 , similar to syn-rift deformation prior to break-up. Transcontinental strike-slip shear zones are not evident but a major NW–SE lithospheric lineament associated with a failed triple junction arm had a major influence on the magmatic history, both prior to and after break-up. Supplementary material: A4 versions of the seismic sections shown in Figures 6 & 7 are available at http://www.geolsoc.org.uk/SUP18563 .

Abstract Understanding the genesis of the very peculiar 600 km-wide Santos Basin–São Paulo Plateau system and its narrow conjugate Namibe Margin is a kinematic and structural problem. Several hypotheses have been proposed in order to explain the genesis of this system that imply the same amount of horizontal movement. We investigate the consequences of the horizontal movement in the Santos Basin, based in plate kinematic reconstructions. The kinematic history of this system that we present here, based on the interpretation of seismic profiles and kinematic constraints, has the following consequences: (1) there is no evidence of a ridge jump sensu stricto but, rather, a southwards propagation in the Central Segment of the South Atlantic that starts in the northern part, between the NE Brazilian and Gabonese margins; (2) the Namibe margin evolved as a transform passive margin; (3) the opening direction of the Santos Basin–São Paulo Plateau system is oblique to the general opening motions of the South American and African plates; and (4) this opening is younger (6 Ma) than those of the other basins of the Central Segment of the South Atlantic.

ABSTRACT Búzios, discovered in 2010, is a supergiant pre-salt field, located in the Santos Basin. The main reservoirs are lacustrine carbonates, deposited from the Barremian until the Aptian. Preliminary estimates indicate a volume of oil in place (OIP) on the order of 29,900 MMBOE, thereby ranking it as the largest of the pre-salt fields. The understanding of pre-salt reservoirs continues to be a challenge because of complex facies distributions and tectono-stratigraphy. This study focuses on describing the tectono-stratigraphic framework of Búzios Field, using criteria from 3-D seismic, well log, and core data. Three-dimensional seismic interpretation reveals the Búzios’ rift configuration as a series of horst, graben, and half-graben structures, which are highly faulted (N30W–N30E) because of a complex transfer zone interpreted in the area. Based on seismic interpretation, the rift section was subdivided into a lower and upper rift section. The lower rift section was strongly affected by normal faults, whereas the upper rift was exposed to a less expressive faulting process and has a thinner sedimentary wedge. The upper section corresponds to a commonly observed coquina interval (the Itapema Formation), which serves as the lower pre-salt reservoir in the Búzios Field. Lastly, prior to salt deposition, the post-rift mega-sequence (sag section) is comprised of the Barra Velha Formation, which is composed of biotic and abiotic carbonate reservoirs in a complex structural setting. Based on core analysis from the 3-BRSA-944A-RJS well, the most common facies in the Itapema Formation reservoirs are rudstone and grainstone, composed of bivalve shells, with an average porosity and permeability of 12.5% and 88.7 md, respectively. The Barra Velha Formation reservoirs consist of four main carbonate facies: spherulites (most common), crystal shrub, carbonate laminates, and rare stromatolites, which display an average porosity and permeability of 9.4% and 122.6 md, respectively.

ABSTRACT The Cabo Frio High corresponds to a regional basement arch located on the continental platform between the Santos and Campos basins. The distal margin of the Cabo Frio Outer High is characterized by gravity and magnetic anomalies suggesting an association with magmatic centers that affected the salt basin. Volcanic rocks are observed both on the proximal margin, where the Cabo Frio Volcanic Complex is marked by several magmatic episodes, and on the distal margin, where the Cabo Frio Outer High is marked by intrusive and extrusive igneous features affecting the pre-salt and post-salt sedimentary successions. The most important magmatic events in the area are related to (a) the pre-rift phase, with massive lava flows both onshore and offshore of the incipient continental margin; (b) the synrift phase, as indicated by several wells that drilled subaerial basaltic lava flows intercalated with lacustrine sediments; (c) the sag basin and transitional evaporitic post-rift phase, as indicated by sills and laccoliths overlain by salt and also by discordant igneous structures intruded into salt layers; and (d) the post-breakup phase, with major magmatic activity registered in the Upper Cretaceous and in the Paleogene. Volcanic events in the Cabo Frio region are a major factor in basin development and greatly impact the petroleum resources assessment, particularly when igneous rocks intrude into pre-salt source rocks and reservoirs. The geochemical data from producing fields and exploratory wells in the Cabo Frio region indicate that the main source rock system for the known accumulations are the upper Barremian calcareous black shales, deposited in brackish-to-saline water lacustrine environments from the Coqueiros Formation. In the continental shelf, the oil fields are characterized by intense biodegradation, which has deteriorated the oil quality. Several factors are important elements that control the prospectivity of the Cabo Frio region, such as thermal maturity of the source rocks, reservoir depth, seal effectiveness, magmatic events, and mixing of oils generated from different maturity pulses.

Abstract The tectonosedimentary development of the South Atlantic is compared with the Central Atlantic margins, which are associated with major episodes of magmatism during the Mesozoic continental break-up. Subsequently, the Cenozoic break-up in the North Atlantic led to the formation of the volcanic Norwegian–Greenland conjugate margins. The DSDP boreholes in the magma-poor Iberian–Newfoundland margins have confirmed the occurrence of exhumed mantle at the ocean–continent transition. This possibility has been suggested for the South Atlantic margins, but still lacks confirmation from drilling. The Red Sea and the Gulf of Aden may be considered as natural laboratories to study the break-up processes and formation of divergent continental margins. Using key geological and geophysical data, we compare some of the structures observed in incipient stages of basin formation between the African and the Arabian plates with the structures observed in older sedimentary basins associated with the Gondwana break-up. We also analyse deep seismic reflection profiles and potential field data at the continent–ocean boundary of these conjugate margins, using palinspastic reconstructions to define the corresponding seismic pairs. We conclude that the Red Sea and the Gulf of Aden display remarkable differences to the Iberian–Newfoundland margins, and notable similarities with the South Atlantic margins.

Abstract Salt–sediment interplay in the Santos Basin is investigated integrating seismic interpretation, kinematic restoration and analogue modelling. Deformation within the post-salt sequence results from thin-skinned gravitational gliding and spreading, driven primarily by halokinesis, greatly affected by massive sediment inflows. The impressive landward-dipping listric Cabo Frio Fault controls the major depocentres updip, whereas salt-cored folds accommodate downdip shortening. Sediment supply from confluent directions creates a complex interference pattern of superposed folds with intervening polygonal minibasins. A new structure is identified (termed the ‘Ilha Grande Gravitational Cell’), a linked system of updip extension and downdip contraction detached on salt, comprising the Cabo Frio Fault and minibasins. It moves to the SE, with eastern and western borders suggesting lateral gradients of slippage. This thin-skinned feature results from the differential load imposed by a thick prograding wedge over the ductile salt and is independent of pre-salt structures. The post-salt sequence moves basinwards due to halokinesis, thereby changing position relative to the pre-salt sequence, which implies that any present-day correspondence between pre- and post-salt structures may not attest to linkage in the past. Application of kinematic restoration techniques allows the true position and geometry of the key elements through time, improving petroleum systems assessment.

Abstract Large gold provinces commonly show complicated mineralization histories, and the Paleoproterozoic Alta Floresta, one of Brazil's most exciting Au–Cu mineral provinces, is a good example. The current models defined four deposit types, all connected to a single (1.88–1.75 Ga) magmatic–hydrothermal event. However, long Province history, diverse geodynamic environment and older ages of Type-1mineralization weaken the single metallogenic event and enable the hypothesis of overprinted mineral events. By scale-integrated analyses, we revise the tectonic–geological context, structural–hydrothermal alterations and chlorite–white mica geothermobarometry and propose the Type-1 as an older, granitoid-hosted orogenic mineralization, with subsequent overprinting by the magmatic–hydrothermal event. The older orogenic gold event developed orogenic gold deposits on WNW-trending shear zones in the Peixoto de Azevedo domain granitic–gneiss rocks. Phengite, biotite and chlorite–carbonate phyllonites (3.3–6.1 kbar, 300–420°C) host fault-fill quartz veins (pyrite–chalcopyrite–magnetite–pyrrhotite–gold–Bi–Ag tellurides). Mg-rich chlorite–phengite is the main alteration footprint for this mineralization type. A younger magmatic–hydrothermal event in the Juruena magmatic-arc rocks produced Fe-rich chlorite–white mica alteration zones (0.6–4.6 kbar, 120–380°C) and disseminated and stockwork–breccia ore (pyrite–chalcopyrite–gold–molybdenite–Ti minerals–allanite) in porphyry–epithermal deposits. Where the younger mineralization overprints the older, phyllic alteration destroyed the phengite orogenic gold phyllonite S n +1 foliation. The ages of two pyrite populations (1979 and 1841 Ma) in the older fault-fill veins and molybdenite in late fractures (1805–1782 Ma) or disseminated in the c. 1.79 Ga syenogranite porphyry suggest more than two episodes of mineralization. These two events differ in their alteration styles, P–T conditions and structural, mineralogical and textural ore styles. The multiscale approach sheds light on the relationships between the various mineralization events, allowing a new explorational potential within the province. Supplementary material: Chlorite and white mica complete chemical composition data and other characteristics of the studied deposits are available at https://doi.org/10.6084/m9.figshare.c.6056324

ABSTRACT The presence of natural seepage slicks and seeps composed of a mixture of cracked and uncracked lacustrine saline oils suggests the existence of active Barremian hydrocarbon source rock systems in the frontier deep and ultra-deep waters of the Santos Basin, Brazil. Acquisition, interpretation, and integration with meteoceanographic data of 24 Radarsat and 50 Sentinel images resulted in the identification of 78 oil slicks spread over the 700 km 2 study area from water depths that range from 400 to 3000 m. The identified seepage slicks resulted from the convergence of optimum tectonic, temporal persistence, and environmental scenarios, confirming that some pre-salt oils are effectively leaking from deep petroleum systems to the sea surface. When integrated with piston core, seismic, geochemical, and 3-D modeling data, it is clear that the seepage slicks are directly related to the salt tectonic processes and the presence of transtensional and listric fault zones, suggesting an origin closely associated with salt windows on the unconformity that defines the top of the sag sequence and seepage features on the seafloor. The geological framework of the Santos Basin’s ultra-deep waters is different from the proximal areas of the basin. In this sense, four geological domains are interpreted: The first domain occurs in shallow water in the platform region and can be called the seal risk zone; the second corresponds to the platform to salt-ramp region that occurs from shallow to continental slope waters and is a gas/condensate-prone zone; the third includes the salt-ramp to mini-basin domains, comprising the Upper Cretaceous reservoir turbidity fairway associated with the axis of the central rift system located from the deep to ultra-deep-water region; and the fourth is composed of mini basins and stratified layers of the evaporitic sequence in the ultra-deep waters where giant oil accumulations are present in the carbonate pre-salt reservoirs. These four structural domains determine different petroleum habitats that depend on salt thickness and the structural configuration of the rift sequence. The main hydrocarbon migration model for the identified seeps and oil slicks associated with the salt-weld or salt-wall domain of the Santos Basin’s ultra-deep waters is related to the existence of major fault zones. This type of feature is known as a transtensional fault zone that developed from the basement to the pre-salt reservoirs, with them sometimes functioning as the trigger for the halokinesis-derived listric normal faults that can displace the entire sedimentary wedge and can be observed on the seafloor. The presence of surface slicks is associated with oil seeps detected through piston cores in areas related to these types of faults, which confirms that such systems are the main oil conduits to charge and recharge pre-salt and post-salt oil and gas accumulations. Therefore, this hydrocarbon migration model should be well understood and considered for the exploration for oil and gas, principally post-salt targets. In summary, the integration of seepage slicks, seismic data, and geochemical analyses of reservoir oils and oil seeps can improve the petroleum system comprehension of frontier areas and, in the case of this chapter, open up a huge exploration frontier for the deep and ultra-deep-water outboard area of the Santos Basin.

ABSTRACT The offshore Santos and Campos basins of the southeastern Brazilian margin are currently the focus of extensive hydrocarbon exploration following some of the largest global oil discoveries made within the so-called pre-salt section. It is widely accepted that these basins initially developed during the Neocomian breakup of Gondwana and separation of Africa from South America. However, significant debate exists concerning the regional tectonic significance and timing of Early Cretaceous tholeiitic basalts drilled across the Pelotas, Santos, and Campos basins; the distribution of continental crust; distribution and temporal development of thickened oceanic crust; and basement influence on basin development and timing. We have reviewed earlier published tectonic analyzes in addition to a comprehensive integration of both old and new seismic reflection and refraction data, gravity, and well calibrations to place new constraints on the tectonic evolution of the Santos and Campos basins. Upper and lower crustal refraction velocities and densities across the São Paulo Plateau were once considered to indicate continental basement. Our reinterpretation shows they are equally consistent with thickened oceanic crust (which we term magmatic crust ). We define tectonic domains within the Santos and Campos basins and show that crustal thicknesses across the Outer Basin High and Jupiter Terrace range from 15 to 20 km, whereas the Deep Basin and standard (Penrose) oceanic crust to the east of the Outer Basin High show crustal thicknesses of 1–3 km and 6–8 km, respectively. We interpret the along- and across-strike variations in crustal thickness variations to be a function of the proximity to the Tristan da Cunha plume and its magma budget combined with structural reworking of this thickened oceanic crust by superimposed late-stage extensional faulting. Seismic reflection profiles from the Pelotas, Santos, and Campos basins show the existence of relatively thick oceanic crust characterized by SDR (seaward dipping reflector) geometries that progressively decrease in age to the east and onlap earlier syn-tectonic volcanic flows and/or extended continental basement that form part of a “necking zone.” Analyzing SDRs from the northern Jacuipe Basin demonstrates that they are upper crustal counterparts to Layer 2 of oceanic crust, whereas the lower crust is equivalent to Layer 3 of oceanic crust even exhibiting a crisscross reflectivity pattern possibly related to shear within magma chambers. In particular, we suggest that SDRs represent subaerial seafloor spreading that laterally merges structurally and petrologically into Layer 2 of Penrose oceanic crust. In this interpretation, the first SDR flows onto thinned continental crust are critical because the causative eruptive center defines the location of continental breakup, the timing of breakup, and the initiation of subaerial magmatic spreading. Based on the identification and distribution of SDRs in the Pelotas, Santos, and Campos basins and seismic mapping calibrated with exploration well data, we propose a general template for the structural and stratigraphic development of southeast Brazil that comprises (1) a relatively thick continental crust in the extreme western, proximal part of the margin, (2) deposition of pre-rift and synrift volcanic flows (equivalent to the Paraná basalts) on extended continental crust, (3) a continental crustal necking zone, (4) an exhumation point (i.e., the complete necking of the continental crust) after which post-breakup, magmatic SDR crust onlaps earlier syn-tectonic basement and volcanics, and (5) for the Campos Basin, a second necking zone involving the extensional deformation of magmatic crust. Continental extension is assumed to span Berriasian–late Valanginian (134–145 Ma), consistent with rift basins along the entire eastern Brazilian margin. Lithospheric breakup is considered to be late Valanginian–early Hauterivian (132–134 Ma), triggered by the rapid emplacement of the Paraná Large Igneous Province. As such, deposition east of the continental necking zones is post-breakup (Arutu-, Buracica-, Jiquia-, and Alagoas-aged sediments) on new “real estate” crust. For the Pelotas and southern Santos basins, subaerial magmatic crust was emplaced east of the continental necking zone with the generation of SDRs that progressively decrease in age to the east. In the northern Santos Basin, post-breakup magmatic crust is emplaced east of the continental necking zone, but SDR geometries are not observed. For the Campos Basin, subaerial seafloor spreading forms oceanic crust east of the continental necking zone, and later, seaward of the magmatic necking zone. This second phase of spreading is characterized by additional SDRs. A time-transgressive distribution of magmatic basement age is implied, with older crust emplaced along the continental necking zone and younger crust to the east; depocenter migration is evidenced by the shift in the easterly limit of Buracia-, Jiquía-, and Alagoas-aged sedimentation. In places, ridge jumps may be superimposed (e.g., Abimael Ridge), which locally reverses this age progression. Although several authors have previously suggested that SDRs may represent subaerial seafloor spreading, this is the first analysis to provide an integrated and coherent, self-consistent tectonic analysis of SDRs that defines the location and timing of continental breakup, the initiation of seafloor spreading, the transition to Penrose oceanic crust, and the timing of margin flooding.