Abstract The Recôncavo basin is located in northeastern Brazil, and occupies an area of 11,500 km 2 . It corresponds to the southern portion of an elongated intracontinental aulacogen that extends to the north, encompassing the Tucano and Jatobá basins (Figure 1). The basin is limited to the east by the Salvador fault, with a maximum dip slip of around 5000 m, and to the west by the Maragogipe fault, with an average vertical displacement of 200 m. To the north, the basin is separated from the Tucano basin by the Aporá high, while to the south its exposed portion is delimited by the Itacaré high (Figure 2). This asymmetric graben is basically filled with Upper Jurassic and Lower Cretaceous sediments, which characterize two major sedimentary sequences: the first, prerift, is composed of an arid alluvial fan system and associated facies; the second, synrift, is composed of alluvial, fluvial, and deltaic lacustrine sediments representing the complete record of infilling of a tectonically active lake basin. A thin package of Upper Cretaceous and Tertiary postrift coarse clastics partially covers the present-day basin. As a whole, the sedimentary section reaches a maximum thickness of about 6000 m, deposited over Archean granulites and, locally, over slightly metamorphosed Proterozoic rocks and Permian-Carboniferous sediments.

Abstract The studied Aptian lacustrine succession of the continental Jatobá Rift Basin varies mainly between pure carbonates (predominantly laminated limestones), marls and shales, with some intercalations of presumably deltaic sandstone complexes. In accordance with geochemical data, the occurrence of dolomite indicates intensive microbial activity in a stratified water column with slightly enhanced salinity. Petrographic data prove mild weathering conditions. Aggregates of authigenic smectite observed in sandstones, probably representing transformed volcanogenic glass particles, strongly indicate explosive volcanic activity. Occasionally occurring dolomite seems to have been formed due to intensive microbial activity under moderately increased salinity conditions. Potential hydrocarbon source rocks containing Type I organic matter (OM) were deposited during various phases of the Aptian. Enhanced biological productivity is indicated by bulk organic geochemical data (C org , hydrogen index, extraction yield) and δ 13 C values of carbonates within peletoidal and laminated limestone layers. Carbon-isotope ratios of carbonates argue for OM cycling and remineralization. High δ 18 O values of carbonates are attributed to periods of lower lake levels. A major contribution of aquatic organisms (green algae, microalgae, zooplankton) and minor input from macrophytes and land plants to OM accumulation is indicated by n -alkane distributions, steroid composition and δ 13 C values of individual biomarkers. Microbial communities included heterotrophic bacteria and cyanobacteria, as well as purple and green sulphur bacteria. The sediments were deposited in an alkaline palaeolake. Highly reducing (saline) bottom water conditions and a stratified water column existed during OM accumulation of the Crato Formation. This is indicated by low pristane/phytane, gammacerane index, and the presence of β-carotane and aryl isoprenoids. Differences in OM composition and stable isotope data reflect the evolution of the basin from a stratified saline lake to a freshwater environment with limited potential for OM preservation.

Abstract A combination of seismic reflection and gravimetric imagery has been used to map four sectors of proto-oceanic crust along conjugate segments of the West African and Brazilian margins. These form corridors isolating oceanic crust, produced about the post-118 Ma pole of rotation, from continental crust. Seaward of the proto-oceanic crust/oceanic crust boundary, relatively uniform, thin oceanic crust (4.2–6.5 km thick) has been generated at the paleo-Mid-Atlantic Ridge. Structural variability is limited largely to fracture zones. Proto-oceanic crust in the northern sectors ( i.e. , Kribi, Mbini, and Ogooue) is up to 10 km thick, block-faulted, compartmentalized, and seismically layered. These sectors of proto-oceanic crust likely were generated by slow spreading, as the relative plate motions evolved from left-lateral dislocation along the Sergipe-Alagoas transform to full-fledged spreading. Thus, proto-oceanic crust in the north is the product of a leaky transform fault and records the evolution from disorganized to organized spreading under a changing stress regime. Proto-oceanic crust in the southern sector, the Gabon sector, may consist of slivers of lower crustal or upper mantle rocks emplaced along detachments and unroofed as the Gabon upper plate detached from the Brazil lower plate. The ocean-continent boundary marks the transition from deeply-subsided proto-oceanic crust to relatively elevated continental crust. Merging the mapped oceanic crust/proto-oceanic crust boundaries from the conjugate margins results in a rigid closure model at about 118 Ma for this part of the Atlantic. Merging the mapped ocean-continent boundaries ( i.e. , removing proto-oceanic crust) produces a Neocomian rigid closure fitting the continental sectors of the African and South American plates. Prior to this stage, and beginning in earliest Neocomian, continental deformation was dominated by sinistral shear along the Sergipe-Alagoas transform, parallel to the West African margin between 3° north–1° south (or parallel to the Brazilian margin between 8°–13° south). Shear along the transform produced a complex swath of transcurrent fault branches, relays, pull-apart basins, and transpressional ridges. Conjugate fits of paired seismic lines from the two margins indicate the South American plate moved more than 100 km southwest relative to the African plate, prior to a 40° change in plate motion direction leading to genesis of proto-oceanic crust. Dislocation along the transform obliquely extended both the Gabon rift zone to the south of the transform, and the Jatobá-Tucano-Recôncavo rift zone marking the western boundary of the Sergipe microplate. Conjugate seismic pairings across the adjoined Brazil and Gabon rift zone margins show that a simple shear mode of extension developed in this area as dislocation along the transform progressed. The low-angle main décollement dips toward the Gabonese side and deepens beneath it, dividing a narrow band of abruptly extended São Francisco cratonic crust (lower plate) from a broad zone of extended Congo fold belt rocks (upper plate). With the 40° change in plate motion direction and the onset of seafloor spreading, extension of the Gabon rift zone ceased and the Jatobá-Tucano-Recôncavo rift zone became an aulacogen. The plate closure scenarios presented here have an important bearing on matching rock units and basins from the two margins, particularly in an exploration context. The scenarios also explain why previous attempts to pair apparent conjugate seismic lines from offshore Brazil and West Africa have been unable to consistently match both continental and oceanic crustal sectors.