Abstract A tectono-stratigraphic analysis of a broadband 3D seismic survey over the outer slope of Côte d'Ivoire margin, west Africa, revealed that Cenomanian and younger strata seal well-developed rift fault blocks up to 15 km across. Growth strata indicate that these were formed during rifting that culminated in seafloor spreading in the late Albian, challenging existing plate reconstructions for the opening of the equatorial Atlantic ocean. A previously unrecognized system of volcanic edifices linked at depth to a network of sill complexes has also been identified. These are aligned along a NE–SW trend, concordant with kilometre-wide ridges, interpreted as folds formed by steep, crustal faults with an oblique-slip component. These trends are similar to those of fracture zones in the region and indicate that the Côte d'Ivoire was a transform margin in the late Albian. These results highlight the potential of offshore Côte d'Ivoire for deep-water rift plays with large traps formed by extensional fault blocks together with prospective Albian reservoirs ponded in their hanging walls. In addition, the volcanoes and ridges generated seabed relief along the newly created transform margin, forming confined basins for potential deposition of Turonian and younger turbidites and the generation of stratigraphic traps.

Abstract The discovery of the Jubilee Oil Field in 2007 in the Tano Basin of Ghana is a primary example of the potential for Late Cretaceous deep-water stratigraphic traps in basins previously overlooked by the exploration industry. The Tano Basin forms the eastern extension of the Deep Ivorian Basin, which resulted from Aptian–Albian trans-tension associated with the opening of the Atlantic between the St Paul and Romanche fracture zones and the subsequent post-rift subsidence. The basin was the focus for deposition of a thick Upper Cretaceous, deep-water clastic sequence, which, in combination with a modest Tertiary section, provided sufficient thickness to mature a Cretaceous source rock in the central part of the Tano Basin. This well-defined reservoir and charge fairway forms the play, which, when draped over a large plunging nose (the South Tano high), resulted in the formation of a stratigraphic–structural combination trapping geometry that is characteristic of the Jubilee Field and subsequent discoveries in this play.

ABSTRACT The discovery of the Jubilee field in the Tano Basin of Ghana opened a new play in the deep water of the Atlantic transform margins. The field is a late Cretaceous combination structural-stratigraphic trap associated with topography created by the transform tectonics during the opening of the Atlantic. Prior to the drilling of the discovery well, the African transform margin had seen very little deep-water exploration with only nine wells drilled over a margin more than 2000 km (1243 mi) long. The field was discovered in June 2007 with the Mahogany 1 well, which encountered 98 m (322 ft) of high-quality oil pay in a Turonian-aged fan sequence trapped in a combination structural-stratigraphic trap. Subsequent to the discovery, accelerated appraisal and phased development resulted in first production in November 2010. The field is currently producing more than 100,000 BOPD and has a planned peak production of 120,000 BOPD. The discovery has resulted in an industry-wide exploration campaign of over 50 wells in the last 8 years. These have resulted in a number of additional discoveries and to date at least one additional development. This chapter describes the exploration play concept and the geology of the field.

Abstract The margin between Côte d’Ivoire and the Niger Delta is a region with a common structural history, this being reflected in similarities in the stratigraphic response and play fairways identified across the region. There has been significant exploration on the narrow shelf characterizing the margin, resulting in a series of modest oil and gas discoveries. It is shown in this paper that many of the aspects of the plays in the unexplored deep-water regions of the margin are considerably more favourable to the development of giant fields than those on the shelf. This play-fairway review is based on the integration of existing publications with focused studies of multiclient 3-D seismic data over a number of areas. Play fairways are classified by seismic sequence and trap type, with an analysis of each undertaken. The most attractive deep-water play types are: (1) anticlinal traps involving late syn-transform (Apto-Albian) and early post-transform (Late Cretaceous) reservoirs, (2) combination traps involving ponded turbidites on the shoreward flanks of these highs, and (3) stratigraphic traps associated with large Late Cretaceous submarine fan complexes. The anticlinal play is associated with the terminations of the St Paul and Romanche fracture zones, with the more recent structuring generally associated with the latter. 3-D imaging and amplitude mapping is critical to prospect delineation, particularly for the combination and stratigraphic plays. Active kitchens are evidenced involving Early and Late Cretaceous source rocks in the Côte d’Ivoire and western Ghana to Nigeria segments of the region, which are consequently upgraded. Considerable volumetric potential is indicated that promises to make the region one of significant new exploration activity in coming years.

Abstract Transform margins are a function of the pre-existing crustal architecture (pre-transform) and the interplay of syn- and post-transform geodynamic processes. We use a suite of geospatial databases to investigate four transform margins: East Africa (Davie Deformational Zone, DDZ), Equatorial Africa, and the South African and Falkland (Malvinas) margins (Agulhas–Falkland Fracture Zone, AFFZ). The East African margin is the most complex of the four. This is a consequence of Late Jurassic–Early Cretaceous transform motion affecting highly heterogeneous crust, and post-transform deformation that varies along the margin. Equatorial Africa most closely adheres to traditional definitions of ‘transform margins’, but actually comprises two principal transform systems – the Romanche and St Pauls, dictated by the pre-transform distribution of mobile belts and West African craton. All four margins are spatially associated with volcanism, and each exhibits narrow uplifts associated with transpression or transtension. But the causal relationship of these features with transform processes differ. Volcanism along the East African margin is pre- and post-transform. Syn-transform volcanism on the AFFZ is spatially limited, with the AFFZ possibly acting as a conduit for magmatism rather than as a causal driver. Transform margins are varied and complex and require an understanding of pre-, syn- and post-transform geodynamics.

Abstract The integrated analysis of the South American and African equatorial basins provide important clues regarding the kinematic evolution of transform margins and has important implications for the thermal and tectonostratigraphy history of the African and Brazilian basins. The distribution of petroleum systems, on both sides of the Equatorial Atlantic, was quite affected by the tectonic history of this entire segment of the South Atlantic Ocean. Conventional extensional processes cannot explain the kinematics and rift geometry of the Equatorial South Atlantic basins. Accepted pure-shear or simple-shear rift mechanisms, typical of divergent margins, cannot be promptly used in basins generated as a response to major transform motions along a continental-scale plate boundary. The commonly accepted causal processes for rifting, such as passive/active or diffuse/discrete rifting, cannot accommodate the South Atlantic Equatorial data set. Even though shearing signatures and pull-apart features are easily recognized throughout the margin, their magnitude and basin architecture varies significantly as a function of the distance from the main transform faults. These factors have resulted in significant differences in thermal evolution, tectonic subsidence, facies distribution and uplift history. The tectonic evolution of the sedimentary basins along the Equatorial Atlantic is better understood by considering three stages: pre, syn, and post-transform movements. These are related to kinematic and dynamic controls provided by the emplacement of fractured swells as proto mid ocean ridges, followed by the creation of oceanic crust and the onset of transform shearing between Africa and Brazil. The fragmentation process started as diffuse magmatic and sedimentary events, which began in late Barremian time because of initiation of lithospheric stretching in the equatorial Atlantic, triggered by the onset of transtensional deformation. This event climaxed during the Aptian, when almost instantaneous extension was responsible for the widespread fracturing of the Equatorial Atlantic, generating relatively wide and shallow precursory basins, but there is no evidence of volcanic margins or widespread development of typical syn-rift basins, as expected in orthogonal extensional regimes. The equatorial splitting evolved during the Albian-Cenomanian interval, through a multi-stage basin development, which is better understood if the kinematic and dynamic controls are considered along with the chronologic activation of transform faults, the emplacement of oceanic crust and the onset of drifting between Africa and South America. The geodynamic evolution on the Equatorial Atlantic is addressed by recognizing tectonic stages that pre-date, are synchronous, or post-date the activation of transform faults in the Equatorial Atlantic. Local tectonics and magmatism played a key role in the “postbreak-up” subsidence. The resultant basin architecture, facies distribution, and subsidence history for any particular basin vary significantly according to its paleogeographic position and to its proximity to active transform faults. This has had major impact on the regional distribution and the stratigraphic position of source beds. Tectonic uplifts, varying in space and time, also have had a major impact on reservoir distribution. The dynamic juxtaposition of continental crust against oceanic crust or spreading centers on the opposite side of a transform fault caused diachronous deformations, recorded on the sedimentary record as important unconformities, amplified or not by synchronous eustatic sea level variations. The hydrocarbon shows and maturation history is quite related to the thermal history of each basin. Besides the petroleum systems of deep-water Nigeria, where the oil-prone Aptian, late Cretaceous, and Tertiary aged source rocks have been responsible for charging a quite impressive oil province, the rest of the Equatorial Atlantic is relying mainly on the facies distribution and thermal history of the Aptian aged source rocks to measure failure and success on the equatorial margin. The African and Brazilian margins share the same source rocks characteristics, either proved or expected (in deep water environments). However major differences arise from the tectonic sedimentary evolution of each margin segment, and it is closely related to the kinematic and thermal consequences of a complex transform margin evolution. Exploratory results from both sides of the Atlantic are still limited to a few basins, and the deep-water potential is still controversial.