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We relate the depositional and structural histories of the sedimentary rocks containing Africa’s primary petroleum systems to four tectonic intervals, which in the light of their widespread and beneficial consequences we designate as ‘Aces’. The Ace of Clubs was the assembly of Gondwana by continental collision and the collapse and erosion of the mountains constructed during that assembly, which generated accommodation space through thermal subsidence over a vast area. Africa’s oldest great reservoir rocks accumulated in that space during Cambro-Ordovician times (520-440 Ma). After a short-lived glacial interval, Silurian and Devonian source rocks formed parts of a thick section that was deposited as long-term subsidence continued. The Ace of Diamonds consists of the collision of Baltica with Laurentia at c. 380 Ma and the collision between Gondwana and Laurussia at c. 310 Ma. It also includes the intracontinental deformation and orogenic collapse associated with the latter event, during the course of which regionally important structures and rifts now containing hydrocarbon-bearing fill were generated. Productive petroleum systems involving older Palaeozoic source rocks are concentrated in the rifts and sedimentary rocks of this phase.The two other aces relate to the plume-dominated break-up of Pangaea. The Aces of Hearts and Spades were the eruption of the Karroo Plume at 183 Ma and the eruption of the Afar Plume at 31 Ma. These plumes, because they both generated huge volumes of basalt during brief intervals, are considered to have come from the deep mantle where, for more than 200 million years there has been a discrete large volume of hot rock over which Africa has been slowly rotating. Perhaps as many as six other deep-seated plumes have risen from that deep hot volume. The importance of the Karroo and Afar Plumes comes from the fact that they arrested the motion of the African Plate and, on each occasion, fostered the establishment of a new shallow-mantle convective circulation pattern. Intracontinental rifts, basins and swells developed above the new convection pattern after both arrests. Organic-rich sedimentary rocks deposited in rifts and at continental margins that formed in response to the Karroo-Plume-induced plate-pinning episode (K-pippe, 183-133 Ma) are being buried today under piles of sedimentary rock eroded from swells that have been rising since the later Afar-Plume-induced plate-pinning episode (A-pippe) began at 31 Ma. The Afar Plume eruption is designated ‘Ace of Spades’ because oil and gas generated following source-rock burial by sediments eroded from Africa’s active swells during the past 31 Ma together make up three-quarters of Africa’s hydrocarbon resource. In addition, half of that petroleum lies in reservoirs deposited during this phase.
We relate the depositional and structural histories of the sedimentary rocks containing Africa’s primary petroleum systems to four tectonic intervals, which in the light of their widespread and beneficial consequences we designate as ‘Aces’. The Ace of Clubs was the assembly of Gondwana by continental collision and the collapse and erosion of the mountains constructed during that assembly, which generated accommodation space through thermal subsidence over a vast area. Africa’s oldest great reservoir rocks accumulated in that space during Cambro-Ordovician times (520-440 Ma). After a short-lived glacial interval, Silurian and Devonian source rocks formed parts of a thick section that was deposited as long-term subsidence continued. The Ace of Diamonds consists of the collision of Baltica with Laurentia at c. 380 Ma and the collision between Gondwana and Laurussia at c. 310 Ma. It also includes the intracontinental deformation and orogenic collapse associated with the latter event, during the course of which regionally important structures and rifts now containing hydrocarbon-bearing fill were generated. Productive petroleum systems involving older Palaeozoic source rocks are concentrated in the rifts and sedimentary rocks of this phase.The two other aces relate to the plume-dominated break-up of Pangaea. The Aces of Hearts and Spades were the eruption of the Karroo Plume at 183 Ma and the eruption of the Afar Plume at 31 Ma. These plumes, because they both generated huge volumes of basalt during brief intervals, are considered to have come from the deep mantle where, for more than 200 million years there has been a discrete large volume of hot rock over which Africa has been slowly rotating. Perhaps as many as six other deep-seated plumes have risen from that deep hot volume. The importance of the Karroo and Afar Plumes comes from the fact that they arrested the motion of the African Plate and, on each occasion, fostered the establishment of a new shallow-mantle convective circulation pattern. Intracontinental rifts, basins and swells developed above the new convection pattern after both arrests. Organic-rich sedimentary rocks deposited in rifts and at continental margins that formed in response to the Karroo-Plume-induced plate-pinning episode (K-pippe, 183-133 Ma) are being buried today under piles of sedimentary rock eroded from swells that have been rising since the later Afar-Plume-induced plate-pinning episode (A-pippe) began at 31 Ma. The Afar Plume eruption is designated ‘Ace of Spades’ because oil and gas generated following source-rock burial by sediments eroded from Africa’s active swells during the past 31 Ma together make up three-quarters of Africa’s hydrocarbon resource. In addition, half of that petroleum lies in reservoirs deposited during this phase.
A B S T R A C TSimple to complex, highly sinuous deep-water channels are common in the subsurface Tertiary off Angola, west Africa, and have been important exploration targets there in recent years. We discuss in this article three examples of these sinuous channels that are generally characterized by high-amplitude seismic reflection events, resulting from reservoir-prone lithologies. The planform characteristics of these channels-sinuosities and sinuous loop wavelengthsare similar to those of the fluvial channels; however, the planform combined with sectional seismic characteristics of the deep-water channels suggest that high sinuosities generally evolved through repeated channel aggradation and lateral migration. In detail, the influence of lateral migration vs. vertical aggradation in the evolution of the deep-water channel sinuosities varies from one channel to another and even along the length of a single channel or across a single sinuous loop. The lateral migrations may be continuous or discrete, separated in distance, and resolvable in seismic. Along some parts of the channels, very high initial sinuosities, not significantly affected by lateral migration, suggest that the initial sea-floor topography and gradients were a major factor in their development. In such cases, the channels essentially aggraded vertically. Thus, the modes of deep-water channel migration and sinuosity evolution are complex and different from those of fluvial channels that exhibit largely lateral (without much aggradational component) shifts within a meander loop. These differences are the result of unique hydrodynamic characteristics of the currents in these systems. The gross reservoir shapes in both the fluvial and deep-water channels are obviously dictated by their high sinuosities. The degree of lateral migration vs. vertical aggradation, however, determines the details of the lateral extent vs. vertical stacking of reservoir lithologies and their connectivities in deep-water sinuous channels. A fluvial,
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