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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.

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Structural and magmatic features of northern Sumatra are reviewed, based on a continuing programme of reconnaissance mapping. Distinction is drawn between Tertiary sedimentation on the W and that in the centre and E, the dividing line being the main outcrop of the Sumatran Fault System (SFS) which traverses the length of the island. Large transcurrent movements on the SFS are indicated by ( a ) regional slivers of oceanic crust trapped at the leading junction of the western continental plate of Sumatra as it moved NW against the main mass of the island; ( b ) palaeomagnetic evidence (N. S. Haile) here interpreted as showing eastern Sumatra as part of the Malaya block and occupying its equatorial position since the Cretaceous in contrast to the NW tip of Sumatra, W of the SFS, for which more southerly palaeolatitudes have been determined; ( c ) juxtaposition of Li-rich and Li-poor geochemical provinces along the SFS. The Sumatran magmatic arc commenced at least in the Mesozoic. The offset of the current volcanic arc to the E at Lake Toba is ascribed to a change in the angle of the Benioff Zone, the dividing line suggested being a split in the descending plate which is coincident with prolongation of the Investigator transform fault. The SFS continues N of Sumatra as a transform of the Andaman spreading complex, and terminates in the S in the Sunda Strait area either at the edge of the continental block or against a major plate junction indicated by the commencement of deep focus earthquakes E of Sumatra.

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