Tectonostratigraphy, sequence stratigraphy, and hydrocarbon potential of the Gamtoos Basin, offshore South Africa

The Gamtoos Basin is a Mesozoic half-graben rift basin that developed in response to the break-up of Gondwana during the Middle Jurassic. It is located in offshore South Africa, where it covers approximately 4300 km 2. The data set used included nine wells and 1700 km of seismic data.; Tectonostratigraphically, the Gamtoos Basin is divided into rift initiation, early rift climax, mid-rift climax, late rift climax, immediate and late post-rift systems tracts. Rift initiation is characterized by chaotic reflectors representing alluvial fan deposition. The early rift climax is characterized by relatively continuous reflectors that are divergent towards the Gamtoos Fault. These are representative of the early stages of marine transgression. The mid-rift climax is characterized by continuous, divergent reflectors representing a tectonic induced marine condensed section with proven source rock potential. The late rift climax is characterized by a uniformly thick package of parallel reflectors representing marine deposition. The immediate post-rift and late post-rift systems are characterized by normal passive margin tectonics and eustatic controlled sedimentation.; Twenty-three third-order and sixteen fourth-order sequences were recognized in the post-rift section. Four third-order composite sequences composed of fourth-order sequences are fully developed in the 121.5 to 117.5 Ma interval. Sequences deposited after 112 Ma, are characterized by fundamental third-order sequences composed of parasequences. These sequences prograde out to the location of the modern day shelf break by 103 Ma. After 103 Ma, the relict shelf break remains in essentially the same location and the basin is characterized by aggradational to slightly progradational sequences.