Evolution of tectonic and stratigraphic geometries in the Southern Outeniqua Basin

• Main Author: Smithard, Travis
• Other Authors: Kahle, Beth, Sloan, Alastair
• Format: Master Thesis
• Language: English
• Published: Faculty of Science 2019
• Subjects: Geological Sciences; Weddell; Weddell Sea; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/11427/30992; https://open.uct.ac.za/bitstream/11427/30992/1/thesis_sci_2019_smithard_travis.pdf

The evolution of the Southern Outeniqua Basin has been analysed within a tectono-stratigraphic framework by the interpretation of 3,700km of 2D seismic data constrained by five exploration wells, drilled on the adjacent shelf. The mapping of different fault families into distinct structural orientations, NE-SW, NNE-SSW and NW-SE, was done and the basin sub-divided into four sectors (far-west, west, central and east) based on the geographical position of these faults. Sequence stratigraphic analysis of the basin lead to the identification of seven secondorder unconformities which have been further defined into five main seismo-stratigraphic units. The variation in major structural orientations suggest the evolution of the basin developed during three phases of extension, which have been related to the broader plate tectonic context during the Mesozoic break-up of Gondwana. Early Jurassic (170-150Ma) rifting between West and East Gondwana is proposed to have created weaknesses in the crust along the Southern African margin in a NNE-SSW orientation leading to the development of small rift basins and the deposition of syn-rift sediments. A series of intra-continental strike slip faults, including the proto-Agulhas Falklands Fracture Zone, are proposed to have developed along the southern margin during the incipient formation of the Weddell Sea (147Ma) between Antarctica and West Gondwana. Later mid-Jurassic (150-130Ma) extension along the North-Falkland rift zone lead to the oblique extension along the southern margin and the development of normal faults orientated NE-SW. Continued rifting (134Ma) in the proto-South Atlantic lead to translation along the southern African margin and the coalescence of the individual segments of the intra-continental strike slip faults and ultimately the formation of the Agulhas Falklands Fracture Zone. This phase of wrench faulting (134- 130Ma) is characterised by the strike-slip deformation of syn-tectonic sediments defined by second-order unconformities BR and B - late Valanginian ...