Deposition and Diagenesis Along the Volcanic Rifted Margins of Angola and Namibia

UoM administered thesis: Phd

  • Authors:
  • Nathan Rochelle-Bates

Abstract

This thesis integrates a variety of datasets in order to investigate the deposition and diagenesis of carbonates on Africa's South Atlantic volcanic rifted margin. The work includes datasets from several Lower Cretaceous deposits in Angola and Namibia. These deposits formed during the late stages of continental break-up, which ultimately led to the creation of the South Atlantic Ocean. The first dataset comes from a core that was drilled in the offshore Kwanza Basin, Angola. Detailed core logging was followed by petrographic and geochemical analysis to better understand the deposition and diagenesis of a recently discovered lacustrine carbonate formation, known as the "Microbialite". The results highlight the role of chemical, kinetic and microbial processes in the precipitation of these cryptic carbonates. A complex diagenetic sequence is also revealed, with evidence for hydrothermal fluids that may have affected the rocks shortly after deposition. The second dataset comes from the onshore Namibe Basin, Angola. Bitumen-bearing travertine samples that were acquired on a previous field campaign were analysed using a recently developed U-Pb dating technique, to constrain the timing bitumen emplacement. The results were integrated with dating results from a nearby volcanic complex to show that bitumen emplacement and volcanism were coeval, implying that the bitumen was likely the product of forced maturation of onshore source rocks. The final dataset is a 3D seismic volume from the Luderitz Basin, Offshore Namibia. The seismic geomorphology of a recently discovered build-up is studied to investigate whether it is part of a new carbonate play on the Namibian margin, or a volcanic structure. The results show that it is unlikely to be a carbonate build-up; instead, this newly described unit could represent the waning stages of volcanic activity along the Namibian margin during the Lower Cretaceous. The results reveal new information about the Lower Cretaceous volcanically influenced depositional environments of the South Atlantic, as well as the diagenetic processes that affected these successions post-deposition. The results can be applied to reduce uncertainty in oil and gas exploration in the South Atlantic and volcanic margins elsewhere.

Details

Original languageEnglish
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Supervisors/Advisors
Award date1 Aug 2020