This thesis examines the interaction of pre-existing and evolving salt-related topography on the temporal and spatial evolution of depositional systems in deepwater. To achieve this, the thesis integrates stratigraphic and structural analysis of 3D seismic data from the Miocene record of the salt-influenced Lower Congo Basin, Offshore Angola. Observations at multiple scales ranging from the semi-regional (> 50 km) to local, kilometre-scale and covering timescales ranging from the entire Miocene (~ 18 Myr) to > 2 Myr are presented. At the semi-regional scale, results from this study shows that the progressive along-strike linkage of short (<10 km) fault segments and salt diapirs into through-going large scale (> 30 km) faults and elongated saltwalls results in long lived diversion and/or confinement of depositional system fairways. Axial confinement of fairways occurs where structural strike is parallel to sediment input, contrasting with ponding or diversion of deposits oriented at a high angle to structural strike. The orientation of the structures remains relatively static, which in combination with the fixed sediment entry points of the fairways results in recurrence of the major styles of interaction, and long term pinning of fairways throughout the Miocene. The development of large (10's of km) "sediment shadow" zones devoid of coarse clastics downdip of diverted and or confined sediment gravity flows is also observed through the Miocene. At the intraslope basin (10's of km) and sub-basin scale ( < 10 km), the role of confinement by salt-related structures on the temporal evolution and dip-and-strike variability of Late Miocene channelised-lobe complexes in an elongate intraslope basin was also investigated. At both of these scales, the morphology of the recieving basin geometry significantly influences the dimensions, planform morphology and vertical stacking patterns of channelised-lobe complexes. A transition from thick, radial shaped lobe-complexes which are aggradationally stacked and deposited via 'fill-and-spill' of sub-basins within an intraslope basin to thinner, elongate, laterally offset and compensationally stacked channelised-lobe complexes in the intraslope basin is observed. This transition occurs as the salt-related structural template evolves and confinement changes from the sub-basin scale to the intraslope basin scale. At the depositional element scale ( < 5 km), results from this study further shed light on the critical and hitherto neglected role of salt-related topography in controlling the location of channel to lobe transition zones in deepwater depositional systems. The location of the transition zones are documented from four case studies, with the transitions spatially controlled by salt-related reduction in gradient e.g. a break in slope downflow of monoclinal structures, and/or a reduction in lateral confinement of depositional fairways downflow of segment boundaries. Overall, the result of this thesis show the significant influence which evolving saltrelated topography exerts on the stratigraphic development, geometry and sediment routing patterns on salt-influenced continental margins. In particular the study highlights how variable the interaction between evolving salt-related topography and deepwater sedimentation is at a range of temporal and spatial scales.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:727791 |
| Date | January 2013 |
| Creators | Oluboyo, Ayodeji |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/deepwater-depositional-systems-and-evolving-saltrelated-topography-miocene-offshore-angola(c6736a94-02e4-494d-ac66-2d375b0b44fb).html |
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