Mass-transport deposits (MTDs) are virtually ubiquitous on the modern seafloor and common in ancient slope successions. Their upper surfaces are often irregular due to surface topography, which may vary significantly in wavelength and geometry. Turbidity currents are highly sensitive to topography, resulting in the modification of their density and velocity profiles during topographic interaction, thus affecting their depositional architecture. It is therefore expected that supra-MTD turbidite systems are also affected so. Previous analysis of the upper surface of MTDs and conformable overlying turbidite systems suggests that the upper surface of MTDs support irregularities that vary in wavelength, from 10 m to greater than 1000 m, by which longer length-scales may compartmentalise turbidite systems. But such studies do not investigate in detail the mechanisms by which topography is generated and the effect of the three-dimensional form of topography on supra-MTD turbidite systems. This study therefore addresses these aspects by the application of spectral analysis methods, synthetic modelling of three-dimensional topography, and architectural and lithofacies relationships of turbidite systems with the upper surface of MTDs, illustrated using an ancient slope succession cropping out at Cerro Bola, Argentina, and a modern deepwater system of the Sabah slope, offshore Brunei. In this thesis, an analytical model is described that characterises the three-dimensional form of the upper surface of MTDs in to two types: isolated topographic highs (termed positive topography) and isolated topographic lows (termed negative topography), which describe topography with a low and high degree of confinement, respectively. The geometry of these 'types' of topography are illustrated to vary significantly depending on the variability in the confinement across the surface in question, the degree of anisotropy and the obliquity of the flow direction to its orientation, which are similarly quantified using the analytical model described. Such topographic variability and anisotropy are demonstrated to relate to horizontal variations in thickness of the underlying MTD, generated by various mechanisms, including: internal structure, basal shear surface topography and post-emplacement creep and compaction. Each mechanism may support a variety of wavelengths that typically vary in length-scale and are generated simultaneously upon syn- and post-MTD emplacement. As a consequence, a turbidity current may interact with multiple length-scales of topography that might be produced contemporaneously with deposition. Topographic interaction may therefore not occur over the same length-scale as topographic ponding and, thus, supra-MTD ponded turbidite systems may have vertical and horizontal facies transitions that occur over similar length and height scales to the underlying topography despite ponding over a longer wavelength. Due to the three-dimensional complexity and variability of MTD topography, facies and architectures of supra-MTD reservoirs cannot be generalised in two-dimensions or extrapolated with ease into the third-dimension from isolated exposures/data.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:633284 |
| Date | January 2014 |
| Creators | Fairweather, Luke |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=215569 |
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