Quantifying channelized submarine depositional systems from bed to basin scale
Lyons, William J.
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LocationZerissenne Turbidite System, Namibia
The challenges of directly observing active turbidity currents necessitates the consideration of preserved deposits for deciphering the behavior of these systems. In this thesis, I take advantage 3-D subsurface seismic data and outcrop exposures to study turbidites at scales ranging from bed to basin. At the basin scale, I develop a method to estimate the time-frame over which sedimentation and subsidence come into equilibrium. Using seismic data from the Fisk Basin, Gulf of Mexico, I find that, during periods of broadly distributed, sheet-like deposition, equilibrium time is on the order of 4.6 x 105 years. In contrast, during periods of confined channel development, that time drops to 2.0 x 105 years. Identifying these equilibrium times is critical because, at times below equilibrium, autogenic and allogenic stratigraphic signals cannot be distinguished. At the scale of turbidite beds, detailed grainsize analyses of sediment samples from the Capistrano Formation, San Clemente, California reveal the potential for misinterpretation that arises when deposits are studied without consideration for the dynamics of sedimentation. Previously interpreted as the result of anomalous sandy turbidites, using simple bed shear calculation and Froude scaling, I show that these coarse sediments are consistent with classical muddy, low-density turbidity currents. Finally, at the scale of amalgamated turbidite beds, I use outcrop mapping and aerial photography of the Zerissenne Turbidite System, Namibia to provide a measure of lateral and vertical continuity of a deepwater turbidite system. Previous studies have been hampered by limited exposure while the extensive continuous exposure of the Zerissenne show that correlation lengths of these systems can exceed 1.5 km.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2004
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