Identification and Analysis of Subsea Gas Emissions and Quantitative Bathymetry of Oceanic Core Complexes



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Subsea gas and fluid emissions point to a variety of geological processes below the seafloor. Geophysical studies of the seafloor have been focused by the climate system modelling and oil and gas communities in particular toward the identification and analysis of such emissions. Multibeam sonar allows for the rapid evaluation of hydrographic anomalies as their geological context. Advanced processing methods fuse bathymetric, acoustic backscatter, and water column data into a 4D scene useful for the interpretation of subsea targets. Studies of the detailed characteristics of subsea gas emissions help in determining the magnitude of emissions, their ability to reach surface waters, and provide further understanding of the lithosphere – hydrosphere boundary. Using the Kongsberg EM122 multibeam echo soundings from cruise AT21-02 to the Barbados Accretionary Complex, several tall 500 – 1000 m vertical water column anomalies have been identified in the water column data above cratered hummocky regions with high backscatter emitted from the seafloor at a water depth of ~1500 m. The occurrence of morphologically defined craters, circled by high amplitude seafloor backscatter values and directly beneath flares imaged in the water column, is consistent with a model of dissociation within the gas hydrate stability zone causing the release of gas bubbles into the water column. The second part of this dissertation presents the quantitative morphology of regions of seafloor that host large-scale low-angle normal detachment faults termed oceanic core complexes. High-resolution multibeam data were used to study the morphology of two regions of oceanic core complex formation: Godzilla Megamullion and the Chaotic Terrain, both in the extinct Parece Vela Basin, but separated by ~10 million years of spreading history. These data provide a basis for mapping and analyzing the bathymetry of the oceanic core complexes at a previously unavailable spatial resolution. Data from over 40 surveys provide a high sounding density that has been used to create surfaces gridded at ~250 m. Both the Chaotic Terrain and Godzilla Megamullion datasets are used to further understand the evolution of oceanic core complexes and the Parece Vela Basin on a regional and local scale.



Geology, Marine


Portions of this document appear in: Barnard, Alex, Julia S. Wellner, and John B. Anderson. "Late Holocene climate change recorded in proxy records from a Bransfield Basin sediment core, Antarctic Peninsula." Polar Research 33, no. 1 (2014): 17236.