Spatial and temporal variability of sedimentary processes associated to the Guilvinec Canyon, Bay of Biscay
Pauwaert, Z. (2014). Spatial and temporal variability of sedimentary processes associated to the Guilvinec Canyon, Bay of Biscay. MSc Thesis. Universiteit Antwerpen/Universiteit Gent/VUB: Antwerpen, Gent, Brussel. 16, 55 pp.
Submarine canyons make for a unique habitat for reef building organisms such as deep water oysters Neopycnodonte zibrowii (Van Rooij et al., 2010)) and cold-water corals Lophelia pertusa (De Mol et al., 2011). They use the hard substrate and concealed space to build their banks, and get their food out of passing currents. However, sedimentary processes and changing hydrographical conditions can endanger the successful survival of these reefs. A case study, researching these sedimentary processes and the hydrographical environment in the Guilvinec canyon, on the Armorican margin, Bay of Biscay, is presented in this dissertation. The environmental and sedimentological conditions were investigated using two CTD casts, high resolution multibeam echosounding data and a seismic site survey. Interpretation of the data and comparison between the different data sets is done in order to determine the general morphology and evolution of the Guilvinec canyon. Hereby, the important stratigraphical units and sedimentary processes shaping the canyon are identified. The different water masses in the canyon are identified and any possible interaction with the canyon system and the canyon flanks is described. This knowledge is used to determine whether this system could be a favourable environment for cold-water corals. Two water masses could be identified: MOW and ENAW. The canyon has an asymmetric cross section, with a steeper western flank and less steep eastern flank. Tributary gullies form incisions with different depths and frequencies, both parameters having higher values for the western flank. Several events of mass wasting could be recognized on the multibeam data and the seismic profiles. Three stratigraphical units are identified: U1, having a transparent acoustic character with some discontinuous low amplitude reflectors, possible Miocene in age; U2 has a less transparent acoustic character, with low amplitude, constant frequency, laminated reflectors and an irregular structure with the same acoustic character, dated as Miocene; U3 is dominated by high amplitude, continuous, laminated reflectors with an increasing frequency, reaching the surface. This latter unit is subdivided into U3a and U3b, both deposited during Plio-Pleistocene times. U3a has the previously described acoustic character. Cutting the surface, some channel-like erosional surfaces can be recognized. The infill has a high amplitude acoustic character with none to a few discontinuous reflectors, identified as U3b. The hydrographical setting of this canyon is ideal to sustain the life of cold-water corals. However, initial settling is more likely on the western flank due to higher turbulence near the bottom causing erosion of loose suspended sediment, favouring stern attachment of the coral specimen to the hard substrate and preventing burial of the reef.
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