Late Cenozoic sedimentary processes on the outer edge of the NW Iberian shelf, Cabo Ortegal
Verreydt, W. (2011). Late Cenozoic sedimentary processes on the outer edge of the NW Iberian shelf, Cabo Ortegal. MSc Thesis. Renard Centre of Marine Geology, Ghent University/Universiteit Gent; MARELAC: Gent. 29 pp.
Cabo Ortegal, situated at the north-western Iberian margin, is a unique location at the southern end of the Bay of Biscay at the corner of Spain which underwent an extensive tectonic history. The combination of this tectonic history with the MOW palaeoceanography sculpted the present-day morphologic features at the seafloor. A multidisciplinary study, consisting of multibeam bathymetry, backscatter imaging, high-resolution single channel seismic profiling, ROV and CTD data was applied to analyse and map these features. In the deep zone, situated below 500 m water depth, the presence of a contourite depositional system (CDS), related to the enhanced circulation caused by Mediterranean Outflow Water (MOW) is observed. The presence of mini mounds with dead cold-water coral debris at the edge of the CDS is related to this current activity in the deep zone. A dense network of pockmarks at the seafloor between 250 and 450 m water depth, was probably created by migration from gaseous Albian deposits. The formation of these pockmarks is related to NE-SW oriented faults associated with the opening of the Central Atlantic Ocean. At present this outer shelf environment is one of low accumulation which is characterised by erosion. However, the onset of the contourite deposits can be related to the opening of the Strait of Gibraltar, which introduced MOW into the Atlantic Ocean, as is shown by the Ca and Cb unconformities. Using high-resolution seismic profiles, a palaeoreconstruction of the area from the Mesozoic to the Cenozoic was established. This led to the recognition of a major C5 unconformity with a Late Eocene age. Furthermore, a living cold-water coral is observed at water depths around 750 m. This coral grows within a narrow density envelope, as opposed to the dead coral debris found on the mini mounds slightly outside this density envelope.
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