This thesis presents one of the most comprehensive studies on submarine canyons yet. It integrates data on the geology, geochemistry, sedimentology and oceanography of the Nazaré, Setúbal and Cascais canyons, west Iberian margin, in order to constrain the processes and controls of past and present sedimentation in this area. The results indicate that, during the glacial stages, turbidity currents are the dominant process of sediment transport, erosion and deposition in these canyons. Turbidity currents are mostly in the form of small-volume, high-frequency events that are generated by fluvial and hydrodynamic processes, and the flows remain mainly within the upper canyon. A smaller proportion of turbidity currents are large-volume, low-frequency, seismictriggered events that flush through the entire canyons. Catastrophic mass wasting is most prominent in Setúbal Canyon due to its closer proximity to the region’s active fault zone along the southern Iberian margin. During the Holocene, sedimentary activity in Setúbal and Cascais canyons continued in the form of frequent, canyon-flushing turbidity currents that ceased abruptly ca 6.4 ka. This interval corresponds to both a regional aridification event that affected the Mediterranean and northern African regions, and to a decline in rising sea level. A combination of the two events is interpreted as being the direct cause of the cessation in sedimentary activity on the continental margin. In Nazaré Canyon, sedimentary activity during the last ~1000 years has been dominated by a mid-canyon resuspension depocentre that is controlled by small-volume, low-energy, hydrodynamic-generated turbidity currents. This depocentre provides a unique high-resolution record of recent sedimentation in a deep-sea setting, preserving a potential forest fire debris signal that is linked to a change in climate during the Little Ice Age. The conclusions from this work are that sedimentation in the west Iberian canyons is controlled by the complex interplay between several variables, the most important ones being the source and supply of sediment, the hydrodynamic conditions on the shelf and slope, and the canyon morphology. The sedimentary activity in the river-fed Setúbal and Cascais canyons is found to be affected more by regional climatic changes than by eustatic sea-level changes, and in Nazaré Canyon by the supply of sediment along the shelf.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:500749 |
| Date | January 2008 |
| Creators | Arzola, Raquel Georgina |
| Publisher | University of Southampton |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://eprints.soton.ac.uk/66341/ |
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