Controls on sedimentation in submarine canyons: Nazare, Setubal and Cascais canyons, West Iberian Margin

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

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2008

Author dc:creator

• Arzola, Raquel Georgina