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Marga García, Instituto de Ciencias del Mar. CSIC (Spain)
F. Javier Hernández Molina, Univ. Vigo (Spain)
Estefania Llave, Instituto Geologico y Minero de España (Spain)
Dorrik Stow, National Oceanography Centre (United Kingdom)
Ricardo Leon, Instituto Geologico y Minero de España (Spain)
M Carmen Fernandez Puga, Univ. de Cadiz (Spain)
Victor Diaz del Rio, Instituto Español de Oceanografia (Spain)
Luis Somoza, Instituto Geologico y Minero de España (Spain)
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Contourite erosive features and associated processes on the Gulf of Cadiz middle slope have been studied in detail based on swath bathymetry data, side-scan imagery and different resolution seismic records. The distribution and character of erosive features reflects (1) the present-day interaction of the Mediterranean Outflow Water (MOW) with the seafloor, and (2) the Quaternary oceanographic and tectonic evolution of the system.
We present a detailed description and classification of the major erosive features: contourite moats, contourite channels, marginal valleys and furrows. The Alvarez Cabral contourite moat is associated with elongated mounded and separated drifts at the foot of the Algarvian lower slope. Five major contourite channels (Diego Cao, Huelva, Gusano, Guadalquivir and Cadiz Channels), with a sinuous NE to NW trend, cut the contourite deposits and are especially incised on the SE flanks of the main middle slope relieves (NE-trending diapiric ridges and structural highs). NE-trending marginal valleys occur at the NW flanks of ridges. Furrows have NE trends and are identified on the southern area.
A new scheme for the MOW circulation includes the simultaneous occurrence of two circulation patterns. The main complex along-slope circulation consists on the MOW being split into an Upper Core, related with the contourite moat,and a Lower Core divided into five branches related with contourite channels and furrows. The secondary down-slope circulation is responsible of the erosion of marginal valleys.
Three evolutionary stages are differentiated:
1) Linear diapiric ridges;
2) Main diapiric ridges segmentation and rotation and
3) Present-day configuration.
They are related with changes in the distribution and splitting of the MOW by neotectonic effects. The combination of the movement of a group of WNW-trending faults and the recent salt- and shale-related activity on the area has produced the lateral displacement and rotation of segments of the diapiric ridges. Local gateways have allowed the splitting of MOW branches and the successive creation of new channels, being the Diego Cao, Gusano and the proximal part of the Huelva contourite channels the most recent ones. Thereafter, the MOW circulation has been controlled by climatic changes. During cool stages the low sea level produces the enhancement of the deeper circulation, while during warm stages, when the sea level is higher, the flow is favoured on the shallower levels.
This study reflects the importance of erosive features contourite systems and their great potential as evidences for the oceanographic and tectonic reconstruction.
The contribution by M. Garcia was supported by a FPI fellowship from Spanish Education Ministry in the Framework of the SAGAS project (CTM2005-08071-C03-02) and the Special Action CGL2007-28815-E. This work has been partially carried out during a research stage of F. J. Hernandez-Molina funded by the Mobility Award from the Spanish Ministry of Education and Science at NOCS (UK) (PR2006-0275).
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