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Francisco Javier Hernandez Molina, University of Vigo (Spain)
Jorge Iglesias, Instituto de Ciencias del Mar CMIMA-CSIC (Spain)
David Van Rooij, Renard Centre of Marine Geology (RCMG) (Belgium)
David Casas, Instituto de Ciencias del Mar CMIMA-CSIC (Spain)
Maria Gomez Ballesteros, Instituto Español de Oceanografía (Spain)
Estefanía Llave, Instituto Geológico y Minero de España (Spain)
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This contribution aims to illustrate the Le Danois Contourite Depositional System (DCDS), an impressive example of a CDS located on the Cantabrian margin (Bay of Biscay, Sapin, 4° 20' W to 5° 20'W). A description of major morphosedimentary features, sedimentary stacking pattern as well as its Pliocene and Quaternary evolution are presented. This work is based on several datasets, including: swath bathymetry data (ECOMARG Project, IEO, Spain) and high and middle resolution reflection seismic profiles from sparker (GALIPOR Project, RCMG, Belgium) and airgun systems (MARCONI Project, CMIMA-CSIC, Spain).
The study area is characterised by a well defined upper continental slope composed of two major domains: a) a proximal domain, located between 200 to 400 - 500 m water depth; and b) a distal domain with a complex physiography between 400 and 1600 m water depth. It comprises two highs: the larger Le Danois Bank (DB) and the smaller Vizco High to the west. The presence of the DB defines a southern intraslope basin (IB).Along the distal domain the Mediterranean Outflow Water (MOW) is flowing as a contour current conditioned by the seafloor irregularities and the Coriolis effect, developing the DCDS.
The DCDS is composed of depositional and erosive features. The depositional features are: a) elongated mounded and separated drifts; b) plastered drifts; and c) sediment waves.
The erosive features are:a) moats, b) scours alignments, c) sub-circular holes structures, and d) slide scars. The seismic stratigraphic analysis carried out on the contourite deposits has allowed to define seismic packages on 3 different scales, sequences, units, and subunits.
The major regional discontinuities (LPR, UPR and MPR) define the three sequences: lower (L), middle (M) and upper (U). Sequences M and U comprises three units each one (Ma, Mb, Mc, and Ua, Ub,Uc). The subunits (A, B, C, D, E, F, G & H) have been defined based on the vertical pattern of the seismic facies and bounding surfaces, showing the same cyclicity pattern: a transparent/weak zone at the base that passes to smooth, parallel reflections of moderate-to-high amplitude in the upper part, and a high-amplitude erosive continuous surface at the top.
The DCDS is a consequence of the MOW and its interaction with the sea floor along the slope. It develops after the LPR discontinuity (tentatively Lower Pliocene in age), with a similar stratigraphic architecture to that defined in the Gulf of Cadiz CDS. From LPR up to MPR discontinuities, the main drifts were confined into two paleobasins within the IB. After the MPR, the DCDS started to form just the way we know with the present depositional and erosive features.
Acknowledgements: The Spain's Comisión Interministerial de Ciencia y Tecnología (CYCIT) supported this research through MARCONI Project (REN2001-1734 C03-01/M) and ECOMARG project (REN2002-00916/MAR). Jorge Iglesias contributtion was possible thanks to the CSIC grant UAC-2005-0044.
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