I l e Congres Frangais de Sedimentologie - Caen 2007 - Livre des resumes, Publ. ASF, n057, 358 p.

LE DANOIS CONTOURITE DEPOSITIONAL SYSTEM: PALEOCEANOGRAPHIC 2 1 5 1.4 2 SIGNIFICANCE OF THE MEDITERRANEAN OUTFLOW WATER IN THE

CANTABRIAN MARGIN (BAY OF BISCAY)

F" Javier HERN~EZ-MOLINA*, Jorge IGLESIAS*, David VAN ROOIJ**, Gernma ERCILLA* * *, Maria GOMEZ-BALLESTEROS****, David CASAS***, Estefania LLAVE*****, Soledad

GARC~A-GIL*, Jean-Pierre HENRIET* *, Juan ACOSTA** * * "UNIVERSIDAD DE VIGO, Geociencias Marinas y Ordenacion del Territorio., 36310, Vigo, Espagne, fjhernan@uvigo.es, jorgei@uvigo.es, sgil@uvigo.es **RCMG, University of Ghent, B-9000, Ghent, Belgium, david.vanrooij @ugent.be, jeanpierre.henriet@ugent.be ***WSTITUT DE CI~NCIES DEL MAR, Passeig Maritim de la Barceloneta 37,08003, Barcelona, Espagne, gemrna@icm.csic.es, davidc@icm.csic.es ****INSTlTUTO E S P ~ O L DE OCEANOGRAF~, Corazdn de Maria, 8,28002, Madrid, Espagne, maria.gomez@md.ieo.es, juan.acosta@md.ieo.es *****TNSTlTUTO GEOLOGICO Y MINER0 DE E S P ~ A , Nos Rosas, 23,, 28003, Madrid, Espagne, e.llave@igme.es

In this contribution we present the preliminary results of Le Danois Contourite Depositional System (CDS) morphosedimentary and seismic stratigraphy study. This CDS is located in the Bay of Biscay, on the slope off northern Spain, between the latitudes of Oviedo and Santander (4" 20' W to 5" 20'W). The study has been executed by using swath bathymetry data (ECOMARG Project, 1330, Spain), high and middle resolution reflection seismic profiles from sparker (GALIPOR Project, RCMG, Belgium) and airgun systems (MARCONI Project, CMIMA-CSIC, Spain). In the study area the upper slope has two major domains: a) a proximal domain with a slope gradient of 6" on average, approximately 10 km wide, 29 km long and its base between 400-450 m water depth; b) a distal domain with a complex physiography located from 450 to 1600 m water depth, which is composed of an inner slope basin landward and a large bank seaward. The inner basin is about 17 to 25 km wide and -30 km long. The bank is namely Le Danois Bank (DB). In plan view this Bank has a convex southward shape around 72 km long, 15 km wide and a minimum depth of 424 m.

The Mediterranean Outflow Water (MOW) turns toward the east after the Galician Bank into the Bay of Biscay flowing regionally between 400 and 1500 m water depth. Le DB introduces isopycnal doming that influences MOW levels that joined with the irregularities of the slope physiography, produce a greater local seafloor interaction of the MOW both on the inner basin and DB, generating the large Le Danois CDS. At present, Le Danois CDS is composed of the following depositional and erosive features. Depositional features: a) Elongated mounded and separated drifts (Gijon & Le Danois drifts); b) Plastered drifts; c) Sheeted drifts and d) Sedimentary waves. Erosive features: a) Moats and b) scours alignments. A seismic stratigraphy analysis has been realised on the large contourite drifts, and 7 main discontinuities have been identified within the Pliocene and Quaternary sedimentary record. These discontinuities allow to differentiate depositional sequences at three different scales: a) Major seismic sequences (lower, middle & upper), which are correlated with those sequences defined in other areas of the Iberian margin i.e., Gulf of Cadiz and Alboran Sea. b) The middle and upper sequences can be subdivided into high order sequences. c) Finally, these high order sequences can be subdivided into minor subunits (or highest order sequences) which are named, from older to younger, A to H .The same cyclicity in seismic facies trend has been observed in all these sequences at aforementioned three different scales: 1) a transparentlweak zone at the base; 2) smooth, parallel reflectors of moderate-to-high amplitude in the upper part and 3) a high-amplitude erosive continuous surface at the top. This facies trend is well established within the Faro-Albufeira, the Porcupine, and the Eirik Drifts, and most likely represents cyclic lithological changes showing long-term coarsening-upward sequences bounded on the top by erosive surfaces related to bottom-current changes.

Major conclusions of this contribution can be summarised as follows: A) A complex CDS is developed after the LPR discontinuity (tentatively Lower Pliocene in age) in the Cantabrian margin by the MOW influence with a similar stratigraphic architecture than the defined in the Gulf of Cadiz. B) Previous physiography and major structural features of the slope were quite important in the CDS development and evolution, with a first stage covering until the MPR discontinuity, where the main drifts were confined, and a second stage after MPR, where the present depositional and erosive features started to be formed and both elongated mounded and separated drifts and plastered drifts were developed. C) The sedimentary record of the drifts allows to decode important paleoceanographic events related to MOW fluctuations, where a progressively increase of MOW velocity can be identified in a great scale (as in the Gulf of Cadiz) being the last upper highest order sequence (H) where the water mass has been more intense.

Acknowledgements: The Spain's Comisi6n Interministerial de Ciencia y Tecnologia (CYCIT) supported this research through MARCONI Project (REN2001-1734 C03-01M) and ECOMARG project (REN2002-00916JMAR). Jorge Iglesias contributtion was possible thanks to the CSIC grant UAC-2005-0044.