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Estefania Llave, Insituto Geológico y Minero de España (Spain)
Fº Javier Hernandez-Molina, Univ. de Vigo, Facultad de Ciencias del Mar (Spain)
Jorge Iglesias, Instituto de Ciencias del Mar CMIMA-CSIC (Spain)
Gemma Ercilla, Instituto de Ciencias del Mar CMIMA-CSIC (Spain)
David Van Rooij, Renard Centre of Marine Geology, Ghent Univ. (Belgium)
Maria Gomez-Ballesteros, Insituto Español de Oceanografía (Spain)
David Casas, Instituto de Ciencias del Mar CMIMA-CSIC (Spain)
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The comparison between two complex Contourite Depositional Systems (CDS) located in different geological context, shows numerous resemblances in the sedimentary stacking pattern and seismic facies. The CDSs are developed off southern and northern Iberian Peninsula, by the Mediterranean Outflow Water (MOW) interaction with the slope. Seismic stratigraphy and chronostratigraphy analyses have been carried out using high and middle resolution reflection seismic, gravity cores and boreholes data.
A well defined hierarchy in the stratigraphic architecture is shown, where two major depositional sequences (DSs), separated by regional erosive discontinuities (QD: 1.8 Ma, MPR: 0.9 Ma, and recent seafloor) are composed of eight high-resolution DS (A to H) also separated by erosive discontinuities. These discontinuities result from more energetic episodes of the MOW, are correlated at least along the Iberian continental margin. The MPR discontinuity marks an important change in the stratigraphy architecture, from oblique mounded drifts (Gulf of Cadiz CDS) or confined drifts (Le Danois CDS), to a thicker and sigmoid-oblique prograding drifts. This MPR discontinuity correlates with the Middle Pleistocene Revolution, one of the most significant paleoclimatic events during the Quaternary, occurred about 0.9 Ma ago, coevall with a significant 3rd order sea level fall, which gave place to the establishment of asymmetric eccentricity cycles (100 ka).
The minor discontinuities have been correlated with climatic and paleoceanographic changes and with 4th order main sea level falls during the Quaternary. The main contourite deposition took place during the transition from warm to cold periods, from regressive to lowstand stages, when an upward enhancement of the MOW is produced. This cyclic climate influence on the MOW is observed in each major and minor DSs seismic facies, characterized by a transparent lower section that changes topward to a more reflective stratified part, and truncated by an erosive surface. An increasing reflectivity towards the last DSs (G & H) is shown indicative of a general intensification of the MOW especially since the late Pleistocene. These common characteristics in both systems evidence the mesoscale influence of the paleoclimate changes in the MOW circulation at short-term and recorded in the CDS along the Iberian margin. However, both morphologic and tectonic settings during the Quaternary, conditioned -in a long-term scale- the interaction and paths of MOW along the sea-floor, the erosional and depositional features locations and therefore the types of contourite drifts. Acknowledgements: The Spain's Comisión Interministerial de Ciencia y Tecnología (CICYT) in collaboration Ghent Univ. Belgium supported this research through Eurocore-Euromargins (REN2002-11669-E and 11668-E), MARCONI (REN2001-1734 C03-01/M) and ECOMARG (REN2002-00916/MAR) projects. This work is also a contribution to the Consolider-Ingenio 2010 CSD2006-0041-TopoIberia.
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