Bay of Biscay and Northeast Atlantic Bathymetric map

The new bathymetric map of the Bay of Biscay and Northeast Atlantic ocean is based on all available conventional and multibeam data. It extends from the European coast to the mid-Atlantic ridge in longitude and from the Azores-Gibraltar fracture zone to 50°N in latitude. Grid spacing is one km. The map is in Mercator projection at a 1/2,400,000 scale. With respect to previously published maps, the detailed morphology of Eurasian and Iberian continental margins, a complete picture of the two fossil trajectories of the Bay of Biscay triple junction, which limit the western extension of the Bay of Biscay, and the precise location of the plate boundary between Eurasia and Iberia, which was active during the Tertiary, are now available. The Bay of Biscay and Northeast Atlantic opened simultaneously between chrons M0 (118 Ma) and 33o (80 Ma). A triple junction existed during that period. Fossil triple junctions trajectories on each of the three Eurasia (EU), Iberia (IB) and North America (NA) plates separate oceanic domains which were formed between the three plate pairs: IB/EU for the Bay of Biscay, EU/NA and IB/NA for the northern and southern portions of the Northeast Atlantic respectively. On each side of the fossil trajectories, rift directions formed between different plate pairs present different azimuths. The two eastern branches have been identified on the basis of available bathymetric, magnetic and seismic data. They are generally associated with a basement ridge whose bathymetric expression is clearly shown in their youngest parts. The intersections of these two fossil trajectories with the base of the continental margins are conjugate points before the opening of the Bay of Biscay, giving an independent constraint for plate reconstructions at M0 time. In addition, two topographic features of similar size, the Armorican and Coruna seamounts are tangential to the fossil trajectories, at about 200 km from the triple junction. They are interpreted as twin features formed simultaneously. The plate boundary between Iberia and Eurasia was active between chrons A33o (80 Ma) and A6 (20 Ma). It runs along the Pyrenees, the north Spanish marginal trough, the Charcot seamounts, the Atalante ridges and the Azores-Biscay rise. Relative motions deduced from the fit of magnetic lineations correspond to the IB/EU rotation about a pole located west of Portugal. Topographic features observed along this plate boundary are interpreted in this framework. In a companion poster, we have used the constraints deduced from the new bathymetric map to derive the IB/EU kinematic motions and discuss their consequences on the formation of Pyrenees.