Oceanographic control of the submarine landslides of the northern Galicia Area (Bay of Biscay, NE Atlantic)

This paper characterizes in detail for the first time the gravitational instabilities in two zones of the northern Galicia Area (Bay of Biscay, NE Atlantic): the Jean Charcot ridge (3700 to 4950 mwd) and the Castro marginal platform (1900 to 2500 mwd). Mass transport deposits (MTDs) show different seismo-stratigraphic structures depending on their physiographic location, mostly determined by the actions of bottom currents. On the Jean Charcot ridge, MTDs are mainly present in intra-basins of the inner part of the ridge, a sector unaffected by strong bottom currents. MTDs appear on the seafloor and inside the sedimentary column as stacked levels of transparent acoustic facies interbedded with an alternation of continuous reflections of high and moderate amplitude. On the southeast flank of this ridge, an area affected by moderate to high bottom currents, several headwall scars have been observed. However, MTDs are only present on the seafloor in bathymetrical entrances that are partially protected from the Atlantic and Antarctic bottom currents. We correlate this lack of MTDs with the erosional and reworking processes of Atlantic and Antarctic bottom currents along the Biscay and Charcot channels. On the Castro marginal platform, MTDs are composed of layers of up to 10 ms two-way travel time in thickness topped by patches of blanking acoustic facies and separated by continuous reflections of high amplitude. MTDs form a complex mixed system (down- and alongslope processes) that may have been generated during the Quaternary cold periods.