Sedimentary evolution of the Le Danois contourite drift systems (southern Bay of Biscay, NE Atlantic) : a reconstruction of the Atlantic Mediterranean Water circulation since the Pliocene

The evolution of the Le Danois contourite depositional systems (CDS) during the Pliocene and Quaternary was investigated based on high-resolution seismic reflection data. From old to young, six seismic units (U1-U6) bounded by major discontinuities (H1-H6) were identified. Regarding variations of the bottom-current circulation, four evolution stages of the Le Danois CDS were identified, including onset (similar to 5.3 to 3.5-3.0 Ma), initial (3.5-3.0 to 2.5-2.1 Ma), intermediate (2.5-2.1 to 0.9-0.7 Ma) and drift-growth (0.9-0.7 Ma to present day) stages. The CDS associated with the Atlantic Mediterranean Water (AMW) along the middle continental slope initiated at similar to 3.5-3 Ma and was widely built after the Mid-Pleistocene Transition (MPT; 0.9-07 Ma). At a shallower water depth, a second CDS associated with the Eastern North Atlantic Central Water (ENACW) started to develop from the late Quaternary (similar to 0.47 Ma) onwards. In the AMW-related drift system, the Le Danois Drift was generated both under glacial and interglacial climatic oscilations. Repeated internal structures in unit 5 that consist of acoustically transparent lower parts, moderate amplitude upper parts and high amplitude erosional surfaces at the top, are compared with interglacial/glacial cycles since the middle Pleistocene to the present day. These cyclic features suggest coarsening-upward sequences of the Le Danois Drift and processes related to enhanced AMW during glacial stages. The estimated sedimentation rate of the Le Danois CDS reached a maximum during the MPT (at least similar to 27 cm/ky) and then decreased until present-day (similar to 5 cm/ky). Variations of sedimentary stacking patterns and processes of the Le Danois CDS imply full domination of the intermediate water mass along the central Atlantic and southwest European continental slopes from the late Pliocene (similar to 3.5-3.0 Ma) onwards