Surveying the flanks of the Mid-Atlantic Ridge: the Atlantis Basin, North Atlantic Ocean (36°N)

New seismic reflection and OKEAN (9.5-kHz) sidescan sonar data were used to characterise the seismic stratigraphy and structure of the region south of the Azores Islands, North Atlantic Ocean. The new data provide constraints on the tectono-sedimentary evolution of deep-ocean basins located on the flanks of slow spreading ridges. South of the Azores, thick sedimentary sequences (>1.0-s two-way travel time) correlated with units in the Madeira Abyssal Plain (ODP Sites 950–952) overlay an irregular basement generated by a combination of volcanic and tectonic processes. Three main Cenozoic depositional events are recognised and signed by distinct seismic megasequences. The moderate deformation of the sedimentary units and the structural fabric of the underlying oceanic crust shown on seismic and sidescan data suggest the existence of a complex tectonic setting south of the Azores. Illustrating this complex setting is the change from a basement with prominent abyssal hills west of 30°W to a segmented oceanic crust denoting an extensional/transtensional tectonic regime east of the latter meridian.