The present morphological expression of the continental margin off NW Britain is a mid- to late Cenozoic phenomenon, initiated by a major phase of rapid subsidence in the Rockall Trough and Hatton-Rockall Basin during the early late Eocene. This led to a deepening of the basins and the onset of bottom-current activity in this region. On seismic-reflection profiles, this basin-subsidence event is manifest in the form of a widespread deep-water unconformity caused by bottom-current erosion. This boundary is particularly enhanced at the basin margins and adjacent to the axial seamounts of Rosemary Bank and Anton Dohrn, where the downwarped and eroded surface of lower upper Eocene and older strata is onlapped by middle to upper Cenozoic sediments. The latter comprise two megasequences of late Eocene to mid-Miocene and mid-Miocene to Holocene age, which consist predominantly of deep-marine contourites both in the Rockall Trough and the Hatton-Rockall Basin, although a clastic wedge has built out along the Hebridean shelf-margin since the mid-Miocene. These megasequences reflect a gross, two-stage, depositional history; a response to intra-plate tectonism which modified sedimentation patterns and palaeoceanographic circulation. The development of the bounding unconformities (early late Eocene and mid-Miocene) was coincident with major phases of regional tectonism.

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