[1] The basement is thought to consist of metamorphic rocks of Paleoproterozoic age, based on sampling from the Rockall High.
The oldest sedimentary rocks proven in the area are Albian (uppermost Lower Cretaceous) mudstones and sandstones, encountered in two British Geological Survey boreholes drilled on the Hatton Bank.
The proven Cenozoic sequence starts with Paleocene lavas, part of the North Atlantic Igneous Province, overlain by Eocene claystones.
There is then a major hiatus, with the next youngest preserved strata above the unconformity (known regionally as C30) being of Upper Eocene to Lower Oligocene age.
[1] From wide-angle seismic profiles over the basin and the adjacent highs, a stretching factor of about 2 has been estimated.