 Beneath the floor of the Ross Sea four rift basins have been detected by marine seismic reflections surveys.Rift basins have been mapped under the West Antarctic Ice Sheet including the Bentley Subglacial Trench.Rifting began in the Late Cretaceous as a result of tectonic extension (stretching and thinning of the crust and mantle) in approximately an east–west orientation, by plate tectonics processes.