The Sub-Paleogene surface is an ancient erosion surface that exists in southern England. In parts the Sub-Paleogene surface appear as tilted plain and parts as an unconformity beneath sediments of Paleogene age. The surface was formed by the erosion of chalklands in England following a regression in the Maastrichtian age. The time during which the surface formed has been estimated by comparing the age of the last Maastrichtian chalk to deposit and the age of the earliest Paleogene sediment to cover the surface. This yields a bracket between 71–73 million years ago (Mya) and 59.3 Mya.