Abstract

The 1:2 million scale map showing the sub-Pleistocene geology of the British Isles and the adjacent continental shelf is described, with particular reference to the offshore post-Hercynian basins trending dominantly NW-SE off the east coast and dominantly NE-SW off the west coast.

Tertiary deposits surround the British Isles, with the exception of parts of the English Channel, and are particularly thick in the North Sea. The Tertiary outcrop extends up into the Celtic Sea and Cardigan Bay, where marine deposits give way to nonmarine. Farther north the Tertiary occurs only as isolated basins of nonmarine sediments. Cretaceous strata crop out beyond the Tertiary cover along much of the North Sea and English Channel coasts and extend up into the sea areas between Ireland and Britain. In general, the base of the Cretaceous is erosive and the map shows it resting on rocks ranging in age from Devonian to Upper Jurassic. Erosion has cut into the fill of most of the post-Hercynian basins with the result that a variable amount of Jurassic strata has been removed and, in many cases, some of the Permo-Triassic as well. Beyond the present limits of the Tertiary and Cretaceous outcrops in the sea areas between Britain and Ireland, Jurassic strata have been completely removed from many of the basins. This is thought to be the result of erosion during the Cretaceous and Tertiary when the northwestern side of the British Isles was relatively more elevated than previously.