The stratigraphy of the Chalk Group (Cretaceous) of the Devon coast, UK

Abstract

An almost continuous layer of Upper Cretaceous deposits up to 1000 m thick was probably deposited across much of SW England. Phases of uplift in the late Cretaceous and early Cenozoic, each of which was followed by extensive erosion and dissolution, resulted in the removal of all except a few outliers of Chalk Group that crop out in east Devon and south Somerset. Those on the Devon coast between Sidmouth and Lyme Regis are some of the best exposed Cenomanian to early Coniacian successions in NW Europe and include the most westerly chalks preserved onshore in England. They form an integral part of the Dorset and East Devon World Heritage Site. In contrast to the Chalk of much of southern England, the older formations in Devon, the Beer Head Limestone, Holywell Nodular Chalk and New Pit Chalk, show marked lateral lithological variations that result from a combination of penecontemporaneous movements on local faults and relatively shallow-water environments close to the western edge of the Chalk depositional basin. The younger parts of the succession, the Lewes Nodular Chalk and Seaford Chalk Formations, comprise chalks that do not appear to have been greatly affected by penecontemporaneous fault movements. These formations include lithological marker beds that have been correlated with marker beds in the Sussex type area. The principal sedimentary breaks in the Devon succession cannot be correlated with confidence with eustatic changes in sea level.