The middle Devonian marine transgression in north Devon and west Somerset

The lithological and faunal changes through the transition from non-marine Hangman Grits to marine Ilfracombe Beds of North Devon and West Somerset suggest the presence of a major depositional marine transgression. A fauna of thick-shelled lamellibranchs and gastropods occurs in beds lying stratigraphically between the flu-viatile Hangman deposits below, and the shallow-water marine Ilfracombe Beds above, and is considered to indicate an intermediate phase of intertidal depositional conditions. The transgression appears to have advanced across the region in a north-north-easterly direction during Lower-Middle Givetian times following coastal subsidence and possibly an associated rise of sea level.