Marine faunas from concealed Devonian rocks of southern England and their reflection of the Frasnian transgression

Abstract

Summary Successive early Upper Devonian deposits penetrated in the Willesden No. 1 Borehole, along with their associated fossils, bear testimony to changing environments attributed to movements of the shoreline. The inferences drawn from these, and from marine-influenced deposits and faunas of similar age encountered elsewhere in the concealed strata, reinforce and refine the concept of a discrete Frasnian marine transgression. The event was probably linked with a similar, mid-Frasnian, movement in northern France. Marine fossils have been recovered from the Downtonian–Devonian sequences of nineteen boreholes in southern England, most of which include strata referable to the Frasnian or early Famennian. A revised, Frasnian, age is suggested for deposits encountered in the Brightling Borehole and part of the Bolney succession. Upper Devonian strata with marine faunas are recognized in the Ashwell, Little Chishill and Northbrook boreholes, and late Silurian or very early Devonian at Lakenheath.