Study of the Aptian and Albian part of the Speeton Clay Formation at Speeton, North Yorkshire, has produced a detailed stratigraphy and a large collection of stratigraphically constrained fossils, despite the general poor state of exposure. This has allowed the development of a readily applicable bed numbering scheme and detailed faunal range charts. The Barremian-Aptian boundary is marked by the appearance of abundant examples of the ammonite Prodeshayesites and a marked lithological change from black shale to sandy mudstone. Higher parts of the Aptian have yielded abundant faunas, including ammonites of the fissicostatus, forbesi and deshayesi Zones; the base of the forbesi Zone marked by the incoming of Ewaldi Marl facies. Poorly fossiliferous silty shales of the Albian tardefurcata Zone are succeeded by a bed with glauconite and phosphate pebbles, interpreted as marking the base of the mammillatum Superzone. This is overlain by fossiliferous clays of the Lower and part of the Middle Albian. Aptian and Lower Albian successions inland are highly variable, probably due to intra mid-Cretaceous fault movements. The same general stratigraphy as at Speeton, however, may be seen across much of the southern North Sea
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