REWORKED EARLY DIAGENETIC CONCRETIONS AND THE BIOEROSIONAL ORIGIN OF A REGIONAL DISCONTINUITY WITHIN BRITISH JURASSIC MARINE MUDSTONES

The Coinstone is a well known hiatus-concretion level in the Lower Lias (Lower Jurassic, Upper Sinemurian) of Dorset. It has long been recognized as a layer of bored and encrusted, early diagenetic, clay-hosted septarian concretions coincident with a biostratigraphic gap of three ammonite subzones. The burrowing activities of a benthic fauna in muds cause resuspension of sediment and facilitate erosion, even in the absence of high energy physical processes. Regional stratigraphic gaps may be formed as a consequence of sea level rises or falls, or as a response to sediment supply reduction independent of sea level change. -from Autho