The Purbeck-Wealden of the type areas in onshore southern Britain (Fig. 1) encompasses the Berria-sian-earliest Aptian stages of the Cretaceous, a time span of approximately 21 Ma. At least some of the lowest part of the succession belongs to the latest Jurassic (Portlandian); how much depends on where the Jurassic-Cretaceous boundary is placed. Ostracods are frequently diverse and abundant in the predominantly calcareous or argillaceous units (e.g. Purbeck Limestone Group, Wadhurst Clay Formation, Grinstead Clay Formation, Weald Clay Group), sometimes forming ostracod limestones, but in clays that have undergone pedogenesis and in arenaceous facies (e.g. Ashdown Beds Formation, Upper and Lower Tunbridge Wells Sand formations) they tend to be rare or poorly preserved. They are essentially non-marine faunas, with only a few convincing indicators of direct marine influence. Although their interpretation is difficult and has given rise to controversy, ostracods are undoubtedly the most useful biostratigraphical tool available in Purbeck-Wealden sequences. They have also been used with some success in correlations of the offshore ‘ Purbeck-Wealden’ facies of Portlandian-Barremian age found in the Celtic Sea and Fastnet basins between southern Ireland and SW England (Fig. 1).
Figures & Tables
This book charts the stratigraphical distribution of ostracods in the Cambrian to Pleistocene deposits of Britain and outlines their utility for dating and correlating rock sequences, as well as indicating aspects of their palaeoenvironmental and palaeogeographical significance. These small bivalved crustaceans are the most abundant arthropods in the fossil record. Indeed, the stratigraphy of Britain, which embraces many type-sequences, provides a particularly rich and full record of them, from at least the basal Ordovician, and from the British Cambrian there is a biostratigraphy based on their ‘relatives’, the bradoriids and phosphatocopids. Ostracod distributions demonstrate the ecological success story of the group, occupying as they do marine, non-marine and even ‘terrestrial’ habitats. Written by current specialists in the field, this book is an authoritative account and will be welcomed by all micropalaeontologists and applied geologists in the industrial and academic world alike. It is richly illustrated with over 80 plates of electron micrographs and specially drawn maps, diagrams and range-charts.