Lower Jurassic (Hettangian–Toarcian)
Earliest Jurassic assemblages are generally of low diversity, often monospecific, but throughout the Lower Jurassic we see diversity increasing steadily with the establishment of what would become typical Mesozoic, marine ostracod assemblages with radiations in all cytheroidean families, particularly the Cytheruridae. The most notable evolutionary event within this period is the global extinction of the Metacopina in the earliest Toarcian that appears to be broadly coincident with a major perturbation in the global carbon cycle at this time.
Although this period is characterized by fluctuating sea levels most Lower Jurassic ostracod assemblages occur in fully marine facies. Shallow-water, condensed sequences are not uncommon in some areas during the Toarcian, as are occasional periods of bottom-water dysaerobia. In general, the Lower Jurassic ostracod record marks the first real recovery and diversification in post-Palaeozoic assemblages following the end-Permian extinction.
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.