Studies on the palaeontology of the Lower Oxford clay of southern England.

The Lower Oxford Clay (Middle Callovian, Upper Jurassic) of southern England has been studied in detail, in order to elucidate the stratigraphy, bivalve taxonomy and palaeoecology of the formation. Examination of four quarries in the Midlands, between Peterborough and Calvert (Bucks.), has allowed a detailed stratigraphy to be established, based upon that of Callomon (1968), and to which it has been possible to relate the range and occurrence of all the invertebrate species collected. The position of the Obductum-Grossouvrei Subzonal boundary at Stewartby (Bedford), which was not located by Callomon, has been established, on the basis of recurrent bivalve populations. The taxonomy of the bivalve fauna has been treated monographically, 48 species, 7 of which are new, having been described. One new genus, Byssentolium gen. nov. is introduced, with B. hudsoni sp. nov, as its type species. The subgenus Trautscholdia Cox , Arkell is elevated to full generic rank, and the generic assignations of several of the most well-known Upper Jurassic bivalve species are amended. The remainder of the Lower Oxford Clay invertebrate fauna has been considered in general terms, and its palaeoautecology inferred; the palaeo-autecology of the bivalve fauna has been dealt with in detail. By using the mass of detailed information collected at the four major quarries, a palaeoecological reconstruction of the environmental conditions established during the deposition of the Lower Oxford Clay has been made. Ten biofacies types have been defined and recognised at all the major quarries, and are characterised by 5 ecologically defined parameters. The benthonic fauna of several other Jurassic and Cretaceous Clay Formations has been compared with that of the Lower Oxford Clay, showing that only the Upper Lias of England is closely comparable. Consideration of the composition of deposit-feeder dominated communities since the Lower Palaeozoic has shown the major difference to be the replacement of the suspension-feeding brachiopods by suspension-feeding bivalves, a consequence of mantle fusion and siphon formation.