Article: Palaeoecology of a bituminous shale—the Lower Oxford Clay of central England
Quantitative palaeoecological studies, using triangular plots, rarefaction curves, trophic nuclei, trophic group composition, and Diversity Index, have allowed the definition of ten different biofacies within the Lower Oxford Clay (Upper Jurassic, Middle Callovian) of central England. Analysis of the distribution of these biofacies and seven lithofacies groups, has led to the recognition of the Lower Oxford Clay as a deepening-water sequence, in which two distinct environmental cycles are present. By comparison with other Mesozoic shale facies, the Lower Oxford Clay appears different in having its fauna dominated by infaunal deposit-feeders and by high-level ('pendent') epifaunal suspension-feeders; only the Upper Lias is comparable. Evolutionary changes are considered between Palaeozoic and Mesozoic deposit-feeder dominated assemblages, with siphonate bivalves occupying most of the niches previously held by articulate brachiopods.