THE TROPHIC STRUCTURE OF THE BIOTA OF THE PETERBOROUGH MEMBER, OXFORD CLAY FORMATION (JURASSIC), UK

The Peterborough Member of the Oxford Clay Formation is organic-rich and contains an abundance of well-preserved vertebrate and invertebrate fossils. A high nutrient input supported a diverse biota. Phytoplankton was exceptionally abundant in the surface water, and formed the basis for an intricate food web in both surface and bottom waters. Top predators include some of the largest known Mesozoic marine reptiles. A giant teleost fish was analogous to modern filter feeding whales and sharks. Benthic faunas depended on organic matter sinking from surface waters, and two parallel food webs may have existed. Trophic partitioning allowed the higher level predators to become diverse, especially the plesiosaurs. Productivity was high in the surface waters, probably high in the mid-water column, and high on the sea floor at times, although benthic diversity may have been reduced due to substrate consistency and/or dysoxia. Bacterial activity within the sediment was also intense. The contribution of organic material to the sea floor was high, but heterotrophic reworking probably reduced the abundance considerably during early diagenesis. A decrease in organic carbon content in the Upper Callovian and Lower Oxfordian parts of the Oxford Clay Formation parallels a decreasing abundance of vertebrate fossils.