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

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