The oppeliid, perisphinctid and aspidoceratid ammonite faunas of the ‘Corallian’ Beds (Upper Jurassic) in Cambridgeshire, England

Abstract

The Upware Limestone Member comprises an enclave of Middle Oxfordian ‘Corallian’ facies limestone situated on the East Midlands Shelf within the more typical mudrock-dominated sequences of eastern England, and is assigned to the West Walton Formation. Recent deep excavations in the district have revealed the base of the Upware Limestone, not exposed since the last century, resting on a mudrock sequence, the Dimmock’s Cote Marl Member. The Upware Limestone and Dimmock’s Cote Marl have yielded an unusually common ammonite fauna, including both Boreal (Cardioceratidae) and Tethyan (Perisphinctinae) elements, and rare Tethyian oppeliids and aspidoceratids. Thirteen nominal species of Perisphinctes are described and figured, as are one species of Neocampylites and one of Euaspidoceras . Three distinct assemblages of Perisphinctes are recognized in the Upware succession. The faunas are correlated with existing zonations for the Middle Oxfordian of Sub-Boreal and Sub-Mediterranean regions, including sub-subzonal schemes (i.e. ‘biohorizons’). Such correlations aid the construction of correlative links between two distinct ammonite provinces and have great potential for resolving some of the outstanding questions of European Middle Oxfordian stratigraphy. The succession is also of great importance within Britain as it is the only known locality to yield faunas that are stratigraphically intermediate between the classic Corallian assemblages of Oxford and the later faunas of the Upper Calcareous Grit of Yorkshire.