Boreal influence on English Ryazanian bivalves

In early Ryazanian times a marine embayment extended from the Southern North Sea Basin onto the East Midlands Shelf (Spilsby Basin) and slightly later also reached into the Yorkshire Basin. The sediments on the shelf are predominantly glauconitic sands tones with phosphates and sideritic clay-ironstones (upper parts of the Spilsby Sandstone and the Sandringham Sands) while those in the Yorkshire Basin are clays (lowest part of the Speeton Clay). The associated bivalve faunas are marine and show strong affinities with East Greenland and Russian Platform faunas. In south central England the ferruginous Whitchurch Sands represent restricted marine conditions and contain a bivalve fauna related in part to that of the late Portland Beds of the Upper Jurassic, although the sands are separated from these by the Lulworth Beds of late Jurassic age. In southern England the Durlston Beds are predominantly limestones and marls and contain various bivalve faunas ranging from restricted marine to freshwater facies. The near marine horizons represent transgression into the Anglo-Paris basin from the north. The more restricted and fresh-water environments are typical of European marginal facies. The various bivalve faunas reflect the fluctuating environments.