OSTRACODE AND CONODONT DISTRIBUTION ACROSS THE LUDLOW PRIDOLI BOUNDARY OF WALES AND THE WELSH BORDERLAND/

The ostracodes and conodonts of the Silurian Ludlow/Pridoli Series bou ndary are documented in detail at Ludlow, and described from across Wa les and the Welsh Borderland. The Upper Whitcliffe Formation and its l ateral equivalents are characterized by the ostracode Calcaribeyrichia torosa and the conodonts Ozarkodina confluens, O. excavata, Panderodu s serratus and Coryssognathus dubius. The Downton Castle Sandstone For mation and its lateral equivalents are characterized by the ostracodes Frostiella groenvalliana, Londinia arisaigensis, L. fissurata and Nod ibeyrichia verrucosa. Conodont faunal trends across the Welsh Borderla nd reflect an increasingly turbulent environment towards the top of th e Ludlow Series. The sudden ostracode faunal change at the base of the Downton Castle Sandstone at Ludlow (shelf) contrasts with a gradual c hange at Long Mountain (basin) and parallels shelf-basin palynofacies. Ostracode faunal variations in the Downton Castle Sandstone Formation at Ludlow coincide with minor lithofacies variations. Local variation s in ostracode and land plant spore frequency may be related to proxim al channels that delivered sediment off an irregularly prograding shor eline. Ostracodes correlate the base of the Downton Castle Sandstone a cross the Welsh Borderland to localities in east central Wales where b one beds are absent. Combined conodont and ostracode evidence suggests that the base of the Pridoli Series is at the base of the Downton Cas tle Sandstone Formation in Britain.