Article: Ostracode and conodont distribution across the Ludlow/Prídolí boundary of Wales and the Welsh Borderland

The ostracodes and conodonts of the Silurian Ludlow/Pridoli Series boundary are documented in detail at Ludlow, and described from across Wales and the Welsh Borderland. The Upper Whitcliffe Formation and its lateral equivalents are characterized by the ostracode Calcaribeyrichia torosa and the conodonts Ozarkodina confluens, O. excavata, Panderodus serratus and Coryssognathus dubius. The Downton Castle Sandstone Formation and its lateral equivalents are characterized by the ostracodes Frostiella groenvalliana, Londinia arisaigensis, L. fissurata and Nodibeyrichia verrucosa. Conodont faunal trends across the Welsh Borderland reflect an increasingly turbulent environment towards the top of the Ludlow Series. The sudden ostracode faunal change at the base of the Downton Castle Sandstone at Ludlow (shelf) contrasts with a gradual change 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 variations in ostracode and land plant spore frequency may be related to proximal channels that delivered sediment off an irregularly prograding shoreline. Ostracodes correlate the base of the Downton Castle Sandstone across the Welsh Borderland to localities in east central Wales where bone beds are absent. Combined conodont and ostracode evidence suggests that the base of the Pridoli Series is at the base of the Downton Castle Sandstone Formation in Britain.