FACIES AND FAUNAS AT THE WENLOCK/LUDLOW BOUNDARY OF WENLOCK EDGE, SHROPSHIRE

Abstract

Variations in facies and faunas are described in the Wenlock Limestone, Lower Elton Beds and basal Middle Elton Beds of Wenlock Edge, Shropshire. As in a number of earlier descriptions the Wenlock Limestone outcrop is divided into reef and non-reef areas; five lithofacies are described from the former and three from the latter. In the Lower Elton Beds two distinct lithofacies embrace three overlapping faunal assemblages, all of which have a dominant Wenlock aspect. Criteria based on lithology and shelly and graptolitic faunas are discussed in relation to the position of the Wenlock/Ludlow boundary. It is concluded that there is no recognisable faunal change across the boundary as currently defined at the junction of the Lower Elton Beds and the Wenlock Limestone. There is, however, a major shelly faunal change at the junction of the Lower and Middle Elton Beds. This horizon, which is also marked by a lithological change, appears to coincide with the base of the graptolite zone of Pristiograptus nilssoni.