| Abstract: | For the first time the stratigraphically important brachiopod Davidsonina septosa (Phillips) has been located in thickly bedded pale grey, late Asbian limestones in North Wales. Above these limestones are thinly bedded dark grey Brigantian limestones, which have yielded a rich and diverse coral-brachiopod fauna, including Lonsdaleia floriformis (Martin). The Girvanella Nodular Bed is recorded for the first time in this region, some distance above the base of the Brigantian. The boundary between the two major lithofacies is marked by a prominent palaeokarstic surface and coincides with a significant faunal change, both in the macrofauna and microfauna that serves to identify the boundary between the Asbian and Brigantian Stages. The discovery within late Dinantian successions of certain diagnostic corals, brachiopods, and algae outside their accepted restricted stratigraphical ranges, casts doubt on their reliable use as Asbian or Brigantian zone fossils. |
