The trilobites and brachiopods of the Wrae Limestone, an Ordovician limestone conglomerate in the Southern Uplands

Publisher Website
Google Scholar
Abstract
Synopsis: The Wrae Limestone is a conglomerate within late Caradoc or Ashgill (late Ordovician) siltstones near the southern edge of the Northern Belt of the Southern Uplands. Its interpretation exemplifies problems common to many orogens: separation of fossiliferous lithoclast ages from timing of final emplacement, separation of biofacies from temporal faunal correlation and the use of biofacies in determining provenance. The trilobites are closest to those of the lower Caradoc rocks at Girvan, north of the supposed Southern Uplands-Midland Valley terrane boundary. The edge of the Midland Valley platform may thus have been the source of the carbonate clasts. Some of the trilobites range through the spectrum of biofacies present in the Lower Caradoc of Girvan. However, species of Phorocephala and Dubhglasina suggest an origin at the margin of the Nileus association. The brachiopod assemblage is not directly comparable with any faunas in the Girvan–Appalachian belt. It is dominated by coarse ribbed orthoids. smooth triplesiids and several plectamboni-toids, having more in common with later Ordovician brachiopod biofacies associated with carbonate mudmounds, but overall the Wrae brachiopod assemblage is not particularly typical of any one benthic assemblage zone or precise substrate type.