Aw. Owen et al., THE TRILOBITES AND BRACHIOPODS OF THE WRAE LIMESTONE, AN ORDOVICIAN LIMESTONE CONGLOMERATE IN THE SOUTHERN UPLANDS, Scottish journal of geology, 32, 1996, pp. 133-149
The Wrae Limestone is a conglomerate within late Caradoc or Ashgill (l
ate Ordovician) siltstones near the southern edge of the Northern Belt
of the Southern Uplands. Its interpretation exemplifies problems comm
on to many orogens: separation of fossiliferous lithoclast ages from t
iming of final emplacement, separation of biofacies from temporal faun
al 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 boundar
y. The edge of the Midland Valley platform may thus have been the sour
ce of the carbonate clasts. Some of the trilobites range through the s
pectrum of biofacies present in the Lower Caradoc of Girvan. However,
species of Phorocephala and Dubhglasina suggest an origin at the margi
n of the Nileus association. The brachiopod assemblage is not directly
comparable with any faunas in the Girvan-Appalachian belt. It is domi
nated by coarse ribbed orthoids, smooth triplesiids and several plecta
mbonitoids, having more in common with later Ordovician brachiopod bio
facies associated with carbonate mudmounds, but overall the Wrae brach
iopod assemblage is not particularly typical of any one benthic assemb
lage zone or precise substrate type.