The Billabong Creek Formation and overlying Gunningbland Formation within the Northparkes Group in the Gunningbland area, 28 km west of Parkes, range in age from late Darriwilian (late Middle Ordovician) to late Eastonian (middle Late Ordovician). These strata provide the most complete sequence through this interval in the central Lachlan Orogen in New South Wales. A biostratigraphic zonation spanning the Darriwilian to Gisbornian is proposed, employing conodonts and corals. This supplements the existing coral/stromatoporoid, brachiopod and trilobite faunal assemblages defining Eastonian and Bolindian shelly fossil zones. The Pygodus anserinus Zone (late Darriwilian) in the basal Billabong Creek Formation is succeeded by the Foerstephyllum-Billingsaria-Stratodictyon Assemblage-Zone (of Gisbornian age) in the middle Billabong Creek Formation. A further five Assemblage-Zones extending through the Eastonian succession are formally defined to replace the existing shelly fossil 'faunas'. New coral species described are Billingsaria domica, Eofletcheria subcerioidea, Foerstephyllum nelungaloo, and ?Paleoalveolites explanatus; a possible new species of the conodont Eoplacognathus is described, but not formally named.
- New South Wales