Siluro-Devonian faunas of central New South Wales
thesisposted on 2022-03-28, 02:12 authored by Lawrence Sherwin
Brachiopods from the Amphitheatre and Winduck Groups (Cobar Supergroup) in The Meadows district of western New South Wales range in age from possible Pridoli to late Lochkovian or early Pragian age. The assemblages occur in sandy sediments deposited by traction currents and thus are likely to have been derived from more than one community. The closest affinities of the fauna are with the Old World Realm brachiopods of Podolia and western Europe. In the Australasian region the most comparable faunas are those from the Mount Ida Formation near Heathcote, Victoria. There are marked resemblances to brachiopods in the Baton Formation of New Zealand. Sixteen brachiopods are described including redescriptions of Mesodouvillina (Mesodouvillina) convexa (Dun), Ancillotoechia duni (Gttrich) and Howellella jaqueti (Dun). Brachiopod faunas are described from the Derriwong, Trundle and Yarra Yarra Creek Groups in central New South Wales. The fauna in the Derriwong Group ranges in age from possible late Ludlow to Lochkovian and has affinities with Late Silurian faunas from the Canberra-Yass district. The faunas in the Trundle and Yarra Yarra Creek Groups are Emsian; dating of all the Groups is based on conodonts. A new species, Leptostrophia (Mitchella) deckerae, is described from the Derriwong Group and Spinella pittmani (Dun) from the Trundle Group is redescribed. There is trend towards increasing provincialism from Ludlow to Emsian time despite the oldest and youngest assemblages being limited in the number of genera represented. Three species of trilobites are described from the Amphitheatre and Winduck Groups (Cobar Supergroup) in The Meadows district west of Cobar, New South Wales. Encrinurus cf. silverdalensis occurs in a sandstone member and Encrinurus cf. mitchelli in pink mudstone of the Amphitheatre Group. A review of Late Silurian (Pridoli) Encrinurus occurrences in central and western New South Wales suggests a correlation of species with lithology. Craspedarges wilcanniae Gttrich is redescribed, based on material from the Early Devonian (Lochkovian) Winduck Group. Trilobites in the Trundle district occur at several horizons in the Late Silurian to Early Devonian Derriwong Group but only those in the Cookeys Plains Formation and Milpose Volcanics are well preserved although disarticulated. The fauna is very similar to that from Yass. The cheirurid Didrepanon is recorded for the first time from Australasia. The external ornament in Odontochile cf. loomesi Mitchell is well preserved and described. Ceratocephala impedita is reassigned to Ceratonurus. The Late Silurian to Early Devonian trilobite and brachiopod faunas of central New South Wales are generally poorly preserved but are still sufficiently distinctive to provide a local biostratigraphic scheme. The oldest fauna, Encrinurus - Molongia elegans capricornae, can be dated by conodonts as spanning most of the Pridoli. The Podolella or Nanothyris fauna is widespread but of probable short duration, being overlain by late Lochkovian conodonts. The faunas with Howellella jaqueti are very widespread but this is a reflectiom of the difficulty in differentiating poorly preserved very similar species. The Reeftonia and Spinella faunas are restricted to the eastern part of the region and of possible late Pragian to Emsian age.