Cambrian stratigraphy and faunas at Mount Arrowsmith, northwestern New South Wales

Mount Arrowsmith is situated 200 km north of Broken Jill in far western N.S.W., near the north-western extremity of the Koonenberry Belt. Formal definitions are provided for formations correlated with part of the Gnalta Group on the south-western flank of Mount Arrowsmith. The Pincally Formation, of latest Early Cambrian (Ordian to Early Templetonian) age, includes shales and then-bedded limestones with a total thickness of 130 m. Fauna present includes the lingulate brachiopods Eoobulus sp., Eothele granulate Roberts, Prototreta millsi n. sp., Micromitra nerranubawu Kruse, molluscs Pelagiella madianensis (Zhou & Xiao) and hyolith taxa associated with small shelly fossils, including chancelloriids, hyolithelminthes, spines of the bivalved arthropod Mongolitubulus and problematic forms. The phosphatic assemblage closely resembles broadly synchronous sequence 1 faunas form the First Discovery Limestone Member of the Coonigan Formation further south along the Koonenberry Belt, carbonate sequences in the Daly, Wiso and Georgina basins of northern Australia, and the Arrowie and Stansbury basins in South Australia. Conformably overlaying the Pincally Formation is the Wydjah Formation, dominated by quartzose sandstones in its lower and upper parts. The Pimpira Member, an interval of thick oncolitic dolostones with interbedded shales in the middle of this formation, yields a sparse fauna dominated by hyoliths and algae, with rare lingulate brachiopods (Prototreta millsi n. sp., Eoobolus sp. And Micromitra nerranubawu Kruse). No fossils have been recorded in the conformabilu overlaying Wyarra Shale at the top of the Cambrian section. The stratigraphic break between the Cambrian Gnalta Group equivalents and the Early Ordovician Mutawintji Group (represented at Mount Arrowsmith by the Yandaminta Quartzite and overlaying Tabita Formation) corresponds to the Delanerian Orogeny.