Ordovician Fauna in a Small Fault Block on the Yarrol Fault, South of Calliope, Central Queensland

Abstract

Fossils, comprising sponge spicules, brachiopods, trilobites and assorted echinoderm plates, from a fault-bounded sliver along the Yarrol Fault 30 km south–south-east from the town of Calliope in central eastern Queensland, are described and illustrated for the first time. Due to their poor preservation, none of the fossils are identifiable to species level, but the trilobites, Arthrorhachis sp. and two pliomerid pygidia, belong to taxa not known outside the Ordovician, and Illaenus sp. compares closest with Middle Ordovician members of the genus. The brachiopods – including orthoids (?Phaceloorthis among others), plectambonitoids (Sericoidea), the protorthide Skenidioides and a siphonotretide – resemble forms previously described from the Late Ordovician (Katian) of central New South Wales and indicate an open marine deep-water habitat (120–200 m depth). This assemblage is significant in representing the first Ordovician fauna (and the oldest fossils) documented from the New England Orogen in Queensland. The tectonic implications of this confirmed Ordovician sedimentary succession within the New England Orogen in central Queensland are yet to be fully appreciated, but it does complement similarly aged successions occurring along the Peel Fault in the southern New England Orogen. Together these tiny fault blocks suggest that the island arc or arcs which developed during the early Palaeozoic were incorporated into the New England Orogen during the middle Palaeozoic, both in its northern part as well as in the south.