Late Cambrian (Iverian; mid-Furongian) trilobites from allochthonous blocks in the Cowra Trough, New South Wales, and their significance for the early Macquarie Arc

Cambrian fossils have not previously been documented from the Macquarie Arc within the Lachlan Orogen of eastern Australia, despite rare geophysical and radiometric evidence suggesting that rocks of this age form part of the arc’s early architecture. We describe a late Cambrian trilobite assemblage from siliciclastic olistoliths within the early Silurian Kabadah Formation on Narrawa property, west of Wellington in the Cowra Trough of central New South Wales. The trilobite fauna includes the agnostid Rhaptagnostus clarki and associated polymerid taxa: Pulchricapitus xenos sp. nov., Macropyge (Promacropyge) sp., Koldinioidia sp., Onchonotellus sp., Dokimocephalidae gen. et sp. indet., and Saukiidae gen. et sp. indet. Associated with the trilobite fauna is the tritoechiid brachiopod Narrawaella wellingtonense. The occurrence of R. clarki supports a middle to late Iverian age, broadly equivalent to the middle to late Jiangshanian in global terms. This assemblage constitutes the first direct palaeontological evidence for Cambrian sedimentary rock associated with the Macquarie Arc region. Geologically, this fauna demonstrates that olistostromal successions of the Cowra Trough can preserve older arc-margin or basement-derived components that are otherwise absent from surface exposures, providing a new fossil constraint on the early development of the Macquarie Arc.Patrick M Smith* [[email protected]], Geological Survey of New South Wales, W.B. Clarke Geoscience Centre, 947–953 Londonderry Road, Londonderry, New South Wales 2753, Australia; School of Natural Sciences, Macquarie University, North Ryde, New South Wales 2109, Australia; Ian G. Percival [[email protected]], Geological Survey of New South Wales, W.B. Clarke Geoscience Centre, 947–953 Londonderry Road, Londonderry, New South Wales 2753, Australia; Yong Yi Zhen [[email protected]], Geological Survey of New South Wales, W.B. Clarke Geoscience Centre, 947–953 Londonderry Road, Londonderry, New South Wales 2753, Australia; Izak Schoon, The Fossil Club of Australia, 2 Hugh Place, Kings Langley, New South Wales 2147, Australia.