The Upper Ordovician Kenyu Formation in the Boorowa Region, southeast New South Wales

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Abstract

Conodonts obtained during mapping of the Boorowa 1:100 000 geological sheet indicate a late Gisbornian to earliest Eastonian age (Late Ordovician: late Sandbian to earliest Katian) for allochthonous limestone in the Kenyu Formation. This age is based on co-occurrence of Belodina compressa, Phragmodus undatus and Yaoxianognathus wrighti, associated with Drepanoistodus suberectus, Panderodus gracilis, Periodon aculeatus, Protopanderodus liripipus, Scabbardella sp. cf. altipes and Yaoxianognathus sp. The faunal association, including acrotretide, discinide and lingulide brachiopods in addition to the conodonts, indicates that the limestone was probably originally deposited on the shelf edge, prior to being dislodged down the flanks of a volcanic island in a mass flow. The late Gisbornian to earliest Eastonian age recognised for the Kenyu Formation provides an important constraint on the age and cessation of contemporaneous volcanism in the central Macquarie Arc, represented more extensively further north by the Walli Volcanics and Fairbridge Volcanics. No significant break intervened between the end of this volcanism and ensuing deposition of widespread limestones of Eastonian age on the Molong Volcanic Belt.