A new Early Ordovician trilobite from the Broken River region, northeastern Australia: taxonomy and palaeogeographic implications

WA Museum Records and Supplements | Updated 9 years ago

Abstract - A trilobite from an olistolithic slab of Ordovician shallow water limestone in the Big Stockyard Creek area south of Greenvale in the Broken River Province, northeastern Australia, is a new representative of the subfamily Asaphinae: Norasaphus (Shergoldina) greenvalensis subgen. nov. and sp. nov. Due to close morphological relation to previously described Norasaphus from the Nora Formation of central Australia, a late Early Ordovician age is inferred for the trilobite-bearing horizon-the first record of Early Ordovician shelly faunas from northeastern Australia. The agespectrum of Ordovician-Silurian carbonate olistoliths and clasts in debris flows of the Broken River region is increased by the recognition of a late Early Ordovician age for the host olistolith. The "lost" Georgetown Block carbonate platform is now inferred from this occurrence to have been in existence through much or all of the time-interval from late Early Ordovician until at least earliest Wenlock times. Autochthonous and allochthonous carbonate units in the southwestern Broken River Province (west of the Grey Creek Fault Zone) confirm that a carbonate platform (or platforms) persisted, intermittently, in the Broken River Province/Georgetown Province until at least two-thirds of the way through Devonian times, until around the Givetian-Frasnian boundary.