Conodonts from a core of the Nita and Goldwyer Formations (Lower Middle Ordovician) of the Canning Basin, Western Australia

The Canning Basin in northern Western Australia includes a thick and areally extensive Lower and Middle Ordovician sequence of dominantly carbonate and shale deposited in an epeiric sea. Ordovician strata outcrop in only two small areas along the northeastern basin margin but have been penetrated in the subsurface by numerous, widely-spaced petroleum exploration drillholes. -- Prioniodontacean conodonts from the Lower Ordovician Emanuel Formation in' the Prices Creek outcrop area were described by McTAVISH (1973) but descriptions of conodonts from the subsurface formations have hot been previously published. This study describes conodonts extracted from a continuous 234m core section through the Middle Ordovician Nita Formation and the underlying upper Goldwyer Formation of the subsurface sequence on the Broome Arch. Approximately 8,700 identifiable conodont elements were recovered from 96 samples with a combined mass of approximately 160kgms. A total of 54 conodont taxa have been identified: 20 multielement genera, including 27 species and 27 form-taxa. New taxa described are as follows: the multielement genus: Onyxodus, the multielement species: Protoprioniocus histion, Onyxodus acuoliratus, Phragmodus polystrophos and Phragmodus spicatus, and the form-species FaIodus keramis. -- The conodont taxa fall into two, stratigraphically discrete faunas: a lower fauna correlated with Midcontinent Fauna 4 (SWEET, ETHINGTON and BARNES, 1971) and an upper fauna correlated with the North Atlantic Eoplacognathus suecicus conodont Zone (BERGSTROM, 1971) and Midcontinent Fauna 5. The boundary between these two faunas is abrupt (occurring within a 4m thick sample gap) and is correlated with similar conodont faunal changes in: the Majiagou Formation of North China (AN et. al., 1983), the Bay Fiord Formation of Arctic Canada (NOWLAN, 1976), the Watson Ranch Quartzite of the Ibex Area of Utah (ETHINGTON and CLARK, 1981) and the Antelope Valley Limestone of the Meiklejohn Peak section of Nevada ( HARRIS et. al., 1979)