Discovery of Iapetognathus fauna from far western New South Wales: towards a more precisely defined Cambrian–Ordovician boundary in Australia

ABSTRACT

Conodont species Iapetognathus fluctivagus and Iapetonudus ibexensis are documented for the first time from Australia. The former is the primary marker internationally defining the base of the Ordovician, and the latter is also a distinctive species previously recorded only from the base of the Ordovician in North America. Both species were recovered from a single sample in the Kandie Tank Limestone of the Kayrunnera Group, located about 50 km west of White Cliffs in far western New South Wales. Other species recovered from this sample include Prooneotodus spp., Cordylodus lindstromi, Cordylodus proavus, Hirsutodontus simplex, Teridontus nakamurai and Variabiloconus sp. Recognition of the Iapetognathus fluctivagus Biozone in the Kandie Tank Limestone supports its correlation with the Green Point section (Global Stratigraphic Section and Point for the base of the Ordovician) in western Newfoundland and the Lawson Cove section of Utah (Auxiliary Stratigraphic Section and Point), as well as sections in Asia and South America. Review of other sections in Australia and elsewhere spanning the Cambrian–Ordovician boundary confirms that, in the absence of I. fluctivagus, the presence of C. lindstromi is a good proxy for this level.

KEYWORDS:

• Cambrian–Ordovician boundary
• conodont
• biostratigraphy
• Iapetognathus
• Koonenberry Belt

Acknowledgements

Y. Y. Zhen acknowledges funding support through a grant from the Betty Mayne Scientific Research Fund of the Linnean Society of NSW in assisting a field trip to far western NSW in September 2009. Paul Meszaros assisted with conodont sample acid leaching and residue separation. SEM study of conodonts was carried out at the Electron Microscope Unit of Macquarie University. James Miller and John Repetski are acknowledged for their careful and constructive reviews of the manuscript. This is a contribution to IGCP Project 653: the onset of the Great Ordovician Biodiversification Event. Zhen and Percival publish with permission of the Executive Director, Geological Survey of NSW.

Disclosure statement

No potential conflict of interest was reported by the authors.