Cambro-Ordovician conodonts from the Burke River Structural Belt, Queensland

Conodonts from the Upper Cambrian Chatsworth Limestone and Gola Beds and the Lower Ordovician (Tremadocian) Ninmaroo Formation were examined in order to determine the sequence of conodont species. Over 5000 specimens from 600 trough-samples representing a total of 10,000 feet of section were identified. Fifty-three species are described, of which 13 are new and 2 have been given open nomenclature. They are referred to 16 genera, of which one, Strigaconus, is new, and two are indeterminate. No Assemblage Zones could be erected for the Upper Cambrian. However, six Assemblage Zones (in ascending order - Cordylodus proavus, Oneotodus bicuspatus-Drepanodus simplex, Cordylodus oklahomensis-C. findstromi, Cordylodus prion-Scolopodus, Cordylodlls rotundatus C. anglllatus, and Chosonodina herfllrthi-AcodllS) are erected in the Tremadocian. Comparison of our zones with previously described conodont sequences from Europe, North America, and Korea shows that they can be used for intercontinental correlation. Local correlation of sections sampled over a distance of 59 miles shows a diachronous rise of the- lithological members of the Ninmaroo Formation to the south. The phylogenetic relationships of Upper Cambrian and Tremadocian conodont species are discussed. Two root-stocks are recognized in the Upper Cambrian - the coelocerodontids, and the westergaardodinids. A development from a coelocerodontid ancestor of Oneotodus nakamllrai Nogami gave rise to the majority of Tremadocian species, which are characterized by diverse cordylodids and scolopodids. The minor westergaardodinid root-stock gave rise to only two species of Chosonodina. Rates of sedimentation (calculated from the thicknesses of the conodont Assemblage Zones) show a general decrease upwards throughout the sequence, and a decrease southwards along the outcrop, from Black Mountain to Mount Datson.