Late Cambrian and early Ordovician trilobites from the Burke River structural belt, Western Queensland, Australia

Trilobite faunas are described from sections at Black Mountain, Mount Ninmaroo, Mount Datson, and Dribbling Bore, in the southern part of the Burke River Structural Belt on the eastern margin of the Georgina Basin, western Queensland: 96 species and subspecies are assigned to 51 genera and subgenera classified into 22 families and subfamilies. Seven genera, 5 subgenera, 46 species, and 3 subspecies are new: 28 species are left under open nomenclature.Eight taxa are of early Ordovician age, Datsonian to early Warendian. The remainder are late Upper Cambrian, ranging in age from the informally designated pre-Payntonian B interval to Payntonian. The Cambrian faunas are late Changshanian to early Wanwanian in terms of Asian stage nomenclature; latest Franconian and Trempealeauan with reference to North American stages; and range upwards from approximately Zone 5b (of Westergaard) when compared with the Atlantic-Baltic biostratigraphical scale. The most complete stratigraphical section is described at Black Mountain, where trilobite faunas are grouped into six successive assemblage-zones on the basis of specific range and association. In ascending order these zones are: Pseudagnostus clarki patulus with Caznaia squamosa, Pseudagnostus clarki prolatus with Caznaia sectatrix, Pseudagnostus bi/ax with Pseudagnostus denticulatus, Pseudagnostus clarki maximus with Pseudagnostus papilio, Sinosaukia impages, Pseudagnostus quasibilobus with Tsinania (Tsinania) nomas. A seventh zone, that of Mictosaukia perplexa, succeeds the quasibilobus-nomas Assemblage-Zone at Mount Datson and Dribbling Bore. Biostratigraphical subdivision has been facilitated by use of the Dice Similarity Coefficient and cluster analysis techniques. The faunal passage from latest Cambrian to earliest Ordovician, which is obscured by dolomitic intervals at Black Mountain, Mount Ninmaroo, and Mount Datson, is documented at Dribbling Bore, where the PayntonianDatsonian boundary, corresponding to the Cambrian-Ordovician boundary, is recognized by the incoming of the conodont assemblage-zone based on Cordylodus proavus. In the early parts of the sequences studied, pre-Payntonian B and early pre-Payntonian A intervals, trilobite assemblages have a high component (often more than half) of cosmopolitan elements, particularly Agnostina, Remopleuridacea, and Asaphacea. In the late pre-Payntonian A and Payntonian, endemic Asian shelf elements or their close relatives, particularly Saukiidae and Leiostegiacea, dominate the assemblages, often in excess of 80 percent of the faunas. Consequently, Asian taxa occurring in western Queensland are revised. Among the Agnostina, late Cambrian representatives of the genus Pseudagnostus occurring in Australia are divided into four species groups based on Pseudagnostus clarki Kobayashi, P. convergens Palmer, P. clavus Shergold, and P. bilobus Shaw. The morphology of these species is discussed in detail, and descriptions of both external testaceous and parietal surfaces are given wherever possible.

Tags: AU-QLD, Bulletin, Earth Sciences, GA Publication, Published_External, palaeontology
Organization: Geoscience Australia Data