Upper Cambrian (Mindyallan) trilobites and stratigraphy of the Kayrunnera Group, western New South Wales

Updated: 2018-04-20

Nine species of trilobites are recorded from three localities within a restricted stratigraphic interval near the base of the newly defined Kayrunnera Group (previously Kayrunnera Beds) on Kayrunnera station, western New South Wales. These occurrences come from the Boshy Formation of the Kayrunnera Group. The trilobites described include species of Ammagnostus, Meteoraspis, Biaverta, Blackwelderia, Bergeronites, and Placosema. This assemblage is early Late Cambrian (Mindyallan), and most closely referable to the late Mindyallan zone of Glyptagnostus stolidotus. The steeply dipping,weakly cleaved Upper Cambrian-basal Ordovician Kayrunnera Group overlies, with a well-defined angular unconformity, a more deformed tightly folded and strongly cleaved, graded, turbidite sandstone sequence. The turbidite succession is considered to be Early to Middle Cambrian, by lithological correlation with similar rocks containing sponge spicules and trace fossils elsewhere in the Wonominta Block. The upright isoclinal folds of this sequence and the angular unconformity were produced during a major orogenic phase, probably an early expression of the Delamerian Orogeny, in late Middle Cambrian time. After uplift and erosion there followed a period of early-middle Late Cambrian marine transgression, during which the lower part of the Kayrunnera Group was deposited. The beds include the trilobite-bearing Boshy Formation, of shallow marine origin.