Article: Upper Cambrian and basal Ordovician trilobites from western New South Wales
B. D. Webby, Wang Qizheng and K. J. Mills
Eleven trilobite species are described from the Upper Cambrian-basal Ordovician succession exposed to the south-eastern side of Koonenberry Mountain in western New South Wales. Included among the forms are six new species, Rhaptagnostus leitchi, Pareuloma aculeatum, Pseudoyuepingia whitei, P. lata, Proceratopyge ocella, and Hysterolenus furcatus. The assemblages come from two stratigraphically distinct horizons near the top of the Watties Bore Formation. The lower has the more diverse fauna with typical Upper Cambrian elements such as Rhaptagnostus, Pseudoyuepingia, Proceratopyge, Hedinaspis, and Prosaukia? The upper horizon contains Hysterolenus usually taken as an indicator of a restricted early Tremadoc age. There are no apparent lithological or physical breaks in the intervening barren, conformable, 100 m thick siltstone and shale succession, and it probably spans the Cambrian-Ordovician boundary. Both assemblages are preserved in silty shaly beds, and are characteristic elements of a deeper, basinal, or slope-type biofacies. Genera such as Pseudoyuepingia, Hedinaspis, Pareuloma, and Hysterolenus are not known from shallow platform successions elsewhere in Australia but occur in equivalent biofacies of Chinese sequences. The common occurrences suggest close zoogeographic links. Similar though less strong connections are suggested with other circum-Pacific regions, in particular with Alaska and New Zealand.