Revision of 'Discomesites' and 'Estaingia' (Trilobita) from the Lower Cambrian Cymbric Vale Formation, Western New South Wales: Taxonomic, Biostratigraphic and Biogeographic Implications

Abstract

The taxonomy of Discomesites and Estaingia from the Lower Cambrian Cymbric Vale Formation of western New South Wales is revised. Discomesites is regarded as a valid subgenus of Pagetides. Pagetides (Discomesites) fragum is considered a senior subjective synonym of P. (D.) lunatulus. Pagetides (Discomesites) spinosus from the Shackleton Limestone in the Holyoake Range, Transantarctic Mountains, is considered to be a junior subjective synonym of P. (D.) fragum. Estaingia cerastes from the Cymbric Vale Formation is considered to be synonymous with Hsuaspis cf. H. bilobata from the Shackleton Limestone. The Cymbric Vale Formation trilobite fauna is of late Early Cambrian (late Botoman) age, equivalent to the Pararaia janeae Zone of South Australia, based on correlation of the Syringocnema favus archaeocyathan fauna. Absolute ages of recently dated tuffs from the Cymbric Vale and Billy Creek Formations are questioned, based on new information regarding the stratigraphic position of the Cymbric Vale Formation tuff in relation to archaeocyathan and trilobite biostratigraphy. The co-occurrence of Pagetides (Discomesites) fragum and Estaingia cerastes in the upper part of the Cymbric Vale Formation and in the Shackleton Limestone represents the first species-level correlation between the Lower Cambrian of Australia and Antarctica using trilobites. The distribution of these trilobite species, in association with the Syringocnema favus archaeocyathan fauna, provides supporting evidence that Australia and Antarctica were connected by a continuous carbonate-detrital shelf during the late Early Cambrian (mid-late Botoman),allowing faunal exchange between these regions.