The Cambrian Series 2–Miaolingian boundary interval in Australia: biostratigraphic subdivision and implications for global multi-proxy correlation

The Cambrian Series 2–Miaolingian boundary interval in Australia—equivalent to the local Ordian and Templetonian stages—has long been a source of controversy, with a practical and consistent subdivision of this interval proving elusive. Recent ratification of the Miaolingian Series and Wuliuan Stage Global Boundary Stratotype Section and Point (GSSP) in South China, based primarily on the first appearance of the trilobite Oryctocephalus indicus and the coincident Redlichiine–Olenelline Extinction Carbon isotope Excursion (ROECE), highlights the importance of resolving this interval in Australia. In this contribution, we present an updated synthesis of Cambrian Series 2, upper Stage 4–Miaolingian, Wuliuan (Ordian–Templetonian) intervals across Australia, focusing on the reported ranges of small shelly fossils (SSF) and δ¹³C/δ¹⁸O isotope chemostratigraphy, in addition to trilobite and agnostid arthropod occurrences. Results show an underappreciated sequential series of taxon lowest occurrences across this interval. Based on these, we define two new organophosphatic brachiopod biozones: an upper Stage 4 (Ordian) Schizopholis napuru Zone, and an uppermost Stage 4–Wuliuan (upper Ordian–Templetonian) Micromitra nerranubawu Zone. Taxon ranges across these zones are consistent with the Cambrian Series 2–Miaolingian boundary at the Miaolingian/Wuliuan GSSP, allowing direct correlation with South China. Preliminary work in the Australian Stansbury and Georgina basins has revealed the promise of high-resolution SSF biostratigraphy coupled with δ¹³C/δ¹⁸O chemostratigraphy in addressing the ongoing issues associated with this interval. It is clear that such multi-proxy studies can assist in locating boundaries and correlating intervals across different Cambrian terranes with a high degree of precision, even when lacking index fossils such as O. indicus. Future work should focus on a systematic program of such studies within this interval, which will greatly assist in resolving correlations both within Australia and globally.