REFINED SOUTHERN AUSTRALIA EARLY CAMBRIAN SMALL SHELLY FOSSIL FIRST APPEARANCES BASED ON DYNAMIC TIME WARPING ALIGNMENTS OF δ13CCARB SEQUENCES

The Cambrian “Explosion” is the defining interval in which modern-day phyla appeared. While the chronology for the Cambrian Terreneuvian Series (~539 – 521 Ma) has been established from U-Pb dated zircons in ash beds interstratified within carbonate in the Anti-Atlas, Morocco, this location lacks the small shelly fossils that are needed to date Cambrian phylum originations. Highly fossiliferous regions across the globe, including Australia, China, Mongolia, and Siberia, have δ¹³C_carb excursions that may represent the global marine carbon cycle, and can therefore be correlated to Morocco to extrapolate this age model to fossil first appearances.

Here we apply dynamic time warping to create libraries of alignments between the nine sections of the Arrowie and Stansbury basins, Australia, reported by Betts et al. (2018). To establish relative ages for fossil first appearances at this location within this Period we select individual section alignments to contribute to regional δ¹³C_carb composites based on three criteria. As the early Cambrian stratigraphy from these basins is divided into three different biozones, we can choose preferred alignments that minimize the diachroneity between the base and/or the top of these biostratigrpahic zones. Alternatively, we can choose alignments that best align lithostratigraphic boundaries. Finally, we can produce a composite based on preferred alignments that maximize how well isotopic data correlate (maximum correlation coefficient). Each of these three regional composites predicts a distinct relative chronology for Australia small shelly fossil first appearances. We adopt dynamic time warping to align these three plausible regional composites to the precise Moroccan chronology whereby we can infer the absolute age for fossil and higher-order taxon first appearances and, hence, explore diversification rates.