Reassessing the chronostratigraphy and tempo of climate change in the Lower-Middle Permian of the southern Sydney Basin, Australia: Integrating evidence from U-Pb zircon geochronology and biostratigraphy

The Permian of the southern Sydney Basin (Australia) comprises both marine and non-marine sedimentary sequences with evidence of glacial deposition and syndepositional magmatism represented by tuffs, lava flows and hypabyssal intrusions. This succession has been well-studied in lithostratigraphy and sedimentology, but the Lower-Middle Permian chronostratigraphy remains poorly constrained due to a lack of radiometric isotope ages and strong faunal endemism. In this study, we report the first suite of reconnaissance U-Pb zircon ages from this succession, comprising two Wandrawandian Siltstone (WS) tuffs (Green Point tuff 272.6 ± 6.5 Ma population, Callala Bay tuff ≥290 Ma Permian populations) and magmatic zircon ages from three discrete syndepositional intrusions: the Termeil Complex intruding the Snapper Point Formation dated 278.9 ± 3.7 Ma (95% confidence), the Milton Complex intruding the Snapper Point Formation and likely the WS dated 275.5 ± 4.3 Ma, and a dyke/sill at Kinghorn Point intruding the WS dated 275.6 ± 4.3 Ma. In light of the new preliminary U-Pb ages, combined with stratigraphic and biostratigraphic evidence, the age of the Wasp Head Formation is reassessed to be late Asselian-Sakmarian, Pebbley Beach Formation Artinskian, Snapper Point Formation early Kungurian, Wandrawandian Siltstone late Kungurian-Roadian, Nowra Sandstone and Berry Siltstone both confined within early Wordian, and Broughton Formation from mid-Wordian to early Capitanian. The ages and duration of the Permian glacial events are also revised, with the first episode (P1) lasting from basal Permian to early Sakmarian (~299-293 Ma), P2 spanning Artinskian (~290-283 Ma), P3, possibly the longest of all Permian glacial intervals, extending from mid-Kungurian to early Capitanian (~278-263 Ma), and P4 from mid-Capitanian to late Wuchiapingian (~260-254.5 Ma). The ≥290 Ma Permian zircon populations in the Callala Bay tuff reflect either an early Permian volcanism or older zircons recycled from elsewhere.