High-precision radiometric dating using Chemical Abrasion-Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-IDTIMS) has allowed the recalibration of the numerical ages of Permian and Triassic spore-pollen palynozones in Australia. These changes have been significant, with some zonal boundaries in the Permian shifting by as much as six million years, and some in the Triassic by more than twice that. Most of the samples analysed came from eastern Australian coal basins (Sydney, Gunnedah, Bowen, Galilee) where abundant volcanic ash beds occur within the coal-bearing successions. The recalibrations of these widely used palynozones have implications for the dating of geological events outside the basins from where samples were obtained. Our revised dates for the Permian palynozones can now be applied to all Permian basins across Australia, including the Perth, Carnarvon, Canning and Bonaparte basins (along the western and northern continental margins), the Cooper and Galilee basins (in central Australia), and the Bowen, Gunnedah and Sydney basins (in eastern Australia). Revised regional stratigraphic frameworks are presented here for some of these basins. The impact of an improved calibration of biostratigraphic zones to the numerical timescale is broad and far-reaching. For example, the more accurate stratigraphic ages are the more closely burial history modelling will reflect the basin history, thereby providing control on the timing of kerogen maturation, and hydrocarbon expulsion and migration. These improvements can in turn be expected to translate in to improved exploration outcomes. We have initially focused on the Permian and provide preliminary results for the Triassic, but intend to expand recalibrations to include Jurassic, Cretaceous and Paleozoic successions beyond the Permian. Preliminary data indicates that significant changes to these calibrations are also likely.

Australia has some of the best documented Permian basins in Gondwana, but much of the succession is nonmarine. Calibration of the local palynostratigraphic scheme (Price, 1997) to the global timescale was indirect and very difficult, having traditionally relied on correlations from relatively sparse, high-latitude, marine strata, within which ammonoids and conodonts are rare, fusulinids are unknown, and much of the other fauna (brachiopods, bivalves) is endemic. Tie points are rare and often tenuous (Mantle et al., 2010): one example is the record of a single specimen of the ammonoid Cyclolobus persulcatus from the Cherrabun Member of the Hardman Formation, in the Canning Basin, Western Australia (Foster and Archbold, 2001), dated as ¿post-Guadalupian¿ by Glenister et al. (1990) and ¿Capitanian¿Dzhulfian¿ by Leonova (1998). In eastern Australia, the Permian succession is replete with felsic ash beds, many of which contain zircons. Ash beds are rare in Western Australia, but some have been found in the Canning Basin. Sampling of ash beds has been coupled with sampling of adjacent clastics for palynomorphs, mostly from drillcore and coalmines in the Sydney, Gunnedah, Bowen and Galilee basins in eastern Australia, and drillcore in the Canning Basin in Western Australia. The zircons have been subjected to the Chemical Abrasion-Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-IDTIMS) technique for U-Pb dating (Mattinson, 2005). The resultant radioisotopic dates, with associated palynostratigraphic determinations, permit the direct calibration of the Price (1997) scheme to the numerical timescale. Some of the data has been cited previously (Smith & Mantle, 2013; Nicoll et al., 2015, 2016; Metcalfe et al., 2015; Phillips et al., 2016). A more detailed synthesis of the Guadalupian and Lopingian will be published soon (Laurie et al., in press) and a study of the Cisuralian is in progress. The results of Laurie et al. (in press) indicate that the palynozones in the Guadalupian and Lopingian of Australia are significantly younger than currently calibrated (Figure 1). The recalibrations indicate: 1. the top of the Praecolpatites sinuosus (APP3.2) Zone lies in the early Roadian; 2. the top of the Microbaculispora villosa (APP3.3) Zone lies in the middle Roadian; 3. the top of the Dulhuntyispora granulata (APP4.1) Zone lies in the Wordian; 4. the top of the Didecitriletes ericianus (APP4.2) Zone lies in the first half of the Wuchiapingian; 5. the entire Dulhuntyispora dulhuntyi (APP4.3) Zone lies within the Wuchiapingian; and 6. the top of the Dulhuntyispora parvithola (APP5) Zone lies at or near the Permian¿Triassic boundary. These new calibrations involve some major changes, the most significant being the base of the Dulhuntyispora parvithola (APP5) Zone, which is about 6 million years younger than previously calibrated. A preliminary assessment of the Cisuralian, in eastern Australia, suggests that the Pseudoreticulatispora pseudoreticulata (APP2.1) Zone and the Microbaculispora trisina (APP2.2) Zone (APP2.2) are both of greater duration than previously thought. Contrastingly, the Pseudoreticulatispora confluens (APP1.2.2) Zone is older and of shorter duration than previously suggested (Mantle et al., 2010). However, at this stage this interpretation is based on relatively few dated ash beds (Figure 1). Preliminary data indicates that similar miscorrelations are also a feature of the current Mesozoic palynomorph zonation, and future work will attempt to remedy this.