--> The Impact of CA-IDTIMS on the Understanding of Permian and Triassic Lithostratigraphy and Correlation in Eastern Australian Coal Basins

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The Impact of CA-IDTIMS on the Understanding of Permian and Triassic Lithostratigraphy and Correlation in Eastern Australian Coal Basins

Abstract

In recent years, numerous correlations of the Permian and Triassic successions in the eastern Australian coal basins (Sydney, Gunnedah, Bowen and Galilee basins) have been attempted based on broad scale lithostratigraphy, sequence stratigraphy and biostratigraphy. However, detailed correlation of these successions has proved difficult. The development of Chemical Abrasion-Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-IDTIMS), with its dramatically increased precision, has allowed more precise correlations to be obtained. This is in part because of the large number of tuffs in these eastern Australian basins, which range from the lowest Permian to the middle Triassic and number in the several hundred. The new correlations have resulted in numerous revisions to the ages of important units in eastern Australian Basins. For example, the uppermost coal successions in the Sydney Basin (Newcastle Coal Measures, Illawarra Coal Measures) extend to very near the Permian-Triassic boundary and have a shorter duration than previously thought. The underlying Tomago Coal Measures/Whittingham Coal measures, rather than extending from the basal Wordian to earliest Wuchiapingian extend from the middle Capitanian to middle Wuchiapingian. Similarly, the top of the Greta Coal Measures, rather than being middle Kungurian are now known to be middle Roadian. In the Gunnedah Basin, the top of the Millie Group was basal Wordian, but is now considered middle Capitanian, while the overlying Brothers Subgroup, which was thought to extend up to the middle Capitanian is now known to be middle Wuchiapingian. The overlying Coogal Subgroup has been dramatically shortened in duration, and now lies entirely within the middle Wuchiapingian. In the Bowen Basin, the changes are similar, with the base of the Peawaddy Formation changed to late Wuchiapingian rather than middle Wordian, the base of the overlying Black Alley Formation now being latest Wuchiapingian rather than late Capitanian, and the base of the Bandanna Formation reassigned to earliest Changhsingian, rather than early Wuchiapingian. This recalibration of stratigraphy allows for a much improved understanding of basin history and the correlations between stratigraphic units, within and between eastern Australian basins.