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Abstract
New evidence is presented on the Triassic–Jurassic boundary in eastern Australia, based on miospore assemblages from three continuously cored drillholes which penetrated the Raceview Formation to Ripley Road succession in the eastern Clarence-Moreton Basin of southeastern Queensland. Evidence for the age of this continental succession is provided by correlation based on the first appearances of five distinctive species. These taxa first appear at or close to the Rhaetian–Hettangian boundary in the marine, ammonite-dated succession of New Zealand and in the lower Ripley Road Sandstone of Queensland. The more gradual introduction of these species in the Queensland succession, as opposed to their near-synchronous appearance in New Zealand, is probably due to their gradual migration into an inland environment in contrast to their origin from a nearshore region in New Zealand. At higher levels the first appearance of intrastriate Classopollis, closely followed by its marked increase in abundance, is regarded as evidence for correlating assemblages from the upper Ripley Road Sandstone in the eastern Clarence-Moreton Basin with the earliest Sinemurian of New Zealand. The views of some previous workers that the Hettangian of eastern Australia is characterised by the appearance of abundant Classopollis must now be modified. From the aspect of biotic change, associated with climate change at the Triassic–Jurassic boundary, this study indicates a rapid local change in New Zealand. A new type of biozone, the Association Zone, is proposed as a type of interval zone. The need for a distinctive biozone to characterise palynofloral assemblages is indicated to allow for the frequent recycling of palynomorphs and also to better define the body of an interval zone. New Early Jurassic miospore zones are proposed for southeastern Queensland. Granamegamonocolpites campbellii sp. nov. is described and one new combination, Anapiculatisporities helidonensis (de Jersey) comb. nov., is proposed. Morphological and stratigraphical evidence is provided for gradualism in the lineage development of intrastructure in Classopollis, from massive (unstructured), to intrapunctate, to intrastriate specimens.
Acknowledgements
This study followed a comprehensive investigation of Early Jurassic ammonites of New Zealand (Stevens 2004) which provided a firm basis for dating, via correlation of palynological sequences, the Queensland sucession recorded here. We are indebted to Graeme Stevens for helpful advice on the dating of certain palynofloral assemblages in New Zealand, for providing access to his manuscript and for reading our final text. Also, in New Zealand, the late Doug Campbell organised collection of material across the Triassic–Jurassic boundary; these samples were processed at the New Zealand Institute of Geological and Nuclear Sciences. This laboratory processing was arranged by Ian Raine, who is participating in an ongoing study of New Zealand Jurassic palynofloras, initially reported on by de Jersey and Raine (2002).
In Australia, important assistance was rendered by Clinton Foster and staff of Geoscience Australia, Canberra, in processing additional samples from a critical part of the succession in GSQ Ipswich 25. John Backhouse (Perth) advised on the palynofloral sequence through the Triassic–Jurassic boundary in offshore Western Australia and was also a reviewer, as was Basil Balme (Perth) who offered supportive and valuable opinions. Len Cranfield (formerly of the Geological Survey of Queensland) gave advice on lithostratigraphical relationships in southeastern Queensland. Also, final drafting of the figures was carried out in the Geological Survey of Queensland by Lesley Blight, Gina Nuttall, Paula Deacon and Liam Hogan. Helpful advice was also given by Alfred Traverse (Pennsylvania), who read our final manuscript.