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Utilisation of Microvertebrates in Biostratigraphy and Chemostratigraphy for the Late Devonian and Early Carboniferous in the Canning Basin, Western Australia


The Late Devonian to Early Carboniferous was a major period in vertebrate evolution and encompasses two significant faunal overturns. The first being the Frasnian/Famennian mass extinction event which is estimated to have resulted in the loss of 60% of all taxa, and the second at the end of the Famennian which primarily affected vertebrates. During the Frasnian/Famennian event, the reefal environments continued largely uninterrupted on the Lennard Shelf in the Canning Basin of Western Australia, whereas in Europe, America and North Africa this extinction period is recorded by the presence of anoxic facies typically known as the Kellwasser events. Locating the precise position of major extinction events in the Lennard Shelf has been difficult as the facies lack the distinct and associated lithological changes common in the Northern Hemisphere. Conodont and goniatite biostratigraphy has been traditionally used to locate these events; but age diagnostic material in the backreef and restricted facies is rare. Recent studies have indicated the usefulness of microvertebrates as biostratigraphic substitutes in such environments. Sampling for conodonts and microvertebrates was carried out within measured sections at Horse Spring, Casey Falls and South Oscar Range within the Virgin Hills Formation, as well as spot sampling in the late Famennian and early Carboniferous Fairfield Group. A Turiniid thelodont (jawless fish) was recorded from the crepida to upper marginifera conodont zones, providing the youngest recorded presence for this taxon and allowing for a refined biostratigraphic scheme to be extended from the Silurian to the end Famennian. As well, a diverse chondrichthyan fauna is present and shows a cosmopolitan nature for many species with strong temporal affinities to taxa in the Middle East and North Africa. Furthermore, the present study shows microvertebrates as potential environmental proxies as the chondrichthyan taxa show consistent d18O values for different environments. This study indicates the usefulness of microvertebrates in biocorrelation across different facies and shows potential correlation between basin, fore-reef and platform environments. This work also illustrates the importance of integrating sedimentology, both outcrop and subsurface, palaeontology and biostratigraphy for interpreting Devonian- Carboniferous reef evolution.