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The Kuanyinchiao Formation (Hirnantian, Upper Ordovician), yielding the typical Hirnantia fauna, has commonly been accepted as representing cool-water sediments deposited during the glacial interval in the Hirnantian Global Boundary Stratotype [...]

This contribution reviews the newly revised biostratigraphy of Middle–Upper Ordovician marine shelf successions from the Junee–Narromine Volcanic Belt in central New South Wales, based on conodont studies from four areas covering the northern, central and southern sectors of the Belt. Seven conodont biozones ranging from the middle Darriwilian (Histiodella holodentata-Eoplacognathus pseudoplanus Biozone) to the lower Katian (Taoqupognathus blandus Biozone) are recognized in the Billabong Creek Formation exposed in the Gunningbland area. This includes the first known biostratigraphic succession in Australia that extends continuously from the middle Darriwilian to the basal Sandbian. These new data are crucial for a better understanding of the geological evolution of this region in central New South Wales, and for the enhanced correlation of Ordovician rocks throughout the Macquarie Volcanic Province, which hosts substantial porphyry Cu–Au mineral deposits. [ABSTRACT FROM AUTHOR]

A complete coral succession through the Ordovician-Silurian transition in South China reveals an adaptive phase during the Hirnantian glaciation, followed by an early survival phase and finally a late survival phase that persisted into the early Silurian. We demonstrate that a coral assemblage of latest Hirnantian to earliest Silurian age, remarkably similar to those from the Edgewood fauna known from Laurentia, occurs stratigraphically above the typical Hirnantian fauna. This, in combination with other evidence (e.g. brachiopods, lithology and chemostratigraphy), suggests the Edgewood fauna probably post-dated the early-middle Hirnantian glaciation, rather than being coeval with the older glacial-related Hirnantia fauna. Evidence from South China shows that the Edgewood fauna appeared in the very latest Hirnantian and extended into the middle Rhuddanian, considerably younger than previously believed. Such a new correlation necessitates a reassessment of the influence of the end-Ordovician glaciation on biotas. We argue that this major glaciation probably would have substantially affected the ecosystem even in tropical regions, as shown by the development there of the Hirnantia fauna or, alternatively, the presence of a conspicuous stratigraphic hiatus. This suggests a surprisingly rapid biotic recovery during the subsequent postglacial transgression, represented by the flourishing of comparatively diverse shelly faunas (e.g. the Edgewood fauna and the Cathaysiorthis brachiopod fauna) in nearshore shallow water environments from Laurentia to eastern peri-Gondwana terranes or blocks (e.g. South China). [ABSTRACT FROM AUTHOR]

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Oxygen isotopic ratios of conodont apatite can be a robust proxy for sea surface temperatures and provide important constraints on global climate. The oxygen isotopic composition of seawater is a function of local, regional, and global processes. To determine the relative importance of regional and local influences (and therefore make global inferences), it is necessary to document high resolution δ18O records from a variety of paleogeographic and environmental settings. Available conodont δ18Ophos records for the Ordovician, however, are biased towards North American samples, often come from multiple discontinuous sections, and tend to focus only on specific intervals (e.g., the Katian Stage). To extend the paleogeographic range and test the generality of Ordovician δ18Ophos trends, we measured δ18Ophos values from species-specific conodont assemblages from New South Wales, Australia. Our results from this region show that Early Ordovician δ18Ophos averages are ∼2‰ lower than those in the Late Ordovician and are consistently ∼2.5‰ lower relative to values reported from North America and central Australia. This offset suggests that regional environmental conditions influenced the δ18Ophos record from New South Wales. Despite evidence suggesting a departure from open ocean conditions, our results still show increasing δ18Ophos values through the Early Ordovician in agreement with documented trends from other regions. This similarity suggests that the δ18Ophos increase (documented on separate continental blocks and different environmental settings) reflects global cooling rather than a change in the oxygen isotopic composition of the Ordovician oceans and strengthens the argument that biodiversification and climate change in the first half of the Ordovician were related. [ABSTRACT FROM AUTHOR]

Late Ordovician conodont fauna from allochthonous limestones in the Wairuna Formation of the Broken River Province, north Queensland, contains 23 species typical of the deeper water Protopanderodus biofacies. Many of these species also occur in allochthonous limestones in the Malongulli Formation and correlative units of the Macquarie Volcanic Province in central New South Wales, and are also recognized in North and South China, which supports assignment of the Wairuna Formation conodont fauna to the Taoqupognathus tumidus-Protopanderodus insculptus Biozone of middle Katian age. Associated linguliformean brachiopods include species of Acrosaccus, Atansoria, Biernatia, Conotreta, Elliptoglossa, Hisingerella, Nushbiella, Paterula and Scaphelasma, which are identical to those known from the Malongulli Formation. Subtle paleoecological differences between faunas of the Malongulli Formation limestones (interpreted as forming in a deeper water peri-platform and upper slope environment) and those of the Wairuna Formation limestones imply that the latter were likely originally deposited on the shelf edge and subsequently reworked downslope. This study provides compelling paleontological evidence of strong affinity between Late Ordovician limestones of the Macquarie Volcanic Province and the Broken River Province, suggesting these regions (today separated by 1600 km) were linked by a volcanic island chain characterized by identical geochemical signatures in volcanic rocks associated with the limestones. [ABSTRACT FROM AUTHOR]

The argument that temperature change and biological change during the Ordovician are correlated and, perhaps, causally related has been advanced by measurements of δ18Ophos values on conodont apatite, a phase more resistant to diagenetic alteration than carbonates. However, the available conodont δ18Ophos records are discontinuous and are biased towards North American samples. To test the generality of global patterns and to expand the geographical range of studied regions, we document δ18Ophos values from conodont apatite as well as δ13C and δ18Ocalcite values from bulk carbonate from New South Wales, Australia. New results span most of the Ordovician and include the first Late Ordovician phosphate δ18Ophos values from the Australian continent. The data from New South Wales show an ~1. 5‰VSMOW increase in δ18Ophos values during the Early and Middle Ordovician. This pattern matches previously documented trends from Laurentia and central Australia, but values in New South Wales are consistently ~2. 5‰VSMOW lower than those from other regions. We attribute these low δ18Ophos values to local paleoceanographic effects on the seawater δ18O value. [ABSTRACT FROM AUTHOR]