Ordovician temperature trends: constraints from δ¹⁸O analysis of conodonts from New South Wales, Australia

The argument that temperature change and biological change during the Ordovician are correlated and, perhaps, causally related has been advanced by measurements of δ¹⁸O_phos values on conodont apatite, a phase more resistant to diagenetic alteration than carbonates. However, the available conodontδ¹⁸O_phos 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 δ¹⁸O_phos values from conodont apatite as well as δ¹³C and δ¹⁸O_calcite values from bulk carbonate from New South Wales, Australia. New results span most of the Ordovician and include the first Late Ordovician phosphate δ¹⁸O values from the Australian continent. The data from New South Wales show an ∼1. 5‰_VSMOW increase in δ¹⁸O_phos 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 δ¹⁸O_phos values to local paleoceanographic effects on the seawater δ¹⁸O value.