MID-LATITUDE SOUTHERN HEMISPHERE TEMPERATURE CHANGE AT THE END OF THE PALAEOGENE GREENHOUSE

The Eocene-Oligocene (E/O) boundary marked the onset of permanent Antarctic glaciation and was the most important Cenozoic global transition from a ‘greenhouse’ to an ‘icehouse’ world. The magnitude of the palaeotemperature and ice volume change across the Eocene-Oligocene transition has been the focus of much debate. Our new palaeomagnetic results, together with biostratigraphic data, confirm the position of the E/O boundary directly above the clay-rich Blanche Point Formation, South Australia. δ¹⁸O, δ¹³C, and Mg/Ca analysis of well-preserved benthic foraminifera suggest that the studied sequence includes Step 1 of the major stable isotopic shift encompassing the E/O boundary, which provides the first high-resolution, shallow water record of palaeotemperature change across Step 1 from the region. Results do not indicate that any significant ice volume change occurred across Step 1. Shallow water temperature dropped ~2 °C across Step 1 at the study site, a similar temperature change to published shallow water results across this interval. Gradients of shallow water temperature with latitude before and after Step 1 are highly variable. This highlights the need for consistent and suitable methods to clean foraminiferal tests prior to Mg/Ca analysis and for palaeotemperature calibrations to be based on better quality data. This study provides a proof-of-concept that clay-rich, Palaeogene, marginal marine sediments, that are presently terrestrially exposed, can contain excellent palaeoclimatic records.