A project undertaken at The University of Melbourne, and supervised by Prof Russell Drysdale.
Australia’s arid zone is one of the nation’s most iconic features, hosting a uniquely adapted flora and fauna, and a geology and geomorphology of remarkable antiquity and geoheritage value. Surprisingly, however, we know very little of the region’s climate history. There is evidence in the landscape that today’s arid interior experienced much wetter conditions in the recent past. How regular were these past ‘pluvial’ episodes, and what caused them? The main obstacle to unravelling this history is the incomplete nature of the environmental record, and the problems of establishing the age of what fragments of that evidence remain.
In this project, we overcome these issues by interrogating a unique series of calcite mineral deposits (called speleothems) from caves in the Flinders Ranges to uncover the hydrological history of the southern margin of Australia’s arid zone. Speleothems only grow when there is sufficient rainfall to enable water to percolate through the overlying bedrock and enter caves, where it forms stalagmites and stalactites. Episodes of speleothem formation provide unequivocal evidence of past wet conditions.
We will conduct a large program of environmentally sensitive speleothem sampling to reconstruct past episodes of regional moisture abundance covering the last half a million years. Each speleothem will be radiometrically dated, enabling us to place each growth phase onto an absolute timescale. By placing this history into a precise time frame, we will be able to compare our results with changes in Earth’s orbital geometry to determine whether particular configurations act like a switch on the region’s hydrological system. We will investigate a unique assemblage of subaqueous speleothems, which only grow when regional waters tables are sufficiently high. Dating of these speleothems will not only tell us when it was wet in the past, but their geochemistry may also unlock vital information about the region’s temperature history over the last 100,000 years.
The results of our study will provide unprecedented insights into what drives our natural climate system, and how this links with concurrent changes observed elsewhere on Earth. This will provide a long-term hydrological context in which to place our rich natural history, including the capstone events of human arrival/dispersal and megafauna extinction.