Cave opening and fossil accumulation in Naracoorte, Australia, through charcoal and pollen in dated speleothems

Caves are important fossil repositories which provide records extending back over million-year timescales. While the physical processes of cave formation are well understood, the timing of initial cave development and opening-a more important parameter to studies of palaeontology, palaeoanthropology and archaeology-has proved more difficult to constrain. Here we investigate speleothems from the Naracoorte Cave Complex in southern Australia, with a rich record of Pleistocene vertebrate fossils (including extinct megafauna) and partly World Heritage-listed, using U-Th-Pb dating and analyses of their charcoal and pollen content. We find that, although speleothem formation began at least 1.34 million years ago, pollen and charcoal only began to be trapped within growing speleothems from 600,000 years ago. We interpret these two ages to represent the timing of initial cave development and the subsequent opening of the caves to the atmosphere respectively. These findings demonstrate the potential of U-Th-Pb dating combined with charcoal and pollen as proxies to assess the potential upper age limit of vertebrate fossil records found within caves. The presence of pollen and charcoal in radiometrically dated speleothems suggest the Naracoorte Cave Complex, South Australia, has been open to the atmosphere for the past 600,000 years, placing an upper limit on the accumulation of fossils inside the caves.

Automated summary

This study investigates the Naracoorte Cave Complex in Australia using dating techniques and analyses of charcoal and pollen. The results show that the caves began forming 1.34 million years ago and opened to the atmosphere 600,000 years ago, providing an upper limit on the accumulation of fossils.