The antiquity of Nullarbor speleothems and implications for karst palaeoclimate archives

Jon D. Woodhead,J. M. Kale Sniderman,Paul Devine,Susan White,Nicholas White,Russell N. Drysdale,Roland Maas,John Hellstrom

doi:10.1038/s41598-018-37097-2

Abstract

Speleothems represent important archives of terrestrial climate variation that host a variety of proxy signals and are also highly amenable to radiometric age determination. Although speleothems have been forming on Earth for at least 400 million years, most studies rely upon the U-Th chronometer which extends only to the mid Pleistocene, leaving important questions over their longer-term preservation potential. To date, older records, exploiting the advantages of the U-Pb chronometer, remain fragmentary ‘snapshots in time’. Here we demonstrate the viability of speleothems as deep time climate archives by showing that a vast system of shallow caves beneath the arid Nullarbor plain of southern Australia, the world’s largest exposed karst terrain, formed largely within the Pliocene epoch, with a median age of 4.2 Ma, and that, in these caves, even the most delicate formations date from this time. The long-term preservation of regional-scale cave networks such as this demonstrates that abundant speleothem archives do survive to permit the reconstruction of climates and environments for much older parts of Earth history than the ~600 ka period to which most previous studies have been limited.

Highlights

Speleothems are increasingly recognised as critical sources of climate history
The ~600 ka limit of the U-Th decay chain, the most widely employed chronometer, provides a biased view of the utility of speleothem archives and the cave levels/systems in which they form - a situation analogous to the radiocarbon limit, which has restricted our understanding of Quaternary climate and environmental change
The U-Pb chronometer, which is able to date suitable minerals of any age, has been applied to a handful of speleothems demonstrating that, under certain conditions, ancient samples can be preserved from the Pleistocene[7,8,9], Pliocene[10,11], Early -and Mid-Miocene[12] and even the Permian[13] (Supplementary Fig. S1)

Summary

Introduction

Speleothems (secondary cave calcite deposits including stalagmites, stalactites and flowstones) are increasingly recognised as critical sources of climate history. The U-Pb chronometer, which is able to date suitable minerals of any age, has been applied to a handful of speleothems demonstrating that, under certain conditions, ancient samples can be preserved from the Pleistocene[7,8,9], Pliocene[10,11], Early -and Mid-Miocene[12] and even the Permian[13] (Supplementary Fig. S1).

Results

Conclusion