High-resolution palaeoenvironmental information from southeast Australian speleothems

Speleothems, chemical cave deposits such as soda-straw stalactites, stalagmites and flowstones, have great potential as archives of high-resolution terrestrial palaeoenvironmental change at both short and long term temporal scales. In this study temporal control is achieved using various high precision radiometric techniques such as TIMS 230Th/234 U dating, AMS radiocarbon dating, and 210Pb excess dating, the latter two methods used to investigate contemporary speleothem material. An additional method adopted only with certain samples, but showing considerable promise, is autocorrelation of annual variations in speleothem minor element concentrations. 43 new TIMS 230Th/234 U speleothem age estimates from several karst areas in Tasmania are presented as a cumulative frequency distribution and are compared with some previously published and unpublished speleothem data from southeast Australian continent. The distribution of ages allows some comments to be made on past environmental conditions and their effect on speleothem growth in southeastern Australia. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been used to investigate minor element variations along the whole growth axis of several speleothems. Some soda-straw stalactites are found to contain quasi-periodical variations in their minor element composition, in some cases it is in phase with surface ridges, ie annual banding, sometimes visible on the surface. Measurements of the surface ridging using dendrochronological equipment allow a temporal framework to be developed and comparisons to be made between this chronology and one established using the annual cyclicity of certain minor elements. The chronologies agree very closely, indicating that soda-straw stalactites can potentially provide annually resolved records. Measurements of the minor element and stable isotope composition of flowstone material have been taken in order to provide records of palaeoenvironmental change in areas not previously studied in southeastern Australia using speleothems as an information source.