A NOVEL METHOD FOR TRACE ELEMENTAL ANALYSES OF SPELEOTHEMS USING µ-XRF

Trace element ratios in speleothems (Sr/Ca, Mg/Ca, Ba/Ca) have been used to interpret the hydrogeochemical processes in the epikarst zone as well as the partitioning that occurs at the calcite-water interface. During periods of low rainfall, trace element ratios generally increase as a result of the longer residence time of water in the soil and epikarst zones. High-resolution time series analyses of these elements in speleothems provide evidence for changing paleohydrological and geochemical conditions over time.

The conventional methods of trace metal analysis of speleothems- Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICPMS) and Inductively-Coupled Plasma Optical Emission Spectroscopy (ICP-OES) have yielded many high-quality data sets. However, these methods can be expensive, time-consuming and require the destruction – either by ablation, micro-milling, or powdering – of speleothem samples. The many caveats of these conventional methods have led to the search for a viable alternative – one that will provide the same high-resolution results, but that is affordable, rapid, and non-destructive.

Presented here are preliminary results using µ-X-ray Fluorescence Spectrometry. The Brüker-AXS ARTAX µ-XRF spectrometer permits a multi-element analysis from Na to U with a spatial resolution of 70 µm. The method is non-contact and non-destructive, therefore preserving the sample for additional analyses (e.g. stable isotopes). A simple calibration method for Sr/Ca using pressed mixed powders will be described.

It will be demonstrated that µ-XRF is an important tool in trace element analysis of speleothems and a viable alternative to conventional methods. Sr/Ca ratios were obtained for multiple speleothems and serve as a preliminary test of µ-XRF suitability. Analyses of variable count times, temporal and spatial reproducibility along transects, and a comparison between µ-XRF spectra and ICP-OES spectra for the same transect of a speleothem growth axis will be presented. In addition, ARTAX multi-transect area-mapping will demonstrate trace element abundances along both calcite bands and the growth axis.