Journal
of Cave and Karst Studies
- ISSN 1090-6924
Volume 66 Number 1: 3-8 - April 2004
A publication of the National Speleological Society
Application
of high-resolution X-ray computed tomography in determining the suitability
of speleothems for use in paleoclimatic, paleohydrologic reconstructions
Patrick J. Mickler, Richard A. Ketcham,Matthew W. Colbert and Jay L. Banner
Abstract
The isotopic and elemental compositions of speleothems can be used as proxies to elucidate past climate changes. Speleothem material is precious, however, and its use in such climate studies must be balanced against the need to preserve fragile cave environments. Accordingly, accurate assessment of the internal speleothem stratigraphy can provide insight into: 1) Overall sample quality for paleoclimate studies, and 2) the position of the central growth axis of the sample prior to destructive sample preparation, which involves bisecting by sawing the sample along its growth axis. Chemical and isotopic samples taken along the growth axis have the greatest potential to reflect the composition of the water from which the speleothem precipitated. The growth axis of speleothems cannot be reliably determined by visual inspection of uncut specimens, and incorrect bisections may compromise their applicability as geochemical climate proxies.
High-resolution X-ray computed tomography (HRXCT) is a non-destructive technique that can identify the position of the growth axis in speleothems by detecting subtle changes in calcite density between growth bands. HRXCT imagery of these variations can be animated as ‘stacks’ of slices and rendered in three dimensions. Such imagery can be used to identify the best plane along which the speleothem should be sectioned for sampling. These images may also reveal samples that have been extensively altered during their history, making them unsatisfactory for climatic studies. Additionally, HRXCT imagery can be used to determine the volume and location of large fluid inclusions for use in reconstructing the H and O isotopic composition of paleoprecipitation.
This page last updated:
5 November, 2004 5:46
Web Author: Jim Pisarowicz