An Atlas of Speleothem Microfabrics
L. Bruce Railsback, Department of Geology, University of Georgia.
DIAGENESIS AND COLUMNAR CALCITE
This section presents images from several different speleothems in which there is evidence that columnar calcite has formed via alteration of pre-existing non-columnar fabrics. The origin of columnar calcite in speleothems has been the subject of vigorous debate (e.g., Kendall (1993) and González et al. (1993)). The point of this section is not to argue that all columnar calcite forms diagenetically, but to show that at least some columnar calcite has evidence of an origin via recrystallization of other fabrics.
The significance of recrystallization to paleoclimatological interpretation of speleothems is that many geochemical characteristics of a speleothem may be altered during recrystallization. U-series ages may be exaggerated by recrystallization, because U is more mobile than Th during diagenesis. Radiocarbon ages may be altered if C is mobilized during recrystallization. Stable isotope compositions, particularly of oxygen, may be altered too. For these reasons, recognition of recrystallization is critical to insure that flawed data are not included in paleonvironmental studies.