Diagenesis of speleothems and its effect on the accuracy of 230 Th/U-ages

Abstract Speleothems can be precisely dated by U-series disequilibrium methods. One basic assumption of the 230Th/U-dating method is that the system remains closed and U and Th isotopes are neither lost nor added after deposition. For stalagmites, this requirement is usually fulfilled due to their protected environment in caves. However, undersaturated drip water may lead to diagenesis of speleothem CaCO3 and altered 230Th/U-ages. Here we present a detailed petrographic investigation using thin sections and 230Th/U-ages of a stalagmite from the Riesenberghohle, northern Germany, which grew during Marine Isotope Stages 5e, c and a. The occurrence of a mosaic fabric in large parts of the stal…