Towards ε-Precision of U-series Age Determinations of Secondary Carbonates

Abstract

In this thesis the measurement protocols and data corrections for U-series dating with the highest achievable precision on a MC-ICP mass spectrometer are described. U and Th isotope ratios of sample solutions with high [U] and [Th] above 6 ppt can be measured reproducibly on a 6 e-scale (e = 1·10−4). U and Th isotope ratios of sample solutions with moderate [U] and [Th] are routinely determined with 8 to 18 e-precision. Results from measurements on various mass spectrometers were reproducible within their uncertainties, confirming the credibility of our dating results. Using high-resolution dating, the beginning of the penultimate deglaciation at the Spannagel Cave (Northern Alps) was dated delayed by 2,000 a at 133,183 ± 833 a BP achieving a higher precision of 400 a compared to formerly published results. This age interval is broadly coincident with the rise in boreal summer insolation and seems more concordant to Milankovitch hypothesis. Furthermore, the growth rates of two stalagmites from adjacent caves in the Swiss Alps were compared on a resolution of Δt = 220 a in the last 6,500 a. Both growth rates show individual growth histories, however when combined with a tree-line record, provide additional insights into the local vegetation history.