Uranium-series disequilibrium dating using energy-filtered ICP magnetic sector multiple collector mass spectrometry

The uranium-series disequilibrium dating of pure and impure carbonate has been investigated using energy-filtered MC-ICPMS (Multiple Collector ICP Mass Spectrometry). A new chemical procedure using TRU-Spec resin has been developed, which achieves both excellent chemical yields and a clean separation of Th and U from one another and other elements. High precision uranium and thorium isotopic analytical protocols have also been established using MC-ICPMS.; Mass spectrometric dating results of microatolls from the South China Sea are obtained for the first time in this study. U-Th ages for these Holocene corals are consistently older than their corresponding 14C ages. These ages agree well with independently determined histories of local sea-level changes. High 232Th contents in these samples are common which is considered to be a result of mechanical entrapment of very fine-grained crustal materials inside coral skeletons. The derived average initial 234U/238U ratio is consistent with other reported values within analytical errors. Our results also show that the sea level history of the South China Sea region is complicated and shows high frequency variations on a timescale of 1,000 years.; The total sample dissolution method for impure carbonate dating is theoretically and experimentally investigated. It is concluded that derivation of a valid age requires that the authigenic end member is completely free of any 232Th or that the other end member has a very large 232Th/ 238U ratio compared to that of the authigenic component. A good linearity for total sample dissolution regression lines is a necessary condition but does not guarantee the validity of a derived age.; Fossil land snail shells collected from paleosols and loess in the Chinese Loess Plateau were found to contain enough uranium to allow the accurate determination of 230Th ages, indicating uranium uptake soon after burial. Large quantities of 232Th are commonly observed for all snail shell samples. Three correction models are proposed to estimate the ages for fossil snail shells from the Chinese loess plateau.