U-series dating

Abstract

Radioactive disequilibrium in the uranium decay series (either238U or235U) is caused by fractionation processes that can occur between isotopes within the chain based on differences in their nuclear or chemical properties. Because the intermediate daughter products are themselves radioactive, the U-series nuclides will tend to return to a state of secular equilibrium at rates that depend on the decay constants of each isotope. As a result, a number of geochronometers have been developed that can be used to date a wide variety of materials at timescales ranging from decades to over a million years. These methods have been devised to date near-surface processes including deposition of authigenic and biogenic precipitates, development of soils, rates of rock weathering and rates of mineral comminution, deposition of young sediments, and sediment transport times, as well as processes occurring at depth within the crust and mantle including dating of young volcanic rocks or dating of crystal residence times in magma chambers. Emerging studies have taken advantage of advances in analytical capabilities that allowed analysis of low-level samples with greater precision or higher spatial resolution. The field of U-series dating has now become a mature technique for dating Quaternary geological or archeological materials of increasing diversity.