U-SERIES DATING OF CONTINENTAL SEDIMENTS: RECENT PROGRESSES AND APPLICATIONS

Among the many numerical dating tools of the Quaternary, those based on uranium-series disequilibria enjoy the widest range in terms of applicable material even if we limit ourselves to considering only the ²³⁰Th-²³⁴U-²³⁸U systematics, as we shall do so in this presentation. Here, we will further confine our discussion to the dating of sedimentary deposits from the continental environment. As the ²³⁰Th-²³⁴U method dates the time of U incorporation into a given sample, the nearly ubiquitous presence of traces of uranium in natural deposits explains the method's wide applicability. In this regard, recent advancement in the analytical capability (precision and sensitivity) of the long-lived U and Th isotopes of ²³⁸U, ²³⁴U, ²³²Th and ²³⁰Th using mass spectrometry has played an important role. In addition to having improved the age precision, this atom-counting technique has significantly expanded the dating range of 10-350 ka commonly quoted for the method when the radiation-counting technique of alpha-spectrometry is used. Examples will be given to show efforts in the dating of lake evaporites and carbonate, groundwater-precipitated and pedogenic carbonate and silica, and permafrost peat deposits. These efforts entail attempts at coping with the problem of correcting the non-in-situ produced ²³⁰Th often present in terrestrial deposits, using isochron schemes or micro-sampling of high U/Th aliquots to minimize the correction effect on ages. The general validity of results through external and internal cross-checks will also be examined.