『Abstract
　Constraints on the timing of weathering processes in the northern Australian regolith have been obtained by in situ measurement of U-series disequilibria in U-rich supergene Fe-oxy/hydroxides using a laser ablation-MC-ICPMS technique. This approach has permitted the measurement of ²³⁴U/²³⁸U and ²³⁰Th/²³⁸U activity ratios in finely crystalline Fe-oxy/hydroxides from the Ranger uranium deposit with sufficient precision and spatial resolution to constrain the age of formation of these phases and to develop a geochronological framework for weathering processes.
　²³⁰Th/²³⁸U systematics in the finely crystalline Fe-oxy/hydroxides yield ²³⁰Th-ages ranging from 60 to 350 ka. The most reliable ²³⁰Th-ages cluster between 122 and 216 ka, suggesting Fe-oxy/hydroxides formation and associated weathering, peaked during the previous 2 interglacial periods. This is supported by the ²³⁰Th-ages and isotope composition of pisolith (Fe-oxy/hydroxide pedogenic nodules) cores which are demonstrated to behave as closed systems. The U isotopic composition of the Fe-oxy.hydroxides is consistent with an origin from groundwater in equilibrium with dissolved uraninite. Secondary overprinting is evident in some samples as a large range in ²³⁴U/²³⁸U. Our results suggest that weathering intensity varies with global climate cycles and that, together with weathering events dated by ⁴⁰Ar/³⁹Ar of Mn-oxides elsewhere in northern Australia ([Feng,Y.X. and Vasconcelos,P., 2001. Quaternary continental weathering geochronology by laser-heating ⁴⁰Ar/³⁹Ar analysis of supergene cryptomelane. Geology, 29(7): 635-638.]), weathering rates in this region are orbitally forced.

Keywords: Weathering; Fe-oxy/hydroxides; LA-MC-ICPMS; U-decay series; Northern Australia; Orbital forcing』

1. Introduction
2. Experimental
　2.1. Samples
　2.2. Analytical methods
3. Results and discussion
　3.1. ²³⁴U/²³⁸U in microcrystalline Fe-oxy/hydroxides
　3.2. ²³⁰Th/²³⁸U in the microcrystalline Fe-oxy/hydroxides and their apparent ²³⁰Th-age
　3.3. U and Th isotopic composition of Fe-oxy/hydroxides as indicators of open or closed system conditions
　3.4. ²³⁸U-²³⁴U-²³⁰Th in pisoliths
　3.5. Implications for geochronology of weathering processes: the age of weathering?
　3.6. Orbital forcing of weathering processes?
4. Conclusions
Acknowledgements
Appendix A. Supplementary data
References