Comminution dating is a developing radiometric dating technique based on the disequilibrium between uranium isotopes in fine-grained sediments.DePaolo, D.J., Maher, K., Christensen, J.N. and McManus, J., 2006. Sediment transport time measured with U-series isotopes: results from ODP North Atlantic drift site 984. Earth and Planetary Science Letters, 248(1), pp.394-410.
Theory An alpha-particle with a finite energy is emitted during the alpha decay of uranium-238 to uranium-234 via the short-lived thorium-234. In order to conserve momentum, the daughter nuclide, uranium-234, is recoiled. In silicate mineral grains with high surface-area-to-volume ratios, a certain fraction of nuclides may be directly ejected into the surrounding medium (water or air).
Applications Comminution dating has been applied to dating of: Ice cores.Aciego, S., Bourdon, B., Schwander, J., Baur, H. and Forieri, A., 2011. Toward a radiometric ice clock: uranium ages of the Dome C ice core. Quaternary Science Reviews, 30(19), pp.2389-2397. Palaeochannel deposits.Dosseto, A., Hesse, P.P., Maher, K., Fryirs, K. and Turner, S., 2010. Climatic and vegetation control on sediment dynamics during the last glacial cycle. Geology, 38(5), pp.395-398. Alluvial fans.Lee, V.E., DePaolo, D.J. and Christensen, J.N., 2010. Uranium-series comminution ages of continental sediments: Case study of a Pleistocene alluvial fan. Earth and Planetary Science Letters, 296(3), pp.244-254.
Developments
In order to calculate reliable comminution ages, authigenic uranium must be removed from the surface and pores of silicate minerals.Martin, A.N., Dosseto, A. and Kinsley, L.P., 2015. Evaluating the removal of non-detrital matter from soils and sediment using uranium isotopes. Chemical Geology, 396, pp.124-133. used an etching procedure to evaluate the completeness of existing sample pre-treatment procedures. It was found that further chemical pre-treatment steps are required to completely remove authigenic uranium from sediments. Further work is required to test this approach of samples from different depositional environments.
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