26Al-10Be-21Ne burial dating

Cosmogenic-nuclide burial dating relies on a pair of cosmic-ray-produced nuclides that are produced in the same rock or mineral target at a fixed ratio, but have different half-lives. For example, Al-26 and Be-10 are produced in quartz at Al-26:Be-10 = 6.75:1. If a sample of quartz is exposed at the surface for a time Al-26 and Be-10 concentrations reflect this ratio; if it is then buried below the penetration depth of cosmic rays, production stops and both nuclides decay. The half-life of Al-26 is half that of Be-10, so the Al-26/Be-10 ratio decreases over time and can be used to date the burial event. Because quartz derived from surface erosion and then buried by sediment accumulation is common, the method is widely applicable for dating Plio-Pleistocene clastic sediments. All (terrestrial) applications of burial dating so far have used the Al-26-Be-10 pair. Here we show that coupling cosmogenic Ne-21. which is also produced in quartz, with Al-26 or Be-10 should improve upon both the age range and accuracy of Al-26-Be-10 burial dating. We establish the feasibility of this approach by Ne-21 measurements at two sites that have already been dated using Al-26-Be-10 burial dating. Burial ages from all three nuclide pairs agree at both sites, which shows that currently accepted values for decay constants and production ratios are internally consistent. Thus, it is possible at present to increase the useful range of cosmogenic-nuclide burial dating by incorporating Ne-21. Fully realizing the potential improvements in accuracy would benefit from additional estimates of Ne-21/Al-26 and Ne-21/Be-10 production ratios that are independent of the Al-26 and Be-10 decay constants. (C) 2009 Elsevier B.V. All rights reserved.