Linus Dep, David Elmore, Stephan Vogt, Pankaj Sharma, Michael Bourgeois, Adam Dunne
Submitted to Nature (1997)
Events that shape terrestrial landforms include glacial erosion, volcanism, floods, earthquakes, landslides, impact craters, and tsunami. Determining accurate absolute ages for these events is important for studies of quaternary geomorphology, climate change, magma production rates, and predictions of natural disasters. Such events can bring buried material to the surface in a relatively short time. Absolute exposure ages of freshly exposed rock surfaces can be determined by measuring the accumulation of cosmogenic nuclides in rock surfaces. However, a major stumbling block for determining reliable ages has been uncertainties in shielding of cosmic rays by material that has eroded since the event being dated. Here we demonstrate a new method for simultaneously determining the absolute exposure age and erosion rate of a rock based on the special depth dependence of 36Cl produced from neutron capture of 35Cl. Although results are best obtained form a 0.5 to 1 meter rock core, similar information can be obtained by measuring 36Cl in tow or more mineral fractions separated from surface samples.