A geologically constrained Monte Carlo approach to modeling exposure ages from profiles of cosmogenic nuclides: An example from Lees Ferry, Arizona

作者：Hidy Alan J^*; Gosse John C; Pederson Joel L; Mattern Jann Paul; Finkel Robert C

来源：Geochemistry Geophysics Geosystems, 2010, 11(9): Q0AA10.

DOI：10.1029/2010GC003084

• (10)Be
• desert pavement
• TCN
• Grand Canyon
• alluvial fan
• active tectonics

We present a user-friendly and versatile Monte Carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides (TCNs). Our program (available online at http://geochronology.earthsciences.dal.ca/downloads-models.html) permits the incorporation of site-specific geologic knowledge to calculate most probable values for exposure age, erosion rate, and inherited nuclide concentration while providing a rigorous treatment of their uncertainties. The simulator is demonstrated with (10)Be data from a fluvial terrace at Lees Ferry, Arizona. Interpreted constraints on erosion, based on local soil properties and terrace morphology, yield a most probable exposure age and inheritance of 83.9(-14.1)(+19.1) ka, and 9.49(-2.52)(+1.21) x 10(4) atoms g(-1), respectively (2 sigma). Without the ability to apply some constraint to either erosion rate or age, shallow depth profiles of any cosmogenic nuclide (except for nuclides produced via thermal and epithermal neutron capture, e. g., (36)Cl) cannot be optimized to resolve either parameter. Contrasting simulations of (10)Be data from both sand-and pebble-sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with TCN depth profiles and, when possible, sand-not pebbles-should be used for depth profile exposure dating.

• 出版日期2010-9-2