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G-Cubed: Geochemistry, Geophysics, Geosystems

 

Keywords

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

Index Terms

  • Geochronology: Cosmogenic-nuclide exposure dating
  • Geochronology: Quaternary geochronology
  • Tectonophysics: Tectonics and landscape evolution
Abstract
Cited By (2)
 

Abstract

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, VOL. 11, Q0AA10, 18 PP., 2010
doi:10.1029/2010GC003084

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

Alan J. Hidy

Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada

John C. Gosse

Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada

Joel L. Pederson

Department of Geology, Utah State University, Logan, Utah 84322-4505, USA

Jann Paul Mattern

Department of Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada

Robert C. Finkel

Earth and Planetary Science Department, University of California, 371 McCone Hall, Berkeley, California 94720-4767, USA

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 10Be 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 × 104 atoms g−1, respectively (2σ). 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., 36Cl) cannot be optimized to resolve either parameter. Contrasting simulations of 10Be 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.

Received 17 February 2010; accepted 29 June 2010; published 2 September 2010.

Citation: Hidy, A. J., J. C. Gosse, J. L. Pederson, J. P. Mattern, and R. C. Finkel (2010), A geologically constrained Monte Carlo approach to modeling exposure ages from profiles of cosmogenic nuclides: An example from Lees Ferry, Arizona, Geochem. Geophys. Geosyst., 11, Q0AA10, doi:10.1029/2010GC003084.

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