Cosmogenic Be-10 Exposure Data for a Boulder Field in Zepp, VA

We have dated a boulder field in Zepp, VA using cosmogenic Be-10 exposure dating. Three samples taken from boulders at three elevations in the boulder field (804 m asl, 818 m asl, and 831 m asl) were processed at the Reston Cosmogenic Nuclide (RECON) Lab and measured via accelerator mass spectrometry at the Purdue Rare Isotope Measurement (PRIME) Lab. The results of this work are summarized in the file “Zepp_Exposure_Beryllium10_Odom.csv”. This file contains all relevant sample location data, as well as input variables for exposure age calculations. We employed the CRONUS v.3 exposure age calculator (Balco et al., 2008) to estimate exposure ages for these samples and report exposure ages derived using the LSDn time-dependent production rate scaling scheme (Lifton et al., 2014). From highest to lowest elevation, the boulders increased in exposure age: 53 ± 4 ka at 831 m, 84 ± 6 ka at 818 m, and 113 ± 7 ka at 804 m. These exposure ages are generally younger than boulder field exposure ages calculated ~330 km to the northeast at Hickory Run, PA (Denn et al., 2017), but older than the Last Glacial Maximum. They produce a linear inverse trend in elevation vs. exposure age (R2 = 0.998), indicating a mean downslope movement rate of approximately -0.45 m/ky for boulders. Future study will include Al-26 measurements to evaluate the possibility of boulder reorientation and changes in cosmic ray shielding over time.

References:

Balco, G., Stone, J. O., Lifton, N. A., & Dunai, T. J. (2008). A complete and easily accessible means of calculating surface exposure ages or erosion rates from 10Be and 26Al measurements. Quaternary Geochronology, 3(3), 174–195. https://doi.org/10.1016/j.quageo.2007.12.001

Denn, A. R., Bierman, P. R., Zimmerman, S. R. H., Caffee, M. W., Corbett, L. B., & Kirby, E. (2018). Cosmogenic nuclides indicate that boulder fields are dynamic, ancient, multigenerational features. GSA Today, 4–10. https://doi.org/10.1130/GSATG340A.1

Lifton, N., Sato, T., & Dunai, T. J. (2014). Scaling in situ cosmogenic nuclide production rates using analytical approximations to atmospheric cosmic-ray fluxes. Earth and Planetary Science Letters, 386, 149–160. https://doi.org/10.1016/j.epsl.2013.10.052