28 Quaternary Geology and Geomorphology (Posters)

Sunday, 4 November 2012
9:00 AM - 6:30 PM
Hall B

EXPOSURE DATING SURFACES IN COMPLEXLY SHIELDED ENVIRONMENTS WITH IN SITU-PRODUCED 10BE, 26AL, AND 14C: AN EXAMPLE FROM SOLOMON'S PILLARS, ISRAEL

Paper number: 28-11
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Terrestrial in situ cosmogenic nuclides (TCNs) are commonly utilized to exposure date a variety of landforms and deposits. Their use, however, hinges on the ability to determine time-averaged nuclide production rates applicable to the sampled material. For samples acquired from steeply dipping surfaces, or surfaces experiencing complex or extreme shielding, accurately determining production rates becomes challenging. This is largely because the majority of secondary cosmic radiation arrives from a small angular window around the zenith. Perturbations on surfaces and obstacles impeding this window can significantly affect the shielding and sample geometry corrections required to calculate sample-specific production rates. Thus, characterizing surface topology and proximal obstacles at a resolution required to accurately make these corrections in complexly shielded environments can be daunting.

In order to circumvent computation of shielding and sample geometry corrections, we present a three-nuclide approach using 10Be, 26Al, and 14C. Using a single quartz sample, exposure ages can be determined without knowledge of TCN production rates or surface erosion rate—eliminating the two largest sources of error in exposure age calculations. This method takes advantage of the fixed production ratios of these three nuclides within quartz and requires knowledge of inherited nuclide concentrations; however, where production rates are more easily quantified it can be inverted to calculate these inheritances. We demonstrate this approach with measurements taken from a near-vertical retreating cliff face and its conjugate boulder pile at Solomon’s Pillars, Israel.