Combining cosmogenic nuclide depth profiles and in situ 14C to measure erosion-adjusted exposure ages of sedimentary landforms.

Abstract

In situ cosmogenic ¹⁴C offers a unique window into the recent erosion and burial histories of sedimentary landform surfaces due to its short mean life (ca. 8,223 yr) relative to other terrestrial cosmogenic nuclides (TCNs). This short mean life makes ¹⁴C sensitive to erosion and burial processes over the past 25–30 kyr – timescales that are poorly resolved by longer-lived nuclides such as ¹⁰Be and ³⁶Cl. Here I present a novel approach to estimate erosion rates on late Pleistocene alluvial fan and shoreline surfaces in Panamint Valley, California, by measuring ¹⁴C saturation concentrations in detrital quartz sand from amalgamated sediment samples collected just below the soil mixing zone. Sample locations were guided by soils and geomorphic observations at four sites. I also describe the development and testing of a ¹⁴C extraction line at Dalhousie University, including validation against the known inter-laboratory standard, CRONUS-A. Erosion rate uncertainty improved by up to 50% compared to soils geomorphology-based estimates, providing tighter constraints on ¹⁰Be depth profile exposure ages at the same sites. Comparison of ¹⁴C-derived erosion rates with independent ¹⁰Be and ³⁶Cl depth profile ages suggests that previous field-based erosion rate estimates may have significantly underestimated uncertainty in paleo-erosion histories. These results demonstrate the utility of in situ ¹⁴C saturation measurements as a practical and powerful complement to conventional TCN depth profile dating of alluvial fan surfaces in arid environments, with broader implications for landscape evolution studies in tectonically active regions.