A mechanistic erosion model for cosmogenic nuclide inheritance in single-clast exposure ages

Abstract

Terrestrial cosmogenic nuclides (TCNs), produced by the bombardment of Earth's surface by cosmic rays, are widely used for age-dating and pacing surface processes. Sediments carry an inherited TCN concentration, useful for quantifying erosion and transport rates, but that must be subtracted when age-dating sedimentary landforms, such as alluvial fans. Here we present a mechanistic model of inheritance based on the contributions of episodic erosion by landsliding and steady, background erosion due to soil formation. The balance of these processes, revealed by the distribution of inheritance recorded by a population of individual surface clasts, affects rates of soil generation and the cycling of material through the Earth's critical zone – the surficial layer upon which all terrestrial life depends. We test our inheritance model on alluvial fan TCN datasets drawn from a global compilation of active-fault slip-rate studies. Inheritance-corrected landform ages are systematically younger than published ages. Our results reveal a consistent signature of spatiotemporal clustering of landslides, important for quantifying hazard and for understanding the coupling of physical and chemical erosion. Application of our inheritance model provides a rigorous approach to correcting landform ages for inheritance and reveals information on landslide frequency, with broad implications for hazard and land use.