Cosmogenic nuclide inheritance as an archive of erosional processes

Abstract:

The advent of cosmogenic nuclide (CN) geochronology in the geosciences has provided a means for constraining Quaternary geomorphic processes. However, estimates of surface age and process rate have traditionally been hampered by the competing influences of surface erosion and inheritance, which bias measured nuclide concentrations to lower and higher values, respectively. We’ve developed a mechanistic model for the inheritance contribution attributable to erosional processes in the source catchment as measured in surface clast datasets (Prush and Oskin, 2020). This model combines the competing influences of steady background erosion with episodic landsliding to provide a flexible inheritance model that can be applied to clast datasets with a spectrum of erosional histories. For surface clast datasets sourced from the steep, arid catchments of the Tibetan Plateau, the best-fit inheritance models indicate high rates of landsliding relative to steady background erosion, consistent with the dry climates and steep topography within this environment. Relatively high rates of landsliding are also reflected in datasets sourced from arid environments in the southwestern U.S., such as Death Valley. In contrast, the best-fit inheritance models for clast datasets sourced from more temperate environments, such as the eastern Sierra Nevada, indicate an increased proportion of sediment flux by steady background erosion. The immediate implications of this model include younger surface ages, generally, resulting in faster rates when applied to tectonic problems. Where multiple geochronometers are available our model also reconciles disparate geochronological surface ages, a chronic issue in surface age dating. In future applications, our model may be applied to sedimentary archives to deduce past erosion rates and to develop a time-integrated history of the competing influences of landslides and steady erosion processes, and their climatic and tectonic drivers, at catchments globally.