Weathering and erosion encapsulate a diverse suite of processes that sculpt landscapes, generate soil, and deliver sediments, nutrients, and solutes to streams and the oceans. Quantifying chemical and physical erosion rates is important across a diverse range of disciplines in geology, geomorphology, and biogeochemistry. Yet, until recently, erosion rates have been difficult to quantify over the timescales of soil formation and transport. This article describes how cosmogenic nuclide methods have provided a wealth of new opportunities for dating surfaces, measuring denudation rates, and quantifying chemical erosion rates.
Cosmogenic nuclides are produced in mineral grains by secondary cosmic rays that penetrate the topmost few meters of soil and rock at the ground surface. Because cosmogenic nuclide production rates are rapidly attenuated with depth, the concentration of cosmogenic nuclides in a mineral grain tells us how much time it has spent near the surface or how rapidly material has been removed from above it (Lal, 1991). From the perspective of cosmogenic nuclide production, denudation can be considered simply in terms of the translocation of mass as mineral grains are eroded from depth, detached from bedrock, and transported through soils by physical and chemical processes.
Four general types of weathering-related problems that can be addressed with cosmogenic nuclides will be discussed. These include (1) surface exposure dating of rock and soil, (2) determining erosion rates of rock and soil from samples at the surface and at depth, (3) determining spatially averaged erosion rates from sediment, and (4) inferring chemical ero- sion rates using a geochemical mass balance approach. Cosmogenic nuclides can also be used in many other ways, including dating sediment burial by radioactive decay. The interested reader is referred to the article on burial dating in archaeology and paleoanthropology by Granger (Chapter 14.7).
Granger, D.E. and Riebe, C.S. (2014): Cosmogenic Nuclides in Weathering and Erosion. in Treatise on Geochemistry, Volume 5: Surface and Ground Water, Weathering, and Soils. (2nd edition): 401-436. DOI: 10.1016/B978-0-08-095975-7.00514-3
This Paper/Book acknowledges NSF CZO grant support.