Geomorphological applications of cosmogenic isotope analysis

Abstract

Cosmogenic isotope analysis involves the measurement of cosmogenic nuclides that have accumulated in the upper few metres of the Earth’s surface as a result of interactions between cosmic rays and target elements. The concentrations of these cosmogenic nuclides can provide quantitative estimates of the timing and rate of geomorphic processes. In dating applications the concentration of cosmogenic nuclides is interpreted as reflecting the time elapsed since a surface exposure event. However, over most of the Earth’s surface for most of the time the landsurface experiences incremental denudation and in these circumstances cosmogenic nuclide concentrations are related to the rate of denudation. Applications of event dating using cosmogenic isotopes include constructional landforms such as volcanic and depositional features, fault displacement, meteorite impacts, rapid mass movement, bedrock surfaces rapidly eroded by fluvial or wave action or exposed by glacial retreat, and the burial of sediment or ice. Strategies for quantifying rates of incremental change include estimates of denudation rates from site-specific samples and from fluvial sediment samples reflecting catchment-wide rates, and measurements of cosmogenic nuclide concentrations in soils and regolith to quantify rates of rock weathering. The past decade has seen a rapid growth in applications of cosmogenic isotope analysis to a wide range of geomorphological problems, and the technique is now playing a major role in dating and quantifying rates of landscape change over timescales of several thousands to several millions of years.