Terrestrial cosmogenic nuclide dating
Concentrations of TCNs are lowest in transported sediment in catchments that have the highest erosion rates (see Portenga and Bierman, 2011 for more details).
Erosion rates based on strath terraces younger than about 35,000 years likely reflect sporadic and accelerated erosion.Until recently, rates of erosion has been estimated by calculating the volumes of sediment produce by erosion and trapped in natural (e.g. reservoirs) traps, or direct measurements of sediment loads in rivers.However, accurately measuring sediment volumes in natural traps is challenging because often the geologic record is incomplete, which may lead to underestimates.Also direct measurements of sediment loads in rivers provide only a short time glimpse at erosion rates, that may be human influenced.
Moreover, studies have shown that rates of erosion may vary considerably over the very short timescale of the study due contrasting weather conditions from one year to the next associated with a monsoon climate.There are lots of caveats that need to be considered when determining an TCN age, for example, if the surface was shielded from cosmic rays by a cover of sediment or soil until recently.