Dating methods: geochronology and

Two exciting areas of research are highlighted in this summary of recent publications in the field of geochronology. These lie at opposite ends of the timescale that is normally of interest to geomorphologists, but both have a common interest since they make it possible to quantify rates of landscape evolution in ways which have been difficult, if not impossible, previously. The first area concerns the developments that have occurred in the use of cosmogenic isotopes, and particularly their use over periods from 104 to 107 years, while the second looks at two absolute dating techniques that are now available for quantifying geomorphological processes within the last 103 years. This is a time interval for which absolute dating control has proved problematic for many years, since it lies beyond the range of many historical data sources and aerial photo coverage, and beyond the limit of 210Pb or 137Cs measurements. Over this time period radiocarbon results are significantly affected by reservoir effects and fluctuations in production rates. I Cosmogenic nuclides The use of cosmogenic isotopes in geochronology is not new. These are isotopes produced in the natural environment as a result of the bombardment of the earth by high-energy gamma rays, or cosmic rays. Radiocarbon dating, probably the most commonly used absolute dating method, is based upon the measurement of 14C, which is produced in the upper atmosphere as a result of cosmic ray interaction with 14N. However, over the last 10–15 years a whole suite of new methods has been developed that exploits the interaction of cosmic rays with lithological materials at the earth’s surface. These involve a range of different target atoms and the production of a range of different cosmogenic isotopes (e.g., 10Be, 21Ne, 26Al, 36Cl). The interpretation of th