ABSOLUTE CHRONOLOGIES IN ARID AND SEMI-ARID ENVIRONMENTS USING OPTICALLY STIMULATED LUMINESCENCE

Optical dating of quartz grains has proven itself a reliable and accurate method for determining the absolute age of deposition of Quaternary sediments over the age range from a few 10's of years to in excess of 100,000 years. The method dates the last exposure of sedimentary grains to daylight, and is thus ideally suited to many deposits from arid and semi-arid environments which typically have high rates of insolation. The last decade has seen significant improvements in luminescence dating techniques, with much greater sophistication in the methods that are available to assess whether ages are reliable or not (Duller 2004).

Desert dunes remain the most straightforward material and can be used to provide a chronology for climatic changes provided that the stratigraphic record is complete. Recent improvements in luminescence techniques have meant that for these materials it is now possible to determine ages as recent as a few tens of years, making it feasible to determine rates of geomorphological processes in arid environments. Waterlain sediments from arid and semi-arid environments are more complex because of the possibility that the grains were not adequately exposed to daylight at deposition to remove any pre-existing luminescence signal. Information on insufficient bleaching can be obtained by the measurement of different components of the signal and by single grain measurements.

Optical dating, together with evidence of structure provided by ground-penetrating radar, has been used to provide an assessment of the rate of migration of various geomorphological components of dunes from the northern Namib sand sea in the interval from the last few decades to the mid-Holocene.

Duller, G. A. T. (2004). Luminescence dating of Quaternary sediments: recent developments. Journal of Quaternary Science 19, 183-192.