Dating Quaternary events by luminescence

Luminescence techniques can provide ages for deposits undatable by routine geochronometric techniques (e.g., 14C, K-Ar, fission track). Two classes of events can be dated by luminescence methods: (I) growth of a mineral or its last cooling, and (II) the last exposure to sunlight. Within the past few years, significant advances in procedures, technology, and understanding of the thermoluminescence (TL) behavior of minerals have been made that place luminescence dating techniques on the verge of widespread application to Quaternary deposits. Most progress has come from studies of known-age material deposited under known conditions. Within class I, both distal and proximal tephra deposits have been dated, using TL techniques originally developed for pottery dating. Within class II, loess, buried soils, and waterlaid silts have been successfully dated. Means have been demonstrated for isolating and controlling several major sources of error, such as the type of TL instability known as anomalous fading, as well as the effects of uncertainty about the degree of zeroing of the luminescence signal in certain depositional environments. In particular, because of different sensitivities to light of the TL of quartz and feldspars, feldspars have been shown to be the preferred component for dating most unheated sediments. Of the competing TL methods for dating the last exposure to sunlight, the partial bleach (R-Gamma or R-Beta) technique, when properly applied, has been shown to yield the best results in general. Nevertheless, in future dating studies of unheated sediments, this laborious method may be displaced by a novel technique that uses laser light, rather than heat, to stimulate the luminescence that is a measure of the past ionizing radiation absorbed dose. This new optical (OSL) method of dating promises to be simple, sensitive, and speedy.