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Abstract Many coastal areas of California and Oregon have emergent Quaternary marine terraces that have been assigned only indirect, approximate ages because of the paucity of suitable datable material for the U-series method, or because of the =40-ka limit of the radiocarbon-dating method. We report three thermoluminescence (TL) ages for clayey estuarine deposits from the San Simeon area of south-central California. A weighted mean TL age of 95±13 ka for clayey silt underlying marine deposits of the San Simeon ( Q ,) terrace suggests that this terrace correlates to oxygen isotope substage 5c (105 ka), or more likely substage 5a (80 ka). A single-analysis TL age of 230±70 ka for clayey beds in tilted estuarine deposits at San Simeon Bay is consistent with the available stratigraphic and age control for the underlying Careaga Formation (early Pleistocene or Pliocene) and the overlying Q p marine terrace (=60 ka). This TL age most probably compares to a time of high sea level at 200±20 ka (equivalent to marine oxygen isotope stage 7). The large analytical error in this TL age is consistent with deposition shortly before or after the =200 ka highstand of sea.

Luminescence techniques can provide ages for deposits undatable by routine geochronometric techniques (e.g., 14 C, 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.