THERMOLUMINESCENCE DATING: RADIOACTIVITY IN QUARTZ

Alpha activities measured for four quartz extracts indicate that, in some samples, the alpha dose-rate to the quartz due to radioactivity within the quartz can be significant. Uranium mapping of the quartz by neutroninduced fission tracks shows that the radioactivity is not homogeneously distributed.     

A NEW THERMOLUMINESCENCE DATING TECHNIQUE FOR HEATED FLINT*

A new thermoluminescence (TL) technique for determining the age of heated flint artefacts from archaeological sites is presented. It is a variant of the SAR protocol, which is usually used for OSL dating of sediment, but it is not based on a presumed model for fitting the dose–response curve. Dose recovery tests as well as comparisons with standard protocols show the accuracy of the new technique. It is found that the sensitivity of the thermoluminescence (TL) signal of flint in the orange–red waveband does not show severe changes due to the heating process while measuring the TL. This allows the application of a short SAR procedure, which requires only two dose points. The technique does not require as much instrument time as other SAR techniques, and thus is advantageous for dating very old samples. The major advantage of this new technique is the small amount of sample material required, which allows the dating of samples that are too small for standard TL dating techniques.     

THE EFFECT OF HF ACID ETCHING ON THE MORPHOLOGY OF QUARTZ INCLUSIONS FOR THERMOLUMINESCENCE DATING

The assumption of isotropic etching in hydrofluoric acid of quartz grains prepared for thermoluminescence dating has been tested by optical and scanning electron microscopy. We have found that the rate of etch is very irregular over the surface of many grains and that some grains are attacked much more severely than others. The uncertainty introduced into TL dating by this effect is discussed.     

THERMOLUMINESCENCE DATING OF STALAGMITIC CALCITE

The thermoluminescence (TL) method of dating stalagmitic calcite has been applied to twenty-seven samples from two paleolithic cave sites; Pontnewydd, Wales, and Caune de l'Arago, Tautavel, France. Environmental dose-rates were evaluated mainly by means of CaF₂ capsule burials. The ages of the stalagmitic samples were independently determined by means of the uranium series disequilibrium method. In general, good agreement is found between the TL and uranium series dates, which cover a range from approximately 15 000 to 300 000 years B.P. It is estimated that the TL method should extend to the order of a million years in good circumstances.     

CHARACTERIZATION AND THERMOLUMINESCENCE DATING OF PREHISTORIC POTTERY SHERDS FROM MILENA

This paper reports the results obtained applying absolute dating methodologies and mineralogical, petrographical and micropalaeontological characterization techniques to prehistoric pottery sherds varying in age from the Sicilian Middle Neolithic to Bronze Age. All samples came from the archaeological area of Milena (Caltanissetta, Sicily); those of the Bronze Age were found on a site with a precise stratigraphic succession. The investigation has contributed to the determination of an absolute chronology for the Milena prehistoric period. The data provide, for the first time in Sicily, absolute dates covering a wide spectrum of cultures following one another in the same area and, for the Bronze Age site, correlated to the precise stratigraphic succession. The petrographical and mineralogical analyses allowed not only the identification of the principal constituents of the pottery, but also the formulation of some hypotheses regarding the specific manufacturing techniques of different epochs. The microfacies, obtained from the presence of fossils in the groundmass of the pottery, were also analysed and compared with the microfauna present in the Miocene clays outcropping in the area. The data identified local Messinian clay as the raw material probably used in the manufacture of the pottery and also support the presence, already assumed by archaeologists, of imported Mycenaean pottery, thus supporting the dates obtained on pottery taken from the same stratum.     

OPTICAL DATING OF SINGLE AND MULTIPLE GRAINS OF QUARTZ FROM JINMIUM ROCK SHELTER,NORTHERN AUSTRALIA: PART II,RESULTS AND IMPLICATIONS*

Quartz sediments from the floor deposit at Jinmium rock shelter have been investigated using the multiple-grain and single-grain optical dating methods described by Galbraith et al. (1999, this volume). Here we present the results of this dating programme and argue that the artefact-bearing sediments were deposited within the last 10000 years. This time interval is consistent with the radiocarbon chronology but is much younger than previous claims for initial human occupation during the Pleistocene. Analysis of individual grains revealed also that the characteristic saturation doses of some grains are unusually high, which may permit dating of deposits older than a few hundred thousand years. Such grain-to-grain differences raise doubts, however, about the validity of using multiple-grain samples to investigate the phenomenology of quartz luminescence.     

FACTORS AFFECTING THE VIABILITY OF THERMOLUMINESCENCE DATING OF GLASS

The aim of this study is to achieve a better understanding of some of the factors that limit the thermoluminescence (TL) dating of glass. Using a‘model system’(lithium-disilicate samples having different levels of crystallinity from 0 to 100%), we show, first, that the TL of glass is reproducible only if the glass is not heated above its temperature glass transition and second, that there is a clear connection between the TL sensitivity and the degree of crvstallinity of the sample. We conclude that thermoluminescence is not a general dating method for archaeological glass, but it can be applied to particular glass samples that haue specified characteristics.     

THERMOLUMINESCENCE DATING OF MATERIALS WHICH EXHIBIT ANOMALOUS FADING

This article reports a generalised and systematic approach to the thermoluminescence (TL) dating of samples which suffer from anomalous fading. We hypothesise that the TL signal from each mineral phase is composed of a stable and an unstable portion. The decay of the unstable TL is accelerated thermally, until only stable TL remains. The dating is then carried out on this stable signal. The results, on four known-age, coeval samples, exhibiting gross anomalous fading (25-50% loss over a few days), indicate that many, if not all, samples may successfully be dated with this approach.