RECOGNIZING THE BURNING STATUS OF ARCHAEOLOGICAL QUARTZ PEBBLES COUPLING THERMOLUMINESCENCE AND ELECTRON PARAMAGNETIC RESONANCE SPECTROSCOPY

Abstract

Although the methodology to date pottery and pebbles by thermoluminescence (TL) is based on identical principles, the procedure followed to retrieve the accumulated dose in burnt pebbles offers extra difficulties. In addition, the distinction between burnt and unburnt pebbles is not always free from the subjective influence inherent to the visual inspection. Based on the dependencies of the 110oC TL peak and the electron paramagnetic resonance (EPR) signal of the E’1 center with the heating temperature of quartz, the aim of this study is to extend the method to classify burnt and unburnt pebbles independently from visual inspection. For this, several pebbles collected from the East block of the Pedra Furada rock shelter (São Raimundo Nonato, Piauí, Brazil) were used to create a burning pattern assessing TL and EPR responses as a function of the heating temperature. The results showed that the 110oC peak was not observed in those pebbles that were heated below 400oC and the intensity of the E’1 signal abruptly decreased with heating above 400oC. TL and EPR signals of specimens previously classified as “burnt” and “unburnt” appeared in good agreement with the values related to the burning pattern. This method offered the possibility to estimate the temperature in which some pebbles were heated in the past.