Dating by thermoluminescence 127 pottery fragments collected from 4 archaeological sites in Taquari valley, Rio grande do Sul state, Brazil

127 fragments of pottery from excavation of four archaeological sites in Taquari Valley, close to Lajeado, State of Rio Grande do Sul, Brazil have been dated by thermoluminescence. After usual crushing, sieving, immersing in HCl solution and then in HF solution, accumulated dose, Dac, (or equivalent or paleodose) has been measured using additive method. The annual dose rate of natural radiation was estimated from uranium, thorium and potassium content in both soil from where these fragments have been collected and in fragments itselves. Cosmic ray contribution was added. The interesting finding is that the glow curves of quartz grains from sites enumerated 101, 110 and 114 indicated rare variety of quartz known as reddish quarts, whereas the glow curves of quartz grains, from the site numbered 107 are equal to these of usual quartz (hyaline). Results of dating and the properties of reddish quartz will be discussed. (author)