Thermoluminescence and electron spin resonance dating of freshwater fossil shells from Pa Toh Roh Shelter archaeological site in southern Thailand

This research aims to compare the dating results by thermoluminescence in comparison with the electron spin resonance techniques. We also intended to resolve the discrepancy on the precision being measured between these two. Based upon the archaeological evidence, six portions of freshwater fossil shells, used as samples, contain calcium carbonate polymorphs acquired from six locations in Pa Toh Roh Shelter archaeological site, Khao Han cave, Satun province, Thailand. The approach requires two important quantities for accurate dating, namely the annual dose and the accumulated dose. Using neutron activation analysis, the annual doses of the shells from different depths were found to be 2.64±0.07 to 7.27±0.11 mGy per year. The accumulated dose is evaluated from calibrated TL and ESR intensity versus accumulated γ-dose. Linear regression was used to fit the dependence of TL intensity on dose with a linear saturation function. The TL intensity at 350(∘)C was used to estimate ages of the fossil shells from all depths. The ESR dating would be also available for aragonite calcite shells using the ESR signal of g = 2.0016. The accumulated dose was found to vary from 10.49±2.09 to 22.50±3.99 Gy and the calculated ages of the shells were between 3,094±551 to 4,479±666 years old. These results confirm that the freshwater fossil shells in the area date back to the Neolithic period are similar to those found in the nearby archaeological sites. In addition, the dates are in agreement with those results from the relative dating as reported by a government agency.