Dating of aragonite fossil shell by ESR for paramagnetic species assignment of Mae Moh basin

Electron spin resonance (ESR) spectroscopy technique has been employed to date the aragonite freshwater fossil shells in bottom sediments collected from Mae Moh basin of northern Thailand in the southwest margin of the coal pit. The samples were given an accumulated dose (AD) of 1100.46 ± 52.72 Gy by the additive irradiation method. The dose response of the ESR signals were found to be suitable for an age determination using a signal at g = 2.0016 corresponding to CO2-. The ESR signal growth curve on additional γ irradiation has been best fitted by a linear saturation function. Based on this model, the accumulated dose value for dating is obtained. The ESR age of the aragonite fossil shells was found to be about 13.02 ± 1.03 Ma. The results show that the ESR age within the Middle Miocene, Mae Moh Group of the geological time scale, which agreed with the stratigraphic level of the fauna.