ESR studies of anatolian gypsum

Electron spin resonance (ESR) was used to date the formation and most recent recrystallization of three types of gypsum samples (massive, bedded and fracture filling gypsum) from the Sakarya Formation at Eskişehir in the middle of Turkey. The ESR spectra had the signals of Fe³⁺ and Mn ²⁺ in addition to those of the G1 and G2 sensitive centers (g=2.002 and 2.008) to artificial γ-irradiation. ESR intensities of G1 and G2 were enhanced by γ-ray irradiation to give equivalent doses D_E for each sample. The ESR ages derived from the annual doses of ²³⁸U, ²³²Th and ⁴⁰K contents of the samples determined by thermal neutron activation analysis (TNAA) were between 43±18ka (massive gypsum) and 1100±466ka (bedded gypsum) as minimal and maximal values. The ages fall into the upper Miocene-Pliocene Epoch of the geological time scale, which agreed with the stratigraphy.