ESR dating of stalagmite from Keloğlan cave in the southwestern part of Turkey

Abstract

The determination of the geological age of two stalagmites (designated as A and B) found in Keloğlan cave (Denizli, Acıpayam, Turkey) was investigated using an electron spin resonance (ESR) technique. The natural ESR spectra had the signals of Mn2+ in addition to the signal at g=2.0006. In the ESR spectra of the γ-irradiated samples, three additional signals appear at g=2.0030, g=20016 and g=1.9972. The radicals produced by irradiation in stalagmites were attributed to orthorhombic and isotropic CO ion radicals. The signal intensity of the CO was used as a dating signal. Stalagmites were irradiated with a 60Co gamma source and measured with an ESR spectrometer (X-band) to obtain the signal intensity vs. dose curve, and fitted with the sum of two single exponential saturation functions. Based on this model, accumulated geological dose (DE) values for dating are obtained by using an additive dose method. The DE values of A and B stalagmites for each section range from 15±1 to 83±4 and 25±1 to 100±6 Gy, respectively. As the 238U, 232Th and 40K concentrations of the stalagmites are very low, the measured in situ value of the external gamma dose rate was used for dating calculations. Because some parts of the stalagmites show secondary calcite recrystallization in the pore spaces, the calculated age values of these parts do not agree with the model of stalagmite growth. Except these porous parts, the ESR ages of other sections between A.5–A.8 and B.3–B.6 range from 14±2 to 86±18 and 24±5 to 92±19 kyr, respectively, which is consistent with the model of stalagmite growth.