The choice of equivalent dose fitting function in ESR dating of old fossil samples

BackgroundIn electron spin resonance dating (ESR) of old fossils, the double saturation exponential (DSE) function is often used for the equivalent dose (DE) determination, it generally requires more than 15 dose points and the maximum irradiation dose (Dmax) greater than 20 kGy to ensure the fitting accuracy, which limit the practical application of dating old fossils by ESR method with insufficient sample size.PurposeThis study aims to explore the feasibility and reliability of using the single saturation exponential (SSE) fitting function to fit fewer dose points with lower Dmax to obtain the DE values of the fossil teeth from the late Miocene to the early Pleistocene, and compared with the ones determined by DSE function.MethodsFirstly, 17 fossil samples were taken from seven fossil sites in different regions of China and Myanmar, and their ages covered the late Miocene to early Pleistocene. Then, three fitting functions, i.e., DSE, SSE and EPL-exponential plus linear, were employed to obtain the DE values of ESR using the additional dose method. Finally, the influence of different Dmax on the DE results of three fitting functions was investigated by comparative analysis.ResultsComparison results show that: (1) The SSE and DSE function are used to fit the 15 dose points with Dmax=50 kGy, and the DE-SSE results of 11 samples are basically consistent with the DE-DSE results, meanwhile the precision of the fitting results of SSE function is generally higher than DSE cases. (2) For samples with DE＞4 500 Gy and 2 000 Gy＜DE＜4 500 Gy, the results of SSE and DSE are basically consistent within the error range under the conditions of Dmax≥6.5×DE and 1.9×DE＜Dmax＜3.5×DE, respectively, which can provide the recommended dose value of Dmax for samples with DE＞2 000 Gy when using SSE function. (3) For fossil samples with 2 000 Gy＜DE＜4 500 Gy, the SSE function can be used to fit the 11 dose points with Dmax≤10 kGy, and the DE results are generally consistent with the DSE function within the error range.ConclusionsBased on above results, it is viable to use SSE function to perform DE fitting on old fossil samples under certain Dmax/DE conditions, and establishing the standardized growth curve of old fossils and the fragmental analysis of the fossil teeth for DE determination will be explored in the future study.