Application of multiple-centers ESR dating to middle Pleistocene fluviolacustrine sediments and insights into the dose underestimation from the Ti–H center at high equivalent doses

The Ti–H center exhibits rapid and complete optical bleaching properties, meaning it has significant potential for dating applications. However, the equivalent dose of Ti–H centers is underestimated when total doses received by quartz during its geological history reaches a higher level, and there appears to be linked to saturation of the equivalent dose obtained from Ti–H centers. To investigate this phenomenon, a series of samples were analyzed from two sections at Ximachi in Heqing County, China, which have strong Ti–H signals. The sample ages were obtained using the electron spin resonance (ESR) multiple-centers approach, and the reliability of the ages was validated by comparison with optically simulated luminescence (OSL) ages and between different paramagnetic centers. The ESR data demonstrate that the Ti–H centers can provide accurate dose estimates up to 750–950 Gy, with varying degrees of underestimation at high doses. Combined with previously published Ti–H data, it is evident that the upper threshold of the accurate data obtained from Ti–H centers depends on the sample, and may be positively correlated with the Ti–H/(Ti–Li + Ti–H) ratio (option C/D). According to the provenance significance of the Ti–H/(Ti–Li + Ti–H) ratio, we propose that the Ximachi samples have high Ti–H/(Ti–Li + Ti–H) ratios and then equivalent dose saturation values of Ti–H centers, which may be related to the thermal history of the analyzed quartz grains.