## 4 Results  
### Dose Rate (\(D_{r}\)s), OSL Signal and \(D_{e}\)s  
The radioisotope activity concentration of the \({}^{238}\)U and \({}^{232}\)Th decay series was similar for all samples (Table 1). Such radioisotope concentration does not depend on the lithology underlying the deposits (either metasediments or granite). No disequilibrium was observed in the \({}^{238}\)U and \({}^{232}\)Th series. Significant variations in \({}^{40}\)K activity were observed between samples, ranging from 78 Bq/ka to 230 Bq/ka (Table 1). The gamma dose component (\(D_{r-gamma}\)) ranges from 0.2 to 1.3 (Gy/ky), the beta dose component (\(D_{r-beta}\)) ranges from 0.3 to 0.8 Gy/ky and the cosmic dose (\(D_{r-cosmic}\)) values are about 0.15 (Gy/ky) [11]. The final \(D_{r}\)s ranges between 0.68 Gy/ka and 1.83 Gy/ka (Table 1). Multigrain aliquots of 100 grains show a better fit to \(D_{e}\) and lower uncertainty than the other tested aliquot sizes (10, 30, 300 or >700 grains). In general, the natural OSL signals show dim signals (<40,000 c/u.t) [11]. This could be related to the origin of the quartz and the expected differences in radioisotope content and natural radiation (dose rate) between metasedimentary and gramitic lithology in the area [11]. However, sample Merco-8 from the gramitic area also shows lower signals than expected (<60,000 c/u.t) (Figure 3). However, all signals show a fast decay, with 95% of the counts being recorded in the first 0.5 s of exposure to blue LEDs. Bleaching tests (between 0.2 s and 1000 s) were performed, showing a reduction in the signal to background levels (>80%) after 1 s of exposure to blue LEDs. No linear correlation (neither exponential nor logarithmic) is observed between signal intensity (natural, regenerated or test-dose) and \(D_{e}\) of aliquots (r < 0.65). The signal/test dose ratios (L\({}_{\rm N}\)/T\({}_{\rm N}\)) are low (<10), although the growth curves show a large and steeply sloping linear interpolation region (Figure 3). In addition, dim OSL signals do not mean higher aliquot rejection in the recovery and recycling tests (the higher percentage of aliquot rejection is due to aberrant growth curves or non-interpolation) [11], indicating their reliability. Furthermore, in all samples, there are some aliquots (20%) with brighter OSL signals (natural, test dose and regenerate), with higher signal/test-dose ratios and a lower relative error (<10%). The \(D_{e}\)s from much more sensitive aliquots are very similar to the central estimators as median, arithmetic mean or weighted mean of the Central Age Model, CAM [11]. The \(D_{e}\)s were estimated by using the CAM [21] (Table 2). The relative deviation of the \(D_{e}\)s ranges between 10 and 20%. The absolute deviation of the \(D_{e}\)s shows an increasing linear trend vs. the \(D_{e}\). The proportion of aliquots rejected for exceeding the saturation threshold (\(\geq\)200 Gy) is below 30%, except for samples Merco-3 \begin{table}
\begin{tabular}{c c c c c c} \hline
**Sample** & **N** & **Dr (Gy/ka)** & **De (Gy)** & **OD (\%)** & **Age (ka)** \\ \hline MERO-1 & 59/141 & 1.50 \(\pm\) 0.25 & 98 \(\pm\) 6 & 35 \(\pm\) 5 & 65 \(\pm\) 13 \\ \hline MERO-2 & 36/202 & 1.83 \(\pm\) 0.14 & 108 \(\pm\) 10 & 50 \(\pm\) 7 & 59 \(\pm\) 8 \\ \hline MERO-3 & 43/168 & 1.21 \(\pm\) 0.20 & 115 \(\pm\) 7 & 30 \(\pm\) 5 & 95 \(\pm\) 19 \\ \hline MERO-4 & 51/91 & 0.90 \(\pm\) 0.13 & 95 \(\pm\) 6 & 39 \(\pm\) 5 & 105 \(\pm\) 23 \\ \hline MERO-5 & 51/125 & 1.15 \(\pm\) 0.07 & 89 \(\pm\) 5 & 32 \(\pm\) 5 & 77 \(\pm\) 11 \\ \hline MERO-6 & 65/188 & 0.68 \(\pm\) 0.10 & 32 \(\pm\) 3 & 78 \(\pm\) 7 & 46.1 \(\pm\) 12 \\ \hline MERO-7 & 26/219 & 1.37 \(\pm\) 0.27 & 135 \(\pm\) 7 & 13 \(\pm\) 5 & 99 \(\pm\) 22 \\ \hline MERO-8 & 26/195 & 1.64 \(\pm\) 0.16 & 139 \(\pm\) 9 & 28 \(\pm\) 5 & 85 \(\pm\) 12 \\ \hline \end{tabular}
\end{table} 
Table 2: Dose rate (\(D_{e}\)), equivalent dose (\(D_{e}\)), overdispersion (\(OD\)) and final ages. N: number of accepted/analysed aliquots. Merco-6 age from central dose (CAM) invalidated by asymmetric distribution.