Data for the De estimates.

Coarse fraction content: weight fraction of the [2mm-1 cm] material over the total (< 1 cm) sediment. Cosmic dose rate are calculated from [80]; gamma dose rates are deduced from in situ dosimetry [81,82]; beta 1 and beta2 are calculated from the activities measured with high resolution gamma spectrometry (see Table 5) using specific dose rates of [83] and attenuation factors of [83]. Beta1 is calculated from the activities of the fine (< 2 mm) fraction; beta2 is calculated from the activities of the total (< 1 cm) fraction. Internal dose rate of quartz was neglected; internal dose rate of feldspar is deduced from the measured K content and from an assumed 400 ppm of Rb, following [84]. Total dose rates take into account the mean of beta1 and beta2 (according to [61,85]). Uncertainties included both systematic and statistic errors.