Luminescence dating of glacigenic deposits from northern Germany: A comparison of multigrain aliquots and single grains K-feldspar methods

Glacigenic sediments are challenging to date with luminescence dating technique, particularly with regard to resetting of the luminescence signal before sediment deposition. In this study, six samples from four different ice-marginal positions in northern Germany were investigated to test different luminescence dating methods that account for heterogeneous bleaching of meltwater deposits. Multigrain measurements exhibited agreement between fading corrected infrared stimulated luminescence (IR) and fading corrected post-infrared IR measured at 225°C (pIRIR 225 ) ages, suggesting the studied samples were likely well bleached, as these signals bleach at different rates. Single-grain measurements showed a high proportion of saturated grains (up to ∼33%) in these samples. The single-grain results were therefore assessed using conventional single-grain analyses and the L n T n method. Accurate estimation of the overdispersion (OD) of a well-bleached grain population (σ b ) is essential for applying statistical age models. Because no suitable well-bleached analogue sample with comparable burial doses was available, σ b was estimated by combining intrinsic OD (from dose recovery tests) and extrinsic OD in quadrature. Both D e and L n / T n OD values exceeded the derived σ b values, confirming that all studied samples are poorly bleached and that the Minimum Age Model (MAM) is required. MAM ages derived from conventional single-grain and L n T n approaches are generally consistent; however, standard MAM ages tend to be slightly younger than L n T n MAM ages, likely due to truncation of the D e distribution through the exclusion of saturated grains. These finding demonstrate that (1) consistent IR 50 and pIRIR 225 ages cannot be considered a reliable indicator of well-bleached samples, and (2) σ b and overdispersion values should be determined and interpreted carefully, especially for old samples with a large number of saturated grains. We recommend applying the L n T n method at the single-grain level when dating partially-bleached samples with grains close to saturation, to obtain more reliable luminescence ages.