(a) Magnetization versus time for the sediment groups A–E (circles, crosses), after normalization by the mean saturation remanence Mrs. The sediments were deposited in a null field (day −5 to day 0). A 60-μT field with 50° inclination was applied during the next 7 days and was turned off thereafter. Lines are best-fit model curves obtained from equations (2 and 3). Group V designates the PDRM decay due to magnetic viscosity in three fully dried samples, where particle reorientation was not possible. (b) PDRM acquisition for the groups A–E in 20-, 40-, 60-, 80-, 100- and 150-μT fields and subsequent zero-field decay. Magnetizations are normalized by the equilibrium PDRM (Meq) that would be reached after an infinite time. Acquisition/decay times are normalized by the median rotational diffusion coefficients, and , as deduced from least-squares fits of the measured curves (Supplementary Note 1). All data collapse onto a single acquisition/decay curve (black lines), as expected when the rotational diffusion coefficients are identically distributed. (c) Median rotational diffusion coefficients and deduced from individual acquisition/decay curves of the sediment groups A–E. has been corrected for the effect of field intensity (Supplementary Note 1). Dashed lines indicate constant values of , with expected for stationary conditions. (d) Probability density function pr of the rotational diffusion coefficient D, reconstructed from the normalized acquisition/decay curves shown in b, and the mean distribution p of particle diameters s for the sediment groups A–E (the shaded band corresponds to ±1 s.d. of 40 measurements). D and s on the lower axis are normalized by their median values.