Viscous magnetization of loess/palaeosol samples from Bulgaria

The processes of acquisition of viscous remanence and its decay in zero mag netic field are studied for three sets of palaeosol and loess samples. A li near behaviour of VRM vs. log t minus is obtained for 10-10(4) min. to 30 d ays of acquisition experiments. Linear correlation between the obtained coe fficients of viscous acquisition normalized to saturation magnetization (Sa /Js) or frequency dependent magnetic susceptibility (Sa/chi fd%) and the ra tio of susceptibility to saturation magnetization (chi /Js), suggests that ultra fine SP/SD grains are mainly involved in the process of viscous acqui sition. Non-linear VRM vs. log t behaviour is observed during viscous decay in mu -metal shielded space, being most pronounced for the first 10 min, o f the experiment. It is supposed that this phenomena is due to the presence of composite grains (core/shell structure), formed as a result of low-temp erature oxidation. The latter increases towards older palaeosol units.