Magnetic viscosity of suevites, a particular class of clastic impact rocks, has been comprehensively studied both in the field by transient electromagnetic (TEM) survey and in the laboratory by AC magnetometry methods. The studied rocks originate from the 14-km wide Zhamanshin impact crater, western Kazakhstan. Parameter Δχ, a difference between the static and dynamic magnetic susceptibility, has been considered as a measure of magnetic viscosity. The Δχ values estimated in the laboratory from the frequency and time domain measurements agree with each other while being an order of magnitude higher than the values obtained from the analysis of the field TEM data. This indicates a high sensitivity of the TEM method to the presence of SPM particles in near-surface layers. Magnetic granulometry of the samples has been analyzed using the model of interacting ferrimagnetic particles. Characteristics of superparamagnetic particles deduced from theoretical modeling agree well with the experimental data obtained using the frequency-dependent susceptibility and magnetic granulometry parameters.