The processes that influence a detrital remanent magnetization as well as the physical microscale factors that control formation of a stable post-depositional remanent magnetization are still not fully understood. Previous laboratory studies and statistical numerical approaches have shown the possibility that sediment suspensions can display complex magnetization phenomena. Such behaviour has been attributed to the effect of magnetostatic interactions in the suspension, which could provide one explanation for spurious magnetizations observed in marine sediment cores. In laboratory experiments we investigated magnetization decay as a function of time in sediment suspensions produced with varying lithologies and particle concentrations. A companion model takes into account the physics of magnetic particle-particle interactions, Brownian motion and hydrodynamic forces to investigate numerically the magnetization behaviour of sediment suspensions. When combined, the experiments and the numerical models reveal a weak effect of magnetostatic interactions in the natural sediment suspensions, which is expressed as an increase in the magnetization decay rate. In addition, a calculation of effective particle size based on the response of each suspension to Brownian motion indicates that the majority of the sedimentary magnetic particles are attached to larger clay particles.