Most records of claimed palaeomagnetic excursions are not accepted as manifestations of geomagnetic field variations, due to poor chronostratigraphic correlation. Post-depositional acquisition of detrital remanent magnetization may attenuate and modify, but not erase, high amplitude palaeomagnetic directions. It is proposed that the complete absence of excursions in continuously accumulated sediments, may be due to remagnetization by transient environmental processes. Results of an in situ bioturbation experiment, performed at 12 metres water depth during 1 year, are presented and demonstrate remagnetization of the upper 2 cm of a marine sand sediment. The results may, however, also be interpreted to reflect the influence of waves affecting the sediment surface of shallow-water sediments.