A 1 mm layer of magnetite powder has been sprinkled into a 3 cm deep, 1 meter long trench in high bioturbation rate tidal flat sediments, Sapelo Island, Georgia (USA). Periodic resampling and replicate remanent magnetization (RM) measurement indicates that within site RM directions and intensities stabilized between 20--50 days after initial sampling. The RM mean after 50 days exhibits an inclination which is -20¿ less than the geomagnetic field inclination at the site and remains low through the Winter and Spring but then nearly disappears during the summer when bioturbation rates are extremely high, leaving a post-depositional RM which is statistically indistinguishable from the earth's geomagnetic field inclination at the site. Since only very high bioturbation rates appear to produce a post-depositional RM in this experiment is is inferred that post-depositional RM development in some low bioturbation rate natural sediments, e.g. locally in the deep-sea, may be dominated by physical rather than biological depositional or post-depositional processes.