A grain mobility model of post-depositional realignment

The rate of acquisition of post-depositional remanent magnetization was measured as a function of the applied field for characterized synthetic sediments. The results were interpreted in terms of a conceptual model in which four modes of grain realignment were envisaged. Free rotation in water-filled voids was limited to a small percentage of the magnetic grains. The mobility and blocking conditions of this fraction is discussed. A further small fraction of the grains could realign by locally disturbing the surrounding grains. The majority of the original remanence was, however, not susceptible to realignment. Compression of the sediment preferentially suppressed reorientations involving matrix distortions whereas drying inhibited all types of grain movement. The additional grain disturbances resulting from drying are discussed. The grain mobility of a natural sediment was measured and found to be in general agreement with the model.