Detrital Remanent Magnetism (DRM)
The paleomagnetism of sediments is known as detrital remanent magnetism (DRM), and it arises from the collective alignment with the Earth's magnetic field of small magnetic carriers in the sediment. In general, the magnetic carriers that contribute most to the paleomagnetic signal are smaller than 10 μ across. Except where the sediment itself is derived from older material containing hematite grains, the primary magnetic mineral is fine-grained magnetite (or titanomagnetite). In a typical situation, the magnetite weathers out of parent rock material and is carried by water into a relatively quiet sedimentary environment where it is deposited with the sediment. As a magnetic carrier settles through the water column, the magnetic moment of the carrier tends to rotate to become parallel to the Earth's magnetic field. Thus when a carrier reaches the sediment/water interface, its orientation has been influenced by the direction of the existing magnetic field.