Geomagnetic stratigraphic dating
Hematite forms through chemical oxidation reactions of other minerals in the rock including magnetite.
Redbeds, clastic sedimentary rocks (such as sandstones) are red because of hematite that formed during sedimentary diagenesis.
Then in 1963, Morley, Vine and Matthews showed that marine magnetic anomalies provided evidence for seafloor spreading.
Paleomagnetism is studied on a number of scales: The study of paleomagnetism is possible because iron-bearing minerals such as magnetite may record past directions of the Earth's magnetic field.
Magnetic stripes are the result of reversals of the Earth's field and seafloor spreading.
New oceanic crust is magnetized as it forms and then it moves away from the ridge in both directions.
Hence, the mineral grains are not rotated physically to align with the Earth's field, but rather they may record the orientation of that field.Nonetheless, the record has been preserved well enough in basalts of the ocean crust to have been critical in the development of theories of sea floor spreading related to plate tectonics.TRM can also be recorded in pottery kilns, hearths, and burned adobe buildings.The discipline based on the study of thermoremanent magnetisation in archaeological materials is called archaeomagnetic dating.
In a completely different process, magnetic grains in sediments may align with the magnetic field during or soon after deposition; this is known as detrital remanent magnetization (DRM).
These include biomagnetism, magnetic fabrics (used as strain indicators in rocks and soils), and environmental magnetism.