Magnetostratigraphy

Magnetostratigraphy dates and correlates rock sequences by identifying changes in Earth’s magnetic-field polarity preserved in rocks and sediments.

Remanent magnetization: Magnetization retained by a material after the external magnetic field that induced it has changed or disappeared. This retained signal preserves the polarity that magnetostratigraphic measurements identify.
Magnetite: An iron oxide mineral that is strongly magnetic and common in many igneous and sedimentary rocks. Magnetite grains often carry the remanent signal used to determine polarity.
Marine magnetic anomaly: A seafloor magnetic pattern formed as basalt records geomagnetic polarity during creation at a spreading ridge. Symmetrical anomaly stripes helped establish the global sequence of polarity reversals.
Magnetic overprint: A secondary magnetization imposed on a rock after its original magnetization formed. An overprint can mask or imitate the polarity recorded during deposition or cooling.
Geomagnetic reversal: A transition in which Earth’s magnetic field changes between normal and reversed polarity. Reversals create the polarity boundaries used to divide a rock sequence into magnetozones.
Thermoremanent magnetization: A stable magnetization acquired by magnetic minerals as they cool through their blocking temperatures in a magnetic field. Cooling lava can lock in the field’s polarity when its minerals acquire this magnetization.
Seafloor spreading: The creation of oceanic crust at ridges and its outward movement as new crust forms. Spreading carries successive polarity records away from ridges in datable stripes.
Secular variation: Short-term changes in the direction and strength of Earth’s magnetic field, distinct from polarity reversals. Directional fluctuations are not polarity chrons and should not be mistaken for reversal boundaries.
Magnetic polarity chron: A time interval during which Earth’s magnetic field maintained one polarity. Recognized polarity intervals are matched to these named units of the geomagnetic timescale.
Detrital remanent magnetization: A depositional magnetization acquired as magnetic grains align with Earth’s field while settling or shortly afterward. It allows sedimentary sequences to preserve polarity records as they accumulate.

Linked from 15 pages