magnetostratigrafia

Magnetostratigrafia is a geochronological and stratigraphic method that uses the record of Earth's magnetic field reversals preserved in rocks to determine ages and correlate sedimentary sequences. As sediments are deposited, magnetic minerals such as magnetite acquire a remanent magnetization aligned with the ambient geomagnetic field. Over time, the field has reversed many times, creating alternating normal and reversed polarity intervals that are captured in rock records and define a global polarity timescale.

In practice, magnetostratigraphic studies involve collecting oriented rock samples, measuring their natural remanent magnetization, and applying demagnetization techniques to isolate the primary depositional magnetization. The polarity of each sample is determined, and the results are compiled into a magnetostratigraphic section. This section is then correlated with the global polarity timescale, which is anchored by radiometric dating and biostratigraphy to convert polarity patterns into age estimates.

The method relies on recognizing continuous or near-continuous records and on distinguishing primary magnetization from later overprints. Types of magnetization considered include detrital remanent magnetization and chemical remanent magnetization, each recording information at different timescales and under varying diagenetic conditions. Magnetostratigraphy is frequently integrated with biostratigraphy and radiometric dating to refine ages and align strata across basins and continents.

Applications include dating and correlating sedimentary sequences, basin analysis, and studies of past plate movements and climate changes. Limitations arise from remagnetization, diagenetic overprinting, tectonic rotations, hiatuses, and uneven sedimentation, all of which can complicate the interpretation of polarity records. Notable anchors include well-dated reversals such as the Brunhes–Matuyama boundary around 0.78 million years ago.