Paleomagnetism Analysis
Also known as: paleomagnetic dating, magnetostratigraphy, paleomagnetic remanence
Paleomagnetism analysis is the study of ancient magnetic properties of rocks, measuring fossil magnetization to determine paleomagnetic field history and assign geological ages. Pioneered by Brunhes (1906) and systematized by Tauxe (2010), this method reveals geomagnetic reversals, polar wander paths, and paleomagnetic chronology independent of fossil biostratigraphy. Analysis integrates laboratory rock magnetism with field sampling to build high-resolution timescales and constrain plate motion.
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When to use it
Paleomagnetism analysis is essential for high-resolution chronostratigraphy, especially in continuous sequences (marine cores, ice cores) where biostratigraphy is limited. It is most effective when samples are abundant (decimeter spacing or better), polarity reversals are numerous and well-resolved, and some independent age constraint (biostratigraphy, radiometric date) anchors the correlation. Assumptions include that magnetization is primary (not remagnetized), that the GPTS is accurate for the relevant time interval, and that the record is complete (no gaps obscure reversals). Analysis is hindered by very slow sedimentation (few reversals recorded) or by remagnetization events that overprint primary signals.
Strengths & limitations
- Age independent of fossils—paleomagnetic chronology relies on reversal patterns, not biostratigraphy; useful in barren sequences
- High temporal resolution—reversals occur every 100,000–1,000,000 years; patterns are distinctive and resolvable in continuous sequences
- Quantitative framework—reversal patterns are matched to the GPTS through correlation, yielding numerical ages with known accuracy
- Integration with plate tectonics—paleomagnetic poles reconstruct paleocontinental positions and reveal apparent polar wander
- Primary magnetization assumption—rocks may have been remagnetized during burial or late diagenesis; secondary overprinting must be detected
- Secular variation bias—short-term wiggles in the paleomagnetic field can be misinterpreted as reversals if data are sparse
- Sedimentation rate sensitivity—very slow sedimentation rates result in few reversals per unit thickness; age resolution is poor
- GPTS uncertainty—the Geomagnetic Polarity Time Scale is calibrated using radiometric dates with inherent uncertainty; paleomagnetic ages inherit this uncertainty
Frequently asked
What is the difference between declination and inclination?
Declination is the compass direction (0–360°) of a magnetic vector, the angle east or west from true north. Inclination is the dip angle below the horizontal (−90° to +90°), with positive values indicating downward dip in the northern hemisphere. Together, declination and inclination fully define the orientation of the ancient magnetic field recorded in a rock sample.
What is primary remanent magnetization (ChRM) and how is it isolated?
Primary remanent magnetization (or characteristic remanent magnetization, ChRM) is the magnetization acquired at the time of rock formation (cooling in igneous rocks, deposition in sediments). Secondary magnetization is acquired later (during burial, reheating, chemical alteration). ChRM is isolated by stepwise heating or AF demagnetization, removing unstable secondary components and revealing the linear decay toward the origin characteristic of primary magnetization.
What is the Geomagnetic Polarity Time Scale (GPTS) and why is it important?
The GPTS is a master chronology showing the reversal patterns of Earth's magnetic field through geological time, calibrated with radiometric dates and astronomical cycles. It serves as a reference: paleomagnetic reversal patterns in unknown sequences are matched to the GPTS pattern, yielding ages. The GPTS is updated periodically as new radiometric and paleomagnetic data improve calibration.
How do you distinguish primary magnetization from remagnetization?
Laboratory tests include analysis of demagnetization curves (ChRM should decay linearly toward origin), isolation of chemical remanent magnetization (IRM) to detect alteration, and analysis of paleomagnetic poles (remagnetized samples may plot off the apparent polar wander path). Comparison with biostratigraphy and other age constraints reveals if paleomagnetic ages are unreasonably young or old (indicators of remagnetization).
What is magnetostratigraphy and how does it work?
Magnetostratigraphy is the application of paleomagnetic methods to stratigraphy: samples are collected at regular intervals through a section, magnetization is measured, and polarity zones are identified. The polarity zonation (a unique barcode of normal and reversed intervals) is then correlated to the GPTS, assigning ages. High sample density (10–50 cm spacing) improves reversal resolution and correlation confidence.
Sources
- Butler, R. F. (1992). Paleomagnetism: Magnetic Domains to Geologic Terranes. Blackwell Scientific Publications. link ↗
- Cande, S. C., & Kent, D. V. (1995). Revised calibration of the geomagnetic polarity time scale for the Late Cretaceous and Cenozoic. Journal of Geophysical Research, 100(B4), 6093–6095. DOI: 10.1029/94JB03098 ↗
- Tauxe, L. (2010). Essentials of Paleomagnetism (1st ed.). University of California Press. link ↗
How to cite this page
ScholarGate. (2026, June 3). Paleomagnetism Analysis. ScholarGate. https://scholargate.app/en/geoscience/paleomagnetism-analysis
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
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