Magnetic Stratigraphy

The paleomagnetic record of the geomagnetic field preserved in sediments provides a range of stratigraphic opportunities at a variety of temporal and spatial scales.

The Geomagnetic Polarity Time Scale (GPTS) has been called the backbone of Cenozoic stratigraphy (See, Magnetic Stratigraphy, Opdyke and Channell, 1996 or Essentials of Paleomagnetism: Web Edition  2014, Ch. 15: The GPTS and magnetostratigraphy). Past changes in the strength of the magnetic field, measured as relative paleointensity, is a developing stratigraphic technique that provides substantial stratigraphic opportunity during times of constant polarity (Fig 1).

Changes in directional paleomagnetic secular variation (PSV) have been widely used and are now becoming increasingly well understood, providing stratigraphic opportunities at an even finer scale (Fig 2). Our lab is working to both develop and employ magnetic methods to solve chronological problems at a variety of timescales and resolutions.

 

References

Channell, J.E.T., Xuan, C., and Hodell, D.A., 2009. Stacking paleointensity and oxygen isotope data for the last 1.5 Myr (PISO-1500). Earth and Planetary Science Letters, 283, 14-23.

Kristjansdottir, G. B., Stoner, J. S., Jennings, A., Andrews, J. T., Grönvold, K., 2007. Geochemistry of Holocene cryptotephras from the North Iceland Shelf (MD99-2269): Intercalibration with radiocarbon and paleomagnetic chronostratigraphies. The Holocene 17, 155– 175.

Opdyke, N. D., Channell, J. E. T. 1996. Magnetic stratigraphy. San Diego, CA: Academic Press.

Stoner, J. S., A. Jennings, G. B. Kristjansdottir, G. Dunhill, J. T. Andrews, and J. Hardardottir, 2007: A paleomagnetic approach toward refining Holocene radiocarbon-based chronologies: Paleoceanographic records from the north Iceland (MD99-2269) and east Greenland (MD99-2322) margins, Paleoceanography, 22, PA1209, doi:10.1029/2006PA001285.

Figure 1. Intercalibration of paleointensity (blue) with the marine oxygen isotope record (red) for the last 1.5 ma (after Channell et al., 2009). The geomagnetic polarity time scale is shown for reference above, black is normal polarity, while white is reversed polarity.

Figure 2. Paleomagnetic secular variations (Inclination and declination), tephrochronology and calibrated radiocarbon ages for cores MD99-2269 and -2322 are intercalibrated, providing a Holocene stratigraphic template for the Denmark Straits region (After Stoner et al., 2007: Kirstjansdottir et al., 2007). Click image to enlarge.