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Palaeomagnetic errors related to sample shape and inhomogeneity
Earth, Planets and Space volume 55, pages 83–91 (2003)
When determining the remanent magnetization (RM) of palaeomagnetic rock samples, it is assumed that the samples can be approximated by a magnetic dipole. This assumption greatly simplifies the inverse problem of determining the RM from the measured magnetic field of the sample. The magnetic field of the normally used cylindrical rock samples is however not identical to that of a dipole and care must be taken not to introduce any systematic errors. A numerical test of the effect of cylindrical sample shape on the determination of RM for a spinner-type magnetometer is presented. We find that for a spinner magnetometer the non-ideal sample shape has an insignificant effect (less than 0.3° error), for even the smallest possible sample-sensor distance. Comparing static and spinner-type magnetometers, it is clear that spinner-type magnetometers are less affected by the sample shape. Inhomogeneously magnetized samples are an obvious source of error when determining the RM. We numerically test the error in the determination of RM for the simple case of a laminated cylindrical sample with constant direction, but varying intensity of magnetization between the laminae. For strongly inhomogeneous samples we find an error of ∼4° for typical spinner-type magnetometer and ∼10° for static-type magnetometers.
Blunk, I., Magnetic susceptibility anisotropy and deformation in Quaternary sediments, Z. Dt. Geol. Ges., 140, 393–403, 1989.
Butler, R. F., Paleomagnetism: Magnetic Domains to Geologic Terranes, 319 pp., Blackwell Scientific Publ., Boston, 1992.
Collinson, D. W., Methods in Rock Magnetism and Palaeomagnetism, 503 pp., Chapman and Hall, London, 1983.
Gallet, Y. and V. Courtillot, Modeling magnetostratigraphy in a borehole, Geophysics, 54, 973–983, 1989.
Larochelle, A. and G. W. Pearce, A possible source of error in determining the remanent magnetization of cylindrical rock specimens with a biastatic magnetometer, Geol. Surv. Can. Pap., 68-62, 1–13, 1969.
McElhinny, M. W. and P. L. McFadden, Paleomagnetism—Continents and Oceans, 382 pp., Academic Press, San Diego, 2000.
Menke, W., Geophysical Data Analysis: Discrete Inverse Theory, 289 pp., Academic Press, San Diego, 1989.
Parker, R. L., Calibration of the pass-through magnetometer-I. Theory, Geophys. J. Int., 142, 371–383, 2000.
Parker, R. L. and J. S. Gee, Calibration of the pass-through magnetometer -II. Application, Geophys. J. Int., 150, 140–152, 2002.
Press, W. H., B. P. Flannery, S. A. Teukolsky, and W. T. Vetterling, Numerical Recipes in Pascal, 759 pp., Cambridge University Press, 1989.
Saarinen, T. J., Paleomagnetic study of Holocene sediments of Lake Päijänne (Central Finland) and Lake Paanajärvi (North-West Russia), Geol. Surv. Finland, Bull, 376, 1–87, 1994.
Sharma, P. Vallabh, On the point dipole representation of a Uniformly Magnetized Cylinder, Helv. Phys. Acta, 38, 234–240, 1965.
Sharma, P. Vallabh, Choice of configuration for measurement of magnetic moment of rock specimen with a fluxgate unit, Geoexploration, 6, 101–108, 1968.
Steele, W. K., Directional errors in remanent magnetization of non-cubic soft sediment specimens measured with spinner magnetometers, Geophys. J. R. astr Soc, 96, 333–341, 1989.
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Riisager, P., Abrahamsen, N. Palaeomagnetic errors related to sample shape and inhomogeneity. Earth Planet Sp 55, 83–91 (2003). https://doi.org/10.1186/BF03351735
- Remanent Magnetization
- Magnetic Monopole
- Magnetic Potential
- Sample Shape
- Dark Layer