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Fig. 9.1 Example of multi-component magnetizations in the Mississippian Mauch Chunk Formation red beds from
northeastern Pennsylvania (Tan & Kodama 2002). These thermal demagnetization data are plotted in vector endpoint
diagrams typically used to represent demagnetization data (Zijderveld 1967). The solid squares indicate the endpoints of the
horizontal component of the paleomagnetic vector at each demagnetization step; the open squares indicate the endpoints of
the vertical magnetization component. An easterly and steeply upward component is removed at temperatures up to 686°C for
sample MC4-6 and then the characteristic magnetization is removed between temperatures of 686°C and up to 707°C. The
characteristic remanence for this sample is directed northwesterly and upward at low inclinations. Butler (1992) presents a
detailed and very clear explanation of these vector endpoint diagrams. X Tan and KP Kodama, Magnetic anisotropy and
paleomagnetic inclination shallowing in red beds: Evidence from the Mississippian Mauch Chunk Formation, Pennsylvania,
Journal of Geophysical Research , 107, B11, doi: 10/1029/2001JB001636, 2002. Copyright 2002 American Geophysical
Union. Reproduced by permission of American Geophysical Union.
ple site mean directions from a formation, and the
amount of work entailed in collecting, measuring and
demagnetizing many samples.
Using Fisher (1953) statistics, Butler (1992) has
shown that to average paleomagnetic directions and
estimate the 95% confi dence limits of a mean direc-
tion, the confi dence limits do not decrease appreciably
after about 20 directions are averaged. Fisher statistics
are the traditional mathematical method used to
average paleomagnetic directions, but these statistics
assume a particular directional distribution of direc-
tions (i.e. a Fisher distribution that is a two-dimensional
unit vector distribution on the surface of a sphere,
either the Earth or a stereonet representation of the
data). The 95% confi dence limits tell you that there is
95% probability that the true mean, were you to
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