On archeomagnetic secular variation curves and archeomagnetic dating

Abstract

Abstract Secular variation (SV) of the Earth’s magnetic field can be used for dating purposes by comparing archeomagnetic directions of unknown ages with a well-dated reference curve. In this study, we propose a dating technique based on the statistics of McFadden and McElhinny [Geophys. J. Int. 103 (1990) 725] for testing the hypothesis that two Fisherian distributions of individual directions share a common mean direction. The statistics are adapted to test the degree of compatibility between one individual Fisherian mean direction and a reference curve constructed using the bivariate extension of the Fisher distribution. Furthermore, as the density of the data which define the archeomagnetic reference curve varies in time, we suggest that one computes the mean directions with moving windows of varying duration, where both the window widths and the time shifts between successive mean directions are fixed when a minimum threshold density of data is reached within each time interval. In our paper, we apply this new procedure to the French archeomagnetic data set.