The dispersion of the geomagnetic field due to secular variation and its determination for remote times from paleomagnetic data

In studies of the paleosecular variation the situation often arises that, although a number of spot readings of the paleogeomagnetic field have been deduced from the fossil magnetization of a rock formation, their stratigraphic sequence is unknown. Hence, in this paper, methods are discussed of deducing the amount of dispersion produced by the paleosecular variation in the magnetization of a rock formation against the background of noise due to experimental errors, partial remagnetization, subsequent tectonic movement, etc. The secular variation recorded at observatories and field stations during the past few centuries does not cover the full range of dispersion of the geomagnetic field in time, and models are considered by means of which this may be estimated. Angular dispersion factors are defined and have been calculated for three models and found to be of the same magnitude as those calculated from various rock formations. Other calculations for these models predict that the secular variation dispersion depends on latitude, and data from a number of igneous rock formations appear to confirm this prediction. It is not possible, however, to calculate the dispersion due to the paleosecular variation from the large body of paleomagnetic data tabulated by various authors, since these data have been computed in different ways.