Holocene geomagnetic field in Europe

Abstract

During the summers of 1975 and 1976, 29 six metre cores of lacustrine sediment were collected from France and Switzerland, and 59 from Poland. All of these cores were collected using a Mackereth type pneumatic corer. Thenaturalremanent magnetization (N.R.M.) of these cores was studied in an attempt to investigate the pattern of long period secular variations of the geomagnetic field. The cores were then dated using palynological and radio-carbon techniques. A correlation between the patterns recorded from the different lakes, and between the lakes and the archaeomagnetic record for Europe was then attempted. The results obtained from the French and Swiss lakes were 1n general better than those from the Polish lakes. Further studies indicated that the percentage of magnetic material in the Polish lakes was much lower than in the French and Swiss ones and hence may be the reason for the poorer results. An investigation into the carrier of the N.R.M. was then made, and in almost all of the cases studied was found to be fine grained magnetite.

Attempts were then made to simulate long period secular variations using an oscillating eccentric radial dipole model. The model allows eight radial dipoles as positioned by Alldredge and Hurwitz (1964) to oscillate as a s1ne function. The period and phase of the oscillations can be varied for each dipole, as can the strength and radial distance. The field at the surface is then calculated by summlng the effects of the dipoles. A modification to the model, allowing the dipoles to drift as well as oscillate was also made.

The effect of varying the different parameters was then studied. An attempt to simulate a geomagnetic excursion was also made.