A 10 000 yr geomagnetic secular variation record from three Australian maars

Abstract

Summary. Detailed within-lake magnetic stratigraphies enable composite declination and inclination versus depth curves to be derived for sets of 6m cores from each of three volcanic crater lakes in western Victoria. Comprehensive radiocarbon chronologies for each sequence enable reliable timescales to be assigned to the variations in direction of the remanence. The resultant time-scaled curves are in satisfactory agreement and are therefore thought to provide an estimate of the geomagnetic secular variation in SE Australia during the last 10 000 yr. Amplitude attenuation occurs as an increasing function of age, and probably results from long time-scale remagnetization processes. Mean directions coincide with the geocentric axial dipole field directions at the three sites. Inclination oscillations are stronger and better resolved than those in declination, whereas the opposite tends to be true for the European records. Reduction of records to a common ‘virtual’ site suggests that the difference is largely of geometrical origin. Comparisons of VGP paths do not reveal a common dipole wobble component. The sense of looping of the magnetic vector favours westward rather than eastward drift of features of the non-dipole field. Relative field strength estimates based on normalization of NRM with respect to measures of the magnetic mineral content do not agree with Australian and worldwide’ archaeointensity results.