Secular variation record of the Earth's magnetic field in Italy during the Holocene: constraints for the construction of a master curve

Abstract

SUMMARY The palaeosecular variation of the geomagnetic field during the Holocene has been investigated in marine and lacustrine cores from the Italian region. U-channel measurements were carried out on two low-resolution cores from the Tyrrhenian Sea (Core ET91-18 and ET95-4) and Ionian Sea (Core ET99-M11 and ET99-M63) representing the Late and Early–Middle Holocene, respectively. Discrete samples were measured on two cores from the Adriatic Sea (PAL94-8 and Pal 94-9) and the maar lake of Nemi (Core PNemi 94-1B) containing an expanded section of the whole Holocene. Temporal variations in inclinations and declinations for each marine site were stacked according to an independently established timescale based on calibrated radiocarbon ages. The timing of the different declination and inclination features is not synchronous between the cores, hampering the possibility of obtaining a master curve by stacking the results. Nevertheless, by using few points with a consistent timing it has been possible to make an age-depth model for the Nemi sediments. The upper part of this core was precisely dated by comparing the core results with the published secular variation data from Italian volcanics emplaced during the last millennium. Comparison of the results with the UK master curve suggests that similar SV features are common to both records although discrepancies exist in the timing and they may be explained by inadequate age determination, time lag in the magnetization lock-in or even by an offset between the two records. Relative palaeointensity of the geomagnetic field established by NRM/ARM ratio for the Adriatic sediments is in agreement with the global dipole-moment compilation suggesting certainly that the sediments recorded the field behaviour.