Palaeosecular variation over the past 5 Myr based on a new generalized database

Abstract

A generalized database of global palaeomagnetic data from 3719 lava flows and thin dykes of age 0-5 Ma has been constructed for use with a relational database management system. The database includes all data whose virtual geomagnetic poles (VGP) lie within 45° of the spin axis and can be used for studies of palaeosecular variation and for geomagnetic field modelling. Because many of these data were collected and processed more than 15-20 years ago, each result has been characterized according to the demagnetization procedures carried out. Analysis of these data in terms of the latitude variation of the angular dispersion of VGPs (palaeosecular variation from lavas) strongly suggests that careful data selection is required and that many of the older studies may need to be redone using more modern methods. Differences between the angular dispersions for separate normal- and reverse-polarity data sets confirm that many older studies have not been adequately cleaned magnetically. Therefore, the use of the database for geomagnetic field modelling should be carried out with some caution. Using a VGP cut-off angle that varies with latitude, the best data set consists of 2636 results that show a smooth increase of VGP angular dispersion with latitude. Model G for palaeosecular variation, which is based on modelling of the antisymmetric (dipole) and symmetric (quadrupole) dynamo families, provides a good fit to these results.