PALAEOSECULAR VARIATION OVER THE PAST 5 MYR BASED ON A NEW GENERALIZED DATABASE

A generalized database of global palaeomagnetic data from 3719 lava fl ows and thin dykes of age 0-5 Ma has been constructed for use with a r elational database management system. The database includes all data w hose virtual geomagnetic poles (VGP) lie within 45 degrees of the spin axis and can be used for studies of palaeosecular variation and for g eomagnetic field modelling. Because many of these data were collected and processed more than 15-20 years ago, each result has been characte rized according to the demagnetization procedures carried out. Analysi s of these data in terms of the latitude variation of the angular disp ersion of VGPs (palaeosecular variation from lavas) strongly suggests that careful data selection is required and that many of the older stu dies may need to be redone using more modern methods. Differences betw een the angular dispersions for separate normal-and reverse-polarity d ata sets confirm that many older studies have not been adequately clea ned magnetically. Therefore, the use of the database for geomagnetic f ield modelling should be carried out with some caution. Using a VGP cu t-off angle that varies with latitude, the best data set consists of 2 636 results that show a smooth increase of VGP angular dispersion with latitude, Model G for palaeosecular variation, which is based on mode lling of the antisymmetric (dipole) and symmetric (quadrupole) dynamo families, provides a good fit to these results.