ARCHAEOMAGNETISM - AN ERROR ASSESSMENT OF FIRED MATERIAL OBSERVATIONSIN THE BRITISH DIRECTIONAL DATABASE

The direction of the geomagnetic field in Britain is now moderately we ll established for the last 2,000 year based on analyses of the direct ions of magnetic remanence isolated at some 466 archaeological sites i n Britain and parts of N.E. France. The vast majority of these observa tions are of fired, in situ archaeological materials, with only 21 sit e observations being based on sediments. Most of these findings are on ly available in virtually inaccessible field reports and theses, or si milar such publications, so the summary mean site British values have been placed into a database; this has then been extended to include ma y directional observations on a global basis. These data are now avail able as Dbase and Access databases, as well as in ASCII form. It is ho ped that such data will enable more detailed secular variation studies to be undertaken and encourage other workers to add their observation s to this database, particularly those that may otherwise be observed scatter with that expected from archaeomagnetic, geomagnetic and archa eological site sources suggest that the precision of the mean directio n is only a partial estimate of the total error, evaluated as being of the order of +/-5 degrees for any given site that may have taken plac e after the last heating. There is also clear evidence for invalid age assignments in some of the published data but increasing archaeomagne tic data are now enabling such errors to be re-evaluated and the techn ique is thus improving as more data accumulate.