A MINERAL MAGNETIC STUDY OF SOME POTTERY SAMPLES - POSSIBLE IMPLICATIONS FOR SAMPLE SELECTION IN ARCHAEOINTENSITY STUDIES

We have related the mineral magnetic properties of some archaeological samples to the quality of the paleointensity data that they produce. We find that samples which have broad unblocking temperature distribut ions and most of their remanences unblocked at intermediate temperatur es produce high-quality paleointensity data. This conclusion is based on a comparative study of pottery samples which had previously produce d reliable and unreliable paleointensity data. For each sample, we det ermined the magnetic mineralogy and the magnetic domain state. In all cases, magnetite (or titanomagnetite) is the primary magnetic carrier, with domain states that extend from superparamagnetic to single domai n, and maybe even to pseudo-single domain. We believe that the magneti c grain size distribution of these samples produces a broad unblocking temperature distribution. The advantage of having such a distribution is that high-quality data can be obtained before the onset of the min eralogical changes that can occur at high temperatures with the Thelli er and Thellier method. The frequency-dependent susceptibility appears to be useful as a non-destructive estimator of the unblocking tempera ture distribution for samples having only magnetite as the magnetic mi neral.