Improved isolation of archeomagnetic signals by combined low temperature and alternating field demagnetization

Conventional alternating field (AF) demagnetization of the magnetite-bearin g claystone foundations of a Saxon or late medieval lime kiln in Lincolnshi re. England fail to isolate stable characteristic remanences. or remanences compatible with possible contemporary geomagnetic field orientations. Cons olidation of the material prevented thermal demagnetization. When low tempe rature demagnetization (LTD) precedes AF demagnetization. however. the vect or plots show a stable characteristic (primary) component. Magnetic anisotr opy measurements show that the LTD did not significantly disturb the minera l fabric of the claystone, that the mineral fabric did not deflect the pala eofield, and that AF demagnetization did not induce a field-impressed aniso tropy during the experiments. Anisotropy of low-field magnetic susceptibili ty (AMS) is affected by all minerals, and therefore the anisotropy of the m agnetite was isolated by measuring anisotropy of anhysteretic remanence (AA RM), this is of more relevance in evaluating the potential for palaeofield deflection. Thus, we conclude that LTD preceding AF demagnetization is resp onsible for improving the isolation of a characteristic remanence, which th en favours a late medieval age for the kiln foundation.