下総台地西部に分布するじょう文時代中期住居し内炉し焼土の考古地磁気

Abstract

Natural remanent magnetization of the baked earth collected from the three dwelling pits (DW-2, 22, 34) found in the Ebigasaku shell-midden site was measured. For checking the reliability of the magnetization of the samples for archeomagnetic purpose, a thermomagnetic analysis was made on magnetic minerals of the baked earth.1. Thermomagnetic curves of the specimens collected from the site DW-22 are observed to be irreversible, while they are reversible for samples from the site DW-34.2. The country soil of the baked earth of the site DW-22 is considered to be weathered volcanic ash (“loam”), and is correlated to the upper Tachikawa Loam Formation on the basis of similarity of both thermomagnetic curves and heavy mineral assemblages.3. The results of thermomagnetic and also microscopic analysis suggest that the ferromagnetic minerals of the samples of the site DW-34 are high-temperature oxidized titanomagnetites. The high-temperature oxidation of titanomagnetite may have been resulted from the common use of this hearth in those days. Meanwhile, in case of the samples from the site DW-22, ferromagnetic minerals are non-oxidized titanomagnetites.4. The presence of the oxidized titanomagnetites in such samples as from the site DW-34 may be employed in checking the reliability of samples for archeomagnetic purpose.