古地磁気学的手法による先土器遺跡の炉址検出法の開発とその有効性

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A Paleomagnetic method for detecting fireplaces in Pre-ceramic sites was established, and its availability was tested in detail.At first, a bonfire experiment was carried out with the purpose of evaluating magnetic property changes of soils through a baking process. When soils were baked, the remanent magnetizations changed (1) to become stronger in intensity by one to two orders, (2) to become more stable in both intensity and direction against alternating-field demagnetization, and (3) to be directed more nearly in an identical direction than before being backed. These magnetic property changes may have been caused by chemical change (dehydration) from goethite to hematite or magnetite in soils through the baking process. These differences before and after baking were adopted as criteria to detect fireplaces and to determine their positions in Pre-ceramic sites (Paleomagnetic method).Secondly, the availability of these criteria was tested using soils in two archeological sites, Tamatu-Tanaka site, Hyogo (Yayoi age) and Ichi-no-Kubo site, Oita (early Jomon age-Preceramic age), where fireplaces have been definitely recognized with the naked eye. The results showed that remanent magnetizations of backed soils sampled from the fireplaces in these sites satisfy the above-mentioned criteria, and that those of unbaked soils sampled in the same sites do not. However, differences between the magnetic properties of the baked and the unbaked soils were not so significant as seen in the results of the bonfire experiment. This is attributed to chemical alteration of magnetic particles induced through a chemical process over a long period. Consequently, it is important to utilize all the above-mentioned criteria with significant care, in order to correctly detect fireplaces in Pre-ceramic sites.
日本第四紀学会の論文

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