17:15 〜 19:15
[SEM16-P14] Rock magnetic investigation of Japanese ceramic coffins: Insights on their magnetic mineralogy and firing temperature
キーワード：岩石磁気学、考古学、考古岩石磁気学
From the middle to late Kofun period, ceramic coffins were used in some parts of Japan. Here we report the results of rock magnetic analyses conducted on ceremic coffins excavated from the Sada-Nishizuka Kofun in Maniwa City, Okayama Prefecture. The paleomagnetic intensity of two of the three pottery coffins excavated from this mound (SADA1 and SADA4) was determined using the Coe-Thellier method (Tema et al., 2023). On the other hand, the sample of the other ceramic coffin (SADA2) that was the subject of the study was excluded from the paleointensity measurements because significant mineralogical changes were observed during heating in the laboratory.
The firing temperature of this ceramic coffin (SADA2) was subsequently estimated by a combination of rock magnetism, thermoluminescence, and X-ray diffraction analysis, which indicated a low firing temperature of about 500°C (Tema et al., 2024). In this presentation, we will present the results of these analyses, as well as the results of additional rock magnetic measurements on SADA4, which is thought to have been fired at a high temperature, and SADA2, which is thought to have been fired at a low temperature, and discuss the differences between the two, and the alteration of magnetic minerals when the soil is fired. For both samples, isothermal remanent magnetization IRM acquisition analyses were taken before and after heating the samples in the laboratory at 600°C for 1 hour. For SADA4 there was almost no change before and after heating, but for SADA2 the amount of magnetite and the peak position and amount of the high remanent coercivity component changed. This supports the idea that the sample was not sufficiently heated during firing. In addition, the results of low-temperature magnetic measurements on both ceramic coffin samples showed that the Verwey transition of magnetite, which was not observed at all in SADA2, was slightly observed in SADA4. This is thought to be due to the fact that the amount and particle size of magnetite changed during firing, and the number of vacancies and impurities in the crystal decreased.
In recent years, rock magnetic measurements have been performed on several archaeological materials, and it can be said that they provide useful information for estimating the heating conditions and environment of pottery and fired clay.
The firing temperature of this ceramic coffin (SADA2) was subsequently estimated by a combination of rock magnetism, thermoluminescence, and X-ray diffraction analysis, which indicated a low firing temperature of about 500°C (Tema et al., 2024). In this presentation, we will present the results of these analyses, as well as the results of additional rock magnetic measurements on SADA4, which is thought to have been fired at a high temperature, and SADA2, which is thought to have been fired at a low temperature, and discuss the differences between the two, and the alteration of magnetic minerals when the soil is fired. For both samples, isothermal remanent magnetization IRM acquisition analyses were taken before and after heating the samples in the laboratory at 600°C for 1 hour. For SADA4 there was almost no change before and after heating, but for SADA2 the amount of magnetite and the peak position and amount of the high remanent coercivity component changed. This supports the idea that the sample was not sufficiently heated during firing. In addition, the results of low-temperature magnetic measurements on both ceramic coffin samples showed that the Verwey transition of magnetite, which was not observed at all in SADA2, was slightly observed in SADA4. This is thought to be due to the fact that the amount and particle size of magnetite changed during firing, and the number of vacancies and impurities in the crystal decreased.
In recent years, rock magnetic measurements have been performed on several archaeological materials, and it can be said that they provide useful information for estimating the heating conditions and environment of pottery and fired clay.