Construction Of New Archaeointensity Reference Curve For East Asia From 200 Ce To 1100 Ce

Archaeomagnetism is a research area that reconstructs ancient geomagnetic fields mainly using baked samples (especially baked artifacts) containing magnetic minerals such as magnetite and hematite. Archaeomagnetism can be applied to reveal temporal changes in the geomagnetic field related to deep-earth dynamics, and to estimate the age of archaeological remains and artifacts. Reconstruction methods for ancient geomagnetic field intensity (archaeointensity) continue to develop rapidly, with various experimental methods having been proposed since 2000. The Tsunakawa-Shaw method is one of the latest experimental methods. The Tsunakawa-Shaw method was applied to reconstruction of the archaeointensity for a large number of samples of baked clay belonging to different ages from archaeological relics in Osaka Prefecture, Japan, and a new archaeointensity reference curve was constructed. The archaeointensities from 98 specimens belonging to 39 kilns were estimated. These data were screened and compiled for each pottery sequence, and finally 6 mean intensity values for the pottery sequence level were obtained. All of the mean intensity values satisfied the selection criteria, which indicates that they have sufficient reliability. It is notable that these newly estimated archaeointensities are lower than those in previous studies in Japan. On the other hand, new archaeointensity values show a complementary trend in the archaeointensity dataset obtained by the IZZI-Thellier method reported in Korea recently. We combined the dataset for Japan obtained in this study and the dataset for Korea, and drew an interpolation curve to construct an archaeointensity reference curve for East Asia covering from ca. 200 CE to ca. 1100 CE. This reference curve includes events of archaeointensity decrease and increase that occurred around 610 CE and around 950 CE, which are a characteristic pattern of the intensity variation found in this study.