11:00 〜 13:00
[SEM15-P08] Archeointensity Study of Yayoi Pottery Excavated from Northern Kyushu using the IZZI Thelleir Method
キーワード：弥生土器、考古地磁気強度
Construction of an archeointensity curve for East Asia has been underway. Kitahara et al. (2021) proposed the latest version of the curve, which is back to as old as ca. 200 CE (hereafter, Kitahara curve). It is important to extend the curve further back in time. For determining archeointensity, so-called Thellier-type techniques have been widely used. Archeointensity data determined by the IZZI-Thellier method (Yu et al., 2004), one of the latest version of the Thellier-type techniques, are included in the Kitahara curve. Archeointensity data determined by the Tsunakawa-Shaw method (Yamamoto et al., 2003), which have been often utilized by Japanese research groups, are also included in the Kitahara curve. The two methods are complementary: the IZZI Thellier method is for blocking temperature space, while the Tsunakawa-Shaw method is for coercivity space. Therefore, in order to estimate an archeointensity more accurately, it is ideal to perform the two methods on a same set of samples.
In this study, we estimated archeointensites from Yayoi potteries excavated from northern Kyushu, aiming to extend the Kitahara curve beyond ca. 200 CE. A total of 43 pottery samples, which have been dated archeologically for early to middle period of Yayoi era, were used for archeointensity measurements by the IZZI-Thellier method and the Tsunakawa-Shaw method. Each of the sample was cut into several pieces, and the two methods were carried out on sister specimens. In this presentation, we report results of the IZZI-Thellier method, including those of progressive thermal demagnetization to confirm the thermal behavior of the samples.
We selected 20 samples for archeointensity measurements using the IZZI-Thellier method. Progressive thermal demagnetization measurements were also carried out on the sister samples, revealing that secondary components are separated at around 450°C in most of the samples (some of the samples consisted of only the primary component). Results from 11 samples passed the specimen-level selection criteria of the IZZI-Thellier method (CCRIT; Cromwell et al., 2015) if the criterion of FRAC was relaxed to 0.350, yielding archeointensities from 32.7 μT to 60.0 μT.
There has been much debate on chronology of the Yayoi era in archeology since 2003, and no unified view has yet been reached. In this presentation, we tentatively adopt a time scale of 300 BCE - 200 CE for the measured samples. Averaged archeointensities for three different time periods are 34.3 μT from 300 BCE to 200 BCE, 39.1 μT from 200 BCE to 0 CE, and 47.3 μT from 0 CE to 200 CE. These are generally consistent with the results of the Tsunakawa-Shaw method obtained from the same sample (Yoshimura et al., 2022JpGU), indicating robustness of the archeointensity results.
In this study, we estimated archeointensites from Yayoi potteries excavated from northern Kyushu, aiming to extend the Kitahara curve beyond ca. 200 CE. A total of 43 pottery samples, which have been dated archeologically for early to middle period of Yayoi era, were used for archeointensity measurements by the IZZI-Thellier method and the Tsunakawa-Shaw method. Each of the sample was cut into several pieces, and the two methods were carried out on sister specimens. In this presentation, we report results of the IZZI-Thellier method, including those of progressive thermal demagnetization to confirm the thermal behavior of the samples.
We selected 20 samples for archeointensity measurements using the IZZI-Thellier method. Progressive thermal demagnetization measurements were also carried out on the sister samples, revealing that secondary components are separated at around 450°C in most of the samples (some of the samples consisted of only the primary component). Results from 11 samples passed the specimen-level selection criteria of the IZZI-Thellier method (CCRIT; Cromwell et al., 2015) if the criterion of FRAC was relaxed to 0.350, yielding archeointensities from 32.7 μT to 60.0 μT.
There has been much debate on chronology of the Yayoi era in archeology since 2003, and no unified view has yet been reached. In this presentation, we tentatively adopt a time scale of 300 BCE - 200 CE for the measured samples. Averaged archeointensities for three different time periods are 34.3 μT from 300 BCE to 200 BCE, 39.1 μT from 200 BCE to 0 CE, and 47.3 μT from 0 CE to 200 CE. These are generally consistent with the results of the Tsunakawa-Shaw method obtained from the same sample (Yoshimura et al., 2022JpGU), indicating robustness of the archeointensity results.