日本地球惑星科学連合2015年大会

講演情報

口頭発表

セッション記号 S (固体地球科学) » S-EM 固体地球電磁気学

[S-EM34] 地磁気・古地磁気・岩石磁気

2015年5月24日(日) 16:15 〜 18:00 102A (1F)

コンビーナ:*望月 伸竜(熊本大学大学院先導機構)、松島 政貴(東京工業大学大学院理工学研究科地球惑星科学専攻)、座長:山本 裕二(高知大学 海洋コア総合研究センター)、福間 浩司(同志社大学理工学部環境システム学科)

17:18 〜 17:21

[SEM34-P02] 須恵器実験窯の焼土試料の考古地磁気強度研究-綱川・ショー法の有効性の検討(続報)

ポスター講演3分口頭発表枠

*山本 裕二1鳥居 雅之2夏原 信義3 (1.高知大学、2.岡山理科大学、3.夏原技研)

A reconstruction experiment of a kiln had been done to imitate completely that of an excavated kiln of the 7th century in Japan. Baked clay samples were taken from floor surface and -20 cm level, and they have been stored after determinations of the paleomagnetic directions by partial alternating field demagnetizations. A suite of the rock magnetic experiments and the scanning electron microprobe observations elucidate that dominant magnetic carriers of the floor surface samples are Ti-poor titanomagnetite grains in ~ 10 nm size with single-domain and/or super-paramagnetic states, whereas contributions of multi-domain grains seem to be relatively large for the -20 cm level samples. We applied the Tsunakawa-Shaw method to the samples to assess how reliable archeointensity results are obtained from the samples. From the floor surface samples, six out of the eight successful results were discriminated and they give an average of 47.3 microT with a standard deviation of 2.2 microT. This is fairly consistent with the in-situ geomagnetic field of 46.4 microT at the timing of the reconstruction. They are obtained with a built-in anisotropy correction using anhysteretic remanent magnetization, and without any cooling rate corrections. In contrast, only one out of the four successful result was obtained from the -20 cm level samples. It yields an archeointensity of 31.6 microT, which is inconsistent with the in-situ geomagnetic field. Considering from the in-situ temperature record during the firing of the kiln, the floor surface samples acquired full thermoremanent magnetizations (TRMs) as their natural remanent magnetizations whereas the -20 cm level samples only acquired partial TRMs, and these differences probably cause the difference in the archeointensity results between the two sample groups. For archeointensity researches, baked clay samples from a kiln floor are considered to be ideal materials.