JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-EM Earth's Electromagnetism

[S-EM18] [EE] General Contributions in Geomagnetism, Paleomagnetism, and Rockmagnetism

Sat. May 20, 2017 3:30 PM - 5:00 PM A07 (Tokyo Bay Makuhari Hall)

convener:Hirokuni Oda(Institute of Geology and Geoinformation, Geological Survey of Japan, AIST), Nobutatsu Mochizuki(Priority Organization for Innovation and Excellence, Kumamoto University), Joshua M Feinberg(University of Minnesota), Myriam Annie Claire Kars(Center for Advanced Marine Core Research), Chairperson:Nobutatsu Mochizuki(Priority Organization for Innovation and Excellence, Kumamoto University), Chairperson:Ioan Lascu(University of Cambridge), Chairperson:Myriam Kars(Center for Advanced Marine Core Research)

4:20 PM - 4:35 PM

[SEM18-04] Further archeointensity study on potteries fired in the reconstructed ancient kiln in Japan

*Yuhji Yamamoto1, Yu Kitahara2, Tadahiro Hatakeyama3, Nobuyoshi Natsuhara4 (1.Center for Advanced Marine Core Research, Kochi University, 2. Graduate School of Integrated Science for Global Society, Kyushu University, 3.Information Processing Center, Okayama University of Science, 4.Natsuhara Giken)

Yamamoto et al. (2015) reported that baked clay samples from the floor of a reconstructed ancient kiln provided a reliable archeointensity estimate of 47.3 +/- 2.2 microT which is fairly consistent with the in situ geomagnetic field of 46.4 microT at the time of the reconstruction. The reconstruction was conducted to reproduce an excavated kiln of the seventh century in Japan and potteries of contemporary style (Sue ware) were also fired (Nakajima et al., 1974). We have been performing archeointensity determinations on the potteries using the Tsunakawa-Shaw (LTD-DHT Shaw) method.

We cut mini specimens from a cup type (CupB-1) and a sake-pitcher type (Tokkuri-1) potteries. For the CupB-1 all the specimens were heated in vacuum for acquisition of laboratory thermoremanent magnetization (TRM), and 15 out of the 17 specimens passed the criteria to yield an archeointensity estimate of 65.8 +/- 2.5 microT. This is significantly higher than the in situ geomagnetic field of 46.4 microT (about 40 per cent high). Anisotropy of remanent magnetization is not seemed to be a possible cause of the high archeointensity estimate because it is only 3 per cent between the natural remanent magnetization (NRM) directions and laboratory TRM directions based on measurements of anhysteretic remanent magnetization (ARM). We reported these preliminary results from the CupB-1 in last November (Yamamoto et al., 2016 SGEPSS meeting).

Other possible cause of the high archeointensity estimate is uncorrectable laboratory alteration using ARMs. It is expected that different type of alterations could occur between heating in vacuum and air. For the Tokkuri-1 the specimens were split into two groups: one was heated in vacuum while the other was in air. So far we have obtained 6 successful results: 67.1 +/- 12.5 microT for the vacuum group (N=2) and 49.1 +/- 2.6 microT for the air group (N=2). We will continue the experiment and discuss these results.