[M-ZZ43] Transdisciplinary Network linking Space-Earth Environmental Science with History and Archaeology

[MZZ43-P04] Estimate of the firing environment of archaeological artifacts based on transition of magnetic mineral assembly upon heating

*Chie Kato¹, Tadahiro Hatakeyama², Tatsuro ADACHI¹ (1.Faculty of Social and Cultural Studies, Kyushu University, 2.Institute of Frontier Science and Technology, Okayama University of Science)

Keywords:rock magnetism, archaeological artifact, firing environment

Heated artifacts and remains are among the most important archaeological materials. Investigating the conditions under which these artifacts were heated is essential to understanding the evolution and propagation of firing techniques and the lives of people at that time. focusing on the fact that magnetic iron minerals take various forms depending on the environment, we are conducting basic research to estimate the heat exposure conditions of archaeological artifacts and remains through magnetic measurements. First, we conducted thermomagnetic experiments on major iron minerals in soils and clays to investigate their transition upon heating. The results show that at relatively low temperatures of <500°C, magnetization increases or decreases at various temperatures depending on the type of iron mineral and whether the heating atmosphere is in air or vacuum. In particular, the magnetization of lepidocrocite, an iron oxide-hydroxide found in paddy fields, increased rapidly at 200°C to 250°C and decreased rapidly around 500°C. It is indicated that maghemite (or magnetite) was formed by dehydration of lepidocrocite, which was subsequently transformed into stable hematite. These results are expected to provide a clue to the temperature of heat exposure of artifacts heated at relatively low temperatures. Next, clay samples imitating the paste of earthenware were heated at different temperatures and redox atmospheres to determine how their magnetic properties change. The magnetization of the samples was maximum when fired at 400°C. The magnetization decreased as the firing temperature increased, and a component with high coercivity tended to appear. It was also shown that heating in a vacuum resulted in stronger magnetization, i.e., a higher percentage of magnetite, than in air. In the future, we would like to clarify the relationship between magnetic parameters and firing conditions by comparing these results with the measurement results of actual excavated artifact and remains and samples fired in a reconstructed kiln.