Abstract
Paleomagnetic information reconstructed from archeological materials can be utilized to estimate the archeological age of excavated relics, in addition to revealing the geomagnetic secular variation and core dynamics. The direction and intensity of the Earth’s magnetic field (archeodirection and archeointensity) can be ascertained using different methods, many of which have been proposed over the past decade. Among the new experimental techniques for archeointensity estimates is the Tsunakawa–Shaw method. This study demonstrates the validity of the Tsunakawa–Shaw method to reconstruct archeointensity from samples of baked clay from archeological relics. The validity of the approach was tested by comparison with the IZZI-Thellier method. The intensity values obtained coincided at the standard deviation (1σ) level. A total of 8 specimens for the Tsunakawa–Shaw method and 16 specimens for the IZZI-Thellier method, from 8 baked clay blocks, collected from the surface of the kiln were used in these experiments. Among them, 8 specimens (for the Tsunakawa–Shaw method) and 3 specimens (for the IZZI-Thellier method) passed a set of strict selection criteria used in the final evaluation of validity. Additionally, we performed rock magnetic experiments, mineral analysis, and paleodirection measurement to evaluate the suitability of the baked clay samples for paleointensity experiments and hence confirmed that the sample properties were ideal for performing paleointensity experiments. It is notable that the newly estimated archaomagnetic intensity values are lower than those in previous studies that used other paleointensity methods for the tenth century in Japan.
Highlights
The Earth’s magnetic field is known to vary significantly with time
Variations with a comparatively short period between several decades and several millennia are referred to as geomagnetic secular variations, and their identification is needed to understand the dynamic behavior in the core using the dynamo calculation and to estimate the archeological age of excavated relics
For the Tsunakawa–Shaw method, many studies have focused on volcanic rocks (e.g., Yamamoto and Tsunakawa 2005; Mochizuki et al 2006; Yamamoto et al 2010; Mochizuki et al 2011, 2013; Yamazaki and Yamamoto 2014; Ahn et al 2016), but only one has applied the method to samples taken from clay from the floor of a reconstructed kiln from the present age that was burnt in a known magnetic field, demonstrating that such samples are suitable for archeointensity research (Yamamoto et al 2015)
Summary
The Earth’s magnetic field (geomagnetic field) is known to vary significantly with time. Age estimation is done by comparing the value of Numerous archeomagnetic studies have been conducted in Japan using oriented baked clay samples collected from several types of burnt relics, such as kilns (e.g., Hirooka 1977). These studies used samples from excavations performed by local government archeological research organizations. For the Tsunakawa–Shaw method, many studies have focused on volcanic rocks (e.g., Yamamoto and Tsunakawa 2005; Mochizuki et al 2006; Yamamoto et al 2010; Mochizuki et al 2011, 2013; Yamazaki and Yamamoto 2014; Ahn et al 2016), but only one has applied the method to samples taken from clay from the floor of a reconstructed kiln from the present age that was burnt in a known magnetic field, demonstrating that such samples are suitable for archeointensity research (Yamamoto et al 2015)
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