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[HQR05-18] Collection method of volcanic ash for making the Usultan-style earthenware in Chalchuapa, El Salvador, demonstrated using WDS analysis of volcanic glass in ceramic paste
Keywords:El Salvador, Arce Tephra, wave-length dispersive X-ray microprobe analyzer(WDS), chemical analysis of volcanic glass, ceramic paste of earthenware pottery
In volcanic areas, volcanic ash is generally used as a material for making earthenware pottery. Then the X-ray microprobe analysis of the volcanic glass contained in the paste of earthenware can provide available data to clarify the producing area and the producing method of the pottery. Analysis of volcanic glass which reflects the chemistry of the magma is most effective to identify volcanic ash, and a wavelength dispersive X-ray microanalyzer (WDS) providing the grain-by-grain chemical analysis of volcanic glass is recognized as an effective analysis tool to identify the volcanic ash.
This method was previously used for revealing production area of the Jomon-style earthenware in Tohoku district in Japan (Shiba, et al., 2014). Kitamura (2022) analyzed volcanic glass contained by a piece of Usulutan-style pottery, which was excavated in the La Cuchilla zone at the archaeological site of Chalchuapa, western El Salvador, using the same method and illustrated that volcanic ash of the Arce tephra was utilized selectively for making pottery.
The Arce Tephra is an extensive pumice fall (72 ka) originated from Coatepeque Caldera located in the neighbor area of Chalchuapa. While Kitamura (2017) demonstrated the chemical composition of volcanic glass in each of units divided into three using WDS, Kutterolf, et al. (2020) divided it more precisely into 10 units based on WDS chemical analysis of volcanic glass by each unit.
In this study, the chemical composition of volcanic glass contained in two pieces of the Usulutan-style earthenware excavated in the La Cuchilla zone at the archaeological site of Chalchuapa were analyzed using WDS (JEOL JXA-8230) in the laboratory of Global Environment and Disaster Prevention Sciences, the Faculty of Science and Technology, Hirosaki University, and were compared with each chemistry of samples from 7 units (I to VII) collected at the location 2 km northwest of the archeological site and from 9 units (III to X) at the 15 km eastern northeast of the site, to clarify which unit of the tephra was used for making the earthenware.
As a result, chemical composition of volcanic glass from the middle unit (unit V) and the lower units (Unit II to IV) of the Arce Tephra shows bimodal (fig. 2 & 3)while chemistry of volcanic glass from the upper units (unit VI and VII) and lowermost unit (Unit I) shows mostly unimodal (fig. 1). On the other hand, volcanic glass in the ceramic paste of earthenware shows chemically bimodal composition (fig.4), and each of the modes is consistent with the each of the modes of middle and lower units of Arce Tephra, respectively. The result indicates that the lower and middle units or a part of them could be used at least for making pottery.
In addition, the number of volcanic glasses belonging to the two modes from the earthenware is roughly the same, and the ratio of chemical plots of volcanic glass that falls between the two modes is small at a few percent. No unit is found that has such feature alone, so that volcanic ash for making pottery was possible to be collected from the several units around the lower part of the Arce Tephra.
This method was previously used for revealing production area of the Jomon-style earthenware in Tohoku district in Japan (Shiba, et al., 2014). Kitamura (2022) analyzed volcanic glass contained by a piece of Usulutan-style pottery, which was excavated in the La Cuchilla zone at the archaeological site of Chalchuapa, western El Salvador, using the same method and illustrated that volcanic ash of the Arce tephra was utilized selectively for making pottery.
The Arce Tephra is an extensive pumice fall (72 ka) originated from Coatepeque Caldera located in the neighbor area of Chalchuapa. While Kitamura (2017) demonstrated the chemical composition of volcanic glass in each of units divided into three using WDS, Kutterolf, et al. (2020) divided it more precisely into 10 units based on WDS chemical analysis of volcanic glass by each unit.
In this study, the chemical composition of volcanic glass contained in two pieces of the Usulutan-style earthenware excavated in the La Cuchilla zone at the archaeological site of Chalchuapa were analyzed using WDS (JEOL JXA-8230) in the laboratory of Global Environment and Disaster Prevention Sciences, the Faculty of Science and Technology, Hirosaki University, and were compared with each chemistry of samples from 7 units (I to VII) collected at the location 2 km northwest of the archeological site and from 9 units (III to X) at the 15 km eastern northeast of the site, to clarify which unit of the tephra was used for making the earthenware.
As a result, chemical composition of volcanic glass from the middle unit (unit V) and the lower units (Unit II to IV) of the Arce Tephra shows bimodal (fig. 2 & 3)while chemistry of volcanic glass from the upper units (unit VI and VII) and lowermost unit (Unit I) shows mostly unimodal (fig. 1). On the other hand, volcanic glass in the ceramic paste of earthenware shows chemically bimodal composition (fig.4), and each of the modes is consistent with the each of the modes of middle and lower units of Arce Tephra, respectively. The result indicates that the lower and middle units or a part of them could be used at least for making pottery.
In addition, the number of volcanic glasses belonging to the two modes from the earthenware is roughly the same, and the ratio of chemical plots of volcanic glass that falls between the two modes is small at a few percent. No unit is found that has such feature alone, so that volcanic ash for making pottery was possible to be collected from the several units around the lower part of the Arce Tephra.