Carbon and nitrogen isotope analysis of carbonized cookies : Case study of the Shimohirooka site, Ibaraki prefecture

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  • クッキー状炭化物の炭素・窒素同位体分析 : 茨城県下広岡遺跡の事例
  • クッキージョウ タンカブツ ノ タンソ ・ チッソ ドウイタイ ブンセキ : イバラキ ケンカ ヒロオカ イセキ ノ ジレイ

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Abstract

In Japan, carbonized archaeological relics, called "Jomon cookies" (carbonized bread or cookie like materials) were excavated, that contain residues of the nut's starch from the Jomon period. In this study, we will attempt to elucidate the content of carbonized cookies by conducting carbon and nitrogen isotope analysis, C/N ratio analysis. The authors have been conducting research using this method since 2009. As a result, it was found that the carbonized cookies were likely to be mainly composed of starch from nuts. We also pointed out that these data had a v叩small dispersion range, so the origin of their content was relatively simple. In analyzes up to 2012, it was possible to distinguish between three types (1: carbonized cookies, 2: perilla seed cluster, 3: asphalt). We have not been able to confirm any evidence of animal origin with a high nitrogen content, such as the''hamburger stealc shaped'" type that was identified in the fatty acid analysis of the Ondashi site in the 1990s. In this paper, we report the analysis results of the Shimohirooka site, where samples were collected in 2016, and discuss them together with previous research results. In this analysis, we conducted carbon and nitrogen isotope analysis, C/N ratio analysis, and radiocarbon dating on a total of 7 samples: 3 carbonized cookies, 2 carbonized oalc seeds, and 2 carbonized walnut kernels. The results for the 3 carbonized cookies showed that the nitrogen isotope ratio and nitrogen content were slightly higher than the carbonized cookies from the previous study and showed a tendency similar to that of perilla seed cluster. This result tends to be slightly different from the isotope ratio results for carbonized oalc seeds. Therefore, it is difficult to think that oalc was used for only one type of content. The result of 1 carbonized cookie may have animal origin, so we need to wait for similar cases in the future and carefully consider the results.

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