Adhering material remained on ancient potsherds represents foods and/or soot that were left after cooking, and therefore it should provide a clue directly related to the cooking in the old time. Although it has been used for radiocarbon dating, its use for the dietary study seems very scarce.

In this study about 700 charred materials adhering to potsherd were measured on carbon isotopes including ¹⁴C, nitrogen isotopes and their elemental ratios. The data were analyzed in the light of (1) marine food, (2) C4 plant and (3) fuels. Food-derived materials were expected inside and also outside as a boil-over. The fuel-derived one was expected in a form of soot on the outside of the pottery.

The measurements showed that delta-13 values of most samples are distributed between -27 to -25 per mil, suggesting that materials are derived from common land plants and animals. The carbon to nitrogen (C/N) ratios are distributed from 6-7 to more than 100, with 15-25 most probable. The ratio probably represents the mixture of plant and meat.

(1) Some of the data (5-10%) indicated the presence of marine food which is characterized by higher delta-¹³C and delta-¹⁵N, lower C/N ratio and older ¹⁴C age. Higher dependence on sea food was indicated for the northern part of Japan, in particular for Hokkaido, the northernmost main island.

(2) A small portion of samples has shown a symptom of C4 plants such as millet. These samples showed higher delta-¹³C value, with ¹⁴C dates consistent in the archaeological contexts, and C/N ratios were fairly high.

(3) The samples from Hokkaido indicated possible use of fossil fuel, peat for instance.

The charred material samples taken from the outside of pottery (Tsuishikari-2 archaeological site) showed similar delta-¹³C values at -24 per mil, high C/N ratios and much older radiocarbon ages than expected.

This work was supported by a Grant-in Aid for Creative Scientific Research of the Japan Society for the Promotion of Science (No.16GS0118, 15300295).