Article Geology

Chinese Science Bulletin

, Volume 56, Issue 14, pp 1495-1502

Open Access This content is freely available online to anyone, anywhere at any time.

Investigation of the ultrastructural characteristics of foxtail and broomcorn millet during carbonization and its application in archaeobotany

  • Qing YangAffiliated withState Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of SciencesGraduate University of Chinese Academy of Sciences
  • , XiaoQiang LiAffiliated withThe Laboratory of Human Evolution, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences Email author 
  • , XinYing ZhouAffiliated withState Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of SciencesThe Laboratory of Human Evolution, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences
  • , KeLiang ZhaoAffiliated withState Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of SciencesGraduate University of Chinese Academy of Sciences
  • , Ming JiAffiliated withGraduate University of Chinese Academy of SciencesNanjing Institute of Geography and Limnology, Chinese Academy of Sciences
  • , Nan SunAffiliated withState Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of SciencesGraduate University of Chinese Academy of Sciences

Abstract

Fossilized caryopses (or grains) of foxtail millet (Setaria italica) and broomcorn millet (Panicum miliaceum) are important archaeobotanical materials for the study of early human agricultural activities. The morphology and ultrastructural characteristics of carbonized modern millets caryopses treated in a drying oven and burning in a field were investigated at different temperatures to study how fossilized millets are formed. The caryopses shrank gradually at temperatures below 200°C, and starch granules in the endosperm retained their crystalline structure. At 250°C the foxtail millet caryopses expanded, whereas the broomcorn millet caryopses were greatly deformed. At this temperature, the structure of the starch granules of both millets became amorphous. At 300°C the caryopses partially turned to ash and became porous, and the ultrastructure of the starch granules was transformed into alveolate cavities. Fossil caryopses from the prehistoric storage cellar at the Beiniu Site retained their crystalline structure and were formed by the dehydrating effect of carbonization, indicating that water molecules were not involved in the starch crystallization. The results of a field burning experiment demonstrated that the ultrastructure of carbonized caryopses placed on the ground under the fire was amorphous. The amorphous ultrastructure of the carbonized caryopses recovered from the archaeological layers is consistent with the expected structure of caryopses that have been carbonized at 250°C. Therefore, we suggest that the recovered caryopses were formed at about 250°C by baking rather than by burning in an open fire.

Keywords

foxtail millet broomcorn millet carbonization process ultrastructural characteristics archaeobotany