Understanding the Possible Contamination of Ancient Starch Residues by Adjacent Sediments and Modern Plants in Northern China

The potential contamination of ancient residues from both modern plant sources and sediments adjacent to archaeological contexts can complicate interpretation in the field of starch grain analysis, thus affecting the sustainable use of the method in archaeobotany. In this study, we examined two potential sources of contamination at a wheat field in Shandong Province and a maize field in Beijing, the Nanzhuangtou site in Hebei Province and the Zhuannian site in Beijing in Northern China. Surface soils from active farmland and its surrounds, as well as deposits from clearly-defined cultural layers, overlying layers, and underlayers at the archaeological sites were subjected to starch grain analysis. No starches were recovered from any of the 16 surface soil samples from fields of wheat and maize, or their environs. This outcome indicates that starches do not preserve well in active surface soils. Further results from the analysis of 33 samples from the two sites demonstrate that starches do not occur in either the overlying layers or underlayers of cultural deposits. Thus, starch grains extracted from the surface residues of artifacts were not deposited from adjacent sediments after the artifacts were abandoned or buried. Further, cultural sediments contained fewer starch grains than the surfaces of artifacts in the same horizon. Thus, if any starch grains on the surfaces of tools are the result of contamination, ancient cultural sediments are the primary source. In conclusion, we offer insights for the prevention of misinterpretation of extraneous residues and sustainable development for the use of starch grain analysis.