Molecular, isotopic and radiocarbon evidence for broomcorn millet cropping in Northeast France since the Bronze Age

Abstract

Molecular and isotopic investigation of lipids from soils filling several structures from an archaeological site located at Obernai (Alsace, NE France) has revealed the presence of miliacin, a triterpenoid marker from Panicum miliaceum (broomcorn millet), indicating that this cereal was cultivated at the site. The concentration profiles of miliacin within silos and its detection in other archaeological structures (e.g. Gaulish pit) suggest that miliacin did not originate from cereals stored in the silos but rather came from remains of millet from cultivated soils which filled the silos after they were abandoned. Furthermore, the 14 C age of miliacin isolated from a silo of the Second Iron Age was shown to be considerably older (Bronze Age) than the structure itself, revealing that the soil filling the silo therefore archived the molecular signature from past millet cropping, predating the digging of the silo. Thus, radiocarbon dating of the isolated miliacin allowed the timing of millet cropping to be determined, showing that it was established during the Bronze Age and the Roman Gaul period at Obernai. This is the first evidence of millet cultivation in Alsace dating back to the Bronze Age, bringing new perspectives on agricultural and past dietary practices in Eastern France. The combination of molecular studies and radiocarbon dating of individual lipids highlights the potential of hollow structures like silos and pits to act as "pedological traps", recording information on past vegetation cover or agricultural practices from the surface horizons of surrounding soils that filled these structures after abandonment.

Direct evidence from lipid residue analysis for the routine consumption of millet in Early Medieval Italy

“…10 μg g −1 ) of the molecule in this sample was much greater than previously reported (Heron et al, 2016) permitting a stable carbon isotope measurement by GC-C-IRMS. The δ 13 C value of this compound was −20.5‰ which is in excellent agreement with reported values from miliacin directed isolated from millet grains and extracted from soils (Courel et al, 2017;Jacob et al, 2008) and slightly enriched (ca. 3‰) compared to fatty acids extracted from previously reported prehistoric pottery associated with miliacin (Heron et al, 2016).…”

Lipid residue analysis of ceramic vessels from the Liujiawa site of the Rui State (early Iron Age, north China)

“…Two other isomers, β-amyrin ME (olean-12-en-3β-ol ME) and α-amyrin ME (urs-12-en-3β-ol ME), were also identified from their significant ions m/z at 440, 425, 218, 203 and 189, as well as their relative retention time on nonpolar columns (Han et al 2016, Avataneo andSablier, 2017). These pentacyclic triterpene compounds have all been previously detected in broomcorn millet and utilised as tracer biomarkers for indications of millet cultivation (Bossard et al 2013, Courel et al 2017. Simulated pottery cooking experiments have also revealed that miliacin can move from the millet into the ceramic matrix during the cooking process and, thus, can be used as biomarker for millet processing in pottery (Heron et al 2016).…”

Making the invisible visible: tracing the origins of plants in West African cuisine through archaeobotanical and organic residue analysis

“…;Motuzaite- Matuzeviciute et al 2016) and, more recently, in archaeological pottery(Heron et al 2016;Courel et al 2017;Kučera et al 2019), although it should be noted that it is not an African…”