The potential of triterpenoids as chemotaxonomic tools to identify and differentiate genuine, adulterated and archaeological balsams

International audiencePlant exudates have been extensively used in the past for different applications related to their olfactory, physical or medical properties. Their identification in archaeological samples relies, notably, on the characterisation of chemotaxonomic molecular markers but is often hampered by the severe alteration of their typical genuine molecular signature due to ageing. Among these exudates, those recovered from Styrax, Liquidambar and Myroxylon tree species – defined as balsams – have been exploited in the past for their pleasant scent and medical properties. They are characterised by a large variety of aromatic compounds, especially of the cinnamate and benzoate series, which can be used to assess their botanical source. These compound series may, however, be subject to alteration over time during exposure to environmental conditions in the case of archaeological material. As a result, their reliability as chemotaxonomic markers to characterise and discriminate archaeological balsams is problematic and questionable. We have, therefore, carried out a comparative analysis of various extant balsams (Styrax officinalis, S. paralleloneurum, S. tonkinensis, Liquidambar styraciflua, L. orientalis and Myroxylon balsamum var. pereirae) using gas chromatography–mass spectrometry to search for more solid lipid markers. The results revealed that a distinction between styrax, liquidambars, Peru and Tolu balsams is possible based on the distribution of pentacyclic triterpenes. The predominance of uncommon 6‑oxygenated derivatives of oleanolic acid among triterpenoids could be specifically related to styrax resins. Liquidambar gums were characterised by the predominance of oleanonic acid together with uncommon 3-epi oleanolic and ursolic acids, whereas Peru balsam was rich in cinnamic and benzoic acids, but devoid of triterpenoids. Thanks to the high specificity of some of these triterpenes, already known for their low volatility and robustness towards alteration processes, they should be considered as reliable molecular tools for the unambiguous identification of archaeological balsams. In addition to archaeological applications, these triterpenic markers might also find an application for the detection of counterfeit balsams

Investigating the formation and diagnostic value of ω-(o-alkylphenyl)alkanoic acids in ancient pottery

Long chain ω‐(o‐alkylphenyl)alkanoic acids (APAAs) derived from the heating of unsaturated fatty acids have been widely used for the identification of aquatic products in archaeological ceramic vessels. To date, little attention has been paid to the diagnostic potential of shorter chain (<C20) APAAs, despite their frequent occurrence. Here, a range of laboratory and field experiments and analyses of archaeological samples were undertaken to investigate whether APAAs could be used to further differentiate different commodities. The results of this study provide new insights regarding conditions for the formation of APAAs and enable us to propose novel criteria to distinguish different natural products

The use of early pottery by hunter-gatherers of the Eastern European forest-steppe

The Eastern European steppe and forest-steppe is a key region for understanding the emergence of pottery in Europe. The vast region encompasses the basins of two major waterways, the Don and the Volga rivers, and was occupied by hunter-gatherer-fisher communities attracted to highly productive forest/aquatic ecotones. The precise dates for the inception of pottery production in this region and the function of pottery is unknown, but such information is vital for charting the pan-Eurasian dispersal of pottery technology and whether there were common motivations for its adoption. To investigate, we conducted AMS dating, including a re-evaluation of legacy radiocarbon dates together with organic residue analysis and microscopy. The dating programme was able to clarify the sequence and show that hunter-gatherer pottery production was unlikely in this region before the 6th millennium BC. Regarding use, stable isotope and molecular analysis of 160 pottery samples from 35 sites across the region shows that terrestrial animal carcass fats were preferentially processed in pots at Middle Volga sites whereas aquatic resources dominate the residues in pottery from the Middle and Upper Don basin. This is supported by fragments of fish, legumes and grasses in the available charred deposits adhering to the inside of pottery from the Don basin. Since the sites from both river basins had similar environmental settings and were broadly contemporaneous, it is posited that pottery use was under strong cultural control, recognisable as separate sub-regional culinary traditions. The ‘aquatic hypothesis’, previously suggested to explain the emergence of Eurasian pottery, cannot be substantiated in this context

The transmission of pottery technology among prehistoric European hunter-gatherers

Human history has been shaped by global dispersals of technologies, although understanding of what enabled these processes is limited. Here, we explore the behavioural mechanisms that led to the emergence of pottery among hunter-gatherer communities in Europe during the mid-Holocene. Through radiocarbon dating, we propose this dispersal occurred at a far faster rate than previously thought. Chemical characterization of organic residues shows that European hunter-gatherer pottery had a function structured around regional culinary practices rather than environmental factors. Analysis of the forms, decoration and technological choices suggests that knowledge of pottery spread through a process of cultural transmission. We demonstrate a correlation between the physical properties of pots and how they were used, reflecting social traditions inherited by successive generations of hunter-gatherers. Taken together the evidence supports kinship-driven, super-regional communication networks that existed long before other major innovations such as agriculture, writing, urbanism or metallurgy

Caractérisation de substances naturelles en contexte archéologique : apport des études moléculaires, isotopiques et de la datation au 14C

In this archaeometric study, lipid biomarkers from archaeological soils and organic substances originating from plants found on artefacts were investigated by GC-MS. In addition, the stable carbon isotopic composition of individual lipids and the 14C age (AMS MICADAS) of soil organic matter, lipid extracts and one isolated compound (miliacin) were determined. Such an archaeometric approach allowed:- the existence of a millet cultivation during the Bronze Age in Alsace to be unveiled for the first time based on preserved molecular remains of this cereal in agricultural soils trapped within grain silos dated from the Iron Age.- the function of uncharacterized archaeological structures to be identified as ancient latrines and a stall area based on the identification of faecal steroidal markers.- reliable chemotaxonomic criteria for the authentication of styrax resins and liquidambar gums to be established using specific organic markers (triterpenoids, notably).- the vegetal component of an organic coating decorating a skull from the 9th millennium BC (Nahal Hemar site, Israel) to be identified as a resin from Styrax officinalis.- the use of birch bark tar as adhesive for the making of a jewellery dated from the Iron Age to be discovered.Ces travaux d'archéométrie concernent l’étude moléculaire par GC-MS de marqueurs lipidiques (biomarqueurs) préservés au sein de sols archéologiques et de substances végétales impliquées en tant qu'ingrédients dans la confection d’artefacts. Des analyses complémentaires en isotopie du carbone de composés individuels et des mesures de datation au 14C (AMS MICADAS) de la matière organique totale des sols, d'extraits lipidiques et d'un composé individuel (miliacine) ont également été effectuées. Cette approche a permis:- de montrer l’existence de la culture de millet dès l’âge du Bronze en Alsace, les sols associés à cette culture et leur contenu organique ayant été piégés et préservés dans des silos à grains enterrés datés de l’âge du Fer.- d'identifier la nature de structures archéologiques comme étant d'anciennes latrines et une aire de stabulation de bétail via l'identification de stéroïdes fécaux.- d'établir des critères chimiotaxonomiques fiables basés sur l'analyse des lipides pour l’authentification de résines de styrax et de liquidambars.- d'identifier la nature d'une résine issue de Styrax officinalis ayant été incorporée dans l’enduit organique ornant un crâne décoré (IXème millénaire av. J.-C., site de Nahal Hemar, Israël).- de mettre en évidence l’emploi de brai de bouleau comme agent collant lors de la confection d’un bijou daté du Premier âge du Fer

Characterization of natural substances in an archaeological context : contribution of the molecular and isotopic studies and of the 14C dating

Ces travaux d'archéométrie concernent l’étude moléculaire par GC-MS de marqueurs lipidiques (biomarqueurs) préservés au sein de sols archéologiques et de substances végétales impliquées en tant qu'ingrédients dans la confection d’artefacts. Des analyses complémentaires en isotopie du carbone de composés individuels et des mesures de datation au 14C (AMS MICADAS) de la matière organique totale des sols, d'extraits lipidiques et d'un composé individuel (miliacine) ont également été effectuées. Cette approche a permis:- de montrer l’existence de la culture de millet dès l’âge du Bronze en Alsace, les sols associés à cette culture et leur contenu organique ayant été piégés et préservés dans des silos à grains enterrés datés de l’âge du Fer.- d'identifier la nature de structures archéologiques comme étant d'anciennes latrines et une aire de stabulation de bétail via l'identification de stéroïdes fécaux.- d'établir des critères chimiotaxonomiques fiables basés sur l'analyse des lipides pour l’authentification de résines de styrax et de liquidambars.- d'identifier la nature d'une résine issue de Styrax officinalis ayant été incorporée dans l’enduit organique ornant un crâne décoré (IXème millénaire av. J.-C., site de Nahal Hemar, Israël).- de mettre en évidence l’emploi de brai de bouleau comme agent collant lors de la confection d’un bijou daté du Premier âge du Fer.In this archaeometric study, lipid biomarkers from archaeological soils and organic substances originating from plants found on artefacts were investigated by GC-MS. In addition, the stable carbon isotopic composition of individual lipids and the 14C age (AMS MICADAS) of soil organic matter, lipid extracts and one isolated compound (miliacin) were determined. Such an archaeometric approach allowed:- the existence of a millet cultivation during the Bronze Age in Alsace to be unveiled for the first time based on preserved molecular remains of this cereal in agricultural soils trapped within grain silos dated from the Iron Age.- the function of uncharacterized archaeological structures to be identified as ancient latrines and a stall area based on the identification of faecal steroidal markers.- reliable chemotaxonomic criteria for the authentication of styrax resins and liquidambar gums to be established using specific organic markers (triterpenoids, notably).- the vegetal component of an organic coating decorating a skull from the 9th millennium BC (Nahal Hemar site, Israel) to be identified as a resin from Styrax officinalis.- the use of birch bark tar as adhesive for the making of a jewellery dated from the Iron Age to be discovered

TRITERPENOIDS FROM BALSAMS: USEFUL MARKERS TO RECOGNIZE GENUINE, ADULTERATED AND ARCHAEOLOGICAL RESINS

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Birch bark tar and jewellery: the case study of a necklace from the Iron Age (Eckwersheim, NE France)

International audienceOrganic residue analysis has been undertaken on an organic material found on a necklace with a pendant unearthed from a necropolis dated to the Early Iron Age (800-475 BC) and located in Eckwersheim (NE France). The molecular composition of the substance, which was investigated using gas chromatography coupled to mass spectrometry, points towards an adhesive used to stick two bronze half-spheres to form a pendant. The predominance of triterpenoids from the lupane series led to the identification of the adhesive as a birch bark tar and constitutes a rare example of the use of such a material in jewellery in the pas

Analyse, isolement et datation au 14C de lipids dans les sols. L’exemple des tétraéthers de diglycérol

We report here the development of an analytical protocol for the specific isolation of isoprenoid and branched glycerol dialkyl glycerol tetraethers (i-and br-GDGTs, respectively) of microbial origin from soil samples for radiocarbon dating. This protocol comprises an extraction step followed by several chromatographic steps combining different techniques (silica gel column chromatography, high performance liquid chromatography and thin layer chromatography). Radiocarbon dating of these two series of compounds, isolated from a surface sample and a deep horizon sample (40-50 cm) from a soil profile, shows that i-and br-GDGTs in the deep sample have a comparable mean residence time (MRT), despite their different biological origin. These MRT are, however, lower than those measured for the soil organic matter (SOM) and for the different compartments of SOM. This result suggests that i-and br-GDGTs originate from microorganisms using the same carbon source, made of a combination of ancient and recent organic matter. It can also be envisaged that these compounds originate from both recent and ancient microbial populations. These preliminary results suggest that the use of (palaeo) proxies based on the distributions of GDGTs might be questionable in the case of soils or, at least, that caution is needed when interpreting soil GDGT signals in terms of (palaeo) environmental reconstructions