Golden artefacts, resin figurines, body adhesives and tomb sediments from the pre-Columbian burial site El Caño (Gran Coclé, Panamá): tracing organic contents using molecular archaeometry

Abstract

This research aimed to determine the origin of organic residues from funerary contexts in the El Caño settlement (Gran Coclé area, Panamá, Central America) by means of multiple molecular probing techniques (GC-MS of organic solvent extracts and pyrolysis-GC-MS, THM-GC-MS and FTIR of solid samples). The samples include particles of precious resin figurines, fillings of golden objects, tomb sediments, plant exudates from extant plants (reference collection) and other reference materials (amber). The labdane diterpene fingerprints (eperuic, iso-ozic, copalic and kolavenic acids and derivatives) of the resin figurines, a resinous bead and several other samples, suggest that they were composed primarily of Hymenaea resin. Besides traditional interpretation approaches (visual comparison of chromatograms and relative proportions data), we used a novel OpenChrom® application that resolves complex pyrolysis chromatograms by screening data from archaeological samples for marker products defined on the basis of a reference collection (ChromIdent). ChromIdent confirmed the Hymenaea origin of many samples and also Burseraceae resin was identified in some samples, which is present as a minor ingredient in resin figurines (indicative of mixing practices) and as the dominant resin in tomb sediment that had been in contact with the corpses (indicating balsaming practices). The degree of polymerization of the Hymenaea resin was higher than for extant resin but diagenetic alteration (especially condensation of cyclic moieties) was much smaller than for amber, implying that the manufacturers used resin (or copal), not amber. These results were confirmed by FTIR, which allowed identification of non-fossil Hymenaea resin as the main constituent of one of the resin figurines. Several golden object infillings contained wax derivatives, probably beeswax, accompanied by various types of plant resin, which may well indicate the use of meliponines' cerumen for manufacturing (lost-wax casting). The findings highlight the potential of complementary molecular techniques to resolve questions on materials and manufacturing of archaeological artefacts, and the need for cross-comparison of molecular and ethnographic information in the study of archaeobotanical remains and the processes involved in their management.