Samples undergoing routine pre-treatment to remove contaminants and isolate the original wood prior to radiocarbon dating. Pre-treatment consists of a sequence of washes with organic solvents, acid and base solution.
One of the key aims of the Trinidad project is to establish a clear chronological framework for the wood artefacts recovered from Pitch Lake, in order to directly link them to the island's (pre)history. This, however, is not without its challenges: pitch itself is of considerable age, and may have soaked into the artefacts immersed in the lake. A small sample of the pitch remaining on the zoomorphic bench provided a radiocarbon date of 41300 ± 800 BP (calibrated to 44342-41402 cal BC). Even small amounts of such a material remaining in a sample can have significant impact on the radiocarbon date, giving it an artificially old age. Another challenge was the ‘old wood’ problem, where an ancient, slow growing tree may have been used to carve the artefact, and without due caution, a sample could give a date of centuries older than when it was felled and carved.
To deal with these problems, 14C samples were first carefully selected from the outer edge of each carving, in order to ensure that a date as close as possible to the felling of the tree. At the same time, experiments involving the deliberate contamination of material of known age with pitch were undertaken in order to ensure that the pitch could be removed, and was not significantly affecting the radiocarbon date. We can therefore be confident in our results.
A transmitted light micrograph of the transverse section of Carapa cf. guianensis.
The scale bar is 500um. Courtesy of Alex Wiedenhoeft.
Another key aim of the project was to determine the types of wood chosen by carvers for their work. This helps us to better understand how indigenous Caribbean populations interacted with their environment and can potentially provide insights into the more complex symbolic meanings behind their choices.
The density and hardness of material had direct impact on the labour involved in carving – for example Guaiacum sp, among the hardest woods known in the world, was used regularly in the carving of large-scale sculpture in the pre-Columbian Greater Antilles. Did the people of Pitch Lake also favour such hard woods, or was there a greater diversity of timbers selected for their needs?
Strontium isotopes and provenance
A school group gathers beneath the branches of an Andira sp. tree, growing on the edge of Pitch Lake. Herbarium and strontium samples were collected from this tree for the isotope study.
Trees take up their nutrients from the groundwater absorbed through their roots, and in so doing incidentally absorb small amounts of strontium (Sr), a chemical element whose isotopic composition varies depending on the underlying geology. The strontium isotope ‘signature’ can be measured in the wood, and can provide some clues as to where the wood used to carve the artefact came from. It is usually not possible to be very specific, but certain locations – sometimes entire islands (for example limestone vs. volcanic islands) – can be ruled out or supported. Identifying the source of the woods enables us to explore such issues as whether the carvings were likely to have been made locally (around Pitch Lake), or whether they may have been imports to the area. This in turn informs our understanding of local vs. regional styles as well as potential inter- and/or intra-island (or mainland) trade links.
But in order to interpret an artefact’s strontium isotope value, we first need to develop a comparative dataset of strontium isotope values from living trees for the region – and this was one of the most rewarding fieldwork elements of the study, which you can read about on the blog. Once we identified which trees to target, selecting the same woods used to carve the original artefacts, we collected both an isotope sample and two herbarium specimens - one for the National Herbarium of Trinidad and Tobago and another for National Museums Liverpool. These not only provide a context for the archaeological isotope results, but also contribute to the growing botanical and geophysical knowledge of the islands.