Anthracological study of a Chalcolithic funerary deposit from Perdigões (Alentejo, Portugal): A new analytical methodology to establish the wood burning temperature

PLoS One. 2023 Jul 7;18(7):e0287531. doi: 10.1371/journal.pone.0287531. eCollection 2023.

Abstract

Anthracological analyses of charcoal samples retrieved from Pit 16 of Perdigões (Reguengos de Monsaraz, Portugal), a secondary deposition of cremated human remains dated back to the middle of the 3rd millennium BC, enabled the identification of 7 different taxa: Olea europaea, Quercus spp. (evergreen), Pinus pinaster, Fraxinus cf. angustifolia, Arbutus unedo, Cistus sp. and Fabaceae. All taxa are characteristic of both deciduous and evergreen Mediterranean vegetation, and this data might indicate that the gathering of woods employed for the human cremation/s occurred either on site, or in its vicinity. However, considering both the large distribution of the identified taxa and data about human mobility, it is not possible to conclusively determine the origin of the wood used in the cremation(s). Chemometric analysis were carried out to estimate the absolute burning temperature of woods employed for the human cremation/s. An in-lab charcoal reference collection was created by burning sound wood samples of the three main taxa identified from Pit 16, Olea europaea var. sylvestris, Quercus suber (evergreen type) and Pinus pinaster, at temperatures between 350 and 600 °C. The archaeological charcoal samples and the charcoal reference collection were chemically characterized by using mid-infrared (MIR) spectroscopy in the 1800-400 cm-1 range, and Partial Least Squares (PLS) regression method was used to build calibration models to predict the absolute combustion temperature of the archaeological woods. Results showed successful PLS forecasting of burn temperature for each taxon (significant (P <0.05) cross validation coefficients). The anthracological and chemometric analysis evidenced differences between the taxa coming from the two stratigraphic units within the Pit, SUs 72 and 74, suggesting that they may come from two different pyres or two different depositional moments.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Charcoal / analysis
  • Cremation*
  • Humans
  • Pinus*
  • Portugal
  • Temperature
  • Wood / chemistry

Substances

  • Charcoal

Grants and funding

This study was developed in the framework of the HERITAS Doctoral Program througha PhD grant to G.C. (FCT (PD/BD/128278/2017) funded by the FCT (Fundação para aCiência e a Tecnologia). Analyses were developed at the HERCULES Laboratory of the University of Évora, also funded by FCT through the projects UIDB/04449/2020 and UIDP/04449/2020. The funder FCT (Fundação para a Ciência e a Tecnologia) had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.