Shell middens - Unlocking hidden archaeological information using Raman spectroscopy

Abstract

The study of shell middens and archaeological marine shells is important to investigate palaeoenvironments and human development. Analytical methods, such as isotope analyses, used for these reconstructions can only be trustworthy if the shells have not been drastically changed by the effect of diagenesis or by human intervention, eg., heating of the shells. These changes are difficult to quantify by the current methods, which are either limited or destructive. In this thesis, a quantitative method for the assessment of diagenesis and the evidence of heating in sea shells has been proposed with Raman spectroscopy (RS), which is based on the inelastic scattering of light, whereby a small difference in the incoming and outgoing light energy provides highly sensitive spectroscopic information. The quantitative analysis of the Raman spectrum involved peak fitting procedures to obtain the peak position, amplitude and full width half maximum (FWHM) parameters, which were then compared between modern and ancient Conomurex fasciatus and Nucella sp. shells to obtain markers of diagenesis. Modern Conomurex fasciatus shells were heated at different temperatures and time conditions with the quantitative Raman parameters compared across different heat-treatments that were later compared to burnt archaeological Conomurex fasciatus fragments obtained from the same shell midden. The results have proven that quantitative RS is responsive to diagenetic alterations and heating of sea shells indicating an increase in the calcium carbonate crystallinity caused by the degradation of the organic macromolecules that supported the strained mineral lattice, demonstrating that RS is sensitive to indicate diagenesis in sea shells.