Shell middens - Unlocking hidden archaeological information using Raman spectroscopy

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.