Strontium isotope tracing of prehistoric human mobility in France
Date
2015
Authors
Willmes, Malte
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Abstract
Human mobility in recent history is well documented and often related to drastic external changes,
including war, famine, and the discovery and exploration of new geographic regions and resources.
Reconstruction of mobility patterns in prehistory is thus a crucial part of understanding the forces that
drove our ancestors, but it is complicated by the fact that the archaeological evidence becomes scarce
as we go back in time. The application of stable isotopes in archaeological research has revolutionised
palaeomobility studies by providing independent data, which can be used to evaluate models of
migration, trade, and cultural change. This research project explores the use of strontium isotope ratios
(87Sr/86Sr) to trace prehistoric human mobility patterns. Strontium isotope ratios vary across the
landscape based on the age and composition of the underlying geology. Through diet humans incorporate
strontium into their skeletal tissues such as bones and teeth. Teeth form during childhood and are
resistant to weathering and geochemical alteration, often preserving the original isotope values. By
comparing the strontium isotope ratios in teeth to the variations of strontium isotopes in the landscape
it becomes possible to investigate mobility across geologically different areas between childhood and
death.
This study establishes the Isotopic Reconstruction of Human Migration (IRHUM) reference database
and provides the first dataset of 87Sr/86Sr isotope ratios of plant and soil samples, covering all major
geologic units of France. This provides a new powerful tool for the archaeological science community
as it allows the mapping of the variations of bioavailable 87Sr/86Sr isotope across the landscape. Utilizing
this dataset, a bioavailable 87Sr/86Sr isotope map for archaeological provenance studies in France is
created.
For the application of this method to human fossil teeth new analytical methods to detect diagenetic
overprint were tested. These now allow for rapid scanning to investigate the suitability of samples,
minimising the damage to fossil remains. Least destructive analytical techniques for strontium isotope
analysis, such as micro drilling thermal ionisation mass spectrometry and in situ laser-ablation MC-ICPMS,
were further developed and applied to a range of materials of known composition, including shark
and dugong teeth, modern and archaeological fauna samples, and fossil and modern human teeth.
Finally, strontium isotope tracing was applied to three key archaeological sites in France, including the
Neanderthal sites of Moula-Guercy, and the Neolithic sites of Le Tumulus des Sables and La Grotte des
Perrats. Strontium isotope tracing proved to be a valuable technique and in combination with additional
strings of evidence from archaeological material and other isotopic tracers, such as oxygen, improved
our understanding of prehistoric human mobility at these sites. By covering different geographic
locations and different time periods this study tests geochemical fingerprinting and offers new insights
into these renowned archaeological sites.
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Keywords
Strontium, Human mobility, Neanderthals, Isotopes, France, Migration, Laser ablation
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