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Information - VGP23 Archaeological Geochemistry
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Event Information |
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‘Archaeological Geochemistry’ is the application of geochemical techniques to solve archaeological questions. Since archaeology is the study of past humans and societies, archaeological geochemistry might be interpreted as the application of geochemistry to the study of past humans and societies. More generally, it encompasses the use of geochemistry to understand past human behaviour, the response of human society to past environmental change, and the impact of past human activity on the environment.
We propose four themes within the session:
1. the geochemistry of archaeological bone and teeth
2. geochemical studies of trade and exchange
3. dendrochemistry – using tree rings to study environmental change and, particularly, as markers of past catastrophic events
4. tephra geochemistry – the use of distal tephra as chronostratigraphic markers in the archaeological record
The Geochemistry of Archaeological Bone and Teeth
There has been considerable interest over the past two decades concerning the use of chemical analysis (stable and heavy isotopes, trace elements, biomolecular analysis) of archaeological human bone and teeth as a source of information on the diet, mobility, status and health of individuals and groups of people. This has included measurements of ä13C and ä15N in bone collagen for dietary information, Sr, Pb and O isotopes in bone and dental enamel for mobility studies, trace elements in bone (Sr, Ba, etc.) for dietary studies, and the identification of microbial lipids as markers of disease. There has been intensive research on questions such as ‘how do different food sources contribute to the isotopic signals in different bone components?’, and ‘what is the effect of post-mortem alteration on the trace element and isotopic composition of bone and teeth?’. Notable applications have included tracing the origins of the Neolithic Alpine Iceman, and identification of incomers in the pre-contact city of Teotihuacan in Mexico, as well as attempting to chart the movement of the ‘Beaker folk’ in Late Neolithic Europe. More recently, interest has developed in palaeodietary studies of hominids and other mammals from ‘deep time’ (millions of years), in an attempt to understand the evolution of human dietary behaviour.
Geochemical Studies of Trade and Exchange
One of the earliest applications of chemistry to archaeology was the use of chemical analysis to determine the geological origin of inorganic raw materials used in antiquity. Studies have been carried out on natural rocks such as obsidian, on the clays used to make pottery, and on the ore minerals used to provide metals such as copper and silver. Analysis was initially of major and minor elements, but with increasing analytical sophistication the trace elements have been used, as well as the rare earths, and, more recently, isotopes such as Sr and Pb. Beyond the obvious complexity of issues such as the potential effects of mixing of raw materials (e.g., clays) or of the finished products (e.g., metals), and the possible effects of post-depositional alteration, an interesting area of research has been in relating the choices of raw materials and processing technologies to human behaviour. This can sometimes introduce ‘non-scientific’ complexity, such as the selection of raw materials because of ownership of mines or trading rights rather than ore richness, or the desire to produce a particular colour of metal rather than a particular composition. Given the relative ease of rapid multielement analytical techniques (e.g., ICP-MS), the main archaeological challenge is now seen as integrating the results of such studies with current models of human behaviour.
Dendrochemistry
Since their original use as a dating technique by Douglass in the US Southwest in the 1920s, it has been realised that the variation in annual ring width in many tree species is a complicated function of climate parameters at the time of growth, combined with issues such as local water availability, levels of insect activity, and proximity to other trees. Isotopic studies of ä13C, ä18O and äD on tree-ring cellulose have been attempted for several years in order to unravel the climate signal from these other factors. There have also been attempts to use the trace element and stable isotope chemistry of annual rings as markers of environmental pollution. More recently, there has been a surge of interest in the possibility of using trace elements in tree-rings as indicators of major catastrophic events such as volcanic activity. The value of these studies for archaeology is that, unlike similar data obtained from the Greenland ice-cores or (to a lesser extent) terrestrial lake sediments, data obtained from tree-rings indicate the conditions at the particular place where humans where living, not on the relatively remote ice-fields.
Geochemistry and Tephrochronology
Tephra is the fine volcanic ejecta from particular sorts of volcanic eruptions, containing within it a vitreous phase which can be widely distributed. Tephrochronology is now becoming extensively applied beyond its traditional geological applications, in fields such as archaeology, quaternary science, and palaeoceanography. These applications raise a number of issues such as the distribution, dispersal and sedimentation mechanisms of the tephra, the chemical homogeneity of particular eruptions, the reliability of the dating of particular tephra horizons, and the overall reliability of the geochemical tephra database. Although visible tephra layers have long been recognised as valuable stratigraphic markers in regions close to active volcanism, it is only relatively recently that interest has turned to distal deposits, which can provide non-visible chronostratigraphic markers in a wide range of sedimentary environments at a considerable distance from the source volcano. Recent improvements in extraction procedures using physical rather than chemical separation methods has shown the wide distribution of such marker horizons. With such distal deposits, however, there is a heavy reliance placed on the geochemistry of the small vitreous particles in order to correlate the deposit with the parent eruption and hence to give an estimated date. There is a growing concern that the chemistry of some tephras might be sufficiently altered over the time of burial (or in some circumstances by aggressive extraction regimes) to render them unidentifiable, or to lead to the spurious identification of new eruptions. There is a need to standardise extraction and identification protocols, and to understand the extent of possible geochemical alteration on small (c. 20-80 µm) vitreous shards in a range of sedimentary environments. Factors to be considered include glass chemistry, environmental pH and Eh, hydrological regime, and the possible presence of chelating agents in groundwaters.
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Preliminary List of Solicited Speakers |
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 Back to Session Programme
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