Multi-Element Analysis of the Soils In and Around Balnreich
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Introduction
Multi-element analysis involves determining the concentrations of a wide range of metals and trace elements in soil. It has been used for decades in archaeology; as a survey technique to establish the location and extent of a site, and as an aid to interpretation of space use and function within buildings. Inputs to the site - crops, animal dung, metal and craft working, building materials, and soil amendments - all bring with them their own loadings of trace elements that accumulate over time in the soil. Previous studies have shown how the distribution of many elements can reflect the presence of archaeological remains. However, the sources of these loadings and the effects of soil processes on the retention of trace elements within the soil are poorly understood, and this seriously limits interpretation of this type of data.The site of Balnreich provided the opportunity of sampling from a documented post-medieval site alongside archaeological excavation and historical investigation. Areas of known function and space use could be identified and this allowed us to 'ground-truth' the multi-element soil data. This work forms part of a larger study evaluating the use of multi-element soil analysis in archaeology, which is being carried out by Stirling and York Universities.
Sampling
| The site was sampled in September 2002. The
archaeological excavations allowed us to identify the house floor, byre
floor and hearth areas; and samples were taken from between the flagstones
and cobbles as well as from the material that had accumulated over them.
In addition, soils were collected from the township's stack/kailyards, and from areas of infield and outfield identified from Farquharson's 1769 map. A historically undisturbed soil profile was also sampled for comparison (the reference profile). |
Sampling the house floor at Balnreich |
Mean soil concentrations and 95% confidence interval of Balnreich
functional areas
Levels of enrichment tend to be highest within the hearth area, followed by the house and byre areas then generally decrease into the field areas. Concentrations of K, P, Ba, Cu, Sr, Zn, La, Ce, Nd, Yb, Dy, and Pb appear to be providing the most information about former land use. P, Nd and Cu are important in differentiating between the building and field areas, whilst Ca, Na, Sr, and Ba appear to help us differentiate between the different building contexts (hearth, house and byre). However, differences in geology, hydrology, and soil properties across the site are also important and influence the patterns of element distribution.
Summary
Multi-element analysis of the soils in and around Balnreich has given us the opportunity to groundtruth this much used technique. Analysis of the data is ongoing and requires greater spatial, historical and background information to make sense of the processes involved. However, already our analyses are highlighting significant patterns and trends in the geochemistry of these soils and archaeological sediments that may, in part, be explained by patterns of former human activity.| Claire Wilson University of Stirling [External Link] |
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