Integrating Multi‐element Geochemical and Magnetic Survey at Ancient Sagalassos (Southwest Turkey): Anthropogenic Versus Natural Anomalies

Abstract

Several studies in the field of archaeological prospection have suggested that multi-element soil geochemical survey holds potential as an archaeological survey method, complementing more common techniques such as magnetometry and fieldwalking. Despite this, only limited research regarding this topic has been carried out. In this study, a geochemical survey was conducted in the Eastern Suburbium of the Roman to Byzantine city of Sagalassos, with the aim of investigating the possibilities and limitations of the technique in facilitating the interpretation of magnetic survey data. To explore the multivariate patterns present within the chemical dataset, the data were statistically analysed using a contiguity-constrained spatial clustering algorithm. The resulting spatial clusters revealed that an area characterized by high-frequency magnetic anomalies was spatially associated with a chemical cluster rich in Cu, K, P, Pb and Zn. This is interpreted as resulting from the accumulation and decomposition of occupational debris. Enhancements of Al, As and Ba helped to interpret an area with a low magnetic signal as a region where limestone bedrock was located close to the soil surface. Finally, two zones of enhanced magnetization were shown to spatially overlap with two clusters of soils containing elevated levels of Co, Cr, Mg, Mn, Ni and (Fe) and Ti, V and (Fe), respectively, indicating the presence of two different types of mafic to ultramafic ophiolitic bedrock near the soil surface. This study confirms that multi-element geochemistry has potential as a survey technique, because it offers direct information on soil bedrock or ancient human disturbance, thereby adding an extra dimension to the interpretation of geophysical survey data. It is shown that soil chemical data are particularly valuable for distinguishing anthropogenic and natural impacts creating geophysical anomalies. Contiguityconstrained clustering was found to be a promising data analysis technique for multivariate geochemical survey data.

Multi-proxy survey of open-air surface scatters in drylands: Archaeological and physico-chemical characterisation of fossilised dunes in North Gujarat (India)

“…Thus, a PC transform was calculated on the dataset of physico-chemical variables and the resulting data matrix of 151 samples x 21 PCs was submitted to a hierarchical clustering using Euclidean distance as similarity measure, and Ward's aggregation method to ensure low variance clusters (Calegari et al, 2013;Dirix et al, 2013aDirix et al, , 2013b. The resulting dendrogram was cut using a dissimilarity threshold defined by the stopping threshold rule proposed by Mojena (1977), which selects the "best" number of clusters based on the distribution of a clustering criterion associated with each hierarchical level.…”

Spatial Distribution of Elemental Enrichments around Archaeological Sites: Insights from the Ancient City of Sagalassos in Southwest Turkey

“…Because Ca contains significant individual outliers, and was found to severely influence results from the multivariate analysis in previous studies (Dirix et al, 2013a(Dirix et al, , 2013b, it was decided to exclude this element from the statistical analyses. All statistical analyses were performed using R software (R core Team, 2012).…”

“…The pattern of Pb is not straightforward. Although it is one of the elements most strongly enriched in and around the city, it is also strongly correlated with Ba, which proved to be a geogenic element in comparable studies in the Sagalassos area (Dirix et al, 2013a(Dirix et al, , 2013b. This raises the question whether the pattern of Pb is mainly governed by natural or human processes.…”

“…The research project mainly focuses on the use of elemental mapping for wider site prospection. The results of two previous papers showed that Cu, K, P, and Zn were elevated on and around potential activity areas (Dirix et al, 2013a(Dirix et al, , 2013b. However, lithological variability around Sagalassos strongly challenges the applicability of elemental prospection in this area.…”

Geochemical insight during archaeological geophysical exploration through in situ X‐ray fluorescence spectrometry

“…By contrast, geochemical analyses are usually conducted in the laboratory, on prepared (often destroyed) samples of material extracted from a site (e.g. Dungworth, ; Wilson, Davidson, & Cresser, ; Cook et al , ; Dirix, Muchez, Degryse, Mušič, & Poblome, ; Vittori Antasari, Cremonini, Desantis, Calastri, & Vianello, ; Carey, Wickstead, Juleff, Anderson, & Barber, ; Scott, Eekelers, & Degryse, ). In situ geochemical analysis using X‐ray fluorescence (XRF) spectrometry has become possible, however, with the development of handheld, field‐portable XRF analysers (e.g.…”