Large‐scale geochemical survey by pXRF spectrometry of archaeological settlements and features: new perspectives on the method

Abstract

Over the past several decades the geochemical study of archaeological sediments has experienced an increase in interest from archaeologists in search of new methods to investigate spatial organization and space function. Used with other proxies like geophysics, archaeobotany and micromorphology, geochemistry provides a new insight into microscopic pollution generated by past human activities, and thus can explain or confirm the function of features and spaces. Portable X‐ray fluorescence (pXRF) spectrometry offers new perspectives to the archaeological community to test, develop and integrate geochemical surveys in the daily routine of fieldwork, especially in the developer‐funded archaeology sector. We have undertaken over 20 geochemical surveys using pXRF spectrometry, both in the field and on bulk samples, and from a wide variety of sites, sedimentological, and chronological contexts. Working exclusively on developer‐funded projects, we present a series of results detailing a range of chemical element associations, including details on how the data is organized spatially and how these data may be interpreted. For some associations, such as that between phosphorus, calcium and strontium, our work confirms and builds on existing studies. For other elements such as zirconium, or the association between potassium, chromium and vanadium, our work presents new data patterns as well as a series of new hypothesis; the interpretation of these patterns remains at an early stage and we hope that further work will be done to test and detail the origins of these chemical associations and enrichments, with the goal of confirming the human activities and/or natural processes from which they originated. The rapidity and cost‐efficiency of pXRF, especially when used in situ in the field, makes it the ideal method for documenting the geochemical characteristics of landscapes; the approach we have developed means that geochemical survey can become a regular part of archaeological practice.

Identifying anthropogenic features at Seoke (Botswana) using pXRF: Expanding the record of southern African Stone Walled Sites

“…The pXRF analysis carried out at Seoke has recorded the most diagnostic elements related to human occupation, including Ca, K, P and Mn. Those elements in particular are associated with a number of daily activities [ 32 , 41 ] and hint at past use of space in our site. Looking at the results of the spatial distribution of the various elements, together with the archaeological features visible on the surface, hypothetical inferences can be made regarding the use of space at Seoke.…”

“…The occurrence of Zirconium in midden 4 in area C has been linked to the presence of pottery, Zr being a common component of clay. Recent research has correlated enrichments of Zr to areas of vessel storage [ 32 ]. In our area C, the chemical elements recorded may fit with the hypothesis of an area used as a ‘workshop’ or storage, where metal tools may have been used for shaping pottery, clearing, breaking wood for fires, trimming plaster (cow dung and mud) walls, as well as sharpening them on stones.…”

“…Human occupations may leave evidence in the form of chemical elements in the archaeological sediments [ 29 ]. Since the seminal works of Barba and Ortiz [ 30 ] and Middleton and Price [ 31 ], the study of such elements has increasingly been applied in archaeology [ 32 , and references therein] and ethnoarchaeology to identify the chemical signatures of many human activities (e.g. food preparation and consumption, craft production, livestock management) [ 33 ].…”

“…For instance, major components of organic occupation waste are Ca, Sr, K, P, Mn and Zn since they are essential nutrients for all living organisms, and their occurrence can be linked to specific features and activities to be found at archaeological sites. Recent reviews [ 32 , 41 , 42 ] have identified the significant relationships between chemical elements and archaeological features, such as burials, hearths, stock enclosures, middens, houses, metal working areas, and food-processing areas. As stressed also by Save and colleagues [ 32 ], “[‥] geochemistry has experienced an increase in interest from archaeologists in search of new methods to investigate the internal spatial organization of sites and/or to determine the specific function of features, structures or spaces within sites”.…”

“…Frahm et al [ 66 ] developed a method to measure P concentration in archaeological sediments and tested the results with ICP OES technique. Save and colleagues [ 32 ] have recently presented the results of large-scale surveys carried out with pXRF, stressing the effectiveness and high potential of this technique. Other case studies [e.g.…”