Identifying activity areas in Neolithic sites through ethnographic analysis of phytoliths and geochemical residues

The Neolithic in southwest Asia (c 11,700-7800 cal BP) is a critical period in human history; it was during this time, that people made the transition from living in small hunter-gatherer groups, occupying temporary camps, to fully fledged agriculturalists living in large sedentary communities.

The reason why people made this transition is one of the great unanswered questions of our time. What is apparent, however, is that this development not only altered the way people interacted with their environment, but also the social structure within communities, ultimately leading to the development of complex societies.

Despite the importance of the Neolithic in southwest Asia, archaeological sites, particularly those from the earlier Pre-Pottery Periods (c 11,700-8250 cal BP), often prove difficult to interpret due to their ephemeral nature and the scarcity of biological remains.

In order to gain a greater understanding of such sites, we will develop and validate a method based on more durable forms of evidence that are often the result of human activities, i.e. phytoliths (bodies of silica that form in and around plant cells) and geochemical elements (traces of chemicals in soils, e.g. phosphorous, calcium and manganese). The aim is to determine if different areas have specific phytolith and geochemical signatures which can be used to recognise these same areas archaeologically.

This will be achieved through ethnographic research using two settlement types: Bedouin tent sites and abandoned mud and stone constructed villages. These have been chosen because they provide the best available analogies for the Neolithic sites which will be analysed as part of this project. The Bedouin tent sites will be the ethnographic analogy for the small scale, ephemeral, pastoralist, and seasonally occupied sites of Wadi el-Jilat and Azraq, while the abandoned villages near Shawbak on the Jordanian plateau and the village of Shammakh, north of Wadi Mousa will be the comparison for the more substantial, stone and mud brick constructed sites of Ain Ghazal, Beidha, and WF16.

Limited existing ethnographic research (conducted in other geographical regions) has focused either on phytoliths or geochemical elements but not both. They demonstrated that these methods are informative about the use of space within settlements. This project will be the first large scale ethnographic study to integrate these two types of analysis. It will also be the first to explore how much taphonomy (i.e. the processes assemblages go through from creation to analysis) affects the composition of phytolith and geochemical assemblages.

We conducted a large scale combined analysis of phytoliths (bodies of silica that form in and around plant cells) and geochemical elements from ethnographic sites to determine if certain activity areas, for example middens, hearths, and floors, have particular phytolith and geochemical signatures that can help us recognise these same areas in archaeological sites . We used southwest Asian Neolithic sites (c 11,700-7800 years ago) as our case study.
As part of this research we investigated how phytolith and geochemical assemblages are altered through time by taphonomy (i.e. the processes assemblages go through from creation to analysis which can alter their composition).
Our research on the ethnographic sites showed positive results and demonstrated that both phytoliths and geochemistry can be used to identify activity areas but when run together in a statistical analysis they are not as robust as when run independently (Jenkins et al 2017). However, the two forms of evidence can be used in tandem to gain more information than can be ascertained from each form of evidence individually. For example, the geochemistry allows us to identify hearths and other fire installations but the phytoliths allow us to identify what was used as fuel e.g. dung, wood, reeds etc.
Analysis of samples from the Neolithic sites demonstrated that phytolith and elemental signatures were strongest for fire deposits and for categories linked to construction practices, particularly for the make-up of floors and features. Other categories such as middens showed more variation in their phytolith and elemental signatures which reflected their mixed nature. The influence of the natural source materials, available local vegetation and specific practices/constructions/alterations meant that for some categories inter-site differences between categories were found. Overall, however, the ethnographic results added greatly to our understanding of the patterns we recorded at the archaeological sites, and offered comparisons to use in our interpretations of the archaeological samples.