Periodic Reporting for period 1 - SEArch (Sea harvesting in the transition from hunter-gatherer to farmer societies. Archeological microscopic and molecular approaches to shell midden stratigraphy)
Período documentado: 2020-09-01 hasta 2022-08-31
Humans have exploited the sea and its resources since prehistory. From xx to xx thousand years ago, prehistoric hunter-gatherers from the Mesolithic times commonly use the sea and its by-products in their diet. These actions generated large shell mounds in coastal settings that can be explored to decipher both how these past populations lived and how were the environment they inhabited. With the advent of farming and food producing societies, we see a decline in the degree that marine resources are being used. However, along the Atlantic shores of Iberia, there are still shell mounds that outlive the transition from the Mesolithic to the farming Neolithic societies. Were they coastal-adapted farmers, or resilient foragers that produced these middens? Project SEArch seeked to address this issue to understand the role of coastal resources in the appearance of food production and the first sedentary lifestyles in Western Europe, a crucial phase of transformation in society. In SEArch, we studied microscopic and molecular datasets retrieved from shell mound deposits, to reconstruct their dynamics of accumulations and abandonments. Another important goal was to detect the use of other coastal resources apart from fish and shellfish, which usually do not leave visible remains, such as molecules of plants and seaweeds to investigate how all these resources were processed at these sites. Finally, the SEArch approach aimed at reconstructing the environmental changes in the coastal ecosystems exploited by these prehistoric populations.
The SEArch project applied state-of-the-art approaches to study archaeological biomolecules from controlled contexts. This work is linked to microstratigraphic analysis of three archaeological shell mounds in the coast of southern Portugal and in the Bay of Biscay in Spain. To study ancient biomolecules of plants and animals, it is necessary to have reference data from modern species. For that, a collection of modern seaweeds and limpets was built to analyse with the same techniques used in the archaeological sediment samples. These techniques are soil micromorphology - the study of intact microstratigraphic contexts under the microscope -, combined with mass spectrometry and isotope analysis for the identification of the nature of the ancient animal and plant molecular signatures preserved in the sediment organic matter, like lipid compounds (oils, fats, resins, waxes). The micromorphological analysis was carried out at the ICArEHB, the Interdisciplinary Centre for Archaeology and Evolution of Human Behaviour, located in the University of Algarve (Portugal). These studies revealed that some shelly deposits result from human actions of direct tossing from one single event, while others result from intentional mixing of shells that had been discarded before, alongside other occupation debris. The studies also revealed that the latter kind of deposits can result both from human maintenance activities and reworking by natural events during phases of site abandonment. It also revealed that some layers contain high amounts of nondescript organic matter, which is the focus of the lipid analysis. The ancient lipid analysis was conducted at the Archaeological Micromorphology and Biomarkers Laboratory (AMBI Lab) in the University of La Laguna, Spain. Results from these analyses is currently being processed. To address the topic of how shellfish was processed at the shell middens, heating alterations in shells’ carbonate phase mineralogy was investigated to infer possible cooking techniques, through micro-FTIR analysis. This task allowed the identification of burning of shells within their microstratigraphic context using direct measures in the micromorphological samples. By combining the degree of burning and their contextual association with other debris, such as charcoals fragments, it was possible to associate and discuss shellfish cooking activities. Some of these results were already presented in international conferences and published in scientific articles.
The SEArch project advanced in the knowledge of discrete, though relevant, sedimentary signatures of different activities carried in shell middens by its inhabitants. However, shell mounds pose a difficult challenge for archaeologists since it is difficult to recognise individual depositional phases during excavation. This greatly limits the study of artefacts and their contexts. The systematic micromorphological analysis of an array of site across Atlantic Iberia, allowed by the EU-funded SEArch project, is a determinant step to overcome this challenge. The preservation of the microstratigraphic integrity in micromorphological samples allowed for the study of in situ shell heating through mineralogical thermal alterations. This study suggested that shellfish was probably processed by simple roasting combustion features (instead of boiling techniques), while the use of fire also occurred unrelated to cooking, in shelly surfaces where the usual traces of archaeological fire use are not evident. Apart from shellfish, it is largely if the organic matter present in the sediments results from local terrestrial plants, or if it corresponds to the use of available aquatic resources (e.g. marine plants and algae). This knowledge gap greatly hampers our understanding of the extent into which past hunter-gatherers made use of the entirety of resources available in marine environments. The biomolecular studies specifically targeting organic matter from shell midden sediments aims to address this question by detecting the presence of such materials and have measurable data to balance the importance of terrestrial vs aquatic resources in these sites. If the resources and modes of shell mound growth show no changes, that would suggest a resilient behaviour from coastal hunter-gatherers. If, in contrast, these aspects show changes between the earlier and later occupations, the possibilities of different coastal adaptations strategies, or environmental changes must be investigated, combining with other paleoenvironmental records from around the sites. The work that is being developed on stable isotope analysis from shell’s growth lines is something not done previously for Portuguese coastal sites. In sum, the evolution of these activities and environmental changes throughout such an impactful process as the neolithization, reveals how this process occurred amongst coastal populations . The project so far has impacted society at both local and national levels, by reaching municipal policy makers regarding the communication and preservation of coastal cultural heritage, and through a partnership with another EU-funded project in the enterprise sector of Archaeology, fostering knowledge transfer between this sector and the academic one.