A hundred years ago, the Count of Vega del Sella laid the foundation for understanding the prehistoric shell middens of Asturias. Now, a century later, an international team of researchers has tested this century-old model using cutting-edge geoarchaeological techniques.

The results, recently published in the journal Quaternary Science Reviews, shed new light on how these enigmatic Mesolithic sites in Asturias were formed and raise questions about the lifestyles of coastal hunter-gatherers from 9,000 years ago.

The study, led by Carlos D. Simões from the University of Algarve, focused on two iconic sites: El Alloru and El Mazo. Through micromorphological and carbonate microfacies analyses, the researchers were able to examine the internal structure of these cemented deposits, which hang from the walls of caves and have been inaccessible to traditional archaeological methods until now.

a) location of the wide Asturian area in Western Europe and foreground in the core of concentration of sites, with location of the sites under study (in black) and sites excavated by Vega del Sella mentioned in the text (in gray) ; b) Asturian peaks recovered during the excavation in 2013 of the Unit 104 of El Alloru.
a) location of the wide Asturian area in Western Europe and foreground in the core of concentration of sites, with location of the sites under study (in black) and sites excavated by Vega del Sella mentioned in the text (in gray) ; b) Asturian peaks recovered during the excavation in 2013 of the Unit 104 of El Alloru. Credit: L. Teira / J. P. Ruas

The results obtained contradict several aspects of the model proposed by Vega del Sella in 1923. According to the Count, these shell middens were formed by the accumulation of waste thrown into the caves, while the habitation areas were outside. However, microscopic evidence reveals a more complex story.

First, the carbonate cements that bind these deposits are not due to water percolating through the walls, as Vega del Sella suggested, but are associated with tufa formations linked to water springs. This implies that during the early Holocene, the water table was higher than it is today, and there was intense spring activity in these coastal caves.

Furthermore, detailed analysis of the microscopic stratigraphy shows successive phases of accumulation of remains and periods of stability, which contradicts the idea of a continuous formation of the shell mound. Moreover, evidence indicates that the formation of tufa and the accumulation of anthropogenic remains were simultaneous processes.

Examples of typical Asturian shell middens: (a) hanging patches of cemented remains in the El Andriz crag; scale bar = 1m (80 cm visible); (b) hanging ledge of the La Llosa crag; scale bar = 1m; (c) large hanging cemented remains from Fronfría cave; scale bar = 1m; note the slopes descending into the interior karst in all these examples, with rock accumulation at the bottom; d) detail of the cemented deposit of Peñavilla cave, showing the abundance of mollusk shells and a boulder (yellow arrow) attached to the wall (scale in cm); e) detail of another Peñavilla stain attached to a small projection of the cave wall, showing mollusk shells with an Asturian peak in situ.
Examples of typical Asturian shell middens: (a) hanging patches of cemented remains in the El Andriz crag; scale bar = 1m (80 cm visible); (b) hanging ledge of the La Llosa crag; scale bar = 1m; (c) large hanging cemented remains from Fronfría cave; scale bar = 1m; note the slopes descending into the interior karst in all these examples, with rock accumulation at the bottom; d) detail of the cemented deposit of Peñavilla cave, showing the abundance of mollusk shells and a boulder (yellow arrow) attached to the wall (scale in cm); e) detail of another Peñavilla stain attached to a small projection of the cave wall, showing mollusk shells with an Asturian peak in situ. Credit: Carlos D. Simões et al.

Perhaps the most surprising finding is that the biogenic and diagenetic cements reveal phreatic conditions, meaning these deposits were formed underwater. This presents a radically different scenario from the one proposed a century ago: instead of mounds of waste exposed to the air, these were deposits submerged in pools or ponds within the caves.

These new pieces of evidence force us to reconsider how Mesolithic groups used these spaces. Far from being mere dumps, microcontextual evidence suggests that shells were also processed and consumed inside the shelters. This opens the possibility that these spaces were used as habitation areas, at least temporarily, and not just for discarding waste.

The study also provides valuable information about paleoenvironmental conditions on the Cantabrian coast during the early Holocene. The indications of a higher water table and greater spring activity coincide with the period of rapid sea level rise following the end of the last glaciation. This would have radically transformed the coastal landscape inhabited by these marine hunter-gatherer groups.

El Alloru shelter: (a) topographic plan of the site; the main shelter is located to the west of the limestone outcrop; note the existence of other minor shelters around it; (b) view towards the main shelter, hidden by the vegetation at the back, showing the archaeological excavation in the open-air area; c) aspect of the cemented shell pit at the back of the shelter before sampling; the dashed yellow lines mark the limits of the block extracted for micromorphological analysis; d and e) west and east profiles, respectively, of Test 1, showing the stratigraphic units (white labels) and the micromorphological samples (black labels).
El Alloru shelter: (a) topographic plan of the site; the main shelter is located to the west of the limestone outcrop; note the existence of other minor shelters around it; (b) view towards the main shelter, hidden by the vegetation at the back, showing the archaeological excavation in the open-air area; c) aspect of the cemented shell pit at the back of the shelter before sampling; the dashed yellow lines mark the limits of the block extracted for micromorphological analysis; d and e) west and east profiles, respectively, of Test 1, showing the stratigraphic units (white labels) and the micromorphological samples (black labels). Credit: Carlos D. Simões et al.

The findings of this study compel a reconsideration of the models of prehistoric shell midden formation in other coastal regions of the world. The study of the Asturian shell middens offers a unique window into a crucial period of European prehistory, when the last hunter-gatherers developed increasingly sedentary lifestyles based on the intensive exploitation of marine resources.

The work published in Quaternary Science Reviews does not close the debate on the formation of the Asturian shell middens but opens new lines of research. The authors highlight the need to expand these studies to other sites in the region to determine whether the pattern observed at El Alloru and El Mazo is generalizable. They also stress the urgency of developing new conservation strategies for these fragile deposits, threatened by coastal erosion and rising sea levels.

In short, this study not only revisits a century-old model but also proposes a new vision of how Mesolithic human groups interacted with their coastal environment. A vision that brings us a little closer to understanding the daily life of those pioneering fishermen and shellfish gatherers who populated the Cantabrian coasts nine millennia ago, laying the foundations for a long maritime tradition that has endured to this day.

SOURCES

Carlos D. Simões, Eneko Iriarte, et al., Carbonate microfacies reveal how Asturian shell middens formed in the Mesolithic. Quaternary Science Reviews, Volume 342, 15 October 2024, 108898. doi.org/10.1016/j.quascirev.2024.108898

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