MegaGeo projectMoving megaliths in the Neolithic: Geology sourcing of dolmen slabs in C entral-South Portugal (PTDC/EPH-ARQ/3971/2012)
Principal Investigator: Rui Boaventura |
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Project Partners: Centro de Arqueologia da Universidade de Lisboa (UNIARQ/FL/UL); Centro de Geofísica da Universidade de Évora (CG/UE); GEOBITEC da Universidade de Aveiro (GEOBIOTEC/UA).
Megalithic tombs, also known as dolmens, are the most conspicuous remains of the populations of the 4th and first half of 3rd millennia BCE. These tombs are impressive not only for their monumentality, but also because of the socioeconomic investment they represent for those Neolithic communities, namely from the Central-South of Portugal, who built them. These constructions are an element of Megalithism, which is viewed by archaeologists as a complex set of magical and religious rules that are related to death and not only a type of funerary architecture. Nevertheless, dolmens appear as the most abundant type of tomb in the region, where thousands have been recorded.
Although dolmens have been studied for their funerary content and typologies, an interdisciplinary approach toward the geological characterization and sourcing of stones used in these constructions has not received enough attention from researchers. When studied, most archaeological analyses of the geology of the tombs and their local geology are limited to brief descriptions of rock types and geology and whether they were the same. When a megalith is found to be made of stones of nonlocal origin, that is usually highlighted but rarely and thoroughly investigated. When rigorous geological identification is conducted for specific dolmens, rarely is any attempt made to verify if there are similar patterns of slab selection on neighboring dolmens and what relationship it might have with its geological background.
Almost a decade ago in Alentejo two projects were conducted on geological identification of megaliths and its sourcing: at Vale de Rodrigo, Évora and at the cluster of Rabuje, Monforte. These projects demonstrated a tendency for the use of local (1-2 km) stones, mainly in small- to middle-sized dolmens (approximately 1-2 m high and 2-4 m long by 2 m wide). In larger tombs there were cases of megaliths sourced to outcrops at greater distances (6-8 km). The proximity and cost/benefit of slab extraction as well as its transport and erection could explain the selection of local stones, but the need for more suitable stones (that were larger or flatter, e.g.), might explain the use of more distant sources. Nevertheless, the intrinsic and phenomenological qualities of certain rocks or geological contexts may have also influenced community’s choices, as much as the prestige and power that those endeavors would give to its members. These hypotheses, however, need to be verified with new studies. In order to provide answers to such questions, an integrated geo-archaeological approach will be applied.
This project intends to assess the relationship between the distribution of dolmens in Central-South Portugal, their source materials, and the geological landscape. GIS will map the information gathered and will be used to analyze these relationships. Three regional case-studies will be analyzed. These cases are from diverse geological backgrounds, and include: 1) Monforte and 2) Redondo, both in Alto Alentejo (Hercynian Massif), and 3) the Lower Estremadura - region of Lisbon (Meso-Cenozoic basin). The selection of these areas, with distinctive geologies, will allow us to verify if human patterns of behavior regarding the selection of megaliths are similar or different regionally. This would be achieved by evaluating the type of rocks used in the constructions of dolmens, the shape, volume and mass of megaliths, as well as identifying and measuring the distances to their potential geological sources. In this case a thorough and detailed geological identification is crucial. Thus, besides macroscopic
description of the megaliths at the tombs, petrography will be conducted by conventional polarized microscopy (transmitted and reflected light) but also recurring to SEM-EDS and RAMAN for semi-quantitate analysis of mineral phases. Elemental whole rock geochemical (IC P-MS) and isotope (TIMS) compositions from megaliths and outcrops are invaluable and supplemental data to guarantee the accuracy of rock differentiation and classification.
The individual expertise of each team member combined within this project is an asset to achieve successfully the multidisciplinary enterprise of project MEGAGEO, to better understand how and why populations of the 4th and first half of 3rd millennia BCE used megaliths and if they were influenced by its geological nature.
August 2014
Megalithic tombs, also known as dolmens, are the most conspicuous remains of the populations of the 4th and first half of 3rd millennia BCE. These tombs are impressive not only for their monumentality, but also because of the socioeconomic investment they represent for those Neolithic communities, namely from the Central-South of Portugal, who built them. These constructions are an element of Megalithism, which is viewed by archaeologists as a complex set of magical and religious rules that are related to death and not only a type of funerary architecture. Nevertheless, dolmens appear as the most abundant type of tomb in the region, where thousands have been recorded.
Although dolmens have been studied for their funerary content and typologies, an interdisciplinary approach toward the geological characterization and sourcing of stones used in these constructions has not received enough attention from researchers. When studied, most archaeological analyses of the geology of the tombs and their local geology are limited to brief descriptions of rock types and geology and whether they were the same. When a megalith is found to be made of stones of nonlocal origin, that is usually highlighted but rarely and thoroughly investigated. When rigorous geological identification is conducted for specific dolmens, rarely is any attempt made to verify if there are similar patterns of slab selection on neighboring dolmens and what relationship it might have with its geological background.
Almost a decade ago in Alentejo two projects were conducted on geological identification of megaliths and its sourcing: at Vale de Rodrigo, Évora and at the cluster of Rabuje, Monforte. These projects demonstrated a tendency for the use of local (1-2 km) stones, mainly in small- to middle-sized dolmens (approximately 1-2 m high and 2-4 m long by 2 m wide). In larger tombs there were cases of megaliths sourced to outcrops at greater distances (6-8 km). The proximity and cost/benefit of slab extraction as well as its transport and erection could explain the selection of local stones, but the need for more suitable stones (that were larger or flatter, e.g.), might explain the use of more distant sources. Nevertheless, the intrinsic and phenomenological qualities of certain rocks or geological contexts may have also influenced community’s choices, as much as the prestige and power that those endeavors would give to its members. These hypotheses, however, need to be verified with new studies. In order to provide answers to such questions, an integrated geo-archaeological approach will be applied.
This project intends to assess the relationship between the distribution of dolmens in Central-South Portugal, their source materials, and the geological landscape. GIS will map the information gathered and will be used to analyze these relationships. Three regional case-studies will be analyzed. These cases are from diverse geological backgrounds, and include: 1) Monforte and 2) Redondo, both in Alto Alentejo (Hercynian Massif), and 3) the Lower Estremadura - region of Lisbon (Meso-Cenozoic basin). The selection of these areas, with distinctive geologies, will allow us to verify if human patterns of behavior regarding the selection of megaliths are similar or different regionally. This would be achieved by evaluating the type of rocks used in the constructions of dolmens, the shape, volume and mass of megaliths, as well as identifying and measuring the distances to their potential geological sources. In this case a thorough and detailed geological identification is crucial. Thus, besides macroscopic
description of the megaliths at the tombs, petrography will be conducted by conventional polarized microscopy (transmitted and reflected light) but also recurring to SEM-EDS and RAMAN for semi-quantitate analysis of mineral phases. Elemental whole rock geochemical (IC P-MS) and isotope (TIMS) compositions from megaliths and outcrops are invaluable and supplemental data to guarantee the accuracy of rock differentiation and classification.
The individual expertise of each team member combined within this project is an asset to achieve successfully the multidisciplinary enterprise of project MEGAGEO, to better understand how and why populations of the 4th and first half of 3rd millennia BCE used megaliths and if they were influenced by its geological nature.
August 2014