NINMACH 2017

Investigating beads from Chalcolithic funerary cremation contexts of Perdigões, Portugal

13 Oct 2017, 11:55

20m

Hungarian Academy of Sciences

Oral presentation Multi-technique approach and complementary techniques Multi-technique approach and complementary techniques 2.

Speaker

Prof. M. Isabel Dias (Centro de Ciências e Tecnologias Nucleares, CAMPUS TECNOLÓGICO E NUCLEAR, INSTITUTO SUPERIOR TÉCNICO)

Description

Beads appear to have been one of the earliest examples of personal adornments. The analyzed beads come from Pit 40, a funerary secondary deposition of cremated remains of more than a hundred individuals. The pit is located in the center of Perdigões (Évora, Portugal) ditched enclosures and is dated from the third quarter of the 3rd millennium BC. The beads were burned and were part of the funerary votive assemblages, also composed by arrowheads ivory figurines, marble idols and pots, phalanx idols, copper awls, Pecten shells and pottery sherds. These beads have between 5 and 10.5 mm in diameter, with a central perforation up to 5 mm and maximum thickness of 3 mm, they are gray or black and of unknown nature. We report the use of prompt-gamma activation analysis (PGAA), external milli-beam particle induced X-ray emission spectroscopy (PIXE) and high-resolution time-of-flight diffractometer (ToF-ND) at the Budapest Neutron Centre, to a large dataset demonstrating that composition can help on identification of beads nature by using non-destructive techniques. Infrared spectroscopic measurements were also performed on some beads. In one broken bead a micro-destructive - Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectrometry (SEM/EDX) analysis was applied at IST. Among the chemical elements obtained by PGAA, calcium (53%<CaO<74%) is the element with major concentrations. Sr, Si and Fe are also present in the majority of the samples. Sr contents can be explained by calcium substitution within the lattice; Si and Fe can be related with soils particles that are still in the beads. The chemical results obtained by PIXE show that the surface is more contaminated with soils particles due to high Si, Fe and K contents, and phosphorous was found in higher proportion, certainly originated from bones. FTIR patterns show that the major part of the beads is calcium carbonate crystallized in calcite form, contaminated with silicates and calcium phosphate. The ToF-ND results also indicate the crystal lattice structure of calcite. Aragonite, a polymorph formed in the biomineralisation process of shells, was not detected, indicating a total phase transformation to calcite due to heating processes during funerary practices. The low amount of Mg, usually present in shells below the detection limits of applied methods, as well as, eventual alterations of elemental proportion derive by the burning and burial processes, may compromise the identification of the marine / estuarine origin of the shells. The SEM-EDS results clearly show the shell nature of the archaeological beads, with the characteristic shell macrostructure, with inner, intermediate and outer layers of calcium carbonate. Thus, the results obtained showed that shells were the raw materials used for the production of these beads, found in funerary contexts and burnt together with bones during funerary practices in Perdigões. Acknowledgments IPERION CH project co-funded by the European Commission within the action Research Infrastructures of the Capacities, at Budapest Neutron Center, GA No.654028. FCT support through the UID/Multi/04349/2013 project.