The necessity of sample quality assessment in 14C AMS dating: The case of Cova des Pas (Menorca – Spain)

doi:10.1016/j.nimb.2009.10.081

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 268, Issues 7–8, April 2010, Pages 990-994

https://doi.org/10.1016/j.nimb.2009.10.081 Get rights and content

Abstract

The Cova des Pas cave is a karstic cave in the cliffs of the Barranc (canyon) de Trebalúger. It is a small cave only 6.5 m deep, 4.5 m wide and 1.7 m high. Yet more than 70 burials, in foetal position, from the Early Iron Age were found in this small cave. The conservation of the archaeological remains was very unusual. Not only wood, ropes and other plant material was found, but also remains of body tissue, hair and leather. In spite of the remarkable preservation of the bodies and artefacts, the state of conservation of the bone material was very bad. The bones contained little and heavily deteriorated collagen and the organic plant material was very fragile. The special environmental conditions of the cave are the cause of these unusual preservation conditions. Although the cave is situated in a limestone cliff, the soil of the cave is very acid. Unexpectedly bad sample quality seemed to be the major drawback for AMS radiocarbon dating on hair, wood, ropes and bone collagen, as well as on bio-apatite.

Introduction

The ‘Cova des Pas’ cave (39°57′N–4°00′E) is situated on the territory of the Son Mercer de Baix farm, near the village of Ferreries, on the Balearic Island of Menorca (Spain). More precisely, the cave is located in the southeast cliff-wall of the barranc (canyon) of Trebalúger, at about 15 m above the canyon floor. The cave is rather small, maximum 6.5 m deep, 4.5 m large and never higher than 1.7 m. The only opening faces west – northwest. Some parts of the cave are modified by human activity. This karstic cave is formed by water erosion of a Miocene calcareous stratum.

During the archaeological excavation of 2005–2006 the remains of minimum 70 humans were excavated, almost half of them have never reached an adult age [1].

The inventory of the metal objects from the cave comprises a number of bronze bracelets, a needle, some small metal rings and a small spear head. No pottery was found but a remarkable find consist of some tabular tubes in leather or antler, with a top and base made of wood or bone. These tubes contain human hair just like the ones found in the Cova des Càrritx [2] indicating that the burial rites in both caves are most probably the same. The Cova des Càrritx is situated in the barranc d’Algendar (Ciutadella, Menorca), a canyon in the same karst formation as Cova des Pas.

Most surprising was the unusual conservation of the organic material. From the inhumated bodies (Fig. 1) not only the bones remained, but fragments of human tissue were also present on some skeletons. Also wood, plant remains and animal skin were preserved in a way that a good reconstruction of the inhumation practice was possible (Fig. 2).

This practice consisted of a primary inhumation in foetal position. According to the archaeological records the bodies were at first disposed near the entrance of the cave, later on in deeper parts. No orientation in the depositions could be noticed. To keep the bodies in the foetal position they were tied up with ropes. The bodies were wrapped in a bovid skin and placed on a wooden bier. This would facilitate the climb to the cave entrance. Under the deceased small branches and leafs were deposited.

Section snippets

Sample pre-treatment

Different remains were sampled for radiocarbon analysis: botanical material, hair, and human bones. From the latter, two products were extracted: collagen and bio-apatite. Collagen extraction from the human bones followed the Longin method [3], downscaled for small samples. In most cases a NaOH wash was introduced between the demineralization and the hydrolisation step. After hydrolisation, the samples were freeze-dried.

For bio-apatite extraction, the crushed bones were treated with 1% acetic

Results and discussion

Although the conditions in the cave seemed ideal for ¹⁴C dating, a test sample sent to Beta Analytic by the archaeologists gave no result, because the bone did not contain any collagen. In spite of this negative result it was still attempted to set up a further dating experiment. It was taken into account that sample yield could be a problem but, due to the extraordinary conditions in this small and dry cave, sample contamination was still not thought to present difficulties. A first set of

Analytical conclusions

The Cova des Pas site is a typical example of the advantages but also of the problems involved in ¹⁴C-AMS dating. None of the samples from this cave could be dated using β-decay counting but the AMS technique did produce results. However, it should always be evaluated whether these results are meaningful. It must not be forgotten that AMS asks for a very severe sample quality assessment. Often samples are submitted for dating by archaeologists without discussing with the dating laboratory the

References (10)

J.M. Fullola, V.M. Guerrero, M.À. Petit, M. Calvo, A. Malgosa, N. Armentano, P. Arnau, S. Cho, X. Esteve, T. Fadrique,...
V. Lull, R. Micó, C. Rihuete-Herrada, R. Risch (Eds.), La Cova des Càrritx y la Cova des Mussol – Ideología y sociedad...
R. Longin
Nature
(1971)
M. Van Strydonck et al.
Bulletin Kon. Inst. v. h. Kunstpatrimonium
(1990-1991)
M.-J. Nadeau et al.
Radiocarbon
(1998)

There are more references available in the full text version of this article.

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On the presence of gypsum in the archaeological burial site of Cova des Pas (Menorca, western Mediterranean)
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The Cova des Pas (Ferreries, Menorca) is a cave that was used as a collective sepulcher during the late Bronze Age (1100–800 B.C.). Apart from the archaeological and paleoanthropological attractiveness of the site, it stands out for its excellent preservation of organic remains.
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Human soft tissue preservation in the Cova des Pas site (Minorca Bronze Age)
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Either way, all the preserved soft tissues in this archaeological site are highly modified due to a decomposition process. Bone material from CdP does not contain enough collagen to perform a C14 analysis (Van Strydonck et al., 2010). Also, molecular analyses from teeth and bones show a low efficiency in the DNA recovery and amplification (Simón et al., 2012).
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Paleodemographic study and radiocarbon dating of the remains indicate that a small community of approximately 15–18 persons used the burial site for one century. This cave would have been the burial site for the entire population except for children under 6 months (Armentano et al., 2010; Van Strydonck et al., 2010). Their remains were completely covered by fine brown sediment, about 3 cm thick, formed by the disintegration of sandstone in the cave.
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Some of the substances found in the environment of each particular site can act as inhibitors for the DNA amplification. In the case of La Cova des Pas, in spite of the remarkable external preservation of the bodies and artefacts, the state of conservation of the bone material was very deficient as it contained little and heavily deteriorated collagen (Van Strydonck et al., 2010). When the routine protocol, the phenol–chloroform method (Malgosa et al., 2005) was applied, the results were disappointing, and an inhibition of the amplification of the samples seemed to be a real possibility.
The site from La Cova des Pas, located in Menorca, is a funerary cave with a collective burial dating from the Late Bronze Age. This cave presents a good conservation of the remains of both humans and other organic elements. In spite of the good preservation, the first DNA amplification tests showed a low amplification success rate, probably owing to the presence of substances from the process of decomposition of the bodies and substances of the soil present in the samples. To overcome this problem, 41 samples were processed by means of two different extraction methods, following sterility criteria used in ancient DNA research. Two fragments of different sizes of mitochondrial DNA were amplified in order to evaluate the success rate of both methods. The results did not show a statistically significant better recovery of DNA from either teeth or bones. For the length of the retrieved DNA, the recovery was significantly better with the QIAamp kit procedure than with the phenol–chloroform method.
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The necessity of sample quality assessment in 14C AMS dating: The case of Cova des Pas (Menorca – Spain)

Abstract

Introduction

Section snippets

Sample pre-treatment

Results and discussion

Analytical conclusions

Nature

Bulletin Kon. Inst. v. h. Kunstpatrimonium

Radiocarbon

The necessity of sample quality assessment in ¹⁴C AMS dating: The case of Cova des Pas (Menorca – Spain)