Collagen Quality Indicators for Radiocarbon Dating of Bones: New Data on Bronze Age Cyprus

Abstract

Radiocarbon dating of bones can be very useful in archaeological contexts, especially when dealing with funerary deposits lacking material culture, e.g. pottery vessels. 14C measurements of bone samples are usually performed on the extracted collagen residue. The content and the quality of collagen can vary significantly, mainly depending on bone preservation and diagenesis. Generally speaking, environmental conditions such as low pH level of soils, high temperatures, and percolating groundwaters, typical of arid and tropical zones, can affect the preservation of collagen; at the same time, bones recovered in such environments are more likely to be contaminated with carbon from the surrounding environment. Possible contamination of samples can also occur in temperate zones. While low collagen content is a condition we cannot overcome, we can use several chemical and elemental indicators in order to assess collagen quality. Among these, the C/N atomic ratio is considered a good parameter for detecting low-quality collagen and possibly contaminated samples. In a combustion and graphitization setup like that installed at INFN-LABEC, Florence, measurement can be easily performed using an elemental analyzer when combusting the sample prior to graphitization, thus requiring no extra effort (or extra amount of sample) during the preparation procedure. Bone samples recently 14C dated at INFN-LABEC have confirmed that the measurement of C/N atomic ratios can give some indications of the collagen quality. The bone material was collected from 3 necropoles of the Bronze Age period in Cyprus (Erimi-Laonin tou Porakou, Lophou-Kolaouzou, and Erimi-Kafkalla&Pitharka, along the Kouris Valley), an area characterized by environmental conditions that do not favor bone preservation. Samples were treated to extract collagen and measured by accelerator mass spectrometry (AMS). 14C results have been compared with the archaeological evidence, showing some relationship between measured C/N atomic ratios and collagen quality. In particular, when grouping the measured samples according to their C/N ratio, the agreement between 14C dates and archaeological evidence is good or inconsistent when the C/N ratio clearly falls inside or outside the “recommended” range, respectively, with a still reasonable agreement also when it is slightly above the upper limit of that range.

Excellent Preservation of Archaeological, Mercury‐Enriched Dental Remains

“…Recall that a C/N ratio between 2.9 and 3.6 is widely utilized as an indicator for acceptable organic preservation for AMS radiocarbon dating (Calabrisotto et al . ). Carbon and nitrogen concentrations were also significantly lower in the pre‐Hispanic specimen of the 30‐year‐old woman compared to the values reported in contemporary teeth (Table ), which is in agreement with a previous study (Ambrose ) showing that carbon and nitrogen concentrations in ‘collagen’ have been demonstrated to drop significantly between well‐preserved and poorly preserved samples (Ambrose ).…”

87Sr/86Sr and 14C evidence for peccary (Tayassuidae) introduction challenges accepted historical interpretation of the 1657 Ligon map of Barbados

“…AMS dating yielded an age of 235 ± 15 BP (UCIAMS-181681; δ 13 C: -21.5 ‰; δ 15 N: 8.0 ‰; 45.4%C; 14.8%N), with a 2σ calibrated range of AD 1645–1670/1780–1800 and median probability of AD 1660 [68]. The C:N ratio (3.58), a proxy measure for collagen quality, falls within the acceptable range of 2.9–3.6 [72, 73], with the ultrafiltered gelatin reported as white, high quality, and showing no signs of contamination from humates or conservants (B. Culleton, personal communication 2018). The two calibrated date ranges, representing 69.7% and 30.3% probability distributions respectively, arise from multiple intercepts of the calibration curve for the measured age.…”

The first evaluation of diagenesis rate of ancient bones by laser-induced breakdown spectroscopy in archaeological context prior to radiocarbon dating

“…The crater volume after 100 laser shot can be estimated by its profile measurement: the diameter is about 200 µm and the depth is about 400 µm from Figure 5c. Therefore, each laser shot ablated about 8 µg with a density of 2 g/cm 3 . In contrast with the traditional method of 1-3 g mechanically cleaned bone, LIBS analysis shows the advantage of fewer sample taking.…”

“…Radiocarbon dating has been a standard tool for archaeologists since the late 1940s [1]. The dating of ancient or archaeological bones is carried out on their organic fraction [2,3], the collagen, which can be extracted according to the Longin method [4]. The most widely used technique today for radiocarbon dating is counting the number of 14 C and 12 C atoms in a given sample via accelerator mass spectrometry, which requires at least 0.5 mg of carbon to be extracted from collagen (corresponding to 1-3 g mechanically cleaned bone) to perform the measurement [5].…”