Improved radiocarbon dating of contaminated protein-containing archaeological samples via cross-flow nanofiltrated amino acids

Carbon-14 (14C) dating of contaminated protein-containing material e.g. bone collagen, hair, wool and silk usually results in unreliable results if conventional pre-treatment methods are used. Therefore, the objective of this PhD thesis was to develop a method to detect 14C contamination in protein-containing archaeological material and develop a method to improve sample quality of contaminated samples to obtain more accurate 14C dates. Quality control is gaining more attention in the 14C community; hence a quality control system was introduced. Contaminated test samples were selected from archaeological sites where the presumed historical date was known by a dendrochronological date, a dated coin, a stylistic date, a funeral stone with inscripted name, written historical sources or typrochonological dated pottery. A non-destructive fluorescence spectroscopy method was developed to monitor the presence of humic substances, one of the major 14C contaminants in archaeological material, in wool, hair and silk. A positive fluorescence slope, calculated using a linear fit (least squares) of the fluorescence intensity measured between the excitation wavelengths 460 and 475nm, indicates presence of humic substances in the sample, while a negative slope is an indication of absence of humic substances. All protein-containing samples were pre-treated with standard methods before subjected to the quality assessment tests. The quality control was checked by analyzing the C:N ratio for bone collagen, silk, wool and hair. The applied C:N ratios to define uncontaminated archaeological samples were: 1. collagen C:N ratio between 2.9 and 3.6; 2. wool and hair C:N ratio between 2.9 and 3.8; 3. silk: C:N ratio between 2.9 and 3.4 . Samples with a higher C:N ratio were defined as contaminated. Uncontaminated samples can be used directly 14C analyses and reliable 14C dates should be obtained. However, contaminated samples need more clean-up to improve the sample quality. Nanofiltration is an option because it is suitable for all types of protein-containing material and should remove low-molecular and high-molecular weight contaminants unlike ultrafiltration that only suits for bone collagen and only eliminates low-molecular contaminants. A new nanofiltration method to improve quality for 14C dating was developed for bone collagen as test material. First, two nanofiltration types were tested: dead-end and cross-flow filtration using a ceramic filter with a molecular weight cut-off of 450 Dalton. Nanofiltration should remove low-and high-molecular weight humic substances. Fluorescence analyses indicated that cross-flow filtration was a more efficient technique than dead-end filtration to remove humic substances. However, 14C dating of cross-flow filtrated hydrolysed artificial collagen-humic substance mixtures, demonstrated a significant but yet incomplete removal of humic material. Hot acid hydrolysis of humic substances may form new chemical compounds, as demonstrated by HPLC analysis. It is possible that these compounds are smaller than the filter cut-off of 450 Dalton and pass through the filter and, hence, causes contamination. Second, cross-flow nanofiltration technique was applied in combination with a quality control procedure on real contaminated archaeological samples. However, a membrane with a molecular weight cut-off of 200 Dalton was used as a means to retain more 14C-containing contaminants, i.e. chemical compounds formed after hot acid hydrolysis and obtain only amino acids from the protein-containing archaeological material. The efficiency of the cross-flow nanofiltration was verified by comparing: 1. C:N ratio of the bulk sample (before nanofiltration) with C:N ratio of the cross-flow nanofiltrated amino acids (permeate) to indicate the quality sample improvement; 2. compare the 14C date of permeate with the presumed historical date. Cross-flow nanofiltration, with a filter cut off of 200 Dalton, of hydrolysed contaminated archaeological protein-containing samples, e.g. bone collagen, hair, wool and silk, decreases the C:N ratio, which indicates contaminant removal and improvement of sample quality for 14C dating. If the C:N ratio of the permeate falls within the boundaries of uncontaminated samples more accurate 14C dates were obtained. Finally the applicability of the cross-flow nanofiltration method was demonstrated on contaminated protein-containing samples by means of a case study of two skeletons and their gars of two bishops from Noyon-Tournai. One burial was assigned to Baldwin I, who died in AD 1068, because: 1. a ring with the inscription “BAL” was found; 2. a funeral stone with text was present on top of the grave mentioning the name “Baldewinus”. The second burial probably belongs to Radbot II who was the successor of Baldwin I and died in AD 1098. However, single cross-flow nanofiltration may not always be sufficient to obtain a C:N ratio within the quality boundaries for uncontaminated samples. Double cross-flow nanofiltration may be a solution as shown by silk sample ’20’ of Radbot II, but requires further investigation. This study resulted in a workflow for 14C dating of archaeological wool, silk, hair and bone collagen. All protein-containing samples are pre-treated with standard methods before quality assessment tests. Samples categorized as uncontaminated can be 14C dated after pre-treatment with the standard protocols. Hence, contaminated samples are treated with cross-flow nanofiltration and subsequently quality control parameters are measured on permeate to verify whether permeate fulfills the criteria for uncontaminated samples or not. Contaminated permeate samples are rejected for 14C dating while uncontaminated undergo 14C analysis

Reliability of AMS 14C dates of moss temper preserved in Neolithic pottery from the Scheldt river valley (Belgium)

Direct dates of pottery obtained from food crusts or other organic residues on the vessel surfaces can be affected by a reservoir effect and/or an old wood effect and therefore be unreliable. Hence, there is a need for alternative ways to directly date pottery. Moss is used as temper by several cultural groups of the late 6th to early 4th millennium cal BC in northwestern Europe. After the pottery is fired, charred moss remains are often preserved in the clay, so that relatively short-lived plant material with a direct chronological link to the pottery and human occupation is available for radiocarbon (C-14) dating. In this study, charred moss temper is extracted for accelerator mass spectrometry (AMS) C-14 dating from pottery of the Swifterbant Culture and Spiere group in the Scheldt river valley (Belgium). The moss dates are then compared to reference dates of organic macro-remains from the same sites and food crust dates with or without a reservoir effect of the same pottery. Eleven out of 13 moss dates are in line with the expected pottery age. The paired dates of moss temper and food crusts from the same potsherds confirm a freshwater reservoir effect (FRE) for the latter. We conclude that moss temper has great potential as a sample material for direct pottery dating. However, more research on the extraction and pretreatment of moss temper as well as on the reliability of moss dates is necessary in the future

An archaeological mystery revealed by radiocarbon dating of cross-flow nanofiltrated amino acids derived from bone collagen, silk, and hair: case study of the bishops Baldwin I and Radbot II from Noyon-Tournai

Excavations in the cathedral of Tournai revealed two sepultures, which were identified by the excavators as those of bishops because of their special location in the cathedral. One burial was assigned to Baldwin I, who died in AD 1068, because (1) a ring with the inscription "BAL" was found and (2) a funeral stone with text was present on top of the grave mentioning the name Baldewinus. The second burial probably belongs to Radbot II, who was the successor of Baldwin I, and died in AD 1098. Both burials contained textiles (silk), the skeleton, a wooden pastoral staff, and human hair was still present on the skull of what was presumed to be Radbot II. All the protein-containing materials were degraded and/or contaminated. Standard sample pretreatment methods were not able to remove all the contaminants. Single and double cross-flow nanofiltration of the hydrolyzed protein-containing materials were performed. The sample quality for radiocarbon dating was improved and C-14 data revealed interesting and surprising results. The C-14 dates of the wooden pastoral staff and permeate femur confirm that the skeleton and tomb belong to bishop Baldwin I. The C-14 dates of hair and permeate skull indicate that the skeleton may indeed belong to bishop Radbot II. The younger C-14 dates of the wooden pastoral staff and silk samples indicate a postburial disturbance of the site burial during the 12th-13th century

Primer intent de mesurar l'edat del compartiment marí de 14C de les aigües costaneres de les illes Balears

[cat] El coneixement de les coves litorals situades entre cala Falcó i cala Varques s’ha vist enriquit amb les aportacions subaquàtiques efectuades a la cova des Coloms de Cala Falcó o cova des Coloms 1, a la cova des Coloms de cala Varques o cova des Coloms 2 i amb la incorporació d’una nova cavitat, la cova des Genet. Dues de les tres cavitats descrites són captures càrstico-marines a on es fan ben evidents les interaccions entre el modelat càrstic i el modelat litoral. La cova des Coloms de Cala Varques actua també de surgència submarina.[eng] The knowledge of the littoral caves located between Cala Falcó and Cala Varques has resulted enriched with several new findings: the diving explorations performed in Cova des Coloms de Cala Falcó (also known as Cova des Coloms 1) and in Cova des Coloms de Cala Varques (also known as Cova des Coloms 2) as well as the documentation of a new cave, the Cova des Genet. Two of the three described caves are complex regarding their genesis, being the result of mixed karstic and marine erosion processes. The Cova des Coloms de Cala Varques acts also as a submarine spring

Can calcined bones be used to date Final Palaeolithic and Mesolithic open-air sites? A case-study from the Scheldt basin (NW Belgium)

This paper presents the results of an inter-comparative study in view of assessing the reliability of radiocarbon dates obtained on calcined bones from open-air Palaeolithic and Mesolithic sites. The results demonstrate that the success rate is largely dependent on site-taphonomy, in particular the speed of covering of the site. Sites quickly covered by aeolian, alluvial or marine sediments yield on average good dating results. At worst they can be affected by an wood-age offset, generally <100 years, caused by the uptake of carbon from the firewood. Sites which are uncovered or have been covered rather late suffer from contamination problems resulting in radiocarbon dates much younger than the reference dates. For these sites, which unfortunately represent the vast majority of open-air Palaeolithic and Mesolithic sites, calcined bones are not a valuable dating material for developing robust, decadal-to-centennial chronologies

Humans and Myotragus: the issue of sample integrity in radiocarbon dating

Una fita clau enla prehistòria de les Illes Balears és la data de l'arribada dels humans i la suposadament consegüent extinció de Myotragus balearicus, degut a les interferències humanes. Al llarg dels anys s'han proposat diferents models cronològics. Els treballs que tracten aquest assumpte discuteixen tots en gran extensió la integritat arqueològica de les mostres emprades per a la datació radiocarbònica d'aquest esdeveniment. Emperò, cap dels treballs discuteix la integritat de les mostres d' ossos (tant d'humans com de Myotragus) emprats a les anàlisis radiocarbòniques. La nostra recerca mostra que la majoria dels ossos d'una localitat clau, la cova de Moleta, estan molt mal conservats. En conseqüència, els resultats no són fiables i en molts de casos la pregunta que caldria respondre és si hi ha alguna relació entre l'edat radíocarbònica de la mostra i l'edat real de l'os. En aquest treball discutim mètodes relativament senzills per contrastar la qualitat dels ossos i la fiabilitat de la data radiocarbònica.A crucial datum in the prehistory of the Balearic Islands is the arrival of humans and the supposed, consequent extinction of Myotragus balearicus due to human interference. Over the years several chronological models have been proposed. The papers dealing with this topic all discuss in great extent the archaeological integrity of the samples used for radiocarbon dating this event. None of the papers, however, discuss the sample integrity of the bones (of both humans and Myotragusi used in the radiocarbon analyses. Our investigation shows that most of the bones from the crucial site of Cova de Moleta are very badly preserved. Consequently, the results are unreliable and in many cases the question should be asked if there is any relationship between the radiocarbon age of the sample and the real age of the bone. In this paper, we discuss relatively simple methods to check the quality of the bone and the reliability of the radiocarbon date