Sample preparation for accelerator-based radiocarbon dating

Although several efficient sample preparation methods have been devised for conventional radiocarbon dating, the advent of the accelerator mass spectrometer (AMS) dating technique with its much smaller sample requirement and different counting method has meant that new preparation routes have had to be developed. Techniques used for the Oxford AMS system are described in this paper.     

The archaeology of radiocarbon accelerator dating

Accelerator mass spectrometry (AMS) allows radiocarbon dating to be carried out by direct counting of¹⁴C atoms, rather than the conventional counting of radioactive disintegrations. The result is that samples up to 1000 times smaller can be handled. The approach was tested in principle by 1977 and for archaeological operation by 1983. More than 2000 samples per year are now being dated worldwide. The machines can now operate to about ± 80 years or better. Dates older than 40,000 years have not yet been achieved, but the ability to use small samples has already had considerable impact on dating the period 10,000–30,000 years ago. Bone is an ideal material for the new technique, since amino acids can normally be isolated and purified from gram-size samples. Studies of the origins of domestication are aided by the dating of individual grains and seeds. Because small samples can be mobile in the soil, careful sample selection strategies and procedures are required. The full impact of the technique can be assessed only through the rapid and comprehensive publication of archaeological results.     

Comparison of fluoride and direct AMS radiocarbon dating of black bear bone from Lawson Cave,Missouri

Abstract

After a 20-year hiatus (1955–1975) during which few archaeologists discussed fluoride dating, the method again received attention in the 1980s and 1990s when some argued for its validity. As a dating method, fluoride dating depends on the rate at which fluorine ions replace hydroxyl ions in osseous tissue. The rate of replacement is influenced by the properties of the skeletal part (SP), sediment chemistry (K), and sediment hydrology (H), and the replacement rate influences estimates of time. Calibrated AMS radiocarbon assays of 10 black bear (Ursus americanus) femora from a natural-trap cave in central Missouri are weakly correlated with fluorine concentrations, determined by neutron activation analysis in the 10 femora. Despite minimal variation in SP, K, and H, results indicate fluoride dating can be considered a valid dating method only in cases when the chronological validity of its results are confirmed with independent chronometric data. As similarities in fluorine amounts across specimens increase, provenience information and bone orientation data as well as fine resolution data on K and H become critical to the application of fluoride dating.     

Radiocarbon dating of marine shell samples. The marine radiocarbon reservoir effect of coastal waters off Atlantic Iberia during Late Neolithic and Chalcolithic Periods

Radiocarbon dates on marine shells have not been used as extensively as charcoal or bone dates for the setting up of absolute chronologies because interpreting these dates is complicated by the marine radiocarbon reservoir effect. Nevertheless marine shellfish were used widely at least during the Holocene and their shells are abundant and usually well preserved in archaeological deposits located near shorelines. Consequently prior research concerning the oceanographic conditions and the marine radiocarbon reservoir effect of a particular coastal area is needed in order to set up reliable chronologies for that region. Values of regional marine radiocarbon reservoir effect – ΔR – of coastal waters off Atlantic Iberia, some of its variability along the Holocene and its correlation with the upwelling phenomenon were determined during previous research. More data related to the ΔR values for western Portuguese coastal waters during the Late Neolithic and the Chalcolithic, a time interval badly sampled in previous research, were recently obtained. These values can be compared with ΔR values already determined for the Gulf of Cadiz. Besides the importance of these values for a better knowledge of the palaeoceanography and palaeoclimatology of Atlantic Iberia, from now on archaeologists can set up reliable chronologies for Late Neolithic and Chalcolithic contexts using marine shell samples of that origin for radiocarbon dating.     

Characterisation and blind testing of radiocarbon dating of cremated bone

The success of radiocarbon dating of burned or cremated bones depends on the exposed temperature during burning and the degree of re-crystallisation of the inorganic bone matrix. We present a method for characterisation of likely cremated bones by employing visual inspection, infrared spectrometry and carbon stable isotope analysis on the bio-apatite fraction. The method of radiocarbon dating of cremated bones was tested by dating paired samples of bone and associated context materials such as pitch, charcoal and a dendrochronologically dated oak coffin. The dating of these paired test samples were largely performed as blind tests and showed excellent agreement between pitch and bone. The weighted mean age difference of all test samples is observed to −9 ± 60 ¹⁴C yr. To test the indicators and the effects of the degree of burning, a Late-Neolithic human individual has been studied, as this individual exhibits the full spectrum from low temperature burning (charred) to high temperature (“cremated”) from one end of a single bone to the other. This is reflected as a marked step in numerous parameters as well as in a significant difference in ¹⁴C age between the charred and the cremated bone samples.     

Pre-screening techniques for identification of samples suitable for radiocarbon dating of poorly preserved bones

Under certain environmental conditions, post-depositional diagenetic loss of bone collagen can severely reduce the number of bones from a particular archaeological site that are suitable for stable isotopic analysis or radiocarbon dating. This study examined nearly 300 bones from 12 archaeological sites across southern England known to yield poor or variable preservation to try to identify one, or more, pre-screening technique(s) that would indicate suitable collagen preservation for radiocarbon dating. The most reliable method was shown to be the percent nitrogen (%N) of whole bone powder, which has an 84% chance of successfully predicting whether or not a bone will yield sufficient (i.e. >1% weight) collagen for dating.     

Radiocarbon dating of bone by accelerator mass spectrometry

A companion article describes the sample preparation method used in the production of graphite targets for the Oxford accelerator mass spectrometer (AMS) system. The chemical pretreatment developed for the dating of bone, ivory and tooth samples is described in this paper.     

New radiocarbon dating of the transition from the Middle to the Upper Paleolithic in Kebara Cave,Israel

The Middle to Upper Paleolithic transition (MP-UP transition) is considered a major technological and cultural threshold, at the time when modern humans spread “out of Africa”, expanded from the Levant into Europe and possibly into central and northern Asia. The dating of this techno-cultural transition has proved to be extremely difficult because it occurred sometime before 40,000 radiocarbon years before present (¹⁴C years BP), which is close to the end of the effective dating range of radiocarbon. Other dating methods such as Thermoluminescence (TL) or Electron Spin Resonance (ESR) are not sufficiently precise to date the recorded archaeological MP-UP transition in the Levant. Here we report a consistent set of stratified radiocarbon ages on freshly excavated charcoal from Kebara Cave, Mt. Carmel (Israel), that span the late Middle Paleolithic (MP) and Early Upper Paleolithic (EUP) This study applied novel strategies to improve sample preparation techniques and data analysis to obtain high-resolution radiocarbon models. From this study it is proposed that the MP-UP transition for this site can be placed immediately after 45,200 ± 700 ¹⁴C years BP and before 43,600 ± 600 ¹⁴C years BP or from 49/48 to 47/46 radiocarbon calibrated years before present (years Cal BP).     

Debates over Palaeolithic chronology – the reliability of C is confirmed

The debate about the complex issues of human development during the Middle to Upper Palaeolithic transition period (45–35 ka BP) has been hampered by concerns about the reliability of the radiocarbon dating method. Large ¹⁴C anomalies were postulated and radiocarbon dating was considered flawed. We show here that these issues are no longer relevant, because the large anomalies are artefacts beyond plausible physical limits for their magnitude. Previous inconsistencies between ¹⁴C radiocarbon datasets have been resolved, and a new radiocarbon calibration curve, IntCal09 (Reimer et al., 2009), was created. Improved procedures for bone collagen extraction and charcoal pre-treatment generally result in older ages, consistent with independently dated time markers.     

Combining an archaeomagnetic and radiocarbon study: dating of medieval fireplaces at the Mühlegasse,Zürich

During the restoration of the Radium cinema located in the old Town of Zürich, a stratigraphic sequence of medieval fireplaces came to light. Based on ceramic finds, a preliminary age of about 1000 AD was assigned. In this paper we show the results from archaeomagnetic and radiocarbon dating, which combined with the stratigraphic information yield a better constrain of the period of use of these fireplaces. Whilst the radiocarbon technique continues to be the most widespread methodology for dating young archeological artifacts, archaeomagnetic dating is becoming increasingly more established in Europe thanks to the increased number of available measurements. A Bayesian model on the period of use of these fireplaces was produced with OxCal, by a combination of magnetic and radiocarbon ages, together with the stratigraphic information. The results show that the fireplaces were probably used during 1 to 2 generations (e.g. 20–40 years each), and are in good agreement with the archaeological context of this site. To make use of the magnetic measurements for future reconstructions of the field, we carried out an additional age model using only the radiocarbon and the stratigraphic information. Although some of the structures show large directional scatter due to poor baking in antiquity, the results confirm the trend of the geomagnetic field around 1000 AD.     

Obsidian hydration dating by infrared spectroscopy: method and calibration

Low temperature (90–190 °C) hydrothermal experiments have been conducted on seven obsidians where composition of the glass varies significantly in the concentration of structural water within the unhydrated bulk material. Infrared transmission spectroscopy was used to track the diffusion of molecular water into the glass surface as a function of time and temperature. Long-term (60–360 days) hydration sequences at 90 °C show a t^0.6 time dependence for the mass uptake of molecular water that forms the hydration layer. The structural water concentration of the unhydrated bulk obsidian is highly correlated with the pre-exponential and activation energy and may be used to estimate the Arrhenius constants. In addition, secondary ion mass spectrometry (SIMS) hydrogen profiling of Napa Glass Mountain obsidian hydrated at 90 °C reveals that the early stages of diffusion exhibit a dynamic behavior that includes a fluctuating hydrogen concentration and a changing diffusion coefficient that slows with time.     

A bayesian approach to wiggle-matching

“Wiggle-matching” is a technique developed to provide calendar dates for a series of samples of known deposition rate using the now well-established high-precision radiocarbon calibration curve. In this paper we describe how the technique may be formulated within the Bayesian framework for statistical analysis and thereby permit the incorporation of uncertainties regarding the deposition rate. The methodology is illustrated by two archaeological examples.     

Ford revisited: A critical review of the chronology and relationships of the earliest ceramic complexes in the New World, 6000-1500 B.C.

In 1969, Ford offered a comprehensive model for the diffusion of ceramic production and Formative lifeways in the New World. Although criticized as simplistic, it was echoed by other unitary models, such as Lathrap's spread of Tropical Forest culture outward from a lowland South American hearth. Radiocarbon dates suggest that the earliest American pottery appears in the Amazon basin as early as 6000 B.C. However, there is little support for an ex Amazonas lux spread of pottery technology. Diffusionary models predict early complexes will resemble one another at first and then diverge over time, but comparative analysis reveals substantial variability even at the earliest time level. Heterogeneity among the earliest complexes indicates several likely hearths for the independent evolution of ceramic production, including (1) lowland Brazil, (2) northern Colombia, (3) coastal Ecuador, (4) coastal Peru, (5) central Panama, (6) southern Mesoamerica, (7) the southeastern United States, and (8) the central United States.     

Bayesian modelling of an absolute chronology for Egypt's 18th Dynasty by astrophysical and radiocarbon methods

Only a few astrophysical points and synchronisms listed in texts provide anchor points for the absolute chronology of Ancient Egypt. At first we will show how we can re-calculate some of these anchor points by using Sothic dating based on the arcus visionis method, and modelling lunar dates using a Bayesian approach. Then, we will discuss two radiocarbon studies carried out on short-lived Egyptian materials held at the Louvre Museum that could be attributed to particular reigns or other precise periods. Using a Bayesian approach, these dates were combined with the known order of succession and the lengths of reigns. Sothic and lunar dates were integrated as priors in the model. This approach has led to a new proposal for the absolute chronology of Egypt's 18th Dynasty.     

A red deer (Cervus elaphus L.) skeleton from seamer carrs, Cleveland, England: Provenance of the skeleton and palaeoecology of the site

A Red deer, Cervus elaphus L., skeleton from Seamer Carrs was excavated and the collagen fraction of one of the bones dated to 4330 ± 100 bp (Birm. 977). The bones were embedded in a limnic sediment that was dated to 7360 ± 120bp(Birm.882). This date was confirmed by the pollen assemblage, which indicated a Flandrian I/II chronozone age. The date of the Cervus bone is explained by its movement vertically downwards in the limnic sediment. Attention is drawn to the number of large mammalian skeletons that have been recovered from Seamer Carrs during drainage operations and subsequently, and to the mesolithic and neolithic artifacts recovered from the slopes around the Carrs.     

Reassessing the Developmental and Chronological Relationships of the Formative of Coastal Ecuador

The Ecuadorian Formative was initially interpreted as a result of long-distance diffusion, and migration, more recent research has changed our perception of the Valdivia, Machalilla, and Chorrera culture complexes. In this analysis, these archaeological investigations are reassessed in order to reevaluate our understanding regarding the nature of these prehistoric cultures. Formative chronologies, distributions, interrelationships are reviewed in the light of Pre-Hispanic occupations in El Oro Province. Previous investigations on the Ecuadorian littoral are examined. Results indicate (1) Valdivia and Machalilla are part of the same ceramic tradition and (2) the interrelationships of these complexes to Late Formative Period ceramic sequences are more complex than previously assumed. (3) A major adaptive shift related to an increased dependence upon agriculture occurred during Valdivia VI–VIII, and continued into the Late Formative with the widespread distribution of Chorrera related material culture. (4) Long-distance interaction with the Ecuadorian highlands resulted in the spread of what may be termed a Chorrera horizon and formed the basis of subsequent Andean cosmology where it was symbolically represented according to local and regional artistic canons and over a vast area of Andean South America.     

A possible case of treponemal disease from England dating to the 11th–12th century AD

This short report describes a human skeleton from an archaeological site in England showing signs of treponemal disease. A radiocarbon determination indicates that it is firmly pre‐Columbian in date. The implications for recent debates concerning the origin of treponemal disease in Europe are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Two radiocarbon dates for freshwater shells from hierakonpolis: Archaeological and geological interpretations

Shells of two species of freshwater bivalve (Unio willcocksi Bullen Newton and Etheria elliptica Lamarck) from the predynastic Gerzean (Nagada II) Decorated Tomb at Hierakonpolis, Egypt have given dates of 5000±90 bp for the tomb, and 12,900±120 bp for an episode of Nile terrace accumulation (correlated here with the Sahaba-Darau aggradation event). The archaeological and geological significance of these results is discussed, together with an outline of problems associated with radiocarbon dating of shell. Comparisons are made with the few other radiocarbon dates available for the Predynastic period in Egypt and possible reasons for the presence of shells in the tomb are considered.     

Luminescence and radiocarbon dating as tools for the recognition of extraterrestrial impacts

Extraterrestrial events and the extraterrestrial origin of both material and impact forms were recognized in the Morasko, Kaali and Przełazy shallow geological profiles by means of luminescence and radiocarbon dating as well as the frequency of magnetic spherules. The obtained results provide a promising tool for proving theat extraterrestrial events affected characteristic lithological and morphological environmental features.