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.     

Prehistoric settlement chronology on Rapa Nui,Chile: obsidian hydration dating using infrared photoacoustic spectroscopy

The prehistoric Polynesian inhabitants of Rapa Nui (Easter Island) utilized obsidian for nearly 700 years in many activities connected with daily life. The near ubiquitous occurrence of the natural glass in both domestic residences and religious structures makes the application of obsidian hydration dating highly suitable for the investigation of cultural change. We have applied previously developed calibrations that estimate hydration rates for obsidian based upon the structural water content of the glass as determined by infrared spectroscopy. The archaeological ages estimated by this method were compared with accelerator mass spectrometry (AMS) dates using short-lived woody species endemic to the island. The convergence between the two dating methods is strong and we suggest that obsidian hydration dating may be used on Rapa Nui to reliably date contexts where suitable material for AMS dating may not be available.     

Dating North Asian surface assemblages with ostrich eggshell: implications for palaeoecology and extirpation

East Asian ostrich (Struthio anderssoni Lowe) was thought to have become extinct sometime in the Late Pleistocene. Petroglyphs portray ostrich with Pleistocene animals, and ostrich eggshell (OES) fragments and ornaments from Holocene sites were considered to be older fossils. Here we summarize previous radiometric dates for ostrich eggshell (OES) and present 15 new calibrated accelerator mass spectrometry (AMS) dates, indicating that ostrich survived in Mongolia and northern China until at least 8.9 ka BP. The dates in our sample population suggest a correlation between Struthio and warm steppe environments, with extirpation probably related to essential changes in Holocene steppe ecosystems including human expansion. This study assesses the usefulness of Asian OES for archaeological dating by AMS, constrains the date of Asian ostrich extirpation, and investigates palaeoenvironmental implications of ostrich survival and extinction.     

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.     

Radiocarbon dating and the “old shell” problem: direct dating of artifacts and cultural chronologies in coastal and other aquatic regions

Archaeologists have long recognized the problem of the “old wood” effect in radiocarbon dating charcoal and wood samples, the age of which may be hundreds of years older than their use by humans. Such problems have resulted in significant changes in how most researchers select wood and charcoal samples for ¹⁴C dating, with many now using relatively short-lived carbonized materials for dating. Despite the significant strides made in our understanding of the potential biases of the “old wood” effect, little emphasis has been placed on the possible impacts of dating “old shell” in archaeological deposits. The use of marine shell for ¹⁴C dating is widespread in coastal areas around the world, including a growing emphasis on the dating of individual shell artifacts via Accelerator Mass Spectrometry (AMS). In dating shell artifacts, we have obtained several dates older than associated ¹⁴C dates for short-lived subsistence remains from the same deposits, including great disparities (>10,000 years) and more subtle differences (≥100 years). These discrepancies appear to be due to the use of old shells by humans to make beads and other artifacts, including shells collected from fossil deposits, older archaeological sites, and beaches. The problems caused by the use of old shells to make beads and other artifacts are surmountable through careful sample selection, analysis of multiple ¹⁴C dates on a variety of materials, and proper calibration procedures.     

岩画断代研究——科技考古学领域中一个亟待解决的问题

探索和研究表明,岩画断代问题仍然是困扰岩画研究的难题之一,其主要原因是岩画本身不能够提供可供断代的直接依据。本文综述了目前岩画断代研究中经常使用的自然科学和考古学方法及其存在的问题,提出应用AMS14C是今后研究我国岩绘画断代问题的首选方法,解决岩刻画的断代问题则主要有赖于微腐蚀方法。     

NEW RADIOCARBON ACCELERATOR DATES ON ARTEFACTS FROM THE EARLY MESOLITHIC SITE OF STAR CARR,NORTH YORKSHIRE*

For the well‐known early Mesolithic site of Star Carr, dating of organic artefacts by accelerator mass spectrometry (AMS) has been hampered by treatment of bone and antler recovered during the original excavations with preservatives. Some, untreated, artefacts were, however, collected after Clark's excavation in 1950. Four of these artefacts were AMS dated in 1995, but two of the dates were significantly younger than the others, and were questionable due to their low collagen yields. These suspect samples have now been re‐analysed, demonstrating that all four artefacts are of similar date. The significance of these dates for the chronology of Star Carr is discussed.     

Radiocarbon dating of prehistoric hearths in alpine northern Sweden: problems and possibilities

The chronology of prehistoric Sami settlement sites has previously been established by conventional radiocarbon dating of bulk charcoal samples associated with hearths from sunken hut floors (stállo-foundations). Here we present results of a comprehensive dating exercise of stállo-foundations in the alpine area of northern Scandinavia using Accelerator Mass Spectrometry (AMS) radiocarbon dating of charcoal. Over a 3 km² study area, AMS calibrated ages of hearth charcoal from 22 stállo-foundations across 12 sites securely date these features to between cal. AD 640 and AD 1180. Only small variations in age were found between charcoal samples from different areas of a given hearth. Statistical analysis of all the charcoal AMS radiocarbon dates obtained reveals that 12 stállo-foundations across nine sites are contemporaneous and date to the Viking Period (AD 800–AD 1050). The tightly constrained AMS-based chronology of stállo-foundations contrasts with the existing chronology based on conventional radiocarbon analysis, which places these features within a significantly greater time-frame of between AD 600 and AD 1900, with most dates ranging between AD 800 and AD 1350.This discrepancy is likely to result from the necessity of collecting composite hearth charcoal particles, which may originate from different phases of occupation, in order to achieve the required final carbon content for conventional radiocarbon analysis. We argue that the new AMS-based radiocarbon chronology of stállo-foundations presented here supersedes the existing chronology based on conventional (Gas Proportional counting) radiocarbon analysis and we advocate the use of AMS radiocarbon dating in future hearth investigations.     

A Multi-regional Analysis of AMS and Radiometric Dates from Carbonized Food Residues

Abstract

Accelerator Mass Spectrometry (AMS) is increasingly employed to date encrusted carbonized food residues on prehistoric pottery sherds, particularly in regions where other datable material is absent or scarce, or where such materials lack good association with objects of chronological interest. The accuracy of AMS dating of residues has recently been questioned in Europe and North America, with skepticism directly or indirectly attributed to the presence of carbonate rich bedrock, a freshwater carbonate reservoir resulting from association with such bedrock, or the cooking of aquatic resources such as mollusk or fish engaged in the uptake of older carbonates. It is argued that carbonized food residues from such contexts or resources are expected to display older apparent ages than dates on other materials. We evaluate this proposition through hypotheses assessing the accuracy and internal consistency of a broad range of data from the northeastern and midwestern United States. We statistically assess dates from 25 site components where either both dates on residue and context dates on other materials have been obtained. Of the 70 dates on residue tested, only 5.7 percent are considered inconsistent with their respective context dates. We also test for consistency 46 dates on residues from 14 site components lacking context dates. Of these, only 4.5 percent are considered internally inconsistent with expectations at the site or regional level. At present, we conclude that AMS dating of residues provides results consistent with those of other datable materials.     

The Timing of Angel Mounds Palisade Construction A Search for the Best Chronological Model

Abstract

Angel Mounds was a heavily fortified Mississippian settlement with several discrete palisades. Although the palisades were identified early on, the construction sequence has remained elusive because the construction episodes do not have stratigraphic relationships with one another. Recent work at the site reexamined old test excavations and collected new material for radiocarbon dating. AMS dating yielded a suite of new dates from palisade contexts. To refine the construction sequence, five Bayesian chronological models were constructed for palisade building. These models indicate that palisades were first built at Angel Mounds sometime between A.D. 1278 and A.D. 1410, which precedes or coincides with regional depopulation in the lower Ohio River valley. These results further indicate that palisade building at Angel Mounds may be a consequence of external competition and conflict caused by resource-induced stress resulting from deteriorating climatic conditions.     

Middle Palaeolithic Refugium,or Archaeological Misconception? A New U-series and Radiocarbon Chronology of Abric Agut (Capellades,Spain)

New U-Series and C14 (AMS) dates are provided for the Abric Agut (Capellades, Barcelona, Spain). This site was previously considered to be of Middle Palaeolithic age according to the characteristics of the lithic assemblage. In addition, human teeth were uncovered and attributed to neandertals. However, radiometric dating clearly indicates a Late Pleistocene-Early Holocene age.     

Radiocarbon dating by the accelerator technique

Radiometric dating of archaeological samples by the accelerator mass spectrometry (AMS) technique is well established today. The main advantage of this method compared to the old decay counting procedure is the small sample size (1 mg carbon equivalent weight) needed to carry out a dating. The basic principles as well as the present status of the technique are presented. Experiences from the first year of routine measurements in the Uppsala laboratory are discussed and some examples of the material analysed are given.     

Calcium oxalate AMS C dating and chronology of post-Palaeolithic rock paintings in the Iberian Peninsula. Two dates from Abrigo de los Oculados (Henarejos,Cuenca, Spain)

Since 2005 we have been utilizing accelerator mass spectrometry (AMS) ¹⁴C dating in research on calcium oxalate crusts associated with open air rock art of the Iberian Peninsula. In this paper we present two dates linked with three eye-idol pictographs at Abrigo de los Oculados (Henarejos, Cuenca, Spain). Radiocarbon ages for these motifs agree with the expected iconography-based archaeological chronology. Such oxalate dates could provide an independent basis for evaluating chronological theories for post-Palaeolithic sites, designated in the UNESCO World Heritage List as Rock Art of the Mediterranean Basin on the Iberian Peninsula.     

Dating oxalate minerals 20–45 ka

We report a test of the dating of oxalate minerals near the radiocarbon limit. Oxalate salts are used for estimating the ages of prehistoric rock paintings and carvings, but uncertainties have existed about the origin of the carbon they contain. Sediments at the Carpenter's Gap 1 rockshelter, Western Australia, have been conventionally radiocarbon dated at about 34 000 years old, providing independent evaluation for the ages of buried oxalate crusts associated with them. Accelerator mass spectrometry radiocarbon (AMS ¹⁴C) assays of carbon in rapidly oxidized oxalate ions from these crusts produce age estimates marginally older than the covering sediments.     

The antiquity of Olivella shell beads at CA-ORA-64: AMS radiocarbon dated between 9420 and 7780 cal BP

Investigations in the 1960s and 1970s showed the Irvine site (CA-ORA-64) to be among the oldest shell middens known from the Pacific Coast of North America. The site chronology, based on conventional analysis of mixed shell samples collected from heavily bioturbated soils, extended back to ca. 8440 RYBP. Recent work at the site provided an opportunity to refine the CA-ORA-64 chronology via AMS ¹⁴C dating of single shell fragments, including 14 Olivella beads. Long considered to be one of the earliest ornament types made by Pacific Coast peoples, such spire-removed Olivella beads were used through much of the Holocene and generally are not good chronological indicators. AMS analysis of the CA-ORA-64 specimens, however, produced a consistent series of Early Holocene dates that includes some of the oldest securely dated shell beads in North America. Along with obsidian from interior sources, Olivella beads played an important role in early exchange networks between coastal and interior peoples. Methodologically, our research demonstrates the utility of AMS ¹⁴C dating in determining the age of key artifact types found in multicomponent sites with assemblages affected by stratigraphic mixing.     

Reevaluating the Age of the Iberomaurusian in Morocco

Chronological evidence for the Iberomaurusian is currently very limited and there are problems with some of the published radiocarbon dates. In this paper we present new AMS dating results from well-stratified cave sequences at Ghar Cahal, Kehf el Hammar and Taforalt in northern and eastern Morocco. The longest of these sequences, from Taforalt, shows an intermittent occupation history spanning the period ca. 18,000–11,000 bp (radiocarbon determinations presented in this paper are expressed as ka bp or bp, whilst approximate calendar ages are expressed as Cal bp) with a marked intensification of cave use soon after ca. 13,000 bp. Using calibrated AMS ages in comparison to sea surface temperature evidence from the Alboran Sea core MD95-2043 and more generally to Greenland ice δ¹⁸O core records, we suggest that there may have been a relationship, albeit a complex one, between climatic events and cave activity on the part of Iberomaurusian populations.     

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 Architectural Mortar: A Case Study in the Maya Region,Quintana Roo,Mexico

Abstract

The use of radiocarbon dating to analyze mortar and charcoal inclusions within mortar or plaster is a useful way to date the construction of architecture, particularly when options for other chronometric methods are limited. In the Yalahau region of northern Quintana Roo, Mexico, members of the Yalahau Regional Human Ecology Project have faced challenges in dating buildings made of large blocks of stone in the Megalithic architectural style. The Megalithic style poses serious problems for any analysis, as excavating into structures with stones weighing several tons can be dangerous, expensive, and time consuming. Additionally, there are no associated sculptures, texts with dates, or other traditionally accessible chronological markers. These factors have resulted in a reliance on a ceramic chronology despite the uncertainty of the dating of many ceramic types in this region, as well as the questionable contextual associations between recovered ceramics and architectural construction phases. Megalithic-style structures at the ancient Maya site of El Naranjal have residual mortar with charcoal inclusions left behind during the mortar-making processes that can be extracted and dated with AMS ¹⁴C methods. Several samples of mortar and charcoal were obtained from structures 1 and 10 from exposed exterior walls and an interior vault. The resulting dates confirm the date for the construction based on ceramics excavated from the same site.     

AMS C dating the Protoaurignacian/Early Aurignacian of Isturitz,France. Implications for Neanderthal–modern human interaction and the timing of technical and cultural innovations in Europe

This paper presents new AMS radiocarbon dating results of six ungulate bones from the current excavation of Isturitz Cave, France, layer C 4c4. The assemblage from this layer exhibits a suite of traits closely aligned with the Early Aurignacian, but with some aspects that bear strong similarities with the Protoaurignacian, with possible in situ technological transformation. Accurate and precise dating of the late Middle Palaeolithic and the early Upper Palaeolithic periods is critical to our understanding of the possible relationship between final Neanderthals and early modern humans in Europe. As such, a rigorous set of sample selection and evaluation protocols was developed and used in this research. Among these, only cutmarked bones were selected and a total of 31 targets were made, giving a weighted average of 37,180 ± 420 BP for this assemblage and providing a terminus ante quem for the ornaments, decorated artefact and amber pendants beneath it. The implications and importance of these results to debates concerning the chronological relationship between the Châtelperronian, Protoaurignacian and Early Aurignacian and associated debates regarding hominin dispersal, interaction and the timing of technical and cultural innovations are discussed.     

RADIOCARBON DATES FROM THE OXFORD AMS SYSTEM: ARCHAEOMETRY DATELIST 34

This is the thirty‐fourth list of AMS radiocarbon determinations measured at the Oxford Radiocarbon Accelerator Unit (ORAU). Amongst the dates obtained for archaeological sites included here are the latest series of determinations from the key sites of Proskynas (Greece), Kova?evo (Bulgaria) and Khirbet Qeiyafa (Israel), as well as others dating to the Palaeolithic, Mesolithic and later periods. Submitters of the material provide comments on the significance of the results.