FURTHER STATISTICAL METHODS FOR THE CALIBRATION OF FLOATING TREE-RING CHRONOLOGIES

This paper describes the application of some further statistical methods for the calibration of floating treering chronologies to data pertaining to the Neolithic settlement at Auvernier. The more general statistical approach utilizes the information contained in the successive time-derivatives as well as the absolute values of the bristlecone pine calibration curve, by fitting polynomial or piecewise polynomial curves, thereby producing better estimates, in general, of the absolute dates of the floating chronologies. Presentation of results in terms of joint confidence regions enables the relevant stratigraphic evidence to be included in the analysis by simple graphical means. In addition, the paper offers a new approach, using only floating tree-ring chronologies, to the testing of Libby's principle of simultaneity.     

RADIOCARBON MEASUREMENTS ON A FLOATING TREE-RING CHRONOLOGY FROM NORTH-EAST SCOTLAND

Radiocarbon measurements have been performed on a 250 year ‘floating’ tree-ring section recovered from an archaeological site in north-east Scotland. Short term fluctuations in atmospheric concentration appear to be superimposed on a general trend of decreasing ambient ¹⁴Cparallel with tree growth. The most significant finding is the range of dates obtained from the sequence, namely 400 years, since it implies that the error on a single radiocarbon date is considerably greater than at present accepted on the basis of analytical precision alone.     

Palaeoenvironmental and chronological investigations of the Magdalenian sites of Goyet Cave and Trou de Chaleux (Belgium), via stable isotope and radiocarbon analyses of horse skeletal remains

Trou de Chaleux and Goyet are caves situated less than 30 km apart in Belgium that contain stratified Magdalenian artefacts and butchered faunal remains. Published radiocarbon dates suggest that both sites were contemporaneously occupied during to the Late-glacial interstadial. It has previously been suggested that the Trou de Chaleux Late-glacial faunal remains might be slightly older than those at Goyet Cave, and that Trou de Chaleux has two phases of occupation during the Late-glacial interstadial. However, the limited number of radiocarbon dates currently available makes it impossible to determine whether the sites are truly contemporaneous, and the assessment of their absolute chronologies is complicated by a plateau in the calibration curve. In this paper, bone collagen δ¹³C and δ¹⁵N signatures of horse bones from the two sites are used to reconstruct local palaeoenvironments. We hypothesise that if occupations at the two sites were contemporaneous, the horse collagen δ¹³C and δ¹⁵N isotope signatures from both sites will be similar, since comparable carbon and nitrogen isotopic values would reflect similar diets, ecologies and environments. To provide clear dating parameters, new AMS radiocarbon determinations are also presented. Results show that horse collagen δ¹³C and δ¹⁵N isotope signatures at the two sites are different, indicating that the populations were not subject to similar diets, ecologies and environments. The new radiocarbon dates confirm that the horse bones from Trou de Chaleux date to the Late-glacial interstadial, but they also show that in Goyet Cave Horizons 1 and 2, older horse remains dating to ca. 32?000–27?000 ¹⁴C yr BP are mixed with Late-glacial horse remains. The δ¹⁵N values of the Goyet Cave horse bones radiocarbon dated to the Pleniglacial are substantially higher than those that have Late-glacial radiocarbon dates. Therefore, we now hypothesise that the majority of the horse bones isotopically analysed from Goyet Cave Horizon 1 are Pleniglacial in age. Statistical analysis of the radiocarbon dates indicates that the Late-glacial occupation at the two sites was contemporaneous, and that while there may appear to be two phases of occupation at Trou de Chaleux, this may be an artefact of the radiocarbon calibration curve.     

PROBLEMS OF THE RADIOCARBON CALENDAR AND ITS CALIBRATION

Both the growing body of literature on the tree-ring calibration of radiocarbon dates, and the variety of statistical approaches used, make it appropriate to review the basic principles involved in the construction of a calibration curve. While its ultimate validity is in part a geophysical problem, the appropriate form for the calibration function, given a specific body of data, is a statistical question centering upon the analysis of the measurement errors involved. The relationship between the calibration function and the inverse calibration function is examined, and the shortcomings of the available published calibration curves considered in the light of this examination. It is concluded that there is no reason to doubt the general principles on which the calibration is based, but a need exists for a more critical handling of the measurement data with a statistical treatment of the errors involved. The quality of the data could itself be improved by the use of replicate samples for inter-laboratory projects specifically designed to investigate the magnitude of measurement error.     

Radiocarbon Dating and the Historical Archaeology of Korea: An Alternative Interpretation of Hongryeonbong Fortress II in the Three Kingdoms Period,Central Korea

Relying heavily upon historical records to build archaeological chronologies, many Korean historical archaeologists question the utility of radiocarbon dating. To challenge this tendency, we test a model based on historical records by analyzing radiocarbon dates. We dated two bulk samples from Hongryeonbong Fortress II, Seoul, South Korea, which is known historically to have been occupied between a.d. 500 and 551. By dividing bulk samples into smaller aliquots, we dated 40 subsamples and statistically estimated consensus dates. The consensus dates do not support expectations of the historical model, as they do not lie within the temporal range provided by historical records. We propose an alternative model that explains both the radiocarbon dates and the historical records. It is suggested that radiocarbon dating can be successfully applied to the reconstruction of historical periods and is a way of mitigating possible biases of models based solely on historical records.     

Stone Age midden deposition assessed by bivalve sclerochronology and radiocarbon wiggle-matching of Arctica islandica shell increments

Sclerochronology, the study of the skeletal diaries of mollusks and corals, is a high-resolution geochronological tool of versatile usage in archaeology and paleontology with increasingly growing opportunities. Much of the recent efforts have concentrated on building multi-centennial bivalve growth records using annually deposited increments in the Holocene shells, comparable to tree-ring chronologies. In the context of geoarchaeology, the hitherto unachieved potential includes the application of sclerochronology to reconstruct long-term settlement histories. Here we contribute to both of these critical issues by presenting the first multi-shell sclerochronology constrained by methods originally developed in tree-ring research, using anthropogenically deposited bivalve shells of Arctica islandica excavated from a Stone Age midden in North Norway. Our systematic chronological approach to shell growth histories lays the foundation for a multi-dimensional dating framework that interacts between the incremental, radioisotopic and stratigraphic evidence. We show how the crossdating within and between the single-shell records yields a 155-year multi-shell sclerochronology, supported by the ¹⁴C AMS dates, that demonstrates minimum midden accumulation of 82 years and a depositional rate of 0.3 cm/yr. Sclerochronology paves the way for radiocarbon wiggle-matching, which narrows the probabilistic 2-σ uncertainty range for the oldest and youngest ¹⁴C AMS dates to 3150–2980 and 3060–2890 BC, respectively. We attribute the spectral characteristics of the chronology primarily to the North Atlantic Oscillation, suggesting essentially similar influences of climate variability on the Stone Age culture and our own society.     

Radiocarbon chronology of Neolithic and Predynastic sites in Upper Egypt and the Delta

Critical evaluation, tree-ring calibration, and statistical analysis of 95 radiocarbon dates from neolithic and predynastic sites in Upper Egypt and the Delta provide the following average age estimates in calendrical years BC. Early Fayum Neolithicca 5200 to 4500 BC Early Merimda Neolithicca 4800 BC Late Merimda Neolithic ?4400 BC Late Fayum Neolithicca 4000 BC Late Badarian? (Hemamieh)ca 4400/4000 BC Early Nagada (Nagada)ca 3750 BC Hierakonpolis (Locs 11 & 29)ca 3550 BC Late Nagada (South Town)ca 3450 BC Other sites or periods are not adequately dated. In addition, further dates are needed to bolster thistentative framework.     

BRISTLECONE PINE AND ANCIENT EGYPT: A RE-APPRAISAL

Previous comparisons of the radiocarbon dates of tree-ring-dated bristlecone pine samples and historicallydated samples from Egyptian archaeological sites have led to conflicting conclusions regarding the validity of the bristlecone pine calibration of radiocarbon dates. However, the new statistical analysis presented in this paper shows that the bristlecone pine calibration of the radiocarbon time-scale is not incompatible with the given Egyptian historical chronology in the period 3000–300 B.C. (calendar years). This analysis is the first to allow for possible additional variability in the radiocarbon dates of short-lived samples (due to short-term fluctuations in the atmospheric carbon-14 level), and to examine the effect on the analysis of any changes in the precision ascribed to the historical dates of the samples. Furthermore, the paper examines the reasons for the conflicting conclusions obtained in previous analyses, and uses the differences in the paired radiocarbon dates on the Egyptian samples to investigate the overall repeatability of these radiocarbon measurements.     

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.     

First dendroarchaeological dates of prehistoric contexts in South America: chullpas in the Central Andes

Despite the existence of long-lived tree species with excellent tree-ring characteristics, the use of dendrochronological techniques for dating archaeological contexts has been very limited in South America. Recent research in the Bolivian Altiplano of the Central Andes has yielded a network of Polylepis tarapacana chronologies that goes back to the 13th century. This species was regularly used by local populations since pre-Columbian times as raw material for beams, lintels, hooks and other architectural features in houses, storage chambers, and sepulchers. The aim of this study is to argue in favor of the potential of P. tarapacana for providing high resolution dates of significant archaeological events during the pre-Columbian era. The chronology of chullpas (burial towers and storage chambers) in the southern Andean Altiplano is used as a case study. Growth rings from P. tarapacana have provided several centennial-length dendrochronological records including a reference regional chronology covering the last 786 years in the Central Andean highlands. Based on this long reference chronology calendar years were assigned to woody pieces from pre-Hispanic chullpas. Dendroarchaeological results are consistent with contextual evidence and most radiocarbon dates from woody samples and related archaeological items. Our results indicate that P. tarapacana has a high potential for providing annually-resolved tree-ring dates for archaeological contexts in the Altiplano since the early 13th century.     

Radiocarbon dating and the “old wood” problem: The case of the Hohokam chronology

Many archaeological chronologies, including that of the Hohokam in southern Arizona, are based on a series of radiocarbon dates on wood. This paper argues that because of variability in rates of wood decay processes (in the environment and in systemic context), such archaeological chronologies are potentially biased towards excessive antiquity by an old wood problem and must be reassessed. Following the theoretical insights of Dean (1978), this paper sets forth principles and procedures for relating radiocarbon dates to cultural events. Emphasis is placed on identifying and taking into account the formation processes of (1) the dated specimens and (2) the deposits that yielded them. This methodological framework is applied to Hohokam radiocarbon dates, and a chronology much shorter than the original Gladwin-Haury formulation is supported.     

The age of the subfossil trunk horizon in deposits of the Warta River valley (central Poland) based on <Superscript>14</Superscript>C dating

The present study focuses on investigations carried out in the Late Vistulian succession of the Warta River deposits (central Poland) in which a horizon of subfossil trees was excavated. Prelim-inary conclusions on time record and past environmental conditions of a forest existence determined from radiocarbon dating, pollen analyses and geological evidence appear promising with view of tree-ring chronologies.     

Radiocarbon and dendrochronological dating of Sub-fossil oaks from Smarhoń riverine sediments

Sub-fossil oaks from Smarhoń in Belarus have been investigated and tree-ring chronologies were assembled. According to radiocarbon dating, the oldest oak grew from 5782–5612 cal BC and the youngest from 1575–1747 cal AD. Radiocarbon and dendrochronological dating of 97 samples, four single series, 10 mean curves (containing 2–9 series) and three chronologies (10–25 series) were constructed. The longest chronology (No. 16), covering 549 years, was absolutely dated against various oak chronologies of Polish/Baltic origin to AD 778–1326. Germination and dying-off phases were assessed from the three best replicated chronologies. A spectral analysis of the chronologies provided cycles of variable length, on average of 25 years.     

Comments on relations West Norway ‐ Western Europe documented in petroglyphs

Dendrochronologic calibration of radiocarbon dates, which is of vital importance when such dates are compared with historical records, is discussed.

The nature and causes of variations in the past atmospheric radiocarbon content are briefly described. Different calibration curves are compared with available high‐precision data on radiocarbon in tree rings, and also with preliminary results from the joint efforts of U.S. scientists to establish an optimal calibration scheme.     

A comparison of the treatment of errors in radiocarbon dating calibration methods

The application of radiocarbon dating to archaeological samples generally requires calibration of ¹⁴C dates to calendar ages and interpretation of dating errors. In this paper, four recent methods of age calibration are assessed, particularly with regard to their quality of error treatment. Recent experimental research has suggested that commonly quoted errors on “raw” ¹⁴C dates may require enlargement to more realistic levels, which, when incorporated in the calibration schemes, produce a considerable increase in the size of the typical calibrated interval. A general decrease in the sensitivity of ¹⁴C dating using single, “normal precision” dates is implied. Thus typical calibrated age intervals range from 300 to 1300 years (approximate 95% confidence level), with little improvement resulting if “high precision” calibration systems are used to correct “normal precision” dates. Of the four methods considered here, that proposed by Neftel is found to provide the most objective, flexible, comprehensive and “easy to use” scheme. This method is particularly recommended for its treatment of errors both on the dates to be calibrated and on the calibration curve itself.     

Fluvial sediments, correlations and palaeoenvironmental reconstruction: The development of robust radiocarbon chronologies

Multiple sequences of radiocarbon dates extracted from organic materials are increasingly being used to provide robust chronologies for landscape development, particularly the timing and correlation of significant climatic and ‘process’ events. Whilst the validity of using such frameworks in sedimentary environments such as lake basins and raised bogs has been the focus of much attention, such debates have not extended to fluvial systems. Using examples from three lowland, vertically accreting river valleys in East Anglia, UK, this paper assesses the robustness of their associated radiocarbon chronologies by assessing the contrasting age estimates that are obtained by dating different parts of the same organic sample (humic, humin and plant macrofossils) at a variety of stratigraphic levels. Overall, the humin and humic acid fraction results were statistically consistent, whilst the plant macrofossil remains were found to be of a slightly younger age. In these examples, it is argued that the younger ages appear to be the result of Phragmites (common reed) roots pushing plant macrossils through the sedimentary sequence or opening up voids for material to fall through, although studies in lacustrine and mire environments suggest alternative explanations may also be possible. Whichever explanation is preferred, this study demonstrates clearly that the complexity of valley floor stratigraphy and processes is such, that using single radiocarbon dates, whether AMS or bulk samples to reconstruct chronologies of ‘geomorphic system response’ may need to be refined and subjected to the same level of assessment that has been applied in other sedimentary systems.     

“The good,the bad,the weird”: Stone Age and Early Metal Period radiocarbon dates and chronology from the Karelian Isthmus,North-West Russia

In this paper all the Stone Age and Early Metal Period (ca. 8600 cal BC — 300 AD) radiocarbon dates from the Karelian Isthmus, Russia, are compiled and their archaeological usability assessed using a set of evaluation principles. The quality of radiometric dates from such a large area has rarely been methodologically examined in Finnish or North-West Russian archaeology, and is applied here for the first time on the present material. Special attention is given to the discussion on the deficiencies and limitations of the current data. Based on the 81 dates evaluated as useful, a tentative radiocarbon chronology is presented for the study area. This is generally in sequence with the chronologies of the nearby areas, but suggests some differences especially towards the end of Stone Age, as well as the presence of biases caused by taphonomic and research-related factors.     

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.     

Radiocarbon dating: Some practical considerations for the archaeologist

The article is divided into four main sections in each of which a key aspect of radio-carbon dating is discussed with emphasis on the practical implications for users of dates. The four topics which the article attempts to deal with are, in turn, (i) the effect on the radiocarbon timescale of the variations in atmospheric ¹⁴C now known to have occurred in the past and the role of other absorlute dating methods in investigating these, (ii) laboratory measurement of ¹⁴C, (iii) selection of optimum samples for dating and (iv) some of the limitations of the final dates. The theme is essentially that the technical difficulties of radiocarbon measurement in the laboratory have been overcome to the extent that the physical measurements can now be made with high precision, that is to within ±1% or better, as a routine. Thus, it is more important than ever (a) that only reliable samples having very firm associations should be dated and (b) that pretreatment of such samples by the dating laboratory to remove any age contaminants should be completely effective. However, in addition to the recognized statistical limitations, the absolute accuracy of radio-carbon dating is limited by the past ¹⁴C variations. Coupled with the requirements of proper association and pretreatment of samples is the long-term need to establish an overall correlation between radiocarbon and calendar years. At present this is still a matter for final agreement by the laboratories concerned. Meanwhile, when all possible steps have been taken to ensure the reliability of the date messurements, these can strictly only be compared with one another in terms of radiocarbon years bp. In practice this is often too restrictive but any attempts at calibration must be regarded as approximations for the time being. In this article the lower and upper case notation advocated in Antiquity46, 265, for radiocarbon and calendar years respectively has been followed.     

High-resolution radiocarbon dating of marine materials in archaeological contexts: radiocarbon marine reservoir variability between Anadara, Gafrarium, Batissa, Polymesoda spp. and Echinoidea at Caution Bay, Southern Coastal Papua New Guinea

The remains of shellfish dominate many coastal archaeological sites in the Pacific and provide a wealth of information about economy, culture, environment and climate. Shells are therefore the logical sample type to develop local and regional radiocarbon chronologies. The calibration of radiocarbon (¹⁴C) dates on marine animals is not straightforward, however, requiring an understanding of habitat and dietary preferences as well as detailed knowledge of local ocean conditions. The most complex situations occur where terrestrial influences impinge on the marine environment resulting in both the enrichment and depletion of ¹⁴C (Ulm Geoarchaeology 17(4):319–348, 2002; Petchey and Clark Quat Geochronol 6:539–549, 2011). A sampling protocol that combines a high-resolution excavation methodology, selection of short-lived samples identified to species level, and a tri-isotope approach using ¹⁴C, δ¹³C and δ¹⁸O, has given us the ability to identify ¹⁴C source variation that would otherwise have been obscured. Here, we present new research that details high-resolution mapping of marine ¹⁴C reservoir variation between Gafrarium tumidum, Gafrarium pectinatum, Anadara granosa, Anadara antiquata, Batissa violacea, Polymesoda erosa and Echinoidea from the Bogi 1 archaeological site, Caution Bay, southern coastal Papua New Guinea. These isotopes highlight specific dietary, habitat and behavioural variations that are key to obtaining chronological information from shell radiocarbon determinations.