Evidence for Complexities in the RHX Dating Method

The rehydroxylation (RHX) dating method applicable to virtually all baked clay fragments still requires testing and new developments. Here, we have obtained new weighing measurements from Syrian medieval ceramic fragments. In particular, they allow us to illustrate the scatter in RHX behaviour that may exist between different potsherds of the same age and found at the same archaeological site, thus having experienced the same effective lifetime temperature, and even between samples collected from the same artefact. Thanks to a so‐called time‐span analysis, we also report on some complexities in data sets previously obtained by Wilson et al. (2009, 2012, 2014).     

The influence of temperature on rehydroxylation [RHX] kinetics in archaeological pottery

Almost all archaeological ceramics undergo slow, progressive rehydroxylation by chemical combination with environmental water. The reaction is accompanied by an expansion, and also by the small but measurable mass gain that provides the basis of the RHX dating method. The rate of the RHX reaction increases with increasing temperature. Here we describe comprehensively the effects of temperature on the RHX process in relation to the dating methodology. We deal in turn with the kinetic model of the RHX reaction, the temperature dependence of the RHX rate, and the influence of varying environmental temperature on the RHX mass gain. We define an effective lifetime temperature and show how this is calculated from an estimated lifetime temperature history. Historical meteorological temperature data are used to estimate the lifetime temperature history, and this can be adjusted for long-term climate variation. We show also how to allow for the effects of burial in archaeological sites on the temperature history. Finally we describe how the uncertainties in estimates of RHX age depend on the estimates of temperature history and effective lifetime temperature.     

Rehydroxylation of Fired‐Clay Ceramics: Factors Affecting Early‐Stage Mass Gain in Dating Experiments

To obtain accurate results in the RHX dating of ceramics, it is essential that the RHX measurements are continued until the rate of mass gain is constant with (time)^1/4. In this paper, we discuss how the initial stages of mass gain are affected by the specific surface area (SSA) of the ceramic material. The paper provides guidance on experimental protocols to avoid dating results being distorted by relatively early‐time mass gain data.     

Rehydroxylation dating of fired clays: an improved time-offset model to account for the effect of cooling on post-reheating mass gain

Dating of fired clay ceramics can be critical in building chronologies of archaeological sites. However, direct dating techniques such as luminescence, archaeomagnetism and radiocarbon dating are not always suitable or even possible. Rehydroxylation dating of fired clays is a developing method that has the potential to provide an alternative/complementary approach. Determination of a second stage, Stage II, mass gain rate in fired/reheated clay ceramics using a time^1/4-based model is central to this method. Experiments on modern brick samples demonstrate that the Stage II mass gain is not linear with t^1/4 as expected. The non-linearity observed can be taken account of through the introduction of a time-offset that represents the additional time required for mass gain at a specific aging temperature to equate to the additional mass gained above this aging temperature during cooling of the sample post-firing/reheating. Simulations of the mass gain curves expected during post-firing/reheating cooling highlight the significant effect of this mass gained during cooling and provide excellent agreement with experiment. Simulations also suggest that the two-stage structure in the mass gain curves observed might be better explained as largely the result of a single t^1/4-based process (Arrhenius in temperature dependence) across both stages; Stage I results from mass gained during cooling with Stage II resulting from mass gained during static temperature conditions. The overall implications for the dating method are that a non-linear Stage II mass gain (as a function of time^1/4) is expected and that an improved time-offset model provides a solution while removing issues of subjectivity in isolating the Stage II mass gain rate. This should lead to an improvement in the accuracy of RHX dates produced on archaeological material and further its development as a viable dating technique.     

Induced hydration of obsidian: a simulation study of accuracy requirements

Determination of the hydration rate constant of obsidian is basic to the use of obsidian for establishing chronologies. The constant can, in principle, be determined in either of two ways: by correlations with archaeological sequences, or by laboratory experiments using induced hydration. Induced hydration holds promise of great accuracy, but results reported to date have been disappointing. This paper is based on the hypothesis that the outcomes are the result of error build-up in the induced hydration protocol, and describes an analysis based on a Monte Carlo simulation of the measurement and analysis process. Data are presented which show that the poor results are due to errors inherent in optical measurement of hydration rim thickness. It is concluded that successful use of induced hydration requires an order of magnitude improvement in accuracy of hydration rim measurement over the accuracies currently claimed for optical microscopy. The results do not affect the validity of hydration dating based on archaeological correlations.     

BAYESIAN ANALYSIS OF PLEISTOCENE CHRONOMETRIC METHODS*

Bayesian analysis of radiocarbon dates on Holocene archaeological sites has become well established. Application to Pleistocene sites dated by multiple techniques would be advantageous. This paper develops the necessary mathematical apparatus in the form of likelihoods for luminescence dating, and uranium‐series dating, and considers the possibility for amino‐acid racemization dating. Application of the new methods is illustrated using the stratigraphic sequences of dates from the sites of Saint‐Césaire and La Chaise‐de‐Vouthon. For application to amino‐acid racemization dating, fuller publication of data is found to be required.     

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.     

An archaeologically validated protocol for computing obsidian hydration rates from laboratory data

This paper reports the computation of hydration rate for Topaz Mountain obsidian from laboratory data, and a comparison with archaeological data from a well-dated site, Camels Back Cave, in western Utah. Topaz Mountain obsidian is found to be slow-hydrating, with a rate of 0.071 ± 0.021 μ/yr^½ at an effective hydration temperature of 16.01 °C. This rate agrees with a rate developed from archaeological data from Camels Back Cave within ∼6%. Activation energy of Topaz Mountain obsidian is 10370 ± 544 K, and its diffusion constant is (1.87 ± 9.13) × 10¹³ μ²/yr, both of which are independent of temperature. Its intra-source variability in hydration rate is very low (CV < 0.01), implying a low variability in intrinsic water. We present a model of chemical erosion which shows why earlier laboratory-determined rates were incorrect, and discuss the implications of our findings on the determination of experimentally derived rates in obsidian hydration dating.     

A NEW THERMOLUMINESCENCE DATING TECHNIQUE FOR HEATED FLINT*

A new thermoluminescence (TL) technique for determining the age of heated flint artefacts from archaeological sites is presented. It is a variant of the SAR protocol, which is usually used for OSL dating of sediment, but it is not based on a presumed model for fitting the dose–response curve. Dose recovery tests as well as comparisons with standard protocols show the accuracy of the new technique. It is found that the sensitivity of the thermoluminescence (TL) signal of flint in the orange–red waveband does not show severe changes due to the heating process while measuring the TL. This allows the application of a short SAR procedure, which requires only two dose points. The technique does not require as much instrument time as other SAR techniques, and thus is advantageous for dating very old samples. The major advantage of this new technique is the small amount of sample material required, which allows the dating of samples that are too small for standard TL dating techniques.     

Timing the Neolithic transition: the application of fluoride dating at Tell Halula,Syria

The study of Near Eastern Neolithic villages provides a unique means of tracing subsistence strategy, population growth, health, and emerging social inequality associated with agricultural origins. However, disentangling these patterns requires a detailed comprehension of the chronological placement of individual households in the site. In this paper, we present a test to determine the reliability and applicability of the fluoride dating method (a relative dating method) on human dentition of 40 samples from 28 Pre-Pottery Neolithic B (or PPNB) burials from the site of Tell Halula, in Syria. This method, applied here for the first time on a Neolithic Near East case study, is an alternative when other dating methods, like radiocarbon dates, do not provide the required temporal resolution to address particular research problems. Nonetheless, the results obtained in the fluoride analysis show how both the age at death of individuals, and the integrity of the burial plug enormously affect the amount of fluoride absorbed by teeth, so that only a small subset of the full dataset was suitable for fluoride dating. Although the distribution of fluoride values of dentine from the small sample of burials from suitable contexts matches the expected chronology, and corroborates the hypothesis that the occupation at Halula extends from the Middle to the Late PPNB, our analysis illustrates the need for a better understanding of the different sources of error in fluoride dating to improve the method itself, and to obtain more reliable fluoride chronologies.     

AUTO-REGENERATIVE THERMOLUMINESCENCE DATING USING ZIRCON INCLUSIONS

Fired ceramics containing zircon inclusions have been dated by allowing the zircons to regenerate their own thermoluminescence (TL) signal, hence auto-regenerative TL dating. The technique is conceptually straightforward. One first measures the TL accrued since the last heating of the material. The zircon grains are then stored for six months and the TL signal regenerated through self-irradiation is measured. Since the internal dose-rate for zircon is dominated by the internal component the age of the sample is simply given by the ratio of the natural to auto-regenerated signal times the laboratory storage period. The technique, however, requires the measurement of a very small auto-regenerated signal, which introduces a number of experimental and physical complications. The methods for overcoming these problems and successfully dating zircons by auto-regeneration are described.     

An Independent Confirmation of the 4 ka Antiquity of a Beeswax Figure in Western Arnhem Land,Northern Australia

Critical to any chronology is reliability in the determination of age for a distinctive artefact that is related to other components in a series. Therefore, the independent testing and verification of the antiquity of an apparent anomalous measurement for an old beeswax figure in northern Australia is of fundamental interest in rock art studies. Replication of the radiocarbon dating process has confirmed that one exceptional figure in early X‐ray style at the Gunbilngmurrung site in western Arnhem Land is indeed c. 4–4.5 ka. The result also confirms the great antiquity of paintings over which the beeswax was applied.     

Thermoluminescent dating in its application to archaeology: A review

This paper sets out to describe the fundamentals of thermoluminescent (TL) dating and to explain the principles of operation of the different methods at present in use. The various complicating factors associated with TL dating are discussed, together with the measures which can be taken to recognize and as far as possible to correct them. Those materials from archaeological contexts which are suitable for dating by the TL technique are described and the criteria for the selection of suitable samples, and the methods of obtaining the desired ancilliary information relating to the environment of the site, are discussed.     

Lake Nuga Nuga: a Levee‐dammed Lake in Central Queensland,Australia

Lake Nuga Nuga is a levee‐dammed lake in the dry sub‐humid tropics of the Fitzroy Basin in Central Queensland, Australia, that has expanded significantly since it was first mapped in 1866. ²¹⁰Pb dating of a sediment core from the lake indicates that the rate of sedimentation has been constant for the past 67 years at 3 mm yr^?1 despite widespread clearing and land use intensification in the catchment during that time. Pollen analysis confirms this and shows that there was little change in vegetation during the early settlement period (1863–1962), but the intensification of land use that started in the early 1960s brought about a dramatic change in the vegetation communities. This study demonstrates that while sediment production may be significantly impacted by land‐use activities, sediment delivery is primarily controlled by topography.     

Iberian Dendrochronology and the Newport Medieval Ship

At the time of the discovery of the Newport medieval ship, it proved impossible to date the timbers used in its original construction through dendrochronology. Associated British timbers and artefacts provided dating to the mid 15th century, with the latter pointing to strong Iberian connections. The development of regional oak ring‐width chronologies in the Basque Country, and their extension back in time to overlap with the ring‐width mean developed for the Newport Ship, has allowed absolute dating and provenance of timbers used in its original construction. Further research is required to clarify the geographical source of the timbers and to develop a high‐resolution network of tree‐ring data for the region.     

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.     

Obsidian hydration dating: accuracy and resolution limitations imposed by intrinsic water variability

Obsidian hydration dating typically yields a range of ages for a single chronometric measurement, even after controlling for source chemistry and effective hydration temperature. Previously published data suggest that this range is due to hydration rate variations caused by variability in the concentration of intrinsic water, and specifically hydroxyl ions, in the obsidian. Such variability exists within any given obsidian source, and even within any particular specimen. This paper analyzes the effect on age estimates of intrinsic water variability and concludes that if a controlled sample of obsidian yields a range of ages, there is no way to tell whether the range is due to long site use or to variations in hydroxyl concentration. At present there is no robust and cost-effective protocol for measuring hydroxyl concentration. Suggested guidelines for obsidian hydration dating are developed using a case study. These findings do not invalidate obsidian hydration as a chronometric technique, but they do suggest limits to the temporal resolution achievable.     

Review and assessment of the potential of post-IR IRSL dating methods to circumvent the problem of anomalous fading in feldspar luminescence

Quartz has been the main mineral used for optically stimulated luminescence (OSL) dating of sediments over the last decade. The quartz OSL signal, however, has been shown to saturate at relatively low doses of ～200–400 Gy, making it difficult to be used for dating beyond about 200 thou-sand years (ka), unless the environmental dose rate is low. The infrared stimulated luminescence (IRSL) from feldspars has been shown to continue to grow to higher dose levels than quartz OSL. The application of IRSL dating of feldspars, however, has long been hampered by the anomalous fading effect. Recent progress in understanding anomalous fading of the infrared stimulated luminescence (IRSL) signals in potassium-feldspar has led to the development of post-IR IRSL (pIRIR) protocols and also a multiple elevated temperature (MET) stimulation (MET-pIRIR) protocol. These procedures have raised the prospect of isolating a non-fading IRSL component for dating Quaternary deposits containing feldspars. In this study, we review the recent progress made on (1) overcoming anomalous fading of feldspar, and (2) the development of pIRIR dating techniques for feldspar. The potential and problems associated with these methods are discussed.     

Lexsyg — A new system for luminescence research

The newly developed lexsyg system by Freiberg Instruments is a versatile luminescence reader, suited for research on the luminescence of materials, fundamental research in luminescence dating, but also for routine mass measurements in retrospective dosimetry as well as in dating application. The 80 sample storage wheel is disconnected from the measurement chamber and therefore crosstalk of optical stimulation is absent and cross-irradiation is negligible from the α- and β-sources, which are providing very uniform irradiations, with the latter especially designed for radiofluores-cence (RF) measurement. Optical excitation sources and filter wheels to vary detection wavelengths can be programmed to change at almost any time within measurement sequences, including the auto-mated change of an optional wheel holding up to four different detectors. Thermoluminescence meas-urements and preheating are possible with a versatile heater, which can be programmed for linear or non-linear heating or cooling, as well as holding a temperature constant. Rates as well as durations can be varied, together with individual ramping, staging and cooling for an almost unlimited number of steps. Violet- and IR-lasers, green and blue LED-arrays can be operated in continuous (CW) or modulated mode (linear/non-linear), and optionally for pulsed as well as time resolved luminescence detection. Six arrays of power LEDs allow the simulation of different bleaching regimes (‘solar simu-lator’), while luminescence detection can be achieved by a variety of photomultiplier tubes and by CCD cameras for spatially resolved measurements and luminescence spectra.     

The Post Medieval Gravellona Toce Boat: an inland watercraft from north‐west Italy assembled using locked dowels

Discovered in 1955, not far from the Roman necropolis of Pedemonte, the Gravellona Toce boat has long been considered evidence of Roman‐period riverine navigation in northern Italy. This initial interpretation, which was not supported by direct dating evidence, has been recently reconsidered on the basis of radiocarbon‐dating and analysis of the timbers retrieved. In this paper, the authors present the results of the recent analysis of the surviving remains which allow the vessel to be interpreted as a post medieval boat built using the traditional bottom‐based construction techniques of the Po Valley region.