RHX Dating: measurement of the Activation Energy of Rehydroxylation for Fired‐Clay Ceramics

In rehydroxylation (RHX) dating, the activation energy of the rehydroxylation reaction is required first in the estimate of a material's effective lifetime temperature (ELT), and second to correct the RHX rate constant obtained at a given measurement temperature to that at the ELT. Measurement of the activation energy is thus integral to the RHX methodology. In this paper, we report a temperature‐step method for the measurement of activation energy and develop fully the underlying theoretical basis. In contrast to obtaining the activation energy from a series of separate experiments (each of which requires the sample to be dehydroxylated prior to measuring the RHX rate constant), the temperature‐step method not only requires a single dehydroxylation at 500°C but also eliminates repeated acquisition of Stage I data, which are not required for dating purposes. Since the first temperature step is set to correspond to the temperature at which a dating determination is carried out, the measurement of rate constants at higher temperatures simply becomes an extension of dating. Consequently, the logistics of obtaining the activation energy of rehydroxylation are greatly simplified.     

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.     

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).     

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.     

Cultural Niche Construction and Remote Sensing of Ancient Anthropogenic Environmental Change in the North Coast of Peru

Archaeological land use results in the modification of natural environments according to cultural templates and strategies. Deeply entrenched environmental legacies can result from such “niche construction,” influencing subsequent cultures and continuing to resonate in modern ecological function. These changes can be better understood through archaeological remote sensing.Here, I describe spectral responses of densely vegetated sugarcane fields in the Chicama Valley (north coast of Peru) to archaeological features and associated anthropogenic soils (anthrosols). Ongoing satellite remote sensing documents approximately 440 previously unrecorded major archaeological monuments and smaller features within a 310 km² sample of the Chicama Valley The majority of these date to the Moche–Chimu periods (ca. AD 300–1400), with others dating to the Cupisnique–Colonial periods. The newly recorded features are significant for accurately reconstructing the socio-ecological history of anthropogenic environmental change in the region.In addition to advancing analyses of archaeological settlement, these results reveal how prehispanic land use legacies result in persistent anthropogenic niches that can affect modern agricultural potentials. The relationships between anthropogenic features and sugarcane development can be directly evaluated through vegetation indices and physically based image transforms. Phenological response is linked to long-term alterations in soil texture, organic-matter content, and moisture capacity. Past land use thus has a significant impact upon contemporary ecological function, resulting in anthropogenic microenvironments. As sugarcane increasingly is an important industrial crop, these results have the potential to be widely applied to archaeological and agronomic problems, including reconstructions of archaeological landscapes, understanding persistent anthropogenic environments, and mitigating heritage loss while potentially improving precision agriculture.     

Human occupation in South America by 20,000 BC: the Toca da Tira Peia site,Piauí, Brazil

When and how did the first human beings settle in the American continent? Numerous data, from archaeological researches as well as from palaeogenetics, anthropological and environmental studies, have led to partially contradictory interpretations in recent years, often because of the lack of a reliable chronological framework. The present study contributes to the establishment of such a framework using luminescence techniques to date a Brazilian archaeological site, the Toca da Tira Peia. It constitutes an exemplary case study: all our observations and measurements tend to prove the good integrity of the site and the anthropological nature of the artifacts and we are confident in the accuracy of the luminescence dating results. All these points underline the importance of the Toca da Tira Peia. The results bring new pieces of evidence of a human presence in the north-east of Brazil as early as 20,000 BC. The Toca da Tira Peia thus contributes to the rewriting of the history of the peopling of the American continent.     

Implications of burial alterations on luminescence dating of archaeological ceramics

Recent mineralogical studies on archaeological pottery samples report significant variations in alkali metal concentrations due to environmental alterations during burial. Here we examine the effects of potassium (K) leaching on luminescence dating. The effect on the estimation of the dose rate is studied by considering four models of leaching (exponential, linear, early and late) and their impact on fine- and coarse-grain dating are calculated. The modeling approaches are applied to two cases of pottery in which evidence for alteration was found. Additionally, TL dating performed on pottery of one of the studied cases, indicates the importance of leaching effects on absolute dating measurements.     

Contemplating the history and future of radiocarbon dating in the American Southeast

We consider the history, present, and future of radiocarbon dating in the American Southeast. We point out some of the past and present flaws related to archaeological research and dating. Our approach to this review is rooted in the perspective that each radiocarbon date collectively adds to our knowledge of the region and not just a particular site. Based on our observations, we suggest some “good” practices with respect to certain aspects of radiocarbon dating. Our concluding discussion considers Bayesian chronological analysis and the growing contribution of chronological modeling to the Southeast.     

Spatial dynamics of human dispersals: Constraints on modelling and archaeological validation

In recent years there has been growing interest in the application of travelling wave models to the spatial dynamics of human dispersals, and their archaeological validation. These models enable predictions of the velocity of population expansion, derived from estimates of reproductive rates and of individual mobility. In this paper we discuss some intrinsic constraints on the application of such models to dispersal events which have been documented in the archaeological record. There is significant uncertainty in radiocarbon dating of first occupation at different locations, and in the reconstruction of evolving population distributions from time-averaged archaeological distribution maps. We calculate some archaeological boundary conditions for the accurate estimation of travelling wave profiles and velocities, and demonstrate their significance for two archaeological case studies: the first peopling of the Americas, and the Neolithic transition in Europe.     

MEASURING CHRONOLOGICAL UNCERTAINTY IN INTENSIVE SURVEY FINDS: A CASE STUDY FROM ANTIKYTHERA,GREECE*

This paper considers how to make the most out of the rather imprecise chronological knowledge that we often have about the past. We focus here on the relative dating of artefacts during archaeological fieldwork, with particular emphasis on new ways to express and analyse chronological uncertainty. A probabilistic method for assigning artefacts to particular chronological periods is advocated and implemented for a large pottery data set from an intensive survey of the Greek island of Antikythera. We also highlight several statistical methods for exploring how uncertainty is shared amongst different periods in this data set and how these observed associations can prompt more sensitive interpretations of landscape‐scale patterns. The concluding discussion re‐emphasizes why these issues are relevant to wider methodological debates in archaeological field practice.     

Architectural Paint Research and the archaeology of buildings

ABSTRACT

Architectural Paint Research (APR) is the archaeological study of interior and exterior applied decoration. Over time, applied layers of paint and other decorative finishes build up on the surface of a built structure, encapsulating microscopic deposits of material evidence. This evidence can be used to inform the phase dating of a structure or illuminate the historic function of a space. It can challenge preconceived ideas of how specific areas were decorated and track the changes in aesthetics over time. It can identify when architects’ ideologies have been balanced by practical considerations. It can provide an insight into the intangible and ephemeral atmosphere that decoration gives to a room. Finally, it can examine the dirt trapped between the layers of decoration and thus categorise the physical environmental conditions that surrounded a building at varying points in its history. Although used in the commercial heritage and conservation sectors, APR is almost completely unknown to building archaeologists. This article aims to introduce APR to a new audience and argues that is an invaluable tool in the archaeological interpretation of buildings.     

Mass Migration and the Polynesian Settlement of New Zealand

This paper reintroduces the concept of mass migration into debates concerning the timing and nature of New Zealand’s settlement by Polynesians. Upward revisions of New Zealand’s chronology show that the appearance of humans on the landscape occurred extremely rapidly, and that within decades settlements had been established across the full range of climatic zones. We show that the rapid appearance of a strong archaeological signature in the early 14th century AD is the result of a mass migration event, not the consequence of gradual demographic growth out of a currently unidentified earlier phase of settlement. Mass migration is not only consistent with the archaeological record but is supported by recent findings in molecular biology and genetics. It also opens the door to a new phase of engagement between archaeological method and indigenous Maori and Polynesian oral history and tradition.     

DATING COINS,DATING WITH COINS

This paper addresses the issue of how coins are dated, and how coins are then used to provide dates on archaeological excavations. Using examples from Roman archaeology, the author examines how patterns of manufacture, supply, loss and retrieval can impact on the value of those dates. The need to examine coin finds within their stratigraphic context is emphasized, as well as the need for the archaeological numismatist and the excavator to collaborate closely to obtain the best from the data. The paper concludes with an analysis of the impact of sample size on dating.     

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.     

Optically stimulated luminescence dating of Southern High Plains archaeological sites

The Southern High Plains of North America is rich in archaeological sites, but many are not well constrained chronologically, owing to a lack of material for radiocarbon dating. A program of optically stimulated luminescence (OSL) dating, applying mainly single-grain analyses, was therefore initiated. Many samples have independent age estimates from radiocarbon to check the OSL results, but OSL age estimates are also provided for those sites that otherwise lack secure chronological control. Sediment samples for OSL were obtained primarily from Paleoindian and Archaic localities, though include deposits of more recent age. Through the analysis of single grains, equivalent dose—the numerator of the age equation—is evaluated independently on numerous grains. The distribution of these values is relatively broad for some samples, and this is attributed to post-depositional mixing. Mixing is also evident in some samples with more narrow distributions. Selecting portions of the mixed distributions for age determination allows more accurate dating for some samples, but the nature of the distributions limits the resolution on others, conclusions that cannot be as easily drawn from multi-grain analysis. Where independent age control is available, most OSL results broadly conform; however, some samples show discrepancies that are not readily explained, but may relate to association or dose rate problems. This underscores the desirability of obtaining where possible suites of chronological evidence.     

Degradation of Archaeological Wood Under Freezing and Thawing Conditions—Effects of Permafrost and Climate Change

The degradation of archaeological wood at freezing and thawing temperatures is studied at the site of Qajaa in West Greenland through a combination of environmental monitoring, measurement of oxygen consumption and microscopy of wood samples. Permanently frozen wood is still very well preserved after 2–4000 years, while wood samples that thaw every summer show attack by soft rot and an average density loss of 0.1 g cm^–3 (corresponding to 25% of the dry mass) over the past 27 years. Future increases in temperature may increase the decay rate significantly (Q₁₀ = 4.2 at 0–10°C) but the effects on site depend on local hydrology.     

Editorial: Palaeolithic America

Abstract

We present the results of the Cerro Jazmín Archaeological Project, a mapping and intensive survey project of a hilltop urban center in the Mixteca Alta, Oaxaca, Mexico. Our archaeological and geomorphological investigations reveal a long history of intermittent occupation with the time of maximum occupation, the Early Postclassic, corresponding with soil formation and landscape stability. Our population estimates are compared with agricultural production projections to assess the city's capability to feed its population and we argue that it functioned as an agricultural center. In a broader discussion of landscape and urbanism, Cerro Jazmín's managed labor was needed to build, manage, and maintain its terrace systems. Our findings show that large urban populations do not necessarily cause environmental degradation.