Prof Christopher Ramsey

Abstract:

When humans consume foods from different radiocarbon reservoirs offset in age to the atmosphere, inaccuracies in the 14C date of bone collagen can occur. Mesolithic human skeletons from the Iron Gates section of the Lower Danube Valley have yielded reservoir offsets of up to ~500 yr. This has been demonstrated through direct dating of bulk collagen from human bones and the remains of ungulate bone projectile points that were found embedded in them (Cook et al. 2001). We present improvements to a novel HPLC method for the detection and separation of underivatized amino acids using a wateronly mobile phase free of organic or inorganic modifiers, ensuring very low carbon backgrounds. Our hypothesis is that direct 14C dating of single essential and non-essential amino acids might allow an improvement in the dating accuracy for reservoiraffected human bones. The method facilitates separation of less polar amino acids (mostly "essential"), currently not possible in the recently published protocol. We discuss methodological developments, demonstrate carbon backgrounds, and present analytical approaches to minimize their effects. We validate the precision and accuracy of the method by accelerator mass spectrometry (AMS) dating relatively modern and 14C-dead, known-age bone standards. Finally, we apply the method to the dating of single amino acids from bone samples with a proven ~500-yr carbon reservoir effect from Mesolithic burials at the Iron Gates sites. We investigate whether differences can be found in AMS dates for essential and non-essential amino acids since, although contemporaneous, these are expected to derive from dietary sources with differing 14C reservoirs. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.

Abstract:

Bayesian methods have been widely used to address the Iron Age chronological debate in Israel, which has implications for the entire eastern Mediterranean Iron Age chronology. However, a consensus has not been reached. This is largely because radiocarbon dates of materials in this period lie on an oscillation in the calibration curve. This study focuses on the modeling of 14C dates from the Iron I and Iron II periods, discusses the underlying assumptions and limitations of existing Bayesian chronologies, and proposes the use of a more appropriate model that allows for the phase transitions not being instantaneous. The new trapezoidal model sheds light on the probable duration of the transitions between the Iron Age phases. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.

Abstract:

Tephra from the Cape Riva (Y-2) eruption of Santorini has been found across the eastern Mediterranean. It presents an important link between marine and terrestrial records. A Poisson process (P Sequence) age-depth prior, with model averaging, is used to model individual previously published radiocarbon sequences, cross-linked with an exponential phase model parameter to obtain a robust age. Multiple sequences and 14C determinations from 3 eastern Mediterranean data sets (Seymour et al. 2004; Margari et al. 2009; Müller et al. 2011; Roeser et al. 2012) are used in the model. The modeled age of the Y-2 tephra produced within this study is 22,329-21,088 cal BP at 95.4% probability. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.

Abstract:

OxCal is a widely used software package for the calibration of radiocarbon dates and the statistical analysis of 14C and other chronological information. The program aims to make statistical methods easily available to researchers and students working in a range of different disciplines. This paper will look at the recent and planned developments of the package. The recent additions to the statistical methods are primarily aimed at providing more robust models, in particular through model averaging for deposition models and through different multiphase models. The paper will look at how these new models have been implemented and explore the implications for researchers who might benefit from their use. In addition, a new approach to the evaluation of marine reservoir offsets will be presented. As the quantity and complexity of chronological data increase, it is also important to have efficient methods for the visualization of such extensive data sets and methods for the presentation of spatial and geographical data embedded within planned future versions of OxCal will also be discussed. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.