Prof Christopher Ramsey

Abstract:

High-quality data from appropriate archives are needed for the continuing improvement of radiocarbon calibration curves. We discuss here the basic assumptions behind 14C dating that necessitate calibration and the relative strengths and weaknesses of archives from which calibration data are obtained. We also highlight the procedures, problems, and uncertainties involved in determining atmospheric and surface ocean 14C/12C in these archives, including a discussion of the various methods used to derive an independent absolute timescale and uncertainty. The types of data required for the current IntCal database and calibration curve model are tabulated with examples.

Abstract:

The Lake Suigetsu 2006 Varved Sediment Core Project (SG06 Project) aims to contribute to the international terrestrial radiocarbon calibration model, extending it to >50,000 cal years BP using the new SG06 sediment record, which shows annual laminations (varves) for most of this period. For varve counting, a novel approach using high resolution X-ray fluorescence (μXRF) and X-radiography was applied, described here in detail for the first time, and applied to the Late Glacial sediments of core SG06. This new technique was carried out alongside conventional varve counting by thin-section microscopy (Schlolaut et al., 2012). This dual approach allows comparison of results from the two independent counting methods on metre to sub-mm scales, enabling the identification and characterisation of differences between the techniques, and quantification of their weaknesses. Combining the results produces a more robust chronology than either counting method could produce alone. The reliability of this dual approach is demonstrated by comparison of the combined chronology with the radiocarbon dataset of SG06, calibrated with the tree-ring derived Late Glacial section of IntCal09. © 2012 Elsevier B.V.

Abstract:

Hublin et al (2012) have published a new series of AMS determinations from the site of the Grotte du Renne at Arcy-sur-Cure, one of the key sites in discussions regarding late Neanderthal behavior and adaptation. The site is well known as one of the very few Châtelperronian sites that appear to contain evidence for the range of ornaments and objects that are usually found in sites of the Proto- or Early Aurignacian in Europe, and therefore associated with anatomically modern humans. For this reason it is important that we have an idea of the chronology of the sequence here, so that we may compare it with other contexts where similar cultural horizons have been excavated. Higham et al (2010) published a series of 31 AMS dates from well-selected humanly-modified material from several layers of the site. They found variation in the results that they ascribed to taphonomic influences, which implied strongly that there was some degree of mixing of material within the site. They recommended that caution was therefore required in literally interpreting the archaeological evidence, especially the relationship between human remains and ornaments from the Châtelperronian levels. Caron et al (2011) and Zilhão et al (2011) criticised this, citing a range of archaeological and stratigraphic evidence which suggested the opposite; that the sequence remained largely intact save for some obvious examples where the excavators had identified some material from a different layer. Hublin et al's (2012) new results have been taken to suggest that: a) the original Oxford series of determinations are largely variable due to low collagen preservation which exacerbates the contamination effect in the dated bones; b) that the selection of humanly-modified material resulted in a biased corpus of poorly preserved samples for dating; c) that the new determinations show no evidence for mixing in the site because the results are consistent with the stratigraphic divisions at the site. In this short paper we comment on these suggestions.