Prof Christopher Ramsey

Abstract:

The Bayesian calibration program OxCal v.4.1.5 is applied to two chronological datasets for early Lapita derived from two comprehensive reviews. The two datasets are supplemented by published ages for early Lapita sites in two key island groups within Remote Oceania: Vanuatu and Fiji. The analyses provide statistically robust chronologies for the emergence of Lapita on Mussau at 3470-3250 cal BP and in the rest of the Bismarck Archipelago at 3360-3240 cal BP. After a period of 130-290 years, Lapita dispersed to Vanuatu by 3250-3100 cal BP and to Fiji by 3130-3010 cal BP.

Abstract:

Single and multiphase models have been used extensively in construction of chronologies. We model more gradual transition between phases with a trapezoid model since it better reflects the nature of the information that goes into the model prior. We find that a simple trapezoid model has a bias that does not reflect prior knowledge, and thus propose an addition of a noninformative element to the prior. We also present an alternative parameterization, which transforms the current abrupt transition model into a model that allows for gradual changes. The addition of a noninformative prior ensures model flexibility. We evaluate these Bayesian models using 2 case studies. © 2012 by the Arizona Board of Regents on behalf of the University of Arizona.

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.