The contribution of new radiocarbon dating pre-treatment techniques to understanding the Middle to Upper Palaeolithic transition in Iberia

Thesis

In the last ten years it has become apparent that the radiocarbon dating method can significantly underestimate the age of samples > 25 ka BP because routine pre-treatment protocols may not remove sufficient contaminants. In response, new pre-treatment protocols have been proposed, and two in particular, ultrafiltration of bone collagen and ABOx-SC of charcoal, show promise. This thesis has tested whether these methods effectively remove contaminants without adding carbon in the laboratory. Subsequently it used them, alongside careful selection of humanly modified material and Bayesian statistical analysis, to test the radiocarbon-based chronology of the Iberian Middle to Upper Palaeolithic transition.

Both protocols were found to effectively remove environmental contaminants, but add small amounts of laboratory-derived carbon. Using known age standards, a correction has been calculated for the ultrafiltration protocol to counter the effect of the laboratory-derived carbon. A similar correction could not be made for the ABOx-SC protocol due to uncertainties in the age of the standards and underlying chemical processes. However, the effect of such contamination did not have a significant effect on the chronologies developed for the sites examined in this thesis.

96 new radiocarbon dates have been obtained from the Iberian Middle to Upper Palaeolithic transition. A further 50 dates recovered from the literature and are regarded as reliable. The most alarming finding of this thesis is that routine pre-treatment protocols may cause dates to be underestimated by more than 10 ka ¹⁴C years. The implication of offsets of this magnitude in Iberia is significant: whereas a prolonged survival of Neanderthals south of the Ebro valley has been observed in the published dataset, this study could not replicate such ages. Preservation did not allow the arrival of anatomically modern humans to be dated in the south. However, using typological arguments and the chronology constructed for the north of the Peninsula, it is unlikely that they were present in this region before 38,080 – 36,680 cal BP (95% probability). This implies a temporal gap of at least 4,490 – 12,740 cal years, although it is unclear whether this is due to taphonomic factors or is a real period of abandonment. This pattern contrasts to northern areas of the Peninsula where the Aurignacian appears at 42,330 – 40,980 cal BP, shortly postdating the start of the Châtelperronian and end of the Mousterian.

It is hoped that the chronology produced will warn against the use of radiocarbon dates produced using poor pre-treatment protocols and has laid the foundations from which a more accurate and more precise chronology can be built in the future.

Authors: Wood, RE

• Publication date: 2011
• DOI: 10.5287/ora-yxa4eog0e
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Archaeology; Paleolithic; Neanderthal; Aurignacian; Palaeolithic; Mousterian; Radiocarbon
• Subjects: Archaeology; Dating