Problems with radiocarbon dating the Middle to Upper Palaeolithic transition in Italy

Abstract

Radiocarbon dating of material from Late Pleistocene archaeological sites is challenging. Small amounts of modern ¹⁴C-labelled contamination will significantly affect the reliability of dates from the period, producing erroneous results. Recent developments in sample pre-treatment chemistry have shown that problems in reliable age determination during this period are surmountable. In this paper we provide an example of one such case, from the Middle to Upper Palaeolithic transitional site of the Grotta di Fumane, in northern Italy. We AMS dated two fractions of the same charcoal samples derived from a series of superimposed Mousterian, Aurignacian and Gravettian levels excavated at the site. One fraction was treated using the routine acid–base–acid (ABA) method, the other with the more rigorous acid–base-oxidation/stepped combustion (ABOx–SC) method. The latter method produced consistently older, and almost certainly more reliable, results. The eruption of the known-age Campanian Ignimbrite from the Phlegrean Fields near present-day Naples at 39.3 ka yr BP seals Ulluzzian and Proto Aurignacian levels in the south of Italy. Equivalent cultural levels are present at Fumane and the results obtained with the ABOx–SC methods are consistent with the ages inferred for sites in the south of Italy based on the presence of the Campanian Ignimbrite. New results from a sample found beneath the Campanian Ignimbrite at the Russian site of Kostenki, obtained using both the ABA and ABOx–SC, methods are also presented. They support the conclusion reached at Fumane by demonstrating that, in many cases, the ABOX–SC treatment effectively removes contamination where the ABA treatment does not. The results of the work offer a sobering examination of the problems inherent in the current radiocarbon database relating to the period, and highlight the dangers of an uncritical use of the corpus of ¹⁴C results obtained over the last few decades. Based on our results, we predict that more than 70% of the 53 previously available determinations from Fumane are erroneously young. A way forward is suggested, using these improved chemical preparation methods, applying analytical methods to characterise the material dated, and testing existing site chronologies to establish which previous determinations are liable to be inaccurate.

Introduction

Radiocarbon dates provide the framework for understanding the chronology of the European Middle and Upper Palaeolithic transition. Unfortunately, the method is plagued with problems in its proper application through this period because the low amount of residual radiocarbon (<3%, equivalent to ∼30,000 BP¹) may be significantly influenced by the trace presence of contaminating carbon of a more recent age. The application of radiocarbon dating over almost 60 years has created a blurred vision of chronology over the latter part of the Late Pleistocene period in Europe, and this has, in turn, provided fertile ground for the strong debates that characterise the discipline (eg. D'Errico et al., 1998, Mellars, 1999, Zilhão and D'Errico, 1999). Several thousand radiocarbon determinations are available on various databases². However, deciphering quite which of them are reliable and which not, is an often impossible task, because the key information we require in order to diagnose this, such as a pre-treatment method description and basic analytical data, is almost always unavailable. Recent developments have signalled that an improvement in the situation is near. A new interim calibration curve reaching ∼55,000 BP is due to be released soon through the INTCAL group and more refined pre-treatment methods are being applied which, along with improved instrumentation, are facilitating increased levels of accuracy. However, much more work remains to be done. In this paper we point to the crucial requirements of sample preparation and chemistry in deriving reliable radiocarbon dates and provide a case study from the Italian Palaeolithic that illustrates the pitfalls and problems apparent.