Direct Radiocarbon Dating of Megalithic Paints from North-West Iberia
Steelman, K. L., Ramirez, F. Carrera, Valcarce, R. Fabregas, Guilderson, T., Rowe, M. W., Antiquity
On the Iberian Peninsula, post-Palaeolithic paintings--in contrast with Palaeolithic images-have received scant attention from the AMS radiometric technique. In fact, only one radiocarbon date consistent with generally expected values has been previously determined on a painted megalith; charcoal from a black-painted tomb panel in a corridor at Antelas, Viseu, Portugal, was dated to 4655 [+ or -] 65 BP (Cruz 1995a,b). Here we present nine accelerator mass spectrometry (AMS) radiocarbon dates for megalithic paintings in north-west Iberia (Figure 1), placing these paintings as the oldest known examples of prehistoric art in Galicia (northwest Spain). Two of us (FCR & RFV) have actively investigated north-west Iberian megalithic art since 1998, systematically locating and recording pictorial remains (doubling the number of known sites in the Galician area) (Carrera Ramirez & Fabregas Valcarce 2003).
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The progressively widespread use of radiocarbon dating using AMS since the late 1980s has overcome an important barrier to dating rock paintings--the ability to analyse small amounts of material available in a paint sample. AMS has opened new possibilities for dating those paintings that contain an organic component (charcoal, blood, fats/oils). The first AMS radiocarbon date for a rock painting was obtained for a charcoal painting located in South Africa (van der Merwe et al. 1987). Since that time, researchers have used AMS to radiocarbon date rock paintings throughout the world (see Rowe 2001 for a review of published dates).
Paintings on stone, whether on a cave wall or a megalithic monument, pose serious and unique challenges for accurate dating: (1) images are often painted on limestone, a carbon-containing mineral; (2) the amount of carbon from the paint sample available for dating is small-orders of magnitude less than a typical artefact; (3) little is known about binders and/or vehicles used in making ancient paints; (4) physical contamination must be removed; and (5) organic material unassociated with painting activity can occur in unpainted rock (see Rowe 2001; Bednarik 2002; Steelman et al. 2002; Steelman & Rowe 2005, for further discussion concerning pictograph dating, as well as Pettit & Bahn 2003; Valladas & Clottes 2003, both published in Antiquity). Charcoal paintings are most commonly dated, but the plasma-chemical extraction method also allows the dating of pictographs with inorganic pigments (if an organic material was added to the paint). Our (MWR & KLS) laboratory has repeatedly attempted to verify our results by dating radiocarbon standards with previously measured ages and rock paintings for which an archaeologist had some inferred age range (Rowe & Steelman 2001).
Using plasma-chemical extraction and AMS, we have obtained nine radiocarbon dates for paint samples taken from six Galician megalithic monuments (Figure 2). These results stand out by their general agreement with one another.
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Description of monuments studied
We sampled black paints from gneiss, granite and schist dolmen stones at Pedra da Moura, Casota do Paramo, Pedra Cuberta, Maimoa de Monte dos Marxos, Forno do Mouros, Anta de Serramo, Coto dos Mouros and Dolmen de Dombate, all located in Galicia (north-west Spain). These monuments are all passage graves, consisting of a polygonal chamber and a short corridor (Figure 3). Typically, the orthostats (vertical upright wall stones) forming the corridor are shorter and smaller than those of the chamber. Unfortunately, these monuments have suffered from vandalism in which some stones were removed as construction material. Inspection of the accessible orthostats reveals visible remnants of paint; however, the graphic images are often highly degraded and unrecognisable.
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Red and black geometric paintings were typically applied over a white plaster coating the interior of the stone monument. …