Chemical and isotopic analyses have been made of pigment samples from two separate rock art sites in Argentina. The purpose of the study has been to establish the feasibility of extracting carbonaceous material from the samples which will permit reliable radiocarbon dates for the time of painting. The two sites, Catamarca and Rio Negro, present quite different problems. Most of the paper is concerned with Catamarca, and here we have shown that the paint pigments contain very little or no organic binder; but they do contain calcium oxalate derived from local cacti, and calcium carbonate derived probably from local plant ash. We describe a method to purify carbon extracted from the calcium oxalate, and present the dates obtained on both components. We show that, though rare, natural deposits containing both calcium oxalate and calcite do occur, but that they are very distinct in both 13C and 14C compositions; and we argue that they are very unlikely to contaminate the pigments to such an extent that the 14C dates are altered. For the Rio Negro site we show that the ground for the paint pigments contains carbon derived from fires burnt inside the cave, and discuss how analytical methods provide information to develop a strategy for extracting material, from both ground and pigment, for more reliable dating.

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Mediante el análisis por difracción de rayos X se buscó determinar si en los pigmentos de las pinturas rupestres de la cueva Comallo I, en la estepa rionegrina, se utilizaron minerales de los afloramientos cercanos. Los resultados indicaron que solo el rojo pudo tener un abastecimiento local. No se localizaron fuentes para los demás colores, por lo que se proponen dos alternativas no excluyentes: los rangos de acción de esas poblaciones variaban desde una escala local a otra regional y/o se recurría a prácticas de intercambio.Palabras clave: arqueología, prehistoria, Patagonia, arte rupestre, pigmentos, tecnología, etnodinamia

Dedicated to Professor Rosa Lederkremer on her 70th anniversary AbstractThe study of organic residues preserved in objects and materials collected in archaeological sites can provide information on the activities of ancient societies. Degraded animal fats, plant oils, beeswax and plant resins are among the most common organic residues found within ceramic vessels or mixed with inorganic pigments in archaeological pastes. The effects of decay of these organic compounds difficult the direct comparison with modern reference data. The purpose of this work was the use of complementary analytical methods, such as GC-MS, NMR, FT-IR and FT-Raman spectroscopy for the characterization of a reference fat and the degradation products of a thermally aged mixture of a red mineral of the Patagonian region and the fat of an American ostrich (Pterocnemia pennata). Our results showed a decrease in the unsaturated fatty acids with formation of C 8 and C 9 dicarboxylic acids in the thermally aged fat.