Micro-spectroscopic analysis of pigments and carbonization layers on prehispanic rock art at the Oyola's caves, Argentina, using a stratigraphic approach

Abstract

Samples of prehispanic rock art from Oyola's archaeological site, near the city of Catamarca, Argentina have been analyzed using micro-Raman spectroscopy, SEM-EDS and BSD, and optical microscopy. These samples are representative of diverse figures and non-painted surface of one of the caves at the site: Oyola 7. The pigments employed in the rock art were fully characterized. The red colors are confirmed to be red ochre (hematite) and clay. White areas of the painting have been identified as gypsum whereas black pigment is attributed to graphite. In addition, it was demonstrated that all the samples analyzed, including underlying strata, contain large amounts of calcium oxalate as the mineral whewellite. Because of the distribution along the sample, it was conclude that the presence of this compound is due to biodeterioration produced by microorganisms, fungi, algae or lichens. Moreover, a methodology to differentiate black painting layers from carbon deposition layers from bonfires and to characterize them is presented. These results have a great impact in both chemical and archaeological sciences because allow an interdisciplinary approach bringing relevant information about relative and absolute dating. Finally, the information collected with this methodology establish a sound basis to develop complementary studies between the wall and painting stratigraphies with archaeological excavations resulting in a new and fundamental tool henceforth.