Oscar Palacios

Provenance study of obsidian samples by using portable and conventional X ray fluorescence spectrometers. Performance comparison of both instrumentations

The potentiality of portable instrumentation lies on the possibility of the in situ determinations. Sampling, packaging and transport of samples from the site to the laboratory are avoided and the analysis becomes non destructive at all. However, detection limits for light elements are, in most cases, a limitation for quantification purposes. In this work a comparison between the results obtained with an X ray fluorescence spectrometer laboratory based and a portable instrument is performed. A set of 76 obsidian archaeological specimens from northwest Patagonia, Argentina was used to carry out the study. Samples were collected in the area of the middle and high basin of the Limay River. The analytical information obtained with both instrumentations was complemented with Principal Component Analysis in order to define groups and identify provenance sources. The information from both instruments allows arriving to the same conclusion about sample provenance and mobility of hunter-gatherer groups. Three groups of sources were identified in both cases matching with the geographical information. Also, same sets of outlier samples or not associated to these sources were found. Artifact samples were associated mainly to the closest sources, but some of them are related to sources located more than three hundred kilometers, evidencing the large mobility of the hunter-gatherers by the obsidian interchange. No significant differences between concentrations values obtained by laboratory based instrument and portable one were found.

Compositional study of prehistoric pigments (Carriqueo rock shelter, Argentina) by synchrotron radiation X-ray diffraction

In this work synchrotron radiation X-ray diffraction technique was successfully applied for the analysis of pigments found in excavation at Carriqueo rock shelter, Neuquen, Argentina. The pigment samples of orange, red, and brown shades were collected from different levels of this archaeological site and compared with a suspected source of provenance La Oficina creek. X-ray diffraction patterns of several yellowish, reddish, and red pigments showed the presence of haematite, goethite, kaolinite, and quartz. The majority of Carriqueo collected samples belonged to the same group of the suspected source, having haematite and quartz as main crystalline phases. The results indicate that the raw material from La Oficina is the source of most of the pigments found at Carriqueo. The present work helps us to understand the strategy of supplying raw materials by human groups in the North Patagonia region.