Magnetic Sourcing of Obsidians in Southern South America: Some Successes and Doubts

Sourcing of archaeological obsidians is of great importance in unravelling the cultural, social and economic development of many ancient societies. Use of magnetic properties of obsidian fragments has been reported as a cheap, fast and versatile tool for these purposes. One hundred and seventy-six obsidians from archaeological sites and sources in Argentina and southern Chile were analysed magnetically using the weight-normalized intensity of JNRM (Intensity of Natural Remanent Magnetization), the intensity of JSIRM (Intensity of Saturation of Isothermal Remanent Magnetization) at 0·35T and the bulk susceptibility. The method allowed identification of at least two different sources for archaeological materials found respectively to the north and south of the Lago Argentino, in SW Santa Cruz province, Argentina. Comparison of values from most samples in south and central Santa Cruz with those from a known source may lead to the interpretation that most of them belong to that source. In contrast, a critical analysis of the resolution of this using a larger than usual number of samples from three well distant obsidian sources in Argentina showed that two of the sources showed an almost complete overlapping of these three parameters, and all displayed a very large dispersion of values. This different result indicates that the magnetic sourcing of obsidians may not always have the resolution previously portrayed, but is applicable in certain localities.