A DATABASE OF OBSIDIAN MAGNETIC PROPERTIES FOR ARCHAEOLOGICAL SOURCING

The eruptive conditions of obsidian flows vary widely, thereby producing a variety of distinctive compositions, microstructures, microlite abundances, and textures. These characteristic properties are frequently used in provenance studies that seek to establish a link between an archaeological artifact and a specific volcanic source. Compositional and geochronologic data are the most commonly used measurements in successful obsidian provenance studies; however, most of these approaches are either destructive, time-consuming, and costly, or lack accuracy. The pioneering study of McDougall et al. (1983) showed that measurements of obsidian’s magnetic properties are a nondestructive, quick, and inexpensive alternative approach that can correctly distinguish groups of obsidian artifacts. Since this initial study, there have been several research groups that have reproduced the results of McDougall et al., or suggested additional magnetic parameters for correlation. Despite the promise of magnetic measurements as an obsidian provenance tool, these studies are limited in the total number of samples analyzed, which in turn, has limited the statistical rigor of the correlations. To overcome this limitation, we have produced a database that includes all measurements from these earlier studies (n=252) as well as measurements from >700 new obsidian specimens from around the world (with exceptional coverage of SW Asia). This database includes parameters for each specimen such as natural remanent magnetization, low-field susceptibility, frequency dependence of susceptibility, saturation magnetization, saturation remanence, bulk coercivity, and coercivity of remanence. When possible, we also seek to measure more advanced magnetic properties such as anisotropy of susceptibility, first-order reversal curves, magnetization and susceptibility as a function of temperature, and on occasion, magnetic palaeointensity. Multivariate statistical techniques are then used to discriminate between groups of obsidian artifacts and to establish correlations with volcanic sources. We encourage other obsidian researchers to add to this database, which will be made publically available, and envision magnetic properties as a complementary technique to compositional and geochronologic provenance studies.