Obsidian source sampling

XRF analyses of Silver Lake and Sycan Marsh obsidian source samples suggested the possibility that the two sources could be differentiated based on small differences in strontium concentrations. However, when the standard error for strontium was taken into account, both groups overlapped at one standard deviation. Because of higher instrumental detection limits for strontium, NAA could not discriminate between the two sources. LA-ICP-MS analyses were conducted to determine if the sensitivity and precision of this analytical technique was sufficient to confirm the existence of the two compositional... 

Figure 4. Comparison ofLA-ICP-MS and XRF data for Sycan Marsh and Silver Lake obsidian source samples.

In the Mediterranean Sea and Middle East area, for example, there are obsidian outflows only in Italy, in some islands in the Aegean Sea, and in Turkey. Artifacts made of obsidian, however, are widely distributed over much of this vast area. Chemical analysis of many of these artifacts has shown that most of the obsidian used to make them originated in one or another of the outflows mentioned, but also in far-distant places such as Armenia and Iran. Plotting on a graph the concentration of selected elements in samples from obsidian sources against that in samples from sites where it was used, enables the identification of the source of the samples (see Fig. 22). Moreover, this type of analysis also makes it possible to trace the routes through which obsidian (and most probably other goods) were traded in antiquity (Renfrew and Dixon 1976). 

Barium (p.p.m). j" G iaii Samples bom obsidian sources Sardinia... 

Geochemical studies by Hughes (1988), Ericson Glascock (2004), and Drucker (2007) employing multivariate statistical analysis have delineated major obsidian sub-sources within the CVF. This study was undertaken to ascertain the extent which LIBS could be applied to the problem of obsidian sourcing through analysis of the same suite of samples that was analyzed by Draucker (2007). 

Until recently, there was no systematic survey, documentation, and chemical and physical analyses of western Mediterranean obsidian sources. Recently, Tykot completed an extensive survey and documentation of western Mediterranean obsidian sources on the islands of Sardinia, Palmarola, Lipari, and Pantelleria (24-27) for a more detailed discussion. Samples from these sources were analyzed at MURR by INAA and/or XRF and LA-ICP-MS. As expected, INAA (and XRF and LA-ICP-MS) of geologic samples from these sources demonstrated that obsidian from each island had a unique chemical signature(s). In the case of Sardinia, six compositional groups were identified. Because of the analytical cost and semi-destructive nature of INAA, artifacts were analyzed by LA-ICP-MS rather than INAA. XRF would have provided a viable analytical alternative, but many of the artifacts were smaller than the minimum size required for this analysis on a standard laboratory-based stationary XRF instrument... 

Figure l. Comparison ofINAA elemental ratios for the four major western Mediterranean Island obsidian sources. Only geologic source samples are... 

Figure 3. Comparison ofLA-ICP-MS elemental ratios for the six Monti Arci (Sardinia) obsidian subgroups. Artifacts are represented by anX. All other symbols represent known source samples that were included in the analyses to verify the accuracy of the assignment ofartifacts.

All obsidian samples were analyzed as unmodified samples they were washed in the field. Each sample was placed in the sample chamber with the flattest part of the surface facing the x-ray beam. All samples were at least 3 cm in length with varying widths and thicknesses. The width of the sample did not produce errors when comparing obsidian artifact to potential obsidian source. Accuracy errors result from inaccuracies of the regression model, statistical error of the calibration spectra, inaccuracy of the intensity of the calibration curve and the energy calibration. When the error is taken into account, the relative analytical uncertainty for this project is less than seven percent with this portable XRF unit (26) ... 

Due to political violence in the Andean highlands, obsidian research in Peru continued only sporadically throughout the 1980s. However, Katharina Schreiber and Paul Trawick successfully located and collected geological samples from the Jampatilla and Alca obsidian sources (see below). Unfortunately, little more was accomplished prior to 1990. 

Geological samples were collected from primary sources and secondary deposits of obsidian. In most cases, the geographic coordinates of source samples were also recorded. The geological samples were shipped to MURR for sample preparation and analysis. 

During archaeological surveys in the Department of Arequipa, Sarah Brooks located two additional obsidian sources and collected geological samples from each for NAA. A secondary source deposit was found 5 km west of Chivay near the pre-Inca archaeological site of Uyo Uyo. The second obsidian source named Caylloma was found about 14 km northwest of the town of Caylloma in a northern province of Arequipa by that name. Compositional analysis of both sources failed to match the data for any artifacts. Thus, it is believed that neither source was used prehistorically. 

This investigation focuses on obsidian reaching two highland Iranian sites during the tinje period from roughly 3500 to 1800 B.c. Geological source samples from two major source regions in Western Asia were used to characterize possible sources of the artifacts. 

This study has demonstrated that precise chemical analysis is a powerful tool for the characterization and provenance determination of Middle Eastern obsidian. Thirteen to 15 chemically distinctive groups were distinguishable in geological source samples collected from eight source... 

Fig. 8.11 The location of obsidian sources and samples in the early Neolithic of Southwest Asia. Major rivers shown on the map are the Nile, Tigris, and Euphrates. Two major sources are shown in Anatolia and two in Armenia. The distribution of obsidian from these sources is seen at settlements across the area. The distributions are largely separate with the exception of one site where obsidian from both source areas is found...

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