Provenance Determination from ICP-MS Elemental and Isotopic Compositions of El Paso Area Ceramics
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59 Mat. Res. Soc. Symp. Proc. Vol. 462 01997 Materials Research Society
sciences, but few applications have been seen in archaeology8' 9 . ICP-MS links a high-temperature plasma excitation source to a mass spectrometer analyzer, rather than to an emitted light detector as in conventional ICP-AES (Atomic Emission Spectroscopy). ICP-MS provides detection limits in solution several orders of magnitude lower than The instrument can analyze ICP-AES, typically in the parts-per-trillion range. simultaneously as many as 70 elements in a sample, in 3 to 5 minutes. It also provides low-resolution (compared to thermal ionization mass spectroscopy) isotopic ratios for such favorable elements as Pb. The detection limits for ICP-MS rival or surpass those of instrumental neutron activation analysis (INAA) for most elements, even in solid samples which must be dissolved and thus diluted for conventional ICP-MS analysis. An ICP-MS facility, including the ICP-MS, microwave sample dissolution system, balance, standards, etc. can be set up for under $ 200,000. ICP-MS instruments are now relatively common in university and contract geological and environmental laboratories. Given the rapid analytical speed of the ICP-MS, elemental range, detection limits, local availability, and reasonable cost of the instrument, we expect that ICP-MS will rival INAA as the technique of choice for bulk elemental analysis of ceramics and other archaeological artifacts. In this study, we have applied the elemental and isotopic capabilities of the ICP-MS to investigation of the provenance of archaeological ceramics. Our sample suite was chosen both to test the ICP-MS technique and to provide information of archaeological significance to researchers in the El Paso region. MATERIALS -- CERAMIC SAMPLES A total of 30 ceramic artifacts was analyzed, comprising six groups of five sherds each. Groups are located geographically in Figure 1. Groups 1 and 2 represent historic period assemblages from sites located within the Rio Grande flood plain on the Tigua Indian Reservation, Ysleta, Texas1 °. Group 1 consists of five red painted ceramics from a late 19t century Tigua farmstead and Group 2 is five plain brownware sherds recovered from a late 18th/early 1 9 th century Tigua jacal structure. Groups 1 and 2 contain both bowl and jar forms and originate from sites within 300 meters of one another. Ethnographic and archival research conducted among the Tigua Indian suggests that the ceramics were derived from clay sources located along the Rio Grande flood plain or on the terraces of the Rio Grande". Petrographic analysis of historic plain brown ceramics documented this conclusion 12 . Group 3 consists of five Hueco Plain jar sherds recovered from a site in the desert lowlands southeast of present-day El Paso, Texas 13. Hueco Plain is a recently named and described fine-pasted brownware that is distinctly different from the locally made brownwares (Group 6, see below) found in the El Paso region. The Hueco Plain sherds were recovered from deposits radiocarbon dated
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