Oxygen stable isotope ratios, sourcing

To refine potential Olivella source zones to more specific sections of the coastline, we have employed two different archaeometric techniques, including determination of elemental composition by inductively coupled plasma-mass spectrometry (ICP-MS) and the use of carbon and oxygen stable isotopes using an isotope ratio-mass spectrometer (IR-MS) (38). Each of these techniques is described below, and the final section evaluates and compares their utility in sourcing Olivella shell beads. 

The provenance of marble is one such case. Early attempts at provenance using trace elements found that trace element concentrations varied by factors of over 100 within the same quarry. However, the stable isotopic ratios of oxygen and carbon have been used to discriminate between marble sources. These isotopic ratios are fractionated during initial formation of the protolith. For example, the will vary... 

For marble provenance studies, the most successful technique seems to be the measurement, through mass spectrometry, of the abundance ratios of the stable isotopes of carbon and oxygen (116). However, no single technique appears to provide unequivocal results, especially in cases such as the different Mediterranean sources, and a combination is often necessary to arrive at an approximate place of origin (117). 

We have applied two distinct techniques, analysis of bulk chemical composition and the ratios of oxygen and caibon stable isotopes, in an effort to determine source provenance of Olivella shell beads in Western North America. These techniques produce varying degrees of success. 

Paint and Varnish Finnigan Mat [86] analyzed the carbon and nitrogen isotope values in paint and varnish samples using an EA-IRMS. Differentiation of these samples was achieved based on a combination of the isotope values of the two elements. Farmer et al. [87] provide an overview of research conducted to determine the stable isotope composition of 51 white architectural paints. Carbon, oxygen and hydrogen isotope values were measured and likehhood ratio analysis applied to the data. While samples originating from different sources were differentiated, a false-positive rate of 2% was observed. 

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