Romita pottery revisited: a reassessment of the provenance of ceramics from Colonial Mexico by LA-MC-ICP-MS

The origin of Romita pottery has been a controversial topic during the last three decades of Colonial Mexico archaeological studies. Lead isotopic analyses of glaze coatings of Spanish and Mexican pottery, and Romita ceramics unearthed from the archaeological site of the Metropolitan Cathedral in Mexico City provide evidence that support a Mexican origin.     

Strontium isotope ratios in fossil teeth from South Africa: assessing laser ablation MC-ICP-MS analysis and the extent of diagenesis

This study tests the precision and accuracy of laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) for measuring strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) in fossil teeth from Swartkrans and Sterkfontein in South Africa, and explores the extent of diagenesis in these specimens. Compared to solution MC-ICP-MS or thermal ionization mass spectrometry (TIMS) methods, LA-MC-ICP-MS can be faster and less expensive, but has lower precision and accuracy. We found that ⁸⁷Sr/⁸⁶Sr ratios in fossil rodent teeth measured by LA-MC-ICP-MS were offset from solution values by a mean of 0.0005 ± 0.0010 (2σ). Because of the very wide spread of biologically available ⁸⁷Sr/⁸⁶Sr ratios (∼0.710 to ∼0.790) in the region, LA-MC-ICP-MS is more than sufficient for assessing the geographic origins of the fossil rodents. The concentration of strontium in modern and fossil enamel from the area is statistically indistinguishable, as is the range of ⁸⁷Sr/⁸⁶Sr ratios in modern rodents and fossil rodents from Swartkrans. Thus, there is little evidence of diagenetic Sr in the fossil enamel. In contrast, the fossil dentine may contain up to ∼50% diagenetic strontium, although many dentine ⁸⁷Sr/⁸⁶Sr ratios are still far removed from the background cave value of 0.729. We propose that LA-MC-ICP-MS will also be of use for investigating the geographic origins of other, non-rodent fossil teeth from the Sterkfontein and Swartkrans collections, and may prove of similar utility at other suitable sites.     

Evidence for long-term averaging of strontium in bovine enamel using TIMS and LA-MC-ICP-MS strontium isotope intra-molar profiles

Abstract

High spatial resolution micro-sampling of tooth enamel offers the possibility of high temporal resolution isotope data to reconstruct climate, environment, diet and mobility. Questions remain about the duration and pattern of the maturation phase of enamel and the existence and direction of chronological 'time-lines'. LA-MC-ICP-MS measurements of c. 400 μm craters and TIMS analyses of transverse enamel sections of an archaeological bovine third molar were undertaken to investigate the long-term averaging of incorporated strontium. The same gradually increasing isotope profile was obtained from both approaches, indicating that the large increase in spatial resolution did not change the response profile obtained. The results suggest that even at the microscopic scale, strontium is incorporated over a period in excess of 12 months. Averaging of the input signal may result from both long-term retention of strontium in the skeleton and recirculation in the body pool, or long-term maturation of enamel on a microscopic scale. Whichever mechanism is responsible, it may not be possible to recover strontium isotope ratios with a high time resolution from cattle molar enamel unless there is a large imbalance in the amount of strontium supplied by different sources. Consequently, strontium isotope profiles may not be synchronous with those of lighter isotope systems.