Provenance analysis of cremated skeletal remains by stable isotopes.

Cremated human remains are a rather neglected research substrate in physical anthropology; its investigation is still mainly restricted to the osteological level. The application of archaeometric methods to cremations is limited because the organic skeletal components are fully combusted at high temperatures. Stable isotope ratios of heavy elements such as strontium and lead, however, are thermally stable and permit research targeting questions of mobility, migration, and trade. In many cremations, neither dental remains nor the petrous bone are preserved. In such case, no skeletal element that retains the isotopic signature of childhood is available and compact bone has to be chosen instead. This raises interpretive problems, since due to its slow remodeling rate, compact bone integrates the element uptake over many years prior to death. This can generate a mixed isotope ratio in migrants. Such mixed ratios are no longer compatible with the place of origin, and not yet with the place of recovery. Provenance analysis with a single isotope ratio (mostly 87Sr/86Sr) therefore has its limits. A combination of strontium and lead stable isotopes in cremations generates a multi-dimensional isotopic fingerprint that is however more difficult to interpret. Data mining methods that permit a similarity search are a promising approach. In this paper, possibilities and limitations of stable isotope analysis of cremated finds are discussed together with the substrate-specific methodological and interpretive problems. The research potential is demonstrated by use of selected examples.

Modelling strontium isotopes in past biospheres - Assessment of bioavailable 87Sr/86Sr ratios in local archaeological vertebrates based on environmental signatures.

87Sr/86Sr isotopic ratios in skeletal remains of archaeological vertebrates are used for provenance analysis since long. However, the definition of the past bioavailable isotopic ratio at the site of recovery is not known beforehand and geological maps can provide no more than gross expectations. Therefore, the assessment of the "local Sr isotopic signature" is still of crucial importance. In this study, we present a tool for the prediction of such local isotopic signatures by creating a concentration weighted mixing model that links lithospheric, biospheric, and atmospheric strontium per site. The major strontium sources and their input into an animal's body were assessed by choosing elemental strontium and its isotopic signature in groundwater, soil, vegetation, and precipitation as components for the mixing model, augmented by literature values. The model was applied to 24 sites located in the alpine transect of the Inn-Eisack-Adige-Brenner passage across the European Alps, a passage used since the Mesolithic. Predicted local bioavailable 87Sr/86Sr ratios were compared with measured values from locally excavated archaeozoological bone samples from three taxa of large and mainly residential vertebrates (cattle, pig, red deer) to verify the models' accuracy. With regard to the fact that the environmental samples predict the past local bioavailable 87Sr/86Sr at a specific site while the vertebrates had different and species-specific home ranges, thereby integrating strontium from a region of primarily unknown size, the model is capable of assigning reasonable expectation values. For 11 sites, up to 100% of the vertebrate isotopic signatures were correctly predicted. Mismatches at the remaining sites are explainable by special environmental factors, and also the fact that some import of animals can never be excluded beforehand. Suggestions for site-specific adjustments of the model are made.

Multi-isotope provenancing of archaeological skeletons including cremations in a reference area of the European Alps.

RATIONALE: Due to the spatial heterogeneity of stable isotope ratios of single elements measured in attempts to georeference bioarchaeological finds, multi-isotope fingerprints are frequently employed under the assumption that similar isotopic signatures are indicative of similar shared environments by the individuals studied. The extraction of the spatial information from multi-isotope datasets, however, is challenging. METHODS: Gaussian mixture clustering of six- to seven-dimensional isotopic fingerprints measured in archaeological animal and human bones was performed. Uncremated animal bones served for an isotopic mapping of a specific reference area of eminent archaeological importance, namely the Inn-Eisack-Adige passage across the European Alps. The fingerprints consist of 87 Sr/86 Sr, 208 Pb/204 Pb, 207 Pb/204 Pb, 206 Pb/204 Pb, 208 Pb/207 Pb, and 206 Pb/207 Pb ratios, and δ18 Ophosphate values in uncremated bone apatite, while the thermally unstable δ18 O values of human cremations from this region were discarded. RESULTS: The bone finds were successfully decontaminated. Animal and human isotope clusters not only reflect individual similarities in the multi-isotopic fingerprints, but also permit a spatial allocation of the finds. This holds also for cremated finds where the δ18 Ophosphate value is no longer informative. To our knowledge, for the first time Pb stable isotopes have been systematically studied in cremated skeletal remains and proved significant in a region that was sought after for its ore deposits in prehistory. CONCLUSIONS: Gaussian mixture clustering is a promising method for the interpretation of multi-isotopic fingerprints aiming at detecting and quantifying migration and trade.