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Isotope ratio analyses of trace elements are applied to tooth enamel, ostrich eggshell, and other archaeological hard tissues to infer mobility and other aspects of hominin and animal paleoecology. It has been assumed that these highly mineralized tissues are resistant to diagenetic alteration, but this is seldom tested and some studies document diagenetic alteration over brief time spans. Here, we build on existing research on Maximum Threshold Concentrations (MTCs) to develop screening tools for diagenesis that can inform heavy isotopic analyses. The premise of the MTC approach is that archaeological tissues are likely contaminated and unsuitable for isotope ratio analysis when they exceed characteristic modern concentration ranges of trace elements. Furthermore, we propose a new metric called the Maximum Threshold Ratio (MTR) of 85Rb/88Sr or whole element Rb/Sr, which can be measured simultaneously with 87Sr/86Sr during laser ablation (LA) MC-ICP-MS or applied during post hoc screening of specimens. We analyzed 56 enamel samples from modern Kenyan mammals and 34 modern ostrich eggshells from South Africa, Namibia, and the United States by solution ICP-MS, as well as a subset of shells using LA-MC-ICP-MS. Our results indicate that thresholds are consistent across taxa at a single location, but likely vary across locations. Therefore, MTCs and MTRs need to be tissue and locality specific, but not necessarily taxon-specific. Other important differences are observed between the inner and outer surfaces of the eggshells and between LA and solution ICP-MS. This exploratory study provides guidelines for building reference thresholds to screen enamel and eggshell for diagenesis potentially impacting biogenic isotope ratios.
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This content will become publicly available on November 1, 2026
Does exposure to heat alter stable isotopes in ostrich eggshell? A controlled experiment and analysis
Little research explores the effect of heat on the isotopic composition of ostrich eggshell (OES), though several studies use stable isotopes in OES to assist in paleoclimatic reconstruction. Archaeological OES often shows signs of heat exposure, though distinguishing lower-temperature exposure remains challenging. This controlled study uses modern OES heated in an electric kiln to examine if exposure to low through high degrees of heat shifts δ13C, δ15N, and δ18O values in the organic and mineral components of ostrich eggshell. Results indicate that the total organic portion of the shell conserves original isotopic signatures with exposure below ~220 ◦C, while the mineral portion conserves signatures up to 500 ◦C. Additionally, the study provides C:N ratios as a reliability criterion for the organic portion of archaeological OES. Data produced in this study allows for a more discriminating selection of archaeological samples for paleoclimatic reconstructions.
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- Award ID(s):
- 2152718
- PAR ID:
- 10654201
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Journal of Archaeological Science: Reports
- Volume:
- 67
- Issue:
- C
- ISSN:
- 2352-409X
- Page Range / eLocation ID:
- 105323
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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