Implications of Ostrich Eggshell Diagenesis Experiments and Observations for Isoscape Analyses

Summary

This is an abstract from the "SAA 2021: General Sessions" session, at the 86th annual meeting of the Society for American Archaeology.

Ostrich eggshell (OES) is widely used for environmental reconstruction with carbon, oxygen and nitrogen isotopes, and radiocarbon dating. Strontium isotope ratios of OES artifacts can be used to reconstruct object biography, human mobility, and interaction networks. OES can provide an isotopic baseline for reconstructing past environments and provenience of artifacts only if diagenetic contamination of archaeological eggshell can be excluded.

OES has two main structural layers with different diagenetic susceptibilities. The palisade (outer) layer is micritic calcite with 1-2% organic matter. It absorbs large amounts of uranium after burial. Its oxygen and carbon isotope ratios decrease systematically above 350°C. The mammilary/cone (inner) layer comprises small translucent columnar calcite crystals. It does not absorb organic staining solutions, uptakes ~100-1000 times less uranium, and does not shift isotope ratios at 450°C. Porous calcite covering the organic-rich cone tips should be removed before sampling.

87Sr/86Sr of inner and outer layers in the same specimen differ substantially in surface-collected modern OES from Kenya and archaeological OES from Malawi, likely due to uptake of soil Sr by the palisade layer. Results of analyses of cone layer crystals decontamination by acid-etching will be presented. This method can insure accurate elemental and isotopic analyses of OES.

This Resource is Part of the Following Collections

• Society for American Archaeology 86th Annual Meeting, Online (2021)   •
• SAA 2021: General Sessions

Keywords

Spatial Coverage

Record Identifiers

Abstract Id(s): 33541