Amino acid geochronology: advances and limitations in bivalve shells

Martina Conti*, Paul Butler, David Reynolds, Harry Kenneth Robson, Nicky Milner, James Scourse, Kirsty Elizabeth Helena Penkman

*Corresponding author for this work

Research output: Contribution to conferencePaperpeer-review


The SEACHANGE project is a multidisciplinary project that aims to reconstruct marine ecosystems prior to and after significant cultural transitions. For robust geochronology, radiocarbon dating of organic material, cross-matched and cross-dated sclerochronology (dating of hard tissues of shells) are employed. Cross-matched floating sclerochronologies (not precisely calendar-dated) can provide annual resolution records spanning decades to as much as 500 years for the longest-lived shells. Developing this record requires visually and statistically comparing growth ring width patterns (cross-matching) across numerous samples. Such an endeavour can be hugely time consuming and therefore needs to be targeted appropriately, especially when dead-collected samples are of unknown antiquity. Radiocarbon dating can be a very precise technique, but it is not always economically viable, especially for a large number of samples (>2,000), and it requires correcting for the marine reservoir effects.

Here we explore the potential for range-finding age estimates of individual dead shells by amino acid (AA) geochronology. AA dating is a relatively fast and cheap technique, which can be used to constrain the time period for any floating sclerochronologies. Previous work on the intra-crystalline protein fraction from calcareous biominerals has resulted in a robust dating method for the Quaternary period. High precision can be achieved in warm environments, for example, cross-dated Porites coral skeletons provided precisions ±24 years across different colonies in samples from the last 150 years.

In addition to the already known caveats of AA geochronology, bivalve shells also present the additional complication of having different microstructures. These have shown significant but consistent variation in AA composition between the microstructural layers, meaning that targeted sampling is necessary to establish a robust and reproducible method for dating bivalve shells. In SEACHANGE, aragonitic Arctica islandica and calcitic Ostrea edulis are targeted in the first instance to constrain mediaeval and Mesolithic-Neolithic shell middens, respectively, showing the range and resolution in dating. These preliminary results indicate that the inner portion of the outer shell layers (iOSL) of A. islandica and foliated layer of O. edulis should be targeted for AA geochronology.
Original languageEnglish
Publication statusPublished - 14 Jul 2023

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