05 Oct 2023
 | 05 Oct 2023
Status: this preprint is open for discussion.

Electron backscatter diffraction analysis unveils foraminiferal calcite microstructure and processes of diagenetic alteration

Frances Alice Procter, Sandra Piazolo, Eleanor Heulwen John, Richard Walshaw, Paul Nicholas Pearson, Caroline Helen Lear, and Tracy Aze

Abstract. Electron backscatter diffraction (EBSD) analysis enables a unique perspective of the internal microstructure of foraminiferal calcite. Specifically, EBSD provides crystallographic data from within the test, highlighting the highly organised “mesocrystal” structure of crystallographically aligned domains throughout the test, formed by sequential deposits of microgranular calcite. We compared EBSD maps across the test walls of both poorly- and well-preserved specimens of the planktonic foraminifera species Globigerinoides ruber and Morozovella crater. The EBSD maps, paired with information about intra-test distributions of Mg/Ca ratios, allowed us to examine the effects of different diagenetic processes on the foraminifera test. In poorly-preserved specimens EBSD data shows extensive reorganisation of the biogenic crystal microstructure, indicating differing phases of dissolution, re-precipitation and overgrowth. The specimens with the greatest degree of microstructural reorganisation also show an absence of higher concentration magnesium bands, which are typical features of well-preserved specimens. These findings provide important insights into the extent of post-depositional changes both in microstructure and geochemical signals that must be considered when utilising foraminifera to generate proxy archive data.

Frances Alice Procter et al.

Status: open (until 11 Dec 2023)

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  • RC1: 'Comment on egusphere-2023-2213', Chiara Consolaro, 15 Nov 2023 reply

Frances Alice Procter et al.

Frances Alice Procter et al.


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Short summary
This study looked at the microstructure of planktonic foraminifera (single celled marine organisms) fossils, to further our understanding of how they form their hard exterior shells, and how the microstructure and chemistry of the shells can change as a result of processes which occur to them after deposition on the seafloor. Understanding these processes is of critical importance for using planktonic foraminifera for robust climate and environmental reconstructions of the past.