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

Procter, Frances A., Piazolo, Sandra, John, Eleanor H., Walshaw, Richard, Pearson, Paul N. ORCID: https://orcid.org/0000-0003-4628-9818, Lear, Caroline H. ORCID: https://orcid.org/0000-0002-7533-4430 and Aze, Tracy 2024. Electron backscatter diffraction analysis unveils foraminiferal calcite microstructure and processes of diagenetic alteration. Biogeosciences 21 (5) , 1213–1233. 10.5194/bg-21-1213-2024

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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 preserved 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 ratios, allowed us to examine the effects of different diagenetic processes on the foraminifera test. In poorly preserved specimens EBSD data show 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, in both microstructure and geochemical signals that must be considered when utilising foraminifera to generate proxy archive data.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Publisher:	European Geosciences Union
ISSN:	1726-4189
Date of First Compliant Deposit:	3 April 2024
Date of Acceptance:	13 January 2024
Last Modified:	08 Apr 2024 09:00
URI:	https://orca.cardiff.ac.uk/id/eprint/167672

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