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SINCE 1952
Earth Science cover
Estonian Journal of Earth Sciences
ISSN 1736-7557 (Electronic)
ISSN 1736-4728 (Print)
Impact Factor (2022): 1.1
Short communication
Early diagenetic transformation stages revealed by micro-analytical studies of shelly phosphorites, Rakvere region; pp. 34–37

Sophie Graul, Toivo Kallaste, Marko Moilanen, Mawo Ndiaye, Rutt Hints

Furongian–Tremadocian phosphorites of Estonia are sandstone rich in biogenic apatite, represented by brachiopod detritus. The study focuses on the mineralogical and micro-analytical characterisation of phosphorites from the Aseri, Toolse, and Kabala deposits based on FE-SEM and EPMA analyses. The shell fragments are composed of alternating compact and porous laminae, but with considerably poor preservation of pristine textures, superseded by the formation of authigenic CAF-apatite during the early diagenesis. In all settings, the shells showed preferential uptake of Sr into the porous cryptocrystalline laminae. The altered areas are composed of massive apatite crystallites with Mn-enriched layers. They are frequently covered with pyrite, indicating progressive recrystallisation under the influence of interstitial fluids and fluctuations in redox gradients in coastal environments.


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