PCI Paleontology

Title

Evidence of high Sr/Ca in a Middle Jurassic murolith coccolith speciesuse asterix (*) to get italics

Authors

Baptiste Suchéras-Marx, Fabienne Giraud, Alexandre Simionovici, Rémi Tucoulou, Isabelle DanielPlease use the format "First name initials family name" as in "Marie S. Curie, Niels H. D. Bohr, Albert Einstein, John R. R. Tolkien, Donna T. Strickland"

Year

2020

Picture

Abstract

<p>Paleoceanographical reconstructions are often based on microfossil geochemical analyses. Coccoliths are the most ancient, abundant and continuous record of pelagic photic zone calcite producer organisms. Hence, they could be valuable substrates for geochemically based paleoenvironmental reconstructions but only Sr/Ca is exploited even if it remains poorly understood. For example, some murolith coccoliths species have very high Sr/Ca compared to the common 1-4 mmol/mol recorded in placolith coccoliths. In this study, we analyzed the elemental composition of the Middle Jurassic murolith *Crepidolithus crassus* by synchrotron-based nanoXRF (X-ray Fluorescence Spectroscopy) mapping focusing on Sr/Ca and compared the record to two placolith species, namely *Watznaueria contracta* and *Discorhabdus striatus*. In *C. crassus*, Sr/Ca is more than ten times higher than in both placoliths and seems higher in the proximal cycle. By comparison with the placoliths analyzed in the same analytical set-up and from the same sample, we exclude the impact of the diagenesis and seawater Sr/Ca to explain the high Sr/Ca in *C. crassus*. Based on comparisons to *Pontosphaera discopora* and *Scyphosphaera apsteinii* which also have high Sr/Ca, it seems more likely that high Sr/Ca in *C. crassus* is either due to the vertical elongation of the R-units of the proximal cycle or related to the action of the special polysaccharide controlling the growth of those vertically elongated R-units that may have affinities to Sr 2+. In order to apply the Sr/Ca proxy to muroliths, further investigations are needed on cultured coccoliths.</p>

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Keywords

Calcareous nannofossils; Coccoliths; ESRF; Muroliths; Sr/Ca; Ultrastructure; XRF

Methods that require specific expertise (optional)

NonePlease indicate the methods that may require specialised expertise during the peer review process (use a comma to separate various required expertises).

Thematic fields

Microfossils, Micropaleontology, Nanofossils

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Submission date

2020-05-18 16:11:35

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Antonino Briguglio

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