HR: 17:15h
AN: B44C-05    [Abstracts]
TI: Uncovering of High Strontium Content in Biogenic Calcite: New Data From a Murolith- producing Coccolithophore
AU: * Hermoso, M
EM: hermoso@ccr.jussieu.fr
AF: Université Pierre et Marie Curie (Paris 6) - JE 2477 Biominéralisations et Paléoenvironnements, 4 place Jussieu, PARIS, 75005, France
EM: hermoso@ccr.jussieu.fr
AF: University of Oxford - Department of Earth Sciences, Parks Road, OXFORD, OX1 3PR, United Kingdom
AU: Minoletti, F
EM: minolet@ccr.jussieu.fr
AF: Université Pierre et Marie Curie (Paris 6) - JE 2477 Biominéralisations et Paléoenvironnements, 4 place Jussieu, PARIS, 75005, France
AU: de Rafélis, M
EM: rafelis@ccr.jussieu.fr
AF: Université Pierre et Marie Curie (Paris 6) - JE 2477 Biominéralisations et Paléoenvironnements, 4 place Jussieu, PARIS, 75005, France
AU: Rickaby, R
EM: rosr@earth.ox.ac.uk
AF: University of Oxford - Department of Earth Sciences, Parks Road, OXFORD, OX1 3PR, United Kingdom
AU: Hesselbo, S
EM: stephess@earth.ox.ac.uk
AF: University of Oxford - Department of Earth Sciences, Parks Road, OXFORD, OX1 3PR, United Kingdom
AB: Biogeochemical studies of modern coccolithophores have demonstrated a link between growth rate and the incorporation of strontium into coccolith calcite. Values for the Sr content of coccolithophores have been quoted as high as 30 mmol/mol. A paleochemical study of the Early Jurassic deposits of the Paris Basin reveals a biogeochemical anomaly. It appears indeed that a coccolithophorid genus, Crepidolithus, contains unexpected amounts of strontium (ca. 12-20% weight) in their calcite lattice that corresponds to a Sr/Ca ratio around 130 mmol/mol. These results have been obtained using a innovative protocol which enables the concentration of Crepidolithus from a polyspecific assemblage. Chemical measurements have then been performed by ICP-GAAS after a weak acid leaching. SEM spot analyses confirm the reproducibility of high values. At the same time, other calcareous particles (such as Schizosphaerella, coccoliths and euhedral monocrystals) do not show such parallel enrichments in strontium. This observation enables us to preclude diagenesis as the cause of the high Sr values. Moreover, further investigations (SEM, XRD, selective leaching) rule out an additional contaminant phase such as sulfates. Finally, in view of the good preservation of Crepidolithus in the sediment, an aragonite precursor for this coccolith genus can also be excluded. If true, these results raise the question about the mode of incorporation of strontium into the calcite lattice because these values require huge K_Sr (>> 0.13) and/or unrealistic Sr content in the seawater (ca. 150 ppm !). We discuss here several explanations to explain this bioincorporation of strontium into these coccoliths. 1. A mineralization of (Crepidolithus from a distinct water mass extraordinarily enriched in Sr. For that, we present the physico-chemical structure of the water column during the Early Toarcian OAE and the geographic repartition of this anomaly. 2. A differential vital effect explained by physiological pathways (cross-membrane transport). 3. A kinetic effect due to the growth mode of this murolith where vertical V-units are dominant. In order to verify that last hypothesis, we also investigate the Sr content from others same-structured coccoliths (e.g., Crucirhabdus).
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0459 Macro- and micropaleontology (3030, 4944)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 0489 Trace element cycling (4875)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting