Journal
COMPTES RENDUS GEOSCIENCE
Volume 345, Issue 3, Pages 160-165Publisher
ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER
DOI: 10.1016/j.crte.2013.02.005
Keywords
Germanium; Flint; Biosilica; Sponges; Diagenesis; Chalk
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Germanium and silicon, dissolved in seawater, are considered to be incorporated into biogenic opal with no or little fractionation, which permitted to use diatoms as reliable recorders of seawater Ge/Si. Does some fractionation occur during diagenesis, preventing the use of Ge/Si in ancient sediments? We examined the Ge/Si ratio of fossil sponges and flint nodules of the Cretaceous Chalk Formation of northern France. Though disputed, silica in this formation is considered to originate from sponges. No fractionation is observed between sponges and diagenetic flints, which allows us to observe whether Ge/Si bears a biogenic or detrital signature. We may thus confirm that sponges were the main silica supplier during the chalk deposition. The Ge/Si ratio may be used to identify a biogenic signature in cherts where the origin of silica is dubious. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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