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Fine-scale growth patterns in coral skeletons: biochemical control over crystallization of aragonite fibres and assessment of early diagenesis

By
J. P. Cuif
J. P. Cuif
UMR 8148 IDES, Faculté des Sciences, Bât 504, F-91405, Orsay, France (e-mail: jean-pierre.cuif@u-psud.fr)
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Y. Dauphin
Y. Dauphin
UMR 8148 IDES, Faculté des Sciences, Bât 504, F-91405, Orsay, France (e-mail: jean-pierre.cuif@u-psud.fr)
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A. Meibom
A. Meibom
MNHN, LEME - Nanoanalyse, 57 rue Cuvier, F-75423 Paris, France
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C. Rollion-Bard
C. Rollion-Bard
CRPG, Rue N-D des Pauvres, F-54501 Vandoeuvre les Nancy, France
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M. Salomé
M. Salomé
ESRF ID21, BP 220, F-38043 Grenoble Cedex 9, France
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J. Susini
J. Susini
ESRF ID21, BP 220, F-38043 Grenoble Cedex 9, France
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C. T. Williams
C. T. Williams
NHM, Analytical Department, Cromwell Road, SW7 5BD London, UK
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Published:
January 01, 2008

Abstract

Recent works have paved the way for an understanding of the scale at which environmental signals might be recorded in coral skeletons. In this paper, the resulting structural and chemical insights are exemplified by a Goniastrea corallite. The bulk of the coral skeleton consists of fibrous aragonite, which in turn is constructed by sequential growth of micrometre thick layers, oriented parallel to the local growth direction. These growth layers consist of nanograins (50–100 nm) of aragonite that appear to be crystallized in close association with a matrix, conceivably proteoglycans, which seem to coat individual nanograins. These observations contradict the traditional notion that coral fibre consists of ‘a single crystal of orthorhombic aragonite’.

Additionally, the ultrastructural observations provide us with criteria to assess early diagenetic effects. Some Lower Norian corals from South Anatolia (Turkey) display extremely well-preserved mineralogy and structures. They have also preserved the organic components of their skeletons from which it has been demonstrated, through a study of the Nitrogen isotopic composition, that photosynthesis was involved in the metabolism of these early Scleractinia. But even in these remarkably preserved corals, we find evidence for diagenetic changes at the nanometre scale, concerning both the amount of organic matrices and the appearance of the aragonitic nano-granular units. Such micro-structural observations call for caution when interpreting isotopic effects in the fossil coral record.

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Contents

Geological Society, London, Special Publications

Biogeochemical Controls on Palaeoceanographic Environmental Proxies

W. E. N. Austin
W. E. N. Austin
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R. H. James
R. H. James
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Geological Society of London
Volume
303
ISBN electronic:
9781862395510
Publication date:
January 01, 2008

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