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Evolution of Clay Minerals in a Chronosequence of Poldered Sediments Under the Influence of a Natural Pasture Development

Published online by Cambridge University Press:  01 January 2024

B. Velde*
Affiliation:
Laboratoire de Géologie, UMR 8538 CNRS Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris, France
B. Goffé
Affiliation:
Laboratoire de Géologie, UMR 8538 CNRS Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris, France
A. Hoellard
Affiliation:
Laboratoire de Géologie, UMR 8538 CNRS Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris, France
*
*E-mail address of corresponding author: [email protected]
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Abstract

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Clay minerals appear to change significantly under the influence of pasture development on poldered sediments in the Baie d'Authie area (Somme, France). Cores 40–90 cm deep from recent salt marsh sediments and poldered sediments developing grass pastures since 1737, 1575 and 1158 indicate that the natural mineral suite of kaolinite, mica, illite, and two disordered mixed-layered illite-smectite (I-S) phases common to the sedimentary input changes gradually but significantly in the materials. In the oldest, best-developed profile, there is a dominance of a disordered, illitic I-S in the humic upper part of the profile and a more abundant, more smectitic I-S mineral below. It appears that grass-derived humic materials tend to stabilize closed (collapsed) or illitic behavior in I-S clays. The natural evolution of the sediment (lower part of the profile) is towards a smectitic clay assemblage. Destruction of organic matter of the smectitic I-S minerals by oxidation indicates that this material can significantly modify the physical behavior of the clays keeping the structure open to polar molecules.

Type
Research Article
Copyright
Copyright © 2003, The Clay Minerals Society

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