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Mineral phases and processes within green peloids from two Recent deposits near the Congo River Mouth

Published online by Cambridge University Press:  09 July 2018

P. Giresse ,
A. Wiewiora  and
B. Lacka
P. Giresse
Affiliation:
Laboratoire de Recherches de Sédimentologie Marine, Université de Perpignan — Avenue de Villeneuve, 66025 Perpignan, France
A. Wiewiora
Affiliation:
Institute of Geological Sciences, Polish Academy of Sciences, al. Zwirki i Wigury 93, 02-089 Warsaw, Poland
B. Lacka
Affiliation:
Institute of Geological Sciences, Polish Academy of Sciences, al. Zwirki i Wigury 93, 02-089 Warsaw, Poland
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Abstract

In the Recent sediments of the Congo River estuary, the green Fe-bearing peloids containing 7 Å phases are nearer to the river mouth than the 10 Å phyllosilicates. Measurements of d060 for 7 Å minerals in various density fractions indicated a progressive transformation of kaolinite into trioctahedral 1:1 phyllosilicates in the zone with a high sedimentation rate. Projection of the chemical composition from the approximate crystallochemical formula on to a classification field confirmed the transformation of kaolinite into a 7 Å Fe-rich phase via substitution of Fe2+ and Mg for Al in the octahedral sheet, with insignificant changes in the tetrahedral sheet. The resultant transition phase has a composition closer to greenalite than berthierine. The possible advancement of the evolution process was stopped by massive formation of goethite. The 10 Å minerals formed in the grains deposited in the off-shore sediments have a homogenous composition and occur in association with goethite and quartz. These peloids show an enrichment in Al although no kaolinite is present.

Type
Research Article
Information
Clay Minerals , Volume 23 , Issue 4 , December 1988 , pp. 447 - 458
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1988

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