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A deep-water glauconitization process on the Ivory Coast-Ghana marginal ridge (ODP Site 959); determination of Fe (super 3+) -rich montmorillonite in green grains

A. Wiewiora, P. Giresse, S. Petit and A. Wilamowski
A deep-water glauconitization process on the Ivory Coast-Ghana marginal ridge (ODP Site 959); determination of Fe (super 3+) -rich montmorillonite in green grains
Clays and Clay Minerals (December 2001) 49 (6): 540-558

Abstract

The mineral and chemical composition of green glauconitic grains from ODP site 959 (2100 m water depth) located on the northern flank of the Ivory Coast-Ghana Marginal Ridge was studied. Recurrent winnowing of a 20 m thick Pleistocene succession resulted in a low accumulation rate and stratigraphic hiatuses. The green clay material typically occurs as fillings in the chambers of pelagic foraminifers. The amount of green clay present in sediments older than 1 Ma is small, and greater in younger material. Mud composed of smectite, kaolinite, traces of mica, calcite and quartz was the precursor material that filled the chambers of the foraminifers. Processes at the water-sediment interface slowly modified this composition. Kaolinite was dissolved; smectite lost Al but gained Fe, K and layer charge. In that matrix, the nanocrystals of neoformed smectite are observed. The infrared (IR) spectra showed OH-stretching and bending vibrations due to groups incorporating Fe (super 3+) . The spectra are in agreement with the crystallochemical formulae of Fe (super 3+) -rich montmorillonite as determined by point-by-point analyses on the neoformed crystallites and on the surrounding matrix. The layer charge in this Fe (super 3+) -rich montmorillonite is almost wholly octahedral as shown in crystallochemical formulae and documented independently by a new IR method. The tetrahedral charge appeared when the Fe content increased by >1.2 Fe per formula unit. With the maturation process, the increased role of the closed layers is observed, with the color of grains becoming greener. We have documented for the first time glauconitization proceeding at a depth of 2100 m at a temperature near 3 degrees C. The most important factors of the process are: accumulation of terrigenous clayey material in the foraminiferal chambers, Fe supply from a nearby continent, and a lengthy residence at the water-sediment interface in the zone of the winnowing and low sediment accumulation rate.


ISSN: 0009-8604
Coden: CLCMAB
Serial Title: Clays and Clay Minerals
Serial Volume: 49
Serial Issue: 6
Title: A deep-water glauconitization process on the Ivory Coast-Ghana marginal ridge (ODP Site 959); determination of Fe (super 3+) -rich montmorillonite in green grains
Affiliation: Polish Academy of Sciences, Institute of Geological Sciences, Warsaw, Poland
Pages: 540-558
Published: 200112
Text Language: English
Publisher: Clay Minerals Society, Clarkson, NY, United States
References: 33
Accession Number: 2002-023397
Categories: Quaternary geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, sketch map
N03°37'40" - N03°37'40", W02°44'08" - W02°44'08"
Secondary Affiliation: Universite de Perpignan, FRA, FranceUniversite de Poitiers, FRA, France
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200209
Program Name: ODPOcean Drilling Program
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