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How reliable is the K-Ar glauconite chronometer? A case study of Eocene sediments from the Isle of Wight

N. Clauer, J. M. Huggett and S. Hillier
How reliable is the K-Ar glauconite chronometer? A case study of Eocene sediments from the Isle of Wight
Clay Minerals (June 2005) 40 (2): 167-176

Abstract

K-Ar ages of Eocene glauconite pellets from the Isle of Wight are related to quantified amounts of older glauconite pellets and to occurrences of detrital mica/illite particles that might have been added to synsedimentary pellets during reworking processes. Addition of older glauconite did not significantly bias the K-Ar dates, as the results most often provide the expected stratigraphic reference ages or even significantly lower ages. Alternatively, K-Ar dates significantly greater than those suggested by the stratigraphy appear to result from non-glauconized detrital mica in the pellets which is not always removable, even by high-gradient magnetic separation. Unexpected "old" K-Ar glauconite ages do not result from misapplication of the method, but from inability to systematically identify and remove the "contaminant" particles from glauconite splits. Analysis of highly evolved glauconite separates is definitely appropriate for reliable isotopic age determinations, but it might not be enough for the final selection, as long-lasting diagenesis might have taken over the synsedimentary process. Much if not all depends on the separation and characterization of the separates, but also on the completion of the glauconitization process which effects cannot always be anticipated.


ISSN: 0009-8558
EISSN: 1471-8030
Coden: CLMIAF
Serial Title: Clay Minerals
Serial Volume: 40
Serial Issue: 2
Title: How reliable is the K-Ar glauconite chronometer? A case study of Eocene sediments from the Isle of Wight
Affiliation: CNRS, Centre de Geochimie de la Surface, Strasbourg, France
Pages: 167-176
Published: 200506
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 17
Accession Number: 2005-062406
Categories: Sedimentary petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch maps
N50°40'00" - N50°45'00", W01°30'00" - W01°00'00"
Secondary Affiliation: Natural History Museum, GBR, United KingdomMacaulay Institute, GBR, United Kingdom
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200538
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