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Testing high-voltage electrical discharges in disintegrating claystone for isotopic and mineralogical studies; an example using opalinus claystone

Horst Zwingmann, Alfons Berger, Urs Eggenberger, Andrew Todd and Marco Herwegh
Testing high-voltage electrical discharges in disintegrating claystone for isotopic and mineralogical studies; an example using opalinus claystone
Clays and Clay Minerals (November 2017) 65 (5): 342-354

Abstract

The radiogenic isotope systematics of clay minerals are complex because of the intimate mixture of minerals from different origins such as detrital and authigenic sources. An important aspect of dating clays is the primary sample preparation and disintegration method. In the present study, a sample of weakly deformed Opalinus claystone from the Mont Terri underground site (Switzerland) was investigated after disintegration by three different methods. The Opalinus Clay was sedimented in the late Toarcian and early Aalenian and reached maximum temperatures of approximately 85 degrees C during burial in the Cretaceous. The present study reports data from a comprehensive investigation comparing the effects of disintegration by: (1) disc milling; (2) repeated freezing and thawing; and (3) high-voltage discharges. K-Ar age values of the finest clay (<0.1 mu m) released by the different disintegration methods are indistinguishable, indicating that the high-voltage liberation method does not influence grains as small as 100 nm. The K-Ar age values of particle-size separates decreased with decreasing particle size. The age values of the 2-6 mu m separates correspond to the Carboniferous Period, which reflects the dominance of Paleozoic detritus in that size range. The age values of the smallest separates (<0.1 mu m), on average 213 + or - 4 Ma, exceed the numerical age of the formation ( approximately 177 -172 Ma), which show predominance of detrital grains over authigenic grains even in the finest illite. In summary, isotope geochronology data suggest that the high-voltage method can be applied reliably for disintegrating claystones.


ISSN: 0009-8604
EISSN: 1552-8367
Coden: CLCMAB
Serial Title: Clays and Clay Minerals
Serial Volume: 65
Serial Issue: 5
Title: Testing high-voltage electrical discharges in disintegrating claystone for isotopic and mineralogical studies; an example using opalinus claystone
Affiliation: Kyoto University, Graduate School of Science, Kyoto, Japan
Pages: 342-354
Published: 201711
Text Language: English
Publisher: Clay Minerals Society, Chantilly, VA, United States
References: 35
Accession Number: 2018-018691
Categories: GeochronologySedimentary petrologyEnvironmental geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch map
N47°23'29" - N47°23'29", E07°09'40" - E07°09'47"
Secondary Affiliation: University of Bern, CHE, SwitzerlandCSIRO Energy, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, Copyright, Clay Minerals Society. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201810
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