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Rb-Sr isotopic and elemental studies of the origin of glauconite in the Permian northern Karoo coal fields, South Africa; evidence for a thermal Mid-Jurassic influence

J. M. Barton, B. Cairncross and I. McLachlan
Rb-Sr isotopic and elemental studies of the origin of glauconite in the Permian northern Karoo coal fields, South Africa; evidence for a thermal Mid-Jurassic influence
South African Journal of Geology (December 2004) 107 (4): 499-504

Abstract

Rb-Sr isotopic analyses of glauconite from Permian sedimentary rocks associated with coal seams in the northern Karoo basin yield ages ranging from approximately 181 to approximately 178 Ma. These ages, being significantly younger than times of deposition of the host rocks, are interpreted to reflect the time of recrystallization and glauconite maturation during the Middle Jurassic. These ages are very similar to the time of widespread volcanism and intrusion of dolerite dykes and sills into Karoo sedimentary strata at approximately 180 Ma. Some link, whether just heating or hydrothermal activity leading to maturation of glauconite is implied. Rb-Sr ages between approximately 400 and approximately 750 Ma for detrital biotite and muscovite from these same sedimentary rocks limit the maximum temperature of the thermal activity to < approximately 250 degrees C, and vitrinite reflectance and the presence of oil in the sediments indicate a maximum temperature of <120 degrees C, well below the approximately 230 degrees C block temperature of glauconite in the Rb-Sr system. Therefore the second possibility seems more probable.


ISSN: 1012-0750
EISSN: 1996-8590
Coden: TGSAA3
Serial Title: South African Journal of Geology
Serial Volume: 107
Serial Issue: 4
Title: Rb-Sr isotopic and elemental studies of the origin of glauconite in the Permian northern Karoo coal fields, South Africa; evidence for a thermal Mid-Jurassic influence
Affiliation: Rand Afrikaans University, Department of Geology, Auckland Park, South Africa
Pages: 499-504
Published: 200412
Text Language: English
Publisher: Bureau for Scientific Publications, Pretoria, South Africa
References: 34
Accession Number: 2005-056811
Categories: Sedimentary petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch map
S27°00'00" - S26°00'00", E28°15'00" - E29°30'00"
Country of Publication: South Africa
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200520
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