Abstract
Research Article| December 01, 2004 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, Jr.; J. M. Barton, Jr. Department of Geology, Rand Afrikaans University, P.O. Box 524, Auckland Park 2006, South Africa, e-mail: jmb@na.rau.ac.za; bc@na.rau.ac.za Search for other works by this author on: GSW Google Scholar B. Cairncross; B. Cairncross Department of Geology, Rand Afrikaans University, P.O. Box 524, Auckland Park 2006, South Africa, e-mail: jmb@na.rau.ac.za; bc@na.rau.ac.za Search for other works by this author on: GSW Google Scholar I. McLachlan I. McLachlan P.O. Box 307, Parow 7499, South Africa, e-mail: mclachlai@petroleumagencysa.com Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2004) 107 (4): 499–504. https://doi.org/10.2113/gssajg.107.4.499 Article history first online: 07 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation J. M. Barton, B. Cairncross, 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 2004;; 107 (4): 499–504. doi: https://doi.org/10.2113/gssajg.107.4.499 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract Rb-Sr isotopic analyses of glauconite from Permian sedimentary rocks associated with coal seams in the northern Karoo basin yield ages ranging from ~181 to ~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 ~180 Ma. Some link, whether just heating or hydrothermal activity leading to maturation of glauconite is implied. Rb-Sr ages between ~400 and ~750 Ma for detrital biotite and muscovite from these same sedimentary rocks limit the maximum temperature of the thermal activity to <~250°C, and vitrinite reflectance and the presence of oil in the sediments indicate a maximum temperature of <120°C, well below the ~230°C block temperature of glauconite in the Rb-Sr system. Therefore the second possibility seems more probable. You do not currently have access to this article.
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