Oxygen and carbon isotopic composition of Silurian brachiopods: Implications for coeval seawater and glaciations

Abstract

Research Article| November 01, 1998 Oxygen and carbon isotopic composition of Silurian brachiopods: Implications for coeval seawater and glaciations Karem Azmy; Karem Azmy 1Ottawa-Carleton Geoscience Centre, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada Search for other works by this author on: GSW Google Scholar Ján Veizer; Ján Veizer 2Ottawa-Carleton Geoscience Centre, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada and Institut für Geologie, Ruhr Universität, 44780 Bochum, Germany Search for other works by this author on: GSW Google Scholar Michael G. Bassett; Michael G. Bassett 3Department of Geology, National Museum of Wales, Cardiff CF1 3NP, Wales, United Kingdom Search for other works by this author on: GSW Google Scholar Paul Copper Paul Copper 4Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Karem Azmy 1Ottawa-Carleton Geoscience Centre, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada Ján Veizer 2Ottawa-Carleton Geoscience Centre, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada and Institut für Geologie, Ruhr Universität, 44780 Bochum, Germany Michael G. Bassett 3Department of Geology, National Museum of Wales, Cardiff CF1 3NP, Wales, United Kingdom Paul Copper 4Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1998) 110 (11): 1499–1512. https://doi.org/10.1130/0016-7606(1998)110<1499:OACICO>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Karem Azmy, Ján Veizer, Michael G. Bassett, Paul Copper; Oxygen and carbon isotopic composition of Silurian brachiopods: Implications for coeval seawater and glaciations. GSA Bulletin 1998;; 110 (11): 1499–1512. doi: https://doi.org/10.1130/0016-7606(1998)110<1499:OACICO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We collected 236 calcitic brachiopod shells, covering the entire Silurian Period (∼30 m.y.), at high temporal resolution from stratotype sections from Anticosti Island (Canada), Wales (United Kingdom), the Oslo region (Norway), Gotland (Sweden), and Podolia (Ukraine), Estonia, Latvia, and Lithuania. Data from petrography, scanning electron microscopy, cathodoluminescence, isotopes, and trace elements all confirmed that there was excellent preservation in most shells, thus arguing for retention of primary isotope signals; exceptions were samples from the Oslo region.The δ18O and δ13C values for the well-preserved samples range from −2‰ to −6.5‰ and from −1‰ to 7.5‰ (Peedee belemnite), respectively. In terms of temporal trends, oxygen and carbon isotopes vary in parallel, with a slight decrease with declining age of ∼1‰ through Silurian time, with superimposed short-term oscillations that are negatively correlated with sea-level changes. Three successive positive δ18O shifts in early Aeronian, latest Aeronian, and early Wenlock time correlate with sea-level lowstands and with glacial diamictite deposits in the Amazon Basin and in Africa. The high δ18O and δ13C values are attributed to cold episodes with low sea levels and low values to warm episodes with high sea levels. During warm Silurian episodes, the δ18O value of seawater is suggested to have been about −3.5‰ standard mean ocean water (SMOW) and the global tropical temperatures of about 20–30 °C, similar to the present-day values in summer. During glacial episodes, seawater is proposed to have had a δ18O value of ∼−2.5‰ (SMOW) and temperature of about 14–23 °C, comparable to tropical temperatures proposed for the last glacial episode (14 to 28 °C). Three positive δ13C peaks, in early and late Wenlock and late Ludlow time, likely of regional to global significance, appear to coincide with sea-level lowstands, but we are as yet unable to propose a convincing causative geologic scenario that would explain their origin. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.