When do black shales tell molybdenum isotope tales?

Abstract

Research Article| June 01, 2009 When do black shales tell molybdenum isotope tales? G.W. Gordon; G.W. Gordon * 1School of Earth & Space Exploration, Arizona State University, Tempe, Arizona 85287-1404, USA *E-mail: Gwyneth.Gordon@asu.edu. Search for other works by this author on: GSW Google Scholar T.W. Lyons; T.W. Lyons 2Department of Earth Sciences, University of California–Riverside, Riverside, California 92521-0423, USA Search for other works by this author on: GSW Google Scholar G.L. Arnold; G.L. Arnold 1School of Earth & Space Exploration, Arizona State University, Tempe, Arizona 85287-1404, USA Search for other works by this author on: GSW Google Scholar J. Roe; J. Roe 3Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA Search for other works by this author on: GSW Google Scholar B.B. Sageman; B.B. Sageman 4Department of Geological Sciences, Northwestern University, Evanston, Illinois 60208, USA Search for other works by this author on: GSW Google Scholar A.D. Anbar A.D. Anbar 1School of Earth & Space Exploration, Arizona State University, Tempe, Arizona 85287-1404, USA 5Department of Chemistry & Biochemistry, Arizona State University, Tempe, Arizona 85287-1404, USA Search for other works by this author on: GSW Google Scholar Author and Article Information G.W. Gordon * 1School of Earth & Space Exploration, Arizona State University, Tempe, Arizona 85287-1404, USA T.W. Lyons 2Department of Earth Sciences, University of California–Riverside, Riverside, California 92521-0423, USA G.L. Arnold 1School of Earth & Space Exploration, Arizona State University, Tempe, Arizona 85287-1404, USA J. Roe 3Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA B.B. Sageman 4Department of Geological Sciences, Northwestern University, Evanston, Illinois 60208, USA A.D. Anbar 1School of Earth & Space Exploration, Arizona State University, Tempe, Arizona 85287-1404, USA 5Department of Chemistry & Biochemistry, Arizona State University, Tempe, Arizona 85287-1404, USA *E-mail: Gwyneth.Gordon@asu.edu. Publisher: Geological Society of America Received: 25 May 2008 Revision Received: 29 Oct 2008 Accepted: 22 Jan 2009 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2009 Geological Society of America Geology (2009) 37 (6): 535–538. https://doi.org/10.1130/G25186A.1 Article history Received: 25 May 2008 Revision Received: 29 Oct 2008 Accepted: 22 Jan 2009 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation G.W. Gordon, T.W. Lyons, G.L. Arnold, J. Roe, B.B. Sageman, A.D. Anbar; When do black shales tell molybdenum isotope tales?. Geology 2009;; 37 (6): 535–538. doi: https://doi.org/10.1130/G25186A.1 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 SocietyGeology Search Advanced Search Abstract Molybdenum (Mo) isotopes in ancient sediments are promising recorders of global ocean paleoredox conditions. Organic-rich black shales can be used to reconstruct ancient ocean Mo isotope compositions if these sediments record the isotopic composition of contemporaneous seawater. Comparison of δ98/95Mo in two Devonian shale sequences of similar age, the New York Oatka Creek and Geneseo Formations, reveals that this assumption cannot be applied to all organic-rich shales. Although both sequences contain laminated intervals, elevated organic carbon, and enrichments of redox-sensitive metals, the mean δ98/95Mo differs systematically between the formations by ~0.59‰. Independent paleoredox indicators reveal that portions of the Oatka Creek Formation were deposited under pervasively euxinic (anoxic and sulfidic) conditions, whereas conditions during deposition of the Geneseo Formation were intermittently euxinic to suboxic (oxygen deficient but not sulfidic in the water column). We infer that reconstruction of ancient ocean δ98/95Mo from organic-rich shales requires independent verification of persistent local euxinia. With these considerations in mind, our data point to δ98/95Mo in the Devonian oceans ~0.6‰ lighter than in today's oceans, consistent with expanded anoxia. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.