Tropical weathering of the Taconic orogeny as a driver for Ordovician cooling

Abstract

Research Article| June 09, 2017 Tropical weathering of the Taconic orogeny as a driver for Ordovician cooling Nicholas L. Swanson-Hysell; Nicholas L. Swanson-Hysell 1Department of Earth and Planetary Science, University of California, Berkeley, California 94720-4767, USA Search for other works by this author on: GSW Google Scholar Francis A. Macdonald Francis A. Macdonald 2Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Nicholas L. Swanson-Hysell 1Department of Earth and Planetary Science, University of California, Berkeley, California 94720-4767, USA Francis A. Macdonald 2Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA Publisher: Geological Society of America Received: 23 Jan 2017 Revision Received: 11 Apr 2017 Accepted: 19 Apr 2017 First Online: 23 Jun 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2017 Geological Society of America Geology (2017) 45 (8): 719–722. https://doi.org/10.1130/G38985.1 Article history Received: 23 Jan 2017 Revision Received: 11 Apr 2017 Accepted: 19 Apr 2017 First Online: 23 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 Nicholas L. Swanson-Hysell, Francis A. Macdonald; Tropical weathering of the Taconic orogeny as a driver for Ordovician cooling. Geology 2017;; 45 (8): 719–722. doi: https://doi.org/10.1130/G38985.1 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 The Earth’s climate cooled through the Ordovician Period leading up to the Hirnantian glaciation. Increased weatherability of silicate rocks associated with topography generated on the Appalachian margin during the Taconic orogeny has been proposed as a mechanism for Ordovician cooling. However, paleogeographic reconstructions typically place the Appalachian margin within the arid subtropics, outside of the warm and wet tropics where chemical weathering rates are highest. In this study, we reanalyze the paleomagnetic database and conclude that Ordovician constraints from cratonic Laurentia are not robust. Instead, we use paleomagnetic data from well-dated volcanic rocks in the accreting terranes to constrain Laurentia’s position given that the Appalachian margin was at, or equatorward of, the paleolatitude of these terranes. To satisfy these allochthonous data, Laurentia must have moved toward the equator during the Ordovician such that the Appalachian margin was within 10° of the equator by 465 Ma. This movement into the tropics coincided with the collision and exhumation of the Taconic arc system, recorded by a shift in neodymium isotope data from shale on the Appalachian margin to more juvenile values. This inflection in detrital neodymium isotope values precedes a major downturn in global seawater strontium isotopic values by more than one million years, as would be predicted from a change in weathering input and the relatively long residence time of strontium in the ocean. These data are consistent with an increase in global weatherability associated with the tropical weathering of mafic and ultramafic lithologies exhumed during the Taconic arc-continent collision. A Taconic related increase in weatherability is a viable mechanism for lowering atmospheric CO2 levels through silicate weathering contributing to long-term Ordovician cooling. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.