High Archean climatic temperature inferred from oxygen isotope geochemistry of cherts in the 3.5 Ga Swaziland Supergroup, South Africa

Abstract

Research Article| May 01, 2003 High Archean climatic temperature inferred from oxygen isotope geochemistry of cherts in the 3.5 Ga Swaziland Supergroup, South Africa L. Paul Knauth; L. Paul Knauth 1Department of Geological Sciences, Arizona State University, Tempe, Arizona 85287-1404, USA Search for other works by this author on: GSW Google Scholar Donald R. Lowe Donald R. Lowe 2Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, USA Search for other works by this author on: GSW Google Scholar Author and Article Information L. Paul Knauth 1Department of Geological Sciences, Arizona State University, Tempe, Arizona 85287-1404, USA Donald R. Lowe 2Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, USA Publisher: Geological Society of America Received: 17 Oct 2001 Revision Received: 03 Sep 2002 Accepted: 05 Sep 2002 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2003) 115 (5): 566–580. https://doi.org/10.1130/0016-7606(2003)115<0566:HACTIF>2.0.CO;2 Article history Received: 17 Oct 2001 Revision Received: 03 Sep 2002 Accepted: 05 Sep 2002 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 L. Paul Knauth, Donald R. Lowe; High Archean climatic temperature inferred from oxygen isotope geochemistry of cherts in the 3.5 Ga Swaziland Supergroup, South Africa. GSA Bulletin 2003;; 115 (5): 566–580. doi: https://doi.org/10.1130/0016-7606(2003)115<0566:HACTIF>2.0.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 New and compiled oxygen isotope data combined with the results of geological and sedimentological studies demonstrate that enclaves of synsedimentary to very early diagenetic cherts are widely preserved in the 3.5–3.2 Ga Swaziland Supergroup, Barberton greenstone belt, South Africa. The low δ18O values of these cherts indicate extremely high ocean temperatures of 55–85 °C. Previously, the large depletion in 18O shown by all Barberton cherts relative to their Phanerozoic counterparts has been attributed to low 18O in Archean oceans, chert formation during late diagenesis, wholesale loss of 18O during alteration, and/or regional silicification of sediments around hot springs. These alternative explanations are not compatible with the new results.Cherts in the Onverwacht Group display an isotopic stratigraphy that is inversely repeated in conglomerates in the overlying Fig Tree and Moodies Groups, demonstrating that the chert δ18O values were fixed prior to Archean uplift and erosion, which started at 3.26 Ga. The maximum δ18O value in Barberton cherts (+22‰) is lower than the minimum values (+23‰) in Phanerozoic bedded cherts, precluding late diagenesis as the explanation of the overall low δ18O values. Regional metamorphic, hydrothermal, or long-term resetting of original δ18O values is also precluded by preservation of δ18O values across different metamorphic grades and by systematic δ18O differences among interbedded chert types, stratigraphic units, and conglomerate clasts.The 7‰ δ18O variation of these Archean cherts is similar to that of Phanerozoic deep-sea cherts—formed when opal converted to microquartz during burial—but the actual Archean values are ∼10‰ lower. Marine opal was apparently converted to microquartz during burial to depths of <1 km. Cherts with δ18O < 15‰ reflect conversion during deepest burial or in local areas of enhanced geothermal gradient and/or hydrothermal activity. Cherts with higher δ18O values formed during early diagenesis and indicate an extremely hot Archean ocean and surface environment. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.