Significance of Oxygen and Carbon Isotope Variations in Early Precambrian Cherts and Carbonate Rocks of Southern Africa

Abstract

Research Article| March 01, 1972 Significance of Oxygen and Carbon Isotope Variations in Early Precambrian Cherts and Carbonate Rocks of Southern Africa E. C PERRY, JR.; E. C PERRY, JR. Minnesota Geological Survey, University of Minnesota, 1633 Eustis Street, St. Paul, Minnesota 55108 Search for other works by this author on: GSW Google Scholar F. C TAN F. C TAN Minnesota Geological Survey, University of Minnesota, 1633 Eustis Street, St. Paul, Minnesota 55108 Search for other works by this author on: GSW Google Scholar Author and Article Information E. C PERRY, JR. Minnesota Geological Survey, University of Minnesota, 1633 Eustis Street, St. Paul, Minnesota 55108 F. C TAN Minnesota Geological Survey, University of Minnesota, 1633 Eustis Street, St. Paul, Minnesota 55108 Publisher: Geological Society of America Received: 14 Jul 1971 Revision Received: 29 Jul 1971 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1972, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1972) 83 (3): 647–664. https://doi.org/10.1130/0016-7606(1972)83[647:SOOACI]2.0.CO;2 Article history Received: 14 Jul 1971 Revision Received: 29 Jul 1971 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation E. C PERRY, F. C TAN; Significance of Oxygen and Carbon Isotope Variations in Early Precambrian Cherts and Carbonate Rocks of Southern Africa. GSA Bulletin 1972;; 83 (3): 647–664. doi: https://doi.org/10.1130/0016-7606(1972)83[647:SOOACI]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 Bedded cherts and carbonates from the early Precambrian Bulawayan Group and the Pongola and Swaziland Sequences of southern Africa have δO18SMOW values ranging from 9.8 to 14.5 ‰ for calcite, 8.4 to 16‰, for dolomite and iron carbonate, and 11.0 to 18.7%,, for SiO2. Values of δC13PDB for calcite and dolomite are similar to those of modern carbonates; they range from −1 to + 1.8‰. In contrast, carbonates from magnetite-bearing iron formations have (δC13PDB values of −3.5 to −9.6‰,. Well-preserved sedimentary magnesite from Barton's Farm, Rhodesia, has a maximum δO18SMOW value of 28.8‰.If the highest δO18 values of these ancient chert and carbonate rocks are primary, δO18 of the ocean probably has increased by about 15‰ since their deposition. Available data on the oxygen isotope composition of crustal rocks indicates a probable large excess in the crustal abundance of O18 compared to the O18 concentration in rocks from the mantle. These observations suggest that large amounts of water have been recycled through the mantle.Our finding that carbon isotope ratios in early Precambrian carbonate rocks of southern Africa are similar to ratios in modern marine carbonates corroborates other studies of carbonates in Precambrian rocks. 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.