Iron formation carbonates: Paleoceanographic proxy or recorder of microbial diagenesis?

Research Article| November 01, 2013 Iron formation carbonates: Paleoceanographic proxy or recorder of microbial diagenesis? Clark M. Johnson; Clark M. Johnson * 1Department of Geoscience, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA2National Aeronautics and Space Administration Astrobiology Institute, USA, https://astrobiology.nasa.gov/nai/ *E-mail: clarkj@geology.wisc.edu. Search for other works by this author on: GSW Google Scholar James M. Ludois; James M. Ludois 1Department of Geoscience, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA2National Aeronautics and Space Administration Astrobiology Institute, USA, https://astrobiology.nasa.gov/nai/ Search for other works by this author on: GSW Google Scholar Brian L. Beard; Brian L. Beard 1Department of Geoscience, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA2National Aeronautics and Space Administration Astrobiology Institute, USA, https://astrobiology.nasa.gov/nai/ Search for other works by this author on: GSW Google Scholar Nicolas J. Beukes; Nicolas J. Beukes 3Department of Geology, University of Johannesburg, Johannesburg, South Africa Search for other works by this author on: GSW Google Scholar Adriana Heimann Adriana Heimann 4Department of Geological Sciences, East Carolina University, 101 Graham Building, Greenville, North Carolina 27858, USA Search for other works by this author on: GSW Google Scholar Geology (2013) 41 (11): 1147–1150. https://doi.org/10.1130/G34698.1 Article history received: 02 May 2013 rev-recd: 09 Jul 2013 accepted: 11 Jul 2013 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Clark M. Johnson, James M. Ludois, Brian L. Beard, Nicolas J. Beukes, Adriana Heimann; Iron formation carbonates: Paleoceanographic proxy or recorder of microbial diagenesis?. Geology 2013;; 41 (11): 1147–1150. doi: https://doi.org/10.1130/G34698.1 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 chemical and isotopic compositions of carbonates are commonly used as proxies for ancient seawater or paleoenvironments. Iron formation (IF) carbonates have been used as evidence for an anoxic, Fe(II)-rich Archean and Paleoproterozoic ocean and high atmospheric CO2 contents. It has been proposed, however, that microbial Fe cycling dominates the chemical and isotopic compositions of IF carbonates, suggesting less direct applicability as an oceanic proxy. Here were use an isotope tracer that is not affected by biological processes or isotopic fractionation, the radiogenic 87Rb-87Sr system, to test the applicability of IF carbonates as a paleoenvironmental proxy. We focus on the 2.5 Ga Campbellrand platform, Transvaal Basin, South Africa, that records a shift from Ca-Mg carbonates to IF carbonates during a marine transgression. When coupled with previously determined Fe, C, and O isotope compositions, it becomes clear that the IF carbonates studied here do not reflect seawater compositions, but instead record extensive microbial Fe cycling in the soft sediment prior to lithification. These results question the use of IF carbonates to infer seawater compositions and paleoenvironmental conditions, including estimates for atmospheric CO2 contents. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.