Did major changes in the stable-isotope composition of Proterozoic seawater occur?

Abstract

Research Article| March 01, 1990 Did major changes in the stable-isotope composition of Proterozoic seawater occur? J. W. Burdett; J. W. Burdett 1Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882 Search for other works by this author on: GSW Google Scholar J. P. Grotzinger; J. P. Grotzinger 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Search for other works by this author on: GSW Google Scholar M. A. Arthur M. A. Arthur 1Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882 Search for other works by this author on: GSW Google Scholar Geology (1990) 18 (3): 227–230. https://doi.org/10.1130/0091-7613(1990)018<0227:DMCITS>2.3.CO;2 Article history first online: 02 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 J. W. Burdett, J. P. Grotzinger, M. A. Arthur; Did major changes in the stable-isotope composition of Proterozoic seawater occur?. Geology 1990;; 18 (3): 227–230. doi: https://doi.org/10.1130/0091-7613(1990)018<0227:DMCITS>2.3.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 SocietyGeology Search Advanced Search Abstract Early Proterozoic marine carbonates of the Rocknest Formation (1.93-1.89 Ga) have very depleted δ18O values (about 8‰) relative to younger, Late Proterozoic marine carbonates that formed in similar depositional environments. Two isotopic trends are superimposed on the data for open-marine components. The first involves stabilization of tidal-flat sediments during early, possibly reflux-type dolomitization by evaporative pore fluids enriched in δ18O The second trend toward isotopically light δ18O values was established during dolomitization of open-marine facies in contact either with meteoric waters (mixing zone) or under conditions of higher temperatures during burial. This resulted in precipitation of blocky, pore-occluding cements.The isotopically most enriched ooids are the best preserved normal marine components and may suggest that the δ18O of seawater was about -9.75‰ ±1.0‰ (SMOW) at 1.9 Ga. This composition would require a major change in the balance of high-temperature oxygen isotopic exchange between seawater and basalt and low-temperature weathering in order to explain the 8‰ positive shift in inferred seawater δ18O between 1.9 and 1.0 Ga. Alternatively, the depleted δ18O values represent an approximately 30-35 °C higher temperature of surface waters at 1.9 Ga. The heaviest carbonate δ13C values are +1.75permil;, more enriched than previously reported for the Early Proterozoic on the basis of bulk-rock data. 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.