Sulfur isotope variability in biogenic pyrite; reflections of heterogeneous bacterial colonization?

Abstract

Other| December 01, 1998 Sulfur isotope variability in biogenic pyrite; reflections of heterogeneous bacterial colonization? Matthew J. Kohn; Matthew J. Kohn Lawrence Livermore National Laboratory, Institute for Geophysics and Planetary Physics, Livermore, CA, United States Search for other works by this author on: GSW Google Scholar Lee R. Riciputi; Lee R. Riciputi Oak Ridge National Laboratory, United States Search for other works by this author on: GSW Google Scholar Debra Stakes; Debra Stakes Monterey Bay Aquarium Research Institute, United States Search for other works by this author on: GSW Google Scholar Daniel L. Orange Daniel L. Orange University of California at Santa Cruz, United States Search for other works by this author on: GSW Google Scholar Author and Article Information Matthew J. Kohn Lawrence Livermore National Laboratory, Institute for Geophysics and Planetary Physics, Livermore, CA, United States Lee R. Riciputi Oak Ridge National Laboratory, United States Debra Stakes Monterey Bay Aquarium Research Institute, United States Daniel L. Orange University of California at Santa Cruz, United States Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X GeoRef, Copyright 2004, American Geological Institute. American Mineralogist (1998) 83 (11-12_Part_2): 1454–1468. https://doi.org/10.2138/am-1998-11-1234 Article history First Online: 02 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 Matthew J. Kohn, Lee R. Riciputi, Debra Stakes, Daniel L. Orange; Sulfur isotope variability in biogenic pyrite; reflections of heterogeneous bacterial colonization?. American Mineralogist 1998;; 83 (11-12_Part_2): 1454–1468. doi: https://doi.org/10.2138/am-1998-11-1234 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 SocietyAmerican Mineralogist Search Advanced Search Abstract The top 20 cm of sediments at active cold seeps in Monterey Bay, coastal California, contain framboidal pyrite that occurs as infillings and pseudomorphs of the chambers of the tests of foraminifera and rarely as irregularly shaped grains. Sulfur isotope compositions obtained with the ion microprobe show depletions in 34 S (delta 34 S = -41 to -5 per mil, CDT), and large variations both within and among these pyrite grains. Intergranular differences in delta 34 S values in the same sediment are as large as 35 per mil, and intragranular zoning reaches 15 per mil. Zoning is regular in some grains, with systematic isotope changes from core to rim or from one foraminiferal chamber to another, but irregular in others. The regular zoning is consistent with an increase in 34 S through time. Backscattered-electron imaging reveals three types of pyrite: isolated framboids in a porous aggregation ("PF-pyrite"), agglomerated framboids with cementing interstitial pyrite ("F+I-pyrite"), and recrystallized pyrite with isolated relicts of framboids ("RF-pyrite"). In individual grains, RF-pyrite cores grade into F+I-pyrite toward grain rims, and F+I-pyrite grades into PF-pyrite at the grain edges. These textures are consistent with a paragenetic sequence whereby framboids first agglomerate (PF-pyrite), then cement (F-I-pyrite), and finally recrystallize (RF-pyrite). The delta 34 S values of RF-pyrite are generally lower than that of F+I-pyrite; if the paragenetic sequence is correct, then this trend parallels the regular core-rim isotopic zoning observed in some grains. The implied increase in delta 34 S with time is consistent with Rayleigh fractionation of sulfur in a closed system. Bacteria are intimately involved in the production of pyrite from our samples, and heterogeneous colonization by bacteria provides a simple explanation for the sulfur isotope heterogeneity among and within grains: The foraminifera provide open space for colonization and local nutrients for bacterial growth, whereas the cell walls of the bacteria may provide a local nucleation site for sulfides. If so, then initial colonization is reflected in lower delta 34 S values, whereas later bacterial emigration to other foraminifera chambers is indicated by higher delta 34 S values. 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.