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Constraints on Pyrite precipitation in a Middle Devonian Pyrite bed, Western New York

Borkow, Philip Samuel
http://rave.ohiolink.edu/etdc/view?acc_num=osu1406640370

Abstract Details

2004, Master of Science, Ohio State University, Geological Sciences.
Studies integrating sedimentary geochemistry, diagenesis, and taphonomic experimentation provide new insight into the development of pyrite concretions and pyrite coatings surrounding organisms. Pyrite is responsible, under certain circumstances, for the preservation of mineralized body parts and the exceptional preservation of nonmineralized tissue. As now interpreted, at least three factors influence the preservation of organisms by pyrite: 1) the Eh of aqueous environments surrounding and their effects on dissolved pyrite saturation; 2) the combined total of sulfide ions and dissolved reactive iron in sediment pore waters and microenvironments; and 3) the presence of reactive biofilms (microbial assemblages or consortia) associated with decaying organic material. Under low oxygen conditions, breakdown of organic matter allow for the release of sulfide ions into sediment pore waters, where they combine with reactive iron ions to form iron sulfides with various textures and proximities to the surface of a decaying mass. A link is hypothesized between Eh levels, the overall concentration of pyritic components (e.g., sulfur and iron), and the development of textures that either hinder or promote preservation of nonmineralized parts in the fossil record. This work builds on a double reservoir model (involving sulfur and iron soruces) for explaining pyrite precipitation associated with deposition associated with decaying organic material by considering also the role of microbial processes. The extent of pyrite precipitation and the types of organic material preserved by FeS2 seem to be related to the development of either reactive bacterial coatings that were in direct contact with decaying organic tissues or microbial assemblages (including bacteria and probably fungi) that formed halos around decaying organic tissue. A new modified double reservoir model explains the precipitation of pyrite under the influence of both the Eh of the macroenvironment and the effects of Eh and ion transport boundaries created by microbial tiering inside the consortium. Precipitation of concretionary material indicates a decaying mass surrounded by a microbial consortium that induced internal reducing conditions. Precipitation is hypothesized to occur either below the oxic-anoxic boundary, with the effect of macroenvironmental Eh predominating in importance, or inside of a microbially-induced low-Eh microenvironment occurring at or above the oxic-anoxic boundary. Low Eh levels (e.g., completely anoxic) create an undersaturation of dissolved pyrite, leading to isolated spots of pyrite nucleation with preferential crystal growth. In contrast, microbial consortia occurring at the oxic-anoxic boundary and lacking facultative anaerobes would be affected most by the Eh of the surrounding macroenvironment. With slightly raised oxygen levels at the boundary, dissolved pyrite would be supersaturated, facilitating impregnation or coating of organic tissue by dissolved iron sulfides and crystal nucleation, developing small (<0.25 µm) pyrite crystals preferentially involved in fossilization of nonmineralized tissues.
Loren E. Babcock (Advisor)
Anne E. Carey (Committee Member)
Matthew R. Saltzman (Committee Member)
105 p.
Geological

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Citations

  • Borkow, P. S. (2004). Constraints on Pyrite precipitation in a Middle Devonian Pyrite bed, Western New York [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406640370

    APA Style (7th edition)

  • Borkow, Philip. Constraints on Pyrite precipitation in a Middle Devonian Pyrite bed, Western New York. 2004. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1406640370.

    MLA Style (8th edition)

  • Borkow, Philip. "Constraints on Pyrite precipitation in a Middle Devonian Pyrite bed, Western New York." Master's thesis, Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406640370

    Chicago Manual of Style (17th edition)

osu1406640370
137
© 2004, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.