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ORIGINAL RESEARCH article

Front. Mar. Sci.
Sec. Marine Biogeochemistry
Volume 11 - 2024 | doi: 10.3389/fmars.2024.1439471

Iron species and sulfur isotopic compositions of authigenic pyrite in deep-sea sediments at southern Hydrate Ridge, Cascadia margin (ODP Leg 204): Implications for non-steady-state depositional and diagenetic processes

Provisionally accepted
Chenhui Liu Chenhui Liu 1,2Shao-Yong Jiang Shao-Yong Jiang 3*Xin Su Xin Su 4Xiaopeng Bian Xiaopeng Bian 5Hai Ding Hai Ding 6Da Li Da Li 7Tao Yang Tao Yang 2
  • 1 Laoshan Laboratory, Qingdao, China
  • 2 Nanjing University, Nanjing, Jiangsu Province, China
  • 3 China University of Geosciences Wuhan, Wuhan, Hubei Province, China
  • 4 China University of Geosciences, Beijing, Beijing Municipality, China
  • 5 University of Southern California, Los Angeles, California, United States
  • 6 Anhui Provincial Bureau of Coal Geology, Hefei, China
  • 7 Nanjing Normal University, Nanjing, Jiangsu Province, China

The final, formatted version of the article will be published soon.

    Two accretionary sediment sequences from Sites 1245 and 1252 recovered during Ocean Drilling Program (ODP) Leg 204 at southern Hydrate Ridge were investigated to explore the response of geochemical partitioning of iron and sulfur isotopic composition of authigenic pyrite to non-steadystate depositional and diagenetic scenarios. Five iron species were characterized by a modified sequential extraction procedure that covers almost all iron-bearing minerals in sediment cores, including: (1) iron-bearing carbonates, mainly siderite; (2) ferric (hydr)oxides, probably ferrihydrite and/or lepidocrocite; (3) magnetite; (4) iron-bearing silicates; and (5) pyrite. Highly reactive iron has been accumulated for a long-term steady-state history and its pyritization, to varying degrees, is limited by availability of dissolved sulfide. This causes pyrite and siderite occurred in the same sedimentary layer and shows an inverse relationship between their concentrations. From this, their proportions to highly reactive iron can be chosen for evaluating the degree of sulfidization. A significant change in sulfur isotopic composition of pyrite (-42.4 to +16.8‰ VCDT) indicates that the steady-state conditions are dramatically limited, where the δ 34 S values higher than -20‰ may result from an upward shift of SMT zone close to the seafloor or a sudden, massive depositional event. To explain the downcore sulfidization effects and pyrite δ 34 S values, we developed two categories of conceptual scenarios based on variations in sedimentation rate and methane flux. The geochemical features similar to those derived from each scenario were searched in the sediment columns and the non-steady-state events behind the scenarios were proved to be consistent with the real observations. Thus, iron species and pyrite δ 34 S values can be regarded as a proxy to differentiate different non-steady-state depositional and diagenetic controls on the sedimentary record.

    Keywords: iron species, authigenic pyrite, Sulfur Isotopes, Non-steady-state, Hydrate Ridge, ODP Leg 204

    Received: 28 May 2024; Accepted: 04 Jul 2024.

    Copyright: © 2024 Liu, Jiang, Su, Bian, Ding, Li and Yang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Shao-Yong Jiang, China University of Geosciences Wuhan, Wuhan, 430074, Hubei Province, China

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