The impact of postdepositional alteration on iron- and molybdenum-based redox proxies.

Eroglu, Suemeyya, Scholz, Florian, Salvatteci, Renato, Siebert, Christopher, Schneider, Ralph and Frank, Martin (2021) The impact of postdepositional alteration on iron- and molybdenum-based redox proxies. Geology, 49 (12). pp. 1411-1415. DOI 10.1130/G49291.1.

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Supplementary data:


Ratios of (un)reactive iron species, authigenic molybdenum contents (Moauth), and molybdenum isotope compositions (δ98Moauth) in sedimentary rocks are geochemical proxies that are widely used to reconstruct past marine redox states, which have been calibrated in modern marine settings covering oxic to euxinic conditions. However, syn- and postdepositional processes can result in alterations and ambiguities of proxy-derived redox signals that can challenge the validity of paleoreconstructions. We present new data from modern organic-rich sediments of two oxygen minimum zone settings in the Gulf of California and the Peruvian margin. The results show that Mo is fully immobilized shortly after deposition by reaction with hydrogen sulfide (H2S) produced during organoclastic sulfate reduction. Thus, any H2S produced deeper in the sediment (e.g., by sulfate reduction coupled to anaerobic methane oxidation) leaves the initially deposited Mo concentrations and δ98Mo signatures unaltered, which supports the robustness of Mo-based redox proxies. In contrast, the Fe speciation data reveal continued pyritization due to constant exposure of Fe minerals to H2S. Importantly, both Fe bound to oxides and carbonates (highly reactive Fe) and also poorly reactive Fe (e.g., sheet silicates) undergo pyritization during early diagenesis. This process generates Fe-based proxy signatures that falsely imply ferruginous or euxinic conditions.

Document Type: Article
Keywords: iron species, molybdenum isotopes, past redox states, postdepositional alteration, Gulf of California, Peruvian margin, oxygen minimum zones
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 754
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Kiel University
Main POF Topic: PT2: Ocean and Cryosphere
Refereed: Yes
Open Access Journal?: No
Publisher: GSA (Geological Society of America)
Projects: SFB754, ICONOX
Date Deposited: 20 Aug 2021 11:09
Last Modified: 08 Feb 2023 09:43

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