Gilleaudeau, GJ, Sahoo, SK, Ostrander, CM et al. (4 more authors) (2020) Molybdenum isotope and trace metal signals in an iron-rich Mesoproterozoic ocean: A snapshot from the Vindhyan Basin, India. Precambrian Research, 343. 105718. ISSN 0301-9268
Abstract
Fundamental questions persist regarding the redox structure and trace metal content of the Mesoproterozoic oceans. Multiple lines of evidence suggest more widespread anoxia in the deep oceans compared to today, and iron speciation indicates that anoxia was largely accompanied by dissolved ferrous iron (ferruginous conditions) rather than free sulfide (euxinia). Still, exceptions exist—euxinic conditions have been reported from some ocean margin and epeiric sea settings, and oxic conditions were reported in one deeper water environment and are also known from shallow waters. Constraining the temporal evolution of Mesoproterozoic marine redox structure is critical because it likely governed redox-sensitive trace metal availability, which in turn played a significant role in marine diazotrophy and the evolution of early eukaryotes. Here, we present a new, multi-proxy geochemical dataset from the ~1.2 Ga Bijaygarh Shale (Kaimur Group, Vindhyan Basin, India) emphasizing total organic carbon, iron speciation, and trace metal concentrations, as well as sulfur, nitrogen, and molybdenum isotopes. This unit was deposited in an open shelf setting near or just below storm wave base. Taken together, our data provide a unique snapshot of a biologically important shallow shelf setting during the Mesoproterozoic Era, which includes: 1) locally ferruginous waters below the zone of wave mixing, 2) muted enrichment of trace metals sensitive to general anoxia (e.g., chromium) and variable enrichment of trace metals sensitive to euxinia (e.g., molybdenum and, to a lesser extent, vanadium), 3) general sulfate limitation, and 4) nitrogen fixation by molybdenum-nitrogenase and a dominantly anaerobic nitrogen cycle in offshore settings. Differential patterns of trace metal enrichment are consistent with data from other basins and suggest a largely anoxic ocean with limited euxinia during the Mesoproterozoic Era. Our new molybdenum isotope data—the first such data from unambiguously marine shales deposited between 1.4 and 0.75 Ga—record values up to +1.18 ± 0.12‰ that are analogous to data from other Mesoproterozoic shale units. Ultimately, this study provides a broad, multi-proxy perspective on the redox conditions that accompanied early eukaryotic evolution.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2020 Elsevier B.V. All rights reserved. This is an author produced version of an article published in Precambrian Research. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | Mesoproterozoic; Redox; Ocean oxygenation; Molybdenum isotopes; Ferruginous conditions |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Earth Surface Science Institute (ESSI) (Leeds) |
Funding Information: | Funder Grant number Royal Society WM150108 Leverhulme Trust Not Known |
Depositing User: | Symplectic Publications |
Date Deposited: | 27 Mar 2020 16:21 |
Last Modified: | 27 Mar 2021 01:39 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.precamres.2020.105718 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:158766 |