Liu, Y, Zhao, M, He, T et al. (2 more authors) (2023) Formation of molar tooth structures in low sulfate Precambrian oceans. Geochimica et Cosmochimica Acta, 354. pp. 62-73. ISSN 0016-7037
Abstract
Molar tooth structures (MTS) comprise calcite microspar-filled voids in fine-grained shallow-water carbonate, and were commonly formed in the Mesoproterozoic and early Neoproterozoic. However, the origin of MTS and links between the temporal distribution of MTS and contemporaneous seawater chemistry remains poorly understood. Here we report elemental and isotopic data for MTS and host rocks from the Mesoproterozoic Gaoyuzhuang Formation (∼1,600–1,550 Ma), North China Craton. The results reveal similar C, S and Sr isotope signatures between MTS and host rocks, which are close to the isotopic compositions of contemporaneous global seawater, suggesting an early diagenetic, seawater-buffered origin for MTS. A small sulfur isotopic fractionation between seawater sulfate and pyrite (Δ³⁴SCAS-Py) of 4.1 ± 1.5‰ in host rocks is consistent with previously reported data, providing support for sub-millimolar sulfate concentrations in Mesoproterozoic seawater. Our observations suggest that the widespread occurrence of MTS through the Mesoproterozoic to early Neoproterozoic was broadly linked to sulfate scarcity in the ocean. We further propose that in Proterozoic oceans with sub-millimolar seawater sulfate concentrations, where aerobic and anaerobic methane oxidation was likely inhibited, methane produced via methanogenesis may have been more prone to accumulate in sediments, creating voids during escape. The absence of MTS across periods of higher sulfate concentrations during the Palaeoproterozoic and after the mid-Neoproterozoic, suggests that elevated sulfate concentrations promoted consumption of methane via anaerobic methane oxidation, thus preventing methane accumulation and the formation of sediment voids. Rapid lithification of the substrate as a result of elevated carbonate saturation may have also hindered the formation of MTS during these intervals. The link between MTS and changes in both oceanic sulfate levels and benthic methane fluxes gives a new perspective on temporal fluctuations in Earth’s redox state through time.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2023 Elsevier Ltd. This is an author produced version of an article published in Geochimica et Cosmochimica Acta. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | Molar tooth structures; Seawater-buffered diagenesis; Seawater sulfate; Mesoproterozoic; Precambrian |
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 NERC (Natural Environment Research Council) NE/R010129/1 |
Depositing User: | Symplectic Publications |
Date Deposited: | 19 Jun 2023 14:08 |
Last Modified: | 17 Jun 2024 00:13 |
Published Version: | https://www.sciencedirect.com/science/article/pii/... |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.gca.2023.06.013 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:200537 |