Abstract
Manganese (Mn) oxidation in marine environments requires oxygen (O2) or other reactive oxygen species in the water column, and widespread Mn oxide deposition in ancient sedimentary rocks has long been used as a proxy for oxidation. The oxygenation of Earth's atmosphere and oceans across the Archean-Proterozoic boundary are associated with massive Mn deposits, whereas the interval from 1.8–1.0 Ga is generally believed to be a time of low atmospheric oxygen with an apparent hiatus in sedimentary Mn deposition. Here, we report geochemical and mineralogical analyses from 1.1 Ga manganiferous marine-shelf siltstones from the Bangemall Supergroup, Western Australia, which underlie recently discovered economically significant manganese deposits. Layers bearing Mn carbonate microspheres, comparable with major global Mn deposits, reveal that intense periods of sedimentary Mn deposition occurred in the late Mesoproterozoic. Iron geochemical data suggest anoxic-ferruginous seafloor conditions at the onset of Mn deposition, followed by oxic conditions in the water column as Mn deposition persisted and eventually ceased. These data imply there was spatially widespread surface oxygenation ~1.1 Ga with sufficiently oxic conditions in shelf environments to oxidize marine Mn(II). Comparable large stratiform Mn carbonate deposits also occur in ~1.4 Ga marine siltstones hosted in underlying sedimentary units. These deposits are greater or at least commensurate in scale (tonnage) to those that followed the major oxygenation transitions from the Neoproterozoic. Such a period of sedimentary manganogenesis is inconsistent with a model of persistently low O2 throughout the entirety of the Mesoproterozoic and provides robust evidence for dynamic redox changes in the mid to late Mesoproterozoic.
Original language | English |
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Pages (from-to) | 28-43 |
Number of pages | 16 |
Journal | Geobiology |
Volume | 21 |
Issue number | 1 |
Early online date | 27 Sept 2022 |
DOIs | |
Publication status | Published - Jan 2023 |
Bibliographical note
This research was funded by the Australian Science and Industry Endowment Fund (SIEF) as part of The Distal Footprints of Giant Ore Systems: UNCOVER Australia Project (RP04-063)—Capricorn Distal Footprints. EAS also thanks the donors of The American Chemical Society Petroleum Research Fund for partial support of this research (61017-ND2).Data Availability Statement
The data that supports the findings of this study are available in the Supplementary Material (Appendices S1 and S2, Tables S1 and S2) of this article.Keywords
- atmospheric oxygenation
- Capricorn Oregon
- iron speciation
- manganese
- Mesoproterozoic
- supergene ore deposits