Paleoproterozoic manganese oxide precipitation in oxic seawater surface and reductive enrichment in anoxic seafloor

Santos, Felipe Holanda dos; Amaral, Wagner da Silva; Fru, Ernest Chi; Souza, Ana Clara Braga de; Bosco-Santos, Alice

doi:10.1016/j.chemgeo.2021.120655

Cited by 4 publications

(2 citation statements)

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“…It is possible that the metamorphosed assemblages of graphite minerals and manganese silicates, respectively, represent organic-rich precursors that were incorporated into manganese silicates during diagenesis. It is suggested that such early burial takes place in a redox-strati ed marine environment, as both oxidized and reduced manganese mineral phases are present 30,31 .…”

Section: Discussionmentioning

confidence: 99%

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The origin and fate of organic carbon in graphite-manganese bearing rocks and implications for the Lomagundi-Jatuli Event

Santos,

Amaral,

Filho

et al. 2024

Preprint

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Our study helps to unravel the complexity of the Lomagundi-Jatuli event, the largest and longest positive carbon isotope excursion ever recorded on the Earth's surface, by providing a unique view of Paleoproterozoic graphitic rocks from the Borborema province of Northeastern Brazil. Through detailed mineralogical, textural, chemical and isotopic analyses, we bring a new perspective that challenges existing views of the global impact of the Lomagundi-Jatuli event. Graphite crystals with distinctive textural features occur in association with silicate and oxidised manganese ores, manganese quartzites, garnetites, and gneisses. The graphites were crystallised at temperatures up to 634ºC, consistent with amphibolite facies metamorphism, according to Raman thermometry. An average carbon content of 2.1 wt%, with δ13C values ranging from -15.0 to -21.5‰, is indicated by whole-rock geochemistry and carbon isotopic composition. Based on these results, our study proposes that these graphitic rocks may represent remnants of organic matter, possibly derived from bacterial biomass associated with manganese-rich sediments, preserved under reducing environmental conditions. Biological mediation on the origin of silicates is suggested by the close relationship between reduced manganese silicates and graphite. These constraints indicate that Paleoproterozoic graphite-rich rocks represent an important but overlooked reservoir of organic carbon that was partially degassed during the metamorphism of organic-rich sequences. Overall, this research highlights the complex interplay between organic carbon, manganese-rich rocks and Earth's evolutionary processes during the Lomagundi-Jatuli event.

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Section: Discussionmentioning

confidence: 99%

“…Several graphitic sequences occur in association with Mn-rich rocks for at least 70 km along a N-NE trending linear belt within the Paleoproterozoic units of the Northern Borborema province 16,30,31 . For this study, we use the Lagoa do Riacho manganese deposit within the graphite and manganese mineralisation trend (Figure 1C).…”

Section: Introductionmentioning

confidence: 99%