
==== Front
Sci Rep
Sci Rep
Scientific Reports
2045-2322
Nature Publishing Group UK London

39261553
71877
10.1038/s41598-024-71877-3
Article
The origin and fate of organic carbon in graphite–manganese bearing rocks and implications for the Lomagundi–Jatuli Event
Santos Felipe Holanda felipeholanda@ufc.br

12
da Silva Amaral Wagner 2
Filho Evilarde Carvalho Uchôa 13
de Andrade Caxito Fabrício 4
Souza Ana Clara Braga 1
Martins Douglas Teixeira 5
de Andrade Feitosa Brenda 6
1 https://ror.org/03srtnf24 grid.8395.7 0000 0001 2160 0329 Departamento de Geologia, Universidade Federal do Ceará (UFC), Fortaleza, Ceará Brazil
2 grid.411087.b 0000 0001 0723 2494 Instituto de Geociências, Universidade Estadual de Campinas (UNICAMP), Campinas, São Paulo Brazil
3 https://ror.org/04ry0c837 grid.452625.2 0000 0001 2175 5929 Serviço Geológico do Brasil (SGB), Fortaleza, Ceará Brazil
4 https://ror.org/0176yjw32 grid.8430.f 0000 0001 2181 4888 Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, Minas Gerais Brazil
5 https://ror.org/033qmpy33 grid.472959.4 0000 0004 0370 5057 Instituto Federal do Piauí, Paulistana, Piauí Brazil
6 https://ror.org/04603xj85 grid.448725.8 0000 0004 0509 0076 Universidade Federal do Oeste do Pará, Santarém, Pará Brazil
11 9 2024
11 9 2024
2024
14 2119112 4 2024
2 9 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
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 provide support to elevated primary productivity and large-scale organic carbon burial during 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 634 °C, consistent with amphibolite facies metamorphism, according to Raman thermometry. An average total 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, respectively. 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 in a redox-stratified marine setting. 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 provides new insights for the enigmatic emergence of the Lomagundi–Jatuli event, highlighting the intricate interplay among organic carbon, manganese-rich rocks and Earth's evolutionary processes during this period.

Keywords

Paleoproterozoic era
Borborema Province
Organic matter
Carbon isotope
Raman thermometry
Subject terms

Geochemistry
Geology
Precambrian geology
National Council for Scientific and Technological Development (CNPq)409918/2023-7 407255/2022-2 408815/2021–3 Santos Felipe Holanda da Silva Amaral Wagner de Andrade Caxito Fabrício Instituto Serra PilheiraSerra-1912-31510 de Andrade Caxito Fabrício issue-copyright-statement© Springer Nature Limited 2024
==== Body
pmcIntroduction

The Earth underwent major climatic, tectonic and biological changes about 2.2 billion years ago. This period coincides with the Lomagundi–Jatuli Event (LJE), the largest and most prolonged positive carbon isotope excursion documented at the Earth’s surface, with δ13C ranging from about + 5 to + 30‰1–4. Moreover, this event is directly linked to a significant rise in oxygen levels in the ocean–atmosphere system, which suggests that the Earth experienced widespread organic carbon burial4,5. However, there is still extensive ongoing debate regarding the primary causes and the mechanisms that give rise to the LJE, as well as its spatial and temporal extent in the geological record.

The most widely accepted explanation or the “canonical model” for the anomalous increase in seawater δ13CDIC, is an increase in primary productivity resulting in a higher fraction of buried organic carbon4,5. However, there are alternative models that have been proposed which do not necessarily require significant changes in the fraction of carbon buried as organic matter relative to the dissolved inorganic reservoir. One notable approach, suggested by Eguchi et al.6,7, involves a combination of factors such as increased volcanism resulting from the supercontinent break-up and the subduction of significant amounts of Corg and Ccarb. Several models have been proposed to explain the LJE. Other models have proposed that the precipitation of authigenic carbonate minerals in sedimentary layers through processes that exhibit notable fractionations (e.g., methanogenesis) in carbon isotopes8–10 could also be responsible. Moreover, there are hypotheses that challenge the magnitude of disturbance to the carbon cycle during the LJE, as contended by Schidlowski et al.1, Melezhik et al.2 and Mayika et al.11. Although these models differ in the nature and depositional context of phases that sequester excess 12C, the role of organic carbon burial remains a key issue in elucidating these discrepancies.

A major criticism of the canonical LJE model is the lack of geological evidence for organic-rich rocks in the Palaeoproterozoic era12–14. However, the global occurrence (Fig. 1A) of graphite-rich rocks chrono-correlated with the LJE reinforces the idea that large amounts of organic matter were buried during this time interval15. Furthermore, detailed analysis of some of these occurrences indicate that they are associated with Mn-rich rocks that are temporally related to the Great Oxidation Event (GOE)16. High concentrations of oxygen are known to be required in the ocean–atmosphere system for the precipitation of Mn oxides17,18. In this context, understanding the origin and fate of these organic-rich associations may help to elucidate not only the role of these rocks in the global carbon cycle, but also the control that they may have exerted on atmospheric oxygenation through time.Fig. 1 General overview of the study area. (A) Distribution of some Paleoproterozoic organic-matter rich-successions in South America and Africa. Excepting South Africa, all deposits were included in a hypothetical Paleoproterozoic (Atlantica?) paleocontinental mass (top left corner). References for the organic-matter rich successions are as follows: (A) Santos et al.30, Fragomeni et al.32; (B) Silva and Xavier33; (C) Miranda et al.34; (D) Mesquita et al.35; (E) Klein et al.36,37; (F) Kríbek et al.38; (G) Canfield et al.39. (B) Geological framework of the Northern Borborema Province highlighting study area in white star. MCD Médio Coreaú Domain, CCD Ceará Central Domain, TBL Transbrasiliano Lineament, OASZ Orós-Aiuaba Shear Zone, PSZ Patos Shear Zone. (C) Local map of the Lagoa do Riacho manganese deposit (left) and schematic cross-section constructed from the core Ocr-1 (right) showing the distribution of the manganese-graphite rich lithological groups investigated in the present study. The maps were created using QGIS v3.28 software (https://qgis.org/en/site/). Figure (A) was designed using the ETOPO Global Relief data, available at https://www.ncei.noaa.gov/products/etopo-global-relief-model.

An excellent opportunity to address questions regarding the magnitude of such carbon cycle anomalies could be provided by studying the LJE event in the Paleoproterozoic terrains of South America, such as the Borborema Province in Northeastern Brazil (Fig. 1B), and its relationship with organic-rich rocks. Here, a detailed geochemical and isotopic analysis of graphite-bearing rocks associated with manganese that are about 2.2 Ga old in the Borborema province19 shows that graphite-bearing rocks can be considered when estimating the processes that triggered the LJE event.

General geology of the Borborema Province and the graphite and manganese-bearing rocks

The Borborema Province, located in the Northeastern region of Brazil (Fig. 1B), was adjacent to the West African Congo and São Francisco cratons before the opening of the Atlantic Ocean following the Phanerozoic breakup of western Gondwana19. In this context, the Borborema province represents the western segment of Gondwana19. This province contains a series of metamorphosed Palaeoproterozoic rocks20–22 overlying an Archean tonalite-trondhjemite-granodiorite (TTG) basement23,24. Neoproterozoic granites, supracrustal rocks and shear zones (e.g., Patos, Pernambuco and Transbrasiliano) are also common in this province25,26.

The Borborema Province is divided into three major structural domains, namely (1) the Northern Borborema Province, including the Médio Coreaú, Ceará Central and Rio Grande do Norte domains; (2) the Central Domain; and (3) the Southern Domain. The northern Borborema province, which is the focus of this study, consists of an expressive Rhyacian metavolcanic-plutonic-sedimentary sequence16,20,21,27–29.

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 province16,30,31. For this study, we use the Lagoa do Riacho manganese deposit within the graphite and manganese mineralisation trend (Fig. 1C). The graphite and manganese mineralisation in the Lagoa do Riacho deposit is hosted within the Paleoproterozoic Canindé do Ceará Complex27,29–31 which is composed of paragneisses and schists interbedded with marbles, quartzites, calc-silicate rocks, amphibolites, orthogneisses and manganese and iron formations. Recently, Santos et al.16 carried out a zircon U–Pb geochronological study in the Lagoa do Riacho manganese deposit and concluded that the sedimentary precursors of these mineralisations have a Rhyacian depositional age (2.22–2.05 Ga). These ages are like other manganese deposits such as the Francevillian and Birimian groups in Gabon and Ghana respectively, and those on the South American platform (e.g. Serra do Navio, Azul, Buritirama and Morro da Mina).

Results

Mineralogy and textural features of the graphite-rich rocks

Graphite crystals occur in silicate-manganese ore (SMO), oxidized manganese ore (OMO), garnetites, quartzites and pelitic gneisses. Several minerals, including tephroite, spessartine-garnet, manganese-pyroxene and rhodochrosite, are associated with graphite crystals in the SMO and OMO lithologies (Fig. 2A). The most abundant silicate minerals associated with graphite in these lithology groups are manganese-pyroxene and spessartine-garnet (Fig. 2B; Supplementary Figs. 1, 2). Manganese-pyroxene crystals can grow up to 6 mm in size and are occasionally replaced by manganese-amphibole, in both cases graphite occurs as an inclusion within these crystals. Tephroite and carbonate minerals are present in small quantities, also in association with graphite, and account for less than 5%. Other minerals of interest in this rock include sulphides, also associated with pentlandite, chalcopyrite, cobaltite and pyrite (Fig. 2C,D; Supplementary Fig. 1), as well as pyrophanite and manganese oxides and hydroxides, such as pyrolusite, cryptomelane and todorokite (Fig. 2E,F; Supplementary Fig. 3). In general, graphite occurs in the rock matrix through foliation planes and is in direct contact with the silicate minerals (Fig. 2G).Fig. 2 Transmitted (A,B,G,H,I); A is under cross polarized and all the others are plane polarized), reflected (E) light photomicrographs, and BSE images (C,D,F) showing petrographic aspects of the graphite and manganese-bearing rocks. (A) Manganese-pyroxene (Pxmn) porphyroblast in contact with minor graphite crystals (Gph). (B) Spessartine (Spss) porphyroblast in a matrix of manganese-oxide (Mn–O) and graphite. (C) Pentlandite (Pt) in contact with graphite flakes. (D) Euhedral cobaltite (Cb) in contact with spessartine and graphite in a silicate matrix. (E) Pyrolusite (Pyro) and todorokite (Td) crystals crosscutting a matrix of manganese-pyroxene. (F) Detailed view of the manganese-oxide-hydroxide minerals (Pyrolusite, todorokite and cryptomelane-Cml) replacing manganese-pyroxene. (G) Graphite along foliation planes in contact with spessartine and quartz (Qtz) agglomerates. At the top of the image is a manganese-rich domain. (H) Graphite (Gph) flakes aligned with a well-developed foliation in contact with spessartine. Two textural graphite types are shown, a “pocket” graphite with low crystallinity and a well-ordered graphite (more common). (I) Graphite flakes in an assemblage composed of biotite (Bt), garnet (Gt), feldspar (Fsp) and quartz along the foliation plane.

A distinctive feature of the garnetite, which is also common in the quartzite, is the presence of fine, millimetre-sized graphite flakes aligned with the rock matrix, indicating primary sedimentation (S0//S1; sedimentary bedding parallel to metamorphic foliation) (Fig. 2G,H). The Garnetite lithological group is also characterised by a thinly banded rock, typically only a few millimetres thick, with alternating layers of garnet and quartz-rich material. Mica and graphite can be found in the interstitial areas near the garnet. Carbonate and sulphide minerals are also present in minor amounts.

The graphitic gneiss consists mainly of minerals such as quartz, feldspar, cordierite, biotite, muscovite, garnet and sillimanite. Graphite flakes are abundant throughout the rock and are distributed parallel to the primary foliation (Fig. 2I). Usually, the mineral assemblage is laminated, some with granoblastic domains of quartz, feldspar and cordierite, others with lepidoblastic domains of muscovite and biotite.

Graphite micro-Raman thermometry

Peak metamorphic temperatures for graphite in the OMO, SMO and garnetite rocks range from 580–652 °C, 509–664 °C and 597–634 °C respectively (Supplementary Information Table S1). These ranges are all within amphibolite facies and are consistent with potential thermometer error, although they are relatively wide. The raman spectra of the analysed graphite crystals are shown in Fig. 3 and a detailed analysis of the micro-Raman thermobarometric results is given in Supplementary Information Table S1 and S2.Fig. 3 Textural features and Raman spectra of the analyzed graphite crystals.

Carbon and manganese geochemistry

The carbon isotope ratio (δ13C) study was carried out on twenty-two (22) samples (Fig. 4A, Supplementary Information Table S3). The δ13C values ranged from − 15.0 to − 21.5‰ with an average of − 17.5‰ relative to the VPDB standard. Sample Ocr-24A had the highest value (− 15.0‰) and sample Ocr-29 had the lowest value (− 21.5‰). Graphitic carbon contents are presented in Fig. 4B and Supplementary Information (Table S3) and consist of thirty-two (32) results. Sample OCR-38 has a carbon content of 1% (the lowest value) and sample OCR-52 has a content of 3.19% carbon (the highest value). The mean carbon content was 2.1%. Figure 4C,D and Supplementary Information Table S3 also show the whole-rock MnO (wt%) content and Raman temperature (T °C) for this study.Fig. 4 General geochemistry dataset. (A) δ13C values of whole-rock samples from different graphite-bearing units at Lagoa do Riacho Deposit. For the box and whisker plots, the boxes extend to the interquartile range and the whiskers extend to furthest data point up to 1.5 times the interquartile range (IQR). (B) Variability of δ13C ratios with amount of graphitic carbon. (C) Percentage of whole-rock manganese content (wt%) in the samples with the δ13C ratios. (D) Comparison between Raman temperature from some selected graphite-rich lithologies and the δ13C ratios.

Discussion

Where does organic carbon come from?

Organic-rich rocks can be found in metamorphosed Palaeoproterozoic sequences throughout the world38–41. In some cases, the conversion of organic matter to graphite has often been the result of changes in temperature and pressure during regional metamorphism. In our study, the correlation of graphitisation temperatures with those of the host rocks30 provides evidence for a primary organic reservoir rather than a secondary or external reservoir for these graphite-bearing sequences. For example, it is expected that the same P–T metamorphic conditions would be imprinted in pelitic metasedimentary rocks associated with genetically related organic matter from an ancient basin involved in a continental collision. Therefore, in these cases where the metamorphic conditions are paired, it is unlikely that the graphite has an origin related to the precipitation of hydrothermal fluids. Moreover, the way in which the graphite crystals are arranged in the rock, distributed in an ordered planar array, also supports a biological origin40–42 (Fig. 2).

It is also noteworthy that these graphitic rocks have δ13C values between − 27 and − 15‰, within the expected range for a biological origin (Fig. 5). However, isotopically heavier values of carbon have been observed. This can be explained by devolatilisation of organic carbon during metamorphism. In a sediment originally rich in organic matter, regional orogenic metamorphism leads to a gradual loss of organic compounds through devolatilisation processes43. In this sense, the δ13CV-PDB values of graphitic rocks can be heavier due to the loss of volatile components, such as CO2 and/or CH4, because of the intense burial and metamorphism that the precursor organic matter has undergone. Typically, in contrast to the Phanerozoic era where δ13CV-PDB values are consistently closer to -30‰, the organic-rich rocks of the ancient (Paleoproterozoic) geological record tend to exhibit a wide range in δ13CV-PDB between (− 40 and − 18‰) (e.g., Fig. 5). This is relevant and partly explained by the fact that the rocks of the Phanerozoic era have not been so deeply affected by multiple orogenic events.Fig. 5 δ13C values of whole-rock samples from different graphite-bearing units at Lagoa do Riacho Deposit compared with potential carbon sources as well as values from other flake graphite deposits. Organic, marine and mantle carbon isotope values are from Schidlowski45. Carbon isotopes from fluid-deposited graphite deposits are from Luque et al.46. Borborema Province (This study and Fragomeni et al.32. Rio Itapicuru33. Quadrilátero Ferrífero34. Northeast Tocantis Province35. Gurupi belt36,37. West Africa Craton38. Franceville basin, Gabon39. The compositional range for other regions is as compiled by Zhu et al.47.

Such isotopic ratios tend to become heavier (more enriched in 13C in relation to 12C) as the rock is diagenetically altered and metamorphosed. Some studies have already documented this by showing that the δ13CV-PDB of metamorphic organic matter is heavier than that of non-metamorphic equivalents, with values ranging from − 17 to − 27‰ respectively32. In this sense, the metamorphic conditions achieved by these rocks are likely to be reflected in the heavier carbon isotope values reported here.

Since the graphitic rocks presented here have been heated to temperatures on the order of 700 °C, it is assumed that a large fraction of the original organic matter has been lost during the progressive regional metamorphism. Rayleigh fractionation of metamorphic fluids from an initially homogeneous δ13C reservoir shows CH4 degassing, with δ13C increasing progressively with metamorphic grade, supporting the above interpretation (Fig. 6). Furthermore, preservation of organic matter in the geological record usually requires rapid burial under oxygen-limited conditions (such as anoxic and/or euxinic environments)44. The prevalence of CH4 release (from the precursor organic material) indicates a reducing environment and supports and explains the reason for the preservation of this organic material, which was later transformed into graphite during metamorphism29,30. In this sense, the data presented here suggest that graphite is a remnant of organic matter, possibly derived from bacterial biomass, living in a photic zone associated with reduced manganese sediments and preserved under reducing environmental conditions. Such evidence opens new perspectives for the understanding of the preservation of ancient microorganisms in rocks subject to high-grade metamorphism.Fig. 6 Results of a multicomponent Rayleigh fractionation model for a starting source composition of δ13Csource =  − 29‰, a temperature of 654 °C, and rCH4-CO2 = 0.99. The graphite-fluid and CH4-CO2 fractionation factors at this temperature are from Bottinga48.

The link between manganese, organic-rich rocks and the primary environment in which they were deposited

The close association of reduced manganese silicates with graphite suggests that this mineral assemblage may have resulted from the maturation/recrystallisation of organic/silicate-rich precursors during early diagenesis. Often, the relationship between organic matter and silicate-rich rocks suggests a biologically mediated origin of the silicates that may include Mn or Fe40,41. In this sense, the isotopic composition of organic matter, with δ13CV-PDB values between (− 40 and − 18‰), would reflect biological activity. This activity would have influenced the precipitation of reduced manganese silicates or their precursors. Santos et al.30, based on the occurrence of kutnohorite-like carbonates as inclusions in garnet-spessartine crystals and manganese-pyroxene, pointed that primary silicic marlstones could be the precursors of these metamorphosed manganese-rich silicate rocks. It is believed that these rocks were originally deposited in a redox-stratified marine setting along with organic-rich pelitic sediments between 2.22 and 2.05 Ga16,31. Santos et al.16,30,31 stated that the manganese-graphite bearing rocks in Northeast Brazil would have originally been very similar to the Paleoproterozoic black-shale-hosted Mn sequence from the Franceville Basin39 in Gabon and chrono-correlated to several others manganese-rich successions in Brazil and Africa. It is also interesting to note that the origin of the black shales from the Franceville Basin may be correlated to a global, large-scale organic carbon burial event that took place in the Great Oxidation Event aftermath, during the Lomagundi–Jatuli Event at ca. 2.2–2.0 Ga39.

In addition, early diagenetic or primary microbial Mn4+ and Mn3+ reduction via oxidation of organic matter and precipitation of Mn silicates and carbonates is well documented49–51. For example, during the diagenesis of an organic-rich rock, a group of heterotrophic bacteria can produce a carbon isotope signal that is particularly light. This leads to the negative values of δ13C in manganese minerals51. In other Precambrian organic-rich rocks, such as those found in Akilian rocks of western Greenland, an association between δ13C-depleted graphitic rocks and manganese and silicate minerals has been suggested as a biological proxy52. It has been extensively studied in various Precambrian sedimentary sequences that this mineral association happens due to the diagenetic process of organic matter40,41,53. Furthermore, modern manganese deposits, including carbonaceous shales, cherts, sedimentary carbonates and BIFs, often contain carbonaceous material in addition to reduced manganese silicate40,41,53. The Cantabria region of Spain, where manganese-rich stromatolites were induced by chemolithotrophic Mn-oxidising microbes, provides a modern example of the interplay between microbial organisms and the genesis of manganese deposits54.

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-stratified marine environment, as both oxidized and reduced manganese mineral phases are present30,31.

One point worth noting is the fact that some carbon isotope signals are still preserved in these high-grade metamorphic rocks. Similar examples to those reported in our study include organic-rich metamorphic rocks found in the Archean Saglek Block, Labrador55. Although the origin of these rocks remains controversial56, they do contain possible evidence of early life. However, why the isotopic signature was preserved is a still unresolved question. The presence of silica might be one hypothesis. South Australia’s Ediacaran Member is perhaps a classic example of silica shielding organic material. In this case, the exceptional preservation of the soft-bodied Ediacara biota would have been facilitated by the rapid and early precipitation of siliceous cement. Silicified organic microstructures are also preserved in coccoidal and filamentous organic microfossils, such as in the 1.9-Gyr-old Gunflint Iron Formation from Canada57 and in the ca. 2.4-Gyr-old Turee Creek Group from Western Australia58.

A combination of factors between manganese oxides and silicates is another hypothesis for shielding of organic matter. For example, the very fine size of the manganese-oxide minerals in combination with silica-rich particles may have been responsible for the exceptional preservation of these ancient microorganisms (?). The latter approach is supported by the fact that the graphites are closely associated with the oxide and silicate phases of the manganese-rich minerals. Graphitic crystals occur as flakes distributed along foliation within crystalline rock matrix, unrelated to crosscutting veins and other filling textures.

A hidden organic carbon reservoir and its implications for the global nature of the Lomagundi–Jatuli event

The Lomagund-Jatuli event (LJE) has been conventionally regarded as a period marked by a global restructuring of the carbon cycle, as evidenced by a pronounced positive carbon isotope excursion (δ13C)3,5. This phenomenon has been extensively documented and is interpreted as indicative of an oxygen-rich atmosphere1,3,5,12,39,59. However, perspectives differ, with some arguing that large positive carbon isotope anomalies observed in certain regions may indicate localized transgressive–regressive cycles11 rather than a truly global event. The limited availability of preserved Paleoproterozoic organic-rich sequences in the geological record is a recurring challenge to the global characterization of the Lomagundi–Jatuli event. This paucity has led some researchers to question the feasibility of such a global anomaly based solely on the existing evidence. As a result, alternative carbon reservoirs have been proposed to address and solve this fascinating puzzle. For example, Eguchi et al.6 argued that around 2.5 billion years ago, a tectonic transition resulted in increased volcanic CO2 emissions, which led to increased deposition of carbonates and organic carbon through weathering and the delivery of nutrients to the oceans. Thus, the increased burial of organic-rich rocks would have allowed for the accumulation of oxygen in the atmosphere and, at the same time, an increase in the supply of carbon to subduction zones.

Alternatively, our work indicates for the first time a possible hidden Paleoproterozoic organic carbon reservoir in the form of ancient graphite-rich sequences. For example, the geological terrains of Africa and Brazil contain several organic-rich sequences that have been metamorphosed during the Paleoproterozoic era (from Santos et al.16 and references therein). Based on the above assumptions, we believe that the regional Palaeoproterozoic metamorphism of these carbonaceous rocks might have caused extensive graphitization because of the increased thickness of the colliding landmasses. Hence, the prolonged duration of the Lomagundi event could be attributed to the elevated gross primary organic productivity and efficient sequestration of organic carbon that occurred during the mountain-building period15. This way, our work helps to solve the enduring puzzle of the most significant positive carbon isotope anomaly in the history of our planet. Furthermore, as noted by Parnell et al.15, the presence of Paleoproterozoic graphite deposits around the globe suggests that an unusually high amount of carbon burial may have had a significant impact on Earth's carbon budget following the GOE.

Supporting this view, the association of metamorphosed organic-rich successions with manganese sequences, as reported in this study, reinforces a causal link between manganese-carbonaceous sedimentation and the climatic-biological crisis60. In this approach, the first large-scale Mn accumulations are thought to have occurred at the Great Oxidation Event that followed the Palaeoproterozoic Lomagundi Event, when oxygen levels on Earth exceeded 10–5 PAL12,61. Moreover, around 2.5–2.3 Gy ago, a transition from stagnant/sluggish lid to plate tectonic and/or near-global glaciation (Snowball Earth) increased volcanic CO2 emissions. In contrast, near-global glaciation (Snowball Earth) might have shut down the silicate weathering CO2 sink. At the same time, atmospheric oxygen levels increased, leading to increased deposition of carbonate and organic carbon through increased erosion and weathering of mountain ranges, and a strong nutrient flux into the seas6,7.

Conclusions

Our study sheds light on the origin of organic carbon in metamorphic Palaeoproterozoic strata. The light, negatively fractionated δ13C values obtained from Paleoproterozoic graphite samples from the Borborema Province of NE Brazil and correlation of graphitization temperatures with host rock temperatures indicates a primary organic reservoir, with graphitic rocks likely derived from photic zone bacterial biomass associated with reduced manganese sediments. An early diagenetic or microbial reduction process is suggested by the preservation of carbon isotopic signatures and association with manganese silicates. Furthermore, our study provide support to elevate primary productivity and large-scale organic carbon burial during the Lomagundi–Jatuli event by suggesting a hidden Paleoproterozoic organic carbon reservoir. In this approach, the metamorphosed organic-rich sequences, such as graphite-rich rocks, may represent a significant but previously overlooked reservoir of partially devolatilized organic carbon. This new perspective helps elucidate the complexity of the carbon cycle dynamics of the Earth during critical periods in geologic time.

Methods

Methods are available as electronic Supplementary Information.

Supplementary Information

Supplementary Information.

Supplementary Table S2.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-024-71877-3.

Acknowledgements

This research was part of the first author’s Ph.D. thesis. FHS is grateful to the Federal University of Western Pará (UFOPA) and Geosciences Graduate Program from University of Campinas for support throughout the thesis development, and to geologist Renato Braz Sue (representing Libra Ligas do Brasil company) for providing full access to drill cores and fieldwork assistance. FHS would like to express gratitude to the Society of Economic Geologists (SEG) and CNPq, Brazil (409918/2023-7) for the research grant. WSA is funded by CNPq, under grant number (407255/2022-2). FAC is supported by Project MOBILE, Instituto Serrapilheira (Serra-1912-31510), and by CNPq, through grant number 408815/2021–3. We truly appreciate the comments, suggestions and criticisms from Dongjie Tang and two anonymous reviewers that helped to improve the quality of this manuscript. In addition, we also thank the editorial handling by Professor Chunfang Cai.

Author contributions

F.H.S. designed the study, developed the idea, performed the analyses and wrote the manuscript. All authors discussed the results and participated in manuscript refinement.

Data availability

All data generated or analyzed during this study are included in this published article (and its Supplementary Information files).

Competing interests

The authors declare no competing interests.

Publisher's note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
==== Refs
References

1. Schidlowski M Eichmann R Junge CE Carbon isotope geochemistry of the Precambrian Lomagundi carbonate Province, Rhodesia Geochim. Cosmochim. Acta 1976 40 449 10.1016/0016-7037(76)90010-7
Schidlowski, M., Eichmann, R. & Junge, C. E. Carbon isotope geochemistry of the Precambrian Lomagundi carbonate Province, Rhodesia. Geochim. Cosmochim. Acta 40, 449 (1976).10.1016/0016-7037(76)90010-7
2. Melezhik VA Fallick AE Medvedev PV Makarikhin VV Extreme 13 C Enrichment in ca. 2.0 Ga carb magnesite-stromatolite-dolomite-’red beds’ association in a global context: A case for the world-wide signal enhanced by a local environment Earth-Sci. Rev. 1999 48 1 10.1016/S0012-8252(99)00027-6
Melezhik, V. A., Fallick, A. E., Medvedev, P. V. & Makarikhin, V. V. Extreme 13 C Enrichment in ca. 2.0 Ga carb magnesite-stromatolite-dolomite-’red beds’ association in a global context: A case for the world-wide signal enhanced by a local environment. Earth-Sci. Rev. 48, 1 (1999).10.1016/S0012-8252(99)00027-6
3. Bekker A Karhu JA Kaufman AJ Carbon isotope record for the onset of the Lomagundi carbon isotope excursion in the Great Lakes area, North America Precamb. Res. 2006 148 145 180 10.1016/j.precamres.2006.03.008
Bekker, A., Karhu, J. A. & Kaufman, A. J. Carbon isotope record for the onset of the Lomagundi carbon isotope excursion in the Great Lakes area, North America. Precamb. Res. 148, 145–180 (2006).10.1016/j.precamres.2006.03.008
4. Hodgskiss, M. S. W., Crockford, P. W. & Turchyn, A. V. Deconstructing the Lomagundi–Jatuli Carbon Isotope Excursion. 10.1146/annurev-earth-031621 (2023).
5. Bekker A Holland HD Oxygen overshoot and recovery during the early Paleoproterozoic Earth Planet Sci. Lett. 2012 317–318 295 304 10.1016/j.epsl.2011.12.012
Bekker, A. & Holland, H. D. Oxygen overshoot and recovery during the early Paleoproterozoic. Earth Planet Sci. Lett. 317–318, 295–304 (2012).10.1016/j.epsl.2011.12.012
6. Eguchi J Seales J Dasgupta R Great oxidation and Lomagundi events linked by deep cycling and enhanced degassing of carbon Nat. Geosci. 2020 13 71 76 10.1038/s41561-019-0492-6
Eguchi, J., Seales, J. & Dasgupta, R. Great oxidation and Lomagundi events linked by deep cycling and enhanced degassing of carbon. Nat. Geosci. 13, 71–76 (2020).10.1038/s41561-019-0492-6
7. Eguchi J Diamond CW Lyons TW Proterozoic supercontinent break-up as a driver for oxygenation events and subsequent carbon isotope excursions PNAS Nexus 2022 1 1 10.1093/pnasnexus/pgac036
Eguchi, J., Diamond, C. W. & Lyons, T. W. Proterozoic supercontinent break-up as a driver for oxygenation events and subsequent carbon isotope excursions. PNAS Nexus 1, 1 (2022).10.1093/pnasnexus/pgac036
8. Hayes JM Waldbauer JR The carbon cycle and associated redox processes through time Philos. Trans. R. Soc. B Biol. Sci. 2006 361 931 950 10.1098/rstb.2006.1840
Hayes, J. M. & Waldbauer, J. R. The carbon cycle and associated redox processes through time. Philos. Trans. R. Soc. B Biol. Sci. 361, 931–950. 10.1098/rstb.2006.1840 (2006).10.1098/rstb.2006.1840
9. Higgins JA Fischer WW Schrag DP Oxygenation of the ocean and sediments: Consequences for the seafloor carbonate factory Earth Planet Sci. Lett. 2009 284 25 33 10.1016/j.epsl.2009.03.039
Higgins, J. A., Fischer, W. W. & Schrag, D. P. Oxygenation of the ocean and sediments: Consequences for the seafloor carbonate factory. Earth Planet Sci. Lett. 284, 25–33 (2009).10.1016/j.epsl.2009.03.039
10. Schrag, D. P., Higgins, J. A., Macdonald, F. A. & Johnston, D. T. Authigenic Carbonate and the History of the Global Carbon Cycle. www.sciencemag.org.
11. Mayika KB The Paleoproterozoic Francevillian succession of Gabon and the Lomagundi–Jatuli event Geology 2020 48 1099 1104 10.1130/G47651.1
Mayika, K. B. et al. The Paleoproterozoic Francevillian succession of Gabon and the Lomagundi–Jatuli event. Geology 48, 1099–1104 (2020).10.1130/G47651.1
12. Karhu, J. A. & Holland, H. D. Carbon Isotopes and the Rise of Atmospheric Oxygen. http://pubs.geoscienceworld.org/gsa/geology/article-pdf/24/10/867/3515968/i0091-7613-24-10-867.pdf.
13. Planavsky NJ Evolution of the structure and impact of Earth’s biosphere Nat. Rev. Earth Environ. 2021 2 123 139 10.1038/s43017-020-00116-w
Planavsky, N. J. et al. Evolution of the structure and impact of Earth’s biosphere. Nat. Rev. Earth Environ. 2, 123–139 (2021).10.1038/s43017-020-00116-w
14. Li Y Satish-Kumar M Kiran S Wan C Zheng J 2.0 Ga orogenic graphite deposits and associated 13C-enriched meta-carbonate rocks from South China Craton: Implications for global Lomagundi event Geosci. Front. 2022 13 101409 10.1016/j.gsf.2022.101409
Li, Y., Satish-Kumar, M., Kiran, S., Wan, C. & Zheng, J. 2.0 Ga orogenic graphite deposits and associated 13C-enriched meta-carbonate rocks from South China Craton: Implications for global Lomagundi event. Geosci. Front. 13, 101409 (2022).10.1016/j.gsf.2022.101409
15. Parnell J Brolly C Boyce AJ Graphite from Palaeoproterozoic enhanced carbon burial, and its metallogenic legacy Geol. Mag. 2021 158 1711 1718 10.1017/S0016756821000583
Parnell, J., Brolly, C. & Boyce, A. J. Graphite from Palaeoproterozoic enhanced carbon burial, and its metallogenic legacy. Geol. Mag. 158, 1711–1718 (2021).10.1017/S0016756821000583
16. dos Santos FH da Silva Amaral W Martins DT de Souza ACB Zircon U-Pb geochronology of manganese-rich rocks from the Borborema Province, Northeast Brazil: Adding a new piece to the global inventory of Paleoproterozoic manganese mineralization Miner. Depos. 2023 58 531 551 10.1007/s00126-022-01140-0
dos Santos, F. H., da Silva Amaral, W., Martins, D. T. & de Souza, A. C. B. Zircon U-Pb geochronology of manganese-rich rocks from the Borborema Province, Northeast Brazil: Adding a new piece to the global inventory of Paleoproterozoic manganese mineralization. Miner. Depos. 58, 531–551 (2023).10.1007/s00126-022-01140-0
17. Calvert SE Pedersen TF Sedimentary geochemistry of manganese: Implications for the environment of formation of Manganiferous Black Shales Econ. Geol. 1996 91 36 10.2113/gsecongeo.91.1.36
Calvert, S. E. & Pedersen, T. F. Sedimentary geochemistry of manganese: Implications for the environment of formation of Manganiferous Black Shales. Econ. Geol. 91, 36 (1996).10.2113/gsecongeo.91.1.36
18. Roy S Sedimentary manganese metallogenesis in response to the evolution of the Earth system Earth Sci. Rev. 2006 77 273 305 10.1016/j.earscirev.2006.03.004
Roy, S. Sedimentary manganese metallogenesis in response to the evolution of the Earth system. Earth Sci. Rev. 77, 273–305 (2006).10.1016/j.earscirev.2006.03.004
19. Neves SP Proterozoic history of the Borborema province (NE Brazil): Correlations with neighboring cratons and Pan-African belts and implications for the evolution of western Gondwana Tectonics 2003 22 1 10.1029/2001TC001352
Neves, S. P. Proterozoic history of the Borborema province (NE Brazil): Correlations with neighboring cratons and Pan-African belts and implications for the evolution of western Gondwana. Tectonics 22, 1 (2003).10.1029/2001TC001352
20. Hollanda MHBM Archanjo CJ Souza LC Dunyi L Armstrong R Long-lived Paleoproterozoic granitic magmatism in the Seridó-Jaguaribe domain, Borborema Province-NE Brazil J. S. Am. Earth Sci. 2011 32 287 300 10.1016/j.jsames.2011.02.008
Hollanda, M. H. B. M., Archanjo, C. J., Souza, L. C., Dunyi, L. & Armstrong, R. Long-lived Paleoproterozoic granitic magmatism in the Seridó-Jaguaribe domain, Borborema Province-NE Brazil. J. S. Am. Earth Sci. 32, 287–300 (2011).10.1016/j.jsames.2011.02.008
21. de Souza ZS Generation of continental crust in the northern part of the Borborema Province, northeastern Brazil, from Archaean to Neoproterozoic J. S. Am. Earth Sci. 2016 68 68 96 10.1016/j.jsames.2015.10.006
de Souza, Z. S. et al. Generation of continental crust in the northern part of the Borborema Province, northeastern Brazil, from Archaean to Neoproterozoic. J. S. Am. Earth Sci. 68, 68–96 (2016).10.1016/j.jsames.2015.10.006
22. da Costa FG Geochemistry and U-Pb–Hf zircon data for plutonic rocks of the Troia Massif, Borborema Province, NE Brazil: Evidence for reworking of Archean and juvenile Paleoproterozoic crust during Rhyacian accretionary and collisional tectonics Precamb. Res. 2018 311 167 194 10.1016/j.precamres.2018.04.008
da Costa, F. G. et al. Geochemistry and U-Pb–Hf zircon data for plutonic rocks of the Troia Massif, Borborema Province, NE Brazil: Evidence for reworking of Archean and juvenile Paleoproterozoic crust during Rhyacian accretionary and collisional tectonics. Precamb. Res. 311, 167–194 (2018).10.1016/j.precamres.2018.04.008
23. Dantas EL Crustal growth in the 3.4-2.7Ga São José de Campestre Massif, Borborema Province, NE Brazil Precamb. Res. 2013 227 120 156 10.1016/j.precamres.2012.08.006
Dantas, E. L. et al. Crustal growth in the 3.4-2.7Ga São José de Campestre Massif, Borborema Province, NE Brazil. Precamb. Res. 227, 120–156 (2013).10.1016/j.precamres.2012.08.006
24. Ganade CE Basei MAS Grandjean FC Armstrong R Brito RS Contrasting Archaean (2.85–2.68 Ga) TTGs from the Tróia Massif (NE-Brazil) and their geodynamic implications for flat to steep subduction transition Precamb. Res. 2017 297 1 18 10.1016/j.precamres.2017.05.007
Ganade, C. E., Basei, M. A. S., Grandjean, F. C., Armstrong, R. & Brito, R. S. Contrasting Archaean (2.85–2.68 Ga) TTGs from the Tróia Massif (NE-Brazil) and their geodynamic implications for flat to steep subduction transition. Precamb. Res. 297, 1–18 (2017).10.1016/j.precamres.2017.05.007
25. Vauchez A The Borborema shear zone system, NE Brazil J. S. Am. Earth Sci. 1995 8 247 10.1016/0895-9811(95)00012-5
Vauchez, A. The Borborema shear zone system, NE Brazil. J. S. Am. Earth Sci. 8, 247 (1995).10.1016/0895-9811(95)00012-5
26. Viegas LGF Archanjo CJ Hollanda MHBM Vauchez A Microfabrics and zircon U-Pb (SHRIMP) chronology of mylonites from the Patos shear zone (Borborema Province, NE Brazil) Precamb. Res. 2014 243 1 17 10.1016/j.precamres.2013.12.020
Viegas, L. G. F., Archanjo, C. J., Hollanda, M. H. B. M. & Vauchez, A. Microfabrics and zircon U-Pb (SHRIMP) chronology of mylonites from the Patos shear zone (Borborema Province, NE Brazil). Precamb. Res. 243, 1–17 (2014).10.1016/j.precamres.2013.12.020
27. Motta Garcia MDG Dos Santos TJS Da Silva Amaral W Provenance and tectonic setting of neoproterozoic supracrustal rocks from the Ceará Central Domain, Borborema Province (NE Brazil): Constraints from geochemistry and detrital zircon ages Int. Geol. Rev. 2014 56 481 500 10.1080/00206814.2013.875489
Motta Garcia, M. D. G., Dos Santos, T. J. S. & Da Silva Amaral, W. Provenance and tectonic setting of neoproterozoic supracrustal rocks from the Ceará Central Domain, Borborema Province (NE Brazil): Constraints from geochemistry and detrital zircon ages. Int. Geol. Rev. 56, 481–500 (2014).10.1080/00206814.2013.875489
28. da Costa FG de Palheta ESM Rodrigues JB Gomes IP Vasconcelos AM Geochemistry and U-Pb zircon ages of plutonic rocks from the Algodões granite-greenstone terrane, Troia Massif, northern Borborema Province, Brazil: Implications for Paleoproterozoic subduction-accretion processes J. S. Am. Earth Sci. 2015 59 45 68 10.1016/j.jsames.2015.01.007
da Costa, F. G., de Palheta, E. S. M., Rodrigues, J. B., Gomes, I. P. & Vasconcelos, A. M. Geochemistry and U-Pb zircon ages of plutonic rocks from the Algodões granite-greenstone terrane, Troia Massif, northern Borborema Province, Brazil: Implications for Paleoproterozoic subduction-accretion processes. J. S. Am. Earth Sci. 59, 45–68 (2015).10.1016/j.jsames.2015.01.007
29. Muniz RL dos Santos TJS Dantas EL Fuck RA Rhyacian-Orosirian Khondalite Belt in the Borborema Province (NE Brazil): An active margin setting based on U-Pb zircon and monazite constraints Geol. J. 2022 57 3808 3828 10.1002/gj.4517
Muniz, R. L., dos Santos, T. J. S., Dantas, E. L. & Fuck, R. A. Rhyacian-Orosirian Khondalite Belt in the Borborema Province (NE Brazil): An active margin setting based on U-Pb zircon and monazite constraints. Geol. J. 57, 3808–3828 (2022).10.1002/gj.4517
30. dos Santos FH Unraveling sedimentary precursors and metal enrichment of high-grade metamorphosed manganese-rich rocks from the Borborema Province, northeastern Brazil Ore Geol. Rev. 2021 137 104283 10.1016/j.oregeorev.2021.104283
dos Santos, F. H. et al. Unraveling sedimentary precursors and metal enrichment of high-grade metamorphosed manganese-rich rocks from the Borborema Province, northeastern Brazil. Ore Geol. Rev. 137, 104283 (2021).10.1016/j.oregeorev.2021.104283
31. dos Santos FH da Silva Amaral W Chi-Fru E de Souza ACB Bosco-Santos A Paleoproterozoic manganese oxide precipitation in oxic seawater surface and reductive enrichment in anoxic seafloor Chem. Geol. 2022 588 120655 10.1016/j.chemgeo.2021.120655
dos Santos, F. H., da Silva Amaral, W., Chi-Fru, E., de Souza, A. C. B. & Bosco-Santos, A. Paleoproterozoic manganese oxide precipitation in oxic seawater surface and reductive enrichment in anoxic seafloor. Chem. Geol. 588, 120655 (2022).10.1016/j.chemgeo.2021.120655
32. Fragomeni PRP Pereira RM The graphite mineralization in the Aracoiába-Baturité District (CE): Geotectonic and metallogenetic implications Braz. J. Geol. 2013 43 223 234 10.5327/Z2317-48892013000200003
Fragomeni, P. R. P. & Pereira, R. M. The graphite mineralization in the Aracoiába-Baturité District (CE): Geotectonic and metallogenetic implications. Braz. J. Geol. 43, 223–234 (2013).10.5327/Z2317-48892013000200003
33. Pereira Silva GDL Xavier RP The gold-carbonaceous matter association in lode deposits of the Rio itapicuru greenstone belt, northeastern Brazil Int. Geol. Rev. 1997 39 688 702 10.1080/00206819709465296
Pereira Silva, G. D. L. & Xavier, R. P. The gold-carbonaceous matter association in lode deposits of the Rio itapicuru greenstone belt, northeastern Brazil. Int. Geol. Rev. 39, 688–702 (1997).10.1080/00206819709465296
34. Miranda DA de Oliveira Chaves A Campello MS de Ramos SLLM Origin and thermometry of graphites from Itapecerica supracrustal succession of the southern Sao Francisco Craton by C isotopes, X-ray diffraction, and Raman spectroscopy Int. Geol. Rev. 2019 61 1864 1875 10.1080/00206814.2018.1564073
Miranda, D. A., de Oliveira Chaves, A., Campello, M. S. & de Ramos, S. L. L. M. Origin and thermometry of graphites from Itapecerica supracrustal succession of the southern Sao Francisco Craton by C isotopes, X-ray diffraction, and Raman spectroscopy. Int. Geol. Rev. 61, 1864–1875 (2019).10.1080/00206814.2018.1564073
35. Mesquita MJ Samson I Hartmann LA de Picanço JL Gomes MEB Shearing and fluid evolution of the Porto Nacional orogenic gold district, western Brazil: Microstructural, fluid inclusion, and C-O isotopic evidence Ore Geol. Rev. 2021 136 104242 10.1016/j.oregeorev.2021.104242
Mesquita, M. J., Samson, I., Hartmann, L. A., de Picanço, J. L. & Gomes, M. E. B. Shearing and fluid evolution of the Porto Nacional orogenic gold district, western Brazil: Microstructural, fluid inclusion, and C-O isotopic evidence. Ore Geol. Rev. 136, 104242 (2021).10.1016/j.oregeorev.2021.104242
36. Klein EL Harris C Giret A Moura CAV Angélica RS Geology and stable isotope (O, H, C, S) constraints on the genesis of the Cachoeira gold deposit, Gurupi Belt, northern Brazil Chem. Geol. 2005 221 188 206 10.1016/j.chemgeo.2005.05.003
Klein, E. L., Harris, C., Giret, A., Moura, C. A. V. & Angélica, R. S. Geology and stable isotope (O, H, C, S) constraints on the genesis of the Cachoeira gold deposit, Gurupi Belt, northern Brazil. Chem. Geol. 221, 188–206 (2005).10.1016/j.chemgeo.2005.05.003
37. Klein EL Fluid inclusion and stable isotope (O, H, C, and S) constraints on the genesis of the Serrinha gold deposit, Gurupi Belt, northern Brazil Miner. Depos. 2006 41 160 178 10.1007/s00126-006-0050-1
Klein, E. L. et al. Fluid inclusion and stable isotope (O, H, C, and S) constraints on the genesis of the Serrinha gold deposit, Gurupi Belt, northern Brazil. Miner. Depos. 41, 160–178 (2006).10.1007/s00126-006-0050-1
38. Kříbek B The origin and hydrothermal mobilization of carbonaceous matter associated with Paleoproterozoic orogenic-type gold deposits of West Africa Precamb. Res. 2015 270 300 317 10.1016/j.precamres.2015.09.017
Kříbek, B. et al. The origin and hydrothermal mobilization of carbonaceous matter associated with Paleoproterozoic orogenic-type gold deposits of West Africa. Precamb. Res. 270, 300–317 (2015).10.1016/j.precamres.2015.09.017
39. Canfield DE Oxygen dynamics in the aftermath of the great oxidation of Earth’s atmosphere Proc. Natl. Acad. Sci. U.S.A. 2013 110 16736 16741 10.1073/pnas.1315570110 24082125
Canfield, D. E. et al. Oxygen dynamics in the aftermath of the great oxidation of Earth’s atmosphere. Proc. Natl. Acad. Sci. U.S.A. 110, 16736–16741 (2013).24082125 10.1073/pnas.1315570110
40. Dodd MS Papineau D Pirajno F Wan Y Karhu JA Minimal biomass deposition in banded iron formations inferred from organic matter and clay relationships Nat. Commun. 2019 10 1 10.1038/s41467-019-12975-z 30602773
Dodd, M. S., Papineau, D., Pirajno, F., Wan, Y. & Karhu, J. A. Minimal biomass deposition in banded iron formations inferred from organic matter and clay relationships. Nat. Commun. 10, 1 (2019).30602773 10.1038/s41467-019-12975-z
41. Dodd MS Widespread occurrences of variably crystalline 13 C-depleted graphitic carbon in banded iron formations Earth Planet Sci. Lett. 2019 512 163 174 10.1016/j.epsl.2019.01.054
Dodd, M. S. et al. Widespread occurrences of variably crystalline 13 C-depleted graphitic carbon in banded iron formations. Earth Planet Sci. Lett. 512, 163–174 (2019).10.1016/j.epsl.2019.01.054
42. Bernard S Papineau D Graphitic carbons and biosignatures Elements 2014 10 435 440 10.2113/gselements.10.6.435
Bernard, S. & Papineau, D. Graphitic carbons and biosignatures. Elements 10, 435–440. 10.2113/gselements.10.6.435 (2014).10.2113/gselements.10.6.435
43. Zhang S Ague JJ Vitale Brovarone A Degassing of organic carbon during regional metamorphism of pelites, Wepawaug Schist, Connecticut, USA Chem. Geol. 2018 490 30 44 10.1016/j.chemgeo.2018.05.003
Zhang, S., Ague, J. J. & Vitale Brovarone, A. Degassing of organic carbon during regional metamorphism of pelites, Wepawaug Schist, Connecticut, USA. Chem. Geol. 490, 30–44 (2018).10.1016/j.chemgeo.2018.05.003
44. Calvert SE Bustin RM Ingall ED Influence of water column anoxia and sediment supply on the burial and preservation of organic carbon in marine shales Pergamon Geochim. Cosmochim. Acta 1996 60 1577 10.1016/0016-7037(96)00041-5
Calvert, S. E., Bustin, R. M. & Ingall, E. D. Influence of water column anoxia and sediment supply on the burial and preservation of organic carbon in marine shales. Pergamon Geochim. Cosmochim. Acta 60, 1577 (1996).10.1016/0016-7037(96)00041-5
45. Schidlowski M Carbon isotopes as biogeochemical recorders of life over 3.8 Ga of earth history: Evolution of a concept Precamb. Res. 2001 106 1 10.1016/S0301-9268(00)00134-0
Schidlowski, M. Carbon isotopes as biogeochemical recorders of life over 3.8 Ga of earth history: Evolution of a concept. Precamb. Res. 106, 1 (2001).10.1016/S0301-9268(00)00134-0
46. Luque FJ Crespo-Feo E Barrenechea JF Ortega L Carbon isotopes of graphite: Implications on fluid history Geosci. Front. 2012 3 197 207 10.1016/j.gsf.2011.11.006
Luque, F. J., Crespo-Feo, E., Barrenechea, J. F. & Ortega, L. Carbon isotopes of graphite: Implications on fluid history. Geosci. Front. 3, 197–207 (2012).10.1016/j.gsf.2011.11.006
47. Zhu J Carbon isotope and geochemical characteristics of the Paleoproterozoic graphite deposits in the Jiao-Liao-Ji belt, North China Craton: Implications for genesis and depositional environment Precamb. Res. 2021 362 106320 10.1016/j.precamres.2021.106320
Zhu, J. et al. Carbon isotope and geochemical characteristics of the Paleoproterozoic graphite deposits in the Jiao-Liao-Ji belt, North China Craton: Implications for genesis and depositional environment. Precamb. Res. 362, 106320 (2021).10.1016/j.precamres.2021.106320
48. Bottinga Y Calculated fractionation factors for carbon and hydrogen isotope exchange in the system calcite-carbon dioxide-graphite-methane-hydrogen-water vapor Geochim. Cosmochim. Acta 1969 33 49 10.1016/0016-7037(69)90092-1
Bottinga, Y. Calculated fractionation factors for carbon and hydrogen isotope exchange in the system calcite-carbon dioxide-graphite-methane-hydrogen-water vapor. Geochim. Cosmochim. Acta 33, 49 (1969).10.1016/0016-7037(69)90092-1
49. Huckriede H Meischner D Origin and environment of manganese-rich sediments within black-shale basins Geochim. Cosmochim. Acta 1996 60 1 10.1016/0016-7037(96)00008-7
Huckriede, H. & Meischner, D. Origin and environment of manganese-rich sediments within black-shale basins. Geochim. Cosmochim. Acta 60, 1 (1996).10.1016/0016-7037(96)00008-7
50. Okita PM Maynard JB Spikers EC Force ER Isotopic evidence for organic matter oxidation by manganese reduction in the formation of stratiform manganese carbonate ore Geochim. Cosmochim. Acta 1988 52 2679 10.1016/0016-7037(88)90036-1
Okita, P. M., Maynard, J. B., Spikers, E. C. & Force, E. R. Isotopic evidence for organic matter oxidation by manganese reduction in the formation of stratiform manganese carbonate ore. Geochim. Cosmochim. Acta 52, 2679 (1988).10.1016/0016-7037(88)90036-1
51. Polgari, M., Okita, P. M. & Hein, J. R. Stable Isotope Evidence for the Origin of the Urkut Manganese Ore Deposit, Hungary. http://pubs.geoscienceworld.org/sepm/jsedres/article-pdf/61/3/384/2810790/384.pdf (1991).
52. Mojzsis SJ Evidence for life on Earth before 3800 million years ago Nature 1996 384 55 59 10.1038/384055a0 8900275
Mojzsis, S. J. et al. Evidence for life on Earth before 3800 million years ago. Nature 384, 55–59 (1996).8900275 10.1038/384055a0
53. Papineau D Ancient graphite in the Eoarchean quartz-pyroxene rocks from Akilia in southern West Greenland I: Petrographic and spectroscopic characterization Geochim. Cosmochim. Acta 2010 74 5862 5883 10.1016/j.gca.2010.05.025
Papineau, D. et al. Ancient graphite in the Eoarchean quartz-pyroxene rocks from Akilia in southern West Greenland I: Petrographic and spectroscopic characterization. Geochim. Cosmochim. Acta 74, 5862–5883 (2010).10.1016/j.gca.2010.05.025
54. Rossi C Lozano RP Isanta N Hellstrom J Manganese stromatolites in caves: El Soplao (Cantabria, Spain) Geology 2010 38 1119 1122 10.1130/G31283.1
Rossi, C., Lozano, R. P., Isanta, N. & Hellstrom, J. Manganese stromatolites in caves: El Soplao (Cantabria, Spain). Geology 38, 1119–1122 (2010).10.1130/G31283.1
55. Tashiro T Early trace of life from 3.95 Ga sedimentary rocks in Labrador, Canada Nature 2017 549 516 518 10.1038/nature24019 28959955
Tashiro, T. et al. Early trace of life from 3.95 Ga sedimentary rocks in Labrador, Canada. Nature 549, 516–518 (2017).28959955 10.1038/nature24019
56. Whitehouse MJ Dunkley DJ Kusiak MA Wilde SA On the true antiquity of Eoarchean chemofossils—Assessing the claim for Earth’s oldest biogenic graphite in the Saglek Block of Labrador Precamb. Res. 2019 323 70 81 10.1016/j.precamres.2019.01.001
Whitehouse, M. J., Dunkley, D. J., Kusiak, M. A. & Wilde, S. A. On the true antiquity of Eoarchean chemofossils—Assessing the claim for Earth’s oldest biogenic graphite in the Saglek Block of Labrador. Precamb. Res. 323, 70–81. 10.1016/j.precamres.2019.01.001 (2019).10.1016/j.precamres.2019.01.001
57. Wacey D Nanoscale analysis of pyritized microfossils reveals differential heterotrophic consumption in the 1.9-Ga Gunflint chert Proc. Natl. Acad. Sci. U.S.A. 2013 110 8020 8024 10.1073/pnas.1221965110 23630257
Wacey, D. et al. Nanoscale analysis of pyritized microfossils reveals differential heterotrophic consumption in the 1.9-Ga Gunflint chert. Proc. Natl. Acad. Sci. U.S.A. 110, 8020–8024 (2013).23630257 10.1073/pnas.1221965110
58. Schopf JW Sulfur-cycling fossil bacteria from the 1.8-Ga Duck Creek formation provide promising evidence of evolution’s null hypothesis Proc. Natl. Acad. Sci. U.S.A. 2015 112 2087 2092 10.1073/pnas.1419241112 25646436
Schopf, J. W. et al. Sulfur-cycling fossil bacteria from the 1.8-Ga Duck Creek formation provide promising evidence of evolution’s null hypothesis. Proc. Natl. Acad. Sci. U.S.A. 112, 2087–2092 (2015).25646436 10.1073/pnas.1419241112
59. Kump LR Isotopic evidence for massive oxidation of organic matter following the great oxidation event Science 2011 334 1694 1696 10.1126/science.1213999 22144465
Kump, L. R. et al. Isotopic evidence for massive oxidation of organic matter following the great oxidation event. Science 334, 1694–1696 (2011).22144465 10.1126/science.1213999
60. Kirschvink, J. L. et al. Paleoproterozoic Snowball Earth: Extreme Climatic and Geochemical Global Change and Its Biological Consequences. www.pnas.org (1999).
61. Holland HD The oxygenation of the atmosphere and oceans Philos. Trans. R. Soc. B Biol. Sci. 2006 361 903 915 10.1098/rstb.2006.1838
Holland, H. D. The oxygenation of the atmosphere and oceans. Philos. Trans. R. Soc. B Biol. Sci. 361, 903–915. 10.1098/rstb.2006.1838 (2006).10.1098/rstb.2006.1838
