Carbon

Measurements of carbon and oxygen isotopic abundances are commonly based on the mass spectrum of carbon dioxide, but analysis of that spectrum is not trivial because three isotope ratios (17O/16O, 18O/16O, and 13C/12C) must be determined from only two readily observable ion-current ratios (45/44 and 46/44). Here, approaches to the problem are reassessed in the light of new information regarding the distribution of oxygen isotopes in natural samples. It is shown that methods of calculation conventionally employed can lead to systematic errors in the computed abundance of 13C and that these errors may be related to incorrect assessment of the absolute abundance of 17O. Further, problems arising during the analysis of samples enriched by admixture of 18O-labeled materials are discussed, and it is shown (i) that serious inaccuracies arise in the computed abundance of 17O and 13C if methods of calculation conventionally employed in the analysis of natural materials are applied to material labeled with 18O but (ii) that computed fractional abundances of 18O are always within 0.4% of the correct result. Methods for exact calculation of two isotope ratios when the third is known are presented and discussed, and a more exact approach to the computation of all three isotope ratios in natural materials is given.

@article{doi101021ac00284a060,
    author = "Santrock, Jeffrey and Studley, Stephen A. and Hayes, John M.",
    title = "Isotopic analyses based on the mass spectra of carbon dioxide",
    year = "1985",
    journal = "Analytical Chemistry",
    abstract = "Measurements of carbon and oxygen isotopic abundances are commonly based on the mass spectrum of carbon dioxide, but analysis of that spectrum is not trivial because three isotope ratios (17O/16O, 18O/16O, and 13C/12C) must be determined from only two readily observable ion-current ratios (45/44 and 46/44). Here, approaches to the problem are reassessed in the light of new information regarding the distribution of oxygen isotopes in natural samples. It is shown that methods of calculation conventionally employed can lead to systematic errors in the computed abundance of 13C and that these errors may be related to incorrect assessment of the absolute abundance of 17O. Further, problems arising during the analysis of samples enriched by admixture of 18O-labeled materials are discussed, and it is shown (i) that serious inaccuracies arise in the computed abundance of 17O and 13C if methods of calculation conventionally employed in the analysis of natural materials are applied to material labeled with 18O but (ii) that computed fractional abundances of 18O are always within 0.4\% of the correct result. Methods for exact calculation of two isotope ratios when the third is known are presented and discussed, and a more exact approach to the computation of all three isotope ratios in natural materials is given.",
    url = "https://doi.org/10.1021/ac00284a060",
    doi = "10.1021/ac00284a060",
    openalex = "W1559756460"
}

@article{doi101038333313a0,
    author = "Schidlowski, M.",
    title = "A 3,800-million-year isotopic record of life from carbon in sedimentary rocks",
    year = "1988",
    journal = "Nature",
    url = "https://www.semanticscholar.org/paper/c6ba4db0ff7b2c3973ecfed3bbe7efc1ebf8c77c",
    doi = "10.1038/333313A0",
    is_oa = "true",
    number = "6171",
    pages = "313-318",
    semanticscholar_citation_count = "751",
    semanticscholar_id = "c6ba4db0ff7b2c3973ecfed3bbe7efc1ebf8c77c",
    volume = "333"
}

@article{schidlowski1988a,
    author = "Schidlowski, Manfred",
    title = "A 3,800-million-year isotopic record of life from carbon in sedimentary rocks",
    year = "1988",
    journal = "Nature",
    url = "https://doi.org/10.1038/333313a0",
    doi = "10.1038/333313a0",
    number = "6171",
    openalex = "W2010626609",
    pages = "313-318",
    volume = "333",
    references = "cloud1976beginnings, doi1010160009254180900479, doi1010160016703753900015, doi1010160016703779900590, doi1010160031942281851345, doi1010160302459880800547, doi101016b9780444422255500012, doi1015159780691220239, openalexw1564144063, openalexw2026796374, openalexw2586781288"
}

@misc{schidlowski1988a1,
    author = "Schidlowski, M",
    title = "A 3,800-million-year isotopic record of life from carbon in sedimentary rocks",
    year = "1988",
    howpublished = "Nature, v. 333, p. 313-318",
    note = "talkorigins\_source = {true}; raw\_reference = {Schidlowski, M., 1988, A 3,800-million-year isotopic record of life from carbon in sedimentary rocks: Nature, v. 333, p. 313-318.}"
}

@incollection{banerjee1992organic,
    author = "Banerjee, D. M. and Deb, M. and Strauss, H.",
    title = "Organic Carbon Isotopic Composition of Proterozoic Sedimentary Rocks from India: Preliminary Results",
    year = "1992",
    booktitle = "Early Organic Evolution",
    url = "https://doi.org/10.1007/978-3-642-76884-2\_17",
    doi = "10.1007/978-3-642-76884-2\_17",
    openalex = "W2182534418",
    pages = "232-240",
    references = "doi1010160301926875900182, doi1010160301926889900028, doi101038321832a0, doi101111j150239311988tb02083x, doi101144gsjgs12510351, doi105860choice304422, openalexw2026796374, openalexw2521241193, openalexw418879830, openalexw565036203"
}

Turbiditic and pelagic sedimentary rocks from the Isua supracrustal belt in west Greenland [more than 3700 million years ago (Ma)] contain reduced carbon that is likely biogenic. The carbon is present as 2- to 5-micrometer graphite globules and has an isotopic composition of delta13C that is about -19 per mil (Pee Dee belemnite standard). These data and the mode of occurrence indicate that the reduced carbon represents biogenic detritus, which was perhaps derived from planktonic organisms.

@article{doi101126science2835402674,
    author = "Rosing, Minik T.",
    title = "13 C-Depleted Carbon Microparticles in >3700-Ma Sea-Floor Sedimentary Rocks from West Greenland",
    year = "1999",
    journal = "Science",
    abstract = "Turbiditic and pelagic sedimentary rocks from the Isua supracrustal belt in west Greenland [more than 3700 million years ago (Ma)] contain reduced carbon that is likely biogenic. The carbon is present as 2- to 5-micrometer graphite globules and has an isotopic composition of delta13C that is about -19 per mil (Pee Dee belemnite standard). These data and the mode of occurrence indicate that the reduced carbon represents biogenic detritus, which was perhaps derived from planktonic organisms.",
    url = "https://doi.org/10.1126/science.283.5402.674",
    doi = "10.1126/science.283.5402.674",
    openalex = "W2085436563",
    references = "doi1010160016703779902382, doi101016001670379090269q, doi101016s0009254196000927, doi101016s0009254197000843, doi101016s0012825297818582, doi101038384055a0, doi101046j13653121199800162x, doi101073pnas91156735, doi1011300091761319960240043epoess23co2, openalexw3120543430, shanmugam1997the"
}

Estimates of the average composition of various Precambrian shields and a variety of estimates of the average composition of upper continental crust show considerable disagreement for a number of trace elements, including Ti, Nb, Ta, Cs, Cr, Ni, V, and Co. For these elements and others that are carried predominantly in terrigenous sediment, rather than in solution (and ultimately into chemical sediment), during the erosion of continents the La/element ratio is relatively uniform in clastic sediments. Since the average rare earth element (REE) pattern of terrigenous sediment is widely accepted to reflect the upper continental crust, such correlations provide robust estimates of upper crustal abundances for these trace elements directly from the sedimentary data. Suggested revisions to the upper crustal abundances of Taylor and McLennan [1985] are as follows (all in parts per million): Sc = 13.6, Ti = 4100, V = 107, Cr = 83, Co = 17, Ni = 44, Nb = 12, Cs = 4.6, Ta = 1.0, and Pb = 17. The upper crustal abundances of Rb, Zr, Ba, Hf, and Th were also directly reevaluated and K, U, and Rb indirectly evaluated (by assuming Th/U, K/U, and K/Rb ratios), and no revisions are warranted for these elements. In the models of crustal composition proposed by Taylor and McLennan [1985] the lower continental crust (75% of the entire crust) is determined by subtraction of the upper crust (25%) from a model composition for the bulk crust, and accordingly, these changes also necessitate revisions to lower crustal abundances for these elements.

@article{doi1010292000gc000109,
    author = "McLennan, S. M.",
    title = "Relationships between the trace element composition of sedimentary rocks and upper continental crust",
    year = "2001",
    journal = "Geochemistry Geophysics Geosystems",
    abstract = "Estimates of the average composition of various Precambrian shields and a variety of estimates of the average composition of upper continental crust show considerable disagreement for a number of trace elements, including Ti, Nb, Ta, Cs, Cr, Ni, V, and Co. For these elements and others that are carried predominantly in terrigenous sediment, rather than in solution (and ultimately into chemical sediment), during the erosion of continents the La/element ratio is relatively uniform in clastic sediments. Since the average rare earth element (REE) pattern of terrigenous sediment is widely accepted to reflect the upper continental crust, such correlations provide robust estimates of upper crustal abundances for these trace elements directly from the sedimentary data. Suggested revisions to the upper crustal abundances of Taylor and McLennan [1985] are as follows (all in parts per million): Sc = 13.6, Ti = 4100, V = 107, Cr = 83, Co = 17, Ni = 44, Nb = 12, Cs = 4.6, Ta = 1.0, and Pb = 17. The upper crustal abundances of Rb, Zr, Ba, Hf, and Th were also directly reevaluated and K, U, and Rb indirectly evaluated (by assuming Th/U, K/U, and K/Rb ratios), and no revisions are warranted for these elements. In the models of crustal composition proposed by Taylor and McLennan [1985] the lower continental crust (75\% of the entire crust) is determined by subtraction of the upper crust (25\%) from a model composition for the bulk crust, and accordingly, these changes also necessitate revisions to lower crustal abundances for these elements.",
    url = "https://doi.org/10.1029/2000gc000109",
    doi = "10.1029/2000gc000109",
    openalex = "W1880555926",
    references = "doi101007bf00375292, doi1010160016703764901292, doi1010160016703776900934, doi101086628992, doi1015159781501509032010, openalexw2094255421"
}

@article{chu2003sulfur,
    author = "Chu, Xuelei and Zhang, Qirui and Zhang, Tonggang and Feng, Lianjun",
    title = "Sulfur and carbon isotopic variations in Neoproterozoic sedimentary rocks from southern China *",
    year = "2003",
    journal = "Progress in Natural Science",
    url = "https://doi.org/10.1080/10020070312331344580",
    doi = "10.1080/10020070312331344580",
    number = "11",
    openalex = "W2073276098",
    pages = "875-880",
    volume = "13",
    references = "doi101016s0012821x02006878, doi101016s0012821x0200804x, doi101016s0301926899000674, doi101021ac50033a056, doi101038325140a0, doi101038382127a0, doi10108010020070312331344430, doi101126science1069651, doi1011300091761319980261059tofng23co2, doi102138gsrmg431637"
}

Glacial deposits of Sturtian and Marinoan age occur in the well-studied Neoproterozoic successions of northern Namibia, South Australia, and northwestern Canada. In all three regions, the Marinoan glaciation is presaged by a large negative δ13C anomaly, and the cap carbonates to both glacial units share a suite of unique sedimentological, stratigraphic, and geochemical features. These global chronostratigraphic markers are the bases of a new correlation scheme for the Neoproterozoic that corroborates radiometric data that indicate that there were three glacial epochs between ca. 750 and 580 Ma. Intraregional correlation of Neoproterozoic successions in the present-day North Atlantic region suggests that glacial diamictite pairs in the Polarisbreen Group in northeastern Svalbard and the Tillite Group in eastern Greenland were deposited during the Marinoan glaciation, whereas the younger of a pair of glacials (Mortensnes Formation) in the Vestertana Group of northern Norway was deposited during the third (Gaskiers) Neoproterozoic glaciation. Gaskiers-aged glacial deposits are neither globally distributed nor overlain by a widespread cap carbonate but are associated with an extremely negative δ13C anomaly. The chronology developed here provides the framework for a new, high-resolution model carbon-isotope record for the Neoproterozoic comprising new δ13C (carbonate) data from Svalbard (Akademikerbreen Group) and Namibia (Otavi Group) and data in the literature from Svalbard, Namibia, and Oman. A new U-Pb zircon age of 760 ± 1 Ma from an ash bed in the Ombombo Subgroup in Namibia provides the oldest direct time-calibration point in the compilation, but the time scale of this preliminary δ13C record remains poorly constrained.

@article{doi101130b256301,
    author = "Halverson, Galen P. and Hoffman, Paul F. and Schrag, Daniel P. and Maloof, Adam C. and Rice, A. H. N.",
    title = "Toward a Neoproterozoic composite carbon-isotope record",
    year = "2005",
    journal = "Geological Society of America Bulletin",
    abstract = "Glacial deposits of Sturtian and Marinoan age occur in the well-studied Neoproterozoic successions of northern Namibia, South Australia, and northwestern Canada. In all three regions, the Marinoan glaciation is presaged by a large negative δ13C anomaly, and the cap carbonates to both glacial units share a suite of unique sedimentological, stratigraphic, and geochemical features. These global chronostratigraphic markers are the bases of a new correlation scheme for the Neoproterozoic that corroborates radiometric data that indicate that there were three glacial epochs between ca. 750 and 580 Ma. Intraregional correlation of Neoproterozoic successions in the present-day North Atlantic region suggests that glacial diamictite pairs in the Polarisbreen Group in northeastern Svalbard and the Tillite Group in eastern Greenland were deposited during the Marinoan glaciation, whereas the younger of a pair of glacials (Mortensnes Formation) in the Vestertana Group of northern Norway was deposited during the third (Gaskiers) Neoproterozoic glaciation. Gaskiers-aged glacial deposits are neither globally distributed nor overlain by a widespread cap carbonate but are associated with an extremely negative δ13C anomaly. The chronology developed here provides the framework for a new, high-resolution model carbon-isotope record for the Neoproterozoic comprising new δ13C (carbonate) data from Svalbard (Akademikerbreen Group) and Namibia (Otavi Group) and data in the literature from Svalbard, Namibia, and Oman. A new U-Pb zircon age of 760 ± 1 Ma from an ash bed in the Ombombo Subgroup in Namibia provides the oldest direct time-calibration point in the compilation, but the time scale of this preliminary δ13C record remains poorly constrained.",
    url = "https://doi.org/10.1130/b25630.1",
    doi = "10.1130/b25630.1",
    openalex = "W2102516422",
    references = "doi1010160016703790901288, doi101016001670379290064p, doi1010160301926894000708, doi1010160301926894000775, doi101016s0009254199000832, doi101016s0301926899000686, doi101016s0301926899000728, doi101016s0301926899000777, doi101016s0301926899000820, doi101017s0016756800007603, doi101038001534a0, doi101038231498a0, doi101038269209a0, doi101038321832a0, doi101038356673a0, doi101046j13653121200200408x, doi101126science28153811342, doi101126science972526482b, doi101130001676061974851869gsaavt20co2, doi10113000917613198210516vosstp20co2, doi1011300091761320030310431eocana20co2, doi101130b250661, doi101130g205191, doi10130603b59b0716d111d78645000102c1865d, doi101306212f7bb72b2411d78648000102c1865d, openalexw2912219260, openalexw45631376"
}

Evidence of life on Earth is manifestly preserved in the rock record. However, the microfossil record only extends to ∼ 3.5 billion years (Ga), the chemofossil record arguably to ∼ 3.8 Ga, and the rock record to 4.0 Ga. Detrital zircons from Jack Hills, Western Australia range in age up to nearly 4.4 Ga. From a population of over 10,000 Jack Hills zircons, we identified one >3.8-Ga zircon that contains primary graphite inclusions. Here, we report carbon isotopic measurements on these inclusions in a concordant, 4.10 ± 0.01-Ga zircon. We interpret these inclusions as primary due to their enclosure in a crack-free host as shown by transmission X-ray microscopy and their crystal habit. Their δ(13)CPDB of -24 ± 5‰ is consistent with a biogenic origin and may be evidence that a terrestrial biosphere had emerged by 4.1 Ga, or ∼ 300 My earlier than has been previously proposed.

@article{doi101073pnas1517557112,
    author = "Bell, Elizabeth A. and Boehnke, P. and Harrison, T. Mark and Mao, Wendy L.",
    title = "Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon",
    year = "2015",
    journal = "Proceedings of the National Academy of Sciences",
    abstract = "Evidence of life on Earth is manifestly preserved in the rock record. However, the microfossil record only extends to ∼ 3.5 billion years (Ga), the chemofossil record arguably to ∼ 3.8 Ga, and the rock record to 4.0 Ga. Detrital zircons from Jack Hills, Western Australia range in age up to nearly 4.4 Ga. From a population of over 10,000 Jack Hills zircons, we identified one >3.8-Ga zircon that contains primary graphite inclusions. Here, we report carbon isotopic measurements on these inclusions in a concordant, 4.10 ± 0.01-Ga zircon. We interpret these inclusions as primary due to their enclosure in a crack-free host as shown by transmission X-ray microscopy and their crystal habit. Their δ(13)CPDB of -24 ± 5‰ is consistent with a biogenic origin and may be evidence that a terrestrial biosphere had emerged by 4.1 Ga, or ∼ 300 My earlier than has been previously proposed.",
    url = "https://doi.org/10.1073/pnas.1517557112",
    doi = "10.1073/pnas.1517557112",
    openalex = "W2161420691"
}

Biological activity is a major factor in Earth's chemical cycles, including facilitating CO2 sequestration and providing climate feedbacks. Thus a key question in Earth's evolution is when did life arise and impact hydrosphere-atmosphere-lithosphere chemical cycles? Until now, evidence for the oldest life on Earth focused on debated stable isotopic signatures of 3,800-3,700 million year (Myr)-old metamorphosed sedimentary rocks and minerals from the Isua supracrustal belt (ISB), southwest Greenland. Here we report evidence for ancient life from a newly exposed outcrop of 3,700-Myr-old metacarbonate rocks in the ISB that contain 1-4-cm-high stromatolites-macroscopically layered structures produced by microbial communities. The ISB stromatolites grew in a shallow marine environment, as indicated by seawater-like rare-earth element plus yttrium trace element signatures of the metacarbonates, and by interlayered detrital sedimentary rocks with cross-lamination and storm-wave generated breccias. The ISB stromatolites predate by 220 Myr the previous most convincing and generally accepted multidisciplinary evidence for oldest life remains in the 3,480-Myr-old Dresser Formation of the Pilbara Craton, Australia. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO2 sequestration by 3,700 million years ago (Ma), near the start of Earth's sedimentary record. A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life's origin in the Hadean eon (>4,000 Ma).

@article{doi101038nature19355,
    author = "Nutman, Allen P and Bennett, Vickie C and Friend, Clark R L and Van Kranendonk, Martin J and Chivas, Allan R",
    title = "Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures.",
    year = "2016",
    journal = "Nature",
    abstract = "Biological activity is a major factor in Earth's chemical cycles, including facilitating CO2 sequestration and providing climate feedbacks. Thus a key question in Earth's evolution is when did life arise and impact hydrosphere-atmosphere-lithosphere chemical cycles? Until now, evidence for the oldest life on Earth focused on debated stable isotopic signatures of 3,800-3,700 million year (Myr)-old metamorphosed sedimentary rocks and minerals from the Isua supracrustal belt (ISB), southwest Greenland. Here we report evidence for ancient life from a newly exposed outcrop of 3,700-Myr-old metacarbonate rocks in the ISB that contain 1-4-cm-high stromatolites-macroscopically layered structures produced by microbial communities. The ISB stromatolites grew in a shallow marine environment, as indicated by seawater-like rare-earth element plus yttrium trace element signatures of the metacarbonates, and by interlayered detrital sedimentary rocks with cross-lamination and storm-wave generated breccias. The ISB stromatolites predate by 220 Myr the previous most convincing and generally accepted multidisciplinary evidence for oldest life remains in the 3,480-Myr-old Dresser Formation of the Pilbara Craton, Australia. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO2 sequestration by 3,700 million years ago (Ma), near the start of Earth's sedimentary record. A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life's origin in the Hadean eon (>4,000 Ma).",
    url = "https://pubmed.ncbi.nlm.nih.gov/27580034/",
    doi = "10.1038/nature19355",
    openalex = "W2511850779",
    pmid = "27580034",
    references = "doi1010160016703786903960, doi101029jc086ic10p09776, doi101038377220a0, doi101038384055a0, doi101038nature04764, doi101038nrg929, doi101126science2835402674, doi1015159781501509032, doi1015159781501509032010, openalexw2338438729"
}

Metasedimentary rocks from Isua, West Greenland (over 3,700 million years old) contain 13C-depleted carbonaceous compounds, with isotopic ratios that are compatible with a biogenic origin. Metamorphic garnet crystals in these rocks contain trails of carbonaceous inclusions that are contiguous with carbon-rich sedimentary beds in the host rock, where carbon is fully graphitized. Previous studies have not been able to document other elements of life (mainly hydrogen, oxygen, nitrogen and phosphorus) structurally bound to this carbonaceous material. Here we study carbonaceous inclusions armoured within garnet porphyroblasts, by in situ infrared absorption on approximately 10-21 m3 domains within these inclusions. We show that the absorption spectra are consistent with carbon bonded to nitrogen and oxygen, and probably also to phosphate. The levels of C-H or O-H bonds were found to be low. These results are consistent with biogenic organic material isolated for billions of years and thermally matured at temperatures of around 500 °C. They therefore provide spatial characterization for potentially the oldest biogenic carbon relics in Earth's geological record. The preservation of Eoarchean organic residues within sedimentary material corroborates earlier claims for the biogenic origins of carbon in Isua metasediments.

@article{doi101038nature23261,
    author = "Hassenkam, T and Andersson, M P and Dalby, K N and Mackenzie, D M A and Rosing, M T",
    title = "Elements of Eoarchean life trapped in mineral inclusions.",
    year = "2017",
    journal = "Nature",
    abstract = "Metasedimentary rocks from Isua, West Greenland (over 3,700 million years old) contain 13C-depleted carbonaceous compounds, with isotopic ratios that are compatible with a biogenic origin. Metamorphic garnet crystals in these rocks contain trails of carbonaceous inclusions that are contiguous with carbon-rich sedimentary beds in the host rock, where carbon is fully graphitized. Previous studies have not been able to document other elements of life (mainly hydrogen, oxygen, nitrogen and phosphorus) structurally bound to this carbonaceous material. Here we study carbonaceous inclusions armoured within garnet porphyroblasts, by in situ infrared absorption on approximately 10-21 m3 domains within these inclusions. We show that the absorption spectra are consistent with carbon bonded to nitrogen and oxygen, and probably also to phosphate. The levels of C-H or O-H bonds were found to be low. These results are consistent with biogenic organic material isolated for billions of years and thermally matured at temperatures of around 500 °C. They therefore provide spatial characterization for potentially the oldest biogenic carbon relics in Earth's geological record. The preservation of Eoarchean organic residues within sedimentary material corroborates earlier claims for the biogenic origins of carbon in Isua metasediments.",
    url = "https://pubmed.ncbi.nlm.nih.gov/28738409/",
    doi = "10.1038/nature23261",
    openalex = "W2738378480",
    pmid = "28738409",
    references = "doi1010020470011149, doi101007bf00372150, doi1010160009261489851188, doi101016jssc200703052, doi101039p29930000799, doi10106311674108, doi1010631463096, doi101103physreva383098, doi101103physrevb338822, doi101180mono4"
}

@article{doi101038s4158601806104,
    author = "Allwood, A. and Rosing, M. and Flannery, D. and Hurowitz, J. and Heirwegh, C.",
    title = "Reassessing evidence of life in 3,700-million-year-old rocks of Greenland",
    year = "2018",
    journal = "Nature",
    url = "https://www.semanticscholar.org/paper/8a47eb81a31aa969e067a4e1238def3b331cfddb",
    doi = "10.1038/s41586-018-0610-4",
    is_oa = "true",
    number = "7730",
    pages = "241-244",
    semanticscholar_citation_count = "135",
    semanticscholar_id = "8a47eb81a31aa969e067a4e1238def3b331cfddb",
    volume = "563"
}

Abstract Spatial correlation of isotopic chemostratigraphy across ancient epeiric basins is of particular interest in the field of geology. This study examines the carbon isotopic compositions of carbonate and organic matter from the Late Ordovician sedimentary succession in the Yangtze Platform, including the Linxiang (LX) Formation deposited in the bottom and the Tiezufeike (TZFK)/Daduhe (DDH)/Wufeng (WF) formations in the top. Paired δ13Ccarb and δ13Corg analyses of the Upper Ordovician strata on the Yangtze Platform were recorded, and the results show that the rocks in the LX Formation have high δ13Ccarb and δ13Corg values relative to those in the DDF/TZFK/WF formations. Additionally, a variation of ~ 2‰ was found between shallow- and deep- water settings during the Late Ordovician: heavier δ13Ccarb and δ13Corg values are observed at the Wukemuchang (WKMC) and Wanhe (WH) sections, representing the shallow regions of the Yangtze Platform, relative to the Tianjiawan (TJW) and Tianba (TB) sections representing the deeper margin of the Yangtze Platform. We suggest that the variations of δ13C in carbonate and organic matter are related to the sea - level eustacy and shoaling of marine chemocline: (1) sea - level rise driven decrease in local scale carbonate weathering; (2) decreased decomposition of organic matter under anoxic conditions; and (3) incorporation of non - photosynthetic chemoautorophic bacteria living in deeper waters. The △13C (△13C = δ13Ccarb – δ13Corg) values in both the WH and WKMC sections display an increasing trend upward from the LX Formation to the overlying strata, varying from 27.8‰ to 31.2‰ and from 28.1‰ to 31.1‰, respectively. These increased △13C values are related to the enhanced nutrients and correspondingly high primary productivity, and thus that, the anoxic water conditions and high primary productivity may be the significant factors in the deposition of Late Ordovician black shales.

@article{doi101016jjseaes2020104540,
    author = "Yang, Xiangrong and Yan, D. and Chen, Daizhao and Liu, Mu and She, Xiaohui and Zhang, Junfeng and Wei, Xiaosong and Lu, Zeyu",
    title = "Spatial variation of carbon isotopic compositions of carbonate and organic matter from the Late Ordovician sedimentary succession in the Yangtze Platform, South China: Implications for sea – Level eustacy and shoaling of marine chemocline",
    year = "2020",
    journal = "Journal of Asian Earth Sciences",
    abstract = "Abstract Spatial correlation of isotopic chemostratigraphy across ancient epeiric basins is of particular interest in the field of geology. This study examines the carbon isotopic compositions of carbonate and organic matter from the Late Ordovician sedimentary succession in the Yangtze Platform, including the Linxiang (LX) Formation deposited in the bottom and the Tiezufeike (TZFK)/Daduhe (DDH)/Wufeng (WF) formations in the top. Paired δ13Ccarb and δ13Corg analyses of the Upper Ordovician strata on the Yangtze Platform were recorded, and the results show that the rocks in the LX Formation have high δ13Ccarb and δ13Corg values relative to those in the DDF/TZFK/WF formations. Additionally, a variation of \textasciitilde\ 2‰ was found between shallow- and deep- water settings during the Late Ordovician: heavier δ13Ccarb and δ13Corg values are observed at the Wukemuchang (WKMC) and Wanhe (WH) sections, representing the shallow regions of the Yangtze Platform, relative to the Tianjiawan (TJW) and Tianba (TB) sections representing the deeper margin of the Yangtze Platform. We suggest that the variations of δ13C in carbonate and organic matter are related to the sea - level eustacy and shoaling of marine chemocline: (1) sea - level rise driven decrease in local scale carbonate weathering; (2) decreased decomposition of organic matter under anoxic conditions; and (3) incorporation of non - photosynthetic chemoautorophic bacteria living in deeper waters. The △13C (△13C = δ13Ccarb – δ13Corg) values in both the WH and WKMC sections display an increasing trend upward from the LX Formation to the overlying strata, varying from 27.8‰ to 31.2‰ and from 28.1‰ to 31.1‰, respectively. These increased △13C values are related to the enhanced nutrients and correspondingly high primary productivity, and thus that, the anoxic water conditions and high primary productivity may be the significant factors in the deposition of Late Ordovician black shales.",
    url = "https://www.semanticscholar.org/paper/c28bad1463c8d6d721e1f5f024d845e327f12b30",
    doi = "10.1016/j.jseaes.2020.104540",
    is_oa = "true",
    pages = "104540",
    semanticscholar_citation_count = "6",
    semanticscholar_id = "c28bad1463c8d6d721e1f5f024d845e327f12b30",
    volume = "202"
}

Much of our understanding of Earth's past climate comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the Cenozoic era and to study their dynamics. Here, we present a new, highly resolved, astronomically dated, continuous composite of benthic foraminifer isotope records developed in our laboratories. Four climate states-Hothouse, Warmhouse, Coolhouse, Icehouse-are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume. Statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of Cenozoic climate dynamics.

@article{doi101126scienceaba6853,
    author = "Westerhold, Thomas and Marwan, Norbert and Drury, Anna Joy and Liebrand, Diederik and Agnini, Claudia and Anagnostou, Eleni and Barnet, James S K and Bohaty, Steven M. and Vleeschouwer, David De and Florindo, Fabio and Frederichs, Thomas and Hodell, David A and Holbourn, Ann and Kroon, Dick and Lauretano, Vittoria and Littler, Kate and Lourens, Lucas Joost and Lyle, Mitchell W and Pälike, Heiko and Röhl, Ursula and Tian, Jun and Wilkens, Roy H. and Wilson, Paul A. and Zachos, James C.",
    title = "An astronomically dated record of Earth’s climate and its predictability over the last 66 million years",
    year = "2020",
    journal = "Science",
    abstract = "Much of our understanding of Earth's past climate comes from the measurement of oxygen and carbon isotope variations in deep-sea benthic foraminifera. Yet, long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the Cenozoic era and to study their dynamics. Here, we present a new, highly resolved, astronomically dated, continuous composite of benthic foraminifer isotope records developed in our laboratories. Four climate states-Hothouse, Warmhouse, Coolhouse, Icehouse-are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume. Statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of Cenozoic climate dynamics.",
    url = "https://doi.org/10.1126/science.aba6853",
    doi = "10.1126/science.aba6853",
    openalex = "W3084856838",
    references = "doi101007s105840110156z, doi1010160025322771900533, doi1010160031018294902518, doi1010160033589473900525, doi101016b9780444594259000287, doi101016b9780444594259000299, doi101016jmargeo200502007, doi1010292001gl012943, doi1010292003pa000908, doi1010292007pa001458, doi1010292019pa003563, doi10102992jb01202, doi10102994jb03098, doi101029jc086ic10p09776, doi101029pa002i001p00001, doi10103835021000, doi101038nature03135, doi101038nature06588, doi101038ncomms14845, doi1010510004636120041335, doi10105100046361201116836, doi101111j1365246x1980tb02601x, doi101126sciadvaaz1346, doi101126science1059412, doi101126science1133822, doi101126science19442701121, doi101126science2875451269, doi105194cp76032011"
}

Abundant and well-preserved fossil microbenthos occurs in siliciclastic deposits of all Earth ages, from the early Archean to today. Studies in modern settings show how microbenthos responds to sediment dynamics by baffling and trapping, binding, biostabilization, and growth. Results of this microbial-sediment interaction are microbially induced sedimentary structures (MISS). Successful prospection for rich MISS occurrences in the terrestrial lithological record requires unraveling genesis and taphonomy of MISS, both of which are defined only by a narrow range of specific conditions. These conditions have to coincide with high detectability which is a function of outcrop quality, bedding character, and rock type. Assertions on biogenicity of MISS morphologies must be based on the presence of microbially induced sedimentary textures (MIST), which are MISS-internal textures comprising replacement minerals arranged into microscopic biological morphologies, ancient carbonaceous matter, trace fossils, and geochemical signals. MISS serve as possible templates for the decryption of ancient life-processes on Mars. This article closes with a perspective on selected deposits and ancient environments in Meridiani Planum, Gale Crater, and Jezero Crater, Mars, regarding their potential for MISS occurrences. The earlier hypothesis of structures on Mars as potentially being MISS is revised.

@article{doi101089ast20210011,
    author = "Noffke, Nora",
    title = "Microbially Induced Sedimentary Structures in Clastic Deposits: Implication for the Prospection for Fossil Life on Mars",
    year = "2021",
    journal = "Astrobiology",
    abstract = "Abundant and well-preserved fossil microbenthos occurs in siliciclastic deposits of all Earth ages, from the early Archean to today. Studies in modern settings show how microbenthos responds to sediment dynamics by baffling and trapping, binding, biostabilization, and growth. Results of this microbial-sediment interaction are microbially induced sedimentary structures (MISS). Successful prospection for rich MISS occurrences in the terrestrial lithological record requires unraveling genesis and taphonomy of MISS, both of which are defined only by a narrow range of specific conditions. These conditions have to coincide with high detectability which is a function of outcrop quality, bedding character, and rock type. Assertions on biogenicity of MISS morphologies must be based on the presence of microbially induced sedimentary textures (MIST), which are MISS-internal textures comprising replacement minerals arranged into microscopic biological morphologies, ancient carbonaceous matter, trace fossils, and geochemical signals. MISS serve as possible templates for the decryption of ancient life-processes on Mars. This article closes with a perspective on selected deposits and ancient environments in Meridiani Planum, Gale Crater, and Jezero Crater, Mars, regarding their potential for MISS occurrences. The earlier hypothesis of structures on Mars as potentially being MISS is revised.",
    url = "https://doi.org/10.1089/ast.2021.0011",
    doi = "10.1089/ast.2021.0011",
    openalex = "W3164244887",
    references = "doi101016jearscirev2019102888, doi101016jearscirev2020103296, doi101016jprecamres201804007, doi102110jsr201957"
}

A response to the Quanta article “Carbon captured”, which reports that a new environmentally colour-coded periodic table had marked carbon as green, red and grey.

@article{cook2022zerocarbon,
    author = "Cook, Nick",
    title = "Zero-carbon carbon",
    year = "2022",
    journal = "Physics World",
    abstract = "A response to the Quanta article “Carbon captured”, which reports that a new environmentally colour-coded periodic table had marked carbon as green, red and grey.",
    url = "https://doi.org/10.1088/2058-7058/35/01/25",
    doi = "10.1088/2058-7058/35/01/25",
    number = "1",
    pages = "26ii-26ii",
    volume = "35"
}

Although Ce anomalies are commonly used to reconstruct past seawater redox conditions, published interpretations are based on various proxy materials and analytical approaches, while no relatively complete compilation of sedimentary Ce anomaly data has yet been made. Here, we report a new compilation comprising >6000 carbonate, iron formation, phosphorite, and chert samples of all ages, of which 1127 passed screening for near primary Ce anomaly values. The Ce anomalies of 592 mudstones were also investigated and found to contain in some cases unambiguous traces of a primary negative Ce anomaly, which was likely inherited during early diagenetic organic degradation or directly from authigenic phases. Here we show that seawater-like rare earth element (REE) patterns may be retained in siliceous mudstones in cases where the detrital REE signature has been diluted by authigenic silica. Mudstone weathering is shown to have a negligible effect on the magnitude of negative Ce anomalies in moderately weathered samples. A critical appraisal of negative Ce anomalies from the published literature, yet to be confirmed through La-Ce isotopic dating, implies that oxygenic photosynthesis likely evolved during 3.0–2.5 Ga. Although our compilation does not capture the onset of the Great Oxidation Episode, a decreasing trend in mean negative Ce anomalies from 2.5 to 2.1 Ga is in accordance with a rise in oxygen levels during the early Paleoproterozoic. Sporadic Ce anomalies might identify transient oxygenation events during 1.8–1.2 Ga with minimum atmospheric concentrations up to 1–6% present atmospheric level. Statistical analysis of Ce anomaly data is consistent with progressive oxygenation of the surface ocean through the late Tonian-early Cambrian interval. While pronounced negative Ce anomalies indicate that shallow marine settings were broadly well oxygenated during the Ediacaran-Cambrian transition, the deeper marine environment remained largely anoxic, consistent with the persistence of a dissolved organic carbon redox buffer. The Ce anomaly compilation also reveals expanded ocean anoxia in the early Paleozoic, followed by more pervasive oxygenation by middle Devonian times, coincident with the emergence and radiation of secondary woody tissues and forests. The redox evolution and estimated pO2 revealed by Ce anomalies are generally compatible with other proxies and modelling results, and therefore we concur that the marine sedimentary Ce anomaly record responds sensitively to oceanic redox changes and can be a useful additional proxy to track Earth system evolution.

@article{doi101016jearscirev2022104015,
    author = "Zhang, Kun and Shields, Graham",
    title = "Sedimentary Ce anomalies: Secular change and implications for paleoenvironmental evolution",
    year = "2022",
    journal = "Earth-Science Reviews",
    abstract = "Although Ce anomalies are commonly used to reconstruct past seawater redox conditions, published interpretations are based on various proxy materials and analytical approaches, while no relatively complete compilation of sedimentary Ce anomaly data has yet been made. Here, we report a new compilation comprising >6000 carbonate, iron formation, phosphorite, and chert samples of all ages, of which 1127 passed screening for near primary Ce anomaly values. The Ce anomalies of 592 mudstones were also investigated and found to contain in some cases unambiguous traces of a primary negative Ce anomaly, which was likely inherited during early diagenetic organic degradation or directly from authigenic phases. Here we show that seawater-like rare earth element (REE) patterns may be retained in siliceous mudstones in cases where the detrital REE signature has been diluted by authigenic silica. Mudstone weathering is shown to have a negligible effect on the magnitude of negative Ce anomalies in moderately weathered samples. A critical appraisal of negative Ce anomalies from the published literature, yet to be confirmed through La-Ce isotopic dating, implies that oxygenic photosynthesis likely evolved during 3.0–2.5 Ga. Although our compilation does not capture the onset of the Great Oxidation Episode, a decreasing trend in mean negative Ce anomalies from 2.5 to 2.1 Ga is in accordance with a rise in oxygen levels during the early Paleoproterozoic. Sporadic Ce anomalies might identify transient oxygenation events during 1.8–1.2 Ga with minimum atmospheric concentrations up to 1–6\% present atmospheric level. Statistical analysis of Ce anomaly data is consistent with progressive oxygenation of the surface ocean through the late Tonian-early Cambrian interval. While pronounced negative Ce anomalies indicate that shallow marine settings were broadly well oxygenated during the Ediacaran-Cambrian transition, the deeper marine environment remained largely anoxic, consistent with the persistence of a dissolved organic carbon redox buffer. The Ce anomaly compilation also reveals expanded ocean anoxia in the early Paleozoic, followed by more pervasive oxygenation by middle Devonian times, coincident with the emergence and radiation of secondary woody tissues and forests. The redox evolution and estimated pO2 revealed by Ce anomalies are generally compatible with other proxies and modelling results, and therefore we concur that the marine sedimentary Ce anomaly record responds sensitively to oceanic redox changes and can be a useful additional proxy to track Earth system evolution.",
    url = "https://doi.org/10.1016/j.earscirev.2022.104015",
    doi = "10.1016/j.earscirev.2022.104015",
    openalex = "W4226459787",
    references = "doi1010160037073894900396, doi101016jearscirev201510006, doi101016jearscirev201706012, doi101038nature25009, doi101038s4155901908216, doi101111gbi12378"
}

Abstract Rock weathering is a key process in global elemental cycling. Life participates in this process with tangible consequences observed from the mineral interface to the planetary scale. Multiple lines of evidence show that microorganisms may play a pivotal—yet overlooked—role in weathering. This topic is reviewed here with an emphasis on the following questions that remain unanswered: What is the quantitative contribution of bacteria and fungi to weathering? What are the associated mechanisms and do they leave characteristic imprints on mineral surfaces or in the geological record? Does biogenic weathering fulfill an ecological function, or does it occur as a side effect of unrelated metabolic functions and biological processes? An overview of efforts to integrate the contribution of living organisms into reactive transport models is provided. We also highlight prospective opportunities to harness microbial weathering in order to support sustainable agroforestry practices and mining activities, soil remediation, and carbon sequestration.

@article{doi101038s41529022003127,
    author = "Wild, Bastien and Gerrits, Ruben and Bonneville, Steeve",
    title = "The contribution of living organisms to rock weathering in the critical zone",
    year = "2022",
    journal = "npj Materials Degradation",
    abstract = "Abstract Rock weathering is a key process in global elemental cycling. Life participates in this process with tangible consequences observed from the mineral interface to the planetary scale. Multiple lines of evidence show that microorganisms may play a pivotal—yet overlooked—role in weathering. This topic is reviewed here with an emphasis on the following questions that remain unanswered: What is the quantitative contribution of bacteria and fungi to weathering? What are the associated mechanisms and do they leave characteristic imprints on mineral surfaces or in the geological record? Does biogenic weathering fulfill an ecological function, or does it occur as a side effect of unrelated metabolic functions and biological processes? An overview of efforts to integrate the contribution of living organisms into reactive transport models is provided. We also highlight prospective opportunities to harness microbial weathering in order to support sustainable agroforestry practices and mining activities, soil remediation, and carbon sequestration.",
    url = "https://doi.org/10.1038/s41529-022-00312-7",
    doi = "10.1038/s41529-022-00312-7",
    openalex = "W4313448281",
    references = "doi101093nsrnwac128"
}

In recent years, the typical crude oil from the Cambrian Lower Ordovician source rocks has been found in the Tarim Basin, and it is characterized by 13C enrichment. The stable carbon isotope of the oil is concentrated at approximately −28‰, which is 3‰–6‰ heavier than that of the crude oil from the Middle and Upper Ordovician source rocks. The stable carbon isotope between crude oil and its kerogen is characterized by inversion, with an amplitude of approximately 3‰–4‰. However, the origin of this phenomenon remains controversial, which restricts the next exploration of crude oil in the Cambrian–Lower Ordovician in the Tarim Basin. Samples were collected from seven outcrop profiles in the Kuruketage region. The basic geochemical features of the Cambrian strata, including total organic carbon abundance, δ13Corg, δ13Ccarb, and δ18Ocarb, were studied and compared with those of well TD2. The results show that the lithologies, isotope stratigraphic evolutional curves, and correlations between the organic carbon and inorganic carbon of the profiles from the northern Kuruketage region are successively comparable with those of the profiles from the southern Kuruketage region and the well TD2. In this study, the carbon isotope records are supposed to indicate a vertical gradient Cambrian oceanic mode, including the shallow decoupled isotope zone, middle gradient‐coupled isotope zone, and deep isotope‐decoupled zone. The discovery of this isotope record reflects the formation of stable carbon and oxygen isotope stratified oceans during the Cambrian period. Additionally, it provides important insights into the origin of the 13C enrichment observed in some Lower Cambrian crude oils in the Tarim Basin.

@article{doi101002gj4809,
    author = "Liu, Hu and Qi, Minghui and Cao, T. and Tan, Jieqing and Yin, Zhongshan and Cheng, B.",
    title = "Influence of dissolved organic carbon on the Cambrian Ocean: Evidence from the carbon isotopes of the sedimentary rocks of the Eastern Tarim Basin, North‐west China",
    year = "2023",
    journal = "Geological Journal",
    abstract = "In recent years, the typical crude oil from the Cambrian Lower Ordovician source rocks has been found in the Tarim Basin, and it is characterized by 13C enrichment. The stable carbon isotope of the oil is concentrated at approximately −28‰, which is 3‰–6‰ heavier than that of the crude oil from the Middle and Upper Ordovician source rocks. The stable carbon isotope between crude oil and its kerogen is characterized by inversion, with an amplitude of approximately 3‰–4‰. However, the origin of this phenomenon remains controversial, which restricts the next exploration of crude oil in the Cambrian–Lower Ordovician in the Tarim Basin. Samples were collected from seven outcrop profiles in the Kuruketage region. The basic geochemical features of the Cambrian strata, including total organic carbon abundance, δ13Corg, δ13Ccarb, and δ18Ocarb, were studied and compared with those of well TD2. The results show that the lithologies, isotope stratigraphic evolutional curves, and correlations between the organic carbon and inorganic carbon of the profiles from the northern Kuruketage region are successively comparable with those of the profiles from the southern Kuruketage region and the well TD2. In this study, the carbon isotope records are supposed to indicate a vertical gradient Cambrian oceanic mode, including the shallow decoupled isotope zone, middle gradient‐coupled isotope zone, and deep isotope‐decoupled zone. The discovery of this isotope record reflects the formation of stable carbon and oxygen isotope stratified oceans during the Cambrian period. Additionally, it provides important insights into the origin of the 13C enrichment observed in some Lower Cambrian crude oils in the Tarim Basin.",
    url = "https://www.semanticscholar.org/paper/649f96e0a4db1a3dba4f4ed55b05d2d9456db77a",
    doi = "10.1002/gj.4809",
    is_oa = "true",
    number = "10",
    pages = "3806-3818",
    semanticscholar_citation_count = "1",
    semanticscholar_id = "649f96e0a4db1a3dba4f4ed55b05d2d9456db77a",
    volume = "58"
}

Abstract The nitrogen isotopic composition of organic matter is controlled by metabolic activity and redox speciation and has therefore largely been used to uncover the early evolution of life and ocean oxygenation. Specifically, positive δ 15 N values found in well‐preserved sedimentary rocks are often interpreted as reflecting the stability of a nitrate pool sustained by water column partial oxygenation. This study adds much‐needed data to the sparse Paleoarchean record, providing carbon and nitrogen concentrations and isotopic compositions for more than fifty samples from the 3.4 Ga Buck Reef Chert sedimentary deposit (BRC, Barberton Greenstone Belt). In the overall anoxic and ferruginous conditions of the BRC depositional environment, these samples yield positive δ 15 N values up to +6.1‰. We argue that without a stable pool of nitrates, these values are best explained by non‐quantitative oxidation of ammonium via the Feammox pathway, a metabolic co‐cycling between iron and nitrogen through the oxidation of ammonium in the presence of iron oxides. Our data contribute to the understanding of how the nitrogen cycle operated under reducing, anoxic, and ferruginous conditions, which are relevant to most of the Archean. Most importantly, they invite to carefully consider the meaning of positive δ 15 N signatures in Archean sediments.

@article{doi101111gbi12540,
    author = "Pellerin, Alice and Thomazo, Christophe and Ader, Magali and Marin‐Carbonne, Johanna and Alléon, Julien and Vennin, Emmanuelle and Hofmann, Axel",
    title = "Iron‐mediated anaerobic ammonium oxidation recorded in the early Archean ferruginous ocean",
    year = "2023",
    journal = "Geobiology",
    abstract = "Abstract The nitrogen isotopic composition of organic matter is controlled by metabolic activity and redox speciation and has therefore largely been used to uncover the early evolution of life and ocean oxygenation. Specifically, positive δ 15 N values found in well‐preserved sedimentary rocks are often interpreted as reflecting the stability of a nitrate pool sustained by water column partial oxygenation. This study adds much‐needed data to the sparse Paleoarchean record, providing carbon and nitrogen concentrations and isotopic compositions for more than fifty samples from the 3.4 Ga Buck Reef Chert sedimentary deposit (BRC, Barberton Greenstone Belt). In the overall anoxic and ferruginous conditions of the BRC depositional environment, these samples yield positive δ 15 N values up to +6.1‰. We argue that without a stable pool of nitrates, these values are best explained by non‐quantitative oxidation of ammonium via the Feammox pathway, a metabolic co‐cycling between iron and nitrogen through the oxidation of ammonium in the presence of iron oxides. Our data contribute to the understanding of how the nitrogen cycle operated under reducing, anoxic, and ferruginous conditions, which are relevant to most of the Archean. Most importantly, they invite to carefully consider the meaning of positive δ 15 N signatures in Archean sediments.",
    url = "https://doi.org/10.1111/gbi.12540",
    doi = "10.1111/gbi.12540",
    openalex = "W4315928646",
    references = "doi101016jearscirev2020103296"
}

The marine carbon isotope record (δ13C) used for chemostratigraphy and reconstruction of carbon cycle dynamics is commonly assembled using carbonate rocks. There is, however, evidence that carbonate cements hosted within fine-grained clastics (shales and mudstones) in some settings may also express δ13C trends that covary with the record from carbonates. We present new carbon and oxygen isotopic data from shale-hosted carbonate cements (herein termed δ13Ccarb-sh and δ18Ocarb-sh, n = 107, <16 wt% CaCO3) of the terminal Ediacaran Nama Group, Namibia (≥550.5 to <539.6 Million years ago; Ma). These data are compared with the published carbon and oxygen isotopic record from coeval carbonates (δ13Ccarb and δ18Ocarb, n = 1611) and total organic carbon (TOC) concentrations. We show that, in the Nama Group, δ13Ccarb-sh compositions in samples of intermediate to high CaCO3/TOC (>0.4) can approximate contemporaneous δ13Ccarb in open marine mixed carbonate-clastic settings. By contrast, δ13Ccarb-sh values in samples with low CaCO3/TOC (<0.4) that were deposited in clastic settings distant from the locus of carbonate deposition are more negative than contemporaneous δ13Ccarb. These data suggest that δ13Ccarb-sh may approach seawater composition in samples with low TOC when deposited in settings characterized by high CO32- concentration, where carbonate can rapidly precipitate from seawater during early diagenesis. However, the use of δ13Ccarb-sh to infill gaps in the existing δ13Ccarb record remains uncertain, even when these criteria are fulfilled. Intervals of δ13C-δ18O co-variability in the Nama Group succession appear to correlate with units where seawater mixing with meteoric fluids was more likely during early diagenesis, such as clastic-dominated settings, which also show significant decreasing δ18O through time with gradual sub-basin infill. We further consider uncertainties in lithostratigraphic correlation of the upper Urusis Formation of the Nama Group that enable three new possible correlations to be proposed for δ13Ccarb-sh data within the terminal Ediacaran to lower Cambrian (<542.65 Ma to >532 Ma) regional and global δ13Ccarb records.

@article{doi102475001c88082,
    author = "Bowyer, F. and Yilales, Mariana and Wood, Rachel A. and Poulton, S.",
    title = "Insights Into the Terminal Ediacaran Marine Carbonate Record From Shale-Hosted Carbonate Carbon Isotopes",
    year = "2023",
    journal = "American Journal of Science",
    abstract = "The marine carbon isotope record (δ13C) used for chemostratigraphy and reconstruction of carbon cycle dynamics is commonly assembled using carbonate rocks. There is, however, evidence that carbonate cements hosted within fine-grained clastics (shales and mudstones) in some settings may also express δ13C trends that covary with the record from carbonates. We present new carbon and oxygen isotopic data from shale-hosted carbonate cements (herein termed δ13Ccarb-sh and δ18Ocarb-sh, n = 107, <16 wt\% CaCO3) of the terminal Ediacaran Nama Group, Namibia (≥550.5 to <539.6 Million years ago; Ma). These data are compared with the published carbon and oxygen isotopic record from coeval carbonates (δ13Ccarb and δ18Ocarb, n = 1611) and total organic carbon (TOC) concentrations. We show that, in the Nama Group, δ13Ccarb-sh compositions in samples of intermediate to high CaCO3/TOC (>0.4) can approximate contemporaneous δ13Ccarb in open marine mixed carbonate-clastic settings. By contrast, δ13Ccarb-sh values in samples with low CaCO3/TOC (<0.4) that were deposited in clastic settings distant from the locus of carbonate deposition are more negative than contemporaneous δ13Ccarb. These data suggest that δ13Ccarb-sh may approach seawater composition in samples with low TOC when deposited in settings characterized by high CO32- concentration, where carbonate can rapidly precipitate from seawater during early diagenesis. However, the use of δ13Ccarb-sh to infill gaps in the existing δ13Ccarb record remains uncertain, even when these criteria are fulfilled. Intervals of δ13C-δ18O co-variability in the Nama Group succession appear to correlate with units where seawater mixing with meteoric fluids was more likely during early diagenesis, such as clastic-dominated settings, which also show significant decreasing δ18O through time with gradual sub-basin infill. We further consider uncertainties in lithostratigraphic correlation of the upper Urusis Formation of the Nama Group that enable three new possible correlations to be proposed for δ13Ccarb-sh data within the terminal Ediacaran to lower Cambrian (<542.65 Ma to >532 Ma) regional and global δ13Ccarb records.",
    url = "https://ajsonline.org/article/88082.pdf",
    doi = "10.2475/001c.88082",
    is_oa = "true",
    semanticscholar_citation_count = "1",
    semanticscholar_id = "d990aa76495e8d7f15c997753b87d47deb1a6dfb",
    volume = "323"
}

Oxidative weathering of organic carbon in sedimentary rocks is a major source of CO2 to the atmosphere over geological timescales, but the size of this emission pathway in Earth's past has not been directly quantified due to a lack of available proxy approaches. We have measured the rhenium isotope composition of organic‐rich rocks sampled from unweathered drill cores and weathered outcrops in south Texas, whose stratigraphic successions can be tightly correlated. Oxidative weathering of more than 90% of the organic carbon and ∼85% of the rhenium is accompanied by a shift to lower rhenium isotope compositions in the weathered outcrops. The calculated isotope composition of rhenium weathered from the initial bedrock for individual samples varies systematically by ∼0.7‰ with different fractions of rhenium loss. This variation can be empirically modeled with isotope fractionation factors of α = 1.0002–1.0008. Our results indicate that the isotope composition of rhenium delivered to the oceans can be altered by weathering intensity of rock organic matter and that the rhenium isotope composition of seawater is sensitive to past oxidative weathering and associated CO2 emissions.

@article{doi1010292024gc011795,
    author = "Dickson, A. and Hilton, R. G. and Prytulak, J. and Minisini, D. and Eldrett, J. S. and Dellinger, M. and Stow, M. and Wang, W.",
    title = "Rhenium Isotopes Record Oxidative Weathering Intensity in Sedimentary Rocks",
    year = "2024",
    journal = "Geochemistry",
    abstract = "Oxidative weathering of organic carbon in sedimentary rocks is a major source of CO2 to the atmosphere over geological timescales, but the size of this emission pathway in Earth's past has not been directly quantified due to a lack of available proxy approaches. We have measured the rhenium isotope composition of organic‐rich rocks sampled from unweathered drill cores and weathered outcrops in south Texas, whose stratigraphic successions can be tightly correlated. Oxidative weathering of more than 90\% of the organic carbon and ∼85\% of the rhenium is accompanied by a shift to lower rhenium isotope compositions in the weathered outcrops. The calculated isotope composition of rhenium weathered from the initial bedrock for individual samples varies systematically by ∼0.7‰ with different fractions of rhenium loss. This variation can be empirically modeled with isotope fractionation factors of α = 1.0002–1.0008. Our results indicate that the isotope composition of rhenium delivered to the oceans can be altered by weathering intensity of rock organic matter and that the rhenium isotope composition of seawater is sensitive to past oxidative weathering and associated CO2 emissions.",
    url = "https://www.semanticscholar.org/paper/058b66535ef71cffe0f9643ea8bd121c1b2a68bd",
    doi = "10.1029/2024GC011795",
    is_oa = "true",
    number = "10",
    semanticscholar_id = "058b66535ef71cffe0f9643ea8bd121c1b2a68bd",
    volume = "25"
}

ABSTRACT The oxygenation of Earth’s atmosphere represents the quintessential transformation of a planetary surface by microbial processes. In turn, atmospheric oxygenation transformed metabolic evolution; molecular clock models indicate the diversification and ecological expansion of respiratory metabolisms in the several hundred million years following atmospheric oxygenation. Across this same interval, the geological record preserves 13C enrichment in some carbonate rocks, called the Lomagundi-Jatuli excursion (LJE). By combining data from geologic and genomic records, a self-consistent metabolic evolution model emerges for the LJE. First, fermentation and methanogenesis were major processes remineralizing organic carbon before atmospheric oxygenation. Once an ozone layer formed, shallow water and exposed environments were shielded from UVB/C radiation, allowing the expansion of cyanobacterial primary productivity. High primary productivity and methanogenesis led to preferential removal of 12C into organic carbon and CH4. Extreme and variable 13C enrichments in carbonates were caused by 13C-depleted CH4 loss to the atmosphere. Through time, aerobic respiration diversified and became ecologically widespread, as did other new metabolisms. Respiration displaced fermentation and methanogenesis as the dominant organic matter remineralization processes. As CH4 loss slowed, dissolved inorganic carbon in shallow environments was no longer highly 13C enriched. Thus, the loss of extreme 13C enrichments in carbonates marks the establishment of a new microbial mat ecosystem structure, one dominated by respiratory processes distributed along steep redox gradients. These gradients allowed the exchange of metabolic by-products among metabolically diverse organisms, providing novel metabolic opportunities. Thus, the microbially induced oxygenation of Earth’s atmosphere led to the transformation of microbial ecosystems, an archetypal example of planetary microbiology. IMPORTANCE The oxygenation of Earth’s atmosphere represents the most extensive known chemical transformation of a planetary surface by microbial processes. In turn, atmospheric oxygenation transformed metabolic evolution by providing oxidants independent of the sites of photosynthesis. Thus, the evolutionary changes during this interval and their effects on planetary-scale biogeochemical cycles are fundamental to our understanding of the interdependencies among genomes, organisms, ecosystems, elemental cycles, and Earth’s surface chemistry through time. The oxygenation of Earth’s atmosphere represents the most extensive known chemical transformation of a planetary surface by microbial processes. In turn, atmospheric oxygenation transformed metabolic evolution by providing oxidants independent of the sites of photosynthesis. Thus, the evolutionary changes during this interval and their effects on planetary-scale biogeochemical cycles are fundamental to our understanding of the interdependencies among genomes, organisms, ecosystems, elemental cycles, and Earth’s surface chemistry through time.

@article{doi101128aem0009324,
    author = "Sumner, D. Y.",
    title = "Oxygenation of Earth’s atmosphere induced metabolic and ecologic transformations recorded in the Lomagundi-Jatuli carbon isotopic excursion",
    year = "2024",
    journal = "Applied and Environmental Microbiology",
    abstract = "ABSTRACT The oxygenation of Earth’s atmosphere represents the quintessential transformation of a planetary surface by microbial processes. In turn, atmospheric oxygenation transformed metabolic evolution; molecular clock models indicate the diversification and ecological expansion of respiratory metabolisms in the several hundred million years following atmospheric oxygenation. Across this same interval, the geological record preserves 13C enrichment in some carbonate rocks, called the Lomagundi-Jatuli excursion (LJE). By combining data from geologic and genomic records, a self-consistent metabolic evolution model emerges for the LJE. First, fermentation and methanogenesis were major processes remineralizing organic carbon before atmospheric oxygenation. Once an ozone layer formed, shallow water and exposed environments were shielded from UVB/C radiation, allowing the expansion of cyanobacterial primary productivity. High primary productivity and methanogenesis led to preferential removal of 12C into organic carbon and CH4. Extreme and variable 13C enrichments in carbonates were caused by 13C-depleted CH4 loss to the atmosphere. Through time, aerobic respiration diversified and became ecologically widespread, as did other new metabolisms. Respiration displaced fermentation and methanogenesis as the dominant organic matter remineralization processes. As CH4 loss slowed, dissolved inorganic carbon in shallow environments was no longer highly 13C enriched. Thus, the loss of extreme 13C enrichments in carbonates marks the establishment of a new microbial mat ecosystem structure, one dominated by respiratory processes distributed along steep redox gradients. These gradients allowed the exchange of metabolic by-products among metabolically diverse organisms, providing novel metabolic opportunities. Thus, the microbially induced oxygenation of Earth’s atmosphere led to the transformation of microbial ecosystems, an archetypal example of planetary microbiology. IMPORTANCE The oxygenation of Earth’s atmosphere represents the most extensive known chemical transformation of a planetary surface by microbial processes. In turn, atmospheric oxygenation transformed metabolic evolution by providing oxidants independent of the sites of photosynthesis. Thus, the evolutionary changes during this interval and their effects on planetary-scale biogeochemical cycles are fundamental to our understanding of the interdependencies among genomes, organisms, ecosystems, elemental cycles, and Earth’s surface chemistry through time. The oxygenation of Earth’s atmosphere represents the most extensive known chemical transformation of a planetary surface by microbial processes. In turn, atmospheric oxygenation transformed metabolic evolution by providing oxidants independent of the sites of photosynthesis. Thus, the evolutionary changes during this interval and their effects on planetary-scale biogeochemical cycles are fundamental to our understanding of the interdependencies among genomes, organisms, ecosystems, elemental cycles, and Earth’s surface chemistry through time.",
    url = "https://www.semanticscholar.org/paper/06f64bfb04c15914b37bfea23f0a710b03c778ea",
    doi = "10.1128/aem.00093-24",
    is_oa = "true",
    number = "6",
    semanticscholar_citation_count = "8",
    semanticscholar_id = "06f64bfb04c15914b37bfea23f0a710b03c778ea",
    volume = "90"
}

The Archean rock record is limited and there is minimal organic matter available to understand the origin and evolution of life on early Earth. Low carbon isotope ratios have been measured in organic and reduced carbon phases in Archean rocks and have been invoked as biosignatures. However, it can be challenging to distinguish whether these low values reflect biotic formation, abiotic reactions, or post-depositional processes. To re-address this long-standing question, we compiled a comprehensive dataset of carbon isotope ratio measurements from organic carbon phases from Archean units that were analyzed using a variety of geochemical techniques. Our compilation also includes available descriptions and measurements of the stratigraphy, mineralogy, elemental ratios, and metamorphic grade for each data point. Our statistical analyses re-enforce a result that has been noted by prior compilations, that the carbon isotopic composition of Archean organic matter (OM) is broadly more 13C-deplete than the composition of Phanerozoic OM: The median δ13C values ( ±SD) of Archean total organic carbon and kerogen were −30.5±8‰ (n=2421) and −33.7±11.3‰ (n=556; Phanerozoic OM δ13C ±SD = −26.7±4.6‰ with n=449 from a prior compilation). Our study also identifies a previously unrecognized bimodality within the δ13C values of Archean OM that is observed even with subsampling of the data to account for geographic and stratigraphic sampling bias. We describe and model the isotopic and structural changes associated with the transformation of marine Type II kerogen from formation through diagenesis, catagenesis and metagenesis, and metamorphism, as described by trends on a van Krevelin diagram. Empirically, early maturation of organic matter during diagenesis results in shifts up to a few per-mille, which can occur in either direction depending on selective preservation and degradation of compounds. Thermal cracking that occurs during catagenesis can drive increases in δ13C of 5–12‰. At temperatures above greenschist metamorphism, carbon atoms exchange with other reactive carbon pools, driving increases in δ13C of up to 20‰. Together, our analyses suggest that the most metamorphosed graphitic samples from the earliest Archean are likely signatures of alteration, while low and multimodal ranges of δ13C values may preserve records of Archean ecology.

@article{doi102475001c116058,
    author = "Zeichner, S. and Fischer, Woodward W. and Lotem, Noam and Moore, K. and Goldford, J. and Eiler, J.",
    title = "The Carbon Isotopic Composition of Archean Kerogen and Its Resilience Through the Rock Cycle",
    year = "2024",
    journal = "American Journal of Science",
    abstract = "The Archean rock record is limited and there is minimal organic matter available to understand the origin and evolution of life on early Earth. Low carbon isotope ratios have been measured in organic and reduced carbon phases in Archean rocks and have been invoked as biosignatures. However, it can be challenging to distinguish whether these low values reflect biotic formation, abiotic reactions, or post-depositional processes. To re-address this long-standing question, we compiled a comprehensive dataset of carbon isotope ratio measurements from organic carbon phases from Archean units that were analyzed using a variety of geochemical techniques. Our compilation also includes available descriptions and measurements of the stratigraphy, mineralogy, elemental ratios, and metamorphic grade for each data point. Our statistical analyses re-enforce a result that has been noted by prior compilations, that the carbon isotopic composition of Archean organic matter (OM) is broadly more 13C-deplete than the composition of Phanerozoic OM: The median δ13C values ( ±SD) of Archean total organic carbon and kerogen were −30.5±8‰ (n=2421) and −33.7±11.3‰ (n=556; Phanerozoic OM δ13C ±SD = −26.7±4.6‰ with n=449 from a prior compilation). Our study also identifies a previously unrecognized bimodality within the δ13C values of Archean OM that is observed even with subsampling of the data to account for geographic and stratigraphic sampling bias. We describe and model the isotopic and structural changes associated with the transformation of marine Type II kerogen from formation through diagenesis, catagenesis and metagenesis, and metamorphism, as described by trends on a van Krevelin diagram. Empirically, early maturation of organic matter during diagenesis results in shifts up to a few per-mille, which can occur in either direction depending on selective preservation and degradation of compounds. Thermal cracking that occurs during catagenesis can drive increases in δ13C of 5–12‰. At temperatures above greenschist metamorphism, carbon atoms exchange with other reactive carbon pools, driving increases in δ13C of up to 20‰. Together, our analyses suggest that the most metamorphosed graphitic samples from the earliest Archean are likely signatures of alteration, while low and multimodal ranges of δ13C values may preserve records of Archean ecology.",
    url = "https://ajsonline.org/article/116058.pdf",
    doi = "10.2475/001c.116058",
    is_oa = "true",
    semanticscholar_citation_count = "1",
    semanticscholar_id = "c6563aa8326439cf3c64d261a454f653303a0def",
    volume = "324"
}

The rapid warming events (hyperthermals) of late Paleocene to early Eocene time—the Paleocene−Eocene Thermal Maximum (PETM), Eocene Thermal Maximum 2 (ETM2/H1), H2, I1, and I2—were recorded in marine and terrestrial facies in the form of negative carbon-isotope excursions (CIEs). Unlike the numerous discoveries of the PETM in terrestrial facies, records of the other hyperthermals (ETM2/H1, H2, I1, and I2) are rare. To better understand these other Paleocene−Eocene hyperthermals and their utility for stratigraphic correlation between marine and terrestrial deposits, we performed carbon- and oxygen-isotope analysis of lacustrine sedimentary rocks from the ZK0303 well in the southwestern Jianghan Basin, Central China. Based on palynological data, the 320−1000 m section of the well represents the stratigraphic period from 65 Ma to 52 Ma. The δ13C records for bulk carbonate (δ13Ccarb) and bulk organic matter (OM; δ13Corg) include three significant negative shifts. Based on a stratigraphic comparison with global marine and continental records from the same period, the three negative CIEs observed were assigned to three hyperthermals: the PETM, the ETM2/H1, and the H2 events. The recorded magnitudes of the CIEs of the δ13Ccarb values of the PETM, ETM2/H1, and H2 (−10.1‰, −6.7‰, and −5.6‰) are greater than those of the δ13Corg values (−4.4‰, −3.6‰, and −2.3‰). In comparison to the vast ocean, which responded more slowly to the increase in humidity and pCO2 concentration and had stronger buffering capacity during the PETM, the smaller Jianghan Basin was more intensely affected by the increase in the pCO2 concentration and especially the increase in humidity. This resulted in a CIE magnitude of the δ13Corg value (−4.40‰) significantly larger than those of marine records. The climate during the PETM was very humid and hot, with flourishing vegetation, enhanced soil respiration, increased OM oxidation, and higher runoff. This resulted in a significant decrease in the δ13C value of dissolved inorganic carbon in the lake. In contrast, the climate was relatively dry during the ETM2/H1 and H2 events, the lake level declined, and groundwater (springs) probably constituted the main water supply to the lake, with runoff playing a lesser role. The discovery of the three hyperthermals in the ZK0303 well reveals that the humid climate of the Paleocene−Eocene in the Jianghan Basin began during the PETM and ended during the ETM2/H1 and H2 events.

@article{doi101130b376501,
    author = "Yan, Kai and Wang, Chunlian and Wang, Jiuyi and Chen, Renyi and Mischke, Steffen and Teng, Xiaohua and Yu, Xiao-can",
    title = "Patterns of carbon-isotope excursions recorded in lacustrine sedimentary rocks of Central China during Paleocene−Eocene hyperthermals",
    year = "2025",
    journal = "Geological Society of America Bulletin",
    abstract = "The rapid warming events (hyperthermals) of late Paleocene to early Eocene time—the Paleocene−Eocene Thermal Maximum (PETM), Eocene Thermal Maximum 2 (ETM2/H1), H2, I1, and I2—were recorded in marine and terrestrial facies in the form of negative carbon-isotope excursions (CIEs). Unlike the numerous discoveries of the PETM in terrestrial facies, records of the other hyperthermals (ETM2/H1, H2, I1, and I2) are rare. To better understand these other Paleocene−Eocene hyperthermals and their utility for stratigraphic correlation between marine and terrestrial deposits, we performed carbon- and oxygen-isotope analysis of lacustrine sedimentary rocks from the ZK0303 well in the southwestern Jianghan Basin, Central China. Based on palynological data, the 320−1000 m section of the well represents the stratigraphic period from 65 Ma to 52 Ma. The δ13C records for bulk carbonate (δ13Ccarb) and bulk organic matter (OM; δ13Corg) include three significant negative shifts. Based on a stratigraphic comparison with global marine and continental records from the same period, the three negative CIEs observed were assigned to three hyperthermals: the PETM, the ETM2/H1, and the H2 events. The recorded magnitudes of the CIEs of the δ13Ccarb values of the PETM, ETM2/H1, and H2 (−10.1‰, −6.7‰, and −5.6‰) are greater than those of the δ13Corg values (−4.4‰, −3.6‰, and −2.3‰). In comparison to the vast ocean, which responded more slowly to the increase in humidity and pCO2 concentration and had stronger buffering capacity during the PETM, the smaller Jianghan Basin was more intensely affected by the increase in the pCO2 concentration and especially the increase in humidity. This resulted in a CIE magnitude of the δ13Corg value (−4.40‰) significantly larger than those of marine records. The climate during the PETM was very humid and hot, with flourishing vegetation, enhanced soil respiration, increased OM oxidation, and higher runoff. This resulted in a significant decrease in the δ13C value of dissolved inorganic carbon in the lake. In contrast, the climate was relatively dry during the ETM2/H1 and H2 events, the lake level declined, and groundwater (springs) probably constituted the main water supply to the lake, with runoff playing a lesser role. The discovery of the three hyperthermals in the ZK0303 well reveals that the humid climate of the Paleocene−Eocene in the Jianghan Basin began during the PETM and ended during the ETM2/H1 and H2 events.",
    url = "https://www.semanticscholar.org/paper/9ad3cbd0daf6426d48d7d6d673c9aafe6ef53272",
    doi = "10.1130/b37650.1",
    is_oa = "true",
    number = "11-12",
    pages = "5424-5434",
    semanticscholar_id = "9ad3cbd0daf6426d48d7d6d673c9aafe6ef53272",
    volume = "137"
}

The Otish Supergroup and Mistassini Group of north-central Quebec are two weakly metamorphosed sedimentary successions deposited during the middle Paleoproterozoic along the modern-day eastern margin of the Archean Superior craton. This study presents new uranium-lead (U-Pb) detrital zircon and shale rhenium-osmium (Re-Os) geochronological data for these two successions, as well as δ13Ccarb data from sedimentary carbonate rocks, which comprise the first such data for the Otish Supergroup. New geochronological data presented here demonstrate that the Mistassini Group was deposited between 2121 Ma and 1825 Ma and postdates the Otish Supergroup by at least ∼20 m.y. The δ13Ccarb data from the Otish Supergroup are strongly enriched, typically +7‰ to +12‰, and therefore consistent with deposition during the Lomagundi-Jatuli carbon isotope excursion (LJE), which is generally considered to have occurred during ca. 2220−2060 Ma. Within the basal ∼200 m of the Mistassini Group, δ13Ccarb values reach almost +8‰, before shifting to near 0‰ in the overlying ∼1800 m of strata, which indicates that it records the termination of the LJE. The Re-Os depositional age of 1825 ± 9 Ma for mudstones of the Kallio Formation, the uppermost formation in the Mistassini Group, provides a minimum constraint for deposition in the basin. Cumulatively, the new radiometric ages and stable isotope ratio data provide a basis for a new tectonostratigraphic reconstruction that closely links the Mistassini and Otish basins to the evolution of the Labrador Trough and other basins along the eastern and southern margins of the Superior craton.

@article{doi101130b379481,
    author = "Hodgskiss, M. and Lechte, Maxwell A. and Rainbird, R. and Whelan, M. and Creaser, R. and Davis, William J. and Slagstad, T. and Mansur, Eduardo T. and Kirsimäe, K. and Kovalick, A. and Bekker, Andrey",
    title = "The Paleoproterozoic Otish and Mistassini basins of Quebec, Canada: A record of Superia supercraton breakup and the end of the Lomagundi-Jatuli carbon isotope excursion",
    year = "2025",
    journal = "Geological Society of America Bulletin",
    abstract = "The Otish Supergroup and Mistassini Group of north-central Quebec are two weakly metamorphosed sedimentary successions deposited during the middle Paleoproterozoic along the modern-day eastern margin of the Archean Superior craton. This study presents new uranium-lead (U-Pb) detrital zircon and shale rhenium-osmium (Re-Os) geochronological data for these two successions, as well as δ13Ccarb data from sedimentary carbonate rocks, which comprise the first such data for the Otish Supergroup. New geochronological data presented here demonstrate that the Mistassini Group was deposited between 2121 Ma and 1825 Ma and postdates the Otish Supergroup by at least ∼20 m.y. The δ13Ccarb data from the Otish Supergroup are strongly enriched, typically +7‰ to +12‰, and therefore consistent with deposition during the Lomagundi-Jatuli carbon isotope excursion (LJE), which is generally considered to have occurred during ca. 2220−2060 Ma. Within the basal ∼200 m of the Mistassini Group, δ13Ccarb values reach almost +8‰, before shifting to near 0‰ in the overlying ∼1800 m of strata, which indicates that it records the termination of the LJE. The Re-Os depositional age of 1825 ± 9 Ma for mudstones of the Kallio Formation, the uppermost formation in the Mistassini Group, provides a minimum constraint for deposition in the basin. Cumulatively, the new radiometric ages and stable isotope ratio data provide a basis for a new tectonostratigraphic reconstruction that closely links the Mistassini and Otish basins to the evolution of the Labrador Trough and other basins along the eastern and southern margins of the Superior craton.",
    url = "https://www.semanticscholar.org/paper/c997d8e98a24ae9921bbf645a49dec84a0d2bcbb",
    doi = "10.1130/b37948.1",
    is_oa = "true",
    number = "7-8",
    pages = "3647-3669",
    semanticscholar_citation_count = "2",
    semanticscholar_id = "c997d8e98a24ae9921bbf645a49dec84a0d2bcbb",
    volume = "137"
}

Over the past few decades, ultraviolet (UV) cured bio-based resins have been widely applied in UV cured. However, most UV cured bio-based resins are plagued by issues such as excessively high viscosity and poor mechanical properties. Epoxy soybean oil acrylate (AESO) is environmentally friendly. A series of AESOs with different contents of carbon-carbon double bonds functionality (from 2.28 to 4.32) were obtained through ring-opening reactions using acrylic acid and Epoxy soybean oil (ESO). The photo curing resins were obtained by mixing AESO with hexanediol diacrylate (HDDA), dicyclopentadieneoxyethyl acrylate (DCPEA), and diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide (TPO). The resins were rapidly cured under a 395 nm ultraviolet light-emitting diode (UV-LED) light source to form cured films. The cured film from AESO with functionality of 4.32 has good mechanical strength, with a tensile strength of 18.73 MPa and an elongation at break of 13.12%. The performance far exceeds that of the pure AESOcured film reported in the literature. This work provides a highly meaningful solution for the development of solvent-free epoxy soybean oil-based UV-LED cured films.

@article{doi101002marc70275,
    author = "Zhang, Qihao and Tang, Chengxing and Wang, Niangui and Wei, Lanhua",
    title = "Effect of Carbon-Carbon Double Bond Functionality on Properties of UV-LED Cured Epoxy Soybean Oil Acrylate Films.",
    year = "2026",
    journal = "Macromolecular rapid communications",
    abstract = "Over the past few decades, ultraviolet (UV) cured bio-based resins have been widely applied in UV cured. However, most UV cured bio-based resins are plagued by issues such as excessively high viscosity and poor mechanical properties. Epoxy soybean oil acrylate (AESO) is environmentally friendly. A series of AESOs with different contents of carbon-carbon double bonds functionality (from 2.28 to 4.32) were obtained through ring-opening reactions using acrylic acid and Epoxy soybean oil (ESO). The photo curing resins were obtained by mixing AESO with hexanediol diacrylate (HDDA), dicyclopentadieneoxyethyl acrylate (DCPEA), and diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide (TPO). The resins were rapidly cured under a 395 nm ultraviolet light-emitting diode (UV-LED) light source to form cured films. The cured film from AESO with functionality of 4.32 has good mechanical strength, with a tensile strength of 18.73 MPa and an elongation at break of 13.12\%. The performance far exceeds that of the pure AESOcured film reported in the literature. This work provides a highly meaningful solution for the development of solvent-free epoxy soybean oil-based UV-LED cured films.",
    url = "https://pubmed.ncbi.nlm.nih.gov/42044210/",
    doi = "10.1002/marc.70275",
    pmid = "42044210"
}

The development of high-performance supercapacitor electrode materials critically depends on the concurrent optimization of porosity and heteroatom doping. Herein, a simple NH4Cl-assisted dual-functional strategy is proposed to convert inedible sprouted potato starch into nitrogen-doped porous carbon, enabling the simultaneous modulation of pore structure and nitrogen configuration within a single thermal process. Systematic comparisons of different nitrogen sources (melamine, urea, and NH4Cl) under identical synthesis conditions reveal that NH4Cl exhibits more evident dual-functional roles in the present system, contributing to both pore regulation and nitrogen incorporation. Its presence is proposed to influence the distribution state of Zn-containing species during activation, which may contribute to the formation of a high-surface-area porous structure (1589 m2 g-1, 97% micropore contribution) favorable for charge storage. Meanwhile, as a nitrogen source, NH4Cl effectively introduces graphitic nitrogen (34.98% of total nitrogen, and 2.51 of absolute content), facilitating electron transport and interfacial charge transfer. The resulting NPCT-N electrode delivers a high specific capacitance of 438 F g-1 at 1 A g-1 and maintains 270 F g-1 under a commercial-level mass loading of 10 mg cm-2. Furthermore, a gel-based quasi-solid-state flexible symmetric supercapacitor assembled with this electrode achieves an energy density of 32 Wh kg-1 at 900 W kg-1, with two devices connected in series providing a stable output voltage of 3.6 V. This NH4Cl-assisted approach provides a simple route for converting inedible sprouted potato starch into nitrogen-doped porous carbon for energy storage applications.

@article{doi101021acslangmuir6c00197,
    author = "Guo, Ziwen and Li, Xinyue and Jiang, Lili and Zhao, Chenglong and Liang, Jingwu and Cai, Yibin and Guo, Huijun and Li, Jianping and Wu, Dai and Geng, Shudong and Tong, Liangliang and Sheng, Lizhi",
    title = "Nitrogen-Doped Porous Carbon Enabled by a Dual-Functional NH4Cl-Assisted Strategy for Quasi-Solid-State Supercapacitors.",
    year = "2026",
    journal = "Langmuir: the ACS journal of surfaces and colloids",
    abstract = "The development of high-performance supercapacitor electrode materials critically depends on the concurrent optimization of porosity and heteroatom doping. Herein, a simple NH4Cl-assisted dual-functional strategy is proposed to convert inedible sprouted potato starch into nitrogen-doped porous carbon, enabling the simultaneous modulation of pore structure and nitrogen configuration within a single thermal process. Systematic comparisons of different nitrogen sources (melamine, urea, and NH4Cl) under identical synthesis conditions reveal that NH4Cl exhibits more evident dual-functional roles in the present system, contributing to both pore regulation and nitrogen incorporation. Its presence is proposed to influence the distribution state of Zn-containing species during activation, which may contribute to the formation of a high-surface-area porous structure (1589 m2 g-1, 97\% micropore contribution) favorable for charge storage. Meanwhile, as a nitrogen source, NH4Cl effectively introduces graphitic nitrogen (34.98\% of total nitrogen, and 2.51 of absolute content), facilitating electron transport and interfacial charge transfer. The resulting NPCT-N electrode delivers a high specific capacitance of 438 F g-1 at 1 A g-1 and maintains 270 F g-1 under a commercial-level mass loading of 10 mg cm-2. Furthermore, a gel-based quasi-solid-state flexible symmetric supercapacitor assembled with this electrode achieves an energy density of 32 Wh kg-1 at 900 W kg-1, with two devices connected in series providing a stable output voltage of 3.6 V. This NH4Cl-assisted approach provides a simple route for converting inedible sprouted potato starch into nitrogen-doped porous carbon for energy storage applications.",
    url = "https://pubmed.ncbi.nlm.nih.gov/42044395/",
    doi = "10.1021/acs.langmuir.6c00197",
    pmid = "42044395"
}