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Martin D Brasier - One of the best experts on this subject based on the ideXlab platform.
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3 46 ga apex chert Microfossils reinterpreted as mineral artefacts produced during phyllosilicate exfoliation
Gondwana Research, 2016Co-Authors: David Wacey, Charlie Kong, Martin Saunders, A T Brasier, Martin D BrasierAbstract:Abstract Filamentous microstructures from the 3.46 billion year (Ga)-old Apex chert of Western Australia have been interpreted as remnants of Earth's oldest cellular life, but their purported biological nature has been robustly questioned on numerous occasions. Despite recent claims to the contrary, the controversy surrounding these famous microstructures remains unresolved. Here we interrogate new material from the original ‘microfossil site’ using high spatial resolution electron microscopy to decode the detailed morphology and chemistry of the Apex filaments. Light microscopy shows that our newly discovered filaments are identical to the previously described ‘microfossil’ holotypes and paratypes. Scanning and transmission electron microscopy data show that the filaments comprise chains of potassium- and barium-rich phyllosilicates, interleaved with carbon, minor quartz and iron oxides. Morphological features previously cited as evidence for cell compartments and dividing cells are shown to be carbon-coated stacks of phyllosilicate crystals. Three-dimensional filament reconstructions reveal non-rounded cross sections and examples of branching incompatible with a filamentous prokaryotic origin for these structures. When examined at the nano-scale, the Apex filaments exhibit no biological morphology nor bear any resemblance to younger bona fide carbonaceous Microfossils. Instead, available evidence indicates that the microstructures formed during fluid-flow events that facilitated the hydration, heating and exfoliation of potassium mica flakes, plus the redistribution and adsorption of barium, iron and carbon within an active hydrothermal system.
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nanoscale analysis of pyritized Microfossils reveals differential heterotrophic consumption in the 1 9 ga gunflint chert
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Nicola Mcloughlin, John B Cliff, David Wacey, Charlie Kong, Martin Saunders, Matt R Kilburn, Mark Barley, Martin D BrasierAbstract:The 1.88-Ga Gunflint biota is one of the most famous Precambrian microfossil lagerstatten and provides a key record of the biosphere at a time of changing oceanic redox structure and chemistry. Here, we report on pyritized replicas of the iconic autotrophic Gunflintia-Huroniospora microfossil assemblage from the Schreiber Locality, Canada, that help capture a view through multiple trophic levels in a Paleoproterozoic ecosystem. Nanoscale analysis of pyritic Gunflintia (sheaths) and Huroniospora (cysts) reveals differing relic carbon and nitrogen distributions caused by contrasting spectra of decay and pyritization between taxa, reflecting in part their primary organic compositions. In situ sulfur isotope measurements from individual Microfossils (δ(34)S(V-CDT) +6.7‰ to +21.5‰) show that pyritization was mediated by sulfate-reducing microbes within sediment pore waters whose sulfate ion concentrations rapidly became depleted, owing to occlusion of pore space by coeval silicification. Three-dimensional nanotomography reveals additional pyritized biomaterial, including hollow, cellular epibionts and extracellular polymeric substances, showing a preference for attachment to Gunflintia over Huroniospora and interpreted as components of a saprophytic heterotrophic, decomposing community. This work also extends the record of remarkable biological preservation in pyrite back to the Paleoproterozoic and provides criteria to assess the authenticity of even older pyritized microstructures that may represent some of the earliest evidence for life on our planet.
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taphonomy of very ancient Microfossils from the 3400ma strelley pool formation and 1900ma gunflint formation new insights using a focused ion beam
Precambrian Research, 2012Co-Authors: David Wacey, Nicola Mcloughlin, Sarath Menon, Leonard Green, Derek Gerstmann, Charlie Kong, Martin Saunders, Martin D BrasierAbstract:Abstract Focused ion beam (FIB) milling permits the accurate extraction of ultrathin (c. 100 nm) cross sectional lamellae from Microfossils found in geological thin sections. Subsequent TEM analysis of these lamellae can provide unique insights into the ultrastructure, chemistry and taphonomy of Precambrian Microfossils at the micrometer to nanometer scale. Combining serial FIB milling with SEM imaging extends this capability to three dimensional (3D) tomographic reconstruction and visualization of Precambrian Microfossils, revealing information not available in light microscopy. Here we apply these techniques to two iconic silicified microfossil assemblages, from the ∼3400 Ma Strelley Pool Formation of Western Australia and the ∼1900 Ma Gunflint Formation of Canada. All the examined Microfossils have carbonaceous walls surrounded by pure silica. Impregnation of microfossil walls by nano-grains of silica is common, together with variable degrees of wall displacement and replacement by silica. All Microfossils are rigidly preserved in 3D and show little or no folding or compression. However, there are also notable differences in taphonomic preservation. Our examples of the spheroidal Gunflint microfossil Huroniospora showed the highest fidelity of preservation with a continuous carbonaceous wall fossilized by spheroidal nano-silica grains that resemble those found on bacterial surfaces in modern silicifying hot-spring environments. The nucleation of these silica nano-spheres on the microfossil walls has induced an artificial ‘saw-tooth-like’ ridged wall texture that may subsequently hinder species-level identification. The Strelley Pool Microfossils in comparison show a lower fidelity of preservation with small parts of the microfossil walls completely replaced by silica, plus extensive recrystallization of spheroidal silica nano-grains to angular micro-quartz. Our examples of the sheath-like filamentous Gunflint microfossil Siphonophycus showed the lowest fidelity of preservation with many gaps in the carbonaceous walls and significant redistribution of carbon by recrystallizing silica grains. A model is presented to explain these observations. Criteria for distinguishing highly probable Microfossils from non-cellular carbonaceous microstructures (e.g., botryoids and grain coatings) using FIB-based imaging are put forward for the first time here, using examples drawn from the Strelley Pool Formation and comparisons with younger Gunflint material. The combined in situ techniques of FIB–TEM and FIB–SEM nano-tomography potentially provide a wealth of new nano-scale information regarding the biogenicity, antiquity and taphonomy of Precambrian Microfossils. However, the destructive nature of both techniques makes their application to unique palaeontological specimens problematical.
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critical testing of earth s oldest putative fossil assemblage from the 3 5ga apex chert chinaman creek western australia
Precambrian Research, 2005Co-Authors: Martin D Brasier, Nicola Mcloughlin, Owen R Green, John F Lindsay, A Steele, Cris StoakesAbstract:Abstract Structures resembling cyanobacterial Microfossils from the ca. 3465 Ma old Apex chert of the Warrawoona Group in Western Australia have until recently been accepted as providing the oldest morphological evidence for life on Earth, and have been taken to support an early beginning for oxygen-releasing photosynthesis. Eleven species of filamentous prokaryote, principally distinguished by shape and geometry, have been put forward as meeting the criteria required of authentic Archaean Microfossils. They were contrasted with other Microfossils that were dismissed as either unreliable or irreproducible. The aim of this paper is to provide a detailed account of research recently reported by us on the type and recollected material, involving optical and electron microscopy, digital image analysis and other techniques. All previously figured holotype materials are illustrated here, and the context for all the published materials is re-evaluated. The Apex chert ‘Microfossils’ occur near the top of a 1.5-km long chert dyke complex associated with major synsedimentary growth faults. Highly localised, glassy felsic tuffs erupted explosively from this and other fissures during the early stages of volcanism, and were followed by the deposition of essentially hydrothermal black and white BaSO4 rich cherts that infiltrated the feeder dykes, underplating and dilating adjacent stratiform cherts before the start of the next volcanic cycle. The Apex chert ‘Microfossils’ occur within multiple generations of these metalliferous hydrothermal vein cherts some 100 m down the dyke system. Comparable structures occur in associated volcanic vent glass and in hydrothermal cherts at least 1 km deep. We find no supporting evidence for a primary biological origin. We reinterpret the purported microfossil-like structures as pseudofossils that formed from the reorganization of carbonaceous matter, mainly during recrystallization from amorphous to spherulitic silica.
Martin J Van Kranendonk - One of the best experts on this subject based on the ideXlab platform.
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snapshot of an early paleoproterozoic ecosystem two diverse microfossil communities from the turee creek group western australia
Geobiology, 2018Co-Authors: Erica Victoria Barlow, Martin J Van KranendonkAbstract:Eighteen microfossil morphotypes from two distinct facies of black chert from a deep-water setting of the c. 2.4 Ga Turee Creek Group, Western Australia, are reported here. A primarily in situ, deep-water benthic community preserved in nodular black chert occurs as a tangled network of a variety of long filamentous Microfossils, unicells of one size distribution and fine filamentous rosettes, together with relatively large spherical aggregates of cells interpreted as in-fallen, likely planktonic, forms. Bedded black cherts, in contrast, preserve Microfossils primarily within, but also between, rounded clasts of organic material that are coated by thin, convoluted carbonaceous films interpreted as preserved extracellular polymeric substance (EPS). Microfossils preserved within the clasts include a wide range of unicells, both much smaller and larger than those in the nodular black chert, along with relatively short, often degraded filaments, four types of star-shaped rosettes and umbrella-like rosettes. Large, complexly branching filamentous Microfossils are found between the clasts. The grainstone clasts in the bedded black chert are interpreted as transported from shallower water, and the contained Microfossils thus likely represent a phototrophic community. Combined, the two black chert facies provide a snapshot of a microbial ecosystem spanning shallow to deeper-water environments, and an insight into the diversity of life present during the rise in atmospheric oxygen. The preserved Microfossils include two new, distinct morphologies previously unknown from the geological record, as well as a number of Microfossils from the bedded black chert that are morphologically similar to-but 400-500 Ma older than-type specimens from the c. 1.88 Ga Gunflint Iron Formation. Thus, the Turee Creek Group microfossil assemblage creates a substantial reference point in the sparse fossil record of the earliest Paleoproterozoic and demonstrates that microbial life diversified quite rapidly after the end of the Archean.
David Wacey - One of the best experts on this subject based on the ideXlab platform.
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pathways of microfossil mineralisation by hematite in the 1878 ma gunflint formation
Chemical Geology, 2021Co-Authors: David Wacey, Kate Eiloart, Martin SaundersAbstract:Abstract The ~1878 Ma Gunflint Formation contains some of the foremost examples of Palaeoproterozoic life but questions remain regarding the potential metabolic and taphonomic pathways within the microfossil assemblage. Here we report on hematite-mineralised examples of the most abundant Gunflint organisms (Gunflintia and Huroniospora), using correlative light-, Raman- and electron-microscopy to document subtle variations in iron oxide mineralisation styles. Data come from two localities where similar stromatolitic facies are found, namely Schreiber Channel and Mink Mountain, Ontario. At Schreiber Channel, rare hematitic Microfossils are found at the margins of small pods of pyritised microorganisms, with some individual cell or sheath walls retaining pyrite cores and hematite rims. Microfossil wall hematite grains form anhedral masses, contain large numbers of quartz inclusions, plus a small number of barium-rich and calcium-rich nano-crystals. Hematitic, pyritic and carbonaceous microfossil preservation styles co-occur within a single petrographic thin section. A sub-set of iron-mineralised fossils at Schreiber have thinner walls, comprising tabular hematite grains plus Fe-Al-silicates and traces of organic material. At Mink Mountain, microfossil walls are ubiquitously preserved as hematite but well-preserved examples occur only in isolated zones of particularly dark brown/purple hematite. Here, hematite grains show a cuspate to anhedral habit with embayment and inclusions of quartz plus rare Ti-rich nano-crystals; nano-particles of iron oxide and rare organic material occur as bridges between some grains. The morphological similarity of microfossil assemblages having walls now preserved with different chemical compositions (carbon, pyrite, Fe-Al-silicate and hematite), and across widely-spaced stromatolitic localities, indicates that iron oxide mineralisation was a taphonomic rather than primary metabolic process. The pyrite and Fe-Al-silicates at Schreiber are interpreted as the earliest stages of iron mineralisation, forming under reducing diagenetic conditions in the presence of excess organic material. Partial replacement of these phases by hematite followed later when oxygen bearing fluids penetrated limited zones within the sediments. At Mink Mountain, we infer that zones of well-preserved Microfossils were initially mineralised as pyrite, followed by the complete oxidation of pyrite plus all surrounding organic material to hematite. This study demonstrates the importance of localised micro-environmental conditions on taphonomic processes and, in turn, the role that taphonomy can play in the modification of the morphology of fossilised organisms. This has implications both for the study of early life on Earth and for the assessment of any putative Microfossils returned from Mars.
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3 46 ga apex chert Microfossils reinterpreted as mineral artefacts produced during phyllosilicate exfoliation
Gondwana Research, 2016Co-Authors: David Wacey, Charlie Kong, Martin Saunders, A T Brasier, Martin D BrasierAbstract:Abstract Filamentous microstructures from the 3.46 billion year (Ga)-old Apex chert of Western Australia have been interpreted as remnants of Earth's oldest cellular life, but their purported biological nature has been robustly questioned on numerous occasions. Despite recent claims to the contrary, the controversy surrounding these famous microstructures remains unresolved. Here we interrogate new material from the original ‘microfossil site’ using high spatial resolution electron microscopy to decode the detailed morphology and chemistry of the Apex filaments. Light microscopy shows that our newly discovered filaments are identical to the previously described ‘microfossil’ holotypes and paratypes. Scanning and transmission electron microscopy data show that the filaments comprise chains of potassium- and barium-rich phyllosilicates, interleaved with carbon, minor quartz and iron oxides. Morphological features previously cited as evidence for cell compartments and dividing cells are shown to be carbon-coated stacks of phyllosilicate crystals. Three-dimensional filament reconstructions reveal non-rounded cross sections and examples of branching incompatible with a filamentous prokaryotic origin for these structures. When examined at the nano-scale, the Apex filaments exhibit no biological morphology nor bear any resemblance to younger bona fide carbonaceous Microfossils. Instead, available evidence indicates that the microstructures formed during fluid-flow events that facilitated the hydration, heating and exfoliation of potassium mica flakes, plus the redistribution and adsorption of barium, iron and carbon within an active hydrothermal system.
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nanoscale analysis of pyritized Microfossils reveals differential heterotrophic consumption in the 1 9 ga gunflint chert
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Nicola Mcloughlin, John B Cliff, David Wacey, Charlie Kong, Martin Saunders, Matt R Kilburn, Mark Barley, Martin D BrasierAbstract:The 1.88-Ga Gunflint biota is one of the most famous Precambrian microfossil lagerstatten and provides a key record of the biosphere at a time of changing oceanic redox structure and chemistry. Here, we report on pyritized replicas of the iconic autotrophic Gunflintia-Huroniospora microfossil assemblage from the Schreiber Locality, Canada, that help capture a view through multiple trophic levels in a Paleoproterozoic ecosystem. Nanoscale analysis of pyritic Gunflintia (sheaths) and Huroniospora (cysts) reveals differing relic carbon and nitrogen distributions caused by contrasting spectra of decay and pyritization between taxa, reflecting in part their primary organic compositions. In situ sulfur isotope measurements from individual Microfossils (δ(34)S(V-CDT) +6.7‰ to +21.5‰) show that pyritization was mediated by sulfate-reducing microbes within sediment pore waters whose sulfate ion concentrations rapidly became depleted, owing to occlusion of pore space by coeval silicification. Three-dimensional nanotomography reveals additional pyritized biomaterial, including hollow, cellular epibionts and extracellular polymeric substances, showing a preference for attachment to Gunflintia over Huroniospora and interpreted as components of a saprophytic heterotrophic, decomposing community. This work also extends the record of remarkable biological preservation in pyrite back to the Paleoproterozoic and provides criteria to assess the authenticity of even older pyritized microstructures that may represent some of the earliest evidence for life on our planet.
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taphonomy of very ancient Microfossils from the 3400ma strelley pool formation and 1900ma gunflint formation new insights using a focused ion beam
Precambrian Research, 2012Co-Authors: David Wacey, Nicola Mcloughlin, Sarath Menon, Leonard Green, Derek Gerstmann, Charlie Kong, Martin Saunders, Martin D BrasierAbstract:Abstract Focused ion beam (FIB) milling permits the accurate extraction of ultrathin (c. 100 nm) cross sectional lamellae from Microfossils found in geological thin sections. Subsequent TEM analysis of these lamellae can provide unique insights into the ultrastructure, chemistry and taphonomy of Precambrian Microfossils at the micrometer to nanometer scale. Combining serial FIB milling with SEM imaging extends this capability to three dimensional (3D) tomographic reconstruction and visualization of Precambrian Microfossils, revealing information not available in light microscopy. Here we apply these techniques to two iconic silicified microfossil assemblages, from the ∼3400 Ma Strelley Pool Formation of Western Australia and the ∼1900 Ma Gunflint Formation of Canada. All the examined Microfossils have carbonaceous walls surrounded by pure silica. Impregnation of microfossil walls by nano-grains of silica is common, together with variable degrees of wall displacement and replacement by silica. All Microfossils are rigidly preserved in 3D and show little or no folding or compression. However, there are also notable differences in taphonomic preservation. Our examples of the spheroidal Gunflint microfossil Huroniospora showed the highest fidelity of preservation with a continuous carbonaceous wall fossilized by spheroidal nano-silica grains that resemble those found on bacterial surfaces in modern silicifying hot-spring environments. The nucleation of these silica nano-spheres on the microfossil walls has induced an artificial ‘saw-tooth-like’ ridged wall texture that may subsequently hinder species-level identification. The Strelley Pool Microfossils in comparison show a lower fidelity of preservation with small parts of the microfossil walls completely replaced by silica, plus extensive recrystallization of spheroidal silica nano-grains to angular micro-quartz. Our examples of the sheath-like filamentous Gunflint microfossil Siphonophycus showed the lowest fidelity of preservation with many gaps in the carbonaceous walls and significant redistribution of carbon by recrystallizing silica grains. A model is presented to explain these observations. Criteria for distinguishing highly probable Microfossils from non-cellular carbonaceous microstructures (e.g., botryoids and grain coatings) using FIB-based imaging are put forward for the first time here, using examples drawn from the Strelley Pool Formation and comparisons with younger Gunflint material. The combined in situ techniques of FIB–TEM and FIB–SEM nano-tomography potentially provide a wealth of new nano-scale information regarding the biogenicity, antiquity and taphonomy of Precambrian Microfossils. However, the destructive nature of both techniques makes their application to unique palaeontological specimens problematical.
Erica Victoria Barlow - One of the best experts on this subject based on the ideXlab platform.
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snapshot of an early paleoproterozoic ecosystem two diverse microfossil communities from the turee creek group western australia
Geobiology, 2018Co-Authors: Erica Victoria Barlow, Martin J Van KranendonkAbstract:Eighteen microfossil morphotypes from two distinct facies of black chert from a deep-water setting of the c. 2.4 Ga Turee Creek Group, Western Australia, are reported here. A primarily in situ, deep-water benthic community preserved in nodular black chert occurs as a tangled network of a variety of long filamentous Microfossils, unicells of one size distribution and fine filamentous rosettes, together with relatively large spherical aggregates of cells interpreted as in-fallen, likely planktonic, forms. Bedded black cherts, in contrast, preserve Microfossils primarily within, but also between, rounded clasts of organic material that are coated by thin, convoluted carbonaceous films interpreted as preserved extracellular polymeric substance (EPS). Microfossils preserved within the clasts include a wide range of unicells, both much smaller and larger than those in the nodular black chert, along with relatively short, often degraded filaments, four types of star-shaped rosettes and umbrella-like rosettes. Large, complexly branching filamentous Microfossils are found between the clasts. The grainstone clasts in the bedded black chert are interpreted as transported from shallower water, and the contained Microfossils thus likely represent a phototrophic community. Combined, the two black chert facies provide a snapshot of a microbial ecosystem spanning shallow to deeper-water environments, and an insight into the diversity of life present during the rise in atmospheric oxygen. The preserved Microfossils include two new, distinct morphologies previously unknown from the geological record, as well as a number of Microfossils from the bedded black chert that are morphologically similar to-but 400-500 Ma older than-type specimens from the c. 1.88 Ga Gunflint Iron Formation. Thus, the Turee Creek Group microfossil assemblage creates a substantial reference point in the sparse fossil record of the earliest Paleoproterozoic and demonstrates that microbial life diversified quite rapidly after the end of the Archean.
David Troadec - One of the best experts on this subject based on the ideXlab platform.
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iron mineralization and taphonomy of Microfossils of the 2 45 2 21 ga turee creek group western australia
Precambrian Research, 2017Co-Authors: Alexandre Fadel, Kevin Lepot, Ahmed Addad, Vincent Busigny, David TroadecAbstract:Abstract We report a new assemblage of carbonaceous Microfossils intimately associated with siderite and Fe-silicates, from a black chert nodule included in iron formation of the ca. 2.45–2.21 Ga Turee Creek Group, Western Australia. This chert comprises microbial fabrics dominated by filaments preserved in matrix of nano- to micrometric quartz. Filaments occur in clumps and in a cobweb-like fabric interspersed with coarse crystalline, void filling quartz granules. We studied this chert with optical microscopy combined with Scanning Transmission Electron Microscope observations of Focused Ion Beam sections of Microfossils. This distinguished three types of well-preserved fossil interpreted as polysaccharide sheaths that usually do not preserve chains of cells (trichomes): Type 1 comprises narrow filaments with thin continuous kerogen sheaths, Type 2 comprises narrow filaments with thick granular sheaths, and Type 3 comprises broad filaments with thin sheaths. Type 4 filaments are poorly preserved as granular kerogen. Organic ultrastructures of Type 2–4 Microfossils are variably replaced by siderite crystals, associated with minor Fe-silicates. Iron isotope analyses on bulk powder and reactive iron fraction show indistinguishable and highly positive δ 56 Fe values (+1.45‰ relative to the reference IRMM-014), indicating that the bulk of siderite derives from reduction of Fe(III)-oxides. This provides indirect evidence that the microbial community was originally associated with Fe(III)-oxides. Siderite and Fe-silicates are found with Type 2–4 but not Type 1 filaments, suggesting that only the former were encrusted by Fe(III)-oxides, which may have been reduced in situ . Siderite and Fe-silicates could result from oxidation of organic matter in filaments coupled with microbial and/or thermal reduction of Fe(III)-bio(?)minerals. The increasing abundance of siderite correlated with decreasing organic matter preservation in filaments supports that this reaction occurred to variable extents, in situ on each microfossil. Type 2–4 Microfossils may thus represent iron-oxidizing bacteria. These microbial mats display strong similarities with those associated with immediately overlying carbonate rocks of the Turee Creek Group, where filaments were interpreted as sulfur-oxidizing bacteria. Some filamentous bacteria can oxidize both iron and sulfur. Such metabolic versatility could have enabled benthic microbial mats to thrive in the drastically changing chemical conditions of the Great Oxidation Event.
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iron minerals within specific microfossil morphospecies of the 1 88 ga gunflint formation
Nature Communications, 2017Co-Authors: Kevin Lepot, Jian Wang, Andrew H Knoll, Ahmed Addad, David Troadec, Armand Beche, Emmanuelle JavauxAbstract:Problematic Microfossils dominate the palaeontological record between the Great Oxidation Event 2.4 billion years ago (Ga) and the last Palaeoproterozoic iron formations, deposited 500–600 million years later. These fossils are often associated with iron-rich sedimentary rocks, but their affinities, metabolism, and, hence, their contributions to Earth surface oxidation and Fe deposition remain unknown. Here we show that specific microfossil populations of the 1.88 Ga Gunflint Iron Formation contain Fe-silicate and Fe-carbonate nanocrystal concentrations in cell interiors. Fe minerals are absent in/on all organically preserved cell walls. These features are consistent with in vivo intracellular Fe biomineralization, with subsequent in situ recrystallization, but contrast with known patterns of post-mortem Fe mineralization. The Gunflint populations that display relatively large cells (thick-walled spheres, filament-forming rods) and intra-microfossil Fe minerals are consistent with oxygenic photosynthesizers but not with other Fe-mineralizing microorganisms studied so far. Fe biomineralization may have protected oxygenic photosynthesizers against Fe2+ toxicity during the Palaeoproterozoic. Fossil microorganisms older than 1.7 billion years are challenging to interpret due to their size, simple shapes, and alteration. Here, in 1.88 billion year old Microfossils, the authors show a pattern of cellular preservation and internal iron nanominerals consistent with oxygenic photosynthetic bacteria.