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Approximate Growth Rates of Early Proterozoic Microstromatolites as Deduced by Biomass Productivity
Abstract
An assemblage of microstromatolites and intraclastic stromatolitic fragments has been found in early carbonate-replacement black chert from a drill core (356 m) in the 2.3 Ga Transvaal Supergroup, South Africa. These materials are characterized by two predominant populations of fossilized microorganisms. Unicellular coccoid microfossils are preserved as patchy cell accumulations of up to 2.4 X 10 9/cm 3 and rod- and vibro-shaped bacterial microfossils occur in normalized densities of up to 1.3 X 10 10 cells/cm 3 as stratified layers within many microstromatolites and stromatolite intraclasts. The bacterial layers are often found beneath dense surficial coccoid layers. Minimum microstromatolite growth rates have been estimated by assuming a steady-state model for stromatolite accretion. The rate of bacterial biomass turnover is calculated by measuring the frequency of fossilized dividing bacterial cells. Minimum growth rates as deduced by the FFDBC method range from 2-40 mu m/day. An average lamination thickness of 27 mu m suggests that individual laminae may represent daily-growth markers. This study underscores the potential application of modern concepts of microbial ecology to fossilized microbial ecosystems (stromatolites). -from Author
... The volume of organic matter determines the thickness of the dark laminae. The subsequent diagenesis in the microbial mat brings out the change in the dark lamina (Lanier, 1986). On this basis banded microstructure has been divided into regular banded, discontinuous thick banded, continuous thick banded, thin banded, irregular banded and grume bearing banded. ...
... After comparative more selective silicification of darker laminae (microbial laminae) they become prominent and protrude out in outcrops. Extensive growth provides a continuum of dark lamine in stromatolites (Lanier, 1986). This biomass provided the thick darker laminae in these stromatolites followed by precipitation of the carbonate mineral for equally long duration might have given rise to continuous thick-banded microstructure structure. ...
... Wavy irregular filiform microstructure is noted among the members of Pseudogymnosolen, Minicolumella and Kanpuria. It may be due to small coccoidal microbes growing on the microbial mats and their low biomass production contributed towards the fine laminations as suggested by (Lanier, 1986). The continuity of the laminae suggests stable environment of formation of stromatolites over long period. ...
... Especially in the sixties to eighties of the last century, when stromatolite research became popular and advanced, numerous reports appeared (e.g. Winter, 1963;Truswell and Eriksson, 1972;Nagy, 1974;Grobler and Emslie, 1976;Mason and von Brunn, 1977;Beukes, 1980;Buck, 1980;Martin et al., 1980;Orpen and Wilson, 1981;De Wit et al., 1982;Abell et al., 1985a,b;Lanier, 1986;Byerly et al., 1986;Beukes, 1987;Beukes and Lowe, 1989; and many Fig Altermann and Schopf (1995). In (c) colonial unnamed coccoids and in (d) a fragmented filament of Siphonophycus transvaalensis are visible. ...
... First, Lanier (1986Lanier ( , 1988 reported on the authentic occurrence of filaments and coccoids as well as rodshaped and ellipsoidal bacterial prokaryotes in the Monte Christo Formation of the Malmani Subgroup. Lanier (1986) calculated organic production rates for these microfossils in the range of modern microbial mat organic production and minimum growth rates of 2-40 lm per day for microstromatolites. ...
... First, Lanier (1986Lanier ( , 1988 reported on the authentic occurrence of filaments and coccoids as well as rodshaped and ellipsoidal bacterial prokaryotes in the Monte Christo Formation of the Malmani Subgroup. Lanier (1986) calculated organic production rates for these microfossils in the range of modern microbial mat organic production and minimum growth rates of 2-40 lm per day for microstromatolites. These calculated growth rates were later supported by computation of sediment accumulation rates by Altermann and Nelson (1998), based on decompaction of Campbellrand Subgroup rocks between tuff layers that were dated by the single zircon SHRIMP method. ...
From the Archean sedimentary rocks of Africa numerous reports of cellularly preserved microfossils were published since 1960. Until the first report of authentic microfossils from the Barberton Greenstone Belt [M.M. Walsh, D.R. Lowe, Nature 314 (1985) 530], however, none of these reports stood up to the criteria for confirming authenticity and originality of Archean microfossils. According to these criteria, only less than 10 microfossil reports from the Archean of Africa can be recognised as indeed cellularly preserved microbes. All of them are from Southern Africa, namely from the territory of the Republic of South Africa. Nevertheless, these few occurrences provide evidence for a very advanced evolutionary stage of Archean microbiota and are thus key contributions to our knowledge of the early life on Earth. They demonstrate the presence of coccoid and filamentous bacteria and cyanobacteria in the Archean and also confirm the development of aerobic and anaerobic photosynthesis and of biogenic calcium precipitation in the Archean. Therefore, the contribution of the African continent to the knowledge of Archean biology and the early evolution of life is of immense value to paleobiological science.
... The Neoarchean carbonates of the Transvaal Supergroup are well know not only for the above controversy, but also for possible correlations to similar carbonates on the Pilbara Craton, Western Australia ( Nelson et al., 1999) and their wealth of stromatolite occurrences ( Eriksson and Truswell, 1974;Beukes, 1987;Altermann, 2002Altermann, , 2008). These carbonates bear the best preserved and least controversial bodily preserved Archean microfossils ( Lanier, 1986;Klein et al., 1987;Altermann and Schopf, 1995;Wright and Altermann, 2000). In particular, the >2588-2549 Ma ( Altermann and Nelson, 1998) Nauga Formation bears the oldest morphological and geochemical evidence for cyanobacteria and their role as producers of widespread and copious, rock-forming, micritic carbonate ( Kazmierczak and Altermann, 2002;Altermann and Kazmierczak, 2003;Altermann et al., 2006), preserved in non-silicified carbonate rocks, rich in organic matter. ...
... Additionally, the above-discussed abundant occurrences of microfossils of entophysalidacean affinity in the rocks of the Campbellrand Subgroup and stratigraphic equivalents in South Africa (e.g. Lanier, 1986;Altermann and Schopf, 1995;), strengthen our interpretation. Concerning the taxonomic position of the cyanobacterial remains studied here, the bio-structures visible in the SEM images are essentially similar to capsules and common mucilage sheaths of modern benthic cyanobacteria. ...
... From the same stratigraphic level, and partly based on the thin section of Klein et al. (1987), Wright and Altermann (2000) reported on possible microbial mediation of calcification and dolomitisation processes, in microbial laminites and oolites. Earlier multiple descriptions of coccoid microfossils including Eoentophysalis, from a similar stratigraphic level of the Campbellrand Subgroup ( Altermann and Schopf, 1995) and from the age-equivalent Chuniespoort Group (Transvaal Supergroup, Transvaal preservational basin; Lanier, 1986) support our findings and interpretation. Further support can be derived from the report of cyanobacterial molecular fossils (steranes and related products of carbon maturation) in Archean shales of similar age, but from Australia ( Brocks et al., 1999;Eigenbrode et al., 2008). ...
Precambrian Research j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / p r e c a m r e s a b s t r a c t The sparse Archean fossil record is based almost entirely on carbonaceous remnants of microorganisms cellularly preserved due to their early post-mortem silicification. Hitherto as an exception, sedimen-tary carbonate rocks from the Neoarchean Nauga Formation of South Africa contain calcified microbial mats composed of microbiota closely resembling modern benthic colonial cyanobacteria (Chroococcales and Pleurocapsales). Their remains, visible under the scanning electron microscope (SEM) after etching of polished rock samples, comprise capsular envelopes, mucilage sheaths, and groups of cells miner-alized by calcium carbonate with an admixture of Al–K–Mg–Fe silicates. The capsular organization of the mucilaginous sheaths surrounding individual cells and cell clusters forming colonies and the mode of mineralization are the characteristic common features of the Neoarchean microbiota described and their modern analogues. The new findings indicate massive production of calcium carbonates by benthic coccoid cyanobacteria in the Neoarchean, and offer a solution to the problem of the origin of Archean carbonate platforms, stromatolites and microbial reefs. © 2009 Published by Elsevier B.V.
... Very small, often millimetric, stromatolite columns, that are widespread and locally abundant in Proterozoic carbonates (Riding, 2008), have variously been termed digitate stromatolite (Donaldson, 1963), microstromatolite (Hofmann, 1969a, p. 15;Raaben, 1980;Lanier, 1986), 'tiny arborescent stromatolite' (Hofmann, 1975), microdigitate stromatolite (Hoffman, 1972;Grotzinger & Read, 1983) and ministromatolite (Hofmann & Jackson, 1987). Their fabrics range from irregularly laminated and peloidal to evenly layered and radially fibrous, and have variously been interpreted as biogenic (Grey & Thorne, 1985) or abiotic (Grotzinger, 1986), and they have often been described from restricted nearshore environments (Hofmann, 1975). ...
Microbial carbonates formed stromatolitic, thrombolitic, dendrolitic and maceriate (mazelike) fabrics in shallow marine Cambrian–Early Ordovician carbonates encircling Laurentia. However, poor preservation often hinders recognition of their specific components. Well‐preserved examples of normal shallow marine limestones in the ca 490 Ma upper Cambrian Point Peak Member, Wilberns Formation, central Texas, include stromatolitic cones, steep‐sided laminated rimmed columns with grainy interiors, and laminated and maceriate domes. Together these decimetre to metre‐thick biostromes. In these examples, a single component, microstromatolite, on its own or with minor calcimicrobes, creates macroscopic stromatolitic, dendrolitic, thrombolitic and maceriate fabrics. Microstromatolites constructed upward widening stromatolitic cones that developed into columns with laminated rims surrounding slightly depressed interiors. These columns accumulated allochthonous sediment by a ‘bucket effect’. Their interiors contain either clusters of dendrolitic microstromatolite or ragged columns of laminated stromatolite–sponge biolithite, and are often characterized by a ‘mottled’ fabric that superficially resembles thrombolite. This mottling was formed by localized dolomitization around millimetric burrows that otherwise do not appear to have significantly influenced the biolithite fabric. Calcimicrobes, including cyanobacteria (Razumovskia) and microproblematica (Renalcis and Tarthinia), impart a mesoscopic clotted appearance to maceriate fabric, and locally to column rims, both of which are dominated by microstromatolite. Similar component‐fabric relationships should be recognizable in rimmed columns and domes that were locally abundant elsewhere in Cambrian–Early Ordovician shallow carbonate seas.
... They are almost identical to the newly obtained spheroids from the Wumishan MDS in this study. In addition, comparable coccoid-like spheroids have been widely reported from the Archean to Paleoproterozoic successions worldwide, for instance, colonial ensheathed coccoidal unicells from the ca 3388 Myr old Strelley Pool Chert of Western Australia (Schopf and Packer, 1987;Schopf, 1992), and solitary or paired microbial coccoidal unicells and bacterium-like rod-shaped unicells from the ~3260 Ma Swartkoppie Formation and the ~2600 Ma Monte Cristo Formation of South Africa (Lanier, 1986;Buick, 2001). All of these Archean-Paleoproterozoic solitary or paired coccoid-like spheroids have been interpreted as a biogenic origin because they are composed of organic matter, and special microstructure with biological characteristics. ...
Stromatolites have been widely reported from the Archean and Paleoproterozoic successions worldwide, and they could represent one of oldest life forms on Earth. Of these, a group of small stromatolites occur as microdigitate low-relief columns, and are also conspicuous in the field. However, biogenicity of these microdigitate stromatolites (MDSs) has long been disputed due to to the abundance of radial-fibrous texture and a lack of convincing microfossils. New examples of MDS are documented from the Mesoproterozoic Wumishan Formation of the Jixian area, North China. Vertically oriented fibrous fabrics are conspicuous and penetrate laminae as well as microscopic spheroids, which point to an abiotic genesis for this specific fabric. Stromatolite laminae contain abundant spheroids, typically 15–30 μm in diameter, with single or double outlines and they occur as solitary coccoid-like microfossils or in small aggregated colonies. Spheroids show strong fluorescence under both green and purple exciting lights, consistent with their composition of organic matter. Spheroids are abundant in the Wumishan stromatolites and they are categorized into two types. The first kind comprises micrite nuclei surrounded by sparitic sheaths, without nano-particle coatings. A smooth to grainy spheroidal surface defines the first kind of spheroids that also has a distinct rounded opening, which is often broken probably due to diagenesis and silicification. The second kind of spheroids is usually covered with nano-particles and lacks circular opening on surface. These spheroids possess large nuclei of single sparitic calcite coated with thin sparry sheaths. Overall, the Wumishan spheroids resemble coccoidal microorganisms reported from other Archean-Paleoproterozoic strata worldwide, but they are also better preserved. The rounded opening on spheroid surface is interpreted as division point of unicells during reproduction of the life cycle of bacteria akin to Myxococcoides grandis. Clump-like micro-particle aggregates in nuclei could represent daughter cells released from the parental envelope, similar to the reproduction process and life cycle suggested for similar spheroidal microfossils from other similar Precambrian occurrences. The Wumishan spheroids therefore may represent fossilized prokaryotes that could have contributed to construct the MDS. Moreover, filamentous microfossils are occasionally present in the coloumns of stromatolites, and they resemble filamentous cyanobacteria, but may not be major constructors of MDS due to their rarity in the buildups. Three types of nano-particles are also conspicuous: (1) putative organic relics, such as fragmented filaments and mucuslike biofilms (purported EPS), (2) organominerals, including nanoglobules, polyhedrons, and their aggregates, and (3) dumbbell-shaped nano-particle aggregates. All of these nano-particles are interpreted to be likely biogenic in origin, and many of them were found from the radial-fibrous fabrics of carbonate precipitates in the MDS, implying that some heterotrophic bacteria may have afficliated the precipitation of radial fibers in deep-time radial-fibrous carbonate precipitates. Therefore, abundant and diverse biosignatures (spheroids, tubular filaments, and nano-particles) are identified in the Wumishan MDSs, and we conclude that diverse filamentous and coccoidal micro-organismscontributed to the formation of the Wumishan stromatolites.
... We advance the suggestion of Cuerno et al. [36], providing a mechanistic demonstration of a biogenic origin for structures that are not readily explicable through the terms defined by mathematical morphogenesis at small scales. A brief literature survey shows that such 'unpredictable' complexity is common in contemporaneous and younger stromatolites of biological origin (e.g., [67][68][69][70][71][72]), but is not present in stromatolite-like structures of more likely abiological origin [73][74][75], where the eventual morphologies and, indeed, a dominantly phototrophic affinity, can be predicted in terms of either KPZ or diffusion-limited dynamics alone. Given the valid application of KPZ, DLA, and DLA-CA models to OSS of varying morphology, the specific model required for morphogenetic studies of Precambrian OSS must be determined on a case-by-case basis, considering the petrological context given by correlative biogeochemical analyses. ...
Morphologically diverse organo-sedimentary structures (including microbial mats and stromatolites) provide a palaeobiological record through more than three billion years of Earth history. Since understanding much of the Archaean fossil record is contingent upon proving the biogenicity of such structures, mechanistic interpretations of well-preserved fossil microbialites can reinforce our understanding of their biogeochemistry and distinguish unambiguous biological characteristics in these structures, which represent some of the earliest records of life. Mechanistic morphogenetic understanding relies upon the analysis of geomicrobiological experiments. Herein, we report morphological-biogeochemical comparisons between micromorphologies observed in growth experiments using photosynthetic mats built by the cyanobacterium Coleofasciculus chthonoplastes (formerly Microcoleus) and green anoxygenic phototrophic Chloroflexus spp. (i.e., Coleofasciculus–Chloroflexus mats), and Precambrian organo-sedimentary structures, demonstrating parallels between them. In elevated ambient concentrations of Cu (toxic to Coleofasciculus), Coleofasciculus–Chloroflexus mats respond by forming centimetre-scale pinnacle-like structures (supra-lamina complexities) associated with large quantities of EPS at their surfaces. μPIXE mapping shows that Cu and other metals become concentrated within surficial sheath-EPS-Chloroflexus-rich layers, producing density-differential micromorphologies with distinct fabric orientations that are detectable using X-ray computed micro-tomography (X-ray μCT). Similar micromorphologies are also detectable in stromatolites from the 3.481 Ga Dresser Formation (Pilbara, Western Australia). The cause and response link between the presence of toxic elements (geochemical stress) and the development of multi-layered topographical complexities in organo-sedimentary structures may thus be considered an indicator of biogenicity, being an indisputably biological and predictable morphogenetic response reflecting, in this case, the differential responses of Coleofasciculus and Chloroflexus to Cu. Growth models for microbialite morphogenesis rely upon linking morphology to intrinsic (biological) and extrinsic (environmental) influences. Since the pinnacles of Coleofasciculus–Chloroflexus mats have an unambiguously biological origin linked to extrinsic geochemistry, we suggest that similar micromorphologies observed in ancient organo-sedimentary structures are indicative of biogenesis. An identical Coleofasciculus–Chloroflexus community subjected to salinity stress also produced supra-lamina complexities (tufts) but did not produce identifiable micromorphologies in three dimensions since salinity seems not to negatively impact either organism, and therefore cannot be used as a morphogenetic tool for the interpretation of density-homogeneous micro-tufted mats—for example, those of the 3.472 Ga Middle Marker horizon. Thus, although correlative microscopy is the keystone to confirming the biogenicity of certain Precambrian stromatolites, it remains crucial to separately interrogate each putative trace of ancient life, ideally using three-dimensional analyses, to determine, where possible, palaeoenvironmental influences on morphologies. Widespread volcanism and hydrothermal effusion into the early oceans likely concentrated toxic elements in early biomes. Morphological diversity in fossil microbialites could, therefore, reflect either (or both of) differential exposure to ambient fluids enriched in toxic elements and/or changing ecosystem structure and tolerance to elements through evolutionary time—for example, after incorporation into enzymes. Proof of biogenicity by deducing morphogenesis (i.e., a process preserved in the fossil record) overcomes many of the shortcomings inherent to the proof of biogenicity by descriptions of morphology alone.
... Archean sedimentary rock successions preserve only relatively simple microfossils including filamentous, unicellular and spindle- shaped microfossils that are often found only in isolated, single populations (e.g., Czaja, Beukes, & Osterhout, 2016;Klein, Beukes, & Schopf, 1987;Knoll & Barghoorn, 1977;Kremer & Kazmierczak, 2017;Lanier, 1986;Sugitani, Grey, Nagaoka, Mimura, & Walter, 2009;Sugitani, Mimura, Nagaoka, Lepot, & Takeuchi, 2013;Sugitani, Mimura, Takeuchi, Lepot, et al., 2015;Sugitani, Mimura, Takeuchi, Yamaguchi, et al., 2015;Wacey, Kilburn, Saunders, Cliff, & Brasier, 2011;Walsh, 1992; amongst others). It is not until the c. 1.88 Ga Gunflint Iron Formation, Canada, that a variety of microbial forms with more complex morphologies are preserved, such as Kakabekia, Eoastrion and Eosphaera (Barghoorn & Tyler, 1965). ...
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.
... Chain-ofbeads and spherical structures similar to Gunflintia and Huroniospora, respectively, may form during abiotic, mineral-free auto-assembly of organic molecules (Fox and Yuyama, 1963). However, the biogenicity of Gunflintia and Huroniospora morphospecies is supported by their distribution in stromatolites with respect to clastic fragments and laminae (Knoll et al., 1988;Lanier, 1986) that is often similar to the distribution of microorganisms in modern stromatolites (Reid et al., 2000). However, other possible microfossils such as Eoastrion remain highly problematic. ...
The FC Formation of the Francevillian of Gabon displays the oldest Gunflint-type assemblage of microfossils that is hosted in shallow-water stromatolites. The FC Formation was deposited between 2.14 and 2.08 billion years ago (Ga), after the Great Oxygenation Event (∼2.4–2.3 Ga) and near the end of the Lomagundi event (∼2.3–2.06 Ga). Although they have been used as a benchmark for the search for older microfossils, the nature of Gunflint-type microfossils has remained elusive due to their simple shapes, their small sizes, and their alteration. Here, we report the first nanoscale study of Francevillian Gunflint-type microfossils. We used a combination of Raman spectroscopy, palynology, in situ focused ion beam sectioning, and analytical electron microscopy. In spite of the relatively high thermal maturity of organic matter (inferred peak burial temperature ∼296 ± 30 °C), spherical cell walls (Huroniospora) and filamentous sheaths (Gunflintia minuta: ≤3 µm in diameter, and broader filaments) are preserved. Organic matter in/on cell walls and sheaths, is associated with nanocrystalline quartz, whereas coarser quartz crystals fill and surround the microfossils. This pattern, likely inherited from recrystallization of texturally heterogenous opal generations, could have allowed the observed preservation of organic structures and limited migrations of organic matter. Moreover, we demonstrate the preservation of thick-sheathed broad (>3 µm) filaments for the first time in a stromatolitic Gunflint-type assemblage; such thick sheaths are common in cyanobacteria, but not in other filamentous bacteria. We distinguished two types of star-shaped organic microstructures (Eoastrion) but found no diagnostic evidence for/against a microfossil nature at the nanoscale. Furthermore, we show that titanium is commonly associated with organic structures of microfossils, likely as a result of diagenetic mineralization. In contrast, iron-rich nanocrystals associated with microfossils occur in quartz, not in organic matter, and could possibly represent recrystallized biominerals.
... These forms have been considered as obvious empty sheaths of fossil hormogonian and chrooococcacean cyanobacteria (Sergeev et al., 2007a). Report of rod shaped heterotrophic bacteria from the same formation (Lanier, 1986) is regarded as pseudofossils. Diverse microstructures have been reported by Sugitani et al. (2007Sugitani et al. ( , 2009) and Grey and Sugitani (2009) from the Mount Goldsworthy-Mount Grant area, Pilbara Craton, Western Australia (> 2.97 Ga). ...
A monographic account is presented on the fossil Proterozoic cyanobacteria. It chronicles the 60 years of history of investigations on the Precambrian microfossils. The researches on Precambrian microfossils have revealed a new, earlier unknown, world of oldest microorganisms and divulged the steps in life’s evolution on the earth. Documented records show that cyanobacteria occupied all available ecological niches of the Precambrian biosphere and filamentous and coccoidal cyanobacteria were the dominant microbial community. Extinct fossilized cyanobacteria in diagenetic cherts of the Precambrian are comparable in morphology and behavior with extant forms. These oxygenic phototrophic microorganisms were masters for at least first 3.0-3.5 billion years of the Earth history and almost did not change for billion years. The unprecedented evolutionary conservatism of the cyanobacteria is established so much so that modern systematics of cyanobacteria can be applied on Proterozoic forms at least, up to the family level. More than half a century of research on Precambrian microfossils demands refinement in taxonomy and allows differentiation between products of taphonomy and primarily biological features of fossilized cyanobacteria as well as those features formed as a result of postmortem degradation and subsequent diagenetic alternations. The paper embodies all cyanobacterial taxa broadly accepted by most of the researchers and provides complete revision of all Precambrian fossil cyanobacterial remains. It presents a comprehensive information on the taxonomy of cyanobacterial and related microorganisms along with emendations with due considerations of possible processes of post-mortem alterations. Detailed analysis of fossil cyanobacteria populations has revealed 50 genera and 92 species as truly acceptable forms. Of this, more than 10 genera and 18 species are recognized as problematic cyanobacterial taxa that could be alternatively interpreted as Protista. The present review contains diagnosis and descriptions of genera as well as type and some other very important species. The information on other species (size, type specimen, distribution) is given in the table format along with the described genera. All valid taxa described from the Proterozoic microbiotas are incorporated in this work. Problematic remains of Archaean (?) cyanobacteria are not included because of their uncertain and disputable biogenic origin. The relevant data of molecular biology and other methods applied in systematics of modern cyanobacteria are discussed in the paper. Besides, main taxonomic part and relevant discussion on the morphology of microfossils the palaeobiology, palaeoecology and geological history of cyanobacteria are also provided. The present paper contains following taxa: Family- CHROOCOCCACEAE: Brachypleganon, Coniunctiophycus, Corymbococcus, Eoaphanocapsa, Eogloeocapsa, Eosynechococcus, Gloeodiniopsis, Gloeotheceopsis, Gyalosphaera, Sphaerophycus, Tetraphycus; Family- ENTOPHYSALIDACEAE: Coccostratus, Eoentophysalis; Family- DERMOCARPACEAE: Polybessurus; Family- HYELLACEAE: Eohyella; Family- PLEUROCAPSACEAE: Palaeopleurocapsa, Scissilisphaera; Family- XENOCOCCACEAE: Synodophycus; Family- OSCILLATORIACEAE: Calyptothrix, Cephalophytarion, Cyanonema, Eomicrocoleus, Eoschizothrix, Filiconstrictosus, Heliconema, Obruchevella, Oscillatoriopsis, Palaeolyngbya, Partitiofilum, Siphonophycus, Uluksanella; Family- NOSTOCACEAE: Eosphaeronostoc, Veteronostocale; Family- SCYTONEMATACEAE: Circumvaginalis, Ramivaginalis; Order- NOSTOCALES OR STIGONEMATALES: Archaeoellipsoides, Orculiphycus, INSERTAE SEDIS: Animikiea, Chlorogloeaopsis, Chuaria, Clonophycus, Glenobotrydion, Gunflintia, Huroniospora, Leiosphaeridia, Leptoteichos, Myxococcoides, Phanerosphaerops, Polysphaeroides, Polytrichoides.
... On the other hand, there is ample evidence, for the cyanobacterial and bacterial communities, that their metabolism was similar to that observed today (Schopf and Klein, 1992;Schopf, 1993). In support of this, Lanier (1986) calculated organic production rates for microfossils from the Malmani Subgroup stromatolites in the range of modern microbial mats, and thus the growth rates of Precambrian and modern stromatolites should be comparable, provided that a similar sediment binding or precipitation mechanism operated. The calculated decompacted sedimentation rates of over 150 B for the stromatolitic carbonates of the Ghaap Plateau also support comparable growth rates for modern and Precambrian stromatolites. ...
W. Altermann, D.R. Nelson / Sedimentary Geology 120 (1998) 225–256
Abstract
Calculation of sedimentation rates of Neoarchaean and Palaeoproterozoic siliciclastic and chemical sediments covering
the Kaapvaal craton imply sedimentation rates comparable to their modern facies equivalents. Zircons from tuff beds
in carbonate facies of the Campbellrand Subgroup in the Ghaap Plateau region of the Griqualand West basin, Transvaal
Supergroup, South Africa were dated using the Perth Consortium Sensitive High Resolution Ion Microprobe II (SHRIMP
II). Dates of 2588 � 6 Ma and 2549 � 7 Ma for the middle and the upper part of the Nauga Formation indicate that
the decompacted sedimentation rate for the peritidal flat to subtidal below-wave-base Stratifera and clastic carbonate
facies, southwest of the Ghaap Plateau at Prieska, was of up to 10 m=Ma, when not corrected for times of erosion and
non-deposition. Dates of 2516 � 4 Ma for the upper Gamohaan Formation and 2555 � 19 for the upper Monteville
Formation, indicate that some 2000 m of carbonate and subordinate shale sedimentation occurred during 16 Ma to
62 Ma on the Ghaap Plateau. For these predominantly peritidal stromatolitic carbonates, decompacted sedimentation
rates were of 40 m=Ma to over 150 m=Ma (Bubnoff units). The mixed siliciclastic and carbonate shelf facies of the
Schmidtsdrif Subgroup and Monteville Formation accumulated with decompacted sedimentation rates of around 20 B. For
the Kuruman Banded Iron Formation a decompacted sedimentation rate of up to 60 B can be calculated. Thus, for the
entire examined deep shelf to tidal facies range, Archaean and Phanerozoic chemical and clastic sedimentation rates are
comparable. Four major transgressive phases over the Kaapvaal craton, followed by shallowing-upward sedimentation,
can be recognized in the Prieska and Ghaap Plateau sub-basins, in Griqualand West, and partly also in the Transvaal
basin, and are attributed to second-order cycles of crustal evolution. First-order cycles of duration longer than 50 Ma
can also be identified. The calculated sedimentation rates reflect the rate of subsidence of a rift-related basin and can be
ascribed to tectonic and thermal subsidence. Comparison of the calculated sedimentation rates to published data from other
Archaean and Proterozoic basins allows discussion of general Precambrian basin development. Siliciclastic and carbonate
sedimentation rates of Archaean and Palaeoproterozoic basins equivalent to those of younger systems suggest that similar
mechanical, chemical and biological processes were active in the Precambrian as found for the Phanerozoic. Particularly
for stromatolitic carbonates, matching modern and Neoarchaean sedimentation rates are interpreted as a strong hint of a
similar evolutionary stage of stromatolite-building microbiota. The new data also allow for improved regional correlations
across the Griqualand West basin and with the Malmani Subgroup carbonates in the Transvaal basin. The Nauga Formation
carbonates in the southwest of the Griqualand West basin are significantly older than the Gamohaan Formation in the
Ghaap Plateau region of this basin, but are in part, correlatives of the Oaktree Formation in the Transvaal and of parts of
the Monteville Formation on the Ghaap Plateau.
Keywords: basin analysis; sedimentation rates; Archaean; Proterozoic; Kaapvaal craton; SHRIMP
... The effects of hydrothermal fluid flow and metamorphism can be seen in the record of silicified microfossils, a rich source of information in Proterozoic deposits, but scarce and contentious in the Archean. Unambiguous microfossils occur in cherts of the 2500 to 2600 Ma Transvaal Supergroup, South Africa, one of the earliest carbonate platforms developed on a large craton (Lanier 1986;Klein et al. 1987;Altermann and Schopf 1995). These fossils could be cyanobacterial, but unlike 2000 Ma assemblages from Canada (Hofmann 1976), their simplicity, relatively poor preservation, and deposition in an anoxic environment (obviating any simple assumptions about electron donors) make systematic interpretation difficult. ...
Microfossils, stromatolites, and chemical biosignatures indicate that Earth became a biological planet more than 3.5 billion years ago, making most of life's history microbial. Proterozoic rocks preserve a rich record of cyanobacteria, including derived forms that differentiate multiple cell types. Stromatolites, in turn, show that microbial communities covered the seafloor from tidal flats to the base of the photic zone. The Archean record is more challenging to interpret, particularly on the question of cyanobacterial antiquity, which remains to be resolved. In the late Neoproterozoic Era, increasing oxygen and radiating eukaryotes altered the biosphere, with planktonic algae gaining ecological prominence in the water column, whereas seaweeds and, eventually, animals spread across shallow seafloors. From a microbial perspective, however, animals, algae, and, later, plants simply provided new opportunities for diversification, and, to this day, microbial metabolisms remain the only essential components of biogeochemical cycles.
Copyright © 2015 Cold Spring Harbor Laboratory Press; all rights reserved.
... The effects of hydrothermal fluid flow and metamorphism can be seen in the record of silicified microfossils, a rich source of information in Proterozoic deposits, but scarce and contentious in the Archean. Unambiguous microfossils occur in cherts of the 2500 to 2600 Ma Transvaal Supergroup, South Africa, one of the earliest carbonate platforms developed on a large craton (Lanier 1986;Klein et al. 1987;Altermann and Schopf 1995). These fossils could be cyanobacterial, but unlike 2000 Ma assemblages from Canada (Hofmann 1976), their simplicity, relatively poor preservation, and deposition in an anoxic environment (obviating any simple assumptions about electron donors) make systematic interpretation difficult. ...
... Traditionally, efforts to assess biogenicity and syngeneity of organic residues in sedimentary rocks have focused on geochemical signatures in kerogen and soluble extracts and/or morphological and chemical signatures of organic materials observable in thin section using optical microscopy and techniques such as Raman spectroscopy. Objectives were to define features likely to be biogenic (e.g., specialized cell types known in modern biology, evidence of cell division in paired unicells [83,84], colonial organization, chemical and isotopic signatures suggestive of living systems, and spatial distributions of carbonaceous remains suggestive of biologic origin such as association with potential biofilms and mat-type architectures [9,10,13]). However, the earlier geochemical investigations lacked the refinements discussed in Waldbauer et al. [25] and French et al. [82] for addressing syngeneity of soluble extracts as well as those introduced by Derenne et al. [26] and Marshall et al. [27] for elucidating molecular composition of syngenetic components of kerogen. ...
The past decade has seen an explosion of new technologies for assessment of biogenicity and syngeneity of carbonaceous material within sedimentary rocks. Advances have been made in techniques for analysis of in situ organic matter as well as for extracted bulk samples of soluble and insoluble (kerogen) organic fractions. The in situ techniques allow analysis of micrometer-to-sub-micrometer-scale organic residues within their host rocks and include Raman and fluorescence spectroscopy/imagery, confocal laser scanning microscopy, and forms of secondary ion/laser-based mass spectrometry, analytical transmission electron microscopy, and X-ray absorption microscopy/spectroscopy. Analyses can be made for chemical, molecular, and isotopic composition coupled with assessment of spatial relationships to surrounding minerals, veins, and fractures. The bulk analyses include improved methods for minimizing contamination and recognizing syngenetic constituents of soluble organic fractions as well as enhanced spectroscopic and pyrolytic techniques for unlocking syngenetic molecular signatures in kerogen. Together, these technologies provide vital tools for the study of some of the oldest and problematic carbonaceous residues and for advancing our understanding of the earliest stages of biological evolution on Earth and the search for evidence of life beyond Earth. We discuss each of these new technologies, emphasizing their advantages and disadvantages, applications, and likely future directions.
... These forms have been considered as obvious empty sheaths of fossil hormogonian and chrooococcacean cyanobacteria (Sergeev et al., 2007a). Report of rod shaped heterotrophic bacteria from the same formation (Lanier, 1986) is regarded as pseudofossils. Diverse microstructures have been reported by Sugitani et al. (2007Sugitani et al. ( , 2009) and Grey and Sugitani (2009) from the Mount Goldsworthy-Mount Grant area, Pilbara Craton, Western Australia (> 2.97 Ga). ...
A monographic account is presented on the fossil Proterozoic cyanobacteria. It chronicles the 60 years of history of investigations on the Precambrian microfossils. The researches on Precambrian microfossils have revealed a new, earlier unknown, world of oldest microorganisms and divulged the steps in life’s evolution on the earth. Documented records show that cyanobacteria occupied all available ecological niches of the Precambrian biosphere and filamentous and
coccoidal cyanobacteria were the dominant microbial community. Extinct fossilized cyanobacteria in diagenetic cherts of the Precambrian are comparable in morphology and behavior with extant forms. These oxygenic phototrophic microorganisms were masters for at least first 3.0-3.5 billion years of the Earth history and almost did not change for billion years. The unprecedented evolutionary conservatism of the cyanobacteria is established so much so that modern systematics of cyanobacteria can be applied on Proterozoic forms at least, up to the family level. More than half a century of research on Precambrian microfossils demands refinement in taxonomy and allows differentiation between products of
taphonomy and primarily biological features of fossilized cyanobacteria as well as those features formed as a result of postmortem degradation and subsequent diagenetic alternations. The paper embodies all cyanobacterial taxa broadly accepted by most of the researchers and provides complete revision of all Precambrian fossil cyanobacterial remains. It presents a comprehensive information on the taxonomy of cyanobacterial and related microorganisms along with emendations with due considerations of possible processes of post-mortem alterations. Detailed analysis of fossil cyanobacteria populations
has revealed 50 genera and 92 species as truly acceptable forms. Of this, more than 10 genera and 18 species are recognized as problematic cyanobacterial taxa that could be alternatively interpreted as Protista. The present review contains diagnosis and descriptions of genera as well as type and some other very important species. The information on other species (size, type specimen, distribution) is given in the table format along with the described genera. All valid taxa described from the Proterozoic microbiotas are incorporated in this work. Problematic remains of Archaean (?)
cyanobacteria are not included because of their uncertain and disputable biogenic origin. The relevant data of molecular biology and other methods applied in systematics of modern cyanobacteria are discussed in the paper. Besides, main taxonomic part and relevant discussion on the morphology of microfossils the palaeobiology, palaeoecology and geological history of cyanobacteria are also provided. The present paper contains following taxa: Family- CHROOCOCCACEAE:
Brachypleganon, Coniunctiophycus, Corymbococcus, Eoaphanocapsa, Eogloeocapsa, Eosynechococcus, Gloeodiniopsis, Gloeotheceopsis, Gyalosphaera, Sphaerophycus, Tetraphycus; Family- ENTOPHYSALIDACEAE: Coccostratus, Eoentophysalis; Family- DERMOCARPACEAE: Polybessurus; Family- HYELLACEAE: Eohyella; Family- PLEUROCAPSACEAE: Palaeopleurocapsa, Scissilisphaera; Family- XENOCOCCACEAE: Synodophycus; Family- OSCILLATORIACEAE: Calyptothrix, Cephalophytarion, Cyanonema, Eomicrocoleus, Eoschizothrix, Filiconstrictosus,
Heliconema, Obruchevella, Oscillatoriopsis, Palaeolyngbya, Partitiofilum, Siphonophycus, Uluksanella; Family-NOSTOCACEAE: Eosphaeronostoc, Veteronostocale; Family- SCYTONEMATACEAE: Circumvaginalis, Ramivaginalis; Order- NOSTOCALES OR STIGONEMATALES: Archaeoellipsoides, Orculiphycus, INSERTAE SEDIS: Animikiea, Chlorogloeaopsis, Chuaria, Clonophycus, Glenobotrydion, Gunflintia, Huroniospora, Leiosphaeridia, Leptoteichos, Myxococcoides, Phanerosphaerops, Polysphaeroides, Polytrichoides.
... Few microfossils have been reported from Archean cherts and shales. Somewhat poorly preserved fossils occur in latest Archean cherts from South Africa (Lanier 1986;Klein et al. 1987;Altermann and Schopf 1995); these could include cyanobacteria, but other alternatives cannot be rejected. More controversial are the nearly 3500 Ma carbonaceous microstructures interpreted as bacterial, and possibly cyanobacterial trichomes by Schopf (1993). ...
This chapter explores two records of past primary producers: morphological fossils and molecular biomarkers. Because these two windows on ancient biology are framed by such different patterns of preservational bias and diagenetic selectivity, they are likely to present a common picture of stratigraphic variation only if that view reflects evolutionary history. Diagenesis can obliterate fossils as well as preserve them: organic walls are subject to postdepositional oxidation and mineralized skeletons may dissolve in undersaturated pore waters. The molecular and morphological records of eukaryotic predominance in shelf primary production are mirrored by indications of relatively low cyanobacterial contributions. Fossils, molecular biomarkers, molecular clocks for individual clades, and the sedimentary silica record all disclose that the modern phytoplankton has Mesozoic roots. Paleozoic primary production is described in detail. Microfossil and biomarker molecules both suggest that green algae played a greater role in marine primary production than they have in the past 100 million years, and biomarkers also suggest a significant role for cyanobacterial production on continental shelves. The later part of the chapterdiscusses about proterozoic primary production and also explains the prokaryotic fossils, eukaryotic fossils, and proterozoic molecular biomarkers. The chapter concludes that improved understanding of Earth's redox history and the evolutionary record of animals and land plants will provide the framework needed to interpret the evolutionary history of marine photoautotrophs as it continues to emerge.
... Regardless of the cause, rates of sediment accumulation and organic production on 2.6 Ga carbonate platforms were comparable to more modern carbonate platforms and recent microbial mats (Lanier, 1986;Altermann & Nelson, 1998). Mechanisms (alone or in combination) proposed to explain the formation of carbonate layers in cyanobacterial stromatolites include: trapping and binding of carbonate grains on cyanobacterial mucus (e.g. ...
Microbially mediated calcification can be traced back for at least 2.6 billion years. Although morphological comparison of fossil and recent microbial carbonates suggests that mineralization processes associated with cyanobacteria and their interactions with heterotrophic bacteria have remained similar from the Archaean until today, the metabolic and chemical details remain poorly constrained. Microbial consortia often exhibit an ability to change solution chemistry and control pH at the microscale, passively or actively. This leads to oversaturation of Ca2+ and ions and to the removal of kinetic inhibitors to carbonate precipitation, like sulphate or phosphate. The kinetic barriers of low carbonate ion activity, ion hydration and ion complexing, especially in saline waters, inhibit spontaneous carbonate mineral precipitation from saturated solutions but oxygenic photosynthesis and sulphate reduction by sulphate-reducing bacteria can overcome these natural barriers. Sulphate in seawater tends to form pairs with Ca2+ and Mg2+ ions. The removal of sulphate reduces complexing, raises carbonate alkalinity, and along with pyrite formation, enhances carbonate precipitation. Cyanobacteria can store Ca2+ and Mg2+ ions in organic envelopes and precipitate carbonates within their sheaths and extracellular polymeric substances, thus, triggering sedimentary carbonate production. We propose that this interplay of cyanobacteria and heterotrophic bacteria has been the major contributor to the carbonate factory for the last 3 billion years of Earth history.
... Judging from morphology and size ranges, empty non-branching sheaths up to 35 µ m in diameter and coccoidal forms 1.0 to 5.0 µ m across from this formation (Klein et al., 1987;Altermann and Schopf, 1995) can be regarded quite safely as empty envelopes of fossil hormogonian and chroococcacean cyanobacteria. Small (a few µ m) rod-shape bodies described from the same formation as remains of heterotrophic bacteria (Lanier, 1986) are now attributed to pseudofossils. In the 1970s-1980s, diverse organicwalled morphotypes of Archean microbiotas were described in North Eurasia (Timofeev, 1982, and references therein). ...
Expounded in this work are the results of critical consideration of published and original data on biologic nature and appearance
chronology of different groups of Archean and Lower Proterozoic (3.5–1.65 Ga) paleontological remains known from geological
record. Conclusions are substantiated by morphological analysis of structurally preserved microfossils, their facies distribution,
and by inferable genesis and principal evolutionary trends of Archean stromatolites. A special attention is paid to variations
of organic and carbonate carbon isotope composition in sedimentary successions with paleontological remains and to recent
information about discovered, most ancient biomarkers of large groups of organic world. As a result of this approach, a detailed
model of Precambrian organic world evolution is suggested.
... The calculation of accumulation rates for carbonates using the age of Schmidtsdrif Formation (2557 _+ 49 Ma, Jahn et al., 1990) also resulted in an extremely low rate of 26 m/Ma. Such slow accumulation conflicts with the calculations based on microstromatolite growth rates from biomass production performed by Lanier (1986) for the Monte Christo Formation of the Malmani Subgroup. Although, the calculated growth rate of 16 gm/day on average (ca. ...
The Campbell Group carbonates were deposited in a basin transgressing from southwest to the east and to northeast. At the southwestern margin of the Kaapvaal craton, in Griqualand West, mainly tidal flat carbonates and shallow marine deposits are found to be followed by subtidal carbonates marking the slow transgression. North of the Griquatown Fault, where the center of the Griqualand West sub-basin developed, continuous subsidence matched by stromatolitic carbonate growth, led to accumulation of the thickest carbonate pile (> 2000 m). There, the largest limestone deposits of South Africa are located. The deposit at Lime Acres and mining operations of the PPC Lime Ltd. are described and discussed in respect to diagenetic processes that permitted limestone preservation.
... For example, Fenchel and Kühl (2000) found artificial mats to grow at 2-3 mm year -1 , which assuming similar levels of organic matter composition as measured in this study, would be biomass accumulation of approximately 600 g organic matter year -1 . Lanier (1986) estimated fossil mats to attain growth rates of 0.7-14.6 mm year -1 , which are likely to be in the range of 130-1,600 g organic matter year -1 . ...
Extensive cyanobacterial mats are a feature of the high intertidal zone in the Exmouth Gulf, Western Australia. This study
provides a description of the position of the mats within the intertidal zone and of the mats elemental composition and productivity.
We found that the mats occupied 40cm elevational range within the intertidal zone. They have a mean organic matter content
of 1,600gm−2. Mean concentrations of nitrogen (N) were 1.82gkg−1 and phosphorus (P) 205mgkg−1. N:P ratio was 19.7 indicating P limitation, but N:P was variable. Rates of photosynthesis and biomass production were similar
to those reported for mats in hypersaline conditions at other sites. When photosynthetic production was scaled-up for the
region our data suggest that cyanobacterial mats are an important contributor to the carbon budget in the Exmouth Gulf, contributing
between 5 and 15% of the total carbon fixed by primary producers. Additionally mats were observed to be a source of soluble
carbohydrates in tidal waters indicating that fixed carbon from high intertidal cyanobacterial mats may enter near shore food
webs through this pathway.
... Microstromatolites have been reported from Proterozoic strata (Hoffman 1969;Lanier 1986), Neoproterozoic Limestone (Tewari 2001), hot spring limestones (Jones et al. 1997;Mountain et al. 2003;Guidry and Chafetz 2003), and cold fluid-generated carbonates (Barbieri and Cavalazzi 2004). The genesis of these microstromatolites may be different from that of microstromatolites in the Midale Beds. ...
Carbonates of Mississippian age (Viséan) in the Midale Beds, Charles Formation of southeastern Saskatchewan, Canada, produce
significant amounts of hydrocarbons. The Midale Beds represent deposition in a shallow-water, periodically restricted, epeiric
setting. The sedimentation is characterized by a variety of shallow-water carbonate lithologies ranging from wackestone, packstone,
grainstone, to microbial boundstone. Algae, calcimicrobes, and related microbial fabrics are common features in these limestones.
Cores and thin sections through the Midale Beds in the Glen Ewen and Midale pools of southeastern Saskatchewan were examined
in order to study the contribution of calcimicrobes and microbial fabrics to the sedimentation of Mississippian carbonate
rocks in southeastern Saskatchewan. Calcimicrobes and microbial fabrics are the important components in the grainstones and
microbial boundstone. The calcimicrobes are commonly found as porostromate forms, including Garwoodia sp. and Ortonella sp., and other forms such as Archaeolithoporella-like, Girvanella-like, Wetheredella-like, and problematic microbes also occur but are not common. Microbial fabrics are characterized by microstromatolites,
microbial laminations, thrombolite, clotted peloids, and fenestrate forms. Calcimicrobes stabilized grains and modified and
created sediments, and the related syndepositional microbial fabrics affected the development of porosity/permeability of
Midale carbonates. Calcimicrobes and microbial fabrics in Midale Beds highlighted a significant account of microbial facies
associated with the Mississippian carbonates worldwide.
KeywordsCalcimicrobes–Microbial fabrics–Midale beds–Mississippian–Saskatchewan
Chemosynthetic microorganisms facilitate microbialite development in many caves throughout the world. In Youqin Cave and Tian'e Cave, located in the Carboniferous–Triassic carbonates on the South China Block, five Quaternary speleothems (stalagmite, stalactite and cave pearl) that are 2.3 to 11.0 cm long were examined for their petrographic, geochemical and microbiological features to reveal how chemotrophs contribute to microbialite growth. In the speleothems, millimetre‐sized stromatolites, thrombolites and calcified microbial mats are characterized by alternating light, calcitic microlaminae and dark, clay and organic‐rich calcite microlaminae. Filamentous (reticulate, smooth, nodular and helical), coccoid and bacilliform microbes, originally carried into the caves from surface soils, are more common in the dark microlaminae/clots than in the light microlaminae. 16S rRNA gene sequencing shows that the biotas in the microbialites are dominated by chemoorganotrophic heterotrophic bacteria, including primarily Sphingomonas , Crossiella and Acinetobacter , and rare Archaea. Diverse metabolic pathways of these prokaryotes, including ureolysis, denitrification and nitrite ammonification, contributed to increases in localized pH and/or dissolved inorganic carbon in these microenvironments, prompting carbonate precipitation. Development of the cave microbialites was probably controlled by the evolution of the cave microbial community as environmental conditions changed. Microbialite growth was probably mediated by the microorganisms that flourished on the speleothem surfaces during periods of low drip water rates and slow calcite precipitation. The change from microstromatolites to microthrombolites was probably linked to a decrease in cell populations in the microbial communities. These cave microbialites provide clear insights regarding the biogenicity and growth mechanisms of chemosynthetic microbialites. Given their association with chemolithotrophic activities that can date back to the Meso‐Archean, cave microbialites provide insights into the biogenicity and growth mechanisms of chemosynthesis‐based microbialites throughout geological history.
The search for life beyond the Earth is the overarching goal of the NASA Astrobiology Program, and it underpins the science of missions that explore the environments of Solar System planets and exoplanets. However, the detection of extraterrestrial life, in our Solar System and beyond, is sufficiently challenging that it is likely that multiple measurements and approaches, spanning disciplines and missions, will be needed to make a convincing claim. Life detection will therefore not be an instantaneous process, and it is unlikely to be unambiguous-yet it is a high-stakes scientific achievement that will garner an enormous amount of public interest. Current and upcoming research efforts and missions aimed at detecting past and extant life could be supported by a consensus framework to plan for, assess and discuss life detection claims (c.f. Green et al., 2021). Such a framework could help increase the robustness of biosignature detection and interpretation, and improve communication with the scientific community and the public. In response to this need, and the call to the community to develop a confidence scale for standards of evidence for biosignature detection (Green et al., 2021), a community-organized workshop was held on July 19-22, 2021. The meeting was designed in a fully virtual (flipped) format. Preparatory materials including readings, instructional videos and activities were made available prior to the workshop, allowing the workshop schedule to be fully dedicated to active community discussion and prompted writing sessions. To maximize global interaction, the discussion components of the workshop were held during business hours in three different time zones, Asia/Pacific, European and US, with daily information hand-off between group organizers.
The biotic and abiotic controls on major shifts in atmospheric oxygen and the persistence of low-oxygen periods over a majority of Earth’s history remain under debate. Explanations of Earth’s stepwise pattern of oxygenation have mostly neglected the effect of changing diel illumination dynamics linked to daylength, which has increased through geological time due to Earth’s rotational deceleration caused by tidal friction. Here we used microsensor measurements and dynamic modelling of interfacial solute fluxes in cyanobacterial mats to investigate the effect of changing daylength on Precambrian benthic ecosystems. Simulated increases in daylength across Earth’s historical range boosted the diel benthic oxygen export, even when the gross photosynthetic production remained constant. This fundamental relationship between net productivity and daylength emerges from the interaction of diffusive mass transfer and diel illumination dynamics, and is amplified by metabolic regulation and microbial behaviour. We found that the resultant daylength-driven surplus organic carbon burial could have shaped the increase in atmospheric oxygen that occurred during the Great and Neoproterozoic Oxidation Events. Our suggested mechanism, which links the coinciding increases in daylength and atmospheric oxygen via enhanced net productivity, reveals a possible contribution of planetary mechanics to the evolution of Earth’s biology and geochemistry.
Le bassin de Franceville d'âge Paléoprotérozoïque (2,2-2,0 Ga) est connu pour ses réacteurs nucléaires naturels, la richesse de son sous-sol (minéralisations uranifères et manganésifère) et ses formations sédimentaires bien préservées qui ont fourni les plus anciens macro-organismes multicellulaires déplaçant la limite de l’apparition de la vie multicellulaire précédemment fixée à 600 Ma à 2,1 Ga. Ces derniers sont retrouvés dans la formation FB dont la mise en place s'est faite durant et immédiatement après le GOE (Grand Evenement d’Oxydation de l’atmosphère terrestre). Cependant, le bassin de Franceville possède également des roches de type cherts qui appartiennent majoritairement au FC et sont le sujet de ce travail.Les observations de terrains, les études pétrographiques et géochimiques sont utilisées pour déterminer l'environnement de dépôts, le mode de formation, et la source de la silice qui compose ces cherts. L'analyse des différents affleurements met en évidence trois faciès distincts : (1) un faciès chert massif d'apparence homogène, (2) un faciès de chert béchique et (3) un faciès stromatolites. Les dômes plats, relativement peu épais, et les formes concentriques à la surface de ces dômes traduisent un milieu supratidal à intertidal. Les observations microscopiques dépeignent trois microfaciès : (1) un microfaciès homogène composé de microquarz dans lequel sont inclus de carbonates et des calcédoines ; ce microfaciès est caractéristique des affleurements de Sucaf et route de Moyabi ; (2) un microfaciès hétérogène montrant des grains qui peuvent être assimilés à des péloïdes à Bambaye, et à des intraclastes et oncoïdes à Lekouba ; (3) un microfaciès laminé (stromatolites) présent dans tous les affleurements. Ces différents microfaciès peuvent être reliés à une précipitation directe de silice, à l'exception des faciès à intraclastes comprenant des inclusions de carbonates qui résultent de la silicification d'un précurseur carbonaté. La formation FC de Francevillien du Gabon renferme les plus vieux microfossiles de Gunflint (Gunflintia, Huroniospora, Eoastrion) qui sont observés dans des stromatolites. Des observations microscopiques (microscopie optiques, microscope électronique à balayage, microscopie électronique à transmission, microscopie laser confocal à balayage et la microspectroscopie Raman) ont été utilisées pour étudier la morphologie et l'ultrastructure dans le but de mieux caractériser leur préservation, leur biogénicité et leur affinité biologique. Malgré un degré de maturation élevé de la matière organique qui les compose, les gaines et les parois des Gunflintia et Huroniospora sont préservées par une recristallisation de plusieurs générations d'opales de différentes textures. Des filaments larges (> 3 μm) à parois épaisses sont reconnus pour la première fois dans un assemblage stromatolitique de type Gunflint et montrent la préservation d'une ultra-structure de gaine épaisse souvent observée dans les cyanobactéries. Deux types de formes en étoiles (Eoastrion) sont distinguées. L'étude palynologique et ultrastructurale révèle un processus de préservation similaire à celui des Gunflintia et Huroniospora. Toutefois, les branches d'un Eoastrion traversant un cristal de chlorite diagénétique tardif sont compatibles avec la formation de branches par migration. De ce fait, leur biogénicité reste discutable.
Cambridge Core - Computational Science and Modelling - Planets and Life - edited by Woodruff T. Sullivan, III
Carbonate minerals such as dolomite, kutnahorite or rhodochrosite are frequently, but not exclusively generated by microbial processes. In recent anoxic sediments, Mn(II)carbonate minerals (e.g. rhodochrosite, kutnahorite) derive mainly from the reduction of Mn(IV) compounds by anaerobic respiration. The formation of huge manganese-rich (carbonate) deposits requires effective manganese redox cycling in an oxygenated atmosphere. However, putative anaerobic pathways such as microbial nitrate-dependent manganese oxidation, anoxygenic photosynthesis and oxidation in ultraviolet light may facilitate manganese cycling even in an early Archean environment, without the availability of oxygen. In addition, manganese carbonates precipitate by microbially induced processes without change of the oxidation state, e.g. by pH shift. Hence, there are several ways how these minerals could have been formed biogenically and deposited in Precambrian sediments. We will summarize microbially induced manganese carbonate deposition in the presence and absence of atmospheric oxygen and we will make some considerations about the biogenic deposition of manganese carbonates in early Archean settings.
Early life processes: A geo- and astrobiological approach - Volume 15 Issue 3 - Jan-Peter Duda, Joachim Reitner
Life on Earth has existed for at least 3.5 billion years. Yet, relatively little is known of its evolution during the first two billion years, due to the scarceness and generally poor preservation of fossilized biological material. Cyanobacteria, formerly known as blue green algae were among the first crown Eubacteria to evolve and for more than 2.5 billion years they have strongly influenced Earth's biosphere. Being the only organism where oxygenic photosynthesis has originated, they have oxygenated Earth's atmosphere and hydrosphere, triggered the evolution of plants --being ancestral to chloroplasts-- and enabled the evolution of complex life based on aerobic respiration. Having such a strong impact on early life, one might expect that the evolutionary success of this group may also have triggered further biosphere changes during early Earth history. However, very little is known about the early evolution of this phylum and ongoing debates about cyanobacterial fossils, biomarkers and molecular clock analyses highlight the difficulties in this field of research. Although phylogenomic analyses have provided promising glimpses into the early evolution of cyanobacteria, estimated divergence ages are often very uncertain, because of vague and insufficient tree-calibrations. Results of molecular clock analyses are intrinsically tied to these prior calibration points, hence improving calibrations will enable more precise divergence time estimations. Here we provide a review of previously described Precambrian microfossils, biomarkers and geochemical markers that inform upon the early evolution of cyanobacteria. Future research in micropalaeontology will require novel analyses and imaging techniques to improve taxonomic affiliation of many Precambrian microfossils. Consequently, a better understanding of early cyanobacterial evolution will not only allow for a more specific calibration of cyanobacterial and eubacterial phylogenies, but also provide new dates for the tree of life.
The history of bacteria spans at least 3.8 billion years (Ga) and may well extend to 4 billion years or more. The oldest indirect evidence for the presence of life on Earth dates from 3.8 Ga and is provided by δ13 isotope ratios, indicative of fractionation by bacterial metabolism, measured in sediments from the Isua Supracrustal province in SW Greenland (Mojzsis et al., 1996). If bacteria were already active and interacting with processes on Earth so as to leave traces of their presence already by 3.8 Ga, then their development must have taken place even before that period. Bacteria are, therefore, the earliest forms of life known, to date, on Earth. However, so far no fossils have been found in the Isua sediments and the oldest known fossil bacteria occur in rocks 3.5 Ga old (Knoll and Barghoorn, 1977, Schopf and Walter, 1983; Schopf, 1993;Walsh and Lowe, 1985; Walsh, 1992; Westall, 1997a; Westall et al., 1977a, b; Westall et al., in prep.). Not only are prokaryotes the oldest known form of life, they were the only form of life for more than 70% of the history of life on Earth until the appearance of the eukaryotes sometime around 2.1 Ga.
Stromatolitic phosphorites of late Early to early Middle Eocene age have recently been found in several sites along the upper northeastern flanks of the Ramon anticline, Negev (southern Israel). As a rule, the stromatolites are associated with condensed Senonian and Paleocene rock-suites with telescoped multi-event unconformities.The stromatolite occurs in two growth forms: 1) as stratiform pseudo-columnar “ministromatolites” 1 cm in height, and 2) as polymorphic columnar “microstromatolites” hundreds of microns high, intermittently intercalated within the ministromatolite edifices and growing on micro-diastems within them. Laminae of both the mini and the microstromatolites are wavy, with a high degree of inheritance, with virtually no clastics embedded. The stromatolites where unweathered, are entirely composed of francolite. SEM study shows that the two growth forms are in large part made up of clustered capsule-like phosphate cells and some multi-enveloped globose structures, respectively tentatively interpreted as the possible remnants of early phosphatized decomposer, and primary producer microbial populations. The attributes of the stromatolitic phosphorites and their areal distribution indicate that they accreted in well-sheltered settings at the margins of the Ramon high. The stromatolitic phosphorites grade distally into phosphate nodules set within glauconite-rich late Early Eocene biomicrites. Globose structures and rod-shaped bodies of bacterial affinities are the support of the phosphate fraction and the “cement” of the nodules. Different growth conditions are considered responsible for the development of these different phosphate constructions in the two settings. These nodular and stromatolitic phosphorites in the Eocene of Negev are assumed to be a faint “echo” of the big phosphogenic event which marked the African Atlantic coastal zone during this time.
Stromatolites are morphologically circumscribed accretionary growth structures with a primary lamination that is, or may be, biologically influenced (biogenic). They are found in Archean sedimentary carbonate rocks, almost always associated with extensive volcanic sequences. Thirty-two occurrences have been reported from n small regional clusters representing the world’s principal preserved Archean cratons: North America 16, Africa 7, Australia 5, Asia 3, and Europe s; none are presently known from Archean rocks of South America and Antarctica; less than two dozen of the occurrences are viewed as definitely Archean and stromatolitic. The earliest stromatolite records date back to nearly 3.5 Ga, and their worldwide distribution and abundance increase as time progresses.
Morphological types include structures with flat, convex-up, concave-up, and globoidal laminae; stacking patterns producing nodular, columnar (unbranched as well as branched), and oncoidal forms are represented. The observed diameters of the structures show a gradual increase in size as the stratigraphic column is ascended, spread over two orders of magnitude in geon 34 (centimetric to decimetric), but ranging over six orders of magnitude by geon 25 (sub-millimetric to dekametric). Unlike Proterozoic stromatolites, most are developed in limestones rather than dolostones, with sideritic/ankeritic and cherty types also present. Microfossils are only very rarely preserved. Ministromatolites with radial-fibrous microstructure, probably almost exclusively the result of chemical precipitation, developed after 3.0 Ga, as did mesoscopic aragonite/calcite crystal fans, indicating carbonate supersaturation of ambient Meso-and Neoarchean ocean waters.
The genesis of carbon-rich rocks (shungite rocks) and accompanying phtanites (lydites) from the Early Proterozoic (2,1-2,0 Ga) of the Transonega Formation in Karelia (Eastern Fennoscandian Shield) is discussed. Some features of composition, structure and texture of these rocks as well as the structure of the deposits is described. Microtextures of lydites were studied by means of scanning electronic microscopy. The organogenic origin of primary sedimentary organic matter as well as the originally colloidal nature of silica could be confirmed.
The satisfactory systematic and functional interpretation of any fossil requires that its features be comparable to those of living organisms. A conundrum facing paleontologists who study Proterozoic microfossils is that many of the cyanobacteria-like remains that are so abundant in microbial mat assemblages have multiple morphological analogues in the modern biota -organisms that range from oxygenic photoautotrophs (the cyanobacteria) to anaerobic heterotrophs. Interpretation, therefore, requires that careful attention be paid to paleoenvironmental, behavioral, and taphonomic considerations, as well as morphology. Analyses of Proterozoic microfossil populations, including species of Eoentophysalis, Polybessurus, Eohyella, and others, demonstrate how paleobiological interpretation is maximized when careful observations on ancient populations are combined with complementary studies of modern morphological, developmental, and behavioral counterparts living in comparable physical environments.
A comprehensive analysis of taxonomic composition of pre-Riphean silicified and organic-walled microfossils described in publications is performed and dynamics of stromatolite abundance during the Archean and Paleoproterozoic is reconstructed based on a calculation of a number of stromatolite-bearing formations in seven time periods 300-400 m.y. long for the Archean and 200-300 m.y. long for the Paleoproterozoic. It is shown that the Jatulian positive δ13Ccarb anomaly, the largest one in the Earth's history that occurred 2.3-2.06 Ga ago was not related to evolutionary innovations in the ancient microbiota but was synchronous with the sharpest, in geological history, increase in the global stromatolite abundance. This event was controlled by a favorable combination of climatic, paleogeographic, and geodynamic factors and occurred under condition of the prevalence of the mantle flux into the World ocean over the continental runoff. Simultaneously, the transition to "normal marine" δ13Ccarb values that marked the termination of the Jatulian anomaly was accompanied by a slight increase in abundance of Paleoproterozoic stromatolites, which was reduced again only 1.8-1.6 Ga ago. It is concluded that the Jatulian anomaly was mainly related to the unique-scale expansion of cyanobacterial ecosystems that is recorded in stromatolite succession and occurred against the background of increasing oxygenation of atmosphere and surficial part of hydrosphere. Peculiarities of the C-isotope and paleontological records of the second half of the Paleoproterozoic are briefly discussed with consideration of probable factors responsible for the disappearance of the anomaly in question.
The Vempalle and the Tadpatri formations of the Cuddapah Supergroup of India are well known for their stromatolites. Absolute dates of the rock containing these stromatolites range between < 1800 Ma to > 1550 Ma. The stromatolites have been grouped into three assemblage zones. The characteristic forms of these three assemblages are (1) Pilbaria-Asperia, (2) Gymnosolen-Tibia and (3) Conophyton-Collumnocollenia in a younging sequence at different stratigraphic levels of the Cuddapah Supergroup. The assemblages consist of some typical Palaeoproterozoic stromatolites, viz., Asperia, Microstylus, Alcheringa, Paraboxonia and Tibia. The morphological features, microstructure and microfabric of these assemblages are comparable with Chinese forms and are characteristic of the Palaeoproterozoic age. Banded and streaky types dominate the microstructures and microfabrics are characterized by the granular, vermiform, pelloidal and tussocky types, and are similar to those recorded in Chinese forms. These microstructure and microfabrics are described and their genesis have been discussed. Comparison of the microstructure and microfabric with microstructure and microfabric of Chinese Palaeoproterozoic and younger stromatolite forms suggest that they may be identical to Chinese forms but these could not exclusively be considered as characteristic of Palaeoproterozic stromatolite assemblage. On the contrary morphological forms of the stromatolites are more reliable from the biostratigraphic point of view and are not frequently repeated in the earth history.
Reveals crucial influence (epicellular biomineralization) of small (<1 μm) coccoid cyanobacteria in the calcification process in Green Lake. Microscopic examination shows that the bioherms are actually modern thrombolitic. Groundwater enters Green Lake along the Syracuse Formation-Vernon Shale contact (~10 m depth) and the contact between the green and red shale facies of the Vernon Shale (~18 m depth). Electron microscopy of the bacteria from the oxic-anoxic interface reveals two predominant species of anoxygenic phototrophic sulfur bacteria and a facultative anoxygenic filamentous cyanobacterium. -from Authors
Fossil evidence of photosynthesis, documented in the geological record by microbially laminated stromatolites, microscopic fossils, and carbon isotopic data consistent with the presence of Rubisco-mediated CO2-fixation, extends to ~3500 million years ago. Such evidence, however, does not resolve the time of origin of oxygenic photosynthesis from its anoxygenic photosynthetic evolutionary precursor. Though it is evident that cyanobacteria, the earliest-evolved O2-producing photoautotrophs, existed before ~2450 million years ago - the onset of the "Great Oxidation Event" (GOE) that forever altered Earth's environment - O2-producing photosynthesis seems certain to have originated hundreds of millions of years earlier. How did Earth's biota respond to the GOE? Four lines of evidence are here suggested to reflect this major environmental transition: (1) rRNA phylogeny-correlated metabolic and biosynthetic pathways document evolution from an anaerobic (pre-GOE) to a dominantly oxygen-requiring (post-GOE) biosphere; (2) consistent with the rRNA phylogeny of cyanobacteria, their fossil record evidences the immediately post-GOE presence of cyanobacterial nostocaceans characterized by specialized cells that protect their oxygen-labile nitrogenase enzyme system; (3) the earliest known fossil eukaryotes, obligately aerobic phytoplankton and putative algae, closely post-date the GOE; and (4) microbial sulfuretums are earliest known from rocks deposited during and immediately after the GOE, their apparent proliferation evidently spurred by an increase of environmental oxygen and a resulting upsurge of metabolically useable sulfate and nitrate. Though the biotic response to the GOE is a question new to paleobiology that is yet largely unexplored, additional evidence of its impact seems certain to be uncovered.
Silica–carbonate biomorphs are inorganic self-organized structures that mimic the morphology of living organisms. In this study, we present the effect that proteins involved in the in vivo biomineralization of silica and calcium carbonate have on the formation of silica–carbonate biomorphs. We tested four different sources of protein: (1) struthiocalcin-1, (2) the catalytic domain of silicatein-α of Tethya aurantia, (3) a protein extract obtained from the spicules of a vitreous sponge (Protosuberitis sp.), and (4) a protein extract obtained from the spines of the sea urchin Echinometra lucunter. In addition to the well-established role that pH plays in biomorph formation, all the proteins tested controlled the morphology of these aggregates. Biomorphs obtained in the presence of the catalytic domain of silicatein-α were similar in shape to those observed in the control though considerably smaller in size. Struthiocalcin-1 affected the availability of carbonate ions and completely inhibited the formation of biomorphs resulting only in worm-like aggregates. Finally, novel biomorphs with shapes such as twisting rods, sunflowers, and mitotic cells were obtained in the presence of protein extracts from the marine sponge spicules and sea urchin spines.
Central European Upper Jurassic sponge-microbial “reefs” are commonly regarded as compact, massive and homogenous facies bodies. A continuous study of borehole cores from SW Germany clearly shows a very systematic architecture of these “reefs” built by sedimentary cycles of various hierarchical levels. Altogether five orders of cycles can be distinguished: decimeter-scale microcycles building meter-scale mesocycles, which in turn are stacked to form several-meter thick macrocycles. These high-frequency cycles in turn are parts of basin-wide medium-scale and large-scale cycles reported in a previous paper. This paper documents the high-frequency micro-, meso- and macrocycles. Microcycles (0.1–0.8 m thick) usually have a sharp erosional base covered by reworked sponges, shells and intraclasts, interpreted as storm events. These bioclastic layers are colonised by a succession of thrombolitic and stromatolitic microbialites. Successive microcycles form distinct stacks that record gradually increasing and decreasing depositional energy, thus defining mesocycles (0.5–4 m thick). Several mesocycles construct macrocycles (3–25 m). The cycle stacking patterns were analysed by means of facies-proportion-diagrams. The dominant microscale cyclicity records changes in water agitation, possibly caused by fluctuating storm wave base. The sponge-microbial mounds could probably build up just to average storm wave base. Within the cycles of larger hierarchical levels the successive smaller-scale cycles show systematic trends in their symmetry and in thickness. This may be caused by variations in the ratio of accomodation space (and associated energy level) to carbonate production. External reef geometries (progradation, aggradation, retrogradation, condensation) can be related to internal cycle stacking patterns. To approximate the duration of the high-frequency cycles two different approaches were used. Firstly, the duration of cycles was determined with the help of published chronostratigraphic time scales. Secondly, cycle duration was estimated using published microbial reef growth rates. Both approximations result in ca. 0.4 Ma for the medium-scale cycles and 0.1 Ma for the macrocycles. Both are regionally correlatable, thus appear to be allocyclic in nature and probably are Milankovitch-driven. In contrast, the microcycles are only locally correlatable and thus indicate an autocyclic (storm-induced) nature. This study poses the question if not more of the apparently homogenous “reef bodies” of other settings and geological ages may possibly also show internal high-frequency cycles.
Carbonate fixation in the ocean proceeds in three basic modes: abiotically, biotically induced (with organic trigger), and biotically controlled (where organisms determine timing, location and composition of the product). The three modes combine in a variety of ways to produce carbonate sediment. When viewed on the scale of formations and global facies belts, three benthic carbonate production systems, or ‘factories’, emerge: (1) the tropical shallow-water system, dominated by biotically controlled (mainly photoautotrophic) and abiotic precipitates; (2) the cool-water system, dominated by biotically controlled (mainly heterotrophic) precipitates; and (3) the mud-mound system, dominated by abiotic and biotically induced (mainly microbial) precipitates.
The sedimentation rates of all three factories decrease as the time span of observation increases. This scaling trend is not just an artifact of ratio correlation; it is almost certainly related to the episodic, pulsating nature of sedimentation.
The growth potential of the three systems can be estimated by drawing the envelope of the maximum observed rates of aggradation. The tropical system shows the highest rates: 10 ⁴ μm a ⁻¹ at 10 ³ years, decreasing to 10 ² μm a ⁻¹ at 10 ⁷ years. The maximum rates of the cool-water system are comparable to those of the tropical carbonates for intervals shorter than 2 × 10 ⁵ years but they amount to only 25% of the tropical standard in the domain of 10 ⁶ –10 ⁸ years. The high short-term rates of cool-water carbonates are probably caused by reworking and local trapping of sediment. The growth rates of the mud-mound system significantly exceed cool-water rates and rival the aggradation rates of tropical shallow-water carbonates. However, the mud-mound system exports less sediment than its tropical counterpart and is, therefore, somewhat less productive.
Silicified stratiform stromatolites of the Mesoproterozoic Gaoyuzhuang Formation (1.4–1.5Ga), China, contain well-preserved microfossils. The cherts also harbor varied synsedimentary precipitates and void-filling cements, replaced by early diagenetic silica minerals. These precipitates disclose microenvironments characterized by supersaturated solutions in protected, shallow depressions within an intertidal setting. The precipitates provided surfaces for selective microbial settlement, and rigid sediment matrix for microbial growth. Together with early silicification, the frequent precipitation events contributed to preservation of microfossils by reducing sediment compaction and shearing. Fossiliferous cherts display fine, flat and wavy lamination, characterized by an alternation of highly silicified, thin organic-rich layers with thick sediment-rich layers. Organic-rich layers are dominated either by coccoid or by filamentous microfossils, whereas sediment-rich layers contain abundant synsedimentary precipitates, within which the microfossils are preserved in their growth position. Four dominant microfossils Coccostratus dispergens n. gen. et sp., Eoentophysalis belcherensis, Eoschizothrix composita and Siphonophycus inornatum occur contiguously through several tens of laminae, and are identified as main frame-building biological components of Gaoyuzhuang stromatolites. Community composition, microbial density, distribution, orientation and developmental patterns of the frame-building microfossils are closely correlated with the changing depositional events of Gaoyuzhuang cherts, contrasting conditions of sedimentary kinetics with those of sedimentary stasis. Each assemblage of frame-building microfossils responded to sedimentation with different mechanisms to escape burial. High sedimentation rates correlate with scattered colonies of coccoids and with loose webs of predominantly upright filaments. Low sedimentation rates correlate with dense, laterally connected colonies of coccoids and with a change in filament orientation from vertical to horizontal. In multi-trichomous microfossil Eoschizothrix composita, low sedimentation rates are also accompanied with an increase in number of trichomes per filament. The observed morphological variability of the frame-building microfossils is explained by microbial development, reproduction and behavior by interactions between sedimentological and biological controls.
The Precambrian Earth: Tempos and Events Edited by EG. Eriksson, W. Altermann, D.R. Nelson, W.U. Mueller and O. Catuneanu Developments in Precambrian Geology, Vol. 12 (K.C. Condie, Series Editor) 9 2004 Elsevier B.V. All rights reserved
Chapter 9
TOWARDS A SYNTHESIS
RG. ERIKSSON, O. CATUNEANU, D.R. NELSON, W.U. MUELLER AND W. ALTERMANN
The principal theme of this book is change through time, or tempos and events in the Precambrian (Preface). Each chapter portrays a different part of the Earth's history but there is a unifying theme: Earth's evolution. Chapter 1 explains the celestial origin of our planet and the early development of the Earth into core, mantle, crust and primitive atmosphere. Chapter 2 discusses the generation of continental crust, with the emphasis on granite-greenstone terranes. Chapter 3 builds further upon its predecessor, empha- sising the interaction between tectonism and mantle plumes through Precambrian time. Chapter 4 examines the volcanic attributes of the Archaean Earth and how they may have changed, as exemplified by plume-generated komatiites, the constant interaction between arc-plume volcanism and subaqueous caldera formation. Chapter 5 deals with the evolution of Earth's atmosphere and hydrosphere, and chapter 6 with related concepts of the evolu- tion of Precambrian life and bio-geology. Chapter 7 details sedimentation regimes through Precambrian time, while chapter 8 discusses the application of sequence stratigraphy to the Precambrian rock record.
9.1. EVOLUTION OF THE SOLAR SYSTEM AND THE EARLY EARTH
Investigation of pre-4 Ga Earth history relies largely upon study of the most ancient rocks thus far identified, and upon modelling of the differentiation of Earth's chemical reservoirs (Nelson, section 1.1). As the known preserved rock record dates from 4030 Ma (Stern and Bleeker, 1998; Bowring and Williams, 1999), more than 500 My of Earth's ear- liest evolution remains essentially speculative. It was only with the identification within meteorites of daughter products from radiogenic decay of long-extinct nuclides (firstly by Reynolds, 1960), that the timing of accretion and differentiation of the early Earth could be investigated (summarised by Nelson, in section 1.2). The short-lived parent nu- clides were synthesised during supernova explosions shortly before formation of our solar system; their short half-lives enable precise determination of the chronology of the earli- est history of the solar system (section 1.2). Collision and amalgamation of smaller, rocky planetesimals within a protoplanetary disk formed the terrestrial planets, including Earth. As proto-Earth and its Moon grew by these violent accretion processes, earlier differenti- ation products were largely obliterated; with the growth of embryonic planets the impact rate decreased and concomitantly, the likelihood of preservation of fragments of the early
Earth increased.
Current evidence (section 1.2) suggests that short-lived nuclides with atomic masses
< 140, together with a part of the heavy elements in our solar system, were synthesised
during a core-collapse supernova event at c. 4571 Ma (Lugmair and Shukolyukov, 2001;
Gilmour and Saxton, 2001 ). Formation of the Sun and solar system may have been initiated
by shock waves from this supernova explosion (probably one of a number of successive
such events); injection of short-lived nuclides into a nearby interstellar gas and dust cloud
may have triggered its collapse, forming a proto-Sun of radius c. five times its present
value, over a time period of < 105 years (Cameron, 1995; Nelson, section 1.2). Progressive
collapse from inner to outer parts of the cloud, together with conservation of angular
momentum, caused it to spin faster; colliding gas and dust particles orbiting the proto-
Sun in the same direction lost their energy, causing flattening of the cloud, especially near
its centre.
Gravitational energy was converted to heat during collapse of the nebula. At some time
during collapse, the density and temperature became high enough for hydrogen burning
to commence, and the proto-Sun began its violent T-Tauri phase (Cameron, 1995;
Nelson, section 1.2). More abundant Fe, Ni and silicate-rich components condensed within
lower temperature parts of the nebula in its medial to central parts, while volatile elements
(e.g., water, ammonia, methane ice) condensed in cold, outer parts of the accretionary disk.
Volatiles were possibly carried by the solar wind from inner to outer reaches of the emerging
solar system (Shu et al., 1994).
Spectroscopy and simulation modelling suggest only a few million years from star formation
and large scale accretion of disks into the young solar-type T-Tauri stars. Larger
planetesimals may have formed within ~< 2 My of solar system formation (Hutchison et al.,
2001). Coagulation consequent upon icy particle collisions within an ice sublimation belt
in the cold outer parts of the nebula being more efficient than that between metal or silicate
particles, large gas-rich proto-planets (Jupiter and Saturn precursors) formed before
the nebula gas dissipated (Cameron, 1995). Collision and amalgamation of chemically refractory
dust particles within the inner part of the disk occurred more slowly. Collisions of
smaller planetesimals with larger bodies continued to rework early planetary-sized bodies
for at least a further 100 My, and triggered large scale melting and magmatic differentiation
of silicate components of the larger planetesimals. Dating of meteoritic remnants from
these early differentiated planetary bodies indicates that planetesimals of at least 10s-100s
of kilometres in diameter underwent internal magmatic differentiation within < 10 My
after the supernova event. 187Re-187Os isotopic data from pallasites and iron meteorites
(Morgan et al., 1995; Shen et al., 1998; Horan et al., 1998) suggest formation of metallic
cores within c. ~< 50 My of formation of the solar system. There is intriguing evidence for
hydrothermal alteration processes involving aqueous fluids within planetesimals ~< 2 My
after solar system formation.
Planetary embryos had thus existed within <~ 5 My of the supernova event that triggered
formation of the solar system. Accretion of these embryos within a c. 0.5-2.5 AU range
of the Sun (Wetherill, 1994) was largely responsible for formation of the terrestrial plan
The unambiguous evidence for the presence of life in the Archean is only limited by the preservation potential of sedimentary
rocks. Throughout Earth’ preserved sedimentary deposits, prokaryotic bodily fossils and geochemical fossils, for example,
products of the Calvin-cycle dependent carbon isotopic fractionation, can be found. Nevertheless, irreproducible analyses
in organic geochemistry, misinterpretations of artifacts from sample preparation and of organic contaminants, and uncertainties
on the age and nature of the Archean rock formations are copious in evaluation of the earliest traces of life.
The understanding of geological processes strongly influence discussions of the ancient, supposed biological relicts from
c. 3.8 billion years old (3.8 Ga) metasedimentary rocks. The evidence for prokaryotic bodily preserved microfossils of the
Neoarchean, at 2.7 to 2.5 Ga is by orders of magnitude stronger, as rocks of this age are abundant and better preserved.
Bacteria and nannobacteria (0.1??m dwarfed forms) are abundant in both non-etched and gently etched travertines deposited by hot springs in Viterbo, Italy. They are also plainly visible in Bahama ooids and hardgrounds, and in Great Salt Lake aragonite ooids and cements. In addition, nannobacteria are found in Paleozoic and Mesozoic rocks. Because of their extraordinary abundance in some specimens, they probably play a prominent role in catalyzing the precipitation of carbonate materials. -Author
IntroductionHow are relics of Archaean life preserved?When did life first appear?What were Archaean organisms like?How did Archaean organisms live?Where did Archaean organisms live?
The Linok Formation is made up of clayey and carbonate strata, 180–300 m thick, formed at the terminal Middle Riphean on the northwestern margin of the Siberian Platform. In the modern structure, it is exposed in the lower part of the Turukhansk Uplift section. The sediments accumulated in the distal part of the epiplatformal basin as a symmetrical transgressive–regressive cycle. Its lower part represents a deep-water basin environment with the mixed carbonate–clayey sedimentation, whereas the upper part reflects the origination and evolution of a carbonate platform. Microstructures discussed in this work suggest not only the ancient existence of benthic microbial assemblages (mats) but their active influence upon the facies pattern of sediments as well. The influence was determined by the ability of mat-forming communities to produce carbonate sediments under certain environmental conditions. The analysis of the facies succession suggested the absence of an appreciable influx of carbonate material to the basin from other sources. Based on the carbonate generation ability, one can distinguish three (carbonate-free, low-productive, and high-productive) groups of microbial communities. Groups 1 and 2 represent deep-water basin mats, whereas group 3 represents relatively shallow-water platformal microbial–mineral systems. The carbonate productivity of communities is inversely proportional to the depth of their dwelling and the relative rate of clayey sedimentation. The morphological reconstruction of microbiolite structures showed that the structures in basins and platforms greatly differed in terms of the size of elements. The ability of microbial communities to generate carbonate could be realized only within large ecosystems.
The vast majority of laminae in the cortex of modern Bahaman ooids and ooids in the Pleistocene Miami Limestone in the Florida
Keys are aragonite. The aragonite has two forms: rod-shaped batons (0.5–3.0 μm long and 0.17–0.7 μm in diameter), and nannoballs
(0.025–0.3 μm in diameter). Nannoballs are always subordinate to batons and are much more common in Bahaman ooids than in
ooids in the Miami Limestone.
Variations in the size and shape of known rod-shaped bacteria correspond exactly or very closely to variations in the size
and shape of batons. Accordingly, batons are interpreted as calcified rod-shaped bacteria
The intimate association of batons and nannoballs suggests a formational link. Aggregates of nannoballs and aggregates of
nannoballs and batons probably originated via the complete decay of original batons in the former cases, and the partial decay
of original batons in the latter case. Nannoballs not in contact with one another may be bacterial spores that become separated
from gram-positive bacterial vegetative cells as a result of a lack of nutrients or some other from of environmental pressure.
Calcification of rod-shaped bacteria probably involved aragonite formation in the bulk phase external to individual bacteria.
It is proposed that calcification of individual bacteria took place in biofilms that were adsorbed to the surface of a nucleus
(such as a fecal pellet) and then to successive laminae as the ooids grew in size. Each lamina would initially, therefore,
represent a single biofilm and, ultimately, a layer of calcified rod-shaped bacteria. Calcification of bacteria in biofilms
probably took place rapidly so that successive biofilms were formed on mostly solid surfaces. Thus, the ooids lithified from
the inside out.
It is hypothesized that ooids stop growing as a result of termination of a nutrient supply necessary to create biofilms on
the surface of developing ooids. The most likely cause is burial of older ooids by younger ooids so that biofilms in older
ooids no longer have access to a nutrient source in the water column.
The diurnal variation in the microgradients of O(2), H(2)S, and Eh were studied in the benthic cyanobacterial mats of a hypersaline desert lake (Solar Lake, Sinai). The results were related to light intensity, light penetration into the mat, temperature, pH, NH(4), photosynthetic activity, pigments, and the zonation of the microbial community. Extreme diurnal variation was found, with an O(2) peak of 0.5 mM at 1 to 2 mm of depth below the mat surface during day and a H(2)S peak of 2.5 mM at 2 to 3 mm of depth at night. At the O(2)-H(2)S interface, the two compounds coexisted over a depth interval of 0.2 to 1 mm and with a turnover time of a few minutes. The photic zone reached 2.5 mm into the mat in summer, and the main CO(2) light fixation took place at 1 to 2 mm of depth. During winter, light and photosynthesis were restricted to the uppermost 1 mm. The quantitative dynamics of O(2) and H(2)S were calculated from the chemical gradients and from the measured diffusion coefficients.
Frequency of dividing cells is suggested to be an indirect measure of the mean growth rate of an aquatic bacterial community. Seasonal changes in frequency of dividing cells were found which covariated with the bacterial uptake of C-labeled phytoplankton exudates. Batch and continuous culture growth experiments, using brackish water bacteria in pure and mixed enrichment cultures, were performed to establish a relationship between frequency of dividing cells and growth rate. An improved technique for bacterial direct counts, using fluorescent staining and epifluorescence microscopy, is presented. Based on a 6-month survey in a coastal area of the Baltic Sea, the bacterial production in the photic zone is estimated. Compared to the total primary production in the area, the bacterial population during this period utilized approximately 25% of the amount of carbon originally fixed by the primary producers.
Laminated mats of unique character in siliceous alkaline hot springs of Yellowstone Park are formed predominantly by two organisms, a unicellular blue-green alga, Synechococcus lividus, and a filamentous, gliding, photosynthetic bacterium, Chloroflexus aurantiacus. The mats can be divided approximately into two major zones: an upper, aerobic zone in which sufficient light penetrates for net photosynthesis, and a lower, anaerobic zone, where photosynthesis does not occur and decomposition is the dominant process. Growth of the mat was followed by marking the mat surface with silicon carbide particles. The motile Chloroflexus migrates vertically at night, due to positive aerotaxis, responding to reduced O(2) levels induced by dark respiration. The growth rates of mats were estimated at about 50 mum/day. Observations of a single mat at Octopus Spring showed that despite the rapid growth rate, the thickness of the mat remained essentially constant, and silicon carbide layers placed on the surface gradually moved to the bottom of the mat, showing that decomposition was taking place. There was a rapid initial rate of decomposition, with an apparent half-time of about 1 month, followed by a slower period of decomposition with a half-time of about 12 months. Within a year, complete decomposition of a mat of about 2-cm thickness can occur. Also, the region in which decomposition occurs is strictly anaerobic, showing that complete decomposition of organic matter from these organisms can occur in the absence of O(2).
Several isolates of bacteria and fungi from soil, together with cells released directly from soil, were studied with respect to buoyant density and dry weight. The specific volume (cubic centimeters per gram) of wet cells as measured in density gradients of colloidal silica was correlated with the percent dry weight of the cells and found to be in general agreement with calculations based on the partial specific volume of major cell components. The buoyant density of pure bacterial cultures ranged from 1.035 to 1.093 g/cm, and their dry-matter content ranged from 12 to 33% (wt/wt). Average values proposed for the conversion of bacterial biovolume into biomass dry weight are 1.09 g/cm and 30% dry matter. Fungal hyphae had buoyant densities ranging from 1.08 to 1.11 g/cm, and their dry-matter content ranged from 18 to 25% (wt/wt). Average values proposed for the conversion of hyphal biovolume into biomass dry weight are 1.09 g/cm and 21% dry matter. Three of the bacterial isolates were found to have cell capsules. The calculated buoyant density and percent dry weight of these capsules varied from 1.029 g/cm and 7% dry weight to 1.084 g/cm and 44% dry weight. The majority of the fungi were found to produce large amounts of extracellular material when grown in liquid cultures. This material was not produced when the fungi were grown on either sterile spruce needles or membrane filters on an agar surface. Fungal hyphae in litter were shown to be free from extracellular materials.
With a microculture technique and time-lapse, phase-contrast photomicrography, it was possible to follow the division of individual cells and the development of microcolonies of bacteria in freshly collected marine water samples. A certain number of marine bacteria, upon inoculation onto a nutrient rich agar surface, displayed an increase in size as well as a high growth rate. Other bacteria were identified as very small marine bacteria (ultramicrobacteria). These had a very slow growth rate when inoculated onto a nutrient-rich agar surface. These latter cells formed very small microcolonies (ultramicrocolonies), and cell size did not increase significantly. These two types of marine heterotrophs could be described in terms of zymogenous and autochthonous bacteria, a concept used by Winogradsky for describing soil microorganisms.
The Sand Bulge is a silicoclastic sabkha lying between Padre Island and the mainland; it is cut on its landward side by the canal of the Intracoastal Waterway. The Sand Bulge is sporadically inundated by rain and by wind- and tide-driven water from Laguna Madre, and by washover from Padre Island. Most of this floodwater is prevented from directly entering the fine sandy sediment by a leathery algal mat; the remainder accumulates and concentrates by evaporation in shallow pools. The sabkha contains saline groundwater. This water-table discharges westward into the Intracoastal Waterway, and possibly also eastward through buried stream channels under Padre Island. Although the salinity of the groundwater (>200per mille) exceeds that required for the precipitation of gypsum, no gypsum is present in the sands. The algal mat contains CaCO 3 as a micrite of high-Mg calcite. Apparently, the algae are responsible for depleting the descending water of sufficient Ca to prevent gypsum saturation.-H.R.B.
This chapter discusses microbiology and morphogenesis of columnar stromatolites from hot springs in Yellowstone national Park. The hot springs of Yellowstone National Park in Wyoming constitute an environment that, in some ways, is analogous to Precambrian marine environments. The great amount of microbiological data on the Yellowstone springs provides an excellent opportunity to study in depth the microbiology of columnar stromatolites. Field observations and laboratory experiments strongly suggest that the morphology and microstructure of the Conophyton stromatolites result from the phototaxis and cohesion of the principal constructing microorganism, Phormidiumtenue var. granuliferum. The Yellowstone conophytons are similar to the Precambrian and the Precambrian Conophytons are astoundingly like those in Yellowstone. The Conophyton–like structures have been induced to form in the laboratory, using pure cultures of this cyanophyte. The results of the work indicate the morphogenetic analysis of at least some fossil stromatolites that can provide physiological data on the constructing microorganisms.
New Rb-Sr and trace element data are reported for the Great Dyke and Bushveld Mafic Phase layered intrusions. It is argued
that geochemical characteristics, such as 87Sr/86Sr ratios and R.E.E. distribution patterns have been little modified by crustal contamination.
Rb-Sr data for whole-rocks of the Great Dyke yield an age of 2514±16 m.y. and an initial 87Sr/86Sr ratio of 0.70261±4. Mineral data are consistent with these results. The low errors on the results indicate no significant
variation of 87Sr/86Sr ratios of successive magmatic influxes emplaced in different magma chambers. Earlier Great Dyke magmas were highly Mg-rich
and represent extensive partial melts of the source material. One such influx is shown to have a high Rb/Sr ratio (∼0.25)
and a fractionated R.E.E. pattern (CeN/YBN∼ 12). These ratios are considered to approximate those of the source region.
The Bushveld Mafic Phase has been dated accurately for the first time and has a Rb-Sr age of 2095±24 m.y. Initial 87Sr/86Sr ratios increase in a stepwise manner upwards in the intrusion from 0.70563±2 to 0.70769±6. Each increase is abrupt and
occurs at a horizon also characterized by a sudden irregularity in cryptic variation. The Mafic Phase was emplaced as a succession
of magmatic influxes each of which had higher 87Sr/86Sr ratio than its predecessor.
The first magma was both Mg-rich (MgO ≥ 21.5 per cent) and SiO2-rich (50–55 per cent SiO2) and was derived by extensive partial melting of a shallow level upper mantle source. This source was characterized by trace
element abundance ratios (e.g. Rb/Sr ∼ 0.25; K/Rb ∼ 90; CeN/YbN ∼ 11), similar to those of kimberlites and some potassic lavas and comparable with those deduced for the Great Dyke source
region.
It is postulated that when the Rhodesian and Kaapvaal cratons stabilized, underlying refractory mantle became fixed thereto
to form a proto-lithosphere. Shortly afterwards, at about 2800 m.y. ago, this proto-lithospheric mantle was enriched by passage
through it of fluids with kimberlitic trace element chemistry. This sub-cratonic mantle thereafter evolved with a relatively
high Rb/Sr ratio. Magmas derived from it have anomalous chemical characteristics with respect to those of ocean-floor basalts,
reflecting major differences in the evolution of their respective source regions.
The littoral sediments of Solar Lake (Sinai) consist of cyanobacterial mats up to 1 m thick. The vertical distributions in these mats of sulfur compounds, organic carbon, carbonate, and of sulfate-reducing and other anaerobic, heterotrophic bacteria are presented. The in situ rate of sulfate reduction measured with a radiotracer technique, decreased 10,000-fold from 5,400 Nmol SOâ/sup 2 -//cm³/d at the surface to less than 1 at the bottom of the mats. Turnover rates of inorganic sulfur compounds and of organic matter were estimated. A high influx down into the cyanobactyerial mats of dissolved organic compounds produced by the epibenthic algae and bacteria could be deduced from the anaerobic respiration rates. A quantitative flow diagram of the sedimentary sulfur and carbon cycle is presented.
Microbial contaminants may be introduced on outcrop as well as en route to or in the laboratory. Micropseudofossils may be natural or man-made. It is possible to recognize such misleading objects and important that they are not allowed to dilute the growing record of authentic pre-Phanerozoic life. Filamentous microbial contaminants from minute cracks in samples of ancient carbonate rocks from Brazil (perhaps 1 Ga old) and South Africa (∼2.3 Ga old) are similar to occurrences previously described as fossils. Published records of supposedly Archean microbial life also include microcontaminants and laboratory artifacts. Although microstructures from sedimentary rocks of the Swaziland system could be fossils, they are not demonstrably so. The oldest structurally preserved fossils yet known seem to be the filaments described by Lois Nagy from stromatolitic limestone in the ∼2.3 Ga old Malmani Dolomite of South Africa. It will be difficult to establish unequivocal older records in the absence of definitive ultrastructural or micro-chemical evidence.
The Malmani Subgroup northwest of Johannesburg consists of dolomite and chert with only minor clastic sediments.A precise upper intertidal to marginal supratidal analogy and the associated relationship of varied structures suggest that much of the succession represents a tidal flat to intertidal complex formed within differing semiprotected to protected conditions. The dolomites from these environments are recrystallized, reflecting a meteoric influence, and the cherts which are commonly developed within them are also related to prevailing lower pH's. This dolomitization is considered to have been enhanced by the influx of meteoric waters which however resulted in the dolomites having undersaturated iron-manganese ratios. Rare colour-banded dolomites containing columnar stromatolites are thought to represent more steeply shelving intertidal conditions than are normally encountered in the epeiric sea. These dolomites contain quartz crystals rather than chert, suggestive of a lower concentration of silica in the original alkaline solutions. The exposure is part of a very widespread carbonate unit, dated at ca. 2.250 m.y.Subtidal conditions in which large elongate stromatolitic domes developed can be related to a marine transgression across a basal clastic beach sand; and secondly to a progradational tidal flat seawards of which a talus breccia developed on a steepened slope leading down to the subtidal regime. These dolomites formed by interaction with marine waters saturated with respect to iron and manganese, while the absence of chert reflects persisting alkaline conditions.A dark chert-free dolomitic facies with high iron and manganese contents of saturated ratios is considered to have developed in an alkaline lagoonal environment behind a subaqueous bar that is now represented by an overlying thick oolitic unit.The succession contains numerous chert breccias with which shales are associated. The breccias represent subaerial exposure phenomena related to regressions which were followed by periods of short-lived terrigenous influx.
Cyanobacterial mats of Solar Lake, studied in the field and by microscopic methods, are classified into four types: flat shallow‐water mat, pinnacle mat on the upper slope, cyanobacterial and other photosynthetic bacterial films on the lower slope, and flocculose mat at the bottom. The annual cycle and development of the four types are described. Measurements of photosynthesis by the flat shallow‐water mat in the field and the laboratory yielded an average value of 10 g C m ⁻² d ⁻¹ . In the flocculose anaerobic bottom mat 5 g C m ⁻² d ⁻¹ was measured. Total accretion rates including organogenic material for the four mat types range between 5 and 50 cm 100 yr ⁻¹ ; aerobic and anaerobic degradation of the organic production of the shallow‐water mat remineralizes more than 99% of the biomass. In the deeper parts of the mat, organic matter is transformed into carbonates. The role of bacteria in this process is demonstrated by ultramorphological analyses and by comparison to laboratory experiments with bacterial isolates.
An association of structures is documented from a Lower Proterozoic carbonate sequence in South Africa: this is dominated by finely laminated material which may display flat (smooth), small domical (blister), crinkled (tufted) and pustular (mamillate) surface. The lamination may display overfolded structures and contain flat encapsulated features. Lens-like flat-pebble breccias are common, while edgewise breccias were seen less frequently. Small-scale features suggestive of vertical algal moulds were also recorded. This facies is considered to be analogous to contemporary tidal flat sedimentation developed in specific settings at Shark Bay in Western Australia, and at Abu Dhabi where it is the dominant growth form. This analogy is most notably clear in relation to the protected embayments at Shark Bay, and as a result, an inner intertidal to marginal supratidal environment is suggested for the specific horizons under consideration from the Transvaal Dolomite.
Other structures are associated with this facies. These include larger domes, coarser bedding, oolites, ripple-marks and, in one case, columnar stromatolites. Using the basic facies as an environmental datum, a model is developed in which these latter structures extend into the outer intertidal zone. They are also considered to be associated with varying states of turbulence in the intertidal regime.
The microfossil Frutexites is known from many Palaeozoic and some Proterozoic carbonate sedimentary rocks. We recently found unusually well-preserved examples in the early Proterozoic Gunflint Iron Formation of Ontario, Canada. These are preserved in chert, along with other microfossils of the Gunflint microbiota. The Gunflint examples have previously been described as laminated, columnar-branching microstromatolites. We have found narrow tubes (interpreted as trichome moulds) axially placed in many of the microcolumns. By comparison with extant organisms, we interpret Frutexites as a thick-sheathed scytonematacean cyanophyte. These are the oldest known fossil scytonemataceans. They apparently grew within mats of other microorganisms. These probably were photosynthetic organisms, which may have significant implications in the interpretation of some occurrences, such as in the fore-reef facies of Devonian reefs in Western Australia.
A basal section of the Lower Proterozoic Transvaal Dolomite from the northern Cape has been re-examined. Numerous associations of stromatolites and other structures have been distinguished in it. Forms of domical stromatolite dominate the structures, but columns, and associations built around spheroidal forms, are also represented. This material accumulated in a telescoped range of environments through the intertidal to a high-energy agitated zone and out into the subtidal.Columnar forms and flat domes from the intertidal zone appear to be remarkably similar to features described from Hamelin Pool at Shark Bay, Western Australia. The subtidal elongate domes and mounds increase in size with depth to reach dimensions of 40 by 10 m, heights of 13 m and relief of 2.5 m. Minor structures on these subtidal forms reflect decreasing energy outwards; included within them are columnar forms in the shallow subtidal zone.It is suggested that deposition within an epeiric sea was away from a headland on a relatively steeply shelving floor affected by currents at right angles to the shore. There are indications that an arid to semi-arid climate existed at that time.
Chapter 1 contains a short historical introduction. Chapter 2, represents an updated review of microbial diversity and systematics. It also provides essential information required for the understanding of the form, function, and systematic relationship of microorganisms. Chapter 3 is devoted to the formation and structure of microbial communities, and deals with this subject both in the evolutionary and successional senses. Chapter 4 describes the interactions between microorganisms, and Chapters 5 and 6 explore the interactions of microorganisms with plants and with animals, respectively. Chapter 7 discusses the quantitative measurement of numbers, biomass, and activity of microorganisms; Chapter 8 examines the influence and the measurement of their environmental determinants. Chapter 9 presents air, water, and soil as microbial habitats and describes the typical composition of their communities. Chapters 10 and 11 contain an expanded discussion of the biogeochemical cycling activities performed by microbial communities. Chapters 12-15 deal with applied aspects of microbial ecology evident in biodeterioration control, sanitation, soil conservation, pollution control, resource recovery, and biological control.
Three techniques for the measurement of bacterial numbers and biomass in the marine environment are described. Two are direct methods for counting bacteria. The first employs an epifluorescence microscope to view bacteria that have been concentrated on membrane filters and stained with acridine orange. The second uses a transmission electron microscope for observing replicas of bacteria that are concentrated on membrane filters. The other technique uses Limulus amebocyte lysate, an aqueous extract from the amebocytes of the horseshoe crab, Limulus polyphemus, to quantitate lipopolysaccharide (LPS) in seawater samples. The biomass of gram-negative (LPS containing) bacteria was shown to be related to the LPS content of the samples. A factor of 6.35 was determined for converting LPS to bacterial carbon.
Upon starvation, Ant-300, a psychrophilic marine vibrio, was observed to decrease in size and change in shape from a rod to a coccus. After 3 weeks of starvation 50% of the starved population was able to pass through a filter with a pore size of 0.4 mum. Electron microscopy of thin sections of the small cells revealed normal cell structure except for an enlarged periplasmic space. When inoculated into a fresh medium, starved cells growth without a significant lag and regained "normal" size and shape within 48 h.
The relationship between specific growth rate of Escherichia coli and the concentration of limiting nutrient (glucose or phosphate or tryptophan) has been determined for populations in a steady state. At high concentrations the specific growth rate is independent of the concentration of nutrient, but at low concentrations the specific growth rate is a strong function of the nutrient concentration. Such a relationship was predicted by Monod; however, Monod's equation does not predict the relationship over the entire range of nutrient concentration. If parameters of the equation are estimated from the results obtained at low concentrations, then at high concentrations of nutrient, the specific growth rate is significantly higher than that predicted by Monod's equation. These results were interpreted on the basis that the rate of growth is controlled by at least two parallel reactions and that the affinities of the enzymes catalyzing these reactions are different. The relationship between specific growth rate and mean cell volume was also measured, and the results indicate that mean cell volume depends not only on the specific growth rate but also on the nature of the limiting nutrient. There are different mean cell volumes at the same specific growth rate established by different limiting nutrients. Therefore, the mean cell volume is not uniquely determined by the specific growth rate.
Ant-300, a psychrophilic marine vibrio isolated from the surface water of the Antarctic convergence, was starved for periods of more than 1 year. During the first week of starvation, cell numbers increased from 100 to 800% of the initial number of cells. Fifty percent of the starved cells remained viable for 6 to 7 weeks while a portion of the population remained viable for more than 1 year. During the first 2 days of starvation, the endogenous respiration of the cells decreased over 80%. After 7 days, respiration had been reduced to 0.0071% total carbon respired per hour and remained constant thereafter. After 6 weeks of starvation, 46% of the cellular deoxyribonucleic acid had been degraded. Observation of the cellular deoxyribonucleic acid with Feulgen staining before starvation showed the average number of nuclear bodies per cell varied from 1.44 to 4.02 depending on the age of the culture. A linear relationship was found between the number of nuclear bodies per cell and the increase in cell numbers upon starvation. Our data suggest that Ant-300 is capable of surviving long periods of time with little or no nutrients and is therefore well adapted for the sparse nutrient conditions of the colder portions of the open ocean.
Stromatolites from the Proterozoic Animikie and Sibley Groups, Ontario: Geological Survey of Canada, Paper 68-69 Attributes of stromatolites: Geological Survey of Canada, Paper 69-35
- H J Hofmann
- H J Hofmann
HOFMANN, H.J., 1969a, Stromatolites from the Proterozoic Animikie and Sibley Groups, Ontario: Geological Survey of Canada, Paper 68-69, 77 p. HOFMANN, H.J., 1969b, Attributes of stromatolites: Geological Survey of Canada, Paper 69-35, 75 p. HOFMANN, H.J., 1976, Precambrian microflora, Belcher Islands, Canada: Significance and Systematics: Journal of Paleontology, v. 50, p. 1040-1073.
Laminated microbial mats
- J Javor
- R W Castenholz
JAVOR, J., and CASTENHOLz, R.W., 1981, Laminated microbial mats, Laguna Guerrero Negro, Mexico: Geomicrobiology Journal, v. 2, p. 237-273.
Optical Mineralogy Stromatolites-the challenge of a term in space and time
- P F Kerr
KERR, P.F., 1977, Optical Mineralogy: New York, McGraw Hill, 492 p. KRUMBEIN, W.E., 1983, Stromatolites-the challenge of a term in space and time: Precambrian Research, v. 20, p. 493-531.
Microstromatolites from the 2.3 G.a. Transvaal Sequence, South Africa [unpubl. Ph.D. dissert.]: Tucson, Arizona, University of Arizona
- W P Lanier
- W B Lyons
- D T Long
- M E Hines
- H E Gaudette
LANIER, W.P., 1984, Microstromatolites from the 2.3 G.a. Transvaal Sequence, South Africa [unpubl. Ph.D. dissert.]: Tucson, Arizona, University of Arizona, 165 pp. LYONS, W.B., LONG, D.T., HINES, M.E., GAUDETTE, H.E., and ARM-STRONG, P. E., 1984, Calcification of cyanobacterial mats in Solar Lake, Sinai: Geology, v. 12, p. 623-626.
Stratigraphy of South Africa Part 1 (Comp. Kent, L.E.); Lithostratigraphy of the Republic of South Africa, South West Africa/Manibia and the Republics of Bophuthatswana, Transkei and Uenda: Handbook of the Geological Survey of South Africa
- South African
- For
- Stratigraphy
SOUTH AFRICAN COMMITTEE FOR STRATIGRAPHY (SACS), 1980, Stratigraphy of South Africa. Part 1 (Comp. Kent, L.E.); Lithostratigraphy of the Republic of South Africa, South West Africa/Manibia and the Republics of Bophuthatswana, Transkei and Uenda: Handbook of the Geological Survey of South Africa, v. 8, p. 191-192.
The morphology of stromato-lites from the Transvaal Dolomite northwest of
- J F Truswell
- K A Eriksson
TRUSWELL, J.F., and ERIKSSON, K.A., 1972, The morphology of stromato-lites from the Transvaal Dolomite northwest of Johannesburg, South Africa: Transactions of the Geological Society of South Africa, v. 75, p. 99-110.