No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Chapter 5.2 An Attempt to Classify Late Precambrian Stromatolite Microstructures
Abstract
This chapter presents an attempt to classify late Precambrian stromatolite microstructures. The stromatolite primary lamination reflects the growth pattern of the algal coenose and the habit of the carbonate precipitated or trapped within the filament framework, among other things. The fossil stromatolite microstructure includes furthermore the imprint of subsequent diagenesis. A carefully detailed description of the actual fabric of the microstructure mixing up original and diagenetic features leads to an excessive number of microstructural patterns, and a very artificial classification. The need of modern models is great because of the excessive attention paid by the geologists to the sedimentary and physical processes. Well-preserved microstructures were proposed for the classification of stromatolites that were well adapted: (1) simple microstructures where the laminations or the dominant fabrics follow the rhythmical growth pattern of the coenose; and (2) complex microstructures where the historical succession of laminations presents microstructural changes due to seasonal differentiation of the algal coenose.
... No fabrics have been observed here that would suggest in situ precipitation, such as vertically oriented crystals with terminations, in the microspar that is juxtaposed with matrix at the stromatolite surface (for example, Fig. 18); therefore, this is regarded as selective alteration of an essentially fine-grained precursor. It resembles 'streaky' or 'platy' (Walter, 1972) and 'film' (Bertrand-Sarfati, 1976, fig. 1) microfabric, which Bertrand-Sarfati (1976) considered to be common near the mid-late Riphean transition (ca 1Á0 Ga). The selective nature of this alteration is seen at column margins where 'streaky' column fabric is juxtaposed against partially dolomitized, but otherwise relatively unaltered, finegrained matrix in the runnels (Fig. 18). ...
... Glauconite is also often localized near column margins (Mei et al., 2008) (Fig. 18D). Column microlayering evidently broadly follows original fabric variations; it includes stromatolitic microcolumns, shows cross-cutting relationships between laminae and preserves small intraclasts that locally include millimetric plates arranged in a pack of cards structure (Fig. 19), together with smaller rounded grains, some of which resemble catagraphs figured by Bertrand-Sarfati (1976, fig. 3b). ...
... In addition to neomorphic microspar, cement spar occurs locally between intraclast plates (Fig. 19D). Bertrand-Sarfati (1976) compared film microfabric with Andros tidal flat mats formed by alternation of layers of carbonate mud, with and without Scytonema (Monty, 1965), and which are similar to 'type A' mats of Black (1933, pl. 22, fig. ...
The Mesoproterozoic Tieling Formation, near Jixian, northern China, contains thick beds of vertically branched, laterally elongate, columnar stromatolites. Carbonate mud is the primary component of both the stromatolites and their intervening matrix. Its abundance is attributed to water-column ‘whiting’ precipitation stimulated by cyanobacterial photosynthesis. Neomorphic microspar gives the stromatolites a ‘streaky’ microfabric and small mud-flakes are common in the matrix. The columns consist of low-relief, mainly non-enveloping, laminae that show erosive truncation and well-defined repetitive lamination. In plan view, the columns form disjunct elongate ridges <10 cm wide separated by narrow matrix filled runnels. The stromatolite surfaces were initially cohesive, rather than rigid, and prone to scour and are interpreted as current aligned microbial mats that trapped carbonate mud. The pervasive ridge–runnel system suggests scale-dependent biophysical feedback between: (i) carbonate mud supply; (ii) current duration, strength and direction; and (iii) growth and trapping by prolific mat growth. Together, these factors determined the size, morphology and arrangement of the stromatolite columns and their laminae, as well as their branching patterns, alignment and ridge–runnel spacing. Ridge–runnel surfaces resemble ripple mark patterns, but whether currents were parallel and/or normal to stromatolite alignment remains unclear. The formation and preservation of Tieling columns required plentiful supply of carbonate mud, mat building microbes well-adapted to cope with this abundant sediment, and absence of both significant early lithification and bioturbation. These factors were time-limited, and Tieling stromatolites closely resemble coeval examples in the Belt-Purcell Supergroup of Laurentia. The dynamic interactions between mat growth, currents and sediment supply that determined the shape of Tieling columns contributed to the morphotypical diversity that characterizes mid-late Proterozoic branched stromatolites. This article is protected by copyright. All rights reserved.
... Some authors have assigned generic and species names to stromatolites based on form (see Logan et al., 1964 for a discussion of nomenclature). In addition, several stromatolite classifications have been proposed, which are typically based on overall geometry (domical or columnar), column shape (where present), presence or absence of branching, the nature of column margins, laminae shape (wavy vs. smooth), and/or presence or absence of linkage between adjacent stromatolites (e.g., Korolyuk, 1960;Logan et al., 1964;Walter, 1972;Bertrand-Sarfati, 1976;Semikhatov and Raaben, 2000 and references therein). ...
... The columnar stromatolites developed discontinuously along the shoreline and were well-cemented, wave-resistant structures as indicated by their upright orientations, lack of evidence of wave scour, and absence of inter-column clasts. The relief of stromatolites in modern peritidal settings is directly proportional to the wave energy they experience (Bertrand-Sarfati, 1976). Therefore, the columnar stromatolites, which have the highest relief of the microbialites described herein, are inferred to have accreted in the low intertidal zone of fair-weather wave sweeping (Sami and James, 1994), which represents the setting of highest energy among the various peritidal zones. ...
... Therefore, coarse detrital grains in the columnar stromatolites are consistent with Bertrand-Sarfati's (1976) premise that the size fraction of detrital particles in stromatolites reflects the turbulence of ambient water. Rare to common detrital grains in the columnar stromatolites indicate that some accretion occurred via grain baffling and trapping. ...
... This would explain why strongly calcified skeletal stromatolites (e.g. Black, 1933;Hudson, 1970;BertranddSarfati, 1976;Riding, 1977;Pentecost & Riding, 1986;Rasmussen et al., 1993;Arp, 1955;Freytet, 2000) include very scarce trapped grains in their microfabrics, as occurs in the Leza Fm examples. Some of the published examples ( Hudson, 1970;BertranddSarfati, 1976;Rasmussen et al., 1993;Freytet, 2000) describe sediment commonly filling the space between stromatolite columns, between filamentous fannlike colonies, or between branching calcified f ilaments, as is also locally observed in the Leza Fm skeletal stromatolites ( Fig..8G). ...
... Black, 1933;Hudson, 1970;BertranddSarfati, 1976;Riding, 1977;Pentecost & Riding, 1986;Rasmussen et al., 1993;Arp, 1955;Freytet, 2000) include very scarce trapped grains in their microfabrics, as occurs in the Leza Fm examples. Some of the published examples ( Hudson, 1970;BertranddSarfati, 1976;Rasmussen et al., 1993;Freytet, 2000) describe sediment commonly filling the space between stromatolite columns, between filamentous fannlike colonies, or between branching calcified f ilaments, as is also locally observed in the Leza Fm skeletal stromatolites ( Fig..8G). This filling process takes place after filament growth and thus it should not be considered an accretionary p rocess of the stromatolite. ...
Stromatolites associated with ooids are often described in the literature, both in marine and continental environments. However, a lateral relationship between them does not necessarily entail that ooids are trapped within the stromatolites. For example, present-day stromatolites that trap ooids (agglutinated oolitic stromatolites) are only found in tidal environments of the Bahamas and Shark Bay, whereas non-agglutinated stromatolites laterally related with oolitic facies are common in different modern and fossil environments. The Leza Fm carbonates (Cameros Basin, N Spain) were formed in a system of coastal-wetlands during Barremian-Aptian times (Early Cretaceous) and they offer an opportunity to elucidate the role of tides in ooid-trapping processes because they contain examples of both agglutinated and non-agglutinated stromatolites associated with oolitic facies. Agglutinated stromatolites are found in tide-influenced oolitic facies from the eastern Leza Fm and they show very scarce calcified microbial filaments. Non-agglutinated stromatolites are found in freshwater-dominated oolitic facies from the western Leza Fm and these stromatolites contain calcified filamentous microfabrics (i.e. skeletal stromatolites) without significant ooids trapped in them. The textural and sedimentological differences between both stromatolites suggest that water chemistry and hydrodynamics were different during their formation. The carbonate saturation state of the water might have been low enough to prevent intense microbial calcification of the tide-influenced stromatolites, developing soft microbial mats; moreover, the cyclic hydrodynamic changes of tides allowed the periodic supply of grains to be trapped by the soft mats. In contrast, the higher carbonate saturation of meteoric waters, which passed through and dissolved the Jurassic carbonate substrate of the basin, probably led to the stronger mat calcification of skeletal stromatolites from the western Leza Fm, without tidal influence. This together with the lower hydrodynamic changes of the environment prevented ooids from being trapped within these stromatolites. The Leza Fm example is therefore a step forward for understanding the processes involved in the development of stromatolites in tidal oolitic depositional environments. Moreover, its study together with a review of the literature suggests that conditions for ooid-trapping by stromatolites may be preferentially achieved in tidal environments.
... This handbook is an attempt to rationalize and standardize stromatolite terminology. Much of the information is already published, but is scattered through the literature (Raaben, 1969a, bi Hofmann, 1969Bertrand-Sarfati, 1976;Walter, , 1976Preiss, , 1976Komar and others, 1965;Krylov, 1976). Terminology adopted is that most commonly used and readily applied (alternatives are listed in the glossary). ...
... 3A). other forms recorded by Bertrand-Sarfati (1976) (Preiss, 1974). Examples: -Omachtenia utschurica Nuzhnov: pelletal microstructure. ...
... Na classificação de microfácies carbonáticas utilizou-se a proposta de Dunham (1962). Bertrand-Sarfati (1976) propôs parâmetros para caracterização de estromatólitos que podem ser divididos em análise de feições primárias (variedade cristalina dos minerais; textura; as relações genéticas entre os cristais e a estrutura da laminação) e análise de feições diagenéticas, como cimentação, compactação, dissolução, precipitação, substituição e fraturamento. ...
A abertura do Oceano Atlântico Sul durante o Cretáceo foi responsável pela geração de extensas bacias marginais ao longo da costa brasileira onde se acumularam espessas sequências siliciclásticas marinhas e transicionais. A Formação Alcântara é o registro de uma sequência costeira-lacustre depositada na Bacia São Luís-Grajaú durante este período. Os principais afloramentos da Formação Alcântara são encontrados em falésias costeiras na região homônima, onde alcançam aproximadamente 20 metros de espessura. Na praia da Baronesa esta unidade é caracterizada por arenitos finos a médios na base sobrepostos por intercalações de pelitos vermelhos e dolomitos esbranquiçados dispostos em ciclos de raseamento ascendente. Neste trabalho os dolomitos são classificados como estromatólitos estratiformes com a ocorrência de icnofósseis ainda não descritos na literatura científica para esta unidade. As camadas de dolomito são contínuas lateralmente por dezenas de metros e exibem espessuras que variam entre 30 e 50 centímetros, formam corpos tabulares de relevo sinóptico baixo (ondulados) com traço laminar plano, sendo classificados como doloboundstone estratiforme. As estruturas microbiais são definidas pela alternância entre laminações irregulares e crenuladas, localmente descontinuas e enrugadas, que são visualizadas como finas linhas de material micrítico mais escuro com espessura de no máximo 1 mm. Microscopicamente são constituídas predominantemente por dolomita microcristalina, peloides e grãos terrígenos, além de raros bioclastos. Localmente estas camadas são maciças, e exibem poros fenestrais, feições microcársticas preenchidas por marga, gretas de contração e icnofósseis. Os icnofósseis ocorrem principalmente no topo das camadas do dolomito, porém distribuídos de forma heterogênea nesta superfície; exibem uma baixa icnodiversidade e abundância, e pouco destroem a laminação interna.Foram descritas seis icnoespécies: Furculosus carpathicus,Palaeophycus tubularis, Phycodes cf. circinatus, Taenidium barretti, Thalassinoides suevicus e Thalassinoides isp. Esta associação de icnofósseis é interpretada como o registro da atividade de organismos sedimentófagos que habitavam substratos semiconsolidados a inconsolidados indicando uma sobreposição das icnofácies Glossifungites e Cruziana. Opadrão estratiforme do doloboundstone denota um ambiente calmo com baixa interferências da hidrodinâmica ou em ambientes restritos como a laguna. O desenvolvimento do estromatólito é interrompido pelo avanço dos processos de exposição subaérea
(e.g. gretas de contração) associado a colonização e predação do substrato. Em resumo a sedimentação carbonática ocorria nas porções mais rasas da laguna que era influenciada pelas variações periódicas na taxa de sedimentação siliciclástica, períodos de exposição subaérea, influxos de águas marinhas e doces, curtos períodos de colonização do substrato por organismos sedimentófagos e variações locais na taxa de nutrientes disponíveis, esta provavelmente relacionada a formação de esteiras microbiais.
... Peloids can be explained in at least three ways (Tucker and Wright 1990;Scholle and Ulmer-Scholle 2003;Tucker and Dias-Brito 2017), not mutually exclusive: micrite intraclasts, formed by mechanical reworking of the sedimentary bottom, clasts of possible fecal origin (pellets sensu stricto) (Macintyre 1985;Flügel 2004), or micrite aggregates generated under cyanobacterial action (Gebelein 1974;Bertrand-Sarfati 1976;Monty 1976;Coniglio and James 1984;Kennard and James 1986;Dupraz and Strasser 1999;Riding 2000Riding , 2002, which would be favored by hypersaline conditions (Paerl et al. 2001;Dupraz et al. 2004;Riding and Tomás 2006;Sánchez-Román et al. 2009;Spadafora et al. 2010;Cabestrero et al. 2018), which in turn favor the precipitation of sulfates. The great homogeneity of shape and size of the peloids (Fig. 7A) supports the hypothesis of a fecal origin, which had already been interpreted by Hachiro and Coimbra (1992) in peloids present in the ''dolomitic bank'' (Bairrinho Bed), attributed to pellets produced by Liocaris. ...
Tepee structures, associated with cracks and intraformational breccias, are found in the basal part of the Thin Rhythmites Bed of the Irati Formation. The rhythmite alternates dark gray mm-thick laminae, formed by dolomicrite with crenulated microlamination rich in organic clay, and intermediate gray laminae, formed by dolarenite with peloids. Some of the rhythmic pairs are separated from each other by thin horizons (< 0.5 mm) with a concentration of quartz pseudomorphs of gypsum and/or pores resulting from bioturbation or dissolution. The close association of the peloids with microrosettes of early authigenic sodium sulfate, a typical salt of nonmarine brines, is suggestive of its formation under cyanobacterial action, favored by hypersaline conditions in inland lakes. This is consistent with the closing of the connection between the Paraná Basin and the Panthalassic Ocean, as has been suggested for the final stages of Irati sedimentation. The tepees analyzed are related to diapiric features of massive light gray dolomicrite, which is distinguished under the microscope as being poorer in organic matter and for presenting coalesced peloids (clots) rich in sodium sulfate. The hydroplastic rheology, overpressure, and density gradient required for the upward injection of light gray dolomicrite are attributed to supersaturation in water and the presence of eodiagenetic low-density hydrated sulfates (e.g., mirabilite and thenardite). Thus, the processes that form the tepees studied here differ from those described in previous models of lacustrine and lagoon tepees, especially regarding the fundamental role of the expansion and mobility of the sulfated dolomite sediment, controlled by the lake's hydrology and by the elevation of groundwater, without necessarily involving subaerial exposure processes.
... These problematic carbonate structures have been identified as 'Catagraphia', which are regarded as a result of the activity of Cyanophycean algae and bac'eria. The organic nature of the oncolites and catagraphs becomes apparent, if the fossil carbonate nodules are compared with the calcareous concretions and tufa formed by recent algae (Zhuravleva, 1964;Bertrand-Sarfati, 1976). The present form of catagraphs appears similar to Vesicularites Reitlinger and Conferta Klinger but detail comparison up to form level is not possible due to distortion of rocks. ...
Cryptarchs namely Granomarginata, Lophosphaeridium and Protoleiosphaeridium belonging to Sphaeromorphitae and catagraphs - Vesicularites and Conferta - are recorded from the subsurface samples of the Cuddapah Supergroup. The catagraphs are supposed to be formed by the exobiogenic activities of Cyanophyceae and bacteria. No comment on the age could be made on the basis of poor occurrence of biota, as they show wide geological distribution from Late Proterozoic to Devonian.
... Stromatolites are laminated organosedimentary structures produced by the interaction of microbial communities, detrital sediment and autochthonous carbonate precipitation (see Grey & Awramik, 2020 for a detailed discussion). Analysis of stromatolite diversity typically focuses on morphology, or macroscopic structure, of individual stromatolitic forms (Bertrand-Sarfati & Moussine-Pouchkine, 1985;Bertrand-Sarfati & Awramik, 1992;Grey & Awramik, 2020), often with only secondary focus on mesoscopic elements, such as laminae structure (Kah et al. , 2009Bartley et al. 2015), or the microscopic elements that comprise laminae (Bertrand-Sarfati, 1976;Turner et al. 1993;Knoll & Semikhatov, 1998;Bartley et al. 2000;Riding, 2008). Here, we examine both synoptic relief and inheritance (Hofmann, 1969;Grey & Awramik, 2020) as comprising macroscopic morphology (i.e. ...
Time-distinctive features within carbonate rocks, specifically the presence, abundance and distribution of stromatolites, molar-tooth fabric and specific morphologies of marine cement, have been identified as potential indicators of global-scale changes in the chemistry of marine environments. Recently, Cantine et al. (2019) introduced a database approach seeking to quantify spatial and temporal patterns in these carbonate features through the Precambrian. Despite the coarse temporal scale, results support earlier inferences of temporal change in carbonate sedimentation. Here, we use original field notes to dissect late Mesoproterozoic (˜1.3 to 1.0 Ga) carbonate strata at a high resolution, analyse time-distinctive carbonate fabrics within a database context and compare sedimentological patterns within this narrow time range to observations of the Proterozoic as a whole. Late Mesoproterozoic strata contain a variety of features (e.g. stromatolites, seafloor precipitates, herringbone carbonate, molar-tooth carbonate), often in close spatial and temporal proximity, that are commonly considered to be temporally restricted during the Precambrian. The spatial distribution of such features within Mesoproterozoic basins demonstrates the importance of recognizing even rare occurrences of time-distinctive facies and permits inference of environmental drivers that may have interacted to affect carbonate precipitation. Such spatial variability reflects a subtle division of Mesoproterozoic carbonate platform environments driven by globally high sea level, elevated carbonate saturation and a low-oxygen water column. The heterogeneous, mosaic nature of environments appears to be a hallmark of Mesoproterozoic carbonate sedimentation and emphasizes the importance of these basins in understanding longer-term trends in carbonate deposition.
... Micritic to microclotted fabrics of microbial carbonates represent calcification of the extracellular polymeric substances of sulphatereducing bacteria (Riding, 2011). Very thin microbial layers are similar to the "filmy structure" of Precambrian stromatolites (Bertrand-Sarfati, 1976;Knoll and Semikhatov, 1998) from the primary growth of microbial organisms (Harwood and Sumner, 2012). ...
Lower Ordovician stromatolite-like columns and thrombolite-like mounds, composed of fossilised keratose sponges (keratolites) and microbial carbonates, are reported from the Tremadocian Mungok Formation, Yeongwol, Korea. The stromatolite-like columns, which are up to 10 cm wide and high, consist of an inner core with low-angled (10–45°) layers that are covered by high-angled (>45°) layers. The inner core is made up of millimetric layers of alternating keratolite and microbial carbonate, and microbial carbonate dominantly comprises the outer cover. The entire columns are surrounded by bioclastic packstone to grainstone. The thrombolite-like mounds are domes a maximum of 100 cm high and 40–60 cm wide embedded within lime mud and shale. These mounds consist of keratolite–microbial carbonate clots and minor lithistid sponge–microbial carbonate clots. The stromatolite-like columns were formed in a high-energy subtidal setting, in which laminoid keratolite and microbial carbonate formed the tight laminar frame columns. Continued growth of the column narrowed the intercolumnar space, resulting in higher-energy hydrodynamic conditions that limited the growth of sponges but promoted growth of microbial organisms. In contrast, thrombolite-like mounds developed in a low-energy environment below fair-weather wave base, where irregular to bulbose keratose sponges with minor lithistid sponge–microstromatolite associations formed cluster reefs. There appear to have been ecological and/or environmental factors that affected the distribution of these sponges; keratose and lithistid sponges rarely occur together in the Mungok reefs, whereas lithistids are pervasive within coeval intermediate-energy microbial reefs elsewhere. These results demonstrate the importance of hydrodynamic controls on overall reef morphology and configurations during the Early Ordovician, and suggest that keratosan–microbial consortia may have been an integral component of the Great Ordovician Biodiversification Event, together with the lithistid sponge–microbial consortium.
... 이 유사 각질해면류는 미생물암 위에 자라나거나 미생물암과는 별개로 생 성된 것으로 해석된다. (Walter, 1972;Bertrand-Sarfati, 1976;Kennard, 1994). 이들이 해면동물 기원일 가능 성도 제기되었으나 (Gürich, 1906), Pratt (1982)는 해 Sepkoski, 1997;Kiessling et al., 2002 andRiding, 2006 Gürich, 1906, pl. ...
... Excluding the purely descriptive term 'peloid', referring to micritic aggregates of uncertain origin (McKee & Gutschick, 1969;Macintyre, 1985;Flügel, 2004), in the literature peloids have often been regarded as being autochthonous and benthic microbial in origin, because they constitute the most common microfabric of modern and ancient microbialites (Gebelein, 1974;Bertrand-Sarfati, 1976;Monty, 1976;Kennard & James, 1986;Dupraz & Strasser, 1999;Riding, 2000Riding, , 2002a. The most common peloidal microfabric consists of micritic peloids surrounded by microspar. ...
In a modern peritidal microbial mat from Qatar, both biomediated carbonates and Mg-rich clay minerals (palygorskite) were identified. The mat, ca 5 cm thick, shows a clear lamination reflecting different microbial communities. The initial precipitates within the top millimetres of the mat are composed of Ca–Mg–Si–Al–S amorphous nanoparticles (few tens of nanometres) that replace the ultrastructure of extracellular polymeric substances. The extracellular polymeric substances are enriched in the same cations and act as a substrate for mineral nucleation. Successively crystallites of palygorskite fibres associated with carbonate nanocrystals develop, commonly surrounding bacterial bodies. Micron-sized crystals of low-Mg calcite are the most common precipitates, together with subordinate aragonite, very high-Mg calcite/dolomite and ankerite. Pyrite nanocrystals and framboids are present in the deeper layers of the mat. Calcite crystallites form conical structures, circular to triangular/hexagonal in cross-section, evolving to crystals with rhombohedral terminations; some crystallite bundles develop into dumb-bell and stellate forms. Spheroidal organo-mineral structures are also common within the mat. Nanospheres, a few tens of nanometres in diameter, occur attached to coccoid bacteria and within their cells; these are interpreted as permineralized viruses, and could be significant as nuclei for crystallite-crystal precipitation. Microspheres, 1 to 10 μm in diameter, result from intracellular permineralization within bacteria or the mineralization of the bacteria themselves. Carbonates and clay minerals are commonly aggregated to form peloids, tens of microns in size, surrounded by residual organic matter. Magnesium-silicate and carbonate precipitation are likely to have been driven by pH – saturation index – redox changes within the mat, related to micro-environmental chemical changes induced by the microbes – extracellular polymeric substances – viruses and their degradation. This article is protected by copyright. All rights reserved.
... Laminated freshwater cyanobacterial mats in shallow lakes of Andros Island show similarities to hybrid stromatolite, with fine-grained incipiently lithified cyanobacterial mats alternating with laminar fenestrae and elongate open voids (Monty, 1976, Fig. 4). If this structure were early lithified, it could resemble some Conophyton and Baicalia fabrics, as Bertrand-Sarfati (1976) suggested. ...
... Consequently, when certain Precambrian stromatolites were discovered to contain laminae with palimpsest radial fabrics, these were attributed to the former growth of calcifying cyanobacteria (e.g. Bertrand-Sarfati 1976, Grey 1984, Walter et al 1988). However, subsequent detailed examination of petrographic textures revealed that these textures were more consistent with recrystallization of former radially arranged crystals than the micritic sheath coatings of cyanobacteria (Fairchild et al 1990, Grotzinger 1986a, Grotzinger & Read 1983, Hofmann & Jackson 1987 ). ...
Stromatolites are attached, lithified sedimentary growth structures, accretionary
away from a point or limited surface of initiation. Though the accretion process is
commonly regarded to result from the sediment trapping or precipitation-inducing
activities of microbial mats, little evidence of this process is preserved in most Precambrian
stromatolites. The successful study and interpretation of stromatolites
requires a process-based approach, oriented toward deconvolving the replacement
textures of ancient stromatolites. The effects of diagenetic recrystallization
first must be accounted for, followed by analysis of lamination textures and deduction
of possible accretion mechanisms. Accretion hypotheses can be tested
using numerical simulations based on modern stromatolite growth processes. Application
of this approach has shown that stromatolites were originally formed
largely through in situ precipitation of laminae during Archean and older Proterozoic
times, but that younger Proterozoic stromatolites grew largely through the
accretion of carbonate sediments, most likely through the physical process of microbial
trapping and binding. This trend most likely reflects long-term evolution
of the earth’s environment rather than microbial communities.
... For example, beside Magdiganites mawsoni, vermiform microstructure was reported from several other Vendian and Cambrian stromatolites (e.g. Preiss 1972;Bertrand-Sarfati 1976), although these examples were not well illustrated and are nowadays hard to access. 'Stromatolites' composed of alternating thin microbial laminae and sponge-like micritic lenses, similar to the PB materials, were described from more than one localities in the Triassic of Germany Krause & Weller 2000). ...
Two ‘stromatolites’ from Carboniferous and Triassic carbonates previously regarded as microbial bioconstructions are analysed and reinterpreted as sponge-microbial build-ups. The automicritic aggregations in these build-ups are similar to the previously reported fossils of keratose demosponges in showing moulded anastomosing filamentous structures. All the studied columnar or domal constructions were formed in turbulent water with high sedimentation rate. The Carboniferous build-ups were constructed in the shallow subtidal zone of an open shelf or a ramp. The laminations within the stromatolite-like columns are composed of alternating dark micritic laminae of sponge fossils and pale laminae of neomorphic microspars. The accretion of these columns is probably related to the repeated cycles of sponge growth, rapid lithification after burial, re-exposure and erosion, and settlement of new generations. The Triassic rocks are presumed to have been precipitated in a slightly evaporitic environment based on lithological features. They show a transition from planar laminae, which were formed under the influence of microbial mats, to stromatolitic columnar or domal build-ups, which are dominated by stacked micritic clumps of probable sponge fossils. The sponge–microbe alternation may have been controlled by variation of salinity. Comparable with a recent study, this work shows that sponge-related bioconstructions can be morphologically similar to microbialites in the level of mega- and mesostructures.
... Banded pattern of fibrous aragonite in bore holes (g) indicates progressive infilling. Precipitation in tunnels that cross between grains leads to welding (h). in thickness to micritic laminae in many ancient stromatolites (Walter 1983, Bertrand-Sarfati 1976. In addition, the microstructure of the layers of fused, microbored grains is identical to that formed by the climax community described above. ...
Research in the burgeoning field of geomicrobiology reveals an “intimate juxtaposition and interdependence” of microbes and minerals that we are only beginning to appreciate (Skinner 1997, p. 1). Future studies of microbe-mineral interactions are likely to lead to major advances in our understanding of such fundamental issues as the dynamics of sedimentation, the flow of energy and matter through the biosphere, and the evolution of life on Earth (Nealson 2000, Nealson and Stahl 1997, Hazen 2001)
... Stromatolites from Formations 1-5 to 1-7 in the Adrar area in the west of the basin were selected for this study, because fabric-destructive dolomitization is less widespread than at other horizons, and because they include excellent examples of contrasting morphologies. Formation 1-5 is notable for Conophyton-jacutophyton biostromes with filmy microstructures (Bertrand-Sarfati and Moussine-Pouchkine, 1985), whereas Formations 1-6 and 1-7 contain a number of horizons of stromatolites with tussocky microstructures (Bertrand-Sarfati, 1976). The change in stromatolite microstructure from 1-5 to 1-6 has been interpreted as a major biological event traceable over 1500 km eastward to the Pan-African Orogenic Belt (Moussine-Pouchkine and others, 1988). ...
In the Atar Group of Mauritania (about 900 Ma), a shift from positive (+0.3 to +2.8 permil) to variably negative (-0.2 to -3.3 permil) carbon isotope values of carbonate carbon occurs between Formation I-5 with its Conophyton-Jacutophyton biostromes and Formation I-6 in which the stromatolites display tussocky microstructure. No biologically-related 13C fractionations can be recognized by comparison of stromatolitic micrites with marine cements so in principle stromatolites seem suitable for studies of secular change in δ13C. Diagenesis of the initially metastable marine Proterozoic precipitates poses the main problem for such studies. A suggested strategy for isotope stratigraphy is to seek out deliberately the diagenetic patterns of alteration and to correct for them. -from Authors
... The appearance of distinct internal structures (microstructures) in many Proterozoic and Camb rian stromatolites (Bertrand -Sarfati 1976, for review) may reflect important evolutionary changes in the mode of organization of coccoid cyanophycean aggregates or colonies. This process found its acme in stromatoporoid stromatolites characterized by many discrete, regular internal skeletal structures appearing successively in relatively short time intervals (Kaimierczak 1971, for review), particularly in Siluri~n and Devonian strata. ...
Stromatoporoids are calcareous fossils common in Early Paleozoic (?Cambrian — Lower Carboniferous) shallow-water carbonate deposits. They have been regarded as remnants of enigmatic organisms possibly related to hydrozoans or sponges (e.g., Galloway 1957, for review). The recent attempts of Hartman (1978), Hartman and Goreau (1966, 1970) and others to homologize stromatoporoids with living sclerosponges are basically ill-founded, since instead of proper stromatoporoids (Early Paleozoic) the authors used as comparative material dubious Late Paleozoic and Mesozoic fossils somewhat resembling stromatoporoids in gross morphology and perhaps being sponges.
... The oldest unquestionable stromatoporoids are known (Galloway 1957) from the Ordovician (Middle Chazyan). However, many Proterozoic and Cambrian calcareous stromatolites (Walter 1972;Bertrand-Sarfati 1976) and doubtful stromatoporoids (Bain 1927;Vlasov 1961) have been reported characterized by distinct internal structures and granular mi.crofabric (called thrombolitic, cIotty or pelletoid), and very reminiscent of those found in stromatoporoids. I therefore postulate that the ancestors of stromatoporoids were weakly morphologically differentiated stratiform colonies of coccoid cyanobacteria as known already from Middle Precambrian deposits (Hofmann 1975). ...
Stromatoporoid stromatolites; new insight into evolution of cyanobacteria. Acta Palaeont. Polonica, 25, 2, 243-251 July, 1980. Common enigmatic fossils called stromatoporoids are recognized as calcareous stromatolitic structures build by coccoid cyanobacteria (= Cyanophyta). The diversified internal structures of stromatoporoids reflect various growth patterns of cyanobacterial cell aggregates or colonies preserved due to a rapid in situ calcification. Stromatoporoid stromatolites are evolutionary advanced descendants of early precamprian stromatolites generated by weakly differentiated Rtratiform mats of coccoid cyanobacteria. The presence of stromatoporoid stromatolites in ancient subtidal environments, often in association with normal marine biota, is a non-actualistic phenomenon which needs to be explained in other than present-day ecological terms.
... Stromatolitic fabrics in this study are considerably less complex than those recorded in Vempalle Formation stromatolites described by Riding and Sharma (1998), who document a wide range of clotted (e.g., grumeleuse; Carozzi, 1970) to radial-fibrous (e.g., asperiform; Hofmann and Jackson, 1987) microfabrics. Clotted textures are interpreted to represent mineral precipitation within cyanobacterial EPS (Hofmann, 1969;Bertrand-Sarfati, 1976;Monty, 1976Monty, , 1981Turner et al., 1993), or potentially within a non-cyanobaterial biofilm (Reitner, 1993;Riding and Sharma, 1998). By constrast, radial fibrous fabrics are interpreted to represent nucleation and growth of seafloor precipitates that may or may not be associated with microbial communities (Hofmann and Jackson, 1987;Grotzinger, 1993;Kah and Knoll, 1996;Knoll et al., 2013). ...
... Similar nanometer-sized spheroidal precipitates are a ubiquitous feature in microbialites (Sprachta et al., 2001;Zavarzin, 2002;Hammes et al., 2003;Dupraz et al., 2004;Benzerara et al., 2006; Aloisi Lepot et al., 2008;Bontognali et al., 2008;Spadafora et al., 2010;Perri et al., 2012). Coalescence of nanospheroids progressively replacing the EOM produces the autochthonous micropeloidal texture (Dupraz et al., 2004;Spadafora et al., 2010;Perri et al., 2012), which constitutes the most common microfabric of modern and fossil microbialites (Gebelein, 1974;Bertrand-Sarfati, 1976;Monty, 1976;Kennard & James, 1986;Dupraz & Strasser, 1999, 2002Riding, 2000;Hardwood & Sumner, 2011;Perri et al., 2012). ...
The initial lamination in young, metabolically active Scytonema knobs developing in Storr's Lake (Bahamas) results from the iterative succession of two different stages of microbial growth at the top of this microbialite. Stage 1 is dominated by vertically oriented cyanobacterial filaments and is characterized by a high porosity of the fabric. Stage 2 shows a higher microbial density with the filaments oriented horizontally and with higher carbonate content. The more developed, dense microbial community associated with Stage 2 of the Scytonema knobs rapidly degrades extracellular organic matter (EOM) and coupled to this, precipitates carbonate. The initial nucleation forms high-Mg calcite nanospheroids that progressively replace the EOM. No precipitation is observed within the thick sheath of the Scytonema filaments, possibly because of strong cross-linking of calcium and EOM (forming EOM-Ca-EOM complexes), which renders Ca unavailable for carbonate nucleation (inhibition process). Eventually, organominerals precipitate and form an initial lamina through physicochemical and microbial processes, including high rates of photosynthetic activity that lead to (13) C-enriched DIC available for initial nucleation. As this lamina moves downward by the iterative production of new laminae at the top of the microbialite, increased heterotrophic activity further alters the initial mineral product at depth. Although some rare relic preservation of 'Stage 1-Stage 2' laminae in subfossil knobs exists, the very fine primary lamination is considerably altered and almost completely lost when the knobs develop into larger and more complex morphologies due to the increased accommodation space and related physicochemical and/or biological alteration. Despite considerable differences in microstructure, the emerging ecological model of community succession leading to laminae formation described here for the Scytonema knobs can be applied to the formation of coarse-grained, open marine stromatolites. Therefore, both fine- and coarse-grained extant stromatolites can be used as model systems to understand the formation of microbialites in the fossil record.
... Streaky microstructure is most prevalent in reef-margin microbialites. It resembles some examples of ''microstructure en tapis'' (mat microstructure) of Bertrand- Sarfati (1972Sarfati ( , 1976, which consists of an upper layer of homogeneous micrite, and a lower, paler, microcrystalline layer. Found in forms of Gymnosolen, Jurusania, and Nouatila, it was attributed tentatively to either episodic growth of a single microbial community or alternating growth of two taxa. ...
Early Neoproterozoic reefs of the Little Dal Group, Northwest Territories, are built by stromatolites and thrombolites containing calcified filamentous cyanobacteria and interstitial cement. Micritic and microcrystalline carbonate grew in or on extracellular cyanobacterial sheaths, preserving filaments when mineralization was early relative to sheath degradation, or grumeaux when mineralization was later. Filamentous microstructure is volumetrically predominant in the reefs; less common are micritic and grumelous microstructures already known from late Proterozoic stromatolites and Phanerozoic thrombolites. Textural intergradation of filamentous-calcimicrobial microstructure with these non-filamentous microstructures reflects microstructural variation developed through differential preservation at the scale of individual filaments and laminae. Textural gradients from filaments to grumeaux, and from calcimicrobial to stromatolitic and thrombolitic microstructure types, imply that a wide variety of microbialite microstructure types can be derived from a single progenitor community. This suggests that taphonomic variables may be as important in the development of microbialite microstructure as the biology of the microbial mat community. It also challenges recent suggestions that the Neoproterozoic increase in thromboids was related to the rise of multicellular organisms. These conclusions have broad implications for the interpretation of fossil microbialites, many of which might have been more closely related in origin than hitherto suspected.
... These are very similar to those described from Precambrian marine calcareous stromatolites (comp. Hofmann 1975;Hofmann and Jackson 1987;Bertrand-Sarfati 1976;Semikhatov et al. 1979;Buick et al. 1981;Walter 1983;Fairchild 1991;Ginsburg 1991;Knoll and Semikhatov 1998;Riding 2000). Further detailed studies of Alchichica stromatolites may provide interesting information that can help in reconstructing the sedimentary environment and morphogenetic processes that ruled stromatolite formation in Earth's early oceans. ...
Remains of silicified microbial mats composed of benthic colonial coccoid cyanobacteria similar to modern entophysalidaceans and/or pleurocapsaleans have been identified in Lower Silurian black radiolarian cherts from central and southwestern Poland. Contrary to widespread views ascribing the genesis of such deposits to permanently anoxic deep-water marine environments, the abundance of benthic mats of phototrophic cyanobacteria suggests that the water-mat interface must have been located at moderate depth, most probably close to the limit of light penetration (dysphotic zone). Depending on ambient sulfide levels, the mats could intermittently perform anoxygenic (PSI) or oxygenic (PSII) photosynthesis, thriving under anoxic, oxic, or dysoxic (microaerophilic) conditions. The open marine (offshore) character of these cherts is consistent with their paleooceanographic location and with the presence of remains of such planktonic organisms as acritarchs, radiolarians, chitinozoans, and graptolites, entrapped by the cyanobacterial mats.
... Throughout Atar Group strata, primary microfacies typically display dull, homogeneous to patchy luminescence, whereas secondary components vary from brightly luminescent to non-luminescent (extinct), and commonly display distinct zoning. Within stromatolitic facies, microstructures are dominated by irregular, filmy to patchy, micritic layers (Fig. 5A) interspersed with crystalline tussocks (cf.Bertrand-Sarfati, 1976;Fairchild et al., 1990). Tussocks are composed of discrete, fan-shaped masses that show a range of crystal sizes from microspar to spar and a range of crystal fabrics from anhedral to euhedral bladed crystals. ...
Sedimentary strata of the Atar/El Mreiti groups, Taoudeni Basin, Mauritania, are characterized by carbon isotope values that fall largely between −2.5‰ and +4.0‰, and contain stratigraphic trends that are strikingly similar to those recorded worldwide in strata with depositional ages from ∼1.2 Ga to 1.1 Ga. Chemostratigraphic results are consistent with recent Re–Os dates of ∼1.1 Ga for Atar/El Mreiti group strata (Rooney et al., 2010) and support an emerging dataset that identifies the Late Mesoproterozoic as an isotopically distinctive interval in Earth history. The relatively low-amplitude carbon isotope variability limits the use of chemostratigraphy in detailed correlation during this time interval. In this study, we combine chemostratigraphic data with key chronostratigraphic horizons and detailed analysis of depositional facies to construct a rigorous and testable model for the intrabasinal correlation of Atar and el Mreiti group strata. Data support a depositional model that results in broadly uniform stratigraphic thicknesses across the West African craton, with predominantly stromatolitic facies of the Atar Group (Mauritania) and the Hank and Dar Cheikh groups (Algeria) representing deposition on shallow-water craton margins, and clayey-carbonate and shale facies of the El Mreiti Group (Mauritania) representing deposition on a broad, shallow-water, epicratonic platform. Within this stratigraphic framework, regional differences in carbon isotope composition are interpreted to reflect spatial differences in water chemistry likely associated with local carbon cycle dynamics in cratonic environments that have limited exchange with the open ocean. Similarly, distinct differences in trace element composition recorded in multilayered marine cements within deeper-water stromatolitic reef facies are interpreted to reflect vertical differences in water chemistry associated with redox-gradients in the water column.
Molecular phylogeny indicates that metazoans (animals) emerged early in the Neoproterozoic era1, but physical evidence is lacking. The search for animal fossils from the Proterozoic eon is hampered by uncertainty about what physical characteristics to expect. Sponges are the most basic known animal type2,3; it is possible that body fossils of hitherto-undiscovered Proterozoic metazoans might resemble aspect(s) of Phanerozoic fossil sponges. Vermiform microstructure4,5, a complex petrographic feature in Phanerozoic reefal and microbial carbonates, is now known to be the body fossil of nonspicular keratosan demosponges6–10. This Article presents petrographically identical vermiform microstructure from approximately 890-million-year-old reefs. The millimetric-to-centimetric vermiform-microstructured organism lived only on, in and immediately beside reefs built by calcifying cyanobacteria (photosynthesizers), and occupied microniches in which these calcimicrobes could not live. If vermiform microstructure is in fact the fossilized tissue of keratose sponges, the material described here would represent the oldest body-fossil evidence of animals known to date, and would provide the first physical evidence that animals emerged before the Neoproterozoic oxygenation event and survived through the glacial episodes of the Cryogenian period. Vermiform microstructure in microbial reefs dating to approximately 890 million years ago resembles the body fossils of Phanerozoic demosponges, and may represent the earliest known physical evidence of animals.
The term keratolite is proposed for keratosan sponge carbonate dominated by vermiform fabric that preserves the outlines of the original spongin skeleton. Thinly (<~2 cm) interlayered keratosan–microbial carbonate consortia in peritidal sediments near the Cambrian–Ordovician boundary in Newfoundland, Canada, are macroscopically indistinguishable from stromatolites. These carbonate domes and columns consist of approximately equal proportions of keratolite and stromatolite. The keratolite is characterized by pervasive microscopic vermiform fabric reflecting the original spongin framework, and the stromatolite by fine-grained carbonate with cross-cutting laminae, primarily formed by sediment trapping. The intimate association of keratolite and stromatolite in these deposits indicates that the sponges and microbes involved shared similar environmental tolerances and requirements. Synchronicity of sponge colonization, followed by stromatolite regrowth, across adjacent columns suggests coordinated responses by both sponges and microbes to local ecophysiological stimuli. Due to their macroscopic similarity, keratolite and fine-grained stromatolite may commonly have been confused with one-another throughout the Phanerozoic, and possibly longer.
Paleontological evidence indicates that terrestrial life existed at least 3500 Ma ago, and it is quite possible that the earliest cells arose well before that time. The early appearance of life on Earth suggests that under appropriate environmental conditions the probability of chemical evolution proceeding to the point of biogenesis may be reasonably high. Most of biological history has been the history of microorganisms, with tissue-grade plants and animals characterizing only the most recent 15% or so of the fossil record. Intelligent life has occupied only the latest instant in geological time. The time table of terrestrial evolution is governed more by the particulars of our planet's physical and biological history than by some universal tempo of evolutionary change. One aspect of terrestrial life that is likely to be universal is the organization of populations into efficient biogeochemical systems.
Several mound-shaped bioherms with a maximum depositional relief of 12 m are developed within and upon a tabular limestone stratum in the middle of the Laborcita Formation (Lower Permian; Wolfcampian) in the Sacramento Mountains, near Tularosa, New Mexico, U.S.A. The bioherms are constructed by a restricted biota of erect codiacean (?) phylloid algae encrusted by wavy-laminar, digitate, and mammillary stromatolites preserved in living habit. Mound morphology, biotic constituents and stratigraphie relations are described elsewhere (Cross and Klosterman, this vol.). Primary void space was created as sheltered cavities within and between phylloid algal fronds during development of the bioherms. Although the algal constituents supported weight and created an interlocking organic constructional framework, penecontemporaneous submarine botryoidal cements precipitated within sheltered cavities contributed significantly to mechanical rigidity and prevented the collapse of the primary biotic framework. In this respect, these cements had a more important mechanical function than similar cement fabrics described from other reef and biohermal structures of Paleozoic through Holocene age, in which precipitation occurs within already rigid framework-supported void space.
Member 3 of the Dalradian Bonahaven Formation of Islay comprises, mixed dolomitic-siliciclastic sediments assignable to 3 facies, all deposited under very shallow marine conditions. The layered facies consists of a centimeter-scale alternation of dolomitic, fine-to-medium-grained sandstones and silty dolomicrites, often containing terrigenous clay. Each sand layer was deposited by one storm event. Deposition was almost entirely sub-aqueous in a 'lagoonal' area suffering varying salinities. The sandstone facies consists of cross-stratified medium-grained sandstones and pure dolostone layers. Deposition was from tidal currents on a tidal sand flat. The stromatolite facies is represented both by bioherms within the sandstone and layered facies, and by biostromes. -from Author
In Hirmer’s treatise on Paleobotany (1927) Pia defined an equivocal class of lower Thallophytes which he called Schizophyceae; this class included definite blue-green algae like the unicellular form Gloeocapsamorpha, the filamentous genera Rivularia and Oscillatoria. The Schizophyceae also included “families” of uncertain affinities: the Spongiostromata and the Porostromata.
The fossil record of prokaryotes extends back 3500 million years and prokaryotes were only forms of life known for the first 2000 million years of Earth history. Understanding the fossil record of these organisms is important for the comprehension of the interaction of geological factors and the evolution of life. Prokaryo-tic microbial fossils, however, do not provide sufficient detailed evidence to help a great deal in this. Stromatolites, the biosedimentary products of microbe-sediment interactions, have the potential to provide significant information on the interaction of the biosphere, atmosphere, hydrosphere, and litho-sphere throughout the entire history of life on this planet.
An unusual type of microstructure occurs in stromatolites of the Upper Proterozoic cover of the West African Craton. These stromatolites bearing the same microstructure are reported from diverse sections along the northern edge of the Taoudenni basin and from the Pan-African fold belt of the Hoggar (Bertrand-Sarfati 1972). Their microstructure has been defined as “tussocky” (Bertrand-Sarfati 1976).
The stromatolites are entirely built by tussocks, absent from the interspaces between columns. They comprise hemispherical bodies, juxtaposed and overgrowing, roughly superimposed to compose irregular but obvious laminae. The tussocks are made of rods which are interpreted as the remnants of previous filaments. Most of the time they are straight, rarely branched. A common feature of the tussocks is the banding, concentrically arranged bands of brown pigmentation. According to Fairchild et al. (1990), the carbonate of the tussock was originally aragonitic and recrystallization into calcite appeared during burial.
In order to compare the tussocks with modern stromatolite builders, a range of measurements were made on Rivularia, Inzeria, and Serizia to clarify their structural relationships. Among 11 characters listed, 7 are shared by Rivularia and the tussocks. The four differences are heliotropism, branching and curvature of the filaments and the interface between adjacent colonies. The observations, however, point to a biogenic origin for the tussocks, but we must accept that they have no modern counterparts. The microorganisms building the tussocks may have been filamentous, weakly heliotropic cyanobacteria with a radiating structure.
Late Cretaceous to Early Miocene series of Southern France and northeastern Spain display an almost continuous record of nonmarine stromatolites. Well preserved organic remains, mainly microbial or algal filaments, are tentatively used as a base for the description of stromatolite microstructures of fluviatile, lacustrine and brackish origins. Four terms can be described as follows:
a)
microstructures with well preserved filaments are subdivided according to filament size and disposition within the lamina,
b)
microstructures with dubious filaments,
c)
zoned structures composed of fibro-radial sparite,
d)
associated non-microbial biogenic microstructures.
Recent petrological works and biological studies on modern fluviatile and lacustrine stromatolites afforded terms of comparisons whereas paleoenvironmental considerations suggest comments on salinity requirements for several of the microstructures.
This descriptive approach should allow for the addition of new categories according to similar criterion: nature of the organic remains, size and habit of filaments and spheres. It furthermore facilitates comparisons with some Proterozoic stromatolite microstructures.
Microbialites comprise the mineralized record of early life on Earth and preserve a spectrum of fabrics that reflect complex physical, chemical, and biological interactions. The relatively rarity of microbialites in modern environments, however, challenges our interpretation of ancient structures. Here we report the occurrence of microbial mats, mineral precipitates, and oncoids in the Laguna Negra, a high-altitude hypersaline Andean lake in Catamarca Province, Argentina. Laguna Negra is a Ca-Na-Cl brine where abundant carbonate precipitation takes place. Extreme environmental conditions, including high UV radiation, elevated salinity, and temperature extremes, restrict multicellular life so that mineralization reflects a combination of local hydrologic conditions, lake geochemistry, and microbial activity. The resulting carbonates consist of micritic laminae, botryoidal cement fans, and isopachous cement laminae that are strikingly similar to those observed in Proterozoic stromatolites, providing insight into mechanisms of mineralization. Here, increased saturation with respect to carbonate minerals reflects mixing of spring-fed inlets and lake waters, favoring microbialite formation and preservation. This highlights the importance of hydrological mixing zones in microbialite formation and as taphonomic windows to record microbial activity. Recent discoveries of minerals related to evaporating playa-lake systems on Mars further highlights the potential of Laguna Negra to provide critical insight into biosignature preservation in both terrestrial and extraterrestrial settings.
Within the upper Proterozoic sedimentary cover of the West African craton, well exposed in the Atar area (Mauritania), the carbonate-rich Atar Formation exhibits a peculiar development of stromatolites. This formation is subdivided into 6 units based on lithology and stromatolite content. Units 1, 3 and 5 are mainly terrigenous (shales and silts), and contain carbonate layers of different facies: laminated and structureless micrite, microbially laminated and detrital carbonates, stromatolitic layers. The environmental conditions were characterized by low energy, sporadically increasing, and shallow water with rare desiccation features. Units 2 and 4 contain Conophyton, Jacutophyton and Tilemsina; unit 6 has a succession of Conophyton jacqueti to Baicalia. These carbonate units were deposited under water, in low energy conditions, without any allochthonous sediment supply. The rhythmic alternation of terrigenous and carbonate units corresponds to rhythmic variations in environmental conditions, related to sea level or climatic changes. The morphological diversity of stromatolites is not related systematically to changes in the environment. Some of the morphological variations are controlled by the evolution of the biological community (e.g., the evolution of Conophyton shape with time and its eventual disappearance).New forms of stromatolite are described: Baicalia safia, Conophyton jacqueti, Jaculophyton sahariensis and Tilemsina agdeireia.
This paper outlines studies of Chinese Precambrian stromatolites, which may be subdivided preliminarily into two ‘stromatolite successions’ and seven assemblages.Secondly, based on Chinese data, stromatolites have undoubted stratigraphic significance for intrabasinal correlation, but it is necessary to depend on some of the ‘bridging elements’ and the ‘related assemblages’, as well as on other methods for interbasinal correlation.Finally, the paper discusses some problems of fossil stromatolites, i.e. the principal classification and the stromatolite cycles.
Nearly 70 new RbSr isochron ages and many KAr conventional ages have been determined between 1975 and 1980 on Proterozoic sedimentary or metasedimentary sequences in western and Central Africa and South America. Some stratigraphic results have been established: 1.(1) five formations have been dated of the Lower Proterozoic;2.(2) a long sedimentation gap occurs, mainly in western African and in some regions of Central Africa and South America between nearly 1600 and 1100 Ma;3.(3) the upper Riphean assemblages of stromatolites have been dated and compared to those of the Eurasian craton;4.(4) two main glacial events have been dated, the first one placed at ca. 950 Ma, the second one during the Vendian, at ca. 650-620 Ma;5.(5) it can be stated that, when applied to Precambrian sequences, all stratigraphic methods must be used together.
We report for the first time micrometer-scale correlation of geologic and microbial processes in modern marine stromatolites. Precipitation of micritic laminae in these stromatolites was studied by comparing microstructure, as observed in petrographic thin sections, with microbial sulfate-reduction activity. Two-dimensional mapping of sulfate-reduction rates was implemented by incubating a vertical section of a stromatolite face on silver foil coated with 35SO42-. Our results show that sulfate-reduction activity is high in zones of CaCO3 precipitation and indicate that microbial activity produces lithified micritic laminae near the surface of the stromatolites. Similarities with micritic laminae in ancient stromatolites suggest that sulfate reduction may also have been an important mechanism of carbonate precipitation in these fossilized structures.
The results of geological, hydrochemical and biosedimentological studies of two main caldera lakes, Vai Lahi and Vai Si‘i, on the volcanic Niuafo‘ou Island (Kingdom of Tonga) are presented. These slightly alkaline lakes support formation of carbonate sediments among which the most spectacular are calcareous cyanobacterial microbialites comparable with ancient, particularly Precambrian, stromatolites. The hydrochemistry of both lakes indicate that they originated and evolved from precipitation-water with some admixture of hydrothermal fluids. The lakes and their microbialites prove to be an excellent model for testing the hypothesis of an early alkaline ocean.
Keywords:Planetary oceans, early ocean chemistry, soda ocean, silicate weathering, Niuafo‘ou Island, Tonga, volcanology, caldera, limnology, alkalinity, carbonate chemistry, stromatolites, stable isotopes
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.
Non-columnar stromatolites occur in the late Precambrian Annijokka Member of the Båtsfjord Formation of the Varanger peninsula, north Norway. The stromatolites form biostromes up to 0.5 m thick embedded within peritidal, shallowing-up, siliciclastic-dolomite cycles. The stromatolite biostromes tend to occur in the upper, dolomite-rich portions of the cycles and are mostly calcite-dominated.Interpretation of the origin of the host sediments, combined with the location of the biostromes in the depositional sequences and with the contrasting mineralogy between the latter and the stromatolites, suggests that the majority of the stromatolite biostromes originated in freshwater and schizohaline supralittoral ponds.
Stromatolites are now used more and more frequently in attempts to solve Precambrian stratigraphic problems. Abundant new data that have become available during the last two years support the view that the methods are valid and useful, provided that rigorous taxonomic procedures are followed. Contrary to earlier indications that Early and Late Proterozoic stromatolites are identical, none of the 53 forms (‘form-species’) now known from the Early Proterozoic are also reported from younger rocks. Nonetheless, it has become increasingly apparent that correlations based only on group (‘form-genus’)-level identifications can be misleading. The problems of establishing identity at the form-level indicate the need to substantially improve descriptive methods, and in particular to make more use of numerical techniques.Stromatolite assemblage zones distinguished in Middle to Late Proterozoic sequences are 100–350 Ma in duration, with boundaries at 1650 ± 50, 1400 ± 50, 1050 ± 50, 650–680 ± 20 and 570 ± 20 Ma.
The radial growth rate and calcification of a cyanobacterium, Rivularia haematites, has been measured in detail for the first time. Maximum radial growth rates of 12-14 mu m d-1 were recorded during the summer and minimum rates of less than 2 mu m d-1 during winter. There was a significant correlation (p < 0.001, r = +0.929) between radial growth and water temperature. Differences in growth between sites were related to variation in water temperature and illumination. All colonies were heavily calcified and two patterns of calcification were noted: (i), a broad, seasonal band formed at the colony surface with calcification proceeding inwards, resulting from inorganic precipitation within the mucilage, probably augmented by particle trapping; and (ii), a series of finer secondary bands, probably formed as a result of photosynthetic activity within meristematic zones of the colonies. Colonization by Rivularia and its tolerance to emersion are also discussed briefly.
Periods of widespread abundance of calcified cyanobacteria in marine environments are here termed cyanobacterial calcification episodes (CCEs). Intense such episodes occurred in the Cambrian-early Ordovician, Late Devonian and Mid-Late Triassic. Mild episodes occurred during the Early Carboniferous and Jurassic-Early Cretaceous. Possible episodes during parts of the Silurian and Permian await confirmation. Cyanobacterial calcification is not obligate but is dependent upon environmental factors favouring carbonate precipitation. Cyanobacterial calcification episodes are therefore interpreted as reflecting periods of increased marine carbonate precipitation. This is supported by the general abundance of marine carbonate cements and oolites during cyanobacterial calcification episodes.
Cyanobacterial calcification episodes correspond with Phanerozoic periods for which elevated global temperatures have been inferred. They do not appear to correlate closely with inferred changes in aragonite/calcite facilitation (the Sandberg curve) and P CO2 through time. It is concluded that variations in the precipitation rates of abiotic and quasi-abiotic marine carbonates through time have been controlled primarily by temperature. The mineralogy of these precipitates appears instead to have been mainly influenced by P CO2 and the Mg/Ca ratio, also linked to sea-level through plate tectonic processes. Thus, the controls on rate and mineralogy of precipitation were independent of one another.
As part of a continuing biostratigraphic study, stromatolites are described and named from the following units: Amelia Dolomite, Tooganinie Formation and Emmerugga Dolomite (McArthur Group), and the Balbirini Dolomite (Nathan Group), McArthur Basin; Lochness Formation (Haslingden Group), Mount Isa Province; Yardida Tillite, Georgina Basin. The latter is Late Proterozoic and all others are Middle Proterozoic. To the previous record of Conophyton garganicum Korolyuk from the McArthur Basin we add Kussiella kussiensis Krylov, Omachtenia omachtensis Nuzhnov, Acaciella emmerugga f. nov. and the components of the Balbirina prima bioherm series, Bukalara tortuosa gr. et f. nov. and Australoconus abnera gr. et f. nov. We introduce a formal taxonomic procedure for bioherm series. ?Segosia isa f. nov. is described from the Mount Isa Province and Yardida delicata gr. et f. nov. from the Georgina Basin. The new groups and forms at present are unknown from elsewhere and so have no biostratigraphic significance at this stage, but the assemblage of stromatolites from the McArthur Basin allows correlation with the Lower Riphean of the USSR, which is consistent with the available geochronologic constraints.
The Beck Spring Dolomite is the medial unit of the Middle to Late Proterozoic Pahrump Group, the oldest sequence of sedimentary rocks in eastern California. Stratigraphic sections of the Beck Spring Dolomite examined in the eastern Mojave Desert and Death Valley regions consist of four members. These are, in ascending order, a lower cherty member, a lower laminated member, an oolitic–pisolitic member, and an upper cherty member. More than 80% of the Beck Spring Dolomite is algal-laminated dolomite with a possible Middle to Late Riphean stromatolite assemblage characterized by cf. Conophyton, eroded, irregular columnar forms similar to Kussiella or Baicalia, and several types of stratiform Stratifera. Petrographic, X-ray diffraction, and atomic absorption spectroscopic analyses indicate that the formation is composed of well-ordered replacement dolomite with less than 25% acid-insoluble residue. Concentrations of Fe and Mn are two to six times higher in the algal-laminated members than in the oolitic–pisolitic member, whereas the concentrations of Ca, Mg, Ba, Sr, Na, and K show no systematic variations. Stratigraphic relationships, primary and secondary sedimentary structures, petrology, and stromatolite assemblages suggest deposition during Middle to Late Proterozoic time on a platform that most likely included offshore shoals, restricted lagoons, and broad tidal flats with ponds, channels, and levees.
The results of geological, hydrochemical and biosedimentological studies of two main caldera lakes, Vai Lahi and Vai Si‘i, on the volcanic Niuafo‘ou Island (Kingdom of Tonga) are presented. These slightly alkaline lakes support formation of carbonate sediments among which the most spectacular are calcareous cyanobacterial microbialites comparable with ancient, particularly Precambrian, stromatolites. The hydrochemistry of both lakes indicate that they originated and evolved from precipitation-water with some admixture of hydrothermal fluids. The lakes and their microbialites prove to be an excellent model for testing the hypothesis of an early alkaline ocean.
Summary of Life on Earth and other Planetary Bodies (Introduction of J. Seckbach, § 5)
This volume has gathered 68 expert authors from around the world to discuss questions of life on Earth and elsewhere. Their chapters deal with primeval seas, the origin of the genetic code, panspermia, and terrestrial habitability. The Extremophiles section includes the halophiles, the polar cyanobacteria, and life without water, as well as microorganisms tolerating, surviving, and flourishing in severe environments. The extremophiles are important for practical uses (enzyme production) and extraction of special proteins. In the Extraterrestrial Life section of this volume there are discussions about the search for extraterrestrial intelligent life, terrestrial analogues for planetary oceans, life in terrestrial lava-caves, as implications for life detection on other planets, habitability of Earth-like exoplanets, Mars water and polar dunes, Antarctica as a model for life on Europa, Saturn and its moons, astrobiology of Titan, habitability of extrasolar planets and cosmic catastrophes.
This volume is number 24 of the Cellular Origin, Life in Extreme Habitats and Astrobiology [COLE] series [J. Seckbach (editor) 1999-2013, www.springer.com/series/5775]. The present book complements previous books of this series discussing also topics associated with this volume, namely, the Science of Astrobiology (2011), Stromatolites (2011), Symbioses and Stress (2010), Algae and Cyanobacteria in Extreme Environments (2007), Enigmatic Microorganisms and Life in Extreme Environments (1999). The target audience for this new book comprises scientists, microbiologists working with extremophiles, biology, geology students, teachers and general readers.
ResearchGate has not been able to resolve any references for this publication.