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Schematic microbial head with idealized sequence of internal fabrics and their relative water depths. The structures often display a vertical sequence of internal fabrics in shallowing-upward arrangement or show truncated fabric sequences depending on environmental setting and timing of growth history.

Schematic microbial head with idealized sequence of internal fabrics and their relative water depths. The structures often display a vertical sequence of internal fabrics in shallowing-upward arrangement or show truncated fabric sequences depending on environmental setting and timing of growth history.

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Article
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The distribution, nature and extent of microbial deposits in Hamelin Pool, Shark Bay have been investigated and mapped with emphasis on the occurrence, external morphologies, internal fabrics, constructional mechanisms, microbial communities, growth rates and sediment associations in the intertidal and previously little researched subtidal zone. De...

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... Most of the microbial constituents in marine carbonate-precipitating mats are not readily identifiable by eye [7,26,27], but Cyanobacteria, the primary producers in modern microbialites, excrete copious extracellular polymeric substances (EPS) that bind sediments ( Figure 2) [7,24]. Sediment-trapping alone cannot build stromatolites-carbonate minerals precipitated in situ cement the microbialites and create some of their textures ( Figure 2C,D), and processes within mats could potentially influence the growth or dissolution of trapped grains, as well. ...
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Here we review the application of molecular biological approaches to mineral precipitation in modern marine microbialites. The review focuses on the nearly two decades of nucleotide sequencing studies of the microbialites of Shark Bay, Australia; and The Bahamas. Molecular methods have successfully characterized the overall community composition of mats, pinpointed microbes involved in key metabolisms, and revealed patterns in the distributions of microbial groups and functional genes. Molecular tools have become widely accessible, and we can now aim to establish firmer links between microbes and mineralization. Two promising future directions include “zooming in” to assess the roles of specific organisms, microbial groups, and surfaces in carbonate biomineralization and “zooming out” to consider broader spans of space and time. A middle ground between the two can include model systems that contain representatives of important microbial groups, processes, and metabolisms in mats and simplify hypothesis testing. These directions will benefit from expanding reference datasets of marine microbes and enzymes and enrichments of representative microbes from mats. Such applications of molecular tools should improve our ability to interpret ancient and modern microbialites and increase the utility of these rocks as long-term recorders of microbial processes and environmental chemistry.
... Most of the microbial constituents in marine carbonate-precipitating mats are not readily identifiable by eye [7,26,27], but Cyanobacteria, the primary producers in modern microbialites, excrete copious extracellular polymeric substances (EPS) that bind sediments ( Figure 2) [7,24]. Sediment-trapping alone cannot build stromatolites-carbonate minerals precipitated in situ cement the microbialites and create some of their textures ( Figure 2C,D), and processes within mats could potentially influence the growth or dissolution of trapped grains, as well. ...
Article
Here we review the application of molecular biological approaches to mineral precipitation in modern marine microbialites. The review focuses on the nearly two decades of nucleotide sequencing studies of the microbialites of Shark Bay, Australia; and The Bahamas. Molecular methods have successfully characterized the overall community composition of mats, pinpointed microbes involved in key metabolisms, and revealed patterns in the distributions of microbial groups and functional genes. Molecular tools have become widely accessible, and we can now aim to establish firmer links between microbes and mineralization. Two promising future directions include “zooming in” to assess the roles of specific organisms, microbial groups, and surfaces in carbonate biomineralization and “zooming out” to consider broader spans of space and time. A middle ground between the two can include model systems that contain representatives of important microbial groups, processes, and metabolisms in mats and simplify hypothesis testing. These directions will benefit from expanding reference datasets of marine microbes and enzymes and enrichments of representative microbes from mats. Such applications of molecular tools should improve our ability to interpret ancient and modern microbialites and increase the utility of these rocks as long-term recorders of microbial processes and environmental chemistry.
... Branch diameter in cyclostome bryozoans has been shown to increase in cyclostome with depth (Taylor et al. 2007), and Figuerola et al. (2015) demonstrated depth-related differences in the levels of skeletal Mgcalcite in modern Antarctic bryozoans, but does the BSI vary with depth? Similarly, colony morphology in stromatolites (Andres and Reid 2006;Jahnert and Collins 2012) varies with depth, and the ability or otherwise to lay down skeleton in bryozoans may be reflected in observable differences in zoarial or zooecial morphology. ...
... The number of a calcareous strain isolated was high in Pudhumadam compared to Vepalodai and Uvari. The number of isolates was high in Pudhumadam, which may be due to the age and size of the calcareous sandstone [17] because of the age and size of the calcareous sandstones identified in the location were higher than the other locations. Qualitative analysis ...
Conference Paper
Diverse biotic communities interact with beach sand which facilitate their survival and growth. The interactions are to achieve few specific functions and analogous to the system required in geotechnical engineering. The biological functions are governed by natural selection, adopting the same physical laws to the engineered environments addresses geotechnical challenges like erosion prevention by stabilizing sand particles. The synthesis of calcium carbonate interveined through soil particles using the Microbial Induced Calcite Precipitation process emerged as a promising technology in stabilizing the loosened sand. The present research focused to isolate the microbes from the coastal environment, which has been studied for their calcite precipitation potential. In the study, 13 isolates were identified from marine sediments, whereas six exhibited Urease positive activity. Among the six isolates, the strain NIOT 1 showed high calcification potential and was recognized as Sporsarcina pausterii NIOT-1. This strain was identified as one of the promising urease producing bacteria in the microbiological world. In the course of the laboratory study, utilizing the identified strain to stabilize the coastal beach sand, success was achieved with a maximum compressive strength of 740 Kpa. In the meantime the maximum ammonium concentration was observed as 323.54 mM with the pH of around 8.1. The gained compressive strength in this study with the beach sand was slightly higher than the international studies, and it is one of its novel types. The current research results have paved a new path to utilize the MICP techniques as a tremendous non-destructive alternate to stabilize the coasts by preventing the beach sand movement and protecting the coastal populace from the eroding shoreline
... However, study from modern coral reef suggests another self-organization possibility (Schlager andPurkis, 2013, 2015;Purkis et al., 2016) that can potentially be applicable to microbial system where spatial interactions between water, topography, sediment transport, and microbialite growth can explain the observed microbialite spatial distributions, such that microbialite mounds self-organize to generate predictable autogenic patterns, independent of the initial conditions, and representing an important record of paleoenvironmental conditions. Previous studies of microbialite morphology and distribution are mostly based on field observations and interpretations, including both modern (Gebelein, 1969;Andres and Reid, 2006;Jahnert and Collins, 2012;Suosaari et al., 2016;Baskin et al., 2021) and ancient examples (Wood et al., 2002;Bosak et al., 2013;Andrews and Trewin, 2014;Bahniuk et al., 2015). However, these studies rarely address how microbial mats interact with adjacent sediment, how the interplay between mound expansion and smothering is linked to macroscopic morphologies, or their large-scale structure and spatial distribution. ...
... Model elements are then progressively added in cases 2, 3, and 4, to explore how each additional factor controls the strata (Table 1). Input parameters are based on reasonable, constrained values used in previous study of marine microbial carbonate systems (Johnson and Grotzinger, 2006;Jahnert and Collins, 2012;Kozlowski, 2016;Curtis et al., 2021). ...
... Modern microbialites commonly have multiple phases of accumulation (Paull et al., 1992;Jahnert and Collins, 2012;Carvalho et al., 2018), and the averaged growth rate decreases with increasing time span of observation (Table 2) (Sadler, 1981;Schlager, 1999), so the input maximum growth rate is set to 5 mm per year, and a total of 250 years EMT can produce microbialites with height of approximately 1 m or less, consistent with observations from modern systems, such as Shark Bay (Playford et al., 2013), Bahamas (Dravis, 1983), and Bermuda (Gebelein, 1969). Maximum accumulation rate of suspended sediment is 4 mm per year, which is a reasonable rate for non-compacted sediment to be deposited and form packstones in marine settings. ...
Article
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Microbialites span a substantial fraction of Earth history, and have important meanings for understanding long-term history of life and environment. Key controls on microbialite morphology and distribution include substrate topography, hydrodynamic conditions, water depth, salinity, light intensity, and sedimentation rates. This leads to potentially complex combinations of control by internal spatial feedbacks and also external factors. This complexity is explored here using Stromatobyte3D, a new numerical stratigraphic forward model that calculates microbialite accumulation due to in-situ precipitation, sediment trapping and binding, and sedimentation from suspension, controlled by evolving topography and water flow due to waves, tides or other currents. Results show that with increasingly strong spatial interactions of microbialite growth with water and suspended sediment, particularly the influence of hydrodynamics on in-situ microbialite growth and suspended sediment deposition patterns, three distinct microbialite morphologies are produced, from isolated columns, through elongated mounds, to ridges elongated in the dominant flow direction. Quantitative analysis demonstrates a dominant antecedent substrate topographic control on microbialite nucleation and growth in the absence of water flow, declining as hydrodynamic processes and strong spatial interactions are introduced causing mounds to accrete and coalesce laterally in the flow direction. Formation of coherent morphological patterns, produced by spatial interactions between topography, hydrodynamics, microbialite growth, and sedimentation from suspension, and independent of initial condition, is evidence of spatial self-organization. Modelled morphologies are strikingly similar to observations from modern marine agglutinated microbialite strata, suggesting modelled processes and their behaviours are realistic, and can therefore be useful to assist field interpretations of observed microbialite morphologies where similar processes were operating together.
... Modern microbialites have the fascinating potential to tell us about environmental changes through Earth history (Grotzinger and Knoll 1999) and although this is not straightforward, a number of features from modern microbialite-forming systems highlight the value of microbialites as paleoecological indicators (e.g., Moore and Burne 1994;Feldmann and McKenzie 1998;Reid et al. 2000;Riding 2000; Andres and Reid 2006;Dupraz et al. 2009;Jahnert and Collins 2012;Gomez et al. 2014Gomez et al. , 2018Pace et al. 2018;Roche et al. 2018;Suosaari et al. 2018;Eymard et al. 2019;Vennin et al. 2019;Grey and Awramik 2020;Shapiro and Awramik 2000) Morphologies (macroscale and megascale) can reveal potential relationships that can help to unravel the environmental controls on microbialite-building biological communities (Shapiro and Awramik 2000). Subsequently, the identification of similar microbialite morphologies from vastly different environments may indicate that a specific morphology is biologically controlled (Suosaari et al. 2018). ...
... According to many authors (Riding 1991;Kennard 1994;Moore and Burne 1994;Dupraz et al. 2009Dupraz et al. , 2011Dupraz et al. , 2013 some examples a distinction can be made between factors that play a major role in the development of microbial fabrics and buildups. For example, it was pointed out that, on a microscale, the differences between lamination (stromatolite) and clotted (thrombolite) textures are mainly controlled by the internal organization and morphologic composition of the successive microbial communities (Winsborough and Golubić 1987;Riding et al. 1991;Kennard 1994;Winsborough et al. 1994;Dupraz et al. 2013;Pace et al. 2018); mesoscale structures are related to a major control by a complex interaction of biological and environmental factors (Guo and Riding 1994;Kennard 1994;Dupraz et al. 2011;Gomez et al. 2014;Suosaari et al. 2016;Buongiorno et al. 2018;Marques Erthal 2018;Warden et al. 2019), and the external morphology (macroscale and megascale) is considered to be mainly controlled by environmental factors such as hydrodynamic conditions, sedimentation rate, and accommodation space, among others (Kennard 1994;Moore and Burne 1994;Riding 2011;Jahnert and Collins 2012;Patterson 2014;Suosaari et al. 2016). ...
... 3D, 4B). These may be related to the fact that wind-driven currents favor CO 2 degassing produced by splashing waves on microbialite surfaces, enhancing carbonate precipitation (Jahnert and Collins 2012;Suosaari et al. 2016) and therefore promoting better development in this zone. ...
Article
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Pozo Bravo is a high-altitude Andean lake that harbors modern microbialites thriving in hypersaline conditions in the Salar de Antofalla, one of the driest sites on Earth and located in the Puna region of Catamarca, northwest Argentine. Due to the lake physiography, microbialites are restricted to a narrow belt following Pozo Bravo lake variations. Microbialites exhibit a wide range of external morphologies including domal, discoidal, tabular, and horseshoe-like bioherms which vary considerably in size, as well as large biostromal terraces. As documented by other studies on modern microbialites, external morphology appears to be mainly the product of the environmental setting. In Pozo Bravo lake, high evaporation rates and hypersalinity (driven by high temperature and strong winds), water-level fluctuations, and lake-bottom topography are major controlling factors. The distinctive feature of Pozo Bravo microbialites is their internal structure, showing a gradual transition from a thrombolitic core to dendrolitic structures and to a sharply overlying stromatolitic layer within a single microbialite. We suggest that these various microbialite textures represent a gradual change within an environmental gradient based on lake-level variations, and the influence of these environmental factors on biological activity, mainly by cyanobacteria and diatoms. The study of this site is particularly relevant given that it represents an active system where progressive changes in microbialite type (from thrombolites to dendrolites and stromatolites) are recorded, providing an excellent natural laboratory to study these textural changes from a mechanistic perspective, and it may provide insights for better understanding of the microbialite geological record. In addition, given that these systems are threatened by human activities (mining of lithium-rich brines), its study and preservation are necessary.
... Modern stromatolites and microbial mats are often considered analogs of life on early Earth; however, they should also be considered as analogs of the environment where eukaryogenesis may have occurred. The stromatolites and microbial mats of Shark Bay on the west coast of Australia are often considered an ideal analog due to the hypersalinity, high UV radiation, and desiccation stress that mimics predicted conditions of the Paleoproterozoic era [73,79]. Moreover, metagenome analysis of functional genes, including arsenic respiration potential, hydrogenases, and the Wood-Ljungdahl pathways, also suggests that these mats may be a functional analog for ancient mat systems [80,81]. ...
Article
One of the most significant events in the evolution of life is the origin of the eukaryotic cell, an increase in cellular complexity that occurred approximately 2 billion years ago. Ground-breaking research has centered around unraveling the characteristics of the Last Eukaryotic Common Ancestor (LECA) and the nuanced archaeal and bacterial contributions in eukaryogenesis, resulting in fundamental changes in our understanding of the Tree of Life. The archaeal and bacterial roles are covered by theories of endosymbiogenesis wherein an ancestral host archaeon and a bacterial endosymbiont merged to create a new complex cell type – Eukarya – and its mitochondrion. Eukarya is often regarded as a unique and distinct domain due to complex innovations not found in archaea or bacteria, despite housing a chimeric genome containing genes of both archaeal and bacterial origin. However, the discovery of complex cell machineries in recently described Asgard archaeal lineages, and the growing support for diverse bacterial gene transfers prior to and during the time of LECA, is redefining our understanding of eukaryogenesis. Indeed, the uniqueness of Eukarya, as a domain, is challenged. It is likely that many microbial syntrophies, encompassing a ‘microbial village’, were required to ‘raise’ a eukaryote during the process of eukaryogenesis.
... The original structure of microbialites can indicate some aspects of their formation environments, such as water depth and hydrodynamic intensity. It is thought that tabular laminated stromatolites form near the average high tide level or subtidal zone with weak hydrodynamic condition, while domal and columnar stromatolites form in intertidal zone of high water energy, and dendritic thrombolites form at lagoons of evaporation platform (Jahnert and Collins 2012;Mettraux et al. 2015). Some researchers analyzed the formational environments of microbialites according to their mesostructures, but not based on the fabrics at microscale, since the relationship between the fabrics and their formation environments have not been determined. ...
Article
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The fabrics of microbialites preserved in limestones are generally better than in dolostones. What are the fabrics of the microbialites preserved in heavily dolomitized dolostones? This paper presents an example of a strongly dolomitized Cambrian microbialite profile. The Xiaoerblak Formation (Cambrian Series 2 Stage 3 and lower Stage 4) of the Sugaitblak section in Aksu, Xinjiang Uygur Autonomous Region, China is mainly composed of microbial dolostones. Due to strong alteration by diagenesis, their features, formation and environments have not been fully understood. Here, based on detailed observation on outcrops and thin sections, we show that this formation comprises four kinds of microbialites: laminite, thrombolite, thrombolitic laminite, and Renalcis framestone, in five intervals (Interval I to Interval V). We identified three main types of microbialite fabrics, i.e., clotted fabric, laminated fabric and skeletal fabric, and established a high-resolution vertical evolution sequence of the microbialites. The clotted fabric and the laminated fabric were further divided into subtypes. We found that the original fabrics were mainly affected by dolomitization, recrystallization and dissolution, and the alteration degree of the microbialite fabric is stronger in the lower part of this formation. The laminated fabric has the strongest resistance to diagenesis, followed by the clotted fabric. Based on studies of different rock types and sedimentary structures, we concluded that the sedimentary environment of Xiaoerblak Formation consists of three settings: a) Intervals I to III formed in restricted tidal flat environments, b) Interval IV and the lower part of Interval V in restricted deep subtidal environments, and c) upper part of Interval V in shallowing-up open subtidal environments.
... Microbial material -precipitated in-situ (authigenic) (Tucker, 1982;Tucker and Wright, 2009); clastic sediment -trapped and bound by microbial material (O'Connell et al., 2020;Tucker and Wright, 2009;Wright, 1984); stratiform microbialite; suspended load, low flow regime, gentle current action (Tucker and Wright, 2009;Chiarella et al., 2017;O'Connell et al., 2020); small tepee structuressame as LF11; large tepee structurescrystallisation expansion in carbonate-supersaturated subaqueous conditions (Shinn, 1969;Kendall and Warren, 1987 Microbial materialsame as LF14; clastic sedimentsame as LF14; stromatolitic buildupsuspended load, higher energy wave activity ( Hoffman, 1974( Hoffman, , 1976Jahnert and Collins, 2012;Kunzmann et al., 2019;Tucker and Wright, 2009;Wanless et al., 1988); columnar buildups -Baicalia burra (Preiss, 1973;Belperio, 1990) Skillogalee Dolomite, Myrtle Springs Formation LF16 Magnesite mud Light grey/cream to white; micritic; massive to laminated (cm scale); rare small (cm scale) tepee structures (SD) ...
... In the upper portion of the Skillogalee Dolomite, large tepee structures in layered microbialites without the presence of brecciation or chert most likely developed from crystallisation expansion in carbonatesupersaturated subaqueous conditions (Shinn, 1969;Kendall and Warren, 1987;O'Connell et al., 2020). These layered microbialites reflect a low energy, quiescent and productive setting (Shinn, 1969;Kendall and Warren, 1987;Belperio, 1990;Jahnert and Collins, 2012;Kunzmann et al., 2019;O'Connell et al., 2020;Thorie et al., 2020). Conversely, inversely graded stromatolitic buildup lithofacies, previously interpreted as Baicalia burra (Preiss, 1973;Belperio, 1990), could reflect deposition from higher energy wave activity (Hoffman, 1976;Wanless et al., 1988;Tucker and Wright, 2009;Jahnert and Collins, 2012;Kunzmann et al., 2019). ...
... These layered microbialites reflect a low energy, quiescent and productive setting (Shinn, 1969;Kendall and Warren, 1987;Belperio, 1990;Jahnert and Collins, 2012;Kunzmann et al., 2019;O'Connell et al., 2020;Thorie et al., 2020). Conversely, inversely graded stromatolitic buildup lithofacies, previously interpreted as Baicalia burra (Preiss, 1973;Belperio, 1990), could reflect deposition from higher energy wave activity (Hoffman, 1976;Wanless et al., 1988;Tucker and Wright, 2009;Jahnert and Collins, 2012;Kunzmann et al., 2019). This facies association is interpreted as an outer platform (E), where layered microbialites with large tepee structures deposit in a low energy, subtidal lagoon (E1) (e.g. ...
Article
The Tonian–Cryogenian transition (ca. 720 Ma) represents a period of significant environmental change in Earth history, involving variations in oceanic and atmospheric oxygenation, significant changes in the biosphere, tectonic reorganisation, and the onset of the global ‘Sturtian’ glaciation. South Australia has some of the thickest, continuous and best exposed sections of this unique interval globally. Here we present detailed palaeoenvironmental interpretations for a complete, ca. 3 km thick, pre- to post-glacial succession near Copley in the northern Flinders Ranges, South Australia. Elemental concentration data, complemented by screening for diagenesis, demonstrates the preservation of marine or primary REE signatures for studied carbonate samples and supports the proposed sedimentological and palaeoenvironmental interpretations. Multiple Tonian regressive-transgressive cycles are defined, which are recorded by deltaic rippled and cross-stratified sandstones (Copley Quartzite), through inner platform intraclastic magnesite and stromatolitic carbonates (Skillogalee Dolomite), to subtidal laminated siltstone and platform carbonates (Myrtle Springs Formation). The REE patterns from carbonate samples in the Skillogalee Dolomite and Myrtle Springs Formation indicate low Y/Ho, slight light rare earth element (LREE) depletion, weak negative Ce/Ce* and high Eu/Eu*. This suggests a nearshore, dysoxic setting fed by anoxic deep waters and more oxic shallow waters. In combination, the sedimentological and geochemical data build a picture of a partially restricted, shallow marine to lagoonal setting for the northern Flinders Ranges directly before the climate pivot to the Sturtian glaciation. These pre-glacial formations are unconformably overlain by Cryogenian subglacial to grounded ice-margin pebbly diamictites with immature, massive sand interbeds (Bolla Bollana Tillite). We suggest these facies reflect glacial grounding-line advance and retreat in a glaciomarine setting. These grade into turbiditic laminated sandstone and mudstone with dropstones (Wilyerpa Formation), which were likely deposited at the onset of deglaciation in a subaqueous proglacial environment. The post-glacial succession (Tapley Hill Formation) consists of subtidal laminated shales and carbonates, which are represented by increased Y/Ho, moderate LREE depletion, slight negative Ce/Ce* and low Eu/Eu*. This significant geochemical shift to a more open, oxic to suboxic subtidal setting coincides with widespread transgression and relative sea level rise after one of the most severe glaciations ever recorded.
... The most efficient instrument for identifying the sedimentary environment and the affecting processes is the facies analysis (Catuneanu 2013;2020). From a petroleum reservoir perspective, sedimentary facies analysis plays an important role in studying the expansion of reservoir zones and can be very effective in discovering new hydrocarbon traps and drilling new wells (Jahnert and Collins 2012). Petrographic studies of the Fahliyan Formation were carried out, aiming to identify microfacies and sedimentary environment based on facies differentiation, type and frequency of skeletal and non-skeletal components, sediment texture and structures and also comparison with the standard facies models (Wilson 1975;Flügel 2010). ...
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In this study, our attempt is to integrate sedimentological and petrophysical data for reservoir evaluation in the sequence stratigraphic framework. Petrographic analysis of the Late Jurassic–Early Cretaceous Fahliyan Formation reservoirs of two oilfields in the northwest of the Persian Gulf led to recognition of twelve microfacies. They can be classified into four facies associations, including open marine, shoal, lagoon and tidal flat, which are deposited in a homoclinal ramp carbonate. Sequence stratigraphy of the studied successions led to the recognition of three third-order depositional sequences based on vertical changes in microfacies and gamma ray analysis. Except for the upper boundary of the third sequence, the other sequence boundaries are type I (SBT.1). Dissolution is the most important diagenetic feature that affected the lower depositional sequence which is caused by the development of subaerial exposure after the deposition of the Fahliyan Formation, whereas cementation is the main diagenetic feature affecting the second- and third depositional sequences, causing their lower reservoir quality. In order to identify the flow units, the flow zone index methods, porosity throat radius (R35) and modified Lorenz based on stratigraphy were applied. The key wells studied in this area have shown good correlation throughout the studied oilfields which may potentially be used for hydrocarbon exploration and field development in the Late Jurassic–Early Cretaceous deposits of the Persian Gulf. This study integrates geological and petrophysical data (rock typing) toward sequence stratigraphic framework.