Development Of Microbial Mats Research Articles

Organic facies variability and paleoenvironmental characterization of the Codó and Itapecuru formations (Aptian-Albian) of Parnaíba Basin, Brazil

The Aptian-Albian sedimentary record of the Parnaíba Basin (NE Brazil), represented by the Codó and Itapecuru formations, is characterized by near-shore, shallow marine, and fluvio-lacustrine clastic sediments deposited in a large shallow sag basin that developed during the breakup of northwestern Gondwana associated with the early opening stages of the South Atlantic. This study aims to precisely characterize the nature, variability, paleoenvironmental significance and preservation conditions of the organic matter of the Aptian-Albian succession of the 2-TV-1-MA borehole (270 m). With these premises, organic petrographic and geochemical techniques were applied for the definition of the organic facies, allowing a better understanding of the Parnaíba Basin evolution during the Aptian-Albian interval. The 2-TV-1-MA borehole presents, at the base, a lacustrine system, with a high contribution of continental components deposited in a high energy, oxic environment, with incipient marine influence. This is intercalated by periods of restriction, with deposition occurring in a dysoxic-anoxic, low energy environment, with high contribution of higher plants. To the top, a relative decrease in the water-column leads to an increase in restriction, the emplacement of a stratified water-column, and the development of microbial mats. This is topped by a return to a high energy, oxic environment, with marine influence, and dominance of higher plants organic components.

Geomorphic and environmental controls on microbial mat fabrics on Little Ambergris Cay, Turks and Caicos Islands

AbstractTo interpret microbially influenced paleoenvironments in the sedimentary record, it is crucial to understand what processes control the development of microbial mats in modern environments. This article reports results from a multiyear study of Little Ambergris Cay, Turks and Caicos Islands, an uninhabited island floored by broad tracts of well‐developed microbial mats on the wind‐dominated and wave‐dominated Caicos Platform. Uncrewed aerial vehicle‐based imaging, differential global positioning system topographic surveys, radiocarbon data, and in situ sedimentological and microbial ecological observations were integrated to identify and quantify the environmental factors that influence the distribution and morphologies of Little Ambergris Cay microbial mats, including their response to large storm events. Based on these data, this study proposes that Little Ambergris Cay initially developed from the accretion and rapid lithification of carbonate sediment delivered by converging wave fronts in the lee of adjacent Big Ambergris Cay. Broad tracts of microbial mats developed during late Holocene time as the interior became restricted due to beach ridge development. Minor elevation differences regulate subaerial exposure time and lead to three categories of microbial mats, differentiated by surface texture and morphology: smooth mats, polygonal mats and blister mats. The surface texture and morphology of the mats is controlled by subaerial exposure time. In addition to elevation, the spatial distribution of mats is largely controlled by hydrodynamics and sediment transport during large storm events. This detailed assessment of the controls on mat formation and preservation at Little Ambergris Cay provides a framework within which to identify and understand the interactions between microbial communities and sediment transport processes in ancient high‐energy carbonate depositional systems.

Spatial comparison and temporal evolution of two marine iron-rich microbial mats from the Lucky Strike Hydrothermal Field, related to environmental variations

In hydrothermal environments, diffuse fluids emanations provide optimal conditions for the development of iron-rich microbial mats. Here, we present a unique spatial and temporal study of phylogenetic and chemical data from this type of mats and their associated hydrothermal fluids from two sites of the Lucky Strike Hydrothermal Field (EMSO-Azores deep-sea observatory), collected annually from 2016 to 2020. Our metabarcoding analyses reveal a completely different microbial community at each site, linked to the distinctive chemical composition of the diffuse fluids nourishing the mats. Capelinhos site is dominated by microorganisms with metabolisms related to iron, methane, and reduced sulphur compounds, coming from hydrothermal fluids, while North Tour Eiffel site presents higher abundances of microorganisms with metabolisms related to nitrogen, organic and oxidized sulphur compounds, coming from seawater. We present for the first time the yearly evolution of these mats over a five-year period. This analysis reveals similar variations of the microbial communities over time at both sites, indicating a regional Lucky Strike influence on the temporal scale. We also highlight more diversified microbial communities at both sites in 2016, pointing out the occurrence of a geological event that could have affected them during this specific year. Except for this year, our study shows that the communities of iron-rich microbial mats remain stable over time at both sites.

Microbial-mat colonization of modern gravel deposits in a siliciclastic coastal setting

ABSTRACTMicrobial mats are layered consortia of microorganisms colonizing surface sediments that alter their physical and chemical characteristics. The northern Patagonia coastline (Argentina) includes gravel deposits (termed rodados Patagónicos) accumulated during the Pleistocene and Holocene by high-energy hydrodynamic processes. In this area, surface sediments in a relict tidal channel (Paso Seco; 40° 38′ 27″ S, 62° 12′ 55″ W) are extensively colonized by microbial mats, appearing to overgrow exposed gravel deposits. To date, such substrates have not been reported as suitable for the development of microbial mats. The objectives of this paper are: 1) to describe the mechanisms of microbial baffling, trapping, and binding of sedimentary particles, and biostabilization that enable epibenthic microbial mats to develop on gravel substrates, 2) to relate microbial mat growth to a variety of hydrodynamic conditions, and 3) to describe resulting microbially induced sedimentary structures (MISS). Our hypothesis is that the alternation of episodic seawater flooding, stagnation, and draining with subsequent subaerial exposure and desiccation are the controlling factors for mat development on gravel. Once stagnant, mud-size sediment particles settle from suspension. At the same time, an initial biofilm may become established on the bottom, using the fine-grained material as substrate. Subsequently introduced particles are baffled, trapped, and bound into the developing biofilm matrix. During the Austral winter comparatively higher values for chlorophyll a and organic matter point towards increased growth of the microbial mat during this season. With increasing coherence, the developing microbial mat may encroach onto individual pebbles, ultimately engulfing them. Eventually, a mature, epibenthic microbial mat levels the sedimentary surface. Hydrodynamic reworking during flooding produces MISS such as mat chips and flipped-over mats.

Sequence stratigraphic and petrological analyses of the Cambrian oncoids exposed in the Liaoning Province, North China Platform

The Cambrian Miaolingian Series strata are continuously exposed in the North China Platform and contain diverse sedimentary phenomena, including substantial with oncoid-rich units. Limestone samples from the Zhangxia Formation in the Sandaogou section were collected to characterise unique macroscale to microscale sedimentary characteristics of the marine carbonate oncoids. In the oncolitic beds (∼4.5 m thick), the individual size of oncoids gradually increases from bottom to top. The oncoid morphology and the presence of a nucleus and laminae in thin-sections are used to classify these oncoids into three types (concentric laminar, lateral growth and multicore oncoids). As evidenced by scanning electron microscopy and energy-dispersive X-ray observations, Girvanella are abundant inside these oncoids and are associated with nanospheres, framboidal pyrite, and spherical and filamentous microbial fossils, confirming the biogenicity of the studied oncoids. These results suggest that the oncolitic–oolitic limestone formed in an upward-shallowing marine environment caused by a forced regression process that resulted in a decrease in accommodation space in a fourth-order sequence. Thus, the conditions became increasingly suitable for the development of cyanobacteria-dominated microbial mats and large oncoids. The late stage of the depositional setting and elevated solar radiation resulted in the formation of the growth termination surface. KEY POINTS Evidence of microbial origin from the oncoids of the Cambrian Miaolingian Series in the North China Platform. Vertical variation in oncoid size and distribution coincide with geochemical data. A shallowing depositional environment is interpreted as the reason for variation in oncoid size and formation of oncoid growth termination surfaces.

The 'classic stromatolite' Cryptozoön is a keratose sponge-microbial consortium.

Animal evolution transformed microbial mat development. Canonically inferred negative effects include grazing, disturbance and competition for space. In contrast, ancient examples of cooperation between microbial mats and invertebrates have rarely been reported. Late Cambrian (~485 million years) Cryptozoön is widely regarded as the first stromatolite to have received a taxonomic name and has been compared with present-day examples at Shark Bay, Australia. Here, we show that Cryptozoön is an interlayered consortium of keratose ('horny') sponge and microbial carbonate in roughly equal proportions. Cryptozoön's well-defined layering reflects repeated alternation of sponge and microbial mat. Its distinctive lateral growth is due to the ability of keratosans to colonize steep and overhanging surfaces. Contrary to the perception of Phanerozoic stromatolites as anachronistic survivors in a eukaryotic world, Cryptozoön suggests mutualistic behaviour in which sponges and microbial mats cooperated to gain support, stability and relief, while sharing substrates, bacteria and metabolites. Keratosan-microbial consortia may have been mistaken for stromatolites throughout the record of the past 500 million years, and possibly longer.

The Vulnerability of Microbial Ecosystems in A Changing Climate: Potential Impact in Shark Bay.

The potential impact of climate change on eukaryotes, including humans, has been relatively well described. In contrast, the contribution and susceptibility of microorganisms to a changing climate have, until recently, received relatively less attention. In this review, the importance of microorganisms in the climate change discourse is highlighted. Microorganisms are responsible for approximately half of all primary production on earth, support all forms of macroscopic life whether directly or indirectly, and often persist in “extreme” environments where most other life are excluded. In short, microorganisms are the life support system of the biosphere and therefore must be included in decision making regarding climate change. Any effects climate change will have on microorganisms will inevitably impact higher eukaryotes and the activity of microbial communities in turn can contribute to or alleviate the severity of the changing climate. It is of vital importance that unique, fragile, microbial ecosystems are a focus of research efforts so that their resilience to extreme weather events and climate change are thoroughly understood and that conservation efforts can be implemented as a response. One such ecosystem under threat are the evolutionarily significant microbial mats and stromatolites, such as those present in Shark Bay, Western Australia. Climate change models have suggested the duration and severity of extreme weather events in this region will increase, along with rising temperatures, sea levels, and ocean acidification. These changes could upset the delicate balance that fosters the development of microbial mats and stromatolites in Shark Bay. Thus, the challenges facing Shark Bay microbial communities will be presented here as a specific case study.

Microbially induced sedimentary structures in late Pennsylvanian glacial settings: A case study from the Gondwanan Paraná Basin

This paper explores microbially induced sedimentary structures (MISS) preserved in Late Paleozoic Ice Age deposits to evaluate the potential microbe-substrate physical interactions in ancient glacial settings. MISS have been recorded worldwide in different modern and ancient settings, mostly in tidal flats. However, their record in ancient glacial settings is still underrepresented. The reported MISS are preserved in the siltstone-claystone glacigenic rhythmites in Trombudo Central region of the Rio do Sul Formation (Paraná Basin, Pennsylvanian, southern Brazil). The recorded structures in these deposits are composed of wrinkle structures, dome structures, mat fragments, mat microfabrics, sinoidal structures, laminated leveling structures, oriented grains and mat-layer bound small grains, kinneyia structure, discoidal microbial colony, elongated filaments, and drab-haloed filaments. They represent the development of endobenthic and epibenthic microbial mats, as well as microbial earths. Endobenthic mat structures predominate in the siltstone beds, suggesting less time for development of microbial mat during deglaciation events and meltwater input. Epibenthic mat structures preserved in the claystone layers indicate episodic quiescence periods that allowed the mat achieve maturity and that cyanobacteria and sulfate-reducing bacteria composed a significant part of the microbial community. The set of MISS observed in the studied rhythmites have been commonly reported in tidal settings, and the presence of microbial earths structures indicate periods of drainage of the water bodies, at least partially. Thus, the microbial communities played an important role in ancient glacial settings during climatic amelioration periods, opening the colonization window for macroorganisms in outwash plains and marginal marine settings. This paper provides a characterization of different sorts of preserved MISS, and evaluate the physical interactions between microbial mats and the substrate, in the ancient glacigenic deposits from the Itararé Group.

Antecedent aeolian dune topographic control on carbonate and evaporite facies: Middle Jurassic Todilto Member, Wanakah Formation, Ghost Ranch, New Mexico, USA

AbstractThe Middle Jurassic Todilto Member of the Wanakah Formation is a carbonate and gypsum unit inset into the underlying aeolian Entrada Sandstone in the San Juan Basin. Field and thin section study of the uppermost Entrada and Todilto at Ghost Ranch, New Mexico, identified Todilto facies and their relationship to remnant Entrada dune topography. Results support the previous interpretation that the Entrada dunes, housed in a basin below sea level, were rapidly flooded by marine waters. Mass wasting of the dunes gave rise to sediment‐gravity flows that largely buried remnant dune topography, leaving ca 12 m of relief that defined the antecedent condition for Todilto deposition. Previously interpreted as seasonal varves deposited in a stratified water body, the Todilto is reinterpreted as a microbial biolaminite. Most diagnostic are organic‐rich laminae with structures characteristic of filamentous microbes and containing trapped aeolian silt, and clotted‐texture laminae with a fabric associated with calcification of extracellular polymeric substances. The spatial arrangement of Todilto facies is controlled by the dune palaeotopography. A continuous basal laminated mudstone thickens over the dune crest, reflecting the optimum conditions for microbial mat development, and is interpreted to have been deposited when marine waters submerged the topography. Subsequent drying caused emergence of the crestal area, and formation of tepee structures and a dissolution breccia. Gypsiferous mudflats and periodic ponds occupied the dune flanks and interdune area, with gypsum concentrated within the interdune area. Entrada sands remained unstable during Todilto deposition with common injection structures into the Todilto, and a remnant slope caused the downslope movement and folding of Todilto strata on the upper lee face. Although some expansion of the gypsum occurred in the subsurface, facies architecture fostered development of a dissolution front adjacent to the interdune gypsum body with section collapse of gypsiferous limestone on the dune flanks.

Fish‐bearing deposits from the Upper Eocene Terminal Complex of the Plana de Vic (Catalonia, NE Spain): Sedimentary context and taphonomy

The Upper Eocene fish‐bearing deposits of the Terminal Complex of the Plana de Vic (Ebro Basin, Catalonia, NE Spain) and its fish assemblage are analysed in detail from a stratigraphic and sedimentological point of view. Moreover, the taphonomic features and taxonomy of the fishes are studied for the first time. Fishes belonging to the families Clupeidae, Synodontidae, and an indeterminate percomorph have been identified, including a new lizardfish taxon, Ausonasynodus almerai gen. et sp. nov. The fish specimens are preserved in finely laminated limestones, resulting from the development of microbial mats on the seafloor. The presence of these microbially induced biolaminations favoured the good preservation of the fossil material. The combination of the stratigraphic and sedimentological context of the studied deposits, together with the taphonomic and paleobiological information obtained from the fishes, suggest that they were likely deposited in a shallow marine setting, probably in restricted or protected areas, under arid climatic conditions.

Givetian-Frasnian arid palaeoenvironments from the northern Gondwana: a case study from the Moesian platform (Bulgaria)

Palaeozoic deposits in the Moesian platform (northern Bulgaria) are known only from deep wells drilled for oil and gas prospecting. Sixteen microfacies (MFT 1–16) have been distinguished and described in the Givetian to Frasnian carbonate and evaporite sequences, represented in thirteen wells from the eastern parts of the platform. They are respectively interpreted as arid peritidal deposits, formed in a variety of carbonate/evaporite environments (from shallow subtidal zones, adjacent to tidal flat, to supratidal sabkha). The shallow subtidal zone is characterised by wave-dominated (possible carbonate sand shoals, MFT 1–3) and protected lagoon (MFT 4–8) settings. The intertidal zone is distinguished by the development of microbial mats with typical lamination (MFT 9 and MFT 10) and “bird’s eyes” type fenestrae (MFT 11). Unfossiliferous laminated mudstones (MFT 12), lag deposits rich in intraclasts (MFT 13), brackish ponds with charophytes (MFT 14), unfossiliferous homogeneous mudstones/dolomudstones (MFT 15) and sabkha evaporites (MFT 16) were formed within the range of the upper intertidal and supratidal zones. These deposits presumably reflect the transition of the platform from carbonate ramp to rimmed shelf. Most of the studied Givetian–Frasnian microfacies are comparable with Wilson’s Standard Microfacies Types and/or with other microfacies described from shallow-marine Middle–Upper Devonian carbonate and evaporite successions in Europe. It seems likely that during the Givetian–Frasnian time the Moesian carbonate platform was located in the arid climate zone on the northern shallow shelf of the Gondwana.

The giant stromatolite field at Santa Rosa de Viterbo, Brazil (Paraná Basin) – A new paleoenvironmental overview and the consequences of the Irati Sea closure in the Permian

The city of Santa Rosa de Viterbo, São Paulo State, Brazil, contains an important geological and paleontological site that is part of the Paraná Basin and presents one of the most significant records of Permian microbial life of southwestern Gondwana: the giant stromatolite field, with structures reaching 3 m high and 6 m wide. This work proposes a new overview of the paleoenvironment, focusing on the growth and development of microbial mats and microbialites. The characterization and association of nine facies were performed: intraformational breccia with wackestone matrix, intraformational breccia with grainstone matrix, packstone, wackestone, microbial mats, peloidal wackestone, laminated peloidal wackestone, laminated peloidal packstone and stromatolites. Four lithologic logs were correlated and used to interpret the history of the establishment of microbial communities during the episode of the Irati Sea closure. Field studies were carried out, thin sections were analyzed, and techniques such as SEM/EDS and Raman spectroscopy were applied for compositional analysis and to aid in the identification of associated fossils. This moment in the Paraná Basin's evolution was important due to the noteworthy increase in rates of organic matter deposition and the significant proliferation of microbial life brought about by the closure of the Irati Sea. One hypothesis is that there was more than one attempt to establish microbial communities during the paleoenvironmental evolution, and success was achieved only after a decrease in water depth and energy of the depositional system, as well as after an increase in salinity. As a result of a reconfiguration of paleogeography in the Gondwana supercontinent, the closure of the Irati Sea significantly affected the development and establishment of microbial communities, which gave rise to extensive microbialitic structures such as those at Santa Rosa de Viterbo.

Last Millennium Meridional Shifts in Hydroclimate in the Central Tropical Pacific

AbstractReconstructing past changes in the spatial structure of tropical Pacific hydroclimate requires archives of past moisture balance across spatial gradients of precipitation. To date, only one, 600‐year, terrestrial record of hydroclimate is available for the central tropical Pacific (CTP) from Washington Lake, Washington Island, limiting the ability to test the hypotheses regarding the location of the CTP Intertropical Convergence Zone (ITCZ) in the last millennium. A new lake sediment record from Lake 30, Kiritimati, Republic of Kiribati, 3° south of Washington Island, provides additional constraints on past CTP ITCZ position. Lake 30 geochemical and sedimentological data indicate an episode of increased microbial mat development and gypsum precipitation from 900 to 1200 CE, coincident with the Medieval Climate Anomaly (MCA). We infer drier conditions during the MCA at Kiritimati as the Washington Lake proxy record indicates wetter conditions, suggesting that the CTP ITCZ was displaced northward during the MCA relative to its position today. At the transition between the MCA and the Little Ice Age (LIA), Lake 30 sediment becomes predominantly carbonate, suggesting a transition to wetter conditions and a southward shift of the ITCZ relative to its MCA position. However, a tropical Pacific synthesis of hydroclimate‐sensitive proxy records does not point to a consistent spatial or temporal pattern of variability in the MCA and LIA, suggesting multiple influences on centennial‐scale tropical Pacific hydroclimate during the last millennium.

Hydraulic sediment penetration and seasonal growth of petalonamean basal discs from the Vendian of Ukraine

Around the Ediacaran-Cambrian transition, about 540 million years ago, marine organisms began to dig in the sediment that has resulted in its better ventilation and further expansion of infaunal life. Few vertical infaunal burrows are known from the Precambrian and they are usually attributed to sea anemones. Here we show that the enigmatic Ediacaran petalonamean ‘sea pens’ were able to penetrate sediment for more than one centimetre depth while anchoring the body in the microbial mat. Their growth, as evidenced by numerous well-preserved basal discs from the late Ediacaran Lomoziv Member of the Mohyliv Formation in Podolia, Ukraine, was under control of rhythmic sedimentation events and periodic microbial mat development. Size frequency distribution in classes of both the final disc size and growth retention stages show that their size increase was stepwise. Each discrete stage corresponds to deposition of a thin sediment layer and development of the microbial mat at its top. Podolia was located near the South Pole in the Ediacaran (Vendian) and such rhythmic sedimentation was probably connected with the local climate seasonality.

Temporal and environmental significance of microbial lamination: Insights from Recent fluvial stromatolites in the River Piedra, Spain

Despite extensive research, the environmental and temporal significance of microbial lamination is still ambiguous because of the complexity of the parameters that control its development. A 13 year monitored record of modern fast-accreting calcite stromatolites (mean 14 mm year−1) from artificial substrates installed in rapid flow in the River Piedra (north-east Spain) allows comparison of the sedimentological attributes of successive six-month depositional packages with the known climatic, hydrophysical and hydrochemical parameters of the depositional system. The stromatolites are formed of dense, porous and macrocrystalline composite laminae. The dense and porous composite laminae, which are composed of two to eight laminae consisting largely of calcified cyanobacteria, are characterized by: (i) dense composite laminae, up to 15 mm thick, mostly with successive dense laminae and minor alternating dense and porous laminae; and (ii) porous composite laminae, up to 12 mm thick, consisting mainly of porous laminae alternating with thinner dense laminae. Most of the dense composite laminae formed during the warm periods (April to September), whereas most of the porous composite laminae developed in the cool periods (October to March). Each dense and porous composite lamina represents up to or slightly longer than six months. The alternation of these two types of composite laminae parallels seasonal changes in temperature. The dense and porous laminae result from shorter (for example, intraseasonal) variations in temperature, insolation and hydrological conditions. The macrocrystalline laminae, with crystals >100 μm long, occur isolated and grouped into composite laminae up to 1·7 mm thick. Their occurrence suggests the absence or poor development of microbial mats over periods of weeks to several months. Thus, stromatolite lamination can record different-order, periodic and non-periodic changes in the magnitude of environmental parameters over a single year. These results hold important implications for the temporal and environmental interpretation of lamination in microbial structures.

Cyanobacteria of the Wadden Sea: seasonality and sediment influence on community composition

Tidal flats are extremely dynamic habitats in several environmental parameters, which enforces severe selection on their microbial inhabitants. Despite good knowledge of the species present, little is known about the temporal dynamics of their communities. Aim of the study was the investigation of cyanobacterial populations in intertidal flats of the German Wadden Sea and their seasonal- and sediment-type related dynamics of community composition based on next generation sequencing of 16S rRNA fragments. Most of the detected cyanobacterial taxa were present throughout the year, but with changing distribution patterns in different sediment types suggesting migration processes between sediment types during the year. Seasonal as well as tidal changes of environmental conditions and the heterogeneity of the study site concerning grain-size and related parameters created a temporally and spatially highly dynamic ecosystem. Development of microbial mats and community composition was mainly influenced by seasons. The annual mat growth started in spring and reached its maximum in late summer with highest richness as well-stabilized laminated structure. Different grain-sizes provided alternative niches for present taxa when conditions change. Coleofasciculus, Hydrocoleum, and Lyngbya were dominating genera in all sediment types. Βeta diversity of seasonal groups was influenced by the interval between sampling dates.

Temporal and environmental significance of microbial lamination: Insights from Recent fluvial stromatolites in the River Piedra, Spain

AbstractDespite extensive research, the environmental and temporal significance of microbial lamination is still ambiguous because of the complexity of the parameters that control its development. A 13 year monitored record of modern fast‐accreting calcite stromatolites (mean 14 mm year−1) from artificial substrates installed in rapid flow in the River Piedra (north‐east Spain) allows comparison of the sedimentological attributes of successive six‐month depositional packages with the known climatic, hydrophysical and hydrochemical parameters of the depositional system. The stromatolites are formed of dense, porous and macrocrystalline composite laminae. The dense and porous composite laminae, which are composed of two to eight laminae consisting largely of calcified cyanobacteria, are characterized by: (i) dense composite laminae, up to 15 mm thick, mostly with successive dense laminae and minor alternating dense and porous laminae; and (ii) porous composite laminae, up to 12 mm thick, consisting mainly of porous laminae alternating with thinner dense laminae. Most of the dense composite laminae formed during the warm periods (April to September), whereas most of the porous composite laminae developed in the cool periods (October to March). Each dense and porous composite lamina represents up to or slightly longer than six months. The alternation of these two types of composite laminae parallels seasonal changes in temperature. The dense and porous laminae result from shorter (for example, intraseasonal) variations in temperature, insolation and hydrological conditions. The macrocrystalline laminae, with crystals >100 μm long, occur isolated and grouped into composite laminae up to 1·7 mm thick. Their occurrence suggests the absence or poor development of microbial mats over periods of weeks to several months. Thus, stromatolite lamination can record different‐order, periodic and non‐periodic changes in the magnitude of environmental parameters over a single year. These results hold important implications for the temporal and environmental interpretation of lamination in microbial structures.

Possible biogenic structures from the Lower Cambrian strata in Yunnan Province, South China

AbstractMicrobially induced sedimentary structures (MISS) are microbial traces in sandy deposits. They have been formed by various modes of microbial behaviour in response to the prevailing physical dynamics in shallow-marine environments since early Archaean time. An association of fossils, phosphatic structures and grains, stromatolites and microbial laminated levelling structures is documented from the Zhongyicun Member of Lower Cambrian strata in the Baideng section dated close to 535 Ma. SEM examination demonstrates that microbial laminated levelling structures are the result of the development of microbial mats composed of filamentous structures. We propose that there was a short hiatus after the dolomite layer deposited when the dolomite layer was weathered to form centimetre-scale valleys firstly, and then microbes accumulated in these valleys and formed the microbial laminated levelling structures.

Stable and Variable Parts of Microbial Community in Siberian Deep Subsurface Thermal Aquifer System Revealed in a Long-Term Monitoring Study.

The goal of this work was to study the diversity of microorganisms inhabiting a deep subsurface aquifer system in order to understand their functional roles and interspecies relations formed in the course of buried organic matter degradation. A microbial community of a deep subsurface thermal aquifer in the Tomsk Region, Western Siberia was monitored over the course of 5 years via a 2.7 km deep borehole 3P, drilled down to a Palaeozoic basement. The borehole water discharges with a temperature of ca. 50°C. Its chemical composition varies, but it steadily contains acetate, propionate, and traces of hydrocarbons and gives rise to microbial mats along the surface flow. Community analysis by PCR-DGGE 16S rRNA genes profiling, repeatedly performed within 5 years, revealed several dominating phylotypes consistently found in the borehole water, and highly variable diversity of prokaryotes, brought to the surface with the borehole outflow. The major planktonic components of the microbial community were Desulfovirgula thermocuniculi and Methanothermobacter spp. The composition of the minor part of the community was unstable, and molecular analysis did not reveal any regularity in its variations, except some predominance of uncultured Firmicutes. Batch cultures with complex organic substrates inoculated with water samples were set in order to enrich prokaryotes from the variable part of the community. PCR-DGGE analysis of these enrichments yielded uncultured Firmicutes, Chloroflexi, and Ignavibacteriae. A continuous-flow microaerophilic enrichment culture with a water sample amended with acetate contained Hydrogenophilus thermoluteolus, which was previously detected in the microbial mat developing at the outflow of the borehole. Cultivation results allowed us to assume that variable components of the 3P well community are hydrolytic organotrophs, degrading buried biopolymers, while the constant planktonic components of the community degrade dissolved fermentation products to methane and CO2, possibly via interspecies hydrogen transfer. Occasional washout of minor community components capable of oxygen respiration leads to the development of microbial mats at the outflow of the borehole where residual dissolved fermentation products are aerobically oxidized. Long-term community analysis with the combination of molecular and cultivation techniques allowed us to characterize stable and variable parts of the community and propose their environmental roles.

External controls on the distribution, fabrics and mineralization of modern microbial mats in a coastal hypersaline lagoon, Cayo Coco (Cuba)

AbstractActive, carbonate‐mineralizing microbial mats flourish in a tropical, highly evaporative, marine‐fed lagoonal network to the south of Cayo Coco Island (Cuba). Hypersaline conditions support the development of a complex sedimentary microbial ecosystem with diverse morphologies, a variable intensity of mineralization and a potential for preservation. In this study, the role of intrinsic (i.e. microbial) and extrinsic (i.e. physicochemical) controls on microbial mat development, mineralization and preservation was investigated. The network consists of lagoons, forming in the interdune depressions of a Pleistocene aeolian substratum; they developed due to a progressive increase in sea‐level since the Holocene. The hydrological budget in the Cayo Coco lagoonal network changes from west to east, increasing the salinity. This change progressively excludes grazers and increases the saturation index of carbonate minerals, favouring the development and mineralization of microbial mats in the easternmost lagoons. Detailed mapping of the easternmost lagoon shows four zones with different flooding regimes. The microbial activity in the mats was recorded using light–dark shifts in conjunction with microelectrode O2 and HS− profiles. High rates of O2 production and consumption, in addition to substantial amounts of exopolymeric substances, are indicative of a potentially strong intrinsic control on mineralization. Seasonal, climate‐driven water fluctuations are key for mat development, mineralization, morphology and distribution. Microbial mats show no mineralization in the permanently submersed zone, and moderate mineralization in zones with alternating immersion and exposure. It is suggested that mineralization is also driven by water‐level fluctuations and evaporation. Mineralized mats are laminated and consist of alternating trapping and binding of grains and microbially induced magnesium calcite and dolomite precipitation. The macrofabrics of the mats evolve from early colonizing Flat mats to complex Cerebroid or Terrace structures. The macrofabrics are influenced by the hydrodynamic regime: wind‐driven waves inducing relief terraces in windward areas and flat morphologies on the leeward side of the lagoon. Other external drivers include: (i) storm events that either promote (for example, by bioclasts covering) or prevent (for example, by causing erosion) microbial mat preservation; and (ii) subsurface degassing, through mangrove roots and desiccation cracks covered by Flat mats (i.e. forming Hemispheroids and Cerebroidal structures). These findings provide in‐depth insights into understanding fossil microbialite morphologies that formed in lagoonal settings.