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1.
<正>Microbial mats are ecosystems that can control or induce the precipitation of calcium(Ca) carbonate on Earth through geological time.In the present study,we report on a novel accumulation of Ca,together with iron(Fe),in a microbial mat collected from a slight acidic hot spring(pH=5.9) in south China.Combining an array of approaches,including environmental scanning electron microscopy,X-ray microanalysis,transmission electron microscopy,and selected area electron diffraction,we provide ultrastructral evidence for amorphous acicular aggregates containing Ca and Fe associated with cyanobacteria precipitating in the microbial mats.Cyanobacterial photosynthesis and exopolymeric organic matrixes are considered to be responsible for the precipitation of Ca.These amorphous acicular aggregates might imply the early stage of calcification occurring in microbial mats.Ca and Fe coprecipitation indicates another potential important way of inorganic element precipitation in hot spring microbial mats.Our results provide insight into the possible mechanism of cyanobacterial calcification and microfossil preservation in slight acidic hot spring environments.  相似文献   

2.
Microbial mats, mainly dominated by filamentous algae Calothrix and Oscillatoria, are well developed in Tibetan hot springs. A great number of fossil microorganisms, which existed as algae lamination in thermal depositional cesium-bearing geyserite in this area, are identified as Calothrix and Oscillatoria through microexamination and culture experiments. These microbial mats show the ability to accumulate cesium from spring water to the extent of cesium concentration of 0.46–1.03% cell dry weight, 900 times higher than that in water, and capture large numbers of cesium-bearing opal grain. Silicon dioxide colloid in spring water replaces and fills with the organism and deposits on it to form algae laminated geyserite after dehydration and congelation. Cesium in the microbial mats and opal grain is then reserved in the geyserite. Eventually, cesium-bearing algae laminated geyserite is formed. Study on cesium distribution in geyserite also shows that cesium content in algae lamination, especially in heavily compacted algae lamination, is higher than in the opal layer. For geyserite with no algae lamination or other organism structure, which is generally formed in spring water with low silicon content, cesium accumulation and cesium-bearing opal grain assembled by the microbial mats are also indispensable. After the microbial mats accumulating cesium from spring water, silicon dioxide colloid poorly replaces and fills with the organism to form opal grain-bearing tremellose microbial mats. The shape and structure of the organisms are then destroyed, resulting in cesium-bearing geyserite with no algae lamination structure after dehydration and congelation. It is then concluded that microbial mats in the spring area contribute to the enrichment of cesium in the formation of cesium-bearing geyserite, and a biological genesis of the geyserite, besides of the physical and chemical genesis, is likely.  相似文献   

3.
The bacteria used in the experiment are Thiobacillus Ferrooxidans separated from acidic mine water in sulphide deposits. The chemoautotrophic bacteria can act directly on sulphides and accelerate the oxidation of sulphides. The experiment shows that the bacteria, as an important microbial factor of gold's supergenous enrichment within the oxidized zones of sulphide deposits, are helpful to dissolve gold and silver in ferric sulphate. In the bacterial oxidation process, the precipitation of goethite is concerned both with the lower activity of ferric ions and with the existence of carbonates in solution. Meanwhile, the acid-resisting and oxidizing ability of the bacteria will certainly lead up to a microbial way of treating the acidic mine water.  相似文献   

4.
A sulfide black smoker chimney exists in the Gaobanhe seabed exhalation massive sulfide deposit in the Xingiong-Kuancheng secondary fault basin of the Proterozoic Yaniiao rift trough in Hebei Province, taking the shape of mounds, individually about 2-3 cm high. Abundant fossils of thermophilous bacteria and algae in perfect preservation are found in the ore surrounding the black smoker chimney. Scanning electron microscopy （SEM） and molecular biomarker studies on the microorganismai ore fabric show that the microorganism in the sulfide ore is in fact a sedimentary product of probiotic bacteria and algae. In the special food chain based on black smoker chimney at ancient seabed- thermophilous bacteria, the thermophilous bacteria and algae reproduce in large quantity. Intermittently erupting of fluid from the chimney creats conditions for formation of sulfide deposit. In the process of exhalation action of hot fluid, thermophilous bacteria and algae grow and reproduce around the sulfide black smoker chimney, absorbing mineralizing substances brought by the fluid. Massive sulfide deposits are formed in this process of absorption of seabed black smoker chimney exhalation-mineralizing fluid pulsation-thermophilous microorganism.  相似文献   

5.
High-sulfur, heavy petroleum is widely occurring in the Tertiary lacustrine Jiyang sub-basin, Bohai Bay Basin. They are differentiated into two families based on the bulk properties and biomarker compositions. Family 1 is characterized by high resins (40%–71%) and sulfur (2%–4%), and low wax (1%–6%), with n-alkanes removed by biodegradation, whereas family 2 is characterized by extremely abundant sulfur (3%–10%), and high asphaltenes (7%–31%) and wax (2%–19%), with no evidence of microbial attack. The oils of family 1 are distributed in the reservoir, lower than 1500 m throughout the sub-basin. Biomarker assemblages, such as low pristane/phytane ratios (<1 Pr/Ph) and a high abundance of carotane, gammacerane, and dinosterane, suggest that they are derived from the calcareous mudstones and shales among the stratified, saline Es4u unit, in addition to the in situ biodegradation-concentrated sulfur content. However, the oils of family 2 are identified only in the western Zhanhua and eastern Chezhen depressions, with a depth deeper than 1700 m. Physical properties, together with biomarker ratios, including even-numbered n-alkanes, <1 Pr/Ph, trace diasteranes, higher C35 homohopanes, and abundant dibenzothiophene series, with >1 dibenzothiophene/phenanthrene, indicate an origin from carbonate source rocks. The X-ray diffraction analysis showed that the carbonate source rock is limited in the Es4u unit of the Bonan sag, which is different from most other source rocks in the same horizon. It is suggested that the high-sulfur, heavy oils are generated at the early stage of the oil window. Bacterial sulfate reduction might be responsible for the occurrence of sulfur species in the high-sulfur, heavy oils, while heavy biodegradation will enhance sulfur concentrations.  相似文献   

6.
The Shimen realgar deposit is characterized by the pipi-shaped orebody and the development of silica sinter and hydrothermal explosive breccia which are typical of hot spring activity.Very similar trace-element associations are noticed between the silica cap and the breccia and modern hot spring waters in the area.The chemistr of ore-forming solutions is also well comparable with that of modern hot spring.,The spring system that gave rise to the mineralization was charged by ground waters heated through thermal conducting systems in the deep crust and,to a lesser extent,by geothermal gradient.ΔD,δ^18O,δ^13CCH4andδ^13CH4andδ^13CCO2values and ^40Ar/^36Ar and 3^He/^4He ratios indicate that the spring system is of crustal derivation.The ore-forming metals were supplied by surrounding strata,particularly those underlying the ore deposits.The mechanim of ore deposition is thought to be hydrothermal explosion and accompanying boiling and abrupt changes in pH and Eh.Located in northwest Hunan,the Shimen realgar deposit is the leading arsenic producer in the country,However,regardless of its long mining history,the genesis of this deposit has long been a puzzle.It was considered to be postmagmatic epithermal in the leading arsenic producer in the puzzle.It Was considered to be postmagmatic epithermal in origin,but this is trongly challenged by filling(metasomatism)in karst environment proposed later by Zhou Zhiquan(1986)also encounters a number of difficulties.For example,why can the pipi-shaped orebody vertically extend up to several hundreds meters without any compatible development in the lateral dimension? A hot spring genesis is suggested in the present paper based on geological observations and laboratory studies conducted by the authors in recent years.  相似文献   

7.
Core V36-06-3, approximately 12m long, was raised from the lower part of the continental slope of the continental South China Sea from a water depth of 2,809 m. Analyses of planktonic foraminifera, CaCO_3 content and oxygen isotopes(δ~(18)O) in shells of Globigerinoides sacculifer show that the trend of the sea surfacetemperature change at this site over the last 130,000 years is consistent with that in other oceans, while the expression of the dissolution cycles of calcium carbonates here is contrary to that in the Pacific Ocean but consistent with that in the Atlantic Ocean, which means that the dissolution was intense and the CaCO_3 content was slightly low during the glacial ages, but the reverse was true for the interglacial ages. The reason for this is that during the glacial ages large quantity of terrigenous detrital materials were brought into the abyssal and bathyal Zones, thus diluting the calcium carbonate deposits and intensifying their dissolution.  相似文献   

8.
http://www.sciencedirect.com/science/article/pii/S1674987111001307   总被引：3，自引：1，他引：2  
South China Sea(SCS) is the largest Western Pacific marginal sea.However,microbial studies have never been performed in the cold seep sediments in the SCS.In 2004."SONNE" 177 cruise found two cold seep areas with different water depth in the northern SCS.Haiyang 4 area,where the water depth is around 3000 m.has already been confirmed for active seeping on the seafloor.such as microbial mats,authigenic carbonate crusts and bivalves.We investigated microbial abundance and diversity in a 5.55-111 sediment core collected from this cold seep area.An integrated approach was employed including geochemistry and 16S rRNA gene phylogenetic analyses.Here,we show that microbial abundance and diversity along with geochemistry profiles of the sediment core revealed a coupled reaction between sulphate reduction and methane oxidation.Acridine orange direct count results showed that microbial abundance ranges from 10~5 to 10~6 cells/g sediment(wet weight).The depth-related variation of the abundance showed the same trend as the methane concentration profile.Phylogenetic analysis indicated the presence of sulphate-reducing bacteria and anaerobic methane-oxidizing archaea.The diversity was much higher at the surface,but decreased sharply with depth in response to changes in the geochemical conditions of the sediments,such as methane,sulphate concentration and total organic carbon.Marine Benthic Group B.Chloroflexi and JSl were predominant phylotypes of the archaeal and bacterial libraries,respectively.  相似文献   

9.
In order to investigate the effect of Thiobacillusferrooxidans on the oxidation of pyrite, two parallel experiments, which employed H2SO4 solutions and acidic solutions inoculated with ThiobaciUus ferrooxidans, were designed and carried out at 30℃. The initial pH of the two solutions was adjusted to 2.5 by dropwise addition of concentrated sulphuric acid. The surfaces of pyrite before exposure to leaching solutions and after exposure to the H2SO4 solutions and acidic solutions inoculated with Thiobacillus ferrooxidans were observed by scanning electron microscopy （SEM）. There were a variety of erosion patterns by Thiobacillusferrooxidans on the bio-leached pyrite surfaces. A conclusion can be drawn that the oxidation of pyrite might have been caused by erosion of the surfaces. Attachment of the bacteria to pyrite surfaces resulted in erosion pits, leading to the oxidation of pyrite. It is possible that the direct mechanism plays the most important role in the oxidation of pyrite. The changes in iron ion concentrations of both the experimental solutions with time suggest that ThiobaciUus ferrooxidans can enhance greatly the oxidation of pyrite.  相似文献   

10.
Pyrite Surface after Thiobacillus ferrooxidans Leaching at 30℃   总被引：4，自引：0，他引：4  
In order to investigate the effect of Thiobacillus ferrooxidans on the oxidation of pyrite, two parallel experiments, which employed H2SO4 solutions and acidic solutions inoculated with Thiobacillus ferrooxidans, were designed and carried out at 30℃. The initial pH of the two solutions was adjusted to 2.5 by dropwise addition of concentrated sulphuric acid. The surfaces of pyrite before exposure to leaching solutions and after exposure to the H2SO4 solutions and acidic solutions inoculated with Thiobacillus ferrooxidans were observed by scanning electron microscopy (SEM). There were a variety of erosion patterns by Thiobacillus ferrooxidans on the bio-leached pyrite surfaces. A conclusion can be drawn that the oxidation of pyrite might have been caused by erosion of the surfaces. Attachment of the bacteria to pyrite surfaces resulted in erosion pits, leading to the oxidation of pyrite. It is possible that the direct mechanism plays the most important role in the oxidation of pyrite. The changes in iron ion concentrations of both the experimental solutions with time suggest that Thiobacillus ferrooxidans can enhance greatly the oxidation of pyrite.  相似文献   

11.
Microbial mat communities host complex biogeochemical processes and play a role in the formation of most carbonate rocks by influencing both carbonate precipitation and dissolution. In this study, the biogeochemistry of microbial mats from the hypersaline Salt Pond, San Salvador, Bahamas are described using scanning electron microscopy, X-ray diffraction, microelectrode profiling, fatty acid methyl esters, and carbon and nitrogen analyses. These microbial mats are distinctly layered both chemically and with regard to composition of microbial community, where significant (?? < 0.05) differences are noted between layers and cores. Furthermore, an oxic upper zone and an H2S-rich lower zone dominate the Salt Pond microbial mats, where H2S concentrations were measured approaching 8 mM. The high H2S concentrations along with the lacking evidence of mineral precipitation in SEM images point to the prevalence of carbonate dissolution. Moreover, the high concentrations of organics (3?C9%) reveal that the mats are self-sourcing and can provide ample fuel to sustain the highly active heterotrophic (both aerobic and anaerobic) metabolism. Seasonal differences in sulfide and oxygen concentrations in Salt Pond mats indicate that the carbonate dissolution and precipitation reactions are dynamic in this hypersaline lake.  相似文献   

12.
The Borra caves, Vishakapatnam, India, can be described as a speleothem cave with significant amounts of unexplored microbial mats in spring waters. Here, we present the first observations and hypotheses on the possible impact of the microorganisms in these mats on the cave formation, focusing on their role on iron mineral precipitation. The spring waters (pH neutral 7.5–7.7) contained dissolved metals like iron and the organic mat sludge (pH 7.0–7.3) had a TOC content of approximately 5.4 wt%. Geochemically, the spring waters deep below the microbial mats contained Fe 369 ppb, Sr 198 ppb; and the organic mat sludge contained Mg 9 ppm, Fe 427 ppb, Zn 149 ppb, Sr 190 ppb. XRD observations displayed Fe minerals (dominantly hematite), minor amounts of zinc gallium sulfide and nitrofuryl compounds. At least four groups of bacteria identified by direct microscopy and SEM-EDX on the basis of morphology could be observed in all samples: Leptothrix-like organisms, entombed bacterial mineral sheaths, a few stalks of Gallionella-like organisms and some additional bacteria that could not be further identified. Leptothrix-like organisms contained 43.22–60.08 wt % Fe and the mineral precipitated near and around these bacteria (in the actual unaltered samples on site) contained 30.76–45.22 wt% Fe as identified and quantified by SEM-EDX. This study indicates that the precipitation of these iron-rich mats in the spring waters could be linked to the presence of abundant active communities of iron precipitating bacteria at Borra caves, Vishakapatanam.  相似文献   

13.
Microbialites (benthic microbial carbonate deposits) were discovered in a hypersaline alkaline lake on Eleuthera Island (Bahamas). From the edge towards the centre of the lake, four main zones of precipitation could be distinguished: (1) millimetre‐sized clumps of Mg‐calcite on a thin microbial mat; (2) thicker and continuous carbonate crusts with columnar morphologies; (3) isolated patches of carbonate crust separated by a dark non‐calcified gelatinous mat; and (4) a dark microbial mat without precipitation. In thin section, the precipitate displayed a micropeloidal structure characterized by micritic micropeloids (strong autofluorescence) surrounded by microspar and spar cement (no fluorescence). Observations using scanning electron microscopy (SEM) equipped with a cryotransfer system indicate that micrite nucleation is initiated within a polymer biofilm that embeds microbial communities. These extracellular polymeric substances (EPS) are progressively replaced with high‐Mg calcite. Discontinuous EPS calcification generates a micropeloidal structure of the micrite, possibly resulting from the presence of clusters of coccoid or remnants of filamentous bacteria. At high magnification, the microstructure of the initial precipitate consists of 200–500 nm spheres. No precipitation is observed in or on the sheaths of cyanobacteria, and only a negligible amount of precipitation is directly associated with the well‐organized and active filamentous cyanobacteria (in deeper layers of the mat), indicating that carbonate precipitation is not associated with CO2 uptake during photosynthesis. Instead, the precipitation occurs at the uppermost layer of the mat, which is composed of EPS, empty filamentous bacteria and coccoids (Gloeocapsa spp.). Two‐dimensional mapping of sulphate reduction shows high activity in close association with the carbonate precipitate at the top of the microbial mat. In combination, these findings suggest that net precipitation of calcium carbonate results from a temporal and spatial decoupling of the various microbial metabolic processes responsible for CaCO3 precipitation and dissolution. Theoretically, partial degradation of EPS by aerobic heterotrophs or UV fuels sulphate‐reducing activity, which increases alkalinity in microdomains, inducing CaCO3 precipitation. This degradation could also be responsible for EPS decarboxylation, which eliminates Ca2+‐binding capacity of the EPS and releases Ca2+ ions that were originally bound by carboxyl groups. At the end of these processes, the EPS biofilm is calcified and exhibits a micritic micropeloidal structure. The EPS‐free precipitate subsequently serves as a substrate for physico‐chemical precipitation of spar cement from the alkaline water of the lake. The micropeloidal structure has an intimate mixture of micrite and microspar comparable to microstructures of some fossil microbialites.  相似文献   

14.
The live and sedimentary components of the flat laminated microbial mat at Laguna Figueroa have been studied since the late sixties. This paper reports the observation and isolation of a variety of micro-organisms, both prokaryotes and eukaryotes. The microbes were taken from the flat laminated mats submerged under at least one meter of water due to the spring rains of 1979 and 1980. Both in situ and enrichment culture observations were made using light and electron microscopic techniques. New strains of the following microbes are reported here: Bacillus megaterium, Bacillus licheniformis, Arthrobacter simplex and Paratetramitus jugosus. Several pseudomonads were isolated, some of which form distinctive subsurface colonial structures. Regular distinctive colony morphologies and desiccation resistant cysts were often observed, several types of which grow to characteristically large sizes and resemble objects found in the pre-Phanerozoic fossil record.Some colonies of manganese oxidizing bacilli and other bacteria are reminiscent of microfossils of the 2 Ga-old Gunflint Iron formation such as Metallogenium, Eosphaera tyleri, Eoastrion and Huronispora. Some manganese oxidizing bacteria form colonial structures that might be mistaken for individual organisms in the tens to hundreds of microns size range. The diversity of microbial structures, including those with preservation potential, must be kept in mind when interpreting the microfossil record.  相似文献   

15.
Methods were developed for stabilizing SO2 in water and gas samples. The pararosaniline colorimetric method, and a gas Chromatographic method using a flame photometric detector specific for sulfur gases were used to assay SO2. Assays were also performed for sulfide, elemental sulfur and sulfate.A large number of acidic, neutral, and alkaline springs in Yellowstone National Park were sampled: SO2 was found in small amounts in most of them. The highest concentration detected in water was 0.5–0.6 μg/ml (expressed as sulfur). Sulfur dioxide was never detected in gases emanating from hot springs, or in fumaroles, although H2S was readily detected. Because of the high solubility of SO2 in water, and its low pK, it is unlikely that environmentally significant quantities are volatilized from geothermal systems of the low-temperature type characteristic of Yellowstone Park. Laboratory studies suggest that in acid waters, ferric iron is the primary oxidant, as H2S is not oxidized by O2 at low pH. At neutral or alkaline pH, O2 is the likely oxidant, because sulfide is oxidized by O2 at these pH values, and neutral and alkaline hot springs are always low in iron. Although bacteria capable of oxidizing sulfide and elemental sulfur are present in most of the springs sampled, it is concluded that the oxidation of reduced sulfur compounds to sulfur dioxide is primarily a chemical process, because of the rapidity with which it occurs and the lack of any evidence that bacteria produce sulfur dioxide.  相似文献   

16.
Siliceous oncoids, up to 4 cm in diameter, are common on the laterally extensive sinter aprons that surround the spectacular geysers and hot springs at El Tatio in northern Chile. Many of these complex oncoids developed close to geyser and spring vents that discharge boiling water. Internally the oncoids, which are composed of precipitated amorphous silica, are formed of complex arrays of spicules and concentric laminae as well as detrital volcanic grains. Spicular growth is dominant in most examples. The formation and growth of the spicules and concentric laminae were mediated by a microbial community which included filamentous microbes, mucus, and possibly bacteria. The microbes and mucus were silicified by replacement and encrustation. In some laminae the filamentous microbes lay parallel to the growth surface; in other laminae most filaments forming the thin mats were suberect. Amorphous silica precipitated between the filaments occluded porosity and commonly disguised the microbial fabric. The oncoids grew on the proximal sinter aprons around the geyser vents and hot spring pools. Most growth took place subaerially with the silica delivered to the precipitation sites by splashing water from the geysers and/or periodic shallow flooding of the discharge aprons. Unlike silica oncoids at other geothermal sites, vertical growth of oncoids that formed in some rimstone pools was not limited by water depth.  相似文献   

17.
Recent studies of continental carbonates revealed that carbonates with similar fabrics can be formed either by biotic, biologically-induced, biologically-influenced or purely abiotic processes, or a combination of all. The aim of this research is to advance knowledge on the formation of carbonates precipitated (or diagenetically altered) in extreme, continental environments by studying biotic versus abiotic mechanisms of crystallization, and to contribute to the astrobiology debate around terrestrial analogues of Martian extreme environments. Both fossil (upper Pleistocene to Holocene) and active carbonate spring mounds from the Great Artesian Basin (South Australia) have been investigated. These carbonates consist of low-Mg to high-Mg calcite tufa. Four facies have been described: (i) carbonate mudstone/wackestone; (ii) phytohermal framestone/boundstone; (iii) micrite boundstone; and (iv) coarsely crystalline boundstone. The presence of filaments encrusted by micrite, rich in organic compounds, including ultraviolet-protectants, in phytohermal framestone/boundstone and micrite boundstone is clear evidence of the existence of microbial mats at the time of deposition. In contrast, peloidal micrite, despite commonly being considered a microbial precipitate, is not directly associated with filaments in the Great Artesian Basin mounds. It has probably formed from nanocrystal aggregation on colloid particulate. Thus, where biofilms have been documented, it is likely that bacteria catalyzed the development of fabrics. It is less certain that microbes induced calcium carbonate precipitation elsewhere. Trace elements, including rare earth element distribution from laminated facies, highlight strongly evaporative settings (for example, high Li contents). Carbon dioxide degassing and evaporation are two of the main drivers for an increase in fluid alkalinity, resulting in precipitation of carbonates. Hence, although the growth of certain fabrics is fostered by the presence of microbial mats, the formation of carbonate crystals might be independent from it and mainly driven by extrinsic factors. More generally, biological processes may be responsible for fabric and facies development in micritic boundstone whilst micrite nucleation and growth are driven by abiotic factors. Non-classical crystallization pathways (aggregation and fusion of nanoparticles from nucleation clusters) may be more common than previously thought in spring carbonate and this should be carefully considered to avoid misinterpretation of certain fabrics as by-products of life. It is proposed here that the term ‘organic-compound catalyzed mineralization’ should be used for crystal growth in the presence of organic compounds when dealing with astrobiological problems. This term would account for the possibility of multiple crystallization pathways (including non-classical crystallization) that occurred directly from an aqueous solution without the direct influence of microbial mats.  相似文献   

18.
Barite (BaSO4) deposits generally arise from mixing of soluble barium-containing fluids with sulfate-rich fluids. While the role of biological processes in modulating barium solubility has been shown, no studies have shown that the biological oxidation of sulfide to sulfate leads to barite deposition. Here we present an example of microbially mediated barite deposition in a continental setting. A spring in the Anadarko Basin of southwestern Oklahoma produces water containing abundant barium and sulfide. As emergent water travels down a stream to a nearby creek, sulfate concentration increases from 0.06 mM to 2.2 mM while Ba2+ concentration drops from 0.4 mM to less than 7 μM. Stable isotope analysis, microbial activity studies, and in situ experiments provide evidence that as sulfide-rich water flows down the stream, anaerobic, anoxygenic, phototrophic bacteria play a dominant role in oxidizing sulfide to sulfate. Sulfate then precipitates with Ba2+ producing barite as travertine, cements, crusts, and accumulations on microbial mats. Our studies suggest that phototrophic sulfide oxidation and concomitant sulfur cycling could prove to be important processes regulating the cycling of barium in continental sulfur-containing systems.  相似文献   

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