Lime mud(i.e.,micrite)is a major component of carbonate deposits.Various mechanisms(biotic versus abiotic)have been proposed for the formation of lime mud in Earth’s history.However,the detailed role that microbes pl...Lime mud(i.e.,micrite)is a major component of carbonate deposits.Various mechanisms(biotic versus abiotic)have been proposed for the formation of lime mud in Earth’s history.However,the detailed role that microbes play in the nucleation and subsequent precipitation of micrites remains to be resolved.Herein we undertook a detailed geobiological characterization of laminated lime mudstone from the Middle Triassic Guanling Formation in Yunnan Province,southwestern China.Morphological features,together with previous geobiological investigations,suggest that the laminated lime mudstones represent the former presence of microbial mats.These lime mudstones consist mainly of calcite,dolomite and quartz,with clay minerals and pyrites as subordinate components.In particular,micro-analysis shows copious nano-globules(65–878 nm)and capsule-shaped nano-rods in laminations.These low-Mg calcite nano-globule aggregates are closely associated with mucilaginous biofilms resembling extracellular polymeric substances(EPS).Nano-sized globules coalesce to form semi-euhedral micrite crystals.We suggest that a decaying hydrolytic destruction of the EPS by microbial communities within microbial mat leads to the precipitation of the nano-globules by enhancing alkalinity in local micro-environment.As an intermediate,these nano-globules further aggregate to form micrite crystals possibly through a dissolution-reprecipitation process.展开更多
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 deposi...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.展开更多
The well-preserved Mesoproterozoic succession in the North China platform consists mainly of three iithological associations including peritidal quartz sandstone, shallow marine and lagoonal dark to black shales, and ...The well-preserved Mesoproterozoic succession in the North China platform consists mainly of three iithological associations including peritidal quartz sandstone, shallow marine and lagoonal dark to black shales, and shallow epeiric carbonates, with a total thickness of up to 8 000 m. In addition to well-documented microplants, macroalgae, and microbial buildups, abundant microbially induced sedimentary structures （MISS） and mat-related sediments have been recognized in these rocks. Intensive microbial mat layers and MISS are especially well preserved in the carbonates of the upper Gaoyuzhuang （高于庄） （ca. 1.5 Ga） and lower Wumishan （雾迷山） （ca. 1.45 Ga） formations, indicating diversified microbial activities and a high organic production. In these petrified biomats, putative microbial fossils （both coccoidal and filamentous） and framboidal pyrites have been identified. The abundance of authigenic carbonate minerals in the host rocks, such as, acicular aragonites, rosette barites, radial siderites, ankerites, and botryoidal carbonate cements, suggests authigenic carbonate precipitation from anaerobic oxidation of methane （AOM） under anoxic/euxinic conditions. Warm climate and anoxic/euxinic conditions in the Mesoproterozoic oceans may have facilitated high microbial productivity and organic burial in sediments. Although authigenic carbonate cements may record carbonate precipitation from anaerobic methane oxidation, gas blister （or dome） structures may indicate gas release from active methanogenesis during shallow burial. Bituminous fragments in mat-related carbonates also provide evidence for hydrocarbon generation. Under proper conditions, the Mesoproterozoic mat-rich carbonates will have the potential for hydrocarbon generation and serve as source rocks. On the basis of petrified biomats, a rough estimation suggests that the Mesoproterozoic carbonates of the North China platform might have a hydrocarbon production potential in the order of 10 ×10^8 t.展开更多
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（F...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.展开更多
A wide spectrum of macroscopic and microscopic features preserved on the bedding planes or frozen between the laminations of fine-to medium-grained sandstones are described from a number of stratigraphically and geogr...A wide spectrum of macroscopic and microscopic features preserved on the bedding planes or frozen between the laminations of fine-to medium-grained sandstones are described from a number of stratigraphically and geographically separated localities within the Chhattisgarh(Bhalukona and Kansapathar Formations)and Khariar basins(Lower sandstone Formation),India and attributed to microbial mat related sedimentary structures.These include bedding plane features viz.wrinkle structures,palimpsest and patchy ripples,spindle-shaped and sub-circular microbial shrinkage cracks indicating original cohesiveness in sand-sized sediments,fragments of torn mat spread on bed surface suggesting mat erosion under high energy flow etc.and bed-perpendicular features e.g.wavy-crinkly laminae,iron oxide specks and stringers etc.The structures suggest different mat-induced biophysical interactions viz.growth,biostabilisation,binding,baffling and trapping or a combination of all.Mat growth also favoured preservation of setulf structure that usually has low preservation potential.The stratigraphic intervals from where the structures are described are assigned Mesoproterozoic time frame(~1.4 Ga)and modelled as products of near-shore environment i.e.wave-influenced shoreface-beach under widely different sea level stands viz.forced regression,low-stand and transgression.It is proposed that prolific mat growth may act as facilitator for preservation of thin forced regressive deposits in Proterozoic low-gradient epeiric basins.展开更多
A stretch of the modern hypersaline coastal plain of the Gulf of Cambay was chosen to examine the distribution of the microbial mat-related structures(MRS) on siliciclastic sediments in the intertidal and supratidal z...A stretch of the modern hypersaline coastal plain of the Gulf of Cambay was chosen to examine the distribution of the microbial mat-related structures(MRS) on siliciclastic sediments in the intertidal and supratidal zones.The abundance of MRS increases from the lower intertidal zone to the upper supratidal zone while the type of MRS records a systematic change.While the lower intertidal zone exhibits wrinkle structures,sieve-like surfaces and patchy ripples in places,the upper intertidal zone exhibits diverse MRS related to reduced current activity on the mat layer and intermittent exposure.MRS in the upper intertidal zone include wrinkle structures,sieve-like surfaces,gas domes,reticulated surfaces,multi-directional ripples,patchy ripples,rolled-up mat fragments,setulfs and occasional petee ridges and cracked mat surfaces.The lower supratidal zone is characterized by increased occurrence of petee ridges,gas domes and cracked mat surfaces compared to the upper intertidal zone.The upper supratidal zone is distinguished by the presence of abundant cracked mat surfaces,petee ridges,gas domes and wrinkle structures.The presence of cm-scale,disc-shaped microbial colonies(DMC) with a variety of internal structures is a unique feature of the Gulf of Cambay study area.While wrinkle structures occur in all the coastal zones,setulfs occur close to the boundary between the upper intertidal and lower supratidal zones.An attempt has been made to compare the distribution of MRS in this modern environment with those in the ~1.6 Ga Chorhat Sandstone of the Vindhyan Supergroup for high-resolution palaeoenvironmental interpretation.The upper part of the intertidal segment of the Chorhat Sandstone is distinguished from its lower part by the presence of abundant cracked mat surfaces,petee ridges and gas domes in the former,while wrinkle structures,Kinneyia,rolled-up mat fragments,patchy ripples and multi-directional ripples are equally abundant in both parts.The lower part of the intertidal segment of the Chorhat Sandstone is thus analogous to the upper intertidal zone of the modern Gulf of Cambay environment,while the upper part of the Chorhat intertidal segment reflects prolonged exposure close to the high tide line.The bottom-most part of the intertidal segment of the Chorhat Sandstone with fewer MRS corresponds to the lower intertidal zone at Cambay.Inferred disc-shaped microbial fossils within Vindhyan sandstones are analogous to the DMC found in the modern environment and these features do not have any biostratigraphic implication.展开更多
Microbes had been the sole occupant of the early biosphere and they strongly controlled the evolution of lithosphere,hydrosphere,biosphere and atmosphere.Many Microbes could form mat like structure on sea floor.During...Microbes had been the sole occupant of the early biosphere and they strongly controlled the evolution of lithosphere,hydrosphere,biosphere and atmosphere.Many Microbes could form mat like structure on sea floor.During the Precambrian these microbial mats had a strong influence on sedimentation,and they facilitated the formation of a variety of mat-induced sedimentary structures(MRS/MISS)in siliciclastic and carbonate rocks.展开更多
A striking feature of the Mongolian plateau is the wide range of air temperatures during a year, -30 to 30~C. High summer temperatures, atmospheric weathering and the arid climate lead to formation of numerous alkalin...A striking feature of the Mongolian plateau is the wide range of air temperatures during a year, -30 to 30~C. High summer temperatures, atmospheric weathering and the arid climate lead to formation of numerous alkaline soda lakes that are covered by ice during 6-7 months per year. During the study period, the lakes had pH values between 8.1 to 10.4 and salinity between 1.8 and 360 g/L. According to chemical composition, the lakes belong to sodium carbonate, sodium chloride-carbonate and sodium sulfate-carbonate types. This paper presents the data on the water chemical composition, results of the determination of the rates of microbial processes in microbial mats and sediments in the lakes studied, and the results of a Principal Component Analysis of environmental variables and microbial activity data. Temperature was the most important factor that influenced both chemical composition and microbial activity, pH and salinity are also important factors for the microbial processes. Dark CO2 fixation is impacted mostly by salinity and the chemical composition of the lake water. Total photosynthesis and sulfate-reduction are impacted mostly by pH. Photosynthesis is the dominant process of primary production, but the highest rate （386 mg C/（L.d）） determined in the lakes studied were 2-3 times lower than in microbial mats of lakes located in tropical zones. This can be explained by the relatively short warm period that lasts only 3-4 months per year. The highest measured rate of dark CO2 assimilation （59.8 mg C/（L·d）） was much lower than photosynthesis. The highest rate of sulfate reduction was 60 mg S/（L·d）, while that of methanogenesis was 75.6 μL CH4/（L·d） in the alkaline lakes of Mongolian plateau. The rate of organic matter consumption during sulfate reduction was 3-4 orders of magnitude higher than that associated with methanogenesis.展开更多
基金supported by the Chinese Academy of Sciences(No.XDB26000000)the CAS Pioneer Hundred Talents Program(No.2018-039)+2 种基金the CAS Open Fund(No.193110)the National Natural Science Foundation of China(Nos.41830323,41930322)the Key Research Program of Frontier Sciences,CAS(No.QYZDY-SSWDQC023)。
文摘Lime mud(i.e.,micrite)is a major component of carbonate deposits.Various mechanisms(biotic versus abiotic)have been proposed for the formation of lime mud in Earth’s history.However,the detailed role that microbes play in the nucleation and subsequent precipitation of micrites remains to be resolved.Herein we undertook a detailed geobiological characterization of laminated lime mudstone from the Middle Triassic Guanling Formation in Yunnan Province,southwestern China.Morphological features,together with previous geobiological investigations,suggest that the laminated lime mudstones represent the former presence of microbial mats.These lime mudstones consist mainly of calcite,dolomite and quartz,with clay minerals and pyrites as subordinate components.In particular,micro-analysis shows copious nano-globules(65–878 nm)and capsule-shaped nano-rods in laminations.These low-Mg calcite nano-globule aggregates are closely associated with mucilaginous biofilms resembling extracellular polymeric substances(EPS).Nano-sized globules coalesce to form semi-euhedral micrite crystals.We suggest that a decaying hydrolytic destruction of the EPS by microbial communities within microbial mat leads to the precipitation of the nano-globules by enhancing alkalinity in local micro-environment.As an intermediate,these nano-globules further aggregate to form micrite crystals possibly through a dissolution-reprecipitation process.
基金co-supported by the National Key Project on Basic Research(2011CB403006)the Special Fund for Scientific Research of Central-leveled Academy(K2007-3-2)National Geological Survey(1212010818057,1212011120046)
文摘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.
基金supported by the SINOPEC project (G0800-06-ZS-319)the National Natural Science Foundation of China (No. 40621002)the Ministry of Education of China (IRT00546, B0711)
文摘The well-preserved Mesoproterozoic succession in the North China platform consists mainly of three iithological associations including peritidal quartz sandstone, shallow marine and lagoonal dark to black shales, and shallow epeiric carbonates, with a total thickness of up to 8 000 m. In addition to well-documented microplants, macroalgae, and microbial buildups, abundant microbially induced sedimentary structures （MISS） and mat-related sediments have been recognized in these rocks. Intensive microbial mat layers and MISS are especially well preserved in the carbonates of the upper Gaoyuzhuang （高于庄） （ca. 1.5 Ga） and lower Wumishan （雾迷山） （ca. 1.45 Ga） formations, indicating diversified microbial activities and a high organic production. In these petrified biomats, putative microbial fossils （both coccoidal and filamentous） and framboidal pyrites have been identified. The abundance of authigenic carbonate minerals in the host rocks, such as, acicular aragonites, rosette barites, radial siderites, ankerites, and botryoidal carbonate cements, suggests authigenic carbonate precipitation from anaerobic oxidation of methane （AOM） under anoxic/euxinic conditions. Warm climate and anoxic/euxinic conditions in the Mesoproterozoic oceans may have facilitated high microbial productivity and organic burial in sediments. Although authigenic carbonate cements may record carbonate precipitation from anaerobic methane oxidation, gas blister （or dome） structures may indicate gas release from active methanogenesis during shallow burial. Bituminous fragments in mat-related carbonates also provide evidence for hydrocarbon generation. Under proper conditions, the Mesoproterozoic mat-rich carbonates will have the potential for hydrocarbon generation and serve as source rocks. On the basis of petrified biomats, a rough estimation suggests that the Mesoproterozoic carbonates of the North China platform might have a hydrocarbon production potential in the order of 10 ×10^8 t.
基金supported by the National Natural Science Foundation of China(Grant No.40532011,40403004,and 40473032).
文摘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.
文摘A wide spectrum of macroscopic and microscopic features preserved on the bedding planes or frozen between the laminations of fine-to medium-grained sandstones are described from a number of stratigraphically and geographically separated localities within the Chhattisgarh(Bhalukona and Kansapathar Formations)and Khariar basins(Lower sandstone Formation),India and attributed to microbial mat related sedimentary structures.These include bedding plane features viz.wrinkle structures,palimpsest and patchy ripples,spindle-shaped and sub-circular microbial shrinkage cracks indicating original cohesiveness in sand-sized sediments,fragments of torn mat spread on bed surface suggesting mat erosion under high energy flow etc.and bed-perpendicular features e.g.wavy-crinkly laminae,iron oxide specks and stringers etc.The structures suggest different mat-induced biophysical interactions viz.growth,biostabilisation,binding,baffling and trapping or a combination of all.Mat growth also favoured preservation of setulf structure that usually has low preservation potential.The stratigraphic intervals from where the structures are described are assigned Mesoproterozoic time frame(~1.4 Ga)and modelled as products of near-shore environment i.e.wave-influenced shoreface-beach under widely different sea level stands viz.forced regression,low-stand and transgression.It is proposed that prolific mat growth may act as facilitator for preservation of thin forced regressive deposits in Proterozoic low-gradient epeiric basins.
文摘A stretch of the modern hypersaline coastal plain of the Gulf of Cambay was chosen to examine the distribution of the microbial mat-related structures(MRS) on siliciclastic sediments in the intertidal and supratidal zones.The abundance of MRS increases from the lower intertidal zone to the upper supratidal zone while the type of MRS records a systematic change.While the lower intertidal zone exhibits wrinkle structures,sieve-like surfaces and patchy ripples in places,the upper intertidal zone exhibits diverse MRS related to reduced current activity on the mat layer and intermittent exposure.MRS in the upper intertidal zone include wrinkle structures,sieve-like surfaces,gas domes,reticulated surfaces,multi-directional ripples,patchy ripples,rolled-up mat fragments,setulfs and occasional petee ridges and cracked mat surfaces.The lower supratidal zone is characterized by increased occurrence of petee ridges,gas domes and cracked mat surfaces compared to the upper intertidal zone.The upper supratidal zone is distinguished by the presence of abundant cracked mat surfaces,petee ridges,gas domes and wrinkle structures.The presence of cm-scale,disc-shaped microbial colonies(DMC) with a variety of internal structures is a unique feature of the Gulf of Cambay study area.While wrinkle structures occur in all the coastal zones,setulfs occur close to the boundary between the upper intertidal and lower supratidal zones.An attempt has been made to compare the distribution of MRS in this modern environment with those in the ~1.6 Ga Chorhat Sandstone of the Vindhyan Supergroup for high-resolution palaeoenvironmental interpretation.The upper part of the intertidal segment of the Chorhat Sandstone is distinguished from its lower part by the presence of abundant cracked mat surfaces,petee ridges and gas domes in the former,while wrinkle structures,Kinneyia,rolled-up mat fragments,patchy ripples and multi-directional ripples are equally abundant in both parts.The lower part of the intertidal segment of the Chorhat Sandstone is thus analogous to the upper intertidal zone of the modern Gulf of Cambay environment,while the upper part of the Chorhat intertidal segment reflects prolonged exposure close to the high tide line.The bottom-most part of the intertidal segment of the Chorhat Sandstone with fewer MRS corresponds to the lower intertidal zone at Cambay.Inferred disc-shaped microbial fossils within Vindhyan sandstones are analogous to the DMC found in the modern environment and these features do not have any biostratigraphic implication.
文摘Microbes had been the sole occupant of the early biosphere and they strongly controlled the evolution of lithosphere,hydrosphere,biosphere and atmosphere.Many Microbes could form mat like structure on sea floor.During the Precambrian these microbial mats had a strong influence on sedimentation,and they facilitated the formation of a variety of mat-induced sedimentary structures(MRS/MISS)in siliciclastic and carbonate rocks.
基金Supported by the Ministry of Education and Science of the Russian Federation(No.1990)the Russian Foundation for Basic Research(No.13-04-00646)the Presidium of the Russian Academy of Sciences Program No.28"Biosphere Origin and Evolution"
文摘A striking feature of the Mongolian plateau is the wide range of air temperatures during a year, -30 to 30~C. High summer temperatures, atmospheric weathering and the arid climate lead to formation of numerous alkaline soda lakes that are covered by ice during 6-7 months per year. During the study period, the lakes had pH values between 8.1 to 10.4 and salinity between 1.8 and 360 g/L. According to chemical composition, the lakes belong to sodium carbonate, sodium chloride-carbonate and sodium sulfate-carbonate types. This paper presents the data on the water chemical composition, results of the determination of the rates of microbial processes in microbial mats and sediments in the lakes studied, and the results of a Principal Component Analysis of environmental variables and microbial activity data. Temperature was the most important factor that influenced both chemical composition and microbial activity, pH and salinity are also important factors for the microbial processes. Dark CO2 fixation is impacted mostly by salinity and the chemical composition of the lake water. Total photosynthesis and sulfate-reduction are impacted mostly by pH. Photosynthesis is the dominant process of primary production, but the highest rate （386 mg C/（L.d）） determined in the lakes studied were 2-3 times lower than in microbial mats of lakes located in tropical zones. This can be explained by the relatively short warm period that lasts only 3-4 months per year. The highest measured rate of dark CO2 assimilation （59.8 mg C/（L·d）） was much lower than photosynthesis. The highest rate of sulfate reduction was 60 mg S/（L·d）, while that of methanogenesis was 75.6 μL CH4/（L·d） in the alkaline lakes of Mongolian plateau. The rate of organic matter consumption during sulfate reduction was 3-4 orders of magnitude higher than that associated with methanogenesis.
