绪论:化石藻类和叠层石

本专辑是第 7届国际化石藻类学术讨论会的产物。该次会议于 1 999年 1 0月 1 3 - 1 7日在南京召开。前 6届学术讨论会相继在德国爱尔兰根 (1 975 ) ,法国巴黎 (1 979) ,美国丹佛 (1 983 ) ,英国卡的夫(1 987) ,意大利卡普里 (1 991 )和土耳其安卡拉(1 995 )召开。本次会议除了学术报告会以外 ,还安排了会前会后地质旅行 ,会前旅行参观山东济南崮山中寒武统张夏组标准剖面的钙质微生物礁 ,会后参观广西桂林泥盆纪生物礁及藻类和微生物组合。本专辑收录了 1 2篇论文。虽然大部分论文著者都在会议上作了学术报告 ,但后来著者在本专辑中发表的论…     

中国叠层石研究的历史和现状

中国前寒武纪地层分布广泛。在20世纪70-80年代,中国学者对晚前寒武纪的叠层石进行了系统的研究,描述了类型众多的叠层石属种,并把叠层石组合应用于地层的划分和对比。近年来,为了揭示叠层石的形态发生,中国学者正在探讨硅质叠层石的生物组构模式和叠层石微层理的成因,以及叠层石中微生物生长、运动和造席过程。     

岩溶洞穴叠层石

岩溶洞穴叠层石系藻类等生物在洞穴弱光带富含钙质的岩溶水中,通过粘结捕获或同化作用沉淀碳酸盐面形成。油穴叠层石均显示双层叠置构造,即背光浅色层和向光深色层,并由细密纹层组成,。向光深色层疏松多孔,表面粗糙可见生物体;背光浅色层致密,表面光滑。因生长微环境的变化,其形态可分为３类：倾斜型,直立型和坝型。     

再论假裸枝叠层石科

概要地介绍了假裸枝科叠层石的特征、分布时限、分类系统、研究方法和形成环境.提出该科叠层石有可能作为我国中元古代乃至蓟县系叠层石标志的意见.     

中国叠层石新属（群）索引

索引材料取自１９６２－１９９４年期间在国内外各种期刊和专著上公开发表过的叠层石文献资料,共录中国学者所创立的叠层石新属１３１个,其中元古宙为１２２个,古生代为６个,中生代为３个,为了统一描述规范,统一对叠层石性状在分类中作用的认识,招集整理中国学者建立的叠层新属,建立中国叠层石数据库,提出了第一批中国叠层石属的索引名单。     

宁夏中上元古界的叠层石

本文描述的叠层石标本采自宁夏北部平罗县王全口剖面,中部同心县青龙山剖面和南部固原县闵家沟剖面(插图1)。这些剖面的叠层石大多未经正式描述,有关名称仅见于某些论     

宁夏中上元古界的叠层石

本文描述的叠层石标本采自宁夏北部平罗县王全口剖面,中部同心县青龙山剖面和南部固原县闵家沟剖面(插图1)。这些剖面的叠层石大多未经正式描述,有关名称仅见于某些论     

徐淮地区新元古代叠层石组合

徐淮地区新元古代海相碳酸盐岩地层分布广泛,其中由微生物生命活动形成的叠层石十分发育,构成了各种形态及规模的礁体,文内拟就该区地层序列中叠层石组合及其演变过程,讨论其环境的变迁及区域地层对比,根据徐淮地区叠层石组合的层位分布特点,可划分为3个亚组合,自上而下分别为：亚组合I,星散分布于贾园组,赵圩组及九里桥组,以Baicalia,Jurusania,Inzeria,Crassphloem,Grmnosolen及Stratifera为特征,形成小型点礁和生物丘,亚组合Ⅱ。广泛分布于倪园组,九顶山组,张渠组,魏集组,史家组,望山组及四顶山组,包括Conophyton,Jacutophyton,Acaciella,Baicalia,Jurusania,Linella,Tungussia,Anabaria,Minjaria,Katavia,Gymnosolen,Colonnella及Stratifera等多种类型,建造起巨大而复杂的堡礁,堤礁,斑礁,环礁及生物丘／层,亚组合Ⅲ,仅见于金山寨组,以Boxonia,Xiehiella及Anabaria为主,构成中型的点礁及生物丘,这套叠层石组合面貌,造礁规模及多样化程度说明,它们显然形成于新元古代大冰期之前的叠层石繁盛期,其层位大致可与我国华北及东北青白口系上部,俄罗斯上里菲系及澳大利亚苦泉组的叠层石组合对比。     

苏,皖北部震旦纪叠层石及其沉积环境学意义

根据苏、皖北部震旦纪叠层石的外形、大小、颜色及纹层特征,结合其它沉积构造特征,探讨水体能量、光照及沉积作用等环境因素对叠层石生长的影响,以此找出叠层石上具有指相意义的某些生态学特征。目前发现,大型层状、层柱状叠层石往往与浅水低能沉积物共生;分叉不发育的大、中型柱状叠层石则与具周期性变化的浅水高能沉积物共生;分叉发育的柱状叠层石与变化不定的浅水高能沉积物共生;平行分叉的小型柱状叠层石则与中-次中等能量沉积物共生。值得注意的是,环境的变化使一些叠层石形态也随之变异,形成一系列过渡类型,引起分类上的混淆。叠层石纹层表面积与水深往往成反比梯变,这也许与藻席受光照的充足程度有关。叠层石及其围岩的原生色也可作为了解当时水体化学性质及生物对矿物的富集作用的线索。     

Microbial Communities and Exopolysaccharides from Polynesian Mats

Microbial mats present in two shallow atolls of French Polynesia were characterized by high amounts of exopolysaccharides associated with cyanobacteria as the predominating species. Cyanobacteria were found in the first centimeters of the gelatinous mats, whereas deeper layers showing the occurrence of the sulfate reducers Desulfovibrio and Desulfobacter species as determined by the presence of specific biomarkers. Exopolysaccharides were extracted from these mats and partially characterized. All fractions contained both neutral sugars and uronic acids with a predominance of the former. The large diversity in monosaccharides can be interpreted as the result of exopolymer biosynthesis by either different or unidentified cyanobacterial species. Received July 25, 2000; accepted October 21, 2000     

ANTARCTIC CYANOBACTERIA: LIGHT,NUTRIENTS, AND PHOTOSYNTHESIS IN THE MICROBIAL MAT ENVIRONMENT1

The microenvironmental and photosynthetic characteristics of Antarctic microbial mats were measured in a series of ponds near McMurdo Sound. As elsewhere in Antarctica, these cold-water benthic communities were dominated by oscillatoriacean cyanobacteria. Despite large variations in mat thickness, surface morphology, and color, all of the communities had a similar pigment organization, with a surface carotenoid-rich layer that overlaid a deep chlorophyll maximum (DCM) enriched in phycocyanin as well as chlorophyll a. Spectroradiometric analyses showed that the DCM population inhabited an orange-red shade environment. In several of the mats, the deep-living trichomes migrated up to the surface of the mat within 2 h in response to a 10-fold decrease in surface irradiance. The euphotic layer of the mats was supersaturated in oxygen and contained ammonium and dissolved reactive phosphorus concentrations in excess of 100 mg N·m^?3 or P·m^?3. Integral photosynthesis by core samples was saturated at low irradiances and varied two- to threefold throughout the continuous 24-h radiation cycle. Oxygen microelectrode analyses showed that the photosynthetic rates were slow to negligible near the surface and maximal in the DCM. These compressed, nutrient-rich euphotic zones have some properties analogous to planktonic systems, but the integrated photosynthetic responses of the community reflect the strong self-shading within the mat and physiological dominance by the motile, DCM populations.     

Characterization of Microbial Mats from a Siliciclastic Tidal Flat (Bahía Blanca Estuary,Argentina)

Biofilms and microbial mats cover the tidal flats of the central zone of the Bahía Blanca estuary (Argentina), creating extensive layers. The objective of this study was to characterize the microphytobenthic communities in these biofilms and mats from sediment cores taken in March, June, September and December 2010. Microorganisms were identified and enumerated by microscopy, and their biomass (chlorophyll a, biovolume) quantified at two different stations in the lower supratidal zone, located ～210 m apart from each other (namely S1 and S2). Additionally, the colloidal carbohydrates produced by these microbial communities were quantified, together with physical parameters such as temperature, granulometry, moisture and organic matter content of the sediment layers that comprise a typical epibenthic mat. On the other hand, changes in biomass and colloidal carbohydrate content were studied through a half-tidal cycle (7 h). There were significant seasonal differences in microphytobenthic biovolume (P < 0.001) with a considerably lower biomass in summer, but no significant differences in microalgal biovolume between stations (P = 0.454). Cyanobacterial biomass (largely composed of the filamentous Microcoleus chthonoplastes) was dominant on all dates at both stations, followed by pennate diatoms. Chlorophyll a and colloidal carbohydrate contents in sediment presented a similar pattern to that of microalgal biovolume; with a 5-fold variation in chlorophyll a for S1 between consecutive sampling events on September and December. There were significant differences between sampling dates in colloidal carbohydrates (P < 0.001) with the lowest values recorded during fall and winter; conversely there were no significant differences between stations (P = 0.324). Silt was the dominant sediment fraction at S1 while sand dominated throughout the uppermost 20 mm at S2. Chlorophyll a contents did not show significant differences throughout a half-tidal cycle, likely the product of vertical migration along the section sampled. Conversely, the content of colloidal carbohydrates varied 5-fold, showing a significant (P < 0.001) and steady increase with time of exposure to air and pointing to the rapid metabolic rates of the community. In conclusion, the microphytobenthic community of the Bahía Blanca estuary presented marked seasonality in its biological parameters and overall physiognomy, also showing elevated metabolic rates when subject to tidal fluctuations.     

Characteristics of oligotrophic hardwater lakes in a postglacial land-rise area in mid-Sweden

1. We describe some remarkable ephemeral, oligotrophic hardwater lakes formed because of land rise in the coastal areas of the Baltic Sea, that are unique in Sweden and probably also worldwide. Two younger, coastal lakes were studied by regular sampling for 1 year and compared with an older (i.e. greater altitude) lake, that passed through the oligotrophic hardwater stage some 3–4000 years ago. 2. Despite some differences in composition of the catchment, the two younger lakes were similar with regard to water chemistry and plankton community composition. The concentration of phosphorus was low while nitrogen was high, resulting in very high N/P quotients (101 and 131). Although water colour was moderate, the concentration of organic carbon was extremely high (average values of ≥ 20 μg TOC L^–1), consisting mainly of dissolved compounds (DOC). 3. While the plankton was poorly developed, sediments in both lakes were covered by a layer of photosynthesising micro‐organisms. This substantial `microbial mat', which has not been described in detail before, was up to 15 cm thick and dominated by cyanobacteria and purple sulphur bacteria. The concentration of sediment phosphorus was extremely low (352 μg g^–1 dw) in one of the lakes and dominated by organic‐bound (residual) phosphorus. 4. Deep sediments in the older lake, representing its oligotrophic hardwater period, differed in phosphorus composition from the currently oligotrophic hardwater lakes by having a strong dominance of HCl‐extractable (Ca‐bound) phosphorus. This indicates that phosphorus, initially organic‐bound within the microbial mat, is subsequently bound to calcium. We hypothesise that this is promoted by the environmental conditions created by the benthic photosynthetic activity, in combination with the prevailing hardwater conditions. 5. The rich and flourishing microbial community on the sediments may also explain the high concentration of DOC in the lake.     

Biogeographical distribution and ecological ranges of benthic cyanobacteria in East Antarctic lakes

For the first time, the cyanobacterial diversity from microbial mats in lakes of Eastern Antarctica was investigated using microscopic and molecular approaches. The present study assessed the biogeographical distribution of cyanobacteria in Antarctica. Five samples were taken from four lakes spanning a range of different ecological environments in Larsemann Hills, Vestfold Hills and Rauer Islands to evaluate the influence of lake characteristics on the cyanobacterial diversity. Seventeen morphospecies and 28 16S rRNA gene-based operational taxonomic units belonging to the Oscillatoriales, Nostocales and Chroococcales were identified. The internal transcribed spacer was evaluated to complement the 16S rRNA gene data and showed similar but more clear-cut tendencies. The molecular approach suggested that potential Antarctic endemic species, including a previously undiscovered diversity, are more abundant than has been estimated by morphological methods. Moreover, operational taxonomic units, also found outside Antarctica, were more widespread over the continent than potential endemics. The cyanobacterial diversity of the most saline lakes was found to differ from the others, and correlations between the sampling depth and the cyanobacterial communities can also be drawn. Comparison with database sequences illustrated the ubiquity of several cyanobacterial operational taxonomic units and their remarkable range of tolerance to harsh environmental conditions.     

SALINITY-DEPENDENT LIMITATION OF PHOTOSYNTHESIS AND OXYGEN EXCHANGE IN MICROBIAL MATS

We used benthic flux chambers and microsensor profiling under standardized incubation conditions to compare the short-term (hours) and long-term (days) functional responses to salinity in eight different hypersaline microbial mats. The short-term response of productivity to changes in salinity was specific for each community and in accordance with optimal performance at the respective salinity of origin. This pattern was lost after long-term exposure to varying salinities when responses to salinity were found to approach a general pattern of decreasing photosynthesis and oxygen exchange capacity with increasing salinity. Exhaustive measurements of oxygen export in the light, oxygen consumption in the dark and gross photosynthesis indicated that a salinity-dependent limitation of all three parameters occurred. Maximal values for all three parameters decreased exponentially with increasing salinity; exponential decay rates (base 10) were around 4–5 mL·g⁻¹. The values of mats in steady state with respect to salinity tended to approach this salinity-dependent limit. On the basis of environmental and ecophysiological data, we argue that this limitation was not caused directly by salinity effects on the microorganisms. Rather, the decreasing diffusive supply of O₂ in the dark and the increasing diffusion barriers to O₂ escape in the light, which intensify with increasing salinity, were likely responsible for the salinity-dependent limitations observed.     

Ultraviolet Radiation-Absorbing “Humic Pigments” of Cyanobacteria in Microbial Mats: Their Presumptive Photoprotective Function and Relevance to Early Precambrian Microbial Ecology and Evolution

Cyanobacteria that form the primary components of microbial mats in freshwater bogs and intertidal marine environments in the Bahamas produce water-soluble brown pigments whose spectral properties imply that they are a type of humic acid. These “humic pigments” are produced by vital processes of living cyanobacteria, not by decomposition of dead ones, as shown by decreases in the concentrations of humic pigments, ultraviolet (UV) radiation-absorbing photoprotective mycosporine-like amino acids (MAAs), and chlorophyll from upper to lower layers of the mats, and by the occurrence of humic pigments in cyanobacterial cultures. Unlike MAAs, which absorb UV radiation only within limited ranges of wavelengths, humic pigments absorb radiation spanning the entire UV spectrum, and absorbance increases with decreasing wavelength. These observations suggest that the biosynthesis of humic pigments originated as a photoprotective adaptation in the early Precambrian, enabling cyanobacteria to colonize shallow-water and terrestrial environments even though the atmosphere was virtually devoid of O₂ and O₃ and therefore transparent to all solar radiation in the UV region of the spectrum. Moreover, the evolution of this photoprotective mechanism may have been linked to the evolution of photosynthesis.     

Biogeochemical processes in the algal-bacterial mats of the Urinskii alkaline hot spring

The structure and production characteristics of microbial communities from the Urinskii alkaline hot spring (Buryat Republic, Russia) have been investigated. A distinctive characteristic of this hot spring is the lack of sulfide in the issuing water. The water temperature near the spring vents ranged from 69 to 38.5°C and pH values ranged from 8.8 to 9.2. The total mineralization of water was less than 0.1 g/liter. Temperature has a profound effect on the species composition and biogeochemical processes occurring in the algal-bacterial mats of the Urinskii hot spring. The maximum diversity of the phototrophic community was observed at the temperatures 40 and 46°C. A total of 12 species of cyanobacteria, 4 species of diatoms, and one species of thermophilic anoxygenic phototrophic bacteria, Chloroflexus aurantiacus, have been isolated from mat samples. At temperatures above 40°C, the filamentous cyanobacterium Phormidium laminosum was predominant; its cell number and biomass concentration comprised 95.1 and 63.9%, respectively. At lower temperatures, the biomass concentrations of the cyanobacterium Oscillatoria limosa and diatoms increased (50.2 and 36.4%, respectively). The cyanobacterium Mastigocladus laminosus, which is normally found in neutral or slightly acidic hydrothermal systems, was detected in microbial communities. As the diatom concentration increases, so does the dry matter concentration in mats, while the content of organic matter decreases. The concentrations of proteins and carbohydrates reached their maximum levels at 45–50°C. The maximum average rate of oxygenic photosynthesis [2.1 g C/(m² day)], chlorophyll a content (343.4 mg/m²), and cell number of phototrophic microorganisms were observed at temperatures from 45 to 50°C. The peak mass of bacterial mats (56.75 g/m²) occurred at a temperature of 65–60°C. The maximum biomass concentration of phototrophs (414.63 × 10^?6 g/ml) and the peak rate of anoxygenic photosynthesis [0.42 g C/(m² day)] were observed at a temperature of 35–40°C.