growth patterns and implications of complex dendrites in calcite travertines from lýsuholl snaefellsnes iceland calcite dendrite crystals are important but poorly understood components of calcite travertine that forms around many hot springs the l suholl hot spring deposits located in western iceland are formed primarily of siliceous sinters that were precipitated around numerous springs that are now inactive calcite travertine formed around the vent and on the discharge apron of one of the springs at the northern edge of the area the travertine is formed largely of two types i and ii of complex calcite dendrite crystals up to 1 cm high that grew through the gradual addition of trilete sub crystals the morphology of the dendrite crystals was controlled by flow direction and the competition for growth space with neighbouring crystals densely crowded dendrites with limited branching characterize the rimstone dams whereas widely spaced dendrites with open branching are found in the pools many dendrite bushes in the pools nucleated around plant stems growth of the dendrite crystals was seasonal and incremental calcite precipitation was driven by rapid co2 degassing of co2 rich spring waters during the spring and summer during winter when snow covered the ground and temperatures were low opal a precipitated on the exposed surfaces of the dendrites segmentation of dendrite branches by discontinuities coated with opal a and overgrowth development around sub crystals resulted from this seasonal growth cycle the calcite dendrite crystals in the l suholl travertine differ in morphology from those at other hot springs such as those at lake bogoria kenya and waikite in new zealand comparison with the calcite dendrite crystals found at those sites shows that dendrite morphology is site specific and probably controlled by carbonate saturation levels that in turn are controlled by the rate of co2 degassing and location in the spring outflow system

speleothems in a wave cut notch cayman brac british west indies the integrated product of subaerial precipitation dissolution and microbes abstract a wave cut notch that is deeply incised into the vertical cliff faces of cayman brac is adorned with stalactites stalagmites and columns the prefix notch is applied to each type of speleothem in order to distinguish them from cave speleothems these speleothemic deposits must have formed since the highstand 125 000 years ago which was responsible for the development of the notch the laminated notch speleothems are formed largely of aragonite small and large crystals and calcite columnar fiber and grain coating mats along with minor amounts of dolomite a mg si precipitate kerolite gypsum and halite laminae typically the notch speleothems are the integrated product of precipitation and dissolution that was in some places microbially mediated interpretations based on their mineralogy and internal structures indicate that the composition of the formative waters must have temporally fluctuated with periods of precipitation being interrupted by periods of dissolution the microbes that formed the subaerial biofilms may have influenced some of these processes the aragonite calcite and kerolite probably formed as evaporation and loss of ca through precipitation progressively increased the mg ca and the si ca mg ratios the dolomite gypsum and halite probably formed during early diagenesis during the evaporation of seawater that percolated into the interiors of the notch speleothems

microbes and mineral precipitation miette hot springs jasper national park alberta canada at miette hot springs so42 h2s ca2 sr2 and co32 rich waters with a mean temperature of 51 2 c are ejected from three spring vents and several minor seeps near the floor of sulphur creek valley runoff channels from the springs are colonized by cyanobacteria oscillatoria phormidium gloeocapsa synechococcus xenococcus that grow in resistant mats and as loose filaments within 0 5 m of the spring vents diatom assemblages cymbella mastagloia brachysira sellaphora rhopalodia nitzschia navicula pinnularia that dominate the flow paths 0 5 2 0 m from the vents and microbial mats with cyanobacteria and diatoms in the distal flow paths sulphate reducing bacteria and green algae are also present gypsum elemental sulphur and lesser quantities of calcite and strontianite precipitate from the spring waters microbial populations influence accumulation of mineral precipitates by i forming mats close to the spring vents on which crystals grow ii forming mats alongside the flow paths t

hot spring systems geobiology abiotic and biotic influences on travertine formation at mammoth hot springs yellowstone national park usa multiple abiotic and biotic factors combine in nature to influence the formation of calcium carbonate limestone deposits systems geobiology studies of how micro organisms respond to or sometimes even control the coupled effects of environmental change and mineralization will permit more accurate interpretation of the fossil record of ancient microbial life mammoth hot springs in yellowstone national park usa serves as a natural laboratory for tracking how the dynamic interplay of physical chemical and biological factors come together to form hot spring limestone called travertine systematic downstream correlations occur at mammoth hot springs between travertine deposition geomorphology crystalline structure and geochemistry microbial communities mat morphology pigmentation and phylogenetic and metabolic diversity and spring water conditions temperature ph geochemistry and flow field based microscale and mesoscale experimentation indicates that microbes directly influence travertine growth rate and crystalline structure at the macroscale time lapse field photography and numerical modelling suggest that travertine terrace geomorphology is influenced strongly by hydrology heat dispersion and geochemistry these results from mammoth hot springs allow establishment of a conceptual framework across broad spatial and temporal scales in which to track how multiple geological and biological factors combine to control caco3 crystal precipitation and the resulting formation of travertine deposits

depositional facies and aqueous solid geochemistry of travertine depositing hot springs angel terrace mammoth hot springs yellowstone national park u s a petrographic and geochemical analyses of travertine de positing hot springs at angel terrace mammoth hot springs yellow stone national park have been used to define five depositional facies along the spring drainage system spring waters are expelled in the vent facies at 71 to 73 8c and precipitate mounded travertine composed of aragonite needle botryoids the apron and channel facies 43 728c is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide oxidizing aquificales bacteria the travertine of the pond facies 30 62 8c varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures calcite ice sheets calcified bubbles and aggregates of aragonite needles fuzzy dumbbells pre cipitate at the air water interface and settle to pond floors the prox imal slope facies 28 54 8c which forms the margins of terracette pools is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face finally the distal slope facies 28 30 8c is composed of calcite spherules and calcite feather crys tals despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization the com positions of spring water and travertine predominantly reflect abiotic physical and chemical processes vigorous co 2 degassing causes a 12 unit increase in spring water ph as well as rayleigh type covariations between the concentration of dissolved inorganic carbon and corre sponding d 13 c travertine d 13 c and d 18 o are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher temperature 50 738c depositional facies conversely

skeletal crystals of calcite and trona from hot spring deposits in kenya and new zealand abstract skeletal crystals are hollow crystals that develop because their outer walls grow before their cores the presence of skeletal crystals of calcite three types trigonal prisms hexagonal prisms and plates and trona in hot 90 c spring deposits in new zealand waikite springs and ohaaki pool and kenya lorusio hot springs shows that they can form in natural sedimentary regimes analysis of samples from these deposits shows that this crystal morphology develops under disequilibrium conditions that are unrelated to a specific environmental or diagenetic setting skeletal crystals transform into solid crystals when subsequent precipitation fills their hollow cores in some cases this may involve precipitation of crystalline material that has a sieve like texture in other xamples the skeletal crystal provides a framework upon which other materials can be precipitated some of the skeletal hexagonal calcite crystals from new zealand for example are thinly coated with amorphous silica walls in the skeletal trigonal calcite prisms from waikite springs are formed of subcrystals that mimic the shape of the parent crystal similarly plate like skeletal crystals from lorusio are formed of densely packed subcrystals that are 0 5 m long conversely the walls of the skeletal hexagonal calcite crystals from ohaaki pool and the skeletal trona crystals from lorusio are not formed of subcrystals recognition of skeletal crystals is important because they represent growth that follows the reverse pattern of normal growth failure to recognize that crystal growth followed the skeletal motif may lead to false interpretations concerning the growth of a crystal for example the standard interpretation of zoned crystals using the a priori assumption that growth proceeded from the crystal core to the crystal face cannot always be used

bacterial extracellular polymeric substances eps mediate caco3 morphology and polymorphism abstract the effect of bacterial extracellular polymers eps on calcium carbonate morphology and polymorphism was investigated by means of free drift mineralisation experiments conducted using cells of the eps producing thermotolerant bacillus licheniformis s 86 the cells either had the eps layer intact native cells or had the eps layer removed eps free cells experiments were also undertaken in the absence of cells but with the addition of the extracted eps solution it was found that the abiotic control and eps free cell experiments contained vaterite and calcite when sampled after 12 h and 48 h whereas the native cell and eps solution experiments contained only calcite these results suggest that the presence of eps inhibits vaterite precipitation it is proposed that dissolved organic carbon doc released from the eps complexes ca 2 ions in solution reducing the calcium carbonate saturation and favouring calcite precipitation over vaterite after 7 days all experiments contained only calcite however distinct morphological differences between the calcite crystals precipitated in the four experiments were preserved after a period of 7 days suggesting that crystal morphology may indicate the biological conditions under which calcite precipitated

late holocene sea levels and coral reef development in vahitahi atoll eastern tuamotu islands pacific ocean abstract preliminary quantitative data are provided on the latest stage of development and morphological evolution of the closed atoll vahitahi in the eastern tuamotus from before 4300 to at least 2400 yrs b p sea level was at least 0 7 m higher than at present during this time the development of a flat reef pavement now slightly emerged gradually separated the lagoon from the ocean at about 1200 yrs b p the water level of the lagoon already closed was still slightly above the present level the response of the reef was a rapid upward accretion until about 3000 yrs b p then an oceanward development at rates averaging from 0 04 to 0 13 m yr 1

influence of thermophilic bacteria on calcite and silica precipitation in hot springs with water temperatures above 90 c evidence from kenya and new zealand hot and boiling springs in kenya and new zealand that are emitting water with temperatures more than 90 c are commonly characterized by a complex array of caco3 and sio2 precipitates that have been formed through abiogenic and biogenic processes thermophilic bacteria are the only microbes that can survive in the boiling water that is discharged into pools around the spring orifice analysis of modern substrates from various springs in the kenya rift valley and the taupo volcanic zone in new zealand shows that they are inhabited by a diverse array of coccoid and filamentous bacteria in some areas these bacteria produce copious amounts of mucus that coat the substrates although the coccoid and filamentous bacteria provide substrates for caco3 and sio2 precipitation the microbes do not seem to have any direct influence on the morphology of the precipitates that are produced conversely the mucus found in these hot spring pools selectively takes up elements such as si mg al and fe but is not calcifi

signatures of biologically influenced caco3 and mg fe silicate precipitation in hot springs case study from the ruidian geothermal area western yunnan province china hot springs at gongxiaoshe and zhuyuan maximum temperatures of 73 to 84 c respectively are characterized by deposits formed of calcite aragonite non crystalline si mg fe deposits and minor amounts of barite and gypsum the deposits at gongxiaoshe are formed largely of alternating calcite and aragonite laminae whereas those at zhuyuan are formed largely of calcite the calcite is in the form of i pseudodendrites that grew as sub crystals stacked upon each other and ii unattached euhedral and incompletely formed dodecahedral and rhombohedral crystals amorphous caco3 formed of nanoparticles 1 m long is common in some of the zhuyuan deposits but minor in the gongxiaoshe deposits the morphologically diverse arrays of aragonite crystals that lie parallel to bedding were not nucleated on a growth surface many substrates in these deposits are covered with reticulate coatings that are formed largely of si and mg with minor fe and micro granular coatings that are formed largely of si and fe biofilms with their extracellular polymeric substances and microbes are common at both springs the compositionally and crystallographically diverse precipitates at these two springs are attributed to a biologically influenced model with precipitation taking place in micro domains that developed in the extracellular polymeric substances according to this model precipitation varied at the micron scale influenced by the elemental concentrations that developed in the hydrogel of extracellular polymeric substances critically the very low preservation potential of the extracellular polymeric substance and its formative microbes means that the precipitates will rapidly lose evidence of their biotic origin the compositional diversity of the precipitates the crystallographic diversity of the calcite and aragonite with numerous incompletely formed crystals and local concentrations of si mg and fe may however serve as proxies of that biologically influenced precipitation

unusual secondary ca mg carbonate kerolite deposits in basaltic caves kauai hawaii abstract aragonite calcite monohydrocalcite dolomite magnesite hydromagnesite and talc like kerolite have been identified in speleothems from basaltic caves on the island of kauai hawaii these secondary minerals have crystallized in the presence of freshwater seeping from the basaltic host rock and the mineralization process is ongoing at some locations the deposits are extremely variable in macroscopic character ranging from millimeter thin powdery coatings to hard crusts several centimeters thick many deposits are associated with actively forming microbial mats and stromatolitic structures are common in the thicker deposits formation of the mineral deposits is a result of a combination of direct precipitation from solution by evaporation and co2 degassing alteration of precursor minerals and or microbial processes and physicochemical conditions within the mats these unusual deposits provide important insights into the mineralogy and geochemistry of low temperature alteration and carb

christmas island lagoonal lakes models for the deposition of carbonate evaporite organic laminated sediments the atoll of christmas island now known as kiritimati in the kiribati republic central pacific lies at about 28n in the intertropical convergence zone much of the surface area of the atoll ca 360 km 2 is occupied by numerous lakes in which carbonate evaporite calcium sulfate halite and organic layers are deposited observations suggest that deposition of these different laminae is controlled by climatic and biologic factors it is thought that periodic climatic variations such as el nino southern oscillations enso events which bring heavy rainfall to the atoll result in the succession of the precipitation of carbonate minerals during periods after dilution of hypersaline waters by heavy rains followed by evaporitic minerals carbonate calcium sulfate halite when salinity increases through evaporation thick up to 5 cm microbial essentially cyanobacterial mats develop continuously on the lake bottom surfaces providing the sediment with an important total organic carbon 2 5 organic contribution in the form of an internal geometrically structured network in which the authigenic minerals precipitate the high bioproductivity of these microbial populations is reflected in low d 13 c values of sedimentary organic carbon 214 to 217 interpreted as being the result of high atmospheric co2 demand geochim cosmochim acta 56 1992 335 the well laminated organic layers present in the sediment profile result from the death and burial of microbial populations at the time of severe climatic events storms heavy rainfall these lagoonal lakes provide a model for the deposition of carbonate and organic matter in an evaporitic environment the high ratio of deposited carbonate vs sulfate 1 chloride when compared to low ratio in evaporitic salinas results from both a lack of limitation of calcium magnesium and carbonate ions in a carbonate reef environment and active processes of high mg calcite precipitation organomineralization q 2001 elsevier science b v all rights reserved

selective mineralization of microbes in fe rich precipitates jarosite hydrous ferric oxides from acid hot springs in the waiotapu geothermal area north island new zealand abstract a group of small springs that are informally called orange spring located near hakereteke stream in the northern part of the waiotapu geothermal area feed hot 80 c acidic ph 2 1 2 4 as rich sulfate waters into a discharge channel that is up to 25 cm deep submerged reddish brown precipitates on the channel floor are formed largely of noncrystalline as rich hydrous ferric oxide hfo mainly goethite poorly crystalline lepidocrocite and crystalline jarosite well preserved coccoid and rod shaped microbes are found in the as rich hfo but not in the lepidocrocite or jarosite the jarosite was probably precipitated when the water had a low ph 4 and lower so4 content the fluctuations in the ph and so4 content which led to precipitation of the different mineral phases may reflect mixing of the spring water with stream water that flowed through the channel when hakereteke stream was in flood stage the goethite probably formed when coccoid and rod shaped bacteria acidithiobacillus ferrooxidans mediated rapid oxidization of the fe2 to fe3 that was then immediately coprecipitated with the as such rapid precipitation promoted mineralization of the microbes the lack of mineralized microbes and the lower as in the lepidocrocite and jarosite may reflect precipitation rates that were slower than the decay rates of the microbes or ecological factors that limited their growth

an unusual modern silica carbonate sinter from pavlova spring ngatamariki new zealand a silica carbonate deposit is forming from the dilute alkali chloride waters of pavlova spring a small thermal pool and outflow channel 85 to 10 times lower accumulation rates than typical siliceous sinters in the tvz and deposition of both silica and calcite is controlled by microchemical conditions and local temperature gradients rather than by bulk spring water chemistry

geothermal fields of china abstract there are over 2500 known occurrences of geothermal phenomena in china these lie mainly in four major geothermal zones xizang tibet yunnan taiwan east coast and north south hot water has also been found in boreholes in major mesozoic cenozoic sedimentary basins this paper presents a summary of present knowledge of these geothermal zones the geological settings of geothermal occurrences are associated mainly with magmatic activity fault uplift and depressional basins and these are described by examples of each type increased multipurpose utilisation of geothermal resources is planned and examples are given of current usages

cyclic development of large complex calcite dendrite crystals in the clinton travertine interior british columbia canada abstract bands of large up to 4 cm long three dimensional crystallographic dendrites form the terrace fronts in an old travertine mound exposed near clinton british columbia the dendrites with their long axes perpendicular to the terrace front are characterized by numerous levels of branching each branch is formed of multitudes of skeletal rhombs four and six sided bipyramidal crystals or prismatic hexagonal crystals that are precisely aligned along crystallographic precepts although individual branches are formed of one type of subcrystal neighbouring branches may be formed of different subcrystal types highly supersaturated waters that were generated by rapid co 2 degassing of the spring water during its turbulent flow over the steep terrace fronts probably drove dendrite precipitation the presence of growth lines indicates that growth was episodic type i growth lines probably formed annually in response to seasonal climate changes whereas type ii growth lines which formed less frequently may reflect changes in the flow velocity and or flow patterns of the spring waters early diagenetic modification of the dendrites involved crystal face enlargement cements formed of trigonal prisms or needle fiber crystals microbial infestation that mediated substrate dissolution and or deposition of detrital calcite crystals that formed in the water column much of the diagenetic modification may have taken place during the periods when the dendrites had temporarily stopped growing the dendrites in the clinton travertine are an excellent example of complex episodic calcite crystal growth that was extensively modified by early diagenetic processes in a surface environment the same spring waters from which the dendrites were precipitated mediated much of the early diagenesis

habit of bacterially induced precipitates of calcium carbonate and the influence of medium viscosity on mineralogy abstract marine bacteria can and do induce the precipitation of calcium carbonate in the laboratory and in nature which results in single crystals and aggregates of crystals crystal bundles the end member forms of the crystal bundles observed are rods and spheres with numerous variations in between these forms the most common of which is the dumbbell rounded dumbbells and single crystals resembling brushes appear to be unique to bacterially induced precipitates and consequently may serve to identify bacterially induced precipitates in the rock record viscosity of the growth medium is the single most important control over the mineral precipitated in the experiments conducted the medium viscosity controls the ion diffusion rate and thus the rate of precipitation and consequently the mineral precipitated in a liquid medium circulation and the ion diffusion rate are both high precipitation is rapid and aragonite forms in a gelatinous medium there is little circulation the ion diffusion rate is slow the rate of precipitation is slow and calcite is precipitated the overall form of the resultant precipitate rods or spheres was the same regardless of the mineral composition

controls on aragonite and calcite precipitation in hot spring travertines at chemurkeu lake bogoria kenya subfossil travertines precipitated around hot spring orifices at chemurkeu on the western shore of lake bogoria kenya are composed of calcite aragonite and minor dolomite aragonite crystal beds which form 5 10 of the travertine by volume are formed of large pseudohexagonal prisms whereas the calcite crystal beds are composed mainly of feather dendrites dolomite is only found between aragonite crystals boundaries between aragonite and calcite crystals commonly display evidence of dissolution but there is no evidence to indicate that calcite formed by inversion of aragonite or that the dolomite replaced the aragonite thus the aragonite calcite and dolomite are each treated as primary precipitates reticulate gelatinous coatings with a high si and mg content cover most external and internal surfaces of the aragonite and calcite crystals the travertines may have formed under more humid conditions than today when the spring waters contained more ca2 the physiochemical conditions at the mo

mid infrared observations of io s volcanism from the ground in 2011 and 2012 abstract we report the latest volcanic activity on io based on our ground based observations made in 2011 and 2012 using just a 1 m telescope at 8 9 m where io s thermal radiation dominates solar reflected light seen at shorter wavelengths a particular result from these observations is that the power we detected from a bright hotspot at the longitude of 282 18 perhaps daedalus patera was 10 13 w which is comparable to that of loki patera the most powerful volcanic hotspot on io we conclude this hotspot is one of the most powerful volcanic hotspots on io but its activation is not as frequent as loki patera

oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate because meteoric water 18 o values decrease with decreasing ambient temperature and increasing latitude 18 o values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures to test this we compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from devonian to modern and in paleolatitude from 3 5 to 83 mean 18 o values for meteoric cements and speleothems both show the same negative correlation with paleolatitude the 18 o vs latitude trend for these carbonates is almost identical to that predicted for modern inland environments but differs from the trend for coastal environments this suggests that the ground water controlling the ultimate composition of meteoric cement is derived predominantly from inland recharge if it is assumed that the modern meteoric water 18 o vs temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation then coastal and inland paleotemperatures can be calculated from the 18 o values of meteoric calcite 18 o mcl and seawater 18 o sw by using the equations t coastal 13 3 32 6 0 231 0 0613 18 o mcl 18 o sw and t inland 17 8 16 2 0 572 0 1233 18 o mcl 18 o sw where t is temperature in c calcite precipitated from coastal meteoric water at temperatures between 0 and 25 c will exhibit a narrow range in 18 o 6 to 4 where 18 o sw 0 the 18 o of calcite precipitated from inland meteoric water will be sensitive to paleotemperature ranging from 14 to 5 where 18 o sw 0 for temperatures of 0 to 25 c

biogenic structure of early sediment fabric visualized by low temperature scanning electron microscopy the accurate visualization of early biogenic sediment fabric is important in the search for modern analogues to relict fossil structure and therefore for the interpretation of past environmental conditions water may have a significant structural role within hydrated material and sample dehydration may be detrimental to the structural interpretation of natural sediments and their associated microbiota water is present in sediments as free water or in the form of bound or hydration water extracellular polymeric substances associated with microbial assemblages have a high content of hydration water and are distorted by dehydration the use of low temperature scanning electron microscopy for the visualization of water saturated sediments and associated biogenic structures is examined low temperature sem allows samples to be examined without the removal of water that is normally associated with the preparatory procedures for traditional ambient sem samples for low temperature sem are first frozen cryofixed and then examined fully hydrated and still frozen at low temperature cf 180 c on the stage of a specially adapted sem the process of low temperature sem for the examination of hydrated sediments is described and several examples of cohesive and mixed flat sediments and their associated biogenic fabrics are given detail of the internal fabric and associated microbiota can be examined by freeze fracture techniques to preserve the natural condition of the sediments

amorphous calcium carbonate associated with biofilms in hot spring deposits abstract calcium carbonate nanoparticles are intimately associated with crystalline calcite and aragonite in the eryuan gongxiaoshe and zhuyuan hot springs water temperature 75 c which are located in yunnan province china the nanoparticles

kopara in polynesian atolls early stages of formation of calcareous stromatolites widespread modern calcareous stromatolites known as kopara in the vernacular language on the tuamotu archipelago have been found accreting on the bottom of shallow generally 1 m depth lakes located on the rims of these french polynesian atolls they are flat gelatinous sediments several tens of centimetres thick with lamination comprised of vertically alternating red organic rich and white carbonate rich millimetre thick laminae they originate from benthic microbial communities mainly composed of cyanobacteria generally dominated by the genus phormidium the living cyanobacteria occupy only the top 1 3 cm of the deposit the red organic matter below being made of remnants of the dead microbes essentially of polysaccharide microfibrils inherited from the sheaths and arranged into a three dimensional network enclosing pores ranging from a few tens of angstroms to a few micrometres wide the carbonates are predominantly high mg calcite 9 19 mole mgco3 which precipitated as micron size bunches within the pores on walls of the organic network it is sometimes accompanied by aragonite less than 22 of the total mineral fraction when present and lesser high mg calcite allochthonous bioclasts which occasionally form up to few centimetres thick detrital intercalations the pore waters are variable mixtures of freshwater rain or ground water and sea water from the ocean or lagoon which are feeding waters of the lakes their chemistry deviate from a straight mixture gradient with respect to ca2 mg2 and alkalinity under the influence of local calcification and bacterial processes e g ammonia production sulphate reduction within the sediments it is hypothesized that the calcification is initiated at carboxylic sites on the walls of the polysaccharide network the pores acting as confining organic compartments with increased internal supersaturation lamination is suggested to be due to the combined effects of the stratification of the microbial activity of the deposits and alternations of fresh and saline periods within the lakes lacustrine environments on oceanic atolls are found to be important habitats of modern microbialite formation

trigonal dendritic calcite crystals forming from hot spring waters at waikite north island new zealand amorphous silica and calcite form the deposits in the vent and on the discharge apron of waikite spring 100 ws 100 which is located in the waikite geothermal area on north island new zealand these precipitates formed from spring water that has a temperature of 90 c and a ph of 8 1 8 8 the opaline silica is restricted to areas around the vent where cooling and evaporation of the spring water triggered precipitation the calcite deposits in the spring vent and on the discharge apron are formed of large up to 15 cm long asymmetrical dendrite crystals that are characterized by multiple levels of branching branches grew preferentially from the downflow side of their parent branch all branches have a trigonal transverse cross section except in areas where competition for growth space induced merger of neighboring crystals the primary branches of the dendrite crystals are sub perpendicular to the substrate even in areas where the discharge apron slopes at a high angle up to 80 on the steeper parts of the discharge apron the plate like primary branches form the floors of the small terrace pools whereas their distal edges form the rims of the pools growth of these dendrite crystals is attributed to abiotic processes high levels of saturation with respect to calcite were caused by rapid co2 degassing of the sheets of spring water that flowed down the steep discharge apron calcite crystals with different crystal morphologies characterize other springs near this spring the variation in crystal morphologies from spring to spring is attributed to different levels of saturation that are related to the initial pco2 of the spring water upon discharge and the rate of co2 degassing at each spring

bacterially induced mineralization of calcium carbonate in terrestrial environments the role of exopolysaccharides and amino acids this study stresses the role of specific bacterial outer structures such as glycocalix and parietal polymers on calcium carbonate crystallization in terrestrial environments the aim is to compare calcium carbonate crystals obtained in bacterial cultures with those obtained during abiotically mediated synthesis to show implications of exopolysaccharides and amino acids in the mineralogy and morphology of calcium carbonate crystals produced by living bacteria this is done using various amounts of purified exopolysaccharide xanthan eps and l amino acids with a range of acidities amino acids and increasing xanthan content enhance sphere formation in calcite and vaterite regarding calcite the morphology of crystals evolves from rhombohedral to needle shape this evolution is characterized by stretching along the c axis as the amino acid changes from glutamine to aspartic acid and as the medium is progressively enriched in eps regarding vaterite the spherulitic habit is preserved throughout the morphological sequence and starts with spheres formed by the agglomeration of short needles which are produced in a xanthan free medium with glutamine monocrystals forming spheres increase in size as xanthan is added and the acidity of amino acids glutamic and aspartic acids is increased at high xanthan concentrations amino acids and mainly aspartic and glutamic acids induce vaterite precipitation the role of the carboxyl group is also probably critical because bacterial outer structures associated with peptidoglycan commonly contain carboxyl groups this role combined with the results presented here clearly demonstrate the influence of bacterial outer structure composition on the morphology and mineralogy of bacterially induced calcium carbonate this point should not be neglected in the interpretation of calcite cements and carbonate accumulations in terrestrial environments

microscopic calcite dendrites in cold water tufa implications for nucleation of micrite and cement dendritic calcite forms in an active cold water tufa system in association with extracellular polymeric substances eps that discontinuously coat bryophytes and cyanobacteria dendrites consist of 100 200 nm thick calcite fibres that form 3d lattice like domains in each dendrite domain fibres have three structurally equal orientations which correspond in disposition to radii from the centre of a calcite unit cell to the convex triple face junctions on its surface fibres do not form in the orientation of the c axis the external form of each dendrite has the shape of half of a shortened octahedron with an upper triangular surface parallel to the substrate dendrite nucleation takes place on or in microbial eps whether microbial cells are present or not and is probably effected by attraction of ca 2 cations to negatively charged eps together with co2 degassing and concomitant ph increase of supersaturated spring water in stream splash zones ensuing dendrite growth is abiogenic and controlled by diffusion dendrite c axes are perpendicular to the substrate probably because the negative charge of eps forces the orientation of ca 2 and co 2 planes within the developing dendrite crystal to be parallel to the eps film surface dendrites are eventually filled and overgrown by solid syntaxial calcite which gradually and completely obliterates the dendrites as more familiar calcite crystal forms develop no trace of the dendritic nucleus remains in the rock record calcite crystal nucleation may take place by this mechanism in many marine and meteoric settings given that microbial eps is now assumed to be virtually ubiquitous in these environments this phenomenon could contribute to the development of familiar fabrics such as marine micrite cement and fibrous calcite cement radial ooids peloids abiogenic stromatolites sea floor precipitates microbialites tufa travertine speleothems and some meteoric cements it may also contribute to the substrate normal orientation of c axes of common cement fabrics

polymeric substances and biofilms as biomarkers in terrestrial materials implications for extraterrestrial samples organic polymeric substances are a fundamental component of microbial biofilms microorganisms especially bacteria secrete extracellular polymeric substances eps to form slime layers in which they reproduce in the sedimentary environment biofilms commonly contain the products of degraded bacteria as well as allochthonous and autochthonous mineral components they are complex structures which serve as protection for the colonies of microorganisms living in them and also act as nutrient traps biofilms are almost ubiquitous wherever there is an interface and moisture liquid liquid liquid solid liquid gas solid gas in sedimentary rocks they are commonly recognized as stromatolites we also discuss the distinction between bacterial biofilms and prebiotic films the eps and cell components of the microbial biofilms contain many cation chelation sites which are implicated in the mineralization of the films eps biofilms and their related components thus have strong preservation potential in the rock record fossilized microbial polymeric substances fps and biofilms appear to retain the same morphological characteristics as the unfossilized material and have been recognized in rock formations dating back to the early archaean 3 5 b y we describe fps and biofilms from hot spring deep sea volcanic lake and shallow marine littoral environments ranging up to 3 5 b y in age fps and biofilms are more commonly observed than fossil bacteria themselves especially in the older part of the terrestrial record the widespread distribution of microbial biofilms and their great survival potential makes their fossilized remains a useful biomarker as a proxy for life with obvious application to the search for life in extraterrestrial materials

bacterial shrubs crystal shrubs and ray crystal shrubs bacterial vs abiotic precipitation hot water travertine deposits commonly contain shrub like morphologies on the centimeter to meter scale that range from highly irregular forms bacterial shrubs to features that display regular geometric patterns crystal shrubs and ray crystal crusts the bacterial shrubs have been previously recognized as the product of bacterially induced precipitation whereas the ray crystal crusts have been described as due to dominantly abiotic precipitation the bacterial shrubs have a highly irregular morphology similar to woody plants in contrast end member crystal shrubs display distinct crystal habits and regular repeating morphologies i e they commonly have attributes of noncrystallographic as well as crystallographic dendrites there is a complete gradational relationship between the bacterial shrubs and crystal shrubs ray crystal crusts are large fan shaped features composed of subparallel extremely coarse bladed crystals of calcite all three types bacterial shrubs crystal shrubs and ray crystal crusts contain either a dense tangle of bacterial body fossils and or micron sized pores the micropores are bacterial molds the immediately enveloping spar crystals around all three morphologic types are devoid of bacterial body fossils and micropores the bacterial shrubs crystal shrubs and ray crystal crusts are to differing degrees the product of bacterially induced precipitation as well as abiotic mineral precipitation the differences in morphology are due to the relative contribution of bacterially induced precipitation as compared with that of abiotic mineral precipitation bacterially induced precipitates can form in environments too chemically harsh or otherwise inhospitable for other taxa to thrive epiphyton and renalcis commonly formed in occult environments under conditions inhospitable to other taxa consideration of the published descriptions and interpretations concerning epiphyton and renalcis and by analogy the origin of bacterial shrubs have led to the conclusion that epiphyton and renalcis also are bacterially induced precipitates

deposition and diagenesis of mammoth hot springs travertine yellowstone national park wyoming u s a strata forming a 113 m long core through mammoth hot springs record the holocene evolution of this travertine accumulation from deposition as part of a lacustrine to a terraced mound environment the deposit is readily divided into four intervals 113 67 m carbonate cemented volcaniclastic with intercalated layers of travertine 67 60 m moderately pure travertine with some volcaniclastics 60 50 m carbonate cemented volcaniclastic rich interval and 50 0 m essentially pure travertine lithologic composition sedimentary structures and the rare ostracode fossils indicate that the lower 67 m predominantly accumulated in a lacustrine environment whereas the upper 40 m are terraced mound deposits all of the travertine is calcite some after aragonite layers of shrubs oncoids and peloids all bacterial in origin form the dominant allochems within the travertine stable isotopic carbon and oxygen values n 128 are strongly positively correlated and decrease up core 4 and 8 respectively reflec

depositional facies and diagenetic alteration in a relict siliceous hot spring accumulation examples from yellowstone national park u s a abstract siliceous precipitates from portions of an 11 m long core drilled through a relict yellowstone hot spring deposit provide valuable insights into the diagenetic facies in this hydrothermal environment most of the core consists of relatively low temperature siliceous sinter containing abundant plant diatom and microbial fossilized remains derived from the distal debris apron and discharge channel flowpath of the hot spring a few intervals contain stromatolitic horizons analogous to modern siliceous pool margin and discharge channel flowpath facies despite the abundance of silicified microbial remains e g silicified stromatolitic horizons as well as individual filamentous microbes diatoms distinctive organic biomarkers are not preserved in the core the apparent lack of distinctive organic biomarkers is attributable to pervasive diagenetic alteration in the presence of high temperature chemically reactive fluids numerous diagenetic features have been superimposed on the siliceous sinter especially considering the relatively shallow depths of burial the uppermost interval 0 to 1 2 m consists of highly porous siliceous sinter opal a and interbedded travertine amorphous manganese oxides and sparry calcite cements are present and are irregularly distributed throughout this interval below is a diagenetic facies 4 8 to 5 3 m that consists of opal ct and minor chalcedony the most pervasive diagenetic alteration in the core is the 6 8 to 11 2 m depth interval where abundant zeolites mordenite heulandite bladed cristobalite lepispheres chalcedony cements and calcite veins are present judging by the assemblage of plant and diatom remains most of this pervasive alteration is superimposed on relatively low temperature siliceous sinters and is likely the result of migration of hot waters through this interval the paragenesis of all these intervals is very complex involving numerous episodes of mineral precipitation and dissolution this diagenetic alteration is facilitated by the porous nature of the siliceous sinter thermal convection of superheated fluids or steam strongly oxidizing spring waters and fluctuating hydrochemical regimes rapid dissolution and or replacement of organic matter indicates that standard morphological means e g petrographic identification of body fossils may be the best method by which to identify that organisms were previously present in ancient hot spring accumulations

geomicrobiology of carbonate silicate microbialites from hawaiian basaltic sea caves abstract modern microbial mats and microbialites are described from basaltic sea caves on the island of kauai hi the mats grow on the ceilings and walls in the photic zone of several open caves where fresh water seeps out of the rock scanning sem and transmission electron microscopy tem showed that the active mats are dominated by filamentous and nonfilamentous cyanobacteria in the surface layers and heterotrophic bacteria in deeper layers energy dispersive x ray analysis revealed that copious amounts of extracellular polymeric substances eps are rich in mg si o and ca likely concentrated from solution petrographic microscopy and electron microprobe analysis of the mineralized microbialites showed textures reminiscent of stromatolitic laminations consisting mainly of alternating calcium carbonate calcite and aragonite and magnesium rich silicate kerolite thin coatings rich in magnesite hydromagnesite and monohydrocalcite surround the microbialites on the rock surfaces and are likely inorganic in origin within the mats minerals tend to form and concentrate within or around dense matrices of eps microenvironments with geochemical conditions favorable for mineral crystallization likely develop in the mats as a result of the mucilaginous extracellular material and the development of bacterial microcolonies in addition copious amounts of extracellular polymers bind ions from solution and provide nucleation sites for mineral crystallization and growth this combination of biological and inorganic processes can explain the occurrence of the secondary minerals in these caves as well as the stromatolitic textures of the microbialites

abiotic versus biotic controls on the development of the fairmont hot springs carbonate deposit british columbia canada the relict fairmont hot springs deposit formed largely of carbonates covers an area of 0ae 5k m 2 and is up to 16 m thick the triangle shaped discharge apron which broadens down valley is divided into a proximal part with beds dipping at 10 and a distal part with beds dipping at 10 to 15 the deposit is formed of the 1 basal macrophyte 2 lower carbonate 3 middle clastic 4 upper carbonate and 5 upper clastic sequences two charcoal samples embedded in the lower carbonate sequence yielded dates of 8690 90 and 8270 70 cal yr bp indicating that much of the deposit formed post glacially during the early to mid holocene deposit aggradation ceased in the mid to late holocene when the fairmont creek valley was incised the lower and upper carbonate sequences which are the thickest sequences are composed of nearly equal parts of travertine abiotic and tufa biotic with feather dendrite travertine radiating dendrite travertine and stromatolite tufa dominating competition between calcite precipitation rates and biotic growth rates controlled the distribution of tufa and travertine across the discharge apron calcite and biotic growth rates were controlled largely by flow velocity across the apron which in turn was controlled by topography and regular fluctuations in spring water discharge volume during times of high spring discharge slow sheet flow over the proximal part of the apron promoted stromatolite growth whereas fast turbulent flow on the distal part of the apron induced rapid feather dendrite formation during times of low spring discharge quiescent shallow evaporative pools conducive to radiating dendrite formation formed on the proximal part of the apron whereas slow flow on the distal part promoted stromatolite growth facies with high calcite supersaturation experienced rapid abiotic dendrite growth that precluded most biotic growth