the role of fungi in the diagenetic alteration of spar calcite fungi may play a far more important role in carbonate diagenesis than has been previously suspected this can be demonstrated by placing known species of fungi on crystals of iceland spar calcite such experiments show that fungi can 1 cause sparmicritization through dissolution 2 produce spiky calcite through dissolution 3 trap and bind loose particles of calcite and 4 promote the growth of new calcite crystals although not observed in this series of experiments fungi can bore into substrates and cause sparmicritization the activity of fungi involves a complex interplay of substrate destruction and construction without the intervention of vast quantities of fluid

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

origin of platy calcite crystals in hot spring deposits in the kenya rift valley abstract platy calcite crystals which have their c axis parallel to their shortest length axis are common components of travertine deposits found around some hot springs in the kenya rift valley they are composite crystals formed of numerous paper thin subcrystals individual plates allowed to grow without obstruction develop a hexagonal motif the kenyan crystals typically form in hot 75 c waters that have a low ca content 1 a high co2 content and a high rate of co2 degassing at chemurkeu aggregates of numerous small platy crystals collectively form lattice crystals that superficially resemble ray crystals the walls of the lattice crystals are formed of large platy crystals that have their long and intermediate length axes aligned parallel to the plane of the long axis of the lattice crystal internally the lattice crystals are formed of small platy calcite crystals arranged in a box like pattern that creates the appearance of a lattice when viewed in thin section lattice crystals are highly porous with each pore being enclosed by platy crystals at lorusio travertines are mainly formed of pseudodentrites that are constructed by numerous small platy crystals attached to a main stem which is a large platy crystal that commonly curves along its long axis the pseudodentrites are the main construction blocks in ledges and lilypads that form in the vent pool and spring outflow channels where the water is too hot for microbes other than hyperthermophiles the platy calcite crystals in the kenyan travertines are morphologically similar to platy calcite crystals that form as scale in pipes in the geothermal fields of new zealand and hydrothermal angel wing calcite from the la fe mine in mexico comparison of the kenyan and new zealand crystals indicates that platy calcite crystals form from waters with a low ca2 content and a high co3 ca ratio due to rapid rates of co2 degassing

the role of magnesium in the crystallization of calcite and aragonite in a porous medium abstract morphological development of calcite crystals is related to supersaturation conditions during growth crystallization of calcium carbonate calcite and aragonite as well as mg calcite was studied under controlled supersaturation conditions by the counter diffusion of ca2 and co32 ions through a porous transport medium a column of silica gel under our experimental conditions where ion transport is constrained to be diffusion controlled nucleation and growth take place under conditions of high supersaturation the actual threshold value of the supersaturation depending on the supersaturation gradient in the pure caco3 system calcite grows at lower supersaturation than aragonite the calcite develops relatively simple rhombohedra whil the aragonite grows as spherulites presence of mg2 in the interstitial fluid inhibits nucleation increasing the threshold supersaturation at which crystallization begins the resulting mg calcite crystals show a range of morphologies depending on the mg content and the supersaturation at the point of crystallization at high values of supersaturation up to 15 mol mgco3 is incorporated into the calcite and the crystals form spheres at lower supersaturations mg content decreases and morphologies change progressively through a well defined and reproducible sequence from spheres to dumbbell like forms to wheat sheaf like bundles and eventually single crystals with steep rhombohedral faces the crystals are compositionally zoned showing both sector and oscillatory zoning the compositional evol tion is related to the supersaturation and interface roughness during crystal growth

processes associated with microbial biofilms in the twilight zone of caves examples from the cayman islands abstract the twilight zone of a cave an environment transitional between the well illuminated environment outside the cave and the dark environment of the cave interior is one of the most unusual microenvironments of the karst terrain walls in the twilight zone of caves on grand cayman and cayman brac are coated with a biofilm that incorporates a diverse assemblage of epilithic microbes and copious mucus most microbes are different from those found elsewhere in the karst terrains of the cayman islands probably because they have adapted to life in the poorly illuminated twilight zone none of the microbes employ an endolithic life mode and less than 10 of them show evidence of calcification the biofilm does however provide a medium in which a broad spectrum of destructive and constructive processes operate etching the dominant destructive process produces residual dolomite residual calcite blocky calcite and spiky calcite constructive processes include precipitation of calcite dolomite gypsum halite and sylvite although filamentous microbes are common examples of detrital grains trapped and bound to the substrate are rare destructive processes are more common than constructive ones

rapid in situ silicification of microbes at loburu hot springs lake bogoria kenya rift valley microbial mats located along the margins of hot spring pools and outflow channels at lake bogoria kenya are commonly silicified forming friable laminated crusts columnar microstromatolites composed of silica and calcite are also forming at several springs in sites of oscillating water level or spray silicification of the microbes involves impregnation of organic tissue by very fine amorphous silica particles and encrustation by small 2 m silica spheroids rapid silicification of the microbes which may begin while some are still alive can preserve sheaths and in some examples the filaments capsules and cells although this provides evidence of their general morphology the biological features that are required for taxonomic identifications are commonly poorly preserved the silica precipitation results mainly from evaporative concentration and rapid cooling of spring waters that have been drawn upward through the mats and microstromatolites by capillary processes almost all the silica at the loburu springs nucleates on microbial substrates this affinity of silica for functional groups on microbial surfaces contributes to the rapid silicification of the microbes and their preservation in modern and ancient cherts

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

noncrystallographic calcite dendrites from hot spring deposits at lake bogoria kenya abstract complex calcite crystals are an integral component of precipitates that form around the orifices of the loburu and mawe moto hot springs on the shores of lake bogoria kenya two types of large up to 4 cm long noncrystallographic dendrites are important components of these deposits feather dendrites are characterized by multiple levels of branching with individual branches developed through crystal splitting and spherulitic growth scandulitic from latin meaning shingle dendrites are formed of stacked calcite crystals and are generally more compact than feather dendrites these developed through the incremental stacking of rectangular shaped calcite crystals that initially grew as skeletal crystals feather and scandulitic dendrites precipitated from the same waters in the same springs the difference in morphology is therefore related to microenvironments in which they grew feather dendrites grew in any direction in pools of free standing water provided that they were in constant contact with the solute conversely scandulitic dendrites grew on rims of dams where water flowed over the surface in concert with the pulses of spring water thus each calcite crystal in these dendrites represents one episode of crystal growth the orientation of the component crystals in scandulitic dendrites is controlled by the topography of the dam or surface not crystallographic criteria the noncrystallographic dendrites formed from spring waters with initial temperatures of 90 99 c surficial water cooling loss of co2 and presence of other elements that can interfere with crystal growth contributed to the formation of these unusual crystals

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

kinetic control of morphology composition and mineralogy of abiotic sedimentary carbonates abstract conventional thinking has long held that the abiotic precipitation of calcium carbonate occurs with a causal relationship between fluid my ca ratios and crystal morphology crystal composition and carbonate mineralogy resulting in the formation of meteoric equant low magnesium calcite and marine acicular high magnesium calcite and aragonite problematically calcites with varying amounts of incorporated magnesium occur either as equant or acicular crystals and aragonite may coexist with calcite in either environment commonly however a systematic relation exists between crystal morphology composition mineralogy and rates of reactant supply to growing crystal surfaces for example equant rather than acicular crystals of calcite form in modern deep and or cold marine meteoric phreatic and deep burial settings where the degree of carbonate saturation and or rates of fluid flow are low in areas of higher saturation and or fluid flow such as in warm shallow marine and meteoric vadose environments acicular calcite may predominate this relation is also seen in systems in which aragonite and calcite form in intimate association aragonite precipitation is favored when rates of reactant supply are high calcite forms when rates are low such relations suggest that crystal morphology composition and mineralogy are controlled by the kinetics of surface nucleation and the amount of reactants principally carbonate ions at growth sites precipitating phases are the ones which can best accommodate such excess reactants ambient mg ca ratios only indirectly control the nature of inorganically precipitated carbonate phases

mineralogical crystal morphological and isotopic characteristics of smooth slope travertine deposits at reshuitang tengchong china abstract reshuitang is an important active hydrothermal area in the tengchong geothermal field and is characterized by many hot springs and their associated deposits detailed mineralogical crystal morphological and stable isotopic investigations of the smooth slope fossil travertines at reshuitang and hydrochemical studies of two active springs around the fossil travertines were conducted to study their genesis the results show that 1 the modern springs discharge waters with high temperature 70 c near neutral ph 6 3 8 34 and high saturation indices of calcite and aragonite 2 the fossil travertines contain calcite and small amounts of mn fe oxides halite thenardite and non carbonate debris 3 the calcite include ray crystals dendrite crystals platy crystals and spike crystals and 4 13c and 18o of the fossil travertines at reshuitang range from 1 59 to 0 87 and 6 48 to 7 80 respectively according to comparison between the travertines at reshuitang and other travertines in tengchong all these travertines are thermogene travertines with a large contribution of mantle degassing to their parent co2 but are formed at different temperatures the fossil travertines at reshuitang similar to those at shuzhishi are formed at high temperatures near 100 c which results in weak microbial activities during the formation of the fossil travertines most of the calcite crystals at reshuitang were non equilibrium products precipitated directly from the spring waters during the deposition process while the spike crystals originated from diagenetic dissolution of large calcite crystals comparison between the fossil travertines at reshuitang and other smooth slope travertines from other areas shows these smooth slope travertines have different lithofacies and fabrics in smooth slope environments temperature may control the distribution and development of microbes and the intensity of co2 degassing and consequently cause the precipitation of contrasting fabrics and lithofacies

origin of endogenetic micrite in karst terrains a case study from the cayman islands abstract cavities in the dolostones of the cayman formation miocene on grand cayman and cayman brae commonly contain spar calcite cements and or a variety of exogenetic derived from sources external to the bedrock and endogenetic derived from sources in the bedrock internal sediments micrite is a common component in many of these internal sediments the exogenetic micrite which is typically laminated and commonly contains fragments of marine biota originated from the nearby shallow lagoons the endogenetic micrite formed as a residue from the breakdown of spar calcite crystals by etching as constructive and destructive envelopes developed around spar calcite crystals by calcification of microbes by breakdown of calcified filamentous microbes and by precipitation from pore waters nce produced the endogenetic micrite may be transported from its place of origin by water flowing through the cavities endogenetic micrite can become mixed with the exogenetic micrite subsequently it is impossible to recognize the origin of individual particles because the particles in endogenetic micrite are morphologically like the particles in exogenetic micrite formation of endogenetic micrite is controlled by numerous extrinsic and intrinsic parameters in the cayman formation for example must endogenetic micrite is produced by etching of meteoric calcite crystals that formed as a cement in the cavities or by microbial calcification as a result the distribution of the endogenetic micrite is ultimately controlled by the distribution of the calcite cement and or the microbes factors controlled by numerous other extrinsic variables irrespective of the factors involved in its formation it is apparent that endogenetic micrite can be produced by a variety of processes that are operating in the confines of cavities in karst terrains

morphology relationship and origin of fiber and dendrite calcite crystals abstract fiber and dendrite calcite crystals formed by abnormal growth conditions are minor but important components of many limestones that have undergone vadose meteoric diagenesis fiber crystals which have a length width ratio of greater than 6 1 are divided into hexagonal fibers rectangular fibers composite fibers and rhomb chains according to their crystal form dendrite crystals are formed of a main stem primary branches and secondary branches random and tangential fiber crystals refer to masses of fibers that have a random distribution or tangentially coat a substrate respectively such crystals may be tightly or loosely packed the shape of fiber and dendrite crystals can be substantially modified by destructive or constructive diagenetic processes destructive modification includes physical breakdown dissolution or micritization constructive modification which usually involves epitaxial growth around the original fiber or dendrite crystal may proceed to the point where the original crystals are completely disguised in extreme cases fiber crystals can be cemented together to form lattices that look like dendrite crystals fiber and dendrite calcite crystals generally form from fluids that are supersaturated with respect to calcium carbonate although experimental data suggest that both types of crystal can form from the same parent fluid there are only rare examples where both are present together in nature such crystals form through biogenically and abiogenically mediated processes the common association of these crystals with plant roots or microorganisms suggests that the organisms can produce conditions suitable for growth of the crystals

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

inorganic calcite morphology roles of fluid chemistry and fluid flow abstract evaluation of calcite crystal habits and fabric and their relation to precipitating fluids in spelean environments indicates that habit variations are controlled primarily by degree of supersaturation at less than 6 times supersaturation crystal habits are limited to those with shallow to steep rhombohedral forms i e 1011 4041 with increasing supersaturation scalenohedrons extremely steep rhombohedrons pinacoids and hexagonal prisms are developed slight elongation due to differences in crystal dimensions of these forms may arise i e scalenohedrons versus shallow rhombohedrons at extreme supersaturation 12 times curvature of crystal faces or curved surfaces appear the development of fibrous versus equant fabrics is the result of changes or modification of reactant supply rates and the number of crystallites nuclei present under rapid flow conditions growth rates are accelerated and greater numbers of nuclei are present thus compromise boundaries parallel to c axis and perpendicular to flow and substrate are rapidly attained in the absence of flow fewer crystallites are present and larger well developed crystals or branching forms dictated by saturation conditions arise in the absence of flow at low supersaturation elongate composite crystals and hence fibrous fabrics may result from migration of the fluid crystal interface as a result of changing or oscillating water levels a flow control mechanism can be applied to numerous geological conditions in which transitions from fibrous to equant crystal morphologies are observed

origins of calcite in a boiling geothermal system the formation of hydrothermal calcite relates to the movement of carbon dioxide in a geothermal system as governed by boiling dilution and condensation in this paper we show how these processes control the occurrence distribution and stable isotope composition of calcite based on a study at broadlands ohaaki the two principal calcite occurrences in the broadlands ohaaki geothermal system are 1 as replacement of rock forming minerals and volcanic glass and 2 as platy crystals infilling voids both are stable over a broad temperature range from 160 degrees c to 300 degrees c replacement calcite is widespread and forms through hydrolysis reactions involving calcium alumino silicates and sub boiling liquids that contain 0 3 to 0 75 m co 2 platy calcite in contrast forms over a restricted vertical interval of a few hundred meters within the upflow zone it precipitates from boiling fluids through exsolution of carbon dioxide as indicated by coeval liquid rich and vapor rich fluid inclusions and its formation in the two phase zone fluid inclusion data help to define the boiling paths of fluids from which platy calcite formed homogenization temperatures range from 160 degrees c to 310 degrees c and are consistent within the present geothermal regime ice melting temperatures range from 0 0 to 1 0 degrees c and indicate the presence of up to 0 5 m dissolved carbon dioxide model boiling curves calculated to match these data show how the concentration of dissolved carbon dioxide in the preboiled fluid dictates the depth of first boiling most fluid inclusion data lie along a model boiling path characteristic of the centre of the upflow zone in which the rising fluid initially containing 0 75 m co 2 begins to boil at approximately 320 degrees c and approximately 2000 m depth data from well br 18 instead matches a curve in which the rising fluid initially containing 0 53 m co 2 begins boiling at approximately 245 degrees c and approximately 900 m depth the shallowing of the depth of first boiling likely results from dilution of dissolved carbon dioxide in the parent chloride water as it rises and mixes with marginal waters calcite precipitates from both shallow formed steam headed groundwater and deeply derived chloride water and these waters are isotopically distinct at broadlands ohaaki the delta 18 0 values of calcite at 200 degrees c range from 0 5 to 7 5 per mil whereas delta 18 0 values of calcite at 200 degrees c range from 4 to 10 per mil taking appropriate temperature dependent fractionation factors into account these data indicate equilibration with chloride water delta 18 0 h2o 4 5 per mil and steam heated groundwater delta 18 o h2o 7 0 per mil respectively oxygen isotopes of hydrothermal calcites in the nearby wairakei and waiotapu geothermal systems show similar patterns consistent with the occurrence of both chloride and steam heated waters there calcite formation is explained by a model that describes the distribution of two phase conditions and aqueous carbon dioxide concentrations in a column of hydrothermal fluid rising through a rock matrix of isotropic permeability in this ideal situation platy calcite forms along the inner margin of the two phase zone having the shape of an inverted cone whereas replacement calcite mostly forms in the surrounding one phase liquid only zone the sparse occurrence of calcite at less than or equal to 800 m depth in the central upflow of the ohaaki sector at broadlands ohaaki is compatible with this model and appears related to the exsolution of dissolved carbon dioxide through boiling deeper in the system

shrub morpho types as indicator for the water flow energy tivoli travertine case central italy abstract travertines from tivoli area central italy possess abundant shrub like fabrics that are laterally continuous over hundreds of square meters they occur dominantly in horizontal layers with aggradational and progradational stacking patterns their fabrics and morphologies are remarkably similar to the shrubs lithotypes reported in literature for the pre salt reservoirs offshore brazil and angola with huge oil accumulations petrographic and micro computer tomography analyses allowed the identification of six shrub morpho types i e narrow dendriform wide dendriform fili dendriform arborescent arbustiform and pustular dendriform shrubs are the most common lithotype in tivoli area and three different subtypes could be distinguished according to the arrangement of their branches the shrubs consist largely of peloidal micritic aggregates engulfed in spar calcite ranging in average from 1 to 3 cm in height the shrubs are interpreted to have developed in very shallow extensive waterlogged slightly inclined flat areas changing laterally into a slope system with crusts as the main lithotype changes in the hydrodynamic conditions with episodes of stagnancy influenced the shrub morpho types making them very variegated shrub morphologies likely reflect specific micro environments that are controlled by water flow rates evaporation and microbial activity the latter processes influenced shrub fabric and morphology under high flow conditions co 2 degassing is the main process leading to carbonate precipitation consequently denser and tightly packed morphologies will precipitate composing mainly the crust lithotype in this scenario microbes are less dominant dendriform shrubs with narrow wide and fili morphologies are interpreted to occur in moderate to low energy water flows narrow dendriform shrubs reflect faster flowing conditions with decreasing impact of flow on the morphological aspects from wide dendriform shrubs to fili dendriform shrubs slow to very slow flowing waters are more characteristic for the arborescent arbustiform and pustular shrubs that possibly are highly influenced by evaporation a decrease of water flow likely allows higher microbial activity and consequently shrub morphologies become more fragile and enriched in peloidal micritic aggregate fabrics

hydrochemical evolution and reaction simulation of travertine deposition of the lianchangping hot springs in yunnan china located in western yunnan of china the lianchangping hot springs are of so 4 hco 3 ca na type with total dissolved solids tds ranging from 3560 to 4240 mg l large amounts of travertine are deposited near the hot springs with a variety of travertine morphology including travertine terrace slope and ridge travertine is precipitating along the slope near one of the spring s thresholds chemical compositions of the hot water samples collected along travertine slope show that p co 2 p co 2 tds and contents of hco 3 and ca decrease downstream along the travertine slope due to travertine deposition the initial milliequivalent ratio of ca 2 hco 3 is greater than 1 5 before travertine precipitation and there is an increasing trend in the ratio downstream along the travertine slope high levels of sulphate are probably the result of gypsum dissolution in the sediments widespread in the lianchangping area the spring waters issuing from the land surface are slightly supersaturated with respect to calcite dolomite fluorite kaolinite halite plagioclase and carbon dioxide hydrochemical evolution of the lianchangping spring water along the slope is calculated with the phreeqc interactive 2 12 5 sets of minerals and gases reacted in appropriate amounts are recognized through reaction simulation quantitatively accounting for the variations in chemical compositions especially depositing minerals along the flow path on the travertine slope

growing spherulitic calcite grains in saline hyperalkaline lakes experimental evaluation of the effects of mg clays and organic acids the origin of spherical radial calcite bodies spherulites in sublacustrine hyperalkaline and saline systems is unclear and therefore their palaeoenvironmental significance as allochems is disputed here we experimentally investigate two hypotheses concerning the origin of spherulites the first is that spherulites precipitate from solutions super saturated with respect to magnesium silicate clays such as stevensite the second is that spherulite precipitation happens in the presence of dissolved organic acid molecules in both cases experiments were performed under sterile conditions using large batches of a synthetic and cell free solution replicating waters found in hyperalkaline saline lakes such as mono lake california our experimental results show that a highly alkaline and highly saline solution supersaturated with respect to calcite control solution will precipitate euhedral to subhedral rhombic and trigonal bladed calcite crystals the same solution supersaturated with respect to stevensite precipitates sheet like stevensite crystals rather than a gel and calcite precipitation is reduced by 50 compared to the control solution producing a mixture of patchy prismatic subhedral to euhedral and minor needle like calcite crystals enhanced magnesium concentration in solution is the likely the cause of decreased volumes of calcite precipitation as this raised equilibrium ion activity ratio in the solution on the other hand when alginic acid was present then the result was widespread development of micron size calcium carbonate spherulite bodies with further growth time but falling supersaturation these spherules fused into botryoidal topped crusts made of micron size fibro radial calcite crystals we conclude that the simplest tested mechanism to deposit significant spherical radial calcite bodies is to begin with a strongly supersaturated solution that contains specific but environmentally common organic acids furthermore we found that this morphology is not a universal consequence of having organic acids dissolved in the solution but rather spherulite development requires specific binding behaviour finally we found that the location of calcite precipitation was altered from the air water interface to the surface of the glassware when organic acids were present implying that attached calcite precipitates reflect precipitation via metal organic intermediaries rather than direct forcing via gas exchange

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

cyclonic brine flow pattern recorded by oriented gypsum crystals in the badenian evaporite basin of the northern carpathian foredeep abstract in the middle miocene badenian within sulfate evaporites formed in the northern carpathian foredeep basin of poland ukraine and the czech republic the apices of the primary bottom grown gypsum crystals selenites are similarly aligned over broad areas and have a common azimuth this crystal orientation is interpreted as the product of a consistent direction of a brine inflow during gypsum crystallization and such a unique commonality is used as a tool for paleocurrent analysis in order to recognize both the local and the regional brine paleocurrents in the basin earlier sedimentologic and stratigraphic studies proved that these beds of oriented selenites were deposited at the same or nearly the same time in a brine not more than a few meters deep it is interpreted that the oriented selenites recorded only the mean flow within the basin mainly from the periods of mixing in the dry season lowstands when the whole brine column down to the bottom was ca sulfate oversaturated the measured paleocurrent vectors showed that the brines flowed along the marginal zone of the carpathian foredeep basin predominantly in a counterclockwise direction this longshore flow is interpreted as a typical cyclonic circulation analogous to those present in recent lakes and semi closed basins in the northern hemisphere where counterclockwise mean water drift is directly or indirectly forced by earth rotation the coriolis effect the detected brine flow directions do not reflect downslope gravity flow of dense brines into the central basinal depths or subbasins that were filling with the halite facies

travertines depositional morphology and the bacterially constructed constituents abstract investigation of travertine accumulations throughout central italy and the west central u s has shown that the carbonate is precipitated in response to both inorganic and organic processes individual deposits range up to 85 m thick and hundreds of square kilometers in areal extent all of the carbonate is low magnesian calcite water chemistry temperature and morphology of the accumulation greatly influence the constituents comprising these deposits harsh environmental situations favor inorganic deposits while increasingly more moderate conditions result in the formation of a greater abundance of organically precipitated material morphological variations of travertine deposits recognized include 1 waterfall or cascade 2 lake fill 3 sloping mound fan or cone 4 terraced ound and 5 fissure ridge gross morphology internal stratification and constituents comprising these deposits vary systematically depending upon the type of accumulation and chemistry of the waters bacterially precipitated calcite forms a large percentage of the carbonate in many travertine accumulations exceeding 90 of the framework grains comprising some of the lake fill deposits bacteria are among the first taxa to inhabit and reproduce in harsh spring environments and produce a variety of fascinating constituents the bacteria are primarily rods generally 0 2 m in diameter and less than 1 0 m in length the rods readily decay resulting in calcite crystals loaded with micropores the basic building block of bacterially constructed travertine is a clump of bacteria averaging 20 m in diameter enclosed in a single crystal of calcite aggregates of these crystals produce a variety of deposits including 1 crudely laminated carbonate mud 2 finely laminat d layers of mud 3 intraclasts 4 foam rock and 5 shrubs the shrubs are most striking commonly forming layers 1 3 cm thick but also producing bacterial pisoids at some locales bacterial stromatolites composed of layers of shrubs alternating with finely laminated layers of bacterial mud comprise essentially the entire deposit the shrub layers are the result of flourishing summer growth of bacteria and furthermore show remarkable daily laminae 0 1 0 5 mm thick the importance of bacteria in the formation of travertine and their universally recognized abundance in modern sediments provides an impetus for a reexamination of the role of bacteria in the origin of other types of ancient deposits

50 million year long record of glacial to postglacial marine environments preserved in a carboniferous lower permian graben northern perth basin western australia abstract the perth basin is an intracratonic rift in western australia and contains a carboniferous to cretaceous infill in excess of 12 km thick some 2 km of mid carboniferous to lower permian glacially influenced marine strata spanning the serpukhovian to kungurian about 50 my form one of the longest late paleozoic cold climate successions preserved anywhere in gondwana and record the transition from full glacial to postglacial conditions at high 70 paleolatitudes the great thickness of the succession reflects an abundant supply of glaciclastic sediment from the adjacent ice covered yilgarn craton and continued subsidence along the darling urella fault system the oldest part of the basin fill comprises a 1 5 km thick succession of massive and laminated marine mudstones with striated dropstones nangetty formation deposited in a fiord like environment from plumes of suspended sediment dilute turbidity currents and icebergs meltwater inputs are recorded by erosionally based multistory channels filled with coarse grained gravity flow facies wicherina member deposited on a fan delta along the steep faulted basin margin the nangetty formation passes upward into a regressive succession of postglacial mudstones holmwood shale with bioclastic calcarenites and marine macrofossils capped by sandstone and mudstone facies high cliff sandstone deposited in a storm influenced inner shelf setting on the outer margins of coalesced fan deltas along the basin margin the overlying irwin river coal measures contain a flora that indicates colonization of fan deltas and the yilgarn craton by ferns and lycopods an overlying thick transgressive shale with ice rafted debris carynginia formation records renewed subsidence but continuing seasonally cool climates where coarse debris was rafted by ice into a marine embayment the sedimentology of the perth basin highlights the key role of glacial meltwaters in transporting coarse and fine grained clastic sediment to marine basins rather than direct glacial processes per se the equivalent terrestrial record of glaciation and climate change across the yilgarn craton at this time is very limited

travertine distinctive depositional fabrics of carbonates from thermal spring systems the terrestrial limestones forming at the emergence of thermal springs show a variety of unusual depositional facies the specific lithological and petrological features of these deposits have few counterparts in the marine and continental karst related carbonates but they are typical of the epigean limestone that has been quarried since antiquity in the surroundings of tivoli rome under the name of travertine where it is still forming in hydro geothermal fields linked to extensional tectonics the physicochemical hydrodynamic and geological conditions specific to the tivoli thermal spring system imply hypersaturated alkaline sulphate warm to hot waters upwelling from springs fed through open fractures faults in extensional and or volcanic regimes these features together with the hydrodynamic behaviour of the water flows running from the vents control the petrogenetic features of the travertine a well bedded mostly finely laminated porous but quite compact limestone the results of a detailed comparative petrological analysis carried out on the lithofacies of travertine limestones and of those observed during formation within numerous active thermal spring fields provide the elements required for an exhaustive textural classification of the travertine lithofacies which has not yet been described systematically according to the genetic processes and fabrics the thermal deposits that originate from such hypersaturated alkaline sulphate warm to hot waters can be subdivided into abiotic crystalline crusts microbially mediated crusts microbialites and granular deposits mostly represented by small accumulations of lime mudstone some of the granular deposits and the microbialites are only partially comparable with analogous sediments forming on tidal flats sabkhas or other continental sites however the facies association of crystalline crusts and laminar curled microbialites has no counterpart in the marine realm the widespread presence of thermophile bacteria and sulphobacteria and the general absence of autochthonous eukaryote organisms unable to live in poisonous sulphate waters are also undeniable evidence of their thermal origin