microbial processes forming daily lamination in a stromatolitic travertine abstract thirty hour continuous observation revealed that cyanobacterial metabolism caused daily lamination of a stromatolitic travertine in the shionoha hot spring sw japan the travertine is mainly composed of dendritic calcite crystals intercalated with bands of micritic particles at sub millimeter intervals cyanobacteria remained in the spaces between the calcite crystals during the daytime rose to the travertine surface to receive illumination as light decreased and formed a biofilm around sunset a micritic band developed on the biofilm where glutinous substances trapped detrital ferrihydrite rich particles transported from upcurrent the trapped particles covered the biofilm and in situ precipitation of calcite crystals became dominant before mid night the depositional model of daily lamination of the shionoha travertine may provide insight into the poorly understood origins and depositional rate of ancient stromatolites

multi scale study of the role of the biofilm in the formation of minerals and fabrics in calcareous tufa abstract three sites of actively forming tufa two barrage systems and one terraced slope system located in northern calabria italy and in north east england have been investigated with the purpose of studying the neo formed carbonate minerals at the interface with the organic components that compose the associated biofilms several depositional facies are distinguished notably peloidal to aphanitic laminar and dendrolitic fabrics composed of micrite and microsparite and isolated botryoids and continuous crusts composed of sparite all fabrics occurring in all depositional facies are organized into layers with a more or less well developed seasonal cyclicity low mg calcite precipitates more or less constantly during all seasons within the active depositional zone this extends for a few hundred microns upon the external surface of the deposits where the biofilm occurs the latter is composed of a heterogeneous community of green algae filamentous cyanobacteria and other types of prokaryotes actinobacteria and fungi with a variable amount of extracellular polymeric substances eps porous micro columns 50 to 150 m in size separated by interstitial spaces characterize the active depositional zone here precipitation always begins with organomineral nanospheres 10 to 20 nm diameter both along the external surfaces and within internal cavities of the micro columns by replacing degraded organic matter and at point sites suspended within living cyanobacterial tufts along the external surface of their sheaths indicating that the biological activities of the biofilm are crucial with its living organisms and non living organic matter organomineral nanospheres successively agglutinate to form irregular to rod shaped crystal aggregates 100 200 nm in size that with their further agglutination create two basic types of larger more ordered crystal structure polyhedrons in the range of 1 2 m and minute triads of calcite fibres varying in length from 0 4 short triads to 1 m long triads basic crystal structures coalesce to form larger crystals mainly tetrahedrons tens of microns in size that constitute the micro columns

microbial mats as bioreactors populations processes and products microbial mats are dynamic and complex ecosystems exhibiting spatial and temporal heterogeneity the physical chemical environment is typified by steep gradients and distinct microenvironments these microenvironments support a great diversity of species with a wide range of metabolic processes these processes often result in coupled reactions and biogeochemical cycles and produce important end products such as trace gases and mineral precipitates the latter can impact the composition and character of the sediment imparting a biosignature these biosignatures can be preserved in the rock record and are useful in the interpretation of fossil record on earth and possibly as an indication of life on other planetary bodies the modern marine stromatolites of the exuma cays bahamas provide an ideal system for studying the populations processes and products in a microbial ecosystem using a multidisciplinary approach in order to acquire redox energy microbial populations need to carry out metabolic reactions at rates faster than the equivalent chemical abiotic reactions as such microbes can be viewed as bioreactors that preferably oxidize carbon to co2 to maximize the energy yield the study of the microbial role in carbonate sedimentation and lithification in these stromatolites provides a picture of microbial mats as bioreactors producing a biosignature

dynamic liquefaction of jurassic sand dunes processes origins and implications soft sediment deformation occurs in ancient eolian dune deposits but understanding its extent and the conditions and forces behind the deformation often remains elusive here we gain insight into the aerial extent and environmental conditions related to intense soft sediment deformation based on an exceptional three dimensional 3d exposure of eolian dune deposits and preserved geomorphic landscape expressions in the jurassic navajo sandstone at white pocket vermilion cliffs national monument arizona deformation features include elongate northeast trending decameter scale mounds and raised ridges cored by deformed and upturned eolian dune sets overlain by a massive blanket sandstone with breccia blocks the geomorphic mounds display 40 60 m spacing roughly perpendicular to the southerly paleoflow dune foreset directions the geometry of the deformation is imaged by oblique aerial photography using cameras mounted on a remote control airplane and high resolution panoramas with a robotic camera mount we interpret the exquisitely preserved deformation features as liquefaction induced ground failure consistent with theoretical and laboratory studies of deformation in saturated sand a shallow water table affected by differential dune loading facilitated lateral spreading and failure the transition to steady state flow liquefaction near the top of the shallow water table destroyed original sedimentary structure creating a massive sand blanket that entrained brecciated blocks ripped up during flow the water pressurized upwelled sediment created the mounds a relief inversion in underlying deformed dune sets deformation was intense but sedimentary structure was not obliterated as deformation progressed from initial cyclic mobility to strain softening but ceased prior to steady state flow liquefaction the spatial extent topographic relief and intensity of dynamic deformation suggest an origin of strong ground motion driven by long duration surface waves of a large earthquake mw 7 8 possibly related to back arc thrusting from jurassic subduction of the pacific plate under north america copyright 2014 john wiley sons ltd

the morphology and function of thrombolitic calcite precipitating biofilms a universal model derived from freshwater mesocosm experiments microbialites with laminar stromatolite and thrombolitic thrombolite fabrics are ubiquitous within the cenozoic freshwater sedimentary record however the biology and physiology of the living prokaryote microphyte biofilms which produced them is only now becoming understood the present contribution describes a flowing water experimental mesocosm study spanning over 2 5 years and run under near natural conditions this work focussed on microbial biofilm precipitation mechanisms which produce thrombolitic carbonate micro fabrics capable of preservation in the geological record in particular the roles of microbial guilds and carbonate precipitation processes were examined and recorded at all stages of thrombolite development the mesocosm experiments convincingly demonstrated that the biofilm community actively encouraged calcium ion precipitation derived from flowing waters this precipitation took the form of amorphous calcium carbonate nanosphere clusters these clusters were not randomly distributed within the biofilm extracellular polymeric substances but were focussed in the close vicinity of living filament and coccoid bacterial clusters within individual living biofilm layers significantly the precipitates never replaced microbial cell walls and never buried the living microbes during nanosphere precipitation extracellular polymeric substances were progressively occluded from between the developing nanosphere clusters however extracellular polymeric substances were never totally removed from within the amorphous calcium carbonate clusters until they had neomorphosed into microspar crystals the orientation of precipitating microspar crystals within the biofilm appeared to be controlled by the host extracellular polymeric substance fabric cf typical crystal growth from solid substrates precipitates were organized around the margins of a cancellate microfabric developed by a range of microbial guilds within each biofilm layer this produced a distinct thrombolitic fabric within the biofilm which was quite distinct from laminar stromatolite fabrics it is concluded that the mesocosm grown freshwater biofilms and their associated microbialite calcite micro fabrics present a universally applicable model importantly they provide a mechanism for thrombolite micro fabric developments throughout the geological record

the influence of diurnal temperatures on the hydrochemistry of a tufa depositing stream at a station diurnal variations in carbonate hydrochemistry were measured during four observation periods at davys creek a tufa depositing stream in central nsw australia major ion concentrations and continuously logged measurements of specific conductivity ph and temperature showed that changes in the amount of caco3 deposited upstream of the study reach were directly related to changes in diurnal water temperatures which control the rate of co2 efflux to the atmosphere the greatest upstream losses occurred during the mid afternoon water temperature peak whereas the lowest upstream losses occurred at sunrise when water temperatures were at their lowest cloudy days at all times of the year produced small diurnal water temperatures ranges c 2 5 c and consequently relatively small changes in upstream caco3 loss 23 50 mg l 1 through the day clear sunny days especially during summer months produced large diurnal water temperature changes up to c 1 1 c which in turn triggered diurnal changes in upstream caco3 loss of up to 100 mg l 1 by implication the active reach of tufa deposition must advance downstream and increase in length during the evening and vice versa during the day given that the temperature of davys creek waters are a function of insolation changes in the reach of tufa deposition under baseflow conditions are a direct function of the prevailing weather this has implications for the palaeoclimatic interpretation of fossil tufa deposits copyright 2003 john wiley sons ltd

submarine fault scarps in the sea of marmara pull apart north anatolian fault implications for seismic hazard in istanbul earthquake scarps associated with recent historical events have been found on the floor of the sea of marmara along the north anatolian fault naf the marmarascarps cruise using an unmanned submersible rov provides direct observations to study the fine scale morphology and geology of those scarps their distribution and geometry the observations are consistent with the diversity of fault mechanisms and the fault segmentation within the north marmara extensional step over between the strike slip ganos and izmit faults smaller strike slip segments and pull apart basins alternate within the main step over commonly combining strike slip and extension rapid sedimentation rates of 1 3 mm yr appear to compete with normal faulting components of up to 6 mm yr at the pull apart margins in spite of the fast sedimentation rates the submarine scarps are preserved and accumulate relief sets of youthful earthquake scarps extend offshore from the ganos and izmit faults on land into the sea of marmara our observations suggest that they correspond to the submarine ruptures of the 1999 izmit mw 7 4 and the 1912 ganos ms 7 4 earthquakes while the 1999 rupture ends at the immediate eastern entrance of the extensional cinarcik basin the 1912 rupture appears to have crossed the ganos restraining bend into the sea of marmara floor for 60 km with a right lateral slip of 5 m ending in the central basin step over from the gulf of saros to marmara the total 1912 rupture length is probably about 140 km not 50 km as previously thought the direct observations of submarine scarps in marmara are critical to defining barriers that have arrested past earthquakes as well as defining a possible segmentation of the contemporary state of loading incorporating the submarine scarp evidence modifies substantially our understanding of the current state of loading along the naf next to istanbul coulomb stress modeling shows a zone of maximum loading with at least 4 5 m of slip deficit encompassing the strike slip segment 70 km long between the cinarcik and central basins that segment alone would be capable of generating a large magnitude earthquake mw 7 2 other segments in marmara appear less loaded

origin of annual laminations in tufa deposits southwest japan abstract laminated tufas and a tufa depositing stream in sw japan shirokawa ehime prefecture were studied monthly over a 3 yr period a series of samples from the tufa clearly reveals the pattern of annual laminations the annual layering pattern was primarily controlled by changes in the rate of calcite precipitation as calculated from water chemistry the concentration of dissolved caco 3 which correlates with the precipitation rate was high in summer autumn and low in winter spring owing to changes in the partial pressure of co 2 in underground air regular seasonal changes in underground pco 2 probably resulted from two temperature dependent processes the diffusion of soil co 2 and the ventilation of underground air these changes in addition to water temperature changes altered the precipitation rate which has a clear seasonal pattern especially in the lower stream the seasonal precipitation rate was high in summer autumn and low in winter spring which is consistent with the seasonal lamination pattern seen in the tufas the textures of collected samples show that the laminations consist of densely calcified summer autumn june october laminae and lightly calcified winter spring november may laminae we infer that the increased precipitation rate stimulated thick calcite encrustation on cyanobacterial filaments to produce the dense textures this interpretation is supported by the lowered organic inorganic carbon production ratio in summer autumn seasonal variations in cyanobacterial assemblages are present but do not reflect the seasonal lamination pattern because the relevant processes are temperature dependent the seasonal lamination pattern at shirokawa is thought to generally apply to other laminated tufas deposited in temperate climates however a reversed pattern can result from local and climatic circumstances dense laminae were deposited in winter near the source of the spring at shirokawa because calcite precipitation was high owing to low underground pco 2 in winter reversed patterns reported from northwestern europe were probably influenced by seasonal rainfall which is reflected in hydrological conditions

maximum earthquake magnitudes along different sections of the north anatolian fault zone abstract constraining the maximum likely magnitude of future earthquakes on continental transform faults has fundamental consequences for the expected seismic hazard since the recurrence time for those earthquakes is typically longer than a century such estimates rely primarily on well documented historical earthquake catalogs when available here we discuss the maximum observed earthquake magnitudes along different sections of the north anatolian fault zone nafz in relation to the age of the fault activity cumulative offset slip rate and maximum length of coherent fault segments the findings are based on a newly compiled catalog of historical earthquakes in the region using the extensive literary sources that exist owing to the long civilization record we find that the largest m7 8 8 0 earthquakes are exclusively observed along the older eastern part of the nafz that also has longer coherent fault segments in contrast the maximum observed events on the younger western part where the fault branches into two or more strands are smaller no first order relations between maximum magnitudes and fault offset or slip rates are found the results suggest that the maximum expected earthquake magnitude in the densely populated marmara istanbul region would probably not exceed m7 5 the findings are consistent with available knowledge for the san andreas fault and dead sea transform and can help in estimating hazard potential associated with different sections of large transform faults

the indarri falls travertine dam lawn hill creek northwestern queensland australia indarri falls is a spectacular travertine dam which impounds lawn hill creek a perennial karst stream draining the barkly tableland in northwest queensland australia the dam is at least 13 5 m high making it the largest feature of its kind known in australia carbonate precipitation at the falls is favoured by downstream changes in the bulk chemistry of the karst spring waters which feed the creek although deposition at the microenvironmental level may be encouraged by biological factors the dam has dramatically altered the hydrology and geomorphology of the area transforming the middle reaches of lawn hill creek from a fluvial to a lacustrine environment 1997 by john wiley sons ltd

asymmetric slip partitioning in the sea of marmara pull apart a clue to propagation processes of the north anatolian fault between 1939 and 1999 the north anatolian fault naf experienced a westward progression of eight large earthquakes over 800 km of its morphological trace the 2000 km long north anatolian transform fault has also grown by westward propagation through continental lithosphere over a much longer timescale 10 myr the sea of marmara is a large pull apart that appears to have been a geometrical mechanical obstacle encountered by the naf during its propagation the present paper focuses on new high resolution data on the submarine fault system that forms a smaller pull apart beneath the northern sea of marmara between two well known strike slip faults on land izmit and ganos faults the outstandingly clear submarine morphology reveals a segmented fault system including pull apart features at a range of scales which indicate a dominant transtensional tectonic regime there is no evidence for a single continuous purely strike slip fault this result is critical to understanding of the seismic behaviour of this region of the naf close to istanbul additionally morphological and geological evidence is found for a stable kinematics consistent both with the long term displacement field determined for the past 5 myr and with present day anatolia eurasia motion determined with gps however within the sea of marmara region the fault kinematics involves asymmetric slip partitioning that appears to have extended throughout the evolution of the pull apart the loading associated with the westward propagation process of the naf may have provided a favourable initial geometry for such a slip separation

seasonal variation in water chemistry and depositional processes in a tufa bearing stream in sw japan based on 5 years of monthly observations abstract annually laminated freshwater carbonate tufa is a potential source of high resolution terrestrial paleoclimate data in order to understand the processes and characteristics of climate information recorded in tufa the chemical components of carbonate rich water its flow rate and soil pco2 were recorded monthly during a 5 year period december 1997 to december 2002 at shimokuraida niimi city okayama prefecture sw japan water issues from a limestone cave there flows along a 450 m long stream and deposits tufa that commonly exhibits distinct annual laminations among observed properties the co2 partial pressures in the soil and the spring water show the clearest seasonal patterns which are similarly high in summer autumn and low in winter spring the spring water pco2 partly reflects soil pco2 but is controlled by another temperature dependent process natural ventilation between the subsurface and the atmosphere the concentration of dissolved caco3 does not mirror the seasonal pattern of spring water pco2 but is largely influenced by rainfall dilution the development of annual laminations results from seasonal changes in the depositional rate of caco3 which was faster from summer to autumn and slower from winter to spring this seasonal pattern is initially controlled by relatively regular changes in water temperature and flow rate both of which correlated positively with the calcite precipitation rate high calcite precipitation in summer autumn formed a densely calcified texture whereas a precipitation low rate winter spring formed a porous texture changes in the concentrations of minor dissolved components mg2 na k cl no3 so42 and sio2 exhibited no seasonal pattern because the amplitude of the mg ca change is very high at shimokuraida the mg ca ratio of tufa calcite does not reflect paleotemperatures while mg ca ratio of water does not correspond to rainfall intensity too

mg ca ratios in freshwater microbial carbonates thermodynamic kinetic and vital effects the ratio of magnesium to calcium mg ca in carbonate minerals in an abiotic setting is conventionally assumed to be predominantly controlled by mg ca solution and a temperature dependant partition coefficient this temperature dependence suggests that both marine e g foraminiferal calcite and corals and freshwater e g speleothems and surface freshwater deposits tufas carbonate deposits may be important archives of palaeotemperature data however there is considerable uncertainty in all these settings in surface freshwater deposits this uncertainty is focussed on the influence of microbial biofilms biogenic or vital effects may arise from microbial metabolic activity and or the presence of extracellular polymeric substances eps this study addresses this key question for the first time via a series of unique through flow microcosm and agitated flask experiments where freshwater calcite was precipitated under controlled conditions these experiments reveal there is no strong relationship between mg ca calcite and temperature so the assumption of thermodynamic fractionation is not viable however there is a pronounced influence on mg ca calcite from precipitation rate so that rapidly forming precipitates develop with very low magnesium content indicating kinetic control on fractionation calcite precipitation rate in these experiments where the solution is only moderately supersaturated is controlled by biofilm growth rate but occurs even when light is excluded indicating that photosynthetic influences are not critical our results thus suggest the apparent kinetic fractionation arises from the electrochemical activity of eps molecules and are therefore likely to occur wherever these molecules occur including stromatolites soil and lake carbonates and via colloidal eps speleothems

geological slip rates along the north anatolian fault in the marmara region 1 reliable piercing points on both sides of the sea of marmara enabled us to obtain an estimate of the slip rate over time scales of 10 15 ka on different fault strands of the north anatolian fault naf system we analyzed geomorphic features in the gulfs of izmit gemlik sea of marmara and saros ne aegean sea which were passively displaced by the naf strands after their abandonment related to the post glacial sea level rise results for the main northern strand consistently similar on both sides of the marmara pull apart are in the order of 10 mm yr about one half of that expected from geodetic measurements and accepted plate tectonic models in the southern branch of the naf the estimated rate of 4 mm yr is only slightly higher than that given by geodetic models our findings have implications for both neo tectonic reconstructions of the submerged portion of the naf system and fault interactions and seismic hazard estimates in the marmara region they suggest that either the total anatolia eurasia plate motion is more diffuse than previously reported or geodetic data are not representative of the geological time scale deformations moreover they suggest that a significant amount of stress is accommodated along the southern strand of the naf system on which the last large m 7 earthquakes dates back to 1419 1855 and 1863 ad

new insights into biological influence on the geochemistry of freshwater carbonate deposits abstract ambient temperature freshwater carbonates tufas have outstanding potential as palaeoclimate archives however it has proven difficult to constrain the behaviour of the geochemical parameters on which important proxy systems rely current thinking on the development of trace element ratios in tufa rests upon an assumption of precipitation driven by degassing of co2 with the final precipitate being in equilibrium with ambient river water this study provides evidence that although supersaturation is largely regulated by degassing precipitation in sterile flowing systems does not occur throughout the air water interface but only at lines of intersection between this interface and a solid surface precipitation at the bottom as is normal in river sites is not found to occur however when benthic microbial communities biofilms are present extensive precipitation does occur within them in preference and or addition to that at the air water interface precipitation is therefore not purely a consequence of degassing and some microbiological influence is necessary to generate precipitates analogous to nature we further investigate whether these biofilms alter the behaviour of trace elements within tufa systems in addition to modulating the sites and mechanisms of precipitation via a series of experiments biofilms are shown to accumulate large inventories of calcium and other dissolved ions ba sr and mg and we demonstrate that this process is chemoselective in favour of ions with low charge densities these observations have consequences for interpretation of trace element records from tufas based on an assumption of equilibrium with river water and also for other carbonate deposits associated with biofilm activity travertines marine stromatolites lacustrine and soil carbonates speleothems conversely our study provides new insight into the reasons for discrepancy of tufa mg ca ratios from expectation and thus provides encouragement for the potential of mg ca palaeothermometry in freshwater carbonate systems

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

micromorphology and genesis of quaternary stromatolitic tufa crust within the exposed cretaceous rayda formation in al jabal al akhdar oman abstract this study aimed to improve the understanding of the causes of lamination in terrestrial tufa using samples of terrestrial quaternary stromatolitic tufa deposits occurring within narrow karst grooves carved along the bedding planes of the exposed cretaceous rayda formation in al jabal al akhdar oman these stromatolitic tufa deposits consist wholly of low mg calcite and are formed of vertically stacked laminated planar and digitate like columnar structures lamination is exhibited as vertically stacked couplets of dark micritic and light sparitic laminae significant variations in the abundance and thickness of the micritic laminae as well as progressive changes in the size and fabric of calcite in the sparitic laminae were recognised thorough microscopic and nanoscopic examinations revealed that these laminations initially developed as stacked indistinct micritic laminae formed of calcitic microbialite that had initially precipitated within a biologically active microbial biofilm which thrived on the wet bedrock surface this was followed by the growth of microglobules at certain horizons within the microbialitic laminae forming incipient discontinuous thin sparitic laminae consisting of laterally stacked biogenic skeletal disphenoidal calcite microcrystals the latter were further growing via abiogenic syntaxial precipitation of calcite forming coarsely crystalline dagger shape bladed calcite crystals these processes resulted in the formation of well developed lamination it is therefore suggested that the stromatolitic lamination has been generated through five consecutive stages of biogenic and abiogenic precipitation of calcite within initially developed microbial biofilms stable isotope values 13c and 18o suggest that these tufa deposits had precipitated from continuously renewed freshwater enriched with bicarbonate dissolved from the marine limestone bedrock during a cold pluvial period

factors controlling tufa deposition in natural waters at waterfall sites abstract study on calcite precipitation has major implications for both the hydrochemical evolutions of river systems and the global carbon cycle the precipitation of calcite generally requires the water to be 5 10 times supersaturated with respect to calcite which is usually achieved by the removal of co2 formation of waterfall tufa has been often simply described as the result of water turbulence in fast flowing water in this paper the formation mechanisms of waterfall tufa are discussed and a series of laboratory experiments are designed to simulate the hydrological conditions at waterfall sites the influences of the air water interface the water flow velocity and the solid water interface on co2 outgassing and calcite precipitation are compared and evaluated quantitatively the results show that the principal cause of waterfall tufa formation is the enhanced inorganic carbon dioxide outgassing resulted from the sudden hydrological changes occurring at waterfall sites rather than organisms evaporation or the solid water interface the air water interface area and the water flow velocity are greatly increased at waterfall sites as a result of the aeration effect low pressure effect and jet flow effect which greatly accelerate co2 outgassing inorganic co2 outgassing drives the waters to become highly supersaturated with respect to calcite and consequently results in much calcite deposition the solid water interface is less important as the air water interface in affecting calcite precipitation at waterfall sites field measurements showed that conductivity ca2 and hco3 concentrations along tianhe creek and hot creek decrease downstream while ph rises field observations also showed that tufa deposition occurred mainly at waterfall sites

freshwater calcite precipitates from in vitro mesocosm flume experiments a case for biomediation of tufas freshwater carbonates tufas develop today from the arctic to the tropics many being localized about springs and upper water courses some quaternary tufas especially in the mediterranean region extend over tens of square kilometres and exceed 30 m in thickness radiometric dating of holocene deposits shows that many have accumulated at an average rate of 1 mm year 1 however local precipitation may be much faster and some holocene deposits may even have outpaced their tropical marine carbonate counterparts recently the study of active sites has attempted to quantify the precipitation mechanisms which lead to tufa deposition however field observation and sampling procedures suffer from the inherent disadvantages of uncontrolled fluctuations in environmental conditions during the study programme these disadvantages compromise any interpretations particularly where controls on spar versus micrite precipitation are concerned many of these problems have been overcome in the current study by the construction and operation of laboratory mesocosm flumes which simulate the natural conditions e g ph flow rate ambient temperature and daylight in which freshwater carbonate tufa is deposited three mesocosms were supplied with natural river water from tufa precipitating streams and two mesocosms were supplied with uv treated sterile river water from the same source one of the untreated flume mesocosms was linked with a calcium reactor which replaced calcium ions removed during the precipitation process in order to maintain tufa growth over extended experimental runs low magnesium calcite precipitates both rhombic sparite grown from long crystallite dendrites and short crystallite dendrite triad precursors and micrite peloids grown from spherulitic precursors were precipitated in intimate association with biofilm extracellular polymeric substances within the four mesocosms supplied with natural river water virtually no tufa like precipitate was obtained from the flumes supplied with uv treated river water a second extended run flume experiment was also carried out for comparison purposes using a calcium hydroxide solution in deionized water collectively these experiments provide convincing evidence confirming that the presence of a microbial biofilm strongly influences the precipitation of carbonates in riverine freshwater settings in particular experimental results show that micropeloidal micrite and short crystallite calcite dendrites are only produced in the presence of microbial extracellular polymeric substances

an explanation of the effect of seawater carbonate concentration on foraminiferal oxygen isotopes abstract stable oxygen isotope ratios of foraminiferal calcite are widely used in paleoceanography to provide a chronology of temperature changes during ocean history it was recently demonstrated that the stable oxygen isotope ratios in planktonic foraminifera are affected by changes of the seawater chemistry carbonate system the 18 o of the foraminiferal calcite decreases with increasing co 3 2 concentration or p h this paper provides a simple explanation for seawater chemistry dependent stable oxygen isotope variations in the planktonic foraminifera orbulina universa which is derived from oxygen isotope partitioning during inorganic precipitation the oxygen isotope fractionation between water and the dissolved carbonate species s h 2 co 3 hco 3 co 3 2 decreases with increasing p h provided that calcium carbonate is formed from a mixture of the carbonate species in proportion to their relative contribution to s the oxygen isotopic composition of caco 3 also decreases with increasing p h the slope of shell 18 o vs co 3 2 of orbulina universa observed in culture experiments is 0 0022 mol kg 1 1 spero et al 1997 whereas the slope derived from inorganic precipitation is 0 0024 mol kg 1 the theory also provides an explanation of the nonequilibrium fractionation effects in synthetic carbonates described by kim and o neil 1997 which can be understood in terms of equilibrium fractionation at different p h the results presented here emphasize that the oxygen isotope fractionation between calcium carbonate and water does not only depend on the temperature but also on the p h of the solution from which it is formed