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

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

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

comparative study of the pleistocene cakmak quarry denizli basin turkey and modern mammoth hot springs deposits yellowstone national park usa this study compares and contrasts the travertine depositional facies of two of the largest sites of travertine formation located in very different geological contexts i e the modern mammoth hot spring mhs system in the active volcanic complex of yellowstone national park usa and the pleistocene cakmak quarry a well exposed example of the ballik travertines in the extensional denizli basin turkey new 2d to 3d facies maps of both travertine systems combined with microscopy assist in proposing an integrated spring depositional model based on the existing mhs facies model understanding general controls on meter to kilometer scale travertine deposit architecture and its preservation and provide quantitative estimates of facies spatial coverage and slope using gis the comparison resulted in the distinction of eight facies grouped in five downstream facies zones from vent to distal slope notwithstanding the different geological context of both travertine systems observations show that several of the facies are strikingly comparable draping apron and channel facies top slope pond facies crystalline proximal slope facies and distal slope facies whereas other facies do not have a precise exposed equivalent vent facies pavement apron and channel facies extended pond facies and phyto proximal slope facies combining observations of active springs at mhs with the cakmak vertical travertine quarry exposures demonstrates that lateral and vertical facies transitions are a sensitive record of changes in the spring dynamics flow intensity and paths that become well preserved in the geological record and can be recognized as prograding aggrading retrograding trends or erosive surfaces traceable over tens to hundreds of meters quantification of facies specific coverage at mhs shows that proximal and distal slope facies deposits cover as much as 90 of the total mapped surface area in addition only 7 of the surface is found to be marked by a waterfilm related to an active flowing spring slope statistics reveal that strong slope breaks can often be related to transgressive apron and channel facies belts and that variable but steep slopes up to 40 are dominated by proximal slope facies in agreement with the cakmak exposures integrating travertine facies and architecture of deposits formed in distinct geological contexts can improve the prediction of general spring facies distributions and controls in other modern and ancient subsurface travertine systems

production and cycling of natural microbial exopolymers eps within a marine stromatolite extracellular polymeric secretions eps that are produced by cyanobacteria represent potential structuring agents in the formation of marine stromatolites the abundance production and degradation of eps in the upper layers of a microbial mat forming shallow subtidal stromatolites at highborne cay bahamas were determined using 14 c tracer experiments and were integrated with measurements of other microbial community parameters the upper regions of a type 2 reid r p visscher p t decho a w stolz j bebout b macintyre i g dupraz c pinckney j paerl h prufert bebout l steppe t des marais d 2000 the role of microbes in accretion lamination and early lithification of modern marine stromatolites nature london 406 989 992 stromatolite mat exhibited a distinct layering of alternating bgreenq cyanobacteria rich layers layers 1 and 3 and bwhiteq layers layers 2 and 4 and the natural abundance of eps varied significantly depending on the mat layer the highest eps abundance occurred in layer 2 the production of new eps as estimated by the incorporation of 14 c bicarbonate into eps occurred in all layers examined with the highest production in layer 1 and during periods of photosynthesis i e daylight hours a large pool i e up to 49 of the total 14 cbicarbonate uptake was released as low molecular weight mw dissolved organic carbon doc this doc was rapidly mineralized to co2 by heterotrophic bacteria eps degradation as determined by the conversion of 14 c eps to 14 co2 was slowest in layer 2 results of slurry experiments examining o2 uptake following additions of organic substrates including eps supported this degradation trend and further demonstrated selective utilization by heterotrophs of specific monomers such as acetate ethanol and uronic acids results indicated that natural eps may be rapidly transformed post secretion by heterotrophic degradation specifically by sulfate reducing bacteria to a more refractory remnant polymer that is relatively slow to accumulate a mass balance analysis suggested that a layer specific pattern in eps and low mw doc turnover may contribute to major carbonate precipitation events within stromatolites our findings represent the first estimate of eps

aragonite laminae in hot water travertine crusts rapolano terme italy small 5 30 m aggregates of aragonite needles occur in calcite crystal crusts of present day hot water slope travertines at rapolano terme in tuscany italy the aggregates are mainly concentrated in irregular wispy and dark laminae which cross cut calcite crystal feathers to create a pervasive millimetre scale banded appearance in the deposit they also occur less commonly scattered irregularly through the calcite layers the aragonite needle aggregates are in the form of crosses fascicles sheaf shaped bundles or dumbbell shaped rosettes and spherulites locally irregular masses of needles also occur the fascicles rosettes and spherulites have hollow centres which resemble microbial components fungal spores bacterial colonies and pollen suggesting that the aragonite crystals are biotically nucleated the lamination is interpreted to reflect diurnal control stimulation of microbial activity during daylight concentrates cells in laminae and promotes aragonite calcification calcite feather crystals although traversed by the aragonite aggregate laminae have a clear appearance under the light microscope they form more or less continuously through the diurnal cycle by abiotic precipitation the constant association of aragonite with organic nuclei irrespective of whether the latter are in laminae or scattered through the calcite layers supports a biotic control on aragonite formation lamination in pleistocene travertines is superficially similar to that in the present day deposits but is diagenetically altered in the pleistocene deposits the calcite feathers appear dark under the light microscope and the aragonite aggregates where they are not altered to dark calcite are dissolved together with parts of the adjacent spar calcite and therefore appear light coloured

ecogeomorphic feedbacks in regrowth of travertine step pool morphology after dam decommissioning fossil creek arizona abstract the linkages between fluvial geomorphology and aquatic ecosystems are commonly conceptualized as a one way causal chain in which geomorphic processes create the physical template for ecological dynamics in streams with a travertine step pool morphology however biotic processes strongly influence the formation and growth of travertine dams creating the potential for numerous feedbacks here we take advantage of the decommissioning of a hydroelectric project on fossil creek arizona where restoration of caco 3 rich baseflow has triggered rapid regrowth of travertine dams to explore the interactions between biotic and abiotic factors in travertine morphodynamics we consider three conceptual frameworks where biotic factors independently modulate the rate of physical and chemical processes that produce travertine dams combine with abiotic factors in a set of feedback loops and work in opposition to abiotic processes such that the travertine step pool morphology reflects a dynamic balance between dominantly biotic constructive processes and dominantly abiotic destructive processes we consider separately three phases of an idealized life cycle of travertine dams dam formation growth and destruction by erosive floods dam formation is catalyzed by abiotic factors e g channel constrictions and bedrock steps and biotic factors e g woody debris and emergent vegetation from measurements of changes over time in travertine thickness on a bedrock step we find evidence for a positive feedback between flow hydraulics and travertine accrual measurements of organic content in travertine samples from this step show that algal growth contributes substantially to travertine accumulation and suggest that growth is most rapid during seasonal algal blooms to document vertical growth of travertine dams we embedded 252 magnets into nascent travertine dams along a 10 km stretch of river growth rates are calculated from changes over time in the magnetic field intensity at the dam surface at each magnet we record a range of hydraulic and travertine composition variables to characterize the dominant mechanism of growth abiotic precipitation algal growth trapping of organic material or in situ plant growth we find 1 rapid growth of travertine dams following flow restoration averaging more than 2 cm year 2 growth rates decline downstream consistent with loss of dissolved constituents because of upstream travertine deposition but also parallel to a decline in organic content in dam surface material and a downstream shift in dominant biotic mechanism 3 biotic mechanisms are associated with faster growth rates and 4 correlations between hydraulic attributes and growth rates are more consistent with biotic than abiotic controls we conclude that the strong influence of living organisms on rates of travertine growth coupled with the beneficial effects of travertine on ecosystem dynamics demonstrate a positive feedback between biology and geomorphology during our two year study period erosive flood flows occurred causing widespread removal of travertine the temporal distribution of travertine growth and erosion over the study period is consistent with a bimodal magnitude frequency relation in which growth dominates except when large infrequent storms occur this model may be useful in other systems where biology exerts strong controls on geomorphic processes

convective circulations induced by surface heterogeneities a simple theory for convective circulations induced by surface heterogeneities is proposed the theory is based on the thermodynamics of heat engines and provides a simple physical explanation for the general characteristics of circulations forced by surface inhomogeneities in sloping terrains in particular the theory is applied to a mesoscale circulation induced by deforestation it predicts that the intensity of the mesoscale convective circulation forced by deforestation depends on the difference of the near surface nonadiabatic temperature and humidity between the forest and cleared regions and on the depth of the convective boundary layer the theory was successfully tested against observations made during a field experiment in the amazon forest and a nearby clearing

periodicity in stromatolitic lamination a potential record of enso nao and sunspot in the miocene lacustrine record of the ebro basin spain abstract the spectral decomposition of time series obtained from ancient rock records can be used to study the similarity between the dynamics of present day and past climate systems a high resolution periodicity analysis of luminance and lamina thickness of lacustrine stromatolites in the ebro basin northeast of iberian peninsula reveals a significant signal of interannual and decadal climatic variability in the miocene this is one out of very few works that presents the use of spectral analysis to estimate the potential of stromatolite lamination as multiple scale recorders of climate parameters the effects of precipitation and evaporation variations on stromatolite lamination have been detected at three orders of cyclicity based on textural and high resolution stable isotope analyses c and o obtained in prior studies these analyses also revealed that the light and dark simple lamina couplets are identified with annual cycles third order isotopic cycles in the present study the spectral analysis results obtained through different paths in five stromatolite specimens reveal significant periods in the power spectrum at around 2 5 3 7 5 7 10 and 22 years these cycles can be correlated with the typical oscillation bands of different climate related agents the 2 5 year period corresponds to the quasi biennial oscillation qbo or to the biennial component of the el nino southern oscillation enso or to the north atlantic oscillation nao the 3 to 5 and 5 to 7 year bands can be linked to enso or nao variability second order isotopic cycles the 8 to 11 year bands fit the 11 year schwabe first order isotopic cycles and 22 to 23 year fit the 22 year hale sunspot cycles thus the stromatolite growth was controlled by enso nao and solar activity cycles the close relationship between these climate related agents makes it difficult to specify the dominant agent controlling the stromatolite growth nevertheless the significant periods obtained from this study within interannual 2 5 3 7 5 7 years decadal 10 22 years and even multidecadal bands 37 42 years support the existence and concurrence of enso and nao precursors during the early and middle miocene

textural transition in an aragonite travertine formed under various flow conditions at pancuran pitu central java indonesia abstract a large travertine mound at pancuran pitu central java indonesia displays various types of lamination reflecting different hydrological conditions to understand the geomicrobiological processes of the laminated travertines we investigated the mound s hydrology water chemistry texture microbial composition and volume percentage of carbonate mineral vpc we identified four types of travertines dense travertine 80 vpc flow rate 200 cm s lithified microbial travertine 60 vpc flow rate 70 cm s fragile microbial travertine 30 vpc flow rate 10 cm s and poorly lithified microbial mat

palaeoproterozoic travertines of volcanic affiliation from a 13c rich rift lake environment abstract the ca 2 2 ga kuetsjarvi sedimentary formation ksf of the pechenga greenstone belt the north east fennoscandian shield contains the oldest travertines so far reported in the literature the travertine hosting succession is composed of flat laminated dolomitic stromatolites micritic and allochemical dolostones all formed in coastal plains of a rift related playa lake system in an arid semiarid climate the travertines are categorised as thermal autochtonous spring travertine crust and spring orifice travertine mounds formed from hot water springs issuing at the playa lakeshore the travertines are represented by crusts and small scale mounds both composed of a series of 1 5 mm thick dark light couplets of fibrous dolomite crystals with compromise boundaries and radiating dolomite crystals travertines are composed of dolomite mg ca 0 42 0 47 exhibiting a general lack of replacement textures travertines exhibit several phases of growth separated by dissolution processes and accompanied by precipitation of sio 2 the upper surface of crusts and mounds are often affected by desiccation joints and covered with thicker sio 2 veneer 18 o 18 6 the host dolostones are characterised by 13 c carb of 6 1 8 8 v pdb and 18 o values ranging from 11 to 19 v smow microcored samples of travertine dolomite exhibit 13 c and 18 o values ranging from 6 1 to 7 7 and from 12 0 to 21 5 respectively the 13 c rich nature of the background stratified dolostones is caused by the 2 4 2 06 ga global shift in 13 c 12 c carbonate carbon associated with enhanced accumulation of c org and perturbation of the global carbon cycle the source of co 2 for the travertines is considered to be of volcanogenic origin with an initial 13 c value of ca 6 0 several processes contributed to carbon and oxygen isotope composition of travertine dolomite i an initial co 2 loss at the spring orifice ii water cooling and rapid co 2 loss during water transit iii persistent evaporation from thermal water ponds pools and iv mixing with co 2 of ambient lake water enriched in 13 c silica is thought to have been dissolved by groundwater from underlying sediments and been transported upwards by a mechanism of capillary rise due to dry climatic condition

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

wet dry seasonal variations of hydrochemistry and carbonate precipitation rates in a travertine depositing canal at baishuitai yunnan sw china implications for the formation of biannual laminae in travertine and for climatic reconstruction travertine or tufa is a chemical sedimentary deposit that is precipitated from springfed stream water supersaturated with calcite due to co2 degassing liu et al 1995 pentecost 1995 ford and pedley 1996 these deposits have biannual laminations which could provide valuable paleoclimatic and paleoenvironmental information with high resolution liu et al 2006 kano et al 2007 brasier et al 2009 lojen et al 2009

transition of microbiological and sedimentological features associated with the geochemical gradient in a travertine mound in northern sumatra indonesia abstract modern travertines carbonate deposits in ca rich hydrothermal water with high pco2 often display a changing environment along the water path with corresponding variability in the microbial communities we investigated a travertine bearing hot spring at the blue pool in northern sumatra indonesia the thermal water of 62 c with high h2s 200 m and pco2 1 atm developed a travertine mound 70 m wide the concentrations of the gas components h2s and co2 decrease immediately after the water is discharged while the dissolved oxygen ph and aragonite saturation increase in the downstream direction responding to the geochemical gradient in the water the surface biofilms change color from white to pink light green dark green and brown as the water flows from the vent this corresponds to microbial communities characterized by chemolithoautotrophs halothiobacillaceae purple sulfur bacteria chromatiaceae anaerolineaceae and co occurrence of green non sulfur bacteria chloroflexales cyanobacteria and green sulfur bacteria chlorobiales respectively in an environment with a certain level of h2s 1 m sulfur digestion and anoxygenic photosynthesis can be more profitable than oxygenic photosynthesis by cyanobacteria the precipitated carbonate mineral consists of aragonite and calcite with the proportion of aragonite increasing downstream due to the larger mg2 ca2 ratio in the water or the development of thicker biofilm where the biofilm is well developed the aragonite travertines often exhibit laminated structures that were likely associated with the daily metabolism of these bacteria the microbiological and sedimentological features at the blue pool may be the modern analogs of geomicrobiological products in the early earth biofilm of anoxygenic photosynthetic bacteria had the potential to form ancient stromatolites that existed before the appearance of cyanobacteria

analysis of the crustal velocity structure of the british isles using teleseismic receiver functions summary the onshore crustal and upper mantle velocity structure of the british isles has been investigated by teleseismic receiver function analysis the results of the study augment the dense offshore and sparse onshore models of the velocity structure beneath the area in total almost 1500 receiver functions have been analysed which have been calculated using teleseismic data from 34 broadband and short period three component seismic recording instruments the crustal structure has primarily been investigated using 1 d grid search and forward modelling techniques returning crustal thicknesses bulk crustal vp vs ratio and velocity depth models h stacking reveals crustal thicknesses between 25 and 36 km and vp vs ratios between 1 6 and 1 9 the crustal thicknesses correlate with the results of previous seismic reflection and refraction profiles to within 2 km the significant exceptions are the stations close to the iapetus suture where the receiver function crustal thicknesses are up to 5 km less than the seismic refraction moho this mismatch could be linked to the presence of underplated magmatic material at the base of the crust 1 d forward modelling has revealed subcrustal structures in northern scotland these correlate with results from other uk receiver function studies and correspond with the flannan and w reflectors the structures are truncated or pinch out before they reach the midland valley of scotland the isolated subcrustal structure at station gim on the isle of man may be related to the closure of the iapetus ocean

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

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

implications for neoarchaean ocean chemistry from primary carbonate mineralogy of the campbellrand malmani platform south africa the precipitation of calcite and aragonite as encrustations directly on the seafloor was an important platform building process during deposition of the 2560 2520 ma campbellrand malmani carbonate platform south africa aragonite fans and fibrous coatings are common in unrestricted shallow subtidal to intertidal facies they are also present in restricted facies but are absent from deep subtidal facies decimetre thick fibrous calcite encrustations are present to abundant in all depositional environments except the deepest slope and basinal facies the proportion of the rock composed of carbonate that precipitated as encrustations or in primary voids ranges from 0 to 65 depending on the facies subtidal facies commonly contain 20 35 in situ precipitated carbonate demonstrating that neoarchaean sea water was supersaturated with respect to aragonite carbonate crystal growth rates were rapid compared with sediment influx rates and the dynamics of carbonate precipitation were different from those in younger carbonate platforms the abundance of aragonite pseudomorphs suggests that sea water ph was neutral to alkaline whereas the paucity of micrite suggests the presence of inhibitors to calcite and aragonite nucleation in the mixed zone of the oceans

isotopic fingerprints of microbial respiration in aragonite from bahamian stromatolites authigenic aragonite preserves a carbon isotopic record of heterotrophic microbial influences on dissolved inorganic carbon dic in microenvironments within shallow subtidal stromatolites from highborne cay bahamas a greater amount of aragonite precipitates when and where respiration rather than photosynthesis influences local dic which is consistent with sulfate reduction promoting carbonate precipitation and calcium release during decay of exopolymeric substances thus heterotrophs play a more direct role than phototrophs in stromatolite lithification cyanobacteria are spatially associated with aragonite containing heterotrophic isotopic signatures hence the absence of an autotrophic isotopic signature in the rock record does not imply the absence of photosynthetic organisms