numerical simulations of marine hydrothermal plumes for europa and other icy worlds abstract the liquid water interiors of europa and other icy moons of the outer solar system are likely to be driven by geothermal heating from the sea floor leading to the development of buoyant hydrothermal plumes these plumes potentially control icy surface geomorphology and are of interest to astrobiologists we have performed a series of simulations of these plumes using the mit gcm ocean circulation model we assume here that europa s ocean is deep of order 100 km and unstratified and that plume buoyancy is controlled by temperature not composition our experiments explore a limited region of parameter space with ocean depth h ranging from 50 to 100 km deep source heat flux q between 0 1 and 10 gw and coriolis parameter f corresponding to europa latitudes between 9 and 47 as predicted by earlier work the plumes in our simulations form narrow cylindrical chimneys a few km across under the influence of the coriolis effect these plumes broaden over time until they become baroclinically unstable breaking up into cone shaped eddies when they become 10 35 km in diameter the shed eddies are of a similar size large scale currents in the region of the plume range between 1 and 5 cm s temperature anomalies in the plume far from the seafloor are tiny varying between 10 and 180 k variations in plume size shape speed and temperature are in excellent agreement with previous laboratory tank experiments and in rough agreement with theoretical predictions plume dynamics and geometry are controlled by a natural rossby number which depends strongly on depth h and coriolis parameter f but only weakly on source heat flux q however some specific theoretical predictions are not borne out by these simulations this may occur because the plumes are reingesting their own emissions a process not considered in our earlier theory

detecting tides and gravity at europa from multiple close flybys 1 this paper presents the expected accuracy of the tides and gravity of europa that can be measured by tracking a spacecraft during close flybys of europa a reference trajectory was designed for flyby science observations and consists of a total of 36 flybys of europa at 100 km altitude earth based doppler measurements were created during 2 hours of each periapsis passage and were simulated with realistic dynamical and measurement assumptions the result shows that the degree 2 tidal love number k2 can be estimated to k2 0 045 and k2 0 009 1 sigma formal uncertainty assuming x band and ka band tracking capabilities respectively which is sufficient to confirm the existence of a global subsurface ocean

deposition diagenetic and hydrothermal processes in the aptian pre salt lacustrine carbonate reservoirs of the northern campos basin offshore brazil abstract the discovery of large oil accumulations in the rift and sag pre salt sections of the campos and santos basins has revived interest in the exploration of the lacustrine carbonate reservoirs in the brazilian and african marginal basins more than half of brazilian oil production originates from the pre salt reservoirs of these offshore basins a study integrating systematic petrography cathodoluminescence scanning electron microscopy microprobe and x ray diffraction was performed on seven wells in the northern campos basin this study highlights the major primary diagenetic and hydrothermal features of the pre salt succession with the aim to improve our understanding of the factors that influence the porosity and permeability distribution in these important lacustrine carbonate reservoirs the pre salt deposits correspond to bioclastic grainstones and rudstones syngenetic crusts of fascicular calcite and intraclastic grainstones and rudstones of reworked crust fragments and calcite spherulites magnesian silicates are frequently associated with carbonate deposits in the sag phase stevensitic laminations constitute the substrate for the precipitation of calcite crusts and spherulites which displace and replace the syngenetic magnesian clay deposits in the rift section stevensitic ooids are mixed with bioclasts or form ooidal arenites pre salt carbonate reservoirs have undergone a complex and heterogeneous diagenetic evolution eodiagenetic processes include the dissolution neomorphism and cementation of bivalve bioclasts in the rift as well as the dissolution of magnesian silicates and their replacement by calcite spherulites silica and dolomite in the sag section burial alterations are commonly associated with hydrothermal fluids carried through faults and fracture systems these fluids promote dolomitization silicification and dissolution at varying degrees and intensities eodiagenetic precipitation and dissolution owing to variations in the lake water chemistry and the episodic flow of hydrothermal fluids under burial conditions control the creation redistribution and obliteration of porosity in the pre salt reservoirs

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

magnetic remote sensing of europa s ocean tides abstract recent analyses of galileo magnetometer and gravity data justifies approximations that allow estimates of the magnetic fields generated by europa s ocean tides to be made even though some of the ocean parameters that would generally be required are unavailable we show solutions for the magnetic fields generated by published estimates of ocean tides on europa and provide simple scaling formulas that can be used to estimate the magnetic field amplitudes for other choices for the ocean tidal state because of the distinguished spatial temporal form of these fields it is expected that europa s ocean tides can be inferred from remote magnetic sensing by an orbiter of sufficient duration

ocean driven heating of europa s icy shell at low latitudes on jupiter s icy moon europa enigmatic chaos terrain where the icy crust is cut by a jumble of ridges and cracks occurs most commonly at lower latitudes simulations of convection in the ocean underlying europa s icy crust suggest that ocean dynamics can control an enhanced flow of heat to europa s equatorial surface and hence geological activity

composition structure and evolution of a lacustrine carbonate margin dominated by microbialites case study from the green river formation eocene wyoming usa abstract during mid eocene times the northwestern margin of the gosiute lake wyoming has been characterised by the extensive development of a microbialite dominated carbonate sequence corresponding to the laney member of the green river formation thus providing a potential analogue for petroleum carbonate reservoirs developed in similar marginal lacustrine settings a detailed sedimentological study carried out on the little mesa plateau near labarge sw wyoming allows the reconstruction of 1 lateral and vertical facies variations of the carbonate sequence across the margin 2 development patterns of complex microbial bioconstructions and 3 the evolution of the margin through time the carbonate sequence up to 18 m thick starts with the deposition of sandy limestones which fill channels in the underlying siliciclastic unit of the cathedral bluff formation the increasing microbial contribution in the upper part of the sequence results in the development of large insect microbial build ups which represent up to 80 of the total volume of the carbonate deposits and which aggregated to form reef like geometries up to several tens of metres in diameter including bioherms spur and groove alignments and reef flat structures the initiation and development of the lacustrine carbonate platform was controlled both by the general lake expansion associated to the eocene climatic optimum and by local drainage diversions responsible for a new water inflow in the basin from the northern volcanic provinces short term lake level changes driven by high frequency climate fluctuations which are superimposed to this general transgressive trend may explain the discontinuous and polygenic growth of the individual insect microbial build ups the basin infilling by prograding alluvial volcaniclastic deposits originated from the northwestern volcanic province caused the rapid turn off of the marginal lacustrine carbonate factory during mid eocene time

simulations of magnetic fields generated by the antarctic circumpolar current at satellite altitude can geomagnetic measurements be used to monitor the flow 1 with a volume transport of 134 106 m3 s at the drake passage the antarctic circumpolar current acc is the strongest ocean current in the interest of estimating the secondary magnetic fields generated by the magnetohydrodynamic interaction of this flow with earth s main field we compare numerical results for the magnetic fields obtained using flow from three different ocean general circulation models these simulations all expect detectable ocean signals in the magnetic records at ground and satellite altitude 400 km the variability of this contribution is highly correlated with the acc transport a very important variable for climate studies observed magnetic fields could then be used in principle to derive an index of variability of the acc however given its small amplitude compared with other magnetic contributions extracting the ocean s signal from observations remains a challenge at this time

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

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

origin and diagenesis of quaternary travertine shrub fabrics rapolano terme central italy millimetre to centimetre sized arborescent shrub like calcite precipitates are common constituents of hot water travertine shallow pool deposits of quaternary age at rapolano terme tuscany italy in the presently forming travertines the shrubs consist of apparently random associations of i micrite aggregates and ii subhedral to euhedral rhombic spar crystal aggregates in thin section the micrite aggregates appear dark and the spar rhomb aggregates light giving the shrubs a mottled appearance travertines are basically produced by caco3 precipitation due to degassing and evaporation of the spring waters although biological influence may also stimulate precipitation the formation of masses of erect shrubs rather than dense crystal crusts that form on slopes is probably due to limited water flow in the pool environments microbes including bacteria and diatoms are important influences on shrub microfabric and external shape the micrite aggregates are associated with bacteriform bodies seen as tiny rods and spheres the micrite precipitates around these bodies and in adjacent biofilm spar rhomb precipitation appears to be external to the biofilm and may be related to the presence of diatoms which are locally closely associated with the spar rhombs although an essentially inorganic origin particularly for the more euhedral rhombs cannot be ruled out in the older quaternary travertines the original microfabric of the shrubs has been diagenetically altered the original mottled appearance of the shrubs has become uniformly dark and micritic and the evidence for the dual micritic and spar rhomb origin of the shrubs is obscured or destroyed spar micritization of the shrubs is probably due to abiotic and locally biotic dissolution previous studies did not recognize the diagenetic micritization and attributed shrub formation entirely to bacterial activity

lateral and vertical variations in sedimentology and geochemistry of sub horizontal laminated travertines cakmak quarry denizli basin turkey abstract the laterally extensive sub horizontal laminated travertine deposits outcropping in the cakmak quarry denizli basin turkey allows reconstructing their three dimensional geobody architecture based on field observations detailed petrographic and geochemical analyses stable carbon and oxygen isotopes major and trace elements the most important controlling porosity permeability parameters in this lacustrine dominated facies in relation to microfacies and diagenetic modifications were constrained sedimentological analyses and the observed architectural geometries allowed to subdivide the sub horizontal carbonate succession into three main depositional units these units in turn based on macro and microscopic observations were subdivided into nine dominant lithotypes reflecting an overall shrub flat and a marsh pool depositional setting the shrub flat facies mainly comprises dendritic shrub crusts boundstone pustular grainstone and clotted micrite mudstone to boundstone in contrast the marsh pool environment is dominated by coated reed rudstone to boundstone cryptalgal silty bioclast rich bioturbated mudstone and peloidal packstones the diagenetic study revealed that the sediments were affected by dissolution cementation sparmicritization recrystallization and local formation of fe oxi hydroxides and chalcedony among the diagenetic products in particular the calcite cements were investigated applying micro analysis of stable carbon and oxygen isotopes accordingly the co variation between the obtained isotopic values and the elemental concentrations sr mg na and s point to a thermogene fluid system that likely circulated through the subsurface limestones dolomites and evaporites of the lycian nappes these findings ensure an in depth understanding of continental carbonate deposition i e sub aqueous travertines in the context of a lacustrine depositional system

the formation of travertine shrubs mammoth hot springs wyoming the structure and microbiology of active travertines is described from canary and minerva springs with emphasis on shrubs growing in terracette pools these dendritic growths of aragonite consist of intricately branched sprays containing thousands of radiating needles shrub microstructure could be explained by the principle of keimauslese and the preferential elongation of sharp protuberances in a rapidly depositing environment the shrubs and other active travertines contain unicellular and filamentous bacteria estimates of total bacteria numbers ranged from 0 6 1 7 10 5 mm 3 but biomass was low and always less than 1 of the travertine by weight no evidence was found to indicate that bacteria played a role in shrub growth or morphology but crystal trapping on bacterial strings may influence travertine fabrics on cascades the shrubs are considered to have developed by inorganic processes in hot spring waters supersaturated with aragonite

empirical constraints on the salinity of the europan ocean and implications for a thin ice shell induced electrical currents within europa inferred from galileo spacecraft magnetometer instrument data have been interpreted as due to a salty europan ocean published compositional models for europa s ocean based on aqueous leaching of carbonaceous chondrites range over five orders of magnitude in predicted magnesium sulfate concentrations we combine the galileo spacecraft magnetometer derived oceanic conductivities and radio doppler data derived interior models with laboratory conductivity vs concentration data for both magnesium sulfate solutions and terrestrial seawater to determine empirically the range of salt concentrations permitted for europa s ocean solutions for both a three layer spherical model and a five layer half space model that satisfy current preferred best fits to magnetometer data imply high near saturation salt concentrations and require a europan ice shell of less than 15 km thick with a best fit at 4 km ice thickness adding a conductive core and mantle has a negligible effect on the amplitude when ocean conductivities are greater than a few siemens per meter similarly we find that including a realistic ionosphere has a negligible effect we examine the implications of these results for the subsurface habitability of europa

a simple formula for estimating the magnetic fields generated by tsunami flow 1 ocean flow is known to generate magnetic fields which reach land and satellite observatories with detectable amplitudes but because the expected signal to noise ratio is poor one must typically know in advance of the data analyses much about the expected behavior in order to identify these small oceanic contributions we show that in the case of ocean flow associated with tsunamis a very simple formula relating both amplitudes and phase allows the expected magnetic fields to be directly related to the sea surface displacement using sea surface data from jason 1 the formula gives maximum magnetic amplitudes of about 2 nt for the recent dec 26 2004 tsunami which occurred near the magnetic equator but near the magnetic poles the maximum amplitudes reach about 20 nt per meter sea surface displacement determining the feasibility for extraction of tsunami generated magnetic signals is of interest in designing early warning systems and for remotely tracking tsunami development

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

the tidal response of europa the tidal response of europa to a time varying potential is determined by solving the quasi static equilibrium equations for a body composed of several uniform maxwell viscoelastic layers models in which europa s surface ice extends all the way to the silicate mantle have weak tidal responses 1 m vertical deflection while models in which a liquid ocean underlies the ice have about 30 m peak vertical deflection the phase lag of the tidal response is very small 2 in the case of an ocean but may be large if there is no ocean and the ice has a viscosity around 1013 pa s for models with an ocean the product of the thickness and strength of the ice determines the tidal response making it difficult to determine the thickness of the ice by observing the tidal deflection of europa

early cambrian reefs reef complexes and associated lithofacies of the shackleton limestone transantarctic mountains the shackleton limestone formed a carbonate platform that bordered part of the greater antarctic craton in middle and late early cambrian time in the holyoake range of the central transantarctic mountains this unit records deposition on a stable shelf on which flourished ecological reefs composed of microorganisms and archaeocyathans burrow mottled lime mudstone wackestone and packstone with patch reefs represent accumulation in shelf areas of relatively low to moderate energy thick ooidal grainstone units reflect deposition in higher energy shoals and as sand sheets that were associated with extensive reef complexes the framework of these reefs was principally the product of micro organisms by inference mostly cyanobacteria archaeocyathans constitute as much as 30 of some reefs but commonly they form less than 10 and are absent from some on the basis of microbial composition three reef types are recognized the first type is a renalcis boundstone that lacks archaeocyathans within these abundant upward directed thalii of renalcis formed a framework that trapped fine grained sediment the second type which forms the core of some larger reefs is composed of stromatactis bearing microbial boundstone the third yet most common reef type is variable in composition it is characterized by the presence of abundant epiphyton but may include archaeocyathans and the microbial microfossils girvanella and renalcis as well as cryptomicrobial clotted micrite in this type of reef frame building organisms typically constructed highly porous structures that had small interparticle and fenestral pores and large growth framework cavities as well as rare metre sized caverns within these spaces epiphyton and less commonly renalcis encrusted framework elements fine grained sediments accumulated and pervasive sea floor cements were precipitated boundstone fabrics in the shackleton limestone are highly complex with fabrics analogous to younger more metazoan rich reefs as well as deep water stromatactis bearing mud mounds the epiphyton girvanella archaeocyathan frameworks and stromatactis bearing boundstones both of which seemingly first appeared in the middle early cambrian are regarded as the precursors in structure composition and preferred hydrologic setting of the more extensive reefs and complex framework styles of later phanerozoic time

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

unusual calcite stromatolites and pisoids from a landfill leachate collection system low magnesium calcite stromatolites and pisoids were found to have precipitated within the leachate collection system piping of a palm beach county florida landfill the stromatolites and pisoids formed in an aphotic and anoxic environment that was at times greatly supersaturated with calcite the stromatolites are composed of branching cylindrical bundles of concentrically laminated radial fibrous crystals the pisoids consist of concentric layers of radial fibrous and microcrystalline calcite bacteria likely sulfate reducing appear to have acted as catalysts for calcite crystal nucleation and thus the formation of the stromatolites and pisoids the leachate system stromatolites provide a recent example of stromatolites that formed largely by cement precipitation by acting as catalysts for calcite nucleation bacteria may cause more rapid cementation than would have occurred under purely abiotic conditions rapid calcite precipitation catalyzed by bacteria has interfered with the operation of the palm beach county landfill leachate collection by obstructing pipes and may be an unrecognized problem at other landfill sites

subsurface oceans on europa and callisto constraints from galileo magnetometer observations magnetic field perturbations measured during galileo flybys of europa and callisto are consistent with dipole fields induced by the temporal variations of the ambient jovian magnetospheric field these fields are close to those expected for perfectly conducting moons we investigate the implications of these observations for the electrical structure of the moon s interiors using a simple shell model it is found that europa and callisto must possess regions where the conductivity exceeds 0 06 and 0 02 s m at a depth of less than 200 and 300 km below the surface respectively this conductivity is unattainable in ice or silicates unless the ice layer is at least partially molten or very large temperature gradients can be maintained below the ice an ionosphere or a cloud of pick up ions are probably also insufficiently conductive global earth like oceans under the surface of both moons could account for the observations provided they are at least a few kilometers thick c 2000 academic press

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

satellite observations of magnetic fields due to ocean tidal flow the ocean is an electrically conducting fluid that generates secondary magnetic fields as it flows through earth s main magnetic field extracting ocean flow signals from remote observations has become possible with the current generation of satellites measuring earth s magnetic field here we consider the magnetic fields generated by the ocean lunar semidiurnal m2 tide and demonstrate that magnetic fields of oceanic origin can be clearly identified in satellite observations

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

ocean tides heat enceladus 1 with a young highly reflective surface and vigorous geological activity saturn s tiny moon enceladus has been one of the most mysterious planetary bodies in the solar system recent observations from the cassini spacecraft show vast plumes of vapor erupting from geysers near the south pole and inferred heat fluxes of about 100 mw m2 for the same region have helped consolidate the essential enigma of enceladus there must be a relatively large and unidentified source of heat in the tiny moon here we present a case for heating from dissipation by tidal flow in an ice covered ocean we show that if the spin axis of enceladus is tilted with respect to its orbital plane by at least 0 05 degree then strong tidal flow will be generated with enough dissipative heating to explain the observed heat flux in an alternative case of a shallow 10 km or less ocean comparable flow velocities and heating may be obtained by eccentricity tidal forces

galileo magnetometer measurements a stronger case for a subsurface ocean at europa on 3 january 2000 the galileo spacecraft passed close to europa when it was located far south of jupiter s magnetic equator in a region where the radial component of the magnetospheric magnetic field points inward toward jupiter this pass with a previously unexamined orientation of the external forcing field distinguished between an induced and a permanent magnetic dipole moment model of europa s internal field the galileo magnetometer measured changes in the magnetic field predicted if a current carrying outer shell such as a planet scale liquid ocean is present beneath the icy surface the evidence that europa s field varies temporally strengthens the argument that a liquid ocean exists beneath the present day surface

planetary science tidal flows in satellite oceans sub surface oceans probably exist on several large satellites of jupiter and saturn an analysis of europa s tides suggests that some of the rossby waves are resonantly enhanced by the obliquity producing sufficient heat and flow to keep the ocean liquid

mn and fe rich black travertine shrubs bacterially and nanobacterially induced precipitates abstract black shrubs i e arborescent forms are present within hot water travertine deposits from morocco the shrubs are commonly a few centimeters high and laterally grouped along individual laminae other than in mineral composition the black shrubs closely resemble the calcite shrubs from other hot water travertine deposits e g bagni di tivoli italy and mammoth hot springs yellowstone national park they are composed of a variety of minerals that are mn rich and also have a significant fe oxide component similar mn and fe rich shrub like forms have been described from desert varnish deep sea mn nodules and marine carbonates frutexites sem analyses show that bacterial bodies are densely packed within the mn rich black travertine shrubs whereas no bacterial bodies are evident within the enclosing aragonite and calcite laminae the bacterial bodies range in shape and size from rods commonly 0 8 m long by 0 1 m in diameter to spherical forms commonly 0 3 m in diameter that form chains up to 1 m long to nanobacterial spheres 150 to 200 nm in diameter that make up densely packed chains commonly 15 m in length it is well documented within the microbiological literature that not only do bacteria have the ability to induce the precipitation of mn and fe they can concentrate mn in mineral precipitates from waters with very low to essentially undetectable concentrations of mn the black mn rich shrubs within the moroccan travertines other hot water travertines and related features such as desert varnish deep sea mn nodules and frutexites are postulated to also be the result of bacterially induced precipitation

europa s differentiated internal structure inferences from four galileo encounters radio doppler data from four encounters of the galileo spacecraft with the jovian moon europa have been used to refine models of europa s interior europa is most likely differentiated into a metallic core surrounded by a rock mantle and a water ice liquid outer shell but the data cannot eliminate the possibility of a uniform mixture of dense silicate and metal beneath the water ice liquid shell the size of a metallic core is uncertain because of its unknown composition but it could be as large as about 50 percent of europa s radius the thickness of europa s outer shell of water ice liquid must lie in the range of about 80 to 170 kilometers

incipient hydrothermal alteration of basalts and the origin of martian soil the martian soil is a fine grained regolith that is chemically basaltic in character with evidence for both gains and losses of volatile and mobile elements compared to martian basalt compositions these chemical fractionations provide clues to geochemical processes on the surface of mars geochemical processes contributing to the soil proposed in the past include the chemical and mechanical breakdown of rocks under surface conditions the addition of volcanic aerosols containing s and cl compounds and the alteration of basaltic glass to palagonite our studies of terrestrial analogs suggest that hydrothermal alteration processes involving impact craters and volcanism could also contribute to the major element trends observed in martian soil data from viking pathfinder and the current mer missions consistently show that relative to basaltic martian meteorite compositions the major element compositions of the soils are 1 depleted in the fluid mobile element calcium 2 generally similar or somewhat enriched in iron oxide and magnesium but mgo depleted compared to gusev rocks 3 locally variable in potassium 4 possibly poorer in aluminum and 6 very enriched in chlorine and sulfur the major element trends aside from the cl and s enrichment could be explained by the formation or addition of palagonite according to mcsween and keil 2000 but the missing cao remains a problem the chlorine and sulfur are probably derived from other processes such as volcanic aerosols and hydrothermal fluids mcsween and keil 2000 also argued that hydrothermal alteration of basalts produce alteration trends that are inconsistent with the mars soil but this study concludes otherwise we have used quantitative mass balance mixing models to investigate possible models involving mixtures of basaltic compositions with different types of alteration materials including palagonite we show that the mars soil composition can be matched with a combination of unweathered basaltic martian meteorites with basaltic feo rich cao poor alteration products palagonite is a possible but not a necessary component of successful model mixtures the hydrothermal alteration materials that form successful model mixtures are formed in low temperature low water rock ratio environments and they can reproduce the required geochemical trends because they are poorer in cao but not in feo compared to their respective protoliths these results argue that material altered by hydrothermal processes could be a plausible component of the soil and that removal of cao from the soil into some undiscovered reservoir after its formation is not required the current soil on mars therefore did not have to undergo an episode of in situ aqueous alteration but could represent a sink for materials that experienced aqueous processes in a different setting before erosion to form the soil the soil can also represent a sink for mobile elements e g s cl and br derived from other sources such as volcanic aerosols and hydrothermal fluids

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