microstructural changes accompanying the opal a to opal ct transition new evidence from the siliceous sinters of geysir haukadalur iceland opaline silica opal a has formed in marine lacustrine and geothermal environments throughout geological time during diagenesis opal a normally changes to opal ct then opal c and finally to quartz such changes commonly destroy the original fabrics and any fossils that opal a contained the physical changes that accompany the opal a to opal ct transition however are known poorly x ray diffraction analyses electron microprobe analyses and high resolution high magnification scanning electron microscope imagery of siliceous sinters from the geysir geothermal area in iceland show that opal a is formed of heterometric arrays of randomly packed microspheres up to 5 m diameter with neighbouring spheres commonly being joined by small connection pads in contrast enlarged spheres lepispheres inverse opal two types and spindle frameworks with hexagonal motifs characterize opal ct the textures in opal ct which vary on a microscale reflect the complex interplay between dissolution e g inverse opal and precipitation e g enlarged spheres spindle frameworks that probably was mediated by groundwater in a near surface environment the processes deciphered from these young rocks should however be applicable to sedimentary opal a and opal ct of all ages irrespective of their origin

magnetic properties of sedimentary greigite fe3s4 an update greigite fe3s4 is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction it can also grow at any time when dissolved iron and sulfide are available during diagenesis greigite is important in paleomagnetic environmental biological biogeochemical tectonic and industrial processes much recent progress has been made in understanding its magnetic properties greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites the crystallographic c axis is the easy axis of magnetization with magnetic properties dominated by magnetocrystalline anisotropy robust empirical estimates of the saturation magnetization anisotropy constant and exchange constant for greigite have been obtained recently for the first time and the first robust estimate of the low field magnetic susceptibility is reported here the curie temperature of greigite remains unknown but must exceed 350 c greigite lacks a low temperature magnetic transition on the basis of preliminary micromagnetic modeling the size range for stable single domain behavior is 17 200 nm for cubic crystals and 17 500 nm for octahedral crystals gradual variation in magnetic properties is observed through the pseudo single domain size range we systematically document the known magnetic properties of greigite at high ambient and low temperatures and with alternating and direct fields and illustrate how grain size variations affect magnetic properties recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records including widespread remagnetizations

nannobacteria and the precipitation of carbonate in unusual environments abstract nannobacteria are abundant not only in normal marine limestones but also in other environments such as continental caliches fresh water streams springs water pipes caves etc cells are typically 50 to 200 nm in diameter

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

microbial control on the precipitation of modern ferrihydrite and carbonate deposits from the cezallier hydrothermal springs massif central france abstract actively precipitating hydrous iron oxides and carbonates are commonly associated with cool co2 rich spring waters in the massif central france chemical isotopic and mineralogical analyses and thermodynamic calculations were undertaken to elucidate the processes involved in the formation of these deposits hydrous iron oxide particles rich in al si ca and as are the first to form in the springs accompanying the iron oxides are layered carbonate deposits composed mainly of well crystallised calcite sem examination of both oxides and carbonates sampled at the outlet of the springs shows that they basically consist of grape shaped agglomerates of small 300 nm to 1 m anhedral crystals light acid etching of these agglomerates reveals colonies of spherical nannobacteria water trace partitioning between oxide and carbonate favours the hydrous oxide with as pb zn th concentration the microscopic features of both types of deposit indicate that microbial mediation probably contributes to their formation

pyrite alteration and neoformed magnetic minerals in the fault zone of the chi chi earthquake mw7 6 1999 evidence for frictional heating and co seismic fluids 1 during an earthquake physical and chemical transformations lead to alteration and formation of minerals in the gouge layer altered and neoformed minerals can be used as tracers of some earthquake processes in this study we investigate pyrite and magnetic minerals within the host chinshui siltstone and the 16 cm thick gouge this gouge hosts the principal slip zone of chi chi earthquake mw7 6 1999 in the chinshui siltstone pyrite framboids of various sizes and euhedral pyrite are observed the magnetic mineral assemblage comprises stoichiometric magnetite greigite and fine grained pyrrhotite the pyrite content is generally reduced in the gouge compared to the wall rock the magnetic mineral assemblage in the gouge consists of goethite pyrrhotite and partially oxidized magnetite the pyrrhotite goethite and some magnetite are neoformed pyrrhotite likely formed from high temperature decomposition of pyrite 500 c generated during co seismic slip of repeated earthquakes goethite is inferred to have formed from hot aqueous co seismic fluid 350 c in association with the 1999 chi chi event elevated fluid temperatures can also explain the partial alteration of magnetite and the retrograde alteration of some pyrrhotite to pyrite we suggest that characterization of neoformed magnetic minerals can provide important information for studying earthquake slip zones in sediment derived fault gouge

mechanoradical h2 generation during simulated faulting implications for an earthquake driven subsurface biosphere 1 molecular hydrogen h2 is the key component to link the inorganic lithosphere with the subsurface biosphere geochemical and microbiological characterizations of natural hydrothermal fields strongly suggested that h2 is an important energy source in subsurface microbial ecosystems because of its metabolic versatility one of the possible sources of h2 has been considered as earthquakes mechanoradical reactions on fault surfaces generate h2 during earthquake faulting however it is unclear whether faulting can generate abundant h2 to sustain subsurface chemolithoautotrophic microorganisms such as methanogens here we present the result of high velocity friction experiments aimed to estimate the amount of h2 generated during earthquakes our results show that h2 generation increases with frictional work i e earthquake magnitude and that a h2 concentration of more than 1 1 mol kg of fluid can be achieved in a fault zone after earthquakes of even small magnitudes the estimated earthquake derived h2 concentration is sufficiently high to sustain a h2 based subsurface lithoautotrophic microbial ecosystem furthermore earthquakes have initiated on the earth at least since tectonic plate movement began 3 8 ga implying the possible existence of ancient earthquake driven ecosystems seismic h2 based subsurface ecosystems might exist not only over the earth but also other planets

grain size dependence of the magnetic behavior of pyrrhotite during its low temperature transition at 34 k the grain size dependent behavior of pyrrhotite during a magnetic lt transition at 34 k is suitable for granulometric purposes cycling down to liquid helium temperature suppresses soft md jrs more than hard sd jrs so that it may be effective in removing soft secondary nrm components the domain structure of large pyrrhotite grains changes from md at room temperature to sd or psd below the lt transition

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

nannobacteria as a by product of enzyme driven tissue decay spheroidal features 50 to 200 nm in size and found in sedimentary rocks have been described as nannobacteria the idea that they are minute fossilized life forms and especially the discovery of such features in martian meteorite alh84001 sparked a lively debate with regard to identification of ancient microbial life because biologists consider 200 300 nm to be the lower viable size limit for microorganisms an alternative explanation is needed for features that have been described as nannobacteria by geologists we report here on tissue decay experiments that produced abundant proteinaceous spheroids in the size range of nannobacteria described as nannoballs in the remainder of this paper experimental conditions were comparable to those found in earth9s surface sediments and diagenetic mineralization of these spheroids may be a common process for preservation of nannoballs that are observed in the rock record

geochemical evidence of microbial activity within ooids ooid formation remains elusive despite their importance as palaeoclimatic indicators and important contributors to global carbonate budget based on stable isotopes nutrient and elemental analyses on solid components and ooidal leachates this study supports the notion of microbial involvement in the development of ooids from great bahama bank carbon and nitrogen isotopic analyses on organic fractions identified geochemical signatures of microbial activity the 13c values for organic carbon in the bulk 11 9 to 16 9 intercrystalline intracrystalline 11 9 to 16 7 and intracrystalline phases 12 4 to 17 7 were similar and except for the more enriched values of ooids from butterfly beach were within the range of photosynthesisers the 15n values for the bulk 0 5 to 0 2 intercrystalline intracrystalline 0 3 to 0 7 and intracrystalline organic matter 0 3 to 1 7 showed a narrow range consistent with nitrogen fixation while positive 15n and 18o values of the leached from the ooids provided evidence of denitrification the carbonate associated sulphate 34scas of the bulk sediments 19 2 to 19 6 and 34s of the leachates 16 6 to 18 3 provided weak indication of sulphate reduction suggesting either that high concentrations of isotopically enriched s are overriding bio signatures of sulphate reduction or that microbes are preferentially using as an electron acceptor in contrast the elevated sulphate concentrations of the leachates suggest the occurrence of microbial sulphide oxidation within ooids the high mg ca of the leachates and scanning electron microscope analyses provide putative evidence of amorphous calcium carbonate and a formative role in caco3 precipitation together these findings indicate that a redox dependent microbial consortium may influence caco3 precipitation in the form of ooid accretion cementation and micritization it is also inferred that ooid deposits are not suitable indicators of palaeoclimate because ooids are affected throughout their life by a complex chain of abiotic and biological processes which can lead to large geochemical offsets

microbes and ooids abstract the bahamian archipelago is one of the few locations in the world where ooid formation is actively occurring ooid cortices from six locations in the region were incrementally dissolved and analyzed for 14c 18o 13c mg ca and sr ca ratios ooids were examined under sem after each step in the incremental analyses to characterize the nature of dissolution radiocarbon dating indicates that ooids presently at the sediment water interface began forming across the archipelago between 1000 and 2800 yr bp and continue to form today the ooids have the same pattern of microboring alteration across the region the surface and outer cortex of the ooids are punctuated with unfilled microborings whereas the inner cortex contains two morphologies of aragonite cement filling the microborings the two morphologies of cement form in association with two different species of cyanobacteria one is solentia sp the other is interpreted to be hyella sp the chemistry of ooids from across the region is remarkably similar 18o and 13c values for all samples vary directly having a slope of approximately 1 the outer cortex has low 18o and 13c values of 3 4 and 0 2 respectively whereas the 18o and 13c values of the inner cortex are high with values of 1 9 and 6 8 respectively the presence of aragonite cement in microborings in the inner cortex increases the overall isotopic composition of both oxygen and carbon in the ooid causing it to appear close to equilibrium with seawater the isotopic variation in 18o and 13c within the cortex can be characterized as a mixing line between the low values in the unaltered ooid laminae and the aragonite cement in the microborings the most exterior portion of the ooid has very high mg ca values and is interpreted as an amorphous calcium carbonate acc coating there are two other phases in the cortex both being aragonite the outer cortex has a higher mg ca ratio and lower sr ca ratio than the inner cortex this difference in chemistry is a result of the presence of aragonite cement in the inner cortex stable isotopic and trace element results coupled with sem investigations indicate that microbes do not play a role in ooid formation but instead alter the texture and chemistry of ooids after they have formed a new model of ooid formation is proposed whereby a veneer of acc precipitates on an ooid while it is at the sediment water interface the active phase this veneer of acc later recrystallizes to aragonite needles and a new cortex layer is formed the stationary phase observations from this study lead to a deeper understanding of the chemical processes involved in ooid genesis which allow a better understanding of paleoenvironments hosting ooid formation

thermal alteration of pyrite to pyrrhotite during earthquakes new evidence of seismic slip in the rock record seismic slip zones convey important information on earthquake energy dissipation and rupture processes however geological records of earthquakes along exhumed faults remain scarce they can be traced with a variety of methods that establish the frictional heating of seismic slip although each has certain assets and disadvantages here we describe a mineral magnetic method to identify seismic slip along with its peak temperature through examination of magnetic mineral assemblages within a fault zone in deep sea sediments cored from the japan trench one of the seismically most active regions around japan during the integrated ocean drilling program expedition 343 the japan trench fast drilling project fault zone sediments and adjacent host sediments were analyzed mineral magnetically supplemented by scanning electron microscope observations with associated energy dispersive x ray spectroscopy analyses the presence of the magnetic mineral pyrrhotite appears to be restricted to three fault zones occurring at 697 720 and 801 m below sea floor in the frontal prism sediments while it is absent in the adjacent host sediments elevated temperatures and coseismic hot fluids as a consequence of frictional heating during earthquake rupture induced partial reaction of preexisting pyrite to pyrrhotite the presence of pyrrhotite in combination with pyrite to pyrrhotite reaction kinetics constrains the peak temperature to between 640 and 800 c the integrated mineral magnetic microscopic and kinetic approach adopted here is a useful tool to identify seismic slip along faults without frictional melt and establish the associated maximum temperature

sem imaging of bacteria and nannobacteria in carbonate sediments and rocks abstract bacteria and nannobacteria 0 1 m dwarfed forms are abundant in both non etched and gently etched travertines deposited by hot springs in viterbo italy they are also plainly visible in bahama ooids and hardgrounds and in great salt lake aragonite ooids and cements in addition nannobacteria are found in paleozoic and mesozoic rocks because of their extraordinary abundance in some specimens they probably play a prominent role in catalyzing the precipitation of carbonate materials

multiphase calcification associated with the atmophytic cyanobacterium scytonema julianum scytonema julianum which is an atmophytic cyanobacterium that lives in small clusters in shaded vadose settings throughout the world is prone to rapid calcification specimens found on cavity walls in an inactive spring tower located in shiqiang stone wall in china and cavity walls in a breccia that fills sinkholes in dolostones of the cayman formation miocene on grand cayman are morphologically identical the microbes 4 11 pm diameter are encased with thick well developed calcified sheaths with external diameters of 11 to 25 pm which developed through the sequential precipitation of amorphous caco3 acc acicular calcite crystals triradiate calcite crystals and dendrite calcite crystals the paragenetic relationship of these precipitates to the skeletal rhombic crystals that cover some specimens is unknown precipitation probably took place in the extracellular polymeric substances eps that covered the microbes when they were alive critically the type of crystal evident on the surface of the sheath depends on the thickness of the calcified sheath which is in accord with the sequential development of the different crystal forms available evidence indicates that precipitation was largely microbially influenced rather than environment influenced and also demonstrates that crystals commonly morphed from one crystal form into another as precipitation progressed there is for example clear evidence that the dendrite crystals developed from the triradiate crystals s julianum can play a significant role in the development of microbialites in vadose settings by acting as nuclei for caco3 precipitation c 2014 elsevier b v all rights reserved

an integrated paleomagnetic rock magnetic and geochemical study of the marcellus shale in the valley and ridge province in pennsylvania and west virginia an integrated paleomagnetic rock magnetic and diagenetic study of the devonian marcellus subgroup from threefolds in the valley and ridge province in pennsylvania and west virginia indicates that the unit contains an intermediate temperature chemical remanent magnetization crm with south southeast declinations and shallow negative inclinations residing in pyrrhotite and a crm with more southerly declinations and shallow positive inclinations residing in magnetite rock magnetic results confirm the presence of pyrrhotite and magnetite tilt tests indicate that pyrrhotite and magnetite crms are syntilting to posttilting and paleopoles for both crms are similar and plot on the permian part of the apparent polar wander path for north america the marcellus subgroup has a complex paragenetic sequence which includes bitumen deposition and vein formation the magnetite and pyrrhotite crms formed in the permian probably due to burial diagenetic processes and not orogenic fluids the base of the unit contains the highest total organic content toc values and highest magnetic intensities both of which decrease up section this connection between toc and magnetic intensity suggests that the magnetite formed as a result of the maturation of the organic matter although more work is needed to test this hypothesis the pyrrhotite may have formed as a result of thermochemical sulfate reduction involving organic matter during the production of methane in this gas reservoir the similar permian crm ages may be explained by thrusting which resulted in rapid burial of the marcellus subgroup as it passed through the oil window and into the gas window quickly producing magnetite and pyrrhotite respectively

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

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

young volcanism and related hydrothermal activity at 5 s on the slow spreading southern mid atlantic ridge the effect of volcanic activity on submarine hydrothermal systems has been well documented along fast and intermediate spreading centers but not from slow spreading ridges indeed volcanic eruptions are expected to be rare on slow spreading axes here we report the presence of hydrothermal venting associated with extremely fresh lava flows at an elevated apparently magmatically robust segment center on the slow spreading southern mid atlantic ridge near 5 s three high temperature vent fields have been recognized so far over a strike length of less than 2 km with two fields venting phase separated vapor type fluids exit temperatures at one of the fields reach up to 407 c at conditions of the critical point of seawater the highest temperatures ever recorded from the seafloor fluid and vent field characteristics show a large variability between the vent fields a variation that is not expected within such a limited area we conclude from mineralogical investigations of hydrothermal precipitates that vent fluid compositions have evolved recently from relatively oxidizing to more reducing conditions a shift that could also be related to renewed magmatic activity in the area current high exit temperatures reducing conditions low silica contents and high hydrogen contents in the fluids of two vent sites are consistent with a shallow magmatic source probably related to a young volcanic eruption event nearby in which basaltic magma is actively crystallizing this is the first reported evidence for direct magmatic hydrothermal interaction on a slow spreading mid ocean ridge

trace element anomaly in fault rock induced by coseismic hydrothermal reactions reproduced in laboratory friction experiments friction experiments at high velocities 0 1 to 0 4 m s at room temperature under high pore fluid pressures 2 or 5 mpa and trace element analyses of the run products were carried out on simulated fault gouge derived from the chelungpu fault taiwan the friction coefficient decreased to 0 1 during sliding and the slip surface temperature reached 300 c by 6 m of slip displacement the slip caused a small but distinct decrease of li in the deformed gouge when the slip surface temperature exceeded 300 c the observed li depletion agreed with calculated results indicating that it resulted from a hydrothermal reaction at a high temperature produced by short duration up to 40 s frictional heating the geochemical data suggest a small fluid rock ratio and low reaction temperature in the simulated fault which is explained by higher normal stress or repeated earthquakes which elevated fluid rock ratios in the natural fault

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

the rupture mode of the shallow large slip surge of the tohoku oki earthquake abstract the remarkable feature of the m w 9 1 tohoku oki earthquake of 2011 was a late shallow surge that propagated from about 12 km depth all the way to the trench this surge had very large slip and was depleted in high frequency radiation it was followed by normal faulting in the outer wedge this requires that the postsurge basal shear stress be close to zero explanations for the surge propagating through the velocity strengthening region by a thermal weakening mechanism fail to produce the near total stress drop required by the postseismic extension the surge propagated in a region of material contrast across the plate interface the combination of a strong nucleation pulse from down dip velocity strengthening and the bimaterial effect satisfies the conditions for wrinkle pulse propagation a wrinkle pulse rupture mode can produce an instability by overcoming velocity strengthening with the normal stress reduction produced by the bimaterial effect it also leads to total stress drop satisfying the extension constraint and explaining the prodigious slip amplitude of the surge because the surfaces are detached in wrinkle pulse mode asperity contact is reduced which explains the dearth of high frequency radiation during the surge this behavior appears to be a common feature of many of the greatest subduction earthquakes

shorter intervals between great earthquakes near sendai scour ponds and a sand layer attributable to a d 1454 overwash a sparsely documented tsunami in 1454 may subdivide the recurrence interval between the 869 and 2011 tsunamis near sendai as judged from geomorphic stratigraphic and archival evidence pond filled breaches cut across beach ridges on century old topographic maps the basal pond deposit in one of these breaches postdates 1454 stratigraphy on sendai plain includes a sand sheet that contains marine and brackish diatoms radiocarbon ages suggest that the sheet dates to 1406 1615 2 and written records for this interval in tohoku mention a tsunami in 1454 the inferred inundation extended 1 0 2 5 km inland from an approximate medieval shoreline simulated tsunamis that best account for the sand sheet require a thrust earthquake of moment magnitude 8 4 or larger if the sand sheet represents the 1454 tsunami the two most recent intervals between great thrust earthquakes in sendai region spanned 585 and 557 years

formation of aragonite cement by nannobacteria in the great salt lake utah brine shrimp egg cases in growth cavities in modern stromatolites in the great salt lake utah are replaced by aragonite and cemented together by aragonite cement the fabric of the cement changes dramatically as the distance from the egg case increases the cement within 50 to 70 m of the egg case exhibits a random fabric of 10 to 20 m equant crystals the surface of the cement is covered by bead like bumps 0 1 m in diameter interpreted as nannobacteria overlying the random beaded fabric with a relatively abrupt transition are epitaxial prismatic aragonite crystals that have smooth crystal surfaces lacking bead like bodies the smooth surfaced prismatic aragonite crystals are interpreted to be normal abiotic precipitates whereas the beaded microspar is interpreted to result from biotic processes where the nannobacteria serve as catalysts for creation of the cement a population explosion of bacteria occurs as the organic material of egg case rots which alters the microchemical environment and induces a rapid precipitation of aragonite enclosing tens of thousands of nannobacteria as the organic material is destroyed reproduction of bacteria slows and epitaxial prismatic aragonite crystals nucleate and grow abiotically on the structureless biotic layer

authigenesis of magnetic minerals in gas hydrate bearing sediments in the nankai trough offshore japan gas hydrate occurrence is one of the possible mechanisms invoked for iron sulfide formation a high resolution rock magnetic study was conducted in iodp expedition 316 hole c0008c located in the megasplay fault zone of the nankai trough offshore japan in this particular zone no bottom simulating reflectors bsr indicating the base of the gas hydrate stability field have been identified two hundred and eighteen pleistocene samples were collected from 70 to 110 m csf in order to document the changes in the concentration grain size and rock magnetic parameters of magnetic minerals through the gas hydrate bearing horizons two different populations of magnetic grains are recognized in the pseudosingle domain range three types of magnetic mineral assemblages are identified iron oxides magnetite ferrimagnetic iron sulfides greigite and pyrrhotite and their mixture greigite and pyrrhotite are authigenic and constitute six layers called is1 is6 is1 is3 is4 and is6 are associated with pore water anomalies suggesting the occurrence of gas hydrates and anoxic conditions is2 and is5 are probable gas hydrates horizons although there is no independent data to confirm it the remaining intervals are mainly composed of detrital iron oxides and paramagnetic iron sulfides two scenarios based on different diagenetic stages are proposed to explain the variations in the magnetic properties and mineralogy over the studied interval the results suggest that rock magnetism appears useful to better constrain the gas hydrate distribution in hole c0008c and counterbalances the low resolution of pore water analyses and the absence of a bsr

microbes produce nanobacteria like structures avoiding cell entombment microsedimentary structures referred to as nanobacteria like particles were described from modern carbonate environments where they form in close spatial association with sulfate reducing bacteria srb however the exact mechanism of their formation as well as their paleontological significance remains controversial here we report on an investigation of microbe mineral interactions in experimentally produced carbonate globules the experiments were carried out under anoxic conditions at 30 c with desulfovibrio brasiliensis a srb known to mediate dolomite formation we observed that extracellular polymeric substances eps secreted by the microbial community play a key role in the mineralization process nanobacteria like particles represent the early stage of carbonate nucleation within the eps which progressively evolve to larger globules displaying a grainy texture we excluded the possibilities that these structures are fossils of nanobacteria dissolution surfaces or artifacts created during sample preparation d brasiliensis cells are predominantly located outside of the eps aggregates where mineral growth takes place as a result they remain mobile and are rarely entombed within the mineral this self preservation behavior may not be limited to d brasiliensis other microbes may produce or may have produced during the geological past biogenic minerals through a similar process mineralization within eps explains why microbial relics are not necessarily present in biogenic carbonates

facies character and depositional architecture of hydrothermal travertine slope aprons pleistocene acquasanta terme central italy abstract hydrothermal travertines develop various depositional geometries from tabular to high relief mounds or aprons with steep slopes under the control of local topography location and geometry of the vents fault activity hydrology water physico chemical properties rates of thermal water flow and carbonate precipitation rates this study focuses on two pleistocene tens of metres thick travertine slope aprons accumulated on fluvial terraces in the tronto river valley acquasanta terme central italy to investigate their facies character geochemical signature porosity and evolution of the depositional geometry through time the two travertine aprons consist of four aggradational progradational units vertically and laterally stacked with onlap and downlap stratal terminations separated by erosional unconformities produced by events of non deposition and erosion due to temporary interruptions of vent activity shifts of the vent location and or deviation of the flow directions the travertine units include various depositional environments 1 smooth slope 2 terraced slope with metre scale sub horizontal pools separated by rounded rims and vertical walls and 3 sub horizontal tens of metres wide ponds smooth slope clinoforms are made of centimetre to decimetre thick layers of crystalline dendrite cementstone laminated boundstone and radial coated grain grainstone precipitated by fast flowing water on inclined substrates rims and walls of terraced slopes are built by crystalline dendrites and laminated boundstone sub horizontal layers of terrace pools and ponds consist of facies precipitated by slow flowing to standing water clotted peloidal micrite dendrite coated bubble boundstone raft rudstone associated with radial coated grains and laminated boundstone carbonate coated reeds occur in distal ponds adjacent to toe of slopes or overlie packstone rudstone with travertine intraclasts and substrate extraclasts marking events of subaerial exposure and erosion travertine facies porosity and permeability range from 4 to 21 and 0 03 to 669 md respectively showing no direct correlation stable isotope values 13 c 5 7 9 3 18 o 9 6 to 12 2 are similar to other travertines precipitated by thermal water in central italy this study identifies the centimetre scale travertine facies variability linking it to the environment of deposition and to the depositional geometry of travertine units affected by the substrate topography and lateral shifts of the active springs despite the different scale and facies composition the geometry of aggradational progradational units of travertine aprons might resemble marine flat topped high relief carbonate platforms travertine units in the subsurface if present with sizes that can be seismically resolved might be wrongly interpreted as carbonate platforms with steep slopes without a detailed facies analysis

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

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

genesis and diagenesis of travertine futamata hot spring japan abstract genetic and diagenetic processes of travertine were examined at futamata hot spring where both active and inactive subfossil and fossil travertines are present geochemical and geomicrobiological analyses of active travertines reveal that abiotic process of caco3 precipitation is predominant photosynthetic inhibition of caco3 precipitation occurs at the upstream while the cyanobacterial population is low in the downstream resulting in photosynthesis induced caco3 precipitation only in the midstream nonetheless microorganisms have an effect upon depositional fabrics and filamentous cyanobacteria possessing non acidic sheaths contribute to the particle trapping binding and the generation of pore space both active and inactive travertines are mainly composed of calcite however active travertine in the up midstream also contains some aragonite due to high rates of co2 degassing active and subfossil travertines are characterized by domal topography and relatively high flow rates are assumed due to the dominance of slope facies on the other hand fossil travertines are characterized by fissure ridge topography and relatively low flow rates are assumed due to the dominance of crest and marsh facies the elemental composition of travertines primarily reflects their constituent minerals and the active travertines consisting of both aragonite and calcite show higher sr ba na and k contents whereas travertines consisting solely of calcite show higher mg and mn contents due to elevated mn content bright cathode luminescence is exhibited by the primary calcite of active travertines most fossil travertines have experienced prominent diagenetic alteration in the vadose zone and are commonly cemented and recrystallized in addition to meteoric water percolating hot spring water was also involved in the diagenetic process combined with the results of u th dating our results suggest that the formation of fissure ridge travertines at futamata hot spring began approximately 20 thousand years ago ka via fault activity which terminated at around 7 ka and the domal travertines were formed by hot spring water discharging from several vents

patterns of biomediated caco3 crystal bushes in hot spring deposits in the eiyuan hot spring located in south china the vent pool is covered with crystal bushes up to 2 cm high 1 cm in diameter that grew in the biofilms that thrive in the spring waters that have a ph of 7 5 and a temperature of 88 degrees c the biofilms are formed largely of phototrophic purple bacteria and green bacteria growth of the crystal bushes which are formed of aragonite crystals wheat sheaves radiating clusters rhombohedral and dodecahedral calcite crystals amorphous caco3 acc and opal a is attributed to precipitation in the micro domains of the biofilms where physiochemical conditions can vary on the sub micron scale there is no evidence that the calcite was formed through recrystallization of the metastable aragonite and most of the calcite crystals developed as mesocrystals that are characterized by incomplete growth and porous crystal faces

structure and composition of the plate boundary slip zone for the 2011 tohoku oki earthquake the mechanics of great subduction earthquakes are influenced by the frictional properties structure and composition of the plate boundary fault we present observations of the structure and composition of the shallow source fault of the 2011 tohoku oki earthquake and tsunami from boreholes drilled by the integrated ocean drilling program expedition 343 and 343t logging while drilling and core sample observations show a single major plate boundary fault accommodated the large slip of the tohoku oki earthquake rupture as well as nearly all the cumulative interplate motion at the drill site the localization of deformation onto a limited thickness less than 5 meters of pelagic clay is the defining characteristic of the shallow earthquake fault suggesting that the pelagic clay may be a regionally important control on tsunamigenic earthquakes

variations in water content in opal a and opal ct from geyser discharge aprons abstract opal a sio2 nh2o and its diagenetic derivative opal ct are found in environments that range from the deep ocean floor to terrestrial spring geyser systems although the loss of water may be a critical factor in the transition from opal a to opal ct analytical difficulties in determining the distributions and quantities of molecular water h2omol and silanols h2osioh has hindered a full understanding of the processes involved with this diagenetic transition electron microprobe emp and micro fourier transform infrared ftir analyses of opal a and opal ct collected from geyser discharge aprons on iceland and the north island of new zealand produce compatible and reliable derivations of the total weight water in opal a and opal ct provided that they contain 1 wt of other elements such as al emp analyses produce excellent results where microscale variations in total water content are required but it cannot determine if that water is formed of molecular water h2omol or silanols h2osioh in contrast ftir analyses yield total water molecular water and silanol contents of the opal microscale variations however are commonly masked because the scale of ftir analysis is coarser than that for emp analyses analyses of sinters from iceland and new zealand show that the opal a contains 2 1 12 1 average 7 3 wt total water whereas the opal ct contains 1 0 8 9 average 5 5 wt total water based on ftir analyses the opal a contains 1 2 9 8 average 6 8 wt molecular water and 0 4 2 4 average 1 0 wt silanols compared to opal ct which contains 3 8 8 2 average 6 7 wt molecular water and 0 1 0 7 average 0 2 wt silanols the dual usage of emp and ftir analyses provide important information on the distribution of different types of water in opal a and opal ct irrespective of the environments where they formed

dynamics of the northern annular mode at weekly time scales abstractrapid onsets of positive and negative tropospheric northern annular mode nam events during boreal winters are studied using era interim datasets the nam anomalies first appear in the north pacific from low frequency rossby wave propagation initiated by anomalous convection in the western tropical pacific around 2 weeks before the peak of the events for negative nam the enhanced convection leads to a zonal acceleration of the pacific jet while for positive nam the reduced convection leads to a poleward deviated jet in its exit region the north atlantic anomalies which correspond to north atlantic oscillation nao anomalies are formed in close connection with the north pacific anomalies via downstream propagation of low frequency planetary scale and high frequency synoptic waves the latter playing a major role during the last onset week prior to positive nam the generation of synoptic waves in the north pacific and their downstream propagation is strong the poleward deviated pacific j

mineralogical crystallographic and isotopic constraints on the precipitation of aragonite and calcite at shiqiang and other hot springs in yunnan province china two active spring vent pools at shiqiang yunnan province china are characterized by a complex array of precipitates that coat the wall around the pool and the narrow ledges that surround the vent pool these precipitates include arrays of aragonite crystals calcite cone dendrites red spar calcite unattached dodecahedral and rhombohedral calcite crystals and late stage calcite that commonly coats and disguises the earlier formed precipitates some of the microbial mats that grow on the ledges around the pools have been partly mineralized by microspheres that are formed of si and minor amounts of fe the calcite and aragonite that are interspersed with each other at all scales are both primary precipitates some laminae for example change laterally from aragonite to calcite over distances of only a few millimetres the precipitates at shiqiang are similar to precipitates found in and around the vent pools of other springs found in yunnan province including those at gongxiaoshe zhuyuan eryuan and jifei in all cases the dwater and 18owater indicate that the spring water is of meteoric origin these are thermogene springs with the carrier co2 being derived largely from the mantle and reaction of the waters with bedrock variations in the 13ctravertine values indicate that the waters in these springs were mixed to varying degrees with cold groundwater and its soil derived co2 calcite and aragonite precipitation took place once the spring waters had become supersaturated with respect to caco3 probably as a result of rapid co2 degassing these precipitates which were not in isotopic equilibrium with the spring water are characterized by their unusual crystal morphologies the precipitation of calcite and aragonite seemingly together can probably be attributed to microscale variations in the saturation levels that are in turn attributable to microscale variations in the rate of co2 degassing

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

magnetic transition at 30 34 kelvin in pyrrhotite insight into a widespread occurrence of this mineral in rocks abstract a characteristic magnetic transition at 30 34 k is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low temperature techniques as applied to magnetite and hematite extended down to liquid helium temperature a review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals unblocking temperature up to 350 c and extreme resistance against af may be encountered in fine grained pyrrhotite

nucleation of calcium carbonate on bacterial nanoglobules nucleation of calcium carbonate on microbial cell material may have been the dominant mode of microbial carbonate formation during most of earth s history current knowledge predicts that nucleation takes place on the cell surface or on extracellular polymeric substances however the initial nucleation steps have not been described in detail and the process remains elusive here we describe the bacterial nucleation of calcium carbonate at the nanometer scale in our precipitation experiment with sulfate reducing bacteria srb the bulk of calcium carbonate precipitates on hundreds of individual globules 60 200 nm in diameter globules originate from the srb cell surface but calcify significantly only when released to the culture medium similar globules have been observed albeit at a much larger scale in other bacterial precipitation experiments and in many natural microbial carbonates suggesting that the process we describe could be an important step in microbial calcification

nanometre scale spheroids on sands vulcano sicily possible nannobacterial alteration spheroids in the size range of 30 200 nm coat sand grains on sediments around the island of vulcano they occur as single individuals as ball shaped clumps resembling biological colonies with radiating chains of bodies and eventually merge into sheets in which the individual nannobacteria are no longer evident rarely they appear to bore into the glass grains older rocks are composed mainly of closely packed nanospheroids these spheroids are believed to be nannobacterial cells based on their resemblance to nannobacteria found in other surficial environments and their occurrence in colony like groups if so nannobacteria play a very important role in the destruction of volcanic materials on vulcano

variations of geothermometry and chemical isotopic compositions of hot spring fluids in the rehai geothermal field southwestern china abstract geothermal variations origins of carbon bearing components and reservoir temperatures in the rehai geothermal field rgf of tengchong volcanic area yunnan province southwestern china are discussed on the basis of carbon isotope compositions combined with helium isotope ratios and geothermal data from 1973 to 2000 13 c values of co 2 ch 4 hco 3 co 3 and travertine in the hot springs range from 7 6 to 1 18 56 9 to 19 48 6 7 to 4 2 6 4 to 4 2 and 27 1 to 0 6 respectively the carbon dioxide probably has a mantle magma origin but ch 4 and he have multiple origins hco 3 and co 3 in rgf thermal fluids are predominantly derived from igneous carbon dioxide but other ions originate from rocks through which the fluids circulate the 13 c values of co 2 hco 3 aq and co 3 aq illustrate that isotopic equilibriums between co 2 and hco 3 aq and co 3 aq and between dic and travertine were not achieved and no carbon isotope fractionation between hco 3 aq and co 3 aq of the hot springs in rgf was found using various geothermometers temperatures of the geothermal reservoirs are estimated in a wide range from 69 c to 450 c that fluctuated from time to time the best estimate of subsurface reservoir temperature may be 250 300 c contributions of mantle fluids and shallow crust fluids in rehai geothermal field varied with time which resulted in variations of chemical and isotopic compositions and reservoir temperatures

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

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

long term temperature records following the mw 7 9 wenchuan china earthquake are consistent with low friction this is the publisher s final pdf the published article is copyrighted by the geological society of america and can be found at http geology gsapubs org

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

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

alternative origins for nannobacteria like objects in calcite more than 40 calcite precipitation experiments were performed under sterile conditions in order to investigate the origins of 25 300 nm spherical rod and ovoid shaped objects that have been widely interpreted as evidence of nanometer scale life i e nannobacteria individual experiments included the addition of soluble organic compounds common species of eubacteria or phage induced eubacterial lysates these experiments indicate that many of the nanometer scale objects have inorganic or nonnannobacterial origins in the precipitation experiments calcite formed euhedral crystals 50 800 nm in diameter and smaller 50 nm anhedral or rounded particles or protocrystals the small anhedral or rounded solids resembled nannobacteria the relative amount of anhedral or rounded calcite was greatest in experiments with a dissolved organic component these controlled experiments are in accord with observations that rounded nanometer scale objects are more common in minerals formed in organic rich environments bacterial fragments occur as rounded to irregularly shaped particles that included cell wall fragments expulsed cytoplasm and relict capsules that also closely resembled nannobacteria acid etching of the large euhedral crystals produced in the precipitation experiments also resulted in the formation of nanometer scale features that resembled nannobacteria in natural carbonates the shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching much caution is advisable in interpreting the origin of rounded features 50 nm

seismic slip record in carbonate bearing fault zones an insight from high velocity friction experiments on siderite gouge pseudotachylyte formed by frictional melting has been the only unequivocal evidence of past seismogenic fault slip we report from high velocity friction experiments on siderite bearing gouge that mineral decomposition due to frictional heating also can leave evidence of paleoseismic events along shallow crustal faults other than pseudotachylyte experiments were conducted room dry on simulated gouge composed of siderite or mixture of siderite calcite and quartz initially at room temperature under normal stresses of 0 6 1 3 mpa and at seismic slip rates of 1 3 2 0 m s in all cases gouge exhibited dramatic slip weakening and siderite was decomposed into nanocrystalline magnetite and co 2 gas as confirmed by co 2 measurement x ray diffraction analyses and transmission electron microscopy the weakening was caused by the low frictional strength of ultrafine decomposition products at seismic slip rates magnetite formation during shearing changed gouge color to black and increased magnetic susceptibility by a few orders of magnitude those changes can be recognized in natural fault zones and black gouge in the chelungpu fault zone in taiwan is perhaps such an example thus our results suggest that thermal decomposition in shallow crustal faults can be an important co seismic process not only for dynamic fault weakening but also for leaving seismic slip records

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

multiscale approach to micro porosity quantification in continental spring carbonate facies case study from the cakmak quarry denizli turkey carbonate spring deposits gained renewed interest as potential contributors to subsurface reservoirs and as continental archives of environmental changes in contrast to their fabrics petrophysical characteristics and especially the importance of microporosity 1 mu m are less understood this study presents the combination of advanced petrophysical and imaging techniques to investigate the pore network characteristics of three common and widespread spring carbonate facies as exposed in the pleistocene cakmak quarry denizli turkey the extended pond the dipping crystalline proximal slope facies and the draping apron and channel facies deposits formed by encrustation of biological substrate integrating mercury injection capillary pressure bulk and diffusion nuclear magnetic resonance nmr nmr profiling and brunauer emmett teller bet measurements with microscopy and micro computer tomography mu ct shows that nmr t 2 distributions systematically display a single group of micro sized pore bodies making up between 6 and 33 of the pore space average nmr t 2 cut off value 62 ms micropore bodies are systematically located within cloudy crystal cores of granular and dendritic crystal textures in all facies the investigated properties therefore do not reveal differences in micropore size or shape with respect to more or less biology associated facies the pore network of the travertine facies is distinctive in terms of i the percentage of microporosity ii the connectivity of micropores with meso to macropores and ii the degree of heterogeneity at micro and macroscale results show that an approach involving different nmr experiments provided the most complete view on the 3 d pore network especially when microporosity and connectivity are of interest

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

the association of gold with calcrete abstract the discovery that au accumulates in calcrete pedogenic carbonate or caliche was made in 1987 by csiro calcrete is a general term describing accumulation of alkaline earth metals in soils of arid and semi arid terrains around the world the principal constituent of calcrete is calcite while au is a noble metal calcrete has been a significant tool in a number of au deposit discoveries so understanding the mechanisms by which these diametrically different components come together is valuable for enhancing future discovery numerous laboratory experiments case histories and exploration models have been published most from australia yet we do not fully understand the mechanisms involved it is timely therefore twenty five years on since the first publication of this phenomenon to review this highly unusual but economically important association critical to any review on au in calcrete is to first consider calcretes themselves the nature of a particular calcrete where it has formed and mode of formation is relevant to how where and why au accumulates within it this review commences with a background nomenclature history classification and some examples of calcrete types found near au deposits how calcretes form their origins and the role of biota is considered their locations in the regolith and landscape as well as exploration models for au in calcrete are discussed a section on the chemistry of au in calcretes details what we know about possible mechanisms of formation and considers what laboratory experiments on microorganisms and abiotic experiments tell us following on is a summary of practical aspects of identifying collecting and analysing samples for exploration purposes selected mineral exploration case histories are described and how they fit into models of exploration and different regolith settings concluding sections include a summary and implications of this accumulated knowledge to discovering au deposits

what do we really know about early diagenesis of non marine carbonates abstract non marine carbonate rocks including cave spring stream calcrete and lacustrine palustrine sediments are susceptible to early diagenetic processes these can profoundly alter the carbonate fabric and affect paleoclimatic proxies this review integrates recent insights into diagenesis of non marine carbonates and in particular the variety of early diagenetic processes and presents a conceptual framework to address them with ability to study at smaller and smaller scales down to nanometers one can now observe diagenesis taking place the moment initial precipitates have formed and continuing thereafter diagenesis may affect whole rocks but it typically starts in nano and micro environments the potential for diagenetic alteration depends on the reactivity of the initial precipitate commonly being metastable phases like vaterite ca oxalates hydrous mg carbonates and aragonite with regard to the ambient fluid furthermore organic compounds commonly play a crucial role in hosting these early transformations processes like neomorphism inversion and recrystallization cementation and replacement generally result in an overall coarsening of the fabric and homogenization of the wide range of complex primary microtextures if early diagenetic modifications are completed in a short time span compared to the annual to millennial time scale of interest then recorded paleoenvironmental signals and trends could still acceptably reflect original depositional conditions however even compact non marine carbonate deposits may behave locally and temporarily as open systems to crystal fluid exchange and overprinting of one or more geochemical proxies is not unexpected looking to the future relatively few studies have examined the behaviour of promising geochemical records such as clumped isotope thermometry and non conventional stable isotopes in well constrained diagenetic settings ongoing and future in vitro and in situ experimental approaches will help to investigate and detangle sequences of intermediate diagenetic products processes and controls and to quantify rates of early diagenesis bridging a gap between nanoscale molecular lab studies and the fossil field rock record of non marine carbonates