cave pearls the integrated product of abiogenic and biogenic processes abstract cave pearls up to 8 cm long collected from dried out rimstone pools in old man village cave on grand cayman british west indies have nuclei e g bone that are encased by laminated cortices these laminae are composed of trigonal prismatic calcite crystals calcite crystal bushes or particulate calcite that is formed of filamentous microbes four morphotypes spores seven morphotypes extracellular polymers eps disorganized and organized calcite fiber crystals and detrital calcite grains syntaxial overgrowths modified many of the fiber crystals and the trigonal calcite crystals thin laterally discontinuous growth lines are formed of micrite that may have been precipitated in a microbial mat growth of the cave pearls involved abiogenic and biogenic processes the trigonal calcite crystals and crystal bushes probably formed abiogenically whereas the particulate calcite laminae appear to have formed as microbes trapped and bound detrital grains to the surfaces of the cave pearls and indirectly mediated precipitation of the fiber crystals water flow into the rimstone pools which was linked to local rainfall controlled the influx of detrital grains water chemistry and microbe growth into the pools and hence the growth of the cave pearls periods of low water influx led to stagnation of pool waters that seemed to trigger periods of rapid abiogenic calcite precipitation and curtail microbial colonization high flow rates slowed abiogenic calcite precipitation promoted microbe growth and fed detrital materials into the pools despite the lightless environment of the cave the evidence clearly shows that the microbes and their associated eps played a critical role in the growth and development of the cave pearls

comment on first records of syn diagenetic non tectonic folding in quaternary thermogene travertines caused by hydrothermal incremental veining by billi et al tectonophysics 700 701 2017 60 79 abstract billi et al 2017 proposed a new interpretation for the origin and internal structure of thermogene travertine deposits on the basis of evidence from two quarries located in southern tuscany italy they interpreted some travertine beds as calcite veins and argued that undulating travertine beds formed by syn diagenetic i e non tectonic folding that was caused by laterally confined volume expansion caused by incremental veining they assumed that such a process causes changes to the rock properties including porosity reduction rock strengthening and age rejuvenation the interpretations by billi et al 2017 challenge and question the current understanding and interpretation of thermogene travertine deposits this understanding based on numerous studies since the 1980s is that these deposits form from thermal water flowing downslope and precipitating calcium carbonate here we explain how the comparison with active depositional systems is essential for the understanding the origin of structures in older inactive travertine deposits such as those studied by billi et al 2017 we further argue that the three dimensional setting of travertine deposits should be taken into account in order to discuss the possible development of secondary structures indeed travertine deposition on slopes typically leads to the formation of terraced morphologies with pools bordered by rounded rims and separated from each other by steep walls the resulting three dimensional structures can be misinterpreted as asymmetric folds in two dimensional views i e in saw cut walls of quarry in this paper we debate the interpretations offered by billi et al 2017 and their criteria to recognise syn diagenetic non tectonic folds in travertine deposits and explain why many of their ideas are questionable

rapid cold water formation and recrystallization of relict bryophyte tufa at the fall creek cold springs alberta canada the fall creek tufa is a relict mid to late holocene freshwater carbonate spring deposit that is formed almost entirely of calcite encased cratoneuron commutatum gametophytes the spring is presently active emitting 13 c meteorically derived waters but it is not precipitating calcite wood embedded in the youngest part of the tufa yielded a radiocarbon 14c date of 310 50 years bp the oldest parts of the deposit could not be dated by radiocarbon methods because of a lack of embedded organics the fall creek tufa however probably began forming 5000 years bp in response to the same wet climatic conditions that initiated calcite precipitation at miette hot springs in jasper national park and the cave and basin hot springs in banff national park the relict deposit is composed largely of calcite cements that were precipitated around the bryophytes with lesser amounts of internal sediments the tufa formed through a repeated four stage developmental process that involved i encrustation ii enc

microbes and mineral precipitation miette hot springs jasper national park alberta canada at miette hot springs so42 h2s ca2 sr2 and co32 rich waters with a mean temperature of 51 2 c are ejected from three spring vents and several minor seeps near the floor of sulphur creek valley runoff channels from the springs are colonized by cyanobacteria oscillatoria phormidium gloeocapsa synechococcus xenococcus that grow in resistant mats and as loose filaments within 0 5 m of the spring vents diatom assemblages cymbella mastagloia brachysira sellaphora rhopalodia nitzschia navicula pinnularia that dominate the flow paths 0 5 2 0 m from the vents and microbial mats with cyanobacteria and diatoms in the distal flow paths sulphate reducing bacteria and green algae are also present gypsum elemental sulphur and lesser quantities of calcite and strontianite precipitate from the spring waters microbial populations influence accumulation of mineral precipitates by i forming mats close to the spring vents on which crystals grow ii forming mats alongside the flow paths t

an overview of permian marine stratigraphy and biostratigraphy of mongolia this paper summarizes the spatial distribution stratigraphical divisions and biostratigraphical zonation schemes of permian marine deposits in mongolia where appropriate correlations of the various permian marine biostratigraphical units with those of adjacent regions are also reviewed and discussed in general permian marine sequences are developed in two separate basins one in central and northeastern mongolia where the permian stratigraphy and marine faunas bear strong similarities with those of the transbaikal verkhoyansk and kolyma omolon regions of southern and eastern russia and the other in southeastern mongolia where the permian marine faunas and rock sequences are closest to those of northeast china and southern primorye of far east russia

the marine permian of east and northeast asia an overview of biostratigraphy palaeobiogeography and palaeogeographical implications abstract the permian marine biostratigraphy faunal successions and mutual correlations where possible throughout east and northeast asia are synthesized region by region based on both published literature and the author s field observations in certain parts of the region the correlation of the permian marine successions of ne asia with the permian international timescale and in particular with gondwanan permian marine sequences remains a major challenge due to profound marine provincialism during the permian however by employing biogeographically mixed faunas from east asia se mongolia ne china south primorye of far east russia and the south kitakami terrane of japan as biostratigraphic gateways coupled with some bipolarly and bi temperately shared permian marine taxa and faunas it has been possible to correlate with reasonable confidence some of the high palaeolatitude permian marine rock units and faunas of ne asia with those of the tethyan region and gondwana palaeobiogeographically the permian marine faunas of east and ne asia are assigned to four major provinces verkolyman sino mongolian japanese cathaysian and panthalassan provinces on the basis of their palaeogeographical distribution patterns and characteristics of faunal assemblages of these the sino mongolian japanese province has considerable significance for regional palaeogeographical plate tectonic and palaeoceanographical reconstructions during the middle permian because of its conspicuously mixed cool and warm water marine biota the origin of this biogeographically mixed marine biota is interpreted to have resulted from a combination of some key factors including the increased tectonic convergence between the bureya jiamusi terrane and the sino korean platform during the permian and the intermingling of both warm and cold water ocean currents off the eastern coastal areas of the bureya jiamusi terrane and the sino korean platform during the middle permian

solonker suture in east asia and its bearing on the final closure of the eastern segment of the palaeo asian ocean abstract the location and tectonic nature of the solonker suture in east asia and hence the late palaeozoic to early mesozoic closure of the palaeo asian ocean have notoriously been enigmatic in the past decades due to limited rock exposure and the absence of unambiguous collision related regional features several tectonic models have been proposed since but in many cases these models were derived only from single key exposures or methodologies often being over simplified or interpreted leading to questionable extrapolations on regional and global scales despite the complexity of the palaeozoic accretionary tectonic framework now the regionally consistent availability of geochronological geochemical stratigraphic and palaeo geographic data enables us to integrate these into a highly detailed and coherent palaeozoic tectonic review of the suture the region across the solonker suture can generally be subdivided into three major palaeozoic tectonic provinces e g i a sino cratonic province that resembles the active palaeozoic northern margin of the north china craton to the south of the suture ii a mongolian province that comprises the south eastern margin of the mongolian terrane to the north of the suture and iii an east asian pre pacific province in north east china that accreted with the late permian initiation of pacific plate subduction the sino cratonic province experienced episodic tectonic activity that includes the accretion of the initially ensialic bainaimiao arc onto the passive northern margin of the north china craton at 437 453 ma subsequent southward directed subduction activity beneath the amalgamated margin until at least 400 ma followed by a temporary cessation of magmatic activity accompanied by a switch from north to southward directed continental drift and finally concluded by renewed subduction activity until the final closure of the palaeo asian ocean the mongolian province is suggested to have been more closely associated with the siberian craton before the presumably late devonian opening of the mongol okhotsk ocean the east asian pre pacific province originally rifted away from the eastern margin of gondwana at 600 750 ma recorded early palaeozoic 500 ma orogenic processes along the then northern margin of the siberian craton the baolidao arc system successively developed along the present day south eastern margin of the mongolian province due to continued subduction activity throughout the palaeozoic after the middle carboniferous opening of the hegenshan back arc basin renewed subduction beneath a matured baolidao arc during carboniferous and permian times led to the obduction of the hegenshan ophiolite not earlier than 270 ma shortly after the palaeo asian ocean diachronously closed from west to east along the solonker suture in the late permian to early triassic the east asian pre pacific province re attached itself by the mid mesozoic followed by a change in the regional stress regime controlled by palaeo pacific plate subduction a divergent double sided subduction model for the closure of the palaeo asian ocean provides based on the reviewed data a tectonic model that is not only able to reasonably well explain the absence of typical collision related features in the region but also the abundance of mesozoic a type granitic magmatism in north east china

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 dynamic evolution of the palaeozoic geography of eastern asia abstract new palaeogeographical reconstructions are presented for eleven time intervals through the palaeozoic of the eastern asia region from the middle cambrian at 510 ma to the end of the permian at 250 ma they centre on the continental blocks of north china south china and annamia indochina and their relationships with northeastern gondwana which was united to form part of pangea from the late carboniferous onwards also shown is the continent of tarim during the lower palaeozoic as well as the hutag uul songliao and khanka jiamasu bureya terranes both of which straddle the russian mongolian and chinese borders today from silurian times onwards we conclude that annamia and south china were united as a single continent throughout the lower palaeozoic and early devonian and were translocated by major strike slip faulting along the northeastern gondwana margin during that period from off afghanistan to outboard of the sibumasu and australian sectors of the superterrane they left the gondwana marginal area together during the lower devonian opening of the palaeotethys ocean but very shortly afterwards they themselves divided into the two separate continental blocks that we recognise today not to reunite until the triassic the various cambrian to permian rocks found in japan largely represent active volcanic arcs which originally lay to the southeast of south china although the carboniferous was more quiescent there the neotethys ocean opened during the permian dividing sibumasu and the tibetan terranes from gondwana and the palaeotethys ocean started to close progressively in the upper palaeozoic as most of the east asian continents and smaller terranes moved towards siberia the positions of the various continents and terranes have been deduced from a mixture of palaeomagnetic and faunal data the positions of large igneous provinces and kimberlites and the need to provide kinematic continuity between maps of successive ages however many uncertainties remain

distribution and characteristics of mixed transitional mid permian late artinskian ufimian marine faunas in asia and their palaeogeographical implications abstract the permian marine biogeography of the asian region is characterised by the development of three broad realms boreal tethyan and gondwanan in the early early permian asselian to early artinskian there seems to have existed sharp biogeographical boundaries with no transitional zones between the realms presumably due to the effect of gondwanan glaciation and sharp climatic zonation the mid permian late artinskian to ufimian of the asian region is distinguished by the rise of two broad transitional zones in which mixed marine faunas flourished the northern transitional zone north and northeast china sikhote alin central and northeast japan is characterised by an admixture of both warm water cathaysian and cold temperate boreal genera the southern transitional zone arabian peninsula iran afghanistan the karakorum southeast and central pamir salt range central and northwest tibet shan thai terrane timor and western irian jaya on the other hand is distinguished by incorporating faunal elements of both gondwanan and cathaysian origin the mixed faunas of both transitional zones share several antitropically distributed genera e g monodiexodina lytvolasma and spiriferella and are succeeded by palaeotropical tethyan faunas of late permian age it has been postulated that the mixed mid permian fauna of the northern transitional zone was probably formed in an epicontinental sea which was connected to both the asian tethys and the arctic which facilitated the migration of cathaysian and boreal forms into the epicontinental sea and subsequent faunal mixing the formation of the mixed faunas of the southern transitional zone on the other hand is probably related to the breaking off of the cimmerian blocks from northern gondwana and subsequent drifting into a lower latitudinal zone with geographical proximity to both gondwana and cathaysia during the mid permian

permian stratigraphy and correlation of northeast china a review palaeontological lithostratigraphical data from the permian strata and correlation of the permian successions for different tectonic units in northeast china are reviewed and summarized in this paper permian strata in northeast china are dominated by brachiopods fusulinoideans and land plants with limited ammonoids conodonts and bivalves the cisuralian early permian in the northern margin of the north china block and in the manchuride belt is composed mostly of marine massive limestone with the characteristic pseudoschwagerina zone in the asselian and sakmarian and the misellina claudiae zone in the kungurian the cisuralian in the xing an block and the northeastern part of inner mongolia is dominated by huge terrestrial deposits with fossil plants the guadalupian middle permian in the manchuride altaid and yanbian belts are characterized by bi temperate roadian or early wordian monodiexodina fauna and the late wordian capitanian codonofusiella schwagerina or neoschwagerina yabeina faunas the mixed brachiopod faunas between the boreal antitropical and the palaeoequatorial cathaysian forms the roadian or early wordian solitary coral faunas and the late wordian capitanian compound waagenophyllum wentzelella fauna the nadanhada terrane contains some exotic limestone blocks with a typical cathaysian neoschwagerina yabeina fauna in a late jurassic early cretaceous melange which is related to mesozoic subduction in the western circum pacific region the lopingian late permian in northeast china is mostly characterized by terrestrial molasse deposits with a mixed flora between the boreal angaran and the palaeoequatorial cathaysian provinces indicating the final closure of the palaeo asian ocean c 2005 elsevier ltd all rights reserved

growth and development of spring towers at shiqiang yunnan province china abstract throughout the world high artesian pressures in hydrothermal areas have led to the growth of tall spring towers that have their vents at their summits the factors that control their development and formative precipitates are poorly understood because these springs irrespective of location are mostly inactive spring towers found at shiqiang yunnan province china which are up to 4 m high and 3 m in diameter are formed largely of calcite and aragonite crystal bushes euhedral calcite crystals and coated grains with alternating fe poor and fe rich zones calcite rafts and cements formed of various combinations of calcite aragonite strontianite mg si reticulate needle fiber calcite calcified and non calcified microbes diatoms and insects collectively the limestones that form the towers can be divided into 1 group a that are friable porous and form the cores of the towers and have 18 o smow values of 15 7 to 19 7 average 17 8 and 13 c pdb values of 5 1 to 6 9 average 5 9 and 2 group b that are hard and well lithified and found largely around the vents and the tower sides and have 18 o smow values of 13 0 to 22 0 average 17 6 and 13 c pdb values of 1 4 to 3 6 average 2 6 the precipitates and the isotopic values indicate that these were thermogene springs growth of the shiqiang spring towers involved 1 phase ia when precipitation of calcite and aragonite bushes formed the core of the tower and phase ib when calcite commonly fe rich was precipitated locally 2 phase ii that involved the precipitation of white cements formed of calcite aragonite strontianite and mg si reticulate coatings in cavities amid the phase i precipitates and 3 phase iii which formed probably after spring activity ceased when needle fiber calcite was precipitated and the mounds were invaded by microbes some now calcified diatoms and insects at various times during this complex history pore waters mediated dissolution of the calcite and aragonite and sometimes partial alteration of the aragonite the diverse array of precipitates depositional fabrics and diagenetic changes clearly indicate that the composition of the spring water changed frequently growth of the spring towers at shiqiang continued until there was insufficient artesian pressure to lift the water above the top of the tower vent

geochronological and hf isotopic variability of detrital zircons in paleozoic strata across the accretionary collision zone between the north china craton and mongolian arcs and tectonic implications the central asian orogenic belt formed by accretion subsequent to the contraction of the paleo asian ocean and its southeastern segment terminated along the solonker suture zone amalgamating the mongolian arcs and the north china craton by the end of the early triassic since typical regional collisional features are absent its tectonic evolution remains speculative an investigation into the variability of detrital zircon u pb ages and hf ratios in permian strata along a southeast northwest transect from the mongolian arcs to the north china craton reveals distinct differences northern basins carry a broad mesoproterozoic to latest precambrian age signature and their sedimentary source terranes are of mixed juvenile to crustal magmatic origin in contrast southern basins contain detritus from the north china craton and their sources are of dominantly crustal contaminated magmatic origin provenance analysis suggests that in the early paleozoic ca 429 ma the paleo asian ocean was consumed along the uliastai arc and the north china craton initiating the formation of the northern and southern accretionary orogens respectively by the end of the middle carboniferous the mongolian arcs were consolidated after the accretion of the uliastai arc in the late carboniferous ca 314 ma the hegenshan back arc basin opened detaching the northern accretionary orogen while subduction continued there it may have temporarily ceased in the south after the accretion of a microcontinent ca 300 ma by the end of the middle permian ca 269 ma back arc basin closure led to the formation and obduction of the suprasubduction zone hegenshan ophiolite eventually the paleo asian ocean closed by double sided subduction such accretionary wedge wedge collision would not involve continental deep subduction unlike other continental collisions the early stages of the sequence likely resembled a pacific type scenario dominated by the subduction of oceanic lithosphere including a japanese sea type back arc basin opening the late stages involved the accretion of large scale continental blocks ultimately leading to final ocean closure which may be similar to the archipelago type setting of present day southeast asia

gypsum in modern kamchatka volcanic hot springs and the lower cambrian black shale applied to the microbial mediated precipitation of sulfates on mars gypsum is a mineral that commonly precipitates in hydrothermal environments this study reports the electron microscopic analyses of gypsum morphologies and crystal sizes found in hot springs on the kamchatka peninsula russia and compares these analyses with gypsum morphologies of hydrothermal genesis found in lower cambrian black shale in sediments of the kamchatka hot springs we observed prismatic prismatic pseudo hexagonal fibrous tubular lenticular and twinned gypsum crystals with crystal sizes ranging from 200 m the coexistence of diverse crystal habits of gypsum implies a constant interaction between hot spring geochemistry and the metabolisms of the microbial community the crystallization of ca and ba sulfates in the black shale of the lower cambrian which shows similar but less varied morphology was influenced by post depositional hydrothermal fluids the partial replacement of pyrite by sulfates in a situation coexisting with rich biomass deposits and animal fossils indicates limited modification of the sedimentary records by biological materials if the gypsum precipitated on mars underwent similar interactions between microbial communities and their geochemical environments the resulting crystal habits could be preserved even better than those on earth due to the weak geodynamics prevailing on mars throughout its evolutionary history

concretion formation in volcaniclastic host rocks evaluating the role of organics mineralogy and geochemistry on early diagenesis abstract the upper part of the brushy basin member of the jurassic morrison formation in the four corners regions of the u s was deposited in an ephemeral alkaline saline lake system with copious input of volcanic ash that resulted in dynamic fluid rock interaction during early diagenesis three broad diagenetic facies defined by color and associated bioturbation features are interpreted red green and intermediate diagenetic facies reflect meter scale paleotopography red facies represent shallow water to subaerial oxidizing conditions green facies reflect saturated conditions and reducing pore water chemistry shortly after deposition and intermediate facies represent a combination of or rapid transition between the previous two conditions three categories of concretions are characterized based on mineralogy carbonate iron oxyhydr oxide and phosphate concretions variation in concretion mineralogy and morphology in the brushy basin member suggests that alkaline saline fluid chemistries created diagenetic microenvironments within a larger lake system to influence concretion precipitation however porosity and permeability are more important factors affecting concretion size morphology and mineralogy than host rock composition diagenetic fluid rock interactions in volcaniclastic sediments can be spatially variable even on tens of centimeters scale

early archean hot springs above epithermal veins north pole western australia new insights from fluid inclusion microanalysis the world s most ancient biogenic structures are found in the north pole dome of western australia where 3 47 gyr old algal mats and stromatolites are closely associated with bedding conformable and discordant laminar quartz chalcedony and barite barite rich quartz hydrothermal veins with similar mineralogy occur throughout the stratigraphy below the conformable biogenic structures with the exception of the large volume of barite these bedding conformable and discordant laminar quartz veins exhibit textures and associated hydrothermal alteration quartz chalcedony chlorite illite calcite adularia pyrite typical of epithermal deposits formed from near neutral ph fluids we characterize the physical and chemical conditions of the ancient water responsible for depositing both the discordant and conformable quartz chalcedony barite as it passed through the upper parts of the archean crust field relationships combined with new fluid inclusion data suggest that the best documented stromatolites in the north pole dome occur adjacent to quartz chalcedony bands formed from cool 120 c low salinity 3 wt nacl equiv waters higher temperature up to 300 c more saline up to 10 wt nacl equiv and co2 h2s rich ch4 aqueous fluids occur in deeper level veins rare inclusions that are unusually rich in co2 containing liquid and gaseous co2 and liquid h2o support the existence of multiple batches of hydrothermal fluids with variable densities and gas contents oxygen isotope data 8 7 3 7 suggest that the causative fluids comprised admixtures of deeply circulated surface water with variable input of magmatic components our findings reveal that the earliest life known on earth lived in and around a hydrothermal system with temperatures from 300 c at depth to 120 c near the paleosurface in an environment closely analogous to modern hot springs developed above epithermal veins evidence exists for the introduction of different batches of hydrothermal fluids with variable densities and gas contents during the development of veins these findings support previous studies that demonstrate that the processes that form epithermal deposits have been active throughout geologic time and the present day distribution of epithermal deposits is dominantly a result of preservation not process

abiogenic growth of needle fiber calcite in spring towers at shiqiang yunnan province china abstract at shiqiang china there are spring towers up to 4 m high and 3 m in diameter that are formed of porous gray to orange to brown bedded limestones that have a multistage diagenetic history the walls of many cavities in these limestones are covered with hypocoatings and or needle fiber calcite nfc that formed during the last stage of diagenesis where present the hypocoatings are 10 m thick appear homogeneous and typically lie under the nfc mats the nfc is divided into nanofibers rods 1 m long 75 100 nm diameter composite fibers bundles of 2 to 16 rods each rod 300 400 nm in diameter up to 25 m wide and 100 m long pyramid fibers pyramid shape with 4 to 6 sides up to 25 wide at base tapering to point up to 100 m long and ribbon fibers blade shape 2 4 m wide 1 m thick up to 100 m long many crystals are highly ornate with epitaxial overgrowths that display elements of skeletal and or dendritic growth the wall covering nfc mats are formed of one crystal type or any combination of different crystal types with or without epitaxial overgrowths precipitation of needle fiber calcite known from a diverse array of geological settings throughout the world is commonly linked to fungi or other biogenic processes in the shiqiang spring towers however no fungi were found with the nfc and only scattered microbes and minor amounts of exopolysaccharides were associated with some of the nfc in some pores the nfc crystals appear to have been precipitated from fluids that were highly saturated with respect to calcite as a result of evaporation the calcium probably came from rainwater groundwater via capillary action and or dissolution of the calcite framework whereas evaporation was mediated by solar radiation and or the wind available evidence indicates that the nfc found in the spring deposits at shiqiang were a late diagenetic product that probably formed through abiogenic precipitation

chemical divides and evaporite assemblages on mars assemblages of evaporite minerals record detailed physical and chemical characteristics of ancient surficial environments accordingly newly discovered regions of saline minerals on mars are high priority targets for exploration the chemical divide concept of evaporite mineral formation is used successfully to predict evaporite mineralogy and brine evolution on earth however basaltic weathering largely controls fluid compositions on mars and the robust predictive capabilities of terrestrial chemical divides cannot be used to interpret martian evaporites here we present a new chemical divide system that predicts evaporite assemblages identified in snc type meteorites ancient evaporites discovered on meridiani planum by the opportunity rover and mars express omega data we suggest that a common fluid type that has been buffered to different ph levels by basaltic weathering controls the variability among martian evaporite assemblages and that evaporite mineralogy and brine evolution is essentially established by the initial composition of the dilute evaporating fluid b 2005 elsevier b v all rights reserved

the hot spring and geyser sinters of el tatio northern chile abstract the siliceous sinter deposits of el tatio geothermal field in northern chile have been examined petrographically and mineralogically these sinters consist of amorphous silica opal a deposited around hot springs and geysers from nearly neutral silica saturated sodium chloride waters water cooling and evaporation to dryness are the main processes that control the opal a deposition in both subaqueous and subaerial settings in close spatial relation to microbial communities all fingerprints of organisms observed in the studied sinter samples represent microbes and suggest that the microbial community is moderately diverse cyanobacteria green bacteria and diatoms the most important ecological parameter is the temperature gradient which is closely related to the observed depositional settings 1 geyser setting water temperature 70 86 c boiling point at el tatio 4200 m a s l coarse laminated sinter macrostructure with rapid local variations biota comprises non photosynthetic hyperthermophilic bacteria 2 splash areas around geysers water temperature 60 75 c laminated spicule and column macrostructure locally forming cupolas

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

stalactite growth mediated by biofilms example from nani cave cayman brac british west indies growth lines evident in cross sections through stalactites from nani cave provide a temporal record of their growth many of these dark organic rich laminae developed as biofilms that are recognized by the presence of 1 a diverse microbial biota that is dominated by actinomycetes 2 calcified filaments 3 films formed of extracellular polymeric substances eps 4 grain coating sheets of calcite crystals that grew in eps 5 biterminal calcite crystals and 6 etching this biosignatures suite encompasses a variety of constructive and destructive processes where fully developed the features generated by the biofilms form a distinctive microstratigraphic succession collectively 50 m thick which can be traced laterally across the stalactite s surface the use of speleothems in paleoclimate studies is commonly framed against a chronology that relies at least in part on annual growth couplets the dark organic rich lamina that forms one part of the growth couplet is typically ascribed to abiotic precipitation that incorporated exogenic organic matter that was flushed into the cave following the first major rainfall of the wet season this assumption ignores the possibility that dark organic rich growth laminae can be the record of biofilms that developed on the surface of the stalactites and hence may not be a record of annual events

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

possible microbial effects on stable carbon isotopes in hot spring travertines recent and older early holocene to pleistocene hot spring travertine carbonates from central italy have two distinctive macrofabrics crystalline crusts and shrubs crystalline crusts are laminated slope deposits that formed abiotically following co 2 degassing from spring water the formation of shrub travertine irregular dendritic precipitates from pool environments is controversial and has been attributed to both abiotic and microbial processes oxygen isotope variation in our travertines can be explained by abiotic processes mainly co 2 degassing in contrast our carbon isotope data cannot be wholly explained by abiotic co 2 degassing invoked in earlier studies because photosynthesis is known to preferentially remove 12 c leaving ambient waters enriched in 13 c this fractionation should be recorded in delta 13 c values of microbially influenced travertine our shrub carbon isotope values are between 0 5 per thousand and 6 0 per thousand larger than values for associated abiotic precipitates and this difference is probably caused by microbial activity these isotope data support previous visual evidence that some shrub fabrics are microbially influenced

impact dust not the cause of the cretaceous tertiary mass extinction most of the 3 mm thick globally distributed chicxulub ejecta layer found at the cretaceous tertiary k t boundary was deposited as condensation droplets from the impact vapor plume a small fraction of this layer 14 g was submicrometer size dust the global mass and grain size distribution of the clastic debris indicate that stratospheric winds spread the debris from north america over the pacific ocean to europe and little debris reached high southern latitudes these findings indicate that the original k t impact extinction hypothesis the shutdown of photosynthesis by submicrometer size dust is not valid because it requires more than two orders of magnitude more fine dust than is estimated here furthermore estimates of future impact hazards which rely upon inaccurate impact dust loadings are greatly overstated

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

travertine mounds of the cave and basin national historic site banff national park the cave and basin national historic site is a fan shaped travertine deposit associated with four thermal spring outlets tentative age dating of the travertine mound indicates growth initiated with onset of the late holocene shift to more humid and cool climate conditions and suggests that the flow of thermal waters was limited during the hypsithermal which in turn places constraints on the evolutionary biology of endemic species in the spring system two large caves and one collapsed cave structure are developed within the deposit cave development is in response to both physical erosion of till underlying the travertine and acid gas attack of calcite that makes up the deposit this process is buffered by formation of reaction crusts of gypsum on the interior cave walls only minor modern travertine growth occurs due to historic flow control measures understanding the flow of water through the historic site is critical for long term preservation

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

differences in the delta 18 o and delta 13 c signatures of seasonal laminae comprising travertine stromatolites abstract alternation of sparry and micritic laminae in modern nonmarine travertine stromatolites from creeks in the arbuckle mountains of oklahoma and from eocene hot water deposits in the palm park formation of new mexico represent seasonal accumulations the sparry laminae with upright biogenic structures represent spring summer accumulations whereas the micritic laminae with flat lying microbial remains represent fall winter accumulations the 18o values of the modern creek waters average 5 04 spring summer and 5 25 fall winter smow and calcite precipitated in equilibrium with these waters should have 18o values of approximately 6 4 and 5 2 pdb for spring summer and fall winter precipitates respectively 18o values for calcite which precipitated during three month periods on test objects in the creek waters average 6 5 for spring summer and 4 9 for fall winter the sparry and micritic laminae comprising the naturally occurring modern stromatolites from these creeks average 6 4 for sparry spring summer and 5 2 for micritic fall winter laminae thus the agreement between 18o values for precipitates which formed in isotopic equilibrium with the creek water composition precipitates on test objects and the sparry and micritic laminae comprising naturally occurring modern stromatolites confirm the seasonal origin of the laminae the 13c values for the creek waters the test objects and the naturally occurring laminae of the stromatolites are higher in the sparry spring summer than the micritic fall winter deposits the 18o values obtained as a result of lamina by lamina analyses of the eocene hot water travertine stromatolites of new mexico do not display a seasonal trend but the 13c values are consistently higher in the sparry laminae than in the micritic laminae in addition increased concentrations of trace elements occur in the sparry relative to the micritic laminae of the hot water stromatolites the lamina by lamina stable isotopic and trace elemental analyses provide confirmation of the seasonal origin of the sparry spring summer and micritic fall winter laminae comprising the ancient stromatolites

dirty water events at rocky mountain hot springs and their correlation with other short lived phenomena the radium british columbia and miette alberta hot springs occasionally produce dirty water that carries varying amounts of solid particles in suspension dirty water events in the period 1959 1983 were caused either by heavy rains or rapid snowmelt or by earthquakes with magnitudes of 6 9 or greater between 740 and 2300 km distant from the springs in alaska idaho and montana rainfall induced events at miette appear to require at least 34 mm of rain within a 48 h period associated decreases in water temperatures and dissolved solids concentrations and changes in the ionic and isotopic compositions of the spring waters result from mixing of deep thermal water with cooler less mineralized shallow water by contrast the earthquake triggered events did not have significant thermal or geochemical effects suspended solids in the dirty waters represent surficial materials including vegetation debris and possibly residues from dissolution of carbonate rocks at miette hot springs the dirt conta

permian ammonoid associations of the verkhoyansk region northeast russia abstract on the basis of a study of the majority of permian ammonoids known in verkhoyansk region and an analysis of their age distribution seven associations and four subassociations are established these ammonoid associations are the khorokyt arkachan endybal mysovy orol takamkyt delendzha and post sverdrupites associations in ascending order the majority of these associations and subassociations include some complementary ammonoid beds the ammonoid associations and subassociations are considered as biostratigraphic divisions of regional stratigraphic extent and are useful for dating and correlating the permian sedimentary sequences of the verkhoyansk region the geographical and stratigraphic distributions of 360 permian ammonoid shells in the verkhoyansk region permits us to not only diagnose each ammonoid association with specific index species but also to elucidate the biogeographic connections and migration patterns of the verkhoyansk ammonoid faunas in relation to these spreading throughout the entire boreal realm

unconformity bounded upper paleozoic megasequences in the beishan region nw china and implications for the timing of the paleo asian ocean closure abstract the upper paleozoic sedimentary sequence in the beishan region northwest china provides a complete record of the complex amalgamation and extension history of the central asian orogenic belt caob for this part of china integrating newly obtained stratigraphic paleontological and radiometric data this paper reviews the upper paleozoic stratigraphic sequences of the beishan region the upper paleozoic strata here are divided into three megasequences ms they are in ascending order devonian mississippian guadalupian and lopingian megasequences ms1 ms2 and ms3 separated by two major unconformities each indicative of a huge sedimentary hiatus ms1 is made up of continental and epicontinental marine deposits in the pre rift stage ms2 of transgressive marine and volcanic strata in the syn rift stage and ms3 of continental sediments in the inversion stage the major unconformity between ms1 and ms2 is interpreted to represent the regional uplift and erosion caused by the final amalgamation of caob in the beishan region the syn rift ms2 represented by transgressive marine and volcanic strata in the beishan region can be well correlated with pennsylvanian guadalupian megasequences in inner mongolia where they rest on a major interregional unconformity this correlation suggests the closure of the paleo asian ocean in beishan and inner mongolia before the carboniferous followed by the development of a synchronous marine rift megasequence in the southern part of the caob

abiotic versus biotic controls on the development of the fairmont hot springs carbonate deposit british columbia canada the relict fairmont hot springs deposit formed largely of carbonates covers an area of 0ae 5k m 2 and is up to 16 m thick the triangle shaped discharge apron which broadens down valley is divided into a proximal part with beds dipping at 10 and a distal part with beds dipping at 10 to 15 the deposit is formed of the 1 basal macrophyte 2 lower carbonate 3 middle clastic 4 upper carbonate and 5 upper clastic sequences two charcoal samples embedded in the lower carbonate sequence yielded dates of 8690 90 and 8270 70 cal yr bp indicating that much of the deposit formed post glacially during the early to mid holocene deposit aggradation ceased in the mid to late holocene when the fairmont creek valley was incised the lower and upper carbonate sequences which are the thickest sequences are composed of nearly equal parts of travertine abiotic and tufa biotic with feather dendrite travertine radiating dendrite travertine and stromatolite tufa dominating competition between calcite precipitation rates and biotic growth rates controlled the distribution of tufa and travertine across the discharge apron calcite and biotic growth rates were controlled largely by flow velocity across the apron which in turn was controlled by topography and regular fluctuations in spring water discharge volume during times of high spring discharge slow sheet flow over the proximal part of the apron promoted stromatolite growth whereas fast turbulent flow on the distal part of the apron induced rapid feather dendrite formation during times of low spring discharge quiescent shallow evaporative pools conducive to radiating dendrite formation formed on the proximal part of the apron whereas slow flow on the distal part promoted stromatolite growth facies with high calcite supersaturation experienced rapid abiotic dendrite growth that precluded most biotic growth

the permian antitropical fusulinoidean genus monodiexodina distribution taxonomy paleobiogeography and paleoecology all the documented occurrences with illustration of specimens of the permian fusulinoidean genus monodiexodina from a total of 33 areas in 11 regions are reviewed and their taxonomic positions are reexamined in this paper among 17 species including two subspecies of monodiexodina in the current taxonomy the following 10 species are recognized as valid m kattaensis m wanneri m caracorumensis m sutchanica m shiptoni m kumensis m wanganensis m neimongolensis m delicata and m rhaphidoformis in addition species once referred to monodiexodina but now should be excluded from the genus are also investigated in terms of their generic positions in reconstructed mid permian paleomap monodiexodina bearing areas can be restored to either northern or southern middle latitudes between high latitudinal cool cold water climatic realm and paleo tropical warm water realm these two middle latitudinal areas each corresponding to the northern and southern transitional zones respectively can be best interpreted climatologically as mesothermal warm temperate belts in both hemispheres thus suggesting the genus to be a paleobiogeographically typical antitropical fusulinoidean taxon moreover the genus is generally found in a monotypic crowded manner in sandy sediments with their shells being often aligned uni directionally this mode of occurrence of monodiexodina strongly suggests that it was adapted to shallow marine high energy environments which would probably be essentially maintained by the acquisition of highly elongated fusiform subcylindrical shells with well developed polar torsion this morphological feature is adapted to increase septal pores per unit area in polar regions thus increasing possibility to develop more pseudopodia on both sides of test it probably has a functional significance for not only locomotion but also anchoring their tests on the surface of bottom sediments in agitated water conditions the genus itself is considered to be a rather long ranging taxon from the late yakhtashian artinskian to the early midian capitanian it is therefore concluded that monodiexodina had an opportunistic character occurring repeatedly only when favorable high energy conditions such as sand shoal appeared in warm temperate climatic belts in both hemispheres monodiexodina originated in the southern transitional zone from an elongated eoparafusulina stock at late early permian around late artinskian time it flourished in southern middle latitudinal areas in latest early and early middle permian time the genus then migrated to the northern hemisphere northern transitional zone by some dispersion mechanism at around the early middle permian and prevailed there during the remaining period of the middle permian