fluviokarst and classical karst examples from the dinarics krk island northern adriatic croatia abstract in order to contribute to the debate on the role of fluvial erosion in the shaping of karst two nearby areas with different karstic landscapes were compared areas a and b are located relatively close to each other on the southern side of the krk island adriatic sea croatia both areas are composed of similar limestone with a very high caco 3 content area a is a typical doline or polygonal type classical of karst with numerous dolines up to 57 km 2 covered with terra rossa red soil and mediterranean maquis shrubland dolines are located in zones which correspond to the strike of the main geological structures dry karstic valleys are visible only on gently inclined coastal slopes bordering the karstic plateau in contrast area b is typical of a bare karst landscape with a strong palaeo fluvial imprint the dolines are absent and the bedrock is only sporadically covered with terra rossa palaeogene marls have been observed in a few elongated depressions and in the coastal zone of area b along steep coastal slopes valleys up to 460 m km 2 are cut into the carbonates the traces of episodic surface flows are visible in some of these valleys in contrast to the valleys in area a remnants of a disrupted ancient fluvial network are clearly visible on the elevated karstic plateau in area b differences in the recent morphology are attributed mainly to varying thicknesses of the palaeogene impermeable marly cover and the intensity of tectonics in the two areas

microstructure of high temperature 73 c siliceous sinter deposited around hot springs and geysers yellowstone national park the role of biological and abiological processes in sedimentation slightly alkaline hot springs and geysers in yellowstone national park exhibit distinctive assemblages of high temperature 73 c siliceous sinter reflecting local hydrodynamic conditions the main depositional zones include subaqueous pool and channel bottoms and intermittently wetted subaerial splash surge and overflow areas subaqueous deposits include particulate siliceous sediment and dendritic and microbial silica framework silica framework forms thin porous microbe rich films coating subaqueous surces spicules with intervening narrow crevices dominate in splash zones surge and overflow deposits include pool and channel rims columns and knobs in thin section subaerial sinter is composed of i dark brown nearly opaque laminated sinter deposited on surfaces that evaporate to dryness ii clear translucent silica deposited subaqueously through precipitation driven by supersaturation iii heterogeneous silica representing silica encrusted microbial filaments and detritus and iv sinter debris brownish laminations form the framework of most sinter deposited in surge and overflow zones pits and cavities are common architectural features of subaerial sinter and show concave upward pseudo cross laminations and micro unconformities developed through migration marked birefringence of silica deposited on surfaces that evaporate to dryness is probably a strain effect repeated wetting and evaporation often to dryness and capillary effects control the deposition morphology and microstructure of most high temperature sinter outside of the fully subaqueous zone microbial filaments are abundant on and within high temperature sinter but do not provide the main controls on morphology or structuring except in biofilms developed on subaqueous surfaces millimetre scale lamination cyclicity in much high temperature sinter represents annual layering and regular seasonal fluctuations in silica sedimentation

diversity of iron and silica precipitation by microbial mats in hydrothermal waters iceland implications for precambrian iron formations direct examination of microbial mats from icelandic hot springs with transmission electron microscopy and energy dispersive x ray spectroscopy revealed a consortium of bacterial cells in varying stages of mineralization differences in observed mineralogy largelyreflectdifferencesinthechemistryofthehydrothermalwaters silica richspheroids formedepicellularlyoncellwallsandsurroundingsheathsandcapsulesofmicroorganisms and insomecases intracellularlywhenpresumablythecell s hadlysed commonly these precipitateswereobservedcoalescingtoformamatrixofamorphoussilicathatcompletely encapsulated the cells and or replaced their cytoplasmic material however in other cells the precipitates were composed of amorphous granules made exclusively of iron and silica inapproximatelyequalproportions atonelocality thebacteriaformedseveralepicellular iron minerals ranging from iron mineralized capsules tofine grained spheroids of amorphous ferric hydroxide and acicular aggregates of goethite the complete encrustation of bacterial cells by silica iron or a combination of both may greatly enhance their preservation potential such that these mineralized microorganisms may conceivably represent future microfossils thus we may be witnessing contemporaneous biomineralization processes that are similar to those of the geologic past particularly with regard to the origin of some precambrian banded iron formations

biogenicity of silica precipitation around geysers and hot spring vents north island new zealand abstract before anthropogenic modifications ohaaki pool broadlands ohaaki and dragon s mouth geyser wairakei emitted waters at temperatures of 93 98 c the siliceous sinter that precipitated around their vents has the characteristics of geyserite a dense laminated deposit of presumed abiogenic origin that was precipitated from waters too hot 73 c to support microbes other than thermophilic bacteria petrographic and sem examinations of the sinters that surround the vent of dragon s mouth geyser and form the pool rim dam of ohaaki pool show that they incorporate columnar stromatolites and silicified laminated stromatolitic mats that contain well preserved filamentous microbes at both localities the microbes lack evidence of desiccation or shrinkage which implies that they were silicified rapidly at or shortly after their death microbe preservation is commonly spectacular even the trichome is recognizable in many specimens although replacement by silica preserved the cells of the trichome cell walls and septae were not preserved possibly because they were destroyed by autolysis before silicification the sheath that surrounded the trichome is normally well preserved however late silica precipitation produced thick external encrustations of amorphous silica around many sheaths although boiling and very hot 90 c waters were discharged temperatures at many sites surrounding the vents remained sufficiently low and moist to support a microbial community that included thermophilic bacteria and cyanobacteria in these cooler niches the microbes and their biofilms served as highly favorable templates for the nucleation and growth of amorphous silica and collectively provided a microbial framework for the laminated accretionary sinter silica was supplied from supersaturated spring and geyser fluids that were delivered to sites of sinter precipitation as air cooled spray as proximal runoff or as the result of oscillations in the surface level of the spring or geyser pool waters in the field and in hand specimen the resulting columnar sinter appear to be identical in morphology to that inferred to originate from abiotic silica precipitation in a sterile environment consequently some columnar spicular and stratiform geyserites are probably not abiotic precipitates but are true silica stromatolites

armoring and sorting simulation in alluvial rivers formulations for bed armoring and hydraulic sorting of bed sediments in alluvial streams are developed and an application to missouri river bed evolution is presented a relation for the areal coverage factor for armoring on a plane bed is first formulated as a function of degradation depth and bed material characteristics and is then modified by introducing correction factors for the effect of bed forms and the stochastic nature of sediment motion for the simulation of hydraulic sorting bed sediments are assumed to be mixed homogeneously in a mixed layer depth approximately equal to average bed form height and the composition of mixed layer materials is adjusted to satisfy the continuity equation for each sediment size fraction these formulations are applied in a 20 year simulation of bed degradation in the middle missouri river reach downstream of gavins point dam it is found that the simulated bed sediment composition including the two layer structure comprising the top armor coat and the underlying finer sediments is in good agreement with the observed missouri river bed characteristics

geometry of geyser plumbing inferred from ground deformation author s ardid a vera e kelly c manga m munoz saez c maksymowicz a ortega culaciati f abstract 2019 american geophysical union all rights reserved broadband seismic data were recorded on the ground surface around an exceptionally regular eruptive system geyser el jefe in the el tatio geyser field chile we identify two stages in the eruption recharge and discharge characterized by a radial expansion and contraction respectively of the surface around the geyser we model the deformation with spherical sources that vary in size location and pressure constrained by pressure observations inside the conduit that are highly correlated with deformation signals we find that in order to fit the data the subsurface pressure sources must be laterally offset from the geyser vent during the recharge phase and that they must migrate upward toward the vent during the eruption phase this pattern is consistent with models in which ascending fluids accumulate and then are released from a bubble trap that is horizontally offset from the shallow conduit of the geyser

analysis of dolines using multiple methods applied to airborne laser scanning data abstract delineating dolines is not a straightforward process especially in densely vegetated areas this paper deals quantitatively with the surface karst morphology of a miocene limestone occurrence in the styrian basin austria the study area is an isolated karst mountain with a smooth morphology former planation surface of pliocene age densely vegetated mixed forest and with a surface area of 1 3 km 2 the study area is located near the city of wildon and is named wildoner buchkogel the aim of this study was to test three different approaches in order to automatically delineate dolines the data basis for this was a high resolution digital terrain model dtm derived from airborne laser scanning als and with a raster resolution of 1 1 m the three different methods for doline boundary delineation are a the traditional method based on the outermost closed contour line b boundary extraction based on a drainage correction algorithm filling up pits and c boundary extraction based on hydrologic modelling watershed extracted features are integrated in a gis environment and analysed statistically regarding spatial distribution shape geometry elongation direction and volume the three methods lead to different doline boundaries and therefore investigated parameters show significant variations the applied methods have been compared with respect to their application purpose depending on delineation process between 118 and 189 dolines could be defined the high density of surface karst features demonstrates that solutional processes are major factors in the landscape development of the wildoner buchkogel furthermore the correlation to the landscape evolution of the grazer bergland is discussed

physico chemical and environmental controls on siliceous sinter formation at the high altitude el tatio geothermal field chile abstract el tatio geothermal field is located 4270 m above sea level in the altiplano northern chile siliceous sinter deposits from el tatio were studied to understand the influence of water chemistry and the extreme climatic conditions on their textures and mineralogy the results of this study show that the mineralogy of el tatio sinters include of opal a and accessory minerals such as halite gypsum and cahnite ca 4 b 2 as 2 o 12 4h 2 o which precipitate by full evaporation of high arsenic boron and calcium thermal waters el tatio sinters show a high degree of structural disorder probably linked to cation incorporation into the silica structure and or the occurrence of micro to nano scale accessory minerals the high content of cations in the thermal waters is strongly tied to relatively high silica precipitation rates considering silica concentration in water 147 285 mg l sio 2 precipitation rate reach 2 5 kg m 2 per year based on in situ precipitation experiments the particular environmental conditions of this high altitude geothermal area that produce high water cooling rate and high evaporation rate may also be responsible for the fast silica precipitation low environmental temperatures create freezing related sinter textures i e silica platelets and micro columns ridges silicified microbial filaments are also characteristic of el tatio sinters and they are indicative of water temperature and hydrodynamic conditions at the moment of sinter formation however sinter textural interpretation in a high altitude andean context must be done carefully as specific relationships between microbial and hydrodynamic textures are found

the growth of siliceous sinter deposits around high temperature eruptive hot springs abstract siliceous hot spring deposits sinter are of interest as they are indicative of hydrothermal resources at depth and may provide evidence for early life on earth and possibly mars numeric models of concurrent evaporation and opal a precipitation around high temperature 73 c eruptive hot spring vents such as geysers show that silica is most efficiently precipitated by complete evaporation owing to very sluggish growth kinetics for silica precipitation from supersaturated hydrothermal water where evaporation is complete between geyser events areas of initially deeper water precipitate more silica that over time fill in topographic lows to produce a smooth surface in contrast incomplete evaporation in which water is left in low areas prior to being washed away by the next geyser event or equivalently where there is continuous surface flow in topographic low areas tends to enhance the growth of minor topographic highs and leads to an increase in surface roughness such as seen in the development of knobby geyserite sinter texture around vents

tracing the continental diagenetic loop of the opal a to opal ct transformation with x ray diffraction abstract opaline silica forms in a variety of continental deposits on the earth s surface the maturation from opaline silica to quartz is traditionally traced with x ray diffraction that suggests a gradual phase transformation and structural ordering however the identification and categorization of the gradual opal a to opal ct transformation remains challenging due to potential mineral impurities and the transient structure of opaline silica here we use x ray powder diffraction to identify peak parameters that characterize the maturation from opal a to opal ct in continental settings we analyzed inclusion free opals from non sinter continental deposits and the products of opal mixing and heating experiments twenty five samples were analyzed from australia ethiopia slovakia usa mexico and madagascar and represent opal from a range of host rocks and formation conditions xrd analysis reveals that opal peak parameters constitute a diagenetic loop and that the structural order is decoupled from the low tridymite cristobalite ratio at large d values systematic changes of the width and position of a subsidiary peak at ca 2 5 a accurately reflect the low tridymite cristobalite ratio and degree of ordering our results suggest that the identification of individual stages in the opal a to opal ct transformation sequence requires the application of multiple peak parameters that complement or replace existing maturation indicators this information is essential for a precise silica identification and genetic reconstruction especially of open continental systems with internal re distribution and external input of aqueous silica

karstic uvala revisited toward a redefinition of the term abstract uvalas are a particular type of karst closed depression while other types of closed depression dolines and poljes are regularly listed and relatively well defined in overviews of karst surface morphology uvalas are either excluded or their vague identification is stressed the leading idea of this paper is to obtain a clearer meaning of the term uvala and prevent its abandonment from karstology and general geomorphology within the study 43 examples of uvalas have been selected the studied uvalas are located in the dinaric karst and karst of the carpatho balkanides all the case examples have been digitally processed in the same way creation of high resolution digital elevation models enabled quantification of morphometric parameters generation of inclination maps and cross sections as well as application of statistical analyses formation of the geographical information system of the studied uvalas was done using raster based and vector based gis software packages in 12 studied uvalas detailed structural geological mapping has been carried out which revealed dominant development of uvalas along regional scale tectonically broken zones a revised definition of the term uvala is suggested leaving the opportunity for further discussion

cryogenic silicification of microorganisms in hydrothermal fluids silica rich hydrothermal fluids that experience freezing temperatures precipitate cryogenic opal a coa within ice bound brine channels we investigated cryogenic silicification as a novel preservation pathway for chemo and photo lithotrophic bacteria and archaea we find that the co partitioning of microbial cells and silica into brine channels causes microorganisms to become fossilised in coa rod and coccoidal form bacteria and archaea produce numerous cell casts on coa particle surfaces while chloroflexus filaments are preserved inside particle interiors coa particles precipitated from natural icelandic hot spring fluids possess similar biomorphic casts including those containing intact microbial cells biomolecules and inorganic metabolic products are also captured by coa precipitation and are detectable with a combination of visible shortwave infrared reflectance ftir and raman spectroscopy we identify cryogenic silicification as a newly described mechanism by which microbial biosignatures can be preserved within silica rich hydrothermal environments this work has implications for the interpretation of biosignatures in relic hydrothermal settings and for life detection on mars and enceladus where opaline silica indicative of hydrothermal activity has been detected and freezing surface conditions predominate

cryogenic opal a deposition from yellowstone hot springs sub zero winter temperatures on the yellowstone plateau alter the opal a precipitation pathway offluid erupting from hot springs and geysers frozen fluid often only meters from boiling pools contains abundant opal a particles comprising sheet and filamentlike aggregations of opal a microspheres which are formed by opal a precipitation in brine pockets channels and veins by natural cryogelling unconsolidated cryogenic opal a sediment accumulates in and below water ice where it is locked until spring thaw conditions sediment is then either remobilized contributing large volumes of opal a particulate to geothermally influenced wetlands or becomes adhered in situ by dehydration and cementation this strongly seasonal opal a precipitation regime has been overlooked in investigations of sinter deposition accretion rates and microbe mineral interactions natural opal a textures recorded fromyellowstonemaybereplicatedsimplybyfreezingandthawingsyntheticsilica saltsolutioninthelaboratory cryogenicprocess may have influenced mineral precipitation and sediment accumulation in many other geothermal areas particularly active terrestrial springs located at high altitude latitude fossil systems influenced by ancient glaciations plus potential astrobiological targets e g mars and europa 2007 elsevier b v all rights reserved

thermophiles early biosphere evolution and the origin of life on earth implications for the exobiological exploration of mars mars holds great interest for exobiology and presently stands center stage in our plans to explore the inner solar system for signs of past or present life with the spectacular success of the pathfinder mission golombek 1997 and upcoming mapping efforts by the mars global surveyor orbiter albee et al 1998 it is an especially appropriate time to revisit some important issues in mars exobiology the papers making up this journal of geophysical research planets special issue on mars were the outgrowth of an american geophysical union special session entitled exploring for a martian biosphere which was presented at the fall meeting in san francisco in 1995 farmer 1995a together these papers provide a context for evaluating some fundamental issues in the exobiological exploration of mars topics covered fall into the following broad categories 1 environments and conditions required for the origin of life hydrothermal environments as sites for prebiotic chemical synthesis shock and schulte this issue 2 early martian environments as a context for the evolution and diversification of life on mars early impact hazards sleep and zahnle this issue early volatile and climate history of mars haberle this issue and ice covered lakes as habitats for early life doran et al this issue 3 exploring for extant martian life results of the viking missions klein this issue environmental extremes for martian life clark this issue and planetary protection and mars sample return devincenzi et al this issue and 4 exploration strategies phosphate minerals as targets for chemofossils mojzsis and arrhenius this issue and the role of robotic surface missions stoker this issue

exploring for a record of ancient martian life the immediate task facing exopaleontology is to define a strategy to explore mars for a fossil record during the decade long exploration program that lies ahead consideration of the quality of paleontological information preserved under different geological conditions is important if we are to develop a strategy with broad applicability the preservation of microbial fossils is strongly influenced by the physical chemical and biological factors of the environment which acting together determine the types of information that will be captured and retained in the rock record in detrital sedimentary systems preservation is favored by rapid burial in fine grained clay rich sediments in chemical sedimentary systems preservation is enhanced by rapid entombment in fine grained chemical precipitates for long term preservation host rocks must be composed of stable minerals that are resistant to chemical weathering and that form an impermeable matrix and closed chemical system to protect biosignatures from alteration during subsequent diagenesis or metamorphism in this context host rocks composed of highly ordered chemically stable mineral phases like silica e g cherts or phosphate e g phosphorites are especially favored such lithologies tend to have very long crustal residence times and along with carbonates and shales are the most common host rocks for the precambrian microfossil record on earth although we make the defensible assumption that mars was more like the earth early in its history clearly the geological and historical differences between the two planets are many such differences must be carefully considered when adapting an earth based strategy to mars

dynamics within geyser conduits and sensitivity to environmental perturbations insights from a periodic geyser in the el tatio geyser field atacama desert chile abstract despite more than 200 years of scientific study the internal dynamics of geyser systems remain poorly characterized as a consequence there remain fundamental questions about what processes initiate and terminate eruptions and where eruptions begin over a one week period in october 2012 we collected down hole measurements of pressure and temperature in the conduit of an exceptionally regular geyser 132 s cycle located in the chilean desert we identified four stages in the geyser cycle 1 recharge of water into the conduit after an eruption driven by the pressure difference between water in the conduit and in a deeper reservoir 2 a pre eruptive stage that follows the recharge and is dominated by addition of steam from below 3 the eruption which occurs by rapid boiling of a large mass of water at the top of the water column and decompression that propagates boiling conditions downward and 4 a relaxation stage during which pressure and temperature decrease until conditions preceding the recharge stage are restored eruptions are triggered by the episodic addition of steam coming from depth suggesting that the dynamics of the eruptions are dominated by geometrical and thermodynamic complexities in the conduit and reservoir further evidence favoring the dominance of internal processes in controlling periodicity is also provided by the absence of responses of the geyser to environmental perturbations air pressure temperature and probably also earth tides

morphologic and mineralogic transitions from opal a to opal ct in low temperature siliceous sinter diagenesis taupo volcanic zone new zealand abstract the opal a to opal ct silica phase transformation in new zealand s siliceous hot spring deposits sinter is accompanied by recurring textural changes at the micron scale recognition of these changes is essential to extract paleohydrological paleoenvironmental and paleobiological signatures from ancient hydrothermal systems and to recognize diagenetic overprints upon primary depositional signals we examined 39 samples of siliceous sinter from the low temperature 35 c palisade microfacies at orakei korako and te kopia geothermal fields taupo volcanic zone new zealand in three different postdepositional environments least disturbed heat affected weathered friable to indurated samples were collected from modern presently silicifying microbial mats in the outflow of nearly neutral alkali chloride springs to sinter 3 500 years old the progressive mineralogical change from noncrystalline opal a to paracrystalline opal ct was traced by x ray powder diffraction and scanning electron microscopy one diagenetic sequence with two morphological pathways spherical and smooth polymeric and monomeric deposition respectively was identified at the micron scale both pathways ultimately lead to formation of typical opal ct bladed lepispheres along the spherical pathway initial morphological restructuring includes formation of circular holes 0 1 to 1 0 m in diameter in opal a spheres 3 0 m in diameter these changes correlate with a shift in the maximum intensity of the opal a x ray scattering broadband from 4 0 a to 4 09 a the characteristic position for opal ct an early transitional diagenetic stage is indicated in both sphere and smooth silica pathways by development of hexagonal platelets and a composite opal a ct scattering broadband that is sharp peaked in comparison and centered at 4 09 a a still sharper peaked composite opal ct a x ray diffraction band follows which has developed an incipient tridymite shoulder it is found in samples that display both hexagonal platelets and incipient fuzzy opal ct lepispheres at this late transitional stage patchy replacement textures are visible at the macroscale only with the appearance of numerous well developed opal ct bladed lepispheres is a typical sharp peaked 4 09 a opal ct x ray trace evident with a well defined tridymite shoulder this diagenetic process can produce either porous or vitreous fabrics depending on the degree to which infill of silica has reduced porosity and increased density of the deposit this study provides a textural mineralogical context for understanding silicification of microbial communities in geothermal settings and their subsequent diagenetic modifications these modifications continue long after geothermal activity has ceased with little or no burial and occur in horizons or localized patches of a given deposit moreover postdepositional conditions such as heat overprinting or weathering influence the diagenesis of siliceous sinter by increasing its maturation rate

coupled and decoupled numerical modeling of flow and morphological evolution in alluvial rivers existing numerical river models are mostly built upon asynchronous solution of simplified governing equations the strong coupling between water flow sediment transport and morphological evolution is thus ignored to a certain extent an earlier study led to the development of a fully coupled model and identified the impacts of simplifications in the water sediment mixture and global bed material continuity equations as well as of the asynchronous solution procedure for aggradation processes this paper presents the results of an extended study along this line highlighting the impacts on both aggradation and degradation processes simplifications in the continuity equations for the water sediment mixture and bed material are found to have negligible effects on degradation this is however in contrast to aggradation processes in which the errors purely due to simplified continuity equations can be significant transiently the asynchronous solution procedure is found to entail appreciable inaccuracy for both aggradation and degradation processes further the asynchronous solution procedure can render the physical problem mathematically ill posed by invoking an extra upstream boundary condition in the supercritical flow regime finally the impacts of simplified continuity equations and an asynchronous solution procedure are shown to be comparable with those of largely tuned friction factors indicating their significance in calibrating numerical river models it is concluded that the coupled system of complete governing equations needs to be synchronously solved for refined modeling of alluvial rivers

modeling of riverbed evolution for bedload sediment mixtures a new computational methodology for fully coupled simulation of unsteady water and sediment movement in mobile bed alluvial rivers has been developed and tested the one dimensional approach treats bedload transport of nonuniform sediment mixtures with sorting and armoring effects considered spatial lag effects in nonequilibrium bedload transport are taken into account through innovative use of the recently developed notion of a loading law the new system of equations for water and sediment movement is solved in a fully coupled implicit manner using the preissmann finite difference scheme implemented to allow for either upstream or downstream induced mobile bed perturbations formal analysis of the coupled system sheds new light on boundary condition requirements for the multiple size class problem the fully coupled implicit solution has proven to be robust and stable and it respects the underlying volumetric conservation laws remarkably well as demonstrated in continuity analyses of computed bed e

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

depositional evolution of an extinct sinter mound from source to outflow el tatio chile siliceous sinter deposits from el tatio chile preserve a wide variety of depositional environments and biosignatures from high temperature 85 c vent proximal facies to distal deposits dominated by silicified microbial mats four cores were drilled into an el tatio sinter mound and associated distal apron to investigate changes in hydrothermal environments over geologic timescales sedimentary and geochemical analysis of multiple sinter cores records the initiation and accretion of diverse depositional features still observed today in el tatio facies adjacent to hydrothermal vents are dominated by laminated sinter crusts on the steep margins of a high temperature pool with sparse microbial preservation outer margins of the same pool contain extensive sinter columns up to ten centimeters in length precipitated during repeated cycles of pool overflow and subsequent evaporation low relief hydrothermal pools also form minor deposits within distal debris aprons and analogous pools are still active close to sampling locations debris aprons are dominated by palisade tufted and arborescent microbial fabrics with distinct mat textures revealing well preserved microfossils surficial deposits in all cores feature detrital rich and microbially influenced sinters overlying higher temperature facies indicating a relative decrease in hydrothermal activity over time geochemical proxies for hydrothermal fluids and de trital input match depositional interpretations based on sedimentary structures 14 c ages from core deposits extend the mound s history by 11 000 years recording at least three thousand years of sinter deposition on top of glacial sandstones 13 337 10 232 y cal bp importantly this work provides a detailed depositional model unavailable through surficial sedimentology alone

morphometric properties of dolines in matarsko podolje sw slovenia matarsko podolje in sw slovenia is a karstic surface with many dolines which appear between the flysch composed brkini hills in the ne and mt slavnik in the sw we have analyzed dolines to find the morphometric parameters of the depth area volume and circularity index and also calculated the doline density and pitting index all parameters were also calculated separately for individual lithological units to explain the variations of the calculated values among these groups morphometry was performed in gis environment on a 1 1 m digital elevation model with bare earth obtained by lidar the results show a high density of dolines 94 dolines km2 and also a high pitting index rp 8 27 compared to other studies there are some significant differences between the measured values in individual lithologies as the depths areas and volumes are largest in dolomitic beds other beds include various types of limestones and carbonate breccia the median values of depth area and volume are 2 98 m 541 m2 and 690 m3 the circularity index is also lowest in dolomite beds and kozina limestones however the differences are not so pronounced as for areas and volumes dolines longer axes are parallel to the directions of major structural elements however more detailed mapping should be done to confirm the influence of faults and fracture zones on the doline geometry

sedimentary facies and mineralogy of the late pleistocene umukuri silica sinter taupo volcanic zone new zealand abstract the umukuri silica sinter is a large late pleistocene hot spring deposit exposed along the eastern upthrown block of the umukuri fault one kilometer southwest of the active orakei korako geothermal area taupo volcanic zone new zealand uplift along the fault has frozen sinter maturation to produce a characteristic silica phase stratigraphy revealed by x ray diffraction paracrystalline opal ct dominates upper layers opal c occurs throughout middle and lower horizons and recrystallized fabrics of microcrystalline quartz constitute lowermost exposed layers original and secondary matrix fabrics in the sinter include fine grained porous friable dense vitreous and massive mottled diffusely layered original fabrics combine with silicified plant matter peloids pisoids sinter fragments detrital grains diatoms ostracodes and filamentous to tufted microbial remains to form nine depositional microfacies thinly laminated plant rich and palisade types dominate sinter breccia and wavy laminated varieties also are common whereas curved laminae with lenticular voids bubble mats clotted peloidal and pisolitic microfacies are minor umukuri microfacies represent silicification in mid to low temperature waters on sinter apron terrace and slope areas and in distal marshy settings closely spaced lateral and vertical intercalation of various microfacies in outcrop implies changing local flow and temperature conditions no facies typical of high temperature proximal vent areas have been identified comparison with modern thermal spring analogs suggests that original umukuri sinter fabrics recorded varying degrees of polymerization vs monomerization of juvenile opal a mineralogical and textural modification of matrix fabrics reflects a microscale incremental continuum following granular or fibrous habits along solution precipitation pathways late stage quartz rims and infills pores throughout the sinter

geochemistry of metals and metalloids in siliceous sinter deposits implications for elemental partitioning into silica phases abstract sinter deposits are formed by precipitation of silica from hydrothermal fluids that have reached the surface environment they are commonly found around hot springs and represent surface expressions of underlying geothermal systems and or low sulfidation epithermal gold silver hydrothermal deposits several studies have reported ppm to weight percent concentrations of metals e g au ag cu and metalloids e g as sb b in sinters capping geothermal systems and epithermal gold silver deposits however the relation between the maturity of the siliceous sinter and its metal enrichment remains unknown here we use geochemical and mineralogical data that link the silica crystallinity degree with trace metal and metalloid contents in sinter in this paper we provide in situ trace element data in metal rich silica sinter samples from the puchuldiza geothermal field in the altiplano of northern chile that record the complete diagenetic sequence from non crystalline opal a to microcrystalline quartz combined sem xrd and la icp ms data show that the concentration of metals and metalloids in sinters from puchuldiza display a strong correspondence with silica crystallinity while arsenic and boron are predominantly enriched in the more amorphous silica phases opal a ct gold and silver show higher concentrations in the more crystalline phases opal c quartz silica structural morphological and geochemical transformations from its initial precipitation to its final maturation after diagenesis are responsible for this differential enrichment during the initial stages gold and silver are incorporated into silica microspheres as cationic species and or metal nanoparticles or colloids while arsenic and boron incorporation is controlled by as bearing accessory minerals and fe oxyhydroxides as diagenesis progresses and the crystallinity of silica increases diffusion driven processes such as ostwald ripening may progressively enrich gold and silver in the sinter while metalloids are depleted owing to the low retention of arsenic by silica these findings indicate that the diagenetic transitions of silica defined by significant structural changes that involve generation of surface defects and the creation of reactive sites may play an important role in elemental uptake by silica in near surface environments

experimental studies on new zealand hot spring sinters rates of growth and textural development to study the rate of growth of sinters in new zealand hot springs field experiments were conducted in seven geothermal areas at wairakei fan shaped subaqueous deposits of amorphous silica grow rapidly 350 kg a 1 m 2 of drain wall and are composed of silicified filaments with subordinate bacillus and spirillium shaped organisms characterization of bacteria revealed isolates sharing 97 16s rrna gene sequence homologies affiliated with thermus meiothermus bacillus tepidomonas thermomonas porphyrobacter thermonema and hydrogenophilus spp as well as previously uncultured bacteria at rotokawa microstromatolites have a slow growth rate 0 004 mm day 1 that is attributed to low ph capillary rise and evaporation at champagne pool sinter growth 0 023 mm day 1 is dominated by wave action building alternating microbe rich and microbe poor layers silica sinter was not observed at waikite where slides developed a layer of calcite 0 026 mm day 1 sinter growth at ngatamariki 0 016 mm day 1 forms by capillary rise evaporation and diffusion and at tokaanu subaqueous growth is slow 0 002 mm day 1 and contains silicified microbes textures at orakei korako indicate similar mechanisms to ngatamariki except that growth is more rapid 0 023 mm day 1 due to a splash contribution silica and calcite saturation indices adequately explain the growth of the sinters and calcite indicating that microbes are not inducing precipitation where it should not occur the rate of precipitation is correlated with silica supersaturation but ph effects can alter this relationship the degree of preservation of microbial material is explained by the effect of ostwald ripening on silica spherules subaqueous growth allows coarsening of spherules and poor preservation of smaller microbes while subaerial nucleation is rapid ostwald ripening is inactive and better preservation can be expected

morphometric analysis of sinkholes in a karst coastal area of southern apulia italy salento the southern portion of apulia region se italy is a narrow and elongated peninsula in carbonate rocks with prevailing low coastlines locally interrupted by high rock cliffs the long stretches of low coasts are marked by typical karst landforms consisting of collapse sinkholes as observed in many other karst coastal settings worldwide development of sinkholes may be particularly severe along the coasts where both natural and anthropogenic processes contribute to accelerate the dissolution of carbonate rocks and subsidence processes even influencing the coastline evolution following a previous study where the main features of sinkholes at torre castiglione taranto province were investigated and described and a preliminary susceptibility map produced at the light of updated data and elaborations in the present paper we perform a detailed morphometric analysis on the sample of identified sinkholes the main morphometric parameters generally used for sinkhole characterization have been considered in this study shape of the sinkhole azimuth and length of maximum and minimum axes depth elongation ratio and distance from the shorelines each of them is described both as individual parameter and in conjunction with the others in the attempt to identify the main factors controlling development of sinkholes in the area and their evolution as well with regard to this latter aspect beside simple morphometry of the sample of sinkholes at torre castiglione we also focused our attention on the likely relationships existing between distribution and shape of the sinkholes and the tectonic discontinuities to investigate the matter a three stage analysis has been carried out in this study by means of field measurements of the fractures bounding the sinkholes field measurement of the long axes azimuth of the elongated sinkholes comparison of the previously described sets with the strikes of the main regional geological structures the obtained results show in addition to the coincidence of the main regional discontinuity systems with the major axis of elongated sinkholes a clear control exerted by development and evolution of the sinkholes on the formation of coastal inlets and bays eventually the approach here presented may be applied in other karst coastal sinkhole prone areas to gain new knowledge on the genesis and evolution of coastal sinkholes and to properly evaluate the hazard they pose to the anthropogenic environment

karst database implementation in minnesota analysis of sinkhole distribution this paper presents the overall sinkhole distributions and conducts hypothesis tests of sinkhole distributions and sinkhole formation using data stored in the karst feature database kfd of minnesota nearest neighbor analysis nna was extended to include different orders of nna different scales of concentrated zones of sinkholes and directions to the nearest sinkholes the statistical results along with the sinkhole density distribution indicate that sinkholes tend to form in highly concentrated zones instead of scattered individuals the pattern changes from clustered to random to regular as the scale of the analysis decreases from 10 100 km2 to 5 30 km2 to 2 10 km2 hypotheses that may explain this phenomenon are 1 areas in the highly concentrated zones of sinkholes have similar geologic and topographical settings that favor sinkhole formation 2 existing sinkholes change the hydraulic gradient in the surrounding area and increase the solution and erosional processes that eventually form more new sinkholes

formation of silica oncoids around geysers and hot springs at el tatio northern chile siliceous oncoids up to 4 cm in diameter are common on the laterally extensive sinter aprons that surround the spectacular geysers and hot springs at el tatio in northern chile many of these complex oncoids developed close to geyser and spring vents that discharge boiling water internally the oncoids which are composed of precipitated amorphous silica are formed of complex arrays of spicules and concentric laminae as well as detrital volcanic grains spicular growth is dominant in most examples the formation and growth of the spicules and concentric laminae were mediated by a microbial community which included filamentous microbes mucus and possibly bacteria the microbes and mucus were silicified by replacement and encrustation in some laminae the filamentous microbes lay parallel to the growth surface in other laminae most filaments forming the thin mats were suberect amorphous silica precipitated between the filaments occluded porosity and commonly disguised the microbial fabric the oncoids grew on the proximal sinter aprons around the geyser vents and hot spring pools most growth took place subaerially with the silica delivered to the precipitation sites by splashing water from the geysers and or periodic shallow flooding of the discharge aprons unlike silica oncoids at other geothermal sites vertical growth of oncoids that formed in some rimstone pools was not limited by water depth

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

relationship between spring and geyser activity and the deposition and morphology of high temperature 73 c siliceous sinter yellowstone national park wyoming u s a abstract six classes of alkaline hot springs and geysers are here distinguished in yellowstone national park based on activity and eruptive style 1 non surging non boiling springs 2 gently surging non boiling springs 3 non surging to gently surging boiling springs 4 strongly surging springs 5 fountain geysers and 6 cone geysers each displays morphologically distinctive siliceous sinter deposits in the high temperature 73 c parts of the vent and outflow systems non surging and gently surging non boiling springs that do not overflow their rims develop thin digitate to lilypad like sinter rims that grow horizontally over the pool surfaces similar springs with rim overflow have rims that accrete vertically boiling springs often have nearly circular steep sided pools and rims dominated by splash and rim overflow and composed mainly of spicular and columnar sinter fountain geysers characterized by broad fountain like eruption bursts have a central vent surrounded by a zone of spicular sinter beyond which is a broad flat bottomed moat but lack steep sinter cones cone geysers have narrow vents jet like discharges that cool rapidly and fall close to the vent and steep sided spicule dominated sinter cones sinter deposition takes place within three main zones 1 fully subaqueous sides and bottoms of vent pools outflow basins and outflow channels 2 periodically wetted splash zones surrounding hot springs and geysers and 3 largely subaerial parts of the rim and outflow areas wetted mainly by overflow and surging and that dry quickly fully subaqueous surfaces are covered by fine earthy particulate siliceous sediment pss composed largely of amorphous silica spherules and spherule aggregates that appear to have precipitated around heterogeneous nuclei including microbes splash zones of hot springs and geysers are characterized by spicular sinter largely subaerial zones wetted mainly by rim overflow and surging with little or no splash show complex varieties of terraced columnar and knobby sinter the highest silica deposition rates occur where surfaces are wetted frequently and evaporate to dryness such as the tops of spicules columns and knobs associated lower areas and crevices that remain wet or moist show slow accumulation of pss most continuously wet surfaces in high temperature 73 c hot spring and geyser vent and outflow systems are probably covered by microbial biofilms although microbes may locally influence rates of silica deposition and sinter microstructure the results of this study suggest that the depositional sites morphology and macrostructuring of high temperature sinter are controlled largely by the processes of surface wetting evaporation and drying

gis based analysis of doline density on taurus mountains turkey the taurus mountain is one of the most important karstic region of the world and dolines are characteristics landforms of this area however the number and distribution of doline are unknown in the study area the aims of this study are to explain the total number of dolines distribution of doline density effects of slope conditions and the change of doline orientation in the taurus mountains according to the 1 25000 scale topographic maps utilized in this study a total of 140 070 dolines were determined in a 13 189 km2 area on eleven high karstic plateaus bordered by steep slopes and deep gorges these plateaus are substantially affected by highly faulted and jointed systems and about 80 of each plateau is covered with neritic limestone the dolines are located at an elevation between 10 and 2870 m average elevation of all dolines is 1842 m 90 of dolines are located between 1300 and 2270 m and only 5 of dolines found under 1330 m according to this results the densest doline zone corresponds to the alpine and periglacial zone above the treeline doline density reaches 100 doline km2 on mt anamas and the seyran geyik and akdag ranges as well as the taseli plateau maximum density 187 doline km2 is found on the akdag mountains however 66 of the study area is characterized by low density 29 9 with moderate density 3 4 with high density and 0 7 with very high density the highest doline densities are seen on gentle slopes 15 25 km2 and steep slopes 35 km2 are limited doline distribution according to the rose diagram formed by the azimuths of the long axis of the dolines at the central taurus two direction are dominant in doline orientations nw se and ne sw however dominant directions are ne sw at eastern ne sw and nw se at central and nw se at western part of the central taurus according to this elongations doline orientations are formed an arc which is formed by tectonic evolution of the central taurus

sinkhole distribution in a rapidly developing urban environment hillsborough county tampa bay area florida sinkhole formation in florida is a common event the florida karst plain is significantly altered by human development and sinkholes cause considerable property damage throughout much of the state we present in this paper a morphometric analysis of karst depressions in the tampa bay area and the relation with the known distribution of sinkholes we selected the tampa bay area because it is particularly susceptible to the evolution of karst depressions in relation with development of the built up environment karst depressions were mapped from the 1 24 000 usgs topographic maps and a morphometric analysis was performed by using parameters such as shape circularity index perimeter area length width and orientation maps showing the distribution of depression density and the sectors with greatest areas of karst depression were produced using a gis these results were compared with data compiled from the database of sinkhole occurrences in florida maintained by the florida geological survey our analysis demonstrates that the distribution of new sinkhole occurrences differs from the distribution of existing sinkholes indicating that there are processes acting today that are influencing karst landscape formation that are different from those acting in the past

iodine budget in surface waters from atacama natural and anthropogenic iodine sources revealed by halogen geochemistry and iodine 129 isotopes abstract iodine enrichment in the atacama desert of northern chile is widespread and varies significantly between reservoirs including nitrate rich caliche soils supergene cu deposits and marine sedimentary rocks recent studies have suggested that groundwater has played a key role in the remobilization transport and deposition of iodine in atacama over scales of millions of years however and considering that natural waters are also anomalously enriched in iodine in the region the relative source contributions of iodine in the waters and its extent of mixing remain unconstrained in this study we provide new halogen data and isotopic ratios of iodine 129 i i in shallow seawater rivers salt lakes cold and thermal spring water rainwater and groundwater that help to constrain the relative influence of meteoric marine and crustal sources in the atacama waters iodine concentrations in surface and ground waters range between 0 35 m and 26 m in the tarapaca region and between 0 25 m and 48 m in the antofagasta region and show strong enrichment when compared with seawater concentrations i 0 4 m in contrast no bromine enrichment is detected 1 3 45 7 m for tarapaca and 1 7 87 4 m for antofagasta relative to seawater br 600 m these data coupled to the high i cl and low br cl ratios are indicative of an organic rich sedimentary source related with an initial fluid that interacted with meteoric water to produce a mixed fluid and preclude an exclusively seawater origin for iodine in atacama natural waters iodine isotopic ratios 129 i i are consistent with halogen chemistry and confirm that most of the iodine present in natural waters derives from a deep initial fluid source i e groundwater which has interacted with jurassic marine basement with variable influence of at least one atmospheric or meteoric source samples with the lowest isotopic ratios 129 i i from 215 to 1000 10 15 strongly suggest mixing between the groundwater and iodine storage in organic rich rocks with variable influence of volcanic fluids and pre anthropogenic meteoric water while samples with higher values 2000 93 700 10 15 indicate the input of anthropogenic meteoric fluid taking into account the geological hydrologic and climatic features of the atacama region we propose that the mean contribution of anthropogenic 129 i is associated with 129 i releases during nuclear weapon tests carried out in the central pacific ocean until the mid 1990 s 129 i i 12 000 10 15 this source reflects rapid redistribution of this radioisotope on a global scale our results support the notion of a long lived continental iodine cycle in the hyperarid margin of western south america which is driven by local hydrological and climate conditions and confirm that groundwater was a key agent for iodine remobilization and formation of the extensive iodine rich soils of atacama

diagenetic transformations opal a to quartz of low and mid temperature microbial textures in siliceous hot spring deposits taupo volcanic zone new zealand silica sinter is a subaerial hot spring deposit formed upon cooling 100 c of discharging alkali chloride waters silica deposition traps and fossilizes living microbes in low temperature 35 c to mid temperature 35 59 c apron terrace outflow channels and pools which record distinctive macrotextures and microtextures along a thermal gradient sinters from four geothermal fields orakei korako northern waiotapu te kopia and umukuri within the taupo volcanic zone new zealand were sampled from two common microbe rich microfacies low temperature palisade mid temperature bubble mat through a range of ages modern to 40 000 years bp we observed morphologic changes in microbial silicification and stepwise transitions in silica phase mineralogy throughout diagenesis opal a to quartz x ray powder diffractometry analysis of taupo volcanic zone sinter samples revealed that mode of microbial fossilization is controlled by silica phase mineralogy which also determines the preservation potent

simulation of missouri river bed degradation the future course of bed degradation in the middle missouri river has been predicted using numerical simulation techniques the simulation required development of the new total load transport model tltm which incorporates the interdependence of friction factor and sediment transport through data based empirical relations tltm was implemented in a mathematical simulation model called ialluvial which computes quasi steady water and sediment flow in natural rivers having nonuniform bed sediments ialluvial also incorporates bed sediment sorting and armoring which are processes of fundamental importance to the future course of missouri river degradation ialluvial was first validated through simulation of the 1960 1980 severe degradation in the missouri river between sioux city iowa and omaha nebraska subsequently ialluvial was used to predict 1980 2000 degradation for several river management scenarios the simulations suggest that the worst of the degradation is now over and that it is the channelization rather than upstream regulation which is primarily responsible for the degradation a companion paper describes the details of ialluvial s armoring and sorting simulation procedures

3d anatomy of a 60 year old siliceous hot spring deposit at hipaua waihi tokaanu geothermal field taupo volcanic zone new zealand abstract in 1941 a 72 m deep bore healy s bore 2 hb2 at the hipaua waihi tokaanu geothermal field taupo volcanic zone new zealand tapped alkali chloride water of 145 c at the bottom of the well since then thermal fluid

tracking crystallinity in siliceous hot spring deposits siliceous hot spring deposits sinters entrap paleoenvironmentally significant components and are used as extreme environment analogs in the search for early earth and extraterrestrial life however sinters undergo a series of textural and mineralogical changes during diagenesis that can modify and overprint original environmental signals for ancient hydrothermal settings including those close to the dawn of life these transformations have long since occurred so that study of diagenetic processes and effects is best undertaken in much younger deposits still undergoing change three young sinters preserve the entire diagenetic sequence of silica phases from opal a to quartz the 6000 to 11 500 years bp 70 years sinter at steamboat springs nevada the 1600 1900 160 years bp opal mound sinter at roosevelt hot springs utah and the 456 35 years bp deposit at sinter island taupo volcanic zone new zealand provide an opportunity to track crystallographic mineralogic and morphologic transitions of sinter diagenesis using standard and new analytical approaches worldwide sinter forms from cooling alkali chloride waters as noncrystalline opal a transforming first into noncrystalline opal a ct then paracrystalline opal ct moganite paracrystalline opal c and eventually to microcrystalline quartz in this study these changes were identified by the novel and combined application of electron backscatter diffraction x ray powder diffraction and scanning electron and optical microscopy techniques we show that mineralogical changes precede morphological and accompanied crystallographic transformations during this modification silica particles grow and shrink several times from the micron to nano meter scales via dissolution reprecipitation and recrystallization and diagenesis follows the ostwald step rule all deposits followed nearly identical diagenetic pathways with time as the only variable in the march toward physicochemically stable quartz crystals diagenesis alters original environmental signatures trapped within sinters after five silica phase changes filamentous microfossils are modified but still remain recognizable within sinter from the opal mound and steamboat springs deposits and during the opal a to opal ct silica phase transformations at sinter island therefore delineating diagenetic components and how they affect sinters is necessary to accurately identify biosignals from ancient hot spring deposits

rare earth elements in sinters from the geothermal waters hot springs on the tibetan plateau china abstract the mineralogical and geochemical composition of sinters from the geothermal areas on the tibetan plateau was determined they occur as siliceous salty and calcareous sinters but biogenic siliceous sinters were also found the analyses indicate that there are no distinct inter element relationships between individual rare earth elements rees and other elements formed from the same geothermal water the mineralogical and chemical composition of the sinters is influenced by their genesis and formation conditions the ree distributions depend on the origin of the sinters fe mn phases in sinters tend to scavenge more rees from geothermal water neither the ree fractionation nor the ce anomaly seems to be associated with fe mn phases in the sinters the fourth tetrads of some sinters display weak w type concave effects in contrast the third tetrads present large effects in some sinters due to positive gd anomalies the origin of the positive eu anomalies in some sinters seems to be caused by preferential dissolution of feldspars during water rock interaction the complexing ligands in geothermal water may contribute significantly to the fractionation of rees in sinters the dominant co 3 2 and hco 3 complexing in geothermal water favors enrichment of heavy rees in calcareous sinters

scour depth prediction under armoring conditions a simple procedure is proposed to predict scour depth on an alluvial bed having graded materials under certain flow conditions that can produce an armor layer at the bed surface the procedure is based on calculation of an active or mixing layer that supplies the fine particles to the sediment load transported by the flow and from where all the heavier and larger particles not transportable under the flow conditions collect at the bed surface and gradually form the armor layer the procedure is validated in both laboratory and field conditions it predicted scour depths in the little and mayer s experimental flume and in the missouri river downstream from gavins point dam as expected the procedure can serve as a useful tool for practicing engineers in making conservative estimates of scour depths downstream of hydraulic structures and in new unlined canals and in selecting materials for canal beds and banks

vnir multispectral observations of aqueous alteration materials by the pancams on the spirit and opportunity mars exploration rovers multispectral visible and near infrared vnir observations from the mars exploration rover pancam multispectral stereo camera systems are consistent with materials having been subjected to various aqueous processes ferric oxides in the form of hematite in the burns and grasberg formations of meridiani planum have been well characterized by opportunity on the basis of strong 535 and 864 nm absorptions and positive 754 1009 nm and 934 1009 nm slopes on the rim of noachian aged endeavour crater opportunity has observed light toned veins with high ca and s as determined by the rover s alpha particle x ray spectrometer apxs and a negative 934 1009 nm slope in vnir spectra extracted from pancam data indicative of a 1000 nm h2o overtone absorption together these observations indicate that the veins are composed of gypsum rocks overturned by opportunity on the murray ridge portion of the endeavour crater rim display dark and light toned coatings the dark toned coatings have a red featureless slope that is consistent with the slope observed in laboratory spectra of high valence manganese oxide minerals potential mn oxide coatings may also be associated with some exposures of the grasberg formation apxs results for high mg and s in the light toned coatings of the murray ridge overturned rocks and a negative 934 1009 nm slope are consistent with hydrated mg sulfates opportunity has also observed spectral features in rocks that are consistent with orbital observations of fe smectites as well as al smectites and possible hydrated silica in light toned fracture fill materials the spirit rover observed sulfate rich light toned soils exposed by the rover s wheels several of these soil observations contained spectral features such as a broad absorption centered near 800 nm consistent with ferric sulfate minerals a finding confirmed by the rover s mossbauer spectrometer spirit also excavated light toned si rich soils these soils have a flat near infrared spectrum with a drop in reflectance from 934 1009 nm that is consistent with free water contained in voids or adsorbed onto the surface of the silica

mineralogical characterization of silica sinters from the el tatio geothermal field chile silica sinters deposited from alkali chloride waters in the el tatio geothermal field in northern chile 22 20 s 68 01 w have been characterized by xrd sem tg dta and ftir the dominant silica phase is opal a minor contents of opal a ct and opal ct are also present together with halite nacl sylvite kcl and realgar ass accessory phases include teruggite ca4mgas2b12o22 oh 12 12 h2o sassolite h3bo3 and detrital quartz sio2 fwhm values reflect the immature nature of the studied opal a dta heating experiments of opal a show cristobalite crystallization at 1000 c whereas dta cooling experiments show the cristobalite transformation at 200 c the total weight loss is related to changes in the sinter microtextures mineral phases and organic matter contents ftir spectra show the effects of silica maturation as consequence of the loss of trapped and absorbed water attached to silanols

hot spring and geyser sinters the integrated product of precipitation replacement and deposition complex ornate sinter deposits are found in many hot spring and geysers systems throughout the world including those located in the taupo volcanic zone on the north island of new zealand those sinters are formed of opal a that replaced microbes opal a precipitated as cement accessory minerals e g kaolinite jarosite calcite biological detritus e g leaves wood pollen grains and lithic detritus the opal a is compositionally variable because of the amount of water oh and h2o and in some cases accessory elements e g au ag bound into its structure the composition and fabric of the siliceous sinter found at any locality reflect the relative balance among the processes of replacement precipitation and deposition the microbes that inhabit these systems are of critical importance because they are commonly replaced by and or encrusted with opal a in many settings copious amounts of opal a are precipitated as cement around the frameworks of silicified filaments the cementation pro

early archean fossil bacteria and biofilms in hydrothermally influenced sediments from the barberton greenstone belt south africa abstract sem imaging of hf etched 3 3 3 5 ga cherts from the onverwacht group south africa reveals small spherical 1 m diameter and rod shaped structures 2 3 8 m in length which are interpreted as probable fossil coccoid and bacillar bacteria prokaryotes respectively preserved by mineral replacement other possibly biogenic structures include smaller rod shaped bacteriomorphs 900 m textures in the sediments in which these biogenic structures occur suggest that they were probably deposited in a shallow water environment which was subjected to intermittent subaerial exposure pervasive hydrothermal activity is evidenced by oxygen isotope studies as well as the penecontemporaneous silicification of all rock types by low temperature 220 c hydrothermal solutions

light hydrocarbons as redox and temperature indicators in the geothermal field of el tatio northern chile abstract el tatio northern chile one of the largest geothermal fields of south america is presently undergoing a new program of geothermal exploration after the failure of the first exploration phase in the early 1970s the geochemical features of the fluid discharges characterizing this system mainly consist of boiling pools and fumaroles and represent the result of a complex mixing process involving 3 main components i hydrothermal ii atmospheric iii magmatic chemical reactions involving light hydrocarbons equilibrate at higher temperature than those directly measured in the geothermal wells and calculated on the basis of the composition of the inorganic gas species this suggests that in the deeper parts of the hydrothermal system temperatures higher than 300 c may be achieved such results can have a strong impact for the evaluation of the potential resources of this geothermal system moreover the chemical characteristics of the organic gas fraction allow the assessment of the chemical physical conditions governing the geochemical processes acting on geothermal fluids at depth

microbial silica interactions in icelandic hot spring sinter possible analogues for some precambrian siliceous stromatolites silicified deposits such as sinters occur in several modern geothermal environments but the mechanisms of silicification and crucially the role of microorganisms in their construction are still largely unresolved detailed examination of siliceous sinter in particular sections of microstromatolites growing at the krisuvik hot spring iceland reveals that biomineralization contributes a major component to the overall structure with approximately half the sinter thickness attributed to silicified microorganisms almost all microorganisms observed under the scanning electron microscope sem are mineralized with epicellular silica ranging in thickness from 5 lm coatings on individual cells to regions where entire colonies are cemented together in an amorphous silica matrix tens of micrometres thick within the overall profile there appears to be two very distinct types of laminae that alternate repeatedly throughout the microstromatolite microbial layers are predominantly consisting of filamentous intact vertically aligned biomineralized cyanobacteria identified as calothrix and fischerella sp and weakly laminated silica layers which appear to be devoid of any microbial component the microbial layers commonly have a sharply defined base overlying the weakly laminated silica and a gradational upper surface merging into the weakly laminated silica these cyclic laminations are probably explained by variations in microbial activity active growth during spring summer allows the microorganisms to keep pace with silicification with the cell surfaces facilitating silicification while during their natural slow growth phase in the dark autumn winter months silicification exceeds the bacteria s ability to compensate i e grow upwards at this stage the microbial colony is probably not essential to microstromatolite formation with silicification presumably occurring abiogenically when conditions once again become favourable for growth recolonization of the solid silica surface by free living bacteria occurs cell motility is not responsible for the laminations we have also observed that microbial populations within the microstromatolite some several mm in depth appear viable i e they still have their pigmentation the trichomes are not collapsed cell walls are unbroken cytoplasm is still present and they proved culturable this suggests that the bulk of silicification occurred rapidly probably while the cells were still alive surprisingly however measurements of light transmittance through sections of the microstromatolite revealed that photosynthetically active light pal only transmitted through the uppermost 2 mm therefore the deeper microbial

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

fluid geochemistry of hydrothermal systems in the arica parinacota tarapaca and antofagasta regions northern chile we investigate the chemical and isotopic composition of water and gas thermal discharges from six hydrothermal systems in the tarapaca and antofagasta regions northern chile surire puchuldiza tuja pampa lirima pampa apacheta el tatio and torta de tocorpuri to determine the chemical physical conditions at the fluid source the chemical facies of the thermal discharges vary from na cl el tatio puchuldiza tuja and part of surire where so42 rich waters also occur to na ca2 cl so42 pampa lirima ca2 so42 hco3 torta de tocorpuri and ca2 so42 pampa apacheta the gas seeps are characterized by the dominance of co2 h2s and ch4 with n2 ar ratios that occasionally are up to 450 significant amounts of so2 and hcl are present at pampa apacheta water and gas geothermometry suggests that el tatio and puchuldiza tuja fluid reservoirs have relatively high reservoir equilibrium temperature up to 270 c gases from pampa apacheta apparently equilibrated at unusually high temperature for hydrothermal fluids up to 350 c being likely related to an active magmatic system as testified by the presence of highly acidic gas compounds such as so2 and hcl on the contrary low equilibrium temperatures were calculated for the surire fluids 200 c suggesting interactions of deep originated fluids with meteoric water at shallow depth shallow low temperature aquifers mask any signal of deep fluids in the pampa lirima and torta de tocorcupi thermal discharges despite the variations in temperatures he isotopic compositions and redox conditions of the fluid reservoirs consistently indicate a significant contribution from magmatic degassing although geophysical studies are necessary to better constrain the geothermal potential of northern chile the geothermometric estimations carried out in the present study indicate that el tatio pampa apacheta surire and puchuldiza tuja can be regarded as the most promising areas and deserve more detailed geological investigations

recurrent shoaling and channel dredging middle and upper mississippi river usa abstract a 34 year record of dredging in a 484 km reach of the middle and upper mississippi river documents the spatial and temporal patterns of bed aggradation in an intensively engineered river between 1964 and 1997 183 million m 3 was removed from the study reach with 112 6 km of the channel undergoing dredging of some kind 12 1 km requiring 5 dredgings during this period 2 6 km requiring 10 dredgings and one site requiring 29 dredgings in 34 years forty three sites were identified where dredging volume was exceptionally high and or were frequently repeated these sites occur in five settings 1 where flow is divided through chutes or side channels 2 at the mouths of largely unregulated tributary streams 3 at thalweg crossings in meander bends 4 in long straight reaches of the channel and 5 near problematic engineered structures the principal one in the study area being the outlet of the chain of rocks canal in the pooled reach of the upper mississippi impoundment has had a major influence on shoaling with 80 of dredged volume required in the upstream halves of the pools although past engineering modifications have reduced sediment aggradation in the mississippi channel structural solutions to continuing shoaling can adversely impact the river s ecology flood response or hydrological function and many structural solutions appear to be approaching their effective limits the exception to this may be at highly localized shoaling locations such as the chain of rocks canal outlet where flaws in the original design may still be remedied by structural means targeted structural solutions may be effective at solving limited local shoaling problems but we suggest that more sweeping new engineering modifications to reduce or eliminate dredging requirements are likely to be ineffective and or outweighed by their adverse effects on the river system

seasonal changes in silica deposition in hot spring systems abstract monthly monitoring of water chemistry at octopus spring yellowstone national park reveals no changes in the chemical composition over this eight month study differences in silica deposition are attributed to flow dynamics and seasonal air temperatures colder air temperatures in winter promote visible accumulation of siliceous sinter probably as a result of decreased solubility periodic drying promotes accumulation and subsequent dehydration of the silica this combination of intermittent supply and periodic dehydration may account for the laminated siliceous deposits observed in the geological record the processes described herein are important in the siliceous preservation of microbial fossils but the following observations underscore the difficulty in preserving microbial fabrics in the geological record pools populated by cyanobacteria are bounded by margins built of silicified microbial mats silicification of the pool margins occurs through an evaporative process called wicking silica rich water is transported upward through the microbial mats by capillary action depositing silica at the surface of the mat as water evaporates the upper surface of such wicking deposits is extremely resistant to brecciation but the underlying support is highly friable and would be difficult to preserve intact in winter months temporary isolation of some pools from active flow causes fragile silica deposition around biological and other debris film coated gas bubbles on the surfaces of microbial mats are observed during all seasons and probably are filled with oxygen released during photosynthesis although this has not been confirmed they become coated with silica during winter months presumably because of increased cooling possibly forming thin discontinuous silica sheets as observed in the geological record