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

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

chemistry of uranium thorium and radium isotopes in the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal abstract the most comprehensive data set on uranium thorium and radium isotopes in the ganga brahmaputra one of the major river systems of the world is reported here the dissolved 238u concentration in these river waters ranges between 0 44 and 8 32 1 and it exhibits a positive correlation with major cations na k mg ca the 238 u cations ratio in waters is very similar to that measured in the suspended sediments indicating congruent weathering of uranium and major cations the regional variations observed in the 234 u 238 u activity ratio are consistent with the lithology of the drainage basins the lowland tributaries chambal betwa ken and son draining through the igneous and metamorphic rocks of the deccan traps and the vindhyan bundelkhand plateau have 234 u 238 u ratio in the range 1 16 to 1 84 this range is significantly higher than the near equilibrium ratio 1 05 observed in the highland rivers which drain through sedimentary terrains the dissolved 226ra concentration ranges between 0 03 and 0 22 dpm 1 the striking feature of the radium isotopes data is the distinct difference in the 228ra and 226ra abundances between the highland and lowland rivers the lowland waters are enriched in 228ra while the highland waters contain more 226ra this difference mainly results from the differences in their weathering regimes the discharge weighted mean concentration of dissolved 238u in the ganga at patna and in the brahmaputra at goalpara are 1 81 and 0 63 1 respectively the ganga brahmaputra river system constitutes the major source of dissolved uranium to the bay of bengal these rivers transport annually about 1000 tons of uranium to their estuaries about 10 of the estimated global supply of dissolved uranium to the oceans via rivers the transport of uranium by these rivers far exceeds that of the amazon although their water discharge is only about 20 of that of the amazon the high intensity of weathering of uranium in the ganga brahmapura river system can also be deduced from the 232 th 238 u and 230 th 238 u activity ratios measured in the suspended sediments 230th is enriched by about 19 in the suspended sediments relative to its parent 238u the flux of excess 230th supplied to the bay of bengal via these river sediments is 980 1012 dpm a about six times more than its in situ production from seawater in the entire bay of bengal

on the possibility of determining rates of removal of uranium from crystalline igneous rocks using u series disequilibria 2 applicability of a u leach model to mineral separates abstract preliminary u series data are presented on the disequilibria of mineral separates of surface samples from the eye dashwa lakes granite canada most analyses of the ferromagnesian quartz plus feldspar and zircon plus sphene grains show that leaching of u has taken place such that 234 u 239 u 1 and 230 th 234 u 1 the simple leach model presented in a companion paper was used to explain these characteristic ratios it is suggested that the leach model may be used on zircon and sphere grains to estimate u leach rates and this is relevant to the suggestion of using sphene like hosts as the primary barrier in the safe disposal of nuclear waste a full analysis of u mobility within a given rock volume was not possible due to our limited data base and to our inability to monitor labile u directly

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

particle transport of 234u 238u in the kalix river and in the baltic sea the role of particles for u isotope transport was investigated in the kalix river watershed a particle poor fe mn rich river in northern sweden and in the baltic sea estuary particles 0 45 m are strongly enriched in u and contain 20 50 of the total riverine uranium budget and 1 of the total u in brackish waters 3 7 psu the particles have high 234 u which is close to that of dissolved u in the associated water indicating that u on particles is dominantly nondetrital and isotopically exchanges rapidly with the ambient dissolved u particles at the river mouth are dominated by nondetrital fe mn oxyhydroxides uranium and fe are strongly correlated clearly demonstrating that secondary fe oxyhydroxide is the major carrier of u in river water there is no evidence for significant association of u with mn oxyhydroxide apparent u distribution coefficients k d fe were calculated for u between the authigenic fe on particles and the solution these values appear to be relatively constant throughout the year this suggests an equilibrium between fe in solution and authigenic fe oxyhydroxides on detrital particles high values of k d fe calculated for one summer as well as high u concentrations in brackish waters can be explained by u scavenging by biogenic phases with low authigenic fe content

time scale and conditions of weathering under tropical climate study of the amazon basin with u series the rio solimoes amazonas amazon river and its major tributaries have been analyzed for u series nuclides 238 u 234 u 230 th 226 ra disequilibria have been measured in the dissolved 0 2 lm as well as bed sands u series disequilibria are closely related to major and trace element compositions and therefore reflect elemental fractionation during chemical weathering moreover while the dissolved load records present day weathering suspended particles integrate the erosion his tory over much longer time scales 100 ka lowland rivers are characterized by long time scales of chemical erosion p100 ka result ing in a high weathering intensity moreover exchange between suspended particles and the dissolved load may explain the u series signature for these rivers by combining u series and pb isotopes in suspended particles we show that erosion in the rio madeira basin occurred as a multi step process whereby the pristine continental crust was eroded several hundreds of ma ago to produce sediments that have then been integrated in the cordillera by crustal shortening and are currently eroded in contrast recent erosion of a pristine crust is more likely for the rio solimoes amazonas 10 ka the suspended particles of the rivers draining the andes solimoes ama zonas madeira suggest time scales of weathering ranging between 4 and 20 ka this indicates that suspended particles transported by those rivers are not stored for long periods in the andean foreland basin and the tropical plain the sediments delivered to the ocean have resided only a few ka in the amazon basin 6 3 1 ka for the rio amazonas at obidos nevertheless a large fraction of the sediments coming out from the andes are trapped in the foreland basin and may never reach the ocean erosion in the andes is not operating in steady state u series systematics shows unambiguously that rivers are exporting a lot more sediments than predicted by steady state erosion and that is a consequence of soil destruction greater than production by relating this observation to the short time scales of weathering inferred for the andes a few ka it appears that the erosion regime has been recently perturbed resulting in high denudation rates a possible explanation would be the increase in precipitation less than 5 ka proposed by recent paleoclimatic studies our results indicate that erosion responds rapidly to high frequency climatic fluctuations

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

rates of weathering rind formation on costa rican basalt weathering rind thicknesses were measured on 200 basaltic clasts collected from three regionally extensive alluvial fill terraces qt 1 qt 2 and qt 3 preserved along the pacific coast of costa rica mass balance calculations suggest that conversion of unweathered basaltic core minerals plagioclase and augite to authigenic minerals in the porous rind kaolinite allophane gibbsite fe oxyhydroxides is iso volumetric and ti and zr are relatively immobile the hierarchy of cation mobility ca na k mg si al fe p is similar to other tropical weathering profiles and is indicative of differential rates of mineral weathering anorthite albite hypersthene orthoclase apatite alteration profiles across the cm thick rinds document dissolution of plagioclase and augite and the growth of kaolinite with subsequent dissolution of kaolinite and precipitation of gibbsite as weathering rinds age the rate of weathering rind advance is evaluated using a diffusion limited model which predicts a parabolic rate law for weathering rind thickness rr as a function of time t rr t and an interface limited model which predicts a linear rate law for weathering rind thickness as a function of time rr kappt in these rate laws is a diffusion parameter and kapp is an apparent rate constant the rate of advance is best fit by the interface model terrace exposures are confined to the lower reaches of streams draining the pacific slope near the coast where the stream gradient is less than 3 m km and terrace deposition is influenced by eustatic sea level fluctuations geomorphological evidence is consistent with terrace deposition coincident with sea level maxima when the stream gradient would be lowest assigning the most weathered regionally extensive terrace qt 1 mean rind thickness 6 9 0 6cm to oxygen isotope stage ois 7 ca 240 ka and assuming that at time 0 rind thickness 0 it is inferred that terrace qt 2 rr 2 9 0 1 cm is coincident with stage 5e ca 125 ka and that qt 3 rr 0 9 0 1 cm is consistent with ois 3 ca 37 ka these assignments yield a value of kapp of 8 6 10 13 cm s 1 r 2 0 99 only this value satisfies both the existing age controls and yields ages coincident with sea level maxima using this value elemental weathering release fluxes across a weathering rind from qt 2 range from 6 0 10 9 mol si m 2 s 1 to 2 5 10 11 mol km 2 s 1 the rate of rind advance for the costa rican terraces is 2 8 10 7 my r 1 basalt rind formation rates in lower temperature settings described in the literature are also consistent with interface controlled weathering with an apparent activation energy of about 50 kj mol 1 rates of rind formation in costa rica are an order of magnitude slower than reported for global averages of soil formation rates copyright 2004 elsevier ltd

distribution and transport of hydrocarbons in surface sediments of the alaskan outer continental shelf abstract surface sediments from the outer continental shelf of alaska were analyzed for hydrocarbons as part of an environmental survey sponsored by noaa blm sediments were collected from the proposed oil lease areas of beaufort sea southeastern bering sea norton sound navarin basin gulf of alaska kodiak shelf and lower cook inlet data on normal and branched alkanes and di and triterpenoids from capillary gas chromatography gc and gas chromatography mass spectrometry gc ms indicate that the area displays little evidence of petroleum hydrocarbons i e seeps except at a few isolated stations beaufort sea sediments have the highest hydrocarbon budget whereas kodiak shelf sediments have the lowest the molecular markers of the hydrocarbons are of a mixed marine autochthonous and terrestrial allochthonous origin norton sound and cook inlet sediments contain the highest levels of terrigenous lipids and kodiak shelf the lowest the abundance of alkenes implies that relatively low oxidizing conditions exist in some of the depositional areas studied suggesting that extraneous petroleum hydrocarbons introduced into these sediments would be expected to have a relatively long residence time the distribution of polynuclear aromatic hydrocarbons pah is complex and shows a pyrolytic origin the data on perylene strongly favor the hypothesis that it is performed from terrigenous precursors and transported into the marine environment with no apparent in situ generation polynuclear aromatic hydrocarbons of diagenetic origin are probably dominant in gulf of alaska and kodiak shelf sediments two stations north of kalgin island in lower cook inlet and one in southeastern bering sea show typical weathered petroleum distribution of n alkanes and triterpenoids probable pathways of transport and fate of petroleum hydrocarbons in case of an oil spill are also briefly discussed

hydrothermal hydrocarbon gases in the sediments of the king george basin bransfield strait antarctica thermogenic hydrocarbons formed by the thermal alteration of organic matter are encountered in several piston core stations in the king george basin anatarctica these hemipelagic sediments are being deposited in an area of active hydrothermalism associated with the back arc spreading in the bransfield strait the lateral extent of sediments infiltrated by the hydrothermally influenced interstitial fluids is characterized by basalt diapirix intrusions and is delineated by an acoustically turbid zone in the sediments of the eastern part of the basin iron sulphide bearing veins and fractures cut across the sediment in several cores they appear to be conduits for flow of hydrothermally altered fluids these zones have the highest c2 and ethene contents the thermogenic hydrocarbons have molecular c1 c2 c3 ratios typically 50 and 13ch4 values between 38 and 48 indicating an organic source which has undergone strong thermal stress several sediment cores also have mixed gas signatures which indicate the presence of substantial amounts of bacterial gas predominantly methane hydrocarbon generation in the king george basin is thought to be a local phenomenon resulting from submarine volcanism with temperatures in the range 70 150 c there are no apparent seepages of hydrocarbons into the water column and it is not believed that significant accumulation of thermogenic hydrocarbons reside in the basin

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

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

transport and exchange of u series nuclides between suspended material dissolved load and colloids in rivers draining basaltic terrains this study presents uranium and thorium concentrations and activity ratios for all riverine phases bedload suspended load dissolved load and colloids from basaltic terrains in iceland and the azores small basaltic islands such as these are thought to account for 25 of co2 consumed by global silicate weathering and for 45 of the flux of suspended material to the oceans these data indicate that u and th in the dissolved and colloidal fractions are strongly controlled by ph and to a much lesser extent by levels of dissolved organic carbon which are low in these environments at high ph basalt glass dissolution is enhanced and secondary mineral formation e g fe oxyhydroxides and allophane is suppressed resulting in high dissolved u and low colloidal u and th indicating a direct chemical weathering control on elemental abundances when the dissolved 234u 238u activity ratio is 1 3 i e when physical weathering groundwater contribution or soil formation are high there is little isotope exchange between dissolved and colloidal fractions at lower activity ratios the dissolved load and colloids have indistinguishable activity ratios suggesting that when chemical weathering rates are high secondary clay formation is also high and colloids rapidly adsorb dissolved u many of the suspended sediment samples have 234u 238u activity ratios of 1 which suggests that uptake of u onto the suspended load is important identical 230th 232th in suspended dissolved and colloidal samples suggests that th like u is exchanged or sorbed rapidly between all riverine phases this particle reactivity combined with poorly constrained contributions from groundwater and hydrothermal water and short term variations in input to soils volcanic and glacial suggests that u series nuclides in riverine material from such basaltic terrains are unlikely to reflect steady state erosion processes

fixation of radionuclides in the 238u decay series in the vicinity of mineralized zones 1 the austatom uranium prospect northern territory australia abstract the minimum age of a zone of secondary uranium mineralization located at the austatom prospect in the alligator rivers region of australia is estimated to be 3 6 10 5 y this is derived from a geochronological model based on retarded leaching of 234 u with respect to 238 u and on ratios within the ore of these members of the 238 u decay series although kaolinite is a dominant mineral in the weathered schist host rocks retarded dissolution of 234 u occurs only in the presence of the clay minerals illite and montmorillonite in their absence the reverse occurs a model is proposed to explain the results ratios of 230 th to 238 u indicate that the mineralization has probably remained stationary within the weathered schist for at least 1 to 2 10 5 y future use of clay minerals as buffers in radioactive waste repositories is supported by the excellent long term retention obtained for oxidized uranium probably due in part to isomorphic substitution into the clay crystal lattice

the effect of curvature on weathering rind formation evidence from uranium series isotopes in basaltic andesite weathering clasts in guadeloupe abstract to quantify rates of rind formation on weathering clasts under tropical and humid climate and to determine factors that control weathering reactions we analyzed uranium series isotope compositions and trace element concentrations in a basaltic andesite weathering clast collected from basse terre island in guadeloupe u th and ti elemental profiles reveal that th and ti behave conservatively during rind formation but that u is added from an external source to the rind in the rind weathering reactions include dissolution of primary minerals such as pyroxene plagioclase and glass matrix as well as formation of fe oxyhydroxides gibbsite and minor kaolinite rare earth element ree profiles reveal a significant eu negative anomaly formed during clast weathering consistent with plagioclase dissolution significant porosity forms in the rind mostly due to plagioclase dissolution the new porosity is inferred to allow influx of soil water carrying externally derived dissolved u due to this influx u precipitates along with newly formed clay minerals and oxyhydroxides in the rind the conservative behavior of th and the continuous addition of u into the rind adequately explain the observed systematic trends of 238 u 232 th and 230 th 232 th activity ratios in the rind rind formation rates determined from the measured u series activity ratios with an open system u addition model increase by a factor of 1 3 0 18 0 24 mm kyr from a low curvature to a high curvature section 0 018 0 12 mm 1 of the core rind boundary revealing that curvature affects rates of rind formation as expected for diffusion limited rind formation u series geochronometry thus provides the first direct evidence that the curvature of the interface controls the rate of regolith formation at the clast scale the weathering rates determined at the clast scale can be reconciled with the weathering rates determined at the watershed or soil profile scale if surface roughness equals values of approximately 1300 2200

basalt and olivine dissolution under cold salty and acidic conditions what can we learn about recent aqueous weathering on mars 1 to test which variables may be important for weathering on mars the effects of temperature 22 c 6 c and 19 c high ionic strength and oxygen concentrations were investigated in batch dissolution experiments containing forsterite fayalite and basalt glass cacl2 nacl h2o brine can remain liquid to temperatures of 55 c and thus may be liquid in the cold dry climate that currently characterizes mars to understand weathering under such conditions dissolution rates were measured in experiments in distilled water with and without cacl2 and nacl as observed by others dissolution rates increased with temperature and only fayalite dissolution was significantly affected by the presence or absence of oxygen enhanced fayalite dissolution under anoxic conditions suggests that fe rich olivine would dissolve more rapidly than mg rich olivine on mars dissolution in the two most dilute experimental solutions deionized water and cacl2 nacl h2o solution of ionic strength 0 7 m were the same within uncertainty but apparent dissolution rate constants in cacl2 nacl h2o brines were significantly slower steady silica concentrations are decreased in the brines consistent with other work and precipitation rates of silica decrease with decreasing temperatures these results suggest that enhanced silica precipitation could be an indicator of high ionic strength solutions on mars consistent with these observations weathering of basalt has been observed to sometimes be accompanied by precipitated layers of silica in cold dry environments on earth if dissolution on mars occurs or occurred under conditions similar to our experiments cation leaching would be expected to be accompanied by silica precipitates on weathering surfaces

geophysical and geochemical evidence for subsurface hydrocarbon leakage in the bering sea alaska abstract geophysical and geochemical surveys were conducted on the bering sea shelf to investigate whether hydrocarbons found in the surficial sediment particularly in association with certain geophysical events indicate the presence and nature of more deeply reservoired oil and gas deposits surface sediment samples were obtained at 1000 sites where high resolution seismic data indicated the presence of gas seepage and or surface faulting in addition sites for background measurements were occupied away from areas of gas seepage results of the geophysical survey show seismic wipeout zones to be present throughout the bering sea shelf sediment samples obtained within the shallow wipeout zones confirm that these features are caused by gas in addition compositional and isotopic analyses indicate that the gas is of biogenic and thermogenic origins the thermogenic leakage appears to be related to localized faulting and shallow structuring the high resolution seismic data therefore provide an excellent tool for locating leakage points thereby enhancing the opportunity of finding migrated thermogenic hydrocarbons in surficial sediments an examination of vertical variability shows the hydrocarbon concentrations to be strongly related to various processes occurring in the surficial sediments core samples must be taken from below the zone of maximum disturbance to obtain unaltered hydrocarbon samples

a porosity related diffusion model of weathering rind development abstract a model of weathering rind growth is proposed based on the study of andesite cobbles sampled from a modern floodplain and four fluvial terraces 0 20 130 290 and 660 ka in central japan the times elapsed since each of the above ages can be assumed to be the weathering periods the 0 ka rocks are not visibly weathered the 20 ka rocks have an alteration layer with white or brown colours and a mean thickness of 0 7 mm on their surface the 130 290 and 660 ka rocks have brown weathering rinds with average thicknesses of 3 6 mm based on the measurements of physical and mechanical properties throughout from the rock surface to the interior weathering rinds are divided into two bands the outer brown band is characterized by ferric hydroxides which experienced both oxidization and leaching the inner band is formed by leaching alone of alkalis alkaline earths the inner border of this band is located at the position where vickers hardness numbers start decreasing with decreasing depth the thickness of each band was determined from its physical and mechanical properties the results show that brown band thickness l i is a function of time however total thickness of the two bands i e total weathering rind thickness l i ii is also controlled by initial rock porosity n their relationships are represented by diffusive equations l i dt 1 2 0 0283 t 1 2 and l i ii dt 1 2 0 0431 exp 0 4287 n t 1 2 these findings indicate that rind characterization and original rock porosity should be taken into consideration when weathering rind thickness is used as a dating tool

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

the evolution of weathering profiles through time new insights from uranium series isotopes the sustainability of soil is a major issue for society in principle the evolution of soil resources can be constrained by comparing the rates of soil erosion and production cosmogenic isotopes provide one measurement of soil erosion rates they can also be used to estimate soil production rates but only if erosion is assumed to be balanced by production this implies that the evolution of soil resources thinning thickening or constant since soil thickness is assumed to be constant with time here we utilise an independent method to estimate soil production rates using uranium series u series isotopes the study of a site in temperate australia undisturbed by human activity shows that soil production rates inferred from u series isotopes are similar to erosion rates derived from beryllium 10 10be measurements implying that at this site there is no net accumulation or loss of soil saprolite production rates the migration rate of the weathering front into the bedrock are also similar to erosion rates so the thickness of the entire weathering profile is effectively in steady state this study demonstrates that the combination of u series and cosmogenic isotopes can be used to quantitatively assess soil evolution and the development of weathering profiles preliminary observations suggest that the rate of bedrock weathering i e saprolite production in temperate australia is of the same order of magnitude as that inferred for laterites in tropical climates this may suggest that for thick weathering profiles although the extent of weathering strongly differs between temperate and tropical climates the migration of the weathering front into the bedrock occurs at a relatively uniform rate regardless of present day climatic conditions

mobilization and redistribution of rees and thorium in a syenitic lateritic profile a mass balance study abstract ree th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite at akongo in sw cameroon ree and th mass balance calculations for the host rock minerals show that at least 70 of the lree s and 50 of the hrees are contained in allanite apatite titanite and epidote and at least 50 of the th is controlled by the same accessory minerals which represent about 2 wt of the unaltered syenite these accessory phases are destroyed during the first stages of weathering causing most of the rees and th to be rapidly released into the soil comparison of the variation in the zr ti and th content as a function of the apparent density of the different zones of the saprolite shows that th is the least mobile element the presence of secondary thorianite tho2 the etched surface on zircon grains and the presence of ti in secondary cerianite support this geochemical interpretation the concentration of thorium was therefore chosen as invariant relative to the concentration of the other elements especially the rees in mass balance calculations most of the rees are leached in the iron rich upper horizons loose nodular horizon iron crust and top of mottled clay horizon where the groundwater table moves saprolite and bottom of the mottled clay horizon the rees are fractionated and redistributed there is a juxtaposition of leached and accumulation zones with precipitation of lree aluminous hydrated phosphates this study supports the existence of two different cycles for the redistribution of elements in the soil 1 1 as dissolved ions in the saprolite horizon and 2 2 as individual particles in the upper part of the profile

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

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

surface geochemical studies in the norwegian barents sea comparison with drilling results during the last 4 years a number of surface geochemical studies have been undertaken in the barents sea acreage in all of the areas has subsequently been licensed for exploration sampling for surface geochemistry has been undertaken using a gravity corer where samples were taken 2 m below the seafloor the sampling grids were either regular or irregular based on known geological features in the areas or a combination of the two the samples were analyzed for interstitial gas adsorbed gas grain size distribution organic and inorganic carbon content fluorescence of the hexane extract and heavy hydrocarbons in the hexane extract the results from the different areas ranged from barren i e no indication of petrogenic hydrocarbons at the surface anomalies of petrogenic hydrocarbons i e indicating the generation of gas condensate or oil to extremely strong anomalies of oil interpreted as indicators of direct leakage from source rocks or a defective caprock

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

hydrocarbon geochemistry in surface sediments of alaskan outer continental shelf part 1 c15 hydrocarbons the c15 hydrocarbons in 220 surface sediments from the outer continental shelf of alaska were analyzed as part of an environmental survey supervised by national oceanic and atmospheric administration and bureau of land management gas chromatography and gas chromatography mass spectrometry were employed for the identification of organic compounds in the bitumen extracts surface sediments from one station in southeastern bering sea and two stations in lower cook inlet display n alkanes and triterpenoid distribution typical of weathered petroleum major faulting in the vicinity of the southeastern bering sea station may account for the leakage of petroleum from subsurface reservoir rocks oil production in upper cook inlet or a hitherto unrecorded seep in the rea could contribute petroleum hydrocarbons to the sediments from the two stations in lower cook inlet apart from these stations there is little evidence of near surface petroleum seeps in the sites investigated

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

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

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

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

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

u th ra fractionation during weathering and river transport the potential of radioactive disequilibria as tracers and chronometers of weathering processes has been recognised since the 1960 s e g rosholt et al 1966 hansen and stout 1968 this interest results from the dual property of the nuclides of the u and th radioactive series 1 to be fractionated during water rock interactions and 2 to have radioactive periods of the same order of magnitude as the time constants of many weathering processes and chemical transfers to ground and river waters therefore the study of radioactive disequilibria in surface environments should help to bring information about the nature the intensity but also the time scale of the water rock interactions produced during weathering and related chemical transfers these different properties have justified many of the studies on u th series in weathering profiles and river waters rosholt 1982 scott 1982 and osmond and ivanovich 1992 gave a synthesis of the studies of u series in weathering and surface hydrology up to the 1980 s and the 1990 s respectively here we present the main directions taken in these domains over the last decade they were partly stimulated by the analytical developments made in the measurement of the medium half life nuclides of 238u series i e 234u 230th 226ra in the mid 1980 s namely the use of thermal ionisation mass spectrometry tims e g chen et al 1986 edwards et al 1987 cohen et al 1991 chabaux 1993 chabaux et al 1994 and more recently the use of mc icp ms turner et al 2001 robinson et al 2002 for u and th isotope analysis details of these developments are given in this volume goldstein and stirling 2003 compared to the radioactive counting methods previously used the new techniques permit 1 a reduction by one order of magnitude or more of the size of the sample required for

hydrocarbon geochemistry in surface sediments of alaskan outer continental shelf part 2 distribution of hydrocarbon gases the distribution of c1 to c4 hydrocarbon gases in surficial sediments from the alaskan continental shelf was determined as part of a regional environmental survey sponsored by national oceanic and atmospheric administration and bureau of land management noaa blm methane ethane ethene propane propene n butane and iso butane were observed in low concentrations 0 1 10 ppb as weight gas to dry weight sediment in nearly all of the 190 sediment samples examined with methane exceeding c2 to c4 hydrocarbons in abundance by about a factor of 10 no gasoline range c5 to c8 hydrocarbons were detected above blank levels ethene was found generally to be more abundant than ethane while propane was slightl more abundant than propene the correlation between these hydrocarbons suggests a common possibly biogenic origin sediments from norton sound have anomalously high methane concentrations probably as a result of biological methanogenesis in subsurface organic rich peat layers most of the regions sampled showed median values of the c1 c2 c3 ratio of 20 the generally low c1 concentrations probably resulted from the selective loss of c1 by biologic oxidation or ebullition from the surface sediments no major c2 to c4 hydrocarbon anomalies were discovered however at some stations in kachemak bay kodiak shelf and norton sound anomalously high c3 c3 1 ratios indicated the poss ble presence of thermogenic gases at depth

seismic and geochemical evidence for shallow gas in sediment on navarin continental margin bering sea marine seismic studies coupled with geochemical investigations demonstrate that hydrocarbon gases are ubiquitous in the near surface 250 m or 820 ft depth sediment of the navarin continental margin in the northern bering sea three types of acoustic anomalies appear to be related to the presence of gas in the sediment these anomalies are most prevalent in the northern half of the navarin basin acoustic anomalies attributed to gas hydrates and to diagenetic boundaries are present on seismic records of the lower slope between navarinsky and zhemchug canyons hydrocarbon gases methane through butanes are common in the surface 5 m or 17 ft depth sediment of the navarin continental margin methane the most abundant hydrocarbon gas is present in amounts ranging from 84 000 to 1 l l of wet sediment these concentrations are two to three orders of magnitude greater than the other hydrocarbon gases the highest concentrations of methane greater than 1 000 l l were measured in sediment of navarinsky canyon and over the central part of the navarin basin the source of methane is mainly biogenic but the hydrocarbon gas compositions in 17 of 141 cores suggest the presence of thermogenic gas most of these 17 cores are from the continental slope at water depths greater than 150 m 490 ft no direct correlation could be found between acoustic anomalies and gas concentrations in the sediment this lack of correlation is probably due to the limited penetration of the gravity corer and the spotty distribution of hydrocarbon concentrations

a reactive transport model for weathering rind formation on basalt abstract saprolite formation rates influence many important geological and environmental issues ranging from agricultural productivity to landscape evolution here we investigate the chemical and physical transformations that occur during weathering by studying small scale saprolites in the form of weathering rinds which form on rock in soil or saprolite and grow in thickness without physical disturbance with time we compare detailed observations of weathered basalt clasts from a chronosequence of alluvial terraces in costa rica to diffusion reaction simulations of rind formation using the fully coupled reactive transport model crunchflow the four characteristic features of the weathered basalts which were specifically used as criteria for model comparisons include 1 the mineralogy of weathering products 2 weathering rind thickness 3 the coincidence of plagioclase and augite reaction fronts and 4 the thickness of the zones of mineral reaction i e reaction fronts four model scenarios were completed with varying levels of complexity and degrees of success in matching the observations to fit the model to all four criteria however it was necessary to 1 treat diffusivity using a threshold in which it increased once porosity exceeded a critical value of 9 and 2 treat mineral surface area as a fitting factor this latter approach was presumably necessary because the mineral water surface area of the connected accessible porosity in the costa rica samples is much less than the total porosity navarre sitchler et al 2009 the model fit surface area here termed reacting surface area was much smaller than the bet measured surface area determined for powdered basaltic material in the parent basalt reacting surface area and diffusivity are low due to low pore connectivity and early weathering is therefore transport controlled however as pore connectivity increases as a result of weathering the reacting surface area and diffusivity also increase and weathering becomes controlled by mineral reaction kinetics the transition point between transport and kinetic control appears to be related to a critical porosity 9 at which pore connectivity is high enough to allow rapid transport based on these simulations we argue that the rate of weathering front advance is controlled by the rate at which porosity is created in the weathering interface and that this porosity increases because of mineral dissolution following a rate that is largely surface reaction controlled

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

sources of hydrocarbon gases in mud volcanoes from the sorokin trough ne black sea based on molecular and carbon isotopic compositions abstract molecular and stable carbon isotope properties of hydrocarbon gases methane through pentanes and sometimes hexanes from seven sediment cores collected from five mud volcanoes mvs in the sorokin trough ne black sea suggest that these gases are initially derived from the comparable hydrocarbon pools and are likely initial products of non microbial oil cracking processes our results state that dry characteristics of gas and 13 c depleted signatures of methane are result of a high admixture of secondary microbial gas formed due to subsequent microbial anaerobic degradation of redeposited hydrocarbons in the shallow reservoirs the wet gas components in all mvs and gas hydrates are related to each other the compositional variations in c 2 content appear to result from a complex of secondary processes such oil cracking in the deep subsurface migration and mixing of resulted gaseous and liquid hydrocarbons biodegradation of possibly redeposited hydrocarbons forming shallow reservoirs and additional alterations of hydrocarbon gases in the surface sediments due to currently active microbial processes such as aom c 2 consumption etc our data show that the most unaltered gas is in the mud breccia from the kazakov mv the gas mixture possibly represents the original properties of the hydrocarbons trapped in the deep subsurface of the sorokin trough analysis of the hydrocarbon gas data complemented with published maturity characteristics of organic matter from maycopian rock clasts and mud breccia matrix implies that the original source of gases is likely to be located below the maycopian shale formation

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

on the possibility of determining rates of removal of uranium from crystalline igneous rocks using u series disequilibria 1 a u leach model and its applicability to whole rock data the removal of u from granitic rocks is characterised by234u 238u 1 and 230th 234u 1 it is notable from weathered eye dashwa lakes canada granite samples and from the published data that230th 234u ratios seldom exceed a limiting value of about 2 a u leach model is discussed in detail which may account for these observations the model assumes that 230th is practically immobile and that the removal of u can then be measured against the decay rate of the unsupported230th a property of the model is that the isotope ratios reach constant values reflecting a kind of secular equilibrium and this implies that u is seldom removed faster than the decay of230th if the limited230th 234u ratios from the data correspond to secular equilibrium ratios then this allows simple calculation of u leach rates from any given subsurface sample a test for the model using235u 231pa ratios is suggested a comparison of leach rates derivable from u th pb systematics of colorado and wyoming granite samples with the corresponding estimates from the model shows that the latter are high by a factor of 10 50 data from rapidly weathered surface rinds suggests that the presence of labile u restricts the application of the model to subsurface low weathered zones

regolith production rates calculated with uranium series isotopes at susquehanna shale hills critical zone observatory abstract in the critical zone where rocks and life interact bedrock equilibrates to earth surface conditions transforming to regolith the factors that control the rates and mechanisms of formation of regolith defined here as material that can be augered are still not fully understood to quantify regolith formation rates on shale lithology we measured uranium series u series isotopes 238 u 234 u and 230 th in three weathering profiles along a planar hillslope at the susquehanna shale hills observatory ssho in central pennsylvania all regolith samples show significant u series disequilibrium 234 u 238 u and 230 th 238 u activity ratios range from 0 934 to 1 072 and from 0 903 to 1 096 respectively these values display depth trends that are consistent with fractionation of u series isotopes during chemical weathering and element transport i e the relative mobility decreases in the order 234 u 238 u 230 th the activity ratios observed in the regolith samples are explained by i loss of u series isotopes during water rock interactions and ii re deposition of u series isotopes downslope loss of u and th initiates in the meter thick zone of bedrock that cannot be augered but that nonetheless consists of up to 40 clay silt sand inferred to have lost k mg al and fe apparent equivalent regolith production rates calculated with these isotopes for these profiles decrease exponentially from 45 m myr to 17 m myr with increasing regolith thickness from the ridge top to the valley floor with increasing distance from the ridge top toward the valley apparent equivalent regolith residence times increase from 7 kyr to 40 kyr given that the ssho experienced peri glacial climate 15 kyr ago and has a catchment wide averaged erosion rate of 15 m myr as inferred from cosmogenic 10 be we conclude that the hillslope retains regolith formed before the peri glacial period and is not at geomorphologic steady state both chemical weathering reactions of clay minerals and translocation of fine particles colloids are shown to contribute to mass loss of u and th from the regolith consistent with major element data at ssho this research documents a case study where u series isotopes are used to constrain the time scales of chemical weathering and regolith production rates regolith production rates at the ssho should be useful as a reference value for future work at other weathering localities

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

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

erosion timescales derived from u decay series measurements in rivers the relative importance of the factors influencing weathering of continental rocks has been a topic of debate for the last few decades the principal reasons are the lack of reliable proxies for chemical weathering and the difficulty in constraining actual physical denudation rates in this study 234u 238u 230th 238u and 226ra 238u were measured by tims and by mc icp ms in the dissolved and suspended loads of rivers from the mackenzie basin northwest territories canada the data show a complementary nature between 234u 238u 230th 238u in the dissolved and suspended loads while 226ra is characterized by a more complex behavior modeling of fractionation of u series nuclides in the particulate matter and the corresponding dissolved phase permits us to constrain the duration of chemical erosion for the suspended load currently sampled in the watershed 9 28 10 ka as well as the rates of release of u series nuclides the results also imply significant recent changes of chemical erosion rates and underline the impact of the last glaciation on current continental fluxes of northern latitude rivers such as the mackenzie river

effects of organic ligands on granite dissolution in batch experiments at ph 6 yosemite granite from the tuolumne river series was dissolved under oxic and anoxic conditions in the presence 0 001 or 0 01 m and absence of organic ligands in batch experiments at ph 6 release of all elements was enhanced considerably in the presence of organic ligands citrate tridentate and gallate tetradentate increased element release to the greatest extent among the aliphatic and aromatic ligands respectively the extent of element mobilization observed for the aliphatic ligands decreased in the order citrate oxalate malonate and for the aromatic ligands gallate salicylate phthalate the effects of the ligands generally followed trends in cation ligand stability constants but aromatic ligands were less effective in element mobilization than aliphatic ligands this was attributed to protonation of the functional groups of aromatic ligands at ph 6 rock dissolution was non stoichiometric regardless of the presence or absence of organic ligands release of p and cu of total element content in the unweathered rock in the presence of organic ligands was considerably greater than that of other elements findings of the present study were compared to the findings of our previous study on dissolution of basalt differences in the mobility patterns of y fe cu ti and zr during dissolution of granite and basalt were observed in basalt release of y was enhanced considerably in the presence of citrate in contrast in the present study release of y from granite with and without citrate was at the detection limit this difference was attributed to the difference in y hosting parent minerals apatite basalt and sphene granite with and without organic ligands no significant differences were observed in the extent of fe released from granite under oxic versus anoxic conditions while the extent of fe release from basalt was considerably greater under anoxic versus oxic conditions with and without organic ligands these differences can be attributed to the difference in major fe hosting phases in the rocks biotite granite versus glass and augite basalt in the granite concentrations of cu released increased considerably in the presence of organic ligands under both oxic and anoxic conditions in contrast concentrations of cu released from basalt were increased considerably only under oxic conditions especially in the presence of organic ligands this difference was attributed to the different extent of fe release from basalt and granite that affected dissolution of cu fe sulfides although both ti and zr can be mobilized in the presence of organic ligands in the rock where zircons hosted zr granite this element was the most immobile while in the rock where fe ti oxides hosted zr basalt ti was the most immobile

active venting at the isis mud volcano offshore egypt origin and migration of hydrocarbons abstract the isis mud volcano is an active camembert like mud expulsion structure in the eastern nile deep sea fan area it has been investigated during the nautinil 2003 and mimes 2004 cruises carried out within the mediflux project active gas rich fluid venting occurs at the isis mud volcano as indicated by enhanced gas content in the sediments having a measured 7 5 mmol of methane per liter of wet sediment in the central area of the mud volcano in addition gas bubble expulsions have resulted in the formation of multiple hydrocarbon plumes in the water column with methane concentrations as high as 1550 nmol l compared to 1 nmol l for background levels in deep water in view of the stable carbon and hydrogen isotopic composition of methane 13 c 55 1 vpdb d 203 vsmow and of higher hydrocarbons 13 c of 30 3 26 1 28 4 and 25 0 vpdb for ethane propane i butane and n butane respectively their origin is mainly thermogenic these isotopic data also show that the wet compounds are co generated with oil and we suggest they predominantly originate from type ii kerogen source rocks of potentially variable maturity levels at the centre of the mud volcano the distinct kink observed in the pore water isotopic and dissolved species composition and its depth level change between subsequent cruises indicates a high frequency of fluid gas expulsion the seawater signature of the pore fluid in the upper part of the sediment column suggests that each expulsion is followed by a downward migration of overlying seawater such downward advection of bottom seawater may not only be related to the replacement of the ejected gas but also to the replacement of lower density pore fluid by bottom seawater this mechanism is thought to be a common feature at mud volcanoes and gas seepage sites in the peripheral zone pore fluid is at seawater concentration and isotopic composition down to a coring depth of 430 cmbsf we suggest that the deeper downward advection of bottom seawater is related to the less frequent fluid gas expulsion occurring at these sites compared to the centre sites in this paper we show that a combination of geochemical tools used for hydrocarbons and pore water geochemistry is a powerful approach to detect sources of ascending fluid and to reveal post eruptional fluidodynamic processes within mud volcanoes

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

molecular and carbon isotopic variability of hydrocarbon gases from mud volcanoes in the gulf of cadiz ne atlantic investigations of molecular and carbon isotopic variability of hydrocarbon gases from methane through butanes pentanes have been performed on six mud volcanoes from two fluid venting provinces located in the gulf of cadiz ne atlantic the main aims were to define the basic gas types to describe their geochemical characteristics in relationship to their sources and to determine the secondary effects due to migration mixing and microbial alteration hydrocarbon gas data reveal two groups of gases despite the different maturation characteristics both gas groups are allochthonous to the erupted mud breccia and represent a complex of redeposited secondary migrated mixed and microbially altered hydrocarbons it may possibly imply the presence of hydrocarbon accumulations in the deep subsurface of the gulf of cadiz

basalt weathering across scales abstract weathering of silicate minerals impacts many geological and ecological processes for example the weathering of basalt contributes significantly to consumption of atmospheric carbon dioxide co2 and must be included in global calculations of such consumption over geological timeframes here we compare weathering advance rates for basalt wd where d and indicate the scale at which the rate is determined and surface area measured respectively from the laboratory to the watershed scales data collected at the laboratory weathering rind soil profile and watershed scales show that weathering advance rate of basalt is a fractal property that can be described by a fractal dimension dr 2 3 by combining the fractal description of rates with an arrhenius relationship for basalt weathering we derive the following equation to predict weathering advance rates at any spatial scale from weathering advance rates measured at the bet scale w d k 0 a d r 2 e e a r t here k0 is the pre exponential factor 1 29 107 mm3 mm 2 yr 1 ea is the activation energy 70 kj mol 1 and a is a spatial constant related to the scale of measurement of bet surface area 10 7 mm the term a d r 2 is the roughness the roughness fractal dimension can be conceptualized as a factor related to both the thickness of the reaction front and the specific surface area within the reaction front however the above equation can also be written in terms of a surface fractal dimension and the hypothetical average grain radius these fractal dimensions provide insight into reaction front geometry and should vary with lithology once the surface area discrepancy has been accounted for using this method we find a one to two order of magnitude range in weathering advance rates measured at any scale or temperature that can be attributed to factors such as changes in erosional regime parent lithology mechanism climate composition of reacting fluid and biological activity our scaled equation when used to predict global basalt co2 consumption based upon global lithologic maps yields an uptake flux 1 75 1013 mol co2 yr 1 within the predicted error of fluxes estimated based upon riverine measurements

thermogenic hydrocarbons in unconsolidated sediment of eel river basin offshore northern california thermally produced hydrocarbons were recovered from unconsolidated sediment ponded within a bathymetric depression on the surface of a shale diapir in the offshore eel river basin of northern california evidence that the hydrocarbons are thermogenic consists of the following 1 very high concentrations of hydrocarbon gases particularly ethane through butanes c2 c4 2 methane having a carbon isotopic composition relative to the pdb standard of 43 and 44 per mil 3 presence of gasoline range c5 hydrocarbons and 4 presence of a complex mixture of heavy hydrocarbons c15 with n alkanes having a petroleumlike distribution this mixture of gaseous and liquid hydrocarbons likely originated deep within the basin an migrated to the surface through fractures and faults developed during the emplacement of the diapir the presence of thermogenic hydrocarbons in unconsolidated surface sediment indicates that conditions for petroleum generation have existed within this offshore basin

u series disequilibria in suspended river sediments and implication for sediment transfer time in alluvial plains the case of the himalayan rivers 238u 234u 230th radioactive disequilibria were analyzed in suspended sediments collected at different depths from the ganges river and one of its main tributaries the narayani gandak river results associated with bedload sediment data suggest that uranium series u series disequilibria in river sediments of the ganges basin vary with grain size and sampling location the range of observed u series disequilibria is explained by a mixing model between a coarse grained sediment end member represented by bedload and bank sediments and a fine grained end member that both originate from himalaya but undergo different transfer histories within the plain the coarse grained sediment end member transits slowly i e several 100 s ky in the plain whereas the fine grained sediment end member is transferred much faster 20 25 ky as indicated by the absence of significant variations in th isotope composition of the fine grained sediment end members these results show that u series isotopes can be used to quantify the various transfer times of river sediments of different sizes and infer that there can be an order of magnitude of difference or more between the transfer time of suspended and bedload sediments this underlines that a good knowledge of the proportion of suspended vs bedload sediments transported in the river is required to accurately assess how fast erosion products are transferred in a catchment and how fast a catchment is likely to respond to external forcing factors

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

chemical mobilizations in laterites evidence from trace elements and 238u 234u 230th disequilibria geochemical and mineralogical investigations including measurements of major and trace elements sr isotope ratios and 238u 234u 230th activity ratios were made on an old african laterite to reconstruct its formation steps and assess recent chemical mobilization the present data support a scenario of discontinuous formation for the laterite with different bedrock weathering conditions during the formation of each unit rather than a scenario of continuous formation absolute accumulation of fe u and lanthanides in the uppermost ferruginous unit suggests an autochthonous origin of this iron cap by leaching of an older overlying profile present chemical distributions of lanthanides as well as of rb k ba and sr within the profile cannot be linked to the mineralogical distribution of both relictual primary and authigenic secondary phases complementary lanthanide patterns indicate that these elements were primarily accumulated in the uppermost ferruginous unit before further remobilization and accumulation in the underlying horizons these redistribution processes may be related to the chemical instability of the ferruginous cap the 238u 234u 230th disequilibria indicate that recent u mobilization occurs in the whole profile and that as for lanthanides there is a vertical redistribution of u from the uppermost ferruginous unit to the underlying horizons moreover these data show that both u losses and gains exist at each level of the profile a simple modeling of this double u mobilization process is proposed to interpret the 238u 234u 230th data differences in the mobilization and fractionation intensities of the u input and removal processes can account for the two evolution trends which distinguish the ferruginous unit from the underlying ones furthermore on the basis of this modeling the profile appears to be in a transient state because of recent changes in the u mobilization conditions which could correspond to major pleistocene climatic variations

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

changing sources of strontium to soils and ecosystems across the hawaiian islands abstract strontium isotope ratios assist ecosystem scientists in constraining the sources of alkaline earth elements but their interpretation can be difficult because of complexities in mineral weathering and in the geographical and environmental controls on elemental additions and losses hawaii is a natural laboratory where a number of important biogeochemical variables have either limited ranges or vary in systematic ways providing a unique opportunity to understand the impact of time climate and atmospheric inputs on the evolution of base cation sources to ecosystems there are three major sources of strontium sr to these ecosystems each with distinct isotopic compositions basalt lava asian dust and rainfall we present sr isotope and concentration data on both bulk soil digests and nh4ac extracts from soil profiles covering a wide range of environments and substrate ages bulk soil material from dry climates and or young substrate ages with 80 g g 1 sr retain basalt like sr isotopic signatures whereas those with sr concentrations 40 by mass at elevated dust levels lava derived sr is low and dust derived sr is the dominant control of 87sr 86sr in bulk soils however 87sr 86sr of nh4ac extractable sr largely reflects atmospheric deposition of marine aerosol in these situations overall whole soil sr isotope values are controlled by complex interactions between sr provided by lava weathering but partially lost by leaching and sr provided by dust but held in more resistant minerals the isotopic composition of nh4ac extractable sr and of the biota is controlled by lava weathering and rainfall contribution of sr with only minor contributions from radiogenic dust sources

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

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

experimental evidence for 234u 238u fractionation during granite weathering with implications for 234u 238u in natural waters abstract the daughter to parent 234u 238u activity ratio in natural waters is often out of secular radioactive equilibrium the major reason for this disequilibrium is related to the energetic decay of 238u and differential release of 234u relative to 238u this disequilibrium originates from 1 preferential release of more loosely bound 234u from damaged mineral lattice sites or 2 direct recoil of 234th into surrounding media from near mineral surface boundaries however it is unclear which of the two mechanisms is most important in nature to better quantify the effects of preferential release of 234u two continuous laboratory granite leaching experiments conducted over 1100 h were performed the leachates were characterized by declining u concentrations with time and 234u 238u initially greater than unity up to 1 15 which changed to below unity during leaching 0 95 the early elevated 234u 238u suggests that additional 234u is released into solution by preferential release of 234u from mineral phases however the excess 234u constitutes a finite pool of easy leachable 234u and the 234u 238u values become lower than unity when this pool is used up a model based on first order kinetics dissolution rates and preferential release of 234u from damaged lattice sites was developed and is able to quantitatively predict the observed pattern of 234u 238u values and u concentrations for the two granite leaching experiments extending the modeling to longer time scales more comparable to natural systems shows that the production of waters with high 234u 238u ratios can be achieved in two distinct regimes 1 slow weathering where the rate of directly recoiled 234u near mineral surfaces into waters is high 2 fast weathering where the role of incipient chemical weathering and preferential release of loosely bound 234u are important the model is able to explain apparent opposite correlations between physical erosion rates and 234u 238u in waters and it provides a new framework that will be useful for examining weathering regimes their timescales and their coupling with physical erosion

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

uranium series isotopes in river materials insights into the timescales of erosion and sediment transport abstract the uranium series isotope signatures of the suspended and dissolved load of rivers have emerged as an important tool for understanding the processes of erosion and chemical weathering at the scale of a watershed these signatures are a function of both time and weathering induced fractionation between the different nuclides provided appropriate models can be developed they can be used to constrain the residence time of river sediment this chronometer is triggered as the bedrock starts weathering and the inferred timescale encompasses the residence time in the weathering profile storage in temporary sediment deposits e g floodplain and transport in the river this approach has been applied to various catchments over the past five years showing that river sediments can reside in a watershed for timescales ranging from a few hundreds of years iceland to several hundreds of thousands of years lowlands of the amazon various factors control how long sediment resides in the watershed the longest residence times are observed on stable cratons unaffected by glacial cycles or more generally climate variability and human disturbance shorter residence times are observed in active orogens andes or fast eroding recently glaciated catchments iceland in several cases the residence time of suspended sediments also corresponds to the time since the last major climate change the u series isotope composition of rivers can also be used to predict the river sediment yield assuming steady state erosion is reached by comparing this estimate with the modern sediment yield obtained by multi year sediment gauging it is clear that steady state is seldom reached this can be explained by climate variability and or human disturbance steady state is reached in those catchments where sediment transport is rapid iceland or where the region has been unaffected by climate change and or human disturbance u series are thus becoming an important tool to study the dynamics of erosion

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

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