high salinity fluid inclusions formed from recycled seawater in deeply subducted alpine serpentinite abstract the origin of high pressure brines has been investigated in the erro tobbio peridotite western alps a mantle slice that was exposed to the seafloor of the mesozoic ligurian piedmontese tethys and was later involved in alpine subduction hydrothermal alteration by seawater derived fluids led to replacement of the mantle assemblage by cl bearing serpentine 0 35 wt cl brucite 0 2 wt cl and alkali bearing phyllosilicates 0 2 wt cl 0 2 0 55 wt na2o 1 5 wt k2o relics of these hydrous phases occur in olivine titanian clinohumite antigorite assemblages formed at 2 5 gpa and 550 600 c during partial devolatilization and veining of the hydrothermally altered peridotite the high pressure phases lack chlorine and alkalis and are coeval with fluid inclusions trapped in the syn eclogitic veins the inclusions are salt saturated and contain up to 50 wt cl na k mg and fe high fluid chlorinity was probably achieved during rehydration of relict mantle minerals and deposition of hydrous phases in the veins the data presented suggest that the seafloor hydrothermal signature was inherited by the eclogitic fluid due to partitioning of chlorine and alkalis into the fluid phase the presence of salty brines in eclogitized hydrous peridotites can indicate deep recycling of seawater derived fluids hydrous ultramafic systems can therefore act as large scale carriers of seawater into the mantle

carbonate control of h2 and ch4 production in serpentinization systems at elevated p ts 1 serpentinization of forsteritic olivine results in the inorganic synthesis of molecular hydrogen h 2 in ultramafic hydrothermal systems e g mid ocean ridge and forearc environments inorganic carbon in those hydrothermal systems may react with h 2 to produce methane ch 4 and other hydrocarbons or react with dissolved metal ions to form carbonate minerals here we report serpentinization experiments at 200 c and 300 bar demonstrating fe 2 being incorporated into carbonates more rapidly than fe 2 oxidation and concomitant h 2 formation leading to diminished yields of h 2 and h 2 dependent ch 4 in addition carbonate formation is temporally fast in carbonate oversaturated fluids our results demonstrate that carbonate chemistry ultimately modulates the abiotic synthesis of both h 2 and ch 4 in hydrothermal ultramafic systems and that ultramafic systems present great potential for co 2 mineral sequestration

authigenic trioctahedral smectites controlling ph alkalinity silica and magnesium concentrations in alkaline lakes abstract the mineralogical composition of salts and the chemical composition of brines of lake yoa ounianga el kebir northern chad both reveal the neoformation of stevensite a trioctahedral smectite accompanied by aragonite the coprecipitation of these two minerals clearly controls the evolution of ph alkalinity and ca mg and silica concentrations in alkaline brines the geochemical evolution characterized by a strong depletion of ca and mg in solution and an increase in alkalinity and ph is confirmed as the dominant process governing the formation of soda alkaline lakes

highly alkaline high temperature hydrothermal fluids in the early archean ocean abstract based on the petrology of hydrothermally altered archean basaltic greenstones thermodynamic calculations of phase equilibria were conducted to estimate the composition of a high temperature 350 c hydrothermal fluid in an archean subseafloor basalt hosted hydrothermal system the results indicate that the hydrothermal fluid was highly alkaline attributed to the presence of calcite in the alteration minerals under a high co2 condition and predict a generation of sio2 rich fe poor hydrothermal fluids in the archean subseafloor hydrothermal system the chemically reactive mixing zones between alkaline hydrothermal fluids and slightly acidic neutral seawater are characterized by inverse ph and chemical polarity to modern hydrothermal systems leading to extensive precipitation of silica and iron oxyhydroxides on under the seafloor such processes can be responsible for the abiotic formation of voluminous chert and subseafloor silica dike the mechanism of silicification and the ph controlled generation of banded iron formation that has been arising mainly from the redox chemistry in the archean ocean such high temperature alkaline fluids could have had a significant role not only in the early ocean geochemical processes but also in the early evolution of life

characterization of hyperalkaline fluids produced by low temperature serpentinization of mantle peridotites in the oman and ligurian ophiolites a regional survey of alkaline springs in oman and ligurian ophiolites shows that the alkaline water compositions significantly vary from one ophiolite to the other and within the same ophiolite the first order correlation between the na and k and cl concentrations points to fluid compositions only partly due to evaporation the scatter around the evaporation line implies that na and cl may not be conservative during the alteration of the ultramafic rocks mg is almost entirely depleted at ph 10 5 as a result of serpentine formation within the ultramafic body and of brucite and minor hydrotalcite precipitation at the springs ca accumulates in the high ph fluids and is consumed by ca carbonate formation at the springs by mixing with river waters or by the co2 supply from the atmosphere thermodynamic calculations show that brucite saturation is reached at ph values around 10 5 which triggers major changes in the water composition the waters evolve from a quartz saturated low ph continental environment to a brucite dominated high ph serpentinizing system at low temperature the highest water salinities are found in springs located along the basal thrust plane of the ophiolite the highest al concentrations are found in some springs located on the crustal side of the mantle crust boundary this poses the question of the hydrologic pathways and of the role of the mineralogical composition of the altered formations key points new temperature and composition of the alkaline waters brucite formation at ph 10 5 triggers major chemical and mineralogical changes relationship between the water compositions and the hydrologic pathways

assessing the extent of carbonate deposition in early rift settings select lacustrine and marine depositional settings show a spectrum of styles of carbonate deposition and illustrate the types of carbonates with an emphasis on microbialites and tufa to be expected in early rift settings early rift lake examples examined in this review article are all from east africa lakes turkana bogoria natron and magadi manyara and tanganyika other lake examples include four from the western united states great salt lake and high lake level lake bonneville mono lake and high lake level russell lake pyramid lake and high lake level lake lahontan and searles lake and two from australia lakes clifton and thetis marine basin examples are the hamelin pool part of shark bay from australia marginal marine and the red sea marine rift landsat images and digital elevation models for each example are used to delineate present and past lake basin margins based on published lake level elevations and for some examples the shorelines representing different lake levels can be compared to evaluate how changes in size shape and lake configuration might have impacted carbonate development the early rift lakes show a range of characteristics to be expected in lacustrine settings during the earliest stages of continental extension and rifting whereas the red sea shows well advanced rifting with marine incursion and reef skeletal sand development collectively the lacustrine examples show a wide range of sizes with several of them being large enough that they could produce carbonate deposits of potential economic interest three of the areas great salt lake and high lake level lake bonneville pyramid lake and high lake level lake lahontan and the red sea are exceedingly complex in that they illustrate a large degree of potential depositional facies heterogeneity because of their size irregular pattern and connectivity of subbasins within the overall basin outline

paleoclimate of the past 4000 years at lake turkana kenya based on the isotopic composition of authigenic calcite abstract authigenic calcite was analyzed for 13 c and 18 o in a 12 m long core from lake turkana that spans the last 4200 yr the 18 o record is interpreted to reflect lake level history and indicates high stands prior to 4000 yr b p from 1800 to 2000 yr b p and within the last century this coincides better with the history of lake level change reported for other lakes in africa than did the previous lake level curve for lake turkana based on 14 c dates of exposed shoreline deposits the 13 c curve roughly parallels the 18 o curve and may reflect the influence of the omo river plume both of the isotope records are strongly cyclic with periodicites common to both at 80 120 150 and 225 yr other somewhat longer periodicites are nearly equal in the two records and there is close agreement with previously published cycles based on carbonate and lamination thickness analyses in the same turkana core

low silica activity for hydrogen generation during serpentinization an example of natural serpentinites in the mineoka ophiolite complex central japan the textural evolution in the serpentinite of the mineoka ophiolite complex has been investigated to constrain the natural environment for hydrogen production in the serpentinite hosted hydrothermal vent systems textural relations of the serpentinites from the mineoka ophiolite indicate at least two stages in the process of serpentinization with the replacement of olivine by a mesh texture of serpentine and brucite followed by the development of magnetite bearing or free serpentine veins the generation of hydrogen during serpentinization which accompanies the formation of magnetite involves a silica depletion reaction as evidenced by the low abundance of serpentine in the magnetite bearing veins and the absence of magnetite in pseudomorphs of orthopyroxene direct evidence for the production of hydrogen and strongly reducing conditions is provided by ch4 and h2 bearing inclusions in relic olivine crystals the production of methane and hydrogen may have provided a suitable environment for microbial activity in hydrothermal vent systems along the seafloor our results indicate that low silica activity plays a key role in the generation of hydrogen during serpentinization and that low silica activity environments are possible in olivine rich rocks such as dunite or during local disequilibrium in other silica poor rocks in the mantle lithosphere

hot spring systems geobiology abiotic and biotic influences on travertine formation at mammoth hot springs yellowstone national park usa multiple abiotic and biotic factors combine in nature to influence the formation of calcium carbonate limestone deposits systems geobiology studies of how micro organisms respond to or sometimes even control the coupled effects of environmental change and mineralization will permit more accurate interpretation of the fossil record of ancient microbial life mammoth hot springs in yellowstone national park usa serves as a natural laboratory for tracking how the dynamic interplay of physical chemical and biological factors come together to form hot spring limestone called travertine systematic downstream correlations occur at mammoth hot springs between travertine deposition geomorphology crystalline structure and geochemistry microbial communities mat morphology pigmentation and phylogenetic and metabolic diversity and spring water conditions temperature ph geochemistry and flow field based microscale and mesoscale experimentation indicates that microbes directly influence travertine growth rate and crystalline structure at the macroscale time lapse field photography and numerical modelling suggest that travertine terrace geomorphology is influenced strongly by hydrology heat dispersion and geochemistry these results from mammoth hot springs allow establishment of a conceptual framework across broad spatial and temporal scales in which to track how multiple geological and biological factors combine to control caco3 crystal precipitation and the resulting formation of travertine deposits

paleo co2 variation trends and the cretaceous greenhouse climate the cretaceous was one of the most remarkable periods in geological history with a greenhouse climate and several important geological events reconstructions of atmospheric co2 using proxies are crucial for understanding the cretaceous greenhouse in this paper we summarize the major approaches for reconstructing co2 based on paleobotanical or geochemical data and synthesize the co2 variations throughout the cretaceous the results show that atmospheric co2 levels remained relatively high throughout the cretaceous but were lower in the early cretaceous highest in the mid cretaceous and gradually declined during the late cretaceous however this overall trend was interrupted by several rapid changes associated with ocean anoxic events oaes and the end cretaceous catastrophic event new data on paleo co2 levels from paleobotanical and paleosol evidences support not only the overall trends indicated by geochemical models but provide more precise records of the short term fluctuations related to brief episodes of climate change temporal resolution within the long quiet magnetic period in the middle cretaceous is one of the obstacles preventing us from a more comprehensive understanding of the co2 climate linkage but new paleo co2 determinations and climatic data from stratigraphic sections of sediments intercalated with datable volcanic rocks will allow a better understanding of the relationships between fluctuations of atmospheric co2 climate change and geological events

facies classification and patterns of lacustrine carbonate deposition of the barra velha formation santos basin brazilian pre salt abstract the lacustrine carbonate rocks of the giant pre salt oil fields in the santos and campos basins differ in a number of important aspects from classic lake deposits prior work has described distinctive and unusual features of deposition early diagenesis and reservoir quality with in these rocks that defy classification using established schemes in addition to their unusual textures debate continues as to how to interpret the vertical stacking pattern of facies a new facies classification scheme is proposed based on the relative abundance of three end member components mud micrite and clay minerals calcite spherulites and fascicular calcite shrubs although focused on the main textural and mineralogical features of the rocks as seen today the proposed scheme takes into account the relative contribution of depositional and early diagenetic components sediment mineralogy and the degree of dissolution application of this scheme offers insight into depositional conditions whilst also linking to reservoir quality basic elementary cycles can be defined using this classification in combination with the variation in the abundance of detrital grains and the chemical composition three possible models are suggested to interpret the origin of the basic cycle within the barra velha formation in the context of variation in climate lake level and water chemistry integration of data from different sources including petrographic core description and chemical data for the basic cycle offers improved process based understanding of metre scale facies patterns and provides a foundation for understanding larger scale vertical variations within and between unconformity bound sequences

sublacustrine precipitation of hydrothermal silica in rift lakes evidence from lake baringo central kenya rift valley abstract many lakes in volcanic regions are fed by hot springs that in some basins can contribute a large percentage of the annual recharge especially during times of aridity it is important to recognize any contemporary hydrothermal contribution in paleoenvironmental reconstruction of lake basins because recharge from thermal waters can potentially confuse paleoclimatic signals preserved in the lacustrine sedimentary record hot spring deposits travertine sinter provide the most tangible evidence for thermal recharge to lakes although subaerial spring deposits have been widely studied lacustrine thermal spring deposits especially sublacustrine siliceous sinters remain poorly known detailed field petrographic and scanning electron microscope sem studies have been made of fossil sublacustrine sinter exposed at soro hot springs along the northeastern shoreline of ol kokwe a volcanic island in lake baringo kenya modern hot springs at soro which discharge na hco3 cl waters from a deep reservoir 180 c have thin 1 10 mm friable microbial silica crusts around their subaerial vents but thicker 1 cm sinter deposits are not forming the fossil sinter which is present as intergranular cements and crusts in littoral conglomerates and sandstones is composed mainly of opaline silica opal a three types of fossil sinter are recognized 1 massive structureless silica which fills intergranular pores and forms crusts up to 5 cm thick 2 pore lining silica some of which is isopachous and 3 laminated silica crusts which formed mainly on the upper surfaces of detrital particles all three types contain well preserved diatoms including lacustrine planktonic forms microbial remains mainly filamentous and coccoid bacteria including cyanobacteria and extracellular polymeric gels are locally abundant in the opaline silica together with detrital clays and thin laminae composed of authigenic chlorite most of the hydrothermal silica precipitated when the thermal springs were submerged by fresh lake water silica precipitated upon rapid cooling of thermal 90 c waters at and just below their interface with the overlying cooler 25 c lake waters microbial mats locally acted as a filter that limited mixing and rapid dilution of the thermal fluids some of the silica originally may have been soft and partly gelatinous planktonic diatoms and detrital clay rained down then became incorporated in the amorphous silica following a fall in lake level the opal a lithified and partly altered to cristobalite opal c and chalcedony the lowest fossil sinters were later encrusted by calcite stromatolites with calcite and quartz forming late pore filling cements the age of the sublacustrine sinters is unknown but some of the deposits could date back to the late pleistocene similar conglomerates cemented by hydrothermal silica are present along fault lines at neighbouring lake bogoria such rocks may provide evidence for deep hot fluid recharge to lakes when encountered in the geological record

seismic characteristics and distribution of hydrothermal vent complexes in the cretaceous offshore rift section of the campos basin offshore brazil abstract hydrothermal vents are structures that occur close to volcanically active areas their occurrence can have considerable impacts on the evaluation of the oil reserves of a basin in the campos basin eastern brazilian continental margin no hydrothermal vents have been previously recognized and related with magmatic events on seismic sections this work aims to map the hydrothemal vents ducts and associated intrusive bodies observed in the rifte section with the use of 2d seismic data and a well with lithologic information the occurrence of ten hydrothermal vents and seven ducts were mapped and the interval with volcanic intrusive rocks was characterized the identification of intrusive rocks in seismic data is given by reflectors with high amplitude and disk or half moon geometry with abrupt endings the vent geometries shows dome and eye shaped types and the ducts are fault related downward tapering cone type this study highlights new geological elements that can influence the petroleum systems of the campos basin such as the identification of hydrothermal vents in seismic sections and the correlation with regional tectono magmatic events

are spherulitic lacustrine carbonates an expression of large scale mineral carbonation a case study from the east kirkton limestone scotland lacustrine carbonate deposits with spherulitic facies are poorly understood but are key to understanding the economically important pre salt mesozoic strata of the south atlantic a major barrier to research into these unique and spectacular facies is the lack of good lacustrine spherulite dominated deposits which are known in outcrop stratigraphy and petrography suggest one of the best analogue systems is found in the carboniferous of scotland the east kirkton limestone here we propose a hydrogeochemical model that explains why the caco3 sio2 mg si al mineral suite associated with spherular radial calcite facies forms in alkaline lakes above basaltic bedrock demonstrating links between igneous bedrock chemistry lake and spring water chemistry and mineral precipitation this model has implications for studies of lacustrine sediments in rift basins of all ages using empirical and theoretical approaches we analyze the relationship between metal mobilization from sub surface volcaniclastic rocks and the potential for precipitation of carbonate minerals various mg bearing minerals and chalcedony in a lacustrine spherulitic carbonate setting this suite of minerals is most likely formed by in gassing of co2 to a carbon limited alkaline spring water consistent with the reaction of alkali igneous rocks in the subsurface with meteoric groundwater we suggest that an analogous system to that at east kirkton caused development of the pre salt spherulitic carbonate deposits

the hydrochemical evolution of alkaline volcanic lakes a model to understand the south atlantic pre salt mineral assemblages abstract understand the origin of the exotic strontium rich calcite magnesium rich clay silica deposits formed during the early cretaceous in the south atlantic pre salt lakes is challenging our ability to comprehend the chemical evolution of alkaline volcanic lakes here we present a new hydrochemical model based on an open basin concept thermodynamic equilibrium and chemical data from lake baringo east african rift to shed light on the mechanisms facilitating carbonate clay silica precipitation this model explores the effects that the leakage to adjacent waterbodies the combination of lake evaporation and lake recharge with river hydrothermal and marine waters and the bathymetric effects of the partial co2 pressure have in the stationary precipitation of pre salt lacustrine mineral assemblages sediment thickness calculations suggest that the facies cyclicity in the pre salt and elsewhere are likely reflecting temporal fluctuations in the type of waters sourcing the lake and in the degree of leakage to aquifers over multiple evaporative freshening cycles a plausible link between enhanced strontium uptake into pre salt calcite allochems and ca2 co32 lake water stoichiometries allows to infer different scenarios for strontium rich calcite formation with or without magnesium clays our conceptual model allows to quantify the role that hydrology groundwater charge discharge to aquifers evaporation exert on carbonate clay silica precipitation providing with a refined framework to understand the basin scale chemical sedimentation in alkaline lakes furthermore this model represents a robust template upon which critically test the superimposed kinetic factors likely attached to the genesis of specific mineral factories such as those encountered in the south atlantic pre salt alkaline lakes

satellite observation of upwelling along the western coast of the south china sea abstract we observed the evolution of upwelling along the western coast of the south china sea scs the data we used are noaa national oceanic and atmospheric administration satellite avhrr advanced very high resolution radiometer ir infrared images taken in 1996 and 1997 summer at the hrpt high resolution picture transmission receiving station built on tai ping island which is located in the central scs an upwelling intensity defined by the total heat loss in the upwelling cold water region is used to determine the relationship between coastal upwelling and the wind stress derived from the ers 2 european remote sensing satellite data the results show that the upwelling intensity has a good linear relationship with the total alongshore wind stress while it has a low correlation with the cross shore component of wind stress these results imply that the alongshore wind stress is the main factor to pump the cold water up to the sea surface layer meanwhile the satellite infrared images also indicate that the centroid of cold water moved southward from 15 n to 11 n during the observation period the size of upwelling area changed as well and finally evolved into a cold jet stretching offshore along 11 n 12 n in the mid august 1997 satellite infrared and altimeteric data show that the evolution of upwelling region is closely associated with the development of two anticyclonic circulations in the western scs

chemistry of springs across the mariana forearc shows progressive devolatilization of the subducting plate abstract cold springs upwelling through large serpentinite mud volcanoes in the outer half of the mariana forearc provide a unique window into processes of devolatilization of the subducting pacific plate we have sampled upwelling pore waters with lower chlorinity than seawater from six sites on five serpentinite mud volcanoes by conventional gravity and piston coring by push coring from the rov jason by drilling on odp legs 125 and 195 and by manned submersible the sites range from 13 47 n to 19 33 n and 52 to 90 km from the mariana trench axis corresponding to approximate depths to the top of the downgoing plate of 16 to 29 km the composition of the springs varies systematically over this distance nearer the trench the upwelling waters have much higher ca and sr than seawater and much lower carbonate alkalinity sulfate na cl k rb and b farther from the trench the waters show the opposite trends relative to seawater chlorinity is consistently lower than in seawater and shows large variations that are not systematic with distance from the trench cs is consistently higher than in seawater and increases with distance from the trench all of the waters have high ph and are heavily depleted in mg si li f and 87sr 86sr relative to seawater they tend to be enriched in o18 o16 except for odp drilling none of the cores was long enough to produce an asymptotic compositional trend with depth we have inferred the end member compositions of the upwelling waters by extrapolation against mg at two sites we were able to compare data from gravity cores with data from drill cores or push cores collected at springs to estimate the effects of reactions that occur at shallow depth below the seafloor on mixing of the upwelling waters with seawater these effects are different for sites high in dissolved ca nearer the trench vs those high in alkalinity farther from the trench common to both are large losses from solution of 1 ca as caco3 and in exchange for na 2 mg in exchange for na or ca and as brucite 3 sulfate probably reduced by microbes or possibly precipitated as gypsum 4 sr ba si and f na is consistently leached from the solids into solution whereas k and o18 o16 are relatively unreactive we infer that the upwelling waters are uniformly saturated with caco3 and that the excess h2o and the trends in ca sr alkalinity and sulfate with distance from the trench result from introduction of h2o and dissolved carbonate and sulfate from an external source the sediment and altered basalt at the top of the subducting plate the concurrent trends in na cl b cs and especially k and rb indicate that these species originate from the top of the subducting plate in response to increasing temperature these systematic variations across the outer forearc imply that the solutions ascend more or less vertically from the source region and do not travel long distances laterally along the decollement before ascending based on leaching of k the 150 c isotherm is crossed approximately beneath big blue seamount at a depth of 22 km below the seafloor 70 km behind the trench by this point it appears that carbonate dissolution has joined dehydration as a significant process at the top of the subducting plate

calcite and aragonite precipitation from seawater solutions of various salinities precipitation rates and overgrowth compositions abstract the reaction rate and composition of calcite and aragonite overgrowths precipitated from seawater solutions of various salinities i e s 5 15 25 35 44 were determined at 25 c and 10 2 5 atm co2 partial pressure using a constant disequilibrium seeded technique the rate data were fitted to an empirical rate law of the form log r n c or a 1 log k where n is the empirical reaction order and k is the rate constant calcite precipitation rates in seawater solutions do not vary appreciably as a result of salinity variations over the range investigated while those for aragonite show an increase in going from the higher i e s 35 44 to the lower i e s 5 15 25 salinity range this study also confirms previously published findings that above a given saturation state i e c 2 6 aragonite precipitates more rapidly than calcite at 25 c the incorporation of sr2 in aragonite and mg2 in calcite overgrowths are independent of the precipitation rate the partition coefficient of sr2 in aragonite is approximately equal to unity and is unaffected by salinity variations between 5 and 44 however the mg2 partition coefficient in calcite increases with decreasing salinity of the parent seawater solutions possibly as a result of variations in the sulfate content of the solutions and solids the experimental results were discussed in the context of a number of geological environments

the effects of wind forcing and background mean currents on the latitudinal structure of equatorial rossby waves abstract the latitudinal structure of annual equatorial rossby waves in the tropical pacific ocean based on sea surface height ssh and thermocline depth observations is equatorially asymmetric which differs from the structure of the linear waves of classical theory that are often presumed to dominate the variability the nature of this asymmetry is such that the northern ssh maximum along 5 5 n is roughly 2 times that of the southern maximum along 6 5 s in addition the observed westward phase speeds are roughly 0 5 times the predicted speed of 90 cm s 1 and are also asymmetric with the northern phase speeds about 25 faster than the southern phase speeds one hypothesized mechanism for the observed annual equatorial rossby wave amplitude asymmetry is modification of the meridional structure by the asymmetric meridional shears associated with the equatorial current system another hypothesis is the asymmetry of the annually varying wind forcing which is stronger north of the equator a reduced g

in situ carbonation of peridotite for co2 storage the rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low temperature alteration can be enhanced to develop a significant sink for atmospheric co2 natural carbonation of peridotite in the samail ophiolite an uplifted slice of oceanic crust and upper mantle in the sultanate of oman is surprisingly rapid carbonate veins in mantle peridotite in oman have an average 14c age of 26 000 years and are not 30 95 million years old as previously believed these data and reconnaissance mapping show that 104 to 105 tons per year of atmospheric co2 are converted to solid carbonate minerals via peridotite weathering in oman peridotite carbonation can be accelerated via drilling hydraulic fracture input of purified co2 at elevated pressure and in particular increased temperature at depth after an initial heating step co2 pumped at 25 or 30 c can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy in situ carbonation of peridotite could consume 1 billion tons of co2 per year in oman alone affording a low cost safe and permanent method to capture and store atmospheric co2

abiotic methane in continental ultramafic rock systems towards a genetic model abstract methane ch4 often in substantial quantities is reported for numerous surface manifestations seeps springs and aquifers in continental serpentinized ultramafic rocks in ophiolites peridotite massifs and intrusions frequently this gas is considered to have a dominant abiotic origin with variable though generally minor components of biotic gas thermogenic or microbial abiotic ch4 production through low temperature fischer tropsch type reactions ftt between a carbon c compound and h2 is endorsed by most of scholars but direct derivation from olivine hydration serpentinization magmatic sources and fluid inclusions have also been suggested here we review the application of ftt in geology discussing the appropriateness of several c compounds co2 co formic acid formate or elemental c as ch4 precursors and of aqueous versus gas phase reactions we examine published gas geochemical and flux data that provide clear constraints on the methane origins in the analysis we add new isotopic and gas seepage data acquired in surface gas manifestations at acquasanta in the voltri ophiolite genova italy multiple lines of evidence including a stable isotope compositions of ch4 co2 and helium b radiocarbon free ch4 c isotopic disequilibrium between ch4 and h2o d low temperatures of ch4 production based on clumped isotopes and heat flow data and e methane seepage forms and intensities suggest that ch4 is not formed directly in water or from magmatic sources or fluid inclusions rather all the lines of evidence taken together are compatible with the hypothesis of low temperature

modeling slippery layers in the northern bay of bengal abstract in this study we model a slippery layer observed during september 2011 at a national institute of ocean technology niot mooring deployed at 18 o n 89 o e in the northern bay of bengal bob the mooring was located close to the mouths of the huge rivers draining the indian subcontinent the lateral advection of riverine water masses past the mooring resulted in a shallow brackish layer 10 15 m deep bounded by a strong halocline below giving rise to the possibility of a slippery layer gliding past the layers below the strong currents in this slippery layer were simulated by a simple slab type dynamical model in addition a second moment turbulence closure based model driven by surface data from the buoy was also used to simulate the water mass structure and upper layer currents during the event both the slab and turbulence closure models reproduce currents in the slippery layer reasonably well overall although the currents are somewhat overestimated this haline slippery layer observed in the bob complements well the thermal slippery layers that have been observed under certain conditions during strong diurnal heating of the upper layers of the ocean

linking serpentinization hyperalkaline mineral waters and abiotic methane production in continental peridotites an integrated hydrogeological bio geochemical model from the cabeco de vide ch4 rich aquifer portugal abstract continental active serpentinization of ultramafic rocks is today recognized as a key process triggering a sequence of phenomena involving the passage from inorganic to organic and metabolic reactions these may have a role in the origin of life and may explain the occurrence of abiotic hydrocarbons on earth and other planets production of hyperalkaline waters and abiotic methane ch4 are two critical steps in this sequence they were described independently by specific hydrogeological and geochemical models here we update and combine these models into a unified scheme using and integrating geological hydrogeological hydrogeochemical gas geochemical and microbial analyses acquired from 2002 to 2014 in the cabeco de vide cdv study site portugal the hyperalkaline ph 10 5 na cl ca oh mineral water of cdv evolve from groundwater peridotite interaction serpentinization generating hydrogen h2 which according to multiple theoretical laboratory and field evidence likely reacted with co2 within metal catalyst rich rocks abiotically producing ch4 up to 1 2 mg l 24 4 oo

a numerical model of the atmospheric boundary layer over a marginal ice zone a two dimensional multilevel model for simulating changes in the atmospheric boundary layer across a marginal ice zone is described and applied to off ice on ice and along ice edge wind conditions the model incorporates a second moment closure for parameterizing the intensification and suppression of turbulent mixing in the boundary layer due to stratification effects for off ice winds as the atmospheric boundary layer passes from cold smooth ice onto warm open water the onset of intense convection raises the inversion over the transition zone of rough rafted ice with open leads the shear stress on the ice cover increases significantly before dropping down to the downstream values over water such nonmonotonic surface stress could be the cause of divergence of sea ice near the ice edge in a marginal ice zone these results are in agreement with the one layer model simulations of off ice winds by overland et al 1983 for on ice wind conditions as the warm flow in the boundary layer encounters the cold ice conditions the resulting stable stratification could rapidly suppress the turbulence in the boundary layer leading to the development of a shallow inversion and an associated jet when the wind is predominantly along the ice edge the temperature contrast between the open water and the ice could produce a thermal front at the ice edge in the boundary layer with strong associated turbulence more observations are needed to verify these model predictions nevertheless these model results suggest that it is important to account for the changes in the characteristics of the atmospheric boundary layer across the marginal ice zone in our attempts to understand the behavior of the ice cover in these regions

serpentinized troctolites exposed near the kairei hydrothermal field central indian ridge insights into the origin of the kairei hydrothermal fluid supporting a unique microbial ecosystem the vent fluids of the kairei hydrothermal field khf on the central indian ridge near the rodriguez triple junction are atypical they have a very high h2 concentration a relatively high si concentration and a remarkably low ch4 h2 ratio recently particular attention has been paid to the khf because the hydrothermal fluids are suggested to support a hydrogen based hyperthermophilic subsurface lithoautotrophic microbial ecosystem hyperslime which is considered to be a likely modern analogue for the early earth ecosystems prior to photosynthesis despite the increasing interest in the fluid chemistry and associated biota the origin of the unusual chemistry of the hydrothermal fluids is still uncertain here we suggest interaction of seawater with troctolite recently discovered from small hills near the khf provide a possible explanation for the composition of the khf fluids dives with the manned submersible shinkai 6500 recovered plagioclase dunite troctolites and olivine gabbros which generally constitute the lower oceanic crust microscopic observations revealed that olivine crystals in the samples were partly to completely replaced by serpentine and magnetite indicating the generation of h2 by serpentinization reactions between olivine and hydrothermal fluids theoretical model calculations predict that the high h2 and high si concentrations of the hydrothermal fluids can be attributed to serpentinization of the troctolites and subsequent hydrothermal reactions with basaltic wall rocks under the khf the unique geological setting of the kairei hydrothermal system where deep crustal rocks are emplaced in the shallower part of oceanic crust is considered to be responsible for the unusual chemistry of the kairei hydrothermal fluids driving the occurrence of the hyperslime

human evolution in a variable environment the amplifier lakes of eastern africa abstract the development of the cenozoic east african rift system ears profoundly re shaped the landscape and significantly increased the amplitude of short term environmental response to climate variation in particular the development of amplifier lakes in rift basins after three million years ago significantly contributed to the exceptional sensitivity of east africa to climate change compared to elsewhere on the african continent amplifier lakes are characterized by tectonically formed graben morphologies in combination with an extreme contrast between high precipitation in the elevated parts of the catchment and high evaporation in the lake area such amplifier lakes respond rapidly to moderate precessional forced climate shifts and as they do so apply dramatic environmental pressure to the biosphere rift basins when either extremely dry or lake filled form important barriers for migration mixing and competition of different populations of animals and hominins amplifier lakes link long term high amplitude tectonic processes and short term environmental fluctuations east africa may have become the place where early humans evolved as a consequence of this strong link between different time scales

shallow submarine seep of abiotic methane from serpentinized peridotite off the island of elba italy abstract abiotic methane ch4 is today widely reported in gas seeps and hyperalkaline springs in ophiolites and peridotite massifs characterized by low temperature continental serpentinization origin and distribution of this gas have far reaching implications in microbiology astrobiology and carbon cycle we report an in depth study of a recently described abiotic ch4 seep occurring in shallow seafloor along the western coast of elba island tyrrhenian sea italy the gas is characterized by stable c and h isotopic compositions of ch4 13c 18 2h 141 and a very low co2 content that are typical of abiotic gas in continental ultramafic rock systems based on local geothermal gradients the temperature of methane production is estimated to be below 100 c the isotope signature of methane is similar to that occurring in the liguria region about 200 km north of elba island where the same ophiolite unit exposed a mantle co2 component suggested by relatively high 3he 4he ratios has likely acted as ch4 precursor the reconstruction of the geological structural setting of elba ophiolite sequence highlighted that the seep occurs in correspondence with a faulted reverse limb of the antiform of the ophiolite unit the gas bearing fault forms a contact between mafic and ultramafic serpentinized rocks as typically observed in other continental seeps and springs related to ophiolites magmatic intrusions in the island may have contributed to the c feedstock of methane

origins of high ph mineral waters from ultramafic rocks central portugal abstract this paper reviews the geochemical isotopic 2h 18o 13c 3h and 14c and numerical modelling approaches to evaluate possible geological sources of the high ph 11 5 na cl ca oh mineral waters from the cabeco de vide region central portugal water rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the cabeco de vide mineral waters which was corroborated by numerical modelling approaches the local shallow groundwaters belong to the mg hco3 type and are derived by interaction with the local serpentinized rocks at depth these type waters evolve into the high ph na cl ca oh mineral waters of cabeco de vide spas issuing from the intrusive contact between mafic ultramafic rocks and an older carbonate sequence the cabeco de vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization magnesium silicate phases brucite and serpentine seem to control mg concentrations in cabeco de vide mineral waters similar 2h and 18o suggest a common meteoric origin and that the mg hco3 type waters have evolved towards cabeco de vide mineral waters the reaction path simulations show that the progressive evolution of the ca hco3 to mg hco3 waters can be attributed to the interaction of meteoric waters with serpentinites the sequential dissolution at co2 g closed system conditions leads to the precipitation of calcite magnesite amorphous silica chrysotile and brucite indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks dunites present at depth the apparent age of cabeco de vide mineral waters was determined as 2790 40 a bp on the basis of 14c and 13c values which is in agreement with the 3h concentrations being below the detection limit

sedimentation in lake malawi east africa during the past 10 000 years a continuous paleoclimatic record from the southern tropics a suite of piston cores recovered from lake malawi 9 14 s 34 35 e east africa in 1986 has been analyzed for major and minor elements organic c and n calcium carbonate and diatoms an internally consistent stratigraphy was constructed from calcium carbonate abundance and variations in the two most abundant diatom genera stephanodiscus and melosira with age control obtained primarily from 14c dating of the carbonate differences with time in fe abundance in a transect of cores from different water depths have been interpreted to reflect changes in chemocline depth the depth to the chemocline was on the order of 100 m shallower than present prior to 3500 yr b p indicating less seasonality carbonate production and preservation appears to be related to climatically induced changes in both salinity and chemical distributions in the water column the carbonate which precipitates from surface waters is most abundant during the interval from about 10 000 to 6000 yr b p this micrite most likely represents periods of low lake level when salinity increased and carbonate precipitation was enhanced sedimentary evidence suggests that lake levels were 100 150 m lower than present during this period this record is different from climatic trends in northern intertropical africa but appears to also be related to changes in insolation and monsoon circulation this is the northernmost basin in africa reported to exhibit a southern hemisphere response to the early holocene northern hemisphere summer insolation maximum the climatic hingeline north of lake malawi 9 s implied by our results is significantly south of that indicated by general circulation model simulations however the cores show evidence for periods of abrupt climate change during the interval of generally arid climate

iron partitioning and hydrogen generation during serpentinization of abyssal peridotites from 15 n on the mid atlantic ridge aqueous dihydrogen h2 aq is produced in copious amounts when seawater interacts with peridotite and h2o oxidizes ferrous iron in olivine to ferric iron in secondary magnetite and serpentine poorly understood in this process is the partitioning of iron and its oxidation state in serpentine although both impose an important control on dihydrogen production we present results of detailed petrographic mineral chemical magnetic and mosbauer analyses of partially to fully serpentinized peridotites from the ocean drilling program odp leg 209 mid atlantic ridge mar 15 n area these results are used to constrain the fate of iron during serpentinization and are compared with phase equilibria considerations and peridotite seawater reaction path models in samples from hole 1274a mesh rims reveal a distinct in to out zoning from brucite at the interface with primary olivine followed by a zone of serpentine brucite magnetite and finally serpentine magnetite in the outermost mesh rim the compositions of coexisting serpentine mg 95 and brucite mg 80 vary little throughout the core about 30 50 of the iron in serpentine brucite mesh rims is trivalent irrespective of subbasement depth and protolith harzburgite versus dunite model calculations suggest that both partitioning and oxidation state of iron are very sensitive to temperature and water to rock ratio during serpentinization at temperatures above 330 c the dissolution of olivine and coeval formation of serpentine magnetite and dihydrogen depends on the availability of an external silica source at these temperatures the extent of olivine serpentinization is insufficient to produce much hydrogen hence conditions are not reducing enough to form awaruite at t 330 c hydrogen generation is facilitated by the formation of brucite as dissolution of olivine to form serpentine magnetite and brucite requires no addition of silica the model calculations suggest that the iron distribution observed in serpentine and brucite is consistent with formation temperatures ranging from 150 to 250 c and bulk water to rock ratios between 0 1 and 5 these conditions coincide with peak hydrogen fugacities during serpentinization and are conducive to awaruite formation during main stage serpentinization the development of the common brucite rims around olivine is either due to an arrested reaction olivine brucite serpentine brucite or reflects metastable olivine brucite equilibria developing in the strong gradient in silica activity between orthopyroxene talc serpentine and olivine serpentine brucite

synmagmatic normal faulting in the lower oceanic crust evidence from the oman ophiolite structural and petrological study of the oman ophiolite shows that normal faults at oceanic spreading centers can root in incompletely crystallized cumulates and form at the same time as melt is being supplied to the magma chamber in the vicinity 200 m of a ridge facing normal fault located a couple of kilometers off a former axial mantle diapir blocks of layered cumulates were tilted at high angles relative to the moho block rotation was accommodated by a swarm of anastomosed fault planes connected to the main fault these planes are underlain by screens of gabbroic micropegmatites former melt layers and by ptygmatic folds pointing to viscous deformation of a compacting crystal mush flat lying undeformed cumulate layers from the same parent melts as the deformed ones settled directly over the tilted blocks water introduction into the melt is evidenced by the crystallization of anomalously high anorthite an 90 95 cumulus plagioclase regardless of the degree of evolution of the magma shearing continued at subsolidus temperatures along some but not all fault planes attested to by the local development of plastic deformation structures the subsolidus development of amphibole spinel coronas around olivine grains points to pervasive percolation of high temperature hydrothermal fluids through the cumulates as the crust cooled further water penetration progressively focused within the main fault zone where the crust was fractured and eventually altered in greenschist facies conditions

travertines associated with hyperalkaline springs evaluation as a proxy for paleoenvironmental conditions and sequestration of atmospheric co2 abstract travertine are found in ophiolite massifs in association with bicarbonate depleted hyperalkaline spring waters ph up to 11 9 in contrast with most continental carbonates e g travertine tufa speleothems that precipitate from calcium bicarbonate enriched waters here travertines formed from bicarbonate depleted hyperalkaline spring water were subjected to a multidisciplinary and multi scale approach to evaluate their potential as proxies of past climatic records and sequestration of atmospheric co 2 two mechanisms of calcium carbonate precipitation were apparent 1 hydration hydroxylation reaction due to the mixing of hyperalkaline and surface runoff waters or 2 dissolution of atmospheric co 2 g into hyperalkaline waters for two sites the bulk chemical signature of travertines mg ca and sr wt are consistent with prior calcite precipitation pcp processes and thus likely records the environmental conditions at the time of their formation however for the third site the trace element concentrations in the various carbonate fabrics indicate some recrystallization constant 18 o values indicate that hydration and hydroxylation reactions completely buffer the oxygen isotope composition of the water equilibrium state from which a paleo temperature can be estimated in contrast 13 c values reflect potential carbon sources either from surface runoff waters or atmospheric co 2 within the framework of continental carbonate calcium carbonate formation in bicarbonate depleted hyperalkaline environments results in a linear and positive co variation of 18 o and 13 c values and defines a unique and distinctive stable isotope field on a 18 o 13 c plot in contrast to carbonates formed in more typical bicarbonate enriched environments moreover the combined variations in 18 o 13 c and 87 sr 86 sr between laminae document the changes in the paleo activity of hyperalkaline spring and surface runoff waters on the time scale of formation the 87 sr 86 sr ratio represents a tracer for quantifying surface runoff water contribution furthermore the amount of co 2 sequestrated in travertine has been estimated following different scenarios of formation the calculated co 2 sequestrated for these deposits ranges from 9 kgco 2 yr 1 to 522 kgco 2 yr 1

springs and streams of the taro ceno valleys northern apennine italy reaction path modeling of waters interacting with serpentinized ultramafic rocks article i nfo in the area of the taro ceno valleys northern apennine emilia romagna region italy waters of meteoric origin interact with ophiolite rocks of the external ligurides fresh water springs issuing from basalts have a ca hco3 composition whereas freshwater springs from ultramafites vary in composition from ca hco3 or mg hco3 to na oh or na so4 types and in ph values from 7 3 8 8 up to ph 11 respectively in addition the boron content of the alkaline waters is up to 13 mg l which is unusually high for freshwaters in general and ultramafites that have undergone oceanic serpentinisation in particular and gives a boric alkalinity to the waters the springs waters show evidence of recent low temperature continental serpentinisation and the process is modeled by reaction paths using an updated geochemical thermodynamic database consistent with the local primary and secondary serpentinite paragenesis for the model bicarbonate waters evolve to alkaline waters supersaturated in ca mg carbonate based on the assumption that the dissolution of serpentinite results in supersaturation with respect to kaolinite ferrihydrite vermiculite fe 2 mg 2 saponite and poorly crystalline serpentine the alkaline composition and the chloride content of the waters suggest a prolonged interaction with the rocks at depth that led to dissolution of albite and leaching of olivine hosted fluid inclusions a similar evolution is also proposed for the more developed springs issuing from the ultramafic rocks of the voltri group liguria region where solutions are supersaturated in brucite and are in equilibrium with enstatite and or chlorite

mineralogical assemblages forming at hyperalkaline warm springs hosted on ultramafic rocks a case study of oman and ligurian ophiolites 1 we report on the mineralogical assemblages found in the hyperalkaline springs hosted on liguria and oman ophiolites based on exhaustive x ray diffraction and scanning electron microprobe analyses in liguria hyperalkaline springs produce a thin brownish calcite precipitate that covers the bedrock due to the concomitant atmospheric co2 uptake and neutralization of the hyperalkaline waters no brucite and portlandite minerals are observed the discharge of alkaline waters in oman ophiolite forms white orange precipitates calcium carbonate minerals calcite and or aragonite are the most abundant and ubiquitous precipitates and are produced by the same mechanism as in liguria this process is observed as a thin surface crust made of rhombohedral calcite morphological features of aragonite vary from needle bouquet dumbbell spheroidal like habitus according to the origin of carbon temperature and ionic composition of the hyperalkaline springs and the biochemical and organic compounds brucite is observed both at hyperalkaline springs located at the thrust plane and at the paleo moho the varying mixing proportions between the surface runoff waters and the hyperalkaline ones control brucite precipitation the layered double hydroxide minerals occur solely in the vicinity of hyperalkaline springs emerging within the bedded gabbros finally the dominant mineralogical associations we found in oman ca bearing carbonates and brucite in a serpentinizing environment driven by the meteoric waters are surprisingly the same as those observed at the lost city hydrothermal site in a totally marine environment

diagenetic pathways linked to labile mg clays in lacustrine carbonate reservoirs a model for the origin of secondary porosity in the cretaceous pre salt barra velha formation offshore brazil

flux and dispersion of gases from the drachenschlund hydrothermal vent at 8 18 s 13 30 w on the mid atlantic ridge hydrothermal emission of mantle helium appears to be directly related to magma production rate but other processes can generate methane and hydrogen on mid ocean ridges in an on going effort to characterize these processes in the south atlantic the flux and distribution of these gases were investigated in the vicinity of a powerful black smoker recently discovered at 8 17 9 s 13 30 4 w the vent lies on the shoulder of an oblique offset in the mid atlantic ridge and discharges high concentrations of methane and hydrogen measurements during expeditions in 2004 and 2006 show that the ratio of ch4 to 3he in the neutrally buoyant plume is quite high 4 108 the ctd stations were accompanied by velocity measurements with lowered acoustic doppler current profilers ladcp and from these data we estimate the methane transport to have been 0 5 mol s 1 in a wsw trending plume that seems to develop during the ebb tidal phase this transport is an order of magnitude greater than the source of ch4 calculated from its concentration in the vent fluid and the rise height of the plume from this range of methane fluxes the source of 3he is estimated to be between 0 14 and 1 2 nmol s 1 in either case the 3he source is significantly lower than expected from the spreading rate of the mid atlantic ridge from the inventory of methane in the rift valley adjacent to the vent it appears that the average specific rate of oxidation is 2 6 to 23 yr 1 corresponding to a turnover time between 140 and 16 days vertical profiles of methane in the surrounding region often exhibited gaussian like distributions and the variances appear to increase with distance from the vent using a gaussian plume model we obtained a range of vertical eddy diffusivities between 0 009 and 0 08 m2m2 s 1 these high values may be due to tidally driven internal waves across the promontory on which the vent is located

the chemical and hydrological evolution of an ancient potash forming evaporite basin as constrained by mineral sequence fluid inclusion composition and numerical simulation the chemical evolution of the brine in a potash evaporite basin has been investigated by x ray microanalysis of frozen primary inclusions trapped in halite a computer program based on thermodynamic equilibrium and mass balance principles has been used to simulate evaporation paths the comparison between the results of calculations the observed mineralogy and mineral sequence and the solute content in fluid inclusions has placed constraints on the hydrological evolution of the basin the upper eocene basin of navarra southern pyrenees spain began as a marine basin evolving from a moderate to a high degree of restriction depositing first a basai anhydrite horizon and then a thick sequence of massive halite an additional inflow of cacl2 in the basin during seawater evaporation is proposed as the process responsible for the sulfate depletion required for sylvite instead of mg sulfates to form mixing of seawater with continental waters bacterial sulfate reduction and in situ dolomitization are discarded the basin subsequently closed to the sea and evolved with decreasing volume alternating bands of clays halite sylvite and then clays halite carnallite were deposited under the influence of seasonal continental recharge before reaching total desiccation the residual brine was diluted by continental water the basin then evolved under an endoreic regime where continental recharge and the recycling of previously formed halite led to deposition of alternating beds of clays and halite

palaeohydrology of the lower cretaceous pre salt lacustrine system from rift to post rift phase santos basin brazil abstract large oil accumulation discoveries in the last decade in the pre salt rock succession off the brazilian coast aroused renewed interest in carbonate reservoirs prompting several studies aiming at unravelling the conditions of formation of these rocks despite that there are still many gaps in the knowledge concerning environmental conditions of the deposition of the pre salt carbonates of santos basin located at the southeastern brazilian margin in this study we present and discuss a new suite of geochemical and biostratigraphic data of the lacustrine rift to post rift succession broadly correlated with itapema and barra velha formations of the santos basin whose deposition occurred in the aptian the integration of the petrographic biostratigraphic and geochemical data serves the ultimate purpose of the study which is to apply the new radiogenic strontium data as a proxy for the reconstruction of the evolution of the lake hydrology associated with the deposition of the carbonates of the itapema and barra velha formations these data are integrated into numerical models whose results bring new ideas on the general hydrologic conditions of the lake system and on its evolution through time the mass balance calculations indicate that two end members alone can account as potential sources of sr to the palaeolake a mafic and a felsic component respectively the latter likely contributed with significantly higher fluxes roughly one to two and up to four orders of magnitude higher than the former end member for most of the depositional history in order to generate the 87sr 86sr trends observed in the carbonate rocks finally the results obtained from the integration of the observations with the numerical models point to decreasing fluxes of water with time as contributed from both sources suggesting that the formation of the deposits became very likely constrained to progressively more evaporitic and alkaline lake waters these results also open up a new window into the environmental conditions of the interior gondwana continent immediately prior to the definitive opening of the south atlantic ocean

fe ni co o s phase relations in peridotite seawater interactions serpentinization of abyssal peridotites is known to produce extremely reducing conditions as a result of dihydrogen h2 aq release upon oxidation of ferrous iron in primary phases to ferric iron in secondary minerals by h2o we have compiled and evaluated thermodynamic data for fe ni co o s phases and computed phase relations in fo2 g fs2 g and ah2 aq ah2s aq diagrams for temperatures between 150 and 4008c at 50 mpa we use the relations and compositions of fe ni co o s phases to trace changes in oxygen and sulfur fugacities during progressive serpentinization and steatitization of peridotites from the mid atlantic ridge in the 15820 0 n fracture zone area ocean drilling program leg 209 petrographic observations suggest a systematic change from awaruite magnetite pentlandite and heazlewoodite magnetite pentlandite assemblages forming in the early stages of serpentinization to millerite pyrite polydymite dominated assemblages in steatized rocks awaruite is observed in all brucite bearing partly serpentinized rocks apparently buffering of silica activities to low values by the presence of brucite facilitates the formation of large amounts of hydrogen which leads to the formation of awaruite associated with the prominent desulfurization of pentlandite sulfide is removed from the rock during the initial stage of serpentinization in contrast steatitization indicates increased silica activities and that highsulfur fugacity sulfides such as polydymite and pyrite vaesite solid solution form as the reducing capacity of the peridotite is exhausted and h2 activities drop under these conditions sulfides will not desulfurize but precipitate and the sulfur content of the rock increases the co evolution of fo2 g fs2 g in the system follows an isopotential of h2s aq indicating that h2s in vent fluids is buffered in contrast h2 in vent fluids is not buffered by fe ni co o s phases which merely monitor the evolution of h2 activities in the fluids in the course of progressive rock alteration the co occurrence of pentlandite awaruite magnetite indicates h2 aq activities in the interacting fluids near the stability limit of water the presence of a hydrogen gas phase would add to the catalyzing capacity of awaruite and would facilitate the abiotic formation of organic compounds

acceleration creation and depletion of wind driven baroclinic rossby waves over an ocean ridge the influences of topography on the propagation spatial patterns and amplitude variations of long baroclinic rossby waves are investigated with a wind forced two layer model above a midocean ridge with steep topography the evolution equation for the baroclinic mode is shown to differ from that for a flat bottom in several ways 1 the phase speed is systematically faster by the factor h h2 where h is the total ocean depth and h2 is the lower layer thickness though the propagation remains westward and nearly nondispersive 2 an effectively dissipative transfer to the barotropic mode occurs whenever the baroclinic mode is locally parallel to f h contours where f is the coriolis frequency and 3 the wind forced response is amplified in proportion to the topographic steepness f h dh dx df dy for a longitudinally varying topography which can be a large factor but the amplification is only by the modest factor h h2 for a latitudinally varying topography effects 2 and 3 are the result of energy exchanges to and from the barotropic mode respectively effect 3 causes freely propagating baroclinic rossby waves to be generated west of the ridge these effects collectively cause distortions of the baroclinic wave pattern as it traverses the ridge these effects account qualitatively for several features seen in altimetric measurements in the vicinity of major topographic features an increase in variance of baroclinic signals on the west side an enhanced phase speed overall compared to flat bottom waves and an abrupt change in the phase speed at midocean ridges

the effects of shear flow on propagation of rossby waves in the equatorial oceans abstract the effects of strong meridional shear of mean flow on propagation of long waves having a wavelength of about 1000 km and period of 25 days observed in the equatorial pacific and atlantic oceans are analyzed in this paper information from the weekly multichannel sea surface temperature images derived from the advanced very high resolution radiometer on board the noaa series satellites from january 1986 to march 1992 is used for the statistics of the visual parameters of the waves the characteristic scales of the waves are estimated based on the results by previous investigators and the statistical results of the present study solving a potential vorticity equation the authors obtain a dispersion relation with an additional term depending on the flow shear strength compared with that of the free rossby wave the theoretical model provides a good explanation for the variable behavior of long wave propagation

geochemical evolution of closed basin lakes general model and application to lakes qinghai and turkana in contrast to most previous models for the evolution of closed basin lakes we present an integrated model which considers various water budget patterns clay regradation so4 reduction and subbottom leakage in addition to the classical equilibrium approach of mineral precipitation the model was applied to lakes qinghai and turkana which significantly differ in the lithologies of their drainage areas but are representative of the carbonate rich sedimentary rock province of the tibet qinghai plateau and the silicate rock province of eastern africa both lakes are now topographically closed but to some degree hydrologically open subbottom leakage major results of the mode calculations show that the lithology controls the ultimate brine which is of na k cl type for qinghai lake and of na hco3 cl type for lake turkana so4 reduction delays the onset of sulfatic mineral precipitation and favours the formation of na carbonates such as trona at the expense of calcite clay mineral regradation plays an important role before the saturation of sulfatic or chlorine minerals is reached in particular magnesite formation may be in competition with mg bearing clay minerals finally simulations with various hydrological scenarios have shown that the modern hydrochemistry of both lakes cannot be reproduced by simply evaporating inflow water but reflects long term accumulation and evolution of solutes by continuous inflow over several thousand years the diversity of lake water composition within a uniform lithological province can thus be largely ascribed to varying hydrological conditions

control of the products of serpentinization by the fe2 mg 1 exchange potential of olivine and orthopyroxene it is argued that the high mg content mg number1 4 95 3 of the serpentine minerals in serpentinized peridotite is a consequence of the environmental femg 1 exchange potential imposed on the system by the abundance of olivine and orthopyroxene mass balance in the serpentinization reaction then requires the precipitation of an ironrich mineral that in most cases is magnetite this causes hydrogen to be evolved in an oxygen conserved reaction the low variance mineral assemblage ol srp brc mag sets the chemical potentials of h2o sio2 and o2 internally at an early stage in the process but the paragenetic assessment of serpentinites is rendered difficult by the variable and usually unknown fe3 content of the serpentine minerals particularly lizardite whole rock analyses of highly to completely serpentinized peridotites reveal fe sfe ratios40 4 with an average value 0 69 similar to that of magnetite 0 67 this feature may be attributed to the presence of high fe lizardite as has been found in mo ssbauer spectroscopy studies electron microprobe and scanning electron microcope analyses in the literature exhibit element trends e g decreasing si vs sfe a p f u for olivinepseudomorph lizardite and with some exceptions for bastite lizardite that show a substitution of the cronstedtite component fe charge balanced ontand m sites cronstedtite substitution will be favoured at low temperature and or low hydrogen fugacity and in these circumstances less magnetite will be evolved during serpentinization in some cases none at all some bastite lizardites from sea floor settings show evidence of m site vacancy substitution of fe for fe in the course of progressive serpentinization micrometer to millimeter scale variations in sio2 potential may well be present but their influence on fe in lizardite seems to be limited to a few cases of lizardite associated with orthopyroxene chrysotile is on average more mg rich and less variable in fe mg ratio than lizardite facts that may be attributed to the greater fe content of lizardite chrysotile veins provide the best record available to us of the environmental femg 1 exchange potential in the pore fluid attending serpentinization this potential serves as a robust control on serpentine and brucite compositions although it may fail after olivine and orthopyroxene have been armoured or eliminated and in more open system environments high water rock ratio such as on the sea floor or at serpentinite host rock contacts the default assumption in microprobe analyses that measured iron is all fe can lead to inappropriate petrological conclusions in the case of serpentinites

a depositional model for spherulitic carbonates associated with alkaline volcanic lakes the south atlantic aptian pre salt reservoirs are formed by a combination of spherulitic carbonates and mg rich clays accumulated in volcanic alkaline lake settings with exotic chemistries so far outcrop analogues characterised by metre thick successions deposited in lacustrine scenarios are elusive so disentangling the genesis of spherulitic carbonates represents a major scientific challenge with business impact in particular the controls on spatial distribution and the environment of spherulitic facies formation remain poorly constrained little studied and hotly debated to shed light on this conundrum a spherulitic carbonate rich alkaline volcanic lacustrine succession has been analysed at outcrop scale the carboniferous east kirkton limestone scotland despite clays being very scarce and limited to layers of amorphous mg si minerals a diverse array of spherulitic calcitic components were formed including coated grains crusts and build ups this setting enables the mechanisms of spherulitic calcite development and the patterns of sediment accumulation to be explored in a geobiological and hydrochemical scenario similar to the pre salt subsurface occurrences but divorced from clay influence the integration of logs borehole data outcrop photomosaics and petrographic observations collectively allowed the reconstruction of a depositional model for the east kirkton lacustrine succession in this model calcite spherule nucleation took place at the sediment water interface in the littoral zone driven by the co occurrence of 1 high alkalinity 2 ca mg rich hydrochemistry and 3 microbial derived colloidal exopolymeric substances these environmental conditions permitted the coeval development of spherulitic cementstone build ups and spherulitic grainstone packstone within the wave agitated zone and the accumulation of floatstones and laminites of spherulitic grains in deeper lake regions by means of downslope reworking this model is consistent with the previously documented microbial bloom occurrences and highlights the need to better understand the complex microbe solution interactions before any reliable facies model is envisaged

diversity and origin of quartz cements in continental carbonates example from the lower cretaceous rift deposits of the south atlantic margin abstract silica precipitation in continental carbonates is a common process occurring during sedimentation and diagenesis the lower cretaceous rift deposits of the south atlantic equatorial margin which are intensively explored by petroleum companies provide good examples of such silicifications in carbonates exhibiting a wide diversity of petrographic habit of early to late quartz cements in order to understand the palaeoenvironmental and diagenetic conditions leading to this diversity we integrated detailed petrography of diagenetic sequences and quartz habit with 18oquartz measurements by sims of individual cements observed in samples from the offshore and onshore basins of the west african margin the petrographic description highlights the omnipresence of early fibrous microquartz cements exhibiting either length fast or length slow habit in addition to laminated microquartz and micro or mega quartz forms amongst the isotopic analysis the 18oquartz data show that length slow cements are generally strongly enriched in 18o 18oquartz ranging from 31 to 37 smow whereas length fast forms show less elevated values 25 c and

sulfur isotopic profile through the oceanic crust sulfur mobility and seawater crustal sulfur exchange during hydrothermal alteration measurements of the abundance of anhydrite and pyrite veins and the distribution of alteration types in oceanic basement enable estimates of global mass and isotopic fluxes of sulfur during hydrothermal alteration of oceanic crust fluxes of 2 5 10 12 g yr s 34 s 2 7 from the volcanic section to seawater and 2 1 10 12 g yr of seawater s 21 into the crust result in an insignificant change in the s content of altered ocean crust these are clearly second order fluxes compared to the riverine input of s to the oceans and the output of sedimentary pyrite most of the anhydrite that forms in the high temperature axial convection cell must later be dissolved at lower temperatures during off axis circulation the mean 34 s of altered oceanic basement is 0 9 only slightly changed from the primary value of 0 1 unless s is preferentially mobilized from 34 s rich sulfide deposits or mineralized zones subduction of altered basaltic crust is unlikely to be the source of high 34 s values of arc volcanic rocks 4 but could contribute to isotopic heterogeneities of s in the mantle

equatorially trapped rossby waves in the presence of meridionally sheared baroclinic flow in the pacific ocean topex poseidon altimeter data are analyzed for the 8 5 year period november 1992 to may 2001 to investigate the sea surface height ssh and geostrophic velocity signatures of quasi annual equatorially trapped rossby waves in the pacific the latitudinal structures of ssh and both components of geostrophic velocity are found to be asymmetric about the equator across the entire pacific with larger amplitude north of the equator the westward phase speeds are estimated by several different methods to be in the range 0 5 0 6 m s 1 these observed characteristics are inconsistent with the classical theory for first vertical first meridional mode equatorially trapped rossby waves which predicts a phase speed of about 0 9 m s 1 with latitudinally symmetric structures of ssh and zonal velocity and antisymmetric structure of meridional velocity the observations are even less consistent with the latitudinal structures of ssh and geostrophic velocity components for other modes of the classical theory the latitudinal asymmetries deduced here have also been consistently observed in past analyses of subsurface thermal data and altimeter data and have been variously attributed to sampling errors in the observational data a superposition of multiple meridional rossby wave modes asymmetric forcing by the wind and forcing by cross equatorial southerly winds in the eastern pacific we propose a different mechanism to account for the observed asymmetric latitudinal structure of low frequency equatorial rossby waves from the free wave solutions of a simple 1 5 layer model it is shown that meridional shears in the mean equatorial current system significantly alter the potential vorticity gradient in the central and eastern tropical pacific the observed asymmetric structures of sea surface height and geostrophic velocity components are found to be a natural consequence of the shear modification of the potential vorticity gradient the mean currents also reduce the predicted westward phase speed of first meridional mode rossby waves improving consistency with the observations

hydrogen generation from mantle source rocks in oman hydrogen gas associated with ca2 oh rich alkaline groundwaters ph 10 12 is at present emanating from ultramafic rocks of the oman ophiolite isotopic and chemical evidence indicates that hydrogen is formed by low temperature redox reactions in a closed groundwater environment this is normally a cryptic process in the hydrosphere but is fortuitously revealed by the unusual hydrogeological conditions in oman where atmospheric oxygen is totally assimilated it is suggested that hydrogen generation in mantle source rocks at depth and in the early archaean surface environment may be more widespread than has hitherto been realised

paleoclimatic reconstruction in northern oman based on carbonates from hyperalkaline groundwaters abstract a paleoclimatic reconstruction for the past 35 000 years for northern oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs high ph groundwaters ph up to 11 9 discharge from the mantle sequence of the oman ophiolite as the product of modern low temperature serpentinization under arid climatic conditions hyperalkaline discharge occurs at the surface uptake of atmospheric co 2 precipitates characteristic laminated travertines accompanied by strong kinetic depletion of 13 c and 18 o pluvial climates supporting a shallow bicarbonate groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite replaced roots and stems all such carbonates have modern initial 14 c contents allowing radiocarbon dating and paleoclimatic reconstruction for the late pleistocene and holocene our reconstruction shows a dominantly wet late pleistocene up to 19 000 yr b p when a phase of climatic deterioration began leading to a period of hyperaridity which dominated from ca 16 300 to 13 000 yr b p the early holocene pluvial occurred from 12 500 to ca 6500 yr b p and was followed by renewed climatic deterioration and the current phase of hyperaridity comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the a rub al khali of central saudi arabia and the summer insolation driven monsoon record of east africa and the arabian sea is remarkably good

geochemistry of high ph waters from serpentinites of the gruppo di voltri genova italy and reaction path modeling of co2 sequestration in serpentinite aquifers abstract the large number of geochemical data gathered on the gruppo di voltri springs confirm that progressive interaction of meteoric waters with ultramafic rocks variably affected by serpentinization leads initially to the formation of mg hco3 waters when the system is open to co2 and na hco3 and ca oh type water upon further interaction with the rock under highly reducing closed system conditions with respect to co2 as indicated by 3h data these high ph waters have had long residence times underground in deep aquifers hosted by serpentinitic rocks these waters are the only available evidence of the presence of such deep aquifers high pressure injection of co2 into these deep aquifers was simulated by reaction path modeling results indicate that this is a feasible methodology to reduce the inputs of anthropogenic co2 into the atmosphere serpentinitic rocks have a high capacity for co2 sequestration mainly through formation of carbonate minerals dissolution of serpentinitic rocks and precipitation of magnesite and silica minerals occurs naturally in areas of high terrestrial co2 fluxes such as in southern tuscany corroborating the feasibility of this methodology of co2 sequestration however this process causes a progressive decrease in the porosity of the aquifer at least under closed system conditions these side effects must be carefully evaluated by means of further laboratory tests and field activities

geochemical bioenergetics during low temperature serpentinization an example from the samail ophiolite sultanate of oman abstract various classes of microbial and biomolecular evidence from global studies in marine and continental settings are used to identify a set of reactions that appear to support microbial metabolism during serpentinization of ultramafic rocks geochemical data from serpentinizing ecosystems in the samail ophiolite of oman are used to evaluate the extent of disequilibria that can support this set of microbial metabolisms and to provide a ranking of potential metabolic energy sources in hyperalkaline fluids that are direct products of serpentinization results are used to construct hypotheses for how microbial metabolism may be supported in the subsurface for two cases ecosystems hosted in rocks that have already undergone significant serpentinization and those hosted by deeper active serpentinization processes

geochemistry of high h2 and ch4 vent fluids issuing from ultramafic rocks at the rainbow hydrothermal field 36 14 n mar the flores diving cruise was part of the mast iii amores 1995 1998 program funded by the european union one of the major achievements of the flores cruise was the discovery of the rainbow hydrothermal field hosted in ultramafic rocks south of the amar segment on the mid atlantic ridge mar the rainbow hydrothermal fluids exhibit temperatures of 365 c ph of 2 8 high chlorinity 750 mmol kg and low silica 6 9 mmol kg the uniformity in endmember major minor trace element concentrations and gas contents suggests that all rainbow fluids originate from the same deep source although h2s content is relatively low 1 20 mmol kg all vent fluids show extraordinary high h2 16 mmol kg ch4 2 5 mmol kg and co 5 mol kg endmember concentrations compared to fluids collected from other vent sites along the mar hydrogen represents more than 40 of the total gas volume extracted from the fluids at rainbow h2 production is likely associated with alteration of olivine and orthopyroxene minerals during serpentinization given that exposures of ultramafic rock may be common particularly along slow spreading ridges the production of h2 may have important implications for microbial activity at and beneath the seafloor

unraveling the sequence of serpentinization reactions petrography mineral chemistry and petrophysics of serpentinites from mar 15 n odp leg 209 site 1274 1 the results of detailed textural mineral chemical and petrophysical studies shed new light on the poorly constrained fluid rock reaction pathways during retrograde serpentinization at mid ocean ridges uniformly depleted harzburgites and dunites from the mid atlantic ridge at 15 n show variable extents of static serpentinization they reveal a simple sequence of reactions serpentinization of olivine and development of a typical mesh texture with serpentine brucite mesh rims followed by replacement of olivine mesh centers by serpentine and brucite the serpentine mesh rims on relic olivine are devoid of magnetite conversely domains in the rock that are completely serpentinized show abundant magnetite we propose that low fluid flux serpentinization of olivine to serpentine and ferroan brucite is followed by later stages of serpentinization under more open system conditions and formation of magnetite by the breakdown of ferroan brucite modeling of this sequence of reactions can account for covariations in magnetic susceptibility and grain density of the rocks citation bach w h paulick c j garrido b ildefonse w p meurer and s e humphris 2006 unraveling the sequence of serpentinization reactions petrography mineral chemistry and petrophysics of serpentinites from mar 15 n odp leg 209 site 1274 geophys res lett 33 l13306

mapping of an ophiolite complex by high resolution visible infrared spectrometry the sumail massif of the oman peridotite has been surveyed by the high spectral resolution imager hymap the field measurements have been taken simultaneously to the hymap campaign with a ger 3700 spectrometer to compare the two data sets further calibration and atmospheric correction are made through empirical line corrections a continuum removal by a modified gaussian model on reflectance is then performed for each pixel to minimize atmospheric scattering and shadowing effects classification from spectral distance is established using field observations and comparisons at full spectral resolution to identify peridotite subunits harzburgites and dunites and to distinguish plagioclase wehrlites from gabbros detections of hydrothermal transformations of olivine in serpentines and their alteration in carbonates along fracture networks characterized by narrow spectral signatures validate the classification this demonstrates the utility of the high spectral resolution and the development of appropriate processing methods for geological identifications

borehole observations of fluid flow from south chamorro seamount an active serpentinite mud volcano in the mariana forearc abstract a sealed borehole observatory cork was deployed on south chamorro seamount an active serpentinite mud volcano in the mariana forearc to explore subduction related processes on a non accretionary convergent plate margin formation fluid was overpressured relative to ambient hydrostatic conditions fluid flowed from the borehole at 0 2 l s when the observatory was opened to recover instruments 2 yr after it was installed the chemical composition of the formation fluid is similar to that extrapolated from trends in pore water data collected during ocean drilling program leg 195 when the observatory was established reduced sulfur is present in this highly alkaline ph 12 4 formation fluid indicative of microbial activity at or below the depth of the screened casing 149 202 m below the seafloor discharge from the open borehole continued for 37 days until the observatory was resealed this discharge requires significant permeability at depth 6 10 14 m2 zones of high permeability may be associated with the formation of headwall scarps consistent with numerous slumps on the southeastern flank of the seamount and likely shape a geochemical environment suitable for an active microbial community

lizardite versus antigorite serpentinite magnetite hydrogen and life the serpentinization of peridotite operates according to one or the other or a combination of two end member mechanisms in low temperature environments 50 300 c where lizardite is the predominant serpentine mineral olivine is consumed by reaction with h2o but its composition mg remains unchanged mg rich lizardite magnetite and dihydrogen gas brucite are products of the reaction at higher temperatures 400 600 c rates of mgfe diffusion in olivine are orders of magnitude faster with the result that the growth of mg rich antigorite can be accommodated by a compositional adjustment of olivine eliminating the need to precipitate magnetite and evolve hydrogen this latter end member mechanism probably best reflects the situation in the forearc mantle wedge

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

ultramafic rock carbonation constraints from listvenite core bt1b oman drilling project the occurrence of the quartz carbonate alteration assemblage listvenite in ophiolites indicates that ultramafic rock represents an effective sink for dissolved co2 however the majority of earlier studies of ultramafic rock carbonation had to rely on the surface exposure of reaction textures and field relationships here we present the first observations on ultramafic rock alteration obtained from the 300 m deep bt1b drill hole icdp oman drilling project allowing for a continuous and high resolution investigation hole bt1b recovered continuous drill core intersecting surface alluvium 200 meters of altered ultramafic rock comprising mainly listvenite and minor serpentinite bands at 90 m and 180 m depth and 100 meters of the underlying metamorphic sole textural evidence suggests that the carbonation of fully serpentinized harzburgite commenced by non equilibrium growth of spheroidal carbonate characterized by sectorial zoning resulting from radially oriented low angle boundaries in the serpentinite carbonate spheroids are composed of alternating magnesite cores and dolomite rims whereas texturally similar carbonate in the listvenite is composed of fe rich magnesite cores and ca fe rich magnesite rims the distinct compositions and mineral inclusions indicate that the carbonation extent was controlled by fluid accessibility resulting in the simultaneous formation of limited carbonate in the serpentinite bands and complete carbonation in the listvenite parts of bt1b the presence of euhedral magnesite overgrowing spheroidal carbonate in the listvenite suggests near equilibrium conditions during the final stage of carbonation the carbonate clumped isotope thermometry constrains carbonate crystallization between 50 c and 250 c implying repeated infiltration of reactive fluids during ophiolite uplift and cooling

seawifs observations of upwelling south of madagascar long term variability and interaction with east madagascar current sea viewing wide field of view sensor data from september 1997 to november 2001 were used to observe upwelling south of madagascar from empirical orthogonal function analysis we found that the upwelling is enhanced in austral winter each year except 1999 and in austral summer each year except 2001 current and wind stress are the mechanisms to cause the upwelling the upwelling borders on the east madagascar current in the east and south the movement and deformation of the boundary between the two contain the information of their interaction mechanism of the interaction can be explained by the shear wave propagation theory

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

three dimensional stratigraphic sedimentological forward modeling of an aptian carbonate reservoir deposited during the sag stage in the santos basin brazil abstract stratigraphic sedimentological forward modeling is a useful technique to test the role of parameters that may act in the depositional processes of sedimentary rocks the technique was applied to the santos basin brazil using the software program dionisos to test possible depositional scenarios for an aptian section of a lacustrine carbonate platform developed during the late sag stage uppermost pre salt section of the basin different parameters were tested in a set of numerical simulations with the aim of reproducing the carbonate facies spatial distribution and the overall stratigraphic stacking pattern of the platform as observed in the available well data several models were simulated and four of them are discussed in this paper based on the available descriptive data from 10 wells model 3 is considered to produce the best fit to explain the development of the 100 m thick aptian carbonate platform occurrences of grainstones and stromatolites as proximal and intermediate facies respectively and the overall carbonate stacking pattern thus based on 3d stratigraphic sedimentological forward modeling the best set of environmental conditions able to explain the pattern of carbonate deposition observed in the study area are 1 a slow carbonate depositional rate 0 08 mm y over an interval of 2 4 my which is indicative of a larger microbial contribution and 2 lake level oscillations which were essentially induced by arid climatic conditions these results also enable new perspectives for the application of stratigraphic sedimentological forward modeling as a predictive tool for hydrocarbon exploration in carbonates and for the development of depositional models of other sag carbonate platform settings

presalt stratigraphy and depositional systems in the kwanza basin offshore angola the lower cretaceous presalt section in the kwanza basin contains an excellent petroleum system that includes synrift strata barremian overlain by a sag interval aptian and capped by the loeme salt the upper synrift is generally limestone with widespread mollusk packstones and grainstones coquinas deposited in a fresh to moderately saline alkaline lake the sag interval is characterized by carbonate platforms and silica rich isolated buildups formed in highly evaporated highly alkaline lakes shrubby dendritic microbially influenced boundstones and intraclast spherulite grainstones accumulated in shallow water on platform tops microbial cherts were deposited as organic buildups on large isolated structural highs basinward west of platforms and they apparently formed at low temperatures in very alkaline lake water shrubby boundstones and microbial cherts have vuggy pores that are primary and result in high permeability wackestones and packstones with calcitic grains mainly spherulites in dolomite or argillaceous dolomite were deposited in slightly deeper low energy sag environments in addition clays especially stevensite precipitated out of the silica rich highly alkaline lake waters during sag deposition calcite precipitated on the shallow lake floor with morphologies that ranged from spherulites to shrubs and included a continuum of intermediate forms spherulites probably precipitated just below the sediment water interface spherulites and shrubby calcites are commonly recrystallized spherulites floating in stevensite probably formed in deeper lacustrine environments organic rich mudstones were deposited in even deeper lacustrine environments in synrift and sag intervals and they are likely the source of most hydrocarbons in this system these interpretations are supported by seismic core petrographic and stable isotope data

role of winds in estimation of ocean heat storage anomaly using satellite data 1 the heat storage anomaly of the upper ocean can be estimated using altimeter data based on the thermal dynamics equation in this study we analyzed both nonthermal and thermal steric height measured by altimetry and removed nonthermal steric height from altimeter measurements to calculate the heat storage anomaly from thermal steric height alone in the global oceans but with a focus on the pacific ocean after examining nonthermal steric height salinity waves and wind we believe that wind stress is a major component to the change in sea surface height blended topex poseidon and ers 1 2 altimeter 1 1 sea surface height anomaly from january 1993 to october 2000 were used to calculation of the heat storage anomaly in addition we used expendable bathythermograph xbt data to the global oceans to determine a reference heat storage from which the altimeter estimation of the heat storage was compared the wind stress curls from scatterometer data obtained from january 1993 to october 2000 were used for analyzing the wind effects on sea surface height variation the correlation coefficients between heat storage from altimeter data halt and that from the xbt hxbt are larger than 0 6 in the global oceans except in the regions of 20 n in the eastern pacific the eastern tropical pacific the tropical atlantic and the western tropical indian ocean the root mean square rms of the differences halt hxbt has large values in the gulf stream and the kuroshio extension regions as well as the eastern and western tropical pacific and eastern indian ocean the wind induced sea surface height variation exhibits strong annual and interannual cycles so the empirical orthogonal function eof method was employed to extract the cycles the annual cycle has two modes whereas the interannual cycle is characterized by el nino events wind stress can affect the estimation of the heat storage through mechanisms derived from quasi geostrophic and barotropic theory we calculated the correlation coefficient between the differences halt hxbt and wind stress curl the result shows that el nino southern oscillation enso related wind stress curl anomalies are responsible for estimating discrepancy in the regions west of south and north america and tropical oceans the high correlation suggests that in these regions the barotropic and linear theory is the dynamic mechanism underlying the wind effects on heat storage estimation furthermore we focus on baroclinic signal in sea level resulting from ekman upwelling in the tropical oceans the effect of wind forcing has the most important role in sea level change during the 1997 1998 el nino event for instance the heat storage anomaly q due to the strong coastal upwelling off the west coast of peru closely relates to sea surface temperature sst wind forcing remnant sea level height anomaly after removing the contributions of the heat salt and waves to the sea level height and ekman depth dek however the q in the west coast of america and western pacific warm pool areas did not closely relate to sst wind forcing and dek

sedimentology and petrophysical analysis of pre salt lacustrine carbonate reservoir from the santos basin southeast brazil lacustrine carbonate deposits mark the rift sag sedimentation stage of the so called pre salt section of the campos and santos basins in the southeast brazilian continental shelf these salt sealed carbonate reservoirs form deep water giant and prolific oil fields that are currently responsible for approximately 70 of the brazilian oil and gas production in the santos basin the sag stage carbonates are represented by the aptian barra velha formation characterized by exotic textural and compositional features whose origin development and correlation with petrophysical properties have been broadly discussed in the last decade a geological and petrophysical study has been performed based on core samples plugs and thin sections of a well in the barra velha formation from the eastern santos basin the analyzed core interval was grouped into six depositional facies constituted by the association of five key textural components 1 crystal shrubs 2 calcite spherulites 3 hybrid forms 4 mud grade carbonates and dolomite and 5 intraclasts the relationship between the depositional framework and the poroperm system as evidenced by petrographic image analysis and ct scan data is highly complex the depositional control over porosity is erratic mainly due to the extensive diagenetic and possible hydrothermal overprint dolomite cementation dolomitization pervasive silicification and dissolution processes are the main primary porosity modifiers petrophysical analysis indicates that intraclastic and spherulitic grainstones rudstones affected by matrix dissolution may present the best reservoir properties in certain intervals even surpassing the shrubby framestones which are widely regarded as the best reservoir facies this study seeks to contribute to an emerging body of research about the brazilian pre salt lacustrine carbonates broadening the geological knowledge about these deposit while providing new data to improve hydrocarbon forecast and recovery

lacustrine carbonate reservoirs from early cretaceous rift lakes of western gondwana pre salt coquinas of brazil and west africa abstract barremian aptian lower cretaceous pre salt lacustrine carbonates host large petroleum reservoirs in south atlantic rift basins yet remain poorly studied in part due to the scarcity of lacustrine carbonate reservoirs throughout the geological record this review provides an integrated discussion of the current state of knowledge on the coquina play having been deposited in extensive rift lakes during the early stages of the opening of the south atlantic thick successions of coquina are recorded from the santos to sergipe alagoas basins and the kwanza to gabon basins on the brazilian and west african continental margins respectively coquinas exhibit similarities in depositional processes across the south atlantic however have distinct diagenetic histories and stratigraphic stacking patterns having been deposited in lakes with different geologies climates and water chemistries west african coquinas exhibit depositional characteristics that are indicative of deposition on distally steepened ramps and rimmed platforms and accordingly facies are somewhat different to those in brazilian basins which were deposited on low angle ramps as petroleum exploration continues into ultra deep waters on the brazilian and west african margins accurate facies models will be important for the predictability of carbonate reservoir intervals to this end onshore outcrop in the sergipe alagoas basin has revealed that the molluscan faunas have marine origins suggesting that facies patterns may be more complex than previously considered it is hoped that this review will provide the impetus for further research on the coquinas especially given the presence of poorly studied easily accessible onshore outcrops

methane and hydrogen in hyperalkaline groundwaters of the serpentinized dinaride ophiolite belt bosnia and herzegovina abstract methane ch 4 in continental serpentinized peridotites msp has been documented in numerous hyperalkaline ph 9 springs and gas seeps worldwide with a dominantly abiotic origin msp is often associated with considerable amounts of hydrogen h 2 produced by serpentinization both gases may fuel microbial activity in igneous rocks and may have played roles in the origin of life msp is also a natural ch 4 source for the atmosphere not included in the global greenhouse gas budget yet here we document a new and major case of msp in the dinaride ophiolite belt in bosnia and herzegovina ch 4 is dissolved 83 2706 m in low temperature 13 30 c hyperalkaline ph 10 to 12 8 waters in six sites sampled through springs and boreholes four sites slanac vlajici kulasi and ljesljani show ch 4 isotopic signatures typical of abiotic msp 13 c 18 5 to 35 7 2 h 221 to 335 4 two sites vaiceva and kiseljak show a dominantly biotic signature 13 c 58 8 and 65 1 2 h 310 8 and 226 8 probably due to mixing with gas from coal beds adjacent to the ultramafic rocks h 2 concentration is highly variable up to 348 m ethane propane and butane reach 0 13 vol in total and helium isotopic composition r ra 0 12 to 0 48 reflects a dominant crustal signature the ljesljani site features the highest ph 12 8 and ch 4 emission 9 ton y 1 in peridotite hosted hyperalkaline groundwater documented so far geological and geochemical data converge towards the hypothesis that as proposed in similar cases ch 4 was mainly generated by sabatier reaction between h 2 from serpentinization and co 2 from c bearing rocks in tectonic contact with the ophiolite or other co 2 sources ch 4 h 2 h 2 o disequilibria and sabatier reaction constraints suggest that ch 4 is not formed in the hyperalkaline water but in water free or unsaturated rocks hosting opportune metal catalysts e g chromitites the amount of methane released to the atmosphere from individual springs is comparable to that of conventional biotic gas seeps springs in sedimentary basins