precipitation of dolomite using sulphate reducing bacteria from the coorong region south australia significance and implications dolomite was successfully precipitated in culture experiments that simulated microbiogeochemical conditions prevailing during late stages of evaporation in ephemeral hypersaline dolomitic lakes of the coorong region south australia analyses of lake and pore water samples document rapid geochemical changes with time and depth in both dolomitic and non dolomitic lakes extremely high sulphate and magnesium ion concentrations in lake waters decline rapidly with depth in pore waters throughout the sulphate reduction zone whereas carbonate concentrations in pore waters reach levels up to 100 times those of normal sea water ultimately sulphate is totally consumed and no solid sulphate is recorded in the dolomitic lake sediments most probable number calculations of lake sediment samples record the presence of large populations of sulphate reducing bacteria whereas sulphur isotope analyses of lake water samples indicate microbial fractionation in all the lakes studied viable populations of microbes from the lake sediments were cultured in anoxic conditions in the laboratory samples were then injected into vials containing sterilized clastic or carbonate grains or glass beads immersed in a solution that simulated the lake water falls in the levels of sulphate and rising ph in positive vials were interpreted as indicating active bacterial sulphate reduction accompanied by increased concentrations of carbonate within 2 months sub spherical sub micron size crystals of dolomite identical to those of lake sediments were precipitated it is concluded that bacterial sulphate reduction overcomes kinetic constraints on dolomite formation by removing sulphate and releasing magnesium and calcium ions from neutral ion pairs and by generating elevated carbonate concentrations in a hypersaline strongly electrolytic solution the results demonstrate that bacterial sulphate reduction controls dolomite precipitation in both the laboratory experiments and lake sediments it is proposed that dolomite formation through bacterial sulphate reduction provides a process analogue applicable to thick platformal dolostones of the past where benthic microbial communities were the sole or dominant colonizers of shallow marine environments

the influence of organic matter in organogenic dolomitization we hypothesize that the decomposition of organic debris derived from plants planktonic animals and algae by sulfate reducing bacteria and specifically by the enzymatic degradation of protein is vital to organogenic dolomitization the role of this degradation is to increase both alkalinity and ph of the pore waters providing the necessary solution and surface chemistries for dolomitization to occur ammonia derived by the enzymatic breakdown of proteins is the only simple base available to supply the ph conditions necessary for dolomitization protein is abundant in organic matter derived from a marine source because of the large enthalpies of hydration of mg super 2 and ca super 2 ions we propose that dolomitization proceeds with the transfer of neutral ion pairs caco 3 and mgco 3 to and from the dolomite surface within a replacement zone for this reason dolomitization will occur only when the concentration of the co 3 super 2 ion is high and in large excess to the hco 3 super ion in solution and at the carbonate crystal surface these conditions will be met when the ph and or ionic strength is high and the carbonate alkalinity is also high

microphysical structure of the marine boundary layer under strong wind and sea spray formation as seen from a 2d explicit microphysical model part iii parameterization of height dependent droplet size distribution abstractthis paper completes a series of studies using a 2d hybrid lagrangian eulerian model to investigate the effect of sea spray on the thermodynamics and microphysics of the hurricane mixed layer the evolution of the mixed layer was simulated by mimicking the motion of an air volume in a lagrangian sense toward a tropical cyclone eyewall along a background airflow during the radial motion sea surface temperature pressure background wind speed sea spray production rate and turbulence intensity were altered according to the available observations analysis of the interaction between the hurricane mixed layer and the upper layers in terms of entrainment heat and moisture fluxes gives a new insight into the role of sea spray in the thermodynamics and microphysics of the mixed layer the evaporation of sea spray leads to an increase in the relative humidity by 10 15 and to a decrease in temperature by about 1 1 5 k as compared to cases where sea spray is excluded sea spray leads to formation o

methane derived authigenic carbonates mdac in northern central adriatic sea relationships between reservoir and methane seepages abstract in the adriatic basin gas venting characterized by pockmarks gas bubbling and other fluid escape related features is diffused and has been linked or to shallow gases trapped in the late pleistocene and below the holocene maximum flooding surface or to leakage from more deeply buried pliocene to pleistocene foredeep succession some seepages are associated with carbonate crusts but a possible correlation between methane leakage and carbonate precipitation in this basin never reached a clear definition carbonate concretions recovered by different areas of the adriatic sea northern central and southern at different depths from ca 30 to ca 300 m have been analysed different fabrics petrography and mineralogy can be evidenced for the different sets of samples all of them show a carbonate content mainly represented by high mg calcite up to 66 in weight of total carbonates for the samples from central adriatic close to bonaccia gas field offshore ancona and 79 to 96 of the total carbonate weight for the other samples that are mainly biogenic these differences are also reflected by the 13 c values ranging between 19 and 29 vpdb for the samples collected in the bonaccia area and moderately positive values for all the other samples bonaccia samples contain carbonate cements that record the contribution of methane derived carbon and have been interpreted as formed below the sea floor in correspondence of the sulphate methane transition zone carbonates recovered from the southern and northern adriatic basin do not show clear evidence of methane derived carbon and are mainly made up by organisms typically recovered in the adriatic coralligenous assemblage nonetheless micro morphological evidences suggest influence of bacterial sulphate reduction and methanogenesis in precipitation of some of these carbonates

the role of sulphate reducing bacteria and cyanobacteria in dolomite formation in distal ephemeral lakes of the coorong region south australia abstract the dolomitic distal ephemeral lakes of the coorong region of south australia are dynamic systems in which the concentrations of solutes generally increase during late spring and summer when the rate of evaporation greatly exceeds aqueous input during late evaporation active bacterial sulphate reduction occurs in uppermost anoxic lake sediments as rising salinity and then h2s toxicity kills off the macrobiota these hypersaline lakewaters are characterised by high ph and elevated concentrations of carbonate and sulphate ions magnesium concentrated in cyanobacterial cells and sheaths is released into the strongly electrolytic alkaline lake brines from lake margin stromatolites and mats during desiccation and may explain the remarkable increase in mg levels recorded at this time continued evaporation of the lakewaters produces a halite crust overlying the dolomite sulphate free residual puddles and the absence of gypsum indicates that all sulphate is removed by sulphate reducing bacteria dolomite forms in situ as a primary precipitate from these microbially mediated lake porewaters and both the morphology and size distribution of dolomite grains is identical to bacterial cells it is not proven exactly when dolomite precipitation occurs but the submicron sized grains and multiple defects in a disordered lattice indicate that precipitation is rapid and follows bacterial removal of sulphate which is known to inhibit dolomite formation bacterial sulphate reduction and cyanobacterial degradation may thus lead to the removal of all kinetic inhibitors to dolomite formation and provide a mechanism for dolomite precipitation around bacterial cells in shallow subsurface sediments during the late stages of evaporation in adjacent non dolomitic lakes sulphate is present throughout evaporation so that other minerals principally aragonite and hydromagnesite are precipitated

microbe mineral interactions early carbonate precipitation in a hypersaline lake eleuthera island bahamas microbialites benthic microbial carbonate deposits were discovered in a hypersaline alkaline lake on eleuthera island bahamas from the edge towards the centre of the lake four main zones of precipitation could be distinguished 1 millimetre sized clumps of mg calcite on a thin microbial mat 2 thicker and continuous carbonate crusts with columnar morphologies 3 isolated patches of carbonate crust separated by a dark non calcified gelatinous mat and 4 a dark microbial mat without precipitation in thin section the precipitate displayed a micropeloidal structure characterized by micritic micropeloids strong autofluorescence surrounded by microspar and spar cement no fluorescence observations using scanning electron microscopy sem equipped with a cryotransfer system indicate that micrite nucleation is initiated within a polymer biofilm that embeds microbial communities these extracellular polymeric substances eps are progressively replaced with high mg calcite discontinuous eps calcification generates a micropeloidal structure of the micrite possibly resulting from the presence of clusters of coccoid or remnants of filamentous bacteria at high magnification the microstructure of the initial precipitate consists of 200 500 nm spheres no precipitation is observed in or on the sheaths of cyanobacteria and only a negligible amount of precipitation is directly associated with the well organized and active filamentous cyanobacteria in deeper layers of the mat indicating that carbonate precipitation is not associated with co2 uptake during photosynthesis instead the precipitation occurs at the uppermost layer of the mat which is composed of eps empty filamentous bacteria and coccoids gloeocapsa spp two dimensional mapping of sulphate reduction shows high activity in close association with the carbonate precipitate at the top of the microbial mat in combination these findings suggest that net precipitation of calcium carbonate results from a temporal and spatial decoupling of the various microbial metabolic processes responsible for caco3 precipitation and dissolution theoretically partial degradation of eps by aerobic heterotrophs or uv fuels sulphate reducing activity which increases alkalinity in microdomains inducing caco3 precipitation this degradation could also be responsible for eps decarboxylation which eliminates ca 2 binding capacity of the eps and releases ca 2 ions that were originally bound by carboxyl groups at the end of these processes the eps biofilm is calcified and exhibits a micritic micropeloidal structure the eps free precipitate subsequently serves as a substrate for physico chemical precipitation of spar cement from the alkaline water of the lake the micropeloidal structure has an intimate mixture of

dependence of tropical cyclone intensification on the boundary layer representation in a numerical model we present idealized numerical model experiments to investigate the dependence of tropical cyclone intensification and in particular the kinematic structure of the tropical cyclone boundary layer on the boundary layer parametrization in the model the study is motivated by recent findings highlighting the important dynamical role of the boundary layer in tropical cyclone intensification the calculations are carried out using the pennsylvania state university national center for atmospheric research fifth generation mesoscale model mm5 predictions using one of five available schemes are compared not only between themselves but where possible with recent observational analyses of boundary layer structure at this stage the study falls short of being able to advocate the use of a particular scheme although certain shortcomings of individual schemes are identified the current inability to determine the optimum scheme has implications for the predictability of tropical cyclone intensification copyright 2010 royal meteorological society

a stable isotope study of microbial dolomite formation in the coorong region south australia abstract the coorong region of south australia is a classic location for the study of modern dolomite formation a number of ephemeral lakes here contain dolomite whilst other lakes in close proximity contain aragonite with minor magnesite our previous field and experimental work has revealed that sulphate reducing bacteria play a key role in overcoming kinetic inhibitors to dolomite formation in this area we here use a combination of oxygen carbon and sulphur isotopes to help to further constrain the processes leading to dolomite precipitation in modern hypersaline environments we report isotopic data from four dolomite and three aragonite containing lakes 34 s data for dissolved lake and porewater sulphates reveal 34 s enrichment of residual sulphate in all seven lakes consistent with bulk closed system microbial fractionation by sulphate reducing bacteria calculations using temperature dependent oxygen isotope fractionation factors between dolomite and the solution from which it precipitated are consistent with a strong microbial component to carbonate precipitation in these lakes a comparison of 18 o data from dolomite and aragonite sediment and from their associated lakewaters indicates seasonal mineral precipitation occurs late in the evaporative cycle of the lakes within a yoghurt like saturated mud horizon coincident with the zone of sulphate reduction surprisingly 13 c data from the carbonates do not show the characteristic wide range of values often associated with organogenic carbonates but instead show that these bacterially mediated precipitates incorporate carbon primarily from the inorganic lakewater reservoir partially diluted by an organic component a coorong type microbial model of dolomite formation may be particularly applicable to for example precambrian sedimentary dolomites where benthic microbial communities which are today restricted to extreme environments dominated the shallow marine ecosystem prior to the emergence of metazoa

bed scale spatial patterns in dolomite abundance part ii effect of varied fluid chemistry flow rate precursor mineralogy temperature textural heterogeneity nucleation density and bed geometry

microbially mediated carbonate precipitation in a hypersaline lake big pond eleuthera bahamas microbial metabolism impacts the degree of carbonate saturation by changing the total alkalinity and calcium availability this can result in the precipitation of carbonate minerals and thus the formation of microbialites here the microbial metabolic activity the characteristics and turnover of the extracellular polymeric substances and the physicochemical conditions in the water column and sediments of a hypersaline lake big pond bahamas were determined to identify the driving forces in microbialite formation a conceptual model for organomineralization within the active part of the microbial mats that cover the lake sediments is presented geochemical modelling indicated an oversaturation with respect to carbonates including calcite aragonite and dolomite but these minerals were never observed to precipitate at the mat water interface this failure is attributed to the capacity of the water column and upper layers of the microbial mat to bind calcium a layer of high mg calcite was present 4 to 6 mm below the surface of the mat just beneath the horizons of maximum photosynthesis and aerobic respiration this carbonate layer was associated with the zone of maximum sulphate reduction it is postulated that extracellular polymeric substances and low molecular weight organic carbon produced at the surface i e the cyanobacterial layer of the mat bind calcium both aerobic and anaerobic heterotrophic microbes consume extracellular polymeric substances each process accounting for approximately half of the total consumption and low molecular weight organic carbon liberating calcium and producing inorganic carbon the combination of these geochemical changes can increase the carbonate saturation index which may result in carbonate precipitation in conclusion the formation and degradation of extracellular polymeric substances as well as sulphate reduction may play a pivotal role in the formation of microbialites both in marine and hypersaline environments

an estimation of turbulent characteristics in the low level region of intense hurricanes allen 1980 and hugo 1989 this study analyzes the flight level data collected by research aircraft that penetrated the eyewalls of category 5 hurricane hugo 1989 and category 4 hurricane allen 1980 between 1 km and the sea surface estimates of turbulent momentum flux turbulent kinetic energy tke and vertical eddy diffusivity are obtained before and during the eyewall penetrations spatial scales of turbulent eddies are determined through a spectral analysis the turbulence parameters estimated for the eyewall penetration leg are found to be nearly an order of magnitude larger than those for the leg outside the eyewall at similar altitudes in the low level intense eyewall region the horizontal length scale of the dominant turbulent eddies is found to be between 500 and 3000 m and the corresponding vertical length scale is approximately 100 m the results suggest also that it is unwise to include eyewall vorticity maxima evm in the turbulence parameter estimation because the evms are likely to be quasi two dimensional vortex structures that are embedded within the three dimensional turbulence on the inside edge of the eyewall this studyis afirstattempt at estimatingthe characteristics of turbulent flow in the low leveltroposphereof an intense eyewall using in situ aircraft observations the authors believe that the results can offer useful guidance in numerical weather prediction efforts aimed at improving the forecast of hurricane intensity because of the small sample size analyzed in this study further analyses of the turbulent characteristics in the high wind region of hurricanes are imperative

on the characteristic height scales of the hurricane boundary layer in this study data from 794 gps dropsondes deployed by research aircraft in 13 hurricanes are analyzed to studythecharacteristicheightscalesofthehurricaneboundarylayer theheightscalesaredefinedinavariety of ways the height of the maximum total wind speed the inflow layer depth and the mixed layer depth the height of the maximumwind speed and the inflow layerdepth are referred to asthe dynamical boundarylayer heights while the mixed layer depth is referred to as the thermodynamical boundary layer height the data analyses show that there is a clear separation of the thermodynamical and dynamical boundary layer heights consistent with previous studies on the boundary layer structure in individual storms the dynamical boundary layer height is found to decrease with decreasing radius to the storm center the thermodynamic boundary layer height which is much shallower than the dynamical boundary layer height is also found to decrease with decreasing radius to the storm center the results also suggest that using the traditional critical richardson number method to determine the boundary layer height may not accurately reproduce the height scale of the hurricane boundary layer these different height scales reveal the complexity of the hurricane boundary layer structure that should be captured in hurricane model simulations

limitation of one dimensional ocean models for coupled hurricane ocean model forecasts abstract wind stress imposed on the upper ocean by a hurricane can limit the hurricane s intensity primarily through shear induced mixing of the upper ocean and subsequent cooling of the sea surface since shear induced mixing is a one dimensional process some recent studies suggest that coupling a one dimensional ocean model to a hurricane model may be sufficient for capturing the storm induced sea surface temperature cooling in the region providing heat energy to the hurricane using both a one dimensional and a three dimensional version of the same ocean model it is shown here that the neglect of upwelling which can only be captured by a three dimensional ocean model underestimates the storm core sea surface cooling for hurricanes translating at 5 m s 1 for hurricanes translating at 2 m s 1 more than half of the storm core sea surface cooling is neglected by the one dimensional ocean model since the majority of hurricanes in the western tropical north atlantic ocean translate at 5 m s 1 the

holocene evolution of the anichab pan on the south west coast of namibia coastal sediment filled depressions pans are one of the few areas that contain quaternary records of sea level and palaeoenvironmental change along the western margin of southern africa anichab is a 128 km2 salt encrusted pan on the hyper arid southern coast of namibia with an emergent well preserved and in place mid holocene mollusc assemblage the molluscs are typical of subtidal sands on the sheltered side of offshore islands but include several warm water species no longer found living along this coast the holocene evolution of the pan was largely influenced by changes in sea level and supply of sand along the coast calibrated radiocarbon ages of mollusc shells indicate a maximum holocene sea level of ca 2 m above mean sea level msl from 7 0 to 6 3 ka and a return to near present day sea level by 5 3 ka the pan surface is 2 m below msl and has been emergent since 4 9 ka from the build up of sandy beaches and coastal dunes a thin 1 4 cm halite crust occurs over much of the pan surface but a layer of halite cemented sand up to 40 cm thick is restricted to the central pan gypsum occurs near the subsurface brine interface and is limited by calcium to the edges of the pan nodules of calcite cemented sand are forming in brackish relatively high alkalinity subsurface waters in the south east corner of the pan and nodules of aragonite cemented sand are forming in brines 1 m below the central pan surface although modern dolomite has been reported from coastal lagoons of brazil and australia carbonate cements are a minor feature of anichab pan and dolomite was restricted to a single reworked nodule most likely of late pleistocene age therefore anichab pan does not appear to be a modern analogue to extensive mixed water dolomite cements found in upper pleistocene sediment filled depressions on the namibian shelf

dolomite in permian paleosols of the bravo dome co2 field u s a permian reflux followed by late recrystallization at elevated temperature abstract lower permian abo tubb subsurface strata of northeastern new mexico u s a consist of 30 to 120 m of fluvial and eolian deposits containing numerous dolomitic paleosols dolomite in the abo tubb interval occurs in discrete intervals interpreted as paleosols on the basis of recognizable horizonation and the presence of associated features such as ped structures and rhizoliths the dolomite commonly forms veins rhizoliths and discrete and coalesced nodules petrographic analysis indicates four dolomite types present in paleosol horizons microsparitic pseudospherulitic clear cement and cloudy inclusion rich cement microsparitic dolomite constitutes most of 70 the dolomite and is stoichiometric with relatively low sr and na and elevated fe and mn pseudospherulitic dolomite forms 15 of the dolomite and consists of stoichiometric microspar and spar with abundant fluid inclusions low sr na and fe and elevated mn clear dolomite cement constitutes approximately 12 of the dolomite and is finely to coarsely crystalline with a relatively calcian composition low sr and na and elevated fe and mn the cloudy cement forms a minor 2 phase of very coarsely crystalline rhombs with a calcian composition low sr and na values and relatively high fe and mn all dolomite types exhibit a mottled texture of moderate to bright orange and red luminescence fluid inclusion analysis was not possible on the most common microsparitic dolomite type but analyses on the coarser varieties reveal homogenization temperatures typically ranging from 70 c to 110 c and final melting temperatures of ice ranging from 20 c to 34 c suggesting fluids of high 25 by weight salinity bulk rock carbon and oxygen isotopes of carbonate nodules and rhizoconcretions from four paleosol profiles most commonly exhibit mean values typically ranging between 3 to 5 5 vpdb and 0 5 to 2 8 vpdb respectively sulfur isotopes were analyzed for the overlying cimarron anhydrite interval and an anhydrite nodule near the base of the study interval both samples yielded similar results suggesting that brines that precipitated the cimarron anhydrite also influenced the study interval the dolomite in the abo tubb interval is interpreted to have precipitated in multiple stages solid calcite microinclusions in microsparitic and pseudospherulitic dolomite suggest that pedogenensis and groundwater penecontemporaneous with early permian deposition led to precipitation of calcite rather than dolomite oxygen and sulfur isotope data indicate dolomitization from later reflux of brines associated with deposition of the overlying leonardian cimarron anhydrite petrographic relations and elevated temperatures and salinities recorded by the fluid inclusions in the coarse dolomite are consistent with recrystallization of the earlier dolomite and precipitation of dolomite cement from warm saline fluids of a possible tertiary hydrothermal origin just predating migration of mantle derived gas into the bravo dome reservoir these findings offer insight into questions about the climate significance of dolomite in paleosols origin of dolomite in hydrothermally altered hydrocarbon reservoirs and the long term effect of co2 sequestration in saline aquifers the results show that dolomitic nodules in paleosols may form as replacements of paleosol calcite long after the paleosol formed primary pedogenic dolomite would undoubtedly have climatic and paleoenvironmental significance but recognizing it as forming during soil formation as opposed to later dolomitization is key in establishing that significance also this study provides an example of high temperature recrystallization of low temperature dolomite a process hotly debated in discussions of dolomitized hydrocarbon reservoirs with evidence for hydrothermal fluid flow finally as a natural co2 reservoir the bravo dome system shows that the long term result of dissolution of co2 into brines is predominantly carbonate mineral dissolution

biotic and abiotic processes in the formation and diagenesis of permian dolomitic stromatolites zechstein group ne england abstract the crinkly bed of the upper permian zechstein group succession roker formation hauptdolomit z2c in northeast england is a distinctive 1 4 meter thick unit that has been interpreted as a stromatolite of microbial origin or alternatively as the result of purely abiotic precipitation close examination of this stratigraphically significant unit shows that it is the result of both physical and microbial processes and was deposited in hypersaline shallow water immediately following lowstand evaporite deposition within the zechstein basin the internal structure of the crinkly bed consists of fine millimeter scale laminae of alternating clotted peloidal or aphanitic micritic layers and granular laminae composed of silt size peloids with rare hollow spheroids the lamination is extremely regular in thickness and laterally persistent for up to 4 meters a microbial community composed of coccoid and filamentous microorganisms inferred from fossil evidence colonized the original sediment surface it is suggested that this biofilm was responsible for the precipitation of both the micrite laminae and most of the peloids of the granular laminae the peloids are consequently interpreted as autochthonous this interpretation of a microbial origin is consistent with the microstructure and geochemical signatures of the micritic dolomite which constitutes both the continuous micritic laminae and the peloids themselves primary dolomite precipitation is hypothesized to have taken place from marine to slightly hypersaline waters mediated by bacterial metabolism similar to the process that operates in modern intertidal microbial mats the crinkly bed shows macro structures that vary along a continuum from symmetrical to asymmetrical centimeter scale ripple like structures some showing interference patterns through to domical and conical structures more typical of stromatolites the more ripple like structures have a lamination of microbial origin identical to that within the domal conical stromatolites there is no internal cross lamination their origin is equivocal they could be the result of physical current or wave induced deformation of a surficial biofilm or their form could be inherited from true mechanically deposited ripples not observed that provided a template for biofilm growth changes in the nature and strength of the wave and or current regime and possibly in the community structure of the microbial mat produced this array of microbially induced macrostructures miss the latter plus the absence of desiccation features indicative of intertidal to supratidal deposition suggest subtidal sedimentation at a depth of several meters intergranular gypsum cement precipitated during early diagenesis and ferroan sparry dolomite precipitated during burial tertiary uplift and the consequent exposure to meteoric waters resulted in the precipitation of calcite cements that replaced gypsum and pre existing dolomite probably via the biological mediation of heterotrophic bacteria the interpretation of this distinctive stratigraphic unit illustrates the difficulty in distinguishing between biotic and abiotic processes in the sedimentary record

turbulence structure of the hurricane boundary layer between the outer rainbands abstract as part of the coupled boundary layers air sea transfer cblast hurricane program flights were conducted to directly measure turbulent fluxes and turbulence properties in the high wind boundary layer of hurricanes between the outer rainbands for the first time vertical profiles of normalized momentum fluxes sensible heat and humidity fluxes and variances of three dimensional wind velocities and specific humidity are presented for the hurricane boundary layer with surface wind speeds ranging from 20 to 30 m s 1 the turbulent kinetic energy budget is estimated indicating that the shear production and dissipation are the major source and sink terms respectively the imbalance in the turbulent kinetic energy budget indicates that the unmeasured terms such as horizontal advection may be important in hurricane boundary layer structure and dynamics finally the thermodynamic boundary layer height estimated based on the virtual potential temperature profiles is roughly half of the boundary

stable isotope study of carbonate sediments from the coorong area south australia the mineralogy and isotope geochemistry of carbonate minerals in the coorong area are determined by the water chemistry of different depositional environments ranging from seawater to evaporitically modified continental water the different isotopic compositions of coexisting calcite and dolomite suggest that each of the above two minerals was formed from water of composition and origin unique to that specific mineral in addition the dolomite was not formed by simple solid state cation exchange the occurrence of two types of dolomite was shown by isotope analysis and sem observations the dolomite which is isotopically light 13c 1 to 2 0 18o 3 to 5 0 and of fine grain size 0 5 m probably precipitated under the influence of evaporitically modified continental water coarser grained dolomite up to 4 m is isotopically heavier 13c 3 to 4 0 18o 5 to 6 0 contains mg in excess of ca and was formed in or close to equilibrium with atmospheric co2 probably by the dolomitization of aragonite

effects of large eddies on the structure of the marine boundary layer under strong wind conditions abstract a model of the atmospheric boundary layer bl is presented that explicitly calculates a two way interaction of the background flow and convective motions the model is utilized for investigation of the formation of large eddies roll vortices and their effects on the structure of the marine boundary layer under conditions resembling those of tropical cyclones it is shown that two main factors controlling the formation of large eddies are the magnitude of the background wind speed and air humidity determining the cloud formation and latent heat release when the wind speed is high enough a strong vertical wind shear develops in the lower part of the bl which triggers turbulent mixing and the formation of a mixed layer as a result the vertical profiles of velocity potential temperature and mixing ratio in the background flow are modified to allow for the development of large eddies via dynamic instability latent heat release in clouds was found to be the major energy source of large eddi

microbial dolomite precipitation using sulfate reducing and halophilic bacteria results from qinghai lake tibetan plateau nw china past studies have revealed the important roles of certain types of microbes in precipitating dolomite in coastal hypersaline lakes and lagoons and marine sediments however it is still poorly known if other types of microbes can precipitate dolomite in low salinity lakes without any marine influence the objective of this study was therefore to expand the microbial dolomite precipitation model by investigating the origin of dolomite in the sediments of qinghai lake an inland slightly saline lake salinity 12 5 g l on the tibetan plateau nw china this objective was accomplished via an integrated approach combining geochemical investigations of natural dolomite present in the lake sediments with laboratory precipitation experiments a 5 m sediment core was collected and pore water chemistry was analyzed calculation of saturation index indicated that dolomite was oversaturated in sediment pore water sub spherical grains of dolomite with abundant pores and microstructures similar to microbially precipitated dolomite were found in the sediments suggesting a biogenic origin dolomite precipitation experiments were set up in the laboratory to simulate the natural conditions of the qinghai lake dolomite was precipitated using sulfate reducing bacterium srb desulfotomaculum ruminis and aerobic halophilic bacterium halomonas marina present in the qinghai lake sediments aqueous geochemistry and mineral characterization data collectively suggest that dolomite precipitation was accomplished via increase of ph and alkalinity to overcome the kinetic inhibitors and exopolymeric substances eps and cell walls as possible nucleation sites these results expand the current microbial dolomite precipitation model and have implications for dolomite formation in slightly saline inland lake environments

why rolls are prevalent in the hurricane boundary layer recent remote sensing observations show that the hurricane boundary layer flow although energetic is not a region of homogeneous turbulence in fact the observations convincingly demonstrate that a large fraction of the turbulent flow in the regions away from the deep convective rainbands is highly organized into intense horizontal roll vortices that are approximately aligned with the mean wind and span the depth of the boundary layer these observations show that rolls strongly increase the flux of momentum between the underlying surface and the main body of the storm compared to an equivalent hurricane boundary layer flow without rolls the linear and nonlinear dynamics of hurricane boundary layer roll formation are outlined and it is shown why rolls are in fact the expected basic hurricane boundary layer state the model presented here explains the hurricane roll features currently documented in field programs and makes predictions that can be tested in future experiments the primary effects of rolls on the boundary layer fluxes are inherently nonlocal and nongradient and hence cannot be captured by standard downgradient turbulence parameterizations used in hurricane simulations however the nonlinear theory is the proper starting point for developing boundary layer parameterizations that include roll modification of the turbulent fluxes

bacterially induced dolomite precipitation in anoxic culture experiments to study the process of microbial mediated dolomite formation growth experiments were carried out with selected bacterial cultures under anoxic environmental conditions simulating those found in lagoa vermelha a hypersaline lagoon in brazil where dolomite precipitation occurs specifically we report the isolation of a particular strain of sulfate reducing bacteria lvform6 from lagoa vermelha sediment which apparently promotes the formation of nonstoichiometric dolomite sulfate reducing bacteria grown in a synthetic liquid medium produced dolomite during 30 days incubation at 30 c the precipitates have morphologies similar to those observed in lagoa vermelha sediment our results demonstrate that sulfate reducing bacteria can influence dolomite precipitation under controlled lowtemperature anoxic conditions and imply that anaerobic microorganisms can play an important role in carbonate sedimentation they may have been particularly significant in earth s earliest history when a more reducing atmosphere existed

carbon and sulfur isotopic compositions of organic carbon and pyrite in sediments from the transvaal supergroup south africa abstract sedimentary organic matter and pyrite from parts of the lower transvaal supergroup and few samples from the olifantshoek group have been studied for their carbon and sulfur isotopic compositions respectively carbon isotopic compositions for minimally altered organic matter range from 43 to 31 sulfur isotope values for sedimentary pyrite display values between 1 3 to 23 6 results from this and previously published work are being interpreted with respect to past biochemical pathways carbon isotope data indicate autotrophic carbon fixation as the process of primary production in addition products of secondary biological reworking contributed to the total organic carbon content sulfur isotope data indicate bacterial sulfate reduction as the main process however changes in sulfate availability and or the rate of sulfate reduction may have caused the observed range in isotopic compositions

mineralogy nucleation and growth of dolomite in the laboratory and sedimentary environment a review dolomite camg co3 2 forms in numerous geological settings usually as a diagenetic replacement of limestone and is an important component of petroleum reservoir rocks rocks hosting base metal deposits and fresh water aquifers dolomite is a rhombohedral carbonate with a structure consisting of an ordered arrangement of alternating layers of ca2 and mg2 cations interspersed with co32 anion layers normal to the c axis dolomite has r3 symmetry lower than the caco3 r3 c symmetry of calcite primarily due to ca mg ordering high magnesium calcite also has r3 c symmetry and differs from dolomite in that ca2 and mg2 ions are not ordered high magnesium calcite with near dolomite stoichiometry 50 mol mgco3 has been observed both in nature and in laboratory products and is referred to in the literature as protodolomite or very high magnesium calcite many dolomites display some degree of cation disorder ca2 on mg2 sites and vice versa which is detectable using transmission electron microscopy and x ray diffractometry laboratory syntheses at high temperature and pressure as well as studies of natural dolomites show that factors affecting dolomite ordering stoichiometry nucleation and growth include temperature alkalinity ph concentration of mg and ca mg to ca ratio fluid to rock ratio mineralogy of the carbonate being replaced and surface area available for nucleation in spite of numerous attempts dolomite has not been synthesized in the laboratory under near surface conditions examination of published x ray diffraction data demonstrates that assertions of dolomite synthesis in the laboratory under near ambient conditions by microbial mediation are unsubstantiated these laboratory products show no evidence of cation ordering and appear to be very high magnesium calcite elevated temperature and elevated pressure experiments demonstrate that dolomite nucleation and growth always are preceded by very high magnesium calcite formation it remains to be demonstrated whether microbial mediated growth of very high magnesium calcite in nature provides a precursor to dolomite nucleation and growth analogous to reaction paths in high temperature experiments

why is the tropical cyclone boundary layer not well mixed abstractplausible diagnostics for the top of the tropical cyclone boundary layer include i the top of the layer of strong frictional inflow and ii the top of the well mixed layer that is the layer over which potential temperature is approximately constant observations show that these two candidate definitions give markedly different results in practice with the inflow layer being roughly twice the depth of the layer of nearly constant here the authors will present an analysis of the thermodynamics of the tropical cyclone boundary layer derived from an axisymmetric model the authors show that the marked dry static stability in the upper part of the inflow layer is due largely to diabatic effects the radial wind varies strongly with height and therefore so does radial advection of this process also stabilizes the boundary layer but to a lesser degree than diabatic effects the authors also show that this differential radial advection contributes to the observed superadiabatic layer ad

microbial sphalerite formation in carbonate hosted zn pb ores bleiberg austria micro to nanotextural and sulfur isotope evidence microglobular sphalerite 90 180 m is a major form of sphalerite in the abandoned triassic carbonate hosted zn pb deposit at bleiberg austria it is common in ores from the crest horizon and the first cardita horizon which contain about 0 5 to 3 mm thick and up to 5 cm long wavy discontinuous sphalerite rich bands composed of agglomerations of microglobular sphalerite based on comparisons with modern environments these textures are interpreted as peloids and probably represent fossil microbial mats these are inter layered with carbonate and marcasite rich as well as finely banded sphalerite layers fibrous galena and relics of oxysulfides resulting in the characteristic rhythmically banded macrotexture of these zn dominated ores microbial nanotextures made visible by field emission scanning electron microscopy fesem after etching include sphalerite nanospheres 10 90 nm and bacterial filaments the sphalerite nanospheres are identical to those previously reported for mixed calcite sphalerite peloids from bleiberg and are very similar to nanotextures observed in recent bacterial biofilms made by desulfobacteriaceae the observed sphalerite nanospheres are interpreted as in situ metabolic products of sulfate reducing bacteria micro and nanotextures suggest that the larger m sized sphalerite globules formed by agglomeration of sphalerite nanospheres as well as by replacement of peloids representing former bacterial colonies the latter are now composed of zn calcite cores surounded by serrated sphalerite rims most samples studied evidence recrystallization of sphalerite that is broadly coeval with formation of fluorite involvement of sulfate reducing bacteria in the formation of this early sphalerite mineralization is supported by sulfur isotope data sphalerite is generally characterized by isotopic light sulfur with 34 s per mil values ranging from 30 5 to 20 3 per mil the most negative sulfur isotope values are recorded from sphalerite 30 5 30 2 and galena with unusual fibrous to dendritic morphology 31 9 31 8 both are associated with oxysulfides microglobular sphalerite with well preserved sphalerite globules has a 34 s value of 28 8 to 28 2 per mil colloform sphalerite schalenblende ranges from 29 0 to 25 0 per mil microglobular sphalerite associated with fine grained fluorite and euhedral sphalerite formed through recrystallization processes show a trend to less negative values i e 26 3 to 22 2 per mil and 22 9 to 20 3 per mil respectively we suggest that the combined biogenic nano to macrotextures and sulfur isotope data are evidence that microbes played a key role in formation of alpine carbonate hosted zn pb deposits results of this study contradict the mvt model suggested for alpine pb zn deposits which calls for formation of pb zn mineralization during late diagenetic burial in the late triassic early jurassic

simulation and parameterization of the turbulent transport in the hurricane boundary layer by large eddies 1 hurricane boundary layer hbl processes especially the structure of the coherent large eddy circulations lecs and their induced vertical transport are not well understood this paper introduces a large eddy simulation les framework in a weather hindcasting mode developed from a multiple scale nested weather research and forecasting wrf model using the wrf les this study investigated the structure of the hbl lecs and the associated vertical transport during the landfall of hurricane ivan 2004 the simulation shows that the hbl lecs exist in a mean stable environment and consist of well defined updraft and downdraft statistically the hbl lecs are only slightly skewed with the updrafts and downdrafts relatively evenly distributed spatially the inversion base basically envelopes the upper boundary of lecs the trough in between two adjacent lecs is where most entrainment takes place whereas the crest of the lecs is where boundary layer air detrains out of the hbl in such a way lecs directly connect the surface the hbl and the main body of a hurricane vortex and enhance the exchange of energy moisture and momentum between them it is found that the current boundary layer schemes significantly underestimate the resolved turbulent fluxes due to the fact that the effects of lecs have not been included in the parameterizations on the basis of the statistical structure of lecs simulated by the wrf les this paper proposes a conceptual updraft downdraft model that can potentially be implemented in weather forecasting models to parameterize the fluxes induced by the hbl lec transport

the role of bacterial sulfate reduction during dolomite precipitation implications from upper jurassic platform carbonates the early diagenetic formation of dolomite in modern aquatic environments is limited mostly to evaporitic and marine anoxic organic rich sediments dominated by bacterial sulfate reduction bsr in such environments bacterial activity lowers the energy barriers for the nucleation and growth of dolomite and thus promotes the formation of non stoichiometric highly disordered and metastable proto dolomite although the boundary conditions for the formation of modern proto dolomites are considered to be generally understood the role of bsr during limestone dolomitization in ancient marine environments remains questionable herein we present a study about the physicochemical conditions and processes which led to the formation of partly dolomitized limestone and dolostone in the presence of bsr on a stable carbonate platform during the upper jurassic at oker northern german basin the dolomite textures the spatial trace elemental patterns of the dolomite and of the surrounding limestone and the results of 18o and 13c isotope analyses reveal that the oker dolomite has been formed by the early diagenetic replacement of magnesian calcite precursors at temperatures between 26 c and 37 c we interpret the mineralizing fluids responsible for dolomitization as pristine marine to slightly evaporitic and reducing seawater being modified during shallow seepage reflux and or evaporitic tidal pumping the elevated 34scas values 17 9 to 19 7 v cdt of the oker dolomite compared to ambient upper jurassic seawater indicate that bsr facilitated dolomite formation for the first time we show that a linear anti correlation exists between decreasing carbonate associated sulfate cas contents in dolomite and increasing ordering ratio of the dolomite lattice structure with the degree of cation order in dolomite to be given by degree of cation order dol 0 018 cas dol 68 3 r2 0 98 this correlation implies that the cas content of sedimentary dolomite can be used as a measure for dolomite maturity the relationships between the ambient paleo environmental controls the resultant dolomitization pathways and subsequently the structure and the composition of the precipitating dolomite are presented and discussed in relation to the stability of modern and ancient proto dolomites throughout burial diagenesis

degree of supersaturation and precipitation of organogenic dolomite this paper integrates the degree of carbonate saturation into a general model for the origin of dolomite in organic rich marine sediments degradation of organic matter by sulfate reducing bacteria promotes early dolomite precipitation by simultaneously increasing the carbonate alkalinity and lowering the sulfate ion concentration to near zero the interstitial water in organic rich sediments of several deep sea drilling project sites where dolomite is believed to be precipitating is up to 10 sup 3 times supersaturated with respect to near ideal dolomite and up to 10 times supersaturated with respect to calcite the highly supersaturated interstitial waters appear to overcome low temperature kinetic barriers to precipitate a nonideal fine grained calcian dolomite the degree of supersaturation with respect to dolomite decreases and the interstitial water approaches carbonate equilibrium with increasing burial depth at several of these sites removal of sulfate ion is important because sulfate ion may inhibit dolomite precipitation a calcareous sediment is not required but the presence of calcite or aragonite appears to greatly enhance dolomitization by providing an additional source of ca and carbonate ions

influence of early diagenesis on geotechnical properties of clay sediments romania black sea abstract the geotechnical properties of clay sediments were investigated using laboratory and in situ measurements as part of the geohazard assessment in the romanian sector of the black sea affected by landslides and seafloor deformation features the sediments were characterized as predominantly high plastic silty clay of high compressibility low undrained shear strength low cohesion and moderate sensitivity a shallow increase in shear strength exceeding the general trend could have been reconciled with evidence for the precipitation of iron sulfides and calcium carbonates related to early diagenetic reactions of sulfate reduction e g cryptic sulfur cycle and anaerobic oxidation of methane comparison of the compression behaviour of natural and reconstituted samples indicated that precipitation of these materials at particle contacts produced cementation the analysis of deeper sediments sharing similar geochemical properties illustrated that the early precipitation of even low quantity of sulfur and carbonate cements allowed clays to develop sufficient strength to preserve an abnormal high water content even under tens of meters burial depth because this cementation process was observed to be associated with an enhanced sensitivity and a strain softening response to undrained shearing it was concluded that such early diagenesis should be considered as a key environmental factor leading to weak layer formation that may influence the susceptibility of seafloor to failure

microbialites in a modern lagoonal environment nature and distribution tikehau atoll french polynesia abstract microbialites including stromatolitic structures gelatinous masses and mats develop in tikehau lagoon tuamotu french polynesia on the flanks and slopes of numerous pinnacles and motu islets between 0 and 25 m deep on coral colonies algal tufts or on lagoonal sediments individual stromatolitic structures consist of hemispherical domes and are produced by monospecific populations of filamentous cyanobacteria belonging to three distinctive phormidium species symploca and possibly to one new species of schizothrix gelatinous masses hanging from the ceiling of caverns are produced by phormidium laysanense microbial mats are well developed at all depths on pinnacle slopes and are produced by either monospecific or mixed cyanobacterial populations the study of micro and ultrastructure of stromatolites reveals that they result both from trapping and binding of sediments and from carbonate precipitation in addition to phototrophic biomineralization pervasive carbonate precipitation occurred in association with decaying organic matter the basic constructional elements of the precipitated carbonate consist of 0 1 0 2 m rounded bodies that form very fine anhedral to subhedral micrite their surfaces comprise extremely small carbonate granules 20 50 nm gradual changes ageing in the ultrastructure of carbonate precipitates include the precipitation of successive euhedral calcite layers around these grains widespread development of microbialites in this pristine lagoonal environment results from rapid blooms of microbial benthic communities possibly induced by temporary and local nutrient pulses nutrients seem to undergo a restricted circulation between the sediment and pinnacle reef frameworks pinnacles and reef islets are repeatedly affected by catastrophic storm events which cause redistribution of sediments and nutrients

3700 ma pre metamorphic dolomite formed by microbial mediation in the isua supracrustal belt w greenland simple evidence for early life chemical meta sedimentary rocks in the amphibolite facies 3700 ma isua supracrustal belt w greenland are mostly strongly deformed so there is only a small chance of the survival of features such as stromatolites or microfossils that would be direct proof of a 3700 ma biosphere therefore the search for evidence of 3700 ma life in isua rocks has focused on chemical signatures particularly c isotopes the new approach presented here is based on whole rock chemistry rather than isotopic signatures isua chemical sedimentary rocks have ca mg fe bulk compositions that coincide with ferroan dolomite siderite fe oxide mixtures most have low al2o3 tio2 contents 0 5 and 0 05 wt respectively showing minimal contamination from terriginous materials identical seawater like ree y shale normalised trace element signatures with la ce eu and y positive anomalies are found in magnetite rich banded iron formation bif such as the geochemical standard if g dolomite rich rocks and quartz carbonate calcsilicate rocks additionally from a rare small area of low deformation in isua there are 3700 ma pillow lava interstices consisting of quartz tremolite calcite derived from pre metamorphic dolomite silica thus the dolomite in the chemical sediments and the pillow interstice was part of the pre metamorphic assemblage and was deposited from seawater and or low temperature groundwater as shown by the ree y chemistry therefore at least some isua carbonate rocks are sedimentary or diagenetic in origin rather than being formed by metasomatism at 600 500

helical circulations in the typhoon boundary layer 1 low level wind data from the wsr 88d in guam obtained in typhoon dale 1996 and typhoon keith 1997 are analyzed for coherent structures consistent with the results of previous studies of atlantic hurricanes velocity anomalies associated with coherent structures were found in the boundary layer of both storms a total of 99 cases of coherent structures also known as roll vortices were documented during a 6 h evaluation period for each storm storm relative roll location roll vorticity asymmetries in the upward and downward momentum fluxes and signatures of circulations transverse to the mean flow associated with roll circulations were explored the effects of terrain and convective precipitation systems such as rainbands on the occurrence of rolls were investigated the results support and extend prior findings of roll observations and can be used to help validate theoretical and numerical models of coherent structures within tropical cyclones moreover the wind variations documented in this study may have application for wave runup and wind damage potential in tropical cyclones

dolomite mountains and the origin of the dolomite rock of which they mainly consist historical developments and new perspectives beginning in the late 18th century the dolomite mountains in northern italy have been the location for major sedimentological developments from the discovery of the mineral dolomite to the formulation of the coral reef hypothesis to explain the origin of the massive dolomite structures that define the splendid scenery of the region further the dolomite mountains have inspired voluminous research into the origin of dolomite questioning whether dolomite is a primary precipitate or a secondary replacement product recently with the recognition that microbes can mediate dolomite precipitation a new geomicrobiological approach combining the study of modern natural environments with bacterial culture experiments is now being used to calibrate or interpret microbial evidence derived from the dolomite rock record this three pronged methodology applied to the study of dolomite formation holds great promise for future research into the dolomite problem and provides a new impetus to revisit the dolomite mountains in the 21st century

observational estimates of the horizontal eddy diffusivity and mixing length in the low level region of intense hurricanes this study examines further the characteristics of turbulent flow in the low level region of intense hurricanes using in situ aircraft observations the data analyzed here are the flight level data collected by research aircraft that penetrated the eyewalls of category 5 hurricane hugo 1989 category 4 hurricane allen 1980 and category 5 hurricane david 1979 between 1 km and the sea surface estimates of horizontal eddy momentum flux horizontal eddy diffusivity and horizontal mixing length are obtained it is found that the horizontal momentum flux and horizontal diffusivity increase with increasing wind speed the horizontal mixing length increases slightly with wind speed also but the mixing length is not significantly dependent on the wind speed the magnitude of the horizontal momentum flux is found to be comparable to that of the vertical momentum flux indicating that horizontal mixing by turbulence becomes nonnegligible in the hurricane boundary layer especially in the eyewall region within the context of simple k theory the results suggest that the average horizontal eddy diffusivity and mixing length are approximately 1500 m 2 s 21 and 750 m respectively at about 500 m in the eyewall region corresponding to the mean wind speed of approximately 52 m s 21 it is recalled also that the mixing length is a virtual scale in numerical models and is quantitatively smaller than the energy containing scale of turbulent eddies the distinction between these two scales is a useful reminder for the modeling community on the representation of small scale turbulence in hurricanes

microscale observations of sulfate reduction correlation of microbial activity with lithified micritic laminae in modern marine stromatolites we report for the first time micrometer scale correlation of geologic and microbial processes in modern marine stromatolites precipitation of micritic laminae in these stromatolites was studied by comparing microstructure as observed in petrographic thin sections with microbial sulfatereduction activity two dimensional mapping of sulfate reduction rates was implemented by incubating a vertical section of a stromatolite face on silver foil coated with 35 so 4 2 our results show that sulfate reduction activity is high in zones of caco 3 precipitation and indicate that microbial activity produces lithified micritic laminae near the surface of the stromatolites similarities with micritic laminae in ancient stromatolites suggest that sulfate reduction may also have been an important mechanism of carbonate precipitation in these fossilized structures

neutralization of acid runoff by groundwater discharge to streams in canadian precambrian shield watersheds abstract application of environmental isotope techniques during storm and snowmelt runoff from the harp lake and turkey lakes watersheds on the precambrian shield of central ontario canada indicates that subsurface pre event water is a major component of the runoff hydrograph storm runoff from two sub basins in the harp lake watershed is comprised of 40 90 groundwater depending on rainfall amount and intensity and antecedent soil moisture conditions and water table depth because the alkalinity of the groundwater is large compared to the acid precipitation ph 3 8 4 5 characteristic of this region groundwater discharge results in significant neutralization of runoff acidity snowmelt runoff studies in the turkey lakes watershed indicate that much of the first meltwater from the acidic ph 4 5 snowpack infiltrates the subsurface displacing higher ph groundwater to the stream since the first meltwater from an ablating snowpack is more acidic than the snow itself meltwater infiltration limits the extent of stream acidification during snowmelt runoff hence the physical displacement of near neutral ph pre event subsurface water during storm and snowmelt runoff periods partially buffers the alkalinity of baseflow as long as the acid neutralization capacity of the geologic materials storing the subsurface water is not exhausted groundwater contributions to runoff will continue to neutralize acid runoff

spectral characteristics of turbulence in the hurricane boundary layer over the ocean between the outer rain bands spectra and cospectra of wind velocity potential temperature and humidity have been analysed using data collected in the atmospheric boundary layer in hurricanes fabian 2003 and isabel 2003 during the coupled boundary layer air sea transfer cblast hurricane experiment the spectra and cospectra are normalized following the surface layer scaling methods according to similarity theory it is found that the cblast data gathered in the mixed layer between the outer rain bands below 400 m can be grouped into well defined curves for spectra of wind velocity potential temperature and humidity and for cospectra of momentum and humidity flux however the cospectra of sensible heat flux do not exhibit well defined universal shape the cblast universal shape spectra and cospectra generally resemble the shapes of those from previous studies but shift to higher frequencies that correspond to smaller wavelengths of turbulent eddies that contain most of the energy this work highlights the structural difference between the hurricane boundary layer and the standard atmospheric boundary layer over land and ocean copyright 2010 royal meteorological society

an observational study of hurricane boundary layer small scale coherent structures abstract data with high temporal and spatial resolution from hurricanes isabel 2003 and frances 2004 were analyzed to provide a detailed study of near surface linear structures with subkilometer wavelengths of the hurricane boundary layer hbl the analysis showed that the features were omnipresent throughout the data collection displayed a horizontal and vertical coherency and maintained an average orientation of 7 left of the low level wind a unique objective wavelength analysis was conducted where wavelength was defined as the distance between two wind maxima or minima perpendicular to the features long axis and revealed that although wavelengths as large as 1400 m were observed the majority of the features had wavelengths between 200 and 650 m the assessed wavelengths differ from those documented in a recent observational study to evaluate the correlation between the features and the underlying near surface wind field time and spectral analyses were completed and ground relative freque

cryptalgal metazoan bioherms of early ordovician age in the st george group western newfoundland bioherms are common in the st george group a sequence of shallow water carbonate rocks deposited on the western continental shelf of iapetus ocean they range from small heads and metre sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent the cores of these bioherms are principally composed of thrombolites unlaminated branching columnar stromatolites structures quite distinct from laminated stromatolites which are common in intertidal beds associated with thrombolites is a diverse fauna of burrowing invertebrates trilobites nautiloids pelmatozoans brachiopods gastropods rostroconchs and archaeoscyphiid sponges on the basis of framework building components three main bioherm types are distinguished 1 thrombolite mounds 2 thrombolite lichenaria or sponge mounds and 3 thrombolite lichenaria renalcis reef complexes the framework of the last is the most complex with abundant cavities and a demonstrably uneven growth surface of thrombolites corals and free standing renalcis heads walls and roofs some cavities were active sediment conduits while others were protected their roofs draped with renalcis and their walls coated by cryptalgal laminites these bioherms possess the attributes of shallow water ecologic reefs they span a critical time gap in the development of reefs the transition period from algal dominated bioherms of the precambrian and cambrian to the metazoan dominated bioherms of the middle ordovician and remaining phanerozoic

dolomite silica stromatolites in miocene lacustrine deposits from the duero basin spain the role of organotemplates in the precipitation of dolomite this research provides an ancient analogue for biologically mediated dolomite precipitation in microbial mats and biofilms and describes the involvement of highly structured extracellular polymeric secretion eps templates in dolomite nucleation the structure of eps is shown to match the hexagonal trigonal lattice geometry of dolomite which favoured the epitaxial crystallization of dolomite on the organic substrate this structure of eps also matches the arrangement of silica nanospheres in opal which further accounts for the organically templated formation of opal enabling the non replacive co existence of dolomite and silica the study is focused on a 50 m thick dolomite succession that is exposed in central areas of the tertiary duero basin and was deposited in a mudflat saline lake sedimentary complex during the middle to late miocene 9 to 15 ma in the intermediate intervals of the succession poorly indurated dolomite beds pass gradually into silica beds on the basis of sedimentological compositional geochemical and petrographic data silica and dolomite beds have been interpreted as mineralized microbial mats the silica beds formed in marginal areas of the lake in response to intense evaporative concentrations this resulted in the rapid and early precipitation of opal silicification accounted for the exceptional preservation of the microbial mat structure including biofilms filamentous and coccoid microbes and eps extracellular polymeric secretions have a layered structure each layer being composed of fibres which are arranged in accordance with a reticular pattern with frequent intersection angles at 120 and 60 therefore the structure of eps matches the lattice geometry of dolomite and the arrangement of silica nanospheres in opal additionally eps binds different elements with preference to si and mg the concurrence of suitable composition and surface lattice morphologies in the eps favoured the crystallization of dolomite on the substrate in some cases dolomite nucleation took place epicellularly on coccoid micro organisms which gave way to spheroid crystals organic surfaces enable the inorganic mineral precipitation by lowering the free energy barrier to nucleation most of the microbial mats probably developed on the lake floor under sub aqueous conditions where the decomposition of organic matter took place the subsequent formation of openly packed dolomite crystals with inter related si enriched fibrils throughout is evidence for the pre existence of fibrillar structures in the mats miocene dolomite crystals are poorly ordered and non stoichiometric with a slight ca excess up to 5 which is indicative of the low diagenetic potential the microbial dolomite has towards a more ordered and stoichiometric structure this confirms that microbial imprints can be preserved in the geological record and validates their use as biosignatures

origins of pyrites in the 2 5 ga mt mcrae shale the hamersley district western australia abstract the mt mcrae shale is the footwall rock unit of the brockman iron formation 2 5 ga in age in the hamersley basin australia it is characterized by a high concentration of organic carbon 2 8 wt an abundance of disseminated pyrite 1 to 10 wt s in the bulk rocks and abundant pyrite nodules 1 10 cm radius we have examined microscale 200 m to 1 cm variations in sulfur isotopic compositions of pyrite and s and c contents in six rock samples from a 27 m drill core section of the base of the mt mcrae shale at the whaleback mine the microanalyses of sulfur isotope compositions were performed in situ on single or aggregates of pyrite crystals eighty four analyses using a nd yag laser microprobe the carbon contents of thirty powdered samples drilled from different parts of the six rock samples are similar 2 to 8 wt c with the exception of one sample 0 5 wt however the occurrence morphology abundance and 34s value of pyrite reveal distinct differences between the two samples from the upper part and the four samples from the lower part of the drill core section pyrite crystals in the upper part occur mostly as disseminated fine grains 5 m the pyrite s contents are uniform within each sample but the 34s values vary from 6 3 to 7 1 these data suggest that pyrite crystals in the upper section were formed by bacterial reduction of seawater sulfate pyrite crystals of the lower section occur in the form of veinlets nodules or laminae of coarse grains 200 m the pyrite contents are highly variable within each specimen 0 to 10 wt and the 34s values vary from 2 2 to 11 8 the formation process of pyrites in the lower section appears to have been complicated pyrite laminae were first formed by bacterial sulfate reduction during early diagenesis and then some of the early pyrites were dissolved and reprecipitated to form pyrite nodules by later diagenetic or hydrothermal solutions in a closed system the sulfur isotope data obtained in this study can be best explained by a model postulating that the seawater about 2 5 ga ago in the hamersley basin had the 34s value of 10 to 15 and that the kinetic isotope effects accompanying bacterial sulfate reduction were 8 13 and 16 21 respectively during the deposition of the lower and upper sections of the mcrae shale the variable 34s values of microscale area and the magnitudes of the kinetic isotope effects suggest that 1 the sulfate concentration of the 2 5 ga seawater was already more than one third of the present seawater value and 2 the activity of sulfate reducing bacteria in the 2 5 ga ocean was generally higher than that in the modern ocean suggestion 1 further implies that by 2 5 ga 3 the atmosphere became oxic and 4 the chemical and isotopic characteristics of sulfur in the earth s near surface reservoirs oceans and sediments were controlled by the phanerozoic style biogeochemical cycles rather than by the mantle buffer i e magmatic mechanism suggestion 2 may imply that 5 the archean oceans were generally warmer compared to the modern oceans and 6 they produced a higher abundance of organic matter that were easily metabolized by sulfate reducing bacteria

an observational case for the prevalence of roll vortices in the hurricane boundary layer abstract doppler velocity data from weather surveillance radar 1988 doppler wsr 88d radars during four hurricane landfalls are analyzed to investigate the presence of organized vortices in the hurricane boundary layer hbl the wavelength depth magnitude and track of velocity anomalies were compiled through analysis of doppler velocity data the analysis reveals alternating bands of enhanced and reduced azimuthal winds closely aligned with the mean wind direction resulting statistics provide compelling evidence for the presence of organized secondary circulations or boundary layer rolls across significant areas during four hurricane landfalls the results confirm previous observations of the presence of rolls in the hbl a potential limitation of the study presented here is the resolution of the wsr 88d data in particular analysis of higher resolution data e g from the doppler on wheels is needed to confirm that data aliasing has not unduly impacted the statistics reported here momentum flux

dolomitization of gas reservoirs the upper permian changxing and lower triassic feixianguan formations northeast sichuan basin china abstract the lower triassic feixianguan formation and to a lesser extent the upper permian changxing formation contain more than ten giant recently discovered dolomite gas fields on either side of a paleo embayment kaijiang liangping bay sichuan basin china this study documents the origin of the dolomite using a combination of petrology fluid inclusion trace element geochemistry and stable isotope and radiogenic isotope analysis of samples from outcrop and core samples from producing gas fields three stages of dolomitization are revealed dolomicrite from the lagoon facies in the feixianguan formation and minor fabric retentive dolomite from reef facies in the changxing formation on the northeast side of kaijiang liangping bay represent the initial dolomite phase caused by reflux of feixianguan brine with salinity close to gypsum saturation 18 wt salinity during the first stage of diagenesis at 30 c the second and dominant dolomite phase fabric retentive dolomite in both the feixianguan and changxing formations on the both sides of kaijiang liangping bay is the result of reflux of diagenetic fluids with salinity ranging from normal feixianguan seawater 3 5 salinity up to mesohaline water 6 5 salinity during early burial diagenesis at about 35 40 c as shown by the dominance of single phase aqueous inclusions shallow formed stylolites that cut the second phase of dolomite and the early triassic marine carbon oxygen and strontium isotope and rare earth element and yttrium ree y signals the subordinate third dolomite phase fabric obliterative dolomite and dolomite cement was due to burial diagenetic recrystallization between 80 and 140 c in the feixianguan and changxing formations on both sides of kaijiang liangping bay the third phase of dolomitization involved water expelled from the slightly younger lower triassic jialingjiang formation marine evaporites and carbonates on the northeast side of kaijiang liangping bay revealed by the high salinity of the aqueous inclusions that homogenize at 80 to 140 c and elevated strontium isotope data the carbon isotope and ree y signals of the third phase of dolomite are similar to earlier dolomite cements confirming the lack of exotic input future exploration should be focused on dolomitized high energy sediments e g reef and oolitic shoal and bank in similar triassic tethyan paleogeographic settings that are associated with restricted facies but underlying dolomitized high energy permian strata may also be good exploration targets