organic matter oxidation and aragonite diagenesis in a coral reef abstract a combination of field and theoretical work is used to study controls on the saturation state of aragonite inside a coral reef framework a closed system ion speciation model is used to evaluate the effect of organic matter oxidation on the saturation state of aragonite the aragonite saturation state initially drops below 1 but becomes oversaturated during sulfate reduction the c n ratio of the organic matter affects the degree of oversaturation with n poor organic material resulting in a system more corrosive to aragonite precipitation of sulfide as fes strongly affects the aragonite saturation state and systems with much fes formation will have a stronger tendency to become oversaturated with respect to aragonite both precipitation and dissolution of aragonite are predicted at different stages of the organic reaction pathway if the model system is maintained at aragonite saturation field data from a coral reef framework indicate that the system maintains itself at aragonite saturation and model predicted changes in dissolved calcium follow those observed in the interstitial waters of the reef aragonite probably acts as a solid phase buffer in regulating the ph of interstitial waters because interstitial water in the reef has a short residence time the observed equilibration suggests rapid kinetics

numerical simulation of katabatic flow with changing slope angle a large eddy simulation les model and the advanced regional prediction system arps model which does not resolve turbulent eddies are used to study the effect of a slope angle decrease on the structure of katabatic slope flows for a simple uniform angle slope simulations from both models produce turbulence kinetic energy and momentum budgets that are in good overall agreement simulations of a compound angle slope are compared to a uniform angle slope to demonstrate how a changing slope angle can strongly affect the strength of katabatic flows both arps and the les model show that slopes with a steep upper slope followed by a shallower lower slope concave shape generate a rapid acceleration on the upper slope followed by a transition to a slower evolving structure characterized by an elevated jet over the lower slope in contrast the case with uniform slope having the same total height change yields a more uniform flow profile with stronger winds at the slope bottom higher average slope in the uniform slope angle case generates greater gravitational potential energy which is converted to kinetic energy at the bottom of the slope analysis of the total energy budget of slope flows indicates a consistent structure where potential energy generated at the top of the slope is transported downslope and converted into kinetic energy near the slope base

water rock interactions and seawater freshwater mixing effects in the coastal dunes aquifer coos bay oregon abstract groundwater from the seawater freshwater interface in sandy sediments was sampled using a unique profile well designed in which separate pvc tube screens were installed at various depths all major ions except chloride showed non conservative behavior in the mixing zone so4 mg2 and k are depleted and hco3 is enriched relative to cl na is enriched in solutions containing less than 20 seawater and depleted in solutions containing higher percentages of seawater the behavior of ca2 is the mirror image ofthat of na the chemical data on the stratification of groundwater above and within the interface zone were obtained using a unique profile well design in which separate pvc tube screens were installed at various depths thus making it possible to extract water samples at close vertical intervals the chemical changes in the groundwater reflect the following processes 1 a ca2 na and ca2 mg2 base exchange reactions 2 b oxidation of organic matter in the sediment 3 c reduction of sulfate probably due to bacterial processes 4 d reaction of hco3 and s2 with fe2 to produce mineral coatings and cements of pyrite and siderite 5 e k feldspar formation producing lower of k concentrations the authigenic phases were identified using scanning electron microscopy thermodynamic calculations suggest that all solutions are saturated with respect to quartz and chalcedony and many are saturated with respect to calcite dolomite siderite and hematite kaolinite is the stable clay mineral in the top of the freshwater column whereas smectite is the stable clay mineral in the lower part of the freshwater column and in the seawater freshwater mixing zone

palaeo mixing zone karst features from palaeocene carbonates of north spain criteria for recognizing a potentially widespread but rarely documented diagenetic system abstract marine meteoric mixing zone dissolution effects are a major feature of present day karst systems in carbonate platforms yet are rarely reported in the geological record an example is described from the upper danian platform limestones of the alava province in the western pyrenees north spain this consists of several narrow zones with sponge like porosity analogous to the swiss cheese features found in present day mixing zones these zones are stained by fe oxides and overlie limestones which are irregularly dolomitized and contain disseminated pyrite these high porosity zones are interpreted as having developed in marine mixing zones where mixing corrosion and microbially mediated processes increased dissolution if collapsed ancient mixing zones could be misinterpreted as terra rossa palaeosols the main criteria to identify them as mixing zone products are their occurrence below a palaeo meteoric phreatic zone their association with stratified oxic and anoxic redox zones and petrographic evidence for highly variable calcite saturation states

large eddy simulation of a katabatic jet along a convexly curved slope 2 evidence of gortler vortices this paper is the second part of a study of katabatic jet along a convexly curved slope with a maximum angle of about 35 5o large eddy simulation is performed with a special focus on the outer layer shear of the katabatic jet in the first part a basic statistical quantitative analysis of the flow was performed here a qualitative and quantitative description of vortical structures is used to gain insight in the present 3d turbulent flow it is shown that gortler vortices oriented in the streamwise downslope direction develop in the shear layer they spread with a specific mushroom shape in the vertical direction up to about 100m height they play a main role with respect to local turbulent mixing in the ground surface boundary layer the present curved slope configuration constitutes a realistic model for alpine orography this paper provides a procedure based on local turbulence anisotropy to track gortler vortices for in situ measurements which has never been proposed in the literature

nocturnal meso beta basin and katabatic flows on a midlatitude island abstract a mesoscale simulation for the island of majorca spain in the western mediterranean sea is used to study the nocturnal system of winds under weak synoptic pressure gradients a very high vertical resolution is used in the first 500 m above ground level to characterize with large detail the thin circulations close to ground namely basin and katabatic flows it is found that the island the basin and the slope scales interact strongly especially when a quasi steady state is reached in the second part of the night a high mountain range creates a high pressure area upwind where local winds can develop katabatic flows converge to the valleys where they interact with a cold pool which is advected slowly to sea by the land sea night breeze effect combined with a topographic forcing the katabatic flows experience small entrainment at the top and have well defined characteristics the results are partially confirmed by the observations and some satellite images

microbial mats as bioreactors populations processes and products microbial mats are dynamic and complex ecosystems exhibiting spatial and temporal heterogeneity the physical chemical environment is typified by steep gradients and distinct microenvironments these microenvironments support a great diversity of species with a wide range of metabolic processes these processes often result in coupled reactions and biogeochemical cycles and produce important end products such as trace gases and mineral precipitates the latter can impact the composition and character of the sediment imparting a biosignature these biosignatures can be preserved in the rock record and are useful in the interpretation of fossil record on earth and possibly as an indication of life on other planetary bodies the modern marine stromatolites of the exuma cays bahamas provide an ideal system for studying the populations processes and products in a microbial ecosystem using a multidisciplinary approach in order to acquire redox energy microbial populations need to carry out metabolic reactions at rates faster than the equivalent chemical abiotic reactions as such microbes can be viewed as bioreactors that preferably oxidize carbon to co2 to maximize the energy yield the study of the microbial role in carbonate sedimentation and lithification in these stromatolites provides a picture of microbial mats as bioreactors producing a biosignature

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

diagenetic salinity cycles and sea level along a major unconformity monte composauro italy abstract in shallow water carbonates position of the water table and the chemistry of early diagenetic fluids are controlled in large part by sea level and climate fluctuations these fluctuations may result in cyclic progression from marine diagenesis or sedimentation to mixing zone meteoric mixing zone and then marine diagenesis or sedimentation herein we term such a cyclic progression as a diagenetic salinity cycle this diagenetic study along a single unconformity in cretaceous limestones of monte camposauro southern apennines italy demonstrates the presence of four diagenetic salinity cycles and their link to relative changes in sea level data consist of field observations transmitted light and cathodoluminescence microscopy fluid inclusions and carbon and oxygen isotopes they show that twenty one unconformity related diagenetic features predated deposition of marine limestones above the unconformity fossiliferous internal sediments and stable isotope data from radiaxial fibrous calcite and recrystallized aragonite are used to indicate marine diagenesis fluid inclusion and stable isotope data are used to indicate precipitation of calcite cement in all mixing ratios of the mixing zone environment and in the freshwater phreatic zone paleocave morphology indicates vadose and water table dissolution and bauxite sediments support extensive vadose diagenesis in each diagenetic salinity cycle there is evidence for relative fall or rise of sea level indicated by transitions from marine sedimentation to mixing zone and freshwater phreatic diagenesis marine phreatic to freshwater vadose diagenesis vadose diagenesis to marine phreatic diagenesis and freshwater phreatic diagenesis to normal marine sedimentation during the time interval of the development of the unconformity beginning some time in the aptian and ending in the early middle cenomanian at least seven third order eustatic fluctuations have been hypothesized during an overall second order eustatic rise at a given elevation the third order eustatic fluctuations would not be able to produce four diagenetic salinity cycles without tectonic uplift of 3 5 to 8 mm ky our study illustrates that the formation and the timing of diagenetic salinity cycles are highly sensitive to paleoelevation diagenetic salinity cycles preserved along unconformities can be used to interpret relative changes of sea level and to predict the presence of depositional sequences in downdip positions conversely downdip depositional sequences tectonic history and sea level history can be used to predict some aspects of diagenetic alteration updip

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

comparing oxygen isotope records of silurian calcite and phosphate δ18o compositions of brachiopods and conodonts oxygen isotope compositions of silurian calcitic brachiopod shells from gotland are compared with those of phosphatic inarticulate brachiopod shells and conodonts from identical stratigraphic horizons the 18ophosphate values of inarticulate brachiopod shells vary widely 13 0 to 17 5 v smow and are significantly lower than those of coeval conodont samples 17 5 to 19 5 v smow conodont samples from individual beds have homogenous 18ophosphate values with variations close to the analytical precision 0 2 together with a significant correlation of conodont 18ophosphate and articulate brachiopod shell 18ocarbonate values r 0 85 this observation suggests that primary marine oxygen isotope compositions are better preserved in conodont apatite than in inarticulate brachiopod shell apatite however with decreasing 18ocarbonate values the 18ophosphate values of conodonts are higher than expected for theoretical isotopic equilibrium with brachiopod calcite different habitats of conodonts and brachiopods cannot account for the observed offset in 18o because both organisms were thriving on a broad shallow marine carbonate platform whereas 18ophosphate values of silurian conodonts are close to 18ophosphate values of modern and mesozoic tropical biogenic apatites most silurian calcitic brachiopod shells from gotland are depleted in 18o when compared to modern or mesozoic brachiopods we therefore suggest that silurian conodonts from gotland record paleotemperature and 18o of silurian sea water more faithfully than coeval calcitic brachiopod shells

a comparison of vitrinite reflectance measurements made on whole rock and dispersed organic matter concentrate mounts abstract a comparison of mean random vitrinite reflectance r v r values calculated from measurements on polished whole rock and on concentrates of dispersed organic matter dom mounts of the same samples generally show little difference compared to measurements on dom mounts r v r measurements by the same microscopist on corresponding whole rock samples are up to a few tenths of a percent lower over the range of 0 6 3 2 r v r and have a slightly higher standard deviation whole rock mounts have an advantage over dom mounts in the identification of first cycle vitrinite and differentiation of solid bitumen from vitrinite

non marine radiaxial fibrous calcites examples of speleothems proved by electron backscatter diffraction abstract the occurrence of radiaxial fibrous calcites rfc in speleothems is documented for the first time using the new electron backscatter diffraction ebsd method up to now in speleothems these precipitates have only been observed as mg containing calcites in close association with aragonite in caves of the temperate to cool central european regions with mean annual temperatures between 4 and 16 c as the four studied occurrences are located in caves in dolomitic and or ankeritic host rocks magnesium is considered to be of particular importance for triggering the formation of radiaxial fibrous mg calcite

climate controlled early dolomite late triassic cyclic platform carbonates hungary abstract the 2 km thick late triassic hungarian carbonate platform has a completely dolomitized lower part and a limestone dominated upper part the platform succession is made up of meter scale possibly precessional 20 ky carbonate cycles in the lower platform main dolomite cycles are completely dolomitized and capped by caliche laminites and pisolites in the upper platform dachstein limestone dolomite is confined to laminite caps of cycles that are bounded by clayey paleosols most of the dolomitization in the platform interior occurred early in tidal flat settings during each high frequency cycle subtidal dolomites are slightly coarser grained are low in fe2 and mn2 and have the heaviest 18o signature this indicates they formed from evaporative oxidizing brines sourced from supratidal flats intertidal supratidal dolomites are fine grained commonly fe2 and or mn2 rich and slightly enriched in 18o compared to the marine calcite cement they formed from marine water that was weakly to moderately reducing dachstein paleosols have light 18o and 13c signatures reflecting meteoric soil waters repeated emergence stabilized the dolomites to low sr2 and na dolomite similar to cenozoic platform dolomites in contrast to these early cyclic dolomites coarse grained platform margin dolomites with very low mn2 and fe2 and light 18o signatures formed as thermally driven warm oxidizing marine water associated with jurassic rifting of the neo tethys pennini ocean circulated through the margin early dolomitization of cycles may have been controlled by high frequency sea level changes but the overall vertical distribution of early dolomite on the platform does not reflect long term eustasy rather the intense dolomitization of the lower platform reflects a semiarid hot subtropical seasonal setting and megamonsoonal climate global cooling and increased humidity toward the latest triassic and early jurassic inhibited pervasive early dolomitization leaving the upper platform largely as limestone

a three dimensional simulation of a tropical squall line convective organization and thermodynamic vertical transport abstract three dimensional convective scale simulations of an african squall line observed during the french copt 81 experiment are presented three simulations with different representations of large scale forcing are performed on a domain of 50 km along the line by 80 km across the line they exhibit a similar circulation pattern characteristic of a squall line but differ in intensity the first simulation supposes an unperturbed environment and produces a slow moving squall line 7 m s 1 with weaker total precipitation rate then observed 25 the second one includes a representation of observed thermodynamic and dynamic environment modifications and produces a fast moving squall line 10 m s 1 still weaker than observations 50 or the rain rate the third simulation takes into account the forcing induced by the rear inflow jet as depicted by smull and houze and observed on that day it allows the system to reach an intensity in agreement with observations the convective region 30 km wid

mixing zone diagenesis in the subsurface of florida and the bahamas abstract three cores from great bahama bank and southern florida contain examples of mixing zone diagenesis where typical shallow water aragonite rich sediments were altered to low mg calcite the 40 50 m thick mixing zones are identified on the basis of downcore covariant trends from depleted meteoric 18o 3 2 0 7 13c 1 6 1 8 to enriched marine isotopic values 18o 1 0 0 3 13c 1 9 0 7 the age of the mixing zones varies from late pliocene to pleistocene so these cores provide three independent examples of mixing zone diagenesis mixing zone diagenesis produced a limestone composed of low mg calcite with petrographic fabrics including moldic porosity blocky to dogtooth calcite cementation and recrystallization of lime mud to micrite and microspar the mixing zone diagenetic model predicts alteration in only part of the mixing zone because the alteration recorded in these cores shows continuous alteration through the entire mixing zone we consider the mixing of waters itself to be largely irrelevant rather diagenesis was probably driven by the difference in solubility between aragonite and calcite with some additional dissolution of aragonite driven by the microbial oxidation of buried organic matter the mixing zone has been proposed as a likely location for dolomitization with the exception of some clearly sea floor dolomite in one core unda the mixing zones in these cores lack dolomite despite the sediment clearly having been altered in the mixing zone the lack of dolomite in these mixing zones combined with the extensive literature questioning the chemical reasoning for mixing zone dolomite supports rejection of the mixing zone dolomite model

differential dissolution of a pleistocene reef in the ground water mixing zone of coastal yucatan mexico a geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the yucatan peninsula mexico mixing of fresh ground water with subterranean caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite mixing zone dissolution caused by ground water discharge is a major geomorphic process in developing caves coves and crescent shaped beaches along the yucatan coast such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record

reactive transport modeling of calcite dissolution in the fresh salt water mixing zone abstract dissolution of calcite in the saltwater mixing zone of coastal carbonate aquifers has been the subject of numerous studies they conclude that dissolution is driven by mixing of freshwater and saltwater which may lead to undersaturation even if both end members are saturated however as transport in the mixing zone is rather complex a fully coupled reactive transport model is needed to properly understand the interplay between transport and chemistry we perform 1 and 2d simulations to gain insight into the processes controlling dissolution rate exploring its sensitivity to the chemistry of end members and the dispersivity of the medium we conclude that the results of sanford and konikow sanford w e konikow l f 1989 simulation of calcite dissolution and porosity changes in saltwater mixing zones in coastal aquifers water resources research 25 655 667 which used a two step method solely transporting the amount of calcite dissolved are essentially correct but their solution is essentially kinetic with a rate dependent on the time increment used the 1d simulations allow us to show that maximum dissolution rates do occur neither at the location nor for the end members of maximum undersaturation for non reactive mixing in the 1d case enhanced transport at the freshwater end causes dissolution to concentrate there however in the 2d case representative of coastal aquifers maximum dissolution occurs at the saline side near the discharge zone because of a very active convection cell that develops there which enhances mixing and thus reaction rates this mechanism may explain observations at blue holes and should display a positive feedback with dissolution causing an increase in permeability that would lead to increased seawater flux and mixing thus enhancing further dissolution

questioning carbonate diagenetic paradigms evidence from the neogene of the bahamas carbonate diagenetic models have been heavily influenced by numerous studies of exposed quaternary limestones as a result meteoric diagenesis is often assumed to be the principle means of altering aragonite rich sediments into calcitic limestones however these models are limited by the scarcity of examples of aragonite rich sediments buried in seawater that have never been influenced by meteoric fluids the bahamas transect cores recovered originally aragonite rich sediments deposited in deep water beyond the easy reach of meteoric waters and provide an opportunity to test current diagenetic paradigms the bahamas transect consists of seven cores drilled in the prograding western margin of great bahama bank the two proximal cores clino and unda were drilled on the platform top and recovered shallow water platform to reef facies overlying deeper margin and proximal slope facies the five distal cores were drilled by odp leg 166 in up to 660 m of water and recovered carbonate slope facies all studied sections are neogene to pleistocene in age diagenetic environments were identified based on petrographic and scanning electron microscopy sem observations xrd mineralogy carbon and oxygen stable isotopic data and trace elements the upper 100 150 m of the two proximal cores were altered in meteoric to mixing zone diagenetic environments but all other intervals were altered exclusively in marine pore fluids during seafloor marineburial and deep burial diagenesis several of the findings of this study question current carbonate diagenetic paradigms these include 1 large scale sea level lowstands may not have chemically active meteoric lenses as we found no meteoric alteration at the 3120 m elevation of the latest pleistocene lowstand rather phreatic meteoric diagenesis appears restricted to within w10 m of the land surface 2 mixing zone diagenesis includes aragonite dissolution and minor lmc cementation but does not show the cavernous porosity or dolomitization predicted by mixing zone diagenetic models current models are based on coastal mixing zones which do not appear to be applicable to these more inland and perhaps more typical locations 3 marine burial diagenesis produces a mature limestone with fabrics formerly considered diagnostic for meteoric diagenesis such as moldic porosity aragonite neomorphism blocky calcite spar and calcite microspar however oxygen stable isotopic data average n 18 o 1x indicate alteration in marine pore fluids only the character of marine burial diagenesis is partially controlled by the nature of the sediment being altered we have identified two end member styles an open system style characterized by dissolution of aragonite without significant cementation and a more closed system style with aragonite dissolution

observations and models of simple nocturnal slope flows abstract measurements of simple nocturnal slope winds were taken on rattlesnake mountain a nearly ideal two dimensional ridge tower and tethered balloon instrumentation allowed the determination of the wind and temperature characteristics of the katabatic layer as well as the ambient conditions two cases were chosen for study these were marked by well defined surface based temperature inversions and a low level maximum in the downslope wind component the downslope development of the slope flow could be determined from the tower measurements and showed a progressive strengthening of the katabatic layer hydraulic models developed by manins and sawford 1979a and briggs 1981 gave useful estimates of drainage layer depths but were not otherwise applicable a simple numerical model that relates the eddy diffusivity to the local turbulent kinetic energy was found to give good agreement with the observed wind and temperature profiles of the slope flows

observations of flow and turbulence in the nocturnal boundary layer over a slope measurements were conducted on an eastern slope of the salt lake basin slb as a part of the vertical transport and mixing experiment vtmx conducted in october 2000 of interest was the nocturnal boundary layer on a slope in particular katabatic flows in the absence of significant synoptic influence extensive measurements of mean flow turbulence temperature and solar radiation were made from which circulation patterns on the slope and the nature of stratified turbulence in katabatic winds were inferred the results show that near the surface 25 50 m the nocturnal flow is highly stratified and directed downslope but at higher levels winds strongly vary in magnitude and direction with height and time implying the domination of upper levels by air intrusions these intrusions may peel off from different slopes surrounding the slb have different densities and flow at their equilibrium density levels the turbulence was generally weak and continuous but sudden increases of turbulence levels were detected as the mean gradient richardson number dropped to rig about unity with a short timescale fluctuated on the order of a few tens of seconds while modulating with rig a longer along slope internal waves sloshing timescale of about half an hour the mixing efficiency or the flux richardson number of the flow was found to be a strong function of similar to that found in laboratory rig experiments with inhomogeneous stratified shear flows the eddy diffusivities of momentum and heat were evaluated and they showed a systematic variation with when scaled with the shear length scale and the rms rig vertical velocity of turbulence

enhanced carbonate petrography using fluorescence microscopy abstract fluorescence microscopy can recognize depositional facies and delineate diagenetic fabrics and porosity relationships in certain highly dolomitized or recrystallized limestones previously uninterpretable using standard petrographic techniques this tool has other valuable applications in the study of carbonate rocks these other applications include differentiating carbonate cements from neomorphic spar enhancing depositional and diagenetic fabrics rapidly evaluating mineralogical stabilization and recrystallization in holocene and pleistocene deposits and improving delineation of porosity and pore geometries in sedimentary rocks fluorescence microscopy is a rapid easily used and nondestructive technique that can be applied to unpolished thin sections or rock slabs by itself or in conjunction with other petrographic and geochemical tools it has the potential to expand our understanding of carbonate diagenetic processes and products in particular dolomitization and neomorphism and carbonate porosity evolution we strongly encourage routine usage of fluorescence microscopy in future carbonate petrographic studies

palaeogeographic significance of black pebbles lower cretaceous prebetic southern spain abstract the presence of black pebbles in carbonate stratigraphic sections constitutes a criterion for identifying emergence episodes which are significant to palaeographic reconstructions and to location of sedimentary cycle boundaries three genetic models can be inferred from the stratigraphic petrologic and geochemical study of black pebbles that occur in sediments of the lower cretaceous of the prebetic southern spain in the first model black pebbles are the product of redeposition in tidal and lacustrine environments from layers rich in organic matter carbonaceous layers in the second model blackening takes place as a result of very mature organic matter mainly generated from terrestrial plants possibly burnt ones selectively staining some of the intraclasts of the storm layers in intertidal environmnts in the third model applicable only to pedogenic and lacustrine environments black pebbles to a large extent originate from a redeposition of pedogenic carbonate materials affected by natural forest fires where blackening was caused by a sudden and rapid increase in temperature the third hypothesis is supported by data obtained from an experiment in which samples underwent progressive heating to monitor the blackening process and accompanying change in isotopic composition in all cases the effects of storms and or currents and waves caused erosion and redeposition

aragonite cycles diagenesis caught in the act organic biomarker and nannofossil assemblages are used in combination with sedimentary petrology to identify the role of diagenesis for the formation of a rhythmic calcareous succession a record from the early pliocene of the maldives ocean drilling program odp leg 115 is presented containing precession and eccentricity cycles expressed as variable aragonite content additional sub milankovitch cycles are caused by rhythmic precipitation of calcite cement in the lower part of the interval comparison with palaeo productivity indicators nannofossils chlorin total organic carbon suggests that cementation occurs preferentially in intervals characterized by increasing or decreasing productivity the coupled variability in productivity and carbonate diagenesis is attributed to the effect of organic matter degradation in the sediment the observed combination of primary and diagenetic factors hampers the interpretation of the cyclicity on milankovitch and sub milankovitch scales diagenetically stable proxies for palaeo productivity such as nannofossil assemblage data were used to distinguish between palaeoclimate and diagenetic influences

kinetic control of morphology composition and mineralogy of abiotic sedimentary carbonates abstract conventional thinking has long held that the abiotic precipitation of calcium carbonate occurs with a causal relationship between fluid my ca ratios and crystal morphology crystal composition and carbonate mineralogy resulting in the formation of meteoric equant low magnesium calcite and marine acicular high magnesium calcite and aragonite problematically calcites with varying amounts of incorporated magnesium occur either as equant or acicular crystals and aragonite may coexist with calcite in either environment commonly however a systematic relation exists between crystal morphology composition mineralogy and rates of reactant supply to growing crystal surfaces for example equant rather than acicular crystals of calcite form in modern deep and or cold marine meteoric phreatic and deep burial settings where the degree of carbonate saturation and or rates of fluid flow are low in areas of higher saturation and or fluid flow such as in warm shallow marine and meteoric vadose environments acicular calcite may predominate this relation is also seen in systems in which aragonite and calcite form in intimate association aragonite precipitation is favored when rates of reactant supply are high calcite forms when rates are low such relations suggest that crystal morphology composition and mineralogy are controlled by the kinetics of surface nucleation and the amount of reactants principally carbonate ions at growth sites precipitating phases are the ones which can best accommodate such excess reactants ambient mg ca ratios only indirectly control the nature of inorganically precipitated carbonate phases

a prominent colour front in false bay south africa cross frontal structure composition and origin abstract colour fronts are a frequent occurrence in false bay south africa and their occurrence has been the subject of previous study and anecdotal conjecture the opportunity arose to make a cross frontal study of this feature in november 2005 photographs were taken and subsequently satellite imagery was obtained measurements were made of temperature salinity turbidity dissolved oxygen suspended solids plant nutrients and chlorophyll a cross frontal comparisons were also made on particulate material using a scanning electron microscope sem and elemental dispersive x ray edx analysis frontal waters were milky white green in colour in stark contrast to the adjacent clearer green blue waters the milky white green water mw gw was found to be warmer apparently less saline more turbid richer in nitrate and silicate and had a higher chlorophyll a concentration the dissolved oxygen signal was less pronounced both water types being supersaturated paradoxically in spite of the higher turbidity in the mw gw both water types had similar weights of suspended solids although the mw gw material was found to be more abundant and fragmentary when compared with its green blue water g bw counterpart the mw gw was rich in calcium whereas the g bw was silicon enriched the central findings of this study are that the strong southerly onshore wind conditions prior to mw gw formation introduced calcium rich fine particulates into the waters of the surf zone the sources of these particulates are thought to be the sea bed sediments and the sea land interface the particulates are close to neutral buoyancy enabling the mw gw to persist over the time scale of days a mechanism reinforced by the warming of this water in the nearshore zone the water was then advected by wind forcing and subsequently its own inertia around the north west corner of false bay at which stage it was easily observed and sampled it is suggested that the eventual collapse of the front was due to the slowing down of inertial movement in combination with the passive sinking of fine particulates and evaporative cooling resulting in downward convection

katabatic winds on ice sheets a refinement of the prandtl model katabatic winds on ice sheets and glaciers are buoyancy driven flows much like turbidity currents in the ocean these winds are driven by radiative cooling of the ice surface and are not resolved by the typical horizontal and vertical discretization of general circulation models therefore a parameterization of their magnitude is desirable in this paper it is shown that the simplest such parameterization based on the classical prandtl model of slope winds is physically inadmissible and an improved model which removes this irregularity is presented it is also shown that the improved model allows favorable comparison with both observations and regional numerical models

early meteoric diagenetic control of upper smackover production oaks field louisiana a comprehensive stable isotopic trace element and petrographic examination of 10 cores in the jurassic upper smackover formation at oaks field louisiana suggests that early meteoric diagenesis was directly responsible for the present observed porosity distribution in the field an isotopic and geochemical model for near surface meteoric diagenesis based on studies of quaternary diagenesis is fundamental to understanding the diagenetic history of the oaks field grainstones near surface meteoric diagenesis develops a characteristic isotopic and chemical signature that is easily recognized when sampled closely in stratigraphic sequence rocks stabilized in high flow freshwater phreatic lens show more negative meteoric dgr18o values and low values of magnesium and strontium relative to the zones above and below furthermore carbon isotopic values show a trend to lighter values upward toward the subaerial exposure surface indicating partial cementation and recrystallization in the presence of isotopically light soil gas in the vadose zone data from oaks field are interpreted in light of this diagenetic model porous zones in oaks field are characterized by more negative dgr18o values and lower magnesium and strontium content the carbon data show a trend to lighter values toward the tops of the wells these data suggest early mineralogic stabilization of the now porous intervals in a high flow near surface meteoric phreatic lens upon burial those intervals that had been stabilized early were less susceptible to solution compaction than those intervals retaining significant proportions of unstable mineralogy porosity reduction through solution compaction occurred because the unstable minerals were more soluble under burial conditions than stable low mg calcite these relationships are noted in all wells here porosity and permeability are well preserved

flow during the evening transition over steep alpine slopes a field campaign the slope experiment near la fouly self 2010 was conducted to monitor the evening transition of slope flows on clear sky days from july to september 2010 in a narrow valley of the swiss alps a steep west facing slope with inclinations ranging from 25 to 45 was instrumented from 1900mto 2200mabove sea level detailed measurements were made along a linear transect of the slope with two turbulence towers two weather stations five surface temperature measurement stations and a tethered balloon system the present study focuses on nine exemplary convective days characterized by weak synoptic flow and clear sky conditions during which thermal circulations prevail the analysis of the observational data shows that topographic shading triggers the evening transition the topographic configuration around the experimental site results in a sharply defined shading front propagating up slope causing a sudden decrease in incoming short wave radiation on the order of several hundreds of wm 2 within a few minutes the slope surface rapidly responds to the advancing shading front in some cases reductions in surface temperatures of some 10 c in less than 10 min are observed this is rapidly followed by an early evening calm period with very small turbulent kinetic energy tke 0 05m2 s 2 and extremely light wind speeds 0 5ms 1 when the inertia driven upslope flow is fully stopped by the katabatic acceleration a shallow local drainage flow forms and reaches a quasi equilibrium 1 5 h after the local sunset an analysis of the tke budget close to the surface shows that the buoyancy flux is much greater than the shear production in the last hours before the local sunset possibly due to valley curvature effects copyright c 2012 royal meteorological society

pleistocene speleothems of mallorca implications for palaeoclimate and carbonate diagenesis in mixing zones the pleistocene speleothems of sa bassa blanca cave mallorca are excellent indicators of palaeoclimate variations and are samples that allow evaluation of the products and processes of mixing zone diagenesis in an open water cave system integrated stratigraphic petrographic and geochemical data from a horizontal core of speleothem identified two main origins for speleothem precipitates meteoric marine mixing zone and meteoric vadose zone mixing zone precipitates formed at and just below the water air interface of cave pools during interglacial times when the cave was flooded as a result of highstand sea level mixing zone precipitates include bladed and dendritic high mg calcite microporous bladed calcite with variable mg content and acicular aragonite their presence suggests that calcium carbonate cementation is significant in the studied mixing zone system fluid inclusion salinities 13c and 18o compositions of the mixing zone precipitates suggest that mixing ratio was not the primary control on whether precipitation or dissolution occurred rather the proximity to the water table and degassing of co2 at the interface were the major controls on precipitation thus simple two end member mixing models may apply only in mixing zones well below the water table meteoric vadose speleothems include calcite and high mg calcite with columnar and bladed morphologies vadose speleothems precipitated during glacial stages when sea level was lower than present progressive increase in 13c and 18o of the vadose speleothems resulted from cooling temperatures and more positive seawater 18o associated with glacial buildup such covariation could be considered as a valid alternative to models predicting invariant 18o and highly variable 13c in meteoric calcite glacio eustatic oscillations of sea level are recorded as alternating vadose and mixing zone speleothems short term climatic variations are recorded as alternating aragonite and calcite speleothems precipitated in the mixing zone fluid inclusion and stable isotope data suggest that aragonite as opposed to calcite precipitated during times of reduced meteoric recharge

large eddy simulation of a katabatic jet along a convexly curved slope part 1 statistical results abstractlarge eddy simulation is performed to study a katabatic jet along a convexly curved slope with a maximum angle of about 35 5 the design of this numerical simulation of turbulent shear flow is discussed and a qualitative assesment of the method is proposed the katabatic flow is artificialy generated by ground surface cooling and a stable atmospheric boundary layer with constant stratification is considered as a reference state a quantitative statistical analysis is used to describe the present turbulent flow with a focus on the outer layer shear of the katabatic jet which extends about 50 m above the jet maximum the prandtl model for a katabatic jet is applied to the present results and revisited versions of the model found in the literature are discussed with an emphasis on specific momentum and turbulent heat diffusion the vertical and downslope variability of the turbulent kinetic energy budget is also discussed and it is shown that advection and production contributions in the downslope

large eddy simulation of the convective atmospheric boundary layer abstract large eddy simulations of a free convective atmospheric boundary layer with an overlying capping inversion are considered attention is given to the dependence of the results upon the various factors influencing the simulation the subgrid model the domain size and the mesh resolution by providing artificial constraints upon the convection the results also provide extra insight into the underlying dynamics the gross features of the boundary layer such as the overall energy budget are not sensitive to the details of the simulations but a number of important factors are revealed it has been found that near the surface the subgrid diffusivity must be larger than is usually supposed in order for the vertical velocity skewness to have the correct sign this region of the flow has a significant subgrid scale heat flux and it seems that the subgrid model requires improvement in such cases a revised model which under statically unstable conditions allows the mixing length of the subgrid scale tu

fulvic acid like organic compounds control nucleation of marine calcite under suboxic conditions intracrystalline organic compounds enclosed within in situ precipitated marine microcrystalline calcite automicrite might represent either an inclusion or the catalyst of such precipitation we use evidence from a lower cretaceous deep water carbonate mound to show 1 the original source 2 the degree of condensation 3 the redox conditions involved and 4 the catalytic role of natural organic matter for the precipitation of automicrite fluorescence spectrometry of the intracrystalline organic fraction extracted from these carbonates identifies a marine fulvic acid like organic compound with a low degree of polycondensation this finding points to a temporal correlation of the initial stage of geopolymer formation with the precipitation of automicrite furthermore the rare earth element ree distribution patterns in the mineral show a consistent positive ce anomaly suggesting an episode of reductive dissolution of iron manganese oxyhydroxides during automicrite formation in general a relative enrichment of middle weight rees is observed resulting in a convex distribution pattern typical for e g phosphate concretions or humic acid material by merging the results of spectrometry and ree geochemistry we thus conclude that the marine calcite precipitation was catalyzed by marine fulvic acid like compounds during the early stages of humification under suboxic conditions this indicates that humification driven by the presence of a benthic biomass is more important for calcite authigenesis than any site specific microbial metabolism the neoproterozoic rise of carbonate mounds supports this hypothesis there is molecular evidence for early metazoan divergence then but not for a major evolutionary episode of microorganisms

two hundred million years of karst history dachstein limestone hungary platform carbonates of the upper triassic dachstein limestone in naszaly hill have been karstified extensively over the past 200 million years they provide an excellent example of polyphase karstic diagenesis that is probably typical of many subaerially exposed carbonate sequences seven karstic phases are recognized in the area each of which include polyphase karstic events the first karst phase was associated with the lofer cycles meteoric waters caused dissolution enlarged fractures and cavities were filled by marine and or vadose silts and cement the second karst phase was caused by local tectonic movements bedding plane controlled phreatic caves were formed and filled by silts the third karst phase lasted from the end of the triassic to the eocene this was a regional multiphase karstic event related to younger composite unconformities bauxitic fill is the most characteristic product of this phase the karst terrain reached its mature or senile stage with very little porosity narrow veins and floating rafts of white calcite marks karst phase 4 which resulted from hydrothermal activity associated with palaeogene magmatism the early rupelian phase of alpine uplift caused large scale rejuvenation of the former karst terrain karst phase 5 subsequently naszaly hill was buried as an area of juvenile karst with significant porosity a second period of hydrothermal activity in the area karst phase 6 was induced by miocene volcanism which resulted in wide pale green calcite veins finally karst phase 7 was of tectonic origin following the most recent miocene uplift of the naszaly hill the carbonates have again become the site of vadose karst development

an evaporation driven salinity maximum zone in australian tropical estuaries abstract the distribution of temperature and salinity in three tropical australian estuaries was measured in october 1983 in the hot dry season as a result of evaporation a salinity maximum zone exists near the mouth of the river where downwelling occurs and a classical and an inverse internal estuarine circulation prevail respectively upstream and downstream of the salinity maximum zone the zone of salinity maximum can be thought of as a high salinity plug inhibiting so much the mixing of estuarine and ocean waters that in some cases freshwater dose not reach the ocean

coupling between sulfur recycling and syndepositional carbonate dissolution evidence from oxygen and sulfur isotope composition of pore water sulfate south florida platform u s a sulfur cycling in fe poor organic rich shelf carbonates known to have rapid rates of so4 2 reduction remains poorly studied despite the volumetric significance of shelf deposits in modern and ancient carbon budgets we investigated sulfur cycling in modern carbonates of the florida platform from end member depositional environments muddy sands from the atlantic reef tract and finer grained mudbank and island flank deposits from florida bay relations between pore water chemistry so4 2 co2 ca 2 cl and oxygen and sulfur stable isotope compositions of so4 2 require direct coupling between sulfur redox cycling and syndepositional carbonate dissolution oxygen isotope compositions of pore water sulfate were remarkably shifted away from the established value for marine so4 2 9 5 despite near normal so4 2 cl ratios chemical evolution was least in reef tract pore waters and greatest in florida bay relative to overlying seawater mudbank sediments exhibited sulfate depletion with 18oso4 and 34sso4 values both increasing by about 7 more bioturbated island flank sediments colonized by thalassia grass had a 5 increase in 18oso4 variable 34sso4 values 17 7 to 23 3 and exceptionally high ca 2 cl ratios the large excess of ca 2 up to 1 7 mm requires a much larger acid source than the amounts derived from utilization of dissolved o2 0 3 mm and small degrees of net so4 2 reduction 0 5 mm reduced a conceptual model was constructed using chemical and isotopic data on natural pore waters and on sulfate isotope fractionation factors obtained from sediment incubation experiments the model outputs show that pore water compositions can be explained by a redox cycle where microbial so4 2 reduction is followed by very efficient h2s oxidation thus maintaining virtually invariant so4 2 cl ratios the enhanced o2 transport may be driven by associated marine grass rhizome systems and microbial communities established in bioturbated sediments the net result of the cycle is that the rate of sulfide oxidation which is largely balanced by the rate of microbial sulfate reduction is stoichiometrically related to the rate of carbonate dissolution this is consistent with previously reported rates of carbonate dissolution 400 mol cm2 yr and average rates of sulfate reduction 200 mol cm2 yr from the florida platform and a 2 1 stoichiometry

diagenesis of fibrous magnesian calcite marine cement implications for the interpretation of δ18o and δ13c values of ancient equivalents fibrous high mg calcite hmc marine cement from the pliocene hope gate formation jamaica occurs as 1 2 mm thick isopachous coatings on skeletal grains in local occurrences of halimeda grainstone and is commonly syntaxially overgrown by clear prismatic low mg calcite lmc interpreted as a mixing zone cement the presence of inclusions at discrete levels in the fibrous marine cement produces internal growth banding wherein clear inclusion free zones alternate with cloudy inclusion rich zones clear zones have uniform mg contents 13 7 0 2 mol mgco3 and stable isotopic compositions 18o 0 8 0 1 13c 3 2 0 1 consistent with a marine origin in contrast inclusion rich zones contain fine scale intergrowths of lmc dolomite and hmc and have carbon and oxygen isotopic compositions that define a linear mixing trend between compositions of inclusion free hmc and prismatic lmc cement overgrowths petrographic observations indicate that the mixing trend defined by isotopic data from inclusion rich zones is related to the addition of large volumes of secondary lmc as cement in primary pore space as intergrowths among fibers of primary hmc marine cement and or as replacements of primary hmc crystallites dolomite is present in inclusion rich zones in volumes generally compatible with amounts predicted to result from the closed system stabilization of hmc to lmc and dolomite in addition isotopic and geochemical data from some areas of inclusion rich zones are consistent with mass balance constraints assuming a closed system which require that bulk isotopic and geochemical compositions are retained these relations suggest that small remnants of hmc in inclusion rich zones of hope gate marine cement have altered to lmc and dolomite while isolated from system pore fluids such that primary marine isotopic signatures were imparted on diagenetic products similar petrographic geochemical and isotopic relations have been noted in ancient occurrences suggesting that 18o and 13c values from some former marine cements should be useful for the determination of isotopic compositions of original marine cements and ultimately for the determination of ocean chemistry in the geologic past

iron bacterial mediation in phanerozoic red limestones state of the art different pathways can be proposed to explain the origin of the red pigmentation present in many phanerozoic limestones we investigate three possible models 1 telogenetic alteration 2 detrital input and 3 role of iron bacteria the third hypothesis is supported by our data for a number of phanerozoic series by this hypothesis not only can we highlight the importance of the microenvironments at the dysoxic anoxic water sediment interfaces for the bacterial fe oxidation but also can conclude that the dred limestonest have no particular paleogeographic meaning the seven studied red successions are rather poor in iron 350 ppm in the ammonitico rosso without large fluctuations the pigmentation is due to the dispersion of submicrometric hydro oxides now hematite formed by bacterial mediation during early diagenesis in various microaerophilitic environments different ferruginous morphs e g filaments coccoids microstromatolites suggest the presence of iron bacteria the limiting factor is the oxygen content which was low in these very quiet and relatively deep environments the presence of iron bacteria is also confirmed by iron isotope analysis on the ammonitico rosso fe isotopic compositions have been analyzed on residues as well as on leachates of red and grey facies of the same interval d 56 fe values are systematically lower in the red residues varying from 1 19x to 0 34x compared to the grey ones 0 27x to 0 09x this indicates a significant accumulation of lighter isotopes in the red parts suggesting that hematite have been formed via a biological pathway d 2005 elsevier b v all rights reserved

a theory for the estimation of surface fluxes in simple katabatic flows the classical prandtl model describes the basic dynamics of katabatic flows but it fails in determining the gradients near the surface because the eddy diffusivity k is independent of height z an improvement is proposed to the prandtl model by using the wkb method to solve the dynamic equation for any prescribed reasonably smooth k z profile the surface fluxes are obtained by extrapolation from the katabatic jet down to the surface thus the fluxes depend primarily on the jet which is well captured by the wkb method the profiles of wind temperature momentum and heat fluxes as well as the surface fluxes calculated using the model are tested against observations from a meteorological field campaign on the pasterze glacier austria in 1994 and their numerical simulations generally there is a good agreement between observations and theory

the middle late jurassic forced regression and disconformity in central portugal eustatic tectonic and climatic effects on a carbonate ramp system successions across the middle upper jurassic disconformity in the lusitanian basin west central portugal are highly varied and were probably developed on a large westward inclined hangingwall of a half graben the disconformity is preceded by a complex forced regression showing marked variations down the ramp and provides an example of the effects of rapid relative sea level falls on carbonate ramp systems in the east middle jurassic inner ramp carbonates candeeiros facies are capped by a palaeokarstic surface veneered by ferruginous clays or thick calcretes in the west mid outer ramp marls and limestones brenha facies are terminated by two contrasting successions 1 a sharp based carbonate sandbody capped by a minor erosion surface overlain by interbedded marine lagoonal deltaic deposits with further minor erosion exposure surfaces 2 a brachiopod rich limestone with a minor irregular surface overlain by marls lignitic marls with marine and reworked non marine fossils and charophytic limestones with further minor irregular surfaces and capped by a higher relief ferruginous erosional surface the age ranges from late bathonian in the east to late callovian in the west this disconformity assemblage is succeeded by widespread lacustrine lagoonal limestones with microbial laminites and evaporites cabacos facies attributed to the middle oxfordian over the whole basin increasingly marine facies were deposited afterwards in middle jurassic inner ramp zones in the east the overall regression is marked by a major exposure surface overlain by continental sediments in middle jurassic outer ramp zones to the west the regression is represented initially by open marine successions followed by either a sharp marine erosion surface overlain by a complex sandbody or minor discontinuities and marginal marine deposits in both cases capped by the major lowstand surface reflooding led to a complex pattern of depositional conditions throughout the basin from freshwater and brackish lagoonal to marginal and shallow marine settings additional complications were produced by possible tilting of the hangingwall of the half graben the input of siliciclastics from westerly sources and climate change from humid to more seasonally semi arid conditions the middle late jurassic sea level fall in the lusitanian basin is also recorded elsewhere within the iberian and other peri atlantic regions and matches a transgressive to regressive change in eustatic sea level curves indicating that it is related in part to a global event

overview of ophiolites and related units in the late palaeozoic early cenozoic magmatic and tectonic development of tethys in the northern part of the balkan region abstract the northern balkan peninsula including serbia montenegro bosnia croatia and the former yugoslavian republic of macedonia represents an excellent region for the study of tectonic processes related to mesozoic tethyan ophiolite genesis and emplacement we first summarise the main tectonic units of the northern balkan peninsula and then use this information to discuss tectonic processes including rifting sea floor spreading ophiolite genesis and emplacement melange accretion ocean basin closure and collision we then discuss alternative models of ophiolite genesis and emplacement for the region and suggest that multi ocean basin interpretations fit the data better than single ocean basin interpretations rifting of adria gondwana during the triassic created a rift in the south budva zone and opened a triassic oceanic basin further north dinaride ocean occurrences of inferred sub continental mantle lithosphere in the dinaride ophiolite belt e g zlatibor may record extensional exhumation within an ocean continent transition zone bordering the adria dinaride continent this was followed by emplacement together with ophiolites and melange during upper jurassic early cretaceous time upper triassic radiolarites and mid ocean ridge type basalts formed at a spreading ridge after continental break up the oceanic lithosphere of the dinaride ophiolite belt was partly generated above a subduction zone the metamorphic soles of the dinaride ophiolites formed during mid late jurassic mainly based on k ar dating widespread melange that is associated with the ophiolites represents a subduction complex controlled by tectonic accretion and sedimentary reworking in trench and fore arc basin settings a possible cause of jurassic dinaride ophiolite emplacement was collision of a subduction trench with a continental margin further north mesozoic oceanic lithosphere subducted northeastwards present coordinates opening a late jurassic marginal basin in the main vardar zone the dinaride ocean in the south closed during late jurassic early cretaceous time tithonian berriasian deformed oceanic crust melange and magmatic arc rocks further north main vardar zone were transgressed by mainly clastic sediments during the early cretaceous however part of the vardar ocean vardar zone western belt or sava zone remained partially open until latest cretaceous time generally northward subduction within this remnant ocean triggered further supra subduction zone ophiolite genesis during the late cretaceous the ocean closed by the maastrichtian followed by early cenozoic regional scale southward thrusting that locally intercalated older and younger mesozoic ophiolites and melanges future progress particularly depends on determining the crystallisation ages of the ophiolites obtaining better structural data on the direction of initial ophiolite emplacement and unravelling the palaeozoic tectonic development of the eurasian continental margin

why is stromatactis so rare in mesozoic carbonate mud mounds the sedimentary diagenetic structure stromatactis is widespread in palaeozoic spiculitic carbonate mud mounds but occurs only sporadically in mesozoic sponge carbonate mud mounds comparative analysis of palaeozoic and mesozoic stromatactis limestones suggests that this variation results from the degree of siliceous sponge skeletal rigidity and the amount of internal sediment accumulation in the original cavity network partial to entire filling by internal sediment resulted in a continuum from a small amount of internal sediment and large amount of cement stromatactis common in the palaeozoic to only internal sediments aborted stromatactis common in the mesozoic these observations match independent lines of evidence concerning the siliceous sponge evolution and sediment recycling e g bioerosion across the palaeozoic to mesozoic biotic revolution

evolution of porosity in the saltwater freshwater mixing zone of coastal carbonate aquifers an alternative modelling approach summary dissolution of calcium carbonate in the saltwater freshwater mixing zone in carbonate islands and coastal aquifers up to now has been treated by coupling geochemical equilibrium programmes to a reactive transport model the result is a complex nonlinearly coupled set of differential transport advection equations which need high computational efforts if dissolution rates of calcite are sufficiently fast such that one can assume the solution to be in equilibrium with respect to calcite a highly simplified modelling approach can be used by use of the concept of phillips in his book flow and reactions in permeable rock cambridge university press new york 1991 and its more general formulation by de simoni et al de simoni m carrera j sanchez vila x guadagnini a 2005 a procedure for the solution of multicomponent reactive transport problems water resource research 41 w11410 it is possible to decouple the complex set of equations to calculate initial changes of porosity in the rock matrix one needs solely to solve the advection transport equation for salinity s current codes on density driven flow such as seawat can be used to obtain the dissolution capacity of the mixed saltwater freshwater solution the calcium equilibrium concentration c eq s is obtained as a function of salinity by phreeqc 2 initial porosity changes can then be calculated by a simple analytical expression of the gradient of the spatial distribution s x y of salinity the distribution of flow fluxes q x y and the second derivative of the calcium equilibrium concentration c eq s with respect to salinity s this approach does no longer require large dispersivities on the order of meters but reasonable results are obtained with dispersivity on the scale of the pore size of the porous rock which correctly describes mixing on the molecular scale the method is applied to a simple 1 d domain without convective flow and a constant gradient of salinity as presented by rezaei et al rezaei m sanz e raeisi e ayora c vazquez sune e carrera j 2005 reactive transport modeling of calcite dissolution in the fresh saltwater mixing zone journal of hydrology 311 1 4 282 298 our results exhibit a sharper dissolution zone close to the freshwater side of the domain which is caused by the properties of the second derivative of c eq s recently singurindy et al water resources research 40 2004 and correction in water resources research 41 2005 performed dissolution experiments in a saltwater freshwater mixing zone in a sandbox the results from our model simulations are in good agreement to their experimental data finally the modelling approach is employed to porosity evolution in homogeneous and heterogeneous carbonate islands the results are in general agreement to earlier work due to the properties of the second derivative however the regions of active dissolution are restricted to more narrow regions

an intercomparison of subgrid models for large eddy simulation of katabatic flows we present an intercomparison of three subgrid scale sgs models for large eddy simulation les of katabatic flows the sgs closures we study include the smagorinsky formulation a scale invariant dynamic model and a scale dependent dynamic model downslope fluxes of mass and buoyancy deficit are highly sensitive to sgs closure choice due to strong shear and strong stratification the dynamic models show a reduction of the smagorinsky coefficient near the surface relative to the smagorinsky model furthermore results from both scale dependent dynamic models suggest that the assumptions of scale invariance in the dynamic model are violated we present a second set of experiments which focus on grid resolution requirements of eddy resolving simulations of drainage flows downslope buoyancy and mass flux predictions produced by the scale dependent dynamic model are more robust with respect to grid resolution and grid anisotropy than the scale invariant dynamic and smagorinsky sgs models predictions of vertically integrated downvalley mass and buoyancy fluxes are more sensitive to vertical grid resolution than horizontal grid resolution

botryoidal aragonite and its diagenesis botryoidal aragonite is a spectacular growth form occurring as mamelons up to 100 mm in diameter three examples of this particular carbonate cement have been discovered in two distinct areas in new caledonia small scale mamelons have been recognized within pleistocene reefal terraces at ouvea an island of the loyalty archipelago and in the red sea large scale mamelons of botryoidal aragonite exist within pleistocene reefal terraces along the um gheig region of the egyptian coast in addition a similar botryoidal cement partly dolomitized but exhibiting aragonite relics occurs within a miocene reef in the same region mamelons of botryoidal aragonite are isolated and or coalescent but grow only on fixed substrates they occur within cavities of varied origin their fabrics are characterized by fans of elongate euhedral crystals of aragonite fibres botryoidal aragonite can be preceded or followed by other types of cements or internal sediment despite similar mineralogy petrography and ultrastructure there are differences between the fabrics of the pleistocene botryoids from the red sea and ouvea and the miocene botryoids from the red sea the former are of submarine origin as confirmed by the strontium content 8500 10 500 ppm and isotopic composition 18o between 0 10 and 0 19 pdb the latter related to a miocene karst are rich in strontium average 13 600 ppm and have an isotopic composition average 18o 10 50 pdb indicative of non marine precipitation diagenesis of these botryoidal aragonites consists of slight dissolution for pleistocene botryoids and mineralogical transformation for the miocene botryoids the latter exhibit the diagenetic sequence aragonite calcite dolomite the aragonite to calcite transformation is a dissolution reprecipitation process the void distribution and size influencing the distribution and the size of the replacement calcite crystals

black pebble occurrence and genesis in holocene carbonate sediments florida keys bahamas and tunisia abstract black carbonate lithoclasts along with blackened peloids ooids skeletal fragments and entire limestone beds are found in the shallow subtidal intertidal and supratidal zones of modern and ancient carbonate environments they are often associated with pedogenic features such as root traces or caliche the blackening is due to impregnation of the sediment by dissolved colloidal or finely particulate organic substances in an anoxic and alkaline environment or microenvironment the organic matter is derived from decayed algae and or decayed or burnt higher terrestrial plants iron sulfides contribute to the blackening especially in samples containing algal matter a complex interplay of adsorption of organic matter on carbonate crystal surfaces neomorphism and microcrystalline cementation in the vadose or freshwater phreatic zones is thought to fix the organic matter and make the black coloration relatively resistant to oxidation black pebbles form through reworking of the preferentially cemented and blackened sediment by coastal erosion they are mostly relics because the less consolidated host sediment is washed away black pebbles may thus be valuable indicators of ancient coastal and terrestrial environments

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

pleistocene shoreline deposition and sea level history at swartklip south africa abstract a 50 m thick succession of poorly cemented sandstone is exposed along the northern shore of false bay south africa this late pleistocene succession is attributed to shorezone estuarine deposition in the last interglacial and dune activity during the highstand and early in the succeeding sea level withdrawal facies analyses allow us to establish that the last interglacial sea level high 120 ka locally reached an elevation between the upper and lower boundaries of a washover sequence that is 5 1 to 8 0 m above present mean sea level four depositional facies are recognized on the basis of distinct lithologies and assemblages of sedimentary structures beachrock is present intermittently in the present intertidal zone as a seaward dipping unit of flatbedded sandstone capped by calcrete we interpret this facies as a beach foreshore wedge which originated in warmer climates of the 135 ka sea level high and which developed its calcrete crust in the lowstand which immediately followed subsequent sea level rise at 120 ka and shoreline progradation is reflected in a two meter thick estuarine fill containing tomichia ventricosta a third facies comprises landward dipping sheetsands which overlie the estuarine fill on the basis of facies relationships and primary sedimentary structures this unit is attributed to washover fan deposition the last and dominant facies comprises calcite cemented sandstone arranged in sets of very large scale crossbeds pulmonate gastropods occur throughout poorly developed calcretes interrupt the succession deposition of this facies is believed to have occurred as parabolic dunes in a coastal foredune complex near the start of the wurm wisconsinan glacial climate when atmospheric circulation was more intense modern pedotubule and hardpan calcretes cap the succession

biofilm architecture of phanerozoic cryptic carbonate marine veneers thin 150 m micritic veneers lining crypts in paleozoic and mesozoic reef microbial and bioclastic carbonates have the dimensions and architecture of modern uncalcified bacterial biofilm morphologic attributes include rounded aggregate nanofabric internal channels external towers mushrooms and plumes all can be interpreted as characteristics of attached bacterial communities i e aggregates as microcolonies originally embedded in a matrix of extracellular polymeric substances channels as water conduits and or uncolonized nutrient poor spaces external protuberances as localized growths and plumes as surface streamers cryptic habitat favored pristine biofilm preservation by precluding disturbance and overgrowth and suggests aphotic and anoxic conditions these examples provide diagnostic morphologic criteria for wider recognition of biofilm in phanerozoic and older carbonates

carbonate dissolution in a modern mixing zone the potential for dissolution of calcite and aragonite and precipitation of dolomite by the mixing of fresh and saline ground waters has been demonstrated theoretically1 3 although geologists have used these processes in the explanation of the diagenesis of recent4 7 and ancient8 12 carbonates there has been only limited investigation of the geochemical processes of modern mixing zones13 14 here we report the results of chemical and rock profiling through a modern mixing zone on andros island in the bahamas our results demonstrate undersaturation of the waters in the mixing zone with respect to aragonite and calcite and corresponding pervasive dissolution of the carbonate rocks at this level undersaturation is significantly enhanced by bacterial processes which are also responsible for precipitation of an iron rich crust despite chemical supersaturation precipitation of dolomite was not observed thereby casting some doubt on the mixing zone model of dolomitization

missing molluscs field testing taphonomic loss in the mesozoic through early large scale aragonite dissolution as a field test for cherns and wright9s previously published hypothesis based on paleozoic faunas that the paucity of certain molluscan groups in the fossil record may be largely a taphonomic not ecologic effect a typical mesozoic molluscan dominated fauna is compared with its early silicified lagerstatten equivalent from a similar depositional setting a lower jurassic offshore carbonate ramp facies in south wales comprises alternating thin limestones and organic rich shales the former are largely diagenetic and carry marine isotopic signatures their typical fauna is mainly well preserved calcitic and bimineralic calcite aragonite epifaunal and semiinfaunal bivalves evidence of aragonitic shells is normally restricted to molds common in inner ramp settings in high energy skeletal grainstones but mostly poorly preserved and restricted to deep burrowing bivalves in offshore deposits however locally early silicification in offshore facies has preserved much more diverse faunas with abundant formerly aragonitic molluscs including many more infaunal burrowers it appears that major aragonite dissolution normally distorted both apparent diversity 65 decrease in bivalve diversity and the trophic structure of the offshore facies providing aragonite that probably sourced the diagenetic carbonates we suggest that aragonitic shells were selectively dissolved in the upper sediment column in lower energy settings where high organic contents favored microbial decay and acidity such early dissolution was absent from the higher energy facies that originally had low organic contents taphonomic loss through early skeletal aragonite dissolution was an equally important process in mesozoic offshore shelf environments and although still leaving depleted molluscan dominated faunas resulted in a massive distortion of diversity

effects of sulfate reduction on caco 3 dissolution and precipitation in mixing zone fluids abstract sulfate reduction in the sea water end member of mixing zone fluids changes the fluid saturation indices for carbonate minerals mixing zone fluids were modeled quantitatively using atlantic sea water and a fresh water end member from barbados for sulfate reduction in the presence of goethite in the absence of goethite and with back oxidation of aqueous sulfide to sulfate minor amounts of sulfate reduction enhance dissolution of caco3 in brackish to saline mixing zone fluids whereas major amounts of sulfate reduction enhance precipitation in all mixing zone fluid compositions secondary reactions produce either caco3 dissolution or precipitation which depend in magnitude on the amount of sulfate reduction dissolution results from the back oxidation of aqueous sulfide to sulfate and precipitation occurs from the transformation of iron oxides to iron sulfides ph buffering due to sulfate reduction prevents a linear correlation of calcite saturation indices with the moles of calcite necessary to dissolve or precipitate to reach equilibrium without iron sulfide precipitation or the back oxidation of aqueous sulfide the moles of calcite that can be dissolved continue to increase up to about 25 sulfate reduction even though the degree of undersaturation begins to decrease with greater than 5 sulfate reduction the effects of iron sulfide precipitation and the back oxidation of aqueous sulfide are greatly enhanced by increasing the amount of sulfate reduction being generally more than 0 1 g of calcite per kg of water dissolved or precipitated respectively at 50 sulfate reduction

selective blackening of bioclasts via mixing zone aragonite neomorphism in late triassic limestone zlatibor mountains serbia a peculiar facies of the norian rhaetian dachstein type platform carbonates which contains large amounts of blackened bioclasts and dissolutional cavities filled by cements and internal sediments occurs in the zlatibor mountains serbia microfacies investigations revealed that the blackened bioclasts are predominantly solenoporaceae with a finely crystalline originally aragonite skeleton of fine cellular structure blackening of other bioclasts also occurs subordinately solenoporacean dominated reefs developed behind the platform margin patch reef tract were the main source of sand sized detritus the blackened and other non blackened bioclasts are incorporated in automicrite cement radiaxial fibrous calcite cements in the dissolutional cavities are also black dark grey or white reworked black pebbles were reported from many occurrences of peritidal deposits in those cases the blackening took place under pedogenic meteoric diagenetic conditions in contrast in the inner platform deposits of the ilidz ya limestone the blackening of bioclasts occurred in a marine meteoric mixing zone as indicated by petrographic features and geochemical data of the skeleton replacing calcite crystals attributes of mixingzone pore waters were controlled by mixing corrosion different solubility of carbonate minerals and microbial decomposition of organic matter in the moderate energy inner platform environment large amounts of microbial organic tissue were accumulated and subsequently decomposed triggering selective blackening in the course of early shallow burial diagenesis the d 18 o and d 13 c values of the mixing zone precipitates and replacive calcite do not produce a linear mixing trend variation mainly resulted from microbial decomposition of organic matter that occurred under mixing zone conditions the paragenetic sequence implies cyclic diagenetic conditions that were determined by marine meteoric and mixing zone pore fluids the diagenetic cycles were controlled by sea level fluctuations of moderate amplitude under a semi arid to semi humid climate

modeling of subsurface calcite dissolution including the respiration and reoxidation processes of marine sediments in the region of equatorial upwelling off gabon abstract mineralization of organic matter and the subsequent dissolution of calcite were simulated for surface sediments of the upper continental slope off gabon by using microsensors to measure o2 ph pco2 and ca2 in situ pore water concentration profiles of no3 nh4 fe2 and mn2 and so42 ex situ as well as sulfate reduction rates derived from incubation experiments the transport and reaction model cotrem was used to simulate the degradation of organic matter by o2 no3 fe oh 3 and so42 reoxidation reactions involving fe2 and mn2 and precipitation of fes model application revealed an overall rate of organic matter mineralization amounting to 50 mol c cm 2 yr 1 of which 77 were due to o2 17 to no3 and 3 to fe oh 3 and 3 to so42 the best fit for the ph profile was achieved by adapting three different dissolution rate constants of calcite ranging between 0 01 and 0 5 d 1 and accounting for different calcite phases in the sediment a reaction order of 4 5 was assumed in the kinetic rate law a caco3 flux to the sediment was estimated to occur at a rate of 42 g m 2 yr 1 in the area of equatorial upwelling the model predicts a redissolution flux of calcite amounting to 36 g m 2 yr 1 thus indicating that 90 of the calcite flux to the sediment is redissolved

mesozoic lower jurassic red stromatactis limestones from the southern alps arzo switzerland calcite mineral authigenesis and syneresis type deformation the broccatello lithological unit lower jurassic hettangian to lower parts of upper sinemurian near the village of arzo southern alps southern switzerland is a mound shaped carbonate deposit that contains patches of red stromatactis limestone within the largely bioclastic broccatello unit the stromatactis limestone is distinguished by its early diagenetic cavity system a relatively fine grained texture and an in situ assemblage of calcified siliceous sponges various demosponges and hexactinellids a complex shallow subsurface diagenetic pathway can be reconstructed from sediment petrography in combination with comparative geochemical analysis carbon and oxygen isotopes trace and rare earth elements ree y this pathway includes organic matter transformation aragonite and skeletal opal dissolution patchy calcification and lithification sediment shrinkage sagging and collapse partial ree remobilization and multiple sediment infiltration these processes occurred under normal marine essentially oxic conditions and were independent from local recurring syn sedimentary faulting it is concluded that the stromatactis results from a combination of calcite mineral authigenesis and syneresis type deformation the natural stromatactis phenomenon may thus be best explained by maturation processes of particulate polymer gels expected to form in fine grained carbonate sediments in the shallow subsurface conditions favorable for the evolution of stromatactis appear to be particularly frequent during drowning of tropical or subtropical carbonate platforms

soluble humic substances from in situ precipitated microcrystalline calcium carbonate internal sediment and spar cement in a cretaceous carbonate mud mound albian carbonate mud mound limestones exposed near iraneta northern spain show a fabric and particle specific fluorescence intense fluorescence is restricted to in situ precipitated microcrystalline automicritic fabrics calcified demosponges and coralline sponges intermediate intensity derives from micritized bioclasts pellets and a rim of marine bladed cement most invertebrate skeletons late diagenetic equant cement and crosscutting zones of dolomitization are weakly to nonfluorescent internal microcrystalline sediment allomicrite and red algae debris have variable fluorescence correlation between rock fluorescence and soluble humic substances was evaluated from 3 g of automicrite allomicrite and cement time resolved laser induced fluorescence spectroscopy trlfs with ultra short pulses on two extracrystalline fractions naoh soluble and two intracrystalline fractions hcl soluble and naoh soluble showed that most of the soluble humic substances of automicrite are within the crystals but conversely are significantly enriched on outer surfaces of allomicrite spar cement is close to detection limits fluorescence lifetimes are in the range of 0 5 2 ns and 3 5 6 ns we conclude that precipitation of automicrite took place during oxidative organic matter diagenesis i e during condensation reactions of degradation products of marine biopolymers by contrast allomicrite formed by skeletal breakdown followed by ingestion organic coating and reingestion during deposit feeding a humic substance based model of marine polymer gels represents a new approach for the understanding of ancient polygenetic carbonate muds so typical of phanerozoic mud mounds in deeper water settings

geomicrobiology its significance for geology abstract some microorganisms including various kinds of bacteria fungi algae and protozoa serve as geochemical agents in the uppermost lithosphere and in the hydrosphere some promote rock weathering by mobilizing mineral constituents with inorganic or organic acids or ligands that they excrete others promote rock weathering by redox attack of mineral constituents such as fe and mn still others cause active or passive mineral formation by precipitation and subsequent nucleation of crystal formation on or in the cell or in the bulk phase they play a role in some phases of fossil fuel formation and accumulation they modulate the terrestrial and marine cycles of c n s and p and some other elements and they influence the composition of the atmosphere in respect to o 2 co 2 and ch 4 some discriminate between stable isotopes of h c o n and s

the structure of stably stratified atmospheric boundary layers a large eddy simulation study dry stably stratified planetary boundary layers have been studied by large eddy simulation results from simulations using two different subgrid scale models are compared a recently suggested improved subgrid scale model version is shown to give improve