natural free convection in porous media first field documentation in groundwater 1 natural free convection is a process of great importance in disciplines from hydrology to meteorology oceanography planetary sciences and economic geology and for applications in carbon sequestration and nuclear waste disposal it has been studied for over a century but almost exclusively in theoretical and laboratory settings despite its importance conclusive primary evidence of free convection in porous media does not currently exist in a natural field setting here we present recent electrical resistivity measurements from a sabkha aquifer near abu dhabi united arab emirates where large density inversions exist the geophysical images from this site provide for the first time compelling field evidence of fingering associated with natural free convection in groundwater

early detection of first time slope failures using acoustic emission measurements large scale physical modelling early warning systems for slope instability need to alert users of accelerating slope deformation behaviour to enable safety critical decisions to be made this study shows that acoustic emission

late quaternary stratigraphic charcoal records from madagascar the classic view regarding the cause of the extinction of at least 17 species of large mammals birds and reptiles in madagascar during the late holocene implicates human use of fire to modify the environment however analysis of the charcoal stratigraphy of three sediment cores from madagascar shows that late pleistocene and early to mid holocene sediments deposited prior to human settlement often contain more charcoal than postsettlement and modern sediments this observation which is confirmed by independent measurements from direct assay and palynological counting techniques suggests that widely held but previously untested beliefs concerning the importance of anthropogenic fires in late holocene environmental changes and megafaunal extinctions of madagascar may be based on an overly simplified version of actual prehistoric conditions moderate to low charcoal values characterized only the late holocene millennia immediately prior to the presumed time of arrival of the first settlers human settlement is probably indicated in the stratigraphy by the sharp rise in charcoal content observed beginning ca 1500 yr b p fire appears to be a significant natural component of prehuman environments in madagascar but some factor probably climate has modulated the extent of natural burning

automatic approach for increasing the location accuracy of slow moving landslide endogenous seismicity the apoloc method seismological observations offer valuable insights on the stress strain states the physical mechanisms and the possible precursory signs of activation of various earth surface processes i e volcanoes glaciers and landslides comprehensive catalogues of the endogenous landslide seismicity that is corresponding to seismic sources generated by the unstable slope from either mechanical or hydrological origins should include the typology and an estimate of the source parameters location magnitude of the event these advanced catalogues constitute a strong basis to better describe the slope deformation and its time evolution and better understand the controlling factors because the number of seismic events in landslide catalogues is generally large automatic approaches must be considered for defining both the typology and the location of the sources we propose here a new location approach called automatic picking optimization and location method apoloc for locating landslide endogenous seismic sources from seismological arrays located at close distance the approach is based on the automatic picking of the p waves arrivals by optimizing the intertrace correlations the method is tested on calibration shots realized at the super sauze landslide southeast french alps and compared to other location approaches by using a realistic velocity model obtained from a seismic tomography campaign apoloc reduces the epicentre errors to 23 m on average compared to ca 40 m for the other approaches apoloc is then applied for documenting the endogenous seismicity i e slopequakes and rockfalls at the landslide

microseismic emissions from flowslide type movements in south wales abstract many of the unstable hillslopes of south wales have landslides that turn into flowslides over part of their tract the valley slopes at pant teg and glynrhigos are unstable as they possess the optimum requirements for slope failure they have probably been affected by repeated movements during the last 10 000 years significant acoustic emissions ae have been recorded from two landslide sites both subsequent to a major failure pant teg and during continuous movement glynrhigos four distinct types of ae have been recognised so far with frequencies in the 1 7 khz bandwidth with particular peaks at 1 2 2 0 4 2 4 9 5 5 and 6 5 khz the results indicate that there is a potential in developing a warning system for identifying increasing instability

charcoal analysis for paleoenvironmental interpretation a chemical assay a nitric acid digestion and ignition technique developed to measure relative frequencies of charcoal in lake and bog sediments measures the weight of charcoal relative to the dry weight of the sample percentage charcoal and gives results comparable to counting of microscopic charcoal differences in the two techniques caused by changes in sediment type were found especially in postsettlement and late glacial parts of cores charcoal values from sediments less than 100 yr old cannot be compared to older charcoal values unless wood charcoal and charcoal from fossil fuel burning are separated microscopically tests of this chemical assay on mixtures of known weights of charcoal leaves and sand give correlations between observed and expected values of 0 99 to 1 00

composition and origin of the sabkha brines and their environmental impact on infrastructure in jizan area red sea coast saudi arabia the sulfate evaporite minerals gypsum and anhydrite and brines of jizan sabkha cause corrosion of the steel reinforcement and deterioration of the concrete and consequently hinder the development activity for building new urban communities and industrial zones in jizan area red sea coastal plain of saudi arabia the sabkha evaporite minerals below the sediment surface are represented by displacive and inclusive growth of lenticular and rosette gypsum and nodular anhydrite in small saline pans halite precipitates form rafts chevrons and cornets the salinity tds of the groundwater in the sabkha area is highly variable and ranges from 12 900 to 495 000 mg l compared to the average value of the red sea water of 40 366 mg l the low salinity values of the sabkha brines are most probably caused by localized influx of groundwater of meteoric origin from direct rain fall and or temporary floods in addition to seepage of sewage water from septic tanks the electric conductivity ec values range from 20 000 to 199 100 s cm which are conformable to the salinity values of the brine the dominant cation concentration order in seawater and brines of the sabkha is na mg2 ca2 k or na mg2 k ca2 the dominant anion concentration order is cl so4 2 hco3 the dominant brine type for most samples is sodium chloride with variable proportions of the major cations ca2 and mg2 and the major anion so4 2 most brine samples indicate their source is of modified marine water having an elevated cacl2 content which may be derived from dissolution of mixed salt from the miocene salt dome in jizan area the chemical composition and origin of the brines and mineralogy and textures of the evaporite minerals in jizan sabkha help in understanding the nature of the corrosive factors to the foundations in jizan area

biotically constrained palaeoenvironmental conditions of a mid holocene intertidal lagoon on the southern shore of the arabian gulf evidence associated with a whale skeleton at musaffah abu dhabi uae whale remains a left and right mandible scapula humerus and fragmentary radius and ulna as well as parts of the cranium and rostrum belonging to a probable humpback whale megaptera cf novaeangliae were found in the well described sabkha sequence exposed in the musaffah industrial channel abu dhabi united arab emirates more precisely the whale remains were found in a series of sediments representing a range of lagoonal facies the sediments surrounding the whale bones were age dated at approximately 5200 14 c yrs bp and are therefore interpreted to correspond to the previously documented late flandrian sea level peak preceding a fall in sea level which culminated in the supratidal sabkha overprint of the carbonates associated with the whale remains is an assemblage of molluscs foraminifera and ostracods together with the inferred presence of sea grass and algae these facies are interpreted to indicate a very shallow subtidal to intertidal lagoonal environment cirripede remains found associated with the skeleton were identified as those of the whale barnacle coronula diadema and hence had their origins with the whale significantly the low species diversity of microfossils suggests that higher salinities existed in the mid holocene lagoon than are present in modern counterparts this is here inferred to be related to the onset of continental aridity in arabia during the mid holocene

evaporitic carbonates in the pre salt of santos basin genesis and tectonic implications abstract since the first discoveries of oil accumulations in the carbonate reservoirs of the lower cretaceous barra velha formation of the santos basin their genesis has been the subject of intense discussion different depositional models have been proposed with some authors advocating a microbial origin while others an abiotic origin as travertines or travertine like rocks this search for a modern carbonate analogue for these unusual rocks may have disregarded an intriguing alternative an evaporative model supported by our petrographical and geochemical data evaporitic sediment patterns in endorheic basins in a depositional framework of brine drawdown are dominated by ephemeral salt pan hydrology bedded salt crusts form a stack of subaqueous aligned crystal beds at the sediment water interface salt grows diagenetically within saline and mud layers beneath the dry pan surface finally laminated sediments are deposited we observe a similar cyclic pattern in the pre salt core we described beds of shrub like crystals and diagenetic spherulites growing in magnesium clay matrix are followed by laminites the model we propose attempts to contribute solving the puzzle of pre salt carbonate deposition by integrating sedimentology and geochemistry with basin tectonics our observations and basin tectonics point to the exciting possibility that the sag phase carbonates of the santos campos basin were deposited as the initial transitional stage of a closed sub sea level evaporite basin whose rising salinities culminated in the deposition of halite and bittern salts carnallite sylvite tachyhydrite basinwide evaporites are singular events in the geological record they form when a giant sub sea level basin becomes a sump of continental marine and hydrothermal fluids producing unexpected brine compositions in unusual depositional settings present in ancient evaporitic basins but absent from most modern ones the novelty in this paper is that we apply to pre salt carbonate deposition the sedimentology hydrology and geochemistry of ancient evaporitic basins with this concept in mind we propose a geochemical model for the unusual pre salt carbonate precipitation of the santos basin regarding the walvis rio grande volcanic high as a topographic barrier during the aptian we suggest that the main sources of calcium to the barra velha paleolake were hydrothermal brines mostly from infiltrating seawater that reacted at depth with the basalts of the volcanic barrier hyperextension of the lithosphere with a shallow moho increased geothermal gradients to levels favorable for the generation of hydrothermal cacl2 brines a process facilitated by the already elevated ca ion and low sulfate concentration of the cretaceous ocean these cacl2 rich fluids would pass through the volcanic barrier into a sub sea level paleolake in the rift basin the high salinity paleolake would become saturated in calcium bicarbonate carbonate as internally drained nahco3 bearing alkaline waters formed by physical chemical weathering of penecontemporaneous basaltic rocks mix with the cacl2 bearing hot brines percolating through the barrier producing a hybrid brine 2nahco3 cacl2 ca hco3 2 2nacl such a depositional system integrating the geochemical depositional controls of sag phase carbonates with those of the south atlantic evaporites has important implications for unravelling the genesis of these exotic deposits

chemical openness and potential for misinterpretation of the solute environment of coastal sabkhat abstract sabkha deposits in the geologic record are commonly used to interpret the environmental conditions of deposition implicit in this use is the assumption that the solute system is chemically closed that is the authigenic minerals represent the composition of the fluids in their environment of origin thermodynamic and mass balance calculations based on measurements of water and solute flux of contemporary abu dhabi coastal sabkha system however demonstrate that the system is open for sodium and chloride where nearly half of the input is lost but closed for sulfur where nearly 100 is retained sulfur and chloride isotopes were consistent with this observation if these sabkha deposits were preserved in the geologic record they would suggest a solute environment rich in sulfate and poor in chloride yet the reverse is true in most coastal sabkha environments capillary forces bring solutes and water to the surface where the water evaporates and halite carnallite sylvite and other soluble minerals are precipitated retrograde minerals such as anhydrite calcite dolomite and gypsum however precipitate and accumulate in the capillary zone beneath the surface of the coastal sabkha because they possess relatively low solubility and are below the surface these retrograde minerals are protected from dissolution and physical erosion occurring from infrequent but intense rainfall events thus they are more likely to be preserved in the geological record than highly soluble minerals formed on the surface

microbially catalyzed dolomite formation from near surface to burial abstract over the past century a number of models have been developed to explain the vast stratigraphic distribution of authigenic dolomite these models include hydrogeological geochemical and geomicrobiological interpretations that shed light on kinetic constraints on low temperature dolomite formation and in particular how certain microbes can overcome such limitations in this review we focus on the direct and indirect mechanisms by which microbes facilitate the nucleation and shallow burial diagenetic stabilization of dolomite in marine sediments we also consider the likely effects of local and global scale biogeochemical perturbations over the distribution and activities of subsurface microbes and thus potentially over the stratigraphic distribution of dolomite considering the many advances that have been made in the fields of geomicrobiology and biogeochemistry during the past 20 years investigating the important role microbes play in sedimentary systems will undoubtedly contribute to a more complete interpretation of dolomite formation in the rock record

microseismic investigation of an unstable mountain slope in the swiss alps 1 risks associated with unstable rocky slopes are growing as a result of climate change and rapid expansions of human habitats and critical infrastructure in mountainous regions to improve our understanding of mountain slope instability we developed a microseismic monitoring system that operates autonomously in remote areas afflicted by harsh weather our microseismic system comprising 12 three component geophones was deployed across 60 000 m 2 of rugged crystalline terrain above a huge 30 million m 3 recent rockfall in the swiss alps during its 31 month lifetime signals from 223 microearthquakes with approximate moment magnitudes ranging from 2 to 0 were recorded determining the hypocenters was challenging for several reasons 1 p wave velocities were highly heterogeneous varying abruptly from 3 8 km s 2 first break picks were either inaccurate or lacking for some microearthquakes 3 there were no reliable s wave picks 4 numerous microearthquakes occurred just outside the network boundaries these issues were addressed by using a three dimensional 3 d p wave velocity model of the mountain slope determined from refraction tomography in a nonlinear inversion for hypocenter parameters and their probability density functions recordings from geophones at different altitudes and in boreholes constrained microearthquake depth estimates most microearthquakes were concentrated within 50 100 m of the surface in two zones one that followed the recent rockslide scarp and one that spanned the volume of highest fracture zone fault density these two active zones delineated a mass of rock that according to geodetic measurements has moved toward the scarp at 1 2 cm yr

late holocene vegetational change in central madagascar abstract a sediment core from lake kavitaha central madagascar provides a stratigraphic record of changes in pollen spectra and charcoal influx in the late holocene the earliest pollen spectra distantly resemble the modern pollen rain of a vegetational mosaic in northern madagascar although results of principal component analysis suggest no close modern analog at about 1300 yr b p a marked rise in charcoal is followed by a decline in pollen of woody taxa culminating in a change to grass dominated pollen spectra within about 4 centuries pollen of woody taxa decline below 15 of total terrestrial pollen and spores beginning about 600 yr b p the influx of charcoal from graminoid sources remains high until recent centuries the late holocene changes in vegetation and fire ecology at the site were approximately contemporaneous with the latest 14 c dates for the extinct megafauna and the earliest dates for human occupation

groundwater seepage controls salinity in a hydrologically terminal basin of semi arid northwest australia abstract very small groundwater outflows have the potential to significantly impact the hydrochemistry and salt accumulation processes of notionally terminal basins in arid environments however this limited groundwater outflow can be very difficult to quantify using classical water budget calculations due to large uncertainties in estimates of evaporation and evapotranspiration rates from the surface of dry lake beds in this study we used a dimensionless time evaporation model to estimate the range of groundwater outflow required to maintain salinity levels observed at the fortescue marsh fm one of the largest wetlands of semi arid northwest australia 1100 km2 the groundwater outflow from aquifers underlying the fm to the lower fortescue catchment is constrained by an extremely low hydraulic gradient of 300 g l after 45 ka we calculated that only a very small seepage of 2g l yr 0 03 of the fm water volume is sufficient to maintain current salinity conditions the minimum time required to develop the current hydrochemical groundwater composition under the fm ranges from 60 to 165 ka we conclude that a dimensionless time evaporation model versus inflow over outflow ratio model is likely more suitable than classical water budget calculations for determining outflow from large saline lakes and to estimate groundwater seepage from hydrologically terminal basins

source of solutes to the coastal sabkha of abu dhabi an ascending brine model is proposed to address the observed isotope geochemistry solute composition and solute and water fluxes in the coastal sabkha of the emirate of abu dhabi mass balance measurements document that 95 of the solutes are derived from ascending continental brines minor amounts are derived from rainfall and from groundwater entering from up gradient areas nearly 100 of the annual water loss is from evaporation and not lateral discharge direct rainfall on the sabkha and subsequent recharge to the underlying aquifer account for 90 of the annual water input to the system the remaining 10 comes from both lateral and ascending groundwater flow thus the water and solutes in this system are from different sources solute concentrations of conservative i e nonreactive elements in the coastal sabkha covered aquifer are consistent with the fluid pore volumes of ascending brine calculated from hydrologic properties calcium to sulfate ratios and sulfur isotopes are consistent with this source of solute from the underlying tertiary formations recharging rainwater dissolves halite and other soluble minerals on the surface causing the solution to become more dense and sink to the bottom of the aquifer where it vertically mixes with less dense ascending brines solutes are returned to the surface by capillary forces and recycled or lost from the system by eolian or fluvial processes thus the system becomes vertically mixed consistent with the presence of tritium throughout the aquifer but there is essentially no horizontal mixing of seawater with groundwater the observed seawater solutes in the supratidal zone come from interstitial seawater trapped by the rapid progradation of the sediments into the arabian gulf and are not refluxed or laterally mixed the ascending brine model contrasts significantly with both the seawater flooding and evaporative pumping models previously proposed as a source of solutes to the coastal sabkha of the emirate of abu dhabi use of these earlier models leads to incorrect conclusions and raises serious questions about their applicability in the evaluation of sabkhat in the geologic record

distinguishing seawater from geologic brine in saline coastal groundwater using radium 226 an example from the sabkha of the uae article sabkhat salt flats are common geographic featuresof low lyingmarinecoastalareas thatdevelopunder hyper aridclimaticconditions theyare characterizedby thepresenceof highlyconcentratedsalinesolutions and evap oritic minerals and have been cited in the geologic literature as present day representations of hyper arid regional paleohydrogeology paleoclimatology coastal processes and sedimentation in the geologic record it is therefore important that a correct understanding of the origin and development of these features be achieved knowledge of the source of solutes is an important first step in understanding these features historically two theories have been advanced as to the main source of solutes in sabkha brines an early concept entailing seawa ter as the obvious source and a more recent and dynamic theory involving ascending geologic brine forced upward into the base of the sabkha by a regional hydraulic gradient in the underlying formations ra 226 coulduniquely distinguish betweenthese sourcesunder certain circumstances asitistypically present atelevat ed activity of hundreds to thousands of bq m 3 becquerels per cubic meter in subsurface formation brines at exceedingly low activities in open ocean and coastal water and not significantly supplied to water from recently formed marine sedimentary framework material the coastal marine sabkha of the emirate of abu dhabi was used to test this hypothesis the distribution of ra 226 in 70 samples of sabkha brine mean 700 bq m 3 7 sam ples of underlying deeper formation brine mean 3416 bq m 3

sulfur isotope signatures in gypsiferous sediments of the estancia and tularosa basins as indicators of sulfate sources hydrological processes and microbial activity abstract in order to reconstruct paleo environmental conditions for the saline playa lakes of the rio grande rift we investigated sediment sulfate sources using sulfur isotope compositions of dissolved so 4 2 ions in modern surface water groundwater and so 4 2 precipitated in the form of gypsum sediments deposited during the pleistocene and holocene in the tularosa and estancia basins the major sulfate sources are lower and middle permian marine evaporites 34s of 10 9 14 4 but the diverse physiography of the tularosa basin led to a complex drainage system which contributed sulfates from various sources depending on the climate at the time of sedimentation as inferred from sulfur isotope mass balance constraints weathering of sulfides of magmatic hydrothermal and sedimentary origin associated with climate oscillations during last glacial maximum contributed about 35 50 of the sulfates and led to deposition of gypsum with 34s values of 1 2 to 2 2 which are substantially lower than permian evaporates in the estancia basin microbial sulfate reduction appears to overprint sulfur isotopic signatures that might elucidate past groundwater flows a rayleigh distillation model indicates that about 3 18 of sulfates from an inorganic groundwater pool 34s of 12 6 13 8 have been metabolized by bacteria and preserved as partially to fully reduced sulfur bearing minerals species elemental sulfur monosulfides disulfides with distinctly negative 34s values 42 3 to 20 3 compared to co existing gypsum 3 8 to 22 4 for the tularosa basin microbial sulfate reduction had negligible effect on 34s value of the gypsiferous sediments most likely because of higher annual temperatures 15 33 c and lower organic carbon content median 0 09 in those sediments leading to more efficient oxidation of h2s and or smaller rates of sulfate reduction compared to the saline playas of the estancia basin 5 28 c median 0 46 of organic carbon the white sands region of the tularosa basin is frequently posited as a hydrothermal analogue for mars high temperatures of groundwater 33 3 c and high 18o h2o values 1 1 in white sands however are controlled predominantly by seasonal evaporation rather than the modern influx of hydrothermal fluids nevertheless it is possible that some of the geochemical processes in white sands such as sulfide weathering during climate oscillations and upwelling of highly mineralized waters might be considered as valid terrestrial analogues for the sulfate cycle in places such as meridiani planum on mars

sequence stratigraphic context of extensive basin margin evaporites middle jurassic gypsum spring formation wyoming u s a abstract ancient marine evaporites are commonly far more extensive than any known modern evaporite system this is true not only for basin central saline giants but also for evaporites that occur in basin margin settings and the origin of these basin margin systems is unclear extensive basin margin evaporites of the middle jurassic gypsum spring formation are well exposed along the eastern flank of the bighorn basin in wyoming usa and a facies and sequence stratigraphic analysis was undertaken to understand the origin of these evaporites and associated deposits the gypsum spring formation was deposited on a northwestward dipping mixed evaporate carbonate siliciclastic ramp with facies and depositional environments that include distal ooid shoal grainstone open marine shallow subtidal peloidal skeletal wackestone to packstone restricted shallow subtidal laminated lime mudstone peritidal dolostone and microbialite as well as red mudstone and gypsum deposited on mud flats sabkhas and salinas three depositional sequences are present with the j 1 j 1a and j 1b sequence boundaries characterized locally by chert pebble lags silicified horizons and iron rich paleosols evaporites accumulated in a basin margin position with 1 6 m beds of gypsum forming in salinas and sabkhas and nodular anhydrite and gypsum forming in red mudstones deposited on sabkhas and mud flats the limited lateral extent of salina type gypsum beds and the variable number of these beds among the exposures indicates substantial autocyclic control on the formation of salinas salinas are well developed in the tst of the j 1 sequence and sabkhas and mud flats are well developed in the j 1 hst the j 1a hst and the j 1b tst the great lateral extent of the gypsum spring evaporites reflects the original expanse of the depositional environment in which they formed and is not the result of diachroneity of a narrow evaporite precipitating belt such as the modern day coastal sabkhas of the trucial coast the great lateral extent of gypsum spring evaporites suggests that they were precipitated mainly from continental brines on an expansive desert mudflat

quantification of landslide velocity from active waveguide generated acoustic emission acoustic emission ae has become an established approach to monitor stability of soil slopes however the challenge has been to develop strategies to interpret and quantify deformation behaviour from the measured ae ae monitoring of soil slopes commonly utilizes an active waveguide that is installed in a borehole through the slope and comprises a metal waveguide rod or tube with a granular backfill surround when the host slope deforms the column of granular backfill also deforms and this generates ae that can propagate along the waveguide results from the commissioning of dynamic shear apparatus used to subject full scale active waveguide models to simulated slope movements are presented the results confirm that ae rates generated are proportional to the rate of deformation and the coefficient of proportionality that defines the relationship has been quantified e g 4 4 105 for the angular gravel examined it is demonstrated that slope velocities can be quantified continuously in real time th

ground water control of evaporite deposition topographically closed basins may be hydrologically open as a result of seepage losses to underlying or surrounding ground water systems in such cases these losses can have a substantial control over the suite and the thicknesses of evaporite minerals formed in the basin the ratio of ground water outflow to inflow flux ratio in hydrologically open basins is as important in determining the mineralogy and thicknesses of evaporite deposits as the solute composition of the inflow water attainment of steady state flux ratios permits large thicknesses of two or three minerals to form rather than thin veneers of many minerals the presence or absence of glauberite mirabilite halite bloedite polyhalite and hexahydrite caused by subtle changes in the ground water seepage is illustrated using an example from the southern high plains of texas and new mexico however the model is general and is applicable with any solute composition including that of seawater and the use of surface rather than ground water an analytical lumped parameter solute mass balance model is developed to define the concept of a ground water flux ratio as it applies to topographically closed basins in which evaporation exceeds precipitation diffusion advection and density driven flow are proposed as mechanisms by which solutes can escape to the ground water from these closed basins the geochemical reaction computer program phrqpitz is used to document the effects of various flux ratios on the mineralogy and thickness of deposits solute analyses used in conjunction with the model can be used to screen prospective basins as well as to provide insights for exploratory drilling program

dolomitization by hypersaline reflux into dense groundwaters as revealed by vertical trends in strontium and oxygen isotopes upper muschelkalk switzerland the trigonodus dolomit is the dolomitized portion of the homoclinal ramp sediments of the middle triassic upper muschelkalk in the se central european basin various dolomitizing mechanisms followed by recrystallization have been previously invoked to explain the low 18o high 87sr 86sr extensive spatial distribution and early nature of the replacive matrix dolomites this study re evaluates the origin timing and characteristics of the dolomitizing fluids by examining petrographic and isotopic trends in the trigonodus dolomit at 11 boreholes in northern switzerland in each borehole the ca 30 m thick unit displays the same vertical trends with increasing depth crystal size increase change from anhedral to euhedral textures uv fluorescence decrease 18ovpdb decrease from 1 at the top to 6 7 at the base and an 87sr 86sr increase from 0 7080 at the top to 0 7117 at the base thus dolomites at the top of the unit record isotopic values similar to middle triassic sea water 18ovsmow 0 87sr 86sr 0 70775 while dolomites at the base record values similar to meteoric groundwaters from the nearby vindelician high 18ovsmow 4 87sr 86sr 0 712 according to water rock interaction modelling a single dolomitizing or recrystallizing fluid cannot have produced the observed isotopic trends instead the combined isotopic geochemical and petrographic data can be explained by dolomitization via seepage reflux of hypersaline brines into dense horizontally advecting groundwaters that already had negative 18o and high 87sr 86sr values evidence for the early groundwaters is found in meteoric calcite cements that preceded dolomitization and in fully recrystallized dolomites with isotopic characteristics identical to the groundwaters following matrix dolomitization this study demonstrates that early groundwaters can play a decisive role in the formation and recrystallization of massive dolomites and that the isotopic and textural signatures of pre existing groundwaters can be preserved during seepage reflux dolomitization in low angle carbonate ramps

seismic monitoring of soft rock landslides the super sauze and valoria case studies this work focuses on the characterization of seismic sources observed in clay shale landslides two landslides are considered super sauze france and valoria italy the two landslides are developed in reworked clay shales but differ in terms of dimensions and displacement rates thousands of seismic signals have been identified by a small seismic array in spite of the high seismic attenuation of the material several detection methods are tested a semi automatic detection method is validated by the comparison with a manual detection seismic signals are classified in three groups based on the frequency content the apparent velocity and the differentiation of p and s waves it is supposed that the first group of seismic signals is associated to shearing or fracture events within the landslide bodies while the second group may correspond to rockfalls or debris flows a last group corresponds to external earthquakes seismic sources are located with an automatic beam forming location method sources are clustered in several parts of the landslide in agreement with geomorphological observations we found that the rate of rockfall and fracture events increases after periods of heavy rainfall or snowmelt the rate of microseismicity and rockfall activity is also positively correlated with landslide displacement rates external earthquakes did not influence the microseismic activity or the landslide movement probably because the earthquake ground motion was too weak to trigger landslide events during the observation periods

early diagenesis driven by widespread meteoric infiltration of a central european carbonate ramp a reinterpretation of the upper muschelkalk abstract meteoric diagenesis of carbonate ramps is often difficult to interpret and can commonly be confused with other coinciding diagenetic processes the middle triassic upper muschelkalk of switzerland provides an insightful case in which the effects of several overprinting diagenetic environments including matrix dolomitization can be clearly unravelled previous studies suggested that diagenesis took place in connate marine waters with later meteoric waters being invoked to explain recrystallization of dolomite in this study diagenetic analyses c o stable isotope ratios thin section point counting cathodoluminescence and uv fluorescence microscopy of calcitic bioclastic samples have revealed that early diagenesis pre stylolitization and the accompanying porosity evolution did not occur exclusively in the presence of marine fluids five sequential stages of diagenesis have been identified marine shallow burial mixing zone meteoric and dolomitization marine diagenesis induced precipitation of bladed and inclusion rich syntaxial cements that fluoresce strongly under uv light both cements account for a mean 7 5 vol reduction in the porosity of bioclastic beds shallow burial diagenesis likely induced mouldic porosity and associated fluorescent dog tooth cementation based on light oxygen isotope and elevated strontium isotope ratios matrix aragonite calcite neomorphism is interpreted to have occurred in a mixture of marine and meteoric fluids the combination of shallow burial and mixing zone processes reduced porosity on average by 4 8 vol evidence for subsequent meteoric diagenesis is found in abundant dog tooth and blocky calcite cements that have mean 18 o vpdb of 9 36 and no signs of recrystallization these meteoric cements reduced porosity by a further 13 4 vol percolation of meteoric water through the ramp was driven by hydraulic gradients on an adjacent basement high which was exposed by a cycle of early ladinian regressions following meteoric diagenesis the upper muschelkalk was dolomitized by refluxing brines this complex history of diagenesis resulted in moderate porosities in dolomitized rocks up to 20 and low porosities

correlation of acoustic emissions with patterns of movement in an extremely slow moving landslide at peace river alberta canada the peace river region alberta canada has experienced extensive landslide activity since deglaciation shear zones within weak lacustrine silt and clay layers typically experience continuous cre

dolomite formation within microbial mats in the coastal sabkha of abu dhabi united arab emirates microbial mediation is the only demonstrated mechanism to precipitate dolomite under earth surface conditions a link between microbial activity and dolomite formation in the sabkha of abu dhabi has until now not been evaluated even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences such an evaluation is the purpose of this study which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of abu dhabi along a transect from the intertidal to the supratidal zone this investigation revealed a close association between microbial mats and dolomite suggesting that microbes are involved in the mineralization process observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats in current models microbial dolomite precipitation is linked to an active microbial activity that sustains high ph and alkalinity and decreased sulphate concentrations in pore waters such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone by contrast these models cannot be applied to the supratidal zone where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity as no abiotic mechanism is known to form dolomite at earth surface conditions two different hypotheses can reconcile this result in a first scenario all of the dolomite present in the supratidal zone formed in the past when the mats were active at the surface in a second scenario dolomite formation continues within the buried and inactive mats in order to explain dolomite formation in the absence of active microbial metabolisms a revised microbial model is proposed in which the mineral template properties of exopolymeric substances play a crucial role

atmospheric bromine flux from the coastal abu dhabi sabkhat a ground water mass balance investigation 1 a solute mass balance study of ground water of the 3000 km2 coastal sabkhat salt flats of the emirate of abu dhabi united arab emirates documents an annual bromide loss of approximately 255 metric tons 0 0032 gmoles or 85 kg km2 this value is an order of magnitude greater than previously published direct measurements from the atmosphere over an evaporative environment of a salar in bolivia laboratory evidence consistent with published reports suggests that this loss is by vapor transport to the atmosphere if this bromine flux to the atmosphere is representative of the total earth area of active salt flats then it is a significant and generally under recognized input to the global atmospheric bromide flux