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Stefano M Bernasconi - One of the best experts on this subject based on the ideXlab platform.
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Precipitation of dolomite from seawater on a Carnian coastal plain (Dolomites, northern Italy): evidence from carbonate petrography and Sr isotopes
Solid Earth, 2019Co-Authors: Maximilian Rieder, Wencke Wegner, Monika Horschinegg, Stephanie Klackl, Anna Breda, Susanne Gier, Nereo Preto, Urs Klotzli, Stefano M BernasconiAbstract:Abstract. The geochemical conditions conducive to dolomite formation in shallow evaporitic environments along the Triassic Tethyan margin are still poorly understood. Large parts of the Triassic dolomites in the Austroalpine and the southern Alpine realm are affected by late diagenetic or hydrothermal overprinting, but recent studies from the Carnian Travenanzes Formation (southern Alps) provide evidence of primary dolomite. Here a petrographic and geochemical study of dolomites intercalated in a 100 m thick Carnian sequence of distal alluvial plain deposits is presented to gain better insight into the conditions and processes of dolomite formation. The dolomites occur as 10 to 50 cm thick homogeneous beds, millimetre-scale laminated beds, and nodules associated with palaeosols. The dolomite is nearly stoichiometric with slightly attenuated ordering reflections. Sedimentary structures indicate that the initial primary dolomite or precursor phase consisted largely of unlithified mud. Strontium isotope ratios ( 87Sr∕86Sr ) of homogeneous and laminated dolomites reflect Triassic seawater composition, suggesting precipitation in evaporating seawater in a coastal ephemeral lake or Sabkha system. However, the setting differed from modern Sabkha or coastal ephemeral lake systems by being exposed to seasonally wet conditions with significant siliciclastic input and the inhibition of significant lateral groundwater flow by impermeable clay deposits. Thus, the ancient Tethyan margin was different from modern analogues of primary dolomite formation.
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dolomite formation within microbial mats in the coastal Sabkha of abu dhabi united arab emirates
Sedimentology, 2010Co-Authors: Tomaso R R Bontognali, Stefano M Bernasconi, Christian J Strohmenger, Crisogono Vasconcelos, Rolf Warthmann, Christophe Dupraz, Judith A MckenzieAbstract: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.
Judith A Mckenzie - One of the best experts on this subject based on the ideXlab platform.
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organomineralization of proto dolomite by a phototrophic microbial mat extracellular polymeric substances control of crystal size and its implication for carbonate depositional systems
American Journal of Science, 2020Co-Authors: Carlos Paulo, Judith A Mckenzie, Basirath Raoof, Jorg Bollmann, Roberta R Fulthorpe, Christian J Strohmenger, Maria DittrichAbstract:Many have postulated that a specific microbial metabolism or the presence of microbes or/and their extracellular polymeric substances (EPS) can lead to the formation of dolomite. Although now there is the consensus that dolomite can be formed in the presence of microorganisms, the exact nature of the involvement of microbes in the dolomite nucleation remains a matter of debate. The focus is now in understanding how microbial mats determine the mineralogy of dolomite. Here we report the effect of the EPS extracted from phototrophic microbial mat isolated from a Sabkha in Qatar dominated by cyanobacteria (Lyngbya aestuarii) in the formation of dolomite precursors at 25 °C and 40 °C. Both the temperature and the presence of EPS impact the size and morphology of minerals, promoting spherulitic and dumbbell growth in sulfate free solutions. The formation of proto-dolomite was enhanced by the abundance of carboxylated molecules in EPS which controlled the polymorphism of carbonates. Our study emphasizes the dual importance of organic matter and temperature in dolomite formation and their impact on mineral morphology and chemical composition in Sabkhas.
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dolomite formation within microbial mats in the coastal Sabkha of abu dhabi united arab emirates
Sedimentology, 2010Co-Authors: Tomaso R R Bontognali, Stefano M Bernasconi, Christian J Strohmenger, Crisogono Vasconcelos, Rolf Warthmann, Christophe Dupraz, Judith A MckenzieAbstract: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.
Warren W Wood - One of the best experts on this subject based on the ideXlab platform.
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distinguishing seawater from geologic brine in saline coastal groundwater using radium 226 an example from the Sabkha of the uae
Chemical Geology, 2014Co-Authors: Thomas F Kraemer, Warren W Wood, Ward E SanfordAbstract: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
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hydrogeologic processes in saline systems playas Sabkhas and saline lakes
Earth-Science Reviews, 2002Co-Authors: Yoseph Yechieli, Warren W WoodAbstract:Abstract Pans, playas, Sabkhas, salinas, saline lakes, and salt flats are hydrologically similar, varying only in their boundary conditions. Thus, in evaluating geochemical processes in these systems, a generic water and solute mass-balance approach can be utilized. A conceptual model of a coastal Sabkha near the Arabian Gulf is used as an example to illustrate the various water and solute fluxes. Analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the Sabkha, but contribute only a small volume of the water. Local rainfall is the main source of water in the modeled Sabkha system with a surprisingly large recharge-to-rainfall ratio of more than 50%. The contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal Sabkha. Because of a short residence time of water, steady-state flow is expected within a short time ( 50,000 years). The solute composition of the brine in a closed saline system depends largely on the original composition of the input water. The high total ion content in the brine limits the efficiency of water–rock interaction and absorption. Because most natural systems are hydrologically open, the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems. Seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation. Thus, during the hot dry season months, minerals exhibit retrograde solubility so that gypsum, anhydrite and calcite precipitate. Evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone (e.g. halite and carnallite), provided that the relative humidity of the atmosphere is less than the activity of water. The slope of the fresh/brine-water interface in saline lake systems is shallower than in fresh/seawater interface because of the greater density difference between the fresh/brine-water bodies. The interface between Sabkha brines and seawater slopes seaward, unlike normal marine–fresh water systems that slope landward. Moreover, the brine/seawater interface does not achieve steady state because it is pushed toward the sea by the Sabkha's brine.
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hydrology of the coastal Sabkhas of abu dhabi united arab emirates
Hydrogeology Journal, 2001Co-Authors: Ward E Sanford, Warren W WoodAbstract:Water fluxes were estimated and a water budget developed for the land surface and a surficial 10-m-deep section of the coastal Sabkhas that extend from the city of Abu Dhabi, United Arab Emirates, west to the border with Saudi Arabia. The fluxes were estimated on the basis of water levels and hydraulic conductivities measured in wells and evaporation rates measured with a humidity chamber. In contrast with conceptual models proposed in earlier studies, groundwater inflow is estimated to be small, whereas the largest components of the water budget are recharge from rainfall and evaporation from the water table. Estimates within a rectilinear volume of Sabkha, defined as 1 m wide by 10 km long by 10 m deep, indicate that about 1 m3/year of water enters and exits by lateral groundwater flow; 40–50 m3/year enters by upward leakage; and 640 m3/year enters by recharge from rainfall. Based on the water and solute fluxes estimated for the upward leakage into the Sabkha, 7–8 pore volumes of brine have entered the Sabkha from below since the time the Sabkha became saturated (7,000 years ago) as a result of the last global sea-level rise.
Jeanmarc Rolain - One of the best experts on this subject based on the ideXlab platform.
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non contiguous finished genome sequence and description of paucisalibacillus algeriensis sp nov
Standards in Genomic Sciences, 2014Co-Authors: Esma Bendjama, Lotfi Loucif, Seydina M Diene, Caroline Michelle, Djamila Gacemikirane, Jeanmarc RolainAbstract:Paucisalibacillus algeriensis strain EB02T is the type strain of Paucisalibacillus algeriensis sp. nov., a new species within the genus Paucisalibacillus. This strain, whose genome is described here, was isolated from soil sample from the hypersaline lake Ezzemoul Sabkha in northeastern Algeria. Paucisalibacillus algeriensis is a Gram-positive and strictly aerobic bacterium. Here we describe the features of this organism, together with the complete genome sequence and annotation. The 4,006,766 bp long genome (1 chromosome but no plasmid) exhibits a low G+C content of 36% and contains 3,956 protein-coding and 82 RNA genes, including 9 rRNA genes.
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non contiguous finished genome sequence and description of bacillus algeriensis sp nov
Standards in Genomic Sciences, 2014Co-Authors: Esma Bendjama, Lotfi Loucif, Seydina M Diene, Caroline Michelle, Djamila Gacemikirane, Jeanmarc RolainAbstract:Strain EB01T sp. nov. is the type strain of Bacillus algeriensis, a new species within the genus Bacillus. This strain, whose genome is described here, was isolated from sediment sample of the hypersaline lake Ezzemoul Sabkha in northeastern Algeria. B. algeriensis is a facultative anaerobic Gram-positive bacillus. Here we describe the features of this organism, together with the complete genome sequence and annotation. The 5,269,577 bp long genome contains 5,098 protein-coding and 95 RNA genes, including 12 rRNA genes.
Ward E Sanford - One of the best experts on this subject based on the ideXlab platform.
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distinguishing seawater from geologic brine in saline coastal groundwater using radium 226 an example from the Sabkha of the uae
Chemical Geology, 2014Co-Authors: Thomas F Kraemer, Warren W Wood, Ward E SanfordAbstract: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
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hydrology of the coastal Sabkhas of abu dhabi united arab emirates
Hydrogeology Journal, 2001Co-Authors: Ward E Sanford, Warren W WoodAbstract:Water fluxes were estimated and a water budget developed for the land surface and a surficial 10-m-deep section of the coastal Sabkhas that extend from the city of Abu Dhabi, United Arab Emirates, west to the border with Saudi Arabia. The fluxes were estimated on the basis of water levels and hydraulic conductivities measured in wells and evaporation rates measured with a humidity chamber. In contrast with conceptual models proposed in earlier studies, groundwater inflow is estimated to be small, whereas the largest components of the water budget are recharge from rainfall and evaporation from the water table. Estimates within a rectilinear volume of Sabkha, defined as 1 m wide by 10 km long by 10 m deep, indicate that about 1 m3/year of water enters and exits by lateral groundwater flow; 40–50 m3/year enters by upward leakage; and 640 m3/year enters by recharge from rainfall. Based on the water and solute fluxes estimated for the upward leakage into the Sabkha, 7–8 pore volumes of brine have entered the Sabkha from below since the time the Sabkha became saturated (7,000 years ago) as a result of the last global sea-level rise.
