petrographic and geochemical analysis of caliche profiles in a bahamian pleistocene dune two caliche profiles from a pleistocene carbonate dune on san salvador island bahamas were examined by petrographic and geochemical analysis profile a is an immature buried caliche profile characterized by caliche pisolites a friable crust and abundant cerion profile b is a more well developed caliche profile at the top of the dune which contains abundant pisolites rhizomorphs laminated calcrete a breccia and abundant cerion geochemical changes in caliche profiles relative to the host rock are an increase in al2o3 fe2o3 and total organic carbon a decrease in mg and sr and a decrease in 13ccarb 18ocarb and 13corg the magnitude of these changes is probably a function of the duration of subaerial exposure and resultant colonization by dune plants and associated microflora abundance of calcified filaments and needle fibre crystals in profile a attests to the importance of microbial processes in the early development of caliche profiles biogenic structures are largely destroyed in profile b due to recrystallization but indirect evidence of biological activity is retained in the form of carbon isotope values

microbial nucleation of mg rich dolomite in exopolymeric substances under anoxic modern seawater salinity new insight into an old enigma sulfate reducing bacteria are known to mediate dolomite formation under hypersaline conditions but details of the crystal nucleation process are still poorly constrained our laboratory study demonstrates for the first time that desulfobulbus mediterraneus a marine sulfate reducing bacterium mediates primary precipitation of mg rich dolomite under anoxic conditions in media replicating modern seawater chemistry at low temperature 21 c precipitation of crystals was associated with extracellular polymeric substances in a monospecific biofilm providing templates for nucleation by altering the molar mg ca ratio after initial nucleation of single nanospherulites 50 nm growth was mediated by aggregation resulting in spherulites of 2 3 m in diameter nucleation led to differences in mg ca ratios and 44 40ca values among the organic material i e biofilm including cells and extracellular polymeric substances 0 87 0 01 2 sd and 0 48 0 11 2 se respectively the crystals 1 02 0 11 2 sd and 0 08 0 24 2 se respectively and the liquid bulk medium after mineral precipitation 4 53 0 04 2 sd and 1 10 0 24 2 se respectively these data indicate a two step fractionation process involved in the sequestration of ca from the solution into the crystal lattice of the mineral precipitated our results demonstrate the capability of extracellular polymeric substances to overcome kinetic inhibition fostering the formation of kinetically less favorable mg rich dolomite and they also question the applicability of the ca isotopic system as a proxy for paleogeochemistry of seawater

supratidal evaporitic dolomite at ojo de liebre lagoon mineralogical and isotopic arguments for primary crystallization abstract this pair deals with a new site of dolomite formation in supratidal evaporite flats at the southernmost edge of the ojo de liebre evaporitic complex baja california mexico the sedimentary context is mostly siliciclastic except for calcareous outcrops around the flats both chemical and isotopic data on the interstitial solutions demonstrate a mixing between mg2 rich marine derived brines and calcium bicarbonate bearing continental waters which are subjected to concentration by capillary evaporation the lack of any in situ solid caco3 in the sedimentary matrix argues for direct crystallization of dolomite from aqueous solutions this is documented by the oxygen isotope compositions of the dolomite which are consistent with deposition under equilibrium conditions of ambient temperature and 18o of water of the interstitial solutions furthermore the low 13c values of the dolomites and the absence of living plants or organisms in the basin indicate that a fraction of the total dissolved inorganic carbon reservoir is biogenic and is mostly provided by continental groundwaters therefore crystallization of dolomite occurs within the sands infiltrated by solutions whose state of saturation relative to dolomite is mainly governed by the chemistry of continental groundwaters mixing with the inflowing marine brines

hydrogeochemical and isotope evidence of groundwater evolution and recharge in minqin basin northwest china a hydrochemical investigation was conducted in the minqin basin to identify the groundwater evolution and recharge in the aquifer the mbr cl ratio is strongly depleted average 0 000451 compared with sea water 0 0035 indicating an evaporite origin the ionic ration plot saturation index si and chloro alkaline indices cai suggest that the dissolution of halite the glauberite gypsum dolomite and calcite determine na cl ca2 mg2 so42 and hco3 chemistry but other processes such as na exchange for ca2 and mg2 and calcite precipitation also contribute to the water composition the 6180 and 62 h in precipitation near the study area are linearly correlated similar to that for the world meteoric water line wmwl with an equation of delta h 2 7 49 delta o 18 5 11 r 2 0 97 according to radiocarbon residence time estimates the deep groundwater is approximatety 40 ka old and was recharged during a period when the climate was wetter and colder the radiocarbon content of shallow groundwater shows a clear evolution along the groundwater flow path from the beginning of the groundwater flow path to similar to 31 km the radiocarbon values are 73 6 pmc whereas beyond this point the values are 42 9 pmc based on radiocarbon content the shallow groundwater is older than 1 ka and represents pataeowaters mixed with a limited quality of modern recharge the rain fed groundwater direct recharge was estimated by chloride mass balance cmb method to range from 1 55 to 1 64 mm yr 1 with a mean value of 1 6 mm yr 1 this value represents about 1 5 of local rainfall the direct recharge volumes is about 0 666 x 10 8 m 3 yr 1 indirect recharge volumes by the surface water is about 0 945 x 10 8 m 3 yr 1 the total natural recharge in the minqin basin is 1 6 x 10 8 m 3 yr 1 whereas the groundwater abstraction has reached 11 6 x 10 8 m 3 yr 1 far exceeding the groundwater natural recharge c 2006 elsevier b v all rights reserved

trapping and binding a review of the factors controlling the development of fossil agglutinated microbialites and their distribution in space and time trapping and binding of allochthonous grains by benthic microbial communities has been considered a fundamental process of microbialite accretion since its discovery in popular shallow marine modern examples bahamas and shark bay however agglutinated textures are rare in fossil microbialites and thus the role of trapping and binding has been debated in the last four decades recently renewed attention on this subject has produced new findings of fossil agglutinated microbialites those mainly formed by trapping and binding and analogous to modern examples but they are still few and geologically recent mainly post paleozoic when compared to the 3 5 gyr long record of microbialites in order to better understand this discrepancy between modern and fossil examples an extensive literature review is presented here providing the first thorough database of agglutinated microbialites which shows that all of them are formed in shallow marine environments and most under tidal influence in addition a lower cretaceous example is described including very diverse microbialites each of them formed in a particular paleoenvironment some of these microbialites developed in grainy settings but only those formed in marginal marine tide influenced environments accreted mainly by trapping and binding the surrounding grains being analogous of modern agglutinated microbialites and matching the environmental pattern observed in the literature database the combination of the literature review with the case study allows to discuss the factors that control and enhance trapping and binding a occurrence of grains in the microbialite environment b frequent currents that mobilize the grains and supply them onto the microbialite surface c high concentration and diversity of electrolytes in the water to increase the adhesiveness of the extracellular polymeric substances eps of the microbialite surface and d a caco3 saturation state not high enough to promote early and strong carbonate precipitation within eps which would eventually decrease its availability to adhere grains therefore this review shows that the keys to solve the trapping and binding debate may be environmental because the conjuction of these hydrodynamic and hydrochemical parameters is preferentially achieved in shallow marine settings and especially in those influenced by tides at least since mesozoic times this explains the limited environmental and stratigraphic distribution of microbialites mainly formed by trapping and binding and opens new ways to look geologically and microbiologically at this process so often cited and yet so rare

two opposing effects of sulfate reduction on carbonate precipitation in normal marine hypersaline and alkaline environments comment sulfate reduction sr has been linked to carbonate mineral precipitation and has been invoked as a possible mechanism for microbialite formation lyons et al 1984 1 kempe 1990 2 although there is evidence to support the contribution of sr in carbonate mineral precipitation from both

growth rate and stable isotopic character of modern stromatolites from san salvador bahamas abstract 14 c 18 o and 13 c stratigraphies were measured on the successive carbonate crusts within large mushroom shaped stromatolitic heads from hypersaline storrs lake san salvador bahamas and also on the finely laminated soft sediment that enclose them 14 c dates show that the carbonate layers in these stromatolites range in age from 2310 70 years b p at the base to modern at the surface this suggests that the heads develop at an overall rate of 16 cm 1000 yr because there are 1 5 macroscopic laminae per cm less than one crustose layer is preserved in the heads per decade thin section examination of the crusts reveals numerous discontinuous micro unconformities which suggest multiple intervals of accretion and erosion these factor complicate any history of slow growth that may occur values of 18 o in the carbonates suggest that the heads were formed in waters with isotopic and temperature conditions similar to those that presently exist in the lake however carbonate 13 c values from the heads and sediments vary over 7 5 1 2 0 pdb and are significantly out of equilibrium with atmospheric co 2 the fluctuations in the 13 c values within the heads could not be correlated between adjacent heads nor with adjacent sediment on the basis of 14 c ages thus the sampled macroscopic layers mm cm in these calcified stromatolites do not appear to be recording simultaneous basin wide events but rather local diagenetic effects and micro environmental conditions in or under the microbial mats these data do not encourage basin wide interpretations of isotopic stratigraphies observed within ancient stromatolites where independent chronologies like 14 c are not available

the importance of melt tio2 in affecting major and trace element partitioning between fe ti oxides and lunar picritic glass melts abstract lunar mare basalts and picritic glasses have tio2 abundances ranging from less than 1 wt to over 16 any high ti mare basalt or picritic glass petrogenetic model must include fe ti oxides in the mantle source or invoke fe ti oxide assimilation during magma ascent to the lunar surface we conducted partitioning experiments to investigate high field strength element hfse rare earth element ree and transition metal distribution between fe ti oxides and lunar picritic glass melts over a range of melt compositions our results suggest that ilmenite melt and armalcolite melt hfse cr and v partition coefficients dhfse dcr dv are strongly dependent on melt tio2 content whereas ilmenite melt ree partition coefficients appear to be insensitive to melt composition as tio2 increases in picritic glass melts hfse cr and v activities in melt also increase and fe ti oxide melt dhfse dcr and dv decrease the effect of ti on partitioning behavior can be attributed to the formation of fe o ti melt species in high ti melts ilmenite dhfse range from compatible in oxides in equilibrium with low ti melts to incompatible in oxides in equilibrium with depolymerized high ti picritic glass melts dhfse are inversely correlated with tio2 abundance in the melt and become nearly constant for melts with more than 6 8 tio2 we present simple partitioning models that utilize the solubility of ilmenite and armalcolite in melt to effectively predict hfse partition coefficients across a wide range of picritic glass melt compositions the hfse budget of ilmenite cumulates that crystallize from the lunar magma ocean strongly depends on the composition of the magma ocean low ti and high ti lunar basalts can be produced by an ilmenite or armalcolite bearing hybridized mantle source or by assimilation of late stage magma ocean cumulates the dependence of dhfse and dcr on melt tio2 is consistent with the formation of lunar type 1 armalcolite from high tio2 picritic glass melt however lunar type 2 and 3 armalcolite have a more complicated yet undetermined history of formation

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

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

controls on microbial activity and tidal flat evolution in shark bay western australia microbial deposits at shark bay constitute a diverse living microbial carbonate system developed in a semi arid highly evaporative marine setting three tidal flats located in different embayments within the world heritage area were investigated in order to compare microbial deposits and their holocene evolution the stressing conditions in the intertidal subtidal environment have produced a microbial ecosystem that is trapping binding and biologically inducing caco3 precipitation producing laminated stromatolites tufted smooth and colloform non laminated thrombolitic forms pustular and cryptomicrobial non laminated forms microbial pavement a general shallowing upwards sedimentary cycle was recognized and correlated with holocene sea level variations where microbial deposits constitute the younger 2360 years bp and shallower sedimentary veneer in addition sediments have been documented with evidence of exposure during the holocene from 1040 to 940 14c years bp when sea level was apparently lower than present filamentous bacteria constitute the dominant group in the blister tufted and smooth mat types and coccus bacteria dominate the pustular colloform and microbial pavement deposit types in the subtidal environment within colloform and pavement structures microbial communities coexist with organisms such as bivalves serpulids diatoms green algae acetabularia crustaceans foraminifera and micro gastropods which are responsible for exoskeleton supply and extensive bioturbation the internal fabric of the microbial deposits is laminated sub laminar scalloped irregular or clotted depending on the amount of fine grained carbonate and the natural ability of microbial communities to trap and bind particles or induce carbonate precipitation nilemah tidal flat contains the thickest 1 3 m and best developed microbial sedimentary system its deposition pre dated the rocky point and garden point tidal flats with the most positive isotope values for 13c and 18o reflecting strong microbial activity in a highly evaporative environment there is an evolutionary series preserved within the tidal flats reflecting relative ages and degree of salinity elevation

an ecology oriented exploitation mode of groundwater resources in the northern tianshan mountains china abstract in recent years ecological degradation caused by irrational groundwater exploitation has been of growing concern in arid and semiarid regions to address the groundwater ecological issues this paper proposes a groundwater resource exploitation mode to evaluate the tradeoff between groundwater development and ecological environment in the northern tianshan mountains northwest china s xinjiang uygur autonomous region field surveys and remote sensing studies were conducted to analyze the relation between the distribution of hydrological conditions and the occurrence of ecological types the results show that there is a good correlation between groundwater depth and the supergene ecological type numerical simulations and ecological assessment models were applied to develop an ecology oriented exploitation mode of groundwater resources the mode allows the groundwater levels in different zones to be regulated by optimizing groundwater exploitation modes the prediction results show that the supergene ecological quality will be better in 2020 and even more groundwater can be exploited in this mode this study provides guidance for regional groundwater management especially in regions with an obvious water scarcity

transient metazoan reefs in the aftermath of the end permian mass extinction microbes were thought to be the dominant reef constructors following the end permian mass extinction sponge microbe reef deposits formed in the early triassic from the western united states suggest that instead metazoan reef building continued immediately following the extinction wherever marine conditions allowed

asymmetric thermal evolution of the moon 1 the moon possesses a clear dichotomy in geological processes between the nearside and farside hemispheres the most pronounced expressions of this dichotomy are the strong concentration of radioactive heat sources on the nearside in a region known as the procellarum kreep terrane pkt and the mare basaltic lava flows that erupted in or adjacent to this terrane we model the thermochemical evolution of the moon using a 3 d spherical thermochemical convection code in order to assess the consequences of a layer enriched in heat sources below the pkt on the moon s global evolution we find that in addition to localizing most of the melt production on the nearside such an enriched concentration of heat sources in the pkt crust has an influence down to the core mantle boundary and leaves a present day temperature anomaly within the nearside mantle moderate gravitational and topographic anomalies that are predicted in the pkt but not observed may be masked either by crustal thinning or gravitational anomalies from dense material in the underlying mantle our models also predict crystallization of an inner core for sulfur concentrations less than 6 wt

significance of subtidal microbial deposits in shark bay australia abstract microbial deposits at shark bay australia constitute one of the largest and most diverse modern occurrences around the world the microbial carbonate system has developed in response to environmental change from near open marine into restricted embayment with hypersalinity and high evaporation bacterial sediments started depositing at about 2000 years bp after the holocene maximum flooding of sea level about 6800 years bp due to increasing salinity as the sea level fell by about 2 5 m within the holocene highstand system tract the extent and types of subtidal microbial substrate in this world heritage area have not previously been fully systematically mapped and described here we document the importance of subtidal microbial deposits occupying as much as 10 times the occurrence area of the intertidal microbial mats and stromatolites and demonstrate that deeper structures have a cerebroid external morphology with a non laminated internal fabric subtidal structures contain consistently different internal fabrics with carbonate grains and fragments interbedded with aragonitic micrite arranged in millimetric laminae or sub spherical patches which display fabrics such as well laminated smooth coarse laminated wavy colloform sub laminar to irregular with voids and biofragments of bivalves microbial pavement irregular clotted pustular and non laminated cerebroid constituting carbonate sediment with stromatolitic facies smooth and colloform thrombolitic facies pustular and cryptomicrobial non laminated cerebroid and microbial pavement each microbial structure grows in specific settings according to water depth msl with cerebroid build ups commonly occurring between 1 and 2 5 m and microbial pavement extending as deep as 6 m because of the late holocene sea level fall microbial structures often record in their internal features a shallowing up carbonate cycle these newly documented extensive subtidal microbial structures with distinctive morphologies and fabrics have importance as modern occurrences and provide potential analogues for understanding ancient microbial systems and environments

temporal evolution of a carbonate coastal system abu dhabi united arab emirates abstract the southern shore of the persian arabian gulf comprises a low angle carbonate evaporite ramp system that provides a rare recent analogue for ancient epeiric settings including many carbonate petroleum reservoirs during the 1960s several studies documented the distribution of naturally occurring shallow marine facies in the shallow marine environments proximal to abu dhabi island subsequent coastal engineering projects have significantly modified the coastline and sublittoral zone many sedimentary environments have been lost with marine sites now sited beneath buildings parks or roads the data from the earlier studies are used as a pre anthropogenic base line in order to document and assess the temporal changes in the characteristics and distribution of carbonate sedimentary facies as observed today the locations of earlier sample sites were revisited in order to represent the complete range of shallow marine sedimentary environments the shallow subtidal environments adjacent to abu dhabi island continue to be areas of active carbonate sedimentation temporal changes in facies belt geometries and occurrence are assessed changes are recorded for most of the investigated sedimentary settings both in terms of sedimentary environment distribution and sediment composition offshore reefs and their associated back reef lagoons are no longer present ooid shoal and delta complexes are much reduced in their aerial extent now being replaced with shoreface facies or dredged channels significant dredging activity has increased tidal flow to lagoon environments thereby increasing connectivity to open marine conditions however land reclamation has substantially reduced the volume of the area of the lagoon environments despite these changes many facies display surprising resilience to anthropogenic activities with no discernible change in sedimentary facies or biotic distributions understanding these modifications and their associated driving mechanisms allows discrimination between anthropogenic and naturally occurring environmental perturbations this in turn develops our understanding of the temporal evolution of shallow marine carbonate facies under natural and anthropogenic influences

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

a 20 m middle pleistocene sea level highstand bermuda and the bahamas due to partial collapse of antarctic ice marine deposits at 20 3 m on the tectonically stable coastlines of bermuda and the bahamas support the hypothesis of a partial collapse of the antarctic ice sheet during the middle pleistocene beach sediments fill a sea cave at 22 m in bermuda and horizontal fenestrae filled beds crop out on platforms at two sites as high as 21 m in eleuthera bahamas carbonate beach sands are bound by an early generation of isopachous fibrous cement that is characteristic of a phreatic marine environment amino acid racemization and tims thermal ionization mass spectrometry dates constrain the age of the deposits to between 390 and 550 ka while proxy evidence supports a correlation with oxygen isotope stage 11 this direct geologic evidence of a 20 decrease in polar ice during the middle pleistocene has important implications for the stability of ice sheets during warm interglaciations

characteristics distribution and morphogenesis of subtidal microbial systems in shark bay australia abstract the distribution nature and extent of microbial deposits in hamelin pool shark bay have been investigated and mapped with emphasis on the occurrence external morphologies internal fabrics constructional mechanisms microbial communities growth rates and sediment associations in the intertidal and previously little researched subtidal zone detailed georeferenced substrate mapping revealed extensive subtidal microbial deposits occupying approximately 300 km 2 of the total holocene 1400 km 2 area of hamelin pool the microbial pavement covers 227 km 2 of the subtidal substrate that together with columnar structures reveals a subtidal microbial habitat which occupies an area 10 times larger than the area of the intertidal deposits microbial carbonate is composed of aragonite 80 98 that reveals high positive values of 13 c 4 46 to 5 88 and 18 o 3 06 to 3 88 as a characteristic of the highly evaporative environment with extensive microbial activity oldest dated heads are 1915 and 1680 14 c years bp and the overall system was deposited in two stages the first between 2000 and 1200 and the last from 900 years bp to the present slow growth rates vary from less than 0 1 mm year to 0 5 mm year different internal fabrics were constructed according to their position in relation to the littoral zone by distinct microbial communities and lateral fabric relations have been established evidence of shallowing upward fabric sequences of microbial origin reflects relative falling sea levels during the late holocene and is likely useful in ancient environmental interpretation a sequence of events and mechanisms are described emphasizing differences between the stromatolitic thrombolitic and cryptomicrobial deposits in shark bay the new substrate map and depositional history for this distinctive and peculiar microbial habitat establish the significance of subtidal structures and emphasize the geoscientific importance of hamelin pool especially with respect to early life studies and ancient analogues for understanding microbial activity deposit characteristics fenestral fabrics and distribution

does the moon possess a molten core probing the deep lunar interior using results from llr and lunar prospector 1 it is the main purpose of this study to examine the deeper structure of the moon in the light of four numbers these are lunar mass m mean moment of inertia i second degree tidal love number k2 and the quality factor q accounting for tidal dissipation within the solid body of the moon the former two have been measured by lunar prospector to high precision and more than 30 years of lunar laser ranging llr data have led to an estimate of the second degree tidal love number and quality factor the inverse problem dealt with here of obtaining information on the lunar density and s wave velocity profile from the four numbers follows our earlier investigations by employing an inverse monte carlo sampling method we present a novel way of analyzing the outcome using the bayes factor the advantage lies in the fact that rather than just looking at a subset of sampled models we investigate all the information sampled in different runs i e take into account all samples in order to estimate their relative plausibility the most likely outcome of our study based on the data their uncertainties and prior information is a central core with a most probable s wave velocity close to 0 km s density of 7 2 g cm3 and radius of about 350 km this is interpreted as implying the presence of a molten or partially molten fe core in line with evidence presented earlier using llr regarding the dissipation within the moon

enhanced development of lacustrine microbialites on gravity flow deposits great salt lake utah usa the great salt lake utah usa is a shallow hypersaline intracontinental lake hosting extensive microbial deposits at a large spatial scale the distribution of these deposits is driven by environmental and geodynamical factors i e water level fluctuations and a fault related framework a detailed mapping of the buffalo point area in the north western part of antelope island indicates the presence of an anomalous concentration of microbial deposits dated ca 5 8 ka bp and distributed along a lobe shaped geometry this uncommon microbial deposit geometry results from an extensive colonization of a conglomerate substrate exhibiting an accumulation of m sized rounded cambrian quartzite boulders we suggest that this conglomerate substrate provides a stable nucleation point that promotes the development and preservation of the lobe shaped microbial deposits microbial deposits may also have protected the conglomerate substrate from erosional processes and thereby increased the preservation potential of the lobe shaped structure based on the characteristics of the conglomerate e g grain size texture and its location i e 200 m beyond the average shoreline this lobe shaped structure likely results from subaqueous debris or a hyperconcentrated density flow that transports sedimentary material from the buffalo point slopes downward to the shore we estimate the age of the conglomerate deposition to be between 21 and 12 ka bp the initiation of the flow may have been triggered by various mechanisms but the existence of a major active normal fault in the vicinity of these deposits suggests that an earthquake could have destabilized the accumulated sediments and resulted in conglomerate emplacement the catastrophic 15 ka bp bonneville flood which led to a drop in the lake level approximately 110 m may also provide an explanation for the initiation of the flow

external controls on the distribution fabrics and mineralization of modern microbial mats in a coastal hypersaline lagoon cayo coco cuba active carbonate mineralizing microbial mats flourish in a tropical highly evaporative marine fed lagoonal network to the south of cayo coco island cuba hypersaline conditions support the development of a complex sedimentary microbial ecosystem with diverse morphologies a variable intensity of mineralization and a potential for preservation in this study the role of intrinsic i e microbial and extrinsic i e physicochemical controls on microbial mat development mineralization and preservation was investigated the network consists of lagoons forming in the interdune depressions of a pleistocene aeolian substratum they developed due to a progressive increase in sea level since the holocene the hydrological budget in the cayo coco lagoonal network changes from west to east increasing the salinity this change progressively excludes grazers and increases the saturation index of carbonate minerals favouring the development and mineralization of microbial mats in the easternmost lagoons detailed mapping of the easternmost lagoon shows four zones with different flooding regimes the microbial activity in the mats was recorded using light dark shifts in conjunction with microelectrode o2 and hs profiles high rates of o2 production and consumption in addition to substantial amounts of exopolymeric substances are indicative of a potentially strong intrinsic control on mineralization seasonal climate driven water fluctuations are key for mat development mineralization morphology and distribution microbial mats show no mineralization in the permanently submersed zone and moderate mineralization in zones with alternating immersion and exposure it is suggested that mineralization is also driven by water level fluctuations and evaporation mineralized mats are laminated and consist of alternating trapping and binding of grains and microbially induced magnesium calcite and dolomite precipitation the macrofabrics of the mats evolve from early colonizing flat mats to complex cerebroid or terrace structures the macrofabrics are influenced by the hydrodynamic regime wind driven waves inducing relief terraces in windward areas and flat morphologies on the leeward side of the lagoon other external drivers include i storm events that either promote for example by bioclasts covering or prevent for example by causing erosion microbial mat preservation and ii subsurface degassing through mangrove roots and desiccation cracks covered by flat mats i e forming hemispheroids and cerebroidal structures these findings provide in depth insights into understanding fossil microbialite morphologies that formed in lagoonal settings

early triassic environmental dynamics and microbial development during the smithian spathian transition lower weber canyon utah usa the early triassic biotic recovery following the end permian mass extinction is well documented in the smithian spathian thaynes group of the western usa basin this sedimentary succession is commonly interpreted as recording harsh conditions of various shallow marine environments where microbial structures flourished however recent studies questioned the relevance of the classical view of long lasting deleterious post crisis conditions and suggested a rapid diversification of some marine ecosystems during the early triassic using field and microfacies analyses we investigate a well preserved early triassic marine sedimentary succession in lower weber canyon utah usa the identification of microbial structures and their depositional settings provide insights on factors controlling their morphologies and distribution the lower weber canyon sediments record the vertical evolution of depositional environments from a middle smithian microbial and dolosiliciclastic peritidal system to a late smithian early spathian bioclastic muddy mid ramp the microbial deposits are interpreted as microbially induced sedimentary structures miss that developed either 1 in a subtidal mid ramp where microbial wrinkles and chips are associated with megaripples characterizing hydrodynamic conditions of lower flow regime or 2 in protected areas of inter to subtidal inner ramp where they formed laminae and domal structures integrated with other published data our investigations highlight that the distribution of these microbial structures was influenced by the combined effects of bathymetry hydrodynamic conditions lithology of the substrat physico chemical characteristics of the depositional environment and by the regional relative sea level fluctuations thus we suggest that local environmental factors and basin dynamics primarily controlled the modalities of microbial development and preservation during the early triassic in the western usa basin

the preservation potential of environmentally diagnostic sedimentary structures from a coastal sabkha abstract the abu dhabi sabkha constitutes the landward portion of the shallow sloping carbonate ramp situated on the northwestern coast of the united arab emirates uae the sabkha in this region is composed of a complex assortment of carbonate organic and evaporitic facies that constitute a regressive sabkha sequence the surface features of the sabkha can be grouped into distinct laterally continuous facies associations that are directly correlatable with elevation above present day sea level previous investigations have suggested the employment of the abu dhabi sabkha as a modern depositional analogue to ancient carbonate evaporite formations however a quantitative analysis of the relationship between sabkha surface and subsurface characteristics has not previously been undertaken this study describes in detail the sedimentary structures and textures seen at the sabkha surface and compares them to the holocene age facies retained in the shallow subsurface of the 36 sedimentary structures observed at the sabkha surface only seven 19 are still identifiable in the early burial realm the majority of the surface structures were lost during early burial as a result of microbial mat decomposition destructive evaporite precipitation and compaction the loss of diagnostic sedimentary features during early burial as a result of fabric destructive processes has considerable implications for the recognition and interpretation of ancient sabkha sequences documenting these processes from a range of modern sedimentary environments will aid in the identification of those diagnostic features that may be reliably employed during paleoenvironmental reconstructions

morphological signatures of microbial activity across sediment and light microenvironments of lake vanda antarctica abstract cyanobacteria dominated microbial mats in lake vanda grow with pinnacles and ridges separated by prostrate mat rocks protrude over microbial mats on the lake bottom to create localized dm scale gradients in sedimentation and irradiance the effects of sedimentation on pinnacle and ridge growth were isolated from photosynthetic activity by contrasting growth across microenvironmental gradients sedimentation rate was measured as the mass of sand and mud sized sediment in mat that accumulated over 11 years and the incident light was modeled near and under rocks by reconstructing topography using structure from motion techniques morphologically diverse pinnacles and ridges were documented in both exposed and sheltered mat microenvironments in addition to growing downward from the underside of overhanging rocks mat that grew with 40 irradiance under overhangs did not have consistent differences in pinnacle density or ridge abundance as a function of sedimentation rates or irradiance when compared to exposed mat however their morphology did change significantly with changes in the direction of incident irradiance where irradiance was

oligo miocene lacustrine microbial and metazoan buildups from the limagne basin french massif central the limagne basin french massif central is an extensive continental lacustrine system accommodating microbial and metazoan buildups from chattian to aquitanian age a description of these buildups and their associated biotic components in grand gandaillat and crechy quarries provides insights into their spatio temporal distribution patterns flats cauliflowers domes cones and coalescent columnar morphologies have been identified with a main laminated mesofabric and laminated columnar filamentous and caddisfly coated microfabrics two low gradient margin models emerged based on the changes in the distribution morphology and size of the microbial and metazoan rich deposits through time the first model applies to the chattian deposits in the grand gandaillat quarry and the second to the aquitanian deposits in the crechy quarry this study emphasizes the heterogeneity of marginal lacustrine carbonate siliciclastic cycles the lacustrine palustrine cycles of the limagne basin record i lacustrine deposits composed of microbial and metazoan buildups and organic matter rich marls indicating periods of high accommodation and ii palustrine deposits composed of mudstone and clayey paleosoils indicative of periods of low accommodation the cycles differ with thin and symmetrical deposits that dominate the chattian cycles whereas thicker and asymmetrical deposits mark the aquitanian cycles in addition the chattian buildups are exclusively microbial and only a few centimeters thick whereas the aquitanian ones are multiple meters in height and are composed of both microbes and metazoans climatic tectonism volcanic and local parameters are involved in the deposition of buildups and their organization in each different cycle climate may control the long term arid humid sedimentary succession tectonic may explain the difference in the deposit thickness between two cycles of different ages and localizations as well as the specific distribution of the buildups throughout the basin volcanism may control the chemical lacustrine conditions and local physiography may impact the soil removal ability of the lake margin

the formation of caliche in soils of the mojave desert california abstract radiocarbon and 230th 234u dates of calcic horizons from calciorthid soil profiles in the mojave desert were used to calculate the rate of deposition of pedogenic caco3 a major period of caco3 deposition appears to have occurred about 20000 ybp forming calcic horizons below 100 cm depth during a climatic regime with greater effective rainfall than in the present the overall rate of deposition has been 1 0 to 3 5 g caco3 m2 yr during soil formation this rate is consistent with present day rates assuming that the atmospheric deposition of ca limits the process stable isotope ratios in calcic horizons indicate that caco3 precipitated from a soil environment with co2 of 15 5 13 c 12 c vs pdb and h2o of 2 0 18 o 16 o vs smow these values suggest that caco3 precipitates when seasonal drought simultaneously lowers soil pore pco2 and enriches soil water 18o by evaporation the role of soil calcic horizons in the global geochemical cycle of carbon is discussed

stromatolite reef crusts early cretaceous spain bacterial origin of in situ precipitated peloid microspar peloidal crusts are significant components of early cretaceous aptian reef carbonates in eastern spain the crusts form steep sided laminated deposits on coral and other skeletal surfaces their microfabric consists almost entirely of silt sized peloids in fenestral microspar matrix this microfabric contrasts with more poorly sorted and generally finer grained detrital wackestone packstone fabrics of the adjacent reef matrix scarcity of incorporated grains indicates that the crusts did not trap many particles it is proposed that the crusts are stromatolites and that peloids and inter peloid space were created concurrently by bacterial degradation of organic matter as they developed inter peloid voids were protected from infiltration of extraneous sediment by the organic rich exterior surface of the stromatolite even spacing of the peloids within microspar may reflect self organization of bacterial colonies in the decaying organic matrix compressed and partly amalgamated peloids marginal to burrows in the stromatolites suggest that the peloid fabrics were initially only partially lithified the grainstone like peloid fabric is therefore interpreted as having formed in situ by very early diagenetic processes driven by heterotrophic bacteria

the biogeomorphology of shark bay s microbialite coasts abstract the world heritage microbialites coquinas and microbialitic sediments of hamelin pool shark bay western australia form through complex community and environmental interactions resulting in surficial co2 sequestration predicted climate change impacts threaten the stability of this setting and the balance of biogeomorphological processes that generate them in this setting long term surficial co2 sequestration occurs through the combination of biomineralisation organomineralisation and lithification which locks atmospheric co2 into caco3 rocks and sediments biogeomorphological processes that control the distribution and effectiveness of these mechanisms including biostabilisation bioconstruction bioerosion and bioturbation have not been addressed in this setting to date a three dimensional biogemorphological mapping unit framework is defined at three locations in hamelin pool within the shallow subtidal to supratidal zones based on historical and recent multiscale datasets this framework is used to review the complex distribution of geomorphological and biogeomorphological processes the distribution of lithification within a biogeomorphological process context is examined and current geological analogue models of microbialite and coquina development are expanded to include biogeomorphological processes the framework is used to understand the impacts of increased water elevation in response to intensification of the leeuwin current during the 2010 2012 ningaloo nino event potential climate change impacts are identified including reduced intertidal bioconstruction and a shift from microbialitic structure generation to increased grain generation reducing stromatolite development review of the uncertainty of impacts of ocean acidification and temperature shifts on biomineralisation organomineralisation and lithification processes crucial to the maintenance of the outstanding universal values in this world heritage location suggests urgent research is required

growth morphologies of modern marine stromatolites a case study from highborne cay bahamas abstract stromatolites are a uniquely coupled geo biosphere system which potentially records important paleoenvironmental and biological information characterizing and distinguishing between the biological and physical factors that control stromatolite morphogenesis therefore has important implications for the understanding of modern stromatolites and the interpretation of ancient systems this paper documents the occurrence and distribution of stromatolites with distinct growth morphologies in the highborne cay reef system and other locations in exuma cays bahamas and explores the relative contributions of physical and biological environmental factors controlling stromatolite shape our observations suggest that macro scale growth morphologies of exuma stromatolites are primarily controlled by accommodation space hydrodynamics and sedimentation patterns the latter are critical for the stromatolite ecosystem in that the suspended sediment provides grains for trapping and binding and thus stromatolite accretion furthermore sediment burial removes macroalgae allowing the prokaryotic community to dominate changes in sedimentation patterns and frequency allow for the colonization of stromatolites by macroalgae and boring macrofauna which in time destroy and degrade the stromatolite structure

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

periodicity in stromatolitic lamination a potential record of enso nao and sunspot in the miocene lacustrine record of the ebro basin spain abstract the spectral decomposition of time series obtained from ancient rock records can be used to study the similarity between the dynamics of present day and past climate systems a high resolution periodicity analysis of luminance and lamina thickness of lacustrine stromatolites in the ebro basin northeast of iberian peninsula reveals a significant signal of interannual and decadal climatic variability in the miocene this is one out of very few works that presents the use of spectral analysis to estimate the potential of stromatolite lamination as multiple scale recorders of climate parameters the effects of precipitation and evaporation variations on stromatolite lamination have been detected at three orders of cyclicity based on textural and high resolution stable isotope analyses c and o obtained in prior studies these analyses also revealed that the light and dark simple lamina couplets are identified with annual cycles third order isotopic cycles in the present study the spectral analysis results obtained through different paths in five stromatolite specimens reveal significant periods in the power spectrum at around 2 5 3 7 5 7 10 and 22 years these cycles can be correlated with the typical oscillation bands of different climate related agents the 2 5 year period corresponds to the quasi biennial oscillation qbo or to the biennial component of the el nino southern oscillation enso or to the north atlantic oscillation nao the 3 to 5 and 5 to 7 year bands can be linked to enso or nao variability second order isotopic cycles the 8 to 11 year bands fit the 11 year schwabe first order isotopic cycles and 22 to 23 year fit the 22 year hale sunspot cycles thus the stromatolite growth was controlled by enso nao and solar activity cycles the close relationship between these climate related agents makes it difficult to specify the dominant agent controlling the stromatolite growth nevertheless the significant periods obtained from this study within interannual 2 5 3 7 5 7 years decadal 10 22 years and even multidecadal bands 37 42 years support the existence and concurrence of enso and nao precursors during the early and middle miocene

a 6000 year record of ecological and hydrological changes from laguna de la leche north coastal cuba abstract laguna de la leche north coastal cuba is a shallow 3 m oligohaline 2 0 4 5 coastal lake surrounded by mangroves and cattail stands a 227 cm core was studied using loss on ignition pollen calcareous microfossils and plant macrofossils from 6200 to 4800 cal yr bp the area was an oligohaline lake the period from 4800 to 4200 cal yr bp saw higher water levels and a freshened system these changes are indicated by an increase in the regional pollen rain as well as by the presence of charophyte oogonia and an increase in freshwater gastropods hydrobiidae by 4000 cal yr bp an open mesohaline lagoon had formed an increase in salt tolerant foraminifers suggests that water level increase was driven by relative sea level rise the initiation of laguna de la leche correlates with a shift to wetter conditions as indicated in pollen records from the southeastern united states e g lake tulane this synchronicity suggests that sea level rise caused middle holocene environmental change region wide two other cores sampled from mangrove swamps in the vicinity of laguna de la leche indicate that a major expansion of mangroves was underway by 1700 cal yr bp

microbialite formation in seawater of increased alkalinity satonda crater lake indonesia abstract the crater lake of the small volcanic island satonda indonesia is unique for its red algal microbial reefs thriving in marine derived water of increased alkalinity the lake is a potential analogue for ancient oceans sustaining microbialites under open marine conditions current reef surfaces are dominated by living red algae covered by non calcified biofilms with scattered cyanobacteria and diatoms minor caco3 precipitates are restricted to the seasonally flooded reef tops which develop biofilms up to 500 m thick dominated by the cyanobacteria pleurocapsa calothrix phormidium and hyella microcrystalline aragonite patches form within the biofilm mucilage and fibrous aragonite cements grow in exopolymer poor spaces such as the inside of dead lysed green algal cells and reef framework voids cementation of lysed hadromerid sponge resting bodies results in the formation of wetheredella like structures hydrochemistry data and model calculations indicate that co2 degassing after seasonal mixis can shift the carbonate equilibrium to cause caco3 precipitation increased concentrations of dissolved inorganic carbon limit the ability of autotrophic biofilm microorganisms to shift the carbonate equilibrium therefore photosynthesis induced cyanobacterial calcification does not occur instead passive diffusion controlled eps mediated permineralization of biofilm mucus at contact with the considerably supersaturated open lake water takes place in contrast to extreme soda lakes the release of ca2 from aerobic degradation of extracellular polymeric substances does not support caco3 precipitation in satonda because the simultaneously released co2 is insufficiently buffered subfossil reef parts comprise green algal tufts encrusted by microstromatolites with layers of fibrous aragonite and an amorphous unidentified mg si phase the microstromatolites probably formed when lake satonda evolved from seawater to ca2 depleted raised alkalinity conditions because of sulfate reduction in bottom sediments and pronounced seasonality with deep mixing events and strong co2 degassing the latter effect caused rapid growth of fibrous aragonite while mg si layers replaced the initially mg calcite impregnated biofilms this could be explained by dissolution of siliceous diatoms and sponge spicules at high ph followed by mg calcite dissolution and mg silica precipitation at low ph due to heterotrophic activity within the entombed biofilms

micritized skeletal grains in northern belize lagoon a major source of mg calcite mud abstract lime mud in northern belize lagoon is composed predominantly of silt size cryptocrystalline grains and clay size clumps both of which consist of anhedral equant crystals less than 0 5 m in size this mud is 70 90 mg calcite containing 9 10 mole mgco3 detailed petrographic morphologic and mineralogic analyses suggest that the cryptocrystalline grains are micritized skeletal grains and that the mud formed by abrasion and bioerosion of these altered grains micritization of skeletal grains occurred primarily by recrystallization of original skeletal carbonate laths prisms and blades of mg calcite aragonite and calcite to equant crystals of micritic mg calcite with additional alteration by micritic infilling of microborings and skeletal cavities because of d fferences between crystal morphologies and mineralogies of original skeletal components and their micritized counterparts mud produced by diminution of micritized grains is distinct from that produced by skeletal breakdown the abundance of cryptocrystalline grains in the bahamas and other shallow carbonate environments suggests that micritized grains are potentially an important source of lime mud that has not previously been identified

lithifying microbial mats in lagoa vermelha brazil modern precambrian relics abstract bacterial populations microbial and mineral forming processes and their products were analyzed in lagoa vermelha brazil the microbial mat and underlying sediment were studied as a unique system to define the boundary conditions responsible for high mg calcite and dolomite formation in the uppermost layers of the microbial mat oxygenic photosynthesis and aerobic respiration resulted in calcite precipitation whereas in the underlying anoxic layers of the mat sulfide oxidation and sulfate reduction induced formation of a range of carbonate minerals with increasing mg concentrations the chemical mineralogical and biological conditions presently found in lagoa vermelha may have been more common in the precambrian the microorganisms performing the metabolic processes related to carbonate mineral formation within lagoa vermelha s hypersaline microbial mat may have already been present in the precambrian thus microbial carbonate as a biomineral could be a record of metabolism throughout geological time

antecedent aeolian dune topographic control on carbonate and evaporite facies middle jurassic todilto member wanakah formation ghost ranch new mexico usa

microbially influenced formation of mg calcite and ca dolomite in the presence of exopolymeric substances produced by sulphate reducing bacteria some species of sulphate reducing bacteria srb are known to mediate the formation of dolomite and mg calcite however their exact role in the mineralization process remains elusive here we present the result of a laboratory experiment that was designed to test whether formation of carbonate minerals by srb can occur in the absence of living cells through passive mineralization of their exopolymeric substances eps srb capable of mediating dolomite were cultivated in the laboratory allowing them to secrete eps microbial activity within the cultures was subsequently inhibited with antibiotics only after this step ca2 and mg2 were added to the solution and carbonate minerals could form mg calcite and disordered ca dolomite precipitated in association with eps the mol of mg2 in the crystals increased with longer incubation times this result demonstrates that organic compounds produced by srb can mediate the formation of ca mg carbonates in the absence of an active metabolism

environmental controls on microbial community cycling in modern marine stromatolites living stromatolites on the margins of exuma sound bahamas are the only examples of modern stromatolites forming in open marine conditions similar to those that may have existed on precambrian platforms six microbial mat types have previously been documented on the surfaces of stromatolites along the eastern side of highborne cay schizothrix solentia heterotrophic biofilm stalked diatom tube diatom and phormidium mats cycling of these communities create laminae with distinct microstructures subsurface laminae thus represent a chronology of former surface mats the present study documents the effects of environmental factors on surface microbial communities of modern marine stromatolites and identifies potential causes of microbial mat cycling mat type and burial state at 43 markers along a stromatolitic reef on the margin of highborne cay were monitored over a two year period 2005 2006 key environmental parameters i e temperature light wind water chemistry were also monitored results indicated that the composition of stromatolite surface mats and transitions from one mat type to another are controlled by both seasonal and stochastic events all six stromatolite mat communities at highborne cay showed significant correlations with water temperature heterotrophic biofilms solentia stalked diatom and phormidium mats showed positive correlations with temperature whereas schizothrix and tube diatom communities showed negative correlations a significant correlation with light photosynthetically active radiation par was detected only for the heterotrophic biofilm community no significant correlations were found between mat type and the monitored wind intensity data but field observations indicated that wind related events such as storms and sand abrasion play important roles in the transitions from one mat type to another an integrated model of stromatolite mat community cycling is developed that includes both predictable seasonal environmental variation and stochastic events the long term monitoring of mat communities on highborne cay stromatolites and the resulting model are an important step in understanding morphogenesis of modern marine stromatolites with implications for interpreting patterns of stromatolite lamination in the geologic record

biogenic laminar calcretes evidence of calcified root mat horizons in paleosols laminar calcretes are described from the lower carboniferous of south wales the upper jurassic of southern england and the upper jurassic lower cretaceous of northern spain they are interpreted as calcified root mats horizontal root systems and are compared with other examples in the geological record and with possible modern analogues all three occurrences consist of virtually identical centimetre to decimetre thick locally organic carbon rich laminar micrites containing up to 50 by volume of millimetre sized typically calcite filled tubular fenestrae set in an irregular but very finely laminated matrix it is suggested that root mat calcretes are probably very common in the geological record in peritidal lacustrine margin and floodplain deposits but owing to their crudely biogenic microstructure they more closely resemble cryptalgal laminites than do other laminar calcretes the recognition of such root mat calcretes in sedimentary sequences not only provides evidence of subaerial exposure and vegetation cover but can also indicate positions of palaeo water tables in certain circumstances

changes in groundwater induced by water diversion in the lower tarim river xinjiang uygur nw china evidence from environmental isotopes and water chemistry summary the lower tarim river in nw china is under severe ecosystem degradation due to stopped stream flow and diminished groundwater recharge since year 2000 eight water diversions from the upper stream and from the neighboring kaidu kongque river have been implemented to alleviate the ecosystem disaster in order to assess the effectiveness of the water diversion project and to identify proper tracers of groundwater dynamics we sampled the riparian groundwater system in 2007 and 2008 along the 350 km long river channel through the 40 monitoring wells situated along nine transects perpendicular to the river and three soil profiles measurements on the samples have included environmental isotopes 18 o 2 h 3 h and water chemistry the results show that remarkable changes have been induced by the water diversions the observed response of riparian groundwater system includes general decrease in total dissolved solid tds and rise of water table scope with greater than 1 m rise in water table is within 700 m from the riverbank in the upper segments and 300 m in the lower ones greater rise of water table occurs near the river bank tritium data show that the extent of modern recharge since 1960s including that from the diverted water is limited to 600 m from the riverbank at the upper segments and 200 m at the lower ones stable isotopes show that groundwaters regardless of modern or pre modern are enriched in heavy isotopes and are plotted in parallel to the meteoric water line in the d d plot attributed to evaporation during recharge groundwater is generally of na mg cl so4 type and is formed by dissolution of minerals such as halite sulfate and carbonates based on component correlation matrices analysis the salinity of groundwater is mainly affected by that of the diverted water and of the local antecedent groundwater salts in the unsaturated zone evapotranspiration during recharge as the zone of smaller groundwater depth less than 5 m suitable for the most existing populus euphratica and tamarix ramosissima the main species targeted by the rescue effort restricts to 200 m from the riverbank and narrows down towards downstream long term stability of the ecosystem cannot be achieved by the current water diversion scheme and regulating saving water in source streams and the upper middle tarim river is crucial for continuing water diversion

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

architecture and sedimentary evolution of the southwestern gissar carbonate platform uzbekistan during the middle late jurassic abstract sedimentological investigations have been carried out in the southwestern part of the gissar range uzbekistan in order to document the stratigraphic evolution of a vast middle upper jurassic carbonate platform developed on the northern margin of the amu darya basin two major sequences are distinguished based on their contrasting facies pattern platform configuration and carbon isotope signature 1 a callovian sequence and 2 an upper jurassic sequence potentially oxfordian to kimmeridgian in age a carbonate ramp with a double proximal distal polarity developed during the callovian sequence oo bioclastic grainstones were produced in two permanently agitated shallow water areas developing to the north and to the south patch and pinnacle reefs mainly built up close to the storm wave base passing distally to pellet and foraminiferal oncoid rich mid to outer ramp deposits the top of the callovian sequence is a regional discontinuity that could have formed by subaerial exposure of the platform this probable hiatus could record a major climatic change associated to the middle late jurassic transition the upper jurassic sequence consists of metre thick alternations of pellet algal pack to grainstones microbial oncoid floatstones ooid grainstones and mudstones which have likely accumulated in a vast lagoon protected by a large scale barrier reef observed south of the study area gypsum and anhydrite content gradually increased towards the top of the upper jurassic sequence ending up with a thick chicken wire gypsum accumulation recording the progradation of a large scale sabkha over the lagoon this phenomenon is related to a progressive aridification and restriction of the amu darya basin that could have begun during the middle late oxfordian and reached its climax during the tithonian with massive halite deposition comparable events occurred in jurassic platforms located along the tethyan margins pointing to regional and global controls on sedimentation

a model for evaluating the influence of water and salt on vegetation in a semi arid desert region northern china a model influence of water and salt on vegetation iwsv was developed to evaluate their influence on plant species the main function of this model was to calculate a comprehensive index value for evaluating the suitability of plant growth this model consists of five explanatory variables vadose zone moisture content vadose zone salinity vadose zone lithology depth to the water table and groundwater mineralization and two response variables plant species and their cover a set of independent data on three plant species artemisia ordosica salix psammophila and carex enervis which are dominant species in the mu us desert of northern china were used to validate the model validation results show an overall correct prediction for the distribution of these three species the results demonstrated that the iwsv model can be a useful tool for groundwater management and nature conservation in a semi arid desert region especially for predicting the vegetation distribution in areas with groundwater extraction

marine carbonate factories a global model of carbonate platform distribution platform carbonates are a major component of the earth system but their spatial distribution through geological times is difficult to reconstruct due to the incompleteness of geological records sampling heterogeneity and their intrinsic complexity beyond this complexity carbonates are not randomly distributed in the world oceans neither in the modern nor in the past and thus global trends exist in the present review we focus on the understanding of the spatial distribution of carbonate production at a global scale we use a deterministic approach which focuses on discriminating components stratigraphic architectures and environmental features to relate shallow water carbonate production to oceanographic parameters the work is based on extensive literature reviews on carbonate platforms ecological niche modelling coupled with deep time general circulation models is used to calibrate a predictive tool of carbonate factory distribution a carbonate factory function is set up that is based on sea surface oceanographic parameters temperature salinity and primary productivity the model was tested using remote sensing and in situ oceanographic data of modern times while outputs of paleoceanographic models are utilized for lower aptian cretaceous modelling the approach allows determining four neritic carbonate factories that are called the marine biochemical photozoan photo c and heterozoan factories the model finely simulates the global distribution of lower aptian and modern carbonate platforms carbonate factories appear to thrive for specific ranges along the environmental gradient of carbonate saturation this conceptual scheme appears to be able to provide a simple universal model of paleoclimatic zones of shallow water marine carbonates

land subsidence due to groundwater withdrawal in the northern beijing plain china abstract beijing is an international metropolis where over exploration of water resource makes land subsidence becoming more and more serious the related problems cannot be avoided in the coming years because of the giant increase of population the aims of this study are to quantify land subsidence over the period 2003 to 2010 grasp the evolution of the process and investigate the relation with the triggering factors in the northern area of the beijing plain various data including deep compaction from vertical multiple borehole extensometers land subsidence from persistent scatterer interferometry and leveling surveys groundwater levels hydrogeological setting from wellbores and landsat tm image were collected and effectively used to detect the spatial and temporal features of land subsidence and its possible relation with groundwater level changes compressible layer thickness and urban development results show that land subsidence is unevenly distributed and continuously increased from 2003 to 2010 the average loss of elevation over the monitoring period amounted to 92 5 mm with rates up to 52 mm y the distribution of the subsidence bowl is only partially consistent with that of the groundwater depression cone because of the variable thickness of the most compressible fine deposits in fact extensometers reveal that silty clay layers account for the larger contribution to land subsidence with the 15 m thick silty clay layer between 102 and 117 m depth accounting for about 25 of the total subsidence finally no clear correlation has been observed between the subsidence rates and the increase of the load on the land surface connected to the impressive urban development this study represents a first step toward the development of a physically based model of the subsidence occurrence to be used for planning remediation strategies in the northern beijing plain

multivariate statistical analysis for the assessment of groundwater quality under different hydrogeological regimes multivariate statistical analysis has been widely used for hydrogeochemical characterization of groundwater quality in this study hydrochemical data from three hydrological basins were used and two methods factor and cluster analyses were applied the first area is the coastal area of eastern thermaikos gulf where groundwater is influenced by seawater intrusion and geothermal fluids the other two areas are the inland basins of gallikos and perdikas in which agricultural and industrial activities constitute the main anthropogenic pollution sources of groundwater initially the aforementioned methods were applied for each area separately and resulted in a different number of significant factors and clusters while the natural and anthropogenic influences were spatially determined in each area additionally factor and cluster analyses were applied coupling data from all areas therefore five clusters and three major factors were determined distinguishing the hydrochemical processes and impacts from anthropogenic activities in more detail it is worth mentioning that the application of cluster analysis in the coupled groundwater samples of all studied areas resulted beneficially in the most hydrochemically complex area salinization dominates in the coastal area while in gallikos and perdikas basins high concentrations of no3 occur mainly due to agricultural activities and small livestock units the numerous hydrochemical samples are identified as the main issue for the higher discretization and reliability of the second approach nevertheless this study is associated with a number of limitations of multivariable statistical analysis regarding extreme concentrations of cl and na this issue stimulates further research in overcoming and understanding these drawbacks

the participation of ilmenite bearing cumulates in lunar mantle overturn abstract the ilmenite bearing cumulates ibc formed from the solidification of the lunar magma ocean are thought to have significantly affected the long term evolution of the lunar interior and surface their high density is considered to trigger rayleigh taylor instabilities which allow them to sink into the solidified cumulates below and drive a large scale overturn in the lunar mantle knowledge of how the ibc participate in the overturn is important for studying the early lunar dynamo chemistry of surface volcanism and the existence of present day partial melt at the lunar core mantle boundary despite early efforts to study this process as rayleigh taylor instabilities no dynamical models have quantified the degree of ibc sinking systematically we have performed quantitative 2 d geodynamical simulations to measure the extent to which ibc participate in the overturn after their solidification and tested the effect of a range of physical and chemical parameters our results show that ibc overturn most likely happened when the magma ocean had not yet fully solidified with the residual melt decoupling the crust and ibc resulting in 50 70 ibc sinking participation of the last dregs of remaining magma ocean melt is unlikely leaving its high concentrations of radiogenic elements close to the surface our simulations further indicate that foundered ibc can stay relatively stable at the core mantle boundary until the present day at temperatures consistent with the presence of a partially molten zone in the deep mantle as inferred from geophysical data 30 50 of the primary ibc remain at shallow depths throughout lunar history enabling their assimilation by rising magma to form high ti basalts