life on mars evaluation of the evidence within martian meteorites alh84001 nakhla and shergotty abstract analyses both support and are in opposition to the hypothesis that the martian meteorite alh84001 contains evidence for possible biogenic activity on mars new observations in two additional martian meteorites nakhla 1 3 ga old and shergotty 300 165 ma old indicate possible biogenic features features in the three martian meteorites compare favorably with the accepted criteria for terrestrial microfossils and evidence for early life on the earth there is strong evidence for the presence of indigenous reduced carbon biogenic magnetite and the low temperature formation of carbonate globules the morphological similarities between terrestrial microfossils biofilms and the features found in the three martian meteorites are intriguing but have not been conclusively proven every investigation must recognize the possibility of terrestrial contamination of the meteorites whether or not the meteorites are martian the search for evidence of ancient life in martian meteorites has emphasized the difficulties confronting the scientific community with the respect to the positive identification of evidence of past biogenic activity

evidence for microbes in early neoproterozoic stromatolites abstract the biogenesis of stromatolites has long been discussed since many lack convincing evidence of their biological origin this has particularly been the case with older precambrian examples where widespread diagenetic and metamorphic processes have commonly destroyed microbial relics in some cases however evidence has been preserved through very early mineralisation precambrian stromatolites are relatively abundant but it is extremely rare that they contain calcified or dolomitized cyanobacteria and biofilms this study provides evidence from early neoproterozoic columnar stromatolites in the jiuliqiao formation from the southeastern margin of the north china platform for fossilized extracellular polymeric substances eps and cyanobacteria along with nanospheres which may represent permineralised viruses or viral like particles a similar chemical composition and colour along with their embedded and cross cutting relationships with the matrix suggest they are syn depositional products and not modern artefacts or the result of sample preparation the interweaving of cyanobacterial filaments with detrital grains such as quartz and intraclasts indicates trapping baffling and binding processes the presence of virus like particles and mineralized eps with anhedral fine grained calcite suggests they may have provided initial nucleation sites for subsequent carbonate precipitation this study demonstrates the use of a high definition scanning electron microscope to detect fossilized calcified filamentous and spheroidal bacteriomorphs within ancient stromatolites in order to confirm their biogenesis

shear coupled pl summary observed teleseismic shear coupled pl waves spl display a variety of waveforms depending on factors such as source depth source type and velocity structure using a wkbj spectral method for sv wave propagation synthetic seismograms of spl are produced to examine the factors important in sv and spl excitation results show that spl is preferentially excited by shallow sources compared to deep sources this is due to large source area reverberations which consequently leak as sv waves into the mantle interaction at the receiver area then sets up the classic prograde elliptical motion by which spl can be identified this is in accordance with the teleseismic observations and indicates that most previous models for the propagation of spl were not appropriate for shallow source since emphasis was placed on wave interactions occurring only near the receiver

potential evidence of fossilised neoproterozoic deep life sem observations on calcite veins from oppaminda creek arkaroola south australia scanning electron microscopy revealed micron sized globular and coccoid objects associated with filaments and mucus like patches in antitaxial fibrous calcite veins from oppaminda creek northern flinders ranges south australia chemically the objects only differ from their calcite caco3 matrix by a higher sulphur content the 585 ma veins formed at about 3 6 km below the surface fluid inclusions indicate a temperature of formation of about 60 80 c and not exceeding 100 c a non biogenic origin of the objects is discussed but considered unlikely instead morphology chemistry and size distribution all indicate that the objects are fossilised microbes that lived in the veins at the time and depth of vein formation

on the use of combined geophysical methods to assess water content and water conductivity of near surface formations abstract we propose to deepen the interpretation of combined geophysical methods georadar seismic and electric to assess physical properties characterizing the near surface porous formations especially the influence of water velocity analysis of multioffset georadar data are used together with seismic methods to estimate lateral and vertical ground water fluctuations this enables us to identify transitions from non saturated to fully saturated porous layers with certainty furthermore the accurate knowledge of seismic velocities helps to estimate the porosity of the ground water formations finally we show how the radar technique may be useful in solving the problem of trade off between bulk resistivity which is deduced from electrical measurements and that of water ionic conductivity and water content these theoretical considerations are illustrated using various measurements conducted at the same test site our interpretation is compared with a few laboratory measurements on water and soil samples this study displays the impact of combined geophysical approaches for providing models of water and ionic transfers down to a depth of several metres

dipping structure under dourbes belgium determined by receiver function modeling and inversion abstract teleseismic broadband p and s waves recorded at the nars station ne06 dourbes belgium are shown to exhibit strong anomalous particle motion not attributable to instrument miscalibration or malfunction azimuthally varying radial and tangential components have been observed on 38 recordings after vector rotation of horizontal p waves into the ray direction the tangenital p waves attain amplitudes comparable to the radial components from the east with negative polarity and west with positive polarity but tend to be zero in the north and south suggesting major discontinuities in the crust dipping southward the sh wave from the east contains a large spmp phase an s to p conversion at the free surface and then reflected back to the surface from the moho the polarity of this spmp phase presents further evidence for a southward dipping moho we employ ray theory for three dimensionally dipping interfaces to compute the p wave response linear inverse theory with smoothness constraints is applied to the simultaneous inversions of p wave receiver functions for four different backazimuths through the progressive change of interface strike and dip and the inversion of layer shear wave velocities a dipping crustal model that is consistent with both the observed waveforms and results of previous local geophysical surveys has been determined the results suggest a large velocity contrast in the shallow structure near the surface another major interface at a depth of 12 km with dip of 10 and a seismically transparent unit below the interface the interface at a depth of 12 km reportedly emerges at the midi fault 50 km north of the station ne06

microbially induced sedimentary structures from the 1 64 ga chuanlinggou formation jixian north china abstract the present study documents abundant exceptionally preserved microbially induced sedimentary structures miss from the 1 64 ga chuanlinggou formation of the jixian area north china craton the chuanlinggou formation is dominated by black silty shale mudstone with fine sandstone of the lower part and was likely deposited in a relatively restricted shallow marine environment varying from fair weather wave action zone to below storm wave action zone both wrinkle structures and sand veins are very abundant in the lower and middle parts of the formation wrinkled layers are dark colored densely laminated and contain floating quartz grains and abundant mica grains both of which are aligned parallel to bedding plane such an arrangement pattern is attributed to the microbe s binding and trapping of miss sem imaging also shows that sticky networks interwoven by filamentous extracellular polymer substances eps and biofilms with distinct pores are very pronounced in clay matrix of wrinkled layers providing direct evidence of microbial activities during the formation of wrinkle structures in addition the circularly arranged quartz grains forming hollow cavities and vertical channels of quartz grains beneath the laminated layers are unique to the wrinkle structures showing initial forming stage of the sand veins sand veins similar to fills of sand cracks are usually preserved in silty shales and occasionally occur beneath the winkled surfaces they were formed due to methane degassing of decay of microbial mats and biofilms abundant nano particles of various epss isolated nanoglobules paired nanoglobules dumbbell shaped nanoglobules and polyhedron aggregates are detected in clay matrix close to sand veins indicating microbial participation in the formation of sand veins wide spatial distribution broadened environmental inhabitation and extremely high abundance and bed surface density of the misss indicate proliferation of miss forming microbial mats in mesoproterozoic times

the vertical component p wave receiver function the vertical component p wave receiver function is an important source of data in studies of the crust mantle transfer function for determining earth structure under isolated receivers or under receiver arrays this waveform illuminates a missing aspect of the wave propagation in receiver function studies that employ only the horizontal components of motion and yields complementary constraints on near receiver heterogeneity and p wave propagation the vertical component p wave receiver function is formed using an array estimate for the effective teleseismic source function that is then deconvolved from all the vertical and horizontal components of ground motion at each station in the array one dimensional three dimensional and stochastic wave propagation models are used to test the robustness of the technique breakdown of single station receiver function deconvolution occurs because of high levels of noncorrelated noise between the ground motion components receiver functions for stations of the southern california terrascope array are investigated using the array technique vertical receiver functions for stations in the los angeles basin and long valley caldera show high amplitude secondary arrivals that cannot be explained by simple 1d structures but probably reflect wave propagation in 3d basin structures three component receiver functions from the station at mammoth lakes california show pathological behavior where the horizontal components of ground motion exceed the amplitude of the vertical components suggesting extreme topographic and 3d velocity heterogeneity use of all three components of the receiver function in modern passive array experiments is encouraged to reduce the problems of nonuniqueness in determining earth models

improved characterization of fine texture soils using on ground gpr full waveform inversion ground penetrating radar gpr uses the recording of electromagnetic waves and is increasingly applied for a wide range of applications traditionally the main focus was on the analysis of the medium permittivity since estimates of the conductivity using the far field approximation contain relatively large errors and cannot be interpreted quantitatively recently a full waveform inversion fwi scheme has been developed that is able to reliably estimate permittivity and conductivity values by analyzing reflected waves present in on ground gpr data it is based on a frequency domain solution of maxwell s equations including far intermediate and near fields assuming a 3 d subsurface here we adapt the fwi scheme for on ground gpr to invert the direct ground wave traveling through the shallow subsurface due to possible interference with the airwaves and other reflections an automated time domain filter needed to be included in the inversion in addition to the obtained permittivity and conductivity values also the wavelet center frequency and amplitude return valuable information that can be used for soil characterization combined geophysical measurements were carried out over a silty loam with significant variability in the soil texture the obtained medium properties are consistent with theta probe electromagnetic resistivity tomography and electromagnetic induction results and enable the formulation of an empirical relationship between soil texture and soil properties the permittivities and conductivities increase with increasing clay and silt and decreasing skeleton content moreover with increasing permittivities and conductivities the wavelet center frequency decreases whereas the wavelet amplitude increases which is consistent with the radiation pattern and the antenna coupling characteristics

bathymetry of mariana trench arc system and formation of the challenger deep as a consequence of weak plate coupling 1 the challenger deep in the southernmost mariana trench western pacific ocean is the deepest point on the earth s surface 10 920 m below sea level its location within a subduction trench where one plate bends and descends below another is not surprising however why is it located in the southernmost mariana trench and not at its central part where the rate of subduction is higher where the lithosphere is the oldest and densest on the earth and where the subducted lithosphere pulling down is the longest in the earth 1000 km or more according to seismic tomography we suggest that although subduction rate and slab age generally control trench depth the width of the plate coupling zone is more important beneath the central marianas the subducted slab is attached to the upper plate along a 150 km wide surface that holds the shallow portion of the subducted plate nearly horizontal in spite of its great load and thus counters trench deepening in contrast along the south mariana trench the subducted length of the lithosphere is much shorter but its attachment to the upper plate is only along a relatively narrow 50 km wide surface in addition a tear in the slab beneath this region helps it to sink rapidly through the mantle and this combination of circumstances allows the slab to steepen and form the deepest trench on the earth in a wider perspective the interrelations shown here between trench deepening ridge shallowing slab steepening and forearc narrowing may shed light on other subduction zones located near edges of rapidly steepening slabs

syndepositional cements associated with nannofossils in the marmolada massif evidences of microbially mediated primary marine cements middle triassic dolomites italy the marmolada platform is characterized by striking globose masses evinosponges arranged in concentric bands of fibrous calcite cements ranging in size from centimeters to several decimeters the lithogenetic importance of these peculiar cements has been recognized in many middle triassic buildups of the western tethys eds microanalyses revealed that these fibrous cements contain 1 3 mol of mg and detectable amounts of sr over 1000 ppm sometimes exceeding 10 000 ppm the strontium geochemical signature in neomorphic calcite could reflect the replacement of an aragonitic carbonate precursor the boundaries between the fibrous calcite bands are marked by alignments of microcrystalline aggregates of fluorapatite and or dolomite the presence of fluorapatite may indicate a depositional microenvironment eutrophic or rich in microbial communities epifluorescence analyses showed bright bands alternated to dark ones confirming that organic matter remains occur within the studied cements and could have played a significant role in supporting the widespread syndepositional cementation high magnification sem observations on bright epifluorescent bands showed the presence of widespread more or less spherical bodies ranging in size 100 300 nm these bodies could represent the relicts of nannobacterial cells

inverting surface gpr data using fdtd simulation and automatic detection of reflections to estimate subsurface water content and geometry abstracta new inversion scheme for common offset ground penetrating radar measurements at multiple antenna separations was proposed which is intermediate between inverting of picked reflectors using ray tracing and full waveform inversion the measurements are modeled similarly to the real data using 2d finite difference time domain simulations these simulations are obtained with a parameterized model of the subsurface that consists of several layers with constant dielectric permittivity and an explicit representation of the layers interfaces then reflections in the modeled and in the real data are detected automatically and the reflections of interest of the real data are selected manually the sum of squared residuals of the reflections traveltime and amplitude is iteratively minimized to estimate subsurface water content and geometry i e the position and shape of the layer interfaces the method was first tested with a synthetic data set and then applied to a real data set the comparison of

biomimetic properties of minerals and the search for life in the martian meteorite alh84001 the existence of extraterrestrial life was heralded by controversial claims made in 1996 that the martian meteorite alh84001 harbored relics of ancient microorganisms we review here the accumulated evidence for and against past extraterrestrial life in this martian meteorite the main pro life arguments the presence of polycyclic aromatic hydrocarbons magnetite crystals carbonate globules and structures resembling terrestrial life forms known as nanobacteria can be deemed ambiguous at best although these criteria are compatible with living processes each one of them can be explained by nonliving chemical processes by undergoing amorphous to crystalline transformations and binding to multiple substrates including other ions and simple organic compounds minerals especially those containing carbonate have been shown to display biomimetic properties producing forms that resemble bacteria this simple and down to earth explanation can account fully for the existence of mineral entities resembling put

exceptionally preserved microbially induced sedimentary structures from the ediacaran post glacial successions in the kimberley region northwestern australia abstract a set of exceptionally preserved microbially induced sedimentary structures miss is described from the post glacial yurabi formation of late ediacaran age in the kimberley region northwestern australia these miss comprise oriented grains bamboo leaf like cracks polygonal cracks worm like cracks sinuous cracks gas domes pyrite concentrated laminae and micrite laminae most of the yurabi miss are morphologically comparable with their ancient and modern counterparts micrometre or nannometre scale bacteria or biofilm like inorganic objects are detected from most miss and are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization oriented grains indirectly support microbial control on their accumulation both pyrite conformable laminae and micrite laminae suggest degradation and decay of original microbial mats upon diagenesis sinuous cracks were likely generated in a soft sediment deformation process whereas other sand cracks bamboo leaf like cracks worm like cracks polygonal cracks could have formed from sediment surface layer microbial organics shrinkage upon desiccation gas domes may have formed as the result of anoxic redox reactions and being filled with gases and sediments transported from below two proxies bedding plane coverage percentage and accumulative thickness of single miss bearing beds are developed to semi quantitatively evaluate miss abundance on bedding plane and vertical outcrop respectively the yurabi miss have substratum preference to fine sandstone facies and intertidal settings the yurabi formation yields the most abundant and diverse post glacial miss assemblages during the late ediacaran worldwide both kimberley and global fossil records indicate that miss may have proliferated in shallow marine ecosystems soon after the retreat of ediacaran gaskiers glaciation during late neoproterozoic

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

constraints on oceanic lithosphere structure from deep focus regional receiver function inversions we extend teleseismic p wave receiver function techniques to include regional p waveforms from deep focus earthquakes and document a new data source for the study of oceanic lithosphere structure high microseismic noise in oceanic environments strongly contaminates waveform recordings for moderate teleseisms the use of high amplitude deep focus regional body waves significantly improves signal to noise ratio deep sources can generate body waves that propagate as direct waves or turning waves at regional distances which have ray parameters similar to the teleseismic body waves the amplitudes of these regional body waves may be 10 to 20 times that of the teleseismic body waves for constant magnitude and same radiation pattern effects simply due to large differences in the geometrical spreading and attenuation along the propagation path to demonstrate the feasibility of utilizing deep focus regional waveform data in studying oceanic lithosphere structure we examine body wave recordings collected at the seismic station gumo guam mariana islands the oceanic lithosphere structure under the island is resolved using a jumping inversion approach that includes a singular value decomposition procedure along with the tikhonov regularization the thickness of the crust appears to be about 15 0 km the shallow structure has large positive velocity gradients and the moho is a broad crust mantle transition zone velocity complexity occurs in the middle crust

an analysis of the ground penetrating radar direct ground wave method for soil water content measurement the spatial variability of soil water content can be measured with the ground wave velocity of ground penetrating radar gpr using short antenna offsets but picking the correct ground wave arrival time is rather difficult in applying the gpr ground wave method to soil water content estimation it is also important to know the effective sampling depth of the method uniform drainage experiments were conducted with 100 and 450 mhz gpr antennas using 1 0a nd 2 0 m fixed antenna separations on a sandy loam soil to investigate time zero picking methodologies and to estimate the sampling depth of the gpr method the gpr water content data were compared with time domain reflectometry tdr measured data using six vertical tdr probes of different lengths time zero was calculated from an air calibration at a 2 0 m antenna separation and from wide angle reflection and refraction data and a difference was found between the two time zero calibration methods a method was analysed to determine the arrival time of the leading edge of the direct ground wavelet using the arrival time of the peak amplitude since the arrival time of the leading edge of the ground wave can be difficult to pick regression analysis showed that the gpr 100 mhz measured water content was not different from the water content measured with tdr at 0 0 1 m depth implying that this may be a reasonable estimate of the gpr ground wave method s sampling depth a similar analysis based on the differences between the 0 0 2 m tdr and the gpr shows that the effective sampling depth of the direct ground wave of the 450 mhz data is less than the sampling depth of the 100 mhz data copyright 2003 john wiley sons ltd

biotic and inorganic control on travertine deposition at bullicame 3 spring viterbo italy a multidisciplinary approach abstract a multidisciplinary characterization of an active thermal spring in central italy has been undertaken with the aim of i ascertaining whether microbiological activity plays a relevant role in hot depositing travertines and ii establishing an experimental protocol able to identify similar effects in fossil travertines water gas and travertine samples were investigated by chemical icp ms sem eds physical dta dtg isotopic 18o d and 13c mineralogical xrpd and spectroscopic epr techniques twenty four samples three for each phase were collected every 5 c temperature drop along a 100 m long artificial channel near viterbo bullicame 3 latium central italy a microbiological characterization was carried out in parallel sampling the channel every 10 c temperature drop the bullicame 3 system is revealed to be composed of two markedly different subsystems a water gas interface where a kinetically fast exchange allows equilibrium of components both in water and in gases a solid water interface where travertine precipitation occurs influenced by microbiological activity a peculiar lattice shrinking of calcite was identified as well as an anomalous value of the zero field splitting parameter from the epr measurements the interpretation of these anomalies is confirmed by the identification of calcifying cyanobacteria throughout the channel path our results point out that microbiological activity can play a significant role in travertine deposition from hot springs furthermore the proposed approach representing a tool to identify crystal chemical remnants of past microbiological activity could be applicable to fossil travertines

high resolution space time quantification of soil moisture along a hillslope using joint analysis of ground penetrating radar and frequency domain reflectometry data we combined ground penetrating radar gpr and frequency domain reflectometry fdr to assess the space time variability of soil moisture along a hillslope time lapse gpr and fdr measurements were conducted weekly during the period 23 03 08 06 2011 along a cultivated hillslope in the belgian loam belt a full wave gpr model a soil dielectric mixing model and the debye equation were combined to directly estimate soil moisture from gpr measurements measured gpr data were well reproduced by the full wave gpr model resulting in a relatively good agreement between the gpr and fdr derived soil moisture subsequently we merged the soil moisture obtained from both techniques in a data fusion framework and we investigated its spatial and temporal variability the results indicate that there was a high correlation between the spatial variability of soil moisture and topography as well as between its temporal variability and rainfall a temporal stability analysis showed that soil moisture at the footslope is higher and more stable than that at the summits and backslopes the proposed approach appears to be promising for assessing soil moisture at the hillslope scale with a relatively high space time resolution

sedimentary pyrite a window into the microbial past early diagenetic pyrite forms as a result of microbial processes in sediments but has received little attention as a potential source of microbial fossils sedimentary pyrite grains archean to jurassic in age were examined by scanning and transmission electron microscopy tem ion milling was essential for the preparation of electron transparent tem samples most pyrite grains revealed coccoid rod shaped and even filamentous features that are interpreted as microbial identification of microbial remains in sedimentary pyrite may greatly expand our knowledge of microbial life in the sedimentary record combined with geochemical characterization the study of pyritized microbes in the geologic record may in the future enable us to interpret changes in geochemical signatures more realistically in terms of different sulfate reducing communities sedimentary pyrite grains may also represent a good prospect to further our knowledge of past life on mars

coupled hydrogeophysical inversion of time lapse surface gpr data to estimate hydraulic properties of a layered subsurface 1 a major challenge in vadose zone hydrology is to obtain accurate information on the temporal changes of the vertical soil water distribution and its feedback with the atmosphere and groundwater a state of the art coupled hydrogeophysical inversion scheme is applied to evaluate soil hydraulic properties of a synthetic model and a field soil in southern ontario based on time lapse monitoring of soil dynamics with surface ground penetrating radar gpr film flow was included in the hydrological model to account for noncapillary water flow in a sandy medium during dry conditions the synthetic study illustrated that gpr data contain sufficient information to accurately constrain soil hydraulic parameters within a coupled inversion framework and led to an accurate estimation of the soil hydraulic properties when film flow was not accounted for within the inversion an equally good fit could still be achieved in this case errors introduced by neglecting film flow were compensated by different hydraulic parameters for the field data the coupled inversion reduced the overall misfit compared to an uncalibrated model using hydraulic parameters obtained from laboratory data although the data fit improved significantly for water content in the deeper soil layers accounting for film flow in the uppermost subsurface layer did not lead to a better fit of the gpr data further research is needed to describe the processes controlling water content in the dry range in particular coupled heat and vapor transport this study illustrates the suitability of surface gpr measurements combined with coupled inversion for near surface characterization of soil hydraulic parameters

microbial primary dolomite from a norian carbonate platform northern calabria southern italy the origin of fine grained dolomite in peritidal rocks has been the subject of much debate recently and evidence is presented here for a microbial origin of this dolomite type in the norian dolomia principale of northern calabria southern italy microbial carbonates there consist of stromatolites thrombolites and aphanitic dolomites high relief thrombolites and stromatolites characterize sub tidal facies and low relief and planar stromatolites with local oncoids typify the inter supratidal facies skeletal remains are very rare in the latter whereas a relatively rich biota of skeletal cyanophycea red algae and foraminifera is present in the sub tidal facies some 75 of the succession consists of fabric preserving dolomite especially within the microbial facies whereas the rest is composed of coarse dolomite with little fabric preservation three end members of dolomite replacement fabric are distinguished type 1 and type 2 fabric retentive with crystal size 5 and 5 60 m respectively and type 3 fabric destructive with larger crystals from 60 to several hundred microns in addition there are dolomite cements precipitated in the central parts of primary cavities during later diagenesis microbialite textures in stromatolites are generally composed of thin dark micritic laminae of type 1 dolomite alternating with thicker lighter coloured laminae of the coarser type 2 dolomite thrombolites are composed of dark micritic clotted fabrics with peloids composed of type 1 dolomite surrounded by coarser type 2 dolomite marine fibrous cement crusts are also present now composed of type 2 dolomite scanning electron microscope observations of the organic rich micritic laminae and clots of the inter supratidal microbialites reveal the presence of spherical structures which are interpreted as mineralized bacterial remains these probably derived from the fossilization of micron sized coccoid bacteria and spheroidal ovoidal nanometre scale dwarf type bacterial forms furthermore there are traces of degraded organic matter probably also of bacterial origin the microbial dolomites were precipitated in a hypersaline environment most likely through evaporative dolomitization as suggested by the excess ca in the dolomites the small crystal size and the positive 18o values the occurrence of fossilized bacteria and organic matter in the fabric preserving dolomite of the microbialites could indicate an involvement of bacteria and organic matter degradation in the precipitation of syn sedimentary dolomite

nanometer scale features in dolomite from pennsylvanian rocks paradox basin utah abstract scanning electron microscopy reveals an association between early dolomite in the pennsylvanian desert creek paradox fm and small approximately 0 1 m nanometer scale textures termed nannobacteria three diagenetically distinct dolomites are present early dolomite limpid dolomite and baroque dolomite in this study only the early dolomite contained nanometer scale features these textures occur as discrete balls and rods clumps of balls and chains of balls precipitation experiments demonstrate that these textures may be the result of precipitation in an organic rich micro environment the presence of these nanometer scale textures in pennsylvanian rocks suggests that these early dolomites precipitated in organic rich bacterial environments

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

bacteria in the tatahouine meteorite nanometric scale life in rocks we present a study of the textural signature of terrestrial weathering and related biological activity in the tatahouine meteorite scanning and transmission electron microscopy images obtained on the weathered samples of the tatahouine meteorite and surrounding soil show two types of bacteria like forms lying on mineral surfaces 1 rod shaped forms rsf about 70 80 nm wide and ranging from 100 nm to 600 nm in length 2 ovoid forms ovf with diameters between 70 and 300 nm they look like single cells surrounded by a cell wall only na k c o and n with traces of p and s are observed in the bulk of these objects the chemical analyses and electron diffraction patterns confirm that the rsf and ovf cannot be magnetite or other iron oxides iron hydroxides silicates or carbonates the rites of the rsf and ovf are below those commonly observed for bacteria but are very similar to some bacteria like forms described in the martian meteorite alh84001 all the previous observations strongly suggest that they are bacteria or their remnants this conclusion is further supported by microbiological experiments in which pleomorphic bacteria with morphology similar to the ovf and rsf objects are obtained from biological culture of the soil surrounding the meteorite pieces the present results show that bacteriomorphs of diameter less than 100 nm may in fact represent real bacteria or their remnants c 2000 elsevier science b v all rights reserved

ground penetrating radar for determining volumetric soil water content results of comparative measurements at two test sites ground penetrating radar gpr can provide information on the soil water content of the unsaturated zone in sandy deposits via measurements from the surface and so avoids drilling proof of this was found from measurements of radar wave velocities carried out ten times over 13 months at two test sites in the netherlands at these same locations and on the same dates soil water content was measured in access robes using a capacitance probe comparison of gpr and capacitance probe observations revealed that 1 the inferred absolute values of soil water content agree well this is remarkable because the soil water content is deduced entirely differently for the two methods 2 seasonal fluctuations in soil water content established for different general depth zones of radar waves correlate well with the fluctuations observed in the access tubes 3 the various methods to determine the propagation velocities of radar waves are complementary together they produce a realistic and reasonably complete image of the vertical distribution of the soil water content of the entire unsaturated zone high frequency 200 mhz direct groundwaves and refracted waves constitute a particularly attractive complementary combination which provides information on consecutive shallow zones in the underground i e the zones of major soil water content fluctuations 4 lateral variations established at one of the test sites where several access tubes have been placed in a transect also follow from the gpr measurements along that profile this non destructive determination of soil water content in practically continuous and detailed sections is one of the great assets of gpr opening the way to mapping preferential soil water flow paths

quaternary phosphorites from the continental margin off chennai southeast india analogs of ancient phosphate stromatolites abstract pleistocene phosphorites occur on the continental margin off chennai abundantly in the depth range of 186 293 m they are associated with outer shelf glauconites and carbonate skeletals including large shells of molluscs and rhodoliths these are primary phosphate deposits and are similar to phosphate stratiform stromatolites this is the first report of phosphate stratiform stromatolites during the quaternary and modern times and they provide a quaternary analog for ancient phosphorites thin sections of phosphorites exhibit laminated phosphatized microbial mats consisting of mechanically deposited clastic particles or of phosphatic molds clay particles are scattered throughout the matrix sem studies reveal that the laminated phosphate matrix is made of thin sheets of tightly packed apatite globules densely packed intertwined microfilaments or filament molds phosphate with obscured laminae is composed of phosphate tubules cell like structures resembling coccoid cyanobacteria or their botryoidal aggregates are common carbonate fluorapatite and low magnesium and high magnesium calcites are the major mineral phases the structural co2 content of apatite ranges from 4 to 5 5 quartz feldspar and goethite are accessory minerals the microbial mats were formed on the outer shelf most probably during conditions of low sea level in the quaternary and microbial processes played a major role in direct phosphatization of these mats the primary phosphorus source seems to have been the continental supply and degradation of organic matter associated with benthic microbial communities the phosphate stratiform stromatolites thus formed were subsequently reworked into a shelf margin depression and resulted in the occurrence of condensed phosphorites

jurassic septarian concretions from nw scotland record interdependent bacterial physical and chemical processes of marine mudrock diagenesis septarian concretions in the staffin shales formation kimmeridgian isle of skye allow controls on concretion rheology and septarian cracking to be investigated stratabound concretions consist of anhedral ferroan calcite microspar enclosing clay and minor pyrite intergranular volumes range from 77 to 88 and calcite 13c and 18o values in most concretion bodies range from 10 0 to 17 3 and 0 3 to 0 6 respectively consistent with rapid and pervasive cementation in marine pore fluids septarian rupture occurred during incipient cementation with a sediment volume reduction of up to 43 crack lining brown fibrous calcite records pore fluid re oxygenation during a depositional hiatus followed by increasing fe content and 13c related to bacterial methanogenesis brown colouration results from an included gel like polar organic fraction that probably represents bacterially degraded biomass a new hypothesis for concretion growth and septarian cracking argues that quasi rigid proto concretions formed via binding of flocculated clays by bacterial extracellular polysaccharide substances eps this provided rheological and chemical conditions for tensional failure subcritical crack growth volume contraction calcite nucleation and incorporation of degraded products into crack lining cements bacterial decay of eps and syneresis of host muds provided internal stresses to initiate rupture at shallow burial development of septarian shrinkage cracks in muds is envisaged to require pervasive in situ bacterial colonization and to depend on rates of carbonate precipitation versus eps degradation and syneresis subsequent modification of septarian concretions included envelopment by siderite and calcite microspar hydraulic fracturing associated with cretaceous shallow burial or palaeogene uplift and cementation by strongly ferroan yellow sparry calcite that records meteoric water invasion of the host mudrocks an abundance of fatty acids in these spars indicates aqueous transport of organic breakdown products and 13c data suggest a predominantly methanogenic bicarbonate source however the wide 18o range for petrographically identical cement 1 3 to 15 6 is difficult to explain

monitoring an underground steam injection process using electrical resistance tomography we used electrical resistance tomography ert to map the subsurface distribution of a steam flood as a function of time as part of a prototype environmental restoration process performed by the dynamic underground stripping project we evaluated the capability of ert to monitor changes in the soil resistivity during the steam injection process using a dipole dipole measurement technique to measure the bulk electrical resistivity distribution in the soil mass the injected steam caused changes in the soil s resistivity because the steam displaced some of the native pore water increased the pore water and soil temperatures and changed the ionic content of the pore water we could detect the effects of steam invasion by mapping changes in the soil resistivity as a function of space and time the ert tomographs are compared with induction well logs formation temperature logs and lithologic logs these comparisons suggest that the ert tomographs mapped the formation regions invaded by the steam flood the data also suggest that steam invasion was limited in vertical extent to a gravel horizon at depth of approximately 43 m the tomographs show that with time the steam invasion zone extended laterally to all areas monitored by the ert technique

effects of sem preparation techniques on the appearance of bacteria and biofilms in the carter sandstone abstract when biofilms aggregations of bacteria and extracellular polymer secretions in samples from the carter sandstone of alabama were prepared for scanning electron microscopy sem using different dehydration techniques the organic material had visibly different textures and distributions in order to assess whether the variation was attributable to sample preparation or to inherent biofilm heterogeneity each of five techniques were tested 3 to 10 times on small 1 cm pieces of the carter sandstone containing either a strain of bacteria cultured from and reintroduced into the rock or an in situ biofilm grown by injection of nutrients through core samples the techniques tested were 1 air drying alone 2 fixation in 10 glutaraldehyde with air drying 3 ethanol dehydration with hexamethyldisilazane hmds drying 2 5 glutaraldehyde ethanol dehydration and hmds 4 ethanol dehydration with critical point drying and 5 ethanol and acetone dehydration with critical point drying unpreserved control samples were either imaged wet in an environmental scanning electron microscope esem or vacuum dried for sem observations were based on sem microscopy of over 60 samples and study of over 150 photomicrographs in both experiments the original morphology of individual bacteria was best preserved by ethanol dehydration with hmds drying ethanol dehydration with critical point drying or ethanol acetone dehydration with critical point drying critical point drying preserved bacteria but stripped away mucilaginous material revealing filamentous structures within the biofilm these filaments along with masses of microspheres nannobacteria and the smooth mucilaginous outer layer also occur in wet samples studied by esem and are therefore not dehydration artifacts however different sample preparation techniques accentuated different components of the heterogeneous biofilm thus resulting in vastly different textures the cultured bacteria produced a biofilm that had a different surface texture and was more susceptible to sample preparation artifacts than the in situ biofilm use of more than one sample preparation technique is recommended in order to avoid bias

microbes produce nanobacteria like structures avoiding cell entombment microsedimentary structures referred to as nanobacteria like particles were described from modern carbonate environments where they form in close spatial association with sulfate reducing bacteria srb however the exact mechanism of their formation as well as their paleontological significance remains controversial here we report on an investigation of microbe mineral interactions in experimentally produced carbonate globules the experiments were carried out under anoxic conditions at 30 c with desulfovibrio brasiliensis a srb known to mediate dolomite formation we observed that extracellular polymeric substances eps secreted by the microbial community play a key role in the mineralization process nanobacteria like particles represent the early stage of carbonate nucleation within the eps which progressively evolve to larger globules displaying a grainy texture we excluded the possibilities that these structures are fossils of nanobacteria dissolution surfaces or artifacts created during sample preparation d brasiliensis cells are predominantly located outside of the eps aggregates where mineral growth takes place as a result they remain mobile and are rarely entombed within the mineral this self preservation behavior may not be limited to d brasiliensis other microbes may produce or may have produced during the geological past biogenic minerals through a similar process mineralization within eps explains why microbial relics are not necessarily present in biogenic carbonates

defining organominerals comment on defining biominerals and organominerals direct and indirect indicators of life by perry et al 2007 sedimentary geology 201 157 179 the paper by perry et al 2007 defining biominerals and organominerals direct and indirect indicators of life sedimentary geology 201 157 179 proposes to introduce the new term organomineral to describe mineral products whose formation is induced by by products of biological activity dead and decaying organisms or nonbiological organic compounds to be distinguished from the biomineral components of living organisms the substantive organomineral however is not new it was first introduced in 1993 with basically the same definition and distinction from biominerals at the 7th international symposium on biomineralization defarge and trichet 1995 from biominerals to organominerals the example of the modern lacustrine calcareous stromatolites from polynesian atolls bulletin de l institut oceanographique de monaco n spec 14 vol 2 pp 265 271 thereafter more than twenty five papers by various authors have been devoted to organominerals and organomineral formation organomineralization processes only two of these papers are cited by perry et al and without any reference to the definitions or even the terms organomineral or organomineralization which they included moreover perry et al tend to enlarge the original concept of organomineral to encompass all minerals containing organic matter whether these organic compounds are active or passive in the mineralization which introduces ambiguities detrimental to a fine understanding of present and past geobiological processes finally perry et al propose to consider organominerals as indirect biosignatures that could be used in the search for evidence of life in the geological record and extraterrestrial bodies this latter proposition also is problematical in that organominerals may be formed in association with prebiotic or abiotic organic matter

imaging and characterisation of subsurface solute transport using electrical resistivity tomography ert and equivalent transport models abstract we assess the usefulness of electrical resistivity tomography ert in imaging and characterising subsurface solute transport in heterogeneous unconfined aquifers a field tracer experiment was conducted at the krauthausen test site germany the spatial and temporal evolution of the injected nabr solute plume was monitored in a 2d ert image plane located downstream of the injection well for 90 days since ert maps changes in bulk electrical conductivity the reconstructed images at selected time intervals are first converted to solute concentration maps by postulating a linear relation the concentration maps are then analysed using an equivalent convection dispersion model cdm which conceptualises the aquifer as a homogeneous medium with a uniform mean flow velocity as demonstrated by associated synthetic model studies ert resolution in terms of recovered equivalent dispersivities is limited due to spatial smoothing inherent to the imaging algorithm since for heterogeneous media local concentrations within the plume deviate from those predicted by the equivalent cdm we also interpret the ert derived pixel breakthrough curves in terms of an equivalent stream tube model stm the stm represents transport in the aquifer by a set of 1d convection dispersion processes allowing the degree of mixing and the heterogeneity of transport within the plume to be quantified we believe that the observed tracer plume is satisfactorily described by the equivalent cdm probably because the tracer plume was small relative to the heterogeneity scale of the aquifer even though application of the stm revealed some deviation from the ideal homogeneous case the equivalent dispersivity in the stm matches the longitudinal dispersivity of the cdm closely consistent with predominantly homogeneous mixing however the stm analysis illustrates how ert results can be used to quantify the variability of parameters relevant to flow and transport in heterogeneous aquifers

proliferation of miss related microbial mats following the end permian mass extinction in terrestrial ecosystems evidence from the lower triassic of the yiyang area henan province north china microbially induced sedimentary structures misss are commonly present in siliciclastic shallow marine settings following the end permian mass extinction but have been rarely reported in the post extinction terrestrial ecosystems here we present six types of well preserved misss from the upper sunjiagou formation and lower liujiagou formation of induan early triassic age in the yiyang area henan province north china these misss include polygonal sand cracks worm like structures wrinkle structures sponge pore fabrics gas domes and leveled ripple marks microanalysis shows that these misss are characterized by thin clayey laminae and filamentous mica grains arranged parallel to bedding plane as well as oriented matrix supported quartz grains which are indicative of biogenic origin facies analysis suggests that the miss hosting sediments were deposited in a fluvial sedimentary system during the early triassic including lake delta riverbeds point bars and flood plain paleoenvironments abundant misss from yiyang indicate that microbes also proliferated in terrestrial ecosystems in the aftermath of the permian triassic p tr biocrisis like they behaved in marine ecosystems microbial blooms together with dramatic loss of metazoans may reflect environmental stress and degradation of terrestrial ecosystems or arid climate immediately after the severe permian triassic ecologic crisis

miocene phosphorites from the murray ridge northwestern arabian sea abstract phosphorites from the murray ridge nw arabian sea comprise nodules bioclasts and bone fragments the nodules are made up of a homogeneous light colored phosphate nucleus consisting of rivulariacean filamentous cyanobacteria and a thin dark grey colored phosphate cortex showing abundant microbial filaments and microborings the bioclasts comprise of 14 14 5 ma old planktonic foraminifers accepted as the time of deposition spherical to ovoid shaped apatite microparticles resembling fossil bacteria are distinct components in the bioclasts bone fragments exhibit apatite fillings the nodules and bone fragments consist entirely of carbonate fluorapatite cfa with low al k and th concentrations suggesting absence of continental detritus shale normalized ree patterns of the samples support a seawater derived composition the highly uniform initial nd values of 4 8 to 5 1 are interpreted as the seawater value at the onset of phosphatization 14 ma ago in contrast 87sr 86sr ratios show a large range of 0 709055 to 0 709124 corresponding to unusually young stratigraphic ages of 1 to 3 ma the data are interpreted as evidence for post depositional sr exchange of the recrystallizing phosphorites with fluids isotopically not much different from modern seawater it is concluded that the phosphorites formed under oxic shallow water conditions where microbial populations assimilated phosphorus primarily from seawater and mediated precipitation of cfa during early diagenesis at the sediment water interface on different substrates

amorphous calcium carbonate associated with biofilms in hot spring deposits abstract calcium carbonate nanoparticles are intimately associated with crystalline calcite and aragonite in the eryuan gongxiaoshe and zhuyuan hot springs water temperature 75 c which are located in yunnan province china the nanoparticles

calcite cemented concretions in cretaceous sandstone wyoming and utah u s a abstract spheroidal cannon ball calcite cemented concretions some of gigantic size were studied from three cretaceous shelf sandstone units ferron frontier and second frontier the concretions have diameters between 2 cm and 6 m those larger than 40 cm in diameter in the ferron and frontier have septarian structure rare concretions in the second frontier with cone in cone also have septaria the pattern of carbon and oxygen isotopic data and intergranular volume igv data across concretions indicate that concretion growth was complex not all concretions grew progressively from their centers toward their edges in many concretions displacive fascicular optic high mg calcite foc precipitated simultaneously throughout the concretions pervasive growth pattern although the earliest cementation was concentrated in and near their centers remaining pores were subsequently filled by poikilotopic calcite of lower mg content displacive foc cement in the bodies of concretions and in cone in cone structure and the large igv values indicate that these carbonate phases formed at burial depths no greater than tens of meters igv values indicate that spar cement continued to depths of at least 50 m and possibly deeper the association of organic matter and microbial structures or microbial byproducts with displacive foc and cone in cone calcite raises the possibility that biogenic processes were responsible for the apparently rapid growth of the displacive calcite the oxygen isotope composition of pore waters was fairly uniform in the range of 18o of 4 to 6 smow during 80 of concretion growth but became even more depleted in 18o during the last stage of growth and during septarian fracture filling ranging into values as depleted as 14 smow 13c in calcite is negative 4 to 18 v pdb but variable reflecting a range of microbial processes under both oxidizing and reducing conditions earlier calcites fall mostly in the range of 10 to 16 v pdb relatively later calcite in veins and on concretion margins is more enriched in 13c fe and mn concentrations in calcites have a rough positive correlation with higher 13c values the concentration of mg derived from seawater and altered volcanic rock fragments covaries positively with the degree of meteoric influence lower mg contents correlate positively with relatively depleted 18o values 87sr 86sr values are typical of sr derived from coeval seawater or marine skeletal debris growth of concretions 4 to 6 m in diameter apparently in 5 my requires some spatial localization of growth sites by a self organization process and probably a large supply of carbonate shells in the original sediment elongation of larger concretions in the plane of bedding suggests that advective rather than diffusive supply of cement components dominated late in concretion growth history concretions formed close to the tops of parasequence boundaries

crosshole gpr full waveform inversion of waveguides acting as preferential flow paths within aquifer systems high contrast layers caused by porosity or clay content changes can have a dominant effect on hydraulic processes within an aquifer these layers can act as low velocity waveguides for gpr waves we used a field example from a hydrological test site in switzerland to show that fullwaveform inversion of crosshole gpr signals could image a subwavelength thickness low velocity waveguiding layer we exploited the full information content of the data whereas ray based inversion techniques are not able to image such thin waveguide layers because they only exploit the first arrival times and first cycle amplitudes this lowvelocity waveguide layer is caused by an increase in porosity and indicates a preferential flow path within the aquifer the waveguide trapping causes anomalously high amplitudes and elongated wavetrains to be observed for a transmitter within thewaveguide and receivers straddling thewaveguide depth range the excellent fit of amplitudes and phase between the measured and modeled data confirms its presence this new method enables detailed aquifer characterization to accurately predict transport and flow and can be applied to a wide range of geologic hydrological and engineering investigations

chemosynthetic microbialites in the devonian carbonate mounds of hamar laghdad anti atlas morocco abstract veins cutting across the devonian conical mounds of the hamar laghdad ridge eastern anti atlas morocco were the carriers of geofluids although not completely determined the composition of these fluids seems related to hydrothermal and seepage fluxes that were the primary contributors to the establishment of sub seafloor cryptic environments linking deeper fluid sources to the seafloor the optical and scanning electron microscope investigation of the laminated carbonate infill of these veins has revealed that they consist of stromatolite and oncolite like fabrics in the early and middle devonian mounds the laminated carbonates contain morphologies that are attributable to microbially mediated processes that in turn suggest a direct biological contribution to the deposition of the veins infill microbial evidence include rod shaped and cocci clusters embedded in amorphous membranes iron rich filaments organized as mat like and biodictyon filamentous aggregates or isolated filaments microbial clotted textures and peloids moreover the oncoids from the veins of the middle devonian hollard mound have been interpreted as the mineral replacement of crypto microorganisms as frutexites other microbial evidence are biominerals and include carbonate with spheroids and pyrite framboids in which typifying hydrocarbon seep environments the hollard mound which is the only one with a well documented origin by hydrocarbon seepage shares a number of geomicrobiological evidence with other early devonian mounds these evidence which are supplemented by 13 c depleted data suggest that the infill of the veins system in the hamar laghdad mounds would be the product of chemotrophic chemosynthetic microbial communities that are adapted to crypto habitats sustained by hydrocarbon and other components fluid fluxes

precipitation and growth morphology of calcium carbonate induced by myxococcus xanthus implications for recognition of bacterial carbonates abstract it is thought that morphologies of bacterial carbonates can be used to identify microbial fossils and or precipitates in sediments and rocks this study shows that calcite and vaterite formed in a gel medium in the presence of myxococcus xanthus display a range of morphologies that depend on whether the bacteria are live or dead metabolic activity of the bacteria induced 1 aggregates of calcified bacteria formed at maximum supersaturation 2 vaterite spheres final growth stage of dumbbell fibrous radiated aggregates and 3 dipyramid and disphenoid like calcite crystals combination of 011 and 0001 forms morphologies 2 and 3 developed at a lower supersaturation and are typically found in gel like media dipyrimidal like calcite crystals were also obtained abiotically in gel medium dead m xanthus cells induced heterogeneous precipitation of calcite with rhombohedral morphologies at low supersaturation a growth mechanism resulting from self assembly of calcium carbonate nanocrystals may account for the observed morphologies crystal microstructure and crystallite size measurements all of the above mentioned morphologies of bacterial carbonate have been observed in other laboratory experiments and in continental and marine environments however all of them have also been produced abiotically with the exception of calcified bacterial cells this may make it more difficult to identify bacterial activity in the rock record nonetheless bacterially induced alkalinization appears to be a prerequisite for the development of spherulitic and dipyramid or disphenoid like forms in natural mucilaginous biofilms and microbial mats the morphologies reported here may facilitate the recognition of early and recent marine and continental microcrystalline bacterial carbonates and cements

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

structural arrangement of sedimentary organic matter nanometer scale spheroids as evidence of a microbial signature in early diagenetic processes abstract nanometer scale spheroidal objects 20 200 nm wide have been widely encountered in geological samples while their origin remains unclear first described as nannobacteria folk 1993 they are more likely associated with various bacterial debris in order to explore their potential role in degradation and preservation of organic matter om in rocks this research investigates a range of recent and fossil occurrences of various microbial imprints using electron and atomic force microscopy selected samples illustrate different stages in om cycle and diagenesis i e from production to accumulation before and after lithification more specifically effects of oxygen and light depleted conditions which occur naturally at the water sediment interface have been evaluated in microbial mats using a specifically tailored laboratory strategy recent sediments reveal a close association between a large occurrence of nanometer scale spheroids and the degree of degradation due to microbial activity wide nanometer scale spheroids appear in fossilized microbial mats and in microbial mats under experimental diagenesis these samples show that nanometer scale spheroids are associated with well preserved om e g intact bacteria this corresponds to reduced physicochemical degradation processes this observation suggests that nanometer scale spheroids i e in the size range of nannobacteria occur concomitantly with a significant microbial degradation shown by numerous organic debris e g cell walls both recent and fossil samples from anoxic settings show a close association of nanometer scale spheroids with extracellular polymeric substances eps and bacterial cell walls and not with algal cell walls or other organic compounds because they occur concomitantly with well preserved organic constituents nanometer scale spheroids indicate a reduced level of om degradation in the diagenetic processes therefore nanometer scale spheroids would be a microbial evidence of early diagenesis in sedimentary rocks

velocity variations and water content estimated from multi offset ground penetrating radar the common midpoint cmp processing technique has been shown to be effective in improving the results of ground penetrating radar gpr profiling when radar data are collected with the cmp multioffset geometry stacking increases the signal to noise ratio of subsurface radar reflections and results in an improved subsurface image an important aspect of cmp processing is normal moveout velocity analysis our objectives are to show the effect of multiple velocity analyses on the stacked radar image and particularly to demonstrate that this velocity information can also be used to determine subsurface water content most gpr surveys are very limited in spatial extent and assume that within the survey range radar velocity structure in the shallow subsurface can be adequately approximated by a single velocity function in data processing in this study we show that variation in radar velocity can be quite significant and that the stacked profile improves as the number of velocity analysis locations is increased interval velocities can be calculated from the normal moveout velocities derived in the cmp velocity analysis with some reasonable assumptions about subsurface conditions necessary for radar propagation interval velocity can be converted to an estimate of volumetric water content therefore by collecting gpr data in the multioffset cmp geometry not only is the radar profile improved but it also allows for an interpretation of subsurface variation in water content we show the application of these techniques to multioffset gpr data from the chalk river test area operated by atomic energy of canada limited

application of a new 2d time domain full waveform inversion scheme to crosshole radar data crosshole radar tomography is a useful tool in diverse investigations in geology hydrogeology and engineering conventional tomograms provided by standard ray based techniques have limited resolution primarily because only a fraction of the information contained in the radar data i e thefirst arrivaltimesandmaximumfirst cycleamplitudesis included in the inversion to increase the resolution of radar tomograms wehavedevelopedaversatilefull waveforminversion scheme that is based on a finite difference time domain solution of maxwell s equations this scheme largely accountsforthe3dnatureofradar wavepropagationandincludes an efficient method for extracting the source wavelet from the radar data after demonstrating the potential of the newschemeontworealisticsyntheticdatasets weapplyitto two crosshole field data sets acquired in very different geologic hydrogeologic environments these are the first applications of full waveform tomography to observed crosshole radar data the resolution of all full waveform tomograms is showntobemarkedlysuperiortothatoftheassociatedraytomograms small subsurface features a fraction of the dominant radar wavelength and boundaries between distinct geological hydrological units are sharply imaged in the fullwaveformtomograms

origin of sr rich magnesian calcite mud in a holocene pond basin lee stocking island bahamas abstract magnesian calcite represents about 90 of carbonate mud that has accumulated in a holocene 30 c hypersaline pond waters at times exceeding gypsum saturation elevated sr content is likely a product of changing sr cafluid ratios in pond water related to gypsum formation by incorporating carbon and oxygen isotope stratigraphies of indigenous biota the foraminifer ammonia beccarii and gastropod cerithidea sp with that of pond mud this sedimentary basin preserves a record of high order environmental changes over the last 1500 years that likely influenced mud precipitation and its accumulation these changes reflect variation in water residence time temperature likely bacterial productivity and bicarbonate sources

microbial fossilization in carbonate sediments a result of the bacterial surface involvement in dolomite precipitation recent dolomitic sediment samples from lagoa vermelha brazil were examined microscopically to study the process of bacterial fossilization in carbonate sediments bacteria like bodies were intimately associated with carbonate mineral surfaces and coatings on the former demonstrate the calcification of single bacterial cells the bacterial fossilization process in lagoa vermelha sediments was simulated in the laboratory by cultivation of mixed and pure cultures of sulphate reducing bacteria which were isolated from the lagoa vermelha sediments these cultures produced carbonate minerals that were studied to provide insight into the initiation of the fossilization process in mixed culture experiments bacterial colonies became calcified whereas in pure culture experiments single bacterial cells were associated with dolomite surfaces dolomite nucleated exclusively in bacterial colonies intimately associated with extracellular organic matter and bacterial cells electrophoretic mobility measurements of the bacterial cells in electrolyte solutions demonstrated the specific adsorption of ca 2 and mg 2 onto the cell surfaces indicating the role of the bacterial surface in carbonate nucleation and bacterial fossilization the affinity of the cells for mg 2 was related to the capability of the strains to mediate dolomite formation combined with sulphate uptake which dissociates the mgso 4 o ion pair and increases the mg 2 availability the concentration of mg 2 ions in the microenvironment around the cells where the conditions are favourable for dolomite precipitation may be the key to overcome the kinetic barrier to dolomite formation these results demonstrate that bacterial fossilization is a consequence of the cell surface involvement in carbonate precipitation implying that fossilized bacterial bodies can be used as a tool to recognize microbially mediated carbonates

mapping the spatial variation of soil water content at the field scale with different ground penetrating radar techniques summary two ground penetrating radar gpr techniques were used to estimate the shallow soil water content at the field scale the first technique is based on the ground wave velocity measured with a bistatic impulse radar connected to 450 mhz ground coupled antennas the second technique is based on inverse modeling of an off ground monostatic tem horn antenna in the 0 8 1 6 ghz frequency range data were collected on a 8 by 9 m partially irrigated intensive research plot and along four 148 5 m transects time domain reflectometry capacitance sensors and volumetric soil samples were used as reference measurements the aim of the study was to test the applicability of the ground wave method and the off ground inverse modeling approach at the field scale for a soil with a silt loam texture the results for the ground wave technique were difficult to interpret due to the strong attenuation of the gpr signal which is related to the silt loam texture at the test site the root mean square error of the ground wave technique was 0 076 m 3 m 3 when compared to the tdr measurements and 0 102 m 3 m 3 when compared with the volumetric soil samples the off ground monostatic gpr measured less within field soil water content variability than the reference measurements resulting in a root mean square error of 0 053 m 3 m 3 when compared with the tdr measurements and an error of 0 051 m 3 m 3 when compared with the volumetric soil samples the variability between the two gpr measurements was even larger with a rsme of 0 115 m 3 m 3 in summary both gpr methods did not provide adequate spatial information on soil water content variation at the field scale the main reason for the deviating results of the ground wave method was the poor data quality due to high silt and clay content at the test site additional reasons were shallow reflections and the dry upper soil layer that cannot be detected by the ground wave method in the case of off ground gpr the high sensitivity to the dry surface layer is the most likely reason for the observed deviations the off ground gpr results might be improved by using a different antenna that allows data acquisition in a lower frequency range

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

alternative origins for nannobacteria like objects in calcite more than 40 calcite precipitation experiments were performed under sterile conditions in order to investigate the origins of 25 300 nm spherical rod and ovoid shaped objects that have been widely interpreted as evidence of nanometer scale life i e nannobacteria individual experiments included the addition of soluble organic compounds common species of eubacteria or phage induced eubacterial lysates these experiments indicate that many of the nanometer scale objects have inorganic or nonnannobacterial origins in the precipitation experiments calcite formed euhedral crystals 50 800 nm in diameter and smaller 50 nm anhedral or rounded particles or protocrystals the small anhedral or rounded solids resembled nannobacteria the relative amount of anhedral or rounded calcite was greatest in experiments with a dissolved organic component these controlled experiments are in accord with observations that rounded nanometer scale objects are more common in minerals formed in organic rich environments bacterial fragments occur as rounded to irregularly shaped particles that included cell wall fragments expulsed cytoplasm and relict capsules that also closely resembled nannobacteria acid etching of the large euhedral crystals produced in the precipitation experiments also resulted in the formation of nanometer scale features that resembled nannobacteria in natural carbonates the shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching much caution is advisable in interpreting the origin of rounded features 50 nm

palaeoenvironmental significance of organic facies and stable isotope signatures the ladinian san giorgio dolomite and meride limestone of monte san giorgio switzerland whl unesco the over 600 m thick ladinian carbonate section of monte san giorgio world heritage list united nations educational scientific and cultural organization switzerland including the san giorgio dolomite and the meride limestone was analysed with respect to its sedimentology organic matter content rock eval and palynofacies and stable carbon and oxygen isotope composition application of geochemical proxies and optical data transmitted light microscopy epifluorescence cathodoluminescence and scanning electron microscopy allowed the assessment of the relative sea level trend and the characterization of the organic matter content three main organic matter assemblages were defined according to their composition and stratigraphic position overall results suggest immature organic matter predominantly of marine bacterial origin with an upsection increasing land plant derived contribution forcing factors controlling organic matter accumulation include changes in sea level productivity and runoff which in turn were probably promoted by periods of rainfall following explosive volcanic activity enhanced productivity during sea level highstands is considered to have played a key role in black shale formation under anoxic sulphidic conditions mainly in the besano formation in contrast sea level lowstands coupled with intensified runoff resulted in increased basin restriction and in deposition of laminated limestone mainly under lower dysoxic to anoxic conditions chiefly in the lower meride limestone under the latter conditions benthic microbial activity produced most of the hydrogen rich organic matter contributed to carbonate precipitation and also played a major role in taphonomic control on vertebrate fossil preservation in more general terms the monte san giorgio section proved to be an excellent testing ground making it possible to compare diverse approaches with each other and more specifically to relate optical evidence to geochemical signatures

the gpr refraction method refracted phases have been a recognized feature in wide angle common midpoint cmp and common shotpoint csp ground penetrating radar gpr surveys for many years but historically their use has been limited and overshadowed by conventional reflection profiling techniques in truth the gpr refraction method holds great promise as we show using four field examples from three sites in the northeastern united states typical refractors are shallow bedrock or coarse grained unconsolidated sediments where the dielectric constant k 6 7 beneath partially saturated fine grained sand or silt k 15 16 under appropriate conditions refracted phases can be detected readily at transmitter receiver tx rx offsets of 15 m and from depths of 2 m adapting procedures from refraction seismology we interpret gpr data from reversed csp soundings using dipping planar interface models and delay time analyses results from the two approaches are quite consistent further corroborated at one of the sites by a gpr

modelling of gpr waves for lossy media obeying a complex power law of frequency for dielectric permittivity the attenuation of ground penetrating radar gpr energy in the subsurface decreases and shifts the amplitude spectrum of the radar pulse to lower frequencies absorption with increasing traveltime and causes also a distortion of wavelet phase dispersion the attenuation is often expressed by the quality factor q for gpr studies q can be estimated from the ratio of the real part to the imaginary part of the dielectric permittivity we consider a complex power function of frequency for the dielectric permittivity and show that this dielectric response corresponds to a frequency independent q or simply a constant q model the phase velocity dispersion relationship and the absorption coefficient of electromagnetic waves also obey a frequency power law this approach is easy to use in the frequency domain and the wave propagation can be described by two parameters only for example q and the phase velocity at an arbitrary reference frequency this simplicity makes it practical for any inversion technique furthermore by using the hilbert transform relating the velocity and the absorption coefficient which obeys a frequency power law we find the same dispersion relationship for the phase velocity both approaches are valid for a constant value of q over a restricted frequency bandwidth and are applicable in a material that is assumed to have no instantaneous dielectric response many gpr profiles acquired in a dry aeolian environment have shown a strong reflectivity inside dunes changes in water content are believed to be the origin of this reflectivity we model the radar reflections from the bottom of a dry aeolian dune using the 1d wavelet modelling method we discuss the choice of the reference wavelet in this modelling approach a trial and error match of modelled and observed data was performed to estimate the optimum set of parameters characterizing the materials composing the site additionally by combining the complex refractive index method crim and or topp equations for the bulk permittivity dielectric constant of moist sandy soils with a frequency power law for the dielectric response we introduce them into the expression for the reflection coefficient using this method we can estimate the water content and explain its effect on the reflection coefficient and on wavelet modelling

the association of gold with calcrete abstract the discovery that au accumulates in calcrete pedogenic carbonate or caliche was made in 1987 by csiro calcrete is a general term describing accumulation of alkaline earth metals in soils of arid and semi arid terrains around the world the principal constituent of calcrete is calcite while au is a noble metal calcrete has been a significant tool in a number of au deposit discoveries so understanding the mechanisms by which these diametrically different components come together is valuable for enhancing future discovery numerous laboratory experiments case histories and exploration models have been published most from australia yet we do not fully understand the mechanisms involved it is timely therefore twenty five years on since the first publication of this phenomenon to review this highly unusual but economically important association critical to any review on au in calcrete is to first consider calcretes themselves the nature of a particular calcrete where it has formed and mode of formation is relevant to how where and why au accumulates within it this review commences with a background nomenclature history classification and some examples of calcrete types found near au deposits how calcretes form their origins and the role of biota is considered their locations in the regolith and landscape as well as exploration models for au in calcrete are discussed a section on the chemistry of au in calcretes details what we know about possible mechanisms of formation and considers what laboratory experiments on microorganisms and abiotic experiments tell us following on is a summary of practical aspects of identifying collecting and analysing samples for exploration purposes selected mineral exploration case histories are described and how they fit into models of exploration and different regolith settings concluding sections include a summary and implications of this accumulated knowledge to discovering au deposits

effects of gas and water filled boreholes on the amplitudes of crosshole georadar data as inferred from experimental evidence a special packer system is developed that replaces the water in a borehole with a gas and thus allows us to isolate the effects of the borehole filling media on crosshole georadar measurements we demonstrate experimentally that the radiative characteristics of borehole georadar antennas differ substantially for gas and water filled boreholes the main differences are a spectral shift to lower frequencies and a less focused radiation pattern in the case of a water filled borehole these effects are correctly predicted by a basic finite difference time domain fdtd modeling approach which offers the prospect for improving the quality of amplitude inversions from crosshole georadar data

a synthetic study to assess the applicability of full waveform inversion to infer snow stratigraphy from upward looking ground penetrating radar data snow stratigraphy and liquid water content are key contributing factors to avalanche formation upward looking groundpenetrating radar upgpr systems allow nondestructive monitoring of the snowpack but deriving density and liquid water content profiles is not yet possible based on the direct analysis of the reflection response we have investigated the feasibility of deducing these quantities using full waveform inversion fwi techniques applied to upgpr data for that purpose we have developed a frequency domain fwi algorithm in which we additionally took advantage of time domain features such as the arrival times of reflected waves our results indicated that fwi applied to upgpr data is generally feasible more specifically we could show that in the case of a dry snowpack it is possible to derive snow densities and layer thicknesses if sufficient a priori information is available in case of a wet snowpack in which it also needs to be inverted for the liquid water content the algorithm might fail even if sufficient a priori information is available particularly in the presence of realistic noise finally we have investigated the capability of fwi to resolve thin layers that play a key role in snow stability evaluation our simulations indicate that layers with thicknesses well below the gpr wavelengths can be identified but in the presence of significant liquid water the thin layer properties may be prone to inaccuracies these results are encouraging and motivate applications to field data but significant issues remain to be resolved such as the determination of the generally unknown upgpr source function and identifying the optimal number of layers in the inversion models furthermore a relatively high level of prior knowledge is required to let the algorithm converge however we feel these are not insurmountable and the new technology has significant potential to improve field data analysis

microbially influenced formation of 2 724 million year old stromatolites nanoscale evidence suggests that the tumbiana formation stromatolites in australia were influenced by microbial activity in the stromatolites clusters of organic globules are closely associated with 2 724 million year old aragonite crystals