precipitation of dolomite using sulphate reducing bacteria from the coorong region south australia significance and implications dolomite was successfully precipitated in culture experiments that simulated microbiogeochemical conditions prevailing during late stages of evaporation in ephemeral hypersaline dolomitic lakes of the coorong region south australia analyses of lake and pore water samples document rapid geochemical changes with time and depth in both dolomitic and non dolomitic lakes extremely high sulphate and magnesium ion concentrations in lake waters decline rapidly with depth in pore waters throughout the sulphate reduction zone whereas carbonate concentrations in pore waters reach levels up to 100 times those of normal sea water ultimately sulphate is totally consumed and no solid sulphate is recorded in the dolomitic lake sediments most probable number calculations of lake sediment samples record the presence of large populations of sulphate reducing bacteria whereas sulphur isotope analyses of lake water samples indicate microbial fractionation in all the lakes studied viable populations of microbes from the lake sediments were cultured in anoxic conditions in the laboratory samples were then injected into vials containing sterilized clastic or carbonate grains or glass beads immersed in a solution that simulated the lake water falls in the levels of sulphate and rising ph in positive vials were interpreted as indicating active bacterial sulphate reduction accompanied by increased concentrations of carbonate within 2 months sub spherical sub micron size crystals of dolomite identical to those of lake sediments were precipitated it is concluded that bacterial sulphate reduction overcomes kinetic constraints on dolomite formation by removing sulphate and releasing magnesium and calcium ions from neutral ion pairs and by generating elevated carbonate concentrations in a hypersaline strongly electrolytic solution the results demonstrate that bacterial sulphate reduction controls dolomite precipitation in both the laboratory experiments and lake sediments it is proposed that dolomite formation through bacterial sulphate reduction provides a process analogue applicable to thick platformal dolostones of the past where benthic microbial communities were the sole or dominant colonizers of shallow marine environments

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

cryosphere applications of nscat data though designed to measure vector winds over the ocean new imaging techniques facilitate the use of nasa scatterometer data nscat in cryosphere studies nscat provides data of unprecedented coverage resolution and quality which when coupled with the scatterometer image reconstruction with filtering sirf algorithm enables images of spl sigma sup o at resolutions approaching 8 km over stationary targets such images are useful in ice mapping and classification and multidecadal studies are possible by comparison with seasat scatterometer sass data the utility of nscat data in polar ice studies is illustrated through a review of two cryosphere applications of nscat data 1 sea ice mapping and tracking and 2 ice sheet change in greenland and antarctica the wide swath and frequent revisit coupled with incidence and azimuth angle diversity makes nscat data very effective in mapping the extent of sea ice in greenland snow and ice facies are clearly delineated on the basis of the seasonally dependent radar backscattering cross section due to sensitivity of radar backscatter to diagenetic changes occurring at and beneath the surface comparison of nscat and sass data enables study of change in greenland between 1978 and 1996

local observations of the onset of a large earthquake 28 june 1992 landers california the landers earthquake mw 7 3 of 28 june 1992 had a very emergent onset the first large amplitude arrivals are delayed by about 3 sec with respect to the origin time and are preceded by smaller scale slip other large earthquakes have been observed to have similar emergent onsets but the landers event is one of the first to be well recorded on nearby stations we used these recordings to investigate the spatial relationship between the hypocenter and the onset of the large energy release and to determine the slip function of the 3 sec nucleation process relative location of the onset of the large energy release with respect to the initial hypocenter indicates its source was between 1 and 4 km north of the hypocenter and delayed by approximately 2 5 sec three station array analysis of the p wave shows that the large amplitude onset arrives with a faster apparent velocity compared to the first arrivals indicating that the large amplitude source was several kilometers deeper than the initial onset an ml 2 8 foreshock located close to the hypocenter was used as an empirical green s function to correct for path and site effects from the first 3 sec of the mainshock seismogram the resultant deconvolution produced a slip function that showed two subevents preceding the main energy release an mw 4 4 followed by an mw 5 6 these subevents do not appear anomalous in comparison to simple moderate sized earthquakes suggesting that they were normal events which just triggered or grew into a much larger earthquake if small and moderate sized earthquakes commonly detonate much larger events this implies that the dynamic stresses during earthquake rupture are at least as important as long term static stresses in causing earthquakes and the prospects of reliable earthquake prediction from premonitory phenomena are not improved

texture of microbial sediments revealed by cryo scanning electron microscopy abstract textures of modern lacustrine stromatolites on kiritimati line islands central pacific ocean and of buried layers in the stromatolitic carbonate sediments from french polynesian atoll lakes kopara have been studied using cryo scanning electron microscopy sem equipped with a freeze drying sample preparation device this study confirms that microscopic three dimensional organic networks built through reorganization of polysaccharide fibers inherited from sheaths of dead cyanobacteria and from other extracellular polymer secretions are common components of microbial sediments of which they may form the framework in addition to this role in sediment cohesion and formation of microstructure the organic framework appears to be involved in carbonate precipitation with n the stromatolites through chemical nucleating steric and hydrodynamical controls the role of the dead organic constituents of the stromatolites is not only confirmed in micrometer size crystal precipitation but extended to the post mortem internal mineralization of cyanobacterial filaments and to the formation of peloids that evolve into spherulites bacterial including nannobacterial carbonate bodies and carbonate impregnated cyanobacterial sheaths are also shown to form in the stromatolites studied all these carbonate precipitation processes may cooperate in lithification of a given sediment

coherence of seismic body waves from local events as measured by a small aperture array eight local earthquakes were recorded during the operation of a small aperture seismic array at pinyon flat california the site was chosen for its homogeneous granitic geology and its planar topography amplitude spectral ratios for the same signal measured at different stations had average values of less than 2 and maximum values of 7 magnitude squared coherences were estimated for all station pairs these estimates were highest for the p wave arrivals on the vertical component and lowest for the p wave recorded on the transverse component at 500 m station separation the p and s waves were incoherent above 15 hz and 10 hz respectively coherence for both the p and s waves decrease as frequency increases and as distance increases the coherence of signals from borehole sensors located at 300 and 150 m depth displays higher average coherence than equally spaced sites located on the surface the results here suggest that even for sites that appear to be very similar that is those which are located on a planar surface within a few meters of granite bedrock the measured seismic wavefield can be distorted substantially over scale lengths of 500 m coherence properties were calculated from synthetic seismograms which were computed for velocity models with exponential and self similar distribution perturbations standard deviations of 10 are not sufficient for the random velocity distributions to approximate the results from the small aperture array

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

the role of sulphate reducing bacteria and cyanobacteria in dolomite formation in distal ephemeral lakes of the coorong region south australia abstract the dolomitic distal ephemeral lakes of the coorong region of south australia are dynamic systems in which the concentrations of solutes generally increase during late spring and summer when the rate of evaporation greatly exceeds aqueous input during late evaporation active bacterial sulphate reduction occurs in uppermost anoxic lake sediments as rising salinity and then h2s toxicity kills off the macrobiota these hypersaline lakewaters are characterised by high ph and elevated concentrations of carbonate and sulphate ions magnesium concentrated in cyanobacterial cells and sheaths is released into the strongly electrolytic alkaline lake brines from lake margin stromatolites and mats during desiccation and may explain the remarkable increase in mg levels recorded at this time continued evaporation of the lakewaters produces a halite crust overlying the dolomite sulphate free residual puddles and the absence of gypsum indicates that all sulphate is removed by sulphate reducing bacteria dolomite forms in situ as a primary precipitate from these microbially mediated lake porewaters and both the morphology and size distribution of dolomite grains is identical to bacterial cells it is not proven exactly when dolomite precipitation occurs but the submicron sized grains and multiple defects in a disordered lattice indicate that precipitation is rapid and follows bacterial removal of sulphate which is known to inhibit dolomite formation bacterial sulphate reduction and cyanobacterial degradation may thus lead to the removal of all kinetic inhibitors to dolomite formation and provide a mechanism for dolomite precipitation around bacterial cells in shallow subsurface sediments during the late stages of evaporation in adjacent non dolomitic lakes sulphate is present throughout evaporation so that other minerals principally aragonite and hydromagnesite are precipitated

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

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

pervasive early diagenetic dolomitization subsequent hydrothermal alteration and late stage hydrocarbon accumulation in a middle triassic carbonate sequence szeged basin se hungary abstract the middle triassic shallow marine carbonates of the se pannonian basin szeged dolomite formation show evidence for multistage dolomitization and a complex diagenetic history in first stage the whole sequence was completely dolomitized by reflux of slightly evaporated seawater this process took place from the near surface till shallow burial realms and resulted in the formation of both fabric preserving and fabric destructive dolomite types in the following stage nonplanar matrix dolomite and saddle dolomite cement were formed in the intermediate and or deep burial realm these later dolomite phases are likely generated by invasion of exotic fluids at relatively high temperature evidenced from the fluid inclusion homogenization temperatures and stable isotope compositions vuggy fracture and solution enhanced porosity are also related to this local hydrothermal event microthermometry performed on saddle dolomite hosted primary fluid inclusions confirm the presence of hot 138 235 c and moderately saline brines 4 1 8 7 mass nacl equivalent the calculated 18owater and the measured dwater values of the fluid inclusions from the saddle dolomite cement together with the relatively low salinity values indicate a metamorphogenic and or magmatic origin of the hydrothermal fluid that probably was channeled along the upper cretaceous subhorizontal overthrust zones the pores formed by the leaching effect of these hydrothermal fluids were subsequently partly occluded by meteoric calcite during the paleogene middle miocene subaerial exposure but a remarkable part was preserved and currently serves as reservoir space such an integrated study of the different dolomite and porosity types the understanding of their genesis and timing relative to hydrocarbon maturation and migration could aid in exploration and development

preservation of organic carbon in dolomitized cambrian stromatolites and implications for microbial biosignatures in diagenetically replaced carbonate rock abstract stromatolites have been a major focus in the search for ancient microbial life however the organic carbon biosignatures of dolomitized stromatolites have not yet been fully characterized or correlated with their dolomitizing conditions although dolomitization rarely preserves microbial morphology the presence of organic carbon can provide valuable information for characterization of fossils biogenicity syngenicity and indigeneity to their host rock the cambrian allentown formation in new jersey usa is an excellent example of dolomitized stromatolites and thrombolites containing diagenetically modified microbial biosignatures based on xrd and epma data the dolomite composition is typically stoichiometric with varying degrees of cationic ordering the outcrop underwent early dolomitization in a marginal marine setting and later burial diagenesis resulting in multi generational dolomite formation 1 microspar dolomite formed by early diagenetic replacement at or near the surface 2 zoned dolomite formed penecontemporaneously with the microspar phase as rhombohedral crystals by infilling primary pore spaces within the microspar matrix the rhombic crystals continued to grow outward in alternating stages of fe enriched and depleted fluids which were preserved in zoned rims and revealed by cathodoluminescence and 3 saddle dolomite formed during late stage deep burial with fe and mn rich fluids and occurs as a void filling high temperature phase organic carbon characterized using confocal raman microscopy has an exclusive distribution within the microspar dolomite and the d and g bands characteristics reveal similar thermal alteration to the host rock indicating that the mapped organic carbon is indigenous and syngenetic with the cambrian carbonates the findings presented in this study reveal organic matter found within microspar of various dolomitized facies deriving from different source pools of organic carbon this study sheds light on biosignatures in secondary dolostones and may aid biosignature detection in older carbonate rocks on earth and mars

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

partially disordered dolomite microstructural characterization of abu dhabi sabkha carbonates transmission and analytical electron microscopy observations document at least three carbonate phases in sediments of the abu dhabi sabkha aragonite ordered dolomite often showing modulated microstructure and a mostly disordered calcium magnesium carbonate with submicrometer sized ordered domains it is suggested that ordered and partially ordered dolomite formed mainly by direct precipitation from pore fluids with changing temperature and chemistry in response to environmental parameters

cenozoic dolomites of carbonate islands their attributes and origin abstract dolomites found on and below carbonate islands atolls and oceanic platforms provide useful insights into the origin of dolomite insights that may not be attainable from the study of more ancient cratonic dolomites for this reason they have been the subject of study for decades a critical mass of case studies now exist and some significant conclusions can be drawn from the cumulative data in most cases the association with an island is causal and not genetic nevertheless these dolomite occurrences are referred to herein as island dolomites one type of dolomite on carbonate islands is penecontemporaneous dolomite a phase that forms while the host sediment is in its original depositional setting island examples are holocene in age occur in holocene sediments and originate as a direct precipitate from either normal or evaporated seawater these are microcrystalline poorly ordered ca rich 18o enriched and geochemically unstable phases that are susceptible to recrystallization in the setting in which they formed post depositional dolomite is the other type of dolomite associated with carbonate islands this type of dolomite replaces older precursors and forms as cement distinctive characteristics include a dominance of fabric preserving texture pore lining cement rims that may exhibit micron scale banding with low mg calcite and formation in association with precursor dissolution sr isotopic dating indicates that all examples are neogene or quaternary in age those formed during the middle miocene through pliocene are massive laterally continuous and often multigenerational in contrast younger examples tend to be localized partial replacements of a single generation sr isotope ages also suggest global synchroneity in many dolomitization events which suggests a connection between dolomitization global eustacy and or global climatic factors geochemical attributes of post depositional island dolomites are ca enrichment positive 18o and 13c low sr contents 150 300 ppm and low fe global similarity in petrography and geochemistry of replacive island dolomites argues for a similar origin inferred origins however depend primarily on how 18o and sr data are interpreted values for 18o and dsr must be assumed due to uncertainties in oxygen isotope fractionation and sr partitioning there is no consensus or uniformity in those assumptions thus interpretations can vary and be biased to a desired result covariant trends in 13c and 18o some negative 13c values and high sr all favor a mixing zone origin but examples with these attributes are few lack of covariance in the isotopes mean 18o of 2 0 to 3 5 and low sr future studies should standardize the type of data collected and the analytical techniques employed multiple geochemical attributes should be measured on microsampled components and quantitative modeling should be employed in order to constraint interpretations as much as possible also needed are a better understanding of the kinetic processes that form these dolomites more careful assessment of their recrystallization status and an improved understanding of dsr and 18o at low temperature

measuring surface wave phase velocities beneath small broad band arrays tests of an improved algorithm and application to the french alps the local measurement of dispersion curves of intermediate period surface waves is particularly difficult because of the long wavelengths involved we suggest an improved procedure for measuring dispersion curves using small aperture broad band arrays the method is based on the hypotheses of plane incoming waves and that averaging over a set of events with a good backazimuth distribution will suppress the effects of diffraction outside the array none of the elements of the processing are new in themselves but each step is optimized so we can obtain a reliable dispersion curve with a well defined uncertainty the method is based on the inversion for the slowness vector at each event and frequency using time delays between pairs of stations where the time delays deltat are obtained by frequency domain wiener filtering the interstation distance projected on to the slowness vector d is then calculated the final dispersion curve is found by at each frequency calculating the inverse of the slope of the best fitting line of all d deltat points to test the algorithm it is applied to synthetic seismograms of fundamental mode rayleigh waves in different configurations 1 the sum of several incident waves 2 an array located next to or above a crustal thickening and 3 added white noise using regular and irregular backazimuth distributions in each case a circular array of 23 km diameter and composed of six stations is used the algorithm is stable over a large range of wavelengths between half and a tenth of the array size depending on the configuration the situations of several simultaneously incoming waves or neighbouring heterogeneities are well handled and the inferred dispersion curve corresponds to that of the underlying medium above a strong lateral heterogeneity the inferred dispersion curve corresponds to that of the underlying medium up to wavelengths of eight times the array size in the configuration considered but further work is needed to better understand the limits under which the obtained dispersion curve is not biased in the case of 5 per cent spectral amplitude white noise the dispersion curve is also stable for wavelengths up to approximately eight times the array size but this limit depends of course strongly on the noise level the method is finally applied to data from two arrays in the french alps located 50 km apart it is possible to measure the dispersion curves up to wavelengths approximately ten times bigger than the array diameter the difference in the dispersion curves is compatible with a crustal and lithospheric thickening under the alps however the observed errors are large which result in severe limits on the interpretation in terms of lithospheric structure longer recording periods may help to reduce the errors otherwise the algorithm is likely to be of use mainly in areas where the lateral variations outside the array are smaller than those of the french alps

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

production and cycling of natural microbial exopolymers eps within a marine stromatolite extracellular polymeric secretions eps that are produced by cyanobacteria represent potential structuring agents in the formation of marine stromatolites the abundance production and degradation of eps in the upper layers of a microbial mat forming shallow subtidal stromatolites at highborne cay bahamas were determined using 14 c tracer experiments and were integrated with measurements of other microbial community parameters the upper regions of a type 2 reid r p visscher p t decho a w stolz j bebout b macintyre i g dupraz c pinckney j paerl h prufert bebout l steppe t des marais d 2000 the role of microbes in accretion lamination and early lithification of modern marine stromatolites nature london 406 989 992 stromatolite mat exhibited a distinct layering of alternating bgreenq cyanobacteria rich layers layers 1 and 3 and bwhiteq layers layers 2 and 4 and the natural abundance of eps varied significantly depending on the mat layer the highest eps abundance occurred in layer 2 the production of new eps as estimated by the incorporation of 14 c bicarbonate into eps occurred in all layers examined with the highest production in layer 1 and during periods of photosynthesis i e daylight hours a large pool i e up to 49 of the total 14 cbicarbonate uptake was released as low molecular weight mw dissolved organic carbon doc this doc was rapidly mineralized to co2 by heterotrophic bacteria eps degradation as determined by the conversion of 14 c eps to 14 co2 was slowest in layer 2 results of slurry experiments examining o2 uptake following additions of organic substrates including eps supported this degradation trend and further demonstrated selective utilization by heterotrophs of specific monomers such as acetate ethanol and uronic acids results indicated that natural eps may be rapidly transformed post secretion by heterotrophic degradation specifically by sulfate reducing bacteria to a more refractory remnant polymer that is relatively slow to accumulate a mass balance analysis suggested that a layer specific pattern in eps and low mw doc turnover may contribute to major carbonate precipitation events within stromatolites our findings represent the first estimate of eps

imprints of hydrocarbon bearing basinal fluids on a karst system mineralogical and fluid inclusion studies from the buda hills hungary calcite veins and related sulphate sulphide mineralisation are common in the buda hills also abundant hypogenic caves are found along fractures filled with these minerals pointing to the fact that young cave forming fluids migrated along the same fractures as the older mineralising fluids did the studied vein filling paragenesis consists of calcite barite fluorite and sulphides the strike of fractures is consistent nnw sse concluding a latest early miocene maximum age for the formation of fracture filling minerals calcite crystals contain coeval primary hydrocarbon bearing and aqueous inclusions indicating that also hydrocarbons have migrated together with the mineralising fluids hydrocarbon inclusions are described here for the first time from the buda hills mixed inclusions i e petroleum with water tail were also detected indicating that transcrystalline water migration took place the coexistence of aqueous and petroleum inclusions permitted to establish the entrapment temperature 80 c and pressure 85 bar of the fluid and thus also the thickness of sediments having been eroded since latest early miocene times was calculated 800 m low salinity of the fluids 1 7 nacl eq wt implies that hydrocarbon bearing fluids were diluted by regional karst water ft ir investigations revealed that co2 and ch4 are associated with hydrocarbons groundwater also contains small amounts of hc and related gases on the basin side even today based on the location of the paleo and recent hydrocarbon indications identical migration pathways were reconstructed for both systems hydrocarbon bearing fluids are supposed to have migrated north westward from the basin east to the buda hills from the miocene on

nannobacteria as a by product of enzyme driven tissue decay spheroidal features 50 to 200 nm in size and found in sedimentary rocks have been described as nannobacteria the idea that they are minute fossilized life forms and especially the discovery of such features in martian meteorite alh84001 sparked a lively debate with regard to identification of ancient microbial life because biologists consider 200 300 nm to be the lower viable size limit for microorganisms an alternative explanation is needed for features that have been described as nannobacteria by geologists we report here on tissue decay experiments that produced abundant proteinaceous spheroids in the size range of nannobacteria described as nannoballs in the remainder of this paper experimental conditions were comparable to those found in earth9s surface sediments and diagenetic mineralization of these spheroids may be a common process for preservation of nannoballs that are observed in the rock record

sem imaging of bacteria and nannobacteria in carbonate sediments and rocks abstract bacteria and nannobacteria 0 1 m dwarfed forms are abundant in both non etched and gently etched travertines deposited by hot springs in viterbo italy they are also plainly visible in bahama ooids and hardgrounds and in great salt lake aragonite ooids and cements in addition nannobacteria are found in paleozoic and mesozoic rocks because of their extraordinary abundance in some specimens they probably play a prominent role in catalyzing the precipitation of carbonate materials

microbially mediated dolomite in cambrian stromatolites from the tarim basin north west china implications for the role of organic substrate on dolomite precipitation abstract dolomite camg co3 2 is abundant in sedimentary rocks throughout the geological record but it is rarely found in modern sediments also it cannot be precipitated under low temperature conditions in the laboratory without microbial mediation and as a result its origin remains a long standing enigma this study reports biologically mediated dolomite precipitation in ancient microbial mats and biofilms from the cambrian tarim basin the ambient temperature at the time of dolomite precipitation was estimated from delta o 18 values from early diagenetic dolomite and the presence of structures associated with extracellular polymeric substances eps is composed of fibres arranged in a reticular pattern would favour epitaxial crystallization of dolomite on an organic substrate in addition poorly crystallized dolomite formed nanocrystal aggregates that strongly resemble the morphology and size distribution observed in microbial culture experiments these lines of evidence confirm that microbial structures can be preserved in ancient dolomite and validate their use as biosignatures

snow facies over ice sheets derived from envisat active and passive observations this paper aims to separate different snow regions over the terrestrial ice sheets based on their measured microwave signatures it takes advantage of coregistered data from passive and active sensors on the environmental satellite envisat to directly derive a snow facies indicator in a point by point basis this paper represents the first attempt of this kind in exploiting nadir viewing and dual frequency data from both altimeter and radiometer sensors the approach is based on a clustering method such representation of the data by means of fewer clusters necessarily loses fine details but achieves simplification in geographical representation and eases the description of the condition of the ice sheets in 2004 our approach broadens the description of the snow pack by taking into account characteristics such as surface roughness grain size stratification and snowmelt effects whereas the latter has often solely been considered in most previous work such partition of the ice sheets might help to better understand relationships between microwave signatures and snow morphology it could also be useful for estimating elevation uncertainty in altimeter data which in turn is essential to correctly interpret the significance of the rates of elevation change in a changing climate and to convert elevation change to snow mass change

greenland ice sheet surface temperature melt and mass loss 2000 06 author posting international glaciological society 2008 this article is posted here by permission of international glaciological society for personal use not for redistribution the definitive version was published in journal of glaciology 54 2008 81 93 doi 10 3189 002214308784409170

measuring snow and glacier ice properties from satellite satellite remote sensing is a convenient tool for studying snow and glacier ice allowing us to conduct research over large and otherwise inaccessible areas this paper reviews various methods for measuring snow and glacier ice properties with satellite remote sensing these methods have been improving with the use of new satellite sensors like the synthetic aperture radar sar during the last decade leading to the development of new and powerful methods such as sar interferometry for glacier velocity digital elevation model generation of ice sheets or snow cover mapping some methods still try to overcome the limitations of present sensors but future satellites will have much increased capability for example the ability to measure the whole optical spectrum or sar sensors with multiple polarization or frequencies among the methods presented are the satellite derived determination of surface albedo snow extent snow volume snow grain size surface temperature glacier facies glacier velocities glacier extent and ice sheet topography in this review emphasis is put on the principles and theory of each satellite remote sensing method an extensive list of references with an emphasis on studies from the 1990s allows the reader to delve into specific topics

satellite derived melt season surface temperature of the greenland ice sheet 2000 2005 and its relationship to mass balance 1 mean clear sky surface temperature of the greenland ice sheet was measured for each melt season from 2000 to 2005 using moderate resolution imaging spectroradiometer modis derived land surface temperature lst data product maps during the period of most active melt the mean clear sky surface temperature of the ice sheet was highest in 2002 8 29 5 29 c and 2005 8 29 5 43 c compared to a 6 year mean of 9 04 5 59 c in agreement with recent work by other investigators showing unusually extensive melt in 2002 and 2005 surface temperature variability shows a correspondence with the dry snow facies of the ice sheet a reduction in area of the dry snow facies would indicate a more negative mass balance surface temperature variability generally increased during the study period and is most pronounced in the 2005 melt season this is consistent with surface instability caused by air temperature fluctuations

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

microbial biomineralization processes forming modern ca mg carbonate stromatolites abstract modern ca mg carbonate stromatolites form in association with the microbialmat in the hypersaline coastal lagoon lagoa vermelha brazil thestromatolites although showing diversi ed fabrics characterized by thin orcrude lamination and or thrombolitic clotting exhibit a pervasive peloidalmicrofabric the peloidal texture consists of dark micritic aggregates of veryhigh mg calcite and or ca dolomite formed by an iso oriented assemblage ofsub micron trigonal polyhedrons and organic matter limpid acicular crystalsof aragonite arranged in spherulites surround these aggregates unlike thearagonite crystals organic matter is present consistently in the dark micriticcarbonate comprising the peloids this organic matter is observed as sub micron at and lamentous mucus like structures inside the interspaces of thehigh mg calcite and ca dolomite crystals and is interpreted as the remains ofdegraded extracellular polymeric substances moreover many fossilizedbacterial cells are associated strictly with both carbonate phases these cellsconsist mainly of 0ae2to4lm in diameter sub spherical rod like and lamentous forms isolated or in colony like clusters the co existence offossil extracellular polymeric substances and bacterial bodies associated withthe polyhedrons of ca mg carbonate implies that the organic matter andmicrobial metabolism played a fundamental role in the precipitation of theminerals that form the peloids by contrast the lack of extracellular polymericsubstances in the aragonitic phase indicates an additional precipitationmechanism the complex processes that induce mineral precipitation in themodern lagoa vermelha microbial mat appear to be recorded in the studiedlithi ed stromatolites sub micron polyhedral crystal formation of high mgcalcite and or ca dolomite results from the coalescence of carbonatenanoglobules around degraded organic matter nuclei sub micron polyhedralcrystals aggregate to form larger ovoidal crystals that constitute peloids subsequent precipitation of aragonitic spherulites around peloids occurs asmicro environmental water conditions around the peloids change keywords bacterial fossils biomineralization microbialite nanoglobules peloids stromatolites

satellite derived surface type and melt area of the greenland ice sheet using modis data from 2000 to 2005 a new surface classification algorithm for monitoring snow and ice masses based on data from the moderate resolution imaging spectroradiometer modis is presented the algorithm is applied to the greenland ice sheet for the period 2000 05 and exploits the spectral variability of ice and snow reflectance to determine the surface classes dry snow wet snow and glacier ice the result is a monthly glacier surface type gst product on a 1 km resolution grid the gst product is based on a grouped criteria technique with spectral thresholds and normalized indices for the classification on a pixel by pixel basis the gst shows the changing surface classes revealing the impact of climate variations on the greenland ice sheet over time the area of wet snow and glacier ice is combined into the glacier melt area gma product the gma is analyzed in relation to the different surface classes in the gst product the results are validated with data from weather stations and similar types of satellite derived products the validation shows that the automated algorithm successfully distinguishes between the different surface types implying that the product is a promising indicator of climate change impact on the greenland ice sheet

mapping of ice layer extent and snow accumulation in the percolation zone of the greenland ice sheet 1 the greenland ice sheet underwent record extensive melt in 2002 and prolonged melt in 2003 the severe melting created a significant and extensive ice layer over the greenland ice sheet an innovative approach is developed to detect the ice layer formation using data acquired by the seawinds scatterometer on the quikscat satellite quikscat backscatter together with in situ data from automatic weather stations of the greenland climate network are used to map the extent of ice layer formation the results reveal areas of extensive ice layer formed by the 2002 melt which is consistent with the maximum melt extent in 2002 moreover during freezing seasons quikscat data show a linear decrease in backscatter in decibels or db that is related to the amount of snow accumulation in the ice layer formation region this snow accumulation signature is caused by the attenuation of radar waves in the snow layer accumulating since the last major melt event whose thickness appears as an exponential function in relation to the backscatter signature we use the greenland climate network data to calibrate the quikscat accumulation rate in order to estimate and map snow accumulation quikscat results capture the extreme snowfall in mid april 2003 which deposited more than 0 5 m of snow in a day as measured by the automated weather station at the nasa south east site large scale quikscat results show an anomalous increase of snow accumulation over the southeast region of greenland during the 2002 2003 freezing season

observations of loma prieta aftershocks from a dense array in sunnyvale california a small aperture 300 m four station array was deployed in sunnyvale california for 5 days to record aftershocks of the loma prieta earthquake of october 1989 the purpose of the array was to study the seismic response of the alluvium filled santa clara valley and the role of surface waves in the seismic shaking of sedimentary basins strong motion records of the loma prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the santa clara valley we use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3 6 and 4 4 apparent velocities are generally observed to decrease with increasing time after the s wave in the seismograms phases arriving less than about 8 sec after the s wave have apparent velocities comparable to the s wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces for times 10 to 30 sec after the direct s wave we observe long period 1 to 6 sec arrivals with apparent velocities decreasing from 2 5 to 0 8 km sec we interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records much of the energy in the 40 sec after the s wave is coming approximately from the direction of the source although some arrivals have backazimuths as much as 60 different from the backazimuths to the epicenters two of the aftershocks show arrivals coming from 30 to 40 more easterly than the epicenters this energy may have been scattered from outcrops along the southeastern edge of the basin in contrast the deepest aftershock studied d 17 km displays later arrivals with backazimuths 30 to 40 more westerly than the epicenter a distinct arrival for one of the aftershocks propagates from the southwest possibly scattered from the western edge of the basin synthetic seismograms derived from a plane layered crustal model do not produce the long period love waves observed in the waveforms of the ml 4 4 aftershock these love waves may be generated by the conversion of incident s waves or rayleigh waves near the edge of the basin

near surface velocities and attenuation at two boreholes near anza california from logging data to investigate near surface site effects in granite rock we drilled 300 m deep boreholes at two sites which are collocated with stations from the digital array at anza california the first borehole was sited at station knw keenwild fire station which is located along a ridge line about 8 7 km east of the san jacinto fault zone station pfo pinon flat observatory chosen for the second site is another 6 km further to the east of station knw and is located on a gently sloping hillside we logged each borehole for p and s wave velocities as well as for crack density and orientation p waves were generated by striking a plate with a hammer at the surface a tool consisting of weighted anvils driven by compressed air against end plates along a 3 5 m beam was used to generate shear waves signals were recorded downhole with a three component sensor package at 2 5 m intervals from the surface to 50 m depth and at 5 m intervals from 50 m depth to the bottom of the hole velocities were determined by differencing the measured arrival times of first arrivals or peaks over each interval in depth travel times were computed for the first breaks at shallow depths however below about 100 m depth times were computed for the first peaks rather than for first breaks since the first arrival was no longer clearly distinguishable the knw site yielded a shear velocity of 1 9 km sec by only 30 m in depth and reached close to 2 6 km sec at the bottom of the hole p wave velocities at knw were also high at 5 4 km sec starting at 120 m depth the pfo site had similar but slightly higher shear wave velocities the bottom hole shear wave velocity reached 3 0 km sec and the p wave velocity was 5 4 km sec shear wave attenuation was computed using both the pulse rise time and spectral ratio methods at station knw attenuation was significant only in an interval between 17 5 and approximately 40 m in depth over the top 50 m attenuation corresponding to a q of about 8 was obtained a total t of 0 004 sec was measured for this interval pulse rise times also increased rapidly in this zone the spectral ratio data for station pfo yields two peaks in attenuation above 50 m similar to the attenuation found for station knw the peak in attenuation corresponds to a q of about 11 averaged over the top 50 m spectra of the seismic pulses produced by the hammer give good signal between 20 to 80 hz significant motion perpendicular to the polarizations of the first shear wave arrival was recorded within a few meters of the surface apparently the rock structure is sufficiently complicated that body waves are being converted sh to sv at oblique incidence very close to the surface the presence of these elliptical particle motions within a mere few m of the pure shear wave source suggests that the detection of polarizations perpendicular to the main shear arrival at a single location at the surface is not by itself a good method for detecting shearwave splitting within the upper few tens of kilometers of the earth s crust crack densities and orientations were determined from televiewer records these records showed cracks with a preferred direction at station knw and of a greater density than at station pfo at station pfo crack densities were smaller and more diffuse in orientation

hydrothermal dolomitization of basinal deposits controlled by a synsedimentary fault system in triassic extensional setting hungary dolomitization of relatively thick carbonate successions occurs via an effective fluid circulation mechanism since the replacement process requires a large amount of mg rich fluid interacting with the caco3 precursor in the western end of the neotethys fault controlled extensional basins developed during the late triassic spreading stage in the buda hills and danube east blocks distinct parts of silica and organic matter rich slope and basinal deposits are dolomitized petrographic geochemical and fluid inclusion data distinguished two dolomite types 1 finely to medium crystalline and 2 medium to coarsely crystalline they commonly co occur and show a gradual transition both exhibit breccia fabric under microscope dolomite texture reveals that the breccia fabric is not inherited from the precursor carbonates but was formed during the dolomitization process and under the influence of repeated seismic shocks dolomitization within the slope and basinal succession as well as within the breccia zones of the underlying basement block is interpreted as being related to fluid originated from the detachment zone and channelled along synsedimentary normal faults the proposed conceptual model of dolomitization suggests that pervasive dolomitization occurred not only within and near the fault zones permeable beds have channelled the fluid towards the basin centre where the fluid was capable of partial dolomitization the fluid inclusion data compared with vitrinite reflectance and maturation data of organic matter suggest that the ascending fluid was likely hydrothermal which cooled down via mixing with marine derived pore fluid thermal gradient is considered as a potential driving force for fluid flow

analysis of topographic amplification of inclined shear waves in a steep coastal bluff abstract the effect of inclined shear waves on the seismic response of a steep bluff is analyzed using generalized consistent transmitting boundaries the results of the frequency domain analysis of a stepped half space subjected to incident shear waves inclined from 0 to 30 show that the motion at the crest of the slope is amplified for waves traveling into the slope and attenuated for waves traveling away from the slope as compared to the motion in the free field behind the crest of the slope this amplification can be as much as twice that observed for vertically propagating waves a time domain analysis of bluffs at seacliff state beach california is used to estimate the effect of topography using realistic conditions taking into account wave inclination and site effects the analysis of the site shows that although topographic amplification does in fact nearly double the amplitude of the motion in some cases this amplification is offset by reduced site amplification and by wave splitting at material interfaces thus the actual peak acceleration occurring at the crest of the slope changes little with incident angle as compared to the amplification of the free field motion and actually decreases in many cases though a more general study is recommended these results suggest that wave orientation and inclination substantially increase topographic amplification however it may be adequate to only account for vertically propagating waves for site response and slope stability analyses where only the magnitude of acceleration is considered

dolomitization of holocene mg calcite supratidal deposits ambergris cay belize dolomitized crusts and associated sediments 845 2925 yr old on ambergris cay belize central america compose a significant portion of the holocene sediment section on many supratidal flats the dolomitic sections are as thick as 0 7 m and contain an average of 70 calcic dolomite dolomite occurs as a replacement of high mg calcite micrite matrix and allochems and as passively precipitated cements isotopic analyses suggest that dolomitization appears to be promoted primarily by reactions of the magnesian calcite supratidal sediments with essentially near normal marine waters the effects of seasonal influxes of meteoric and hybrid fluids however are also clearly evident in the crusts as indicated by isotopes dolomite crystal etching the selective leaching of aragonite and the local loss of mg 2 from the host micrite and included skeletal fragments the amounts rapid rates of dolomitization and initial mg calcite mineralogy of the sediments make the ambergris cay supratidal flats exceptional in the holocene and this area may be a model for the genesis of some ancient peritidal dolomites

array analysis using circular wave front geometry an application to locate the nearby seismo volcanic source summary the zero lag cross correlation technique used for array analysis in the hypothesis of plane waves has been modified to allow the wave front to be circular synthetic tests have been performed to check the capability of the method which returns the input test data when the source array distances are not greater than two or three times the array aperture for this distance range the method furnishes an estimate of the apparent velocity and the epicentral coordinates of the source for more distant sources the method becomes equivalent to that based on the planar wave approximation which gives an estimate of the backazimuth to the source and the apparent velocity the method has been applied to seismic data recorded at the active volcano located at deception island antarctica 35 volcanic long period events occurring in a small swarm were selected results show that the epicentres are close to the array between 0 4 and 2 km and aligned in a sw direction in agreement with one of the main directions of the fracture system of deception volcano

directional site resonances observed from aftershocks of the 18 october 1989 loma prieta earthquake abstract two weeks after the 18 october 1989 loma prieta california earthquake 18 three component digital seismometers were deployed in the epicentral area to form three six station subarrays the subarray configuration allowed us to investigate the presence of direction and frequency dependent site resonances we measured the shear wave polarization from the recordings of 10 aftershocks from the loma prieta earthquake our observations show that the site response has a strong azimuthal dependence and that both the shear wave polarization and the spectral amplitude of the ground motions are affected by site characteristics in the frequency range from 1 to 18 hz the majority of stations examined showed preferred azimuths of ground motion for the scattered waves that did not depend either on the earthquake location or on the polarization of the shear waves expected from the known focal mechanism the measurements were made from 5 sec windows that included direct and scattered shear waves which contain the largest amplitude motions in the near source region and are therefore of most interest to earthquake engineers however in the 0 to 2 hz frequency range the first pulse of shear waves shows a polarization that is well predicted by the mechanism and location of the earthquake the rapid spatial variation of the preferred directions and their corresponding frequencies indicate that geologic structures within a distance of the order of 50 m probably control these site effects we suggest that the site amplified the motion of scattered waves in one preferred direction altering the resulting polarization and modulating the spectral amplitude

pretreatment for removal of organic material is not necessary for x ray diffraction determination of mineralogy in temperate skeletal carbonate abstract quantifying the effects of ocean acidification requires understanding the skeletal carbonate mineralogy in living marine organisms x ray diffractometry xrd is the simplest and most commonly used technique for determining this samples being analyzed by xrd are typically pretreated to remove organic material prior to grinding to a crystallite powder this pretreatment was traditionally performed as organic material may obscure the mineral peaks on xrd traces this study compared controls with no pretreatment with the most common pretreatment methods roasting immersion in chlorine bleach and immersion in hydrogen peroxide the latter two methods were performed at two strengths and two durations we test the hypothesis that bleaching and or roasting of skeletal carbonate to remove organic material does not affect the mineralogy of temperate skeletal carbonate at a scale detectable by xrd this was done with biogenic skeletal carbonate from temperate marine environments around southern new zealand specimens included 5 species of bivalve mollusks 4 species of bryozoans 2 species of barnacles as well as 1 species each of serpulid worm echinoid gastropod mollusk brachiopod and coralline algae comparison to the untreated control showed that all pretreatments removed some organic matter and that the presence of organic matter in temperate skeletal carbonate does not affect the ability to qualitatively interpret mineralogy or semiquantitatively measure mineralogy using xrd given that pretreatment does not appear to be necessary and that some methods at least can cause unacceptable changes in mineralogy we recommend that pretreatment for the removal of organic material be abandoned

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

from rifting to drifting tectonic evolution of the south alpine upper crust from the triassic to the early cretaceous abstract the tectonic evolution of the south alpine rifted margin is discussed on the base of four palinspastic upper crustal profiles extension related to the movements between adria and europe began in the norian after variscan orogeny late carboniferous to middle permian orogenic collapse and continental scale wrenching from the late triassic to the early liassic stretching was mostly limited to the lombardian basin during this time extension was mainly controlled by four major listric faults symmetrically centred around the late carboniferous early permian collio grabens smaller faults which also started in the norian were progressively de activated during the late triassic after the middle liassic faulting in the lombardian basin gradually ceased and the site of extension shifted westwards i e towards the future site of crustal separation extension was then controlled by a set of west dipping normal faults oceanic crust was formed not later than 157 ma the overall extension along the profile which had a final length of 290 km was 52 km which corresponds to a stretching factor of 1 22 for the whole length of the preserved margin the strain rate is ca 1 10 16 s the sedimentation history suggests that the extension of the south alpine margin was a continuous process from the norian to the middle jurassic the changes in tectonic pattern are related to progressive hardening of the lithospheric segment undergoing slow extension

holocene dolomitization of calcium carbonate sediments from the coastal sabkhas of abu dhabi u a e a stable isotope study secondary dolomitization of holocene calcium carbonate sediments occurs beneath the coastal sabkhas of abu dhabi u a e a stable isotope study of the sabhka sediments and brines indicates that the

tertiary paleomagnetic results and structural analysis from the transdanubian range hungary rotational disintegration of the alcapa unit abstract we carried out an integrated paleomagnetic and structural study in the transdanubian range western and central hungary as a result the tertiary tectonic history of this area can be characterized by three events of counterclockwise ccw rotation and four or five phases of brittle deformation the change of the orientation of stress axes between phases is mainly apparent and reflects the rotation of the faults predating a particular rotation event the first two rotation events r1 and r2 were probably governed by the rollback mechanism of the subducting european plate we suggest that these rotations were taking place from 18 17 and 16 14 5 ma respectively i e simultaneously with the rotations of the north hungarian paleogene basin and the main part of the western carpathians however the angle of both rotations was less in the transdanubian range due to increasing distance from the subduction front the differential rotation was accommodated by extensional faulting by formation of a graben system on the other hand the youngest rotation event r3 seems to be connected to the renewed rotation of the adriatic plate around 5 ma our combined data set strongly supports earlier conclusions namely that the different subunits of the eastern alpine western carpathian northern pannonian unit alcapa did not form a rigid unit although they moved in similar manner

role of sulfide oxidation in dolomitization sediment and pore water geochemistry of a modern hypersaline lagoon system dolomite precipitation has been reported in sediments of marginal marine hypersaline lagoons near rio de janeiro brazil and has been related to microbial sulfate reduction our field study of pore water and sediment geochemistry in two lagoons reveals only modest degrees of so4 reduction and even h2s oxidation significant differences in dolomite contents salinity and carbon sulfur cycling occur in the two lagoons pore waters from the most dolomite rich sediments exhibit significantly elevated so4 cl ratios relative to seawater moreover the o isotope composition of so4 in all lagoonal waters has evolved significantly from seawater values this suggests active sulfur recycling via h2s oxidation which provides acid that decreases pore water saturation state for high mg calcite and aragonite thermodynamically favoring the precipitation of dolomite the open hydrogeochemical nature of these lagoons maintains so4 concentrations below gypsum saturation allowing dolomite to form from fluids with normal marine mg ca

mesozoic plate tectonic reconstruction of the carpathian region abstract palaeomagnetic palaeobiogeographic and structural comparisons of different parts of the alpine carpathian region suggest that four terranes comprise this area the alcapa tisza dacia and adria terranes these terranes are composed of different mesozoic continental and oceanic fragments that were each assembled during a complex late jurassic cretaceous palaeogene history palaeomagnetic and tectonic data suggest that the carpathians are built up by two major oroclinal bends the alcapa bend has the meliata oceanic unit correlated with the dinaric vardar ophiolite in its core it is composed of the western carpathians eastern alps and southern alcapa units transdanubian range bukk this terrane finds its continuation in the high karst margin of the dinarides further elements of the alcapa terrane are thought to be derived from collided microcontinents czorsztyn in the n and a carbonate unit tisza in the se the tisza dacia bend has the vardar oceanic unit in its core it is composed of the bihor and getic microcontinents this terrane finds its continuation in the serbo macedonian massif of the balkans the bihor getic microcontinent originally laid east of the western carpathians and filled the present carpathian embayment in the late palaeozoic early mesozoic the vardar ocean occupied an intermediate position between the western carpathian austroalpine transdanubian high karst margin and the bihor getic serbo macedonian microcontinent the vardar and pindos oceans were opened in the heart of the mediterranean adriatic microcontinent in the late permian middle triassic vardar subducted by the end of jurassic causing the bihor getic serbo macedonian microcontinent to collide with the internal dinaric western carpathian margin an external penninic vahic ocean tract began opening in the early jurassic separating the austroalpine western carpathian microcontinent and its fauna from the european shelf further east the severin ceahlau magura also began opening in the early jurassic but final separation of the bihor getic ribbon and its fauna from the european shelf did not take place until the late middle jurassic the alcapa and the tisza dacia were bending during the albian maastrichtian the two oroclinal bends were finally opposed and pushed into the gates of the carpathian embayment during the palaeogene and neogene at that time the main n s shortening in distant alpine and hellenic sectors was linked by a broader right lateral shear zone along the former vardar suture

syn sedimentary hydrothermal dolomites in a lacustrine rift basin petrographic and geochemical evidence from the lower cretaceous erlian basin northern china

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

spatial patterns of diagenesis during geothermal circulation in carbonate platforms geothermal convection of seawater deep in carbonate platforms could provide the necessary supply of magnesium for dolomitization at temperatures high enough to overcome kinetic limitations we used reactive transport simulations to predict the rates and spatial patterns of dolomitization during geothermal convection in a platform that was 40 km across and 2 km thick in the simulations porosity and permeability decrease with depth to account for sediment compaction dolomitization of a platform consisting of medium grained 0 0 5 mm sediments occurred in a broad band ranging from 2 5 km depth near the margin to 1 5 km depth near the platform center the area of dolomitization is deep enough that temperatures exceed 50 c but not so deep that low permeabilities restrict mass transport complete dolomitization in the center of this zone is estimated to require at least 60 my incorporation of permeability contrasts permeable beds and reactive beds focused dolomitization strongly and reduced the estimated time required for dolomitization by as much as 50 percent dolomitization created magnesium depleted calcium rich fluids in less than 10 ky and results support a link between dolomitization and anhydrite precipitation where adequate sulfate is available

microbialites in a modern lagoonal environment nature and distribution tikehau atoll french polynesia abstract microbialites including stromatolitic structures gelatinous masses and mats develop in tikehau lagoon tuamotu french polynesia on the flanks and slopes of numerous pinnacles and motu islets between 0 and 25 m deep on coral colonies algal tufts or on lagoonal sediments individual stromatolitic structures consist of hemispherical domes and are produced by monospecific populations of filamentous cyanobacteria belonging to three distinctive phormidium species symploca and possibly to one new species of schizothrix gelatinous masses hanging from the ceiling of caverns are produced by phormidium laysanense microbial mats are well developed at all depths on pinnacle slopes and are produced by either monospecific or mixed cyanobacterial populations the study of micro and ultrastructure of stromatolites reveals that they result both from trapping and binding of sediments and from carbonate precipitation in addition to phototrophic biomineralization pervasive carbonate precipitation occurred in association with decaying organic matter the basic constructional elements of the precipitated carbonate consist of 0 1 0 2 m rounded bodies that form very fine anhedral to subhedral micrite their surfaces comprise extremely small carbonate granules 20 50 nm gradual changes ageing in the ultrastructure of carbonate precipitates include the precipitation of successive euhedral calcite layers around these grains widespread development of microbialites in this pristine lagoonal environment results from rapid blooms of microbial benthic communities possibly induced by temporary and local nutrient pulses nutrients seem to undergo a restricted circulation between the sediment and pinnacle reef frameworks pinnacles and reef islets are repeatedly affected by catastrophic storm events which cause redistribution of sediments and nutrients

early diagenetic recrystallization of holocene 3000 years old peritidal dolomites ambergris cay belize three peritidal carbonate crusts and associated intercrust sediments total thickness of 30cm aged 3000 years bp on ambergris cay belize contain 32 100 calcian dolomite x 72 5 dolomite ranging in composition from 40 to 46 mol mgco3 x 43 3 dolomite replaced high mg calcite foraminiferal muds penecontemporaneously with sedimentation forming partially dolomitized sediments and lithified crusts dolomitization probably occurred in normal to moderately evaporated seawater and is apparently continuing at the present detailed scanning electron microscope analysis shows a linear increase in mean dolomite crystal size with depth 0 4 m near the top of the section to 1 0 m near the base of the dolomitized section this size increase is not accompanied by any significant decrease in porosity crystal size distributions appear to be log normal and become increasingly broad and flat with depth rietveld x ray pattern fitting structure refinements indicate increasing ca and mg concentrations on their respective sites cation ordering as a function of increasing depth most of the ordering occurs within the first 15 cm of the surface stoichiometry does not increase with depth indicating no relationship between the ca mg ratio and cation ordering strong geochemical trends were observed down section in the dolomite including 1 increasing mn content 44 to 274 ppm and 2 decreasing 13c values 0 9 to 5 5 pdb oxygen isotope values range from 18o 1 3 pdb in the upper part of the section to 2 6 pdb in the lower part of the section and are interpreted to represent two distinct groups of values rather than a continuous trend down section dolomite crystal size increase and shapes of crystal size distributions are consistent with recrystallization via a surface energy driven dissolution reprecipitation process ostwald ripening the observed trends in carbon isotopes and mn content probably result from geochemical re equilibration during recrystallization and reflect reducing conditions and an isotopically light organically derived carbon source oxygen isotope compositions probably reflect relict original dolomite values and are a result of decreasing evaporation due to rising sea level

seismic wave field observations at a dense small aperture array located on a landslide in the santa cruz mountains california abstract a rectangular 4 by 5 array of short period three component seismometers with 15 m spacing was deployed to record several u s geological survey calibration explosions detonated around the santa cruz mountains the array was located at a site where an earlier station had recorded frequency dependent polarized site resonances for aftershocks of the 1989 loma prieta earthquake the site is on a hillside believed to be a landslide structure with the near surface consisting of poorly sorted sediments and weathered rocks with dipping subsurface layers the primary objective was to explore the site effects in this complex three dimensional soft rock environment characteristic of much of the loma prieta source region the direct p waves from four nearby 15 to 20 km explosions at easterly azimuths from the array show counterclockwise arrival azimuth anomalies of 30 to 50 these deflections are attributed to the presence of more than one dipping velocity contrast beneath the array with dips of from 10 to 50 and dip directions generally toward the south one such boundary may correspond to the landslide slip surface and the presence of dipping velocity contrasts underlying the site is probably responsible for some of the observed directional site resonance a slowness vector analysis demonstrates that arrivals early in the p coda have similar azimuthal anomalies while later scattered arrivals come from many azimuths particle motions indicate that the more coherent arrivals in the coda are comprised of scattered p waves and rayleigh waves probably associated with scattering from the rough topography in the region the coda displays greater spatial coherency along the hill strike than down the slope consistent with a wedge shaped landslide the overall wave field spatial coherence ccc f x decreases with increasing frequency f and spatial offset x and on average can be well represented by ccc f x e cf x with c 0 6 km 1 hz 1 for the vertical p wave in the first 1 sec window this behavior is comparable to that found for previously studied hard rock locations

dolomitization of triassic microbial mat deposits hungary origin of microcrystalline dolomite abstract dolomite most commonly forms via replacement of precursor carbonate minerals for this reason diagnosing primarily precipitated organogenic dolomite in microbial mat deposits from the rock record is not straightforward even though the deposits exhibit microbial fabric single and multiple dolomite crusts exhibiting microbial fabric occur in a pervasively dolomitized middle triassic platform succession two sections were studied in the transdanubian range in both sections two fabric types occur in the upper part of the metre scale cycles one of that is microbial boundstone fabric type 1 characterised by clusters of dolomite microcrystals which display diagnostic microbial features such as calcimicrobes clotted spherular aggregates and globules the other one is different in the two sections in section 1 it is micritic dolomite fabric type 2 that is characterised by predominantly fine crystals and contains obscured microbial components in section 2 it is bioclastic dolomite fabric type 3 that is rich in reworked dasycladalean alga fragments and consists of dolomite crystals of wide size range from fine to coarse the precipitation of the microcrystalline dolomite phase is interpreted as being facilitated by mats and biofilms favouring tolerating an increasing frequency of subaerial conditions in the upper intertidal setting petrographic analyses revealed that organogenic calcite was also precipitated especially in mat deposits rich in bioclasts synsedimentary dolomitization resulting in fine crystals was coupled with aragonite dissolution and it postdated the organogenic precipitation it took place only in the peritidal caps of the shallowing upward depositional units petrographic analyses provide circumstantial evidence constraining that microcrystalline dolomite did not form via mimetic replacement accordingly the microcrystalline dolomite which shows microbial microfabrics in the studied samples is interpreted as an organogenic primary precipitate both peritidal processes dolomite precipitation and replacement were likely controlled by the environmental factors in a semi arid climate those components of the platform succession that were not dolomitized in the peritidal environment were replaced and cemented by medium and coarsely crystalline dolomite during further burial at elevated temperature as shown by fluid inclusion homogenisation temperature 62 to 83 c and negative stable oxygen isotope values thus the majority of the studied formation consists of fabric destructive dolomite fabric type 4

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

dolomitization of holocene shallow marine deposits mediated by sulfate reduction and methanogenesis in normal salinity seawater northern belize abstract dolomite constitutes an average of 12 of the holocene organic rich sediments over a 15 km2 area of the cangrejo shoals mudbank in northern belize although it defines a laterally persistent stratiform body that averages 3 m thick it is present throughout the 7 6 m thick sediment section these transgressive sediments are less than 6400 years old and were deposited in shallow marine environments of normal salinity the dolomite is dominantly cement and average crystal size is 7 m there are no significant correlations among amount of dolomite vs sediment texture mineralogy porosity or mole mgco3 in associated particulate high mg calcite depth or location on the shoals the dolomites are poorly ordered and calcic 39 5 44 5 mole mgco3 with low mean mn 210 ppm and relatively high mean sr 1034 ppm concentrations there is no evidence of recrystallization or geochemical alteration of the dolomite 18o values of the dolomites range from 0 5 to 2 8o oopdb and the mean value 2 1o oo suggests that the dolomite precipitated from normal salinity pore water dolomite 13c values range from 5 2o oo to 11 6o oopdb mean seawater 13c 0 5o oo which suggests dolomitization promoted by both bacterial sulfate reduction and methanogenesis in environments with anoxic pore water dolomitization attending these organodiagenetic reactions apparently was reversible over time and episodic rather than continual precipitation is indicated requisite mg and ca were provided by seawater and by some dissolution of host sediments the most rapid period of dolomitization may have been during early transgression when relatively high sedimentation rates sustained high levels of organodiagenesis and pore water alkalinities

microbially induced dolomite precipitates in eocene lacustrine siliciclastic sequences in the dongying depression bohai bay basin china evidence from petrology geochemistry and numerical modeling this study investigates the origin of dolomite by examining thick lacustrine sequences of evaporites mudstones and deep water sublacustrine fan sandstones in the lower unit of the fourth member of the eocene shahejie formation es4x in bohai bay basin china this petrographic geochemical and numerical modeling study recognizes evidence for microbially mediated dolomite precipitates in the es4x sandstones including the following 1 spherical or elliptical dolomite aggregates consisting of submicrometer sized crystals 2 negative 13cvpdb vpdb refers to vienna peedee belemnite values of the dolomite cements 6 56 to 3 35 3 relatively low precipitation temperatures of dolomite cements 39 c 65 c 102 f 149 f based on 18ovpdb values from 8 76 to 4 65 and 4 negative 34svcdt vcdt refers to vienna canon diablo troilite values of associated framboidal pyrite 3 9 to 5 7 with respect to an anhydrite precursor 21 2 to 37 8 one dimensional reactive transport modeling incorporating biodegradation kinetics was conducted to evaluate the link between biodegradation of organic matter and geochemical reactions of inorganic minerals during microbial sulfate reduction msr microbial metabolism in the model creates favorable geochemical conditions for dolomite precipitation by increasing ph carbonate alkalinity and mg2 ca2 ratio the modeling results reproduce petrographic observations associated with the msr process and indicate that the kinetics of microbial growth can significantly modify the geochemistry of simulated waters and enhance microbially mediated dolomite precipitation therefore this study illustrates the effect of msr in dolomite precipitation in a semiclosed and reducing continental lacustrine basin

nucleation of calcium carbonate on bacterial nanoglobules nucleation of calcium carbonate on microbial cell material may have been the dominant mode of microbial carbonate formation during most of earth s history current knowledge predicts that nucleation takes place on the cell surface or on extracellular polymeric substances however the initial nucleation steps have not been described in detail and the process remains elusive here we describe the bacterial nucleation of calcium carbonate at the nanometer scale in our precipitation experiment with sulfate reducing bacteria srb the bulk of calcium carbonate precipitates on hundreds of individual globules 60 200 nm in diameter globules originate from the srb cell surface but calcify significantly only when released to the culture medium similar globules have been observed albeit at a much larger scale in other bacterial precipitation experiments and in many natural microbial carbonates suggesting that the process we describe could be an important step in microbial calcification

bacterial fossils and microbial dolomite in triassic stromatolites triassic stromatolitic dolomite from italy preserves mineralized bacterial remains one of the first unequivocal identifications of such structures in the geological record they consist of empty spheroids 1 0 m diameter resembling coccoid bacteria and smaller 150 400 nm objects interpreted as dwarf bacterial forms occurring within and between syn sedimentary dolomite crystals moreover gently folded sheets 100 200 nm thick and several micrometers long form a sub polygonal network reminiscent of eps extracellular polymeric substance their granular textured surfaces suggest bacterial degradation of original organic matter these features confirm a biological origin for the stromatolites as in modern microbial mats and the preserved original geochemical signatures indicate early precipitation of mg carbonates induced through microbial sulfate reducing metabolic activities

polarization and coherence of 5 to 30 hz seismic wave fields at a hard rock site and their relevance to velocity heterogeneities in the crust abstract except for its very onset the p wave of earthquakes and chemical explosions observed at two narrow aperture arrays on hard rock sites in the adirondack mountains have a nearly random polarization the amount of energy on the vertical radial and transverse components is about equal over the frequency range 5 to 30 hz for the entire seismogram the spatial coherence of the seismograms is approximately exp cf x where c is in the range 0 4 to 0 7 km 1 hz 1 f is frequency and x is the distance between array elements vertical radial and transverse components were quite coherent over the aperture of the array indicating that the transverse motion of the compressional wave is a property of relatively large 10 6 m 3 volumes of rock and not just an anomaly caused by a malfunctioning instrument poor instrument rock coupling or out crop scale effects the spatial coherence is approximately independent of component epicentral azimuth and range and whether p or s wave coda is being considered at least for propagation distances between 5 and 170 km these results imply a strongly and three dimensionally heterogeneous crust with near receiver scattering in the uppermost crust controlling the coherence properties of the waves

microscale observations of sulfate reduction correlation of microbial activity with lithified micritic laminae in modern marine stromatolites we report for the first time micrometer scale correlation of geologic and microbial processes in modern marine stromatolites precipitation of micritic laminae in these stromatolites was studied by comparing microstructure as observed in petrographic thin sections with microbial sulfatereduction activity two dimensional mapping of sulfate reduction rates was implemented by incubating a vertical section of a stromatolite face on silver foil coated with 35 so 4 2 our results show that sulfate reduction activity is high in zones of caco 3 precipitation and indicate that microbial activity produces lithified micritic laminae near the surface of the stromatolites similarities with micritic laminae in ancient stromatolites suggest that sulfate reduction may also have been an important mechanism of carbonate precipitation in these fossilized structures

shallow burial dolomite cement a major component of many ancient sucrosic dolomites dolomite cement is a significant and widespread component of phanerozoic sucrosic dolomites cements in dolomites that were never deeply buried are limpid have planar faces non saddle forms often distinct zonation in cathodoluminescence and form syntaxial overgrowths on crystals facing pores five samples of sucrosic dolomites interpreted as having had mostly limemudstone or wackestone precursors in four carbonate aquifers provide insights into the abundance of planar cements in sucrosic dolomites such cement comprises 11 to 45 32 mean of peritidal to sub tidal dolomites on an outcrop in the edwards aquifer early cretaceous of central texas 19 to 33 25 mean of ramp dolomites in the hawthorn group oligomiocene and 50 to 70 in shelf dolomites of the avon park formation eocene in the upper floridan aquifer of sub surface peninsular florida 18 to 45 32 mean of sub tidal shelf dolomites in quarry sections of the burlington keokuk formation early mississippian in south eastern iowa and 18 to 76 50 mean in shallow cores and outcrops of outer shelf dolomites from the gambier limestone oligo miocene of south australia backstripping the cement phases revealed by cathodoluminescence colour photomicrographs documents the effects of cements on textural coarsening pore space reduction induration and general maturation of these dolomites most pre holocene dolomites are multiphase crystalline rocks composed of i seed crystals or cores ii crystal cortices that concentrically enlarged the cores and iii free space syntaxial precipitates of limpid cement around the crystals remaining caco3 grains and micrite can be replaced by dolomite but typically they are dissolved between stages ii and iii creating systems of intercrystal and mouldic pores typical of sucrosic dolomites networks of cement overgrowths aided by water filled pore systems under hydrostatic to lithostatic pressure are judged to slow or prevent compaction in sucrosic dolomites it can be argued that cortex growth involves both replacement of caco3 particles and microcementation of their interparticle pores this interpretation and the abundance of cements in so many dolomites would obviate the controversy over the volumetrics of replacement dolomitization limpid planar and syntaxial dolomite cements of early diagenetic origin are interpreted to have precipitated from clear pore waters at low temperatures 30 to 35 c and shallow burial depths 100 m in water saturated networks of dolomite silt and sand cements in many dolomites in island and continental aquifer systems appear to result from event driven processes related to sea level highstands cementation events can follow replacement

the melt anomaly of 2002 on the greenland ice sheet from active and passive microwave satellite observations 1 active and passive microwave satellite data are used to map snowmelt extent and duration on the greenland ice sheet the passive microwave pm data reveal the extreme melt extent of 690 000 km2 in 2002 as compared with an average extent of 455 000 km2 from 1979 2003 a statistical analysis of the melt time series affirms an increased melt extent earlier in the melt season the quikscat qscat or am analysis for 1999 to 2004 confirms the extreme melt situation in 2002 qscat data show a significant increase in melt season length over several areas in 2003 ssm i and qscat melt data reveal that the later detects melt earlier and is more sensitive to surface melt qscat detects an earlier stage of melt and ssm i detects a later stage of melt the ssm i xgpr melt extent is approximately confined to the qscat melt areas experiencing 2 weeks or more of melting time

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

holocene dolomitization of supratidal sediments by active tidal pumping sugarloaf key florida abstract sugarloaf key is an area where holocene dolomitization is occurring calcium rich dolomite is found in a 0 25 to 10 cm thick surface crust which transgresses a thin layer of carbonate mud overlying the karsted pleistocene miami oolite radiocarbon ages of the crust range from 160 years b p to 1420 years b p with a corresponding increase in dolomite content from 0 to 80 the relatively high permeability of the underlying pleistocene oolite and low permeability of the holocene carbonate mud results in a tidal lag between surface water and the partly confined aquifer consequently seawater is pumped upward and downward through the holocene sediment during spring tides the highest concentration of dolomite is found in areas where the sediment layer is thinnest and tidal pumping is most effective limited analyses of surface and subsurface water taken at intervals throughout the pumping cycle suggest that the dolomitizing fluid is essentially florida bay water the earliest diagenesis is caused by precipitation of dolomite cement which occurs as 0 1 to 0 3 micron subrounded crystallites that show no distinct crystal form during further cementation and somewhat later during replacement of preexisting crystallites poorly ordered dolomite forms as 1 to 5 micron euhedral rhombs x ray diffraction data indicate that the crystallized dolomite is better ordered and less calcium rich than the dolomite composed of crystallites

analysis of wave propagation in the valley of mexico from a dense array of seismometers a dense array of seismometers was installed and operated in the botanical garden of unam within the valley of mexico during april and may 1994 the slow surface velocities at the array require an approach to array analysis with the capability of measuring arrival time differences between stations of less than the sampling interval of the data applying the method to principal component seismograms from earthquakes at local and regional ranges from a number of directions provides the first quantitative information on the composition of the wave field incident upon mexico city phases that propagate through the entire crust such as the initial p and lg waves cross the array with the expected backazimuth on the other hand surface waves in the 2 5 to 5 sec period band which are sensitive to uppercrustal structure show systematic rotations of backazimuth these suggest changes in upper crustal structure or point scatterers located north and south of mexico city for earthquakes outside of the valley of mexico no significant energy was observed propagating across the array from the east from the lake zone thus although it is clear that seismic waves resonate within the lake zone little if any of this energy is transmitted into the hill zone where the array was located however long duration ground motions are observed at the array with evidence of multipathing a back projection of these late off azimuth arrivals indicates that their sources correlate with the boundaries of the quaternary volcanics of the trans mexican volcanic belt

permian paleogeography of west central pangea reconstruction using sabkha type gypsum bearing deposits of parnaiba basin northern brazil abstract extreme aridity during late permian early triassic period was the main factor for resetting the entire paleoclimate of the planet permian evaporite basins and lacustrine red beds were widely distributed along the supercontinent of pangea sulphate deposits in western pangea particularly in northern brazil accumulated in an extensive playa lake system outcrop based facies and stratigraphic analysis of up to 20 m thick evaporite siliciclastic deposits reveal the predominance of laminated reddish mudstone with subordinate limestone marl and lenses of gypsum the succession was deposited in shallow lacustrine and inland sabkha environments associated with saline pans and mudflats gypsum deposits comprise six lithofacies 1 bottom growth gypsum 2 nodular micronodular gypsum 3 mosaic gypsum 4 fibrous prismatic gypsum 5 alabastrine gypsum and 6 rosettes of gypsum gypsum types 1 and 2 are interpreted as primary deposition in saline pans bottom growth gypsum forms grass like crusts while nodular micronodular gypsum indicates displacive precipitation of the crust in shallow water and the groundwater capillary zone types 3 and 4 are early diagenetic precipitates abundant inclusions of tiny lath like anhydrite crystals suggest a primary origin of anhydrite alabastrine gypsum fibrous gypsum satinspar and rosettes of gypsum probably derived from near surface hydration of anhydrite the gypsum bearing deposits in the parnaiba basin contribute towards understanding paleogeographic changes in western pangea a progressive uplift of east pangea culminated in the forced regression and retreat of epicontinental seas to the west restricted seas or large lakes were formed before the definitive onset of desert conditions in pangea leading to the development of extensive ergs

a new present day temperature parameterization for greenland near surface air temperature 2 m over the greenland ice sheet gris is parameterized using data from automatic weather stations located on land and on the ice sheet the parameterization is expressed in terms of mean annual temperatures and mean july temperatures both depending linearly on altitude latitude and longitude the temperature parameterization is compared to a previous study and is shown to be in better agreement with observations the temperature parameterization is tested in a positive degree day model to simulate the present 1996 2006 mean melt area extent of the gris the model accounts for firn warming rainfall and refreezing of meltwater with different degree day factors for ice and snow under warm and cold climate conditions the simulated melt area extent is found to have reasonable agreement with satellite derived observations

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

comparison of satellite thermochron and air temperatures at summit greenland during the winter of 2008 09 current trends show a rise in arctic surface and air temperatures including over the greenland ice sheet where rising temperatures will contribute to increased sea level rise through increased melt we aim to establish the uncertainties in using satellite derived surface temperature for measuring arctic surface temperature as satellite data are increasingly being used to assess temperature trends to accomplish this satellite derived surface temperature or land surface temperature lst must be validated and limitations of the satellite data must be assessed quantitatively during the 2008 09 boreal winter at summit greenland we employed data from standard us national oceanic and atmospheric administration noaa air temperature instruments button sized temperature sensors called thermochrons and the moderate resolution imaging spectroradiometer modis satellite instrument to 1 assess the accuracy and utility of thermochrons in an ice sheet environment and 2 compare modis derived lsts with thermochron derived surface and air temperatures the thermochron derived air temperatures were very accurate within 0 1 0 3 c of the noaa derived air temperature but thermochron derived surface temperatures were 3 c higher than modis derived lsts though surface temperature is largely determined by air temperature these variables can differ significantly furthermore we show that the winter time mean air temperature adjusted to surface temperature was 11 c higher than the winter time mean modis derived lst this marked difference occurs largely because satellite derived lsts cannot be measured through cloud cover so caution must be exercised in using time series of satellite lst data to study seasonal temperature trends

reactive transport modeling of early burial dolomitization of carbonate platforms by geothermal convection reactive transport models rtms permit quantitative investigation of diagenesis and its effects on reservoir quality the rtm toughreact is used to investigate diagenesis in an isolated platform driven by geothermal kohout convection of seawater which has been invoked to explain dolomitization during early burial previous short 0 1 m y rtm simulations suggested that convection can drive dolomitization mostly at greater than 50c and anhydritization but complete dolomitization requires greater than 30 60 m y our more extended rtm simulations 30 m y indicate significant nonlinearities in the system consistent with high temperature experiments with parts of the platform completely dolomitized within 10 15 m y as dolomitization proceeds the process becomes predominantly flux controlled with development of a wedge shaped dolomite body which thins from the margin to the interior at considerably shallower depth and cooler temperatures 20 30c than suggested by short simulations dolomitization is relatively insensitive to boundary conditions such as relative sea level and platform geometry but is significantly slower in circular than elongate platforms sediment permeability and reactive surface area commonly inversely related are key controls dolomitization is limited to the margin of low permeability muddy platforms despite a high reactive surface area dolomitization of more permeable grainy platforms is limited by a lower reactive surface area occurring only in the platform core due to widespread cooling sedimentary layering produces a complex diagenetic stratigraphy dolomitization favoring more reactive beds at shallow depth where permeability is not limiting but switching to more permeable beds at depth bank marginal fracturing limits dolomitization of the platform interior whether the fractures are baffles or conduits for flow

measurements of p and s wave fronts from the dense three dimensional array at garni armenia the p and s wave arrivals from local earthquakes were studied using an array of 10 three component instruments in and around a tunnel at garni observatory armenia the array has a three dimensional configuration with lateral dimensions of 300 to 500 m and a depth extent of 100 m estimates of the horizontal and vertical components of slowness for p and s wave fronts were used to determine the angles of approach and the propagation velocity the results showed that the region around the array has low average velocities for both the p 1 43 km sec and s 0 61 km sec waves so wave fronts approach the array at steep angles of incidence waveforms from one event show clear reflections from the free surface for both p and s waves the timing of these reflections gives the velocity variation with depth within the array we estimated a p velocity of 0 33 km sec within a few meters of the surface increasing to several kilometers per second for the deepest portion of the array local site variations can greatly complicate the high frequency waveforms even for tunnel stations in bedrock the s waves exhibit stronger site dependent waveforms and time delays than do the p waves

observations of high frequency scattered waves using dense arrays at teide volcano abstract a study of the seismic coda of seven small earthquakes recorded on the teide volcano canary islands spain was carried out using a temporary small aperture 12 station seismic array the purpose was to measure backazimuth apparent velocity and the type of waves that compose the coda in the frequency range 4 to 6 hz we used the zero lag cross correlation zlc method to obtain the components of the wave vector and three component analysis techniques based on the covariance matrix of the signal in the time domain to investigate the polarization properties of the signals the results show that a great part of the coda signals in the analyzed frequency range are almost uncorrelated while a low number of isolated correlated arrivals show an apparent slowness between 2 10 3 and 2 5 10 4 sec m and an almost random distribution of backazimuths the correlated arrivals have been interpreted as generated by strong scatterers probably related to the presence in the study area of surface topography irregularities the volcanic cone and the caldera rim the wave type varies from pure s type waves to mixed surface waves with some rayleigh components

microbial biomass a catalyst for caco3 precipitation in advection dominated transport regimes microorganisms have long been thought to impact caco3 precipitation but determining the extent of their influence on sediment formation has been hampered by our inability to obtain direct experimental evidence about mineral formation processes in natural environments we address this problem by conducting kinetic experiments within a modern terrestrial carbonate spring to determine aragonite precipitation rates and to quantify the relative influences of aragonite saturation state a microbial biomass concentration and microbial viability on caco3 mineralization in advection dominated transport regimes at an a value consistent with modern seawater 3 63 0 09 our controlled in situ kinetic experiments show that 1 the natural steady state aragonite precipitation rate is more than twice that determined when microbial biomass on the aragonite mineral surface is depleted by 0 2 m filtration and 2 inhibiting microbial viability with ultraviolet uv irradiation has no significant effect on the mean precipitation rate furthermore our modeling of the caco3 precipitation process which uses the empirical crystal growth rate expression and additional in situ kinetic measurements reveals that reducing biomass concentrations by 45 can decrease the empirical rate constant by more than an order of magnitude these findings strongly suggest that microorganisms catalyze caco3 precipitation in advection dominated systems and imply that changes in carbonate mineralization rates may have resulted from changes in local microbial biomass concentration throughout geologic history

freshwater forcing of abrupt climate change during the last glaciation large millennial scale fluctuations of the southern margin of the north american laurentide ice sheet occurred during the last deglaciation when the margin was located between about 43 and 49 n fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the north atlantic by rerouting continental runoff from the mississippi river drainage to the hudson or st lawrence rivers we found that periods of increased freshwater flow to the north atlantic occurred at the same time as reductions in the formation of north atlantic deep water thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume