geochemical and textural evidence for early shallow diagenetic growth of stratigraphically confined carbonate concretions upper devonian rhinestreet black shale western new york laterally persistent carbonate concretionary horizons are conspicuous to the upper devonian frasnian rhinestreet black shale of the western new york state appalachian plateau field observations including randomly tilted concretions and differential compaction of host sediment laminae around concretions are consistent with early diagenetic growth in unconsolidated sediment further estimates of pre cementation host sediment porosity based on the volume percentage of caco3 cement 74 93 and perhaps most importantly the preservation of a cardhouse clay fabric in mudstones collected from concretion pressure shadow regions suggest that concretionary growth occurred rapidly within perhaps a meter of the seafloor petrographic examination sem of matrix carbonate samples collected from six concretions reveals a relatively porous 4 7 framework of calcite micrite and microsparite euhedral pyrite most abundant near concretion rims disseminated pyrite framboids and randomly oriented detrital clay platelets and domains c isotopic compositions of rhinestreet concretion matrix carbonate range from 13 9 to 1 7 pdb suggesting derivation of c from a mixed source that included depleted and isotopically heavy c slightly to moderately depleted o isotopic compositions 3 8 to 6 8 pdb do not corroborate the shallow depth of concretion growth suggested by field and textural observations the vertically confined nature of most rhinestreet concretions their large size oblate ellipsoidal shape variable c isotope compositions and absence of any evidence that concretions were sited at local concentrations of organic matter suggest an origin by anaerobic ch4 oxidation early pre concretion sulfate reduction and associated pyrite framboid formation that occurred throughout the host sediment was renewed in thin shallow zones of uncompacted sediment the concretionary horizons by ch4 and isotopically heavy dissolved carbonate diffusing upward from the zone of biogenic methanogenesis to the base of the sulfate reduction zone probably little more than a meter below the seabed local variations in the mix of isotopically light ch4 and heavier dissolved carbonate may have been responsible for the wide range of 13c isotopic compositions of rhinestreet concretions crucial to this mechanism is a pause in deposition that would have held the zone of carbonate precipitation at a fixed distance below the ocean floor long enough for the large concretions to grow evidence that sedimentation slowed or even stopped during concretion growth includes 1 laminae that can be traced through concretions with no observed systematic changes in thickness and 2 minimal concretion center to edge variations in estimated pre cementation porosity a resumption of sedimentation and related burial brought concretion growth in each horizon to an end the moderately depleted 18o values of rhinestreet concretions probably reflect the resetting of o isotopic compositions by warm fluids migrating through the permeable concretions during burial

stable carbon and oxygen isotope evidence of cretaceous sea level fluctuations recorded in septarian concretions from pueblo colorado u s a abstract limestone concretions in the blue hill member of the carlile formation middle middle turonian exposed in the lake pueblo state park colorado u s a range in size from 20 cm diameter approximately spherical forms to flattened spheroids 2 m in width and 1 m in height the earliest matrix and septarian calcite cement with 13c and 18o values ranging mostly from 18o oo to 8o oo pdb and 3o oo to 8o oo pdb respectively precipitated from diluted seawater during shallow burial where sulfate reduction largely controlled pore water bicarbonate composition in contrast the latest septarian cements exhibit very depleted 18o values 16o oo with 13c values approaching values of 1o oo to 3o oo reflecting a strong meteoric water component to pore fluids overall 13c and 18o values are inversely covariant concretion matrix calcite and septarian cements precipitated from mixtures of modified marine and meteoric fluids pore water reversals resulted from sea level fluctuations leading up to and associated with the formation of a sequence boundary or possibly the development of parasequences near the top of the blue hill member relative sea level falls caused pore water freshening as the coastal mixing zone migrated seaward similarly modified marine derived pore waters replaced fresher pore fluids accompanying subsequent marine flooding carbonate cements precipitated during this active hydrologic history recorded the isotopic characteristics of their parent fluids negative 18o values of the meteoric end member calcite compositions suggest derivation from high altitude precipitation in the sevier highlands to the west septarian cements in concretions despite their enclosure in relatively impermeable host sediment can act as sensitive indicators of relative sea level fluctuations

effects of grand cycle cessation on the diagenesis of upper cambrian carbonate deposits in the southern appalachians u s a abstract the vertical transition from the mainly subtidal alternating shale and carbonate units or grand cycles of the conasauga group middle to upper cambrian to the peritidal dolostone of the knox group upper cambrian to lower ordovician marks a major change in the early paleozoic passive margin sedimentation of the southern appalachians the grand cycles represent an interplay between intrashelf shale basin and carbonate platform deposition the end of grand cycle deposition occurred in response to carbonate platform progradation over the infilled intrashelf basin and is associated with a prominent change in diagenetic patterns observed in the uppermost conasauga group strata the maynardville formation the maynardville records upward shallowing from subtidal shale and limestone into peritidal dolostone this change from a subtidal into a peritidal depositional regime influenced the early diagenesis of the maynardville and in conjunction with the changes in the regional facies distribution at the end of grand cycle deposition extended its influence upon the burial diagenesis of these deposits the subtidal deposits of the maynardville contain a variety of calcite cements dolomite is not abundant in these deposits where it occurs mainly as a fine crystalline ferroan phase associated with argillaceous layers and pressure dissolution features the local source for this dolomite during burial was provided by expulsion of pore fluids from interbedded shale deposits diagenesis of clay minerals and pressure dissolution of carbonates ferruginous coatings on hardgrounds in the subtidal deposits provided an additional local source of iron for the formation of replacement saddle dolomite the subtidal deposits also contain saddle dolomite cement associated with mississippi valley type mvt minerals which indicate the involvement of externally derived fluids during late burial diagenesis of these strata the peritidal deposits on the other hand are extensively dolomitized fine crystalline dolomite most likely represents early diagenetic replacement of tidal flat carbonate sediment coarse crystalline replacement dolomite formed during burial by recrystallization of early dolomite and dolomitization by warm burial brines fenestrae desiccation cracks and evaporite dissolution voids are occluded with dolomite cement which is commonly complexly zoned zoned dolomite precipitated during shallow to intermediate burial and is postdated by saddle dolomite cement saddle dolomite in pore centers dissolutional voids and tectonic fractures formed during late burial from warm fluids associated with the migration of mvt brines the effects of changes in the depositional setting on diagenesis are reflected in similar early diagenesis between the subtidal maynardville and the underlying conasauga group carbonate deposits and between the peritidal deposits of the upper maynardville and the rest of the overlying knox group the depositional environments and early diagenesis also affected the burial diagenesis the changes in regional facies distribution caused by carbonate platform progradation at the end of grand cycle deposition resulted in a decrease in the proportion of siliciclastic components this decrease was accompanied by a decline in the amount of ferroan carbonate in the peritidal deposits the maynardville is conformably overlain by carbonate deposits of the knox group this allowed the maynardville knox succession to behave as a single hydrologic unit for the migration of burial fluids in response to the formation of the ordovician foreland sevier basin to the southeast during the conversion from a passive into a convergent continental margin the nolichucky shale separates the maynardville knox succession from the carbonate deposits of the underlying conasauga group which were in contrast affected by the migration of burial fluids from the cambrian intrashelf shale basin to the west

constraining pathways of microbial mediation for carbonate concretions of the miocene monterey formation using carbonate associated sulfate abstract carbonate concretions can form as a result of organic matter degradation within sediments however the ability to determine specific processes and timing relationships to particular concretions has remained elusive previously employed proxies e g carbon and oxygen isotopes cannot uniquely distinguish among diagenetic alkalinity sources generated by microbial oxidation of organic matter using oxygen nitrate metal oxides and sulfate as electron acceptors in addition to degradation by thermal decarboxylation here we employ concentrations of carbonate associated sulfate cas and 34scas along with more traditional approaches to determine the specific nature of concretion authigenesis within the miocene monterey formation integrated geochemical analyses reveal that at least three specific organo diagenetic reaction pathways can be tied to concretion formation and that these reactions are largely sample site specific one calcitic concretion from the phosphatic shale member at naples beach yields 34scas values near miocene seawater sulfate 22 vcdt abundant cas ca 1000 ppm depleted 13ccarb 11 vpdb and very low concentrations of fe ca 700 ppm and mn ca 15 ppm characteristics most consistent with shallow formation in association with organic matter degradation by nitrate iron oxides and or minor sulfate reduction cemented concretionary layers of the phosphatic shale member at shell beach display elevated 34scas up to 37 cas concentrations of 600 ppm mildly depleted 13ccarb 6 moderate amounts of mn ca 250 ppm and relatively low fe ca 1700 ppm indicative of formation in sediments dominated by sulfate reduction finally concretions within a siliceous host at montana de oro and naples beach show minimal cas concentrations positive 13c values and the highest concentrations of fe ca 11 300 ppm and mn ca 440 ppm consistent with formation in sediments experiencing methanogenesis in a highly reducing environment this study highlights the promise in combining cas analysis with more traditional techniques to differentiate among diagenetic reactions as preserved in the geologic record and shows potential for unraveling subsurface biospheric processes in ancient samples with a high degree of specificity

carbon oxygen and sulphur isotope variations in concretions from the upper lias of n e england carbon oxygen and sulphur isotope data for transects across two pyrite bearmg carbonate concretions and their host sediments from the upper lias of n e england show symmetrical zonation 13cpdb values of the calcite cement 12 9 to 15 4 indicate that most of it originated from organic matter by bacterial reduction of sulphate augmented with marine and to a lesser extent fermentation derived carbonate organic carbon 13cpdb 26 1 to 37 0 reflects the admixture of allochtho nous terrestrial organic matter with marine material and the selective preservation of isotopically light organic material through microbiological degradation two phases of pyrite are present in each concretion the earlier framboidal pyrite formed throughout the sediment prior to concretionary growth and has 34scd values of 22 to 26 indicating formation by open system sulphate reduction the later euhedral phase is more abundant and reaches values of 2 5 to 5 5 at concretion margins this phase of sulphate reduction provided the carbonate source for concretionary growth and occurred in a partially closed system the 13c and 34s data are consistent with mineralogical and chemical evidence which suggest that both concretions formed close to the sediment surface the 18o values of the calcite in one concretion 18opdb 2 3 to 4 8 indicate precipitation in pore waters whose temperature and isotopic composition was close to that of overlying seawater the other concretion is isotopically much lighter 18opdb 8 9 to 9 9 and large 18o differences between concretions in closely spaced horizons imply that local factors control the isotopic composition of pore waters

field relationships and stable isotope geochemistry of concretions from james ross island antarctica abstract early diagenetic precompactional concretions are abundant throughout the cretaceous tertiary marambio group larsen basin antarctica four distinct concretion types are recognised 1 spherical subspherical concretions 2 sheet concretions 3 fossil nucleated concretions and 4 concretionary burrow networks all concretion types have a micritic to microsparry variably non ferroan to ferroan calcite cement stable isotope analyses show a wide spread in both 18o and 13c 13c values are typically negative ranging between 3 38 and 39 15 o pdb usually 16 to 230 18o ranges between 1 28 and 13 81 pdb with most of the values between 5 and 10 the 13c signature is interpreted to represent carbon sourced from sulphate reduction and or methane oxidation with minor input from shell dissolution and is consistent with a shallow burial early diagenetic origin a single mudstone hosted concretion has a 18o composition indicative of precipitation of carbonate from seawater the low 18o signatures in the sandstone and siltstone hosted concretions are possibly due to early diagenetic modification of the pore water composition through volcaniclastic mineral dissolution reprecipitation reactions and perhaps through input of meteoric water concretion distribution is related to a changes in sedimentation rate and b the dominance of diffusion on concretion cementation

another look at downslope windstorms part i the development of analogs to supercritical flow in an infinitely deep continuously stratified fluid abstract numerical simulations are conducted to examine the role played by different amplification mechanisms in the development of large amplitude mountain waves it is shown that when the static stability has a two layer structure the nonlinear response can differ significantly from the solution to the equivalent linear problem when the parameter nh u is as small as 0 3 in the cases where the nonlinear waves are much larger than their linear counterparts the highest stability is found in the lower layer and the flow resembles a hydraulic jump simulations of the 11 january 1972 boulder windstorm are presented which suggest that the transition to supercritical flow forced by the presence of a low level inversion plays an essential role in triggering the windstorm the similarities between breaking waves and nonbreaking waves which undergo a transition to supercritical flow are discussed

petrographic and sims pyrite sulfur isotope analyses of ediacaran chert nodules implications for microbial processes in pyrite rim formation silicification and exceptional fossil preservation abstract the lower ediacaran doushantuo formation in the yangtze gorges area contains exceptionally preserved microfossils including the earliest known animal resting eggs and embryos these fossils are preserved in cm sized chert nodules which typically have a microbial mat fragment in the center a silica cortex a pyrite rim and an outer rim of blocky calcite petrographic analysis indicates that the formation of the blocky calcite rim postdates that of the pyrite rim and silica cortex the pyrite rim grew centripetally during early diagenesis representing a reaction front that was determined by the dynamics between ambient fe2 and h2s the latter of which was derived from bacterial sulfate reduction bsr of mat fragment in nodule center the silica cortex was formed pervasively through replacement of carbonate sediments prior to compaction secondary ion mass spectroscopy sims sulfur isotopes of individual pyrite crystals 34spy sims in pyrite rims and matrices show highly positive values 15 2 39 8 the pyrite rims do not show an isotopic gradient between small crystals formed in outer rim during early diagenesis and large crystals formed in inner rim during subsequent overgrowth although rim pyrite in the same chert nodule has consistent 34spy sims values there are significant spatial and stratigraphic variations in 34spy sims values of both matrix and rim pyrite overall isotopic fractionation between pyrite and carbonate associated sulfate cas is small

deciphering the impact of diagenesis overprint on negative δ13c excursions using rock magnetism case study of ediacaran carbonates yangjiaping section south china rock magnetism is used here to investigate the genesis of one of the puzzling negative carbon isotopic excursions of the neoproterozoic in the yangtze platform south china a detailed characterization of the magnetic mineralogy which includes low temperature and high field magnetometry and classical magnetic measurement arm irm susceptibility was therefore performed along upper doushantuo and lower dengying formations outcropping in the yangjiaping section the derived magnetic parameters show variations that can be interpreted as variations in magnetic grains size and in oxide contents they show that the magnetic content is significantly reduced in samples presenting negative 13ccalcite values we interpret this as a result of magnetite dissolution and secondary carbonate precipitation during early diagenesis bacterial sulfate reduction combined with c and o isotopic data paleomagnetic techniques thus show that the upper doushantuo lower dengying negative excursion of the yangjiaping section is largely due to diagenesis although the preservation of a genuine 13c excursion of lower magnitude from 7 down to 0 instead of down to 9 as usually considered cannot be ruled out a corrected 13ccarbonate chemostratigraphic curve is therefore proposed the unambiguous identification of a strong diagenetic component for this excursion casts doubts on the primary nature of other potentially time equivalent negative excursions of the yangtze platform and thus to its correlation to negative excursions in other cratons i e shuram excursion more generally this study illustrates the potential of magnetic mineralogy characterization a low cost time efficient and non destructive technique as screening tool for diagenetic overprints of 13c and 18o

spatial resolution of time reversal arrays in shallow water a series of time reversal experiments was performed in shallow water including a range dependent slope environment time reversal arrays implemented with center frequencies of 445 and 3500 hz achieved sharp focal regions up to ranges of 30 and 13 km respectively in 110 130 m shallow water in this paper resolution expressions are derived using an image method to describe the focal sizes achieved with time reversal arrays in various ocean environments analysis for the measured data indicates that the focal size approaches the diffraction limit of an array for given waveguide conditions i e waveguide geometry and attenuation the measured focal size has implications for the maximum achievable resolution of linear matched field processing which is a computational implementation of the time reversal process

seismic fault zone trapped noise systematic velocity contrasts across and within fault zones can lead to head and trapped waves that provide direct information on structural units that are important for many aspects of earthquake and fault mechanics here we construct trapped waves from the scattered seismic wavefield recorded by a fault zone array the frequency dependent interaction between the ambient wavefield and the fault zone environment is studied using properties of the noise correlation field a critical frequency fc 0 5 hz defines a threshold above which the in fault scattered wavefield has increased isotropy and coherency compared to the ambient noise the increased randomization of in fault propagation directions produces a wavefield that is trapped in a waveguide cavity like structure associated with the low velocity damage zone dense spatial sampling allows the resolution of a near field focal spot which emerges from the superposition of a collapsing time reversed wavefront the shape of the focal spot depends on local medium properties and a focal spot based fault normal distribution of wave speeds indicates a 50 velocity reduction consistent with estimates from a far field travel time inversion the arrival time pattern of a synthetic correlation field can be tuned to match properties of an observed pattern providing a noise based imaging tool that can complement analyses of trapped ballistic waves the results can have wide applicability for investigating the internal properties of fault damage zones because mechanisms controlling the emergence of trapped noise have less limitations compared to trapped ballistic waves

fluid flow methane fluxes carbonate precipitation and biogeochemical turnover in gas hydrate bearing sediments at hydrate ridge cascadia margin numerical modeling and mass balances a numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate bearing surface sediments from a cold vent site situated at hydrate ridge an accretionary structure located in the cascadia margin subduction zone steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below the model results underline the dominance of advective fluid flow that forces a large inflow of methane from below 869 mumol cm 2 a 1 inducing high oxidation rates in the surface layers anaerobic methane oxidation is the major process proceeding at a depth integrated rate of 870 mumol cm 2 a 1 a significant fraction 14 of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite the total rate of carbonate precipitation 120 mumol cm 2 a 1 allows for the build up of a massive carbonate layer with a thickness of i m over a period of 20 000 years aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane charge fluids is high enough greater than or equal to10 cm a 1 to maintain super saturation with respect to this highly soluble carbonate phase it precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments suggesting microbial catalysis the investigated station is characterized by high carbon and oxygen turnover rates approximate to1000 mumol cm 2 a 1 that are well beyond the rates observed at other continental slope sites not affected by fluid venting this underlines the strong impact of fluid venting on the benthic system even though the flow velocity of 10 cm a 1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites non steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow moreover they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities 80 cm a 1 only at flow rates exceeding approximately 100 cm a 1 does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol ch4 cm 2 a 1 into the overlying bottom water

the structure of raylike arrivals in a shallow water waveguide acoustic remote sensing of the oceans requires a detailed understanding of the acoustic forward problem the results of a shallow water transmission experiment between a vertical array of sources and a vertical array of receivers are reported the source array is used to provide additional degrees of freedom to isolate and track raylike arrivals by beamforming over both source and receiver arrays the coordinated source receiver array processing procedure is presented and its effectiveness in an example of tracking raylike arrivals in a fluctuating ocean environment is shown many of these arrivals can be tracked over an hour or more and show slowly varying amplitude and phase the use of a double beamforming algorithm lays the foundation for shallow water acoustic remote sensing using travel time and source and receive angles of selected eigenrays

the diagenetic history of some septarian concretions from the kimmeridge clay england abstract large septarian concretions from the kimmeridge clay up to 1 2 m in diameter have centres comprising anhedral calcite microspar passing into margins of radiating fibrous calcite microspar with a pyrite rich zone at the transition septarian veins formed and were lined with brown calcite synchronously with fibrous matrix growth with white calcite precipitated in septarian cavities after concretion growth ceased septarian veins filled only with white calcite formed later at the same time as the outermost calcite microspar crystals were enlarged the concretions were buried in the late jurassic to about 130 m and in the late cretaceous to about 550 m with uplift between oxygen isotopes show that the concretion grew throughout the first burial with septarian veins forming from about 30 m depth onwards later septarian veins formed between about 200 and 500 m during the second burial carbon isotopes show that the compact inner matrix grew in the sulphate reduction zone the end of which is marked by the pyrite enriched zone dissolving shells and possibly minor methanogenic carbonate slowly diluted sulphate reduction zone carbonate during deeper burial during early concretion growth mg and sr were depleted in the pore water during later stages of the first burial mg sr mn and fe all increased especially after concretion growth ceased during the second burial fe mn and mg decreased as calcite precipitated implying relatively closed systems for these elements synchronous formation of septarian fractures and fibrous calcite matrix shows that the kimmeridge clay became overpressured during the later stages of both burials

turning point filters analysis of sound propagation on a gyre scale acoustic transmissions from pioneer seamount off california to a vertical array near hawaii are analyzed using a technique which we call a turning point filter the observables travel time and axial inclination are interpreted in terms of the ocean sound speed field the method permits a uniform treatment of the arrival pattern from the early ray like arrivals to the late mode like arrivals including peak arrivals which cannot be identified as either rays or modes an adiabatic range dependence is assumed and wentzel kramers brillouin jeffreys formalism is applied

using a time based subarray method to extract and invert noise derived body waves at long beach california the reconstruction of body waves from the cross correlation of random wavefields has recently emerged as a promising approach to probe the fine scale structure of the earth however because of the nature of the ambient noise field the retrieval of body waves from seismic noise recordings is highly challenging and has only been successful in a few cases here we use seismic noise data from a 5 200 node oil company survey to reconstruct body waves and determine the velocity structure beneath long beach california to isolate the body wave energy from the ambient noise field we divide the entire survey into small aperture subarrays and apply a modified double beamforming scheme to enhance coherent arrivals within the cross correlated waveforms the resulting beamed traces allow us to identify clear refracted p waves traveling between different subarray pairs which we then use to construct a high resolution 3d velocity model of the region the inverted velocity model reveals velocity variations of the order of 3 and strong lateral discontinuities caused by the presence of sharp geologic structures such as the newport inglewood fault nif additionally we show that the resolution that is achieved through the use of high frequency body waves allows us to illuminate small geometric variations of the nif that were previously unresolved with traditional passive imaging methods

coupled fe and s isotope variations in pyrite nodules from archean shale ron and sulfur isotope compositions recorded in ancient rocks and minerals such as pyrite fes2 have been widely used as a proxy for early microbial metabolisms and redox evolution of the oceans however most previous studies focused on only one of these isotopic systems herein we illustrate the importance of in situ and coupled study of fe and s isotopes on two pyrite nodules in a c 2 7 ga shale from the bubi greenstone belt zimbabwe fe and s isotope compositions were measured both by bulk sample mass spectrometry techniques and by ion microprobe in situ methods secondary ion mass spectrometry sims spatially resolved analysis across the nodules shows a large range of variations at micrometer scale for both fe and s isotope compositions with 56 fe and 34 s values from 2 1 to 0 7 and from 0 5 to 8 2 respectively and 33 s values from 1 6 to 2 9 the fe and s isotope variations in these nodules cannot be explained by tandem operation of dissimilatory iron reduction dir and bacterial sulfate reduction bsr as was previously proposed but rather they reflect the contributions of different fe and s sources during a complex diagenetic history pyrite formed from two different mineral precursors 1 mackinawite precipitated in the water column and 2 greigite formed in the sediment during early diagenesis the in situ analytical approach reveals a complex history of the pyrite nodule growth and allows us to better constrain environmental conditions during the archean

petrography and geochemistry of floodplain limestones from the clarks fork basin wyoming u s a carbonate deposition and fossil accumulation on a paleocene eocene floodplain abstract floodplain limestones are increasingly important sources of fossil vertebrates from the clarks fork basin the northern extension of wyoming s bighorn basin despite their importance for understanding paleogene floodplain faunas little work has addressed the depositional history of these carbonates or evaluated potential taphonomic biases affecting the assemblages they produce recent studies of bighorn basin paleosols have increased our understanding of parameters affecting the paleo floodplain and large collections of limestones now exist this has allowed detailed investigation of limestone petrography and geochemistry and the proposal of a new model for their formation floodplain limestones record a complex depositional and diagenetic history precipitation of micritic low mg calcite and accumulation of bone occurred in low energy ponded water at the earth s surface pedogenic overprinting obscured primary textures and produced diagenetic grainstones packstones and wackestones biological and chemical pedogenic processes formed most carbonate allochems including micrite grains and calcified plant cells microbial fermentation occurred at shallow burial depths and methane production migration and oxidation affected the carbon isotope composition of diagenetic carbonate and primary micrite pore space was fully occluded by phreatic calcite cements during late stage diagenesis fossil assemblages contained within the limestones likely represent fauna derived from rarely sampled floodplain microenvironments hydraulic transport of bones was minimal accumulation of fossil material occurred episodically and bones were rapidly encased in micrite the uncommon body size distribution characteristic of limestone faunas is attributed in part to buffering of chemical and physical processes normally effecting bone decomposition during surface exposure and pedogenesis

timelapse ultrasonic tomography for measuring damage localization in geomechanics laboratory tests variation of mechanical properties in materials can be detected non destructively using ultrasonic measurements in particular changes in elastic wave velocity can occur due to damage i e micro cracking and particles debonding here the challenge of characterizing damage in geomaterials i e rocks and soils is addressed geomaterials are naturally heterogeneous media in which the deformation can localize so that few measurements of acoustic velocity across the sample are not sufficient to capture the heterogeneities therefore an ultrasonic tomography procedure has been implemented to map the spatial and temporal variations in propagation velocity which provides information on the damage process moreover double beamforming has been successfully applied to identify and isolate multiple arrivals that are caused by strong heterogeneities natural or induced by the deformation process the applicability of the developed experimental technique to laboratory geomechanics testing is illustrated using data acquired on a sample of natural rock before and after being deformed under triaxial compression the approach is then validated and extended to time lapse monitoring using data acquired during plane strain compression of a sample including a well defined layer with different mechanical properties than the matrix

an investigation of boundary forcing sensitivities in a regional climate model the sensitivity of a regional climate model to lateral upper and lower dynamical forcing is evaluated for a pan arctic domain the experiments focus on a month long case study of may 1990 but the results are shown to be extendable to january and july 1990 although the control simulation is found to adequately represent major tropospheric circulation features a large negative geopotential height bias of up to 700m is found at the upper levels of the model experiments find these biases are remedied through the replacement of a reflective rigid lid upper boundary condition with a local wave absorbing layer geopotential height biases are reduced to a maximum underestimation of only 50m at the upper boundary substantial improvement is also found in the simulated temperature and zonal wind profiles transient heat and momentum fluxes and stationary eddies as seen through the eliassen palm flux divergence with this wave absorbing upper boundary condition in place additional improvement is found using a gravity wave drag parameterization appropriate for this domain s 100km horizontal resolution additional sensitivity to lateral forcing is examined and the relative role of the upper boundary condition to skillful simulations within the arctic basin domain is discussed

early diagenesis and its relationship to depositional environment and relative sea level fluctuations upper cretaceous marshybank formation alberta and british columbia early diagenesis of the upper cretaceous late coniacian to early santonian marshybank formation was controlled by depositional environment composition of depositional water fe and organic content of the sediment sedimentation rate proximity to the shoreline and influx of meteoric water related to relative sea level fall five depositional environments each characterized by a distinct early diagenetic mineral assemblage have been recognized offshore shelf sediments that were deposited in a dysaerobic environment are characterized by abundant framboidal pyrite and rare septarian concretions composed of early calcite and siderite intense sulphate reduction promoted by the dysaerobic depositional water was the primary influence on early diagenesis offshore shelf sediments deposited under aerobic conditions are characterized by abundant concretions composed of two generations of siderite s1 and s2 in this environment methanogenesis rather than sulphate reduction was more important early diagenesis of the inner shelf sands was generally limited however in sands deposited proximal to the shoreline mixing of marine and meteoric waters promoted crystallization of fe rich chlorite and siderite the shoreface was characterized by dissolution of detrital minerals in the upper portion and precipitation of kaolinite or illite smectite in the lower portion in the coastal plain environment brackish water and early reducing conditions resulted in formation of abundant euhedral pyrite ankerite rather than siderite is the typical early diagenetic carbonate the 18o values of the earliest cements i e early calcite siderite s1 inner shelf siderite indicate crystallization from a low 18o marine derived porewater assuming crystallization at 25 c a 18o value of about 7 smow can be estimated for the seaway during marshybank formation time similar calculations for the overlying dowling member puskwaskau formation suggest that the 18o value of the seaway increased to about 4 smow consistent with its transgressive nature very low 18o values are exhibited by siderite s2 these results indicate crystallization during intermediate diagenesis 60 c from meteoric water 15 smow that entered the marshybank formation during sea level lowstand

material flux and porosity changes during sediment diagenesis understanding the changes in porosity that occur during burial of sediments is of importance both in modelling fluid flow in sedimentary basins and for prediction of petroleum reservoir quality when deposited up to 50 of the volume of sands is intergranular pore space porosity generally decreases with depth because of compaction and precipitation of diagenetic minerals but some sandstones retain an anomalously high porosity whether this is due to dissolution and removal of material or to its local redistribution is not clear we originally intended to quantify losses of major chemical components during burial of a complete sedimentary unit we have investigated ten reservoir sandstones of permian to tertiary age from oilfields worldwide these show consistent results and here we present detailed data from four of them we found that the silica content of these sandstones actually increased by 220 to 350 kg m 3 following compaction no statistically significant changes were observed for aluminium potassium or sodium the flux of silica cannot be modelled satisfactorily using currently accepted values of permeability silica solubility and flow rates posing a challenge for existing models of fluid flow and ore emplacement

the origin of late spar cements in the lincolnshire limestone jurassic of central england the carbon and oxygen isotopic compositions of the lincolnshire limestone bajocian of the east midlands are shown to be determined largely by two end member components marine precipitates and later sparry burial cements the origin of major quantities of such burial cement is controversial the extreme possibilities ranging from calcite precipitation from meteoric groundwaters to precipitation from highly saline brines with contrasting flow regimes this study demonstrates how formation wide sampling and mapping of stable isotopic compositions of burial cements from the lincolnshire limestone combined with a detailed knowledge of its burial history and associated thermal evolution can be employed to distinguish the influence of different water types two 9provinces9 are differentiated with respect to the stable isotopic compositions of the latest volumetrically most significant ferroan burial cements 1 a 9southern province9 associated with thinning of the limestone shallower depths of maximum burial approx 300 m and light 18 o and i3 c cement compositions 2 a 9central province9 associated with deeper burial approx 550 m but less 18 o and 13 c depleted cement compositions the relative isotopic depletion of the southern province ferroan burial cements is considered to be a function of their precipitation from meteoric waters with a depleted i8 o signature relative to seawater at temperatures of approximately 24 c 13 c depletion is tentatively ascribed to the persistence of 13 c depleted soil gas co 2 in the precipitating waters in the central province basinal waters of both meteoric and marine derivation are considered to have precipitated the late spar with associated up dip fluid movement at temperatures between 29 and 39 c 13 c depletion is believed to be controlled by the input of co 2 derived from thermal oxidation of organic matter

diagenetic evolution and porosity destruction of turbiditic hybrid arenites and siliciclastic sandstones of foreland basins evidence from the eocene hecho group pyrenees spain abstract this study aims to unravel the impact of diagenetic alterations on porosity loss of foreland basin turbiditic hybrid arenites and associated siliciclastic sandstones of the eocene hecho group south central pyrenees spain in this succession hybrid arenites and calclithites are extensively cemented by mesogenetic calcite cement 18ovpdb 10 0 to 5 8 th mode 80 c salinity mode 18 8 wt eq nacl fe dolomite 18ovpdb 8 5 to 6 3 and trace amounts of siderite the extent of carbonate cementation is interpreted to be related to the amounts of extrabasinal and intrabasinal carbonate grains which provided nuclei and sources for the precipitation and growth of carbonate cements other diagenetic alterations such as pyrite and albitization had no impact on reservoir quality scarce early diagenetic cements coupled with abundant ductile carbonate and siliciclastic framework grains have led to rapid porosity loss owing to compaction conversely abundant quartz in the sandstones prevented rapid loss of porosity by mechanical compaction reservoir quality was affected by mesogenetic cementation by quartz overgrowths calcite and dolomite intergranular pressure dissolution of quartz grains and formation of fracture filling calcite cement 18ov pdb values from 10 4 to 7 8 th temperatures of 150 c which are attributed to deep circulation of hot meteoric waters during extensional stages of tectonism the results of this study illustrate that diagenetic evolution pathways of the arenites and sandstones are closely linked to the variation in detrital composition particularly the proportion and types of extrabasinal noncarbonates extrabasinal carbonates and intrabasinal carbonate grains these insights suggest that marine turbiditic hybrid arenites and calclithites of foreland basins are subjected to more rapid and extensive porosity loss owing to compaction and cementation than associated siliciclastic sandstones degradation of reservoir quality makes these hybrid arenites calclithites and sandstones suitable as tight gas reservoirs but only if fracture porosity and permeability develop during tectonic deformation

application of the coherent to incoherent intensity ratio to estimation of ocean surface roughness from high frequency shallow water propagation measurements for acoustic propagation through a shallow ocean channel or waveguide the coherence between different transmissions is controlled primarily by the roughness of the ocean surface and to a lesser degree by fluctuations in the volume in this study the coherent to incoherent intensity ratio ctir is defined as a way to quantify the coherence between multipath transmissions and ocean surface rms wave height and wind speed a theory that connects the ctir and the coherent surface reflection coefficient is developed using both kirchhoff and small slope approximations as rough surface scattering models the ctirs have been evaluated over a period of several days using broad band experimental results from shallow water deployment of source and receiver arrays that span most of the water column estimates of wind speed and rms wave height obtained using these ctir calculations are compared with environmental measurements to demonstrate the validity of the theory

upwelling on the continental slope of the alaskan beaufort sea storms ice and oceanographic response 1 the characteristics of pacific born storms that cause upwelling along the beaufort sea continental slope the oceanographic response and the modulation of the response due to sea ice are investigated in fall 2002 a mooring array located near 152w measured 11 significant upwelling events that brought warm and salty atlantic water to shallow depths when comparing the storms that caused these events to other aleutian lows that did not induce upwelling interesting trends emerged upwelling occurred most frequently when storms were located in a region near the eastern end of the aleutian island arc and alaskan peninsula not only were these storms deep but they generally had northward tending trajectories while the steering flow aloft aided this northward progression the occurrence of lee cyclogenesis due to the orography of alaska seems to play a role as well in expanding the meridional influence of the storms in late fall and early winter both the intensity and frequency of the upwelling diminished significantly at the array site it is argued that the reduction in amplitude was due to the onset of heavy pack ice while the decreased frequency was due to two different upper level atmospheric blocking patterns inhibiting the far field influence of the storms

anomalous geochemical signals from phosphatic middle cambrian rocks in the southern georgina basin australia middle cambrian rocks of the georgina basin contain both phosphatic and organic rich sediments the former often occurring as commercially viable phosphate deposits and the latter as minor oil shale occurrences both kinds of rocks occur in the hay river formation penetrated by bureau of mineral resources bmr stratigraphic corehole tobermory 14 detailed sampling and analysis of this core has been undertaken to assess the chemostratigraphy of the hay river formation to examine the possible use as a palaeoceanographic tool of changes in 13c values of carbonates and kerogens and to gain an understanding of phosphate deposition in this part of the basin the upper hay river formation was deposited in a normal marine environment characterized by oxic bottom conditions it contains several episodes of significant trace metal enrichment which appear to indicate periodic replacement of the water body the lower hay river formation however was deposited in an abnormal marine environment low in sulphate and mo and enriched in p its carbonate phase has positive 13c values 1 1 5 0 enriched over the accepted cambrian marine carbonate value of 0 57 0 17 0 the very low sulphate concentration mo depletion and spiking of carbonate 18o values suggests there was an influx of deeper ocean water of sufficient volume to maintain prolonged stable anoxic bottom waters these data support a previous suggestion that phosphogenesis in the georgina basin was related to oceanic anoxic events

body and surface wave reconstruction from seismic noise correlations between arrays at piton de la fournaise volcano body wave reconstruction from ambient seismic noise correlations is an important step toward improving volcano imaging and monitoring here we extract body and surface waves that propagate in piton de la fournaise volcano on la reunion island using ambient noise cross correlation and array processing techniques ambient noise was continuously recorded at three dense arrays each comprising 49 geophones to identify and enhance the green s function from the ambient noise correlation we apply a double beamforming dbf technique between the array pairs the dbf allows us to separate surface and body waves direct and reflected waves and multipathing waves based on their azimuths and slownesses we successfully extract body waves between all the combinations of arrays including the wave that propagates through the active magmatic system of the volcano additionally we identify the effects of uneven noise source distribution and interpret the surface wave reflections

spheroidal dolomites in a visean karst system bacterial induced origin spheroidal dolomite crystals occur in the karstified top of a dinantian dolomite sequence in eastern belgium the spheroidal dolomite crystals are best developed at the base of the karst system the dolomite crystals are characterized by a spherulitic or dumb bell inclusion pattern and are overgrown by dolomite cements with a rhombohedral outline they are considered to be bacterially related precipitates based on 1 textural similarities with documented bacteriogenic precipitates 2 the presence of bacterial microspheres and framboidal pyrite embedded within the dolomite and 3 their general geological setting the geochemical characteristics of the dolomites and associated minerals support a bacterial origin the ubiquity of framboidal pyrite depleted in 34s 34s 22 4 to 25 5 ocdt testifies to a period of bacterial sulphate reduction the isotopic composition of the spheroidal dolomites 13c 2 4 to 3 2 opdb and 18o 3 8 to 3 4 opdb suggest a contribution from oxidized organic carbon produced during bacterial sulphate reduction sulphate reduction may also result in a concomitant 18o depletion if the system is nearly closed it is however evident from the sulphur isotopic composition of associated framboidal pyrite that the system was fairly open the 18o depletion of the spheroidal dolomite crystals 18o 3 8 to 3 4 opdb and their occurrence adjacent to and within karst cavities suggests a mixing zone origin with a significant proportion of freshwater in it the rhombohedral cement overgrowths have calculated 18o values in the range of 0 to 5 3 opdb which reflect precipitation from normal to slightly evaporated contemporaneous seawater

interaction between hemipelagic sediment and a hydrothermal system middle valley northern juan de fuca ridge subarctic northeast pacific abstract slightly hydrothermally altered sediments were recovered from a sedimented rift valley with active hydrothermal discharge the sediment consists mainly of terrigenous material with a low content of biogenic components in spite of the alteration glacial and non glacial periods are still discernable based on lithology mineralogy carbonate content and bulk sediment geochemistry in the vicinity of the core studied extremely high heat flow anomalies and the presence of active black smokers suggest a rapid discharge of hydrothermal fluids along discrete pathways such as coarse grained turbidite layers or faults in the biogenic rich fine grained sediments diffuse transport can supply the components and allow the time necessary for the formation of authigenic phases such as carbonate concretions gypsum barite often mg rich amorphous silica and mg rich silicates stevensite mg rich amorphous silica could be the precursor of the mg rich silicates commonly found associated with hydrothermal deposits carbon and oxygen isotopic results on the carbonate nodules suggest 1 that the carbon in the nodules could be partly derived from methane which would have been oxidized at the oxic anoxic boundary and in the sulphate reduction zone and 2 that successive cycles of hydrothermal fluid migration through the sediment could explain the variability in the results

sulphur isotope geochemistry of pyrite from the upper cretaceous marshybank formation western interior basin abstract variations in the texture and sulphur isotopic composition of pyrite in the upper cretaceous marshybank formation are linked to depositional environment abundant framboidal and lesser euhedral pyrite precipitated in offshore marine rocks moderate quantities of pyrite also crystallized in brackish coastal plain rocks however in contrast to marine pyrite coastal plain pyrite is dominantly euhedral in texture reflecting direct precipitation from a porewater with a relatively low dissolved sulphide concentration in the marine rocks pyrite 34s values range from 35 7 to 27 4 avg 4 8 canyon diablo troilite cdt pyrite within carbonate concretions hosted in these marine rocks has a similar isotopic composition 49 8 to 10 6 cdt however isotopic values are often highly variable within individual concretions as a result of the heterogeneous nature of sulphate reduction and pyrite formation within marine sediments pyrite in coastal plain rocks is characterized by relatively high 34s values 4 2 to 35 5 avg 13 2 cdt while the overlying sideritized conglomerates have the lowest 34s values reported for cretaceous rocks from the western interior basin of north america 49 8 to 41 7 cdt very low 34s values which are only observed in the marine rocks are indicative of microbial sulphate reduction and pyrite formation in a sulphate replete i e open system higher 34s values up to 18 which were obtained for both the marine and coastal plain rocks are indicative of progressive pyrite crystallization in a sulphate limited i e closed system such conditions are expected in marine sediments as burial occurs and in brackish i e low sulphate sediments pyrite with very high 34s values 18 is common in the coastal plain rocks these high values are the result of influx of 34s enriched residual sulphide derived from overlying marine units a minor amount of 34s enriched pyrite is also present within and proximal to marine sedimentary unit h which was deposited at the same time as the coastal plain rocks we hypothesize that porewater containing 34s enriched residual sulphide flowed from the coastal plain and along unit h into the marine sediments thus producing anomalously high 34s pyrite

reduction of systematic forecast errors in the ecmwf model through the introduction of an envelope orography day 1 forecast errors in the ecmwf model geopotential height fields during wintertime show a distinctive and highly reproducible signature with negative biases over the major mountain barriers these biases are largest on days when the 500mb flow over the mountains is strong and they tend to shift position from day to day so as to remain close to the region where the jet stream crosses the mountain barrier these systematic errors evolve through the forecast interval until by day 10 they assume an equivalent barotropic structure which strongly resembles the upper level stationary wave pattern but has the opposite sign which indicates that the model does not have sufficient presumably orographic forcing to maintain the stationary waves the time evolution of the systematic error pattern is investigated by means of a series of experiments with a barotropic model in which the observed mean wintertime 300 mb flow is perturbed by a steady forcing derived from the day 1 forecast error pattern the day 10 error patterns as simulated by the barotropic model bear a strong similarity to the observed ones the forcing in the vicinity of the northern rockies makes a particularly large contribution to the simulated day 10 error pattern whereas that in the himalaya region appears to be relatively less important the impact of an enhanced orography upon the climate of the ecmwf model is investigated by carrying out a pair of extended integrations out to 50 days the control run is based on the conventional average type orography used for operational forecasting the other run is based on an envelope orography constructed by adding to the conventional grid square averaged orography an increment proportional to the standard deviation of the sub grid scale variance results for this one rather short pair of integrations suggest that the envelope orography may be capable of yielding a more realistic simulation of the observed wintertime flow pattern particularly with respect to features in the pacific and western north american sectors certain aspects of the zonally averaged circulation are also more realistic in this envelope simulation a series of 21 successive ten day forecast integrations has also been carried out with this envelope orography from february 1982 data results indicate that the introduction of the envelope orography results in a slight degradation of the short range forecasts together with a distinct improvement of the forecast beyond four days the beneficial impact towards the end of the forecast interval appears to be large enough to increase the forecast usefulness by perhaps as much as half a day

concretion formation in volcaniclastic host rocks evaluating the role of organics mineralogy and geochemistry on early diagenesis abstract the upper part of the brushy basin member of the jurassic morrison formation in the four corners regions of the u s was deposited in an ephemeral alkaline saline lake system with copious input of volcanic ash that resulted in dynamic fluid rock interaction during early diagenesis three broad diagenetic facies defined by color and associated bioturbation features are interpreted red green and intermediate diagenetic facies reflect meter scale paleotopography red facies represent shallow water to subaerial oxidizing conditions green facies reflect saturated conditions and reducing pore water chemistry shortly after deposition and intermediate facies represent a combination of or rapid transition between the previous two conditions three categories of concretions are characterized based on mineralogy carbonate iron oxyhydr oxide and phosphate concretions variation in concretion mineralogy and morphology in the brushy basin member suggests that alkaline saline fluid chemistries created diagenetic microenvironments within a larger lake system to influence concretion precipitation however porosity and permeability are more important factors affecting concretion size morphology and mineralogy than host rock composition diagenetic fluid rock interactions in volcaniclastic sediments can be spatially variable even on tens of centimeters scale

travel time tomography in shallow water experimental demonstration at an ultrasonic scale acoustic tomography in a shallow ultrasonic waveguide is demonstrated at the laboratory scale between two source receiver arrays at a 1 1 000 scale the waveguide represents a 1 1 km long 52 m deep ocean acoustic channel in the kilohertz frequency range two coplanar arrays record the transfer matrix in the time domain of the waveguide between each pair of source receiver transducers a time domain double beamforming algorithm is simultaneously performed on the source and receiver arrays that projects the multi reflected acoustic echoes into an equivalent set of eigenrays which are characterized by their travel times and their launch and arrival angles travel time differences are measured for each eigenray every 0 1 s when a thermal plume is generated at a given location in the waveguide travel time tomography inversion is then performed using two forward models based either on ray theory or on the diffraction based sensitivity kernel the spatially resolved range and depth inversion data confirm th

evidence for surface reaction controlled growth of carbonate concretions in shales estimates for the rate of concretionary growth in shales are based on models which assume that growth is diffusion controlled however laboratory and field studies of caco3 precipitation in organic carbon rich sediments indicate that surface reactions control growth due to inhibition by various dissolved species the spatial distribution of carbonate concretions in the jet rock lower jurassic england is also inconsistent with diffusion controlled precipitation of caco3 into concretions and growth must have been at least partly surface reaction controlled

a long range and variable focus phase conjugation experiment in shallow water a second phase conjugation experiment was conducted in the mediterranean sea in may 1997 extending the results of the earlier time reversal mirror experiment kuperman et al j acoust soc am 103 25 40 1998 new results reported here include 1 extending the range of focus from the earlier result of 6 km out to 30 km 2 verifying a new technique to refocus at ranges other than that of the probe source song et al j acoust soc am 103 3234 3240 1998 and 3 demonstrating that probe source pulses up to 1 week old can be refocused successfully

determining the diagenetic conditions of concretion formation assessing temperatures and pore waters using clumped isotopes carbonate 18 o paleothermometry is used in many diagenetic studies to unravel the thermal history of basins however this approach generally requires an assumed pore water 18 o 18 o pw value a parameter that is difficult to quantify in past regimes in addition many processes can change the original isotopic composition of pore water which further complicates the assignment of an initial 18 o pw and can lead to erroneous temperature estimates here we use clumped isotope thermometry a proxy based on the 13 c 18 o bond abundance in carbonate minerals to evaluate the temperatures of concretion formation in the miocene monterey formation and the cretaceous holz shale california these temperatures are combined with established carbonate water fractionation factors to calculate the associated 18 o pw results demonstrate that diagenetic processes can modify the 18 o of ancient pore water confounding attempts to estimate diagenetic temperatures using standard approaches clumped isotope based temperature estimates for monterey formation concretions range from 17 to 35 c up to 12 c higher than traditional 18 o carbonate water paleothermometry when 18 o pw values are assumed to equal miocene seawater values calculated 18 o pw values range from 0 3 to 2 5 vsmow higher than coeval miocene seawater likely due to 18 o pw modification accompanying diagenesis of sedimentary siliceous phases clumped isotope temperatures for the holz shale concretions range from 33 to 44 c about 15 to 30 c lower than temperatures derived using the traditional method calculated 18 o pw values range from 5 0 to 2 9 and likely reflect the influx of meteoric fluids we conclude that the use of clumped isotopes both improves the accuracy of temperature reconstructions and provides insight into the evolution of 18 o pw during diagenesis addressing a longstanding conundrum in basin evolution research

topographically generated gravity waves in the brooks range alaska amplified wind events are identified over the brooks range in alaska with observed wind speed increasing from calm to 5 ms 1 over 24 to 36 hours in simulations using an limited area climate system model the wind events are captured consistently although generally display greater strength than observed cooling associated with the wind events lead to an identification of the ne region of the north slope of alaska below the inversion as the source region for the air flow analysis of the wind event of 7th january 1992 supports the nonlinear hydraulic model of gravity waves

the alaskan arctic frontal zone forcing by orography coastal contrast and the boreal forest abstract experiments have been conducted with a regional climate model to indicate the conditions required to generate preferred regions of frontal activity in the alaskan region several objective methods of frontal identification were first investigated it was found that the vertical component of relative vorticity a thermal front parameter t850 n where t850 is the 850 hpa temperature and n is a unit vector in the direction of the 850 hpa temperature gradient and a parameter derived from the q vector as a measure of vertical motionwere useful in combination to determine the occurrence of fronts the preferred locations for frontal activity were located to the southern side of the eastern brooks range and over the alaska range these diagnostics were then used to characterize frontal frequency in a series of experiments removing topographic and vegetation contrasts it was found that the removal of the treeline contrast and its associated heating gradient had a small effect on frontal frequ

tracking of velocity variations at depth in the presence of surface velocity fluctuations we tested a small scale experiment that is dedicated to the study of the wave separation algorithm and to the velocity variations monitoring problem itself it handles the case in which velocity variations at depth are hidden by near surface velocity fluctuations using an acquisition system that combines an array of sources and an array of receivers coupled with controlled velocity variations we tested the ability of beam forming techniques to track velocity variations separately for body waves and surface waves after wave separation through double beam forming the arrival time variations of the different waves were measured through the phase difference between the extracted wavelets finally a method was tested to estimate near surface velocity variations using surface waves or shallow reflection and compute a correction to isolate target velocity variations at depth

a methodological approach towards high resolution surface wave imaging of the san jacinto fault zone using ambient noise recordings at a spatially dense array we present a new technique for deriving detailed information on seismic velocities of the subsurface material from continuous ambient noise recorded by spatially dense seismic arrays this method uses iterative double beamforming between various subarrays to extract surface wave contributions from the ambient noise data in complex environments with unfavourable noise source distributions the iterative double beamforming extraction makes it possible to retrieve large amounts of rayleigh wave traveltime information in a wide frequency band the method is applied to data recorded by a highly dense nodal array with 1108 vertical geophones centred on the damage zone of the clark branch of the san jacinto fault zone south of anza california the array covers a region of 650 700 m 2 with instrument spacing of 10 30 m and continuous recording at 500 samples s 1 over 30 d in 2014 using this iterative double beamforming on subarrays of 25 sensors and cross correlations between all of the station pairs we separate surface waves from body waves that are abundant in the raw cross correlation data focusing solely on surface waves maps of traveltimes are obtained at different frequencies with unprecedented accuracy at each point of a 15 m spacing grid group velocity inversions at 2 4 hz reveal depth and lateral variations in the structural properties within and around the san jacinto fault zone in the study area this method can be used over wider frequency ranges and can be combined with other imaging techniques such as eikonal tomography to provide unprecedented detailed structural images of the subsurface material

methane derived authigenic carbonates of mid cretaceous age in southern tibet types of carbonate concretions carbon sources and formation processes abstract methane derived authigenic carbonates with distinctive structures and morphologies have been documented worldwide but they are rarely found from ancient strata in the eastern tethys ocean the methane derived authigenic carbonates found in southern tibet are developed in calcareous or silty shales of mid cretaceous age in the xigaze forearc basin and in the tethyan himalaya tectonic zone the morphology mineralogy elemental geochemistry and composition of carbon and oxygen isotopes of these carbonates are studied in detail the carbonates have nodular tubular and tabular morphologies they are primarily composed of carbonate cement that binds and partly replaces host sediment grains host siliciclastic sediments are composed mainly of quartz and plagioclase feldspar a few foraminifers and framboidal or subhedral to euhedral pyrite carbonate cements dominantly are micritic calcite with minor contribution of dolomite nodular concretions are characterized by depleted 13c values commonly ranging from 30 to 5 the 13c values show a gradual decrease from the periphery to the center and the cao sio2 fe2o3 al2o3 k2o and tio2 contents generally show a gradual change these features indicate that the nodular concretions grew from an early formed center toward the periphery and that the carbon source of the nodular concretions was derived from a mixture of methane methanogenic co2 and seawater dissolved inorganic carbon the tubular concretions are characterized by 13c values of 8 85 to 3 47 in the shangba section and 27 37 to 23 85 in the upper gamba section unlike the nodular concretions the tubular concretions show central conduits which are possible pathways of methane rich fluids suggesting that the cementation of tubular concretions begins at the periphery and proceeds inward moreover the tubular concretions show morphological similarity with the methane derived carbonate chimneys pipes and slabs reported in present day cold seep settings we suggest that the carbon source of the tubular concretions was derived from a mixture of seawater dissolved inorganic carbon and oxidized methane formed by released hydrate the tabular concretions are characterized by 13c values of 21 87 to 6 67 in the xiege sections these depleted 13c values suggest that the carbon of the tabular concretions was derived at least in part from aom the tabular concretions are characterized by 13c values of 28 81 to 12 99 in the gamba section according to the 13c values and field observation we infer that their carbon source was more likely to be a mixture of the oxidized methane formed by released hydrate and seawater dissolved inorganic carbon

acoustic travel time perturbations due to shallow water internal waves and internal tides in the barents sea polar front theory and experiment during august 1992 a combined acoustics physical oceanography experiment was performed to study both the acoustical properties and the ocean dynamics of the barents sea polar front in the region near bear island oceanographic observations from shipboard hydrography and moored sensors allowed the construction of the internal wave frequency spectrum for the area a rapidly sampled tomographic section from a 224 hz 16 hz bandwidth acoustic source to a 16 element vertical receiving array enabled the monitoring of travel time fluctuations over the internal wave frequency band to describe the measured acoustic fluctuations theoretical expressions have been developed for the travel time variances which are functions of the internal wave oceanographic field the local acoustic propagation characteristics and the acoustical system s properties both ray and mode theory expressions are generated as the experiment was performed in shallow water and both ray and mode arrivals were resolvable comparison of the

geochemistry and diagenesis of stratabound calcite cement layers within the rannoch formation of the brent group murchison field north viking graben northern north sea abstract up to four calcite cemented horizons doggers form impermeable barriers to fluid flow within the middle jurassic rannoch formation and are correlatable across the murchison field calcite precipitated during early diagenesis within high porosity permeability sandstones at the top of coarsening shoaling upward shoreface cycles calcite 13c and 18o compositions range from 4 1 to 13 4 pdb and 6 6 to 16 7 pdb respectively sr concentrations of up to 1334 ppm are consistent with marine carbonate sources probably shell fragments but no viable intraformational carbonate source has been identified in the murchison field area initial 87sr 86sr compositions 0 71109 0 71266 are higher than middle jurassic seawater 0 7073 and consistent with precipitation from modified porewaters containing significant proportions of continentally derived meteoric fluids enriched in 87sr as a result of basement weathering or percolation through hinterland soils unconsolidated detritus an internal source of 87sr is not considered viable in view of the high proportion up to 25 clastic constituents of unaltered detrital alkali feldspar and mica within the rannoch formation geochemical and isotope data indicate correlations between increasing 18o composition and increasing iron and magnesium content within calcite calcium concentrations decrease with increasing 18o for calcites geochemical data trends can be interpreted differently in terms of either static or evolving 18o porewater models static 18o porewater models using jurassic early cretaceous meteoric water 18 o 6 smow predict cement precipitation temperatures of 17 77 c however 13c compositions are more depleted than those typical of carbon derived from shell debris and correlation between decreasing 18o and decreasing 13c suggests modification of a meteoric derived porewater system during burial via contribution of low 13c carbon derived from a deep basinal source however it is difficult to constrain accurately the degree to which porewater 18o may have evolved during burial the degree to which porewater 18o could have evolved from that of a jurassic early cretaceous meteoric water can be loosely constrained as from 18 o 6 smow to 18 o 2 smow if the temperature at which the most 18o depleted cements precipitated is limited by present day bottom hole temperatures 110 c for wells currently at maximum burial depth

peloidal fabrics in upper jurassic reefal limestones weald basin southern england abstract coraliferous limestones from the corallian group upper jurassic of subsurface of the weald basin southern england record the localized development of superimposed patch reefs and banks the reefal limestones exhibit a variety of peloidal fabrics in particular well sorted peloids 10 60 m in diameter with a well developed euhedral rim of fibrous sparry calcite around a micritic anhedral nucleus they occur in confined intraskeletal pores corals molluscs and borings growth cavities between framebuilders and as stromatolitic crusts the peloids in interskeletal cavities and as crusts resemble microbial precipitates and merge into spongiostromate fabrics the distribution of these peloidal fabrics seems to be facies related and is best developed in zones which had relatively low framework growth rates low sedimentation rates and moderate energy levels the peloids are identical in form and occurrence to those in some ancient and quaternary reefs the association of the peloids with stromatolitic coatings and spongiostromate fabrics leads us to interpret the peloids as microbial precipitates either by direct precipitation or by induction the abundance of microbial carbonate in these reefal limestones places them in an intermediate category between frame built reefs and microbial mud mounds

the concretions of the bearreraig sandstone formation geometry and geochemistry the sandbodies of the bearreraig sandstone formation inner hebrides uk are cemented by two generations of calcite the first generation an inhomogeneous ferroan calcite 0 05 3 28 mol feco3 formed during sulphate reduction 13c 24 to 32 o pdb in marine porewaters 18o of cement from 1 to 4 o pdb at very shallow burial depths a few centimetres these cements are rare but form millimetre scale clusters of crystals which acted as nuclei to the later concretionary cements the second generation of cements are more homogeneous ferroan calcites mean 1 58 mol feco3 which evolve to progressively higher fe mg ratios they are sourced by shell dissolution 13c of cement from 1 to 3 o pdb into meteoric 18o of cement from 6 to 10 o pdb or mixed marine meteoric waters 18o of cement from 4 to 6 o smow these were introduced into the formation either during bathonian times as a freshwater lens or subsequent to partial inversion by confined aquifer flow corroded feldspars within the concretions suggest that an interval of at least 8 ma separated the deposition of the sediments from the onset of concretion growth abundant concretions are preferentially developed at certain horizons within the sandbodies where the early generation of ferroan calcite cements provided nuclei the latter formed close to the sediment water interface the concentration of cement within the sediment being related to sedimentation rate the relatively high concentrations of the first generation of cement upon which the concretionary horizons are nucleated formed during periods of minimal sedimentation

microfabric mineralogy and early diagenetic history of the whitby mudstone formation toarcian cleveland basin u k the whitby mudstone formation in northeast england contains three shale facies normal restricted and bituminous which have previously been differentiated on the basis of sedimentary structures and faunal assemblages this paper shows that the three facies can also be differentiated by mineralogical geochemical and microtextural criteria determined using bsem edxra xrd and xrf the bituminous shale facies consists of finely laminated shales containing an early diagenetic mineral assemblage dominated by pyrite calcite and dolomite the weakly laminated restricted facies shales contain an early diagenetic assemblage dominated by pyrite the normal facies shales are very weakly laminated and contain siderite in addition to pyrite the geochemical conditions which left a dominant early diagenetic imprint on the three facies are interpreted to be carbon rich sulphidic carbon poor sulphidic and very carbon poor sulphidic respectively

geoacoustic inversion with two source receiver arrays in shallow water a geoacoustic inversion scheme based on a double beamforming algorithm in shallow water is proposed and tested double beamforming allows identification of multi reverberated eigenrays propagating between two vertical transducer arrays according to their emission and reception angles and arrival times analysis of eigenray intensities yields the bottom reflection coefficient as a function of angle of incidence by fitting the experimental reflection coefficient with a theoretical prediction values of the acoustic parameters of the waveguide bottom can be extracted the procedure was initially tested in a small scale tank experiment for a waveguide with a plexiglas bottom inversion results for the speed of shear waves in plexiglas are in good agreement with the table values a similar analysis was applied to data collected during an at sea experiment in shallow coastal waters of the mediterranean bottom reflection coefficient was fitted with the theory in which bottom sediments are modeled as a multi layered system retrieved bottom parameters are in quantitative agreement with those determined from a prior inversion scheme performed in the same area the present study confirms the interest in processing source receiver array data through the double beamforming algorithm and indicates the potential for application of eigenray intensity analysis to geoacoustic inversion problems

analyzing sound speed fluctuations in shallow water from group velocity versus phase velocity data representation data collected over more than eight consecutive hours between two source receiver arrays in a shallow water environment are analyzed through the physics of the waveguide invariant in particular the use of vertical arrays on both the source and receiver sides provides source and receiver angles in addition to travel times associated with a set of eigenray paths in the waveguide from the travel times and the source receiver angles the eigenrays are projected into a group velocity versus phase velocity vg vp plot for each acquisition the time evolution of the vg vp representation over the 8 5 h long experiment is discussed group speed fluctuations observed for a set of eigenrays with turning points at different depths in the water column are compared to the brunt vaisala frequency