meteoric like fabrics forming in marine waters implications for the use of petrography to identify diagenetic environments petrographic fabrics have long been used to identify meteoric diagenesis of carbonate sediments however on the basis of oxygen isotopic data we document similar fabrics forming in marine pore fluids in the shallow subsurface of great bahama bank therefore petrographic fabrics alone are not reliable indicators of diagenetic environments even for shallow water sediments in our study skeletal grainstones show two distinct diagenetic assemblages either dissolution of aragonitic grains and minimal cementation high permeability intervals or abundant blocky spar cement and neomorphism of aragonitic skeletal grains low permeability intervals these marine burial fabrics are present as shallow as 110 m below sea level well above the aragonite compensation depth a feature that must be considered for models of diagenesis in ancient carbonate sediments marine burial diagenesis may be important in ancient carbonate sediments deposited in moderate water depths or in shallow water during rising sea level where meteoric diagenesis is suppressed

tidal wave propagation along the mekong deltaic coast a two dimensional barotropic numerical model was employed to investigate the dynamics of tidal wave propagation in the south china sea with a particular interest for its characteristics along the mekong deltaic coast the study indicates that tidal waves propagate from the pacific ocean into the south china sea mainly through the luzon strait ls where the k 1 diurnal tide dominates due to a quarter wavelength resonance in this semi enclosed basin and that the incoming tidal waves from the celebes open boundary play a more important role than those from the andaman and flores open boundaries previous studies have not explained why both adjacent seas including the south china sea and the gulf of thailand are dominated by a diurnal tide while a semidiurnal tide dominates along the eastern mekong deltaic coast by means of green s law continental shelf tidal resonance theory and standing wave theory this study clarifies that the large amplified m 2 semidiurnal amplitude leading to a prevailing mixed semidiurnal tide is caused not only by the shoaling effect and the continental shelf oscillation resonance phenomenon but also by the position on the standing wave anti node line moreover the finding of radial tidal currents occurring along the southern mekong estuarine coast has not been revealed in earlier studies based on a number of numerical geometrically schematised experiments we suggest that the interaction between the large amplified amplitude near the shoreline associated with the adjacent low amplitude band system causing convex hydraulic gradients of tidal amplitude due to basin geometry as well as sloping topography is the mechanism for developing these radial tidal current systems the results reveal that wind monsoon climate could cause either damped or amplified tidal amplitudes around the mekong deltaic coast of which approximately 2 3 cm is due to the changing atmospheric pressure the tangential stress of wind over the water surface and wind enhanced bottom friction also this study suggests that the tidal generating forces should be considered to achieve accurate model results depending on the geographical region of interest findings achieved from this study contribute to a deeper insight of tidal wave propagation from a deep ocean to a shallow flat basin similar to the south china sea and its mekong deltaic coast

wave attenuation in partially saturated porous rocks new observations and interpretations across scales abstract seismic waves propagating in porous rocks saturated with two immiscible fluids can be strongly attenuated predicting saturation effects on seismic responses requires a sound understanding of attenuation and velocity dependencies on the fluid distribution decoding these effects involves interpreting laboratory experiments analyzing well log data and performing numerical simulations despite striking differences among scales flow regimes and frequency bands some aspects of wave attenuation can be explained with a single mechanism wave induced pressure diffusion different facets of wave induced pressure diffusion can be revealed across scales

a lowstand epikarstic intertidal flat from the middle silurian of gotland sweden this paper describes the sedimentology morphology and diagenesis of recently discovered middle silurian low relief micro epikarst from the klintehamn area on western gotland sweden the epikarst represents the most distal portion of an unconformity that truncates stratigraphic units across a major part of the baltic palaeo basin it formed in the intertidal area during the late stage of platform development and following a short period of regression and siliciclastic influx to the basin at the closing of the cyrtograptus lundgreni chron an overlying oncolite shows signs of repeated exposure to meteoric and marine waters supporting the interpretation of a karstic flat setting four microfacies with different stable isotopic signatures are recognised across the unconformity dolomitic siltstone and altered siltstone in the topmost frojel formation below the contact and ferruginous crinoid algal packstone and ferruginous oncolite grainstone above the contact in the basal lag of the transgressive halla formation endolithic structures of inferred fungal algal origin occur frequently in the two transgressive microfacies the set of observations pointing towards subaerial exposure and karstic processes include a an understanding of the regional geology b erosional relief with undercutting and an associated conglomerate c vertical and subvertical conduits karren indicating gravitationally controlled waters d widening of fissures and subsequent polyphase fillings splitkarren e eluviated internal sediment e g crystal silt f blackening g repeated etching of carbonate allochems h a fitted grain fabric i circum granular cracking j pendant nonluminescent cements k abundant intercrystalline and intergranular secondary porosity and 1 anomalous stable isotopes a synsedimentary iron crust at the contact was not related to karstification but formed a few centimetres below the sediment surface during the ensuing transgression c 2002 elsevier science b v all rights reserved

towards a parametrization of river discharges into ocean general circulation models a closure through energy conservation diagnostic methods are defined in order to compare two numerical simulations of ocean dynamics in a region of freshwater influence the first one is a river plume simulation based on a high resolution numerical configuration of the pom coastal ocean model in which mixing parametrizations have been previously defined the second one is a simulation based on the nemo global ocean model used for climate simulations in its half a degree configuration in which a river inflow is represented as precipitation on two coastal grid cells both simulations are forced with the same freshwater inflows and wind stresses the divergence of volumetric fluxes above and below the halocline are compared results show that when an upwelling wind blows the two models display similar behavior although the impact of lack of precision can be observed in the nemo configuration when a downwelling wind blows the nemo global ocean configuration can not reproduce the coastally trapped baroclinic dynamics because its grid resolution is too coarse to find a parametrization to help represent these dynamics in ocean general circulation models a method based on energy conservation is investigated this method shows that it is possible to link the energy fluxes provided by river inflows to the divergence of energy fluxes integrated over the grid cells of ocean general circulation models a parametrization of the dynamics created by freshwater inflows is deduced from this method this enabled creation of a box model that proved to have the same behavior as the fluxes previously computed from the high resolution configuration

high resolution geochemical and biotic records of the tethyan bonarelli level oae2 latest cenomanian from the calabianca guidaloca composite section northwestern sicily italy abstract high resolution micropalaeontological and chemostratigraphic records for the upper cenomanian portion of the calabianca guidaloca composite section nw sicily provide new insight into the palaeoclimatic and palaeoceanographic evolution of the tethys ocean the bonarelli level equivalent was identified on the basis of lithology and well constrained by calcareous plankton biostratigraphy and radiolarian assemblages as well as by the 13 c curve showing a marked positive excursion up to 4 7 the bonarelli level equivalent deposition is characterized by highly eutrophic conditions as testified by radiolarian proliferation black shale samples from the calabianca guidaloca composite section contain very high toc up to 26 and moderate to high amounts of caco 3 on average 20 among the planktonic foraminifera hedbergellids and globigerinelloids tolerated the environmental stress induced by the oceanic anoxic event 2 oae2 the occurrence of some benthic foraminifera testifies to dysoxic rather than completely anoxic conditions at the sea floor during the deposition of some portions of the bonarelli level equivalent based on micropalaeontological results and geochemical proxies 13 c d rb ti v ni ba si cr the bonarelli level equivalent is interpreted as a high productivity event driven by increasingly warm and humid climatic conditions promoting an accelerated hydrological cycle we propose that periodically increased riverine influxes triggered by enhanced humidity resulted in a sluggish circulation mode and consequent anoxic euxinic conditions favouring the preservation of organic matter at the sea floor spectral analyses performed on selected geochemical signals reveal within the main high productivity event a strong orbital climatic forcing represented by a long term eccentricity steered humidity cyclicity that amplifies a short term precession controlled productivity fluctuation

surfaces with a long history the aptian top shu aiba formation unconformity sultanate of oman discontinuity surfaces in shallow marine carbonate successions may represent significant time gaps in the geological record of ancient epeiric neritic seas understanding the hidden geological information contained in major discontinuities is thus of key significance in palaeo environmental analysis sequence stratigraphy reconstructions of sea level change and basin evolution in the present paper the aptian top lower shu aiba formation discontinuity in the sultanate of oman is taken as a prominent example of a regionally extensive 100 000 km2 surface with a long up to 10 myr and complex geological history the top shu aiba discontinuity formed on the topographically elevated domain of the oman platform and represents in essence the late aptian time interval coeval carbonates in the intrashelf bab basin and oceanic rim indicate forced regression and sequence wise gradual down stepping available regional sedimentological sequence stratigraphic petrographic palaeontological and geochemical evidence from outcrops and cored wells in oman is summarized in part complemented by new data and reviewed in a process oriented context in the field the discontinuity is expressed as a low relief stained surface with evidence for a marine hardground stage being dominant indistinct features that indicate a transient meteoric precursor stage isotope shifts meteoric cements circumgranular cracks etc are present but their interpretation requires careful and detailed work this feature is remarkable as a series of relative sea level falls with amplitudes of up to several tens of metres from the early to late aptian boundary to the end of the aptian are reported from the middle east and elsewhere despite the palaeogeographic position of the study area in the tropical climate zone evidence of deep cutting karst features characteristic for many long term exposure surfaces worldwide is scarce acknowledging the fact that the modern world offers no genuine analogues for the lower aptian carbonate system in oman morphological similarities between actualistic wave eroded coastal terraces and the top shu aiba discontinuity are discussed critically this discussion may imply that during an exposure time of several million years the top shu aiba discontinuity experienced repeated stages of shallow flooding and emergence with each transgression removing portions of the underlying rock record the data shown here exemplify the complexity of hiatal surfaces in epeiric neritic carbonates and may serve as a case example for other major discontinuities

saturation path dependency of p wave velocity and attenuation in sandstone saturated with co2 and brine revealed by simultaneous measurements of waveforms and x ray computed tomography images abstractwe performed a laboratory experiment to measure compressional p wave velocity and its attenuation in low permeability striped sandstone at ultrasonic frequency during drainage co2 injection and imbibition brine injection x ray computed tomography ct images of the rock sample were simultaneously recorded during the injections on the basis of the ct images we calculated the co2 saturation inside a prolate spheroid shaped volume the first fresnel zone that enclosed the wave propagation path the relationship of p wave velocity and that of attenuation to the co2 fraction were then obtained both relationships showed nonuniqueness with remarkable hysteresis in a drainage imbibition cycle to explain the nonunique relationship of p wave velocity to the co2 fraction we investigated the continuous random patchy saturation model by using exponent type autocorrelation the nonunique relationship of velocity to the co2 fraction was explained by the model with a correlation length from an order

equivalent viscoelastic solids for heterogeneous fluid saturated porous rocks differenttheoreticalandlaboratorystudiesonthepropagation ofelasticwavesinrealrockshaveshownthatthepresenceofheterogeneities larger than the pore size but smaller than the predominant wavelengths mesoscopic scale heterogeneities may producesignificantattenuationandvelocitydispersioneffectson seismic waves such phenomena are known as mesoscopic effects and are caused by equilibration of wave induced fluid pressure gradients we propose a numerical upscaling procedure to obtain equivalent viscoelastic solids for heterogeneous fluidsaturated rocks it consists in simulating oscillatory compressibility and shear tests in the space frequency domain which enable us to obtain the equivalent complex undrained plane wave and shear moduli of the rock sample we assume that the behavior of the porous media obeys biot s equations and use a finiteelementproceduretoapproximatethesolutionsoftheassociated boundary value problems also because at mesoscopic scales rock parameter distributions are generally uncertain and of stochastic nature we propose applying the compressibility and sheartestsinamontecarlofashion thisfacilitatesthedefinition of average equivalent viscoelastic media by computing the moments of the equivalent phase velocities and inverse quality factors over a set of realizations of stochastic rock parameters described by a given spectral density distribution we analyzed the sensitivity of the mesoscopic effects to different kinds of heterogeneities in the rock and fluid properties using numerical examples also theapplicationofthemontecarloprocedureallowed us to determine the statistical properties of phase velocities and inverse quality factors for the particular case of quasi fractal heterogeneities

comparison of p wave attenuation models of wave induced flow abstract wave induced oscillatory fluid flow in the vicinity of inclusions embedded in porous rocks is one of the main causes for p wave dispersion and attenuation at seismic frequencies hence the p wave velocity depends on wave frequency porosity saturation and other rock parameters several analytical models quantify this wave induced flow attenuation and result in characteristic velocity saturation relations here we compare some of these models by analyzing their low and high frequency asymptotic behaviours and by applying them to measured velocity saturation relations specifically the biot rayleigh model considering spherical inclusions embedded in an isotropic rock matrix is compared with white s and johnson s models of patchy saturation the modeling of laboratory data for tight sandstone and limestone indicates that by selecting appropriate inclusion size the biot rayleigh predictions are close to the measured values particularly for intermediate and high water saturations

time lapse sonic logs reveal patchy co2 saturation in situ 1 based on time lapse sonic and neutron porosity logs from the nagaoka co2 sequestration experiment a p wave velocity saturation relation at reservoir depth is retrieved it does not coincide with either of the end member models of uniform and patchy saturation but falls in between even if realistic error estimates for the host rock properties are considered assuming a random distribution of co2 patches it is shown that the mechanism of wave induced flow can be evoked to explain this velocity saturation relation characteristic co2 patch size estimates range from 1 to 5 mm such mesoscopic heterogeneity can be responsible for attenuation and dispersion in the well logging frequency band

neptunic dikes and their relation to the hydrodynamic circulation of submarine hydrothermal systems neptunic dikes in lower jurassic sedimentary rocks of the tethyan margins consist of internal sediment in cavities and submarine cement the textures of the infilling sediment indicate downward and lateral movements of seawater beneath what was probably a deep sea floor this circulation probably was part of the hydrodynamic circulation that supplied hot ore bearing solutions to hydrothermal vents near a spreading ridge system this working hypothesis is being tested by stable isotope studies now in progress

analysis of velocity dispersion using full waveform multichannel sonic logging data a case study seismic attenuation and velocity dispersion are potentially able to reveal the rock physical properties of the subsurface conventionally a frequency independent quality factor q is measured this q is equivalent to the total velocity dispersion in a seismic record and is inadequate for analysing the attenuation mechanism or rock physical properties here a new method is proposed to extract the velocity dispersion curves so that more attributes can be obtained from full waveform multichannel sonic logging data especially the critical frequency fc if it is within the bandwidth of the data this method first decomposes the seismic data into a series of frequency components computes the semblance of each frequency component for different velocity values cross correlates the semblance matrices of adjacent frequency components to get the velocity gradients and finally integrates to obtain a velocity dispersion curve results of this method are of satisfactory accuracy and robustness this method is applied to the data acquired in mallik 5l 38 gas hydrate research well in mackenzie delta northwest territories canada the observed p wave velocity dispersion compares well with the geological setting in the gas hydrate zone about 900 m 1100 m high concentration of gas hydrate causes very strong velocity dispersion and a distinct fc at about 15 khz likely due to strong scattering of centimetre scale inclusions of gas hydrate concurrently water flow in connected cracks in some ranges of this zone adds a large part of velocity dispersion and a dimmer fc at about 9 5 khz immediate underneath the gas hydrate zone abundant free water in weakly laminated sediments causes quite strong velocity dispersion and an fc at about 6 5 khz velocity dispersion is mild and without an obvious fc in sediments above the gas hydrate zone

petrography and high resolution geochemical records of lower jurassic manganese rich deposits from monte mangart julian alps abstract deposits with unusually high mn contents sampled at monte mangart in the julian alps include organic rich marlstone and black shale with interbedded manganoan and siliceous limestone which were deposited during the early toarcian oceanic anoxic event mn enrichment during that period has been related to global sea level change coincident with increasing subsidence rate the formation of fe mn nodules marking a hardground at the base of the monte mangart section seems to be triggered by release of mn from remote hydrothermal vents into a region of relatively elevated submarine topography where oxidizing conditions prevailed however very high mn contents in carbonate phases above the hardground imply an additional diagenetic source of this element in the lower part of this section the whole stratigraphic sequence ca 30 m displays a transition from mn rich up to 8 8 sediments in the lower part to mn poor less than 1 8 sediments in the middle and upper parts the drastic decrease in mn content s up section is accompanied by a clear decrease in the mean size of pyrite framboids indicating more intense anoxia euxinia in the water column in the presence of mn2 conditions of high alkalinity induced precipitation of mn carbonates during early diagenetic processes negative 13ccarb values coincident with high mn contents indicate involvement of organic matter in the mineralization process the striking similarity of ce ce and mn profiles demonstrates that consistent with redox chemistry of mn and ce under anoxic conditions ce3 and mn2 were mobilized and released into pore water where precipitation of mn carbonates occurred

lithospheric bulges recorded by regional unconformities the case of mesozoic tertiary apulia abstract cyclic shallow water carbonate sequences in the cretaceous of southern italy are punctuated by regional unconformities associated with bauxites and palaeokarst features direct and indirect evidence strongly suggests that despite their apparent plate interior position tectonics rather than eustasy was responsible for subaerial exposure long enough to form bauxites in plane stress related lithospheric arching caused by orogenic deformation along the distant active margins of apulia is invoked to explain the vertical stacking of a series of regional unconformities one of them marked by bauxites on land and under the sea the case history of apulian bauxites associated with a turonian arching allows a first estimate of the duration of a stress related distant perturbation of a subsiding passive continental margin

fluid distribution effect on sonic attenuation in partially saturated limestones extensional and torsional wave attenuation measurements are obtained at a sonic frequency around 1 khz on partially saturated limestones using large resonant bars 1 m long to study the influence of the fluid distribution we use two different saturation methods drying and depressurization when water saturation sw is higher than 70 the extensional wave attenuation is found to depend on whether the resonant bar is jacketed this can be interpreted as the biot gardner white effect the experimental results obtained on jacketed samples show that during a drying experiment extensional wave attenuation is influenced strongly by the fluid content when sw is between approximately 60 and 100 this sensitivity to fluid saturation vanishes when saturation is obtained through depressurization using a computer assisted tomographic ct scan we found that during depressurization the fluid distribution is homogeneous at the millimetric scale at all saturations in contrast during drying heterogeneous s

acoustic measures of partial gas saturation in tight sandstones the acoustic properties of tight sandstones are very sensitive to partial gas water saturation measurements at 5 khz show that compressional velocity drops sharply with undersaturation extensional and shear losses at 5 khz are large in both fully and partially saturated sands the shear loss qs 1 declines linearly with increasing gas content the extensional loss qe 1 peaks at 0 80 water saturation q 1 is frequency dependent the attenuation is well explained by hydrodynamic relaxation in the grain contacts the measurements indicate velocity dispersions consistent with this mechanism ultrasonic velocities at 500 khz are roughly 10 25 higher than acoustic velocities at 5 khz the ultrasonic velocities exhibit a weak dependence on saturation frame moduli are unrelaxed at these frequencies

neptunian dykes and associated features in southern spain mechanics of formation and tectonic implications neptunian dykes and sills in jurassic carbonate platform strata of the betic region of spain occupy spaces created by wholly mechanical fracturing and displacement of the host strata and later filled by pelagic sediments from above or by precipitation of calcite from circulating solutions in some places joint bounded blocks of platform carbonates have been wholly removed possibly by sliding down submarine slopes leaving a staircase topography commonly fe encrusted that was subsequently filled by pelagic sediments other cavities that formed during cretaceous times were developed by dissolution and current erosion in moderately deep submarine environments and then filled by pelagic sediments from above none of the cavities hosted by either platform or pelagic strata contain evidence for their formation by dissolution in a subaerial environment the jurassic and cretaceous history of subsidence of the betic margins is thus simpler than in versions requiring repeated emergence to form subaerial karstic cavities

understanding the geological record of carbonate platform drowning across rifted tethyan margins examples from the lower jurassic of the apennines and sicily italy abstract in the geological record a drowning process is documented by various types of shallow water to pelagic or shallow water to mixed benthic pelagic carbonate transitions drowning unconformities are paraconformities to disconformities to angular unconformities and their drowning surfaces range from planar to highly irregular morphologies drowning successions display a mix of products of both the benthic and pelagic carbonate factories these successions can be also bounded by unconformities drowning unconformities and drowning successions are contrasted through a description and discussion of examples of escarpment bounded platforms from the jurassic of the northern apennines and subordinately from sicily and other tethyan sectors the areal distribution of drowning unconformities and successions is discussed with reference to a complex depositional system whose architecture was the product of the rift induced fragmentation of a regional hettangian carbonate megabank the examples in this study show drowning unconformities to be exclusive to intrabasinal highs while drowning successions are found both on highs and in hangingwall basins drowning unconformities with their long associated hiatuses and drowning successions are often seen to merge laterally into one another over very short distances on the same intrabasinal high the deposits of the drowning succession are sometimes missing on the top of the platform while they are found forming clinoforms along its flanks evidence that sediment could be permanently swept from the highs in these depositional systems at this stage

seismic attenuation due to wave induced flow analytical expressions for three p wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework two of the models concern wave induced flow due to heterogeneity in the elastic moduli at mesoscopic scales scales greater than grain sizes but smaller than wavelengths in the first model the heterogeneity is due to lithological variations e g mixtures of sands and clays with a single fluid saturating all the pores in the second model a single uniform lithology is saturated in mesoscopic patches by two immiscible fluids e g air and water in the third model the heterogeneity is at microscopic grain scales broken grain contacts and or micro cracks in the grains and the associated fluid response corresponds to squirt flow the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus crack porosity and or frequency is reduced to zero it is shown that squirt flow is incapable of explaining the measured level of loss 10 sup 2 q sup 1 10 sup 1 within the seismic band of frequencies 1 to 10 sup 4 hz however either of the two mesoscopic scale models easily produce enough attenuation to explain the field data

major palaeoenvironmental perturbation in an early aptian carbonate platform prelude of the oceanic anoxic event 1a the early aptian oceanic anoxic event oae 1a was characterized by intensified greenhouse climate conditions widespread accumulation of organic deposits in open marine settings major perturbations in the c cycle and a generalized increase in terrestrial runoff sedimentological diagenetic and chemostratigraphic analyses of lower aptian platform carbonates from the north cantabrian basin n spain illustrate the regional impact and effects of those global conditions on shallow marine environments the studied interval outlines four stages of platform evolution stage 1 earliest bedoulian is defined by an initial rapid marine transgression that led to deposition of shallow water oligotrophic photozoan skeletal assemblages and by a later interval of subaerial exposure stage 2 early bedoulian starts with a rapid transgression followed by deposition of grainstones that yield heterozoan assemblages more typical of mesotrophic conditions along with ferruginized oolites stage 3 early bedoulian is defined by the drowning of the carbonate platform and subsequent deposition of open marine marls which are thought to represent the local expression of the oae 1a finally stage 4 shows the return of shallow water photozoan carbonate sedimentation the carbonate o and c stable isotope records have revealed prominent negative excursions during deposition of the marly interval of the stage 3 which may be associated with the important global changes that occurred at the onset of the oae 1a the change in skeletal assemblages that preceded the isotopic excursions and the platform drowning documents conditions of environmental stress caused by a combination of local and global factors the global change coupled with increased basin subsidence triggered the drowning of the platform by progressive reduction of the growth potential of the carbonate factory

sedimentation fracturing and sliding on a pelagic plateau margin the middle jurassic to lower cretaceous succession of rocca busambra western sicily italy the jurassic succession of rocca busambra consists of two lithostratigraphic units a pile of peritidal limestones several hundreds of metres thick inici formation hettangian to sinemurian and a 2 to 15 m thick sequence of rosso ammonitico type pelagic limestones toarcian to lowermost berriasian an extensive interval of non deposition is evidenced by a thick fe mn oxide crust on the bounding disconformity and is recorded partially in the material contained within a complex network of neptunian dykes and sills seven lithofacies are distinguished in the rosso ammonitico these lithofacies show that the rosso ammonitico limestones differ from most analogues both in sicily and elsewhere sediments are mostly grain supported and non nodular obviously bottom currents were important during deposition of these sediments these currents were pulsating at different frequencies and induced winnowing intraclast production and early cement precipitation other rosso ammonitico lithosomes of late jurassic to earliest cretaceous age usually decimetre thick and discontinuous overlie the inici formation without any fe mn crust their anomalous stratigraphical and geometrical relationships show that they were deposited on an inclined stepped erosional surface incised in the sub horizontal inici formation this ancient escarpment is interpreted as the result of a mainly gravitational collapse of the margin of a pelagic plateau such mass wasting was probably due to the backstepping of the tectonic plateau basin margin that is not observable directly but may be inferred from circumstantial evidence this observation clearly shows that tectonic activity affected the rocca busambra sector of the west tethys continental margins a few tens of millions of years after the end of the rifting stage the anomalous rosso ammonitico sediments are the only indication of the escarpment and their occurrence in the stratigraphic record is probably more widespread than reported in the literature more accurate palaeoenvironmental and palaeogeographic reconstructions may depend on the identification of these sediments

mesozoic tectonics and volcanism of tethyan rifted continental margins in western sicily abstract the paleotectonic and volcanic features of the jurassic cretaceous carbonate successions outcropping in central western sicily allow us to restore the tectono sedimentary evolution of a sector of the african continental margin these successions consist of shallow to deep water mesozoic deposits that have formed in the carbonate platform to pelagic plateau depositional setting of the so called trapanese paleogeographic domain fieldwork including structural analyses has indicated the occurrence of lateral facies changes resedimented materials volcanic products pillow lavas and tuffitic deposits unconformity surfaces and paleofaults of different trends and age these data combined with facies and a physical stratigraphic analysis allow one to distinguish between the different tectono stratigraphic settings a structural low filled with thick pillow lavas and reworked deposits appears bordered by two main structural highs an articulate carbonate pelagic platform with a stepped fault margin and the flank of a structural high where the volcanoclastic deposits are interlayered with reworked reef materials suggest the occurrence of a submarine volcano that evolved into an atoll type carbonate shelf setting tectonic and magmatic events punctuated the sedimentary evolution during the early jurassic middle late jurassic early and late cretaceous the horst and graben structures connected by steeped margins and the occurrence of distinctive types of volcanic products suggest that the study areas could represent a sector of the jurassic cretaceous southern tethyan passive continental margin situated at the edge of the continental platform bordering those basinal areas where rifting and possible spreading processes were active during the mesozoic

laboratory experiments simulating a coastal river inflow the dynamics of buoyant water entering a rotating basin are studied using a series of laboratory experiments designed to elucidate the alongshore transport mechanisms in river plumes inflowing water which is discharged perpendicular to the tank wall is observed to form a growing anticyclonic bulge and a coastal current downstream of the bulge detailed simultaneous measurements of the velocity and buoyancy fields in the plume confirm that the bulge momentum is in a gradient wind balance and the coastal current is geostrophic the growth of the bulge and accumulation of fluid within it coincides with a reduction in coastal current transport to approximately 50 of the inflow discharge the bulge is characterized by a depth scale h w hich is proportional to the geostrophic depth hg and two time dependent horizontal length scales yc the displacement of the bulge centre from the wall and rb the effective radius of the bulge these two length scales are proportional to the inertial radius

seismic attenuation in porous rocks with random patchy saturation saturation of porous rocks with a mixture of two fluids has a substantial effect on seismic wave propagation in particular partial saturation causes significant attenuation and dispersion of the propagating waves due to the mechanism of wave induced fluid flow such flow arises when a passing wave induces different fluid pressures in regions of rock saturated by different fluids most models of attenuation and dispersion due to mesoscopic heterogeneities imply that fluid heterogeneities are distributed in a regular way however recent experimental studies show that mesoscopic heterogeneities have less idealized distributions and that the distribution itself affects attenuation and dispersion based on an approximation for the coherent wavefield in random porous media we develop a model which assumes a continuous distribution of fluid heterogeneities as this continuous random media approach assumes that there will be a distribution of different patch sizes it is expected to be better suited to modelling experimental data we also show how to relate the random functions to experimentally measurable parameters

velocity saturation relation in partially saturated rocks modelling the effect of injection rate changes the relationship between p wave velocity and fluid saturation in a porous medium is of importance for reservoir rock characterization forced imbibition experiments in the laboratory reveal rather complicated velocity saturation relations including rollover like patterns induced by injection rate changes poroelasticity theory based patchy saturation models using a constant fluid patch size are not able to describe these velocity saturation relations therefore we incorporate a saturation dependent patch size function into two models for patchy saturation this recipe allows us to model observed velocity saturation relations obtained for different and variable injection rates the results reveal an increase in patch size with fluid saturation and show a reduction in the patch size for decreasing injection rate this indicates that there can exist a distinct relation between patch size and injection rate we assess the relative importance of capillarity on velocity saturation relations and find that capillarity stiffening impairs the impact of patch size changes capillarity stiffening appears to be a plausible explanation when a decrease in the injection rate is expected to boost the importance of capillarity

seismic wave attenuation in the uppermost glacier ice of storglaciaren sweden we conducted seismic refraction surveys in the upper ablation area of storglaciaren a small valley glacier located in swedish lapland we estimated seismic wave attenuation using the spectral ratio method on the energy travelling in the uppermost ice with an average temperature of approximately 1 c attenuation values were derived between 100 and 300 hz using the p wave quality factor q p the inverse of the internal friction by assuming constant attenuation along the seismic line we obtained mean q p 6 1 we also observed that q p varies from 8 1 to 5 1 from the near offset to the far offset region of the line respectively since the wave propagates deeper at far offsets this variation is interpreted by considering the temperature profile of the study area far offset arrivals sampled warmer and thus more attenuative ice our estimates are considerably lower than those reported for field studies in polar ice 500 1700 at 28 c and 50 160 at 10 c and hence are supportive of laboratory experiments that show attenuation increases with rising ice temperature our results provide new in situ estimates of q p for glacier ice and demonstrate a valuable method for future investigations in both alpine and polar ice

semidiurnal switching of stratification in the region of freshwater influence of the rhine observations in the rhine region of freshwater influence rofi system in the north sea show evidence of large semidiurnal oscillations in stability superimposed on a mean stratification occurring throughout the stratified region at times of reduced mixing the amplitude of this semidiurnal variation is of the same order as the mean stability and frequently results in conditions being mixed or nearly mixed once per tide it is deduced that this semidiurnal variation results primarily from cross shore tidal straining which interacts with the density gradient to induce stratification this conceptual picture of the contributing processes has been tested in a one dimensional point model forced by the observed slopes and the local density gradients the model exhibits the same qualitative behavior as the observations produces oscillations in stratification of the amplitude observed and confirms the critical role of cross shore tidal straining the large cross shore shear nder stratified conditions is identified with the changes in ellipse configuration which are observed between mixed and stratified conditions the occurrence of semidiurnal variations in stability in the rhine rofi is thus inferred to be a consequence of the development of mean stability whenever the horizontal density gradients relax in conditions of low stirring

interpreting laboratory velocity measurements in partially gas saturated rocks it is an old problem in rock physics that the saturation dependence of high frequency laboratory velocities does not match the biot gassmann theory commonly used to predict the effects of gas on seismic velocities a new interpretation of laboratory velocity data shows that the saturation dependence is controlled by two previously published high frequency acoustic mechanisms 1 a gas pocket model that describes pressure equilibration between liquid and gas saturated regions of the pore space and 2 local fluid flow induced by pressure equilibration in pores with different aspect ratios when these two mechanisms are added to biot theory the result describes published velocity versus gas saturation data for a wide range of rock types these two mechanisms are negligible at the lower frequencies of seismic data so the saturation dependence of laboratory velocities cannot be used to predict the saturation dependence at seismic frequencies the one laboratory measurement that is relevant for predicting the seismic velocity is the ultrasonic velocity of the dry rock the dry rock velocities should be used in the biot gassmann theory to predict the full saturation dependence of the seismic velocities

geochemistry of speleothems from jurassic palaeokarst subbetic southern spain abstract speleothems growing on jurassic palaeokarstic cavity walls from the subbetic southern spain have been geochemically studied these speleothems contain more than one generation of low magnesian calcite lmc cements which grow into the cavities the simplest case is composed of two generations of precipitate the first cement is a non luminescent nl radiaxial fibrous calcite rfc with a fe mn ratio between 2 8 and 6 1 the second cement is a zoned dull luminescent zdl columnar palisade calcite cpc with a lower fe mn ratio the more complex case is composed of several generations of precipitate nl rfc and zdl cpc with interbedded mechanically deposited internal sediments petrographic and isotopic data of the host rocks suggest that they have been formed in the marine phreatic environment in contrast the isotopic composition of the internal sediment and of non skeletal grains of the host rocks suggest that they underwent diagenetic alteration in the marine meteoric mixing zone the isotopic composition of cements in speleothems and complete infillings of small cavities shows a typical meteoric inverted j trend the alternation of the nl and zdl cement stages in the speleothems is interpreted to be a result of hydrodynamic changes in the cementation environments these changes can be related to sea level fluctuations which affected the subbetic continental margin during the jurassic

quantitative estimation of water storage and residence time in the epikarst with time lapse refraction seismic the hydrodynamic characterization of the epikarst the shallow part of the unsaturated zone in karstic systems has always been challenging for geophysical methods this work investigates the feasibility of coupling time lapse refraction seismic data with petrophysical and hydrologic models for the quantitative determination of water storage and residence time at shallow depth in carbonate rocks the biot gassmann fluid substitution model describing the seismic velocity variations with water saturation at low frequencies needs to be modified for this lithology i propose to include a saturation dependent rock frame weakening to take into account water rock interactions a bayesian inversion workflow is presented to estimate the water content from seismic velocities measured at variable saturations the procedure is tested first with already published laboratory measurements on core samples and the results show that it is possible to estimate the water content and its uncertainty the validated procedure is then applied to a time lapse seismic study to locate and quantify seasonal water storage at shallow depth along a seismic profile the residence time of the water in the shallow layers is estimated by coupling the time lapse seismic measurements with rainfall chronicles simple flow equations and the petrophysical model the daily water input computed from the chronicles is used to constraint the inversion of seismic velocities for the daily saturation state and the hydrodynamic parameters of the flow model the workflow is applied to a real monitoring case and the results show that the average residence time of the water in the epikarst is generally around three months but it is only 18 days near an infiltration pathway during the winter season the residence times are three times shorter in response to the increase in the effective rainfall

saturation scale effect on time lapse seismic signatures quantitative interpretation of time lapse seismic signatures aims at assisting reservoir engineering and management operations time lapse signatures are thought to be primarily induced by saturation and pressure changes core flooding and reservoir flow simulations indicate that a change of the driving forces during dynamic fluid injection gives rise to a varying saturation scale this saturation scale is yet another variable controlling the time lapse seismic signal in this work we investigate the saturation scale effect on time lapse seismic signatures by analysing simple modelling scenarios we consider three characteristic saturation scales ranging from few millimetres to metres which may form during gas injection in an unconsolidated water saturated reservoir using the random patchy saturation model we compare the corresponding acoustic signatures i e attenuation reflectivity and seismic gather associated with each saturation scale the results show that the millimetre saturation scale produces minimum attenuation and the same seismic signatures with those obtained from the elastic modelling the centimetre saturation scale produces maximum attenuation whereas the metre saturation scale causes highest velocity dispersion the analyses of the time shift and amplitude change indicate that ignoring a time dependent saturation scale can result in biased estimation discrimination of the saturation and the fluid pressure in particular the 4d signal can be strongly affected by the saturationscale change when the reservoir gas saturation is low and the effective pressure is high in the presence of an increasing decreasing saturation scale during injection interpreting an observed time shift and amplitude change using the gassmann model will lead to underestimation overestimation of the change in gas saturation and fluid pressure we show that including the effects of capillarity and residual saturation into the rock physics modelling can potentially reduce the interpretation uncertainty due to the saturation scale change

relating river plume structure to vertical mixing abstract the structure of a river plume is related to the vertical mixing using an isohaline based coordinate system salinity coordinates offer the advantage of translating with the plume as it moves or expanding as the plume grows this coordinate system is used to compare the relative importance of different dynamical processes acting within the plume and to describe the effect each process has on the structure of the plume vertical mixing due to inertial shear in the outflow of a narrow estuary and wind mixing are examined using a numerical model of a wind forced river plume vertical mixing and the corresponding entrainment of background waters is greatest near the estuary mouth where inertial shear mixing is large this region is defined as the near field with the more saline far field plume beyond wind mixing increases the mixing throughout the plume but has the greatest effect on plume structure at salinity ranges just beyond the near field wind mixing is weaker at high salinity classes tha

seismic signatures of permeability in heterogeneous porous media in homogeneous poroelastic systems the permeability tensor practically does not influence propagating seismic waves in the low frequency range 0 1000 hz see e g schmitt 1989 gelinsky and shapiro 1996 in this paper we show that this situation changes in heterogeneous systems such as layered or fractured sediments due to the heterogeneities of poroelastic structures the attenuation of p waves is influenced by the permeability in an enhanced way we show however that such a seismic permeability can differ very strongly from the hydraulic permeability

stable isotopic and elemental relationships of ancient shallow marine slope carbonates cambro ordovician cow head group newfoundland implications for fluid flux abstract carbon and oxygen stable isotopic and trace elemental variations in diagenetic calcite and dolomite from slope and platform margin carbonates of the cambro ordovician cow head group western newfoundland are explained by calculations that consider variations in the water rock ratio during burial history of a reconstructed cross section of the continental margin platform margin deposits are preserved as blocks of limestone with calcified algae in slope strata the blocks contain neomorphic radial 18o 9 3 to 5 8 pdb 13c 0 7 to 1 4 pdb and blocky spar 18o 8 3 to 6 7 pdb 13c 0 6 to 1 2 pdb calcite sparry dolomite x18o 5 8 pdb x13c 0 6 pdb and lutecite length slow chalcedony 18o 27 9 to 29 7 smow reaction of these almost isotopically homogeneous rocks with sea water meteoric water and upward migrated basinal water is suggested by their distinctive fabrics and isotopic compositions the beds of slope limestone contain abundant calcite microspar and pseudospar 18o 9 2 to 6 6 pdb 13c 5 6 to 0 6 pdb dolomite 18o 9 3 to 2 8 pdb 13c 3 0 to 1 0 pdb and minor chert 18o 23 4 to 29 1 smow the three dolomite fabrics are fine crystalline rhombohedra that grew in clay rich carbonate mudstone medium crystalline replacive mosaics that are nonfabric selective and coarse white sparry rhombohedra associated with stylolites and fractures the microspar and pseudospar grew by widespread neomorphism of 1 fine grained detrital calcite or aragonite in lime mudstone and 2 calcite cement in calcarenite cathode luminescent patterns of calcites and dolomites suggest a prolonged history of recrystallizations dissolution precipitation on a fine scale during burial diagenesis with increasing distance basinward from the platform margin diagenetic calcite and dolomite are systematically depleted in the heavy isotopes of oxygen and carbon and diagenetic calcite is enriched in magnesium suggesting crystal growth and recrystallizations in evolved disgenetic fluids these data along with the burial history indicate that the limestones of the cow head group were systematically altered as greater amounts of burial fluids were either focused along preferred permeability pathways during compactive expulsion or recirculated during possible convective flow through strata farther from the platform margin

subaerial exposure and drowning processes in a carbonate platform during the mesozoic tethyan rifting the case of the jurassic succession of western sicily central mediterranean abstract the liassic carbonate platform succession outcropping at monte maranfusa central western sicily consists of a shallowing upward sequence of peritidal carbonates with jurassic to paleogene pelagic limestone and siliciclastic tertiary covers above the cyclic sequences of subtidal wackestones packstones intertidal microcrystalline carbonates with bird s eye pores and supratidal bioclastic grainstones are interbedded with dark layers of the following composition 1 dark gray compact and well cemented limestone with blackish clasts interpreted as calcretes a type of carbonate soil and 2 reddish calcite laminae deformed by elongated cavities filled with vadose silt interpreted as paleokarst this succession is crossed by almost vertical faults of the late liassic to miocene which often coincides with neptunian dykes filled by several generations of toarcian early miocene pelagic sediments another system of dykes known as neptunian sills filled by injected upper lias dogger pelagic sediments lies parallel to the stratification the parallel dykes were caused by the flexure of the platform during the jurassic and presumably by a planar slip in the carbonate rocks whereas neptunian dykes are caused by faulting episodes here we present evidence that the dark layers in the liassic succession of monte maranfusa previously described by many authors only as parallel dykes can actually be interpreted as a neptunian sills b pedogenic calcretes and c paleospeleothems therefore we found evidence of exposure flooding intervals in the evolution of the carbonate platform during the liassic linked to different pulses in both the subsidence tectonic activity and the sea level oscillations at the top fe mn crusts hardgrounds seal the carbonate platform succession which is in turn overlain by condensed pelagic deposits confirming its drowning during rifting processes

permian circumpacific deep water faunas from the western tethys sicily italy new evidences for the position of the permian tethys abstract circumpacific deep water faunas characterized mainly by radiolarians paleopsychrospheric ostracods and conodonts were found in the early middle and late permian deposits pertaining to the sicanian paleogeographic domain of western sicily near the western end of the eurasiatic tethys similar permian deep water faunas are known from the phyllite unit of crete and from oman in the latter area partly above oceanic crust all these occurrences indicate the presence of a late paleozoic tethys ocean immediately north of gondwana

chemistry and mineralogy of pyrite enriched sediments at a passive margin sulfide brine seep abyssal gulf of mexico pyrite is rapidly accumulating at the contact between the cretaceous limestones of the florida platform and the hemipelagic sediments of the abyssal gulf of mexico sediments sampled with the submersible alvin in 3266 m of water are associated with a dense community of organisms that depend on chemosynthetic primary production as a food source analysis of the chemistry mineralogy and textural composition of these sediments indicate that iron sulfide mineralization is occurring at the seafloor within an anoxic micro habitat sustained by the advection of hydrogen sulfide charged saline brines from the adjacent platform the chemosynthetic bacteria that directly overlie the sediments oxidize hydrogen sulfide for energy and provide elemental sulfur that reacts with iron monosulfide to form some of the pyrite the sediments are mixtures of pyrite 30 wt basr sulfates 4 wt clays and locally derived biogenic carbonates and are progressively being cemented by iron sulfides oxidation of hydrogen sulfide produces locally acidic conditions that corrode the adjacent limestones potential sources of s h2s fe ba and sr are discussed

continental margin brine seeps their geological consequences local dissolution observed at the base of the florida escarpment appears to result from acid generated by sea floor oxidation of dissolved sulfide species carried in brines that seep from the base of the escarpment the extent of seep corrosion depends upon the amount of sulfide that has exited the platform and the efficiency with which the acid attacks the limestones of the escarpment calculations suggest that brine seepage influences the shape of these escarpments by undercutting and steepening the carbonate continental margin edges other processes competing for the dissolved sulfides are bacterial chemosynthesis and sulfide mineralization which produces organic carbon and sulfide mineral rich deposits along the unconformity that separates the buried escarpment from onlapping abyssal sediments

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

remote monitoring of the mechanical instability induced by fluid substitution and water weakening in the laboratory abstract we studied the effect of fluid injection on the mechanical behaviour of the poorly consolidated and layered sherwood sandstone under varying stresses with micro seismic ms monitoring in order to highlight possible weakening effects water and inert oil have been injected into critically loaded samples to assess their effect on strength and elastic properties derive the ultrasonic signature of the saturation front for each fluid and the potential development of damage to this end the specimens were instrumented with 16 ultrasonic p wave transducers used for both passive and active monitoring during loading and fluid injection a first set of injection tests in hydrostatic conditions using either water or inert oil has been performed on samples subjected to low confining pressure water invasion in the pore space induces a significant decrease of the p wave velocity whereas oil invasion shows a velocity increase the velocity decrease associated with water injection is analysed in terms of attenuation mechanisms and corresponding critical frequencies a second series of injection tests with the same fluids has been performed during creep tests on critically loaded samples the development of mechanical instability inducing micro seismic activity is observed only when water is injected into the sample the recorded micro seismic events are spatially and temporally located thanks to the dedicated velocity models accounting for the initially homogeneous sample anisotropy and for the heterogeneous velocity field associated with fluid migration within the sample the consistency between the relocated clusters of events and the final damage pattern is verified thanks to x ray computed tomography images of the samples taken post mortem

evolution of pore space in the poza rica trend mid cretaceous mexico the poza rica trend of the tampico embayment mexico will ultimately produce more than 2 3 109 barrels of oil from mid cretaceous albian cenomanian basin margin deposits bioclastic grainstone packstone and wackestone are interbedded with polymictic lime breccia and dolomitized debris all were deposited by sediment gravity flow indigenous sediment was pelagic lime mud typical reservoir porosities are about 10 permeabilities average 2 md and rarely exceed 100 md porosity is largely the result of selective dissolution of rudist fragments which were originally aragonite detailed petrographic study with emphasis on the diagenetic products allows quantitative assessment of porosity at various diagenetic stages from original sediment to reservoir rock a relatively simple diagenetic history is reflected by about 90 of the samples studied primary porosity was reduced through lithification of matrix mud and initial cementation by clear equant to bladed non ferroan calcite later dissolution produced extensive skelmoldic and minor vuggy porosity subsequently non ferroan calcite cement reduced porosity before the emplacement of hydrocarbons reconstructed sediment porosities are comparable to but lower than modern counterparts the initial phase of cementation and presumed lithification of mud greatly reduced porosity in all lithologies but appreciably more porosity persisted in grainstone and packstone than in wackestone or mudstone dissolution produced a porosity resurrection which exceeded that of the initial sediment in some grainstones calcite cementation and local multiphase quartz cementation and dolomitization reduced porosity to present average values of 8 12 in grain supported rocks and 3 in mud supported rocks the greater persistence of primary porosity and therefore permeability in grain supported rocks probably accounts for their greater secondary porosity development and ultimate reservoir quality geometrically averaged permeabilities range from only 0 17 md in wackestone to 3 85 md in dolomite but differ significantly with rock type and grain size permeability increases with porosity in all lithologies the rate of increase is greater at higher porosities and with coarser grain sizes the agent for both early cementation and development of secondary porosity appears to have been meteoric water subaerial exposure appears to be ruled out however by a basin margin depositional environment and continued burial beneath upper cretaceous pelagic sediments early exposure to meteoric water can be explained by a hydrologic head developed during penecontemporaenous exposure that produced cavernous porosity in the adjacent golden lane trend descending meteoric water likely emerged as submarine springs along the tamabra trend deposition of pelagic limestone during the turonian blanketed part of the golden lane escarpment to enhance development of a large freshwater lens gaps in the blanket localized springs and influenced flow patterns within the poza rica field analogous freshwater circulation exists today in northern florida

acoustic signatures of partial saturation the relationship between elastic wave velocities and water saturation in a water gas reservoir depends strongly on whether saturation is heterogeneous patchy or homogeneous heterogeneity in saturation may result from lithologic heterogeneity because under conditions of capillary equilibrium different lithologies within a reservoir can have different saturations depending on their porosities and permeabilities we investigate this phenomenon by generating models of a reservoir in which we control the distribution of lithologic units and theoretically determine the corresponding velocity saturation relationship we assume a state of capillary equilibrium in the reservoir and determine the saturation level of each region within the reservoir from the corresponding capillary pressure curve for the lithologic unit at that location the velocities we calculate for these models show that saturation heterogeneity caused by lithologic variation can lead to a distinct dependence of velocity on saturation in a water gas saturated reservoir a patchy distribution of the different lithologic units is found to cause p wave velocity to exhibit a noticeable and almost continuous velocity variation across the entire saturation range this is in distinct contrast to the response of a homogeneous reservoir where there is only a large change in velocity at water saturations close to 100

fe mn encrusted kamenitza and associated features in the jurassic of monte kumeta sicily subaerial and or submarine dissolution abstract an unusually jagged dissolution surface capped by a thick fe mn crust is well exposed in small quarry cuts of the jurassic of monte kumeta it was formed on a crinoidal limestone substrate of pliensbachian age and is covered by upper bajocian ammonitico rosso type sediments all cross cut by several generations of neptunian dykes this peculiar surface is more or less coeval with hardgrounds fe mn capped dissolution surfaces and associated neptunian dykes described from other localities of the western tethys and currently subject to fierce debates as to their purely submarine or perhaps partly subaerial origin the major goal of this paper is to add new arguments to this debate by revealing the finest details of field relationships at a site particularly adapted to the study of this phenomenon field observations are supported by petrography and to a lesser extent by geochemistry results are as follows i vertical dissolution grooves pointing to dissolution by gravitationally controlled waters were detected on the sides of several micro topographic highs ii extensive intergranular dissolution predating the formation of the fe mn crust was proved in the substrate both on the micro and meso scale iii intense micro bio erosion and local phosphate enrichment were detected immediately underneath the crust iv a toarcian fauna was identified from the hollows of the irregular surface v synsedimentary faults and fractures clearly predating the major fe mn encrusted surface were observed and vi a meso scale synsedimentary growth structure post dating the fe mn crust which controlled the liassic depositional environment of monte kumeta is documented our conclusion is that the studied surface records at least three separate events of dissolution and precipitation sedimentation each having either erased or overprinted the effects of the previous one and therefore not permitting the exact reconstruction of all the details of the complex story to form the irregular surface in addition to a transient phase of subaerial exposure a complex history of bio erosion and submarine dissolution by fluids of widely different chemical composition is proposed to permit the mixing of sea water with fault controlled waters of higher temperature and with groundwaters introduced by deep circulation a scenario of down faulted blocks and an adjoining distant subaerially exposed region is invoked such a region provided the hydraulic drive for the postulated circulation the ultimate cause for the unusual phenomena under scrutiny was the combined effect of tectonics the local manifestation of early liassic rifting in the western tethys and the well known pliensbachian toarcian sea level rise

estimating rock porosity and fluid saturation using only seismic velocities evaluation of the fluid content in deep earth reservoirs or fluid contaminants in shallow earth environments has required the use of geophysical imaging methods such as seismic reflection prospecting interpretation of seismic velocities and amplitudes is based on theories of fluid saturated and partially saturated rocks that have been available since the 1950s here we present a new synthesis of the same physical concepts that uses compressional wave velocities together with shear wave velocities in a scheme that is much simpler to understand and apply yet yields detailed information about porosity and fluid saturation magnitudes and spatial distribution the key idea revolves around the fact that the density and the lame elastic parameter are the only two parameters determining seismic velocities that also contain information about fluid saturation at low enough frequencies gassmann s well known equations show that the shear modulus is independent of the fluid saturation level we use these facts to

tethyan ferromanganese oxide deposits from jurassic rocks in hungary fossil manganese nodules and encrustations from seamount and basin localities in the transdanubian central mountains of hungary are lithologically mineralogically and chemically similar to some modern marine ferromanganese oxide deposits and show no evidence of postdepositional changes other than cementation five groups of deposits were encountered fe mn nodules encrusted shells pavements stains and fe oxide encrusted intraclasts the first three of which are specific to the 9seamount9 environment and the last to the basins optical and electron microprobe investigation of the samples shows them to exhibit many similarities with modern ferromanganese oxide deposits and that many of the nodules are surrounded by a halo of dispersed ferromanganese oxides strongly suggesting that they continued to accrete metals through the pore waters of unlithified sediments for a period after burial by contrast pavements which appear to have grown on hardgrounds at the sea floor show little or no evidence of derivation of metals from underlying sediments geochemical investigations on the deposits show the seamount varieties to be closer in composition to most modern nodules and crusts than the basin varieties and that the latter are essentially manganese and trace element poor ferruginous deposits nevertheless all can be more or less compositionally equated with modern ferromanganese oxide deposits forming in marginal atlantic environments which would be in accord with the proposed depositional environment of the transdanubian central mountains based on other evidence

variation in p wave modulus with frequency and water saturation extension of dynamic equivalent medium approach abstractwe have developed a new modeling approach for the complex valued p wave modulus of a rock saturated with two phase fluid accounting for the variation with frequency and water saturation our method is based on the dynamic equivalent medium approach theory which predicts p wave modulus dispersion due to mesoscopic scale wave induced fluid flow wiff although the application of the original theory was limited to small fluctuation media we have extended it to also be applicable for high fluctuation media such as partially saturated rock our modification and extension consists of two components the first is introducing a scaling by the rigorous bounds for p wave velocity dispersion by mesoscopic scale wiff the second is to develop a model representing the effective patch size of stiffer fluid that controls the location of the dispersion curve we have found that the spatial correlation length of heterogeneity of saturated rock used in the original theory does not appropriately capture the effec

a simple theory for the fate of buoyant coastal discharges abstract a simple theory that predicts the vertical structure and offshore spreading of a localized buoyant inflow onto a continental shelf is formulated the theory is based on two competing mechanisms that move the buoyant fluid offshore 1 the radial spread of the lighter water over the ambient water being deflected by the coriolis force and producing an anticyclonic cyclostrophic plume and 2 offshore transport of buoyant water in the frictional bottom boundary layer that moves the entire plume offshore while maintaining contact with the bottom the surface expression of the cyclostrophic plume moves offshore a distance ys 2 3g h0 2i 2g h0 2i 1 2f where g is reduced gravity based on the inflow density anomaly h0 is the inflow depth i is the inflow velocity and f is the coriolis parameter the plume remains attached to the bottom to a depth given by hb 2l ih0f g 1 2 where l is the inflow width both scales are based solely on parameters of the buoyant inflow at its source there

proterozoic microbial reef complexes and associated hydrothermal mineralizations in the banfora cliffs burkina faso abstract the proterozoic guena souroukoundinga formation of the mopti arm gourma aulacogen southerm taoudeni basin consists of a shale dominated succession up to 200 m thick with scattered microbial reef complexes quarry exposures of the tiara reef complex allow reconstruction of a transect across back reef peritidal laminites reef margin and peri reef ooidal shoals and fore reef slope strata microbial carbonate productivity nucleated on isolated palaeohighs during transgression whereas its end was controlled by two tectonically induced drowning pulses that led to the successive record of onlapping kerogenous limestones and pelagic shales reef carbonates are crosscut by fractures and fissures occluded by hydrothermal mineralizations which are related to the rifting activity of the gourma aulacogen the tiara reef complex is similar to other proterozoic reefs in being composed nearly entirely of stromatolites although calcimicrobial filamentous and thromboid textures are locally abundant which contrast with their scarcity or absence in coeval stable platform microbial reefs of the northern taoudeni basin

formation and significance of a middle silurian ravinement surface on gotland sweden a laterally extensive and conspicuously smooth erosional surface is exposed near the wenlock ludlow boundary on east central gotland sweden it occurs in the reef complex area of a carbonate platform has an undulating topography and separates truncated bioherms and biostromes from overlying allochthonous high energy deposits on a basin regional scale the surface is associated to a shift from a prograding to a retrograding platform and to a substantial hiatus in basin marginal areas estonia the significance of the surface is further indicated by a clear cut truncation of the reef complex including m sized stromatoporoids along a distance of at least 20 km b an erosional relief exceeding 2 08 in c a conspicuously smooth nature in both palaeolows and palaeohighs d present although scarce subaerial diagenetic indications e g shallow karst features at the unconformity surface and pendant meniscus cement in the lowermost part of overlying strata e a locally occurring basal conglomeratic lag in overlying strata and 0 peritidal indications and as evident from at least one quarry onlapping geometry in overlying strata the unconformity has implications for the analysis of the middle silurian baltic basin evolution as well as for the interpretation of erosional surfaces on carbonate platforms in general based on the above characteristics the formation of the unconformity is attributed to a relative sea level fall causing subaerial exposure followed by transgressive abrasion in a rocky shore environment the unconformity hence constitutes a ravinement surface which based on the associated basin regional sedimentary changes is interpreted as coinciding with a regional exposure surface sequence boundary it thus increases our understanding of the hitherto poorly understood palaeogeographic evolution of the middle silurian baltic basin further the transgressive erosion was significant as well as recurrent as indicated by the clear cut truncation of large stromatoporoids at the unconformity surface and by truncated marine fossil fragments in upper edges of karst infills the unconformity therefore constitutes a good example of the capability of transgressive erosion in creating stratigraphic incompleteness and hence in removing subaerial indications on previously exposed carbonate platforms c 2004 elsevier b v all rights reserved less

microbially induced fe and mn oxides in condensed pelagic sediments middle upper jurassic western sicily abstract this article presents a petrographic comparison of the rosso ammonitico facies of western sicily and the original rosso ammonitico veronese of northern italy based on a total of 27 sections the rosso ammonitico has been the subject of numerous controversies that range from bathyal to shallow water platform sedimentation therefore it seemed interesting to verify if the term rosso ammonitico has the same geologic connotation from region to region the middle upper jurassic rosso ammonitico of western sicily is a condensed succession formed during a period of extensional synsedimentary tectonics related to the spreading of the ionian ocean slope to basin or pelagic carbonate deposits characterize the sedimentation which consists of reddish mudstones and wackestones the abundant fauna is composed of radiolarians protoglobigerinids saccocoma bositra associated with ammonites a few ferruginous hardgrounds fe mn oxide crusts and mn coated condensation horizons are also present the red matrices contain abundant fe mn encrusted microbored and bioeroded bioclasts sporadic fe mn oncolites composed of amorphous mn minerals and goethite are also conspicuous the matrix as well as the shells and the fillings of the complex associated veinlets are frequently altered into calcite microsparite submicronic iron bacterial and fungal filaments associated with mineralized extracellular polymeric substances eps are observed in the matrix they record dysaerobic microenvironments at or near the sediment water interfaces early mineralized discontinuities enhanced by subsequent pressure dissolution are reported in the succession mn ni bacterial filaments are exceptionally observed in the cortex of the fe mn oncolites as a consequence of an early lithification the mn filaments are poorly preserved the pigmentation of the rock is due to the dispersion of submicronic oxyhydroxides now goethite and amorphous iron formed by bacterial mediation during early diagenesis in microaerophilitic environments as in the case of the original rosso ammonitico veronese fe and mn bacteria fungi were able to produce bioconstructions which have no bathymetric significance the limiting factor must have been the oxygen content which was low in these very quiet and relatively deep environments thus the rosso ammonitico of northern and southern italy have a number of points in common but some obvious dissimilarities are observed that explain some of the various sedimentological interpretations among them the chemical composition is of particular importance more fe is present in veneto northern italy while mn is associated with the sicilian rosso ammonitico the sicilian localities were more proximal to oceanic magmatic sources which were related to the activity of the oceanic crust

seismic attenuation due to patchy saturation 1 in porous rocks saturated in patches by two immiscible fluids seismic compression causes the fluid with the larger bulk modulus to respond with a larger change in fluid pressure than the fluid with the smaller bulk modulus which results in fluid movement and seismic attenuation for virtual rock samples having fluid distributions obtained using the invasion percolation model attenuation is determined using finite difference numerical experiments based on the laws of poroelasticity analytical models are also proposed to explain the numerical results when oil invades water the equilibration is controlled by the geometry of the invading oil which has a narrow range of small diffusion lengths resulting in a single relaxation frequency at high frequencies and not much seismic band attenuation when water invades oil the defending oil controls the equilibration and a power law emerges for how attenuation varies with frequency due to the fractal nature of how saturation is varying with scale in the defending oil for air invading water the geometry of the defending water controls the equilibration and a large amount of attenuation is observed over a wide range of frequencies including the seismic band due to the wide range in water patch sizes however when water invades air the narrow fingers of invading water control the equilibration and there is a single relaxation frequency at high frequencies that does not result in much seismic band attenuation

the role of stratification dependent mixing for the stability of the atlantic overturning in a global climate model using the climber 3 coupled climate model of intermediate complexity the effect of a stratification dependent vertical diffusivity on the sensitivity of the atlantic ocean meridional overturning circulation to perturbations in freshwater forcing is investigated the vertical diffusivity is calculated as n where n is the local buoyancy frequency and the parameter is a measure of the sensitivity of the vertical diffusivity to changes in stratification independent of the stratification of the deep ocean is weakly increased as a response to an anomalous freshwater flux in the north atlantic in these experiments in the region of freshwater forcing and north of it this is caused by the freshwater anomaly itself but farther south it is associated with anomalously warm surface waters caused by a reduction of the northward oceanic heat transport subsequently and in opposition to results from previous studies the overturning is reduced by the anomalous freshwater flux independent of the choice of however the amount of reduction in overturning following a freshwater perturbation is found to depend critically on the choice of the mixing sensitivity i f cr the response is similar to the model s response using constant vertical diffusivity 0 for cr a sharp increase of the sensitivity is found the value of cr is found to be between 0 5 and 1 a general feedback is proposed explaining this threshold behavior if is large both positive and negative perturbations of stratification are amplified by associated changes in diffusivity in the experiments presented here this enhances the initial positive stratification anomaly in northern high latitudes which is created by the anomalous freshwater flux as a result convection is strongly reduced and the overturning is significantly weakened

improved understanding of velocity saturation relationships using 4d computer tomography acoustic measurements a recently developed laboratory method allows for simultaneous imaging of fluid distribution and measurements of acoustic wave velocities during flooding experiments using a specially developed acoustic sample holder that combines high pressure capacity with good transparency for x rays it becomes possible to investigate relationships between velocity and fluid saturation at reservoir stress levels high resolution 3d images can be constructed from thin slices of cross sectional computer tomography scans ct scans covering the entire rock core volume and from imaging the distribution of fluid at different saturation levels the x ray imaging clearly adds a new dimension to rock physics measurements it can be used in the explanation of variations in measured velocities from core scale heterogeneities computer tomography gives a detailed visualization of density regimes in reservoir rocks within a core this allows an examination of the interior of core samples revealing inhomogeneities porosity and fluid distribution this mapping will not only lead to an explanation of acoustic velocity measurements it may also contribute to an increased understanding of the fluid flow process and gas liquid mixing mechanisms in rock immiscible and miscible flow in core plugs can be mapped simultaneously with acoustic measurements the effects of core heterogeneity and experimentally introduced effects can be separated to clarify the validity of measured velocity relationships

discontinuities in carbonate successions identification interpretation and classification of some italian examples abstract the growing use of unconformities as bounding surfaces for new types of stratigraphic units seems not to be matched by a corresponding effort on process oriented researches on unconformities themselves this paper aims at giving a contribution to classification and understanding of discontinuities in carbonate successions from the outcrop perspective based on some italian examples a number of integrated criteria geometry sedimentology diagenesis biostratigraphy is proposed to recognise stratigraphic breaks old terms are discussed and sometimes redefined while some new terms are introduced the term discontinuity surface ds is proposed as a general one to indicate any stratigraphic interface where an interruption of sedimentation can be proved a ds can be characterized as a firm ground or a rock ground depending on its coherence at the moment of the renewal of sedimentation polygenic and simple omission surfaces are separated within firm grounds if a recognizable gap is either present or not a third kind of firm ground revealed only by biostratigraphy has been called hidden discontinuity surface two categories of rock grounds are also distinguished hard grounds and inherited rock grounds if respectively generation of the ds and or deposition of the overlying sediments took place in the same environment of the underlying sediments or not a genetic interpretation for each type of discontinuity is proposed the largest variety of ds s occurs in pelagic sediments some discontinuities hard grounds and simple omission surfaces are attributed to increased bottom current activity during sea level falls others polygenic omission surfaces and hidden ds s are interpreted as submarine slide scars either with or without the overprint due to exposure on the seafloor the ds s separating different facies e g platform and pelagic ones are interpreted to be due to tectonics the relevance of the recognized ds s to sequence stratigraphy is briefly discussed

subaerial exposure and deposition of shallowing upward sequences evidence from stable isotopes of purbeckian peritidal carbonates basal cretaceous swiss and french jura mountains purbeckian lowermost cretaceous peritidal carbonates are characterized by open marine lagoonal intertidal and lacustrine facies arranged in milankovitch type shallowing upward sequences shallowing upward sequences typically consist of 2 6 individual beds the sequences may be i complete ii incomplete or ii pedogenetically overprinted reflecting the duration of subaerial exposure and or the extent of erosion and pedogenetic modification at the cycle tops the stable isotopic composition of the peritidal micrites reveals homogenous 6 o values attributed to diagenetic stabilization in a meteoric water buffered system carbon isotopes show three distinctly different carbon isotope patterns dependent on the completeness of the shallowing upward sequences complete shallowing upward sequences consist of l6 individual carbonate beds the carbon isotope values show a facies dependent pattern open marine carbonate muds record enriched 6i3c values of 0 28 while lagoonal 0 82 intertidal 2 46 10 and lacustrine micrites 2 96 are increasingly depleted this distinct pattern is explained by carbonate mud deposition in environments of differing salinity and marine influence incomplete sequences 2 5 carbonate beds are characterized by depleted 6 c values below subaerial exposure surfaces that become progressively enriched in c with increasing depth pedogenetically overprinted sequences 1 3 carbonate beds show strong i3c depletion throughout the sequence with little variation in the carbon isotopic composition the depleted values 4 51 10 of the pedogenetically altered micrites suggest that modification during subaerial exposure was associated with equilibration with meteoric solutions enriched in isotopically light soil gas coz the duration of subaerial exposure is the most crucial factor determining the extent of pedogenetic alterations the completeness of the shallowing upward sequences and the carbon isotope pattern the recorded patterns clearly illustrate that micrites have a good potential for the preservation of their primary carbon isotopic composition if the duration of subaerial exposure is rather brief otherwise the recorded carbon isotope patterns may support sequence stratigraphic analysis by providing a refinement of the time stratigraphic interpretation

characterization of fractured reservoirs using a consistent stiffness permeability model focus on the effects of fracture aperture in this paper we propose a method for the characterization of naturally fractured reservoirs by quantitative integration of seismic and production data the method is based on a consistent theoretical frame work to model both effective hydraulic and elastic properties of fractured porous media and a non linear bayesian method of inversion that provides information about uncertainties as well as mean ormaximum likelihood values we model a fractured reservoir as a porous medium containing a single set of vertical fractures characterized by an unknown fracture density azimuthal orientation and aperture we then look at the problem of fracture parameter estimation as a non linear inverse problem and try to estimate the unknown fracture parameters by joint inversion of seismic amplitude versus angle and azimuth data and dynamic production data once the fracture parameters have been estimated the corresponding effective stiffness and permeability tensors can be estimated using consistent models a synthetic example is provided to clearly explain and test the workflow it shows that seismic and production data complement each other in the sense that the seismic data resolve a non uniqueness in the fracture orientation and the production data help to recover the true fracture aperture and permeability because production data are more sensitive to the fracture aperture than the seismic data

one dimensional random patchy saturation model for velocity and attenuation in porous rocks porous rocks encountered in hydrocarbon reservoirs are often saturated with a mixture of two or more fluids generation of synthetic seismograms as well as interpretation of in situ attenuation measurements require a theoretical understanding of the relation between the heterogeneous distribution of fluid patches and the acoustic properties of rocks thus the problem of calculating acoustic properties of rocks saturated with a mixture of two fluids has attracted considerable interest white 1975 murphy 1982 gist 1994 mavko and mukerji 1998 pride et al 2004 at the same time this problem is also interesting from the theoretical point of view because partially saturated rocks represent a particularly interesting situation when the effects of dynamic poroelasticity may be significant at seismic or sonic frequencies indeed it is a radical departure from the situation with a porous material fully saturated with a single fluid such a fully saturated material exhibits frequency dependent effects only at frequencies comparable with biot9s characteristic frequency bourbie et al 1987 c f where f is the fluid density is fluid viscosity is permeability and is porosity for frequencies much lower than c the dynamic effects can be ignored and gassmann theory applies

finite difference modeling of wave propagation and diffusion in poroelastic media numerical modeling of seismic waves in heterogeneous porous reservoir rocks is an important tool for interpreting seismic surveys in reservoir engineering various theoretical studies derive effective elastic moduli and seismic attributes from complex rock properties involving patchy saturation and fractured media to confirm and further develop rock physics theories for reservoir rocks accurate numerical modeling tools are required our 2d velocity stress finite difference scheme simulates waves within poroelastic media as described by biot s theory the scheme is second order in time contains high order spatial derivative operators and is parallelized using the domain decomposition technique a series of numerical experiments that are compared to exact analytical solutions allow us to assess the stability conditions and dispersion relations of the explicit poroelastic finite differ ence method the focus of the experiments is to model wave induced flow accurately in the vicinity of mesoscopic hete

interference between shallow and deep seated structures in the sicilian fold and thrust belt italy abstract the fold and thrust belt in western sicily is characterized by the presence and interference of shallow and deep seated compressional structures which were generated and developed at different structural levels the shallow structures consist of imbricated thrusts and asymmetric folds with a typical wavelength of 2 km involving relatively thin deep water units these units are superimposed on thick platform carbonate units along a wide and originally almost flat floor thrust the axial trend of the folds is variable as multi phase folding often occurred producing a characteristic interference pattern reflecting continuous variations of the apparent transport direction during the emplacement i e rotation of the allochthonous thrust sheets the deep seated structures consist of large double verging pop up structures with a typical wavelength of 5 10 km involving thicker platform carbonate successions the deep seated structures are characterized by large folds with vertical to overturned limbs caused by high angle transpressive ramps that reactivated previous i e mesozoic synsedimentary normal or transtensional faults the floor thrust of the shallow structures was passively deformed by the subsequent growth of the underlying younger deep seated structures large clockwise rotations of the tectonic units occurred during the compressional deformation and the amount of rotation is apparently related to the timing and amount of the tectonic transport

an equivalent medium model for wave simulation in fractured porous rocks seismic wave propagation in reservoir rocks is often strongly affected by fractures and micropores elastic properties of fractured reservoirs are studied using a fractured porous rock model in which fractures are considered to be embedded in a homogeneous porous background the paper presents an equivalent media model for fractured porous rocks fractures are described in a stress strain relationship in terms of fracture induced anisotropy the equations of poroelasticity are used to describe the background porous matrix and the contents of the fractures are inserted into a matrix based on the fractured equivalent medium theory and biot s equations of poroelasticity two sets of porosity are considered in a constitutive equation the porous matrix permeability and fracture permeability are analysed by using the continuum media seepage theory in equations of motion we then design a fractured porous equivalent medium and derive the modified effective constants for low frequency elastic constants due to the presence of fractures the expressions of elastic constants are concise and are directly related to the properties of the main porous matrix the inserted fractures and the pore fluid the phase velocity and attenuation of the fractured porous equivalent media are investigated based on this model numerical simulations are performed we show that the fractures and pores strongly influence wave propagation induce anisotropy and cause poroelastic behaviour in the wavefields we observe that the presence of fractures gives rise to changes in phase velocity and attenuation especially for the slow p wave in the direction parallel to the fracture plane

paleogeography and structure of the central mediterranean sicily and its offshore area abstract the geology of the mainland and offshore of sicily is illustrated by a few geologic sections and seismic profiles across the late cenozoic orogenic belt of central and western sicily and across the sardinia channel and sicily straits this belt is the result of several tectonic events deformation involved mainly the sedimentary cover of the old african continental margin characterized by a broad basinal domain flanked along its external southern margin by a shallow water carbonate platform attached to africa in the triassic compressional deformation started in the more internal basinal rock assemblages overlying a thinned crust the most important structural characteristic of the early phase of thrusting is the duplex pile forming the bulk of the chain in central western sicily the structure consists of a basal allochthon made up of permian to middle triassic layers an intermediate duplex wedge composed of competent mesozoic carbonates and a roof complex including upper mesozoic lower tertiary less competent rocks large scale clockwise rotation of the thrusts accompanied transpressional movements in the hinterland during the pliocene right oblique reverse faults modified the previous tectonic contacts between the allochthons in the hinterland zones contemporaneous south directed imbrications affected the southern external areas progressively incorporating foreland and piggyback basins development of the gela thrust system appears to be linked to the transpressional event its accretion is also related to contemporaneous underthrusting at deeper levels of mesozoic carbonate substratum the older buried thrust sheets were pushed up to the surface breaching the deformed tertiary cover of the gela ts northwards in the belt post messinian normal growth faults opened half graben whose sedimentary fill underwent structural inversion alternation of extension and compression tectonics characterizes the sicilian continental margin in the last million years

black shales and carbon isotopes in pelagic sediments from the tethyan lower jurassic detailed sampling and analysis of jurassic pelagic limestones and marls from italy hungary and switzerland have enabled construction of an isotope stratigraphy across the pliensbachian toarcian boundary with resolution to the zonal level the oxygen isotope record is unremarkable the carbon isotopes however show two positive excursions one relatively minor during the pliensbachian margaritatus zone subnodosus subzone the other more major during the toarcian early falciferum zone where a maximum 13c value of 4 52 pdb is attained these intervals are known to be favoured periods of organic rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record a comparable phenomenon has been documented from the cenomanian turonian boundary in the cretaceous where it has been referred to the influence of an oceanic anoxic event some italian sections spanning this lower jurassic interval contain organic rich shales in the falciferum zone the isotopic signatures from their included locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve carbon isotopes from the organic carbon itself are extremely negative falling to 33 pdb and in one section examined in detail correlate with the calcium carbonate content of the shales they may reflect a partial change to a non calcified planktonic biota during deposition of this lime poor interval possibly responding to upwelling and increased fertility of near surface waters the onset of upwelling may have been as early as spinatum tenuicostatum zone time that is at the pliensbachian toarcian boundary

seismic study of the low permeability volume in southern france karst systems locating groundwater in deep seated karst aquifers is inherently difficult with seismic methods we studied the upper epikarst and the underneath low permeability volume lpv of several karst systems located in the southern quercy and larzac regions of france and found that refraction tomography was effective only in the epikarst and not in the lpv we evaluated a 3d case study using a combination of surface records and downhole receivers to overcome this limitation this 3d approach unveiled a set of elongated furrows at the base of the epikarst and identified heterogeneities deep inside the lpv that may represent high permeability preferred pathways for water inside the karst to achieve the same result when no borehole was available we studied seismic amplitudes of the wavefield recognizing that wave induced fluid flow in low permeability carbonates is a driving mechanism of seismic attenuation we developed a workflow describing the heterogeneity of the lpv with spectral attributes derived from surface consistent decomposition principles and we validated its effectiveness at benchmark locations we applied this workflow to the 3d study and found a low amplitude signal area at depth we interpreted this anomaly as a water saturated body perched above the aquifer

repeated events of hardground formation and colonisation by endo epilithozoans on the sediment starved pontine continental slope tyrrhenian sea italy abstract rock samples dredged offshore the pontine archipelago 400 2000 m water depth were studied by palaeontological analyses of planktic foraminifera and endo epilithozoan faunas colonising fe mn crusts and by petrographic analyses of volcanic samples palaeontological and petrographic analyses have revealed a complex plio pleistocene depositional history controlled by hemipelagic sedimentation and volcanic activity with episodic non depositional phases the sedimentary deposits are associated with ferromanganese hardgrounds more or less colonised by endolithic and epilithozoan organisms the presence of foraminifera typical of tropical and subtropical waters such as globigerinoides ruber globigerinoides trilobus pulleniatina obliquiloculata and sphaeroidinella dehiscens indicates that the micritic deposition occurred during warm climatic periods whilst micrite cementation and hardground formation are here attributed to colder climates the depositional processes recognised on the pontine continental slope reveal a sediment starved condition that locally resemble those of seamount environment the slope sedimentation found in the pontine archipelago can be helpful in the interpretation of ancient deposits from seamounts and continental slope depositional environments characterised by hardground and hiatuses

large microbial foraminiferal oncoids from condensed lower middle jurassic deposits a case study from the tatra mountains poland abstract microbial foraminiferal macrooncoids have been found in the toarcian aalenian limestones of the kri na unit in the tatra mountains western carpathians the oncoids were formed by the consortium of microbes bacteria and fungi and encrusting foraminifers dominated by nubecularia aff mazoviensis dolosella sp 1 and tolypammina sp the microbial bodies and biofilms are mineralized with iron hydrooxides and or oxides the association of foraminifers with microbes is supposed to be an adaptation of foraminifers to oligotrophic conditions on the sea floor it is very likely that the biofilm served as a continuous food source for the encrusting foraminifers formation of the oncoids was possible under conditions of low rates of deposition and periodic weak water agitation deposition of the oncoid bearing limestones took place during gradual deepening of the basin and associated with increasing oligotrophy at the sea floor

bounds on low frequency seismic velocities in partially saturated rocks the most common technique for estimating seismic velocities in rocks with mixed pore fluid saturations is to use gassmann s relations with an effective fluid whose density and compressibility are averages of the individual pore fluid properties this approach is applicable only if the gas oil and brine phases are mixed uniformly at a very small scale so the different wave induced increments of pore pressure in each phase have time to diffuse and equilibrate during a seismic period in contrast saturations that are heterogeneous over scales larger than the characteristic diffusion length i e patchy saturation will always lead to higher seismic velocities than if the same fluids are mixed uniformly at a fine scale critical saturation scales separating uniform from patchy behavior are typically of the order 0 1 1 cm for laboratory measurements and tens of centimeters for field seismic frequencies for low seismic frequencies velocities corresponding to patchy and homogeneous saturations represent a

effect of fracture fill on frequency dependent anisotropy of fractured porous rocks in fractured reservoirs seismic wave velocity and amplitude depend on frequency and incidence angle the frequency dependency is believed to be principally caused by the wave induced flow of pore fluid at the mesoscopic scale in recent years two particular phenomena patchy saturation and flow between fractures and pores have been identified as significant mechanisms of wave induced flow however these two phenomena are studied separately recently a unified model was proposed for a porous rock with a set of aligned fractures with pores and fractures filled with two different fluids existing models treat waves propagating perpendicular to the fractures in this paper we extend the model to all propagation angles by assuming that the flow direction is perpendicular to the layering plane and is independent of the loading direction we first consider the limiting cases through poroelastic backus averaging and then we obtain the five complex and frequency dependent stiffnesses of the equivalent ti medium as a function of the frequency the numerical results show that when the bulk modulus of the fracture filling fluid is relatively large the dispersion and attenuation of p waves are mainly caused by fractures and the values decrease as angles increase almost vanishing when the incidence angle is 90 propagation parallel to the fracture plane while the bulk modulus of fluid in fractures is much smaller than that of matrix pores the attenuation due to the partial saturation mechanism makes the fluid flow from pores into fractures which is almost independent of the incidence angle this article is protected by copyright all rights reserved