burial history of palaeozoic strata in belgium as revealed by conodont colour alteration data and thickness distributions thickness distributions of devono carboniferous formations and their relationship to conodont colour alteration indices cais from over 500 sample locations in belgium and northern france have been studied to reconstruct the thermal alteration and burial history of palaeozoic rocks the depositional centre during eifelian through visean times was located in the subsiding southern part of the dinant basin forming a thick sedimentary pile of probably more than 3 5 km in order to explain conodont cais chiefly resulting from upper carboniferous sedimentation two different depositional centres are considered giving rise to approximately 4 5 km of sediment in the central part of the dinant and namur basins as a consequence of the northward shifting variscan fold belt the upper carboniferous succession in the southern part of the dinant basin and in the rocroi area was reduced or absent conodont cais together with other thermal alteration data from the condroz massif indicate that this area was a structural high for most of the devonian the brabant massif was probably covered with approximately 1 5 2 0 km of upper carboniferous sediments in the south and less than 1 0 km in the central and northern parts in the central campine basin visean strata could have been buried by 3 5 4 5 km of upper carboniferous rocks

microstructural observations on natural syntectonic fibrous veins implications for the growth process abstract syntectonic antitaxial and ataxial fibrous veins were investigated using sem microprobe cathodoluminescence cl and optical microscopy in antitaxial calcite veins fibres and surrounding selvage grew simultaneously with similar growth rates of crystallographically differently oriented grains new material precipitated at the vein margin in antitaxial and bi mineralic ataxial microstructures bridges of country rock material formed during vein growth in an initial en echelon vein system in our antitaxial and bi mineralic ataxial samples the spacing of solid inclusions does not reflect individual crack seal openings

vertical tectonics and the origins of bsrs along the peru margin abstract the distribution of bottom simulating reflections bsrs which mark the base of the gas hydrate zone on marine seismic records across the peru margin is examined with respect to tectonic uplift sedimentation and carbon content of sediment where accretion of only deep ocean pelagic sediment containing less than 1 carbon is seismically imaged no bsr is observed no bsr is apparent on seismic records of carbon rich 4 8 sediment of rapidly subsiding basins bsrs are abundant on records of carbon rich sediment affected by tectonic uplift and or rapid sedimentation in areas of uplift the bottom simulating reflectors contain small amounts of free gas in contact with sediment containing small amounts of gas hydrate during uplift free gas is released from gas hydrates by dissociation as the hydrate phase boundary shifts upward with respect to sea level the strong effects of free gas in reducing seismic velocity and gas hydrate in increasing velocity can explain the relatively small total quantities of gas and hydrate indicated by observations of bsrs off peru

observation and tentative interpretation of a double bsr on the nankai slope seismic data collected during the french japanese kaiko tokai cruise of r v l atalante on the upper slope of the eastern nankai margin reveal the simultaneous presence at two distinct depths below the seafloor of two bottom simulating reflector bsr type reflectors the upper bsr is traced as a continuous reflector over about 10 km as water depth decreases from 850 m to 550 m its depth below seafloor decreases from 200 m to 40 m the lower bsr is traced at 50 100 m below the upper one the two bsrs end abruptly near the summit of the daichii tenryu knoll into an area where the 3 5 khz record suggests active gas expulsion through the seabed the observed depth of the upper bsr fits the predicted one for the base of the methane gas hydrate stability zone as estimated from present temperature and pressure conditions at the seafloor and in the slope sediments thus we interpret the upper bsr as an active methane hydrate bsr we further suggest that the lower bsr is a residual hydrate related bsr this could have followed a recent migration of the base of the methane hydrate stability zone from the lower bsr to the upper one as possible causes for this migration we discuss sea bottom warming and tectonic uplift the bsr migration could have occurred as a response to a 1 2 c sea bottom warming or with an equivalent effect an event of fast uplift of the seafloor by about 90 m we do not discard other interpretations of the lower bsr such as an active hydrate related bsr formed from a mixture of gases

on the critical state characteristics of methane hydrate bearing sediments abstract reasonable prediction of marine ground stability is vital for the safe exploitation of methane gas from the seabed and development of relevant technologies for gas production constitutive models based on a critical state soil mechanics framework for methane hydrate bearing sediments have been proposed in recent decades they required careful calibration of laboratory results to obtain accurate information on model parameters this study presents a comprehensive analysis of triaxial shear test data to examine the effects of hydrate saturation on the geomechanical characteristics of methane hydrate bearing sediments particularly at the critical state multiple critical state lines are identified for methane hydrate bearing sediments with different levels of hydrate saturation on the specific volume and logarithm of mean stress plane a rise in hydrate saturation shifts the critical state line of methane hydrate bearing sediments upward and slightly increases the gradient of critical state line in the v ln p plane non unique critical state lines are observed for methane hydrate bearing sediments under plane strain loading conditions considering methane hydrate saturation as an extra dimension of critical states the critical state line in the plane of specific volume and logarithm of mean stress becomes a three dimensional critical state surface

large scale sea ice drift and deformation comparison between models and observations in the western weddell sea during 1992 statistical comparisons between numerical sea ice models and an observed large scale strain array in the western weddell sea during 1992 are used to evaluate the performance of three of the more generally utilized sea ice rheology formulations results show that sea ice velocity is reproduced with relatively high accuracy 90 coherence 80 normalized cross correlation in models having high quality atmospheric forcing fields e g the european centre for medium range weather forecasts on the other hand temporal and spatial variability of the velocity field as exemplified by progressive vector plots and ice deformation respectively are reproduced less accurately coherence and normalized cross correlation 50 in terms of model sensitivity this means that deformation and temporal variability are more discriminating in terms of elucidating specifics about the constitutive relation and mechanical properties of sea ice on a large scale for example inclusion of both compressive and shear stresses is important in attaining a proper probability distribution of deformation relative to observations additional analysis shows that adjustments to specific model parameters improve the model results for either drift or select deformation components but no best solution could be found given the models examined here results suggest that inclusion of more physically based processes such as subdaily tidal and inertial oscillations reconsideration of the boundary layer formulation and consideration of anisotropy may be necessary to include in next generation sea ice models especially those that are intended for coupling with high resolution eddy resolving ocean models

long term sea ice dynamics simulations using an elastic plastic constitutive law a quasi steady elastic plastic sea ice dynamics model is introduced for long term simulations tidal and inertial oscillations are removed by discarding the negligible inertia term with this assumption the model is integrated using an implicit numerical scheme results are shown for a one dimensional case this approach eliminates the elastic waves that typically contaminate elastic plastic simulations and allows the elastic plastic constitutive law to be integrated over longer time periods with the potential for being used effectively for climate dynamics studies

role of off shelf to on shelf transitions for east antarctic sea ice dynamics during spring 2003 1 during austral spring 2003 mesoscale sea ice drift and deformation off east antarctica were investigated using in situ data from a nine buoy array upon deployment the array comprised an area of about 4000 km2 with a mean ice concentration of 96 half hourly sea ice velocities were coherent across all buoys at zonal meridional separations of less than 160 km 70 km regional cross spectral correlation was high at synoptic scales and also at semidiurnal periods off the continental shelf atmospheric synoptic scale forcing explained in excess of 85 of the ice drift variability this is significantly more than found in the weddell sea where significant ice drift variability is derived from oceanic forcing peak frequencies of semidiurnal contributions covaried with latitude and are largely associated with the inertial response over the continental shelf coincident diurnal and semidiurnal variances in ice motion arose from tidal forcing net divergence over 37 days resulted in an expansion to 270 of the initial area although regional ice concentration reduced only slightly high frequency processes namely inertial response and to a lesser degree tidal forcing dominated the variability of all deformation parameters in contrast to ice motion low frequency processes played a secondary role in sea ice deformation this high frequency dominance is similar to what has been found in the weddell sea although many observations there were limited to the continental shelf where tidal processes dominate sea ice motion and deformation were not affected by a seasonal transition nor did the regional ice characteristics show any signal of seasonal change instead local ice dynamics were strongly influenced by bathymetrically dependent processes

evolution of metamorphic fluids at the variscan fold and thrust belt in eastern belgium abstract quartz veins in the southern greenschist facies metamorphic border of the stavelot venn massif belgium have been examined a detailed petrographical study of these quartz veins indicates the presence of eleven quartz stages a microthermometric analysis shows the expulsion of three main fluid types during the palaeozoic in the first quartz stage i of caledonian age mixed aqueous gaseous h 2 o co 2 nacl fluid inclusions are present the post caledonian and pre variscan second stage ii is characterised by gaseous co 2 n 2 inclusions occurring along inter crystal grain boundaries and by aqueous h 2 o nacl intra crystal inclusions the quartz stages iii vi which formed during the variscan period contain primary mixed aqueous gaseous h 2 o co 2 nacl inclusions all with an equal bulk chemical composition post variscan quartz stages vii xi could not be investigated microthermometrically the combination of microthermometry chlorite geothermometry and geothermal gradients reveals minimum trapping conditions of 200 mpa and 200 c for stage i quartz and 175 275 mpa and 385 435 c for quartz stages iii vi the trapping conditions of stage ii quartz could not be determined due to the strong recrystallisation of the quartz veins at the lower metamorphic variscan thrust front distinct temperature anomalies are associated with thrust faults as indicated by conodont colour alteration index cai vitrinite reflectance data chlorite geothermometry and fluid inclusion microthermometry the expulsion of metamorphic fluids generated at the southern part of the stavelot venn massif could have caused the distinct temperature anomalies along variscan thrust faults alternatively some of these anomalies could have been induced by deeply circulating meteoric fluids

a double bottom simulating reflector in the western ross sea antarctica 1 we present seismic evidence of the presence of gas hydrates and free gas in victoria land basin western ross sea antarctica the occurrence of gas hydrates is inferred from a bottom simulating reflector bsr the first identified in the ross sea area the gas presence was analyzed through targeted reprocessing of the multichannel seismic reflection data 3000 m streamer 120 channels 60 fold acquired in 1990 by the italian r v ogs explora the seismic data were reprocessed in order to increase the signal to noise ratio by adopting a true amplitude approach allowing a subsequent amplitude variations with offset avo analysis to extract information on both p and s wave reflectivity along a profile from the deeper basin to an intrabasin structural high the bsr evolves into crosscutting reflectors ccrs and enhanced amplitude reflectors ears locally another seismic event is interpreted to be a second bsr bsr0 identified about 150 m below the first bsr and is possibly related to the presence of a mixture of gases comprising methane and hydrocarbons with heavier molecular weight and therefore associated with a deeper hydrate stability zone the presence of faults controls the upward gas migration connecting the free gas zone below the bsr and the mud volcanoes and pockmarks on the seafloor the modeling of the hydrate equilibrium zone shows that the observed bsr bsr0 could be stable at the present pressure temperature conditions

fluid inclusion evidence for progressive folding during decompression in metasediments of the voltri group western alps italy abstract quartz veins syntectonic to distinct folding events in metasediments from the voltri group ligurian alps were studied in order to compare fluid and structural evolution studied veins vs1 vs2 vs3 pertain to three distinct generations of folds f 1 f 2 f 3 that formed during the retrograde metamorphic evolution two types of fluids characterize the different generations of veins and are represented essentially by aqueo carbonic mixtures of moderate salinity with decreasing densities 1 01 0 41 g cm 3 the chemical evolution is characterised by a progressive decrease of h 2 o from early fluids associated with opening of vs1 and vs2 xco 2 0 08 to fluids related to vs3 formation xco 2 0 3 the close match between the fluids in vs1 and vs2 suggests that the development of two superimposed systems of folds f 1 and f 2 folds occurs under very similar p t conditions during a progressive and continuous deformational event at glaucophanic and or barroisitic metamorphic grade a different evolution is outlined for the formation of vs3 during low greenschist grade successive isochores allow us to define a retrograde decompression path for the voltri group present results indicate that fluid inclusions are powerful markers to constrain the p t t conditions of different folding events

the boudinage question in the high ardenne slate belt belgium a combined structural and fluid inclusion approach abstract the terms boudin and boudinage 1 were first introduced as descriptive terms for particular geometric features associated with quartz veins in competent metaquartzitic layers in the high ardenne slate belt belgium the occurrence of the boudins has subsequently been used to draw kinematic conclusions on a pre variscan extensional event in the rhenohercynian belt in this paper a combined structural and fluid inclusion approach allows proposing a new and more representative kinematic model for the development of the veins and associated structures moreover the kinematic significance of interboudin veins is emphasized in this regard microthermometry of primary co 2 n 2 fluid inclusions in the quartz of the interboudin veins suggests that the origin of vein development is hydraulic fracturing in an already compressional setting this suggestion implies the presence of fluid and near lithostatic fluid pressures to permit fracturing at great depths where the rocks otherwise would be either stable or in the realm of ductile behaviour the vein filling fluid had a local origin and was most likely related to the formation of bedding parallel dissolution seams within the host rock veining is followed by layer parallel shortening resulting in the development of double sided mullions at both interfaces of metaquartzitic layers pinned by pre existing veins subsequently these polyphase structures behave passively in the variscan deformation

velocity structure of a bottom simulating reflector offshore peru results from full waveform inversion abstract much of our knowledge of the worldwide distribution of submarine gas hydrates comes from seismic observations of bottom simulating reflectors bsrs full waveform inversion has proven to be a reliable technique for studying the fine structure of bsrs using the compressional wave velocity we applied a non linear full waveform inversion technique to a bsr at a location offshore peru we first determined the large scale features of seismic velocity variations using a statistical inversion technique to maximise coherent energy along travel time curves these velocities were used for a starting velocity model for the full waveform inversion which yielded a detailed velocity depth model in the vicinity of the bsr we found that the data are best fit by a model in which the bsr consists of a thin low velocity layer the compressional wave velocity drops from 2 15 km s down to an average of 1 70 km s in an 18 m thick interval with a minimum velocity of 1 62 km s in a 6 m interval the resulting compressional wave velocity was used to estimate gas content in the sediments our results suggest that the low velocity layer is a 6 18 m thick zone containing a few percent of free gas in the pore space the presence of the bsr coincides with a region of vertical uplift therefore we suggest that gas at this bsr is formed by a dissociation of hydrates at the base of the hydrate stability zone due to uplift and subsequently a decrease in pressure

simulation of gas hydrate dissociation caused by repeated tectonic uplift events gas hydrate dissociation by tectonic uplift is often used to explain geologic and geophysical phenomena such as hydrate accumulation probably caused by hydrate recycling and the occurrence of double bottom simulating reflectors in tectonically active areas however little is known of gas hydrate dissociation resulting from tectonic uplift this study investigates gas hydrate dissociation in marine sediments caused by repeated tectonic uplift events using a numerical model incorporating the latent heat of gas hydrate dissociation the simulations showed that tectonic uplift causes upward movement of some depth interval of hydrate bearing sediment immediately above the base of gas hydrate stability bghs to the gas hydrate instability zone because the sediment initially maintains its temperature in that interval gas hydrate dissociates while absorbing heat consequently the temperature of the interval decreases to that of the hydrate stability boundary at that depth until the next uplift event endothermic gas hydrate dissociation proceeds at the bghs using heat mainly supplied from the sediment around the bghs lowering the temperature of that sediment the cumulative effects of these two endothermic gas hydrate dissociations caused by repeated uplift events lower the sediment temperature around the bghs suggesting that in a marine area in which sediment with a highly concentrated hydrate bearing layer just above the bghs has been frequently uplifted the endothermic gas hydrate dissociation produces a gradual decrease in thermal gradient from the seafloor to the bghs sensitivity analysis for model parameters showed that water depth amount of uplift gas hydrate saturation and basal heat flow strongly influence the gas hydrate dissociation rate and sediment temperature around the bghs

inversion of needle probe data for sediment thermal properties of the eastern flank of the juan de fuca ridge 1 an estimation method is introduced for measuring thermal conductivity thermal diffusivity and heat capacity of sediment from temperatures using a needle probe this method is based on the continuous cylindrical heat source model thermal conductivity is estimated from needle probe temperature data using asymptotic approximation of the model heat capacity is then inverted from early time temperature data using a complete form of the model finally thermal diffusivity is calculated from the estimated thermal conductivity and heat capacity numerical experiments with synthetic temperature data indicate that the estimation error of the sediment s heat capacity is 12 the error of thermal diffusivity is thought to be greater than that of heat capacity we apply the method to needle probe temperature data obtained during integrated ocean drilling program expedition 301 carried out on the eastern flank of the juan de fuca ridge and estimate the sediments thermal properties the results indicate that thermal properties of sediments are strongly dependent on lithology and porosity examination results of the relations of heat capacity and thermal diffusivity to thermal conductivity show that these relations depend on the amount of quartz the empirical formulas for these relations are provided and they differ from those which are commonly used in thermal conductivity reduction schemes

modeling linear kinematic features in sea ice abstract sea ice deformation is localized in narrow zones of high strain rate that extend hundreds of kilometers for example across the arctic basin this paper demonstrates that these failure zones may be modeled with a viscous plastic sea ice model using an isotropic rheology if the ice is assumed to be heterogeneous at the grid scale and allowed to weaken in time intersecting failure zones propagate across the region the direction of failure propagation depends upon the stress applied to the ice wind stress and boundary conditions and the rheological model describing plastic failure of the ice the spacing between failure zones is controlled by the magnitude of the wind stress and the distribution describing spatial variability of ice strength sea ice motion and deformation oscillate at close to a 12 h period throughout the arctic and antarctic pack ice this oscillation is found at all spatial scales from hundreds of kilometers to the lead scale it is shown that with an inertial embedded mo

effect of layer orientation on the failure of layered sandstone under brazilian test conditions abstract the experimental research in this paper focuses at macro scale on the effect of the layer orientation on failure strength and fractures induced by the brazilian tensile test for one particular sandstone sandstone from modave in the south of belgium the variation in the strength the applied energy and the failure pattern are examined as a function of the inclination angle between the layer plane and the loading direction for each sample the length of fractures parallel to the layers as well as corresponding to other directions is measured for the layered sandstone in this study the transition angle range is determined whereby the relative importance of both types of fractures switches

geochemical constraints on the origin and migration of palaeofluids at the northern margin of the variscan foreland southern belgium three major fracture types in the dinantian of the namur syncline at the northern margin of the variscan foreland in southern belgium have been investigated by fluid inclusion and stable isotope analysis the oldest and volumetrically most important fracture type is characterized by conjugated and sigmoidal en echelon calcite veins which formed during the variscan folding these veins and the surrounding limestones have both a similar dull brown orange luminescence and stable isotopic composition 18o 11 to 8 pdb and 13c 0 to 3 pdb this indicates precipitation of the calcite cement from a fluid buffered by the rock in the area studied only a limited amount of fluids was expelled through the dinantian during the main phase of variscan compressional tectonism fractures filled with ferroan calcites cross cut the variscan folds fluid inclusion and stable isotopic evidence indicates that the calcites precipitated at 40 60 c from a saline fluid 9 2 to 23 2 eq wt nacl with an estimated 18o composition between 2 0 and 0 6 smow the most likely origin of these high salinity fluids with a relatively low oxygen isotopic composition is a gravity driven meteoric water which underwent an intense water rock interaction the topographic relief created by the variscan tectonism could have allowed groundwater to penetrate into the deeper subsurface and to migrate towards the margin of the foreland basin non ferroan fracture filling calcites formed later during the mesozoic or tertiary low salinity meteoric waters and high salinity cacl2 nacl brines with a temperature around 50 c migrated through this fracture system along these fractures meteoric water migrated down into the subsurface and the brines could have flowed upward from the basement

gas hydrate fluid flow and free gas formation of the bottom simulating reflector abstract gas hydrate in continental margins is commonly indicated by a prominent bottom simulating seismic reflector bsr that occurs a few hundred metres below the seabed the bsr marks the boundary between sediments containing gas hydrate above and free gas below most of the reflection amplitude is caused by the underlying free gas gas hydrate can occur without a bsr however and the controls on its formation are not well understood here we describe two complementary mechanisms for free gas accumulation beneath the gas hydrate stability zone ghsz the first is the well recognised hydrate recycling mechanism that generates gas from dissociating hydrate when the base of the ghsz moves upward relative to hydrate bearing sediment the second is a recently identified mechanism in which the relationship between the advection and diffusion of dissolved gas with the local solubility curve allows the liquid phase to become saturated in a thick layer beneath the ghsz when hydrate is present near its base this mechanism for gas production called the solubility curvature mechanism is possible in systems where the influence of diffusion becomes important relative to the influence of advection and where the gas water solubility decreases to a minimum several hundred metres below the ghsz we investigate a number of areas in which gas hydrate occurs to determine where gas formation is dominated by the solubility curvature mechanism and where it is dominated by hydrate recycling we show that the former is dominant in areas with low rates of upward fluid flow such as old rifted continental margins low rates of seafloor uplift and high geothermal gradient and or pressure conversely free gas formation is dominated by hydrate recycling where there are rapid rates of upward fluid flow and seabed uplift such as in subduction zone accretionary wedges using these two mechanisms to investigate the formation of free gas beneath gas hydrate in continental margins we are able to resolve a number of problems these include why sub bsr free gas zones are generally thin in convergent margins and thick in passive margins and why areas such as the gulf of mexico and mackenzie delta do not have regional bsrs finally we use our understanding of how bsrs are formed to show that regional gas hydrate is unlikely to exist in substantial quantities in passive continental margins outside areas with an observable bsr

evolution of palaeofluids at the variscan thrust front in eastern belgium the geochemical evolution of the fluids migra ting at the variscan thrust front in eastern belgium has been investigated by a petrographic mineralogical and geoche mical study of ankerite quartz and ferroan calcite veins hosted by lower devonian rocks three vein generations have been recognized the first generation consists of quartz chlorite and ankerite filling pre to early variscan extensional fractures the second generation is present as shear veins of variscan age and contains quartz chlorite and ferroan calcite the third generation consists of ankerite filling post variscan fractures the oxygen and carbon isotopic composition of the two ankerite phases and of the ferroan calcites are respectively between 16 4 and 11 4 pdb between 17 8 and 1 7 pdb this range is greater than that of calcite nodules in the lower devonian siliciclastic sediments 18o 15 6 to 11 1 pdb and 13c 13 4 to 10 2 pdb this suggests precipitation of the carbonate veins from a fluid which was at most only partly isotopically buffered by the calcite nodules in the host rock the calculated oxygen isotopic composition of the ambient fluid from which the calcite veins formed is between 7 8 and 10 0 smow two main fluid types have been recognized in fluid inclusions in the quartz and carbonates the first fluid type is present as secondary fluid inclusions in the first and second vein generations the fluid has a salinity of 0 5 7 2 eq wt nacl and a high but variable homogenization temperature th 124 188 c two origins can be proposed for this fluid it could have been expelled from the lower devonian or could have been derived from the metamorphic zone to the south of the area studied taking into account the microthermometric and stable isotope data and the regional geological setting the fluid most likely originated from metamorphic rocks and interacted with the lower devonian along its migration path this is in agreement with numerical simulations of the palaeofluid and especially the palaeotempera ture field which is based on chlorite geothermometry and vitrinite reflectance data the second fluid type occurs as secondary inclusions in the shear veins and as fluid inclusions of unknown origin in post variscan ankerite veins therefore it has a post variscan age the inclusions are characterized by a high salinity 18 6 22 9 eq wt cacl2 the composition of the fluid is similar to that which caused the development of mississippi valley type pb zn deposits in belgium

shear sense indicators in striped bedding veins striped bedding veins are veins that lie subparallel to bedding and have an internal layering or lineation at a small angle to the veins long axis they form during bedding parallel slip and can be used as shear sense indicators solid inclusion trails produce the visible internal layering or lineation and track the opening direction of the veins elongate quartz crystals however can be oriented at an angle of up to 80 to the opening direction are non tracking and contain almost no information on the shear sense the striped bedding veins can be separated into three types according to the geometry of their internal segmentation veins of type b opened parallel to jogs oriented at a low angle to bedding veins of type j opened parallel to jogs oriented at a high angle to bedding and veins of type o opened orthogonal to bedding and jogs striped bedding veins of types b and j contain crack seal inclusion bands and displacement parallel inclusion trails striped bedding veins of type o feature only crack seal inclusion bands the example of striped bedding veins presented in this paper from the orobic alps of italy belongs to type b the lineation in the veins and the orientation of the inclusion bands and inclusion trails as well as the orientation of steps in the vein wall can be used to determine the sense of shear and the direction and amount of vein opening or bedding parallel slip

stress state evolution of the brittle upper crust during compressional tectonic inversion as defined by successive quartz vein types high ardenne slate belt germany abstract in the frontal part of the rhenohercynian fold and thrust belt high ardenne slate belt germany two successive types of quartz veins oriented normal and parallel to bedding respectively are interpreted to reflect the early variscan compressional tectonic inversion of the ardenne eifel sedimentary basin fracturing and sealing occurred in lower devonian siliciclastic multilayers under very low grade metamorphic conditions in a brittle upper crust a geometrical and microthermometric analysis of these veins has helped to constrain the kinematic and pressure temperature conditions of both vein types allowing the reconstruction of the stress state evolution in a basin during tectonic inversion it is demonstrated that bedding normal extension veins which developed under low differential stresses and repeatedly opened and sealed crack seal under near lithostatic fluid pressures reflect the latest stage of an extensional stress regime bedding parallel veins which developed at differential stresses that were still low enough to allow the formation of extension veins cross cut the bedding normal veins and preceded the regional fold and cleavage development these veins show a pronounced bedding parallel fabric reflecting bedding normal uplift and bedding parallel shearing under lithostatic to supra lithostatic fluid pressures during the early stages of a compressional stress regime this kinematic history corroborates that fluid overpressures are easy to maintain during compressional tectonic inversion at the onset of orogeny

a comprehensive review on the geomechanical properties of gas hydrate bearing sediments abstract natural gas hydrates ngh that form in sediments beneath the ocean beds are a potential source to meet growing global energy demand gas hydrate bearing sediments ghbs exhibit improved geomechanical properties viz shear strength stiffness compressibility and poisson s ratio that are responsible for their greater stability as compared to the native sediments however dissociation of gas hydrates during extraction of gas instability in the ghbs could trigger submarine slope failures seabed subsidence and failure of the foundations of seafloor installations in order to reduce the risk of occurrence of such geohazards it is imperative to ascertain the stability of ghbs by understanding the variations in their geomechanical properties through field and laboratory investigations which are time consuming and prohibitively expensive for many researchers with this in view the present study attempts to decipher the variation of geomechanical properties with respect to various parameters that affect them viz hydrate saturation sh hydrate morphology and confining pressure temperature conditions by critically synthesizing the existing data in the literature it has been noticed that the shear strength and stiffness are the major parameters influencing the stability of ghbs and both share power law relationship with sh further it is noticed that the cohesion is the predominant component of the shear strength of ghbs and shows significant improvement for sh values greater than 15 50 the variability of cohesion and stiffness with respect to sh have been analysed in tandem with the volumetric deformation during the shearing process to propose particle level mechanism hypothesis that provides an insight in to the stress strain behavior of ghbs the proposed relationships and mechanisms would aid in understanding the behavior and development of improved modeling of geomechanical properties of ghbs

role of naturally occurring gas hydrates in sediment transport naturally occurring gas hydrates have the potential to store enormous volumes of both gas and water in semi solid form in ocean bottom sediments and then to release that gas and water when the hydrate s equilibrium conditions are disturbed therefore hydrates provide a potential mechanism for transporting large volumes of sediments under the combined low bottom water temperatures and moderate hydrostatic pressures that exist over most of the continental slopes and all of the continental rises and abyssal plains hydrocarbon gases at or near saturation in the interstitial waters of the near bottom sediments will form hydrates the gas can either be autochthonous microbially produced gas or allochthonous catagenic gas from deeper sediments equilibrium conditions that stabilize hydrated sediments may be disturbed for example by continued sedimentation or by lowering of sea level in either case some of the solid gas water matrix decomposes released gas and water volume exceeds the volume occupied by the hydrate so the internal pressure rises drastically if large volumes of hydrate are decomposed part of the once rigid sediment is converted to a gas and water rich relatively low density mud when the internal pressure due to the presence of the compressed gas or to buoyancy is sufficiently high the overlying sediment may be lifted and or breached and the less dense gas cut mud may break through such hydrate related phenomena can cause mud diapirs mud volcanos mud slides or turbidite flows depending on s diment configuration and bottom topography

laminated veins and hydrothermal breccia as markers of low angle faulting rhenish massif germany abstract the emplacement of bedding veins and vein breccia in a fold and thrust belt setting is discussed we relate vein types to thrusting regimes using the rhenish massif in germany as case example the rhenish massif is a slate belt in a hercynian fold and thrust system the slate belt cleavage generally dips to the southeast and locally has been rotated into low angle shear zones parts of these are parallel to bedding and marked by quartz carbonate veins both shear veins and extensional veins are distinguished on the basis of fibrous crack seal microstructures most shear veins grew by incremental pull apart between en echelon slip surfaces s0 the overlap of which produced a vein stack the stacks have a lineation l0 resulting from a combination of slip fibre growth and dissolution pressure solution slip the attitude of l0 relative to fold axes and the asymmetry of vein microstructures are consistent with vein emplacement during the hercynian thrusting early shear zone veins were thrusted mylonitized and finally boudinaged or folded depending on their setting the shear veins include coeval sheets of vein hosted breccia the breccia contains angular fragments of mylonitized veins and slate the orientation of s0 and s1 in the breccia varies randomly per fragment indicating random fragment rotation unencumbered spin of country rock debris implies rock expansion possibly by rapid pull apart events during the thrusting

fluid inclusions in crack seal veins at dugald river mount isa inlier implications for palaeostress states and deformation conditions during orogenesis abstract an integrated geometrical investigation and microthermometric analysis of fluid inclusion trails in fibrous crack seal veins at dugald river mount isa inlier allowed distinction of two general types of fluid inclusions a co 2 ch 4 rich variety and a h 2 o rich variety at least three stages of fluid percolation are identified to be related to the vein formation trails of pseudosecondary inclusions have a constant orientation relative to the direction of the regional maximum principal shortening direction 3 this relationship allows the trails to be regarded as potential structural markers however trails of secondary inclusions generally show a deviation from the established bulk shortening direction and possibly reflect the overprinting of a later deformation event microthermometric data combined with knowledge of metamorphic reactions suggest that the p t path of crackseal deformation started at about 450 c and 2 8 kbar then crossed 340 c and 1 2 kbar and possibly terminated around 130 c and at near surface pressure corresponding to the regional crustal uplift this study shows the importance of combined geometrical and microthermometric studies of fluid inclusions for understanding the physical conditions of crack seal deformation a common phenomenon in low grade metamorphic terrains

heat transfer through the sediments of the mounds hydrothermal area galapagos spreading center at 86 w heat transfer processes at the mounds area of the galapagos spreading center at 86 w are revealed by temperatures measured at 10 m intervals in the 30 10m sediment at each of 12 holes at dsdp leg 70 sites 506 509 and by temperatures of up to five thermistors on eleven 8 12 m long piston cores the 325 needle probe values show a significant linear increase of thermal conductivity with depth in each core about half of the temperature thermal resistance profiles are nonlinear and are fit to a steady state vertical pore water advection model results indicate high and variable total heat flow and localized hydrothermal discharge at 10 8 m s associated with individual mounds recharge is indicated at similar rates in the low heat flow belt 5 km south of the mounds and is suggested at slower rates in the intermediate heat flow 0 17 0 42 w m2 belt surrounding the mounds heat flow high possible slow entrained recharge within 100 m of discharging mounds is suggested also suggested is strong local discharge along the major fault bounding the mounds crustal block to the north about 95 km north of the spreading axis at dsdp site 510 temperatures in the 114 m sediment cover on 2 7 m y crust are linear consistent with the suggestion that the hydraulic resistance of this layer is sufficient to seal off free hydrothermal exchange between basement and bottom water the combination of heat flow data and the physical properties data of karato and becker this issue suggests that 50 m of sediment may be a threshold thickness for sealing of hydrothermal circulation within basement where the topography is smooth we suggest that the formation of mounds may be associated with the forced localization of hydrothermal discharge through the sediment as its thickness approaches this threshold value

the flexural slip mechanism abstract detailed field studies of turbiditic sequences from south georgia south atlantic north devon england and cardigan bay wales show that flexural slip occurs on discrete movement horizons between rock packets in which the beds have welded contacts stair stepping displacements of sedimentary dykes and of early quartz veins show that the movement horizons generally have a decimetre to metre spacing and are marked by bedding parallel quartz veins these veins are from 1 mm to several cm thick and can be used to identify movement horizons in the absence of displaced markers they consist of several sheets of quartz fibres which each carry a slickenfibre lineation and which together preserve a record of the displacements on an individual surface complex slickenfibre patterns and departures from ideal behaviour in which slip occurs orthogonal to the fold hinge probably result from changes in slip vector on the limbs of growing non cylindrical folds movement horizons show many of the features associated with large scale thrusting such as ramps duplexes and imbricate structures and the shear sense given by fibre steps on these surfaces and by duplexes within stratigraphically restricted packages changes across fold hinges chevron folds are thought to develop mainly by flexural flow in the early stages with flexural slip becoming dominant later as the beds become lithified new slip surfaces are generated as the dip of the fold limbs increases

effect of gas hydrates melting on seafloor slope instability we present a theoretical study of the thermodynamic chemical equilibrium of gas hydrate in soil by taking into account the influence of temperature pressure pore water chemistry and the mean pore size distribution the model uses a new formulation based on the enthalpy form of the law of conservation of energy the developed model shows that due to a temperature and pressure increase hydrates may dissociate at the top of the hydrate occurrence zone to ensure a chemical equilibrium with the surrounding bulk water this original result confirms what has been already shown through experiments the second part of the paper presents an application of the model through a back analysis of the giant storegga slide on the norwegian margin two of the most important changes during and since the last deglaciation hydrostatic pressure due to the change of the sea level and the increase of the sea water temperature were considered in the calculation simulation results show that melting of gas hydrate due to the change of the gas solubility can be at the origin of a retrogressive failure initiated at the lower part of the storegga slope once again the developed model leads to predictions which are supported by laboratory experiment results but contradictory to previous interpretations and beliefs considering that hydrate dissociation occurs only at the bottom of the gas hydrate stability zone

variscan transpressive inversion in the northwestern central rhenohercynian belt of western germany abstract important orogen parallel strike slip components during the convergence of the variscan orogen of central europe have been increasingly recognized these oblique slip faults often develop from pre existing tectonic boundaries and are influenced by pre existing structural trends in the basement in this paper evidence is presented for a 3 6 km wide distributed shear zone here named the monschau shear zone in epizone metamorphic cambro ordovician and lower devonian clastic rocks of the northwestern rhenohercynian belt kinematic indicators including field observations of anomalous mullion and fold axes patterns a set of two cleavages stretching lineations and shear and kink bands microscopical observations of stretching parallel asymmetric pressure shadows of quartz on prekinematic epizone metamorphic pyrite porphyroblasts and microfabrics of phyllosilicates by x ray texture goniometry point to a sinistral tranpressive shear zone with emplacement of the southeast hangingwall under retrograde conditions coincidence of the anchizone epizone metamorphic boundary with the change along strike from penetrative shearing to distributed thrusting suggests a ductile brittle transition the monschau shear zone is situated on the backlimb of an allochthonous anticlinorium located above a basement ramp that corresponds roughly to a pre orogenic synsedimentary normal fault its continuation shows up clearly in a dekorp seismic reflection profile to a depth of 12 15 km

regional uplift gas hydrate dissociation and the origins of the paleocene eocene thermal maximum much of the north atlantic region experienced hundreds of metres of transient uplift during the latest paleocene regional uplift should cause dissociation of gas hydrates stored in marine sedimentary strata and the subsequent release of carbon to the atmosphere should enhance warming through the greenhouse effect we have developed models of the spatial distribution of uplift to match observational constraints from sedimentary basins fringing the north atlantic in order to provide quantitative estimates of the carbon released upon uplift these models are coupled to a simple parameterisation of carbon storage in sub seafloor gas hydrates results of modelling indicate that large quantities of carbon can be released by uplift with some models generating over 2000 gt of carbon release the possibility that latest paleocene regional uplift occurred over the same time interval as onset of the paleocene eocene thermal maximum petm around 30 kyr cannot be ruled out using current stratigraphical observations or mantle convection models in this case the uplift mechanism alone can account for the magnitude and timing of the carbon isotope excursion associated with the petm alternatively if the duration of latest paleocene uplift was closer to the upper bound of around 1 myr or if other paleocene uplift events were equally significant then gas hydrate dissociation upon uplift could have contributed to longer term changes in ocean temperature and carbon isotope composition through the late paleocene these temperature changes in combination with development of the north atlantic land bridge during the latest paleocene culmination of uplift may be able to force rapid changes in ocean circulation and cause phenomena such as the petm

modeling the high frequency component of arctic sea ice drift and deformation abstract buoy observations of sea ice drift show that sea ice motion and deformation contain substantial high frequency variability at subdaily timescales however numerical simulations of the sea ice dynamics normally do not include processes on such short timescales instead by applying traditional water drag formulations for the ocean sea ice boundary layer the inertial frequencies tend to be omitted in the spectra of modeled sea ice motion and deformation due to fictitious ocean damping here a dynamic thermodynamic sea ice model is presented that includes inertial embedding of the sea ice into the oceanic boundary layer to reproduce sea ice motion and deformation not only at daily and lower frequencies but also at subdaily frequencies up to 2 cycles per day and higher comparison with buoy data shows that the embedded model much more successfully simulates the observed sea ice motion in regard to the high frequency component the results demonstrate that both inertial embedding of the sea ice oc

thermal properties of methane hydrate bearing sediments and surrounding mud recovered from nankai trough wells this paper presents the measurement of the thermal constants of natural methane hydrate bearing sediments and mud layer samples recovered from wells core samples were recovered from the tokai oki test wells nankai trough japan in 2004 the thermal conductivity thermal diffusivity and specific heat of the samples were simultaneously determined using the hot disk transient method the thermal conductivity of natural hydrate bearing sediments decreased slightly with increasing porosity in addition the thermal diffusivity of hydrate bearing sediments decreased as the porosity increased moreover we also used simple models to calculate the thermal conductivity and diffusivity estimations of the distribution model geometric mean model were relatively consistent with the measured results suggesting that sand grains and hydrates should be independently distributed for hydrate bearing sediments which exhibit a pore filling pattern the measurement results were also consistent with the thermal diffusivity which was estimated by dividing the thermal conductivity obtained from the distribution model by the specific heat taken from the arithmetic mean finally our estimate of the thermal conductivity of silt soil was much lower than that for sand soil in hydrate bearing sediment which suggests that the small grains influence thermal conductivity

bedding parallel veins and their relationship to folding abstract laminated bedding parallel veins hosted in turbiditic sandstone shale sequences from central victoria australia consist of stacked millimetre thick sub parallel sheets of quartz separated by micaceous layers wall rock slivers and pressure solution seams they have very high length to thickness ratios are laterally continuous over tens to hundreds of metres and have relatively uniform thickness compared to other vein types they are intimately associated with and folded by chevron folds and the quartz grain shape elongation lineation is commonly orthogonal to mesoscopic and macroscopic fold hinge lines the bedding parallel veins have two morphological forms type i are thin commonly 5 10 cm laminated veins which have complex microstructures dominated by phyllosilicate inclusion surfaces related to oblique opening along bedding with varying rates of deposition opening relative to shear displacement slip along the bedding surfaces more common are type ii thicker generally

excess pore pressure resulting from methane hydrate dissociation in marine sediments a theoretical approach 1 this study quantifies the excess pore pressure resulting from gas hydrate dissociation in marine sediments the excess pore pressure in confined pore spaces can be up to several tens of megapascals due to the tendency for volume expansion associated with gas hydrate dissociation on the other hand the magnitude of excess pore pressure in well connected sediment pores is generally smaller depending primarily on the hydrate dissociation rate and the sediment permeability volume expansion due to gas hydrate dissociation in well connected pore spaces is related via darcy s law to an increase in pore pressure and its gradient in sediment which drives an additional upward fluid flow through the sediment layer overlying the gas hydrate dissociation area the magnitude of this excess pore pressure is found to be proportional to the rate of gas hydrate dissociation and the depth below seafloor and inversely proportional to sediment permeability and the depth below sea level the excess pore pressure is the greatest at low initial pressures and decreases rapidly with increasing initial pressure excess pore pressure may be the result of gas hydrate dissociation due to continuous sedimentation tectonic uplift sea level fall heating or inhibitor injection the excess pore pressure is found to be potentially able 1 to facilitate or trigger submarine landslides in shallow water environments 2 to result in the formation of vertical columns of focused fluid flow and gas migration and 3 to cause the failure of a sediment layer confined by low permeability barriers in relatively deep water environments

upward shifts in the southern hydrate ridge gas hydrate stability zone following postglacial warming offshore oregon 1 high resolution three dimensional 3 d seismic reflection data acquired on the r v thomas g thompson in 2000 reveal a pair of bottom simulating reflections bsrs across a broad region of southern hydrate ridge offshore oregon the primary bsr bsrp is a regionally extensive reflection that lies 120 150 m below seafloor and exhibits typical characteristics of a gas hydrate bsr we also imaged a second weaker bsr bsrs 20 40 m below bsrp with similar characteristics bsrs is interpreted as a remnant of a bsr that probably formed during the last glacial maximum 18 000 years ago when the base of the gas hydrate stability zone ghsz was deeper an increase in bottom water temperatures of 1 75 2 25 and a corresponding sea level rise of 120 m could have produced the bsr shift the preservation of bsrs for at least 5000 years which is the time since subseafloor temperatures stabilized following ocean warming after the last glacial maximum implies very slow upward advective and diffusive flow of methane 1 m 1000 years in the vicinity of bsrs bsrs appears where there are no resolvable steeply dipping faults and fractures consistent with very low advective flow rates and has dispersed where vertical fractures are visible free gas released by the shift in the bsr either migrates so slowly that it remains stable beneath the ghsz or is directed upward along fractures to reform as hydrate in the ghsz there is no evidence for release of this free gas into the ocean or atmosphere

palaeoseismic events recorded in archaean gold quartz vein networks val d or abitibi quebec canada archaean gold quartz vein deposits are commonly hosted in high angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment this paper presents the results of a combined structural and fluid inclusion study on three gold quartz vein deposits of the val d or area abitibi quebec consisting of subhorizontal extensional veins and e w steeply dipping shear veins crack seal structures tourmaline fibres stretched quartz crystals and open space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure co2 rich and h2o nacl fluid inclusions interpreted as two coexisting immiscible fluids occur typically in microcracks of different orientations interpreted to have formed in the 1 2 plane horizontal co2 rich fluid inclusion planes are contemporaneous with the opening of these veins 3 vertical vertical h2o nacl fluid inclusion planes as well as some microstructures such as deformed minerals indicate that the same extensional veins have experienced episodic vertical shortening 3 horizontal alternating with the opening events deformation and slip opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear except that the h2o nacl fluid inclusion planes tend to be oriented at high angles to the slip direction the successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip opening events in shear veins respectively and are attributed to cyclic fluid pressure fluctuations in the system they are thus consistent with the fault valve model sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post failure following seismic rupturing along the shear zone sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form the intermittent change in orientation of 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture the complex internal structures of the gold quartz veins provide an excellent record of archaean seismic activity along high angle reverse faults

linked fluid and tectonic evolution in the high himalaya mountains nepal fluid inclusions were studied in a quartz lens from the structurally highest unit of the himalaya mountains in nepal from a textural geometrical chemical and isotopic point of view six types of fluid inclusions were distinguished one of these types consists of annular inclusions this shape is attributed to a confining pressure increase in a non isotropic stress field two successive stress fields were deduced from the orientation of the inclusion planes relative to the schistosity the bulk composition of the fluid was dominated by co2 84 mol and h2o the composition remained constant during the whole history of the sample indicating that it was buffered by the carbonaceous host rock and or that one single fluid was reworked in situ by decrepitation stable isotope of fluids and minerals indicate 1 that fluids were buffered by surrounding rocks for o and c and 2 that at least two types of water metamorphic and meteoric were involved finally a p t t e path is proposed for the sample taking into account the southward thrusting along the main central thrust the northward tectonic denudation of the himalaya mountains inducing tectonic burying below the annapurna range and lastly rapid uplift

flexural slip generated bedding parallel veins from central victoria australia abstract thin continuous laminated bedding parallel quartz veins bpvs with slip striated and fibred vein walls occur within slates or at their contact with sandstones on the limbs of chevron folds in the bendigo castlemaine goldfields southeastern australia two microstructural types of bpv i and ii have been previously recognized and are confirmed in this study both types are concluded to have formed during and or after crenulation cleavage the first tectonic axial planar structure in the wallrock slates and during flexural slip folding type i bpvs consist of syntaxial phyllosilicate inclusion trails parallel to bedding enclosing inclined inclusion bands the latter formed by detachment of wallrock phyllosilicate particles from the walls of pressure solution segmented discordant tension veins type i bpvs are formed by bedding parallel shear and grow in width by propagation of the discordant veins into the bpv walls type ii veins are composed of quartz bands separated by wallrock slate seams which have split away from the vein wall during dilatant shear opening they incorporate numerous torn apart fragments of crenulated wallrock slate type i bpv inclusion band average spacing of 0 5 mm probably represents the magnitude of slip increments during stick slip flexural slip folding activity

late variscan fluid migration at the variscan thrust front of eastern belgium numerical modelling of the palaeothermal and fluid flow field modelling of the palaeothermal field at the variscan thrust front in eastern belgium indicates significant temperature modifications by late variscan palaeofluids migrating from internal to peripheral parts of the orogen a detailed set of calibration data chlorite geothermometry microthermometry organic rank gives evidence of temporary palaeotemperature variations at the variscan thrust front obviously connected to the migration of hot low saline palaeofluids these thermal events likely enhanced organic maturation vitrinite reflectance conodont alteration of devonian and carboniferous sediments which accumulated long before the variscan orogeny occurred numerical simulation 2d finite element method of the palaeothermal field includes coupled heat transport by thermal conduction and fluid flow palaeothermal scenarios yield successive palaeotemperatures 200 300 c which are indicated by the control data due to relatively short term fluid ascent along the detachment and the imbricate thrust front the simulated flow velocities are up to tens of metre per year lasting several thousand years non steady state solution in the scenarios modelled these thermal events occur in a realm of enhanced bulk temperatures due to elevated basal heat flow densities 90 mw m 2 and an additional burial depth of some kilometres the simulated temperature enhancement due to fluids ascending at the variscan thrust front is several tens degrees the scenarios demonstrate long distance fluid migration during or after deformation of the palaeozoic basin and its effect on the palaeothermal field

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

coincident buoy and sar derived surface fluxes in the western weddell sea during ice station weddell 1992 propagation shows lower agreement for divergence 47 4 rmse 7 46 10 8 s 1 but we find these results sufficient for integrated surface flux comparisons using a toy model we test the effects of aliasing in surface flux determination the results show that variability associated with storms ocean tides inertial oscillations and other highfrequency forcing affects integrated sea ice growth rates along this continental slope location integrated salt and new ice production rates computed from buoys are found to be two times larger than those computed from ers 1 sar motion products we show that these differences in salt and ice production rates result primarily from inadequate temporal resolution of heat flux variability and sea ice divergence comparison with other studies shows that the problem is widespread thereby impacting the modeling of sea ice mass balance and variability the small scale processes cited here have significant ramifications for larger scales and the global thermohaline circulation

high and low density fluids in a quartz vein from the irish variscides abstract combined microstructural and fluid inclusion studies on a multiple quartz vein from the irish variscides reveal a kinematic history consisting of three separate dynamically distinct extensional opening events the first of these is characterized by trapped fluid at densities of 0 87 0 98 g cm 3 indicative of pressures approximating the estimated lithostatic load while fluid densities associated with the following two events 0 76 0 91 g cm 3 clearly indicate sub lithostatic fluid pressures the combined evidence suggests that these later two opening events were extensional fractures occurring well below the critical depth for tensional 3 least effective principal stress it is argued here that the preservation of such low density fluids in an environment that conventionally requires supra lithostatic fluid pressures for hydraulic failure is due to i the influence of a preexisting material anisotropy in the rock that would result in hybrid extensional failure ii the effect of stress heterogeneities associated with the development of crude boudins in the vein

simulating transient ice ocean ekman transport in the regional arctic system model and community earth system model this work evaluates the fidelity of the polar marine ekman layer in the regional arctic system model rasm and community earth system model cesm using sea ice inertial oscillations as a proxy for ice ocean ekman transport a case study is presented that demonstrates that rasm replicates inertial oscillations in close agreement with motion derived using the gps this result is obtained from a year long case study pre dating the recent decline in perennial arctic sea ice using rasm with sub hourly coupling between the atmosphere sea ice and ocean components to place this work in context the rasm coupling method is applied to cesm increasing the frequency of oceanic flux exchange from once per day in the standard cesm configuration to every 30 min for a single year simulation this change causes a considerable increase in the median inertial ice speed across large areas of the southern ocean and parts of the arctic sea ice zone the result suggests that processes associated with the passage of storms over sea ice e g oceanic mixing sea ice deformation and surface energy exchange are underestimated in earth system models that do not resolve inertial frequencies in their marine coupling cycle

paleostress directions from the preferred orientation of closed microfractures fluid inclusion planes in sandstone east texas basin u s a abstract closed extensional microfractures are useful indicators of paleostress directions in shallowly buried quartz cemented quartz arenites of the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 670 m thick that was deposited in the gradually subsiding northern gulf of mexico basin the closed microfractures are syndiagenetic fluid inclusion rich planes that have an ene strike that is subparallel to contemporary quartz filled extension veins and regional normal faults indicating that closed microfractures contain the maximum paleostress direction these microstructures are potentially useful for mapping paleostress trajectories in passive margin and platform settings particularly where samples are obtained from core previous experimental studies of microfracture closure suggest that microfractures evolved into fluid inclusion planes by dendritic quartz precipitation in east texas microfracture closure may have occurred at temperatures as low as 85 c and depths as shallow as 1500 m