the thickness of faults from laboratory experiments to field scale observations to assess the role of the fault thickness on its mechanical behavior we first present the results of an experimental modeling of a thick fault core our laboratory setup consists in an annular simple shear apparatus in which we can apply very large shear displacements 50 m to 100 particle thick granular samples thanks to a window in the apparatus pictures of the microstructures can be continuously taken during shear we observe from a correlation image velocimetry technique that a significant strain field exists outside of the observable shear band this strain field though of small magnitude compared to that existing inside the shear band is very structured and extends in a region much wider than expected from individual static observations i e wider than the directly observable shear band moreover this strain field controls most of the evolution of the shear strength of the fault we then propose plausible comparisons of our experimental results to geological observations of fault cores in the region of aigion corinth gulf greece the studied faults indeed display spectacular indurated fault planes lying on weakly cohesive material signatures of cementation clay mineral distribution and porosity profile of one of the studied fault cores are included and discussed in the light of the experimental results our observations suggest that the maximum shear strain during earthquakes might occur not in the center but on the border of the fault cores it is presumably localized in a transition zone which exhibits a significant cementation owing to a process of mechanical smearing by fine particles this zone may also act as a very low permeability layer responsible for a channeling of the fluid flow such a scheme of progressive multi sub localizations is different from classical descriptions of faults and consistent with a layering of the core consisting of separated zones of high strains or large cataclastic flows

a pressure solution creep law for quartz from indentation experiments 1 indenter experiments have been performed on quartz crystals in order to establish a pressure solution creep law relevant at upper to middle crustal conditions this deformation mechanism contributes to earth s crust geodynamics controlling processes as different as fault permeability strength and stress evolution during interseismic periods or mechanochemical differentiation during diagenesis and metamorphism indenter experiments have been performed at 350 c and 20 120 mpa during months with differential stress varying from 25 to 350 mpa several experimental parameters were varied nature of quartz synthetic or natural nature of fluid manner in which the solid solution solid interface was filled and orientation of the indented surfaces versus quartz crystallographic c axis significant strain rates could only be obtained when using high solubility solutions naoh 1 mol l 1 displacement rates of the indenter were found activated by differential stress with exponential dependence as theoretically predicted the mean thickness of the trapped fluid phase below the indenter was estimated in the range 2 10 nm moreover the development of this trapped fluid phase was relatively fast and allowed fluid penetration into previously dry contact regions by marginal dissolution the indenter displacement rate was driven by differential stress and its kinetics was controlled by diffusion along the trapped fluid and the development of a morphological roughness along the interface conversely marginal strain energy driven dissolution was observed around the indenter and its kinetics was controlled by free surface reaction these experimental results are applied to model the interactions between pressure solution and brittle processes in fault zones providing characteristic time scales for postseismic transitory creep and sealing processes in quartz rich rocks

development of cleavage in limestones of a fold thrust belt in eastern new york abstract tectonic cleavage has developed in lower devonian limestones of the hudson valley fold thrust belt in new york state morphology and distribution of cleavage in these limestones is controlled by the amount of clay quartz matrix present and by strain only limestones with greater than 10 clay quartz matrix developed widespread cleavage x ray diffraction analyses indicate that the clay matrix was altered during deformation the width of the 001 illite peak in cleaved lime wackestone is less than that in uncleaved lime wackestone from the same stratigraphic level a minimum of 10 clay is necessary to provide interconnectivity between sites of dissolution and the free fluid system preliminary analyses of bulk chemistry indicate that calcite is removed from the local rock system during cleavage development supporting proposals that circulation of fluid through the rock plays a major role in the development of cleavage textural evidence suggests that both pressure solution and free face dissolution contribute to the removal of ions at grain boundaries cross cutting relations indicate that cleavage was initiated early during the development of the fold thrust belt but continued to develop during the late stages of folding

experimental pressure solution in halite the effect of grain interphase boundary structure to investigate the mechanisms and kinetics of pressure solution we measured deformation at contacts between polished convex lenses of halite and polished flat lenses of either halite or fused silica in saturated brine at 50 2 0 2 c and fluid pressures of 0 1 mpa loads applied using small springs ranged from 0 1 4 2 n mean effective normal stresses within the contact zone ranged from 1 14 mpa the geometry and diametric growth rate of the contact spot neck growth and the rate at which the lenses approached one another convergence were monitored during deformation using transmitted and reflected light photomicrography time dependent convergence did not occur at measurable rates when two halite lenses were pressed together in saturated brine but did occur when halite and fused silica lenses were pressed together in brine convergence rates in the halite silica experiments were 0 01 0 05 m day although the initial deformation during loading involved elastic and plastic processes control experiments without brine showed no time dependent convergence indicating that dislocation creep did not contribute to the observed rates no undercutting or cataclasis was observed in any experiments residual fluid inclusions were formed along grain boundaries between two halite lenses loaded in brine indicating non zero wetting angles

quantitative analysis of reservoir rocks by microfocus x ray computerised tomography abstract microfocus computer tomography ct is a non destructive imaging technique that allows visualisation of internal features within non transparent objects such as sedimentary rocks with resolution as good as 10 m in three dimensions this technique is highly superior to medical ct widely used in geology and material sciences superior resolution is achieved by decreasing the x ray spot size which allows a decrease in the penumbra effect and an increase in primary magnification by placing the sample close to the x ray source since polychromatic x ray sources are used the technique is not free of artefacts application of filtering techniques is recommended to circumvent these artefacts and to achieve good quality images for quantitative analysis application of a dual energy approach allows quantification of density as well as effective atomic number distribution of internal features as the technique acquires data in 3d ct provides an ideal tool to link 2d thin section petrography to 3d petrophysical measurements or to be used within an upscaling approach a number of applications and the use of dual energy density and effective atomic number characterisations are presented attention is also paid to some of the limitations of this technique

hydraulic sealing due to pressure solution contact zone growth in siliciclastic rock fractures thermo hydro mechanical chemical simulations at the pore scale are conducted to study the hydraulic sealing of siliciclastic rock fractures as contact zones grow driven by pressure dissolution the evolving fluid saturated three dimensional pore space of the fracture results from the elastic contact between self affine randomly rough surfaces in response to the effective confining pressure a diffusion reaction equation controls pressure solution over contact zones as a function of their emergent geometry and stress variations results show that three coupled processes govern the evolution of the fracture s hydraulic properties 1 the dissolution driven convergence of the opposing fracture walls acts to compact the pore space 2 the growth of contact zones reduces the elastic compression of the pore space and 3 the growth of contact zones leads to flow channeling and the presence of stagnant zones in the flow field the dominant early time compaction mechanism is the elastic compression of the fracture void space but this eventually becomes overshadowed by the irreversible process of pressure dissolution growing contact zones isolate void space and cause an increasing disproportion between average and hydraulic aperture this results in the loss of hydraulic conductivity when the mean aperture is a third of its initial value and the contact ratio approaches the characteristic value of one half convergence rates depend on small wavelength roughness initially and on long wavelength roughness in the late time the assumption of a characteristic roughness length scale therefore leads to a characteristic time scale with an underestimation of dissolution rates before and an overestimation thereafter

diagenetically enhanced bedding in argillaceous platform limestones stratified cementation and selective compaction a field and petrographic study has been made of 34 massive beds in argillaceous limestones of open marine platform facies in the u k lithologies include grainstones packstones wackestones and lime mudstones the rocks are of silurian carboniferous and jurassic ages additional information was obtained from other limestones in the u k the u s a canada and continental europe the beds are parts of sequences composed of couplets of strata fissile limestones alternating with hard limestones in the fissile limestones the effects of mechanical compaction and pressure dissolution have been concentrated whereas in the hard limestones they are minimal or absent bedding planes visible in outcrop are diagenetic in origin and lie in the middle parts of the fissile limestones where compaction has been most severe the features produced by pressure dissolution are dissolution seams and fitted fabric there are no stylolites the original carbonate sediments were bioturbated and any structures produced by flowing water were destroyed the vertical distribution of the bedding planes bears no relation to primary depositional bedding planes which are rare or absent it is inferred that the strata which were to become the hard limestones were selectively cemented before mechanical compaction had been completed thenceforth mechanical compaction and then pressure dissolution were concentrated in the less cemented strata these became the fissile limestones pressure dissolution acted late in the diagenetic history and provided only an insignificant part if any of the carbonate for cementation it is concluded that the orientation of beds couplets is parallel to successive sea floors and that the sediments that eventually became single beds accumulated synchronously similar couplets in platform limestones of the mississippian and pennsylvanian of the u s a extend over thousands of square kilometres the signal that controlled the initial selective cementation must have been widespread and synchronous and also syndepositional in its timing but otherwise cannot be further defined on the basis of the data so far collected the presumed order of events was 1 accumulation of carbonate sediment terrigenous clay and organic matter 2 hydrodynamic reworking and bioturbation the latter finally overprinting the former 3 selective cementation of the more carbonate rich strata yielding couplets each consisting of a relatively well cemented stratum and a poorly cemented stratum 4 mechanical compaction concentrated in the less cemented strata 5 pressure dissolution concentrated in the same strata

pull aparts shear fractures and pressure solution vein arrays are often composed of pull aparts which are linked by shear fractures good examples of which occur in the lower jurassic limestones of somerset southwestern england such pull apart arrays have displacement distance characteristics which are similar to fault zones with maximum displacement indicated by the largest pull apart widths near the centre of the array and with displacement decreasing towards the tips pull apart arrays usually die out into enechelon or pinnate veins evidence for pressure solution along the shear fractures which connect pull aparts include their dark and braided nature their obliquity to the displacement direction the high dihedral angles often 90 between conjugate shear fractures and the dissolution of earlier structures a range of geometries occurs with varying relative amounts of veins and pressure solution being related to varying amounts of transtension or transpression there is a general trend for an increase in the angle between vein segments and the shear fractures as contraction increases there is therefore a trend for increased pressure solution on the shear fractures in more contractional arrays the concentration of insoluble material along shear fractures has important implications for the mechanics and sealing of faults

electromagnetic induction studies recent developments in electromagnetic induction studies of the lithosphere and the asthenosphere are reviewed attention is given to geoelectrical studies of active tectonic areas in terms of the major zones of crustal extension the basin and range province along western regions of north america and the rio grande rift studies have also been performed of tectonic activity around iceland the salton trough and cerro prieto and the subduction zones of the cascade mountains volcanic belt where magnetotelluric and geomagnetic variation studies have been done geomagnetic variations experiments have been reported in the central appalachians and submarine electromagnetic studies along the juan de fuca ridge controlled source electromagnetic and dc resistivity investigations have been carried out in nevada hawaii and in the adirondacks mountains laboratory examinations on the conductivity of representative materials over a broad range of temperature pressure and chemistry are described

controls on stylolite development morphologic lithologic and temporal evidence from bedding parallel and transverse stylolites from the u s appalachians quantification of morphology of bedding parallel and transverse or tectonic stylolites from the southern appalachians reveals that regardless of tectonic setting or stylolite orientation lithologic heterogeneity controls stylolite development for example stylolites in more heterogeneous carbonate lithologies packstones and grainstones are more serrate than those in wackestones and mudstones similarly early forming stylolites are more serrate than late forming stylolites and computer simulations suggest that decreases in porosity or other lithologic heterogeneity cause the less serrate nature of late forming stylolites the linkage of a stylolite s morphology to its time of development should allow field estimation of timing of stylolitization and thus of timing of loading or compression although bedding parallel and transverse stylolites generally result from different kinds of compression morphological relations indicate that their development follows the same fundamental patterns bedding

fracture surface energy of the punchbowl fault san andreas system the energetics of earthquake rupture slip weakening and rupture surface formation are poorly understood by measuring the energy associated with fracture damage along the punchbowl fault in the devil s punchbowl los angeles county park part of the san andreas system chester et al show that the fracture surface energy for rupture along a mature fault of this type accounts for only a small fraction of the energy released during large earthquakes as determined by seismologists this suggests that mechanisms such as melt lubrication and thermal pressurization are responsible for slip weakening fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening1 2 3 fracture energy has been estimated from seismological and experimental rock deformation data4 5 6 7 8 yet its magnitude mechanisms of rupture surface formation and processes leading to slip weakening are not well defined8 9 10 here we quantify structural observations of the punchbowl fault a large displacement exhumed fault11 12 in the san andreas fault system and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake if fracture energy is attributed entirely to the production of fracture surfaces then all of the fracture surface area in the punchbowl fault could have been produced by earthquake displacements totalling 1 km but this would only account for a small fraction of the total energy budget and therefore additional processes probably contributed to slip weakening during earthquake rupture

development and scaling relationships of a stylolite population abstract the frequencies amplitudes and insoluble residue thicknesses of 4639 stylolites have been measured from 674 3 m of core from four vertical wells in the khuff formation a permo triassic carbonate reservoir offshore abu dhabi although there are similar numbers of stylolites per metre of core in dolomites and limestones the stylolites in the limestones have approximately double the cumulative amplitudes and insoluble residue thicknesses than the stylolites in dolomites this indicates that stylolites in the limestones have grown at approximately twice the speed or for twice as long as the stylolites in the dolomites stylolite amplitudes in dolomites and limestones together appear to obey a power law scaling relationship over about one order of magnitude 20 150 mm stylolite amplitudes in dolomites however have a higher power law exponent than those in the limestones and appear to obey a power law down to 10 mm this indicates that stylolites in the limestones have merged more than the stylolites in the dolomites the amount of pressure solution and possibly the scaling of a population of stylolites may also be controlled by location within the fold with less pressure solution in the hinge region into which hydrocarbons migrated earlier than in the limbs

nanometre scale faulting in quartz under an atomic force microscope abstract we conducted nano indentation tests of quartz under a load of 294 mn at room temperature and ambient pressure using an atomic force microscope we performed topographic mapping of the indented surface immediately after the nano indentation test and again 46 h later differences in the contour patterns of the two surface topographies reveal that a new fault developed in the quartz specimen while it was secured on the specimen stage of the atomic force microscope between the two mapping times the fault length is 2 m and the maximum displacement on the fault plane is 20 nm when combined with existing displacement length data from natural faults the data suggest that a linear displacement length scaling relationship can be extrapolated to nanometre scale faulting

modeling porosity evolution and cementation of sandstones abstract recent models of quartz cementation of sandstones attribute the source of silica to dissolution of quartz at stylolites bjorkum 1993 walderhaug 1994 aase et al 1996 oelkers et al 1996 quartz dissolution is believed to be catalyzed by the presence of mica illitic clayswhich are not dissolved or destroyed during the quartz dissolution process bjorkum1993 a supersaturation of silica is created at the stylolites which leads to a diffusive transport of silica into the interstylolite regionwhere the silica precipitates as cement interstylolite cementation is observed to be smooth which has led to the conclusion that the precipitation step is the slowest step in the entire quartz cementation process this is because the silica supersaturationcreated by dissolution of quartz at the stylolites is almost uniform throughout the interstylolite region the supersaturation is estimated to be 1 above the silica equilibrium concentration aase et al 1996 oelkers et al 1996 this estimate is based on the increase in the silica equilibrium concentration needed to grow microcrystalline quartz grains of a size 1 m petrographic studies of deeply buried jurassic north sea sandstones show that sandstones with microcrystalline quartz coatings have well preserved porosities microcrystalline quartz coatings are able to inhibit quartz cementation because the supersaturation created by dissolution of quartz at the stylolites is insufficient to grow the microcrystalline quarts aase et al 1996 the idea that stylolites are the source for silica cement was already suggested by heald et al 1955

kinematics of stylolite formation and physics of the pressure solution process abstract a kinematical model for stylolite formation is proposed which is consistent with the geometry of all types of observed stylolites the model is based on the assumption that every surface element of an evolving stylolite behaves as a bistable system i e dissolution operates only on alternate sides of the rock bodies in contact along the stylolitic surface the proposed kinematics of stylolite production leads to the suggestion of a new physical process in some way different from the pressure solution phenomenon as it is currently conceived transfer of material from the solid state into an activated state in a supposed thin fluid film should be promoted and controlled by a spontaneous polarization of the contact region the search for conditions responsible for the setting up of this inferred process and the identification of its nature are beyond the aim of the present paper

mechanics of the formation of orthogonal sets of solution seams and solution seams and veins and parallel solution seams and veins abstract commonly observed networks of pressure solution seams psss and psss and veins can be broken down to three basic assemblages orthogonal pss sets orthogonal pss vein sets and parallel pss vein sets we investigate stress distributions around psss idealized as localized volume reduction structures lvrss to identify the conditions for forming these three fundamental assemblages various geometries of lvrss are taken into account including elliptical lvrss with smooth flanks lvrss with triangular and rectangular asperities on their flanks and lvrss with overall irregular geometries such as columnar and conical shapes the modeling results indicate that if the first pss set has elliptical shapes with smooth flanks the conditions for generating the fundamental assemblages listed above are highly restrictive primarily due to relatively large average aspect ratios of psss as measured in the field which indicate lower stresses around psss as they grow however both laboratory and field observations have shown that pss surfaces are extremely rough we find that psss with relatively rough flanks and psss with overall irregular trace geometry such as sutured and zig zag or wiggly are much more favorable for generating the stresses for the formation of these fundamental structural assemblages based on a series of stress domain maps from our mechanical model we evaluated the stress strain and geometric conditions for the formation of each of the three assemblages it turns out that there are a wide variety of loading and geometric factors favoring the formation of a particular type of assemblage

contribution at satellite altitude of electromagnetically induced anomalies arising from a three dimensional heterogeneously conducting earth using sq as an inducing source field summary the induced magnetic signature at satellite altitude associated with crustal and mantle electrical heterogeneities is examined using five different earth models the three dimensional induction problem is solved in these models using the solar quiet daily variation as an inducing source field every model has an upper shell representing the land ocean electrical conductivity distribution the different models have either a homogeneous mantle or a heterogeneous mantle containing either subduction zones a ridge system or conductive blocks electromagnetic anomalies presented in the form of geographical maps are calculated for wavelengths related to spherical harmonics of degrees in the ranges 1 12 and 13 27 respectively magnetic anomalies are calculated at an altitude of 400 km and for three different local times 6 12 and 18 h

a model for intergranular pressure solution in open systems abstract intergranular pressure solution ips represents a well known mechanism of bulk deformation and pore volume change especially in sedimentary rocks which has been documented in the field and reproduced in laboratory experiments theoretical descriptions of the process in terms of simple pressure solution creep laws can explain features such as grain size dependence of creep rates but have typically remained restricted to closed system conditions with negligible long range transport in the fluid phase and somewhat biased toward grain boundary diffusion controlled creep the recasting of the classical weyl rutter model of ips considered in this paper emphasizes open system conditions and the competition between diffusion and dissolution reaction rate processes the thermodynamic force which drives ips is expressed in terms of an effective grain boundary normal traction and a solute supersaturation this suggests the occurrence of a transition from ips to grain boundary healing at a certain level of supersaturation of the pore fluid although the process of healing is not studied here the explicit appearance of the solute concentration in the driving force highlights the coupling of the ips deformation process to the long range transport of dissolved material and the need to model the diagenesis of compacting sedimentary sequences accordingly the conceptual grain boundary model used in this paper is that of a fluid invaded grain to grain contact zone which is visualized to remain in a roughened state during continued ips the use of simple linear phenomenological rate laws for dissolution and grain boundary diffusion allows the ranges of rate control by dissolution or diffusion to be succinctly characterized in terms of the ratio of corresponding time constants the associated compaction behaviour is explored quantitatively in this paper by presenting solutions for the uniaxial and isotropic compaction creep strain vs time for a simple cubic packing of spheres

fluid control of localized mineral domains in limestone pressure solution structures grain to grain and stylolitic solution structures in two central appalachian siluro devonian limestone macroscale folds contain one of four distinct mineral assemblages that are characterized by the dominant iron phase mineral present 1 chloritegillitegpyritegcalciteg quartzgtio2ggoethite 2 chloritegillitegpyrite altered to iron oxide hydroxidegcalcite gquartzgtio2 3 chloritegilliteg magnetitegcalcitegquartz and 4 chloritegilliteggoethitegcalcitegquartzgtio2 optical reflectance microscopy and sem eds was used to characterize the mineralogy and mineral morphology of these structures geochemical modeling was used to constrain the conditions of formation and preservation the primary control on solution structure mineral assemblage was the redox conditions present in the solution structures during burial and deformation the redox conditions on the microscale may have been controlled by the local fluid chemistry and the presence absence of hydrocarbons and organic acids within the formation fluids and the influx of externally derived fluids by fracture formation during the folding process the wide variation in mineralogy of the solution structures shows that they were chemical factories where a variety of chemical reactions took place during rock dissolution in particular the formation of authigenic magnetite in solution structures has significant implications for paleomagnetic applications and use of anisotropy of anhysteretic remanent magnetization and anisotropy of magnetic susceptibility fabrics q 2005 elsevier ltd all rights reserved

finite element modelling of the evolution of pressure solution cleavage abstract deformation by pressure solution or water assisted stress induced diffusion transfer is modelled by incorporating volume transfers driven by variations in mean stress and competency contrast into a finite element code for viscous deformation the model assumes a two component quartz mica mixture with a composition dependent rheology in which the viscosity of an element is solely dependent upon the volume fraction of the mobile quartz component both quartz rich and mica rich compositions are given a high competency with a minimum viscosity at some intermediate fraction the model is able to reproduce many structures observed in natural tectonites propagation and coalescence of pressure solution seams formation of microlithons and anastomosing cleavage and more generally tectonic segregation

the formation and growth of pressure solution seams in clastic rocks a field and analytical study abstract pressure solution seams psss are closing mode structures of localised dissolution resulting in a volume reduction we present new observations constraining the processes by which psss initiate and grow in low porosity clastic rocks from southern ireland psss initiate as inter granular psss at quartz grain to grain contacts as quartz dissolves clay remains as a residue along the contacts as well as filling the adjacent pores to form incipient psss involving multiple grain boundaries further lengthening and thickening occurs by lateral linkage and transverse coalescence of neighbouring segments of incipient psss multiple pss segments are observed to concentrate in thin tabular zones that appear as single macroscopic psss visible in hand samples published numerical modelling results show the ability of both lateral and transverse growth of psss due to the presence of asperities on their flanks which confirm our interpretations based on our laboratory and field observations

anisotropic scaling of tectonic stylolites a fossilized signature of the stress field 1 vertical stylolites are pressure solution features which are considered to be caused by horizontal tectonic loading with the largest principal compressive stress being sub parallel to the earth s surface in the present study we analyze the roughness of such tectonic stylolites from two tectonic settings in southern germany and northeastern spain aiming to investigate their scaling properties with respect to the stress during formation high resolution laser profilometry was carried out on opened stylolite surfaces of nine samples these data sets were then analyzed using one and two dimensional fourier power spectral approaches we found that tectonic stylolites show two self affine scaling regimes separated by a distinct crossover length l as known for bedding parallel stylolites in addition tectonic stylolites exhibit a clear in plane scaling anisotropy that modifies l since the largest and smallest crossover lengths are oriented with the sample vertical and horizontal directions i e 2 and 3 and l is a function of the stress field during formation as analytically predicted we conclude that the scaling anisotropy of tectonic stylolites is possibly a function of the stress field knowledge of this crossover length anisotropy would enable the reconstruction of the full three dimensional stress tensor if independent constraints of the depth of formation can be obtained

chronology of fracture sealing under a meteoric fluid environment microtectonic and isotopic evidence of major cainozoic events in the eastern paris basin france abstract a detailed reappraisal of the sequence of tectonic stages that has affected the eastern part of the paris basin from the late jurassic to the end of cainozoic is presented in order to improve knowledge of the relationships between tectonics and fluid mass palaeo transfers in that basin this goal was performed in two steps i establishing a relative tectonic chronology on the basis of numerous observations and detailed analysis of geometrical relationships between striated planes vertical and bedding stylolites and tension gashes and ii discussing the geochemical signatures 18 o and 13 c of calcite from fracture infillings well positioned within the relative tectonic chronology the resulting tectonic sequence agrees with the main events described by previous papers but the present work details the pyrenean s l eocene oligocene and alpine miocene pliocene convergence stages and explains the mechanisms of the oligocene miocene transition between the two previous events the different tectonic stages are as follows i late jurassic to early cretaceous extension starting with a wnw ese direction but changing to e w ii the pyrenean convergence eocene changing from nne ssw to ne sw and finally ene wsw compression iii oligocene transition from pyrenean to alpine convergence marked by a drastic evolution of main stress which swaps from a horizontal position to a vertical one and radial extension marked by a strong reactivation of bedding stylolitisation iv the alpine convergence late miocene to present day changing from wnw ese to nnw sse direction of shortening 18 o and 13 c values of calcite from tension gashes associated to each tectonic stage spread from 18 to 27 smow and from 0 8 to 3 pdb respectively according to the maximum thermal history of this part of the basin t max 40 c or 60 c according to the available published estimates the calculated 18 o values of fluids 7 to 4 involved in mass transfer processes are interpreted as meteoric the lowest 18 o values 18 20 are located around the main regional faults and associated with 13 c values that are rather different from those of host rocks in contrast calcites from non faulted area present a higher 18 o 20 and 13 c values close to those of host rocks these data are explainable in terms of differences in the fluid rock ratios prevailing during carbonate redistribution the highest ratios being associated to discontinuities faults sometimes with hydraulic breccias that were active during the tertiary tectonic events outside the fault zones the isotopic compositions of calcite from tension gashes are similar at the regional scale to those of calcite from geodes or cements analysed in previous studies on localized areas as a result we emphasize the fact that a significant part of the carbonate redistribution in the middle to upper jurassic limestones from the eastern paris basin occurred during the tertiary s l enlightening the influence of distant orogenic systems extensive or compressive in the matter redistribution within sedimentary basins at variance of models inferring a porosity cementation predominantly during burial

joints microfractures and the formation of solution cleavage in limestone the geometry of solution cleavage surfaces in limestones indicates a close connection between cleavage formation and joint and microfracture surfaces these relations suggest that networks of microfractures and joints act both as conduits for transport of dissolved phases and as surfaces on which the cleavage nucleates material transport is by darcyian type bulk flow and is thus not a rate limiting process this contrasts with metamorphic terranes where the transport mechanism diffusion has been identified as a rate limiting step cleavage surfaces of weak to moderate intensities or spacing may form parallel to nonprincipal planes of finite strain

the fractal geometry of some stylolites from the calcare massiccio formation italy stylolites are serrated surfaces that form by stress enhanced dissolution though their geometry and morphology reflects their formation and evolution only a few studies have attempted to quantify them here we present results indicating that stylolites in limestone of the calcare massiccio formation jurassic italy are fractal over 4 5 orders of magnitude in spatial bandwidth with an average fractal dimension obtained by spectral and scaled windowed variance analyses clustering at 1 47 some stylolites from the skene cambrian usa and tamar cenomanian israel formations are fractal over 3 orders of magnitude with fractal dimensions of 1 26 and 1 43 these values are high relative to other natural surfaces and reflect the jagged topography of the stylolites preliminary results indicate that the fractal dimension and power are constant throughout the stylolite surface and are not orientation dependent furthermore we show that stylolite contours are fractal too the grain size does not register in our analyses implying that the grain is not a cutoff between processes rather stylolite generating processes operate similarly below and above the grain size our results suggest that the geometry of these stylolites especially at long wavelengths may not be sensitive to the immediate fabric surrounding them

pressure solution in chalk pressure solution residues in the cretaceous to paleocene chalk from the north sea area were studied to understand the pressure solution process and fluid flow residue seams reach lengths and thickness of more than 800 and 0 15 m 2625 and 0 5 ft respectively seams can present significant barriers to fluid flow because they have nannodarcy permeability and hold back large pressure differentials stylolite amplitudes decrease when they merge making it difficult to quantify volume loss measuring amplitudes allows volume loss estimates using a new dissolution ratio method the sum of the thicknesses of all residues is multiplied by the maximum amplitude to residue thickness ratio on average 30 mm 1 2 in of chalk had to be dissolved to produce a 1 mm 0 04 in thick residue the volume loss of chalk from flamborough averages about 50 and is 60 in the machar oil field united kingdom central graben the minimum fluid volume required to produce the volume loss in 1 unit volume of preserved chalk on the machar field is estimated to be 8000 unit volumes this and the stable isotopes of vein carbonates imply that the pressure solution process involved an open fluid system high illite content in mixed layered illite smectite and high illite crystallinity of clays in the pressure solution seams in the machar reservoir indicate high diagenetic maturity with implied temperatures in the range of 200 360c 392 680f which is greater than the present day reservoir temperature of 85c 185f the anomalously hot temperatures are interpreted to be produced by deep mineralizing fluids transported from the central graben the lack of abundant veining in the chalk and the large fluid volumes involved in the chalk dissolution suggest that this was an open pressure solution system

the influence of rock heterogeneity on the scaling properties of simulated and natural stylolites abstract stylolites are among the most prominent deformation patterns in sedimentary rocks that document localized pressure solution recent studies revealed that stylolite roughness is characterized by two distinct scaling regimes the main goal of the present study is to decipher whether this complex scaling behavior of stylolites is caused by the composition of the host rock i e heterogeneities in the material or is governed by inherent processes on respective scales namely the transition from a surface energy to an elastic energy dominated regime as theoretically predicted for this purpose we have developed a discrete numerical technique based on a lattice spring model to simulate the competition between stress strain and dissolution during stylolite roughening we varied systematically the quenched noise initially present in the material which controls the roughening we also changed the size amount and dissolution rate of the heterogeneities introduced in our model and evaluated the influence on the scaling exponents our findings demonstrate that the roughness and growth exponents are independent of the exact nature of the heterogeneities we discovered two coinciding crossover phenomena in space and time that separate length and time scales for which the roughening process is either balanced by surface or elastic energies our observations are consistent with analytical predictions and with investigations quantifying the scaling laws in the morphology of natural stylolites the findings presented here can further be used to refine volume loss compaction estimates from the finite strain pattern of stylolites

stylolites as open fluid conduits abstract stylolites have hitherto been regarded as a direct result of dissolution in response to stresses applied during compaction zones of cementation and dolomitization and in some rocks associated internal sediments indicate that they were pathways to fluid flow yet clay residues and impermeable zones suggest that they are now less able to transmit fluids it is proposed that some stylolites represent former open fluid pathways developed in an over pressured system and that the familiar morphologies were only imposed during compaction as formation pore water pressures declined

stress sensitivity of stylolite morphology abstract stylolites are rough surfaces that form by localized stress induced dissolution using a set of limestone rock samples collected at different depths from a vertical section in cirque de navacelles france we study the influence of the lithostatic stress on the stylolites morphology on the basis of a recent morphogenesis model we measured the roughness of a series of bedding parallel stylolites and show that their morphology exhibits a scaling invariance with two self affine scaling regimes separated by a crossover length l at the millimeter scale consistent with previous studies the importance of the present contribution is to estimate the stylolite formation stress from the sample position in the stratigraphic series and compare it to the crossover length l using the expected relationship l 2 we obtained a successful prediction of the crossover behavior and reasonable absolute stress magnitude estimates using relevant parameters depth of stylolite formation between 300 to 600 m with corresponding normal stress in the range of 10 18 mpa accordingly the stylolite morphology contains a signature of the stress field during formation and we thus suggest that stylolites could be used as paleo stress gauges of deformation processes in the upper crust

observing geomagnetic induction in magnetic satellite measurements and associated implications for mantle conductivity 1 currents induced in earth by temporal variations in the external magnetic field have long been used to probe mantle electrical conductivity but almost exclusively from sparsely distributed land observatories satellite borne magnetometers such as flown on magsat orsted and champ offer the prospect of improved spatial coverage the approach we have taken is to isolate induction by harmonic dst disturbance storm time excitation of the magnetospheric ring current in satellite magnetic measurements this is done by removing the magnetic contributions of the main core magnetic field the crustal magnetic field and ionospheric fields cause of the daily variation using sabaka et al s 2000 2002 cmp3 comprehensive model the dst signal is then clearly evident in the midlatitude satellite passes lower than 50 degrees geomagnetic latitude at higher latitudes auroral and field aligned currents contaminate the data we fit the internal and external components of the dst signal for each equatorial pass exploiting the fact that the geometry for the internal and external components is different for the azimuthal and radial vector components the resulting timeseries of internal and external field variations shows that the dst signals for the dawn passes are half those of the dusk passes the sum of equatorial external and internal components of the field averaged over dawn and dusk passes provides an excellent estimate for the dst index and may in fact be superior when used as a proxy for the purposes of removing induced and magnetospheric fields from satellite magnetic data we call this estimate satellite dst cross spectral analysis of the internal and external timeseries shows both greater power and higher coherence in the dusk data we processed the transfer function between internal and external dusk timeseries to provide globally averaged frequency dependent impedances that agree well with independently derived estimates we estimate earth s radial electrical conductivity structure from these impedances using standard regularized inversion techniques a near surface conductor is required of thickness less than 10 km with a conductivity thickness product almost exactly that of an average earth ocean inversions suggest that an increase in conductivity at 440 km depth predicted by recent laboratory measurements on high pressure phases of olivine is not favored by the data although as in previous studies the 670 km discontinuity between the upper and lower mantle is associated with a two orders of magnitude jump in conductivity a new feature in our inversions is a further increase in lower mantle conductivity at a depth of 1300 km a global map of the internal induced component of the magnetic field provides a qualitative estimate of three dimensional 3 d variations in earth electrical conductivity demonstrating graphically that the satellite data are responsive to lateral variations in electrical conductivity caused by the continents and oceans

three dimensional morphology and connectivity of stylolites hyperactivated during veining abstract the limestone of the palaeozoic jack formation in north queensland australia contains bedding parallel stylolites that locally increase in amplitude adjacent to calcite veins the veins formed in response to inhomogeneous strain locally superposed on the tightly folded strata stylolites were locally hyperactivated during vein formation and provided calcite for vein filling three dimensional reconstructions of the morphology of the stylolites based on detailed serial profiles demonstrate that the side faces of columnar stylolites form an interconnected fluid pathway through the rock the connective morphology defines a drainage network comprising highly tortuous major trunks of high amplitude side faces linked locally by minor pathways of variable amplitude the permeability pathway anastomoses in three dimensions making it impossible to image in two dimensions alone

growth of stylolite teeth patterns depending on normal stress and finite compaction abstract stylolites are spectacular rough dissolution surfaces that are found in many rock types they are formed during a slow irreversible deformation in sedimentary rocks and therefore participate to the dissipation of tectonic stresses in the earth s upper crust despite many studies their genesis is still debated particularly the time scales of their formation and the relationship between this time and their morphology we developed a new discrete simulation technique to explore the dynamic growth of the stylolite roughness starting from an initially flat dissolution surface we demonstrate that the typical steep stylolite teeth geometry can accurately be modelled and reproduce natural patterns the growth of the roughness takes place in two successive time regimes i an initial non linear increase in roughness amplitude that follows a power law in time up to ii a critical time where the roughness amplitude saturates and stays constant we also find two different spatial scaling regimes at small spatial scales surface energy is dominant and the growth of the roughness amplitude follows a power law in time with an exponent of 0 5 and reaches an early saturation conversely at large spatial scales elastic energy is dominant and the growth follows a power law in time with an exponent of 0 8 in this elastic regime the roughness does not saturate within the given simulation time our findings show that a stylolite s roughness amplitude only captures a very small part of the actual compaction that a rock experienced moreover the memory of the compaction history may be lost once the roughness growth saturates we also show that the stylolite teeth geometry tracks the main compressive stress direction if we rotate the external main compressive stress direction the teeth are always tracking the new direction finally we present a model that explains why teeth geometries form and grow non linearly with time why they are relatively stable and why their geometry is strongly deterministic while their location is random

modeling the growth of stylolites in sedimentary rocks stylolites are ubiquitous pressure solution seams found in sedimentary rocks their morphology is shown to follow two self affine regimes analyzing the scaling properties of their height over their average direction shows that at small scale they are self affine surfaces with a hurst exponent around 1 and at large scale they follow another self affine scaling with hurst exponent around 0 5 in the present paper we show theoretically the influence of the main principal stress and the local geometry of the stylolitic interface on the dissolution reaction rate we compute how it is affected by the deviation between the principal stress axis and the local interface between the rock and the soft material in the stylolite the free energy entering in the dissolution reaction kinetics is expressed from the surface energy term and via integration from the stress perturbations due to these local misalignments the resulting model shows the interface evolution at different stress conditions in the stylolitic case i e when the main principal stress is normal to the interface two different stabilizing terms dominate at small and large scales which are linked respectively to the surface energy and to the elastic interactions integrating the presence of small scale heterogeneities related to the rock properties of the grains in the model leads to the formulation of a langevin equation predicting the dynamic evolution of the surface this equation leads to saturated surfaces obeying the two observed scaling laws analytical and numerical analysis of this surface evolution model shows that the cross over length separating both scaling regimes depends directly on the applied far field stress magnitude this method gives the basis for the development of a paleostress magnitude marker we apply the computation of this marker i e the morphological analysis on a stylolite found in the dogger limestone layer located in the neighborhood of the andra underground research laboratory at bure eastern france the results are consistent with the two scaling regimes expected and the practical determination of the major principal paleostress from the estimation of a cross over length is illustrated on this example

tectonic analysis of the dead sea rift region since the late cretaceous based on mesostructures we have measured the orientations of small faults slickensides tectonic stylolites vein with secondary mineralization small folds and dikes in israel and sinai these structures are indicators of paleo stress or strain and provide the pattern of tectonic deformation data were collected at 130 stations most with tens of separate measurements most stations showed consistent deformation stations were located on exposures ranging from precambrian crystalline rocks to pleistocene sediments we have defined two tectonic stress fields each relatively uniform in both time and space one stress field with dominating maximum horizontal compression trending w to wnw in the late cretaceous to eocene rocks in the folds and plateaus west of the dead sea rift the second field with dominating horizontal extension trending e to ene in all rocks inside the rift and proximal thereto the first stress field is called the syrian arc stress and the second is called the dead sea stress a change in style of tectonic deformation which corresponds to the two stress fields is manifested also in the major structures in israel the late cretaceous to neogene deformation is characterized by long wavelength folds and monoclines whereas the neogene to recent deformation is characterized by normal and strike slip faults and volcanic activity

pressure solution seams in carbonatic fault rocks mineralogy micro nanostructures and deformation mechanism we have investigated mineralogy and micro nanostructures of pressure solution seams in four different carbonatic faults with kilometric displacement cropping out in the northern apennines italy disregarding the different protoliths and deformation conditions the stylolite filling material has almost constant mineralogical characteristics being invariably formed by an ultrafine matrix that encloses relic insoluble grains among which quartz feldspars and detritic micas the ultrafine matrix also hosts syn and post dynamic phases e g foliation parallel goethite flakes and apatite euhedral nanocrystals in random orientation the ultrafine matrix is formed by smectitic clays in nanosized 001 lamellae showing pervasive interlayer fissuring layer bending and preferred orientation parallel to the slipping surface stylolite mineralogy and micro nanostructures may affect deformation mechanisms and permeability properties of the fault rock in particular we propose that the extremely low friction coefficient of smectite would favour frictional sliding along the faults and that the fissured and oriented nanostructure of the smectite dominated seams would enhance the sealing attitude of the structures in the fault perpendicular direction

generation of evenly spaced pressure solution seams during late diagenesis a kinetic theory stylolites and pressure solution seams can form during diagenesis of rocks subjected to stress through a feedback involving texture and pore fluid solute concentration this feedback destabilizes the state of uniform texture represented here only by porosity for simplicity a mathematical kinetic model that includes pressure solution diffusion and reprecipitation predicts the spontaneous generation even in initially uniform rocks of regions alternatingly in space more and less soluble a region that becomes more soluble also becomes simultaneously more porous the kinetic theory predicts that stylolites can form at roughly constant spacings this agrees with many field and petrographic observations bedding planes between beds that have initially different texture are shown by the theory to be the focus of a porosity instability that can lead to the formation of a stylolite and to the generation of more stylolites within each bed this prediction agrees with the observation that many stylolites have developed at bedding planes

revealing the natural complexity of fluvial morphology through 2d hydrodynamic delineation of river landforms abstract fluvial landforms at the morphological unit scale 1 10 channel widths are typically delineated and mapped either by breaking up the one dimensional longitudinal profile with no accounting of lateral variations or by manually classifying surface water patterns and two dimensional areal extents in situ or with aerial imagery mapping errors arise from user subjectivity varying surface water patterns when the same area is observed at different discharges and viewpoints and difficulty in creating a complete map with no gaps or overlaps in delineated polygons this study presents a new theory for delineating and mapping channel landforms at the morphological unit scale that eliminates in field subjective decision making adds full transparency for map users and enables future systemic alterations without having to remap in the field delineation is accomplished through a few basic steps first near census topographic and bathymetric data are used in a two dimensional hydrodynamic model to create meter scale depth and velocity rasters for a representative base flow second expert judgment and local knowledge determine the number and nomenclature of landform types as well as the range of base flow depth and velocity over each type this step does require subjectivity but it is transparent and adjustable at any time third the hydraulic landform classification is applied to hydraulic rasters to quickly completely and objectively map the planform pattern of laterally explicit landforms application of this theory will reveal the true natural complexity yet systematic organization of channel morphology

kaolin coating of stylolites effect on quartz cementation and general implications for dissolution at mineral interfaces abstract the deeply buried 4 km 160 c quartz rich sandstones of the middle jurassic garn formation in well 6507 7 1 offshore mid norway typically contain 20 30 quartz cement and only 3 9 porosity the exception is a less than 1 5 m thick interval at the top of the formation where quartz cement volumes typically drop to 8 16 and porosities are in the range 7 19 the uppermost part of the garn formation is not isolated from the rest of the formation by any type of impermeable barrier the sandstones are water filled indicating that the change in cementation does not correspond to a hydrocarbon contact and there are no significant changes in grain size grain coating abundance grain mineralogy or other factors that could give a lower quartz surface area for development of quartz overgrowths within the uppermost 1 5 m of the sandstones however in the samples from the less cemented interval illitization of authigenic kaolin is either not detectable or very restricted compared to deeper down in the cores where illitization of kaolin is usually complete we propose that the cause of reduced quartz cementation in the top of the garn formation may be the coating of stylolites developed from primary illitic clay rich and micaceous laminae with authigenic kaolin as quartz cementation proceeds and the authigenic kaolin rich rock adjacent to the stylolites is dissolved although we do not have evidence indicating that this may be a common phenomenon of major importance for preservation of reservoir quality our observations may help to unravel the mechanisms of quartz dissolution at stylolites specifically we suggest that the lack of significant surface charge on kaolin compared to illite and mica may lead to a reduced thermodynamic drive for quartz dissolution at kaolin quartz contacts similarly lack of dissolution at clean quartz quartz surfaces may be due to smaller and equal surface charges setting up oppositely directed electric fields that cancel each other whereas the positive surface charge of carbonate minerals may actually enhance the electric fields from negatively charged illitic clay and mica which may explain the extensive dissolution often seen at stylolites in limestones

stylolites a review abstract stylolites are ubiquitous geo patterns observed in rocks in the upper crust from geological reservoirs in sedimentary rocks to deformation zones in folds faults and shear zones these rough surfaces play a major role in the dissolution of rocks around stressed contacts the transport of dissolved material and the precipitation in surrounding pores consequently they play an active role in the evolution of rock microstructures and rheological properties in the earth s crust they are observed individually or in networks in proximity to fractures and joints and in numerous geological settings this review article deals with their geometrical and compositional characteristics and the factors leading to their genesis the main questions this review focuses on are the following how do they form how can they be used to measure strain and formation stress how do they control fluid flow in the upper crust geometrically stylolites have fractal roughness with fractal geometrical properties exhibiting typically three scaling regimes a self affine scaling with hurst exponent 1 1 0 1 at small scale up to tens or hundreds of microns another one with hurst exponent around 0 5 to 0 6 at intermediate scale up to millimeters or centimeters and in the case of sedimentary stylolites a flat scaling at large scale more complicated anisotropic scaling scaling laws depending of the direction of the profile considered is found in the case of tectonic stylolites we report models based on first principles from physical chemistry and statistical physics including a mechanical component for the free energy associated with stress concentrations and a precise tracking of the influence of grain scale heterogeneities and disorder on the resulting micro structures experimental efforts to reproduce stylolites in the laboratory are also reviewed we show that although micrometer size stylolite teeth are obtained in laboratory experiments teeth deforming numerous grains have not yet been obtained experimentally which is understandable given the very long formation time of such geometries finally the applications of stylolites as strain and stress markers to determine paleostress magnitude are reviewed we show that the scalings in stylolite heights and the crossover scale between these scalings can be used to determine the stress magnitude its scalar value perpendicular to the stylolite surface during the stylolite formation and that the stress anisotropy in the stylolite plane can be determined for the case of tectonic stylolites we also show that the crossover between medium millimetric scales and large pluricentimetric scales in the case of sedimentary stylolites provides a good marker for the total amount of dissolution which is still valid even when the largest teeth start to dissolve which leads to the loss of information since the total deformation is not anymore recorded in a single marker structure we discuss the impact of the stylolites on the evolution of the transport properties of the hosting rock and show that they promote a permeability increase parallel to the stylolites whereas their effect on the permeability transverse to the stylolite can be negligible or may reduce the permeability depending on the development of the stylolite

pressure solution and hydrothermal recrystallization of carbonate sediments an experimental study reply abstract the extent of calcite recrystallization was determined in pressure solution and hydrothermal experiments which were conducted on deep sea carbonates of low mg calcite iceland spar and reagent grade calcite powder in the pressure solution experiments wet sediments were subjected to confining pressures of 500 1500 bars and pore pressures of 150 500 bars at temperatures between 22 and 180 c for 21 240 h the hydrothermal experiments were performed in sealed teflon coated bombs at 200 c zero effective stress in sulfate free sea water for two weeks the hydrothermal system was solution dominated the extent of calcite recrystallization was determined by measuring the oxygen isotopic compositions of the pore fluids and solids before and after each experiment scanning electron microscope observations porosity and specific surface area measurements were performed in fine grained carbonate samples subjected to high effective stresses the mechanism for recrystallization apparently involves both relief of strain energy at grain to grain contacts and decrease in surface free energy by decreasing the surface area while in coarse grained carbonates relief of strain energy appears to be the most important control of recrystallization in the hydrothermal experiments however decrease in surface free energy is the only driving force for recrystallization effective stress increased the rate of calcite recrystallization in both pressure solution and hydrothermal experiments clay minerals retarded the reaction the effects of diatomite and basaltic glass on the extent of calcite recrystallization was investigated only in the hydrothermal experiments both admixed non carbonate materials retarded the reaction diatomite being the most effective inhibitor surface chemical reactions seem to be responsible for the observed inhibitions of calcite recrystallization increases in the extent of calcite recrystallization with increasing ionic strength were observed in hydrothermal experiments in nacl solutions of five different ionic strengths

effects of phosphate ions on intergranular pressure solution in calcite an experimental study abstract intergranular pressure solution ips is a coupled chemical mechanical process of widespread importance that occurs during diagenesis and low temperature deformation of sedimentary rocks laboratory experiments on ips in halite quartz and calcite have largely concentrated on the mechanical aspects of the process in this study we report the effects of pore fluid chemistry specifically varying phosphate ion concentration on the mechanical compaction by ips of fine grained calcite powders at room temperature and 1 to 4 mpa applied effective stress phosphate was investigated because of its importance as a biogenic constituent of sea and pore waters increasing the pore fluid phosphate concentration from 0 to 10 3 mol l systematically reduced compaction strain rates by up to two orders of magnitude the sensitivity of the compaction strain rate to phosphate concentration was the same as the sensitivity of calcite precipitation rates to the addition of phosphate ions reported in the literature suggesting that the rate of ips in phosphate bearing samples was controlled by calcite precipitation on pore walls the results imply that ips and associated porosity permeability reduction rates in calcite sediments may be strongly reduced when pore fluids are enriched in phosphates for example through high biologic productivity or a seawater origin future modeling of ips related processes in carbonates must therefore take into account the effects of pore fluid chemistry specifically the inhibition of interfacial reactions

sedimentary stylolite networks and connectivity in limestone large scale field observations and implications for structure evolution stylolites are rough surfaces formed by localized rock dissolution and prevalent in carbonates and other sedimentary rocks their impact on porosity and permeability and capacity to accommodate compactive strain are well documented this paper presents a meso scale field study on sedimentary stylolites in carbonates characterizing large scale distributions of stylolites including measurements conducted on longer than kilometer long stylolites our field study suggests that on large scales connections between stylolites become important since connectivity and also lack of connectivity are expected to play a significant role in strain accommodation and hydraulic rock properties we suggest that large scale analysis may require a new characterization scheme for stylolites populations based on their connectivity we therefore divide sedimentary stylolite populations into three end member types which are correlated with the three possibilities for percolation of such systems isolated stylolites with zero percolation connectivity long parallel stylolites with 2 dimensional percolation connectivity and interconnected stylolite networks with 3 dimensional percolation connectivity new statistical parameters and measures are devised and used to quantitatively characterize the different population types schematic mechanistic models are then offered to explain the evolution of the three end member connectivity classes in addition we discuss the effect on fluid flow of the different population types

stylolites in the caballos novaculite west texas stylolites within the caballos novaculite developed by pressure solution in response to lithostatic pressure after the original sediment had been converted to a novaculite estimates of minimum stratigraphic thinning of the novaculite are fairly uniform across the marathon basin they range from 3 5 to 5 6 on the basis of stylolite column amplitude

magnetovariational sounding of the earth using observatory and magsat satellite data abstract deep magnetovariational soundings have been carried out using data from the geomagnetic observatory net and the magsat satellite complex apparent resistivities have been estimated from satellite data by two independent methods the joint results have been interpreted assuming spherical symmetry of the earth s layers the global estimation of the electrical structure of the earth s mantle has confirmed the existence of a layer with high conductance at a depth of approximately 600 700 km the nature and possible causes of this layer are discussed

an integrated model for transitional pressure solution in sandstones abstract a key aspect of the deformation of sedimentary rocks during diagenesis is pressure solution however it is often not clear why some rocks of a given mineralogy depth and pressure exhibit a great deal of pressure solution while very similar rocks under similar conditions do not to address such difficulties which we believe arise from the natural non linear physico chemical processes a quantitative model for pressure solution applied to sandstones has been developed this model subsumes various factors 1 pressure temperature and burial rate 2 grain size shape and packing of the mineral grains 3 the variability of water film thickness and coefficient of diffusion between any two grains in contact as a function of stress across the contact pore fluid pressure salinity ph and temperature in this study we distinguish several types of surface sites over quartz grains in a sandstone with corresponding differences in chemical potential thus allowing the diffusive transfer of matter from one site to another the contact between two grains is divided into two parts the actual true contact between two grains is a site of water film diffusion and the inclusions inside the contact the free face inclusion contacts are sites of free face pressure solution on the pore surface site precipitation occurs it is shown that a kinetics transition from a reaction limited deformation to a diffusion limited deformation occurs in the upper crust a geometric transition occurs too due to the textural evolution of the rock with deformation the main goal of this paper is to show the dynamics of the shifting importance of actual and free face inclusion contacts using a unified model including both features the result is a predictive model for porosity variations with depth due to pressure solution in sandstones

extensional veins induced by self similar dissolution at stylolites analytical modeling abstract stylolites are surfaces of localized dissolution observed in rocks many stylolites share a common morphological feature the amount of dissolved rock in the center of the seam is proportional to the stylolite s length field observations demonstrate that stylolites can locally influence formation of veins the developed analytical model of the indirect solution of eshelby s transformation problem calculates the stress field within and around the stylolite the results suggest that growth of a stylolite with an elliptic dissolution pattern generates a local non uniform stress field in the host rock which is in turn accommodated by brittle mode i fracturing in the stylolite midsection further resulting in veins formation parametric analysis and qualitative comparison with anticrack model describing stress field within and around stylolite are conducted

stylolite interfaces and surrounding matrix material nature and role of heterogeneities in roughness and microstructural development rough pressure solution interfaces like stylolites are one of the most evident features of localized slow deformation in rocks of the upper crust there is a general consensus that the development of these rough structures is a result of localized stress enhanced dissolution of material along a fluid filled interface but little is known on the initiation of this roughness the aim of this article is to reveal the role of heterogeneities initially present in the host rock on roughness initiation this should give insights on whether stylolite roughness is generated by a stress induced instability or by the presence of disorder in the material i e quenched noise we use a microstructural approach based on sem ebsd analysis combined with orientation contrast oc image analysis of stylolites in limestones we found that the stylolite roughness is induced by heterogeneities in the host rock clay particles and detrital quartz grains in our case in addition close to mature stylolite interfaces matrix modifications occur which can be attributed to the compaction along the stylolite the grain size decreases by 15 25 and a pre existing shape and lattice preferred orientation spo lpo are significantly modified in the vicinity of the stylolite the results presented here imply that localized pressure solution along stylolites is not necessarily restricted to the actual interface but influences the adjacent matrix the heterogeneity data might serve as a quantitative basis for elaborate numerical models of localized compaction

the electrical conductivity of the upper mantle as estimated from satellite magnetic field data the electrical conductivity of the upper mantle is estimated from low latitude magnetic field variations magnetic storms caused by large fluctuations in the equatorial ring current the data base is derived from magnetic field magnitude data measured by satellites ogo 2 4 and 6 which offer better global coverage than land based observatories the procedure of analysis consist of 1 separation of the disturbance field into internal and external parts relative to the surface of the earth 2 estimation of an electromagnetic response function q omega which relates the internally generated magnetic field variations to the external variations due to the ring current and 3 interpretation of the estimated response function using theoretical response functions for assumed conductivity profiles special consideration is given to possible oceanic and ionospheric effects best estimates of the geomagnetic response function q omega for 0 2 to 2 0 cpd indicate an upper mantle conductivity of the order of 10 sup 2 s m this conductivity is reasonable especially when laboratory measurements of conductivity versus temperature for olivine are considered

rock matrix structures in a zone influenced by a stylolite abstract a stylolitic structure is one of the visible manifestations of the pressure solution process in a rock the stylolitic process zone as defined in previous studies on both sides of a stylolite is studied by sem the chosen samples concern tectonic stylolites within a high porosity limestone 16 without tension gashes this zone corresponds to a local increase of porosity and comprises a large number of stylolitic joints showing a decreasing size from the macroscopic structure to simple contact between two grains two hypotheses are presented for the stylolite formation 1 the macroscopic stylolite is the result of the coalescence of earlier minor pressure solution structures 2 small stylolites nucleate gradually from a major stylolite joint the mass transfer can be realized either by diffusion between particles or by seepage through previously undescribed process zone fractures the mass deposition can be localized in the porous volume and the microcracks without requiring any additional tectonic openings including tension gashes the rock deformation is therefore limited to shortening parallel to 1 without normal extension

experimental pressure solution deposition on quartz grains the crucial effect of the nature of the fluid abstract experimental deformation by pressure solution was performed on an aggregate of small grains subjected to deviatoric stress 50 mpa for a long time several weeks or months at relatively high temperature and pressure in contact with various fluids air water 0 1 to 1 n naoh for quartz water and 5 nh 4 cl for calcite the change in shape of the grains by solution deposition depended on the duration of the experiment with the same fluid and on the concentration of the solid in solution with the same duration but various fluids significant shape changes were obtained for quartz grains but only with both long duration and very good solvents 1 n naoh by comparison with previously obtained results on the change of shape of fluid inclusions where the kinetics of dissolution was the rate controlling process the limiting process of the deformation of the quartz grains was inferred to be the rate of diffusion along grain boundaries saturated with trapped fluid

stylolitization as source of cement in mississippian salem limestone west central indiana the mississippian salem limestone of west central indiana is a homogeneous cross bedded grainstone containing numerous stylolites with amplitudes ranging up to 25 cm petrographic and geochemical analyses of closely spaced samples from four 1 m thick stylolite bounded units document spatial trends in grainstone texture and composition which correlate with proximity to bounding solution seams textural data indicate that stylolitization was locally preceded by grain compaction and that seam solution preferentially occurred within layers where grain packing was tightest amount of cement largely corresponds to volume of available pore space and remaining porosity varies inversely to stylolite proximity trace element compositions demonstrate that intergranular spar is enriched in mn and depleted in mg relative to grains and suggest a significant contribution of carbonate cement to grainstone pores from bounding solution seams data on grainstone and stylolite insoluble contents indicate that stylolite amplitude records 43 of actual section shortening on average seam solution within the salem limestone could have provided no less than 47 and no more than 90 of the caco 3 fe and mn mass now in grainstone pores as intergranular spar cement as such stylolitization has played an important role during burial diagenesis porosity occlusion and permeability reduction within this mississippian grainstone sequence

compaction creep of wet granular calcite by pressure solution at 28 c to 150 c 1 uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone analytical grade calcite and superpure calcite the tests were performed at 28 c 150 c effective stresses of 20 47 mpa and a pore pressure of 20 mpa using presaturated caco3 solution as the pore fluid sample grain sizes ranged from 12 to 86 m the aim was to determine if creep occurs by intergranular pressure solution ips under these conditions and to identify the rate controlling process the wet samples showed significant creep while dry and oil flooded samples did not wet samples were also characterized by microstructures such as sutured grain contacts grain indentations and overgrowths suggesting the operation of ips the behavior of the wet samples at low strains 4 5 agreed well with the predictions of standard models for diffusion controlled pressure solution however at higher strains 5 10 creep slowed down compared with the model predictions transient flow through tests performed in this regime led to an acceleration of creep consistent with models for precipitation controlled ips and demonstrated an increase in the impurity content of the pore fluid toward higher strains since some of these impurities notably mg2 retard precipitation in calcite we suggest that creep occurred by diffusion controlled ips at low strain giving way to precipitation control at larger strains as impurities accumulated fitting of the diffusion controlled ips model to the low strain data yielded values of the grain boundary diffusion product ds in calcite of 10 19 m3 s 1 at 150 c

a tem study of microstructures associated with solution cleavage in limestone abstract microstructures associated with clay filled seams in the scaglia rossa limestone from the umbria marche apennines italy were characterized with transmission electron microscopy tem in order to study one of the mechanisms that presently falls under the heading of pressure solution only seams that formed after lithification often called solution of spaced cleavage were examined although some observations supported suggestions that much of the clay in the solution cleavage seam could be authigenic this report focuses primarily on the limestone microstructures no evidence of plastic deformation could be observed around the seams with an optical microscope however the tem resolved dislocations concentrated within limited areas of single grains comparisons with experimentally deformed calcite microstructures and with computer simulations of tem dislocation contrast allowed further interpretation of the character and density of dislocations dislocation concentrations were frequently associated with voids and pits the pits and voids were usually elongate in a calcite dislocation slip plane and were interpreted as dissolution features these and other observations suggested that selective dissolution of localized dislocation tangles was responsible for solution cleavage formation similar microstructures associated with the stress corrosion cracking have been interpreted elsewhere as evidence of plastic strain enhanced heterogeneous dissolution further interpretations indicated that a solution cleavage surface grows laterally like a fracture tip

effects of interfacial energy on compaction creep by intergranular pressure solution theory versus experiments on a rock analog nano3 groundwater systems are increasingly used for seasonal aquifer thermal energy storage sates for periodic heating and cooling of buildings its use is hampered in contaminated aquifers because of the potential environmental risks associated with the spreading of contaminated groundwater but positive side effects such as enhanced contaminant remediation might also occur a first reactive transport study is presented to assess the effect of sates on the fate of chlorinated solvents by means of scenario modeling with emphasis on the effects of transient sates pumping and applicable kinetic degradation regime temperature effects on physical chemical and biological reactions were excluded as calculations and initial simulations showed that the small temperature range commonly involved t 15 c only caused minor effects the results show that a significant decrease of the contaminant mass and eventually plume volume occurs when degradation is described as sediment limited with a constant rate in space and time provided that dense non aqueous phase liquid dnapl is absent however in the presence of dnapl dissolution particularly when the dissolved contaminant reaches sates wells a considerably larger contaminant plume is created depending on the balance between dnapl dissolution and mass removal by degradation under conditions where degradation is contaminant limited and degradation rates depend on contaminant concentrations in the aquifer a sates system does not result in enhanced remediation of a contaminant plume although field data are lacking and existing regulatory constraints do not yet permit the application of sates in contaminated aquifers reactive transport modeling provides a means of assessing the risks of sates application in contaminated aquifers the results from this study are considered to be a first step in identifying the subsurface conditions under which sates can be applied in a safe or even beneficial manner

stylolites porosity depositional texture and silicates in chalk facies sediments ontong java plateau gorm and tyra fields north sea comparison of chalk on the ontong java plateau and chalk in the central north sea indicates that whereas pressure dissolution is controlled by effective burial stress pore filling cementation is controlled by temperature effective burial stress is caused by the weight of all overlying water and sediments as counteracted by the pressure in the pore fluid so the regional overpressure in the central north sea is one reason why the two localities have different relationships between temperature and effective burial stress in the chalk of the ontong java plateau the onset of calcite silicate pressure dissolution around 490 m below sea floor bsf corresponds to an interval of waning porosity decline and even the occurrence of proper stylolites from 830 m bsf is accompanied by only minor porosity reduction because opal is present the pore water is relatively rich in si which through the formation of ca silica complexes causes an apparent super saturation of ca and retards cementation the onset of massive pore filling cementation at 1100 m bsf may be controlled by the temperature dependent transition from opal ct to quartz in the stylolite bearing chalk of two wells in the gorm and tyra fields the nannofossil matrix shows recrystallization but only minor pore filling cement whereas microfossils are cemented cementation in gorm and tyra is thus partial and has apparently not been retarded by opal controlled pore water a possible explanation is that due to the relatively high temperature silica has equilibrated to quartz before the onset of pressure dissolution and thus in this case dissolution and precipitation of calcite have no lag this temperature versus effective burial stress induced difference in diagenetic history is of particular relevance when exploring for hydrocarbons in normally pressured chalk while most experience has been accumulated in the over pressured chalk of the central north sea

compaction creep of quartz sand at 400 600 c experimental evidence for dissolution controlled pressure solution intergranular pressure solution ips is an important compaction and deformation mechanism in quartzose rocks but the kinetics and rate controlling process remain unclear the aim of the present study is to test microphysical models for compaction creep by ips against isostatic hot pressing experiments performed on quartz sand under conditions expected to favor pressure solution confining pressure 300 mpa pore water pressure 150 250 mpa temperature 400 600 c microstructural observations revealed widespread intergranular indentation features and confirmed that intergranular pressure solution was indeed the dominant deformation mechanism under the chosen conditions for porosities down to 15 the mechanical data agree satisfactorily with a microphysical model incorporating a previously determined kinetic law for dissolution of loose granular quartz suggesting that the rate limiting mechanism of ips was dissolution the model also predicts ips rates within one order of magnitude of those measured in previous experiments at 150 350 c and thus seem robust enough to model sandstone compaction in nature such applications may not be straightforward however as the present evidence for dissolution control implies that the compositional variability of natural pore fluids may strongly influence ips rates in sandstones

finite element modelling of the propagation of a pressure solution cleavage seam abstract the propagation of a cleavage seam is modelled by a two dimensional finite element technique which extends fletcher and pollard s elastic anticrack theory to a composition dependent viscous rheology the viscous solution is obtained by repeated solutions of the force equilibrium equations at successive time steps with the viscosity of each element varying as a function of its strain history the rheology assumed follows previous modelling by robin the rock is modelled as a quartz mica mixture in which deformation proceeds by diffusion of silica the viscosity of an element depends on its proportion of quartz varying from a minimum for intermediate quartz mica mixtures to higher values for either pure quartz or pure micas as a result of its incremental strain an element either loses or gains quartz i e volume and therefore changes its viscosity for the next strain increment the system can be either open silica escapes the system all individual elements lose volume or closed individual elements may gain or lose volume but the total volume of the system is preserved at the start of a run a nucleus of a cleavage seam is introduced as a thin layer of elements with a lower viscosity corresponding to a higher mica content than the rest of the rock the stress concentration at the tip of the seam leads to a weakening of the elements in front of it through loss of quartz this results in crack propagation for both open and closed systems all other parameters being equal the speed of propagation is greater for open systems than for closed ones

postseismic pressure solution creep evidence and time dependent change from dynamic indenting experiments active faults in the earth s upper crust can slide either steadily by aseismic creep or abruptly causing earthquakes seismic and aseismic processes are closely related earthquakes are often followed by transient afterslip creep postseismic displacement rates progressively decrease with time over a period of years or decades so seismic fracturing activates the creep rate and various healing processes progressively reduce it this article presents pressure solution indenter experiments on halite calcite and plaster that show how fracturing and comminution processes induced by dynamic stress loading applied by dropping steel balls drastically accelerate the displacement rates accommodated by pressure solution creep by decreasing the dissolution contact area and the diffusive mass transfer distance along this contact however as fractures progressively heal and dissolution contacts flatten these effects disappear and the displacement rates slow down the time dependent change in indenter displacement after dynamic stress loading has been measured and is best fitted by power laws with exponents that change with time from 0 3 to 1 when healing is achieved natural postseismic afterslip displacement time relationships have been analyzed and also show a power law change with a power law exponent in the range of 0 25 0 4 it is proposed that the variation in power law exponent with time is related to the change in morphology of the dissolution contact that is fractured or comminuted during the dynamic event and is then progressively healed and smoothed in natural faults monitoring the power law parameters could give access to the characteristic healing time in the fault

compaction of porous rock by dissolution on discrete stylolites a one dimensional model 1 compaction of sedimentary porous rock by dissolution and precipitation is a complex deformation mechanism that is often localized on stylolites and pressure solution seams we consider a one dimensional model of compaction near a thin clay rich stylolite embedded in a porous rock under the assumption that the clay enhances solubility the model predicts a reactive transport away from the clay layer followed by pore cementation the evolution of the porosity reactant transport and compaction rate are studied as functions of model parameters and shown to reach a stationary state we find good agreement between the porosity distribution predicted by the model and previously reported field measurements the model provides quantitative estimates for compaction rates on stylolitic surfaces