coral ages and island subsidence hilo drill hole a 25 8 m thick sedimentary section containing coral fragments occurs directly below a surface lava flow the 1340 year old panaewa lava flow at the hilo drill hole ten coral samples from this section dated by accelerator mass spectrometry ams radiocarbon and five by thermal infrared multispectral scanner tims 230th u methods show good agreement the calcareous unit is 9790 years old at the bottom and 1690 years old at the top and was deposited in a shallow lagoon behind an actively growing reef this sedimentary unit is underlain by a 34 m thick lava flow which in turn overlies a thin volcaniclastic silt with coral fragments that yield a single 14c date of 10 340 years the age depth relations of the dated samples can be compared with proposed eustatic sea level curves after allowance for island subsidence is taken island subsidence averages 2 2 mm yr for the last 47 years based on measurements from a tide gage near the drill hole or 2 5 2 6 mm yr for the last 500 000 years based on the ages and depths of a series of drowned coral reefs offshore from west hawaii the age depth measurements of coral fragments are more consistent with eustatic sea levels as determined by coral dating at barbados and albrolhos islands than those based on oxygen isotopic data from deep sea cores the panaewa lava flow entered a lagoon underlain by coral debris and covered the drill site with 30 9 m of lava of which 11 m was above sea level this surface has now subsided to 4 2 m above sea level but it demonstrates how a modern lava flow entering hilo bay would not only change the coastline but could extensively modify the offshore shelf

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

partial homogenization of cryptoperthites in an ignimbrite cooling unit a single crystal x ray study of alkali feldspars of bulk composition or39 43 and or62 64 from a single cooling unit of battleship rock tuff northern new mexico reveals a trend of decreasing degree of exsolution from the non welded zone toward the densely welded center of the cooling unit crystals of bulk composition or62 64 range from cryptoperthite with both phases monoclinic in the nonwelded zone to virtually unexsolved crystals in the welded center of the cooling unit crystals of bulk composition or39 43 include crytpoperthites with both phases monoclinic and cryptoperthites with pericline twinned sodic lamellae with of the sodic phase increasing systematically from 87 3 in the nonwelded zone to 90 in the densely welded zone composition estimates based on unitcell parameters show decreasing compositional differences between coexisting lamellae toward the welded zone the feldspar crystals studied are interpreted to be xenocrysts which had undergone exsolution prior to incorporation in the erupting magma and which were then partially homogenized during emplacement and post emplacement cooling the data indicate a maximum re equilibration temperature of the feldspars of about 500 c and a more rapid cooling of the tuff than calculated for simple conduction in a uniform slab

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