an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

boudinage and composite boudinage in superposed deformations and syntectonic migmatization abstract the banded gneisses of the jasidih deoghar area of east india behaved as a complex geological multilayer which evolved through the combined effects of deformation and leucosome emplacement the early foliation and banding were transposed and retransposed by two generations of isoclinal folds the intensity of foliation development the layer thickness ratios and the rheological contrasts within the gneisses changed both in space and in time under layer normal compression these complex multilayers gave rise to a variety of boudins and of their pegmatite filled separation zones the geometrical relations with successive generations of folds can distinguish the closely associated pre f 1 syn f 1 and syn f 2 boudins d 2 boudinage occurred at an advanced stage of f 2 folding so that boudinage induced subhorizontal extension was considerably less than the total subhorizontal extension during d 2 composite boudinage occurred during progressive syntectonic leucosome emplacement in the course of which a group of boudinaged layers with a profusion of coarse quartz feldspar leucosome became more competent than the adjoining rocks and underwent boudinage as a whole

nitrogen isotope hydrochemistry and denitrification within the chalk aquifer system of north norfolk uk abstract although there has been much debate over the potential health risks of nitrate in drinking water there is a real issue of the costs associated with removing nitrate from drinking water supplies in the chalk aquifer system of north east norfolk modern contaminants of a mainly agricultural origin produce high levels of nitrate 15 mg l no3 n in the unconfined valley areas whereas in confined regions the levels of nitrate are low and commonly below detection limits

methodology of the last climatic cycle reconstruction in france from pollen data abstract a numerical method has been devised to reconstruct the climate of the last climatic cycle from pollen data reliable annual reconstructions have been published recently for the two french long sequences of la grande pile and les echets covering the last 140 millennia this paper gives more details on the method used it proposes new reconstructions based on an extended modern pollen data base these reconstructions are consistent with the previous ones especially detailed information is obtained on the seasonal characteristics of climate computations of gcm on the climate variations from 125 kyr to 115 kyr b p are confirmed for western europe the insolation variations have induced at that time a decrease of seasonality accompanied by an increased cyclonic activity in winter this has been the beginning of the first ice growth after the last interglacial other glacier growth phases are detected at the end of substage 5c and particularly at the end of substage 5a

twenty years of groundwater evolution in the triassic sandstone aquifer of lorraine impacts on baseline water quality abstract the lorraine triassic sandstone aquifer ltsa which has already been the subject of a chemical and radioisotopic study 1979 is used to investigate the impacts of 20 a of large scale pumping on baseline water quality in parallel new sampling of the aquifer 2001 provides new inorganic geochemical data including trace elements that allow improving the knowledge of baseline conditions and hydrochemical functioning of a major sandstone aquifer the good correlation between 14 c activities temperature and depth along the main flow line indicate regular downgradient trends and possible water stratification unreactive tracers mainly stable isotope ratios 18 o and 2 h as well as c isotopes are used to define a timescale for the aquifer showing two groups of groundwater namely of modern and holocene age and late pleistocene age with a mixing zone baseline quality is then represented by a wide range of concentrations mainly the result of time dependent water rock interaction as already observed elsewhere in triassic sandstone aquifers some trace elements such as li rb cs which are not limited by solubility constraints show linear trends during saturated flow downgradient the chemistry is also specifically characterised by a regular increase in na and cl and locally so 4 as a result of evaporite dissolution related to overlying or basement limits the aquifer is mostly oxidising with a redox boundary marked by u decrease some 40 km from outcrop groundwater abstraction since the 1970s has created a strong lowering 10 150 m of the water table especially from 1970 to 1980 based on nine boreholes previously sampled in 1979 a decreasing evolution in radiocarbon content of the tdic together with significant evolution of 18 o content indicate that old groundwater has moved upgradient the major difference in terms of baseline evolution is observed using cl and na concentration and locally so 4 indicating an increasing influence of water circulation involving overlying or basement formations or of mixing with permian waters from the point of view of aquifer management the perceptible no 3 increase could provide information on the progress of any contamination under the aerobic conditions in addition the few key elements indicators of disequilibrium related to overlying or deep waters should be included in regular monitoring programmes

microstructure and texture in experimentally folded single layer rock salt abstract buckling experiments on single layers of fine grained artificial polycrystalline rock salt embedded in a plasticine matrix have been performed in the temperature range of 185 200 c under a confining pressure of 10 bars in a plane strain pure shear apparatus strain rates ranged from 2 5 10 7 to 4 7 10 7 layers with an aspect ratio of 7 deformed without buckling but when this ratio was increased to 13 layers deformed by buckling and produced one wavelength of a sinusoidal fold the stress strain and time strain curves indicate that folding is initiated at about 7 to 8 of bulk deformation the layer parallel shortening and thickening continues with progressive folding the changes in the arclength thickness and limb dip show that initially the fold growth is slow and then becomes rapid the inner fold are is characterized by strong preferred dimensional grain orientation with the longer axis normal to the layer surface the axial ratio of grains gradually decreases towards the outer arc the stresses on the outer are have been relieved mainly by the development of tension fractures in the limbs the grains are elongated normal to the layer however close to the surfaces the grains are very fine and exhibit a tendency to elongate along the layer surface the preferred lattice orientation of 100 110 and 111 planes in halite have been determined by x ray texture goniometry and the pole figures are partially comparable to the textures in natural fold from salt domes

the development of subgrain misorientations with strain in dry synthetic nacl measured using ebsd abstract the development of subgrain boundary misorientations with strain in dry synthetic nacl polycrystals deformed at elevated temperature has been investigated using electron backscattered diffraction ebsd at low natural strains up to 0 5 average misorientations of subgrain boundaries increase with strain and a power law relationship exists between strain and average misorientations the average misorientations are strongly influenced by grain orientation suggesting that the misorientation strain relationship may also be texture dependent in materials with high plastic anisotropy like nacl a slight grain size dependency of the average misorientations was observed the results indicate that with suitable calibration average subgrain boundary misorientations may offer a method for estimating the strain accommodated by dislocation creep in nacl and thus perhaps in other geological materials although current theories for polycrystalline plasticity imply that misorientations may also depend on stress in some situations

the effect of dispersion on the establishment of a paleoclimatic record from groundwater a mathematical model which can account for the dispersion of solute in underground water over time scales exceeding 104 yr is described in its simplest form the model postulates a diffusion limited exchange of material between flowing groundwater and the stationary water in the confining aquiclude leading to the spreading of the solute in the mobile water and a consequent reduction in its concentration variability the model is used to study the increasing attenuation with age of the perturbations in groundwater composition induced by paleoclimatic oscillations in the late quaternary specific reference is made to noble gas concentrations stable isotope ratios and chloride levels the extreme attenuation of stable isotope ratios in the australian great artesian basin cannot yet be adequately explained and may provide the basis of a critical evaluation of different dispersion models in large hydraulic basins

closely spaced fractures in layered rocks initiation mechanism and propagation kinematics spacings of opening mode fractures joints and veins in layered sedimentary rocks often scale with the layer thickness field observations reveal that the ratio of fracture spacing to the thickness of the fractured layer s tf ranges from less than 0 1 to greater than 10 there is a critical spacing to layer thickness ratio that defines the condition of fracture saturation and explains the observed spacing ratios between 0 8 and 1 2 values of s tf 1 2 are explained as the results of the fracturing process having not reached the saturation level to explain ratios of s tf 0 8 we study the possibility for further fracture infilling by considering flaw distributions between adjacent fractures loaded by extension of the layer results show that infilling fractures grow more easily from flaws located near the interface than from those in the middle of the fractured layer the propagation of a flaw located in the middle of the fractured layer is unstable but for the flaw to propagate toward the interfaces its height has to be greater than a critical size this critical size decreases with increasing s tf the propagation behavior of a flaw with one of its tips at the interface depends on s tf the propagation is unstable when s tf is greater than a critical value when s tf is less than this critical value the propagation is first unstable then stable and then unstable again an infilling fracture can cut through the fractured layer only if s tf is greater than another critical value otherwise the infilling fracture can only partially cut the fractured layer for models with the same elastic constants for the fractured layer and the neighboring layers this critical value is 0 546 and the minimum spacing to layer thickness ratio of fractures formed by the in filling process under extension is 0 273

geochemical evolution of groundwater in the carbonate aquifers of sierra de segura betic cordillera southern spain summary sierra de segura betic cordillera with a total area of over 3000 km 2 is the source of the two principal rivers in southern spain the guadalquivir and the segura due to the orographic effect of these mountains precipitations are considerably more abundant than in nearby lowland areas where the climate is semi arid sierra de segura is constituted of mesozoic and cenozoic sedimentary rocks among which there are thick limestone dolomitic formations which have given rise to extensive outcrops of permeable materials in geomorphological terms there is a large plateau intensively karstified that constitutes the main recharge area discharge takes place via a large number of springs of which the 50 most important add up to a mean spring flow of about 13 500 l s the active geochemical processes in aquifers of sierra de segura with their corresponding time sequence are dissolution of co 2 dissolution of calcite incongruent dissolution of dolomite dedolomitization exsolution of co 2 and precipitation of calcite more evolved water has higher temperature magnesium content and mg ca ratio therefore these parameters can be utilised as indicators of the degree of hydrochemical evolution in addition a good correlation between water temperature and magnesium concentration or mg ca ratio indicates that an increase in temperature accelerates the kinetics of the dissolution of dolomite finally the distribution of the temperatures in the vadose zone determined by atmospheric thermal gradient implies an apparent stratification of the predominant hydrochemical processes and of the groundwater physical and chemical characteristics

chemical and isotopic evidence for hydrogeochemical processes occurring in the lincolnshire limestone over 150 groundwater samples from the lincolnshire limestone have been analysed for ph major ions and 13c ratios where possible field eh and iodide concentrations were measured and methane concentrations were determined for 12 samples stable isotope ratios were determined for soil and rock carbonate samples a system of zonation allows the division of hydrogeochemical processes occurring in the aquifer the use of hydrochemical and isotope data in modelling exercises enables the re evaluation and possible enhancement of the understanding of hydrogeochemical processes the carbonate chemistry of outcrop groundwaters is explained by calcite saturation being achieved under open system conditions in the soil zone 13c ratios in the range 15 99 to 10 57 may be generated from a stoichiometric reaction with possible additional partial and or simultaneous exchange with soil co2 or carbonate the isotopic composition of soil carbonate shows the effects of precipitation from soil waters the incongruent dissolution of primary depositional limestone carbonate results in increasing magnesium and strontium concentrations and increasing 13c ratios for the groundwaters with flow down the hydraulic gradient as a result of incongruent dissolution secondary calcite may be precipitated onto fissure surfaces significant nitrate and sulphate reduction in non saline groundwaters is not supported by the results of hydrochemical and isotope modelling exercises however sulphate reduction and methane fermentation may be affecting the isotopic and chemical compositions of saline groundwaters sodium calcium ion exchange leads to limited calcite dissolution deep in the aquifer but the evolution of these groundwaters is confused by the uncertain effects of oxidation of organic carbon and mixing with a saline end member solution

nature of seismic reflections and velocities from vsp experiments and borehole measurements at the ktb deep drilling site in southeast germany abstract the 1989 vsp program at the ktb pilot hole was complemented in 1992 by a standard vsp in the ktb super deep borehole from 3000 to 6013 m p wave velocities oscillate around 5 8 km s in the upper 3150 m in accordance with sonic log velocities and correlate with paragneisses which prevail in this depth range at about 3150 m depth velocities increase to 6 4 km s correlating with metabasites which dominate in the depth range 3150 to 7500 m laboratory measurements and petrophysical modelling provide evidence that the intrinsic velocities were reduced by 5 10 by fracture density and porosity at all depth ranges subvertical dip 50 70 in structures and textures prevail causing about 10 s wave anisotropy indicated by direct observations of s wave splitting pronounced p wave reflections accompanied by p to s wave conversions and a lack of s wave reflections occur in the lower depth range only 3000 6000 m and correlate with fluid filled fracture systems lithological contrasts gneiss amphibolite play a minor role in generating reflections the most prominent reflecting elements known from surface profiling and 3d surveys i e the franconian lineament reflector at about 7 km and p wave reflections at 8 3 km with notably absent associated s wave reflections coincide with pronounced anomalies observed in the logging data indicating the presence of major fracture zones

hydrogeochemistry of a clayey till 2 sources of co2 the spatial distributions of inorganic and organic carbon in gas aqueous and solid phases were studied in an 18 m thick surficial deposit of fractured clayey calcareous till large pco2 increases were observed with increasing depth at the bottoms of vadose zones from which solid organic carbon had been depleted hydrochemical reaction simulations indentified a reaction path consistent with pco2 o2 major element chemistry 13c and 14c isotope observations this path is open to a biogenic co2 reservoir with pco2 higher than and 14c composition considerably different from that of the soil zone such co2 reservoirs occurring in deep vadose shallow saturated zones and thus isolated by overlying sediments from temperature fluctuations which limit soil zone respiration may be common in the western glaciated plains as evidenced by prevalence of hard high pco2 waters in the region s intertill aquifers carbon 14 data suggest that in the till both dissolved organic c and dissolved inorganic c have two sources soil organic matter and kerogen in the till matrix regardless of source s initial 14c activities of both aqueous c pools at the water table are diluted substantially relative to the actual residence time of the water unappreciated this could cause large relative errors in the calculation of radiocarbon based groundwater age dates

the structural geology of boulby potash mine cleveland united kingdom abstract this is the first description of the structural geology of the upper permian potash and salt of the third zechstein cycle exposed in boulby mine the near seam lithologies are described briefly and the associated veins vein networks shear zones and slides are introduced it is argued that the boulby potash migrated from lower levels to those at which it is now found to fill fractures which developed in a grey anhydrite shale produced by the reduction and wetting of the lower parts of the carnallitic rotten marl continued introduction of chlorides of na and k into vein networks dispersed the shale as clasts of ever decreasing size in a sub horizontal zone of gneissose sylvinite which when it reached a significant thickness began to flow in an extraordinary manner hundreds of asymmetric sub horizontal lobes of gneissose sylvinite root to and repeat the first formed layer in structures which developed to various degrees in different parts of the mine these are shown to represent small scale movement cells e g 15 30 to 100m in axial section in which the movements integrate within a pattern of larger scale movement cells 15 200 to 400 m where the sylvinite was thickest these movement cells progressed to a stage which involved the complete circulation of a compound layer of sylvinite and grey shale continued circulation almost homogenised this compound layer to sylvinite in which the grey shale has been disrupted and dispersed to small aggregates and individual clay particles included within the chloride grains the circulation cells in the sylvinite are rectilinear rolls close to where thin but extensive sub horizontal lobes of boulby halite moved through and over them late in the structural history away from such salt lobes the small scale circulation cells are concentric within the boundaries of larger cells which have polygonal planforms after rejecting explanations invoking near surface slumping for the small scale circulation cells it is argued that they developed near their maximum depth of burial in late jurassic or cretaceous times the multiwavelength circulation pattern in the boulby potash is interpreted as due to thermal convection influenced by primary gravitational instabilities on a larger scale the sub horizontal lobes of boulby halite are assigned to a final laramide transcurrent reactivation of faults inherited from the basement during earlier phases of movement

sinking of a fragmented anhydrite layer in rock salt abstract two dimensional numerical models are used to study the gravity driven sinking of a dense boudinaged anhydrite layer within rock salt we analyze models with an infinite array of regularly spaced blocks two and three block clusters and irregularly spaced blocks we show that the mass of the blocks their shapes and spatial arrangement are the dominating factors that control sinking velocity variation of the block separation distance can modify the velocity by many orders of magnitude for the model with the regularly spaced cuboidal blocks we derive a new approximate formula for their terminal velocity the solution works best when the block separation distance to block width is smaller than 1 and the block height to block separation distance is larger than 1 the horizontally aligned and regularly spaced blocks sink vertically with a constant velocity for clustered blocks the velocity depends on the number of blocks in the cluster and their arrangement and it is larger than for the case of the regularly aligned blocks the blocks can exhibit swinging or rotational motions and can change their spatial arrangement which in turn affects their sinking velocity additionally we show examples of complex structures that develop during block sinking through a stratified salt in the case of two block clusters in the case of an irregularly spaced array the blocks sink faster up to few orders of magnitude than in the regularly spaced arrangement and the mean sinking velocity generally increases with the increasing irregularity of the blocks positions the blocks often tend to cluster initiating a locally fast downward flow that generates backflow which can lead to the upward motion of non clustered blocks the irregular spacing differentiates sinking velocities of individual blocks and promotes their vertical separation distance we show that the mechanical interaction between the blocks can explain low sinking rates of anhydrite blocks observed in zechstein basin

rheology of rocksalt abstract we review progress in experimental determinations of transient and steady state flow properties and processes of natural rocksalt aggregates focusing primarily on results from avery island louisiana domal salt the steady state flow field established from constant stress and constant strain rate tests at temperatures from 50 to 200 c strain rates from 10 5 to 10 9 s 1 and differential stresses from 20 7 to 2 5 mpa has been separated into two flow regimes each fit by a power law relation at the higher stresses and strain rates this relation is e 1 6 10 4 exp 68 1 rt 10 3 5 3 for which the pre exponential constant is expressed in mpa 5 3 s 1 and the apparent activation energy is in j mol 1 creep rates predicted by equation a do not differ appreciably from those predicted previously the relatively low stress low strain rate data are very well fit by e 8 1 10 5 exp 51 6 rt 10 3 2 4 which is comparable conditions predicts creep rates higher and equivalent viscosities lower than does equation a by two orders of magnitude the change in behavior from a to b is ascribed to a change in rate limiting mechanism from cross slip of screw dislocations to the climb of edge dislocations in this dry material subgrain formation dominates microstructural development during steady state flow of salt and from determinations of average subgrain diameters in crystals from 20 different rocksalt bodies flow stress levels between 0 6 and 1 4 mpa have been estimated these values do not bear directly on arguments concerning the nature of forces initiating salt pillow growth because apparently evidence relating to the early deformational history has been overprinted at that stage fluid assisted grain boundary diffusional processes might dominate dislocation creep leading to a linear stress strain rate mechanical response considering buoyancy forces alone behavior described by equation b rather than a reduces the relief necessary to initiate pillow growth but a 1000 fold amplification is required to produce stress differences near 1 mpa that forces other than buoyancy are important is indicated by the occurrence of these same paleostress levels in bedded salts and in shallow offshore concordant intrusions differential loading generally provides the most plausible initial driving force for the growth of diapiric salt structures

anatomy of mushroom shaped diapirs we produced more than 100 mushroom shaped diapirs in eight centrifuged models under acceleration of 1200 g the modelling results allow natural examples to be recognized mushroom diapirs have an overhanging bulb fringed by one or more skirts which can curl inward to form vortices capable of entraining cover material to various degrees most of the internal folds are downward facing the oldest buoyant unit occurs in the skirt and in the diapiric core younger buoyant units or their immediate cover are infolded in crescentic patterns external mushroom diapirs have skirts that infold cover material with greater maturity the skirts can curl inward to form an external vortex entraining cover in contrast internal mushroom diapirs have skirts confined entirely within the intrusion again with greater maturity these confined skirts may curl inward but they entrain only diapiric material internal mushroom structure results from toroidal circulation confined within the diapir where isoviscosity prevails external mushroom structure results where source and entrained cover have similar effective viscosities entrained inclusions of more permeable country rock threaten the integrity of a mined cavern by creating a plumbing system

the application of high resolution x ray computed tomography on naturally deformed rock salt multi scale investigations of the structural inventory abstract x ray computed tomography ct represents a useful technique providing new perspectives and insights for the structural investigation of naturally deformed rock salt several samples of permian rock salt from gorleben asse and teutschenthal germany were investigated by exploiting the non destructive nature of ct and nct techniques particularly for salt rocks ct imaging enabled the visualization and quantification of anhydrite impurities pore space and fluid phases located along grain boundaries or trapped as intracrystalline inclusions disseminated grains and aggregates of anhydrite in rock salt of the gorleben salt dome have been visualized and quantified by ct for the first time in order to portray their spatial occurrence the visualization of anhydrite aggregates and pore space shows no correlation between their spatial distributions this independence excludes the anhydrite to be responsible for elevated porosity 0 87 0 07 vol high resolution nct scans 1 m voxel size of single intracrystalline and grain boundary fluid inclusions from gorleben and asse rock salt allowed the visualization and quantification of their various phase components a major achievement is the detailed description of the morphology and shape of the fluid inclusions and of their phase components which has not been conducted in rock salt research by high resolution x ray ct imaging before

deformation experiments on anhydrite rocks of different grain sizes rheology and microfabric miiller w h schmid s m and briegel u 1981 deformation experiments on anhydrite rocks of different grain sizes rheology and microfabric in g s lister h j behr k weber and h zwart editors the effect of deformation on rocks tectonophysics 78 527 543 three anhydrite rocks of different grain size were experimentally deformed in the 20 to 45o c temperature range the strength of the finegrained varieties becomes strongly temperature and strain rate dependent above 3oo c and a flow law of the form 6 a exp h rt sinh o a with an activation energy h of 27 36 kcal mole and a very low value for the exponent n of 1 5 2 was found the course grained rock remains relatively insensitive to strain rate and temperature even at 45o c microstructural and x ray texture analyses suggest that intracrystalline glide and twinning are the major deformation mechanisms the transition from strong work hardening observed at high stresses into steady state flow at low stresses was found to correlate with the onset of dynamic recrystallization by grain boundary migration

small scale faulting in the upper cretaceous of the groningen block the netherlands 3d seismic interpretation fault plane analysis and regional paleostress abstract over the last years field based studies have shown that fault surfaces can exhibit a considerable self affine topography it is reasonable to assume that similar undulations are also present in fault interpretations from 3d reflection seismic data however both the interpretation uncertainty and geophysical resolution limits hinder their analysis this study analyses a set of small scale non reactivated faults in the upper cretaceous chalk group upper ommelanden formation of the nw part of the groningen block the netherlands in a high quality pre stack depth migrated 3d seismic data set the studied faults are fully contained inside the chalk group in an area located between the major tectonic bounding faults of the nw groningen block over 200 faults with offsets in the order of 30 50 m were interpreted across an area of ca 150 km 2 showing a clear preferential orientation for strike dip and dip direction detailed interpretations and 3d fault plane analyses show undulations on the fault plane we show that these undulations are not an interpretation or gridding artefact and interpret these to indicate direction of fault slip these results were used to calculate a paleostress tensor using all faults to calculate a single stress tensor for the entire study area by numerical dynamic analysis based on the orientation position and a thickness analysis it is interpreted that these faults formed due to the tectonic reactivation of salt structures in the latest cretaceous the calculated paleostress state shows a general nw se extension with a vertical maximum principle stress and a stress ratio of about 0 3 indicating that the studied faults are not the result of dewatering this interpretation agrees both with a nearby salt tectonic reconstruction as well as field based paleostress results from the uk belgium and france a first look at other surveys from the dutch sector indicates that similar faults are present in other areas with different orientations we propose that a dedicated analysis of these faults across on and offshore europe would allow extending the stress map of the late cretaceous into areas where the chalk is not outcropping

contributions of c3 c4 organic materials and carbonate rock to dissolved inorganic carbon in a karst groundwater system on miyakojima island southwestern japan summary groundwater 13 c values and chemical compositions were employed to quantitatively evaluate the controlling processes and sources of dissolved inorganic carbon in a karst aquifer system on miyakojima island mi southwestern japan most mi groundwater is ca hco 3 type water but some na cl ca cl or na hco 3 type groundwaters occur formed mainly by seawater intrusion and partly by cation exchange reactions calculations using the wateq4f and phreeqc programs revealed that all mi groundwater not just the ca hco 3 type was strongly influenced by calcite dissolution in a karst aquifer system open with respect to soil co 2 initially derived from organic materials with mainly around 10 50 matm as pco 2 and that most groundwater was saturated with respect to calcite moreover oxidation of ammonium sulfate applied as fertilizer added h to the mi groundwater resulting in surplus calcite dissolution these processes sufficiently explained contents of alkalinity dic and ca 2 in the groundwater and were evaluated by model calculation using the phreeqc program with measured groundwater 13 c and ph values the results showed that the average mass fractions of dissolved inorganic carbon dic initially from calcite dissolution and c3 and c4 organic materials in the groundwater were 46 4 18 5 and 35 1 respectively the model results regarding the origins of dic in the groundwater agreed fairly well with land use distributions on mi in particular with the spatial distribution of forest and sugarcane fields and gave us some constrains of groundwater recharge areas and flowpaths

formation of chocolate tablet boudins in a foreland fold and thrust belt a case study from the external variscides almograve portugal abstract chocolate tablet boudins of quartzite are restricted to steep limbs of d 1 folds along the sw coast of portugal the chocolate tablet geometry results from older vertical and younger horizontal quartz veins both sets of veins developed during similar conditions by extension fracture in pre existing necked domains 1 both veins show stretched crystal fibers 2 the boudin aspect ratio is the same in vertical 3 0 1 4 and in horizontal sections 2 9 1 2 3 temperatures obtained from fluid inclusions are similar 200 20 for vertical and 230 22 c for horizontal veins and are compatible with temperatures obtained from illite crystallinity ca 200 ca 250 c given thermal equilibrium between the host rock and the precipitating fluid the chocolate tablet boudins formed close to the metamorphic peak we interpret that the vertical veins developed after the limbs of the d 1 folds had attained their steep attitude and the orientation of the greatest and intermediate principal strain axes had interchanged subsequently the initial strain field was restored and opening of horizontal veins led to the chocolate tablet geometry the direction of the main shortening direction was constant from the initial buckling stage via isoclinal folding and during all boudinage stages

coeval folding and boudinage in four dimensions scaled analogue experiments have been carried out incrementally to demonstrate the growth of constrictional folds and boudins through space and time pure constriction acted on a single stiff layer that was embedded in a weak matrix with the layer trending parallel to the x axis of the constrictional strain ellipsoid the viscosity ratio between non linear viscous layer and matrix was set at ca 13 three dimensional images of the incrementally deformed layer have been obtained using computer tomography they yielded clear evidence that d1 folds and d1 boudins show striking interactions when growing simultaneously at low to moderate finite strain the axes of d1 folds are subparallel and the axes of d1 boudins are subperpendicular to the x axis of the constrictional strain ellipsoid the normalized wavelengths of d1 folds and d1 boudins and the amplitudes of d1 folds are fixed already at low finite strain 5 and do not significantly change as deformation proceeds the normalized wavelength of both structures is not so in line as suggested by theoretical studies at higher degrees of finite strain d1 boudins are affected by d2 folds and rotated limbs of the latter show d2 boudinage resulting in complex deformation patterns that are difficult to identify in the field the model results are important for the analysis and interpretation of deformation structures in rheologically stratified rocks undergoing dislocation creep under bulk constriction tectonic settings where constrictional folds and boudins may develop simultaneously are stems of salt diapirs subduction zones or thermal plumes

tablet boudinage of an anhydrite layer in rock salt matrix results from thermomechanical experiments abstract a single competent layer of anhydrite embedded in a matrix of incompetent rock salt was deformed in a flattening type of bulk deformation at temperature t 345 c strain rate 10 7 s 1 to a maximum finite strain e z 30 as the anhydrite layer was oriented perpendicular to the main shortening direction z the layer underwent equal layer parallel extension in all directions resulting in tablet shaped boudins boudinage results from tensile fracture of anhydrite the rock salt matrix on the other hand behaved viscously crystal plastic deformation of halite was accommodated by slip on 110 which led to formation and rotation of subgrains and a 001 maximum parallel to the principal shortening axis z an axisymmetric texture of halite however is present only in high strain domains at the contact to the anhydrite layer where the differential stress obtained from subgrain size of halite reaches maximum values of ca 6 mpa subgrains remote from the anhydrite layer yielded 2 3 mpa which is consistent with the flow stress recorded by the load cell of the machine the non isometric shape of the tablet boudins in plan view is indicated by the ratio between long and short axis r 1 2 1 9 and can be explained by the interaction of concentric and radial tensile fractures both the mean diameter of the tablet boudins in plan view w a and the number of boudins n show a linear relation to the layer thickness progressive finite strain results in a higher number and a smaller mean diameter of the boudins the thickness of the boudins h f is almost the same like the initial layer thickness h i while the aspect ratio w d w a h f decreases with finite strain the mean w d values obtained from all runs are ranging from ca 0 8 to ca 1 5 this range is much lower than the aspect ratio of boudins in viscous or brittle viscous layers but is similar to the aspect ratio expected from fracture saturation models the aspect ratio of the tablet shaped anhydrite boudins is further consistent with aspect ratios published so far for tensile fracture boudins which developed in a plane or constrictional type of bulk deformation

use of 14c modelling to determine vulnerability and pollution of a carbonate aquifer the lincolnshire limestone eastern england abstract the lincolnshire limestone is an important and well studied british aquifer it has been demonstrated by previous workers that the aquifer is affected by agrichemical polution and aquifer protection policy requires in part a knowledge of timescales of groundwater movement this study uses new 14 c data to speculate on such timescales by calculating model ages in non saline groundwaters the main corrections applied to carbon isotope data are for the effects of congruent dissolution and dissolution reprecipitation of soil carbonate and incongruent dissolution of aquifer carbonate although an appropriate small correction is made for ca 2 2na ion exchange no correction is applied for redox processes because they are established as having negligible effects negative model ages calculated for many non saline groundwater support a rapid recharge mechanism to the southern outcrop and suggest that post bomb post 1963 recharge has penetrated deep into the confined aquifer this serves to demonstrate the vulnerability of the southern aquifer to contamination and as a marker of antrhopogenic pollution by so 4 and cl in the confined aquifer however the presence of post bomb c in some no 3 free groundwaters supports the capability of the confined aquifer for in situ denitrification a maximum model age of 5 7 ka is calculated for non saline groundwater the practical problems associated with model ages leads to the recommendation that groundwater 14 c data are best expressed as corrected per cent modern c values in future studies

multipathing and spectral modulation of the downgoing wavefield in a complex crust an example from the ktb germany borehole vsp data collected in the ktb germany borehole to a depth of 8 5 km in 1999 show a surprising spectral modulation of the downgoing wavefield after filtering the data with the singular value decomposition technique it was found that below about 6 2 km there are two depth intervals where the modulation can be explained in terms of a basic wavelet plus two weighted and delayed copies of that wavelet with the delay for each wavelet remaining almost constant in each interval the boundary between the two intervals is at about 7 25 km depth and above and below this depth the delay for the second wavelet is almost the same while the delay for the third wavelet is significantly different neither the modulation nor its depth variation are source related and cannot be explained in terms of multiple reflections in a subhorizontal low velocity layer on the other hand finite difference synthetic data show that subvertical layering which is prevalent in the borehole area provides a mechanism that can explain the observations this mechanism has analogies with the generation of the standard refracted i e head waves when a plane wave front propagates perpendicular to the boundaries of a vertical low velocity layer surrounded by two vertical high velocity layers refracted wave fronts are generated in the low velocity layer which in turn generate secondary wave fronts in the high velocity layers these wave fronts trail the primary wave fronts by a constant delay whose magnitude has a simple dependence on the thickness of the low velocity layer and the velocities involved this process creates multipath arrivals that in geological settings with steeply inclined and faulted layers may appear and disappear rather abruptly which may contribute to a scattered appearance of the wavefield

the value of iodide as a parameter in the chemical characterisation of groundwaters abstract brackish and saline groundwaters can severely constrain the use of fresh groundwaters their chemical characterisation is important in understanding the hydraulic conditions controlling their presence in an aquifer major ions are frequently of limited value but minor ions can be used iodide in groundwater is particularly significant in many environments due to the presence of soluble iodine in aquifer matrix materials iodide is found in groundwaters in parts of the english chalk aquifer in concentrations higher than are present in modern seawater its presence is considered as a indication of groundwater residence and is of use in the characterisation of fresh as well as saline waters under certain circumstances modern seawater intrusion into aquifers along english estuaries produces groundwaters which are easily identified due to iodide enrichment from estuarine muds in other environments iodide concentrations are of value in distinguishing between groundwaters in limestones and shaly gypsiferous rocks as shown by a study in qatar while in an alluvial aquifer study in peru iodide has been used to identify groundwaters entering the aquifer from adjacent granodiorites

stress orientation and fracturing during three dimensional buckling numerical simulation and application to chocolate tablet structures in folded turbidites sw portugal abstract two orthogonal sets of veins both orthogonal to bedding form chocolate tablet structures on the limbs of folded quartzwackes of carboniferous turbidites in sw portugal structural observations suggest that 1 mode 1 fractures transverse to the fold axes formed while fold amplitudes were small and limbs were under layer subparallel compression and 2 mode 1 fractures parallel to the fold axes formed while fold amplitudes were large and limbs were brought to be under layer subparallel tension we performed two and three dimensional numerical simulations investigating the evolution of stress orientations during viscous folding to test whether and how these two successive sets of fractures were related to folding we employed ellipses and ellipsoids for the visualization and quantification of the local stress field the numerical simulations show a change in the orientation of the local 1 direction by almost 90 with respect to the bedding plane in the fold limbs the coeval 3 direction rotates from parallel to the fold axis at low fold amplitudes to orthogonal to the fold axis at high fold amplitudes the stress orientation changes faster in multilayers than in single layers the numerical simulations are consistent with observation and provide a mechanical interpretation for the formation of the chocolate tablet structures through consecutive sets of fractures on rotating limbs of folded competent layers

lateglacial and early flandrian coleoptera from la taphanel massif central france climatic and ecological implications a lateglacial and early holocene sequence of coleopteran assemblages is described from la taphanel in the massif central france the site is a sediment filled small lake at an altitude of almost 1000 m the insect fauna provides evidence for a detailed palaeoecological reconstruction and in particular enables a reconstruction of climatic changes at the close of the last glaciation a sudden climatic warming occurs at about 13000 yr bp followed by a temperate episode equivalent in time to the bolling period there is clear evidence of a short cold period between the bolling and allerod that is approximately equivalent to the older dryas period the allerod phase is decidedly cooler than the bolling as is shown by the coleoptera from several sites in northwest europe a clear younger dryas signal is provided by the coleoptera with climates similar in severity to those of the glacial period the climatic improvement at the start of the holocene is also sudden so that by preboreal times temperatures were equivalent to those of the present day

ktb the structure of a variscan terrane boundary seismic investigation drilling models abstract on october 12 1994 the hauptbohrung main hole of the german continental deep drilling program ktb in the oberpfalz ne bavaria reached its final depth of 9101 m the drilling results provide a test of the validity of the initial structural concept for the ktb location in the boundary zone between the saxothuringian and moldanubian terranes of the variscan orogen this paper outlines some of the geological results as well as additional information from seismic investigations and discusses briefly alternative structural models the interpretation of local and regional seismic structures leads in connection with the drilled profile to the conclusion that the zev zone erbendorf vohenstrauss with the ktb drill site is derived from and linked with the erbendorf body and equivalents of the marianske lazn complex and or the bohemicum in the middle and lower crust instead of a rootless klippe resting on the saxothuringian moldanubian suture the zev appears to be a part of the suture itself the present position of the zev is tied to the junction of the ene wsw suture with the nnw sse oberpfalz block as a part of a large wrench system and developed probably by a two stage transpressive exhumation process prior to and during the variscan collision

experimental deformation of a single layer anhydrite in halite matrix under bulk constriction part 2 deformation mechanisms and the role of fluids abstract composite natural samples consisting of a single layer of anhydrite embedded in matrix of rock salt were experimentally deformed at temperature t 345 c and strain rate 10 7 s 1 the geometry and kinematics of folds and boudins which affect the stiff anhydrite layers were described in part 1 of the present study zulauf et al 2009 the microfabrics deformation mechanisms and the role of fluids are treated in the present paper anhydrite was deformed under brittle viscous conditions as is indicated by fracturing twinning and local recrystallization the latter based on strain induced grain boundary migration viscous deformation of halite was accommodated by slip on 110 110 which led to formation and rotation of subgrains and a striking 001 maximum parallel to the long axis x of the strain ellipsoid differential stress obtained from subgrain size of halite is largely consistent with stresses recorded by the load cells of the machine despite of the high deformation temperature and the low water content of the starting samples nacl brine and hydrocarbons expelled from fluid inclusions of both halite and anhydrite led to hydraulic fracturing and redistribution of matter the fluids migrated along newly formed microfractures in anhydrite and along halite anhydrite boundaries released hydrocarbons and nacl brine were redeposited in open space of neck domains in the form of black organic coatings condensate and fine grained halite respectively as these fluid controlled phenomena are common in salt domes of northern germany and released fluids may led to contamination of bed rock and biosphere the results of the present study should be important for workers who are dealing with radioactive waste deposits in rock salt

a deformation apparatus for three dimensional coaxial deformation and its application to rheologically stratified analogue material abstract a new apparatus is described that supports all types of three dimensional coaxial deformation from pure constriction to pure flattening up to 78 shortening is possible at strain rates ranging from 4 10 6 to 1 10 2 s 1 the apparatus has been used to study the influence of the deformation regime on the geometry of a deforming stiff layer embedded in a weak matrix layer and matrix consist of plasticine the apparent viscosity and stress exponent n of which vary from 2 10 6 to 2 10 7 pa s and 6 9 respectively first results suggest a considerable influence of the deformation regime on the geometry of the deformed layer including its thickness if the viscosity ratio between layer and matrix is small 2 1 5 folding is restricted to the flattening and plane strain regime the latter if the layer is initially oriented perpendicular to the long axis x of the finite strain ellipsoid if the layer is oriented perpendicular to the intermediate y axis under plane and constrictional strain low viscosity ratios result in boudinage but folding is hardly developed however simultaneous growth of folds and boudins is possible under pure constriction at a viscosity ratio of 10 three dimensional images based on computer tomography suggest a strong interaction between such coeval folds and boudins resulting in characteristic deformation patterns that should not occur if both structures form in sequence during polyphase deformation

spectral evidence for source multiplicity in explosions application to regional discrimination of earthquakes and explosions abstract spectral and cepstral analysis were performed on regional array noress recordings of mining explosions in scandinavia and russia in order to detect the effects of delayed explosions or ripple firing commonly used in mine blasting practice noress array stacked spectra corrected for instrument and noise were computed in windows on pn pg sn and lg waves from the mine blasts by averaging individual channel spectra frequency by frequency across the array for comparison spectra were also computed for six western norway earthquakes located near the blasjo and titania norwegian mines also stack spectra of p coda sn and lg were computed using norsar seismograms for presumed peaceful nuclear explosions pnes located at near regional distances 10 in western russia the norsar spectra were determined in the same manner as the noress spectra except that an individual source correction was applied to the spectra comparison of western norway mine blast spectra and nearby earthquakes shows that the earthquake pn spectra are peaked in the 8 to 16 hz band with little energy below 6 hz whereas the explosion spectra have flatter spectra from 3 to 16 hz this difference in the pn spectra may be caused by the earthquakes occurring at greater depths than the explosions differences in the near source media or source mechanism effects in the earthquake spectra the main difference between earthquake and explosion spectra is that the explosion spectra exhibit marked scalloping or modulation patterns not observed in the earthquake spectra the modulation patterns are identical in spectra of all phases indicating that they are caused by multiple shot sequences or ripple firing simulated multiple source spectra determined using the noress seismograms for one of the western norway earthquakes resulted in spectra that resembled many of the explosion modulation patterns based on the simulation studies and cepstral analysis of the spectra the mine explosions appear to be composed of two to three separate explosions delayed by between 80 to 150 msec moreover the norsar spectra of pnes indicate that these signals are also produced by multiple explosions although they have larger delay times of between 0 9 to 1 5 sec these results show that spectral modulations in seismogram spectra of economic explosions including mine explosions and nuclear explosions fired for peaceful economic purposes can be used to distinguish them from earthquakes and nuclear explosion weapons tests

microfabrics and 3d grain shape of gorleben rock salt constraints on deformation mechanisms and paleodifferential stress abstract the permian knauel and streifensalz formations z2hs1 and z2hs2 are main constituents of the gorleben salt dome northern germany and show different amounts and distributions of anhydrite the reconstruction of 3d halite grain shape ellipsoids reveals small grain size 3 4 0 6 mm and heterogeneous grain shapes in both formations the latter attributed to the polyphase deformation of the rock salt during diapirism the halite microfabrics of both formations indicate that strain induced grain boundary migration was active during deformation crystal plastic deformation of halite is further documented by lattice bending subgrain formation and minor subgrain rotation evidence for pressure solution of halite has not been found but cannot be excluded because of the small grain size the lack of lpo and the low differential stress 1 1 1 3 mpa as deduced from subgrain size piezometry anhydrite has been deformed in the brittle ductile regime by solution precipitation creep minor dislocation creep and brittle boudinage no continuous anhydrite layers are preserved and halite has acted as a sealing matrix embedding the disrupted anhydrite fragments prohibiting any potential migration pathways for fluids thus anhydrite should not have a negative effect on the barrier properties of the gorleben rock salts investigated in this study

identification of presumed shallow underwater chemical explosions using land based regional arrays abstract seismic events located in the gulf of bothnia the baltic sea and the north sea recorded at the regional seismic arrays noress and finesa have characteristics of underwater blasts observed hydroacoustically spectral analysis of regional phases associated with the events reveals strong time independent spectral scalloping indicating that the waveforms are made up of correlated pulse echo type signals cepstral analysis gives consistent delay times between the pulse echo pairs with the most common delays between 400 and 600 msec some cepstra also have negative peaks at quefrencies between 150 and 350 msec the cepstral peaks are observed in all phases associated with the event and events recorded at both arrays have the same delay times the higher time delays are consistent with bubble pulse delays commonly observed in underwater blasts recorded hydroacoustically the lower quefrency negative peaks are caused by echoes with reversed polarities relative to the primary pulse and are consistent with reflections from the top of the water column generally these events have large pn lg amplitude ratios similar to those observed from quarry blasts somewhat smaller high frequency pn lg ratios are observed for baltic sea events compared with the north sea events which may be due to differences in the water bottom geologies of the two regions simple source models of underwater blasts explain many of the features of the observed cepstra and indicate that the shot depths had to be shallow around 40 to 80 m for shot sizes between 75 and 150 kg this study shows that the seismic sensor network called for by the comprehensive test ban treaty ctbt can augment the smaller network of hydroacoustic stations for the detection and identification of clandestine under water nuclear explosion tests in the near offshore environment

isotopic composition of sulfate as a tracer of natural and anthropogenic influences on groundwater geochemistry in an urban sandstone aquifer birmingham uk abstract development and management of urban groundwater resources is limited in practice by a lack of knowledge of the nature distribution and sources of groundwater contamination in an urban aquifer that may have had complex land use and abstraction history sulfate is associated with many of the solute sources to urban groundwater and in this study the use of dual isotope 18o and 34s fingerprinting of so 4 2 in groundwater to assess the contribution of different sources to urban groundwater is investigated groundwater 70 locations and surface water samples from the city of birmingham on the triassic sherwood sandstone aquifer have been analyzed for inorganic chemical and so 4 2 isotopic composition isotopic compositions of so 4 2 associated with various solute sources have also been determined sulfate derived from pyrite oxidation during recharge through quaternary drift deposits is characteristically depleted in 18o and 34s compared to other sources and is ubiquitous in unconfined zone groundwater though the contribution from this source has increased markedly following draw down induced by abstraction from the aquifer in unpolluted groundwaters other so 4 2 sources are dissolution of evaporite minerals confined zone and rainfall unconfined zone unfortunately so 4 2 isotopic composition cannot distinguish between made ground i e artificial man made ground usually demolition waste and sewage sources of so 4 2 which constitute the major contributions to so 4 2 in polluted urban groundwater at most sites contributions of so 4 2 from spilt industrial acids do have a distinctive isotopic composition seen at many metal working and former metal working sites estimates of solute contributions derived from these sources derived in this way provide a useful check on the calibration of aquifer and pollutant flux recharge models for urban groundwater

theory of chocolate tablet boudinage two dimensional boudinage in a flattening type of bulk deformation with equal layer parallel extensions in all directions leads to the development of roundish or polygonal outlines of boudins in plan view as combined experimental and theoretical studies show chocolate tablet boudinage with two sets of mutually perpendicular boudin axes may form in different ways 1 unequal layer parallel extension in the matrix results in one set of extension fractures forming perpendicular to the greatest principal stress in the matrix once these long narrow boudins are formed the greatest principal stress in the brittle layer becomes approximately parallel to the long axis of the boudin as a result a second set of fractures forms normal to the first set 2 in lineated rocks the anisotropy of tensile strength leads to the sequential formation of two sets of extension fractures parallel and perpendicular to the lineation depending on the orientation of the lineation the boudin axes may or may not be parallel to the principal stresses in the matrix 3 boudins with rectangular plan view may also form when two successive events of unidirectional boudinage are superposed on one another irrespective of the direction of principal extensional strain rate in the matrix the second generation extension fractures are likely to form approximately perpendicular to the first generation boudin axes

hydrochemical effects of saltwater intrusion in a limestone and dolomitic limestone aquifer in lebanon this study demonstrates groundwater quality differences between a limestone and a dolomitic limestone sub oxic coastal aquifer in the eastern mediterranean lebanon with and without ongoing moderate salinization since the last decades for this purpose 8 major and 50 trace elements tes were analyzed in 80 water and 65 rock samples and interpreted with a quad fold approach utilizing 1 nonparametric statistical tests 2 concentration deviations from ideal conservative freshwater seawater mixing lines 3 a new parameter called mixing enrichment factor to assess the mobility of chemical constituents under salinizing conditions and 4 1 d dual porosity flow path modeling with phreeqc dissolution precipitation of caxmgysrzco3 and cation exchange were the main disclosed hydrogeochemical processes besides minor signs of organic matter oxidation in the dolomitic limestone aquifer less carbonate dissolved as compared to the limestone aquifer partly because of lower pco2 in addition to seawater inflow triggering mg calcite precipitation by cation exchange saltwater intrusion led to mobilization of as ba cu ni rb sr and u in both aquifers sometimes likely by cation exchange e g ba and sr some of these tes notably cu and ni recorded higher concentrations in the dolomitic limestone regardless of salinization other elements like al be ce cr nb pb v y and zr revealed no or a low mobilization tendency the concentration of all tes in groundwater remained below drinking water limits notwithstanding moderate salinization this classifies carbonate rocks as a weak geogenic source of tes whereas encroaching seawater appears to be a more important source

the internal geometry of salt structures a first look using 3d seismic data from the zechstein of the netherlands abstract we present a first look at the large scale complexly folded and faulted internal structure of zechstein salt bodies in nw europe using 3d reflection seismic reflection data from two surveys on the groningen high and the cleaver bank high we focus on a relatively brittle folded and boudinaged claystone carbonate anhydrite layer the z3 stringer enclosed in ductile salt a first classification of the structures is presented and compared with observations from salt mines and analogue and numerical models z3 stringers not only are reservoirs for hydrocarbons but can also present a serious drilling problem in some areas results of this study could provide the basis for better prediction of zones of drilling problems more generally the techniques presented here can be used to predict the internal structure of salt bodies to estimate the geometry of economic deposits of all kinds and locate zones suitable for storage caverns structures observed include an extensive network of zones with increased thickness of the stringer these we infer to have formed by early diagenesis karstification gravitational sliding and associated local sedimentation later this template was deformed into large scale folds and boudins during salt tectonics salt flow was rarely plane strain producing complex fold and boudin geometries deformation was further complicated by the stronger zones of increased thickness which led to strongly non cylindrical structures we present some indications that the thicker zones also influence the locations of later suprasalt structures suggesting a feedback between the early internal evolution of this salt giant and later salt tectonics this study opens the possibility to study the internal structure of the zechstein and other salt giants in 3d using this technique exposing a previously poorly known structure which is comparable in size and complexity to the internal parts of some orogens

palaeohydrogeological reconstructions of the north lincolnshire chalk uk for the last 140 000 years abstract the influence of climatic change on hydrogeology is investigated by studying the evolution of the north lincolnshire chalk aquifer system during the last 140 000 years a numerical modelling approach is adopted using a density coupled finite difference model to reconstruct past groundwater environments two major controls on groundwater circulation are considered the position of sea level which determines the base level condition and the amount of recharge associated with different climates the quaternary history of the region is used to define aquifer boundary conditions and climate analogue data are used to determine likely recharge amounts model results cannot be compared against groundwater flow volumes or head other than for the present day situation and so hydrochemical evidence is used to constrain the model simulations the main finding is that recharge to the chalk aquifer during the last 140 000 years has been restricted to periods when the climate and sea level position have been similar to those of the present day the devensian cold period experienced very minor recharge with no chalk permeability development forest clearance since about 5000 years ago is predicted to have permitted an increase in the volume of freshwater recharge which increased the rate of chalk permeability development the presence of saline water at depth in the aquifer is argued on the basis of the model behaviour to be contributed by a component of upward cross formational flow

microstructural evolution of deformation modified primary halite from the middle triassic rot formation at hengelo the netherlands the microstructure of halite from the subhorizontal bedded main rot evaporite member at hengelo the netherlands akzo well 382 depth interval of 420 460 m was studied by transmitted and reflected light microscopy of gamma irradiation decorated samples primary microstructures compare favourably with those found in recent ephemeral salt pans large blocky fluid inclusion poor halite grains and elongated chevrons are interpreted to have formed in the saline lake stage while void filling clear halite is interpreted to have formed during the desiccation stage of the salt pan in addition in all layers the grains are rich in deformation related substructures such as slip bands and subgrains indicating strains of a few percent the study of gamma irradiation decorated thin sections shows that the main recrystallization mechanism is grain boundary migration grain boundary migration removes primary fluid inclusions and produces clear strain free new grains differential stresses as determined by subgrain size piezometry were 0 45 0 97 mpa the deformation of the salt layers is probably related to cretaceous inversion in the area

formation of chocolate tablet boudins results from scaled analogue models abstract we used power law viscous plasticine as a rock analogue to simulate chocolate tablet boudinage of rocks undergoing dislocation creep a competent plasticine layer oriented perpendicular to the main shortening direction z underwent two phases of plane strain in a weaker plasticine matrix with the principal stretching axis x and the axis of no change y replacing each other from the first to the second phase in each phase of plane strain boudinage was controlled by an initial phase of viscous necking followed by extension fracture along the neck domain increase in the magnitude of finite strain e and decrease in layer thickness h i result in a decrease in the boudin width w a and an increase in the number of boudins n given the viscosity ratio between layer and matrix m is higher than ca 5 the number of boudins decreases and the boudin width increases with increasing values of m an unexpected result of the present study is that in each experiment the number of boudins was significantly higher during the second phase of plane strain this difference should be related to additional drag of the matrix plasticine on the stiff layer in the neck domains formed during the first phase of boudinage the aspect ratio of the second generation of boudins w d w a h i is compatible with aspect ratios of natural boudins and with aspect ratios calculated using analytical solutions

early cretaceous slumps and turbidites with peculiar soft sediment deformation structures on lingshan island qingdao china indicating a tensional tectonic regime abstract some sections on lingshan island in the yellow sea close to the city of qingdao show the early cretaceous lingshandao formation the exposed succession consists mainly of turbidites some of which show uncommon soft sediment deformation structures and contains well developed large scale slumps that consist of sets of turbidites the sediments were deposited as part of lobes of turbidites and hyperpycnites deposits of flood generated sediment laden bottom currents derived from an estuary in a deep sea environment that formed part of an inter arc basin with a tensional tectonic regime some of the slumps have dimensions of the order of metres to tens of metres they consist of the turbidites that build most of the succession the soft sediment deformation structures in the turbidites represent a wide variety of types most of which are common in subaqueous environments with a high accumulation rate the most interesting are however structures that indicate active tectonic tension these structures are boudins which are present with two subtypes the most common are pinch and swell structures sometimes leading to isolated parts of the affected sandy layer enveloped by shales of the under and overlying shale layers the second type consists of domino boudins which have as far as we are aware of not earlier been described from sediments that were still unlithified during their formation the presence of the boudins and associated structures which indicate synsedimentary stretching related to an extensional tectonic setting form an additional argument in the long lasting debate about the question of whether a compressional or an extensional tectonic regime dominated in the area during the early cretaceous

constraints on geological strain rates arguments from finite strain states of naturally deformed rocks a summary of known finite strain states is presented longitudinal strains 1 e as measured in many rocks often range from 1 to 40 and 1 to 0 025 the time span available to produce such measureable strains in young orogenic zones seems to be less than 10 m y possibly less than 1 m y which constrains conventional strain rates into the range of 10 sup 13 s sup 1 to 10 sup 15 s sup 1 for both pure and simple shear the most efficient way and much less efficient way to accumulate incremental strains respectively the ellipticity of the finite strain ellipse increases in a nonlinear manner finite strain variations in adjacent layers which give rise to features such as cleavage refraction arise with only slight differences in the strain rates within these layers

a stress transfer model for the development of extension fracture boudinage abstract the term boudinage is used to describe a wide variety of extensional structures in deformed rocks this paper is mainly concerned with boudinage resulting from through layer extension fractures followed by separation of the layer segments thus forming boudins with more or less rectangular cross sections in principle this process is similar to the break up of fibres in fibre reinforced composite materials extended parallel to the fibre direction both processes are controlled by the transfer of stress from the matrix to the fibre or layer and a mathematical model for fibre matrix stress transfer the fibre loading model is well established we have used this as a basis for developing a stress transfer model for boudinage the only difference in the basic mathematical formulation results from geometric differences between the two systems the geometric expressions in the fibre loading model have therefore been rederived for the layer matrix case stress transfer theory predicts that the tensile stress in a layer segment rises from a minimum at the end of a segment to a maximum at the centre this behaviour which is clearly shown by finite element models of boudinage structure suggests that extension fracture boudinage develops by successive mid point fracturing according to stress transfer theory the process will continue until a layer is reduced to segments boudins all of which are shorter than some critical length for which the tensile fracture strength of the layer is equal to the tensile stress at the mid point in practice successive fracturing will be influenced by two other factors 1 in nature the controlling material properties tensile fracture strength elastic moduli will not be single valued but will have a distribution reflecting local variations in lithology and microstructure and 2 major pre deformation flaws may be present in a layer which will control the starting length of layer segments these factors are incorporated with the stress transfer theory into a statistical monte carlo model for extension fracture boudinage which results in a prediction of boudin aspect ratios the predicted distribution compares very closely with the observed distribution of 91 quartzite boudins within lower carboniferous slates at tintagel cornwall the stress transfer model implies that boudin defining fractures occur sequentially so that inter boudin gap lengths will be unequal strain estimates based on boudinage structure will vary according to which part and how much of a layer is sampled a much improved strain estimate is possible based on sequentially closing the inter boudin gaps the stress transfer theory also leads to the possibility of estimating palaeostress from boudinage structure and is the only model available which predicts an aspect ratio distribution of boudins formed by extension fracture other than our own we know of no published data on boudin aspect ratio distributions hence further elaboration of the model is not possible until more field data is available we hope that our work will encourage the systematic measurement of boudinage as well as the development of alternative models

residence time of chalk groundwaters in the paris basin and the north german basin a geochemical approach the comparative geochemical and isotopic study of confined and unconfined chalk groundwaters of the paris basin and the n german basin proves a significant chemical evolution during groundwater flow from the recharge zones to the deep confined aquifer different time dependent geochemical parameters have been tested as dating tools cation ratios sr2 ca2 mg2 ca2 n no 3 noble gas contents as paleotemperature indicators ne ar kr xe radiogenic he 13c 14c 18o 2h 3h cation ratios and 13c show the importance of incongruent dissolution processes in the chalk aquifer water rock interactions were taken into account in a multi step dissolution model to determine radiocarbon groundwater ages the oldest waters in the confined part of the paris basin chalk with maximum 14c ages of 14 000 a b p contain pleistocene recharge components as can be shown by a stable isotope depletion and noble gas temperatures significantly lower than in recent groundwaters chalk waters at the lagerdorf site in northern germany show a distinct stratification with respect to residence times and hydrochemistry

assessment of recharge components for a chalk aquifer unit abstract recharge to aquifer systems involves an understanding of the flow processes at the soil surface and in the deposits overlying the aquifer three major recharge components are identified in a chalk catchment which is partly overlain by boulder clay a fourth recharge component occurs due to river aquifer interaction this paper describes how field evidence is used in association with mathematical models to quantify the recharge components

polyphase development of chocolate tablet boudins in the sat zone kumaun lesser himalaya india abstract a combination of two groups of boudins exposed in orthogonal sections is observed as chocolate tablet structures in the south almora thrust sat zone kumaun lesser himalaya evidence from boudin associated veins fractures folds and microstructures suggest that the chocolate tablet boudins were developed as a consequence of layer parallel stretching in two orthogonal directions during two successive phases of ductile shearing in the sat zone the early phase of top to nw shearing is speculated as a pre himalayan deformation during which the early boudins were developed this deformation was superposed by a late phase of top to sw himalayan shearing and development of the attendant late boudins it is concluded that the interference of two phases of successively developed boudins has resulted into development of the chocolate tablet structures in the sat fluid inclusion and microstructures indicate a low temperature about 300 c growth of the chocolate tablet boudins the finite strain analysis reveals that a maximum strain ratio rs of 1 7 was accumulated during the pre himalayan phase of deformation whereas rs was of the order of 2 1 in the himalayan phase of deformation

groundwater chemistry in southeast suffolk u k and its relation to quaternary geology abstract east anglia has a complex pleistocene geological history having been affected both by major changes in the level of the adjacent north sea and by glacial processes the resulting geology has a profound effect on the distribution of water chemistry in the chalk aquifer which underlies the pleistocene deposits a detailed study of the chemistry of the chalk groundwater including strontium fluoride and iodide as well as major elements has shown that this chemistry results from three phases of saline intrusion early pleistocene to modern and at least two periods of freshwater flushing climatic changes and erosional history were important in controlling flushing periods

experimental deformation of a single layer anhydrite in halite matrix under bulk constriction part 1 geometric and kinematic aspects a new deformation apparatus has been used to model the internal kinematics of salt diapirs composite natural samples consisting of a single layer of anhydrite embedded in halite matrix were constrictionally deformed at temperature t 345 c strain rate 10 7 s 1 maximum viscosity 2 1013 pa s and maximum finite strain ex 122 the anhydrite layer oriented parallel to the major stretching axis x was deformed by fracturing whereas halite behaved viscously at advanced state of constriction ex 90 a strong increase in strain hardening of halite led to a transient tension fracture that healed up and was shortened by folding during the final phase of viscous deformation tiny prismatic anhydrite inclusions disseminated inside the halite matrix were reoriented during constriction resulting in a linear grain shape fabric 3d images of the anhydrite layer based on computer tomography revealed rare kink folds with axes subparallel to x and boudins which result from tension fracture with increasing layer thickness hi the width of boudins wa increases linearly wa 0 3 1 3 hi the normalized width of boudins wd wa hi is almost constant at 1 5 1 0 these geometrical parameters can be used to reveal fracture boudinage under bulk constriction the oblique orientation of most of the boudins with respect to the principal strain axes results from folding of the boudins by a second generation of folds the latter with axes subperpendicular to the layer

microstructural evolution during initial stages of static recovery and recrystallization new insights from in situ heating experiments combined with electron backscatter diffraction analysis we present in situ observations performed using electron backscatter diffraction of static recovery and recrystallization processes occurring in a plastically deformed geological material namely rocksalt static heating experiments carried out in a scanning electron microscope at temperatures of up to 450 c allowed direct detailed observations of grain boundary migration between substructured grains in deformed polycrystalline samples contrary to expectations crystallographic orientation maps reveal that behind slowly migrating grain boundaries new subgrain boundaries form while pre existing subgrain boundaries are sometimes inherited moreover the crystallographic character especially the preferred orientation of misorientation axes of the new substructures reflects the character of the previous deformation history these results imply that substructural features such as subgrain misorientation distributions may be relatively robust indicators of deformation mechanisms and conditions even in tectonites that have undergone late static recrystallization in addition our observations suggest that the process of static grain boundary migration does not necessarily reset earlier deformation microstructures as commonly assumed the kinematic observations of boundary migrations are inconsistent with simple models in which migration is achieved by single atoms jumping across the boundary

rheological behaviour of synthetic rocksalt the interplay between water dynamic recrystallization and deformation mechanisms abstract the ductile deformation of rocks in nature can be greatly enhanced by the presence of water part of the water induced weakening of rocks at depth may come from fluid assisted deformation or recrystallization mechanisms that are absent in dry rocks in this study we investigate the effect of water on the rheological behaviour of rocksalt we focus on quantification of the contribution of individual deformation and recrystallization mechanisms to deformation we also aim to calibrate a flow law that incorporates the effect of all the relevant microphysical processes and hence more accurately describes the flow of rocksalt in nature for this purpose the mechanical behaviour and microstructural evolution of synthetic rocksalt samples that are similar except for differences in water content determined using ftir analysis are investigated the samples are deformed to natural strains of 0 07 0 46 at 50 mpa confining pressure strain rates of 5 10 7 1 10 4 s 1 and temperatures of 75 240 c resulting in flow stresses of 7 22 mpa the flow stress of samples with a water content below 5 ppm dry is higher than that of samples with a water content of 9 46 ppm wet at all strains under the investigated conditions the difference in flow stress can be explained as due to the operation of only work hardening dislocation creep without dynamic recrystallization in the dry material versus combined dislocation and solution precipitation creep plus fluid assisted grain boundary migration in the wet material the results allow us to calibrate a flow law for wet rocksalt that incorporates the effects of solution precipitation creep and fluid assisted grain boundary migration the results also suggest that strain localization in natural rocksalt is more likely to be localized due to fluid infiltration and associated rheological weakening than due to progressive removal of strain hardening substructure by grain boundary migration

aquitard characteristics of clay rich till deposits in east anglia eastern england summary an extensive area of quaternary glacial deposits lowestoft till of elsterian anglian age overlies the regionally important cretaceous chalk aquifer in east anglia in eastern england the glacial deposits act as an aquitard potentially affording protection from surface derived mainly agricultural contaminants however there has been little previous research on the physical and chemical characteristics of the glacial tills and contained pore waters in east anglia to demonstrate this benefit hence this study presents the results from the drilling of two boreholes in northern and southern east anglia at morley and cowlinge respectively and the construction of a high pressure squeezing rig to obtain pore water for major and minor ion stable isotope 18 o 2 h and dissolved organic carbon analysis special features of the mechanical squeezing rig included a high diameter to length ratio of the squeezer dual seepage faces and a unique pore water collection system designed to eliminate the risk of alteration of in situ pore water redox characteristics the hydrochemistry of the pore waters is found to be controlled by i incongruent carbonate dissolution given the high proportion of chalk clasts contained in the till ii cation exchange in the unweathered clay rich till and iii pyrite oxidation associated with the mineralogy of both the chalk and clay material content that comprises the till matrix the clay material is sourced from upper jurassic clays oxford and kimmeridge clay formations found to the west of the region these clays are also considered to be the source of organic material contributing relatively high concentrations of dissolved organic carbon above 2 mg l found in till pore waters below the soil zone concentrations of dissolved inorganic constituents increase with depth with a high total dissolved solids tds content in excess of 1500 mg l measured in the unweathered till below a depth of 5 m below ground level with the highest concentrations maximum of 3738 mg l associated with low permeability clay rich till the stable isotope composition of the pore waters with mean values for 18 o and 2 h of 7 01 and 51 7 at cowlinge and 6 44 and 49 9 at morley respectively are similar to local meteoric water and indicate that groundwater recharge of the tills has occurred during the holocene in the last 10 000 years overall the physical and chemical characteristics of the lowestoft till suggest only limited groundwater recharge of the order of 10 mm a or less in interfluve areas where the till deposits are greater than 15 m thick although higher rates are expected where the till becomes more sand rich for example at valley margins and also northwards in east anglia where the lowestoft till is influenced by the component of anglian ice that advanced from the north containing sand material derived from the floor of the north sea basin

the origin of tablet boudinage results from experiments using power law rock analogs abstract we used power law viscous plasticine n ca 7 as a rock analog to simulate boudinage of rocks undergoing dislocation creep and brittle fracture a competent plasticine layer oriented perpendicular to the main shortening direction z underwent bulk pure flattening inside a less competent plasticine matrix computer tomographic analyses of the deformed samples revealed that boudinage results from an initial phase of viscous necking followed by tensile failure along the previously formed necks the resulting boudins display a polygonal shape in plan view and are referred to as tablet boudins in contrast to the square to rectangular shaped chocolate tablet boudins the ratio between the plan view long and short axis r ranges from 1 2 to 2 6 the polygonal non isometric shape of the tablet boudins can be explained by the strong interaction of concentric and radial tensile fractures with increasing layer thickness h i the mean diameter of the boudin tablets w a increases while the number of boudins n decreases progressive finite strain results in a higher number of the boudins and a smaller mean diameter the thickness of the boudins h f is almost the same as the initial layer thickness h i while the aspect ratio w d w a h f decreases with layer thickness and finite strain the mean w d values obtained from all experiments span from ca 4 to ca 11 tablet boudins described in the present paper have yet not been described from natural outcrops the reasons might be that pure flattening strain is not common in nature and the characterization and evaluation of tablet boudins requires geometrical analysis in three dimensions which is a difficult task when such structures occur in nature

deformation and recrystallization mechanisms in mylonitic shear zones in naturally deformed extrusive eocene oligocene rocksalt from eyvanekey plateau and garmsar hills central iran abstract microstructural processes in mylonitic shear zones from extrusions of eocene oligocene rocksalts from garmsar hills and eyvanekey plateau central iran are described and analyzed the halite samples were studied by transmitted light microscopy of gamma irradiated thin sections subgrain size palaeopiezometry of polished and chemically etched samples and texture measurements by electron backscatter diffraction ebsd the studied shear zones are thin using published flow laws the strain rate in the fine grained mylonites is about 10 10 l s which is in a good agreement with earlier in situ measurements on glacier salt flow rate

basalts water or shear zones in the lower continental crust abstract bright sub horizontal laterally extensive multi cyclic layered reflections have now been recorded in the lower continental crust from many areas in contrast this reflection signature is rare in the continental upper crystalline crust and upper mantle and in the oceanic lithosphere with the present state of knowledge it is sensible to seek a single quantitative explanation for all such layering qualitative explanations for lower crustal layering abound and include igneous metamorphic structural and fluid related models measurements of reflection coefficients from the lower crust place strong quantitative constraints on possible models structurally induced anisotropy metamorphic layering or free fluids cannot realistically produce sufficiently bright reflections igneous layering or the juxtaposition of pre existing heterogeneities by shear zones can produce strong reflections results from crustal xenoliths helium isotope ratios palaeo geothermal gradients and chemistry of flood basalts together with numerical modelling of lithospheric extension and asthenospheric melting suggest that underplating and intrusion of the lower crust with mantle derived mafic igneous rocks is common the apparent spatial relationship between lower crustal layering and continental extension and the strength and continuity of the reflections suggest that underplating related to extension and or elevated mantle temperatures is a good explanation for lower crustal layering

controls on stable isotope profiles in the chalk aquifer of north east norfolk uk with special reference to dissolved sulphate groundwater samples were collected at a site in n norfolk uk comprising a borehole penetrating upper chalk and piezometers open within the overlyinf glacial deposits and intervening weathered putty chalk the samples were analyzed for 18o water 34s and 18o so4 and 13c hco3 as well as major ions variations in solute concentration and isotopic composition with depth were found to be caused by limited groundwater circulation at the site and incomplete flushing of old groundwater the isotopic data prove the existence of a mineralized palaeowater at depth which has undergone so4 reduction and is being slowly modified by mixing with recent groundwater circulating at a shallow depth in a more transmissive chalk horizon one measured 18o h2o value of 8 25 vsmow represents the lightest value reported for the norfolk chalk aquifer and is evidence for a component of late pleistocene recharge trapped at depth the wide range of observed isotope ratios at the site e g 34s and 18o so4 between 7 8 to 27 8 cdt and 5 2 to 20 0 ovsmow respectively demonstrates the importance of vertical stratification of solutes and the implications this has for interpreting spatial hydrochemical surveys of groundwater

quantification of the geometrical parameters of non cylindrical folds abstract the geometrical parameters of natural folds are used by structural geologists to estimate finite strain and rheological properties of deformed rocks the relation between geometry and rheology is well understood in cases of cylindrical folds but is still limited for non cylindrical folds although the latter are frequent in nature the sparsity of quantitative geometrical data of non cylindrical folds can be explained by the small number of 3d exposures and by the lack of robust methods to quantify their geometrical parameters in 3d space we present a new workflow which can be used to quantify geometrical parameters of non cylindrical folds 3d fold geometry is described using fold wavelength arc length l and amplitude a as most natural folds do not show ideal shapes but are affected by various types of discontinuities the new procedure is not fully automatic but requires the manual selection of measuring profiles along which the geometrical parameters are constrained the new workflow is tested using natural and experimentally produced non cylindrical folds the geometric parameters obtained can be used to improve our understanding of fold kinematics and fold mechanics and should assist the quantitative analysis of non cylindrical folds present in gneiss and salt domes and in rocks containing reservoirs of hydrocarbons and minerals deposits

textural evolution of synthetic anhydrite halite mylonites the rheology and textural evolution of mylonites for both crustal and mantle rocks are generally poorly understood stress and strain partitioning between shear zones and wall rock foliation development flow mechanisms and constitutive relations are little known to address these problems we have begun an experimental study in which anhydrite and halite aggregates are deformed in simple shear homogeneous mixes at intervals of 10 vol of anhydrite and halite powders of 90 to 180 m grain size comprise the 1 mm thick zone between the 35 precut surfaces in 2 by 4 cm right circular cylinders of anhydrite all specimens are confined under 200 mpa pc and tested at 300 c t producing an aggregate of near zero porosity all specimens are shortened at an axial displacement rate of 5 l0 6 cm s to shear strains of about 2 0 most stress strain curves have a similar form they are characterized by an initial linear response that is followed by a work hardening region that leads to a plateau of constant stress whilst strain continues to accumulate this apparent steady state behavior is followed by a drop in stress to a second apparent steady state stress the strain at this stress drop and the magnitude of the drop increase with increasing anhydrite content the second lower steady state stress for all mixes approaches that of sheared pure halite optical examination of the fabrics shows that straining under the initial apparent steady state is accommodated by both mineral phases a foliation evolves as defined by mineral segregation and grain elongation of halite at 15 to 30 to the shear zone walls anhydrite grains rotate until their 001 010 slip system parallels the foliation the anhydrite also exhibits twin lamellae kinks and microfractures following the stress drop rheologic behavior is dominated by dynamic recovery in halite the recrystallized grain size increasing consistent with the lower stress level

carbonate chemistry of recent chalk groundwater in a part of east anglia u k abstract an example of apparent open system dissolution is described from a region where a limestone aquifer is recharged through thick calcareous soils developed on till groundwaters in the area have higher alkalinities and lower ph values than are generally reported for carbonate terrains apparently as a consequence of open system dissolution however limited 13 c isotope data are incompatible with this conclusion indicating that exchange with the gas phase does not control the isotope chemistry and therefore that the system is isotopically closed this paradox can be resolved if the dynamics of the system are considered it is shown that back diffusion of gas from the solution to the gas reservoir is prevented and therefore isotopic equilibrium between gas and solution is not achieved isotope data also show that limited transfer of carbon between soil water and soil calcite occurs

chemical evolution of groundwater in triassic gypsum bearing carbonate aquifers las alpujarras southern spain a hydrochemical study employing modelling techniques was carried out using samples taken at 65 points springs and wells in triassic carbonate aquifers lujar gador unit alpujarride complex betic cordillera these aquifers are made up of limestones and dolomites with some gypsum scattered or interbedded though the area is semi arid recharge is relatively high because of their mountainous nature the carbonate rocks contain dense microfissuration the groundwater flow regime is predominantly diffuse the karstic forms are in general poorly developed two main hydrochemical processes have been identified in these aquifers one is incongruent dissolution of dolomite that determines the chemical composition of the less mineralised water the other is dedolomitisation dolomite dissolution together with calcite precipitation caused by dissolution of gypsum which becomes predominant when the flow encounters interbedded gypsum this reaction is also frequently associated with low temperature thermalism and can play a part in more intense local karstification cavities sinkholes high transmisivity in wells observed in the sectors of these aquifers where gypsum is more abundant a reaction path model has been used to simulate the geochemical processes through a hypothetical aquifer with similar lithology to the alpujarride carbonate aquifers successive stages of evolution through the carbonate sequence represented by different saturation states with respect to calcite dolomite gypsum and co2 have been modelled and then compared with the field data

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

the influence of pre devensian glacial deposits on the hydrogeochemistry of the chalk aquifer system of north norfolk uk the distribution of hydrochemical facies in the chalk aquifer system of north norfolk uk is interpreted to reveal the hydraulic and hydrogeochemical processes operating in the area the occurrence of two distinct glacial tills covering the chalk aquifer is shown to dominate aquifer conditions chalk groundwater in the interfluve regions covered by chalky boulder clay is characteristically of the order of 10 000 years old and compares with chalk groundwater of about 1000 2000 years old in areas covered by north sea drift the difference in age reflects the different mechanical compositions of the two glacial tills with the chalky boulder clay containing a higher clay content and lower sand content than the north sea drift hydrochemically chalk groundwater from beneath chalky boulder clay is distinguished from groundwater associated with north sea drift by a hco3 concentration of 300 mgl 1 with higher values occurring beneath chalky boulder clay the reason for the difference is that recharge water entering the carbonatedepleted soils developed on north sea drift attains calcite saturation for low values of soil pco2 in the range 10 2 5 10 2 0 whereas recharge entering carbonate rich soils developed on chalky boulder clay achieves calcite saturation for higher values of soil pco2 in the range 10 2 1 10 2 0 additionally pyrite oxidation and so4 reduction associated with the chalky boulder clay interfluve regions evolve further hco3 and to maintain calcite equilibrium increase the dissolved pco2 of the chalk groundwater in the interfluve regions mg sr and sio2 are able to increase because of the groundwater residence time which favours incongruent dissolution of the rock carbonate and breakdown of clay minerals contained in the glacial deposits and the chalk in contrast modern valley zone chalk groundwaters contain high concentrations of no3 up to 120 mgl 1 so4 up to 130 mgl 1 and cl up to 100 mgl 1 contributed by contamination mainly from an agricultural source the hydrochemical interpretation demonstrates that the varying glacial deposits are important in controlling recharge and groundwater flow within the chalk aquifer the chalk aquifer in the interfluvial areas experiences minor recharge whereas the chalk in the valley zone receives direct modern recharge water at the fluvial margin glacial sands and gravels control the storage and release of water transferred laterally through the glacial tills to the high transmissivity chalk in the valley zone

late quaternary climatic change in france estimated from multivariate pollen time series abstract in regions like southern france where usual analytical techniques are unsatisfactory due to the heavy influence of human activity and the existence of a complex climate the quantitative reconstruction of climate from pollen is particularly difficult that is why an original method has been performed the first step of the method based on best analogs estimation and multiple regression is to calculate a relationship between climate monthly temperature and precipitation and modern pollen spectra for data from 182 sites the result is called the analog climate the second step of the method an original combination of canonical correlation and principal components analyses extracts the common information from several fossil pollen sequences to produce a so called paleobioclimate this step removes the effects of local differences in the vegetation among nearby sites and also reduces the effects of human disturbance in the third step the signals obtained from the first two steps are merged by kalman filter into a final reconstruction where the noise is reduced by around 37 the results presented with a 95 confidence level suggest that the pleni wurm was 7 to 13 c colder than present and had 20 to 60 less precipitation than today this large confidence takes into account the climatic diversity of the region at 13 000 yr b p the climate reached the modern level of precipitation but the temperature was just less than present the subsequent decrease of precipitation is less important than that of temperature this fact may explain the advance of alpine glaciers during the younger dryas preboreal warming was abrupt 3 to 4 c per 500 yr and precipitation increased more slowly

geology and models of salt extrusion at qum kuh central iran profiles through the summit of a small nearly axisymmetric extrusion of oligocene and miocene salt and simple analogue models of it simulate the profiles of piles of ductile nappes extruded from convergent orogens the salt extrudes from a reactive diapir along a major strike slip fault at about 82 mm a 1 and rises 315 m above the central plateau of iran the salt has the distinctive smooth profile of a viscous fountain in which an asymmetric apron of allochthonous salt gravity spreads over its surroundings from a summit dome curtain folds developed in the source layer extrude from the diapir and are refolded by major recumbent folds with circumferential axes that simulate nappes minor flow folds with circumferential axes refold major folds in the top 10 50 m of surficial salt master joints 100 m long indicate brittle failure of dilated salt by regional stress fields tuned to the dimensions of qum kuh analytical and analogue models of viscous extrusions constrain the dynamic salt budget and a time of extrusion of at least 42 000 years new analogue models suggest that the number amplitude and spacing of major recumbent folds within the extruded salt and ductile nappe piles record the number amount and relative timing of fluctuations in the driving forces

rheology of petrolatum paraffin oil mixtures applications to analogue modelling of geological processes abstract paraffins have been widely used in analogue modelling of geological processes petrolatum and paraffin oil are commonly used to lubricate model boundaries and to simulate weak layers in this paper we present rheological tests of petrolatum paraffin oil and several homogeneous mixtures of the two the results show that petrolatum and all petrolatum paraffin oil mixtures are strain strain rate and temperature dependent under typical experimental strain rates 10 3 10 1 s 1 for the same conditions pure paraffin oil is a slightly temperature dependent linear newtonian fluid all mixtures have yield stress and flow stress strain softening values that decrease with decreasing shear rate and with increasing relative amounts of paraffin oil the degree of strain rate dependence shear thinning also decreases with increasing paraffin oil content because these materials have rheologies that can be characterized and controlled they are suitable for use in a large number of analogue model settings either as a lubricant or to simulate weak layers when used as a lubricant mixtures with higher paraffin oil content should perform better than pure petrolatum

linear to non linear relationship between vein spacing and layer thickness in centimetre to decimetre scale siliciclastic multilayers from the high ardenne slate belt belgium germany abstract typical spacing distributions have frequently been described for fractures in thin sedimentary layers 40 cm vein spacing tends to increase to a maximum value becoming more or less independent of layer thickness the resemblance with fracture spacing suggests that in an unfractured rock vein saturation can occur high fluid pressures are responsible for vein nucleation but the stress state around the initial veins controls the spacing pattern subsequently in a vein saturated rock or the existing veins will thicken by the process of crack sealing or a new cross cutting vein generation will develop in case the regional stress field changes relatively with respect to the existing veins

hydrochemistry of the saline groundwaters of the lower mersey basin permo triassic sandstone aquifer uk saline groundwater occurs at depth in the triassic sandstones of the northern end of the cheshire basin in northwest england major and minor ion data suggest that the origin of the salinity is dissolution of evaporite deposits the salinity probably developed in an interval following the tertiary inversion of the basin which would have allowed faulted contact between the sandstones and the overlying evaporite sequence of the mercia mudstone group isotope evidence suggests the saline waters to have been considerably diluted by presumably dispersive mixing with a meteoric water recharged under cool and therefore quaternary climatic conditions comparison with other uk permo triassic basin brines suggests the merseyside waters are not unusual except in terms of the importance of exchange reactions and dilution by quaternary recharge waters these factors are due to the shallow maximum burial depth of the aquifer and the preservation of smectites and also to the geometry of the aquifer and its low permeability faults in the light of the water chemistry data it is suggested in a slight modification of the proposal of naylor et al q geol soc lond 146 685 699 1988 that the cheshire basin mineralization resulted from mixing of the relatively oxidized so4 rich evaporite brines with the reduced so4 poor metal rich barich coal measures brines which were expelled through faults from the coal measures during basin inversion some degree of oxyhydroxide stripping of the sandstones by the coal measures brines would have enhanced metal concentrations the water resulting from the mixing of brines would have been far from equilibrium and the barite and sulphide precipitation followed along the faults

nature of crustal reflectivity along the dekorp profiles in germany in comparison with reflection patterns from different tectonic units worldwide a review reflectivity of the continental crust displays many different patterns the dekorp lines are used as a basis for comparing and reviewing reflectivity in different tectonic units the brittle upper crust generally exhibits only two types of reflectivity it is either rather transparent preferably in some extensional provinces or and it shows traces of thrust and shear zones of former or present ruptures as these zones have a low impedance interior with few exceptions their first reflection onsets have a negative polarity and evince strong but short signals which sometimes can be correlated over several kilometers the generally ductile lower crust displays a completely different reflectivity in warm extensional and thin crusts the lower part is full of reflecting lamellae it is suggested that this type of reflectivity has a thermo rheological origin the creation of lamellae must take place in a ductile material with contrasting impedance under extensional stresses it can be associated with mineral alignment and corresponding seismic anisotropy destruction of lamellae may take place by a cooling process transforming parts of the lower crust into a brittle regime small stresses might deform or break the lamellae and leave a certain dispersed reflectivity like that in some old and cold shields there are no observations of reflecting lamellae in the upper crust or in the upper mantle in all areas the moho is the last reflecting band reflection moho which most often is identical with the classical refraction moho there are isolated mostly dipping reflections in the uppermost mantle in zones where the last tectonic event a delamination or subduction was not succeeded by a heating process the uppermost mantle is brittle again in most areas and may keep the memory of a cold collision over billions of years

hydrochemical and stable isotope evidence for the extent and nature of the effective chalk aquifer of north norfolk uk in eastern england the chalk aquifer is covered by extensive pleistocene deposits which influence the hydraulic conditions and hydrochemical nature of the underlying aquifer in this study the results of geophysical borehole logging of groundwater temperature and electrical conductivity and depth sampling for major ion concentrations and stable isotope compositions 18o and 2h are interpreted to reveal the extent and nature of the effective chalk aquifer of north norfolk it is found that the chalk aquifer can be divided into an upper region of fresh groundwater with a cl concentration of typically less than 100 mg l 1 and a lower region of increasingly saline water the transition between the two regions is approximately 50 m below sea level and results in an effective aquifer thickness of 50 60 m in the west of the area but less than 25 m where the eocene london clay boundary is met in the east of the area hydrochemical variations in the effective aquifer are related to different hydraulic conditions developed in the chalk where the chalk is confined by low permeability chalky boulder clay isotopically depleted groundwater 18o less than 7 5 is present in contrast to those areas of unconfined chalk where glacial deposits are thin or absent 18o about 7 0 the isotopically depleted groundwater is evidence for groundwater recharge during the late pleistocene under conditions when mean surface air temperatures are estimated to have been 4 5 c cooler than at the present day and suggests long groundwater residence times in the confined aquifer elevated molar mg ca ratios of more than 0 2 resulting from progressive rock water interaction in the confined aquifer also indicate long residence times a conceptual hydrochemical model for the present situation proposes that isotopically depleted groundwater occupying areas where confined groundwater dates from the late pleistocene is being slowly modified by both diffusion and downward infiltration of modem meteoric water and diffusive mixing from below with an old saline water body

paleowaters in silurian devonian carbonate aquifers geochemical evolution of groundwater in the great lakes region since the late pleistocene abstract changes in the climatic conditions during the late quaternary and holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the great lakes region increased hydraulic gradients from melting of kilometer thick pleistocene ice sheets reorganized regional scale groundwater flow in paleozoic aquifers in underlying intracratonic basins here we present new elemental and isotopic analyses of 134 groundwaters from silurian devonian carbonate and overlying glacial drift aquifers along the margins of the illinois and michigan basins to evaluate the paleohydrology age distribution and geochemical evolution of confined aquifer systems this study significantly extends the spatial coverage of previously published groundwaters in carbonate and drift aquifers across the midcontinent region and extends into deeper portions of the illinois and michigan basins focused on the freshwater saline water mixing zones in addition the hydrogeochemical data from silurian devonian aquifers were integrated with deeper basinal fluids and brines in upper devonian black shales and underlying cambrian ordovician aquifers to reveal a regionally extensive recharge system of pleistocene age waters in glaciated sedimentary basins elemental and isotope geochemistry of confined groundwaters in silurian devonian carbonate and glacial drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals dissolution of halite and anhydrite cation exchange microbial processes and mixing with basinal brines carbon isotope values of dissolved inorganic carbon dic range from 10 to 2 87sr 86sr ratios range from 0 7080 to 0 7090 and 34 s so 4 values range from 10 to 30 a few waters have elevated 13cdic values 15 from microbial methanogenesis in adjacent organic rich upper devonian shales radiocarbon ages and 18o and d values of confined groundwaters indicate they originated as subglacial recharge beneath the laurentide ice sheet 14 50 ka bp 15 to 13 18o these paleowaters are isolated from shallow flow systems in overlying glacial drift aquifers by lake bed clays and or shales the presence of isotopically depleted waters in paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional scale groundwater flow modern groundwater flow in the great lakes region is primarily restricted to shallow unconfined glacial drift aquifers recharge waters in silurian devonian and unconfined drift aquifers have 18o values within the range of holocene precipitation 11 to 8 and 7 to 4 5 for northern michigan and northern indiana ohio respectively carbon and sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions 13cdic 14 7 to 11 1 and 87sr 86sr 0 7080 0 7103 the distinct elemental and isotope geochemistry of pleistocene versus holocene age waters further confirms that surficial flow systems are out of contact with the deeper basinal scale flow systems these results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes which are important for determining the sustainability of present day water resources and stability of saline fluids in sedimentary basins

identification of connate water in interstitial solution of chalk sediment interstitial solution was recovered from core samples of a borehole through 472 m of the upper cretaceous chalk formation in eastern england the solution has been analysed for major and some minor components and also for oxygen and hydrogen isotopic composition samples of the carbonate rock have also been analysed following acid dissolution the general feature of interstitial solution chemistry is a progressive dilution of dissolved species with decreasing depth from a near marine composition found in the deepest samples which are identified as connate water departures from the expected dilution trend are interpreted as evidence for diagenetic reactions during burial or as a result of freshwater circulation following subaerial uplift sr2 li and f have been enriched in interstitial solution and k has been slightly depleted the profile of chalk chemistry with depth shows no conclusive evidence for changes in the mg and sr content of the bulk carbonate due to freshwater diagenesis the 18o and d of the interstitial water reflect the same mixing as that shown by dissolved species however an apparent depletion of 18o and d in the deepest fluids with respect to the expected marine isotopic composition is tentatively explained as a result of the differences in diffusion rates of aqueous oxygen and hydrogen and of ionic solutes

hydrogeochemical effects of groundwater mining of the sierra de crevillente aquifer alicante spain the groundwater mining of the crevillente aquifer southeastern spain has resulted in the progressive deterioration of water quality with particularly significant increases in chloride sulfate and sodium the possibility of a vertical hydrochemical zoning is deduced that would require examining the importance of the geometry and lithology evaporitic materials in the salinization process the time of water rock contact residence time and dilution by infiltration of rainwater also influences the hydrogeochemistry of the aquifer the hydrochemical data are useful in defining the conceptual model of the aquifer completely karstified with relative homogeneity

microstructural evolution and grain boundary structure during static recrystallization in synthetic polycrystals of sodium chloride containing saturated brine the effects of brine on recrystallization in halite are well known however properties of brine such as morphology connectivity diffusivity and the resulting influences on deformation mechanisms are still a matter of debate this paper presents a microstructural study of dense statically recrystallizing synthetic polycrystalline halite containing small amounts of brine we used powders of two different grain size classes 10 m and 200 355 m the aggregates were compacted to brine filled porosities less than about 2 and annealed at room temperature without an external stress field

the groundwater chemistry of the lower mersey basin permo triassic sandstone aquifer system uk 1980 and pre industrialisation urbanisation abstract the lower mersey basin permo triassic sandstone aquifer lies in a heavily urbanised and industrial area of nw england extensive pumping has lowered the piezometric surface considerably causing the sandstone aquifer which is overlain by a variable sequence of glacial deposits to become extensively unconfined the groundwater chemistry of the system appears to be controlled by the geometry of the sandstones faulting the variable distribution and permeability of the quaternary deposits and by the pumping the water in the present day recharge areas is affected by pollution with high no 3 so 4 and cl concentrations it has ph values as low as 4 3 the oldest fresh waters in the area age less than a few thousand years are strongly ion exchanged as a result of the flushing of saline water from the system these waters grade into similar but much less ion exchanged waters with zero no 3 very low so 4 and high hco 3 a fourth group of waters appears to be the result of mixing between the latter waters and pumping induced leakage through the quaternary deposits a final group of waters is characterised by very low alkalinity and is strongly associated with particular geological units poor in carbonates minor ion distributions confirm the patterns suggested by the major ions the distribution of the water chemistry preserves some of the features of the pre pumping system in this low transmissivity high storage system and reconstruction of the pre pumping chemical distributions is attempted to highlight the effects of industrial man on the system

baseline geochemical conditions in the chalk aquifer berkshire u k a basis for groundwater quality management the chalk aquifer is the most important british aquifer and is also important over much of northern europe aquifer protection requires a sound knowledge of the baseline conditions and how these might vary or have varied with time this detailed geochemical study of a representative area of chalk in berkshire u k includes a consideration of several components 1 the inputs from the atmosphere 2 the interstitial water of the soil and the unsaturated zone 3 the interstitial water in the confined and unconfined sections of the aquifer and 4 the saturated mainly fissure flow along the hydraulic gradient which forms an important water supply of the thames valley region atmospheric inputs form an important source of some elements but the dominant chemical characteristics of the chalk groundwater are acquired during percolation through the soil and the upper unsaturated zone during saturated flow downgradient the chemistry is modified mainly by incongruent reactions of the carbonate matrix and by redox reactions and only to a minor extent by exchange reactions and mixing with residual saline connate water the incongruent reaction of carbonate results in a marked increase in the mg ca ratio and the sr and 13c contents of the groundwater with increased residence time oxygen concentrations are reduced mainly by oxidation of fe2 and the onset of reducing conditions allows dissolved fe2 to increase and rapid denitrification to occur the salinity profile through the confined chalk confirms that residual connate water up to one fifth sea water concentration still remains at depth and this accounts for some salinity increase in the confined groundwater resulting from fissure water pore water diffusional exchange timescales for groundwater movement have been established using tritium radiocarbon and indirectly using inert gas ratios and stable isotope ratios on balance it is concluded that all abstracted water is of holocene age although inert gas temperatures indicate cooler climatic conditions for recharge for some of the confined groundwater the implications for development and aquifer protection are discussed especially the prospect of natural in situ denitrification problems of fe solubility and the recognition of groundwater of different maturities