hydrogeochemical conditions and evolution at the aspo hrl sweden abstract the overall hydrogeochemical conditions at and in the near vicinity of the underground experimental aspo hard rock laboratory hrl in se sweden have been investigated groundwater data from more than 400 samples have been compiled and evaluated the groundwater samples represent depths down to 1700 m below sea level and sampling has been performed prior to and during the hrl tunnel excavation episodic events have to a great extent influenced the hydrochemical evolution since the last glaciation which ended some 13 ka ago at that time glacial melt water was flushed under hydraulic pressure down into the fracture system to a depth of at least several hundred metres the next episodic event took place when the baltic freshwater lake transformed into the brackish litorina sea some 7 ka ago at this time aspo was covered by the sea and these denser more saline waters partly replaced the glacial water down to a depth where the density equilibrated with the replacement sea water at some time around 3 4 ka ago aspo started to rise above sea level and meteoric water began to infiltrate the rock the overall trend of increasing salinity with depth may easily be misinterpreted as a fairly simple groundwater system evolving from a two component evolution path between non saline and saline groundwaters however when combining the results from environmental isotopes and the chemical parameters using a new modelling tool named m3 multivariate mixing and mass balance calculations a higher resolution was obtained and a more complex groundwater pattern which reflects the present and paleo hydrogeological events can be recognised the measured groundwater composition was modelled to be a mixture of meteoric past and present baltic seawater glacial or cold climate recharge and brine type of waters the modelling result shows that the processes considered to have a dominating impact on the present aspo groundwater chemistry are mixing both in disturbed and undisturbed systems calcite dissolution and precipitation redox reactions and biological processes the undisturbed groundwater conditions prior to the hrl tunnel construction at aspo consisted of 1 a dominating proportion of meteoric fresh water in the upper 250 m of the aquifer 2 a brackish saline water consisting of mixing proportions of present and ancient baltic sea water and glacial melt water present to a depth of 250 600 m 3 saline water still containing proportions of glacial water which could represent even older glaciations and brines a large portion of which have been stagnant for perhaps millions of years below a depth of 600 m during the hrl tunnel construction there were changes in the composition of the water flowing into the tunnel at different locations although the variation in salinity was relatively small the variations in the mixing proportions of the different water types were substantial

quantification of rock mass damage in underground excavations from microseismic event monitoring abstract rock mass damage assessment is required for many applications in rock engineering practice including support design contamination transport control stope design amongst others while various methods such as displacement measurement seismic refraction and direct observation using borehole camera have been used relatively few efforts have been made to use microseismic monitoring to quantify the rock mass damage from laboratory tests it is well known that microseismic events are indicators of fracturing or rock damage as the rock mass is brought to failure at high stress by capturing the microseismic events underground excavation induced rock mass degradation or damage can be located but can the amount of damage in terms of changes to strength or deformation properties be measured in the present study a method of characterizing rock mass damage near excavations based on microseismic event monitoring is developed and a damage driven numerical model is presented that takes the microseismic data as input to determine the damage state described by fracture density the approach is built on the discovery that a realistic crack size corresponding to a seismic event can be established by applying a tensile cracking model instead of the traditional shear model commonly used in earthquake analysis the rock mass is softened by the introduction of cracks and this is simulated by a micro mechanics based constitutive model the material property input for the model are young s modulus poisson s ratio of the intact rock and information obtained from the monitoring of microseismic events such as the location and the source size of each event calculated from source parameters using data from the atomic energy of canada limited mine by experiment this model has been verified by investigating the linkage between microseismicity rock mass damage and ground deformation it is found that when damage related softening based on microseismic data is considered predicted rock mass displacements are in good agreement with extensometer measurements

hydrochemical disturbances measured in groundwater during the construction and operation of a large scale underground facility in deep crystalline rock in japan changes in the hydrochemical conditions of groundwater were evaluated following the construction of a large scale underground facility at the mizunami underground research laboratory miu japan the facility was constructed to a depth of 500 m in sedimentary and granitic rocks drawdown of the groundwater level in the range of several tens to hundreds of meters was observed up to hundreds of meters away from the shafts during the first ten years of facility construction and operation subsequent changes in groundwater chemistry occurred due to upconing of high salinity groundwater from the deepest part of the shaft and the infiltration of low salinity shallow groundwater we predict that future deep groundwater chemistry in the vicinity of the miu facility will resemble that of the present day shallow groundwater multivariate statistical analysis provides fundamental insights into such a site we found that the extent of hydrochemical variability related to miu construction and operation was dependent on the distance from the facility shafts and galleries and on hydrogeological compartmentalization resulting from lithological boundaries such as permeable conglomerates vs more compact lithological units and other features such as faults or clay layers we conclude that hydrochemical impact assessment of groundwater in low permeability rock is essential prior to the construction of such a facility this should include characterization of hydrogeological structures and compartments to propose suitable location of shafts and galleries

the bow city structure southern alberta canada the deep roots of a complex impact structure geological and geophysical evidence is presented for a newly discovered probable remnant complex impact structure the structure located near bow city southern alberta has no obvious morphological expression at surface the geometry of the structure in the shallow subsurface mapped using downhole geophysical well logs is a semicircular structural depression approximately 8 km in diameter with a semicircular uplifted central region detailed subsurface mapping revealed evidence of localized duplication of stratigraphic section in the central uplift area and omission of strata within the surrounding annular region field mapping of outcrop confirmed an inlier of older rocks present within the center of the structure evidence of deformation along the eastern margin of the central uplift includes thrust faulting folding and steeply dipping bedding normal faults were mapped along the northern margin of the annular region isopach maps reveal that structural thickening and thinning were accommodated primarily within the belly river group evidence from legacy 2 d seismic data is consistent with the subsurface mapping and reveals additional insight into the geometry of the structure including a series of listric normal faults in the annular region and complex faulting within the central uplift the absence of any ejecta blanket breccia suevite or melt sheet based on available data is consistent with the bow city structure being the remnant of a deeply eroded complex impact structure accordingly the bow city structure may provide rare access and insight into zones of deformation remaining beneath an excavated transient crater in stratified siliciclastic target rocks

thermochronology and the three dimensional cooling pattern of a granitic pluton an example from the toki granite central japan the three dimensional spatial variations in the cooling pattern of the toki granitic body a zoned pluton in central japan have been evaluated quantitatively by thermochronology using cooling age determination based on the different closure temperatures for target mineral species the toki granite has hornblende k ar ages of about 74 3 3 7 ma n 2 closure temperature of 510 25 c biotite k ar ages of 78 5 3 9 to 59 7 1 5 ma n 33 300 50 c and zircon fission track ages of 75 6 3 3 to 52 8 2 6 ma n 44 240 50 c the spatial variation in the biotite k ar age is similar to that in the zircon fission track age in samples collected from 11 boreholes and seven outcrop sites in the toki granite indicating that cooling was effectively from the roof and also from the northwest margin this cooling pattern shows a strong correlation with the alumina saturation index asi distribution of the body larger asi values correspond to earlier and more rapid cooling after emplacement and smaller value to slower cooling toki granite was effectively cooled from the peraluminous regions where assimilation of country sedimentary rock was most extensive

the toms canyon structure new jersey outer continental shelf a possible late eocene impact crater abstract the toms canyon structure 20 22 km wide is located on the new jersey outer continental shelf beneath 80 100 m of water and is buried by 1 km of upper eocene to holocene sedimentary strata the structure displays several characteristics typical of terrestrial impact craters flat floor upraised faulted rim brecciated sedimentary fill but several other characteristics are atypical an unusually thin ejecta blanket lack of an inner basin peak ring or central peak being nearly completely filled with breccia seismostratigraphic and biostratigraphic analyses show that the structure formed during planktonic foraminiferal biochron p15 of the early to middle late eocene the fill unit is stratigraphically correlative with impact ejecta cored nearby at deep sea drilling project dsdp site 612 and at ocean drilling program odp sites 903 and 904 22 35 km southeast of the toms canyon structure the toms canyon fill unit also correlates with the exmore breccia which fills the much larger chesapeake bay impact crater 90 km diameter 335 km to the southwest on the basis of our analyses we postulate that the toms canyon structure is an impact crater formed when a cluster of relatively small meteorites approached the target site bearing n 50 e and struck the sea floor obliquely

sedimentary signatures and processes during marine bolide impacts a review abstract studies of submarine impact craters resulting from impacts of comets or asteroids demonstrate that the presence of water and the physical properties of target rocks have a major influence on sedimentary processes associated with meteorite impacts this results in difference in sedimentary signature of bolide impacts in marine environments compared to subaerial impact craters in subaerial impacts the targets are commonly hard rocks frequently of igneous and or metamorphic origin whereas in submarine impacts the targets are mostly unconsolidated or poorly lithified sediments or sedimentary rocks with high volumes of pore water such differences result in variability in crater morphology and in sedimentary processes inside and outside the impact area impacts in shallow water marine neritic environments produced craters with low or absent rims and wide and shallow brims as characterize by both the montagnais on the scotian shelf the mjolnir in the barents sea 45 and 40 km in diameter respectively and the chesapeake bay 90 km in diameter lack of elevated rims is thought to be the result of current reworking and resurge of the water back into the excavated cavity as the water in the crater is vaporized during this process resurge gullies can be cut across the rim while mass and debris flows turbidites and other gravity deposits are produced as results of tsunami and crater wall and central high collapse during and after the crater excavation stage such deposits are found both within and outside the crater structure the only difference between gravity deposits triggered by an impact or other rare events such as earthquakes is the admixture of various melt particles and possible enrichments in iridium in the former impacts near the shelf edge may cause partial collapse of the continental margin as shown by the montagnais and chicxulub impacts some of the gravity and debris flows generated by margin collapse may be channelized with final deposits up to several hundred meters thick extending for hundreds of kilometers from the impact site other impact features such as shatter cones tektites spherules and ni spinels shocked quartz isotropication and partial melts are common to both submarine and subaerial impacts theoretical calculations of the destructive forces of mega tsunami waves triggered by meteorite impact in the ocean greatly exceed those based on geologic evidence a dearth of gigantic tsunami evidence for the chicxulub impact outside of the gulf of mexico where from theoretical modelling the maximum near bottom orbital velocity of water flow crossing the deep north atlantic basin should have been 1 m s could be the result of the mitigating effect of the bathymetry of surrounding area causing wave diffraction and interference calculated maximum horizontal orbital velocity near the seafloor at the shelf for the montagnais impact is 22 m s for a 200 m high wave 5 5 m s for a 50 m high wave at 500 km decreasing to 0 5 m s at 1000 km strong enough to scour the deep ocean bottom and produce distinct erosion surfaces and disconformities in marine sedimentary record however lack of cores across impact horizon prevents confirmation of occurrence of such bottom water flows

cometary impacts into ocean their recognition and the threshold constraint for biological extinctions the montagnais impact crater is presently the only site in the ocean where the effect of a meteorite fall on marine organisms has been studied the impact crater is 45 km in diameter and was formed at 50 8 ma by a fall of probably an old cometary nucleus 3 4 km in diameter into shallow 600 m ocean comparison of the impact structure and related deposits with those on land shows several major differences of which the most significant is the absence of an elevated crater rim instead the crater perimeter is bevelled and eroded as a consequence of impact induced bottom currents and turbulent return water flow into the excavating cavity by this process most of the fall out breccia is reworked back into the crater cavity where it accumulates in much larger thickness than in impact craters on land at a microscopic scale the shock metamorphism features are about the same as those for land impacts geochemically impacts of comet nucleii may not leave a recognizable signature at the impact horizon except for a minor increase in iridium thus stratigraphic horizons associated with extinctions and or major changes in biota have to be closely examined for other impact indicators like the presence of tectites glass spherules and quartz grains with shock features occurrence of megatsunami wave deposits extensive erosion on continental margins margin failures and faunal mixing above erosional unconformities are other potential impact indicators there is no single indicator that can provide sufficient proof of an impact event such interpretations have to be based on multiparameter studies of global extent since many of the impact indicators are only of regional extent the lack of extinction of any marine plankton genera or of bottom dwellers at the montagnais impact site allows us to place a lower limit for biological extinctions caused by cometary impacts on those with nucleus 4 km in diameter the calculated frequency for a cometary impact which could result in a 10 extinction of marine genera is about 6 10 7 yr 1 and for the k t boundary type of extinctions about 2 10 8 yr 1 even allowing for a large degree of uncertainty in these estimates it is unlikely that the biological extinction events for the last 250 ma identified by sepkoski 1990 could have been all caused by meteorite impacts

geological and hydraulic characterisation of the excavation disturbed zone in the opalinus clay of the mont terri rock laboratory abstract the fracture network in the excavation disturbed zone edz of an argillaceous formation the opalinus clay in the mont terri rock laboratory in northwest switzerland is characterised using structural and hydrogeological techniques sampling of unloading fractures is done by analysing resin injected overcores taken from the edz resulting in a structural data set of fracture orientations frequencies and extent of the edz these parameters are derived in tunnel sections which were excavated by blasting pneumatic hammering and road header techniques pneumatic and hydrogeological tests are subsequently carried out to derive hydraulic parameters such as permeability and transmissivity distributions of the fracture network synthesis of the structural and hydrogeological data led to a conceptual model of the edz in the mont terri rock laboratory which is defined by a 2 m plastically deformed zone around the tunnel this plastic zone is further divided into an inner 1 m zone consisting of an air filled fracture network and an outer zone with mostly saturated and isolated fractures transmissivities in the inner zone are orders of magnitude higher than those of the undisturbed opalinus clay finally a methodology is proposed for the structural and hydrogeological characterisation of the edz this methodology is not site specific and is thus applicable at any argillaceous underground facility

geochemical influences on the design construction and operation of a nuclear waste vault abstract the design construction and operation of a vault for used nuclear fuel in crystalline rock may be influenced by a number of geochemical factors during the period when a site is being selected information is needed regarding the rock type heterogeneities in its composition and the mineralogy of permeable zones because these will cause variations in thermal conductivity strength and radionuclide sorptive properties of the rock these factors may affect decisions regarding depth of vault construction tunnel dimensions and spacing of panels and waste containers during site characterization borehole drilling from the surface and subsequent hydraulic testing will introduce both chemical and microbiological contaminants that may further influence this decision during vault construction the geochemistry of the rock may cause changes to the design and construction methods used high salinity fluids in the rock matrix could limit the ability of radar surveys to detect fractures in the surrounding rock and may also cause unacceptably high total dissolved solids loadings in water discharged from the facility the presence of toxic corrosive or radioactive constituents in inflowing groundwater may require grouting or development of treatment facilities both above and below ground the use of explosives will cause high organic and nitrate loadings in service water as well as the possible impregnation of these chemicals in the disturbed wall rock surrounding an excavation these chemicals may remain despite cleaning efforts and act as nutrients to promote microbial activity in the post closure phase in the operational phase inflow of increasingly saline groundwater may affect predicted container corrosion rates and buffer and grout stabilities following vault resaturation and increase in temperature this in turn may affect designs for container materials and spacing salt accumulations and microbial growths on vault walls may extend into the rock mass and require skimming of wall rock before closure this paper describes geochemical influences that might be anticipated in the disposal of nuclear waste with examples from the construction and operation of canada s underground research laboratory manitoba in a granitic batholith on the canadian shield

structural outer rim of chesapeake bay impact crater seismic and bore hole evidence nine seismic reflection profiles and four continuous core holes define the gross structural and stratigraphic framework of the outer rim of the chesapeake bay impact crater the rim is manifested as a 90 km diameter ring of terraced normal fault blocks which forms a 320 m 1200 m high rim escarpment the top of the rim escarpment is covered by a 20 m 30 m thick ejecta blanket the escarpment encircles a flat floored annular trough which is partly filled with an 250 m thick breccia lens exmore breccia the exmore breccia overlies a 200 m 800 m thick interval of slumped sedimentary megablocks which in turn rests on crystalline basement rocks all postimpact strata upper eocene to quaternary sag structurally into the annular trough and most units also thicken as they cross the rim into the crater postimpact compaction and subsidence of the exmore breccia have created extensive normal faulting in overlying strata

characterization of rare earth elements rees associated with suspended particles in deep granitic groundwater and their post closure behavior from a simulated underground facility abstract understanding radionuclide transport processes deep underground is indispensable for safety assessments of the geological disposal of radioactive wastes this study investigated the behavior of rare earth elements rees associated with suspended particles in deep granitic groundwater and in a sealed drift at a depth of 500 m in the mizunami underground research laboratory url in japan as an analogue study of radionuclide behavior around an underground waste disposal facility particles suspended in natural groundwater consist of silicate minerals including clays and iron hydroxide calcite sulfide and organic substances approximately 10 60 of rees in groundwater are associated with suspended particles furthermore sequential chemical extraction analyses of the suspended materials trapped on membrane filters suggests that rees are primarily sorbed onto carbonate particles in deep granitic groundwater carbonate particles in groundwater are most likely derived from in situ precipitation of supersaturated carbonate minerals such as calcite the concentration of lanthanum associated with suspended particles as an example is highest when the calcite saturation index shows equilibrium si 0 and decreases as the calcite saturation index increase because deep granitic groundwater is generally in equilibrium with the saturated condition for calcite the results of this study suggest that calcite particles inevitably exist in groundwater and preferentially sorb rees the ree concentrations in the water and suspended particles from the closed drift are significantly lower compared with concentrations in the surrounding groundwater thermodynamic calculations show that the dissolved ree carbonate complexes in the closed drift decreased in the drift closure period these complexes may have been absorbed or co precipitated within the shotcrete on the drift wall in the closed drift zns particles and large amounts of organic suspensions as artificial suspended particles were observed in addition to the particles observed in natural groundwater a sequential chemical extraction analysis indicates that rees are primarily sorbed onto the carbonate particles and not on the large quantity of organic particles there may be little ree adsorption onto organic suspensions or rees may have preferentially adsorbed onto calcite particles or shotcrete rather than organic matter the occurrence of calcite particles under the cementitious conditions of the closed drift changes from the large suspended particles to aggregates of relatively small particles with time precipitation of carbonate particle borne rees is probably one of reasons for the decrease in the suspended rees concentrations the usage of cement based materials would generate environmental conditions in which rees are fundamentally immobile in and around the underground facilities

in situ experiments on an excavation disturbed zone induced by mechanical excavation in neogene sedimentary rock at tono mine central japan abstract the excavation disturbed zone edz is defined as the rock zone where rock properties and conditions have been changed due to the processes induced by excavation such as fracturing stress redistribution and desaturation based on our results of the in situ blasting excavation disturbance experiment at the tono mines the rock mass around the drift behaved elastically and the excavation damage induced by blasting was considered to be a primary factor in causing a change in rock properties the excavation damage was considered to depend on the excavation method so we performed an excavation disturbance experiment with mechanical excavation using a boom header in the neogene sedimentary soft rock to compare the rock property change and width of the edz induced by blasting geological observation rock mass displacement and vibration measurement were performed during the drift excavation seismic refraction and tomographic surveys borehole expansion test and hydraulic test were performed before and after the drift excavation a low seismic velocity layer of the edz with a width of ca 0 3 m and a seismic velocity of 65 70 of the intact rock was detected by a seismic refraction survey along the drift wall deformability and hydraulic conductivity were not changed in the rock mass up to 0 3 m from the drift wall the change in rock properties and width of the edz was shown to depend on the excavation method in this geological setting the mechanical excavation method is more effective in limiting the extent of the edz and change in rock mass properties

assessment of seawater intrusion into underground oil storage cavern and prediction of its sustainability operation of underground oil gas storage cavern in coastal area can induce seawater intrusion because excavation of underground storage cavern causes the groundwater level decrease of coastal aquifer seawater intrusion has the potential to cause the corrosion of underground cavern facility and leakage of gas and oil from the storage caverns therefore seawater intrusion into the underground storage caverns should be evaluated carefully to avoid unexpected operation problems in this study the extent of seawater intrusion into underground oil storage cavern in yeosu korea was assessed through field monitoring and numerical modeling to evaluate the storage cavern sustainability against seawater intrusion the mean values of seawater mixing ratios of seepage water in each cavern estimated through modeling range from 0 01 to 8 70 which are less than the measured mixing ratio 2 3 12 8 based on the cl concentrations this result indicates that other source of cl may have contributed to the observed salinity in the cavern seepage water spatial and temporal variations in monitoring data and numerical modeling demonstrate that the location of storage seepage water flow rate and the fracture zones are important factors controlling seawater mixing ratio seawater intrusion barrier wells located along the coastline were shown to be important to prevent seawater intrusion into the storage caverns significantly the predicted seawater mixing ratio after 100 years of cavern operation is 0 06 12 7 varying depending on the caverns location

hydrochemical baseline condition of groundwater at the mizunami underground research laboratory miu abstract hydrochemical conditions up to depths of 1000 m below ground level around the mizunami underground research laboratory were investigated to construct a baseline condition model describing the undisturbed hydrochemical environment prior to excavation of the underground facilities at mizunami gifu japan groundwater chemistry in this area was classified into a na ca hco 3 type of groundwater in the upper part of sedimentary rock sequence and a na ca cl type of groundwater in the deeper part of the sedimentary rock sequence and basement granite the residence time of the groundwaters was estimated from their 14 c contents to be approximately 9 3 ka in the middle part of the sedimentary rock and older than 50 ka in the deep part of the granite the evolution processes of these groundwaters were inferred to be water rock interactions such as weathering of plagioclase dissolution of marine sulphate sulphide minerals and carbonate minerals in the na ca hco 3 type of groundwater and mixing between low salinity water in the shallow part and higher salinity water in the deeper part of the granite in the na ca cl type of groundwater the source of salinity in the deeper part of the granite was possibly a palaeo hydrothermal water or a fossil seawater that recharged in the miocene subsequently being modified by long term water rock interaction the cl depth trend in granitic groundwater changes at a depth of 400 m below sea level the hydrogeological properties controlling the groundwater flow and or mixing processes such as advection and diffusion were inferred to be different at this depth in the granite this hydrochemical conceptual model is indispensable not only when constructing the numerical model for evaluating the hydrochemical disturbance during construction and operation of the miu facility but also when confirming a hydrogeological model

how big was the chesapeake bay impact insight from numerical modeling the chesapeake bay impact structure virginia is the largest impact crater in the united states the important question of how large the impactor was that formed the crater remains unanswered this is primarily due to peculiarities of the crater structure revealed by seismic exploration that complicate comparisons with other terrestrial and extraterrestrial craters one potential explanation for the unusual structure of the chesapeake bay crater is that the cratering process was affected by rheologic variations in the target at the time of impact using numerical modeling we find that for a sufficient contrast in material strength between the sedimentary and crystalline units at the chesapeake bay impact site we can produce a model of the final crater that is consistent with observational constraints and hence we can infer the energy released during the impact 1 75 3 10 6 mt in the absence of target strength variations the final crater diameter is likely to have been 40 km rather than the observed 80 90 km

the mont terri rock laboratory a new international research project in a mesozoic shale formation in switzerland abstract in many countries argillaceous formations are being considered as potential host rocks for repositories of radioactive waste therefore in 1995 several organisations decided to start an international research project in the reconnaissance gallery of the mont terri motorway tunnel in north western switzerland in a mesozoic shale formation the opalinus clay aalenian this project is under the patronage of the swiss national hydrological and geological survey the following organisations are also partners in the project andra and ipsn france bgr germany enresa spain nagra switzerland jnc and obayashi japan sckcen belgium the aims of the project are to analyse the hydrogeological geochemical and rock mechanical properties of an argillaceous formation the changes of these properties induced by the excavation of galleries and to evaluate and improve appropriate investigation techniques in january 1996 eight niches were excavated for the project and 15 experiments were started in boreholes of no more than 30 m in length in the winter of 1997 1998 a new research gallery was excavated to host further experiments different excavation drilling and investigation techniques have been tested and improved significant results of the different experiments are already available some of those dealing with hydrochemistry porewater pressure measurements and the evolution of the excavation disturbed zone edz are reported in this paper

large scale intrusion of shallow water into a vertical fracture zone in crystalline bedrock initial hydrochemical perturbation during tunnel construction at the aspo hard rock laboratory southeastern sweden on march 13 1991 construction of the entrance tunnel to the aspo hard rock laboratory opened a vertical fracture zone at a depth of 70 m this provides an opportunity to study geochemical changes resulting from shallow water inflow into a crystalline bedrock aquifer as anticipated during construction and operation of a deep repository for spent nuclear fuel chloride ion is a natural conservative tracer for mixing between the dilute cl 10 mg l 1 shallow groundwater and the saline cl 5000 mg l 1 native groundwater of the fracture zone a sharp dilution front corresponding to 80 dilution of the native groundwater indicated arrival of shallow groundwater in the entrance tunnel after 3 weeks in spite of this large input of shallow water the fracture zone remains predominantly anoxic major element hydrochemistry and carbon and oxygen stable isotope data indicate large inputs of alkalinity and biogenic co2 g input of organic carbon with shallow groundwater provides a possible energy and carbon source for anaerobic respiration there is no evidence for sulfate reduction and fe iii oxyhydroxide fracture minerals are the only other dominant electron acceptor observed

the anatomy of a buried complex impact structure the mjolnir structure barents sea analysis of the prominent seismic disturbance at the 40 km diameter mjolnir impact structure based on an extensive seismic reflection database shows that the observed broad brimmed bowl shaped disturbance was formed as a result of the impact of an asteroid or comet during volgian berriasian time 149 141 m seismic mapping exhibits and visualizes a 850 1400 km3 disturbed volume and analysis of several structural features within the disturbance provides insight into major cratering processes such as brecciation and excavation melting gravitational collapse of the transient crater and structural uplift a transient crater of 16 km in diameter and 4 5 km in depth is determined from transient and final crater dimensions we obtain an estimate of the degree of gravitational collapse of the order of 2 5 considerably larger than the average expected values for typical terrestrial craters the extensive collapse took place by low angle decollement surfaces at the periphery and by chaotic debris mass flows toward the center furthermore we estimate the mjolnir projectile to have been 0 9 3 km in diameter and that the physical impact released energy in the range of 2 4 53 1020 j corresponding to an earthquake of magnitude 8 3 the mjolnir impact is not associated with a significant mass extinction however dissipation of the energy released during the mjolnir impact was sufficient to have caused several short term near field perturbations such as large amplitude tsunami waves affecting the barents sea region and possibly adjacent areas in the arctic

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

a methodology to interpret cross hole tests in a granite block water flow through low permeability fractured media is often concentrated in a small number of fractures this fractures need to be characterized in order to simulate accurately the hydraulic behaviour of such media we present a methodology to identify the most significant water conductive fractures the method is based on the interpretation of cross hole tests and is supported by geology geophysics and hydraulic data the methodology has been applied to the hydrogeological characterization of a granitic block around the febex experiment at the grimsel underground laboratory switzerland geology and geophysics are used for identifying candidates to flow controlling fractures single borehole hydraulic tests help in neglecting those with low transmissivity but the only means to assess connectivity consists of performing cross hole tests the resulting geometry is later implemented into a 3d finite element mesh where the fractures are simulated as 2d elements embedded into a 3d porous medium the latter includes the effect of minor fracturing and can be heterogeneous and anisotropic the resulting model is calibrated to obtain an integrated model this methodology has proven capable of reproducing single hole and cross hole tests and steady state heads and also of quantifying groundwater flow to the experimental area of the febex tunnel

impact origin of the chesapeake bay structure and the source of the north american tektites seismic profiles drill core samples and gravity data suggest that a complex impact crater 35 5 million years old and 90 kilometers in diameter is buried beneath the lower chesapeake bay the breccia that fills the structure contains evidence of shock metamorphism including impact melt breccias and multiple sets of planar deformation features shock lamellae in quartz and feldspar the age of the crater and the composition of some breccia clasts are consistent with the chesapeake bay impact structure being the source of the north american tektites

the terrestrial impact cratering record approximately 130 terrestrial hypervelocity impact craters are currently known due to variations in preservation and in geologic knowledge this sample is biased towards young x 20 km craters on the cratons of australia europe including the former u s s r and north america the rate of discovery of new craters is 3 5 craters per year although modified by erosion terrestrial impact craters exhibit the range of morphologies observed for craters on other terrestrial planetary bodies such as the moon terrestrial craters provide essential ground truth data on the geologic effects of impact and the subsurface structure of impact craters which can be used to constrain interpretations of lunar samples and models of crater formation due to erosion and its effects on form terrestrial craters are recognized primarily by the occurrence of shock metamorphic effects these include shatter cones microscopic planar deformation features solid state and fusion glasses high pressure polymorphs and whole rock melting and vaporization shock recovery experiments indicate that these features occur over shock pressures of 5 gpa to x 100 gpa terrestrial craters have a set of geophysical characteristics which are largely the result of the passage of a shock wave and impact induced fracturing they include gravity and magnetic lows and reductions in seismic velocity the gravity anomalies are seldom greater than 30 mgal due to the limiting effects of lithostatic pressure on fracturing at large complex craters the gravity signature may include a central relative gravity high due to uplift and short wavelength central magnetic anomalies due to a variety of processes much current work is focused on the effects of impact on earth evolution previous work on shock metamorphism and the contamination of impact melt rocks by meteoritic siderophile elements provides a basis for the interpretation of the physical and chemical evidence from cretaceous tertiary boundary sites as resulting from a major impact suggestions that other biological boundaries in the stratigraphie record are due to periodic impacts are not supported by time series analysis of the terrestrial cratering record by analogy with the lunar record and modelling of the effects of very large impacts it has been proposed that biological and atmospheric evolution of the earth could not stabilize before the end of the late heavy bombardment 3 8 ga ago the present terrestrial cratering rate is 5 4 2 7 10 15 km 2a 1 for a diameter 20 km this represents a local threat on historic time scales on a global scale a major impact sufficient to cripple human civilization severely will occur on time scales of 106 a

seismic response of major regional unconformities in atlantic coastal plain sediments at smith point virginia as part of an evaluation of the acoustic response of relatively unconsolidated sediments of cretaceous and younger age beneath the atlantic coastal plain a seismic reflection survey was conducted in northumberland county smith point virginia the seismic data were acquired by the vp1 su vibroseis crew using a single y 1100 vibrator the survey area is on the flank of a negative gravity anomaly centered east of smith point and covering much of chesapeake bay the purpose of the study was to confirm the depth to and the nature of acoustic basement and to investigate the continuity of reflectors in the overlying sedimentary sequence seismic and drill hole data from many sites in the northern virginia and maryland area provided a generalized stratigraphy from which to interpret the seismic data seismic data indicate an average basement depth of 950 m data quality is sufficient to identify two normal basement faults with displacements of 40 m and 15 m bounding a tilted basement fault block the presence of a large negative gravity anomaly and the known high heat flow 64 9 mw m 2 at this location suggest that the basement rock type is granite analysis of velocity spectra reveals the presence of an indurated unit 90 m thick of triassic age overlying crystalline basement shallow reflections marking regional eocene and cretaceous unconformities can be correlated with lithostratigraphy at three drill sites in northumberland county

deep sea drilling project site 612 bolide event new evidence of a late eocene impact wave deposit and a possible impact site u s east coast a remarkable 60 m thick upward fining polymictic marine boulder bed is distributed over 15 000 km sup 2 beneath chesapeake bay and the surrounding middle atlantic coastal plain and inner continental shelf the wide varieties of clast lithologies and microfossil assemblages were derived from at least seven known cretaceous paleocene and eocene stratigraphic units the supporting pebbly matrix contains variably mixed assemblages of microfossils from the same seven stratigraphic units along with trace quantities of impact ejecta tektite glass and shocked quartz the youngest microfossils in the boulder bed are of early late eocene age on the basis of its unusual characteristics and its stratigraphic equivalence to a layer of impact ejecta at deep sea drilling project dsdp site 612 new jersey continental slope the authors postulate that this boulder bed was formed by a powerful bolide generated wave train that scoured the ancient inner shelf and coastal plain of southeastern virginia the most promising candidate for the bolide impact site identified on seismic reflection profiles is 40 km north northwest of dsdp site 612 on the new jersey outer continental shelf

understanding the patterns of biological response to physical forcing in the alboran sea western mediterranean 1 a singular value decomposition svd analysis was performed to determine the coupled modes of variability of satellite surface chlorophyll chl and absolute dynamic topography adt data for the alboran sea western mediterranean during a 12 year period 1998 2009 from this analysis we have been able to detect features of the alboran sea dynamics that had not been recognized in previous research on the primary production of this basin we have found that the two leading svd modes represent more than 97 of the total squared covariance the first mode is associated with the inverse barometer and its impact on chlorophyll distribution whereas the second physical mode can explain the distribution of eutrophic and oligotrophic waters in the alboran sea the results also confirm that the phytoplankton in the basin is very tightly controlled by meteorological and physical processes via the advection of properties through the strait by the influence of atlantic jet intensity which controls the gyres of the basin and by the activation of up or down welling coastal processes by wind

rare earth elements ree in deep groundwater from granite and fracture filling calcite in the tono area central japan prediction of ree fractionation in paleo to present day groundwater rare earth elements rees combined with yttrium yree in deep groundwater from granite and fracture filling calcite are being studied at the mizunami underground research laboratory miu tono area central japan the groundwater was sampled from cored boreholes drilled from the miu galleries at 200 300 400 and 500 m depths the fracture filling calcite was collected from the same boreholes and dissolved in 1 m nh4 acetate buffer solution ph 4 8 major chemical composition of groundwater changed with depth and the concentrations of some major elements na k ca2 mg2 cl br and b increased with depth while alkalinity so42 and f decreased isotopic compositions of 18o and d indicated that the groundwater originated from meteoric water yree patterns of groundwater also changed with depth with heavy ree hree enrichment in shallow groundwater 200 to 400 m and light ree lree enrichment in deep groundwater 500 m the predominant yree species are yreeco3 and yree co3 2 laco3 65 70 la co3 2 8 27 luco3 20 38 and lu co3 2 53 77 the lree enrichment in the shallow groundwater resulted in preferential scavenging of positively charged yreeco3 by negatively charged bedrock surfaces in slightly alkaline groundwater ph 7 4 8 6 because of the construction and operation of the underground facility the shallow groundwater has been influenced by infiltration of surface water undersaturated in calcite in contrast the deep groundwater was barely affected by the mixing of surface water indicating that the yree originated from yree fractionation by bedrock granite irrespective of depth a negative ce anomaly preserved in the groundwater is probably indicative of paleo oxic conditions during paleo recharge the negative ce anomaly in the groundwater was possibly fractionated from sedimentary calcite with positive ce anomalies during the paleo recharge the yree patterns of the fracture filling calcite were enriched in lree the isotopic variations of 18o and 13c in the fracture filling calcite indicated that it originated from a mixture of sea water and fresh water at a temperature 100 c the yree patterns of paleo groundwater from which the fracture calcite precipitated were calculated using yree abundances in the fracture calcite and distribution coefficient reported in previous laboratory experiments the paleo groundwater was found to be enriched in lree and hree depending on the aqueous yree species our results suggest that changes in the paleo to present day yree fractionation range roughly from that of present day shallow to deep groundwater

influence of reaction kinetics and mesh refinement on the numerical modelling of concrete clay interactions large quantities of cements and concretes need to be incorporated in geological disposal facilities for long lived radwaste an alkaline plume diffusing from an aged concrete ph 12 5 through argillite type rocks has been modelled considering feedback of porosity value variations on transport properties using the reactive transport code toughreact the mineralogical composition of the argillite is modified at the interface with the concrete diffusion of cementitious elements leads to rapid and strong porosity occlusion in the argillite numerical results show that both reaction rates and spatial refinement affect mineralogical transformation pathways the variations in porosity and the extension of the zone affected by the alkaline perturbation are compared at different times the major effects of mineral precipitation under kinetic constraints rather than local equilibrium are a delay in the porosity clogging and an increase in the extension of the alkaline perturbation in the clay formation the same time delay rise for the porosity occlusion also appears for the roughest spatial resolutions a simulation as representative as possible of temporal and spatial scales of cementation processes must then be supported by more comparative data such as long term experimental investigations or natural analogues

numerical simulations of the mjolnir marine impact crater 1 the 40 km diameter mjolnir crater in the barents sea was created by a meteoroid impact into a 400 m shallow sea about 142 ma we have used a multimaterial hydrocode with depth depending target strength to model numerically the cratering and early modification stages of the mjolnir impact our models are constrained by the observed crater morphology and structure the best results were obtained for a composite target strength structure very low strength for the upper 3 km of sedimentary rocks and gradual increase from 3 to 6 5 km depth before using strength values typical for granitic rocks at greater depths the low strength of the target sediments at shallow depths led to exceptionally intensive slumping and gravitational collapse of the order of 2 0 2 5 considerably larger than the average expected values for typical terrestrial craters as a result we obtain a crater collapse in between simple and complex where slumping and gravitational collapse counteract the crater floor uplift and lead to suppression and burial of the central high the mjolnir impact in a shallow sea was responsible for a major disturbance of the water column following the impact induced outward water surge large amplitude tsunamis were formed and the rapid resurge of seawater into the excavated crater transported large amounts of ejecta and crater wall material back into the crater accounting for the redestribution of ejecta material and extensive infilling

hydrology of yucca mountain nevada yucca mountain located in southern nevada in the mojave desert is being considered as a geologic repository for high level radioactive waste although the site is arid previous studies indicate net infiltration rates of 5 10 mm yr 1 under current climate conditions unsaturated flow of water through the mountain generally is vertical and rapid through the fractures of the welded tuffs and slow through the matrix of the nonwelded tuffs the vitric zeolitic boundary of the nonwelded tuffs below the potential repository where it exists causes perching and substantial lateral flow that eventually flows through faults near the eastern edge of the potential repository and recharges the underlying groundwater system fast pathways are located where water flows relatively quickly through the unsaturated zone to the water table for the bulk of the water a large part of the travel time from land surface to the potential repository horizon 300 m below land surface is through the interlayered low fracture density nonwelded tuff where flow is predominately through the matrix the unsaturated zone at yucca mountain is being modeled using a three dimensional dual continuum numerical model to predict the results of measurements and observations in new boreholes and excavations the interaction between experimentalists and modelers is providing confidence in the conceptual model and the numerical model and is providing researchers with the ability to plan further testing and to evaluate the usefulness or necessity of further data collection

meteoroid mayhem in ole virginny source of the north american tektite strewn field new seismic reflection data from chesapeake bay reveal a buried 85 km wide 1 5 2 0 km deep peak ring impact crater carved through upper eocene to lower cretaceous sedimentary strata and into underlying pre mesozoic crystalline basement rocks a polymictic late eocene impact breccia composed mainly of locally derived sedimentary debris determined from four continuous cores surrounds and partly fills the crater structural and sedimentary characteristics of the chesapeake bay crater closely resemble those of the miocene ries peakring crater in southern germany we speculate that the chesapeake bay crater is the source of the north american tektite strewn field

dynamic changes in hydrogeochemical conditions caused by tunnel excavation at the aspo hard rock laboratory hrl sweden abstract hydraulic changes caused by tunneling at the aspo hard rock laboratory hrl in sweden have been investigated over a period of 2a using different hydrochemical approaches i e noble gas content isotopic measurements and major ion concentrations the dissolved noble gases 4he and ne contents and the ratio of 3he 4he 40ar 36ar stable isotopes chemical concentrations of major ions and 36cl cl ratios were determined in groundwater samples collected in the tunnel from borehole sections isolated by inflated packers groundwater was categorized into 3 groups based on 4he and cl contents undisturbed groundwater i e prior to tunnel construction with high 4he and cl contents groundwater that has been gradually changed by mixing with baltic seawater and whose 4he and cl contents have gradually increased with increasing depth and groundwater that has been totally changed due to a rapid mixing of baltic seawater and or shallow groundwater and whose 4he and cl contents are extremely low compared with other samples collected at the same surrounding depth the oldest groundwater with a high salinity of more than 14 000 mg l 1 of cl is estimated to be more than 1 8 ma old the groundwater residence time ranges from 0 9 to 900 ka in the mixing zone groundwater in the disturbed zone where rapid mixing has occurred is hard to date reliably and its primary hydrochemical character has already been lost