sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

gravity gradiometry resurfaces the red october was heading southwest on gorshkov s railroad his speed was thirteen knots installed in the keel was a highly sensitive device called a gradiometer essentially two large lead weights separated by a space of one hundred yards a laser computer system measured the space between the weights down to a fraction of an angstrom distortion of that distance or lateral movement of the weights indicated variations in the local gravitational field with careful use of gravitometers he could plot the vessel s location to within a hundred meters

reliability of subtidal sediments as geochemical recorders of pollution input san simon bay ria de vigo nw spain the concentrations of both major and trace elements in san simon bay s subtidal sediments were determined for the purposes of 1 evaluating the influence of anthropogenic activities on metal content against pre anthropogenic background values attained via the deepest core samples 2 establishing the subtidal sediments degrees of pollution in recent decades and 3 determining the influence of mussel raft systems on the composition of bottom sediments subtidal sediments consist of laminated organic rich fine grained sediments with low carbonate content and a notable presence of gas in their lower part the recent sedimentary record revealed pollution mainly from pb and cu rising toward the sediment surface the sources of various heavy metals were accordingly identified with the application of principal component analysis to discriminate among the different metal sources it has been found that the mineralogy of the catchment area determines the overall composition whereas biogenic production and anthropogenic activities contribute to the total metal content at the same time mariculture influences the composition of underlying sea bottom sediments by changing the inorganic carbon content finally evidence is provided to show how sediment composition is tied mainly to aquaculture and watershed characteristics via conditioning by anthropogenic activities

the spatial distribution and source of arsenic copper tin and zinc within the surface sediments of the fal estuary cornwall uk abstract estuarine sediments commonly form major sinks for contaminants released during industrial activity many industrial processes lead to the release of metals initially in solution which can then be adsorbed on to for example fe hydroxides or clay minerals however in the mining industry there are two major contaminant waste streams 1 metals discharged in solution via mine drainage and 2 particulate grains of the ore forming or related minerals released after ore processing the release of particulate waste can have a major long term impact on environmental geochemistry in this study we have mapped the distribution of arsenic copper tin and zinc within the surficial sediments of the fal estuary cornwall uk an area that drains a historically important polymetallic mining district there are clear spatial variations in the contaminants with the highest levels 2800 p p m as 5000 p p m cu 3000 p p m sn and 6000 p p m zn within restronguet creek on the western side of the estuary mineralogical studies show that small 20 m grains of detrital arsenopyrite chalcopyrite cassiterite and sphalerite are very abundant within the surface sediments most of the sulphide grains are fractured but mineralogically unaltered although some grains show alteration rims caused by oxidation of the sulphides the geochemistry and mineralogy are indicative of sediment supply from the discharge of particulate waste into the estuary during historical mining activity subsequently this particulate waste has been largely physically and biologically reworked within the surface sediments although considerable effort has been made to minimize contaminants released via mine drainage into the estuary the potential flux of contaminants present within the intertidal and subtidal sediments has not been addressed benthic invertebrates living within the area have adapted to be metal tolerant and it is likely that the dominant source of bioavailable metals is a result of alteration of the particulate mine waste present within the intertidal and subtidal sediments

relative sea level rise and climate change over the last 1500 years we constructed a detailed relative sea level rise curve for the last 1500 years using a novel approach i e charting the rate of relative sea level rise using microfaunal and geochemical data from a coastal salt marsh sequence clinton ct usa the composition of benthic foraminiferal assemblages and the iron abundance in peats were used to describe shifts in marsh environment through time quantitatively the resulting sea level rise curve with age control from 14c dating and the onset of anthropogenic metal pollution shows strong increases in the rate of relative sea level rise during modern global warming since the late nineteenth century but not during the little climate optimum ad 1000 1300 there was virtually no rise in sea level during the little ice age ad 1400 1700 most of the relative sea level rise over the last 1200 years in clinton appears to have occurred during two warm episodes that jointly lasted less than 600 years changes from slow to fast rates of relative sea level rise apparently occurred over periods of only a few decades we suggest that changes in ocean circulation could contribute to the sudden increases in the rate of relative sea level rise along the northeastern usa seaboard relative sea level rise in that area is currently faster than the worldwide average which may result partially from an ocean surface effect caused by hydrodynamics our data show no unequivocal correlation between warm periods on a decaal to centennial time scale and accelerated sea level rise one period of acclerated sea level rise may have occurred between about ad 1200 and 1450 which was the transition for the little climate optimum to the little ice age i e a period of cooling at least in northwestern europe local changes in tidal range might also have contributed to this apparent increase in the rate of relative sea level however the second period of accelerated sea level rise occurred during the period of modern global warming that started at the end of the last century

sedimentological characteristics heavy metal distribution and magnetic properties in subtidal sediments ria de pontevedra nw spain the rias of nw spain are coastal ecosystems of high biological productivity and great economic importance they are intensively exploited by man for fish and shellfish there are a number of important centres of population and industrial activity along their margins which serve as sources of contamination in this context it is desirable to achieve the best possible understanding of the physico chemical processes that control spatial and temporal variations in the geochemical mineralogical and sedimentological characteristics of near surface sediments in the ria de pontevedra and in particular the distribution and mobility of heavy metal contaminants thus adequate environmental planning can be achieved for this site and understanding gained for comparable contexts core samples were examined from the inner middle and outer parts of the ria grain size distributions reflect the presence of two main populations one dominated by silt and clay derived mainly from terrestrial sources and the other by fine sand to coarse silt which is derived mainly from continental shelf and ria mouth sources mineralogical analysis shows an abundance of terrestrial intensive weathering products near the ria head a dominance of shelf derived sediment towards the mouth and the presence of several diagenetic minerals whose nature varies with location within the ria in the inner ria the near surface sediments are slightly enriched in pb cu and zn from anthropogenic sources these sediments are fine grained and have a high organic content hence they have a higher potential to sorb contaminants than the coarser grained less organic rich sediments of the mid and outer ria the estimated sedimentation rates for the fine grained organic rich sediments from the inner part of the ria are about 1 mm year 1 the dominant authigenic minerals in the inner ria are iron sulphides whereas in the mid and outer ria iron silicates and oxyhydroxides are more important these differences in authigenic iron mineralogy are clearly reflected by the magnetic properties of the sediments

metalliferous mining geophysics state of the art after a decade in the new millennium mining exploration was very active during the first decade of the twenty first century because there were numerous advances in the science and technology that geophysicists were using for mineral exploration development came from different sources instrumentation improvements new numerical algorithms and cross fertilization with the seismic industry in gravity gradiometry kept its promise and is on the cusp of becoming a key technology for mining exploration in potential field methods in general numerous techniques have been developed for automatic interpretation and 3d inversion schemes came into frequent use these inversions will have even greater use when geologic constraints can be applied easily in airborne electromagnetic em methods the development of time domain helicopter em systems changed the industry in parallel improvements in em modeling and interpretation occurred in particular the strengths and weaknesses of the various algorithms became better understood simpler imaging schemes came into standard use whereas layered inversion seldom is used in the mining industry today improvements in ground em methods were associated with the development of squid technology and distributed acquisition systems the latter also impacted ground induced polarization ip methods developments in borehole geophysics for mining and exploration were numerous borehole logging to measure physical properties received significant interest perhaps one reason for that interest was the desire to develop links between geophysical and geologic results which also is a topic of great importance to mining geologists and geophysicists

ultrasonic velocity survey in callovo oxfordian argillaceous rock during shaft excavation the excavation of a deep underground structure induces a stress field redistribution that could create an excavation damaged zone edz the study of the edz is important in the framework of nuclear waste storage where such edz could constitute a preferential pathway of stored material towards the biosphere analysis of ultrasonic wave propagation across the rock media around the excavation is one technique that can be used to characterize such zones this method has been applied in the meuse haute marne underground research laboratory url in france to characterize the initialization and evolution of damage around the url access shaft to achieve this a device comprising 21 ultrasonic sensors was spread out at different distances from the shaft wall at depths between 465 and 475 m a transversely isotropic model enabled the measured experimental velocities on each ray path during shaft excavation to be integrated the results highlighted the initialization and extension of the damage as the shaft front proceeded they also showed a polarization of the velocity field and an oscillation of the transversal isotropy with a preferential orientation of the stress release and the microcracking monitoring of the velocity field also highlighted some significantly different behaviour linked to the complex mechanical behaviour of the argillaceous rock

aseismic mining subsidence in an abandoned mine influence factors and consequences for post mining risk management in the lorraine area of eastern france decades of iron ore mining from 1850 to 1997 have left vast underground cavities beneath or in the vicinity of urban areas several major collapses occurred in the southern part of this iron ore basin in the 1990s after the mine closure and the flooding of underground mine workings following these large scale collapses the french government initiated a strategy of post mining risk management to prevent and control risks associated with these ground failures the high risk zones are secured either by reducing the vulnerability while the moderate risk zones are monitored for public safety purposes by using in situ monitoring this monitoring relies mainly on real time microseismic systems to detect precursors to a rapid large scale collapse after the progressive closing and then flooding of the northern iron basin ending in 2008 subsidence was observed in a town of the lorraine basin in autumn of 2009 however this local subsidence with a low velocity of few centimeters per month was not clearly detected by the borehole microseismic monitoring station located nearby only some microseismic events were recorded which could not be unambiguously related to the beginning of the subsidence event to better understand this lack of microseismic precursor a geophysical investigation was launched a calibration blast experiment was carried out from a remaining old underground access in order to answer to the following questions 1 what is the seismic wave attenuation field 2 what is the minimum source power that can be detected by the sensors 3 what is the impact of the geology the faults corridor and the integral pillar extraction zone on the wave propagation field the results of this study show strong anelastic attenuation of the seismic waves though the monitored overburden most likely related to the extensive fault system intersecting the study site strong attenuation might explain the lack of detected microseismicity during the subsidence event in order to clarify this issue a mobile gps monitoring system was designed and tested to address this type of situation in future

sediment transport pathways in a dredged ria system southwest england abstract the fowey ria system southwest england comprises the river fowey catchment the fowey estuary the cliffs and bays adjacent to the ria mouth and part of the inner continental shelf of the english channel previously large quantities of sediment were introduced into the upper ria by ore mining activity today in common with other rias the fowey receives a low riverine sediment input material from maintenance dredging in the lower ria is dumped in a spoil ground outside the ria mouth the sediments of the system are investigated using an integrated approach to determine sediment distribution and sediment transport pathways surface sediments are analysed for grain size and mineralogy grain size trend analysis is used to examine sediment dispersal patterns away from the locus of deposition in the spoil ground archived data are used to investigate the seabed morphology and to determine long term 100 year bathymetric changes within the ria mixing of sediment from several sources occurs in the upper reaches riverine and locally eroded sediment is transported seawards towards the main area of commercial activity sand and finer grained material moves into the ria from offshore the bed of the inner continental shelf comprises interfluves covered by a thin veneer of sediment with a natural composition of locally derived lithic fragments and biogenic material the area is mainly low non depositional in character except within the partially infilled palaeovalley and its tributaries sediments dumped in the spoil ground disperse in a complex pattern coarse grained material is moved by the action of waves and tidal currents towards the southwest and northeast fine grained material is transported either to the east or the west depending upon the prevailing wave and tidal current regime because of its geomorphology the lower ria acts as an efficient sediment trap retaining a riverine material and sediment eroded from the upper reaches and b sediment entering the ria from offshore despite being subjected to major anthropogenic disturbance from past mining and present day dredging activities the fowey ria conforms to the general sediment model for southwest england rias castaing p guilcher a 1995 geomorphology and sedimentology of rias in perillo g m e ed geomorphology and sedimentology of estuaries developments in sedimentology no 53 elsevier science amsterdam pp 69 111 a conceptual model of sediment transport pathways for the fowey ria system is presented as the basis for further investigations

acoustic wave velocity and permeability evolution during pressure cycles on a thermally cracked granite abstract compressional waves velocity vp and water permeability k were measured during long term experiments in a high pressure vessel in the range 11 75 mpa for confining pressures and 10 70 mpa for pore pressures experiments were carried out on fractured granite specimens prepared by a controlled heating treatment at 510 c which generated thermal cracks a distinct effective pressure law was derived from the measurements within specific p c p p ranges for each of these properties data analysis emphasizes the differences in vp and k evolution during pressure cycles vp shows a regular increase during effective pressure increase but some crack lips sticking is thought to be responsible for the hysteresis found during the first stages of effective pressure decrease k decreases exponentially with effective pressure increase whereas during effective pressure decrease k values are systematically lower which attest to irreversible changes in the connected crack network likely to be the result of irreversible crack closure of a subset of cracks such study of the simultaneous evolution of physical properties of the rocks as a function of the applied stresses is relevant for man induced applications like radioactive waste disposal where perturbations of the environmental stresses may modify the rock structure thus leading to changes in mechanical or transport properties of the host rock

diagenesis in anoxic sediments from the california continental borderland and its influence on iron sulfur and magnetite behavior solid phase and pore water profiles of compounds containing iron and sulfur have been determined by wet chemical magnetic and x ray diffraction techniques in three california continental borderland basins the observed profiles have been fit by simple reaction diffusion models in order to determine reaction rates and constrain budgets for iron and sulfur more than 95 of the solid phase reduced sulfur is pyrite and down core profiles are well fit by a model in which net sulfate reduction rates decrease exponentially with depth net sulfate reduction rates determined from models fit to solid phase reduced sulfur measurements and pore water sulfate profiles yield results that are consistent depth integrated sulfate reduction rates for modern sediments in san pedro santa catalina and san nicolas basins are 11 4 6 3 and 6 3 8 8 mol cm 2yr 1 respectively measurements of solid phase iron species indicate that surficial sediments are enriched in easily reducible ferric oxyhydroxides the enrichment is maintained by a combination of oxidation of fe2 diffusing upward from underlying anoxic sediments as well as input of fresh sediment enriched in ferric oxyhydroxides the three primary sources for iron converted to pyrite and the sequence in which they are utilized are ferric oxyhydroxides magnetite and other crystalline oxides and exchangeable iron in phyllosilicates the majority 50 80 of the iron converted to pyrite is from the silicates and budgetary calculations indicate the amount of iron released from san pedro basin silicates agrees within 35 with the amount of magnesium removed from pore water to solid phases fe2 is enriched in near surface pore waters because rates of dissolved iron production by oxyhydroxide reduction exceed rates of sulfate reduction and pyrite formation at depth pore waters are sulfidic because rates of sulfate reduction exceed rates of iron release from silicates sulfide produced at depth diffuses upward until it reaches sediments with available iron causing a step like increase in solid phase sulfur concentration over 90 of the magnetite present in surficial sediments is dissolved at depth due to reaction with h2s a model is developed to predict the depth at which magnetite dissolution should occur based on sulfate reduction rates and the flux of ferric oxyhydroxides the results of this model predict the onset of dissolution at depths of 5 40 cm in different basins and agree well with the observed depths of magnetite dissolution

a study of cut blasting for one step raise excavation based on numerical simulation and field blast tests abstract over the past several decades raise excavation has been widely employed in underground mining civil engineering and military engineering one step raise excavation with burn cuts where all the boreholes are pre drilled and detonated at one time and no workers need to be underneath the freshly blasted and dangerous ground is an important and promising method in raise excavation cut parameters especially the parameters of prime cut which used empty hole as a free surface and swelling space have significant influence on the effect of raise formed in this study two small scale experimental methods spiral hole spacing method and observation hole method are designed to determine the prime cut parameters such as hole spacing l stemming length ls1 ls2 and air deck length la which are normally determined by empirical formula in order to study the feasibility of the two methods numerical analysis and experimental tests are conducted in v zone of sandaozhuang molybdenum mine smm in which there are large numbers of underground goafs need to be controlled by filled raise the riedel hiermaier thoma rht material model which considers compression damage and tension damage effect under blasting loading is employed in the ls dyna software to study the rock damage zone meanwhile the field tests are carried out according to the two small scale experimental methods the comparison results show that the damage zone of numerical simulation has a good agreement with the experimental data further the optimal prime cut parameters obtained from experimental tests are applied in one step filled raise excavation and a 23 m raise that meets the design requirements is formed through the proposed technology the results indicate that these cut parameters determined by the small scale experiments are suited for one step raise excavation this study can provide two simple field experiments to determine the important prime cut parameters of one step raise excavation

geochemical and mineralogical characterization of surficial sediments from the northern rias implications for sediment provenance and impact of the source rocks abstract a multidisciplinary study of the elemental geochemistry and mineralogical characteristics of the marine surficial sediment in the northern rias nw iberian peninsula has been carried out the linkages between the marine sediment composition and their potential sources were examined the influence of the river borne sediments is only detected in the innermost part of the three rias regional variations of the mineral assemblages are governed by the source rock composition of the different geological complexes and the relative source rock contribution controlled by the continental hydrology mineralogical composition of the ortigueira ria and adjacent shelf surficial sediments are mainly made up of mafic and ultramafic rocks of the cape ortegal complex indicated by the high content of mg mn and chrysotile and riebeckite minerals in areas nearby ortegal complex the imprint of heavy minerals present in the surrounding rocks has also been recorded barqueiro and viveiro rias bed sediments are influenced by granitic and metamorphic rocks from the ollo de sapo complex as revealed by the high contribution of muscovite and quartz mining activities in the continental domain left strong imprints on marine surficial sediments pyrite content is high in the innermost areas of the ortigueira ria since this mineral is exploited in the mera river basin whereas high muscovite percentages characterize the viveiro ria owing to the abundance of granitic rocks and its exploitation in the landro river basin quartz content is high nearby cape estaca de bares induced by the presence of an important excavation of this material

eigenvector analysis of gravity gradient tensor to locate geologic bodies we have developed a new method to locate geologic bodies using the gravity gradient tensor the eigenvectors of the symmetric gravity gradient tensor can be used to estimate the position of the source body as well as its strike direction for a given measurement point the eigenvector corresponding to the maximum eigenvalue points approximately toward the center of mass of the causative body for a collection of measurement points a robust least squares procedure is used to estimate the source point as the point that has the smallest sum of square distances to the lines defined by the eigenvectors and the measurement positions it s assumed that the maximum of the first vertical derivative of the vertical component of gravity vector gzz is approximately located above the center of mass observation points enclosed in a square window centered at the maximum of gzz are used to estimate the source location by increasing the size of the window the number of eigenvectors used in the robust least squares and

consistency investigation vertical gravity estimation and inversion of airborne gravity gradient data a case study from northern sweden for airborne gravity gradient data it is a challenge to distinguish between high frequency intrinsic and dynamically produced noise caused by the aircraft and small scale effects from shallow dens

a simple three dimensional model of diffusion with precipitation applied to localised pyrite formation in framboids fossils and detrital iron minerals a three dimensional diffusion with precipitation model is constructed to estimate radial variations in the amounts of pyrite which precipitate where a spherical mass of organic matter producing h2s by sulphate reduction is enveloped in a dissolved iron bearing porewater the model indicates that higher rates of sulphate reduction more readily metabolisable organic matter and larger organic masses require increasingly high dissolved iron concentrations in order to confine pyrite or iron sulphide precipitation to the decay site the maximum size sphere of exceedingly metabolisable organic matter equivalent to fresh planktonic material which can be pyritised is about 50 m radius where decay occurs in porewaters with typical dissolved iron levels this radius is close to the maximum radius of framboidal pyrite the formation of which could involve model type processes fossil carcases although mainly composed of less readily metabolisable organic matter may be orders of magnitude larger and the model demonstrates that their pyritisation requires unusually high porewater dissolved iron concentrations these inferred chemical conditions are consistent with sedimentological observations of pyritisation in beecher s trilobite bed new york state at greater depths within the sediment pyritisation is controlled by the kinetics of iron mineral reactivity towards h2s sediments vary widely in their exposure times to h2s which can range at least from 50 to 106 years at low exposure times only iron oxides are pyritised whereas at high exposure times even the most refractory iron silicates can become pyritised

appraisal of waveform repeatability for crosshole and hole to tunnel seismic monitoring of radioactive waste repositories countries worldwide are seeking solutions for the permanent removal of high level radioactive waste from the environment surrounding the waste with multiple engineered barriers and emplacement in deep geological repositories is widely accepted as a safe means of isolating it from the biosphere for the necessary 105 106 years as a precautionary measure society demands that repositories be monitored for 100 300 years after they are backfilled and sealed effective monitoring that does not compromise the engineered and natural barriers is challenging to address this issue we investigate the viability of crosshole and hole to tunnel seismic methods for remotely monitoring high level radioactive waste repositories measurements are made at two underground rock laboratories in switzerland one within granitic rock and one within clay rich sediments numerical simulations demonstrate that temporal changes of the monitored features i e bentonite plug excavation damage zone sand filled microtunnel sh

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

degree of pyritization of iron as a paleoenvironmental indicator of bottom water oxygenation abstract a new method is presented for recognizing the degree of bottom water oxygenation in organic carbon bearing rock the method uses the parameter degree of pyritization dop which is the ratio of pyritic fe to pyritic fe acid soluble fe sediments with ages ranging from devonian to cretaceous have been classified on paleoecological and sedimentological criteria as having been deposited in aerobic conditions deposited in fully oxygenated bottom waters restricted marine conditions deposited in waters with low oxygen concentrations or inhospitable bottom conditions where little or no oxygen is present and h2s may be continually or intermittently present aerobic dop

high resolution velocity field imaging around a borehole excavation damaged zone characterization the excavation of a deep underground structure induces stress field redistribution that creates an excavation damaged zone edz the study of edz physical properties is of prime importance in the framework of nuclear waste geologic storage where edz constitutes a preferential pathway for storage materials toward the biosphere a probe for measuring the ultrasonic velocity field around a cylindrical excavation zone has been developed the probe uses pzt transducers operating at 150 khz to collect all required data with high accuracy and minimum effort the probe is fully monitored for automatic data acquisition also a numerical inversion method reconstructs a stress field using the measured velocity field this method was partially validated in the laboratory on a multilayer test bed following laboratory tests and probe development an in situ experiment was performed in the meuse haute marne underground research laboratory france to assess the safety of nuclear waste storage in the callovo oxfordian argillaceous layer the damaged zone extends up to 0 175 diameter of depth with an anisotropic damage pattern oriented according to the regional stress field the results show the potential of the method to forecast damage of similar larger structures

seismic monitoring of radioactive waste repositories abstractsafe isolation of high level radioactive waste hlw and spent nuclear fuel sf from the biosphere is an important concern for humanity many countries consider monitoring the evolving conditions of a hlw sf repository over a long period noninvasively in such a way as to not compromise the sealing of the repository remote active seismic methods are possible options we performed extensive seismic measurements at the mont terri rock laboratory located within a clay formation that is a potential host rock in the swiss hlw sf program a scaled down hlw sf repository was simulated as a 13 m long microtunnel of 1 m diameter the dry sand filled microtunnel was progressively water saturated and slightly overpressured the monitoring system consisted of a pressure seismic source and a hydrophone cable located in two boreholes drilled perpendicular to the microtunnel and eight geophones equally distributed around the periphery of the microtunnel nonlinear anisotropic tomography of crosshole traveltim

the assessment of damage around critical engineering structures using induced seismicity and ultrasonic techniques two large diameter boreholes have been excavated vertically from the floor of a tunnel at the aspo hard rock laboratory sweden the two deposition holes will have simulated high level radioactive waste canisters installed in them in an experiment undertaken to test the retrievability of waste from a proposed repository induced seismicity and other acoustic monitoring techniques have been used to investigate the excavation damaged zone edz around the two holes high frequency acoustic emission ae monitoring has been used to delineate regions of stress induced microfracturing on the millimetre scale this has been shown to locate in clusters around the perimeter of the deposition hole at azimuths orthogonal to the far field maximum principal stress three dimensional velocity surveys have been conducted along ray paths that pass through the damaged region and through a stress disturbed zone around the excavation induced microfracturing and stress disturbance have been observed as sharp decreases in velocity as the excavation proceeds through the rock mass the combination of the high resolution velocity measurements and the ae source locations has allowed the linking of the velocity measurements to a volume of excavation damaged rock this has provided a quantitative estimate of the effect of the edz on the rock mass

early diagenesis of organic matter rich sediments in a ria environment organic matter sources pyrites morphology and limitation of pyritization at depth abstract the subtidal sediments of the inner ria de vigo nw spain are fine grained rich in organic matter and accumulate at rates of around 3 mm yr redoxomorphic pyrites formation was studied in four sediment cores four operationally defined iron fractions were determined hcl extracted silicate bound organic and pyritic and the dimensions and morphology of pyrites which mainly occurred as isolated framboids 3 5 m in diameter were studied by sem sediment appearance and degree of pyritization dop identified an oxic zone limited to the top few millimetres a suboxic zone that in most cores was just a few decimetres thick the exception was a core obtained in an area of strong turbulent currents and an underlying anoxic zone with dop values of around 60 pyritic iron increased at the expense of the hcl extracted fraction in approximately the top metre but no further pyrite formation occurred at greater depths pyrite formation in these lower levels was not limited by lack of either hcl extracted iron or metabolizable organic matter but apparently by lack of sulphate ion the diffusion of which to these depths was probably prevented by the fine texture of the sediments our findings highlight the interest of studying transitional sedimentary environments in order to explore in detail the geochemical parameters controlling pyrite formation

noise reduction through joint processing of gravity and gravity gradient data in mineral and oil exploration gravity gradient data can help to delineate small scale features that cannot be retrieved from gravity measurements removing high frequency noise while preserving the high frequency real signal is one of the most challenging tasks associated with gravity gradiometry data processing we present a method to reduce gravity and gravity gradient data noise when both are measured in the same area based on a least squares simultaneous inversion of observations and physical constraints inferred from the gravity gradient tensor definition and its mathematical properties instead of handling profiles individually our noise reduction method uses simultaneously measured values of the tensor components and of gravity in the whole survey area benefiting from all available information synthetic examples show that more than half of the random noise can be removed from all tensor components and nearly all the noise from the gravity anomaly without altering the high frequency information we apply our method to a set of marine gravity gradiometry data acquired by bell geospace in the faroe shetland basin to demonstrate its power to resolve small scale features

chemostratigraphic and lithostratigraphic signatures of the anthropocene in estuarine areas from the eastern cantabrian coast n spain abstract a range of chemostratigraphic and lithostratigraphic markers of human impacts can be recorded in four estuaries located in the eastern cantabrian coast northern spain metal enriched levels and stable pb isotopic ratios in dated sediment cores allowed the recognition of an ancient local episode of pb contamination associated with mining activities during roman times as well as the widespread fingerprint of the industrial revolution and the great acceleration of human pressure after the second world war micropalaeontological data variations in foraminiferal assemblages provided key information to identify agricultural soils in previously reclaimed and currently regenerated salt marshes whereas anthropogenic beachrocks offered an example of the incorporation of technofossils to the coastal sedimentary record

from space to lithosphere inversion of the goce gravity gradients supply to the earth s interior study the emergence of high resolution satellite measurements of the gravitational field goce mission offers promising perspectives for the study of the earth s interior these new data call for the development of innovant analysis and interpretation methods here we combine a forward prism computation with a bayesian resolution approach to invert for these gravity gradient data configuration we apply and test our new method on satellite data configuration i e 225 km height with a global and homogeneous geographic distribution we first quantify the resolution of our method according to both data and parameteriza tion characteristics it appears that for reasonable density contrast values 0 1 g cm 3 crustal structures have to be wider than 28 km to be detectable in the goce signal deeper bodies are distinguishable for greater size 35 km size at 50 km depth 80 km at 300 km depth we invert the six tensor components among which five are independent by carefully testing each of them and their different combinations we enlighten a trade off between the recovery of data and the sensitivity to inversion parameters we particularly discussed this characteristic in terms of geometry of the synthetic model tested 2 plasman et al structures orientation 3 d geometry etc in terms of rms value each component is always better explained if inverted solely but the result is strongly affected by the inversion parameterization smoothing variances etc on the contrary the simultaneous inversion of several components displays a significant improvement for the global ten sor recovery more dependent on data than on density variance or on smoothness control comparing gravity and gradient inversions we highlight the superiority of the gg data to better reproduce the structures especially in terms of vertical location we succesfully test our method on a realistic case of a complex subduction case for both gradient and gravity data while the imaging of small crustal structures requires terrestrial gravity dataset the longest wavelength of the slab is well recovered with both data sets the precision and homogeneous coverage of goce data however counterbalance the heterogeneous and often quite nonexistance coverage of terrestrial gravity data this is particularly true in large areas which requires a coherent assemblage of heterogeneous data sets or in high relief vegetally covered and offshore zones

natural and anthropocene fluxes of trace elements in estuarine sediments of galician rias the anthropocene has been proposed as a new geo stratigraphic epoch where humans have become a global factor affecting the ecosystems estuarine sediments constitute a biogeochemical reservoir where trace elements tes from natural sources mix with a fraction generated by human activities this study assessed the natural lithogenic imprint of tes from uncontaminated sedimentary records to study anthropogenic changes sediment cores were sampled in the estuarine part of the low populated and low industrialized rias of ares a betanzos b and cedeira c which are located in the nw of the iberian peninsula cores were dated by the 210pb method covering up to the last century period sedimentation rates in mm yr 1 were 3 4 0 6 older than 1961 and 8 2 3 2 younger than 1961 for core a 0 9 0 2 1940 and 4 2 2 3 for core b and 13 4 1 4 for core c the background fluxes of tes were in the ranges of in g m 2 yr 1 50 560 for al and fe 20 320 for poc and 8 100 for ps and in mg m 2 yr 1 20 120 for as 0 2 2 0 for cd 7 110 for co 40 870 for cr 20 230 for cu 0 1 0 6 for hg 290 2800 for mn 4 24 for mo 20 410 for ni 20 150 for pb 60 800 for v and 70 700 for zn the three cores showed an anthropogenic influence since the mid 20th century the detected human impact during the anthropocene was due to the eume river damming and as pontes lignite mining the largest mine open pit in the iberian peninsula in core a by bridge road constructions vehicles emissions and river mouth urbanization in core b and changes in land use in core c sediment accumulation rates increased 2 4 core a and 4 7 times core b while tes fluxes increased 2 4 times in core a and between 3 6 and 5 1 times in core b pre industrial sedimentary records showed the lithogenic differences of the drainage basins mainly granitic watersheds for cores a and b and the prevalence of basic rocks of the ortegal geological complex for core c this explains the high concentrations and fluxes of cr ni and v of core c the different lithogenic imprints highlight the value of using local background references in contamination studies such as those on the anthropocene influence in estuaries which occurred after the spanish civil war in the studied rias

rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the california continental borderland the rock magnetic properties of marine sediments from the california continental borderland san pedro santa catalina and san nicolas basins have been studied in order to quantitatively assess the effects of sediment diagenesis on magnetic minerals previous studies have noted that the natural remanent magnetization in these sediments primarily carried by detrital magnetite decays to 10 or less of its surface value soon after deposition this decrease is caused by magnetite dissolution related to sediment diagenesis and is unrelated to paleoclimatic variations or changes in the regional influx of detrital magnetic material detailed rock magnetic measurements show that shifts to softer remanent coercivity and differences in the rate and degree of magnetic intensity loss with depth can be related to the dissolution process the shift to softer remanent coercivity is related to a coarsening of the magnetic mineral grain sizes with depth due to preferential dissolution of the finest grained magnetic material the intensity decreases which are linearly proportional to magnetite concentration decreases indicate that dissolution occurs with rate constants ranging from 0 3 to 1 6 kyr 1 the rate constants sulfide concentrations and magnetite grain size estimates from the borderland are consistant with previous studies of magnetite dissolution our results demonstrate the importance of both sulfide and magnetite surface area in the dissolution process anomalous peaks in viscous remanence within the sediments suggest the authigenic growth of greigite and its subsequent transformation to pyrite

a seeping sea floor in a ria environment ria de vigo nw spain the occurrence of gas accumulations in the ria de vigo nw spain have been characterized by the authors in previous research pockmarks frequently appear on seismic and sonar records covering ca 45 of the sea floor of the study area which indicates that gas expulsion is not an uncommon phenomena in the coastal ria environment here we report the occurrence of gas seepage for the first time along the coast of nw spain side scan sonar echo sounder and high resolution seismic techniques were used for mapping gas expulsion features some expulsion pockmarks sit over elongated features that represent bottom marks created by anthropogenic activity thus these anthropogenic sites may act as preferential venting zones for gas as well as being potential hazards on a muddy sea bed such as that of the ria where gas accumulates just below the surface of the sea floor

geochemistry and mineralogy of sediments and authigenic carbonates from the malta plateau strait of sicily central mediterranean relationships with mud fluid release from a mud volcano system a mud volcano field was recently discovered within the malta plateau in the strait of sicily central mediterranean sea box core sediments and associated authigenic carbonates have been collected in water depths of 140 170 m from two distinctive sectors of the area and analyzed for major trace and rare earth elements stable isotopes and mineralogy relative homogeneity in the mineralogy and geochemistry of bulk sediments and 210pb activity distributions argue against an active mud ejection activity in the malta plateau western sector the sediments show high concentrations of fe as sb and mo exceeding the background values estimated for the strait of sicily active fluid seepage in this area is thought to be responsible for these enrichments and for the formation of authigenic carbonate crusts evidence of bacterial involvement in carbonate mainly aragonite formation is recorded in the authigenic crusts which contain flat and spiralled filaments resembling beggiatoa like sulphide oxidising bacteria and biofilm like remains which occur inside the interspaces carbonate crusts consistently show extremely negative 13c values down to 49 that suggest contribution of carbon originating from anaerobic methane oxidation heavy oxygen isotopic compositions of the authigenic carbonates 2 3 higher than those in box core sediments are interpreted as due to precipitation from fluids enriched in 18o due to seepage of deep isotopically heavy relict messinian brines

accumulation of zn pb cu cr and ni in sediments between roots of the tagus estuary salt marshes portugal abstract sediment cores of 60 cm length were collected from two tagus estuary salt marshes at each salt marsh samples were taken from a non vegetated zone and one from each of areas dominated byhalimione portulacoides spartina maritimaandarthrocnemum fruticosum cores were slicedin situand at each sediment layer redox potential and ph were measured and the organic matter content loi grain size and concentrations of zn cu pb ni and cr were determined sediment between roots and non vegetated sediments of the same depth 5 15 cm were extracted with several acid solutions and the metal concentrations were compared metal residues were determined in roots of vascular plants sediment between roots was more oxidative more acidic and richer in organic matter than non vegetated sediment profiles of zn pb and cu concentrations in vegetated sediments differed from those recorded in non vegetated areas at subsurface layers where root density is higher zn pb and cu were enriched the percentages of zn pb and cu removed by acetic acid nitric acid and dtpa extractions from sediment between roots were much lower than those from non vegetated sediments being preferentially linked to the residual fraction chromium and ni behave differently no subsurface enrichment being found and their associations being similar in the two types of sediment furthermore ni concentrations in roots were much lower than in bulk sediments while levels of zn and pb were similar and cu values higher these results point out that plants are an important feature for metal accumulation in salt marshes