comparison of geoelectrical imaging and tunnel documentation at the hallandsas tunnel sweden article i nfo for construction in rock a thorough pre investigation is important in order to avoid unforeseen conditions which may delay the work it is crucial to remember the results from this investigation in the further work and use the experience from the construction to update the geological prognosis and reduce the uncertainties different geophysical methods have proved valuable tools in such investigations in this work the electrical imaging is evaluated with regards to the method s applicability the evaluation is done qualitatively by comparing the electrical imaging with tunnel documentation from a tunnel in southern sweden by evaluating the result continuously when making the tunnel a more detailed geological prognosis can be compiled and used in the continued work with the tunnel the parameters used for the comparison are lithology q rqd weathering and water leakage the result was that virtually every change in electrical resistivity image coincides with a change in rock conditions the general trend was that high resistivity corresponded with good quality gneiss whereas low resistivity corresponds to poor quality rock e g high weathering low rqd low q and or several lithological contacts the intermediate resistivity is often amphibolites or rock with water bearing fractures the results were supported by in situ resistivity measurements inside the tunnel and resistivity logging in a core drilling geoelectrical imaging proved to give valuable information for a detailed geological model which could be compiled for a section where the tunnel had not yet been drilled as a help for planning of the continued tunnel work as is the case other geophysical methods it is clear that for the interpretation of data a priori information about the geological setting is necessary

data driven approach to identify field scale biogeochemical transitions using geochemical and geophysical data and hidden markov models development and application at a uranium contaminated aquifer 1 although mechanistic reaction networks have been developed to quantify the biogeochemical evolution of subsurface systems associated with bioremediation it is difficult in practice to quantify the onset and distribution of these transitions at the field scale using commonly collected wellbore datasets as an alternative approach to the mechanistic methods we develop a data driven statistical model to identify biogeochemical transitions using various time lapse aqueous geochemical data e g fe ii sulfate sulfide acetate and uranium concentrations and induced polarization ip data we assume that the biogeochemical transitions can be classified as several dominant states that correspond to redox transitions and test the method at a uranium contaminated site the relationships between the geophysical observations and geochemical time series vary depending upon the unknown underlying redox status which is modeled as a hidden markov random field we estimate unknown parameters by maximizing the joint likelihood function using the maximization expectation algorithm the case study results show that when considered together aqueous geochemical data and ip imaginary conductivity provide a key diagnostic signature of biogeochemical stages the developed method provides useful information for evaluating the effectiveness of bioremediation such as the probability of being in specific redox stages following biostimulation where desirable pathways e g uranium removal are more highly favored the use of geophysical data in the approach advances the possibility of using noninvasive methods to monitor critical biogeochemical system stages and transitions remotely and over field relevant scales e g from square meters to several hectares

controls on facies and sequence stratigraphy of an upper miocene carbonate ramp and platform melilla basin ne morocco abstract upwelling of cool seawater paleoceanographic circulation paleoclimate local tectonics and relative sea level change controlled the lithofacies and sequence stratigraphy of a carbonate ramp and overlying platform that are part of a temporally well constrained carbonate complex in the melilla basin northeastern morocco at melilla from oldest to youngest a third order depositional sequence within the carbonate complex contains 1 a retrogradational transgressive warm temperate type rhodalgal ramp 2 an early highstand progradational bioclastic platform composed mainly of a temperate type bivalve rich molechfor facies and 3 late highstand progradational to downstepping subtropical tropical type chlorozoan fringing porites reefs the change from rhodalgal ramp to molechfor platform occurred at 7 0 0 14 ma near the tortonian messinian boundary during a late stage in the development of the bioclastic platform a transition from temperate type molechfor facies to subtropical tropical type chlorozoan facies occurred and is bracketed by chron 3an 2n 6 3 6 6 ma comparison to a well dated carbonate complex in southeastern spain at cabo de gata suggests that upwelling of cool seawater influenced production of temperate type limestone within the ramp and platform at melilla during postulated late tortonian early messinian subtropical tropical paleoclimatic conditions in the western paleo mediterranean region the upwelling of cool seawater across the bioclastic platform at melilla could be related to the beginning of siphoning of deep cold atlantic waters into the paleo mediterranean sea at 7 17 ma the facies change within the bioclastic platform from molechfor to chlorozoan facies may be coincident with a reduction of the siphoning of atlantic waters and the end of upwelling at melilla during chron 3an 2n the ramp contains one retrogradational parasequence and the bioclastic platform three progradational parasequences minor erosional surfaces that bound the upper surface of the ramp and upper surface of the oldest platform parasequence are related to relative falls in sea level induced by local volcanism and associated tectonic uplift these local relative falls had little influence on a broader scale rise to stillstand in relative sea level that controlled development of the transgressive and early highstand systems tracts represented in the ramp and platform respectively

boat towed radio magnetotelluric and controlled source audio magnetotelluric study to resolve fracture zones at aspo hard rock laboratory site sweden boat towed radio magnetotelluric rmt measurements using signals between 14 and 250 khz have attracted increasing attention in the near surface applications for shallow water and archipelago areas

evaluation of δ13c chemostratigraphy for intrabasinal correlation vendian strata of northeast siberia integrated sedimentologic stratigraphic and geochemical 13 c 18 o fe mn and sr data from vendian cambrian carbonate ramp deposits of the northeast siberian platform olenek uplift and kharaulakh mountains region are used to constrain primary time dependent oscillations in the carbon isotope record and to evaluate 13 c chemostratigraphy for high resolution intrabasinal correlation the vendian 13 c record of northeast siberia reflects global variations seen elsewhere by displaying in ascending order a strong positive isotopic shift to values near 6 herein named the p interval an intermediate interval of relatively little isotopic change i interval which shows in some sections a monotonic decrease in 13c from 2 at the base to near 0 at the top and a negative excursion to 4 n interval just beneath the vendian cambrian boundary in addition to secular isotopic shifts these strata exhibit local small scale signals related to intrabasinal variations in subsidence erosion and diagenetic alteration e g degradation of organic matter dolomitization and hydrothermal and burial effects these local intrabasinal processes in some cases have modified both the magnitude and form of the primary isotopic excursions which are used as the basis for correlation in all studies carbon isotope profiles provide an important method to evaluate intrabasinal variations in subsidence erosion and stratigraphic completeness these profiles reflect increasing subsidence along the platform to basin transition whereas progressive truncation of isotopic profiles along this trend illustrate pronounced uplift and erosion of ramp strata along unconformity surfaces

evolution of a terminal neoproterozoic carbonate ramp system buah formation sultanate of oman effects of basement paleotopography the buah formation is a carbonate unit of late neoproterozoic age exposed in the jabal akhdar of northern oman and the huqf region of central oman the buah formation is interpreted as a distally steepened storm dominated ramp containing inner ramp tidally influenced oolitic shoal and back shoal lagoon fades and storm dominated mid ramp facies a slope break separates mid ramp facies from outer ramp facies characterized by accumulation of redeposited carbonates on gently inclined slopes 1 2 degrees combined facies stacking patterns and outcrop correlation via 1 3 c profiles suggest that buah carbonates formed as a highstand systems tract characterized by a general upward shallowing of facies and strong lateral progradation on a regional scale buah facies distributions across oman were controlled by the presence of basement highs defining areas of reduced subsidence which promoted lateral progradation of the buah carbonate ramp for tens of kilometers while the faster subsiding areas became sites of deep water deposition

subsurface investigation of the neogene mygdonian basin greece using magnetic data a high resolution ground and marine magnetic survey was executed to determine the structure of the subsurface and the thickness of the sedimentary cover in the mygdonian basin a spacing of approximately 250 m or 500 m between measurement stations was selected to cover an area of 15 km 22 km edge detectors such as total horizontal derivative thdr analytic signal as tilt derivative tdr enhanced total horizontal gradient of tilt derivative ethdr were applied to map the subsurface structure depth was estimated by power spectrum analysis tilt derivative source parameter imaging spi and 2d forward modeling techniques spectral analysis and spi suggest a depth to the basement ranging from near surface to 600 m for some selected locations depth was also calculated using the tdr technique suggesting depths from 160 to 400 m 2d forward magnetic modeling using existing boreholes as constraints was carried out along four selected profiles and confirmed the presence of alternative horsts and grabens formed by parallel normal faults the dominant structural trends inferred from thdr as tdr and ethdr are n s nw se ne sw and e w this corresponds with the known structural trends in the area finally a detailed structural map showing the magnetic blocks and the structural architecture of the mygdonian basin was drawn up by collating all of the results

extinction of cloudina and namacalathus at the precambrian cambrian boundary in oman biostratigraphic carbon isotope and u pb zircon geochronological data from the ara group of oman indicate an abrupt last appearance of cloudina and namacalathus coincident with a large magnitude but short lived negative excursion in the carbon isotope composition of seawater that is globally coincident with the precambrian cambrian boundary u pb zircon age data from an intercalated ash bed directly define this negative excursion to be at 542 0 0 3 ma consistent with previous age constraints from siberia and namibia combined with the global biostratigraphic record these new data strengthen hypotheses invoking mass extinction within terminal proterozoic ecosystems at or near the precambrian cambrian boundary

planning of urban underground infrastructure using a broadband seismic landstreamer tomography results and uncertainty quantifications from a case study in southwestern sweden abstractwe have developed a multicomponent broadband seismic landstreamer system based on digital sensors and particularly suitable for noisy environments and areas in which high resolution images of the subsurface are desired we have evaluated results interpretations and approaches using the streamer in the planning of an approximately 3 km long underground tunnel in the city of varberg in the southwestern sweden prospective targets were imaging of the shallow 20 m bedrock surface and weak zones such as fracture and shear zones over the course of three weeks 25 profiles were acquired with a total length of approximately 7 5 km using a source and receiver spacing of 2 4 m a novel approach of the data acquisition was to integrate the landstreamer with wireless sensors in areas in which the accessibility was restricted by roads and also to increase the source receiver distances offsets although the area was highly noisy the seismic data in conjunction with available boreholes successfully l

2d joint inversion of rmt and ert data versus individual 3d inversion of full tensor rmt data an example from trecate site in italy tensor radiomagnetotelluric rmt and electrical resistivity tomography ert data were acquired along 10 parallel lines to image electrical resistivity of the vadose and the saturated zone in an a

depth of investigation in electromagnetic sounding methods the time or frequency at which the electromagnetic em response of a buried inhomogeneity can first be measured is determined by its depth of burial and the average conductivity of the overlying section it is relatively independent of the type of source or receiver and their separation the ability to make measurements at this time or frequency however depends on the sensitivity and accuracy of the instrumentation the signal strength and the ambient noise level these factors affect different em sounding systems in surprisingly different ways for the magnetotelluric mt method it is possible to detect a buried half space under about 1 5 skin depths of overburden the maximum depth of investigation is virtually unbounded because of high signal strengths at low frequencies transient electromagnetic tem soundings on the other hand have a limited depth of penetration but are less affected by static shift errors for tem a buried inhomogeneity can be detected under about one diffusion depth of overburden for conventional near zone sounding in which induced voltage is measured impulse response the depth of investigation is proportional to the 1 5 power of the source moment and ground resistivity by contrast if the receiver is a magnetometer step response system the depth of investigation is proportional to the 1 3 power of source moment and is no longer a function of resistivity magnetic field measurements may therefore be superior for exploration in conductive areas such as sedimentary basins far zone or long offset tem soundings are traditionally used for deep exploration the depth of investigation for a voltage receiver is proportional to the 1 4 power of source moment and resistivity and is inversely proportional to the source receiver separation magnetic field measurements are difficult to make at long offsets because instrumental accuracy limits the measurement of the very slow decay of the magnetic field frequency domain controlled source systems are ideally suited for sounding at the very shallow depths needed for engineering archaeological and groundwater applications because of the relative ease of extending the measurements to arbitrarily high frequencies and also because geometric soundings can be made at low induction numbers

magnetotelluric measurements across the sorgenfrei tornquist zone in southern sweden and denmark the results of a magnetotelluric experiment across the sorgenfrei tornquist zone stz in the southwestern part of the baltic shield are presented the stz marks the border between the proterozoic

sedimentation during carbonate ramp to slope evolution in a tectonically active area bowland basin dinantian northern england the bowland basin northern england contains a series of carbonates and terrigenous mudstones deposited during the ivorian to early brigantian two regional depositional environments are indicated by facies and facies associations wackestone packstone and calcarenite facies indicate deposition in a carbonate ramp environment while lime mudstone wackestone calcarenite and limestone breccia conglomerate facies often extensively slumped represent a carbonate slope environment stratigraphic relations suggest that the depositional environment evolved from a ramp into a slope through the dinantian two main sediment sources are indicated by the sequence an extra basinal terrigenous mud source and a supply of carbonate from the margins of the basin deposition from suspension and from sediment gravity flows in situ production and remobilization of sediment during sedimentary sliding were important processes operating within the basin periods of enhanced tectonic activity in the late chadian to early arundian and late asbian to early brigantian are indicated by basin wide horizons of sedimentary slide and mass flow deposits both intervals were marked by a decline in carbonate production resulting from inundation and uplift emergence the first of these intervals separates deposition on a seafloor with gentle topography carbonate ramp from a situation where major lateral thickness and facies variations were present and deposition took place in a carbonate slope environment the second interval marks the end of major carbonate deposition within the bowland basin and the onset of regional terrigenous sedimentation

on the recognition of areas with problematic sulphidic sediments using multi disciplinary data increased concentrations of several trace elements have been observed in water draining areas with sulphidic sediments along the baltic sea coast of sweden and finland some of these elements are harmful to the water environment the increased leaching of trace elements is often caused by antrophogenic activities such as ditching which cause oxidation of the sulphides and thereby acid soil conditions it is therefore important to recognise areas with sulphidic sediments and if possible avoid land use which causes sulphide oxidation the aim of this study was to find time effective methods which can be used to delineate areas with sulphidic sediments three areas in sweden with known occurrences of sulphidic sediments were studied data obtained from the mapping program at the geological survey of sweden sgu were first studied selected sites were thereafter visited and geoelectrical measurements were carried out by the use of several instruments the results imply that areas with sulphidic sediments are reflected as areas with high trace element contents on sgus biogeochemical maps which are based on analyses of trace elements in aquatic plants the same deposits are often shown as gyttja clay on the maps of quaternary deposits furthermore models derived from airborne electromagnetic measurements show that areas with sulphidic sediments often have a lower electric resistivity than surrounding sediments also the results from ground geoelectrical measurements suggest that the sulphidic sediments have a lower resistivity than surrounding fine grained deposits that interpretation was verified after stratigraphical studies and analyses of the sulphur contents of the sediments it is therefore suggested that data from ground geophysical measurements can be used for a detailed delineation of sulphidic sediments whereas data obtained from airborne geophysical and geological maps give an overview over potential areas with these sediments the absolute resistivity of the sulphidic sediments varies however between the three investigated areas complementary corings and stratigraphical descriptions are therefore always necessary to verify the occurrence of these sediments

hardened subtidal stromatolites bahamas hardened high relief stromatolites have been discovered along the margins of some bahamian platforms they occur in high energy tidal oolitic sand environments in waters ranging in depth from about 1 to 5 meters physical stress produced by actively migrating bed forms of oolitic sand appears to exclude grazing gastropods and subsequent community successions permitting stromatolite growth

the dinantian stratigraphy of the east midlands a seismostratigraphic approach six tectonically controlled seismic sequences have been identified in the dinantian succession of the widmerpool gulf east midlands and they have also been recognized in outcrop sections in derbyshire and the bowland basin these correlations are made possible by integrating and calibrating sequence boundaries with the biostratigraphical evidence from foraminifers conodonts and palynomorphs and relating these to the tectonostratigraphical evolution of the basin it is suggested that the current chronostratigraphical stages of the dinantian do not always reflect major regional stratigraphical events and that the seismic sequence stratigraphy erected herein may provide a more applicable chronostratigraphical subdivision of the dinantian of the east midlands and northern england

joint inversion of lake floor electrical resistivity tomography and boat towed radio magnetotelluric data illustrated on synthetic data and an application from the aspo hard rock laboratory site sweden joint inversion of lake floor electrical resistivity tomography and boat towed radio magnetotelluric data illustrated on synthetic data and an application from the aspo hard rock laboratory site sweden

a radio magnetotelluric study to evaluate the extents of a limestone quarry in estonia electromagnetic signals from distant radio transmitters in the frequency range 15250 khz were measured to model an electrical resistivity structure beneath 7 profiles in the vicinity of the karinu limestone quarry in estonia with the aim to map the extent of the economically exploitable limestone the resistivity models from a 2d inversion of determinant resistivity and phase values using an occam type of regularization contained reasonably accurate information about the geometry namely depth to the top and the bottom of the target high resistivity limestone the resistivity models correlated well with existing geological evidences as well as information from closely located boreholes however the sharp lithological boundaries seen in the boreholes were not resolved exactly in the resistivity models this is probably because of the smoothing regularization used in the inversion process combined use of borehole data together with resistivity models resulted in two major geological interpretations a towards the western part of the existing limestone quarry there is a nnw to ns striking fault covered by post glacial sediments b a potential cost effective exploitable area containing high quality highly resistive limestone is located south of the existing quarry this case study shows the applicability of the reasonably fast radio magnetotelluric rmt method for the exploration of near surface resources

understanding carbonate ramp dynamics using δ13c profiles examples from the neoproterozoic buah formation of oman the late neoproterozoic buah formation nafun group oman is a carbonate unit outcropping in the jabal akhdar and huqf areas it is composed mostly of shallow water carbonates deposited on a distally steepened carbonate ramp correlation of two 13c isotope shifts shows that in the jabal akhdar ramp differentiation into fast and slow subsiding areas was followed by lateral progradation in the huqf area however a uniform scenario of upward shallowing of the facies and lateral progradation is demonstrated by chemostratigraphic timelines cross cutting the facies belts the chemostratigraphic profiles show that the buah formation was deposited during sea level highstand conditions and that ramp differentiation was due to synsedimentary tectonics high resolution correlation of 13c profiles from the same lithostratigraphic unit whether precambrian or phanerozoic in age lacking biostratigraphic data can shed light on carbonate systems dynamics tectonic vs eustatic controls on depositional sequences and basin subsidence

giant subtidal stromatolites forming in normal salinity waters we report here the discovery of giant lithified subtidal columnar stromatolites 2 m high growing in 7 8 m of clear oceanic water in current swept channels between the exuma islands on the eastern bahama bank they grow by trapping ooid and pelletal carbonate sand and synsedimentary precipitation of carbonate cement within a field of giant megaripples the discovery is important to geologists and biologists because similar organo sedimentary structures built by a combination of cementation and the trapping of sediment by microbes were the dominant fossil types during the precambrian stromatolites are thought to have been responsible for the production of free oxygen and thus the evolution of animal life1 2 until the discovery of small lithified subtidal columnar stromatolites in the bahamas3 the only subtidal marine examples known to be living while undergoing lithification were in the hypersaline waters of hamelin pool at shark bay western australia4 7 shark bay stromatolites range from intertidal to the shallow subtidal with the larger columns reaching 1 m in height the shark bay stromatolites have strongly influenced geological interpretation by analogy many ancient stromatolites have been considered to have grown in intertidal and or hypersaline conditions8 although hypersalinity was not a necessity for growth during the precambrian because grazing metazoan life had not then evolved

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

integrated 2d modeling and interpretation of geophysical and geotechnical data to delineate quick clays at a landslide site in southwest sweden radio magnetotellurics rmt electrical resistivity tomography ert and high resolution reflection seismic data were collected along four lines to characterize the geometry and physical properties of geologic structures at a quick clay landslide site in southwest sweden the site is situated in the gota river valley where the normally consolidated materials mainly consist of glacial and postglacial sediments geotechnical data suggest the presence of quick clays above coarse grained layers these layers play a key role in the formation of quick clays and landslide triggering the rmt and ert data were individually and jointly inverted in 2d to study the resolution of resulting models for each data set the resistivity models from the joint inversions demonstrate superior resolution and accuracy compared with individual ones the geometry and location of shallower structures resolved in the 2d resistivity models from joint rmt ert inversions correlated well with those imaged in the reflection seismic data and observed in the existing geotechnical boreholes the models were poor in resolving deeper resistive bedrock at locations where the thickness of the conductive overburden exceeds a certain limit however information from the reflection seismic data could be used to estimate the depth to the top of the bedrock along all the four lines comparison between the geotechnical data and the resistivity models suggested that quick clays overlying the coarse grained layer have higher electrical resistivity than the marine clays we further validated and refined the obtained results by performing synthetic tests we showed that integration of ertand rmt data with reflection seismic data is ideal for quick clay landslide studies especially when the clay materials are thick

the potential of rotary wing uav based magnetic surveys for mineral exploration a case study from central sweden abstract unmanned aerial vehicle uav based geophysical surveys are attractive for land mineral exploration and are gradually opening extraordinary opportunities in providing high resolution definition of geologic structures and for direct targeting of mineral deposits there are however challenges such as electromagnetic noise from the uav limited load capacity and short flight times if these are overcome there will be a new era in using uav based geophysical systems for mineral exploration and for a number of mining related purposes in this study we have tested the potential of rotary wing uav systems given their flight flexibility and robustness for direct targeting of iron oxide deposits in central sweden a walking mode high precision overhauser magnetometer was reassembled so that it could be lifted by the rotary wing system successful backyard tests were performed but during the real experiment several issues related to high uav noise level and extreme magnetic field from the mineraliza

hydrogeophysical investigations of the former s 3 ponds contaminant plumes oak ridge integrated field research challenge site tennessee abstractat the oak ridge integrated field research challenge site near oak ridge tennessee contaminants from the former s 3 ponds have infiltrated the shallow saprolite for over 60 years two and three dimensional dc resistivity tomography is used to characterize the number and location of the main contaminant plumes which include high concentration of nitrate these contaminant plumes have typically an electrical resistivity in the range 2 20 ohm m while the background saprolite resistivity is in the range 60 120 ohm m so the difference of resistivity can be easily mapped using dc resistivity tomography to locate the contaminant pathways we develop a relationship to derive the in situ nitrate concentrations from the 3d resistivity tomograms accounting for the effect of surface conductivity the footprint of the contamination upon the resistivity is found to be much stronger than the local variations associated with changes in the porosity and the clay content with this method we identified a tot

float transient electromagnetic method in loop transient electromagnetic measurements on lake holzmaar germany lake sediments may serve as archives on paleoclimatic fluctuations geomagnetic field variations and volcanic activities lake holzmaar in eifel germany is a maar lake and its lacustrine sediments provide paleoclimatic proxy data therefore knowledge about the geometry and especially about the thickness of the sediments is very important for determining an optimum drilling location for paleoclimatic studies we have developed a floating in loop transient electromagnetic method field set up float transient electromagnetic method with a transmitter and receiver size of 18 18 m2 and 6 6 m2 respectively this special set up enables in loop transient electromagnetic method measurements on the surface of freshwater lakes that define the geometry and the thickness of sediments beneath such lakes thus helping to determine optimum drilling locations due to the modular design of the new float transient electromagnetic method field set up this system can be handled by two operators and can easily be transported sixteen in loop soundings were carried out on the surface of lake holzmaar the transient electromagnetic method data could not be interpreted by conventional 1d inversions because of the 3d distribution of subsurface conductivity caused by the lake s geometry three dimensional finite element modelling was applied to explain the observed transients and the 3d conductivity distribution beneath the lake was recovered by taking its geometry into account the 3d interpretation revealed approximately 55 m thick sediments beneath 20 m deep water in the central part of the lake

stratigraphy and sedimentology of the great oolite group in the humbly grove oilfield hampshire abstract the main reservoir of the humbly grove oilfield comprises variably dolomitic grainstones and packstones representing the bathonian great oolite group the bathonian sequence commences in lower fuller s earth claystones which coarsen upwards into oncolitic claystones and skeletal packstones probably equivalent to the fuller s earth rock above is a variable succession of wackestones and thin packstones which have a distinctive sandstone at their base this sequence is named here the hester s copse formation the succeeding great oolite limestone is predominantly oolitic and cross bedded on a variety of scales it exhibits both coarsening and fining sequences which have locally well developed capping hardgrounds and burrowed horizons the great oolite limestone is subdivided into three members the lowest the humbly grove member and the highest the herriard member begin with massive shoal oolite deposition but each then pass upward into more interbedded sequences representing a more transgressive environment the middle member the hoddington is a thin but widely correlatable wackestone the overlying forest marble commences abruptly in claystones but there is an upward increase in both the incidence and thickness of discrete oolitic limestones both the great oolite limestone and forest marble were affected by early fresh water dissolution and cementation in addition to the localized development of submarine cements the top of the great oolite group is represented by the cornbrash the lower cornbrash is a thin micritic limestone while the upper cornbrash is a calcareous claystone which passes upwards into the kellaways clay the bathonian sequence overlies the dolomitic limestones of the inferior oolite the lower fuller s earth claystones being interpreted as a basinal marine mudstone sequence marking a substantial deepening and transgressive phase at the opening of the bathonian these mudstones shoal upwards into the quiet but photic water deposits of the fuller s earth rock the hester s copse formation represents the temporary development of wave dominated terrigenous shoreface and lagoonal conditions renewed transgression established a high energy tide dominated carbonate shelf upon which the great oolite limestone was deposited as a series of shoal oolites channels tidal deltas and spill overs periodic exposure of the carbonate sand bodies led to the production of early dissolutional and cementation fabrics that post date and largely obliterate submarine cements the forest marble opened with a further phase of deepening and the temporary establishment of muddy facies subsequently discrete tide dominated ridges and linear channelized oolitic sands prograded into the area the latest bathonian is marked by subsidence of the carbonate ramp to the south of the london platform the cornbrash kellaways clay sequence accumulating under progressively deepening waters

airborne doppler radar analysis of a toga coare waterspout storm abstract an airborne doppler radar analysis of a waterspout parent storm is presented an 8 min window centered around the time of the visual observation of the waterspout is presented the waterspout was associated with a small intense cloud that developed ahead of a squall line it was observed by radar from a distance of 3 km with a cross beam resolution of approximately 70 m one radar scan cut through the vortex revealing the structure the high resolution dual doppler analysis of the electra doppler radar was used to investigate the velocity and vorticity structure of the parent storm these observations were consistent with a low level vorticity source no cloud scale vorticity was observed until the time of the visual observation of the storm

boat towed radio magnetotellurics a new technique and case study from the city of stockholm we have developed a new data acquisition system and technique to measure the radio magnetotelluric rmt signals from distant radio transmitters with the objective of mapping and modeling electric

delineating hydrothermal stockwork copper deposits using controlled source and radio magnetotelluric methods a case study from northeast iran radio and controlled source tensor magnetotelluric rmt and cstmt methods are used to target hydrothermal veins of copper mineralization the data were acquired along six eastwest and three

combined magnetic electromagnetic and resistivity study over a highly conductive formation in orrivaara northern sweden different geophysical methods were used to determine the characteristics of a highly conductive structure in northern sweden first discovered on airborne data airborne electromagnetic very low frequency data indicate a high conductivity structure coincident with low magnetic patterns the airborne data were processed in different ways to enhance various structures features in particular we introduce a new transformation to current density that is suitable for delineating conductive structures ground measurements of the total magnetic field radiomagnetotelluric measurements and resistivity imaging provided valuable information that was used in the compilation of a new bedrock map over the area the results of our measurements indicate that the conducting structure consists of metasedimentary rocks containing thin horizons of pyrrhotite and graphite

delineating a road salt plume in lakebed sediments using electrical resistivity piezometers and seepage meters at mirror lake new hampshire u s a electrical resistivity surveys seepage meter measurements and drive point piezometers have been used to characterize chloride enriched groundwater in lakebed sediments of mirror lake new hampshire u s a a combination of bottom cable and floating cable electrical resistivity surveys identified a conductive zone 100 ohm m overlying resistive bedrock 1000 ohm mbeneaththelake shallowpore watersamples frompiezometersinlakebedsedimentshavechlorideconcentrations of 200 1800 eq liter and lake water has a chloride concentrationof104 eq liter theextentoftheplumewasestimated and mapped using resistivity and water sample data the plume2035 mwideandatleast3 mthickextendsnearlythe full length and width of a small inlet overlying the top of a basin formed by the bedrock it would not have been possible to map

geophysical characterization of areas prone to quick clay landslides using radio magnetotelluric and seismic methods landslides attributed to quick clays have not only considerable influences on surface geomorphology they have caused delays in transportation systems environmental problems and human fatalities