ground penetrating radar assisted saturation and permeability estimation in bimodal systems near surface investigations often require characterization of vadose zone hydraulic parameters conventional sampling or borehole techniques for estimating these parameters are costly time consuming and invasive all of which limit collection of hydrogeological data at a spacing needed for detailed site characterization incorporation of two or three dimensional densely sampled geophysical data with conventional hydrological data increases the amount of data available for the characterization and thus has the potential to significantly improve the hydraulic parameter estimates over those obtained from borehole data alone the hydraulic estimation procedure can be greatly improved by incorporating dielectric information potentially available from ground penetrating radar gpr a noninvasive high resolution geophysical method the procedures for collecting and processing gpr data in the format needed for the proposed estimation technique are relatively new and still a topic of research our method requires as a starting point the ability to estimate dielectric constants from gpr data numerical experiments were performed to investigate the general utility of the gpr assisted estimation technique under a range of conditions three bimodal systems were investigated each system being composed of a sand facies together with another facies with a larger clay volume fraction each facies was defined using characteristic values of clay content porosity and permeability using dielectric information and petrophysical relations degree of saturation and intrinsic permeability values at each location within the three systems were identified for bimodal systems a dielectric constant measurement corresponds to two possible values of saturation and intrinsic permeability at each location single values of saturation and intrinsic permeability were estimated from these values using the principle of maximum likelihood results from case studies demonstrate that a combination of gpr data with conventional borehole data significantly improves the estimates of saturation and has the potential to improve the estimates of permeability over those obtained from well bore data alone the proposed method should be especially advantageous for vadose zone characterization in areas favorable for gpr data acquisition where detailed hydraulic parameter information is required but the drilling of numerous boreholes is prohibited

detecting the thermal aureole of a magmatic intrusion in immature to mature sediments a case study in the east greenland basin 73 n the cretaceous and triassic argillaceous rocks from the passive margin of greenland have been investigated in order to detect the thermal aureole of magmatic intrusions ranging from metric dyke to kilometric syenite pluton rock eval data tmax generally 0 3 all indicate a maximum of 5km burial for the argillaceous rocks whatever the distance to an intrusion the k ar dating of the clays 2 m fraction suggests that illites are mostly detrital except near magmatic intrusions where younger ages are recorded to get more information about the extent of the thermal aureole rock magnetism data were determined at distance away from the thermal aureole of the syenite intrusion triassic argillaceous rocks reveal a standard magnetic assemblage compatible with their burial r 0 4 percent it is constituted essentially by neoformed stoichiometric magnetite fe o in contrast within the thermal aureole of the magmatic intrusions the cretaceous argillaceous rocks contain micron sized pyrrhotite fe s firmly identified through the recognition of besnus transition at 35k the thermal demagnetization of natural remanence carried by this pyrrhotite shows a diagnostic square shouldered pattern indicating a narrow grain size distribution of pyrrhotite the extension of this diagnostic pyrrhotite maps a 10 km thick aureole around the syenitic pluton away from this aureole the magnetic assemblage is diagnostic of those found in argillaceous rocks where organic matter is mature

chemical and isotopic characterization of water rock interactions in shales induced by the intrusion of a basaltic dike a natural analogue for radioactive waste disposal abstract disposal of nuclear waste in deep geological formations is expected to induce thermal fluxes for hundreds of years with maximum temperature reaching about 100 150 c in the nearfield argillaceous environment the long term behavior of clays subjected to such thermal gradients needs to be perfectly understood in safety assessment considerations in this respect a toarcian argillaceous unit thermally disturbed by the intrusion of a 1 1 m wide basaltic dike at the perthus pass herault france was studied in detail as a natural analogue the thermal imprint induced by the dike was evaluated by a mineralogical chemical and k ar study of the at the eastern contact with the dike the mineral and chemical compositions of both the shales and the basalt suggest water rock interactions subsequent to the intrusion with precipitation of palagonite and renewed but discrete deposition of carbonate a pencil cleavage developed in the shales during the dike emplacement probably favored water circulation along the contact strontium isotopic data suggest that the fluids of probable meteoric origin reacted with bathonian and bajocian limestones before entering the underlying toarcian shales by analogy with deep geological radioactive waste repositories the results report discrete mineralogical variations of the clays when subjected to temperatures of 100 150 c that are expected in deep storage conditions beyond 150 c significant mineralogical changes may alter the physical and chemical properties of the shales especially of the clay fraction also the development of structural discontinuities in the so called thermally disturbed zone might be of importance as these discontinuities might become zones for preferential fluid circulation finally the study emphasizes the use of rb sr and k ar isotopic systems as tracers of local circulating fluids related to low grade thermal imprints

magnetic properties of sedimentary greigite fe3s4 an update greigite fe3s4 is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction it can also grow at any time when dissolved iron and sulfide are available during diagenesis greigite is important in paleomagnetic environmental biological biogeochemical tectonic and industrial processes much recent progress has been made in understanding its magnetic properties greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites the crystallographic c axis is the easy axis of magnetization with magnetic properties dominated by magnetocrystalline anisotropy robust empirical estimates of the saturation magnetization anisotropy constant and exchange constant for greigite have been obtained recently for the first time and the first robust estimate of the low field magnetic susceptibility is reported here the curie temperature of greigite remains unknown but must exceed 350 c greigite lacks a low temperature magnetic transition on the basis of preliminary micromagnetic modeling the size range for stable single domain behavior is 17 200 nm for cubic crystals and 17 500 nm for octahedral crystals gradual variation in magnetic properties is observed through the pseudo single domain size range we systematically document the known magnetic properties of greigite at high ambient and low temperatures and with alternating and direct fields and illustrate how grain size variations affect magnetic properties recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records including widespread remagnetizations

biomarker distribution in the lacustrine shales of the upper triassic lower jurassic kap stewart formation jameson land greenland abstract freshwater lacustrine shales with a good to excellent petroleum source potential from the upper triassic lower jurassic kap stewart formation in jameson land eastern greenland have been investigated by rock eval pyrolysis toc and sulphur determinations gas chromatography mass spectrometry and pyrolysis gas chromatography distributions of n alkanes isoprenoids steranes and hopanes together with rock eval data and sulphur contents have been used to describe depositional environment and thermal maturity the lacustrine shales are characterized by long chain n alkanes high cpi values high pristane phytane ratios high hopane sterane ratios and very low sulphur contents good potential for generation of liquid petroleum is confined to samples having the highest relative contents of c 27 steranes gammacerane and 17 h trisnorhopane ts regional maturity levels correspond to an immature stage perturbed by local heating from sills comparison with the time equivalent are formation on haltenbanken offshore mid norway has been made with respect to biomarker distribution and petroleum potential the biomarker distributions of the two formations are similar and can be ascribed to the clastic non marine nature of both depositional areas the petroleum potential of the are formation is poorer than that of the kap stewart formation probably due to a predominantly deltaic facies of the former with major terrestrial organic matter input

colour banding in a latest neoproterozoic cambrian microbially variegated sabkha of the taoudeni basin adrar of mauritania abstract the taoudeni basin is a large intracratonic trough located in the west african craton with more than 2 km of neoproterozoic lower palaeozoic sedimentary thickness the occurrence of late ediacaran cambrian sabkha deposits in which playa lake evaporites are bounded by proximal braided fluvial and distal shoal complexes is easily distinguishable in the field by their variegated colour banding the diagenetic processes recorded in the sabkha substrates were largely facies controlled associated with microbial development and mat decay mineralization due to anaerobic decay of mat microorganisms chemical conditions beneath mats and biofilms tended to be strongly reducing as a result precipitation of authigenic indicators of anoxic conditions such as pyritic crusts led to variegated colours parallel to stratification reworking of microbial mats and structures by ephemeral streams also generated isolated reduction spots around their microbial clasts leading to the formation of pyritic haloes the subsequent alteration of pyrite to amorphous reddish hematite and subsequent recrystallization to brownish to yellow goethite contributed to the variegated aspect of the unit final reddening of the sediment took place irregularly as a result of dehydration of ferric hydroxides a process relatively common in desert environments

the continental margin of central east greenland in relation to north atlantic plate tectonic evolution the east greenland continental margin is inferred to have formed in three stages during the tertiary evolution of the adjacent north atlantic ocean the east greenland basaltic volcanism occurred over a period of 2 3 ma which was just prior to the probable date of onset of seafloor spreading in the early eocene shortly before magnetic anomaly 24b 52 ma the associated coastal flexure is interpreted as marking the edge of a zone of stretched and thinned continental crust beneath the inner denmark strait shelf and jan mayen microcontinent this represents a short lived rifting phase just prior to break up according to the evolutionary model the initial break up produced the margins south of the faeroe transform fault 68 5 n and north of the jan mayen fracture zone 72 n but in the intervening region the microcontinent remained attached to east greenland after break up the outer shelf of denmark strait formed from anomalously thick oceanic crust complementary to the iceland faeroe ridge the blosseville kyst margin 68 5 n to 70 n was initiated after anomaly 20 time 42 ma as the jan mayen microcontinent started to separate from greenland with spreading on both sides the new split occupied the line of the pre existing coastal dyke swarm and flexure the liverpool land margin 70 n to 72 n was also initiated at this time but the main separation of the northern part of the microcontinent only commenced after anomaly 7 time 26 ma when a single spreading axis was relocated west of the microcontinent it is suggested that the blosseville lavas subsided during deposition by loading and slight crustal stretching doming occurred near kangerdlugssuaq at the time of break up otherwise the topography of the lavas remained subdued until the relocation of the spreading axis at 26 ma after which the main regional uplift took place

magnetism in rocks rock magnetism is the study of induced and remanent magnetization of ferrimagnetic mineral grains in rocks sediments soils and organisms its applications include environmental magnetism magnetic anisotropy sources of continental and oceanic magnetic anomalies records of geomagnetic field variations and polarity reversals and the paleomagnetic record of plate motions and the wilson cycle this paper reviews the beginnings of rock magnetism and then traces the development of six particularly interesting areas pseudo single domain behavior magnetic domains and micromagnetic structures diagnostic tests of the type and stability of remanent magnetization magnetic microanalysis thermoviscous remagnetization and chemical remanent magnetization other areas including sediment and soil magnetism are covered in a companion paper by verosub and roberts on environmental magnetism

the magnetization of clay rich rocks in sedimentary basins low temperature experimental formation of magnetic carriers in natural samples abstract rocks are often magnetically altered during burial thus providing a useful method to study their thermo chemical history in order to improve the understanding of burial diagenetic magnetization we experimentally synthesized magnetite in natural samples lower jurassic argillites from the paris basin were heated to 150 c under a confined atmosphere of argon when a magnetic field was applied during the heating a chemical remanent magnetization was acquired rock magnetism studies reveal that most of the newly formed magnetic carriers were magnetite using anhysteretic remanent magnetization as a measure of the quantity of magnetite an increase of up to 150 after heating was observed ferrimagnetic iron sulphide and hematite are observed to have formed in samples composed of less than 3 calcite and new magnetite is sometimes completely absent in samples containing less than 0 5 calcite hysteresis measurements suggest that the new magnetite is in the pseudo single domain state scanning electron microscope studies indicate that the new magnetic carriers are associated with pre existing pyrite the magnetic transformations during the experiments involved a fluid which reacted with iron bearing and sulfur bearing minerals in ways depending on local redox conditions this study shows that magnetite can be produced in argillaceous sediments at the normal temperatures and pressures found in sedimentary basins without any external supply from long range fluid flow

oxygen isotopes versus climap 18 ka temperatures a comparison from the tropical atlantic glacial interglacial differences in 18 o values of globigerinoides sacculifer have been mapped in the western and central tropical atlantic using data from surface and core sediments glacial interglacial differences in the western tropical atlantic if attributed to temperature changes only are at odds with temperature reconstructions performed by climap in the ceara rise region delta 18 o values exceeding 2 are recorded they can only be partly attributed to changes in the precipitation evaporation regime i e higher salinities and 18 o enriched precipitation an additional cooling of 1 2 c as compared to climap9s results is required to balance the 18 o record thus temperature changes from glacial to modern times amount to 2 3 c in the tropical atlantic off the northern coast of brazil

new constraints on the thermal history of north east greenland from apatite fission track analysis apatite fission track analyses from the area north of jameson land east greenland indicate that the region has undergone at least three phases of cooling during the mesozoic and cenozoic two major periods of cooling during the tertiary have been identified a middle tertiary episode in which cooling began between 40 and 30 ma and a late tertiary episode in which cooling began between 10 and 5 ma the middle tertiary event is synchronous with emplacement of major intrusive bodies associated with continental rifting and may be due either to uplift and erosion or hydrothermal effects the late tertiary event appears to be related to erosion associated with uplift resulting from changes in the north atlantic spreading direction and associated events no paleothermal effects have been identified related to the onset of rifting in the early tertiary results from samples farthest from the continental margin reveal an earlier event in which cooling began between 225 and 165 ma the origin of this event is not clear but it may reflect uplift and erosion associated with recognized unconformities within the jurassic section

grain size dependence of the magnetic behavior of pyrrhotite during its low temperature transition at 34 k the grain size dependent behavior of pyrrhotite during a magnetic lt transition at 34 k is suitable for granulometric purposes cycling down to liquid helium temperature suppresses soft md jrs more than hard sd jrs so that it may be effective in removing soft secondary nrm components the domain structure of large pyrrhotite grains changes from md at room temperature to sd or psd below the lt transition

pyrrhotite ptrm acquisition in metamorphic limestones in the light of microscopic observations abstract the potential of pyrrhotite as a recorder of successive independent ptrms in graphite bearing metacarbonates depends on the amount and composition of metamorphic fluids during its formation very low amounts of h2s dominated fluids will favour an in situ epitaxy of pyrrhotite at the expense of iron bearing minerals in its surroundings the resulting particle assemblage of pyrrhotite is within the single domain grain size range and exhibits a broad blocking temperature spectrum with increasing fluid content the desulfidation of pyrite controls the pyrrhotite formation and results in large crystals up to several millimeters where independent ptrms cannot be expected as both types are present in regional and contact metamorphic rocks the existence of pervasive fluids determines whether or not pyrrhotite will be able to record successive ptrms i e changes of the earth magnetic field emf during metamorphic cooling

acquisition and processing of wide aperture ground penetrating radar data a 40 channel wide aperture ground penetrating radar gpr data set was recorded in a complicated fluvial aeolian environment in eastern canada the data were collected in the multichannel format usually associated with seismic reflection surveys and were input directly into a standard seismic processing sequence filtering static corrections common midpoint gathering velocity analysis normal and dip moveout corrections stacking and depth migration the results show significant improvements over single channel recordings in noise reduction and depth of penetration by stacking and in spatial positioning and reduction of diffraction artifacts by migration these characteristics increase the potential for reliable interpretation of structural and stratigraphic details thus without having to develop any new software gpr data processing technology is brought to the same level of capability flexibility and accessibility that is current in seismic exploration

alteration of a basaltic glass in an argillaceous medium the salagou dike of the lodeve permian basin france analogy with an underground nuclear waste repository abstract volcanic basaltic glasses are commonly considered to be very suitable natural analogs of vitrified waste packages intended for geological disposal the studied basaltic glass of the salagou dike lodeve basin france intruded into a permian argillaceous formation about 1 4 ma ago provides a means of assessing the long term behavior of nuclear waste glass in an argillaceous repository concept this study is based on combining chemical mineralogical and isotopic investigations the occurrence of a palagonite film no more than 1 2 mm thick characterizes the basaltic glass alteration in contact with the argillaceous host rock the chemical and structural properties of the palagonite suggest constant volume alteration the alteration rates estimated from palagonite thickness and age of the glass are comparable to those measured on natural glasses altered in nonargillaceous media the occurrence of the studied argillaceous material in contact with the basaltic glass did not result in long term alteration kinetics significantly different from those measured in simple glass water systems mineralogical chemical and isotopic data obtained on the basaltic and argillaceous components suggest that an aqueous fluid flowed primarily at the glass argillite interface and did not propagate in the argillaceous host rock beyond 5 cm from the basaltic dike the elements released by alteration of the basaltic glass notably strontium did not diffuse into the surrounding clay this conclusion is important from the perspective of a natural analog for a deep geological repository for nuclear waste and highlights the major role of the structural properties of the clayey barrier

changes in remanence coercivity and domain state at low temperature in magnetite abstract submicron magnetite crystals with mean sizes of 0 037 0 10 and 0 22 m undergo major changes in hysteresis properties and domain states in crossing the verwey transition t v 120 k the 0 037 m crystals are single domain sd both in the cubic phase at room temperature t 0 and in the monoclinic phase below t v the 0 10 and 0 22 m crystals have a mixture of sd and two domain 2d states at room temperature t 0 but mainly sd structures below t v in agreement with micromagnetic calculations coercive force h c increases on cooling through t v by a factor 3 5 in the submicron magnetites and 40 in a 1 3 mm single crystal because of the high crystalline anisotropy and magnetostriction of monoclinic magnetite as a result domain walls and sd moments are so effectively pinned below t v that all remanence variations in warming or cooling are reversible however between 100 k and t 0 remanence behavior is variable saturation remanence sirm produced in monoclinic magnetite at 5 k drops by 70 100 in warming across t v with minor recovery in cooling back through t v ultimate levels at 5 k of 23 37 for the submicron crystals and 3 for the 1 3 mm crystal in contrast sirm produced in the cubic phase at 300 k decreases 5 35 submicron or 95 1 3 mm during cooling from 300 to 120 k due to continuous re equilibration of domain walls but there is little further change in cooling through t v itself however the submicron magnetites lose a further 5 15 of their remanence when reheated through t v these irreversible changes in cycling across t v and the amounts of the changes have potential value in determining submicron magnetite grain sizes the irreversibility is mainly caused by 2d sd transformations on cooling through t v which preserve or enhance remanence while sd 2d transformations on warming through t v cause remanence to demagnetize

improving groundwater project analysis with geophysical data when interpreting the earth s subsurface for groundwater contamination we face a fundamental problem we typically sample one millionth of the relevant material if only these data are used to determine the material between boreholes and the continuity of high hydraulic conductivity units the answers will be ambiguous for example consider a site where three boreholes intersect two hydrofacies figure 1 if no other information is available all of the interpretations shown and many more not shown are equally likely

the transition from the continent to the ocean a deeper view on the norwegian margin we present a regional crustal scale 3d structural model of the norwegian continental margin integrating sedimentary and crustal layers from the continental and the oceanic domain the model includes six sedimentary units underlain on the continental side by a thinned crystalline crust and a lower crustal high velocity body in the oceanic domain three crustal layers 2ab 3a and 3b thickened at the continent ocean transition cot are modelled below the post breakup deposits two major rift phases with different rift axes late jurassic early cretaceous and late cretaceous early tertiary have caused post jurassic subsidence and post depositional deformation of the pre cretaceous units the modelled cot suggests that the pre breakup rifting event was related to differential stretching focused at the outer margin and that breakup took place in a base up magmatic process as a continuation of underplating for the earlier rift event stretching was distributed over the entire margin and led to accumulation of up to 12 km of cretaceous deposits the large sediment thickness of the cretaceous units requires deep water conditions and abundant sediment supply and thus coeval offshore subsidence and onshore uplift all layers indicate a sinistral offset along the jan mayen fracture zone and its continentward continuation

three dimensional reverse time migration of ground penetrating radar signals three dimensional 3d ground penetrating radar gpr systems and 3d seismic imaging techniques have been developing fast and evolving rapidly in the last decade ray based migration methods have been successfully applied to processing 3d gpr signals based on the similarity between electromagnetic and seismic waves however reverse time migration rtm of 3d gpr signals has not been well studied in the past in this paper we present a 3d rtm based on maxwell s equations for 3d gpr surveys migration recovers the true subsurface structure from a distorted and unfocused time profile and suppresses common electromagnetic clutter and noise rtm based on maxwell s equations can consider conductivity directly and compensate for the attenuation within a high conductivity zone compared with 2d rtm 3d rtm back propagates both in line and cross line signals simultaneously and can include complex 3d permittivity and conductivity models we have integrated a parallel finite difference time domain fdtd algorithm based on a hybrid mpi and openmp scheme to reduce the computational cost of 3d problems the 3d rtm experiments on an anomaly of em shape and a realistic sand dune model demonstrate the effective recovery of 3d subsurface structures

low temperature magnetic behaviour near 35 k in unmetamorphosed claystones summary there is growing evidence that the magnetic assemblage of claystones illustrated by low temperature magnetic transitions at 120 k and 35 k may be representative of the peak burial temperature in the so called oil window 60 150 c in previous studies it was proposed that this magnetic assemblage is characterized by fine grained pyrrhotite fe7s8 and magnetite fe3o4 however evidence of pyrrhotite was not so obvious and the magnetic transition near 35 k of fine grained pyrrhotite has similarities with those of siderite feco3 or rhodochrosite mnco3 here we propose some diagnostic tests to distinct 50 k behaviours by studying claystones from netherlands borehole and borneo prism that experienced different peak burial temperatures we perform magnetic susceptibility temperature dependency of sirm zfc rt sirm and field cooled hysteresis loops on cooling of rt sirm 300 k to 10 k we applied a magnetic field of 5 t to enhance neel type magnetic transition it is found that our samples can be classified in two categories based on the shape of the rt sirm curve one displaying an abrupt break in slope in the remanence at 30 k called n behaviour and the other one characterized by a progressive increase of the remanent magnetization by 80 k named p behaviour the first category contains essentially magnetite and fe mn carbonates the second one magnetite and probably iron sulphides

investigating the geoelectrical response of hydrocarbon contamination undergoing biodegradation 1 a newly proposed geoelectrical model for hydrocarbon contaminated sites predicts high conductivities coincident with the contaminated zone as opposed to the traditionally accepted low conductivity the model attributes the high conductivities to mineral weathering resulting from byproducts of microbial redox processes to evaluate this conductive model in situ vertical conductivity measurements were acquired from a light non aqueous phase liquid lnapl contaminated site the results showed high conductivities coincident with the zone of contamination and within the smear zone influenced by seasonal water table fluctuations we infer this zone as an active zone of biodegradation and suggest significant microbial degradation under partially water saturated conditions a simple archie s law analysis shows large pore water conductivities necessary to reproduce the bulk conductivity measured at the contaminated location this study supports the conductive layer model and demonstrates the potential of geoelectrical investigations for assessing microbial degradation of lnapl impacted soils

spectral induced polarization signatures of abiotic fes precipitation in recent years geophysical methods have been shown to be sensitive to microbial induced mineralization processes the spectral induced polarization sip method appears to be very promising for monitoring mineralization and microbial processes with this work we study the links of mineralization and sip signals in the absence of microbial activity we recorded the sip response during abiotic fes precipitation we show that the sip signals are diagnostic of fes mineralization and can be differentiated from sip signals from biomineralization processes more specifically the imaginary conductivity shows almost linear dependence on the amount of fes precipitating out of solution above the threshold value 0 006 gr under our experimental conditions this research has direct implications for the use of the sip method as a monitoring and decision making tool for sustainable remediation of metals in contaminated soils and groundwater

temporal geophysical signatures from contaminant mass remediation we have previously documented changes in bulk electrical conductivity self potential sp and ground penetrating radar gpr reflections in a field setting caused by biogeochemical transformations of hydrocarbon contaminated media these transformations are associated with hydrocarbon biodegradation the results of surface geophysical surveys acquired in 1996 2003 and 2007 document changes in geophysical signatures associated with removing hydrocarbon mass in the contaminated zone initial investigations in 1996 showed that relative to background the contaminated area was characterized by higher bulk electrical conductivity positive sp anomaly and attenuated gpr reflections repeated surveys in 2003 and 2007 over the contaminated area showed that in 2007 the bulk electrical conductivityhad reverted to near background conditions the positive sp anomaly became more negative and the zone of attenuated gpr reflections showed increased signal strength removal of hydrocarbon mass in the vadose zone o

the recognition of hailstone impressions in clay rich sediment experimental results and relation to the neoproterozoic case abstract based on experimental impacts of hailstone and rain droplets on clayey sediment distinct differences between their imprints are shown the key difference that unequivocally differentiates these impact structures is that raindrop imprints are always part of a sphere even after different degrees of compaction whereas hailstone imprints never have such a shape forming a more or less regular funnel terminated by a nipple like structure that usually retains the original shape of the hailstone we show and discuss the reasons why hailstone imprints have never been reported in the sedimentary record albeit their fossilization potential seems to be much higher than that of raindrop imprints which are commonly reported from various types of sedimentary rocks of widely differing ages inferred hailstone imprints are illustrated from the fossil record for the first time from the neoproterozoic cambrian transition of western africa the origin of paleohailstones required specific dynamic conditions of the atmosphere similar to those of the recent atmosphere present day hailstorms are generally restricted to specific geographic regions e g mid latitude along mountain ranges and they are largely absent from circum polar and circum equatorial areas correspondingly hailstone impact structures preserved in the sedimentary record may possess interpretational value regarding fundamental questions concerning the dynamics of the paleoatmosphere and perhaps paleogeography of ancient continents

rock water interaction in dielectric properties experiments with hydrophobic sandstones the dielectric constant of a partially saturated sandstone varies as a function of the level of water saturation experimental data indicate that rock water interaction at low saturations has a large effect on the measured dielectric response to theoretically predict the dielectric constant of the rock water air system this rock water interaction must be accounted for by including the effect of the water wetting the rock solid alternatively if the rock water interaction can be eliminated a three component dry rock water and air mixing law can be used to model the dielectric behavior in this laboratory study a chemical treatment is used to change four water wet sandstones into hydrophobic sandstones in three hydrophobic samples the rock water interaction seen in the data for the water wet samples is eliminated and the dielectric constant of the partially saturated sandstones can be simply modeled as a dry rock water air system this experimental study illustrates the importance of the chemical state of the rock surfaces in determining the dielectric behavior of sandstones

towards pyrrhotite magnetite geothermometry in low grade metamorphic carbonates of the tethyan himalayas shiar khola central nepal abstract in mesozoic metacarbonates of the tethyan himalayas shiar khola area central nepal two characteristic remanent magnetisations chrm1 and chrm2 were identified by their unblocking temperature spectra the chrm1 is carried by pyrrhotite unblocking temperature 270 360 c and the chrm2 by magnetite unblocking temperature spectra 430 580 c the temperature related formation of pyrrhotite at the expense of primary magnetite during low grade metamorphism in marly carbonates allows the determination of thermal gradients by the pyrrhotite magnetite ratio this new method can be used as a geothermometer for t 300 c in low grade metamorphic carbonates where other methods are not available this method is applied for the first time in the tethyan himalayas of central nepal in the shiar khola valley systematic variations in the ferrimagnetic content of the metacarbonates along an e w profile were detected by the ratio of remanence intensity of pyrrhotite to magnetite derived from natural remanent magnetisation rpyr mag and saturation magnetisation spyr mag over a stretch of 10 km the rpyr mag and spyr mag increase from w to e from 0 42 to 0 91 and 0 48 to 1 0 respectively based on temperature estimates the eastern part experienced upper anchizone epizone 250 300 c conditions while the western part underwent only diagenesis 200 c the temperature gradient and the temperature ranges suggested are consistent with the findings of the calcite twin lamellae geothermometry which is a non magnetic method

geophysical investigation using resistivity and gpr methods a case study of a lubricant oil waste disposal area in the city of ribeirao preto sao paulo brazil geophysics has been shown to be effective in identifying areas contaminated by waste disposal contributing to the greater efficiency of soundings programs and the installation of monitoring wells in the study area four trenches were constructed with a total volume of about 25 000 m3 they were almost totally filled with re refined lubricating oil waste for approximately 25 years no protection liners were used in the bottoms and laterals of the disposal trenches the purpose of this work is to evaluate the potential of the resistivity and ground penetrating radar gpr methods in characterizing the contamination of this lubricant oil waste disposal area in ribeirao preto sp situated on the geological domain of the basalt spills of the serra geral formation and the sandstones of the botucatu formation geophysical results were shown in 2d profiles the geophysical methods used enabled the identification of geophysical anomalies which characterized the contamination produced by the trenches filled with lubricant oil waste conductive anomalies smaller than 185 m immediately below the trenches suggest the action of bacteria in the hydrocarbons as has been observed in several sites contaminated by hydrocarbons in previously reported cases in the literature it was also possible to define the geometry of the trenches as evidenced by the gpr method direct sampling chemical analysis of the soil and the water in the monitoring well confirmed the contamination in the soil analysis low concentrations of several polycyclic aromatic hydrocarbons pahs were found mainly naphthalene and phenanthrene in the water samples an analysis verified contamination of the groundwater by lead pb the geophysical methods used in the investigation provided an excellent tool for environmental characterization in this study of a lubricant oil waste disposal area and could be applied in the study of similar areas

the late diagenetic conversion of pyrite to magnetite by organically complexed ferric iron abstract the geochemistry of late stage diagenetic replacement of pyrite by magnetite was investigated by laboratory experiments of pyrite dissolution and magnetite precipitation involving organically complexed ferric iron the design of the experiments is based on the hypothesized geochemical conditions for in situ diagenesis in the pennsylvanian age belden formation an organic rich carbonate in northwestern colorado with pyrite grains rimmed with magnetite that contains a cretaceous paleopole position the geochemistry is applicable to both deep and near surface reactions involving pyrite magnetite and organic matter and bears upon the geologic interpretation of secondary chemical remanent magnetizations crm aqueous solutions of ferric ligand complexes and pyrite were heated 60 c for 60 days in the absence of light and at low partial pressures of oxygen additional experiments with each ligand were performed both in the presence of bentonite and without ferric iron ligand only raising the ph to 8 5 produced a ferrous hydroxide precipitate and subsequent heating 90 c resulted in the formation of magnetite ferric complexes of oxalate salicylate and acetylacetonate resulted in pyrite dissolution and magnetite formation the activity of strongly reducing ligands e g catechol or unsaturated fe iii exchange capacity particularly in experiments with bentonite or with solutions of uncomplexed ligands can result in an effective reduction of ferric iron concentration and prevent pyrite dissolution and or interfere with the crystallization of magnetite the bentonite acted to adsorb dissolved species and also underwent direct dissolution especially by the oxalate ligands although these reactions could occur at any depth a continuing supply of molecular oxygen more available in near surface settings would result in the formation of hematite or the production of acidic sulfate conditions whereas at greater depths or restricted porosity the redox gradation is halted at magnetite the results of this study thus provide a likely geochemical mechanism for the replacement of pyrite by magnetite during the latter stages of diagenesis

raindrop imprints in the late archaean early proterozoic ventersdorp supergroup south africa abstract well preserved raindrop imprints occur in ventersdorp rocks of randian age 2 7 ga on mudflakes at five different stratigraphic levels in a sequence which consists of alternating beds of arkose and tuff the raindrop imprints indicate that an atmosphere did exist and that the arkose was deposited in an environment periodically exposed to the atmosphere these are as far as is known the oldest raindrop craters ever to be described special conditions governing their formation and preservation are given

a comparison of the correlation structure in gpr images of deltaic and barrier spit depositional environments we have used geostatistical analysis of radar reflections to quantify the correlation structures found in 2 d ground penetrating radar gpr images we find that the experimental semivariogram the product of the geostatistical analysis of the gpr data is well defined and can be modeled using standard geostatistical models to obtain an estimate of the range or correlation length and the maximum correlation direction in the 2 d gpr image when we compare the results from geostatistical analysis of gpr data from selected deltaic and barrier spit depositional environments we find different correlation structures in gpr images from different depositional environments gpr images from braid deltas have near horizontal correlation directions and correlation lengths on the order of a few meters in contrast the gpr image of a fan foreset delta has a very long 24 m correlation length and a maximum correlation direction plunging 20 in the gpr images from barrier spits we find maximum correlation directio

high precision three dimensional paleothermometry derived from paleomagnetic data in an alpine metamorphic unit in the dauphinoise zone of the french western alps a posttectonic thermoremanent magnetization carried by pyrrhotite has been isolated the paleomagnetic signature is interpreted as the record of successive partial thermoremanent magnetizations of opposite directions acquired during the early miocene slow cooling of the epimetamorphic marly limestones of the studied area a local vertical thermal gradient of 22 2 c km was derived from the unblocking temperature of a reversal recorded at different altitudes using this vertical gradient we have produced a paleotemperature map at the time of the reversal about 20 ma the map shows a horizontal regional thermal gradient of 7 c km the higher temperatures were toward the crystalline basement paleomagnetic directions demonstrate that this horizontal gradient was present during cooling its origin can be explained by large volume fluid circulation along the major fault that forms the boundary between the crystalline basement and its liassic cover

coupling ground penetrating radar and fluid flow modeling for oilfield monitoring applications the recent introduction of smart well technology allows for new geophysical monitoring opportunities smart wells which allow zonal production control combined with monitoring techniques capable of capturing the arrival of undesired fluids have the potential to significantly increase the oil recovery we consider borehole radar as a valuable technology for monitoring of the near well region by coupling a drainage process of a bottom water drive reservoir with electromagnetic simulations we find that radar sensors located in the production well can successfully map the fluid saturation evolution in low conductivity reservoirs 0 02 s m a system performance above 80 db is necessary to record reflections in the range of 10 m higher conductivity values strongly reduce the radar investigation depth despite the technical challenges to implement a permanent down hole radar system the potential semi continuous acquisition would make 4d ground penetrating radar a promising technology in capturing the near well fluid dynamics suitable environments are bottom water drive reservoirs with thin oil layer and heavy oil reservoirs exploited by steam assisted gravity drainage processes

the jameson land basin east greenland a fission track study of the tectonic and thermal evolution in the cenozoic north atlantic spreading regime abstract the late mesozoic and cenozoic thermal history of the jameson land basin is constrained by new apatite and zircon fission track ft data of surface permian to jurassic sedimentary rocks the results show a general regional thermal evolution related to burial to temperatures close to and in excess of the maximum temperatures of the apatite annealing interval 125 c followed by cooling mainly due to cenozoic uplift and erosion faulting and differential movements in the basin generally occurred after cooling below the apatite partial annealing zone paz 75 125 c however in the northern part of the basin the data suggest a thicker sediment cover or localized heating related to an earlier fracture zone both apatite ft analysis and vitrinite reflectance values reveal a postmature signature for the studied rocks in the northeastern jameson land and premature to mature for the western central and southern jameson land rocks with respect to generation of hydrocarbons the chemical variations of apatite enhance the possibility of recognizing sample positions near maximum temperatures in the paz furthermore the pb zn mineralization pattern closely follows the tertiary maturity trend given by the ft data the type and distribution of mineralization suggest that it was influenced by the regional thermal evolution of the basin in the northeast domain circulating fluids may have overprinted the regional thermal record before ca 20 ma basaltic dyke and sill intrusions 55 45 ma locally caused resetting of apatite ft ages but generally the direct influence from upper crustal magmatic activity played only a minor role the thermal evolution in northeast jameson land is related to the late tectonic evolution of the northeast atlantic involving a change in ridge position at ca 25 ma which followed the passage of the proto icelandic mantle plume at 63 40 ma

a new oil window indicator the magnetic assemblage of claystones from the baffin bay volcanic margin greenland identifying independent parameters to bracket the oil window in sedimentary basins is of first importance for petroleum exploration we investigate the magnetic assemblage of cretaceous claystones collected from the western volcanic margin of greenland these claystones experienced low grade burial 300 k properties of isothermal remanent magnetization the magnetic assemblage of immature claystones lower ro resides in goethite greigite and some magnetite the magnetic assemblage of immature to early mature claystones higher ro resides in stoichiometric magnetite and fine grained pyrrhotite by comparing these results with those from claystones from the paris basin france and the jura mountains switzerland we suggest the existence of similar mechanisms for the formation of magnetic minerals during burial if confirmed by further studies the magnetic assemblage of claystones may be diagnostic of oil windows

deep structures and breakup along volcanic rifted margins insights from integrated studies along the outer voring basin norway three dimensional multichannel seismic survey and well data allows a deeper insight into rifting mechanisms and crustal structure of the norwegian volcanic rifted margin a surprising high velocity lower crustal dome marked by a strong amplitude reflection t reflection is described below the north gjallar ridge ngr near the volcanic plateau formed during the late paleocene early eocene breakup faulting along the ngr occurs during early campanian paleocene and is controlled by the crustal dome the t reflection was previously related to either the top of mafic underplated crust or soft lower crust updomed during the continental breakup the influence and timing of the crustal dome on the basin structure shows clearly that the dome predates the continental breakup based on the structural relationship and the results of the modelling it is therefore concluded that the t reflection does not necessarily originate from an anomalous tertiary magmatic event related to the breakup underplated material but could be also partly attributed to pre breakup mafic material or and inherited high pressure granulite eclogite rocks in the continental domain q 2004 elsevier ltd all rights reserved

low temperature magnetic properties of siderite and magnetite in marine sediments low temperature magnetic techniques provide useful tools to detect the presence of magnetite and pyrrhotite in sediments through identification of their low temperature transitions to determine the amount of ultrafine grained superparamagnetic material in sediments and can potentially detect the presence of certain types of magnetotactic bacteria application of these types of experiments to nannofossil chalks from beneath the barbados accretionary prism led to some unusual results which are attributed to the presence of siderite thermal demagnetization of low temperature remanence after cooling in zero field and in a 2 5 t field both displayed large remanence losses from 20 k to 40 k below 40 k the magnetization of the chalks was much higher in the field cooled experiments than in the zero field cooled experiments low temperature hysteresis experiments made after cooling in a 2 5 t field displayed offsets in magnetization parallel to the direction of the initial applied field when measured below 40 k the offset loops can be due to either an exchange anisotropy between siderite and magnetite phases in the sediments a defect moment in the siderites or a canted moment in the siderites apparent similarity between the low temperature thermal demagnetization results from these siderite bearing sediments pure siderite and pure rhodochrosite samples and the well known 34 k transition in pyrrhotite should lead to caution in identification of pyrrhotite in marine sediments based on low temperature remanence studies alone

evidence for eight great earthquake subsidence events detected with ground penetrating radar willapa barrier washington a new approach to detect holocene subduction zone earthquakes combines the results from ground penetrating radar gpr vibracores and accelerator mass spectrometry ams dates from a barrier spit located west of willapa bay southwest washington gpr data show a 10 m thick facies of beach sand within which we identify and vibracores confirm beach parallel wave eroded buried scarps mantled with multiple beds of magnetite the eight gpr detected buried scarps are interpreted to be eroded by minor transgressions caused by instantaneous barrier subsidence during earthquakes associated with the juan de fuca plate subducting under the north american plate of these scarps four have been ams dated at 300 1110 2540 and 4250 radiocarbon yr b p no datable material has yet been found for the other four radar detected scarps but we interpolate and extrapolate dates of 1800 3400 5000 and 5800 yr b p

ground penetrating radar images of selected fluvial deposits in the netherlands ground penetrating radar gpr surveys have been carried out in order to characterise reflection patterns and to assess the method s potential for imaging palaeofluvial sediments in the mass rhine former confluence area in the southern netherlands the results show that the deposits of meandering braided and transitional river types produce characteristic radar facies representative examples of each of these river types were selected where the gpr data could be directly correlated with sedimentary information derived from exposures and detailed drilling and geomorphological data could be supplied individual channels may be distinguished by the radar facies of their fills the floodplains of the different river types also show a characteristic radar facies in gpr data from the meander floodplain parallel dipping reflections represent point bar structures while irregular intersecting small channel patterns that alternate with parallel continuous reflections are more typical in the braid plain a transitional river type shows characteristics of both of these types typical examples of gpr sections recorded in each of the different fluvial palaeoenvironments are presented in an interpretative radar facies chart

examples of reverse time migration of single channel ground penetrating radar profiles a single channel ground penetrating radar gpr profile portrays a distorted unfocused image of subsurface structure due to apparent position shifts associated with dipping reflectors and to diffractions from corners and edges a focused image may be produced from such data by using any of the migration algorithms previously developed for seismic data we use reverse time migration based on the scalar wave equation field work was performed over a simple stratigraphic soil sequence and a complicated fluvial environment in the migrated images reflector continuity is enhanced and the level of detail available for high resolution interpretation is significantly increased

searching for single domain magnetite in the pseudo single domain sedimentary haystack implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations 1 magnetic hysteresis measurements of sediments have resulted in widespread reporting of pseudo single domain like magnetic properties in contrast the ideal single domain sd properties that would be expected to be responsible for high quality paleomagnetic records are rare determining whether sd particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment we apply a range of such techniques and find that sd particles are much more common than has been reported in the literature and that magnetite magnetofossils the inorganic remains of magnetotactic bacteria are widely preserved at depth in a range of sediment types including biogenic pelagic carbonates lacustrine and marine clays and possibly even in glaci marine sediments thus instead of being rarely preserved in the geological record we find that magnetofossils are widespread this observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments magnetofossils also have grain sizes that are substantially smaller than the 1 15 m size range for which there is reasonable empirical support for relative paleointensity studies the different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies this issue needs much closer attention despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years much remains to be understood about how they become magnetized

laboratory chemical remanent magnetization in a natural claystone a record of two magnetic polarities summary a record of two magnetic polarities during the acquisition by heating of a laboratory chemical remanent magnetization crm in a natural pyrite rich claystone was investigated the samples were heated for 22 hr at 250 ci na controlled magnetic field 1 0 mt under an argon atmosphere we interpret the origin of crm as the surface oxidation of pyrite to magnetite which in turn is progressively oxidized into haematite we carried out experiments under a constant polarity magnetic field and under two opposite polarities the resulting crm was measured after cooling in zero field it is parallel to the applied field and has the direction of the last polarity thermal demagnetization under an argon atmosphere isolates an unexpected lowunblocking temperature component t ub 220 c this component probably results from thermal alteration of magnetic carriers during subsequent thermal demagnetization in the onepolarity experiments thermal demagnetization of crm above 220 c isolates a well defined component parallel to the imparted field direction in the experiments with two magnetic polarities thermal demagnetization of crm reveals two components of opposite polarity the component which is parallel to the direction of the last applied field is well defined while the other component which has the polarity of the first applied field is ill defined oppositely directed components are also detected by using alternating field demagnetization

sedimentary response to mantle plumes implications from paleocene onshore successions west and east greenland the uplift history of the upper cretaceous paleocene sedimentary successions underneath the extensive tertiary flood basalts of west and east greenland supports recently described models for the generation of flood basalt provinces in response to rising hot mantle plumes however the sedimentary development indicates that the period of plume related uplift prior to eruption of volcanic rocks was very short 5 m y substantial regional uplift and faulting took place in west and east greenland in the early paleocene to earliest late paleocene resulting in a basinwide unconformity in west greenland the uplift was associated with fluvial peneplanation valley incision and catastrophic deposition in east greenland it was associated with fluvial peneplanation the cumulative uplift in west greenland is probably on the order of several hundred meters whereas in east greenland the observed uplift cannot be quantified in both west and east greenland this phase was shortly followed by rapid major subsidence associated with extensive volcanism it is suggested that this sequence of events reflects the arrival of the north atlantic mantle plume or plumes

pyrrhotite as a tracer for denudation of the taiwan orogen 1 the use of pyrrhotite as an index mineral to delineate metamorphic isograds has long been proposed however details of the occurrence of pyrrhotite in different metamorphic facies and its implications have rarely been explored here by simple characterization of magnetic properties and mineral identification we demonstrate that pyrrhotite is widely distributed in low grade metamorphic terranes of taiwan s central range and in sediments derived therefrom by coupling the distribution of pyrrhotite in rocks with that in dated sediment strata we have studied the denudation history of taiwan s orogen from a source to sink perspective we suggest that pyrrhotite is a potential tracer for studying surface processes in orogens with high denudation rates similar to that in taiwan

theoretical constraints on oxygen and carbon dioxide concentrations in the precambrian atmosphere simple one dimensional climate models suggest that carbon dioxide concentrations during the archean must have been at least 100 1000 times the present level to keep the earth s surface temperature above freezing in the face of decreased solar luminosity such models provide only lower bounds on co2 so it is possible that co2 levels were substantially higher than this and that the archean climate was much warmer than today periods of extensive glaciation during the early and late proterozoic on the other hand indicate that the climate at these times was relatively cool to be consistent with climate models co2 partial pressures must have declined from approximately 0 03 to 0 3 bar around 2 5 ga ago to between 10 3 and 10 2 bar at 0 8 ga ago this steep decrease in carbon dioxide concentrations may be inconsistent with paleosol data which implies that pco2 did not change appreciably during that time oxygen was essentially absent from the earth s atmosphere and oceans prior to the emergence of a photosynthetic source probably during the late archean during the early proterozoic the atmosphere and surface ocean were apparently oxidizing while the deep ocean remained reducing an upper limit of 6 x 10 3 bar for po2 at this time can be derived by balancing the burial rate of organic carbon with the rate of oxidation of ferrous iron in the deep ocean the establishment of oxidizing conditions in the deep ocean marked by the disappearance of banded iron formations approximately 1 7 ga ago permitted atmospheric oxygen to climb to its present level o2 concentrations may have remained substantially lower than today however until well into the phanerozoic

evidence for microbial enhanced electrical conductivity in hydrocarbon contaminated sediments 1 bulk electrical conductivity of sediments during microbial mineralization of diesel was investigated in a mesoscale laboratory experiment consisting of biotic contaminated and uncontaminated columns population numbers of oil degrading microorganisms increased with a clear pattern of depth zonation within the contaminated column not observed in the uncontaminated column microbial community structure determined from ribosomal dna intergenic spacer analysis showed a highly specialized microbial community in the contaminated column the contaminated column showed temporal increases in bulk conductivity dissolved inorganic carbon and calcium suggesting that the high bulk conductivity is due to enhanced mineral weathering from microbial activity the greatest change in bulk conductivity occurred in sediments above the water table saturated with diesel variations in electrical conductivity magnitude and microbial populations and their depth distribution in the contaminated column are similar to field observations the results of this study suggest that geophysical methodologies may potentially be used to investigate microbial activity

magnetic transition at 30 34 kelvin in pyrrhotite insight into a widespread occurrence of this mineral in rocks abstract a characteristic magnetic transition at 30 34 k is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low temperature techniques as applied to magnetite and hematite extended down to liquid helium temperature a review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals unblocking temperature up to 350 c and extreme resistance against af may be encountered in fine grained pyrrhotite

using gpr data as constraints in rmt data inversion for water content estimation a case study in heby sweden this study uses ground penetrating radar gpr data as constraints in the inversion of radio magnetotelluric rmt data to provide an improved model at shallow depth we show that modification of the model regularization matrix using all gpr common offset co reflections can mislead the constrained inversion of rmt data to avoid such problems common mid point cmp gpr data are translated to a resistivity model by introducing a new petrophysical relationship based on a combination of topp s and archie s equations this model is updated through a semi iterative method and is employed as an initial and prior model in the subsequent inversion of rmt data finally a water content model that fits the gpr cmp and rmt data is derived from the resistivity model computed by the constrained inversion of rmt data to assess the proposed scheme it is applied to a synthetic data set then real rmt data collected along an 870 m long profile across a known aquifer situated in the north of heby central sweden are inverted by removing the smoothness constraints across gpr co interfaces or using cmp based inversion thick 10 m vadose and saturated zones are resolved and shown to correlate with logs from nearby boreholes nevertheless the application of our cmp based inversion was the only efficient scheme to retrieve thin 3 m saturated zones and the water table at a depth of 7 15 m in the rmt models the estimated models of water content are in good agreement with the available hydrogeological information in the study area

experimental evaluation of thermal recording of successive polarities during uplift of metasediments summary the discovery of a post tectonic natural remanent magnetization nrm carried by pyrrhotite in the dauphinoise zone of the western alps allows us to test the ability of these rocks to record a sequence of magnetic polarity versus temperature acquired during their slow cooling several laboratory experiments composite partial thermal remanent magnetizations ptrms thellier thellier experiments trm thermal demagnetization as well as nrm demagnetization were performed this shows that the pyrrhotite grains are single domain sized and that they are able to record successive independent ptrms the nrm thermal demagnetization analysis demonstrates the occurrence of several antiparallel components a comparison between nrm and trm thermal demagnetizations is attempted in order to highlight small ptrms naturally recorded in a temperature interval of only a few degrees we attempt to retrieve the temperature at which each reversal occurs during the post metamorphic cooling this method called thermopalaeomagnetism is discussed and developed in order to delineate the sequence of polarity chrons recorded versus temperature

ground penetrating radar of northern lacustrine deltas ground penetrating radar gpr was used in several selected deltaic sedimentary environments to better understand subsurface stratigraphy and reconstruct former depositional environments the profiles provide high resolution continuous subsurface data on facies thickness and depths orientation of major sedimentary structures postdepositional failure planes and depth of peat deposits field experiments were carried out on six river deltas records from four of the deltas exhibit sedimentary facies a record from one delta shows a possible slump and records from another delta reveal the thickness and stratigraphic relationships of peat deposits the delta types are i sandy wave influenced ii sandy immature wave influenced steeper middle and lower shoreface iii sandy braided and iv gravelly fan foreset in areas of limited subsurface control stratigraphic logs from drill core cutbank exposure or geophysical logs radar profiles can provide big picture perspectives of the subsurface

biogeophysics a new frontier in earth science research 1 biogeophysics is a rapidly evolving earth science discipline concerned with the geophysical signatures of microbial interactions with geologic media it spans the established disciplines of geomicrobiology biogeoscience and geophysics biogeophysics research in the last decade has confirmed the potential for geophysical techniques to measure not simply the physical and chemical properties of the subsurface as already well established but also to detect microbes microbial growth and microbe mineral interactions thus representing a major paradigm shift in geophysical thinking in this review we begin by defining biogeophysics and provide a historical perspective we then consider microbial alterations of petrophysical properties as such alteration is the source of most biogeophysical signals our review then focuses on geophysical interrogation of microbial processes including the direct detection of microbial cells and biofilm formation microbial metabolic by products microbe mediated redox processes and biogeochemical and microbe mineral transformations we conclude by discussing challenges opportunities and potential new applications of biogeophysics to the exploration of life in extreme environments e g the deep biosphere the cryosphere and other planets we find that published biogeophysics studies to date are mostly observation based presenting only empirical relationships between microbial and geophysical variables future research endeavors must focus on developing theoretical and or numerical models for predicting geophysical signals arising from microbial activity

continuous production of nanosized magnetite through low grade burial geological processes such as burial can lead to remagnetization in rocks due to neoformed magnetic minerals that have passed a critical volume called blocking volume in this study we designed a heating experiment for claystones obtained from the paris basin france in the 50 130 c temperature range in order to simulate 20 nm and 20 nm minerals respectively this result led us to propose a conceptual model of nucleation and growth process of magnetite during low grade burial from 2 to 4 km depth ultrafine magnetite 20 nm was predominant over single domain magnetite 20 nm for 4 km depth transposed to natural conditions our heating steps experiment suggested that claystone type rocks are remagnetized during burial for temperatures higher than 200 c the extrapolation of our results indicated that burial remagnetization due to the chemical remanent magnetization might be larger than the natural remanent magnetization 2012 american geophysical union all rights reserved

kar systematics of clay to mica minerals in a multi stage low grade metamorphic evolution the behavior of the ar isotopic system of clay to mica fractions was studied in cambrian greywacke samples along a transect of northwestern morocco these rocks were affected by a progressively increasing metamorphic overprint spanning from diagenetic to epizonal metamorphic conditions k ar isotopic data of 0 2 10 m size fractions recovered from seven samples allowed to recognized three episodes of illite crystallization 1 during an upper ordovician thermal event at 445 ma which is characterized by an illite chlorite mineral paragenesis in the northernmost part of the transect 2 during a carboniferous low grade overprint at 305 ma which is characterized by a similar mineral paragenesis and 3 during a triassic to liassic hydrothermal activity at 205 ma which generated a smectite dominated paragenesis the ages were examined in combining x ray mineralogic and k ar isotopic data in terms of linear arrays in both isochron and harper diagrams to differentiate true isochrons from mixing lines it could also be shown that mixtures of two generations of micaceous minerals can induce different trends in the k ar dates depending whether the first generation of minerals was either or not affected by the event inducing the later generation

ground penetrating radar for environmental applications abstract ground penetrating radar gpr is a near surface geophysical technique that can provide high resolution images of the dielectric properties of the top few tens of meters of the earth in applications in contaminant hydrology radar data can be used to detect the presence of liquid organic contaminants many of which have dielectric properties distinctly different from those of the other solid and fluid components in the subsurface the resolution approximately meter scale of the radar imaging method is such that it can also be used in the development of hydrogeologic models of the subsurface required to predict the fate and transport of contaminants gpr images are interpreted to obtain models of the large scale architecture of the subsurface and to assist in estimating hydrogeologic properties such as water content porosity and permeability its noninvasive capabilities make gpr an attractive alternative to the traditional methods used for subsurface characterization

field evidence for geophysical detection of subsurface zones of enhanced microbial activity 1 geochemical data from closely spaced vertical intervals in a hydrocarbon impacted aquifer were used to assess the relationship between bulk conductivity and zones of enhanced microbial activity the bulk conductivity was measured using in situ vertical resistivity probes microbial activity was verified using terminal electron acceptors nitrate sulfate iron and manganese dissolved inorganic carbon dic and major ion chemistry peaks in bulk conductivity in the aquifer overlapped with zones where nitrates and sulfates were depleted total petroleum hydrocarbon iron manganese dissolved ions and dic were elevated suggesting a link between higher electrical conductivity and zones of enhanced microbial activity stimulated by the presence of hydrocarbon thus the subsurface expression of microbial activity is apparently recorded in the bulk conductivity measurements our results argue for combining geophysics with biogeochemistry studies to delineate subsurface zones of enhanced microbial activity

cenozoic remagnetization of the paleozoic rocks in the kitakami massif of northeast japan and its tectonic implications abstract secondary remanent magnetization is identified in the paleozoic igneous and sedimentary rocks of the kitakami massif the secondary nature is shown by a negative fold test for the permo carboniferous sedimentary rocks the northwesterly paleomagnetic declination with moderate inclination d 321 2 i 56 5 95 5 2 n 18 of this secondary remanent magnetization is almost parallel to the primary magnetization reported for the cenozoic welded tuffs of northeast japan indicating that the paleozoic rocks were subjected to remagnetization at any period between 62 and 16 ma the secondary magnetization of the serpentinized ultramafic rocks is carried by magnetite which grew in veins and mesh rims of serpentine whereas the carrier of the magnetization in limestones is fine grained pyrrhotite combining this with the previously reported remagnetization of the kitakami granitic rocks it is suggested that rocks in the kitakami massif were subjected to crystallization remanent magnetization at low temperature conditions since serpentinization requires fluid migration one of the most likely events is the eastward lateral migration of water into the kitakami massif we postulate a cenozoic suturing of the kitakami massif with the asian continent as a plausible tectonic event for this fluid migration

velocity variations and water content estimated from multi offset ground penetrating radar the common midpoint cmp processing technique has been shown to be effective in improving the results of ground penetrating radar gpr profiling when radar data are collected with the cmp multioffset geometry stacking increases the signal to noise ratio of subsurface radar reflections and results in an improved subsurface image an important aspect of cmp processing is normal moveout velocity analysis our objectives are to show the effect of multiple velocity analyses on the stacked radar image and particularly to demonstrate that this velocity information can also be used to determine subsurface water content most gpr surveys are very limited in spatial extent and assume that within the survey range radar velocity structure in the shallow subsurface can be adequately approximated by a single velocity function in data processing in this study we show that variation in radar velocity can be quite significant and that the stacked profile improves as the number of velocity analysis locations is increased interval velocities can be calculated from the normal moveout velocities derived in the cmp velocity analysis with some reasonable assumptions about subsurface conditions necessary for radar propagation interval velocity can be converted to an estimate of volumetric water content therefore by collecting gpr data in the multioffset cmp geometry not only is the radar profile improved but it also allows for an interpretation of subsurface variation in water content we show the application of these techniques to multioffset gpr data from the chalk river test area operated by atomic energy of canada limited

influence of oil wettability upon spectral induced polarization of oil bearing sands the presence of oil in an unconsolidated granular porous material like a sand changes both the resistivity of the material and the value of the phase lag between the current and the voltage we performed laboratory experiments to investigate the influence of oil wettability and water saturation upon the complex resistivity of oil bearing sands in the frequency range 1 mhz 1 khz for a sand saturated by a nonwetting oil both the resistivity and the magnitude of the phase increase with the oil saturation as expected from theoretical considerations in the case of a sand partially saturated by a wetting oil we found that both the magnitude of the phase and the resistivity decrease with the oil saturation the quadrature conductivity decreases with the oil with the same trend in presence of wetting and nonwetting oils for relative water saturation above 0 5 in the case of a nonwetting oil the results are quantitatively predicted by available theories in the case of a wet oil our results could be inte

a new concept in modeling the dielectric response of sandstones defining a wetted rock and bulk water system experimental data for the real part of the dielectric constant k of three sandstone samples are considered as a function of the level of water saturation sw in the frequency range 60 khz to 4 mhz existing theoretical models have previously shown poor agreement with k versus sw data for rock samples undoubtedly due to the complexity involved in adequately accounting for geometrical and electrochemical effects in analyzing the data presented here we find a pronounced increase in k in the low saturation region which in all cases can be attributed to the establishment of geometrical and surface effects associated with the rock water interface when this increase in k is accounted for by defining wetted matrix parameters the data show excellent agreement with existing theoretical models

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

paleomagnetism of the notch peak contact metamorphic aureole revisited pyrrhotite from magnetite pyrite under submetamorphic conditions 1 on the basis of new demagnetization and rock magnetic experiments a scattered two polarity remagnetization extending throughout the contact metamorphic aureole surrounding the jurassic notch peak granitic stock in western utah is now thought to reside in metamorphic pyrrhotite rather than in fine grained hematite in part the pyrrhotite formed by in situ reduction of magnetite by pyrite and organic compounds it could not have been formed by the large scale introduction of reducing fluids as isotopic evidence indicates that these metalimestones remained impermeable at higher grades some pyrrhotite probably also formed by the reaction of pyrite and fe bearing silicates as magnetite destruction and pyrrhotite formation extends into rocks that are not obviously metamorphosed the reactions responsible could proceed at very low less than 200 c temperatures and the feasibility of such low temperature reactions in a closed system is shown by detailed thermodynamic calculations this study demonstrates that under reducing conditions in the presence of sufficient pyrite pyrrhotite can form at the expense of magnetite under very mild conditions indeed magnetite may be destroyed merely by deep burial such a mechanism may help explain the paucity of primary magnetite in ancient sedimentary rocks particularly since the single domain and pseudo single domain grains capable of retaining a stable paleomagnetic signature over geologic time are extremely fine grained and hence particularly vulnerable to destruction

why not raindrop impressions abstract field observations show that most raindrop impressions are produced during the last vestiges of shower activity when the rain has almost ceased to fall these fewer number of raindrops impact upon portions of the mud surface that have the right degree of saturation to retain impressions this accounts for the isolated nature of most modern and fossil raindrop impressions while not all so called raindrop impressions are considered to have formed due to the impact of raindrops one can not eliminate their important role

intrusion history of the portrush sill county antrim northern ireland evidence for rapid emplacement and high temperature contact metamorphism the gabbroic portrush sill in northern ireland part of the north atlantic igneous province intruded lower jurassic mudstones and siltstones about 55 ma ago we used petrologic observations and geochemical analyses to study how the sill interacted with the sedimentary rocks field relationships show that an upper sill and numerous associated minor intrusions were emplaced in the sedimentary host rocks before intrusion of the main sill some 10 m above its upper contact geochemical analyses reveal two magma contamination processes nb and ta anomalies coupled with incompatible element enrichment record contamination by deep crustal rocks whereas li pb and ba anomalies reveal a superficial contamination through fluid circulation at the contact between magmatic and sedimentary rocks analysis of mineral assemblages and geochemical data from the contact aureole demonstrate uniform metamorphic conditions between the two main intrusions and an absence of a thermal gradient the identification of pyrrhotite by magnetization analyses and of orthopyroxene by microprobe analyses indicates very high temperatures up to 660 c thermal modelling explains these temperatures as the coupled effects of the main sill and the earlier intruded upper sill and minor intrusions even though the chemical composition of the main sill suggests another type of parental liquid all three units were emplaced in a very short time certainly less than five years

vitrinite reflectance and molecular geochemistry of jurassic sediments the influence of heating by tertiary dykes northwest scotland vitrinite reflectance measurements from sedimentary rocks adjacent to six dykes from sites across the inner hebrides indicate that the lateral extent of thermal alteration is reasonably similar and proportional to dyke thickness d t with alteration starting to take effect at 70 d t detailed sampling of a jurassic siltstone adjacent to a 0 9 m dyke reveals that the zone of maximum extractable organic matter eom wt g rock equivalent to the oil window is relatively narrow ca 25 of the d t the position of this oil window relative o the vitrinite reflectance profile is comparable with that from burial maturation gas chromatograms of the aliphatic hydrocarbon fractions reveal i a shift from branched and cyclic dominated hydrocarbons to an increasing predominance of straight chain components and ii the carbon number distribution of the n alkanes shifts towards the shorter chain homologues with decreasing distance from the dyke contact apart from the methylphenanthrene index mpi1 changes in each of the molecular maturity parameters are initiated by the the thermal effects of the dyke between 80 and 70 d t from the contact the mpi1 parameter was the most sensitive maturity indicator in that it responded to the dyke emplacement even in the distal samples i e distance from dyke contact 140 d t a significant reduction in toc at the dyke contact suggests that the synthesis gas reaction may have occurred i e the reaction of organic matter with steam resulting in the formation of carbon monoxide this reaction may be associated with the vitrinite reflectance reversal this study suggests that these particular dykes have had only a local effect on the maturity of the intruded sediments

geostatistical analysis of ground penetrating radar data a means of describing spatial variation in the subsurface we have investigated the use of ground penetrating radar gfr as a means of characterizing the heterogeneity of the subsurface radar data were collected at several sites in southwestern british columbia underlain by glaciodeltaic sediments a cliff face study was conducted in which geostatistical analysis of a digitized photograph of the face and the radar image of the face showed excellent agreement in the maximum correlation direction and the correlation length determined from these two data sets other two dimensional 2 d sections of radar data were divided into sedimentary architectural elements on the basis of the distinct radar appearance of these sedimentary units examples of four sedimentary units were used to obtain semivariograms from the radar data and resulted in maximum correlation lengths between 0 5 and 4 8 m a 3 d radar survey collected over a package of gravel and sand foresets was analyzed to determine the paleoflow direction a correlation length of 4 m was found in that direction

ground penetrating radar monitoring of a controlled dnapl release 200 mhz radar a controlled release of tetrachloroethylene was performed in a saturated natural sandy aquifer to evaluate the effectiveness of various geophysical techniques for detecting and monitoring dense nonaqueous phase liquids dnapls in the subsurface tetrachloroethylene typical of most dnapls has a low relative dielectric permittivity 2 3 which contrasts with the high relative permittivity 80 of the pore water it displaces making it a potential target for detection by ground penetrating radar gpr gpr data were acquired using 200 mhz antennas radar sections collected at different times over the same spatial location clearly show the changes induced by the movement of dnapl in the subsurface temporal changes can be examined through the evolution of a radar data trace collected at a single spatial location normal moveout analysis of common midpoint cmp data demonstrates induced changes in electromagnetic em wave velocities of up to 30 percent caused by the presence of dnapl the distribution o

metamorphic control of the magnetic mineralogy of black shales in the swiss alps toward the use of magnetic isogrades abstract the magnetic susceptibility of the helvetic jurassic black shales sampled around the aar and gothard massifs in the swiss alps is due to iron bearing silicates magnetite or pyrrhotite it exhibits a clear correlation with the alpine metamorphism from zeolite to amphibolite facies it firstly decreases due to the breakdown of original magnetite then sharply increases when pyrite is transformed into magnetic pyrrhotite using numerous field measurements of the susceptibility it was possible to carry out a fast and precise mapping of the pyrrhotite in isograde which appears to correspond closely to the stilpnomelane out isograde the matrix susceptibility obtained by means of high field measurements with a cryogenic magnetometer is due to iron bearing silicates and shows only smooth variations with metamorphism both monoclinic and hexagonal pyrrhotites are observed in the high grade area

petrogenesis of late stage magmatism at hold with hope east greenland the myggbukta caldera complex and a swarm of basic dykes constitute the latest tertiary magmatism in the hold with hope region east greenland the sr and nd isotope ratios of these rocks show coherent variations which extend to high 87sr 86sr and low 143nd 144nd values and require a contribution from continental lithosphere broad correlations with major element differentiation indices suggest that the continental component was incorporated during magmatic differentiation thereby favouring a crustal contamination process trace element concentrations are strongly correlated with isotopic compositions but display ranges for many incompatible elements which extend beyond likely crustal contaminant compositions this is readily modelled by afc processes in which the dominant cause of trace element enrichment is the concentration effect of fractional crystallisation rather than the composition of the contaminant the simplest such models still require unrealistically high degrees of fractional crystallisation to explain the ten fold enrichment of some trace elements this can be overcome if the primary magmas entering the crust already had highly variable trace element compositions such variability is readily achieved if melts from different parts of the melting column escape without thorough homogenization an afc model which incorporates variability in parental magma composition is then able to simulate the range of compositions observed at hold with hope this carries the implication that the variations observed are more readily attributed to changes in uncontaminated parental magma than to variations in the composition or amount of contaminant

spatial correlation structure estimation using geophysical and hydrogeological data the large spatial variability of hydraulic properties in natural geologic systems over a wide range of scales and the difficulty of collecting representative and sufficient hydraulic property measurements using conventional sampling techniques render estimation of spatial correlation parameters difficult further compounding the estimation problem is the observation that the integral scale estimate is a function of the measurement support scale to mitigate these problems we investigate the use of tomographic geophysical data in combination with hydrogeological data in the spatial correlation estimation procedure two synthetic case studies were investigated where the scale of the geophysical measurements were varied relative to the scale of the hydrogeological properties the spatial correlation structure parameter estimation procedure was performed in the spectral domain where analysis of data having different support scales and spatial sampling windows was facilitated comparison of the spatial correlation structure parameters estimated from measured data with those of the synthetic aquifers revealed which type of data tomographic hydrogeological or a combination of both was most effective for recovering spatial correlation statistics under different sampling heterogeneity conditions these synthetic case studies suggest that collection of a few tomographic profiles and interpretation of these profiles together with limited well bore data can yield correlation structure information that is otherwise obtainable only from extensive hydrological sampling

a late diagenetic syn folding magnetization carried by pyrrhotite implications for paleomagnetic studies from magnetic iron sulphide bearing sediments paleomagnetic rock magnetic and sedimentary micro textural data from an early miocene mudstone sequence exposed in okhta river sakhalin russia indicate the presence of pyrrhotite and magnetite at different stratigraphic levels sites that contain only magnetite have a reversed polarity characteristic remanent magnetization chrm with a low coercivity overprint which coincides with the present day geomagnetic field direction pyrrhotite bearing sites have stable normal polarity chrms that are significantly different from the present day field direction after correction for bedding tilt the chrm data fail a reversals test however the normal polarity pyrrhotite chrm directions become antipodal to the tilt corrected magnetite chrm directions and are consistent with the expected geocentric axial dipole field direction at the site latitude after 40 partial unfolding these data suggest that the pyrrhotite magnetization was acquired during folding and after lock in of the magnetite remanences electron microscope observations of polished sections indicate that fluid associated halos surround iron sulphide nodules pyrrhotite is present in randomly oriented laths in and around the nodules and the nodules do not appear to have been deformed by sediment compaction this observation is consistent with a late diagenetic origin of pyrrhotite documentation of a late diagenetic magnetization in pyrrhotite bearing sediments here and in recent studies of greigite bearing sediments suggests that care should be taken to preclude a late origin of magnetic iron sulphides before using such sediments for geomagnetic studies where it is usually crucial to establish a syn depositional magnetization

authigenesis of magnetite in organic rich sediment next to a dike implications for thermoviscous and chemical remagnetizations rock magnetic results from organic rich sediment around a tertiary dike in scotland indicate changes in magnetic mineralogy and magnetite content as well as grain size in the contact zone sediment specimens within 85 cm of a 90 cm thick dike contain a tertiary magnetization that is equivalent in direction to the thermal remanent magnetization in the dike whereas the sediment at greater distances does not carry a stable remanence based on acquisition of isothermal remanent magnetization irm thermal decay of triaxial irms and s ratio determinations magnetite is the dominant magnetic phase in the sediment except near the dike 8 cm where hematite is abundant maximum laboratory unblocking temperatures tbmax for the magnetization are higher than predicted by a thermal cooling model at distances greater than 40 cm but the tbmax values are not corrected for gradual cooling of the dike and are therefore overestimates trends in rock magnetic parameters such as irm at 300 mt and anhysteretic remanence arm are consistent with an increasing contribution of single domain pseudosingle domain magnetite towards the dike an increase in saturation irm sirm along with a decrease in arm sirm values 25 cm from the dike also suggest an increase in multidomain magnetite low temperature experiments indicate the presence of abundant superparamagnetic magnetite changes in hysteresis parameters are consistent with changes in the relative amounts of the different magnetite size fractions towards the dike the onset of changes in the magnetite grain size budget starting at 85 cm or approximately one dike width suggests that chemical processes contributed to the remanence at temperatures as low as 220 c petrographic and geochemical studies suggest that the contact zone was not pervasively altered by hydrothermal fluids utilizing the dike as an analog for thermal processes that occur during burial the results of this study suggest that moderately elevated burial temperatures are sufficient to cause magneto chemical changes

the effect of vertical measurement resolution on the correlation structure of a ground penetrating radar reflection image 1 geostatistical analysis of a ground penetrating radar reflection image can be used to quantify the maximum correlation direction and the range of horizontal and sub horizontal radar reflections a review of previous work and an analysis of a photograph of layered sediments suggest that the vertical resolution of a radar image strongly affects its lateral correlation structure numerical modeling was used to generate synthetic radar sections and investigate the effect of the vertical resolution of the radar measurement on the link between the correlation structure of the radar reflections and the true correlation structure of subsurface water content the horizontal range of the radar reflections decreased as the vertical resolution improved closely matching that of the water content when the vertical resolution was approximately equal to the vertical range of the water content

subsurface radar propagation deconvolution the frequency dependence of attenuation is typically far greater for subsurface radar waves than for seismic waves since this frequency dependence causes the subsurface radar pulse shape to change as it propagates through the earth conventional wavelet deconvolution techniques are often inadequate to reconstruct the earth s reflectivity series the application of a time variant filter that undoes the effect of frequency dependent attenuation can substantially improve the resolution of subsurface radar data this filter is minimum phase with amplitude characteristics equal to the inverse of the attenuation function of the medium investigated preliminary tests on data from surveys over a water tank an underground mine stope and fractured granite suggest that good results can also be achieved by assuming attenuation is linearly proportional to frequency similar to a constant q model

the need to adapt the exploration model from the oil patch to contaminated site characterization a case from hill afb utah usa for decades the oil industry has employed a working model for hydrocarbon exploration in which large scale geophysical surveys are undertaken prior to a second phase of intensive targeted drilling this latter phase may be conducted in conjunction with further focused geophysical studies the geophysical surveys provide lateral coverage and continuity that are used to drive placement of drilling locations the reason for this approach is simple wells are expensive relative to geophysical surveys also practical limits on lateral coverage preclude optimization of exploration targets based on well information alone