research note compact depth from extreme points a tool for fast potential field imaging we propose a fast method for imaging potential field sources the new method is a variant of the depth from extreme points which yields an image of a quantity proportional to the source distribution magnetization or density such transformed field is here transformed into source density units by determining a constant with adequate physical dimension by a linear regression of the observed field versus the field computed from the depth from extreme points image such source images are often smooth and too extended reflecting the loss of spatial resolution for increasing altitudes consequently they also present too low values of the source density we here show that this initial image can be improved and made more compact to achieve a more realistic model which reproduces a field consistent with the observed one the new algorithm which is called compact depth from extreme points iteratively produces different source distributions models with an increasing degree of compactness and correspondingly increasing source density values this is done through weighting the model with a compacting function the compacting function may be conveniently expressed as a matrix that is modified at any iteration based on the model obtained in the previous step at any iteration step the process may be stopped when the density reaches values higher than prefixed bounds based on known or assumed geological information as no matrix inversion is needed the method is fast and allows analysing massive datasets due to the high stability of the depth from extreme points transformation the algorithm may be also applied to any derivatives of the measured field thus yielding an improved resolution the method is investigated by application to 2d and 3d synthetic gravity source distributions and the imaged sources are a good reconstruction of the geometry and density distributions of the causative bodies finally the method is applied to microgravity data to model underground crypts in st venceslas church tovacov czech republic

a combined analytic signal and euler method an eul for automatic interpretation of magnetic data we present a new automatic method of interpretation of magnetic data called an eul pronounced an oil the derivation is based on a combination of the analytic signal and the euler deconvolution methods with an eul both the location and the approximate geometry of a magnetic source can be deduced the method is tested using theoretical simulations with different magnetic models placed at different depths with respect to the observation height in all cases the method estimated the locations and the approximate geometries of the sources the method is tested further using ground magnetic data acquired above a shallow geological dike whose source parameters are known from drill logs and also from airborne magnetic data measured over a known ferrometallic object in both these cases the method correctly estimated the locations and the nature of these sources

spatio temporal variability in volcanic sulphate deposition over the past 2 kyr in snow pits and firn cores from amundsenisen antarctica in the framework of the european project for ice coring in antarctica epica a comprehensive glaciological pre site survey has been carried out on amund senisen dronning maud land east antarctica in the past decade within this survey four intermediate depth ice cores and 13 snow pits were analyzed for their ionic compos ition and interpreted with respect to the spatial and temporal variability of volcanic sul phate deposition the comparison of the non sea salt nss sulphate peaks that are related to the well known eruptions of pinatubo and cerro hudson in ad1991 revealed sulphate depositions of comparable size 15 8 3 4 kg km 2 in 11 snow pits there is a tendency to higher annual concentrations for smaller snow accumulation rates the combination of seasonal sodium and annually resolved nss sulphate records allowed the establishment of a time scale derived by annual layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition using a robust outlier detection algo rithm 49 volcanic eruptions were identified between ad165 and 1997 the dating uncer tainty is 3 years between ad1997 and 1601 around 5 years between ad1601 and 1257 and increasing to 24 years at ad165 improving the accuracy of the volcanic chronology during the penultimate millennium considerably abstract in the framework of the european project for ice coring in antarctica epica a comprehensive glaciological pre site survey has been carried out on amund senisen dronning maud land east antarctica in the past decade within this survey four intermediate depth ice cores and 13 snow pits were analyzed for their ionic compos ition and interpreted with respect to the spatial and temporal variability of volcanic sul phate deposition the comparison of the non sea salt nss sulphate peaks that are related to the well known eruptions of pinatubo and cerro hudson in ad1991 revealed sulphate depositions of comparable size 15 8 3 4 kg km 2 in 11 snow pits there is a tendency to higher annual concentrations for smaller snow accumulation rates the combination of seasonal sodium and annually resolved nss sulphate records allowed the establishment of a time scale derived by annual layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition using a robust outlier detection algo rithm 49 volcanic eruptions were identified between ad165 and 1997 the dating uncer tainty is 3 years between ad1997 and 1601 around 5 years between ad1601 and 1257 and increasing to 24 years at ad165 improving the accuracy of the volcanic chronology during the penultimate millennium considerably

a 220 year continuous record of volcanic h2so4 in the antarctic ice sheet continuous h2so4 profiles observed in snow from several antarctic locations reveal four major volcanic events of the past two centuries agung krakatoa tambora and another large scale event not recorded historically acid deposition and interhemispheric distribution mechanisms are quantified and then used to obtain an order of magnitude estimate for the h2so4 emissions from these eruptions

3 d magnetotelluric inversion and model validation with gravity data for the investigation of flood basalts and associated volcanic rifted margins summary 20 magnetotelluric mt soundings were collected on the isle of skye scotland to provide a high resolution three dimensional 3 d electrical resistivity model of a volcanic province within the framework of a project jointly interpreting gravity seismic geological and mt data the full 3 d inversion of the mt data jointly interpreted with gravity data reveals upper crustal structure the main features of the model are interpreted in conjunction with previous geological mapping and borehole data our model extends to 13 km depth several kilometres below the top of the lewisian basement the top of the lewisian basement is at approximately 7 8 km depth and the topography of its surface was controlled by precambrian rifting during which a 4 5 km thick sequence of torridonian sediments was deposited the mesozoic sediments above which can reach up to 2 2 km thick have small scale depocentres and are covered by up to 600 m of tertiary lava flows the interpretation of the resistivity model shows that 3 d mt inversion is an appropriate tool to image sedimentary structures beneath extrusive basalt units where conventional seismic reflection methods may fail

shallow stratigraphic drilling applied in hydrocarbon exploration of the nordkapp basin barents sea abstract the nordkapp basin is a late palaeozoic rift basin characterised by numerous salt diapirs the salt was deposited in the late carboniferous early permian and has been remobilised several times upper palaeozoic and mesozoic sediments filled in the basin and were uplifted by salt diapirism in the early middle triassic late jurassic late cretaceous and tertiary regional uplift and erosion in the early tertiary and extensive glacial erosion in the late pliocene pleistocene removed up to 1200 m of the mesozoic and cenozoic strata and left them heavily tilted and truncated around the salt diapirs only covered by a thin sheet of glacial sediments during much of the triassic and jurassic the nordkapp basin was a large marine embayment open to the ocean in the southwest this allowed deposition of potential hydrocarbon source rocks in anoxic basins during transgressive periods in the triassic and late jurassic coastal processes improved the reservoir quality of upper triassic to middle jurassic sands during regressive periods one exploration well within the basin and three wells surrounding the basin have produced oil shows but no commercial discoveries have been made so far during the review period of the present paper an exploration well encountered oil and gas in triassic sandstones in the southwestern segment of the basin this is the first direct indication of a mature oil producing source rock in the nordkapp basin and will be important for future exploration of the basin

evolution of heat flow hydrothermal circulation and permeability on the young southern flank of the costa rica rift we analyze 67 new conductive heat flow measurements on the southern flank of the costa rica rift crr heat flow measurements cover five sites ranging in oceanic crustal age between approximately 1 6 and 5 7 ma and are co located with a high resolution multi channel seismic line that extends from slightly north of the first heat flow site 1 6 ma to beyond odp hole 504b in 6 9 ma crust for the five heat flow sites the mean observed conductive heat flow is 85 mwm 2 this value is approximately 30 per cent of the mean lithospheric heat flux expected from a half space conductive cooling model indicating that hydrothermal processes account for about 70 per cent of the heat loss the advective heat loss fraction varies from site to site and is explained by a combination of outcrop to outcrop circulation through exposed basement outcrops and discharge through faults super critical convection in layer 2a extrusives occurs between 1 6 and 3 5 ma and flow through a thinly sedimented basement high occurs at 4 6 ma advective heat loss diminishes rapidly between 4 5 and 5 7 ma which contrasts with plate cooling reference models that predict a significant deficit in conductive heat flow up to ages 65 10 ma at 5 7 ma the crr topography is buried under sediment with an average thickness 150 m and hydrothermal circulation in the basement becomes sub critical or perhaps marginally critical the absence of significant advective heat loss at 5 7 ma at the crr is thus a function of both burial of basement exposure under the sediment load and a reduction in basement permeability that possibly occurs as result of mineral precipitation and original permeability at the time of formation permeability is a non monotonic function of age along the southern flank of the crr in general agreement with seismic velocity tomography interpretations that reflect variations in the degree of ridge axis magma supply and tectonic extension hydrothermal circulation in the young oceanic crust at southern flank of crr is affected by the interplay and complex interconnectedness of variations in permeability sediment thickness topographical structure and tectonic and magmatic activities with age

magnetic expression of salt diapir related structures in the nordkapp basin western barents sea high resolution aeromagnetic surveys in the nordkapp basin western barents sea demonstrate the capability of modern high resolution aeromagnetic surveys to provide an efficient and promising tool for mapping features related to salt diapirism salt diapirs are clearly visible by a small low amplitude negative round to ellipsoidal magnetic pattern this pattern coincides with shallow sedimentary layers deformed by the rising salt during active and passive diapirism the dimensions of these features coincide in shape and size with those interpreted on gravity and seismic surveys

assessment of the record of the 1982 el chichon eruption as preserved in greenland snow variability in the so42 and cl time series for the 1980s from 12 shallow snow pits across the greenland ice sheet is used to evaluate the record of the 1982 el chichon eruption and the potential for recording a moderate northern equatorial eruption in a single greenland ice core composition of volcanic glass found in spring 1983 snow in one of the pits in the summit region matches that from el chichon glass thereby verifying the deposition of material from the eruption high na and cl concentrations in this same layer probably represent deposition of the reaction products of halite and h2so4 as observed in the stratosphere following the eruption these findings and the presence of a cl signal in five of the other pits indicate that the cl aerosol component of some eruptions has the potential to remain aloft for at least 1 year after the eruption some of these aerosols may be adsorbed onto tephra particles distinct so42 peaks that can be confidently linked to el chichon were found in only 50 of the records developed through subseasonal sampling however in several other pits an elevated baseline thought to represent more lengthy periods of el chichon aerosol deposition as opposed to deposition from a single snowfall event were observed smoothing of the original data by the calculation of annual so42 flux resulted in the presence of high flux values between 1982 and 1984 years thought to be affected by el chichon aerosol deposition in 9 of the 12 pits these results suggest that a single ice core from anywhere in greenland may record a signal from a northern equatorial eruption of magnitude similar to that of el chichon about 75 of the time this is despite the overall high levels of so2 4 deposition from anthropogenic sources that now make identification and quantification of the volcanic so2 portion of the record more difficult than obtaining the same data for preindustrial volcanism nevertheless composite records from all the pits sampled yielded stratospheric loading 20 mt and optical depth 0 13 estimates similar to stratospheric and satellite based measurements following the eruption equally high so42 concentration and flux values in snow from 1980 to 1982 reflect deposition from the series of middle to high northern latitude volcanic eruptions 1979 1981

accumulation rates in dronning maud land antarctica as revealed by dielectric profiling measurements of shallow firn cores the european programme for ice coring in antarctica includes a comprehensive pre site survey on the inland ice plateau of dronning maud land antarctica the german glaciological programme during the 1997 98 field season was carried out along a 1200 km traverse on amundsenisen and involved sampling the snow cover in pits and by shallow firn cores this paper focuses on the accumulation studies the cores were dated by dielectric profiling and continuous flow analysis distinct volcanogenic peaks and seasonal signals in the profiles served to establish a depth time scale the eruptions of krakatoa tambora an unknown volcano kuwae and el chichon are well documented in the ice variations of the accumulation rates over different times were inferred from the depth time scales a composite record of accumulation rates for the last 200 years was produced by stacking 12 annually resolved records according to this accumulation rates decreased in the 19th century and increased in the 20th century the recent values are by no means extraordinary as they do not exceed the values at the beginning of the 19th century variations in accumulation rates are most probably linked to temperature variations indicated in 18o records from amundsenisen

salt diapirs of the southwest nordkapp basin analogue modelling the geometry and evolution of the salt diapirs in the southwestern segment of the nordkapp basin sw nkb were interpreted on reflection seismic data reflection seismic profiles were used to build

annually resolved southern hemisphere volcanic history from two antarctic ice cores the continuous sulfate analysis of two antarctic ice cores one from the antarctic peninsula region and one from west antarctica provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century the dating is accurate within 3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis the two sulfate records are consistent with each other a systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals the resulting volcanic chronology covering 1417 1989 a d resolves temporal ambiguities about several recently discovered events a number of previously unknown moderate eruptions during late 1600s are uncovered in this chronology the eruption of tambora 1815 and the recently discovered eruption of kuwae 1453 in the tropical south pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium a technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux for the same eruptions the variability of the volcanic sulfate flux between the cores is within 20 of the sulfate flux from the tambora eruption

improved salt imaging in a basin context by high resolution potential field data nordkapp basin barents sea abstract the seismic imaging of salt diapirs in the nordkapp basin gave rise to considerable problems in defining their shape and volume independent information was added by integrating the interpretation with high resolution gravity and magnetic data we developed a novel iterative workflow separated into sub categories sediments salt structures basement and moho distinctions between the sources of the anomalies from different depths was achieved by utilizing the different decay characteristics of gravity gravity gradiometry and high resolution magnetic anomalies the workflow was applied to the southern part of the nordkapp basin it started with the sedimentary model derived from seismics populated with measured densities and magnetic susceptibilities and a starting model for the base salt the residual after the removal of this model was interpreted in terms of a crustal model including flexural isostatic calculations for the moho with the sedimentary load the residual after the removal of crustal and early sedimentary model was used to tune the salt model as these major and minor modelling steps depend on each other an iterative process was applied to stepwise improve the density and magnetic susceptibility model the first vertical gradient of gravity and the magnetic field were found to give most information about the cap rock of the diapirs the improvement in salt imaging integrated with results from controlled source electromagnetic and magneto telluric modelling is shown for the salt diapir uranus where a well terminated in the salt constrains the minimum of the depth to base salt

conforming falcon gravity and the global gravity anomaly gravity derived only from airborne gravity gradient measurements with a normal error distribution will have an error that increases with wavelength it is straightforward in principle to use sparsely sampled regional gravimeter data to provide the long wavelength information thereby conforming the derived gravity to the regional gravity regional surface or airborne gravimeter data are not always available and can be difficult and expensive to collect in many of the areas where an airborne gravity gradiometer survey is flown however the recent release by the danish national space centre of the dnsc08 global gravity anomaly data has provided regional gravity data for the entire earth of adequate quality for this purpose studies over three areas including comparisons with ground marine and airborne gravimetry demonstrate the validity of this approach future improvements in global gravity anomaly data are expected particularly as the product from the recently launched gravity field and steady state ocean circulation explorer goce satellite becomes available and these will lead directly to an improvement in the very wide bandwidth gravity available after conforming gravity derived from gravity gradiometry with the global gravity

structural style and evolution of the nordkapp basin norwegian barents sea after three decades of research and hydrocarbon exploration in the nordkapp basin norwegian barents sea the dynamics of mesozoic salt mobilization is still poorly understood both progradationa

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

potential field migration for rapid imaging of gravity gradiometry data the geological interpretation of gravity gradiometry data is a very challenging problem while maps of different gravity gradients may be correlated with geological structures present maps alone cannot quantify 3d density distributions related to geological structures 3d inversion represents the only practical tool for the quantitative interpretation of gravity gradiometry data however 3d inversion is a complicated and time consuming procedure that is very dependent on the a priori model and constraints used to overcome these difficulties for the initial stages of an interpretation workflow we introduce the concept of potential field migration and demonstrate how it can be applied for rapid 3d imaging of entire gravity gradiometry surveys this method is based on a direct integral transformation of the observed gravity gradients into a subsurface density distribution that can be used for interpretation or as an a priori model for subsequent 3d regularized inversion for large scale surveys we show how migration runs on the order of minutes compared to hours for 3d regularized inversion moreover the results obtained from potential field migration are comparable to those obtained from regularized inversion with smooth stabilizers we present a case study for the 3d imaging of falcon airborne gravity gradiometry data from broken hill australia we observe good agreement between results obtained from potential field migration and those generated by 3d regularized inversion

quantifying the pinatubo volcanic signal in south polar snow recent snow and firn core samples from south pole contain increased sulfate so42 concentrations during 1992 1994 as a result of the june 1991 pinatubo eruption and the august 1991 cerro hudson eruption in chile traces of pinatubo tephra volcanic ash were identified in the 1993 and 1994 snow layers supporting the conclusion that increased so42 in 1993 1994 is from the pinatubo eruption although the pinatubo eruption preceded hudson its so42 signal in south polar snow follows and is resolved from that of hudson the deposition of the pinatubo so42 aerosol was delayed due to the long transport to the high southern latitudes and its initial existence at high altitudes in the antarctic atmosphere multi year multi site sampling demonstrates that the volcanic signals are well preserved and spatially consistent measurements on 2 firn cores show that the south pole so so42 flux from pinatubo is 10 9 1 2 kg km 2 over 2 2 years while the hudson flux is 3 2 0 6 kg km 2 in 1 1 years these results when combined with satellite determined pinatubo sulfur dioxide so2 emission make it possible to link quantitatively the atmospheric aerosol mass loading from a low latitude volcanic eruption to its signal in polar ice cores

ice cores as an index of global volcanism from 1850 to the present to evaluate an important cause of past climate change climate researchers need reliable estimates of volcanic aerosol loading in the atmosphere previous indices the dust veil index volcanic explosivity index and those by mitchell 1970 sato et al 1993 and khmelevtsov et al unpublished manuscript 1993 all have drawbacks ice core acidity and sulfate records because they contain physical evidence of atmospheric loading are a promising source of information on past volcanic aerosols but these records contain large nonvolcanic signals as well we have compared northern hemisphere nh and southern hemisphere sh annual average versions of five indices with eight nh and six sh ice core records for the period 1850 to the present in an attempt to identify the volcanic signal common to all records the indices are all highly correlated with each other for the nh although the individual ice core records are in general not well correlated with each other or with any of the indices a composite derived from averaging the cores the ice core volcano index ivi shows promise as a new index of volcanic aerosol loading this new index correlates well with the existing non ice core volcanic indices and with high frequency temperature records for the sh the individual ice cores and indices are better correlated the shivi is again highly correlated with all indices and individual ice cores but not with high frequency temperature records for both hemispheres the southern oscillation index shows no significant correlation with the volcanic indices ice cores or the ivi thus providing no evidence for the impact of volcanic eruptions on el nino southern oscillation events

3d gravity modeling of buyuk menderes basin in western anatolia using parabolic density function abstract a method to model 3d sedimentary basins with parabolic density contrast is applied to buyuk menderes basin in western anatolia the measured gravity fields reduced to a horizontal plane are assumed to be available at grid nodes of a rectangular square mesh juxtaposed 3d vertical prisms with their geometrical epicenters on top coincide with grid nodes of a mesh to approximate a sedimentary basin the algorithm based on newton s forward difference formula automatically calculates the initial depth estimates of a sedimentary basin assuming that 2d infinite horizontal slabs can generate the measured gravity fields and among these slabs the density contrast varies with depth the lower boundary of a sedimentary basin is formulated by estimating the depth values of the 3d prisms with in predetermined limits measured gravity fields pertaining to the buyuk menderes basin turkey where the density contrast varies with depth are interpreted to show the applicability of the method

three dimensional regularized focusing inversion of gravity gradient tensor component data we develop a new method for interpretation of tensor gravity field component data based on regularized focusing inversion the focusing inversion makes its possible to reconstruct a sharper image of the geological target than conventional maximum smoothness inversion this new technique can be efficiently applied for the interpretation of gravity gradiometer data which are sensitive to local density anomalies the numerical modeling and inversion results show that the resolution of the gravity method can be improved significantly if we use tensor gravity data for interpretation we also apply our method for inversion of the gradient gravity data collected by bhp billiton over the cannington ag pb zn orebody in queensland australia the comparison with the drilling results demonstrates a remarkable correlation between the density anomaly reconstructed by the gravity gradient data and the true structure of the orebody this result indicates that the emerging new geophysical technology of the airborne gravity gradient observations can improve significantly the practical effectiveness of the gravity method in mineral exploration

a glacio chemical characterization of the new epica deep drilling site on amundsenisen dronning maud land antarctica in the framework of the european project for ice coring in antarctica epica a glacio chemical pre sitesurvey was carried out in dronning maud land dml antarctica up to now three intermediate deep icecores and twelve snow pits have been analysed by ion chromatography the spatial and seasonal variationsof the snow chemistry in dml covering the time period 1997 to 1865 are presented summer maxima insulphate and winter maxima in sea salt components are well archived in the area under investigation while for nitrate and methanesulphonic acid msa seasonal variations could not be unambiguouslydetected due to postdepositional changes average concentrations of sea salt components and nitrateare spatially uniform in the plateau region however sea salt shows an exponential decline with altitudefor elevations below 2800 m a s l non seasalt sulphate shows a 40 increase with lower snowaccumulation while msa shows a 50 decline with higher elevation and lower accumulation the outcomeof this study supports that the data of the new epica deep drilling site in dml 0 04 07 e 75 00 10 s will be geographical representative for this region high resolution analytical methods will allow accuratestratigraphic dating of the core at least for the holocene period

three dimensional gravity inversion using simulated annealing constraints on the diapiric roots of allochthonous salt structures in the northern continental slope of the gulf of mexico large oil and gas reservoirs are often found beneath sheetlike allochthonous salt structures that are laterally extensive some of these salt structures retain their diapiric feeders or roots beneath them these hidden roots are difficult to image seismically in this study we develop a method to locate and constrain the geometry of such roots through 3 d inverse modeling of the gravity anomalies observed over the salt structures this inversion method utilizes a priori information such as the upper surface topography of the salt which can be delineated by a limited coverage of 2 d seismic data the sediment compaction curve in the region and the continuity of the salt body the inversion computation is based on the simulated annealing sa global optimization algorithm the sa based gravity inversion has some advantages over the approach based on damped least squares inversion it is computationally efficient can solve underdetermined inverse problems can more easily implement complex a priori information and does not introduce smoothing effects in the final density structure model we test this inversion method using synthetic gravity data for a type of salt geometry that is common among the allochthonous salt structures in the gulf of mexico and show that it is highly effective in constraining the diapiric root we also show that carrying out multiple inversion runs helps reduce the uncertainty in the final density model

focusing iterative migration of gravity gradiometry data acquired in the nordkapp basin barents sea abstract geological interpretation based on gravity gradiometry data constitutes a very challenging problem rigorous 3d inversion is the main technique used in quantitative interpretation of the gravity gradiometry data an alternative approach to the quantitative analysis of the gravity gradiometry data is based on 3d smooth potential field migration this rapid imaging approach however has the shortcomings of providing smooth images since it is based on direct integral transformation of the observed gravity tensor data another limitation of migration transformation is related to the fact that in a general case the gravity data generated by the migration image do not fit the observed data well in this paper we describe a new approach to rapid imaging that allows us to produce the density distribution which adequately describes the observed data and at the same time images the structures with anomalous densities having sharp boundaries this approach is based on the basic theory of potential field migration with a focusing stabilizer in the framework of regularized scheme which iteratively transfers the observed gravity tensor field into an image of the density distribution in the subsurface formations the results of gravity migration can also be considered as an a priori model for conventional inversion subsequently we demonstrate the practical application of migration imaging using both synthetic and real gravity gradiometry data sets acquired for the nordkapp basin in the barents sea

seismic interpretation and characterization of anhydrite caprocks in the tromso basin sw barents sea abstract the origin of anhydrite caprocks found in many evaporite basins is currently under debate existing models in the literature for anhydrite formation include rotated stratigraphic layering rotated crestal caprock and diagenetic anhydrite in this work we interpret high quality 2d seismic reflection data to understand the processes associated with anhydrite caprock formation our study focuses on anhydrite caprock formation in the tromso basin which represents one of several underexplored salt basins in the arctic we use well log data and seismic stratigraphic as well as seismic attribute analyses to characterize the anhydrite layers associated with salt diapirs our results reveal that the anhydrite layers are high amplitude reflections at the crests which are often found close to the seabed and lateral caprocks on the flanks of salt diapirs a third class of anhydrite layers is folded faulted and boudinaged intrasalt stringers encased by the salt diapirs lateral caprocks in the tromso basin are formed in response to rotated crestal caprock failure the crestal caprocks are secondary in origin occur at shallow depths and are formed as insoluble residues from the dissolution of halite by the ingress of basinal fluids into the tops of diapirs anhydrite stringers or floaters originate from tectonic related multi dimensional salt flow salt diapirs in the tromso basin are associated with varied anhydrite caprocks their formation cannot be fully explained using a single model our work demonstrates from seismic reflection data the occurrence of caprock events that formed progressively on the flanks of salt diapirs due to local folding

euler deconvolution using differential similarity transformations of gravity or magnetic anomalies euler deconvolution of gravity and magnetic anomalies can be used to estimate the coordinates of a simple point source and the level of a constant background in the deconvolved field by testing a series of structural indices by using differential similarity transformations dsts joint estimations of the source coordinates the structural index and the coefficients of a linear background trend become possible dsts calculated from the derivatives of the interpreted field depend on the position of a chosen central point of similarity with respect to the source position on this basis techniques for euler deconvolution of anomalous fields are presented the theoretical formulations of dst and the deduced sets of equations for euler deconvolution are tested and verified on model and field examples of magnetic anomalies caused by one point and two point sources such as thin and thick dikes semi infinite and finite sills contacts steps faulted beds etc the possibility of an optimum estimation of the structural index can be used to define a second acceptance criterion along with the criterion of relative standard deviations the joint application of these two criteria ensures the selection of reliable results the suggested dst techniques are suitable for initial rapid estimations of the source type depth and plane location they may be applied to either profile or gridded data acquired from onecomponent measurements as well as from gradient or three component measurements additional data on the density or magnetization of the sources are not necessary

an inter hemispheric volcanic time marker in ice cores from greenland and antarctica a strong volcanic acid signal is clearly registered using an acidity measuring technique in the a d 1259 ice layer in four different greenland ice cores camp century milcent crete and dye 3 this signal is similar in amplitude to the laki iceland a d 1783 volcanic event as recorded in the central and south greenland ice cores measurement of ice layers from corresponding age levels in antarctic ice cores byrd station south pole and j 9 on the ross ice shelf provides similar strong acid signals there is no historical record of a significant volcanic eruption for the period around a d 1260 in the northern hemisphere subsequent chemical analyses of all a d 1259 ice layers show similar compositions we suggest that the a d 1259 signals registered in both greenland and antarctica were caused by the same volcanic disturbance and that its epicenter was located at the earth s equatorial zone which enabled global distribution of the acid gases these results indicate that inter hemispheric dating of ice sheets is possible by the chemical identification of major eruptive volcanic events in the equatorial zone

3 d gravity analysis of the dniepr donets basin and donbas foldbelt ukraine abstract the dniepr donets basin ddb is a linear nw se trending late palaeozoic and younger sedimentary basin on the east european platform separating the ukrainian shield from the voronezh massif its northwestern dniepr segment has the characteristics of a typical rift basin to the southeast through a transition zone of approximately 200 km length the ddb is progressively uplifted and compressionally deformed into the correlatable donbas foldbelt df along the axis of the dniepr segment a series of gravity highs has been previously explained by high density crystalline crust beneath the axis of the basin caused by intrusion of mafic and ultramafic rocks in this paper the results of a 3 d gravity analysis using a gravity backstripping technique is described that investigates the crustal and upper mantle structure in the region of the ddb df transition zone and df a residual gravity field i obtained by subtracting the gravity influence of the sedimentary succession of the ddb from the observed field reveals a distinct positive anomaly along the axis of the rift basin increasing in amplitude to the southeast in concert with increasing sedimentary thickness a residual gravity field ii derived by removing the gravity effects of a modelled homogeneous crystalline crust from residual field i reaches 200 and 100 mgal amplitude in the df for two respective moho models based on different interpretations of the published crust and upper mantle seismic velocity models the first of these model a assumes crustal thickening beneath the transition zone and df to a moho depth up to 50 km whereas the second model b assumes a moho shallowing to depths in the range 35 37 km along the whole basin axis for each residual anomaly ii the best fitting 3 d distribution of average density in the crystalline crust has been computed both models indicate the existence of a high density body in the crystalline crust along the ddb axis increasing in density from the dniepr segment to the df with higher average crustal density required in the case of moho model a 3 17 103 kg m 3 versus 3 06 103 kg m 3 for model b the preferred interpretation of the density models is one in which the denser crystalline crust underlying the ddb df transition zone and df is explained by intrusion of mafic and ultramafic rocks during late palaeozoic rifting processes invocation of processes related to the uplift and inversion in the df are not required to explain the observed gravity field although reworking of the crust during permian and younger tectonism in the df cannot be ruled out