true polar wander driven by late stage volcanism and the distribution of paleopolar deposits on mars article i nfo the areal centroids of the youngest polar deposits on mars are offset from those of adjacent paleopolar deposits by 5 10 we test the hypothesis that the offset is the result of true polar wander tpw the motion of the solid surface with respect to the spin axis caused by a mass redistribution within or on the surface of mars in particular we consider the possibility that tpw is driven by late stage volcanism during the late hesperian to amazonian there is observational and qualitative support for this hypothesis in both north and south observed offsets lie close to a great circle 90 from tharsis as expected for polar wander after tharsis formed we calculate the magnitude and direction of tpw produced by mapped late stage lavas for a range of lithospheric thicknesses lava thicknesses eruption histories and prior polar wander events we find that if tharsis formed close to the equator the stabilizing effect of a fossil rotational bulge located close to the equator leads to predicted tpw of b2 too small to account for observed offsets if however tharsis formed far from the equator late stage tpw driven by low latitude late stage volcanism would be 6 33 similar to that inferred from the location of paleopolar deposits a volume of 4 4 1 3 10 19 kg of young erupted lava can account for the offset of the dorsa argentea formation from the present day south rotation pole this volume is consistent with prior mapping based estimates and would imply a mass release of co2 by volcanic degassing similar to that in the atmosphere at the present time the south polar layered deposits are offset from the present rotation pole in a direction that is opposite to the other paleopolar deposits this can be explained by either a sequential eruption of late stage lavas or an additional contribution from a plume beneath elysium we predict that significant volcanic activity occurred during the time interval represented by the basal unit planum boreum unconformity planum boreum postdates the promethei lingula lobe and that the north polar deposits span a substantial fraction of solar system history if the additional contribution to tpw from plumes is small then we would also predict that tharsis montes formation postdates the promethei lingula lobe of the south polar layered deposits we conclude with a list of observational tests of the tpw hypothesis

gas hydrate systems in petroleum provinces of the sw barents sea abstract 3d seismic data of the sw barents sea provided information about the existence of structure ii gas hydrates and shallow gas in marine sediments gas hydrates and shallow gas exist in the sw barents sea in conjunction with deep hydrocarbon reservoir leakage available conventional 3d seismic data show acoustic chimneys that extend to depths 1700 ms two way travel time below the seafloor the location of the chimneys coincides with structural boundaries and fault complexes cutting through mostly jurassic and triassic strata vertical fluid flow through these chimneys transports thermogenic gas to the gas hydrate stability zone causing the formation of a bottom simulating reflector bsr in addition variations of fluid flux across deep seated fault complexes cause changes in heat flow which explains the shoaling of the bsr and the formation of a tilted bsr tbsr at the border between the ringvassoya fault complex and the loppa high the stability model using thermogenic gas composition type i and ii shows gas hydrates are stable at 225 m 345 m depth corresponding to variation in the geothermal gradient for upper bsr 28 7 c km and 37 c km and lower bsr levels 23 4 c km and 28 3 c km these lateral changes in the temperature gradient can be reconciled with changes in upward fluid flow rates of 1 8 2 2 mm yr 1 such gas hydrate and fluid flow systems on arctic continental margins especially in shallow water depths are potential gas emitters due to their sensitivity to warming ocean temperatures

a complete formalism for the inversion of post glacial rebound data resolving power analysis summary a formal inverse theory for mantle viscosity based upon the data of glacial isostatic adjustment is here formulated and applied to synthetic data in this theory full account has been taken of the normal mode nature of the forward problem for realistic viscoelastic maxwell models of the planet since it is impossible to accurately infer the excitation and decay constants of the individual normal modes from the observations the formalism is cast in terms of the observed gross earth data in the time domain in this analysis expressions are required for the first order perturbations in both the modal amplitudes and relaxation times that are induced by an arbitrary radial perturbation to the starting viscosity profile a numerical technique is developed which enables us to accurately determine differential kernels for the modal amplitudes the analogous kernels for the modal decay times are derived analytically peltier 1976 and the complete set of kernels is shown to satisfy the physical constraint imposed by the uniqueness of the state of isostatic equilibrium for the viscously incompressible maxwell models that we employ when the problem is parametrized in terms of the logarithm of viscosity the kernels are capable of accurately predicting shifts in the normal mode characteristics for at least an order of magnitude variation in mantle viscosity using bayesian statistics a formal inversion is applied to a set of synthetically generated data these data chosen to reproduce the space time coverage of the actual observables include a subset related to the global gravity field and a large sequence of idealized relative sea level rsl curves it is found that even very weak a priori constraints can provide a stable and accurate inversion a resolving power analysis indicates a spatial resolution of approximately 1200km near the core mantle boundary cmb with a gradual improvement to better than 350km in the middle of the upper mantle subsets of the synthetic data are inverted in order to examine conditions on stability and accuracy and to determine their relative contributions to the spatial resolution data from progressively older beaches are shown to contribute most to the spatial resolution at all depths though the improvement in lower mantle resolution converges for data obtained from beaches formed within the last 5000 yr furthermore the rsl curves in the vicinity of the peripheral bulge of the ancient laurentide ice sheet are significant contributors to lower mantle resolution as demonstrated in previous analyses of the forward problem the inversion of this subset of the data also appears to be encouragingly stable

constraints on mantle anelasticity from geodetic observations and implications for the j2 anomaly summary we use geodetic observations of the earth to constrain anelasticity in the earth s mantle at periods between 12 hr and 18 6 yr the observations include satellite laser ranging slr measurements of 12 hr and 18 6 yr tides in the j 2 component of the gravity field spacebased observations of tidal variations in the earth s rotation rate and optical and space based measurements of the chandler wobble period and damping these geophysical signals are mostly sensitive to the lower mantle the results suggest the dissipative process could consist of a single absorption band that extends across seismic periods out at least as far as 20 yr the results also require values of the anelastic parameter q that are smaller than those required by seismic observations we interpret this as evidence that q in the lower mantle is frequency dependent the frequency dependence suggested by the geodetic observations is reasonably consistent with laboratory measurements though those measurements have only been done on rocks at upper mantle conditions after fitting and removing the 18 6 yr tide from the slr j 2 results we find that the 1998 2002 anomaly present in the original j 2 observations is no longer a singular anomaly in the j 2 residuals but becomes one of a series of maxima in a quasi decadal oscillation

controls on gas hydrate system evolution in a region of active fluid flow in the sw barents sea abstract the location and stability of gas hydrates in the sw barents sea is poorly constrained due to complex geological geochemical and geophysical conditions including poor controls on regional heat flow and gas chemistry understanding the stability of gas hydrates in this region is important as recent studies suggest destabilizing hydrates may lead to methane discharge into the ocean and possibly in to the atmosphere here we use high resolution 3d p cable seismic data combined with 3d heat flow and fluid flow models to place new constraints on gas hydrate stability in this region the 3d p cable seismic data acquired in 2009 west of loppa high show cross cutting reverse polarity high amplitude reflectors interpreted as the base of gas hydrate stability to constrain heat flow fluid flow and gas hydrate stability within the 3d seismic volume we use a 3d steady state finite difference diffusive thermal model that incorporates regional bottom water temperature from ctd casts expected geothermal gradients and gas composition derived from well data in general modelled bottom simulating reflectors are deeper than observed bsrs our analysis weighs multiple factors that might explain the discrepancy between observed and modelled bottom simulating reflector depths from this analysis we propose that the most significant discrepancies in bsr depth are likely related to changes in regional fluid heat flow and fluid geochemistry the anomalously shallow bottom simulating reflectors can be explained via vertical fluid flow that might include ensuing potential effects on gas composition pore water salinity and temperature our estimate suggest that a maximum vertical fluid flux of approximately 12 mm y is necessary to explain the most significant anomalies our study provides new insight into regional heat flow geochemistry and end member vertical fluid flux rates in the barents sea moreover it documents that the fluid flow system is active and most likely very dynamic

horizontal movements in the eastern barents sea constrained by numerical models and plate reconstructions summary the eastern barents sea basins west of novaya zemlya were mildly inverted between late permian and early jurassic times as indicated by mild folds in the basin sediments previous studies have suggested that the crustal part of novaya zemlya was thrust westward but the magnitude of this compressive movement is not well known our aim is to provide an order of magnitude constraint on the amount of shortening associated with the displacement of novaya zemlya and inversion of the eastern barents sea basins by combining numerical models and plate reconstructions in an iterative process we use a 2 d finite element method to model inversion of a pre defined basin the total amount of shortening imposed on the models is first constrained by plate reconstructions for the barents sea region for the late palaeozoic to early mesozoic we assume that the shortening is caused by westward movement of the siberian plate but the magnitude of this westward displacement in plate reconstructions is highly uncertain due to the allochthonous nature of the rocks of novaya zemlya and the scarcity of palaeomagnetic data in the region our models show that shortening localizes in the model basin and at novaya zemlya and that westward propagation of deformation is more efficient when the strength of the lower crust is reduced part of the movement of the siberian plate could be accommodated by thrusts at novaya zemlya and perhaps in the domain of the kara sea at the western margin of the siberian plate by comparing the inversion obtained in the numerical models to the inferred inversion structures in the eastern barents sea basins we further constrain the amount of shortening that caused the inversion and therewith improve the plate reconstructions for the region our models indicate that the westward movement of novaya zemlya occurred in the late triassic early jurassic 220 190 ma and was limited in magnitude to 100 200 km which is considerably less than previous estimates 500 700 km

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

solid tidal friction above a liquid water reservoir as the origin of the south pole hotspot on enceladus abstract earth jupiter s moon io and saturn s tiny moon enceladus are the only solid objects in the solar system to be sufficiently geologically active for their internal heat to be detected by remote sensing interestingly the endogenic activity on enceladus is only located on a specific region at the south pole from which jets of water vapor and ice particles have been observed spencer j r and 9 colleagues 2006 science 311 1401 1405 porco c c and 24 colleagues 2006 science 311 1393 1401 the current polar location of the thermal anomaly can possibly be explained by diapir induced reorientation of the satellite nimmo f pappalardo r t 2006 nature 441 614 616 but the thermal anomaly triggering and the heat power required to sustain it over geological timescales remain problematic using a three dimensional viscoelastic numerical model simulating the response of enceladus to tidal forcing we explore the effect of a low viscosity anomaly in the ice shell localized to the south polar region on the tidal dissipation patterns we demonstrate that only interior models with a liquid water layer at depth can explain the observed magnitude of dissipation rate and its particular location at the south pole moreover we show that tidally induced heat must be generated over a relatively broad region in the southern hemisphere and it is then transferred toward the south pole where it is episodically released during relatively short resurfacing events as large tidal dissipation and internal melting cannot be induced in the south polar region in the absence of a pre existing liquid decoupling layer we propose that liquid water must have been present in the interior for a very long period of time and possibly since the satellite formation owing to the orbital equilibrium requirement meyer j wisdom j 2007 icarus 188 535 539 sustaining some liquid water at depth is impossible if heat is continuously emitted at a rate of 4 8 gw at the south pole based on that requirement we propose that the current thermal emission is not in equilibrium with the heat production and that the thermal emission rate is abnormally high at present time alternatively continuous dissipation at a rate of 1 2 gw in the ice shell at the south pole should be sufficient to induce internal melting and it could sustain a layer of liquid water at depth over geologic timescales

seismic architecture stratigraphy and evolution of a subtropical marine embayment maputo bay mozambique abstract the seismic stratigraphy architecture and evolution of a large subtropical embayment maputo bay southern mozambique is described nine seismic units are documented and show repeated phases of incised valley formation and transgressive infilling trangressive infilling alternates between the classic wave dominated transgressive succession of fluvial and central estuarine bay deposits and the filling by intertidal flat and tidal bedforms developed during stages of inlet restriction and shallowing associated with barrier growth at stillstand intervals imprinted on the succession are several key facets of subtropical stratigraphy hurricane generated erosional surfaces and beachrock horizons the upper stratigraphy comprises the highstand bayhead delta a prograding feature constructed by several flood events in comparison with literature from other similar systems such as lagoons coastal lakes and estuaries a generic three stage stratigraphic model of large marine embayments is proposed that includes incision during glaciations transgressive infilling during deglaciations and shallowing during the stillstand episodes of the recent deglaciation

acoustic evidence for a gas migration and release system in arctic glaciated continental margins offshore nw svalbard abstract high resolution 3d and 2d seismic data offshore nw svalbard west of prins karls forland provide geophysical evidence for geologically controlled fluid migration pathways gas hydrate occurrence and an active seabed gas expulsion system the investigated seabed area covers 1600 km2 and lies between kongsfjorden cross shelf trough in the north and isfjorden cross shelf trough in the south ranging in water depths from 200 m on the shelf to 800 m on the upper continental slope acoustic evidence for present day methane release from the seabed to the water column comes from more than 220 gas flares at the outer shelf while past methane release activity at the mid shelf area is evident from pockmarks without flares the fluid migration pathways towards the seabed can be drawn from sub seabed acoustic anomalies fluid migration towards the upper slope occurs mostly along strata in upslope direction and largely prevails over vertical focused migration fluids accumulate in the uppermost part of the slope just westward of the shelf break where they are trapped beneath the prograding glacigenic sequence which is not permeable enough for fluids to migrate through fluids are expelled on the shelf where the base of the glacigenic sequence outcrops some gas charged fluids may originate from deep seated hydrocarbon reservoirs and can be temporally stored in gas hydrates in the shallow subsurface though evidence for hydrates on the uppermost slope is missing the seismic data from the lower slope clearly suggest the occurrence of gas hydrate

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

the early carboniferous mageroy dykes northern norway palaeomagnetism and palaeogeography palaeomagnetic data from the 337 ma mageroy dykes northern norway are of exceptionally high quality and a positive contact test along with an existing regional result from the silurian honningsvag igneous suite attests to a primary early carboniferous magnetic signature the palaeomagnetic pole s 14 8degrees e320 1degrees dp dm 4 4 8 6degrees is the first early carboniferous pole from baltica and implies that northernmost norway greenland the barents sea and svalbard were located at tropical to low northerly latitudes at this time northward drift during carboniferous times 5 6 cm yr as demonstrated from palaeomagnetic data is also reflected in the sedimentary facies in the barents sea realm that is a change from tropical early carboniferous to subtropical 20 30degrees n carbonates and evaporites in the late carboniferous the mageroy dykes are continental tholeiites which intruded into a set of nw se trending normal faults parallel to the trollfjorden komagelva fault zone and the mageroysundet fault immediately to the north and south of mageroya respectively these and many other nw se trending faults onshore and offshore were active during late palaeozoic extension and the dykes were probably contemporaneous with the earliest syn rift sedimentation in the barents sea for example the nordkapp basin less

deformation structures in organic rich shales seismic images of upper jurassic organic rich siliciclastic rocks are studied along the 2000 km 1243 mi norwegian margin these rocks are considered the main source rock for most of the large oil and gas fields in the north sea and norwegian sea we report characteristic seismic expressions of thin skinned gravitational gliding structures that are strata bound to the organic rich formations the most characteristic structures are listric faults that offset and rotate the upper part and sole out near the base of the organic rich zone these may be present in large areas 10 000 km2 3861 mi2 but are usually restricted to tilted areas the strike of the faults was perpendicular to the downdip direction of the movement of mass and fault directions can therefore be used as paleodip indicators several types of contraction structures are observed and all are formed at a maximum of a few hundred meters of burial although they are not limited to organic rich shales such strata bound structures may help identify organic rich intervals in basins where their presence is unknown we suggest that adding organic material to clay leads to reduced permeability compaction related vertical fluid flow may cause fluid overpressure to build up at the base of a less permeable organic rich layer during early burial this high fluid pressure zone becomes a low friction decollement surface on which overlying sediments slide to form characteristic thin skinned deformation structures

the history and future trends of ocean warming induced gas hydrate dissociation in the sw barents sea the barents sea is a major part of the arctic where the gulf stream mixes with the cold arctic waters late cenozoic uplift and glacial erosion have resulted in hydrocarbon leakage from reservoirs evolution of fluid flow systems shallow gas accumulations and hydrate formation throughout the barents sea here we integrate seismic data observations of gas hydrate accumulations along with gas hydrate stability modeling to analyze the impact of warming ocean waters in the recent past and future 1960 2060 seismic observations of bottom simulating reflectors bsrs indicate significant thermogenic gas input into the hydrate stability zone throughout the sw barents sea the distribution of bsr is controlled primarily by fluid flow focusing features such as gas chimneys and faults warming ocean bottom temperatures over the recent past and in future 1960 2060 can result in hydrate dissociation over an area covering 0 03 38 of the sw barents sea

mantle viscosity inferences from joint inversions of pleistocene deglaciatio induced changes in geopotential with a new slr analysis and polar wander joint inversions of post glacial rebound induced secular changes in low degree harmonics of the geopotential and true polar wander tpw systematically indicate that the upper mantle viscosity has a value that is considerably smaller than 10 21 pas the lower mantle viscosity is about one order of magnitude larger than the upper mantle viscosity discrepancies in the viscosity profiles inferred from even and odd zonals are likely an indication of recent unmodeled glacial forcings and or insufficient precision in the evaluation of the mass loss from pleistocene ice sheets the influence of systematic errors in slr data reduction due to thermal drag on the lageos satellites for the uneven zonals of the geopotential is avoided by making use of the starlette and stella satellites to recover the uneven zonals and by considering lumped coefficients for these uneven terms

hydromechanical insight of fracture opening and closure during in situ hydraulic fracturing in crystalline rock abstract six hydraulic fracturing hf experiments were conducted in situ at the grimsel test site gts switzerland using two boreholes drilled in sparsely fractured crystalline rock high spatial and temporal resolution monitoring of fracture fluid pressure and strain improve our understanding of fracturing dynamics during and directly following high pressure fluid injection in three out of the six experiments a shear thinning fluid with an initial static viscosity approximately 30 times higher than water was used to understand the importance of fracture leak off better diagnostic analyses of the shut in phases were used to determine the minimum principal stress magnitude for the fracture closure cycles yielding an estimate of the effective instantaneous shut in pressure effective isip 4 49 0 22 mpa the jacking pressure of the hydraulic fracture was measured during the pressure controlled step test a new method was developed using the uniaxial fibre bragg grating strain signals to estimate the jacking pressure which agrees with the traditional flow versus pressure method the technique has the advantage of observing the behavior of natural fractures next to the injection interval the experiments can be divided into two groups depending on the injection location i e south or north to a brittle ductile s3 shear zone the experiments executed south of this zone have a jacking pressure above the effective isip the proximity to the s3 shear zone and the complex geological structure led to near wellbore tortuosity and heterogeneous stress effects masking the jacking pressure in comparison the experiments north of the s3 shear zone has a jacking pressure below the effective isip this is an effect related to shear dislocation and fracture opening both processes can occur almost synchronously and provide new insights into the complicated mixed mode deformation processes triggered by high pressure injection

hydrate occurrence in europe a review of available evidence abstract large national programs in the united states and several asian countries have defined and characterised their marine methane hydrate occurrences in some detail but european hydrate occurrence has received less attention the european union funded project marine gas hydrate an indigenous resource of natural gas for europe migrate aimed to determine the european potential inventory of exploitable gas hydrate to assess current technologies for their production and to evaluate the associated risks we present a synthesis of results from a migrate working group that focused on the definition and assessment of hydrate in europe our review includes the western and eastern margins of greenland the barents sea and onshore and offshore svalbard the atlantic margin of europe extending south to the northwestern margin of morocco the mediterranean sea the sea of marmara and the western and southern margins of the black sea we have not attempted to cover the high arctic the russian ukrainian and georgian sectors of the black sea or overseas territories of european nations following a formalised process we defined a range of indicators of hydrate presence based on geophysical geochemical and geological data our study was framed by the constraint of the hydrate stability field in european seas direct hydrate indicators included sampling of hydrate the presence of bottom simulating reflectors in seismic reflection profiles gas seepage into the ocean and chlorinity anomalies in sediment cores indirect indicators included geophysical survey evidence for seismic velocity and or resistivity anomalies seismic reflectivity anomalies or subsurface gas escape structures various seabed features associated with gas escape and the presence of an underlying conventional petroleum system we used these indicators to develop a database of hydrate occurrence across europe we identified a series of regions where there is substantial evidence for hydrate occurrence some areas offshore greenland offshore west svalbard the barents sea the mid norwegian margin the gulf of cadiz parts of the eastern mediterranean the sea of marmara and the black sea and regions where the evidence is more tenuous other areas offshore greenland and of the eastern mediterranean onshore svalbard offshore ireland and offshore northwest iberia we provide an overview of the evidence for hydrate occurrence in each of these regions we conclude that around europe areas with strong evidence for the presence of hydrate commonly coincide with conventional thermogenic hydrocarbon provinces

polar wandering of a dynamic earth summary the rotational behaviour of a stratified visco elastic planet submitted to changes in its inertia tensor is studied in a viscous quasi fluid approximation this approximation allows for large displacements of the earth rotation axis with respect to the entire mantle but is only valid for mass redistribution within the planet occurring on the time scale of a few million years such a motion called true polar wander tpw is detected by palaeomagneticiens assuming that the earth s magnetic field remains on average aligned with the spin axis our model shows that a downgoing cold slab induces a tpw which quickly brings this slab to the pole for a mantle of uniform viscosity the same slab is slowly moved toward the equator when a large viscosity increase with depth takes place in the mantle our model is also suitable to investigate the effects of a non steady state convection on the earth s rotation we discuss these effects using a simple mass redistribution model inspired by the pioneering paper of goldreich toomre 1969 it consists of studying the tpw induced by a random distribution of slabs sinking into the mantle for such a mass redistribution only a strongly stratified mantle can reduce the earth s pole velocity below l ma which is the upper bound value observed by palaeomagnetic investigations for the last 200 ma our model also shows that when corrected for the hydrostatic flattening the earth s polar inertia generally corresponds to the maximum inertia as it is presently observed however this may not be the case during some short time periods we also discuss the amount of excess polar flattening that can be related to tidal deceleration this frozen component is found to be negligible

low viscosity of the bottom of the earth s mantle inferred from the analysis of chandler wobble and tidal deformation abstract viscosity of the d layer of the earth s mantle the lowermost layer in the earth s mantle controls a number of geodynamic processes but a robust estimate of its viscosity has been hampered by the lack of relevant observations a commonly used analysis of geophysical signals in terms of heterogeneity in seismic wave velocities suffers from major uncertainties in the velocity to density conversion factor and the glacial rebound observations have little sensitivity to the d layer viscosity we show that the decay of chandler wobble and semi diurnal to 18 6 years tidal deformation combined with the constraints from the postglacial isostatic adjustment observations suggest that the effective viscosity in the bottom 300 km layer is 1019 1020 pa s and also the effective viscosity of the bottom part of the d layer 100 km thickness is less than 1018 pa s such a viscosity structure of the d layer would be a natural consequence of a steep temperature gradient in the d layer and will facilitate small scale convection and melt segregation in the d layer

chronology of tertiary fan deposits off the western barents sea implications for the uplift and erosion history of the barents shelf abstract a combined biostratigraphic and seismic study was performed on three holes drilled in the western barents sea two holes penetrate the thick sedimentary wedge which forms a large fan located off a trough on the barents sea shelf the bjornoyrenna fan the study shows that the fan was built over a short time span in the late pliocene pleistocene mainly due to glacial erosion of the barents shelf region this contrasts earlier age assignments which concluded that fan deposition started in the oligocene the results have a major impact on the understanding of trough mouth fan formation and has important bearing on the history of the sedimentary basins of the barents shelf

depositional history of the upper triassic kapp toscana group on svalbard norway inferred from palynofacies analysis and organic geochemistry abstract upper triassic sediments in the svalbard archipelago were deposited in several transgressive regressive cycles understanding their deposition and distribution is of vital importance because of their potential as hydrocarbon reservoir rocks in this study we integrate palynofacies with organic geochemistry in order to reconstruct the depositional environment of the upper botneheia fm up to the lower the knorringfjellet fm from two sections located in central spitsbergen for which distinctive palynofacies zones have been distinguished these are mainly terrestrially dominated but occasionally contain amorphous organic matter and marine palynomorphs rock eval pyrolysis reveals overall mature kerogen type iii iv samples our results indicate that at least partially restricted marine conditions prevailed during deposition of the botneheia fm the botneheia fm is overlain by a regressive cycle from the lower part of the tschermakfjellet fm up to the top of the de geerdalen fm with terrestrially dominated palynofacies assemblages the knorringfjellet fm contains increased marine palynofacies and marine dinoflagellate cysts which is in accordance with a transgression at the base of this unit this study integrates for the first time in the spitsbergen area quantitative palynofacies and sedimentary organic matter characterization and shows the generally accepted paleo environmental development for the svalbard archipelago

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

climate variations in the boreal triassic inferred from palynological records from the barents sea this paper presents palynological evidence from the late early triassic late smithian to the late triassic rhaetian of the barents sea area a continuous palynological succession from an exploration well 7228 7 1a in the nordkapp basin sw barents sea and palynological data from a series of shallow cores drilled at the svalis dome central barents sea representing selected triassic intervals these fully marine sediments are independently dated by marine faunas both records show significant shifts in the distribution of the main floral elements changing ratios of spore pollen taxa grouped as hygrophytes versus xerophytes and spores versus pollen reveal major changes of the floras within the studied interval one distinct turnover coincides with the smithian spathian boundary where lycopsid and pteridophyte spores dominated assemblages change to pollen pteridosperms and conifers dominated assemblages lower middle triassic assemblages are again dominated by lycopsid spores while the assemblages from the upper part of the middle triassic and the lower part of the late triassic are characterised by dominance of coniferous pollen and show the decline of pteridosperms in the latest triassic fern spores are abundant and diverse in contrast to the middle triassic the pollen assemblages are characterized by cycadophytes and araucariacites these distribution patterns are interpreted to reflect climatic changes the presented results from norwegian boreal areas confirm the significant differences between quantitative distribution of specific taxa as well as diversity of major groups in plant assemblages from low and mid latitudes the present survey opens new perspectives for more detailed comparisons and climatic interpretations of floras from the triassic period a time during which mesozoic vegetation established the major changes in the dominance of specific floral elements especially the diversification and spreading of the conifers can probably be related to climatic changes

late palaeozoic evolution of the north atlantic margin of pangea abstract eleven palaeogeographic maps spanning the earliest carboniferous tournaisian to late permian kazanian have been constructed for the northern north atlantic based on available onshore and offshore data each palaeogeographic map corresponds to an epoch i e 4 17 ma there are no reconstructions of the serpukhovian and tatarian and the kungurian ufimian are treated as one the palaeogeographic reconstructions outline a change in the overall depositional environment of the barents sea north greenland area from huge humid flood plains in the early carboniferous over shallow warm seas in the mid carboniferous to mid permian to cooler and possibly deeper marine environments in the late permian in east greenland non marine conditions occurred during the entire carboniferous and following a prolonged early permian hiatus warm water carbonates were deposited during the late permian the changes reflect large scale shifts in palaeoclimatic and subsidence patterns related to the northward drift of the area and ongoing rifting in the region

quantification of thermal conductivity uncertainty for basin modeling thermal conductivity is a major influencing factor on subsurface conductive heat transport and resulting temperature distribution which in turn is a key parameter in basin modeling basin modeling studies commonly use representative literature values of thermal conductivity despite their impact on modeling results we introduce a workflow for quantifying the effect of uncertain thermal conductivity on subsurface temperature distribution and thus on basin modeling results and test this workflow on a two dimensional generic model from the nordkapp basin a prior ensemble of possible models is conditioned according to bayes theorem to incorporate prior knowledge of temperature data this conditional probability yields a posterior ensemble of temperature fields with a significantly reduced standard deviation to verify our approach we use five characteristic scenarios from the posterior ensemble for transient petroleum systems modeling how considering uncertain thermal conductivity affects variance in hydrocarbon generation is assessed by modeling corresponding vitrinite reflectances ro temperature uncertainty increases with depth it also increases with increasing offset from the salt diapirs which can be associated with a large lateral heat flow component in the complex tectonic environment of the nordkapp basin the introduced workflow can reduce temperature uncertainty significantly especially in regions with high prior uncertainty the ro is very sensitive to changes in thermal conductivity because the onset depth of the gas window in the nordkapp basin may vary by up to 800 m 2600 ft within the 95 confidence interval this demonstrates the importance of quantification of the uncertainty in thermal conductivity on thermal basin modeling

glacial isostatic adjustment on a rotating earth summary we extend and complete previous work to compute the influence of perturbations to the rotation vector on a suite of observables associated with glacial isostatic adjustment gia we emphasize observables relevant to present and future geodetic missions for example present day 3 d crustal motions relative sea level change and geoid or absolute sea level variations our calculations adopt spherically symmetric self gravitating maxwell viscoelastic earth models while incorporating realistic mass ice plus ocean load and rotation variations the predicted rotation induced signals are dominated by the influence of true polar wander tpw the spatial geometry of the tpw induced relative sea level geoid and radial velocity fields is primarily that of a degree two order one surface spherical harmonic the spatial variation of the horizontal velocity vectors is given by the gradient of this harmonic the peak radial and horizontal velocities are of the order of 0 5 mm yr 1 however we show that this value is sensitive to the adopted profile of mantle viscosity we also demonstrate that an accurate prediction of tpw induced sea level and 3 d crustal deformation rates requires that a realistic number of glacial cycles be incorporated into the ice load history we conclude that geodetic observations of the gia process should be analysed using a gia theory valid for a rotating planet finally we also consider variations in rotation driven by simple present day polar melting scenarios and predict the influence of these variations on a suite of geophysical observables we find that the rotational feedback associated with greenland melting is capable of significantly perturbing both relative and absolute sea level variations

origin of marine petroleum source rocks from the late jurassic to early cretaceous norwegian greenland seaway evidence for stagnation and upwelling abstract forty samples were selected from upper jurassic to lower cretaceous black shales of iku sites 6307 07 u 02 and 6814 04 u 02 located on the mid norwegian shelf for a detailed maceral analysis the penetrated rocks include the spekk and hekkingen formations which represent major potential petroleum source rocks in the region it was our first objective to reveal the type of organic material that is responsible for the source rock potential of these sediments the results suggest that black shale formation has occurred in two different paleoceanographic settings 1 in a high productive and 2 an anoxic stagnant environment this conclusion is supported by inorganic and sedimentological data in addition sedimentation rates sr from recent biostratigraphic and sedimentological work on these sequences gave impulse for using accumulation rates to estimate the original organic carbon flux to the sediment organic carbon accumulation rates are relatively low but similar to mid cretaceous black shales from other ocean areas average 10 300 mg cm 2 ka supported by redox sensitive re mo ratios sr toc relationships and paleoproductivity estimates we suggest that the formation and preservation of organic carbon during black shale formation in the spekk formation has followed largely the conditions of the stagnation model whereas the hekkingen formation is likely one possible example for the productivity model

why does not lithology correlate with gamma ray spikes in the shaley source rocks of the upper jurassic alge member southwestern barents sea abstract prominent high value gamma ray spikes in the maximum flooding surfaces of the middle oxfordian kimmeridgian succession alge member display stratigraphic and regional variations in the southwestern barents sea these variations suggest heterogeneities in the composition of the alge member thus challenging the common perception that this interval is a homogenous succession of organic rich black shale this study explores the overall variation in clay mineral composition source rock quality minerals and macerals core logs and seismic facies of the alge member gamma log fluctuations were found to be independent of these variations uranium precipitates on sea bottom sediments when conditions change from oxic to anoxic fluctuations in sea level may result in such changes and hence guide gamma ray responses sea level fluctuations also lead to a changing distance to the shoreline which again influences sediment types grain sizes and source rock quality thus indirectly sea level appears to be the common denominator which sometimes matches source rock richness with spikes on gamma logs presence and absence of gamma ray spikes are hence an additional tool to reveal the redox conditions in the sw barents sea which has implications for the understanding of the paleogeography or paleobathymetry during deposition

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

late jurassic to early cretaceous black shale formation and paleoenvironment in high northern latitudes examples from the norwegian greenland seaway 1 the late jurassic to early cretaceous volgian ryazanian was a period of a second order sea level low stand and it provided excellent conditions for the formation of shallow marine black shales in the norwegiangreenland seaway ngs iku petroleum research drilling cores taken offshore along the norwegian shelf were investigated with geochemical and microscopic approaches to 1 determine the composition of the organic matter 2 characterize the depositional environments and 3 discuss the mechanisms which may have controlled production accumulation and preservation of the organic matter the black shale sequences show a wide range of organic carbon contents 0 5 7 0 wt and consist of thermally immature organic matter of type ii to ii iii kerogen rock eval pyrolysis revealed fair to very good petroleum source rock potential suggesting a deposition in restricted shallow marine basins well developed lamination and the formation of autochthonous pyrite framboids further indicate suboxic to anoxic bottom water conditions in combination with very low sedimentation rates it seems likely that preservation was the principal control on organic matter accumulation however a decrease of organic carbon preservation and an increase of refractory organic matter from the volgian to the hauterivian are superimposed on short term variations probably reflecting milankovitch cycles various parameters indicate that black shale formation in the ngs was gradually terminated by increased oxidative conditions in the course of a sea level rise index terms 1055 geochemistry organic geochemistry 4802 oceanography biological and chemical anoxic environments 9609 information related to geologic time mesozoic 8105 tectonophysics continental margins and sedimentary basins 1212 keywords black shale formation depositional environment norwegian greenland seaway mesozoic organic petrography citation langrock u r stein m lipinski and h j brumsack late jurassic to early cretaceous black shale formation and paleoenvironment in high northern latitudes examples from the norwegian greenland seaway paleoceanography 18 3 1074 doi 10 1029 2002pa000867 2003

enhancement and sharpening the migration images of the gravity field and its gradients potential field migration represents a rapid technique for imaging the subsurface based on gravity data however migration transformation usually produces a smooth and unfocused image of the targets due to the diffusive nature of the potential fields in this paper we introduce a method of the migration image enhancement and sharpening based on the application of the hybrid focusing stabilizer which combines the edge preserving smoothing filter with the minimum support functional the method is based on the model resolution matrix of the migration operator we also improve the migration image with a novel target oriented migration method the developed method of migration image enhancement and sharpening is illustrated by synthetic model studies and case studies the case study involves imaging the full tensor gravity gradient data collected in the nordkapp basin of the barents sea

impacts of small scale faults on continental to coastal plain deposition evidence from the realgrunnen subgroup in the goliat field southwest barents sea norway abstract in this study we synthesise sedimentological fault and amplitude versus angle ava analysis and propose that the fruholmen and tubaen formations realgrunnen subgroup are syn kinematic deposits that record a previously undocumented early phase of mesozoic rifting on the troms finnmark fault complex and within the hammerfest basin the realgrunnen subgroup hosts one of two triassic reservoirs currently being produced in the goliat field here the subgroup sits unconformably on top of the storfjorden subgroup carnian snadd formation away from the goliat field which is characterised by a periclinal anticline the realgrunnen subgroup also comprises the lower middle jurassic nordmela and sto formations sedimentological analysis of six exploration wells reveals that the fruholmen formation was deposited in a prodelta to delta plain environment where tide influenced and fluvial dominated distributary channels are represented by clay siltstones and very fine grained sandstones the overlying tubaen formation is characterised by medium to very coarse grained deposits locally conglomeratic and represents a widespread braid plain with localised alluvial fans displacement profiles of faults and along fault thickness variations demonstrate that an immature fault system was active during deposition of the realgrunnen subgroup a series of unconnected fault segments hosted isolated sub basins and erosional catchment areas in their hanging and footwalls respectively an ava attribute map generated from a 10 ms interval of the uppermost part of the subgroup reveals gross sand prone depositional bodies i e individual and amalgamated channels some of which show meandering geometries ox bow lakes and alluvial fans sand bodies frequently show elongate geometries parallel to faults indicative of syn depositional fault related subsidence driving mechanisms responsible for the norian to rhaetian event may relate to contemporaneous rejuvenation of the fennoscandian hinterland development of the novaya zemlya fold and thrust belt and or the early cimmerian tectonic phase in northern europe

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

new insights into mantle convection true polar wander and rotational bulge readjustment the earth s rotation axis is constantly tracking the main inertia axis of the planet that evolves due to internal and surface mass rearrangements this motion called true polar wander tpw is due to mantle convection on the million years time scale most studies assumed that on this long time scale the planet readjusts without delay and that the earth s rotation axis and the maximum inertia direction of mantle convection mid mc coincide we herein overcome this approximation that leads to inaccurate tpw predictions and we provide a new treatment of earth s rotation discussing both analytical and numerical solutions we obtain an average tpw rate in the range 0 5 1 5 myr 1 and a sizeable offset of several degrees between the rotation axis and the mid mc this is in distinct contrast with the general belief that these two axes should coincide or that the delay of the readjustment of the rotational bulge can be neglected in tpw studies we thus clarify a fundamental issue related to mantle mass heterogeneities and to tpw dynamics

postglacial sea level change on a rotating earth summary we present a complete derivation of the equation governing long term sea level variations on a spherically symmetric self gravitating maxwell viscoelastic planet this new sea level equation extends earlier work by incorporating in a gravitationally self consistent manner both a time dependent ocean continent geometry and the in uence of contemporaneous perturbations to the rotation vector of the planet we also outline an e cient pseudo spectral numerical methodology for the solution of this equation and present a variety of predictions based on a suite of earth models of relative sea level rsl variations due to glacial isostatic adjustment gia these results show that the contribution to the predicted rsl signal from gia induced perturbations to the rotation vector can reach 7 8 m over the postglacial period in geographic regions where the rotationally induced signal is a maximum this result is sensitive to variations in the adopted lower mantle viscosity and is relatively insensitive to variations in the adopted lithospheric thickness we also show that the rotationally induced component of rsl change is su cient to in uence previous estimates of late holocene melting events and ongoing sea level change due to giawhich were based on a rsl theory for a non rotating earth in particular estimates of antarctic melting over the last 5 kyr based on the amplitude of sea level highstands from the australian region may require an adjustment downwards of the order of 0 5 m of equivalent sea level rise furthermore present day rates of sea level change are perturbed by as much as 0 2 mm yr 1 by the rotational component of sea level change and this has implications for gia corrections of the global tide gauge record over the period from the last glacial maximum to the present we predict a distinctly non monotonic variation in the rotation induced component of rsl this is in agreement with our previous preliminary study milne mitrovica 1996 but contrasts signi cantly with predictions presented by han wahr 1989 and bills james 1996 we demonstrate that the disagreement arises as a consequence of approximations adopted in the latter studies we furthermore refute an assertion by bills james 1996 that previously published constraints on mantle viscosity and ice sheet histories which did not incorporate a rotation induced rsl component are largely invalidated by this omission

multiple episodes of fluid flow in the sw barents sea loppa high evidenced by gas flares pockmarks and gas hydrate accumulation abstract gas and gas hydrates have gained considerable attention in the last 20 yr due to their possible impact on global climate change from methane escalations our study area the sw barents sea is unique in its evolution due to the effect of glaciations which removed thick layers of sediment from the seabed unloading due to erosion and deglaciation resulted in opening of pre existing faults and creation of new ones facilitating fluid migration and eventually escape into the water from the subsurface expressions of hydrocarbon gas accumulation and fluid flow such as gas hydrates and pockmarks are widely distributed in the barents sea several gas flares some of them 200 m high in echograms occur along a segment of the ringvassoy loppa fault complex indicating open fractures and active fluid flow observation of gas flares along regional fault complexes outside pockmark regions indicates that present gas escape occurs along faults only the pockmark formation and gas flares belong to different episodes of fluid flow the pockmarks are absent outside soft sediment depocentres indicating that their existence is related to the presence of recording medium the thin sediment cover in pockmarks and their penetration down into glaciomarine sediments indicate that they formed after deposition of these sediments and that fluid escape was active to the very recent past methane hydrate stability zone mhsz modelling shows that after the last glacial maximum 18 000 20 000 14c years ago the mhsz has thinned from 600 m to zero in most parts of the sw barents sea the fluid expulsion probably happened after retreat of the glaciers causing release of methane from dissociation of methane hydrates through fluid escape processes which lasted until recently bottom simulating reflectors bsr observed are probably due to structure ii hydrates formed from gas containing higher order hydrocarbon components such as ethane propane etc along with methane the study area falls close to the new gigantic oil discoveries skrugard and havis and north of the snohvit hydrocarbon field

re os identification of glide faulting and precise ages for correlation from the upper jurassic hekkingen formation southwestern barents sea abstract re os geochronology of black shales provides absolute time pins in sedimentary successions and os isotopic constraints on paleo environmental conditions recognition and reconstruction of pre faulting chronology within a visually monotonous shale section are critical to interpretation of the paleo environmental record and have relevance for fluid migration routes and basin modelling re os isochrons for five core intervals spanning 14 m of black shale from the hekkingen formation on the northern margin of the hammerfest basin document within unit reverse faulting which is corroborated by detailed petrography geochemical profiles and the os isotope record the reverse fault is coincident with a beef like carbonate vein the five core intervals provide six isochrons with increasingly younger depositional ages of 153 3 4 1 1 7 ma to 148 6 3 0 4 1 ma with increasingly higher initial 187 os 188 os ratios 0 475 0 025 0 060 to 0 593 0 134 0 098 consistent with original stratigraphic position our age data and inferred sedimentation rates suggest a vertical displacement of several meters across the fault we suggest such compressional features are the distal i e down dip components of gravity gliding structures the rocks of the hekkingen formation at the studied locality record a period of water column euxinia with the geochemical data in the correct stratigraphic order we identify two periods of increased sulfide deposition with distinct trace metal characteristics that reflect differences in the sharpness of the chemocline these sulfide producing events create complexity in cross plots traditionally used to infer oceanographic conditions stratigraphically corrected os isotope profiles allow us to correlate this stratigraphic interval of the hekkingen formation from the northern margin of the hammerfest basin with other sections in the barents sea and offshore norway

a benchmark study for glacial isostatic adjustment codes the study of glacial isostatic adjustment gia is gaining an increasingly im portant role within the geophysical community understanding the response of the earth to loading is crucial in various contexts ranging from the the interpretation of modern satellite geodetic measurements e g grace and goce to the projections of future sea level trends in response to climate change modern modeling approaches to gia are based on various techniques that range from purely analytical formulations to fully numerical methods despite various teams independently investigating gia we do not have a suitably large set of explicitly validated numerical results through which they may be validated a community benchmark data set would clearly be valuable following the example of the mantle convection community here we present for the first time the results of a benchmark study of codes designed to model gia the approaches benchmarked are based on significantly different codes and different techniques this effort is performed within the working group 4 wg4 of the esf cost action es0701 improved constraints on models of glacial isostatic adjustment our aims are i testing the codes currently in use by the various teams ii establish a sufficiently large set of agreed results iii correct possible systematic errors embedded in the various physical formulations or computer implementations and iv facilitate the dissemination of numerical tools for surface loading studies to the community and to young scientists the test computations are mainly based on models with spherical symmetry and maxwell rheology and include inputs from various different methods and solution techniques viscoelastic normal modes spectral finite elements and finite elements the tests involve the loading and tidal love numbers and their relaxation spectra the deformation and gravity variations driven by surface loads characterized by simple geometry and time history and the rotational fluctuations in response to glacial unloading in spite of the significant differences in the numerical methods employed the test computations show a satisfactory agreement between the results provided by the participants most of the existing misfits have been addressed during the preparation of the manuscript some others are currently the subject of analysis within the wg4 community

gas hydrate stability zone modelling in areas of salt tectonics and pockmarks of the barents sea suggests an active hydrocarbon venting system the barents sea seabed exhibits an area of major glacial erosion exposing parts of the old hydrocarbon basins in this region we modelled the gas hydrate stability field in a 3d perspective including the effects of higher order hydrocarbon gases we used 3d seismic data to analyse the linkage between fluid flow expressions and hydrate occurrences above old sedimentary basin systems and vertical faults pockmarks showed a relation to fault systems where some of them are directly connected to hydrocarbon bearing sedimentary formations the influence of bottom water temperature pore water salinity and geothermal gradient variation on gas hydrate stability zone ghsz thickness is critically analysed in relation to both geological formations and salt tectonics our analysis suggests a highly variable ghsz in the barents sea region controlled by local variations in the parameters of stability conditions recovery of gas hydrate sample from the region and presence of gas enhanced reflections below estimated bsr depths may indicate a prevalent gas hydrate stable condition

sequence stratigraphy and lateral variability of lower cretaceous clinoforms in the southwestern barents sea an extensive seismic database covering an area of 100 000 km2 38 610 mi2 and 16 wells are integrated to define a sequence stratigraphic framework for the lower cretaceous succession in the southwestern barents sea seven sequences s0 s6 are defined and the geometry trajectory and lateral variability of decompacted seismic clinoforms are described to elucidate the depositional history of the basin and to better understand coarse grained sediment transport from the shelf to basin three different clinoform scales are recognized 1 clinoform sets with 35 60 m 115 197 ft height interpreted as deltaic or shoreline clinoforms 2 clinoform sets with 60 110 m 197 361 ft height interpreted as sediments prograding on a continental shelf and 3 clinoforms with greater than 150 m 492 ft height which represent shelf margin clinoforms furthermore clinoforms are grouped into two main progradation directions 1 clinoforms prograded to the southeast in sequences 2 3 in the fingerdjupet subbasin and the western bjarmeland platform indicating a source of sediments located in the west northwestern barents sea and 2 clinoforms prograded to the southwest in sequences 1 6 in the eastern part of the bjarmeland platform nordkapp basin and finnmark platform indicating a second source of sediments located in the east northeast additionally in the hammerfest basin clinoforms prograded to the southeast off the loppa high in sequences 5 6 low relief 35 60 m 115 197 ft high gradient and oblique clinoforms are observed within sequence 2 in the western bjarmeland platform the high gradient foresets are interpreted as potential coarse grained deposits or as a result of clinoforms prograding to progressive deeper waters resulting in steeper foresets clinoforms located in the eastern part of the study area are interpreted as sourced by a mud rich system reflecting a long transportation distance however thin heterolithic patterns in the gamma ray log possibly reflect thin sheetlike sands the height of the clinoforms seems to be a factor controlling the sediment bypass to deep water in the study area when the height is more than 200 m 656 ft bottomset deposits are common this study contributes to a better understanding of the paleogeography and the evolution of the frontier southwestern barents sea during the early cretaceous and to comprehending the variables increasing the bypass of coarse grained sediments to deep water settings

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

pleistocene deglaciation and the earth s rotation a new analysis summary this paper is concerned with an analysis of the effect of the pleistocene glacial cycle upon the earth s rotation we demonstrate that two important geophysical observables may be explained as aspects of the rotational response to surface mass loading by ice sheets these are the astronomically observed non tidal component of the acceleration of planetary rotation and the secular drift of the rotation pole relative to the surface geography which is evident in the ils pole path the former observation is shown to provide an unambiguous constraint upon the viscosity of the planetary mantle and requires a depth dependence of this parameter which is the same as that which has previously been inferred in studies of the relative sea level variations and free air gravity anomalies associated with post glacial rebound the observed secular drift of the pole cannot provide an independent estimate of the viscosity of the mantle because it depends jointly upon mantle viscosity and lithospheric thickness with the viscosity profile fixed by the rebound data the observed speed of polar wander suggests a continental lithospheric thickness which is in excess of that appropriate for old ocean basins but nevertheless in accord with independent constraints

topography and geoid induced by a convecting mantle beneath an elastic lithosphere summary in the absence of seismological measurements observations of the topography and gravity fields of solid planets are the primary constraints on their internal structure to compute the synthetic geoid and topography induced by the dynamics of planetary interiors we introduce a 3 d numerical tool describing mantle convection beneath an elastic lithosphere although the energy conservation is treated in the whole spherical domain the deformation aspect is solved using a hybrid technique finite volume method for the viscous flow spectral method for elastic deformation the mechanical coupling is achieved via the imposition of the traction at the surface of the viscous flow as a basal boundary condition for the elastic deformation we present both response functions and full thermal convection cases computed with our new method for planetary bodies of varying dimensions the filtering effect of the lithosphere on the dynamic topography and geoid is specific for each planetary body justifying the importance of such a tool furthermore since our approach specifically focuses on the mechanical coupling at the base of the lithosphere it will permit future more elaborate rheological treatments it also enables to discriminate between the radial and tangential components of the viscous traction the latter is found to have a significant influence on the elastic deformation the effect on geoid is prominent more specifically while a thin elastic lithosphere is usually considered to play little role on the dynamic topography and geoid of venus a 35 per cent reduction is obtained for geoid height in the numerical example we propose on a planet with thicker elastic lithosphere such as mars the consequence of this filtering effect is to rule out the possibility of a dynamical support for the tharsis rise even for the lowest admissible values of elastic thickness in this region

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

timing duration and causes for late jurassic early cretaceous anoxia in the barents sea abstract re os isochron ages for black shales of the hekkingen formation in the barents sea constrain the onset 157 7 1 3 ma and termination 138 8 1 0 ma and thereby indicate a long duration 19 myr of widespread jurassic cretaceous anoxia in the arctic integration of these new re os ages with published radiometric ages ammonite biostratigraphy and geomagnetic polarity chrons shows shorter late oxfordian late kimmeridgian and longer berriasian stages relative to estimates in the 2012 and 2016 geological time scales late jurassic anoxia was likely the result of warming climate due to high atmospheric co2 levels from increased oceanic crust production rising temperatures enhanced weathering and nutrient supply increased productivity and slowed ocean circulation before a sea level rise brought anoxic waters onto continental shelves assessment of new and published os and sr isotopic data suggests that prolonged oceanic anoxia required a sustained co2 source from fast spreading rates and or longer subduction zones and spreading ridges to balance large burial of carbon in voluminous upper jurassic and lower cretaceous black shales

the influence of paleo bathymetry on total organic carbon distribution tested in the cretaceous hammerfest basin barents sea abstract in basin modelling and petroleum system analysis geometries during deposition of sediments paleo water depth and distribution of organic matter are initial parameters used for further interpretation or modelling this paper presents an approach combining backstripping with a probabilistic forward sedimentary model to calibrate paleo water depth pwd the stochastic pwd results serve as an input for organic facies models and the study demonstrates how pwd will influence models for total organic carbon distribution in a sedimentary basin for the early cretaceous hammerfest basin mainly shelfal to upper bathyal bathymetries average pwd values vary between 118 and 318 m result in average total organic carbon toc varying between 0 47 and 5 24 wt across the basin for the different models basin averaged toc values are similar but vertical and lateral distribution pattern change significantly especially towards the shallow end member pwd the results indicate that pwd uncertainties propagate non linearly into source rock distributions

polar wandering and the forced responses of a rotating multilayered viscoelastic planet changes in the earth s rotation produced by the waxing and waning of large mobile ice sheets can be used to infer the viscosity of the mantle from a comparison with the recent secular polar drift as revealed in the international latitude service data and also in the estimates of the nontidal acceleration of the length of the day we have developed by using an analytical approach a physical model of a rotating earth consisting of an elastic lithosphere a viscoelastic mantle and an inviscid core forcings from the two major ice sheets laurentide and fennoscandia have been considered sensitivity analysis of the parameters governing the external forcings such as the length and the time of termination of the deglaciation phase show in general that there exist two families of mean mantle viscosities 0 1022 p and 0 1023 p which can match the data satisfactorily however we find it an improvement to incorporate some amount of shrinkage from the antarctic ice sheet obtaining simultaneously a better fit with the two rotational data sets to the lower viscosity solutions hence forcings from the southern hemisphere may be able to remove the ambiguity associated with the extraction of mantle viscosity from rotational data we have also solved the initial value problem of the components of instantaneous angular velocity by means of the laplace transform for applied loads characterizing the continental ice sheets which since the mid pliocene have periodically expanded and contracted over the northern hemisphere in consequence of this continual forcing polar wander of around 5 10 degrees can take place for a mean mantle viscosity 0 1022 p recent reanalysis of paleomagnetic data in conjunction with hot spot tracks have revealed that several degrees of true polar wander could have occurred in the last 5 m y these calculations thus provide a physical explanation for the observed movement of the rotation axis membrane stresses of 0 10 bars can develop from this secular polar motion