rock physics modeling of static and dynamic reservoir properties a heuristic approach for cemented sandstone reservoirs rock physics models for fluid and stress dependency in reservoir rocks are essential for quantification and interpretation of 4d seismic signatures during reservoir depletion and injection however our ability to predict the sensitivity to pressure from first principles is poor the current state of the art requires that we calibrate the pressure dependence of velocity with core measurements a major challenge is the fact that consolidated rocks often break up during coring and hence the stress sensitivity is likely to be overpredicted in the laboratory relative to the in situ conditions furre et al 2009 for unconsolidated sands acquisition of core samples is not very feasible due to the friable nature of the sediments one physical model that has been applied to predict pressure sensitivity in unconsolidated granular media is the hertz mindlin contact theory several authors vernik and hamman 2009 among others have suggested empirical models with fitting parameters that correlate with microcr

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

selective glacial erosion and weathering zones in the coastal mountains of marie byrd land antarctica in the coastal mountains of marie byrd land antarctica there is a juxtaposition of ice moulded landforms at lower altitudes and upstanding summits with weathered surfaces bearing tors this paper uses geomorphological mapping and exposure dating to test two hypotheses commonly used to explain such a landscape contrast either the pattern reflects contrasts in glacial erosion related to the basal thermal regime beneath a former ice sheet or it represents a periglacial trimline marking the upper limit of ice cover during the last glacial maximum lgm cosmogenic nuclide measurements on erratics show that the mountains were covered by ice on several occasions most recently during the lgm similar measurements on bedrock show that fragile landforms on weathered surfaces survived many glaciations nuclide concentrations in bedrock indicate both that subglacial erosion is insignificant and that ice free periods of periglacial weathering are longer at higher elevations we conclude that the pattern of landscape modification reflects both topographically controlled contrasts in the basal thermal regime of overriding ice and the longer exposure to periglacial conditions at higher elevations in addition the combination of nuclide data and the wider pattern of striations shows that the lgm ice cover was thinner than predicted by ice sheet models assuming equilibrium conditions that ice sheet thinning has occurred from 10 400 years ago to the present and that regional flow by overriding ice has been replaced by radial ice flow from local glaciers centred on individual mountain massifs

rock physics modeling of stress sensitivity and 4d time shifts in patchy cemented sandstones application to the visund field north sea the patchy cement model predicts stress sensitivity in poorly to moderately consolidated sandstones using a multiply nested hashin shtrikman approach combined with contact theory this model can be used to quantify stress sensitivity in reservoir sandstones where core samples are lacking or unreliable we demonstrate a strategy based on this model that can be used to quantify 4d seismic time shifts and time shift derivatives associated with stress changes the time shifts will be a function of the rock stiffness i e volume of patchy cement therefore it is important to determine the local changes in rock properties before we can predict stress and fluid changes from time shift attributes we apply this approach to four exploration wells in the visund field area where we have good control on the rock properties we first compare modeled time shifts with observed 4d time shifts in the visund s1 segment where pressure data are available and we obtain a very good match at two selected well locations next we use the observed seismic time shifts as constraints to estimate the pore pressure changes in the pan and pandora segments just south of the depleting s1 segment pressure changes are significantly lower than in the s1 segment but still indicate potential pressure communication between these segments and the main visund in spite of fault barriers and deeper fluid contacts

an approach to combined rock physics and seismic modelling of fluid substitution effects the aim of seismic reservoir monitoring is to map the spatial and temporal distributions and contact interfaces of various hydrocarbon fluids and water within a reservoir rock during the production of hydrocarbons the fluids produced are generally displaced by an injection fluid we discuss possible seismic effects which may occur when the pore volume contains two or more fluids in particular we investigate the effect of immiscible pore fluids i e when the pore fluids occupy different parts of the pore volume the modelling of seismic velocities is performed using a differential effective medium theory in which the various pore fluids are allowed to occupy the pore space in different ways the p wave velocity is seen to depend strongly on the bulk modulus of the pore fluids in the most compliant low aspect ratio pores various scenarios of the microscopic fluid distribution across a gas oil contact goc zone have been designed and the corresponding seismic properties modelled such goc transition zones generally give diffuse reflection regions instead of the typical distinct goc interface hence such transition zones generally should be modelled by finite difference or finite element techniques we have combined rock physics modelling and seismic modelling to simulate the seismic responses of some gas oil zones applying various fluid distribution models the seismic responses may vary both in the reflection time amplitude and phase characteristics our results indicate that when performing a reservoir monitoring experiment erroneous conclusions about a goc movement may be drawn if the microscopic fluid distribution effects are neglected

how burial diagenesis of chalk sediments controls sonic velocity and porosity based on p wave velocity and density data a new elastic model for chalk sediments is established the model allows the construction of a series of isoframe if curves each representing a constant part of the mineral phase contributing to the solid frame the if curves can be related to the progress of burial diagenesis of chalk which is revised as follows newly deposited carbonate ooze and mixed sediments range in porosity from 60 to 80 depending on the prevalence of hollow microfossils despite the high porosity these sediments are not in suspension as reflected in ifs of 0 1 or higher upon burial the sediments lose porosity by mechanical compaction and concurrently the calcite particles recrystallize into progressively more equant shapes high compaction rates may keep the particles in relative motion whereas low compaction rates allow the formation of contact cement whereby if increases and chalk forms rock mechanical tests show that when compaction requires more than in situ stress porosity reduction is arrested during subsequent burial crystals and pores grow in size as a consequence of the continuing recrystallization the lack of porosity loss during this process testifies to the absence of chemical compaction by calcite calcite pressure dissolution as well as to the porosity preserving effect of contact cementation at sufficient burial stress the presence of stylolites indicates that pressure dissolution takes place between calcite and silicates and depending on pore water chemistry and temperature pore filling cementation may occur over a relatively short depth interval limestone and mixed sedimentary rock form and porosity may be reduced to less than 20 isoframe increases to more than 0 6 in hydrocarbon reservoirs in north sea chalk relatively high porosity and high ifs are found the reason may be that recrystallization and porosity preserving contact cementation progress whereas pore filling cementation is small probably because pressure dissolution along stylolites is arrested pressure dissolution may be arrested for two reasons 1 the introduction of hydrocarbons causes a fall in effective burial stress and 2 adsorption of polar hydrocarbons on the silicates may shield calcite from the silicates

simulation of snow shielding corrections for cosmogenic nuclide surface exposure studies abstract snow cover reduces cosmogenic nuclide production rates in bedrock corrections for snow cover can be more than 10 in mountainous mid latitude regions where many glacial chronologies have been constructed using cosmogenic nuclide surface dating of landforms most published snow corrections use historic climate data of limited duration that are not likely to reflect adequately the full range of snow conditions over the time of exposure we present a model for describing the impact of snow burial on long term exposure histories of landforms the model applies an energy balance approach to snowpack evolution and incorporates both historic and long term climate proxy data attenuation of cosmogenic fast neutrons is modeled alternatively as a simple exponential decrease with increased shielding or as a thin surface layer with constant production followed by an exponential decrease with increasing depth the choice of attenuation model has little effect on the modeled results for the cairngorms but will have a more significant effect in regions characterized by thinner less dense snowpacks spatial variability in snow cover is modeled as a function of elevation only ignoring local variability in snow accumulation as a result of slope aspect wind redistribution and local topography thus model results reveal general spatial and temporal trends in snow shielding effects rather than site specific corrections applications to data from the cairngorm mountains of scotland show that the constant plus exponential cpe production rate depth profile reduces but does not eliminate snow shielding effects under present day conditions snow at 900 m in the cairngorm mountains reduces average production rates by 6 using the cpe profile and 9 with the exponential profile ep long term climate simulations from 15 5 ka through today produce larger snow shielding effects mainly because they predict an increased proportion of precipitation as snowfall during the younger dryas at 900 m this long term simulation reduces average cosmogenic isotope production rates by 12 cpe and 14 ep these results indicate that snow shielding corrections based on historic climate records may be a potential source of systematic error in midlatitude mountainous regions

rapid erosion drumlin formation and changing hydrology beneath an antarctic ice stream what happens beneath a glacier affects the way it flows and the landforms left behind when it retreats direct observations from beneath glaciers are however rare and the subglacial environment remains poorly understood we present new repeat observations from west antarctica that show active processes beneath a modern glacier which can normally only be postulated from the geological record we interpret erosion at a rate of 1 m a 1 beneath a fast flowing ice stream followed by cessation of erosion and the formation of a drumlin from mobilized sediment we also interpret both mobilization and increased compaction of basal sediment with associated hydrological changes within the glacier bed all these changes occurred on time scales of a few years or less this variability suggests that an ice stream can reorganize its bed rapidly and that present models of ice dynamics may not simulate all the relevant subglacial processes

early holocene history of the west greenland ice sheet and the gh 8 2 event abstract the margin of the greenland ice sheet retreated rapidly during the first few thousand years of the holocene during this period of relative warmth known as the holocene thermal maximum ice core records identify a significant short lived cooling event at approximately 8 4 8 0 ka cal yr bp the gh 8 2 event associated with a 5 7 c fall in mean annual air temperature over the centre of the ice sheet in this paper we constrain the history of the ice sheet margin in disko bugt west greenland and that of a major ice stream jakobshavns isbrae during the early holocene which incorporates the interval of the gh 8 2 event our work is based on a new relative sea level curve and minimum age estimates for the timing of deglaciation from two field sites combined with a review of previously published research from the study area we identify important differences in the chronology of ice margin recession during the early holocene most noticeably the margin of jakobshavns isbrae retreated well inland of the adjacent ice sheet at this time we conclude that the early holocene fjord stade moraines in disko bugt do not record a uniform ice sheet margin response to the gh 8 2 event rather these moraines are diachronous and formed between c 10 8 ka cal yr bp their age varying as a function of the interplay between topography and ice sheet ice stream dynamics we hypothesise that one cause for the lack of an identifiable response to the gh 8 2 event is because topographic controls dominated ice sheet behaviour at this time in lowland areas any increase in ice sheet mass balance was probably associated with an increase in calving rather than any major advance of a grounded ice sheet margin

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

observations and analyses of an intense waves in ice event in the sea of okhotsk 1 ice draft ice velocity ice concentration and current profile data gathered at an array of eight continental shelf monitoring sites east of sakhalin island were analyzed in conjunction with regional meteorological data to document and explain intense wave occurrences several hundred kilometers inside the sea of okhotsk ice pack the studied event was associated with the 19 21 march 1998 passage of an intense cyclone which produced waves with amplitudes in excess of 1 m at the most offshore monitoring location the relatively monochromatic character of the waves allowed extraction of wave intensity time series from ice draft time series data spatial and temporal variations in these data were used to establish directions and speeds of wave energy propagation for comparisons with an earlier interpretation liu and mollo christensen 1988 of an antarctic intense waves in ice event it was concluded that although both events are compatible with a two stage process in which initially slowly advancing wave activity increases subsequent ice cover wave transmissivity the first stage of the sea of okhotsk event was not explicable in terms of the static stress induced changes in the waves in ice dispersion relationship proposed by liu and mollo christensen an alternative explanation is offered that eschews the linkage between wave group velocities and the observed slow rates of wave energy propagation and attributes the subsequent transition to more normal wave propagation behavior to ice pack divergence

the effect of clay distribution on the elastic properties of sandstones the shape and location of clay within sandstones have a large impact on the p wave and s wave velocities of the rock they also have a large effect on reservoir properties and the interpretation of those properties from seismic data and well logs numerical models of different distributions of clay structural laminar and dispersed clay can lead to an understanding of these effects clay which is located between quartz grains structural clay will reduce the p wave and s wave velocities of the rock if the clay particles become aligned or form layers the velocities perpendicular to the alignment will be reduced further s wave velocities decrease more rapidly than p wave velocities with increasing clay content and therefore poisson s ratios will increase as the velocities decrease these effects are more pronounced for compacted sandstones small amounts of clay that are located in the pore space will have little effect on the p wave velocity due to the competing influence of the density effect and pore fluid stiffening the s wave velocity will decrease due to the density effect and thus the poisson s ratio will increase when there is sufficient clay to bridge the gaps between the quartz grains p wave and s wave velocities rise rapidly and the poisson s ratios decrease these effects are more pronounced for under compacted sandstones these general results are only slightly modified when the intrinsic anisotropy of the clay material is taken into account numerical models indicate that there is a strong nearly linear relationship between p wave and s wave velocity which is almost independent of clay distribution s wave velocities can be predicted reasonably accurately from p wave velocities based on empirical relationships however this does not provide any connection between the elastic and petrophysical properties of the rocks numerical modelling offers this connection but requires the inclusion of clay distribution and anisotropy to provide a model that is consistent with both the elastic and petrophysical properties if clay distribution is ignored predicting porosities from p wave or s wave data for example can result in large errors estimation of the clay distribution from p wave and s wave velocities requires good estimates of the porosity and clay volume and verification from petrographic analyses of core or cuttings for a real data example numerical models of the elastic properties suggest the predominance of dispersed clay in a fluvial sand from matching p wave and s wave velocity well log data using log based estimates of the clay volume and porosity this is consistent with an interpretation of other log data

study of traveltime and amplitude time lapse tomography using physical model data in seismic tomography the observed traveltimes or amplitudes of direct waves are inverted to obtain an estimate of seismic velocity or absorption of the section surveyed there has been much recent interest in using cross well traveltime tomography to observe the progress of fluids injected into the reservoir rocks during enhanced oil recovery eor processes if repeated surveys are carried out then eor processes may monitored over a period of time this paper describe the results of simulated time lapse tomography experiment to image the flood zone in an eor process two physical models were made out of epoxy resins to simulate an essentially plane layered sedimentary sequence containing a reservoir layer and simple geological structure the models differed only in the reservoir layer which was uniform in the pre flood model and contained a flood zone of known geometry in the post flood model data sets were acquired from each model using a cross well survey geometry traveltime and amplitude tomographic imaging techniques have been applied to these data in an attempt to locate the extent of the flood zone traveltime tomography locates the flood zone quite accurately amplitude tomography shows the flood zone as a region of higher absorption but does not image itsmore boundaries as precisely this is primarily because of multipathing and diffraction effects which are not accounted for by the ray based techniques for inverting seismic amplitudes less

felsenmeer persistence under non erosive ice in the torngat and kaumajet mountains quebec and labrador as determined by soil weathering and cosmogenic nuclide exposure dating soil analyses and terrestrial cosmogenic nuclide exposure dating are combined and a conceptual model proposed to explain altitudinal weathering contrasts in high latitude highlands we show that summits in the torngat and kaumajet mountains were covered by ice during the last glacial maximum and that their felsenmeer cover probably survived multiple glaciation events for similar lithologies soils on felsenmeer covered summits are signigicantly more weathered than those below the felsenmeer limit displaying higher concentrations of crystalline iron amorphous aluminium and silicium extracted with oxalate secondary minerals such as gibbsite and kaolinite occur in felsenmeer soils whereas those formed in till lacked these secondary minerals 10be and 26al exposure ages for nine of ten samples from high elevation tors and autochthonous felsenmeer blocks range from 73 6 to 157 15 ka by contrast ages of 11 4 1 0 and 11 7 1 0 ka are measured for bedrock in the much lower saglek zone indicating extensive 3 m glacial erosion of this zone during late wisconsinan glaciation 26al 10be ratios demonstrate that exposure of the high elevation surfaces was interrupted during at least one cosmic ray shielding event by either ice or till cover in either case late wisconsinan glaciers could not have extensively eroded these surfaces five erratics dated above the saglek zone including one in the felsenmeer zone have exposure ages ranging from 11 6 1 0 to 13 6 0 7 ka this indicates that valley and high elevation ice persisted through the younger dryas chron and provides further evidence that the highlands were not nunataks during the late wisconsinan period

estimation of clay content in soil based on resistivity modelling and laboratory measurements the determination of clay content in near surface formations is crucial for geotechnical hydrogeological and oil contamination studies we have developed a technique for estimating clay content that consists of the minimization of the difference between the theoretically calculated and measured soil resistivities as a function of water salinity to calculate the resistivity we used a model that takes into account the electrochemical processes in the clay micropores the experimental measurements of soil resistivity were performed on soil samples completely saturated by brines at different concentrations of nacl salt in the range 0 6 100 g l to obtain the resistivity versus salinity curve the parameters obtained with this curve inversion are the clay content the total porosity and the cation exchange capacity to verify the new technique we determined clay concentrations of artificial mixtures of calibrated sand and clay the relative mean error in the clay content does not exceed 20 for a 5 fitting error of the resistivity versus salinity curves such evaluations allow the correct separation of the main lithological groups sand sandy loam loam and light medium and heavy clay we applied this technique to estimate the petrophysical parameters of soils clay content porosity and cation exchange capacity at various sites in mexico the results improved the interpretation of the vertical electrical soundings the lithological soil characterization and the delineation of oil contaminated areas

fluid substitution in rocks saturated with viscoelastic fluids heavyoilshavehighdensitiesandextremelyhighviscosities and they exhibit viscoelastic behavior traditional rock physics based on gassmann theory does not apply to materials saturated with viscoelastic fluids we use an effective medium approach known as coherent potential approximation cpa as an alternativefluid substitutionschemeforrockssaturatedwithviscoelasticfluids suchrocksaremodeledassolidswithellipticalfluidinclusions when fluid concentration is small and as suspensions of solid particles in the fluid when the solid concentration is small thisapproachisconsistentwithconceptsofpercolationandcritical porosity and it allows one to model sandstones and unconsolidated sands we model the viscoelastic properties of a heavyoil saturated rock sample using cpaand a measured frequencydependent complex shear modulus of the heavy oil comparison of modeled results with measured properties of the heavy oil rock reveals a large discrepancy over a range of frequencies and temperatures we modify the cpascheme to account for the effect of binary pore structure by introducing a compliant porosity term this dramatically improves the predictions the predicted values of the effective shear modulus of the rock are in good agreement with laboratory data for the range of frequencies and temperatures this confirms that our scheme realistically estimates the frequency and temperature dependent properties of heavy oil rocks and can be used as an approximate fluid substitutionapproachforrockssaturatedwithviscoelasticfluids

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

clay squirt local flow dispersion in shale bearing sandstones abstractdispersion of elastic wave velocity is common in sandstone and larger in shaly sandstone than in clean sandstone dispersion in fluid saturated shaly sandstone often exceeds the level expected from the stress dependent elastic moduli of dry sandstone the large dispersion has been coined clay squirt and is proposed to originate from a pressure gradient between the clay microporosity and the effective porosity we have formulated a simple model that quantifies the clay squirt effect on bulk moduli of sandstone with homogeneously distributed shale laminae or dispersed shale the model predictions were compared with the literature data for sandstones with dispersed shale agreement was found whereas other sandstones have larger fluid saturated bulk modulus possibly due to partially load bearing shales or heterogeneous shale distribution the data that agree with the clay squirt model indicated nonuniform pore pressure in the high frequency regime and uniform pore pressure in the low frequency regi

holocene deglaciation of marie byrd land west antarctica surface exposure ages of glacial deposits in the ford ranges of western marie byrd land indicate continuous thinning of the west antarctic ice sheet by more than 700 meters near the coast throughout the past 10 000 years deglaciation lagged the disappearance of ice sheets in the northern hemisphere by thousands of years and may still be under way these results provide further evidence that parts of the west antarctic ice sheet are on a long term trajectory of decline west antarctic melting contributed water to the oceans in the late holocene and may continue to do so in the future

early holocene palaeoceanography and deglacial chronology of disko bugt west greenland two new cores from disko bugt a large marine embayment in west greenland are used to assess the deglacial chronology and palaeoceanography of the area during the early holocene deglaciation of the main part of disko bugt is directly dated for the first time to a minimum of ca 10 2 ka cal bp by this time the jakobshavn isbrae ice stream had retreated to the eastern margins of disko bugt initial deglaciation took place before the relatively warm west greenland current wgc was initiated a strengthening in the wgc is identified from ca 9 2 ka cal bp accompanied by retreat of the ice stream to a shallow bank immediately west of the present day jakobshavn isfjord while in this position the calving and melting ice stream produced large volumes of sediment and meltwater the large volumes of meltwater prevented the relatively warm waters of the wgc reaching the eastern margins of disko bugt the ice stream remained grounded on this bank for over a thousand years until ca 7 9 ka cal bp when reduced sedimentation rates and an increase in boreal fauna point to its retreat inside the present day fjord system

paired bedrock and boulder 10be concentrations resulting from early holocene ice retreat near jakobshavn isfjord western greenland we measured in situ cosmogenic 10 be in 16 bedrock and 14 boulder samples collected along a 40 km transect outside of and normal to the modern ice margin near sikuijuitsoq fjord in central west

extraction of marginal ice zone thickness using gravity wave imagery synthetic aperture radar sar imagery of gravity waves in the marginal ice zone miz was acquired during 1987 and 1989 using aircraft flying over the greenland sea the dominant gravity wavelengths acquired during 1987 exhibit a systematic lengthening with penetration distance into the miz for three different regions examined the extracted dominant wavelengths were analyzed using a linear least squares fit with penetration distance and a flexure gravity wave model to estimate mean ice thickness the extracted mean thickness varies from about 1 0 4 m near the ice edge to approximately 2 0 4m near the deepest detectable penetration of the waves about 20 km these thicknesses are in agreement with 31 in situ measurements taken in the fram strait miz within 2 weeks of the sar measurements we also acquired wave imagery across a 150 km section of newly forming ice called the odden a tongue shaped region during 1989 these sar images at l c and x bands display small wave modulation signatures at the northern edge of the odden which we interpret as arising from rapidly growing new ice

rock physics modelling of 4d time shifts and time shift derivatives using well log data a north sea demonstration abstract rock physics models for fluid and stress dependency in reservoir rocks are essential for quantification and interpretation of 4d seismic signatures during reservoir depletion and injection for siliciclastic sandstone reservoirs the gassmann theory successfully predicts changes in seismic properties associated with fluid changes however our ability to predict the sensitivity to pressure from first principles is poor especially for cemented sandstones in this study we demonstrate how we can use a patchy cement rock physics model to quantify the combined effect of stress and fluid changes in terms of seismic time shifts and time shift derivatives during depletion or injection the time shifts are estimated directly from well log data without core calibration of stress sensitivity by assuming non uniform grain contacts where some grain contacts are cemented and others are loose we can combine the contact theory for cemented sandstones with the contact theory for loose sands in order to predict stress sensitivity in a patchy cemented sandstone reservoir time shift derivatives are also useful estimates as this parameter reveals which part of the reservoir is most stress sensitive and contributes most to the cumulative time shift we test out our new approach on well log data from troll east north sea and compare the predicted time shifts with observed 4d seismic time shifts we find that there are good agreements between predicted time shifts and observed time shifts furthermore we confirm that there are local geological trends controlling the fluid and stress sensitivity of the reservoir sands on troll east in particular we observe a lateral stiffening of the reservoir from west to east probably associated with the tectonic and burial history of the area the combined effect of a thinning gas cap and stiffening reservoir sands amplifies the eastward decrease in time shifts associated with reservoir depletion we manage to disentangle these two effects using rock physics analysis it is essential to identify and map the static rock stiffness spatial trends before interpreting time shifts and time shift derivatives in terms of dynamic i e 4d pressure and fluid changes

a relict landscape in the centre of fennoscandian glaciation cosmogenic radionuclide evidence of tors preserved through multiple glacial cycles the presence of well developed tors boulder fields and weathering mantles in the parkajoki area of northeastern sweden near the centre of fennoscandian glaciation has been used to suggest that these landscapes were preserved during all glacial cycles since ice sheet initiation in the late cainozoic this implies that all successive large scale glaciations must have had frozen bed conditions across this area to allow for subglacial landscape preservation cosmogenic 10be and 26al data from three tors and a meltwater channel in the parkajoki area were used to test this hypothesis of landscape preservation through multiple glacial cycles apparent exposure ages of tor summit bedrock surfaces ranging between 79 and 37 ka in an area deglaciated at 11 ka are consistent with the interpretation of these features as relict landforms that have survived glaciation with little or no erosion single nuclide minimum exposure age data require that the tors have survived at least two complete glacial cycles this estimate is based on i the approximate duration of periods of ice sheet cover versus ice free conditions as deduced from the dsdp 607 marine benthic foraminifer oxygen isotope record in conjunction with ii a record of fennoscandian ice sheet flow traces and hence ice sheet extent and iii noting that cosmogenic nuclides are accumulated only during ice free periods in addition mean cosmogenic 26al 10be concentration ratios from two of the sites indicate a minimum model total history of 605 ka and a maximum erosion rate of 1 6 m ma 1 thus the numerical ages confirm the overall qualitative interpretation of landscape preservation through multiple glacial cycles

geophysical and oceanographic information in the marginal ice zone from ocean wave measurements consequent to recent experiments in marginal ice zones miz advances in remote sensing and theoretical progress studies have been published which invoke wave ice interactions to explain or predict certain geophysical phenomena while admirable and desirable in principle these works are based on a refutable surface boundary condition intended for a sheet or plate of solid ice rather than a medium made up of individual ice floes a case is argued for prudence as derived results may originate entirely from the application of an inappropriate miz model

wave effects on ocean ice interaction in the marginal ice zone the effects of wave train on ice ocean interaction in the marginal ice zone are studied through numerical modeling a coupled two dimensional ice ocean model has been developed to include wave effects and wind stress for the predictions of ice edge dynamics the sea ice model is coupled to the reduced gravity ocean model through interfacial stresses the main dynamic balance in the ice momentum is between water ice stress wind stress and wave radiation stresses by considering the exchange of momentum between waves and ice pack through radiation stress for decaying waves a parametric study of the effects of wave stress and wind stress on ice edge dynamics has been performed the numerical results show significant effects from wave action the ice edge is sharper and ice edge meanders form in the marginal ice zone owing to forcing by wave action and refraction of swell system after a couple of days upwelling at the ice edge and eddy formation can be enhanced by the nonlinear effects of wave action wave action sharpens the ice edge and can produce ice meandering which enhances local ekman pumping and pycnocline anomalies the resulting ice concentration pycnocline changes and flow velocity field are shown to be consistent with previous observations

geomorphic and tectonic process rates effects of measured time interval analysis of the original numerical components of diverse geomorphic and tectonic process rates indicates that process rate is not independent of measured time interval this implies that direct comparison of geologic process rates measured over variable time intervals may not be valid and that conclusions based on those comparisons regarding changes in rates through geologic time may be misleading in some cases calculation of statistically derived scaling functions is one approach that can be used to account for this measurement interval bias and to improve comparisons of geologic process rate data when this approach is used a 10 4 or 10 5 yr variation in the measured time interval accounts for approximately one order of magnitude change in the measured process rate the magnitude of the correction can substantially affect conclusions of studies that compare uncorrected process rates calculated from variable time intervals

pore filling material and its effect on velocity in rocks a new method estimates the dependence of p and s velocities in rocks on elastic properties of the pore filling material by going beyond gassmann s relations and accounting for pore filling materials with nonzero shear stiffness the resulting estimates are in good agreement with experimental data and gassmann s relations for values of velocity in water saturated rocks predicted from velocity measured on dry rocks the method successfully predicts the temperature dependence of velocity 1 in frozen rocks at the ice water phase transition and 2 in rocks saturated with heavy hydrocarbon undergoing solid liquid phase transition

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet

cosmogenic chlorine 36 chronology for glacial deposits at bloody canyon eastern sierra nevada deposits from mountain glaciers provide an important record of quaternary climatic fluctuations but have proved difficult to date directly a chronology has been obtained for glacial deposits at bloody canyon california by measurement ofthe accumulation of chlorine 36 produced by cosmic rays in boulders exposed on moraine crests the accumulation ofchlorine 36 indicates that episodes of glaciation occurred at about 21 24 65 115 145 and 200 ka thousand years ago although the timing of the glaciations correlates well with peaks of global ice volume inferred from the marine oxygen isotope record the relative magnitudes differ markedly the lengths of the moraines dating from 115 ka and 65 ka show that the early glacial episodes were more extensive than those during the later wisconsin and indicate that the transition from interglacial to full glacial conditions was rapid