variations in the provenance of sediment from ice sheets surrounding baffin bay during mis 2 and 3 and export to the labrador shelf sea site hu2008029 0008 davis strait based on quantitative x ray diffraction mineralogical analysis of cores hu2008029 0006 0008 857 m water depth located south of the davis strait sill we seek answers to two questions i the temporal correlation of nw labrador shelf sea heinrich h and baffin bay detrital carbonate bbdc events and ii the provenance of the sediments a sediment unmixing model sedunmix is used to determine provenance variations although 12 radiocarbon dates were obtained there were many age reversals and we favour a depth age model for hu2008029 0008pc based on correlations to well dated neighbouring cores north and south of davis strait we find no correlation between h and bbdc events except for h 0 which appears to be a broadly synchronous event along the ne canadian margin and is correlative with an episode of major moraine building along this flank of the laurentide ice sheet unmixing of the sediment composition based on six potential glacial source regions indicates that the bulk of the sediment in 0008pc is derived from glacial erosion of west greenland but is punctuated by intervals when dolomite rich sediments derived from outcrops north of baffin bay dominate the composition estimated dates on these bbdc events are 13 25 and 30 38 cal ka bp copyright 2013 john wiley sons ltd

ocean forcing of the greenland ice sheet calving fronts and patterns of retreat identified by automatic satellite monitoring of eastern outlet glaciers 1 we have developed an automatic method to identify changes in the position of calving glacier margins using daily modis imagery application of the method to 32 ocean terminating glaciers in east greenland produced 26 802 margin positions for a 10 year long period 2000 2009 we report these high resolution data and show that the glaciers exhibit seasonal cycles with magnitudes of advance and retreat proportional to glacier width despite similar seasonality there is a distinct difference between the interannual trends of calving front positions north and south of 69 n all glaciers above this latitude showed very limited or no change when seasonality was excluded while glaciers south of 69 n retreated significantly between 2001 and 2005 2 3 km on average approximately 26 of the retreat of southern glaciers was regained by readvance from 2005 to 2009 to explain the latitudinal boundary of glacier dynamics we review basic climatic factors including summer and winter atmospheric forcing sea ice conditions and ocean temperature we conclude that the southern retreats were strongly influenced by warm oceanic conditions associated with increased transport of subtropical waters to the irminger sea and to fjords and coastal regions south of 69 n northern glaciers remained stable despite significant increase in runoff in this region because fjords at latitudes higher than 69 n are less exposed to subtropical waters the southern retreats illustrate sensitive behavior of calving glaciers and we hypothesize that the calving fronts retreated because they were exposed to rapid ice front melting

modern concepts of earth dynamics anticipated by alfred wegener in 1912 in his first publication on continental drift alfred wegener anticipated sea floor spreading the functional relationship between bathymetry and age or temperature below the sea floor perhaps mantle convection and some aspects of plate tectonics some of these insights such as sea floor spreading and bathymetry with age did not appear in his later work others such as convection and plate tectonics were taken up when new evidence became available his intuition led him to these insights and he had a very clear perception of the distinction between facts and speculation

intrinsic elasticity of a textured transversely isotropic muscovite aggregate comparisons to the seismic anisotropy of schists and shales 1 the anisotropic properties of phyllosilicate rocks are investigated through the modeling of the pore free intrinsic elasticity of a textured muscovite aggregate the elastic constants were calculated for textures as defined using orientation distribution functions odfs ranging from perfectly aligned to completely random the odfs were described using a gaussian distribution the width of which is controlled by the standard deviation of the orientations of the crystal c axis with respect to the sample foliation plane under the assumption that the sample has hexagonal transversely isotropic symmetry the values were obtained using the widely used voigt reuss hill averaging techniques as well as the geometric mean average gma the gma is more physically meaningful in that it requires that the elastic constants determined in either the stiffness or the compliance domains be invertible comparisons between these different averages indicate that strictly the voigt and reuss values do not necessarily provide the limiting bounds as is expected for the isotropic case despite this some characteristics of the elastic wave p wave anisotropy are only weakly dependent on the averaging procedure employed the calculated elastic constants are converted to the anisotropic and parameters in order to allow for comparison to existing measurements in the literature however these intrinsic results are not intended to provide a measure of the properties of phyllites per se but to provide a reference against which more sophisticated models that incorporate porosity layering and composition may be constructed

an approach for predicting stress induced anisotropy around a borehole abstractformation elastic properties near a borehole may be altered from their original state due to the stress concentration around the borehole this could result in a biased estimation of formation properties but could provide a means to estimate in situ stress from sonic logging data to properly account for the formation property alteration we propose an iterative numerical approach to calculate stress induced anisotropy around a borehole by combining a rock physics model and a finite element method we tested the validity and accuracy of our approach by comparing numerical results to laboratory measurements of the stress strain relation of a sample of berea sandstone which contains a borehole and is subjected to a uniaxial stress loading our iterative approach converges very fast and can be applied to calculate the spatially varying stiffness tensor of the formation around a borehole for any given stress state

the variability of baffin bay seafloor sediment mineralogy the identification of discrete glacial sediment sources and application to late quaternary downcore analysis quantitative x ray diffraction qxrd mineralogy of bedrock ice rafted and fluvial clasts 239 seafloor samples 2 mm and samples from two long piston cores were used to i define regional pa

velocity anisotropy of upper jurassic organic rich shales norwegian continental shelf abstractthis study investigates the seismic velocity anisotropy of two organic rich shales from the norwegian continental shelf the tested organic rich shale samples were from the upper jurassic draupne and hekkingen formations collected from two wells 16 8 3s and 7125 1 1 drilled in the central north sea and western barents sea respectively the two tested shales are different in organic matter richness and thermal maturation and they have experienced different burial histories the shale core plugs were tested in a triaxial cell under controlled pore pressure seismic velocities vp and vs were measured along different orientations with respect to layering to identify the complete tensor of the rock elastic moduli and to investigate the velocity anisotropy as a function of increasing effective stress the measured velocity values exhibit strong anisotropy for the two tested organic rich shales the anisotropy for both shales is strongest for vs seismic velocities follow an increasing trend as th

parameterization of elastic stress sensitivity in shales stress dependency and anisotropy of dynamic elastic properties of shales is important for a number of geophysical applications including seismic interpretation fluid identification and 4d seismic monitoring using sayerskachanov formalism we developed a new model for transversely isotropic ti media that describes stress sensitivity behavior of all five elastic coefficients using four physically meaningful parameters the model is used to parameterize elastic properties of about 20 shales obtained from laboratory measurements and the literature the four fitting parameters namely specific tangential compliance of a single crack ratio of normal to tangential compliances characteristic pressure and crack orientation anisotropy parameter show moderate to good correlations with the depth from which the shale was extracted with increasing depth the tangential compliance exponentially decreases the crack orientation anisotropy parameter broadly increases with depth for most of the shales indicating that cracks are getting more aligned in the bedding plane the ratio of normal to shear compliance and characteristic pressure decreases with depth to 2500 m and then increases below this to 3600 m the suggested model allows us to evaluate the stress dependency of all five elastic compliances of a ti medium even if only some of them are known this may allow the reconstruction of the stress dependency of all five elastic compliances of a shale from log data for example

fabric anisotropy induced by primary depositional variations in the silt clay ratio in two fine grained slope fan complexes texas gulf coast and northern north sea article i nfo high resolution x ray texture goniometry hrxtg has been used to quantify the alignment anisotropy of phyllosilicate minerals in a series of diagenetically altered mudstone samples from the deep subsurface of the texas gulf coast and the northern north sea the sampled formations have undergone a simple burial history with no overprint of tectonic deformation that may have influenced the phyllosilicate orientation observations have been made in two constrained temperature windows 148 150 c north sea data and 169 210 c texas gulf coast wherein less than 20 smectite remains in the mixed layer phase illite smectite quantitative x ray powder diffraction xrpd shows quartz which is dominantly detrital and phyllosilicate content having an inverse relationship quantified illite smectite fabric intensity phyllosi licate alignments ranges from low alignment values of 2 42 m r d multiples of a random distribution to high alignment values 6 75 m r d and chlorite kaolinite ranges from 1 80 to 6 46 m r d we propose that the broad range of phyllosilicate fabric intensity observed reflects the range of quartz phyllosilicate ratios that are the imprint of depositional setting bedform truncation and initial grain size detrital quartz acts to disrupt fabric intensity by being non platy producing areas sheltered from effective stress pressure shadows and acting as a matrix support there is no evidence that bioturbation is a significant control on phyllosilicate alignment in these quartz phyllosilicate mixtures these findings have important implications for the role of grain scale alignment on seismic anisotropy in mudstone systems fabric intensity in post diagenetic samples can be predicted from 1 quartz content and 2 total clay content where

r a daly s early model of seafloor generation 40 years before the vine matthews hypothesis an outstanding theoretical achievement inspired by field work on st helena in 1921 1922 large scale lateral mobility of the earth s lithosphere mobilism was a hotly debated issue in earth sciences during some two decades following publication of wegener s 1912 theory of continental displacement the final acceptance of lithospheric mobility was brought about with the plate tectonics revolution during the late 1960s support for mobilism was rather popular in certain european countries during the 1920s whereas the reactions in north america were mostly hostile one of the very few influential mobilists in the new world was reginald aldworth daly of harvard university the present paper discusses his model of continental displacement which is very remarkable in many aspects we focus on the hitherto neglected fact that daly proposed in the mid 1920s a mechanism to create oceanic crust which would have been totally consistent with the vine matthews hypothesis of seafloor generation published in 1963 it is furthermore suggested that daly s geotectonic proposals were inspired by small scale

velocity anisotropy of shales and depth estimation in the north sea basin it is known that in the north sea basin the depths to major reflectors as determined from surface seismic data are often larger than the well log depths from a study of data sets which tie 21 wells i found a strong correlation between the occurrence of the depth error and the presence of shales in the subsurface assuming that the error is caused by elliptical velocity anisotropy in shales i measured the anisotropy from a comparison of the well log sonic data and the interval velocity profile obtained from the surface seismic data and also from a comparison of the seismic depth and the well log depth it was found that the two methods of measurements agree with each other and also agree qualitatively with the previous laboratory measurements of anisotropy in shale samples the results strongly suggest that the depth anomaly in the north sea basin is caused by the velocity anisotropy of shales a simple method to correct the seismic depth is given

a multiscale methodology for the analysis of velocity anisotropy in organic rich shale abstractchanges in the sources of velocity anisotropy and their relative magnitude as maturation progresses in organic rich shale are still incompletely characterized in the rock physics literature as a result of the increasing importance of organic rich shale as unconventional reservoirs a more thorough understanding of the elastic behavior of shale is needed we have formulated a comprehensive multiphysics multiscale experimental methodology for the characterization of the intrinsic syn lithification and extrinsic postlithification factors contributing to velocity anisotropy application of this methodology to unsaturated samples also enabled the characterization of the shale frame for fluid substitution modeling the methodological framework was then tested on a set of five naturally matured organic rich shale samples in this experimental methodology we combined classical rock physics measurements e g ultrasonic velocity and emergent high resolution imaging techniques such as x ray diffra

denmark strait during the late glacial maximum and marine isotope stage 3 sediment sources and transport processes abstract the sediment records from north and south of denmark strait cores ps2644 and md99 2323 and on the kangerlussuaq trough mouth fan ktmf md99 2260 are evaluated for the period 12 to 60 cal ka bp with the goal of evaluating 1 the relative roles of the greenland and iceland ice sheets in sediment composition 2 the processes of sediment supply and 3 the relationship if any between the atmospheric derived ice core records and glacial marine sediment history these questions were addressed using counts of coarse 2 mm ice rafted debris ird magnetic susceptibility grain size spectra and sediment mineral composition a significant difference in these variables occurred between ms3 and mis2 with the latter showing small to modest abrupt changes in felsic and mafic minerals and in ird compared to larger and less variable changes during mis2 the dominant bedrock source archived in the cores is the cenozoic basaltic outcrops from east greenland and iceland 60 but there are frequent pulses of felsic rich sediments 17 36 which coincided with greenland stadials there is also a persistent detrital carbonate input the largest shift in most sediment proxies occurred 28 30 cal ka bp reflecting the sustained expansion of the ice sheets the grain size spectra on the snorri drift md99 2323 reflected complex depositional histories involving the supply of poorly sorted glacially derived sediment sand silt and clay and reworking by bottom currents

a cross anisotropic elastoplastic model applied to sedimentary rocks abstract strength and deformability properties of sedimentary rocks are difficult to characterize as these geomaterials show anisotropic mechanical behavior which cannot be adequately evaluated by an isotropic constitutive model this essay proposes a cross anisotropic elastoplastic model to evaluate stress strain relationships of sedimentary rocks the approach couples the twelve parameter lade kim isotropic model with a non uniform scaling of the stress tensor and includes two scaling parameters that link the orientation of the bedding planes with the loading direction the anisotropic model parameters can be conveniently determined using bayesian analysis we illustrate our method using triaxial tests on a variety of confining stresses and bedding plane orientations for a travertine and a tournemire shale our results demonstrate that the predicted maximum deviatoric stresses and the simulated stress strain curves are shown to be in good agreement with the measured data

microcrack induced elastic wave anisotropy of brittle rocks the failure of brittle rocks during compression is preceded by the formation growth and coalescence of microcracks elastic wave velocities are reduced in the presence of open microcracks and fractures and may therefore be used to monitor the progressive damage of the rock in general these microcracks are not randomly oriented and the rock displays an elastic anisotropy the elastic anisotropy due to cracks can be expressed in terms of a second rank and fourth rank crack density tensor for open cracks the contribution of the fourth rank crack density tensor to the elastic wave velocities is small these results are compared with recent measurements of the ultrasonic compressional and shear wave velocities for propagation parallel and perpendicular to an increasing axial stress applied at constant confining stress to berea sandstone inversion of the velocity measurements indicates that the microcracks propagate parallel to the maximum compressive stress in agreement with current rock mechanics theory a reasonable fit to the data is obtained using only the second rank crack density tensor even though at high confining stress the cracks are expected to be in partial contact along their length this is consistent with the model of elastic wave propagation in a medium containing partially contacting fractures published by white however measurements of off axis wave velocities are required to fully quantify the contribution of the fourth rank crack density tensor

source to sink statistical identification of regional variations in the mineralogy of surface sediments in the western nordic seas 58 n 75 n 10 w 40 w the non clay and clay mineralogies of the 2 mm sediment fraction from 157 seafloor samples in the western nordic seas is calculated by quantitative x ray diffraction analysis our sample coverage includes the iceland shelf the ice impacted east greenland margin and the greenland iceland and irminger seas the bedrock geology of source areas includes precambrian basement rocks devonian red beds and younger marine and fluvial sediments and large outcrops of early tertiary to recent flood basalts and other volcanic facies sediment erosion and transport in the area are associated with ice sea ice and icebergs and glacial meltwater and fluvial sediment plumes we use principal component analysis fuzzy k means clustering and discriminant function analysis to reduce the original 31 minerals 157 sites matrix to more manageable 5 regional coherent clusters of sites which are well discriminated by the weight of six minerals namely quartz pyroxene illites magnetite and maghemite amorphous silica e g glass and muscovite the close spatial relationship between bedrock geology and discrete cluster membership stresses the importance of this variable and indicates that far distant sediment transport by sea ice icebergs or other mechanisms although occurring does not radically change the mineral composition of present day sea floor sediments our improved knowledge of the regional mineral assemblages allows for tracking distinct eastern greenland and icelandic sources

microfracturing and microporosity in shales shales are ubiquitous rocks in sedimentary basins where their low permeability makes them efficient seals for conventional oil and gas reservoirs and underground waste storage repositories waste waters co2 nuclear fuels moreover when they contain organic matter they form source rocks for hydrocarbons that may escape towards a more porous reservoir during burial a process referred to as primary migration and when the hydrocarbons cannot escape these rocks can be exploited as oil or shale gas reservoirs while the presence of fractures at the outcrop scale has been described the existence of fractures at smaller scales their link with microporosity the mechanisms that created them their persistence over geological times and their effect on the petrophysical properties of shales represent scientific challenges for which drillings in various sedimentary basins over the past decades may hold timely key data here we review and synthetize the current knowledge on how microfractures and micropores in shales can be imaged and characterized and how they control their anisotropic mechanical properties and permeability one question is whether such microfractures when observed in outcrops or in drilled core samples extracted from boreholes are related to decompaction and do not exist at depth another question is whether veins observed in shales represent microfractures that were open long enough to have acted as flow paths across the formation the mechanisms of microfracture development are described some have an internal origin fracturing by maturation of organic matter dehydration of clays while others are caused by external factors tectonic loading importantly the amount of microfracturing in shales is shown to depend strongly on the content in 1 organic matter and 2 strong minerals the nucleation of microfractures depends on the existence of mechanical heterogeneities down to the nanometer scale their propagation and linkage to create a percolating network will depend on the presence of heterogeneities at the meso to macro scales such percolating microfracture networks could control both the long term sealing capabilities of cap rocks and the further propagation of hydraulic fracturing cracks finally possible areas of research for describing the mechanism of microfracture formation in greater detail and how this impacts the transport and mechanical properties of shales are also discussed

variations in felsic versus mafic sources in the western nordic seas during mis 1 to mis 4 abstract the goal of this paper is to employ quantitative methods to first describe the spatial variations in the quantitative non clay and clay mineral composition of seafloor surface sediments secondly use those data to describe the temporal variations in mineral compositions of nine cores that extend variously between the present day and 85 ka bp and thirdly describe regional variations in the transport of felsic versus mafic rich glacial marine sediments at four sites close to denmark strait k mean clusters of recent seafloor samples n 156 distinguished four mineral facies which characterize a range of mafic to felsic compositions these samples serve as a training set to identify the down core mineral facies in eight cores n 1053 the degree of provenance mixing is measured by fuzzy clustering on an unsupervised cluster analysis classification decision trees validate the mineral facies only 6 misclassified and indicate that variations in the weight of pyroxene are of primary importance in defining cluster membership mineral compositions identify two end member core sites jm07 174gc greenland sea and lo9 18 reykjanes ridge while the cores north and south of the greenland faroes ridge cores ps2644 md99 2274 2280 and 2323 are a mixture of mafic rich and felsic rich mineral facies variations in magnetic susceptibility and quartz wt exhibit coherent runs of values above or below their medians in three of the cores occurred indicating that these cannot be ascribed to random variations p

impact of fabric microcracks and stress field on shale anisotropy summary few data are available on shales in terms of seismic to ultrasonic properties and anisotropy although all are important with regards to imaging problems often encountered in such lithologies additionally mechanisms causing changes in these properties are not well documented due to the fine grain size of such materials and time required for testing under controlled pore pressure conditions the results presented here are derived from a set of experiments run on muderong shale with pore pressure control in order to evaluate the effect of stress magnitude and stress anisotropy on ultrasonic response this shale was noted to have a linear velocitymean effective stress response and extremely high anisotropy both likely the result of the presence of fluid filled cracks in a low permeability porous medium changes in velocity and vp vs ratios are dependent on both stress and smectite content s wave velocity is significantly affected by the presence of smectite in this and other shales and at low stress 20 mpa is less sensitive to stress change than p wave velocity vp vs ratios are noted to increase in this shale up to 20 mpa effective stress then decrease slightly due to stress induced loss of interlayer water in smectite intrinsic anisotropy comes from composition a strong compaction fabric and the presence of microfractures changes to ultrasonic anisotropy are the result of the magnitude of the stresses their orientation with respect to the fractures and the degree of stress anisotropy

stress induced seismic azimuthal anisotropy sand shale content and depth trends offshore north west australia abstractseismic azimuthal anisotropy is apparent when p wave velocities vary with source receiver azimuth and downward propagating s waves split into two quasi s waves polarized in orthogonal directions not accounting for these effects can degrade seismic image quality and result in erroneous amplitude analysis and geologic interpretations there are currently no physical models available to describe how azimuthal anisotropy induced by differential horizontal stress varies with sand shale lithology and depth we develop a model that does so in unconsolidated sand shale sequences offshore north west australia our method naturally introduces two new concepts critical anisotropy and anisotropic depth limit critical anisotropy is the maximum amount of azimuthal anisotropy expected to be observed at the shallowest sediment burial depth where the confining pressure and sediment compaction are minimal the anisotropic depth limit is the maximum depth where the stress induced azimuthal anisotropy is ex

preferred orientation of phyllosilicates effects of composition and stress on resedimented mudstone microfabrics abstract development of a preferred orientation of clay minerals is investigated in response to changes in vertical effective stress and composition in resedimented material boston blue clay boston blue clay bbc an illitic glacio marine clay composed of 57 clay sized particles

tracer transport in the greenland ice sheet three dimensional isotopic stratigraphy abstract polar ice cores can provide both a record of climate history and a sharp test of the performance of numerical ice dynamics models the stratigraphic structure of an ice sheet is an expression of its full depositional and dynamic history and thus presents a greater challenge to computer models than merely matching the contemporary ice thickness and areal extent we describe a coupled model of ice and tracer dynamics that is realized by adding a semi lagrangian tracer transport scheme to a conventional thermomechanical ice dynamics model model skill is demonstrated by using ice core data from the grip site near summit greenland to successfully predict the isotopic stratigraphy of ice cores at other deep drilling sites the success of this effort indicates that when compensated for the effects of ice flow and elevation all the deep cores relate a coherent glacial history over the past 120 000 years according to the simulation results the oldest greenland ice lies beneath the grip gisp2 and northgrip sites although comparably old ice may also be found in north greenland and east central greenland

predrill pore pressure prediction using seismic data 1a predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform but the seismic velocities need to be derived using methods having sufficient resolution for well planning purposes for a deepwater gulf of mexico example significant differences are found between the velocity field obtained using reflection tomography and that obtained using a conventional method based on the dix equation these lead to significant differences in the predicted pore pressure parameters in the velocity to pore pressure transform are estimated using seismic interval velocities and pressure data from nearby calibration wells the uncertainty in the pore pressure prediction is analyzed by examining the spread in the predicted pore pressure obtained using parameter combinations which sample the region of parameter space consistent with the available well data if calibration wells are not available the ideas proposed in this paper can be used with measurements made whi

late quaternary sedimentation in baffin bay baffin bay is a small ocean basin that connects the arctic and atlantic oceans the adjacent continental shelves have been extensively reworked during quaternary glaciation the shelf break generally lies between 200 and 500 m the continental slope passes directly into the abyssal plain of baffin bay basin without any major submarine canyon deep sea fan system being present except for a large smooth sediment apron in northern baffin bay on the basis of over 50 piston cores six quaternary sediment facies are distinguished from detrital mineralogy reflected in colour and sediment texture facies a b and c are predominantly ice rafted or are debris flow deposits each with a distinct mineralogy facies d is turbidites and bottom current sorted sands silts and muds facies e is hemipelagic sediment facies f consists of sediments ranging from slumps through debris flow deposits to fine grained turbidites with a distinctive provenance in northern baffin bay these sediment facies appear to be part

the elastic anisotrophy of shales shales constitute about 75 of the clastic fill sedimentary basins and have a decisive effect on fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure the elastic stiffnesses of a shale with partially oriented clay particles is expressed in terms of the coefficients w sub lmn in an expansion of the clay particle orientation distribution function in generalized legendre functions application is made to the determination of the anellipticity of shales for transverse isotrophy the anellipticity quantifies the deviation of the p wave slowness curve from an ellipse and is shown to depend on a single coefficient w sub 400 in the expansion of the clay particle orientation distribution function if w sub 400 is small the anellipticity may be neglected as is apparently the case for a near surface late tertiary shale studied by winterstein and paulson strongly aligned clay particles result in a positive value of w sub 400 and a positive anellipticity in agreement with the majority of the field measurements however less well ordered shales could have a significantly positive second moment w sub 200 but only a small positive or even negative value of w sub 400 for such shales the anellipticity would be small or negative despite amore preferred alignment of clay particles in the bedding plane numerical examples of clay particle orientation distribution functions leading to zero or negative anellipticity are given less

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

the geometry of continental displacement and its application to arctic geology eugen wegmann s early approaches published in the geologische rundschau in 1943 plate tectonics developed around 1965 as a powerful tool to describe the tectonic movements of the earth s crust the article demonstrates that basically four already existing theoretical concepts subduction seafloor spreading the application of euler s theorem and transform faults had to be combined to arrive at the modern theory alfred wegener father of the theory of continental displacement is often credited as the most direct forerunner of plate tectonics however none of the aforementioned concepts had been developed by him the present article deals with the hitherto not duly credited contributions of the swiss geologist eugen wegmann 1896 1982 he developed in a series of highly original papers published between 1943 and 1948 one of them in the geologische rundschau a critical test of the theory of continental displacement based on the regional geology of the arctic furthermore he gave a very concise account on the geometrical principles of drift movements as a result he developed for the first time 25 years before mckenzie and parker s nature 216 1276 1280 landmark paper on the pacific 1967 the geometrical basis to graphically test plate motion directions however his work has not yet received the credit it deserves neither by scientist nor by historians of science

stress anisotropy and velocity anisotropy in low porosity shale abstract shales are known for often marked intrinsic anisotropy of many of their properties including strength permeability and velocity for example in addition it is well known that anisotropic stress fields can also have a significant impact on anisotropy of velocity even in an isotropic medium this paper sets out to investigate the ultrasonic velocity response of well characterised low porosity shales from the officer basin in western australia to both isotropic and anisotropic stress fields and to evaluate the velocity response to the changing stress field during consolidated undrained multi stage triaxial tests on core plugs cut normal to bedding vpv increases monotonically with increasing effective stress and vs1 behaves similarly although with some scatter vph and vsh remain constant initially but then decrease within each stage of the multi stage test although velocity from stage to stage at any given differential stress increases this has the impact of decreasing both p wave e and s wave anisotropy through application of differential stress within each loading stage however increasing the magnitude of an isotropic stress field has little effect on the velocity anisotropies the intrinsic anisotropy of the shale remains reasonably high at the highest confining pressures the results indicate the magnitude and orientation of the stress anisotropy with respect to the shale microfabric has a significant impact on the velocity response to changing stress fields

determination of sediment provenance by unmixing the mineralogy of source area sediments the sedunmix program abstract along the margins of areas such as greenland and baffin bay sediment composition reflects a complex mixture of sources associated with the transport of sediment in sea ice icebergs melt water and turbidite plumes similar situations arise in many contexts associated with sediment transport and with the mixing of sediments from different source areas the question is can contributions from discrete sediment bedrock sources be distinguished in a mixed sediment by using mineralogy and if so how accurately to solve this problem four end member source sediments were mixed in various proportions to form eleven artificial mixtures two of the end member sediments are felsic and the other two have more mafic compositions end member and mixed sediment mineralogies were measured for the

ultrasonic velocities in cretaceous shales from the williston basin compressional and shear wave velocities were measured in the laboratory from 1 bar to 4 kbar confining pressure for wet undrained samples of cretaceous shales from depths of 3200 and 5000 ft in the williston basin north dakota these shales behave as transversely isotropic elastic media the plane of circular symmetry coinciding with the bedding plane for compressional waves the velocity is higher for propagation in the bedding plane than at right angles to it and the anisotropy is greater for the 5000 ft shale for shear waves the sh wave perpendicular to bedding and the sv wave parallel to bedding propagate with the same speed which is about 25 percent lower than that for the sh wave parallel to bedding in general compressional and shear velocities are higher for the indurated 5000 ft shale than for the friable 3200 ft shale all velocities increase with in increasing confining pressure to 4 kbar the 3200 ft shale exhibits velocity hysteresis as a function of pressure whereas this effect is a

t matrix approach to shale acoustics summary the t matrix approach of quantum scattering theory is used here to place many long wavelength equivalent medium approximations for porous composites polycrystals and cracked media on a common footing and to indicate their limitations but also to derive some new results based on two point statistics in this way we have obtained an insight into the difficult problem of elastic inclusions at finite concentrations which is of foremost relevance when estimating the effective material parameters of porous cracked shales involving stacks of more or less horizontally aligned clay platelets mixed together with more rounded silt minerals and with fluid filling the spaces a rather involved perturbative analysis of the effects of interactions between or structural correlations among the various inclusions minerals and cavities making up a real shale of hexagonal symmetry was performed in an attempt to obtain a better match between theoretical predictions based on a combination of coherent and optical potential approximations and experimental results recovered from ultrasonic wave speeds for the effective elastic stiffness tensor for the particular data set considered in this study the t matrix approach was able to match the data better than the approach of hornby et al but the match was not completely satisfactory further progress in theoretical shale modelling may come from a better knowledge of the elastic properties of pure clay minerals a more detailed knowledge of the microstructure of shales the incorporation of constraints obtained from comparisons between theoretical predictions and experimental results as well as a continuing development of the t matrix approach numerical results also for the effect of bedding parallel microcracks on the elasticity of such a real shale have value in illustrating the importance of taking into account the effects of spatial distribution when trying to deal with non dilute mixtures of highly contrasting material properties

the effect of anisotropy on the young s moduli and poisson s ratios of shales young s modulus and poisson s ratio are required for geomechanics applications such as hydraulic fracture design analysis of wellbore stability and rock failure determination of in situ stress and assessment of the response of reservoirs and surrounding rocks to changes in pore pressure and stress shales are usually anisotropic and models that neglect shale anisotropy may fail to describe geomechanical behaviour correctly anisotropy in shales results from a partial alignment of anisotropic clay particles kerogen inclusions microcracks low aspect ratio pores and layering for shales the young s modulus measured parallel to bedding e1 is usually greater than the young s modulus measured perpendicular to bedding e3 however the poisson s ratio 31 corresponding to stress applied perpendicular to bedding and strain measured parallel to bedding can be greater than equal to or less than the poisson s ratio 12 for stress applied parallel to bedding and strain measured parallel to bedding for transverse isotropy the elastic anisotropy resulting from a partial alignment of clay particles can be written in terms of the coefficients w200 and w400 which describe the impact of clay particle orientation on the anisotropy of shales disorder in the orientation of clay particles acts to reduce w400 faster than w200 since w400 is a higher order moment of the clay particle orientation distribution function than w200 this is confirmed by analysis of measured anisotropy parameters for shales a partial alignment of clay particles is consistent with the measured young s moduli for shales and with values of poisson s ratio 31 12 but not with values 31 12 these values can be explained if there exist kerogen inclusions microcracks or low aspect ratio pores aligned parallel to the bedding plane

north eastern laurentide western greenland and southern innuitian ice stream dynamics during the last glacial cycle precise relationships between high frequency ice sheet dynamics and late quaternary climate variability are still poorly understood notably with regard to their relative timing and causal mechanisms baffin bay is of particular interest in this regard due to the influence of ice streaming activities from the north eastern laurentide southern innuitian and western greenland ice margins on its sedimentary regimes during glacial times here we document such ice margin dynamics using a sedimentological analysis performed on a piston core from central baffin bay and spanning the last 115 ka lithofacies analysis and mineralogical assemblages are used to reconstruct sediment sources using the sedunmix program and depositional mechanisms coarse detrital carbonate dc dolomite rich layers are attributed either to north eastern laurentide and innuitian ice stream surges or to pervasive ice rafted debris delivery processes at distinct periods out of phase fine grained glaciomarine sediments with a mineralogical signature from western greenland linked to uummannaq ice streaming activity are interbedded with the coarse dc layers the new results suggest that during the last glacial cycle the north eastern laurentide and southern innuitian ice streams were sensitive to high frequency climate fluctuations such as the dansgaard oeschger events while the western greenland margins were more sensitive to large scale climatic oceanic reorganizations such as relative sea level changes and or advection of warmer atlantic waters into the bay copyright 2013 john wiley sons ltd

seasonal speedup of a greenland marine terminating outlet glacier forced by surface melt induced changes in subglacial hydrology we present subdaily ice flow measurements at four gps sites between 36 and 72 km from the margin of a marine terminating greenland outlet glacier spanning the 2009 melt season our data show that 35 km from the margin seasonal and shorter time scale ice flow variations are controlled by surface melt induced changes in subglacial hydrology following the onset of melting at each site ice motion increased above background for up to 2 months with resultant up glacier migration of both the onset and peak of acceleration later in our survey ice flow at all sites decreased to below background multiple 1 to 15 day speedups increased ice motion by up to 40 above background these events were typically accompanied by uplift and coincided with enhanced surface melt or lake drainage our results indicate that the subglacial drainage system evolved through the season with efficient drainage extending to at least 48 km inland during the melt season while we can explain our observations with reference to evolution of the glacier drainage system the net effect of the summer speed variations on annual motion is small 1 this in part is because the speedups are compensated for by slowdowns beneath background associated with the establishment of an efficient subglacial drainage system in addition the speedups are less pronounced in comparison to land terminating systems our results reveal similarities between the inland ice flow response of greenland marine and land terminating outlet glaciers

calcium carbonate saturation states in the waters of the canadian arctic archipelago and the labrador sea 1 ocean acidification is predicted to occur first in polar oceans we investigated the saturation state of waters with respect to calcite cal and aragonite arg in six sections along an arctic outflow pathway through the canadian arctic archipelago caa and into the northwestern atlantic using dissolved inorganic carbon and total alkalinity measurements from 2003 to 2005 the study area a key region connecting the arctic and the north atlantic includes smith sound barrow strait baffin bay davis strait hudson strait and the labrador sea the average arg in the arctic outflow was 1 18 0 17 in barrow strait and 1 31 0 14 in smith sound with areas where arg 1 the arctic outflow through the caa has a high content of pacific waters which have a low saturation state these waters can be traced along the western baffin bay to davis strait south of davis strait this outflow is modified by mixing with slope and offshore waters of atlantic origin and with the outflow from hudson strait despite the mixing low saturation state water can still be identified on the southern labrador shelf the aragonite saturation horizon is found at 150 m in barrow strait at 200 m in baffin bay davis strait and hudson strait and at 2300 m in the labrador sea this study provides baseline data of the saturation states for the waters of the caa and the northwest atlantic it also illustrates the downstream evolution of low saturation state arctic outflow in the northwest atlantic

geomechanical and ultrasonic characterization of a norwegian sea shale anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical interpretation including depth conversion and fluid identification in addition mechanical and dynamic elastic shale behavior is not well understood because few tests have been performed on well preserved samples multiple stage triaxial tests were performed upon horizontal core plugs of a shale from the norwegian sea with a view to evaluating rock strength and the evolution of ultrasonic response during rock deformation in addition standard rock physical properties were characterized as well as composition the shale microfabric is seen to be strongly laminated with alternating thick clay rich laminae and thin silt rich laminae occasional microfractures are also noted parallel to these laminations the shale has low friction coefficient and cohesive strength and shows anisotropy of these parameters when the maximum principal stress is oriented parallel to and at 45 to the microfabric the orientation of the maximum principal stress parallel to the intrinsic fabric and microcracks was seen to significantly impact on velocity normal to the fabric as stress parallel to the fabric increased s wave anisotropy was significantly affected by the increasing stress anisotropy stress orientation with respect to fabric orientation was therefore found to be an important control on the degree of anisotropy of dynamic elastic properties in this shale

tectonic discrimination of basalts with classification trees traditionally geochemical classification of basaltic rocks of unknown tectonic affinity has been performed by discrimination diagrams although easy to use this method is fairly inaccurate because it only uses bi or trivariate data furthermore many popular discrimination diagrams are statistically not very rigorous because the decision boundaries are drawn by eye and they ignore closure thus violating the rules of compositional data analysis classification trees approximate the data space by a stepwise constant function and are a more rigorous and potentially more effective way to determine tectonic affinity trees allow the simultaneous use of an unlimited number of geochemical features while still permitting visualization by an easy to use two dimensional graph two classification trees are presented for the discrimination of basalts of mid ocean ridge ocean island and island arc affinities the first tree uses 51 major minor and trace elements and isotopic ratios and should be used for the classification of fresh basalt samples a second tree only uses high field strength element analyses and isotopic ratios and can also be used for basalts that have undergone alteration the probability of successful classification is 89 for the first and 84 for the second tree as determined by 10 fold cross validation even though the trees presented in this paper use many geochemical features it is not a problem if some of these are missing in the unknown sample classification trees solve this problem with surrogate variables which give more or less the same decision as the primary variables the advantages of the classification tree approach over discrimination diagrams are illustrated by a comparative test on a sample dataset of known tectonic affinities although arguably better than discrimination diagrams classification trees are not perfect and the limitations of the method are illustrated on a published dataset of basalts from the pindos basin greece

source rock seismic velocity models gassmann versus backus source rocks are described by a porous transversely isotropic medium composed of illite and organic matter kerogen oil and gas the bulk modulus of the oil gas mixture is calculated by using a model of patchy saturation then the moduli of the kerogen fluid mixture are obtained with the kuster and toksoz model assuming that oil is the inclusion in a kerogen matrix to obtain the seismic velocities of the shale we used backus averaging and gassmann equations generalized to the anisotropic case with a solid pore infill in the latter case the dry rock elastic constants are calculated with a generalization of krief equations to the anisotropic case we considered 11 samples of the bakken shale data set with a kerogen pore infill the backus model provides lower and upper bounds of the velocities whereas the krief gassmann model provides a good match to the data alternatively we obtain the dry rock elastic moduli by using the inverse gassmann equation instead of using krief equations four cases

microcrack induced versus intrinsic elastic anisotropy in mature hc source shales recent experimental studies of ultrasonic velocity anisotropy in kerogen rich shales indicate that these rocks are characterized by a very strong anisotropic response related to a very fine bedding parallel lamination of organic matter and preferred orientation of clay particles in the rock matrix vernik and nur 1992 this intrinsic anisotropy is further enhanced in thermally mature shales by bedding parallel microcracks caused by the processes of hydrocarbon generation vernik paper in preparation however the potential of recognizing mature source rocks in situ using downhole sonic crosshole seismic or vsp data clearly depends on our ability to discriminate between these two major causes of elastic anisotropy remove the effect of the intrinsic anisotropy and estimate crack density and crack porosity from velocity measurements

measurement of the normal tangential fracture compliance ratio zn zt during hydraulic fracture stimulation using s wave splitting data we develop a method to invert s wave splitting sws observations measured on microseismic event data for the ratio of normal to tangential compliance zn zt of sets of aligned fractures we demonstrate this method by inverting for zn zt using sws measurements made during hydraulic fracture stimulation of the cotton valley tight gas reservoir texas when the full sws data set is inverted we find that zn zt 0 74 0 04 windowing the data by time we were able to observe variations in zn zt as the fracture stimulation progresses most notably we observe an increase in zn zt contemporaneous with proppant injection rock physics models and laboratory observations have shown that zn zt can be sensitive to 1 the stiffness of the fluid filling the fracture 2 the extent to which this fluid can flow in and out of the fracture during the passage of a seismic wave and 3 the internal architecture of the fracture including the roughness of the fracture surfaces the number and size of any asperities and the presence of material filling the fracture these factors have direct implications for modelling the fluid flow properties of fractures consequently the ability to image zn zt using sws will provide useful information about fractured rocks and allow additional constraints to be placed on reservoir behaviour

stress associated intrinsic and scattering attenuation from laboratory ultrasonic measurements on shales seismic attenuation is sensitive to stress induced subtle changes in the physical state of rocks in this study the stress and frequency associated attenuation is quantified through ultrasonic measurements on three differently oriented cylindrical shale samples under various axial stresses as an improvement to the single scattering model the elastic monte carlo method is employed to investigate multiple scattering attenuations by incorporating the boundary reflections and wave conversions our results show that as the axial stress increases the intrinsic attenuation decreases in all directions while the scattering attenuation decreases slightly in the direction perpendicular to the bedding but increases largely and nonlinearly in other directions these discrepancies result from different attenuation mechanisms both the intrinsic and scattering attenuation are found to be largest in the direction 45 to the bedding but least in the perpendicular direction the s wave attenuation is larger and more sensitive to stress changes than p wave attenuation due to its shorter wavelength as expected from sandstone examples the scattering attenuation in shales is significantly larger and more sensitive to stress changes than the intrinsic attenuation the frequency dependence of scattering attenuation suggests that the peak frequency with the maximum scattering attenuation is independent of axial stresses but varies in different directions of an individual rock with different heterogeneity and anisotropy scales the peak frequency of s coda is smaller and its peak scattering attenuation is larger than p coda in conclusion the stress and frequency dependence of ultrasonic attenuations in shales differ largely in various directions indicating significant anisotropy and heterogeneity

microfabric and rock properties of experimentally compressed silt clay mixtures abstract oedometric mechanical compaction tests were performed on brine saturated synthetic samples consisting of silt clay mixtures to study changes in microfabric and rock properties as a function of effective stress the silt consisted of crushed quartz 100 with grain size range between 4 and 40 m whereas the clay consisted of 81 kaolinite 14 mica illite and 5 microcline of grain size between 0 4 and 30 m five sample pairs ranging in composition from pure silt to pure clay were compacted to 5 and 50 mpa effective stress respectively sem studies were carried out to investigate microfabric changes in the mechanically compacted silt clay mixtures the degree of alignment of the different minerals present quartz mica illite and kaolinite were computed by using an image analysis software experimental compaction have measured the changes in the rock properties such as porosity and velocity as a function of effective stress for different mixtures of clay and silt clay rich samples showed a higher degree of mineral orientation and lower porosity compared to silt dominated samples as a function of effective stress pure clay sample had 11 porosity at 50 mpa effective stress whereas the pure silt sample retained about 29 porosity at the same effective stress the experiments showed that low porosity down to 11 is possible by mechanical compaction only a systematic increase in strain was observed in the silt clay mixtures with increasing clay content but the porosity values found for the 50 50 silt clay mixture were lower than that of 25 75 silt clay mixture no preferential mineral orientation is expected before compaction owing to the high initial porosity suggesting that the final fabric is a direct result of the effective stress both p and s wave velocities increased in all silt clay mixtures with increasing effective stress the maximum p and s wave velocities were observed in the 25 75 silt clay mixture whereas the minimum vp and vs were recorded in the pure silt mixture at 50 mpa effective stress p wave velocities as high as 3 km s resulted from experimental mechanical compaction alone the results show that fine grained sediment porosity and velocity are dependent on microfabric which in turn is a function of grain size distribution particle shape sediment composition and stress at 5 mpa effective stress quartz orientation increased as a function of the amount of clay indicating that clay facilitate rotation of angular quartz grains adding clay from 25 to 75 in the silt clay mixtures at 50 mpa effective stress decreased the quartz alignment the clay mineral orientation increased by increasing both the amount of clay and the effective stress the mica illite fabric alignment being systematically higher than that of kaolinite even small amount of silt 25 added to pure clay reduced the degree of clay alignment significantly this study demonstrates that experimental compaction of well characterized synthetic mudstones can be a useful tool to understand microfabric and rock properties of shallow natural mudstones where mechanical compaction is the dominant process

why plate tectonics was not invented in the alps in the alps folds were recognized in the early eighteenth century thrusts in the middle of the nineteenth century the nappe theory developed from 1884 to 1902 led to a mobilistic approach implying large scale relative movements of europe and of a prong of africa argand staub the existence of mesozoic oceans or ocean like basins was also realized ampferer introduced the concept of subduction verschluckung around 1935 alpine geologists somehow became afraid of their own courage and failed to present a coherent interpretation of the structure and evolution of the chain the theory of plate tectonics was developed primarily by geophysicists at sea who took little account of the alpine evidence

late quaternary detrital carbonate dc layers in baffin bay marine sediments 67 74 n correlation with heinrich events in the north atlantic abstract episodes of glaciation in the region north of baffin bay resulted in the erosion of paleozoic carbonate outcrops in nw greenland and the canadian high arctic these events are recognized in the marine sediments of baffin bay bb as a series of detrital carbonate rich dc layers bbdc layers thin southward within baffin bay thus the contribution of baffin bay ice rafted carbonate rich sediments to the north atlantic is probably slight especially compared with sediment output from hudson strait during heinrich events we reexamine cf aksu 1981 a series of nine piston cores from the axis of baffin bay and across the davis strait sill and provide a suite of 21 ams 14 c dates on foramininfera which bracket the ages of several dc layers the onset of the last dc event is dated in six cores and has an age of ca 12 4 ka in northern and central baffin bay a thick dc layer occurs at around 4 m in the cores and is dated 40 ka there were three to six dc intervening events the youngest bbdc event possibly a double event lags heinrich event 1 h 1 off hudson strait dated at 14 5 ka but it is coeval with the pronounced warming seen in gisp2 records from the greenland ice sheet during interstadial 1 we hypothesize that bbdc episodes are coeval with major interstadial 18 o peaks from gisp2 and other greenland ice core records and are caused by or associated with the advection of atlantic water into baffin bay cf hiscott et al 1989 and the subsequent rapid retreat of ice streams in the northern approaches to baffin bay

pressure dependent seismic velocities based on effective compliance theory and an asperity deformation model abstractseismic velocities of rocks depend strongly on confining pressure which is often explained by the fracture compliances changes within the rocks it is important to have an accurate model describing the relations between confining pressure and seismic velocities for applications such as time lapse reservoir characterization we propose a new model to address this problem by combining the existing effective compliance theory with new solutions for the pressure dependence of fracture compliances specifically we assume the fracture contact surface can be represented by a set of elastic hemispheres with radii following power law distribution and the pressure dependence of seismic velocities can be expressed through pressure dependent normal and tangential fracture compliances that are derived from hertzian contact theory joint data fittings of p and s wave velocity laboratory data show that our model is accurate we also implement fluid substitution using our model to explain the similar stress i

along slope variations in sediment lithofacies and depositional processes since the last glacial maximum on the northeast baffin margin canada abstract twelve piston cores were used to characterize late quaternary lithofacies depositional processes and deglacial history along the baffin bay slope between lancaster sound and home bay core investigations show four distinct laterally correlatable lithofacies along the slope basal and upper diamicton laminated red brown mud tan carbonate gravelly sandy mud and bioturbated brown mud basal diamicton largely represents glacigenic debris flow deposits during a glacial advance from baffin island at 25 cal ka the distribution and character of laminated red brown mud suggests a lateral supply to baffin bay slope from ice proximal meltwater plumes and turbidity currents sourced in glacial ice from both baffin bay shelf and home bay between 41 5 cal ka to 14 2 cal ka an upper diamicton records a lesser localized glacial advance that ended at about 14 2 cal ka tan carbonate mud events represent ice rafted enhanced detrital carbonate delivery to the slope between 25 cal ka and 11 cal ka a gradual thinning of these events from northern to southern baffin bay corroborates a northern baffin bay lancaster sound or nares strait iceberg source proglacial facies seaward of home bay contain beds with slightly elevated detrital carbonate that may represent the distal edge of carbonate ice rafted from lancaster sound baffin bay is a type example of a polar glacial basin in which direct glacial supply predominates over the effects of glacial meltwater as a result axial supply from the large ice streams north of baffin bay particularly lancaster sound is dominant in the baffin bay basin and lateral supply from smaller ice streams on baffin island predominates on the ne baffin slope

analysis of antarctic glacigenic sediment provenance through geochemical and petrologic applications abstract the number of provenance studies of glacigenic sediments in antarctica has increased dramatically over the past decade providing an enhanced understanding of ice sheet history and dynamics along with the broader geologic history such data have been used to assess glacial erosion patterns at the catchment scale flow path reconstructions over a wide range of scales and ice sheet fluctuations indicated by iceberg rafted debris in circumantarctic glacial marine sediments it is notable that even though most of the bedrock of the continent is ice covered and inaccessible provenance data can provide such valuable information about antarctic ice and can even be used to infer buried rock types along with their geo and thermochronologic history glacigenic sediments provide a broader array of provenance analysis opportunities than any other sediment type because of their wide range of grain sizes and in this paper we review methods and examples from all size fractions that have been applied to the antarctic glacigenic sedimentary record interpretations of these records must take careful consideration of the choice of analytical methods uneven patterns of erosion and spatial variability in sediment transport and rock types which all may lead to a preferential identification of different elements of sources in the provenance analyses because of this we advocate a multi proxy approach and highlight studies that demonstrate the value of selecting complementary provenance methods

stress induced anisotropy in brine saturated shale summary this paper reports the intrinsic and crack induced anisotropic properties of a set of preserved brine saturated shale samples and their response to external stresses we used undrained multistage triaxial tests to evaluate how the ultrasonic wave velocities and their anisotropy changed with increasing isotropic and differential stress conditions in addition the impact of stress orientation with respect to fabric orientation was evaluated an array of ultrasonic transducers allowed to measure five independent wave velocities which were used to calculate the elastic properties of the shale results indicate that in this shale p and s wave velocities vary with stress in a different manner dependent on the maximum principal stress orientation with respect to the fabric where the maximum stress is normal to bedding vpv and vs1 increase monotonically with increasing effective stress however vph and vsh decrease during individual loading stages but increase from stage to stage as confining pressure increases the reverse occurs when the microfabric is parallel to the maximum principal stress where the maximum stress is bedding normal velocity anisotropy decreases as differential stress increases when maximum stress is fabric parallel anisotropy increases elastic anisotropy is related to the initial composition and the spatial distribution of the different minerals fabric in the sediment and the presence of microfractures while changes in elastic anisotropy result from the applied stresses their orientation with respect to the rock fabric and the degree of stress anisotropy

the role of the cryosphere in source to sink systems abstract glacial erosion and sediment production are of interest to diverse scientific communities concerned with the interaction of climatic tectonic and surface processes that influence the evolution of orogens and with the climatic signals archived in glacigenic strata we review the current state of knowledge on the generation transfer and accumulation of glacigenic sediment from land to sea we draw from geomorphology marine geology geochronology numerical modeling of surface processes and landscape evolution and experimental and field observations of glacier erosion and deposition and the interaction of ice with its bed and the ocean boundary our primary goal is to examine glacial systems using a holistic source to sink approach with a focus on describing a how glacial motion produces sediment b how the sediments sink record the dynamic nature of glacial systems under different climatic thermal regimes c the challenges in using the sedimentary record to interpret these dynamics in space and time and d the approaches still needed to further our understanding of how ice and associated sediment fluxes respond to climatic and other perturbations the dynamic state of ice i e the ice flux and ice extent is defined differently between the source and sink communities reflecting the challenges of establishing a stratigraphic signal that volumetrically constrains glacigenic sediment production as a function of the ice response to climate advances in marine geophysics have greatly assisted our understanding of mass transfer pathways and of former ice extents as a measure of ice dynamics and have identified the primary depocenters and key lithofacies of glacial sinks sediment fluxes associated with the dynamic state of the ice are best constrained where sediment volumes derived from key lithofacies and seismic reflection isopachs can be temporally partitioned of which there are few examples rather than from discrete point measures of sediment flux that are subject to sediment transfer biases forward numerical modeling of sediment fluxes as a function of ice dynamics agree with observational data at the continental margin scale but finer time space scale ice dynamic models do not yet recreate observed ice extent or flowpaths future source to sink work in glaciated systems should focus on refining empirical relationships between ice velocity and sediment production and expand the application of existing methods to develop sediment volumes and fluxes in known depocenters of former and modern ice streams

stress dependent seismic anisotropy of shales a simple theory for the stress dependent seismic anisotropy of shales can be obtained in terms of a second rank tensor and a fourth rank tensor that depend on the orientation distribution of contacts between clay platelets the theory allows the normal and shear stiffness of the contact regions between clay platelets to be obtained as a function of stress from measurements of seismic p and s wave velocities for shales the ratio of the normal to shear compliance bn bt of the contact regions between clay particles is found to be sensitive to the saturation state of the shale inversion of velocity measurements for fully saturated shales shows a low value of bn bt when compared with measurements on air dry shales consistent with the expected reduction in normal compliance in a fluid saturated low permeability rock for all shales considered bn bt is found to be less than unity the contacts between clay particles are therefore more compliant in shear than in compression

multi scale approach for modeling the transversely isotropic elastic properties of shale considering multi inclusions and interfacial transition zone multiscale approach based explicit analytic predictions are obtained for the transversely isotropic properties of shale rock considering the multi inclusion and interfacial transition zone itz effects representative volume elements rves are utilized to describe the material s hierarchical microstructures from the nanoscale to the macroscale a new multilevel micromechanical homogenization scheme is presented to quantitatively estimate the material s transversely isotropic properties with the multi inclusion and itz effects the itz is characterized by the interphase material whose effects are calculated by modifying the generalized self consistent model furthermore the explicit form solutions for the transversely isotropic properties are obtained by utilizing the hill polarization tensor without numerical integration and the standard tensorial basis with the analytic inversions of fourth rank tensors to verify the proposed multiscale framework predictions obtained via the proposed model are compared with experimental data and results estimated by the previous work which show that the proposed multi scaling approaches are capable of predicting the macroscopic behaviors of shale rocks with the multi inclusion and itz effects finally the influences of itz and inclusion properties on the material s macroscopic properties are discussed based on the proposed multiscale framework

margin segmentation of baffin bay davis strait eastern canada based on seismic reflection and potential field data abstract the continental margin of baffin island was interpreted from a compilation of seismic reflection and potential field data based on these data it was divided into volcanic and non volcanic segments in the northernmost area coast parallel grabens and continental basement highs are superseded beneath the slope by irregular basement topography in combination with the velocities from refraction data and the lack of a magnetic slope anomaly we propose a non volcanic margin in the central region the seismic data show a limited region with a seaward dipping reflector sequence that may be intercalated with a sedimentary section both north and south of cape dyer extensive volcanic rocks are interpreted at and below seabed consistent with a volcanic margin in the southern region the depth to basement drops rapidly offshore a thick prograding sedimentary wedge produces a high amplitude long wavelength free air gravity anomaly that was previously confused with the continent ocean boundary although some volcanic rocks are mapped in the region this area is adjacent to the non volcanic labrador sea margin and is interpreted to be of similar structure segmentation of the margin by major faults can explain the abrupt transitions from volcanic to non volcanic margin segments the continent ocean boundary for the region is determined based on the potential field and seismic data along the greenland plate in davis strait the continent ocean boundary coincides with the ungava fault zone the continent ocean boundary is used in conjunction with published poles of rotation to evaluate plate reconstructions at chrons 33n and 27n the earlier reconstruction produces an extensive overlap of boundaries in the north the later reconstruction shows a gap in the southern region thus additional information is required to refine the reconstructions

surface sea floor and near surface box cores sediment mineralogy in baffin bay as a key to sediment provenance and ice sheet variations to better understand the glacial history of the ice sheets surrounding baffin bay and to provide information on sediment pathways samples from 82 seafloor grabs and core tops and from seven box cores were subjected to quantitative x ray diffraction weight percent wt analysis of the 2000 m all show an abrupt drop in calcite wt post 5 cal ka bp following a major peak in detrital carbonate mainly dolomite this dolomite rich detrital carbonate dc event in jr175bc06 is possibly coeval with the younger dryas cold event four possible glacial sourced end mem bers were employed in a compositional unmixing algorithm to gain insight into down core changes in sediment provenance at the deep central basin estimates of the rates of sediment accumulation in the central basin are only in the range of 2 to 4 cm cal ka surprisingly low given the glaciated nature of the surrounding land

pyrolysis induced p wave velocity anisotropy in organic rich shales abstractthe sources of elastic anisotropy in organic rich shale and their relative contribution therein remain poorly understood in the rock physics literature given the importance of organic rich shale as source rocks and unconventional reservoirs it is imperative that a thorough understanding of shale rock physics is developed we made a first attempt at establishing cause and effect relationships between geochemical parameters and microstructure rock physics as organic rich shales thermally mature to minimize auxiliary effects e g mineralogical variations among samples we studied the induced evolution of three pairs of vertical and horizontal shale plugs through dry pyrolysis experiments in lieu of traditional samples from a range of in situ thermal maturities the sensitivity of p wave velocity to pressure showed a significant increase post pyrolysis indicating the development of considerable soft porosity e g microcracks time lapse high resolution backscattered electron scanning electron

baffin bay nares strait surface seafloor sediment mineralogy further investigations and methods to elucidate spatial variations in provenance the goal of the paper is to ascertain whether there are significant regional variations in sediment mineral composition that might be used to elucidate ice sheet histories the weight percentages o

anisotropy of elastic wave velocities in deformed shales part 1 experimental results elastic wave velocity measurements in the laboratory are used to assess the evolution of the microstructure of shales under triaxial stresses which are representative of in situ conditions microstructural parameters such as crack aperture are of primary importance when permeability is a concern the purpose of these experiments is to understand the micromechanical behavior of the callovo oxfordian shale in response to external perturbations the available experimental setup allows for the continuous simultaneous measurement of five independent elastic wave velocities and two directions of strain axial and circumferential performed on the same cylindrical rock sample during deformation in an axisymmetric triaxial cell the main results are 1 identification of the complete tensor of elastic moduli of the transversely isotropic shales using elastic wave velocity measurements 2 assessment of the evolution of these moduli under triaxial loading and 3 assessment of the evolution of the elastic ani

investigation of present day in situ stresses and pore pressure in the south cambay basin western india implications for drilling reservoir development and fault reactivation abstract this work presents the assessment of present day stresses and pore pressures in a prolific onshore hydrocarbon bearing field located in the southern cambay basin western india through the development of a comprehensive geomechanical model a c quality wellbore breakouts inferred from the available four arm caliper logs and anisotropy analyses of dipole shear sonic logs indicate a ne n40 e to n50 e azimuth for maximum horizontal stress shmax pore pressure characterisation reveals mild overpressure in the lower eocene shale caused by disequilibrium compaction resulting from high sedimentation rates vertical stress sv was derived from density logs and a poroelastic strain model was employed to quantify the minimum shmin and maximum horizontal stress components shmax being later validated with leak off tests based on the relative magnitudes of three principal in situ stress components post rift strata upper eocene and younger reveal a normal faulting regime sv shmax shmin whereas a normal fault to strike slip faulting shmax sv shmin transition is observed in the syn rift unit lower eocene and older the mohr coulomb rock failure criterion was utilised to depict the shear failure gradient to prevent wellbore instability and results were validated with caliper logs we have also analysed the fault reactivation potential at reservoir level using frictional fault theory and stress polygons the results indicate that a minimum of 31 increase in pore pressure by fluid injection and hydraulic fracturing treatment can cause shear slippage of critically oriented faults resulting in induced seismicity our study has helped to understand the interplay between stress states and pore fluid pressure and their impact on reservoir development drilling and completion design and fault stability analysis in any given oil and gas field

seismic anisotropy of shales shales are a major component of sedimentary basins and they play a decisive role in fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure shale anisotropy needs to be quantified to obtain reliable information on reservoir fluid lithology and pore pressure from seismic data and to understand time to depth conversion errors and non hyperbolic moveout a single anisotropy parameter thomsen s parameter is sufficient to explain the difference between the small offset normal moveout velocity and vertical velocity and to interpret the small offset avo response the sign of this parameter is poorly understood with both positive and negative values having been reported in the literature is sensitive to the compliance of the contact regions between clay particles and to the degree of disorder in the orientation of clay particles if the ratio of the normal to shear compliance of the contact regions exceeds a critical value the presence of these regions acts to increase and a change in the sign of from the negative values characteristic of clay minerals to the positive values commonly reported for shales may occur misalignment of the clay particles can also lead to a positive value of for transverse isotropy the elastic anisotropy parameters can be written in terms of the coefficients w 200 and w 400 in an expansion of the clay particle orientation distribution function in generalized legendre functions for a given value of w 200 decreasing w 400 leads to an increase in while for fixed w 400 increases with increasing w 200 perfect alignment of clay particles with normals along the symmetry axis corresponds to the maximum values of w 200 and w 400 given by w max 200 10 8 2 and w max 400 3 2 8 2 a comparison of the predictions of the theory with laboratory measurements shows that most shales lie in a region of the w 200 w 400 plane defined by w 400 w 200 w max 400 w max 200

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints