erosion of the laurentide region of north america by glacial and glaciofluvial processes collection of seismic reflection data from continental margins and ocean basins surrounding north america makes it possible to estimate the amount of material eroded from the area formerly covered by laurentide ice sheets since major glaciation began in north america a minimum estimate is made of 1 62 106 km3 or an average 120 m of rock physically eroded from the laurentide region this figure is an order of magnitude higher than earlier estimates based on the volume of glacial drift cenozoic marine sediments and modern sediment loads of rivers most of the sediment produced during laurentide glaciation has already been transported to the oceans the importance of continental glaciation as a geomorphic agency in north america may have to be reevaluated evidence from sedimentation rates in ocean basins surrounding greenland and antarctica suggests that sediment production sediment transport and possibly denudation by permanent ice caps may be substantially lower than by periodic ice caps such as the laurentide low rates of sediment survival from the time of the permo carboniferous and precambrian glaciations suggest that predominance of marine deposition during some glacial epochs results in shorter lived sediment because of preferential tectonism and cycling of oceanic crust versus continental crust

multiple wisconsinan glacigenic sequences at wedron illinois lithofacies and their relationships sedimentological and glaciotectonic structures pebble fabrics and laboratory data were used to delineate seven facies associations in a classic upper wisconsinan glacigenic succession near wedron illinois each association is interpreted to represent a different depositional environment proglacial facies include massive and laminated silt lacustrine bedded sand fluvial and massive silt eolian subglacial facies consist of homogeneous diamicton lodgement till and variable diamicton and sorted sediment deformed by folding and shearing deformed till an ice marginal facies of heterogenous diamicton and sorted sediment supraglacial redeposited sediment and a paraglacial facies of laminated silt lacustrine also are present stratigraphic relationships among the facies allow the delineation of three glacigenic sequences from which three glacial events are inferred each sequence consists of proglacial fluvial and or lacustrine sediment subglacial till and fluvial deposits and supraglacial and ice marginal sediment flow fluvial and lacustrine deposits the complete nature of these glacigenic sequences suggests that the area was located primarily in the depositional zone of the laurentide ice sheet during the late wisconsinan erosional contacts and localized sorted sediment between three lithologically distinct till facies in the lowest sequence are interpreted to be subglacial in origin the three facies were deposited during the same event rather than separate events as previously inferred spatial and temporal variability among the subglacial processes of erosion transportation deformation and lodgement is evident within that sequence

ice divide flow at hans tausen iskappe north greenland from surface movement data surface strain rates around the southeastern dome of hans tausen iskappe in peary land north greenland 82 5 n 27 5 w are determined from global positioning system surveys of a strain net average longitudinal surface strain rate increases towards the dome from 1 4 0 2 x 10 4 a 1 at 5 10 ice thicknesses from the divide to 2 4 1 0 x 10 4 a within 1 ice thickness from the divide analysis of the data shows that the ice cap is presently building up within the strain net with an average rate of 0 04 0 02 m a assuming a uniform thickening the shape factor of the horizontal velocity the ratio between the vertically averaged horizontal velocity and the horizontal surface velocity decreases towards the dome from 0 9 at a distance of 10 ice thicknesses from the dome to 0 5 at the dome based on application of the continuity equation our results indicate that a region with anomalous flow is formed around the dome supporting recent indications reported by vaughan and others 1999 it is not possible from our data to constrain parameters of the flow law because there is no independent estimate of the significant present thickening of the central part of the ice cap and its pattern around the dome

anisotropic behavior of grip ices and flow in central greenland abstract mechanical tests have been performed on strongly textured ice samples coming from a wide range of depths from 1328 down to 2868 m of the greenland ice core project grip for different sample orientations with respect to the prescribed stress in this way two directional viscosities corresponding to the easy glide and to the hard glide orientations were determined along the core the viscoplastic anisotropy gradually increases down to a depth of 2600 m and slightly decreases below revealing a clear correlation between rheology and texture the experimental mechanical response compares well with that predicted by the viscoplastic self consistent vpsc model the vpsc model is also applied to ice samples that exhibit an axisymmetric texture to show in more detail the sensitivity of the rheology to specific texture parameters this leads to a number of recommendations for future mechanical tests on anisotropic samples a large scale ice flow model is finally used to estimate the influence of ice anisotropy on the flow along the grip gisp2 flow line the particular mechanical behavior of deep grip ices in the stress regime corresponding to an ice divide leads to deformation rates that are highly sensitive to bedrock topography and texture pattern this feature is likely to favour the formation of stratigraphic disturbances in deep ice layers as observed in the last 300 m of both grip and gisp2 cores

relation between neighbouring grains in the upper part of the northgrip ice core implications for rotation recrystallization abstract we propose a new method to investigate the relationships between neighbouring crystals and apply it to the textures measured along the upper 900 m of the northgrip ice core this method shows unexpected correlations between neighbours in the so called normal grain growth regime questioning the classical view on the onset of rotation recrystallization in ice sheets moreover the fractionation rate associated to the rotation recrystallization appears constant through time finally grains with low angle boundaries do not present a special distribution pattern of their c axes this suggests that rotation recrystallization is an isotropic process not affected by the direction of the macroscopic strain

new evidence for a grounded irish sea glaciation of the isles of scilly uk abstract new geomorphological and sedimentological data support previously published reconstructions of an irish sea glacier advance as far south as the northern shores of the isles of scilly in the celtic sea 49 58 n offshore boulder covered bars with cores of diamicton are interpreted as moraines which together with onshore moraine ridges and trimlines mark the maximal extent of the irish sea glacier at bread and cheese cove st martin s a heterogeneous sediment unit wedged between periglacial gelifluctates is interpreted as a mixture of glacitectonized and cannibalized glacilacustrine and marine deposits as well as primary subglacial tills macrofabric signatures reflect a subglacial origin but the whole unit has been subject to down slope mass movement micromorphological analysis indicates highly variable response to deformation and glacitectonism with most features relating to ductile behaviour and wet deformation the characteristics suggest deposition during a short lived advance of the irish sea glacier over pre existing marine and contemporaneous proglacial lacustrine sediments once blocks of stratified sediment and diamicton had been driven onshore they were subject to paraglacial remobilization resulting at most locations in complete disaggregation the distribution of re worked glacigenic sediments coincides with the glacial limits inferred from the geomorphological evidence

thermo mechanically coupled ice sheet response cold polythermal temperate classical mixture concepts are the appropriate vehicle for describing the dynamics of ice masses containing some water we review and derive respectively the theoretical formulations of cold polythermal and temperate ice masses emphasize the peculiarities of the model equations and point to difficulties that were encountered with the proposed models the focus is both on the adequate physical motivation of the models and the consistency of their mathematical representation

glaciodynamically upthrusted bands of englacially transported debris in the pleistocene of central poland two kinds of buried structures are described from dzirzenin north east of warsaw where they occur within a glaciofluvial landform 1 narrow till ridges showing vertically oriented structures excavated from stratified gravel and sands and 2 a narrow vertical zone of massive gravelly sandy material involving vertically oriented lens like layers composed of massive sand with pebbles or of diamicton the gravelly sandy zone is also closely surrounded by stratified glaciofluvial sediments in spite of their vertical position and internal deformation the till ridges and gravelly sandy zone show non tectonic contacts with the surrounding stratified undisturbed sediments the glaciofluvial sediments that occur immediately next to the structures under discussion are characterized by the occurrence of comparatively coarse material and interbeddings of diamicton which wedge out away from these structures the gravelly sandy zone separates different kinds of water laid deposits the buried structures are interpreted as former debris laden bands thrust upwards within the frontal part of the ice sheet and then transformed into still frozen debris ridges projecting over the already dead ice further melting of the decaying ice resulted in abundant glaciofluvial sedimentation and the debris ridges also supplied material for the deposition of the neighbouring stratified deposits one of the ridges separated different glaciofluvial environments the glaciofluvial sediments completely buried the ice cemented ridges which were finally transformed by a melting out process into the till ridges and the gravelly sandy zone the former are interpreted as having been transformed from upturned debris laden bands with a high concentration of debris or from the bands composed of frozen up sediment slabs the gravelly sandy zone is interpreted as having most probably been deposited from upturned bands characterized by a lesser concentration of debris

multiple subglacial till deposition a modern exemplar for quaternary palaeoglaciology the sedimentology of a vertical succession of alternating beds of massive and fissile diamictons on a orisjokull plateau icefield outlet foreland is employed to assess the evolution of subglacial traction tills at the margins of active temperate glaciers with deformable substrates where tills appear to form sub marginal incrementally thickened wedges that display multiple till emplacement events potentially of annual scale lodged boulders display strong a axes and surface striae alignments which parallel surface flutings indicating that fluting construction and till emplacement were related to moulding by consistent glacier flow from the ssw during the little ice age in contrast clast macrofabrics at the sub boulder size not unlike those reported from other icelandic tills are not as strong as would be expected in a subglacially sheared medium indicating shear strains too low for a steady state strain signature this separation of fabric data has isolated the strain signatures of the lodgement and deformation components of subglacial traction till whereby the orientations of the largest lodged clasts record high cumulative shear strains and those of the sub boulder sized clasts record greater susceptibility to deformation of their enclosing matrix this is likely due to the effect of clast collisions in clast rich till and the perturbations set up by the numerous large boulders consistent with observations on till fabrics in flutings and around lodged clasts a b plane macrofabric data display unusually high degrees of isotropy reflective of the more variable orientations of a b planes which are thought to reflect a b plane susceptibility to dip parallel or anastomosing shear planes a wide range of clast angularity values reflects the localized input of freshly plucked and hence relatively highly angular blocks to the deforming layer a characteristic of stepped bedrock profiles beneath the snouts of mountain glaciers finally we hypothesize that the massive and fissile units may represent a and b horizons of subglacial deforming layer couplets and that each couplet could record seasonal emplacement and partial inter couplet modification near the ice margin if the latter is the case then less than 1 m of subglacial till is advected to the glacier margin per annual deformation event

the deforming bed debris rich basal ice continuum and its implications for the formation of glacial landforms flutes and sediments melt out till abstract there are two potentially important shear zones at the base of the glacier the deforming layer and or the debris rich basal ice layer these two layers have a significant effect on glacier motion and glacial erosional depositional and sedimentary processes however it is shown that most of the processes operating within these two layers are very similar this includes compression at the ice margin longitudinal extension and simple shear upglacier similar styles of shear zone and associated fabric development and similar incorporation transport and depositional processes in the past many criterion have been developed to identify distinct deposition from the deforming layer and the debris rich basal ice layer however if the processes within these layers are similar then it makes the distinct identification of these two separate layers in the geological record very difficult however it is also shown that the main differences between the two layers include rates of sediment movement processes and preservation potential the later is very important as it appears that the two layers are interconnected and that material is melted out from the debris rich basal ice to form a significant component of the deforming layer in this way the final depositional imprint is from the deforming layer and there is little likelihood of the debris rich basal ice layer being preserved undeformed this is demonstrated from modern glacial environments pleistocene flute studies and studies of pleistocene melt out tills from the u k u s a and germany

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

deformation in the vicinity of ice divides calculs numeriques aux elements finis de la variation de la vitesse horizontale avec la profondeur au voisinage d une difference de la glace symetrique isotherme et ou glissement sur un lit plat

the shallow ice approximation for anisotropic ice formulation and limits ice sheet flow modeling is generally based on the shallow ice approximation sia developed for isotropic ice we extend this approximation to anisotropic ice and check its validity for both the isotropic and anisotropic cases by comparing the results of up to second order sia with those obtained from a model solving the full set of mechanical equations the theory is developed for a constitutive relation describing newtonian and non newtonian behavior but numerical results are shown only for a newtonian behavior the results are compared for plane flow of isothermal ice under steady state conditions sia gives an excellent representation of the newtonian flow of an isotropic ice sheet and a good description for the anisotropic case the zero order approximation is sufficient to describe ice flow precisely over flat bedrock for the anisotropic and isotropic cases even close to an ice divide for uneven bedrock the second order sia gives excellent results for isotropic ice and acceptable results for anisotropic ice finally we quantify the error introduced by using an enhancement factor to represent the anisotropy when longitudinal stresses are taken into account

internal architecture of a till sheet tiskilwa formation north central illinois usa application of architectural element analysis thick till sheets deposited during the quaternary form significant aquitards in many areas of north america however the detailed sedimentary heterogeneity and architecture and depositional history of till units are not well understood this study utilizes architectural element analysis to delineate the internal sedimentary architecture of the tiskilwa formation exposed at two outcrop sections in north central illinois usa architectural element analysis facilitates systematic delineation of sedimentary architecture based on the nature of facies contacts and change in facies associations delineation of unit geometries and understanding of depositional processes at different scales of resolution making architectural element analysis suitable for the sedimentological analysis and palaeoenvironmental reconstruction of subglacial deposits eleven facies types are identified in this study including sand gravel and diamict facies that record a suite of subglacial depositional processes detailed analysis of facies contacts bounding surface hierarchy and change in facies associations allows the delineation of five architectural elements including coarse grained lens coarse grained sheet mixed zone diamict lens and diamict sheet elements the spatial arrangement and genetic interpretation of elements and their spatial relationship with fifth order bounding surfaces allows the delineation of five larger scale architectural units element associations which can be mapped in the local study area and record at least three stacked successions of meltwater accumulation and till deposition the results of this study can be utilized for architectural analysis of till sheets and provide insight to groundwater flow pathways through till in the study area and elsewhere

on the effects of anisotropic rheology on ice flow internal structure and the age depth relationship at ice divides we use numerical modeling with a full system stokes solver to elucidate the effects of nonlinear rheology and strain induced anisotropy on ice flow at ice divides we find that anisotropic rheology profoundly affects the shape of both isochrone layering and surface topography anisotropic effects cause the formation of a downward curving fold i e a syncline in isochrones in the lower central area beneath the ice divide when the resulting syncline is superimposed on the well known raymond anticline a double peaked raymond bump is formed furthermore to each side of the raymond bump flanking synclines are formed in addition anisotropic effects are found to give rise to a subtle concavity in the surface profile to both sides of the summit the lower center syncline the flanking synclines and the near summit surface concavity have all previously been observed in nature but hitherto no explanation for the genesis of these features has been given we compare modeling results with radiograms collected from fuchs ice piedmont and kealey ice rise antarctica good overall agreement is found in particular we are able to reproduce all observed qualitative features of surface geometry and internal layering by including and only by including the effects of induced nonlinear rheological anisotropy on flow rheological anisotropy has the potential to profoundly affect the age distribution with depth and caution must be exercised when estimating age of ice from ice cores with an isotropic model the occurrence of linear features parallel to the ridge of ice divides often seen in satellite imagery is indicative of long term stability rather than signs of ongoing ice divide migration as previously suggested such ice divides are ideal locations for extracting ice cores

multiscale modeling of ice deformation behavior understanding the flow of ice in glaciers and polar ice sheets is of increasing relevance in a time of potentially significant climate change the flow of ice has hitherto received relatively little attention from the structural geological community this paper aims to provide an overview of methods and results of ice deformation modeling from the single crystal to the polycrystal scale and beyond to the scale of polar ice sheets all through these scales various models have been developed to understand describe and predict the processes that operate during deformation of ice with the aim to correctly represent ice rheology and self induced anisotropy most of the modeling tools presented in this paper originate from the material science community and are currently used and further developed for other materials and environments we will show that this community has deeply integrated ice as a very useful model material to develop and validate approaches in conditions of a highly anisotropic behavior this review by no means exhaustive aims at providing an overview of methods at different scales and levels of complexity

textures and fabrics in the grip ice core a comprehensive study of textures and fabrics has been carried out on the greenland ice core project grip ice core crystal sizes and c axis orientations have been measured on thin sections with conventional techniques yielding new information on the growth rotation and recrystallization of ice crystals in the greenland ice sheet normal grain growth is found to persist to a depth of 700 m in the core where the onset of polygonization due to increasing strain prevents a further increase in grain size in the holocene ice smaller crystals are observed in the wisconsin ice larger crystals are found in the eemian ice and the crystal size is found to vary with climatic parameters in these periods this dependence which probably results from variable impurity content in the ice persists to a depth of 2930 m coarse grained ice probably resulting from rapid growth of crystals at comparatively high temperatures is found in the lowest 100 m of the core the data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet a significant strengthening is not observed at the holocene wisconsin transition the fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m the evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth stretched fabrics in coarse grained ice in the lowest 100 m could be due to tensional stresses this ice is unlikely to be undergoing any significant horizontal deformation at the present time

sonic methods for measuring crystal orientation fabric in ice and results from the west antarctic ice sheet wais divide we describe methods for measuring crystal orientation fabric with sonic waves in an ice core borehole with special attention paid to vertical girdle fabrics that are prevalent at the wais divide the speed of vertically propagating compressional waves in ice is influenced by vertical clustering of the ice crystal c axes shear wave speeds particularly the speed separation between fast and slow shear polarizations are sensitive to azimuthal anisotropy sonic data from the wais divide complement thin section measurements of fabric thin sections show a steady transition to strong girdle fabrics in the upper 2000 m of ice followed by a transition to vertical pole fabrics below 2500 m depth compressional wave sonic data are inconclusive in the upper ice due to noise as well as the method s inherent insensitivity to girdle fabrics compared with available thin sections sonic data provide better resolution of the transition to pole fabrics below 2500 m notably including an abrupt increase in vertical clustering near 3000 m our compressional wave measurements resolve fabric changes occurring over depth ranges of a few meters that cannot be inferred from available thin sections but are sensitive only to zenithal anisotropy future logging tools should be designed to measure shear waves in addition to compressional waves especially for logging in regions where ice flow patterns favor the development of girdle fabrics

a flow law for anisotropic ice and its application to ice sheets a new formulation of the flow law of polycrystalline ice was derived for an rbitrary c axis orientation fabric pattern the rate factor of the flow law is given by a geometrical factor that can be calculated with c axis fabric data and stress condition a theoretical calculation combining this flow law with a lattice rotation model by intracrystalline slip in the constituent grains predicts the development of characteristic fabric patterns observed in many laboratory experiments and in the field according to this flow model of polycrystalline ice if significant recrystallization does not occur uniaxial compression makes the ice body harder with increasing strain whereas simple shear makes the ice body softer with strain this may significantly affect ice sheet dynamics

the reconstruction of former ice sheets and their mass balance characteristics using a non linearly viscous flow model on a utilise un modele d ecoulement visqueux non lineaire pour etudier l influence des caracteristiques du bilan de masse des conditions aux limites sur le fond rocheux et de la topographie sous glaciaire sur l etendue et la forme des calottes glaciaires le but est de rendre possible l utilisation des traces geologiques de l extension glaciaire passee pour reconstituer les paleoclimats

carbonate submarine fan facies along a paleozoic prograding continental margin western united states abstract mass transport deposits though common in carbonate basins normally occur as widespread sheets or debris wedges as in the devonian of canada and elsewhere or in modern interplatform troughs of the bahamas reexamination of a seaward prograding cambrian and ordovician continental margin section in central nevada reveals a 150 m thick interval whose facies resemble current models of submarine fan deposition the upper 100 m of sediment is assigned to an inner fan setting and is characterized by submarine slides and several entrenched channels 10 m deep and 500 m wide the channels are filled with disorganized boulder bearing conglomerates but are not arranged in any well defined thinning and fining upward sequences stratigraphically below this interval are thinning and fining upward organized pebble to cobble bearing channelized conglomerates 30 to 50 m thick these channels are 1 to 5 m deep 20 to 100 m wide and rapidly coalesce laterally and vertically the conglomerates grade la erally into and are interbedded with thin and discontinuously bedded ripple laminated and graded calcarenites similar to detrital overbank levee and interchannel deposits these sedimentary units probably represent a system of braided channels in a mid fan position below the braided channels are 10 to 20 m of thickening and coarsening upward cycles of virtually nonchanneled beds beds in the cycles are composed of calcarenites exhibiting bouma divisions these carbonate sand sequences are interpreted to represent prograding outer fan lobes the recognition of carbonate submarine fan sequences raises several questions 1 what sedimentologic and tectonic conditions are conducive to fan development in carbonate provinces 2 do these conditions resemble those for clastic fan development or do carbonate provinces have unique requirements by recognizing carbonate submarine fans and the geologic conditions that control their sediment dispersal patterns areas of maximum sediment accumulation may be predicted as an aid in exploring for petroleum reservoirs of deeper water carbonate environments end of article last page 913

quaternary geology and geomorphology of the dinosaur provincial park area and surrounding plains alberta canada the identification of former glacial lobes drainage diversions and meltwater flood tracks abstract the quaternary geology and geomorphology of the lower red deer river drainage basin centred on the dinosaur provincial park badlands provides information on pre late wisconsinan drainage patterns and the dynamics of former lobes of the laurentide ice sheet in western canada patterns of deglaciation proglacial lake evolution and spillway incision are also reconstructed based upon the distribution of surface materials and glacial glaciofluvial landforms the empress group fluvial and glaciolacustrine sediments which could be as young as 27 ka bp infill the precursor red deer river and its tributaries and document the initial advance of glacier ice into southern alberta glaciotectonic disturbance of older sediments and bedrock the production of deformation tills and the construction of a megafluting complex and cupola hills record the advances of a glacier lobe centred over the study area stratified inter and intra till beds record pulses of subglacial meltwater between phases of subsole deformation the thickening of tills towards the margin of the lobe represents a till wedge an expected product of sediment advection by glaciers moving over deformable beds the eastern margin of the glacier lobe is demarcated by the interlobate suffield hummocky moraine belt which contains overprinted thrust ridges which record diachronous oscillations of neighbouring lobes within the ice sheet proglacial and glaciofluvial sediments were deposited in the area in association with proglacial lake bassano patricia which drained eastwards when the suffield moraine was dissected by spillways changes in the size of glacial lake bassano patricia are clearly documented by a sequence of spillway incisions which culminated in the erosion of scabland topography and the initiation of a new course for the red deer river a 15 km southward diversion of the main channel in distinct contrast to the documented incision histories of other small rivers in alberta one tree creek and little sandhill creek did not start major incisions of the quaternary sediments over buried valley positions until the late holocene when environmental conditions were characterized by higher precipitation

comparison of the measured and finite element predicted ground deformations of a stiff lodgement till the use of the finite element method to model excavations and tunnels in dublin black boulder clay has in the past had limited success owing to the failure of the available constitutive models in commercially available software programs to adequately represent the essential features of a stiff soil a stiff soil lodgement till underlies much of the city of dublin ireland consequently the successful prediction of deformations in this soil arising from structural and infrastructural projects is of considerable importance research has shown that the stress strain response of a stiff soil is complex and depends on many factors including stress history stress level and strain direction these important features are included in the hardening plasticity small strain stiffness hss soil model that is incorporated in the plaxis v8 4 finite element code this paper describes the field and laboratory methods that were used to determine the parameters for incorporation in this soil model and the validati

atokan pennsylvanian berlin field genesis of recycled detrital dolomite reservoir deep anadarko basin oklahoma the berlin gas field in beckham county oklahoma was discovered in 1977 and is the largest atoka pennsylvanian hydrocarbon accumulation in the anadarko basin it is an overpressured reservoir 15 000 ft 4 572 m deep and occupies a surface area of 41 mi2 106 km2 the reservoir rock consists primarily of recycled detrital arbuckle dolomite cambrian ordovician and contains ultimate recoverable reserves of 242 to 362 bcf 6 850 to 10 250 106 m3 the arbuckle dolomite and limited exposures of precambrian granite rocks were eroded from the amarillo wichita mountains during the atokan and were deposited as a terrigenous sandy dolomite clastic wedge adjacent to the uplift during the late atokan the elk city structure was uplifted and subaerially exposed in the vicinity of the northern limit of the dolomite clastic wedge the detrital dolomite on the structure was concurrently eroded and recycled northward as a shallow marine fan delta subsequent recrystallization destroyed the detrital depositional texture and created the present intercrystalline porosity the deep elk city structure consists of an upthrust block bounded by the late atokan unconformity which is genetically associated with the berlin fan delta the present relief on the upthrust block and overlying anticlinal folds was formed during post atokan growth of the structure the berlin field provides a model of a large localized detrital deposit derived from uplift and erosion of a prominent structure and it is an example of the potential for large detrital stratigraphic traps around the perimeters of prominent structures containing crestal unconformities

deformation of the batestown till of the lake michigan lobe laurentide ice sheet deep pervasive shear deformation of the bed to high strains 100 may have been primarily responsible for flow and sediment transport of the lake michigan lobe of the laurentide ice sheet to test this hypothesis we sampled at 0 2 m increments a basal till from one advance of the lobe batestown till along vertical profiles and measured fabrics due to both anisotropy of magnetic susceptibility and sand grain preferred orientation unlike past fabric studies interpretations were guided by results of laboratory experiments in which this till was deformed in simple shear to high strains fabric strengths indicate that more than half of the till sampled has a 5 probability of having been sheared to moderate strains 7 30 secular changes in fabric azimuth over the thickness of the till probably due to changing ice flow direction as the lobe receded indicate that the bed accreted with time and that the depth of deformation of the bed did not exceed a few decimeters orientations of principal magnetic susceptibilities show that the state of strain was commonly complex deviating from bed parallel simple shear deformation is inferred to have been focused in shallow temporally variable patches during till deposition from ice

the experimental basis for interpreting particle and magnetic fabrics of sheared till particle fabrics of basal tills may allow testing of the bed deformation model of glacier flow which requires high bed shear strains 100 field studies however have not yielded a systematic relationship between shear strain magnitude and fabric development to isolate this relationship four basal tills and viscous putty were sheared in a ring shear device to strains as high as 714 fabric was characterized within a zone of shear deformation using the long axis orientations of fine gravel and sand particles and the anisotropy of magnetic susceptibility ams of small 5 8 cm3 intact samples results indicate that till particles rotate toward the plane of shearing with long axis orientations that become tightly clustered in the direction of shear 0 78 s1 0 94 for three dimensional data these strong steady state fabrics are attained at shear strains of 7 30 with no evidence of fabric weakening with further strain regardless of the specific till or particle size fraction under consideration these results do not support the jeffery model of particle rotation which correctly describes particle rotation in the viscous putty but not in the tills owing to fluid mechanical assumptions of the model that are violated in till the sensitivity of fabric development to shear strain magnitude indicates that for most till units where shear strain magnitude is poorly known attributing fabric variations to spatial differences in other variables such as till thickness or water content will be inherently speculative attributing fabric characteristics to particular basal till facies is uncertain because shear strain magnitude is unlikely to be closely correlated to till facies weak or spatially variable fabrics in the absence of post depositional disturbance or major deviations from unidirectional simple shear indicate that till has not been pervasively sheared to the high strains required by the bed deformation model strong flow parallel fabrics are a necessary but insufficient criterion for confirming the model copyright 2008 john wiley sons ltd

method for anisotropic crystal orientation fabrics detection using radio wave depolarization in radar sounding of mars polar layered deposits the polar layered deposits plds provide a wealth of information about the past climate evolution of mars surface mass fluxes and ice flow mainly governed topography and layering of the pld china s mars probe including an orbiter and a landing rover will be launched by 2020 a new type satellite borne mars penetrating radar instrument has been selected to be a part of the payloads on the orbiter its main scientific objectives are to map the distribution of water water ice and to detect the soil characteristics at global scale on the martian crust compared with mars advanced radar for subsurface and ionospheric sounding and shallow radar the biggest difference is that the antenna system of this mars penetrating radar consists of two dipole antennas mutually perpendicular this special configuration enables the investigation of the ice flow of pld by detecting and analyzing the features of anisotropic crystal orientation fabric cof thus relying on the fact that the radio waves are depolarized while passing through an anisotropic cof layer in this paper a method for anisotropic cof detection based on this radar system is proposed the radar echo formulation of anisotropic cof is derived and the ratio of the signals measured by the two perpendicular antennas is used to analyze the anisotropy of cof we demonstrate that the ratio is an ideal criterion for the detection and analysis of cof since it contains all parameters about the anisotropy feature of cof and it is independent of the attenuation in the propagation path and the reflection coefficient in order to verify the validity of the derived analytical expression of the ratio for the detection of cof finite different time domain simulations are carried out based on a simple model of the subsurface of pld which contains an anisotropic cof layer the advantages of this method the potential application scenarios and the effects of the martian environment are also discussed

isothermal flow of an anisotropic ice sheet in the vicinity of an ice divide simulations of glacier flow are commonly based on the assumption that ice has an isotropic viscosity here we examine the plane flow of ice in the special region of an ice divide using a constitutive relation for an anisotropic incompressible viscous body that is orthotropic and transversally isotropic ice is assumed to be isotropic at the ice sheet surface with the continuous development of a vertical single maximum c axis fabric with increasing depth we consider the theoretical case of an isothermal ice sheet over a horizontal bedrock with no slip at the ice bedrock interface the ice sheet surface elevation is imposed and the flow corresponding to the steady state is calculated using a two dimensional finite difference model based on the resolution of a pressure poisson equation in this model all components of the stress and strain rate tensor are calculated the main conclusion is that for a fixed surface elevation the general flow pattern accelerates when the anisotropic behavior of the ice is taken into account due to the greater fluidity with respect to shear stress the downward motion of the ice is faster despite a higher resistance to vertical deformation as a result the dominance of shear strain rate in the flow of polar ice is stronger in the anisotropic case than in the isotropic case the shear stresses are slightly relaxed while the longitudinal stresses are significantly increased in the anisotropic case

permo carboniferous hydrocarbon accumulations mid continent u s a approximately 19 4 billion bbl of oil and 119 tcf of nonassociated gas have been discovered in the mid continent as of january 1 1978 although these volumes of hydrocarbons were trapped in thousands of fields throughout the mid continent the bulk of these resources were emplaced in a relatively few fields about 14 2 billion bbl of oil have been found in 111 significant and giant oil fields and 103 tcf of nonassociated gas have been discovered in 57 significant and giant gas fields permo carboniferous reservoirs are important in 101 of the large oil fields and 55 of the large gas fields these fields contained 9 5 billion bbl of oil and 99 tcf of gas respectively our calculations of the total oil and gas accumulations in permo carboniferous reservoirs are extrapola ed from these data about 2 1 billion bbl of oil and 5 1 tcf of nonassociated gas accumulated in lower carboniferous mississippian reservoirs most of this oil and gas was stratigraphically trapped in upper mississippian sandstones and carbonates which are truncated at the pre pennsylvanian unconformity surface approximately 8 8 billion bbl of oil and about 31 9 tcf of nonassociated gas have been found in upper carboniferous pennsylvanian reservoirs in the mid continent most of these oil and gas accumulations were stratigraphically trapped in lenticular sandstone bodies the environments in which the majority of these sandstones were deposited range from fluvial deltaic to shallow marine about 2 billion bbl of oil and 77 7 tcf of nonassociated gas accumulated in permian reservoirs most of these hydrocarbons accumulated in rocks of lower permian age in the hugoton panhandle panoma fields the oil and gas in these fields were trapped by regional changes in lithofacies with associated hydrodynamic gradients significant stratigraphic accumulations of oil and gas will continue to be discovered in the mid continent even though much of this region is now in a late mature stage of exploration and development

selective dolomitization by syntaxial overgrowth around detrital dolomite nuclei a case from the jurassic of the ligurian brianconnais ligurian alps abstract dolomite crystals occurring in middle jurassic dolostones and dolomitic limestones of the ligurian brianconnais domain french italian ligurian alps show irregular complex zoning evidenced by cathodoluminescence cl and backscattered electron imaging comparable zoning patterns from other study areas have been attributed alternatively to recrystallization or dissolution precipitation processes however none of these mechanisms can account for the range of observations from the ligurian brianconnais domain which include 1 the presence of multiple core types each with different cl characteristics 2 marked compositional differences between cores and surrounding rims ferroan vs nonferroan mg ca ratio 3 a marked shape difference between cores with irregular outlines and rims which progressively approach a well developed rhombohedral habit these features are most reasonably interpreted as dolomitic rims that formed as syntaxial overgrowths around detrital dolomite nuclei which in turn originated from erosion of underlying triassic rocks and triggered selective replacement of fine grained calcareous sediment failure to recognize the exact nature of this type of dolomite crystal may lead to overestimating the degree of dolomitization and to overlooking possible detrital inputs in a basin otherwise supplied with pure allochemical sediments with consequent loss of information on the tectonosedimentary evolution

a new fully three dimensional numerical model for ice dynamics the problem of describing ice dynamics has been faced by many researchers in this paper a fully three dimensional model for ice dynamics is presented and tested using an approach followed by other researchers ice is considered a non linear incompressible viscous fluid so that a fluid dynamic approach can be used the model is based on the full three dimensional stokes equations for the description of pressure and velocity fields on the saint venant equation for the description of the free surface time evolution and on a constitutive law derived from glen s law for the description of ice viscosity the model computes the complete pressure field by considering both the hydrostatic and hydrodynamic pressure components it is time evolutive and uses high order numerical approximation for equations and boundary conditions moreover it can deal with both constant and variable viscosity three theoretical tests and two applications to priestley glacier antarctica are presented in order to evaluate the performance of the model and to investigate important phenomena of ice dynamics such as the influence of viscosity on pressure and velocity fields basal sliding and flow over perturbed bedrocks all these applications demonstrate the importance of treating the complete pressure and stress fields

reflections on soft subglacial beds as a mosaic of deforming and stable spots abstract much discussion regarding subglacial processes is centred around the question of how soft beds respond to ice overriding in particular how widespread and penetrative is their deformation how does it affect the ice stability and what are the consequences for large scale sediment redistribution patterns contrasting views have been proposed which are difficult to verify and reconcile in the light of scarcity of agreed criteria to identify deforming beds here we suggest that soft beds under warm based glaciers can be envisaged as a mosaic of deforming and stable spots transient in time and space according to changes in the control parameters at the ice bed interface the subglacial mosaic model is consistent with field data showing heavily deformed beds interspersed with largely undisturbed beds it is suggested that deformation found in tills is a cumulative effect of strain within a relatively thin ephemeral deforming spots under the ice sole affecting the till as it accretes during ice overriding in accord with the coulomb plastic rheology the role of clast ploughing in bed deformation is emphasised

landform and sediment imprints of fast glacier flow in the southwest laurentide ice sheet evidence for former fast glacier flow ice streaming in the southwest laurentide ice sheet is identified on the basis of regional glacial geomorphology and sedimentology highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream preliminary mapping from a digital elevation model of alberta identifies corridors of smoothed topography and corridor parallel streamlined landforms megaflutes to mega lineations that display high levels of spatial coherency ridges that lie transverse to the dominant streamlining patterns are interpreted as a series of minor recessional push moraines b thrust block moraines or composite ridges hill hole pairs constructed during readvances surges and c overridden moraines cupola hills apparently of thrust origin together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms localised cross cutting and or misalignment of flow sets indicates temporal separation and the overprinting of ice streams lobes the fast flow tracks are separated by areas of interlobate or inter stream terrain in which moraines have been constructed at the margins of neighbouring competing ice streams outlet glaciers this inter stream terrain was covered by more sluggish non streaming ice during full glacial conditions thin tills at the centres of the fast flow corridors in many places unconformably overlying stratified sediments suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams outlet glaciers is consistent with subglacial deformation theory in this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory sometimes with fast flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally the occurrence of minor push moraines and flutings and associated landforms because of their similarity to modern active temperate glacial landsystems are interpreted as indicative of ice lobe marginal oscillations possibly in response to seasonal climatic forcing in locations where meltwater was more effectively drained from the glacier bed further north the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice bed decoupling and drawdown initiated by the development of ice dammed lakes copyright 2008 john wiley sons ltd

sedimentary signatures of basal ice formation and their preservation in ice marginal sediments reconstruction of subglacial processes from sedimentological evidence is central to our understanding of glaciological conditions beneath former ice masses at svinafellsjokull southeast iceland we assess the extent to which two different processes of basal ice formation regelation and glaciohydraulic supercooling can be identified from ice marginal sediments our results indicate that the sedimentary characteristics of deposits produced by these two processes can be distinguished from one another and that it may be possible to recognise evidence of these processes in quaternary sediments and to reconstruct their spatial pervasiveness sediments derived from the melting of regelation basal ice have i a massive structure ii a sediment matrix 0 to 10 dominated by coarse sand and iii a higher proportion of angular clasts than supercool basal ice and associated sediments sediments derived from supercool basal ice i can be either massive or layered ii tend to have a silt dominated matrix and iii contain a slightly higher proportion of rounded and well rounded clasts than regelation basal ice and sediments previous studies indicate that the dominance of silt within supercool basal ice may be unique to this process and hence supercooling should leave a readily recognisable signature in the sedimentary record our results from svinafellsjokull lend support to that idea although we suggest that further work is required to assess whether silt dominance is a process signature diagnostic of supercooling and in particular the extent to which subglacial sediment supply determines the sedimentary character of basal ice facies and associated sediments

past precipitation rates derived from ice core measurements methods and data analysis ice cores in which annual layers can be identified or particular horizons dated provide a record of past precipitation rates if measured layer thicknesses can be corrected for thinning by flow since deposition total strain is usually calculated from steady state flow models because of lack of information about the ice cap s history an assumption of uniform vertical strain rate is valid at best in the upper half of the ice column complex models are needed to take account of uneven bedrock and variations in precipitation rate upstream of the borehole drilling at an ice divide avoids these complications new data analyses suggest that precipitation at camp century has fluctuated by only plus or minus 10 for the past 8500 years whereas at devon island on the opposite side of baffin bay precipitation has been uniform only for the past 1300 years with significantly higher values before that estimation of pre holocene precipitation rates is especially difficult because that ice may have an effective viscosity different from holocene ice three published estimates of pre holocene precipitation at camp century are unreliable the authors did not allow for thinning and their time scales differ appreciably data from three antarctic stations show some inconsistencies measuring concentrations of 10be in ice cores may be an alternative method of determining past precipitation rates

late wisconsinan sub glacial clastic intrusive sheets along lake erie bluffs at bradtville ontario canada abstract numerous clastic intrusive sheets a few decimetres to more than 16 m long 1 120 cm thick and extending one to more than 25 m laterally occur along a 350 m long section of the late wisconsinan catfish creek drift in the lake erie bluffs at bradtville southwestern ontario most of them are downglacier dipping dikes the largest one terminating in the underlying middle wisconsinan tyrconnell formation most dikes strike nne ssw at right angles to the local direction of glacier movement during the deposition of catfish creek drift the tops of some of them are truncated or displaced downglacier by shearing the main concentration of clastic intrusive sheets is on the upglacier side of a glaciotectonically folded anticline of tyrconnell formation clays and silts underlying the catfish creek drift the host sediments are catfish creek till gravel sand and silt and tyrconnell formation silt and clay most intrusive sheets particularly the small to medium ones consist of massive to crudely laminated sand and silt intruded from below by a dewatering process the largest dike reflects in its composition mainly the adjoining or higher lying host sediment materials and its main part was formed by downward infilling or by gravity flows into an open fracture the large dike is flanked by small laminated silty sand sheets and several small apophyses some of them injected downward and sideways others upward by dewatering the clastic intrusive sheets were formed under a moving glacier the erie lobe probably both at the beginning and towards the end of the deposition of catfish creek till their location and position was predetermined by glaciotectonically induced listric planar structures and zones of weakness mainly tension fractures that strike transverse to glacier movement and dip downglacier and also by confinement of pore water in a permeable sediment wedge between the less pervious tyrconnell formation and massive catfish creek basal till

distribution of glacial geomorphic features on the antarctic continental shelf and correlation with substrate implications for ice behavior surveys were conducted seaward of all the major drainage outlets of the antarctic ice sheet from the pennell coast north victoria land to marguerite bay antarctic peninsula the results show that the ice sheet extended onto the outer shelf glacial troughs occur offshore of all major glacial outlets where the substrate is crystalline bedrock ice flow tended to follow the structural grain of the bedrock deposited little sediment and eroded the underlying bedrock where ice flowed over relatively soft more easily eroded sedimentary strata the direction of ice flow was more directly offshore and depositional features characterize the sea floor in these areas the signature of the grounded ice consists of till deposits and large scale geomorphic features drumlins occur within the region of contact between crystalline and sedimentary substrates the different geological substrates are interpreted to have exerted a fundamental control on the behavior of past ice sheets the troughs in the areas of bedrock composed of sedimentary substrate are interpreted to have been occupied by relatively fast flowing ice ice streams and the troughs in the areas of crystalline substrate are interpreted to have been occupied by slower moving ice the area between these two zones was characterized by ice acceleration and is marked by drumlins

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

a highly mobile laurentide ice sheet revealed by satellite images of glacial lineations satellite images of the north american continent reveal previously unrecognized patterns of crossing drift lineations reflecting unexpected shifts of centres of mass of the laurentide ice sheet throughout the last glacial cycle such shifts must must have been associated with major global atmospheric circulation changes

the history of quaternary sedimentation in the uk sector of the north sea basin reconnaissance seismic and sampling surveys have shown that up to 500 m of lower and early middle pleistocene deltaic sediments are preserved in the uk sector of the north sea the distributions of delta related facies record the progressive expansion of peripheral delta systems northwards across the southern north sea during the early pleistocene a late middle pleistocene unconformity is present throughout the uk sector and sedimentation above the unconformity was dominated by glacial erosional and depositional processes a complex system of deeply incised valleys was eroded during each of three regional middle and upper pleistocene glaciations and the valleys have been filled or partially filled by glaciolacustrine or glaciomarine and interglacial marine sediments the valleys of the earliest elsterian glaciation are up to 400 m deep in the southern north sea the saalian and weichselian valleys are commonly more than 100 m deep they are eroded through their contemporary tills nearshore but occur well beyond the limits of these tills offshore the origins of these valleys are attributed to a combination of fluvial subglacial and periglacial processes

the role of crystal fabric in flow near an ice divide polycrystalline ice near an ice divide typically shows a crystal fabric crystal preferred orientation with c axes clustered vertically we explore the effect of this fabric on the large scale flow pattern near an ice divide we incorporate an analytical formulation for anisotropy into a non linear flow law within a finite element ice sheet flow model with four different depth profiles of crystal fabric we find that the effect of fabric is significant only when a profile has a minimum cone angle of less than 25 for a steady state divide the shape and size of the isochrone arch can depend as much on the crystal fabric as it does on the non linearity of ice flow a vertically oriented fabric tends to increase the size of the isochrone arch never to reduce it also non random fabric has little effect on the ice divide flow pattern when ice is modeled as a linear newtonian fluid finally when we use a crystal fabric profile that closely approximates the measured profile for siple dome west antarctica the model predicts concentrated bed parallel shearing 300 m above the bed

fossil remnants of up turned debris bands in pleistocene glacial deposits of poland fossil remnants of up turned debris rich bands of glacial ice are recorded from three localities in the polish lowlands in each case the fossil debris bands occur in proximal parts of hills built of glacitectonically disturbed sediments the characteristics of these remnants and of the associated deposits and structures are described and they are compared to present day examples from spitsbergen

two orthotropic models for strain induced anisotropy of polar ice as polar ice descends from the free surface to depth in a large ice sheet it undergoes deformations which give rise to the formation and subsequent evolution of a fabric and associated anisotropy in this paper two orthotropic models of such strain induced anisotropy are considered model a is based on analysis ofthe microscopic behaviour of an individual ice crystal with transversely isotropic response and assumed uniform stress in a polycrystal the macroscopic response of the ice aggregate is then derived by applying the concept of an orientation distribution function and the resulting viscous law relates the strain rate to the stress and three structure tensors in model b it is assumed that the macroscopic response of ice is determined by the fabric induced entirely by macroscopic deformations and all microprocesses taking place at the grain level are ignored a constitutive relation is derived from a general frame indifferent law for orthotropic materials and expresses the stress in terms of the strain rate strain and three structure tensors the two models are applied to determine the viscous response of ice to continued uniaxial compression and simple shearing in order to compare the predictions of both theories

a numerical study of anisotropic low reynolds number free surface flow for ice sheet modeling few ice sheet flow models have been developed that solve the complete set of mechanical equations until now these models were limited to isotropic conditions we present here a two dimensional finite difference method capable of solving the equations for the steady flow of a viscous incompressible anisotropic fluid with a free surface under isothermal conditions it is not a standard method especially with respect to the time discretization of the numerical scheme and converges for very low reynolds numbers this method is applied here to the planar flow of anisotropic ice over flat or irregular bedrock with no slip boundary conditions at the ice bedrock interface the results are presented here for newtonian behavior in the vicinity of an ice divide the ice is assumed to be isotropic at the ice sheet surface with continuous and prescribed development of anisotropy with increasing depth going from isotropic to anisotropic situations our results indicate that the free surface becomes flatter and the shear strain rates larger and more concentrated near the bedrock the flow is less sensitive to variations of the bedrock topography in the anisotropic case than in the isotropic case furthermore a new phenomenon appears in the anisotropic case the partial stagnation of ice in the holes of the bedrock these effects have significant consequences when dating the ice the isochrones obtained in the anisotropic case are flatter and the anisotropic ice is more than 10 younger above the bumps and more than 100 older within the holes than for the isotropic ice

genesis of hummocky moraines by thrusting in glacier ice evidence from svalbard and britain irregular mounds of glacial debris commonly referred to as 9hummocky moraine9 until recently were linked to ice stagnation during rapid climatic amelioration however recent work in scotland has demonstrated that some hummocky moraine dating from the younger dryas event c 10 000 years bp was the product of deposition at active ice margins observations at modern high arctic glacier margins in svalbard 76 80 n indicate that some moraines of this type form under a dynamic glaciological regime mainly by thrusting in active polythermal ice undergoing strong longitudinal compression this situation is particularly common where there is a transition from warm based ice in the interior of a glacier to cold based ice at the margins or snout from their morphological similarity rectilinear slopes facing up glacier and irregular downglacier faces and apparent stacking of slabs of sediment of subglacial derivation it is concluded that some assemblages of british moraines are also the product of thrusting this process appears to be most dominant in polythermal glaciers rather than in temperate glaciers on this basis it is tentatively suggested that the younger dryas in britain was characterized by a climatic regime similar to that in svalbard today mean annual temperature 5 c 400 1000 mm precipitation and that the associated glaciers may have been of polythermal character

flow law hypotheses for ice sheet modeling ice flow modeling requires a flow law relating strain rates to stresses in situ but a flow law cannot be measured directly in ice sheets microscopic processes such as dislocation glide and boundary diffusion control both the flow law for ice and the development of physical properties such as grain size and c axis fabric these microscopic processes can be inferred from observations of the physical properties and the flow law can then be estimated from the microscopic processes a review of available literature shows that this approach can be imperfectly successful interior regions of large ice sheets probably have depth varying flow law constants with the stress exponent n for power law creep less than 3 in upper regions and equal to 3 only in deep ice n probably equals 3 through most of the thickness of ice shelves and ice streams

modelling of kealey ice rise antarctica reveals stable ice flow conditions in east ellsworth land over millennia flow at ice divides their shape size and internal structure depend not only on local conditions but also on the flow regimes and past histories of the surrounding ice masses here we use field data from kealey ice rise ellsworth land west antarctica in combination with flow modelling to investigate any possible signs of transients in the flow of the surrounding ice masses kealey ice rise shows linear surface features running parallel to its ridge in satellite imagery and a conspicuous layering in the ground penetrating radar data known as double peaked raymond bumps through numerical modelling by using an anisotropic full stokes thermomechanical flow solver we analyse the evolution of kealey ice rise and the timescales involved we conclude that the features observed in the stratigraphy of kealey ice rise require at least 3 ka of near stationary flow conditions however we cannot exclude the possibility of a recent flow reorganization in the last century we stress that the signs of stationary flow in radar stratigraphy observed in kealey ice rise have been observed in other ice divides in the east ellsworth land area suggesting stationary flow conditions over a millennial timescale in the region

an analytical approach to deformation of anisotropic ice crystal aggregates deformation rates of single hexagonal crystals deforming by glide on the basal plane are described as a function of stress state and crystal orientation these results are used to infer the deformation rate of crystal aggregates assuming that the stress distribution within the crystal aggregate is homogeneous analytical equations for the deformation rate of anisotropic ice aggregates are derived for vertically symmetric girdle fabric this type of fabric is approximated by a uniform distribution of c axis orientations between a cone angle and a smaller girdle angle relative to the symmetry axis for simple shear stress acting on a single maximum fabric there is a slight de enhancement for cone angles of 60 90 in uniaxial compression a maximum enhancement of 1 7 occurs at a cone angle of 57 a pure shear stress state has similar features with the additional complication that it causes a non zero transverse strain rate except for perfect vertical alignment of crystals and isotropic fabric in combined states of stress the contribution of each stress component to the strain rate depends on fabric a single enhancement factor is not adequate to describe the effects of anisotropy for complex stress states

ice flow directions of the last scandinavian ice sheet in central poland abstract the article presents the results of studies on the ice flow directions of the last scandinavian ice sheet sis in central poland at the southern periphery of the sis and particularly within the plock lobe the ice flow pattern was derived mainly from direct indices such as till fabric vergence of glaciotectonic compression structures orientation of small scale subglacial deformations formed beneath the flowing ice orientation of pavement stone longitudinal axes stone lee ends and clast surface striae the study is supplemented with a reconstruction of ice movement directions based on orientation analysis of both concave tunnel valley and convex eskers glacial morpholineaments linear glacial landforms till age was also determined using luminescence osl datings from sand deposits these were collected directly at numerous sites from under and above the last sis till unit combined with previously published data the results of the present investigation of the last ice sheet advance during the late weichselian ca 23 18 ka indicate that there were two different ice flow phases and that the maximum extent was asynchronous the western part of the said area experienced two advances during the leszno brandenburg and poznan frankfurt phases while during the earlier one the ice masses came from the nw presumably along the eastern limb of the odranian b2 after punkari 1997 ice stream and then from the n along the vistulian b3 stream the last sis occupied the eastern sector of the area only once during the younger poznan phase building the plock lobe the lobe shaped ice margin with a fan like flow pattern within the lobe may be indicative of a palaeo ice stream terminal zone

irregular oscillations of the west antarctic ice sheet model simulations of the west antarctic ice sheet suggest that sporadic perhaps chaotic collapse complete mobilization of the ice sheet occurred throughout the past one million years the irregular behaviour is due to the slow equilibration time of the distribution of basal till which lubricates ice sheet motion this nonlinear response means that predictions of future collapse of the ice sheet in response to global warming must take into account its past history and in particular whether the present basal till distribution predisposes the ice sheet towards rapid change

flow law for ice in polar ice sheets theories of glacier flow are based commonly on the assumption that ice is not a newtonian fluid but has a non linear stress dependent viscosity1 5 here we re examine the spreading of antarctic ice shelves and suggest that the data cannot define a unique flow law tilt measurements in four boreholes in both the arctic and antarctic seem to show that a linear flow law e a1 where a1 10 15 s 1 pa 1 at 28 c where e is the effective strain rate and the effective shear stress may be just as appropriate for describing the flow of polar ice sheets

till and moraine emplacement in a deforming bed surge an example from a marine environment the glacier sefstrombreen in spitsbergen surged across an arm of the sea between qsr 1882 and 1886 and rode up onto the island coraholmen marine and terrestrial geological observations and archive records show that the glacier advanced on a deforming carpet of marine mud which was eroded from its original location transported and smeared over the sea bed and coraholmen as a deformation till the glacier emplaced about 210sm 0 2 km 3 of drift in the terminal 2 km of its advance in a maximum of 14 years leaving a thickness of up to 20 m on coraholmen which was doubled in size as a result during the surge subglacial muds were characterised by high water pressures low effective pressures and low frictional resistance to glacier movement original sedimentary inhomogenities permit fold structures to be identified but repeated refolding and progressive remoulding produce mixing and homogenisation of deformation tills the surge was probably shortlived and as the heavily crevassed glacier stagnated underlying water saturated muds were intruded into crevasses and then extruded on the glacier surface reticulate crevasse intrusion ridges on coraholmen and the sea floor reflect the orientation of surge generated crevasses water and sediment was also extruded beyond the glacier at its maximum extent to form extensive flows producing till tongues both on coraholmen and the sea floor extending over 1 3 km from the glacier it is argued that subglacial deformation of pre existing sediment will almost invariably be associated with glaciation of marine areas and that this process will not only produce deformation tills through remoulding of pre existing sediments but will also play a fundamental role in glacier dynamics criteria which perrait glacial tills produced by such events from marine and glaciomarine muds are discussed copyright 1996 elsevier science ltd