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

the mixed bed glacial landform imprint of the north sea lobe in the western north sea 2018 john wiley sons ltd during the last glacial cycle an intriguing feature of the british irish ice sheet was the north sea lobe nsl fed from the firth of forth and which flowed south and parallel to the english east coast the controls on the formation and behaviour of the nsl have long been debated but in the southern north sea recent work suggests the nsl formed a dynamic oscillating terrestrial margin operating over a deforming bed further north however little is known of the behaviour of the nsl or under what conditions it operated this paper analyses new acoustic sedimentary and geomorphic data in order to evaluate the glacial landsystem imprint and deglacial history of the nsl offshore from ne england subglacial tills af2 3 form a discontinuous mosaic interspersed with bedrock outcrops across the seafloor with the partial excavation and advection of subglacial sediment during both advance and retreat producing mega scale glacial lineations and grounding zone wedges the resultant mixed bed glacial landsystem is the product of a dynamic switch from a terrestrial piedmont lobe margin with a net surplus of sediment to a partially erosive quasi stable marine terminating ice stream lobe as the nsl withdrew northwards glaciomarine sediments af4 drape the underlying subglacial mixed bed imprint and point to a switch to tidewater conditions between 19 9 and 16 5 ka cal bp as the north sea became inundated the dominant controls on nsl recession during this period were changing ice flux through the firth of forth ice stream onset zone and water depths at the grounding line the development of the mixed bed landsystem being a response to grounding line instability 2018 john wiley sons ltd

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

microscale evidence of liquefaction and its potential triggers during soft bed deformation within subglacial traction tills published conceptual models argue that much of the forward motion of modern and ancient glaciers is accommodated by deformation of soft sediments within the underlying bed at a microscale this deformation results in the development of a range of ductile and brittle structures in water saturated sediments as they accommodate the stresses being applied by the overriding glacier detailed micromorphological studies of subglacial traction tills reveal that these polydeformed sediments may also contain evidence of having undergone repeated phases of liquefaction followed by solid state shear deformation this spatially and temporally restricted liquefaction of subglacial traction tills lowers the shear strength of the sediment and promotes the formation of transient mobile zones within the bed which accommodate the shear imposed by the overriding ice this process of soft bed sliding alternating with bed deformation facilitates glacier movement by way of stick slip events the various controls on the slip events have previously been identified as i the introduction of pressurised meltwater into the bed a process limited by the porosity and permeability of the till and ii pressurisation of porewater as a result of subglacial deformation to which we include iii episodic liquefaction of water saturated subglacial traction tills in response to glacier seismic activity icequakes which are increasingly being recognized as significant processes in modern glaciers and ice sheets as liquefaction operates only in materials already at very low values of effective stress its process form signatures are likely indicative of glacier sub marginal tills

deforming beds viscous and plastic scales of deformation small scale field and laboratory observations of sub glacial sediment deformation suggest that failure is the predominant method of sediment deformation while large scale modelling studies using a viscous model of till deformation have been reasonably successful in predicting the geological consequences of ice sheet action this suggests that the cross over scale between viscous and plastic deformation occurs at a much larger scale than the grain grain interaction scale previously thought to be appropriate to deforming till sediment deformation and the drainage of sub glacial areas are considered at different scales and how these interact to produce failure and viscous behaviour is discussed a fluctuation length scale is proposed whose horizontal dimensions are of the order of the depth of the base of deformation 1 10 m on this length scale the glacier deforming bed system is highly variable in time as well as in space till deformation occurring at this length scale is plastic happening though failure events three other specific scales are proposed whose different properties depend on the relative spatial variability of static and seepage pressures and topography the key theoretical problem which has yet to be solved is how multiple small scale failure events combine into a viscous type flow this is discussed in the context of self organised criticality it is argued that the length scales appropriate for some drainage features are not appreciably larger than the scale for plastic failure events implying that modelling sub glacial drainage channels by balancing erosion rates against viscous closure of the channel is misconceived the outlines of an alternative model involving percolation theory are presented certain key questions which can only be settled through observations by glaciologists and glacial geologists are discussed it is suggested that the difference between lodgement tills and deformation tills reflects the rate of motion of till by deformation and that lodgement from the ice is unimportant

ice stream surface texture sticky spots waves and breathers the coupled flow of ice till and water this paper addresses the coupling of flows of ice till and water and the issue of whether such coupling provides mechanisms for meso scale kilometres to tens of kilometres variability in ice sheet flow and texture the question of whether effective pressures at the ice bed interface are statically or hydraulically controlled is examined in this paper the answer is scale dependent and has a significant effect on the relationship between ice surface and basal topography the consequences of these considerations on till flow coupled ice till flow and coupled ice till and water flow are examined an analysis of till flow kinematics and shock formation is carried out the linear stability of coupled long wavelength ice till flow is analysed and regions in parameter space where this flow is unstable with rather small rate constants are found upstream moving ice surface waves are predicted the linear stablity of coupled ice till water flow is examined where water flow is modelled using a basal flow system with effective pressure dependent properties again regions in parameter space where the system is linearly unstable are found this time with relatively rapid rate constants the water pressure exhibits breather modes these analyses assume that there is a substantial basal traction a problem with models of ice streams wholly restrained at the side is identified they seem to predict erosion rates which are unfeasibly large there appears to be sufficient variability in the ice till water system to potentially explain texture in ice stream surfaces variations in ice stream thickness of tens of metres not directly relatable to topography and waves moving upstream or downstream most importantly the ice stream bed system is shown to exhibit meso scale variability simply by coupling ice flow according to the shallow ice approximation till flow according to the hydrostatic thin till approximation and water flow according to an effective pressure dependent hydraulics

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

re advance of scottish ice into the solway lowlands cumbria uk during the main late devensian deglaciation the complex glacial geomorphology and stratigraphy of the solway lowlands cumbria uk reflects dynamic ice flow during the main late devensian glaciation with numerous ice flow shifts and re advances now recognised the final incursion of scottish ice into the region scottish re advance during a late stage of deglaciation has provoked widespread debate and even scepticism arising from ill defined marginal limits and a paucity of landforms sediments and dates in an attempt to resolve some of these issues this paper has applied both geomorphological and stratigraphic techniques to critically review evidence pertaining to the scottish re advance a major deltaic landform sediment assemblage at holme st cuthbert a thin patchy till sheet and eskers at thursby and sowerby wood verify that scottish ice re advanced into the solway lowlands at a late stage of deglaciation the thin patchy till sheet associated with the re advance is indicative of a short lived pulse with ice thought to have flowed rapidly across water saturated sediment and into proglacial lakes dammed up against higher ground to the east the holme st cuthbert delta which evolved from a subaqueous outwash fan marks a major still stand and development of a large ice contact lake in the vicinity of wigton the extent of the glaciation is difficult to elucidate with the till sheet disparately exposed as far east as lannercost although identification of the blackhall wood re advance till member probably limits its se extent to just south of carlisle coeval re advance of lake district ice is possible given that a final stage lobate movement of ice out of the vale of eden and into the solway lowlands is now recognised however there is no direct stratigraphic correlation or dating control

microfabric and microshear evolution in deformed till abstract the bed deformation model of glacier movement requires that ice masses shear their beds to high strains for homogeneous basal tills that can result from such deformation however there are no sedimentological criteria for estimating strain magnitude thus a large ring shear device was used to shear two basal tills and their particle fabrics and microshears were studied at various strains up to 108 sand particle fabrics in a longitudinal flow plane became steady at shear strains of 7 39 steady fabrics were moderately strong with s1 eigenvalues of 0 71 0 74 these values are smaller than those from experiments with pebble sized particles perhaps reflecting the greater probability of sand particles colliding with larger grains fabrics parallel to flow strengthened progressively indicating that particles did not reorient with their long axes transverse to flow r1 and r2 microshears developed and persisted to the highest strains attained r1 shears became more pervasive with strain and oriented closer to the shear plane movement along both sets of shears provides an explanation for the plunge of the steady state sand fabric approximately 10 upglacier these experiments provide a basis for estimating till deformation magnitude but results will require cautious application to the geologic record where deformation processes may be ambiguous

ice streams as the arteries of an ice sheet their mechanics stability and significance ice streams are corridors of fast ice flow ca 0 8 km year within an ice sheet and are responsible for discharging the majority of the ice and sediment within them consequently like the arteries in our body their behaviour and stability is essential to the well being of an ice sheet ice streams may either be constrained by topography topographic ice streams or by areas of slow moving ice pure ice streams the latter show spatial and temporal patterns of variability that may indicate a potential for instability and are therefore of particular interest today pure ice streams are largely restricted to the siple coast of antarctica and these ice streams have been extensively investigated over the last 20 years this paper provides an introduction to this substantial body of research and describes the morphology dynamics and temporal behaviour of these contemporary ice streams before exploring the basal conditions that exist beneath them and the mechanisms that drive the fast flow within them the paper concludes by reviewing the potential of ice streams as unstable elements within ice sheets that may impact on the earth s dynamic system d 2002 elsevier science b v all rights reserved

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

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

late ordovician glacial pavements revisited a reappraisal of the origin of striated surfaces late ordovician glacial pavements revisited

a near synthesis of pre illinoian till stratigraphy in the central united states iowa nebraska and missouri abstract nearly identical sequences of pre illinoian glacial till are present throughout the north central united states in iowa nebraska and missouri in each of these states three tills with normal magnetic remanence have been found above two three tills with reversed remanence and the lithologic differences among successive tills are nearly the same each till is capped by a mature paleosol except for the two youngest reversed polarity tills which are nearly identical in lithology and separated by immature weathering profiles these results seem to indicate that deposits from five major pre illinoian glaciations are present throughout this entire region cosmogenic nuclide burial ages provide relatively precise ages for the three earliest glaciations that reached northeast missouri ca 2 4 1 3 and 0 76 ma ages of the youngest two glaciations in this area are less precise but both are between 0 2 and 0 4 ma the tills in nebraska and western iowa have not been dated directly but are constrained by the ages of interbedded tephra and these limits are consistent with the burial ages in missouri for tills in the same relative stratigraphic positions with one exception two of the three normal polarity tills in nebraska western iowa are present below the 0 64 ma lava creek b tephra and thus should be between 0 64 and 0 78 ma in age however only one of the normal polarity tills in northeast missouri is within this range this discrepancy indicates either a problem with the age constraints or that the till sequence is more complex than yet recognized

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

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

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

structural analysis of coseismic normal fault zones of the 2011 mw 6 6 fukushima earthquake northeast japan the 2011 m w 6 6 fukushima earthquake occurred in iwaki city 250 km southwest of the epicenter of the 2011 m w 9 0 tohoku japan earthquake and produced two subparallel 15 23 km long surface rupture zones with distinct displacements along two pre existing normal faults the shionohira and yunodake faults which strike north northwest south southeast and northwest southeast both dipping southwest respectively field investigations and structural analysis of the coseismic shear zones developed within the shionohira and yunodake fault zones reveal that 1 the coseismic shear zones consist of a fault core that includes a narrow fault gouge zone of 10 cm in width generally 1 5 cm a fault breccia zone of 50 cm in width and a damage zone of 5 50 m in width that is composed of cataclastic rocks fractures and subsidiary faults 2 the foliations characterized by s c fabrics developed in the shear zones indicate a dominantly normal fault slip sense consistent with that observed along the coseismic surface ruptures and 3 veinlet cataclastic rocks composed of unconsolidated fault gouges and fine grained materials occur as simple discrete veinlets and multiple cross cutting interconnected networks of veinlets these newly documented structural characteristics for two coseismic fault shear zones and associated cataclastic rocks indicate that the locations of coseismic slip zones associated with the 2011 fukushima earthquake were controlled by pre existing fault shear zones central to the shionohira and yunodake faults which have repeatedly moved as seismogenic normal faults since the timing of formation of associated cataclastic rocks our results demonstrate that the structural analyses of coseismic shear fault zones provide a powerful tool to study the nature and active faulting history of seismological faults

the submarine eruption of the bombarda volcano milos island cyclades greece the milos volcanic field includes a well exposed volcaniclastic succession which records a long history of submarine explosive volcanism the bombarda volcano a rhyolitic monogenetic center erupted 1 7 ma at a depth 200 m below sea level the aphyric products are represented by a volcaniclastic apron up to 50 m thick and a lava dome the apron is composed of pale gray juvenile fragments and accessory lithic clasts ranging from ash to blocks the juvenile clasts are highly vesicular to non vesicular the vesicles are dominantly tube vesicles the volcaniclastic apron is made up of three fades massive to normally graded pumice lithic breccia stratified pumice lithic breccia and laminated ash with pumice blocks we interpret the apron beds to be the result of water supported volcaniclastic mass how emplacement derived directly from the collapse of a small volume subaqueous eruption column and from syn eruptive down slope resedimentation of volcaniclastic debris during this eruptive phase the activity could have involved a complex combination of phreatomagmatic explosions and minor submarine effusion the lava dome emplaced later in the source area is made up of flow banded lava and separated from the apron by an obsidian carapace a few meters thick the near vertical orientation of the carapace suggests that the dome was intruded within the apron remobilization of pyroclastic debris could have been triggered by seismic activity and the lava dome emplacement

scale invariant sheath folds in salt sediments and shear zones abstract sheath folds are developed in a broad spectrum of geological environments in which material flow occurs including gravity driven surficial deformation in ignimbrites unconsolidated sediments and salt together with deeper level ductile shear zones in metamorphic rocks this study represents the first geometric comparison of sheath folds in these different settings across a wide range of scales elliptical closures defining eye folds represent y z cross sections through highly curvilinear sheath folds our analysis of the published literature coupled with field observations reveals remarkably similar ellipticities r yz for sheath folds in metamorphic shear zones r yz 4 23 salt r yz 4 29 sediment slumps r yz 4 34 glaciotectonites r yz 4 48 and ignimbrites r yz 4 34 nested eye folds across this range of materials n 1800 reveal distinct and consistent differences in ellipticity from the outer r yz to the inner most r y z elliptical rings of individual sheath folds the variation in ratios from outer to inner rings r r yz r y z in gravity driven surficial flows typically displays a relative increase in ellipticity to define cats eye folds r r yz that are remarkably constant r 2 0 99 across 9 orders of magnitude sheath y axes range from 0 1 mm to 75 km our findings lead us to conclude that the geometric properties of sheath folds are scale invariant and primarily controlled by the type and amount of strain with r also reflecting the rheological significance of layering associated with original buckle fold mechanisms the scaling pattern of sheath folds reflects the length scales of the precursor buckle folds and width of deformation zones across a broad range of materials and environments with continued deformation the layering marking the original folds may become increasingly passive to define sheath folds these empirical relationships suggest sheath folding is a fundamental mode of viscous response across a broad spectrum of materials strain rates and scales encompassing a variety of deformation settings

coupled ice till dynamics and the seeding of drumlins and bedrock forms the geomorphological effects of ice sliding over till internal deformation of till and till sliding over bedrock are considered two questions are examined 1 is the till sheet flow unstable i e is a layer of uniform thickness maintained or not and 2 does the slip of till over bedrock cause amplification of relief of the bedrock such instabilities seem to be necessary to explain such features as drumlins and whaleback forms it is found that the answer to 1 and 2 depends on the position of the system in a parameter space defined by the till rheology and applied shear stress the effective pressure at the ice till interface the thickness of ice and till and the wavelength of the instability two configurations are considered one where the wavelength of the perturbation is much less than the the ice thickness which is related to the classical nye kamb solution for flow over bumps and one where the wavelength is much greater than the ice thickness where the mechanics are described by the shallow ice approximation in both cases substantial areas of parameter space where till sheet and bedrock modes are unstable are found the conceptually related smalley unwin bifurcation is re examined the physical mechanisms by which ice and till flows couple are examined at very short wavelengths 10 m the ice is so rigid that it forces till waves to move at the ice velocity while at long wavelengths 1000 m the flows become essentially uncoupled and till waves move at the kinematic velocity at intermediate wavelengths 100 m high growth rates occur this is postulated to be the scale of drumlin seeding

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

antarctic ice and sediment flux in the oligocene simulated by a climate ice sheet sediment model abstract a model of deforming sediment is added to a climate ice sheet model and applied to the eocene oligocene transition in antarctic ice volume around 34 ma the coupling between the global climate and ice sheet models is asynchronous with a climate simulation performed once every 10 000 years and only for the first 40 000 years these global climate model solutions are re used to perform runs of 400 000 years in length with orbital forcing and different levels of co2 the sediment model includes bulk transport under ice generation of sub ice till and river transport and predicts the continental scale evolution of sediment thickness and coastal discharge for the first few 10 000 s of years after the onset of substantial ice triggered by co2 falling below 3 pre industrial level sediment discharge to the ocean is relatively uniform around the coast derived from nearby pre existing regolith after that most discharge is concentrated into 4 sites at the mouths of major trough systems with orbitally paced pulses on 104 yr scales these sites and the average magnitudes of the fluxes agree generally with those deduced from offshore seismic and core data although longer 10 my integrations are needed to model the real sediment evolution

a critical assessment of subglacial mega floods a case study of glacial sediments and landforms in south central alberta canada the existing subglacial megaflood explanation of glacial sediment deposition and landform production in south central alberta relies upon four sets of observations and associated interpretations 1 a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt out till or ice stagnation facies 2 a melt out genesis for the ice stagnation facies 3 a syn depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice bed re coupling and 4 a subglacial megaflood origin for a truncation surface and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area we provide alternative interpretations of the sediment landform assemblages of the area and demonstrate that alternative simpler interpretations of the evidence can be proposed specifically we propose 1 a proglacial rather than subglacial origin of glacilacustrine sediments 2 a glacilacustrine origin for the melt out till and its subsequent glacitectonic disturbance by minor glacier readvances 3 postdepositional rather than syn depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments 4 that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting 5 that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water the mega flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis aligned and cross cutting flow sets terminating at series of inset and locally cross cutting and lobate transverse ridges moraines these landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines the similarity of the glacial landforms of this region to the active temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments where sheetfloods have not been influential in subglacial landform production allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding

till melange at amsdorf central germany sediment erosion transport and deposition in a complex soft bedded subglacial system abstract glacial melange in the open cast mine at amsdorf central germany consists of several square meters of large sorted sediment blocks embedded in till the blocks are composed of largely intact to slightly deformed glaciofluvial and glaciolacustrine sand silt and clay initially deposited in a proglacial lake 2 3 km up ice and subsequently overridden by a glacier the blocks typically have cuboid to subrounded outlines are randomly distributed in the till and the contacts with the surrounding till are distinctly sharp underneath the melange are varved clays which exhibit strong deformations occasionally intervening with entirely undisturbed areas it is suggested that the blocks were entrained into debris rich basal ice by bulk freeze on when the glacier sole was lowered onto the bottom of an overridden lake after entrainment the blocks were transported englacially and re deposited with far traveled till matrix as a melt out till from stagnant ice the glacier moved mainly by sliding enhanced by low permeability varved clays in the substratum the glacier is believed to have been of a polythermal type these results show that bulk freeze on can lead to entrainment of soft sediment blocks at least 20 m2 in size and that these blocks can be englacially transported with little or no deformation for several kilometers and more the occurrence of deformed and undeformed clays under the till melange indicates a possible mosaic of coupled and decoupled ice the latter caused by a thin transient subglacial water film separating the bed from the glacier

sedimentology of latero frontal moraines and fans on the west coast of south island new zealand exposures through the lgm latero frontal moraine loops at sites along the west coast of south island new zealand reveal a depositional environment that was dominated by the progradation of steep fronted debris flow fed fans manifest in crudely stratified to massive diamictons arranged in sub horizontal to steeply dipping clinoforms and containing discontinuous bodies of variably sorted stratified sediment lfa 1 the fans were constructed by debris covered glaciers advancing over outwash plains as recorded by well stratified and horizontally bedded gravels sands and diamicts lfa 0 the ice contact slopes of the fans are offlapped by retreat phase deposits in the form of glacilacustrine depo centres lfa 2 which record the existence of moraine dammed lakes interdigitation of lake rhythmites and subaerial to subaqueous sediment gravity flow deposits documents intense debris flow activity on unstable moraine fan surfaces glacier readvances in all catchments are documented by glacitectonic disturbance and localized hydrofracturing of lfa 2 followed by the emplacement of schist dominated debris flow fed fans lfa 3 inside and over the top of the earlier latero frontal moraine fan loops contorted and disturbed bedding in lfa 3 reflects its partial deposition in supraglacial positions clast lithologies in lfas 1 and 3 reveal that two distinct transport pathways operated during moraine construction with an early period of latero frontal fan construction involving mixed lithologies and a later period of ice contact supraglacial fan construction dominated by schist lithologies from the mountains these two periods of deposition were separated by a period of moraine abandonment and paraglacial reworking of ice contact slopes to produce lfa 2 the occurrence of lfa 3 at all sites indicates that the glacier readvance phase responsible for its deposition was not localized or glacier specific and involved the transfer of large volumes of schist possibly due to rock slope failures onto glacier surfaces the absence of any sediment that could be unequivocally classified as subglacial till reflects the dominance of debris flow and glacifluvial processes in latero frontal moraine construction in this hyper humid west coast setting

phased occupation and retreat of the last british irish ice sheet in the southern north sea geomorphic and seismostratigraphic evidence of a dynamic ice lobe along the terrestrial margin of the southern north sea previous studies of the mis 2 glaciation impacting eastern britain have played a significant role in the development of principles relating to ice sheet dynamics e g deformable beds and the practice of reconstructing the style timing and spatial configuration of palaeo ice sheets these detailed terrestrially based findings have however relied on observations made from only the outer edges of the former ice mass as the north sea lobe nsl of the british irish ice sheet biis occupied an area that is now almost entirely submarine c 21 15 ka compounded by the fact that marine acquired data have been primarily of insufficient quality and density the configuration and behaviour of the last biis in the southern north sea remains surprisingly poorly constrained this paper presents analysis of a new integrated set of extensive seabed geomorphological and seismo stratigraphic observations that both advances the principles developed previously onshore e g multiple advance and retreat cycles and provides a more detailed and accurate reconstruction of the biis at its southern most extent in the north sea a new bathymetry compilation of the region reveals a series of broad sedimentary wedges and associated moraines that represent several terminal positions of the nsl these former still stand ice margins 1 4 are also found to relate to newly identified architectural patterns shallow stacked sedimentary wedges in the region s seismic stratigraphy previously mapped singularly as the bolders bank formation with ground truthing constraint provided by sediment cores these wedges are interpreted as sub marginal till wedges formed by complex subglacial accretionary processes that resulted in till thickening towards the former ice sheet margins the newly sub divided shallow seismic stratigraphy at least five units also provides an indication of the relative event chronology of the nsl while there is a general record of south to north retreat seismic data also indicate episodes of ice sheet re advance suggestive of an oscillating margin e g mis 2 maximum not related to first incursion of ice into region demonstrating further landform interdependence geographically grouped sets of tunnel valleys are shown to be genetically related to these individual ice margins providing clear insight into how meltwater drainage was organised at the evolving termini of this dynamic ice lobe the newly reconstructed offshore ice margins are found to be well correlated with previously observed terrestrial limits in lincolnshire and e yorkshire holderness e g mis 2 maximum and withernsea till this reconstruction will hopefully provide a useful framework for studies targeting the climatic mass balance and external glaciological factors i e fennoscandian ice sheet that influenced late stage advance and deglaciation important for accurately characterising both modern and palaeo ice sheets

till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams case study of the western canadian prairies and high plains complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western canada represent the terrestrial equivalents of the trough mouth fans of the marine palaeo ice stream record intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed first glacier marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time stacks of subglacial traction tills potentially record annual sub marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing second proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub marginal till wedges and moraines glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls resulting in the widespread development of glacitectonites and megablocks the occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots

geomorphology and sedimentology of surging glaciers a land systems approach the identification of surging glaciers and ice streams in glaciated landscapes is of major importance to the understanding of ice sheet dynamics and for reconstructing ice sheets and climate no single landform or diagnostic criterion has yet been found with which to identify surging glaciers a surging glacier land system model is constructed using observations and measurements from contemporary surging glacier snouts in iceland svalbard u s a and canada for differentiating ancient surging margins from other non surging palaeoglaciers this integrates the suite of landforms sediments and stratigraphy produced at surging glacier margins landforms produced during surging include thrust moraines concertina eskers and subglacial crevasse squeeze ridges sedimentary sequences are usually characterized by multiple stacked diamictons and stratified interbeds which display severe glaciotectonic contortion and faulting hummocky moraine comprising interbedded stratified sediments and mass flow diamictons has also been associated with surge margins where large quantities of supraglacial and englacial debris entrained during the surge event have melted out in situ an example of the application of the land system model is presented for east central alberta canada a surging palaeo ice stream is identified within this part of the southwestern laurentide ice sheet where thrust block moraines crevasse squeeze ridges flutings hummocky moraine and glaciotectonized sediments are juxtaposed

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

styles of till deposition at the margin of the last glacial maximum north sea lobe of the british irish ice sheet an assessment based on geochemical properties of glacigenic deposits in eastern england the geochemical composition of last glacial maximum lgm tills and glacitectonites in east yorkshire and lincolnshire was analysed to assess vertical changes in their geochemical signature with respect to the current regional stratigraphic division and generic models of till deposition results fail to precisely differentiate the traditional basement skipsea and withernsea till types instead there is often more variability within these till types than between them the geochemical signatures are also laterally discontinuous and are often repeated vertically at a number of sites suggesting that the till sequences are composed of a number of lithologically distinct rafts which have been tectonically stacked or elevated to higher levels in the sediment pile at dimlington the production of a glacitectonically folded and stacked moraine is proposed as a mechanism to explain the remarkably thick sequence of withernsea till and the repetitions in geochemical composition we argue that the changes in till matrix geochemistry are related to changes in the dominance of ice lobes of different provenance which reworked pre existing quaternary sediments excavated local bedrock and progressively mixed these sediments with more far travelled material from further north the most significant implication of these findings is that the current lgm till stratigraphy of east yorkshire and lincolnshire is too simplified and therefore does not recognise the sedimentary and structural complexity produced by repeated onshore possibly surging flow by a dynamic north sea lobe at the eastern margin of the british irish ice sheet

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

rogen moraine an example of glacial reshaping of pre existing landforms abstract rogen moraine is widely distributed in the core areas of the former scandinavian and laurentide ice sheets it is generally agreed upon that these gently arched ice flow transverse ridges can be used in reconstructions of paleo ice flow patterns and that they indicate a melted bed or poly thermal basal ice regime however the processes of ridge generation have been contentious this study proposes a two stage formation of rogen moraine based on detailed sedimentological and structural investigations in excavated trenches in a rogen moraine landscape in the province of dalarna central sweden field data suggest that rogen moraine ridges are the reshaped remains of pre existing transverse moraine ridges originally deposited from ice cored moraines in an ice marginal zone due to back and down wasting of ice cores inter ridge troughs were filled with debris flow and fluvial deposits which after landscape inversion were transformed to areas of transverse and hummocky moraines it is proposed that this primary landscape formation occurred during an early weichselian deglaciation this relict landscape was later preserved beneath cold based mid to late weichselian ice sheet s which turned wet based during the preboreal deglaciation phase and re moulded the precursor landforms into rogen moraine

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

glaciology of the british isles ice sheet during the last glacial cycle form flow streams and lobes abstract the last ice sheet over the british isles together with other mid latitude pleistocene ice sheets and in contrast to the modern ice sheets of greenland and antarctica had a relatively low profile low summit elevation and extensive elongated lobes at its margin a thermo mechanically coupled numerical ice sheet model driven by a proxy climate has been used to explore the properties that would have permitted these characteristics to develop the approach the key to quantitative palaeoglaciology is to determine the boundary conditions that permit the simulated ice sheet to mimic the evolution of the real ice sheet through the last glacial cycle simulations show how a british ice sheet may have been confluent with a scandinavian ice sheet during some parts of its history and how unforced periodic and asynchronous oscillations could occur in different parts of its margins marginal lobes are a reflection of streaming within the ice sheet such streams can be ephemeral dynamic streams located because of ice sheet properties or fixed streams whose location is determined by bed properties the simulations that best satisfy constraints of extent elevation and relative sea levels are those with major fixed streams that strongly draw down the ice sheet surface in these the core upland areas of the ice sheet were cold based at the last glacial maximum basal streaming velocities were between 500 and 1000 ma 1 compared with surface velocities of 10 50 ma 1 in inter stream zones shear stresses were as low as 15 25 kpa in streams compared with 70 110 kpa in upland areas and 60 84 of the ice flux was delivered to the margin via streams

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

till deposition by glacier submarginal incremental thickening macro and micro scale sedimentological analyses of recently deposited tills and complex push squeeze moraines on the forelands of icelandic glaciers and in a stacked till sequence at the former younger dryas margin of the loch lomond glacier lobe in scotland are used to assess the depositional processes involved in glacier submarginal emplacement of sediment where subglacial meltwater is unable to flush out subglacial sediment or construct thick debris rich basal ice by cumulative freeze on processes glacier submarginal processes are dictated by seasonal cycles of refreezing and melt out of tills advected from up ice by a combination of lodgement deformation and ice keel and clast ploughing although individual till layers may display typical a and b horizon deformation characteristics the spatially and temporally variable mosaic of subglacial processes will overprint sedimentary and structural signatures on till sequences to the extent that they would be almost impossible to classify genetically in the ancient sediment record at the macro scale icelandic tills display moderately strong clast fabrics that conform to the ice flow directions documented by surface flutings very strong fabrics typify unequivocally lodged clasts despite previous interpretations of these tills as subglacial deforming layers micro morphological analysis reveals that shearing played only a partial role in the emplacement of till matrixes and water escape and sediment flowage features are widespread a model of submarginal incremental thickening is presented as an explanation of these data involving till slab emplacement over several seasonal cycles each cycle involves 1 late summer subglacial lodgement bedrock and sediment plucking subglacial deformation and ice keel ploughing 2 early winter freeze on of subglacial sediment to the thin outer snout 3 late winter readvance and failure along a decollement plane within the till resulting in the carriage of till onto the proximal side of the previous year s push moraine 4 early summer melt out of the till slab initiating porewater migration water escape and sediment flow and extrusion repeated reworking of the thin end of submarginal till wedges produces overprinted strain signatures and clast pavements

numerical modelling of subglacial erosion and sediment transport and its application to the north american ice sheets over the last glacial cycle abstract present day sediment distribution offers a potentially strong constraint on past ice sheet evolution glacial system models gsms however cannot address this constraint while lacking appropriate representations of subglacial sediment production and transport incorporating these elements in gsms is also required in order to quantify the impact of a changing sediment cover on glacial cycle dynamics towards these goals we present a subglacial process model hereafter referred to as the sediment model that incorporates mechanisms for sediment production entrainment transport and deposition bedrock erosion is calculated by both hallet s and boulton s abrasion laws separately and by a novel quarrying law parametrized as a function of subglacial cavity extent these process oriented erosion laws are compared against a simple empirical relationship between erosion rate and the work done by basal stress sediment entrainment is represented by philip s law for regelation intrusion and soft bed deformation is included as a subglacial sediment transport mechanism the model is driven by the data calibrated mun 3d gsm and a newly developed subglacial hydrology module the sediment model is applied to the last north american glacial cycle and predicts sediment thickness and cumulative erosion patterns results are obtained in the context of a sensitivity analysis and are compared against the present day distribution of glacigenic sediment and geological estimates of laurentide ice sheet erosion given plausible ranges for the sensitivity parameters chosen a priori based on available literature or on heuristic arguments the calculated erosion depths overlap with the geological estimates of laurentide erosion most of the runs in the sensitivity set produce unrealistically thick and continuous moraines along the eastern southern and western margins of the north american ice complex which suggests that the model overestimates sediment entrainment and thus englacial transport a realistic sediment distribution is only obtained when the entrainment rate is capped at the average basal melting rate which suggests that modelled entrainment and basal melting rates should be of the same order of magnitude

glacial sediments and landforms of holderness eastern england a glacial depositional model for the north sea lobe of the british irish ice sheet abstract borehole records and exposures at coastal cliffs and inland quarries around holderness are used in a critical assessment of the glacial depositional environments that operated at the margin of the north sea lobe of the british irish ice sheet at the last glacial maximum four lithofacies associations lfa are recognized in the area lfas 1 and 4 are laminated to massive diamictons traditionally called the skipsea and withernsea tills members and display deformation structures indicative of stress from the ne attenuated rafts of soft bedrock lithologies ice bed separation canal fill features and pseudo stratification and clast macrofabric data predominantly indicate deformation only to low strains they are interpreted as subaqueous deposits subsequently deformed by glacier ice to create end products that lie on the glacitectonite continuum localized increases in strain signature are equated with the development of shear zones between onshore thickening wedges of deformed pre existing lake sediment lfa 2 comprises cross bedded clinoforms locally steepening into foresets at the core of linear hummocks along the central spine of holderness lfa 2a and rhythmically laminated silts and sands with dropstones lfa 2b these sediments are interpreted as coalescent glacilacustrine subaqueous outwash fans fining distally to lake bottom rhythmites and varves ice contact deposition is evident in compressional folding faulting and hydrofracture filling due to ice overriding and extensional faulting associated with localized ice melt out depressions produced by folding or sagging provided the accommodation space for the later deposition of lfa 2 and 3 through syntectonic sedimentation lfa 3 comprises flat lying beds of well to poorly sorted cross stratified sands and gravels interpreted as proximal proglacial braided outwash deposits laid down largely in ribbon sandar defined by the topography of abandoned ice contact glacilacustrine depo centres well developed ice wedge pseudomorphs in lfa 3 record permafrost conditions during ice sheet marginal recession indicating that north sea lobe oscillations may have been non climatic or surge related a depositional model is proposed in which advance and retreat phase tills glacitectonites and associated ice contact lake sediments are the geological imprint of a single glaciation the initial advance of the north sea lobe is recorded by a westerly thinning advance till lfa 1 later lfa 1 and 4 retreat tills are strictly glacitectonites and are thicker depositional units because later ice readvances encroached upon and cannibalized more substantial sequences of deglacial lake sediment and subaqueous ice contact fans lfa 2 similar regional till architectures will be manifest wherever the palaeogeography resulted in the onshore flow of ice and the concomitant production of glacitectonites from glacial lake sediments

the active temperate glacial landsystem a model based on breiðamerkurjokull and fjallsjokull iceland accurate interpretations of ancient glaciated terrains rely heavily on our knowledge of process form relationships in contemporary glacierized basins a landsystems model for temperate actively receding glaciers is presented based upon brei amerkurjokull and fjallsjokull iceland historical documentation maps and or aerial photography documenting recession since 1903 provide a unique series of snapshots of the evolving glacial geomorphology at these snouts this documentation is employed in association with sedimentological investigations to assess the evolution of sediment landform assemblages at active temperate glacier margins using the wealth of geomorphological and sedimentological information produced during the recent recession of brei amerkurjokull and fjallsjokull three depositional domains are recognized 1 areas of extensive low amplitude marginal dump push and squeeze moraines derived largely from material on the glacier foreland and often recording annual recession of active ice 2 incised and terraced glacifluvial forms such as recessional ice contact fans and hochsandur fans and simple and complex anabranched eskers and small areas of pitted outwash 3 subglacial landform assemblages of flutes drumlins and overridden push moraines located between ice marginal glacifluvial depo centres the lack of supraglacial sediment in active temperate glaciers like brei amerkurjokull and fjallsjokull generally precludes the widespread development of chaotic hummocky moraine the hummocky terrain previously termed kame and kettle topography has mostly evolved by melt out into a complex network of anabranched eskers over the period 1945 1998 or actually comprises pitted or kettled outwash sandar the tills across the foreland were emplaced by subglacial deformation and lodgement and comprise materials derived from pre existing stratified sediments in addition to localized abrasion of rock surfaces and patches of lake sediments till sequences thicker than 2 m have been constructed by the sequential plastering of till layers onto stratified sediments and bedrock because this stacking is a sub marginal process it is suggested that complex till sequences similar to those observed at brei amerkurjokull fjallsjokull may be employed in the reconstruction of ancient glacier margins additionally the geomorphology of the active temperate landsystem at east brei amerkurjokull may contain subtle surge signatures verifying the historical record of small surges by this part of the glacier this illustrates the danger of employing landform sediment associations from restricted study areas e g parts of landsystems as representative process form models for glaciated terrains

geomorphology and till architecture of terrestrial palaeo ice streams of the southwest laurentide ice sheet a borehole stratigraphic approach abstract a multidimensional study utilising geomorphological mapping and the analysis of regional borehole stratigraphy is employed to elucidate the regional till architecture of terrestrial palaeo ice streams relating to the late wisconsinan southwest laurentide ice sheet detailed mapping over a 57 400 km2 area of southwestern saskatchewan confirms previous reconstructions of a former southerly flowing ice stream demarcated by a 800 km long corridor of megaflutes and mega scale glacial lineations ice stream 1 and cross cut by three formerly southeast flowing ice streams ice streams 2a b and c analysis of the lithologic and geophysical characteristics of 197 borehole samples within these corridors reveals 17 stratigraphic units comprising multiple tills and associated stratified sediments overlying preglacial deposits the till thicknesses varying with both topography and distance down corridor reconciling this regional till architecture with the surficial geomorphology reveals that surficial units are spatially consistent with a dynamic switch in flow direction recorded by the cross cutting corridors of ice streams 1 2a b and c the general thickening of tills towards lobate ice stream margins is consistent with subglacial deformation theory and variations in this pattern on a more localised scale are attributed to influences of subglacial topography including thickening at buried valley margins thinning over uplands and thickening in overridden ice marginal landforms

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

retreat signature of a polar ice stream sub glacial geomorphic features and sediments from the ross sea antarctica abstract three research expeditions to the ross sea antarctica resulted in collection of a dataset of more than 270 km of side scan and chirp sonar data more than 330 km of swath bathymetry and 3 5 khz data and 24 cores within a glacially carved trough the former ice stream flow path is divided into six zones covering a distance of approximately 370 km distinguished by unique stratigraphic signatures and geomorphic features an erosional surface with thin patchy lodgement till characterizes zone 1 this region is interpreted as having experienced relatively high basal shear stress conditions zones 2 3 and 4 are characterized by an erosional surface and thin time transgressive subglacial and grounding line proximal deposits that include back stepping moraines flutes transverse moraines and corrugation moraines these zones represent the transition between erosional and depositional regimes under the expanded lgm ice sheet material eroded from the inner shelf was transported toward the outer shelf possibly as a thin deforming till layer the two outer zones are depositional and include maximum grounding line zone 5 and pro glacial deposits that were overridden subsequently by the ice sheet zone 6 surface features include mega scale glacial lineations corrugation moraines and iceberg furrows ice in these zones is interpreted as having experienced relatively lower basal shear stress an extensional regime and faster flow this advance may have destabilized the ice sheet initiating local draw down and production of icebergs that furrowed the sea floor corrugation moraines are thought to represent annual retreat moraines constraining the retreat rate of the ice sheet across the continental shelf to a consistent 40 to 100 m a 1

magnetic fabric of sheared till a strain indicator for evaluating the bed deformation model of glacier flow wet based portions of ice sheets may move primarily by shearing their till beds resulting in high sediment fluxes and the development of subglacial landforms this model of glacier movement which requires high bed shear strains can be tested using till microstructural characteristics that evolve during till deformation here we examine the development of magnetic fabric using a ring shear device to deform two wisconsin age basal tills to shear strains as high as 70 hysteresis experiments and the dependence of magnetic susceptibility of these tills on temperature demonstrate that anisotropy of magnetic susceptibility ams develops during shear due to the rotation of primarily magnetite particles that are silt sized or smaller at moderate shear strains 6 25 principal axes of maximum magnetic susceptibility develop a strong fabric s 1 eignevalues of 0 83 0 96 without further strengthening at higher strains during deformation directions of maximum susceptibility cluster strongly in the direction of shear and plunge up glacier consistent with the behavior of pebbles and sand particles studied in earlier experiments in contrast the magnitude of ams does not vary systematically with strain and is small relative to its variability among samples this is because most magnetite grains are contained as inclusions in larger particles and hence do not align during shear although processes other than pervasive bed deformation may result in strong flow parallel fabrics ams fabrics provide a rapid and objective means of identifying basal tills that have not been sheared sufficiently to be compatible with the bed deformation model

glacial geomorphology of terrestrial terminating fast flow lobes ice stream margins in the southwest laurentide ice sheet glacial geomorphological mapping of southern alberta canada reveals landform assemblages that are diagnostic of terrestrial terminating ice streams fast flowing outlet glaciers with lobate snouts spatial variability in features that comprise the landform assemblages reflects changes in a palaeo ice stream activity switch on off and b snout basal thermal regimes associated with climate sensitive steady state flow palaeo ice stream tracks reveal distinct inset sequences of fan shaped flowsets indicative of receding lobate ice stream margins former ice lobe margins are demarcated by a major often glacially overridden transverse moraine ridges commonly comprising glacitectonically thrust bedrock and b minor closely spaced recessional push moraines and hummocky moraine arcs details of these landform types are well exhibited around the former southern margins of the central alberta ice stream where larger scale more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges mtr types 1 3 hummocky terrain ht types 1 3 flutings and meltwater channels spillways the mtr type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined the mtr type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts the mtr type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain the close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin where the ht type 3 hummocks represent former ice walled lake plains the ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream fast flow lobes of the southern laurentide ice sheet where alternate cold polythermal and temperate marginal conditions associated with climate sensitive steady state flow sequentially gave way to more dynamic streaming and surging activity

drumlin sedimentology in a hard bed lowland setting connemara western ireland implications for subglacial bedform generation in areas of sparse till cover cores of coastal drumlins in connemara contain stratified diamictons that interdigitate with gravelly clinoforms and finer grained rhythmites the diamictons are interpreted as subaqueous mud apron deposits delivered by subglacial till advection to continuously failing subaqueous ice contact fans whose strata were being syn depositionally over steepened by glacitectonic deformation the localized nature of the stratified sediments reflects the emergence of subglacial deforming tills and meltwater deposits in a glacilacustrine environment to produce interdigitated mass flow diamictons and grounding line fans wedges these depo centres became glacitectonized and subglacially streamlined during glacier overriding and hence regional drumlin sedimentology reflects the varying degrees of inheritance of pre existing glacigenic deposits and suggests that drumlin production relates more to the position of localized sediment accumulations at the glacier bed than full depth till deformation processes e g instability mechanisms within the same drumlin field till cored drumlins give way down ice to stratified cored drumlins with till caps and then to stratified drumlins this zonation is compatible with the increased lateral variability in drumlin composition that would arise from the occurrence of linear assemblages of glacifluvial esker and subaqueous grounding line sediments in an otherwise marginal thickening till sheet

fast flow of the lake michigan lobe evidence from sediment landform assemblages in southwestern michigan usa abstract the dynamics of the late wisconsin lake michigan lobe of the laurentide ice sheet as interpreted by sediment landform assemblages along its southeastern margin are consistent with fast flow driven by high subglacial pore pressures a major advance of the lake michigan lobe terminated at the kalamazoo moraine where proglacial glaciotectonic activity marginal stagnation and release of subglacial meltwater marked the extent of the advance a large portion of the valparaiso moraine west of the kalamazoo moraine is actually a drumlinized till capped upland plain rather than an ice marginal landform assemblage lacustrine sediment underlying the surficial diamicton in the valparaiso upland is glaciotectonically deformed to a depth of 10 m the deformed interval consists of folded sandy and silty lacustrine sediment which is in places sharply truncated by the overlying diamicton decoupling of the glacier from its bed is suggested by a discontinous thin bed of sand at the base of the diamicton and by the sharp truncation of deformed lacustrine sediment the association of drumlins proglacial and subglacial deformation marginal stagnation and major ice marginal outwash fan deposition are indicative of fast flow perhaps in a surge these characteristics are consistent with a terrestrial ice stream model for the lake michigan lobe

structural and depositional evidence for repeated ice marginal oscillation along the eastern margin of the late devensian irish sea ice stream abstract late devensian glacigenic sediments and landforms along the north west coast of wales document the advance and subsequent retreat of the eastern margin of an irish sea ice stream that met coalesced and ultimately uncoupled from ice radiating outwards from the adjacent welsh ice cap centred over snowdonia across the boundary between the two former ice masses is a set of sediment landform assemblages that reflect rapidly changing erosional and depositional conditions during ice interaction from the inner part of the ice stream the assemblages range outwards from a subglacial depositional assemblage characterised by drumlin swarms through a subglacial erosional assemblage marked by prominent bedrock scours and large subglacial rock channels through an ice marginal assemblage identified by closely spaced glaciotectonised push moraines and intervening marginal sandur troughs into a freely expanding proglacial sandur and lacustrine delta assemblage the ice marginal assemblage provides evidence for numerous oscillatory episodes during retreat and at least 20 ice marginal limits can be identified at least 11 of these display multiple criteria for identifying readvance and in the ideal case is characterised by a moraine form built by localised tectonic stacking of diamict to the rear fronted by a clastic wedge of ice front alluvial fan gravel and intercalated flow till the distribution of sediment landform assemblages suggests a highly dynamic convergent ice stream flow pattern with high ice velocity a sharply delineated lateral shear margin pervasive ice marginal glaciotectonic deformation and a tightly focused ice marginal sediment delivery system all signature characteristics of contemporary ice streams

pleistocene glacitectonic landforms and sediments around central magellan strait southernmost chile evidence for fast outlet glaciers with cold based margins abstract proglacial and subglacial glacitectonic sediments and landforms around the margins of the strait of magellan southernmost chile record the advance and retreat of outlet glaciers of the patagonian ice cap during the last glacial cycle the spatial arrangement of glacitectonic landforms in the area is inferred to have resulted from the advance of ice lobes with cold based margins and wet based interiors as the ice advanced subglacial basins were excavated beneath the glacier margins and the eroded material was pushed up into thrust moraines probably because frozen bed conditions formed a thermal dam against the free drainage of subglacial meltwater these ice marginal glacitectonic landforms were then overridden and streamlined into drumlins and flutes as thicker wet based ice passed over the area evidence for permafrost near sea level in patagonia during the last glaciation suggests that mean annual temperatures were several degrees lower than indicated by recent modelling studies the results indicate that future modelling experiments should incorporate more realistic basal boundary conditions particularly the presence of a weak deforming layer at the glacier bed to improve climatic reconstructions of southern south america

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

subglacial and proglacial glacitectonic deformation in the neoproterozoic port askaig formation scotland abstract the recognition and interpretation of glacigenic sediments in the ancient rock record has important implications for understanding processes and patterns of climate change diamictite facies from the neoproterozoic port askaig formation scotland have been variously interpreted as evidence for grounded glacier ice mass movements on a glacially influenced submarine slope and subaqueous mass movements in a non glacial environment these contrasting interpretations imply widely differing degrees of ice cover and have contrasting implications for neoproterozoic snowball glaciations in this paper we focus on the great breccia and the disrupted beds two controversial units in the port askaig formation we present evidence that they were formed by the proglacial and subglacial deformation respectively of pre existing shallow marine facies during an advance of grounded ice quaternary examples provide remarkably exact analogues for the great breccia and disrupted beds illustrating the potential value of applying litho and tectono facies models to ancient sedimentary successions

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

deformation styles as a key for interpreting glacial depositional environments lithostratigraphical and lithofacies approaches used to interpret glacial sediments often ignore deformation structures that can provide the key to environment of formation we propose a classification of deformation styles based on the geometry of structures rather than inferred environment of formation five styles are recognised pure shear p simple shear s compressional c vertical v and undeformed u these dictate the first letter of the codes the remaining letters conveying the evidence this information can be used to reconstruct palaeostress fields and to infer physical properties of sediments when they deformed individual structures are not diagnostic of particular environments but the suite of structures their relative scale stratigraphical relationships and orientation relative to palaeoslopes and to palaeoice flow directions can be used to infer the environment in which they formed this scheme is applied at five sites in west wales the typical succession is interpreted as subglacial sediments overlain by meltout tills flow tills and sediment flows paraglacial redistribution of glacial sediments is widespread large scale compressional deformation is restricted to sites where glaciers readvanced large scale vertical deformation occurs where water was locally ponded near the ice margin there is no evidence for glaciomarine conditions copyright 2003 john wiley sons ltd

sediment deformation beneath glaciers and its coupling to the subglacial hydraulic system abstract the extent and style of shear deformation in sediments beneath modern glaciers and the geological evidence for such deformation in deposited sediments are reviewed new evidence is presented from beneath a modern glacier of the spatial and temporal patterns of water pressure fluctuation and of time dependent patterns of deformation in sediments it is concluded that in most experimental sites beneath soft bedded modern glaciers deformation is a significant or major contributor to glacier movement and the resultant discharge of till is large enough to make sediment deformation a major till forming process particular modes of deformation facilitate incorporation of underlying material into the till whilst the capacity of a deforming till to absorb strain can protect the underlying strata from deformation leading to the commonly found relationship where till overlies other strata with a sharp planar interface it is argued that the almost ubiquitous occurrence of drumlins on the beds of former ice sheets is a reflection of the widespread occurrence of sediment deformation beneath them with important implications for the coupling of ice sheet flow and bed properties it is argued that the mechanical behaviour of the subglacial system is not simply determined by till properties but largely controlled by the subglacial water pressure regime determined by the nature of subglacial drainage results of field experiments show how the nature of the basal hydraulic system can play a vital role in controlling the coupling between the glacier and till deformation processes they show that rapid glacier advances can produce undrained loading of sediments that effective pressure may increase either upwards or downwards in a till according to the direction of drainage and that interstitial water pressures in subglacial sediments can show large and rapid variations producing strong variations in the rate and distribution of strain and in the partitioning of basal movement between sliding and deformation

streamlined erosional residuals and drumlins in central british columbia canada abstract the upland lowland pattern in the plateau region of central british columbia canada forms an extremely large anastomosing channel network with the uplands representing interfluves between channels the study area landscape is remarkably similar in form to water produced channel systems and qualitatively resembles flood landscapes from the channelled scablands and the margins of the laurentide ice sheet numerical shape analysis of the area erosional residuals gives similar results as those derived from known flood landscapes the length to width ratios of the uplands l w 2 38 r2 0 89 are similar to those reported for braid bars and erosional residuals formed by glacial outburst floods thus the study area landscape records a megaflood or floods that almost completely immersed the landscape drumlins with in places ubiquitous hairpin furrows locations downstream from steep slopes facing into the flow and eroded into till and bedrock similarly reflect regional scale meltwater flow that immersed the landscape the regional flow submerged the anastomosing channels at the time of drumlin formation drumlins likely formed as the anastomosing network developed divergent drumlin orientations probably reflect either late flow or separate drumlin forming events that did not appreciably alter the anastomosing system

subglacial conditions and scandinavian ice sheet dynamics at the coarse grained substratum of the fore mountain area of southern poland abstract the fore mountain areas of southern poland are locally composed of the coarse grained sediments of alluvial fans which created unusual conditions under the advancing scandinavian ice sheet during the elsterian glaciation this highly permeable substratum potentially enabled rapid outflow of meltwater from the ice sheet base thereby reducing the water pressure and strongly influencing the ice sheet dynamics the subglacial conditions and the relationship between the ice sheet behaviour and its coarse grained substratum were studied at the foreland of the western carpathian mountains the sedimentological and structural analysis of the till and related sediments that were deposited above the alluvial gravel of the fore mountain fans are presented the study indicates that despite the high permeability of the coarse grained substratum it did not slow the ice sheet movement conversely the ice sheet moved mainly due to basal slip and locally shallow deformations this was a consequence of very high basal water pressure which resulted largely from the presence of permafrost that restricted subglacial groundwater outflow in addition the ice sheet substratum was inclined opposite to the direction of its movement increasing the pressure of the subglacial water numerous subhorizontal sandy laminae within the till indicate that the meltwater from the ice sheet base was drained by a water film along the ice bed interface the water escape structures within the till and subtill sediments indicate the occasional instability of the ice sheet hydrological system and suggest that the meltwater was periodically stored in the ice sheet base temporal changes occurring in the ice sheet hydrological system might indicate variations in the ice sheet behaviour i e phases of relatively fast ice flow and phases of ice stagnation the latter were probably correlated with the freezing of the ice margin to its base the study shows how the coarse grained substratum could potentially influence ice sheet behaviour and provides a broader look on the factors controlling the dynamics of the pleistocene ice sheets which soft sediment substrata in many areas were texturally varied

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

formation mechanisms for ice stream lateral shear margin moraines the lateral shear margins of palaeo ice stream beds are occasionally marked by large curvilinear moraines but little work has addressed how they might form in this paper we review the characteristics of lateral shear margin moraines and present two quantitative models for their formation i differential erosion rates related to lateral variations in the stream velocity and ii lateral incursion from inter stream ridges after the thinner stream retreats where the shear margin moraine is consequently just a terminal moraine of the inter stream ridge other possible mechanisms of formation are addressed qualitatively both of our quantitative theories are in principle feasible but the incursion model is less plausible and inconsistent with observations the differential erosion model can predict moraines tens of metres thick and several kilometres wide which can be formed in a thousand years the width of the moraine depends on the competition between a term that varies across the ice stream because it is dependent on ice velocity and that always causes erosion and a term related to the local accumulation rate which causes erosion if is positive and deposition if negative these terms combine to create the possibility of deposition at the shear margins of ice streams in ablation areas the width of the moraine has a tendency to increase with the width of the stream the conditions that permit shear margin moraines to form are quite constrained too much ablation and deposition occurs everywhere rather than just near the lateral margins of the ice streams too little ablation and there is erosion everywhere this is consistent with the infrequent observations of lateral shear margin moraines

sequence stratigraphy of a glaciated basin fill with a focus on esker sedimentation a large integrated data set of cores outcrop data and seismic transects from the mud buried vars winchester esker in the champlain sea basin canada was studied to gain insight into how muddy glaciated basins fill with sediment and how esker sedimentary systems contribute to this process three stratigraphic units a till sheet over carbonate bedrock the vars winchester esker and overlying champlain sea mud are identified in the data set the till is massive mud rich carbonate rich and drumlinized the esker is also carbonate rich and rests erosively on till or bedrock it consists of two elements a narrow gravelly central ridge and a broad sandy carapace three units comprise the overlying mud package gray carbonate rich rhythmites massive bioturbated mud and carbonate poor red and gray rhythmites a sequence stratigraphic model is proposed to explain these observations emphasis is placed on gradual ice front translation superimposed by rapid meltwater events the esker is interpreted to have been derived from the underlying till by water that flowed through a subglacial conduit r channel within which the narrow gravelly central ridge was deposited most mud and finer sand bypassed the conduit and was deposited proglacially on the floor of the champlain sea first as sandy outwash and farther basinward as muddy carbonate rich rhythmites gradual ice front retreat superposed distal facies over proximal facies generating the upward fining succession that starts with the esker gravel and ends with muddy rhythmites most esker sediment appears to have been deposited during rapid jokulhlaup like floods that punctuated gradual retreat discharges are estimated to have been high possibly on the order of several hundred to perhaps more commonly several thousand cubic meters per second the chaotic and random looking appearance of the resultant sedimentological signatures in the esker sensu stricto is sharply contrasted with the regularity of the muddy rhythmites if the rhythmites are indeed correlative to the esker which seems reasonable given their geochemistry and the fact that their volume scales to the volume of mud in the till the flood events that deposited the esker must have been seasonally mediated and the basin water must have attenuated the flood signal resulting in a rhythmic on off signature in more distal portions of the system the regularity of the rhythmites does not betray the chaotic nature of the esker sensu stricto and vice versa studying either one in isolation would lead to a very different end member impression of how eskers form and how esker sedimentary systems operate during the infilling of glaciated basins

laminated sediments in glacimarine environments diagnostic criteria for their interpretation abstract fine grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences laminated glacimarine sediments form by a variety of processes including suspension settling from turbid overflow plumes turbidity current deposition and contour current activity subglacial deformation of pre existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till the development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important both for their correct interpretation in sedimentary sequences and also for the accurate reconstruction of former glacier extent and geometry as laminated sediments may form in subglacial ice proximal and ice distal environments this paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology the aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record laminated sediments are genetically differentiated on the basis of sedimentary structures bedding contacts stratigraphic relationships and macrofaunal content bioturbation these attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites the paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology reconstructions of former ice dynamics and basal thermal regime