rheology of till beneath storglaciaren sweden in order to study in situ the rheology of a deforming subglacial till various instruments were emplaced in till beneath storglaciaren sweden boreholes were used to gain access to the till beneath about 100 m of ice tiltmeters provided an estimate of the shear strain rate in the till two other instruments yielded measures of till strength in addition water pressures were recorded in boreholes and in the till a computer controlled distance meter provided an effectively continuous record of the surface velocity and data from frequent surveys of a stake network were used to estimate the mean basal drag based on a force balance calculation tilt rates varied directly with effective pressure so decreases in water pressure apparently increased the coupling between the glacier and the bed surface speed was either out of phase with tilt or varied independently of tilt thus increases in speed were apparently a consequence either of longitudinal coupling or of reduced coupling between the glacier and the bed they were not a result of till deformation till strength varied directly with effective pressure which is consistent with it being a mohr coulomb or frictional material the devices measuring till strength are presumed to have been pulled through the till at a speed that varied in phase with the surface speed but till strength did not vary systematically with surface speed this implies that the residual strength of the till is insensitive to strain rate thus the appropriate constitutive equation for till rheology may be of the form e e k where k is a constant this is consistent with experimental data reported in the geotechnical literature

distributed shear of subglacial till due to coulomb slip in most models of the flow of glaciers on till beds it has been assumed that till behaves as a viscoplastic fluid despite contradictory evidence from laboratory studies in accord with this assumption displacement profiles measured in subglacial till have been fitted with viscoplastic models by estimating the stress distribution here we present a model that illustrates how observed displacement profiles can result from till deformation resisted solely by coulomb friction motion in the till bed is assumed to be driven by brief departures from static equilibrium caused by fluctuations in effective normal stress these fluctuations result from chains of particles that support intergranular forces that are higher than average and that form and fail at various depths in the bed during shearing newton s second law is used to calculate displacements along slip planes and the depth to which deformation extends in the bed consequent displacement profiles are convex upward similar to those measured by boulton and colleagues at breidamerkur jokull iceland the model results when considered together with the long term and widespread empirical support for coulomb models in soils engineering indicate that efforts to fit viscoplastic flow models to till displacement profiles may be misguided

till beneath ice stream b 4 a coupled ice till flow model a nonsteady model of an ice stream flowing on deforming till shows that the system responds rapidly and in a stable manner to reasonable marginal perturbations for the model we require one dimensional flow and continuity of ice and till and we assume linear viscous till rheology and balance between the driving stress for ice flow and the resistive stress at the bed this allows us to write coupled equations for the time rate of change of the ice thickness and the till thickness in terms of these thicknesses and the till viscosity an analytic steady state solution for ice stream b west antarctica shows that till viscosity decreases slowly downstream probably in response to decreasing effective pressure downstream nonsteady numerical experiments with fixed ice thicknesses at the ends show that a marginal perturbation causes a wave of adjustment to travel the length of the ice stream in about 50 years with a new steady state in about 200 years changes in till thickness tend to moderate perturbations in the ice and thus stabilize the system

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

tectonic heredity and tectonic wedging along an oblique hanging wall ramp the southern termination of the misty thrust sheet southern canadian rocky mountains the misty range is a homoclinal southwest dipping panel of paleozoic carbonate rocks in the canadian rocky mountains southwest of calgary that has been juxtaposed against underlying mesozoic siliciclastic rocks along the northeast verging misty thrust fault at the south end of the misty range a steep oblique ramp marks an abrupt southward change along the hanging wall of the misty thrust from a detachment zone in the upper devonian palliser formation to another detachment zone in the jurassic fernie group this 2 km high ramp is expressed in the hanging wall rocks as a large oblique southeast plunging fold a west verging back thrust that rises from a detachment zone in the mississippian mount head formation extends across the hanging wall ramp fold and is truncated by the misty thrust the misty thrust evidently propagated southward as an oblique tectonic wedge into this detachment zone forming a triangle zone structure with the back thrust as the roof thrust as displacement on the misty thrust increased and the hanging wall ramp of the misty thrust moved into the triangle zone the back thrust was progressively back folded and became convex subsequently the lower part of the back thrust was partly overridden by the misty thrust and became overturned before becoming detached and incorporated in the misty thrust sheet the configuration and evolution of the tectonic wedge and the oblique hanging wall ramp provide a natural prototype for the interpretation of ramps that mark the lateral terminations of oil and gas reservoir structures in the foothills belt but which are concealed by overlying deformed mesozoic rocks

reconstruction of taconian and acadian paleostress regimes in the quebec and northern new brunswick appalachians a numerical analysis of fault populations was applied in the quebec and northern new brunswick appalachians to characterize paleostress fields attributed to the taconian and acadian orogenies the first brittle deformation documented in the external domain of the humber zone is associated with the thin skinned tectonics of the taconian orogen the taconian brittle deformation characterized by north south to ne sw reverse conjugated brittle faults evolved under a pure shear compressional regime vertical 3 axes with 1 axes oriented ese wnw the ene wsw dextral and nw se sinistral faults that are observed in the st lawrence lowlands are also attributed to taconian compression the first brittle deformation recognized in the dunnage zone and the gaspe belt is attributed to an ese wnw compression during the acadian orogeny in the dunnage zone of southern quebec the acadian paleostress axes are similar to the directions of 1 axes and to the pure shear compressional regime computed for the silurian and devonian rocks of the gaspe belt in the gaspe peninsula the acadian stresses are oriented ese wnw and are mechanically compatible with transpressional regimes reverse brittle faults and pure shear stress are identified along regional and secondary sets of ne sw brittle faults whereas a strike slip stress regime is reconstructed along major east west faults in the humber zone of the quebec appalachians a second compression is identified it is characterized by conjugate ene wsw dextral and nw se sinistral strike slip faults that crosscut taconian thrust faults this late deformation event is attributed to a distal expression of the acadian orogeny

diachronous tectonic collapse of the ordovician continental margin eastern canada comparison between the quebec reentrant and st lawrence promontory the upper ordovician trenton group of southern quebec represents the last taconian foreland basin carbonate unit in the quebec reentrant prior to final collapse of laurentia s continental margin and its burial under synorogenic flysch the trenton group either conformably or unconformably overlies the black river group and is in turn conformably overlain by the utica shales the tripartite trenton carbonate unit records progressive deepening 1 very shallow to shallow subtidal 2 shallow to deep carbonate ramp and 3 shallow to deep outer shelf regional facies distribution lithotectonic elements and thickness variations indicate that the trenton shelf was dissected by extensional faults delineating blocks subsiding at various rates this scenario compares favourably with taconian foreland basin development in the middle ordovician table head group at the st lawrence promontory newfoundland a similar stratigraphic succession and tectono sedimentary history occurring 10 15 ma earlier at the s

stratigraphie framework for the cambrian ordovician rift and passive margin successions from southern quebec to western newfoundland the taconian humber zone stretches from western newfoundland to southern quebec the early cambrian slope succession in newfoundland is found in the curling group whereas in quebec various units were deposited during that first time slice biostratigraphic data allow correlation of the curling group with the labrador group in newfoundland and with the newly time constrained slope succession in quebec the end of the rift drift transition is marked by a sea level lowstand at the end of the early cambrian the middle cambrian to latest early ordovician passive margin history recorded five cyclic sea level fluctuations three of these cycles are recorded in the shallow marine middle to late cambrian platform port au port group and slope sediments preserved in the cow head and northern head groups in newfoundland the biostratigraphic information assists correlation with cambrian passive margin units in quebec major sea level lowstands are recognized along the continental margin in early middle late camb

scale independence of till rheology representation of till rheology in glaciological models of ice motion over deformable sediments has until now focused largely on two end member cases 1 linear or mildly non linear viscous rheology and 2 nearly plastic rheology most laboratory and in situ experiments support the latter model hindmarsh 1997 and fowler 2002 2003 proposed that experimental results represent the behavior of small till samples characteristic length scales of 0 1 to 1 m but that till behaves viscously over length scales that are relevant to determination of ice flow rates in glaciers and ice sheets 1 km or more observations of short speed up events on the ice plain of whillans ice stream west antarctica provide an opportunity to compare the in situ rheology of this till integrated over 10 100 km with the rheology of till from beneath the same ice stream determined on small laboratory samples and in local borehole experiments this comparison indicates that the rheology of the subglacial till beneath whillans ice stream is independent of scale

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

a ring shear device for the study of till deformation tests on tills with contrasting clay contents abstract deformation of subglacial sediment may have had a profound influence on the geomorphic effects and dynamics of pleistocene ice sheets but data that bear on the rheology of such sediment are few and contradictory a means of studying systematically the mechanical properties of glacial tills is provided by a ring shear device that shears a large annular specimen to high strains at variable rates special features of the device allow continuous observation of the distribution of shear strain measurement of local stresses normal to the direction of shear and isolation of wall effects thus far a linear viscous putty and two tills with different clay contents 4 and 32 by weight have been tested the experiments with till indicate as expected that the presence of dispersed clay minerals reduces markedly both the residual strength and hydraulic diffusivity of till clay also reduces spatial variations in normal stress associated with grain bridges the walls bounding the specimen support only 9 17 of the total resistance to shearing strain was localized in both tills but not in the linear viscous putty strain localization in the tills indicates that their theology departs significantly from linear and bingham viscous models

coupled ice till deformation near subglacial channels and cavities previous models of ice till deformation near subglacial channels or cavities neglect the fact that the motions of the two materials are coupled and thus the interface between ice and till may not remain stationary here we analyze in succession two models which address the effect of such coupling via specification of appropriate continuity conditions for stress and velocity across the interface the modelled scenario is that of a shallow channel cavity with its long axis parallel to the principal ice flow direction overlying actively deforming till sediments by applying asymptotic techniques we investigate how the pattern and velocity of the creep flow depend generally on the ratio between the ice and till viscosities and on the deforming till thickness a more sophisticated non linear rheology for till sediments is then introduced it reveals that the two way interaction between water percolation and deformation in the till will enhance the localization of sediment flow near the channel margins the length scale over which transition of effective stress in the till takes place from its relatively high far field value to the low channel value is found to depend critically on a dimensionless permeability parameter a in any case coupled deformation causes sediment and ice flow towards the channel subsidence of the ice till interface just outside the channel and extension of the area over which the ice is in contact with till apart from having direct implications for subglacial sediment transport these results indicate that coupled deformation can contribute significantly to the spatial evolution of stress distribution under a glacier and thus its incorporation into future sliding and drainage theories for a soft bed should be considered essential

pressure dependent viscosity and interfacial instability in coupled ice sediment flow we study an interfacial instability in the coupled flow of ice and subglacial sediment both modelled as viscous media unlike other interfacial instabilities in coupled viscous flows at zero reynolds number the mechanism considered here does not rely on buoyancy or the effect of an upper free surface but on the pressure dependence of the sediment viscosity specifically the instability relies on sediment rheology being such that when sediment flows in simple shear sediment flux increases with compressive normal stress at the ice sediment interface when the velocity of the interface is kept constant when ice moves over a shallow bump in the interface it generates a higher compressive stress on the bump s upstream side than in its lee if in addition the effective sediment viscosity is low compared with that of ice interfacial velocity remains approximately constant and this then implies that more sediment flows into the bump than out of it causing it to grow modelling ice as a newtonian material we show that this mechanism works for a wide range of sediment rheologies including the highly nonlinear shear thinning ones typically thought most appropriate for the description of nearly plastic sediment the instabilities predicted are essentially two dimensional with infinite transverse wavelength and a nonlinear model shows that growth is unbounded until cavitation occurs in the lee of evolving bumps on the interface the instability mechanism does not seem to predict the formation of common glacial landforms but may explain the formation of water filled cavities on deformable glacier beds

the evolution of mesoscopic imbricate thrust faults an example from the vermont foreland u s a abstract an outcrop of a thin 30 cm bed of micrite surrounded by thicker sequences of well cleaved calcareous shale in the ordovician flysch of western vermont records a complex history of imbricate faulting and associated folding the calcareous shale has been shortened by pressure solution cross cutting relations among the floor ramp and roof faults indicate that faulting progressed from the hinterland east to the foreland west all the ramp faults developed from arrays of w climbing enechelon extension fractures all other faults were controlled by the weaker bedding planes that surround the micrite and are found at various levels in the shale each fault is marked by layers of highly twinned sparry calcite and black carbonaceous shale selvedge simple shear along the floor thrust has rotated the s1 cleavage toward the foreland and produced along with volume change a pressure solution cleavage in the fault zone all cleavages have progressively developed from the hinterland to the foreland during folding and faulting of the micrite layer parallel shortening measured in both rock types is between 11 and 16

crustal profile of mountain belt cocorp deep seismic reflection profiling in new england appalachians and implications for architecture of convergent mountain chains relatively shallow reflections from beneath the taconic allochthon and green mountain anticlinorium are suggested to mark a zone of detachment that carries precambrian grenville basement of the green mountains in its upper plate the data suggest that tectonic thickening of the shelf sedimentary and synorogenic flysch sequence beneath the taconic allochthon has occurred and that major thrust fault systems champlain thrust of western vermont which imbricate shelf lithologies project downplunge into the seismic profile eastward dipping reflections beneath the east flank of the green mountains appear to project across the connecticut river valley into new hampshire because some of these reflections can be projected into an exposed zone of probable thrust imbricated precambrian grenville basement and younger metasediments there is a strong implication that similar rock types exist in the deeper crust beneath new hampshire the gross geometry of the eastward dipping zone is a large thrust ramp that facilitated faulting of continental basement in the green mountains to higher structural levels thus suggesting the anticlinorium is a large hanging wall structure or ramp anticlinorium highly deformed satellitic massifs of grenville basement such as the chester dome and sub silurian and silurian devonian rocks of the bronson hill anticlinorium and merrimack synclinorium are probably transported along intracrustal detachments as well data suggest the possiblity of a tectonically buried continental margin transition zone much like that interpreted for the southern appalachians this zone would have been preserved from prior rifting of the proto atlantic ocean and its inherited geometry could have controlled subsequent convergent deformation during appalachian orogenesis although regional deep seismic reflection profiling has not been carried out across the alps existing data imply lateral changes in crustal reflection character similar to those observed in the appalachians deep seismic reflection data from convergent mountain belts raises the possibility of such preserved transition zones beneath transported rocks and provides an alternative interpretation to lithosphere penetrating sutures in explaining lateral geologic and geophysical contrasts in the crust modified journal abstract

stratigraphic relationships and detrital composition of the medial ordovician flysch of western new england implications for the tectonic evolution of the taconic orogeny a reply to rodgers we present new stratigraphic and petrographic data on the easterly derived medial ordovician flysch sequence of western new england and eastern new york state a conformable relationship exists between the flysch and underlying early paleozoic continental rise sediments within the western taconic allochthon farther east in the allochthon we observe a possibly disconformable relationship contrary to previous interpretations these facts suggest that at any place within this paleogeographic realm the sediments were undeformed and untransported at the initiation of flysch deposition at least three sources contributed detritus to the flysch 1 taconic sequence sediments 2 deformed and metamorphosed pelitic psammitic and volcanic lithologies and 3 igneous rocks of dominantly mafic ultramafic affinities these three sources are respectively interpretable as continental rise accretionary prism and ophiolitic volcanic arc assemblages which are recognized in the regional geology of western new eng

flow thermal structure and subglacial conditions of a surge type glacier temperature measurements in a subpolar surge type glacier reveal a distinctive thermal structure associated with the boundary between the ice reservoir and receiving areas in the receiving area the glacier is cold based but bottom temperature has increased as much as 0 5 c between 1981 and 1982 and the basal heat flux is roughly 10 times the expected geothermal flux water percolation through permeable subglacial material is the probable energy source deformation of the substrate could destroy this drainage system and trigger a surge

a model for the development of crenulations in shear zones with applications from the southern appalachian piedmont abstract two sets of crenulations are associated with a major alleghanian dextral shear zone which deformed stratigraphic and structural boundaries in the eastern piedmont of south carolina both sets of crenulation planes are oblique to the boundaries of the shear zone the morphologies and orientations of the crenulation sets and their spatial distributions indicate that they are related to slip along foliation planes and that they serve to compensate for displacement components of foliation slip normal to the overall movement direction in the shear zone the crenulations act to maintain the initial thickness of the shear zone our evaluation of the recent literature on shear zones suggests that crenulations related to foliation slip are abundant and constitute a reliable sense of shear indicator

present day stress analysis of the st lawrence lowlands sedimentary basin canada and implications for caprock integrity during co2 injection operations abstract a geomechanical analysis of the st lawrence lowlands sedimentary basin is important to reliably estimate the maximum sustainable fluid pressures for co 2 injection that will not reactivate pre existing faults in the caprock thereby inducing a breeched co 2 reservoir this requires the determination of prevailing stresses orientations and magnitudes fault and fractures geometries and rock strengths the average maximum horizontal stress orientation s hmax is estimated n59 e 20 in the st lawrence lowlands the stress orientations were obtained from stress induced wellbore breakouts inferred from four arm dipmeter caliper data in 17 wells these wellbore failure features are confined to paleozoic lithological units of the st lawrence platform succession and frontal thrusts of the quebec appalachians at depths from 250 m to 4 km our results are consistent with the regional ne sw s hmax stress orientation trend that is generally observed in eastern canada and the u s the stresses pressure gradients estimated for the st lawrence lowlands depths hmin 20 5 3 kpa m s v 25 6 kpa m s hmax 40 7 5 kpa m pore pressure p p 9 8 kpa m indicating a strike slip stress regime s hmin v hmax the high angle ne sw regional faults and fractures in the paleozoic sedimentary succession and the grenvillian basement are oblique to the s hmax stress orientations 10 to 36 and could be reactivated slip tendency 0 34 to 0 58 under the present day stress field if fluid pressures exceeded the critical threshold further refinement of regional geomechanical model is required to estimate the maximum sustainable injection pressure necessary for shear reactivation along the regional faults the regional pore pressure stress coupling ratio under assumed parameters is about 0 5 0 65 and may contribute to reduce the risk of shear reactivation of faults and fractures the maximum sustainable p p that would not cause opening of vertical tensile fractures during co 2 operations is about 18 5 20 mpa for the depth of 1 km

abrupt glacier motion and reorganization of basal shear stress following the establishment of a connected drainage system three episodes of strong basal motion occurred at trapridge glacier yukon territory canada on 11 june 1995 following the establishment of a connected subglacial drainage system responses to these spring events are noted in the records for 42 instruments and were recorded throughout the 60 000 m study area strong basal motion during the events is indicated by ploughmeter load bolt and vertical strain records and abrupt pressure changes in several transducer records denote damage caused by extreme pressure pulses these pressure pulses generated by the abrupt basal motion also resulted in the failure of seven pressure sensors records for pressure turbidity and conductivity sensors indicate that basal drainage patterns did not change significantly during the events geophone records suggest that the episodes of basal motion were precipitated by the gradual failure of a sticky spot following hydraulic connection of part of the study area this failure resulted in the transfer of basal stress to the unconnected region of the bed during the course of the events no evidence for strong basal motion is seen in the instrument records for several weeks following the events suggesting that the mechanical adjustments resulted in a stable configuration of basal stresses this event illustrates how unstable situations can be quickly accommodated by mechanical adjustments at the glacier bed

effects of irregular basement structure on the geometry and emplacement of frontal thrusts and duplexes in the quebec appalachians interpretations from well and seismic reflection data abstract irregular basement geometry may affect thrust propagation in foreland fold thrust belts creating a perturbation in structural continuity of hydrocarbon fields here we investigate how the irregular pattern of normal faults along with the presence of uplifts and transverse faults in the grenvillian basement has influenced the geometry and emplacement of frontal thrusts and duplexes in the parautochthonous domain of the southern quebec appalachians during the middle late ordovician taconian orogeny integration of data from surface geology wells and 2d and 3d seismic reflection surveys into a regional scale structural model is used to reconstruct the 3d geometry and emplacement history of one and two horse duplexes in the joly saint flavien gas storage area the normal hinterland to foreland sequence of thrusting in this area is complicated by the differential emplacement of tectonic slices along strike of the orogenic front starting in the sw and developing subsequently to the ne within each structural level the shortening related to duplex emplacement decreases laterally over the distance of 20 km from 49 in the sw joly area to 31 in the ne saint flavien area duplex emplacement resulted from the differential forward propagation deflexion and vertical axis rotation of the roof thrust logan s line which in turn has been induced by the presence of frontal uplift and transverse faults in the basement the structural lithological analysis of tectonic slices and restoration of their initial location allows us to consider the lower slice of the joly duplex as a structural trap comparable to the fractured reservoir in lower ordovician dolomites of the saint flavien duplex

rheological nonlinearity and flow instability in the deforming bed mechanism of ice stream motion contrary to what has recently been assumed in modeling the proposed deforming bed mechanism for the rapid motion of antarctic ice streams the rheology of water saturated till is probably highly nonlinear according to information from soil mechanics and preliminary experiments on till from the base of ice stream b the equivalent flow law exponent n is probably as high as 100 and the nonlinearities of the shear stress and effective pressure dependences are closely linked the high nonlinearity has important consequences for the deforming bed mechanism a flow system operating by this mechanism can be unstable as a result of feedback from the generation of basal water by shear heating of basal till the short term feedback effect is analyzed for a perturbation in a model ice stream in which the basal meltwater is transported through a distributed system of narrow gap conduits at the ice till interface although the analysis is approximate and some of the system parameters are poorly known the results suggest that the deforming bed mechanism is unstable for n 20 the apparent lack of such an instability in the currently active ice streams implies that their motion is controlled not by the deforming bed mechanism but by some other as yet unidentified mechanism

lower plate geometry controlling the development of a thrust top basin the tectonosedimentary evolution of the ofanto basin southern apennines the ofanto basin is a pliocene pleistocene thrust top basin that formed with an unusual east west orientation along the frontal part of the southern apennine allochthon during the latest stages of tectonic transport its tectonic and sedimentary evolution was studied integrating field surveys biostratigraphic analyses and the interpretation of a large seismic grid well data and seismic interpretation indicate that a large east west trending normal fault underlies the northern margin of the basin displacing the apulian carbonates that form the foreland and the footwall of the southern apennine allochthon in our reconstruction the ofanto basin formed at the rear of the bulge caused by buttressing of the southern apennine allochthon against this normal fault in a second stage of contraction the footwall of the southern apennine allochthon was involved in deformation with a different trend from the normal faulting and buttressing this caused eastward tilting of the basin and broad folding around its eastern termination good stratigraphic constraints permit the age of buttressing to be defined as early pliocene and that of the shortening in the apulian carbonates as early pleistocene this study highlights the importance of early orogenic normal faults in conditioning the evolution of the frontal parts of orogenic wedges supplementary material a 3d reconstruction of the base of the pliocene deposits of the ofanto basin based on seismic interpretation is available at www geolsoc org uk sup18559

basal mechanics of ice stream b west antarctica 1 till mechanics data from laboratory geotechnical tests on till recovered from beneath ice stream b west antarctica at the upstream b camp hereinafter the upb till show that failure strength of this till is strongly dependent on effective stress but is practically independent of strain and strain rate these data support use of a coulomb plastic rheology in modeling of ice stream behavior and subglacial till deformation our testing program combined triaxial ring shear and confined uniaxial tests to investigate till strength and compressibility results show that the upb till follows closely coulomb s equation in which shear strength is a linear function of normal effective stress apparent cohesion near zero and internal friction angle equal to 24 till compressibility is best described by a logarithmic function that relates void ratio to normal effective stress in general the behavior of the upb till is consistent with other experimental evidence regarding mechanical behavior of granular materials based on our laboratory results we formulate the compressible coulomb plastic till model in which there are three interrelated primary state variables shear strength void ratio and normal effective stress this model is used in the second part of our study to simulate response of subglacial till to realistic effective stress forcings these simulations demonstrate that the model is capable of reproducing fundamental aspects of subglacial till kinematics 1 occurrence of tilt rate oscillations and negative tilt rates in tiltmeter records and 2 distributed till deformation to depths of 0 1 1 0 m beneath the ice base our laboratory and modeling results substantiate application of the compressible coulomb plastic model in simulations of the motion of ice stream b over its weak till bed

normal faults in thrust sheets pre orogenic extension post orogenic extension or both abstract in fold and thrust belts that experienced both pre orogenic and post orogenic extension it may be difficult to establish whether observed normal faults pre dated post dated or were synchronous with thrusting geometrical structural patterns may be insufficient to constrain the relative chronology of extensional and contractional deformations the systematic use of kinematic criteria makes it possible to unequivocally define the timing relationships of reverse and normal fault development and hence to correctly unravel complex structural evolutions kinematic analysis in the southernmost umbria marche apennines of italy where both normal and thrust faults are present revealed a history of repeated tectonic inversion characterised by two distinct stages of extension separated by an episode of folding and thrusting structural overprinting relationships observed at thrust normal fault intersections were useful for i removing sequentially younger deformations and hence ii separating and quantifying the effects of orogenic contraction from those of both pre orogenic and post orogenic extension

pre syn and post imbrication deformation of carbonate slices along the southern quebec appalachian front implications for hydrocarbon exploration thrust imbricated shelf carbonate slices form a wide but poorly understood part of the southernmost quebec appalachian structural front comprehensive structural analysis of two slices exposed at surface the saint dominique and philipsburg slices shows that pre and post imbrication structures are important in defining the final architecture of the slices the dominant structural style is characterized by thrusts and associated asymmetrical folds tear faults oblique ramps and incipient backthrusts developed during wnw ese shortening a forward breaking piggy back sequence of thrusting is recognised as well as minor out of sequence thrusting the complexity and diversity of contractional structures is directly influenced by lithology bed thickness and shale content bedding parallel slip planes are important in the concentration activation and reactivation of deformation in that there are the loci for veining faulting and folding recognition of lithostructural units provides guidelines for t

strike slip interpretation of basin bounding faults of the st lawrence lowlands basin in the quebec city area canada traditional structural interpretations of faults identified in the autochthonous ordovician platform rocks of the st lawrence lowlands basin of quebec canada assert that the primary sense of faulting is normal extensional and dip slip in motion interpretation of field observations such as the offset of facies boundaries in outcrop fault surface features fracture patterns and fault volume considerations lead directly to difficulties with a mobile crustal bulge model for normal faulting newly reprocessed seismic data and well log correlations support this interpretation and indicate a need for a different model for the deformation of the platform margin a left lateral basement involved wrench system resolves stratigraphic discordances across fault zones contradictions in the observed geometry of hanging wall blocks problems concerning timing of tectonic events and the difficulty of using extensional deformation models in a compressional setting this reinterpretation places the timing of the platform faulting just prior to the arrival of the taconic thrust sheet the lateral offset of subsurface and surface depositional facies fault trace features well correlations and seismic expressions document approximately 60 km of left lateral strike slip motion in the st lawrence lowlands basin

deformation styles at the appalachian structural front western newfoundland implications of new industry seismic reflection data new seismic reflection data gathered during hydrocarbon exploration in and adjacent to the external humber zone western newfoundland have important implications for the interpretation of structural style at the appalachian front these new data indicate that the structural front is influenced by both thin skinned and thick skinned structures where the structural front is thin skinned it is characterized by a triangle zone or tectonic wedge similar to structures observed at the southeastern margin of the canadian cordillera and at other orogenic fronts the thin skinned tectonic wedge is overridden locally by thick skinned thrusts which are generally emergent but are locally blind forming a thick skinned tectonic wedge timing relationships indicate that although initial motion occurred during the early to middle ordovician taconian orogeny the thin skinned allochthonous slices in western newfoundland were not emplaced until devonian time the acadian orogeny thick skinned deformation which p

including strain data in balanced cross sections abstract almost all published balanced cross sections include cleaved and or strained rocks and may therefore violate the requirement that bed lengths and formation areas are preserved between undeformed and deformed states knowledge of distortions presence and type of cleavage and overprinting relations in poly deformed segments are necessary to define area changes related to volume loss strike elongation and poly deformation work in the southern and central appalachians has shown variation in structural complexity and changing deformation styles both along and across the thrust belt this necessitates separate treatment of individual sheets during balancing regions of little or no interstratal slip pinning points should be chosen for each thrust sheet and each fold strain in the sheet in external sheets where deformation intensity increases towards thrusts pin points should be back limb inflection points in intermediate and internal sheets where cleavage is approximately coeval with folding pin points should be at fold hinges where cleavage and strain are heterogeneously developed throughout a stratigraphic sequence a line length balance using massive relatively uncleaved beds e g knox group southern appalachians can be used as a basis for restoring the section unstraining of deformed layers given strain data and cleavage trajectories for individual thrust sheets provides line lengths and formation areas which can be fitted to the key bed of the undeformed section cleavages which partially or fully postdate folding indicate continued shortening in the thrust wedge and modify earlier pinning points in upper sheets these cleavages and poly deformed segments are difficult to restore as strain data are generally scarce in the metamorphosed internal thrust sheets

reactivation of prethrusting synconvergence normal faults as ramps within the ordovician champlain taconic thrust system we present new geologic maps of the lake champlain region of west central vermont and east central new york state this region contains a shallow crustal section of an ordovician foreland basin and a far traveled thrust system that transported the upper cambrian lower ordovician platform sequence allochthonous rise facies pelites and arenites and middle ordovician basinal shales and flysch early foreland and shelf sections are cut by post depositional cross faults within the thrust system and the required stratigraphic throw across the cross faults is not matched by the amount they offset the thrust planes as thrust structures these cross faults control structural style and kinematics by laterally bounding regions that contrast sharply in amount of thrust imbrication duplexing and net transport the dominant set of normal faults in the autochthon which had time correlative slip with the thrust system cross faults is oriented parallel to the paleotrench though there is also a subordinate transverse linking set the normal faults developed in response to the migrating flexural forebulge during convergence between the laurentian margin and the accretionary prism above an outboard facing subduction zone within the thrust system any prethrust normal faults that were parallel to the paleotrench are largely masked by thrust structures however an out of sequence thrust which emplaced shelf rocks above the westernmost allochthon and surrounding parautochthonous shale may have localized on a paleotrenchparallel normal fault in the outer shelf we also identify a postthrust normal fault that significantly obscures the original thrust map pattern reactivation of synconvergence prethrust flexure induced normal faults adequately explains many otherwise puzzling stratigraphic and structural relationships in the taconic foreland

distribution and characteristics of taconian and acadian deformation southern quebec appalachians the regional structure of the southern quebec appalachians is redefined in terms of superposed taconian and acadian deformation events taconian structures and metamorphism dominate in cambro ordovician rocks west of the baie verte brompton line bbl the taconian orogen is subdivided into a northwestern external zone composed of fault imbricated continental rocks displaying single phase foreland structures and a south eastern internal zone of polydeformed and metamorphosed continental and oceanic rocks the structural relationships of cambro ordovician rocks astride the bbl demonstrate that the continent ocean contact was deformed by both southeast verging late taconian and upright acadian folds east of the bbl syn and post taconian rocks were mainly affected by acadian deformation the acadian external zone consists of cambro ordovician and post ordovician rock units characterized by a single phase of folding the zone is bounded to the southeast by the riviere victoria fault the acadian internal zone displays polyphase deformation in the easternmost part of the quebec appalachians the acadian deformation shows a significant overlap with taconian structures and metamorphism and structural windows of the taconian orogen are found within both the external and internal zones of the acadian orogen

peritidal origin of the lower ordovician upton group southern quebec appalachians the lower ordovician upton group is part of the cambrian ordovician external domain of the appalachian orogen of southern quebec it is a mixed carbonate siliciclastic volcanic succession occurring

multiple origin and regional significance of bedding parallel veins in a fold and thrust belt the example of a carbonate slice along the appalachian structural front abstract the development and evolution of bedding parallel veins bpv are investigated in the saint dominique carbonate slice southern quebec appalachian structural front in order to emphasize the regional significance of bpv in a fold and thrust belt and their importance in establishing its structural and diagenetic evolution structural and microstructural analyses reveal that most bpv display a laminated structure locally crosscut by a massive one both structures show mutual crosscutting relationships with bedding parallel or bedding perpendicular stylolites and with bedding perpendicular veinlets indicating that bpv cementation and deformation are continuous processes opening both sub parallel and sub perpendicular to the bpv walls are documented early bpv are planes of weakness that focus later reactivation and evidence of successive and sometimes opposite senses of opening are locally preserved within a single bpv the bedding parallel orientation of these veins proved particularly helpful in establishing the structural evolution of an area mostly characterized by front parallel structures with little crosscutting relationships otherwise petrographic and geochemical 18 o vpdb and 13 c analyses of structural cements suggest a common locally derived source for the fluids that percolated through bpv non bedding parallel veins and faults the isotopic ratios also reveal a significant enrichment in 18 o and 13 c through time this evolution is tentatively correlated with tectonic syn convergence exhumation of the saint dominique slice during its imbrication along the appalachian structural front after its burial under taconian thrust sheets

experiments on the dynamics and sedimentary products of glacier slip abstract experimental work in glacial geomorphology is focused almost entirely on processes in the thin shear zone at the beds of sliding glaciers where ice at its pressure melting temperature moves over either rigid rock or deformable till experiments with rotary shear devices illuminate constitutive behavior there central to the dynamics of fast moving glaciers and provide a foundation for interpreting the sedimentary record of glacier slip and associated sediment transport results from experiments designed to study ice sliding over a rigid wavy bed shear deformation of till and plowing of clasts across the surface of a till bed point to a common conclusion drag at the bed can decrease with increasing slip velocity thereby concentrating driving stress elsewhere and promoting rapid glacier flow this rate weakening behavior at glacier beds is in contrast to the viscous slip resistance assumed in ice sheet models and most efforts to determine distributions of basal drag from glacier surface velocities ring shear experiments in which various basal tills and more idealized materials are sheared to high strains provide quantitative insight into grain size evolution mixing at contacts between basal tills microstructure development particle fabric development and development of anisotropy of magnetic susceptibility preferred orientations of principal magnetic susceptibilities provide the most dependable and complete description of till shear patterns when applied to basal tills of the geologic record magnetic till fabrics measured along thick till sections and calibrated experimentally indicate that deformation of the bed by two lobes of the laurentide ice sheet was shallow

discrimination of the flow law for subglacial sediment using in situ measurements and an interpretation model 1 subglacial hydrological and mechanical processes play a critical role in determining the flow characteristics and stability of glaciers and ice sheets to study these processes we have measured simultaneously basal water pressure pore water pressure sediment deformation glacier sliding and sediment strength beneath trapridge glacier yukon territory canada to interpret these data we have developed a simple hydromechanical model of processes beneath a soft bedded alpine glacier the glacier bed is divided into soft bedded regions that are hydraulically connected to the subglacial drainage system soft bedded but hydraulically unconnected regions and hard bedded regions each region is represented as a one dimensional column the columns are coupled by a simple ice dynamics model that accounts for water pressure driven changes in basal shear stress distribution synthetic responses for subglacial instruments are calculated from the modeled basal conditions providing a framework for improving interpretation of field records the model is used to determine which of several till flow laws best represents conditions beneath trapridge glacier investigated are linear viscous nonlinear viscous nonlinear bingham and coulomb plastic tills pore water pressures sediment deformation profiles and sliding rates are calculated for each flow law comparison of synthetic and field instrument responses suggests that till behavior is best represented as coulomb plastic model results also suggest that the ploughmeter is the most diagnostic in situ indicator of till behavior currently available and that using long term observations of sediment deformation profiles in regions of varying pore water pressure can result in an underestimation of flow law nonlinearity

the stability of a viscous till sheet coupled with ice flow considered at wavelengths less than the ice thickness a turbation method is used to analyse the stability of a thin till layer overlain by a deep ice layer ice is modelled as a linearly viscous fluid while the till viscosity has power law dependence on stress and effective pressure a linearized set of equations yields descriptions of the coupling of the ice flow with the sediment flow and reveals parameter ranges where the till perturbation amplitude can grow this shect flow instability is an essential part of any theory of drumlin formation and shows that viscous models of till have the ability to explain typical deforming bed features this is of great significance for large scale ice shect modelling

tectonic synthesis of the taconian orogeny in western new england a tectonic synthesis based on stratigraphic and structural analysis of western new england is proposed for the ordovician taconian orogeny it emphasizes arc continental collision in which ocean floor continental margin and ensialic rift rocks were imbricated westward in a repeatedly deformed accretionary wedge continued compression displaced segments of the north american sialic crust to the west and deformed the earlier emplaced slices of the taconic allochthons which were derived from the continental margin critical arguments for this synthesis are 1 the west to east stratigraphic relations among the basal rift clastic rocks of the dalton pinnacle and hoosac formations of late precambrian to early cambrian age 2 the stratigraphic and sedimentological similarities between the rocks of the lower taconic sequence and rocks in the pinney hollow and underhill slices to the east and north of the green mountain massif 3 the environmental similarities between the cambrian and lower ordovician section of the giddings brook slice and the age equivalent section in the st albans synclinorium 4 the presence of carbonate platform rocks as slivers between each of the successively higher and younger premetamorphic slices groups 1 and 2 of the taconic allochthons 5 the presence of synmetamorphic fault related structures in the youngest and highest slices group 3 of the taconic allochthons 6 the recognition of extensive thrust zones in the pre silurian eugeoclinal sequence east of the middle proterozoic basement of the housatonic berkshire green mountain and lincoln massifs 7 the location of the taconic root zone within the pre silurian eugeoclinal sequence 8 the recognition of numerous faults in the serpentinite belt 9 the similarity between the rocks of the moretown formation and modern fore arc basin sequences 10 the recognition that the volcanic arc continental complexes of the ascot weedon and bronson hill have been displaced westward over the moretown and or hawley formations along such faults as the bristol and coburn hill thrusts 11 the allochthonous and internally imbricated nature of the north american basement in the berkshire massif 12 the proposition that the housatonic green mountain and lincoln massifs as well as the middle proterozoic cored domes of southeastern vermont are also thick sialic slices of north american basement 13 the recognition of medium high to high pressure metamorphic mineral assemblages in the pre silurian eugeoclinal rocks of vermont and 14 the recent synthesis of isotopic age data by sutter and others 1985 on the basis of an analysis of the foregoing arguments and relationships a chronological sequence of seven structural sections between albany new york and the bronson hill anticlinorium in central massachusetts is used to depict the evolution of the taconian orogeny retrodeformed distances are based on structural overlap and restoration of the taconic slices to their depositional setting along the ancient north american continental margin these easterly younging diverticulated slices formed as a result of horizontal compression rather than gravity sliding this palinspastic analysis implies the following 1 approximately 1 000 km of shortening has occurred during the emplacement of the taconic allochthons and the subsequent imbrication of north american basement as thick sialic slices approximately 330 km of this shortening is attributed to multiple cleavage generations 2 repeated movement along such major surfaces as the cameron9s line whitcomb summit belvidere mountain thrust zone has buried the taconic root zone we suggest that the northern extension of this root zone is exposed to the east of the lincoln massif in vermont where the underhill pinney hollow and hazens notch formations are exposed these formations here considered thrust slices disappear along the belvidere mountain whitcomb summit thrust zone as it is traced southward into western massachusetts and western connecticut 3 taconian metamorphic rocks particularly the older medium high pressure rocks in northern vermont have been transported westward on such reactivated surfaces as the belvidere mountain thrust 4 the anticlinorial form of the middle proterozoic basement in the green mountain and lincoln massifs may have resulted from fault bend folding on deep mantle involved thrusts that developed late in the taconian orogeny

taconian melanges in the parautochthonous zone of the quebec appalachians revisited implications for foreland basin and thrust belt evolution in the quebec appalachians disruption imbrication and thrusting of the taconian foreland basin sequence are responsible for the development of chaotic units within the turbiditic sequence of the caradocian sainte rosalie group the main lithologic assemblage of the parautochthonous zone these chaotic units have been termed olistostromes or tectonosomes on the basis of field criteria and following pini s 1999 classification olistostromal units containing blocks of the middle mudstone utica shale and upper turbidite units ste rosalie group of the foreland basin and spanning the caradocian n gracilis c americanus o ruedemanni and c spiniferus graptolite zones were deposited and incorporated into the sainte rosalie group disruption of more competent beds of the flyschic sequence and fault stacking and slicing of older rock units occurred along major thrust faults and now form structurally aligned corridors or tectonosomes graptolites and new chitinozoan data from both olistostromes and tec

till beneath ice stream b 1 properties derived from seismic travel times seismic experiments conducted on ice stream b part of the marine ice sheet of west antarctica show a meters thick layer immediately beneath the 1000 m thick ice a seismic experiment consisting of wide angle reflection profiling along a line parallel to ice stream flow was conducted to determine the properties of this layer inversion of seismic travel times yields a compressional wave speed of less than 1700 m s 1 and a shear wave speed less than 160 m s 1 for the layer these very low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure based on wave speeds in other saturated unconsolidated sediments we believe that a porosity substantially greater than 0 32 probably around 0 4 and an excess of overburden pressure over pore pressure of only 50 kpa 0 5 bar characterize the layer at this location

the opening of the atlantic the mesozoic new england igneous province and mechanisms of continental breakup abstract plume and tensionally induced rifting models have been proposed as causes of continental rifting and breakup mantle plumes should produce early lithospheric doming events associated with alkaline magmatism however the triassic alkaline rocks on the east north american e n a margin are structurally localized the uplifts are mostly jurassic in age and voluminous plateau magmatism post dates the initiation of taphrogenesis by 10 to 20 ma in addition there are no chains of anorogenic igneous rocks leading to any of the postulated triassic plumes these facts argue against the plume generated rifting model for the e n a margin but are consistent with the predicted effects of the tensionally induced rifting model the genesis of linear chains of alkaline rocks has been attributed to passage of a lithospheric plate over a mantle plume this explanation has been proposed for the cretaceous monteregian and white mountain intrusive series and the kelvin seamount chain however these rocks are distributed along structurally controlled e w trending lineaments the monteregians are localized by the presence of a paleorift ottawa bonnechere graben in the underlying grenvillian basement and the kelvin seamounts are emplaced along the early jurassic kelvin fracture zone the structures localizing the southern white mountain lineament are less well defined the spatial temporal and geochemical relationships along and between these lineaments are consistent with an origin as a southeastward propagating tensional event the intra plate stresses are probably the result of shifts in the pole of rotation of the north american plate due to irregular northward extensions of seafloor spreading during the cretaceous

geometry and style of post obduction thrusting in a paleozoic orogen the taconic frontal thrust system the taconic frontal thrust system associated with the later stages of the medial ordovician taconic orogeny a continental margin volcanic arc collision defines the present western boundary of the taconic allochthon in eastern new york and west central vermont the frontal thrust emplaces regionally folded and foliated taconic rocks over deformed but essentially unmetamorphosed flysch the frontal thrust is temporally and kinematically related to the champlain and orwell faults to the north that emplace variably deformed sections of early paleozoic shelf rocks over partially coeval sections of the early paleozoic platform major movement on these faults occurred after initial obduction of the allochthon onto the early paleozoic north american continental shelf and prior to being unconformably overlapped by the early devonian this fault system is considered to be part of the final phase of a continuum of thrusts that evolved during the taconic orogeny and therefore records only the final emplacement

maturation thermique de la matiere organique dans un bassin du paleozoique inferieur basses terres du saint laurent quebec canada the organic matter om sampled in 15 oil exploration wells and 102 outcrops of cambrian ordovician rocks in the st lawrence lowlands consists of zooclasts chitinozoans graptolites and scolecodonts and solid bitumen mainly pyrobitumen the reflectance of pyrobitumen transformed in vitrinite equivalent ro std b indicates that the upper part of the platform sequence is mature condensate zone in the quebec area but overmature in the montreal area the platform is divided into three domains based on optical texture of om and types of bitumen domain 1 south of montreal contains a highly reflecting and coked pyrobitumen showing alteration rims domain 3 east of trois rivieres contains low reflecting late solid bitumen commonly associated with oil impregnations domain 2 located midway contains a pyrobitumen with moderate reflectance and locally fine mosaic texture the thermal maturation in the autochthonous sequences of the st lawrence lowlands and in the appalachian allochthons increas

brittle fault evolution of the montreal area st lawrence lowlands canada rift related structural inheritance and tectonism approached by palaeostress analysis the montreal area belongs to the st lawrence lowlands a cambrian early ordovician passive margin of the iapetus ocean later covered by appalachian middle to upper ordovician foreland deposits a structural and palaeostress analysis has been carried out in order to reconstruct its tectonic evolution the structural map has been revised with new data palaeostresses are reconstructed based on inversion of fault slip data and these results are independently corroborated by the microstructural study of calcite mechanical twinning field relationships are used to establish the relative chronology of fractures and to deduce the motion on regional faults the reconstructed structural and tectonic evolution brings to light some relationships between structural inheritance and tectonic events that have affected the area since early palaeozoic times an early nw se extension is responsible for n040 trending faults along the northern border of the st lawrence lowlands and for n090 and n120 trending faults cross cutting the montreal area this extension is followed by wnw ese and nnw compressions which have induced reverse motion on pre existing faults and generated strike slip conjugate faults subsequent ne sw and nnw sse directed extensions have reactivated previous faults with normal to strike slip motions a late ne sw compression is recorded in the monteregian plutons compressions in wnw ese and nnw directions are consistent with appalachian collisional tectonism but n040 and n090 trending faults cross cut appalachian folds and foreland deposits although the early nw se extension is consistent with the collapse of the iapetan margin in early palaeozoic times most of the present geometry of the st lawrence lowlands could be attributed to mesozoic tectonism recorded as nearly n s directed extensional events

exploring glacier dynamics with subglacial water pressure pulses evidence for self organized criticality 1 in order to determine whether brief excursions or pulses in subglacial water pressure inferred by kavanaugh and clarke 2000 2001 occur water pressures at the bed of trapridge glacier yukon canada were recorded using an interface board that continuously monitored a pressure transducer during the 231 day period between 16 july 2005 and 4 march 2006 more than 7000 pressure pulses were recorded with magnitudes reaching nearly 3 times the flotation value comparison of the pressure pulse record with those from a number of other instruments installed in this soft bedded glacier indicates that these pulses are generated by stress transients that compress the water within the borehole calculations suggest that these transients are as large as 75 times the nominal driving stress both the magnitudes and interevent times for these pulses are well fitted by power law distributions that are remarkably similar to those exhibited by earthquakes these similarities suggest that the ice bed interface of a soft bedded glacier behaves much like an earthquake fault and raises the possibility that such glaciers self organize to a critical state further evidence for self organized criticality soc of soft bedded glaciers is suggested by an examination of well known ice dynamical properties and the rheological properties of subglacial sediments which suggests that soc might be a natural consequence of the rate independent behavior of subglacial sediments

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

alleghanian paleostress reconstruction in the northern appalachians intraplate deformation between laurentia and gondwana a numerical paleostress tensor analysis using striated fault planes has been conducted in the quebec reentrant of the northern appalachians to characterize the stress field of late paleozoic deformations three directions of maximum compressional stress axes s1 have been found and correlated to 1 an early north northwest south southeast compression 2 a north northeast south southwest compression and 3 a late west northwest east southeast compression fault populations associated with these stress regimes are present in all tectonic zones of the quebec and northern new brunswick appalachians directions of 1 axes determined in the northern appalachians resemble in orientation and in relative chronology layer parallel shortening fabrics and joint patterns found in the appalachian foreland of the central appalachians the paleostress regimes are interpreted as the record of intraplate deformation related to the indentation of gondwana into laurentia during the late paleozoic alleghanian orogeny

subglacial till a physical framework for its properties and processes the continuum theory of mixtures provides a framework around which present knowledge of subglacial till can be organized the proposed framework is provisional in two senses the constitutive description of till will require improvement and not all potentially significant processes have been included till is treated as a three component mixture of water clasts coarse grained solids and fine grained matrix solids these components obey mass balance equations and their behavior is subject to constitutive relations that describe such processes as darcian water transport fine grained sediment transport consolidation shear deformation dilatancy and comminution five state variables uniquely determine the compressibility permeability shear strength and other physical properties numerical solutions of the state evolutions equations illustrate that the properties of till are highly responsive to changes in the subglacial environment