seismic reflection borehole and outcrop geometry of late wisconsin tills at a proposed landfill near toronto ontario the search for new landfill sites in the greater toronto area of southern ontario canada is producing a wealth of data regarding the subsurface stratigraphy and geometry of late wisconsin 25 ka

mg perovskite silicate melt and majorite garnet silicate melt partition coefficients in the system cao mgo sio2 at high temperatures and pressures we report the results of a mg perovskite silicate melt and a majorite garnet silicate melt elemental partitioning experiment conducted at high pressures and temperatures in the synthetic system cao mgo sio2 partition coefficients for some refractory lithophile elements e g sc sm deviate significantly from unity if mg perovskite segregated from a terrestrial magma ocean it would impart nonchondritic refractory lithophile element ratios such as sc sm to the primitive upper mantle of earth contrary to inference based on analyses of naturally occurring samples either earth was never substantially molten at the end of accretion or segregation of minerals from magmas was suppressed by vigorous convection it is difficult to avoid melting earth during accretion so the latter alternative seems more plausible

were deforming subglacial beds beneath past ice sheets really widespread abstract the concept of widespread large strain deformation of subglacial unconsolidated unfrozen sediments during pleistocene glaciations has inconsistencies in the geological record numerous properties of tills and related sediments are difficult to reconcile with pervasive strains as predicted by the deforming bed theory while accepting glacier bed deformation as a geological process occurring under certain circumstances we propose that it was much less widespread than believed by some instead we believe that basal sliding and englacial transport are major ice movement and debris transport mechanisms

facies architecture and sequence stratigraphy in glacially influenced basins basic problems and water level glacier input point controls with an example from the quaternary of ontario canada abstract sequence architecture is controlled by two fundamental factors the water level relative to the depositional surface which controls accommodation space and the points or areas of sediment injection which control how this space is filled in relative water level accommodation space and injection points normally vary together and various genetic terms are used to define systems tracts but in glacially influenced basins accommodation space is controlled not only by water level but also by the glacier injection points are similarly dually controlled by water level and by the terminus of the glacier during high lake levels the injection point of the glacier may be underwater at the base of the slope genetic terms like highstand and lowstand therefore are meaningless in successions controlled by sediment input points which are independent of water levels and accommodation space distinct water level and glacier input point systems can occur side by side the water level system controlled by lake level or sea level the glacier input point system controlled by the position of the subaqueous glacier front and both can form juxtaposed systems passing laterally into each other a bewildering and incompatible terminology is needed if the terms of genetic sequence stratigraphy are used for both water level and glacier input point systems because the sedimentary injection points and sequence boundaries of the two systems fluctuate out of phase with one another sequences developed by movement of the glacier are completely independent of those controlled by water levels if genetic sequence stratigraphy is applied to a basin with both lake level and glacier input point systems then each needs separate genetic terminologies to describe them which leads only to confusion however descriptive sequence stratigraphy allostratigraphy can be readily applied to successions like the quaternary of lake ontario we therefore suggest that genetic sequence terms be discarded and simpler allostratigraphic terminology used in glacially influenced basins

no liquid immiscibility in the system mgsio3sio2 at 5 0 gpa liquid us phase relationships in the system mgsio3 sio2 at 5 0 gpa have been determined using a multianvil apparatus compared to phase relationships at 1 atm the mgsio3 sio2 phase diagram at 5 0 gpa is significantly different in two respects first the composition of the eutectic between mgsio3 and sio2 moves from 65 0 wt sio2 at 1 atm 1547 c protoenstatite cristobalite eutectic bowen and andersen 1914 to 68 8 wt sio2 orthoenstatite coesite eutectic at 5 0 gpa 1930 c second no stable two liquid field is present in the mgsio3 sio2 system at 5 0 gpa the unbroken coesite liquidus curve is inflected indicating the presence of a submerged metastable miscibility gap below the liquidus thus although the temperature of the solvus critical point is likely to increase with pressure the dt dp slope of the sio2 liquidus is much steeper and as a result the immiscibility dome has become submerged completely the reduction in liquid immiscibility in the mgsio3 sio2 system at 5 0 gpa implies that in more complex systems relevant to the earth immiscibility will also be suppressed at high pressures copyright 1997 elsevier science ltd

environmental significance of bedrock jointing in southern ontario canada the bedrock surface of many glaciated areas is obscured by thick drift deposits in southern ontario canada the buried bedrock surface is dissected by channels infilled with glacial deposits as much as 150 m thick that are part of a wider mid continent preglacial fluvial system that predates formation of the modern great lake basins the infills of bedrock channels form major groundwater aquifers influence regional groundwater flows and contaminant migration to lake ontario and may localize the release of thermogenic methane and radon within heavily urbanized surface environments a quantitative comparison of the regional pattern of bedrock joints and the orientation pattern of buried bedrock channels and modern river valleys shows that all these orientation patterns are virtually coincident buried bedrock channels in south central ontario are not part of a simple antecedent drainage system but were likely predesigned by bedrock joint patterns that have subsequently been propagated upward into overlying pleistocene sediments joints in sediments are of considerable environmental significance for example subsurface contaminant and gas migration in fine grained clayey sediments and of many origins stress release desiccation etc but are widely assumed to be a predominantly surface related phenomena the existence of deeper joints has been noted by some authors but their origin is obscure data presented herein from south central ontario confirm that in addition to surface related joints a second population of bedrock related joints reflecting the upward propagation of bedrock fractures is present in pleistocene sediments of south central ontario

sedimentation in a large lake a reinterpretation of the late pleistocene stratigraphy at scarborough bluffs ontario canada a lithofacies code developed for diamicts emphasizes facies variability in the classic upper pleistocene glaciogenic sequence at scarborough bluffs ontario canada lithological breaks along the bluffs are traditionally assigned to incursions of grounded ice margins and to interstadial lakes formed during ice retreat during the early and middle wisconsin detailed sedimentological logging through three diamict units previously formalized as sunnybrook seminary and meadowcliffe tills and intervening sandy lithofacies shows absence of glaciotectonic structures and diamicts associated with grounded glacier ice traction current activity during diamict accumulation postdepositional resedimentation of diamicts into topographic lows accompanied by turbidite activity a subaqueous deltaic origin for intervening sandy lithofacies and loaded transitional and interbedded contacts between sand and diamict the scarborough bluffs sequence may be the preserved bottom stratigraphy of a large lake the bottom stratigraphy results from repeated basinward progradation of deltaic sandy lithofacies over glaciolacustrine diamicts deposited below floating ice whether ice shelf ramp bergs or lake ice a facies model is presented for glaciolacustrine diamict deposition on the floors of enlarged pleistocene lakes trapping substantial volumes of fine grained suspended sediment

borehole geophysical log signatures and stratigraphic assessment in a glacial basin southern ontario over the past two decades the geological survey of canada has used a standardized suite of slim hole geophysical tools to log 57 polyvinyl chloride cased boreholes drilled in the glacial sediments of southern ontario this article documents downhole tool responses natural gamma apparent conductivity magnetic susceptibility and seismic velocity in the context of mineralogical characteristics of the region and grain size data from 28 of the 57 boreholes characteristic geophysical properties and or patterns are identified within the units of a regional hydrostratigraphic framework in southern ontario the importance of a calibrated suite of tools is emphasized as stratigraphic units may have variable response from site to site the use of a high sensitivity magnetic susceptibility induction probe is shown to be an important tool in the log suite for lithostratigraphic interpretation and more broadly for provenance studies of source rock across the region ranges of compressional p and shear s

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

shear resistance and continuity of subglacial till hydrology rules the field observations of g s boulton stimulated widespread interest in deformable beds shear resistance of till in its critical state is insensitive to strain rate and increases linearly with effective pressure during unsteady deformation pseudo viscous shear resistance can be caused by dilation of consolidated tills and resultant pore pressure decline this effect is probably uncommon however because susceptible tills of low hydraulic diffusivity are also those least likely to consolidate significantly during effective pressure transients stick slip motion at whillans ice stream antarctica indicates that its basal till must weaken during rapid slip and strengthen during longer periods of slower slip recurrence intervals for rapid slip episodes there 6 18 hours indicate that till strength variations if driven by changes in pore pressure either related or unrelated to basal freezing are focused in the uppermost several centimeters of the bed ploughing of grains at the bed surface and associated excess pore pressures in adjacent till can account for rate weakening during rapid slip with pore pressure decay causing strengthening between slip episodes by promoting shallow sluggish subglacial water flow and low effective pressure soft beds may help sustain themselves by slowing their own transport soft bed shear resistance kinematics and continuity are problems rooted in subglacial hydrology

last interglacial sediments of the don valley brickyard toronto canada and their paleoenvironmental significance the don valley brickyard in toronto is an internationally designated type site in recognition of diverse faunal remains in the don beds of last sangamonian interglacial age pollen in overlying strata record the climatic deterioration marking the onset of the last wisconsinan glacial cycle new sedimentological descriptions show that the don beds about 8 m thick were deposited in a lacustrine lower shoreface environment subject to episodic storms storm deposited sand facies are interbedded with peaty muds that are extensively bioturbated water depths derived from wave formed ripples using linear wave theory appear to have increased during deposition of the don beds from about 2 m to about 18 m 12 28 m above the modern lake level a change that is recorded by an overall fining up sequence increasing water depths may have been the result of isostatic recovery of the lake outlet to the east the don beds overlie a thin bouldery deposit possibly a remnant of older illinoian glacial sediments yo

evidence for the subglacial meltwater origin and late quaternary lacustrine environment of bateau channel eastern lake ontario bateau channel is the smallest and most northerly of the three outlets of lake ontario near its narrowest point 125 m at present water level it is 60 m deep making it one of the deepest places

geophysical geological and hydrogeological characterization of a tributary buried bedrock valley in southern ontario buried bedrock valleys infilled with quaternary aged sediment have the potential to become productive aquifers owing to prevalent sand and gravel deposits often associated with these topographic lo

melting and subsolidus relations of sio2 at 9 14 gpa experiments were performed on amorphous silica at temperatures of 1000 2850 c and pressures of 9 14 gpa using a 2000 t uniaxial split sphere multianvil apparatus ussa 2000 the melting curve of coesite was extended from 8 to 13 7 gpa and the melting temperatures indicate a slope that is almost independent of pressure melting of stishovite was observed at 2850 c and 14 gpa the triple point for coexisting coesite stishovite and melt was located at 2800 c and 13 7 gpa the coesite stishovite phase transition was determined between 2000 and 2800 c and is described by the equation p gpa 5 8 4 0 0028 2 t c the resulting dp dt slope is more than twice that determined in the in situ x ray study of yagi and akimoto 1976 the present coesite stishovite boundary cannot be predicted by existing thermodynamic data e g fei et al 1990 which suggests some uncertainties in the extrapolation of heat capacities of coesite and stishovite at high temperatures thermodynamic extrapolations of the metastable melting curves of quartz and coesite show a strongly negative slope and thus are consistent with the proposal that the room temperature amorphization of quartz and coesite results from crossing of the metastable extension of their melting curves

nature and origin of sediments infilling poorly defined buried bedrock valleys adjacent to the niagara escarpment southern ontario canada the buried paleozoic bedrock surface of southern ontario is dissected by an interconnected system of valleys these buried valleys are infilled with thick successions of glacial interglacial and fluvial sediments that contain a lengthy record of changing environmental conditions during the late quaternary detailed logging of over 500 m of sediment recovered from 11 continuously cored boreholes provides the basis for this study the boreholes were drilled within two poorly defined bedrock valleys located east of the niagara escarpment in southern ontario as part of a groundwater exploration program six distinct facies types were identified within the cores sand gravel fine grained sediment and sand rich mud rich and clast rich diamict textural characteristics of the cored sediments and vertical changes in facies types were used to identify six stratigraphic units su i through su vi within the valley infill deposits these units are interpreted to record fluvial or colluvial su i lacustrine su ii fluvial glaciofluvial or deltaic su iii subglacial su iv glaciofluvial su v and subglacial or ice marginal su vi conditions sediment characteristics and stratigraphic relationships allow tentative correlation with known surficial deposits analysis of the subsurface characteristics and geometries of this stacked succession of coarse and fine grained stratigraphic units also allows identification of the geometry of potential aquifers

sedimentation beneath ice shelves the view from ice stream b abstract ice shelf development is favored by rapid flow of cold ice from outlet glaciers or ice streams into protected embayments with localized high spots basal melting of ice shelves is rapid near the ice front and may occur near the grounding line ice from outlet glaciers may contain significant englacial debris that is deposited as a dropstone diamicton in regions of basal melting englacial debris is sparse or absent in ice streams evidence from ice stream b draining into the ross ice shelf of west antarctica suggests that the rapid ice velocity arises from deformation of a several meter thick water saturated basal till layer that is eroding an unconformity on sediments beneath and that has deposited a till delta tens of meters thick and tens of kilometers long at the grounding line sea level fall would cause conveyor belt recycling of this till delta and grounding line advance across the ross sea to the edge of the continental shelf forming an ice sheet with a low ice stream profile resting on a several meter thick deforming till layer eroding an unconformity the modern ross sea is characterized by a regional unconformity overlain by a diamicton of probable latest pliocene pleistocene age measuring several meters to tens of meters thick we hypothesize that this diamicton is a deformed glacial till and that the ross sea sediments record one or more expansions of the till lubricated west antarctic ice sheet to the edge of the continental shelf

regional unconformities and the sedimentary architecture of the oak ridges moraine area southern ontario seismic stratigraphy geometry and sediment facies within the oak ridges moraine orm area of ontario record major structural elements and surfaces of the quaternary sedimentary sequence the derived stratigraphic architecture can be used to identify the key elements of a regional erosional surface represented by an unconformity in the subsurface and associated overlying channel sediments the erosional surface unconformity forms a distinct time datum in the quaternary sequence which provides an important aid to lithostratigraphic correlation the architecture also gives improved understanding of the effects of erosion on the late glacial landscape the surfaces of erosional drumlins and intervening troughs and the beds and banks of meltwater channels in the orm area define the regional unconformity highlighted by seismic profiles linked to continuously cored boreholes these features are attributed to regional scale subglacial meltwater flow events the sculpted surfaces which are analogous to water eroded forms the presence of boulder lags and coarse grained deposits on the regional erosional surface and the channels with undulating profiles provide the vital supporting evidence for a meltwater interpretation the inter regional extent of the unconformity is inferred from the coherence of regional paleoflows and the extent of drumlinized uplands tunnel channels and scoured bedrock terrain across 75 of the landscape from the orm area east and south to the finger lakes new york the implied magnitude of erosion suggests a pressing need for directed sedimentological study in those ocean basins that were probable depositional sites for flood deposits

evaluating the groundwater resource potential of the dundas buried bedrock valley southwestern ontario an integrated geological and hydrogeological case study population growth in the groundwater dependent municipalities of southwestern ontario has prompted interest in the exploration for new previously untapped groundwater resources in this study th

late pleistocene depositional systems of metropolitan toronto and their engineering and glacial geological significance the municipality of metropolitan toronto area 480 km2 population 2 15 million is centrally located on the late pleistocene sedimentary infill of the laurentian channel a broad bedrock low up to 115 km wide connecting the huron and ontario basins this channel forms part of a relict late tertiary drainage network the laurentian river modified by pleistocene glacial erosion and infilled by over 100 m of glacial and interglacial sediments the subsurface stratigraphy of the channel fill below metropolitan toronto has been established from many different data sources and is depicted in this paper as a series of cross sections with a total length of nearly 105 km the subsurface stratigraphy has been divided provisionally into five depositional complexes which have been mapped in the subsurface along several transects these are 1 a glacial complex of illinoian age 2 a lacustrine complex of sangamon interglacial and earliest wisconsinan sediments 120 000 75 000 bp 3 a glaciolacust

melting of enstatite mgsio3 from 10 to 16 5 gpa and the forsterite mg2sio4 majorite mgsio3 eutectic at 16 5 gpa implications for the origin of the mantle a split sphere multianvil apparatus clissa 2000 has been used to determine the melting curve of enstatite mgsio3 from 10 to 16 5 gpa and the forsterile mgio majoritc mgsio3 euteetic at 16 5 gpa use of a new capsule material rhenium allowed long runs of up to 2 hours at temperatures up to 2380oc with no observed contamination of the sample and with stable temperature control melting temperatures of enstatite are up to 160oc higher than those of kato and kumazawa 1986a two invariant points have been located one for orthoenstatite linoenstatite liquid at 2230oc 11 9 gpa and one for clinoenstatite majoritc liquid at 2370oc 16 4 gpa forsteritc melts incongruently at 2350oc 16 5 gpa to liquid and anhb 0vlglnsiso24 in the system mg2sio4 mgsio3 at 16 5 gpa the forsterite majorite eutectic has been located at 34 wt mg2sio4 a composition similar to that determined by karo and kumazawa 1986a at 20 gpa but much lower in mg2sio4 than several previous estimates based on melting experiments on mantle peridotitc compositions this forstefite poor location for the cuteerie is in apparent conflict with the suggestion that the peridotitic upper mantle is a crystallized cuteeric like liquid formed at about 16 gpa

the sedimentary record of drifting ice early wisconsin sunnybrook deposit in an ancestral ice dammed lake ontario canada abstract outcrops of pebbly mud diamict at scarborough in southern ontario canada the so called sunnybrook till are associated with the earliest incursion of the laurentide ice sheet lis into mid continent north america some 45 000 years ago the sunnybrook is a blanket like deposit containing deepwater ostracodes and occurs conformably within a thick 100 m succession of deltaic and glaciolacustrine facies that record water depth changes in a large proglacial lake contextual evidence associated facies sedimentary structures deposit geometry and landforms indicates a low energy depositional setting in an ice dammed ancestral lake ontario in which scouring by floating ice masses was an important process u shaped iceberg cut scours with lateral berms up to 7 m deep occur on the upper surface of the sunnybrook and are underlain by sub scour structures that extend several meters below the scour base ice rafted concentrations of clasts clast layers grooved surfaces formed by floating ice glissading over a muddy lake floor soft sediment striations and melanges of sand and mud mixed by grounding ice keels ice keel turbates are present and are all well known from modern cold environments the wider significance of this depositional model is that the lis margin lay east of scarborough and did not overrun southern ontario this finding is in agreement with recent data from the erie basin of canada ohio and indiana where deposits formerly correlated with the sunnybrook and thus implying an extensive early wisconsin ice sheet are now regarded as illinoian a speculative hypothesis is proposed that relates deposition of the sunnybrook and two younger deposits of similar sedimentology to surge like instabilities of the southern lis margin

how glaciers entrain and transport basal sediment physical constraints abstract simple insights from the physics of ice water and sediment place constraints on the possible sediment transport behavior of glaciers and ice sheets because glaciers concentrate runoff streams generated by glaciers transport much sediment and may erode bedrock rapidly deforming glacier beds also can transport much sediment particularly in marginal regions rapid sediment entrainment producing thick debris rich basal zones may occur by regelation into subglacial materials and by freeze on from rising supercooled waters numerous other mechanisms may be important but primarily near ice margins especially those of advancing or fluctuating glaciers several sediment entrainment mechanisms may be active beneath a single glacier but one process is likely to be dominant at any place and time

evidence for rapid sedimentation in a tunnel channel oak ridges moraine southern ontario canada abstract in south central ontario a late wisconsinan regional unconformity consisting of tunnel channels and drumlinized till crops out north of lake ontario the tunnel channels are locally infilled and the unconformity buried by sediment of the oak ridges moraine based on seismic reflection profiling and drillcore the tunnel channels are known to continue beneath the moraine detailed sedimentological analysis of 300 m of continuous core from two drillholes located 7 km apart in subparallel tunnel channels identified three facies the gravel facies is 17 m thick and occurs in only one of the cores it directly overlies the unconformity and may include a number of upward fining units seismic reflection data suggests the gravel forms stacked gravel mesoforms or quasi horizontal gravel layers bed load sheets deposited from fluidal flows along the deep channel axis the graded massive sand facies up to 37 m thick is the most common facies and consists of silty medium sand with minor coarse sand strata are reverse graded normal graded or massive with isolated silt intraclasts and evidence locally for dewatering this facies is interpreted to have been deposited from hyperconcentrated dispersions downflow of a hydraulic jump or major channel confluence the third facies consists of medium scale and small scale cross stratified sand medium scale cross stratification occurs predominantly in the lower 37 m of the core and is interbedded with the graded massive sand facies small scale cross stratified sand is progressively more common upward in core medium and small scale cross stratified sands was deposited respectively by subaqueous dunes and ripples formed in dilute fluid flows the complete succession is interpreted to have been deposited very rapidly within a subglacial tunnel channel before discharge ceased along the channel deposition followed closely and in part coincided with rapid expansion of the channel by erosion in a hydraulic jump or at a major channel confluence along the grounding line of a subglacial lake scour into unconsolidated sediment contributed to the sediment flux and quickly overloaded the flow with suspended sediment which in turn resulted in extremely high rates of sedimentation immediately downflow such depositional conditions support the notion that tunnel channels in the study area formed and or served as conduits for subglacial jokulhlaup discharges and that the laurentide ice sheet most probably did not generally drain by steady state processes but instead by short lived catastrophic events

seismic facies and regional architecture of the oak ridges moraine area southern ontario analysis of over 50 line kilometres of land based shallow seismic reflection profiles has provided a means of investigating the subsurface architecture and stratigraphic relationships of the glac

buried ancestral drainage between lakes erie and ontario the bedrock topography for the eastern niagara peninsula of ontario and for adjacent areas of new york was reconstructed using more than 7 600 well records and geophysical data this topography reveals an elaborate system of buried channels dominated by three main passageways connecting lake erie to lake ontario these channels are the erigan crystal beach and st davids the erigan with a depth near 150 ft below lake erie water level precludes the existence of a lake in the erie basin north of the niagara escarpment the erigan channel bifurcates into three outlets that extend into lake ontario the extensive widths and differences in elevation of the outlet valleys suggest that the erigan channel was active at least three times elevations in two of the outlets indicate that water levels in the ancestral lake ontario were similar to those of the present day lake the third outlet requires water levels at least 30 ft lower than present conditions the crystal beach channel originates west of buffalo and trends north along part of the present day course of the niagara river at niagara falls it changes to a southwesterly direction to join the erigan channel near its southern end the crystal beach system received inflow from lake erie through at least 4 inlets with bed elevations only 10 30 ft below the present lake erie water level this suggests the existence of an ancestral lake erie similar to present day conditions limited retreat in the waterfall of the erigan channel indicates that during the active period of the crystal beach and erigan drainage systems only the lake erie watershed emptied through the niagara peninsula the upper great lakes may have drained through the buried laurentian valley between georgian bay and lake ontario drainage of the upper great lakes through the niagara peninsula may have first occurred through the st davids buried channel the limited retreat of the st davids waterfall suggests a history of only a few thousand years its channel above the niagara escarpment probably occupied part of the bedrock depression formed by the crystal beach drainage system but at a higher elevation

architecture of buried valleys in glaciated canadian prairie regions based on high resolution geophysical data abstract airborne electromagnetic and high resolution seismic geophysical data provide insight into complex buried valley geometry and internal sedimentary architecture of buried valleys in the canadian prairies buried valleys with an extent in excess of 20 000 km beneath the canadian prairie landscape have been previously interpolated using borehole data however they provide only limited insight into the geometry and spatial relationships of these valleys the collected high quality geophysical datasets a three dimensional airborne electromagnetic survey and high resolution seismic profile data provide much greater resolution of buried valley geometry and internal sedimentary architecture of buried valleys several generations of valleys at different scales are identified we interpret multiple erosion surfaces bounding thick diamicton sequences that fill the largest valleys the youngest valleys are filled with variable sediment types three valley morphologies are identified and process origins inferred 1 regional scale extensive subaerial and pre interglacial named type valley 2 regional scale narrow and mainly proglacial type valley and 3 local scale apparently discontinuous subglacial type valley within the glacial sediment stratigraphy filling type valleys are thick diamicton sequences bounded by erosional surfaces the type and type valleys are filled with variable sediment types the proglacial valleys erode bedrock and also occur within the type valley fill conversely the subglacial valleys are observed to crosscut other valleys and may be shallow and wide or deep and narrow the reported geophysical datasets supported by borehole data are able to map buried valleys in three dimensions and hence identify the morphologic and stratigraphic relationships that permit improved constraints on process and erosional origin and fill of buried valleys results provide insight into the relationship between valleys formed as part of tertiary fluvial erosion multiple glaciations and glaciofluvial events these data provide significant insights on the distribution and character of potential groundwater reservoirs in prairie regions

the pre late wisconsin stratigraphy of southern simcoe county ontario implications for ice sheet buildup decay and great lakes drainage evolution1 recent three dimensional mapping investigations in southern simcoe county ontario allow refinement of the existing regional stratigraphic framework analysis of 25 continuously cored boreholes ha

experimental investigation and optimization of thermodynamic properties and phase diagrams in the systems cao sio2 mgo sio2 camgsi2o6 sio2 and camgsi2o6 mg2sio4 to 1 0 gpa using experimental results at 1 0 gpa for the systems cao sio2 mgo sio2 camgsi2o6 sio2 and camgsi2o6 mg2sio4 and all the currently available phase equilibria and thermodynamic data at 1 bar we have optimized the thermodynamic properties of the liquid phase at 1 0 gpa the new optimized thermodynamic parameters indicate that pressure has little effect on the topology of the cao sio2 camgsi2o6 sio2 and camgsi2o6 mg2sio4 systems but a pronounced one on the mgo sio2 binary the most striking change concerns passage of the mgsio3 phase from peritectic melting at 1 bar to eutectic melting at 1 0 gpa this transition is estimated to occur at 0 41 gpa for the camgsi2o6 sio2 and camgsi2o6 mg2sio4 pseudo binaries the size of the field clinopyroxene liquid increases with increasing pressure this change is related to the shift of the piercing points clinopyroxene silica liquid from 0 375mol fraction sio2 at 1 bar to 0 414 at 1 0 gpa and clinopyroxene olivine liquid from 0 191mol fraction sio2 at 1 bar to 0 331 at 1 0 gpa that bound the clinopyroxene liquid field in the camgsi2o6 sio2 and camgsi2o6 mg2sio4 pseudo binaries respectively

thermodynamics of the mgo sio2 liquid system in earth s lowermost mantle from first principles abstract knowledge of the multi component thermodynamics and phase equilibria of silicate melts in earth s deep interior are key to understanding the thermal and chemical evolution of the planet yet the melting phase diagram of the lower mantle remains poorly constrained with large uncertainties in both eutectic composition and temperature we use results from first principles molecular dynamics of nine compositions along the mgo sio 2 binary to investigate the compositional dependence of liquid state thermodynamics applying our results to describe incongruent melting for the system at deep lower mantle pressures our phase diagram is bi eutectic throughout the lower mantle with no liquid immiscibility accounting for solid liquid partitioning of fe we find partial melts of basaltic and peridotitic lithologies to be gravitationally stable at the core mantle boundary while liquidus density contrasts predict that perovskite will sink and periclase will float in a crystallizing pyrolytic magma ocean

erosion and infill of new york finger lakes implications for laurentide ice sheet deglaciation a comprehensive seismic reflection profile investigation of the new york finger lakes has revealed the extent of bedrock erosion and nature of sediment fill beneath the lakes bedrock deepens to the south where gorgelike profiles have been eroded to as much as 304 m below sea level and infilled with up to 275 m of late quaternary age 14 ka sediment we propose a working hypothesis that invokes ice streaming and pressurized subglacial meltwater and sediment to account for regional geomorphology this working hypothesis is consistent with recent concepts of the collapse of continental ice sheets via ice streaming and the marine isotopic record for a meltwater spike at 13 14 ka the finger lakes may provide a critical testing ground for deglaciation models of the southern laurentide ice sheet because they contain a thick well preserved and now seismically defined record of the deglaciation process

modelling north american palaeo subglacial lakes and their meltwater drainage pathways this paper presents predictions of palaeo subglacial lakes and their drainage pathways beneath the north american ice sheet during the last glaciation we utilise data on the current topography and seafloor bathymetry and elevation models of the ice and ground surface topography from data calibrated glaciological modelling to calculate the hydraulic potential surface at the ice sheets bed given that specific ice surface elevations are only known from modelled outputs and thus contain significant uncertainty we utilise many such outputs to examine where on the bed that subglacial lakes are likely to have occurred our analysis demonstrates the potential for subglacial lake genesis particularly beneath the former cordilleran ice sheet along the suture zone between the laurentide and cordilleran ice sheets in hudson bay in the great lake basins and deep trenches of the canadian archipelago during the last glacial maximum we suggest that at least 1000 km3 of meltwater could have been stored subglacially as the ice sheet and the bed evolved subglacial lakes repeatedly formed and emptied particularly in hudson bay and the suture zone between the laurentide and cordilleran ice sheets where lakes were characteristically broad and shallow 10 m deep in contrast the cordilleran ice sheet was characterised by deep up to 90 m and persistent lake genesis significantly similar distributions and modes of predicted subglacial lakes are obtained irrespective of the model or model run which suggests the results are robust subglacial meltwater drainage varied between stable networks typically associated with strong topographic controls and convoluted networks that underwent considerable dynamism including repeated meltwater network capture these lake likelihood predictions could usefully form targets for detailed field and remote investigations and we hypothesise and explore the potential that numerous deposits and spillways previously interpreted as arising from ice marginal lakes may have emanated from their subglacial cousins

geological framework of the laurentian trough aquifer system southern ontario the laurentian trough lt a depression 100 km long 3000 km2 in area and 100 m deep at the base of the niagara escarpment extends from within georgian bay to lake ontario it has a complex er

a revised depositional setting for halton sediments in the oak ridges moraine area ontario outcrop and continuous core descriptions high resolution seismic profiling and downhole geophysical data are integrated with detailed mapping to update sedimentary and stratigraphic frameworks for halton sediment a complex mud rich lithofacies succession halton sediment has a gradational transition from underlying oak ridges moraine orm sediment and can abruptly overlie newmarket till halton strata thin and fine upwards from orm sand and gravel to graded sand silt and clay rhythmites with muddy diamicton and sand and gravel interbeds these strata fill basin lows and drape orm sediment lobes and newmarket till drumlins these distinct sedimentary units are here informally referred to as halton formation formal halton till is a proposed subunit of halton formation a clay rich diamicton mapped from niagara peninsula to orm and eastward halton till has traditionally been inferred to represent a late climatically induced readvance of grounded ice from lake ontario basin which deposited drumlini

multicomponent high resolution seismic reflection profiling multicomponent seismic reflection methods are a new tool for oil and gas exploration and reservoir monitoring miles 1988 but such technologies have not yet been extensively exploited for near surface exploration related to hydrogeological and or geotechnical investigations with the advantage of relatively inexpensive recording systems for near surface applications we show that the use of multicomponent high resolution seismic reflection methods has great potential as a new means of observing and characterizing the physical parameters of the shallow subsurface and in particular of groundwater reservoirs

buried valley aquifers in the canadian prairies geology hydrogeology and origin11earth science sector ess contribution 20120131 we review over 100 years of literature on prairie buried valleys to provide a platform for future research and policy development prairie buried valley fills commonly function as aquifers that yie

dissolved organic carbon and methane in a regional confined aquifer southern ontario canada carbon isotope evidence for associated subsurface sources information regarding the origin composition and transport of natural dissolved organic carbon doc in groundwater is necessary to understand the transport of metals and organic pollutants as well as for the use of14c in doc as an isotopic groundwater dating method previous research in several groundwater systems has suggested soil organic c is the predominant source of high molecular weight doc to the subsurface through the use of stable isotopes 14c and geochemical analyses this study shows that significant concentrations of doc and ch4 in a regional confined aquifer can be generated in situ from subsurface sedimentary organic sources the doc and ch4 produced is a combined result of degradation of buried peats and bacterial action resulting in high doc concentrations and strongly methanogenic conditions in the aquifer the doc and ch4 comprise on average nearly 50 of the total dissolved c pool in the central part of the aquifer methanogenic conditions complicate isotopic groundwater dating by the conventional dissolved inorganic carbon dic method estimates of isotopic groundwater residence time using doc14c data are proposed by the application of14c isotope and mass balance corrections

erosion of bedrock by subglacial meltwater georgian bay ontario a regional view a spectacular series of sculpted erosional forms s forms is mapped and described from a 70 km wide area along the shore of georgian bay ontario which except for a scattered boulder lag has been swept clean of sediment a great variety of sculpted forms is described and illustrated and grouped into three classes transverse longitudinal and nondirectional forms transverse forms comprise transverse troughs muschelbruche sichelwannen and comma forms longitudinal forms comprise spindle flutes cavettos and furrows and nondirectional forms consist of undulating surfaces and potholes transverse forms are preferentially located on stoss slopes and longitudinal forms on lee slopes of rock rises undulating nondirectional forms are found on distal slopes and potholes at major breaks in slope this correlation of form and bed topography suggests that relief exerts considerable control on both form and location form geometry is also inferred to be related to coherent flow structures and their int

quantitative assessment of the hydraulic role of subglaciofluvial interbeds in promoting deposition of deformation till northern till ontario the northern till is a thick 65 m deformation till underlying some 7500 km2 of southern ontario canada including the peterborough drumlin field it was deposited below the lake ontario ice stream of the laurentide ice sheet the till rests on glaciotectonized aquifer sediments and consists of multiple beds of till up to 6 m thick these are separated by boulder lags sometimes in the form of striated pavements with thin 30 cm interbeds of poorly sorted waterlaid sand the composite till stratigraphy indicates punctuated aggradation where the subglacial bed was built up incrementally by the repeated immobilization of deforming overpressured till layers boulders and sands indicate pauses in subglacial aggradation marked by sluggish sheet flows of water that reworked the top of the underlying till interbeds are laterally extensive and correlated using downhole electrical conductivity core recovery and natural gamma data a 3 d finite element model feflow using data from 200 cored and geophysically logged boreholes and a large digital water well dataset of 3400 individual records shows that the till functions as a leaky aquitard as a consequence of water flow through interbeds it is proposed that interbeds played a similar role in the subglacial hydraulic system below the laurentide ice sheet by allowing drainage of excess porewater pressures in deforming sediment and promoting deposition of till this is in agreement with theoretical studies of deforming bed dynamics and observations at modern glaciers where porewater in the deforming layer is discharged into underlying aquifers in this way the presence of interbeds may be fundamental in retarding downglacier transport of deforming bed material thereby promoting the build up of thick subglacial till successions

on the origin of the oak ridges moraine landscape analysis mapping sedimentology shallow geophysics and borehole data are integrated to better understand the complex landform sediment geometries and event sequences of the oak ridges moraine southern ontario a model for the origin of the oak ridges moraine is based on the recognition that the moraine is built on a high relief erosional surface unconformity consisting of drumlin uplands and a network of deep steep walled interconnected valleys tunnel channels the development of the moraine is thought to have occurred in four stages i subglacial sedimentation ii subaqueous fan sedimentation iii fan to delta sedimentation iv ice marginal sedimentation the model traces the transition from subglacial to proglacial conditions during moraine formation and examines the order and timing of sedimentation it is thought that the early stages of moraine construction are better exposed in the east in the west these stages are buried by later stages resume les etudes de paysage cartographie sedimentologie geophysique de subsurface et des carottes de trous des sondages ont ete menees conjointement pour chercher a mieux comprendre les configurations complexes des formes de relief sediments et les sequences des evenements qui ont affecte la moraine d oak ridges dans le sud de l ontario un modele interpretant l origine de la moraine d oak ridges est fonde sur le fait que cette moraine fut edifiee sur une surface d erosion discordance en terrain a topographie accentuee comprenant des drumlins sur terres elevees et des vallees a parois subverticales interconnectees chenaux tunnels le modele propose un developpement de la moraine en quatre phases i sedimentation sous glaciaire ii sedimentation d un eventail sous aquatique iii sedimentation de l eventail evoluant vers un depot deltaique iv sedimentation en bordure d un glacier le modele retrace la transition de conditions sous glaciaires a proglaciaires durant la formation de la moraine et traite de l ordre et de la chronologie du sediment il apparait que c est dans le secteur oriental que les premieres phases de l edification de la moraine sont le mieux exposees tandis que dans le secteur partie occidental elles sont enfouies sous le sediment des phases plus tardives

basement controlled faulting of paleozoic strata in southern ontario canada new evidence from geophysical lineament mapping abstract basement fault reactivation is now recognized as an important control on sedimentation and fault propagation in intracratonic basins in southern ontario the basement consists of complexly structured mid proterozoic ca 1 2 ga crystalline rocks and metasedimentary rocks that are overlain by up to 1500 m of paleozoic sedimentary strata reactivation of basement structures is suspected to control the location of paleozoic fault and fracture systems but evaluation has been hindered by a limited understanding of the regional structural characteristics of the buried basement new aeromagnetic and gravimetric lineament mapping presented in this paper better resolves the location of basement discontinuities and provides further evidence for basement controls on the distribution of paleozoic fault and fracture systems lineament mapping was facilitated by reprocessing and digital image enhancement micro levelling regional residual separation derivative filtering of existing regional gravity and aeromagnetic datasets reprocessed images identify new details of the structural fabric of the basement below southern ontario and delineate several previously unrecognized aeromagnetic and gravity lineaments and linear zones linear zones parallel the projected trends of mid proterozoic terrane boundaries identified by field mapping on the exposed shield to the north of the study area and are interpreted as zones of shearing and basement faulting mapped aeromagnetic and gravity lineaments show similar trends to paleozoic faults and fracture networks and broad zones of seismicity in southern ontario these new data support an inheritance model for paleozoic faulting involving repeated reactivation and upward propagation of basement faults and fractures into overlying cover strata

recharge of a subglacial lake by surface meltwater in northeast greenland observations of rapid persistent elevation gains that occur on the ice surface above a subglacial lake as the lake is refilled with surface meltwater during the summer melt period in greenland show that surface meltwater may be trapped and stored at the bed of an ice sheet affecting ice dynamics downstream the discovery of a 70 metre deep collapse basin near the summit of the largest and most northerly peripheral ice cap of greenland and the use of high resolution stereo satellite imagery to monitor its evolution suggests that surface meltwater can be trapped and stored beneath the greenland ice sheet previously meltwater from the surface of the ice sheet had been assumed to drain efficiently through the basal hydrologic system during the summer melt period rapid persistent elevation gains occur on the ice surface above a subglacial lake as the lake is refilled with surface meltwater and stored at least on annual time scales these findings have potential implications for our understanding of ice sheet temperature and velocity in a warming climate surface meltwater production on large ice sheets is expected to increase if this water is delivered to the ice sheet base it may have important consequences for ice dynamics for example basal water distributed in a diffuse network can decrease basal friction1 2 and accelerate ice flow3 4 5 6 7 8 whereas channelized basal water can move quickly to the ice margin where it can alter fjord circulation and submarine melt rates9 10 less certain is whether surface meltwater can be trapped and stored in subglacial lakes beneath large ice sheets here we show that a subglacial lake in greenland drained quickly as seen in the collapse of the ice surface and then refilled from surface meltwater input we use digital elevation models from stereo satellite imagery and airborne measurements to resolve elevation changes during the evolution of the surface and basal hydrologic systems at the flade isblink ice cap in northeast greenland during the autumn of 2011 a collapse basin about 70 metres deep and about 0 4 cubic kilometres in volume formed near the southern summit of the ice cap as a subglacial lake drained into a nearby fjord over the next two years rapid uplift of the floor of the basin which is approximately 8 4 square kilometres in area occurred as surface meltwater flowed into crevasses around the basin margin and refilled the subglacial lake our observations show that surface meltwater can be trapped and stored at the bed of an ice sheet sensible and latent heat released by this trapped meltwater could soften nearby colder basal ice11 and alter downstream ice dynamics12 13 heat transport associated with meltwater trapped in subglacial lakes should be considered when predicting how ice sheet behaviour will change in a warming climate

tunnel valleys concepts and controversies a review abstract although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate the most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin time transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge probably catastrophically and rapid erosion during widespread catastrophic basal sheetflood events recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages in addition new advances in understanding of subglacial hydrology both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds this work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed because of the inability of groundwater flow to account for all the meltwater produced by basal melting other drainage mechanisms involving both non channelized and channelized meltwater flow have been proposed the notion of catastrophic drainage of impounded basal meltwater is still favored by many and the discovery of hundreds of subglacial lakes beneath the antarctic ice sheet and the likelihood of similar lakes beneath pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them tunnel valleys produced by the scandinavian ice sheet have been described and mapped on land as well as on the sea bed valleys and networks of valleys some of which are totally buried have been linked to 3 or more glaciations tunnel valley networks from the last weichselian glaciation in denmark can be related to specific ice margins developed during ice retreat in north america most research has focused on tunnel valleys associated with ice margins formed by the last wisconsin glaciation along the southern margin of the laurentide ice sheet

evidence for large scale subglacial meltwater flood events in southern ontario and northern new york state flow line patterns constructed from the orientation of drumlin long axes are used to infer two major subglacial meltwater floods in southern ontario and northern new york state in this interpretation the flood waters of the first event the algonquin surged southward in the later ontarian event powerful floods streamed southwestward along the basins of lakes ontario and erie bedrock fluting upstream pointing noses on escarpments and tunnel channels give supporting evidence for the regional flood hypothesis regional distributions of drift thickness may be explained by this hypothesis

controls on the sedimentary architecture of a single event englacial esker skeiðararjokull iceland eskers have been used to infer the dynamics and palaeo hydrology of large ice sheets yet there are few suitable contemporary analogues for esker sedimentation during quaternary glaciations consequently models of esker sedimentation have been derived from morpho sedimentary analyses of quaternary eskers but these lack rigorous constraints on their depositional timescales we identify the controls on the large scale sedimentary architecture of a large 700 m long 10 inclined reflections interpreted as backset accretion associated with large scale bedform development 4 down flow dipping high angle 15 inclined reflections interpreted as foreset accretion associated with macroform progradation 5 quasi hyperbolic reflections interpreted as zones of boulder clustering and 6 zones of enhanced noise and em signal attenuation bounded on the upper surface by a continuous reflection sub parallel to the ground surface interpreted as buried ice associated with the conduit channel base these data suggest that deposition took place within a non uniform englacial conduit which has resulted in major up flow to down flow variations in sedimentary architecture the complexities observed are a direct consequence of variations in sediment supply and the within event evolution of conduit geometry this study provides the first detailed insight into the large scale sedimentary architecture of a single event jokulhlaup proto esker

architectural element analysis applied to glacial deposits internal geometry of a late pleistocene till sheet ontario canada deposits left by continental ice sheets are characterized by sedimentological complexity and stratigraphic heterogeneity but stratigraphic descriptions of such deposits and resulting first generation facies models are still based primarily on one or two dimensional borehole or outcrop data reconstruction of depositional environments hydrogeological investigations of pleistocene glacial deposits and hydrocarbon exploration in pre pleistocene glaciated basin fills require a more detailed understanding of the form and heterogeneity of lithofacies sequences in three dimensions architectural element analysis is used widely by sedimentologists for categorizing internal stratigraphic heterogeneity in sandstones particularly those of fluvial origin this paper demonstrates the first application of architectural element analysis to glacial deposits such as tills outcrop borehole and a broad range of subsurface geophysical data were collected from a thick 60 m till sheet present across an 80 km 2 study area near toronto canada the till sheet is not homogeneous but is composed of three distinct architectural elements and associated lithofacies viz diamict elements interbeds of subglaciofluvial sediments and glaciotectonically deformed zones application of architectural element analysis to these subglacial strata provides insights into the origin of drumlin bedforms and subglacial processes below the laurentide ice sheet and creates a framework for understanding ground water and contaminant movement in underlying aquifers

thermoluminescence chronology of toronto area quaternary sediments and implications for the extent of the midcontinent ice sheet s we report direct dating by thermoluminescence tl methods of key quaternary stratigraphic horizons in the toronto area tl ages indicate that 1 most of the exposed sediments of the don formation at the sampled site were probably deposited during the closing phase of the sangamon interglacial 80 ka oxygen isotope stage 5a not the climatic optimum substage 5e 120 130 ka as generally supposed 2 overlying deltaic strata of the scarborough formation which accumulated in an ice dammed ancestral lake ontario were deposited between 60 and 50 ka early wisconsin oxygen isotope stage 4 3 the sunnybrook diamict overlying the scarborough formation was deposited in the middle wisconsin at 40 45 ka oxygen isotope stage 3 likely by glaciolacustrine processes rather than before 65 ka as previously supposed 4 sediments of the upper thorncliffe formation lying stratigraphically just beneath the last glacial maximum hallton till were deposited at 23 ka consistent with reliable 14 c dating thus the earliest wisconsin incursion of the proto laurentide ice sheet into the lake ontario basin as recorded by the scarborough formation probably did not take place until at least 60 ka and did not extend south and southwest of the toronto area until after 25 ka ice free conditions probably persisted over large areas of midcontinent north america from the end of the illinoian glaciation at 130 ka to the late wisconsin glacial maximum at 20 ka

on the formation of large subglacial lakes the role of subglacial water storage beneath continental ice sheets is investigated primarily for a deformable bed subglacial ponding is shown to occur under most regions of warm based ice sheets and large subglacial lakes can become established for example in the hudson bay basin the formation of large lakes depends upon the fact that the ice surface gradient is reduced once subglacial ponding occurs and upon the feedback between the reduced ice surface gradient and increased subglacial ponding subglacial ponding likely played a large role in determining the ice sheet topography during late deglaciation and in speeding up the deglaciation process

converging ice streams a new paradigm for reconstructions of the laurentide ice sheet in southern ontario and deposition of the oak ridges moraine geomorphometric analyses of high resolution 5 m digital elevation datasets shows that the greater toronto area and its immediate environs is built across the former till beds of two fast flowing ice streams the newly named the simcoe ice stream sis and the halton ice stream ois within the last laurentide ice sheet lis these formed during regional deglaciation sometime around 13 000 ybp and are directly analogous to fast flowing 3 km yr 1 ice streams in today s antarctic and greenland ice sheets their subglacial footprint in southern ontario consists of flow sets of highly elongated flow parallel till ridges up to 4 km in length and 100 m in width megascale glacial lineations msgls that converge on the oak ridges moraine orm from the north sis and south his orm is southern ontario s largest glacial landform extending from the niagara escarpment to kingston over some 160 km and was deposited as a series of en echelon glaciolacustrine fan deltas in a complexly evolving glaciolacustr

quaternary sequences along the north shore of lake ontario oshawa port hope we describe six major stratigraphic units from the hitherto neglected quaternary sequences along the north shore of lake ontario between oshawa and port hope these units from the base upwards co

morphodynamic response of a two barred beach to a shoreface nourishment abstract the response to a shoreface nourishment of the two bar system at noordwijk the netherlands is analyzed based on a daily data set of time exposure video images collected during about 6 years complemented with topographic and bathymetric surveys the 1 7 mm 3 nourishment implemented as a 3 km alongshore bump seaward of the outer bar migrated more than 300 m onshore in 4 years before losing its integrity furthermore the nourishment interrupted the autonomous seaward migration of both bars for the entire duration of the study period and allaying earlier fears did not intensify the three dimensional patterns in the bars such as the crescentic plan shape and rip channels the nourishment did result in clear head effects on both flanks with the bar becoming discontinuous and the flank section decaying or becoming attached to an offshore located bar while the section of bar landward of the nourishment became attached to a landward located bar this sequence of morphologies is known as bar switching each switching episode took almost one year to complete and can therefore not be ascribed to individual wave events we suspect that shoreface nourishments enhance the possibility of bar switching by creating alongshore variability in the position and depth of the outer bar and in its cross shore migration rate and direction the noordwijk nourishment did not influence the shoreline position as its trend did not undergo distinctive variations after 1998 differences in the response of the noordwijk sandbars to the shoreface nourishment compared with other dutch nourishments are attributed to the location and size volume per unit length of the nourishment with respect to the sandbars and to the median grain size of the nourished material

reply inferred subglacial meltwater origin of lakes on the southern border of the canadian shield paleozoic rocks form an escarpment up to 35 m high at the border with the frontenac axis of the canadian shield in southeastern ontario the escarpment which lies nearly transverse to the flow direction of pleistocene ice and subglacial meltwater in the region is cut by a series of deep channels locally incised into the bedrock at the escarpment a subbottom acoustic survey of two of these channels and mapping of a third partly flooded channel revealed the shape of the bedrock surface beneath the water and glacial and postglacial sediments of lakes now occupying the channels most cross sections show a smooth walled dominant depression eroded up to 100 m below the land surface nearby and flanked by one or more secondary depressions the pattern changes considerably in detail making secondary depressions especially difficult to trace along the length of the lake the pattern is similar to that of subglacial fluvial erosion marks more than three orders of magnitude smaller found in bedrock throughout

pleistocene glacio lacustrine deltaic deposits of the scarborough formation ontario canada abstract the late pleistocene scarborough formation of the lake ontario basin represents a lacustrine deltaic sequence strongly affected by a nearby glacier it shows gradual upward coarsening and thickening of layers from varve like clay rich rhythmites at the base to channelized cross bedded sands at the top thick lensing massive layers cm of silty sand are found interstratified with thin layers of silt and clay in the lower and middle parts of the sequence these massive layers were probably formed by subaqueous gravity flows of material in part derived directly from a glacier absence of pebbles and of other features such as glacial silt pellets suggests dispersal away from the foot of the glacier rather than deposition under floating ice varve like rhythmites pollen and insect fauna indicate subarctic to arctic climatic conditions at the time of sediment deposition the large amount of sand in the upper part of the formation is best explained as derived from active outwash fans similar fans were formed during the last deglaciation in southern ontario and can be observed on the landscape

outburst flooding and the initiation of ice stream surges in response to climatic cooling a hypothesis abstract outburst flooding from subglacial reservoirs and associated surging of ice streams are caused by processes following climatic cooling that produce ice shelf grounding on proglacial sills trapping subglacial water according to an hypothesis presented here glaciers often advance into proglacial water bodies cooling may allow ice shelf formation and advance causing grounding on a proglacial sill trapping subglacial water ice shelf freeze on to the sill and development of a local reversal in ice air surface slope over the sill then are likely allowing ice thickening and water overpressurization if basal thawing then occurs as is likely an outburst flood and a surge may be triggered these processes may have been involved in heinrich events generation of antarctic subglacial lakes and meltwater scouring of some regions

buried bedrock valleys and glacial and subglacial meltwater erosion in southern ontario canada morphometric features from a recently compiled bedrock topography map by the ontario geological survey suggest a glacial erosion origin for the buried large bedrock valleys and troughs in southern ontario the bedrock valleys at milverton wingham and mount forest are tunnel valleys resulting from subglacial meltwater erosion beneath the huron ice lobe probably during or shortly after the late wisconsinan glacial maximum diagnostic features for this interpretation include abrupt valley beginning and termination uneven longitudinal valley profiles and up slope gradients the dundas bedrock valley is the western extension of the lake ontario basin no comparable bedrock valleys were found to connect it to the milverton valley for a joint drainage system as previously suggested the laurentian bedrock trough is the southeastward extension of the georgian bay basin both developed along shale bedrock between the precambrian shield highlands and the niagara escarpment resulting from long term mechanical weathering associated with pleistocene glacial erosion this bedrock low has a floor that exceeds 50 km in width and is 26 m and more below the current water level of georgian bay it could drain georgian bay should the drift cover be removed there is no evidence to suggest that a preglacial river channel if it existed is still preserved in the floor of the laurentian trough as previously suggested the framework for an intensely glacially sculpted bedrock surface differs from the previous view for simple modification of a preglacial landscape and is therefore important in regional subsurface geological mapping and groundwater studies

illinoian to late wisconsinan stratigraphy at woodbridge ontario near woodbridge northwest of toronto ontario a 15 metre high railroad cut and associated borrow pit first excavated in 1962 exposed a multiple till sequence and intervening fossiliferous sediments work over the next 35 years revealed that illinoian york till early wisconsinan sunnybrook till and late wisconsinan humber till halton till and wildfield till are interbedded with fossiliferous sediments equivalent to the sangamonian don formation early wisconsinan scarborough formation 50 ka bp and middle wisconsinan thorncliffe formation 45 ka bp a complex periglacial record displays multistage fossil frost wedges indicating intervals of severe climate in late illinoian and early wisconsinan time cored boreholes indicate deep gravel below and a till on ordovician shale bedrock georgian bay formation vertebrates molluscs ostracodes insects and plants diatoms wood seeds pollen indicate mostly cool conditions boreal to tundra for interstadial sediments interglacial conditions a

tunnel channels and associated landforms south central ontario their implications for ice sheet hydrology the peterborough trenton drumlin field and associated meltwater erosion marks s forms were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet the algonquin event recent theoretical modelling of ice sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet inductive testing of this hypothesis using observations in south central ontario forms the crux of this paper a geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns such a rough interactive geometry is suggested as the bed is drumlinized and flows responsible for drumlins may be expected to have eroded similar forms into the ice base three landforms in south central ontario namely tunnel channels megachannels and late stage sheet flow scours are described and interpreted as evidence of progressive channelization and flow diversion processes governed by the geometri

subglacial water sheet floods drumlins and ice sheet lobes the effect of subglacial lakes upon ice sheet topography and the velocity patterns of subglacial water sheet floods is investigated a subglacial lake in the combined michigan green bay basin great lakes north america leads to 1 an ice sheet lobe in the lee of lake michigan 2 a change in orientations offlood velocities across the site of a supraglacial trough aligned closely with green bay in agreement with drumlin orientations 3 low water velocities in the lee of lake michigan where drumlins are absent and 4 drumlinization occurring in regions of predicted high water velocities the extraordinary divergence of drumlin orientations near lake ontario is explained by the presence of subglacial lakes in the ontario and erie basins along with ice sheet displacements of up to 30 km in eastern lake ontario the megagrooves on the islands in western lake erie are likely to be the product of the late stage of a water sheet flood when outflow from eastern lake ontario was dammed by displaced ice and instead flowed westward along the erie basin the finger lakes of northern new york state northeastern u s a occur in a region of likely ice sheet grounding where water sheets became channelized green bay and grand traverse bay are probably the products of erosion along paths of strongly convergent water sheet flow

simulating groundwater flow and runoff for the oro moraine aquifer system part i model formulation and conceptual analysis a steady state groundwater model that incorporates the vadose zone in an approximate fashion is developed to account for situations where recharge may be significantly affected by heterogeneity above the water table the model is intended for basin scale applications where the exact representation of the unsaturated zone is no longer feasible the pseudo unsaturated model is compared to a variably saturated model making use of an idealized cross section approximating the complex oro moraine aquifer system differences in predicted flow regimes between the two models arise from the coarser mesh used in the pseudo unsaturated simulations but are minimal below the water table the pseudo unsaturated model yields an accurate overall system water mass balance although a loss in spatial resolution of predicted fluxes may occur such accuracy losses are offset by drastically lower computer memory requirements the flow simulations further show that near surface heterogeneity has a profound impact on the sustainable capacity of a groundwater system and the location of sensitive recharge areas the pseudo unsaturated model is then coupled to a high conductivity layer atop the model domain to simulate rainfall runoff an important advantage of this model formulation is that precipitation and evapotranspiration measurements can be directly used as model input while groundwater infiltration is part of the flow solution runoff and baseflow contributions to long term streamflow generation are also calculated and can be compared to data from gauging stations during model calibration

rock drumlins and megaflutes of the niagara escarpment ontario canada a hard bed landform assemblage cut by the saginaw huron ice stream abstract the late wisconsin c 18 000 ybp saginaw huron ice stream shis of the laurentide ice sheet was as much as 800 km long and 250 km wide in the great lakes basin of mid continent north america in its onset zone in the upper lake huron basin of ontario canada it flowed south from the high standing canadian shield to move over gently dipping ordovician and silurian dolostones devoid of glacial sediment cover the onset zone is recorded by a distinct hard bed landform assemblage across 3000 km2 of north facing escarpments niagara fossil hill and kagawong and dip slope pavements on the bruce peninsula and manitoulin island and the adjacent floor of lake huron a wide range of glacially streamlined rock landforms were carved into dolostones below fast flowing ice the largest are 30 km wide bullet shaped escarpment promontories that face upglacier superposed on these are swarms of rock drumlins up to 5 km wide with downglacier lengths of as much as 10 km promontories and drumlins record streaming of dirty basal ice around escarpment highs and create a distinct zig zag planform to the escarpments in turn down dip trailing edge dolostone pavements are corrugated by kilometre long megagrooves and megaflutes cut by basal ice flowing around resistant high standing bioherm mounds on dolostone bedding planes the geomorphology of the niagara escarpment does not primarily reflect a lengthy history of preglacial cenozoic fluvial erosion as classically argued but geologically brief episodes of accelerated abrasion and quarrying below ice streams within successive pleistocene ice sheets

deformation till in the great lakes region implications for rapid flow along the south central margin of the laurentide ice sheet structural and lithologic data indicate that while deposited under actively moving ice considerable portions of three muddy calcareous subglacial tills in the great lakes region probably experienced some component of ductile deformation viscous till flow and ductile shear are invoked to explain a combination of features such as recumbent isoclinal folds unlithified sediment clasts mixed ostracode shells reversed stone lee ends girdle and transverse fabrics irregular stone pavements fine striae following stone curves and inconsistent stone striae and a axes deforming fine textured subglacial till is considered as a subhorizontal shear zone rheologically layered with associated structures in descending order ductile e g isoclinal folds brittle ductile e g fissility and brittle e g till wedges rheology would be controlled mainly by till pore water content matrix texture and stone content spatial and temporal superposition of rheologies and subglacial processes probably occur