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

drumlins carved by deforming till streams below the laurentide ice sheet the peterborough drumlin field 5000 km 2 is the largest in central canada and was formed during readvance of the laurentide ice sheet shortly after 13 000 b p morphometric analysis of 998 drumlins combined with study of 6921 borehole logs and downhole geophysical data has established the distribution of drumlin types and their stratigraphy along a 70 km flow line through the drumlin field in the north drumlins are spindle shaped composed of till resting directly on bedrock and were formed by deformation of till into low pressure zones in the lee of bedrock scarps eskers record subglacial drainage by channeled meltwaters flowing on bedrock to the south drift thickness increases and eskers are absent drumlins are larger and more ovoid and are composed of overridden proglacial and glaciolacustrine sediments overlain erosively by deformation till till is thin over drumlin crests and thick in interdrumlin swales and records subglacial cannibalization and mixing of overridden sediments the drumlin form is the product of erosion by streams of deforming till flowing in swales separating cores composed of older sediments systematic down field changes in drumlin shape and size can be related to decreased duration of subglacial deformation toward the limit of the readvance and increased thickness of preexisting sediments available for dissection by subglacial till streams absence of eskers in the central and southern parts of the drumlin field suggests that the ice base was drained by mass flow of the deforming substrate the substantial subsurface data available from the peterborough area indicate that drumlins are predominantly erosional in origin and are the geomorphological expression of a deforming subglacial bed below the margin of the laurentide ice sheet

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

sunnybrook drift indicates a grounded early wisconsin glacier in the lake ontario basin glaciotectonic analysis of sunnybrook diamicton and underlying sediments in scarborough bluffs ontario canada indicates that the diamicton investigated is lodgment and or deformation till the early wisconsin overriding of deformable glaciolacustrine mud by the ontario ice lobe was a significant glacial event in the eastern great lakes region this has important implications for understanding interactions between laurentide ice proglacial lakes and water laid sediments

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

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

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

fresh arguments against the shaw megaflood hypothesis a reply to comments by david sharpe on paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event

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

evidence for pre cretaceous history and partial neogene 19 9 ma reequilibration in the karakorum nw himalayan syntaxis from 40ar 39ar amphibole dating amphiboles and a biotite from amphibolites and amphibolitic gneisses of the karakorum metamorphic complex kmc nw himalaya were dated using the 40ar 39ar method isotope correlations were compared to electron microprobe analyses both aliv and alvi contents of amphibole increase from the south near the shyok suture zone to the dassu askole area in the north with an increase in metamorphic grade from anchizone to upper amphibolite facies in the lower metamorphic zone discordant age spectra were obtained they are related to epidote amphibolite overgrowth of amphibole rims on older precambrian to mesozoic magmatic cores in the shyok suture zone ar ar ages of 38 62 ma are contemporaneous with the emplacement of the ladakh batholith granodiorites while middle cretaceous magmatic ar ar ages w120 ma are locally preserved in tschermakite relics in the southern karakorum basement a minimum ar ar age of 651 ma was preserved while an age of 208 5g2 ma was preserved in panjal trap like diorites at the margin of the domes zone more recent metamorphism resulted in mineral growth at 20 5 ma in the domes zone amphibole ar ar ages of 17 ma askole and bimodal age spectra of 15 17 and 9 13 ma dassu extend towards the east the zone of neogene amphibolite to granulite facies metamorphism known in the nanga parbat syntaxis

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

itawa bhopji l3 5 chondrite regolith breccia fall classification and cosmogenic records a stony meteorite fell at itawa bhopji rajasthan india on 2000 may 30 this is the fifth recorded fall in a small area of rajasthan during the past decade the meteorite is an ordinary chondrite with light clasts in a dark matrix consisting of a mixture of equilibrated mainly type 5 and unequilibrated components olivine is fa24 26 and pyroxene fs20 22 but within the unequilibrated components olivine fa5 29 and low calcium pyroxene fs5 37 are highly variable based on petrographic studies and chemical analyses it is classified as l 3 5 regolith breccia studies of various cosmogenic records including several gamma emitting radionuclides varying in half life from 5 6 day 52mn to 0 73 ma 26al tracks and rare gases have been carried out the exposure age of the meteorite is estimated from cosmogenic components of rare gases to be 19 6 ma the track density varies by a factor of 3 from 4 to 12 x 10 6 cm 2 within the meteorite indicating a preatmospheric body of 9 cm radius corresponding to a meteoroid mass of 11 kg and small ablation 1 5 to 3 6 cm trapped components in various rare gases are high and the solar component is present in the dark portion of the meteorite large excess of neutron produced 82kr and 128xe in both the light and the dark lithology but very low 60co indicating low neutron fluxes received by the meteoroid in the interplanetary space are clear signatures of an additional irradiation on the parent body

bedrock jointing and geomorphology in southwestern ontario canada an example of tectonic predesign in southwestern ontario canada palaeozoic sedimentary strata are covered by pleistocene glacial sediments the topography of the buried bedrock surface has been mapped over an area of some 45 000 km2 using new computerised depth to bedrock data from more than 200 000 waterwells this information shows that arching of the underlying proterozoic basement canadian shield and differential erosion of carbonate and shale strata are first order regional controls on bedrock geomorphology these data also define a network of buried bedrock channels quantitative analysis of the trends of these channels reveals a statistical correspondence between channel orientation and regional bedrock joint sets formed in response to the mid continent stress field the orientations of bedrock channels and joints correspond regionally with mean trends at 153 and 164 respectively in addition two dominant orientations of postglacial river valleys and bedrock joints correspond with mean trends at 104 vs 104 and 54 vs 52 respectively our findings show that the erosional channelled topography cut on bedrock together with the postglacial drainage pattern cut into younger glacial sediments are related to the trend of bedrock joints and consequently can be described as tectonically predesigned in addition this study yields new insights into the form of the preglacial tertiary drainage system in southern ontario prior to pleistocene glaciation regardless of the precise age of this preglacial system and degree of subsequent glacial modification an important factor in its geomorphic development has been the mid continent stress field

storm influenced deltas and ice scouring in a late pleistocene glacial lake this paper identifies the sedimentary record of storms and bottom scouring ice masses that is preserved in upper pleistocene glaciolacustrine delta sediments deltaic sedimentation occurred on the margin of an enlarged ice dammed ancestral lake ontario with a surface elevation at least 80 m above the modern level beds of amalgamated hummocky and swaley cross strata separated by fairweather muds represent delta front storm deposits and overlie laminated prodelta clays the central and thickest part of a 5 km long outcrop exposes variably cross stratified sand in multiple channels inset within tabular sheets of rippled sand this complex represents a broad distributary channel system about 1 6 km wide and 20 m deep cut into delta front storm sequences a large scour and related deformation structures are attributed to bottom dragging ice masses possibly pressure ridged lake ice the depositional setting outlined in this paper emphasizes the importance of storm waves in large continental glacial lakes and provides a contrast with better known low energy conditions in small glacial lake basins

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

hydrochemical interpretation of groundwater flow systems in quaternary sediments of southern ontario shallow aquifer systems in surficial quaternary sediments are geometrically complex with highly variable hydraulic characteristics consequently these systems are extremely difficult to assess hydrogeologically using conventional investigation techniques and are often poorly understood in a 500 km2 area of southern ontario hydrochemical techniques were used to investigate the hydraulic integrity and regional flow behaviour of 14 aquifer systems defined within 100 m of quaternary overburden this type of approach had been used successfully in more extensive bedrock aquifer systems but had not previously been applied on a regional scale to shallow quaternary systems where sediment geochemistry and flow conditions are highly variable and rarely known the study involved analysis of over 260 well waters for ph major ions ca mg na k hco3 cl and so4 and subsidiary ions no3 i br and f selected samples were analyzed for tritium the groundwaters are classified into eight water types two of which

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

evidence for recent groundwater flow through late wisconsinan till near toronto ontario the northern till is a thick 50 m late winsconsinan diamict unit that occurs throughout south central ontario the till has generally been regarded as massive and uniform with a very low vertical hydraulic conductivity it is similar to many other till units of mid continental north american glaciated terrain in that it is believed to inhibit recharge to underlying aquifers and afford a high degree of protection to these aquifers from surface and near surface sources of contamination standard methods of estimating hydraulic conductivity k for the northern till such as laboratory testing of core samples other studies and rising falling head field piezometer tests this study and other studies characteristically yield values on the order of 10 11 to 10 9 m s typically these values indicate advective traveltimes through the till on the order of hundreds to thousands of years in contrast isotopic evidence 2h 18o and 3h from till pore waters indicates the presence of modern post 1952 wate

restricted regional extent of the laurentide ice sheet in the great lakes basins during early wisconsin glaciation it is conventional wisdom that the last continental ice sheet in north america extended beyond the southern margins of the great lakes basins during both early ca 75 ka and late 30 ka phases of wisconsin glaciation this model hinges on the presence of a regionally extensive diamict traditionally interpreted as a subglacial till exposed in the ontario basin at toronto between last interglacial lacustrine sediments and late wisconsin tills the discovery of an in situ lacustrine ostracode fauna confirms previous sedimentological and geophysical investigations which concluded that the early wisconsin diamict is not a subglacial deposit but a stony mud deposited on the floor of an extensive glacial lake the unit together with younger mid wisconsin sediments was only overridden by the laurentide ice sheet during the late wisconsin after 30 ka we argue that during the early phase of wisconsin glaciation the laurentide ice sheet was thin highly dynamic and of insufficient volume to extend fully across the great lakes basins a situation more closely in accordance with the marine 18o 16o record and other proxy climatic data that show maximum cooling and global ice volumes at about 20 ka