the interrelation of glaciotectonic and glaciodepositional processes within the glacial environment abstract in recent years it has been recognised that ice sediment coupling occurred beneath the quaternary ice sheets that advanced over the soft sediments of lowland areas this paper looks in detail at the effects of this coupling on the sediments which results in glaciotectonic deformation and also discusses the interaction of deformation and deposition within the subglacial environment two types of glaciotectonic deformation are discussed that are produced by the active movement of ice 1 proglacial tectonics at the margin which include compressive fold styles such as listric thrusts and faults and open folding 2 subglacial tectonics formed beneath the glacier which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone styles of deformation associated with stagnant ice are also investigated we argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets it is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats it is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare whilst deformed till is very common

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

genesis of streamlined landforms and flow history of the green bay lobe wisconsin usa abstract the distribution of streamlined landforms in southeastern wisconsin suggests that drumlins and flutes formed during several phases of the green bay lobe between 18 and 14 000 bp the largest group of drumlins formed during a still stand of the ice margin during the johnstown phase presumably about 18 16 000 bp flutes and smaller drumlins are superimposed on larger forms and larger drumlins are remolded this indicates that drumlin modification continued during retreat three fields containing smaller drumlins formed after ice re advanced a short distance or stabilized during the green lake rush lake and st anna phases about 16 14 000 bp the drumlin forming process included erosion and deformation of pre existing ice marginal and proglacial sediments drumlins associated with the johnstown phase show an increase in length up glacier this is probably the result of variations in flow velocity length of time of drumlin formation and sediment availability flutes and small drumlins are associated with retreat moraines and formed near a thin retreating ice margin ice surface profile reconstructions suggest that margins were relatively steep during the johnstown milton green lake and early rush lake phases during the lake mills and late rush lake phases when flutes were forming the ice surface slopes were lower and margins were retreating during retreat minor sublobes developed some perhaps resulting from surges into small proglacial lake basins thus steep ice margins and driving stresses on the order of 15 25 kpa were typical during drumlin formation the formation of flutes and the remolding of larger drumlins into smaller forms took place beneath gently sloping ice of retreating margins associated with lower driving stresses

timing of pleistocene glacial events in new york state this review of age data for the pleistocene of new york identifies both strengths and weaknesses in the temporal framework relating the glacial chronology of the great lakes region to that of the middle atlantic seaboard the pre wisconsinan record involves saprolith and till in the adirondack mountains marine clay on long island multiple tills at fernbank otto and gowanda and major drainage derangement of the allegheny river middle wisconsinan ice spread into the allegheny plateau damming high level lakes in cayuga trough and southern ontario long island pollen data show late middle wisconsinan warming the plum point interstade glacially overridden organic matter at rush creek lord hill and st davids shows that this episode ended by 24 000 bp maximum late wisconsinan glaciation occurred during the nissouri stade 21 750 18 570 bp the concept of an erie interstade implies that ice recession 15 000 16 000 bp permitted lake drainage across new york new york evidence allows this interpr

origin of drumlins on the floor of lake ontario and in upper new york state abstract upper new york state usa contains one of the largest drumlin fields 12 000 km2 on the north america continent consisting of some 10 000 drumlins located between lake ontario in the north and the finger lakes drumlin like bedforms have also recently been discovered in deep water 200 m on the nearby floor of the rochester basin in lake ontario the new york state drumlin field was produced under the laurentide ice sheet 18 000 years ago when it extended southwards to terminate against the allegheny plateau outcrops of drumlin cores exposed by erosion along the lake ontario shoreline provide windows into the stratigraphy and sedimentology of the northern part of the field sedimentological description of 10 coastal drumlin cores combined with quantitative morphometric analysis of 1487 drumlins shows that they are the product of subglacial erosion of till sheets separated by glaciolacustrine deposits a two phase subglacial model for drumlin formation is suggested consisting of initial aggradation of extensive till deposits during ice advance followed by erosion and streamlining possibly accompanying stillstand of the ice margin and building of moraines systematic changes in drumlin morphometry and spacing are evident ranging from small numbers 60 closely spaced ovoid drumlins l w ratios between 1 and 3 drumlin shape appears to be systematically related to sediment thickness available for erosional streamlining elongate spindle forms occur on the crests and lee sides of bedrock escarpments where sediment cover is thin larger ovoid drumlins occur in topographic depressions where sediment thickness is greater offshore streamlined forms on the floor of the deep water rochester basin in lake ontario have long axes at right angles to the trend of onshore drumlins these are composed of rock rock drumlins and have an orientation structurally controlled by a newly identified inlier of proterozoic grenville province metasediments

evidence from microstructures of deformable bed conditions within drumlins chimney bluffs new york state abstract discussion on the process of drumlin formation has been ongoing for over a century at present two dominant schools of thought prevail viz formation by a subglacial hydraulic mechanisms and b due to subglacial sediment deformation the latter mechanism depends on the existence of a subglacial deformable bed evidence from part of the large central new york drumlin field reveals evidence of syn depositional deformation during the emplacement of diamictons that constitute the major portion of drumlins exposed along shore bluffs in chimney bluffs state park these diamictons cannot be lodgement till facies members but appear to comprise facies indicative of melange style deposition under subglacial deformable bed conditions the evidence obtained from microstructures and plasma fabric within these diamictons supports the existence of a deformable bed during diamicton emplacement it is likely that formation of the drumlins occurred under these same subglacial bed conditions

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

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

a geological view of drumlins in ireland facies modelling of the internal structure of drumlins has resulted in recognition of five major facies associations within the irish drumlin belt the facies associations are linked with a sequence of depositional events during the last deglacial phase ca 20 16 ka bp drumlin sediments were formed by basal till deposition subglacial fluvial lacustrine sedimentation sheet flow debris flow and subglacial cavity deposition subglacial deposition was initiated by the infilling and blocking of subglacial networks which caused a reduction in hydraulic transmissibility at the base of the ice sheet prior to drumlinisation drumlins then formed as subglacial erosional forms during surge type events when subglacial hydraulic transportational processes were active and sediment fluxes to the ice margins were high it is argued on geologic evidence that basal boundary conditions of this type coupled with high rates of ice wastage by calving at the ice margin contributed to rapid disintegration of the last ice sheet in western britain

paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event abstract during the last deglaciation of north america huge proglacial lakes formed along the southern margin of the laurentide ice sheet the largest of these was glacial lake agassiz which formed about 11 7 14 c kyr and drained into hudson bay about 7 7 14 c kyr 8 45 cal kyr overflow from these lakes was variably directed to the mississippi st lawrence and mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events when the ice dam across hudson bay finally was breached a massive flood drained lake agassiz which was routed through hudson strait to the labrador sea in terms of stored water volume the largest reservoir was associated with the kinojevis level of lake agassiz for this maximum filling the impounded water volume available to produce floods is estimated as 40 000 151 000 km 3 depending on the location of the ice margin and route used the timing of this rapid release of stored freshwater just precedes the early holocene cooling event at 8 2 cal kyr bp we use the spring hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are 5 sv and 0 5 yr multiple fillings and floods are possible as are single floods having a complex multipulse structure modelling results suggest that the outburst flood from lake agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established connecting lake agassiz to the tyrrell sea

genesis of boston harbor drumlins massachusetts abstract drumlins in boston harbor are composed of two superposed silty sandy diamicton units and subordinate sand and gravel the lower compact undifferentiated diamicton is interpreted as a pre wisconsin till based on truncated weathering profiles preserved below an erosion surface the upper less compact diamicton contains numerous discontinuous and poorly sorted lenses and stringers of sand and sandy gravel that tend to parallel the erosion surface the upper diamicton and subordinate sandy gravel lenses are interpreted to date from the late wisconsin glaciation along the exposed sections of the long island drumlin complex the preserved weathering profile on the lower diamicton is thicker beneath the drumlin axes and is either thin or missing in the interdrumlin areas this suggests that glacial erosion and streamlining of pre wisconsin deposits and their weathering profile took place after the weathering profile developed and before subsequent deposition of the overlying diamicton unit the latter drapes the erosional drumlin form without contributing substantially to relief of the drumlin form

seismic modeling and analysis of a prototype heated nuclear waste storage tunnel yucca mountain nevada wehavedevelopedseismicvelocitymodelsfortheheated rock surrounding a tunnel in yucca mountain tuff and compared the results with field data obtained at theyucca mountain drift scale test dst facility from 1998 to 2002 during that time the tunnel was heated to replicate the effects of long term storage of decaying nuclear waste and to study the effects of extreme temperatures on the surrounding rock and groundwater flow our velocity models are based on borehole temperature data thermal models and laboratory measurements on granite comparisons between field and synthetic seismograms show that superheating the rock around the tunnel causes thermally induced variations in p and s wave arrival time separation barring out of plane reflections 2d spectral element waveform modeling in the source planeconsistentlyreplicatesseismicreceiverwaveformsand classicbehaviorofpulsesreflectedfromcylinders ourmodels constrain the in situ v 1 dv dt velocity temperature derivative of the tuff to be approximately 0 5 per 100 c this velocity change is consistent with thermally induced wavespeedchangesindryrocksamplesandislowerthanexpected for water to steam conversion in saturated rock we infer that velocity changes are controlled by thermal expansion and fracturing additionally we have developed an improved method for monitoring tunnel conditions that uses waves diffracted around the tunnel in the region of changing velocity

wave field processing of data from the 1986 program for array seismic studies of the continental lithosphere ouachita experiment in may 1986 a wide aperture seismic field experiment was conducted in southwestern arkansas and northwestern louisiana this experiment was sponsored by the incorporated research institutions for seismology as part of the program for array seismic studies of the continental lithosphere the survey line runs from the south edge of the ouachita mountains out into the gulf coastal plain the experiment involved 21 shot points and two major deployments each of 400 recorders with an effective aperture of 200 km the goal of the experiment was to attempt to provide constraints on the diverse development sequences that have been proposed to explain the structure of the area the data were processed using a previously developed prestack common source acoustic finite difference migration to produce images of reflectivity in a slice 200 km long and 40 km deep this migration algorithm has no dip restrictions and uses a two dimensional variable velocity distribution for wave extrapolation interpretation of the results of the prestack processing together with the results of complementary two dimensional ray trace modeling not shown here of the data provides an enhanced picture of the structure of the paleozoic continental margin that is consistent with the observations in most previous geophysical and geological studies the main physical and temporal features of the model are crustal thinning during precambrian rifting a continent ocean boundary sedimentary wedge and carbonate bank thrusting of deepwater sediments during the ouachita orogeny and triassic rifting

seismic images of a tectonic subdivision of the grenville orogen beneath lakes ontario and erie new seismic data from marine air gun and vibroseis profiles in lake ontario and lake erie provide images of subhorizontal phanerozoic sediments underlain by a remarkable series of easterly dipping reflections that extends from the crystalline basement to the lower crust these reflections are interpreted as structural features of crustal scale subdivisions within the grenville orogen broadly deformed imbricated and overlapping thrust sheets within the western central metasedimentary belt are succeeded to the west by a complex zone of easterly dipping apparent thrust faults that are interpreted as a southwest subsurface extension of the boundary zone between the central metasedimentary belt and the central gneiss belt the interpreted central metasedimentary belt boundary zone has a characteristic magnetic anomaly that provides a link from the adjacent ends of lakes ontario and erie to structures exposed 150 km to the north less reflective west dipping events are interpreted as structures within the

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

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

drumlin evolution and ice sheet oscillations along the ne atlantic margin donegal bay western ireland abstract satellite imagery of donegal bay northwestern ireland reveals two streamlined subglacial bedform sets produced during the late devensian glaciation ca 22 000 15 000 yrs b p the first bedform set trends northeast southwest and records fast ice flow from inland ice domes onto the eastern atlantic continental shelf the second bedform set trending east west crosscuts and partially reorientates the first morphological and sedimentary evidence show that the second set corresponds to the last phase of fast ice flow drumlinization in northwestern ireland morphological characteristics of the donegal bay drumlin field and sedimentary characteristics of the mullinasole drumlin donegal bay support a two stage interpretation of drumlin evolution these are the following 1 deposition of glaciomarine mud and diamict facies at a tidewater glacier margin stratified diamicts record debris flow events and sediment reworking this facies sequence is erosionally truncated 2 deposition of subglacial diamict and sand facies recording ice readvance and drumlinization drumlinization sediment streamlining reflects ice mass balance destabilization episodic fast ice flow and ice marginal oscillation and may be correlated with millennial time scale climate changes in the circum north atlantic

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

deep structure beneath lake ontario crustal scale grenville subdivisions lake ontario marine seismic data reveal major grenville crustal subdivisions beneath central and southern lake ontario separated by interpreted shear zones that extend to the lower crust a shear zone bounded transition between the elzevir and frontenac terranes exposed north of lake ontario is linked to a seismically defined shear zone beneath central lake ontario by prominent aeromagnetic and gravity anomalies easterly dipping wide angle reflections and fractures in paleozoic strata we suggest the central lake ontario zone represents crustal scale deformation along an elzevir frontenac boundary zone that extends from outcrop to the south shore of lake ontario seismic images from lake ontario and the exposed western central metasedimentary belt are dominated by crustal scale shear zones and reflection geometries featuring arcuate reflections truncated at their bases by apparent east dipping linear reflections the images show that zones analogous to the interpreted grenville front tectonic zone are al

the meltwater hypothesis for subglacial bedforms this paper presents an historical and in places informal account of the meltwater hypothesis which invokes enormous outburst floods for the formation of subglacial bedforms it begins with a brief discussion of the difficulties of determining processes of formation for landforms which are not seen in formation analogy provides a solution to these difficulties analogy between erosional marks at the bases of turbidites and drumlins which were the starting point for this hypothesis rests on the idea that inverted erosional marks at the ice bed are subsequently infilled to form drumlins field tests on the sedimentology architecture and landform associations of drumlins in the livingstone lake drumlin field are outlined before more extensive work on bedrock erosional forms and flood routes is introduced bedrock erosional forms played a central part in establishing the hypothesis since their form and ornamentation are confidently interpreted as fluvial their form and genesis are discussed mainly with reference to sites at french river and wilton creek ontario though some remarkable bedrock erosional forms in antarctica support their regional extent initially in the meltwater hypothesis drumlins were thought to be cavity fills and erosional drumlins were recognized later this development is shown to be central to the realization that drumlin composition may be inferred from drumlin form the scale of drumlin fields measured at about 10 3 km 2 and the magnitude of the inferred floods require that the flood events were regional regional scale flood tracts in ontario quebec alberta and the northwest territories extending over 1000 km in length and several hundred kilometers in width support this suggestion floods had they occurred would have caused rapid rates of sea level rise and may have changed climate through their effects on ocean stratification and sea surface temperatures the meltwater hypothesis covers a range of bedforms besides drumlins and bedrock erosional marksffluting rogen moraine hummocky terrain and transverse ridges recent work shows how these forms are best explained by the meltwater hypothesis the roles of water storage and release which underpin the theory of the meltwater hypothesis remain poorly understood r 2002 published by elsevier science ltd