the influence of shelf crossing glaciation on continental slope sedimentation flemish pass eastern canadian continental margin abstract flemish pass is a small perched slope basin seaward of the grand banks on the eastern canadian continental margin glacial ice crossed the grand banks to reach the upper continental slope during some mid to late quaternary glaciations but terminated on the middle shelf 200 km distant at the last glacial maximum this study investigates the effect of ice extent on slope sedimentation processes sediment in flemish pass comprises muds of hemipelagic and proglacial plume origin minor thin bedded turbidite sands and thick bedded mass transport deposits mtds a regional stratigraphy based on 500 km of high resolution seismic profiles and 60 piston cores up to 11 m long was dated using 30 radiocarbon dates the presence of ash zone ii and oxygen isotope stratigraphy this provided stratigraphic control for till tongues in water depths

relative sea level changes from ne ireland during the last glacial termination deglacial sea level records from ne ireland between 21 and 11 cal ka bp record marine transgressions and sensitive lithospheric responses to ice loading the sawtooth sea level curve contains four intervals characterized by 1 strong net uplift subaerial channelling and a global meltwater pulse 21 19 cal ka bp 2 ice loading isostatic depression and high relative sea level 19 17 5 cal ka bp 3 ice loading renewed isostatic depression and high relative sea level for 1000 years 17 14 5 cal ka bp 4 catastrophic ice wastage rapid uplift and lowstand 14 5 13 cal ka bp geophysical models do not capture these fluctuations

lift off moraines markers of last ice flow directions on the scotian shelf lift off moraines are acoustically incoherent subparallel ridges observed on sidescan sonograms and high resolution reflection seismic profiles on the southeastern continental margin of canada they are up to 3 m high 20 80 m wide and are commonly overlain by stratified proglacial sediments although little is known about them detailed study of high resolution seismic profiles from the emerald basin and the lahave basin on the scotian shelf show that their height width ratio varies with the sounder seabed separation suggesting that the ridges may be narrower than they appear their morphology is similar to degeer moraines or cross valley moraines which form perpendicular to ice flow direction as their orientations can be estimated at the intersection of seismic lines they can be used to estimate ice flow directions since proglacial sediments are draped directly over top of them they are assumed to record the direction of last ice flow this directional data suggests that ice retreated not only

pre caledonian granulite and gabbro enclaves in the western gneiss region norway indications of incomplete transition at high pressure the western gneiss region of norway is a continental terrane that experienced caledonian high pressure and ultrahigh pressure metamorphism most rocks in this terrane show either peak caledonian eclogite facies assemblages or are highly strained and equilibrated under late caledonian amphibolite facies conditions however three kilometre size rock bodies flatraket ulvesund and krakenes in outer nordfjord preserve pre caledonian igneous and granulite facies assemblages and structures where these assemblages are preserved the rocks are consistently unaffected by caledonian deformation the three bodies experienced high pressure conditions 20 23 kbar but show only very localized about 5 eclogitization in felsic and mafic rocks commonly related to shear zones the preservation of pre caledonian felsic and mafic igneous and granulite facies assemblages in these bodies therefore indicates widespread 95 metastability at pressures higher than other metastable domains in norway late caledonian amphibolite facies retrogression was limited the degree of reaction is related to the protolith composition and the interaction of fluid and deformation during the orogenic cycle whereby metastability is associated with a lack of deformation and lack of fluids either as a catalyst or as a component in hydration reactions the three bodies appear to have been far less reactive than the external gneisses in this region even though they followed a similar pressure temperature evolution the extent of metastable behaviour has implications for the protolith of the western gneiss region for the density evolution of high pressure terranes and hence for the geodynamic evolution of mountain belts

late glacial impacts on dispersal and colonization of atlantic canada and maine by freshwater fishes late glacial scenarios of ice retreat and biogeography databases constrain the dispersal routes of obligate freshwater fishes into atlantic canada and maine evidence indicates glacial ice covered the present day mainland and offshore islands at 18 000 14c yr before present possible refugia for extirpated freshwater fishes were the exposed outer edge of the grand banks east exposed georges bank south atlantic refugium and the mississippi refugium in the west it is improbable that the region was recolonized from the offshore refugia rather fishes recolonized from the east via the upper st lawrence river valley into the upper saint john river maine lake madawaska from 11 000 to 12 000 14c yr bp the short period of entry resulted in the low diversity of obligate freshwater species in the region lake madawaska was breached and dispersal continued into the remainder of the region after 8000 14c yr bp by 6000 14c yr bp access routes to the east along low lying coastal zones were blocked by rising sea levels which isolated prince edward island cape breton island and most probably nova scotia natural dispersal across the region appeared complete by this time

submarine moraines in newfoundland coastal waters implications for the deglaciation of newfoundland and adjacent areas abstract submarine moraines near modern coasts of newfoundland show regional variations in architecture off the west coast arcuate moraines in shallow water were altered to varying degrees by postglacial sea level lowering off the southwest coast arcuate moraines on deep fiord mouth sills interdigitate with glaciomarine deposits whose maximum age is 14 17 ka bp off the northeast coast submarine moraines are absent at the mouths of the deep fiords morainal ridges outside the fiords are coast parallel it is proposed that the moraines formed during deglaciation of the region the late wisconsinan ice sheet extended to the edge of the continental shelf and was divided into catchments with fast flow concentrated in deep channels ice calved back along channels isolating the newfoundland ice cap and ice caps on the offshore banks ca 14 ka drawdown from the interior was localized in fiords and ice margins stabilized just offshore forming the submarine moraines described here off the southwest coasts the ice margin was maintained for up to 1 5 ka at fiord mouths off the northeast coast many of the deep wide fiords are without sills and retreat was nearly continual until the margin stabilized at fiord heads just before 13 ka

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

wisconsinan glacial and sea level history of maritime canada and the adjacent continental shelf a correlation of land and sea events the wisconsinan glacial history of maritime canada records the interaction of land based glaciers with the sea which dissects the region along the deep embayments of the bay of fundy and the laurentian channel ice centers collectively termed the appalachian ice complex shifted in a clockwise manner across the varied bedrock terranes of the region producing cross striated bedrock outcrops and compositionally distinct till sheets on land offshore glacial sediments can be correlated to their terrestrial counterparts on the basis of provenance thus establishing crucial land sea links in the glacial record five glacier flow events have been recognized during the caledonia phase in early to middle wisconsinan time ice from eastern appalachian upland sources crossed nova scotia and extended to the continental shelf edge where a calving margin was established slumping at this margin produced proximal wedge shaped bodies of diamicton that interfinger with glaciomarine sediments the caledonia phase glacier retreated during middle wisconsinan time to the inner scotian shelf during the escuminac phase in late wisconsinan time 22 19 ka an ice center formed over the magdalen shelf escuminac ice center and transported large quantities of local red bed material southward to the outer shelf slope margin this glacier retreated about 18 ka to a tidewater margin at sable island bank and banquereau sea level during this time was falling as a result of isostatic recovery from earlier escuminac phase maximum ice loads just after 18 ka ice wasted back across the midshelf basins to the tidewater margin of the scotian shelf end moraine complex and was stabilized by falling sea levels escuminac ice was reorganized into the scotian ice divide scotian phase over mainland nova scotia and the continental shelf south of cape breton island between 15 and 13 ka another period of glacier retreat ensued and the margin settled close to the present day land areas between 13 and 12 5 ka an ice margin was established from local terrestrial ice centers in northern nova scotia chignecto phase into the bay of fundy and just beyond the present day atlantic coast responding to increasing climatic warming these smaller glaciers dissipated and their margins retreated landward a sea level lowstand of 65 m on the inner shelf occurred ca 11 7 ka isolated terrestrial remnants of chignecto phase glaciers were reactivated as a result of cooling during the collins pond phase younger dryas ca 10 8 ka enhanced ice rafting evident in the north atlantic deep oceanic record appears to correlate with periods of glacier retreat in the appalachian ice complex during melting and sea level rise both the quantity and thickness of icebergs increased due to grounding line retreat within the magdalen shelf thereby increasing the net flux of hematite stained quartz to the north atlantic

the origin and flux of icebergs released into the last glacial maximum northern hemisphere oceans the impact of ice sheet topography the precipitation fields of a palaeoatmospheric general circulation model are used to derive estimates of the geographical distribution and flux of icebergs from the laurentide fennoscandinavian and eastern siberian ice sheets at the last glacial maximum lgm the atmospheric model fields from lgm simulations using climap or peltier ice 4g ice orography were studied to test the sensitivity of the predicted flux the estimated northern hemispheric lgm iceberg flux is 3500 4000 km3 yr 1 of which about 60 issued directly into the north atlantic the iceberg flux from the st lawrence area is of similar significance to that issuing from hudson strait in all estimates both the north pacific and the arctic received substantial iceberg fluxes ca 700 km3 yr 1 with relatively minor differences occurring between the two ice sheet reconstructions apparent discrepancies between arctic deep sea core samples of ice rafted debris and our estimates of mean glacial iceberg flux may be ascribed to coastal trapping of bergs the existence of floating ice tongues or a rapid exit of icebergs from the arctic basin into the greenland sea through the fram strait copyright 2001 john wiley sons ltd

relative sea level changes and glacio isostatic adjustment on the magdalen islands archipelago atlantic canada from mis 5 to the late holocene abstract the magdalen islands quebec canada in the centre of the gulf of st lawrence are located in a strategic position for providing an overview of the relative sea level rsl history of the maritime provinces of eastern canada although data are available for the coastal terrestrial areas of the maritimes data from the gulf are very scarce and both the rsl and glacio isostatic adjustment gia models extrapolate for this central region this study provides new stratigraphic and chronological data from four outcrops and two coring sites on the magdalen islands in addition to the five samples used mainly for age control purposes nine new luminescence ages are presented with these new data added to the available literature a new rsl curve is reconstructed for the lgm to the late holocene period and a partial curve is proposed for the interval between the late mis 4 to the mis 3 data also indicate a few insights for the mis 5 period results reveal that for the lgm to the late holocene the curve corresponds to the j shaped curve scenario recognized in the literature the rsl changes during this period are the result of glacio isostatic rebound migration and collapse of the peripheral forebulge and eustatic sea level changes for the lgm to the early holocene glacio isostatic depression curves displaying a few local differences are also proposed for the late holocene the data constrain the curve between two types of indicators i e marine and terrestrial and indicate that the rsl has risen at least 3 m during the last two millennia sediments dated to the mis 5 and the interval between the late mis 4 and the mis 3 illustrate that the gia following the lgm also occurred for the mis 5 interglacial and the mis 3 interstadial finally recent gia models are discussed in light of the results of this paper

a multi proxy lithostratigraphic record of late glacial and holocene climate variability from piper lake nova scotia a multi proxy lithostratigraphic record from piper lake nova scotia reveals environmental variability during the late glacial and holocene piper lake is a small shallow 3 m closed dystrophic basin located in the eastern nova scotia highlands the site was deglaciated about 14 5 cal calibrated ka bp and elevated loss on ignition values and relatively low carbon nitrogen c n isotope ratios indicate the establishment of a productive aquatic environment consistent with allerod warming the late glacial lake record is punctuated by two thin very fine grained clay layers that are correlative to the killarney and younger dryas yd oscillations they were deposited when perennial ice covered the lake the post yd lithostratigraphy indicates the rapid establishment of an increasingly productive and stable landscape this trend is reversed three times during the holocene by minerogenic units a complex 25 cm thick diamicton unique to piper lake was deposited ca 10 8 10 3 cal ka bp by slumping that was associated with periglacial slope processes and or lake level changes a direct correlation to early holocene preboreal cooling appears unlikely two thin minerogenic units deposited at ca 8 1 and ca 4 9 cal ka bp were likely the result of regional cooling and are broadly correlative with events noted in the gisp2 greenland ice sheet project 2 ice core record the holocene lithostratigraphic record from piper lake may be a consequence of unique limnological factors alternatively the strong lithostratigraphic response may be the result of the absence of a strong and persistent regional climate mechanism north atlantic oscillation which if present might have obscured the impact of hemispheric or larger scale climate forcing

major end moraines of younger dryas age on wollaston peninsula victoria island canadian arctic implications for paleoclimate and for formation of hummocky moraine some of the most extensive and massive end moraines of younger dryas age 11 10 14c ka bp yet recognized in north america occur on wollaston peninsula of victoria island on the western part of the peninsula numerous closely spaced end moraines formed in the interval starting 11 100 100 radiocarbon years ago and ending about 10 500 10 200 years ago net recession was generally slow throughout and was punctuated by moraine building and at least two readvances recession is mapped with a resolution that is approximately decadal the moraines form an orderly nested succession and are consistently associated with westward shedding of meltwater which formed a sequence of marine limit deltas we lack firm independent proxy climate evidence needed to assess whether these moraines formed because of cold younger dryas climate rather than because of controls such as topographic setting and water depth but climatic control seems probable the moraines evidently retain glacier ice cores as do most similarly

a late glacial holocene palaeoecological record from pye lake on the eastern shore of nova scotia canadageological survey of canada contribution 20080395 pollen and chironomid analyses and radiocarbon dating at pye lake on the eastern shore of nova scotia are used to outline the vegetation and climatic history of the area the coast was deglaciated prior to 12 200 14c bp 14 300 cal bp and herbaceous tundra vegetation invaded the area midge inferred maximum summer surface water temperatures in the lake ranged between 9 and 11 c subsequent gradual warming to 18 c by 10 800 14c bp 12 725 cal bp favoured the migration of a variety of herbaceous and shrub taxa into the region rapid cooling to 10 c saw vegetation revert to herbaceous tundra communities this interval related to the younger dryas cold interval of the north atlantic and europe lasted until 10 000 14c bp 11 630 cal bp the climate then warmed again to conditions similar to those that prevailed immediately before onset of younger dryas cooling further warming saw successive tree species migrate into the area until by the mid holocene the forests contained most of the taxa preva

late glacial stratigraphy and history of the gulf of st lawrence reply the three dimensional configuration of the quaternary sediments in the gulf of st lawrence is described based on analysis of 8000 km of high resolution seismic reflection data complemented by anal

sedimentary and rock magnetic signatures and event scenarios of deglacial outburst floods from the laurentian channel ice stream abstract eastern canadian margin sediments bear testimony to several catastrophic deglacial meltwater discharges from the retreating laurentide ice sheet the reddish brown plumite layers deposited on the levees of the laurentian fan valleys have been recognized as indications of multiple outburst floods between heinrich events 2 and 1 five event layers have been consistently recorded in three new gravity cores retrieved on the sw grand banks slope and comply with the previously published laurentian fan core md95 2029 the apparently huge extent of these outburst plumes around the laurentian fan as well as their causes and consequences are investigated in this study using physical properties rock magnetic and grain size analyses together with seismoacoustic profiling we provide the first detailed 14c ages of the outburst event sequence and discuss their recurrence intervals in the context of regional ice retreat compared to the hemipelagic interlayers event layers have overall uniform and systematic changes of rock magnetic properties hematite contents increase over time and proximally while magnetite grain sizes fine upwards and spatially away from the fan based on the sediment composition and load we argue that these plumites were formed by recurrent erosion of glacial mud deposits in the laurentian channel by meltwater outbursts three alternative glaciological scenarios are evaluated in each case the provenance of the transported sediment is not an indicator of the precise source of the meltwater

late cenozoic architecture of the st pierre slope the late cenozoic seismic stratigraphy of the continental slope south of western newfoundland is interpreted using new seismic reflection profiles new miocene pliocene biostratigraphic palynology age determinations on the hermine e 94 well on the northwestern grand banks of newfoundland are correlated to the study area the quaternary section of st pierre slope is disrupted by numerous failure scarps and mass transport deposits but correlation from the mid slope to the continental rise is achieved using major mass transport deposits as markers on the upper slope stacked downslope thinning wedges of acoustically incoherent sediment are interpreted as till deposits of mid to late pleistocene age sedimentation rates in the youngest part of the succession are estimated from a 30 ka radiocarbon date 25 m below the horizon of the youngest till tongue which is exposed on a 60 m deep failure surface extrapolation of sedimentation rates and comparison with dated sections on the j anomaly ridge and bermuda rise provides a consistent interpreted age model for the till tongues that corresponds to marine isotope stages 2 4 6 8 10 and 12

mapping subtle structures with light detection and ranging lidar flow units and phreatomagmatic rootless cones in the north mountain basalt nova scotia light detection and ranging lidar is an emerging technology to generate high resolution digital elevation models dems subtle topographical differences among three flow units of the jurassic north mountain basalt eastern canada are visible on a lidar derived dem the boundaries were verified by field mapping and allow a simple projection of the contact planes through the terrain model to provide a three dimensional visualization of the flow units several ring structures in the lower flow unit distinguishable only in the lidar data are interpreted to be the remnants of rootless phreatomagmatic cones glacial erosion has since excavated the highly fractured cone material leaving the more resistant dike and quenched melt to form protruding ring structures the ability to detect subtle variations in topography using lidar may identify previously undetected landscape elements

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

quaternary geology and surficial sediment processes browns bank scotian shelf based on multibeam bathymetry abstract browns bank is located on the glaciated continental shelf off southern nova scotia geological mapping of browns bank is based on interpretation of multibeam bathymetric and backscatter data in conjunction with 220 line km of seismic reflection profiles and sidescan sonograms sea floor sediment samples and bottom photographs the fundian moraine part of the previously identified end moraine system on the continental shelf off nova scotia is a prominent west east flat topped multi lobate ridge identifiable in the multibeam bathymetric data and in geophysical records the fundian moraine was subjected to erosion in the surf zone during sea level rise in depths less than 100 m a series of north south roughly parallel till ridges continuous in the subsurface with the fundian moraine is interpreted as interlobate moraines suggesting formation by a tidewater glacier the browns bank moraine connected to the fundian moraine is evidence of a newly identified grounded ice position farther seaward than the latter bedforms including obstacle marks comet marks sand waves and megaripples are evidence of a vigorous anticyclonic current pattern on browns bank the combination of multibeam bathymetric imagery with high resolution geoscientific information represents a powerful technique for sea floor geological investigations

sea level change and inner shelf stratigraphy off northern ireland new seismic stratigraphic vibracore and ams c 14 dates from two sites off the northern ireland coast yield information on the deglacial to present sea level history and shelf evolution of the region a lowstand of sea level at about 30 m below present sea level recorded by fossils in a lowstand shoreline deposit occurred around 13 4 cal ka b p following a period of rapid isostatic uplift associated with a rsl fall of 6 7 cm yr following the lowstand contrasting styles of sedimentation characterized the two study sites in the sheltered environment of belfast lough the lowstand shoreline was overtopped and buried by transgressive facies of intertidal and shallow sub tidal mud and sandy mud on the high energy portrush coast the inner shelf sedimentary sequence is characterized by a basal conglomerate overlain by well sorted sands with occasional interbedded gravel c 2006 elsevier b v all rights reserved

evidence from 40ar 39ar ages of individual hornblende grains for varying laurentide sources of iceberg discharges 22 000 to 10 500 yr b p the abundance and lithic content of ice rafted detritus in glacial north atlantic sediment cores vary abruptly on millennial time scales that have been correlated to dansgaard oeschger cycles in the greenland ice cores there is growing evidence that various ice sheet outlets contributed increased iceberg fluxes at multiple discrete intervals and the relative timing of iceberg discharges from different sources is important for understanding interactions between oceans and ice sheets we present a provenance study based on 40ar 39ar dates of individual hornblende grains from 20 samples taken at 600 to 700 yr spacing between 10 500 and 22 000 yr b p from orphan knoll core ew9303 ggc31 heinrich layers are characterized by a dominant paleoproterozoic hornblende provenance consistent with published studies a change in provenance between heinrich events h2 and h1 indicates contributions of iceberg calving from the newfoundland and southern labrador margins between h1 and the younger dryas interval paleoproterozoic ice rafted grains remained dominant the dominance of baffin island or greenland sources to the ice rafted detritus is ascribed to the retreat of the southern laurentide ice sheet at about the time of h1 a retreat that isolated newfoundland and southern labrador ice from the shelf slope boundary

paleoceanographic significance of sediment color on western north atlantic drifts i origin of color reflectance spectra collected during odp leg 172 were used in concert with solid phase iron chemistry carbonate content and organic carbon content measurements to evaluate the agents responsible for setting the color in sediments factor analysis has proved a valuable and rapid technique to detect the local and regional primary factors that influence sediment color on the western north atlantic drifts sediment color is the result of primary mineralogy as well as diagenetic changes sediment lightness is controlled by the carbonate content while the hue is primarily due to the presence of hematite and fe 2 fe 3 changes in clay minerals hematite most likely derived from the permo carboniferous red beds of the canadian maritimes is differentially preserved at various sites due to differences in reductive diagenesis and dilution by other sedimentary components various intensities for diagenesis result from changes in organic carbon content sedimentation rates and h2s production via anaerobic methane oxidation iron monosulfides occur extensively at all high sedimentation sites especially in glacial periods suggesting increased high terrigenous flux and or increased reactive iron flux in glacials 7 2002 elsevier science b v all rights reserved

subtropical iceberg scours and meltwater routing in the deglacial western north atlantic during the last deglaciation northern hemisphere ice sheets discharged ice and meltwater seafloor scours and numerical modelling suggest that freshwater and icebergs from the laurentide ice sheet reached the subtropical north atlantic

late quaternary sedimentation on the southwestern scotian slope eastern canada relationship to glaciationgeological survey of canada contribution 20070176 the sedimentary record on continental slopes has the potential to preserve a record of glacial retreat on the adjacent continental shelf the glacial history of the southwestern part of the scotian shelf is poorly known air gun and high resolution sparker profiles and numerous sediment cores up to 10 m long have been used to determine the character of sedimentation on the southwestern scotian slope since the last glacial maximum lgm seismic reflection profiles show that glacial till was deposited at shallow depths on the upper continental slope and correlation to dated piston cores farther downslope show that this till dates from the lgm slope sedimentation at this time was dominated by local ice and deposited as plume fallout and turbidites progressively increasing importance of red brown sediment derived from glacial supply to laurentian channel indicates retreat of ice from the shelf edge and diminishing supply of proglacial sediment from the calving embayment in the mid scotian shelf with the

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

a reexamination of pleistocene tunnel valley distribution on the central scotian shelf tunnel valleys are an erosional channel characterized by anastomosing steep sided channel systems formed by subglacial confined meltwater flow our study uses two dimensional 2d industry reflection seismic on the scotian shelf near sable island to better constrain the geometry of tunnel valleys in the area here u to v shaped buried channels north and west of sable island extensively branch reconnect and meander they average 2 5 km wide and 150 700 m deep below sea level and have a dominantly north south orientation immediately to the south and southwest of sable island the channels become narrower 1 1 5 km shallower 300 400 m maximum and more widely spaced multiple tunnel valley generations may be present but could not be separately mapped there is a notable gap of 20 30 km between the ends of the detectable tunnel valleys and the shelf edge south of sable island an exception is erosive features at the shelf edge at the head of logan canyon but these channels are disconnected from the tunnel valley network further north and may not be tunnel valleys the reason for the gap south of sable island is not clear however we do not believe it is due to data coverage or resolution issues if the tunnel valleys genuinely end south of sable island then the gap between them and the shelf edge means that between the gully and logan canyon these subglacial meltwater channels did not empty directly at the shelf edge this implies direct meltwater and sediment delivery by tunnel valleys to the scotian slope during the pleistocene may have been limited in this area

differences between the last two glacial maxima and implications for ice sheet δ18o and sea level reconstructions studies of past glacial cycles yield critical information about climate and sea level ice volume variability including the sensitivity of climate to radiative change and impacts of crustal rebound on sea level reconstructions for past interglacials here we identify significant differences between the last and penultimate glacial maxima lgm and pgm in terms of global volume and distribution of land ice despite similar temperatures and radiative forcing our analysis challenges conventional views of relationships between global ice volume sea level seawater oxygen isotope values and deep sea temperature and supports the potential presence of large floating arctic ice shelves during the pgm the existence of different glacial modes calls for focussed research on the complex processes behind ice age development we present a glacioisostatic assessment to demonstrate how a different pgm ice sheet configuration might affect sea level estimates for the last interglacial results suggest that this may alter existing last interglacial sea level estimates which often use an lgm like ice configuration by several metres likely upward

north american ice sheet build up during the last glacial cycle 115 21 kyr the last glacial maximum lgm outline and subsequent retreat pattern 21e7 kyr of north americanice sheets are reasonably well established however the evolution of the ice sheets during their build upphase towards the lgm between 115 and 21 kyr has remained elusive making it difficult to verifynumerical ice sheet models for this important time interval in this paper we outline the pre lgm icesheet evolution of the laurentide and cordilleran ice sheets by using glacial geological and geomorphologicalrecords to make a first order reconstruction of ice sheet extent and flow pattern we mappedthe entire area covered by the laurentide and cordilleran ice sheets in landsat mss images andapproximately 40 of this area in higher resolution landsat etm images mapping in aerial photographsadded further detail primarily in quebec labrador the cordilleran region and on baffin island our analysis includes the recognition of approximately 500 relative age relationships from crosscuttinglineations together with previously published striae and till fabric data these are used as the basis forrelative age assignments of regional flow patterns for the reconstruction of the most probable ice sheetevolution sequence we employ a stepwise inversion scheme with a clearly defined strategy for delineatingcoherent landforms swarms reflecting flow direction and configuration and linking these topreviously published constraints on relative and absolute chronology our results reveal that icedispersalcentres in keewatin and quebec were dynamically independent for most of pre lgm time andthat a massive quebec dispersal centre rivalling the lgm in extent existed at times when the sw sectorof the ice sheet had not yet developed the oldest flow system in eastern quebec labrador atlanticswarm had an ice divide closer to the labrador coast than later configurations a northern keewatin central arctic ice sheet existed prior to the lgm but is poorly chronologically constrained there is alsoevidence for older and more easterly cordilleran ice sheet divide locations than those that prevailedduring the late wisconsinan in terms of ice sheet build up dynamics it appears that residual ice capsafter warming phases may have played an important role in particular the location and size of remnantice masses at the end of major interstadials i e ois 5c and 5a must have been critical for subsequentbuild up patterns because such remnant uplands may have fostered much more rapid ice sheetgrowth than what would have occurred on a fully deglaciated terrain the ice sheet configuration duringstadials would also be governed largely by the additional topography that such residual ice constitutesbecause of inherent mass balance topography feedbacks

the drift des demoiselles on the magdalen islands quebec canada sedimentological and micromorphological evidence of a late wisconsinan glacial diamict the deposits identified as being the drift des demoiselles which is the upper unit of the southern magdalen islands quebec canada belong to two units of different origin glacial and glaciomar

numerical modeling of flow and scour below a pipeline in currents part ii scour simulation abstract a vertical two dimensional 2d numerical model for time dependent local scour below offshore pipelines subject to unidirectional steady flow is developed the governing equations for the flow and sediment transport are solved by using finite difference method in a general curvilinear coordinate system the performance of two turbulence models the standard k model and smagorinsky subgrid scale sgs model on modeling time dependent scour processes is examined both suspended load and bed load are considered in the scour model the suspended load model is verified against two channel sediment transport cases the change of bed level is calculated from the continuity equation of total sediment transport a new time marching scheme and a sand slide scheme are proposed for the scour calculation it is found that the proposed time marching scheme and sand slide model work well for both clear water and live bed scour situations and the standard k turbulence closure is more preferable than the sgs model in the 2d scour model developed in this study

late glacial stratigraphy and history of the gulf of st lawrence discussion the cruise of the c s s hudson in 1990 was a memorable introduction to marine geoscience and north atlantic storms land and sea based geologists were thrown together to link land and sea sedimentary records and get a better understanding of the complex glaciation of atlantic canada atlantic canada is an amalgam of distinctive tectonic terranes where lithic markers can be used to reconstruct glacial flow patterns e g stea and pe piper 1999 provenance analysis can also help to establish correlations between terrestrial and marine stratigraphic records once offshore ice margins and onshore flow lines are linked up former pleistocene glaciers can be modelled stea et al 1998 used these methods to develop an ice advance and retreat history of maritime canada the gulf of st lawrence region was a critical area for the reconstruction and little data was available josenhans and lehman 1999 have made a significant advance in the understanding of the marine record to complete the link with the terrestrial records in the gulf of st lawrence while on the cruise i logged piston cores and examined the lithologies of large 1t iku grab samples from the till units in the gulf of st lawrence that were mapped using high resolution seismic data stea 1991 much of that lithic data was not presented in the summary paper by josenhans and lehman 1999 which is unfortunate because of its important ramifications for ice reconstructions the lithic data and terrestrial radiocarbon dates from the surrounding land areas imply a much greater thickness and extent of late glacial ice than in the model presented by josenhans and lehman 1999 i will briefly review the pebble lithological results addressing the questions of ice flow paths and ice thickness then discuss contradictions between the josenhans lehman model of deglaciation of the gulf of st lawrence and the stea et

ice rafted detritus evidence from 40ar 39ar ages of individual hornblende grains for evolution of the eastern margin of the laurentide ice sheet since 43 14cky abstract during the last glacial interval the north atlantic ice sheets expanded and contracted in approximate synchronicity with orbitally forced global climate change variation in ice rafted detritus content in north atlantic marine sediment cores record the waxing and waning of glaciers as well as the abrupt temperature changes at millennial time scales the background variations of ice rafting are punctuated by heinrich layers which appear to record the catastrophic collapse of the laurentide ice sheet through the hudson strait the objective of this paper is to document the evolution of glaciation on laurentia during the last 43 14c kyr we present a provenance study based on 40ar 39ar dates of individual hornblende grains from 57 samples taken at 2 cm spacing between 4 and 134 cm from core v23 14 43 4 n 45 25 w 3177 m sedimentation rates outside of the heinrich layers are very low in this core but the heinrich layers are easily identified laurentide glaciation did not extend into the ocean south of 55 n until about 26 14c kyr and retreated to the coastline or beyond by 14 14c kyr documenting the history of this major ice sheet has significant implications for understanding ice rafting sources in more distal locations where mixing among different ice sheets is likely

karst geology and hydrogeology of cape breton island nova scotia an overview approximately 23 2700 km2 of cape breton island consists of a wide variety of glaciated bedrock meta carbonates carbonates and evaporites that has the potential for karst development an additional 1100 km2 of such strata have been inundated by post glacial sea level rise there have been three main episodes of karstification the island represents a portion of the tectonically ancient deep crustal eroded terrain of the appalachian orogen more recently influenced by the interplay of sea level change ice sheet stability transient ice aquifers climate change and isostatic rebound lowland karst units are generally characterized by broad scale till covered thick evaporite sequences within this zone are solution trenches near basin boundaries salt diapirs and extensive foundering zones due to salt dissolution which allowed development of karst breccias to depths exceeding 300 m the presence of local salt springs suggests a process to move saline water up from depth through foundering brec

petrographic evidence from the eastern canadian margin of shelf crossing glaciations abstract it is difficult to evaluate when and where glaciers extended across the outer continental shelf off eastern canada the outer shelf and upper slope are commonly hard bottomed or have a great thickness of post glacial sediment in either case making direct sampling and dating of ice margin sediment impossible the timing and extent of glacier ice is important for understanding continental slope sedimentation and ice sheet dynamics we have therefore determined the lithologic components of the 1 4 mm granule fraction of over 100 well dated samples from 40 cores from the more distal parts of the deep water margin off nova scotia and newfoundland this fraction is demonstrably ice rafted in these cores and geographic variation in component results from input of icebergs at different calving margins the samples show that heinrich layers have a distinctive granule fraction that shows some areal variation as a result of dilution by sources other than hudson strait heinrich event 2 ca 21 ka is widespread as far southwest as the west scotian slope but by the last glacial maximum lgm numerous discrete sources of ice rafted granules are recognised implying that calving ice margins were present in several places off newfoundland and nova scotia including off banquereau a distinctive purplish lgm gravelly mud is recognised on the eastern newfoundland margin derived from a calving margin on the ne newfoundland shelf at the time of heinrich event 1 ca 14 ka there was a calving ice outlet somewhere on the grand banks and another in halibut channel retreat of ice from the gulf of st lawrence can be tracked by changing granule petrology from the lgm to 13 ka these data suggest that final ice retreat from many parts of the outer shelf was later than is shown in many recent ice margin reconstructions

laurentide ice sheet dynamics in the bay of fundy canada revealed through multibeam sonar mapping of glacial landsystems abstract recent multibeam sonar data collected in the bay of fundy canada interpreted in conjunction with geophysical profiling and sediment sampling reveal in unprecedented detail a suite of glacial landforms associated with the southwest margin of the laurentide ice sheet these landforms constitute four glacial landsystems 1 subglacial landsystem i in southwestern bay of fundy the elongated grand manan basin contains ice contact sediments of possible mid wisconsinan age overlain by late wisconsinan ice contact sediments strongly imprinted by iceberg furrows and pits in places possible mid wisconsinan glaciomarine sediments have been eroded by late wisconsinan ice creating streamlined landforms eroded bedrock and megafluted ice contact sediment on the flanks of grand manan basin indicate the southwest direction of topographically steered ice 2 subglacial landsystem ii along the southern margin of the bay of fundy an array of drumlins with superimposed esker complexes was formed by glacial ice that emanated northwest from the interior of nova scotia and was deflected to the southwest by the ice flowing out of the bay of fundy to the gulf of maine the esker complexes formed later when the nova scotia ice sheet stagnated and meltwater escaped northwest via topographic gaps 3 ice marginal landsystem i in northern bay of fundy both small de geer moraines and larger basin bounding moraines were created when retreating late wisconsinan ice became grounded in relatively shallow water new radiocarbon ages show that the owen basin moraine in this landsystem was abandoned prior to c 14 600 14 c yr bp cal bp 17 015 17 270 0 7 17 286 17 405 0 3 4 ice marginal landsystem ii this distinctive landsystem consists of numerous arcuate moraines commonly superimposed on one another this landsystem was formed by thin 170 m lightly grounded ice that retreated northeast into the bay of fundy the splayed pattern of the ice margin was a response to a large accommodation space and velocity variations within the ice the isle haute moraine is a large lobate moraine its age is poorly constrained by shells from glaciomarine sediments 13 750 60 14 c yr bp cal bp 15 970 15 996 0 03 16 047 16 665 0 97 but the moraine may be coeval with the onset of a terrestrial ice margin established at the head of the bay of fundy by c 14 300 14 c yr bp cal bp 16 824 17 013

a conceptual model of the deglaciation of atlantic canada abstract we present a conceptual model for the deglaciation of atlantic canada in which a role is played by ice streams the ice margin lay close to the edge of the continental shelf at the last glacial maximum ice streams occupying shelf troughs comprised 1 a major ice stream in the laurentian channel 2 secondary streams in the bay of fundy gulf of maine trinity trough and notre dame channel and 3 lesser ice streams elsewhere early retreat in the northeast notre dame bay and in the southwest bay of fundy gulf of maine was mainly by calving along embayments by 18 ka radiocarbon years a calving embayment had opened on emerald basin scotian shelf retreat along channels marooned ice on intervening banks a major calving episode beginning just before 14 ka removed ice from the gulf of st lawrence triggering re advances down secondary troughs isolation of a newfoundland ice cap produced radial drainage via fiords and more extensive flow into the st george s bay lowlands on the west coast by 13 ka most ice was on land and was ablating by melting rather than calving shelf ice caps persisted until 11 ka

late holocene sea level changes and isostatic crustal movements in atlantic canada abstract it has long been recognised that sea levels along the shores of atlantic canada have been rising rapidly during the holocene in response to isostatic crustal movements new sea level data for the bay of fundy coast of southern new brunswick little dipper harbour and the atlantic coast of nova scotia chezzetcook inlet show that late holocene average rates of sea level rise in these areas have been 1 0 and 2 5 m per 1000 yr respectively numerical model calculations suggest that the high rates of sea level rise are due to crustal subsidence produced by the combined effects of laurentide ice loading forebulge collapse and ocean loading of the scotian shelf although ice loading is the dominant contributor to the regional sea level pattern ocean loading is also important contributing up to 40 of the total crustal subsidence in some areas tide gauges record rates of sea level rise during the 20th century that are 0 7 1 9 mm yr higher than late holocene trends with the highest residuals occurring in the bay of fundy

provenance of sediment in the labrador current a record of hinterland glaciation over the past 125 ka the labrador current flows southward along the continental margin off eastern canada and is the principal source of sediment to the outer continental margin areas where ice sheets did not cross the continental shelf we present multi proxy mineralogical and geochemical records based principally on x ray diffraction and x ray fluorescence for core 2011031 059 from northern flemish cap to determine changes in supply and hence to reconstruct provenance evolution during the last glacial cycle the calcite to dolomite ratios in heinrich layers ranged from 2 to 4 suggesting carbonate layers derived from hudson strait as early as marine isotope stage mis 5a d mineral abundance shows three time dependent predominant sediment sources other than in heinrich layers i baffin bay shelves and adjacent land in mis 5 and 1 with high ca sr kaolinite and feldspars and low clay minerals and calcite dolomite ratios ii labrador in mis 3 with low clays and grey color and iii north east newfoundland shelf in mis 2 and 4 with higher concentrations of clay minerals red sandstones and transition elements these results allow a reconstruction of principal ice streams supplying the north west atlantic over the last full glacial cycle

geologic evolution of the gulf of maine region abstract in this study we reconstruct the evolution of the northern new england passive margin whose development has been influenced by pleistocene glaciations the morphology of the northern new england shelf is rather unique consisting of a inner lowland the gulf of maine with an average depth of 150 m and an area of 90 700 km2 and georges bank a high whose crest is less than 40 m deep and has an area of 27 000 km2 the bank s northern slope facing the gulf of maine has a maximum relief of 377 m on the seaward side of georges bank is the 2000 m high continental slope deeply cut by canyons two channels northeast and great south channels east and west of georges bank provide passageways from the gulf of maine to the open sea this morphology was acquired by a combination of tertiary fluvial erosion pleistocene glacial erosion deposition and pleistocene holocene marine processes fluvial glacial erosion in the gulf of maine was so extensive as to expose basement thus making it possible to map the various terranes making up this foundation these terranes include the pre carboniferous avalon and meguma units a carboniferous permian rift basin formed by the oblique continental collision during the closure of the paleozoic proto atlantic and a late triassic early jurassic rift system created during the opening of the present atlantic basement in the gulf of maine remained above sea level from the opening of the atlantic 190 ma early jurassic to the eocene 55 ma that the gulf of maine remained a high for so long may have been due to igneous activity along the northwest trending boston ottawa lineation extending from the vicinity of the st lawrence river canada to gulf of maine from late triassic to early cretaceous the northwest trending new england seamounts south of georges bank may represent a seaward extension of this lineation on georges bank rising hundreds of meters above the gulf of maine the basement exposed in the gulf is mantled by sediments thousands of meters thick included in these sediments are early jurassic to earliest cretaceous reefs along the continental slope and carbonates north of the reefs grading landward into continental sediments cretaceous cenozoic continental marine terrigenous sediments and pleistocene glacial deposits the continental slope on the seaward flank of georges bank has a complex history of early to mid mesozoic carbonate accretion mid to late mesozoic and cenozoic calcareous terrigenous sediments and canyon erosion burial and exhumation going back to early cretaceous