ice flow patterns and glacial transport in the eastern hudson bay region implications for the late quaternary dynamics of the laurentide ice sheet recent field surveys in the eastern hudson bay region have led to the discovery of regional ice flow sequences that require a significant reassessment of the late quaternary dynamics of the laurentide ice sheet two regional ice flow phases can be recognized from till compositional data and from crosscutting relationships observed on striated bedrock surfaces the oldest is directed toward the northwest and north northwest while the youngest is directed toward the west and includes a late glacial deflection toward the southwest the wide regional distribution of striae formed during the early northwestward glacial movement together with the recognition of palimpsest glacial dispersal trains associated with this phase suggest that it was a long lived time transgressive regional event the ensuing glacial movement is a regionally dominant westward ice flow phase during which several large glacial dispersal trains were formed downglacier from distinctive bedrock sources the largest of these trains extends

a low order model of the heinrich event cycle if heinrich events result from free oscillations in the size and basal melting conditions of the laurentide ice sheet a rigorous quantitative analysis of ice sheet physics should describe their dynamics to explore this possibility i exploit two characteristic timescales which arise from ice sheet physics to construct a relaxation oscillator model of the north atlantic s heinrich events the numerical implementation of this model confirms the notion that the periodicity of heinrich events approximately 7 000 years is determined by the gross properties of a steady glacial climate e g an annual average sea level temperature of 10 c and an adiabatic lapse rate

origins of the ice contact stratified ridges eskers of ireland abstract an extensive system of ridged landforms composed of ice contact stratified sediment was deposited in the central lowland of ireland during the most recent deglaciation 18 000 bp the ridges have been interpreted by others as deposits of an ice sheet drainage system i e eskers and as such have been used with other data to reconstruct the deglacial history the traditional deglaciation model shows systematic retreat of ice from south to north our study which involves an analysis of the ridged landforms using lithofacies sedimentary structures and paleocurrent data in conjunction with the geomorphology indicates that the pattern and nature of the ridges are not compatible with this model and support a new model of deglaciation warren 1991 in which the esker system fo med in an interlobate area during the simultaneous shrinking of two main glacial outflow centers an extensive lake system developed in the lowland between the two outflow centers ridges formed both perpendicular and parallel to ice margins involved both active and stagnating ice are both continuous and segmented beaded and were deposited in subaqueous and subaerial environments almost all of the ridges are associated with lacustrine sediments ice contact ridges are polygenetic and a genetic classification is proposed those that formed perpendicular to the ice margin are termed eskers those that formed parallel are termed moraines distinction between esker types continuous or beaded subglacial tunnel fills fluvial ice channel fills and subaqueous fans and moraine types s baqueous or subaerial is crucial to a reconstruction of the mode and pattern of deglaciation in the central irish lowlands

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

ice streams as the arteries of an ice sheet their mechanics stability and significance ice streams are corridors of fast ice flow ca 0 8 km year within an ice sheet and are responsible for discharging the majority of the ice and sediment within them consequently like the arteries in our body their behaviour and stability is essential to the well being of an ice sheet ice streams may either be constrained by topography topographic ice streams or by areas of slow moving ice pure ice streams the latter show spatial and temporal patterns of variability that may indicate a potential for instability and are therefore of particular interest today pure ice streams are largely restricted to the siple coast of antarctica and these ice streams have been extensively investigated over the last 20 years this paper provides an introduction to this substantial body of research and describes the morphology dynamics and temporal behaviour of these contemporary ice streams before exploring the basal conditions that exist beneath them and the mechanisms that drive the fast flow within them the paper concludes by reviewing the potential of ice streams as unstable elements within ice sheets that may impact on the earth s dynamic system d 2002 elsevier science b v all rights reserved

thermokarst and export of sediment and organic carbon in the sheldrake river watershed nunavik canada 1 a spatiotemporal computation of permafrost decay covering the period from 1957 to 2009 and validated by field investigations was made over a 76 km2 river catchment straddling the tree line in the discontinuous permafrost zone east of hudson bay in order to estimate the amounts of sediments and organic carbon released by thermokarst lithalsas and palsas are the dominant permafrost landforms whereas thermokarst ponds landslides active layer failures and gullies are the main features of permafrost degradation results show that 21 of the existing permafrost in 1957 had disappeared in 2009 resulting in a 96 growth of the thermokarst pond cover and a 46 to 217 increase of the number of active erosion landforms an increase of stream connectivity related with the degradation of permafrost potentially allowed for an increase of sediments and carbon delivery to the main stream by a factor of 1 6 volume of active landslides and gullies also increased by 12 to 38 enhancing sediment and organic matter yields significant differences in permafrost degradation and in sediment and carbon inputs were observed along an east west transect from sites located at the head of the watershed near the tree line to sites located downstream close to the hudson bay coast thermokarst ponds in the forest tundra area released 2 3 times more sediments and dissolved organic carbon per unit of area in the fluvial system than in the shrub tundra area despite these yields by thermokarst the sheldrake river catchment currently does not seem to be yielding proportionally more sediments and carbon than a permafrost free river catchment

continental slope morphology and sedimentary processes at the mouth of an antarctic palaeo ice stream abstract continental slope and shelf edge morphology off marguerite bay western antarctic peninsula is investigated using swath bathymetric data and parametric sub bottom profiler records together with sediment cores marguerite bay has a well defined cross shelf trough and a relatively steep continental slope the slope beyond the trough mouth is convex in longitudinal profile whereas to the north and south it is concave and reaches a maximum of 12 there are no deep canyons cutting into the prograding outer shelf and slope instead a series of gullies runs down the upper slope reaching depths of 200 m south of the trough mouth but

kinematics of the inntal shear zone sub tauern ramp fault system and the interpretation of the transalp seismic section eastern alps austria abstract a new interpretation of the inntal tauern sector of the transalp seismic section is presented one of the most prominent contrasts in reflectivity in the transalp seismic section is the contact between the bajuvaric unit in the footwall and the overlying tirolic unit and its basement across a moderately south dipping interface we trace this contact from the surface at the southern margin of the inn valley to a depth of 5 km there the contact is deformed or cut by the tauern window northern margin we define the contact between bajuvaric and tirolic units as brixlegg thrust which is older than miocene tauern window exhumation and has a paleogene age the sub tauern ramp connects with the inntal fault system at the surface and roots below the tauern window oblique thrust movements across this fault system in the miocene caused exhumation of the hanging wall where the fault has a ramp geometry which is in the area of the transalp cross section and west of it east of the transalp cross section the fault system merges with alpine basal thrust which is a flat no miocene exhumation occurred above the flat

pollen based quantitative reconstructions of holocene climate variability in nw romania abstract a modern analogue technique is applied to two high resolution pollen sequences from nw romania to provide the first quantitative evidence for winter summer and annual temperatures and for precipitation across the holocene in this region the pollen based climate reconstructions allow the identification of four main intervals i an early less stable period between 11 700 and 11 200 cal yr bp ii generally stable conditions between 11 200 and 8300 cal yr bp with winter and annual temperatures and precipitation higher than at present and summer temperatures about the same iii lower winter and annual temperatures and higher summer temperatures and precipitation between 8000 and 2400 cal yr bp iv warmer winter and annual temperatures and lower precipitation for the last 2400 years whereas summer temperatures became cooler at steregoiu and remained stable at preluca tiganului the pollen based climate reconstructions at the two sites show similar patterns in annual and winter temperatures and precipitation changes during the holocene but the trends appear to be less consistent for summer temperatures our pollen based reconstructions revealed several short term climatic oscillations during the holocene the strongest of which occur between 10 300 10 100 8300 8000 6800 6400 5100 4900 4000 3600 and 3200 3000 cal yr bp

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

late holocene history of the moldova river valley romania abstract this paper describes the results of geomorphological sedimentological and 14 c analyses of late holocene fluvial sequences in the moldova river valley of romania this river originates from the carpathians mountains and is known for the extent of its large floodplain and sediment thickness between the molid and timisesti localities river length 86 km numerous large fossil trunks of oak poplar and beech trees are exposed in the riverbanks six wood samples were selected for radiocarbon absolute dating conventional method and their ages ranged from 410 to 3200 cal yrs bp the thickness of the alluvial sediments above the sampled fossil trunks varied between 2 and 3 m and these sediments predominantly consisted of coarse gravel materials that had similar granulometry to sediments that were present in the modern riverbed additionally in the same investigated areas successive floodplain cross sections were constructed based on more than 20 hydrogeological boreholes for each cross section all data were used to calculate the local values of bed loads and these values were compared to the absolute ages of the fossil trunks and were in the range of 300 m 3 m and 5500 m 3 m based on the calculated values during the last 780 years the floodplain sedimentation rates were estimated to be in the range of 0 4 m 3 year at the molid section which was located in the mountainous area of the valley and 44 km downstream from the river headwater and during the last 410 years the sedimentation rate at the praxia section which was located 125 km downstream from the river headwater was 13 3 m 3 year in the past 100 years the fluvial processes along the moldova river were dominated by a narrowing by an average of 76 and an incision up to 2 5 m and a channel metamorphosis from braided to wandering was reported these results are discussed in the context of late holocene regional and local palaeoclimatic reconstructions as well as that of human interventions

dynamics of the laurentide ice sheet in hudson bay canada abstract interpretation of sidescan sonar and high resolution sub bottom seismic data from hudson bay has led to the development of a model for final disintegration of the laurentide ice sheet the well preserved geomorphic features observed from the bay floor are similar to subaerially exposed glaciogenic features observed around the perimeter of hudson bay and can be related to the following three paleoenvironments subglacial erosion deposition ice margin deposition and reworking and post glacial reworking and burial subglacial features observed include fluted terrains with superimposed rogen moraines relief attributed to ice surging eskers subglacial channels and dead ice topography de geer moraines and recessional moraine complexes indicate the mechanism and orientation of ice breakup retreat the orientations of these features are locally consistent with regional trends indicating the overall direction of ice sheet flow and retreat during the last phase of the laurentide ice sheet subglacial channel complexes incised into the till and bedrock and high energy bedforms deposited on the till surface occur in present day water depths down to 160 m due to isostatic depression these could have been as much as 315 m deeper at the time of formation they indicate a wet based glacier with high energy subglacial drainage during the late phases of ice retreat the sidescan sonar data also reveal numerous zones of distinctive morphology attributed to ice breakup and post glacial processes cross cutting relationships allow the determination of the relative ages of these zones from oldest to youngest these zones are interpreted to represent scouring of the bedrock and overburden by the remnants of the ice sheet seafloor scouring by tabular icebergs which moved in a tidally induced arcuate pattern or under the influence of massive glacial lake outflows development of dead ice topography under residual ice masses and random iceberg scouring by smaller icebergs restricted to present day water depths of less than 180 m recently published reconstructions of the collapse of the laurentide ice sheet based on dated quaternary sections on land suggest that the bay was rapidly deglaciated in approximately 400 years the well preserved and distinctive glaciogenic and stratigraphic indicators observed from the bay floor suggest that they were formed by a succession of mechanisms which were too short lived to obliterate the underlying evidence of deglaciation this supports the interpretation of extremely rapid deglaciation of hudson bay and points out that subsequent marine processes have not been sufficient to obliterate the glacial features

early holocene deglaciation of northern hudson bay and foxe channel constrained by new radiocarbon ages and marine reservoir correction abstract radiocarbon ages from southampton island canada provide new chronological control on the deglaciation of foxe channel and northern hudson bay a strategic area for understanding the demise of a marine based portion of the laurentide ice sheet a regional marine reservoir age of 630 45 yr and a reservoir offset r of 263 48 yr were calculated from two early to mid holocene terrestrial marine radiocarbon age pairs these values are consistent with corrections based on early 20th century mollusks suggesting that following deglaciation the oceanic conditions controlling the regional reservoir effect rapidly became similar to those of modern times however our r value is 352 52 yr less than another correction from eastern foxe basin which may be affected by 14 c dilution from carbonate rocks our r value is used to calibrate new marine radiocarbon ages which help further develop the deglaciation history of southampton island especially along the north coast where deglaciation of foxe channel appears to have been completed by 8100 7800 cal yr bp 2 this provides key chronological constraints on the development of a long marine ice margin in southern foxe basin prior to the final breakup of the foxe ice dome

palaeo ice streams abstract the location and behaviour of ice streams is one of the most important controls on ice sheet configuration and stability in order to reconstruct former ice sheets we need to know ice stream location and timing once identified the beds of palaeo ice streams provide an unprecedented opportunity to glean information about their basal environment something that remains very difficult under contemporary ice streams this paper represents the first synthesis and discussion of palaeo ice stream research from a variety of former ice sheets and includes new insights relating their configuration and activity to the evidence they leave behind the ambiguous use of the term ice stream is addressed and four possible configurations for ice streams are presented diagnostic landforms and landform assemblages that we would expect an ice stream to produce are discussed and the temporal context of bedform generation is described as either a rubber stamped or smudged bedform imprint resulting from isochronous or time transgressive landform generation in particular we focus on the configuration of terrestrially terminating ice streams for which there are no modern analogues technological advances in marine geophysics are helping to generate a convergence of interest between antarctic glaciology and palaeo glaciology it is suggested that investigations around the fringes of contemporary ice sheets i e west antarctica can provide evidence that directly links the geomorphological record of palaeo ice streams with their contemporary counterparts in addition computational advances and modelling adaptations have permitted the incorporation of ice streams within ice sheet models we argue that data from palaeo ice stream beds are invaluable to ice sheet stream modelling experiments and will help us understand ice stream operation and the linkages between climate perturbations and both palaeo and contemporary ice sheets

early holocene deglaciation of the eastern coast of hudson bay abstract the final stage of deglaciation of hudson bay was a major holocene catastrophic event marked by the drainage of lake agassiz ojibway at 8 47 ka cal bp and the rapid collapse of the laurentide ice sheet previous work undertaken in the nastapoka river area eastern hudson bay demonstrated that during the relative sea level highstand that shortly followed the drainage of the lake the western margin of the quebec labrador ice sector rapidly retreated eastward to reach a stillstand position in a coastal hill range in this study an analysis of landsat 7tm images has allowed a mapping of large scale glacial landforms outwash deposits eskers flutings and de geer and rogen moraines between kuujjuaraapik se hudson bay and puvirnituq ne hudson bay the key results from this mapping are i ice contact outwash deposits mapped along the entire arc shaped coastline of the eastern hudson bay outline a major ice stillstand phase in the coastal hills that extended at least from kuujjuaraapik to inukjuak the presence of these hills allowed a stabilisation of the ice margin that led to the accumulation of thick and extensive ice contact submarine fans ii the position of these deposits on the down ice side west of large sets of flutings indicates an important phase of sediment delivery by a rapid ice flow phase toward a marine based ice margin iii a second system of outwash deposits observed farther inland indicates a subsequent phase of stabilisation of the ice margin during its retreat toward central quebec labrador

push moraines and glacier contact fans in marine and terrestrial environments the local climatic regime and the mass balance state are important determinants of the dynamics of terrestrial and marine glacier fronts which in turn determine the sediments and landforms produced at the glacier front many modern glaciers undergoing overall retreat in areas of maritime climate produce winter push moraines during a late winter readvance followed by a summer retreat whilst in more continental regions no significant winter readvance occurs and annual push moraines are absent the frontal dynamics which lead to these changes are analysed and the form structure sequence and field relations of both terrestrial and marine push moraines are described from iceland spitsbergen and baffin island long term changes in mass balance leading to major glacier advances or readvances also generate large push moraines in terrestrial environments push moraine formation is accompanied by uplift rejuvenation and down cutting of outwash systems whose sediments become closely associated with glaciotectonic structures which permit pre syn and post tectonic sequences to be identified the development of ice marginal fan moraine complexes is modelled as a function of the relative magnitude of two parameters the velocity of ice movement and the calving rate a high ice velocity just exceeded by the calving rate gives closely spaced push moraines and confluent ice marginal fans a high velocity far exceeded by the calving rate produces closely spaced moraines but separate ice marginal fans a low ice velocity in combination with a high calving rate results in well separated and feebly developed push moraines while a low ice velocity and a low calving rate produces feeble push moraines and coalescent fans

glaciomarine sediments of the isle of man as a key to late pleistocene stratigraphic investigations in the irish sea basin the northern part of the isle of man in the central irish sea basin is identified as a raised marine foreland containing the largest subaerial exposure of last glaciation marine and glaciomarine sediments yet recognized on the british continental shelf a large push ridge that crosses the foreland identifies a major ice limit the ridge divides the foreland stratigraphy into a coarsening upward marine sequence of pelagic muds with dropstones sand and gravel to the south from offlapping stratified and massive sandy diamict assemblages overlying glaciotectonized marine sediments to the north coarse grained diamicts are argued to form part of a push ridge subaqueous outwash depositional system deposited when processes of suspension deposition density underflow ice rafting highly variable traction current activity and sediment gravity flow were operative adjacent to a grounded marine ice margin the identification of large offshore submarine banks aligned parallel to the bride moraine suggests that construction of the push ridge subaqueous outwash depositional system may have been repeated during ice recession this and published descriptions of other irish sea tills indicate that analogous structures and sediments are present offshore and around the irish sea basin

large scale ice moulding a discussion of genesis and glaciological significance abstract landsat images reveal a previously unsuspected large scale pattern of streamlining within drift which comprises a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain consideration of the genesis and glaciological significance of such landforms leads to a number of conclusions it is suggested that mega scale glacial lineations were formed under conditions of fast ice flow and their presence may thus record former locations of ice streams or surge events many lineations of varying scales display a pattern that reveals that they were not formed in sub marginal positions extensive sets of lineations must have been formed approximately synchronously thus indicating that lineation generation occurs over a wide range of glaciodynamic conditions from sub marginal positions to interior portions of ice sheets subglacial deformation of tills has been widely invoked to account for rapid glacier motion criteria for identifying such tills are restricted to structures viewed in cross section and it is thus hard to assess how widespread the processes of deformation may have been lineations provide a surface marker of structure that records subsequent deformation from other ice flow events it is argued that the palaeo flow record including cross cutting patterns provides the surface or plan expression of subglacial deformation the degree of modification to pre existing lineations should permit the identification of zones favoured by deformation and thus assist in an assessment of how pervasive deforming bed processes were in influencing ice sheet dynamics

climate change and recent sedimentation in nastapoka sound eastern coast of hudson bay in an attempt to determine to what extent the impact of recent climate changes that occurred east of hudson bay including important reduction of areas in permafrost had on the coastal marine environment a series of shallow cores were extracted from the seabed off the mouth of the sheldrake river in nastapoka sound a total of 25 cores were taken in april 2009 from the ice cover a preliminary seafloor map was first done to help in the selection of the coring sites nastapoka sound has a complex subaqueous relief formed of asymmetric ridges and deep basins after preliminary sedimentological analyses six of the cores were selected for physical and chronological analyses 14c 210pb and 137cs dating among them three were selected for elemental c n oc tn and isotopic 13c 15n analyses to identify sedimentary organic matter sources sedimentation processes are complex and are primarily driven by bottom currents this is confirmed by the absence of a clay fraction in several cores some erosi

deglacial and postglacial evolution of the pingualuit crater lake basin northern quebec canada abstract the pingualuit crater located in the ungava peninsula northern quebec canada is a 1 4 ma old impact crater hosting a 245 m deep lake the lake has a great potential to preserve unique paleoclimatic and paleoecological sedimentary records of the last glacial interglacial cycles in the terrestrial canadian arctic in order to investigate the stratigraphy in the lake and the late quaternary glacial history of the pingualuit crater this study compiles data from three expeditions carried out in may 2007 9 m long sediment core in august 2010 50 km of seismic lines and in september 2012 high resolution terrestrial lidar topography of the inner slopes despite the weak penetration 10 m of the 3 5 khz subbottom profiling caused by the presence of boulders in the sedimentary column seismic data coupled with the stratigraphy established from the sediment core enabled the identification of two glaciolacustrine units deposited during the final stages of the laurentide ice sheet lis retreat in the crater two episodes of postglacial mass wasting events were also identified on the slopes and in the deep basin of the crater the high resolution topography of the internal slopes of the crater generated from the lidar data permitted the confirmation of a paleolake level at 545 m and determination of the elevation of drainage outlets together with the mapping of glacial and deglacial landforms from air photographs the lidar data allowed the development of a new deglaciation and drainage scenario for the pingualuit crater lake and surrounding area the model proposes three main phases of lake drainage based on the activation of seven outlets following the retreat of the lis front toward the southwest finally as opposed to other high latitude crater lake basins such as lake el gygytgyn or laguna potrok aike where high resolution paleoclimatic records were obtained owing to high sediment accumulation rates the seismic data from the pingualuit crater lake suggest extremely low sedimentation rates after the retreat of the lis owing to the absence of tributaries

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

sakami moraine quebec a 500 km long moraine without climatic control the laurentide ice sheet in eastern canada disintegrated step by step as evidenced by several morainic complexes although commonly interpreted as reflecting climatic events it seems probable that the disintegration simply related to changes in the dynamics of the ice margin without climatic control from the example of the late glacial sakami moraine in quebec formed during the drainage of lake ojibway into the tyrrell sea the concept of a re equilibration moraine already briefly proposed is developed the construction of such a moraine implies a stabilization of the ice front when the glacier margin previously floating or calving in a lacustrine or marine basin is suddenly grounded because of topographic blocking or abrupt drop of water level due to drainage the glacial retreat then pauses until the equilibrium profile of the ice is restored and a morainic accumulation can form during the halt

marginal formation of de geer moraines and their implications to the dynamics of grounding line recession de geer moraine ridges occur in abundance in the coastal zone of northern sweden preferentially in areas with proglacial water depths in excess of 150 m at deglaciation from detailed sedimentological and structural investigations in machine dug trenches across de geer ridges it is concluded that the moraines formed due to subglacial sediment advection to the ice margin during temporary halts in grounding line retreat forming gradually thickening sediment wedges the proximal part of the moraines were built up in submarginal position as stacked sequences of deforming bed diamictons intercalated with glaciofluvial canal infill sediments whereas the distal parts were built up from the grounding line by prograding sediment gravity flow deposits distally interfingering with glaciolacustrine sediments the rapid grounding line retreat ca 400 m yr 1 was driven by rapid calving in turn enhanced by fast iceflow and marginal thinning of ice due to deforming bed conditions the spatial distribution of the moraine ridges indicates stepwise retreat of the grounding line it is suggested that this is due to slab and flake calving of the ice cliff above the waterline forming a gradually widening subaqueous ice ledge which eventually breaks off to a new grounding line followed by regained sediment delivery and ridge build up less

sedimentology and geochemistry of thermokarst ponds in discontinuous permafrost subarctic quebec canada 1 thermokarst thaw ponds and lakes are distributed throughout arctic and subarctic regions however their natural variability and temporal evolution recorded in the bottom sediments are poorly understood this paper presents a multiproxy study conducted in a subarctic site with many thermokarst ponds near kuujjuarapik whapmagoostui on the eastern shore of hudson bay sedimentological geochemical and chronological analyses have been performed on short sediment cores 10 20 cm retrieved from limnologically contrasted ponds analyses revealed two distinct sedimentary facies from bottom to top 1 massive marine silts and clays deposited during postglacial tyrrell sea transgression ca 8000 to 6000 cal yr bp subsequently emerged by glacio isostatic rebound and more recently ca 1500 to 400 cal yr bp affected by permafrost inception and growth 2 laminated organic rich lacustrine muds deposited since permafrost thawing and subsidence i e since thermokarst pond inception the last centuries despite displaying strikingly different water colors the study ponds showed similar long term developmental patterns regarding their physico chemical properties as recorded in the sediments such as decreasing mineral grain size from silts to clays decreasing major chemical element concentrations increasing organic matter content and decreasing bottom water oxygen concentrations from well oxygenated to anoxic hypoxic conditions

deep structure and kinematics of the northern calcareous alps transalp profile the northern calcareous alps nca of southern bavaria and northern tyrol constitute a carbonate dominated polyphase fold thrust wedge together with its grauwacken zone basement it is the northernmost part of the far travelled upper austroalpine thrust complex of the eastern alps the present geometry developed in several kinematic stages jurassic extensional faults that affected large parts of the nca and their basement originated when the main part of the nca was still located southeast of the central alpine otztal silvretta complex these faults and related facies transitions influenced the later style of detachment of the nca thrust sheets mid to late cretaceous detachment thrust sheet stacking and motion over the central alpine complex are registered in clastic deposits of syntectonic basins the latest cretaceous to cenozoic nne to n directed motion of the nca towards europe in front of the central alpine complex created another set of significant contraction structures which at depth overprinted all previous structures during cretaceous to cenozoic deformation the nca experienced about 80 km of shortening i e about 73 along the transalp profile the european basement and autochthonous mesozoic cover beneath the allochthonous nca thrust sheets and flysch complexes seem to have remained relatively undeformed

frozen bed fennoscandian and laurentide ice sheets during the last glacial maximum the areal extents of the laurentide and fennoscandian ice sheets during the last glacial maximum about 20 000 years ago are well known1 but thickness estimates range widely from high domed2 to thin3 with large implications for our reconstruction of the climate system regarding for example northern hemisphere atmospheric circulation and global sea levels this uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials4 a knowledge of which would better constrain reconstructions of ice sheet thickness here we show that in the absence of direct data the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen and thawed bed conditions we argue that ribbed moraines were formed by brittle fracture of subglacial sediments induced by the excessive stress at the boundary between frozen and thawed bed conditions resulting from the across boundary difference in basal ice velocity maps of glacial landforms from aerial photographs of canada and scandinavia reveal a concentration of ribbed moraines around the ice sheet retreat centres of quebec keewatin newfoundland and west central fennoscandia together with the evidence from relict landscapes that mark glacial areas with frozen bed conditions the distribution of ribbed moraines on both continents suggest that a large area of the laurentide and fennoscandian ice sheets was frozen based and therefore high domed and stable during the last glacial maximum

numerical models of the inversion of half graben basins 1 we investigate the dynamic evolution of fold and thrust structures which form by compression and inversion of a sequence of half graben basins the choice for a half graben geometry is motivated by seismic studies and reconstructions of preinversion geometry of inverted regions which show that rifting often leads to a series of half grabens to examine the deformational structures which result from basin inversion we use a two dimensional viscous plastic numerical model and start our experiments from a preexisting extensional geometry we find that synrift and postrift sediments are uplifted in the initial stages of basin inversion this uplift is accompanied by rotation of the basement blocks beneath the basins in the postrift sequence new shear zones form which are a continuation of basin bounding faults with continuing shortening further inversion is more difficult owing to relative strengthening of the half graben region significant surface erosion facilitates inversion back thrusts mainly develop in association with listric basin bounding faults and less for planar domino array faults weak sediments such as salt or shales at the base of the basins promote the development of basement shortcut faults the presence of a postrift decollement layer tends to decouple deformation of the postrift sediments from the material below it in our model preexisting weak basin bounding shear zones are a requirement for substantial amounts of basin inversion to occur our numerical model results display many first order characteristics of examples from nature and analogue studies

an updated radiocarbon based ice margin chronology for the last deglaciation of the north american ice sheet complex abstract the north american ice sheet complex naisc consisting of the laurentide cordilleran and innuitian ice sheets was the largest ice mass to repeatedly grow and decay in the northern hemisphere during the quaternary understanding its pattern of retreat following the last glacial maximum is critical for studying many facets of the late quaternary including ice sheet behaviour the evolution of holocene landscapes sea level atmospheric circulation and the peopling of the americas currently the most up to date and authoritative margin chronology for the entire ice sheet complex is featured in two publications geological survey of canada open file 1574 dyke et al 2003 quaternary glaciations extent and chronology part ii dyke 2004 these often cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka all ages in uncalibrated radiocarbon years using a combination of geomorphology stratigraphy and radiocarbon dating however by virtue of being over 15 years old the ice margin chronology requires updating to reflect new work and important revisions this paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies we also update the original radiocarbon dataset from the 2003 2004 papers with 1541 new ages to reflect work up to and including 2018 a major revision is made to the 18 ka ice margin where banks and eglinton islands once considered to be glacial refugia are now shown to be fully glaciated our updated 18 ka ice sheet increased in areal extent from 17 81 to 18 37 million km2 which is an increase of 3 1 in spatial coverage of the naisc at that time elsewhere we also summarize region by region significant changes to the deglaciation sequence this paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of dyke et al 2003 and dyke 2004 where new information is lacking this is a pragmatic solution to satisfy the needs of a quaternary research community that requires up to date knowledge of the pattern of ice margin recession of what was once the world s largest ice mass the 36 updated isochrones are available in pdf and shapefile format together with a spreadsheet of the expanded radiocarbon dataset n 5195 ages and estimates of uncertainty for each interval

ice flow evolution of the labrador sector of the laurentide ice sheet a review with new evidence from northern quebec abstract outcrops bearing stained striated facets indicative of north northeastward moving ice truncated by unstained striated facets indicative of various younger flows occur in the caniapiscau area of north central quebec this is the first report of differential staining of striated facets in the region we propose that the staining occurred in an ice free interval of probable interglacial age this early ice flow probably occurred during ice retreat toward the quebec highlands ice flow and glacial transport data from the southern hudson bay and james bay basins indicate that the next major regional ice flow was toward the northwest and resulted from the expansion of an early wisconsinan glacier in the quebec highlands the northern part of this flow was diverted northwestward through hudson bay and the southern part southwestward across james bay following a progressive counterclockwise rotation of flow a zone of intersection zi of two major glacier bedform systems often referred to as the horseshoe shaped labrador ice divide represents the head of a large northward convergent ice flow system that extended to ungava bay and beyond the ungava flow propagated southward and captured the head of the opposing flow from an outflow centre located east of caniaspiscau reservoir we propose that this capture event correlates with the gold cove advance in ungava bay and on baffin island at about 9900 14c yr bp it is the largest advance of quebec labrador ice yet proposed for the region this correlation is based on the relative ice flow chronology accommodation of glacial lakes naskaupi and mclean in the deglaciation sequence the constraints placed on last glacial maximum lgm ice configuration by the postglacial uplift pattern and events in the deep sea record therefore the ungava ice flow pattern is not a relict pre wisconsinan glacial landscape as recently proposed

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

holocene forest dynamics in northwestern romnania pollen analyses and ams radiocarbon measurements were carried out on peat deposits from the former crater lake preluca tiganului located in a mid altitude area of the gutaiului mountains nw romania in order to reconstruct the postglacial vegetation history at the lateglacial holocene transition the open vegetation was replaced by forest suggesting a fast response to climatic warming the rapid expansion of pinus betula and later picea may be due to their existence in the area during the lateglacial at approximately 11 250 cal yr bp the dense forest was composed primarily of ulmus and some picea betula and pinus a small population of ulmus might also have survived in the area during the lateglacial at 10750 cal yr bp quercus tilia and fraxinus followed by corylus at c 10200 cal yr bp expanded significantly in the forest the delay of approximately 550 years in their establishment as compared to the expansion of ulmus was probably due to their immigration from more distant localities

late miocene vegetation reconstruction with the caraib model abstract climatic outputs from the atmospheric general circulation model echam4 coupled to a mixed layer ocean model are used as inputs to the caraib global vegetation model to reconstruct the distribution of vegetation and the biosphere carbon stocks over the continents during the late miocene tortonian the results show significant changes in the geographical distribution of vegetation during the late miocene compared to the present with a reduction of desert areas and an expansion of tropical seasonal forests which reached temperate latitudes these changes in vegetation distribution are accompanied by a moderate increase of the total biosphere carbon stock by 159 gt sensitivity tests to atmospheric co 2 have also been performed with the vegetation model only i e while keeping constant all climatic variables to their reference tortonian state these tests point out the potential importance of co 2 fertilization both regarding vegetation distribution and biosphere carbon storage the impact of an atmospheric co 2 decrease from 280 to 200 ppmv or increase from 280 to 560 ppmv on the vegetation distribution appears to be at least as large as that of the climate change between the tortonian and the present while in terms of carbon storage the impact of atmospheric co 2 is far much larger than the climatic one although the actual response of vegetation to co 2 fertilization may be much smaller than its theoretical response in the model these results emphasize the need to consider atmospheric co 2 as an important parameter for palaeovegetation reconstructions

multi proxy records of environmental changes in hudson bay and strait since the final outburst flood of lake agassiz ojibway abstract in this study postglacial continuous high resolution data from five marine sediment cores from hudson bay and hudson strait are presented up to now studies in this area focused on the distinction between large scale climatic variations like the glacial postglacial transition or most recent processes however as demonstrated in this study using sedimentological geochemical and geophysical parameters postglacial sediments provide provenance signals distinguishing between proterozoic dubawnt group sediments paleozoic limestone sources underlying parts of hudson bay and strait and precambrian granitoids from the canadian shield for example it is shown that redistribution of dubawnt group sediments is of minor importance after the outburst flood of lake agassiz paleoproductivity indicators also give insights into paleotemperature trends these are in phase with terrestrial reconstructions from that area colder conditions in hudson strait until ca 4500 cal bp followed by a signal of warmth until ca 4000 cal bp are suggested subsequently a cool interval lasting until approximately 2000 cal bp occurred thereafter a gradual decrease in temperature was observed reaching lowest values during the little ice age period and increasing again afterwards

genesis of de geer moraines in finland abstract the proposed model of the genesis of de geer moraines in finland is based mainly on the distribution of the moraine areas in relation to the palaeohydrological environment and on the composition and two and three dimensional fabrics of the material in order to shed some light on the geochronological problem involved the distances between successive ridges in a number of de geer moraine series are also compared with clay varve data on deglaciation rates in finland granulometrically petrographically and morphometrically de geer moraine till does not differ significantly from tills of surrounding areas two dimensional fabrics stress orientations at right angles to the ridge crest and three dimensional analyses reveal the slope conformable character of pebble inclinations generally spacings of the de geer moraine ridges do not confirm annual deglaciation rates as conveyed by clay varve data it is suggested the moraines were formed in basal crevasses of the ice following active flow phases of a local surging nature during the quiescent phase of the surge cycle the ice subsided into a water soaked till mattress filling up basal cavities from the proximal or the distal side finnish de geer moraines are thus neither annual nor end moraines they are subglacial bedforms with no geochronological meaning except that they formed during one single surge cycle as the marginal zone of the ice sheet calved and thinned it was lifted by proglacial water and the whole group of moraines became free of ice almost simultaneously

sedimentary facies and depositional architecture of ice contact glaciomarine systems abstract the characteristics of ice contact glaciomarine systems are reviewed based on a range of weichselian and holocene examples from the fjordal basins in norway and svalbard these depositional systems occur as large morphological ridges end moraines including push moraines which are coarse grained and show large scale foreset bedding the paper addresses some of the major problems with regard to the recognition classification and stratigraphic analysis of these systems the ice proximal glaciomarine systems are classified here into three categories 1 ice contact submarine fans 2 ice contact deltas and 3 glaciofluvial deltas this classification integrates morphological and sedimentological criteria and renders these glaciomarine systems not only easier to recognize in the stratigraphic record but also possible to compare with common non glacial deltaic systems the emphasis is on the criteria for the recognition of the ice contact glaciomarine systems i e ice contact fans and ice contact deltas and their discrimination from common gilbert type deltas and fan deltas the review further focuses on ice contact glaciomarine systems as highly sensitive recorders of glacier dynamics and climatic fluctuations it is shown that both the periods of ice front stability and changes in the ice front position as well as the magnitude and rate of those changes are all recorded in the ice contact depositional system the sedimentary record further reflects glacio isostatic sea level changes and local palaeogeography a new conceptual model is suggested which places these ice contact glaciomarine systems in a dynamic stratigraphic context the model integrates sedimentary facies and their depositional architecture in an allostratigraphic framework and is meant to be a guide for the analysis of the sedimentary record of ice contact systems

a highly mobile laurentide ice sheet revealed by satellite images of glacial lineations satellite images of the north american continent reveal previously unrecognized patterns of crossing drift lineations reflecting unexpected shifts of centres of mass of the laurentide ice sheet throughout the last glacial cycle such shifts must must have been associated with major global atmospheric circulation changes

isotopic climate record in a holocene stalagmite from ursilor cave romania the pu 2 stalagmite from ursilor cave provides the first dated romanian isotope record for the holocene the overall growth rate of the speleothem was 3 5 cm kyr 1 corresponding to a temporal resolution of 142 y between each isotope analysis the hendy tests indicate that isotopic equilibrium conditions occurred during the formation of pu 2 and hence that it is suitable for palaeoclimatic studies the relationship between 18 o and temperature was found to be positive this can be interpreted either as rain out with distance from the west northwest ocean source of evaporation or shifts in air mass source with changing north atlantic oscillation indices applying five u th thermal ionisation mass spectrometric tims dates to a 17 5 cm isotope profile 18 o

a 9000 year record of cyclic vegetation changes identified in a montane peatland deposit located in the eastern carpathians central eastern europe autogenic succession or regional climatic influences abstract we present a high resolution continuous plant macrofossil remains record complemented by a pollen sequence from t ul muced bog in the eastern carpathian mountains romania the record spans the last 9000 years and we test whether peatland development in the eastern carpathians is linked to climate change or to autogenic succession we find that sphagnum magellanicum was the dominant peat forming species for ca 8000 years but we also identify ten phases of increased representation of eriophorum vaginatum at approximately 8100 7550 6850 6650 5900 4650 3150 1950 1450 and 750 cal yr bp visual inspection and wavelet analysis show that the episodic increases in the relative abundances of eriophorum vaginatum were simultaneous with decreased abundances of sphagnum magellanicum and sphagnum angustifolium comparison with published palaeoclimatic records in this region suggests that these cyclical successions of s magellanicum and e vaginatum appear to be primarily a result of climate changes with e vaginatum developing mainly during dry phases and s magellanicum during wetter periods we therefore suggest that the development of this peatland was largely influenced by changing climatic conditions although the role of autogenic plant succession cannot be excluded our results show the value of ombrotrophic peat deposits as archives of past climate change

sedimentology of an ice contact glaciomarine fan complex nastapoka hills eastern hudson bay northern quebec abstract emerged holocene coalescing glaciomarine fans are exposed along the nastapoka hills eastern hudson bay the fans form part of a regional stratified drift belt associated with terrestrial and submarine frontal moraines and other grounding lines deposits these thick extensive and in many cases coalescent sediment bodies were deposited during a stillstand of the quebec labrador sector qls of the laurentide ice sheet lis that pinned on the hills during eastward retreat from hudson bay the fans are composed of basal interbedded and interlaminated sand silt and silty clay facies association i fa i deposited by suspension settling from overflow plumes sediment gravity flows and ice rafting towards the ice contact zone fa i interfingers with diamict layers fa ii deposited by gravity flows and ice rafting these two sedimentary units are overlain by interbedded sand and gravel fa iii formed by reworking during subsequent emergence parts of fa i and fa ii were remobilized by submarine gravity flows which prevailed long after ice retreat the sedimentology of the nastapoka hills provides information on the processes operating near the grounding line of a temperate ice sheet reaching tidewater

fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model the evolution of ice sheet configuration and flow pattern in fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model i e a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets the model uses mapped flow traces and deglacial melt water landforms as well as relative chronologies derived from cross cutting striae and till lineations as input data flow trace systems were classified into four types i time transgressive wet bed deglacial fans ii time transgressive frozen bed deglacial fans iii surge fans and iv synchronous non deglacial event fans using relative chronologies and aggregation of fans into glaciologically plausible patterns a series of ice sheet configurations at different time slices was erected a chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume geological evidence exists for several discrete ice sheet configurations centred over the scandinavian mountain range during the early weichselian the build up of the main weichselian fennoscandian ice sheet started at approximately 70 ka and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern norway this configuration had a flow pattern which is poorly reproduced by current numerical models of the fennoscandian ice sheet at the last glacial maximum the main ice divide was located overthe gulf of bothnia a major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the scandinavian mountain chain widespread areas of preserved pre late weichselian landscapes indicate that the ice sheet had a frozen bed core area which was only partly diminished in size by inward transgressive wet bed zones during the decay phase

deglaciation landforms and c 14 chronology of the lac guillaume delisle area eastern hudson bay a report on field evidence abstract this paper presents new field data pertaining to the deglaciation of the lac guillaume delisle area aiming to establish its emplacement in time and space between the breaching of the laurentide ice sheet lis over hudson bay and the final ice disintegration over northern quebec and labrador the deglaciation of the east coast of hudson bay started at 8200 cal bp in the south western sector of the lac guillaume delisle estuary when the marine limit was at 271 m above sea level asl by 8000 cal bp frontal moraines and proximal glacio marine sediments were deposited in the transverse valleys along the coastal cuesta ridges at a mean elevation of 250 m asl they are associated with a regional topographic pinning event of the western margin of the quebec labrador ice sheet qlis on the high coastal relief at that time the coastal relief encouraged a change in deglaciation mode from fast calving in the open and deep tyrrell sea to a tidewater ice sheet controlled by the topography the ice front thereafter retreated eastward under very large and fast crustal unloading where ice contact deltas fed by short sandar and eskers were deposited between 7900 and 7400 cal bp between 240 and 195 m asl as the ice front was receding inland and lost contact with tyrrell sea a series of deposits and landforms characterize this modification in the sedimentation regime when the ice sheet margin changed from tidewater to terrestrial dating shows that the deglaciation of the western margin of qlis on land was very fast i e faster than when the front of the ice sheet was in contact with the tyrrell sea as the fall of the relative sea level continued a large volume of paraglacial sediments was deposited in the river valleys making up vast fluvial terraces and deltas between 6500 and 5800 cal bp between 125 and 100 m asl since then land emergence has continued at a rate of about 1 3 m century downcutting by rivers post glacial deltaic sedimentation and shoreline changes still continue today

the nastapoka drift belt eastern hudson bay implications of a stillstand of the quebec labrador ice margin in the tyrrell sea at 8 ka bp during deglaciation of eastern hudson bay the western margin of the quebec labrador sector of the laurentide ice sheet came to a stillstand about 8 14c ka bp along the nastapoka hills a series of topographic highs along the bay these hills are the northward continuation of the eastern hudson bay cuesta system it left a drift belt consisting of ice contact submarine fans along the western slopes of the hills small frontal moraines on hilltops and grounding line deposits on sills between the hills geomorphological sedimentary and radiometric evidence suggest that the stillstand responsible for deposition of the nastapoka drift belt was either entirely or partly synchronous with the deposition of the sakami moraine farther south there was a period when these two morainic systems marked a continuous ice margin these stillstands occurred due to reduction of ablation at the ice margin in the nastapoka hills ablation slowed down when the ice margin was anchored on higher relief and stood at a region

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

subglacial landforms and deposits in central and northern quebec canada with emphasis on rogen moraines abstract the development of the anatomy and the morphology of a relatively simple till sheet deposited over parts of the canadian shield is discussed this is characterized by the common occurrence of well developed streamlined landforms and rogen moraines the sedimentation of the till sheet was an alternating succession of depositional and erosional or landforming events the former leading to the sedimentation of various till lithofacies the latter leading to the development of various morainic terrains this orderly sequence of subglacial events occurred during the deglaciation of central and northern quebec with the controlling factors being bed rock topography and geology ice thickness and basal ice temperatures till lithofacies include in ascending stratigraphic order lodgement till subglacial melt out till immature lodgement till and varieties of supra glacial ablation deposits morainic terrains include drumlinized and fluted ground moraine rogen moraines as well as fluted and unfluted hummocky moraine rogen moraines are formed subglacially a few kilometers behind the glacier margin as a consequence of localized compressive stresses which result in shearing and stacking of slices of near base englacial debris later deposited as a basal melt out till the moraines are believed to be a characteristic landform associated with shield type rock surfaces namely an irregular topography of asymmetric rock basins of all sizes resulting from the areal scouring of hard rocks as well the moraines are believed to be as well a characteristic landform resulting from the flattening profile of the margin of the waning ice sheet the formation of the moraines led to enhanced flow in marginal areas generating late events of streamlining and boulder plucking

first deep seismic reflection images of the eastern alps reveal giant crustal wedges and transcrustal ramps 1 the alps are considered as a classical example for an orogen created by continental plate collision in this study we present new images obtained from deep seismic reflection profiling in the eastern alps between munich and venice which give rise to examine and revise existing concepts the seismic sections exhibit a prominent bi verging reflection pattern at crustal scale a major ramp like structure outcropping at the inn valley fault can be traced southward over 80 km into the mountain root where relics of the subducted penninic ocean are expected new models of the evolution of the eastern alps show an upper lower crustal decoupling along transcrustal thrust faults with opposite thrust directions of both the european and the adriatic african continents

increased atmospheric dust deposition during the neoglacial in a boreal peat bog from north eastern canada abstract dust deposition in north eastern canada was estimated from the geochemical signature of a boreal peat bog from the james bay lowlands the rare earth elements and other lithogenic elements as well as nd isotopes were measured by q icp ms icp oes and mc icp ms respectively along a 4 20 m peat core covering the last 7000 years a principal component analysis performed on the geochemical dataset shows that rees display the same chemical behavior as other lithogenic elements such as al and ti which suggests that they are immobile in the peat column and can be used as tracers of dust deposition after 4000 cal yr bp peaks in dust deposition associated with greater variability in testate amoebae assemblages and plant macrofossil composition as well as a change in nd values are observed between 7000 and 4100 cal yr bp the nd values varied from 36 to 29 while they gradually increased from 4100 cal yr bp until 1500 cal yr bp suggesting proportionally less dust from local source s is deposited in favor of more regional source s from 1500 cal yr bp nd values remained relatively stable around 15 and 12 most of the dust peaks correspond to documented cold and dry periods likely linked to intrusion of arctic air masses a migration of the polar front might explain the more frequent intrusion of arctic air masses in the region and the greater variability in the lg2 record over the last 4000 years

postglacial emergence of ungava peninsula and its relationship to glacial history a series of 178 radiocarbon dates of late glacial and postglacial age from raised marine terraces on the hudson strait hudson bay and ungava bay coasts permit a new synthesis of deglaciation h

geomorphological reconstruction of the labrador sector of the laurentide ice sheet abstract the labrador sector formed one of three major domes of the laurentide ice sheet during the last wisconsinan glaciation reconstruction of its evolution is important because it modulated atmospheric and oceanic circulation over 1 100 ka time scales this paper reports new geomorphological evidence of ice flow which is used to reconstruct glimpses of the behaviour of the labrador sector during its evolution flow evidence indicates a southern position 51 n of the labrador ice divide presumed to be the usual location when the ice sheet was close to its maximum extent a previously inferred dramatic surge of labrador ice across hudson strait and onto baffin island at 9 9 9 4 ka is verified seemingly contradictory evidence regarding deglaciation in northern quebec has been analysed and a reconstruction developed that solves this problem deglacial retreat of the labrador ice sheet was highly asymmetric with rapid retreat of the southern margin northwards migration of the centre of mass by 500 km and slow retreat along the northern margin as it shrank its thermal regime changed from cold centred to entirely cold based and it finally fragmented into many residual ice caps and glaciers this dynamic and asymmetric behaviour may be due to destabilisation of the labrador ice sheet triggered by heinrich event ice streaming through hudson strait

trough mouth fans palaeoclimate and ice sheet monitors abstract trough mouth fans are fans at the mouth of transverse troughs channels on glaciated continental shelves on the northwest european glaciated continental margin eight trough mouth fans varying in size between 2700 and 215 000 km 2 have been identified the trough mouth fans are depocentres dominated by debris flows accumulated in front of ice streams draining the former large northwest european ice sheets the debris flow units are separated by hemmipelagic interglacial interstadial sediments it is inferred that the number of debris flow units record the number of shelfbreak positions of the ice sheet margins the number found varies between three in the south and eight in the north typical trough mouth fans and related debris flow units seem to have been formed later than the early mid pleistocene thus the north european ice sheets did not form ice streams extending to the shelfbreak in any appreciable length before the mid pleistocene besides being loci for sediment deposition the trough mouth fans were also the main sites of fresh water supply to the ocean in the form of icebergs during the mid late pleistocene ice ages