the morphology structural evolution and significance of push moraines abstract push moraines glaciotectonic ice marginal moraines have a restricted distribution at modern glacier margins and consequently are of potential value in reconstructing pleistocene ice sheets providing data both on former glaciodynamics and on the palaeoenvironment of the glacial foreland to the wider earth science community push moraines are of interest as analogues for thin skin tectonics within orogenic belts this paper reviews the morphology structural geology formation and significance of push moraines the morphological and structural characteristics of small seasonal push moraines through to large multi crested examples produced by sustained glacier advances are reported before the primary controls on push moraine formation are examined these controls include the nature of the applied glacial stress field the presence and properties of decollement horizons and the shear strength and rheology of the glacial foreland a conceptual model of push moraine formation is introduced in which the range of observed morphological and structural forms are viewed within a matrix defined by the main variables which control their formation the absence of consensus over which of these variables is of greatest importance currently limits the significance of push moraines in palaeoglaciological research as a consequence this review emphasises the need for future research in order to realise the true potential of push moraine in the reconstruction of pleistocene environments

groundwater flow beneath ice sheets part ii its impact on glacier tectonic structures and moraine formation abstract meltwater flowing as groundwater from beneath the margin of an ice sheet determines the distribution of sub surface heads and effective pressures a subglacial groundwater flow model is used together with an ice sheet loading model to compute the magnitudes and directions of the principal effective stresses in the subsurface from which the distribution of different types of sub surface failure in the subglacial and proglacial zones are deduced zones of hydrofracturing shear fracture and pervasive shear failure are distinguished beneath the ice sheet divide area intact rocks of high tensile strength may fail hydrofracturing and liquefaction are two coupled processes which lead to the formation of upward filled and downward filled sediment dykes and till wedges quicksand conditions are developed where strong vertical seepage pressures occur producing sediment diapirism it is suggested that subglacial permeability magnitude may be the product of a self organising process certain types of moraine extrusion moraines are suggested to be a consequence of upward movement and surface extrusion of sediment driven by rising groundwater it is suggested that groundwater over pressure associated with narrow proglacial permafrost plates are conductive to the formation of large push moraines and that many large ancient and modern examples are produced in this setting

internal tides and baroclinicity in the southern weddell sea 1 model description near the continental shelf break in the southern weddell sea warm deep water and western shelf water meet mixing mechanisms such as internal tides have the potential to mix these water masses and form antarctic bottom water a modified version of the princeton ocean model was utilized to investigate the internal tidal fields generated by the interaction of the m 2 barotropic tide with topography for transects across the continental shelf and slope in the southern weddell sea internal tides were generated over the upper continental slope as predicted by linear internal wave theory although the essentially two dimensional domain resulted in differences between the model elevations and the observations exceeding the observational uncertainties the cross slope velocities agreed well with differences less than the uncertainties for 78 of the existing observations

the paleoclimatic significance of deformation structures in neoproterozoic successions abstract this paper reviews the different types of soft sediment deformation structures that can form in glacial and non glacial settings and explores the potential use of these structures in resolving long standing debates in paleoenvironmental reconstructions of neoproterozoic glacigenic successions soft sediment deformation structures are created when compressional gravitational or shear stress is applied to unlithified sediments during or shortly after deposition in subglacial or ice marginal glacial settings shear and compressional stress imparted by ice moving on top of a deformable substrate or advancing ice buldozing unlithified ice marginal sediments can result in a wide range of folding faulting and shear structures in glaciofluvial or stagnant ice marginal setting gravitational collapse and remobilization of sediments associated with the melting of buried ice can result in normal faulting and broad folding in glaciolacustrine or glaciomarine settings compressional shear and gravitational types of deformation structures can occur as a result of grounding ice or icebergs rapid sedimentation and reworking downslope associated with high sedimentation rates in non glacial settings similar deformation structures can form as a result of slope instability and reworking of sediments downslope rapid sedimentation seismic shaking wave induced shearing or loading in this context two case studies are presented to demonstrate the type of paleoenvironmental information that an analysis of deformation structures can provide in the first case study analysis of deformation in the port askaig formation scotland reveals a distinctive stratigraphic distribution of deformation structures the types of deformation observed together with their recurrence over several 100s of meters and their basinal context are used to infer a seismic origin for the deformation which in turn suggests a significant tectonic control on sedimentation atop a record of ice margin fluctuations in a glaciomarine setting in the second example analysis of deformation in the smalfjord formation northern norway provides strong evidence for deformation by active ice overriding glaciofluvial deposits the types of deformation in this example together with its complexity scale and associated facies provide the strongest case for ice marginal deformation in sum analysis of deformation structures together with analysis of structural geology stratigraphy facies and facies associations can provide additional constraints on paleoenvironmental conditions at the time of deposition which can help us refine or test paleoenvironmental models proposed for this critical time period in earth history

the sedimentary and structural evolution of a recent push moraine complex holmstrombreen spitsbergen abstract the glacier holmstrombreen in spitsbergen surged into the ice contact scarp of a proglacial outwash sequence at some time during its neoglacial maximum the outwash sediments were pushed along a decollement to produce a moraine in which deformation extended for 1 5 km beyond the furthest extent of the glacier front the style of folding and faulting and the nature of the pre syn and post tectonic sedimentary sequence across the whole push moraine is described from a continuously exposed section of the push moraine which extends from its proximal to distal extremities the precise extent of incremental compressive shortening of the pushed sediments of some 900 m is established the depth to the underlying decollement is inferred to be an average of about 30 m indicating that stresses and movement were transmitted through a thin nappe with an aspect ratio of about 1 in 30 it is suggested that this nappe was frozen and that an artesian water pressure head of 60 m immediately beneath it reduced friction along its base to a very low value it is calculated that a glacially generated force of about 1 5 10 7 kn was responsible for pushing the sediment nappe the nature of the glacially controlled groundwater flow system rather than the magnitude of longitudinal forces generated by the glacier is the principle determinant of large scale push moraine characteristics the changing ice topography produced by the pushing event during the surge and in the post surge decay had a major influence on the evolution of the meltwater drainage system and the style of fluvial sedimentation the structure sedimentary architecture and evolution of the whole glacitectonic fluvial complex can best be understood by considering the impact of the surge on a complete outwash system it is suggested that the setting and processes which produced the holmstrombreen push moraine could account for many broad multi ridge and fold push moraines which formed proglacially and that the thickness of original sediments above the decollement can be a guide to the thickness of contemporary permafrost

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

the structural glaciology of kongsvegen svalbard and its role in landform genesis mapping of the structural glaciology of kongsvegen svalbard reveals evidence for four main deformational structures these are stratification longitudinal foliation thrusts and crevasse traces these structures are considered in terms of their contribution to debris entrainment transport and subsequent landform development stratification is associated with small amounts of supraglacial debris that has been folded with flow parallel axes longitudinal foliation in places incorporates basal glacial sediments along folds with flow parallel axes and thrusts transport basal debris to the glacier surface crevasse traces are not significant in terms of debris entrainment the entrainment of basal debris along longitudinal foliation is not a universally recognised process at kongsvegen this process is attributed to the development of a transposition foliation in combination with incorporation of debris rich basal ice or soft basal sediment in the fold complex mapping of the landforms in the proglacial area shows that debris incorporated along longitudinal foliation is released as foliation parallel ridges and that transverse ridges mark debris bearing thrusts the role of longitudinal foliation in landform development has never been documented in this manner although the preservation potential of such ridges may be limited recognition of foliation parallel ridges in the pleistocene landform record has important implications for the interpretation of the dynamics of former ire masses

geomorphology and sedimentology of surging glaciers a land systems approach the identification of surging glaciers and ice streams in glaciated landscapes is of major importance to the understanding of ice sheet dynamics and for reconstructing ice sheets and climate no single landform or diagnostic criterion has yet been found with which to identify surging glaciers a surging glacier land system model is constructed using observations and measurements from contemporary surging glacier snouts in iceland svalbard u s a and canada for differentiating ancient surging margins from other non surging palaeoglaciers this integrates the suite of landforms sediments and stratigraphy produced at surging glacier margins landforms produced during surging include thrust moraines concertina eskers and subglacial crevasse squeeze ridges sedimentary sequences are usually characterized by multiple stacked diamictons and stratified interbeds which display severe glaciotectonic contortion and faulting hummocky moraine comprising interbedded stratified sediments and mass flow diamictons has also been associated with surge margins where large quantities of supraglacial and englacial debris entrained during the surge event have melted out in situ an example of the application of the land system model is presented for east central alberta canada a surging palaeo ice stream is identified within this part of the southwestern laurentide ice sheet where thrust block moraines crevasse squeeze ridges flutings hummocky moraine and glaciotectonized sediments are juxtaposed

short lived streamlined bedforms annual small flutes formed under clean ice turtmann glacier switzerland abstract at the turtmann glacier in switzerland small flutes ranging in length from a few decimetres to a few metres have been formed and destroyed annually since 1986 as the overlying ice is debris free the sediment in the flutes has to come from within the bed flutes form only where sediment distribution and properties of the bed the thickness of the ice and its horizontal velocity are within a certain range the most likely process is squeeze of fines from between coarse material in the bed

glacial landsystems of the southwest laurentide ice sheet modern icelandic analogues landform assemblages and associated stratigraphy sedimentology and structure are used in the reconstruction of palaeo ice sheet dynamics in alberta western canada interpretations are based upon the modern analogues from four outlet glaciers at the margins of vatnajokull and myrdalsjokull iceland in the area between lloydminster and lac la biche central alberta an extensive landform assemblage of megaflutings crevasse squeeze ridges and thrust block moraine arcs document the former surging of part of the margin of the laurentide ice sheet during later stages of recession this landform assemblage including numerous exposures of glacitectonised bedrock and quaternary sediments is comparable to the landsystem of the surging glaciers eyjabakkajokull and bruarjokull in iceland near high river southern alberta the former existence of an ice lobe characterised by active recession is recorded by closely spaced low amplitude recessional push moraines that drape tunnel valleys these are comparable in form and pattern to annual push moraines and fluted till surfaces produced by breidamerkurjokull and sandfellsjokull iceland and also include rimmed depressions produced by the escape of artesian water during ice marginal pushing this study provides interpretations of the regional glacial geomorphology of alberta based upon comparisons of form and stratigraphy with modern glacial analogues and provides an alternative to recent models which invoke large floods of subglacial meltwater to explain many of these same features implications for ice dynamics and regional till stratigraphies are discussed copyright 1999 john wiley sons ltd

the interpretation and classification of subglacially deformed materials abstract a general classification of subglacially deformed materials is proposed based on sediment properties and their relationship to styles of subglacial strain deformation till is defined as homogenized usually diamictic material formed by glacially induced shear of subsole materials three types are recognized type a formed by pervasive ductile deformation type b formed by brittle shear and comminution till produced by the reduction of void space by in situ crushing and abrasion the term glacitectonite is adopted for materials that have undergone subglacial shear but retain some of the structural characteristics of the parent material original structures may be truncated by glacitectonic fabric elements type a or distorted but not truncated type b the principles of strain and material response particle orientation mechanisms fabric development and drainage conditions are reviewed examples of deformation tills and glacitectonites from breidamerkurjokull iceland slettmarkbreen norway loch lomond scotland and east yorkshire england are used to illustrate the nature of subglacially deformed materials and their relationship to former subglacial strain and drainage conditions the geologic evidence suggests a continuum of bed strengths can be recognized in deforming substrata ranging from high strength low strain type b deformation till and comminution till to low strength high strain type a deformation till

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

genesis of an imbricate push moraine hofdabrekkujokull iceland observations on a push moraine now being formed at the margin of the advancing glacier hofdabrekkujokull in iceland provide a background for interpreting the geomorphic and paleoclimatic significance of pleistocene push moraines this moraine up to 10 m high consists partly of unfrozen thrust slabs of glaciofluvial sand and partly of debris derived from the glacier surface during the present advance 10 to 12 m yr 1982 thrust planes intersect the glacier foreland and recurrent thrusting produces an imbricate structure as the moraine grows in height folds and faults are produced as the first formed slabs are rotated slowly backward up the glacier front and the whole moraine deforms under its own weight simultaneously the moraine receives a cover of supraglacial debris from the glacier surface above during the summer of 1982 the push moraine moved forward at a rate averaging about 4 cm day

controls on glacier surging in svalbard the geographical distribution of surge type glaciers worldwide displays a remarkably non random pattern surge type glaciers tend to be concentrated in certain glacierized areas and to be completely absent in others this observation suggests that special conditions are required for surges to occur however the factors controlling the spatial occurrence of surge type behaviour are not known to investigate this problem we performed probability statistical analysis on a sample population of 615 glaciers in svalbard the probability that a glacier in the sample population is surge type is 36 4 within the sampled area there is a spatial variation in the concentration of surge type glaciers several geometric and environmental factors associated with glaciers in the sample population were measured and tested to determine if they are related to the probability of surging of the geometric factors tested length slope elevation orientation and presence or absence of tributaries only glacier length is related to surging with surge probability increasing with increasing length elevated probabilities of surging were also found for glaciers associated with sedimentary subglacial rocks and sub polar thermal regimes the distributions of related factors were used to predict the spatial distribution of surge type glaciers however in each case the individual factors were unable to reproduce the observed pattern of surge type glacier distribution

genesis stability and preservation potential of large lateral moraines of alpine valley glaciers towards a unifying theory based on findelengletscher switzerland abstract lateral moraines are prominent features of glaciated landscapes in high mountain environments and key landforms in glacier and palaeoclimatic reconstructions yet compared to smaller moraines they have been little studied and several aspects are not well understood we here present detailed sedimentological results from the lateral moraines of findelengletscher in sw switzerland to gain new insights into the formation of these landforms the lateral moraines studied here stand up to 140 m above the valley floor are over 3 km long and strongly asymmetrical in cross profile with distal slopes between 29 and 36 and proximal slopes that are commonly 41 64 but locally reach angles of up to 80 recorded lithofacies comprise loose clast and matrix supported stratified diamicts and intercalated sorted sediments in the distal slopes and near the crestline overconsolidated matrix supported massive and weakly stratified diamicts and streaked out sorted sediment lenses in the core and proximal slopes and partly intercalated dark brown layers overlain by loose and consolidated diamicts exposed in near vertical walls in the proximal flank these are interpreted as supraglacial debris flow units with intercalated fluvial wash horizons glaciotectonised and subglacial traction till with boudinaged and streaked out sediment lenses and palaeosoils overlain by sediment produced by overtopping of the former moraine surface during a subsequent advance of the glacier clast shape analysis and process observations reveal that the dominant mode of transport is subglacial and glaciofluvial and that the main mode of sediment delivery to the moraines is by debris flows after the material has been transferred from the bed via englacial debris bands and meltout at the surface this differs from previous studies that found that a supraglacial source was dominant sedimentary structures clast fabric and process observations during the 1979 1980 readvance of findelengletscher strongly suggest that proximal layers of reworked pre existing sediments and or basal traction zone till have been plastered onto the moraine core in several locations causing a high degree of overconsolidation and strongly clustered fabric eigenvalues s 1 0 94 with clustering parallel to the moraine crestline this suggests that a combination of basal lateral drag and lateral plastering produces the observed proximal stability and ensures a high preservation potential we develop a conceptual model that describes alpine lateral moraines as structurally complex landforms that do not just record a single event as often surmised and we discuss implications for palaeo glacier reconstruction and the application of numerical dating methods

distribution and characteristics of lacustrine tight oil reservoirs in china abstract lacustrine tight oil resources in china are significant exploration targets similar to the marine tight oil resources in north america while there are clear differences in terms of the forming environment as well as reservoir properties of these two systems in this study the geological characteristics of lacustrine tight rocks are discussed including the distribution petrology storage space and movable fluid saturation the tight rocks are consisted of tight sandstone tight carbonate rock tight peperite and tight sedimentary tuff in which intergranular pores and dissolved pores with the dimensions of 30 900 nm are mainly dominated by the storage space the oil saturation typically exceeds 50 and the oil mobility is basically controlled by pore throats with diameter less than 1 m these four types of reservoirs show different potentials for tight oil in which tight sandstone plays in the ordos basin and the songliao basin are taken as the preferred targets into account for exploration and development although the distribution area physical properties and mobility of lacustrine tight oil in china are not as good as those of tight oil in north america the lacustrine reservoirs are often stacked in multiple layers resulting in a great thickness and possess relatively high oil saturation making them producible and commercially viable fluid properties are critical to effectively recovery of tight oil and more comprehensive geological evaluation on fluid mobility should be undertaken

influence of glacier advance on the development of the multipart riffeltal rock glacier central austrian alps the multipart riffeltal rock glacier located in a tributary valley of the kaunertal tyrol austria is investigated to enlarge the knowledge about spatial and temporal development of rock glaciers in and at the margins of pro glacial areas and to get a better understanding of glacier rock glacier interactions the subject of interest consists of a complex system of two adjacent rock glacier tongues and various superposed lobes with differing ages origin and root zones and therefore diverse development to determine the reasons for their diverging development the internal structure and permafrost occurrence on and in the surrounding area of the rock glacier were studied by application of geomorphological mapping geophysical methods and measurement of the basal temperature of the winter snow cover bts permafrost modelling was performed on the basis of bts data and land surface parameters derived from a high resolution airborne laser scanning als digital elevation model dem additionally the als data were used to measure vertical and horizontal changes of the rock glacier surface between 2006 and 2012 glacier rock glacier interactions during and since the little ice age lia are evident for the development of the studied rock glacier a geomorphic map gives important information about the connection between glacial advance or retreat and permafrost or ground ice occurrence the combination of all information helps in the analysis of diverse kinematic action of neighbouring rock glacier tongues copyright 2014 john wiley sons ltd

the formation of a geometrical ridge network by the surge type glacier kongsvegen svalbard traditionally geometrical ridge networks are interpreted as the product of the flow of subglacial sediment into open basal crevasses at the cessation of a glacier surge crevasse fill ridges they are widely regarded as a characteristic landform of glacier surges understanding the range of processes by which these ridge networks form is therefore of importance in the recognition of palaeosurges within the landform record the geometrical ridge network at the surge type glacier kongsvegen in svalbard does not form by crevasse filling the networks consist of transverse and longitudinal ridges that can be seen forming at the current ice margin the transverse ridges form as a result of the incorporation of basal debris along thrust planes within the ice the thrusts were apparently formed during a glacier surge in 1948 longitudinal ridges form through the meltout of elongated pods of debris which on the glacier surface are subparallel to the ice foliation and pre date the surge this work adds to the range of landforms associated with glacier surges

glacio tectonic structures a mesoscale model of thin skinned thrust sheets abstract a series of seven groups of push ridges ranging from 7 to 40 m in height 50 to 280 m in length and occupying a total width of more than 2 km mark the marginal zone of the a d 1890 maximum of eyjabakkajokull an outlet glacier of the vatnajokull ice cap iceland the internal structure of one ridge complex comprises two distinct elements a proglacial part which has been subject to compressional stresses resulting in the development of imbricate thrust sheets and a subglacial part which comprises low angle normal fault structures the two sub systems appear to be linked via a floor thrust and to have evolved together as the glacier reached the limit of its rapid advance in a d 1890

an integrated approach to the study of glaciolacustrine landforms and sediments a case study from hagavatn iceland abstract this paper describes the landform assemblage associated with the neoglacial fluctuation of hagafellsjokull eystri into proglacial hagavatn iceland this landform assemblage is dominated by three components firstly a series of moraines formed both by thrusting within the glacier margin and by proglacial subglacial deformation the internal sedimentary architecture of these moraines ranges from stacked sediment slabs separated by listric thrusts to complexly folded and faulted sequences all in glaciolacustrine sediments the second component is a morainal bank and associated ice contact delta the morainal bank consists of a series of low amplitude ridges composed of laminated silts and clays which have been deformed proglacially during the neoglacial ice advance 1890 this morainal bank helped stabilise the 1890 ice limit within the proglacial lake and was the focus for subaqueous outwash first in the form of a subaqueous out wash fan and subsequently as an ice contact delta the third component is a series of lake bed kame terraces formed by rapid sedimentation in a canal like lake formed as the ice retreated away from the push moraines a range of glaciolacustrine facies is present within the lake bed kame terraces and the sedimentary architecture records a complex pattern of ice marginal oscillations and changes in lake level this detailed case study provides an important analogue for the interpretation of both glaciolacustrine and glaciomarine landform sediment assemblages of pleistocene age and illustrates a range of styles of glaciolacustrine sedimentation and glaciotectonic deformation

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

pleistocene glacitectonic landforms and sediments around central magellan strait southernmost chile evidence for fast outlet glaciers with cold based margins abstract proglacial and subglacial glacitectonic sediments and landforms around the margins of the strait of magellan southernmost chile record the advance and retreat of outlet glaciers of the patagonian ice cap during the last glacial cycle the spatial arrangement of glacitectonic landforms in the area is inferred to have resulted from the advance of ice lobes with cold based margins and wet based interiors as the ice advanced subglacial basins were excavated beneath the glacier margins and the eroded material was pushed up into thrust moraines probably because frozen bed conditions formed a thermal dam against the free drainage of subglacial meltwater these ice marginal glacitectonic landforms were then overridden and streamlined into drumlins and flutes as thicker wet based ice passed over the area evidence for permafrost near sea level in patagonia during the last glaciation suggests that mean annual temperatures were several degrees lower than indicated by recent modelling studies the results indicate that future modelling experiments should incorporate more realistic basal boundary conditions particularly the presence of a weak deforming layer at the glacier bed to improve climatic reconstructions of southern south america

glaciotectonics of the ltterbeck uelsen push moraines germany the two saalian push moraines of ltterbeck uelsen formed during the older saalian glaciation consist of tertiary and quaternary deposits locally glaciofluvial deposits are prominent as a result of reworking of older deposits by meltwater the push moraines are built up from a number of imbricated and folded structural units which have moved laterally and in part frontally from two glacial basins dominant structures are large shallow and flat lying glaciotectonic nappes that have been displaced over distances of at lest 1 km in the direction of tectonic transport overprinting relations of two deformation phases give a relative age difference between the two push morianes

glaciotectonized quaternary sediments at dinas dinlle gwynedd north wales and their bearing on the style of deglaciation in the eastern irish sea abstract the sedimentology and structure of late quaternary sediments exposed in a coastal section at dinas dinlle north wales are described the deposits from two small hills the northern one being more prominent and containing northward dipping units of gravel and diamicton bounded by clay lined thrust faults the southern hill comprises complex folded sands and gravels overlying a basal till surface high resolution seismic surveys along the beach 50 m west of the cliffs show a roughly horizontal rockhead lying some 35 m below beach level and demonstrate that thrust faults penetrate the entire quaternary sequence to a detachment immediately above rockhead thrust units in the exposed cliff section show excellent correlation with the seismic sequence 50 m to the west indicating a strike of 080 260 balanced cross section techniques were applied to an initial simple layered sequence comprising a lower irish sea till overlain by a coarsening upwards sand to gravel unit followed by upper till mixed lithology including welsh and northern provenance and finally an upper gravel unit shortening of approximately 54 is estimated within the thrust sequence it is concluded that the two isolated hills at dinas dinlle are erosional remnants of a formerly more extensive push moraine extending westwards into caernarfon bay which has now been truncated by coastal retreat deglaciation of the area was interrupted by ice sheet readvance towards 170 across a proglacial surface

a comparison of the styles of deformation associated with two recent push moraines south van keulenfjorden svalbard in this paper two push moraine systems associated with two small subpolar glaciers finsterwalderbreen and penckbreen were investigated this study showed that at these glaciers the push moraines were formed in association with surges which produced a different style of moraine depending on the rheology of the deformed material and the glacial history the moraines are similar in that they are formed by folded outwash sediments and contain little till however the forms of these moraines are very different the penckbreen moraine is composed of a lower shallow marine sand silt and clay and an upper fluvial sand and gravel deformation at this site led to the formation of large anticlines in the silts and clays with disharmonic smaller folds and thrusts in the upper gravels above a detachment surface between the fine grained and overlying coarse grained lithologies this deformation decreases towards the foreland with marine and fluvial sediments responding differently because of their different rheological properties this moraine was formed during one surge event which occured during the early 19th century in contrast the finsterwalderbreen moraine is composed of outwash sand and gravel and was formed as the result of a series of surge events these advances all reached a similar limit and occurred at regular intervals 1997 john wiley sons ltd

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

drumlin formation in southern anglesey and arvon northwest wales this is a study of late devensian drumlins formed in southern anglesey and arvon northwest wales this area was affected by ice sheet coalescence when the welsh ice sheet met with the lrish sea ice sheet and drumlins were formed once the two had coalesced it is suggested that the drumlins were the result of net subglacial soft bed erosion and that they represent more resistant cores within the subglacial deforming layer the drumlins have either gravel or till cores and where the core was deformable large scale compressive glaciotectonic structures were seen e g dinas dinlle with local subglacial compression of 59 where the cores were more resistant e g lleiniog these were not deformed but remained as more competent masses within the deforming layer it is suggested that the less competent material flowed around the cores some remaining as a thin carapace but most of the material being removed down glacier leaving the drumlins as erosional remnants in northwest wales there is a multi till sequence that traditionally has been interpreted as having been deposited as the result of separate ice sheet advances and retreats however in this study it is suggested that the different tills were deposited as the result of ice sheet coalescence and that sites such as dinas dinlle do not show evidence of a major readvance in the retreat of the devensian ice but are indicative of continuously changing conditions within the subglacial deforming bed

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

reconstruction of palaeo ice sheets the use of geomorphological data the article discusses the nature of the glacial inversion problem which is defined as the extraction of time slice ice sheet flow patterns from the patchy and partly overprinted landform record present in former ice sheet areas a coherent inversion model for derivation of flow patterns and interior ice sheet configuration from geomorphological data is presented glacial landscapes are classified according to the three criteria of internal age gradients presence or absence of meltwater traces aligned to flow traces and basal condition frozen bed thawed bed inferred from morphology the inversion model uses landscapes classified accordingly spatially delineated into fans as input data relative chronologies at fan intersections are used to sort fans in a relative age stack that can be linked to stratigraphic dating information

englacial and proglacial glaciotectonic processes at the snout of a thermally complex glacier in svalbard many glaciers in svalbard which tend to be thermally complex with both warm and cold ice produced complex push moraines or thrust moraine complexes at the time of their maximum neoglacial advance and during their subsequent recession uv rsbreen which nearly reaches the coast of northwest spitsbergen has a push moraine 50 m high comprising gravel and sand of fluvial origin and diamicton derived from basal ice as well as thrust masses of dead ice the push moraine is almost entirely a product of the tectonic processes especially thrusting that occurred in the snout of the glacier and in the frozen sediments immediately in journal of quaternary science front thrusting is probably initiated where the glacier switches from a sliding mode to a state of being frozen to the bed thrusting in the foreland is an extension of the same processes that occur within the ice itself and a sole thrust probably extends from the frozen sediment that underlies the base of the glacier near its snout thrusting results in subglacial sediment being uplifted to a high level within the glacier or even to the surface subsidiary near horizontal thrusts parallel to the bedding plane link thrusts dipping up glacier and result in local thickening of individual subglacial sedimentary units gravels incorporated in this way retain their integrity but sands are folded whereas uplifted debris rich basal ice is intensely folded the distinctive tectonic style of low dip bedding in gravels truncated by high angle 30 40 thrusts and only localised folding in less competent material differs from most descriptions of such ridges but may be typical of many push moraines composed principally of fluvial material

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

the role of the deep ocean in north atlantic climate change between 70 and 130 kyr ago the suggestion1 that changes in north atlantic deep water nadw production are linked through surface heat flux to the atmospheric temperature over greenland is supported by earlier indications2 3 that nadw production decreased during glacial times and by the subsequent finding4 6 that it declined during the younger dryas cool period at the end of the last glaciation changes in north atlantic surface temperatures have been found7 to mirror high frequency temperature changes recorded in greenland ice cores over the past 80 kyr but the connection to abyssal circulation has yet to be established except for one or two isolated oscillations8 9 here we present carbon and oxygen isotope analyses of benthic foraminifera in a high resolution north atlantic deep sea sediment core for the period 70 130 kyr ago these data allow us to reconstruct the history of nadw production which shows a close correlation with greenland climate variability for much of this time interval suggesting that the climate influence of nadw variability was widespread we see no evidence however for changes in nadw production during substage 5e the eemian interglacial period in contrast with recent ice core data10 which suggest severe climate instability in greenland during this time period our results may support suggestions based on data from a second ice core that this apparent instability is an artefact caused by ice flow11 alternatively the eemian climate instability may have had a different origin from the subsequent climate events

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

genesis of hummocky moraines by thrusting in glacier ice evidence from svalbard and britain irregular mounds of glacial debris commonly referred to as 9hummocky moraine9 until recently were linked to ice stagnation during rapid climatic amelioration however recent work in scotland has demonstrated that some hummocky moraine dating from the younger dryas event c 10 000 years bp was the product of deposition at active ice margins observations at modern high arctic glacier margins in svalbard 76 80 n indicate that some moraines of this type form under a dynamic glaciological regime mainly by thrusting in active polythermal ice undergoing strong longitudinal compression this situation is particularly common where there is a transition from warm based ice in the interior of a glacier to cold based ice at the margins or snout from their morphological similarity rectilinear slopes facing up glacier and irregular downglacier faces and apparent stacking of slabs of sediment of subglacial derivation it is concluded that some assemblages of british moraines are also the product of thrusting this process appears to be most dominant in polythermal glaciers rather than in temperate glaciers on this basis it is tentatively suggested that the younger dryas in britain was characterized by a climatic regime similar to that in svalbard today mean annual temperature 5 c 400 1000 mm precipitation and that the associated glaciers may have been of polythermal character

deglacial meltwater drainage and glaciodynamics inferences from laurentide eskers canada abstract this paper evaluates current knowledge of laurentide eskers in canada in the light of developments in glacier hydrology and glacial sedimentology questions regarding the morpho sedimentary relations of eskers the synchroneity and operation of r channel systems the role of supraglacial meltwater input and proglacial water bodies the controls on esker pattern and the glaciodynamic condition of the ice sheet at the time of esker formation are discussed a morphologic classification of eskers is proposed five types of eskers are identified and investigated type i eskers likely formed in extensive synchronous dendritic r channel networks under regionally stagnant ice that terminated in standing water type ii eskers likely formed in short subaqueously terminating r channels or reentrants close to an ice front or grounding line that may have actively retreated during esker sedimentation type iii eskers plausibly formed in short r channels that drained either to interior lakes in or tunnel channels under regionally stagnant ice type iv eskers may have formed as time transgressive segments in short subaerially terminating r channels or reentrants that developed close to the ice margin as the ice front underwent stagnation zone retreat or downwasted and backwasted regionally stagnant ice however formation in synchronous r channels cannot be discounted on the basis of reported observations type v eskers may have formed in h channels that terminated subaerially the spatial distribution of these esker types is discussed the factors that determined laurentide r channel pattern and operation were likely a complex combination of i supraglacial meltwater discharge ii the number and location of sink holes iii the ice surface slope thickness and velocity and iv the permeability topography and rigidity of the bed these factors cause and respond to changes in ice dynamics and thermal regime over the glacial cycle

a reinterpretation of scottish hummocky moraine and its significance for the deglaciation of the scottish highlands during the younger dryas or loch lomond stadial the aim of this paper is to demonstrate that much of the hummocky moraine present within the northern part of the lochlomond readvance ice cap formerly situated in the north west scottish highlands may be interpreted as suites of ice front moraines deposited during active decay these landforms can be used to reconstruct ice cap decay whichleads to important insights into the shrinking form of the ice cap and associated environmental conditions evidence has been collected from 10803 airphotographs and from detailed field survey it is presented at three spatial scales

the landform and sediment assemblage produced by a tidewater glacier surge in kongsfjorden svalbard abstract this paper describes the landform and sediment assemblage produced by a surge in 1948 of the kongsvegen kronebreen tidewater glacier complex in northwest spitsbergen the main geomorphological products of this advance are two large thrustmoraine complexes on opposite sides of the fjord and a system of geometrical ridges revealed on glacier decay the thrust moraines are composed largely of diamicton sandy and muddy gravel gravelly sand sand and mud with minor laminites all of these appear to be derived from the fjord floor and represent both fine fjord basin sediments and coarse grounding line fan deposits thrusting was the principal mode of emplacement of the sediment onto the adjacent land areas during the 1948 advance however the geomorphology of the thrust moraine complexes on either side of the fjord is quite different reflecting a transpressive regime on the southwest side mainly long ridges and a normal compressive regime on the northeast side short ridges and pinnacles of a hummocky nature the advance which produced the moraine complex has previously been attributed to a surge of kongsvegen but the glaciological and geomorphological evidence suggests that the advance involved both kongsvegen and kronebreen comparison of the landform assemblage produced by this event with that produced by other tidewater glacier surges demonstrates the diverse range of landform assemblages associated with glacier surges or other episodes of rapid flow within glaciomarine environments

proglacial subaquatic outwash fan and delta sediments in push moraines indicators of subglacial meltwater activity abstract a significant proportion of the glaciofluvial sediments in the rehburg stage saalian glaciation push moraines in germany appears to be subaquatic in origin they form subaquatic fans deltas and lacustrine deposits composed mainly of reworked autochthonous sediments with only minor amounts of erratic mainly scandinavian material subaquatic sediments occur in three positions with respect to the push moraines 1 pre tectonic and early syn tectonic sediments incorporated in the push moraine and overlying preglacial sediments 2 syn tectonic sediments overlying angular unconformities and filling depressions between anticlinal ridges on top of the push moraine and 3 post tectonic sediments on the distal push moraine slopes this indicates that lakes existed prior to and during the advance of the scandinavian ice sheet onto the north german lowlands and also after formation of the push moraines and prior to their overriding the topsets are commonly overlain by a deformation till produced by subglacial shearing of these sediments the rehburg push moraines closely follow the northern margin of the hercynian highlands in germany blocking of the ice marginal drainage by advancing ice lobes produced vast lakes between the ice sheet and the northern slopes of these highlands both the sedimentology and the petrology of the sediments in the rehburg push moraines suggest that these subaquatic sediments are products of subglacial erosion beneath ice lobes or ice streams since the pre tectonic lakes formed at the ice margin the subaquatic fans and deltas were constructed from the mouths of subglacial tunnels thus it is proposed that these sediments are eskerine in origin a subglacial provenance is supported by the occurrence in some of these sediments of layers and lenses of a pure and uniform petrology intercalated with strata of a more mixed petrology these are interpreted as the products of meltwater tunnelling in the saturated sediments beneath the ice lobes which produced the push moraines

till and moraine emplacement in a deforming bed surge an example from a marine environment the glacier sefstrombreen in spitsbergen surged across an arm of the sea between qsr 1882 and 1886 and rode up onto the island coraholmen marine and terrestrial geological observations and archive records show that the glacier advanced on a deforming carpet of marine mud which was eroded from its original location transported and smeared over the sea bed and coraholmen as a deformation till the glacier emplaced about 210sm 0 2 km 3 of drift in the terminal 2 km of its advance in a maximum of 14 years leaving a thickness of up to 20 m on coraholmen which was doubled in size as a result during the surge subglacial muds were characterised by high water pressures low effective pressures and low frictional resistance to glacier movement original sedimentary inhomogenities permit fold structures to be identified but repeated refolding and progressive remoulding produce mixing and homogenisation of deformation tills the surge was probably shortlived and as the heavily crevassed glacier stagnated underlying water saturated muds were intruded into crevasses and then extruded on the glacier surface reticulate crevasse intrusion ridges on coraholmen and the sea floor reflect the orientation of surge generated crevasses water and sediment was also extruded beyond the glacier at its maximum extent to form extensive flows producing till tongues both on coraholmen and the sea floor extending over 1 3 km from the glacier it is argued that subglacial deformation of pre existing sediment will almost invariably be associated with glaciation of marine areas and that this process will not only produce deformation tills through remoulding of pre existing sediments but will also play a fundamental role in glacier dynamics criteria which perrait glacial tills produced by such events from marine and glaciomarine muds are discussed copyright 1996 elsevier science ltd