submarginal debris transport and till formation in active temperate glacier systems the southeast iceland type locality abstract exhaustive sedimentological analysis of freshly exposed subglacial surfaces and moraines in southern iceland provides diagnostic sedimentological signatures of a debris transport pathways through active temperate glacier snouts and b till production in subglacial traction zones dominated by deforming layers three till end members are recognised based on stratigraphic architecture 1 thin and patchy tills over eroded bedrock 2 single push moraines and complexes and 3 overridden moraines or outwash fans typical till thicknesses are 0 10 1 40 m with each till relating to a deformation event driven by the seasonally tuned processes of glacier sub marginal shearing freeze on squeezing and bulldozing clast form trends demonstrate progressive modification towards mature forms in subglacial traction zones with till being clearly differentiated from scree and glacifluvial deposits clast macrofabric strengths are variable rarely matching those of laboratory shearing experiments except where obviously lodged clasts are abundant they also consistently record former glacier flow directions but localized variability is introduced by bedrock protuberances cavity infill clast interference and freshly imported plucked clasts within tills macrofabrics strengthen from lower b horizon to upper a horizon tills but at the outer edges of sub marginally thickening till wedges or push moraines seasonally driven cycles of squeezing flowage freeze on melt out and bulldozing give rise to a range of clast macrofabric strengths as well as superimposed deformation signatures this reflects two extremes of till emplacement including the more mobile flowing and often liquefied matrixes in push squeeze moraines and in contrast the lodgement deformation and ploughing at the thin end of sub marginal till wedges

the glacial and interstadial sediments at the burn of benholm kincardineshire evidence for onshore pre devensian ice movement in northeast scotland pebbly clays and diamictons containing marine shell fragments and peat lenses exposed beneath subglacially deposited late devensian till at the burn of benholm provide new insights into the glacial history of quaternary sequences in eastern scotland the peat yielded pollen of interstadial affinity including bruckenthalia spiculifolia and non finite radiocarbon dates comparisons with other pre late devensian pollen records in northern scotland suggest that the peat lenses are remnants of an early devensian interstadial deposit of oxygen isotope substage 5c or 5a age reworked faunal assemblages in the shelly sediments include quaternary marine molluscs of low boreal aspect as well as mesozoic and palaeozoic microfossils amino acid ratios from fragments of arctica islandica suggest that the shells are of oxygen isotope stage 9 age or older the fabric and composition of the shelly sediments are consistent with their emplacement as deformation till during the onshore movement of glacially transported rafts of marine sediment folded and sheared contacts between the shelly deposits peat lenses and the overlying late devensian till indicate that the fossiliferous sediments were glacitectonised during the main late devensian glaciation when ice moved from strathmore and overrode the site from the southwest british geological survey nerc 2000

late precambrian glacially related grooved and striated surfaces in the tillite group of central east greenland abstract the tillite group of central east greenland comprises five formations of which two are dominantly glacigenic the ulveso formation formerly lower tillite and the storeelv formation formerly upper tillite both of which embrace a wide range of facies including glaciomarine nearshore and terrestrial glacial sediments evidence of periodic terrestrial conditions is indicated especially by a variety of grooved and striated surfaces on the island ella o in the ulveso formation grooves of complex geometry 0 4 m wide and 0 3 m deep were cut into a cemented conglomerate horizon they are interpreted as having formed as a result of subglacial meltwater cavitation at the base of the storeelv formation boulders thought to have been dropped into partially cemented sandstone by floating glacier ice were largely planed off by a subsequent advance of grounded ice in the middle of the storeelv formation a striated boulder pavement occurs within diamictite on the basis of stone fabric striation orientation and cross bedding data this pavement is inferred to have formed by the packing of stones along a shear surface within an accumulating lodgement till such features have rarely been observed in pre pleistocene glacigenic sequences they imply that each glacigenic formation accumulated during a complex series of advances and retreats rather than just one

fabric and origin of multiple diamictons within the pre illinoian kennedy drift east of waterton glacier international peace park alberta canada and montana usa pebble fabrics and sedimentological properties indicate a glacigenic origin for multiple superposed diamictons within the pre illinoian kennedy drift east of waterton glacier international peace park alberta canada and montana usa determining the origin of these diamictons is particularly important in light of their antiquity eight diamictons on mokowan butte saint mary ridge and two medicine ridge have reversed magnetic polarity and are correlated with the matuyama chron 2 6 0 78 ma on mokowan butte two diamictons with normal polarity underlying two reversed diamictons are correlated with the gauss chron 3 6 2 6 ma or possibly the reunion or olduvai events 2 23 2 20 and 1 93 1 76 ma respectively fabrics were taken from 17 units within the kennedy drift on five interfluves on the basis of comparison of properties of these diamictons with those of modern glacial deposits eight including the uppermost one or two units on each interfluve are probably undeformed lodgment tills these are typically massive matrix supported bouldery sandy loam with strong unimodal fabric orientations relatively high eigenvalue s 1 s 3 ratios and striations on resistant clasts some include boulder pavements bullet shaped boulders and weak fissility eight other units have weaker fabrics typical of either deformed lodgment tills or glacigenic sediment flows because these also include bullet shaped boulders stone pavements and striated clasts most are probably deformed lodgment tills a colluvial or mudflow origin for the material is ruled out on the basis of the lateral and vertical extent of the diamictons at least 300 m wide and 5 10 m thick wide range of clast lithologies and sizes and distance from the mountain front 2 10 km as well as pebble fabrics and sedimentological properties

multiple subglacial till deposition a modern exemplar for quaternary palaeoglaciology the sedimentology of a vertical succession of alternating beds of massive and fissile diamictons on a orisjokull plateau icefield outlet foreland is employed to assess the evolution of subglacial traction tills at the margins of active temperate glaciers with deformable substrates where tills appear to form sub marginal incrementally thickened wedges that display multiple till emplacement events potentially of annual scale lodged boulders display strong a axes and surface striae alignments which parallel surface flutings indicating that fluting construction and till emplacement were related to moulding by consistent glacier flow from the ssw during the little ice age in contrast clast macrofabrics at the sub boulder size not unlike those reported from other icelandic tills are not as strong as would be expected in a subglacially sheared medium indicating shear strains too low for a steady state strain signature this separation of fabric data has isolated the strain signatures of the lodgement and deformation components of subglacial traction till whereby the orientations of the largest lodged clasts record high cumulative shear strains and those of the sub boulder sized clasts record greater susceptibility to deformation of their enclosing matrix this is likely due to the effect of clast collisions in clast rich till and the perturbations set up by the numerous large boulders consistent with observations on till fabrics in flutings and around lodged clasts a b plane macrofabric data display unusually high degrees of isotropy reflective of the more variable orientations of a b planes which are thought to reflect a b plane susceptibility to dip parallel or anastomosing shear planes a wide range of clast angularity values reflects the localized input of freshly plucked and hence relatively highly angular blocks to the deforming layer a characteristic of stepped bedrock profiles beneath the snouts of mountain glaciers finally we hypothesize that the massive and fissile units may represent a and b horizons of subglacial deforming layer couplets and that each couplet could record seasonal emplacement and partial inter couplet modification near the ice margin if the latter is the case then less than 1 m of subglacial till is advected to the glacier margin per annual deformation event

laboratory study of fabric development in shearing till the importance of effective pressure and shearing rate abstract herein we present data on the shearing rate glacier velocity and effective pressure difference between the ice overburden pressure and pore water pressure in the development of magnetic fabric anisotropy of magnetic susceptibility using a rotary ring shear device a wisconsin age basal till was used in the experiments and deformed to its critical state at shear strains as high as 93 we also present data from hysteresis and high temperature susceptibility experiments to identify the magnetic carrier in the basal till results showed little change in fabric strength when varying the shearing rate in the speed range of 110 860 m year 1 moreover the effective pressure tests also showed an inconsistency in fabric between 30 and 150 kpa however a slight strengthening effect was documented thus the k 1 magnetic fabric strength is independent of the shearing rate and effective pressure this suggests that the fabric strength upon these variables cannot be used as a benchmark for estimating shear deformation to the geological record the k 1 fabric strength in this study however remained consistent with respect to other till particle fabric methods e g sand and pebble in which the same conclusion was drawn all particles align parallel to the direction of shear and plunge mildly up glacier

the composition and internal structure of drumlins complexity commonality and implications for a unifying theory of their formation investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory unifying explanation of their formation this paper presents the first systematic survey of the vast literature on this subject with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain results confirm that investigations are often limited by availability of suitable sediment exposures 40 of studies report data from 5 drumlins and 44 do not specify sample size although borehole data and geophysical techniques can alleviate this problem however it is clear that the constituents of drumlins are incredibly diverse in terms of their composition e g a range of lithologies clast shapes sizes and fabrics structure e g sediments that are sorted homogeneous surface conformable unconformable and evidence of deformation e g ranging from pervasive to non pervasive limited to absent despite this diversity our review leads us to suggest that drumlin composition can be simplified to five basic types i mainly bedrock ii part bedrock part till iii mainly till iv part till part sorted sediments and v mainly sorted sediments this is a potentially significant step in that it reduces the oft cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target the various types can occur within the same drumlin field which leaves us with two possible implications for drumlin formation 1 different types of drumlin are formed seeded by different processes despite being morphologically similar equifinality investigation of drumlin composition may therefore reveal diagnostic processes explanations for these different types of drumlin and we argue that bedrock drumlins are an example 2 a single process occurs across large parts of the ice bed interface to create drumlinised terrain in a variety of sediments investigation of drumlin composition may in this case simply reflect pre existing sediments but importantly the way in which the drumlin forming mechanism modifies is modified by them we argue that the latter simpler explanation applies to all other types of drumlin excluding purely bedrock forms and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory

recent drumlins flutes and lineations at vestari hagafellsjokull iceland in the foreland of the vestari hagafellsjokull glacier langajokull central iceland three scales of subglacial bed forms are found drumlins flutes and lineations the smaller bed forms are superimposed upon the larger these three bed forms probably formed as a result of the presence of a rigid subglacial core producing a lee side low pressure area into which sediment flowed and collected the cores of the drumlins are tumuli lava blisters whilst the cores of the flutes and lineations were large clasts differences between the three scales of bed forms are that a the flutes and lineations are far more mobile features as their cores could move within the deforming layer whilst the drumlin bedrock cores were fixed b the lineations formed in association with a clast pavement the change in scale of the bed forms may be related to changes in thickness of the deforming layer and size of the core at this site smaller bed forms were superimposed upon larger bed forms and these may have formed as the deforming layer progressively thinned in association with glacial retreat

glacier fluctuations equilibrium line altitudes and palaeoclimate in lyngen northern norway during the lateglacial and holocene based on lacustrine and morpho stratigraphical evidence from lyngen in troms northern norway 13 marginal moraines have been mapped in front of lenangsbreene in strupskardet moraines m1 m13 are inferred to represent glacier halts or advance readvance taking place during the lateglacial and holocene the presence of collapse depressions suggests that some of them were ice cored m1 m3 a chronological framework taking into account a combination of former shorelines and related glacier meltwater channels lichenometry and ams radiocarbon dated lacustrine sediments spanning the last 20 000 cal yr bp has been established the distal glacier fed lake aspvatnet was isolated from the sea c 10 300 cal yr bp and the lacustrine sediments have been investigated by use of loss on ignition loi magnetic susceptibility water content wet and dry bulk density dbd and the magnetic parameters anhysteretic remanent magnetization arm and saturation remanent magnetization sirm there is in general good agr

subglacial deformation evidence from microfabric studies of particles and voids in till from the upper urumqi river valley tien shan china microfabrics formed by flat particles and voids in till samples from the upper urumqi river valley tien shan northwestern china were analyzed using three mutually perpendicular thin sections chi squared tests were used to determine significance levels of the orientations of both particles and voids the basal tills in an end moraine on the stoss sides of two roche moutonnees on the stoss sides of a drumlin with a rock core and on the lee side of the same drumlin far from the rock core have strong particle and void microfabrics field evidence suggests that these tills were deformed in a subglacial setting thus consistent with recent laboratory studies of till fabric development deformation is believed to be responsible for the strong particle and void microfabrics in the same end moraine particle microfabrics in an overlying till were strong but void microfabrics were weak this till is believed to have been formed by dumping and rolling of debris from hill slopes and of ablation moraine from the glacier surface the weak void microfabric is interpreted to indicate that the till was not consolidated and hence not sheared under the weight of the glacier despite the strong particle microfabric basal tills on the lee sides of the roche moutonnees and on the lee side of the drumlin but near its core have weak microfabrics

an investigation of subglacial processes at the microscale from briksdalsbreen norway the subglacial processes at briksdalsbreen norway are examined by a combination of sedimentology thin section and scanning electron microscope sem analysis of till samples from an exposed subglacial surface and from beneath the glacier studies of a fluted surface indicate that subglacial deformation is occurring on a field scale with flutes forming behind most clasts 0 6 m high at the thin section scale 0 014 2 0 mm it is seen that deformation is by rotation and attenuation and is dependent on till texture at the sem scale 0 1 0 4 mm it is seen that erosion is controlled by abrasion and percussion which produces distinct grain styles as part of an erosional continuum overall it is shown that rotation and attenuation is a dominant process at all scales and that the clast interactions associated with different scale perturbations within the shear zone control erosion and deposition as well as landform and fabric production

pebble fabric in an ice rafted diamicton pebble fabric studies on ice rafted diamictons have been limited to general observations with authors noting preferences toward vertical random or horizontal orientations to clarify such observations pebble fabric data were collected from a fossiliferous diamicton of late pleistocene age located on whidbey island washington the ice rafted origin of this unit is supported by several independent characteristics including in situ macrofauna and microfauna conformity with subaqueous lithofacies containing dropstones lower bulk densities and higher void ratios than associated tills soft sediment deformation structures suggestive of iceberg dumping textural gradations and facies relationships analysis using the eigenvalue method indicates that ice rafted fabrics are nearly random with little consistency of vector orientations between sites and without any relationship to the probable direction of glacial flow the weak fabric is mainly the product of settling through the water column and impact wit

glacial dynamics and transport of debris during the final phases of the weichselian glaciation southwest skane sweden late weichselian glacial sediments were studied in three sections west of lund southwest sweden the lowermost sedimentary unit is a lodgement till containing rock fragments derived from the northeast east fabric analyses indicate successive ice flow directions from the northeast east northeast south southeast and then east the last active ice movement in the area was from the east above the lodgement till are deglaciation sediments consisting of meltout till flow till and glaciofluvial sand and gravel deposited in a subaerial stagnant ice environment the uppermost unit consists of glaciolacustrine clay and silt containing abundant ice rafted debris deposited during a short lived transgression phase when stagnant ice was still present in the area at the westernmost site investigated the petrographical composition of the deglaciation deposits displays a gradual change with upwards increasing components of cretaceous chalky limestone the presence of this rock type requires a period of glacial transport from the south this stratigraphy cannot be explained with traditional glaciodynamic models a possible scenario can however be constructed using a previously published model lagerlund 1987 where marginal ice domes in the southwestern baltic area interact with the main scandinavian ice sheet

rogen moraine an example of glacial reshaping of pre existing landforms abstract rogen moraine is widely distributed in the core areas of the former scandinavian and laurentide ice sheets it is generally agreed upon that these gently arched ice flow transverse ridges can be used in reconstructions of paleo ice flow patterns and that they indicate a melted bed or poly thermal basal ice regime however the processes of ridge generation have been contentious this study proposes a two stage formation of rogen moraine based on detailed sedimentological and structural investigations in excavated trenches in a rogen moraine landscape in the province of dalarna central sweden field data suggest that rogen moraine ridges are the reshaped remains of pre existing transverse moraine ridges originally deposited from ice cored moraines in an ice marginal zone due to back and down wasting of ice cores inter ridge troughs were filled with debris flow and fluvial deposits which after landscape inversion were transformed to areas of transverse and hummocky moraines it is proposed that this primary landscape formation occurred during an early weichselian deglaciation this relict landscape was later preserved beneath cold based mid to late weichselian ice sheet s which turned wet based during the preboreal deglaciation phase and re moulded the precursor landforms into rogen moraine

characterization of pebble fabrics in modern terrestrial glacigenic sediments pebble fabric data are available from several facies of glacigenic sediments deposited by modern glaciers where sedimentary processes can be observed or inferred with relatively little ambiguity over 100 samples from contemporary environments illustrate fabrics characterizing melt out till deformed and undeformed lodgement till sediment flow deposits and ice slope colluvium lodgement till fabric variability is related to the two layer structure of these sediments a structureless friable upper layer with low shear strength and high consolidation coefficient overlying a very compact material of horizontal platy structure fabric strength assessed by eigenvalue analysis is weaker and pebble dip is more dispersed in the upper structureless horizon stronger fabrics in the lower platy horizon may be primary depositional fabrics which are destroyed by subglacial shearing to give weaker fabrics in the upper horizon alternatively upper horizon fabrics may be characteristic of all recently deposited lodgement tills with stronger fabrics developing at depth by dewatering and consolidation there is a general reduction in fabric strength and an increase in particle dip associated with the transition from melt out tills through undeformed and deformed lodgement tills to sediment flow deposits and ice slope colluvium there is however considerable overlap in the fabric strengths characteristic of sediment flow deposits and deformed lodgement tills fabric data from modern glacial sedimentary facies are used to assist in interpreting the mode of deposition of some quaternary glacial sediments relatively strong fabrics characteristic of melt out tills and undeformed lodgement tills are more likely to be diagnostic of genesis than weaker fabrics associated with deformed sediments

melt out till in the edmonton area alberta canada till at two localities in the edmonton area alberta was formed mainly by passive melt out from glacier ice and not by lodgment by active ice or as a result of supraglacially derived flows this interpretation is based on the implications of in situ stratified glacial sediment below and within till and of large unlithified clasts of sediment derived from subtill deposits the interpretation is also supported by more general regional stratigraphic and structural observations such associated properties as subtill deformation a sharply planar till preglacial sediment contact sole marks and fabric support formation by melt out or illustrate local exceptions to this process regionally consistent preferred orientation of clasts is interpreted to represent preferred englacial orientation collective analysis of the principal eigenvectors of individual englacial fabrics and flow or resedimented till fabrics from a modem glacial environment and similar analysis for till at villeneuve near edmonton show the edmonton till to occupy the intermediate position in terms of orientation strength predicted by the melt out hypothesis in places preferred orientation is considered to have been disturbed by flow and diapirism induced by the process of thaw consolidation thus preferred clast orientation in till may show considerable deviation from a regional trend stratigraphy and sedimentology are used to classify the till and to relate individual exposures to regional environments of deposition

approaches to the study of glacier bed deformation investigation of glacier bed conditions and subglacial processes is an obligatory requirement for the modelling and understanding of contemporary glacier behaviour past glacier behaviour glacier response to both spatial and temporal variations in bed material and glacier response to external forcing factors such as climate change the recognition of the importance of coupling between the glacier and its bed resulted in a paradigm shift in the subject and drew attention to the critical importance of subglacial deformation as opposed to simply subglacial deposition and sliding a number of methods have been adopted to measure glacier bed deformation ranging from direct observation and instrumentation the interpretation of macroscale and microscale sedimentary structures to the interpretation of glacier bedforms and glacier bed modelling this paper is concerned to describe the methods used by the two authors and co workers and attention is given to field methods the type and arrangement of sedimentary structures thin section micromorphology and microfabric and clast microfabric and glacier bedform morphology as evidence of subglacial deformation sedimentary structures macro and mesoscale are used to identify constructional deformation where deformational units are preserved one on top of another due to the formation of a thin deforming layer by low basal stresses and excavational deformation in which the deformational style is superimposed on pre existing styles due to increasing thicknesses of glacier deformation caused by increasing basal shear stresses thin section micromorphology has been used to define a range of glacial processes of which subglacial deformation is just one but has drawn attention to critical criteria such as discrete microscale shears orientated matrix kink structures and fractured grains as well as deformed intraclasts that can be used to recognise deformational processes more recently individual aggregates taking the form of rounded pebbles within till matrix have been shown to reflect rotational processes during glacial deformation and provide an additional mechanism to discrete shear within subglacial deformation and an explanation for the transport paths of subglacial materials finally measurements of sediment flow directions using clast macrofabric characteristics coupled with measurement of quantities of sediment transfered and detailed palaeoglacial properties have been used to determine the rates and scales of subglacial deformation associated with the formation of small scale glacier bedforms

the experimental basis for interpreting particle and magnetic fabrics of sheared till particle fabrics of basal tills may allow testing of the bed deformation model of glacier flow which requires high bed shear strains 100 field studies however have not yielded a systematic relationship between shear strain magnitude and fabric development to isolate this relationship four basal tills and viscous putty were sheared in a ring shear device to strains as high as 714 fabric was characterized within a zone of shear deformation using the long axis orientations of fine gravel and sand particles and the anisotropy of magnetic susceptibility ams of small 5 8 cm3 intact samples results indicate that till particles rotate toward the plane of shearing with long axis orientations that become tightly clustered in the direction of shear 0 78 s1 0 94 for three dimensional data these strong steady state fabrics are attained at shear strains of 7 30 with no evidence of fabric weakening with further strain regardless of the specific till or particle size fraction under consideration these results do not support the jeffery model of particle rotation which correctly describes particle rotation in the viscous putty but not in the tills owing to fluid mechanical assumptions of the model that are violated in till the sensitivity of fabric development to shear strain magnitude indicates that for most till units where shear strain magnitude is poorly known attributing fabric variations to spatial differences in other variables such as till thickness or water content will be inherently speculative attributing fabric characteristics to particular basal till facies is uncertain because shear strain magnitude is unlikely to be closely correlated to till facies weak or spatially variable fabrics in the absence of post depositional disturbance or major deviations from unidirectional simple shear indicate that till has not been pervasively sheared to the high strains required by the bed deformation model strong flow parallel fabrics are a necessary but insufficient criterion for confirming the model copyright 2008 john wiley sons ltd

development of the topography controlled upper odra ice lobe scandinavian ice sheet in the fore mountain area of southern poland during the saalian glaciation abstract during the saalian drenthe glaciation the upper odra ice lobe constituted the most southern part of the scandinavian ice sheet in central europe the lobe was situated in an area with varied topography in the foreland of a mountain range the ice lobe had a complex form because it was subdivided into several smaller sublobes the primary factors that controlled the lobe were investigated it was found that the ice lobe development depended largely on the topography but the lithology of the ice sheet substratum was also highly important the topography controlled the main movement direction of the ice and caused a concentration of the ice flow in the axial part of the silesian lowland between subglacial morphological barriers which thereby formed a corridor of relatively fast flowing ice which was probably streaming and which supplied the lobe the topography also determined the ice flow within the lobe which strongly matched the valley system the presence of sediments with relatively low permeability at the base of the lobe the quaternary deposits are underlain by neogene clays caused high pore water pressure in the subglacial zone and triggered the basal movement of the ice sheet which promoted a rapid flow of the ice and favoured the development of the lobe the basal tills deposited from the active and passive ice and extant till patches without a fluvioglacial cover atop some parts of the studied area indicate spatially varying ice flow dynamics especially in the later stage of glaciation certain parts of the lobe underwent stagnation while in other parts the ice was probably still active the varied behaviour of the ice within the lobe was determined primarily by the topography and lithology of the substratum which produced spatially varied marginal compression and basal friction a model of the development of the lobe is proposed

late devonian carbon isotope stratigraphy and sea level fluctuations canning basin western australia the upper devonian reef complexes of the canning basin contain some of the world s best exposed continuous stratigraphic sections through the frasnian famennian boundary the facies distribution and composition of these reef complexes record interactions among sea level changes sediment supply ocean chemistry and paleoecology changes in relative sea level produced spatial shifts in reef platform development and regional changes in sediment supply that can be correlated across facies boundaries using a combination of sequence stratigraphy biostratigraphy and carbon isotope stratigraphy during the lowstand interval below the frasnian famennian boundary the reef margin advanced down the reef slope in shallow water environments and siliciclastics locally dominated in the marginal slope environment compilation of a broad late frasnian to early famennian sequence stratigraphic framework for the canning basin demonstrates that transgressive intervals correlate to positive carbon isotopic excursions within the basin these isotopic shifts also can be correlated to time equivalent positive carbon isotopic excursions reported from transgressive intervals in europe thus the late frasnian transgressions in the canning basin were primarily eustatic rather than tectonic in origin and positive carbon isotopic signatures of the kellwasser horizons are globally correlative c 2002 elsevier science b v all rights reserved

sedimentary record of a scandinavian ice sheet drainage system and till deposition over subglacial obstacles promoting basal sliding an example from southern poland abstract subglacial obstacles occurring in the path of advancing ice sheets generally generate higher longitudinal compression and higher frictional drag than a flat substrate however in the case of a soft sediment substratum they can have a very different effect on ice sheet behaviour this study concerns a substrate composed of very fine grained sediments with low permeability the relationship between subglacial obstacles and the overriding scandinavian ice sheet was studied in an area of southern poland where a small intervalley neogene clay ridge 40 m high was present based on sedimentological and structural analysis of subglacial till and gravelly sandy sediments the basal depositional processes and subglacial conditions and their influence on ice sheet behaviour were analysed the till and related deposits within the ridge reflecting high water pressure conditions and lack of glacitectonic deformations indicate that the clay ridge did not generate much resistance against the advancing ice sheet but instead favoured basal slip the impermeable substratum weakened the ice bed coupling and promoted ice detachment from the substratum gravelly sandy inclusions at the till clay contact indicate that during the first stage of ice sheet overriding a canal drainage system developed at the ice substrate interface varied geometry size and location of inclusions of sorted sediments suggest periodic instability of the canal system which could lead to its transformation from initially uniform to being composed of conduits of different sizes during later stages of ice sheet overriding a traction till was deposited and occasional drainage through a water film was sufficient to evacuate basal meltwater the resulting change in the character of subglacial drainage was probably related to variations in water pressure gradient during progressive ice sheet advance

temporal changes in subglacial meltwater activity field evidence from the late devensian in the north of ireland abstract temporal changes in meltwater abundance distribution and characteristics controlling subglacial processes and ice sheet dynamics can be inferred from subglacial sediment successions field evidence for changes in subglacial meltwater characteristics over time is presented from two sites doonan drummee near a former late weichselian devensian ice centre in the north of ireland on a macroscale both sites investigated show subglacial diamicton overlying glacially planated bedrock platforms in more detail primary sedimentary structures and facies variability show a complex relationship between depositional processes and meltwater characteristics at the ice bed interface ibi sedimentary evidence suggests sediment transport and deposition took place by low viscosity subglacial slurries mobile sediment meltwater admixtures which are part of a continuum between the processes of subglacial sediment deformation and subglacial meltwater flooding subtle changes in meltwater abundance and distribution at the ibi controlled slurry rheology mechanisms of particle support and detailed sediment depositional processes

neogene glacial record from the sirius group of the shackleton glacier region central transantarctic mountains antarctica neogene glacigenic strata collectively referred to as the sirius group are widely distributed throughout the transantarctic mountains the group is particularly well exposed near the head of shackleton glacier 858109 to 858409s on roberts massif and at bennett platform these deposits are critical for examining the nature of former ice flow from the east antarctic ice sheet into the ross embayment the sirius group rests on a glacially grooved and striated pavement named herein the shackleton erosion surface the sub sirius group surface on roberts massif was of low relief and glaciogenic sediment was deposited on it as a sheet of uniform thickness at bennett platform stratigraphic sections attain a thickness of 110 m thick and are subdivided into the shackleton glacier formation maximum thickness 98 m and the overlying bennett platform formation 44 m separated by an unconformity a third older lithified diamictite containing wood fragments occurs as clasts within these formations and as boulders in the modern lateral moraines of shackleton glacier the dominant facies massive diamict is interpreted primarily as lodgement till other facies indicate glaciofluvial and glaciolacustrine deposition facies associations suggest deposition either by sliding temperate or by polythermal glaciers under much warmer conditions than those of today widespread large and small scale faulting has affected the sirius group and underlying rocks to the extent that inland exposures are over 500 m higher than those to the north over a distance of 30 km thus at the time of deposition of the sirius group the mountains were probably lower and the ice sheet was much thinner

fabric analysis of till clasts in the upper urumqi river tian shan china abstract in situ measurement of clast fabric within till and other sediment was performed at locations in hayisa hy upper wangfeng uw lower wangfeng lw and balatigou bl in the upper urumqi river in the tian shan of nw china subglacial tills have stronger fabric of both a axis and a b plane than supraglacial till this can be explained as a result from the different stress and transport histories of till clasts the preferred orientation of a axes of till fabrics intersect the former ice flow direction at a sharp angle 62 16 whereas the a b plane with its normal intersecting the former ice flow at 84 4 is oriented approximately parallel to the ice flow direction thereby subglacial relief appears to strongly influence the till fabric in particular the a axis fabric is more sensitive to landforms than that of the a b plane in simple straight troughs such as the wangfeng valley fabric varies little in the complex section of the trough such as the hayisa lipolith fabric characteristics are different at different sites of the hayisa drumlin the fabric data can be used to understand glacial sedimentary processes in the study area

experiments on the dynamics and sedimentary products of glacier slip abstract experimental work in glacial geomorphology is focused almost entirely on processes in the thin shear zone at the beds of sliding glaciers where ice at its pressure melting temperature moves over either rigid rock or deformable till experiments with rotary shear devices illuminate constitutive behavior there central to the dynamics of fast moving glaciers and provide a foundation for interpreting the sedimentary record of glacier slip and associated sediment transport results from experiments designed to study ice sliding over a rigid wavy bed shear deformation of till and plowing of clasts across the surface of a till bed point to a common conclusion drag at the bed can decrease with increasing slip velocity thereby concentrating driving stress elsewhere and promoting rapid glacier flow this rate weakening behavior at glacier beds is in contrast to the viscous slip resistance assumed in ice sheet models and most efforts to determine distributions of basal drag from glacier surface velocities ring shear experiments in which various basal tills and more idealized materials are sheared to high strains provide quantitative insight into grain size evolution mixing at contacts between basal tills microstructure development particle fabric development and development of anisotropy of magnetic susceptibility preferred orientations of principal magnetic susceptibilities provide the most dependable and complete description of till shear patterns when applied to basal tills of the geologic record magnetic till fabrics measured along thick till sections and calibrated experimentally indicate that deformation of the bed by two lobes of the laurentide ice sheet was shallow

basin scale patterns of subglacial sediment mobility implications for glaciological inversion modelling abstract patterns of glacial bedforms and their internal sediments are described from the omagh basin north central ireland here drumlins and ribbed moraines were variously formed preserved and remoulded during several late devensian ice flow stages and their patterns can be used as input into glaciological inversion models more detailed examination of the morphology and internal sediments of these bedforms shows a complex pattern of reworking driven by local scale basal thermal and hydrological regime sediment lithofacies associations and patterns of erratic carriage can be used to better evaluate ice bed conditions and basal processes than bedforms alone the sedimentary evidence suggests that bedforms were unlikely to have been formed during a single glacial episode as is implicit in glaciological inversion models and more likely formed during several episodes that cannot be resolved by crosscutting or superimposed bedform relationships alone

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

host rock and structural controls on the nature and timing of gold mineralization at the holloway mine abitibi subprovince ontario the holloway mine a mesothermal gold deposit is located within the western abitibi subprovince ontario mineralized zones that contain microscopic gold within pyrite are hosted by a sequence of metakomatiites mafic to felsic metavolcanic and metasedimentary rocks there were two mineralization events however the early one was the main event in terms of the amount of gold mineralization this event was associated with albitization silicification chloritization and sericitization in addition to pyritization the later mineralization is associated with sericitization and pyritization carbonate and sericite alterations are associated with both mineralizing events results of u pb zircon age dating of rocks within the sequence constrains the main mineralization event to 2672 ma ore lenses of the holloway deposit are enveloped by 080 striking steeply south dipping zones of intense deformation and fabric development within the porcupine destor deformation zone the shear zones are characterized by a strong foliation and locally an associated extension lineation the ore lenses are interpreted to represent lithons that were formed by boudinage of the more competent mineralized zones which are pervasively albitized analysis of geochemical data demonstrates that the ree th nb hf ti fe and al were largely immobile with respect to the albite quartz chlorite sericite and hematite alterations locally preserved textures such as abundant varioles and spherulites indicate that the host metavolcanics were relatively evolved rocks geochemical data show they have an iron enrichment trend typical of tholeiitic mafic to felsic suites and that they were derived through fractional crystallization of parent basalt because of their high fe mg ratios the rocks reacted with hydrothermal solutions carrying gold presumably as thio complexes to form pyrite which scavenged the gold

microfabric analysis by manual and automated stereological procedures a methodological approach to antarctic tillite fabric analysis is commonly used to infer former movement directions of diamictons however analysis techniques are typically time consuming and partly subjective stereological analysis provides an alternative for objective determination of the preferred orientation of particles the ability of manual and automated stereological procedures to determine the preferred orientation of particles 120 4000 m in tillite is assessed using core samples from mount feather mcmurdo dry valleys antarctica orthogonal sets of vertical thin sections were subjected to directed secant analysis involving the determination of the number of intersections between particle outlines and a rotating series of parallel lines the manual analysis reveals a weakly developed three dimensional tilt angle plunge of 68 this reflects the depth averaged subglacial deformational structure of the deposit because the preferred orientation signal is weak in the automated set up this signal is obscured by the effect of digitization hampering the reliable assessment of the orientation direction the study shows microfabric variability within the studied cored section that is interpreted as a shear fabric reliable macrostructural information that might constrain ice flow directions requires a larger number of randomly or systematically drawn core samples from which averaged microstructural fabrics can be derived

the mendel formation evidence for late miocene climatic cyclicity at the northern tip of the antarctic peninsula abstract a detailed description of the newly defined mendel formation is presented this late miocene 5 9 5 4 ma sedimentary sequence with an overall thickness of more than 80 m comprises cyclic deposition in terrestrial glacigenic glaciomarine and marine environments subglacial till was deposited by a thick grounded antarctic peninsula ice stream advancing eastwards through the prince gustav channel crossing the northernmost part of present day james ross island with most of the material carried actively at the base of the warm based glacier the form of the prince gustav channel originated before the late miocene and its present glacial over deepening resulted in multiple grounded glacier advances during the neogene and quaternary the sea prograded from the east and the glacier margin became buoyant building a small ice shelf below and in front of which glaciomarine and marine sediments were deposited these sedimentary deposits are composed of material that was transported mostly by small glaciers and subsequently by the floating ice shelf and by calving icebergs towards the open sea these environmental and glaciological conditions differ strongly from the present cold based local glaciers of james ross island and the antarctic peninsula these changes were triggered by the global sea level fluctuation connected with climatic changes due to antarctic ice sheet build up and decay this reveals late miocene obliquity driven cyclicity with a 41 ka period the mendel formation sedimentary sequence is comprised of at least two glacial periods and one interglacial period sea level rise at the northern tip of the antarctic peninsula between glacial lowstand and interglacial highstand was more than 50 m during the late miocene and was followed by a subsequent sea level fall of at least the same magnitude the presence of well preserved articulated pectinid bivalves support interglacial open sea conditions the re deposition of palaeontological material was shown to be important for the mendel formation reworked pectinid shells revealed an open marine interglacial condition in this part of the antarctic peninsula during the early to mid miocene 20 5 17 5 ma unfortunately relevant sedimentary deposits have not been found on land

water throughflow and the physical effects of deformation on sedimentary glacier beds the sediment comprising a deformable bed beneath an ice mass is typically modeled as a homogeneous fluid without internal structure although clearly deformation must result from the spatial rearrangement of the particles that make up the sediment laboratory deformation experiments were used to simulate the effects of active deformation on subglacial sediments these experiments indicate that deformation results in the rearrangement of particles and changes in sediment structure scanning electron and optical microscopy of postdeformation sediments revealed both 1 particle alignment parallel or subparallel to the direction of principal strain and 2 dilation where active deformation had occurred both of these effects will alter the permeability and hence hydraulic conductivity of the sediment body increasing the rate of water flow through the bed parallel to deformation microscopic examination of these sediments allows estimation of postdeformation permeabilities these permeabilities may be anisotropic furthermore water throughflow by darcian processes enhanced by the effects of deformation may increase the proportion of basal water that can be evacuated by throughflow water will tend to be retained in the high permeability actively deforming layer and may destabilize this layer

rhythmic till sedimentation evidence for repeated hydraulic lifting of a stagnant ice mass the youngest sedimentary facies exposed in erosional hummocky terrain in south central alberta canada is composed of alternating beds of massive silty clay diamicton and sorted sand and or silt diamicton beds are similar in thickness 5 20 cm both laterally and vertically within the sequence and sedimentary structures and consistent clast orientations support a subglacial origin for both the diamicton and the sorted sediment alternation between diamicton and sorted strata document rhythmic sedimentary sequences deposition of melt out till followed by current deposition laterally extensive sorted beds indicate that the currents responsible for sand and silt deposition must have flowed as a sheet this flow was shallow no more than 20 cm indicated by scours below boulders that were suspended from the base of glacial ice sheet flow requires that the water was stored beneath the ice prior to drainage consequently some of the diamicton may have been deposited by rain out through the shallow stored water and hence each diamicton bed may represent a combination of direct melt out onto the bed and rain out through the water column inferred cycles of water accumulation and drainage may have been annual

stratigraphy and sedimentology of devensian dimlington stadial glacial deposits east yorkshire england the stratigraphy and sedimentology of the glacial deposits exposed along the coast of east yorkshire are reviewed critical sections at filey brigg barmston and skipsea are examined to reassess the stratigraphy of devensian dimlington stadial glacial deposits in the light of recent developments in glacial sedimentology sedimentary and glaciotectonic structures studied in the field and by using scanning electron microscopy are emphasised two hypotheses are considered for the genesis of the interbedded diamictons and stratified sediments the first involves the deposition of lodgement till and or deformation till followed by meltout till which was overridden to produce more deformation till reflecting periods of ice stagnation punctuated by glacier thickening the second hypothesis which is favoured on the basis of field evidence and micromorphology involves the vertical accretion of a deforming till layer associated with cavity channel or tunnel valley fills beneath active ice at barmston the upper part of the diamicton contains elongate pendant structures containing gravels indicating that the diamicton was saturated and able to flow the diamictons therefore represent a complex sequence of tills deposited and deformed by active ice during the dimlington stadial previously published stratigraphical schemes involving classifications of multiple tills in east yorkshire should be simplified and it is more appropriate to assign these to a single formation the skipsea till formation rhythmic glaciolacustrine and proglacial glaciofluvial sediments overlie the tills at barmston and skipsea these were deposited in sag basins during deglaciation as the tills settled and deformed under thickening sediment and as buried ice melted out extensive sands and gravels cap the succession and were deposited on a sandur during the later stages of deglaciation

unexpected ice flow directions during the late weichselian deglaciation of the south baltic area indicated by a new lithostratigraphy in nw poland and ne germany

grain textural analysis across a range of glacial facies a technique proposed by hooke and iverson 1995 to identify deformed subglacial sediments is reviewed and tested based on two main objectives first an investigation of whether the fractal dimension can distinguish between non deformed and deformed facies for which we compare supraglacial and subglacial facies explicitly second an evaluation of whether the fractal dimension can be used as a diagnostic criteria to discriminate between different styles and degrees of basal deformation this is tested using a range of sediments from the deformation continuum suggested by hart and boulton 1991b sixteen subglacial samples were selected from quaternary sites in england and three supraglacial samples from the modern haut glacier d arolla switzerland the mean fractal dimension for the subglacial diamicton matrix facies was 2 92 similar to findings of 2 90 by hooke and iverson 1995 for their basal tills the supraglacial facies displayed a mean fractal dimension of 2 83 which is unusually high for facies which are assumed to be undeformed a mann whitney u test showed that fractal dimensions of supraglacial and subglacial diamicton matrix facies were not significantly different no significant difference was found between the fractal dimensions of the different tectonic facies within the subglacial group it may be impossible to separate the subglacial and supraglacial facies because of complex debris paths within the glacier grain fracture or parent lithology may affect the particle size distribution of subglacial facies

contrasting styles of glacial dispersal in newfoundland and labrador methods and case studies a review of practical approaches to drift exploration is presented it is intended for use by exploration geologists working in drift covered areas there are contrasts in style of glacial dispersal between labrador dominated by the affects of the laurentide ice sheet and newfoundland affected by small coalescing ice caps at the glacial maximum and smaller topographically controlled ice centres during deglaciation the result has been to produce longer ribbon shaped dispersal trains in labrador except in the labrador trough near the centre of the labrador sector of the laurentide ice sheet in newfoundland the glacial dispersal patterns are more diffuse

sedimentation in a drumlin lee side subglacial wave cavity northwest ireland abstract lee side stratification sequences in a late pleistocene drumlin in northwest ireland are used to assess sedimentation patterns in subglacial wave cavities formed on the lee sides of drumlins three major subglacial cavity sub environments are identified 1 high energy divergent trough like closed conduit characterised by channel fill pebbly sand facies 2 low energy closed conduit characterised by alternating sand silts 3 trough margin dominated by stratified diamicts facies arrangements suggest two major transient states reflecting variations in subglacial meltwater flux the active phase showed meltwater flow directed across the drumlin apex suggesting complete uncoupling from the glacier bed supercavitation as flow velocities waned pebbly sand facies were deposited by in situ freezing of within conduit sediment admixtures the later quiescent phase was characterised by meltwater flow directed transverse to ice flow cavity shrinkage and concomitant deposition of subglacial sheetwash and cohesive sediment flows along cavity margins cavity closure resulted in complete coupling at the ice substrate interface with localised glaciotectonic loading on underlying lee side stratification sequences and concomitant till deposition these late stage sedimentation events at shinnan hill produced a very complex polygene endform which cannot be simply attributed to one formative process more realistically they reflect the influence of a rather complex and very dynamic subglacial system subject to complex spatial and temporal variations in subglacial erosion deposition and meltwater flux at the time of drumlinisation

recognition and palaeoclimatic implications of late quaternary niche glaciation in eastern lesotho geomorphic evidence of former glaciation in the high drakensberg of southern africa has proven controversial with conflicting glacial and non glacial interpretations suggested for many landforms this paper presents new geomorphological sedimentological and micromorphological data and glacier mass balance modelling for a site in the leqooa valley eastern lesotho preserving what are considered to be moraines of a former niche glacier that existed during the last glacial maximum lgm the geomorphology and macro sedimentology of the deposits display characteristics of both active and passive transport by glacial processes however micromorphological analyses indicate a more complex history of glacial deposition and subsequent reworking by mass movement processes the application of a glacier reconstruction technique to determine whether this site could have supported a glacier indicates a reconstructed glacier equilibrium line altitude ela of 3136 m a s l and palaeoglacier mass balance characteristics comparable with modern analogues reflecting viable if marginal glaciation radiocarbon dates obtained from organic sediment within the moraines indicate that these are of lgm age the reconstructed palaeoclimatic conditions during the lgm suggest that snow accumulation in the drakensberg was significantly higher than considered by other studies and has substantial relevance for tuning regional climate models for southern africa during the last glacial cycle copyright 2009 john wiley sons ltd