artifact orientations and site formation processes from total station proveniences it is well understood that the orientation of clasts within a deposit can yield information on site formation processes although the term clast usually refers to the natural component of a deposit the artifactual and faunal components are also known to be sensitive to site formation processes there are a number of ways in which orientations can be recorded and analyzed and this paper describes how orientations can be recorded as part of piece proveniencing artifacts with a total station after the method is described the calculation statistical analysis and presentation of artifact orientations are considered the final part of the paper presents orientation data from pech de l aze iv recorded and analyzed in this way the example demonstrates the effectiveness of the total station method of recording orientations their sensitivity to site formation processes and the importance of using multiple methods of data analysis and presentation to assess and interpret patterning

reinterpreting rotherslade gower peninsula implications for last glacial ice limits and quaternary stratigraphy of the british isles rotherslade on the gowerpeninsula in southwales has beenviewed asa keysite for the reconstruction of quaternary depositional environments in the british isles since the early 20th century and certainly since the 1980s the accepted view has been that rotherslade is the most westerly location on the south gower coast where there is in situ basal till exposed and that logically this location marks the position of the lgm ice limit however reinvestigation of the sediments and their architecture and analysis of clast fabrics and thin sections of critical sedimentary units show that none of the exposed sediments has properties diagnostic of subglacial deposition or deformation we postulate here that lgm ice terminated at the western side of swansea bay a few kilometres to the north east of rotherslade and propose that the sedimentary sequence comprises early to middle devensian periglacial sediments overlain by a complex of late devensian ice proximal outwash fan deposits an assemblage of paraglacial debris and finally periglacial mass movement deposits the proposed repositioning of the late devensian ice limit and the associated new subaerial interpretation of the sediments suggest that a reassessment of sedimentary sequences hunts bay western slade and landforms paviland moraine farther west on gower which have attained similar stratigraphical status is now warranted copyright 2008 john wiley sons ltd

origin of a washboard moraine of the des moines lobe inferred from sediment properties abstract geometric characteristics of the washboard moraines of the des moines lobe dml of the laurentide ice sheet agree with their proposed origin as crevasse squeeze ridges but study of their sediments is required to help further test this hypothesis a 70 m long 3 5 m high section through a moraine ridge in central iowa revealed till with irregular isolated lenses of silt sand and gravel that dip to varying extents upglacier the texture and density of the till are like those of the basal till of the dml studied elsewhere in iowa and preconsolidation pressures determined from tests on till and silt of the ridge indicate that it developed subglacially rather than at the glacier margin preconsolidation pressures additionally demonstrate that pore water pressures in the bed supported most of the glacier s weight which would have contributed to till mobility fabrics based on the anisotropy of magnetic susceptibility of 3125 intact till specimens collected at 125 locations in the section indicate two end member states of strain that varied with location in the ridge and caused sediment mounding simple shear that was directed downglacier along shear planes inclined upglacier together with pure shear where an overlying crevasse allowed the sediment bed to extend upward and laterally meltwater that likely flowed along the crevasse deposited sorted sediments that were incorporated in till deformed and rotated this positive test of the crevasse squeeze hypothesis indicates that the dml was in longitudinal extension near its margin reinforcing previous arguments that the lobe surged the predominance of fabrics caused by simple shear demonstrates that crevasse filling was underway before the surge had fully halted this study should prompt caution in using similar transverse ridges such as those geophysically imaged in some submarine glacier forefields as indicators of retreat rates

basal ice facies and supraglacial melt out till of the laurentide ice sheet tuktoyaktuk coastlands western arctic canada glacially deformed massive ice and icy sediments mi is in the eskimo lakes fingerlands and summer island area of the tuktoyaktuk coastlands western arctic canada show in the same stratigraphic sequences features characteristic of both basal glacier ice and intrasedimental ice basal ice features comprise 1 ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers and ice sheets in alaska greenland and iceland 2 ice crystal fabrics similar to those from basal ice in antarctica and ice cored moraines on axel heiberg island canada and 3 a thaw or erosional unconformity along the top of the mi is buried by glacigenic or aeolian sediments intrasedimental ice consists of pore ice and segregated ice formed within pleistocene sands deposited before glacial overriding the co existence of basal and intrasedimental ice within the mi is records their occurrence within the basal ice layer of the laurentide ice sheet stagnation of the ice sheet and melt out of till from the ice surface allowed burial and preservation of the basal ice layer on a regional scale the widespread occurrence of supraglacial melt out till with clast fabrics similar to those in the underlying ice suggests that such till can be well preserved during partial thaw of a continental ice sheet in lowlands underlain by continuous permafrost

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

zarqa megafacies widespread subglacial deformation in the sarah formation of saudi arabia and implications for the sequence stratigraphy of the hirnantian glaciation

fluid pressure controlled soft bed deformation sequence beneath the surging breiðamerkurjokull iceland little ice age abstract the general subject of this paper is subglacial deformation beneath brei amerkurjokull a surging icelandic glacier more specifically it discusses the evolution and the role of fluid pressure on the behaviour of subglacial sediments during deformation during little ice age maximum the two outcrops studied north jokulsarlon n jk and brennhola alda ba were located at 2550 m and 550 m respectively from the front of the brei amerkurjokull sedimentological analysis at the forefield of the glacier shows thick coarse glaciofluvial deposits interbedded with thin fine grained shallow lacustrine swamp deposits overlain by a deformed till unit at n jk ba outcrop shows fine grained shallow lacustrine swamp deposits overlain by a deformed till unit the sequence of deformation events from one outcrop to the other is similar first major thrust planes which were rooted in shallow lacustrine swamp deposits developed by glacially induced simple shear next the thrusts were folded indicating the deformation of hydroplastic sediment assisted by moderate fluid pressure then clastic dyke swarms crosscut the sedimentary succession proving that fluid overpressure caused hydrofracturing associated with fluidisation finally as water escaped from the glacier bed fluid pressure dropped and normal faulting occurred in brittle state subglacial sediments fluid pressure variations are related to glacier dynamics they control the deformation sequence by modifying subglacial rheological behaviour and the nature of the subglacial tectonism

characterization of sand lenses embedded in tills abstract tills dominate large parts of the superficial sediments on the northern hemisphere these glacial diamictons are extremely heterogeneous and riddled with fractures and lenses of sand or gravel the frequency and geometry of sand lenses within tills are strongly linked to glaciodynamic processes occurring in various glacial environments this study specifically focuses on the appearance and spatial distribution of sand lenses in tills it introduces a methodology on how to measure and characterize sand lenses in the field with regard to size shape and degree of deformation a set of geometric parameters is defined to allow characterization of sand lenses the proposed classification scheme uses a stringent terminology to distinguish several types of sand lenses based on the geometry it includes sand layers sand sheets sand bodies sand pockets and sand stringers the methodology has been applied at the kallerup field site in the eastern part of denmark the site offers exposures in a number of till types that underwent different levels of glaciotectonic deformation sand lenses show high spatial variability and only weak uniformity in terms of extent and shape secondly the genesis of the various types of sand lenses is discussed primarily in relation to the depositional and glaciotectonic processes they underwent detailed characterization of sand lenses facilitates such interpretations finally the observations are linked to a more general overview of the distribution of sand lenses in various glacial environments due to the complex and mutable appearance of sand lenses geometric descriptions can reveal the deformation history and even give indications on the palaeo glaciological conditions during the deposition of the surrounding tills this information can support the understanding of till genesis and further inform till classifications in this regard structural heterogeneity such as sand lenses can supplement traditional directional element analysis to identify till types and may be used as a novel tool in till investigations

new evidence for a grounded irish sea glaciation of the isles of scilly uk abstract new geomorphological and sedimentological data support previously published reconstructions of an irish sea glacier advance as far south as the northern shores of the isles of scilly in the celtic sea 49 58 n offshore boulder covered bars with cores of diamicton are interpreted as moraines which together with onshore moraine ridges and trimlines mark the maximal extent of the irish sea glacier at bread and cheese cove st martin s a heterogeneous sediment unit wedged between periglacial gelifluctates is interpreted as a mixture of glacitectonized and cannibalized glacilacustrine and marine deposits as well as primary subglacial tills macrofabric signatures reflect a subglacial origin but the whole unit has been subject to down slope mass movement micromorphological analysis indicates highly variable response to deformation and glacitectonism with most features relating to ductile behaviour and wet deformation the characteristics suggest deposition during a short lived advance of the irish sea glacier over pre existing marine and contemporaneous proglacial lacustrine sediments once blocks of stratified sediment and diamicton had been driven onshore they were subject to paraglacial remobilization resulting at most locations in complete disaggregation the distribution of re worked glacigenic sediments coincides with the glacial limits inferred from the geomorphological evidence

trampling experiments at cova gran de santa linya pre pyrenees spain their relevance for archaeological fabrics of the upper middle paleolithic assemblages the study of fabrics that is the analysis of the orientation and slope of archaeological and sedimentary materials associated with the middle palaeolithic upper palaeolithic mp up transition at cova gran shows substantial differences archaeological assemblages are characterised by greater isotropy in the fabrics than the sedimentary levels within which they are located indicating that these differences may be generated by anthropic processes one of the anthropogenic processes associated with horizontal and vertical displacement of archaeological artefacts is trampling and circulation caused by later occupations in order to evaluate the effect of movement on materials we undertook experiments simulating geological and archaeological conditions at cova gran the results show that human trampling does not cause major isotropy in fabrics but arranges archaeological assemblages towards planar or linear materials according to surface geometry we were not able to replicate the fabric pattern of materials from the archaeological levels of cova gran suggesting that they must be associated with the activities of human occupation at each level

a mid holocene candidate tsunami deposit from the nw cape western australia although extreme wave events are frequent along the northwestern coast of western australia and tsunamis in 1994 and 2006 induced considerable coastal flooding locally robust stratigraphical evidence of prehistoric tropical cyclones and tsunamis from this area is lacking based on the analyses of x ray computed microtomography ct of oriented sediment cores multi proxy sediment and microfaunal analyses optically stimulated luminescence osl and 14c ams dating this study presents detailed investigations on an allochthonous sand layer of marine origin found in a back barrier depression on the nw cape range peninsula the event layer consists of material from the adjacent beach and dune fines and thins inland and was traced up to 400 m onshore although a cyclone induced origin cannot entirely be ruled out the particular architecture and fabric of the sediment rip up clasts and three subunits point to deposition by a tsunami as such it represents the first stratigraphical evidence of a prehistoric mid holocene tsunami in nw western australia it was osl dated to 5400 4300 years ago thus postdating the regional mid holocene sea level highstand

beyond maps patterns of formation processes at the middle pleistocene open air site of marathousa 1 megalopolis basin greece abstract recent excavations at the middle pleistocene open air site of marathousa 1 have unearthed in one of the two investigated areas area a a partial skeleton of a single individual of palaeoloxodon antiquus and other faunal remains in spatial and stratigraphic association with lithic artefacts in area b a much higher number of lithic artefacts was collected spatially and stratigraphically associated also with faunal remains the two areas are stratigraphically correlated the main fossiliferous layers representing an en mass depositional process in a lake margin context evidence of butchering cut marks has been identified on bones of the elephant skeleton as well on elephant and other mammal bones from area b however due to the secondary deposition of the main find bearing units it is of primary importance to evaluate the degree and reliability of the spatial association of the lithic artefacts with the faunal remains indeed spatial association does not necessarily imply causation since natural syn and post depositional processes may equally produce spatial association assessing the degree and extent of post depositional reworking processes is crucial to fully comprehend the archaeological record and therefore to reliably interpret past human behaviours the present study uses a comprehensive set of spatial statistics in order to disentangle the depositional processes behind the distribution of the archaeological and palaeontological record at marathousa 1 preliminary results of our analyses suggest that a high energy erosional process attributed to a hyperconcentrated flow deposited at the margin of a swamp reworked an autochthonous exposed or slightly buried scatter of lithic artefacts and faunal remains minor reworking and substantial spatial association of the lithic and faunal assemblages support the current interpretation of marathousa 1 as a butchering site

diamictic sediments within high arctic lake sediment cores evidence for lake ice rafting along the lateral glacial margin sediment cores from six small lake basins in the canadian high arctic reveal a gravel rich 30 by weight to gravel poor 2 diamict facies underlying massive post glacial clayey silt ten other lakes contain a second diamict facies within what are interpreted to be glaciolacustrine sedimentary assemblages the sedimentology clast fabrics and fossil remains diatoms ostracodes and chironomid head capsules within both diamict facies suggest that these deposits are not tills clast fabrics yielded low s1 0 41 0 57 and high s3 0 09 0 22 eigenvalues placing them within the range of ice rafted diamictons and glacigenic sediment flows the high percentage of clast dip angles 45 15 61 random clast azimuth and lower diamict contacts conformable to underlying current bedded sediment favours an origin as a rain out or settling deposit samples of the matrix and scrapings of clasts from the diamicts revealed a diatom assemblage dominated by littoral and planktonic forms such as are found in the littoral regions of the lakes today this contrasts sharply with the assemblages within the overlying clayey silt in which benthic forms predominate clasts are thus interpreted to have been rafted from the littoral areas of the lake the process proposed to explain this is rafting by the lake ice cover in a glacial marginal environment early season meltwater impounded along the lateral margin of retreating cold based glaciers would buoyantly lift the lake ice cover and any adfrozen lake sediment higher lake levels and increased areal extent of seasonal freeze on between the lake ice cover and the lake bed would allow the redeposition of littoral sediments to the benthic regions through greater lateral shifting of the ice cover as it broke up incision by meltwater streams into the lateral glacial margins would later isolate the lake allowing seasonal warming of lake water enough to support the growth and maturation of the ostracode and chironomid species found as fossils within the diamicts

sedimentary fabric characterized by x ray tomography a case study from tsunami deposits on the marquesas islands french polynesia x ray tomography is used to analyse the grain size and sedimentary fabric of two tsunami deposits in the marquesas islands french polynesia pacific ocean which are particularly exposed to trans pacific tsunamis one site is located on the southern coast of nuku hiva island hooumi and the other one is on the southern coast of hiva oa island tahauku results are compared with other techniques such as two dimensional image analysis on bulk samples particle analyser and anisotropy of magnetic susceptibility the sedimentary fabric is characterized through three dimensional stacks of horizontal slices following a vertical step of 2 5 mm along the cores while grain size distribution is estimated from two dimensional vertical slices following a step of 2 mm four types of fabric are distinguished a moderate to high angle 15 to 75 b bimodal low angle 15 c low to high angle with at least two different orientations and d dispersed fabric the fabric geometry in a tsunami deposit is not only controlled by the characteristics of the flow itself current strength flow regime etc but also sediment concentration deposition rate and grain size distribution there is a notable correlation between unimodal high angle fabric type a and finely skewed grain size distribution the two tsunami deposits studied represent two different scenarios of inundation as demonstrated here x ray tomography is an essential method for characterizing past tsunamis from their deposits the method can be applied to many other types of sediments and sedimentary rocks

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

islands in a stream reconstructing site formation processes in the late middle paleolithic site of ein qashish northern israel abstract information retrieved from open air sites is necessary for a more complete reconstruction of middle paleolithic behaviors which is currently often based mainly on data from caves and rockshelters however open air sites present methodological and analytical challenges that differ from those encountered in cave sites being essentially an integral part of their paleo landscape open air sites are affected by localized as well as landscape scale processes that need to be distinguished from the anthropogenic signatures ein qashish is an open air late middle paleolithic occurrence located in the yizra el valley just east of mt carmel situated on the pleistocene floodplain of the qishon stream the site is found at the interface of the sediments deposited by the qishon stream which drains the yizra el valley and paleo wadi qashish which flowed off mt carmel artifacts and bones are dispersed over a vertical distance of some 90 cm observations in geological trenches located at variable distances from the excavated area indicate that this cluster of finds occurred at a circumscribed locality on the landscape rather than as a part of a continuous distribution on the paleo surface we reverse engineer site formation processes starting with the latest post depositional moving to earlier syn depositional processes and relate them to their most likely causative agents through the examination of a series of explicit models gis techniques were applied in order to parse the variable lines of information which include lithic and faunal taphonomy size distributions and spatial and stratigraphic dispersal of objects fabric analysis and osl results we discuss the implications of the results for distinguishing anthropogenic from non anthropogenic effects and for reconstructing the timeline of depositional events that led to the current distribution of artifacts insights into these questions inform our understanding of human activities at the site suggesting that the excavation samples the margins of an occupation horizon where activities focused on knapping and resource processing rather than task specific behaviors such as hunting

progressive proglacial to subglacial deformation and syntectonic sedimentation at the margins of the mid pleistocene british ice sheet evidence from north norfolk uk abstract detailed analysis and interpretation of the stratigraphy and structures developed within polydeformed sediments exposed in the coastal section between west runton and sheringham eastern england has allowed the characterisation of the glacitectonic signature associated with the advance of a major mid pleistocene anglian ice sheet the sequence of pre glacial deposits and glacial sediments laid down during earlier southerly directed ice advances d1 d2 is deformed and disrupted by an ice advance from the west southwest that marks a major change in ice flow dynamics in northern east anglia the simplest interpretation of this deformation event d3 is in terms of a progressive proglacial to subglacial deformation model proglacial deformation occurred in advance of the ice margin and was dominated by thrusting positive topographic features which developed above the propagating thrusts controlled sediment dispersal patterns within outwash sandur leading to the formation of small sub basins between these morainic ridges the accretion of the wedge shaped proglacial thrust moraines to the main push moraine formed at the margin of the advancing glacier may have temporarily stalled forward motion of the ice thrusting and large scale folding associated with ice marginal deformation led to the stacking of material excavated from further up ice onto the stoss side of these accreted thrust related moraines that allowed the glacier to override the obstruction subglacial deformation was highly variable in its style and intensity ranging from heterogeneous folding and thrusting through to more pervasive ductile shearing associated with the formation of a subglacial shear zone the thickness and complexity of this shear zone increases up ice where it is characterised by a thick glacitectonic melange the pore water content of the deforming sediments controlled the pattern of deformation within the shear zone however an increase in the efficiency of the drainage system towards the front of the glacier would have led to a rapid thinning of this water enhanced zone of ductile shear evidence from north norfolk suggests that zones of preferential pore water flow within the glacier bed are a major controlling factor on the location of the subglacial shear zone consequently the bulk of the forward motion of the glacier may not be accommodated by shearing within the sediments immediately below its base but occur at a deeper level within the deforming bed

late wisconsin ice flow history in the buffalo head hills kimberlite field north central alberta ice flow of the last glaciation in the buffalo head hills kimberlite field of northern alberta is reconstructed from landform interpretations and clast orientations for the purpose of aiding kimberlite exploration in the region the paucity of bedrock outcrop and the absence of preserved striae and other erosional ice flow indicators on the soft cretaceous marine sediments inhibit detailed interpretations on glacial flow chronology poorly developed bedrock drumlins on the buffalo head hills and erosional ice flow indicators preserved on the kimberlite outcrops indicate southwestward ice flow during the maximum extent of ice during the last glaciation during the deglaciation of northern alberta later phases of ice flow were controlled by lobes of surging ice which surged into proglacial lakes west of the buffalo head hills the maximum phase of southwest flow was followed by southeastward ice movement of the peace river ice lobe similarly east of the buffalo head hills the maximum phase of ice flow was superceded by a south southwest ice advance of the wasbasca ice lobe

x ray tomography of tsunami deposits towards a new depositional model of tsunami deposits x ray computed microtomography is used to obtain high resolution imagery of a historical tsunami deposit in andalusia spain 1755 lisbon tsunami the technique allows characterization of grain size distribution structures component analysis and sedimentary fabric of fine grained unconsolidated tsunami deposits at resolutions down to particle scale the results are validated by comparing to data obtained using other techniques such as laser diffraction anisotropy of magnetic susceptibility and x ray microfluorescence on the same deposits specific technical details such as sampling scanning and image processing methods and further improvements are addressed the use of x ray computed microtomography provides new insights into the stratigraphy of the deposits and gives access to significantly more detailed view of key sedimentary features such as mudlines rip up clasts crude laminations convolutions floating outsized clasts and contacts between successive units this analysis of the 1755 tsunami deposits using x ray computed microtomography allows the proposal of new hypotheses for the sedimentary processes forming tsunami deposits deposition by settling is limited and the section analysed here is dominated by a high shear stress leading to the development of traction carpets with laminated mudlines corresponding to the basal frictional region of these carpets the onset of the tsunami backwash is marked by a micro vortex resembling kelvin helmoltz instabilities

facies architecture within a regional glaciolacustrine basin copper river alaska abstract this paper defines the principal architectural elements present within the pleistocene glaciolacustrine basin fill of the copper river basin in alaska the copper river drains an intermontane basin via a single deeply incised trench through the chugach mountains to the gulf of alaska this trench was blocked by ice during the last glacial cycle and a large ice dammed lake referred to as lake atna filled much of the copper basin facies analysis within the basin floor allows a series of associations to be defined consistent with the basinward transport of sediment deposited along calving ice margins and at the basin edge basinward transport involves a continuum of gravity driven processes including slumping cohesive debris flow hyperconcentrated concentrated density flows and turbidity currents this basinward transport results in the deposition of a series of subaqueous fans of which two main types are recognised 1 large stratified basin floor fans which extend over at least 5 km and are exposed in the basin centre these fans are composed of multiple lobes incised by large mega channels giving fan architectures that are dominated by horizontal strata and large cross cutting channel fills individual lobes and channel fills consist of combinations of diamict derived from iceberg rainout and the ice marginal release of subglacial sediment multiple units of fining upward gravels which grade vertically into parallel laminated and rippled fine sands and silts deposited by a range of density flows and currents derived from the subaqueous discharge of meltwater and rhythmites grading vertically into diamicts deposited from a range of sediment density flows re mobilising sediment deposited by either iceberg rainout or the ice marginal release of sediment 2 small complex proximal fans which extend over less than 2 km and are exposed in the southern part of the basin these fans are composed of coalescing and prograding lobes of diamict and gravel deposited both directly by subaqueous meltwater and from sediment density flows these lobes are cross cut by a range of sand and gravel filled troughs and channels cut by subaqueous outwash and either overlie or are overlain by horizontal sheets of gravel and diamict deposited from a range of sediment density flows the fans are therefore characterised by a complex and laterally variable facies architecture water depth proglacial topography stability of meltwater portals and sediment supply may all be important in determining the type of subaqueous fan present at any one location we suggest that the copper river basin fill is dominated by packages of sediment containing multiple subaqueous fans with individual fans separated by units of diamict each sediment package is in turn separated from the next by a palaeo landsurface shaped by interstadial interglacial fluvial processes and by volcanic debris flows

formation of mega scale glacial lineations on the dubawnt lake ice stream bed 2 sedimentology and stratigraphy mega scale glacial lineations msgls are highly elongate subglacial landforms produced beneath zones of fast flowing ice while qualitative data on their morphology have existed for several decades studies of their composition and sedimentology are comparatively rare sediment exposures along the course of the finnie river in nunavut northern canada provide a window into the internal stratigraphy and sedimentology of msgls formed by the dubawnt lake palaeo ice stream during regional deglaciation of the laurentide ice sheet stratigraphic sections record evidence for an initial advance of ice into the study area followed by ice sheet recession and deposition of glacifluvial and glacilacustrine outwash subsequently the dubawnt lake palaeo ice stream overrode and reworked this outwash subglacially forming an msgl till this till comprises a sandy red diamicton facies forming the core of the msgl ridges and containing variably deformed lenses stringers and rafts of outwash the sedimentology of this diamicton is consistent with an origin as a glacitectonite and hybrid till formed by a combination of non pervasive subglacial sediment deformation and lodgement facies variations from stratified to massive diamicton reflect in turn variations in strain and subglacial transport distance the occurrence of stratified glacifluvial sediments within these ridges and the well preserved nature of many of the sandy inclusions within the diamicton imply relatively short transport distances and incomplete mixing msgls under the dubawnt lake palaeo ice stream formed through a combination of subglacial erosion and deposition this included non pervasive subglacial sediment deformation and the reworking of pre existing sediment depocentres during streaming flow these results highlight the importance of sediment supply to msgl formation with the presence of abundant pre existing sediments which were subsequently overridden being critical to lineation formation

influence of clast axial ratio on macrofabric strength in periglacial colluvium samples of fabric data collected from periglacial solifluction lobes in central alaska show a systematic positive relation between clast axial ratio and fabric strength samples composed of clasts with low a b axial ratios have relatively low fabric strength restricting sampling to clasts with axial ratios of 1 5 1 or higher increases fabric strength and decreases its variability to enhance comparability between fabric studies and the utility of fabric interpretation sampling should be restricted to clasts with relatively large 1 5 1 axial ratios

the use of integrated sedimentological and geophysical methods in drumlin research a case study of pigeon point clew bay northwest ireland despite significant advances over the past decades our understanding of drumlin formation and associated ice bed processes is still incomplete in this paper we present the integrated use of geomorphological sedimentological and geophysical techniques as a powerful means to force a breakthrough towards solving the drumlin enigma we report on investigations of the anatomy of the pigeon point drumlin clew bay ireland we found that the bulk of the landform which displays a classical drumlin shape consists of silty clayey diamicton showing evidence of deformation hydrofracturing and comminution the unit is interpreted as a sub glacial traction till comminution till the thin unit overlying this basal till consists of silty sandy diamicton and is interpreted as a para glacially modified melt out till the partly cemented third unit consists of stratified massive to graded sands and gravels its contact with the sub glacial traction till consists of a series of concave shapes which suggests that it was deposited in meltwater channels that flowed in sub glacial cavities and that cut laterally into the drumlin we propose that highs in the undulating rockhead relief as shown in the seismic profile have provided nuclei which initiated drumlin formation this idea is supported by the observation of local detached bedrock slabs that grade upwards into a comminution till in the long profile very high normalized induced polarization ip values form a wedge shape which is interpreted as a set of conjugate thrusts or a pop up structure the structure is positioned directly above one of the undulations in the bedrock suggesting a direct relationship the high values are thought to reflect the presence of pre existing clays which were sheared into the till thus forming linings in the thrust features it is concluded that glacitectonic processes notably differential bedrock weathering and thrusting have played a key role in the formation of this drumlin

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

late pleistocene stratigraphy and implications for deglaciation and subglacial processes of the flathead lobe of the cordilleran ice sheet flathead valley montana usa abstract the flathead lobe of the cordilleran ice sheet advanced and retreated across the flathead valley a 90 km long by 15 25 km wide basin the glacier terminated at the southern end of the flathead valley during its last glacial maximum i used geologic mapping sedimentologic study and mapping from 3300 descriptive water well logs to define the stratigraphy of glacial and post glacial deposits in the flathead valley and to infer subglacial processes and retreat rates units in the 30 200 m thick stratigraphic sequence include deep sand and gravel proglacial alluvium diamicton till locally gravelly silt and clay coarse grained subaqueous deposits at recessional moraines and glaciolacustrine deposits and surficial sand and gravel outwash and holocene stream deposits a nearly continuous till overlies alluvium and is in turn directly overlain by glaciolacustrine deposits glaciolacustrine shoreline indicators at altitudes of 940 958 m show that the flathead lobe receded as a proglacial lake expanded in that range of altitudes this lake the ancestral flathead lake was impounded behind bedrock that was downcut 60 78 m since the late pleistocene glaciolacustrine deposits are as much as 180 m thick in discontinuous troughs that locally cut through till to alluvium and bedrock the troughs are mostly 1 5 km in width 6 25 km in length sinuous in plan view and undulatory in longitudinal profile the troughs extend below the elevation of flathead lake and have been below local base level since glaciation these characteristics point to incision by meltwater hydrostatically pressurized beneath the flathead lobe in subglacial tunnel channels sand and gravel at the trough bases and part of the glaciolacustrine fill in the troughs are subglacial deposits tunnel channels that terminate at recessional moraines suggest excavation occurred sporadically during deglaciation the distribution of glaciolacustrine silts indicates that the flathead lobe retreated and the ancestral flathead lake expanded by 87 km before the lake outlet stream could downcut its dam by 500 m year 1

ribbed moraines in northern manitoba canada characteristics and preservation as part of a subglacial bed mosaic near the core regions of ice sheets abstract ribbed moraines are enigmatic glacial landforms for which different models with contrasting paleoglaciologic implications have been proposed to explain their formation despite the great deal of attention this type of landform has received over the last several decades ribbed moraine fields in northern manitoba canada are among the largest in the world but have been seldom studied ribbed moraines in this part of the world overlie the low relief canadian shield are not constrained by topography and are part of a spatial subglacial landform assemblage associated with drumlinoid ridges within palimpsest and relict type glacial terrain zones field observations herein provide new insights into the characteristics of these transverse to ice flow ridges at landscape mapping and spatial analysis and landform internal structure using high resolution shear wave s wave seismic reflection surveys sedimentological characteristics clast fabric analyses scales two main types of ribbed moraine are recognized pristine high amplitude straight crested ridges and secondarily modified subdued drumlinized ridges ribbed moraine in northeast manitoba consist of massive matrix supported till at surface which is similar in matrix texture and composition to the regional till sheet though pristine moraines show a higher concentration of boulders a seismic profile reveals subparallel to surface layered stratigraphy with only minor folding and no major unconformities stacking or faulting the demonstrated fragmentary nature of ribbed moraine fields the inherited signature of the till within these fields the secondary patchy drumlinization of the ridges and the more abundant granitoid outcrops in areas of intense modification all suggest that subglacial ribbed moraine formed from pre existing sediments and were later preserved and or partially reworked through a regional mosaic of shifting subglacial bed conditions we therefore make the case that pristine unmodified moraines were preserved beneath stable sticky spots we support a link between ribbed moraine and widespread cold based and or dewatered subglacial conditions in inner core regions of ice sheets but for reasons of preservation and not necessarily formation

resedimentation of debris on an ice cored lateral moraine in the high arctic kongsvegen svalbard abstract in ice cored landform assemblages the process of resedimentation via sediment flow is important in determining the morphology and sedimentary facies distribution after the ice core has melted this paper documents the sediment flow processes associated with the resedimentation of an ice cored lateral moraine at kongsvegen svalbard decay of the ice cored lateral moraine is dominated by the development of a sediment flow fan which has an hour glass form in plan the fan comprises a broad source area on the crest of the lateral moraine separated from the fan surface composed of tessellated flow lobes by a narrow ice floored channel system the principle sedimentary facies associated with this fan include matrix supported diamictons laminated silts and fine sands the evolution of this fan and the likely end products after complete deglaciation are discussed and this paper contributes modern analogue data relevant to the interpretation of the pleistocene landform and sediment record

fabric signature of subglacial till deformation breidamerkurjokull iceland the foreland of breidamerkurjokull iceland is the only locality where tills known to have undergone subglacial deformation are exposed till on the foreland has a two tiered structure consisting of a dilatant upper horizon c 0 5 m thick and a compact lower till these horizons correspond to the ductile deforming a horizon and the brittle ductile b horizon observed below the glacier by g s boulton and co workers the relationship between known strain history and a variety of macrofabric elements is examined for these two genetic facies of deformation till the upper horizon exhibits variable a axis fabrics and abundant evidence for clast re alignment reflecting ductile flow and rapid clast response to transient strains in contrast the lower horizon has consistently well organized a axis fabrics with a narrow range of dip values recording clast rotation into parallel with strain axes during brittle or brittle ductile shear the data indicate that till strain history imparts identifiable macrofabric signatures providing important analogues to guide the interpretation of pleistocene tills

solidification and turbulence non laminar during magma ascent insights from 2d and 3d analyses of bubbles and minerals in an etnean dyke

magnetic mineral diagenesis abstract reduction oxidation redox reactions occur during burial because sediments contain reactive mixtures of oxidised and reduced components diagenetic chemical reactions represent the approach of all sedimentary components toward equilibrium and control the long term stability of sedimentary iron bearing minerals magnetic minerals are sensitive indicators of sedimentary redox conditions and of changes in these conditions through time with diagenetic effects ranging from subtle to pervasive despite the importance of magnetic mineral diagenesis in paleomagnetism rock magnetism and environmental magnetism and the usefulness of these subjects in the earth and environmental sciences there is no systematic single published treatment of magnetic mineral diagenesis this paper is an attempt to provide such a treatment for the full range of diagenetic environments magnetic mineral diagenesis during early burial is driven largely by chemical changes associated with organic matter degradation in a succession of environments that range from oxic to nitrogenous to manganiferous to ferruginous to sulphidic to methanic where the free energy yielded by different oxidants decreases progressively in each environment in oxic environments the most important diagenetic processes involve surface oxidation of detrital minerals and precipitation of fe3 bearing minerals from solution in ferruginous environments the most reactive detrital and authigenic iron oxides undergo dissolution often mediated by dissimilatory iron reducing bacteria which releases fe2 that becomes available for other reactions the fe2 in solution can diffuse upward where it is oxidised to form new authigenic iron oxyhydr oxide minerals or it can become bioavailable to enable magnetotactic bacteria to biomineralise magnetite generally at the base of the overlying nitrogenous zone alternatively dissimilatory iron reducing bacteria can produce extracellular magnetite within ferruginous environments in sulphidic environments iron bearing detrital mineral assemblages undergo more radical alteration hydrogen sulphide which is a byproduct of bacterial sulphate reduction or of anaerobic oxidation of methane reacts with the fe2 released from iron mineral dissolution or directly with solid iron oxyhydr oxide minerals to form iron sulphide minerals mackinawite greigite and pyrite authigenic growth of ferrimagnetic greigite has important implications for paleomagnetic recording secondary iron sulphide formation can also occur as a result of anaerobic oxidation of methane methane migration through sediments in association with biogenic or thermogenic methane production or in association with gas hydrate dissociation can disrupt the diagenetic steady state and give rise to greigite and monoclinic pyrrhotite formation that remagnetises sediments most of the above described diagenetic processes occur below 50 c with continuing burial above 50 c but at sub metamorphic temperatures magnetic minerals can undergo further thermally induced chemical changes that give rise to a wide range of mineralogical transformations that affect the magnetic record of the host sediment these changes include remagnetisations magnetic analysis can provide much valuable information concerning diagenesis in environmental processes the range of processes discussed in this paper should assist researchers in analysing sediment magnetic properties for which the assessment of diagenetic effects has become a necessary component

till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams case study of the western canadian prairies and high plains complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western canada represent the terrestrial equivalents of the trough mouth fans of the marine palaeo ice stream record intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed first glacier marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time stacks of subglacial traction tills potentially record annual sub marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing second proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub marginal till wedges and moraines glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls resulting in the widespread development of glacitectonites and megablocks the occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots

the impact of periglacial processes on palaeolithic sites the case of sorted patterned grounds during the last glaciation western europe witnessed recurrent millennial scale episodes of periglacial climates that had significant impact on palaeolithic site preservation after a review on the genesis and climatic meaning of sorted patterned grounds examples of polygons stripes and stone banked solifluction lobes taken from archaeological contexts are described sorted features in palaeolithic sites imply that caution should be taken in site patterning analysis for reconstructing past human behaviours since spatial alteration of the original anthropogenic pattern took place on low gradients artefact movements remain limited but may increase dramatically on slopes when solifluction adds to sorting processes although these features are widespread in modern periglacial environments archaeological examples remain scarce multiple factors are probably involved including lack of knowledge of periglacial processes and landforms by archaeologists leading to misinterpretation but also more or less complete obliteration of surface features by sedimentary processes upon burial however it is assumed that scarcity of clear anthropogenic patterning in french palaeolithic sites before the late glacial is due for a large part to post depositional disturbance by periglacial processes

formation of subglacial till under transient bed conditions deposition deformation and basal decoupling under a weichselian ice sheet lobe central poland a multi proxy approach involving a study of sediment architecture grain size grain roundness and crushing index petrographic and clay mineral composition till fabric and till micromorphology was applied to infer processes of till formation and deformation under a weichselian ice sheet at kurzetnik poland the succession consists of three superposed till units overlying outwash sediments deformed at the top the textural characteristics of tills vary little throughout the till thickness whereas structural appearance is diversified including massive and bedded regions indicators of intergranular bed deformation include overturned attenuated folds boudinage structures a sediment mixing zone grain crushing microstructural lineations grain stacking and high fabric strength lodgement proxies are grooved intra till surfaces ploughing marks and consistently striated clast surfaces basal decoupling by pressurized meltwater is indicated by undisturbed sand stringers sand filled meltwater scours under pebbles and partly armoured till pellets it is suggested that the till experienced multiple transitions between lodgement deformation and basal decoupling cumulative strain was high but the depth of time transgressive deformation much lower centimetre range than the entire till thickness ca 2 m at any point in time consistent with the deforming bed mosaic model throughout most of ice overriding porewater pressure was high in the vicinity of glacier floatation pressure indicating that the substratum consisting of 11 m thick sand was unable to drain subglacial meltwater sufficiently

the deforming bed characteristics of a stratified till assemblage in north east anglia uk investigating controls on sediment rheology and strain signatures the glacial coastal exposures of north norfolk are a type site for subglacial glaciotectonic deforming bed sediments this investigation of the lower stratified diamict within the north sea drift at west runton reveals two distinct lamina types type 1 laminae are the product of primary extensional glaciotectonism with ductile intergranular pervasive shear predominating over brittle shear type 2 laminae also exhibit structures that can be attributed to ductile intergranular pervasive shear and brittle shear but the lateral continuity of type 2 laminae and the presence of dropstone like structures supports a primary subaqueous origin with secondary subglacial deformation when coupled with micromorphological analysis these findings show that ductile viscous creep mechanisms control sedimentary architecture and that shear stratification in particular has the potential to affect the rheological properties of the sediment pile and the hydraulic routing of basal water ultimately influencing critical effective pressure fluctuations and the thresholds controlling the subglacial drainage system

timing and depositional environments of a middle pleistocene glaciation of northeast england new evidence from warren house gill county durham at various times during the quaternary north eastern england was a zone of confluence between dynamic ice lobes sourced from the pennines northern scotland the cheviots and scandinavia the region thus has some of the most complex exposures of middle to late pleistocene sediments in britain with both interglacial and glacial sediments deposited in terrestrial and marine settings we investigated sedimentary sequences exposed on the coastline of county durham at warren house gill and present a new model of british and fennoscandian ice sheet interaction in the north sea basin during the middle pleistocene the stratigraphy at warren house gill consists of a lower diamicton and upper estuarine sediments both part of the warren house formation they are separated from the overlying weichselian blackhall and horden tills by a substantial unconformity the lower diamicton of the warren house formation is re interpreted here as an mis 8 to 12 glaciomarine deposit containing ice rafted lithics from north eastern scotland and the northeast north sea and is renamed the ash gill member it is dated by lithological comparison to the easington raised beach middle pleistocene amino acid racemisation values and indirectly by optically stimulated luminescence the overlying shallow subaqueous sediments were deposited in an estuarine environment by suspension settling and bottom current activity they are named the whitesides member and form the uppermost member of the warren house formation during glaciation ice rafted material was deposited in a marine embayment there is no evidence of a grounded onshore scandinavian ice sheet in county durham during mis 6 which has long been held as the accepted stratigraphy this has major implications for the currently accepted british quaternary stratigraphy combined with recent work on the middle pleistocene north sea drift from norfolk which is now suggested to have been deposited by a scottish ice sheet the presence of a scandinavian ice sheet in eastern england at any time during the quaternary is becoming increasingly doubtful

the athabasca fluting field alberta canada implications for the formation of large scale fluting erosional lineations abstract current drumlin and fluting hypotheses centred on processes of formation erosion and deposition by subglacial deformation accretion by lodgement glacial erosion and meltwater erosion and deposition rarely receive comprehensive field testing this paper documents the morphology internal structure and landscape associations of the athabasca fluting field alberta and discusses how well these characteristics are explained by postulated fluting forming processes fluting hypotheses are comprehensively tested by this approach and their rejection or acceptance are firmly based on field observation and knowledge of processes using multiple criteria fluting is shown to be erosional and not to be a product of pervasive subglacial deformation or accretion by lodgement morphology landscape associations bed truncation plus glaciofluvial lags and gravel on fluting ridges are inferred to support erosion by meltwater intact primary bedding synsedimentary faults and injection structures very close to the landsurface showing no sign of shear deformation are used to reject erosion by subglacial deformation fluting is shown to be closely associated with tunnel channels and indicates that these channels were overtopped by broad floods that formed the fluting field and eroded anabranching tracts over the length of the alberta plains prior to fluting formation sequences with melt out and lodgement till conduit sediment and boulder lags record net deposition over an extended time period diapirism prior to fluting formation marks a period of extreme pressure gradients which are related to bed separation following fluting formation there was only minimal landscape modification dominated by glaciofluvial and glaciolacustrine deposition not glacial processes this progression is presented as evidence for two very different glacial regimes separated by a short period with diapirism and extensive landscape modification by meltwater erosion we note that the study area was glaciated only once during the late wisconsinian and it follows that glacial sedimentation and landscape modification were confirmed to this single glacial episode

neogene glacigenic debris flows on james ross island northern antarctic peninsula and their implications for regional climate history detailed sedimentological and microtextural analyses of newly discovered late neogene diamictites and other coarse grained facies mostly sandwiched between hyaloclastite of the james ross island volcanic group and cretaceous sandstone and mudstone indicate deposition mainly by glacigenic debris flows the deposits on james ross island northern antarctic peninsula constrain the depositional setting ice bed dynamics and regional palaeoclimate the sequences on james ross island vary in age but are mainly late miocene and pliocene unlike neogene sedimentary sequences elsewhere in antarctica those on james ross island are unusually well dated by a combination of 40ar 39ar and 87sr 86sr analyses on fresh interbedded lavas and pristine bivalve molluscs respectively the sr isotopic ages of the debris flows cluster around 4 74 4 89 5 44 5 78 and 6 31 ma and probably date relatively warm periods in the northern antarctic peninsula region when the bivalves lived under ice poor or seasonally ice free conditions the bivalves are often remarkably well preserved lack adhering lithified sediment and in at least two locations are large mainly unfragmented and sometimes articulated suggesting that they were alive immediately prior to their incorporation in subaqueous debris flows at the margins of an advancing glacier these fossiliferous glacigenic debris flows signify episodes of ice expansion during relatively warm periods or interglacials of the late miocene and pliocene the james ross island glacigenic sedimentary successions attain thicknesses of up to 150 m and extend over 4 km laterally the high volume of glacigenic sediment delivery implicit in the james ross island successions indicates that a series of dynamic ice fronts crossed the region during the late miocene and pliocene epochs associated evidence in the form of clast abrasion including striations and faceting and bedrock erosion is indicative of basal sliding and subglacial sediment deformation active at the ice bed interface and wet based temperate or polythermal regimes prior to remobilisation the evidence further suggests two local ice caps on james ross island during the warm periods as well as ice overriding by the antarctic peninsula ice sheet from the west and northwest

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

an assessment of fluting and till esker formation on the foreland of sandfellsjokull iceland abstract intensive sedimentological analysis of tills parallel sided flutings and a conduit fill till esker on the recently deglaciated foreland of sandfellsjokull a temperate actively receding piedmont lobe draining the eastern margin of the m rdalsjokull ice cap in southern iceland reveals that subglacial sediment was emplaced predominantly as a dilatant a horizon after an initial phase of glacitectonite production from local outwash clast macrofabric strengths weakened through time presumably in response to increasingly wetter substrate conditions until the emplacement of the fluted till when clast alignment was more tightly constrained the fluting phase was initiated only after boulders were plucked from an adjacent bedrock cliff and lodged at the ice till interface this suggests that the parallel sided flutings constrained shearing at the ice bed interface in a similar fashion to a fault gouge thereby strengthening clast alignments but allowing the till to mould around larger obstacles to produce herringbone fabric patterns strong clast macrofabric strengths in the till esker are not parallel to the ice flow direction but instead align parallel with the local axis of the meandering ridge this suggests that the till esker was likely produced by the squeezing of a dilatant till into an elongated cavity or r channel after meltwater evacuation followed by localized deformation constrained by the channel walls as the channel moved downvalley because of ice flow the short period over which the deformation took place was enough to impart weaker fabrics in parts of the conduit that lie transverse to the ice flow direction and stronger fabrics where the conduit trends toward parallelism with the ice flow

quaternary geology and geomorphology of the dinosaur provincial park area and surrounding plains alberta canada the identification of former glacial lobes drainage diversions and meltwater flood tracks abstract the quaternary geology and geomorphology of the lower red deer river drainage basin centred on the dinosaur provincial park badlands provides information on pre late wisconsinan drainage patterns and the dynamics of former lobes of the laurentide ice sheet in western canada patterns of deglaciation proglacial lake evolution and spillway incision are also reconstructed based upon the distribution of surface materials and glacial glaciofluvial landforms the empress group fluvial and glaciolacustrine sediments which could be as young as 27 ka bp infill the precursor red deer river and its tributaries and document the initial advance of glacier ice into southern alberta glaciotectonic disturbance of older sediments and bedrock the production of deformation tills and the construction of a megafluting complex and cupola hills record the advances of a glacier lobe centred over the study area stratified inter and intra till beds record pulses of subglacial meltwater between phases of subsole deformation the thickening of tills towards the margin of the lobe represents a till wedge an expected product of sediment advection by glaciers moving over deformable beds the eastern margin of the glacier lobe is demarcated by the interlobate suffield hummocky moraine belt which contains overprinted thrust ridges which record diachronous oscillations of neighbouring lobes within the ice sheet proglacial and glaciofluvial sediments were deposited in the area in association with proglacial lake bassano patricia which drained eastwards when the suffield moraine was dissected by spillways changes in the size of glacial lake bassano patricia are clearly documented by a sequence of spillway incisions which culminated in the erosion of scabland topography and the initiation of a new course for the red deer river a 15 km southward diversion of the main channel in distinct contrast to the documented incision histories of other small rivers in alberta one tree creek and little sandhill creek did not start major incisions of the quaternary sediments over buried valley positions until the late holocene when environmental conditions were characterized by higher precipitation

the 1992 summer circulation in the northeast water polynya from acoustic doppler current profiler measurements a july august 1992 snapshot of the circulation in the northeast water polynya located off the coast of greenland is presented using data collected with an acoustic doppler current profiler adcp during the cruise of the uscgc polar sea the data reveal anticyclonic circulation with velocity and transport cores aligned with the local topographic trough transport through the trough is between 0 5 and 0 9 sv the total adcp measured velocities are generally less than 10 cm s 1 but some regions have velocities larger than 20 cm s 1 the ratio of the average velocity of the upper 100 m to the average velocity below 100 m shows surface layer flows faster by a factor of between 1 2 and 2 this ratio in the ice free northwest portion of the polynya is smaller 1 5 than found over the adjacent continental shelf 2 0 indicating smaller vertical shear the data show northward flow along the coast supporting the idea that ice carried by this flow is blocked from entering the polynya by a persistent ice wedge to the south that extends from the coast east over the topographic trough to a shallow central bank by blocking ice advecting from the south the ice wedge enhances the polynya supporting the idea that the northeast water polynya is a latent heat polynya

deformation of the batestown till of the lake michigan lobe laurentide ice sheet deep pervasive shear deformation of the bed to high strains 100 may have been primarily responsible for flow and sediment transport of the lake michigan lobe of the laurentide ice sheet to test this hypothesis we sampled at 0 2 m increments a basal till from one advance of the lobe batestown till along vertical profiles and measured fabrics due to both anisotropy of magnetic susceptibility and sand grain preferred orientation unlike past fabric studies interpretations were guided by results of laboratory experiments in which this till was deformed in simple shear to high strains fabric strengths indicate that more than half of the till sampled has a 5 probability of having been sheared to moderate strains 7 30 secular changes in fabric azimuth over the thickness of the till probably due to changing ice flow direction as the lobe receded indicate that the bed accreted with time and that the depth of deformation of the bed did not exceed a few decimeters orientations of principal magnetic susceptibilities show that the state of strain was commonly complex deviating from bed parallel simple shear deformation is inferred to have been focused in shallow temporally variable patches during till deposition from ice

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

rapid locking of tectonic magnetic fabrics in weakly deformed mudrocks abstract the anisotropy of magnetic susceptibility ams has provided important insights into early deformation conditions in compressive settings through characterization of tectonic fabrics in mudrocks that appear otherwise undeformed the validity of these insights relies on the assumption that tectonic fabrics are rapidly locked shortly after sediment deposition however the time lag between deposition and the tectonic overprint has yet to be quantified to verify this assumption here we present ams data from late holocene sediments recovered in two cores from lake issyk kul in the kyrgyz tien shan fold and thrust belt these sediments in which magnetic fabrics reflect the preferred orientation of phyllosillicates have typical tectonic magnetic fabrics with varying degrees of tectonic overprint likely controlled by small scale active faults the mean orientation of the susceptibility maxima parallels neighbouring active thrust faults and is perpendicular to the geodetically derived local shortening direction the age model for one of the studied cores which is based on 7 calibrated accelerator mass spectrometer radiocarbon dates indicates that sediments as young as 25 yr record this clear tectonic fabric which is locked within sediments older than 1180 cal yr bp our demonstration of rapid locking of tectonic fabrics in weakly deformed mudrocks shortly after deposition provides the required validation of their reliability for tectonic studies and opens new opportunities for providing quantitative insights into the relationship between magnetic ellipsoids shortening rates and stress directions in compressive settings

quaternary geology of the duck hawk bluffs southwest banks island arctic canada a re investigation of a critical terrestrial type locality for glacial and interglacial events bordering the arctic ocean duck hawk bluffs southwest banks island is a primary section 8 km long and 60 m high in the western canadian arctic archipelago exposing a long record of quaternary sedimentation adjacent to the arctic ocean a reinvestigation of duck hawk bluffs demonstrates that it is a previously unrecognized thrust block moraine emplaced from the northeast by laurentide ice previous stratigraphic models of duck hawk bluffs reported a basal unit of preglacial fluvial sand and gravel beaufort fm forested arctic overlain by a succession of three glaciations and at least two interglacials our observations dismiss the occurrence of preglacial sediments and amalgamate the entire record into three glacial intervals and one prominent interglacial the first glacigenic sedimentation is recorded by an ice contact sandur containing redeposited allochthonous organics previously assigned to the beaufort fm this is overlain by fine grained sediments with ice wedge pseudomorphs and well preserved bryophyte assemblages corresponding to an interglacial environment similar to modern the second glacial interval is recorded by ice proximal mass flows and marine rhythmites that were glacitectonized when laurentide ice overrode the site from amundsen gulf to the south sediments of this interval have been reported to be magnetically reversed 780 ka the third interval of glacigenic sedimentation includes glacifluvial sand and gravel recording the arrival of laurentide ice that overrode the site from the northeast island interior depositing a glacitectonite and constructing the thrust block moraine that comprises duck hawk bluffs sediments of this interval have been reported to be magnetically normal 780 ka the glacitectonite contains a highly deformed melange of pre existing sediments that were previously assigned to several formally named marine and interglacial deposits resting in an undeformed sequence in contrast the tectonism associated with the thrust block moraine imparted pervasive deformation throughout all underlying units highlighted by a previously unrecognized raft of cretaceous bedrock during this advance laurentide ice from the interior of banks island coalesced with an ice stream in amundsen gulf depositing the interlobate sachs moraine that contains shells as young as 24 cal ka bp late wisconsinan during deglaciation meltwater emanating from these separating ice lobes deposited outwash that extended to deglacial marine limit 11 m asl along the west coast of banks island our new stratigraphic synthesis fundamentally revises and simplifies the record of past quaternary environments preserved on southwest banks island which serves as a key terrestrial archive for palaeoenvironmental change

glacial sediments and landforms of holderness eastern england a glacial depositional model for the north sea lobe of the british irish ice sheet abstract borehole records and exposures at coastal cliffs and inland quarries around holderness are used in a critical assessment of the glacial depositional environments that operated at the margin of the north sea lobe of the british irish ice sheet at the last glacial maximum four lithofacies associations lfa are recognized in the area lfas 1 and 4 are laminated to massive diamictons traditionally called the skipsea and withernsea tills members and display deformation structures indicative of stress from the ne attenuated rafts of soft bedrock lithologies ice bed separation canal fill features and pseudo stratification and clast macrofabric data predominantly indicate deformation only to low strains they are interpreted as subaqueous deposits subsequently deformed by glacier ice to create end products that lie on the glacitectonite continuum localized increases in strain signature are equated with the development of shear zones between onshore thickening wedges of deformed pre existing lake sediment lfa 2 comprises cross bedded clinoforms locally steepening into foresets at the core of linear hummocks along the central spine of holderness lfa 2a and rhythmically laminated silts and sands with dropstones lfa 2b these sediments are interpreted as coalescent glacilacustrine subaqueous outwash fans fining distally to lake bottom rhythmites and varves ice contact deposition is evident in compressional folding faulting and hydrofracture filling due to ice overriding and extensional faulting associated with localized ice melt out depressions produced by folding or sagging provided the accommodation space for the later deposition of lfa 2 and 3 through syntectonic sedimentation lfa 3 comprises flat lying beds of well to poorly sorted cross stratified sands and gravels interpreted as proximal proglacial braided outwash deposits laid down largely in ribbon sandar defined by the topography of abandoned ice contact glacilacustrine depo centres well developed ice wedge pseudomorphs in lfa 3 record permafrost conditions during ice sheet marginal recession indicating that north sea lobe oscillations may have been non climatic or surge related a depositional model is proposed in which advance and retreat phase tills glacitectonites and associated ice contact lake sediments are the geological imprint of a single glaciation the initial advance of the north sea lobe is recorded by a westerly thinning advance till lfa 1 later lfa 1 and 4 retreat tills are strictly glacitectonites and are thicker depositional units because later ice readvances encroached upon and cannibalized more substantial sequences of deglacial lake sediment and subaqueous ice contact fans lfa 2 similar regional till architectures will be manifest wherever the palaeogeography resulted in the onshore flow of ice and the concomitant production of glacitectonites from glacial lake sediments

simulation of the crystal growth of platelet sea ice with diffusive heat and mass transfer antarctic coastal sea ice often grows in water that has been supercooled by interaction with an ice shelf in these situations ice crystals can form at depth rise and deposit under the sea ice cover to form a porous layer that eventually consolidates near the base of the existing sea ice the least consolidated portion is called the sub ice platelet layer congelation growth eventually causes the sub ice platelet layer to become frozen into the sea ice cover as incorporated platelet ice in this study we simulate these processes in three dimensions using voronoi dynamics to govern crystal growth kinetics platelet deposition in situ growth and incorporation into the sea ice cover are integrated into the model heat and mass transfer are controlled by diffusion we extract and compare spatial temporal distributions of porosity salinity temperature and crystallographic c axes with observations from mcmurdo sound antarctica the model captures the crystallographic structure of incorporated platelet ice as well as the topology of the sub ice platelet layer the solid fraction which has previously been poorly constrained is simulated to be 0 22 in good agreement with an earlier estimate of 0 25 0 06 this property of the sub ice platelet layer is important for biological processes and for the freeboard thickness relationship around antarctica

stratigraphy and glaciotectonic structures of permafrost deformed beneath the northwest margin of the laurentide ice sheet tuktoyaktuk coastlands canada the upper 5 20 m of ice rich permafrost at three sites overridden by the northwest margin of the laurentide ice sheet in the tuktoyaktuk coastlands western arctic canada comprise massive ice beneath ice rich diamicton or sandy silt the diamicton and silt contain 1 truncated ice blocks up to 15 m long 2 sand lenses and layers 3 ice veins dipping at 20 30 4 ice lenses adjacent and parallel to sedimentary contacts and 5 ice wedges the massive ice is interpreted as intrasedimental or buried basal glacier ice and the diamicton and silt as glacitectonite that has never thawed deformation of frozen ground was mainly ductile in character deformation was accompanied by sub marginal erosion of permafrost which formed an angular unconformity along the top of the massive ice and supplied ice clasts and sand bodies to the overlying glacitectonite after deformation and erosion ceased postglacial segregated ice and ice wedge ice developed within the deformed permafrost

the glacial sedimentology and geomorphological evolution of an outwash head moraine dammed lake south island new zealand extensive exposures through the glacial landforms around southern lake pukaki new zealand comprise seven lithofacies lfs 1 7 lfs 1 3 are grouped together as lfa 1 pukaki member and record pulsed subaqueous grounding line fan progradation cohesionless debris flows underflow activity and rhythmite deposition by suspension settling iceberg rafting of dropstones and pulsed traction current activity localized disturbance of these deposits by glacitectonic deformation and multi generational hydrofracture fills records minor readvances by the glacier snout and the emplacement of a glacitectonite lf 4 derived from cannibalization of glacilacustrine sediments lfs 4 6 are grouped together as lfa 2 twizel member and record direct glacigenic deposition of glacitectonite lf 4 subglacial traction till lf 5 and supraglacially dumped boulder rubble lf 6 stratigraphic relationships between lfa 1 with lfa 2 record the oscillatory behaviour of the former tasman glacier snout when it formed a calving margin in a proglacial and locally supraglacial lake dammed by a glacitectonically disturbed outwash head and lateral moraine ridges this is entirely consistent with the landform sediment record of its coeval terrestrial margins where flutings and push moraines are diagnostic of active temperate glacier recession from a glacially overridden outwash head the latter being recorded by the vertically stacked sub horizontally bedded and coarse grained gravels of lf 7 waitaki member previous proposals that late pleistocene lake damming was initiated by an ice cored moraine arc appear unfounded because the glacilacustrine deposits only lie above the altitude of the outwash head lateral moraine arc in locations where they have been glacitectonically compressed alternatively it is proposed that the overdeepened subglacial topography was produced by the construction of an outwash head leading to a glacilacustrine sediment sink which operates at times when the expanded tasman glacier actively retreats from the outwash head apex the changing landsystem imprint related to the shrinkage of the tasman glacier records spatio temporal landsystem change involving evolution from a coupled landsystem to a moraine dammed to an uncoupled landsystem

reliability of magnetic fabric of weakly deformed mudrocks as a palaeostress indicator in compressive settings abstract in this work we compare the results of anisotropy of magnetic susceptibility ams with palaeostress analysis at local scale the ams data refer to 14 sites from weakly deformed mudrocks lower and middle miocene lacustrine sediments from two areas of the internal part of the ebro foreland basin the bardenas reales and monegros areas nine sites display a magnetic fabric related to a subtle tectonic overprint showing a roughly e w magnetic lineation whereas the rest of sites most of them located at the monegros area show a sedimentary fabric without a well defined magnetic lineation palaeostress data result from fault populations and joint sets exposed in the limestone beds interbedded with the mudrocks at the nearest possible outcrop from the ams site the origin of the magnetic lineation is related to a n s compression coeval with the earliest diagenesis of the studied sediments prior to consolidation the comparison between magnetic fabric and palaeostress data demonstrates the coaxiality between the ams and palaeostress ellipsoids both at local and regional scales thereby validating the reliability of ams as palaeostress indicator in compressive settings

structural architecture and glacitectonic evolution of the mud buttes cupola hill complex southern alberta canada this paper presents the results of a detailed multidisciplinary study of the deformed bedrock and overlying quaternary sediments exposed at the mud buttes in southern alberta canada this large arcuate cupola hill is composed of intensely folded and thrust sandstones siltstones and mudstones of the cretaceous belly river group glacitectonism responsible for the development of this internally complex landform occurred at the margin of the newly defined prospect valley lobe of the laurentide ice sheet analysis of the deformation structures reveals that construction of this landform occurred in response to at least two phases of south directed ice sheet advance separated by a period of retreat the first phase led to the formation of a forward propagating imbricate thrust stack leading to polyphase deformation of the belly river group d1 thrusting led to the detachment of thrust bound slices of bedrock which were accreted to the base of the developing imbricate stack this process resulted in the structurally higher and older thrust slices being progressively back rotated tilted accompanied by d2 thrusting and folding further thrusting during d3 was restricted to the core of the mud buttes as the deforming sequence accommodated further compression imposed by the advancing ice minor oscillations of the ice margin led to localised brittle ductile shearing d4 of the bedrock immediately adjacent to the ice contact part of the thrust stack the second phase of ice advance led to the accretion of a relatively simple thrust and folded sequence seen the northern side of mud buttes the resulting composite thrust moraine was subsequently overridden by ice advancing from the nnw to form a dome like cupola hill this readvance of the prospect valley lobe led to the formation of a thin carapace of quaternary sediments mantling the mud buttes which include glacitectonite till and an organic rich clay silt palaeosol

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

subglacial to proglacial depositional environments in an ordovician glacial tunnel valley alnif morocco abstract this paper presents the sedimentary analysis of an exceptional ordovician glacial tunnel valley in the eastern part of the anti atlas the valley infill comprises two major glacial erosion surfaces striated pavements each overlain by a fining upward glacial unit these units are composed of five distinct facies associations recording the evolution from subglacial to proglacial environments and an additional sixth facies association overtopping the tunnel valley infill and associated with post glacial environments the tunnel valley infill also records a transitional environment between the subglacial and proglacial settings which is compared with the antarctic ice sheet margin these three environments are defined by the position of the grounding line and the coupling line the new proposed depositional model also differs from usual ordovician depositional models in which the main tunnel valley infill is interpreted as essentially proglacial outwash deposits in a range of glaciomarine to glaciofluvial environments overall a substantial part of the valley infill 50 of volume was deposited in a subglacial setting the sedimentary bodies could form potentially thick and laterally extended although these were limited by the shape and extent of the subglacial accommodation space finally the sedimentary record when compared with regional analogues also provides information for the palaeogeographic reconstruction of the ordovician ice sheet in this region

sedimentary and stratigraphic evidence for subglacial flooding south central michigan usa abstract the glacial landscape in south central michigan is a dissected surface with streamlined residual and upland blocks surrounded by lowland valleys dominated by outwash the upland surface has ridges hills and hummocks composed of boulder gravel which are transitional to drumlins in a down ice direction and is dissected by tunnel channels with eskers within them sedimentary descriptions from 14 gravel pits indicate a consistent stratigraphy across a width of 15 km the upland consists of bedrock covered by a lower till with subglacial melt out or lodgment characteristics above the lower till is a sand and gravel facies that passes upward into a boulder gravel facies nestled within depressions on the boulder gravel surface is a discontinuous facies of laminated sand and silt above the gravel is an upper till with supraglacial melt out and flow till characteristics analyses of the till and gravel indicate an upward change in clast lithology from locally derived carbonates to clastics and finally to crystallines from the lower till through the gravel facies into the upper till the transition mimics the bedrock lithology up ice of the study area and is explained by meltwater erosion of bedrock previously deposited subglacial sediment and overlying debris rich basal ice the systematic change in clast lithology and the stratigraphic position of the gravel facies between a subglacial and supraglacial till strongly suggests that the gravel facies sediment was deposited subglacially and that the entire till gravel till sequence resulted from the same glacial advance

experimental archaeology in a mid latitude periglacial context insight into site formation and taphonomic processes abstract experiments have been carried out at two sites in periglacial maat 0 c and alpine maat 4 c contexts in the pyrenees including open air and cave loci to document in detail the role of site formation processes and taphonomic agents in the degradation of archaeological assemblages in both sites the experimental cells have undergone significant changes over the five years of measurements these are marked by slow downslope creep of lithic artefacts due to solifluction rain creep and the impact of debris fallen from the wall in the cave the behaviour of bone material was significantly different from that of lithics due to the activity of scavengers this was responsible for scattering a high proportion of bone remains and displacements were typically significant such activity was also responsible for a high number of bone elements being lost 1 3 to 2 3 of the bones weathering mostly cracking and exfoliation also affected dry bone material in the open air cells the measurements have highlighted the specific nature of the cave context which plays a protective role for bone remains against meteoric agents the talus at the entrance of the cavity was also characterized by a strong spatial heterogeneity in sedimentary processes which may generate a differential preservation of the assemblages

fabric shape and the interpretation of sedimentary fabric data abstract the concept of fabric shape provides a powerful means of visualizing and analyzing data on sedimentary fabric the shape of a fabric is defined in terms of the ratios between eigenvalues s1 s2 and s3 derived using the orientation tensor method a continuum of all possible orthorhombic fabric shapes can be clearly represented on equilateral ternary diagrams originally developed for the presentation of particle shape data two indices are of particular value in scaling these diagrams fabric isotropy i s3 s1 and fabric elongation e 1 s2 s1 together these indices uniquely define the shape of any orthorhombic fabric and provide a rational and quantitative basis for reconstructing depositional and de ormational processes equilateral ternary diagrams provide a more versatile and powerful basis for analyzing fabric data than other eigenvalue diagrams now in use use of the diagrams in reconstructing processes of sediment transport and deposition is illustrated using fabric data from subglacial tills and a variety of slope deposits

fabric of palaeolithic levels methods and implications for site formation processes fabric analysis in archaeological contexts i e the study of the orientation and dip of artefacts has been significantly improved during the last decade mainly with respect to the statistical treatment of data the development of a reference base for natural sedimentary processes as well as the increased number of data for palaeolithic levels these works show that fabrics are an efficient tool for assessing site formation processes fabrics allow discrimination between i undisturbed or minimally disturbed levels ii levels that have undergone strong pedoturbations due to biological activity or to shrinking and swelling of clayey sediments and iii levels that have been significantly reworked by slope processes such as periglacial solifluction or overland flow however in the present state of knowledge fabrics do not allow precise estimation of the degree of perturbation if not associated with other archaeological and geological criteria from the set of data on french palaeolithic sites used here it is demonstrated that slope dynamics and particularly solifluction for sites predating the late glacial may have played an important role in site formation

morphology and texture of particles along the spirit rover traverse from sol 450 to sol 745 1 we quantified and classified the shape roundness size and texture of 935 loose surface particles along the spirit rover traverse from sols 450 745 to assess origin transport and other alteration mechanisms that altered particles during and after formation variation in particle morphologic parameters along traverse is consistent with crossing mapped geologic unit boundaries texture is divided into four types vesicular smooth and flat faceted rough and flat faceted and very rough sphericity and roundness are intermediate and low respectively comparable to particles moved by high energy transport or to crushed particles this indicates intermittent high energy emplacement or modification of a single lithology rather than systematic continuous low energy abrasion or wear over time comparison with particle morphology at other mars landing sites is consistent with the hypothesis that no secondary systematic transport or wide scale chemical alteration was active at a significant enough level to alter macromorphology in particular particle morphology at the mars pathfinder site shows stronger evidence of abrasion than along the spirit traverse suggesting mars pathfinder particles have undergone abrasion processes that particles in this study area have not additionally morphology indices have correlation coefficients near zero indicating that a fluvial transport mechanism is likely not responsible for morphology morphology and texture are instead related to origin and composition rather than subsequent modification morphology and texture support a volcanic origin possibly without modification but most likely altered primarily by ballistic impact implying that the spirit landing site and traverse may be utilized in the future as a standard site for characterization of impact derived morphology

rock glacier dynamics in marginal periglacial environments vertical electric sounding bottom temperature of winter snowcover bts and ground thermal measurement debris surface analysis and a differential global positioning system dgps survey were performed on the posets rock glacier pyrenees between 2001 and 2008 high precision records of horizontal and vertical movements of the rock glacier were measured using a dgps on ten steel rods total and annual average displacements and thickness changes for each control point were derived from the field survey horizontal and vertical displacement rates in different sectors of the rock glacier were compared and these compared with thermal structural and morphological maps the inferred surface deformation was characterized by extensional and compressive flows in which two dynamic types were found the first type of movement is defined by the slide and flows related to the existence of an ice body over the frost body the second dynamic type involved the displacement generated by deformation of the frozen body the study attempts to understand the surface movement and dynamics of rock glaciers in marginal cold environments and their usefulness as environmental geoindicators copyright 2010 john wiley sons ltd

sea ice salinity and structure a winter time series of salinity and its distribution 1 we present a winter time series of antarctic sea ice salinity from eastern mcmurdo sound an area close to an ice shelf where a subice platelet layer forms below the sea ice late in winter this dramatically changes the sea ice structure as the sea ice grows into the subice platelet layer every 2 weeks during the 5 months of sea ice formation salinity profiles were measured along with detailed measurements of ice structure and growth rates once the influence of growth rate on sea ice bulk salinity is removed the data from 69 cores and the results of a basic parameterization demonstrate that bulk salinity for platelet ice is higher than that for columnar sea ice we also present measurements of the salinity profile close to the ice water interface and use these to investigate the expected regime of fluid flow within the permeable portions of the sea ice with particular reference to mushy layer and percolation theory finally we provide a new distribution of sea ice salinity from 740 measurements which can be interpreted as the sum of two spatial fields that we attribute to sea ice samples with and without brine channels and which should be reproduced by any realistic sea ice models this distribution suggests that two measurements of quantities linearly linked to sea ice salinity must differ by 29 if they are to be considered different with 90 confidence

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

nondestructive high resolution visualization and measurement of anisotropic effective porosity in complex lithologies using high resolution x ray computed tomography abstract new methods are presented that allow high resolution x ray computed tomography hrxct to be utilized for imaging and measuring the effective porosity field of mineralogically complex specimens at resolutions in the 5 100 m range these methods extend previous established approaches by allowing sample displacement between successive imaging runs and eliminating the need for a highly attenuating tracer a highly detailed map of partial porosity can be generated by scanning a sample in a dry state and infiltrated by distilled water and performing a three dimensional alignment of the two data sets this map can then be used to obtain a number of quantitative analyses such as the frequency distribution of partial porosity and directional analysis to infer flow anisotropy it can also be used for petrographic study of the relationship of porosity to evolving mineralogy in a dynamic system these methods are demonstrated on a series of altered volcanic rocks from a deep sea hydrothermal field

debris ridges along the southern drakensberg escarpment as evidence for quaternary glaciation in southern africa considerable geomorphological work has been undertaken on periglacial and possible glacial landforms found in the eastern lesotho highlands however the origin of several of these landforms remains controversial and differences in opinion concerning their original process mechanisms and associated climatic implications is unresolved debris ridges were recently found on south facing slopes along the tsatsa la mangaung and leqooa ranges in the southern drakensberg the objective is to use a variety of approaches to test a number of possible hypotheses to their origin these include an analysis of topographic and spatial positioning geomorphology sedimentology ams dating and palaeo climatological extrapolations a variety of possible geomorphological process origins for particular deposits are tested against the results of the above mentioned approaches the possible origins considered include debris flows water flow pronival ramparts seasonal perennial snow patches glacial moraine permanent glacier ice and variations in landscape denudation i e erosional remnant e g valley fill the results support the contention that the ridges are moraines which relate to the former presence of small glaciers

quantitative morphology of rocks at the mars pathfinder landing site 1 we adapt and test a standard terrestrial technique of assessing morphology quantitatively for use with sites on mars based on two dimensional equations and particle outlines whereby images of particles obtained remotely may yield dimensionless numerical shape and roundness values consistent with previous knowledge of the lithology and sedimentary transport history our test site was the particle rich rock garden at the mars pathfinder landing site a location where the primary geologic processes and lithology have been determined by other means a total of 575 particles were assessed in terms of size sphericity elongation and roundness qualitative roundness was determined for 460 particles particles are mostly pebble to cobble sized and have an average sphericity of 0 75 elongation of 0 63 and relative roundness of 0 083 69 of particles are subangular or subrounded particle sphericity is unimodal with a size sphericity profile matching trends for terrestrial populations of similar lithology and elongations nearly identical to those for particles at vikings 1 and 2 this matches the predictions for a site with the single overall lithology implied from other analyses roundness data indicate one or possibly two particle populations representing the primary processes that likely affected particle roundness most strongly impact and catastrophic flooding finally we tested a hypothesis suggesting that darker smaller more angular particles comprise a population transported through impact cratering while larger less dark more rounded particles are associated with catastrophic flood transport the opposite result is seen larger particles throughout the rock garden are more angular than smaller ones

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

structural composition and sediment transfer in a composite cirque glacier glacier de st sorlin france robserson s 2008 structural composition and sediment transfer in a composite cirque glacier glacier de st sorlin france earth surface processes and landforms 33 13 1931 1947

the glacial origins of relict pingos wales uk ramparted depressions doughnut shaped debris cored ridges with peat and or sediment filled central basins are commonly perceived to represent the relict collapsed forms of permafrost ground ice mounds i e pingos or lithalsas in wales uk ramparted depressions of late pleistocene age have been widely attributed to permafrost related processes however a variety of alternative glacial origins for these enigmatic landforms are also consistent with the available geological and geomorphological evidence although previous studies have barely considered such alternative processes of formation from detailed geophysical sedimentological and remote sensing studies at two field sites we demonstrate that i the wastage of stagnating glacier ice is a viable alternative explanation for the formation of ramparted depressions in wales ii the glacial geomorphology and geology of these landforms is analogous to supraglacial and subglacial landforms from the last laurentide and fennoscandian ice sheets iii these landforms have significant potential for characterising the nature of deglaciation around the margins of the irish sea during the last glacial cycle and may record evidence for the overextension and stagnation of the south eastern margin of the irish sea ice stream and iv investigations of ramparted depressions within formerly glaciated terrains must consider both glacial and periglacial mechanisms of formation

till fabric patterns and significance particle response to subglacial stress abstract the analysis of particle arrangements within glacial sediments fabric has long been considered to reflect the behaviour of the ice that transported and deposited or deformed the sediment particles can develop specific fabric arrangements as a response to bulk sediment strain driven by effective stress at the bed of a glacier as such fabric analysis has been used to try and understand the complex relationship between glacier and ice sheet dynamics and the geological evidence of former glaciation developments have focused on the use of stereonet patterns and statistical measures vector and eigenvector analysis of clast fabric to infer the process of sediment deposition deformation and consequent ice flow directions and dynamics however as this study identifies fundamental processes of particle orientation march jeffery and taylor rotation mechanisms would suggest more complex explanations than have been previously reported this study reports the results of a detailed field and laboratory investigation of macro scale clast and microfabrics from a till sequence in central scotland the results suggest a systematic behaviour of different particle size fractions which may be interpreted in terms of the strain response of sediment three fabric patterns are identified that illustrate consistent progressively shifting and more complex particle behaviour it is suggested these orientation patterns indicate the degree to which subglacial sediment has undergone strain and the nature of the deforming bed erosional or accretionary it is concluded that this approach may yield fundamental information about the strain conditions underlying different ice masses providing critical data linking glaciological modelling with the sedimentary evidence of glaciation

glacitectonism subglacial and glacilacustrine processes during a neoproterozoic panglaciation north east svalbard

signatures of supercooling mcmurdo sound platelet ice near ice shelves around antarctica the ocean becomes supercooled and has been observed to carry small suspended ice crystals our measurements demonstrate that these small crystals are persistently present in the water column beneath the winter fast ice and when incorporated in sea ice they reduce the mean grain size of the sea ice cover by midwinter larger ice crystals below the ice water interface are observed to form a porous sub ice platelet layer with an ice volume fraction of 0 25 0 06 the magnitude and direction of the oceanic heat flux varied between 5 6 wm 2 upwards and 15 10 wm 2 downwards in may but by september it settled between 6 2 and 11 2 w m 2 the negative values imply that the ocean acts as a heat sink which is responsible for the growth of 12 of the ice thickness between june and september this oceanic contribution should not be ignored in models of antarctic sea ice thickness close to an ice shelf

successive subglacial depositional processes as interpreted from basal tills in the lower vistula valley n poland abstract three basal till facies from the lower vistula valley were examined the lowest facies a sandy diamicton with characteristic sand inclusions forming detached and attenuated folds is overlain by a bedded till characterized by alternating diamictons and sorted sediment layers the uppermost till facies is a homogeneous diamicton the three till facies must have been formed by complex subglacial sedimentary processes during the first late weichselian ice advance the lowest till facies is interpreted as a deformation till and accumulated during the initial stage of the ice advance the middle facies represents a stagnation phase during the initial ice advance and was deposited during recurrent periods of subglacial melt out followed by meltwater sedimentation the upper till facies was deposited by direct subglacial melt out during a stage of stagnant ice it is suggested that bed deformation and temporarily enhanced basal sliding have been caused by ice streaming at the time of the ice sheet advance and just before its stagnation

sedimentary facies and landform genesis at a temperate outlet glacier soler glacier north patagonian icefield glasser n f hambrey m j 2002 sedimentary facies and landform genesis at a temperate outlet glacier soler glacier north patagonian icefield 49 1 43 64

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

discussion and reply clast fabric development in a shearing granular material implications for subglacial till and fault gouge discussion hooyer and iverson 2000 1 presented the results of shear box experiments performed on till matrix material obtained from below storglaciaren and they discussed their implications for mechanisms of fabric development in subglacial deforming layers and fault gouge the results of their well

late wisconsinan stratigraphy and chronology at highlands southern st george s bay southwest newfoundland abstract this paper provides detailed sedimentological and chronological data of coastal exposures at highlands in southern st george s bay southwest newfoundland the highlands section shows a coarsening upward sequence from mud to sand and gravel and diamicton and represents an ice distal to ice proximal glaciomarine environment where sediment was introduced via a subglacial meltwater jet and deposited by underflow current flow debris flow and overflow on a grounding line fan diamicton forms a continuous unit along the top of the section grading laterally from structureless to stratified and has characteristics of subglacial sediment gravity flow and rainout depositional processes at one site a fossiliferous diamicton is interpreted to be deposited by rainout through a combination of suspension settling from meltwater plumes and ice rafting with subsequent modification by sediment gravity flow on the fan slope a radiocarbon date of 13 680 90 bp beta 120124 on paired shells from this diamicton is interpreted to represent the date of its emplacement this date lies within the range of all other dates 13 1 14 ka bp on marine organisms from sediments along the coast of southern st george s bay and suggests that deposition of the diamicton was contemporaneous with sedimentation in all areas along the coast evidence to support a previously interpreted late glacial readvance at 12 6 ka bp was not found