striated clast pavements products of deforming subglacial sediment studies of modern glaciers have recently drawn attention to the importance of subglacial sediment deformation to glacier dynamics and processes inferences regarding the probable shear strength of this sediment imply that large clasts may in some cases sink to underlying rigid sediment where abrasion by overlying deforming sediment could occur this scenario provides a formative mechanism for striated clast pavements commonly described from the base of fine grained massive diamictons associated with the late pleistocene laurentide ice sheet such a mechanism indicates that at the time of formation of clast pavements overlying diamictons associated with pavements had a low yield strength 0 5 kpa and were deforming mechanically like a debris flow clast pavements may therefore be an important criterion for recognition of sediments deposited by subglacial deformation transport

glacial advance and retreat sequences in a permo carboniferous section central transantarctic mountains episodes of glacial advance and retreat can be recognized through analysis of vertical facies sequences in the permo carboniferous pagoda formation of the beardmore glacier area antarctica the formation includes a remarkably complete record of continental sedimentation near the terminus of a temperate glacier facies sequence is pre eminent for inferring glacial advance and retreat other important criteria are abundance and geometry of sandstone interbedded with diamictite diamictite character and nature of bed contacts using these characteristics advance and retreat sequences 5 60 m thick are recognized a sharp contact with a striated surface and erosional relief overlain by structureless diamictite lodgement till is typical of grounded ice advance grounded ice retreat is characterized by structureless diamictite lodgement till overlain by crudely stratified diamictite melt out till and then by diamictite interbedded with sandstone and conglomerate flow till and glacio fluvial or glacio lacustrine deposits gradational contacts between shale overlain by diamictite and diamictite overlain by shale characterize advance and retreat respectively in subaqueous settings pauses in sediment accumulation minor fluctuations of the ice margin and or changes in subglacial dynamics are indicated by specific features within diamictite units such as probable frost wedge casts single layer boulder beds sharp sedimentary contacts and changes in diamictite character these minor events are superimposed upon the main advance retreat cycles study of both the overall facies sequence and of individual diagnostic structures albeit in an incomplete stratigraphic record permits a distinction between major and minor advance retreat events as many as six major advance retreat cycles exist in some pagoda sections but the number of cycles present varies in different sections

modification of clast shape in high arctic glacial environments abstract clast shape data from a range of different glacial environments at several high arctic valley glaciers in svalbard are presented these data add to the growing body of reference information about clast shape in modern glacial environments and is used to explore the role of lithology in clast morphogenesis and to evaluate the different methodological approaches to the analysis of clast shape data the following conclusions are drawn 1 it is possible to distinguish clasts transported subglacially from those moved supraglacially 2 it is not possible to differentiate among different types of subglacial sediment or to distinguish them collectively from glaciofluvial samples 3 lithology has some influence on clast shape although not as much as previously suggested and 4 covaria t plots of the ra percentage of angular and very angular clasts versus c40 percentage of clasts with c to a axial ratio 0 4 index give superior data visualization and discriminate more effectively among different glacial sediments than sphericity and roundness plots

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 facies of a glacially influenced continental succession in the pennsylvanian jericho formation galilee basin australia recent work on the late palaeozoic ice age in eastern australia has shown the joe joe group in the eastern galilee basin queensland to be of critical importance as it is one of few records of pennsylvanian glacial activity outside south america this paper presents detailed sedimentological data from which the late palaeozoic environment of the region is reconstructed and which consequently allows for robust comment on the broader gondwanan glaciation the jericho formation in the lower joe joe group was deposited in an active extensional basin in lacustrine to fluvial environments during the mid namurian to early stephanian the region experienced a cool climate during this time and polythermal mountain or valley type glaciers periodically advanced into the area from highlands to the north east the jericho formation preserves a suite of proglacial to terminal glacial facies that is characterized by massive and stratified diamictites deposited from debris flows massive and horizontally laminated conglomerates and sandstones deposited from hyperconcentrated density flows laminated siltstones with outsized clasts and interlaminated siltstone conglomerate deposited through ice rafting into lakes and sedimentary dykes and breccias deposited through overpressurization of groundwater beneath permafrost non glacial facies are dominated by fluvial sandstones and lacustrine overbank siltstones the glacigenic rocks of the jericho formation are confined to discrete packages recording three separate glacial advances during the latest namurian to late westphalian this arrangement is consistent with the temporal distribution of glacigenic rocks from around the remainder of australia and gondwana which supports the theory that glacial deposits occurred in discrete intervals the joe joe group is a key succession in the world in this context as at this time eastern australia provides the only unequivocal evidence of a namurian westphalian glaciation outside south america the continuous record of sedimentation through the pennsylvanian and early permian is indicative of significant warming between glacial intervals which is difficult to reconcile with the development of long lived cold based ice sheets across the supercontinent 2007 the authors journal compilation

estimating carboniferous sea level fluctuations from gondwanan ice extent the magnitude of carboniferous sea level fluctuations is not well known but the estimates are important for constraining cyclothem models in this paper we apply area volume relations developed for quaternary ice sheets to estimate the glacio eustatic component of sea level fluctuations in the carboniferous utilizing the best estimate of gondwanan ice area at the time of its greatest extent we arrive at a figure of 60 15 m for the isostasy corrected glacio eustatic component this value is nearer the lower limit of sea level estimates for cyclothem fluctuations from other sources

ice marginal environment and ecosystem prior to initial advance of the late palaeozoic ice sheet in the mount butters area of the central transantarctic mountains antarctica basal rocks of the upper carboniferous to lower permian pagoda formation at mount butters provide an unusual view of periglacial conditions in the central transantarctic mountains region prior to the initial advance of the gondwanide ice sheet these rocks were deposited on a high relief unconformity that developed on granite deposition within relief on the unconformity possibly in the lee of a granite buttress protected the rocks from erosion during subsequent overriding by the ice sheet the succession reflects deposition in a glacial fed to ice contact lake that contained a freshwater crustacean fauna centimetre to decimetre scale basal layers include breccia and coarse grained sandstone the occurrence of breccia resting on weathered granite suggests sedimentation as scree and as mass flow deposits overlying decimetre to metre scale stratified diamictites interbedded with metre scale coarsening upward successions of siltstone to cross laminated sandstone suggest lacustrine deposition by suspension settling rain out of ice rafted debris and deltaic progradation thin zones with abundant conchostracans and or with prolific trace fossils in addition to less common remains of other crustaceans attest to the presence of a low diversity benthic fauna conchostracans are concentrated in a series of thin beds that reflect moderately lengthy perhaps seasonal periods of free flowing water patchy vertical and lateral distribution of intense bioturbation and profuse trace fossils probably reflect repeated colonization events during times of favourable environmental conditions massive diamictite overlies the basal rocks and indicates that the ice marginal lake was subsequently overridden by the late palaeozoic ice sheet occurrences of lodgement till glacitectonite and deformation till suggest deposition from temperate or warm based ice whereas underlying lacustrine and deltaic deposits along with a crustacean and trace fossil fauna suggest temperate periglacial conditions previous studies have stressed that upper palaeozoic glacigenic deposits in antarctica and in gondwanaland record deglaciation events in contrast rocks at mt butters provide an unusual glimpse into an ice margin lake and its fauna just prior to ice sheet advance

till fabric associated with deformable beds this paper investigates the development of till fabric associated with glaciers overlying deformable beds first the till fabrics from both modern and ancient soft bed and hard bed subglacial environments are investigated and then soft bedded sites with specific strain histories are examined the results indicate that lodgement tills had a strong fabric whilst there is a wide range of much weaker fabric strengths associated with soft bed tills it is suggested from a theoretical study of soft bed till deposition that longitudinal and vertical processes in the subglacial deforming layer are important in fabric development field sites were chosen to isolate these two factors and fabrics investigated in areas of known relative shear strain and known relative thickness of the deforming layer the results indicate that 1 for a fixed deforming layer fabric strength does increase with increasing deformation except at very high strains where the development of a transverse fabric can lead to a reduction in the overall fabric strain and 2 lodgement tills and soft bed tills associated with a thin deforming layer have a high fabric strength whilst soft bed tills associated with a thick deforming layer have a low fabric strength where the deforming layer is thin clasts are oriented parallel with the glacier direction either by lodging against a hard bed or ploughing against a soft bed however where the deforming layer is thicker and shear strains are high melt out processes encourage a parallel fabric but the increased shear strain and changes in the deforming layer thickness cause the clasts to develop both a parallel and transverse fabric these processes combine to reduce the overall fabric strength till fabric studies are a further sedimentological technique to separate the depositional processes associated with a homogeneous till

modeling late paleozoic glaciation late paleozoic glaciation on gondwana is associated with changes in geography solar luminosity and estimated co sub 2 levels to assess the relative importance of these boundary conditions the authors conducted a suite of climate model simulations for the periods before during and after peak mid carboniferous approximately 300 ma glaciation 340 300 and 255 and 225 ma respectively orbital insolation values favorable for glaciation and interglaciation were used for each time interval results indicate that changes in geography cause significant changes in snow area but the temporal trend is not consistent with the geologic record for glaciation combined co sub 2 plus geography changes yield the best agreement with observations in addition interglacial orbital configurations result in almost ice free conditions for the glacial interval at 300 ma at a time of low co sub 2 the large simulated glacial interglacial snowline fluctuations for permian carboniferous time may explain cyclothem fluctuations at these times overall results support the importance of the co sub 2 paradigm but also indicate that a fuller understanding of past climate change requires consideration of paleogeographic luminosity and orbital insolation changes

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

depositional chronology and fabric of siwalik group sediments in central nepal from magnetostratigraphy and magnetic anisotropy abstract magnetostratigraphic research undertaken within the past 15 years in the siwaliks distributed along 400 km of the sub himalaya in central nepal has proved that the sediments possess highly reliable hematite based primary detrital remanent magnetization suitable to determine depositional chronology in order to bring out the polarity sequences in a common chronological frame all available data are newly correlated to the latest global magnetic polarity time scale of cande and kent s c cande d v kent 1995 revised calibration of the geomagnetic polarity timescale for the late cretaceous and cenozoic journal of geophysical research 100 6093 6095 chronological data presented are referred in relation to the diverse lithological nomenclature to the formations whose ages are not constrained by isotopic or paleontologic ages the age of the sections dated by magnetostratigraphy ranges between 14 and

on subglacial stone pavements in till four pavements from central and western canada display uneven pavement surfaces abundant tilted and inverted stones reversed lee ends fine crossing striae in various directions weak striae around curves worn facets distributed evenly on rounded stones and till fabric girdles collectively inconsistent with the popular concept of stones firmly held in till being abraded by overriding ice based on these data new models are offered that involve stone rotation in viscously deforming till to produce deformation pavements in the specific model increased pore water pressure under moving ice locally mobilizes previously formed lodgment and or erosional pavements into deformation pavements in the more general model stones released from the sole of a wet based glacier rotate interact and settle into a viscous suspension zone in deforming till according to velocity density and viscosity gradients stone axes and striae settle into various orientations following dewatering and till stiffening conceptu

development of the late paleozoic glaciations of the south american gondwana in western argentina abstract the late paleozoic ice age in the south american segment of gondwana consisted of several glaciations which can be grouped into two main glacial periods the oldest of them occurred in late early to early late carboniferous time and the younger in early permian time paleontological evidence in the western argentine precordillera supports a late visean age for the beginning and a probable early westphalian age for the end of the carboniferous glacial period in this span of time subsidence and deposition of glacial debris took place in the western mobile belt and in patagonia but no sediments of that age were deposited in the eastern portion of the south american gondwana where subsidence started later a carboniferous glacial sequence is remarkably well preserved in the san eduardo group on the western flank of the precordillera where at least three distinct glaciations are recognized this sequence can be taken as a reference section for the carboniferous glacial deposits shorter than the former and probably restricted to the asselian epoch the permian glacial period is better known the evidence for it is well developed in eastern south american gondwana although a relic is also present in the precordillera the recognition of two glacial periods within the late paleozoic ice age is supported by the existence of a long lasting interglacial which seemingly began in the late westphalian and lasted until the end of the carboniferous period this major interglacial period is inferred from the total absence of glacial features in the upper carboniferous sequences in spite of the existence of a mountainous belt parallel to the pacific during the carboniferous period the presence of marine beds and glacial drift well to the east of these ranges suggests that it was not altitude that was the main factor in determining the formation of glaciers but latitude plus a global change in temperature it is argued that the ice sheets extended greatly during the carboniferous glaciations and reached neighboring areas of the paganzo basin in central argentina

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

stratified interglacial lacustrine sediments from baffin island arctic canada chronology and paleoenvironmental implications abstract thirteen of 18 piston cores recovered from robinson lake in the mid arctic vegetation zone of baffin island arctic canada penetrated stratified lacustrine sediment beneath a thin over consolidated diamict till and postglacial lacustrine sediment the sub till lacustrine units are up to 120 cm thick of which the upper several decimeters frequently contain thick layered mats of aquatic moss pollen and diatoms are common throughout both lacustrine units a series of 23 ams 14c dates defines the chronology of the postglacial sequence which records a succession from a pioneer grass and oxyria dominated tundra between 10 4 and 8 ka bp to a sedge dominated tundra after 8 ka bp limiting 14c dates place the sub till lacustrine sediments more than 40 ka bp 10 luminescence dates centered on 85 ka indicate they were deposited late in oxygen isotope stage ois 5 the dominance of shrub and tree pollen especially shrub birch and alder in sub till lacustrine samples indicates low arctic tundra farther north than at any time during the holocene pollen concentrations are comparable to or higher than in the holocene units cooling late in the interglacial is indicated by declining birch and alder pollen percentages in the upper part of the section diatom floras in both the sub till and postglacial lacustrine sequences indicate similar development of lake water chemistry but input of silica and weathering products was greater in the older lake cycle suggesting more vigorous catchment processes macrofossils in the sub till units are characteristic of lakes ice free in summer based on pollen assemblages indicating local and regional vegetation diagnostic of summer temperatures higher than the holocene we interpret the sub till lacustrine units to be of interglacial character by analogy with holocene plant succession in central and eastern canada all of keewatin and labrador ungava must have been ice free throughout this interval suggesting essentially complete deglaciation of the laurentide ice sheet at the time

styles of sedimentation beneath svalbard valley glaciers under changing dynamic and thermal regimes glacier beds provide crucial information concerning past and present ice dynamics and thermal regime in this paper we present structural and sedimentological data from four valley glaciers austre lovenbreen midtre lovenbreen vestre lovenbreen and austre broggerbreen on broggerhalvoya nw spitsbergen the main focus of this paper is midtre and austre lovenbreen two typical high arctic land based polythermal valley glaciers the former has a long record of documentation regarding its response to twentieth century climatic warming structural mapping on the glacier surface and analysis of sediments in the proglacial area of midtre lovenbreen indicate that the dynamic regime and thermal structure of the glacier have changed through time dynamically midtre lovenbreen was once heavily crevassed and relatively fast moving but now is virtually crevasse free and slow moving the sedimentary record indicates that extensive areas of this glacier were wet based when it was in a more advanced state probably at its neoglacial maximum late nineteenth early twentieth centuries during this advance a thin deforming layer of diamicton commonly fluted was draped over the existing morphology in the presently exposed proglacial area this morphology consisted of large streamlined ridges aligned parallel to ice flow erosion of the underlying bedrock appears to have been limited radio echo soundings of the glacier show that at present it is characterized by a polythermal basal thermal regime with wet based subglacial conditions only beneath its thicker parts modification of the bed is limited under this thermal regime and as a result the supraglacial environment dominates modern sedimentation comparative studies on austre lovenbreen which also is probably polythermal indicate similar sedimentary characteristics and facies associations although here there are much more extensive areas of striated bedrock indicative of former basal sliding in contrast both austre broggerbreen and by analogy vestre lovenbreen are known to be predominantly cold based collectively these four glaciers suggest a trend of glacier recession and thinning accompanied by a change in thermal regime from predominantly wet based through partly frozen to completely frozen this study suggests that svalbard valley glaciers have several dynamic modes and that glaciers switch between these modes largely as a reaction to changes in mass balance

problems of a late palaeozoic glaciation in australia and subsequent climate in the permian the most recent information suggests two periods of glaciation separated by a considerable time interval the first is found in the namurian early carboniferous and may extend into the beginning of the late carboniferous evidence for the carboniferous glaciation is largely or entirely redeposited striated clasts known only from the new england area of northeastern new south wales these are considered to represent montane type glaciation associated with a developing alpine chain after a long interval glacial deposits are then found in many parts of australia in the asselian the lowest stage of the permian and the glaciation may extend into the beginning of the sakmarian the following stage in western australia a number of major fluctuations are recorded in the asselian the end of the glaciation seems to be associated with a worldwide eustatic rise in sea level in the tastubian the lower stage of the sakmarian after the tastubian no direct verifiable evidence indicates glaciation in the permian in australia or any other part of the world in australia there is no clear evidence on the climate in the interval between the two glacial periods but in south america and other parts of the world a warm interval is reported at this time most of the glacial debris is now found in sedimentary basins which were developing contemporaneously with the glaciation and is of a wet based type glaciers were active on steep hinterland carrying debris in adjacent water covered basins but how far the ice may have spread over lower lying land areas in not clear there is no real evidence of a thick dry based ice sheet like that of present antarctica after the tastubian there are a number of major fluctuations in climate during the rest of the permian at times seasonal ice and or perhaps icebergs may have been active but fluctuations which were cool or warm temperate or in some places in australia even subtropical or tropical are found in the sterlitamakian upper sakmarian beginning and end of the baighenzhinian upper artinskian kungurian kazanian and dzhulfian all separated probably by colder and in some cases considerably colder periods comparison of the marine faunas of the carboniferous and permian suggests that the levipustula fauna may not represent as cold sea water as the eurydesma fauna

neoproterozoic environmental change recorded in the port askaig formation scotland climatic vs tectonic controls abstract the snowball earth hypothesis suggests that the neoproterozoic was characterized by several prolonged and severe global glaciations followed by very rapid climate change to hot house conditions the neoproterozoic port askaig formation of scotland consists of a thick succession of diamictite sandstone conglomerate and mudstone sedimentological and stratigraphic analysis of port askaig deposits exposed on the garvellach islands was carried out to establish the nature of neoproterozoic palaeoenvironmental change preserved in this thick succession particular emphasis was placed on identifying and distinguishing between climatic and tectonic controls on sedimentation port askaig formation diamictite units are attributed to deposition by sediment gravity flow processes or rainout of fine grained sediment and ice rafted debris in a glacially influenced marine setting associated facies record various depositional processes ranging from sediment gravity flows conglomerate massive sandstone and laminated mudstone to deposition under other unidirectional currents cross bedded and horizontally laminated sandstone the port askaig formation is also characterized by abundant soft sediment deformation features that occur at discrete intervals and are interpreted to record episodic seismic activity stratigraphic analysis of the port askaig formation on the garvellach islands reveals three phases of deposition phase i was dominated by sediment gravity flow processes and sedimentation was primarily tectonically controlled phase ii was a transitional phase characterized by continued tectonic instability an increased supply of sand to the basin and the preservation of current generated facies in the third and final phase of deposition the interbedded units of sandstone and diamictite are interpreted to reflect development of large sandy bedforms and ice margin fluctuations in a tectonically stable marine setting sedimentological and stratigraphic analysis of the port askaig formation demonstrates that tectonic activity had a significant influence on development of the lowermost parts of the succession climatic influences on sedimentation are difficult to identify during such phases of tectonic activity but are more easily discerned during episodes of tectonic quiescence e g phase iii of the port askaig formation the thick succession of diamictite interbedded with current deposited sandstone preserved within the port askaig formation is not consistent with deep freeze conditions proposed by the snowball earth hypothesis

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

internal structures in part of the south mountain batholith nova scotia canada the devonian south mountain batholith smb in southern nova scotia provides an opportunity to examine the deformation produced in a magma during emplacement the smb was emplaced in three principal stages from oldest to youngest 1 granodiorite 2 monzogranite and 3 late granite porphyry aplite and pegmatite this investigation focuses on the monzogranite that underlies the eastern end of the batholith approximately 15 km south of the city of halifax the deformation consists of various types of mesoscopic and macroscopic flow folds defined by mapping the preferred orientation of alkali feldspar megacrysts the fold geometry is similar to that produced during melt dominated 30 liquid flow in migmatites the deformation did not affect the envelope of cambrian ordovician metasedimentary rocks of the meguma group hence the stresses that caused the folding were internal the response to the stresses was by ductile deformation folding and only locally by fracturing schlieren megacrystic dikes during the late stages of consolidation the magma behaved as a bingham substance during emplacement alternately plastic or brittle depending on the stress

devensian glacigenic sedimentation and landscape evolution in the cardigan area of southwest wales hambrey michael davies j r glasser n f waters r a 2001 devensian glacigenic sedimentation and landscape evolution in the cardigan area of southwest wales journal of quaternary science 16 5 pp 455 482 rae2008

formation of glaciolacustrine late pleistocene end moraines in the tasman valley new zealand abstract detailed examination of the tekapo formation in the tasman valley new zealand has identified 20 facies and five facies associations these associations are delta foresets and bottomsets sediment density flows ice contact lake sediments with ice rafted debris and resedimentation deposits and outwash gravels interpretation of the sediment landform associations informed by observations at modern glacier termini suggests that the late pleistocene tekapo formation moraines have been formed by downwasting of a more expanded tasman glacier during the early stages of glacier retreat ponds on the glacier surface develop into thermokarst lakes which enlarge and coalesce to form a large supraglacial lake continued downwasting causes the lake outlet river to entrench into the impounding latero frontal ice cored moraine lowering the lake level this exposes lake bottom sediments and forms shorelines on the proximal slopes of the ice cored moraine as the ice cored moraine melts these lake sediments are deformed and deposited against the mt john moraine the observations and interpretations reported here suggest the late pleistocene end moraine is a constructional feature not a structural glaciotectonic feature as suggested by previous studies

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

depositional processes in large scale debris flow experiments this study examines the depositional process and characteristics of deposits of large scale experimental debris flows to 15 m3 composed of mixtures of gravel to 32 mm sand and mud the experiments were performed using a 95 m long 2 m wide debris flow flume that slopes 31 following release experimental debris flows invariably developed numerous shallow 10 cm deep surges sediment transported by surges accumulated abruptly on a 3 runout slope at the mouth of the flume deposits developed in a complex manner through a combination of shoving forward and shouldering aside previously deposited debris and through progressive vertical accretion progressive accretion by the experimental flows is contrary to commonly assumed en masse sedimentation by debris flows despite progressive sediment emplacement deposits were composed of unstratified accumulations of generally unsorted debris hence massively textured poorly sorted debris flow deposits are not emplaced uniquely en masse the depositional

reconstructing the transport history of glacigenic sediments a new approach based on the co variance of clast form indices abstract two indices are used to describe the aggregate shape and roundness characteristics of glacially transported clasts the c40 index the percentage of clasts with c a ratios 0 4 and the ra index the percentage of very angular and angular clasts in a sample analysis of the between and within sample co variance of these indices provides a powerful tool for discriminating actively and passively transported clasts in glacigenic deposits use of these indices is illustrated in an analysis of the form characteristics of clasts from lateral and frontal moraines at storbreen jotunheimen these fall between those of actively transported clasts in basal till low c40 and ra values and those of unmodified frost weathered clasts high c40 and ra values both indices decline down moraine within sample analyses of clast shape demonstrates that these aggregate clast form gradients reflect changes in the relative proportions of actively and passively transported debris on the moraines rather than progressive modification of actively transported clasts these analyses also indicate that actively transported clasts form the dominant component of the moraines particularly near the former glacier terminus further applications of the approach developed here are suggested

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