interpretation of lithofacies of the ashtabula till along the south shore of lake erie northeastern ohio the final advance of the erie lobe into ohio during the port bruce stade of the late wisconsinan deposited the ashtabula till wave erosion and mass wasting along the south shore of lake erie show

saalian to weichselian stratigraphy and sedimentation along the lagjaeren hogjaeren escarpment southwest norway quaternary sediments along a profile crossing the southern part of the jaeren escarpment southwestern norway have been investigated with regard to their glacial history and sea level variations deposits from at least three glaciations and two ice free periods between oxygen isotope stage 6 and the late weichselian have been identified subglacial till directly overlain by a glaciomarine regressional succession indicates a deglaciation and amino acid ratios in elphidium excavatum between 0 083 and 0 118 date this event to oxygen isotope stage 6 sea level dropped from 130 to below 110 m a s l subsequently a short lived ice advance deposited a marginal moraine and a sandur locally on the escarpment stratigraphical position and luminescence dates around 148 ka bp suggest deposition during the final stage 6 deglaciation a late weichselian till covers most of the surface of jaeren in addition to a well documented westerly ice flow glaciotectonic indications of ice flow towards the north have been found ice flow directions and a hiatus between oxygen isotope stage 6 and the weichselian indicate enhanced erosion along the escarpment and the influence of a norwegian channel ice stream copyright 1999 john wiley sons ltd

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

quaternary geology of the buchans area newfoundland implications for mineral exploration mineral exploration for volcanogenic massive sulphide deposits in the buchans area of central newfoundland is hindered by thick and widespread quaternary overburden comprising glacial glaciolacustrine glaciofluvial and resedimented deposits mapping of striations and indicator erratics suggests that the area was affected by four ice flow events i southward ii northeastward and westward to southwestward iii southward and iv northeastward and southwestward vertical and areal distributions of lead copper and zinc indicate that till and glaciolacustrine sediments overlying sulphide deposits can be enriched in mineralized debris near mines at buchans surficial debris flow deposits contain much material derived from the topsails igneous terrane and are generally impoverished in mineralized debris southwest of buchans however they can be enriched mineral exploration in the buchans area must take into account that i sulphide rich debris in till does not reflect only the youngest ice flow even

influence of depositional processes on the geotechnical parameters of chicago glacial clays abstract the effects of depositional environment on properties stress history and undrained and drained shear strength parameters are evaluated for chicago glacial clay recent geology and basic depositional environments are described both laboratory and in situ shear strength evaluations have been conducted at several sites in the study area results of the investigations indicate that while depositional environment has a large impact on the engineering properties of these clays identification of the depositional environment is in itself insufficient to strength parameters post depositional events are shown to alter the stress history imparted during deposition and thus impact shear strength parameters

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

re advance of scottish ice into the solway lowlands cumbria uk during the main late devensian deglaciation the complex glacial geomorphology and stratigraphy of the solway lowlands cumbria uk reflects dynamic ice flow during the main late devensian glaciation with numerous ice flow shifts and re advances now recognised the final incursion of scottish ice into the region scottish re advance during a late stage of deglaciation has provoked widespread debate and even scepticism arising from ill defined marginal limits and a paucity of landforms sediments and dates in an attempt to resolve some of these issues this paper has applied both geomorphological and stratigraphic techniques to critically review evidence pertaining to the scottish re advance a major deltaic landform sediment assemblage at holme st cuthbert a thin patchy till sheet and eskers at thursby and sowerby wood verify that scottish ice re advanced into the solway lowlands at a late stage of deglaciation the thin patchy till sheet associated with the re advance is indicative of a short lived pulse with ice thought to have flowed rapidly across water saturated sediment and into proglacial lakes dammed up against higher ground to the east the holme st cuthbert delta which evolved from a subaqueous outwash fan marks a major still stand and development of a large ice contact lake in the vicinity of wigton the extent of the glaciation is difficult to elucidate with the till sheet disparately exposed as far east as lannercost although identification of the blackhall wood re advance till member probably limits its se extent to just south of carlisle coeval re advance of lake district ice is possible given that a final stage lobate movement of ice out of the vale of eden and into the solway lowlands is now recognised however there is no direct stratigraphic correlation or dating control

glaciohydraulic supercooling in former ice sheets glaciohydraulic supercooling has been observed at many modern glaciers and has been shown to generate thick zones of debrisladen basal ice which when exposed to melting can produce debris flow and melt out till deposits as well as hummocky terrain glaciohydraulic supercooling probably occurred in former continental ice sheets especially where ice flowed out of deep basins or up steep slopes evidence to support glaciohydraulic supercooling in former ice sheets however is limited but may include sedimentary sequences of melt out till and debris flow deposits and hummocky terrain along the distal rim of overdeepenings and crests of adverse bed slopes d 2005 elsevier b v all rights reserved

mt etna a model for the 1989 eruption abstract during the 1989 eruption of mt etna one of the most important in the last 20 years in terms of effusion rate a pair of fractures formed on the slopes of the southeast crater cone and propagated in a few days trending ca northeast and southeast with large quantities of magma being drained from the northern fracture in contrast the southern fracture after a short initial eruptive phase grew by 5 km in five days without eruptive or seismic activity when the fracture system crossed the southern scarp of the valle del bove wall some 6 km se of the active crater an intense seismic swarm started in the same area this lasted about four days and consisted of several hundred events clustering in a small focal volume although such a sequence of failure events contains elements of compatibility with a shallow dyke intrusion it did not lead to the expected flank eruption which would have threatened settlements just a few kilometres from the distal end of the fracture the question arises therefore whether or not the fracture system was dyke related and if so to what extent we attempt here to answer such a question by integration and interpretation of the available field observation and geophysical data indeed field observation constraints on the southern fracture system and the typical depth 2 km of the swarm do not contain evidence for shallow dyke emplacement beneath the lowermost part of the sse fracture conversely the inferred direction and shape of the tremor source the location and extent of a gravity anomaly observed a few months before the eruption the near horizontal migration of the seismic focii during the swarm and the change with time of related focal mechanisms lead us to hypothesize that the extreme development of the fracture system at its south was due to a deeper intrusion beneath the southern slope of the volcano

geological evolution of mount etna volcano italy from earliest products until the first central volcanism between 500 and 100 ka ago inferred from geochronological and stratigraphic data we present an updated geological evolution of mount etna volcano based on new 40ar 39ar age determinations and stratigraphic data integrating the previous k ar ages volcanism began at about 500 ka ago through submarine eruptions on the gela catania foredeep basin about 300 ka ago fissure type eruptions occurred on the ancient alluvial plain of the simeto river forming a lava plateau from about 220 ka ago the eruptive activity was localised mainly along the ionian coast where fissure type eruptions built a shield volcano between 129 and 126 ka ago volcanism shifted westward toward the central portion of the present volcano val calanna moscarello area furthermore scattered effusive eruptions on the southern periphery of etna edifice occurred until about 121 ka ago the stabilization of the plumbing system on the valle del bove area is marked by the building of two small polygenic edifices tarderia and rocche volcanoes their eruptive activity was rather coeval ending 106 and 102 ka ago respectively during the investigated time span volcanism in etna region was controlled by a main e w extensional tectonic related to the reactivation of malta escarpment fault system in eastern sicily

glacial marine or subglacial origin of diamicton units from the southwest and north iceland shelf implications for the glacial history of iceland abstract the extent and timing of ice advances onto the north and southwest iceland shelf is reconstructed by identifying the depositional environment of four diamicton units present in two marine cores from shelf troughs we analyze a combination of properties including sedimentological parameters microfabric analyses radiocarbon dates and foraminiferal assemblage data this multi proxy approach for understanding depositional environments of diamicton units is critical in areas where ice sheets extended into the marine environment the two cores studied contain a lower diamicton unit that is interpreted as subglacial till and an overlying diamicton unit that is interpreted as glacial marine sediment our analysis showed that in general till is classified by lower water content lower total organic carbon and coarser grain size than glacial marine sediment anisotropy of magnetic susceptibility shows that the till has a sheared fabric low inclination of the short k3 axis whereas the glacial marine sediment has a high inclination of the short k3 axis and a more random unsheared fabric grain counts on the 106 1000 m fraction in till contain a higher percentage of basalt whereas the glacial marine sediments contain a higher percentage of quartz volcanic glass and foraminifera foraminiferal assemblage data support the interpretations from the sedimentology and microfabric data radiocarbon dates on shells and or foraminifera in sediments directly above the diamicton units show that the ice retreated from these shelf areas by approximately 13 ka

pattern of deglaciation of the last late devensian scottish ice sheet evidence from ice marginal deposits in the dee valley northeast scotland the mode of deglaciation of the last scottish ice sheet is assessed from evidence provided by geomorphological mapping and sedimentology ice marginal deposits in the dee valley have a distinctive morphological expression and a characteristically varied sedimentology that strongly resembles those from subpolar glaciers the deposits tend to occur in certain topographic situations which can be accounted for by compression of ice near the margin and formation of an ice cored supraglacial land system a series of recessional stages of the ice front can be mapped demonstrating that active retreat occurred however additional evidence shows there was probably a thin marginal zone of stagnant ice recessional stages are inferred to be stillstands that are considered to be topographically controlled rather than related to climate development of the supraglacial land system during deglaciation suggests that the ice sheet had a polythermal basal regime with a cold based margin this implies that deglaciation took place in northeast scotland while the climate remained cold probably due to a precipitation deficit which agrees well with chronostratigraphic data

morphology and gpr stratigraphy of a frontal part of an end moraine of the laurentide ice sheet paris moraine near guelph on canada abstract during deglaciation the laurentide ice sheet developed lobate ice termini in the great lakes area where the lobes remained quasi stationary for considerable time and sediment was supplied by the glacier end moraines fronted by outwash plains were formed one of the best examples in southern ontario is the paris moraine formed by the lake ontario lobe this study is a detailed examination of the morphology transverse and longitudinal of part of the paris moraine near guelph ontario and an analysis of the stratigraphy as derived from borehole information and ground penetrating radar gpr surveys parts of the northwestern frontal zone of the moraine are characterized by c 30 m high semi isolated hills composed in great part by aprons fans of debris flow and waterlaid sediments to the southeast these hills are backed by moat like depressions similar to those formed by ice push generating hill hole morphology the ice push effect is corroborated by evidence of folding and dislocation in the gpr profiles farther southeastward still the main body of the end moraine is characterized by hummocky topography typical of differential melting of sediment charged stagnant ice

depositional models for moraine formation in east antarctic coastal oases this paper examines the origin of moraine ridges in east antarctic coastal oases and derives depositional models appropriate for the reconstruction of quaternary history on the basis of morphology structure and sedimentology four principal types of ridge may be identified 1 type a moraines form whenthe basal debris zone crops out near an ice margin 2 type b moraines form when large recumbent folds develop in the basal debris zone 3 type c moraines are ice contact screes and fans which form when debris accumulates at streep or cliffed ice margins and 4 type d moraines are thrust block moraines that form when unconsolidated sediment is entrained by freezing shearing and thrusting of sediment blocks at the base of the glacier simple calcumations of the rate of debris accumulation at ice margins suggest that type a b and c moraines take thousands of years to form and record stable ice margins type d moraines are structural features that may form relatively quickly when ice margins override unconsolidated sediment constructing models to explain the origin of the moraines is an important part of reconstructing the quaternary history of antarctic coastal oases because the models provide a basis for reconstructing the position and behaviour of the ice sheet during advance and retreat

sedimentation and erosion at the weichselian ice marginal zone near golczewo northwestern poland abstract the golczewo end moraine was formed during the general ice sheet recession after the pomerania phase of the late weichselian glaciation and represents a short period of steady state conditions at the ice sheet margin the end moraine is a sw ne oriented zone formed of several isolated 10 15 m high ramparts separated by low areas gates the end moraine zone is located along the axis of the elevated jurassic bedrock that much influenced the subglacial hydrology the golczewo end moraine is formed of two types of subaerial fan its major and morphologically exposed part hills is represented by short glacial terminal fans these fans have been partly eroded especially at tunnel valley mouths the eroded zones gates have been filled with fluvial deposits forming flat sandur fans that extend across the end moraine foreland plain these morphological units ramparts gates and sandur fans which together form the end moraine zone were formed synchronously the ramparts are distinctly elongate hills commonly asymmetrical with steep proximal slopes they comprise a complex sedimentary sequence that suggest alternating phases of sediment gravity flows and fluvial sheet floods flow tills indicate the ice contact conditions the gates between hills and sandur fans are flat to gently inclined they were formed by braided rivers with sheet floods dominating at the fan apexes at the gates and channelised braided rivers in more distal parts

early holocene glacier fluctuations in krundalen south central norway palaeoglacier dynamics and palaeoclimate krundalen a valley occupied by three eastern outlet glaciers of the jostedalsbre ice cap contains three groups of moraines two of which are outside the dated neoglacial little ice age lia l

the polonez cove formation of king george island antarctica stratigraphy facies and implications for mid cenozoic cryosphere development the middle to late oligocene polonez cove formation exposed on south eastern king george island south shetland islands provides rare evidence of mid cenozoic west antarctic cryosphere evolution a revised lithostratigraphy and facies analysis and a review of the palaeoenvironmental significance of the formation are presented here the diamictite dominated basal member of the formation krakowiak glacier member records the presence and retreat of marine based ice on a shallow continental shelf five overlying members are recognized these consist of basaltic sourced sedimentary rocks and lavas and represent a variety of shoreface and shallow continental shelf environments in an active volcanic setting these units contain diverse reworked and ice rafted exotic clasts that become sparse towards the top of the formation suggesting a continuing but waning glacial influence new 40ar 39ar dates from interbedded lava flows indicate a late oligocene age 25 6 27 2 ma for the polonez cove formation but are slightly younger than skeletal carbonate sr isotope ages obtained previously 28 5 29 8 ma there is evidence for wet based subice conditions at the base of the polonez cove formation but no sedimentary facies to suggest substantial meltwater this may reflect a subpolar setting or may result from lack of preservation or a high energy depositional environment a northern antarctic peninsula south shetland islands provenance is probable for most non basaltic clasts but certain lithologies with possible origins in the transantarctic and ellsworth mountains also occur sparsely throughout the formation there is evidence to suggest that the presence of such far travelled clasts within subglacially deposited facies at the base of the formation reflects the advance of a local ice cap across marine sediments containing the clasts as ice rafted material the presence of these clasts suggests that extensive marine based ice drained into the southern weddell sea region and that a strong weddell sea surface current operated both before and during deposition of the polonez cove formation

sediment fans and sediment flows generated by snowmelt observations at austerdalsisen norway sediments in the austerdalsisen basin norway are re worked annually during the short snowmelt period in the last 10 15 years several fans have been constructed largely by sediment flows sediment water mixtures which move downslope under the influence of gravity the viscosity of the flows varies considerably and a single flow may change as a result of water or sediment loss fan characteristics reflect the nature of the sediments the mechanics of flow modes of deposition and the annual periodicity of activity

formation and preservation of a tertiary to pleistocene fluvial gold placer in northwest british columbia abstract a unique longitudinal section through 2 km of a fluvial placer deposit in northwest british columbia provides an excellent sedimentologic and stratigraphic record of the placer sequence and insight into the pleistocene history of the region the section is exposed as a result of long term open pit placer gold mining along otter creek deposition of the auriferous gravels is believed to have occurred mainly in the tertiary and early pleistocene although parts of the uppermost gravels may have been deposited as recently as the late wisconsinan the gold bearing strata are mainly coarse grained gravels that were deposited by high energy fluvial flows in a narrow bedrock confined valley the proposed depositional model shows that ice damming of otter creek during an early glaciation resulted in a dramatic shift from a mainly erosional fluvial system to an aggrading glaciofluvial environment deltaic foresets can be traced upsection into delta topsets upvalley into braided stream deposits and downvalley into deformed proximal and then distal prodelta glaciolacustrine sediments late wisconsinan glaciation appears to be the most erosive glacial event but a pronounced and widespread unconformity at the base of the till did not penetrate to the placer gravels in the mine area preservation of the gravels is attributed to ice damming and rapid aggradation of the overlying glaciofluvial and glaciolacustrine sediments in addition local glaciers did not flow down the valley prior to the damming event and the valley is oriented oblique to the regional ice flow direction further inhibiting erosion sites with similar stratigraphic and geomorphic settings and glacial histories are potential exploration targets for gold bearing paleochannel deposits placer gold has been recently recovered from at least one such site in the area where paleoplacer potential was previously inferred using geologic criteria

internal architecture of a till sheet tiskilwa formation north central illinois usa application of architectural element analysis thick till sheets deposited during the quaternary form significant aquitards in many areas of north america however the detailed sedimentary heterogeneity and architecture and depositional history of till units are not well understood this study utilizes architectural element analysis to delineate the internal sedimentary architecture of the tiskilwa formation exposed at two outcrop sections in north central illinois usa architectural element analysis facilitates systematic delineation of sedimentary architecture based on the nature of facies contacts and change in facies associations delineation of unit geometries and understanding of depositional processes at different scales of resolution making architectural element analysis suitable for the sedimentological analysis and palaeoenvironmental reconstruction of subglacial deposits eleven facies types are identified in this study including sand gravel and diamict facies that record a suite of subglacial depositional processes detailed analysis of facies contacts bounding surface hierarchy and change in facies associations allows the delineation of five architectural elements including coarse grained lens coarse grained sheet mixed zone diamict lens and diamict sheet elements the spatial arrangement and genetic interpretation of elements and their spatial relationship with fifth order bounding surfaces allows the delineation of five larger scale architectural units element associations which can be mapped in the local study area and record at least three stacked successions of meltwater accumulation and till deposition the results of this study can be utilized for architectural analysis of till sheets and provide insight to groundwater flow pathways through till in the study area and elsewhere

lithofacies and depositional history of a late devensian ice contact deltaic complex northeast scotland abstract the late devensian sediments exposed at the mill of dyce near aberdeen were deposited in an ice contact deltaic setting extensively deformed debris flows deposited close to the ice pass down dip into less deformed matrix rich boulder gravel also deposited by debris flow processes and subsequently reworked by en and supra glacial meltwaters farther down dip proximal braided outwash sand and gravel deposits are incised into the ice marginal deposits this braided outwash erosively overlies fine grained bottomset sediments the deltaic succession is locally capped by planar bedded sand upper flow regime deposited by overflow currents from lake waters ponded behind the deltaic sediments at mill of dyce following ice retreat drainage of this lake post dated 11 550 b p

till as a glacial tectomict its internal architecture and the development of a typing method for till differentiation abstract till has been studied for over a century yet still a clear understanding of the mechanics of deposition and or emplacement of till eludes us tills in the past have been generally subdivided into sediments formed in various sub environments of the glacial system as such it has been generally agreed that tills can be separated in terms of these types based on various attributes such as clast fabric increasingly such separation into various sub types of till has become however highly debatable and tenuous based upon the use of micromorphology and a greater in depth appreciation of the internal architecture of till it has become apparent that previously established classifications of till are erroneous micromorphology reveals that deposition and or emplacement of tills is a complex tectonic process such that lodgement melt out and flow tills as previously defined do not appear to exist rather a new term better describes tills as glacial tectomicts by using micromorphology in establishing the presence of sets of microstructures a statistical method is introduced that permits differentiation of tills from other diamictons the implications for this new understanding of tills allied to statistical typing is considerable in terms of till formation glacial stratigraphy and understanding glacial environments in terms of stress histories porewater transmission subglacial deformation mechanics till rheological phase changes and the timeline of till formation

the vendian succession of northeastern spitsbergen petrogenesis of a dolomite tillite association abstract the sedimentary record of late precambrian time is magnificently displayed in the highland snowfields of northeastern spitsbergen svalbard vendian strata are represented essentially by the polarisbreen group which consists mostly of dolostone and includes two dolomitic glacial units the oldest sediments in the polarisbreen group compose the elbobreen formation c 400 m which is divided into four laterally persistent members the lower carbonate member e1 125 m contains a distinctive basal dark grey limestone with microspar filled synaeresis cracks suggested to be of lagoonal origin and associated with minor dolostone shale and chert higher parts of the member are dominantly dolostone partly stromatolitic with some shale and sandstone shallow subtidal to intertidal deposition is indicated by the dominance of intraclastic lithologies and relics of anhydrite penecontemporaneous dolomite is partially overprinted by microsparry dolomite thought to be of groundwater origin the redefined petrovbreen member e2 consists of diamictite and other detrital dolostone pronounced thickness variations 2 40 m are thought to be original depositional features the member represents the deposits of a short glacial period in which the following depositional processes are inferred lodgement massive diamictite subaqueous meltout massive and bedded diamictite ice rafting lithologies bearing dropstones and possibly also diamictite redeposition by sediment gravity flows some diamictite and conglomerate rhythmite and shale current winnowing thin tabular conglomerate subaerial or subaqueous meltwater action channelled conglomerate and sandstone periglacial shrinkage diamictite wedge fillings the macdonaldryggen member e3 230 m is a monotonous succession of shaly dolostone of lagoonal origin it grades up into the slangen member e4 25 m which consists of subtidal to intertidal dolarenite with anhydrite relics succeeded by fenestral dolostone that was fractured and cemented by saline groundwaters in an emergent environment the wilsonbreen formation 160 m represents a return to glacial deposition but this time longer lasting and with substantial extra basinal material represented the gropbreen member w1 28 107 m and the ormen member w3 44 139 m consist dominantly of dolomitic diamictite with subordinate conglomerate and sandstone and are separated by a middle carbonate member w2 3 30 m which contains distinctive rhythmitic and stromatolitic limestone as well as sandstone the same depositional processes can be recognised as in the petrovbreen member but the wilsonbreen formation is overall of somewhat more continental aspect lower proportion of rhythmite and dropstone structures in addition there are basal breccia and crack fillings formed by frost shattering of the underlying cemented dolostone tabular sandstone thought to be formed by wave reworking of outwash a striated terrestrial cobble pavement supraglacially derived breccia horizons periglacial wedges filled by sand and the w2 assemblage of possible lacustrine origin the dracoisen formation 525 m represents an abrupt return to non glacial conditions an upward deepening wave dominated succession of pure dolostone d1 20 m and impure dolostone d2 105 m is succeeded by offshore black shale d3 150 m and then by a very shallow water succession of evaporite lacustrine aspect with a dolostone containing evaporite relics d5 10 m separating dolomitic sandstone and shale d4 80 m and d6 150 m the contact with the transgressive cambrian sandstones above is poorly exposed deposition of the succession dominantly under marine conditions is inferred but it is difficult to rule out a lacustrine environment at any particular horizon this dolomite tillite association can be explained by penecontemporaneous and minor secondary dolomite formation in marginal environments with warm climatic indicators at some levels being sharply interrupted because of rapid climatic changes by glacial sediments containing abundant detrital dolomite since the latter sediments make up only 17 of the 1080m thick succession glacial conditions only occupied a small proportion of vendian time

contrasting triggering mechanisms of the 2001 and 2002 2003 eruptions of mount etna italy abstract mount etna produced two significant eruptions in 2001 and 2002 2003 which we have analysed using geological seismic and deformation data these eruptions showed some similarities such as the activating of two magmatic plumbing systems central lateral and eccentric but they differed in their triggering mechanisms while the 2001 eruption was largely the result of the emplacement of a n s eccentric dike independent from the central conduits consistent with e w regional extension the 2002 2003 eruption occurred in response to a major flank slip on the eastern and southeastern sides of the volcano this is demonstrated by the spatial and temporal distribution of seismicity and deformation preceding and accompanying the two eruptions during the months prior to the 2001 eruption most epicenters were concentrated on the southern flank at depths of 5 15 km below sea level during the 4 days before the eruption earthquake hypocenters migrated to shallower levels from 5 km bsl upward indicating the emplacement of the eccentric dike this is confirmed by the patterns of ground fracturing observed in the field and deformation documented by electronic distance measurements edm in contrast the months before the 2002 2003 eruption were characterised by shallower seismicity mainly concentrated along the active faults bordering the slipping flank sector flank slip accelerated in september 2002 and a second more vigorous acceleration of flank slip occurred on 26 27 october 2002 accompanying the opening of eruptive vents the very short 2 h seismic crisis preceding the onset of eruptive activity stands in neat contrast with the 4 days of intense seismicity before the 2001 eruption subsequently flank slip deformation extended all over the eastern and southeastern flanks of the volcano causing serious damage in this sector the events of 2001 2003 can be seen as a continuous chain of intimately interacting processes including regional tectonics magma accumulation and eruption and flank instability in this scenario the 2001 eruption led to increased flank instability that subsequently accelerated and culminated with the massive flank slip which in turn facilitated the 2002 2003 eruption this sequence of events points to a long term feedback mechanism between magmatism and flank instability at etna

preservation of basal ice sediment texture in ice sheet moraines ice sheet moraines near kangerlussuaq in west greenland inherit distinctive particle size distributions from basal ice although debris structures from the basal ice are commonly destroyed by deposition and resedimentation processes the abundance of clay and silt in the dispersed faciesa basal ice at the ice sheet margin is clearly re ected in the sedimentology of the ice sheet moraine geographical variations in the texture or grain size of moraine sediments may thus re ect geographical variations in basal ice this o ers a new approach to reconstructing the basal ice characteristics and hence the thermal and dynamic properties of former ice sheets 2000 elsevier science ltd all rights reserved

a major ice drainage pathway of the last british irish ice sheet the tyne gap northern england the tyne gap is a wide pass situated between the scottish southern uplands and the english pennines that connects western and eastern england it was a major ice flow drainage pathway of the last british irish ice sheet this study presents new glacial geomorphological and sedimentological data from the tyne gap region that has allowed detailed reconstructions of palaeo ice flow dynamics during the late devensian marine isotope stage 2 mapped lineations reveal a complex palimpsest pattern which shows that ice flow was subject to multiple switches in direction these are summarised into three major ice flow phases stage i was characterised by convergent lake district and scottish ice that flowed east through the tyne gap as a topographically controlled ice stream this ice stream was identified from glacial geomorphological evidence in the form of convergent bedforms streamlined subglacial bedforms and evidence for deformable bed conditions stage ii involved northerly migration of the solway firth ice divide back into the southern uplands causing the easterly flow of ice to be weakened and resulting in southeasterly flow of ice down the north tyne valley and stage iii was characterised by strong drawdown of ice into the irish sea ice basin thus starving the tyne gap of ice and causing progressive ice sheet retreat westwards back across the watershed prior to ice stagnation copyright 2009 john wiley sons ltd

identification of basal layer debris in ice marginal moraines russell glacier west greenland different processes of ice formation and deformation at the glacier bed create distinctive basal ice facies the geographical distribution of these facies at the glacier margin can indicate the distribution of subglacial environments previous research has shown that debris in dispersed facies basal ice at the margin of the greenland ice sheet has a distinctive particle size distribution that can also be recognised in moraines deposited where the dispersed facies is present this permits reconstruction of the distribution of basal ice characteristics and subglacial conditions from moraine sediments here we study stratified and debris band facies of the basal ice layer at the same site we find that contrary to previous suggestions these two facies can also be distinguished sedimentologically co variant plots of the c40 aggregate shape and ra aggregate roundness indices show that pebble and cobble sized clasts 2 to 7 in the debris bands are statistically more angular than those in the stratified facies sedimentological characteristics of the parent facies are retained in ice marginal moraines combined with previous work these new observations suggest that the geographical distribution of basal ice facies at a glacier margin can be reconstructed from sedimentological characteristics preserved in moraines

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

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

chronicle of the 1865 ne flank eruption of mt etna and geomorphologic survey of the mts sartorius area the row of pyroclastic cones named mts sartorius outcropping on the ne flank of etna formed in 1865 during a lateral eruption that lasted about 6 months the event was eye witnessed and described by numerous scientists and reporters in this work we use their observations to reconstruct the eruption chronology and scenario and carry out a detailed geomorphologic survey to identify the eruptive features and pyroclastic deposits the 1865 eruption began on 29 january along a segment of the main system of fractures oriented ene wsw radial to the central conduit after 30 january a secondary system of fractures trending nnw sse was simultaneously active the six larger mts sartorius cones developed since 3 february along the lower extension of the radial system they are markedly asymmetric due to the persistent winds blowing at the time and to the pre existing topography formed on underlying deposits previously unreported that we have recognized now about 150 years after the eruption most of the eruptive vents and fractures are no longer observable in the field being mostly hidden by products of subsequent phases of the eruption and by younger epiclastic deposits

the final phase of dead ice moraine development processes and sediment architecture kotlujokull iceland consecutive phases of de icing of ice cored moraines and the formation of dead ice moraine were monitored over a 4 year period at the terminus of the kotlujokull glacier iceland particularly the transition from partially ice cored moraine with isolated dead ice blocks to the ice free landscape receives attention in this paper in order to link the final melting processes to the architecture of the sedimentary end product in the current humid sub polar climate of south iceland de icing of partially ice cored moraines results chiefly from melting along the bottom surface of ice cores with an annual average rate of 25 cm the final de icing is associated with an interrelated group of re sedimentation processes and surface features series of sinkholes evolve at the toe of dead ice blocks which initiate retrogressive rotational sliding or backslumping of the ice cored slopes and the formation of distinct edges and fractures in the adjacent basins although backslumping is the dominant process in this phase of re sedimentation structures resulting from this process are rarely recognized in the ice free landscape as ice cores gradually diminish the effect of the latest re sedimentation events will overprint or destroy most existing sedimentary characteristics thus in the ice free landscape structures mainly related to the formation of sinkholes and fractures remain imprinted on the sediment succession generally no inversion of the topography occurs during the final phase of de icing the overall topography recognized in the late phase of the fully ice cored terrain is merely lowered and the amplitude of the relief reduced as de icing progresses the sediment architecture of the ice free landscape is characterized by heterogeneous and often slumped diamict sediments with variable thickness and lateral distribution clast orientation is related to the direction of slopes and boulders are found in isolated groups or in linear arrangements

late pleistocene tidewater glaciers and glaciomarine sequences from north county mayo republic of ireland late pleistocene deposits in north county mayo were deposited in three main glacigenic environments 1 drumlins and basal tills were formed when ice moved from the irish lowlands and local mountain catchments into donegal bay 2 gilbert type deltas accumulated up to 80m i o d on the lowlands and subaqueous moraines formed across minor valleys when marine based ice grounded inland 3 a thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice rafting immediately outside of these ice limits the muds contain an elphidium clavatum dominated low diversity microfauna which is characteristic of cold water conditions adjacent to glacier termini valves of macoma calcarea from the mud have been 14c dated at 16940 120 and 17300 100 bp the high level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north county mayo although the field evidence cannot be used to determine former sea level history with any accuracy it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of ireland raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in ireland and represent marine transgressions prior to glacial unloading it is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in ireland than hitherto realised

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

sedimentary signatures of basal ice formation and their preservation in ice marginal sediments reconstruction of subglacial processes from sedimentological evidence is central to our understanding of glaciological conditions beneath former ice masses at svinafellsjokull southeast iceland we assess the extent to which two different processes of basal ice formation regelation and glaciohydraulic supercooling can be identified from ice marginal sediments our results indicate that the sedimentary characteristics of deposits produced by these two processes can be distinguished from one another and that it may be possible to recognise evidence of these processes in quaternary sediments and to reconstruct their spatial pervasiveness sediments derived from the melting of regelation basal ice have i a massive structure ii a sediment matrix 0 to 10 dominated by coarse sand and iii a higher proportion of angular clasts than supercool basal ice and associated sediments sediments derived from supercool basal ice i can be either massive or layered ii tend to have a silt dominated matrix and iii contain a slightly higher proportion of rounded and well rounded clasts than regelation basal ice and sediments previous studies indicate that the dominance of silt within supercool basal ice may be unique to this process and hence supercooling should leave a readily recognisable signature in the sedimentary record our results from svinafellsjokull lend support to that idea although we suggest that further work is required to assess whether silt dominance is a process signature diagnostic of supercooling and in particular the extent to which subglacial sediment supply determines the sedimentary character of basal ice facies and associated sediments

evidence of cordilleran late wisconsinan glaciers in the ice free corridor abstract glaciers flowing down the athabasca river valley during the last glacial period were fed both by local montane glaciers and by cordilleran ice moving easterly across the continental divide from british columbia resulting in a major eastward surge into the ice free corridor the timing of this event has been disputed for many years and has important implications for the study of paleoenvironmental conditions and the north south migration of biota in the corridor chronologic and lithostratigraphic data from the jasper region suggest that this event took place in the late wisconsinan subtill radiocarbon dates on wood in the athabasca river valley indicate that non glacial alluvial sediments began accumulating there sometime before 48 ka a finite date of 29 100 560 bp gsc 3792 on wood under till near jasper provides a maximum age for the onset of the last glaciation in the region although ice from west of the rocky mountain trench probably did not cross the continental divide until after 21 5 ka the occurrence of supraglacial metamorphic erratics as well as the distribution and nature of mapped glacial deposits and the trend of subglacial paleoflow indicators in the region east of the rockies suggests that late wisconsinan glaciers flowing from the mountains coalesced with laurentide glaciers and were deflected southeasterly along the mountain front an even more extensive glacial event may have effected the region in pre late wisconsinan times the model of late wisconsinan glaciation presented here is in agreement with all known radiocarbon data from the area and is especially attractive when supratill dates on non woody lacustrine organics are viewed in light of possible contamination by old carbon

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice i field evidence debris laden ice accretes to the base of matanuska glacier alaska u s a from water that supercools while flowing in a distributed drainage system up the adverse slope of an overdeepening frazil ice grows in the water column and forms aggregates while other ice grows on the glacier sole or on substrate materials sediment is trapped by this growing ice forming stratified debris laden basal ice growth rates of 0 1 m a 1 of debris rich basal ice are possible the large sediment fluxes that this mechanism allows may have implications for interpretation of the widespread deposits from ice that flowed through other overdeepenings including heinrich events and the till sheets south of the laurentian great lakes

melt out till and ribbed moraine formation a case study from south sweden abstract hummocky moraine with dispersed agglomerations of ribbed moraine here named asnen type ribbed moraine forms a 20 40 km wide zone over smaland south sweden terminated to the north by a sharp boundary to streamlined terrain the hummocky ribbed moraine zone can be geomorphologically linked to the subaqueous goteborg moraine formed at an oscillation stand still phase during the deglaciation of the swedish west coast based on detailed sedimentological and structural investigations of ribbed moraine ridges it is concluded that diamict sequences and associated sorted sediment were deposited due to passive melt out from stagnant debris rich ice with synsedimentary deposition of sorted sediments preferentially at a melting ice bed interface to accommodate for the geomorphological expression such an interpretation further implies that debris rich ice formed in an intermediate adfreezing zone between ice at the pressure melting point and a frontal frozen zone at deglaciation basal debris rich ice was stacked into transversally arranged zones controlled moraine forming ribbed moraine embryos the active phase of ridge formation the stacked sequences of debris rich ice eventually melted out beneath a stable and melt retarding supraglacial ablation complex to form the final moraine ridges the passive phase of ridge formation in areas with no stable supraglacial ablation complex the resulting landform after final de icing was a hummocky moraine landscape internal composition of moraine hummocks suggests that most of them are composed of sediment gravity flow sediments intercalated with stream deposited sediments all resting on a platform of subglacial melt out till de icing of the zone now occupied by hummocky and ribbed moraine took a considerable time deglacial 14 c age differences from lake basins on either side of the geomorphic boundary to the streamlined terrain indicate a separation between active and stagnant ice along that boundary and that it took another 200 300 yr for the stagnant ice zone to melt during the final formation of present day landforms

ice marginal sedimentation and processes of diamicton deposition in large proglacial lakes lake erie ontario canada detailed studies of coastal cliff exposures through two end moraines form the basis for a model of ice marginal sedimentation in large ice contact glacier fed lakes the input to the ice marginal environment directly from the glacier included subglacial till and subaquatic flow tills the subaquatic flow till thinly bedded diamicton was deposited in an apron up to 1 km wide along the ice margin an upward gradient of pore water pressure immediately beyond the ice margin causing heaving and dilation of the sediments initiated debris flows of glacially derived debris subaquatic flow tills most of the stratified sediments in the ice marginal zone entered the lake by way of a large proglacial stream sedimentation was dominated by quasi or near continuous density underflows that resulted in the deposition of a sequence of thick rhythmites the glacier in the lake erie basin most likely behaved like an ice stream with its movement controlled predominantly by a deforming bed of glacial debris separa

collapse of sediment filled crevasses associated with floods and mass flows in the proximal zone of the pernunnummi sandurdelta iii salpausselka sw finland abstract we aim to explain the complex geomorphology and sedimentology of the proximal zone of the pernunnummi sandurdelta which forms the most prominent portion of the iii salpausselka ice marginal complex of the former scandinavian ice sheet in sw finland we focus on the sedimentology of distinct diamicton covered glaciofluvial and glaciolacustrine landforms kames making accurate interpretations of both proximal diamictons and related sedimentary facies a crucial approach in the reconstruction of the depositional history of ice marginal zones we propose that the build up of the sandurdelta was followed by the formation of a glaciofluvially dominated supraglacial landsystem within a stagnant ice zone which fringed a glacial embayment between sub lobes of different deglacial dynamics the role of an integrated meltwater system including a major subglacial tunnel and water filled crevasses was crucial in constructing the controlled topography of this supraglacial landsystem the stagnant ice zone contributed to the incremental retreat of the ice margin within a shallow water environment where growing end moraines and proglacial deposits led to the development of supra aquatic conditions our results also evoke temporary dammed water bodies which were supported by ice marginal frozen bed conditions within the baltic sea icestream the collapse of crevasses with ice contact glaciofluvial and glaciolacustrine sediments during the continued deglaciation led to outbursts of dammed meltwater accompanied by extensive mass flows that formed the diamictons partially covering the ice proximal zone because ice marginal and esker related glaciofluvially dominated landform complexes with disintegration topography are relatively common along the main ice marginal deposits of the last great ice sheets the interpreted sedimentary record must be more common than previously reported thus extensive surficial and proximal diamictons of the ice marginal complexes do not always indicate either a re advance or a major oscillation of the ice front this study promotes the understanding of deglacial icestream dynamics with no known modern analogues and hence helps to improve both palaeogeographic reconstructions and the future compilation of even more accurate ice sheet models

applications of quaternary geology to placer deposit investigations in glaciated areas a case study atlin british columbia abstract quaternary geology has numerous applications in the identification of surface and buried placer deposits in glaciated areas including recognition of potentially auriferous stratigraphic units and lithofacies determination of deposit volume grade and geometry and estimation of overburden thickness and composition understanding of the quaternary geology is also required to evaluate the suitability of different exploration mining and processing methods a study of the distribution nature and extent of quaternary deposits in the atlin region british columbia canada is presented to illustrate some of these applications potentially productive fluvial channel and alluvial fan facies and geomorphic settings are identified they are distinguished from colluvial morainal and glaciofluvial deposits that have little placer potential deep glacial erosion and thick over consolidated tills are typical of the region and create special exploration and mining problems

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

subglacial processes of the scandinavian ice sheet in fennoscandia inferred from flow parallel features and lithostratigraphy abstract subglacial processes of the last scandinavian ice sheet in fennoscandia were investigated on two different scales a detailed case study in southwestern finland and a generalized study in the central parts of the ice sheet previously reconstructed time transgressive glacial flow patterns were correlated with different types of glacial flow parallel features and lithostratigraphic units the comparison of orientations of each flow parallel feature with relative ages of different flow patterns enabled estimations of relative distances of the orientation generating processes in relation to the receding ice margin this method was also used to infer sedimentary environments of each lithostratigraphic facies identified generalized lithostratigraphic sequences were compiled in fennoscandia using sections described previously in areas of ice streams a sandy till showing mature deformation structures forms till sheets drumlins and some ribbed moraines the facies is overlain by occasional glaciofluvial deposits and partly washed deformation till both indicating abundant excess water at the ice bed interface in interlobate areas glaciofluvial material is under and overlain by a silty till showing ductile deformation structures in places uppermost thin clayey till interpreted to be a subglacial melt out till mantles underlying till and subglacial glaciofluvial deposits the characteristics of different units are controlled by ice flow velocities subglacial hydrology and deformation type of the substratum the time transgressive origin of till beds and intervening washed sediment as well as divergent ice flow patterns is emphasized ice flow was concentrated in streams which generated marginal fan shaped lobes interstream areas of low basal velocities and melting rates were left between adjacent ice streams in areas of ice streams fast basal ice flow velocities continuously generated heat and meltwater which flowed at first in the sediment and closer to the margin also in thin discontinuous sheets at the ice bed interface excess water may have subsequently formed a linked cavity system and channelized to a tunnel network initiating esker deposition or incision of tunnel channels most processes operated continuously during deglaciation with spatial and temporal differences in their activity the mode of subglacial drainage changed periodically during deglaciation and was probably controlled by the volume of subglacial meltwater available in some periods sheet flow of basal water deposited major marginal complexes and subsequently tunnel networks were re established esker pattern and sedimentation rates of proglacial varved clays indicate that tunnel drainage of subglacial water was partly episodic

glacigenic clast fabrics genetic fingerprint or wishful thinking the interpretation of glacigenic diamictons is a subjective process for which quantitative support is frequently sought from parameters such as clast shape and fabric it has been widely suggested that different glacigenic diamicton facies possess distinct clast fabric signatures this paper examines this concept using a data set of 111 clast fabrics and a synthesis of published results eigenvalues are calculated and compared for a variety sedimentary facies it is concluded that clast fabric alone is not able to discriminate between different glacigenic facies and it is argued that clast fabric offers little quantitative support in the interpretation of glacigenic sediments it is suggested therefore that although clast fabric may continue to have a role as an indicator of relative strain at specific sites its use in the discrimination of glacigenic facies is limited consequently we should be much more selective in undertaking such analyses in the future copyright 1999 john wiley sons ltd

sedimentation and stratigraphy at eyjabakkajokull an icelandic surging glacier a model for sedimentation by surging glaciers is developed from analysis of the debris load sedimentary processes and proglacial stratigraphy observed at the icelandic surging glacier eyjabakkajokull three aspects of the behavior of surging glaciers explain the distinctive landformsediment associations which they may produce a sudden loading of proglacial sediments during rapid glacier advances results in the buildup of excess pore pressures failure and glacitectonic deformation of the overridden sediments b reactivation of stagnant marginal ice by the downglacier propagation of surges is associated with large longitudinal compressive stresses these induce intense folding and thrusting during which basal debris rich ice is elevated into an englacial position in a narrow marginal zone as the terminal area of the glacier stagnates between surges debris from this ice is released supraglacially and deposited by meltout and sediment flows c local variations in overburden pressure beneath stagnant crevassed ice cause subglacial lodgement tills which are sheared during surges to flow into open crevasses and form crevasse fill ridges

structure and modeling of surf zone turbulence due to wave breaking the turbulence structure under breaking waves in the surf zone is investigated through reference to experimental measurements and turbulence closure modeling this includes a unique set of recent turbulence measurements that have extended into the roller area through the application of digital particle image velocimetry measurements highlight the surface roller as the primary agent for turbulence production from where it is transported downward principally because of turbulent diffusion reflecting the breaker transition process turbulence intensities are largest some distance shoreward of the breaker point where the roller is fully developed the temporal variation of turbulence at a fixed point below the wave trough level is generally found to be minimal supporting the present use of a time independent turbulence closure model production of turbulent kinetic energy in the two equation k e model is presumed to occur in the vicinity of the surface roller from where it is transported downward through the water column by diffusion this production which is estimated from the rate of energy dissipation in the wave roller is the principal input parameter for the k e model froude scaled turbulence measurements from laboratory and field experiments are found to be satisfactorily predicted within the limits of the developed surf zone with improved methods of incorporating wave breaker transition zone effects leading to further model refinement the turbulence closure model is further shown to be effective in predicting time mean suspended sediment concentration and undertow velocity profiles in the surf zone

de icing progression of ice cored moraines in a humid subpolar climate kotlujokull iceland modes and rates of de icing ice cored moraines under humid subpolar conditions have been determ ined for two dead ice fields of different age representing a mature and a final stage of collapse in the kotlujokull terminus region south iceland the melting processes considered are backwasting defined as the lateral retreat of near vertical ice walls or steep ice cored slopes and downwasting defined as the thinning of the ice core by melting along the top and bottom surfaces in the mature stage of collapse where there is less than 1 m of sediment cover major faces of ice exposed for rapid melting are ordinarily significant and long lived due to intense precipitation in this fully ice cored terrain the predominating processes are backwasting of exposed ice walls and downwasting by bottom melt each contributing to the annual surface lowering of about 0 5 m or 35 the total annual surface lowering melt rate due to all processes averages 1 4 m in those parts of the fully ice cored dead ice field

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

the pleistocene end moraine fans controls on their sedimentation and location abstract this paper presents a model of end moraine sedimentation based on data from pleistocene ice sheet margins according to this model end moraines quite often constitute alluvial fans or coalesced fans formed at the ice margin by redeposition of supraglacial material three types of end moraine fan have been recognized those composed mainly of mass flow deposits type a equivalent to dry alluvial fan in nonglacial settings those containing both mass flow and waterlain sediments type b and those that contain mainly sorted waterlain material type c equivalent to wet alluvial fan in nonglacial settings for each type of fan several sedimentary subenvironments differentiated by distance from the ice front are identified the diagnostic processes on the end moraine fans are cohesive and cohesionless debris flows or grain flows types a and b or hyperconcentrated flows and sheetflows types b and c the type b fan seems to represent the most typical sequence in the end moraine zones but the type c fan is also quite common at the pleistocene ice sheet margins our studies also suggest that the terminal supraglacial drainage controls the type of end moraine fan sedimentary subenvironment moraine types a b c whereas subglacial hydrology and ice stream regime which determine the mobility of the ice front and larger scale conditions of sediment supply to the ice margin control the location and size of the end moraine fan

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