origins of the ice contact stratified ridges eskers of ireland abstract an extensive system of ridged landforms composed of ice contact stratified sediment was deposited in the central lowland of ireland during the most recent deglaciation 18 000 bp the ridges have been interpreted by others as deposits of an ice sheet drainage system i e eskers and as such have been used with other data to reconstruct the deglacial history the traditional deglaciation model shows systematic retreat of ice from south to north our study which involves an analysis of the ridged landforms using lithofacies sedimentary structures and paleocurrent data in conjunction with the geomorphology indicates that the pattern and nature of the ridges are not compatible with this model and support a new model of deglaciation warren 1991 in which the esker system fo med in an interlobate area during the simultaneous shrinking of two main glacial outflow centers an extensive lake system developed in the lowland between the two outflow centers ridges formed both perpendicular and parallel to ice margins involved both active and stagnating ice are both continuous and segmented beaded and were deposited in subaqueous and subaerial environments almost all of the ridges are associated with lacustrine sediments ice contact ridges are polygenetic and a genetic classification is proposed those that formed perpendicular to the ice margin are termed eskers those that formed parallel are termed moraines distinction between esker types continuous or beaded subglacial tunnel fills fluvial ice channel fills and subaqueous fans and moraine types s baqueous or subaerial is crucial to a reconstruction of the mode and pattern of deglaciation in the central irish lowlands

late weichselian and early holocene shore displacement in the central baltic sea abstract the glacial unloading and resulting isostatic land uplift have together with hydro isostasy eustatic rise of sea level and geoidal changes ruled the shore displacement of fennoscandia within the baltic basin periods of damming and shifts of outlet further complicated the shore displacement during the period studied ca 12 2 8 4 ka bp information on the baltic history was derived from shoreline observations and studies on sediment cores from lakes formerly directly affected by the baltic these cores were analyzed with respect to pollen diatoms and lithology to determine sequences of baltic sediments and dated by a combination of radiocarbon dates and biostratigraphy the studied areas of southeastern sweden mainly central gotland and the oskarshamn area eastern smaland display a similar course of shore displacement the late weichselian period shows a regression of a slightly decreasing rate between ca 12 2 and 10 3 ka bp then followed a fast drop 25 m of the baltic s water level the final drainage of the baltic ice lake during the next ca 700 years the yoldia stage a regression of ca 17 m occurred this period is mainly characterized by freshwater diatoms in the baltic but at ca 10 ka bp there is evidence of a shortlasting 100 150 year period with brackish water the ancylus transgression of ca 11 m began ca 9 6 ka bp and culminated ca 9 3 ka bp it was followed by a fast regression of 8 10 m thereafter the rate of regression decreased shoreline gradients showed that the fastest shoreline tilting occurred around 10 ka bp thus ca 2 ka after deglaciation

proglacial lakes character behaviour and geological importance proglacial lakes are ubiquitous within the quaternary record and can provide exceptional breadth and depth of palaeoenvironmental information present deglaciation is increasing the number and size of proglacial lakes around the world this study provides a synthesis of knowledge on proglacial lake character and behaviour and critically evaluates the importance of proglacial lakes from a geological perspective we show how ice marginal or ice contact lakes and other distal proglacial lakes can be distinguished from each other by geomorphological sedimentological chemical and biological characteristics the key controls on proglacial lake geomorphology and sedimentology are outlined and discussed proglacial lakes can exacerbate mountain glacier and ice sheet margin ablation via mechanical and thermal stresses but very large lakes can moderate summer air temperatures and relatively retard summer ice ablation proglacial lakes interrupt meltwater flux and are very efficient sediment traps hydrological routing and consequent geomorphological activity can be radically modified by sudden drainage of proglacial lakes and resultant glacial lake outburst floods exceptionally large proglacial lake drainages affected global ocean circulation and global climate during the quaternary overall analyses of proglacial lakes can provide a valuable insight into i patterns character and behaviour of mountain glaciers ice sheets and glaciations and ii the impacts of past present and future deglaciation

understanding phengite argon closure using single grain fusion age distributions in the cycladic blueschist unit on syros greece abstract the preservation of 40ar 39ar ages of high pressure hp metamorphic white mica reflects an interplay of processes that mobilise 40ar either through mica recrystallisation or by diffusive 40ar loss the applicability of resulting ages for dating tectonic processes is critically dependent on whether either of these processes can be proven to be efficient and exclusively active in removing 40ar from mica if not preservation of an inherited or mixed age signal in a sample must be considered for interpretation the cycladic blueschist unit on syros has become a new focal area in the discussion of the geological significance of argon age results from multi grain step heating experiments while some argue that age results can directly be linked to deformation or metamorphic growth events others interpret age results to reflect the interplay of protracted recrystallisation and partial resetting preserving a mixed age signal here we demonstrate the potential of a new approach of multiple single grain fusion dating using the distribution of ages at the sample section and regional scale we show that in northern syros mica ages display systematic trends that can be understood as the result of three competing processes 1 crystallisation along the prograde to peak metamorphic path 2 a southward trend of increasing 40ar loss by diffusion and 3 localised and rock type dependent deformation or metamorphic reactions leading to an observed age spread typically limited to 10 myr at the section scale none of the sections yielded the anomalously old age results that would be diagnostic for significant excess 40ar the recorded trends in ages for each of the studied sections reflect a range of p t conditions and duration of metamorphism diffusion modelling shows that in a typical subduction metamorphic loop subtle variations in p t t history can explain that age contrasts occur on a regional scale but are limited on the outcrop scale our new approach provides a comprehensive inventory of the range of ages present in different rocks and at different scales which results in a more refined understanding of argon retention and isotopic closure of phengite and the geological significance of the ages we verify the added value of our new approach by comparison with multi grain step heating experiments on selected samples from the same sections

active faults and paleoseismicity in fennoscandia especially sweden primary structures and secondary effects abstract fennoscandia today a region of low to moderately low seismicity was at the time of deglaciation with rates of uplift on the order of tens of centimetres per year a region of very high seismicity and active tectonics this is evident both from primary fault structures and from secondary sedimentary and hard rock effects in the region around the epicentral areas the map of active faults in fennoscandia includes numerous structures previously not recognised despite this the recording of active faults and paleoseismic events is still in its initial phase much more data will surely accumulate in the near future

superposed deformed beds produced by single earthquakes tecopa basin california insights into paleoseismology abstract well exposed soft sediment deformation ssd structures occur in tecopa paleolake beds largely composed of ash from the bishop 760 kyr and the lava creek 640 kyr ultra plinian eruptions in both cases the ssd structures affected volcaniclastic deposits concentrated by overland flow from the surrounding topography into the lower slope and lake environments re sedimentation of ash produced alternations of volcaniclastic layers with different grain sizes and ash content that allowed for reverse density gradients which favoured liquefaction and deformation in the tecopa basin extensive outcrops show these deformed strata continuing laterally for hundreds of metres along with three dimensional exposures this study illustrates the 3 d complexity of soft sediment deformation including some novel morphologic features of particular interest were examples of superposed deformed beds that laterally change into one single deformed horizon heterogeneities in ash concentration grain size and water content produced contrasting permeabilities that were barriers to liquefaction and soft sediment deformation the probable causes for liquefaction were middle pleistocene paleo earthquakes there are several active faults in the region with enough seismic potential to produce moderate to large earthquakes the fact that a single deformed deposit laterally merges into multiple superposed deformed beds indicates that multilayer liquefaction could be produced by a single shaking event in these cases ssd layers are insufficient and unreliable indicators of paleo seismic recurrence intervals

soft sediment deformation structures in the earth s oldest seismites abstract the chaibasa formation in eastern india which was deposited between 2100 and 1600 million years ago shows deformations that must have formed when the sediments were not yet consolidated some of these deformation structures have never been described before here they are described depicted and their origin is analysed we show that they must be the result of shocks which can only be explained satisfactorily as triggered by earthquakes the layers containing these deformation structures are termed seismites they are among the earliest records of earthquakes known in the earth s history

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

lodgement till and deformation till abstract the use of the terms lodgement till and deformation till are discussed it is proposed that the term hard lodgement till and soft lodgement till are used for sediments deposited subglacially by active ice and existing tectonic names are used for glaciotectonically deformed substructures

the significance of giant seismites in the plio pleistocene baza palaeo lake s spain terra nova 22 172 179 2010 abstract giant load type seismites uncommon in the geological record are described in plio pleistocene lacustrine deposits of the baza basin betic cordillera s iberia deformed beds of the marginal lacustrine and distal alluvial facies of the baza palaeo lake can be traced continuously for several kilometres soft sediment deformation is represented by load type structures of large dimensions pillows around 4 m in width and 2 m in height three dimensional exposures show ellipsoidal pillows separated by fluidized channels without any preferred orientation the final size of these load type seismites is strongly influenced by sedimentary factors such as the presence of a reverse density gradient in sediments and the bed thickness the giant seismites of the baza basin are located in a region which is unlikely to have been subjected to high magnitude earthquakes maximum around 7 0 therefore magnitude is not the main factor that controls the size of these load type structures

palaeoseismicity and de geer moraines abstract de geer moraines are small moraine ridges formed partly in crevasses at the base of glacier ice there may be several different origins of the crevasses one possibility proposed by gerard de geer who first studied these ridges was seismic activity in connection with the isostatic rebound during the deglaciation the present study shows a close connection between occurrences of de geer moraines in fennoscandia and seismic activity or fresh looking fault lines and other features indicating neotectonic movements this supports de geer s theory but does not exclude formation in crevasses formed in other ways there is no real proof that the tectonic movements took place in the quaternary but the close connection between the moraines and tectonic features is evidence pointing in this direction if this is correct it has important implications for the stability within cratons of precambrian crystalline bedrock

marginal formation of de geer moraines and their implications to the dynamics of grounding line recession de geer moraine ridges occur in abundance in the coastal zone of northern sweden preferentially in areas with proglacial water depths in excess of 150 m at deglaciation from detailed sedimentological and structural investigations in machine dug trenches across de geer ridges it is concluded that the moraines formed due to subglacial sediment advection to the ice margin during temporary halts in grounding line retreat forming gradually thickening sediment wedges the proximal part of the moraines were built up in submarginal position as stacked sequences of deforming bed diamictons intercalated with glaciofluvial canal infill sediments whereas the distal parts were built up from the grounding line by prograding sediment gravity flow deposits distally interfingering with glaciolacustrine sediments the rapid grounding line retreat ca 400 m yr 1 was driven by rapid calving in turn enhanced by fast iceflow and marginal thinning of ice due to deforming bed conditions the spatial distribution of the moraine ridges indicates stepwise retreat of the grounding line it is suggested that this is due to slab and flake calving of the ice cliff above the waterline forming a gradually widening subaqueous ice ledge which eventually breaks off to a new grounding line followed by regained sediment delivery and ridge build up less

the baltic ice lake and yoldia sea stages based on data from diatom analysis in the central south eastern and eastern baltic abstract this paper is the first attempt to summarize the results of diatom analyses from sediments of late glacial and preboreal age in the central south eastern and eastern baltic the baltic ice lake deposits are poor in diatoms and amongst those present planktonic freshwater species dominate the yoldia stage sediments however are richer in diatoms and it is possible to recognize these sediments from changes in the composition of the diatom flora i e the occurrence of brackish marine and halophilous species the decrease in planktonic forms and the increase in periphytic ones

the ice contact environment abstract water plays a key role in glacial sedimentation subglacial and englacial hydraulic flow is through a unique form of karstic conduit network which is kept open trough a delicate balance between hydraulic and cryostatic pressures during periods of low water flow some conduits are kept open by the sediment which had previously been deposited during periods of maximum meltwater production esker sediments are deposited in increments sequentially younging towards the source as they are deposited in tunnels relatively close to the ice margin and only survive in situations where the ice margin is receding proglacial lakes seem to have triggered sedimentation by dampening flow in feeding conduits in some palaeogeological situations coarse grained alluvial braid plains are common in the ice marginal situation but chaotic and ephemeral conditions are also characteristic and catastrophic flow events are common complex sequences of lacustrine fluvial debris flow and direct glacial sediments result deformation due to collapse of supporting ice walls or buried ice blocks is common such is the volatility of the ice marginal environment that much of the sedimentary record is destroyed almost as soon as it is deposited

an event stratigraphy for the last glacial holocene transition in eastern middle sweden results from investigations of varved clay and terrestrial sequences this paper presents an event stratigraphy for the last glacial holocene transition in eastern middle sweden the event stratigraphy for eastern middle sweden comprises ten events and covers the tim

lateral variability of ancient seismites related to differences in sedimentary facies the synrift escucha formation mid cretaceous eastern spain abstract lateral extent and continuity of deformation has been used as criterion for the recognition of a seismic origin of soft sediment deformations particular problems are posed by ancient seismites developed in deposits that show lateral variability of sedimentary facies in such a context the lateral continuity of deformation will depend on the lateral variability of physical properties of sediments that ultimately results in the lateral variability of seismites in a single deformation event a variety of decimetre scale soft sediment deformation structures occurs in the synrift escucha formation late aptian middle albian in teruel spain these structures which include pseudonodules ball and pillow structures slumps water escape structures multi phase deformed structures folds sagging like structures and synsedimentary faults were developed contemporaneous to the formation of dark grey silty mudstones and grey clayey siltstones in a shallow marine environment the soft sediment deformation is constrained to a 1 2 m thick horizon exposed in four outcrops consisting of quiet water mudstones and heterolithic storm deposits the deformed horizon can be sub divided into two parts each reflecting a deformation event that affected both cohesive and granular non cohesive sediments the deformed structures occur in the vicinity of the gargallo normal growth fault which is several kilometres long activity along this fault controlled the facies distribution of the unit bearing soft sediment deformations high energy facies were located in the fault tip while low energy facies developed in both the down tilted hanging wall and footwall blocks in addition fault induced shocks released enough kinetic energy to trigger soft sediment deformation the soft sediment deformation in the escucha formation represents different responses of deformation susceptible sediments to earthquakes which reflect the lateral variability of sedimentary facies

liquefaction features interpreted as seismites in the pleistocene fluvio lacustrine deposits of the neuquen basin northern patagonia abstract superbly exposed soft sediment deformation structures in pleistocene fluvio lacustrine deposits along the southern border of the depression area called bajo de anelo departamento de anelo neuquen basin have been analysed in the study area five stratigraphic sections were measured in detail facies distributions and stacking patterns show that these sediments result from the interaction between fluvial and lacustrine systems represented by cross bedded and rippled strata and varved deposits the lateral extent of the deformation is some hundred metres and the deformed bed involves the lower mid part of the 30 metre thick succession deformation affects about 1 5 m of coarse grained sand fine grained sand and rare gravel alternations the base and top of the deformed layer are defined by planar surfaces undeformed beds of similar thickness lithology and facies to the deformed layer occur above and below deformation is represented by a complex vertical succession of disturbed layers each layer shows a general load structure morphology it can be described as a multilayered unstable density gradient system in each bed a partial gravitational re adjustment occurred after liquefaction unequal loading related to lateral variation of both bed thickness and grain packing and porosity is a probable additional driving force that can be described in the undeformed beds trigger mechanism recognition for the observed liquefaction features can be based on the study of the geometry of deformed beds and on facies analysis results two key factors drive our interpretation 1 the occurrence of undeformed beds below and above the deformed bed 2 deformed and undeformed beds showing the same sedimentological features these field data allow us to exclude the action of internal erosive and or sedimentary processes such as overloading wave action etc as possible trigger agents for liquefaction since deformation is totally absent in beds with similar sedimentary features furthermore each internal erosive and or sedimentary process can be discussed and easily excluded by analysing its specific signature in the geological record having excluded every possible internal trigger autokinetic processes the observed liquefaction effects can reasonably be interpreted as seismically induced allokinetic trigger from this point of view this deformed bed is an important record of seismic activity in this sector of the neuquen basin during the pleistocene

deformation of an early preboreal deposit at nykvarn se sweden as a result of the bulldozing effect of a grounding iceberg abstract an early preboreal glaciomarine deposit near nykvarn se sweden consists from bottom to top of a submarine outwash fan a full glacio marine deposit and a near coast marine unit of poorly sorted ice rafted debris the top part of the succession shows soft sediment deformations that have the same characteristics as material moved forward by a bulldozer these deformation structures are interpreted as being due to grounding of an eastward moving iceberg this caused detachment of the lower part of the succession in the way that sand is pushed forward by a bulldozer the iceberg most likely calved off the retreating ice front which extended into sea due to a sudden subglacial discharge of meltwater jokulhlaup which event seems related to the breakthrough of an ice dam that could no longer withstand the pressure of a growing water volume produced by increased ice melting

genesis of de geer moraines in finland abstract the proposed model of the genesis of de geer moraines in finland is based mainly on the distribution of the moraine areas in relation to the palaeohydrological environment and on the composition and two and three dimensional fabrics of the material in order to shed some light on the geochronological problem involved the distances between successive ridges in a number of de geer moraine series are also compared with clay varve data on deglaciation rates in finland granulometrically petrographically and morphometrically de geer moraine till does not differ significantly from tills of surrounding areas two dimensional fabrics stress orientations at right angles to the ridge crest and three dimensional analyses reveal the slope conformable character of pebble inclinations generally spacings of the de geer moraine ridges do not confirm annual deglaciation rates as conveyed by clay varve data it is suggested the moraines were formed in basal crevasses of the ice following active flow phases of a local surging nature during the quiescent phase of the surge cycle the ice subsided into a water soaked till mattress filling up basal cavities from the proximal or the distal side finnish de geer moraines are thus neither annual nor end moraines they are subglacial bedforms with no geochronological meaning except that they formed during one single surge cycle as the marginal zone of the ice sheet calved and thinned it was lifted by proglacial water and the whole group of moraines became free of ice almost simultaneously

subglacial conditions in a branching saalian esker in north central poland abstract the results of a sedimentological study of a branching esker system near uniszki north central poland provide a deeper insight into the depositional processes that took place within a subglacial tunnel formed during the wartanian late saalian glaciation the internal structure of the esker deposits is complex and coarse grained debris intercalates with silt and clay layers ten main lithofacies types are recognized including one formed in a tunnel mouth environment and three other lithofacies which must have been deposited in a truly subglacial environment a subglacial tunnel association is defined fluctuations in meltwater discharge through the tunnels resulted in cyclicity in the sedimentary succession deposition of fine grained facies took place during low discharge whereas boulder and gravel lithofacies formed in the tunnel mouth during high discharge changes in the hydrostatic conditions finally resulted in the collapse of the tunnel roof so that the succession became covered with supraglacial deposits the uniszki deposits record deposition under highly variable sedimentary hydrostatic conditions which is typical of environments in the polish lowlands the results of the present study provide some criteria for the interpretation of subglacial meltwater debris and thus may contribute to the current discussion on subglacial tunnel sedimentation

early holocene history of the baltic sea as reflected in coastal sediments in blekinge southeastern sweden integrated palaeoecological studies of two fiord sediment sequences in the province of blekinge se sweden covering the time span 11 000 5000 cal bp reveal the timing and the environment for the ancylus lake littorina sea transition 9800 8500 cal bp the first ingression of saline water into the baltic sea through the danish straits occurred earlier than formerly assumed new evidence particularly mineral magnetic and palaeobotanical analyses demonstrate that on the general trend of the eustatically caused littorina transgression several minor fluctuations of the water level can be identified between 8500 and 5000 cal years bp a distinct regression phase around 8 100 cal bp is correlated with the greenland ice core cold event dated to 8200 ice core years bp this is described as a regional climatic catastrophe for the baltic sea region the coastal stratigraphy is compared with the offshore stratigraphy earlier studied a tentative shore displacement curve for early and middle holocene is presented

seismites an attempt at critical analysis and classification abstract the main types of seismites are reviewed following the proposed classification and are illustrated by our own case studies the large variety of seismites depends on the sedimentologic hydrodynamic and diagenetic characters of the deposits subject to seismic shocks on a given site generally different types of seismites cane be related to the same seismic event these peculiar but widespread sedimentary structures are not always univocal and may often be related to different causes therefore the structures discussed must necessarily be placed in a detailed geological context

recognition of trigger mechanisms for soft sediment deformation in the pleistocene lacustrine deposits of the santʻarcangelo basin southern italy seismic shock vs overloading abstract the lacustrine deposits of the san lorenzo cycle belong to the infill succession of the sant arcangelo basin a pliocene to pleistocene satellite basin developed close to the front of the south apennines thrust belt the lower to middle pleistocene lacustrine succession is made up of siltstone and claystone interbedded with sandstone carbonate and volcaniclastic beds arranged in fining upward sequences the upper to middle part about 50 m thick of the succession about 200 m thick has been investigated in detail in the depocentral sector of the lacustrine basin here soft sediment deformation structures occur in fine grained sandstone and claystone alternations and show a wide morphological variability deformed laminations slumps load structures large vertical water escape structures and neptunian dykes their formation occurred during and after sedimentation with different mechanisms of deformation some structures are related to liquefaction and fluidization processes viscous fluid behaviour while others occurred when sediment had already undergone lithification and its behaviour was plastic and or brittle facies analysis and detailed morphologic study of the soft sediment deformation structures indicate that the main trigger agents for deformation were seismic shocks and overloading induced by sudden deposition of coarser sediments on clays due to the arrival of density currents thus the soft sediment deformation structures provide a continuous record of the tectonic and sedimentary processes that acted in the lacustrine basin from sedimentation until diagenesis

are arc type rocks the products of magma crystallisation observations from a simple oceanic arc volcano raoul island kermadec arc sw pacific raoul island is the emergent summit of a large intra oceanic strato volcano in what is globally one of the simplest of subduction settings in this simple setting erupted magmas span the compositional range from basalt to dacite but none have the high mg numbers and high ni and cr expected of primitive mantle derived melts the lavas range from aphyric to highly porphyritic and are characterised by phenocryst assemblages dominated by plagioclase accompanied by clinopyroxene olivine orthopyroxene and spinel phenocryst core compositions and zoning profiles are remarkably uniform irrespective of total phenocryst content or geochemical composition indicating a decoupling of melt and crystal components in the system a consistent model for the raoul magmatic system is that primitive high mg magma generated in a melt column within the underlying mantle wedge is transformed into a series of derivative low mg magmas by fractional crystallisation within the lower crust low mg magma accumulates variable quantities of crystal cargo as it ascends toward the surface through a crystal mush zone these processes are essentially those that characterise continental subduction related magmatic systems but differ only in the absence of an evolved crustal component

a fluctuating ice front over an esker near ryssjon s sweden as a cause of a giant load cast abstract a well exposed section in an esker near ryssjon s sweden strongly affected by several phases of glacitectonism showed two phenomena that are uncommon and that seem to have a causal relationship the first phenomenon is the occurrence of a load cast consisting predominantly of gravel in deposits formed just inside or outside a tunnel mouth the load cast is over 3 m high and 8 m wide a size that has previously not been described from unconsolidated sediments two nearby somewhat smaller load casts consisting mainly of sand also have dimensions of over 2 m indicating that the formation of huge load casts was apparently a feature related to the special conditions under which loading could develop at this site the second remarkable feature is that not only is a till present in the succession above the load cast thus indicating re advance of the ice but deposits overlying this till are also deformed by glacitectonism proving that at least a second phase of ice re advance must have occurred this situation has not previously been documented it is concluded that the varying differential overburden of sediment and particularly the retreating and re advancing ice in this area were responsible for the formation of the extremely large load casts possibly triggered by seismic shocks related to isostatic adjustment caused by oscillations of the ice front

an interpretation and catalogue of paleoseismicity in sweden abstract paleoseismic data provide a long term record of seismic activity to predict hazards for periods longer than one to a few centuries in sweden the analysis reveals there was a drastic change in dominant seismic mode from a high to super high deglacial mode to a low to moderately low mode in present and late holocene time paleoseismic criteria and characteristics include numerous different sources of information viz primary faults bedrock deformation sedimentary deformation rock and sediment slides liquefaction sorting by shaking tsunamis differing geomorphic expressions disordering and ordering of magnetic particles by applying multiple criteria it was possible to identify 44 paleoseismic events including 23 events of estimated m 6 7 12 events of m 7 8 and 6 events of m 8 varve dating often allows a precision as to a single year in one case even to the season of a year the key for paleoseismic reconstruction and testing is the application of multiple criteria

observations on terminal moraine ridge formation during recent advances of southern norwegian glaciers abstract the formation of terminal moraines dating from glacier advances during the a d 1990s was investigated at six temperate glaciers in the jostedalsbreen and jotunheimen regions of southern norway morphological and sedimentological information was analysed and combined with detailed observations photographic evidence and length variation measurements bulldozing pushing of proglacial sediments was the predominant process at the low lying glacier termini of the debris free outlets of the jostedalsbreen ice cap evidence for bulldozing includes the relocation and rotation of boulders and the presence of lichen covered boulders in the distal slopes of moraines differences in moraine sedimentology between the individual sites are attributed to variations in the pre existing material pushed up rather than to specific processes in jotunheimen several modes of moraine ridge formation were active dumping of supraglacial debris and the marginal freezing on and subsequent melting out of subglacial sediment slabs were more important than bulldozing at some sites and in some years low air temperatures in winter at the higher altitude glacier termini enabled freezing on to occur however the forelands are below the lower limit of discontinuous permafrost and evidence of thrusting is absent whereas discrete terminal moraine ridges at jostedalsbreen are related to seasonal advances the less dynamic glaciers of jotunheimen allow the accretion of successive ridges during consecutive years no single regional mode of moraine formation is characteristic for southern norway several processes are involved depending on individual glacier morphology and dynamics the glaciological regime and environmental conditions especially climate on the glacier forelands the importance of specific processes varies within and between glacier forelands thus spatial and temporal variation and local individuality has to be taken into account in the interpretation of moraine ridge formation similar variability is likely to have been characteristic of terminal moraines deposited during the little ice age and earlier in the quaternary

sedimentological evidence of pleistocene earthquakes in nw poland induced by glacio isostatic rebound abstract soft sediment deformation structures are abundantly present in two levels within warthanian eemian lacustrine sediments at siekierki near the polish german border the two event horizons show intense folding collapse sag and load structures indicative of liquidization and fluidization the structures must have been caused by sudden shocks most probably resulting from earthquakes that were induced by glacio isostatic rebound probably after the warthanian deglaciation such seismites have not been previously recognized in polish quaternary sediments they provide supporting evidence for glacio isostatic movements that were interpreted up till now based on drilling lithostratigraphic geophysical and geodetic data the recognition of seismites in nw poland may help recognize other deformed event horizons in pleistocene sediments as glacio isostatic or neotectonic seismites

record of the vistula ice lobe advances in the late weichselian glacial sequence in north central poland during the last glacial maximum lgm the vistula ice lobe was one of the key morphological elements at the southern margin of the scandinavian ice sheet in north central poland the area of the vistula ice lobe experienced two ice sheet advances of varied extent the older one is correlated with the leszno brandenburg phase and the younger one is correlated with the poznan frankfurt phase sedimentological research and luminescence dating of the late weichselian glacial sequence in the vistula ice lobe area was conducted a new scenario of the late weichselian ice events in the area is presented the limit of the leszno phase within the vistula ice lobe was much smaller than had been accepted previously and its age is estimated to be about 20 300 bp significant ice sheet retreat was

a model of subaqueous sedimentation at the margin of the late midlandian irish ice sheet connemara ireland and its implications for regionally high isostatic sea levels abstract the geomorphology and sedimentology of a series of late midlandian glacigenic sites in connemara western ireland are described and a set of commonly occurring sedimentary assemblages identified these form components of a simple model of ice contact subaqueous sedimentation involving progressive down current transition from subglacial esker tunnel fill through proximal tunnel mouth fans proximal and distal subaqueous fans into basin floor sediments in two of the sites aggradation to the water line passes into fan delta topsets and foresets all sites abut into inferred water bodies to their west and imply minimum water surface heights of between 35 and 65 m irish od or in the case of the two deltaic sites shoreline heights of between 75 and 80 m these high water levels very close to and facing directly into the immediately adjacent open atlantic ocean are difficult to explain as ice dammed glaciolacustrine water bodies without invoking improbable ice sheet marginal geometries they may however be explained as a set of successive fjord head grounding line depositional systems that trace temporary still stands in the phased retreat of the irish ice sheet from its offshore maximum this possibility not yet confirmed by the discovery of in situ marine fauna implies a degree of late midlandian isostatic depression and subsequent response unexplained by currently applied crustal response models but supported by previously constructed glacio sedimentary models

subglacial drainage by groundwater channel coupling and the origin of esker systems part 1 glaciological observations this work is presented in two parts part i presents observations on the coupling between subglacial channel flow and groundwater flow in determining subglacial hydraulic regime and creating eskers from an icelandic glacier that is suggested as an analogue for many parts of pleistocene ice sheets part ii develops a theory of perennial subglacial stream flow and the origin of esker systems and models the evolution of the subglacial stream system and associated groundwater flow in a glacier of the type described in part i it is suggested that groundwater flow may be the predominant mechanism whereby meltwater at the glacier bed finds its way to the major subglacial streams that discharge water to glacier margins

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

genesis of a giant gravity induced depression gravifossum in the enkoping esker s sweden abstract a structure in the enkoping esker in southern sweden appears to result from a series of deformations that followed essentially loading because of an unstable density gradient diamicton on top of water saturated sands the more or less symmetrical structure which is in fact a structure within a graben structure is some 12 m wide at its top 2 5 m wide at its visible base and some 13 m high it shows a variety of both synthetic and antithetic faults in addition numerous folds are present so that a complex structure results both the structural characteristics and the shape resemble those of the much smaller gravifossums that have been described from subrecent lagoonal silty deposits in the netherlands it is the first time that a gravifossum has been described from glacigenic deposits and consequently also the first time that such a structure has been found in esker deposits

the baltic ice lake yoldia sea transition abstract the baltic ice lake the yoldia sea the ancylus lake and the littorina sea are the four classical stages in the postglacial evolution of the baltic basin the picture is complicated by what concerns the details of each of these stages between the baltic ice lake and the yoldia sea it is necessary to introduce a separate lake stage an entirely lacustrine phase of 300 years right after the drainage of the baltic ice lake and before the ingression of salt water that by definition signifies the onset of the yoldia sea during this lake stage a fully lacustrine ancylusfauna lived along the coasts of the islands of gotland and oland for historical reasons and mistakes we term this new stage the yoldia lake stage thus avoiding too much reorganization