the stratigraphic and sedimentological significance of late devensian ice sheet surging in holderness yorkshire u k amino acid analyses of marine mollusc valves show that the basement till of holderness yorkshire is of late devensian age ca 20 000 bp and not pre ipswichian 125 000 bp as is traditionally supposed together with the overlying skipsea and withernsea tills the basement till is argued to be a deformation till resulting from the repeated onshore surging of late devensian ice over a muddy sea floor and the subglacial transport attenuation and mixing of marine sediment silts on the surface of the basement till yielding 14c dates of 18 500 and 18 240 bp have been regarded as minimum ages for late devensian glaciation in eastern england e g the dimlington stadial of rose 1985 1989 the amino acid data presented here indicates that the maximum of the late devensian glaciation in eastern england occurred earlier sedimentological interpretation of the late devensian tills of holderness as glacially reworked marine sediments supports previous glaciological models of the british ice sheet involving surging of ice lobes along the coast of eastern england the basement skipsea and withernsea tills are separated by shallow marine sediments and may be representative of deformable bed till facies deposited below pleistocene ice sheets moving over soft fine grained sediments

dating sequences of buried horizons of podzols developed in wind blown sand at ulfborg western jutland abstract the ulfborg project is investigating the interactions of natural and anthropogenic influences on a typical west jutland landscape through the holocene with emphasis on the last millennium pollen analysis and ams 14c dates of buried podzols were used to date periods of blown sand transport and the development of man made calluna vulgaris heath hydrochloric acid extractable carbon expected to represent the most mobile fraction of carbon derived from the youngest soil was a non negligible fraction of the total carbon in the buried soils the age of the humic acid fraction in the bs horizons seems to indicate the start of podzolisation whereas the fulvic acid fraction in the mor layer indicates the time of burial dates for the three alkali extracted fractions within the individual mor layers were similar they agree with the results of pollen analyses which indicate that the original forest was transformed into pure calluna heath and kept as such by burning and cutting thus preventing continuous accumulation of organic matter the first large scale sand movement event was dated to about 6000 bc covering soils on which forest had earlier established the vegetational disturbance and sand movement were probably triggered by a climatic change to cooler conditions in contrast later sand movement seems to be connected with human activity in soils covered by sand at 800 600 bc the pollen record shows that the change from forest to pure calluna vulgaris heath had already taken place together with evidence from lacustrine pollen records the pollen assemblages from all younger mor layers indicate that the area was kept as pure calluna heath until the 19th century 14c dates of the lower bs horizons indicate that podzolisation started soon after the sand was deposited so some parent materials had been leached before deposition

the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

repeated short term bioproductivity changes in a coastal lake on store koldewey northeast greenland an indicator of varying sea ice coverage a lacustrine sediment core from store koldewey northeast greenland was biogeochemically biologically and sedimentologically investigated in order to reconstruct long and short term climatic and environmental variability the chronology of the uppermost 189 cm of the record is based on ten 14c ams age determinations of aquatic mosses the record covers almost the entire holocene and revealed changes on multidecadal to centennial scales dating of the oldest mosses shows that lacustrine biogenic productivity already began at around 11 cal kyr bp this age pre dates the onset of biogenic productivity in other lakes on store koldewey by about 2 kyr in spite of the early onset of biogenic production organic matter accumulation remained low and minerogenic sedimentation dominated at about 9 5 cal kyr bp moss sulphur organic carbon and biogenic silica content started to increase indicating that the environment stabilized and the biogenic production in the lake adjusted to more preferable conditions s

multiple late holocene surges of a high arctic tidewater glacier system in svalbard abstract most large tidewater glaciers in svalbard are known to have surged at least once in the last few hundred years however very little information exists on the frequency timing or magnitude of surges prior to the little ice age lia maximum in 1900 we investigate the sediment landform assemblages produced by multiple advances of the nathorstbreen glacier system ngs in order to reconstruct its late holocene surge history the glacier has recently undergone one of the largest surges ever observed in svalbard advancing 16 km from 2008 to 2016 we present flow velocities and ice marginal observations terminus change proglacial geomorphological processes from the later stages of this surge a first detailed assessment of the development of a glaciotectonic mud apron within the fjord during a surge is provided geomorphological and sedimentological examination of the terrestrial moraine areas formed prior to the most recent surge reveals that at least two advances were responsible for their formation based on the identification of a previously unrecognised ice contact zone recorded by the distribution of sediment facies in coastal exposures we distinguish between an outer older advance to the distal part of the moraine system and an inner younger advance to a position 2 km upfjord radiocarbon dating of shells embedded in glaciotectonic composite ridges formed by the onshore bulldozing of marine mud during the outer older of the two advances shows that it occurred at some point during the interval 700 890 cal yr bp i e 1160 ad and not during the lia as previously assumed we instead attribute the inner younger advance to the lia at 1890 by combining these data with previous marine geological investigations in inner and outer van keulenfjorden we demonstrate that ngs has advanced at least four times prior to the recent 2008 2016 surge twice at 2 7 kyr bp at 1160 ad and in 1890 this represents a unique record of the timing and magnitude of late holocene tidewater glacier surges in svalbard

the origin and glaciodynamic significance of sandstone ridge networks from the hirnantian glaciation of the djado basin niger the djado basin niger was located beneath the inner part of the late ordovician ice sheet the felar felar formation consists mainly of glaciomarine deposits associated with the major ice sheet recession within the glaciation and is bounded by two glacial unconformities structures corresponding to sandstone ridges are found within the felar felar formation sandstone ridges are several metres high about 10 m wide and hundreds of metres long these structures are organized in extensive anastomosed to subpolygonal networks the association of sandstone ridge networks with the later glacial unconformity and with other glacial evidence suggests sub glacial conditions for their origin sandstone ridge sedimentological characteristics indicate that sandstone ridges result from the scouring of the felar felar formation by sub glacial turbulent and pressurized meltwater then subglacial cavities were infilled with sand derived from glacial abrasion sandstone ridge networks are comparable with tunnel channels and document unusual drainage structures of the inner part of the palaeo ice sheet

lift off moraines markers of last ice flow directions on the scotian shelf lift off moraines are acoustically incoherent subparallel ridges observed on sidescan sonograms and high resolution reflection seismic profiles on the southeastern continental margin of canada they are up to 3 m high 20 80 m wide and are commonly overlain by stratified proglacial sediments although little is known about them detailed study of high resolution seismic profiles from the emerald basin and the lahave basin on the scotian shelf show that their height width ratio varies with the sounder seabed separation suggesting that the ridges may be narrower than they appear their morphology is similar to degeer moraines or cross valley moraines which form perpendicular to ice flow direction as their orientations can be estimated at the intersection of seismic lines they can be used to estimate ice flow directions since proglacial sediments are draped directly over top of them they are assumed to record the direction of last ice flow this directional data suggests that ice retreated not only

compositional heterogeneity in tephra deposits resulting from the eruption of multiple magma bodies implications for tephrochronology abstract tephra deposits of unknown age and or occurring in distal sequences that lack stratigraphic markers are commonly identified by their glass compositions and mineralogical assemblages recent studies of widespread rhyolitic tephra deposits from okataina volcanic centre ovc new zealand reveal a hitherto unrecognised geochemical and mineralogical diversity within individual deposits and sometimes between and within individual lapilli in these deposits these variations subtle in some units can occur both vertically and laterally through a tephra deposit and result from the sequential or simultaneous eruption of separate batches of rhyolitic magma this process often includes mingling of magmas in the eruption conduits as demonstrated by disequilibrium mineral assemblages in pumice clasts some eruption episodes e g 36 cal ka hauparu 17 6 cal ka rerewhakaaitu have tapped two or more magmas simultaneously while others 0 7 cal ka kaharoa 15 4 cal ka rotorua have tapped multiple magmas sequentially some tephra deposits display the sequential and or simultaneous emissions of different magmas from multiple vents through temporal phases of the episode 5 5 cal ka whakatane the resulting deposits can also show variations between different azimuths around the vent due to changes of wind direction during the episode the internal heterogeneity in ovc tephra deposits was only recognised after comprehensive sampling through their thick proximal pyroclastic sequences and associated lavas the internal heterogeneity highlights the inadequacy of fingerprinting tephra deposits from a small number of samples of restricted dispersal magma mingling at a single clast scale also has implications for geochronological techniques that use accessory phases u series and or require uniform melt geochemistry fission track on glass

evidence for a mazama like tephra deposited ca 10 000 bp at copper lake banff national park alberta mazama tephra is a widespread mid holocene stratigraphic marker dating to ca 6845 bp and is considered useful for the correlation of holocene events in western north america we present evidence from copper lake alberta for a tephra layer that underlies mazama tephra and appears to be a discrete tephra layer but that is indistinguishable from the conventional mazama tephra by microprobe analysis of glass shards three alternative hypotheses are considered to explain this tephra underlying mazama in situ position of an earlier mazama like tephra recycling of tephras and settling of tephra slabs through the gyttja the size distributions of birch pollen grains indicate that the mazama like tephra is in primary stratigraphic position in the early holocene gyttja and that sediment recycling has not destroyed the integrity of copper lake sediment stratigraphy it is concluded that most probably a mazama like tephra was deposited between 9700 and 10 500 bp if this in situ hypothesis is correct the id

timing and climate forcing of volcanic eruptions for the past 2 500 years volcanic eruptions contribute to climate variability but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual to decadal temperature variability in the northern hemisphere during the past 2 500 years our results are based on new records of atmospheric aerosol loading developed from high resolution multi parameter measurements from an array of greenland and antarctic ice cores as well as distinctive age markers to constrain chronologies overall cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth century pandemics famines and socioeconomic disruptions in eurasia and mesoamerica while allowing multi millennium quantification of climate response to volcanic forcing

dawson tephra a prominent stratigraphic marker of late wisconsinan age in west central yukon canada dawson tephra is the most prominent tephra bed in the quaternary deposits of the klondike and sixtymile areas of the yukon it occurs in organic rich reworked late wisconsinan loess deposits that occupy valley bottom sites and has a maximum thickness of 30 cm although most values are in the range of 15 30 cm the tephra consists of thin bubble wall shards that have a distinctive rhyolitic composition orthopyroxene plagioclase magnetite and ilmenite are relatively abundant in the small crystal component which also contains minor amounts of clinopyroxene apatite and zircon overall the composition of dawson tephra bears a close resemblance to that of the well known old crow tephra and like that tephra demonstrates a source in the aleutian alaska peninsula region given that the nearest vent in the alaska peninsula is 700 km distant from the klondike it follows that this explosive eruption must have been of great magnitude distributing tephra over southern and central alaska and the yukon

holocene environmental reconstruction from deltaic deposits in northeast greenland terraces of different age in the zackenberg delta located at 74 n in northeast greenland have provided the opportunity for an interdisciplinary approach to the investigation of holocene glacial periglacial pedological biological and archaeological conditions that existed during and after delta deposition the raised zackenberg delta accumulated mainly during the holocene climatic optimum starting slightly prior to 9500 cal yr bp 30 m a s l and continued until at least 6300 cal yr bp 0 5 m a s l evidence of sea level change is based on conventional 14c dates of shells from the marine delta bottomsets 14c ams dating of macroscopic plant material from the foresets and of fluvial deposits arthropod and plant remains from 7960 cal yr bp in the delta foresets include the oldest evidence of the arctic hare in greenland and evidence of a rich herb flora slightly different from the modern flora empetrum nigrum and salix herbacea remains indicate a summer temperature at least as high as today during delta deposition post depositional nivation activity dated by luminescence lichenometry and schmidt hammer measurements indicate mainly late holocene activity at least since 2900 yr bp including little ice age lia avalanche activity pedological analyses of fossil podsols in the zackenberg delta including 14c ams dating of selected organic rich b horizons show continued podsol development during the holocene climatic optimum and into the subsequent colder period of the late holocene until 3000 2400 yr bp a neo eskimo house ruin found on the lower part of the delta presently being eroded by the sea is dated to ad 1800 it presumably was abandoned prior to ad 1869 and suggests that some of the last eskimos that lived in northeast greenland might have occupied the zackenberg delta copyright 2002 john wiley sons ltd

deglaciation of the central barents sea abstract the marine based barents sea ice sheet covered the polar continental shelf north of norway and western russia during the last glacial maximum initial ice sheet retreat along the western margin is well established while the retreat pattern in the interior parts of the ice sheet remains poorly known here we present new geological data from the central barents sea the results are based on analysis of several marine geophysical datasets including geomorphological mapping of multibeam swath bathymetry data and analysis of seismic and acoustic stratigraphy the new results provide insights into the configuration and dynamics of the ice sheet during its retreat across the central barents sea in particular they show clear changes in the location of the main ice divides and domes with ice flow becoming gradually more topographically controlled as deglaciation progressed major troughs were characterised by episodic retreat and reoccurring cycles of fast and slow ice flow sometimes leading to stagnation and ice shelf formation meanwhile adjacent bank areas were covered by comparatively slowly retreating ice although evidence of streaming ice is also seen locally

permanent fast flow versus cyclic surge behaviour numerical simulations of the austfonna ice cap svalbard a large part of the ice flux within ice caps occurs through spatially limited fast flowing units some of them permanently maintain fast flow whereas others operate in an oscillatory mode characterized by short lived active phases followed by long quiescent phases this surge type behaviour results from intrinsic rather than external factors thus complicating estimates of glacier response to climate change here we present numerical model results from austfonna an ice cap on svalbard that comprises several surge type basins previous studies have suggested a thermally controlled soft bed surge mechanism for svalbard we systematically change the parameters that govern the nature of basal motion and thereby control the transition between permanent and oscillatory fast flow surge type behaviour is realized by a relatively abrupt onset of basal sliding when basal temperatures approach the pressure melting point and enhanced sliding of marine grounded ice irrespective of the dynamic regime the absence of considerable volumes of temperate ice both in the observed and simulated ice cap indicates that fast flow is accomplished by basal motion over a temperate bed given an idealized present day climate the equilibrium ice cap size varies significantly depending on the chosen parameters

geomorphological and cryostratigraphical analyses of the zackenberg valley ne greenland and significance of holocene alluvial fans abstract in high arctic northern greenland future responses to climatic changes are poorly understood on a landscape scale here we present a study of the geomorphology and cryostratigraphy in the zackenberg valley in ne greenland 74 n containing a geomorphological map and a simplified geocryological map combined with analyses of 13 permafrost cores and two exposures cores from a solifluction sheet alluvial fans and an emerged delta were studied with regards to cryostructures ice and total carbon contents grain size distribution and pore water electrical conductivity and the samples were ams 14c dated the near surface permafrost on slopes and alluvial fans is ice rich as opposed to the ice poor epigenetic permafrost in the emerged delta ground ice and carbon distribution are closely linked to sediment transport processes which largely depend on lithology and topography holocene alluvial fans on the lowermost hillslopes covering 12 of the study area represent paleoenvironmental archives during the contrasting climates of the holocene the alluvial fans continued to aggrade through the warmer early holocene optimum the colder late holocene and the following climate warming and by 0 45 mm a 1 on average this is caused by three factors sedimentation ground ice aggradation and vegetation growth and is reflected by ams 14c dating and continuously alternating cryostructures highly variable sedimentation rates in space and time at the alluvial fans have been detected this is also reflected by alternating lenticular and microlenticular cryostructures indicating syngenetic permafrost aggradation during sedimentation with suspended and organic matrix cryostructures indicating quasi syngenetic permafrost aggradation in response to vegetation growth in periods with reduced or no sedimentation over time this causes organic matter to become buried indicating that alluvial fans represent effective carbon sinks that have previously been overlooked

northern cordilleran volcanic province a northern basin and range introductionthe western margin of north america hosts adiverse assemblage of large cenozoic igneousprovinces fig 1 inset the temporal spatial andpetrological characteristics of these provinces areattributed to a variety of magmatic processes andtectonic environments including lithosphericextension e g basin and range migration ofmantle plumes e g snake river plain and sub duction e g cascade magmatic arc however neogene alkaline volcanic rocks in the cordilleraof northwestern canada between 55 and 64 n fig 1 currently lack a clear linkage to tectonicprocesses these volcanic centers constitute thenorthern cordilleran volcanic province and repre sent a significant gap in our understanding of thecenozoic tectonomagmatic activity in westernnorth america fig 1 inset our objective is to demonstrate that an exten sional tectonic model adequately explains thepetrologic radiometric and tectonic data forneogene quaternary volcanic rocks in the north ern cordillera furthermore the model we pro pose is consistent with models for neogene quaternary interactions between the pacific andnorth american plates northern cordilleran volcanicprovincethe northern cordilleran volcanic provinceencompasses a broad area of neogene to qua ternary volcanism approximately 1200 km longand 400 km wide in the northern part of west ern canada fig 1 the majority of the vol canoes within this region formed east of thedenali fault system and west of the tintinatrench fig 1 volcanic expressions of magma tism in the province range from large basalticplateaus and stratovolcanoes to individual cin der cones lava flows and eroded vents petrologyneogene to quaternary volcanic rocks withinthe northern cordilleran volcanic province arealkaline and chemically bimodal at least 70 ofthe volcanic rocks comprise alkali olivine basaltand hawaiite fig 2a basaltic lavas are gener ally olivine and plagioclase phyric with plagio clase olivine titanaugite and magnetite in thegroundmass the province also hosts a variety of other alka line and peralkaline rock types that are uncom mon in the north american cordillera such asnephelinite basanite phonolite trachyte and

retreat patterns and dynamics of the sentralbankrenna glacial system central barents sea accepted manuscript version published version available at https doi org 10 1016 j quascirev 2017 06 004 accepted manuscript version licensed cc by nc nd 4 0

holocene sea level reconstruction in the young sound region northeast greenland a relative sea level curve over the holocene is constructed for the young sound region in northeastern greenland the reconstruction is derived by dating the heights of raised beach ridges in coastal plains using optically stimulated luminiscence osl and by dating palaeoterrestrial surface levels now buried beneath the intertidal frame using the 14 c technique the relative sea level curve reveals a rapid fall of at least 10 mm a 1 from ca 9500 to 7500 a ago which slowed to 2 mm a 1 until it reached the present sea level ca 3000 a ago this part of the curve is based on the raised beach ridge data thereafter relative sea level continued to fall to reach a minimum level at about 0 5 m below the present sea level ca 2300 a ago since then relative sea level has experienced a slow rise of about 0 2 mm a 1 this part of the curve uses the data from the palaeoterrestrial surfaces the study supplements other estimates of holocene relative sea level changes and supports the observations of a decreasing trend in the timing of the cross point and in minimum relative sea level from south to north greenland copyright 2011 john wiley sons ltd

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

marine debris flows late precambrian tillites of the avalonian cadomian orogenic belt abstract correlative late precambrian strata of the avalonian cadomian orogenic cycle deposited after 670 and before 550 ma are now widely dispersed around the margins of the north atlantic these contain several prominent diamictite horizons long interpreted as tillites within thick turbidite successions associated with volcanic horizons the granville formation of the armorican massif in normandy france contains many pebby mud diamicite beds up to 20 m thick that have been interpreted as glaciogenic regionally the granville formation occurs within the lowest part of the upper brioverian supergroup which consists of several kilometres of turbidites and volcanogenic rocks at granville diamictites can be traced along striked into deformed and intermixed graded conglomerates and mudstones diamictites are identified as debris flows generated on a submarine slope by the emplacement of gravel turbidites on a mud substrate and their mixing during downslope slumping a glacial influence cannot be identified in north america the conception group of the avalon peninsula newfoundland canada contains nearly 4 km of turbidites with a conformable sequence of diamictites the gaskiers formation near its base massive and crudely stratified diamicite beds the diamictite successions of the granville and gaskiers formations provide significant data regarding facies types associations and the geometry of resedimented diamictite sequences in deep marine basins along active plate margins similar deposits at the same tectonic stratigraphic horizon occur in new england and africa this paper emphasizes the difficulty of identifying a direct glacial influence on diamictite sedimentation in such settings and the need for a sedimentological reappraisal of other supposed late precambrian tillites preserved in orogenic belts this is a necessary first step prior to modelling late precambrian paleoclimates

the intav intercomparison of electron beam microanalysis of glass by tephrochronology laboratories results and recommendations abstract the international focus group on tephrochronology and volcanism intav of the international union for quaternary research inqua has conducted an intercomparison of tephrochronology laboratories with electron beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries this assessment includes most active tephrochronology laboratories and represents the largest intercomparison exercise yet conducted by the tephrochronology community the intercomparison was motivated by the desire to assess the quality of data currently being produced and to stimulate improvements in analytical protocols and data reporting that will increase the efficacy of tephra fingerprinting and correlation participating laboratories were each supplied with a mount containing three samples for analysis 1 rhyolitic lipari obsidian id3506 2 phonolitic sheep track tephra from mt edziza british columbia canada and 3 basaltic laki 1783 a d tephra a fourth sample rhyolitic old crow tephra was also distributed most laboratories submitted extensive details of their analytical procedures in addition to their analytical results most used some combination of defocused or rastered beam and modest beam current to reduce alkali element migration approximately two thirds reported that they routinely analyze one or more secondary standards to evaluate data quality and instrument performance despite substantial variety in procedures and calibration standards most mean concentrations compare favorably between laboratories and with other data typically four or fewer data contributions had means for a given element on a given sample that differed by more than 2 standard deviations from the overall means obtaining accurate na 2 o concentrations for the phonolitic tephra proved to be a challenge for many laboratories only one half of the data sets had means within 1 standard deviation of the 8 2 wt na 2 o value obtained by other methods one mean is higher and 14 are lower three of the data set means fall below 7 wt na 2 o most submissions had relative precision better than 1 5 for the major elements for low abundance elements the precision varied substantially with relative standard deviations as small as 10 and as large as 110 because of the strong response to this project the tephrochronology community now has a large comparative data set derived from common reference materials that will facilitate improvements in accuracy and precision and which can enable improved use of published data produced by the participating laboratories finally recommendations are provided for improving accuracy precision and reporting of electron beam microanalytical data from glasses

the changing extent of marine terminating glaciers and ice caps in northeastern svalbard since the little ice age from marine geophysical records climate warming in svalbard since the end of the little ice age early in the 20th century has reduced glacier extent in the archipelago previous attempts to reconstruct little ice age glacier

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

submarine glacial landforms and sedimentary environments in vaigattbogen northeastern spitsbergen abstract vaigattbogen is located in northern svalbard the area is currently affected by several tidewater glaciers this study uses multibeam sub bottom acoustic data and four sediment cores to reconstruct the late weichselian and holocene glacial history in vaigattbogen during the last glacial ice flowed northwards through vaigattbogen and fed into the hinlopen strait ice stream streamlined bedforms indicate relatively fast ice flow and their increasing elongation ratios towards the north suggest increasing flow velocities de geer moraines in the shallower parts of vaigattbogen imply that multiple halts and or re advances interrupted the ice retreat in these areas a sediment core suggests that the north basin deglaciated prior to 9 1 cal ka bp in the south basin two large moraine ridges and networks of crevasse squeeze ridges suggest that at least two surge type advances occurred during the holocene the hinlopenbreen glacier surged in the early 1970s and deposited the inner r 2 of the two large moraine ridges radiocarbon ages from a sediment core recovered from the crest of the outer r 1 ridge yield a basal age of 2 6 cal ka bp however the core did not sample subglacial diamict and the age of the ridge could be anything between 2 6 cal ka bp and early holocene the r 1 ridge formed prior to the little ice age lia implying that more than one tidewater glacier has experienced a pre lia surge on the east coast of spitsbergen suggesting that surging during the holocene was a regional phenomenon the r 1 ridge is double crested with small crevasse squeeze ridges between the crests suggesting that more than one surge type advance occurred during the holocene reaching approximately the same location data from eastern svalbard indicate differences in surge landform assemblages suggesting that different mechanisms could have governed surge cycles throughout the holocene

holocene climate history of geographical society o east greenland evidence from lake sediments abstract sediment cores from two lakes in the outer coastal region of east greenland were investigated for chronology lithology palynology and biogeochemistry a 10 m long sequence recovered in basaltso comprises the entire lake history following the last glaciation of the area probably during the preboreal oscillation this is indicated by a succession from glacial via glaciolimnic to limnic sediments deglaciation of the area was associated with a high sedimentation rate mirrored also in the basal part of a 2 6 m long core from a smaller lake b1 about 1 km south of basaltso limnic sedimentation without glacial influence commenced about 10 000 cal yr bp according to radiocarbon dated terrestrial plant remains biogeochemical and palynological data indicate an early holocene climatic optimum from 9000 to 6500 cal yr bp a climatic deterioration began at 6500 cal yr bp with an increase in snow accumulation documented by a change in the pollen assemblage and a coinciding change in the grain size distribution at least since 5000 cal yr bp a decrease in the biogeochemical parameters in both lake sediment successions indicates a temperature decline this deterioration culminated at about 3000 1000 cal yr bp when the climate was cold and dry a slight warming is indicated in the pollen assemblage between ca 1000 and 800 cal yr bp following a subsequent rise in precipitation cooling during the little ice age is mirrored in lowest dwarf shrub pollen percentages and in low contents of organic components

the mount edgecumbe tephra deposits a marker horizon in southeastern alaska near the pleistocene holocene boundary late pleistocene tephra deposits found from sitka to juneau and lituya bay are assigned to a source at the mount edgecumbe volcanic field based on similarity of glass compositions to nearvent deposits and on thinning away from kruzof island the sequence of near vent layers is basaltic andesite and andesite at the base rhyolite and mixed dacite and rhyolite on top the only breaks in the tephra sequence are two 1 mm thick silt partings in a lake sediment core indicating a depositional interval from basaltic andesite to dacite of no more than about a millennium tephra deposits at sites 30 km from the vent are solely dacite and rhyolite and are 10 600 to 11 400 14c yr old based on interpretation of 18 radiocarbon ages including 5 by accelerator mass spectrometry ams basaltic andesite and andesite deposits nearer the vent are as much as 12 000 yr old discrepancy among radiocarbon ages of upland tephra deposits provisionally correlated as the same grainfall is resolvable within 2 of analytical uncertainty comparison of bulk and ams ages in one sediment core indicates a systematic bias of 600 to 1100 yr for the bulk ages correlation of tephra deposits among upland and lacustrine sites implies an additional discrepancy of 200 400 yr between upland relatively too young and lacustrine ages in any case the mount edgecumbe tephra deposits are a widespread latest pleistocene stratigraphic marker that serves to emphasize the uncertainty in dating biogenic material from southeastern alaska

chronology of the peralkaline late cenozoic mount edziza volcanic complex northern british columbia canada the late cenozoic mount edziza volcanic complex covers an area of about 1 000 km 2 in north central british columbia 300 km east of the transcurrent boundary between the north american and pacific plates it is made up of a group of overlapping basaltic shields and intermediate to salic peralkaline composite domes flows and central volcanoes that are associated with extensional structures in the underlying basement new k ar and fission track dates 45 and rb sr and sr isotope analyses 12 from the mount edziza volcanic complex are reported the age dates are for the most part consistent with the stratigraphy and indicate that frequent eruptive activity occurred during the past 8 m y five major magmatic cycles each began with the eruption of basalt and culminated with the eruption of oversaturated peralkaline magma low 87 sr 86 sr initial ratios 0 7028 0 0001 indicate a mantle source for the basalts low sr contents and high 87 sr 86 sr ratios in the salic end members suggest that the oversaturated rocks were derived from the basaltic magma by crystal fractionation in crustal reservoirs rb sr isochrons suggest that residence times for the fractionating magma were about 0 7 to 1 m y early removal of large amounts of plagioclase followed by fractionation of potash feldspar can account for most of the observed petrological and isotopic relationships a few individual compositions and one suite of mainly intermediate samples contain anomalously large amounts of both 87 sr and radiogenic argon this indicates that contamination with crustal material and possibly mixing of parental basalt with partly fractionated magma from previous events may have produced the relatively small volume of intermediate rocks

mud aprons in front of svalbard surge moraines evidence of subglacial deforming layers or proglacial glaciotectonics abstract large debris flow units commonly occur on the distal sides of subaqueous end moraines deposited by surges of svalbard tidewater glaciers but have rarely been described in terrestrial settings some researchers have argued that these kinds of debris flows reflect processes unique to the subaqueous environment such as the extrusion of subglacial deforming layers or extensive failure of oversteepened moraine fronts in this paper we describe terrestrial and subaqueous parts of a single late holocene moraine system deposited by a major surge of the tidewater glacier paulabreen in west spitsbergen the ice marginal landforms on land closely resemble the corresponding landforms on the seabed as evidenced by geomorphic mapping and geophysical profiles from both environments both onland and offshore extensive areas of hummocky moraine occur on the proximal side of the maximum glacier position and large mud aprons interpreted as debris flows occur on the distal side we show that the debris flow sediments were pushed in front of the advancing glacier as a continuously failing mobile push moraine we propose that the mud aprons are end members of a proglacial landforms continuum that has thrust block moraines as the opposite end member two clusters of dates 8000 ybp and 700 ybp have previously been interpreted to indicate two separate surges responsible for the moraine formation new dates suggest that the early cluster indicates a local extinction of the abounded species chlamys islandica other changes corresponding to the widespread 8 2 ka event within the fjord may suggest that the extinction of the c islandica corresponds to that time

a depositional model for hydromagnesite magnesite playas near atlin british columbia canada this study formulates a comprehensive depositional model for hydromagnesite magnesite playas mineralogical isotopic and hydrogeochemical data are coupled with electron microscopy and field observations of the hydromagnesite magnesite playas near atlin british columbia canada four surface environments are recognized wetlands grasslands localized mounds metre scale and amalgamated mounds composed primarily of hydromagnesite mg co oh 4ho which are interpreted to represent stages in playa genesis water chemistry precipitation kinetics and depositional environment are primary controls on sediment mineralogy at depth average 2 m ca mg carbonate sediments overlay early holocene glaciolacustrine sediments indicating deposition within a lake post deglaciation this mineralogical change corresponds to a shift from siliciclastic to chemical carbonate deposition as the supply of fresh surface water for example glacier meltwater ceased and was replaced by alkaline groundwater weathering of ultramafic bedrock in the region produces mg hco groundwater that concentrates by evaporation upon discharging into closed basins occupied by the playas an uppermost unit of mg carbonate sediments hydromagnesite mounds overlies the ca mg carbonate sediments this second mineralogical shift corresponds to a change in the depositional environment from subaqueous to subaerial occurring once sediments emerged from the water surface capillary action and evaporation draw mg hco water up towards the ground surface precipitating mg carbonate minerals evaporation at the water table causes precipitation of lansfordite mgco 5ho which partially cements pre existing sediments forming a hardpan as carbonate deposition continues the weight of the overlying sediments causes compaction and minor lateral movement of the mounds leading to amalgamation of localized mounds radiocarbon dating of buried vegetation at the ca mg carbonate boundary indicates that there has been ca 8000 years of continuous mg carbonate deposition at a rate of 0 4 mm yr the depositional model accounts for the many sedimentological mineralogical and geochemical processes that occur in the four surface environments elucidating past and present carbonate deposition

compositional variation and provenance of late cenozoic distal tephra beds fairbanks area alaska abstract thin fine grained discontinuous tephra beds from interior alaska can be divided into two compositional groups by their mineralogy and major and trace element glass geochemistry the source vents of these beds are unknown but are believed to be in the aleutian arc alaskan peninsula and wrangell volcanic field type i tephra has evolved trace element profiles while type ii is primitive type ii contains abundant hydrous minerals that are absent or rare in type i trace elements were used to compare the fairbanks tephra beds to volcanic rocks in the potential source areas there are very few published glass trace element analyses from these regions this necessitates comparing whole rock with glass analyses for this reason incompatible elements particularly rare earth elements are most useful whole rock analyses and petrography of lavas throughout the aleutian arc alaskan peninsula and the wrangell volcanic field are similar to type i tephra lavas and intrusive rocks similar to type ii tephra are rare and occur at one volcano in the alaskan peninsula and at three volcanoes in the wrangell volcanic field

luminescence dating of archaeological materials using a new technique based on single aliquot measurements abstract a dating method based on single aliquot luminescence dose determination was applied to quartz and feldspars from heated archaeological materials the problem of changes of sensitivity to radiation resulting from signal erasure in regeneration measurements was studied in some detail and a new method based on single aliquot regeneration measurements within an added dose framework which appears to eliminate the problem of sensitivity change is proposed preliminary dating results mainly using quartz obtained with the new method are presented

paleoceanography of the last interglacial glacial cycle in the polar north atlantic abstract using to its position close to the sites of waxing and waning of the major northern hemisphere ice sheets during the late quaternary climatic cycles the polar north atlantic plays a key role in driving global change therefore analyzing the present day sedimentation processes and reconstructing the late quaternary paleoceanography in this region has been a focus of major scientific interest through the last fifteen years this paper aims to combine the vast amount of new results about modern sediment fluxes surface sediment distribution and the paleoceanographic record and to present a comprehensive overview of the paleoceanography in the polar north atlantic through the last 200 000 years which is based on the basinwide analysis of carbonate and ice rafted detritus records during the last fifteen years the climap paleoceanographic view of the glacial polar north atlantic as an almost permanently isolated sea covered by heavy sea ice throughout the year has been shifted to a much more dynamic view of the environmental conditions a meridional current system similar to the present day conditions secured the exchange of water ice and heat between the polar north atlantic and the alantic and arctic oceans although affected by variations in strength and intensity this meridional current pattern resulted in an almost permanent presence of at least some seasonally ice free areas with all the consequences for e g marine life and deep water formation in addition the development of the continental ice sheets namely the fennoscandian and the barents sea ice sheets is closely related to this dynamic circulation pattern during the so called nordway events the pronounced inflow of temperate waters from the south provided moisture for the growth of the ice sheets the most prominent of these events stage 6 stage 4 and substage 3 1 2 ended in major glaciations reflected in the terrestrial sequences and in the deep sea ird records

holocene tephras in lake cores from northern british columbia canada sediment cores recovered from alpine and subalpine lakes up to 250 km apart in northern british columbia contain five previously unrecognized tephras two black phonolitic tephras each 5 10 mm thick occur within 2 4 cm of each other in basal sediments from seven lakes in the finlay river dease lake area the upper and lower finlay tephras are slightly older than 10 220 10 560 cal year b p and likely originate from two closely spaced eruptions of one or two large volcanoes in the northern cordilleran volcanic province the finlay tephras occur at the transition between deglacial sediments and organic rich postglacial mud in the lake cores and therefore closely delimit the termination of the fraser glaciation in northern british columbia sediments in bob quinn lake which lies on the east edge of the northern coast mountains contain two black tephras that differ in age and composition from the finlay tephras the lower bob quinn tephra is 3 4 mm thick basaltic in composition and is derived from

characterization identity distribution and source of late cenozoic tephra beds in the klondike district of the yukon canada a large number of distal silicic tephra beds have been preserved in the late cenozoic deposits of the klondike region yukon territory forty one tephra samples representing twelve distinctive beds are detailed in this study they range in composition from basaltic andesite to high silica rhyolite and were deposited during the late pliocene to late wisconsinan time interval seven tephra beds are derived from volcanoes in the wrangell volcanic field and four come from the more distant eastern aleutian arc alaska peninsula region but the source of the single andesitic tephra is unknown the widespread and well known old crow and sheep creek tephra beds have been identified in the klondike district but all the other tephra units are characterized in detail for the first time the ages of most tephra beds are poorly constrained but will undoubtedly become better known with the application of recently developed glass fission track methods hence prospects are favourable for the eventual development

sediment rich meltwater plumes and ice proximal fans at the margins of modern and ancient tidewater glaciers observations and modelling turbid meltwater plumes and ice proximal fans occur where subglacial streams reach the grounded marine margins of modern and ancient tidewater glaciers however the spacing and temporal stability of these subglacial channels is poorly understood this has significant implications for understanding the geometry and distribution of quaternary and ancient ice proximal fans that can form important aquifers and hydrocarbon reservoirs remote sensing and numerical modelling techniques are applied to the 200 km long marine margin of a svalbard ice cap austfonna to quantify turbid meltwater plume distribution and predict its temporal stability results are combined with observations from geophysical data close to the modern ice front to refine existing depositional models for ice proximal fans plumes are spaced ca 3 km apart and their distribution along the ice front is stable over decades numerical modelling also predicts the drainage pattern and meltwater discharge beneath the ice cap modelled water routing patterns are in reasonable agreement with satellite mapped plume locations however glacial retreat of several kilometres over the past 40 years has limited build up of significant ice proximal fans a single fan and moraine ridge is noted from marine geophysical surveys closer to the ice front there are smaller recessional moraines and polygonal sediment lobes but no identifiable fans schematic models of ice proximal deposits represent varying glacier terminus stability i stable terminus where meltwater sedimentation produces an ice proximal fan ii quasi stable terminus where glacier readvance pushes or thrusts up ice proximal deposits into a morainal bank and iii retreating terminus with short still stands allowing only small sediment lobes to build up at melt stream portals these modern investigations are complemented with outcrop and subsurface observations and numerical modelling of an ancient ordovician glacial system thick turbidite successions and large fans in the late ordovician suggest either high magnitude events or sustained high discharge consistent with a relatively mild palaeo glacial setting for the former north african ice sheet

ice stream retreat dynamics inferred from an assemblage of landforms in the northern barents sea abstract palaeo records of rapid ice stream retreat are important as they can be used to identify the processes involved and inform investigations of present day ice masses here we document a previously unknown retreat stage in northernmost bjornoyrenna bear island trough in the northern barents sea representing the youngest stage in a stepwise retreat of the bjornoyrenna ice stream we present a descriptive landsystem model for retreat of a marine based ice stream which provides new insights into the glacial dynamics of the episodic retreat stages this model captures the landforms produced during a cycle of 1 fast ice stream flow 2 intense calving of large icebergs locked in a dense matrix of smaller icebergs probably from a collapsed ice shelf 3 ice stream stagnation 4 ice stream floating off forming an ice shelf as the grounding line retreats and eventually 5 ice shelf disintegration we hypothesize that the presented ice stream retreat model reflects glacial surging the formation of corrugated furrows in the study area is consistent with interpretation of similar features in pine island bay west antarctica which are interpreted to have been formed during a massive ice shelf break up and associated grounding line retreat two directions of past ice flow are indicated from streamlined glacial landforms in the study area ice flow from north north east is indicated for the last glacial maximum and an early phase of deglaciation whereas a shift to flow from north north west from an ice dome located over hinlopenstretet svalbard is indicated for the latest deglaciation phases of the bjornoyrenna ice stream

tephrochronology of late cenozoic loess at fairbanks central alaska nineteen distinctive distal tephra beds from the gold hill loess in the fairbanks region central alaska are divided into two groups based on their color mineralogy glass shard morphology and the major and trace element composition of their glass shards this dichotomy in tephra composition is believed to reflect the two source regions namely the eastern aleutian arc alaska peninsula region and the wrangell volcanic field despite the fragmentary nature of the preserved loess record which contains many local unconformities these tephra beds can be used to link the numerous loess exposures in the fairbanks region in their proper time sequence establishing thereby a comprehensive reliable time stratigraphic framework because these distal tephra beds are related to large magnitude volcanic eruptions given the long distance to the nearest possible source vent they will also enable correlation of the late cenozoic sedimentary sequence at fairbanks to those of adjacent regions of alaska and the yukon tephra beds with bubble wall or chunky glass shards have been dated by the isothermal plateau fission track method results demonstrate that the gold hill loess spans a long interval of time from late pliocene time to the last interglacial about 125 ka however the age of the basal part of this formation is not well constrained due to the apparent absence of tephra beds paleomagnetic studies suggest that loess deposition in the fairbanks region began about 3 ma

the schmidt hammer as a relative age dating tool and its potential for calibrated age dating in holocene glaciated environments the schmidt hammer is a relatively cheap portable sturdy instrument with proven value over the last two decades or so in rapidly dating coarse inorganic deposits of diverse origins early views were that its dating role was limited to distinguishing recently exposed from much older typically either a few sites of possibly different ages or occasional older surfaces amongst many young sites were studied more recently calibration curves based on individual r value means from small numbers 2 4 of sites of known ages have been used to estimate the ages of undated sites we present schmidt hammer rebound r values from 28 little ice age and younger 23 preboreal and 7 younger dryas glaciated surfaces in southern norway in order first to test rigorously the robustness of the instrument as a relative age dating tool despite being obtained from different surfaces moraines glaciofluvial deposits and bedrock and varied metamorphic lithologies the r value overall means and 95 confidence intervals for the little ice age preboreal and younger dryas age categories respectively 60 0 1 6 41 6 1 4 and 34 2 2 0 are statistically significantly different only two outlying sites in the two younger age categories have overlapping confidence intervals demonstrating remarkable robustness in differentiating early and late holocene surfaces the distinction between preboreal and younger dryas sites with terminal dates 2000 years apart is less clear but still statistically significant though possibly partly because of enhanced weathering conditions at the predominantly well vegetated younger dryas sites second we examine the feasibility and desirability of controlling non age related factors including some previously considered critical instrument wear operator bias initial rock surface texture which emerge either as less important than previously argued or as relatively unimportant together with others previously unreported e g long term changes in lichen soil snow and vegetation covers third we investigate the potential for calibrated age dating by applying exploratory linear rates of r value decline to selected combinations of sites the results suggest that error limits of ca 700 to 1600 years should be achievable over the holocene timescale this improved dating capability however will require adequate numbers of site means not only for each age category used to define these curves but also for each set of test surfaces of the same ages recommendations are made for a suitable sampling protocol for developing further the schmidt hammer as a calibrated age dating tool

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

the formation of a geometrical ridge network by the surge type glacier kongsvegen svalbard traditionally geometrical ridge networks are interpreted as the product of the flow of subglacial sediment into open basal crevasses at the cessation of a glacier surge crevasse fill ridges they are widely regarded as a characteristic landform of glacier surges understanding the range of processes by which these ridge networks form is therefore of importance in the recognition of palaeosurges within the landform record the geometrical ridge network at the surge type glacier kongsvegen in svalbard does not form by crevasse filling the networks consist of transverse and longitudinal ridges that can be seen forming at the current ice margin the transverse ridges form as a result of the incorporation of basal debris along thrust planes within the ice the thrusts were apparently formed during a glacier surge in 1948 longitudinal ridges form through the meltout of elongated pods of debris which on the glacier surface are subparallel to the ice foliation and pre date the surge this work adds to the range of landforms associated with glacier surges

sea floor morphology outside a grounded surging glacier brasvellbreen svalbard abstract acoustical profiling and bottom photography reveal several different sea floor morphological features adjacent to the grounded brasvellbreen glacier on svalbard northwestern barents sea some of the features and their distribution may be closely related to a major glacial surge in 1936 1938 and as such are valuable in identifying former surges in other locations a continuous wide ridge with a characteristic asymmetrical cross section running subparallel to the glacier is the end moraine defining the maximum extent of the surge a large part of the material forming this ridge is most likely rapidly deposited from meltwater during the surge a rhombohedral pattern of smaller mounds inside the ridge is probably an expression of relief in the glacier sole during the surge discontinuous arcuate ridges define local minor oscillations during retreat of the ice at a later stage iceberg plough marks are most frequent seaward of the end moraine their orientation is controlled by the combination of a coastal current offshore katabatic winds and topography superimposed on plough marks are secondary features such as a washboard pattern and striae most likely caused by push up of overconsolidated material during gouging and multi keel icebergs respectively bottom sediments observed in photographs and cores are loose pebbly muds with high variability in clast content resting on overconsolidated material probably basal till mud deposition presently prevails close to the glacier

history of a stable ice margin east greenland during the middle and upper pleistocene abstract the east greenland record of glaciation and environmental change is based on a combination of onshore and offshore studies glaciological work on contemporary outlet glaciers provides background for interpreting the glaciation styles of the past the scoresby sund fjord system the single largest outlet of the inland ice in east greenland and the adjacent continental shelf and slope were the main working areas the regionality of these results was tested with onshore and offshore work on sites further to the north in the east greenland fjord zone the record spans the period since isotope stage 7 ca 240 ka the most extensive glaciation phases were the lollandselv and scoresby sund glaciations isotope stages 7 and 6 the langelandselv interglaciation isotope substage 5e comprises shallow marine sediments at more than 20 sites onshore and cibicides wuellerstorfii carrying sediments on the continental slope summer temperatures were 2 3 warmer than the holocene optimum and there was vigorous advection of warm atlantic water into the fjords the warm period seems to be accompanied by a eustatic sea level rise of ca 20 m during the weichselian there were three major glacier advances the aucellaelv jyllandselv and flakkerhuk stades isotope substages 5d 5b and stages 3 2 all three advances mark a shift from one topographically determined stable position to another in each phase the glaciers occupied almost the same space in the fjord basins and had their fronts on the inner shelf but the glacial regime and duration was different the aucellaelv stade lasted ca 10 ka and the regime resembled that of present day outlet glaciers 600 km further to the north the flakkerhuk stade lasted for ca 50 ka but left only thin and sporadic till as well as glaciolacustrine sediments in ice dammed river valleys the regime was polar similar to present day glaciers in antarctica its culmination the last glacial maximum in the period between 22 and 14 ka is shown by a maximum in ird deposition on the continental slope after 12 ka and before 10 ka the outer fjord basins in the southern fjord zone had been abandoned by the glaciers and at ca 9 5 ka the last resurgence the milne land stade had ended

glaciofluvial crevasse and conduit fills as indicators of supraglacial dewatering during a surge skeiðararjokull iceland

distribution nature and origin of neogene quaternary magmatism in the northern cordilleran volcanic province canada the northern cordilleran volcanic province encompasses a broad area of neogene to quaternary volcanism in northwestern british columbia the yukon territory and adjacent eastern alaska volcanic rocks of the northern cordilleran volcanic province range in age from 20 ma to ca 200 yr b p and are dominantly alkali olivine basalt and hawaiite a variety of more strongly alkaline rock types not commonly found in the north american cordillera are locally abundant in the northern cordilleran volcanic province these include nephelinite basanite and peralkaline phonolite trachyte and comendite the most mgo rich nephelinites basanites and alkaline basalts from throughout the northern cordilleran volcanic province show trace element abundances and isotopic compositions that are consistent with an asthenospheric source region similar to that for average oceanic island basalt and for post 5 ma alkaline basalts from the basin and range our petrologic observations help constrain the origin of northern cordilleran volcanic province magmatism as well as lithosphere changes between the four major basement terranes that underlie the province results from phase equilibria calculations and the spatial distributions of volcanic rock types and magmatic inclusions are more consistent with the existence of thicker lithosphere beneath stikinia which underlies the southern part of the northern cordilleran volcanic province than beneath the cache creek and yukon tanana terranes which underlie the northern part of the northern cordilleran volcanic province our results support a model for initiation of northern cordilleran volcanic province magmatism due to incipient rifting of the northern cordillera driven by changes in relative plate motion between the pacific and north american plates ca 15 10 ma

nivation forms and processes in unconsolidated sediments ne greenland in the periglacial unconsolidated sediment landscape of zackenberg in high arctic ne greenland perennial and seasonal snowpatches dominate the geomorphological development in large areas and control the distribution of the vegetation the existence and distribution of snowpatches and their associated landforms are mainly controlled by the dominating winter wind direction and the amount of snow precipitation with aspect exerting much less influence this makes them an important source of information on past environmental change and knowledge of the combination of geomorphological processes and forms that result from their existence is thus essential the main nivation processes are backwall failure sliding and flow niveo aeolian sediment transport supra and ennival sediment flows niveo fluvial erosion development of pronival stone pavements accumulation of alluvial fans and basins and pronival solifluction the importance of failure sliding and flow in the continuous retrogressive extension of nivation hollows and niches is emphasized under the term backwall failure a morphological assemblage of landforms clearly demonstrates the direct nival sediment transfer link between the eroded nivation hollows their associated meltwater eroded channels and the pronival alluvial fans or basins all landform elements and their formative processes are integrated into a comprehensive model 1998 john wiley sons ltd

sedimentary facies and depositional architecture of ice contact glaciomarine systems abstract the characteristics of ice contact glaciomarine systems are reviewed based on a range of weichselian and holocene examples from the fjordal basins in norway and svalbard these depositional systems occur as large morphological ridges end moraines including push moraines which are coarse grained and show large scale foreset bedding the paper addresses some of the major problems with regard to the recognition classification and stratigraphic analysis of these systems the ice proximal glaciomarine systems are classified here into three categories 1 ice contact submarine fans 2 ice contact deltas and 3 glaciofluvial deltas this classification integrates morphological and sedimentological criteria and renders these glaciomarine systems not only easier to recognize in the stratigraphic record but also possible to compare with common non glacial deltaic systems the emphasis is on the criteria for the recognition of the ice contact glaciomarine systems i e ice contact fans and ice contact deltas and their discrimination from common gilbert type deltas and fan deltas the review further focuses on ice contact glaciomarine systems as highly sensitive recorders of glacier dynamics and climatic fluctuations it is shown that both the periods of ice front stability and changes in the ice front position as well as the magnitude and rate of those changes are all recorded in the ice contact depositional system the sedimentary record further reflects glacio isostatic sea level changes and local palaeogeography a new conceptual model is suggested which places these ice contact glaciomarine systems in a dynamic stratigraphic context the model integrates sedimentary facies and their depositional architecture in an allostratigraphic framework and is meant to be a guide for the analysis of the sedimentary record of ice contact systems

deglaciation chronology sea level changes and environmental changes from holocene lake sediments of germania havn so sabine o northeast greenland abstract germania havn so is located at the outermost coast of northeastern greenland according to radiocarbon dating the lake basin was deglaciated in the early holocene around 11 000 cal yr bp at that time the lake was a marine bay but the lake was isolated soon after deglaciation at 10 600 cal yr bp the marine fauna was species poor indicating harsh conditions with a high sedimentation rate and lowered salinity due to glacial meltwater supply the pioneer vegetation around the lake was dominated by mosses and herbs deposition of relatively coarse sediments during the early holocene indicates erosion of the newly deglaciated terrain remains of the first woody plant salix herbacea appear at 7600 cal yr bp and remains of other woody plants salix arctica dryas octopetala cassiope tetragona and empetrum nigrum appear around one millennium later declining concentrations of d octopetala and the caddis fly apatania zonella in the late holocene probably imply falling summer temperatures only moderate changes in the granulometric and geochemical record during the holocene indicate relatively stable environmental settings in the lake which can probably be explained by its location at the outer coast and the buffering effect of the neighboring ocean

submarine landforms and glacimarine sedimentary processes in lomfjorden east spitsbergen understanding the role of fjords in modulating the long term interaction between ice sheets and glaciers with the surrounding ocean requires the investigation of glacigenic landform and sediment archives in svalbard there is a wealth of data from fjords in west spitsbergen that constrains the glacial history of this sector of the svalbard barents sea ice sheet sbis since the last glacial maximum lgm and the nature and timing of subsequent ice retreat in contrast however very little is known about the glacial history of fjords in east spitsbergen this paper combines multibeam swath bathymetry sub bottom profiles lithological data and radiocarbon dates from lomfjorden svalbard to provide the first insights into the dynamics of tidewater glaciers and associated glacimarine sedimentary processes in a northeast spitsbergen fjord at the lgm a fast flowing ice stream drained the sbis through lomfjorden serving as a tributary to a south north flowing ice stream in hinlopenstretet ice advance is recorded by streamlined bedrock glacial lineations and drumlins a radiocarbon date of 9 7 ka bp from the outer fjord provides a minimum date for retreat of this ice stream and suggests that lomfjorden was ice free earlier than fjords in west spitsbergen ice retreat occurred in a slow and step wise manner indicated by the presence of recessional moraines and de geer moraines by 4 5 ka bp the local tidewater glaciers had probably retreated inland of their present positions the limited extent of glacigenic landform assemblages in front of these glaciers implies that any holocene re advances were probably restricted the principal sedimentary processes during deglaciation were suspension settling from meltwater causing deposition of weakly stratified bioturbated mud in ice distal settings at rates of 0 02 0 08 cm a 1 and gravitational mass flows forming sandy turbidites in ice proximal areas iceberg ploughmarks and ice rafted debris provide evidence for the presence of large icebergs during deglaciation our data suggest an early and extensive deglaciation in east spitsbergen fjords and show that previous reconstructions of the extent of the sbis need to be revised as new data emerges from east spitsbergen the data confirm that tidewater glaciers from different regions of spitsbergen behaved differently since the lgm and that variations in landform sediment assemblages occur even within geographically adjacent fjords

mount churchill alaska source of the late holocene white river ash although the white river ash was first recognized by f schwatka in 1883 the source of this widespread bilobate plinian deposit in northwestern canada and adjoining eastern alaska has not been definitively identified recent investigations disclose that mount churchill in the st elias mountains of south central alaska contains a summit crater whose rim is chiefly composed of ash coarse pumice and exotic rock fragments the pumice clasts decrease in size and the exotic rock fragments disappear with increasing distance from the summit area pumice from the mount churchill summit and from the white river ash deposits up to 25 km from the summit area are mineralogically and chemically similar microprobe analyses of the summit pumice glass are virtually identical to those of more distant proximal white river ash glass fe ti oxide compositions in the mount churchill proximal tephra indicate that all tephra sampled during this study is from the younger eastern lobe of the white river ash these field

response of the high latitude northern hemisphere to orbital climate forcing evidence from the nordic seas sediment cores from the nordic greenland iceland and norwegian seas provide evidence that this area acts as an initial responder to the forcing effect of orbitally driven changes in insolation on the climate system as postulated by j imbrie et al the 18 o record of the cores documents a widespread initial deglacial signal in the area between 15 and 13 ka 1000 yr before other deglacial signals from other parts of the northern hemisphere an even earlier meltwater event has been dated to 16 090 185 yr b p north of iceland at the initial rise of northern hemisphere insolation after the last glacial maximum during the period with lowered surface salinities the nordic seas were still cold reconstructions of the surface water conditions of the area show that as the summer insolation values of the northern hemisphere reached half of maximum values a sea ice free corridor opened along norway at 13 4 ka nearly contemporaneous fluctuations of the polar front and the sea surface temperatures with the insolation changes indicate that the nordic seas are very sensitive to insolation forcing especially in regions close to the sea ice margin a decrease in sea surface temperature and an increase in the areal extent of sea ice cover since 7 ka indicate that the area is currently on the way to glacial conditions supporting the predictions made earlier by j imbrie et al

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

the schmidt hammer as a holocene calibrated age dating technique testing the form of the r value age relationship and defining the predicted age errors most recent developments of schmidt hammer exposure age dating shd as a calibrated age dating tool have been limited by the use of locations at two age control points this has necessitated 1 making assumptions about a linear r value age relationship and 2 basing predictions of age errors only on r value variance at the two age control points this paper analyses 9900 r values obtained from multiple age control points on a sequence of glacio isostatically raised shorelines with well constrained ages skuleskogen high coast world heritage site and environs gulf of bothnia northern sweden ranging from modern to 10 5 ka in age the sampling design involved 30 measurements on granite beach boulders from 30 sites at 11 age control points the r value age relationship is best described by a linear function ordinary least squares ols with an r 2 of 0 89 p 0 0001 predicted age errors are calculated using two approaches 1 ols regression which takes account of the uncertainties associated with the regression line and the age control points and 2 weighted total least squares wtls regression which in addition takes account of possible shoreline age errors and the heteroscedasticity of r value residuals with increasing age with both approaches 95 predicted age errors are relatively modest 355 455 years and 300 515 years respectively with larger r value variance and hence uncertainty for older surfaces and the possibility of further improvement from a more selective field sampling scheme that differentiates between age related and non age related rock surface variability our results also indicate that for certain lithologies and weathering environments it is possible to construct reliable calibrated age curves from relatively few age control points

an assessment of surge induced crevassing and the formation of crevasse squeeze ridges 1 evidence for extensive crevassing is preserved on the deglaciated forelands of many surging glaciers as crevasse squeeze ridges csrs at some point these crevasses make direct connection with the bed in order to become sediment filled and full depth connections have been inferred from turbid water up wellings in crevasses and the formation of concertina eskers the dynamics of seven surging glaciers are assessed using a linear elastic fracture mechanics approach to determine the likely directions of fracture and controlling parameters for mode i crevasses extensional surface strain rates are insufficient to promote top down full depth penetration for small crevasse spacing 5 m surface strain rates are sufficient for top down crevassing to depths of 4 12 m explaining the extensive surface crevassing associated with glacier surging as has been shown in other settings top down full depth crevassing is only possible when water is added and approaches 97 of the crevasse depth the provision of sufficient meltwater to facilitate this is problematic due to the extensive surface crevassing unless water can move along connected crevasses to a dominant water capturing crevasse for ice thicknesses greater than 200 m basal water pressures in excess of 80 90 of flotation are required for full depth bottom up crevassing field evidence suggests that this is the default for surging glaciers and that on occasion water pressures may even become artesian csrs found across many surging glacier forelands and ice margins most likely result from the infilling of basal crevasses driven for the most part bottom up by high basal water pressures

new dates on late pleistocene dacitic tephra from the mount edgecumbe volcanic field southeastern alaska new radiocarbon dates on charcoal incorporated in proximal airfall deposits indicate the largest late pleistocene eruption from the mt edgecumbe volcanic field in southeast alaska occurred ca 11 250 5014c yr b p the more precise dating of the principal edgecumbe tephra layer greatly improves its utility as a tephrochronologic marker horizon in southeastern alaska

advance of alpine glaciers during final retreat of the cordilleran ice sheet in the finlay river area northern british columbia canada abstract sharp crested moraines up to 120 m high and 9 km beyond little ice age glacier limits record a late pleistocene advance of alpine glaciers in the finlay river area in northern british columbia the moraines are regional in extent and record climatic deterioration near the end of the last glaciation several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern cordilleran ice sheet other lateral moraines merge with ice stagnation deposits in trunk valleys these relationships confirm the interaction of advancing alpine glaciers with the regionally decaying cordilleran ice sheet and verify a late glacial age for the moraines sediment cores were collected from eight lakes dammed by the moraines two tephras occur in basal sediments of five lakes demonstrating that the moraines are the same age plant macrofossils from sediment cores provide a minimum limiting age of 10 550 10 250 cal yr bp 9230 50 14c yr bp for abandonment of the moraines the advance that left the moraines may date to the younger dryas period the finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late glacial glacier advances

a model of greenland ice sheet deglaciation constrained by observations of relative sea level and ice extent an ice sheet model was constrained to reconstruct the evolution of the greenland ice sheet gris from the last glacial maximum lgm to present to improve our understanding of its response to climate change the study involved applying a glaciological model in series with a glacial isostatic adjustment and relative sea level rsl model the model reconstruction builds upon the work of simpson et al 2009 through four main extensions 1 a larger constraint database consisting of rsl and ice extent data model improvements to the 2 climate and 3 sea level forcing components 4 accounting for uncertainties in non greenland ice the research was conducted primarily to address data model misfits and to quantify inherent model uncertainties with the earth structure and non greenland ice our new model termed huy3 fits the majority of observations and is characterised by a number of defining features during the lgm the ice sheet had an excess of 4 7 m ice equivalent sea level iesl which reached a maximum volume of 5 1 m iesl at 16 5 cal ka bp modelled retreat of ice from the continental shelf progressed at different rates and timings in different sectors southwest and southeast greenland began to retreat from the continental shelf by 16 to 14 cal ka bp thus responding in part to the bolling allerod warm event c 14 5 cal ka bp subsequently ice at the southern tip of greenland readvanced during the younger dryas cold event in northern greenland the ice retreated rapidly from the continental shelf upon the climatic recovery out of the younger dryas to present day conditions upon entering the holocene 11 7 cal ka bp the ice sheet soon became land based during the holocene thermal maximum htm 9 5 cal ka bp air temperatures across greenland were marginally higher than those at present and the gris margin retreated inland of its present day southwest position by 40 60 km at 4 cal ka bp which produced a deficit volume of 0 16 m iesl relative to present in response to the htm warmth our optimal model reconstruction lost mass at a maximum centennial rate of c 103 4 gt yr our results suggest that remaining data model discrepancies are affiliated with missing physics and sub grid processes of the glaciological model uncertainties in the climate forcing lateral earth structure and non greenland ice particularly the north american component finally applying the huy3 greenland reconstruction with our optimal earth model we generate present day uplift rates across greenland due to past changes in the ocean and ice loads with explicit error bars due to uncertainties in the earth structure present day uplift rates due to past changes are spatially variable and range from 3 5 to 7 mm a including earth model uncertainty

subglacial imprints associated with the isolation and decay of an ice mass in the lower lough erne basin co fermanagh nw ireland high resolution chirp sub bottom profiler and side scan sonar data record the final phases of ice margin activity in the lower lough erne basin at the end of the last cycle of quaternary glaciations in ireland relative to the terrestrial glacial landforms the features in the lough are smaller in scale and are considered to represent local ice mass dynamics that followed regional scale events four phases are identified 1 after the last ice sheet wide readvance associated with the killard point stadial between 15 0 and 14 1 14 c ka bp stagnation zone retreat resulted in isolation of a residual ice block in the lower lough erne basin 2 proglacial waters developed coeval with retreat of the western margin of the ice block drawdown induced localized surging and the generation of push features and lineations 3 squeeze up features reflecting a heavily crevassed ice margin mark the quiescent phase of the local surge cycle 4 iceberg grounding pits and keel marks record calving and rapid disintegration of the lough erne ice margin the well preserved glacigenic features observed in the lake basin suggest formation by a succession of mechanisms that were too short lived to obliterate the underlying evidence of ice margin dynamics

subglacial meltwater discharge in the open marine tidewater glacier environment observations from nordaustlandet svalbard archipelago the ice proximal environment of the nordaustlandet tidewater ice cap svalbard archipelago is one of the best analogues for understanding glacial geologic processes of northern continental shelves during initial pleistocene deglaciation investigations of the proglacial region in 1980 1983 showed that the sedimentary environment is dominated by numerous meltwater outflows which discharge sediment laden water from subglacial meltwater streams during the summer two large stable meltwater outflows were observed in embayments along the southern part of the ice front landsat images show that both outflows have been in approximately the same position since at least 1976 they are located at the intersection of glacial drainage basins and centered over depressions in the underlying bedrock an outflow valley extending away from the ice front was observed in front of the western meltwater outflow sidescan sonar profiling along the glacier front showed a 200 m wide gap in acoustic reflection at the base of the western meltwater outflow probably caused by meltwater effluence enhanced sediment accumulations in this region observed as a 3 ms sediment drape in front of the outflow and large arcuate ridges in the outflow valley testify to the transport efficiency of the subglacial meltwater stream several mounds up to about 25 m high and 200 m wide are observed on sidescan and 3 5 khz profiles directly in front of the outflow although samples from these structures are absent they are most likely composed of sediment and are similar to beaded eskers observed in pleistocene glacimarine sequences indicating locally very high sedimentation rates fine grained components of the subglacial discharge incorporated in the buoyant meltwater plume are usually entrained in a westerly coastal current elevated suspended particulate material concentrations are observed within the coastal waters in a region extending about 15 km perpendicular to the glacier front and at least 60 km along the ice front extending into the northwestern barents sea

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

a continuous 5300 yr holocene cryptotephrostratigraphic record from northern new zealand and implications for tephrochronology and volcanic hazard assessment a continuous 5280 calendar cal yr long cryptotephrostratigraphic record of a peat core from northern new zealand demonstrates that cryptotephra studies can enhance conventional tephra records by extending the known distribution of ash fall and enabling re assessment of volcanic hazards a systematic sampling strategy was used to locate peaks in glass shard concentrations and to determine loci of individual geochemical populations and a palynological method involving spiking samples with lycopodium spores was adapted to facilitate accurate counting of glass shard concentrations using glass shard major element compositions and a core chronology based on eight ams 14c ages and two visible macroscopic tephra layers taupo tephra unit y 1688 1748 cal bp and tuhua tephra 6800 7230 cal bp 2cr age ranges four cryptotephras were correlated with known eruptions whakaipo unit v 2743 2782 cal bp stent unit q 4240 4510 cal bp and unit k 4970 5290 cal bp erupted from taupo volcanic ce

late pleistocene and holocene tephrostratigraphy of interior alaska and yukon key beds and chronologies over the past 30 000 years abstract the aleutian arc alaska peninsula and wrangell volcanic field are the main source areas for tephra deposits found across alaska and northern canada and increasingly tephra from these eruptions have been found further afield in north america greenland and europe however there have been no broad scale reviews of the late pleistocene and holocene tephrostratigraphy for this region since the 1980s and this lack of data is hindering progress in identifying these tephra both locally and regionally to address this gap and the variable quality of associated geochemical and chronological data we undertake a detailed review of the latest pleistocene to holocene tephra found in interior alaska and yukon this paper discusses nineteen tephra that have distributions beyond southwest alaska and that have the potential to become or already are important regional markers this includes three modern events from the 20th century ten with limited data availability but potentially broad distributions and six that are widely reported in interior alaska and yukon each tephra is assessed in terms of chronology geochemistry and distribution with new bayesian age estimates and geochemical data when possible this includes new major element geochemical data for crater peak 1992 redoubt 1989 90 and two andesitic tephra from st michael island tephra d as well as revised age estimates for dawson tephra oshetna hayes set h aniakchak cfe ii and the white river ashes northern and eastern lobes

sinking of volcanic ash in uncompacted sediment in williams lake washington volcanic ash from the eruption of mount st helens on 18 may 1980 fell into williams lake in eastern washington and was temporarily suspended at the sediment water interface after several months of compaction the ash layer broke up and sank into lower density uncompacted lake sediment stratigraphic time displacements of several hundred years and a failure to recognize discontinuous ash layers in sediment cores are possible consequences of this process

little ice age nivation activity in northeast greenland during the little ice age lia the periglacial landscape in northeast greenland responded rela tively quickly to the climatic deterioration with increased nivation activity resulting nivation landforms and associated sediment basins are used as palaeoclimatic archives documenting the significant geomorphological effect of nivation during the lia period in the zackenberg area a nival basin studied in detail showed the onset and dominance of niveo fluvial sedimentation in the period ad 1250 1420 followed by increasing niveo aeolian sedimentation between ad 1420 1500 1580 finally very rapid niveo aeolian sedimentation prevailed during the period ad 1500 1580 1690 in the same period some large nival fans accumulated in the zackenberg lowland as a result of increased niveo fluvial activity and niveo fluvial sediments were also deposited in pre existing fluvial valleys demonstrating the large areal extension of the nivation activity the chronology is based on nine ams 14c determinations the inte

improved age estimates for the white river and bridge river tephras western canada new 14c ages date the eruptions that produced the white river and bridge river tephras two important holocene marker beds in western canada the 14c ages were obtained on trees in growth position buried in coarse tephra and a pyroclastic flow near the source vents the mean calendric age of the white river eruption based on four 14c ages is 1147 cal years bp calibrated years approximately equivalent to calendric years or ad 803 the 2 age range obtained from the two most precise 14c ages is 1014 1256 cal years bp or ad 694 936 the mean age of the bridge river eruption determined both from i the single most precise outer ring 14c age and ii the weighted mean of six outer ring 14c ages is 2360 cal years bp or 411 bc 2 age range 2349 2704 cal years bp or 755 400 bc

till and moraine emplacement in a deforming bed surge an example from a marine environment the glacier sefstrombreen in spitsbergen surged across an arm of the sea between qsr 1882 and 1886 and rode up onto the island coraholmen marine and terrestrial geological observations and archive records show that the glacier advanced on a deforming carpet of marine mud which was eroded from its original location transported and smeared over the sea bed and coraholmen as a deformation till the glacier emplaced about 210sm 0 2 km 3 of drift in the terminal 2 km of its advance in a maximum of 14 years leaving a thickness of up to 20 m on coraholmen which was doubled in size as a result during the surge subglacial muds were characterised by high water pressures low effective pressures and low frictional resistance to glacier movement original sedimentary inhomogenities permit fold structures to be identified but repeated refolding and progressive remoulding produce mixing and homogenisation of deformation tills the surge was probably shortlived and as the heavily crevassed glacier stagnated underlying water saturated muds were intruded into crevasses and then extruded on the glacier surface reticulate crevasse intrusion ridges on coraholmen and the sea floor reflect the orientation of surge generated crevasses water and sediment was also extruded beyond the glacier at its maximum extent to form extensive flows producing till tongues both on coraholmen and the sea floor extending over 1 3 km from the glacier it is argued that subglacial deformation of pre existing sediment will almost invariably be associated with glaciation of marine areas and that this process will not only produce deformation tills through remoulding of pre existing sediments but will also play a fundamental role in glacier dynamics criteria which perrait glacial tills produced by such events from marine and glaciomarine muds are discussed copyright 1996 elsevier science ltd