investigating the glacial history of the northern sector of the cordilleran ice sheet with cosmogenic 10be concentrations in quartz exposure durations of glacial landforms in widely separated areas of central yukon territory affected by the northern sector of the cordilleran ice sheet cis and alpine glaciers have been determined using cosmogenic 10be in quartz the aim of our research is to test previous reconstructions of glacial history and to begin to address the paucity of chronological control for the lateral and vertical extent of the northern cis chronological evidence for cis expansion predating the last glacial maximum comes from minimum surface exposure durations of c 100 ka for two bedrock samples within the reid glacial limit indicating a possible marine oxygen isotope stage ois 6 age for this event and from minimum exposure durations of about 40 ka for boulders on moraines constructed by alpine glaciers on a nunatak within the mcconnell glacial limit ois 2 indicating a possible ois 4 age high elevation minimum surface exposure durations within the mcconnell limit indicate that some areas formerly mapped as nunataks were covered by cold based ice prior to 30 ka montane glaciation in the mackenzie mountains outside the mcconnell glacial limit was contemporaneous with nearby cis advance at 17 ka with cis retreat by 15 ka deglaciation of the tintina trench a major ice discharge route was completed by 12 ka at this time ice in an adjacent discharge route to the south was still entering higher elevation valleys in the pelly mountains a lateglacial readvance may have peaked at ca 10 ka in the ogilvie mountains considerable variation in ages from individual landforms and possible complex histories require additional cosmogenic nuclide measurements to confirm interpretations

cosmogenic 10be and 26al exposure ages of tors and erratics cairngorm mountains scotland timescales for the development of a classic landscape of selective linear glacial erosion abstract the occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre quaternary landscapes beneath protective covers of non erosive dry based ice here we test for the preservation of pre quaternary landscapes with cosmogenic surface exposure dating of tors numerous granite tors are present on summit plateaus in the cairngorm mountains of scotland where they were covered by local ice caps many times during the pleistocene cosmogenic 10be and 26al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected many cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides as the surfaces have been subject to episodic burial by ice an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data exposure ages and weathering characteristics of tors are closely correlated glacially modified tors and boulder erratics with slightly weathered surfaces have 10be exposure ages of about 15 to 43 ka nuclide inheritance is present in many of these surfaces correction for inheritance indicates that the eastern cairngorms were deglaciated at 15 6 0 9 ka glacially modified tors with moderate to advanced weathering features have 10be exposure ages of 19 to 92 ka these surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine oxygen isotope stage 5 or earlier tors lacking evidence of glacial modification and exhibiting advanced weathering have 10be exposure ages between 52 and 297 ka nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events maximum erosion rates estimated from 10be range from 2 8 to 12 0 mm ka with an error weighted mean of 4 1 0 2 mm ka three of these surfaces yield model exposure plus burial ages of 295 71 84 520 141 178 and 626 85 102 ka a vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long term emergence rate of 31 2 mm ka these findings show that dry based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous too old exposure ages while many cairngorm tors have survived multiple glacial cycles rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre quaternary rock surfaces

in situ 10be exposure ages from southeastern norway implications for the geometry of the weichselian scandinavian ice sheet abstract as an initial attempt to constrain the geometry and history of the southern part of the scandinavian ice sheet in situ 10 be concentrations in bedrock samples have been measured from four sites in southeastern norway among our results are a number of pre last glacial maximum lgm exposure ages bedrock outcrops in high elevation blockfields typically give surface exposure ages older than 20 10 be ka whereas glacially moulded bedrock surfaces at lower elevations yield surface exposure ages younger than 15 10 be ka these results clearly indicate the preservation of surfaces and landforms predating the lgm most ice sheet models predict a thick ice mass in southeastern norway at the lgm pre lgm 10 be ages either contradict the models supporting geomorphological reconstructions of a thin lgm ice sheet or indicate preservation of previously exposed surfaces beneath cold based ice in the latter case models of 10 be production incorporating regional glacial chronology and periodic burial suggest that the surfaces with the highest 10 be concentrations may have existed for more than one million years

the cryptotephra record of the marine isotope stage 12 to 10 interval 460 335 ka at tenaghi philippon greece exploring chronological markers for the middle pleistocene of the mediterranean region abstract precise chronologies that allow direct correlation of paleoclimate archives are a prerequisite for deciphering the spatiotemporal characteristics of short term climate variability such chronologies can be established through the analysis of tephra layers that are preserved in the respective sedimentary archives here we explore the yet untapped tephrochronological potential of the eastern mediterranean region for the middle pleistocene specifically for the interval spanning marine isotope stages mis 12 10 460 335 ka high resolution cryptotephra analysis was carried out on peat cores spanning the mis 12 10 interval that have been recovered from the iconic climate archive of tenaghi philippon ne greece eighteen primary cryptotephras were identified and major and trace element analyses of single glass shards from all cryptotephras were performed in order to correlate them with their eruptive sources the results suggest origins from both italian and aegean arc volcanoes specifically one cryptotephra layer could be firmly correlated with the cape therma 1 eruption from santorini which makes it the first distal tephra finding for this eruptive event while eight further cryptotephras could be tentatively correlated with their volcanic or even eruptive sources the provenance of another nine cryptotephras as yet remains unknown the relatively large number of cryptotephras that could not be assigned to specific volcanic sources and eruptive events reflects the still considerable knowledge gap regarding the geochronology and geochemistry of proximal tephra deposits from the middle pleistocene of the central and eastern mediterranean regions due to the lack of well dated middle pleistocene eruptions we provide age estimates for all cryptotephra layers identified in the mis 12 10 interval at tenaghi philippon based on high resolution pollen data from the same cores while eight of the identified cryptotephras were deposited within mis 12 438 427 ka one cryptotephra was deposited at the onset of mis 11 419 ka five cryptotephras during the younger part of mis 11 391 367 ka and four cryptotephras during mis 10 359 336 ka the high number of cryptotephras from multiple sources as recorded in the mis 12 10 interval at tenaghi philippon highlights the key role of this archive for linking tephrostratigraphic lattices for the middle pleistocene of the central and eastern mediterranean regions

relict non glacial surfaces in formerly glaciated landscapes abstract relict non glacial surfaces occur within many formerly glaciated landscapes and contain important information on past surface processes and long term landscape evolution relict non glacial surfaces are distinguishable from glacial surfaces by large scale morphologies including rounded summits fluvial valleys and cryoplanation terraces and pediments and the presence of tors blockfields and or saprolites preservation during glaciation occurs either through coverage by non erosive cold based ice or as nunataks although surface morphologies and denudation rates indicate a continuous non glacial surface history since preglacial times relict non glacial surfaces are dynamic features that have evolved during the quaternary depending on spatial variables such as lithology slope regolith depth and the abundance of fine matrix and water some surfaces are denuding very slowly while others display more rapid denudation high spatial variability in denudation rates results in changing surface morphologies over time denudation rates also display high temporal variability with much surface evolution having perhaps occurred soon after the initial onset of glaciation or during paraglacial phases while some parts of non glacial landscapes are currently active others may be largely inactive relicts of past higher energy regimes although non glacial surfaces are dynamic much remains to be determined regarding surface denudation rates and the magnitude of morphological changes over time

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

the terrestrial end permian mass extinction in south china abstract the end permian mass extinction reflects the most severe life crisis during the phanerozoic and was associated with major global environmental changes however the consistency of the time and pattern of the terrestrial and marine extinctions remains controversial in this paper we presented detailed analyses of the high resolution biostratigraphical and geochemical data from terrestrial sections in south china our analyses show that the transitional kayitou formation actually recorded the process of terrestrial mass extinction as evidenced by the mass disappearance of the gigantopteris megaflora in the lower part the dramatic reduction in abundance of palynomorphs in the middle and the last occurrences of plant remains and abundant charcoal fossils in the uppermost part it is associated with a distinct negative shift of 13corg beginning in the middle part of the formation which is correlative with that in the top of bed 26 at the marine meishan section in addition the kayitou formation is characterized by a distinct shift of lithofacies of fresh lake swamp or river flat environment from olive grey black mudstone siltstone fine to coarse sandstone in the lower part to gradually increasing maroon rocks to purely maroon mudrocks with poorly sorted breccia calcic palaeosols and calcareous nodules in the lowest part of the dongchuan formation which indicates a dramatic collapse of soil system associated with rapid deforestation and climatic warming and drying in the coastal area the kayitou formation contains marine beds with the typical permian triassic mixed faunas and floras which are correlative with the latest changhsingian marine mixed fauna 1 at meishan the kayitou formation also recorded a distinct transgression that began in the latest changhsingian all above phenomena suggest that the kayitou formation is actually the witness of the terrestrial end permian mass extinction and it is mostly or entirely of latest changhsingian permian rather than triassic age

occurrence stratigraphy and geochemistry of late quaternary tephra layers in the aegean sea and the marmara sea abstract several discrete tephra layers occur in 2 5 10 3 m long cores from the aegean sea whereas a single tephra is identified in 3 5 9 7 m long cores from the marmara sea major and trace element data on these tephras delineate eight distinct groups the geochemical data and multivariate statistics allow the correlation of the tephra layers with six previously described marine tephras from the eastern mediterranean sea potential terrestrial sources are suggested for the others the chronostratigraphy of the tephra layers was established using several radiocarbon dates and the oxygen isotope stratigraphy from two long piston cores four widespread tephra layers occur within the upper quaternary sediments of the aegean sea the two youngest widespread tephra layers were derived from the santorini volcano of south central aegean sea z2 the minoan eruption ca 3 6 ka and y2 the cape riva eruption ca 21 7 ka the y2 tephra is also identified in three piston cores from the marmara sea the two older widespread tephra layers originated from the eruptions which emplaced the campanian ignimbrite of the italian volcanic provinces i e the y5 tephra ca 39 3 ka and from the nisyros volcano of the southeastern aegean sea the consistent occurrence of the nisyros tephra below the y5 tephra confirms similar findings in a lake core on the island of lesbos linear extrapolations using the oxygen isotope stratigraphy suggest an age of 42 44 ka for the nisyros eruption three additional tephra layers with a limited regional distribution are identified in the aegean sea cores two of these tephras originated from the yali volcano of the southeastern aegean sea and from the aeolian islands i e x1 tephra a series of six mugearite tephra beds in the south skiros basin is interpreted as a set of redeposited turbidites

revised chronology of the sulmona lacustrine succession central italy we present new stratigraphic palaeomagnetic 87sr 86sr and 40ar 39ar data from a lacustrine succession of the sulmona basin central italy which according to an early study included six unconformity bounded lacustrine units from sul6 oldest to sul1 youngest spanning the interval 600 to 2 ka the results of the present study on the one hand confirm some of the previous conclusions but by contrast reveal that units sul2 and sul1 previously attributed to the holocene are actually equivalent to the older sul6 and sul5 units here dated to 814 530 ka and 530 457 ka respectively and that the u series dates previously published for both former sul2 and sul1 units yielded abnormally young ages in light of the present results a reassessment of the chronology of the sulmona basin succession and a revision of the tephrostratigraphy of the sul2 sul6 and sul1 sul5 units is in order copyright 2013 john wiley sons ltd

exposure dating and validation of periglacial weathering limits northwest scotland periglacial weathering limits on two mountains in northwest scotland separate zones of contrasting exposure history exposure dating of bedrock below the weathering limits gives ages consistent with late devensian deglaciation but six out of seven samples from above the weathering limits give minimum exposure ages older than late devensian ice expansion these results suggest that mountain summits stood as nunataks above the last ice sheet surface and rule out formation of weathering limits by periglacial rock breakdown since deglaciation trimming of frost debris during an ice sheet readvance or enhanced weathering prior to climatic warming during ice sheet downwastage the dating results do not preclude the possibility that weathering limits mark a former englacial boundary between passive cold based ice on mountain summits and erosive warm based ice at lower elevations although 26 al 10 be ratios for high level bedrock surfaces provide no evidence of prolonged static ice cover

postglacial uplift neotectonics and seismicity in fennoscandia abstract fennoscandia has experienced major uplift in postglacial time which is assumed to reflect a glacial isostatic process connected to the melting of the last ice sheets extensive modelling of the isostatic movements show that the applied deglaciation and uplift model fit the observations well there are however areas with significant deviations between uplift measurements and regional model predictions the misfit between observations and the isostatic uplift modelling is interpreted here to reflect a tectonic component of the uplift the objective of the present investigation is to isolate this tectonic uplift component interestingly enough the areas found partly correspond to areas with pronounced seismic activity and the assumption that the postglacial rebound is responsible for much of the observed onshore seismicity is substantiated we conclude that there seems to be present day deformation along the shoreline of mid norway southern norway shoreline and mountain areas and along the swedish east coast with the centre northeast of the gulf of bothnia that cannot be explained by glacial isostasy not all of the deformations in these areas are necessarily co seismic the study suggests that such vertical deformations are small in magnitude and overprint the glacial rebound the deformations may be a consequence of the plio pleistocene erosional pattern which is of glacial origin

selective glacial erosion and weathering zones in the coastal mountains of marie byrd land antarctica in the coastal mountains of marie byrd land antarctica there is a juxtaposition of ice moulded landforms at lower altitudes and upstanding summits with weathered surfaces bearing tors this paper uses geomorphological mapping and exposure dating to test two hypotheses commonly used to explain such a landscape contrast either the pattern reflects contrasts in glacial erosion related to the basal thermal regime beneath a former ice sheet or it represents a periglacial trimline marking the upper limit of ice cover during the last glacial maximum lgm cosmogenic nuclide measurements on erratics show that the mountains were covered by ice on several occasions most recently during the lgm similar measurements on bedrock show that fragile landforms on weathered surfaces survived many glaciations nuclide concentrations in bedrock indicate both that subglacial erosion is insignificant and that ice free periods of periglacial weathering are longer at higher elevations we conclude that the pattern of landscape modification reflects both topographically controlled contrasts in the basal thermal regime of overriding ice and the longer exposure to periglacial conditions at higher elevations in addition the combination of nuclide data and the wider pattern of striations shows that the lgm ice cover was thinner than predicted by ice sheet models assuming equilibrium conditions that ice sheet thinning has occurred from 10 400 years ago to the present and that regional flow by overriding ice has been replaced by radial ice flow from local glaciers centred on individual mountain massifs

tephrochronological dating of varved interglacial lake deposits from pianico sellere southern alps italy to around 400 ka the sediment record from the pianico palaeolake in the southern alps is continuously varved spans more than 15 500 years and represents a key archive for interglacial climate variability at seasonal resolution the stratigraphic position of the pianico interglacial has been controversial in the past the identification of two volcanic ash layers and their microscopic analysis provides distinct marker layers for tephrochronological dating of these interglacial deposits in addition to micro facies analyses reconstructing depositional processes of both tephra layers within the lake environment their mineralogical and geochemical composition has been determined through major element electron probe micro analysis on glass shards comparison with published tephra data traced the volcanic source regions of the pianico tephras to the campanian volcanic complex of roccamonfina italy and probably the puy de sancy volcano in the french massif central available dating of near vent deposits from the roccamonfina volcano provides a robust tephrochronological anchor point at around 400 ka for the pianico interglacial these deposits correlate with marine oxygen isotope stage mis 11 and thus are younger than early to middle pleistocene previously suggested by k ar dating and older than the last interglacial as inferred from macrofloral remains and the geo logical setting copyright 2006 john wiley sons ltd

four climate cycles of recurring deep and surface water destabilizations on the iberian margin centennial climate variability over the last ice age exhibits clear bipolar behavior high resolution analyses of marine sediment cores from the iberian margin trace a number of associated changes simultaneously proxies of sea surface temperature and water mass distribution as well as relative biomarker content demonstrate that this typical north south coupling was pervasive for the cold phases of climate during the past 420 000 years cold episodes after relatively warm and largely ice free periods occurred when the predominance of deep water formation changed from northern to southern sources these results reinforce the connection between rapid climate changes at mediterranean latitudes and century to millennial variability in northern and southern polar regions

eruptive history of a low frequency and low output rate pleistocene volcano ciomadul south harghita mts romania based on a new set of k ar age data and detailed field observations the eruptive history of the youngest volcano in the whole carpathian pannonian region was reconstructed ciomadul volcano is a dacitic dome complex located at the southeastern end of the c limani gurghiu harghita neogene volcanic range in the east carpathians it consists of a central group of extrusive domes the ciomadul mare and haramul mare dome clusters and the koves ponk dome surrounded by a number of isolated peripheral domes some of them strongly eroded balvanyos puturosul and others topographically well preserved haramul mic dealul mare one of the domes dealul cet ii still preserves part of its original breccia envelope a large number of bread crust bombs found mostly along the southern slopes of the volcano suggest that the dome building activity at ciomadul was punctuated by short vulcanian type explosive events two late stage explosive events that ended the volcanic activity of ciomadul left behind two topographically well preserved craters disrupting the central group of domes the larger diameter shallower and older mohos phreatomagmatic crater and the smaller deeper and younger sf ana sub plinian crater phreatomagmatic products of the mohos center including accretionary lapilli bearing base surge deposits and poorly sorted airfall deposits with impact sags are known close to the eastern crater rim a key section studied in detail south of b ile tusnad shows the temporal succession of eruptive episodes related to the sf ana sub plinian event as well as relationships with the older dome building stages the age of this last eruptive event is loosely constrained by radiocarbon dating of charcoal pieces and paleosoil organic matter at ca 27 35 ka the age of the mohos eruption is not constrained but we suggest that it is closely related to the sf ana eruption the whole volcanic history of ciomadul spans over ca 1 myr starting with the building up of peripheral domes and then concentrating in its central part ciomadul appears as a small volume ca 8 74 km3 and very low frequency and low output rate volcano ca 9 km3 myr at the terminus of a gradually diminishing and extinguishing volcanic range a number of geodynamically active features strongly suggest that the magma plumbing system beneath ciomadul is not completely frozen so future activity cannot be ruled out

a younger dryas plateau icefield in the monadhliath scotland and implications for regional palaeoclimate a record of younger dryas glaciation in scotland is well established however the role of the monadhliath a significant plateau area extending over 840 km2 in central scotland has never been investigated systematically we present the first systematic glacial geomorphological mapping across the whole region which has led to the identification of hitherto unrecorded glacial and associated landforms the spatial distribution of these landforms indicates that the last phase of glaciation in the area was that of a local plateau icefield in addition a clear morphostratigraphical signature provides a strong indication that the icefield dates to the younger dryas 12 9 11 7 ka which is supported by numerical ages in the southeast of the study area based on the geomorphological evidence and 2d glacier surface profile modelling a 280 km2 icefield is reconstructed a novel approach is introduced to quantify plateau icefield thickness for equilibrium line altitude ela and palaeoprecipitation calculations resulting in greater overall data confidence compared to traditional reconstruction methods the ela for the whole icefield is calculated to be 714 25 m whilst the elas of individual outlet glaciers range from 560 m in the west to 816 m in the east demonstrating a significant w e precipitation gradient across the region during the younger dryas these elas compare well with those calculated for younger dryas ice masses reconstructed in neighbouring regions and are in good agreement with overall precipitation patterns suggested for scotland during this time whilst the total amount of precipitation calculated from these elas is highly dependent on the method used irrespective of this the study suggests a more arid younger dryas climate in the region compared to the present day

neogene quaternary magmatism and geodynamics in the carpathian pannonian region a synthesis in the carpathian pannonian region in neogene times westward dipping subduction in a land locked basin caused collision of two lithospheric blocks alcapa and tisia with the southeastern border of the european plate calc alkaline and alkaline magmatism was closely related to subduction rollback collision and extension from the spatial distribution of the magmatic activity four segments can be defined western segment magmatism occurring on the alcapa block central segment magmatism occurring on both alcapa and the tisia blocks south eastern segment and interior segment both on the tisia block most calc alkaline magmatism in the region resulted from melting of a heterogeneous asthenospheric mantle source modified by addition of fluids and sediment assimilation and fractionation processes at shallow crustal levels occurred in most of the segments strongly masking the deeper source processes long term subduction rollback and or delamination led to contamination of the asthenosphere beneath the western segment here large volume partial melts of the contaminated mantle caused underplating and crustal anatexis leading to mixing of mantle derived calc alkaline magmas with crustal melts in the central segment calc alkaline magmas were formed by subduction and rollback followed by back arc extension and slab breakoff avariable mantle source is indicated in the back arc setting and larger amount of fluid induced metasomatism source enrichment and assimilation nearer to the trench in the interior segment evolution from typical calc alkaline magmas to adakite like ones was related to extension due to fast rotations and transtensional tectonics here calc alkaline magmas formed by decompression melting of a heterogeneous crust mantle lithosphere while adakite like melts resulted from fliud dominated melting of the lithosphere along the south eastern segment slab breakoff was responsible for the generation of typical calcalkaline magmas but in the extreme south of the segment shallow level tearing of the slab followed breakoff strike slip tectonics allowed the rise of hot asthenosphere and generation of adakite like magmas via slab melting along the torn edge of the east european plate alkalic basaltic volcanism with an oib like asthenosphere source followed the calc alkaline stage

impact of volcanism on the evolution of lake van ii temporal evolution of explosive volcanism of nemrut volcano eastern anatolia during the past ca 0 4ma thirty two new single crystal ages document 400 000 years of widespread explosive volcanism of historically active nemrut volcano towering over huge alkaline lake van eastern anatolia the dated deposits were selected to monitor the volcanic and compositional evolution of nemrut volcano through time and thus to provide a rigorous temporal framework for the tephra record of the paleovan drilling project tephra samples were taken from large volume deposits or those that occur in medial to distal localities well exposed stratigraphic sections or from the initial phase of an eruptive sequence mainly fallout deposits were chosen because most ignimbrites show more complex and corroded feldspar populations owing to compositional zoning and magma mixing moreover fallout deposits held the promise to be more clearly identifiable with and correlatable to 300 tephra layers in the paleovan drill cores even though commonly in amounts marginal or insufficient in thickness to allow well supported single crystal dating the crystals dated are dominantly anorthoclase the main phenoctyst phase in the trachytic to rhyolitic slightly to strongly peralkaline nemrut magmas ages obtained so far range from ca 400 ka to ca 30 ka for nemrut volcano the causes of significant changes in the frequency volume and composition of tephra layers per unit time are discussed in terms of external erosion climate changes geodynamic factors and internal forcing changes in magma supply and composition and incubation periods preceding large volume rhyolitic eruptions for example the low frequency of tephra layers deposited prior to ca 200 ka may be due to low explosive activity severe erosion between mis 9 and mis 11 or both nevertheless the overall frequency of explosive eruptions appears to have increased during the past ca 200 ka we also recognize a slight peak in explosive eruptions during warm periods e g mis 5 and mis 7 and speculate on lithospheric unloading triggering increased partial melting or magma reservoir unloading following massive glacier melting the ages of 5 dated ignimbrites span ca 250 000 years suggesting that nemrut volcano went through a polycyclic evolution with multiple caldera collapses and major pyroclastic flow eruptions the oldest dated so far as 265 ka the widely held view of the impressive nemrut caldera now dated to have formed at ca 30 ka as the main paroxysmal event during the evolution of the volcano is no longer tenable distinct and coherent compositional characteristics especially in trace element concentrations characterize several groups of trachytic tephras we speculate that the growth of nemrut volcano caused the isolation of the lake van basin on account of their mineralogical anorthoclase hedenbergite fayalite aenigmatite and alkalic chemical compositions and large volume dated nemrut fallout tephras are likely to represent excellent markers in lakes and other sites of paleoclimatological or archeological interest in neighboring countries to the northeast of lake van as far as the caspian sea in what may be called the east anatolian tephra province

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

lightning as a geomorphic agent on mountain summits evidence from southern africa abstract the presence of angular bedrock derived debris on mountain summits worldwide has usually been associated with present or past periglacial frost shattering thermal fracturing and other climatically mediated weathering processes climatic inferences are commonly made based on such geomorphological evidence even if frost shattering and other processes are unlikely under present climatic conditions this paper questions this assumed genetic link between present past climate and production of angular bedrock derived debris by describing the geomorphological impacts of lightning strikes on exposed mountain summits using examples from the high drakensberg of eastern lesotho southern africa the impacts of lightning strikes are described which include the generation of angular fractured bedrock derived debris these impacts are identified in the field based on clear and unambiguous criteria that can be used to distinguish between lightning induced weathering processes and those processes associated with more typical alpine weathering this paper argues that lightning strikes are an important geomorphic agent of in particular low latitude mountain summits and that to make uncritical climatic inferences based on the presence of frost shattered debris on mountain summits is wholly erroneous

sorted clastic polygons in the argyre region mars and possible evidence of pre and post glacial periglaciation in the late amazonian epoch abstract the argyre basin and associated rim materials in the southern highlands of mars are ancient having been formed by the impact of a large body 3 9 gya despite its age the regional landscape exhibits a wide range of geological geomorphological modifications and or features e g fluvial lacustrine aeolian glacial and periglacial collectively this bears witness to the dynamic evolution of the argyre region from the deep past through to perhaps the present day here we present three principal findings that point to at least two distinct episodes of periglaciation separated by a possible glacial interval during the very late amazonian epoch in eastern aonia terra at i e on the western flank of the argyre basin these findings are the product of our circum argyre study of all hirise images 35 65 s and 290 350 e 1 a the first periglacial episode involves the development of small sized 15 25 m in diam and clastically sorted polygons sps the sps are observed at eighteen locations within eastern at hitherto the presence of sps in this region has been reported at one location alone no other observations of sps in the southern hemisphere of mars have been documented morphologically similar landforms develop in cold climate permafrost landscapes on earth by means of periglacial processes i e freeze thaw cycling segregated ice formation cryoturbation and frost heave b we ascribe a periglacial origin to the sps in eastern at on the basis of this similarity of form and no less importantly on the close spatial association of the sps with blockfields whose weathered clastic products are the building blocks of periglacial sorting on earth gelifluction like lobes and possible wet gullies where similar assemblages occur in terrestrial permafrost landscapes the presence of liquid water and of boundary conditions tolerant of freeze thaw cycling are observed or inferred c fifteen of the eighteen sp locations are clustered longitudinally 44 4 57 5 s 289 9 302 4 e this is inconsistent with the latitudinal and obliquity driven dependency of freeze thaw cycling in the late amazonian epoch hypothesised by many workers in the discipline 2 the second periglacial episode is highlighted by the development of small sized and clastically non sorted polygons nsps these polygons could have formed by means of a dry cryotic process i e thermal contraction cracking 3 the nsps incise and thus postdate a light toned mantle thought by numerous workers to comprise an ice dust admixture at some of the locations where the putatively icy mantle has undergone apparent ablation underlying sps are observed this suggests that the sps predate the mantle and derivatively the nsps as well the proposed geochronology of wet based sp icy mantle dry based nsp periods and interval is entirely new to the community moreover it underlines the possibility that periglacial and glacial boundary conditions at least in our study area may have oscillated much more substantially in the very late amazonian epoch than many workers have thought possible

acigol rhyolite field central anatolia part 1 high resolution dating of eruption episodes and zircon growth rates protracted pre eruptive zircon residence is frequently detected in continental rhyolites and can conflict with thermal models indicating briefer magma cooling durations if scaled to erupted volumes here we present combined u th and u th he zircon ages from the acigol rhyolite field central anatolia turkey which is part of a quaternary bimodal volcanic complex unlike other geochronometers this approach dates crystallization and eruption on the same crystals allowing for internal consistency testing despite the overall longevity of acigol rhyolite volcanism and systematic trends of progressive depletion in compatible trace elements and decreasing zircon saturation temperatures we find that zircon crystallized in two brief pulses corresponding to eruptions in the eastern and western part of the field during middle and late pleistocene times respectively for late pleistocene zircon resolvable differences exist between interior average 30 7 0 9 ka 1 error and rim 21 9 1 3 ka crystallization ages these translate into radial crystal growth rates of 10 13 to 10 14 cm s broadly consistent with those constrained by diffusion experiments rim crystallization and u th he eruption ages 24 2 0 4 ka overlap within uncertainty evidence for brief zircon residence at acigol contrasts with many other rhyolite fields suggesting that protracted zircon crystallization in or recycling from long lived crystal mushes is not ubiquitous in continental silicic magma systems instead the span of pre eruptive zircon ages is consistent with autochthonous crystallization in individual small volume magma batches that originated from basaltic precursors

the reset project constructing a european tephra lattice for refined synchronisation of environmental and archaeological events during the last c 100 ka this paper introduces the aims and scope of the reset project response of humans to abrupt environmental transitions a programme of research funded by the natural environment research council uk between 2008 and 2013 it also provides the context and rationale for papers included in a special volume of quaternary science reviews that report some of the project s findings reset examined the chronological and correlation methods employed to establish causal links between the timing of abrupt environmental transitions aets on the one hand and of human dispersal and development on the other with a focus on the middle and upper palaeolithic periods the period of interest is the last glacial cycle and the early holocene c 100 8 ka during which time a number of pronounced aets occurred a long running topic of debate is the degree to which human history in europe and the mediterranean region during the palaeolithic was shaped by these aets but this has proved difficult to assess because of poor dating control in an attempt to move the science forward reset examined the potential that tephra isochrons and in particular non visible ash layers cryptotephras might offer for synchronising palaeo records with a greater degree of finesse new tephrostratigraphical data generated by the project augment previously established tephra frameworks for the region and underpin a more evolved tephra lattice that links palaeo records between greenland the european mainland sub marine sequences in the mediterranean and north africa the paper also outlines the significance of other contributions to this special volume collectively these illustrate how the lattice was constructed how it links with cognate tephra research in europe and elsewhere and how the evidence of tephra isochrons is beginning to challenge long held views about the impacts of environmental change on humans during the palaeolithic

a relict landscape in the centre of fennoscandian glaciation geomorphological evidence of minimal quaternary glacial erosion abstract the parkajoki area in northeastern sweden is situated near the central area of fennoscandian glaciation despite its location the area is dominated by landforms induced by subaerial weathering and erosion processes such as well developed tors and associated saprolites boulder fields and boulder depressions the glacial geomorphology is dominated by lateral and proglacial meltwater channels subglacial imprints indicative of thawed bed conditions and reshaping by glacier sliding e g fluting drumlins striae are lacking hence most of the landscape still exhibits a preglacial appearance because of its location near the central area of glaciation we attribute preservation to frozen bed conditions of overriding ice sheets the widespread distribution of well developed tors and boulder fields and the degree of chemical weathering of the bedrock indicate that the area has been protected from glacial erosion during all glacial cycles since ice sheet initiation in the late cenozoic unlike most other areas with tors in glaciated regions the parkajoki area is uniquely situated in the lowlands at 150 400 m a s l moreover this relict landscape is surrounded by glacial landscapes including drumlins ribbed moraine and eskers of varying age and at similar elevation hence topographical reasons for this area being persistently cold based cannot be invoked by inference we conclude that strain heat release never managed to cancel the initial subglacial permafrost conditions we attribute this to divergent ice flow towards the convex outline of the ice sheet margin during deglaciations and to the relative roughness of the area compared to its surroundings the implication is that to explain preservation throughout the quaternary all large scale glaciations must have had a similar evolution concerning ice sheet configuration and internal dynamics as the last glaciation for which good constraints on evolution and outline are available

last glacial maximum ice sheet dynamics in arctic canada inferred from young erratics perched on ancient tors along standing debate regarding the reconstruction of former ice sheets revolves around the use of relative weathering of landscapes i e the assumption that highly weathered landscapes have not been recently glaciated new cosmogenic isotope measurements from upland bedrock surfaces and erratics along the northeastern margin of the laurentide ice sheet lis shed light on this debate 10 be and 26 al concentrations from three perched erratics yielding cosmogenic exposure ages of 17 11 ka are much lower than those measured in two unmodified highly weathered tors upon which they lie which yield cosmogenic exposure ages of 60 ka these findings suggest that non erosive ice covered weathered upland surfaces along the northeastern margin of the lis during the last glacial maximum these data challenge the use of relative weathering to define the margins of pleistocene ice sheets the juxtaposition of non erosive ice over upland plateaus and erosive ice in adjacent fiords requires strong gradients in basal thermal regimes suggestive of an ice stream mode of glaciation r 2003 elsevier science ltd all rights reserved

cosmogenic nuclide exposure ages along a vertical transect in western norway implications for the height of the fennoscandian ice sheet 10 be and 26 al exposure ages for bedrock samples from a vertical transect at skala in western norway provide new constraints on the history of the fennoscandian ice sheet the weathered bedrock surface autochthonous block field mantling the summit of skala has an exposure age of 55 ka suggesting that this surface formed before the last glacial maximum 18 14 c ka or 21 calendar ka the block field is truncated by a glacial trimline at 1660 m above sea level glaciated bedrock below the trimline has an exposure age of 26 21 ka the range depends on assumptions about erosion rate ice therefore receded from this altitude at about the time of the last glacial maximum the 10 be age for bedrock immediately below a second lower trimline at skala suggests a glacial advance or stillstand at 18 13 ka consistent with previously documented readvances or stillstands at the western and southern margins of the ice sheet

improved age estimates for key late quaternary european tephra horizons in the reset lattice abstract the research project response of humans to abrupt environmental transitions reset used tephra layers to tie together and synchronise the chronologies of stratigraphic records at archaeological and environmental sites with the increasing importance of tephra as chronological markers in sedimentary sequences both in this project and more generally comes a requirement to have good estimates for the absolute age of these volcanic horizons this paper summarises the chronology of the key tephra in the reset tephra lattice in the time range 10 60 ka bp from the existing literature from papers produced as part of the reset project and reanalysis conducted for this paper the paper outlines the chronological approach taken to the dating of tephra within the reset project and the basis for further work as part of the intimate integrating ice core marine and terrestrial records initiative for each of the tephra layers in the lattice the existing literature is discussed and where relevant date estimates updated using the latest radiocarbon calibration curves intcal13 and marine13 and methods maps show the approximate extent of tephra finds giving a visual indication of the coverage of the lattice in different time periods

geophysical approach to the study of a periglacial blockfield in a mountain area ztracene kameny eastern sudetes czech republic abstract fluctuation of climatic events in central europe with oceanic and continental influences intensified during the pleistocene especially above the timberline enabled the analysis of this record on the ridge and slopes of the ztracene kameny massif 1245 m a s l czech republic seismic refraction tomography srt and electrical resistivity tomography ert are geophysical methods that that allow the comprehensive recognition of shallow geological structures in a strongly folded area of the high jesenik mountains geophysical surveys were performed to determine structure and thickness of the quartzite blockfield and its boundary with consolidated rock the measured resistivity values were compared with the seismic wave velocities the resistivity values of the block cover show significant differences according to its morphology slope orientation and altitude the data analysis indicates an occurrence of remnants of pleistocene permafrost the subnival traces within the blockfield demonstrate the intensity of past slope processes and the role of frost weathering even during the holocene

felsenmeer persistence under non erosive ice in the torngat and kaumajet mountains quebec and labrador as determined by soil weathering and cosmogenic nuclide exposure dating soil analyses and terrestrial cosmogenic nuclide exposure dating are combined and a conceptual model proposed to explain altitudinal weathering contrasts in high latitude highlands we show that summits in the torngat and kaumajet mountains were covered by ice during the last glacial maximum and that their felsenmeer cover probably survived multiple glaciation events for similar lithologies soils on felsenmeer covered summits are signigicantly more weathered than those below the felsenmeer limit displaying higher concentrations of crystalline iron amorphous aluminium and silicium extracted with oxalate secondary minerals such as gibbsite and kaolinite occur in felsenmeer soils whereas those formed in till lacked these secondary minerals 10be and 26al exposure ages for nine of ten samples from high elevation tors and autochthonous felsenmeer blocks range from 73 6 to 157 15 ka by contrast ages of 11 4 1 0 and 11 7 1 0 ka are measured for bedrock in the much lower saglek zone indicating extensive 3 m glacial erosion of this zone during late wisconsinan glaciation 26al 10be ratios demonstrate that exposure of the high elevation surfaces was interrupted during at least one cosmic ray shielding event by either ice or till cover in either case late wisconsinan glaciers could not have extensively eroded these surfaces five erratics dated above the saglek zone including one in the felsenmeer zone have exposure ages ranging from 11 6 1 0 to 13 6 0 7 ka this indicates that valley and high elevation ice persisted through the younger dryas chron and provides further evidence that the highlands were not nunataks during the late wisconsinan period

periglacial trimlines and the extent of the kerry cork ice cap sw ireland abstract periglacial trimlines on the mountains of sw ireland demarcate a contrast between glacially scoured bedrock on lower ground and thick periglacial regolith covers on summits and plateaus and have previously been interpreted as marking the maximum altitude of the kerry cork ice cap kcic glacially eroded bedrock extends to the highest points on the beara peninsula but the highest summits on the iveragh peninsula support thick regolith covers trimline altitudes on the iveragh peninsula decline radially from a former ice divide near the head of kenmare river from 700 m altitude near the divide to 470 m near dingle bay contrasts in the clay mineral content of above and below trimline soils and cosmogenic isotope exposure ages indicate a lgm age for the trimlines assumption that the trimlines represent the maximum thickness of the kcic implies an ice divide altitude of 825 m however modelling of ice surface profiles demonstrates that an ice divide at 825 m is irreconcilable with stratigraphic evidence for extension of the kcic at least as far as garryvoe 115 km east of the divide we infer that the iveragh trimlines represent a former englacial transition between warm based sliding ice on low ground and cold based ice on high ground rather than delimiting nunataks as previously interpreted modelling of ice surface altitudes suggests that during the lgm the kcic probably overtopped all of the mountains in sw ireland the trimlines of sw ireland thus define the minimum rather than maximum altitude of the kcic at the lgm as well as the sites of former cold patches within the kcic

northwest svalbard during the last glaciation ice free areas existed the possibility that ice free areas existed during the late weichselian glaciation of the svalbard archipelago has been debated for several decades this study reveals the first geologic evidence that nunataks existed on the islands of northwest svalbard several 10 be exposure ages were obtained from bedrock and glacial erratics on danskoya and amsterdamoya islands exposure ages for glacial erratics laid down in block field covered plateaus 300 m above sea level show that the last ice sheet that completely covered the islands deglaciated 80 k y ago dating of marine sediments close to sea level reveals that full ice free conditions were achieved by ca 50 ka during the late weichselian the coastal lowlands were glaciated and the major fjords and troughs controlled glacier flow the existence of nunataks at this time opens the possibility for glacial survival of plant species

importance of sampling across an assemblage of glacial landforms for interpreting cosmogenic ages of deglaciation deglaciation chronologies for some sectors of former ice sheets are relatively poorly constrained because of the paucity of features or materials traditionally used to constrain the timing of deglaciation in areas without good deglaciation varve chronologies and or without widespread occurrence of material that indicates the start of earliest organic radiocarbon accumulations suitable for radiocarbon dating typically only general patterns and chronologies of deglaciation have been deduced however mid latitude ice sheets that had warm based conditions close to their margins often produced distinctive deglaciation landform assemblages including eskers deltas meltwater channels and aligned lineation systems because these features were formed or significantly altered during the last glaciation boulder or bedrock samples from them have the potential to yield reliable deglaciation ages using terrestrial cosmogenic nuclides tcn for exposure age dating here we present the results of a methodological study designed to examine the consistency of tcn based deglaciation ages from a range of deglaciation landforms at a site in northern norway the strong coherence between exposure ages across several landforms indicates great potential for using tcn techniques on features such as eskers deltas and meltwater channels to enhance the temporal resolution of ice sheet deglaciation chronologies over a range of spatial scales

a high resolution tephrochronological record of mis 14 12 in the southern apennines acerno basin italy abstract lithological mineralogical and glass chemical analyses on juvenile fragments extracted from 20 tephra layers embedded within the lacustrine sediments of the acerno basin southern apennines italy were carried out together with four sanidine 40 ar 39 ar age determinations the measured ages span the interval between 561 and 493 ka middle pleistocene eruptive activity at roman province volcanoes was identified as the main possible source of the investigated tephra layers some of them were correlated with precise terrestrial counterparts corresponding to large explosive events of the sabatini e g tufo giallo della via tiberina and alban hills volcanic districts e g tufo pisolitico di trigoria the integration of tephrochronology and pollen analyses allowed the acerno lacustrine sedimentation to be constrained between mis 14 and 12 which overlaps with several well studied lacustrine successions of the southern apennines the correlation with other tephrostratigraphic records from intramontane basins in central southern apennines testifies to the wide dispersal of at least three tephra layers that serve as marker layers thus improving the resolution of the middle pleistocene italian tephrostratotype

the concept of cryo conditioning in landscape evolution recent accounts suggest that periglacial processes are unimportant for large scale landscape evolution and that true large scale periglacial landscapes are rare or non existent the lack of a large scale topographical fingerprint due to periglacial processes may be considered of little relevance as linear process landscape development relationships rarely can be substantiated instead periglacial landscapes may be classified in terms of specific landform associations we propose cryo conditioning defined as the interaction of cryotic surface and subsurface thermal regimes and geomorphic processes as an overarching concept linking landform and landscape evolution in cold regions by focusing on the controls on processes this concept circumvents scaling problems in interpreting long term landscape evolution derived from short term processes it also contributes to an unambiguous conceptualization of periglacial geomorphology we propose that the development of several key elements in the norwegian geomorphic landscape can be explained in terms of cryo conditioning

too young or too old evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages cosmogenic exposure dating has greatly enhanced our ability to define glacial chronologies spanning several global cold periods and glacial boulder exposure ages are now routinely used to constrai

new ways of studying ice sheet flow directions and glacial erosion by computer modelling examples from fennoscandia a computer ice sheet model has been used to study regional ice flow directions and glacial erosion of the weichselian ice sheet adopting a new method of presenting modelled ice flow directions ice sheet model results from different time periods during the weichselian were extracted for five regions and presented in rose diagrams when comparing these computer generated results with information on flow directions obtained from current conceptual geological models based on field data large similarities were observed in comparing the ice flow directions as such the similarities were strikingly good in many cases there was also a good agreement in the timing of the events while in some cases a certain flow direction was assigned to a different time period by the ice sheet model than in the current interpretation of geological information nevertheless the overall agreement between the data sets shows that results from ice sheet models can aid in placing geological information into a coarse timeframe and chronostratigraphic context and also fill in time gaps in the glacial geological record where chronological control is sparse ice sheet model results thus constitute a new data set against which glacial geological information can be compared and tested a new quantity basal sliding distance has also been calculated from the ice sheet model results describing the over time accumulated length of ice that has passed over the landscape by basal sliding the results show high basal sliding distance values in sw sweden se norway in skagerrak and along the gulf of bothnia implying relatively large amounts of glacial erosion in these regions on elevated parts of the scandinavian mountain range and on adjacent plains in the east the basal sliding distance values are low implying weaker glacial erosion this compares well with different types of geological and morphological data suggesting that basal sliding distance is a useful entity for studying regional patterns of glacial erosion intensity

tephrostratigraphy and tephrochronology in the philippi peat basin macedonia northern hellas greece abstract three tephra layers have been identified in the upper 15 m of a 190 m section of peat beneath the philippi fen they provide significant lithological and chronological markers throughout the fen and the aegean region the upper tephra pht1 consists of shards of a transparent calcalkaline felsic glass and fragments of plagioclase augite hypersthene and rare hornblende magnetite apatite and quartz peat directly beneath pht1 gave a radiocarbon approximate age of 13 000 yr the middle tephra layer pht2 which resembles pht1 in chemistry and petrography but contains more crystals and lithic fragments rests on peat dated ca 18 000 14 c yr bp the lower tephra pht3 has colorless to brown glass shards with a trachytic chemistry and a mineral assemblage of sanidine sodic plagioclase biotite aegirine augite hornblende titanite and apatite bracketing radiocarbon ages imply that pht3 accumulated about 30 000 14 c yr bp the likely ages of pht1 and pht2 together with their mineralogical and chemical characteristics suggest that these tephras came from the volcanic field of thera in the hellenic arc pht2 particularly was derived from a major known explosive eruption ca 18 000 yr bp the cape riva eruption correlative to the y 2 tephra layer evidence for pht3 suggests derivation from the campanian province of italy and correlation with the campanian ignimbrite and the y 5 ash beneath the mediterranean sea

geological factors influencing the concentration of trace elements in the philippi peatland eastern macedonia greece abstract six peat samples obtained from the holocene and the weichselian of the philippi peat deposit eastern macedonia greece were analyzed for 48 trace elements by inductively coupled plasma mass spectrometry icp ms the ash contents of these samples were also determined most of the trace elements are associated with the minerals in the peat while ge mo pb se ta tl u and w display a greater affinity with the organic matter compared with crustal averages clarke concentrations the philippi peat is enriched in some elements ag as au cd mo se te u and w because of the respective mineralizations in the area the philippi peat is also enriched in cr cu mo pb sc sn t v y and zn in comparison with typical fen peats as well as in as cr mo se and u in comparison with typical coals climatic and hydrogeological conditions strongly influenced the peat forming environment resulting in a differentiation between holocene and weichselian peat generally the holocene peat contains lower concentrations of trace elements in the northern and southern part of the fen than the weichselian one the opposite trend is observed in the fen area close to the western basin margins

age assessment and implications of late quaternary periglacial and paraglacial landforms on muckish mountain northwest ireland based on schmidt hammer exposure age dating shd abstract schmidt hammer exposure age dating shd was applied to a variety of late quaternary periglacial and paraglacial landforms composed of coarse rock debris on muckish mountain northwest ireland landform ages were determined using a linear high precision age calibration curve derived from young and old control surfaces of known age on the same rock type the shd ages represent maximum estimates of the time elapsed since the boulders stabilised and the landforms became inactive most ages are also minimum estimates for the start of landform development because older boulders are buried beneath the sampled surface boulders ages and 95 confidence intervals obtained for blockfield boulder lobes and talus indicate these features were likely active during several of the early holocene cold events evidenced in greenland ice cores and north atlantic sediment records activity ceased at different times 9 7 ka bp these landforms are the first indication of a geomorphological response to early holocene cooling in the oceanic mountains of ireland late holocene ages obtained for rock slope failure run out debris and debris cone boulders overlap with shifts to cooler and or wetter conditions including the little ice age geomorphological impacts associated with these changes in climate have not previously been recorded in the irish uplands the shd results indicate that previously implied timings for the stabilisation of some accumulations of coarse rock debris on mountain slopes are in need of revision

a granulometry and secondary mineral fingerprint of chemical weathering in periglacial landscapes and its application to blockfield origins abstract a review of published literature was undertaken to determine if there was a fingerprint of chemical weathering in regoliths subjected to periglacial conditions during their formation if present this fingerprint would be applied to the question of when blockfields in periglacial landscapes were initiated these blocky diamicts are usually considered to represent remnants of regoliths that were chemically weathered under a warm neogene climate and therefore indicate surfaces that have undergone only a few metres to a few 10s of metres of erosion during the quaternary based on a comparison of clay and silt abundances and secondary mineral assemblages from blockfields other regoliths in periglacial settings and regoliths from non periglacial settings a fingerprint of chemical weathering in periglacial landscapes was identified a mobile regolith origin under at least seasonal periglacial conditions is indicated where clay 0 5 silt 8 across a sample batch this contrasts with a mobile regolith origin under non periglacial conditions which is indicated where clay 0 5 silt 6 across a sample batch with clay 0 5 silt 8 in at least one sample a range of secondary minerals which frequently includes interstratified minerals and indicates high local variability in leaching conditions is also commonly present in regoliths exposed to periglacial conditions during their formation clay silt ratios display a threshold response to temperature related to the freezing point of water but there is little response to precipitation or regolith residence time lithology controls clay and silt abundances which increase from felsic through intermediate to mafic compositions but does not control clay silt ratios use of a sedigraph or coulter counter to determine regolith granulometry systematically indicates lower clay abundances and intra site variability than use of a pipette or hydrometer in contrast to clay silt ratios secondary mineral assemblages vary according to regolith residence time temperature and or precipitation a microsystems model is invoked as a conceptual framework in which to interpret the concurrent formation of the observed secondary mineral ranges according to the fingerprint of chemical weathering in periglacial landscapes there is generally no evidence of blockfield origins under warm neogene climates nearly all blockfields appear to be a product of quaternary physical and chemical weathering a more dominant role for periglacial processes in further bevelling elevated low relief non glacial surface remnants in otherwise glacially eroded landscapes is therefore indicated

zooming in on frozen bed patches scale dependent controls on fennoscandian ice sheet basal thermal zonation in this paper we explore geomorphological evidence allowing a first order reconstruction of the extent and pattern of frozen bed conditions under the last fennoscandian ice sheet we mapped relict landscapes i e glacial landforms and subaerially developed ground surfaces predating the last ice sheet and marking sustained frozen bed conditions at four different spatial scales at the ice sheet scale relict landscapes are most abundant between the last glacial maximum ice divide and the elevation axis of the scandinavian mountain range the location of frozen bed zones was mainly a function of dispersal centre location low surface temperatures and small strain heating and small ice thickness over the eastern flank of the mountain range at the mesoscale 260 360 km map area the pattern of relict surfaces is governed by inward cutting ice stream erosion topographical control was weak but relation to flow pattern was strong with the major frozen bed zone located where ice flow was strongly divergent at the regional scale 40 65 km map area in hilly terrain topographical control was strong with relict surfaces only appearing above a plane dipping in the up ice direction at the local scale 12 14 km map area control by topography was likewise strong but the detailed boundary pattern was irregular with specific landforms occurring both up and down ice of frozen patches

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

dimensions and deglacial chronology of the outer hebrides ice cap northwest scotland implications of cosmic ray exposure dating cosmic ray exposure ages of frost weathered bedrock from mountain summits in the outer hebrides exceed the age of late devensian glaciation exposure ages of most glacially abraded bedrock surfaces at low and intermediate elevations are younger than the age of maximum late devensian glaciation these results confirm that previously mapped periglacial trimlines in the outer hebrides define the upper limit of bedrock erosion by late devensian ice they are consistent with the interpretation based on geomorphological evidence that the trimlines mark the approximate upper limit of a late devensian outer hebrides ice cap a postglacial exposure age from the summit of oreval 662 m suggests that this mountain was overrun during the last glaciation indicating thicker ice cover and a lower surface gradient west of the ice cap divide than previously inferred although bedrock surfaces below the trimlines are strongly ice moulded some show evidence of prior cosmic ray exposure which we attribute to limited erosion during late devensian glaciation if this interpretation is correct the youngest apparent ages from these surfaces give the most reliable dates for deglaciation at ca 14 5 14 ka this implies that ice persisted at favourable sites through the warm opening phase of the windermere interstade comparison with radiocarbon dated evidence from offshore cores suggests net ice margin retreat of 74 km eastwards across the adjacent shelf in 2 3 1 0 ka the dating evidence is consistent with relatively rapid retreat of calving margins to the coast then slower withdrawal of ice margins to high ground copyright 2005 john wiley sons ltd

glacial survival of blockfields on the varanger peninsula northern norway for more than hundred years it has been debated whether blockfields in mountain summit areas can be used to delimit the vertical extent of pleistocene ice sheets in this study the relationship between blockfields developed in quartzites and sandstones on the varanger peninsula northern norway and glacially derived features have been evaluated erratics and circular ablation moraines are superimposed on the blockfields and lateral meltwater channels are eroded into them glacial striations and other signs of glacial sculpturing are restricted to low lying areas with channelled ice flow relative ages of the blockfields and the features in them are inferred and the first measurements of in situ produced cosmogenic nuclides from the varanger peninsula are reported we conclude that the blockfields have survived underneath at least one thick cold based ice sheet thus these blockfields cannot be used as indicators of ice free conditions as previously suggested for southern norway our results have implications for the potential for land surface preservation beneath ice sheets and for glacial reconstructions in northern fennoscandia

cosmogenic 36cl exposure ages reveal a 9 3 ka bp glacier advance and the late weichselian early holocene glacial history of the drangajokull region northwest iceland abstract we present twenty four new cosmogenic isotope 36 cl surface exposure ages from erratic boulders moraine boulders and glacially eroded bedrock that constrain the late weichselian to holocene glacial history of the drangajokull region northwest iceland the results suggest a topographically controlled ice sheet over the vestfir ir westfjords peninsula during the last glaciation cold based non erosive sectors of the ice sheet covered most of the mountains while fjords and valleys were occupied with erosive warm based ice old 36 cl exposure ages from highlands and mountain plateaux l8 76 5 ka and h1 41 6 ka in combination with younger erratic boulders l7 26 2 and k1 k4 15 0 13 8 ka superimposed on such surfaces suggest the presence of non erosive ice over uplands and plateaux in the vestfir ir peninsula during the last glaciation glacially scoured terrain and erratic boulders yielding younger exposure ages l1 l6 11 3 9 1 ka and r1 r6 r7 10 6 9 4 ka in the lowland areas indicate that the valleys and fjords of the vestfir ir peninsula were occupied by warm based dynamic ice during the last glaciation the deglaciation of mountain leirufjall by 26 2 ka bp suggests that ice thinning and deglaciation of some mountains and plateaux preceded any significant lateral retreat of the ice sheet subsequently this initial ice thinning was followed by break up of the shelf based ice sheet off vestfir ir about 15 ka bp hence the new exposure ages suggest a stepwise asynchronous deglaciation on land following the shelf break up with some valleys and most of the highlands ice free by 14 15 ka bp the outermost moraine at the mouth of leirufjor ur is dated to 9 3 ka bp and we suggest the moraine to be formed by a glacier re advance in response to a cooler climate forced by the reduced atlantic meridional overturning circulation at around 9 3 ka bp a system of moraines proximal to the 9 3 ka moraine in leirufjor ur as well as a 9 4 ka deglaciation age in the coastal area of reykjarfjor ur suggest that an extensive ice cap persisted over the eastern vestfir ir peninsula at least until c 9 ka bp

the last glacial maximum of svalbard and the barents sea area ice sheet extent and configuration abstract the timing extent and configuration of the late weichselian barents ice sheet has been debated for several decades this debate has arisen largely because of the limited or conflicting field evidence on which most models have been based in particular reconstruction of the marine parts of the former barents ice sheet has been controversial this paper aims to review the geological observations and interpretations regarding the size and timing of the late weichselian ice sheet combined with numerical modelling of its formation in order to produce a reconstruction of ice sheet extent and behaviour sub glacial till with overlying glacimarine deposits dated to the late weichselian is found over most of the barents sea floor and the continental shelf west of svalbard glacially induced debris flow deposits on the large bjonoya and isfjorden trough mouth fans strongly support the idea of ice sheet extension to the shelf edge during maximum glaciation isobase maps show a centre of post glacial uplift in the north central barents sea and glaciological and isostatic modelling suggest that the ice sheet was 2000 3000 m thick in this area the ice sheet was confluent with ice over the kara sea but the interaction between the barents and kara ice sheets is not yet fully understood the deglaciation of the barents ice sheet started ca 15 ka probably by calving within the deeper troughs by 12 ka most of the central barents sea was ice free and ice remained over the svalbard franz josef land and novaja zemlya archipelagos and adjacent shallow shelf areas the coasts and fjords of these islands were ice free by 10 ka

an unusual stone circle chilcotin range british columbia canada a unique circular feature of uncertain origin lies above the tree line on the eastern flanks of the coast range of british columbia canada it is composed of white fractured angular cobbles to boulders predominantly under 1 m across arrayed in a slightly flattened circle nearly 50 m in diameter with the ring mostly about 4 m in width the felsic granitoid lithology of the circle is unlike any in the immediate region and no clasts of this composition occur within the circle the debris rests on soliflucted soil containing rounded pebbles to cobbles of granodiorite that forms the regional lithology the age of the circle is deglacial with post glacial modification given the absence of similar lithologic units in the region and no obvious symbolic purpose for such a feature an anthropogenic origin for the circle is improbable mechanisms for transporting the foreign rock unit to its final location distributing fragments into a circle and preserving it include flow of alpine and fringing continental

scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces abstract the decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains sloped surfaces and local rock formations that block them when a large part of the sky is blocked this correction is large and requires detailed model calculations this paper considers three geometries a rectangular obstruction a triangular obstruction and a sloped surface other geometries can be considered as a combination of these the results are presented in terms of formulas and graphs so that the reader can easily apply them to common field situations any use of cosmogenic nuclides in the study of geomorphic processes or forms must consider factors that introduce variations in the production of nuclides

trimlines blockfields mountain top erratics and the vertical dimensions of the last british irish ice sheet in nw scotland periglacial trimlines separating glacially eroded lower slopes from blockfield covered plateaus on british and irish mountains have been interpreted either 1 in terms of representing the maximum altitude of the last ice sheet during the last glacial maximum lgm or 2 as a thermal boundary separating wet based ice at pressure melting point from cold based ice on summit plateaus we test these competing hypotheses through 10be exposure dating of high level erratic boulders above trimlines on five mountains in nw scotland nine out of 14 erratics yielded post lgm exposure ages ranging from 14 0 0 7 ka to 16 5 0 9 ka or from 14 9 0 9 ka to 17 6 1 1 ka depending on the 10be production rate employed in exposure age calculation these ages refute hypothesis 1 as they imply that the last ice sheet overtopped the mountains preservation of apparently intact blockfields on the summits implies cold based ice cover supporting hypothesis 2 as altitudinally consistent high level trimlines extend from our sampled sites across much of nw scotland and the hebrides our conclusions apply to all trimlines in this broader area and probably to all high level trimlines elsewhere in the british isles preservation of blockfields under cold based ice is consistent with blockfield evolution on plateaus throughout much or all of the quaternary averaged exposure ages of 15 16 ka for plateau top erratics implies nunatak emergence from the downwasting ice sheet prior to a regional readvance of the ice margin the wester ross readvance and before rapid warming at 14 7 ka at the onset of the lateglacial interstade but after the timing of ice sheet thinning as retrodicted by recent proxy climate driven thermo mechanical coupled models our findings provide an additional constraint on the future development of such models by implying that high level trimlines represent the altitude of a former transition zone between ice at pressure melting point and ice below pressure melting point

periglacial trimlines in the scottish highlands abstract two periglacial weathering limits have been identified on mountains in the highlands of scotland the lower has been interpreted as a periglacial trimline marking the upper limits of loch lomond younger dryas stade glaciers and has been employed to reconstruct the dimensions of parts of the main west highland icefield and certain smaller glaciers and icefields interpretation of the upper weathering limit has been more contentious but recent research has demonstrated 1 significant contrasts in the degree of bedrock weathering above and below this limit 2 that gibbsite a pre devensian weathering product is abundant above the limit but rare in soils farther downslope 3 that the isotopic 26al age of bedrock exposures above the limit greatly exceeds that at lower altitudes and 4 that the altitude of the weathering limit descends regularly along former ice sheet flowlines collectively these attributes suggest that the upper weathering limit is a periglacial trimline defining the maximum altitude of the last ice sheet calculated basal shear stress values are consistent with this interpretation which implies that the mainland ice shed lay at ca 900 m in wester ross and descended gently northwards whilst harris and lewis in the outer hebrides supported an independent ice cap that achieved a maximum altitude of ca 700 m wider implications of this interpretation and the future potential for ice sheet reconstruction are explored

cryptotephras the revolution in correlation and precision dating from its icelandic origins in the study of visible tephra horizons tephrochronology took a remarkable step in the late 1980 s with the discovery of a ca 4300 year old microscopic ash layer in a scottish peat bog since then the search for these cryptotephra deposits in distal areas has gone from strength to strength indeed a recent discovery demonstrates how a few fine grained glass shards from an alaskan eruption have been dispersed more than 7000 km to northern europe instantaneous deposition of geochemically distinct volcanic ash over such large geographical areas gives rise to a powerful correlation tool with considerable potential for addressing a range of scientific questions a prerequisite of this work is the establishment of regional tephrochronological frameworks that include well constrained age estimates and robust geochemical signatures for each deposit with distal sites revealing a complex record of previously unknown volcanic events frameworks are regularly revised and it has become apparent that some closely timed eruptions have similar geochemical signatures the search for unique and robust geochemical fingerprints thus hinges on rigorous analysis by electron microprobe and laser ablation inductively coupled plasma mass spectrometry historical developments and significant breakthroughs are presented to chart the revolution in correlation and precision dating over the last 50 years using tephrochronology and cryptotephrochronology

numerical reconstructions of the eurasian ice sheet and climate during the late weichselian abstract geological investigations undertaken through the quaternary environments of the eurasian north programme established ice sheet limits for the eurasian arctic at the last glacial maximum lgm sedimentary records of palaeo ice streams and uplift information relating to ice sheet configuration and the pattern of deglaciation ice sheet numerical modelling was used to reconstruct a history of the eurasian ice sheet compatible with these geological datasets the result was a quantitative assessment of the time dependent behaviour of the ice sheet its mass balance and climate and predictions of glaciological products including sediments icebergs and meltwater at the lgm ice cover was continuous from scandinavia to the arctic ocean margin of the barents sea to the north and the kara sea to the east in the west along the continental margin between the norwegian channel and svalbard the ice sheet was characterised by fast flowing ice streams occupying bathymetric troughs which fed large volumes of sediment to the continental margin that were deposited as a series of trough mouth fans ice streams may also have been present in bathymetric troughs to the north between svalbard and franz josef land further east however the ice sheet was thinner across the kara sea the ice thickness was predicted to be less than 300 m while on severnaya zemlya the ice cover may have been thinner at the lgm than at present it is likely that the taymyr peninsula was mainly free of ice at the lgm in the south the ice margin was located close to the shoreline of the russian mainland the climate associated with this ice sheet is maritime to the west and in stark contrast desert like in the east atmospheric general circulation modelling has revealed that such a contrast is possible under relatively warm north atlantic conditions because a circulation system develops across the kara sea isolating it from the moisture laden westerlies which are diverted to the south ice sheet decay began through enhanced iceberg calving in the deepest regions of the barents sea which caused a significant ice embayment within the bear island trough by about 12 000 years ago further iceberg calving reduced ice extent to the northern archipelagos and their surrounding shallow seas ice decay was complete by about 10 000 years ago

fault and basin depocentre migration over the last 2 ma in the l aquila 2009 earthquake region central italian apennines abstract morphological stratigraphical and structural investigations integrated with palaeomagnetic and tephrostratigraphic studies and 40 ar 39 ar measurements allowed us to define the quaternary tectonic sedimentary evolution of the epicentral area of the l aquila 2009 earthquake m w 6 3 this area roughly matches the paganica san demetrio castelnuovo psc intermountain basin filled by a fluvio lacustrine succession that is variously deformed by normal faults at its early stage early pleistocene ca 2 ma the basin hosted a lake that was characterised by whitish carbonate silt and mud deposition towards the end of the early pleistocene this was partly filled by a south eastward prograding deltaic system the south easternmost portion of the deltaic system was successively abandoned and eroded while sedimentation of a braided river system developed in a smaller area westwards before 780 ka this fluvio lacustrine system the lower psc syntheme ended and the area underwent erosional and pedogenic processes these processes continued up to 460 ka with the onset of fluvial gravel and volcanic rich silty sand deposition over a narrow area of the south western psc basin an earlier unit of the upper psc syntheme early middle pleistocene around 460 ka when most of this area was again subjected to denudational processes the sedimentation migrated into the previously exposed north western area of the psc basin where fluvial alluvial sediments were deposited between ca 460 ka and ca 350 ka a later unit of the upper psc syntheme between ca 350 ka and the present the sedimentation continued uninterrupted in a slight westwards restricted area of the psc basin upper late psc syntheme the significant contraction of the basin the shifting of its depocentre the variation in its geometry and in the spatial distributions and thicknesses of the units constituting the lower upper and late psc synthemes provide evidence for strong tectonic control this resulted in progressive reduction of the activity of the south easternmost tectonic structures and parallel migration of the fault activity on the westernmost structures in this perspective the fault system responsible for the l aquila 2009 earthquake can be seen as the most recent expression of a long lasting westwards polarised process of tectonic activity transfer

lateglacial retreat chronology of the scandinavian ice sheet in finnmark northern norway reconstructed from surface exposure dating of major end moraines abstract we report results from a comprehensive surface exposure dating campaign in eastern finnmark located in the northernmost part of norway and close to the norwegian russian border this is a palaeo glaciologically important region as it sits near the proposed border zone between the former scandinavian and barents sea ice sheets however until now the deglaciation history has few direct dates onshore and the chronology of ice front retreat is instead found by correlating ice marginal deposits with isostatically raised shorelines and marine sediment cores we measured the content of 10 be n 22 and 36 cl n 17 from boulders located at the crest of major moraine ridges at four localities kjaes kongsfjorden vardo and kirkenes these are key localities of existing regional reconstructions of ice recession in this area despite some spread in age results from each locality due to methodological challenges associated with surface exposure dating the large numbers of samples from each site except kjaes still allow for obtaining clusters of similar ages which are used for arriving at a likely chronology of ice front retreat our results show that the kongsfjorden and vardo moraines were deposited 14 3 1 7 ka and 13 6 1 4 ka respectively and thus point to a older dryas age of the proposed outer porsanger deglaciation sub stage moraine ridges belonging to the main sub stage near kirkenes were dated to 11 9 1 2 ka corresponding well with the ice retreat chronology farther west in northern norway and suggesting that the maximum younger dryas ice sheet extent was attained in the late younger dryas along a more than 500 km long stretch in northernmost scandinavia

weathering patterns in high latitude regolith 1 large areas distributed on the earth s surface are covered by regolith an unconsolidated heterogeneous material overlying bedrock in high latitude areas most of the land surface has been reworked and eroded by both glacial and fluvial processes leaving only remnants of formerly extensive regolith covers in an effort to further the understanding of weathering patterns and processes in old regolith covers a comprehensive study of localities spread across norway was carried out on the basis of the distribution of minerals and elements within regolith as well as its internal structure and geomorphologic setting we ascertained that it was formed in situ and originated in pre quaternary times there are similarities between the study sites with respect to regolith thickness zonation and composition the chemical index of alteration cia and the weathering index of parker wip suggests that the degree of chemical weathering in the regolith is advanced compared to the parental bedrock with a maximum change of over 80 which indicates a substantial increase in the proportion of secondary versus primary minerals mineral analysis identified kaolinite and gibbsite which are considered indicative of advanced weathering and therefore support this observation on the basis of statistical relationships between different grain size fractions 125 m we observed a consistent pattern which revealed that physical weathering becomes progressively less important in the production of grains smaller than 32 m on the basis of this finding we infer that chemical weathering progressively dominates the production of fine silt very fine silt and clay whereas physical weathering primarily controls the production of grain size fractions larger than 32 m this particular pattern is suggested to be an intrinsic feature in the formation of weathered high latitude regolith

the barents sea ice sheet a model of its growth and decay during the last ice maximum on the basis of geomorphological and sedimentological data we believe that the entire barents sea was covered by grounded ice during the last glacial maximum 14c dates on shells embedded in tills suggest marine conditions in the barents sea as late as 22 ka bp and models of the deglaciation history based on uplift data from the northern norwegian coast suggest that significant parts of the barents sea ice sheet calved off as early as 15 ka bp the growth of the ice sheet is related to glacioeustatic fall and the exposure of shallow banks in the central barents sea where ice caps may develop and expand to finally coalesce with the expanding ice masses from svalbard and fennoscandia the outlined model for growth and decay of the barents sea ice sheet suggests a system which developed and existed under periods of maximum climatic deterioration and where its growth and decay were strongly related to the fall and rise of sea level

constraints on the late weichselian ice sheet over the barents sea from observations of raised shorelines abstract direct evidence for late weichselian grounded glacier ice over extensive areas of the barents sea is based largely on indirect observations including elevations of old shorelines on svalbard and arguments of isostatic rebound such isostatic models are discussed here for two cases representing maximum and minimum ice sheet reconstructions in the former model the ice extends over the kara sea whereas in the latter the ice is limited to the barents sea and island archipelagos comparisons of predictions with observations from a number of areas including spitsbergen nordaustlandet edgeoya kong karls land franz josef land novaya zemlya and finnmark support arguments for the existence of a large ice sheet over the region at the time of the last glacial maximum this ice sheet is likely to have had the following characteristics conclusions that are independent of assumptions made about the earth s rheological parameters i the maximum thickness of this ice was about 1500 2000 m with the centre of the load occurring to the south and east of kong karls land ii the ice sheet extended out to the western edge of the continental shelf and its maximum thickness over western spitsbergen was about 800 m iii to the north of svalberg and frans josef land the ice sheet extended out to the northern shelf edge iv retreat of the grounded ice across the southern barents sea occurred relatively early such that this region was largely ice free by about 15 000 bp v by 12 000 bp the grounded ice had retreated to the northern archipelagos and was largely gone by 10 000 bp vi the ice sheet may have extended to the kara sea but ice thicknesses were only a fraction of those proposed in those reconstructions where the maximum ice thickness is centered on novaya zemlya models for the palaeobathymetry for the barents sea at the time of the last glacial maximum indicate that large parts of the barents sea were either very shallow or above sea level providing the opportunity for ice growth on the emerged plateaux as well as on the islands but only towards the end of the period of fennoscandian ice sheet build up

glacial and periglacial buzzsaws fitting mechanisms to metaphors the buzzsaw hypothesis refers to the potential for glacial and periglacial processes to rapidly denude mountains at and above glacier equilibrium line altitudes elas irrespective of uplift rates rock type or pre existing topography here the appropriateness of the buzzsaw metaphor is examined alongside questions of the links between glacial erosion and elas and whether the glacial system can produce low relief surfaces or limit summit heights plateau fragments in mountains on both active orogens and passive margins that have been cited as products of glacial and periglacial buzzsaw erosion instead generally represent dissected remnants of largely inherited pre glacial relief summit heights may correlate with elas but no causal link need be implied as summit erosion rates are low cirque headwalls may not directly abut summits and on passive margins cirques are cut into pre existing mountain topography any simple links between elas and glacial erosion break down on passive margins due to topographic forcing of ice sheet growth and to the km scale vertical swaths through which elas have shifted through the quaternary glaciers destroy rather than create low relief rock surfaces through the innate tendency for ice flow to be faster thicker and warmer along valleys the glacial buzzsaw cuts down

preservation of landforms under ice sheets and ice caps abstract this article addresses the question of whether or not distinct glacial and non glacial landforms can survive beneath ice sheets and ice caps with little or no morphological alteration a review of recent work documents the existence of pre last stadial landforms and landscapes in areas covered by the fennoscandian and laurentide ice sheets a substantial number of independent works indicate that landforms such as eskers drainage channels and boulder fields have escaped destruction despite complete ice overriding during several tens of millenia full preservation of former ground surfaces or delicate landforms probably is linked to areas where the ice sheet base was continuously frozen to its bed larger robust landforms such as large drumlins appear to have been preserved even under wet based conditions in glaciated areas patches preserved under dry cold based conditions provide important windows towards the past showing landscapes that were destroyed in surrounding areas affected by wet based and eroding ice some consequences for the research fields of non glacial geomorphology archaeology and botany include the possibility of subglacial museums and refugia a time space model describes geomorphological access to information from older events in glaciated areas

quantification of subaerial and episodic subglacial erosion rates on high latitude upland plateaus cumberland peninsula baffin island arctic canada abstract long term rates of subaerial and episodic subglacial erosion by predominately cold based ice cover are determined for tors on weathered plateaus on cumberland peninsula by measuring terrestrial cosmogenic nuclide concentrations in differentially weathered surfaces on a given tor we reconstruct the complex exposure and erosion history involving recurring cold based ice cover the style and rate of subaerial and subglacial erosion at multiple tor sites on cumberland peninsula are assessed with a monte carlo approach that computes plausible exposure histories based on a proxy record of global ice volume constant subaerial erosion rates by weathering are low

circular moraine features on the varanger peninsula northern norway and their possible relation to polythermal ice sheet coverage abstract this paper introduces a new hypothesis about the formation of circular moraine features cmfs on felsenmeer covered plateaux of the varanger peninsula northern norway cmfs and glacial lineations in the northwestern part of the varanger peninsula were mapped from aerial photographs in two cmf rich areas basec rro plateau and batsfjordfjellet the cmfs were investigated during fieldwork the aim was to investigate possible entrainment transport and deposition mechanisms of the cmfs in connection to ice sheet properties the cmfs were deposited in connection with a polythermal ice cover during glaciations the ice sheet was cold based on the boulder field plateaux and warm based in valleys especially in ice drainage pathways towards fjords the cmf material was probably entrained en masse on the varanger peninsula in transition zones between warm and cold based ice the debris transport took place close to the ice base during deglaciation the debris formed dirt cones slowing down the melting of underlying dead ice blocks as material slid down the margins of the cones the typical cmf shape was formed

revised tuning of ocean drilling program site 964 and kc01b mediterranean and implications for the δ18o tephra calcareous nannofossil and geomagnetic reversal chronologies of the past 1 1 myr 1 high resolution color reflectance records of kc01 and kc01b calabrian ridge ionian sea are presented and compared with a modified spliced high resolution color reflectance record of ocean drilling program odp site 964 this comparison revealed that kc01b is characterized by intensive deformation between 27 and 28 5 m piston depth and that some sapropels are tectonically reduced in thickness moreover the piston coring has caused considerable stretching in the top of kc01 and kc01b using a new splice of odp site 964 as guide previous astronomical tuned timescales of kc01b and odp site 964 were evaluated this evaluation resulted in a new sapropel based astronomical timescale for the last 1 1 myr the new timescale implies a much more uniform change in sedimentation rate for the ionian sea cores two prominent excursions to lighter values in the 18o record of the planktonic foraminiferal species globigerinoides ruber occur during marine isotopic stages 12 and 16 applying the new timescale these shifts correspond with maxima in obliquity and are punctuated by minima in the precession cycle they are absent in global ice volume records and are interpreted as reflecting a summer low salinity surface water lens that floats on top of extremely saline intermediate and deep waters at times of the very low sea levels during these glacial periods all biostratigraphic and magnetostratigraphic events found in kc01b and odp site 964 were re dated according to the new timescale and the ages of 33 tephra layers were reviewed the new ages for the calabrian ridge 2 and 3 magnetic events in the brunhes are concordant with minima in the global sint800 composite record derived from worldwide deep sea records of relative paleointensity and have been attributed to the big lost and la palma excursions respectively

formation of plateau landscapes on glaciated continental margins plateaus separated by deeply incised fjords are hallmarks of glaciated passive continental margins computational experiments show that they arise from evolving feedbacks between topography ice dynamics and erosion over millions of years

late cenozoic environmental changes along the norwegian margin abstract our ability to understand the rates and consequences of contemporary climate change is limited by the insufficient duration of instrumental records thus we are not able to fully understand the processes that provide a fundamental control in driving climate changes across different timescales palaeo climate archives like those preserved offshore norway provide our only real window through which to observe long term rates and styles of climate change this paper reviews the extensive geological and geophysical data available from the late cenozoic atlantic margin of norway along the margin periods of erosion and deposition have been controlled by agents including fluvial glacial and oceanographic processes current controlled sedimentation along the margin provides insight into the connection of the arctic and atlantic oceans from the miocene onward plio pleistocene shelf edge progradation of up to 150 km can be linked to the grounding of ice sheets on the continental shelf through observations of buried grounding zone wedges and mega scale glacial lineations the margin is also important for understanding the ability of glaciation to cause topographic relief changes and generate offshore geohazards such as the storegga slide which mobilised some 3000 km 3 of sediments during the holocene whilst the processes operating along the norwegian margin are well understood through the late cenozoic there is little geochronological control with which to constrain the environmental changes that have been observed concomitant with the wealth of knowledge and the extensive data that are currently available we propose that the norwegian margin is an ideal location to be considered for future ocean drilling the observations of multiple processes acting independently and together means ocean drilling could yield information of global significance due to the bridging location of norway s atlantic margin between the arctic and lower latitudes

blockfields old or new evidence and implications from some plateaus in northern norway evidence is presented from investigations on plateau top blockfields in still glaciated regions of north norway pits dug into these blockfields typically show profile depths 0 5 m and sometimes in excess of 1 m analysis of fines shows enrichment in the silt and clay sized fraction suggestive of prolonged chemical weathering chemical alteration of parent material is supported by xrd analysis which identifies a number of clay minerals present in blockfield samples a chemical weathering origin suggests that these plateau top blockfields are features which have considerable longevity in the landscape and have been forming since perhaps tertiary times the original weathering profiles have been destroyed by frost heaving mechanisms protection of the blockfield by cold based ice occurred during periods of glacial coverage

landscape preservation under fennoscandian ice sheets determined from in situ produced 10be and 26al some areas within ice sheet boundaries retain pre existing landforms and thus either remained as ice free islands nunataks during glaciation or were preserved under ice differentiating between these alternatives has significant implications for paleoenvironment ice sheet surface elevation and ice volume reconstructions in the northern swedish mountains in situ cosmogenic 10be and 26al concentrations from glacial erratics on relict surfaces as well as glacially eroded bedrock adjacent to these surfaces provide consistent last deglaciation exposure ages 8 13 kyr confirming ice sheet overriding as opposed to ice free conditions however these ages contrast with exposure ages of 34 61 kyr on bedrock surfaces in these same relict areas demonstrating that relict areas were preserved with little erosion through multiple glacial cycles based on the difference in radioactive decay between 26al and 10be the measured nuclide concentration in one of these bedrock surfaces suggests that it remained largely unmodified for a minimum period of 845 418 461 kyr these results indicate that relict areas need to be accounted for as frozen bed patches in basal boundary conditions for ice sheet models and in landscape development models subglacial preservation also implies that source areas for glacial sediments in ocean cores are considerably smaller than the total area covered by ice sheets these relict areas also have significance as potential long term subglacial biologic refugia

glacial trimlines to identify former ice margins and subglacial thermal boundaries a review and classification scheme for trimline expression abstract reconstructions of former ice sheets and glaciers provide important palaeoglaciological information about their behaviour in response to climate changes glacial trimlines record both the margin positions and palaeo ice thickness enabling the production of empirically constrained 3 dimensional reconstructions however the literature review into the characteristics interpretation and use of glacial trimlines here presented shows that these features have been under utilised and are poorly described in the existing literature with a confusing terminology currently in use a new classification scheme and terminology for trimline identification and interpretation is developed to better facilitate further research into these common features of glacierised and formerly glaciated landscapes

the detailed tephrostratigraphy of a core from the south east black sea spanning the last 60 ka one visible volcanic ash layer and 21 non visible cryptotephra horizons have been identified in the m72 5 25 gc1 core from the south east black sea that spans the last 60 ka glass chemistry suggests that the tephras derive from italian hellenic and turkish sources the visible tephra layer is trachytic in composition and has been correlated to the 39 ka campanian ignimbrite super eruption from campi flegrei caldera italy two cryptotephra layers are associated with eruptions from acigol volcano turkey around the last glacial maximum another is linked to activity at erciyes dagi in the early holocene perikartini or karagullu and a cryptotephra layer near the top of the core correlates to the 3 6k cal a bp minoan marine z2 tephra from santorini thera greece this extends the known dispersal area for all these volcanic ash units many other calc alkaline rhyolite layers preserved in the core are likely to be from central anatolian sources but the lack of detailed proximal data for many of the volcanoes in the region prohibits further correlations the tephrostratigraphy and glass compositional data presented here allow the tephra layers to be used to correlate sedimentary archives across the region and help to extend the mediterranean tephrochronology framework towards the east