development of glacial llyn teifi west wales evidence for lake level fluctuations at the margins of the irish sea ice sheet a thick sequence of quaternary laminated silt and clay sand gravel and diamict has recently been proven at llandudoch st dogmaels west wales most of these deposits accumulated in a tributary valley of afon river teifi that formed prior to the last glaciation the laminated silt and clay occur up to 103 m above present sea level and are considered to have been deposited in llyn lake teifi a large ice dammed lake that developed in the teifi valley as the irish sea ice sheet impinged onto the welsh mainland during the late devensian rhythmic units are interpreted as annual varves whose composition was determined by the distance from the sediment discharge point short term climate fluctuations during the summer months are evident in some of the varve units stratigraphic variations within the laminated deposits are considered to reflect different levels of llyn teifi which varied according to the position of the irish sea ice sheet in the teifi valley and the elevations of three overspill channels the overlying diamict sand and gravel deposits are thought to have accumulated close to the ice front as it encroached into llyn teifi during the final retreat of the irish sea ice sheet a series of kamiform sand and gravel deposits formed along the margins of the glacier

the late devensian glaciation along the western margin of the cheshire shroshire iowland the glacial succession in the western part of the cheshire shropshire lowland records the advance coalescence and subsequent uncoupling of irish sea and welsh ice sheets during the late devensian stage during advance a discontinuous sheet of basal till was emplaced across the floor of the region by subglacial lodgement on retreat compression of the irish sea ice sheet against bedrock obstruction generated a zone of supraglacial sedimentation resulting in the creation of the wrexham ellesmere wem whitchurch moraine system and the formation of a wide range of sedimentary environments including ice marginal sandur troughs ice front alluvial fans proglacial ribbon sandur and subglacial ice contact and proglacial lakes the geometry of sedimentary units and their lithologic and geomorphic characteristics display spatially ordered patterns of sediment landform assemblage which show that the statigraphic succession is a response to rapidly changing depositional conditions at a retreating supraglacial ice margin punctuated by minor still stands and ice front oscillations

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

a new varve sequence from windermere uk records rapid ice retreat prior to the lateglacial interstadial gi 1 abstract annually laminated sediments varves provide excellent temporal resolution to study rapid environmental change but are rare in the early part of the last termination 19 11 7 ka bp we present a new 400 varve year vyr varve sequence in two floating parts from windermere a lake at the southern margin of the mountains of northwest england this sequence records the final retreat of the windermere glacier at the southern edge of the lake district ice cap during the transition from heinrich stadial 1 18 14 7 ka bp into the lateglacial interstadial 14 7 12 9 ka bp laminated sediments from four lake cores from windermere s northern and southern basins were investigated and shown to be varved these sequences are integrated with seismic reflection evidence to reconstruct south to north deglaciation seismic and sedimentological evidence is consistent with gradual stepped ice retreat along the entire southern basin and into the northern basin between 255 and 700 vyr prior to the appearance of significant biota in the sediment that heralded the lateglacial interstadial and had retreated past a recessional moraine rm8 in the northern basin by 121 vyr prior to the interstadial the lateglacial interstadial age of this biota bearing unit was confirmed by 14c dating including one date from the northernmost core of 13 5 cal ka bp a change in mineralogy in all four cores as the glacier retreated north of the dent group the northernmost source of calcareous bedrock and a decrease in coarse grains in the varves shows that the ice had retreated along the entire north basin at 70 vyr prior to the lateglacial interstadial the estimated retreat rate is 70 114 m yr 1 although buried de geer moraines if annual may indicate retreat of 120 m yr 1 with a 3 year stillstand at a recessional moraine halfway along the basin the glacier then retreated north of the lake basin becoming land terminating and retreating at 92 5 49 m yr 1 the northernmost core has a varve sequence ending at least 111 vyr after the other core chronologies due to the increased proximity to remnant ice in the catchment uplands into the early lateglacial interstadial we show that almost all of the glacier retreat in the windermere catchment occurred before the abrupt warming at the onset of the lateglacial interstadial in keeping with similar findings from around the irish sea basin and suggesting a similar retreat timescale for other radial valley glaciers of the lake district ice cap the seismic and core evidence also show the potential for a much longer varve chronology extending at least 400 and potentially over 1000 vyr further back into heinrich stadial 1 18 14 7 ka bp suggesting that glacier retreat in the windermere valley initiated at least before 15 5 ka bp and perhaps 16 ka bp

the slip fiber chrysotile asbestos deposit in the zidani area northern greece abstract the chrysotile asbestos deposit of zidani in northern greece is an example of a slip fiber deposit associated with alpine type peridotites the deposit occurs in the northern part of an antigorite serpentinite and peridotite body tectonically emplaced on the pelagonian basement of the area a continuous retrograde alteration event is recognizable along the thrust fault between a metaclastic and carbonate sequence and the serpentinite body a phase of ductile deformation that formed antigorite mylonites was followed by a brittle one which formed schistose serpentinite the sense of shear of the overthrusting metaclastic mylonite coincides with that of the immediate underlying schistose and mylonite serpentinites thus retrogression of both groups of rocks is assumed to be the result of the thrust event the numerous altered amphibolite dikes crosscutting the ore created planar anisotropies during the thrust related deformation these planar anisotropies localized the deformation and consequently the formation of the schistose serpentinite and the asbestos ore in the northern part of the serpentinite body slip fiber chrysotile asbestos was formed along anastomosing non penetrating shear surfaces in the schistose serpentinite the chrysotile fibers replaced antigorite in situ in shear planes most likely at a transitional stage of deformation exhibiting both ductile and brittle fabrics however syntectonic filling of shear veins at the brittle stage is the major cause of the origin of the asbestos deposit

the last ice sheet in snowdonia in snowdonia there is a marked contrast between weathered summits often with well developed blockfields or tors and lower ice moulded terrain the boundary is interpreted as a trimline marking the upper surface of the last ice sheet this interpretation is supported by the presence of gibbsite an end product of prolonged weathering at the base of soils above but not below the trimline the reconstructed ice surface reaches about 850 m above present sea level along an ice divide running ne sw through the massif there is no evidence to support the popular view that ice centred further south extended over snowdonia and breaching to form the major glacial troughs can be explained by the action of local ice the field evidence presented here demonstrates that most models of the southern british and irish sea ice sheets are significantly flawed the earliest being far too thick and the most recent far too thin copyright 2000 john wiley sons ltd

a new approach for luminescence dating glaciofluvial deposits high precision optical dating of cobbles abstract in recent years luminescence dating has increasingly been applied to date glaciofluvial sediments but uncertainties about the degree of bleaching of the luminescence signal at deposition make dating of such sediments challenging here we test a new approach for luminescence dating of glaciofluvial sediments based on the analysis of rock cores drilled from granite cobbles and compare the luminescence ages generated against independent age control luminescence measurements from rock slices in cobble sized clasts can be used to reconstruct the extent of bleaching thereby giving greater confidence in the ages produced this study illustrates that another important advantage of using cobbles is that at depths of 2 mm or more below the cobble surface 90 of the total dose rate arises from the cobble itself making the dose rate insensitive to the water content of the sediment matrix ordinarily uncertainties in estimating water content during burial are one of the largest sources of uncertainty in luminescence dating methods and hence reducing the reliance upon the dose rate could be particularly advantageous for glacial deposits where water contents can potentially be large and highly variable measurements of cobbles from orrisdale head isle of man demonstrate that the luminescence signal was completely bleached to depths of up to 12 mm into the cobble sampling of orientated cobbles from lithofacies diagnostic of bar top environments was used to maximise the chances of exposure to sunlight the upper faces of these orientated cobble surfaces appear to be bleached to a greater depth than the lowermost faces data from 45 rock slices from these cobbles were tightly clustered yielding a mean age of 20 7 0 3 ka that is in agreement with independent age control one of the well bleached cobbles shows evidence of two discrete exposure events potentially recording both the advance at 26 2 0 8 ka and retreat at 20 7 0 3 ka of the irish sea ice stream

internal dynamics condition centennial scale oscillations in marine based ice stream retreat this paper was supported by a natural environment research council consortium grant briticechrono ne j008672 1

age determination of glacially transported boulders in ireland and scotland using schmidt hammer exposure age dating shd and terrestrial cosmogenic nuclide tcn exposure age dating schmidt hammer exposure age dating shd was applied at 15 sites with glacially transported granite boulders in parts of northern and western ireland and southwest scotland that had been exposed by retreat of the last british irish ice sheet biis or younger dryas yd ice masses seven of these surfaces had previously been dated using terrestrial cosmogenic nuclide tcn exposure age dating application of the granite calibration equation of tomkins et al 2018c indicated a close correspondence between the shd ages and the tcn ages within 1 or 2 uncertainties these findings demonstrate that shd ages can be of comparable accuracy precision and reliability to tcn ages and are a strong argument for the more extensive use of shd in some quaternary dating projects however surface ages obtained by both shd and tcn dating should not be accepted uncritically they must be assessed in relation to the wider geological geomorphological and geochronological evidence evaluation of eight shd ages for which corresponding tcn ages are not available indicate that most are consistent with current theory and field evidence but some anomalous age estimates occur

dynamic cycles ice streams and their impact on the extent chronology and deglaciation of the british irish ice sheet we present results from a suite of forward transient numerical modelling experiments of the british and irish ice sheet biis consisting of scottish welsh and irish accumulation centres spanning the last glacial period from 38 to 10 ka bp the 3d thermomechanical model employed uses higher order physics to solve longitudinal membrane stresses and to reproduce grounding line dynamics surface mass balance is derived using a distributed degree day calculation based on a reference climatology from mean 1961 1990 precipitation and temperature patterns the model is perturbed from this reference state by a scaled ngrip oxygen isotope curve and the specmap sea level reconstruction isostatic response to ice loading is computed using an elastic lithosphere relaxed asthenosphere scheme a suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities to yield a subset of experiments that showed close correspondence to offshore and onshore ice directional indicators broad biis chronology and the relative sea level record three of these simulations are described in further detail and indicate that the separate ice centres of the modelled biis complex are dynamically interdependent during the build up to maximum conditions but remain largely independent throughout much of the simulation the modelled biis is extremely dynamic drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time scale a series of binge purge advance retreat cycles are identified which correspond to alternating periods of relatively cold based ice associated with a high aspect ratio and net growth and wet based ice with a lower aspect ratio characterised by streaming the timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling but are modulated and phase lagged to the oscillations within the ngrip record of climate forcing phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate resulting in major iceberg melt discharge events into the north sea and atlantic ocean the broad chronology of the modelled biis indicates a maximum extent at 20 ka with fast flowing ice across its western and northern sectors that extended to the continental shelf edge fast flowing streams also dominate the irish sea and north sea basin sectors and impinge onto sw england and east anglia from 19 ka bp deglaciation is achieved in less than 2000 years discharging the freshwater equivalent of 2 m global sea level rise a much reduced ice sheet centred on scotland undergoes subsequent retrenchment and a series of advance retreat cycles into the north sea basin from 17 ka onwards culminating in a sustained younger dryas event from 13 to 11 5 ka bp modelled ice cover is persistent across the western and central highlands until the last remnant glaciers disappear around 10 5 ka bp

rapid thinning of the welsh ice cap at 20 19 ka based on 10be ages abstract new 10 be ages from the summits of three mountain areas of north wales reveal a very similar exposure timing as the welsh ice cap thinned after the global last glacial maximum eight bedrock and one boulder sample gave a combined arithmetic mean exposure age of 19 08 0 80 ka 4 2 1 similar exposure ages over a 320 m vertical range 824 to 581 m altitude show that ice cap thinning was very rapid and spatially uniform using the same production rate and scaling scheme we recalculated six published 10 be exposure ages from the nearby arans which also covered a similar elevation range from 608 to 901 m and obtained an arithmetic mean of 19 41 1 45 ka 7 5 1 the average exposure age of all 15 accepted deglaciation ages is 19 21 1 07 5 6 1 the complete dataset from north wales provides very strong evidence indicating that these summits became exposed as nunataks at 20 19 ka this result provides important insight to the magnitude of ice surface lowering and behavior of the welsh ice cap during the last deglaciation that can be compared to other ice masses that made up the british irish ice sheet

the origin of rodingites from cassiar british columbia and their use to estimate t and p h2o during serpentinization abstract the cassiar serpentinite located in north central british columbia is a low grade alpine type serpentinite within the sylvester allochthon two stages of rodingitization have occurred at cassiar and these correlate with two stages of serpentinization that have occurred in the ultramafic rock the first stage is characterised by an increase in ca activity and decreases in mg and sio 2 activities in the rodingite culminating in the crystallization of grossular in the rodingite and by the formation of lizardite in the serpentinite at a later time a second event occurred characterised by a decrease in ca activity and increases in mg and sio 2 activities both in the rodingite and the serpentinite this was marked by the crystallization of diopside prehnite and lizardite in the rodingite and by the recrystallization of lizardite to chrysotile and antigorite in the serpentinite the serpentine recrystallization and the development of the second stage rodingite minerals indicate that the changes in rodingite and serpentine mineral assemblages were driven by similar changes in the bulk rock compositions this suggests that the second stage event in both rodingite and serpentinite was caused by an externally derived fluid measurements on fluid inclusions in the rodingite minerals clinozoisite grossular and diopside of the second event indicate that the externally derived fluid was co 2 poor but relatively saline 8 1 5 equiv wt nacl by combining the pressure dependant temperature measurements from fluid inclusions with the pressure independant temperature measurements on 18 o in coexisting serpentine magnetite pairs the pressure of formation can be estimated the second event of serpentine recrystallization and rodingitization was an isothermal process at 300 c 36 c p h 2 o

bayesian modelling the retreat of the irish sea ice stream we present an 8000 year history spanning 650km of ice margin retreat for the largest marine terminating ice stream draining the former british irish ice sheet bayesian modelling of the geochronological data shows the isis expanded 34 0 25 3ka accelerating into the celtic sea to reach maximum limits 25 3 24 5ka before a collapse with rapid marginal retreat to the northern irish sea basin isb this retreat was rapid and driven by climatic warming sea level rise mega tidal amplitudes and reactivation of meridional circulation in the north atlantic the retreat though rapid is uneven with the stepped retreat pattern possibly a function of the passage of the ice stream between normal and adverse ice bed gradients and changing ice stream geometry initially wide calving margins and adverse slopes encouraged rapid retreat 550m a 1 that slowed 100m a 1 at the topographic constriction and bathymetric high between southern ireland and wales before rates increased 200m a 1 across adverse bed slopes and wider and deeper basin configuration in the northern isb these data point to the importance of the ice bed slope and lateral extent in predicting the longer term 1000 a patterns and rates of ice marginal retreat during phases of rapid collapse which has implications for the modelling of projected rapid retreat of present day ice streams copyright 2013 john wiley sons ltd

evidence for an upwelling mantle plume beneath the songliao basin northeast china abstract a mushroom like low velocity body mllvb was defined by tomography beneath northeast china which may be linked to a vestige of the mesozoic upwelling mantle plume however multiple lines of evidence indicate that the necessary condition of the upwelling is that the upwelling mantle plume has a temperature sufficiently higher than that of the surrounding mantle the upwelling mantle plume cannot be defined only based on the low velocity structure to investigate this issue i conducted common conversion point ccp stacking of receiver functions in northeast china and designed six ccp stacking profiles crossing northeast china the results show that when the ccp stacking profiles cross the location of the mllvb the topography of the 410 and 660 km discontinuities did not exhibit obvious variations instead two 520 km discontinuities merged into a single discontinuity which indicates that the mllvb had an upwelling temperature condition the ccp stacking image of the receiver functions also reveals a deepening of the 410 km discontinuity and shallowing of the 660 km discontinuity at the center of the songliao basin along the 45 n profiles which might be associated with the mesozoic upwelling mantle plume

new age constraints for the maximum extent of the last british irish ice sheet nw sector this paper presents the first terrestrial age constraints from the outer continental shelf for the maximum extent of the nw sector of the last british irish ice sheet cosmogenic 10be ages from eight glacially transported boulders on the island of north rona show that the late devensian late weichselian british irish ice sheet overrode the island at its maximal stage and retreated c 25 ka bp these new dates supported by other geological evidence indicate that the north western part of the ice sheet was most extensive between 27 and 25 ka bp reaching the outer continental shelf during the global eustatic sea level minimum at the last glacial maximum

origin of an esker like ridge erosion or channel fill sedimentology of the monington esker in southwest wales abstract a ridge of stratified gravel and sand near cardigan in southwest wales has previously been interpreted as an esker its sedimentology is exposed in sand pits and consists of cross bedded gravel and sand incised into a complex of climbing ripple cross laminated sand interbedded with silt and clay the succession records the progradation of fluvial channels across a former lake floor there is no clear sedimentological evidence that the sediments were deposited in an ice contact setting and therefore the feature should not be called an esker the interpretation favoured here is that the ridge is an erosional remnant either of a formerly more extensive outwash plain or of a kame terrace deposited when the adjacent valley was filled with dead ice recognition of an esker needs to be based on sedimentology and regional setting as well as on geomorphology

domainal failure of serpentinite in shear zones state line mafic complex pennsylvania u s a abstract deformation within 0 2 1 4 km wide dextral strike slip shear zones in the serpentinite portion of the state line mafic complex pennsylvania maryland is partitioned into two types anastomosing throughgoing mylonitic faults experienced a long relatively simple deformational history of unidirectional dextral transcurrent shearing the relatively less deformed lenticular shaped areas between these faults deformed in a complex sequence of faulting the lenticular pods contain early e striking extensional veins and brittle reverse faults with north strikes northeast striking dextral strike slip faults deformed the veins and reverse faults east striking shear bands developed in both the throughgoing faults and the mylonitic dextral faults within the lenticular pods northwest striking sinistral strike slip faults transected the lenticular pods and earlier faults the sinistral mylonites formed shear bands late in their movement history a similar sequence of faulting occurred in microscopic lenticular pods within mylonitic serpentinite these faults exhibit the same orientation and sequence as their larger counterparts but are clearly not synchronous with them each lenticular pod may have acted as a separate system and therefore like faults between pods of any size may not have been synchronous

10be and 26al exposure age dating of bedrock surfaces on the aran ridge wales evidence for a thick welsh ice cap at the last glacial maximum this paper presents results of the analysis of paired cosmogenic isotopes 10be and 26al from eight quartz rich samples collected from ice moulded bedrock on the aran ridge the highest land in the british isles south of snowdon on the aran ridge comprising the summits of aran fawddwy 905 m a s l and aran benllyn 885 m a s l 26al and 10be ages indicate complete ice coverage and glacial erosion at the global last glacial maximum lgm six samples from the summit ridge above 750 800 m a s l yielded paired 10be and 26al ages ranging from 17 2 to 34 4 ka respectively four of these samples are very close in age 10be ages of 17 5 0 6 17 5 0 7 19 7 0 8 and 20 0 0 7 ka and are interpreted as representing the exposure age of the summit ridge two other summit samples are much older 10be ages of 27 5 1 0 and 33 9 1 2 ka and these results may indicate nuclide inheritance the 26al 10be ratios for all samples are indistinguishable within one sigma uncertainty from the production rate ratio line indicating that there is no evidence for a complex exposure history these results indicate that the last welsh ice cap was thick enough to completely cover the aran ridge and achieve glacial erosion at the lgm however between c 20 and 17 ka ridge summits were exposed as nunataks at a time when glacial erosion at lower elevations below 750 800 m a s l was achieved by large outlet glaciers in the valleys surrounding the mountains copyright 2011 john wiley sons ltd

growth dynamics and deglaciation of the last british irish ice sheet the deep sea ice rafted detritus record the evolution and dynamics of the last british irish ice sheet biis have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data this reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary in order to enhance biis reconstruction we present a compilation of new and previously published ice rafted detritus ird flux and concentration data from high resolution sediment cores recovered from the ne atlantic deep sea continental slope adjacent to the last biis these cores are situated adjacent to the full latitudinal extent of the last biis and cover marine isotope stages mis 2 and 3 age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera neogloboquadrina pachyderma sinistral nps to the greenland gisp2 ice core record multiple ird fingerprinting techniques indicate that at the selected locations most ird are sourced from adjacent biis ice streams except in the centre of heinrich h layers in which ird shows a prominent laurentide ice sheet provenance ird flux data are interpreted with reference to a conceptual model explaining the relations between flux north atlantic hydrography and ice dynamics both positive and rapid negative mass balance can cause increases and prominent peaks in ird flux first order interpretation of the ird record indicates the timing of the presence of the biis with an actively calving marine margin the records show a coherent latitudinal but partly phased signal during mis 3 and 2 published data indicate that the last biis initiated during the mis 5 4 cooling transition renewed growth just before h5 46 ka was succeeded by very strong millennial scale variability apparently corresponding with dansgaard oeschger do cycles closely coupled to millennial scale climate variability in the north atlantic region involving latitudinal migration of the north atlantic polar front this indicates that the previously defined precursor events are not uniquely associated with h events but are part of the millennial scale variability major growth of the ice sheet occurred after 29 ka with the barra ice stream attaining a shelf edge position and generating turbiditic flows on the barra donegal fan at 27 ka the ice sheet reached its maximum extent at h2 24 ka earlier than interpreted in previous studies rapid retreat initially characterised by peak ird flux during greenland interstadial 2 23 ka was followed by readvance between 22 and 16 ka readvance during h1 was only characterised by biis ice streams draining central dome s of the ice sheet and was followed by rapid deglaciation and ice exhaustion the evidence for a calving margin and ird supply from the biis during greenland stadial 1 younger dryas event is equivocal the timing of the initiation maximum extent deglacial and readvance phases of the biis interpreted from the ird flux record is strongly supported by recent independent data from both the irish sea and north sea sectors of the ice sheet

tephrochronology and the extended intimate integration of ice core marine and terrestrial records event stratigraphy 8 128 ka b2k the comparison of palaeoclimate records on their own independent timescales is central to the work of the intimate integrating ice core marine and terrestrial records network for the north atlantic region an event stratigraphy has been established from the high precision greenland ice core records and the integrated gicc05 chronology this stratotype provides a palaeoclimate signal to which the timing and nature of palaeoenvironmental change recorded in marine and terrestrial archives can be compared to facilitate this wider comparison without assuming synchroneity of climatic change proxy response intimate has also focussed on the development of tools to achieve this in particular the use of time parallel marker horizons e g tephra layers volcanic ash coupled with the recent temporal extension of the greenland stratotype as part of this special issue we present an updated intimate event stratigraphy highlighting key tephra horizons used for correlation across europe and the north atlantic we discuss the advantages of such an approach and the key challenges for the further integration of terrestrial palaeoenvironmental records with those from ice cores and the marine realm

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

exposure age constraints on the extent timing and rate of retreat of the last irish sea ice stream abstract we report 23 cosmogenic isotope exposure ages 10be and 36cl relating to the maximum extent and deglaciation chronology of the irish sea ice stream isis which drained the sw sector of the last british irish ice sheet these show that the isis failed to reach the preseli hills of north pembrokeshire yet extended southwards to impinge on northern isles of scilly 50 n during the last glacial maximum four samples from western anglesey demonstrate deglaciation of the southern irish sea basin by c 20 18 ka and two from the ll n peninsula in northwest wales if valid suggest deglaciation by c 23 22 ka followed by gradual oscillatory northwards retreat of the ice margin for over 3000 years an alternative interpretation of our data suggests that ice reached scilly as late as 22 21 ka then retreated 450 km northwards within the following three millennia possibly in response to sea level rise and or intrinsic reorganisation within the last british irish ice sheet samples from upland source areas of the isis in nw england and sw scotland produced exposure ages 14 3 ka suggesting possible persistence of ice in such areas into the lateglacial interstade of 14 7 12 9 ka

high resolution numerical simulation of younger dryas glaciation in scotland golledge n r hubbard a sugden d e 2008 high resolution numerical simulation of younger dryas glaciation in scotland quaternary science reviews 27 9 10 888 904 sponsorship nerc

late devensian and holocene shorelines of the british isles and north sea from models of glacio hydro isostatic rebound sea level change around the british isles since the time of the last glacial maximum is largely due to of the crustal rebound from the glacial unloading of northern britain and the concomitant melt water loading of the adjacent seas and atlantic ocean minor but not insignificant contributions also result from the rebound caused by the unloading of the distant ice sheets including fennoscandia and north america observations of sea level change for this period constrain the glacio hydro isostatic rebound model parameters describing the effective lithospheric thickness or rigidity and the effective mantle viscosity as well as certain ice sheet characteristics such as the ice thickness at the time of the last glacial maximum the models permit palaeobathymetry and palaeoshorelines to be predicted for the british isles region including the north sea the resulting evolution of the coastlines exhibits a complex behaviour through time one that is quite different from the usual models in which sea level change is assumed to be a function of time only in part this is because of the delayed response of the mantle to the spatially variable and time dependent ice and water loads and in part because the unloading history of the british ice sheet is different from those of the major global ice sheets thus maximum emergence of the north sea occurred after deglaciation had started and lasted for an extended period from about 15 000 to 12 000 radiocarbon years bp during this relative sea level still stand shoreline features could have formed for example along the western edge of the norwegian trough when access to the firths of eastern scotland would have been via a long and shallow marine inlet shoreline retreat across the north sea became relatively rapid after about 10000 years the model predictions for the irish and celtic seas also suggest a complex behaviour with the formation of a wide land bridge between about 20000 and 13 000 years ago the model also suggests that as long as the scottish ice extended across the northern irish sea until about 14 000 years ago there would have been a large freshwater periglacial lake located further south both the predicted sea level height age relations and the shoreline positions are consistent with a large body of observational evidence but some discrepancies occur particularly in northern scotland and ireland where the ice heights may have been somewhat greater than assumed in the model

flow pattern evolution of the last british ice sheet we present a 10 stage reconstruction of the evolution in ice flow patterns of the last british ice sheet from build up to demise derived from geomorphological evidence 100 flowsets identified in the subglacial bedform record drumlins mega scale glacial lineations and ribbed moraine are combined with ancillary evidence erratic transport paths absolute dates and a semi independently reconstructed retreat pattern to define flow patterns ice divides and ice sheet margins during build up maximum glaciation and retreat overprinting and cross cutting of landform assemblages are used to define the relative chronology of flow patterns and a tentative absolute chronology is presented based on a collation of available dates for ice advance and retreat the ice flow configuration of the last british ice sheet was not static some ice divides were remarkably stable persisting through multiple stages of the ice sheet evolution whereas others were transient features existing for a short time and or shifting in position 10s km the 10 reconstructed stages of ice sheet geometry capture two main modes of operation first as an integrated ice sheet with a broadly n s orientated ice divide and second as a multi domed ice sheet orientated parallel with the shelf edge a thick integrated ice sheet developed as ice expanded out of source areas in scotland to envelop southerly ice caps in northern england and wales and connect with the irish ice sheet to the west and the scandinavian ice sheet across the north sea following break up of ice over the north sea ice streaming probably drove mass loss and ice sheet thinning to create a more complex divide structure where ice flow patterns were largely controlled by the form of the underlying topography ice surface lowering occurred before separation of and retreat to multiple ice centres centred over high ground we consider this 10 stage reconstruction of the evolution in ice sheet configuration to be the simplest palaeo glaciological interpretation of the flowsets identified from the geomorphological record and their relative timing this empirically based reconstruction of flow pattern geometry provides a framework for more detailed local and regional studies and numerical modelling to provide robust explanations of the observed changes in ice sheet structure in terms of climate and glacial dynamics as a minimum numerical model outputs should be able to reproduce the identified flowset patterns in space and satisfy their chronological order

new age constraints for the limit of the british irish ice sheet on the isles of scilly the southernmost terrestrial extent of the irish sea ice stream isis which drained a large proportion of the last british irish ice sheet impinged on to the isles of scilly during marine isotope stage 2 however the age of this ice limit has been contested and the interpretation that this occurred during the last glacial maximum lgm remains controversial this study reports new ages using optically stimulated luminescence osl dating of outwash sediments at battery tresco 25 5 1 5 ka and terrestrial cosmogenic nuclide exposure dating of boulders overlying till on scilly rock 25 9 1 6 ka which confirm that the isis reached the isles of scilly during the lgm the ages demonstrate this ice advance on to the northern isles of scilly occurred at 26 ka around the time of increased ice rafted debris in the adjacent marine record from the continental margin which coincided with heinrich event 2 at 24 ka osl dating 19 6 1 5 ka of the post glacial hell bay gravel at battery suggests there was then an 5 ka delay between primary deposition and aeolian reworking of the glacigenic sediment during a time when the isis ice front was oscillating on and around the ll n peninsula 390 km to the north

structural and depositional evidence for repeated ice marginal oscillation along the eastern margin of the late devensian irish sea ice stream abstract late devensian glacigenic sediments and landforms along the north west coast of wales document the advance and subsequent retreat of the eastern margin of an irish sea ice stream that met coalesced and ultimately uncoupled from ice radiating outwards from the adjacent welsh ice cap centred over snowdonia across the boundary between the two former ice masses is a set of sediment landform assemblages that reflect rapidly changing erosional and depositional conditions during ice interaction from the inner part of the ice stream the assemblages range outwards from a subglacial depositional assemblage characterised by drumlin swarms through a subglacial erosional assemblage marked by prominent bedrock scours and large subglacial rock channels through an ice marginal assemblage identified by closely spaced glaciotectonised push moraines and intervening marginal sandur troughs into a freely expanding proglacial sandur and lacustrine delta assemblage the ice marginal assemblage provides evidence for numerous oscillatory episodes during retreat and at least 20 ice marginal limits can be identified at least 11 of these display multiple criteria for identifying readvance and in the ideal case is characterised by a moraine form built by localised tectonic stacking of diamict to the rear fronted by a clastic wedge of ice front alluvial fan gravel and intercalated flow till the distribution of sediment landform assemblages suggests a highly dynamic convergent ice stream flow pattern with high ice velocity a sharply delineated lateral shear margin pervasive ice marginal glaciotectonic deformation and a tightly focused ice marginal sediment delivery system all signature characteristics of contemporary ice streams

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

extent and deglacial chronology of the last british irish ice sheet implications of exposure dating using cosmogenic isotopes over 160 10be and 36cl exposure ages pertaining to the extent and chronology of the last british irish ice sheet biis are critically reviewed despite uncertainties inherent in the use of exposure ages this approach has demonstrated that at the last glacial maximum lgm ca 26 21 ka the biis extended over all low ground in scotland and all or almost all of ireland consistent with recent models depicting extension of the last biis to the atlantic shelf edge all exposure ages obtained for high level sites above trimlines on the mountains of northwestern scotland and ireland pre date the lgm this finding confirms that high plateaux in these areas escaped significant glacial erosion probably under a protective cover of cold based glacier ice that remained frozen to the underlying substrate in terms of deglaciation chronology the southern irish sea basin was probably deglaciated by 19 18 ka with extensive deglaciation of low ground in ireland and northeastern scotland prior to ca 14 5 ka ice cover on low ground in northwestern scotland apparently persisted after 14 0 ka suggesting survival of ice in favourable locations during the lateglacial interstade ca 14 5 12 9 ka attempts to date readvances have had mixed success the wester ross readvance in northwestern scotland was initially dated to ca 16 3 ka but more recent research implies a much younger age ca 14 0 13 5 ka exposure ages indicating a prolonged stillstand during ice sheet retreat in the cairngorms at ca 14 5 14 0 ka conflict with ages obtained on postglacial rockslides and basal radiocarbon dates which indicate deglaciation before ca 15 5 15 0 ka exposure dating has been successfully employed to confirm a loch lomond stadial ca 12 9 11 5 ka age for moraines in several mountain areas and to constrain the minimum altitude of the ice cap that extended over the western grampians at that time copyright 2009 john wiley sons ltd

the origin of alpine peridotite hosted cross fiber chrysotile asbestos deposits cross fiber chrysotile asbestos deposits within serpentinized alpine type peridotites are syntectonic the asbestos veins fill tension fractures induced by regional stress fields moderated by local structural heterogeneities inverting this process by measuring the orientation of the veins yields the regional stress regime at the time the veins were formed measurements at several asbestos mines cassiar mine british columbia thetford mines quebec and woodsreef mine new south wales suggest that the asbestos develops during a change in the orientation of the regional stress which appears kinematically as a change from dip slip to strike slip fault motion this interpretation is compatible with other independent sets of structural data several factors determine whether or not an asbestos deposit is developed first the serpentinite must have a nonfoliated texture mineralogy does not appear to be important second it must be situated near a fault that is active during a change in the orientation of the stress field third the serpentinite must be in the stability field of chrysotile when the change in orientation occurs last subsequent deformation must not continue or temperature increase such that the fiber is destroyed

the glacial origins of relict pingos wales uk ramparted depressions doughnut shaped debris cored ridges with peat and or sediment filled central basins are commonly perceived to represent the relict collapsed forms of permafrost ground ice mounds i e pingos or lithalsas in wales uk ramparted depressions of late pleistocene age have been widely attributed to permafrost related processes however a variety of alternative glacial origins for these enigmatic landforms are also consistent with the available geological and geomorphological evidence although previous studies have barely considered such alternative processes of formation from detailed geophysical sedimentological and remote sensing studies at two field sites we demonstrate that i the wastage of stagnating glacier ice is a viable alternative explanation for the formation of ramparted depressions in wales ii the glacial geomorphology and geology of these landforms is analogous to supraglacial and subglacial landforms from the last laurentide and fennoscandian ice sheets iii these landforms have significant potential for characterising the nature of deglaciation around the margins of the irish sea during the last glacial cycle and may record evidence for the overextension and stagnation of the south eastern margin of the irish sea ice stream and iv investigations of ramparted depressions within formerly glaciated terrains must consider both glacial and periglacial mechanisms of formation

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

palaeoenvironmental interpretation of an ice contact glacial lake succession an example from the late devensian of southwest wales uk abstract during the late devensian late weichselian glaciation a number of large proglacial lakes developed in dammed river valleys along the southwest coast of wales u k this paper presents sedimentological data together with a digital terrain model to establish the sedimentation history dynamics and evolution of the largest lake glacial llyn lake teifi buried valley fill sequences within the margins of the former lake basin reveal a thick succession of glaciolacustrine muds which coarsen upward into or are locally abruptly overlain by proximal deltaic subglacial and glaciofluvial deposits sediment delivery pathways represented in the lacustrine succession include gravity flows suspension settling deltaic aggradation and iceberg rafting the latter indicating ice contact conditions the lacustrine muds are variably deformed with a range of syn and post depositional structures some of which indicate subglacial deformation associated with overriding of the lacustrine succession syn depositional structures indicate high sedimentation rates which may explain an absence of bioturbation structures the overall coarsening upward succession and cap of subglacial and or glaciofluvial deposits support recent theories suggesting that glacial llyn teifi formed during glacial advance there is no evidence to support glaciomarine conditions of sedimentation in this area of the irish sea basin

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 john wiley sons ltd

glacial rebound of the british isles ii a high resolution high precision model summary observations of ice movements across the british isles and of sea level changes around the shorelines during late devensian time after about 25 000 yr bp have been used to establish a high spatial and temporal resolution model for the rebound of great britain and associated sea level change the sea level observations include sites within the margins of the former ice sheet as well as observations outside the glaciated regions such that it has been possible to separate unknown earth model parameters from some ice sheet model parameters in the inversion of the glaciohydro isostatic equations the mantle viscosity profile is approximated by a number of radially symmetric layers representing the lithosphere the upper mantle as two layers from the base of the lithosphere to the phase transition boundary at 400 km the transition zone down to 670 km depth and the lower mantle no evidence is found to support a strong layering in viscosity above 670 km other than the high viscosity lithospheric layer models with a low viscosity zone in the upper mantle or models with a marked higher viscosity in the transition zone are less satisfactory than models in which the viscosity is constant from the base of the lithosphere to the 670 km boundary in contrast a marked increase in viscosity is required across this latter boundary the optimum effective parameters for the mantle beneath great britain are a lithospheric thickness of about 65 km a mantle viscosity above 670 km of about 4 5 lo2 pa s and a viscosity below 670 km greater than 4 x lo2 pas

palaeoglaciology of the welsh sector of the british irish ice sheet this palaeoglaciological reconstruction based on the distribution of glacial lineations interpreted from satellite imagery considers the extent thickness and dynamics of the welsh ice cap and its interaction with the british irish ice sheet two major ice flow events were identified the oldest phase of ice flow event i is characterized by ice flowing from an ice dispersal centre situated over the higher terrain in north central wales and by ice thick enough to cover the mountain summits at this time the interior of the ice cap is inferred to have been dominated by cold based ice during the growth of the welsh ice cap it became confluent with the british irish ice sheet the welsh ice cap at this time was again sufficiently thick to submerge the highest mountain summits the youngest detected phase of ice flow event ii was marked by an abrupt change in the dynamics of the welsh ice cap during event ii the welsh ice cap was drained by at least four ice streams which followed major troughs in northern and eastern wales

did large ice caps persist on low ground in north west scotland during the lateglacial interstade recent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north west scotland throughout the lateglacial interstade greenland interstade 1 ca 14 7 12 9 ka and that glacier ice was much more extensive in this area during the older dryas chronozone ca 14 0 ka than during the younger dryas stade ca 12 9 11 7 ka we have recalibrated the same exposure age data using locally derived 10be production rates this increases the original mean ages by 6 5 12 implying moraine deposition between ca 14 3 and ca 15 1 ka and we infer a most probable age of ca 14 7 ka based on palaeoclimatic considerations the internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin the wester ross readvance pollen stratigraphic evidence from a lateglacial site at loch droma on the present drainage divide demonstrates deglaciation before ca 14 0 ka and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade ca 14 7 14 0 ka this inference appears consistent with lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in scotland between 14 and 13 ka that large active glaciers probably survived throughout the lateglacial interstade and that ice extent was greater during the older dryas period than during the younger dryas stade copyright 2011 john wiley sons ltd