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

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

permafrost tectonics and past and future regional climate change yukon and adjacent northwest territories late tertiary changes in the general circulation of the atmosphere regionally enhanced by uplift of the wrangell saint elias and coast mountains were sufficient to promote permafrost development in the western arctic permafrost developed in yukon territory and adjacent northwest territories during early pleistocene glacial periods after continued tectonic activity led to further modification of regional climate but degraded in the interglacials permafrost has been present in northern parts of the region since the illinoian glaciation but most ground ice in central yukon formed in the late wisconsinan the present interglacial is the only one with widespread evidence of permafrost which is maintained in the valleys of central and southern yukon by the saint elias mountains blocking continental penetration of maritime air from the gulf of alaska this reduces snow depth in winter while cold air drainage in the dissected terrain of the yukon plateaus enhances the near surface inversion leading t

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 chronology of speleothem deposition in northern yukon and its relationships to permafrost in the northern yukon there is a significant group of limestone caves in an area that was not glaciated during the quaternary permafrost appears to have played an important role in restricting calcite speleothem deposition in the caves u th dating and stable isotopic studies indicate that the deposits form two distinct groups a first group younger than 350 ka and a second group older than the 350 ka bp limit of the conventional u th alpha spectrometric dating method two large samples from the second group yield sequences of magnetic declinations and inclinations with reversed and normal polarity perhaps from the tertiary the pollen content of five speleothems the modes of calcite deposition and stable isotopic analyses indicate that the speleothems were deposited under a cold regime it is suggested that the ancient speleothems were deposited at a time when permafrost was absent during the later tertiary or at the beginning of the quaternary period the establishment and maintenance of permafros

cosmogenic 36cl accumulation in unstable landforms 1 effects of the thermal neutron distribution cosmogenic nuclides produced in situ within minerals at the surface of the earth are proving to be an effective means of assessing geomorphic histories the use of multiple cosmogenic nuclides permits both exposure times and erosion rates to be determined however if two nuclides are produced only by spallation reactions the systematic differences in their accumulation rates depend only on the differences in their production rates and half lives the relatively small differences that result require a high degree of analytical precision to yield useful results in contrast to other spallogenic nuclides sup 36 cl is also produced by low energy neutron absorption which creates a different pattern of production as a function of depth we have measured the thermal flux with depth in a concrete block using sup 3 he filled neutron detectors the measured thermal neutron profile agrees well with predictions from a simple diffusion based thermal neutron distribution model calculations of sup 36 cl production using the model suggest that the use of sup 36 cl along with a purely spallogenic nuclide to determine erosion rates and exposure times should be less sensitive to analytical error than are determinations from two purely spallogenic nuclides 31 refs 7 figs 3 tabs

investigating absolute chronologies of glacial advances in the nw sector of the cordilleran ice sheet with terrestrial in situ cosmogenic nuclides abstract geologic mapping in yukon territory canada over the past 100 years has revealed a consistent pattern of diminishing cordilleran ice sheet cis extent during successively younger glaciations although this pattern is generally accepted there is still much uncertainty about the number of glaciations their ages and the dynamics of the different lobes that constituted the digitate ice sheet margin their subglacial thermal regimes and ice thicknesses we address uncertainties in the timing of glaciation using cosmogenic nuclide exposure dating at key localities that straddle several major lobes of the cis in west central yukon territory differences in exposure duration within what are thought to be the same map units are perhaps due to inheritance older than expected but more likely result from postglacial shielding younger than expected or surface erosion despite a significant spread in exposure durations on moraines and within map units and tending to rely on longest exposure durations on moraines due to postglacial degradation and shielding our results indicate that the mcconnell glacial advance occurred during marine oxygen isotope stage mis 2 judging from oldest minimum apparent exposure ages of 15 7 1 5 and 17 7 1 6 ka a gladstone glacial advance occurred before 51 8 4 7 ka mis 4 and reid glacial advances before 79 8 7 3 and 82 8 7 5 ka consistent with mis 6 traces of even older glacial advances predate 100 ka 107 5 9 9 154 3 14 2 ka

geologic evolution of the yukon river implications for placer gold abstract the greatest placer potential in northwest canada lies in preglacial drainage systems the largest placer gold deposits are associated with pliocene pre glacial fluvial gravels of the dawson range in particular klondike plateau of west central yukon the abundance and or the lack of gold concentration in this area were controlled by the ability of the streams to aggrade in response to changes caused by extensional faulting in the tintina trench differential uplift and regional denudation gold bearing gravels in the northern and eastern slopes of the dawson range are found in low order tributaries of the pre glacial south flowing yukon river glaciation played an important role in masking and changing the direction of drainage and creating new channels in this region the earliest known drainage changes relate to late miocene formation of the tintina trench and early pliocene uplift of the st elias mountains prior to these events the yukon river drained south into the gulf of alaska initial regional glaciation 2 6 2 9 ma diverted the southward drainage toward the northwest becoming part of the kwikhpak river in alaska the present yukon river drainage basin is about 27 5 larger than the ancestral kwikhpak river basin the evolution of the river is described here in three stages 1 drainage in pre late miocene 2 drainage in early pliocene and 3 drainage after earliest pliocene glaciation

degradation of unconsolidated quaternary landforms in the western north america abstract one of the major goals of geomorphology is to understand the rate of landscape evolution and the constraints that erosion sets on the longevity of land surfaces the latter has also turned out to be vital in modern applications of cosmogenic exposure dating and interpretation of lichenometric data from unconsolidated landforms because the effects of landform degradation have not been well documented disagreements exist among researchers regarding the importance of degradation processes in the dating techniques applied to exposures here we show that all existing qualitative data and quantitative markers of landform degradation collectively suggest considerable lowering of the surface of unconsolidated landforms over the typical life span of quaternary moraines or fault scarps degradation is ubiquitous and considerable even on short time scales of hundreds of years on steeply sloping landforms these conservative analyses are based entirely on field observations of decreasing slope angles of landforms over the typical range of ages in western north america and widely accepted modeling of landscape degradation we found that the maximum depth of erosion on fault scarps and moraines is on average 34 of the initial height of the scarp and 25 of the final height of the moraine although our observations are limited to fault scarps and moraines the results apply to any sloping unconsolidated landform in the western north america these results invalidate the prevailing assumption of no or little surface lowering on sloping unconsolidated landforms over the quaternary period and affirm that accurate interpretations of lichen ages and cosmogenically dated boulder ages require keen understanding of the ever present erosion in our view the most important results are twofold 1 to show with a large data set that degradation affects universally all sloping unconsolidated landforms and 2 to unambiguously show that even conservative estimates of the total lowering of the surface operate at time and depth scales that significantly interfere with cosmogenic exposure and lichen dating

mapping brittle fracture zones in three dimensions high resolution traveltime seismic tomography in a granitic pluton summary fractured and altered zones within a granitic pluton are mapped in three dimensions by means of high resolution seismic traveltime tomography the input traveltimes were picked from offset and azimuth variable vertical seismic profiles ovsp acquired in three boreholes and from seismic shot gathers of four cdp high resolution seismic reflection profiles recorded on the surface for the ovsp data a hydrophone streamer placed in the boreholes recorded the acoustic energy generated a signal with a frequency content between 15 to 150 hz by a vibroseis truck at source points distributed every 30 m in a rectangular grid of 620 m by 150 m the combination of borehole and surface seismic data resulted in an increase in the ray density of the shallow subsurface the tomographic algorithm uses a variable model grid with a finer grid spacing close to the surface were ray density is highest and the velocity variations are strongest therefore the resulting velocity models feature more detail at shallow levels a simple and smooth starting velocity model was derived from p wave velocity logs careful surface geological mapping and borehole geophysical data p and s wave velocity logs and poisson s ratio depth functions provided key constraints for a physically reasonable 3 d interpretation of the tomograms the low velocity anomalies constrained by the tomographic images were interpreted as unconsolidated rock fractures and altered zones which correlate with structures mapped at the surface or velocity anomalies identified in the logs subsequent resolution analysis revealed that the derived velocity model is well constrained to depths of 60 m

timing of terminal pleistocene deglaciation at high elevations in southern and central british columbia constrained by 10be exposure dating abstract the cordilleran ice sheet cis covered most of british columbia and southern yukon territory at the local last glacial maximum llgm during marine oxygen isotope stage 2 however its subsequent demise is not well understood particularly at high elevations east of its ocean terminating margin we present 10be exposure ages from two high elevation sites in southern and central british columbia that help constrain the time of initial deglaciation at these sites we sampled granodiorite erratics at elevations of 2126 2230 m a s l in the marble range and 1608 1785 m a s l in the telkwa range at the western margin of the interior plateau the erratics at both sites are near ice marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation the locations of the erratics and their relations to meltwater channels ensure that the resulting 10be ages date cis deglaciation and not the retreat of local montane glaciers our sample sites emerged above the surface of the cis as its divide migrated westward from the interior plateau to the axis of the coast mountains two of the four samples from the summit area of the marble range yielded apparent exposure ages of 14 0 0 7 and 15 2 0 8 ka these ages are 1 8 3 0 ka younger than the well established llgm age of ca 17 ka for the puget lobe of the cis in washington state they are 1 7 ka younger than the llgm age for the puget lobe if a snow shielding correction to their uncertainty weighted mean age is applied the other two samples yielded much older apparent exposure ages 20 6 1 4 and 33 0 1 5 ka indicating the presence of inherited isotopes four samples collected from the summit area of the telkwa range in the hazelton mountains yielded well clustered apparent exposure ages of 10 1 0 6 10 2 0 7 10 4 0 5 and 11 5 1 1 ka significant present day snow cover introduces a large uncertainty in the apparent exposure ages from this site a snow shielding correction based on present day snow cover data increases the uncertainty weighted mean exposure age of the telkwa range erratics to 12 4 0 7 ka consistent with deglacial 14c ages from areas near sea level to the west our exposure ages show a thinning of the southern portion of the cis shortly after the llgm and persistence of a remnant mountain ice cap in the central coast mountains into the younger dryas chronozone our data also show that the summit area of the marble range was ice covered during the llgm the presence of an ice body of considerable dimension in north central british columbia until or possibly even after the younger dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the skeena mountains in northwest british columbia and the need for better understanding of the response of the cis to lateglacial climate fluctuations

an 18 million year record of vegetation and climate change in northwestern canada and alaska tectonic and global climatic correlates abstract we reconstruct long term vegetation paleoclimatic trends spanning the last 18 million years in alaska yukon and far western northwest territories twenty one average percentage spectra for pollen and spores are assembled from eight surface subsurface sections the sections are dated independently or by correlation pollen and spore ratios indicate the direction of change in vegetation and climatic parameters growing season temperature test tree canopy density cest and paludification at study sites pest a global warm peak ca 15 ma is shown by the abundance of thermophilous taxa including fagus and quercus a temperature decline immediately following 15 ma parallels climatic reconstructions based on marine oxygen isotopes subsequent declines correlate to the messinian event and the onset of late pliocene pleistocene glaciation after 7 ma herbs and shrubs become more important elements of the palynological assemblages suggesting a more continental colder drier climate however a late pliocene warm interval is evident vegetation climatic changes during the early to late miocene show synchrony with and are most economically attributable to global events after 7 ma vegetation climate change is attributed primarily to latest miocene to pleistocene uplift of the alaska range and st elias mts the continuing influence of global climatic patterns is shown in the late pliocene warm interval despite uplift to the south the opening of the bering strait ca 3 ma may have moderated the climate in the study area

nunataks and valley glaciers over the mountains and through the ice models of the first peopling of the americas characterize arrival routes either along the coast or through the ice free corridor following the last glacial maximum while the pendulum has currently swung somewhat towards the coastal route archaeological evidence for either entry is lacking in this paper we introduce a third option an icy corridors entry route we argue that the traditionally envisioned corridor is an unnecessary feature for the terrestrial arrival of clovis or clovis predecessors below the ice sheets the recent genomic data is fully compatible with a re envisioned peopling route

tertiary quaternary drainage of the pre glacial mackenzie basin abstract pre glacial drainage in the northwestern mackenzie region was established in early tertiary time with the uplift of the mountains during the laramide orogeny and persisted until near the end of the pleistocene rivers arose in the mackenzie and richardson mountains and followed a generally eastward direction across piedmont surfaces from the mountains towards the plains the evidence to support this hypothesis includes geomorphology provenance of sediments reconstruction of paleo surfaces and stratigraphy two major drainage systems developed one to the atlantic ocean and another to the arctic ocean the atlantic drainage is composed of the northwestern tributaries of an integrated drainage system that flowed towards hudson bay traces of this drainage are found in the canyon ranges of the mackenzie mountains iroquois upland and in the norman range of the franklin mountains the arctic drainage included two main basins the porcupine basin that drained from west to east across the richardson mountains and the anderson basin that included the peel and snake rivers as its tributaries late wisconsinan laurentide glaciation deranged these drainage systems establishing the porcupine river as a tributary of the yukon river and integrating the tertiary drainage systems into the mackenzie river system flowing to the arctic ocean

a record of early pleistocene glaciation on the mount edziza plateau northwestern british columbia mount edziza is a plio pleistocene volcanic complex that is located in the stikine terrane in northwestern british columbia a sequence of diamictites preserved between ice peak formation basalts on the northwestern blank of mount edziza records an early pleistocene regional glaciation the lowest ice peak formation basalt flow ip1 about 1 ma was probably extruded onto glacial ice because it is deformed and brecciated it is pillowed at the base it lies directly on hyaloclastite deposits and there is a lack of fluvial and lacustrine sediments at the base fabric measurements from the underlying diamictites are consistent with lodgement processes and indicate northwest and southwest transport directions these data and an abundance of striated exotic cobbles indicate that the sediment was deposited by coast mountain ice radiometric paleomagnetic and stratigraphic data all support the interpretation that diamictites at the section are the sedimentary record of an early pleistocene about 1 1 ma i

late glacial drainage systems along the northwestern margin of the laurentide ice sheet abstract the evolution of drainage systems along the retreating northwestern laurentide ice sheet was complex the interaction of ice margin configuration topography and glacioisostasy resulted in a network of meltwater rivers that variably overflowed to the arctic and pacific oceans and to the gulf of mexico glacial lakes also changed dramatically in size and location during the period of deglaciation at the last and all time glacial maximum the ice sheet extended into the eastern cordillera blocking northward and eastward drainage to the arctic ocean some meltwater and most non glacial runoff were diverted through the mountains to the yukon river basin into alaska and the pacific ocean retreat from the glacial maximum prior to 21 ka bp allowed proglacial drainage from the western margin of the ice sheet to flow into the beaufort sea arctic ocean deglaciation was rapid after about 13 ka bp with the present route of the lower mackenzie river established between 13 and 11 5 ka bp continued ice retreat led to significant southward expansion of the mackenzie beaufort drainage basin at about 11 5 ka bp through drainage capture of glacial lake peace which previously had drained southeastward into the missouri river and to the gulf of mexico very rapid ice retreat between 10 5 and 10 ka bp allowed glacial lake mcconnell to expand down slope in contact with the ice margin numerous glacial lakes occurred along the northwestern margin of the ice sheet during the maximum and retreat phases these include ice dammed glacial lake old crow which occupied unglaciated terrain of the northern yukon and glacial lake peace which utilized a number of outlets as it migrated eastward with the ice front along the peace valley the largest glacial lakes in the region were the result of glacioisostatic depression reversing the regional drainage the mackenzie phase of glacial lake mcconnell was the second largest pleistocene lake in north america 215 000 km 2 late glacial and post glacial changes in drainage systems were largely in response to isostatic rebound

lateglacial ice dynamics of the cordilleran ice sheet in northern british columbia and southern yukon territory retreat pattern of the liard lobe reconstructed from the glacial landform record the liard lobe formed a part of the northeastern sector of the cordilleran ice sheet and drained ice from accumulation areas in the selwyn pelly cassiar and skeena mountains this study reconstru

laurentide and montane glaciation along the rocky mountain foothills of northeastern british columbia mapping the surficial geology of the trutch map area nts 94g provides new data on the timing of continental and montane glaciations along the foothills of northeastern british columbia striated surfaces on mountain crests were dated to the late wisconsinan substage by cosmogenic dating the striations were produced by eastward flowing ice emanating from the region of the continental divide this ice was thick enough to cross the main ranges and overtop the rocky mountain foothill summits at 2000 m above sea level asl it is argued here that such a flow unhindered by topography could only have been produced by the cordilleran ice sheet and not by local cirque glaciation during this time the cordilleran ice sheet dispersed limestone and schist erratics of western provenance onto the plains beyond the mountain front conversely the laurentide ice sheet did not reach its western limit in the foothills until after cordilleran ice retreated from the area during its maximum the laurentide ice penetra

paleomagnetic evidence for late cenozoic glaciations in the mackenzie mountains of the northwest territories canada the mackenzie mountains were affected by montane valley glaciers during the pleistocene and peripherally by the laurentide ice sheet during the last glaciation in this paper we report on magnetostratigraphic dating and correlation of three sections recording late pliocene to late pleistocene glaciations katherine creek little bear river and inlin brook located around 65 n 127 w each section consists of a colluvial unit overlying a pliocene pediment surface cut into proterozoic or paleozoic bedrock or tertiary gravel which is in turn overlain by a stack of five and in places six montane tills usually with soils developed at their surfaces and capped by a laurentide till normal and reversed magnetizations were recognized with single domain magnetite as a dominant remanence carrier the katherine creek section has a normally magnetized colluvium at its base which is overlain by two reversed tills succeeded by three normal tills we interpret the top two tills to be of brunhes age 780 ka

last glacial maximum age for the northwest laurentide maximum from the eagle river spillway and delta complex northern yukon abstract the eagle river spillway and braid delta complex provide a record of the maximum extent of the northwest laurentide ice sheet and diversion of meltwater from bonnet plume basin into the interior basins of non glaciated northern yukon development of the spillway can be characterized in three distinct zones based on the distribution of erosion and deposition along each reach erosion dominated channel initiation and incision followed by channelization and coarse clastic deposition along channel margins and into tributary valleys and lastly fine grained deltaic and lacustrine sedimentation in the lower channel reach deltaic sedimentation within the spillway is crudely coarsening upward from alternating beds of massive clay and silt to ripple cross bedded sand all sediments occur in rapidly aggrading forms with no evidence for a significant hiatus in deposition radiocarbon ages on woody plant macrofossils and spruce needles are non finite while radiocarbon ages on macrofossils from herbaceous plant taxa and insects with steppe tundra ecological affinity from the upper part of the delta range from 15 840 90 to 21 600 1300 14c yr bp these ages coupled with the rapidly aggrading nature of the delta sediments and landform suggest an age of ca 15 16 000 14c yr bp non finite and mixed ages underscore the significant problem of reworked well preserved macrofossils in arctic environments and the need for careful selection of both fragile and ecologically representative macrofossils to establish reliable chronologies

evidence for early glaciation of southeastern beringia between the klondike plateau and yukon tanana highlands of yukon and alaska respectively current maps explain glaciated alpine locales and periglacial areas in terms of localized pliocene pleisto

pleistocene stratigraphy paleopedology and paleoecology of a multiple till sequence exposed on the little bear river western district of mackenzie n w t canada the little bear river section lies in a transition zone between mackenzie lowland and canyon ranges of mackenzie mountains within the transition zone the maximum extent of the laurentide ice sheet overlaps the former extent of montane glaciers that emanated from the higher parts of canyon ranges or from the still higher backbone ranges to the southwest five montane tills each with a paleosol developed in its upper part indicate five separate glaciations during each of which a valley glacier emanating from the headwaters of little bear river extended eastward into the transition zone the uppermost of the montane tills is overlain by boulder gravel containing rocks of canadian shield origin deposited by the laurentide ice sheet solum and b horizon depths red colours and lack of leaching and cryoturbation indicate that although each successive interglacial interval was cooler than the preceding one even the last of the intervals was warmer than the holocene climatic conditions during one of the int

paleomagnetic evidence for multiple late pliocene early pleistocene glaciations in the klondike area yukon territory the late pliocene early pleistocene terraces of the klondike area provide a conformal record of sedimentation which marks the transition from preglacial to glacial conditions and is one of the most complete records of glaciation and interglaciation in the northern cordillera preglacial sedimentation is recorded in the lower white channel gravel that contains a reverse normal polarity sequence a re aggradation of the nonglaciated valleys of the goldfields in response to late pliocene cooling is recorded by the upper white channel gravel which is characterized by a dominant normal polarity with a lower reversal likely associated with the first ice wedge casts klondike gravel interfingers with upper white channel and is normally magnetized indicating an equivalent magnetostratigraphic unit this glaciofluvial gravel provides evidence of extra basinal clasts marking a major reorganization of drainage associated with the first advance of the cordilleran ice sheet in western yukon territory correlated

the last koy yukon interglaciation in the yukon comparisons with holocene and interstadial pollen records paleoclimatic reconstructions for the last interglacial lig isotope substage 5e have achieved new importance for testing climate model simulations and predicting the outcome of global warming lig deposits at ch ijee s bluff northern yukon display high fossil spruce pollen frequencies extralimital species and a lack of interglacial permafrost all evidence of a warmer than present climate at the site comparisons between the ch ijee s bluff lig pollen record and late glacial holocene pollen stratigraphy demonstrates a high degree of similarity that implies similar patterns and rates of species migration and regugia compared to mid and early wisconsinan pollen stratigraphy the climate of the wisconsinan interstades was not as warm as that of the lig or today s lig warmth was insufficient for the spread of pine into northern yukon alder so important in the northern forests now appears to have had a less important role during the lig perhaps indicating less widespread permafrost and paludification fossiliferous deposits beneath hungry creek till hughes et al 1981 are reassigned to the lig

differences between the last two glacial maxima and implications for ice sheet δ18o and sea level reconstructions studies of past glacial cycles yield critical information about climate and sea level ice volume variability including the sensitivity of climate to radiative change and impacts of crustal rebound on sea level reconstructions for past interglacials here we identify significant differences between the last and penultimate glacial maxima lgm and pgm in terms of global volume and distribution of land ice despite similar temperatures and radiative forcing our analysis challenges conventional views of relationships between global ice volume sea level seawater oxygen isotope values and deep sea temperature and supports the potential presence of large floating arctic ice shelves during the pgm the existence of different glacial modes calls for focussed research on the complex processes behind ice age development we present a glacioisostatic assessment to demonstrate how a different pgm ice sheet configuration might affect sea level estimates for the last interglacial results suggest that this may alter existing last interglacial sea level estimates which often use an lgm like ice configuration by several metres likely upward

a latest pliocene age for the earliest and most extensive cordilleran ice sheet in northwestern canada abstract the klondike gravel is a widespread glaciofluvial gravel marking the earliest and most extensive cordilleran ice sheet cis in nw north america new terrestrial cosmogenic nuclide tcn burial ages indicate this gravel was emplaced 2 64 0 20 0 18 ma 1 coupled with previously interpreted paleomagnetic stratigraphy this numerical age constrains the timing of the earliest cis to the late gauss chron and provides a minimum age for the upper white channel gravel a significant placer gold source in the yukon this implies the first cis glacial maximum pre dates the maximum extent of the laurentide ice sheet indicating that during the initial stages of northern hemisphere glaciation the most extensive glaciers were present in the relatively cold and high elevation northern cordillera our results verify the cis as a likely source of persistent coeval ice rafted debris in the northern pacific and suggest that the first cis formed as a response to the establishment of the northern pacific halocline and emergence of the 41 ka obliquity cycle during the plio pliocene transition

paleomagnetic evidence for multiple late cenozoic glaciations in the tintina trench west central yukon canadathis article is a companion paper to duk rodkin et al also in this issue the tintina trench in west central yukon has preserved an extensive record of late cenozoic preglacial glacial and interglacial deposits these deposits comprise multiple sequences of tills outwash loesses and paleosols the sediments that were laid down directly by ice tills are of both local montane and regional cordilleran provenance the tintina trench area was impacted repeatedly by montane ice from the southern ogilvie mountains to the northwest 2500 m above sea level asl and also repeatedly along its southern extent by cordilleran ice from the selwyn mountains to the east 2759 m asl the latter forming the continental divide in this region we report here the magnetostratigraphy of three sections rock creek 64 13 n 139 07 w west fifteenmile river 64 29 n 139 55 w and east fifteenmile river 64 23 n 139 48 w the majority of the units identified at these sections record late pliocene to mid pleistocene glaciations although relatively thin surficial sequences of late mid

early pleistocene volcanism and glaciation in central yukon a new chronology from field studies and paleomagnetism the paleomagnetism of the selkirk volcanics and nearby stratified pleistocene sediments was investigated to resolve the chronology of early pleistocene glaciations in central yukon radiometric dates on these low k basalts have proven to be erroneously old most sampled sediments and all basalts accurately record the paleofield and true reversals the valley filling phase of the selkirk volcanics was in part coeval with the younger pre reid glaciation it was erupted during the matuyarna chron either post cobb mountain subchron or post jararnillo subchron over a period too brief to average secular variation the older pre reid glaciation occurred after ca 1 60 ma and prior to the eruption of the fort selkirk tephra pre jaramillo or pre cobb mountain sediments investigated at revenue creek and braden s canyon are normally magnetized the assigned brunhes age is compatible with their occurrence in valleys that were cut or deepened sometime after the pre reid glaciations

paleomagnetism of quaternary and late tertiary sediments on mokowan butte southwestern alberta mokowan butte in southwestern alberta is capped by 32 m of unconsolidated sediment comprising five tills and their associated paleosols previous stratigraphic work has indicated that the older til

dating early and middle reid pleistocene glaciations in central yukon by tephrochronology abstract the late cenozoic deposits of central yukon contain numerous distal tephra beds derived from vents in the wrangell mountains and aleutian arc alaska peninsula region we use a few of these tephra beds to gain a better understanding on the timing of extensive pleistocene glaciations that affected this area exposures at fort selkirk show that the cordilleran ice sheet advanced close to the outer limit of glaciation about 1 5 myr ago at the midnight dome terrace near dawson city exposed outwash gravel aeolian sand and loess related to valley glaciers in the adjacent ogilvie mountains are of the same age reid glacial deposits at ash bend on the stewart river are older than oxygen isotope stage ois 6 and likely of ois 8 age that is about 250 000 yr b p supporting evidence for this chronology comes from major peaks in the rates of terrigeneous sediment input into the gulf of alaska at 1 5 and 0 25 myr b p

late tertiary to late quaternary record in the mackenzie mountains northwest territories canada stratigraphy paleosols paleomagnetism and chlorine 36 a stratigraphic sequence of unconsolidated sediments ranging in age from late pliocene to late pleistocene is recorded in the canyon ranges of the mackenzie mountains three of the sections katherine creek little bear river and inlin brook expose bedrock and tertiary gravel overlain by colluvium and a multiple till sequence of montane origin separated by paleosols and capped by a till of laurentide origin the sections are correlated on the basis of lithology paleosol development paleomagnetism and chlorine dating of surface boulder erratics a formal stratigraphic nomenclature is proposed for the deposits of this region the sequence of glacial tills separated by paleosols reflects a long record of glacial interglacial cycles soil properties from the oldest paleosol to modern soil show a general decrease in the degree of soil development suggesting a progressive deterioration of interglacial climatic conditions a normal reverse normal sequence of remanent magnetization was determined within th

the cambrian araba formation in northeastern egypt facies and depositional environments abstract the cambrian araba formation exposed in gabal el zeit and in the sinai peninsula unconformably overlies precambrian basement rocks and is in turn overlain unconformably by the ordovician naqus formation the araba formation has been subdivided into three informal lithologic units lower middle and upper from field observations seven sedimentary facies assignable to three facies associations fluvial tidal and coastal to open marine are recognized within the araba formation the lower unit comprises two main facies matrix supported conglomerate facies a in the south gabal araba and wadi feiran and interbeds of granulestone and sandstone facies b in the north gabal dhalal and taba deposited in fluvial conditions the middle unit includes four facies cross bedded sandstone facies c thin laminated sandstone facies d burrowed massive sandstone facies e and rhythmically bedded sandstone mudstone facies f deposited mainly under tidal conditions in the coastal zone the upper unit consists mainly of interbeds of burrowed mudstone siltstone with skolithos probably deposited in open marine environment the sequence records the southward transgression of the tethys ocean over a horst and graben system developed in the late precambrian on the northern margin of the arabo nubian continent

the pattern and style of deglaciation at the late wisconsinan laurentide and cordilleran ice sheet limits in northeastern british columbia this paper reports on the landform assemblages at the northern confluence of the late wisconsinan laurentide and cordilleran ice sheets with montane and piedmont glaciers in the northern rockies and southern mackenzie mountains recent observations in northeastern british columbia refine our knowledge of the pattern and style of ice sheet retreat glacial lake formation and meltwater drainage at the onset of deglaciation confluent laurentide and cordilleran terminal ice margins lay between 59 n 124 30 w and 60 n 125 15 w from this terminal limit ice sheets retreated into north central british columbia and yukon territory with remnant cordilleran ice and montane glaciers confined to mountain valleys and the liard plateau distinctive end moraines are not associated with the retreat of cordilleran ice in these areas laurentide ice retreated northeastward from uplands and the plateaus then separated into lobes occupying the fort nelson and petitot river valleys ice retreat landforms include recessional end moraines sometimes overridden and drumlinized hill hole pairs crevasse fill deposits de geer like ribbed till ridges hummocky moraines kames meltwater features and glacial lake deposits that fall within the elevation range of glacial lake liard and glacial lake fort nelson ca 840 380 m meltwater and sediment transport into glacial lakes fort nelson liard nahanni and mackenzie was sustained by remnant ice in the liard river and fort nelson river drainage basins until the end of glaciation optical dating of sand from stabilized parabolic dunes on the liard plateau indicates that proglacial conditions lake formation and drainage began before 13 0 0 5 ka calendar years the petitot fort nelson and liard rivers all occupy spillways incised into glacial deposits and bedrock by meltwater overflow from glacial lakes peace and hay

pleistocene volcanic damming of yukon river and the maximum age of the reid glaciation west central yukon stratigraphic paleomagnetic and radioisotope investigations of the selkirk volcanic group have identified a new eruptive period and constrained the age of the reid glaciation the most extensive middle pleistocene cordilleran advance recognized in central yukon downstream from fort selkirk a complex of valley filling compound pahoehoe basalt flows and pillow basalt is exposed for 10 km along the yukon river and is overlain by outwash deposited during the reid glaciation the flows have an 40ar 39ar age of 311 32 ka this age is consistent with the normal magnetization of the flows and their termination below the level of the contemporary yukon river flood plain taken with the ca 190 ka sheep creek tephra which overlies reid drift elsewhere in yukon territory the reid glaciation is constrained to oxygen isotope stage 8 not stage 6 as previously thought the presence of thick foreset bedded pillow breccia units intercalated with the subaerial flows indicates that this eruption caused damming of t

late quaternary glaciation in the northern ogilvie mountains revised correlations and implications for the stratigraphic record new geomorphic paleolimnological and radiocarbon data suggest that a terminal moraine complex in the northern ogilvie mountains yukon territory canada may represent the mcconnell glaciation late wisconsinan rather than the reid glaciation marine isotope stage 8 illinoian as previously thought relict fluvial channels on the surface of the moraine and analysis of a suite of lake sediment cores from chapman lake a closed basin kettle on the surface of the moraine suggest that flow from the blackstone river passed over the moraine and through the lake until ca 12 500 bp at which time the blackstone river was captured by the east blackstone river diverting flow from the lake subsequent incision by the blackstone river has left its base level more than 10 m below the level of chapman lake perched former outlets from chapman lake indicate that this incision must postdate stream capture because the chapman lake moraine is a topographic barrier across the blackstone river valley incision must