impact processes permafrost dynamics and climate and environmental variability in the terrestrial arctic as inferred from the unique 3 6 myr record of lake el gygytgyn far east russia a review lake el gygytgyn in far east russia is a 3 6 myr old impact crater lake located in an area that has never been affected by cenozoic glaciations nor desiccation the unique sediment record of the l

10be inventories in alpine soils and their potential for dating land surfaces abstract to exploit natural sedimentary archives and geomorphic landforms it is necessary to date them first landscape evolution of alpine areas is often strongly related to the activities of glaciers in the pleistocene and holocene at sites where no organic matter for radiocarbon dating exists and where suitable boulders for surface exposure dating using in situ produced cosmogenic nuclides are absent dating of soils could give information about the timing of landscape evolution this paper explores the applicability of soil dating using the inventory of meteoric 10be in alpine soils for this purpose a set of 6 soil profiles in the swiss and italian alps was investigated the surface at these sites had already been dated using the radiocarbon technique or the surface exposure determination using in situ produced 10be consequently a direct comparison of the ages of the soils using meteoric 10be and other dating techniques was made possible the estimation of 10be deposition rates is subject to severe limitations and strongly influences the obtained results we tested three scenarios using a the meteoric 10be deposition rates as a function of the annual precipitation rate b a constant 10be input for the central alps and c as b but assuming a pre exposure of the parent material the obtained ages that are based on the 10be inventory in soils and on scenario a for the 10be input agreed reasonably well with the age using surface exposure or radiocarbon dating the ages obtained from soils using scenario b produced ages that were mostly too old whereas the approach using scenario c seemed to yield better results than scenario b erosion calculations can in theory be performed using the 10be inventory and 10be deposition rates an erosion estimation was possible using scenario a and c but not using b the calculated erosion rates using these scenarios seemed to be plausible with values in the range of 0 57 mm ky the dating of soils using 10be has several potential error sources analytical errors as well as errors from other parameters such as bulk soil density and soil skeleton content have to be taken into account the error range was from 8 up to 21 furthermore uncertainties in estimating 10be deposition rates substantially influence the calculated ages relative age estimates and under optimal conditions absolute dating can be carried out age determination of alpine soils using 10be gives another possibility to date surfaces when other methods fail or are not possible at all it is however not straightforward quite laborious and may consequently have some distinct limitations

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

pliocene and early pleistocene glaciation and landscape evolution on the patagonian steppe santa cruz province argentina abstract at least seven late pliocene tills cap plateaus mesetas south of lago viedma just east of the andes in argentine patagonia chronologic constraints on the tills are provided by 40ar 39ar ages and magnetic polarities on associated basalt flows and sediments the tills were deposited by piedmont glaciers that reached at least 80 km east of the crest of the andes and flowed on a low relief surface sloping gently downward in that direction the oldest of the tills is about 3 6 ma old glacial deposits dating to the pliocene pleistocene transition are present at least 40 km beyond the east limit of the pliocene tills at lago viedma and tills of similar age occur at condor cliff in the rio santa cruz valley to the southeast a sequence of at least seven early pleistocene 2 1 1 1 ma tills is present between basalt flows in the cerro del fraile meseta south of lago argentino the glaciers that deposited these early pleistocene tills reached far beyond the marine isotope stage 2 limit in the rio santa cruz valley based on positions extents and ages of the un deformed basalt capped mesetas flanking lago viedma we conclude that the topography in this area was profoundly changed during the pleistocene the low to moderate relief pliocene surface was deeply incised by glaciers that became increasingly confined to and flowed within troughs the valley floors today are up to 1350 m below the late pliocene surface

a near synthesis of pre illinoian till stratigraphy in the central united states iowa nebraska and missouri abstract nearly identical sequences of pre illinoian glacial till are present throughout the north central united states in iowa nebraska and missouri in each of these states three tills with normal magnetic remanence have been found above two three tills with reversed remanence and the lithologic differences among successive tills are nearly the same each till is capped by a mature paleosol except for the two youngest reversed polarity tills which are nearly identical in lithology and separated by immature weathering profiles these results seem to indicate that deposits from five major pre illinoian glaciations are present throughout this entire region cosmogenic nuclide burial ages provide relatively precise ages for the three earliest glaciations that reached northeast missouri ca 2 4 1 3 and 0 76 ma ages of the youngest two glaciations in this area are less precise but both are between 0 2 and 0 4 ma the tills in nebraska and western iowa have not been dated directly but are constrained by the ages of interbedded tephra and these limits are consistent with the burial ages in missouri for tills in the same relative stratigraphic positions with one exception two of the three normal polarity tills in nebraska western iowa are present below the 0 64 ma lava creek b tephra and thus should be between 0 64 and 0 78 ma in age however only one of the normal polarity tills in northeast missouri is within this range this discrepancy indicates either a problem with the age constraints or that the till sequence is more complex than yet recognized

large scale erosion rates from in situ produced cosmogenic nuclides in european river sediments abstract we have calculated long term erosion rates of 20 100 mm kyr from quartz contained 10be in the bedload of middle european rivers for catchments ranging from 102 to 105 km2 these rates average over 10 40 kyr and agree broadly with rock uplift incision and exhumation rates historic soil erosion rates and erosion rates calculated from the measured sediment loads of the same rivers moreover our new erosion rate estimates correlate well with lithology and relief however in the regen neckar loire and meuse catchments cosmogenic nuclide derived erosion rates are consistently 1 5 4 times greater than the equivalent rates derived from measured river loads this may be due to the systematic under representation of high magnitude low frequency transport events in the gauging records which cover less than a century alternatively the discrepancy may derive from spatially non uniform erosion and preferential tapping of deeper sections of the irradiation profile a third explanation relates the high cosmogenic nuclide derived erosion rates to inheritance of an elevated pleistocene erosion signal uncertainties associated with the cosmogenic nuclide derived erosion rate estimates are not greater than the potential errors in conventional estimates therefore the cosmogenic nuclide approach is an effective tool for rapid catchment wide assessment of time integrated rates of bedrock weathering and erosion and we anticipate its fruitful application to the quaternary sedimentary record

cosmogenic nuclides and the dating of lateglacial and early holocene glacier variations the alpine perspective abstract based on cosmogenic 10 be data from four sites in the alps we discuss geological uncertainties associated with the dating of former cirque and small valley glacier margins at the early lateglacial gschnitz site trins austria a 3000 yr spread in 10 be exposure ages points to prolonged boulder instability three out of seven ages are not included in the mean age calculation which yielded 15 400 1000 yr indistinguishable from the oldest boulder age of 16 130 1040 yr as a result of the distinctive morphology at julier pass switzerland site we are able to exposure date the early 12 300 1300 yr and the late 11 300 600 yr egesen stadial glacier advances younger dryas equivalent not just final retreat at the kromer site austria 10 be exposure ages from five clast supported boulders are indistinguishable within the analytical uncertainties mean age 8400 500 yr in addition to moraine age key factors that may lead to too young ages include degree of matrix vs clast support of the boulders post depositional periglacial activity and tree coverage at the nagelisgratli bedrock site near grimsel pass switzerland exposure ages of 10 760 11 720 yr are consistent with early holocene cirque glacier retreat and underline the marked lack of nuclide inheritance in bedrock exposures in the alps

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

new chronology for the southern kalahari group sediments with implications for sediment cycle dynamics and early hominin occupation abstract kalahari group sediments accumulated in the kalahari basin which started forming during the breakup of gondwana in the early cretaceous these sediments cover an extensive part of southern africa and form a low relief landscape current models assume that the kalahari group accumulated throughout the entire cenozoic however chronology has been restricted to early middle cenozoic biostratigraphic correlations and to osl dating of only the past 300 ka we present a new chronological framework that reveals a dynamic nature of sedimentation in the southern kalahari cosmogenic burial ages obtained from a 55 m section of kalahari group sediments from the mamatwan mine southern kalahari indicate that the majority of deposition at this location occurred rapidly at 1 1 2 ma this pleistocene sequence overlies the archaean basement forming a significant hiatus that permits the possibility of many phanerozoic cycles of deposition and erosion no longer preserved in the sedimentary record our data also establish the existence of a shallow early middle pleistocene water body that persisted for 450 ka prior to this rapid period of deposition evidence from neighboring archeological excavations in southern africa suggests an association of high density hominin occupation with this water body

application of cosmogenic 10be to dating soils on the raised coral reef terraces of kikai island southwest japan 10be concentrations of six soils on the raised coral reef terraces of kikai island southwest japan range from 0 80 to 7 17 109 atoms g 1 the annual deposition rate of 10be from the atmosphere to kikai island from 2000 to 2002 ranges from 2 0 to 3 5 106 atoms cm 2 year 1 with a mean of 2 8 0 7 106 atoms cm 2 year 1 minimum absolute ages calculated from the inventory of meteoric 10be in the soils and the annual deposition rate of 10be are initial rendzina like soil 8 ka rendzina like soil 18 ka brown rendzina like soil 56 ka terra fusca like soil 127 ka terra rossa like soil 136 ka and intergrade between terra rossa like and red yellow soil 102 ka therefore it was concluded that soil formation during the first 60 000 years would be as rendzina like soils and more than 100 000 years would be required for red yellow soils to develop on raised coral reef terraces under subtropical humid climatic conditions

limits to quantifying climate driven changes in denudation rates with cosmogenic radionuclides abstract the hypothesis that climate change significantly modifies the denudation history of an orogen can be tested by reconstructing catchment wide denudation histories cosmogenic radionuclides measured in sediment deposits of known age e g a sequence of fluvial terraces offer one approach for quantifying catchment wide paleo denudation rates we present a numerical model and two case studies that evaluate the utility of this technique for reconstructing different denudation histories the concentration of cosmogenic beryllium 10 10 be is calculated for a sequence of sediments produced from climate driven variations in the mean denudation rate of a drainage basin at sea level and high latitude the model accounts for the nucleonic and muonic production and decay of 10 be as sediment is eroded and stored in deposits of different ages two scenarios for different climate driven denudation histories are considered 1 a sinusoidal variation in the input denudation rate with free parameters of periodicity 23 41 100 kyr amplitude 0 1 0 5 1 0 and mean denudation rate 0 01 0 1 1 0 mm yr 1 2 a climate driven denudation history based on oscillations of a global benthic foraminiferal oxygen isotope 18 o record over the last 2 myr results from both scenarios suggest cosmogenic radionuclides measured in a system with high denudation rates 0 5 mm yr 1 longer periodicity 100 kyr and low amplitude have the highest potential for reconstructing climate driven paleo denudation rates unfortunately the high denudation rates preferred in the theoretical consideration are not suitable for paleo denudation rate determination due to overprinting of nuclides accumulated during denudation by post depositional decay and irradiation hence a compromise between the capability to determine changes in paleo denudation rates and the determination of true denudation rates has to be accepted application of the model to previous data sets from northwest europe and southwest north america produce a good agreement but highlight the need for future work to consider how geomorphic processes e g landsliding respond to climate change and influence catchment wide denudation rates in addition other climate proxies than the benthic foraminiferal 18 o record should be used for specific sample locations

combined use of relative and absolute dating techniques for detecting signals of alpine landscape evolution during the late pleistocene and early holocene article i nfo a combination of three relative and two absolute numerical dating techniques applied on nine soil profiles in an alpine environment located in val di rabbi trentino northern italy was used to improve the investigation methodology of alpine sites in response to climate change and to reconstruct the chronology of late pleistocene and early holocene landscape evolution the degree of podzolisation clay mineral evolution and the element mass balances of each site were investigated furthermore the stable fraction of the soil organic matter som was extracted with 10 h2o2 and 14 c dated the age of the organic residues was compared with the age of charcoal fragments found in one of the studied soils and with the age of rock boulders obtained by surface exposure dating sed with cosmogenic 10 be numerical dating and weathering characteristics of the soils showed a fairly good agreement and enabled a relative and absolute differentiation of landscape elements the combination of 14 c dating of som and sed indicated that deglaciation processes in val di rabbi were already far advanced by around 14000 cal bp and that glacier oscillations affected the highest part of the region until about 9000 cal bp the development of clay minerals is time dependent and reflects weathering intensity we found a close link between secondary clay minerals like smectite or vermiculite and soil age as obtained by the dating of the organic residues after the h2o2 treatment calculated element mass balances strongly correlated with the ages derived from 14 c measurements old soils have lost a major part of base cations up to 75 compared to the parent material fe and al which indicates a continuous high weathering intensity results of the chemical and mineralogical analyses were in good agreement with numerical dating techniques showing the dynamics of an alpine landscape within a relatively small area the combination of relative and absolute dating techniques is a promising tool for the reconstruction of landscape history in high elevation alpine areas on siliceous substrates

a catalogue of late cenozoic tephra beds in the klondike goldfields and adjacent areas yukon territory preece s j westgate j a froese d g pearce n j g perkins w t 2011 a catlogue of late cenozioc tephra beds in the klondike goldfields and adjacent areas yukon canadian journal of earth sciences 48 10 1386 1418

the global average production rate of10be precipitation collected in continuously open containers for about a year at seven sites around the united states was analyzed for10be 90sr 210pb and238u based on these data and long term precipitation 90sr and210pb delivery patterns the stratospheric tropospheric and recycled10be components in the collections were estimated and the global10be production rate was assessed single station production rate estimates range from 0 52 106 atoms cm 2 yr 1 to 2 64 106 atoms cm 2 yr 1 the mean value is 1 21 106 atoms cm 2 yr 1 with a standard error of 0 26 106 atoms cm 2 yr 1

modest global scale cooling despite extensive early pleistocene ice sheets abstract expanded continental ice sheets and lowered greenhouse gases were the major radiative perturbations at the last glacial maximum lgm and while they had similar magnitudes when averaged over the globe their spatial distributions were dramatically different it is consequently unclear how much each contributed to cooling around the world and the overall global mean cooling in turn part of the difficulty in separating their effects is that ice sheets and greenhouse gases closely covaried over the late pleistocene the situation may have been different during the early pleistocene though then the ice sheets seem to have at least on occasion reached extents comparable to the lgm but co 2 levels were relatively high similar to those of late pleistocene interglacials a global compilation of 11 sea surface temperature records shows substantially less cooling in most regions during the marine isotope stage 100 and 98 glacials at 2 5 ma than during the lgm suggesting that the thermal reach of the ice sheets was relatively limited and perhaps consistent with a more important role for greenhouse gases in driving temperatures around much of the world

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

pre glacial and interglacial pollen records over the last 3 ma from northwest canada why do holocene forests differ from those of previous interglaciations we synthesize pollen spectra from eleven dated stratigraphic sections from central and northern yukon palaeomagnetic and tephra dating indicates the earliest assemblages representing closed canopy pinus and picea forest are middle late pliocene age more open forest conditions indicated by increased poaceae and with evidence of permafrost are dated at ca 3 ma while pinus pollen is abundant at 3 ma it is reduced in records after 2 6 ma and subsequent pleistocene interglacial forest records are repeatedly dominated by picea along with alnus and small but significant amounts of abies surface sample comparisons indicate that abies was more widespread and abundant in past interglaciations than at present and that middle pleistocene piceaeabies forest grew in the northern yukon porcupine basin 500 km beyond modern abies limits in contrast pinus which occurs today in southern and central yukon was not a significant component of these pleistocene interglacial forests late holocene pollen assemblages with rare abies and high pinus are the most distinct in the past 2 6 ma possible factors driving holocene difference are paleoclimate paludification changes in megafaunal herbivory and an unusual fire regime anthropogenic burning is a factor unique to the holocene and if it is shown to be important in this case it would challenge our notion of what constitutes boreal wilderness

beryllium geochemistry in soils evaluation of 10be 9be ratios in authigenic minerals as a basis for age models soils contain a diverse and complex set of chemicals and minerals being an open system both in the chemical and nuclear sense soils have defied quantitative nuclear dating however based on the published studies of the cosmogenic atmospheric 10be in soils its relatively long half life 1 5 ma and the fact that 10be gets quickly incorporated in most soil minerals this radionuclide appears to be potentially the most useful for soil dating we therefore studied the natural variations in the specific activities of 10be with respect to the isotope 9be in mineral phases in eight profiles of diverse soils from temperate to tropical climatic regimes and evaluated the implications of the data for determining the time of formation of soil minerals following an earlier suggestion lal et al 1991 development of cosmogenic nuclear methods for the study of soil erosion and formation rates current sci 61 636 639 we find that the 10be 9be ratios in both bulk soils and in the authigenic mineral phases are confined within a narrower range than in 10be concentrations also the highest 10be 9be ratios in authigenic minerals are observed at the soil rock interface as predicted by the model we present model 10be 9be ages of the b horizon and the corresponding soil formation rates for several soil profiles the present study demonstrates that the 10be 9be ratios in the authigenic phases e g clay and fe hydroxides can indeed be used for obtaining useful model ages for soils younger than 10 15 ma however the present work has to be pushed considerably further to take into account more realistic age models in which for instance downward transport 10be and clays and in situ dissolution of clay minerals at depths altering the 10be 9be ratios of the acidic solutions are included we show that in the case of younger soils 1 ma studied here their 10be inventories and 10be 9be ratios have been significantly disturbed possibly by mixing with transported soils

an extensive late cenozoic terrestrial record of multiple glaciations preserved in the tintina trench of west central yukon stratigraphy paleomagnetism paleosols and pollenthis is a companion paper to barendregt et al also in this issue geological survey of canada contribution 20100035 the tintina trench in west central yukon is a late miocene graben formed along the antecedent early tertiary tintina fault since its formation the trench has served as a sediment trap for alluvial and glacial deposits an extensive record of preglacial glacial and interglacial sediments spanning the late pliocene to late pleistocene has been preserved and is exposed today in modern landslide scars this sedimentary record comprises multiple sequences of tills outwash mudflows loess and paleosols the glacial sediments are the product of both local montane and regional cordilleran ice advances that channeled into the trench while loess and well developed paleosols brunisols and luvisols reflect nonglacial and interglacial conditions respectively the tintina trench exposures provide the most complete record of glaciations for the region paleomagnetism paleosols and palynology provide age constraints for the geological events a formal stratigraphic nomenclature is proposed for this region

millennial scale vegetation changes in the north eastern russian arctic during the pliocene pleistocene transition 2 7 2 5 ma inferred from the pollen record of lake el gygytgyn abstract the sediment record of lake el gygytgyn 67 30 n 172 05 e spans the past 3 6 ma and provides unique opportunities for qualitative and quantitative reconstructions of the regional paleoenvironmental history of the terrestrial arctic millennial scale pollen studies of the sediments that accumulated during the late pliocene and early pleistocene ca 2 7 to 2 5 ma demonstrate orbitally driven vegetation and climate changes during this transitional interval pollen spectra show a significant vegetation shift at the pliocene pleistocene boundary that is however delayed by a few thousand years compared to lacustrine response about 2 70 2 68 ma the vegetation at lake el gygytgyn currently a tundra area was mostly dominated by larch forests with some shrub pine shrub alder and dwarf birch in understory during the marine isotope stages g3 and g1 ca 2 665 2 647 and 2 625 2 617 ma some spruce trees grew in the local larch pine forests pointing to relatively warm climate conditions at the beginning of the pleistocene around 2 588 ma a prominent climatic deterioration led to a change from larch dominated forests to predominantly treeless steppe and tundra like habitats between ca 2 56 2 53 ma some climate amelioration is reflected by the higher presence of coniferous taxa mostly pine and larch but probably also spruce in the area after 2 53 ma a relatively cold and dry climate became dominant again leading to open steppe like and shrubby environments followed by climate amelioration between ca 2 510 and 2 495 ma when pollen assemblages show that larch forests with dwarf birch and shrub alder still grew in the lake s vicinity increased contents of green algae colonies botryococcus remains and zygnema cysts around 2 691 2 689 2 679 2 677 2 601 2 594 2 564 2 545 and 2 532 2 510 ma suggest a spread of shallow water environments most likely due to a lake level lowering these events occurred simultaneously with dry climate conditions inferred from broad distribution of steppe habitats with artemisia and other herbs

the rhine linth glacier in the upper wurm a model of the last alpine glaciation abstract the wurmian glaciation of the alpine foreland has been reconstructed in different phases as a result of investigations in the rhine bodan region as well as in the linth area the whole high glacial is divided in four main phases ice advance into the piedmont basins building up of the foreland glaciation high stages and retreat into the inner alps this epoch took up perhaps less than 12 000 years during the period of building an average increase of ice thickness of about 12 cm per year was sufficient to form an extensive foreland glacier within 5000 7000 years the snow lines of the stades of the piedmont glaciation as well as of the local glaciers are calculated snow lines at about 1500 m a s l led to an inner alpine ice build up and an advance of glaciers towards the piedmont basins to produce the foreland ice sheet low snow lines of 900 1000 m a s l were necessary an interstadial phase before the maximum glaciation is evidenced by sediment sequences and a 14c date of 22 100 bp the chronology of ice retreat after 18 ka bp is still uncertain

absolute chronology for major pleistocene advances of the laurentide ice sheet we used a 26 al 10 be burial isochron method to date the glacial stratigraphic section in missouri usa that records the largest advances of the laurentide ice sheet this permits an improved comparison of terrestrial and marine records of glaciation the first recorded advance of the laurentide ice sheet reached 39 n near the extreme southern limit of north american glaciation 2 4 ma the next advance to this latitude took place near the beginning of the mid pleistocene transition 1 3 ma and three more took place from 0 75 to 0 2 ma there is no evidence that the laurentide ice sheet advanced south of 45 47 n between 2 4 and 1 3 ma this chronology 1 shows that north american continental glaciation postdated cordilleran alpine glaciation 2 is consistent with the hypothesis that both of these events were threshold responses to tropical cooling 3 is consistent with the hypothesis that the first advance of the laurentide ice sheet was glaciologically anomalous due to the presence of deformable preglacial regolith 4 is not consistent with the hypothesis that this deformable regolith persisted until the mid pleistocene transition and 5 indicates that the increase in global ice volume at the mid pleistocene transition was at least in part the result of a more extensive laurentide ice sheet

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

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

paleotopography and erosion rates in the central hangay dome mongolia landscape evolution since the mid miocene abstract standing over 2 km above the surrounding topography and flanked by orogen scale strike slip faults the hangay dome in central mongolia is characterized by long wavelength high topography basaltic eruptions spanning 30 million years and an abundance of flat topped summit plateaus however despite decades of research the origin and timing of the intraplate hangay dome uplift continues to be debated using landsat imagery gis and cosmogenic beryllium 10 we employ geomorphic investigations of 1 paleotopography preserved beneath basalt flows of known age 2 erosion rates at various temporal scales and 3 the relative contribution of glacial activity to total erosion to provide insight into the nature of landscape evolution in the egiin davaa region of the central hangay dome since the middle miocene reconstruction of paleo valleys cut into paleozoic basement rock that exhibit a degree of local relief 600 m similar to the modern landscape sluggish mean erosion rates

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

glacial interglacial variation in denudation rates from interior texas usa established with cosmogenic nuclides abstract the brazos colorado and trinity rivers of texas drain a tectonically quiescent non glaciated and low relief landscape inland from the gulf of mexico where long term 10 3 10 5 a changes in denudation rates are probably driven largely by climate change here we use cosmogenic 10be to obtain spatially averaged denudation rates for these river catchments primarily from terrace deposits associated with glacial or interglacial intervals over the past half million years the denudation rates are 30 35 higher during interglacial periods than during glacial periods and correlate broadly with temperature the results are consistent with predictions from the bqart sediment flux model and support the hypothesis that increased weathering rates associated with warmer climates will accelerate landscape erosion furthermore by analyzing 26al 10be in these deposits we can estimate the bed load sourced from up catchment surfaces the stored coastal plain fraction varies from 10 to 30 and is greater during times of relatively lower sea level the results indicate that although sediment flux is moderated by coastal plain storage increased up catchment flux during warmer interglacial periods outpaces evacuation of stored sediment during glacial periods resulting in a net increase in sediment flux to the ocean during warm intervals if this temperature sediment flux relationship is valid beyond the plio pleistocene transition then global sediment flux to the ocean from passive non glaciated and low relief landscapes would have been greater during the pliocene than in the cooler quaternary

beryllium isotope geochemistry in tropical river basins abstract the distributions of beryllium 9 and beryllium 10 in rivers within the orinoco and amazon basins have been examined to extend our understanding of their geochemical cycles and to develop their use both in geochronometry and in studying erosional processes beryllium 9 the stable isotope is weathered from mineral lattices before entering the riverine dissolved or exchangeable phase the cosmogenic radioisotope 10be t 1 2 1 5 myr is produced primarily in the atmosphere and is brought into riverine systems via rainfall in dissolved or exchangeable form it may be used to examine the processes which affect beryllium partitioning between the dissolved and particulate phases ancillary data such as major ion distributions provide a basis for selecting regions in which riverine chemistry is dominated by a single geochemical process allowing examination of its effects on be distributions in isolation analyses of 9be in dissolved and suspended material from rivers with a wide range of chemical compositions indicate that its geochemistry is primarily controlled by two major factors 1 1 its abundance in the rocks of the watershed and 2 2 the extent of its adsorption onto particle surfaces the relative importance of these parameters in individual rivers is determined by the extent of interaction with flood plain sediments and the riverine ph this understanding of 9be geochemistry forms a basis for examination of the geochemical cycling of 10be in rivers which are dominated by interaction with sediments the riverine concentration of dissolved 10be is far lower than that in the incoming rainwater indicating that a substantial proportion of it is retained within the soils of the basin or is adsorbed onto riverine particles however in acidic rivers in which the stable dissolved be concentration is determined by the be level in the rocks of the drainage basin dissolved 10be has essentially the same concentration as in precipitation these observations imply that the soil column in such regions must be saturated with respect to 10be and that the ratio of the inventory to the flux does not represent an age as may be the case in temperate latitudes but rather a residence time

evolution of a deep water ferromanganese nodule in the south china sea in response to pacific deep water circulation and continental weathering during the plio pleistocene abstract the south china sea scs is connected to the west pacific through a deep channel in the luzon strait thus the scs deep water is sensitive to the evolution of pacific ocean circulation which significantly influences the global climate system geochemical data pb isotope and redox sensitive elements data and magnetic data were determined for a fe mn nodule obtained from jiaolong seamount in the central scs these records reflect interactions between changes in ice sheets deep pacific circulation and weathering inputs to the deep scs during the pliocene and quaternary our results show that the scs deep water environment can be divided into three major stages stages 1 3 stage 1 4 8 1 4 ma was characterized by a well oxygenated pacific deep water pdw and lower dust inputs then moderate stable deep water ventilation and greater inputs of asian dust occurred during stage 2 1 4 0 9 ma during stage 3

chronology of the last glacial cycle in the european alps chronological data for glacier advances in the european alps between the last interglacial eemian and the holocene are summarised 115 to 11 ka during this time glaciers were most extensive extending tens of kilometres out onto the forelands between 30 and 18 ka that is synchronous with the global ice volume maximum of marine isotope stage mis 2 evidence for ice expanding to just past the mountain front for an earlier major glacier advance comes from swiss sites where advances have been luminescence dated to mis 5d 100 ka and mis 4 70 ka up to now no such evidence has been found in the eastern alps by 18 ka more than 80 of the late wurmian ice volume had gone subsequently glaciers readvanced reaching into the upper reaches of the main valleys during the lateglacial gschnitz stadial which likely occurred around 17 ka with final moraine stabilisation no later than 15 4 ka the link of the egesen stadial with the younger dryas climate deterioration is supported by exposure ages from four sites as well as minimum limiting radiocarbon dates from bogs within former glacier tongue areas key questions on the spatial and temporal variability of ice extents throughout the last glacial cycle have yet to be answered copyright 2008 john wiley sons ltd

10be analysis of a quaternary weathering profile in the virginia piedmont samples from a residual weathering profile in the virginia piedmont have been analyzed for cosmogenic 10be concentrations are highest in clay rich soil and decrease exponentially to a depth of about 15 m despite uncertainties about the processes by which 10be may be intercepted before entering the solum and eroded after incorporation a minimum age may be calculated for the regolith this calculation is based on the delivery rate of 10be and its decay rate and suggests that this residual profile developed during a period no shorter than 8 105 yr the calculated minimum age may be within a factor of 2 of maximum age estimates based on surface lowering by erosion and on the rate of rock weathering to saprolite the vertical distribution of 10be in the profile could result from a steady state balance of deposition weathering radioactive decay and erosion

an isochron method for cosmogenic nuclide dating of buried soils and sediments we describe an improved method for dating buried paleosols using measurements of the cosmic ray produced radionuclides 10be and 26al in quartz grains and apply it to a sequence of intercalated tills and paleosols in central missouri usa that record plio pleistocene advances of the laurentide ice sheet a buried paleosol implies a period of surface exposure and nuclide accumulation followed by burial and a halt to nuclide production if the paleosol is formed in a sedimentary unit such as till this unit may also have been emplaced with unknown 26al and 10be concentrations inherited from past surface exposure if the inherited nuclide concentrations are the same at all depths in the soil as is true for well mixed sediments such as till then the 26al and 10be concentrations at different depths in the paleosol will show a linear relationship the slope of this line depends on the duration of burial of the paleosol but not on the inherited nuclide concentrations or on the sample depths thus one can date strata overlying buried paleosols by measuring 26al and 10be at multiple depths in the paleosol and calculating the burial age of the paleosol from the resulting isochron we focus on applying this approach to till paleosol sequences but the basic idea of forming an 26al 10be burial isochron with a set of samples that share the same burial age but differ in other aspects of their exposure history applies to other stratigraphic settings as well the method yields ages for four tills in missouri that are stratigraphically consistent agree with paleomagnetic age constraints and show that ice advanced into missouri near 1 25 ma near 0 8 ma and twice between ca 0 4 and 0 2 ma

production of cosmogenic radionuclides at great depth a multi element approach abstract for the last two decades in situ produced cosmogenic nuclides are increasingly applied in earth sciences to quantify surface processes in parallel significant reduction of the analytical uncertainties linked to advances in accelerator mass spectrometry ams allows more precise measurements however among all the published works on cosmogenic nuclides only few studies are dedicated to a better understanding of their production systematic or to a better constrain of the physical parameters involved in their production thus an approach to investigate in situ produced cosmogenic nuclides 10 be 26 al and 36 cl along a single 11 meter long core drilled from the surface and composed of carbonates and quartzose conglomerates has been launched these measurements have been used to quantify muon induced productions based on natural samples for each studied nuclide contrary to the current most oftenly used calculation of muon induced production parameters which are based on irradiation experiments at discrete energies productions based on natural samples are considering the entire energy range of particles reaching the ground surface the evolution of 36 cl concentrations with depth needs to agree with those parameters deduced from 10 be and 26 al data this is optimized when considering a fast muon induced 36 cl production contribution and a spallation production rate at sea level high latitude slhl of 42 0 2 0 atoms 36 cl g ca 1 a 1 1 sigma uncertainty

the contribution of orbital forcing to the progressive intensification of northern hemisphere glaciation in this study we reconstruct the timing of the onset of northern hemisphere glaciation this began in the late miocene with a significant build up of ice on southern greenland however progressive intensification of glaciation did not begin until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia were glaciated at approximately 2 74 ma 40 ka before the glaciation of alaska 2 70 ma and about 200 ka before significant glaciation of the north east american continent 2 54 ma we also review the suggested causes of northern hemisphere glaciation tectonic changes such as the uplift of the himalayan and tibetan plateau the deepening of the bering strait and the emergence of the panama isthmus are too gradual to account entirely for the speed of northern hemisphere glaciation we therefore postulate that tectonic changes may have brought global climate to a critical threshold but the relatively rapid variations in the earth s orbital parameters and thus insolation triggered the intensification of northern hemisphere glaciation this theory is supported by computer simulations which despite the relative simplicity of the model and the approximation of some factors e g using a linear carbon dioxide scenario neglecting the geographical difference between the pliocene and the present suggest that it is possible to build up northern hemisphere ice sheets between 2 75 and 2 55 ma by varying only the insolation controlled by the orbital parameters c 1998 elsevier science ltd all rights reserved

tertiary ice sheet dynamics the snow gun hypothesis we observe strong negative correlation between tertiary low to mid latitude planktonic foraminiferal 18o and the difference between these data and coeval benthic foraminiferal 18o late quaternary data do not show this correlation coupling statistical model 18o comparisons and evidence for antarctic ice and ocean temperature variation we infer that tertiary ice volume recorded by tropical planktonic 18o increased as the deep ocean warmed because the isotopic signatures of deepwater temperature variation and ice volume change were of opposite sign the sum of these signals in tertiary benthic 18o became lost in the noise this renders low correlation between tertiary planktonic and benthic 18o time series compared to late quaternary data we contend that tertiary ice sheet growth was commonly driven by warming of deep water from low to mid latitude marginal seas snow gun hypothesis in contrast late quaternary ice sheets grew as deep water formed at high latitude cooled because tectonic forcing and orbital forcing at low latitude primarily controlled production and temperature variations of this warm saline deep water these influences largely dictated tertiary ice volume fluctuations through the tertiary we infer ice volume fluctuations to be an important component of sea level history on timescales between 103 and 107 years

10be accumulation in a soil chronosequence we have measured the concentration of the cosmogenic isotope10be in soil samples from various horizons at six sites including three independently dated rappahannock river terraces and a previously undated piedmont soil to which we have assigned an age all of the incident10be can be accounted for in one of these soils and a second is within a factor of two in three soils whose concentrations vary widely with depth a significant fraction of the incident10be cannot be accounted for incomplete sampling and enhanced be mobility caused by organic components are the probable reasons for the low inventory of be from these three soils overall the data from these six sites indicate that10be accumulation could be used to assign ages to soils if be is not mobilized and lost from the soil profile

beryllium 10 dating of the duration and retreat of the last pinedale glacial sequence accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes cosmogenic beryllium 10 measurements in the wind river range indicate that the last glacial maximum marine oxygen isotope stage 2 was achieved there by 21 700 700 beryllium 10 years and lasted 5900 years ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12 100 500 beryllium 10 years

late cenozoic climate change paces landscape adjustments to yukon river capture late cenozoic cooling and changes in glacial interglacial cycle tempo are thought to increase global rates of erosion starting 3 million years ago ma bedrock rivers set rates and patterns of erosion in most landscapes but constraints on river response to late cenozoic climate change remain elusive here we determine cosmogenic isotope and luminescence ages of well preserved bedrock terraces along the fortymile river yukon river basin to reconstruct an 5 myr history of fluvial adjustment to late cenozoic climate and yukon river headwater capture at 2 6 ma post capture yukon river downcutting lowered the fortymile river outlet forcing subsequent bedrock incision throughout the fortymile basin in two pulses from 2 4 to 1 8 ma and at 1 ma these pulses of incision disrupted longer intervals of slow river channel sedimentation under near consistent climate forcing from 4 8 to 2 4 ma and from 1 8 to 1 ma the fortymile river delivers sediment to the bering sea where provenance and accumulation rate changes since 4 3 ma match observed variations in incision our results link alluviation and incision to late cenozoic climate steadiness and change respectively and support the hypothesis that climate forced changes in precipitation and runoff fundamentally control the pace of river incision and landscape erosion increased river incision and landscape erosion can be attributed to late cenozoic cooling changes in hydroclimate according to cosmogenic isotope and luminescence ages of a sequence of bedrock terraces in the yukon river basin

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

meteoric 10be dating of highly weathered soils from fluvial terraces in taiwan abstract stream terraces are geomorphic markers that can be used to gauge surface deformation in response to tectonic uplift the surface deposits of the terraces form a chronosequence that indicates the rate and process of soil development placing a time or age constraint upon soil development has become one of the most important factors in the disciplines of soil science and fluvial geomorphology the radiocarbon 14c method is unable to date old terraces or soils but the longer half life of cosmogenic beryllium 10 10be permits this isotope to be useful to determine soil ages and rates of formation red soils redder than 7 5yr are commonly distributed on old high altitude stream terraces throughout taiwan in this study three pedons of alluvium related red soils were sampled from the taoyang ty ym pakua pk 1 and chiayi terraces cy 1 respectively located in northern central and southern taiwan according to field morphology and chemical analyses these red soils are characterized in soil taxonomy as being highly weathered and they are classified as typic hapludox ty ym and pk 1 and typic paleudult cy 1 meteoric 10be dating shows ages of 261 ka for ty ym 124 ka for pk 1 and 386 ka for cy 1 however the trend of these ages does not agree with the degree of soil development the former two ages are likely underestimated through loss of 10be due to strong leaching and considerable erosion the age obtained from cy 1 may represent the required time for soils develop into oxisols in taiwan

10be in lake lisan sediments a proxy for production or climate abstract the geochemical behavior of 10 be in the modern dead sea hydrological limnological system was studied in order to evaluate the feasibility of using dead sea and lake lisan the late pleistocene precursor of the dead sea sediments as archives of the variations in the 10 be production rate 10 be concentrations in detrital and aragonite material from lake lisan laminated sediments were compared to those measured in modern dust terra rossa soil aeolian in origin loess from the negev desert flood suspended load and waters along a rain flood development pathway the transition from rain to incipient runoff and fully developed floods 10 be concentrations decreased throughout the flood development profile from 8 2 10 3 atoms g 1 in the runoff down to 1 10 3 atoms g 1 in dead sea brine due to fast removal of 10 be by the soil and dust particles thus most of the 10 be in the lake is contained within the detrital sediments that collect the 10 be transported by particles from the surrounding terrain e g desert dust with 1 6 0 8 10 8 atoms g 1 and terra rossa soil material with up to 12 5 0 5 10 8 atoms g 1 the high stand periods of lake lisan were characterized by annual deposition of silty detritus sediments reflecting rapid transfer of desert dust to the lake by floods indeed the bulk sediments of lake lisan in which 10 be is associated mainly with silty detritus display 10 be concentrations similar to those of desert dust this demonstrates that 10 be variations were modulated by climate i e particle transport significant positive 10 be peaks up to 1 6 10 8 atoms g 1 appear during intervals of geomagnetic anomalies in lake lisan stratigraphy and in the global record i e during the laschamp geomagnetic event at 41 ka bp this indicates that 10 be atmospheric production signal is superimposed on the climatic 10 be variations we conclude that after de trending of the climatic signal lake lisan sediments may be used as an archive for atmospheric 10 be production

variable be 10 fluxes in lacustrine sediments from tristan da cunha south atlantic a solar record a 650 yr long sediment sequence from a crater lake on tristan da cunha south atlantic was analysed for its be 10 content based on c 14 dating and sedimentary geochemical magnetic and palynological records the period between 900 and 1450 ad appears to have been unusually stable in terms of sedimentation and vegetation and therefore this period was chosen for analysis of the be 10 content during this period of highly organic sedimentation and closed vegetation the pattern of be 10 flux variations follows the be 10 fluctuations from the grip ice core and estimated c 14 production rates well however before and after this stable period variable sedimentation rates have to be accounted for to obtain results that are comparable to the established be 10 c 14 records our data show not only the possibility of obtaining detailed enough be 10 flux data from sedimentary sequences to reconstruct past solar forcing but also how sensitive this type of record is to sedimentary and environmental changes if suitable archives can be found they have the potential to improve reconstructions of solar activity far back in time c 2007 elsevier ltd all rights reserved less

age erosion constraints on an early pleistocene paleosol in yukon canada with profiles of 10be and 26al evidence for a significant loess cover effect on cosmogenic nuclide production rates abstract wounded moose type paleosols developed on remnant deposits of late pliocene to early pleistocene pre reid cordilleran ice sheet cis glaciations in central yukon canada it is an important regional soil geomorphic marker at the boundary between early cis advances and the non glaciated regions of yukon and alaska yet at present its age is poorly constrained between the reid 0 2 ma and earliest 2 84 ma cis advances here we apply depth profiles of in situ produced cosmogenic 26al and 10be to obtain both a minimum exposure age 1 12 0 44 0 36 ma 2 and maximum erosion rate 1 1 0 9 0 5 m myr 1 for the wounded moose paleosol our results show that this soil formed under exceptionally stable conditions max erosion rate similar to polar bedrock erosion rates and that it pre dates the emergence of the 100 ka eccentricity climate cycle contrasting our results from single and joint nuclide depth profile models reveals a significant discrepancy between calculated and effective 10be and 26al production rates 40 65 of expected values we interpret this discrepancy as the result of intermittent loess cover with a time averaged depth between 60 and 110 cm which significantly reduced apparent exposure ages obtained from the single nuclide model the observation of such a significant loess cover effect on cosmogenic nuclide production has implications for exposure dating in glacial and periglacial environments a multi nuclide sampling strategy is required to quantify this effect

in situ produced 10be measurements at great depths implications for production rates by fast muons in situ cosmogenic 10be values have been used to investigate a brazilian quartz vein from the surface to a depth of 15 m at depths greater than 1000 g cm2 deep enough for neutron induced reactions to be insignificant there is only a slight decrease in 10be concentration with increasing depth our results are consistent with deep production of 10be by a mechanism presumably induced by fast muons with an attenuation length of 5300 950 g cm2 and a contribution of 0 65 0 25 to the total surface production results are compared with values from the literature and implications of this re evaluation are discussed

a 3 m y record of pliocene pleistocene loess in interior alaska many distal tephra beds exist in the thick fossiliferous loess deposits near fairbanks interior alaska isothermal plateau fission track ages determined on glass shards from tephra beds in conjunction with tephrostratigraphic and magnetostratigraphic techniques indicate that loess deposition began in the late pliocene an antiquity previously unsuspected hence there is the opportunity now to reconstruct a detailed well dated record of environmental changes in interior alaska during the past 3 m y

pliocene warmth polar amplification and stepped pleistocene cooling recorded in ne arctic russia understanding the evolution of arctic polar climate from the protracted warmth of the middle pliocene into the earliest glacial cycles in the northern hemisphere has been hindered by the lack of co

formation rates of smectites derived from two holocene chronosequences in the swiss alps the formation rate of smectitic components in alpine soils is derived from two chronosequences in the swiss alps covering a time span of 11 500 years the soils developed on granitic parent material the lithologies between the two chronosequences investigation areas however showed some distinct differences with respect to the main mineralogy and to a lower extent to the chemistry the chronofunctions of smectitic phase formation g kgclay year were fitted to data using an exponential formation model extensive mineral weathering resulted in significant losses of chlorite and mica and the corresponding formation of smectite and regularly and irregularly interstratified mica smectite this formation is especially pronounced in the early stages of soil formation our investigations reveal that the greatest changes in soil clay mineralogy of alpine soils on granitic or gneiss host material occur within the first 1000 3000 years of soil development at both investigation sites the annual formation rates are in a similar order of magnitude with 0 1 g kg year or even higher at the start of soil formation and with values 0 01 g kg year after about 7000 years the pedogenetic smectites from the e or bs horizons included several populations with various interlayer charges this heterogeneity seems to be related to the nature of their precursors

10be concentrations and the long term fate of particle reactive nuclides in five soil profiles from california concentration depth profiles of cosmic ray produced 10 be t 1 2 1 5m y have been measured by accelerator mass spectrometry in five soil profiles these measurements were made in an effort 1 to understand the retentivity of soil surfaces for particle reactive tracers depositing from the atmosphere on time scales of 10 4 10 6 years and 2 to explore the application of 10 be as a chronometer of geomorphic surface age the profiles sampled are from two wave cut terraces located near mendocino california a table mountain top and an alluvial fan both located near friant california the ages of the mendocino terraces are inferred to be 1 5 10 5 years based on amino stratigraphic correlations and models of terrace evolution those of the table mountain top and alluvial fan are 9 5 10 6 years and 6 0 10 5 years respectively based on k ar analyses all the surfaces sampled are nearly flat and exhibit few erosional features in addition to 10 be we measured 210 pb 239 240 pu and 7 be to ascertain the retentivity of the soils for particle reactive nuclides and to assess the present day delivery rate of nuclides from the atmosphere the 7 be inventory is 4 0 dpm cm 2 similar to those observed at nearby locations the inventories of 210 pb and pu isotopes conform to those predicted from model calculations and suggest that the soil surfaces sampled retain the entire burden of particle reactive nuclides delivered to them over short time scales 100 years the 10 be concentrations in the sample range between 0 2 and 7 10 8 atoms g soil and show strong correlations with leachable fe and or al the inventory of 10 be in the soil domain sampled is 1 2 orders of magnitude lower than that expected from the geological age of the surface and an average delivery rate of 10 be from the atmosphere 5 2 10 5 atoms cm 2 yr the low inventory of 10 be is attributed to its loss from the soil domain sampled by solution transport based on a simple model type calculation with a first order removal process for 10 be the residence time of 10 be in the soil domains sampled is determined to be of the order of 10 4 years the low residence time of 10 be in the soil domains sampled requires that it be found either deeper in the regolith or in ground waters in either case the application of 10 be as a chronometer of geomorphic surface age is severely constrained however the study of 10 be in soils provides the only entry into the long term 10 4 10 6 years behavior of particle reactive nuclides in soils and hence could be important for understanding the behavior of analogous nuclides introduced into soils by natural and anthropogenic processes

mid pleistocene climate transition drives net mass loss from rapidly uplifting st elias mountains alaska erosion sediment production and routing on a tectonically active continental margin reflect both tectonic and climatic processes partitioning the relative importance of these processes remains controversial gulf of alaska contains a preserved sedimentary record of the yakutat terrane collision with north america because tectonic convergence in the coastal st elias orogen has been roughly constant for 6 my variations in its eroded sediments preserved in the offshore surveyor fan constrain a budget of tectonic material influx erosion and sediment output seismically imaged sediment volumes calibrated with chronologies derived from integrated ocean drilling program boreholes show that erosion accelerated in response to northern hemisphere glacial intensification 2 7 ma and that the 900 km long surveyor channel inception appears to correlate with this event however tectonic influx exceeded integrated sediment efflux over the interval 2 8 1 2 ma volumetric erosion accelerated following the onset of quasi periodic 100 ky glacial cycles in the mid pleistocene climate transition 1 2 0 7 ma since then erosion and transport of material out of the orogen has outpaced tectonic influx by 50 80 such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out of sequence fault patterns the 1 2 my mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response millions of years the st elias range provides a key example of how active orogenic systems respond to transient mass fluxes and of the possible influence of climate driven erosive processes that diverge from equilibrium on the million year scale

dating sediment burial with in situ produced cosmogenic nuclides theory techniques and limitations abstract dating sediment burial over million year time scales is crucial in many areas of the earth sciences and archeology but is often difficult using traditional techniques sediment burial can be dated by the radioactive decay of cosmogenic nuclides provided that the sediment was exposed to cosmic rays prior to burial dating calculations are straightforward if sediment is buried deeply and rapidly enough to prevent cosmogenic nuclide production after burial however the analysis can be complicated by postburial production if sediment is insufficiently shielded from secondary cosmic ray nucleons and muons this paper discusses how buried sediments can be dated over timescales up to 5 myr using 26 al and 10 be in quartz

ice streams of the late wisconsin cordilleran ice sheet in western north america abstract the late wisconsin cordilleran ice sheet cis of western north america is thought to have reached its maximum extent 2 5 106 km2 as late at c 14 5 ka most 80 of the ice sheet s bed consists of high mountains but its core zone sited on plateaux of the intermontane belt of british columbia and coterminous parts of the usa shows broad swaths of subglacially streamlined rock and sediment broad scale mapping from new digital imagery data identifies three subglacial bed types 1 hard beds of variably streamlined bedrock 2 drumlinized soft beds of deformation till reworked from antecedent sediment and 3 mixed beds of variably streamlined bedrock protruding through drumlinized sediment drumlins on soft beds appear to be erosional features cut into till and antecedent sediments and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations msgls grooved and cloned drumlins appear to record the transition from drumlins to msgls the location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow rock cut msgls are also present locally on the floors of outlet valleys cis disintegrated in

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

biogeochemical cycling in the bering sea over the onset of major northern hemisphere glaciation the bering sea is one of the most biologically productive regions in the marine system and plays a key role in regulating the flow of waters to the arctic ocean and into the subarctic north pacific ocean cores from iodp expedition 323 to the bering sea provide the first opportunity to obtain reconstructions from the region that extend back to the pliocene previous research at bowers ridge south bering sea has revealed stable levels of siliceous productivity over the onset of major northern hemisphere glaciation nhg c 2 85 2 73 ma however diatom silica isotope records of oxygen 18odiatom and silicon 30sidiatom presented here demonstrate that this interval was associated with a progressive increase in the supply of silicic acid to the region superimposed on shift to a more dynamic environment characterized by colder temperatures and increased sea ice this concluded at 2 58 ma with a sharp increase in diatom productivity further increases in photic zone nutrient availability and a permanent shift to colder sea surface conditions these transitions are suggested to reflect a gradually more intense nutrient leakage from the subarctic northwest pacific ocean with increases in productivity further aided by increased sea ice and wind driven mixing in the bering sea in suggesting a linkage in biogeochemical cycling between the south bering sea and subarctic northwest pacific ocean mainly via the kamchatka strait this work highlights the need to consider the inter connectivity of these two systems when future reconstructions are carried out in the region

landscape antiquity and cenozoic drainage development of southern yukon through restoration modeling of the tintina fault the impact of tintina fault displacement on the development of the yukon river and drainage basins of central yukon is investigated through geophysical and hydrological modeling of digital terrain model data regional geological evidence suggests that the age of the planation of the klondike plateau is at least late cretaceous rather than neogene as previously assumed and that surprisingly there has been little net incision in the region since the late mesozoic the tintina fault has been previously interpreted to have experienced 430 km of dextral displacement primarily during the eocene however the alignment of river channels across the fault at specific displacements coupled with recent seismic events and related fault activity suggests that the fault may have moved in stages over a longer time span topographic restoration and hydrological models show that the drainage of the yukon river northwestward into alaska via the ancestral kwikhpak river was only possible at restored displacements of u

plio pleistocene climate sensitivity evaluated using high resolution co2 records theory and climate modelling suggest that the sensitivity of earth s climate to changes in radiative forcing could depend on the background climate however palaeoclimate data have thus far been insufficient to provide a conclusive test of this prediction here we present atmospheric carbon dioxide co2 reconstructions based on multi site boron isotope records from the late pliocene epoch 3 3 to 2 3 million years ago we find that earth s climate sensitivity to co2 based radiative forcing earth system sensitivity was half as strong during the warm pliocene as during the cold late pleistocene epoch 0 8 to 0 01 million years ago we attribute this difference to the radiative impacts of continental ice volume changes the ice albedo feedback during the late pleistocene because equilibrium climate sensitivity is identical for the two intervals when we account for such impacts using sea level reconstructions we conclude that on a global scale no unexpected climate feedbacks operated during the warm pliocene and that predictions of equilibrium climate sensitivity excluding long term ice albedo feedbacks for our pliocene like future with co2 levels up to maximum pliocene levels of 450 parts per million are well described by the currently accepted range of an increase of 1 5 k to 4 5 k per doubling of co2

alteration processes of alkenones and related lipids in water columns and sediments 1 alkenones produced by the haptophyte algae are currently being used as indices of sea surface temperature in recent and past ocean environments but limited information is available concerning the impact of biotic and abiotic processes on the integrity of these long chain lipids this synthesis provides selected background information on major alteration processes that must be considered before such indices can be used with confidence a number of processes in the water column and surface sediments have the potential to impact the structural integrity of alkenones and compromise their ability as temperature markers processes discussed include the alteration of alkenone structure during early diagenesis direct biotic and abiotic impacts and the effect of digestive processes by grazers current literature suggests that despite substantial changes in concentration from biological processing the temperature signal is preserved for each of these processes information on the integrity of the alkenone isotopic signature is also needed and limited information available is reviewed in addition to the alkenones related lipids including the long chain alkadienes and akyl alkenoates that might serve as ancillary markers are discussed

numerical ages for plio pleistocene glacial sediment sequences by 26al 10be dating of quartz in buried paleosols abstract we describe a method for dating plio pleistocene sediments by analysing 26 al and 10 be in quartz from buried paleosols the method amounts to a generalization of the technique of burial dating which has previously been used to date river sands deposited in caves as well as fluvial terraces we a measure nuclide concentrations at multiple depths in the paleosol b use the geologic context of the sample to construct an exposure burial history an exposure model that can be used to predict the nuclide concentrations in the samples as a function of whatever unknown parameters are of geological interest e g the ages of geologic units and then c find the parameters in the exposure model that result in the best fit between predicted and observed nuclide concentrations we apply the method to a paleosol developed on the uppermost till in eastern nebraska which is buried by several middle to late pleistocene loess units the ages of some of which are known independently the lowest loess unit whose age was not previously known was deposited 0 58 0 12 ma and the till was emplaced 0 65 0 14 ma which agrees with existing age constraints from paleomagnetic measurements and the position of the lava creek ash in the regional stratigraphy the most important source of uncertainty in these age determinations is the analytical uncertainty in 26 al and 10 be measurements uncertainties in either the nuclide production rates or the geologic model are comparatively unimportant

last glacial to post glacial 10be fluctuations in a sediment core from the academician ridge lake baikal 10be concentrations sediment composition and sediment accumulation rates were determined in a sediment core from the academician ridge of lake baikal the 10be concentrations vary from 5 07 108 atoms g in the last glacial section to 11 25 108 atoms g in the section representing the post glacial climate stage 10be fluxes on the other hand increase toward the last glacial stage coinciding with an increase of the sediment accumulation rate these facts imply that climate related sedimentation is related to both flux and concentration of the nuclide in the sediment core during the last glacial stage arid conditions in the lake s watershed caused a marked increase in flux of clay particles with low 10be content to the lake resulting in an increased flux but lowered concentration of 10be in the sediments it is suggested that the 10be record of the bottom sediments of lake baikal can be used as a proxy indicator of climate change in central asia

an alternative suggestion for the pliocene onset of major northern hemisphere glaciation based on the geochemical provenance of north atlantic ocean ice rafted debris abstract the onset of abundant ice rafted debris ird deposition in the nordic seas and subpolar north atlantic ocean 2 72 millions of years ago ma is thought to record the pliocene onset of major northern hemisphere glaciation nhg due to a synchronous advance of north american laurentide scandinavian and greenland ice sheets to their marine calving margins during marine isotope stage mis g6 numerous marine and terrestrial records from the nordic seas region indicate that extensive ice sheets on greenland and scandinavia increased ird inputs to these seas from 2 72 ma the timing of ice sheet expansion on north america as tracked by ird deposition in the subpolar north atlantic ocean however is less clear because both europe and north america are potential sources for icebergs in this region moreover cosmogenic dating of terrestrial tills on north america indicate that the laurentide ice sheet did not extend to 39 n until 2 4 0 14 ma at least 180 ka after the onset of major ird deposition at 2 72 ma to address this problem we present the first detailed analysis of the geochemical provenance of individual sand sized ird deposited in the subpolar north atlantic ocean between mis g6 and 100 2 72 2 52 ma ird provenance is assessed using laser ablation lead pb isotope analyses of single ice rafted 150 m feldspar grains to track when an ice rafting setting consistent with major nhg first occurred in the north atlantic ocean during the pliocene intensification of nhg inhg we investigate when the pb isotope composition 206pb 204pb 207pb 204pb 208pb 204pb of feldspars deposited at dsdp site 611 first resembles that determined for ird deposited at this site during mis 100 2 52 ma the oldest glacial for which there exists convincing evidence for widespread glaciation of north america whilst quaternary magnitude ird fluxes exist at site 611 during glacials from 2 72 ma we find that the provenance of this ird is not constant instead we find that the pb isotope composition of ird at our study site is not consistent with major nhg until mis g2 2 64 ma we hypothesise that ird deposition in the north atlantic ocean prior to mis g2 was dominated by iceberg calving from greenland and scandinavia we further suggest that the grounding line of continental ice on northeast america may not have extended onto the continental shelf and calved significant numbers of icebergs to the north atlantic ocean during glacials until 2 64 ma

pliocene and pleistocene chronostratigraphy of continental sediments underlying the altiplano at la paz bolivia abstract continental sediments underlying the altiplano plateau provide insight into the late cenozoic evolution of the central andes we characterize the magnetostratigraphy and lithostratigraphy of the upper part of this fill sequence along a transect extending southwestward from the cordillera real at la paz bolivia where it is best exposed multiple polarity reversals and the locally extensive 2 74 ma chijini tuff enable correlation between our six sections and three previously reported sections the tuff ties the composite polarity sequence to the geomagnetic polarity time scale demonstrating that the stratigraphic record extends from the latest gilbert chron ca 3 8 ma to the late olduvai subchron ca 1 8 ma or possibly jaramillo subchron ca 1 0 ma the sequence provides earth s longest known record of low latitude glaciation and the only record of pliocene tropical glaciation it includes evidence for 16 late pliocene and early pleistocene glaciations separated by interglacials of sufficient length 103 104 a to produce mature soil profiles successively larger ice caps formed directly before during and after the globally warm mid piacenzian 3 265 3 025 ma and throughout plio pleistocene climate deterioration the late pliocene glacial units predate the onset of widespread northern hemisphere continental glaciation and in most cases unambiguously correspond to specific cool peaks of the astronomically tuned benthic oxygen isotope 18o record including marine isotope stages mg2 m2 km2 and g10 the glacial events broadly coincide with those nearer both poles suggesting inter hemispheric climate linkages the early formation and subsequent expansion of ice caps beyond glacier margins of the last glacial maximum suggest that the cordillera real likely attained its modern height before ca 3 4 ma the number and timing of glaciations and long term sediment accumulation and incision rates suggest that the local altiplano surface formed by ca 1 8 ma after which headwaters of the amazon river system breached the cordillera real and began to incise the fill sequence the sequence spans at least 2 ma before and during the first main pulses of the great american biotic interchange providing an important record of faunal migration the arrival of savanna adapted north american mammals in the central andes during this period points to the influence of glaciation on faunal migration in the southern tropics similar to influences proposed in north and central america

combining cosmogenic nuclides and major elements from moraine soil profiles to improve weathering rate estimates abstract previous studies of chemical weathering rates for soil developed on glacial moraines generally assumed little or no physical erosion of the soil surface in this study we investigate the influence of physical erosion on soil profile weathering rate calculations the calculation of chemical weathering rates is based on the assumption that soil profiles represent the integrated amount of weathering since the time of moraine deposition the weathering rate of a surface subjected to denudation is the sum of the weathering loss from the existing soil profile added to the weathering loss in the material removed by denudation divided by the deposition age in this study the amount of weathered material removed since moraine deposition is calculated using the denudation rate estimated from cosmogenic nuclide data and the deposition age of the moraine weathering rates accounting for denudation since moraine deposition are compared to weathering rates based on the assumption of no physical erosion and on the assumption of steady state denudation for the type pinedale moraine 21 ka and the bull lake age moraine 140 ka in the fremont lake area wind river mountains wyoming usa the total weathering rates accounting for denudation are 8 15 1 05 g oxide m 2 y 1 for the type pinedale moraine and 4 78 0 89 g oxide m 2 y 1 for the bull lake age moraine which are 2 to 4 times higher respectively than weathering rates based on the assumption of no physical erosion the weathering rates based on denudation since moraine deposition are comparable or smaller than weathering rates assuming steady state denudation we find the assumption of steady state denudation is not valid in depositional landscapes with young deposition ages or slow denudation rates the decrease in weathering rates over time between the type pinedale and bull lake age soils that is observed in the case of no physical erosion is decreased when the influence of denudation on the total weathering rates is taken into account fresh unweathered material with high reactive mineral surface area is continuously provided to the surface layer by denudation diminishing the effect of decreasing weathering rate over time

mcgee till oldest glacial deposit in the sierra nevada california and quaternary evolution of the rangefront escarpment abstract the mcgee till is an early pleistocene glacial diamict as thick as 50 m preserved over an area of 1 65 km2 on a relict low relief pliocene plateau that stands 900 m higher than mouths of its bounding canyons on the rangefront of the sierra nevada although recognized 90 years ago as the oldest till in the sierra its age and relation to the next oldest sierran till have remained uncertain even controversial this contribution seeks to clarify both the mcgee till consists predominantly of grussy boulders and sandy granular matrix derived largely from a distinctive cretaceous granodiorite that walls mcgee creek canyon 4 8 km to the south the till rests directly upon two different basaltic units that yield 40ar 39ar ages of 2 8 and 2 6 ma and show little or no evidence of preglacial erosion the basalts preserve a minimum of 165 255 m of relief on steep slopes that existed around the plateau margins at the time of their eruption mcgee creek consists of two segments a north directed reach that confined the glacier that deposited the till and now diverging at a right bend just upvalley from the till a northeast flowing reach that was incised later the base of the mcgee till is at 3160 m elevation on the present day rim of mcgee creek 610 m above the bend the base of the 130 ka tahoe till mis 6 is at 2550 m elevation directly downslope from the mcgee till and at 2300 m at the rangefront mouth of the canyon s northeast reach the base of the 900 866 ka sherwin till mis 22 is at 2400 m at the nearby rangefront mouth of rock creek as the canyons were cut to nearly modern depths before the sherwin glaciation the high perched mcgee till is probably older than 2 ma and possibly close in age to the 2 6 ma basalt it overlies growth in rangefront relief since about 3 0 2 5 ma owes to normal slip on the hilton creek and round valley faults east of mcgee mountain as well as to the 767 ka collapse of long valley caldera to its north